Combined in situ and ex situ analysis of hydrogen radical and thermal removal of native oxides from (001) GaAs

Abstract

We are currently involved in the study of regrowth of InAs on nanopatterned GaAs surfaces. The nanopatterning is accomplished through the movement of the sample while in contact with a diamond tip maintained at a constant load. Native oxides present on these surfaces introduce an obstacle to the subsequent regrowth. Therefore, the removal of this oxide is a prerequisite step for the study of the subsequent regrowth on these patterned surfaces. In this study we used in situ spectroscopic ellipsometry (SE) and reflection high energy electron diffraction (RHEED) as well as ex situ atomic force microscopy to follow the hydrogen cleaning and thermal removal of the native oxides from the GaAs surface. SE and RHEED were used to follow the oxide desorption process in situ and were used to determine when the surface was clean. Post AFM analysis indicated that the thermally desorbed oxide surface contained pits which were approximately 100 Å deep and covered 15% of the surface. Hydrogen radical cleaning was studied at substrate temperatures between 400–535 °C using a pressure of approximately 1×10−6Torr and a cracking thermocouple reading of 900 °C. The time to produce a clean surface was found to decrease as the temperature was increased. At the highest temperatures, cleaning took less than 10 min. AFM analysis indicated smooth surfaces were produced up to 500 °C. Above 500 °C, pitting was seen to occur similar to that observed for thermal oxide desorption. It was found that the onset of this pitting coincided with time at which spectroscopic ellipsometry indicated a change in the oxide layer.