Droplet-induced dot, dot-in-hole, and hole structures in GaGe thin films grown by MOCVD on GaAs substrates

Abstract

We report observations and origins of Ga-rich GaGe droplets and the localized etching of Ge-rich GaGe thin films grown on GaAs (100) substrates by metalorganic chemical vapor deposition. Micron and sub-micron dots, dot-in-holes, and holes have been fabricated by controlling the partial pressures of the Ga and Ge precursors as well as the substrate temperatures. The dot-in-hole features can also be converted to empty holes via post-growth sonication in hot deionized water due to the low melting point of the Ga-rich dots. Enhanced Raman scattering (ERS) of the Ge–Ge lattice vibrational mode has been observed at the wall of the concentric dot-in-hole structures as well as in the empty holes. To interpret the ERS mechanism, we have carried out finite-difference time-domain (FDTD) simulations, which reveal an enhanced electrical field for the obtained structures as a result of interference between the incident and reflected waves at the surface of the thin films that, in turn, results in the observed ERS. These findings greatly enrich the conventional droplet epitaxy and etching techniques and widen their applications.