Analysis of the red optical emission in cubic GaN grown by molecular-beam epitaxy

The red optical emission band in cubic GaN is examined for the first time b y cathodoluminescence as well as steady-state and time-resolved photolumine scence. We establish a close analogy between the red emission band in cubic GaN and the yellow emission in wurtzite GaN, and assign it to a donor-acce ptor process involving a shallow donor and a deep acceptor with similar ion ization energies in both phases. We show a range of properties of the red e mission which clearly indicate its donor-acceptor pair origin, namely the b lueshift with excitation intensity, the power-law evolution at increasing e xcitation, and the blueshift with temperature. The line shape of the red ba nd indicates that the deep acceptor is strongly coupled to the lattice. The photoluminescence decay curves show a fast decay at higher energies within the emission band, while at lower energies the decay is much slower, typic al of donor-acceptor pair transitions. An analytical expression for the tim e-dependent emission intensity for donor-acceptor pair transitions in which one of the centers is strongly coupled to the lattice is derived, extendin g the theory of Thomas et al. [Phys. Rev. B 140, A202 (1995)]. The observed decay curves are found to be well described by the theory using the donor Bohr radius of 1.7 nm, while temperature quenching of the: emission gives a n activation energy of 15+/-5 meV. Evidence of Coulomb attraction between a shallow donor and a deep acceptor is presented. [S0163-1829(99)07631-6].