Growth and characterization of GaAs on sapphire (0001) by molecular beam epitaxy

Crystal epilayers of (111)-oriented GaAs have been grown successfully on sapphire (0001) substrates by molecular beam epitaxy. Although the epilayers were found to have a very high twin density, large areas (cm2) with no grain boundaries were observed. Both substrate surface preparation and temperature controlled the crystallinity. Reflection high-energy electron diffraction (RHEED) was used to characterize the sapphire surface after ozone cleaning. RHEED patterns taken at several azimuths were consistent with an outermost layer of oxygen atoms. Powder x-ray diffraction and rotation x-ray photographs were used to determine growth conditions that resulted in an improvement in the crystalline order. Cross-sectional transmission electron microscopy confirmed the crystalline nature of the GaAs epilayers. The quality of the GaAs was also characterized by photoluminescence. Finally, crystalline quality was assessed using double-crystal x-ray diffraction rocking curves.