The present paper describes the evolution of native defects and the introduction of new defects by transient annealing on unimplanted Bridgman (B) or Liquid Phase Epitaxy (LPE) Gallium Arsenide (GaAs). Three techniques covering all the timescales below those available with the conventional furnace annealing were used: Pulsed Electron Beam Annealing (PEBA), Continuous Wave Laser (CWLA) and Rapid Thermal Annealing (RTA). Electronic defects have been investigated by Deep Level Transient Spectroscopy (DLTS). The evolution of native defects and the introduction of new defects, are strongly dependent on the annealing technique. A significant decrease of EL2 concentration has been observed after PEBA, but it is not affected by CWLA or RTA under our annealing conditions. On the contrary, the other native defects EL6 and EL3 are completely annealed by RTA and PEBA. Furthermore, both DLTS spectra recorded after PEBA and RTA on the B substrates show introduction of new defects. However, CWLA does not affect the defects present in B GaAs, but an electron trap termed PL1 was introduced by this treatment in a thin oxide layer formed on the LPE grown GaAs.

We discuss Extended X-ray Absorption Fine Structure (EXAFS) experiments on impurities in semiconductors. The local structure of the impurity site is determined for the first, second and third neighbor shells. These studies are carried out on absorption edges in the soft x-ray region using a novel fluorescence detection scheme which reveals improved detection sensitivity when compared with more standard electron Auger yield methods. The higher detection sensitivity allows structural studies at atomic densities as low as 1018 at/cm3 and this technique is used to study the local structure of P and S impurities in GaAs and of S in Alx Gal−x, As at concentrations of 1019–1020 at/cm3. The P atoms are substitutional on As sites, and a breathing relaxation of the P first shell Ga atoms is responsible for a P-Ga distance of 2.38Å, which is 0.07Å shorter than the As-Ga distance in GaAs(2.45Å). No detectable relaxation is observed in the P second and third atomic shells. In S-doped GaAs we find two different populations of S-Ga bonds with nearly equal intensity and both with S located on the As sub-lattice. These findings indicate two different configurations of substitutional S in GaAs. The coexistence of two similarly populated, charge compensating configurations is the first structural evidence which allows us to explain the observation that in n-doped GaAs the electrical activity of donors is lower than the atomic concentration. Finally, we present experimental results on S impurities in AlxGal−x, As (0.2<x<0.5). In this system, at the Al concentrations we studied, the S impurities are bound only to Al and not to Ga atoms. We report the formation of an extended complex which is discussed in connection with the structural identification of DX centers in these materials.

Te atoms were implanted in GaAs with doses ranging from 1013 to 1016 atoms/cm2, and annealed with the rapid thermal annealing technique. The samples were studied by Mössbauer Spectroscopy, Rutherford Backscattering Spectroscopy – Channeling, and the Van der Pauw-method. While at the lowest implantation dose an unperturbed substitutional site is observed at all annealing temperatures, at the highest implantation dose a strong deviation from a central position in an unperturbed configuration is observed at all temperatures. At the intermediate doses a high degree of substitutionality is observed between annealing temperatures of 200°C and 500°C only.

In GaAs and InSb common residual contaminants introduce both shallow donor states and other levels normally resonant with the conduction band but taking their predominant character from higher conduction band minima. These states can be made to emerge into the forbidden gap by applying hydrostatic pressure. Judged by the measured pressure coefficients two sets of levels are closely tied to the L- and X-conduction band minima. At low temperatures the X-associated states show local relaxation effects and metastability (i.e., D(X) behaviour). Pressure experiments have also been performed with spike-doped GaAs both in single layer and in superlattice form. Shubnikov-de Haas peaks can be observed above 3T. Fourier analysis of these shows that up to six sub-bands can be occupied. The application of hydrostatic pressure of up to 20kbar dramatically increases the mobility of the electrons in the lowest sub-band by as much as an order of magnitude with smaller increases occurring the higher sub-bands. The increases in mobility arise from the diffusion of the silicon donors during growth. Localised donor states associated with the L-conduction band drop below the Fermi energy in the centre of diffused distribution of donors on the application of pressure and become neutralised. This reduction of ionised scattering centres affects the most confined electron states and thus the mobility of the lowest sub-band increases very substantially.

Epitaxial layers of GaAs grown by MBE or MOCVD and doped with silicon impurities have been studied using FTIR spectroscopy. Vibrational modes are observed for Si(Ga), Si(As), Si(Ga)-Si(As) and a defect labelled SI-X. This latter defect appears to be responsible for the compensation effects found in some highly doped material. The Si(Ga) mode is modified in AlGaAs but understood in terms of a simple statistical model. Epitaxial GaAs layers doped with silicon or beryllium are passivated by exposing the samples to an RF hydrogen plasma which leads to the formation of Si-H and Be-H close pairs.

The origin of the complex photoluminescence line series often observed in MBE-grown GaAs has been the subject of considerable recent study. We report on the results of high resolution, high sensitivity resonant excitation measurements which conclusively prove the lines to result from the recombination of excitons bound to a series of acceptors. New details of the properties of the bound excitons and acceptors are revealed. The direct connection between this acceptor series and an often-observed series of broader, lower energy lines is also established. Some preliminary studies of this line series under applied magnetic fields are also described.

Optical and magnetic properties of donors in high AlAs-fraction AlxGa1−x As have been determined using optically-detected magnetic resonance. Many samples exhibit a sharp resonance at g = 1.95 detected on midgap luminescence. One high-quality sample exhibits an exhange-broadened line which reveals a distribution in donor-acceptor pair separations on moderately deep emission. A second high-quality sample exhibits the donor ODMR on donor-to-shallow- acceptor photoluminescence.

The DX center, the lowest energy state of the donor in AlGaAs with x > 0.22, is responsible for the reduced conductivity as well as the persistent photoconductivity observed in this material at low temperature. Extensive studies of the properties of this level and of its effects on the characteristics of some heterojunction devices are reviewed here. Recent measurements are presented showing that the characteristics of the DX center remain essentially unchanged when it is resonant with the conduction band (x < 0.22) and that, independent of other compensation mechanisms, the DX center therefore limits the free carrier concentration in GaAs to a maximum of about 2×1019 cm− 3.

Deep Level Transient Spectroscopies (DLTS) and capacitance transient techniques have been applied to GaAs:Si and to Ga1−xAlxAs:Te (x=0.35) under quasi-hydrostatic pressure using a diamond anvil cell. By substituting the experimental pressure coefficients of the defect energies into a model proposed by Li and Yu (Solid State Commun. 61, 13 (1987)) we concluded that both the DX center in the GaAlAs alloy and the pressure-induced deep donor (PIDD) in GaAs have large lattice relaxations associated with them.

Capacitance as well as photovoltage response methods have been used to analyse DX centers in the N–type AlGaAs:Sn layer of double heterostructures. DLTS spectra have revealed two deep traps. The first center (ΔE1 = 0.20eV) has been interpreted as the DX center related to Sn. In this paper, it is suggested that the second trap, with thermal activation energy equal to ΔE2 = 0.33eV, is also a DX center due to Sn, connected with another final state (the L minimum) of thermal processes. C-T characteristics and DLTS spectra have been compared with photovoltage spectra to find a correlation between the trap populations and Al content. The binding energy of the trap 2, as well as the temperature dependence of the electron capture cross-section, have been determined from measurements of the transition region width. Photoionization measurements confirm that there is large lattice relaxation when an electron is captured at the trap.

Pressure dependent Deep Level Transient Spectroscopy (DLTS) experiments are used to measure the properties of the deep donors (DX-centers) responsible for the persistent photoconductivity effect in Si-doped AlGaAs. The sample dependence of the DLTS spectra shows evidence for a defect complex involved in the DX-center.

A capacitance study of GaAs1−xPx : Te. x > 0.2, obtained by vapor phase epitaxy, has revealed two DX centers, characterized by thermal activation energies ΔEA = 0.18 eV and ΔEB = 0.39 eV. and photoionization energies 0.6 eV and 1.1 eV, respectively. Both traps show strong non-exponential behavior in thermal emission and capture processes. It is shown that correct parameter values for DX centers can be determined from measurements of the transition region width. This method, which allows us to circumvent alloy effects, has been used to study DX center parameters as a function of the phosphorus content. It is demonstrated that the level B is linked to the X minimum, and that the barrier height for electron capture at this trap, with respect to the indirect minimum, is independent of alloy composition.

This paper reviews the principal processes involved in the enhanced interdiffusion of elements across interfaces between two III-V compound semiconductors. Implantation enhanced interdiffusion effects in GaAs-Gal−xAlxAs are compared for single Quantum Well structures and Superlattice structures. Measurements indicate a marked difference in the annealing and enhanced interdiffusion kinetics between these 2 types of structures.

Recently available Ga-Al interdiffusion results in GaAs/AlAs superlattices allow to conclude that Ga self-diffusion in GaAs is carried by triply-negatively charged Ga vacancies under intrinsic and n-doping conditions. The mechanism of the Si enhanced superlattice disordering is the Fermi-level effect which increases the concentrations of the charged point defect species. For the effect of the p-dopants Be and Zn, the Fermi-level effect has to be considered together with dopant diffusion induced Ga self-interstitial supersaturation or undersaturation. Self-diffusion of Ga in GaAs under heavy p-doping conditions is governed by positively charged Ga self-interstitials.

The growth of the epitaxial silicides NiSi2 and CoSi2 on Si is discussed from observations made by in-situ transmission electron microscopy. In particular, we observe the occurrence of epitaxial metastable phases which arise from the dominance of interface energy in extremely thin films. Such phases relate to the thickness dependence of the microstructure in these silicides and may be expected to occur in many binary and more complex thin film systems.

Σ=3 lateral twin boundaries and a Σ=19 boundary have been investigated by highresolution electron microscopy. The lateral twin boundary was produced by growth on single crystal (110) Ge substrate and was observed to facet parallel to the common (112) plane and the (111)/{115} planes. The Σ=19 boundary was grown on a bicrystal substrate and faceted parallel to the common {331} plane. In this case, convergent-beam electron diffraction was used to determine the polarity of the adjoining grains. A possible model for the atomic configuration is proposed for each of the observed boundaries. GaAs-AlxGa1−xAs heterolayers were grown on a (001) Ge substrates to examine the interaction of antiphase boundaries with heterojunctions.

The nucleation and propagation of misfit dislocations in Ge-Si strained epilayers on (100) Si have been investigated using transmission electron microscopy and X-ray diffraction topography at low lattice parameter mismatch (˜ 0.8%). Misfit dislocations nucleate as half loops which are predominantly unfaulted (> 90%) at the advancing growth interface. Under the driving force of the epilayer strain, unfaulted half loops glide and expand on inclined { 111 }planes toward the heterointerface (i.e. substrate/epilayer interface). These unfaulted half loops consist of a 60°-dislocation segment which lies along < 011> in a plane parallel to the heterointerface (i.e. (100)) and this segment is connected to the growth interface by two screw dislocation segments which both lie on the same inclined {111} glide plane. As 60° dislocations reach the heterointerface on each of the four inclined {111} variants, they form an orthogonal array of misfit dislocations which lie along [011] and [011]. At higher lattice parameter mismatch (˜ 2%), there appear to be some important changes in the dislocation behavior and these changes result in orthogonal arrays of heterointerface dislocations which are predominantly edge type (i.e. 90°dislocations).

The relaxation mechanisms of ZnSe/ZnSxSe1−x superlattices grown by molecular beam epitaxy was studied by transmission rAeclmn icroscopy. The relaxation of misfit strain occured in part by conventional misfit dislocations that reside in the superlattice-buffer layer interface and in part by dislocations pinned at individual layer interfaces of the superlattice. The generation of misfit dislocations at the superlattice-buffer layer interface is inhibited by the misfit strain between individual superlattice layers. Therefore a significant amount of overall strain is present even after 1 μm of growth. Because misfit dislocations are not sufficient in relief of the misfit strain cracks are able to propagate

The defect structure of lattice-mismatched one micron In0.12 Ga0.88As epilayers on (001) GaAs was studied with scanning cathodoluminescence (CL) and transmission electron microscopy (TEM). CL examination of the GaAs buffer layer revealed the formation of a segmented network of defects below the interface. Cross-sectional TEM analysis shows that these defects are dislocation half-loops extending from the interface, and the vast majority of these loops lie on the GaAs side of the interface. The dislocations in the GaAs buffer layer were determined to be edge dislocations. Thus, CL images show that edge dislocations in this system are centers for non-radiative recombination. We propose that two 60° dislocations with opposite screw and interface tilt components can glide into the buffer layer to form edge dislocations. Potential energy plots for 60° dislocations near the interface and interacting with interface dislocations supports this model.

GaxIn(1−x)P epilayers grown on GaAs substrates by MOVPE, for different growth temperatures and values of x∼0.5, have been studied by electron microscopy. The results indicate that under certain conditions the ternary epilayer is ordered parallel to the (111) plane. Dark-field images obtained using the superlattice reflections reveal ordered domains of different orientations. High-resolution images have been obtained from the ordered domains. The structure of these domains is not perfect but contains many planar faults parallel to the growth surface.