||Electronic properties of the residual donor in unintentionally doped beta-Ga2O3
Electron paramagnetic resonance (EPR) was used to study the donor that is responsible for the n-type conductivity in unintentionally doped (UID) beta-Ga2O3 substrates. We show that in as-grown material, the donor requires high temperature annealing to be activated. In partly activated material with the donor concentration in the e16 cm-3 range or lower, the donor is found to behave as a negative-U center (often called a DX center) with the negative charge state DX-lying ~16-20 meV below the neutral charge state d0 (or Ed), which is estimated to be ~28-29 meV below the conduction band minimum. This corresponds to a donor activation energy of Ea ~44-49 meV. In fully activated material with the donor spin density close to ~1e18 cm-3, donor electrons become delocalized, leading to the formation of impurity bands, which reduces the donor activation energy to Ea ~15-17 meV. The results clarify the electronic structure of the dominant donor in UID beta-Ga2O3.
||Journal of Applied Physics
Q. T. Thieu