Subscriber access provided by CORNELL UNIVERSITY LIBRARY
Article
TlSn2I5, a Robust Halide Anti-perovskite Semiconductor for #-Ray Detection at Room Temperature Wenwen Lin, Constantinos C. Stoumpos, Zhifu Liu, Sanjib Das, Oleg Y. Kontsevoi, Yihui He, Christos D. Malliakas, Haijie Chen, Bruce W. Wessels, and Mercouri G. Kanatzidis ACS Photonics, Just Accepted Manuscript • Publication Date (Web): 08 Jun 2017 Downloaded from http://pubs.acs.org on June 8, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Photonics is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
1
TlSn2I5, a Robust Halide Anti-perovskite Semiconductor for
2
γ-Ray Detection at Room Temperature
3
Wenwen Lin,† Constantinos C. Stoumpos,† Zhifu Liu,‡ Sanjib Das,‡ Oleg Y. Kontsevoi,§ Yihui He,
4
†
5
†
6
of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, United States.
Christos D. Malliakas, † Haijie Chen, † Bruce W. Wessels, ‡ and Mercouri G. Kanatzidis†,*
Department of Chemistry, ‡Department of Materials Science and Engineering, and §Department
7 8
ABSTRACT: The semiconductor TlSn2I5 with a two-dimensional crystal structure and an
9
anti-perovskite topology is a promising novel detection material. The compound crystallizes in the
10
I4/mcm space group, has an indirect bandgap of 2.14 eV and melts congruently at 314 oC.
11
Electronic band structure calculations reveal that the most facile carrier transport is along the ab
12
layered plane. Compared to the CH3NH3PbX3, TlSn2I5 features higher long term stability, higher
13
photon stopping power (average atomic number of 55), higher resistivity (~1010 Ω·cm) and robust
14
mechanical properties. Centimeter-size TlSn2I5 single crystals grown from the melt by the
15
Bridgman method can be used to fabricate detector devices, which detect Ag Κα X-rays (22 keV),
16
57
17
mobility for electrons were estimated to be 1.1×10-3 cm2·V-1 and 94±16 cm2·V-1·s-1, respectively.
18
Unlike other halide perovskites, TlSn2I5 shows no signs of ionic polarization under long-term,
19
high voltage bias.
Co γ-rays (122 keV), and
241
Am α-particles (5.5 MeV). The mobility-lifetime product and
20
21 22
KEYWORDS: hard radiation detection, γ-ray, crystal growth, semiconductor detector, halide
23
perovskite and photon detection. 1
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 20
24 25
Wide-band-gap semiconductors with high mass density are of great importance for
26
room-temperature radiation detection applications including homeland security, medical imaging,
27
and the non-proliferation of nuclear materials. Compared with scintillator detectors which require
28
a photomultiplier that reduces the resolution of the output signal1, semiconductor detectors can
29
provide a direct, simple and efficient method for the conversion of hard radiation into electric
30
signals. To date, only a handful of compounds have been identified as potential hard radiation
31
detector materials, as a set of strict physical property requirements such as high density, high
32
resistivity, high mobility-lifetime product, and robust mechanical properties must be
33
simultaneously satisfied2-4. Even the commercial grade room temperature detector, Cd0.9Zn0.1Te
34
(CZT)5, still suffers from growth problems related to its intrinsic defects such as Te precipitates
35
and poor uniformity6-7, which in part result in the high cost of the CZT devices. TlBr is another
36
candidate detection material showing a high mobility-lifetime product (µτ) (electron: ~10-3
37
cm2·V-1) with a high energy resolution of 1-2% under γ-rays8-11. However, TlBr is subject to
38
polarization-induced instability and low hardness which is detrimental to mechanical processing2,
39
12
40
very low yield of homogeneous crystals with high quality and poor mechanical stability13-15. On
41
the other hand, the recently developed halide perovskite high-performance semiconductors16,
42
show considerable promise due to their remarkable mobility-lifetime products which range
43
between µeτe = 10-3-10-2 cm2·V-1 17-19. However, because of the polar organic groups and ionic
44
conductivity intrinsic to the materials, halide perovskites exhibit space-charge effects which
45
significantly reduce the charge collection efficiency20-21. Despite the loss of collection efficiency
46
and low signal resolution, X-ray18,
47
CH3NH3PbBr3 (MAPbBr3) and CH3NH3PbI3 (MAPbI3) hybrid inorganic-organic perovskites, but
48
also in the alternative composition HC(NH2)2PbI319 and the all-inorganic analogue CsPbBr317
49
demonstrating X-ray and γ-ray photoresponse, respectively. CH3NH3PbX3, are subject to strong
50
polarization upon the application of high electric fields (e.g. >200 V/cm), exhibit hysteresis loops
51
on electric field cycling and has no long term stability due to a structural phase transition24. The
52
chemical instability, high ionic conduction16, low mass density (3.80-4.15 g·cm-3) space-charge
53
and phase transition issues associated with the halide perovskites prompted us to look for
. Other simple semiconductors studied as detection materials such as HgI2 and PbI2 suffer from
22-23
and γ-ray19-20 responses have been reported for
2
ACS Paragon Plus Environment
Page 3 of 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
54
alternative perovskite-like compounds that maintain the high quality semiconducting properties of
55
the perovskites but at the same time address their deficits.
56
We report here on TlSn2I5, an inorganic iodide semiconductor with two-dimensional (2D) crystal
57
structure and an anti-perovskite topology. TlSn2I5 features elements of high atomic number (Tl:81,
58
Sn:50, I:53) and high density (6.05 g·cm-3) that guarantee a superior absorption coefficient to both
59
halide perovskites and CZT against hard radiation25, as shown in Figure 1a and 1b. TlSn2I5 is a
60
brick-red compound26 with a desirable wide bandgap of Eg = 2.14 eV, melts congruently at a low
61
temperature (315 oC)27, which allows for simple purification/crystal growth protocols and
62
low-concentration of thermally activated defects. The compound has no phase transitions between
63
melting and ambient temperature and is stable in air. Large crystals of TlSn2I5 were grown from
64
the melt by the vertical Bridgman method28, yielding single-crystalline ingot which can be
65
subsequently processed to fabricate detectors. The compound has a very high resistivity of 4×1010
66
Ω·cm and exhibits no signs of electrical polarization, thus being suitable for fabrication of
67
detectors with low background dark current. TlSn2I5 detectors are photoresponsive to hard X-rays,
68
γ-rays and α-particles showing an electron mobility-lifetime product, µeτe =1.1×10-3 cm2·V-1 and
69
µeτe = 4.5×10-5 cm2·V-1 for high-flux X-rays and low-flux γ-rays, respectively. Drift mobility
70
measurements using α-particles reveal an electron mobility µe = 94±16 cm2·V-1·s-1 which is
71
comparable to those of the top performing halide perovskites20. Contrary to the halide perovskites,
72
however, the detector performance of TlSn2I5 shows long-term stability under constant applied
73
bias without suffering any polarization effects. Based on its detector characteristics, TlSn2I5, the
74
new addition to the class of halide perovskites, is a highly promising hard radiation detector
75
material.
76 77
RESULTS AND DISCUSSION
78
Crystal growth and characterization. Bulk TlSn2I5 was prepared by a stoichiometric
79
direct combination of the Sn, I2 elements and TlI precursor. The obtained raw compound was then
80
used to grow single-crystals using the vertical Bridgman method. The as-grown crystal is phase
81
pure as evidenced by powder X-ray diffraction on a powdered ingot specimen (Supporting
82
Information (SI), Figure S1). Figure 1c shows the pristine crystal of TlSn2I5 under ambient light.
83
The whole crystal ingot has a brick-red color and it is optically transparent with no visible cracks. 3
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 20
84
The absence of cracks suggests that the crystal can endure the large temperature gradient of 23
85
o
86
surface, which is parallel to the growth direction. X-ray diffraction on the cleaved crystal facet (SI,
87
Figure S2) shows two diffraction peaks which match well with the (002) and (006) peaks of the
88
simulated pattern at 2θ = 11.595ο and 2θ = 35.280ο, respectively, suggesting that the cleaved
89
surface consists of (00l) planes that orient perfectly perpendicular to the growth direction. The
90
performance of hard radiation detection materials strongly depends on the defect density, as
91
defects can act as shallow impurity levels, trapping centers or scattering centers. Optical
92
spectroscopy can provide useful insights into the defect states and thus the absorption spectrum of
93
TlSn2I5 were measured. Figure 1e shows the optical absorption spectrum of TlSn2I5 indicating a
94
bandgap of Eg = 2.14 eV, consistent with the brick-red color of the crystal. The bandgap is large
95
enough to suppress the formation of thermally activated charge carriers, yet sufficiently narrow to
96
generate photoinduced electron-hole pairs due to a lower pair creation energy29-31.
C·cm-1 during growth. Figure 1d shows a crystal chunk with a naturally cleaved mirror-like
97
98 99
Figure 1. (a). Estimated attenuation length as a function of incident photon energy in TlSn2I5,
100
Cd0.9Zn0.1Te and CH3NH3PbI3. (b). Estimated attenuation efficiency as a function of thickness in
101
TlSn2I5, Cd0.9Zn0.1Te and CH3NH3PbI3 to 122 keV γ-ray from
102
under ambient light. (d). A TlSn2I5 chunk with a naturally cleaved (00l) face parallel to the growth
57
Co. (c). Image of TlSn2I5 ingot
4
ACS Paragon Plus Environment
Page 5 of 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
103
direction. (e). The UV-vis-Near IR optical absorption spectrum of TlSn2I5.
104 105
TlSn2I5 melts congruently at 314 oC (SI, Figure S3) and is free of phase transitions between
106
melting and ambient temperatures. Importantly, its low melting point is beneficial to suppress
107
formation of thermally activated defects32, which in turn can enhance its detection performance.
108
The compound is environmentally stable, mechanically robust as shown from Vickers hardness
109
measurements (SI, Figure S4). The Vickers hardness of polished TlSn2I5 is 75±3.0 kg·mm-2 on the
110
(00l) plane, which is significantly higher than that of CH3NH3PbI3 (22±0.9 kg·mm-2).
111 112
Crystal Structure. TlSn2I5 adopts the (NH4)Pb2Br5 structure type26, crystallizing in the
113
tetragonal I4/mcm space group, with a=8.8019(5) Å, c=15.2514(11) Å, V=1181.58(13) Å3 with a
114
calculated density of 6.05 g·cm-3. Figure 2 shows the crystal structure of TlSn2I5. Detailed
115
crystallographic data are listed in SI Table S1 while atomic coordinates, atomic displacement
116
parameters and bond distances and angles are given in SI Tables S2 and S3. The compound
117
consists of two-dimensional (2D) infinite (Sn2I5)- layers with the Tl+ ions occupying the interlayer
118
voids.
119
120 121 122
Figure 2. (a). View of the unit cell along the ab crystallographic plane. (b). The building block of
123
the {Sn2I5}- layers indicating the Sn-I bond lengths. (c). Extended view of the {Sn2I5}- layers
124
emphasizing on the connectivity of the planar {ISn4}7+ units. The arrows indicate the most likely 5
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 20
125
location of the lone pair. Panel (d).-(f). show the coordination polyhedral of (d). Tl(1), (e). Sn(1),
126
(f). I(1). Comparison between the (g). Anti-perovskite topology of TlSn2I5 and (h). The perovskite
127
topology of the hybrid inorganic-organic perovskite CH3NH3PbI3. The lattice of the TlSn2I5 is
128
significantly more distorted than that of CH3NH3PbI3.
129 130
When viewed without chemical bonding restrictions, the lattice formed between I(1), Tl(1) and
131
Sn(1) adopts an anti-perovskite structure with I being in the center of an axially elongated
132
octahedron with its equatorial plane occupied by four Sn ions and its polar positions by two Tl
133
ions to form an cationic [ISn2Tl]4+ framework (Figure 2g and 2h). Four of the “ignored” iodide
134
ions (I(2)) occupy the perovskite cavity forming “dangling bonds” within the hollow cavity
135
(chemically these are still bonded to Sn(1)) assembling a nearly regular {I4}4- tetrahedron.
136
Interestingly, the volume of this void tetrahedron is comparable to that of SnI4 (Sn-I=2.70Å) with
137
a centroid-iodide distance of 2.58 Å33. The framework has a distorted perovskite structure with the
138
octahedra tilting out-of-phase in the same fashion with hybrid perovskite semiconductor
139
CH3NH3PbI3 which crystallizes in the non-centrosymmetric version of the I4/mcm space group
140
(due to the asymmetric CH3NH3+ cation)34.
141
TlSn2I5 is an unusual compound for several reasons. The majority of halide compounds
142
crystallizing in the AM2X5 crystal structure consist of an NH4+ or an alkali metal cation (K, Rb, Cs)
143
in the A site, a lighter halide anion (Cl, Br) in the X site. The limitations for the structure
144
stabilization come mainly from the necessity to accommodate the halide ion in the square planar
145
cavity of the layer, which is too small in the case of X=F and too large in the case of X=I. Thus, in
146
order to stabilize the crystal structure for X=I, it is required to introduce a group 13 metal ion (In+,
147
Tl+) at the A site26, so that some electronic stabilization is introduced through weak bonding
148
interactions, as opposed to the alkali metal ions which are electronically inert. This electronic
149
contribution is evident by the intense red color of TlSn2I5, as opposed to all other compounds in
150
the AM2X5 type which are colorless35-37. The electronic stabilization has further implications. For
151
example, it makes these tin compounds air stable, in contrast to the notoriously sensitive tin iodide
152
perovskites such as CsSnI3 and CH3NH3SnI324. It thus represents a very rare example of air stable
153
iodostannate27, 38.
154 6
ACS Paragon Plus Environment
Page 7 of 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
155
Electronic band structure. The calculated electronic band structure is shown in Figure 3a
156
plotted along the lines between the high-symmetry points in the Brillouin zone. Figure 3b shows
157
the first Brillouin zone in reciprocal space showing the principle directions and points. The
158
electronic density of states (DOS) projected onto the atomic sites are shown in Figure 3c. The
159
band structure shows that TlSn2I5 has an indirect band gap. The primary valence band (VB)
160
maximum (VBM) is located on the line between Γ and Σ points (close to Σ point) and the
161
conduction band (CB) minimum (CBM) is located at Z point. Interestingly, there is a secondary
162
VBM located on the line between N and Σ1 points (close to Σ1) which is only 0.02 eV lower in
163
energy than the main VBM. Similarly, a secondary CBM, which is just 0.01 eV higher than the
164
primary CBM, is at the Γ point. CBM is very anisotropic: CB is almost flat in the Γ−Z direction,
165
and highly dispersive in other directions (Z−Σ1, Z-Y1), suggesting that there is no electronic
166
communication between the layers. Such behavior translates into highly anisotropic effective
167
masses: the calculated principle electron effective masses are as follows: me,xx= 0.21 m0, me,yy=
168
0.21 m0, and me,zz= 21.5 m0. This result suggests that for properly oriented crystals a high µτ value
169
for electrons can be achieved. If the applied electric field is along the ab plane which is parallel to
170
the cleaved (00l) planes, a higher µτ value could be expected for adetector made of TlSn2I5. The
171
VBM is flater and the calculated values of hole effective masses are mh,xx= 0.50 m0, mh,yy= 1.2 m0,
172
me,zz= 1.9 m0, therefore hole mobility is expected to be lower. The high anisotropy of both band
173
extrema is due to the layered, 2D structure of the TlSn2I5 compound.
174
The PDOS calculations indicate that the VBM is composed of I p and Sn s orbitals, which,
175
however are not strongly coupled. The CBM has mainly pure Sn p character in the Γ−Z direction of
176
the flat band, but changes to the strongly coupled Sn p-I p orbital character in other directions. The
177
lone pairs of Sn p orbitals lead to the localized character of CBM along the Γ−Z line, while the
178
hybridization between Sn p and I p orbitals is responsible for the highly dispersive character of the
179
CBM in other directions. Tl atoms do not contribute to electronic states near the band edges.
180
7
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 8 of 20
181 182 183
Figure 3. (a). Electronic band structure of TlSn2I5. (b). View of first Brillouin zone in reciprocal
184
space showing the principle directions and points in comparison with real space. (c). Projected
185
electronic density of states of TlSn2I5. The Fermi level (EF) is set to zero energy.
186 187
Charge transport and detector performance. The dark current of the detector made from
188
TlSn2I5 wafers was measured Figure 4a shows the typical detector made from 1 mm thick TlSn2I5
189
wafer with a carbon electrode of ~2 mm in diameter. The orientation of TlSn2I5 crystal is
190
perpendicular to the cleaved (00l) planes, thus the electric field of detector is along the ab plane.
191
According to the calculations on the effective electron masses along different directions, the
192
present direction of electric field is preferred for obtaining a better charge collection efficiency. As
193
shown in Figure 4b, the I-V curve of detector is linear in range of ±100 V, indicating the absence
194
of space charge which is an inherent problem in MAPbX3 perovskites39. The resistivity estimated
195
from the I-V curve is 4.0×1010 Ω·cm, which is well above those of MAPbX3 perovskites (107~108
196
Ω·cm)18, suggesting this material is better for obtaining a high signal-to-noise ratio. Most
197
importantly, the high resistivity does not degrade after 24 h’s biasing at 100 V, indicating high
198
stability against ionic movement. The photoresponse of the detector to a Ag Kα source (22 keV)
199
X-ray source was demonstrated in Figure 4c. The photocurrent at various biases is at least two
200
orders of magnitude higher than dark current, indicating that this material is responsive to X-rays.
201
In order to assess the quality of the detector, the mobility-lifetime products for electrons and holes
202
were estimated using the Hecht equation40, based on X-ray photocurrent measurements (see
203
Methods). The electron mobility-lifetime product µeτe (1.1×10-3 cm2·V-1) is 14 times higher than
204
that of the holes µhτh (7.2×10-5 cm2·V-1). The great disparity in µτ values agree well with the great
205
difference between the calculated effective electron masses and hole masses. Figure 4d illustrates 8
ACS Paragon Plus Environment
Page 9 of 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
206
the photoresponse to Ag X-rays at 100 V applied bias exhibiting high contrast and spontaneous
207
response between the beam on and off states. The X-ray photoresponse for electrons in TlSn2I5 is
208
comparable with those obtained for the MAPbX3 halide perovskites under high photon flux
209
conditions (>1018 pairs·s-1·cm-2) and represents a good measure of the expected device
210
performance. However, at it is discussed below, this is not necessarily indicative of a good spectral
211
resolution because the high photon flux causes filling of the electronic trap states. In the excited
212
state the detector is able to produce a stable photocurrent, but the deficiencies of this approach
213
become apparent when the photon flux is drastically reduced below the levels of trap
214
concentration (typically ~1010 cm-3 for the halide perovskites)20-21. In the low photon flux case, the
215
traps start dominating the charge transport in the crystal, leading to a reduced charge collection
216
efficiency and a significant decrease in the detector resolution.
217
218 219 220
Figure 4. (a). The TlSn2I5 detector made of a 0.1 cm thick wafer with a dimension of 5 mm×9 mm.
221
(b). I-V characteristics. (c). Photocurrent response to 22 keV Ag X-rays at various biases and µτ
222
derived from X-ray photocurrent measurements using single-carrier Hecht equation. (d).
223
Photocurrent response to Ag X-rays by switching the X-ray source on and off at a bias of 100 V.
224 225
Having established the high sensitivity of TlSn2I5 as a hard radiation detector, we subsequently 9
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 10 of 20
226
tested the detection performance for low flux weak source of γ-rays and α-particles. Figures 5a
227
shows the
228
electron-collection configuration (cathode irradiation). The detector clearly shows a response to
229
γ-rays as indicated by the significant count rate of the detected photons, which allows the γ-rays
230
induced signal to be easily distinguished from the background noise. Importantly, the shoulder
231
accompanying the spectral tail shifts to higher energy channels with increasing applied bias
232
voltage, a decisive criterion to confirm that the signal arises from the γ-ray source rather than
233
artificial effects induced by the high voltage. Despite the clear response of the TlSn2I5 detector, the
234
characteristic peak of the
235
resolution can be assigned to the insufficiently high carrier collection efficiency due to electron
236
trapping and recombination centers. The effect of the traps can be estimated by γ-ray spectroscopy
237
measurements (see Methods), where the µeτe (4.5×10-5 cm2·V-1) obtained from the Hecht equation
238
is two orders of magnitude lower than the one obtained from X-ray photocurrent measurements
239
(1.1×10-3 cm2·V-1, see above). This is because the X-ray photocurrent measurements are
240
performed under photon flooded conditions, as the estimated generation rate of e-h pairs (around
241
1018 pairs·s-1·cm-2 at 40 kV X-ray tube voltage and 2 mA tube current)41 is many orders of
242
magnitude higher than the removal rate of carriers under bias. Therefore, the electronic system is
243
not in thermal equilibrium but in a dynamic equilibrium with the photon field. Subsequently, the
244
flooded electrons fill all the active electron trapping centers, and then deactivate the electron
245
trapping centers41. In this case, the deactivation of traps provides a higher µeτe which further
246
indicates the strong potential of this detection material. On the other hand, the γ-ray spectroscopy
247
measurement is performed under a photon poor condition, as the estimated generation rate of e-h
248
pairs (around 108 pairs·s-1·cm-2 for 122 keV γ-rays from a 0.2 mCi radiation source, see SI) is
249
comparable to the removal rate of carrier under bias. Under these conditions the electronic system
250
is in thermal equilibrium allowing for the unfilled electron trap centers to determine the charge
251
transport thereby reducing the effective electron mobility and lifetime.
252
57
Co (122 keV) γ-ray spectral response as a function of applied voltage under
57
Co radiation source could not be resolved. The absence of spectral
We further measured its detection performance using un-collimated 241Am α-particles (5.5 MeV)
253
whose energy is significantly higher than 57Co but are not able to penetrate through the detector.
254
Figure 5c shows the α-particles spectrum recorded by irradiating the cathode of the TlSn2I5
255
detector. The signal clearly indicates that TlSn2I5 is photoresponsive to 5.5 MeV α-particles from 10
ACS Paragon Plus Environment
Page 11 of 20
256
an un-collimated 241Am source with an activity of only ~1 µCi. The detector performance does not
257
degrade after 10 h’s biasing at 200 V, indicating absence of polarization effect. The absence of
258
polarization is a unique property of TlSn2I5 among the halide high performance semiconductors
259
including TlBr and the halide perovskites. The electron mobility (µe) of TlSn2I5 detector was
260
estimated by measuring the photoexcited electron drift time (tdrift) using α-particles from an 241Am
261
source42. The µe can be estimated by the following equation:
262
ߤୣ = ா௧
263
, where D and E are the detector thickness and the applied electric field, respectively. The electron
264
drift time tdrift is measured by recording the electron rise time from the detector output pulse. One
265
hundred measurements of electron rise time were performed and averaged in order to enhance the
266
accuracy of the data. Figure 5d demonstrates one typical electron output pulse of the TlSn2I5
267
detector using α-source from
268
1.06±0.18 µs was calculated at an applied electric field of 1000 V/cm and a detector thickness of
269
0.1 cm. Since the attenuation length of α-particle in the materials is much smaller than the detector
270
thickness, the electron drift time approximates the electron rise time. Based on equation (1), the
271
electron drift mobility of TlSn2I5 detector can be estimated to be µe= 94±16 cm2·V-1·s-1. Based on
272
the estimated µeτe (~4.5×10-5 cm2·V-1) and measured µe (94±16 cm2·V-1·s-1), the lifetime of
273
electron τe under 122 keV γ-ray irradiation condition can be derived to be ~ 0.47 µs.
(1)
ೝ
241
Am. As shown in Figure 5e, an average value of rise time of
274
10
102
10 minutes after 200 V posi bias 10 hours after 200 V posi bias
e.
101 10
275
3
200 400 600 800 Channel
0
0
1500 3000 4500 Channel
c. 104 103 Fitting Curve Measured Data
Counts
1.0 0.8 0.6 0.4 0.2 0.0 0
102
200 400 600 800 Bias Voltage (V)
0
1500 3000 4500 Channel
f. 10
0.012
8
0.009 0.006 0.003 0.000
250 V BKGD 100 V posi 150 V posi 200 V posi 250 V posi
101
Counts
104
posi 700 V BKGD posi 100V posi 300V posi 500V posi 700V
Amplitude (V)
Counts
d.
105 104 103 102 101 100 0
Charge Collection Efficiency
b.
a.
Counts
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
2.0x10-5 Time (s)
6 4 2 0 0.0
2.0x10-6 Time (s)
4.0x10-6
276 11
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 12 of 20
57
277
Figure 5. (a). 122 keV γ-ray spectral responses of
278
curve “700V posi BKGD” refers to the background of energy spectrum at 700 V. (b). µeτe
279
estimation based on 122 keV γ-ray spectroscopy measurements using Hecht equation. (c)
280
α-particles spectral response obtained with TlSn2I5 detector. (d).
281
response of TlSn2I5 detector at 250 V at different time periods. (e). A typical electron pulse
282
induced by
283
electron rise times at 100 V bias for a TlSn2I5 detector from α-particles. Among all the new
284
candidates that have been proposed in the past decade,43-55 TlSn2I5 is among the top in terms of
285
promise in view of its easy of crystal growth and initial photoresponse properties.
241
Co source at various applied voltages. The
241
241
Am
Am α-particles spectral
Am α-particles at 100 V bias for estimating electron rise time. (f). Statistics of
286 287
CONCLUSIONS
288
In conclusion, TlSn2I5 is a promising stable tin iodide semiconductor capable of room temperature
289
hard radiation detection and belongs to the larger emerging family of main group metal halide
290
perovskite and related materials. One centimeter-size single-crystals can be easily grown using
291
two-zone vertical Bridgman method thanks to its low melting point and nature of congruent
292
melting. Band structure calculations reveal favorable electron transport along ab plane, parallel to
293
the [Sn2I5]- layers, predicting a high mobility-lifetime product with proper sample orientation. The
294
crystal has a high resistivity on the order of 1010 Ω·cm, which guarantees low noise levels and can
295
withstand electric fields in excess of 7×105 Volts/m. Detectors made of TlSn2I5 shows a clear
296
response to Ag Κα X-rays (22 keV), 57Co γ-rays (122 keV), and 241Am α-particles (5.5 MeV) and
297
they demonstrate high µeτe (1.1×10-3 cm2·V-1) and µe (94±16 cm2·V-1·s-1). Most importantly, the
298
detectors show no severe polarization effects after long-term bias. These features render the iodide
299
TlSn2I5 an excellent new candidate detector material, which can produce even higher performance
300
devices upon further development.
301 302
METHODS
303
Synthesis and Crystal Growth. The synthesis of TlSn2I5 polycrystalline raw material was
304
performed by the direct combination of precursors (TlI, 99.999%; Sn, 99.999%; I2, 99.9%; all
305
from Alfa Aesar) in an evacuated silica ampoule at 500 °C for 12 h in a rocking furnace, and then
306
followed by slow cooling to room temperature in 12 h. The TlI raw material was preheated at 12
ACS Paragon Plus Environment
Page 13 of 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
307
80 °C for 12 h to remove surface moisture before synthesis. As reported, TlSn2I5 congruently melts
308
at 315 °C27. The heating temperature of 500 °C for synthesis can ensure complete melting of
309
TlSn2I5. The temperature of the furnace was increased slowly to avoid any possibility of explosion
310
due to high vapor pressure of I2 precursor. Subsequently, the polycrystalline raw material was put
311
into a conical-tip quartz ampoule with a thickness of 1.5 mm and an inner diameter of 11 mm,
312
which was sealed at a vacuum pressure of 1×10-4 mbar. Single crystalline ingot of TlSn2I5 was
313
grown from stoichiometric melt by the vertical Bridgman method. At the beginning of the growth
314
process, the ampoule was held in the hot zone (520 °C) of a two-zone Bridgman furnace for 12 h
315
to achieve complete melting of polycrystalline raw material. The ampoule was subsequently
316
translated from the hot zone to cold zone at a speed of 0.5 mm/h. In order to generate a
317
temperature gradient of 23 °C/cm, the temperature of cold zone was set at 200 °C. SI Figure S5
318
shows the temperature profile in the Bridgman furnace. After crystal growth, the ingot was
319
annealed in-situ at 250 °C for 24 h in the Bridgman furnace without translation. Finally, the ingot
320
was cooled down to room temperature in 24 h to avoid cracks due to thermal stress. The ingot can
321
easily slide out from ampoule, indicating that the raw material does not contain oxidation
322
impurities which can react with the silica ampoule. Warning: Due to the toxicity of Tl, great care
323
should be exerted with appropriate protective equipment in both the synthesis and handling of Tl
324
containing precursors and TlSn2I5 single crystals.
325
Crystal Processing and Characterization. Boule was cut along the direction perpendicular to
326
the growth direction by using a diamond saw. One wafer was extracted from the tip section of
327
ingot. Subsequently, the sample was polished with silicon carbide sand paper and alumina slurries
328
with a particle size of 0.05-1 µm. After fine polishing with slurries, no further surface etching and
329
passivation were performed on the polished surface. In order to analyze phase purity of as-grown
330
crystal, PXRD pattern of ground crystals was collected using a Si-calibrated CPS 120 INEL
331
diffractometer operating at 40 kV and 20 mA (Cu Ka radiation λ=1.5418 Å). The powder XRD
332
pattern was recorded using the Windif data acquisition program. One chunk with a naturally
333
cleaved surface was selected, and then mounted onto the sample holder of PXRD instrument. The
334
XRD pattern was collected from the cleaved surface in the Si-calibrated CPS 120 INEL
335
diffractometer as well. The orientation of a naturally cleaved surface of the crystal was directly
13
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 14 of 20
336
determined by XRD to be the (00l) direction, indicating that [Sn2I5]- layers are parallel to the
337
growth direction.
338
Single Crystal X-ray diffraction. Single-crystal X-ray diffraction was performed at 298(2) K
339
with a Stoe imageplate diffraction system (IPDS) II diffractometer using graphite-monochromated
340
Mo Kα radiation (λ = 0.71073 Å). Data reduction and numerical absorption corrections were done
341
on the structures using Stoe X-Area software. Structures were solved by direct methods and
342
refined by full-matrix least-squares on F2 (all data) using the SHELXTL software suite.56 Thermal
343
displacement parameters were refined anisotropically for all atomic positions.
344
Thermal Analysis. To assess the thermal stability of TlSn2I5, differential thermal analysis (DTA)
345
was performed using a Shimadzu DTA-50 thermogravimetric analyzer. Ground crystalline
346
material (∼30 mg) was flame sealed in a silica ampoule evacuated to 10−4 mbar. As a reference, a
347
similarly sealed ampoule of ∼30 mg of Al2O3 was used. Samples were heated to ~400 °C at
348
5 °C/min and then cooled at 5 °C/min to ~20 °C.
349
Mechanical Property Assessment. The Vickers hardness tests were performed on a Struers
350
Duramin 5 automated micro hardness test instrument. The Vickers hardness test method comprises
351
of indenting the test material with a diamond indenter, in the form of a right pyramid with a square
352
base and an angle of 136 degrees between opposite faces subjected to a load of 0.01 kgf. The full
353
load is applied on the surface of fine polished wafer for 5 s. The two diagonals of the indentation
354
left in the surface of the material after removal of the load are measured using a built-in
355
microscope and their average is calculated (SI Figure S6). Therefore, the area of the sloping
356
surface of the indentation is estimated. As shown in Function 2, the Vickers hardness is the
357
quotient obtained by dividing the kgf load by the square mm area of indentation. భయల మ ௗమ
ଶிୗ୧୬
358
= ܸܪ
359
F is the load in kgf, and d is the arithmetic mean of the two diagonals, d1 and d2 in mm. Three
360
indents from different locations were obtained for measurements.
(2)
361
Optical Properties Measurements. Solid-state diffuse reflectance UV-vis-Near IR
362
spectroscopy was performed with a Shimadzu UV-3600PC double-beam, double-monochromator
363
spectrophotometer operating in the 200-2500 nm region using BaSO4 as the 100% reflectance
364
reference. 14
ACS Paragon Plus Environment
Page 15 of 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
365
Band Structure Calculations. First-principles electronic structure calculations were carried out
366
within the density functional theory formalism using the Projector Augmented Wave method57
367
implemented in Vienna Ab-initio Simulation Package58-59. The energy cut off for plane wave basis
368
was set to 350 eV and 7×7×7 k-point mesh was chosen for Brillouin zone (BZ) sampling. For
369
exchange-correlation function, the generalized gradient approximation (GGA) was employed
370
within Perdew-Burke-Ernzerhof (PBE) formalism60.
371
Device fabrication and X-ray Photocurrent Measurements. The sample was mounted on
372
1-square inch glass substrate. The contacts were fabricated by applying fast-dry carbon paint
373
purchased from TED Pella. The diameter of the electrode on the top of sample is around 2 mm,
374
while the whole area of the bottom of sample was covered by the fast-dry carbon paint for bottom
375
electrode parallel to the top electrode. Cu wires were attached to the contacts made by carbon
376
paint, and then attached to Cu foil attached to the glass substrate. The thicknesses of device is
377
around 1.0 mm, and the area is about 5 mm×9 mm. The DC I-V measurements under dark were
378
performed. DC conductivity was measured using a Keithley 6517B electrometer and a Keithley
379
6105 resistivity adapter. Electromagnetic interface and photoconductive responses are eliminated
380
by an enclosure. In order to estimate mobility-lifetime products for carriers, photocurrent
381
measurements were performed using 22 keV Ag X-ray as irradiation source. Ag X-ray was
382
generated from a Si-calibrated CPS 120 INEL diffractometer operating at 40 kV and 2 mA. The
383
single-carrier Hecht equation was adopted to determine the mobility-lifetime product for electrons
384
40
385
=ܫ
386
, Where I0 is the saturated photocurrent, and L (0.1 cm) is the thickness of detector.
387
, based on X-ray photocurrent measurements. The single-carrier Hecht equation is ூబ ఓఛ మ
ቆ1 − ݁
ಽమ ഋഓೇ
ି
ቇ
(3)
Hard radiation spectroscopy measurements. 122 keV γ-ray spectroscopy measurements were 57
388
carried out in the atmosphere and the distance between
Co radiation source (0.2 mCi) and
389
detector was set to ~5 cm. The fabricated device was connected to an eV-550 preamplifier box.
390
Various bias voltages from 100 to 700 V were applied. The signals were transferred to an ORTEC
391
amplifier (Model 572A) with a gain of 500, shaping time of 0.5 µs and collection time of 180 s
392
before it is evaluated by a dual 16 K input multichannel analyzer (Model ASPEC-927) and read
393
into the MAESTRO-32 software. The linear amplifier gain, amplifier shaping time and the 15
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 16 of 20
241
394
recorded time are 500, 0.5 µs and 180 s, respectively. An un-collimated
395
used to characterize the detector radiation response upon 5.5 MeV alpha particles. The activity of
396
the alpha source was around 1.0 µCi. The measurements were carried out also in the atmosphere
397
with a source-detector distance of ~4 mm. The linear amplifier gain, amplifier shaping time and
398
the recorded time are 100, 2.0 µs and 500 s, respectively. The single-carrier Hecht equation was
399
adopted to determine the mobility-lifetime product for electrons as well40, based on γ-ray
400
spectroscopy measurements. The single-carrier Hecht equation is
401
= )ܸ(ܧܥܥ
402
, where CCE(V) is the charge collection efficiency at certain bias applied, Ch(V) is the peak
403
channel number at certain bias applied, and L (0.1 cm) is the thickness of detector. The µeτe and the
404
constant can be derived from the experimental data of CCE(V) and Ch(V). Since there is no
405
photopeak in the spectra, the maximum channel positions instead of peak channel numbers were
406
used to fit the single-carrier Hecht equation.
()
େ୭୬ୱ୲ୟ୬୲
=
ఓఛ మ
ቆ1 − ݁
ಽమ ഋഓೇ
ି
Am alpha source was
ቇ
(4)
407 408
Supporting Information
409
The Supporting Information is available (X-ray data, Vickers hardness measurements).
410 411
AUTHOR INFORMATION
412
Corresponding Author
413
*E-mail:
[email protected] 414
Author contributions
415
M. K. conceived and supervised the project. W. L. conceived and conducted experiments on
416
synthesis, crystal growth and characterization, detector fabrication, charge transport, detection
417
performance and mobility estimation. C. S. solved and refined crystal structure. Z. L. conducted
418
experiments on detection performance. O.Y. K. conducted calculations on electronic band
419
structure. S. D conducted optical measurements. Y. H. conducted hardness tests. C. M. helped with
420
I-V measurements. H. C conducted DTA measurement. B. W conceived and supervised the charge
421
transport measurements in the project.
422 16
ACS Paragon Plus Environment
Page 17 of 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
423
Notes
424
The authors declare no competing financial interests.
425 426
ACKNOWLEDGMENTS
427
This work is supported by a Department of Energy NNSA grant (DE-NA0002522). O.Y.K. is
428
supported by DHS-ARI grant 2014-DN-077-ARI086-01 (theoretical calculations). This work
429
made use of the EPIC facility of the NUANCE Center and IMSERC at Northwestern University,
430
which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE)
431
Resource (NSF NNCI-1542205). Computing resources were provided by the National Energy
432
Research Scientific Computing Center, a DOE Office of Science User Facility supported by the
433
Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
434 435
REFERENCES
436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460
1.
Pani, R.; Pellegrini, R.; Cinti, M. N.; Bennati, P.; Betti, M.; Vittorini, F.; Mattioli, M.; Trotta, G.;
Cencelli, V. O.; Scafe, R.; Montani, L.; Navarria, F.; Bollini, D.; Baldazzi, G.; Moschini, G.; Rossi, P.; de Notaristefani, F. LaBr3:Ce crystal: The latest advance for scintillation cameras. Nucl. Instrum. Meth. A 2007, 572, 268-269. 2.
Owens, A.; Peacock, A. Compound semiconductor radiation detectors. Nucl. Instrum. Meth. A
2004, 531, 18-37. 3.
Owens, A.; Peacock, A.; Bavdaz, M. Progress in compound semiconductors. P. Soc. Photo-Opt
Ins. 2003, 4851, 1059-1070. 4.
McGregor, D. S.; Hermon, H. Room-temperature compound semiconductor radiation detectors.
Nucl. Instrum. Meth. A 1997, 395, 101-124. 5.
Zhang, F.; He, Z.; Seifert, C. E. A prototype three-dimensional position, sensitive CdZnTe detector
array. IEEE T. Nucl. Sci. 2007, 54, 843-848. 6.
Szeles, C. Advances in the crystal growth and device fabrication technology of CdZnTe room
temperature radiation detectors. IEEE T. Nucl. Sci. 2004, 51, 1242-1249. 7.
Milbrath, B. D.; Peurrung, A. J.; Bliss, M.; Weber, W. J. Radiation detector materials: An
overview. J. Mater. Res. 2008, 23, 2561-2581. 8.
Churilov, A. V.; Ciampi, G.; Kim, H.; Cirignano, L. J.; Higgins, W. M.; Olschner, F.; Shah, K. S.
Thallium bromide nuclear radiation detector development. IEEE T. Nucl. Sci. 2009, 56, 1875-1881. 9.
Churilov, A. V.; Ciampi, G.; Kim, H.; Higgins, W. M.; Cirignano, L. J.; Olschner, F.; Biteman, V.;
Minchello, M.; Shah, K. S. TlBr and TlBrxI1-x crystals for gamma-ray detectors. J. Cryst. Growth 2010, 312, 1221-1227. 10. Churilov, A. V.; Higgins, W. M.; Ciampi, G.; Kim, H.; Cirignano, L. J.; Olschner, F.; Shah, K. S. Purification, crystal growth and detector performance of TlBr. Hard X-Ray, Gamma-Ray, and Neutron Detector Physics X 2008, 7079, 79790K1-79790K8. 11. Kim, H.; Cirignano, L.; Churilov, A.; Ciampi, G.; Higgins, W.; Olschner, F.; Shah, K. Developing 17
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504
Page 18 of 20
larger TlBr detectors-detector performance. IEEE T. Nucl. Sci. 2009, 56, 819-823. 12. Hitomi, K.; Shoji, T.; Ishii, K. Advances in TlBr detector development. J. Cryst. Growth 2013, 379, 93-98. 13. Li, W. T.; Li, Z. H.; Zhu, S. F.; Yin, S. J.; Zhao, B. J.; Chen, G. X. Improved method for HgI2 crystal growth and detector fabrication. Nucl. Instrum. Meth. A 1996, 370, 435-437. 14. Hayashi, T.; Kinpara, M.; Wang, J. F.; Mimura, K.; Isshiki, M. Growth of PbI2 single crystals from stoichiometric and Pb excess melts. J. Cryst. Growth 2008, 310, 47-50. 15. He, Y.; Zhu, S. F.; Zhao, B. J.; Jin, Y. R.; He, Z. Y.; Chen, B. J. Improved growth of PbI2 single crystals. J. Cryst. Growth. 2007, 300, 448-451. 16. Stoumpos, C. C.; Kanatzidis, M. G. Halide perovskites: poor man's high-performance semiconductors. Adv. Mater. 2016, 28 , 5778-5793. 17. Stoumpos, C. C.; Malliakas, C. D.; Peters, J. A.; Liu, Z.; Sebastian, M.; Im, J.; Chasapis, T. C.; Wibowo, A. C.; Chung, D. Y.; Freeman, A. J.; Wessels, B. W.; Kanatzidis, M. G. Crystal growth of the perovskite semiconductor CsPbBr3: a new material for high-energy radiation detection. Cryst. Growth Des. 2013, 13, 2722-2727. 18. Wei, H. T.; Fang, Y. J.; Mulligan, P.; Chuirazzi, W.; Fang, H. H.; Wang, C. C.; Ecker, B. R.; Gao, Y. L.; Loi, M. A.; Cao, L.; Huang, J. S. Sensitive X-ray detectors made of methylammonium lead tribromide perovskite single crystals. Nat. Photonics 2016, 10, 333-339. 19. Yakunin, S.; Dirin, D. N.; Shynkarenko, Y.; Morad, V.; Cherniukh, I.; Nazarenko, O.; Kreil, D.; Nauser, T.; Kovalenko, M. V. Detection of gamma photons using solution-grown single crystals of hybrid lead halide perovskites. Nat. Photon 2016, 10, 585-589. 20. Dong, Q.; Fang, Y.; Shao, Y.; Mulligan, P.; Qiu, J.; Cao, L.; Huang, J. Electron-hole diffusion lengths >175 µm in solution-grown CH3NH3PbI3 single crystals. Science 2015, 347, 967-970. 21. Shi, D.; Adinolfi, V.; Comin, R.; Yuan, M.; Alarousu, E.; Buin, A.; Chen, Y.; Hoogland, S.; Rothenberger, A.; Katsiev, K.; Losovyj, Y.; Zhang, X.; Dowben, P. A.; Mohammed, O. F.; Sargent, E. H.; Bakr, O. M. Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals. Science 2015, 347, 519-522. 22. Nafradi, B.; Nafradi, G.; Forro, L.; Horvath, E. Methylammonium lead iodide for efficient x-ray energy conversion. J. Phys. Chem. C 2015, 119, 25204-25208. 23. Yakunin, S.; Sytnyk, M.; Kriegner, D.; Shrestha, S.; Richter, M.; Matt, G. J.; Azimi, H.; Brabec, C. J.; Stangl, J.; Kovalenko, M. V.; Heiss, W. Detection of X-ray photons by solution-processed lead halide perovskites. Nat. Photon 2015, 9, 444-449. 24. Stoumpos, C. C.; Malliakas, C. D.; Kanatzidis, M. G. Semiconducting tin and lead iodide perovskites with organic cations: phase transitions, high mobilities, and near-infrared photoluminescent properties. Inorg. Chem. 2013, 52, 9019-9038. 25. Seltzer, S. M. Calculation of photon mass energy-transfer and mass energy-absorption coefficients. Radiat. Res. 1993, 136, 147-170. 26. Beck, H. P.; Clicque, G.; Nau, H. A study on AB2X5 compounds (A:K, In, Tl; B:Sr, Sn, Pb; X:Cl, Br, I). Z. Anorg. Allg. Chem. 1986, 536, 35-44. 27. Stowe, K.; Beck, H. P. Redetermination of the phase-diagram TlI-SnI2. Z. Anorg. Allg. Chem. 1992, 608, 119-122. 28. Bridgman, P. W. Certain physical properties of single crystals of tungsten, antimony, bismuth, tellurium, cadmium, zinc, and tin. Proc. Am. Acad. Arts. Sci. 1925, 60, 305-383. 29. Alig, R. C.; Bloom, S. Electron-hole-pair creation energies in semiconductors. Physical Review 18
ACS Paragon Plus Environment
Page 19 of 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548
Letters 1975, 35, 1522-1525. 30. Alig, R. C.; Bloom, S.; Struck, C. W. Electron-hole-pair creation energies in semiconductors. B Am. Phys. Soc. 1980, 25, 175-175. 31. Ozawa, L.; Hersh, H. N. Creation energy of electron-hole pairs in luminescent semiconductors. J. Electrochem. Soc. 1976, 123, C258-C258. 32. Tuller, H. L.; Bishop, S. R. Point defects in oxides: tailoring materials through defect engineering. Annu. Rev. Mater. Res. 2011, 41, 369-398. 33. R., R. H. P. Zinnhalogenverbindungen. II. Die Molekül- und Kristallstrukturen von Zinn(IV)-bromid und -iodid. Z. Kristallogr. 2009, 216, 34-38. 34. Stoumpos, C. C.; Kanatzidis, M. G. The renaissance of halide perovskites and their evolution as emerging semiconductors. Accounts Chem. Res. 2015, 48, 2791-2802. 35. Hommerich, U.; Nyein, E. E.; Trivedi, S. B. Crystal growth, upconversion, and infrared emission properties of Er3+-doped KPb2Br5. J. Lumin. 2005, 113, 100-108. 36. Tarasova, A. Y.; Isaenko, L. I.; Kesler, V. G.; Pashkov, V. M.; Yelisseyev, A. P.; Denysyuk, N. M.; Khyzhun, O. Y. Electronic structure and fundamental absorption edges of KPb2Br5, K0.5Rb0.5Pb2Br5, and RbPb2Br5 single crystals. J. Phys. Chem. Solids 2012, 73, 674-682. 37. Rademaker, K.; Payne, S. A.; Huber, G.; Isaenko, L. I.; Osiac, E. Optical pump-probe processes in Nd3+-doped KPb2Br5, RbPb2Br5, and KPb2Cl5. J. Opt. Soc. Am. B 2005, 22, 2610-2618. 38. Pfister, D.; Schäfer, K.; Ott, C.; Gerke, B.; Pöttgen, R.; Janka, O.; Baumgartner, M.; Efimova, A.; Hohmann, A.; Schmidt, P.; Venkatachalam, S.; van Wüllen, L.; Schürmann, U.; Kienle, L.; Duppel, V.; Parzinger, E.; Miller, B.; Becker, J.; Holleitner, A.; Weihrich, R.; Nilges, T. Inorganic double helices in semiconducting SnIP. Adv. Mater. 2016, 28, 9783-9791. 39. Leijtens, T.; Eperon, G. E.; Noel, N. K.; Habisreutinger, S. N.; Petrozza, A.; Snaith, H. J. S Stability of metal halide perovskite solar cells. Adv. Energy Mater. 2015, 5, 1500963. 40. Hecht, K. Zum Mechanismus des lichtelektrischen primärstromes in isolierenden kristallen. Z. Phys. 1932, 77, 235-245. 41. Bale, D. S.; Szeles, C. Nature of polarization in wide-bandgap semiconductor detectors under high-flux irradiation: Application to semi-insulating Cd1-xZnxTe. Phys. Rev. B 2008, 77, 035205. 42. Erickson, J. C.; Yao, H. W.; James, R. B.; Hermon, H.; Greaves, M. Time of flight experimental studies of CdZnTe radiation detectors. J. Electron Mater. 2000, 29, 699-703. 43. Androulakis, J.; Peter, S. C.; Li, H.; Malliakas, C. D.; Peters, J. A.; Liu, Z. F.; Wessels, B. W.; Song, J. H.; Jin, H.; Freeman, A. J.; Kanatzidis, M. G., Dimensional reduction: a design tool for new radiation detection materials. Adv. Mater. 2011, 23, 4163-4167. 44. Li, H.; Malliakas, C. D.; Liu, Z. F.; Peters, J. A.; Sebastian, M.; Zhao, L. D.; Chung, D. Y.; Wessels, B. W.; Kanatzidis, M. G., Investigation of semi-insulating Cs2Hg6S7 and Cs2Hg6-xCdxS7 alloy for hard radiation detection. Cryst. Growth & Des. 2014, 14, 5949-5956. 45. Li, H.; Malliakas, C. D.; Peters, J. A.; Liu, Z. F.; Im, J.; Jin, H.; Morris, C. D.; Zhao, L. D.; Wessels, B. W.; Freeman, A. J.; Kanatzidis, M. G., CsCdInQ(3) (Q = Se, Te): new photoconductive compounds as potential materials for hard radiation detection. Chem. Mater. 2013, 25, 2089-2099. 46. Liu, Z.; Peters, J. A.; Sebastian, M.; Kanatzidis, M. G.; Im, J.; Freeman, A. J.; Wessels, B. W., Photo-induced current transient spectroscopy of single crystal Tl6I4Se. Semicond Sci. Tech. 2014, 29, 115002. 47. Morris, C. D.; Li, H.; Jin, H.; Malliakas, C. D.; Peters, J. A.; Trikalitis, P. N.; Freeman, A. J.; Wessels, B. W.; Kanatzidis, M. G., Cs(2)M(II)M(3)(IV)Q(8) (Q=S, Se, Te): an extensive family of 19
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580
Page 20 of 20
layered semiconductors with diverse band gaps. Chem. Mater. 2013, 25, 3344-3356. 48. Nguyen, S. L.; Malliakas, C. D.; Peters, J. A.; Liu, Z. F.; Im, J.; Zhao, L. D.; Sebastian, M.; Jin, H.; Li, H.; Johnsen, S.; Wessels, B. W.; Freeman, A. J.; Kanatzidis, M. G., Photoconductivity in Tl6SI4: a novel semiconductor for hard radiation detection. Chem. Mater. 2013, 25, 2868-2877. 49. Wang, P. L.; Kostina, S. S.; Meng, F.; Kontsevoi, O. Y.; Liu, Z. F.; Chen, P.; Peters, J. A.; Hanson, M.; He, Y. H.; Chung, D. Y.; Freeman, A. J.; Wessels, B. W.; Kanatzidis, M. G., Refined synthesis and crystal growth of Pb2P2Se6 for hard radiation detectors. Cryst. Growth & Des. 2016, 16, 5100-5109. 50. Wang, P. L.; Liu, Z. F.; Chen, P.; Peters, J. A.; Tan, G. J.; Im, J.; Lin, W. W.; Freeman, A. J.; Wessels, B. W.; Kanatzidis, M. G., Hard radiation detection from the selenophosphate Pb2P2Se6. Adv. Funct. Mater. 2015, 25, 4874-4881. 51. Wang, S. C.; Liu, Z. F.; Peters, J. A.; Sebastian, M.; Nguyen, S. L.; Malliakas, C. D.; Stoumpos, C. C.; Im, J.; Freeman, A. J.; Wessels, B. W.; Kanatzidis, M. G., Crystal growth of Tl4Cdl6: a wide band gap semiconductor for hard radiation detection. Cryst. Growth & Des. 2014, 14, 2401-2410. 52. Wibowo, A. C.; Malliakas, C. D.; Liu, Z. F.; Peters, J. A.; Sebastian, M.; Chung, D. Y.; Wessels, B. W.; Kanatzidis, M. G., Photoconductivity in the chalcohalide semiconductor, SbSeI: a new candidate for hard radiation detection. Inorg. Chem. 2013, 52, 7045-7050. 53. Das, S.; Peters, J. A.; Lin, W.; Kostina, S. S.; Chen, P.; Kim, J.-I.; Kanatzidis, M. G.; Wessels, B. W., Charge transport and observation of persistent photoconductivity in Tl6SeI4 single crystals. J. Phys. Chem. Lett. 2017, 8, 1538-1544. 54. Kostina, S. S.; Peters, J. A.; Lin, W.; Chen, P.; Liu, Z.; Wang, P. L.; Kanatzidis, M. G.; Wessels, B. W., Photoluminescence fatigue and inhomogeneous line broadening in semi-insulating Tl6SeI4 single crystals. Semicond Sci. Tech. 2016, 31, 065009. 55. Shi, H.; Lin, W.; Kanatzidis, M. G.; Szeles, C.; Du, M.-H., Impurity-induced deep centers in Tl6SI4. J. Appl. Phys. 2017, 121, 145102. 56. Sheldrick, G. A short history of SHELX. Acta Crystallogr. Sect. A 2008, 64, 112-122. 57. Blöchl, P. E. Projector augmented-wave method. Physical Review B 1994, 50, 17953-17979. 58. Kresse,
G.;
Hafner,
J.
Ab
initio
molecular-dynamics
simulation
of
the
liquid-metal-amorphous-semiconductor transition in germanium. Phys. Rev. B 1994, 49, 14251-14269. 59. Kresse, G.; Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 1996, 54, 11169-11186. 60. Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 1996, 77, 3865-3868.
581
20
ACS Paragon Plus Environment
