Stability and mechanism of selective etching of ultrathin Ge films on the Si(100) surface upon chlorine adsorption

Abstract

This work investigates the effect of chlorine termination on the stability and the etching of ultra thin Ge layers on a Si(100) surface, using scanning tunneling microscopy (STM) and synchrotron radiation photoemission spectroscopy. The initial growth of Ge on the Si(100) surface is known to occur layer by layer. The intensities of the Ge $3d,$ Si $2p,$ and Cl $2p$ core levels, after the chlorine passivation of Ge/Si(100) surfaces, together with the STM images reveal that most of the deposited Ge atoms have been randomly dispersed on the surface layer during initial submonolayer growth. They occupy only $\ensuremath{\sim}90%$ of the surface after a 2-ML (monolayer) coverage. Chlorine termination drastically alters the atomic composition of the surface (dimer) layer and in the thin films when annealing at elevated temperatures occurs. Specifically, Cl termination of the Ge/Si(100) surfaces causes Ge, which initially form Cl-Ge bonds in the surface layer, to move into the subsurface layers after annealing at 650\char21{}750 K. Silicon is extracted from the subsurface layers to form Cl-Si bonds. Above 900 K, chlorine is desorbed in the form of ${\mathrm{SiCl}}_{2},$ leaving the initial thin Ge films on the Si(100) surface almost intact.