Photocurrent spectroscopy of GaN and AlGaN epilayers grown on 6H (0001) silicon carbide

We have investigated the photocurrent of GaN and AlGaN epilayers grown on S iC substrates. The peculiar temperature and intensity dependence of the exc iton photocurrent reveal the existence of two different carrier localizatio n mechanisms, one due to shallow point defects, which is thermally activate d above 150 K and the other due to extended defects, which causes the subli near intensity dependence of the photocurrent in the whole temperature rang e comprised between 10 and 300 K. Comparison with temperature dependent pho toluminescence experiments suggests that Ga-vacancies can be responsible fo r the observed localization at point defects, whereas the high-density of n ative extended defects (as inferred by Rutherford back-scattering experimen ts) is responsible for the intensity dependence of the photocurrent. Howeve r they are localized close to the interface and do not propagate across the bulk of the layer resulting in a good quality of the sample. (C) 2000 Else vier Science Ltd. All rights reserved.