Large electron capture-cross-section of the major nonradiative recombination centers in Mg-doped GaN epilayers grown on a GaN substrate

Complementary time-resolved photoluminescence and positron annihilation measurements were carried out at room temperature on Mg-doped p-type GaN homoepitaxial films for identifying the origin and estimating the electron capture-cross-section (sigma(n)) of the major nonradiative recombination centers (NRCs). To eliminate any influence by threading dislocations, free-standing GaN substrates were used. In Mg-doped p-type GaN, defect complexes composed of a Ga-vacancy (V-Ga) and multiple N-vacancies (V(N)s), namely, V-Ga(V-N)(2) [or even V-Ga(V-N)(3)], are identified as the major intrinsic NRCs. Different from the case of 4H-SiC, atomic structures of intrinsic NRCs in p-type and n-type GaN are different: VGaVN divacancies are the major NRCs in n-type GaN. The sigma(n) value approximately the middle of 10(-13) cm(2) is obtained for V-Ga(V-N)(n), which is larger than the hole capture-cross-section (sigma(p) = 7 x 10(-14) cm(2)) of VGaVN in n-type GaN. Combined with larger thermal velocity of an electron, minority carrier lifetime in Mg-doped GaN becomes much shorter than that of n-type GaN. Published by AIP Publishing.