Showing papers on "Band offset published in 2018"
TL;DR: It is demonstrated that gradual substitution of F- into the SnO2 ETL can effectively reduce the band offset and result in a substantial increase in device VOC, providing a simple pathway to tailor ETL/perovskite band offset to increase built-in electric field of planar heterojunction PSCs for maximizing VOC and charge collection simultaneously.
Abstract: Electron transport layers (ETLs) with suitable energy level alignment for facilitating charge carrier transport as well as electron extraction are essential for planar heterojunction perovskite solar cells (PSCs) to achieve high open-circuit voltage (VOC) and short-circuit current. Herein we systematically investigate band offset between ETL and perovskite absorber by tuning F doping level in SnO2 nanocrystal. We demonstrate that gradual substitution of F– into the SnO2 ETL can effectively reduce the band offset and result in a substantial increase in device VOC. Consequently, a power conversion efficiency of 20.2% with VOC of 1.13 V can be achieved under AM 1.5 G illumination for planar heterojunction PSCs using F-doped SnO2 bilayer ETL. Our finding provides a simple pathway to tailor ETL/perovskite band offset to increase built-in electric field of planar heterojunction PSCs for maximizing VOC and charge collection simultaneously.
131 citations
TL;DR: In this paper, the properties of the quasi-type-II structure in a single quantum well nanowire have been investigated and the authors showed that due to the small band offset of conduction bands, both type-I like and type-II like emission exist in the nanowires.
Abstract: The GaAsSb-based quantum well plays a very important role in optoelectronic devices due to its excellent wavelength tunability. When the dimension reduces, the quantum confinement effect will take place and the quantum well in nanowires will show many interesting characteristics. GaAsSb-based quantum-well nanowires are of contemporary interest. However, the properties of the quasi-type-II structure in a single quantum well nanowire have been rarely investigated. Here, we grow GaAs/GaAs0.92Sb0.08/GaAs coaxial single quantum-well nanowires and discussed their power-dependent and temperature-dependent photoluminescence. We find that due to the small band offset of conduction bands, both type-I like and type-II like emission exist in our nanowires. When electrons obtain enough thermal energy through collisions or surrounding environment, they will overcome the barrier and diffuse to the GaAs conduction band, which contributes to the type-II like recombination. These results show the optical property of the quasi-type-II quantum well in nanowires, which can pave the way toward future nanoscale quantum well devices.
115 citations
TL;DR: In this paper, an epitaxial β-Ga2O3/GaN-based vertical metal-heterojunction-metal (MHM) broadband UV-A/UV-C photodetectors with high responsivity (3.7 A/W) at 256 and 365 nm, UVto-visible rejection >103, and a photo-to-dark current ratio of ~100.
Abstract: We demonstrate epitaxial β-Ga2O3/GaN-based vertical metal–heterojunction-metal (MHM) broadband UV-A/UV-C photodetectors with high responsivity (3.7 A/W) at 256 and 365 nm, UV-to-visible rejection >103, and a photo-to-dark current ratio of ~100. A small (large) conduction (valence) band offset at the heterojunction of pulsed laser deposition (PLD)-grown β-Ga2O3 on metal organic chemical vapor deposition (MOCVD)-grown GaN-on-silicon with epitaxial registry, as confirmed by X-ray diffraction (XRD) azimuthal scanning, is exploited to realize detectors with an asymmetric photoresponse and is explained with one-dimensional (1D) band diagram simulations. The demonstrated novel vertical MHM detectors on silicon are fully scalable and promising for enabling focal plane arrays for broadband ultraviolet sensing.
76 citations
TL;DR: In this paper, electron-beam-evaporated molybdenum oxide and magnesium oxide (MgO x ) are directly deposited upon the front and rear surface of c-Si substrates, respectively, to form CSCs with asymmetric band offset for holes and electrons.
68 citations
TL;DR: A Kelvin probe force microscopy investigation carried out on a type-II photovoltaic heterojunction based on WSe2 monolayer flakes and a bilayer MoS2 film stacked in vertical configuration reveals the dynamics of delayed recombination processes originating from photocarriers trapping at the SiO2/TMDC interfaces.
Abstract: Atomically thin transition-metal dichalcogenides (TMDC) have become a new platform for the development of next-generation optoelectronic and light-harvesting devices. Here, we report a Kelvin probe force microscopy (KPFM) investigation carried out on a type-II photovoltaic heterojunction based on WSe2 monolayer flakes and a bilayer MoS2 film stacked in vertical configuration on a Si/SiO2 substrate. Band offset characterized by a significant interfacial dipole is pointed out at the WSe2/MoS2 vertical junction. The photocarrier generation process and phototransport are studied by applying a differential technique allowing to map directly two-dimensional images of the surface photovoltage (SPV) over the vertical heterojunctions (vHJ) and in its immediate vicinity. Differential SPV reveals the impact of chemical defects on the photocarrier generation and that negative charges diffuse in the MoS2 a few hundreds of nanometers away from the vHJ. The analysis of the SPV data confirms unambiguously that light abso...
56 citations
TL;DR: In this article, the authors performed a systematic study of the factors that determine the accuracy of heterostructure band alignments in density functional calculations, and they found that the potential alignments calculated within the generalized gradient approximation (GGA) are in agreement with those calculated using HSE to within 50
52 citations
TL;DR: In this article, the authors evaluated the type-I band alignment at an α-Ga2O3/α-(Al x Ga1− x ) 2O3 heterointerface, with different Al compositions (x), grown on a c-plane sapphire substrate was evaluated by X-ray photoelectron spectroscopy.
Abstract: The band alignment at an α-Ga2O3/α-(Al x Ga1− x )2O3 heterointerface, with different Al compositions (x), grown on a c-plane sapphire substrate was evaluated by X-ray photoelectron spectroscopy. The experimental results show that the heterointerface has the type-I band discontinuity with the valence band offsets of 0.090, 0.12, and 0.14 eV, and the conduction band offsets of 0.34, 0.79, and 1.87 eV, for x values of 0.1, 0.4, and 0.8, respectively. The small band offset for the valence band is attributed to the fact that the valence band of oxides is constituted by the localized O 2p level, which is dominated by the nature of oxygen atoms. The type-I band discontinuity is desirable for a variety of heterostructure devices.
51 citations
TL;DR: In this article, Cd-free n-type buffer layers with two different Mg-doped ZnO layers (Mg0.26Zn0.74O, Mg 0.30Zn 0.70O) have been examined using ultraviolet photoelectron spectroscopy.
40 citations
TL;DR: Light is shed on the physical pictures in the TMD lateral homojunction, and a practicable and general approach to engineer a type-I homojunctions based 2D semiconductor materials is provided.
Abstract: Transition metal dichalcogenide (TMD) heterostructures have been widely explored due to the formation of type-II band alignment and interlayer exciton. However, the studies of type-I TMD heterostructures are still lacking, which limit their applications in luminescence devices. Here, the 1L/nL MX2 (n = 2, 3, 4; M = Mo, W; X = S, Se) lateral homojunction based on the layer-dependent band gaps of TMD nanosheets is theoretically simulated. The studies show that the TMD homojunction presents with high thermal stability and type-I band alignment. The band offset and quantum confinement of carriers can be easily tuned by controlling the thickness of the multilayer region. Moreover, the electric field can decrease the band gaps of 1L/3L and 1L/4L homojunctions linearly. Interestingly, for the 1L/2L MX2 homojunction, the gap value is robust to the weak electric field, while it drops sharply under a strong electric field. This study sheds light on the physical pictures in the TMD lateral homojunction, and provides a practicable and general approach to engineer a type-I homojunction based 2D semiconductor materials.
40 citations
TL;DR: In this paper, the authors demonstrate the ZnSnN2-based P-N and P-i-N heterojunctions to study the band offset engineering for the development of high-efficiency inorganic solar cell.
Abstract: A new ternary-alloy, zinc–tin nitride (ZnSnN2), is considered as one of the most promising absorber materials for photovoltaic applications due to its ideal band gap, rich ternary-chemistry, robust optical absorption, and low cost. In the present work, we demonstrate the ZnSnN2-based P–N and P–i–N heterojunctions to study the band offset engineering for the development of high-efficiency inorganic solar cell. The P–i–N heterojunction is composed of p-SnO, i-Al2O3, and n-ZnSnN2 constituents. The inclusion of the i-Al2O3 buffer layer has remarkably improved the solar cell efficiency by regulating the conduction band offset and interface energy gap. It is believed that our present work will offer a promising approach to manufacture ZnSnN2-based heterojunctions with better band alignment for novel photovoltaic applications.
39 citations
TL;DR: In this paper, a core ZnO/CuO core-shell heterojunction nanowires (NWs) with large area by a catalyst free vapor deposition and oxidation approach has been investigated.
TL;DR: Machine learning has been utilized to accurately predict band gap and band alignment of wurtzite nitrides in a large design space.
Abstract: Nitride has been drawing much attention due to its wide range of applications in optoelectronics and remains plenty of room for materials design and discovery. Here, a large set of nitrides have been designed, with their band gap and alignment being studied by first-principles calculations combined with machine learning. Band gap and band offset against wurtzite GaN accurately calculated by the combination of screened hybrid functional of HSE and DFT-PBE were used to train and test machine learning models. After comparison among different techniques of machine learning, when elemental properties are taken as features, support vector regression (SVR) with radial kernel performs best for predicting both band gap and band offset with prediction root mean square error (RMSE) of 0.298 eV and 0.183 eV, respectively. The former is within HSE calculation uncertainty and the latter is small enough to provide reliable predictions. Additionally, when band gap calculated by DFT-PBE was added into the feature space, band gap prediction RMSE decreases to 0.099 eV. Through a feature engineering algorithm, elemental feature space based band gap prediction RMSE further drops by around 0.005 eV and the relative importance of elemental properties for band gap prediction was revealed. Finally, band gap and band offset of all designed nitrides were predicted and two trends were noticed that as the number of cation types increases, band gap tends to narrow down while band offset tends to go up. The predicted results will be a useful guidance for precise investigation on nitride engineering.
TL;DR: In this paper, the 1D interface exciton has giant binding energy in the same order as 2D excitons in pristine monolayer TMDs, although the effective radius (electron-hole separation) of interfaceexciton is much larger than that of 2Dexcitons.
Abstract: We study the interface exciton at lateral type II heterojunctions of monolayer transition metal dichalcogenides (TMDs), where the electron and hole prefer to stay at complementary sides of the junction. We find that the 1D interface exciton has giant binding energy in the same order as 2D excitons in pristine monolayer TMDs although the effective radius (electron-hole separation) of interface exciton is much larger than that of 2D excitons. The binding energy, exciton radius, and optical dipole strongly depends on the band offset at the junction. The intervalley coupling induced by the electron-hole Coulomb exchange interaction and the quantum confinement effect at interfaces of a closed triangular shape are also investigated. Small triangles realize 0D quantum dot confinement of excitons, and we find a transition from nondegenerate ground state to degenerate ones when the size of the triangle varies. Our findings may facilitate the implementation of the optoelectronic devices based on the lateral heterojunction structures in monolayer semiconductors.
23 Nov 2018
TL;DR: In this article, a Si/ZnO solar cell is modeled and the carrier transport mechanisms are carefully examined by analyzing the band edge discontinuities, electric field distributions at the Si/znO interface, carrier generation-recombination profile for varying ZnO thickness, carrier density and affinity values.
Abstract: Currently, crystalline and polycrystalline silicon wafer based solar cells dominate the photovoltaic market, which employs expensive manufacturing processes. Zinc oxide is one among the inexpensive alternatives for acting as emitter/anti-reflection coating layer which can be used in combination with widely available p-type silicon. Hence it becomes essential to gain in-depth knowledge about the charge transport mechanisms involved in the n-type ZnO/p-type silicon (Si) heterojunction devices. Therefore, Si/ZnO solar cell is modeled and the carrier transport mechanisms are carefully examined by analyzing the band edge discontinuities, electric field distributions at the Si/ZnO interface, carrier generation-recombination profile for varying ZnO thickness, carrier density and affinity values. The photo- generation rate degrades with the increase in ZnO emitter thickness owing to increased absorption in the blue region and is independent of ZnO affinity and donor concentration. The cliff like configuration with high conduction band discontinuity at the Si/ZnO interface for higher values of ZnO affinity has resulted in the formation of poor electric field and the lattice mismatch resulting in high defects formation (recombination centers) at Si/ZnO interface are the predominant causes for deficit in open circuit voltage and fill factor. Hence the conduction band offset alignment is further engineered by designing Si/MgZnO solar cell model and Mg doped ZnO emitter has significantly improved the band offset alignment at the p-n heterojunction when compared to ZnO emitter. Moreover, the simulation results revealed that the stronger electric field strength developed at the heterojunction is suggested to favor the carrier separation process by drift motion thereby improving the open circuit voltage and fill factor of the device. As a next step, both the models are optimized for varying emitter parameters like thickness, carrier density etc using Silvaco ATLAS simulator. Based on this investigation, the optimized Si/ZnO and Si/MgZnO designs anticipate improved conversion efficiencies of 11.57% and 14.46% respectively.
TL;DR: In this article, the authors cross-correlate nanoscale spectral imaging by near-field scanning optical microscopy with a transmission electron microscopy analysis of the very same polytypic GaAs nanowire dispersed onto a Si wafer.
Abstract: III-V compound semiconductor nanowires are generally characterized by the coexistence of zincblende and wurtzite structures. So far, this polytypism has impeded the determination of the electronic properties of the metastable wurtzite phase of GaAs, which thus remain highly controversial. In an effort to obtain new insights into this topic, we cross-correlate nanoscale spectral imaging by near-field scanning optical microscopy with a transmission electron microscopy analysis of the very same polytypic GaAs nanowire dispersed onto a Si wafer. Thus, spatially resolved photoluminescence spectra could be unambiguously assigned to nanowire segments whose structure is known with lattice-resolved accuracy. An emission energy of 1.528 eV was observed from extended zincblende segments, revealing that the dispersed nanowire was under uniaxial strain presumably due to interaction with its supporting substrate. These crucial information and the emission energy obtained for extended pure wurtzite segments were used to perform envelope function calculations of zincblende quantum disks in a wurtzite matrix as well as the inverse structure. In these calculations, we varied the fundamental bandgap, the electron mass, and the band offset between zincblende and wurtzite GaAs. From this multi-parameter comparison with the experimental data, we deduced that the bandgap between the Γ8 conduction and A valence band ranges from 1.532 to 1.539 eV in strain-free wurtzite GaAs, and estimated values of 1.507 to 1.514 eV for the Γ7–A bandgap.
TL;DR: It is concluded that the electrons and holes show a strong overlap in momentum space, despite recent proposals that Rashba splitting leads to a band offset suppressing such an overlap.
Abstract: The generation and recombination of charge carriers in semiconductors through photons controls photovoltaic and light-emitting diode operation. Understanding of these processes in hybrid perovskites has advanced, but remains incomplete. Using femtosecond transient absorption and photoluminescence, it is observed that the luminescence signal shows a rise over 2 ps, while initially hot photogenerated carriers cool to the band edge. This indicates that the luminescence from hot carriers is weaker than that of cold carriers, as expected from strongly radiative transitions in direct gap semiconductors. It is concluded that the electrons and holes show a strong overlap in momentum space, despite recent proposals that Rashba splitting leads to a band offset suppressing such an overlap. A number of possible resolutions to this, including lattice dynamics that remove the Rashba splitting at room temperature, and localization of luminescence events to length scales below 10 nm are considered.
27 Apr 2018
TL;DR: In this article, the electronic properties of in-plane heterostructure of WS2/WSe2/MoS2 are studied by means of the first-principles calculations based on density functional theory.
Abstract: In-plane heterostructure of two-dimensional (2D) transition metal dichalcogenides (TMDs) means the formation of one-dimensional (1D) interfaces, and promises exciting properties. The electronic properties of in-plane heterostructure of WS2/WSe2/MoS2 are studied by means of the first-principles calculations based on density functional theory (DFT). We find that the band gap can be continuously tuned by changing the length of the components of the in-plane heterostructure, which can be explained by confinement effects. Lattice mismatch induced strain play a crucial role in determining the electronic properties, such as direct-indirect band gap transition, band alignment and the band offset of band edge. Our results suggest that the rich and tunable electronic properties endow in-plane heterostructure of WS2/WSe2/MoS2 great potential in applications in such as light emitting and photovoltaics.
TL;DR: In this article, the electronic structures of InSe and black phosphorus (BP) heterostructure modulated by an external electric field (E ⊥ ) have been investigated based on first-principles calculations.
TL;DR: In this article, a comparative study on the cleaning effect of the intrinsic oxide covering GaAs surface using TMA precursor and Al2O3 buffer layer was performed, and the combined results of X-ray photoemission spectroscopy (XPS) analysis and electrical evaluation indicates that the trimethylaluminum (TMA) precursor can effectively remove surface oxides on the GaAs substrate and inhibit oxygen diffusion in a manner similar to the Al 2 O 3 buffer layer, thus avoiding the generation of the low-k Al 2O3 interface layer.
Abstract: In this work, comparative study on the cleaning effect of the intrinsic oxide covering GaAs surface using TMA precursor and Al2O3 buffer layer were performed. GaAs substrates were either exposed to the TMA precursor or Al2O3 buffer layer was deposited on them under the same cycle prior to the deposition of HfGdO films. The combined results of X-ray photoemission spectroscopy (XPS) analysis and electrical evaluation indicates that the trimethylaluminum (TMA) precursor can effectively remove surface oxides on the GaAs substrate and inhibit oxygen diffusion in a manner similar to the Al2O3 buffer layer, thus avoiding the generation of the low-k Al2O3 interface layer. Moreover, the reduction in valence band offset and the increase in conduction band offset were obtained through passivated atomic-layer-deposition (ALD) of the TMA precursor. The MOS capacitor with GaAs passivated by 20 cycles TMA ALD showed almost no hysteresis, minimum interface state density (∼1.5 × 1012 cm−2 eV−1), greatest band offset (∼2.86 eV), and smaller oxide charge density (∼−2.76 × 1013 cm−2), which led to the maximum dielectric constant (∼35.9) and the lowest leakage current density (∼1.4 × 10−5 A cm−2). Furthermore, the leakage current density–voltage (J–V) characteristic curves at low temperature determined that the device showed stable and reliable electrical properties.
TL;DR: In this paper, the detailed analyses of interface properties and device performance of inorganic perovskite CaMnO3-based buffer layer hybrid perovsite solar cell have been undertaken based on ab initio simulations and macroscopic modelling.
TL;DR: In this article, the optical gain of cylindrical quantum dot structures as functions of surface carrier concentration and the dot radius is investigated, and the results may be useful for the potential applications in optical devices.
TL;DR: The large output voltage of nanoscale partial or full vertical heterostructures of 2D WSe2/MoS2 atomic layers in addition to the increased output voltage through the series connection of multiple nanoscales piezoelectric devices will enable the realization of nano-electromechanical systems (NEMS) with TMDC heterostructure atomic layers.
Abstract: A two-dimensional heterostructure of WSe2/MoS2 atomic layers has unique piezoelectric characteristics which depend on the number of atomic layers, stacking type and interlayer interaction size. The van der Waals heterostructure of p- and n-type TMDC atomic layers with different work functions forms a type-II staggered gap alignment. The large band offset of the conduction band minimum and the valence band maximum between p-type WSe2 and n-type MoS2 atomic layers leads to large electric polarization and piezoelectricity. The output voltages for a MoS2/WSe2 partial vertical heterostructure with a size of 3.0 nm × 1.5 nm were 0.137 V and 0.183 V under 4% and 8% tensile strains, respectively. The output voltage of an AB-stacking MoS2/WSe2 heterostructure was larger than that of an AA-stacking heterostructure under 4% tensile strain due to the contribution of intrinsic piezoelectricity and symmetric out-of-plane conditions. The AB-stacking has a lower formation energy and better structural stability compared to AA-stacking. The large output voltage of nanoscale partial or full vertical heterostructures of 2D WSe2/MoS2 atomic layers in addition to the increased output voltage through the series connection of multiple nanoscale piezoelectric devices will enable the realization of nano-electromechanical systems (NEMS) with TMDC heterostructure atomic layers.
TL;DR: In this article, the authors calculate the band offset of CZTS(Se) with CdS and find that increasing temperature significantly enhances the spike-type offset, and use these to estimate the upper limit of electron and hole mobilities based on optic phonon Frohlich scattering.
Abstract: The efficiencies of solar cells based on kesterite Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) are limited by a low open-circuit voltage due to high rates of non-radiative electron-hole recombination. To probe the origin of this bottleneck, we calculate the band offset of CZTS(Se) with CdS, confirming a weak spike of 0.1 eV for CZTS/wurtzite-CdS and a strong spike of 0.4 eV for CZTSe/wurtzite-CdS. We also consider the effects of temperature on the band alignment, finding that increasing temperature significantly enhances the spike-type offset. We further resolve an outstanding discrepancy between the measured and calculated phonon frequencies for the kesterites, and use these to estimate the upper limit of electron and hole mobilities based on optic phonon Frohlich scattering, which uncovers an intrinsic asymmetry with faster (minority carrier) electron mobility.
TL;DR: In this article, the authors analyzed the interfacial electric field caused by photo-generated electron-hole pairs to be easily separated and transferred in the opposite direction at the interface, which is important for improving the photocatalytic activity.
TL;DR: In this article, the authors calculate the band offset of CZTS(Se) with CdS, confirming a weak spike of 0.1 eV for CZTSe/wurtzite-CdS. They also consider the effects of temperature on the band alignment, finding that increasing temperature significantly enhances the spike type offset.
Abstract: The efficiencies of solar cells based on kesterite Cu$_2$ZnSnS$_4$ (CZTS) and Cu$_2$ZnSnSe$_4$ (CZTSe) are limited by a low open-circuit voltage due to high rates of non-radiative electron-hole recombination. To probe the origin of this bottleneck, we calculate the band offset of CZTS(Se) with CdS, confirming a weak spike of 0.1 eV for CZTS/wurtzite-CdS and a strong spike of 0.4 eV for CZTSe/wurtzite-CdS. We also consider the effects of temperature on the band alignment, finding that increasing temperature significantly enhances the spike-type offset. We further resolve an outstanding discrepancy between measured and calculated phonon frequencies for the kesterites, and use these to estimate the upper limit of electron and hole mobilities based on optic phonon Frohlich scattering, which uncovers an intrinsic asymmetry with faster (minority carrier) electron mobility.
TL;DR: In this paper, the electron affinity of SnSe2 has been shown to be larger than that of most semiconductors and can be combined with other appropriate semiconductorors to form near broken-gap heterojunctions for the tunnel field effect transistor that can potentially achieve high on-currents.
Abstract: SnSe2 is currently considered a potential two-dimensional material that can form a near-broken gap heterojunction in a tunnel field-effect transistor due to its large electron affinity which is experimentally confirmed in this letter. With the results from internal photoemission and angle-resolved photoemission spectroscopy performed on Al/Al2O3/SnSe2/GaAs and SnSe2/GaAs test structures where SnSe2 is grown on GaAs by molecular beam epitaxy, we ascertain a (5.2 ± 0.1) eV electron affinity of SnSe2. The band offset from the SnSe2 Fermi level to the Al2O3 conduction band minimum is found to be (3.3 ± 0.05) eV and SnSe2 is seen to have a high level of intrinsic electron (n-type) doping with the Fermi level positioned at about 0.2 eV above its conduction band minimum. It is concluded that the electron affinity of SnSe2 is larger than that of most semiconductors and can be combined with other appropriate semiconductors to form near broken-gap heterojunctions for the tunnel field-effect transistor that can potentially achieve high on-currents.
TL;DR: In this paper, a high-quality γ-In2Se3/p-Si heterojunction was prepared using pulse laser deposition (PLD) and the band structure was found to be type II structure.
Abstract: High-quality γ-In2Se3 thin films and a γ-In2Se3/p-Si heterojunction were prepared using pulse laser deposition (PLD). The band offset of this heterojunction was studied by XPS and the band structure was found to be type II structure. The valence band offset (ΔEv) and the conduction band offset (ΔEc) of the heterojunction were determined to be 1.2 ± 0.1 eV and 0.27 ± 0.1 eV, respectively. The γ-In2Se3/p-Si heterojunction photodetector has high responsivity under UV to visible light illumination. The heterojunction exhibits highly stable photodetection characteristics with an ultrafast response/recovery time of 15/366 μs. The ultrafast response time was attributed to type II structure band alignment, which was good for the separation of electron–hole pairs and it can quickly reduce recombination. These excellent properties make γ-In2Se3/p-Si heterojunctions a promising candidate for photodetector applications.
TL;DR: It is demonstrated that the newly designed BN/BX LHS have profound implications for developing advanced optoelectronics, such as high-performance light-emitting diodes and lasers, and shed new light on overcoming the enormous hurdle of ineffective and laborious material design.
Abstract: Identifying heterostructures with tunable band alignments remains a difficult challenge. Here, based on bond-orbital theory, we propose a series of new BN/BX (X = P, As, Sb) lateral heterostructures (LHS). Our first principles calculations reveal that the LHS interlines have a substantial impact on the electronic properties. Importantly, we start with the chemical concepts, such as bond length and strength as well as orbital overlap interaction, in an attempt to thoroughly investigate the electronic properties, namely the band offset, the band gap (Eg) and the state of the energy level. We demonstrate that the newly designed BN/BX LHS have profound implications for developing advanced optoelectronics, such as high-performance light-emitting diodes and lasers. Furthermore, the new BN/BX LHS designed from the chemical viewpoint can shed new light on overcoming the enormous hurdle of ineffective and laborious material design.
TL;DR: Using density functional theory (DFT), it is revealed that van der Waals heterostructures composed of monolayers of hexagonal boron nitride (h-BN) and the latest P allotrope blue phosphorus (blue phosphorene, BlueP) forms a straddling type I band offset for which the band edges exclusively belong to BlueP.
Abstract: Van der Waals heterostructures (vdWHs), a new class of materials made of a vertically selective assembly of various 2D monolayers held together by vdW forces, have attracted a great deal of attention due to their premise to design novel electronic and optoelectronic properties which is not achievable by individual 2D crystals. Using the density functional theory (DFT), we have revealed that vdWH composed of monolayers of h-BN and the latest blue phosphorus (blue phosphorene, BlueP) forms straddling type-I band offset where the band edges exclusively belong to BlueP. This feature enables h-BN to be a protective coating material of BlueP to beneficially resolve its so-called air-instability. Furthermore, substitutional doping of C to h-BN at a suitable concentration provokes h-BCN/BlueP into staggered type-II band offset. The type-II band alignment triggered by the intensified built-in electric field across the sheets implies the improved carrier mobility and the suppressed recombination of photogenerated hole-pairs. These major benefits can pave the way for the potential functionality of h-BCN/BlueP for efficient photovoltaic devices.
TL;DR: In this article, X-ray photoelectron spectroscopy (XPS) was performed on thin layers of GaP grown on Si by metal organic chemical vapor deposition and molecular beam epitaxy.
Abstract: We have investigated the GaP/Si heterojunction interface for application in silicon heterojunction solar cells. We performed X-ray photoelectron spectroscopy (XPS) on thin layers of GaP grown on Si by metal organic chemical vapor deposition and molecular beam epitaxy. The conduction band offset was determined to be 0.9 ± 0.2 eV, which is significantly higher than predicted by Anderson's rule (0.3 eV). XPS also revealed the presence of Ga–Si bonds at the interface that are likely to be the cause of the observed interface dipole. Via cross-sectional Kelvin probe force microscopy ( x -KPFM), we observed a charge transport barrier at the Si/GaP interface which is consistent with the high-conduction band offset determined by XPS and explains the low open-circuit voltage and low fill factor observed in GaP/Si heterojunction solar cells.