MOLECULAR-BEAM EPITAXY-GROWN III-V STRAIN RELAXED BUFFER LAYERS AND SUPERLATTICES CHARACTERIZED BY ATOMIC-FORCE MICROSCOPY

Using atomic force microscopy (AFM), we have investigated the effects of growth temperature and dopant incorporation on the surface morphology of molecular beam epitaxy grown graded buffer layers and strained layer superlattices (SLSs) in the InGaAlAs/GaAs and InAsSb/InSb material systems. Our AFM results show quantitatively that over the temperature range from 380 to 545-degrees-C, graded InxAl1-xAs (x = 0.05-0.32) buffer layers grown at high temperatures (approximately 520-degrees-C) and graded InxGa1-xAs (x = 0.05-0.33) buffer layers and In0.4Ga0.6As/In0.26Al0.35Ga0.39As SLSs grown at low temperatures (approximately 400-degrees-C) have the lowest rms roughness. Also, for SLSs of InAS0.21Sb0.79/InSb, undoped layers grown at 470-degrees-C were smoother than undoped layers grown at 420-degrees-C and Be-doped layers grown at 470-degrees-C. These results illustrate the role of surface tension in the growth of strained layer materials near the melting temperature of the InAsxSb1-x/InSb superlattice. Nomarski interference and transmission electron microscopies, IR photoluminescence, x-ray diffraction, and photocurrent spectroscopy were also used to evaluate the relative quality of the material, but usually the results were not conclusive.