Photoreflectance and Double Crystal X-Ray Study of Strained InGaAsP Layers on InP Substrates

Abstract

ABSTRACTDetermining the composition of quaternary epitaxial films requires accurate measurements of both the lattice parameter and the bandgap energy. Complications arise in lattice-mismatched material, because the mismatch produces tetragonal distortion of the epi-layer and splitting of the valence band energies in a manner which depends on the film composition. We present studies on strained InGaAsP grown on (100) InP. Using room temperature photoreflectance (PR) we observe shifting of the band gap and splitting of the valence band energies, and using the (115) and (004) reflections from double crystal x-ray diffraction (DXRD) we determine the values of the parallel and perpendicular lattice constants. By combining the lattice parameter measurements with band splitting data, we accurately determine the quaternary composition from a self-consistent model using an iterative procedure. By linear interpolation of the elastic-stiffness constants, C11 and C12. as well as the shear and hydrostatic deformation potentials for the four binary compounds in the InGaAsP system, we relate the state of biaxial stress to the induced shifts in the valence band energies.