Photoconductivity in AlxGa1-xN with different Al contents

We report on the photoconductivity (PC) of AlxGa1-xN on GaN epitaxial films grown by metal organic vapor phase epitaxy (MOVPE) with Al contents betwee n x = 0% and 18%. The concentration of the free carriers and mobilities of majority carriers are derived from Hall effect measurements. Temperature de pendent photoconductivity measurements between 4.2 and 500 K have been perf ormed. The ratio between the photoconductivity far sub-bandgap excitation a nd that for excitation in the excitonic region drops down with increasing t emperature to a value around 10(5) due to a decreasing relevance of electro nic traps. Time transients after sub-bandgap and UV-excitation exhibit a pr olonged non-exponential decay of photoconductivity. We find a power law del ay for the time transient of the photocurrent I-ph(t) similar to t(-m) (m = 0.27 to 0.33) which can be explained in the picture of bandtails.