Formation of highly conductive polycrystalline GaAs from annealed amorphous (Ga,As)

Polycrystalline (Ga,As) grown by molecular-beam epitaxy (MBE) is compared to polycrystalline (Ga,As) formed by annealing amorphous (Ga,As) also grown by MBE. Both amorphous and polycrystalline materials were grown at 100 deg. C and crystallinity is controlled by the As overpressure. As the amorphous material was annealed at varying temperatures from 300 to 500 deg. C several properties of the material changed such as levels of excess As in the material, grain structure of annealed material, strength and adhesion of crystallized layer, and conductivity of the material. After annealing at temperatures around 400 deg. C, the material is specular, polycrystalline, has good adhesion, and is very conductive. Resistivity values of less than 2 mΩ cm and acceptor concentrations near 5x1020 cm-3 were detected according to Hall/van der Pauw measurements. Conduction is believed to be due to the large amount of excess As in the material forming an As conduction path when the material is annealed. Material grown in a polycrystalline form by MBE differs in both grain structure and conductivity from material crystallized from an amorphous form