LPE growth of GaAs: Formation of nuclei and surface terraces

Observations, analyses and measurements of LPE GaAs are presented on the formation of nuclei and surface terraces. The observations show that nuclei grow into well-defined prismatic hillocks bounded by only {100} and {111} planes and are unique to each substrate orientation, and hillocks tend to coalesce into chains and then into parallel surface terraces. An analysis of these results indicates that growth is limited to interface attachment on {100} planes, and {111} planes and curved surfaces are composed of {100} planes interlocked along 〈100〉 directions. To determine the surface terrace width a model of parallel nuclei on the substrate is analyzed to show that the heat of formation creates a diffuse liquid-solid interface region that can stabilize the nuclei separation and subject the interface to thermal fluctuations. When the thermal fluctuations are superimposed on a temperature gradient normal to the liquid-solid interface, the diffuse interface region is shown to decrease in size. Corresponding measurements of the terrace width for different temperature gradients are then shown to be in excellent agreement with this model.