Nucleation and Surface Roughness in Self-Limiting Monolayer Epitaxy of GaAs

The surface morphology produced by molecular layer epitaxy (MLE) was investigated using atomic force microscopy (AFM). The surface morphology and roughness estimated quantitatively were not consistent with the temperature dependence of self-limiting growth. The degree of roughness had two states in the monolayer growth temperature range from 445 to 534°C. In the growth temperature region over 475°C, nucleated islands along [110] the direction one monolayer high were observed on the grown surface. When the growth temperature was less than 475°C, such nucleation did not occur and a smooth surface without islands was obtained with a roughness of less than one monolayer. To understand island formation, the nucleation and the islands at each growth cycle were investigated.