Systematic optical study of In x Ga 1-x As on InP using photoluminescence, photoreflectance, and micro-Raman spectroscopy

Abstract

We present a systematic study of the optical and structural properties of InGaAs grown on InP:Fe by molecular beam epitaxy (MBE) and metalorganic molecular beam epitaxy (MOMBE). The properties of these films were measured using photoluminescence, photoreflectance, and micro-Raman spectroscopy and correlated to double-crystal x-ray diffractometry. Lineshape analysis of low temperature Fourier transform photoluminescence (FTPL) allowed the identification of four optical transitions; bound exciton, donor-to-acceptor pair, and two bands which are impurity or defect related. The band-gap energy to XRD composition, relationship demonstrates films off the lattice match composition are under biaxial strain. Room temperature photoreflectance (PR) with a complex Airy functional model were used to directly yield band-gap energies (light and heavy hole). The complex Airy lineshapes were applied to both intermediate electric field (Franz-Keldysh oscillations) and low field PR spectra illustrating that the complex Airy analysis represents a generalized treatment. We correlate the band-gap energies from the PR spectral fits to those determined from PL measurements. Micro-Raman spectroscopy was performed in the <100> and <011> backscattering directions to identify four phonon modes; InAs-like TO (226 cm<SUP>-1</SUP>), InAs-like LO (233 cm<SUP>-1</SUP>), GaAs-like TO (255 cm<SUP>-1</SUP>), and GaAs-like LO (270 cm<SUP>-1</SUP>), and one alloy disorder mode R<SUP>*</SUP> (244 cm<SUP>-1</SUP>) for InGaAs on InP. For all five Raman features, a linear relationship between the Raman frequency and composition was determined for near lattice matched conditions (0.04 < 1 - x < 0.52).