ANTIPHASE DOMAIN-FREE GROWTH OF GAAS ON OFFCUT (001)GE WAFERS BY MOLECULAR-BEAM EPITAXY WITH SUPPRESSED GE OUTDIFFUSION

The nucleation and growth of GaAs films on offcut (001) Ge wafers by s olid source molecular beam epitaxy (MBE) is investigated, with the obj ective of establishing nucleation conditions which reproducibly yield GaAs films which are free of antiphase domains (APDs) and which have s uppressed Ge outdiffusion into the GaAs layer. The nucleation process is monitored by in-situ reflection high energy electron diffraction an d Auger electron spectroscopy. Several nucleation variables are studie d, including the state of the initial Ge surface (single-domain 2 x 1 or mixed-domain 2 x 1:1 x 2), the initial prelayer (As, Ga, or mixed), and the initial GaAs growth temperature (350 or 500 degrees C). Condi tions are identified which simultaneously produce APD-free GaAs layers several microns in thickness on Ge wafers with undetectable Ge outdif fusion and with surface roughness equivalent to that of GaAs/GaAs homo epitaxy. APD-free material is obtained using either As or Ga nucleatio n layers, with the GaAs domain dependent upon the initial exposure che mical species. Key growth steps for APD-free GaAs/Ge growth by solid s ource MBE include an epitaxial Ge buffer deposited in the MBE chamber to bury carbon contamination from the underlying Ge wafer, an anneal o f the Ge buffer at 640 degrees C to generate a predominantly double at omic-height stepped surface, and nucleation of GaAs growth by a ten mo nolayer migration enhanced epitaxy step initiated with either pure As or Ga. We identify this last step as being responsible for blocking Ge outdiffusion to below 10(15) cm(-3) within 0.5 microns of the GaAs/Ge interface.