Low temperature photoluminescence and photoreflectance of metamorphic HEMT structures with high mole fraction of in

Low-temperature photoluminescence and photoreflectance have been studied in several metamorphic HEMT (MHEMT) heterostructures with the In_0.7Ga_0.3As active regions and different buffer layer designs. It was found that structures with step-graded metamorphic buffer have better quality. Also it was shown that mismatched superlattices in metamorphic buffer can influence on the half-width of photoluminescence spectra. The possible attribution of photoluminescence spectral lines and their thermal behaviour are critically discussed. The photoreflectance spectrum shows a lot of features in energy region, where none of PL features observed.