Gallium oxide is an ultra-wide bandgap semiconductor with excellent opto-electronic properties, making it a highly promising material for a wide range of applications and devices. In this article, we report how the optical, morphological, structural, and compositional properties of $\beta$-Ga₂O₃ thin films deposited by RF Sputtering on silicon substrates are affected by thermal treatments. Ellipsometric spectra recorded at multiple angles of incidence from several samples subjected to thermal annealing in the range of 550–1000 °C were analyzed to extract the optical functions using appropriate multilayer models. This analysis is complemented by compositional, structural, and morphological characterization techniques. We observed two main stages of crystallization with increasing annealing temperature; up to 700 °C, there is an increase in density and then, for 700–1000 °C, there is an improvement in crystallinity. While the refractive index increases continuously throughout this process, we found that the polarizability of the samples decreases in the first stage and increases in the second. These observations demonstrate that thermal treatments are a powerful tool to tune the optical properties of Ga₂O₃ thin films for device applications.

This paper reports the implementation of two critical technologies used in LiDARs: 1) A microchip Q-switched laser breadboard and 2) breadboard of an Indium gallium arsenide avalanche photodiode working at 300 K with high reverse polarization voltages. Microchip Q-switched lasers are small solid state back pumped lasers, that can generate high energy short pulses. The implemented breadboard used an Erbium and Ytterbium co doped phosphate glass, a COMALO crystal with 98% (initial transparency) and an output coupler of 98% reflectivity. For the sensor test, a system for the simultaneous operation in vacuum and wide range of temperatures was developed. Avalanche photodiodes are reverse polarized photodiodes with high internal gain, due to their multiple layer composition, capable of building up high values of photocurrent from small optical signals by exploiting the avalanche breakdown effects. The test avalanche photodetector was assembled to be operated in two modes: Linear and Geiger mode, to achieve this behavior, a transimpedance amplifier circuit was implemented. These two technologies are critical for mobile LiDAR applications, due to its low mass and high efficiency. The paper describes the breadboard implementation method and sensor characterization at low temperature and high voltage (beyond breakdown voltage).

Gallium oxide is a wide-bandgap semiconductor which has been steadily growing in popularity due to its ultra-wide bandgap, suitability for harsh environments and distinctive opto-electrical properties. Notable applications include deep-UV photodetectors, low loss waveguides or even transparent solar cells. RF sputtering stands out among possible techniques for the epitaxial deposition of Ga$_{2}$O$_{3}$ thin films with high quality and at a low cost. By using sapphire substrates, and through thermal annealing, we can form a $β$-(Al$_{x}$Ga$_{1-x}$)$_{2}$O$_{3}$ alloy by Al diffusion, which has tunable opto-electrical properties such as the bandgap and breakdown electric field. In this work, techniques such as X-ray diffraction, Rutherford backscattering spectrometry, Raman spectroscopy, atomic force microscopy and optical transmission are used to determine the optical properties, morphology and composition of Ga$_{2}$O$_{3}$ deposited and annealed thin films. To explore the formation of the $β$-(Al$_{x}$Ga$_{1-x}$)$_{2}$O$_{3}$ alloy, annealing was performed at variable temperature, in ambient air. It was determined that the bandgap can indeed be tuned between 4.85 and 5.30 eV by varying the annealing temperature, corresponding to an Al content between 0$-$68.5.