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Effects of Strain on Highly Mismatched AlGaN/GaN Multiple Quantum Wells

Photoluminescence (PL) spectra, surface morphologies and cross-sectional images of transmission microscopy (TEM) were examined after changing the thickness of barriers or wells in AlGaN/GaN multiple quantum wells. When the wells are thin and the barriers are thick, multi quantum wells (MQWs) are partially relaxed. This brings about changes in the electric field and the band-gap of the wells. Thus, the PL spectrum becomes broad. Although few cracks were observed, cross-sectional TEM images indicated that the crystalline quality was poor. Even when the wells are thin, however, the strain energy can be lowered by reducing the barrier thickness. Thus, an improved PL spectrum can be obtained.