Acceptors in undoped GaN studied by transient photo luminescence

Acceptors responsible for the 2.2, 2.9 and 3.27 eV photoluminescence (PL) bands in undoped GaN were studied by transient PL. A non-exponential decay of PL intensity for all the three bands is observed at low temperature consistent with donor acceptor pair recombination. The transitions are attributed to recombination involving a shallow donor and three different acceptors. At temperatures in excess of about 100 K a new recombination process emerges as evident from the nearly exponential PL decay. We attribute this to free-to-bound transitions involving free electrons and acceptors. Electron-capture cross-sections of 3 x 10(-19), 2 x 10(-20) and 3 x 10(-21) cm(2) are calculated for the acceptors responsible for the 3.27, 2.9 and 2.2eV bands. These acceptors are attributed to multiply charged defects involving a gallium vacancy. (C) 2002 Elsevier Science B.V. All rights reserved.