Research Article www.acsami.org
Rectifying Characteristics and Semiconductor−Metal Transition Induced by Interfacial Potential in the Mn3CuN/n-Si Intermetallic Heterojunction Kewen Shi,† Cong Wang,† Ying Sun,*,† Lei Wang,*,† Sihao Deng,† Pengwei Hu,† Huiqing Lu,† Weichang Hao,† Tianmin Wang,† and Weihua Tang‡ †
Center for Condensed Matter and Materials Physics, Department of Physics, Beihang University, Beijing 100191, People’s Republic of China ‡ State Key Laboratory of Information Photonics and Optical Telecommunications, School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, People’s Republic of China S Supporting Information *
ABSTRACT: The Mn3CuN/n-Si heterojunction device is first designed in the antiperovskite compound, and excellent rectifying characteristics are obtained. The rectification ratio (RR) reaches as large as 38.9 at 10 V, and the open-circuit voltage Voc of 1.13 V is observed under temperature of 410 K. The rectifying behaviors can be well described by the Shockley equation, indicating the existence of a Schottky diode. Simultaneously, a particular semiconductor−metal transition (SMT) behavior at 250 K is also observed in the Mn3CuN/nSi heterojunction. The interfacial band bending induced inversion layer, which is clarified by the interfacial schematic band diagrams, is believed to be responsible for the SMT and rectifying effects. This study can develop a new class of materials for heterojunction, rectifying devices, and SMT behaviors. KEYWORDS: rectifying characteristics, semiconductor−metal transition, intermetallic heterojunction device, interface, inversion layer, antiperovskite compound
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INTRODUCTION In recent decades, the semiconductor electronic devices have become an important subject in materials science for a variety of unique properties such as photoelectric,1 magnetoelectric,2 and quantum effect3,4 and thus obtained great attention for the potential applications, such as p−n diodes,5 Schottky diodes,6 tunnel diodes,7 field effect transistors (FETs),8 and nanowires (NWs).9 Due to the limitation of the complex fabrication for most electronic devices, the growing demand for a new class of heterojunction devices to obtain novel electronic properties is one of the ways to broaden the potential applications.10 Many research works have shown that the interface interactions should be the key factor for the physical properties in the electronic devices11 since it could lead to band discontinuity and easily form a space charge layer or specific defects. Therefore, modifying the band discontinuity by introducing or tuning interfaces is an effective way to design a new class of heterojunction devices and develop their specific properties. The traditional heterojunction devices are mainly focused on the metals or semiconductors. However, the heterojunctions based on intermetallic compounds have rarely been reported. The intermetallic heterojunction as a new type of heterojunction has a number of advantages. (1) The electrical and © 2017 American Chemical Society
thermal conductivity of the intermetallic heterojunction is usually higher than a traditional oxide heterojunction. (2) The intermetallic heterojunction is usually more stable than metal which can overcome the oxidation at the metal interface. As a typical intermetallic compound, the antiperovskite compound, which shows the same crystal structure and similar lattice constant with perovskite, is a good candidate for intermetallic heterojunctions devices. The antiperovskite compounds have been actively investigated for the abundant magnetic and electronic properties, such as superconductivity,12 magnetoresistance,13 magnetostriction,14 barocaloric,15 piezomagnetic,16 and baromagentic17 effects, which are mainly due to the complex electronic structure and magnetic structure. Particularly, the antiperovskite films18−21 have shown novel properties which are different from their bulk samples. Therefore, it is expected to obtain novel properties in heterojunction devices by introducing and tuning the interface. Herein, we try to prepare intermetallic heterojunction devices based on antiperovskite compound Mn3CuN (labeled as Received: January 15, 2017 Accepted: March 21, 2017 Published: March 21, 2017 12592
DOI: 10.1021/acsami.7b00700 ACS Appl. Mater. Interfaces 2017, 9, 12592−12600
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ACS Applied Materials & Interfaces
Figure 1. (a) Cross-sectional SEM result of MCN/n-Si. Inset shows the crystal structure of Mn3CuN antiperovskite. (b) Overview of morphology of the MCN thin film from TEM. (c) HR-TEM image of MCN thin film. (d) The corresponding electron diffraction pattern with indexing. the sputtering. After the deposition, the films were immediately cooled to room temperature. The scanning electron microscope (SEM) images and the highresolution transmission electron microscopy (HR-TEM) image with Electron Diffraction Pattern were obtained by field emission scanning electron microcopy (JSM7500) and high-resolution transmission electron microscopy (JEM-2100), respectively. We prepared a new MCN thin film on the NaCl(001) substrate to carry out the HR-TEM experiment in order to determine the crystal structure of deposited MCN films by PLD. The temperature dependence of resistivity and voltage dependence of current (labeled as I−V curves) during 10−410 K were measured on a Physical Property Measurement System (PPMS). The resistivity measurements were performed with the standard four-probe method (Cu lines and Ag conductive adhesive), while the I−V curve measurements were carried out with two probes (Cu lines and Ag conductive adhesive) on the MCN film surface and substrate surface, respectively. Both the contact of probes at the film surface and substrate surface were well ohmic contact. The experimental structures for electronic transport properties are shown in detail: n-Si (10 mm × 10 mm × 0.5 mm), MCN film (10 mm × 10 mm × 172 mm), and Ag conductive adhesive (∼4 mm × 1.2 mm), and the distance between two probes is 1.1 mm in the four-probe method. First-principles calculations within density functional theory (DFT) were performed here using the projector-augmented wave (PAW) method initially proposed by Blöchl.25 The execution of Kresse and Joubert26 in Vienna Ab-initio Simulation Package (VASP) code with the Perdew−Burke−Ernzerhof (PBE)27 functional within the
MCN) film by the pulsed laser deposition (PLD) method. The results indicate that the Mn3CuN/n-Si intermetallic heterojunction was successfully fabricated for the first time. Correspondingly, an excellent rectifying characteristic with a large rectification ratio (RR) of 38.9 at 10 V under 410 K and a particular semiconductor−metal transition (SMT) behavior at 250 K are observed. The interfacial potential for the Mn3CuN/ n-Si heterojunction is analyzed and calculated using the Shockley equation based on thermionic emission (TE) theory22−24 to understand the interface effect. Moreover, the inversion space charge layer induced by the band bending at the interface is discussed in detail to clarify the electronic properties obtained here. Our results can possibly launch a new class of heterojunction devices and develop novel properties.
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EXPERIMENTAL SECTION
A disk-type Mn3CuN target (25 mm) was first prepared using homemade Mn3CuN powder. Details on the preparation of Mn3CuN powder are described elsewhere.13 The MCN thin films were deposited by pulsed laser deposition (PLD). Si (001, N type), Si (001, P type), and NaCl (001) were used as the substrates (2sp). Deposition parameters for the MCN thin films were 1 × 10−3 Pa for the chamber vacuum, 600 °C for the substrate temperatures Ts, and 1.5 h for the deposition time. The laser was operated at energy of 400 mJ and a repetition rate of 1 Hz (2 Hz for NaCl substrate). The distance between the substrate and target was kept at 75 mm during 12593
DOI: 10.1021/acsami.7b00700 ACS Appl. Mater. Interfaces 2017, 9, 12592−12600
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Figure 2. (a) Temperature dependences of J−V curves from 70 to 410 K for the MCN/n-Si in the warming process, respectively. Inset graphs display the absolute value of current at voltage from −5 to −10 V and also the model for I−V curve measurement. (b) RR as a function of voltage at the selected temperature from 290 to 410 K. (c) The voltage dependent on absolute value of current in logarithmic scales at temperature from 290 to 410 K. The arrows inside show the current change with increasing temperature. (d) Open-circuit voltage Voc as a function of temperature. generalized gradient approximation (GGA)16 is used. Calculation of MCN thin film was constructed using a slab-supercell within a thin layer of Mn3CuN (containing three primitive unit cells) and a separated layer of vacuum (∼12 Å) in the z direction. The cutoff energy of 500 eV and γ-centered k points with a 12 × 12 × 2 grid were used. The work function is the minimum energy for removing an electron though the surface outside the bulk materials.28 Due to this definition, in slab-supercell geometries, calculation of the work function is to determine the Fermi energy and vacuum potential, which is observed from the average potential in the vacuum region.29
an effective way to estimate the macrocrystal structure of a thin film. Figure 1(b) shows the overview of morphology presenting irregular particles of the MCN thin film. The HR-TEM image shown in Figure 1(c) states that the MCN thin film is well polycrystalline. The selected area electron diffraction taken within the MCN film shown in Figure 1(d) distinctly reveals that the crystal structure for polycrystalline MCN film is antiperovskite cubic crystal (Pm-3m), which confirmed that we successfully obtained antiperovskite MCN film by the PLD method. The inset view in Figure 1(a) presents the crystal structure of antiperovskite Mn3CuN. Then we carry out the experiment of electronic transport properties for the MCN/nSi heterojunction. First, voltage dependence of current−density (labeled as J− V) characteristics of MCN/n-Si at selected temperature points from 70 to 410 K is shown in Figure 2(a). Strongly asymmetric characterization for the J−V curves was observed, indicating excellent rectifying behaviors. The current is tiny in the zerobias limit and remains small when the absolute value of the reverse bias increases at a long range from 0 to 7 V, whereas it grows gradually with voltage bias in the forward direction. When the value increases further from 7 to 10 V, the current starts to increase rapidly to a much higher value. The increasing temperature has only a minor effect on the shift of the J−V curve along the V-axis but induces obvious increase of the current value under positive bias. In the reverse condition, the obtained breakdown voltage is higher than 8 V, and the current increases gradually as the reverse bias voltage increases. To deeply understand the breakdown mechanism, we enlarge the temperature-dependent J−V behaviors from 110 to 410 K
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RESULTS AND DISCUSSION The X-ray diffraction (XRD) patterns of Mn3CuN thin films basically indicate that the films deposited on Si substrates should be Mn3CuN films with (111) preferred orientation (see Supporting Information). In order to deeply clarify the crystal structure and element composition of the deposited films by PLD, the electron diffraction pattern (EDP) and the highresolution TEM (HR-TEM) have been carried out as shown in Figure 1. The energy-dispersive spectrometer (EDS) measurements on the different regions of the Mn3CuN film show a homogeneous distribution of the entire Mn3CuN film on n-Si substrate. An average elemental composition ratio of Mn:Cu:N = 3:1.07:0.78 (normalized to Mn = 3) was identified. Therefore, roughly it is Mn3CuN taking consideration on the accuracy of nitrogen content detected by EDS, which is labeled as MCN thin film in the following. Meanwhile, the crosssectional image is also obtained by scanning electron microscope (SEM) equipment shown in Figure 1(a), which displays that the thickness for the MCN film on the n-Si substrate is 172 nm. Furthermore, the EDP obtained in TEM is 12594
DOI: 10.1021/acsami.7b00700 ACS Appl. Mater. Interfaces 2017, 9, 12592−12600
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ACS Applied Materials & Interfaces under reverse bias voltage range from −5 V to −10 V as shown in the inset graph in Figure 2(a). The absolute value of current under −10 V decreases from 0.0015 A/cm2 at 110 K to 0.0005 A/cm2 at 410 K with increasing temperature. As far as our knowledge, this overall downward trend of the absolute value of currents results from the shifts of the breakdown voltages to higher absolute value of voltages as the temperature increases. This positive temperature dependence of breakdown voltage of about +2 mV/K is a clear signature of the avalanche breakdown mechanism.30,31 Due to the mechanism, in the reverse bias condition, the conduction will only take place with minority carriers. When the voltage increases, these minority carriers tend to accelerate and knock out more valence electrons by means of collision, i.e., carrier multiplication. Due to the energy imparted by colliding accelerated minority carries, the valence electrons are pushed into the conduction band. When the temperature increases, the thermal vibration increases, and the mean free path decreases.31 Since the path length becomes smaller, the carriers will need larger electric field to acquire kinetic energy equal for jumping over the energy gap, which will hence lead to the observed positive temperature dependence of breakdown voltage. The rectification ratio (RR) is a general standard to judge the rectifying properties for diodes following the formula RR (nV) = I (+nV)/I (−nV), i.e., the ratio of current at a fixed positive voltage (+nV) to that at the same negative voltage (−nV). As shown in Figure 2(b), the RR (10 V) may increase from 1.3 to 38.9 when the temperature increases from 290 to 410 K shown in Figure 2(b). Finally the highest RR (10 V) for the MCN/nSi is 38.9 at 410 K. Meanwhile, the voltage dependences of the RR at the selected temperature points from 290 to 410 K are also shown in Figure 2(b). With increasing temperature, the RR increases at 10 V, whereas it decreases at 1 V. As the fixed voltage decreases from 10 to 1 V the order of magnitude of RR regularity increases from 101 at 10 V to 104 at 1 V. The highest RR at 1 V and at 290 K (near room temperature) is nearly 1.6 × 104 which is extremely larger than the reported value of 8.0 for LSMO/TiO2,32 17.8 for LSMO/NSTO p−n heterojunctions,33 and 8.0 × 102 for ITO/i-ZnO/CuPc/Au devices34 at room temperature. Figure 2(c) displays the voltage dependence on absolute value of current in logarithmic scales at temperature from 290 to 410 K. With increasing the temperature, the absolute value of currents at −1, 1, and 10 V increase, and the absolute value of currents at −10 V decreases due to the avalanche breakdown mechanism. That is the reason for the positive temperature dependence of the RR at 10 V. However, in the reverse range of 1 V, the conductivity is much smaller than that at forward voltage of 1 V. With increasing the temperature, a thermionic effect may have more influence on the colliding accelerated minority carriers and knock out more valence electrons (increasing the carrier concentration) at −1 V. As a result, the multiple of the current increase at −1 V is bigger than at 1 V which leads to a negative temperature dependence of RR at 1 V. Moreover, from the cross-point between the tangent lines of the current in the positive bias direction and the x-axis, the temperature dependence of the open-circuit voltage Voc, i.e., diffusion potential from 210 to 410 K, was also obtained as shown in Figure 2(d). The open-circuit voltage Voc of 0.7 V at 290 K (room temperature) is observed. It is clear that the Voc increases as the temperature increases which is reversed with the results about the M−I transition behaviors in the LSMO/ TiO2 heterostructure.32 The highest Voc of MCN/n-Si devices
is 1.13 V at 410 K. The Voc in a p−n junction is generally supposed to be the work function or Fermi energy difference Δε between the p-type semiconductor and n-type semiconductor following the formula Δε = e · Voc, which is related to the modulation of the interfacial electronic structure of the device. As a result, the Fermi energy difference Δε of the interface could be obtained to be near 0.7 eV at room temperature for the MCN/n-Si heterojunction. More interestingly, the introduction of an interface meanwhile induces another particular electronic transport property for the MCN film grown on the n-Si substrate. Figure 3 shows
Figure 3. Temperature dependence of resistivity of the MCN thin film on n-Si and p-Si(001) substrates (left axes) and the Mn3CuN bulk (right axes). The inset shows the model for resistivity measurement.
the temperature dependence of resistivity for the obtained MCN films on n-Si and p-Si substrates in the warming and cooling processes. From the ρ − T curves for the MCN/n-Si heterojunction, a giant resistivity change was observed near TSMT = 250 K; i.e., transition of the resistivity occurred. Above and below the transition temperature, the sloped of the resistivity variations are positive and negative, respectively, which display metallic and semiconducting behaviors, i.e., the so-called SMT behavior.35 Noteworthy, near the transition, the resistivity change for the MCN/n-Si reaches as high as 1.28 × 102 from 3.95 × 10−1 Ω cm at 200 K to 3.09 × 10−3 Ω cm at 270 K, which is higher than the ∼50 for NiS 36 in semiconductor−metal transition, ∼10 for Ti2O3,37 and comparable with ∼102 for VO237,38 in metal−insulator transition. Generally, the reported metal−insulator transition behaviors39 are always correlated with the magnetic phase transition. To our knowledge, the Mn3CuN compound has undergone a magnetic phase transition from ferromagnetic to paramagnetic with a correlated tetragonal to cubic structure transition at about 148 K.40 However, the M−T curves of the MCN/n-Si (shown in Supporting Information S2) indicate an obvious magnetic phase transition at 47 K, which is different from the pure Mn3CuN powder and importantly far away from the semiconductor−metal transition point of the MCN/n-Si. This reveals that the semiconductor−metal transition behavior in the MCN/n-Si is independent of the magnetic transition. Furthermore, our investigation indicates that the resistivity of MCN film grown on p-Si always increases linearly as the temperature increases, presenting a metallic conducting behavior, which is different from the behavior of the MCN/ n-Si. We have also tried to deposit MCN on several other 12595
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Figure 4. Temperature dependences of (a) carrier density and (b) mobility in the warming (up triangle) and cooling (down triangle) processes of the MCN/n-Si.
Figure 5. (a) Temperature dependences of logarithmic plots of current−voltage characteristics (|J|−V) of MCN/Si (001, N type). Inset shows the | J|−V plots for 110 and 290 K. (b) Ideality factor (η) (left) and barrier height of Schottky heterojunction MCN/Si (001, N type) (right) as a function of temperature. (c) Ideality factor (η) (left) as a function of 1000/T. (d) Richardson plots of ln(Js/T2) versus 1000/(ηT) and ln(Js/T2) versus 1000/ T.
these cases, one of the main differences should be the interface phenomena between the top layer and bottom layer. Therefore, we believe that the interface interaction between MCN and n-Si should be a key factor for the particularity of the MCN/n-Si heterojunction. Generally, the electronic transport in thin film is known to be strongly affected by interfacial phenomena. The scattering of the conduction electrons at interfaces defined by the top and bottom surfaces of the film can contribute significantly to the resistivity.41,42 For example the spin dependence interface scattering between ferromagnetic and nonmagnetic metal layers leads to the giant magnetoresist-
substrates, such as STO:Fe (001, 0.05 Wt % Fe doped) and STO:Nb (001, 0.7 Wt % Nb doped), but no SMT behavior was found in these samples. As shown in Figure 3, the resistivity of Mn3CuN bulk increases when the temperature increases from 10 to 130 K and then exhibits a near zero temperature coefficient of resistivity (NZTCR) behavior when the temperature increases higher than 150 K which is in agreement with the reported result for Mn3CuN.40 The electronic transport behaviors are quite different among Mn3CuN bulk sample and Mn3CuN thin films on the different substrates, although the crystal structure and composition are the same. However, in 12596
DOI: 10.1021/acsami.7b00700 ACS Appl. Mater. Interfaces 2017, 9, 12592−12600
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ACS Applied Materials & Interfaces ance.43 Also, in two-dimensional electron−gas, interface scattering can seriously limit the electron mobility.44 The interface scattering will decrease with increasing the thickness of the thin film which induces the decreasing of the resistivity, such as the thickness dependence of the resistivities in Sn films deposited on SnOx substrate45 or Cu and Cu/C60 films on sapphire substrates.46 In our case, the different resistivity behaviors of the MCN two-dimensional films on different substrates such as n-Si and p-Si represent that the interface factor makes an important role. Furthermore, as shown in Figure 4(b), the electron mobility is limited at a very low value for MCN film on n-Si substrate before the SMT transition temperature in the warming process, which indicates that the interface scattering should be taken into account to clarify the semiconductor behavior before SMT transition in MCN films on n-Si substrate as previous works44 discussed. The measurements of Hall effect are further carried out to help the understanding of the SMT behavior for the MCN/nSi. Carrier density and mobility as a function of temperature in the warming and cooling processes are shown in Figure 4(a) and (b). As Figure 4(a) shows, the carrier density first increases below 200 K and decreases slowly from 200 to 250 K near the resistivity transition. Finally it stays at a constant level with further increasing temperature from 250 to 410 K. The mobility is nearly constant at a quite small value below 220 K and then increases rapidly to about 1400 cm2 V−1 s−1 from 220 to 270 K (corresponding to transition) as shown in Figure 4(b). With further increasing temperature, the mobility decreases due to the electron−phonon scatting. According to the Hall effect results, the mobility should be the main reason for the abnormal resistivity behavior since the carrier density has a comparable value between low temperature (∼100 K) and room temperature. Based on the above discussion, the interfacial factors must be taken into consideration for clarifying the change of the mobility and carrier density. Generally, the interface can induce the discontinuity in interface band structure and band bend. The SMT behavior and the rectifying characteristics obtained here are surely correlated with the interfacial potential and the formation of an inversion layer. Therefore, more interfacial information, especially about interfacial electronic structure, is desired to further clarify the nature of the related properties. The temperature dependences of the logarithm of absolute current density versus voltage (log|J|−V) are shown in Figure 5(a). The inset shows the log|J|−V curves of 110 and 290 K which clearly display a significant change in the J−V behaviors at reverse regions. The absolute value of current increases gradually with increasing the reverse bias voltage at 290 K, whereas a current “step” appears at the reverse voltage at 110 K. At low reverse voltage (from −2 V to −6 V), MCN/n-Si stays with a high resistivity and low current value. When increasing the reverse voltage from −6 to −10 V, the absolute value of current value increases drastically which indicates the existence of the resistive switching behavior47 in the MCN/n-Si heterojunction at low temperature of 110 K. When the temperature increases, the current “step” becomes narrow at 170 K and disappears at about 230 K, while the drastic increase of current at reverse voltage totally disappears at about 290 K. The resistive switching behavior, due to the accumulation of the positive carriers at the interface region in previous works,48,49 disappears at almost the same transition temperature range of SMT behavior indicating that the same interfacial factor (accumulation layer) should be taken into consideration to
clarify the typical SMT behavior which we will discuss in the following. Primarily, the Shockley equation is used to analyze the rectifying characteristics at the different temperatures, and then the interfacial potential in the MCN/n-Si heterojunction is obtained. According to the thermionic emission (TE) theory,22−24 the J−V characteristic of a Schottky diode is given by ⎛ ⎛ eV ⎞ ⎞ J = Js ⎜⎜exp⎜ ⎟ − 1⎟⎟ ⎝ ⎝ ηkBT ⎠ ⎠ ⎞ ⎛ e ⌀ ⎞⎛ ⎛ eV ⎞ = A*T 2 exp⎜⎜ − B ⎟⎟⎜⎜exp⎜ ⎟ − 1⎟⎟ ⎠ ⎝ kBT ⎠⎝ ⎝ ηkBT ⎠
(1)
where prefactor Js is the reverse saturation current; η is the ideality factor; e is the electron charge; T is the absolute temperature; kB is the Boltzmann constant; and A* is the effective Richardson constant (114 A cm−2 K−2 for n-Si).23 The temperature dependence of η and Js can be obtained by the slope and the intercept of the linear region of the positive bias ln|J|−V characteristics from Figure 5(a). Furthermore, the temperature dependence of barrier height e⌀B could be determined by the ln(Js/T2)−1/T curve (shown in Supporting Information S4). The barrier height at 290 K (near room temperature) is e⌀B = 0.61 eV. In agreement with the analysis result of open-circuit voltage and Δε, the barrier height here is also increasing in the warming process. The barrier height of the MCN/n-Si according to the Shockley equation at room temperature e⌀B = 0.61 eV is slightly smaller than the Δε = 0.7 eV obtained by open-circuit voltage analysis. The interfacial potential (barrier height) at room temperature should be about 0.61 (0.7) eV in the MCN/n-Si Schottky diode. On the other hand, the ideality factor η obtained by the slope of the linear region of the positive bias ln|J|−V characteristics decreases with increasing temperature shown in Figure 5(b), that is, the so-called T0 effect.50 However, it is always larger than 4, which suggests that the interface should play an important role in the electronic transport process. According to the Tung model51 and the TE theory, both linearity of ideality factor η vs 1000/T shown in Figure 5(c) and the modified Richardson plot of ln(Js/T2) near linearity versus (ηT−1) shown in Figure 5(d) indicate the existence of inhomogeneous barriers and potential fluctuations at the interface between MCN and nSi (discussed in Supporting Information). Therefore, we can draw an interfacial schematic band diagram of the MCN/n-Si heterojunction as shown in Figure 6. The density of state (DOS) and the work function (ϕMCN = 4.52 eV) for the MCN are obtained by the first-principles calculation methods. The resistivity of the n-Si(001) substrate is 1.67 × 103 Ω cm, and the electron concentration is n = 2.55 × 1013/cm3 obtained from the Hall-effect measurement at room temperature. According to the fundamental relations for electron densities in nondegenerate semiconductor6 C n = Neff exp[(E F − EC)/kT ]
(2)
the difference between conduction band and Fermi level EC − EF = 0.36 eV is obtained at room temperature, where NCeff = 2.8 × 1019/cm3 is the effective density of state of the conduction band for Si and k is the Boltzmann constant. The work function of n-Si can be given by ϕSi = χSi + (EC − EF), i.e., ϕSi = 4.41 eV since χSi = 4.05 eV is the electron affinity for silicon. EF − EV = 0.75 eV, where the band gap for Si is 1.11 eV. The intrinsic 12597
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(PLD) method. An excellent rectifying characteristic of this MCN/n-Si heterojunction with a high rectifying ratio of 38.9 at 10 V and open-circuit voltage Voc 1.13 V under 410 K is first revealed, and the mechanism is well analyzed by the Shockley equation according to thermionic emission (TE) theory. In addition, a remarkable semiconductor−metal transition behavior at 250 K for electronic transport property in the antiperovskite film MCN on the n-Si substrate is also first found. Based on the first-principles calculation of work function and the band bending theory, the inversion layer at the interface is considered to be the critical factor of the SMT behavior and the rectifying characteristics in the MCN/n-Si device. These results will also open new research areas in electronic device design and applications for antiperovskite compounds or even the intermetallic materials.
Figure 6. Schematic band diagrams for the interface of the MCN/n-Si heterojunction. The Fermi level is at 0 eV.
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ASSOCIATED CONTENT
S Supporting Information *
energy Ei = −0.18 eV at the middle of the gap for n-Si which means that the Si substrate is n-type in agreement with the Hall result, when the Fermi level is at 0 eV. The barrier height e⌀B between the MCN film and n-Si is about 0.61 (0.7) eV as discussed above. The work function difference between the MCN film and the n-Si substrate ϕMCN − ϕSi = 0.11 eV is positive, which induces an upward band bending at the MCN/ n-Si interface. This will lead to a space charge layer at the interface. Considering the values of Ei, e⌀B, and EC − EF, Ei is higher than EF at the interface which leads to an accumulation of holes in the inversion layer (space charge layer). Our results show that the inversion layer formed at the MCN/n-Si interface plays an important role in the SMT behavior. At low temperature (
