Extended defects and precipitates in LT-GaAs, LT-InAlAs and LT-InP
We review the main structural characteristics of low temperature molecular beam epitaxially produced GaAs (LT-GaAs), LT-InAlAs, and LT-InP. These materials exhibit almost identical behaviours with respect to growth and annealing conditions. For too low growth temperatures or too high As pressures, defects are seen in these layers with characteristic pyramidal shapes which result from multiple twinning. The increase in the strain energy stored in the layers that are slightly mismatched on the substrate is responsible for the formation of these defects. On annealing the excess group V atoms dispersed in the matrix condense to form precipitates except in LT-InAlAs. Sizes and orientation relationships of the precipitates depend on the crystalline quality of the layers. An important difference between LT-GaAs and LT-InP is that As precipitates are metallic while the structure in which P condenses is thought to be insulating.
Source:European Materials Research Society Symposia Proceedings