Systematic study of shockley-read-hall and radiative recombination in GaN on Al₂O₃, freestanding GaN, and GaN on Si

Here we study and correlate structural, electrical, and optical properties of three GaN samples: GaN grown by metalorganic chemical vapor deposition on sapphire (GaN/Al₂O₃), freestanding GaN crystals grown by the high nitrogen pressure solution method (HNPS GaN), and GaN grown by hydride vapor phase epitaxy on silicon (GaN/Si). Defect and impurity densities and carrier concentrations are quantified by x-ray diffraction, secondary mass ion spectroscopy, and Hall effect studies, respectively. Power-dependent photoluminescence measurements reveal GaN near-band-edge emissions from all samples having mixtures of free exciton and band-to-band transitions. Only the defect luminescence in the GaN/Si sample remains unsaturated, in contrast to those from the HNPS GaN and GaN/Al₂O₃ samples. Carrier lifetimes, extracted from time-resolved photoluminescence measurements, and internal quantum efficiencies, extracted from temperature-dependent photoluminescence measurements, are used to extract radiative and nonradiative lifetimes. Shockley–Read–Hall (A) and radiative recombination coefficients (B) are then calculated accordingly. Overall, the A coefficient is observed to be highly sensitive to the point defect density rather than dislocation density, as evidenced by three orders of magnitude reduction in threading dislocation density reducing the A coefficient by one order of magnitude only. The B coefficient, while comparable in the higher quality and lowly doped GaN/Al₂O₃ and HNPS GaN samples, was severely degraded in the GaN/Si sample due to high threading dislocation density and doping concentration.