Carrier recombination under one-photon and two-photon excitation in GaN epilayers

Luminescence properties of 100-μm thick GaN epilayers grown by hydride vapor phase epitaxy (HVPE) over three different substrates: high-pressure grown n-type bulk GaN (HP-n-GaN), high-pressure bulk GaN doped with magnesium (HP-GaN:Mg), and free-standing HVPE lifted-off from sapphire (FS-HVPE-GaN), were compared by means of one-photon and two-photon excitations. The contribution of carrier capture to nonradiative traps was estimated by the analysis of luminescence transients with carrier diffusion taken into account. The estimated values of carrier lifetime of about 3 ns and diffusion coefficient of 1 cm2/s indicate the highest quality of GaN epilayers on FS-HVPE-GaN substrates.