group-V Atoms Research Articles

Tuning the electronic structures and anisotropic transport behaviors of GeSe monolayer by substitutional doping

The electronic structures and anisotropic transport properties of doped-GeSe monolayers are systematically explored by performing the density functional theory combined with non-equilibrium Green’s function method. Numerical results of the cohesive energy and formation energy show that it is possible to substitute Ge/Se with isovalent atoms and group-V atoms at room temperature. Isovalent substitutions of Ge/Se atoms can maintain the semiconducting features of monolayer GeSe. While the doping of group-V atoms modifies drastically the electronic structures of doped-GeSe and makes metallic properties appear. In addition, the anisotropy of electronic transport of monolayer GeSe also can be effectively manipulated by substitutional doping. In particular, the isotropic electronic transport properties are shown in the devices based on GeSe with P substituting Ge atom. An obvious negative differential resistance behavior with a large current peak-to-valley ratio up to the radio of 103 is gained in N-dope device. These results are useful for the future potential applications of GeSe materials in next-generation high-efficiency electronic devices.

Effects of substitution of group-V atoms for carbon or silicon atoms on optical properties of silicon carbide nanotubes* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11574261 and 51132002) and the Natural Science Foundation of Hebei Province, China (Grant No. A2015203261).

Silicon carbide nanotubes (SiCNTs) have broad application prospects in the field of micro-nanodevices due to their excellent physical properties. Based on first-principles, the difference between optical properties of SiCNTs where C atom or Si atom is replaced by group-V element is studied. The results show that the optical absorptions of SiCNTs doped by different elements are significantly different in the band of 600 nm–1500 nm. The differences in photoconductivity, caused by different doping elements, are reflected mainly in the band above 620 nm, the difference in dielectric function and refractive index of SiCNTs are reflected mainly in the band above 500 nm. Further analysis shows that SiCNTs doped with different elements change their band structures, resulting in the differences among their optical properties. The calculation of formation energy shows that SiCNTs are more stable when group-V element replaces Si atom, except N atom. These research results will be beneficial to the applications of SiC nanomaterials in optoelectronic devices and provide a theoretical basis for selecting the SiCNTs’ dopants.

High Efficiency Solution-Processed Aluminum-Alloyed Chalcopyrite Thin Film Solar Cells

CuInGaSe2 (CIGSe) chalcopyrite is one most efficient materials for light conversion to electricity with a record efficiency surpassing all other thin film photovoltaic technologies, achieving 23.4% efficiency. Record efficiencies of CIGSe are typically achieved using 1.16 eV absorbers even though Shockley-Queisser (SQL) limit predicts an optimum bandgap of around 1.4 eV for a single junction solar cell. In theory, higher efficiencies can be expected from wider gap chalcopyrite, however, all attempts to increase efficiency with wide bandgap Ga-rich CIGSe have led to defective materials. Another alternative to increase the band gap of chalcopyrites is by partial replacement of In with other group-V atoms, such as aluminum (Al). The band gap energy of CuInAlSe2 (CIASe) can be tuned from 1.0 eV (CISe) to 2.7 eV (CASe). In addition, Al is also very appealing to reduce the raw materials' cost since it is much more abundant in the earth’s crust than Ga (Al: 82,000 ppm, Ga: 19 ppm) and significantly cheaper (Al: ~$2/kg, Ga: ~$200/kg).In an attempt to fabricate high-efficiency CIASe devices, we demonstrated an alternative and low cost method by fabricating bandgap tunable Cu(In,Al)(S,Se)2 (CIASSe) utilizing molecular ink consisted of Cu, In, Al, and sulfur containing salts dissolved in methanol. In this study, Cu-In-Al-S containing ink was spin coated into a molybdenum substrate and followed by selenization at high temperature to form selenium-rich CIASSe. We are able to achieve a device with maximum efficiency of 11.6% using CIASSe having relatively low-content of Al (Al/(Al+In)~0.1), significantly higher efficiency than CISSe (no Al) fabricated with the same process (8.3%-efficient). To our understanding, this study is the first demonstration of a relatively high-efficiency Aluminum-alloyed chalcopyrite solar cells through solution-based process. Details of the fabrication process and materials characterization will be discussed.

Hole-Doped 2D InSe for Spintronic Applications

Using first-principles calculations based on density functional theory, we study the magnetic and electronic properties of hole-doped two-dimensional InSe. Our simulations reveal that although 2D InSe is intrinsically nonmagnetic, a stable ferromagnetic phase appears for a wide range of hole densities. Interestingly, hole doping induces not only spontaneous magnetization but also half-metallicity, and hole-doped InSe, presenting one conducting and one insulating spin channel, could be highly promising for next generation spintronic nanodevices. The possibility of inducing hole doping and a subsequent ferromagnetic order by intrinsic and extrinsic defects was also investigated. We found that In vacancy creates spin-polarized states close to the valence band and leads to a p-type behavior. Similar to In vacancies, group-V atoms replacing Se atoms lead to a p-type behavior, potentially stabilizing a ferromagnetic order in 2D InSe.

Parity-breaking in single-element phases: ferroelectric-like elemental polar metals

Polar metals based on binary and ternary compounds have been demonstrated in literature. Here, we propose a design principle for ferroelectric-like elemental polar metals and relate it to real materials. The design principle is that, to be an elemental polar metal, atoms should occupy at least two inequivalent Wyckoff positions in a crystal with a polar space group, where inversion symmetry is spontaneously broken. According to this rule, we propose the first class of potential ferroelectric-like elemental polar metals in a distorted α-La-like structure with a polar space group P63mc in which two inequivalent Wyckoff positions 2a (0, 0, z) and 2b (1/3, 2/3, z) are occupied by group-V elements (phosphorus, arsenic, antimony, and bismuth). Analyses based on first-principles calculations indicate that the dynamically stable polar phase results from a lone pair driven polar distortion of the nonploar phase in P63/mmc symmetry where two inequivalent Wyckoff positions 2a (0, 0, 0) and 2c (1/3, 2/3, 1/4) are occupied. This ferroelectric-like transition involves a transition from a metallic state to a semimetallic state. These predicted polar phases are metastable with respect to their corresponding ground phases. Moreover, ionic bonding characters are found due to the inequivalence in Wyckoff positions between group-V atoms. Our work opens a route to single-element parity-breaking phases.

Effect of irradiation with 15-MeV protons on the compensation of Ge〈Sb〉 conductivity

The processes of the compensation of n-type conductivity in germanium irradiated with 15-MeV protons are investigated. Irradiation results in a considerable reduction in the density of shallow donor states of Group-V atoms. The rate of removal of shallow donor states due to the interaction between impurity atoms and radiation-induced intrinsic point defects is ~215 cm–1. The majority of secondary defects produced under proton irradiation are electrically neutral in an n-type material. Radiation-induced acceptors are of little importance in this case. Numerical modeling is performed, and the distribution of the energy transferred to recoil atoms is obtained. Two energy intervals are considered in the analysis of distribution histograms. At low energies, individual Frenkel pairs with closely spaced components are produced. The energy of recoil atoms in the second energy region is sufficient to induce a displacement cascade. Nanoscopic regions with high densities of intrinsic point defects and their complexes with dopant atoms are formed in such cascades. A model of the generation of intrinsic defects in germanium under proton irradiation is discussed.

Suppression of the surface “dead region” for fabrication of GaInAsSb thermophotovoltaic cells

Zn diffusion processes in n-Ga0.78In0.22As0.2Sb0.8 epitaxial films are studied using different diffusion sources, a series of the Zn profiles with single and double humps are obtained. The group V-atoms (As and Sb) are found to have little effect on suppressing the surface “dead region”. The Ga and In atoms have entirely different effect on diffusion although they are both group III-atoms. The “dead region” is suppressed completely under Ga-rich conditions, while the suppression will not occur under In-rich conditions. The GaInAsSb cells are fabricated under pure Zn and Ga-rich conditions. An electrical heating thermophotovoltaic system is fabricated for cell testing. Under the radiation from 1055°C-SiN ceramics emitter, the output power density of the GaInAsSb cell obtained under Ga-rich condition is much larger than that of the cell obtained under pure Zn condition, which demonstrated that the GaInAsSb cells can be fabricated without precise etching under Ga-rich conditions.

Investigation of the abnormal Zn diffusion phenomenon in III-V compound semiconductors induced by the surface self-diffusion of matrix atoms

Zn diffusion in III-V compound semiconductorsare commonly processed under group V-atoms rich conditions because the vapor pressure of group V-atoms is relatively high. In this paper, we found that group V-atoms in the diffusion sources would not change the shaped of Zn profiles, while the Zn diffusion would change dramatically undergroup III-atoms rich conditions. The Zn diffusions were investigated in typical III-V semiconductors: GaAs, GaSb and InAs. We found that under group V-atoms rich or pure Zn conditions, the double-hump Zn profiles would be formed in all materials except InAs. While under group III-atoms rich conditions, single-hump Zn profiles would be formed in all materials. Detailed diffusion models were established to explain the Zn diffusion process; the surface self-diffusion of matrix atoms is the origin of the abnormal Zn diffusion phenomenon.

The Effect of Self-Diffusion on the Zn Diffusion in III-V Compound Semiconductors

Zn diffusion in III-V compound semiconductors are commonly processed under group V-atoms rich conditions because the vapor pressure of group V-atoms is relatively high. In this paper, we found that group V-atoms in the diffusion sources would not change the shaped of Zn profiles, while the Zn diffusion would change dramatically under group III-atoms rich conditions. The Zn diffusions were investigated in typical III-V semiconductors: GaAs, GaSb and InAs. We found that under group V-atoms rich or pure Zn conditions, the double-hump Zn profiles would be formed in all materials except In As. While under group III-atoms rich conditions, single-hump Zn profiles would be formed in all materials. Detailed diffusion models were established to explain the Zn diffusion process; the surface self-diffusion of matrix atoms is the origin of the abnormal Zn diffusion phenomenon.

Theoretical discovery of stable structures of group III-V monolayers: The materials for semiconductor devices

Group III-V compounds are very important as the materials of semiconductor devices. Stable structures of the monolayers of group III-V binary compounds have been discovered by using first-principles calculations. The primitive unit cell of the discovered structures is a rectangle, which includes four group-III atoms and four group-V atoms. A group-III atom and its three nearest-neighbor group-V atoms are placed on the same plane; however, these connections are not the sp2 hybridization. The bond angles around the group-V atoms are less than the bond angle of sp3 hybridization. The discovered structure of GaP is an indirect transition semiconductor, while the discovered structures of GaAs, InP, and InAs are direct transition semiconductors. Therefore, the discovered structures of these compounds have the potential of the materials for semiconductor devices, for example, water splitting photocatalysts. The discovered structures may become the most stable structures of monolayers which consist of other materials.

Optical Emission of a Strained Direct-Band-Gap Ge Quantum Well Embedded Inside InGaAs Alloy Layers

We studied the optical properties of a strain-induced direct-band-gap Ge quantum well embedded in InGaAs. We showed that the band offsets depend on the electronegativity of the layer in contact with Ge, leading to different types of optical transitions in the heterostructure. When group-V atoms compose the interfaces, only electrons are confined in Ge, whereas both carriers are confined when the interface consists of group-III atoms. The different carrier confinement results in different emission dynamics behavior. This study provides a solution to obtain efficient light emission from Ge.

Ga and As composition profiles in InP/GaInAs/InP heterostructures—x-ray CTRscattering and cross-sectional STM measurements

Changes of composition profiles in GaInAs layers sandwiched by InP, due to the layerthicknesses, were measured by the x-ray CTR scattering and cross-sectional STMtechniques. Both techniques showed quite similar results, which indicates that the x-rayCTR scattering measurements and analyses give us correct composition profiles both forgroup-III and group-V atoms in the buried heterostructures non-destructively. Limits of theCTR analysis are discussed, especially on the spatial resolution and composition gradingbelow the bottom interface.

Effects of group-V impurities on the elastic properties of silicon

Abstract Besides reduction in device size the application of strained silicon in transistor design plays a crucial role in improving device speed and power consumption. Microscopic investigations are fundamental to understand the mechanical behaviour of strained Si layers, especially in combination with impurity atoms. In the present work, the influence of group-V impurities on strain fields in silicon was studied by means of the perturbed angular correlation method using the acceptor 111 In as probe. This nuclear technique is well suited for studying strain on an atomic scale. After ion implantation of the group-V atoms and subsequent annealing the Si samples were bent along the 〈1 1 0〉 crystal axis resulting in a uniaxial tensile strain. For nitrogen-implanted silicon the response of the crystal lattice to mechanical stress shows no difference to undoped samples, which means that nitrogen has no influence on strain fields in silicon. However, after implantation of the donors P, As and Sb a significant strain relaxation is observed which is probably due to dislocations. We show that this relaxation caused by n-doping also extends to undoped areas which are adjacent to the implanted region.

III–V semiconductor nanowire growth: does arsenic diffuse through the metal nanoparticlecatalyst?

The synthesis of III–V semiconductor nanowires (NWs) is based on the delivery of atomsfrom a vapor phase to a catalytic metal nanoparticle (NP). Although there hasbeen extensive work on such systems, the incorporation pathways of group Vatoms remain an open issue. Here, we have performed a detailed structural andchemical analysis of the catalyst NP in NWs where we switch the V atomic elementduring growth (heterostructured InP/InAs/InP NWs). Our experimental resultsindicate a group V pathway where these atoms actually diffuse through the catalyticNP by formation of a stable phase containing As under growth conditions. Wehave observed distinct NW growth behavior within a narrow temperature range (30 °C) suggesting a transition between vapor–liquid–solid and vapor–solid–solid growth modes.

Effects of absorbed group-V atoms on the size distribution and optical properties of InAsP quantum dots fabricated by the droplet hetero-epitaxy

Abstract We fabricated InAsP quantum dots on GaInP lattice-matched to GaAs (0 0 1) using three types of growth sequences by the droplet hetero-epitaxy. By changing group-V ambient before In droplets formation, we investigated the effects of absorbed group-V atoms on the lateral size, height, density, and luminescence intensity of InAsP quantum dots. By supplying tertiarybutylphosphine and tertiarybutylarsine mixed gases before In droplets formation, the lateral size and height of dots decreased, and the luminescence intensity increased by 550 times. It was revealed that the group-V ambient before In droplets formation was very important for the lateral size, height, and the luminescence intensity.

Atomic scale analysis of MOVPE grown heterostructures by X-ray crystal truncation rod scattering measurement

The origin of the X-ray CTR scattering have been described in brief in order to make it clear why the X-ray CTR scattering measurement can reveal the interface structure. Then, some examples of the results obtained by the X-ray CTR scattering measurement have been shown. The distributions of group-V and III atoms in InP/GaInAs/InP double-heterostructure samples have mainly been discussed. The change of the distribution of As at the interface with the change of H 2 -purge time has been quantitatively shown at an atomic scale by the X-ray CTR scattering measurement, which has demonstrated the high resolution and significance of the X-ray CTR scattering measurement in the investigation of the III–V compound semiconductor heterostructures. The distribution of group-III atoms has also been investigated by the X-ray CTR scattering measurement. The results have suggested that the interface has not been so abrupt as expected, and it has been more difficult to control the distributions of group-III atoms than group-V atoms. The results have shown how important the observation by the X-ray CTR scattering has been to understand the interface structure.

MOVPE growth conditions of the novel direct band gap, diluted nitride Ga(NAsP) material system pseudomorphically strained on GaP-substrate

Multi-quantum well heterostructures (MQWHs) in the novel dilute nitride Ga(NAsP)/GaP material system have been grown pseudomorphically strained on GaP-substrate by metal organic vapour phase epitaxy (MOVPE). The group V-incorporation has been clarified as a function of growth temperature, chemical composition, gas phase V/V-ratios and macroscopic strain. An overall complex incorporation behaviour of the group V-atoms is observed. The precise adjustment of the V/V competition processes on the crystal surface allows, however, for a control of the solid composition of the Ga(NAsP)/GaP material system.

Novel gas-switching sequence using group-III pre-flow (GIIIP) method for fabrication of InGaP on GaAs hetero-interface by MOVPE

InGaP/GaAs is an attractive material system to realize ultra fast electronic devices and optical devices. Fabrication of a monolayer abrupt hetero-interface by metal organic vapor phase epitaxy (MOVPE) is difficult, however, due to the rapid As/P exchange on the growth surface. Here, adsorption/desorption kinetics of group-V atoms on GaAs surface during a gas-switching sequence to form InGaP/GaAs structure was studied by using in situ kinetic ellipsometry. The in situ monitoring of the GaAs dielectric constant revealed that P diffuses easily and quickly into GaAs and that excess As adsorbed on the GaAs surface in MOVPE is difficult to desorb during the gas-switching sequence. Based on these results, we developed a novel gas-switching sequence in which an additional TMGa supply and a group-III pre-flow (GIIIP) were introduced for the first time. By optimizing this GIIIP sequence (i.e., by controlling the additional TMGa supply time), we successfully fabricated an abrupt interface of InGaP on GaAs. The effectiveness of this sequence was confirmed based on photo-luminescence measurements.

On quantifying the group-V to group-III interdiffusion rates in InxGa1−xAs/InP quantum wells

The interdiffusion rate of group-V and group-III sublattice atoms in InxGa1−xAs/InP quantum well structures induced by proton implantation has been investigated using differential reflectance (DR), photoluminescence (PL) and theoretical modelling. Based on DR, PL and modelling results, we found the unique value of k (LV/LIII) ratio for three different InGaAs quantum well structures, namely lattice matched (LM), tensile strained (TS) and compressively strained (CS). The k ratio of TS, LM and CS was 1.05, 1.25 and 1.40 respectively. These ratios were slightly higher than unity indicating that the diffusion coefficient of the group-V sublattice was larger than that of the diffusion coefficient of the group-III sublattice. Change in the interdiffusion rate of group V and group III in the lattice-matched and strained (TS, CS) quantum well structures was most likely due to the different strain profile developed in the quantum well region as a result of changing the quantum well composition.

Atomic layer diffusion and electronic structure at In0.53Ga0.47As/InP interfaces

We have used secondary ion mass spectrometry and cathodoluminescence spectroscopy to determine the effects that growth and postgrowth conditions have on interdiffusion and near band edge emissions in In0.53Ga0.47As/InP heterojunctions grown by molecular beam epitaxy. This lattice-matched interface represents a model system for the study of atomic movements and electronic changes with controlled anion overlap during growth. Structures subjected to anneals ranging from 440 to 495 °C provide a quantitative measure of concentration-driven cross diffusion of group-III and group-V atoms. By measuring anneal-induced broadening at the InGaAs-on-InP interface we have determined an activation energy for As diffusion into InP of ∼2.44±0.40 eV. An interface layer with Ga–P bonds indicates Ga competes favorably versus As for bonding in the preannealed InP near-surface region. In addition, we present evidence that interface chemical effects manifest themselves electronically as variations of the InGaAs band gap energy.