Self-limiting and step-propagating nature of GaAs atomic layer epitaxy revealed by atomic force microscopy

The self-limiting and step-propagating nature of GaAs atomic layer epitaxy (ALE) is verified by using atomic force microscopy (AFM). AFM measurements reveal that the GaAs surface having a monolayer-height step structure does not change regardless of the trimethylgallium (TMG) flow rate at the ALE growth condition. This indeed confirms the self-limiting nature of ALE. Moreover, it is found that lateral growths such as step-propagation and two-dimensional nucleation take place in ALE. The TMG migration lenght of Group-III species is evaluated to be as large as several hundred nanometers in spite of the low temperature growth at 440°C. The undecomposed TMG on As-stabilized surface is responsible for the large migration length in ALE.