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 (σ 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_Ns), 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: V_GaV_N divacancies are the major NRCs in n-type GaN. The σ n value approximately the middle of 10^-13 cm² is obtained for V_Ga(V_N)_n, which is larger than the hole capture-cross-section (σ_p = 7 × 10^-14 cm²) of V_GaV_N 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.