GaN Tunnel Junction Nanowire White-Light

Subscriber access provided by UNIV OF NEBRASKA - LINCOLN

Communication

Alternating-current InGaN/GaN tunnel junction nanowire white-light emitting diodes Sharif Md. Sadaf, Yong-Ho Ra, Hieu Pham Trung Nguyen, Mehrdad Djavid, and Zetian Mi Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.5b02515 • Publication Date (Web): 18 Sep 2015 Downloaded from http://pubs.acs.org on September 21, 2015

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.

Nano Letters 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 25

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

Nano Letters

1

Alternating-current InGaN/GaN tunnel junction nanowire

2

white-light emitting diodes

3 4 5

S. M. Sadaf, Y.-H. Ra, H. P. T. Nguyen, M. Djavid, and Z. Mi*

6

Department of Electrical and Computer Engineering, McGill University, 3480 University Street,

7

Montreal, Quebec H3A 0E9, Canada

8

*

: E-mail: [email protected]; Phone: 1 514 398 7114

9 10 11 12

1 ACS Paragon Plus Environment

Nano Letters

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

13

Table of Contents Graphic

14 15 16 17

18 19 20 21 22 23 24 25


Page 2 of 25

Page 3 of 25

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

26

Nano Letters

ABSTRACT

27 28

The current LED lighting technology relies on the use of a driver to convert alternating current

29

(AC) to low-voltage direct current (DC) power, a resistive p-GaN contact layer to inject positive

30

charge carriers (holes) for blue light emission, and rare-earth doped phosphors to down-convert blue

31

photons into green/red light, which have been identified as some of the major factors limiting the

32

device efficiency, light quality, and cost. Here, we show that multiple-active region phosphor-free

33

InGaN nanowire white LEDs connected through a polarization engineered tunnel junction can

34

fundamentally address the afore-described challenges. Such a p-GaN contact-free LED offers the

35

benefit of carrier regeneration, leading to enhanced light intensity and reduced efficiency droop.

36

Moreover, through the monolithic integration of p-GaN up and p-GaN down nanowire LED

37

structures on the same substrate, we have demonstrated, for the first time, AC operated LEDs on a Si

38

platform, which can operate efficiently in both polarity (positive and negative) of applied voltage.

39 40

Key words: Nanowire, quantum dot, GaN, light emitting diode, tunnel junction, AC LED

41 42


Nano Letters

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 25

43

Compared to the conventional inefficient incandescent and fluorescent lighting technologies,

44

LED light bulbs can, in principle, operate at an efficiency level of 100%. The current LED lighting

45

technology, however, is not even close to reach this limit, which has been limited by several factors.

46

First, the current LED lamps still rely on the use of phosphors to down-convert blue light into green

47

and red light. Associated with this down-conversion process is an energy loss of ~30%, or more.

48

Second, the performance of GaN-based LEDs has been limited by the inefficient current conduction

49

of p-GaN, which typically has a resistance ~ 100 times higher than that of n-GaN1, leading to poor

50

current spreading2, 3, reduced efficiency, and efficiency droop. Third, unlike conventional light bulbs,

51

LEDs are low voltage devices and cannot operate on an alternating current voltage. As a consequence,

52

an electrical circuit is required to convert AC power to low-voltage DC power (typically 2-4V)4, 5.

53

Such a driver adds a significant level of complexity, cost, and efficiency loss to the LED devices and

54

systems.

55

These critical challenges can be potentially addressed by employing the scheme of tunnel

56

junction and the integration with nanowire LED structures. Since the first demonstration by Esaki in

57

19586, tunnel diodes and their integration with a vast number of electronic and photonic devices have

58

been extensively studied. With the use of tunnel junction, the resistive p-GaN contact layer can be

59

replaced by an n-GaN contact, leading to significantly reduced device resistance3, 7-10, voltage loss,

60

and heating effect11, 12. Tunnel junction also enables the stacking of multiple p-n junctions/LEDs7, 11,

61

13-16

62

operation can be achieved at low injection current, leading to enhanced efficiency18 and reduced

63

efficiency

64

GaN/InGaN/GaN1, 2, 21-25, and GaN/GdN/GaN11, 26 tunnel junctions have been implemented in GaN-

65

based LED structures. However, the tunneling probability has been severely limited by the difficulty

66

in creating a highly doped p-region.8,

, providing the unique opportunity of repeated carrier usage11,

droop18,

19

.

Various

design

22, 23

schemes,

including

12, 17

. As such, high power

GaN/Al(Ga)N/GaN8-10,

20

,

Recently, it has been demonstrated that dopant 4

ACS Paragon Plus Environment

Page 5 of 25

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

Nano Letters

67

incorporation can be significantly enhanced in nanowire structures, due to the much reduced

68

formation energy in the near-surface region27-29. Moreover, compared to conventional GaN quantum

69

well devices, GaN nanowire LEDs can exhibit significantly reduced dislocation densities and

70

polarization fields.30-35 Nanowire LEDs with tunable, multi-color emission have been demonstrated,

71

which can be epitaxially grown on extremely low cost, large area Si substrates.31, 36-43 In spite of these

72

intensive studies, the incorporation of tunnel junction in nanowire LEDs has not been reported to our

73

knowledge.

74

In this context, we have investigated the incorporation of GaN/InGaN/GaN polarization-

75

enhanced tunnel junction in nearly defect-free InGaN/GaN phosphor-free nanowire white LED

76

heterostructures. We have demonstrated, for the first time, p-contact free InGaN/GaN nanowire

77

LEDs. With the use of tunnel junction interconnect, we have shown that multi-junction phosphor-free

78

nanowire LEDs can exhibit improved light intensity and reduced efficiency droop. Due to the

79

repeated carrier usage, such devices operate at low current and high voltage. Moreover, through the

80

monolithic integration of p-GaN up and p-GaN down nanowire LED structures on the same substrate,

81

we have demonstrated, for the first time, AC LEDs on a Si platform, which can operate efficiently in

82

both positive and negative polarity of applied voltage. This work offers a new avenue for realizing

83

high efficiency LEDs that can operate under a large range of voltage biasing conditions and can

84

possibly eliminate, or greatly simplify the electrical driver required in today’s LED lighting systems.

85

Schematically shown in Figure 1a, we have first studied four types of nanowire LEDs,

86

including a conventional InGaN/GaN dot-in-a-wire p-GaN up LED (LED A), single active region

87

(SAR) (n=1) tunnel junction dot-in-a-wire p-GaN down LED (LED B), and multiple-active region

88

(MAR) (n=3) tunnel junction dot-in-a-wire LEDs (LEDs C and D). The device active region consists

89

of multiple InGaN/GaN quantum dots. Each InGaN quantum dot has a height of ~3 nm and is capped

90

by ~3 nm GaN layer. Self-organized InGaN/GaN dot-in-a-wire LED heterostructures were grown on 5 ACS Paragon Plus Environment

Nano Letters

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 25

91

n-Si (111) substrates by radio frequency plasma-assisted molecular beam epitaxy (MBE) under

92

nitrogen rich conditions. The substrate surface oxide was desorbed in situ at 770 oC. The growth

93

conditions for Si-doped GaN nanowires included a growth temperature of 750 oC, nitrogen flow rate

94

of 1.0 standard cubic centimeter per minute (sccm), forward plasma power of 350 W, and Ga beam

95

equivalent pressure of 6×10-8 Torr. The InGaN quantum dots were grown at relatively low

96

temperatures (~650 oC) to enhance the In incorporation into the dots. Each quantum dot layer was

97

subsequently capped by a GaN layer of ~3 nm. In this experiment, 10 InGaN/GaN quantum dots were

98

incorporated in each GaN nanowire for SAR devices, and 5 InGaN/GaN quantum dots were

99

incorporated for MAR tunnel junction devices. During the growth of tunnel junction region, the

100

substrate temperature was reduced to 650 oC. Each active region of LED C is nearly identical to that

101

of LEDs A and B, with peak emission at ~ 540 nm. The multiple active regions of LED D are

102

designed to emit at blue (~ 450 nm), green (~ 550 nm), and red (~ 620 nm) spectral range,

103

respectively, thereby leading to phosphor-free white light emission. In order to compare the intrinsic

104

performance of these devices, no electron blocking layer was incorporated in the device active region.

105

The GaN/InGaN/GaN tunnel junction consists of ~12 nm Si-doped GaN (ND~5×1019 cm-3), 3 nm

106

InGaN with In concentration of ~32% and 20 nm Mg-doped GaN (NA~1×1020 cm-3). The doping

107

together with In concentration and thickness were carefully optimized to maximize tunneling

108

efficiency. The large area nanowire LED device is schematically shown in Figure 1b.

109

Shown in Figure 1c, electrons from the valence band of p-GaN tunnel into conduction band of

110

n-GaN, and, as such, holes are injected into p-GaN and also into the device active region (quantum

111

dots). The use of tunnel junction increases the concentration of holes in the p-GaN, thereby

112

minimizing the restriction of low hole injection efficiency in wide bandgap nitride materials. The

113

injected holes recombine with injected electrons from n-GaN in the active region to give rise to

114

efficient photon emission. This process repeats itself through the rest of the tunnel junctions and 6 ACS Paragon Plus Environment

Page 7 of 25

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

Nano Letters

115

stacked active regions. Consequently, a single electron injection can lead to multiple photon emission

116

in LEDs C and D, due to the repeated carrier regeneration in each tunnel junction. The output power,

117

energy band diagram, and electron and hole distributions of the tunnel junction integrated dot-in-a-

118

wire LEDs were numerically calculated using the APSYS simulation software (see Supplementary

119

Figure S1).

120

The nanowires are of wurtzite crystal structure and possess N-polarity44-46. The MAR tunnel

121

junction LEDs were epitaxially grown by stacking the multiple active regions with tunnel junction

122

interconnects. The dot-in-a-wire LEDs exhibit excellent structural properties. Shown in Figure 2a is

123

the scanning electron microscopy (SEM) image of the nanowire structures for LED C. The nanowire

124

diameters are in the range of 150 nm (See Supplementary Figure S2 for SEM images of LED A and

125

LED B). A 405 nm laser was used as the excitation source for the photoluminescence (PL)

126

measurement of the nanowire heterostructures. Figure 2b illustrates the normalized PL spectra of

127

LED C measured at room temperature, which is nearly identical to that measured from LEDs A and

128

B. The peak at ~550 nm is related to the emission from the quantum dot active region; there are no

129

noticeable additional peaks from the tunnel junctions. PL spectrum of LED D is also shown in the

130

figure for comparison. The broad spectral linewidth (white-light emission) of LED D is due to the

131

stacking of multiple active regions with different emission colors (indicated by the arrows in Figure

132

2b).

133

Structural properties of the tunnel junction LED heterostructures were characterized by

134

scanning transmission electron microscopy (STEM), high angle annular dark field (HAADF) and

135

energy dispersive X-ray spectrometry (EDXS) analysis. JEOL JEM-2100F equipped with a field

136

emission gun with an accelerating voltage of 200 kV was used to obtain bright-field TEM images.

137

For STEM and STEM-HAADF imaging, the same equipment with a cold field emission emitter

138

operated at 200 kV and with an electron beam diameter of approximately 0.1 nm was used. The Ga 7 ACS Paragon Plus Environment

Nano Letters

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 25

139

and In Lα lines were used for the EDXS microanalysis. Figure 2c shows the HAADF of the MAR

140

tunnel junction nanowire structure (LED C). The presence of multiple quantum dot active regions can

141

be clearly identified. No noticeable extended defects or misfit dislocations were observed. It is seen

142

that multiple InGaN/GaN quantum dots are positioned in the center of the nanowires, due to the

143

strain-induced self-organization36,44. The InGaN thickness is ~ 3 nm in each tunnel junction, shown in

144

Figure 2d. To further confirm compositional variations of the tunnel junction and active region,

145

EDXS analysis was performed. The signal variations of Ga, In, and N across different tunnel

146

junctions and the quantum dot active region along the growth direction of LED C are displayed in the

147

lower panel of Figure 2d. Clear In peaks reveals the existence of the InGaN layer in each tunnel

148

junction. Also we observed regular peaks and dips of In and Ga throughout the quantum dot region.

149

The EDXS elemental mapping image of the tunnel junction region, illustrated in Figure 2e, further

150

provides unambiguous evidence for the presence of GaN/InGaN/GaN tunnel junction.

151

The nanowire LED fabrication process included the following steps. First, a polyimide resist

152

layer was spin-coated to fully cover the nanowires, followed by O2 plasma etching to expose the

153

nanowire top surface. Thin Ni (8 nm)/Au (8 nm) and Ti (20 nm)/Au (120nm) metal layers were then

154

deposited on the nanowire surface and the backside of the Si substrates to serve as p- and n-metal

155

contacts, respectively. For the tunnel junction LEDs, thin Ti (8 nm)/Au (8 nm) was deposited on the

156

nanowire top surface to serve as the n-metal contact. Subsequently, a 150 nm indium tin oxide (ITO)

157

layer was deposited to serve as a transparent electrode and current spreading layer. The fabricated

158

devices with metal contacts were annealed at ~500 oC for 1 min in nitrogen ambient, and the

159

complete devices with ITO contacts were annealed at 300 oC for 1 hour in vacuum.

160

Figure 3a shows typical current-voltage (I-V) characteristics of the three sets of devices,

161

including conventional LED A, SAR tunnel junction LED B, and MAR (n=3) tunnel junction LED

162

(LED C). The mesa size of the measured device is 500 × 500 µm2. The turn-on voltages of the 8 ACS Paragon Plus Environment

Page 9 of 25

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

Nano Letters

163

devices approximately scale with the number of active regions (n). The measured voltage drop at 20

164

mA for LEDs A, B and C are 5.5 V, 4.9 V, and 16 V, respectively. We also modeled these tunnel

165

junction integrated SAR and MAR dot-in-a-wire LEDs. The simulation results are consistent with the

166

experimental results (Supplementary Figure S4a). Figure 3b shows the temperature-dependent I-V

167

curves for the multiple-stacked devices (LED C). There are no significant changes in the I-V

168

characteristics, further confirming that the tunnel junction interconnect functions well even at low

169

temperature. It is also worthwhile mentioning that the relatively high turn on voltage for the

170

presented single junction nanowire LEDs is partly related to the non-uniform current injection due to

171

variations of the height of the spontaneously formed nanowire arrays as well as the presence of a

172

SiNx layer at the nanowire-Si interface.47-50 Compared to LED A, LED B shows reduced turn on

173

voltage, due to the efficient hole injection with the incorporation of tunnel junction and lower contact

174

resistance for n-GaN.

175

Figure 4a shows the light intensity vs. current characteristics of the devices.

176

Electroluminescence (EL) spectra of the LEDs are shown in Supplementary Figure S3. An optical

177

image of the device is illustrated in the inset of Figure 4a, showing green light emission. Compared to

178

the reference LED A, SAR tunnel junction dot-in-a-wire LED B shows higher light intensity owing

179

to the better current spreading through the low resistant n-GaN contact, and also the improved hole

180

injection inside the dots19, 21. MAR tunnel junction dot-in-a-wire devices (LED C) shows significantly

181

enhanced light intensity compared to the SAR tunnel junction devices (LED B), due to the repeated

182

carrier regeneration at each tunnel junction and the resulting multiple opportunities for radiative

183

recombination. These measurements are consistent with the simulated results (Supplementary Figure

184

S4b). Figure 4b shows the external quantum efficiency (EQE) trend of the measured devices under

185

pulsed biasing conditions (10% duty cycle). All of the devices show efficiency droop at high

186

injection current. It is worthwhile mentioning that no electron blocking layers were incorporated in 9 ACS Paragon Plus Environment

Nano Letters

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 25

187

the device active regions.

The intriguing part of the result is that, for LED C, the current

188

corresponding to the maximum efficiency point is almost identical to LED A and LED B, suggesting

189

that MAR tunnel junction LED C can be operated at a higher output power while maintaining the

190

same level of efficiency loss of the conventional LEDs. This can be better illustrated in the variations

191

of EQE vs. input power, shown in the inset of Figure 4b. It is seen that efficiency droop occurs at

192

higher input power for LED C, compared to LEDs A and B. An output power of a few mW was

193

measured for the MAR tunnel junction LED C under an injection current of 350 mA. Recent studies

194

have shown that the output power of axial nanowire LEDs can be drastically enhanced by

195

incorporating a large band gap AlGaN shell to minimize nonradiative surface recombination and

196

increase carrier injection efficiency.37, 51

197

In general, stacking multiple quantum wells/dots in planar structures is not a suitable route to

198

realize low current, high voltage operation since it also significantly increases the densities of defects

199

and dislocations. Such issues can be fundamentally addressed in tunnel junction nanowire LED

200

structures, as demonstrated in this work. Moreover, such MAR tunnel junction nanowire LEDs can

201

be designed to operate in a broad wavelength range, leading to phosphor-free white light emission. In

202

LED D, the three interconnected active regions consist of blue, green, and red-emitting quantum dots,

203

respectively, shown in Figure 2b. The HAADF TEM image and EDXS line scan are shown in

204

Supplementary Figure S5. Figure 5a shows the EL spectra. Three distinct peaks positioned at around

205

445 nm, 570 nm, and 625 nm can be clearly measured. The resulting strong, nearly white-light

206

emission is shown in the inset of Figure 5a. No noticeable wavelength shift was measured with

207

increasing injection current. SEM image, I-V and L-I characteristics are shown in Supplementary

208

Figure S6. The device emission characteristics are illustrated in the CIE diagram, shown in Figure 5b.

209

The correlated color temperature is ∼ 3000 K. The x and y values stay nearly constant in the range of

210

0.47 and 0.49 for injection currents varying from 20 mA to 250 mA. 10 ACS Paragon Plus Environment

Page 11 of 25

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

Nano Letters

211

Schematically shown in Figure 6, we have further demonstrated, for the first time, AC LEDs

212

consisting of p-GaN up and p-GaN down tunnel junction dot-in-a-wire structures monolithically

213

grown on the same Si chip using the technique of selective area growth. This AC operated nanowire

214

LED array emits green light at positive and negative polarity of AC voltage. For the selective area

215

growth of AC nanowire LEDs, a 100 nm SiO2 was first deposited on Si substrate by plasma enhanced

216

chemical vapor deposition (PECVD). Various openings with sizes from 300 × 300 µm2 to 50 × 50

217

µm2 were then defined on SiO2/Si substrate by standard photolithography and wet etching process.

218

Conventional p-GaN up InGaN/GaN nanowire LEDs was first grown. Subsequently, the sample was

219

soaked in BOE solution to selectively remove SiO2 and also nanowires on SiO2. Prior to the second

220

growth step, a SiO2 layer was deposited onto the previously grown p-GaN up nanowire LEDs to

221

protect these nanowires. The second reverse polarity p-GaN down nanowire LEDs were then

222

selectively grown on the opening areas. Tunnel junction connects the p-GaN layer with the n-type Si

223

substrate, thereby enabling reverse polarity LED operation. The selective area growth process is

224

illustrated in Figures 6a, b, and c. SEM images of the nanowire devices grown on Si (111) substrates

225

are also shown in Figure 6d (also Supplementary Figure S7 for SEM images of p-GaN up and p-GaN

226

down AC LED devices). The electrical measurements were done with a frequency of 20-60 Hz at a

227

peak to peak voltage of 10 V using an Agilent 6812B AC power source. Shown in Figure 6e, both

228

devices emit green color under AC operation (also see the Supplementary Video). The presence of

229

discrete electroluminescence spots is directly related to the non-uniform current injection, due to

230

variations of nanowire height in the two-step selective area growth process. Highly uniform light

231

emission can be achieved by further optimizing the growth and fabrication conditions. The flickering

232

effect can be minimized by using nanowire LED arrays with nearly identical performance and by

233

operating at relatively high frequency. At a frequency of 60 Hz, these devices are almost flicker free,


Nano Letters

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 25

234

and are suited for practical applications. These devices can also be operated independently by DC

235

bias as shown in Supplementary Figure S8.

236

In summary, we have developed tunnel junction nanowire LEDs that can eliminate the use of

237

resistive p-GaN contact layers, leading to reduced voltage loss and enhanced hole injection.

238

Moreover, by using tunnel junction interconnect, we have demonstrated multiple-active-region

239

nanowire LEDs with significantly enhanced light intensity. We have also realized AC operated

240

nanowire LEDs on a Si platform. Compared to the current quantum well LEDs, the demonstrated

241

tunnel junction nanowire LED technology enables phosphor-free white emission and reduced

242

efficiency droop. Moreover, it offers extreme flexibility in the operation voltage and can completely

243

eliminate the use of an AC/DC converter required in conventional LED lighting technologies, thereby

244

leading to reduced cost and further enhanced efficiency.

245 246 247

ACKNOWLEDGMENT

248

This work was supported by the Natural Sciences and Engineering Research Council of Canada

249

(NSERC). Part of the work was performed in the Micro-fabrication Facility at McGill University.

250

Electron microscopy images and analysis were carried out at Facility for Electron Microscopy

251

Research (FEMR), McGill University. The authors would like to express special thanks to Dr. A.

252

Connie and Mr. J. Kang for CIE and AC LED measurements and also many useful discussions over

253

the course of this study. We would like to acknowledge CMC Microsystems for the provision of

254

products and services that facilitated this research, including Crosslight simulation package,

255

fabrication fund assistance using the facilities of McGill Nanotools Microfab.

256 257


Page 13 of 25

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

Nano Letters

258

SUPPORTING INFORMATION

259

Simulation of tunnel junction nanowire LED devices, simulated I-V and L-I curves of tunnel junction

260

nanowire LED devices, Figures S1−S8, supporting video. This material is available free of charge

261

via the Internet at http://pubs.acs.org.

262 263

COMPETING FINANCIAL INTEREST

264

The authors declare no competing financial interests.

265 266 267 268 269 270 271 272


Nano Letters

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 25

273

REFERENCES

274

1.

275

Kamiyama, S.; Akasaki, I. Japanese Journal of Applied Physics 2013, 52, (8S), 08JH06.

276

2.

277

113503.

278

3.

279

Letters 2001, 78, (21), 3265.

280

4.

281

Photonics Technology Letters 2009, 21, (1-4), 33-35.

282

5.

283

Y.; Yoon, E. Japanese Journal of Applied Physics 2007, 46, (No. 48), L1194-L1196.

284

6.

Esaki, L. Physical Review 1958, 109, (2), 603-604.

285

7.

M. J. Grundmann, U. K. M. Phys. Stat. Sol. (c) 2007, 4, (7), 2830–2833.

286

8.

Simon, J.; Zhang, Z.; Goodman, K.; Xing, H.; Kosel, T.; Fay, P.; Jena, D. Physical Review

287

Letters 2009, 103, (2).

288

9.

289

Y.; Du, G. Scientific Reports 2014, 4, 6322.

290

10.

291

Physics Letters 2014, 104, (5), 053507.

292

11.

Akyol, F.; Krishnamoorthy, S.; Rajan, S. Applied Physics Letters 2013, 103, (8), 081107.

293

12.

Guo, X.; Shen, G.-D.; Ji, Y.; Wang, X.-Z.; Du, J.-Y.; Zou, D.-S.; Wang, G.-H.; Gao, G.; Balk,

294

L. J.; Heiderhoff, R.; Lee, T. H.; Wang, K. L. Applied Physics Letters 2003, 82, (25), 4417.

295

13.

296

2001, 79, (16), 2532.

Kaga, M.; Morita, T.; Kuwano, Y.; Yamashita, K.; Yagi, K.; Iwaya, M.; Takeuchi, T.;

Krishnamoorthy, S.; Akyol, F.; Park, P. S.; Rajan, S. Applied Physics Letters 2013, 102, (11),

Jeon, S.-R.; Song, Y.-H.; Jang, H.-J.; Yang, G. M.; Hwang, S. W.; Son, S. J. Applied Physics

Onushkin, G. A.; Lee, Y. J.; Yang, J. J.; Kim, H. K.; Son, J. K.; Park, G. H.; Park, Y. IEEE

Cho, J.; Jung, J.; Chae, J. H.; Kim, H.; Kim, H.; Lee, J. W.; Yoon, S.; Sone, C.; Jang, T.; Park,

Zhang, K.; Liang, H.; Liu, Y.; Shen, R.; Guo, W.; Wang, D.; Xia, X.; Tao, P.; Yang, C.; Luo,

Zhang, K.; Liang, H.; Shen, R.; Wang, D.; Tao, P.; Liu, Y.; Xia, X.; Luo, Y.; Du, G. Applied

Ozden, I.; Makarona, E.; Nurmikko, A. V.; Takeuchi, T.; Krames, M. Applied Physics Letters


Page 15 of 25

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

Nano Letters

297

14.

Akyol, F.; Krishnamoorthy, S.; Zhang, Y.; Rajan, S. Applied Physics Express 2015, 8, (8),

298

082103.

299

15.

300

368.

301

16.

302

(8), 1-5.

303

17.

304

Ma, X.-Y.; Chen, L.-H. Applied Physics Letters 2001, 79, (18), 2985.

305

18.

Piprek, J. Physica Status Solidi (RRL) - Rapid Research Letters 2014, 8, (5), 424-426.

306

19.

Piprek, J. Applied Physics Letters 2014, 104, (5), 051118.

307

20.

Schubert, M. F. Physical Review B 2010, 81, (3).

308

21.

Krishnamoorthy, S.; Akyol, F.; Rajan, S. Applied Physics Letters 2014, 105, (14), 141104.

309

22.

Krishnamoorthy, S.; Nath, D. N.; Akyol, F.; Park, P. S.; Esposto, M.; Rajan, S. Applied

310

Physics Letters 2010, 97, (20), 203502.

311

23.

Krishnamoorthy, S.; Park, P. S.; Rajan, S. Applied Physics Letters 2011, 99, (23), 233504.

312

24.

Zhang, Z.-H.; Tiam Tan, S.; Kyaw, Z.; Ji, Y.; Liu, W.; Ju, Z.; Hasanov, N.; Wei Sun, X.;

313

Volkan Demir, H. Applied Physics Letters 2013, 102, (19), 193508.

314

25.

315

Physics Letters 2015, 106, (21), 213105.

316

26.

317

2013, 13, (6), 2570-5.

318

27.

319

X. D.; Shih, I.; Guo, H.; Mi, Z. Scientific Reports 2015, 5, 8332.

Shoou-Jinn Chang, W.-H. L., Chun-Ta Yu. IEEE Electron Device Letters 2015, 36, (4), 366-

Shoou-Jinn, C.; Wei-Heng, L.; Wei-Shou, C. IEEE Journal of Quantum Electronics 2015, 51,

Guo, X.; Shen, G.-D.; Wang, G.-H.; Zhu, W.-J.; Du, J.-Y.; Gao, G.; Zou, D.-S.; Chen, Y.-H.;

Connie, A. T.; Zhao, S.; Sadaf, S. M.; Shih, I.; Mi, Z.; Du, X.; Lin, J.; Jiang, H. Applied

Krishnamoorthy, S.; Kent, T. F.; Yang, J.; Park, P. S.; Myers, R. C.; Rajan, S. Nano Letters

Zhao, S.; Connie, A. T.; Dastjerdi, M. H.; Kong, X. H.; Wang, Q.; Djavid, M.; Sadaf, S.; Liu,


Nano Letters

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

320

28.

321

H.; Mi, Z. Nano Letters 2012, 12, (6), 2877-82.

322

29.

323

Letters 2013, 13, (11), 5509-13.

324

30.

Ra, Y. H.; Navamathavan, R.; Park, J. H.; Lee, C. R. Nano Letters 2013, 13, (8), 3506-16.

325

31.

Guo, W.; Zhang, M.; Banerjee, A.; Bhattacharya, P. Nano Letters 2010, 10, (9), 3355-9.

326

32.

Li, S.; Waag, A. Journal of Applied Physics 2012, 111, (7), 071101.

327

33.

Fang Qian, S. G., Yat Li, Cheng-Yen Wen, and Charles M. Lieber. Nano Letters 2005, 5,

328

(11), 2287-2291.

329

34.

330

Journal of Crystal Growth 2008, 310, (18), 4035-4045.

331

35.

332

Physical Review B 2005, 72, (8).

333

36.

334

Letters 2012, 12, (3), 1317-23.

335

37.

336

Letters 2013, 13, (11), 5437-42.

337

38.

Kishino, K.; Nagashima, K.; Yamano, K. Applied Physics Express 2013, 6, (1), 012101.

338

39.

Lin, H.-W.; Lu, Y.-J.; Chen, H.-Y.; Lee, H.-M.; Gwo, S. Applied Physics Letters 2010, 97,

339

(7), 073101.

340

40.

Kishino, K.; Ishizawa, S. Nanotechnology 2015, 26, (22), 225602.

341

41.

Naka, J.; Inose, Y.; Kunugita, H.; Ramesh, V.; Kikuchi, A.; Kishino, K.; Ema, K. Physica

342

Status Solidi (c) 2012, 9, (12), 2477-2480.

343

42.

Page 16 of 25

Zhao, S.; Fathololoumi, S.; Bevan, K. H.; Liu, D. P.; Kibria, M. G.; Li, Q.; Wang, G. T.; Guo,

Zhao, S.; Le, B. H.; Liu, D. P.; Liu, X. D.; Kibria, M. G.; Szkopek, T.; Guo, H.; Mi, Z. Nano

Ristić, J.; Calleja, E.; Fernández-Garrido, S.; Cerutti, L.; Trampert, A.; Jahn, U.; Ploog, K. H.

Ristić, J.; Rivera, C.; Calleja, E.; Fernández-Garrido, S.; Povoloskyi, M.; Di Carlo, A.

Nguyen, H. P.; Cui, K.; Zhang, S.; Djavid, M.; Korinek, A.; Botton, G. A.; Mi, Z. Nano

Nguyen, H. P.; Zhang, S.; Connie, A. T.; Kibria, M. G.; Wang, Q.; Shih, I.; Mi, Z. Nano

Armitage, R.; Tsubaki, K. Nanotechnology 2010, 21, (19), 195202. 16 ACS Paragon Plus Environment

Page 17 of 25

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

Nano Letters

344

43.

Connie, A. T.; Nguyen, H. P. T.; Sadaf, S. M.; Shih, I.; Mi, Z. Journal of Vacuum Science &

345

Technology B: Microelectronics and Nanometer Structures 2014, 32, (2), 02C113.

346

44.

347

Botton, G. A.; Shih, I.; Mi, Z. Scientific Reports 2015, 5, 7744.

348

45.

349

Brandt, O. Nano Letters 2012, 12, (12), 6119-25.

350

46.

351

84, (24).

352

47.

Park, Y.; Jahangir, S.; Park, Y.; Bhattacharya, P.; Heo, J. Opt Express 2015, 23, (11), A650-6.

353

48.

Zhao, S.; Kibria, M. G.; Wang, Q.; Nguyen, H. P.; Mi, Z. Nanoscale 2013, 5, (12), 5283-7.

354

49.

Stoica, T.; Sutter, E.; Meijers, R. J.; Debnath, R. K.; Calarco, R.; Luth, H.; Grutzmacher, D.

355

Small 2008, 4, (6), 751-4.

356

50.

357

Trampert, A.; Jahn, U.; Sánchez, G.; Griol, A.; Sánchez, B. Physica Status Solidi (b) 2007, 244, (8),

358

2816-2837.

359

51.

Nguyen, H. P. T.; Djavid, M.; Woo, S. Y.; Liu, X.; Connie, A. T.; Sadaf, S.; Wang, Q.;

Fernandez-Garrido, S.; Kong, X.; Gotschke, T.; Calarco, R.; Geelhaar, L.; Trampert, A.;

Hestroffer, K.; Leclere, C.; Bougerol, C.; Renevier, H.; Daudin, B. Physical Review B 2011,

Calleja, E.; Ristić, J.; Fernández-Garrido, S.; Cerutti, L.; Sánchez-García, M. A.; Grandal, J.;

Wang, R.; Liu, X.; Shih, I.; Mi, Z. Applied Physics Letters 2015, 106, (26), 261104.

360 361


Nano Letters

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 18 of 25

362

FIGURE CAPTIONS

363

Figure 1. Schematic and energy band diagram of tunnel junction (TJ) integrated dot-in-a-wire

364

LEDs. (a) Schematic illustration of the dot-in-a-wire LEDs, including LEDs A, B, C and

365

D. (b) Schematic illustration of the fabricated large area nanowire LEDs. (c) Simulated

366

energy band diagram of GaN/InGaN/GaN tunnel junction showing carrier regeneration

367

and injection process under reverse bias.

368

Figure 2. Structural characterization by SEM, TEM and photoluminescence. (a) A 45˚ tilted SEM

369

image of MAR TJ dot-in-a-wire LED. The scale bar denotes 1 µm. (b) Room temperature

370

photoluminescence spectra of LED C and LED D. (c) HR-TEM of MAR TJ dot-in-a-wire

371

LED structure. (d) High angle annular dark field (HAADF) image showing the MAR

372

tunnel junction dot-in-a-wire LED structure with the presence of tunnel junctions and

373

quantum dot active regions. EDXS line profile along c-axis (growth direction) showing In

374

peaks in the tunnel junctions and Ga dips and In peaks in dot region (lower panel). (e)

375

EDXS elemental mapping image of tunnel junction region showing the In, Ga, and N

376

variations. Scale bar represents 30 nm.

377

Figure 3. Current-voltage (I-V) characteristics of tunnel junction dot-in-a-wire LEDs. (a) I-V

378

characteristics of LEDs A, B, and C measured at room temperature. (b) Temperature-

379

dependent I-V characteristics of LED C.

380

Figure 4. Electroluminescence characteristics of tunnel junction dot-in-a-wire LEDs. (a) Light-

381

current (L-I) characteristics of LEDs A, B, and C. (b) Relative external quantum

382

efficiency (EQE) of LEDs A, B, and C. The inset shows the relative EQE comparison for

383

the three LEDs as a function of input power measured at room temperature.

384

Figure 5. Phosphor-free white light emission of tunnel junction MAR dot-in-a-wire LEDs. (a)

385

Electroluminescence spectra LED D measured under different injection currents. The 18 ACS Paragon Plus Environment

Page 19 of 25

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

Nano Letters

386

inset shows the device optical image. (b) Correlated color temperature (CCT) properties

387

of the device.

388

Figure 6. Alternating current tunnel junction dot-in-a-wire LED arrays. (a) Two-step selective area

389

growth of p-GaN up and p-GaN down AC nanowire LEDs on Si substrate. p-Up

390

nanowire LED arrays were first grown on the opening areas of SiOx coated Si substrate.

391

Then the SiOx and the nanowires on top were selectively removed using chemical

392

etching. The p-up nanowire LED structures were then covered with SiOx and additional

393

opening areas were created prior to the growth of the p-down nanowire LED structures.

394

Subsequently, the SiOx and the nanowires on top were selectively etched. This leads to

395

the formation of p-up and p-down nanowire LED arrays on the same Si chip. (b), (c)

396

Device schematics. (d) 45° tilted SEM images of as grown p-GaN up and p-GaN down

397

nanowire LED structures. (e) Optical image of green light emitting nanowire LED arrays

398

on Si under AC biasing conditions.

399 400 401 402 403 404 405 406 407 408 409


Nano Letters

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

410 411 412

413 414 415 416

Figure 1.

417 418


Page 20 of 25

Page 21 of 25

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

Nano Letters

419

420 421 422

Figure 2.

423 424


Nano Letters

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

425 426 427 428 429 430

431 432 433 434

Figure 3.

435

436

437

438

439

440


Page 22 of 25

Page 23 of 25

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

Nano Letters

441

442

443

444

445 446

447

Figure 4

448

449

450

451

452

453


Nano Letters

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

454

455

456

457

458 459

460

461

Figure 5

462

463

464

465


Page 24 of 25

Page 25 of 25

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

Nano Letters

466 467

Figure 6.

468 469


GaN Tunnel Junction Nanowire White-Light

Recommend Documents