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Showing papers in "Semiconductor Science and Technology in 2002"


Journal ArticleDOI
TL;DR: In this paper, materials design of new functional diluted magnetic semiconductors (DMSs) is presented based on first principles calculations, and the stability of the ferromagnetic state in ZnO-, ZnS-, Zns, ZnSe and ZnTe-based DMSs is investigated systematically.
Abstract: Materials design of new functional diluted magnetic semiconductors (DMSs) is presented based on first principles calculations. The stability of the ferromagnetic state in ZnO-, ZnS-, ZnSe-, ZnTe-, GaAs- and GaN-based DMSs is investigated systematically and it is suggested that V- or Cr-doped ZnO, ZnS, ZnSe and ZnTe are candidates for high-TC ferromagnetic DMSs. V-, Cr- or Mn-doped GaAs and GaN are also candidates for high-TC ferromagnets. It is also shown that Fe-, Co- or Ni-doped ZnO is ferromagnetic. In particular, the carrier-induced ferromagnetism in ZnO-based DMSs is investigated and it is found that their magnetic states are controllable by changing the carrier density. The origin of the ferromagnetism in the DMSs is also discussed.

771 citations


Journal ArticleDOI
TL;DR: In this paper, the main roadblock to the development of these solar cell devices is poor minority-carrier transport in the III-N-V materials, and the present understanding of the material properties of GaInNAs lattice matched to GaAs and GaNPAs matched to Si is reviewed.
Abstract: III–N–V semiconductors are promising materials for use in next-generation multijunction solar cells because these materials can be lattice matched to substrates such as GaAs, Ge and Si, with a range of bandgaps that are complementary to those of other III–V semiconductors. Several potentially high-efficiency multijunction photovoltaic device designs using III–N–V materials are discussed. The main roadblock to the development of these solar cell devices is poor minority-carrier transport in the III–N–V materials. The present understanding of the material properties of GaInNAs lattice matched to GaAs and GaNPAs lattice matched to Si is reviewed.

324 citations


Journal ArticleDOI
TL;DR: In this paper, the band anticrossing model is extended over the entire Brillouin zone to explain the pressure behaviour of the lowest conduction band minimum in GaP1−xNx.
Abstract: In this paper we review the basic theoretical aspects as well as some important experimental results of the band anticrossing effects in highly electronegativity-mismatched semiconductor alloys, such as GaAs1−xNx and InyGa1−yAs1−xNx. The many-impurity Anderson model treated in the coherent potential approximation is applied to these semiconductor alloys, in which metallic anion atoms are partially substituted by a highly electronegative element at low concentrations. Analytical solutions of the Green's function provide dispersion relations and state broadenings for the restructured conduction bands. The solutions also lead to the physically intuitive and widely used two-level band anticrossing model. Significant experimental observations, including large bandgap reduction, great electron effective mass enhancement and unusual pressure behaviour of the bandgap, are compared with the predictions of the band anticrossing model. The band anticrossing model is extended over the entire Brillouin zone to explain the pressure behaviour of the lowest conduction band minimum in GaP1−xNx. Finally, we show that the band anticrossing can also account for the large bandgap bowing parameters observed in GaAsxSb1−x, InAsySb1−y and GaPxSb1−x alloys.

321 citations


Journal ArticleDOI
TL;DR: In this article, the authors report effective lifetime measurements for a variety of commercially available float-zone silicon wafers that have been carefully passivated using alnealed silicon oxide, and demonstrate that very low bulk and surface recombination rates can be maintained during high-temperature oxidation (1050 °C).
Abstract: Bulk and surface processes determine the recombination rate in crystalline silicon wafers. In this paper we report effective lifetime measurements for a variety of commercially available float-zone silicon wafers that have been carefully passivated using alnealed silicon oxide. Different substrate resistivities have been explored, including both p-type (boron) and n-type (phosphorus) dopants. Record high effective lifetimes of 29 and 32 ms have been measured for 90 Ω cm n-type and 150 Ω cm p-type silicon wafers, respectively. The dependence of the effective lifetime has been measured for excess carrier densities in the range of 1012–1017 cm−3. These results demonstrate that very low bulk and surface recombination rates can be maintained during high-temperature oxidation (1050 °C) by carefully optimizing the processing conditions.

260 citations


Journal ArticleDOI
TL;DR: In this article, the authors review both the materials challenges and progress in growth of the metastable GaInNAs alloys required to reach the 1.3-1.55 μm communication wavelengths and the challenges and advances in device design for both vertical-cavity surface-emitting lasers and higher power edge-EMitting lasers.
Abstract: Research to realize long-wavelength, GaInNAs quantum well lasers has been intense in the past three years. The results have been very promising considering the relative immaturity and challenges of this new materials system. This paper reviews both the materials challenges and progress in growth of the metastable GaInNAs alloys required to reach the 1.3–1.55 μm communication wavelengths and the challenges and progress in device design for both vertical-cavity surface-emitting lasers and higher power edge-emitting lasers.

208 citations


Journal ArticleDOI
TL;DR: In this article, the authors review and extend the physics governing electrical spin injection into non-magnetic semiconductors and provide a critical evaluation of several approaches to circumvent the impedance mismatch that prohibits spin injection in the diffusive transport regime.
Abstract: In this paper we review and extend our modelling of the physics governing electrical spin injection into non-magnetic semiconductors. A critical evaluation is given of several approaches to circumvent the impedance mismatch that prohibits spin injection in the diffusive transport regime, i.e. ballistic transport, the use of tunnel barriers and the physics of a Schottky contact. We conclude by discussing an experimental illustration of our modelling. In an all-electrical geometry, we utilize spin injection from a paramagnetic injector to demonstrate a novel magnetoresistance effect.

145 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the tight-binding method to understand the electronic structure of GaInNAs alloys, and used it to derive a modified k?p model for the electronic structures of GaNAs/GaAs heterostructures.
Abstract: We review how the tight-binding method provides a particularly useful approach to understand the electronic structure of GaInNAs alloys, and use it to derive a modified k?p model for the electronic structure of GaInNAs heterostructures. Using the tight-binding model, we first confirm that N forms a resonant defect level above the conduction band edge in Ga(In)As. We show that the interaction of the resonant N level with the conduction band edge accounts for the strong bandgap bowing observed in GaInNxAs1?x, in agreement with experimental analysis but contrary to some theoretical interpretations. We then use a Green function model to derive explicitly the two-level band-anti-crossing model describing the interaction between the resonant states and the conduction band edge in ordered Ga(In)NxAs1?x. We extend the Green function model to show that the conventional k?p model must be modified to include two extra spin-degenerate nitrogen states, giving a 10-band k?p model to describe the band structure of GaNAs/GaAs and related heterostructures. We describe how this 10-band model provides excellent quantitative agreement with a wide range of experimental data and finally discuss briefly the effects of disorder on the electronic structure in dilute nitride alloys.

142 citations


Journal ArticleDOI
TL;DR: In this article, the InAlN/(In)GaN HEMTs quantum well free electron densities, transistor open channel drain currents and threshold voltages are calculated for different In molar fractions considering the maximal acceptable strain.
Abstract: The replacement of the AlGaN barrier layer of the AlGaN/GaN high electron mobility transistors (HEMTs) with InAlN of various In molar fractions is suggested. Internal polarization fields in the InAlN/(In)GaN quantum well are described using analytical formulae. InAlN/(In)GaN HEMTs quantum well free electron densities, transistor open channel drain currents and threshold voltages are calculated for different In molar fractions considering the maximal acceptable strain. It is suggested that 0.08 ≤ x ≤ 0.27 for a 15 nm thick InxAl1−xN barrier or 0 ≤ y ≤ 0.18 for a 5–10 nm thick InyGa1−yN channel can be applied for strain without layer relaxation while the quantum well free electron densities up to 4.6 × 1017 m−2 and the transistor open channel drain currents up to 4.5 A mm−1 can be expected.

139 citations


Journal ArticleDOI
TL;DR: The injection level dependence of the effective surface recombination velocity (Seff) for the interface between crystalline silicon and stoichiometric silicon nitride, prepared by high-frequency direct plasma enhanced chemical vapour deposition (PECVD), has been comprehensively studied in this article.
Abstract: The injection level dependence of the effective surface recombination velocity (Seff) for the interface between crystalline silicon and stoichiometric silicon nitride, prepared by high-frequency direct plasma enhanced chemical vapour deposition (PECVD), has been comprehensively studied. A wide variety of substrate resistivities for both n-type and p-type dopants have been investigated for minority carrier injection levels (Δn) between 1012 and 1017 cm−3. Effective lifetimes of 10 ms have been measured for high resistivity n-type and p-type silicon, the highest ever measured for silicon nitride passivated wafers, resulting in Seff values of 1 cm s−1 being unambiguously determined. The Seff(Δn) dependence is shown to be constant for n-type silicon under low injection conditions, while for p-type silicon, there is a clear minimum to Seff for injection levels close to the doping density. Further, the Seff(Δn) dependence for these stoichiometric silicon nitride films appears to be weaker than that for other high-quality, silicon-rich silicon nitride films prepared by remote PECVD.

134 citations


Journal ArticleDOI
TL;DR: In this article, the status of InGaAsN-based vertical-cavity surface-emitting lasers (VCSELs) emitting in the wavelength range 1.2-1.3 μm was reviewed.
Abstract: We review the status of InGaAsN-based vertical-cavity surface-emitting lasers (VCSELs) emitting in the wavelength range 1.2–1.3 μm and compare them with similar devices that have been realized using other approaches. To prove the potential of InGaAsN-based VCSELs, we present our results for monolithically MBE- and MOVPE-grown and electrically pumped VCSELs on GaAs substrates. Our MBE-grown devices emit at a wavelength of up to 1305 nm with cw output power at room temperature exceeding 1 mW and a threshold current of 2.2 mA. With an oxide-confined current aperture of about 5 μm diameter, they emit up to 700 μW in single-mode operation at room temperature. Bit-error rates of less than 10−11 are achieved for transmission over 20.5 km of standard single-mode fibre at 2.5 Gbit s−1. Our MOVPE-grown VCSELs with a similar device structure emit single mode at a wavelength of 1293 nm with a cw output power of 1.4 mW and a threshold current of 1.25 mA at room temperature. In back-to-back transmission, we reach a data rate of 10 Gbit s−1, proving the feasibility of high-speed data transmission using InGaAsN VCSELs.

134 citations


Journal ArticleDOI
TL;DR: In this article, the authors review the technology and materials aspects of both the MRAM and spintronics fields that highlight the challenges that must be overcome in order to make magnetic (multilayer) films a standard ingredient in future electronics.
Abstract: There has been an increased interest in the introduction of magnetic thin films into semiconductors. This interest is motivated by the benefit found in using the magnetic thin-film properties (giant or tunnelling magnetoresistance and hysteresis) in magnetic memory (MRAM) products. Furthermore, the use of the electron spin in electronic, spintronic devices requires intimate ferromagnetic/semiconductor combinations. We review the technology and materials aspects of both the MRAM and spintronics fields that highlight the challenges that must be overcome in order to make magnetic (multilayer) films a standard ingredient in future electronics.

Journal ArticleDOI
TL;DR: In this article, the authors present a systematic study of the tube diameter as a function of bilayer thicknesses, taking into account that 2-4 monolayers of the top GaAs layer are consumed due to oxidation during the overall tube formation process.
Abstract: Free-standing nanotubes are formed by rolling-up InGaAs/GaAs bilayers on a GaAs substrate. We present a systematic study of the tube diameter as a function of bilayer thicknesses. In our study we take into account that 2–4 monolayers of the top GaAs layer are consumed due to oxidation during the overall tube formation process. We find that a macroscopic continuum mechanical model can well describe the diameter of the nanotubes from 80 nm to 600 nm for nearly symmetric layers and from 21 nm to 550 nm for asymmetric bilayers. For thin symmetric layers the diameter is slightly smaller than predicted by theory. We find that the growth temperature significantly influences the nanotube diameter.

Journal ArticleDOI
TL;DR: In this paper, the authors review the studies on the molecular beam epitaxy (MBE) growth of ferromagnet (MnAs)/III-V semiconductor layered heterostructures and nanoscale granular structures, and their magnetic, magnetotransport and magneto-optical properties.
Abstract: Ferromagnet/semiconductor hybrid structures are attractive and promising as artificial materials for 'semiconductor spintronics', because they can possess magnetic and/or spin-related functions and they have excellent compatibility with semiconductor device structures. We review our studies on the molecular beam epitaxy (MBE) growth of ferromagnet (MnAs)/III–V semiconductor layered heterostructures and nanoscale granular structures, and their magnetic, magneto-transport and magneto-optical properties. We show that, by careful control of MBE growth and processing, some useful magnetic or spin-related functions can be realized at room temperature.

Journal ArticleDOI
TL;DR: In this article, it has been clarified that dislocation-free III-V-N alloys can be grown on Si substrates whose lattice constants are matched to those of Si.
Abstract: The key issues for growing III–V compound layers, free of structural defects, on Si substrates are clarified. The technologies for overcoming the fundamental problems have been developed. As a result, it has been clarified that dislocation-free III–V–N alloys can be grown on Si substrates whose lattice constants are matched to those of Si. Device structures of the GaAsPN/GaPN quantum well structure and the Si/GaPN/Si structure have been successfully grown on a Si (100) substrate covered with a thin GaP initial layer. The grown layers and hetero-interfaces contained no threading dislocations and no misfit dislocations, respectively. Neither stacking faults nor anti-phase domains were observed. A key issue for application to novel devices is the increase in nitrogen composition without degrading optical and electrical properties.

Journal ArticleDOI
TL;DR: In this paper, the growth and properties of GaNAsSb alloys are investigated and compared with those of other dilute III-N-V-V alloys.
Abstract: Growth and properties of GaNAsSb alloys are investigated and compared with those of other dilute III–N–V alloys. Similar properties are observed including very high bandgap bowing, carrier localization at low temperature, sensitivity to thermal annealing and passivation of N-related electronic states by hydrogen. On the other hand, we point out some features of this alloy system and evaluate its potential for device applications. Probably, GaNAsSb can achieve emission at longer wavelengths than GaInNAs alloys grown to date. Its conduction- and valence-band offsets can be independently tuned by adjusting the N and Sb composition, respectively. Since this compound has a single group III element, its electronic structure should be less dependent on alloy configuration than GaInNAs.

Journal ArticleDOI
TL;DR: In this paper, a comprehensive review of nitrogen-induced modifications of the electronic structure of Ga1−yInyNxAs1−x alloys is carried out, and the results are analyzed in terms of the analytical band anti-crossing model as well as the local density approximation calculations and empirical pseudopotential models.
Abstract: In this paper, we carry out a comprehensive review of the nitrogen-induced modifications of the electronic structure of Ga1−yInyNxAs1−x alloys. We study in detail the behaviour of the conduction-band effective mass as a function of Fermi energy, nitrogen content and pressure. From measurements of the plasma frequency for samples with different electron concentrations we have determined the dispersion relation for the lowest conduction band. We have also studied composition, temperature and pressure dependent optical absorption spectra on free-standing layers of Ga1−yInyNxAs1−x (0 ≤ x ≤ 0.025 and 0 ≤ y ≤ 0.09) lattice-matched to GaAs. Spectroscopic ellipsometry measurements performed in a wide photon energy range from 1.5 to 5.5 eV have been used to determine the energy dependence of the dielectric function as well as the energies of E1, E0' and E2 critical point transitions. Experiments have shown that nitrogen has a large effect on the dispersion relations and on the optical spectra for the conduction-band states close to the Γ point. A much smaller effect has been observed for X and L minima as well as for the valence-band states. We have compared our results with other available experimental data. The results are analysed in terms of the analytical band anti-crossing model as well as the local density approximation calculations and empirical pseudopotential models.

Journal ArticleDOI
TL;DR: In this paper, the authors carried out the electrical and optical characterization of thin films of compounds based on SnS bonds (SnS2, Sn2S3), prepared by plasmaenhanced chemical vapour deposition (PECVD), as a function of the relative concentration of the precursor vapours, SnCl4 and H2S, keeping all other deposition parameters constant.
Abstract: We have carried out the electrical and optical characterization of thin films of compounds based on Sn–S bonds (SnS2, Sn2S3), prepared by plasma-enhanced chemical vapour deposition (PECVD), as a function of the relative concentration of the precursor vapours, SnCl4 and H2S, keeping all other deposition parameters constant. In all studied cases, the deposited films were formed by polycrystalline materials. The optical bandgap values of deposited materials were calculated from optical transmittance and reflectance measurements. The SnS2 compound produced under certain deposition conditions has a forbidden bandgap around 2.2 eV. This compound shows n-type electrical conductivity, whose dark value at room temperature is 2 × 10−2 (Ω cm)−1. Also, it shows the typical semiconductor dependence of its electrical conductivity on the temperature with an activation energy of about 0.15 eV. However, thin films of a mixture of SnS2 and Sn2S3 compounds were deposited with higher values of the relative concentration of source vapours than those used to obtain the SnS2 compound. The optical bandgap shows a decreasing trend as the relative concentration increases. A similar trend is observed for dark electrical conductivity. These results create the opportunity to use SnX SY compounds in thin films for building heterojunction solar cells prepared completely by PECVD.

Journal ArticleDOI
TL;DR: In this article, a correlation between data extracted from the currentvoltage characteristics of a junction in dark, deep level transient spectroscopy and the variations of the short-circuit current and open voltage of solar cells versus the logarithm of the irradiation fluence is proposed.
Abstract: Although the defects introduced by irradiation in Si and GaAs have been extensively studied, the centres giving rise to non-radiative recombination have been neither characterized nor identified. We propose here a method allowing one to fully characterize recombination centres, i.e. to obtain their electron and hole capture cross sections as well as their concentration. It is based on a correlation between data extracted from the current–voltage characteristics of a junction in dark, deep level transient spectroscopy and the variations of the short-circuit current and open voltage of solar cells versus the logarithm of the irradiation fluence. The method is applied to characterize and tentatively identify the recombination centres introduced by electron irradiation in Si, GaAs and InGaP.

Journal ArticleDOI
TL;DR: In this paper, the Raman scattering of thermally oxidized gallium selenide (GaSe) and InSe single crystals is discussed and the presence of the Me2Se3 phase (where Me is Ga or In) is common for both of the semiconductors.
Abstract: We discuss the Raman scattering of thermally oxidized gallium selenide (GaSe) and indium selenide (InSe) single crystals. It has been established that the oxidation mechanisms of these compounds are rather different. For InSe, an increase of the oxidation temperature leads to the formation of (SeO4) complexes. For GaSe, it is characteristic that only Ga2O3 is formed as an oxygen-containing phase during the oxidation. The presence of the Me2Se3 phase (where Me is Ga or In) in its own oxide is common for both of the semiconductors.

Journal ArticleDOI
TL;DR: In this paper, the electrodeposition of zinc telluride (ZnTe) thin films on tin conductive oxide substrates in aqueous solution containing TeO2 and ZnSO4 was studied.
Abstract: The electrodeposition of zinc telluride (ZnTe) thin films on tin conductive oxide substrates in aqueous solution containing TeO2 and ZnSO4 was studied. The electrodeposition mechanism was investigated by cyclic voltammetry. The appropriate potential region where formation of stoichiometric ZnTe semiconductor occurs, was found to be −1.1 V versus saturated calomel electrode, and the pH was maintained at 3.5 ± 0.1. The crystallographic structure of the deposited film is seen to be cubic with a preferential orientation along the (111) phase. Optical absorption studies reveal a bandgap of 2.26 eV and optical constants (n and k) are evaluated. Scanning electron microscopy imaging was used to study the surface morphology. The composition of ZnTe films was analysed using an electron microprobe analyser, and the results are discussed.

Journal ArticleDOI
TL;DR: In this paper, the empirical pseudopotential method and its recent applications to the III-V nitride alloys GaAsN, GaPN, GaInAsN and GaAsPN were discussed.
Abstract: We review the empirical pseudopotential method and its recent applications to the III–V nitride alloys GaAsN, GaPN, GaInAsN and GaAsPN. We discuss how studies using this method have provided an explanation for many experimentally observed anomalous nitride phenomena, including sharp photoluminescence lines in dilute alloys, high effective masses, Stoke's shift between emission and absorption in higher concentration alloys for GaAsN and GaPN ternaries. We also discuss predictions of unusual effects that remain to be experimentally discovered in GaInAsN quaternaries and complex GaAsPN solid solutions.

Journal ArticleDOI
TL;DR: In this article, a detailed impact ionization (II) analysis of electrons is presented for AlGaN alloys as a vital resource for solar-blind avalanche photodiode and high power transistor applications.
Abstract: Detailed impact ionization (II) analysis of electrons is presented for AlGaN alloys as a vital resource for solar-blind avalanche photodiode and high power transistor applications. Necessary ingredients for the II characterization are supplied from a recent experiment on the GaN end, and a Keldysh analysis for the AlN end, of the alloy AlGaN. High-field electron dynamics are simulated using an ensemble Monte Carlo framework, accounting for all valleys in the lowest two conduction bands, obtained from accurate empirical pseudopotential band structure computations. The effect of alloy scattering on II is considered and observed to be significant. For any AlxGa1−xN alloy, the electron II coefficients are found to obey the form, A exp(−K/F), for the electric field, F.

Journal ArticleDOI
TL;DR: In this article, a ring geometry with self-aligned in-plane gates was directly written into a GaAs/AlGaAs heterostructure using an atomic force microscope, and the tuning via inplane gates allowed one to study the Aharonov-Bohm effect in the whole range from the open ring to the Coulomb-blockade regime.
Abstract: Using an atomic force microscope a ring geometry with self-aligned in-plane gates was directly written into a GaAs/AlGaAs heterostructure. Transport measurements in the open regime show only one transmitting mode and Aharonov–Bohm oscillations with more than 50% modulation are observed in the conductance. The tuning via in-plane gates allows one to study the Aharonov–Bohm effect in the whole range from the open ring to the Coulomb-blockade regime.

Journal ArticleDOI
TL;DR: A real TE cooler with a finite-rate heat transfer between the surroundings is investigated and a set of theoretical performance formulae is derived from the thermal network model, based on which a general expression for the total cost of a TE cooler is presented.
Abstract: The design goal of a thermoelectric (TE) device is to determine the optimum structure of the semiconductor thermoelements so as to meet the required specifications with a minimum cost. The cost usually consists of the construction costs of semiconductor materials and heat exchangers and the running cost of supplied electricity. A real TE cooler with a finite-rate heat transfer between the surroundings is investigated in this paper. A set of theoretical performance formulae is derived from the thermal network model, based on which a general expression for the total cost of a TE cooler is presented. A practical procedure for optimizing a TE cooler in order to minimize its total cost is described. Furthermore, the optimum design parameters are calculated at some practical operative conditions, for example, maximum cooling power density and maximum benefit of semiconductor materials, etc. The results obtained in this paper could be useful for the designers of TE coolers as well as designers of power generators.

Journal ArticleDOI
TL;DR: In this article, an alternative model for glass/conducting glass/CdS/cdTe/metal solar cells has been formulated, which explains the device behaviour in terms of a combination of a hetero-junction and a large Schottky barrier at the CdTe and metal interface.
Abstract: Making use of the authors' experimental results and the evidence available in the literature, an alternative model for glass/conducting glass/CdS/CdTe/metal solar cells has been formulated. This model explains the device behaviour in terms of a combination of a hetero-junction and a large Schottky barrier at the CdTe/metal interface. The main experimental observations available to date are described and compared with the currently assumed p–n junction model and this proposed new model. It is shown that the proposed model explains almost all the experimental results more satisfactorily. The paper describes the guidelines to further increase the performance efficiencies based on the new model. Following these new guidelines, the authors have fabricated improved devices producing open circuit voltage (Voc) values over 600 mV, fill factor (FF) values over 0.60 and the short-circuit current density (Jsc) values over 60 mA cm−2 for best devices. Although the Voc and FF could be further improved, the remarkable improvement of Jsc indicates the possibility of further development of multilayer graded band gap tandem solar cells based on CdS/CdTe system.

Journal ArticleDOI
TL;DR: In this article, the Hall mobilities of electrons at temperatures between 300-1300 K and holes between 225-600 K were measured and the measured mobilities agree very well with theoretical calculations.
Abstract: We have developed a novel technology for forming high-temperature stable ohmic contacts on CdTe, and we have measured the Hall mobilities of electrons at temperatures between 300–1300 K and holes between 225–600 K. The temperature interval also covers the region 300–600 K, where no data have yet been presented. The measured mobilities agree very well with theoretical calculations.

Journal ArticleDOI
TL;DR: In this article, a stress and strain analysis of InAs islands embedded in a matrix of GaAs substrate and cap layer is presented, where the initial shape of the islands is pyramidal.
Abstract: We report on a stress and strain analysis, using the finite element method, of the heterosystem of InAs quantum dots embedded in GaAs. The methodology of using the finite element method to simulate the lattice mismatch is discussed and a three-dimensional (3D) model of the heterostructure shows the 3D stress distribution in the InAs islands embedded in a matrix of GaAs substrate and cap layer. The initial shape of the InAs islands is pyramidal. The stress and strain distribution calculated corresponds well with the strain induced by the lattice mismatch. Factors such as the height of the spacer layer and the height of the island are found to play an important role in the stress and strain distribution. With the island having the shape of a truncated pyramid, the stress and strain distribution deviates from that of a full pyramidal island showing the effects that a change of shape in the islands has on the stress field. The stress distribution contributes to the driving force for the mechanism of surface diffusion in molecular beam epitaxy. The effects of anisotropy on the strain distribution are also studied.

Journal ArticleDOI
TL;DR: In this article, simple analytical approximations are proposed for describing the temperature and concentration dependences of low-field mobility in the main polytypes of silicon carbide (SiC): 6H, 4H and 3C in wide ranges of temperatures and concentration.
Abstract: Simple analytical approximations are proposed for describing the temperature and concentration dependences of low-field mobility in the main polytypes of silicon carbide (SiC): 6H, 4H and 3C in wide ranges of temperature and concentration. The obtained results can be directly used for the computer simulation of SiC-based devices. Different approaches to the analytical approximation of SiC parameters are critically correlated and analysed.

Journal ArticleDOI
TL;DR: In this paper, a robust method for rolling planar strained heterofilms in preset directions to obtain three-dimensional (3D) free-standing shells of complex geometry is presented.
Abstract: We have developed a new robust method for rolling lithographically defined planar strained heterofilms in preset directions to obtain three-dimensional (3D) free-standing shells of complex geometry. With the example of InGaAs/GaAs strained heterofilms, we show the possibility of forming 3D shells that may be used for creating various microelectromechanical systems. The method features natural compatibility with the well-developed integration technology, which allows formation of micro- (nano-) mechanical and electronic device components on one and the same chip. The simplicity of the proposed method and its applicability to a broad range of heterostructures give us all grounds to anticipate its great potential in device application.

Journal ArticleDOI
Abstract: An unexpected observation in the current–voltage curves of Schottky diodes, containing barrier inhomogeneities generated using the analytical results based on a Gaussian distribution model of barrier heights is reported Calculations based on these results show that, at very low temperatures, Schottky diodes exhibit higher currents than at higher temperatures This is an unusual observation, indicating a high current through the Schottky diodes at lower temperatures, which is inconsistent with the thermionic emission diffusion theory The effects causing this unusual behaviour are explored by analysing a conventional model A more accurate approach is presented which explains this unusual behaviour and yields results consistent with the theoretical behaviour of the Schottky diodes