Luminescence studies of GaN grown on GaN and GaN/AlN buffer layers by metalorganic chemical vapor deposition

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Abstract
A detailed study of the luminescence properties of GaN layers grown by metalorganic chemical vapor deposition on sapphire substrates with GaN/AlN double buffer layers or GaN single buffer layers was carried out with photoluminescence and cathodoluminescence (CL) spectroscopy. It was discovered that the use of the double buffer layer resulted in an improved surface morphology, but also increased the strain in the samples relative to samples grown on single GaN buffer layers. Free exciton (A exciton), neutral donor-bound exciton, and acceptor-bound exciton photoluminescence peaks were observed for GaN films grown on GaN, AlN, and GaN/AlN buffer layers. Acceptor free-to-bound luminescence was also observed and the thermal activation energy of the acceptors was measured. From these data we are able to determine the acceptor binding energy, EA, to be 231.5 meV and the donor binding energy ED to be 29.5 meV. An exciton peak, the acceptor free-to-bound luminescence, and an unidentified lower energy peak were observed with CL. CL imaging also allowed us to correlate luminescence with surface features of the films. e-beam annealing of both n-type and p-type films was investigated.