Deep level defects in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy

Deep level defects were characterized in Ge-doped (010) beta-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy (PAMBE) using deep level optical spectroscopy (DLOS) and deep level transient (thermal) spectroscopy (DLTS) applied to Ni/beta-Ga2O3: Ge (010) Schottky diodes that displayed Schottky barrier heights of 1.50 eV. DLOS revealed states at E-C - 2.00 eV, E-C - 3.25 eV, and E-C - 4.37 eV with concentrations on the order of 10(16) cm(-3), and a lower concentration level at E-C - 1.27 eV. In contrast to these states within the middle and lower parts of the bandgap probed by DLOS, DLTS measurements revealed much lower concentrations of states within the upper bandgap region at E-C - 0.1 - 0.2 eV and E-C - 0.98 eV. There was no evidence of the commonly observed trap state at similar to E-C - 0.82 eV that has been reported to dominate the DLTS spectrum in substrate materials synthesized by melt-based growth methods such as edge defined film fed growth (EFG) and Czochralski methods [Zhang et al., Appl. Phys. Lett. 108, 052105 (2016) and Irmscher et al., J. Appl. Phys. 110, 063720 (2011)]. This strong sensitivity of defect incorporation on crystal growth method and conditions is unsurprising, which for PAMBE-grown b-Ga2O3: Ge manifests as a relatively "clean" upper part of the bandgap. However, the states at similar to E-C - 0.98 eV, E-C - 2.00 eV, and E-C - 4.37 eV are reminiscent of similar findings from these earlier results on EFG-grown materials, suggesting that possible common sources might also be present irrespective of growth method. Published by AIP Publishing.