AIIIBV Semiconductors Research Articles

Effects of local field and inherent strain in reflectance anisotropy spectra of AIIIBV semiconductors with naturally oxidized surfaces

Reflectance anisotropy (RA) spectra of naturally oxidized (001) surfaces of GaAs and InAs crystals are measured for photon energies from 1.5 up to 5.5 eV. The differential high-accuracy RA spectra reveal features substantially different from those caused by either a reconstruction of clean surface or a built-in near-surface electric field. Models of atomic structure with anisotropic transition layers of excess arsenic atoms specific for GaAs(001)/oxide and InAs(001)/oxide interfaces are proposed. In conformity with these models, a general theory of reflectance anisotropy is developed for semiconductor/oxide interfaces within the Green's function technique. The theory takes into account the combined effect of local field due to interface dipoles and of intrinsic near-surface strain of the crystal. Measured RA spectra are analyzed in the model of valence-bond dipoles occupying a rectangular lattice in a multilayer medium. Comparing the measured and calculated spectra, we conclude that RA spectra of oxidized GaAs(001) and InAs(001) surfaces are simultaneously influenced by interface and near-surface anisotropies. The former is responsible for the broad-band spectral features which are associated with polarizability of the valence bonds attached to As atoms at the crystal/oxide interface. The near-surface anisotropy is due to inherent uniaxial straining the near-surface region of crystal. The effect of strain on RA spectra is experimentally and theoretically substantiated for GaAs crystal wafers undergone a uniaxial applied stress. Basically, this work results in the following. It establishes the physical nature of different levels of RA spectra observed in a majority of papers, but never analyzed. It demonstrates how the studied features of RA spectra could be applied for optical characterization of strained interfaces and atomic layers.

Boundary processes in the electrolyte–silicon interface area during the self-organization of the mosaic structure of 3D islets of porous silicon nanocrystallites in the long-term anode etching of p-Si (100) in electrolyte with an internal current source

The formation and self-organization of a porous silicon (por-Si) surface mosaic structure in the long-term anodic etching of p-type conductivity Si (100) (p-Si) in electrolytes with an internal power source is considered. We show that the formation of 3D islets of mosaic structure nanocrystallites of por-Si occurs with the participation of the adsorbed deposited silicon atoms formed as a result of disporportionation reactions during the etching of silicon single crystals, as in the case of the epitaxial growth of nanocrystallites by molecular beam deposition of silicon atoms on the AIIIBV and Si semiconductor surface and their further spontaneous self-organization. The quantum-size effects occurring in the local areas of the atomically rough surfaces of a real silicon crystal are taken into account. We note the significant role of oxidation of the silicon surface in the formation and self-organization of a mosaic structure of por-Si during long-term anodic etching of p-Si (100) in the HF: H2O2 electrolyte.

Synthesis and properties of colloidal indium phosphide quantum dots

Semiconductor colloidal quantum dots possessing unique spectral-luminescent characteristics are of great interest for the development of novel materials and devices, which are promising to be used in various fields. However, the contemporary high-quality quantum dots contain Cd, Pb, Hg, Se, and Te ions and are toxic, with this circumstance limiting their wide practical application. Therefore, the attention of researchers has recently been focused on AIIIBV semiconductor quantum dots—in particular, InP ones, which are markedly more environmentally safe. InP quantum dots have spectral characteristics similar to those of well-studied CdSe quantum dots and can, in principle, replace the latter in many cases, especially, taking into account their more pronounced size effect caused by the narrow energy gap and the large Bohr radius of the exciton. Moreover, the stronger InP covalent bond than the ionic one in AIIBVI semiconductors makes it possible to expect that they have a higher photostability and stability in active media. This work presents a review of the modern literature devoted to the synthesis and properties of colloidal indium phosphide quantum dots, which are very promising for use as substitutes of toxic cadmium-based quantum dots.

Structural and phase transformation of A III B V(100) semiconductor surface in interaction with selenium

Surfaces of GaAs(100), InAs(100), and GaP(100) substrates thermally treated in selenium vapor have been investigated by transmission electron microscopy and electron probe X-ray microanalysis. Some specific features and regularities of the formation of A3IIIB4VI (100)c(2 × 2) surface phases and thin layers of gallium or indium selenides A2IIIB3VI (100) on surfaces of different AIIIBV(100) semiconductors are discussed within the vacancy model of surface atomic structure.

Spin-dependent processes in heterostructures based on AIIIBV and AIIBVI semiconductors doped with transition metals

In heterostructures based on AIIIBV and AIIBVI semiconductors doped with transition metals, viz., GaSb(59%)—MnSb(41%), GaAs/InGaAs/GaAs/GaAs:Mn, and ZnSe/ZnMgSSe/ZnSSe:Cr, we observe effects caused by the influence of charge carriers on magnetic properties and reverse effects consisting of a change in the electric and optical properties of the heterostructure caused by ferromagnetic ordering. Spin polarization of the charge carriers is the principal condition for establishing an interrelation of magnetic and other properties of magnetic semiconductor heterostructures.

AP-MOVPE Technology and Characterization of InGaAsN p-i-n Subcell for InGaAsN/GaAs Tandem Solar Cell

Abstract Tandem (two p-n junctions connected by tunnel junction) and multijunction solar cells (MJSCs) based on AIIIBV semiconductor compounds and alloys are the most effective photovoltaic devices. Record efficiency of the MJSCs exceeds 44% under concentrated sunlight. Individual subcells connected in series by tunnel junctions are crucial components of these devices. In this paper we present atmospheric pressure metal organic vapour phase epitaxy (AP-MOVPE) of InGaAsN based subcell for InGaAsN/GaAs tandem solar cell. The parameters of epitaxial structure (optical and electrical), fabrication process of the test solar cell devices and current-voltage (J-V) characteristics are presented and discussed.

Internal Photoemission at Interfaces of ALD TaSiOx Insulating Layers Deposited on Si, InP and In0.53Ga0.47As

Electrical analysis of interfaces of (100)Si, (100)InP, and (100)In0.53Ga0.47As with TaSiOx (Ta/Si≈1) films atomic-layer deposited using SiCl4, TaCl5, and H2O precursors suggests Ta silicate as a good insulating and surface passivating layer on all three semiconductors. However, when a positive voltage is applied to the top metal electrode in a metal/ TaSiOx /semiconductor configuration, considerable hysteresis of the capacitance-voltage curves, both at 300 and 77 K, is universally observed indicating electron injection and trapping in the insulator. To shed some light on the origin of this charge instability, we analyzed interface band alignment of the studied interfaces using the spectroscopies of internal photoemission and photoconductivity measurements. The latter reveals that independently of the semiconductor substrate material, TaSiOx layers exhibit a bandgap of only 4.5±0.1 eV, typical for a Ta2O5 network. The density of electron states associated with this narrow-gap network may account for the enhanced electron injection and trapping. Furthermore, while a sufficiently high energy barrier for electrons between Si and TaSiOx (3.1±0.1 eV) is found, much lower IPE thresholds are encountered at the (100)InP/TaSiOx and (100) In0.53Ga0.47As/TaSiOx interfaces, i.e., 2.4 and 2.0 eV, respectively. The lower barrier may be related by the formation of narrow-gap In-rich interlayers between AIIIBV semiconductors and TaSiOx.

Mathematical Model for the Formation of Porous AIIIBV Semiconductors

not Available.

Thermal oxidation of AIIIBV semiconductors with V2O5 nanolayers on the surface

The specific features of the interaction of vanadium(V) oxide nanofilms with the surface of gallium arsenide and indium phosphide semiconductors under thermal oxidation conditions have been considered. The kinetics and mechanism of thermal oxidation of GaAs and InP with deposited V2O5 layers 15 and 25 nm in thickness have been studied. It has been revealed that vanadium(V) oxide exerts a specific effect on the oxidation of gallium arsenide and indium phosphide as compared to other d-metal oxides. It has been established that the oxidation occurs with the formation of a phase predominantly consisting of indium phosphates or gallium arsenates and intermediate products based on vanadium compounds in different oxidation states. Schemes have been proposed for the development of the oxidation processes with due regard for the chemical nature of vanadium(V) oxide.

Electron States at Interfaces of Semiconductors and Metals with Insulating Films

Evolution of electron energy barriers at interfaces of AIV (Si, Ge), AIVBIV (GexSi1-x, SiC), and AIIIBV (GaAs, InxGa1-xAs, InP, GaSb) semiconductors with wide-gap oxide insulators is overviewed. Over a wide spectrum of studied materials no significant interface dipole contribution to the barrier height is found. Instead, it appears that the energy position of the top of the O2p-derived oxide valence band remains nearly constant, which can be used to evaluate the interface band alignment between oxides and semiconductors as well as between dissimilar oxides materials. By contrast, barriers for electrons at metal/oxide interfaces appear to be strongly affected by the interface processing indicating that near-interface oxide charges in combination with a resulting polarized metal surface may provide significant dipole contribution to the interface barrier height.

Solid state voltammetry for diagnostics of functional materials

Solid state voltammetry was used for phase analysis of the natural oxide films on AIIIBV semiconductors. Such films, both anodic and thermal, were shown to be inhomogeneous mixtures of various phases and their structural modifications. Unstable state of the natural oxide layers on AIIIBV semiconductors was caused by their surface oxidation leading to the formation of nonequilibrium set of phases, their amorphous and unstable crystalline forms. A technique for express identification of superconducting phases and their characteristics was developed. All electrochemical characteristics of the detected signal indicate the presence of oxygen in superconducting phases, which is able to accept electrons and thus provide electroneutrality of the molecule.

Ferromagnetic semiconductor nanostructures—future spintronics

The review analyzes and summarizes the principal results of research on the magnetic properties of ferromagnetic semiconductor nanostructures. These materials possess unique physical properties, which attracts great attention both from the scintific and practical viewpoints. The review shows that group AIIBVI and AIIIBV ferromagnetic semiconductors, as well as group IV elemental semiconductors hold the greatest promise for spintronic applications. Nanostructuring allows to increase the Curie temperature corresponding to the percolation transition in elemental semiconductors. Approaches to overcoming the principal barrier to spintronics applications of ferromagnetic semiconductors-the necessity of their deep cooling-are considered. Comparison of the magnetic and magnetotransport properties of quasi-one-dimensional Ge1−x Mn x nanowires with quasi-two-dimensional nanofilms of the same composition reveals an effect of limited size on the ferromagnetic ordering temperature and magnetic resistance.

Solid solutions in In2S3–MnIn2S4 system

AbstractThe research of semiconductors displaying ferromagnetic properties at room temperature has attracted more and more attention to investigations of doped AIIBVI, AIIIBV and A2IIIB3VI binary semiconductors (CdMnTe, GaMnAs, In2S3:Mn etc.) with Mn [1, 2]. During the last few years growing interest has been shown to spintronics or electronics using spin effects due to its potential applicability to new functional devices combining both transport and magnetic properties and possibility to work at room temperature [3]. A number of exciting new properties such as spin injection, carrier‐induced and optically controlled ferromagnetism have been discovered in III‐V‐based diluted semiconductors [4, 5]. Doping of In2S3 with ferromagnetic atoms of Mn shall lead to a change of existing and appearance of new unique physical properties in this compound, combining both semiconductor and magnetic properties. Results of study of In2S3‐MnIn2S4 system have been presented in the given work for the first time. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Lattice energy of zinc blende (AIIIBV and AIIBVI) solids

AbstractIn this paper we present an expression relating the lattice energy (U in kcal/mol) for the AIIIBV and AIIBVI semiconductors with the product of ionic charges (Z1Z2) and nearest‐neighbor distance d (Å). The lattice energy of these compounds exhibit a linear relationship when plotted on a log–log scale against the nearest‐neighbor distance d (Å), but fall on different straight lines according to the ionic charge product of the compounds. A fairly good agreement has been found between the observed and calculated values of the lattice energy for AIIIBV and AIIBVI semiconductors. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

AFM tip-induced ripple pattern on AIII-BV semiconductor surfaces

Modification of c(8x2) InSb(0 0 1) surface induced by prolonged scanning with an atomic force microscope tip has been investigated. The experiment performed with loads of few tens of nanoNewtons resulted in creation of ripples perpendicular to the fast scan direction. It was found that terrace edges are acting as initial instabilities leading to development of the ripple pattern. As a result, information about initial surface topography is preserved in the ripple amplitude, even so the final height of the ripples and their periodicity are determined by the tip curvature.

Technology and characterisation of GaAsN/GaAs heterostructures for photodetector applications

AbstractThe nitrogen-containing conventional AIIIBV semiconductor alloys, so-called diluted nitrides (AIIIBV-N), have been extensively studied recently. Unusual properties of these materials make them very promising for applications in lasers and very efficient multijunction solar cells. This work presents the technology and properties of undoped GaAs1-xNx/GaAs heterostructures used as active regions in the construction of metal-semiconductor-metal (MSM) photodetectors. The atmospheric pressure metal organic vapour phase epitaxy (APMOVPE) was applied for growing MSM test structures. Their structural and optical properties were examined using high resolution X-ray diffraction (HRXRD), photoluminescence (PL), and photoreflectance spectroscopy (PR). Chemical wet etching was applied for forming an active region and a multifinger Schottky metallization was used as MSM contacts. Dark and illuminated current-voltage characteristics were measured. Based on the obtained results, the main detector parameters as responsivity and spectral response were estimated

Laser-induced formation of periodical structures on the AIIBVI semiconductors surfaces

Periodical relief structures were formed on the surface of AIIBVI semiconductor crystals after pulse irradiation using Nd:YAG laser with the pulse duration 30ps working at 532nm. This work was performed on monocrystals of CdZnTe, CdMnTe, HgCdTe, CdTe grown by means of Bridgman method. In order to determine the surface periodic structures (SPS), atomic force microscopy (AFM) has been used. Analyses of the profilograms obtained from these AFM images were performed by means of amplitudes of their discrete Fourier spectra, which allow determining periodicity of surface periodical structures (SPS) and their orientation. The theoretical model of laser-induced SPS correlates with experimental results.

Electrochemical and chemical dimensional treatment as a method for manufacturing nanocomposites based on indium phosphide

Problems, associated with electrochemical dimensional treatment and chemical deposition as methods of manufacturing nanocomposites based on the AIIIBV semiconductors, are considered by studying indium phosphide (n-InP). The results of manufacturing nanocomposites Cu-n-InP and Ag-n-InP by chemical deposition of copper and silver into pores produced by electrochemical anodic dissolution are described. The metallization kinetics and peculiarities of metal distribution inside nanopores at large values of A are described (A = h/d is a geometrical factor or an aspect ratio, where h and d are the pore’s depth and diameter). It is shown that the degree of the nanopores’ filling is defined by the chemical deposition rate. A relatively high copper deposition rate pertaining to the manufacturing of Cu-n-InP leads to a low throwing power of electrolyte and, as a consequence, to a low level of the pores’ filling. Conversely, the substantially lower rate of the silver chemical deposition from a triethanolamine-containing solution leads to a better uniformness of deposition and to the reaching of conditions conducive to a higher degree of the pores’ filling with metal.

Determination of surface recombination velocity so and carrier lifetime τo from IF(VG) characteristics of Al/PECVD-SiNx/pn-GaAs gated diodes

Investigations on Al/SiNx/pn-GaAs gated diodes reveal that the forward current IF in the recombination current region consists of a bulk current part being generated in the depletion region of the metallurgical p–n junction, and a surface recombination current part occurring at the intersection plane of this depletion region with the semiconductor surface. A variation of the gate length influences neither surface current nor HF capacitance of the p–n junction. However, the surface current can be controlled by the gate bias. A simple model using surface recombination at the junction perimeter enables evaluation of surface recombination velocity so and carrier lifetime τo in the depletion region of the p–n junction. Thus the 2kT recombination current of the gated diodes can be separated into a surface and a bulk part. This method can also be applied to other AIIIBV semiconductors.

Strongly compensated InAs obtained by proton irradiation

Proton irradiation of undoped n-InAs allowed a compensated material to be obtained with the degree of compensation K∼0.6. A regime of irradiation was selected to provide for a uniform distribution of radiation defects in depth of the semiconductor plate. The free electron density in irradiated InAs reaches up to 1×1018 cm−3, which corresponds to the Fermi level fixed in the region of allowed states with a wave vector of κ=0 in the conduction band (in contrast to other AIIIBV semiconductor compounds, in which the Fermi level of a material with radiation defects occurs in the middle of the bandgap). The obtained results confirm the model of Brudnyi et al. [1].