Table of contents

This paper reviews the current knowledge of reliability and degradation issues connected with the presence of hot electron and impact ionization conditions in GaAs and InP HEMTs for high frequency analogue applications. The physical phenomena taking place in HEMTs at large drain-source electric fields (electron heating, real-space transfer, impact ionization, light emission, gate-drain breakdown) are first described, then the paper moves on to list and discuss the main degradation modes and mechanisms these conditions may bear. Finally, some conclusive remarks are given as to the main requisites for achieving hot electron robustness in HEMTs.

In the charged device model (CDM) test, the relationship between the failure voltage, the capacitance of LSIs and the failure charge was made clear by a new CDM tester. The mobile charge measurement apparatus was fabricated in the tester, and the capacity and the charge could be measured simultaneously in the CDM test. The CDM sensitivity of the logic MOS LSIs was represented as an inherent quantity of charge for each LSI. Furthermore, using the experimental results, a basic protection circuit to withstand the high quantity of charge in the CDM test was described. The practical use of the data gives us methods to prevent electrostatic discharge (ESD) trouble for quarter-micron LSIs.

A theoretical analysis of the photon drag arising from intersubband transitions in a single quantum well embedded in a microcavity has been performed. Based on the density-matrix theory, the expression for the integrated photon drag current is explicitly given. To determine the field, starting from the Maxwell-Lorentz equations, the field in each layer consisting of the quantum-well microcavity structure is explicitly obtained. Then, by matching the boundary conditions, the field in the quantum-well microcavity structure is precisely determined and used to calculate the photon drag current. Detailed numerical calculations show that the photon drag current can be significantly modified due to the coupling between the quantum well and the microcavity.

We study theoretically excitons in semiconductor quantum wells in which the confining potential has a parabolic shape. In particular, we compare results of the variational calculations of the exciton binding energy using two different types of trial wavefunctions, namely we assume the trial function either has a simple form with the variables describing the motion within the quantum well plane separated from those describing the motion along the growth axis or, alternatively, has the form where these variables are not separable. It is shown that with a good accuracy one can use the separable trial wavefunction in a variational calculation for the exciton even in the range of the well widths where such choice leads to sizable errors in the case of rectangular quantum wells. By introducing a new characteristic length scale we also applied the fractional dimension approach to the exciton problem in parabolic quantum well structures and compared this result with the variational approaches.

In a spherical-harmonics expansion formulation of the semi-classical Boltzmann transport equation the influence of surface scattering mechanisms on device characteristics has been investigated. The main feature of this work is to account for global as well as for local scattering mechanisms. The models associated with the surface scattering mechanisms have been applied to the simulation of MOS devices and they proved able to reproduce the mobility degradation of semi-empirical mobility models and experimental data. Moreover, the experimentally detected universal mobility behaviour of inversion layers is quantitatively reproduced by our model.

A new model is proposed for optical absorption in heavily doped p-type semiconductors and quantum wells. The model gives good agreement with experiment for bulk Ge and for the photoresponse of SiGe quantum wells. For wide wells it is found that the second spin-orbit split-off level dominates the quantum well response.

The anomalous `hole' trap like peaks observed in conductance DLTS spectra of GaAs MESFETs have been previously studied and have been associated with surface states present in the ungated regions at the GaAs-passivant interface. Besides these peaks, the conductance DLTS study of thermal emission and capture by these interface traps also indicates the presence of an associated surface conducting layer. These results show that electrons from this thin conducting layer interact with the interface states giving rise to a temperature-dependent surface leakage current when the Schottky gate is reverse biased with respect to the source and/or drain. This surface current affects both the capture and the emission processes of the interface traps. From the conductance DLTS measurements on GaAs MESFETs passivated with films, we have extracted a characteristic thermal activation energy of 0.43 eV for the interface electron traps, in both of these modes. A two-dimensional interface state band model has been used to explain our experimental results reported in this work.

Optical absorption and optically detected magnetic resonance in highly compensated undoped semi-insulating GaAs have been used to study the charge transfer processes between EL2 and an intrinsic trigonal acceptor (TA) pair defect during the photoquenching and thermal recovery of the EL2 defect. The concentrations of the TA acceptors are determined to be at least of the order of . One of its ionization levels is between the two ionization levels of EL2, i.e. 0.54 and 0.76 eV respectively above the valence band. It is concluded that the TA is a deep acceptor which plays an important role in the compensation mechanism of undoped semi-insulating GaAs.

Shubnikov-de Haas measurements between 0.06 and 1.6 K have been performed on two modulation-doped n-type heterostructures, and analysed to extract the quantum lifetime. Use of the conventional Dingle formula resulted in deviations from the expected theoretical behaviour above . The corresponding quantum lifetime appeared to increase with temperature in the same range. The data were then re-analysed using a modified expression, in which the thermal damping term was neglected. This gave plots with the correct characteristics, and a quantum lifetime which was approximately constant with temperature, as expected for ionized impurity scattering in a degenerate electron gas. A decrease in the quantum lifetime was observed above , and this is attributed to increased small-angle scattering due to acoustic phonons.

The structure of porous silicon carbide has been studied using transmission electron microscopy both in planar geometry and in a cross-section of a porous film. Peculiar structures in the form of shared rosettes with petals of about 3-8 m in size and a density of were found in the subsurface layer. These formations are pierced by thin channels (pores) with an average diameter of 10 nm. Near the surface of the layer the channels in the `lobes' may be directed at small angles to the surface, but, with increasing depth, all of them become approximately perpendicular to the surface, with branching observed. On channel walls there is a rather thick layer of fine particles with characteristic dimensions of the order of 0.8-1.0 nm.

Spectral cathodoluminescence studies have been performed with luminescence excited by a narrow (2 m) electron probe on parts of the initial sample and porous film having varied thickness (0.03-3 m). A layered structure was revealed in the porous film, with the layer responsible for the `blue' luminescence band ( eV) due to the presence of fine crystallites located at a certain depth, rather than immediately near the surface.

Second-harmonic (SH) rotational anisotropy measurements performed on epitaxial (CMT) layers grown on CdTe B substrate exhibits an interference in the SH signal originating from the bulk and from the CMT surfaces. The threefold symmetry of the epilayer was shown to be sensitive to the nature of adsorbed species at the surface when in contact with an electrolyte solution despite the strong SH generation in the bulk of the layer. The modification of the SH response from a non-centrosymmetric semiconducting material to such an extent is unusual since bulk SH generation is considered as the dominant contributor in these instances. The case of CMT is, however, rather specific in that the observed SH signal originates from, at most, only the top 40 nm of the CMT epilayer. This important difference means that surface modification by means of electron donating or withdrawing groups will play a large role in the observed SHG signal.

The electrical and photoluminescence properties of heavily doped GaAs:Zn(100) layers grown by liquid phase epitaxy from gallium and bismuth solutions at various temperatures have been studied. It is shown that a new line at 1.35 eV appears in low-temperature photoluminescence spectra of the layers doped at a level over . It is found that this line is associated with a novel defect. The concentration of defects increases with the doping level proportionally to the concentration of free holes to the power . The exponent is independent of the growth solution used (gallium or bismuth) and growth temperature. It has been found that the defect is a neutral complex consisting of native point defects of GaAs - an antisite defect of gallium in an arsenic site and two arsenic vacancies.

Be-doped GaN layers have been grown on Si(111) by molecular beam epitaxy. The relative Be concentration was measured by secondary ion mass spectroscopy analysis. Photoluminescence spectra have been taken under continuous wave and time-resolved conditions. A new emission at 3.384 eV, which is probably related to substitutional Be, is reported, together with its first and second order phonon replica. Clear blue-shifts are observed when increasing temperature and excitation power, suggesting that this emission is associated with a transition from a residual donor to the Be acceptor. From time-resolved spectra, a very slow and strongly non-exponential decay, as well as a red-shift of the peak energy position with time, confirm the donor-acceptor character of the Be-related emission. The estimated ionization energy of the acceptor is around 90 meV, so Be is the shallowest p-dopant ever reported in GaN.

This paper is devoted to the investigation of the effect of electron irradiation (T = 300 K, E = 6 MeV, ) on the galvanomagnetic properties of Se (x = 0.20, 0.25) alloys. Experimental results were explained in the frame of the earlier proposed model of the energy spectrum for electron-irradiated alloys, assuming that electron irradiation leads to appearance of a wide radiation defect band of the acceptor type in the forbidden band of the alloys and to redistribution of electrons between the conduction band and the radiation defect band. By comparing theoretical and experimental dependences of the electron concentration on the radiation flux the main model parameters of the defect formation process (the defect generation rate , the width and the energy position of the band ) were determined in the alloys under investigation. It was shown that agreement between experimental and theoretical data took place only under the assumption that the introduction rate of radiation defects decreases with an increase in the radiation flux. In the present work we put forward the model according to which the major mechanism of the defect formation process in the alloys is the generation of complexes including the primary radiation defects and the intrinsic structure defects typical of initial crystals.

A strong dependence of the intensity of the ordering-induced phonon bands on thermal treatment (rapid cooling and annealing) was observed in room temperature Raman spectra (RS) of -ordered alloys. The changes of the Raman intensity occur only in diagonal backscattering configuration: , where the polarization of light is parallel to the mirror planes of the ordered structure. The changes are absent in the configuration, where the polarization of light is perpendicular to the mirror planes. We found that there are at least two different intensity distributions of the optical phonon bands, the appearance of which in the RS of are determined by thermal treatment and by the alloy film thickness. A bond polarizability model analysis is presented here which shows that the observed RS behaviour can be described in terms of a martensitic transition involving trigonal lattice sites. This is the first observation of the martensitic transition in spontaneously ordered semiconductor alloys.

N-type amorphous silicon-carbon on p-type crystalline silicon heterojunction diodes have been fabricated and electrically characterized. The a-:H film was deposited by plasma-enhanced chemical vapour deposition. The electrical properties were investigated by capacitance-voltage and current-voltage measurements at different temperatures. Current-voltage characteristics present good rectifying properties, 60 000:1 at at room temperature. The analysis of current-voltage characteristics at different temperatures indicates that the current is dominated by recombination at the a-:H side of the space charge region in forward bias. The reverse characteristics show a leakage current which increases exponentially with the applied voltage. Finally, numerical simulations are presented which explain the experimental results throughout the temperature range.

The luminescent properties of undoped ZnO quantum dots encapsulated in various stabilizing agents have been investigated at room temperature. Stoichiometric as well as non-stochiometric ZnO quantum dots have been prepared by different routes. These studies indicate the importance of OH radical on the surface of ZnO quantum dots. In general, it has been observed that surface defects play an active role in the luminescence behaviour of quantum dots. ZnO quantum dots, doped with copper, have also been studied. Doping Cu in ZnO quantum dots, which have OH radical on its surface, is responsible for quenching green luminescence at 530 nm.

Silicide formation on polysilicon from deposited titanium films and effects of subsequent thermal annealing at different temperatures (C-C) have been investigated by grazing-angle XRD, AFM, ESCA and sheet resistance measurements. The results indicated formation of a high-resistivity isomorphic phase (C49), polymorphic phases (C49 and C54) and low-resistivity isomorphic C54 films at low, medium and high annealing temperatures from C to C. The complete conversion from C49 to isomorphic C54 phase occurs at about C. The influence of phase formations and polymorphic transformation on the surface morphology is studied by estimating the r.m.s. surface roughness using AFM. Samples annealed at C have the highest surface roughness of 15.47 nm owing to agglomeration of C54 grains in films. XPS studies showed the formation of a thin layer of on the surface of .

Thin films of copper sulphide with thickness up to m were deposited at C on glass substrates from a solution containing copper(II) chloride, sodium thiosulphate and dimethylthiourea. As prepared and after annealing at C in (100 millitorr), these films showed x-ray diffraction patterns matching that of the mineral covellite (CuS). Annealing the films for 1 h each at C and C in nitrogen resulted in their conversion to S (digenite) and S (chalcocite), respectively. The reduction in sulphur content of the films is evident in the x-ray florescence spectra. The sheet resistance of the films varied with annealing temperature. For a film of m thickness, the observed sheet resistance values are: (as prepared), (C), (C) and (C). The low sheet resistance (and thus the high conductivity, ) leads to a high near-infrared reflectance for the films, 65% (CuS) and 40% (S), at a wavelength of 2500 nm. Analyses of the optical band gap of the films indicate an indirect gap of 1.55 eV for CuS and S and 1.4 eV for S.

Unprecedented Hall mobility, electron concentration and photoconductivity are demonstrated in semiconducting - thin films prepared on Si(111) surfaces by co-sputtering of iron and silicon followed by post-anneal. Characterization of the silicide as a function of the initial temperature and post-treatment shows that annealing temperatures above C are needed to obtain single phase -. Reactive deposition on substrates heated at C leads to textured films. Majority carriers are electrons in all these unintentionally doped films. Hall concentrations between and electrons and respective Hall mobilities from 290 to are measured at room temperature, involving two different conduction band minima in these two extreme cases. Only deep centres exist in the samples having the lower carrier concentration. In such a situation, raw data must be corrected for the substrate contribution to extract values which are relevant for the - film alone. Photoconductivity also takes place in these samples: at 80 K, it shows a maximum value at the direct band gap of - while at 296 K a step still appears at the same energy. Such results are a consequence of the important decrease of the residual impurity concentration in comparison to values previously published.

A comparison of GaInP/GaAs HBTs with and without a base epitaxial regrowth is undertaken via static and low-frequency noise measurements. Current gain values and behaviour versus emitter area are different in both types of transistor. From low-frequency noise measurements emitter series resistances are extracted. Values of resistances are much smaller by about a factor of ten on samples without regrowth. The and g-r noise components are then analysed versus bias and geometry. For samples without regrowth, the and the g-r noise sources are mostly located at the extrinsic base surface and are due to recombinations. These recombinations are suppressed on samples with a base regrowth. On these devices, the noise sources related both to intrinsic and extrinsic phenomena are present. The g-r noise sources are located within the intrinsic transistor and more particularly in the base-collector space-charge region. This is partly explained by a thermal treatment induced by the process technology. Finally, it is shown that the base epitaxial regrowth brings a correlation between base and collector currents.

In this paper, we demonstrate the qualitative influence of a -doping sheet and setback layer on the performance of an InGaP/GaAs heterojunction bipolar transistor (HBT). The results of a theoretical simulation show that the potential spike is reduced by the simultaneous employment of an appropriate setback layer and -doping sheet. Due to the reduction in the potential spike, a high current gain, even at a small collector current regime, and small offset voltage can be attained. Experimentally, an offset voltage as small as 55 mV and current gain of 11 at collector current of A are obtained without a passivation structure.

Le transistor bipolaire à grille isolée (IGBT) est un composant de puissance largement utilisé car il associe, à fort courant et haute tension, la rapidité du MOSFET et la faible chute de tension à l'état passant du transistor bipolaire. Afin d'étendre encore le champ des applications de ce composant, les fabricants tentent de réaliser l'intégration monolithique de circuits de détection, de protection et de commande du sur-courant, de la sur-tension et de la sur-température. Sur des circuits-tests des effets parasites ont été observés, en l'occurrence la perturbation du composant de puissance sur sa logique de contrôle. En s'aidant d'une simulation électrique bidimensionnelle, nous avons mis en évidence les phénomènes perturbateurs et proposer des remèdes.

We obtained high-performance InGaAsP/InP buried heterostructure lasers integrated with butt-coupled waveguides using reactive ion etching (RIE) for mesa definition, brief chemical cleaning for damage relief and low-pressure metalorganic vapour phase epitaxy for the epitaxial layer growth. We measured a coupling efficiency between the active layer and the passive waveguide layer of over per facet across a quarter of a 2 inch InP wafer. The threshold current and the slope efficiency were 13 mA and , respectively, of the long integrated laser. This excellent uniformity and high performance demonstrate that RIE coupled with slight chemical treatments can be successfully used to fabricate high-quality integrated photonic devices. Transmission electron microscopy observation revealed RIE-induced strains and dislocation loops around the etched mesa after the regrowth, which were proposed to be responsible for the inferior characteristics of the lasers with mesas that were reactive ion etched but had not been cleaned in HBr-based solution.

A new multi-heterojunction photovoltaic infrared photodetector is presented. The device has been developed specifically for operation at elevated temperatures for detection of infrared radiation in the mid- and long-wavelength range of the infrared spectrum. The new structure solves the perennial problems of poor quantum efficiency and low dynamic resistance found in conventional long-wavelength infrared photovoltaic detectors when operated near room temperature. Analysis indicates that practical devices with properly optimized multiple heterojunction layers are capable of achieving the performance limits imposed by the statistical nature of thermal generation-recombination processes. In order to demonstrate the technology, multiple heterojunction devices have been fabricated on epilayers grown by isothermal vapour phase epitaxy of HgCdTe and in situ As p-type doping. The detector structures were formed using a combination of conventional dry etching, angled ion milling and angled thermal evaporation for contact metal deposition. These multi-junction HgCdTe heterostructure devices exhibit performances comparable to, or better than, existing long-wavelength photoconductors and photoelectromagnetic detectors operated under the same conditions. A typical of optically immersed multiple heterostructure photovoltaic detectors of approximately can be achieved at a signal wavelength of and for operation at 230 K.

Leakage currents originating in the virtual substrates which are required in many Si heterostructure systems have been measured. Both ohmic (AuSb) and Schottky (Pt) contacts to a modulation-doped Si:SiGe heterostructure show significant leakage when the contacts cover deep pits originating from growth defects and contaminants. Shallower pits emerging later in the growth process do not contribute to extra conduction. These pits appear after growth of the graded layer which leads us to conclude that carrier transport from the contact along the dense network of dislocations formed in the graded buffer layer is responsible for the leakage found in Si:SiGe systems making use of virtual substrates.

Hydrogenation studies in p-GaAs have been performed by fabricating Pd/p-GaAs devices. The devices have been studied by I-V and C-V measurements. Hydrogenation has been found to improve the ideality factor of the diode. The forward C-V characteristics have shown the presence of interfacial deep donors at and , the density of which decreased on hydrogenation. The content of hydrogen in Pd/p-GaAs has been measured both in the semiconducting substrates and the palladium thin film by ERDA using 55 MeV Si ions.