Hole capture-coefficient of intrinsic nonradiative recombination centers that commonly exist in bulk, epitaxial, and proton-irradiated ZnO

Wurtzite ZnO and related MgxZn1-xO alloys are attractive semiconductors for the use in radiation-resistant and/or visible-light-transparent transistors and ultraviolet light-emitters. As free-carrier lifetime controls the device performances, the accurate understanding of the carrier capture-coefficients of dominant nonradiative recombination channels is essential. In this paper, the hole capture-coefficient (C p) at room temperature of major intrinsic nonradiative recombination centers (NRCs) that commonly exist in various low dislocation density n-type epitaxial films and nearly dislocation-free bulk single crystals of ZnO with and without irradiation by an 8 MeV proton beam is determined. A two-component density functional theory calculation with positron annihilation measurement reveals that major vacancy-type defects are divacancies comprised of a Zn-vacancy and an O-vacancy (VZnVO). Because the weak-excitation nonradiative photoluminescence lifetime (t NR) decreases with increasing VZnVO concentration ([VZnVO]), VZnVO are assigned as major NRCs in n-type ZnO. From the relationship between t NR and [VZnVO], the values of C p and hole capture-cross section of VZnVO are obtained to be 3 × 10 - 7 c m 3 s - 1 and 2 × 10 - 14 c m 2, respectively, according to the Shockley-Read-Hall approach. These values are an order of magnitude larger than those of 3d transition metals such as Ni or Mn but are comparable to those of major intrinsic NRCs in n-type GaN, i.e., divacancies comprised of a Ga-vacancy and a N-vacancy (VGaVN), being 6 × 10 - 7 c m 3 s - 1 and 7 × 10 - 14 c m 2, respectively [S. F. Chichibu, A. Uedono, K. Kojima, H. Ikeda, K. Fujito, S. Takashima, M. Edo, K. Ueno, and S. Ishibashi, J. Appl. Phys. 123, 161413 (2018)].