Zn acceptors in β-Ga2O3 crystals

Electron paramagnetic resonance (EPR) is used to identify and characterize neutral zinc acceptors in Zn-doped beta-Ga2O3 crystals. Two EPR spectra are observed at low temperatures, one from Zn ions at tetrahedral Ga(1) sites (the Zn-Ga (0)(1) acceptor) and one from Zn ions at octahedral Ga(2) sites (the Zn-Ga (0)(2) 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 Ga-69 and Ga-71 nuclei allow the EPR spectra from the two acceptors to be easily distinguished: Zn-Ga (0)(1) acceptors interact equally with two Ga(2) ions and Zn-Ga (0)(2) 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-Ga (-)(1) and Zn-Ga (-)(2)). Exposing a crystal to 325 nm laser light, while being held at 140K, primarily produces neutral Zn-Ga (0)(2) acceptors when photoinduced holes are trapped at Zn-Ga (-)(2) 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 Zn-Ga (0)(2) acceptors and produces the EPR spectrum from the more stable Zn-Ga (0)(1) acceptors. The Zn-Ga (0)(2) acceptors decay in the 240-260K region with a thermal activation energy near 0.65eV, similar to Mg-Ga (0)(2) acceptors, whereas the slightly deeper Zn-Ga (0)(1) acceptors decay close to room temperature with an approximate thermal activation energy of 0.78eV.

Automated summary

Electron paramagnetic resonance (EPR) is utilized to identify and characterize neutral zinc acceptors in Zn-doped beta-Ga2O3 crystals. The study reveals the presence of two types of Zn acceptors, Zn-Ga (0)(1) and Zn-Ga (0)(2), and investigates their interactions and thermal stability.