Electron paramagnetic resonance (EPR) is used to identify and characterize neutral zinc acceptors in Zn-doped β-Ga2O3 crystals. Two EPR spectra are observed at low temperatures, one from Zn ions at tetrahedral Ga(1) sites (the Zn0Ga1 acceptor) and one from Zn ions at octahedral Ga(2) sites (the Zn0Ga2 acceptor). These Zn acceptors are small polarons, with the unpaired spin localized in each case on a threefold coordinated oxygen O(I) ion adjacent to the Zn ion. Resolved hyperfine interactions with neighboring 69Ga and 71Ga nuclei allow the EPR spectra from the two acceptors to be easily distinguished: Zn0Ga1 acceptors interact equally with two Ga(2) ions and Zn0Ga2 acceptors interact unequally with a Ga(1) ion and a Ga(2) ion. The as-grown crystals are compensated, with the Zn ions initially present as singly ionized acceptors (Zn-Ga1 and Zn-Ga2). Exposing a crystal to 325 nm laser light, while being held at 140 K, primarily produces neutral Zn0Ga2 acceptors when photoinduced holes are trapped at Zn−Ga2 acceptors. This suggests that there may be significantly more Zn ions at Ga(2) sites than at Ga(1) sites. Warming the crystal briefly to room temperature, after removing the light, destroys the EPR spectrum from the shallower Zn0Ga2 acceptors and produces the EPR spectrum from the more stable Zn0Ga1 acceptors. The Zn0Ga2 acceptors decay in the 240–260 K region with a thermal activation energy near 0.65 eV, similar to Mg0Ga2 acceptors, whereas the slightly deeper Zn0Ga1 acceptors decay close to room temperature with an approximate thermal activation energy of 0.78 eV.
Journal of Applied Physics
Gustafson, T. D., Jesenovec, J., Lenyk, C. A., Giles, N. C., McCloy, J. S., McCluskey, M. D., & Halliburton, L. E. (2021). Zn acceptors in β-Ga 2 O 3 crystals. Journal of Applied Physics, 129(15), 155701. https://doi.org/10.1063/5.0047947