Native defects and their complexes in spinel LiGa5O8: the puzzle of p-type doping

Recently, LiGa$_5$O$_8$ was identified as a cubic spinel type ultra-wide-band-gap semiconductor with a gap of about 5.36 eV and reported to be unintentionally p-type. Here we present first-principles calculations of the native defects and various of their complexes to try to explain the occurrence of p-type doping. Although we find Li-vacancies to be somewhat shallower acceptors than in LiGaO$_2$, and becoming slightly shallower in complexes with donors such as V$_{\rm O}$ and Ga$_{\rm Li}$ antisites, these $V_{\rm Li}$ based defects are not sufficiently shallow to explain p-type doping. The dominant defects are donors and in equilibrium the Fermi level would be determined by compensation between donors and acceptors, and pinned deep in the gap.