STRUCTURAL AND OPTICAL INVESTIGATIONS OF HIGH-QUALITY INGAAS INALAS SHORT-PERIOD SUPERLATTICES GROWN ON AN INGAAS QUASISUBSTRATE/

Unstrained InGaAs (4.5 nm)/InAlAs (1.0 nm) short-period superlattices grown on a (100) GaAs substrate were studied. To achieve this growth, an In-composition-graded buffer layer and a thick InGaAs buffer layer were adopted. Structural properties were investigated by x-ray diffrac tion, atomic force microscopy, and a compositional analysis by the thi ckness fringe method. X-ray diffraction patterns showed clear periodic ity in the superlattices and atomic-force spectroscopy images showed c ross-hatch morphology for the main ridge along the (01(1) over bar) di rection. Clear thickness fringes in the bright-field electron microsco pe images for the superlattice region and ambiguous fringes for the gr aded buffer layer indicate that misfit dislocation due to lattice mism atch concentrates in the graded buffer and a high-quality superlattice is successfully grown in spite of the large lattice mismatch between the superlattice and the substrate. Optical characteristics measured b y photocurrent spectroscopy reveal a clear Wannier-Stark localization effect at room temperature. The experimental absorption energies agree well with calculated values by a transfer matrix method using paramet ers for bulk InGaAs and InAlAs. (C) 1996 American Institute of Physics .