Influence of Ultralow Temperature on Quasi-2-D $\beta $ -Ga $_{\text{2}}$ O $_{\text{3}}$ Field-Effect Transistors

Understanding the low-temperature stability and degradation mechanism of Ga $_{\text{2}}$ O $_{\text{3}}$ -based transistors is important for their harsh-environment applications. This study examines the ultralow-temperature-dependent (i.e., 50–150 K) behavior of the $\beta $ -Ga $_{\text{2}}$ O $_{\text{3}}$ nanosheet field-effect transistor (FET). The $\beta $ -Ga $_{\text{2}}$ O $_{\text{3}}$ nanosheet with a thickness of 170 nm was peeled off from the single crystal and held on the substrate via van der Waals (vdWs) integration. At room temperature (i.e., 300 K), the vdW-integrated $\beta $ -Ga $_{\text{2}}$ O $_{\text{3}}$ transistor exhibits well-behaved performance, such as low subthreshold slope ( SS , 120.1 mV/dec), large $I_{\text{ON}}$ / $I_{\text{OFF}}$ ratio ( $\sim$ 1.28 $\times $ 10 $^{\text{8}})$ , and small OFF-state current ( $<$ 100 fA). At temperatures ranging from 150 down to 50 K, the electrical parameters were measured and analyzed. The conductive channel still maintains high quality without evident interfacial defects even at 50 K, whereas the mobility decreases considerably. Greater degradation occurs in the contacts between the electrodes and $\beta $ -Ga $_{\text{2}}$ O $_{\text{3}}$ compared to the channel layer. The degradation in the device performance of the $\beta $ -Ga $_{\text{2}}$ O $_{\text{3}}$ nanosheet transistor is associated with severely degraded electrical contact at extremely low temperatures. Nevertheless, optimized Ohmic electrodes (i.e., higher carrier density of $\sim$ 10 $^{\text{18}}$ cm $^{-\text{3}}$ and annealed at 420 $^{\circ}$ C) can effectively relieve the low-temperature effects on the contacts. Different from the high-temperature operation, the contact deterioration induced by low-temperature is reversible. The contact performance can recover to the original state after low-temperature experiments. The obtained results have significance in developing robust Ga $_{\text{2}}$ O $_{\text{3}}$ -based electronic devices and circuits for extreme-environment applications.