Showing papers in "Semiconductor Science and Technology in 1992"
TL;DR: In this paper, modulation-doped Si/SiGe heterostructures were grown on different types of partly relaxed SiGe buffer layers, which are required in this material system to obtain a large enough conduction band offset.
Abstract: n-type modulation-doped Si/SiGe heterostructures were grown on different types of partly relaxed SiGe buffer layers, which are required in this material system to obtain a large enough conduction band offset. The samples were characterized by secondary-ion mass spectroscopy, X-ray rocking analysis, transmission electron microscopy, Rutherford backscattering and temperature-dependent Hall measurements. The highest Hall mobilities of 173000 cm2 V-1 s-1 at 1.5 K were found in a sample grown on a thick, linearly graded SiGe buffer layer deposited at 750 degrees C. Such layer sequences reach room-temperature mobilities around 1800 cm2 V-1 s-1. Mainly at lower temperatures, a strong reduction of the Hall mobility is found if either a conventional buffer layer without Ge grading is used, or if the modulation-doped SiGe barrier of the active layers begins to relax with respect to the strained Si channel.
254 citations
TL;DR: In this article, an analytical review of the last five or six years of research and development in SiC is presented, which outlines the major achievements in single crystal growth and device technology.
Abstract: The present paper is an analytical review of the last five or six years of research and development in SiC. It outlines the major achievements in single crystal growth and device technology. Electrical performance of SiC devices designed during these years and some new trends in SiC electronics are also discussed. During the 1980s the studies on sublimation and liquid-phase epitaxial growth of SiC single crystal were continued successfully. At that time, such methods as chemical vapour deposition, thermal oxidation, 'dry' plasma etching and ion implantation which yielded good results with silicon, came into use. As a result of the technological progress, discrete devices appeared, which incorporated the potential advantages of SiC as a wide bandgap material. Among these were high temperature (500-600 degrees C) rectifier diodes and field-effect transistors, high efficiency light-emitting diodes for the short-wave region of the visible spectrum, and detectors of ultraviolet radiation. It should be stressed that the devices were of commercial quality and could be applied in various fields (control systems of automobile engines, aerospace apparatus, geophysical equipment, colour displays in information systems, etc.). The developments in technology and the promising results of research on electrical performance of the devices already available give hope that in the near future SiC may become the basic material for power microwave devices, and for thermo- and radiation-resistant integrated circuits. This process can be stimulated by further perfection of single-crystal substrates of large area, by development of stable high temperature ohmic contacts, micro- and heterostructures.
247 citations
TL;DR: In this article, a quantum point contact is used as a miniature thermometer to measure the thermal conductance and the Peltier coefficient of a point contact, and the quantum size effects of these properties are investigated.
Abstract: The conductance, the thermal conductance, the thermopower and the Peltier coefficient of a quantum point contact all exhibit quantum size effects. The authors review and extend the theory of these effects. In addition, they review their experimental work on the quantum oscillations in the thermopower, observed using a current heating technique. New data are presented showing evidence for quantum steps in the thermal conductance, and (less unequivocally) for quantum oscillations in the Peltier coefficient. For these new experiments the authors have used a quantum point contact as a miniature thermometer.
130 citations
TL;DR: In this paper, the authors present the principles and application examples of a recently refined, computerised, surface photovoltage (SPV) method, capable of wafer-scale, non-contact mapping of metal contaminants in the bulk and on the surface with sensitivities as high at 1010 atoms cm-3.
Abstract: The authors present the principles and application examples of a recently refined, computerised, surface photovoltage (SPV) method. This new method is capable of wafer-scale, non-contact mapping of metal contaminants in the bulk and on the surface with sensitivities as high at 1010 atoms cm-3. They demonstrate the unique ability of SPV to measure product wafers with finished integrated circuits.
126 citations
TL;DR: In this article, the energy and oscillator strengths of the bandgap and intersubband transitions have been studied theoretically for SimGen SLS with a variety of period lengths, particularly those of m+n=10.
Abstract: Ultrathin SimGen (m monolayers (ML) Si, n ML Ge) strained layer superlattices (SLS) have been grown by molecular beam epitaxy. The optical properties of these structures depend on the concept of band-structure engineering by Brillouin zone folding and strain adjustment of the SLS by a Si1-ybGeyb alloy buffer layer. The energies and the oscillator strengths of the bandgap and intersubband transitions have been studied theoretically for SimGen SLS with a variety of period lengths, particularly those of m+n=10. Various characterization tools such as X-ray diffraction, transmission electron microscopy, Raman spectroscopy, photoluminescence (PL) and photocapacitance measurements have been used to analyse growth quality, interface sharpness, morphology, strain distribution and optical properties of the superlattice experimentally. The PL data indicative of the quasidirect energy gap of the 10 ML strain-symmetrized SLS in the near-infrared spectral regime (h nu approximately 0.8 eV) are presented and discussed as well as complementary photocapacitance measurements on a p-n doped Si4Ge4 SLS diode. The fabrication of test mesa diodes from Si/Ge SLS structures is described. Finally, device applications offering the possibility of monolithic integration of superlattice devices with complex silicon-based electronic circuits are outlined.
119 citations
TL;DR: In this paper, a method for revealing point defects in silicon single crystals has been investigated using preferential etching technique using Secco's etchant, showing that the flow patterns were so characteristic that the D region could be distinguished very easily.
Abstract: A method for revealing point defects in silicon single crystals has been investigated. D or A defects could be revealed by a preferential etching technique using Secco's etchant. Wedge-shaped flow patterns and etch pits were recognised in the D and A regions, respectively. The flow patterns were so characteristic that the D region could be distinguished very easily.
116 citations
TL;DR: In this paper, a polycrystalline films of ZnS with a slight excess of S have been grown on (100) Si by congruent sublimation from a single Knudsen cell.
Abstract: Polycrystalline films of ZnS with a slight excess of S have been grown on (100) Si by congruent sublimation from a single Knudsen cell. Intense blue emission is observed at 460 nm from room-temperature photoluminescence studies, and is ascribed to S-Zn vacancies acting as self-activated (SA) centres. The emission is quenched by the addition of Zn from a second Knudsen cell, which also causes the growth of a luminescent peak centred on 678 nm. No reduction in the SA luminescence is seen when co-sublimating ZnS and AgS, implying that it is not possible to remove the S-vacancy completely. Quenching of the blue emission occurs when Mn, instead of Zn, is added to the ZnS films, providing direct evidence of Mn incorporation into Zn vacancies. At the optimum Mn concentration, the intensity of the Mn emission at 580 nm is comparable to the blue emission (460 nm) from the undoped ZnS films.
89 citations
TL;DR: In this article, the k.p theory of the band structure of IV-VI compounds is presented, taking into account the narrow energy gaps and strong spin-orbit interactions in the materials.
Abstract: Magneto-optical properties of PbTe and PbSe alloyed with paramagnetic ions Mn and Eu are reviewed. The k.p theory of the band structure of IV-VI compounds is presented, taking into account the narrow energy gaps and strong spin-orbit interactions in the materials. The exchange interaction between the paramagnetic ions and mobile carriers is included in the framework of the mean-field approximation. The experimental data of various authors on magnetization, interband magneto-optics, intraband magneto-optics and four-wave mixing are presented. All results are successfully described by the theory, treating the exchange integrals as adjustable parameters. It is shown that the exchange interaction is of particular importance for the valence bands. Differences between semimagnetic behaviours of Mn-based and Eu-based systems are emphasized as well as those between the IV-VI and II-VI semimagnetic compounds.
85 citations
TL;DR: In this paper, chemical deposition of good quality ZnS thin films from aqueous solutions containing zinc sulphate, NH3/NH4Cl buffer (pH 10), triethanolamine and thioacetamide is described.
Abstract: Chemical deposition of good quality ZnS thin films from aqueous solutions containing zinc sulphate, NH3/NH4Cl buffer (pH 10), triethanolamine and thioacetamide is described. It is shown that the presence of these films on glass substrates offers various advantages in the case of chemically deposited metal sulphide thin films: (i) improved adhesion of Bi2S3 thin films, which is vital for growing films of thickness >0.2 mu m for semiconductor applications and in metal sulphide thin film (MSTF) photography based on photoaccelerated chemical deposition; (ii) improved adhesion of CuxS films, offering the choice of different shades of colours for the same integrated transmittance in the visible region of approximately 20% in solar control coatings and the possibility of multiple-dip deposition of CuxS films to enhance the film thickness, enabling the realization of solar absorptance of approximately 90%; and (iii) reduced reflectance in the visible light which can reduce the glare from PbS solar control coatings and improve the solar absorptance in thicker PbS coatings and offer better contrast in MSTF photography.
74 citations
TL;DR: In this article, the effect of crystal growth conditions on oxygen precipitation in silicon crystals with uniform oxygen distribution and concentration of (1.1-1.2)*1018 cm-3.
Abstract: The effect was studied of crystal growth conditions on oxygen precipitation in silicon crystals with uniform oxygen distribution and concentration of (1.1-1.2)*1018 cm-3. Following annealing at 800-1000 degrees C X-ray topographs were obtained and the concentration of precipitated oxygen was measured. The results show that the process of formation of oxygen precipitation centres during crystal growth has several stages and intrinsic point defects play a decisive role in all these stages. The type of dominating intrinsic point defects, their concentration, the crystal cooling rate at the stage of grown-in microdefect formation and the duration of low-temperature stage are all critical. A qualitative model for the formation of oxygen precipitation centres is proposed which takes into account the crystal cooling curve, type of intrinsic point defects, their concentration and distribution in the crystal volume. Depending on the crystal growth conditions different types of oxygen precipitation centres may arise. In the case of the 'interstitial' regime ( xi xi t) centres of two kinds may coexist: high-temperature oxygen microprecipitates (grown-in A' defects) and low-temperature centres. Nucleation of A' defects occurs at 1150-1000 degrees C (depending upon the crystal pulling rate), the low-temperature centres are formed in the range 760-610 degrees C. The low-temperature centres have been found to depend on the high-temperature ones. The dependence is hypothesized to be due to vacancy supersaturation established at the onset of the low-temperature stage.
73 citations
TL;DR: In this paper, the authors have investigated InSb layers grown heteroepitaxially on GaAs(100) substrates by molecular beam epitaxy (MBE), and the dependence of electron mobilities on the MBE-growth conditions was investigated.
Abstract: The authors have investigated InSb layers grown heteroepitaxially on GaAs(100) substrates by molecular beam epitaxy (MBE). The dependence of electron mobilities on the MBE-growth conditions was investigated. The best room temperature mobility, 55000 cm2 V-1 s-1 for a 2 mu m thick layer, was obtained for a growth temperature of 420 degrees C with an antimony over indium ratio of 1.4. The 14.6% lattice mismatch between epilayer and substrate gives rise to threading dislocations and microtwins, as evidenced by transmission electron microscopy. The defects are shown to reduce the mobility for thin samples. One of the most interesting results of the work is the evidence of an electron accumulation layer at the InSb(100) surface. This result is obtained from temperature-dependent Hall measurements which exhibited two singularities in the carrier concentration versus temperature plot. Calculations of the Hall constant considering parallel conduction is successfully used to model this temperature dependence. The MBE-grown InSb layers are shown to have an unintentional acceptor background. The authors also investigated n-type doping using silicon. It is shown that the measured low temperature carrier concentrations and mobilities in undoped samples are considerably influenced by compensation effects.
TL;DR: In this paper, the electrical quality of InAs films grown on GaAs substrates by MBE is found to be optimum for growth temperatures close to 490 degrees C. The Hall mobility for such samples is 80000 cm2 V-1 s-1 at 77 K for film thicknesses of 5 mu m but falls to about 10000 cm2V-1s-1 with a thickness of 0.05 mu m.
Abstract: The electrical quality of InAs films grown on GaAs substrates by MBE is found to be optimum for growth temperatures close to 490 degrees C. The Hall mobility for such samples is 80000 cm2 V-1 s-1 at 77 K for film thicknesses of 5 mu m but falls to about 10000 cm2V-1s-1 at a thickness of 0.05 mu m. The carrier concentration in the bulk of the films is believed to be less than 1015 cm-3. The carrier concentration rises and the mobility falls as the growth temperature is varied on either side of this optimum value, reaching 2.5 *1016 cm-3 and 15000 cm2 V-1 s-1 at 77 K respectively for a growth temperature of 350 degrees C. Extremely sharp free-carrier cyclotron resonance and shallow donor lines are observed from the bulk of the film in far-infrared magneto-optical measurements, together with a very broad but strong cyclotron resonance line from an electron accumulation layer believed to be at the surface. The width of the cyclotron resonance line is consistent with a bulk mobility of the order of 200000 cm2 V-1 s-1 and the decrease in Hall mobility, together with the apparent increase in carrier concentration with decreasing film thickness, can be explained by the parallel conductance from the two-dimensional electron gas at the surface. There is no evidence for a significant reduction in mobility from the high density of threading dislocations caused by the mismatch with the GaAs substrate. The sharpness of the cyclotron resonance allows an accurate value for the band edge effective mass to be determined of 0.0236+or-0.0003 me with a pressure coefficient of +2.0% kbar-1. The donor lines are sufficiently sharp that central cell structure due to two different donor contaminants can be detected, and these donors are thought to be sulphur and selenium originating from the As source material. Certain of the transitions detected are too energetic to be from the shallow donors and these are thought to arise from singly ionized double donors which may be arsenic antisites. Silicon is found to act as a donor dopant up to high concentrations (6*1019 cm-3 where the mobility is 2000 cm2 V-1 s-1).
TL;DR: In this article, the authors reviewed and discussed the mechanism of arsenic precipitation from the viewpoint of stoichiometry and showed that these arsenic precipitates affect the device properties of chloride epitaxial-type MESFETS.
Abstract: It is well known that there are many arsenic precipitates in LEC GaAs, the dimensions of which are 500-2000 AA. The authors have recently found that these arsenic precipitates affect the device properties of chloride epitaxial-type MESFETS. They also affect the formation of small surface oval defects on MBE layers. To reduce the density of these arsenic precipitates, a multiple-wafer-annealing (MWA) technology has been developed in which wafers are annealed first at 1100 degrees C and then at 950 degrees C. By this annealing, highly uniform substrates with low arsenic precipitate densities, uniform PL and CL, uniform microscopic resistivity distributions and uniform surface morphology after AB etching can be obtained. These MWA wafers showed low threshold voltage variations for condensed ion-implantation-type MESFETS. In the present paper recent works are reviewed and the mechanism of arsenic precipitation is discussed from the viewpoint of stoichiometry.
TL;DR: In this article, a diffusion coefficient of 3*10-12 cm2 s-1 was derived for polycrystalline silicon thin film transistors formed with undensified gate oxides.
Abstract: Polycrystalline silicon thin film transistors formed with undensified gate oxides have shown instability phenomena not observed for TFTS formed with oxides annealed at 600 degrees C or above. These instabilities are related to ionized water in the oxide, with positive (H+) and negative (OH-) ions drifting on the application of gate bias to produce both negative and positive threshold voltage shifts. The mobility for the OH- ions is found to be lower than that for the H+ ions, as might be expected. In addition, kinks in the subthreshold characteristic are sometimes seen, and these are shown to be due to a sidewall effect. The water diffuses in from the atmosphere laterally under the gate electrode, and this gives rise to a gate length dependence of the effects. From this dependence a diffusion coefficient approximately 3*10-12 cm2 s-1 is deduced at room temperature. This is some eight orders of magnitude higher than that for fused silica, and confirms the porosity of the material.
TL;DR: The charge injection transistor (CHINT) as discussed by the authors is a three-terminal semiconductor device based on controlled real-space transfer of hot electrons between two conducting layers separated by a potential barrier.
Abstract: The charge injection transistor, or CHINT, is a three-terminal semiconductor device based on controlled real-space transfer of hot electrons between two conducting layers separated by a potential barrier. The symmetry of hot-electron injection by real-space transfer with respect to the polarity of the heating field allows the implementation of novel circuit elements. Thus, in the basic CHINT structure, the collector current is an exclusive OR function of voltages applied to the emitter electrodes. Moreover, the authors have proposed and demonstrated a multiterminal device structure with three symmetric logic inputs that performs both the NOR and the AND logic functions, and can be switched between these functions in the course of the circuit operation. Symmetry properties of real-space transfer transistors have been studied theoretically, with the help of continuation modeling and transient device simulation. These studies reveal a variety of instabilities and a striking novelty of multiply connected current-voltage characteristics. The authors have found that the CHINT can support anomalous steady states in which hot-electron injection occurs in the absence of any voltage between the emitter electrodes. In these states, some of which are not only stationary but also stable with respect to small perturbations, the electron heating is due to the fringing field from the collector electrode. Some of the anomalous states break the reflection symmetry in the plane normal to the channel at midpoint. The study elucidates the formation of hot-electron domains.
TL;DR: In this paper, the reduction of tungsten oxide WO3.xH2O in contact with TiO2 grains suspended in water is found to reduce to WO2.96.
Abstract: Hydrated tungsten oxide WO3.xH2O in contact with TiO2 grains suspended in water is found to reduce to WO2.96.xH2O upon irradiation with UV light. Measurement of the band position of WO3.xH2O suggests that electron transfer from TiO2 to WO3.xH2O is responsible for the reduction.
TL;DR: In this paper, the quantum-confined Stark shift was calculated for eight differently shaped simple Al0.4Ga0.6As/AlxGa1-xAs quantum wells.
Abstract: The quantum-confined Stark shift was calculated, using a numerical method, for eight differently shaped simple Al0.4Ga0.6As/AlxGa1-xAs quantum wells. The dependence of the electron and heavy-hole ground-state interband transition energy on external electric field, quantum well profile and its thickness was investigated. Calculations also include the excitation binding energy, the overlap of the electron and hole wavefunctions and their average spatial separation. A wider well has a larger Stark shift, independent of its shape. An extensive comparison was made of the field response to differently shaped wells having the same zero-field electron ground-state energy (78 meV). The thinnest was a 51 AA wide square well and the thickest a 261 AA asymmetric triangular well. The symmetric and asymmetric triangular wells were found to exhibit the largest Stark shifts but also had a larger reduction of the overlap and exciton binding energy. The square well, on the contrary, had the smallest Stark shift but also smaller variation of the overlap and exciton binding energy. Other wells exhibited characteristics between these two extreme cases.
TL;DR: In this article, a charge collection contrast of a small spherical defect or a straight dislocation parallel to the surface of a semiconductor is calculated by a direct, though approximate, solution of the integral equation for the excess minority carrier density in the presence of each defect.
Abstract: The charge collection contrast of a small spherical defect or a straight dislocation parallel to the surface of a semiconductor is calculated by a direct, though approximate, solution of the integral equation for the excess minority carrier density in the presence of each defect. The analysis is carried out for a semi-infinite semiconductor where the surface acts as a collector, and holds for arbitrary recombination activity of the defect. The new expressions for the effective strength are shown to extend earlier results obtained for the dislocation case with the iteration-perturbation method. The relation between measured defect strength and defect characteristics is illustrated and the range of validity of the first-order contrast analysis is discussed.
TL;DR: In this article, the authors used contactless transient photoconductivity measurements to study excess charge carrier transport in single-crystal silicon wafers and determined the minority carrier lifetime from the decay behavior by varying the thickness of the wafer.
Abstract: Contactless transient photoconductivity measurements are used to study excess charge carrier transport in single-crystal silicon wafers. It is shown that the minority carrier diffusion constant and the minority carrier lifetime can be determined from the decay behaviour by varying the thickness of the wafer. The presence of non-uniform defect densities can be studied by their influence on the diffusion of excess carriers. This is demonstrated by investigation of a proton-irradiated wafer and of a wafer after an internal gettering treatmen.
TL;DR: In this article, a new As antisite-related defect was detected with a reduced 75As hyperfine splitting as compared with that of EL2+ in higher temperatures (325 degrees C, 400 degrees C).
Abstract: GaAs layers grown by the molecular beam epitaxy (MBE) method at low temperatures (200 degrees C) and also MBE samples grown at 300 degrees C highly doped with Be or Si show high concentrations of As antisite-related defects in the optical absorption and in the magnetic circular dichroism of the absorption (MCDA). With optical detection of EPR it is shown that these antisite-related defects have properties similar to those of the EL2 defects except for the EL2 bleaching characteristics and the so called zero phonon line. Their spin-lattice relaxation time is strongly reduced compared with that of EL2+. These differences may be related to their high concentrations, which are of the order of approximately 1019-1020 cm-3. In MBE samples grown at higher temperatures (325 degrees C, 400 degrees C) a new As antisite-related defect was detected with a reduced 75As hyperfine splitting as compared with that of EL2+. This new As antisite-related defect has properties very similar to those of another As antisite-related defect previously detected in horizontal Bridgman n-type GaAs. A comparison of four different As antisite-related defects with similar reduced 75As hyperfine splittings is presented.
TL;DR: In this article, the authors estimate the peak energies of Zn(Cd)S(Se) semiconductors using the available photoluminescence data and construct a band alignment diagram which predicts that CdSe-CdS and CdS-ZnSe are type-II superlattices with electron confinement in the cdS layers; these predictions are borne out by experiment.
Abstract: The authors estimate, by reviewing the available photoluminescence data, the band alignments at heterojunctions of Zn(Cd)S(Se) semiconductors. The photoluminescence peak energies of ZnSe-ZnS, CdS-ZnS and CdSe-ZnSe strained layer superlattices (SLS), with a range of well and barrier widths, have been calculated using Kronig-Penney theory and assumed values of the band offsets which yield acceptable fits to both the experiments and data taken from the literature. For ZnSe-ZnS SLS, fair agreement is obtained between calculation and experiment by assuming, in line with previous work, a negligible conduction band offset. At the same time, good estimates of the photoluminescence peak energies of CdS-ZnS and CdSe-ZnSe superlattices are obtained by assuming a negligible valence band offset in each case. The authors construct a band alignment diagram which predicts that CdSe-CdS and CdS-ZnSe are type-II SLS with electron confinement in the CdS layers; these predictions are borne out by experiment.
TL;DR: In this paper, the authors used heat pulse techniques to study the energy relaxation of a hot two-dimensional electron gas (2 DEG) in a GaAs/AlGaAs heterojunction.
Abstract: The authors have used heat pulse techniques to study the energy relaxation of a hot two-dimensional electron gas (2 DEG) in a GaAs/AlGaAs heterojunction. The 2 DEG was heated by applying short ( approximately=100 ns) electrical pulses to the drain-source contacts of the device. The electrons lost energy by emitting phonons which were detected by a CdS bolometer on the opposite side of the GaAs substrate. A change in the nature of the phonon signal occurring at an excitation level of about 5 pW per electron indicated a change in the phonon emission process. The corresponding electron temperature, Te, at which optic phonon emission is expected to become the dominant energy relaxation process was estimated to be about 60 K. At powers well below the change-over, the authors found that the energy loss rate per electron, Pe, due to acoustic phonon emission is proportional to Te3. At much higher powers, Pe varies as exp(-h(cross) omega LO/kTe), where h(cross) omega LO is the longitudinal optic phonon energy. They obtained a value of 3.3 ps for the electron-optic phonon scattering time, which is consistent with the range of values found in the literature.
TL;DR: In this article, the properties of amorphous silicon carbide (a-SiC) on p-type crystalline silicon (c-Si) have been investigated by measuring their currentvoltage and capacitance-voltage (C-V) characteristics, as well as the temperature dependence of their current.
Abstract: Electrical properties of heterojunctions consisting of amorphous silicon carbide (a-SiC) on p-type crystalline silicon (c-Si) have been investigated by measuring their current-voltage (I-V) and capacitance-voltage (C-V) characteristics, as well as the temperature dependence of their current (I). The I-V characteristics of a-SiC/c-Si(p) heterojunctions exhibit a low turn-on voltage and a high reverse breakdown voltage (about 140 V). It was found that a model of an abrupt anisotype crystalline heterojunction is valid for the a-SiC/c-Si(p) structure. This model, for values of forward-bias voltage lower than a critical value VT, predicts that at low temperatures (T 250 K) recombination-diffusion becomes the dominant transport mechanism. For higher voltages (V>VT), the tunnelling process dominates in the whole temperature range studied. From I-V measurements of a-SiC/c-Si(p) heterojunctions it was concluded that the conductivity of undoped a-SiC is n-type. Finally, from C-V measurements, the value of electron affinity of a-SiC was obtained, for the first time, and it was found to be chi 1=4.12+or-0.04 eV.
TL;DR: In this paper, a new approach to Monte Carlo simulation of electron transport in semiconductors, which has recently appeared in the literature, is reviewed, and applications of the weighted Monte Carlo technique to the evaluation of high-energy tails of the distribution function and of the electron current through a potential barrier are presented.
Abstract: The theory of electron transport in semiconductors is traditionally formulated in terms of the semiclassical Boltzmann equation. In nonlinear transport such an equation must be solved without linearization with respect to the external driving fields. This task is practically impossible by analytical means, but for many years a Monte Carlo numerical technique has been successfully applied to all sorts of problems in semiconductor electron transport. In this paper a new approach to Monte Carlo simulation of electron transport in semiconductors, which has recently appeared in the literature, is reviewed. In the traditional Monte Carlo approach a direct simulation of the electron motion is realized, where all possible events (scattering processes) occur with the same probability as in the 'real' world. On the contrary, in the new approach, called the weighted Monte Carlo technique, events occur with arbitrary probabilities, and the weight of the particle in the simulation is accordingly modified in such a way as to maintain an unbiased result. In this way it is possible to emphasize, during the simulation, the analysis of the effect of rare events that in standard simulations would occur too rarely. The traditional Monte Carlo approach is recovered as a special case of this new more general technique. Applications of the weighted Monte Carlo technique to the evaluation of high-energy tails of the distribution function and of the electron current through a potential barrier are presented. A generalization of the method to quantum electron transport is also reviewed.
TL;DR: In this article, a generalized method of DC and high-frequency analysis for microwave transit time diodes in mixed tunnelling and avalanche mode is reported, which can be applied to any type of diode structure.
Abstract: A generalized method of DC and high-frequency analysis for microwave transit time diodes in mixed tunnelling and avalanche mode, which can be applied to any type of diode structure is reported. Taking a purely field-dependent tunnel generation rate for electrons, the same is computed for holes from a simulated energy band diagram within the depletion layer of the diode. The method has been applied to a variety of Si, GaAs and InP diode structures. The results show a substantial degradation of IMPATT properties due to phase distortion caused by the tunnelling current.
TL;DR: In this article, the temperature coefficient of the barrier height ( alpha ) and the Richardson constant (A**) for Schottky diodes consisting of Au and Cu contacts on GaAs were measured.
Abstract: Careful measurements have been made of the temperature coefficient of the barrier height ( alpha ) and the Richardson constant (A**) for Schottky diodes consisting of Au and Cu contacts on GaAs. The metals were deposited at a pressure of approximately 10-10 Torr so that there is no possibility of an oxide film between metal and semiconductor. The values obtained for alpha were (-2.3+or-0.3)*10-4 eV K-1 and (-3.2+or-0.3)*10-4 eV K-1 for Au and Cu, respectively, the corresponding values of A** being 1.5*104 A m-2 K-2 and 16*104 A m-2 K-2. The values for Al/GaAs diodes obtained previously were (-3.8+or-0.3)*10-4 eV K-1 and 0.41*104 A m-2 K-2. The variation of alpha between metals implies that the interface states which determine the barrier height depend on the metal, and the substantial difference between the values of A** suggest that the band structure of the metal plays a role in determining the reflection coefficient for electron at the interface.
TL;DR: AugAuger recombination in quantum well (QW) semiconductors is re-investigated taking into account a realistic band structure instead of the usual parabolic approximation in this article, since direct AR is negligible in QWS phonon-assisted AR is treated.
Abstract: Auger recombination (AR) in quantum well (QW) semiconductors is re-investigated taking into account a realistic band structure instead of the usual parabolic approximation. Since direct AR is negligible in QWS phonon-assisted AR is treated. The theoretical results are in good agreement with experimental investigations. In contrast, the description of QWS by a reduced heavy-hole mass is insufficient. The influence of AR on the temperature dependence of semiconductor lasers is discussed.
TL;DR: In this paper, the L+ branch of the plasmon-phonon-plasmon system was observed for the first time in Raman experiments with InAs.
Abstract: Raman scattering by coupled plasmon-phonon modes is studied with Si-doped InAs epilayers grown by MBE with carrier concentrations from 7.5*1017 cm-3 to 4*1019 cm-3. Unexpectedly, an unscreened LO line is observed throughout the whole carrier concentration range together with a low frequency (L-) line arising from wavevector dependent LO phonon-plasmon coupling. The frequency of the L- branch lies between the LO and TO phonon frequencies and approaches the TO frequency asymptotically from the high-frequency side as the carrier concentration increases. This behaviour is attributed to competition between screening (dominant in the high-density limit) and large-wavevector induced decoupling. The L+ branch of the plasmon-phonon system is observed for the first time in Raman experiments with InAs.
TL;DR: In this article, a photoluminescence investigation of heavily Si-doped (111)A-oriented GaAs samples was performed with different As overpressures, and the authors suggested that their relative equilibrium is given by VAs to or from VGa+GaAs, where GaAs is a gallium antisite, and that by increasing the As pressure this reaction is moved to the left.
Abstract: The authors report on a photoluminescence investigation of heavily Si-doped (111)A-oriented GaAs samples. Molecular beam epitaxial growth has been performed with different As overpressures. The increase of the As pressure induces a site switching of Si from an As site (where Si is an acceptor) to a Ga site (where Si is a donor). This conversion from p- to n-type coincides with a change in the main point defect present in the sample: As vacancy (VAs) for low As pressure and Ga vacancy (VGa) for high As pressure. The authors suggest that their relative equilibrium is given by VAs to or from VGa+GaAs, where GaAs is a gallium antisite, and that by increasing the As pressure this reaction is moved to the left.
TL;DR: In this article, a unique Monte Carlo simulation of the bandstructure of the semiconductor, the anisotropy of the scattering rates due to both the density-of-states and the electron-phonon matrix elements, and the realistic phonon dispersion, including the impact ionization scattering rate and the intracollisional field effect is presented.
Abstract: The authors have constructed a unique Monte Carlo simulation which takes into account (i) the bandstructure of the semiconductor, (ii) the anisotropy of the scattering rates due to both the density-of-states and the electron-phonon matrix elements (iii) realistic phonon dispersion, and (iv) an impact ionization scattering rate including the anisotropy of the rate and the intracollisional field effect. The sole inputs to the simulation are the empirical local pseudopotential form factors of the semiconductor, and an appropriate dynamical matrix to describe the lattice dynamics. The only freedom they have in constructing the transport model is in choosing an interpolation of the pseudopotential between 'known' form factors. This is necessary for the calculation of the rigid pseudo-ion matrix elements. This computational model provides the authors for the first time with a rigorous test of the ability to formulate and calculate semiclassical transport properties based on fundamental physical principles, i.e. they calculate both the bandstructure and the electron-phonon interaction using the same pseudopotentials to describe the periodic crystal potential.