Hydrogen induced roughening and smoothing in surface morphology during synchrotron-radiation-excited GeH4-source homoepitaxy on Ge(001)

Abstract

The kinetics of roughening and smoothing in Ge(001) surface morphology during synchrotron-radiation-excited GeH4-source homoepitaxy has been investigated. At high GeH4 pressures and low substrate temperatures, two-dimensionally flat surface morphology is maintained while passivating the epitaxially growing surface with a Ge hydride layer. After exceeding the critical temperature (330°C), the delivery of GeHx species to the partially dangling bond terminated surface and the accelerated migration of Ge atoms result in roughening from the initial stage of growth, the onset of which can be detected in terms of a small loop in real-time ψ-Δ trajectories of ellipsometric monitoring. The roughening tendency is enhanced with increasing synchroton radiation beam intensity and substrate temperature and with decreasing GeH4 pressure. Submicrometer tall islands consisting of a (001) top surface surrounded by (113) sidewalls are produced. Roughening is terminated when all dangling bonds are tied up with H atoms, i.e., when the surface free energy is minimized. Then, preferential embedding into valleys between islands yields sinusoidal-like ripple morphology, which is eventually converted into a flat Ge epilayer with no inner defects.