HETEROSTRUCTURE BUFFER LAYERS

Abstract

The problem of choosing the architecture of buffer layers is considered. This is typical problem faced when standard models of different heterostructures with a controlled level of mechanical stresses and low defect density in the bulk and at the layer boundaries are developed. It has been shown that the abovementioned characteristics depend on the quality of the initial substrate surface. They are also dependent on the substrate preparation procedure for epitaxy and the composition of the buffer layers. We note that the quality of the substrate surface is most objectively estimated from the bonding strength of the spliced plates. It has been also shown that if the bonding strength is below 107 Pa (this is the most frequent experimental value), the substrate surface is characterized by noticeable roughness. There are different contaminating elements and chemical compounds, clusters and dust particles, structural defects of different dimensionality on the substrate surface. In addition the substrate surface is restructured so that the «broken» bonds are brought closer to each other. The effect of the real substrate surface structure and the compatibility of the materials on the quality of the epitaxial film has been demonstrated. The analysis provided in this work shows the feasibility of growing a preliminary low−temperature (LT) underlying layer on the substrate for small lattice mismatch. Additional transition layers with changing component ratios in the composition or in the form of superlattices are required for largely differing lattice parameters.