Optical spectroscopy of Si-related donor and acceptor levels in Si-doped GaN grown by hydride vapor phase epitaxy

The optical properties of n-type GaN grown by hydride vapor phase epitaxy, with intentional Si doping levels ranging from nominally undoped to N_D-N_A=4×10¹⁷cm^-3, are investigated using low temperature photoluminescence. We identify free and neutral donor-bound exciton transitions and two-electron satellites (TES) at 1.7 K. The energy difference between the principal neutral donor-bound exciton peak and its TES yields a Si donor binding energy of 22 meV. The intensity of the Si-related TES increases with increasing Si concentration. The Si donor is much shallower than the two residual donors, which have binding energies of 28 and 34 meV. This result suggests that the main residual donors in this material (and possibly in many layers grown by metal organic chemical vapor deposition and metal organic molecular beam epitaxy as well) are not Si. Silicon doping also introduces an acceptor level with a binding energy of about 224 meV.