23 - Nucleation and Surface Diffusion in Molecular Beam Epitaxy

Abstract

Nucleation and surface diffusion in molecular beam epitaxy (MBE) are discussed in this chapter, using III-V compound semiconductors as examples. Real-time detection of the nucleation is possible by monitoring the intensity oscillation of reflection high-energy electron diffraction (RHEED). Behavior of nucleation and surface diffusion in MBE can be understood by investigating the growth on vicinal (stepped) surface using RHEED intensity oscillation. It is shown that there are two modes of the growth, two-dimensional nucleation and step flow. High-resolution scanning electron microscope installed in MBE (microprobe-RHEED) makes it possible to measure the local growth velocity by RHEED intensity oscillation in real time with a spatial resolution less than 50nm. This tool also makes it possible to conduct in situ observation of the morphology change of growing microstructures. In the growth of the microstructure, surface diffusion between surfaces (intersurface diffusion) plays a key role. The origin and the behavior of the intersurface diffusion are described, and the change of morphology during a pyramid growth was observed in real time. The theoretical analysis for the pyramid formation shows that the agreement with the experiment is fairly good. By employing intersurface diffusion as a tool for fabricating the required microstructure, growth elimination and lateral growth enhancement are conducted. These techniques are applied to the fabrication of nanostructures and microchannel epitaxy with high aspect ratios.