Studies of oxide desorption from GaAs substrates via Ga2O3 to Ga2O conversion by exposure to Ga flux

Abstract

Removal of the native oxide from GaAs wafers in the process of thermal desorption in the presence of As flux causes very significant surface degradation. We examine the merits of an alternative oxide desorption method that consists in a standard thermal oxide removal procedure preceded by a partial oxide removal at lower temperatures via conversion of the stable Ga2O3 surface oxide into a volatile Ga2O oxide by a pulsed supply of Ga in the absence of As flux. We find that a reduction of the substrate roughness by more than one order of magnitude is obtained on most epi-ready GaAs substrates regardless of their age, even if only 70% of the original gallium oxide is removed with Ga pulses, and that nearly atomically smooth surfaces are obtained with 90% oxide removal. In addition, we demonstrate that the Ga-induced oxide removal process is laterally inhomogeneous, making this method vulnerable to the accumulation of Ga droplets on the GaAs surface when more than about 90% of the surface oxide is removed. The Ga2O desorption pattern monitored with quadrupole mass spectrometry indicates that other nonvolatile species initially present on the top of the gallium oxide are also converted to a volatile species by Ga exposure before large areas of Ga2O3 become exposed. We examine the residual surface contamination left at the substrate–epilayer interface and find no significant influence of the age of the substrate, or the oxide removal method, on the measured levels of silicon, oxygen, and carbon.