## 3 Results  
### Basic Characteristics  
p-SnO was used as the CBL while all other factors remain unchanged. The output curve of the device is shown in Figure 2a, when the gate voltage was 0-6 v (the step size was 1 V) and the saturated leakage current density of the device was 0.029 kA/cm\({}^{2}\) at 6 V. Additionally, the V\({}_{\text{th}}\) of the device was positive, which was 2.8 V. This shows that, after replacing the CBL material with p-SnO, the threshold voltage of the device is less affected and the device can still be in the enhanced mode. Here, the p-type doping concentration of CBL is equivalent to the original one.  
As seen in Figure 2b, the breakdown voltage of the device reached 379 V. Compared with the original device, the breakdown voltage of the heterojunction device increased by  
Figure 1: (**a**) Semi-symmetric device structure of Ga\({}_{2}\)O\({}_{3}\) MOSFET with CBL used in the simulation, (**b**) transfer and output curves in the model, and (**c**) breakdown voltage curve in the model.  
Figure 2: (**a**) Transfer and output curves of Ga\({}_{2}\)O\({}_{3}\) MOSFET with the p-SnO CBL and (**b**) breakdown voltage curve of Ga\({}_{2}\)O\({}_{3}\) MOSFET with the p-SnO CBL.  
44% when other parameters (such as the doping concentration and thickness of each part) remained unchanged, except for the change in material.  
To better analyze the change in threshold voltage after replacing the CBL material, the transverse and longitudinal conduction band diagrams of the device were extracted from the simulation results. The transverse extraction range is shown by the red solid line in Figure 1a (in the channel near the bottom of Al\({}_{2}\)O\({}_{3}\)), and the longitudinal extraction range is shown by the red dotted line in Figure 1a. The extraction results are shown in Figure 3a,b. It can be seen from Figure 3a that, when SnO is used as the CBL material, the average conduction band height in n-Ga\({}_{2}\)O\({}_{3}\) channel layer is lower than that of Ga\({}_{2}\)O\({}_{3}\) as the CBL. Through ouv study and analysis of the electron affinity and band gap width of SnO and Ga\({}_{2}\)O\({}_{3}\), it was found that, because the electron affinity and band gap width of SnO are less than Ga\({}_{2}\)O\({}_{3}\), a II-type heterojunction formed at the interface between the p-SnO CBL and the n-Ga\({}_{2}\)O\({}_{3}\) channel layer. When the heterojunction formed, a \"spike\" and \"notch\" formed at the interface of SnO and Ga\({}_{2}\)O\({}_{3}\) materials with different band gap widths, resulting in a sudden change in the energy band at the interface. It can be seen in the heterojunction at the circle in Figure 3a. After the heterojunction formed, the conduction band energy in the channel of SnO heterojunction MOSFET became lower than that in Ga\({}_{2}\)O\({}_{3}\) MOSFET due to the sudden change in energy band at the interface, and finally, the threshold voltage of SnO heterojunction MOSFET became slightly lower than that of Ga\({}_{2}\)O\({}_{3}\) MOSFET. This can also be seen from Figure 3b, which shows the conduction band diagram of the channel at 0 V gate voltage and the threshold voltage. The channel barrier of SnO heterojunction MOSFET in the cut-off state was lower than that of the original device, so when the gate voltage increased, the gate voltage required to reach the channel conduction condition was relatively reduced.  
Figure 3: (**a**) The conduction band diagram at 0 V gate voltage in the vertical direction of the oxide layer, channel, and CBL, and a heterojunction formed at the interface between channel and SnO CBL. (**b**) The conduction band diagram at 0 V gate voltage and threshold voltage with Ga\({}_{2}\)O\({}_{3}\) CBL or p-SnO CBL. (**c**) Comparison of the depletion layers of Ga\({}_{2}\)O\({}_{3}\) CBL and p-SnO CBL at breakdown voltage.