R.C. Newman

Hydrogen diffusion and the catalysis of enhanced oxygen diffusion in silicon at temperatures below 500°C

The relaxation of stress‐induced dichroism of the 9‐μm oxygen infrared absorption band has been investigated for Czochralski silicon annealed isothermally at various temperatures in the range 225–350 °C while the material was immersed in a hydrogen plasma. The in‐diffusion of hydrogen atoms enhanced the rate of oxygen diffusion so that the dichroism was lost progressively from the external surfaces of samples. Comprehensive ancillary measurements demonstrated that the oxygen diffusion jumps were catalyzed by collisions with diffusing hydrogen atoms, rather than some other fast‐diffusing species. The measurements allowed the hydrogen diffusion coefficient to be estimated as 1.7 × 102 exp( − 1.2 eV/kT) cm2 s−1 for the range of temperatures investigated. Increased rates of thermal donor formation were also found due to enhanced long‐range oxygen diffusion. The new data are related to previous reports of enhanced oxygen diffusion jumps found in Czochralski silicon given post‐growth heat treatments in hydrogen...

The lattice locations of silicon atoms in delta‐doped layers in GaAs

We have used secondary ion mass spectrometry, local vibrational mode infrared absorption, and electrical characterization to study the incorporation of Si delta‐doped planes in GaAs grown by molecular beam epitaxy at 400 °C, in the concentration range 0.01–0.5 monolayers. A correspondence is observed between the density of SiGa donors, the free electron concentration and the total Si coverage, up to a coverage of ∼1013 cm−2; however, above this value, the electron density falls, while [SiGa] remains constant up to a coverage of ∼1014 cm−2, and then falls below the detection limit at 0.5 monolayer coverage. These effects have been interpreted in terms of a model which takes account of Si migration and aggregation on the delta‐doped plane during deposition.

Light impurities and their interactions in silicon

Abstract The properties of isolated oxygen, carbon, nitrogen and hydrogen impurities in silicon are outlined. The precipitation of oxygen from solution is then discussed, first for temperatures above 500 °C and then for temperatures below 500 °C. It is at these lower temperatures that thermal donors are formed. To generate oxygen clusters containing up to say 10 atoms at 450 °C it is necessary to take dissociation of smaller oxygen clusters into account and also to invoke rapid diffusion of O 2 dimers. It is demonstrated that as-grown Czochralski crystals may contain hydrogen impurities that enhance the diffusion of single oxygen atoms, while these impurities are also incorporated in certain oxygen clusters that act as shallow donors. It is possible that dimer interactions with O i atoms lead to enhancements in D oxy .

X‐ray characterization of Si δ‐doping in GaAs

High‐resolution triple‐axis x‐ray diffractometry has been used to examine the structural properties of a δ‐doped superlattice of sixty periods, each consisting of half a monolayer of Si and 500 A of GaAs, grown by molecular beam epitaxy (MBE) at 400 °C under an arsenic flux. The measurements indicated that the superlattice was of high structural quality. Using dynamical simulation, it was demonstrated that the period variation was equal to 3%, while the silicon spreading was no greater than 2 monolayers. It was possible to extract this information because of the high‐resolution diffractometer which produced the theoretical line shape and wide dynamic range. Using a simple model, it was deduced that virtually all Si atoms were located on Ga lattice sites.

Heavily Si or Be doped MBE GaAs grown at low temperatures

Abstract Infrared absorption due to the localized vibrational modes of Si and Be has been investigated in low temperature molecular beam epitaxial GaAs. A spectrum from SiGa-VGa has been found, but pairing of BeGa was not detected. Anneals of the Si doped layers led to Si-site switching and an apparent loss of silicon from solution. A comparison is made with a previous study of neutron irradiated Si doped GaAs.

Electrical, magnetic circular dichroism and Raman spectroscopic investigations on the EK2 double acceptor (78/203 meV) in GaAs

The electrical and optical properties of liquid encapsulated Czochralski grown, Ga‐rich (melt composed of 55% Ga and 45% As), p‐type GaAs were studied by the Hall effect, capacitance‐voltage measurements, magnetic circular dichroism, optically detected electron spin resonance, deep level transient spectroscopy (DLTS), and Raman spectroscopy. Two levels with ionization energies of 78 and 203 meV above the valence band edge were examined and fitted to the singly and doubly charged ground states of a double acceptor which is designated an EK2 center. The Raman scattering cross sections for electronic excitations were determined from the defect concentrations measured by DLTS. The EK2 center is electrically passivated via a remote microwave hydrogen plasma technique. It can be reactivated by heat treatments with an activation energy of Ea=1.4 eV. The concentrations of the two levels were equal to each other in four as‐grown samples, in samples following passivation, and at all stages during the subsequent rea...

Optical waveguides formed by deuterium passivation of acceptors in Si doped p‐type GaAs epilayers

We report on the use of plasma hydrogenation of Si doped, p‐type GaAs crystalline samples to form infrared waveguides through acceptor passivation. Epilayers grown by liquid phase epitaxy were exposed to a deuterium plasma for ninety minutes at three different temperatures. Secondary‐ion mass spectrometry (SIMS) analysis indicated that the deuterium concentrations in the crystals after plasma exposure were nearly equal to the acceptor level and extended to depths between 2.0 and 4.0 μm. Reflectivity measurements showed that the epilayers had passivated regions whose thicknesses corresponded to those determined by SIMS analysis. Laser coupling experiments at 1.15 μm showed optical waveguiding in each sample and lowest propagation losses were on the order of 35 dB/cm. At a wavelength of 1.523 μm, only the sample processed at the highest temperature exhibited laser guiding and losses were considerably higher.

The upper limits of useful n- and p-type doping in GaAs and AlAs

The maximum carrier concentration found for GaAs:Si is n MAX ∼ 2 × 10 19 cm -3 , limited by the amphoteric behaviour of the Si impurities, the generation of gallium vacancies and Si precipitation. After annealing, a more typical concentration is 4 -5 × 10 18 cm -3 . GaAs:C doped to a level greater than p MAX ∼10 19 cm -3 is unstable during post-growth heat treatments, with the formation of C-C dimers that are deep donors. This process also occurs in AlAs, but p MAX has not been determined.

The role of rapidly diffusing dimers in oxygen loss and the association of thermal donors with small oxygen clusters

The loss of interstitial oxygen from solution is shown to exhibit second order kinetics provided dimer dissociation is not significant at the anneal temperature. Measured changes in the kinetics of the process for anneals at T ≥ 450 °C can be explained by the increasing effect of this dissociation provided dimers diffuse much more rapidly than isolated atoms and are trapped efficiently. The magnitude of the changes indicates that weakly bound clusters are responsible for this trapping. The formation of two seperate series of oxygen clusters containing odd and even numbers of oxygen atoms would be a consequence of clustering by dimer addition. The assignment of thermal donors to the odd-numbered series is suggested.

Gallium vacancy related defects in silicon doped GaAs grown at low temperatures

Abstract Point defects and complexes in silicon doped GaAs grown at low temperatures were investigated. Large differences between the donor and carrier concentrations imply that the crystals contain high concentrations of compensating defects. The detection of Si Ga –V Ga pairs confirms the expectation that they are gallium vacancies and their concentration appears to be controlled by the Fermi level or silicon concentration. The lattice expansion of the low temperature GaAs is related to the concentration of As Ga antisite related defects which do not appear to affect significantly the electrical properties of the material. The annealing behaviour may be explained by the nucleation of Si clustering by V Ga related defects.