Vol. 107 (2005) ACTA PHYSICA POLONICA A No. 1 Proceedings of the 12th International Symposium UFPS, Vilnius, Lithuania 2004 Photoluminescence and Photoconductivity Dynamics in Semi-Insulating Epitaxial GaN Layers E. Gaubas * , S. Jur ˇ s ˙ enas, K. Kazlauskas, S. Miasojedovas, J. Vaitkus and A. ˇ Zukauskas Institute of Materials Science and Applied Research, Vilnius University Saul˙ etekio al. 10, 10223 Vilnius, Lithuania The transients of fast free-carrier recombination and of multi-trapping processes due to different species of defects have been investigated by photo- luminescence and by contact and microwave photoconductivity. Three dis- tinct stages of relaxation, namely, of stimulated emission, of recombination due to point defects and capture into trapping centers associated with dislo- cations, and a non-exponential stage with a stretched-exponent asymptotic decay ascribed to dislocations mediated multi-trapping were distinguished by correlated examination of time-resolved photoluminescence and photo- conductivity transients. PACS numbers: 61.72.Hh, 72.40.+w 1. Introduction GaN-based materials are widely used in fabrication of efficient short- -wavelength light emitters [1, 2]. The key issue of materials quality in GaN is high dislocation density (10 8 -10 10 cm −2 ), when radiative and non-radiative recombi- nation depends on a dislocation type [3]. Luminescence and photoconductivity transients [1, 4] provide direct information on the carrier lifetime, which indicates the dominant recombination processes and defects. In this paper, correlated investigations of the transients of time-resolved photoluminescence (TRPL), contact photoconductivity (CPC) and microwave ab- sorption (MWA) are presented and analyzed in order to identify the behavior of different defects residing in the GaN epilayers. Distinct stages of relaxation, due to * corresponding author; e-mail: eugenijus.gaubas@ff.vu.lt (215)