Semiconductors, 2023, Vol. 57, No. 7 Investigation of the Cr 3+ impurity luminescence in proton-irradiated β -Ga 2 O 3 © V.Yu. Davydov 1 , A.N. Smirnov 1 , I.A. Eliseyev 1 , Yu.E. Kitaev 1 , S.S. Sharofidinov 1 , A.A. Lebedev 1 , D.Yu. Panov 2 , V.A. Spiridonov 2 , D.A. Bauman 2 , A.E. Romanov 1,2 , V.V. Kozlovski 3 1 Ioffe Institute, 194021 St. Petersburg, Russia 2 National Research University ITMO, 197101 St. Petersburg, Russia 3 Peter the Great St. Petersburg Polytechnic University, 195251 St. Petersburg, Russia E-mail: valery.davydov@mail.ioffe.ru Received May 19, 2023 Revised July 18, 2023 Accepted October 30, 2023 Proton irradiation of β -Ga 2 O 3 crystals has been established to lead to a significant increase in the amount of Cr 3+ ions being active in luminescence. Using angle-resolved luminescence, the features of the spectra of Cr 3+ ions were studied. The high sensitivity of photoluminescence spectra and the related selection rules to the local symmetry of Cr 3+ ions in the β -Ga 2 O 3 matrix has been found. The results obtained indicate the potential possibility of using β -Ga 2 O 3 crystals as optical dosimeters of proton irradiation. Keywords: β -Ga 2 O 3 , α-Ga 2 O 3 , proton irradiation, photoluminescence, symmetry analysis. DOI: 10.61011/SC.2023.07.57425.5202C Polytype β -Ga 2 O 3 with a band gap width of ∼ 4. 9 eV possesses electronic and electrophysical properties that are promising for use in UV detectors, high-temperature gas sensors, nanophotonic switches, etc. e.There is quite a considerable amount of research devoted to studying the effects of radiation exposure on β -Ga 2 O 3 oxide-based devices (see, for example, the review [1] and references therein). However, many questions related to the influence of radiation exposure on the nature of impurity states and structural defects in this material have not been sufficiently studied. The aim of the present study was to obtain new information on the possibility of using electron and proton irradiation for controlled change of the charge state of impurities in hboxβ -Ga 2 O 3 in order to identify them by optical methods. Initially undoped and chromium-doped bulk crystals β -Ga 2 O 3 , grown by the Czochralsky [2] method and epitax- ial layers α-Ga 2 O 3 :Cr, grown on Al 2 O 3 (0001) substrate by chloride-hydride epitaxy were studied. Unalloyed β -Ga 2 O 3 crystals were irradiated with electrons at energies of 0. 9 MeV doses 2. 0 · 10 16 and 5. 0 · 10 16 cm -2 at the electron accelerator RTE-1V and protons with energy 15 MeV dose 1. 0 · 10 16 cm -2 at the isochron cyclotron MGC-20 in SPbPU named after Peter the Great. The vibrational and electronic characteristics of crystals by micro-combination light scat- tering (μ-RS) and micro-photoluminescence (μ-PL) were measured using a LabRAM HREvo UV-VIS-NIR-Open spectrometer (Horiba, France). λ = 532 nm (2.33 eV) Nd:YAG-laser line was used to excite the μ-RS spectra. Angle-resolved μ-PL spectra over a temperature range (80-300 K) were measured using a wide range of excitation radiation energies (2.33-5.82 eV). μ-QW studies confirmed that bulk unalloyed and Cr of samples Ga 2 O 3 samples belong to the β - polytype, and epitaxial layers of Ga 2 O 3 : Cr/Al 2 O 3 — to α-E polytype. No noticeable changes were found in the μ-RS spectra of samples irradiated with electrons or protons compared to the spectra of the original samples. Also, no noticeable changes were found in the μ-PL spectra of the electron- irradiated samples. However, the μ-PL spectrum of the proton-irradiated sample β -Ga 2 O 3 was significantly different from that of the non-irradiated sample. The μ-PL spectra of unirradiated, proton-irradiated and chromium-doped samples β -Ga 2 O 3 , measured at room temperature and T = 80 K are shown in Figure 1. In all spectra, a broad band with a maximum at ∼ 3. 25 eV is observed in the UV band, the parameters of which depend weakly on the type of the investigated sample. This feature has been reported in works related to studies of the PL spectra of β -Ga 2 O 3 , crystals grown by different methods [3–5]. In most cases, this band is decomposed into three components: ultraviolet (UV), blue (BL), and green (GR). The UV component is generally independent of impurities and is attributed to the recombination of free electrons and autolocalized holes. The GR component was attributed to donor-acceptor pair transitions involving deep donors and deep acceptors. As for the GR component, the nature of its origin needs further research. As can be seen in Figure 1, the spectrum of the proton- irradiated β -Ga 2 O 3 , in addition to the band in the UV, 557