Direct observation of Ga-rich microdomains in crack-free AlGaN grown on patterned GaN/sapphire substrates

Abstract

The strong three-dimensional modulation of the optical and structural properties due to the self-organized formation of Ga-rich AlGaN microdomains is directly imaged by spectrally and spatially resolved cathodoluminescence microscopy. The 5-μm-thick, crack-free AlGaN was grown on patterned GaN/sapphire templates periodically structured into trenches and terraces. During initial AlGaN overgrowth, the modulation of the local AlGaN stochiometry results in marble-like striations of Ga accumulation clearly reflecting the pattern periodicity. In contrast, after subsequent overgrowth, a homogeneous emission wavelength, i.e., a homogeneous aluminum content, is found near the sample surface. However, the strong rise of quantum efficiency directly above the trenches indicates a drastic improvement of material quality.