Complete removal of threading dislocations from mismatched layers by patterned heteroepitaxial processing

Abstract

We report the effectiveness of patterned heteroepitaxial processing (PHP) in removing threading dislocations (TDs) from ZnSe epitaxial layers grown on GaAs substrates by metalorganic vapor phase epitaxy. The PHP approach used here involves postgrowth patterning of continuous epitaxial layers followed by annealing. In this study, each as-grown ZnSe/GaAs sample was first cut into pieces forming four types of samples, namely: (1) as grown, (2) postgrowth annealed, (3) postgrowth patterned, and (4) PHP prepared (patterned and annealed). The epitaxial layers with thicknesses of 2000–6000 Å were patterned to create 500–6000-Å-high and 3–70-μm-wide square mesas that were separated by 20 μm trenches. TD densities were determined by the etch pit density (EPD) technique and comparisons were made between the four types of samples. The first three types of samples exhibited EPDs of approximately 107 cm−2, which indicate that neither patterning alone nor annealing alone was effective at reducing TDs. In contrast, PHP resulted in a complete removal of TDs from 70 μm×70 μm square layers with thicknesses of >3000 Å. This corresponds to an EPD less than 2.0×104 cm−2, and at least a 500-fold reduction compared to as-grown layers; in fact, this value is even lower than that of the GaAs substrate (EPD=105 cm−2). Thus TDs can be removed in PHP by glide to the sidewalls, as promoted by the presence of image forces.