Point Defects In GaAs Research Articles

The generation of point defects in GaAs by electron-hole recombination at dislocations

The degradation of GaAs heterojunction lasers results in the formation of long dislocation dipoles which grow by a climb process involving point defect concentrations of the order of 1019 cm−3. The driving force for this climb process is not understood and it has been suggested that the material contains a supersaturation of native interstitials which condense on the dislocation during device operation. An alternative model proposed that the driving force is related to the energy released by electron-hole recombination on the dislocation which is partially dissipated by the dislocation emitting vacancies into the surrounding lattice.Gallium arsenide substrates containing greater than 2 × 1018 tellurium atoms cm−3 contain interstitial concentrations of the order of 1017 cm−3 which condense out to form small dislocation loops during an anneal at 880°C. The presence of these loops indicates that the annealed material does not contain excess interstitials in solution. This annealed material was optically pumped and examined by transmission electron microscopy. It was found that the loops developed into dipoles typical of degraded lasers. The number of point defects involved in this climb process increased with increasing pumping power and time. These results are discussed in terms of the two mechanisms listed above and it is concluded that the energy released by electron-hole recombination at the dislocation provides the driving force for the climb process.

Calculations of point defect concentrations and nonstoichiometry in GaAs

A study of point defects and nonstoichiometry in GaAs is presented. Standard methods of chemical thermodynamics are used to derive expressions for the equilibrium concentrations, as a function of temperature and arsenic pressure, of the following defects; arsenic monovacancies, gallium monovacancies, gallium divacancies and appropriately charged versions of these three. This choice of defects is made on the strength of the evidence of the published experimental results relating directly to point defects in GaAs. Values for the required equilibrium constants are obtained by a combination of a priori estimates and matching with this experimental data at certain points. Consistent agreement with the experimental data is obtained, indicating for example that defect concentration in the region 10 18–10 19 cm −3 in melt grown material are not unreasonable. The set of equilibrium constants on which the calculations are based must, however, be regarded as provisional until more extensive data is available for comparison. Using these equilibrium constants the minimum practical deviation from stoichiometry and the width of the existence region of solid GaAs are calculated as a function of temperature.