β-Ga2O3, an emerging wide bandgap semiconductor material, holds significant potential for various applications. However, challenges persist in improving the crystal quality and achieving controllable doping of β-Ga2O3. In particular, the relationship between these factors and the mechanisms behind them are not fully understood. Molecular beam epitaxy (MBE) is viewed as one of the most sophisticated techniques for growing high-quality crystalline films. It also provides a platform for studying the effects of doping and defects in heteroepitaxial β-Ga2O3. In our study, we tackled the issue of Si source passivation during the MBE growth of Si-doped β-Ga2O3. We did this by using an electron beam vaporize module, a departure from the traditional Si effusion cell. Our research extensively explores the correlation between Si doping concentration and film properties. These properties include microstructure, morphology, defects, carrier conductivity, and mobility. The results from these investigations are mutually supportive and indicate that a high density of defects in heteroepitaxial β-Ga2O3 is the primary reason for the challenges in controllable doping and conductivity. These insights are valuable for the ongoing development and enhancement of β-Ga2O3-based device techniques.

The effect of high temperature annealing under O2 and N2 atmospheres on the electrical properties and defect formation on Sn doped n-type β-Ga2O3 bulk samples was investigated by electron paramagnetic resonance (EPR) spectroscopy. EPR, being a volume sensitive technique, probes the entire sample volume. Our results show an electrical compensation being correlated with the formation of a negatively charged Ga vacancy defect VGa2−. This VGa center is different from the one observed after particle irradiation. The associated shift of the Fermi level reveals the presence of Fe3+, Cu2+, and Cr3+, which are residuals related to the growth conditions. The 1100 °C N2 annealed sample is fully compensated, and the neutral donor resonance is no longer observed. Our results directly confirm the thermal instability of Ga and Sn in n-type conducting samples. No oxygen vacancy related centers were detected. We discuss the various Ga vacancy centers reported previously.

We report the realization of high-performance long-wavelength infrared detectors with n-on-p polarity based on InAs/GaSb type-II superlattices grown by metal-organic chemical vapor deposition (MOCVD) on InAs substrate. In a normal n-on-p device with PNn heterostructure, Zinc (Zn) is found to diffuse into the critical n-type barrier layer and lead to a high leakage current. By inserting a 200 nm undoped spacer layer after the p-type region is grown, Zn diffusion is completely confined in the spacer layer. The n-on-p device with the spacer shows performances equivalent to those of a p-on-n counterpart, with a dark current density of 6×10-4 A/cm2 at -0.1 V at 80 K, a peak quantum efficiency of ∼24%, and 100% cut-off wavelength of ∼12 μm.