Chip-Scale Electron Spin Resonance Spectroscopy of Spin-Active Defects in Epitaxial β-Ga₂O₃

We demonstrate the use of a chip-scale, coplanar waveguide resonator in temperature-dependent Electron Spin Resonance (ESR) spectroscopy of defects in the ultra-wide bandgap semiconductor β-Ga₂O₃. The study of point defects in β-Ga₂O₃, many of which are spin active, is essential to establish it as a material platform for high-power electronics. Further, ESR spectroscopy has been a useful tool in the study of defects in semiconductors owing to its sensitivity to a low density of spin-active defects, its ability to readily differentiate between various defect charge states, and to discern asymmetries in the defects’ environment by extracting the associated g-tensor. However, commercially available ESR spectrometers utilize bulky cavity resonators which are not sensitive to a low density of spin-defects in sub-micron epitaxial thin-films, at interfaces, or on surfaces due to the resonator’s mode volume being much larger than the region being probed. The two-dimensional nature of our high-Q resonator allows us to overcome this limitation. We present results on the nature of defects in micron and sub-micron epitaxial β-Ga₂O₃. Our measurements show the presence of additional defect signatures in epitaxial β-Ga₂O₃ beyond those that can be observed by commercial X-Band spectrometers. We will discuss the characteristics and possible sources of these additional signatures, as well as the wider applicability of our chip-scale ESR technique in probing spin defects in semiconductor thin films, interfaces, and surfaces.