# 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 6a shows the impact of channel doping concentration on transfer characteristics. As shown in this figure, the ON-state current of DMMG-HJLTFET stays at the order of \(10^{-6}\) A/\(\upmu\)m at Vds = 2 V when channel doping concentration increases from \(1\times 10^{18}\) cm\({}^{-3}\) to \(1\times 10^{19}\) cm\({}^{-3}\). Moreover, the ON-state current of DMMG-HJLTFET increases while the OFF-state current of DMMG-HJLTFET always remains at the order of \(10^{-18}\) A/\(\upmu\)m, as a result, the ratio of Ion/Ioff keeps at level of \(10^{13}\) with increase of channel doping concentration as shown in inserted small figure at Figure 6b.Therefore, channel doping concentration is selected as \(1\times 10^{19}\) cm\({}^{-3}\) in order to obtain a maximal ON-state current. Figure 7a shows the impact of polar gate work function(\(\Phi_{\text{PG}}\)) on transfer characteristics with keeping \(\Phi_{\text{M1}}=\Phi_{\text{M3}}=4.1\) eV and keeping \(\Phi_{\text{M2}}=4.6\) eV. As can be seen clearly from the Figure 7a appropriate selection of polar gate work function is required to achieve higher ON-state current, the  
Figure 5: (a) Simulated output characteristics and (b) Simulated output transconductance of JLTFET, HJLTFET and DMMG-HJLTFET at Vgs = 1 V.  
Figure 6: (a) Simulated log scale and linear scale transfer characteristics of DMMG-HJLTFET with different channel doping concentration; (b) ON-state current, OFF-state current and Ion/Ioff at different channel doping concentration. ON-state current of DMMG-HJLTFET increases with the increase of polar gate work function while the OFF-state current of DMMG-HJLTFET stays at the order of 10\({}^{-18}\) A/\(\upmu\)m, the reason for this is that polar gate work function has a large influence on the polarization charge formation in source region, as a result, the ON-state current of DMMG-HJLTFET increases with the increase of polar gate work function. Figure 7b shows the variation of energy band with different polar gate work function, the position of conduction band and valance band in the source region increases as the polar gate work function goes up, as illustrated in Figure 7b, which leads to the enhancement of the effective tunneling area at channel/source interface, and further explains the conclusion of Figure 7a. We mentioned above that the gate electrode is divided into three parts namely auxiliary gate (M1), control gate (M2), and tunnel gate (M3) with work functions \(\Phi_{\text{M1}}\), \(\Phi_{\text{M2}}\) and \(\Phi_{\text{M3}}\), respectively, where \(\Phi_{\text{M1}}=\Phi_{\text{M3}}<\Phi_{\text{M2}}\). Figure 8a-d shows the impact of control gate work function(\(\Phi_{\text{M2}}\)) on transfer characteristics, electric field and band diagram with keeping \(\Phi_{\text{M1}}=\Phi_{\text{M3}}=4.1\) eV and \(\Phi_{\text{PG}}=5.9\) eV. As depicted in Figure 8a, the selection of control gate work function is very important to obtain higher ratio of Ion/Ioff, the ON-state current and the OFF-state current of DMMG-HJLTFET decrease with the increase of control gate work function. The variation of electric field is shown in Figure 8b, it is very clear that value of electric field in channel region increases with the decrease of control gate work function, which makes the surface potential under control gate increase and the energy band bend severely in this region, as shown in Figure 8c,d shows the energy band diagram in OFF-state, where it is observed that tunneling barrier height increases with the increase of control gate work function in the channel region. As a result, the overall performance of the DMMG-HJLTFET is significantly affected by the control gate work function, and the optimal value of the control gate work function is chosen as 4.6 eV.