REDUCTION OF OUTDIFFUSION AT THE GE/GAAS(100) INTERFACE BY LOW-TEMPERATURE GROWTH

Ga outdiffusion into Ge layers grown epitaxially by molecular beam epitaxy was observed by secondary ion mass spectroscopy, x-ray photoemission spectroscopy, capacitance-voltage, and temperature dependent Hall-effect measurements. Films were initially grown at low rates (0.03-0.04 nm/s) and low temperatures (150-300-degrees-C) on GaAs buffer layers on GaAs (100) substrates. The temperature and rate were then increased to 500-degrees-C and 0.1 nm/s. The amount of Ga outdiffusion was greatest for films initially grown at 300-degrees-C. No direct evidence of As outdiffusion at any temperature or Ga outdiffusion for initiation temperatures below 300-degrees-C was found. Hall-effect measurements showed higher hole concentrations and greater levels of compensation in films initiated at 300-degrees-C, consistent with outdiffusion of both Ga and As at this temperature. No degradation in the electrical characteristics of Ge-GaAs diodes was observed when the initial Ge growth temperature was reduced from 300 to 200-degrees-C.