Topography of epitaxial GaAs surfaces for growth

Abstract

The topography and surface roughness of (100) GaAs substrates and buffers after different preparation procedures were determined from atomic force microscopy (AFM) measurements. In order to characterize the topography over a wide range of length scales, multiple large 5×5 μm2 AFM scans were acquired for each sample. These scans were analyzed both by histogramming the distribution of pixel heights and by finding the rms roughness at length scales from 10 nm to 5 μm using a tiling analysis. The influence of substrate aging and chemical etching on buffers grown by molecular beam epitaxy was studied, as was the effect of different buffer growth procedures. Immediately after thermal desorption of the surface oxide, all wafers were extremely rough, as expected, with wafers etched in HCl:H20 (1:1) somewhat smoother than untreated epiready wafers, while wafers etched in H2O2:NH4OH:H2O (3:1:10) were rougher. After as little as 100 nm of buffer growth, however, there was no significant difference in roughness of etched or as-received substrates, and all samples were quite smooth with a rms roughness around 0.27 nm. The buffer growth conditions were found to significantly affect surface roughness. Interrupting the supply of Ga at the start of the growth enhanced mounding on the wafer surface, while postgrowth annealing at the growth temperature reduced the surface roughness and changed the characteristic topography of the surface.