Abstract
The influence of the growth procedure on the optical quality of InGaN grown on GaN has been investigated. The photoluminescence spectrum of the sample with a low-temperature-grown GaN cap layer or a graded-temperature-grown GaN cap layer has a shorter peak wavelength than that of the sample grown with a normal-temperature-grown GaN layer. The shift of the peak wavelength increases with the increase of the layer thickness for the sample with the low-temperature-grown GaN. This is because the defects contained in the low-temperature-grown GaN cap layer induce the outdiffusion of In atoms during the temperature-ramped procedure. The narrower linewidths and higher intensities of the PL spectra for InGaN after In outdiffusion may be due to the reduction of the strains, dislocations or defects. The Raman spectra and the Auger electron spectra also indicate that the low-temperature-grown GaN has a lot of defects which reduce the phonon peak intensity and induce the interdiffusion of In atom during the growth of GaN/InGaN heterostructures.