High-resolution X-ray diffraction and micro-Raman scattering studies of Ge(:Ga) thin films grown on GaAs (001) substrates by MOCVD

Abstract

We have employed high-resolution X-ray diffraction (HRXRD) and micro-Raman scattering to study the structural and lattice vibrational dynamic properties of heavy Ga-doped Ge thin films (i.e., Ge:Ga) epitaxially grown by metalorganic chemical vapor deposition on GaAs (001) substrates. Reciprocal space mapping revealed that the ∼1.0 μm thick Ge:Ga films are coherently stressed on the GaAs (001) substrates and the in-plane compressive strain increases with Ga incorporations. In contrast, ∼90% strain has been relaxed in a 10 μm thick unintentionally doped Ge thin film. The compressive strain caused by such Ga incorporations in the Ga-doped Ge thin films, having a maximum of 866 PPM, plays a minor role in the Raman shift of the Ge–Ge longitudinal optical (LO) phonon that has been observed up to −11.63 cm⁻¹. The large phonon softening has been discussed on the bases of hole concentrations and ‘alloy-disorder’ of the ‘self-annealing’ induced atomic interdiffusions, specifically with the help of Raman scattering and HRXRD from the cross-section of the Ge(:Ga)/GaAs (001) heterostructures.