Detailed photoluminescence (PL) studies of high-quality MBE-grown single-crystal cubic and hexagonal GaN are presented. We identify free and bound exciton recombination. By means of a line-shape analysis, we quantitatively analyze our spectra, which were taken as a function of temperature (T = 4 - 300 K) and excitation density (P
ex = 0.3 - 200W/cm2). We show the dominant recombination channel at 300 K to be free-excitonic in nature with an internal small-signal quantum efficiency of 6 · 10−3 for both cubic and hexagonal material. Based on a three-level model, activation energies for exciton dissociation are evaluated. Radiative (τrad ≈ 2 ns) and nonradiative lifetimes (τ
≈ 1μs, τ
≈ 20 ps) are determined, where in the latter case, electron and hole trapping are considered separately. Furthermore, we show that the dominant nonradiative recombination center, being a hole trap, saturates at P
ex ≥ 20 W/cm2.