# Improvement of Electrical Performance in Heterostructure Junctions TFET Based on Dual Material Gate
## 3 Results and Discussion
### Effect of Device Sizes on the Transfer Characteristics
Figure 8: _Cont._  
Figure 7: (a) Simulated log scale and linear scale transfer characteristics of DMMG-HJLTFET with different polar gate work function (\(\Phi_{\text{PG}}\)); (b) the variation of energy band with different polar gate work function (\(\Phi_{\text{PG}}\)). Figure 9a-d shows the impact of auxiliary gate work function (\(\Phi_{\text{M1}}\)) and tunnel gate work function (\(\Phi_{\text{M3}}\)) on transfer characteristics, surface potential, electric field and band diagram with keeping \(\Phi_{\text{M2}}\) = 4.6 eV and \(\Phi_{\text{PG}}\) = 5.9 eV. It can be found through the observation of Figure 9a that the ON-state current of DMMG-HJLTFET decreases and the OFF-state current of DMMG-HJLTFET increases with the increase of auxiliary gate work function, i.e., appropriate selection for auxiliary gate work function should be small in terms of ON-state current. At the same time, the surface potential and electric field are also markedly influenced by auxiliary gate work function, as shown in Figure 9b,c, it can be notified that the DMMG-HJLTFET exhibits higher surface potential and electric field at the position of M1 and M3 with small auxiliary gate work function, which helps M1 suppress the ambipolar leakage current and reduce hot carrier effects (HCEs) by diminishing lateral electric field at drain/channel interface together with SiO2 near the drain and helps M3 improve the ON-state current by increasing the tunneling probability at source/ channel interface, as a result, a higher tunneling rate at the source/channel interface and higher barrier height at drain/channel interface are introduced simultaneously, as shown in Figure 9d. So, auxiliary gate work function should be small in terms of ON-state current and OFF-state current, and the auxiliary gate work function should be large in terms of barrier height at drain/channel interface. All things considered, the optimal value of auxiliary gate work function is chosen as 4.1 eV. Figure 8: (**a**) Simulated log scale and linear scale transfer characteristics of DMMG-HJLTFET with different control gate work function (\(\Phi_{\text{M2}}\)); (**b**) the distribution of electric field at the surface with different control gate work function (\(\Phi_{\text{M2}}\)); (**c**) the variation of ON-state energy band with different control gate work function (\(\Phi_{\text{M2}}\)); (**d**) the variation of OFF-state energy band with different control gate work function(\(\Phi_{\text{M2}}\)). Figure 9: _Cont._  
Figure 10a shows the impact of the thickness of silicon (T\({}_{\text{S}}\)) in a sandwich stack structure (GaAs/Si/GaAs) on transfer characteristics. It can be seen clearly from the Figure 10a, the ON-state current of DMMG-HJLTFET is minimal when T\({}_{\text{S}}\) = 5 nm, this is because DMMG-HJLTFET is converted into HJLTFET when T\({}_{\text{S}}\) = 5 nm, the current level of this condition is consistent with HJLTFET mentioned previous section. Meanwhile, the ON-state current of DMMG-HJLTFET increases visibly when T\({}_{\text{S}}\) varies from 4 nm to 1 nm, the reason is that thickness of GaAs in sandwich stack structure (GaAs/Si/GaAs) increases from 0.5 nm to 3 nm when T\({}_{\text{S}}\) decreases from 4 nm to 1 nm, which improves the electric field distribution at the surface of DMMG-HJLTFET, as shown in Figure 10b. It is not difficult to find that electric field of channel region increases and electric field of drain region decreases when T\({}_{\text{S}}\) increases from 1 nm to 4 nm, which enhances the lateral electric field at drain/channel interface and improves the tunneling probability at source/channel interface. The reason for the improvement of the ON-state current and electric field distribution in Figure 10a,b is that GaAs is a direct bandgap semiconductor while Si is an indirect bandgap semiconductor, the bandgap width of GaAs is larger than that of Si, and the electron mobility of GaAs is much higher than that of Si.