Transients of Carrier Recombination and Diffusion in Highly Excited GaN Studied by Photoluminescence and Four-Wave Mixing Techniques

S. Juršėnas, S. Miasojedovas, G. Kurilčik, A. Žukauskas, R. Aleksiejūnas, T. Malinauskas, M. Sūdžius and K. Jarašiūnas Institute of Materials Science and Applied Research, Vilnius University, Saulėtekio 9-III, 10222 Vilnius, Lithuania

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Received: 22 08 2004;

Time-resolved photoluminescence and four-wave mixing techniques have been combined for studies of carrier relaxation dynamics in a highly photoexcited GaN epilayer. For a moderate excitation density below 1 mJ/cm2, carrier recombination was due to free carrier capture by deep traps. The characteristic time of carrier capture,τe=550 ps, was measured under deep trap saturation regime. The ambipolar diffusion coefficient for free carriers, D=1.7 cm2/s, was estimated from the analysis of the transients of the light-induced gratings of various periods. A complete saturation of the four-wave mixing efficiency was observed for the excitation energy density exceeding 1.5 mJ/cm2. The latter saturation effect was shown to be related to electron--hole plasma degeneration, which results in a significant enhancement of carrier recombination rate due to onset of stimulated emission.

DOI: 10.12693/APhysPolA.107.240 PACS numbers:72.80.Ey, 72.20.Jv, 78.55.Cr