【International Papers】Photoluminescence study of optical transitions in spinel zinc gallium oxide thin films

      Researchers from the University of California have published a dissertation titled "Photoluminescence study of optical transitions in spinel zinc gallium oxide thin films" in Scientific Reports.

Abstract

      Spinel ZnGa₂O₄ is an ultra-wide bandgap material that can have a great potential for deep ultraviolet (UV) photonics and other applications. In this work, zinc gallium oxide (ZnGaO) samples with Zn composition ranging from 0.0 to 48.0 at% were grown in a plasma-assisted molecular beam epitaxy system. The change of crystal structure from beta to spinel was determined using reciprocal space mapping in x-ray diffraction. When Zn composition is at 0.0, 0.9, 3.4, and above 7.3 at%, the crystal structure exhibits beta phase, mixture phase, weak spinel phase, and strong spinel phase, respectively. Comprehensive photoluminescence (PL) of the samples were carried out using an ArF laser excitation, and PL peak deconvolution was performed to understand the optical transitions and energy levels within the forbidden gap. For spinel ZnGaO samples, five deconvoluted peaks were observed, revealing the energy levels of three oxygen vacancies, self-trapped holes binding energy, and acceptor levels.

Conclusion

      In this work, 9 ZnGaO samples with Zn composition ranging from 0.0 to 48.0 at% were grown using a plasma-assisted MBE system. When Zn composition is increased to 0.9 at%, the sample exhibits a mixture of beta and spinel structure. When Zn composition is 3.4 at%, the sample exhibits weak spinel structure. When Zn composition is larger than 7.3 at%, all samples exhibit spinel structure. PL studies of these samples using a 193 nm laser as excitation were carried out to systematically analyze and understand the optical transition of these samples. The STH binding energy and the position of the three oxygen vacancies and acceptor levels were revealed. This study paves a way towards the application of spinel ZnGa₂O₄ for deep ultraviolet photodetectors and other optoelectronic applications.