A technology to reduce the dislocation density in GaN thin films by lateral overgrowth from trenches (LOFT) is reported. In LOFT, a GaN thin film was grown on sapphire substrate first, then trenches were formed into the thin film by etching. GaN material was regrown laterally from the trench sidewalls to form a continuous thin film. The average surface density of threading dislocations is reduced from 8×109/cm2 in the first GaN thin film to 6×107/cm2 in the regrown GaN thin film.

Recently, it has been shown that the etching of deep trenches in close proximity to GaAs vertical-cavity surface-emitting laser (VCSEL) apertures causes the linearly polarized TE emission to be pinned in a direction parallel to the line etch. In this letter, we show that etching introduces compressive strain or relaxes tensile strain through the creation of free interfaces. An anisotropic variation of strain is the origin of the polarization pinning effect. We report on the enhancement of polarization pinning by postannealing after etching. Photoluminescence and Raman measurements of the VCSEL wafer were taken before and after etching and annealing. The observed shift in the Fabry–Perot mode was used to model the strain, giving 4×108 dyn/cm2, or 0.05%, compressive strain perpendicular to the etch.

Up to 20 dB of photocurrent amplification with a frequency response of 2 GHz has been observed in GaAs Schottky photodiodes. The amplification may be caused by a reduction in Schottky built-in potential under illumination. The device may find application in improving the sensitivity of optical receivers.

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