Abstract
In this study, InGaAs/GaAs and AlGaAs/GaAs multiple quantum well (MQW) structures have been grown by molecular beam epitaxy (MBE) at low substrate temperatures (~230℃). This results in an excess of arsenic incorporated in the epilayers and upon subsequent annealing (500~700℃), the excess arsenic precipitates. The coarsening of the As clusters is observed to increase with the temperature or time of annealing. In the AlGaAs/GaAs MQW structures, there are obvious As precipitates accumulation zones (PAD) and precipitates depletion zones (PDZ) near the interfaces of the AlGaAs/GaAs heterostructure annealed at 500℃ for 30s. For the InGaAs/GaAs MQW structures, arsenic precipitates form two dot arrays near each InGaAs/GaAs interface when annealed at 500 and 600℃ and lose this confinement at higher annealing temperature (~700℃). The results are due to the diffusion of arsenic atoms across the interfaces of the heterostructures. The process of arsenic precipitates in the LT heterostructure can be explained by the reduction in the arsenic precipitates/matrix interfacial energy or the lattice-mismatch strain near the interfaces. For an increase of annealing temperature and time, the coarsening of As precipitates follows the process of Ostwald ripening. The annealing processes controlling the final sizes and distribution of As precipitates are important, and the properties of the two-phase system are useful in many electronic and optoelectronic applications.