Mechanism of donor-acceptor pair recombination in Mg-doped GaN epilayers grown on sapphire substrates

Temperature-dependent photoluminescence (PL) measurements in Mg-doped GaN epitaxial layers grown on sapphire substrates by plasma-assisted molecular beam epitaxy have been performed in order to investigate the process of donor-acceptor pair (DAP) recombination. The PL intensity of the DAP peak decreases below 35 K, and then it increases as the temperature increases in the temperature range between 35 and 100 K. This behavior originates from the interaction between two different Mg-related traps, one shallow and the other deep level. The ionization energies of the shallow trap and the deep level trap determined from the calculations and the PL experiments are 126 and 160 meV, respectively. The DAP recombination process suggests that holes are caught in the shallow trap and that they subsequently transfer, via a tunneling process, from the shallow trap to the deep trap, where recombination with electrons takes place. (C) 1998 American Institute of Physics. [S0021-8979(98)06916-3].