Enhancement of excitonic and defect-related luminescence in neutron transmutation doped beta-Ga2O3

Neutron irradiation analysis, inductively coupled plasma mass spectrometry (ICPMS), and cathodolumi-nescence (CL) spectroscopy are used to investigate the influence of transmuted Ge incorporation on the luminescence properties of beta-Ga2O3 single crystals. Calculations based on Ga2O3-neutron interaction reveal temporal variations of both Ge and Zn concentrations as a function of time during and after neutron irradiation. To produce a concentration of 5 x 10(18) Ge donors/cm(3) from the neutron transmutation of Ga, the beta-Ga2O3 crystal was irradiated for 27 h, which was accompanied by the incorporation of 10(16) Zn acceptors/cm(3). These calculated dopant concentrations are confirmed by ICPMS. The beta-Ga2O3 crystals exhibit a UV band at 3.40 eV due to self-trapped holes (STHs) and two blue donor-acceptor pair (DAP) peaks at 3.14 eV (BL1) and 2.92 eV (BL2). In addition to the neutron-induced incorporation of substitutional Ge donors and Zn acceptors on Ga sites, Ga vacancies (V-Ga) were created by high-energy neutrons in the flux, which strongly enhanced the BL1 peak. The VGa acceptors compensate the neutron-induced Ge donors, making the Ga2O3 crystal highly resistive. Concurrent temperature-resolved CL measurements of the beta-Ga2O3 before and after neutron irradiation reveal a twofold increase in both the STH and BL1 peaks. This result suggests that STHs are preferentially localized at an O site adjacent to V-Ga, as theoretically predicted by Kananen et al. [Appl. Phys. Lett. 110, 202104 (2017).]. Analysis of the Ga2O3 CL temperature dependence reveals that the UV and BL1 bands after the neutron irradiation exhibit an equivalent activation energy of 100 +/- 10 meV due to the presence of a neutron-induced defect that acts as an efficient competitive nonradiative recombination channel. The results also provide evidence that the BL1 and BL2 bands arise from different DAP pairs.