Incident wavelength and polarization dependence of spectral shifts in β-Ga2O3 UV photoluminescence

Abstract

We report polarization dependent photoluminescence studies on unintentionally-, Mg-, and Ca-doped β-Ga2O3 bulk crystals grown by the Czochralski method. In particular, we observe a wavelength shift of the highest-energy UV emission which is dependent on the pump photon energy and polarization. For 240 nm (5.17 eV) excitation almost no shift of the UV emission is observed between E||b and E||c, while a shift of the UV emission centroid is clearly observed for 266 nm (4.66 eV), a photon energy lying between the band absorption onsets for the two polarizations. These results are consistent with UV emission originating from transitions between conduction band electrons and two differentially-populated self-trapped hole (STH) states. Calcuations based on hybrid and self-interaction-corrected density functional theories further validate that the polarization dependence is consistent with the relative stability of two STHs. This observation implies that the STHs form primarily at the oxygen atoms involved in the original photon absorption event, thus providing the connection between incident polarization and emission wavelength. The data imposes a lower bound on the energy separation between the self-trapped hole states of ~70–160 meV, which is supported by the calculations.

Synthesis and Characterization of Large‐Area Nanometer‐Thin β‐Ga2O3 Films from Oxide Printing of Liquid Metal Gallium

“…Figure shows the results of the PL emission along with deconvoluted emission bands for Ga 2 O 3 films on SiO 2 /Si and sapphire substrates before and after annealing. The spectrum is composed of four emission bands at UV, UV′, blue, and green wavelengths in agreement with the observations in bulk Ga 2 O 3 crystals, as previously reported in the literature . These four emission bands are identified in all samples.…”

“…These four emission bands are identified in all samples. The UV emission band is attributed to the recombination of free electrons and self‐trapped holes . Computational studies attribute the blue band to ( V Ga + V O ) divacancies in the (1‐) charged state with some contribution of V Ga with (2‐) charge state.…”

On the origin of red luminescence from iron-doped β-Ga2O3 bulk crystals

“…This shows that these samples contain low enough concentrations of transition metals that their intracenter absorption bands are below detection limits. The UID sample shows the typical UV, UV', blue, and green emissions 27 . The Fe-doped samples show UV', blue, and green peaks of ~100 times lower in intensity as compared to those from the UID samples.…”

Terahertz Emission Spectroscopy and Microscopy on Ultrawide Bandgap Semiconductor β-Ga2O3

“…The LTEM and PL images are given in Figure 7a and 7b, respectively. The PL image was obtained at an fs laser power of 20 mW at a wavelength of 365 nm, which corresponds to the UV luminescence as described in Figure 1a [39]. Both images show a similar intensity distribution.…”