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 mm 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 mm 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 À11.63 cm À1 . 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.

Enhanced photoemission from surface modulated GaAs:Ge

“…In contrast, use of other group IV elements involve some fundamental problems associated with large lattice mismatch (∼4% for silicon) and different thermal expansion coefficients. In-diffusion of Ge in GaAs [7,22,23] can results in GaAs 1-x Ge x structures [20,23] exhibiting direct band-gap with superior optical properties. [19] For semiconductors, bringing the structure down to nanoscale may fundamentally modify the properties of materials by inducing low-dimensional charge carrier confinement [24] and self-assembling, allowing the growth of well-defined random or aligned nano/quantum structures [24] without the need of sophisticated lithography techniques.…”