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.