Carrier dynamics under two- and single-photon excitation in bulk GaN

• Published in: physica status solidi (b) 2012-03, Vol.249 (3), p.503-506
• Main Authors: Ščajev, Patrik, Jarašiūnas, Kęstutis, Okur, Serdal, Özgür, Ümit, Morkoç, Hadis
• Format: Article
• Language: English
• Subjects: diffusion; free-carrier absorption; GaN; photoluminescence; recombination; transient gratings; two photon absorption
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/pssb.201100307

Carrier diffusion and recombination features in freestanding 200 µm thick GaN were studied using light‐induced transient grating, time‐resolved free‐carrier absorption, and photoluminescence techniques. Under two‐photon excitation (527 nm, 8 ps), in‐plane carrier diffusion paved the way for determining the hole and ambipolar carrier diffusion coefficients (Dh = 0.8 and Da = 1.6 cm2/s) and their temperature dependence. The nearly inverse correlation between the diffusivity and carrier lifetime in the 80–800 K range was ascribed to nonradiative carrier recombination at the extended defects. Very low density of dislocations, in mid‐105 cm−2, provided extremely long lifetime values, up to 40 ns at 300 K and 120 ns at 800 K. Under single‐photon excitation (267 nm, 100 fs), the initial very fast transient of photoluminescence decay at 3.4 eV was described by carrier diffusion normal to the surface, reabsorption of emission, and surface recombination. The nonequilibrium processes in the entire 80–800 K range can be reliably analyzed by a free electron–hole model.