## 3 Results and Discussion
### Effect of Device Parameters on the Transfer Characteristics  
Figure 6a shows the impact of source doping concentration on transfer characteristics. As can be seen from this figure, the ON-state current of the DMGE-HJLTFET decreased with the increase of source doping concentration, and it was easy to find that the ON-state current of the DMGE-HJLTFET went from \(5.46\times 10^{-4}\) A/\(\mu\)m to \(3.61\times 10^{-4}\) A/\(\mu\)m when the source doping concentration increased from \(1\times 10^{17}\) cm\({}^{-3}\) to \(1\times 10^{19}\) cm\({}^{-3}\), the reason for this was that we adopted uniform N-type doping in the source, channel and drain region, and used the charge plasma concept to form a P\({}^{+}\)-I-N\({}^{+}\) structure with the appropriate workfunction for PG and CG. As a result, the hole concentration formed by polarization in the source region decreased with the increase of the N-type concentration of the lightly doped source. Since the tunnel process was the hole of source valance band to channel conduction band, the ON-state current decreased when we increased the source doping concentration. Moreover, the OFF-state current of DMGE-HJLTFET always remained at the order of \(10^{-17}\) A/\(\mu\)m. Figure 6b presents the variation of the ON-state current and the OFF-state current with the increase of source doping concentration, it was very clear that the OFF-state current was minimal when source doping concentration was \(5\times 10^{17}\) cm\({}^{-3}\), as a consequence, the ratio of Ion/Ioff comes up to maximum at this doping concentration as shown in the inserted small graph at Figure 6b. Therefore, the source doping concentration was selected as \(5\times 10^{17}\) cm\({}^{-3}\) in order to obtain maximal Ion/Ioff value. We mentioned above that the gate electrode was divided into three parts namely auxiliary gate (M1), control gate (M2) and tunnel gate (M3) with workfunctions \(\Phi_{\text{M1}}\), \(\Phi_{\text{M2}}\) and \(\Phi_{\text{M3}}\), respectively, where \(\Phi_{\text{M1}}=\Phi_{\text{M3}}<\Phi_{\text{M2}}\). Next, the effects of the three parameters on the transfer characteristics will be discussed. Figure 7a shows the impact of polar gate workfunction (\(\Phi_{\text{PG}}\)) on transfer characteristics with keeping \(\Phi_{\text{M1}}=\Phi_{\text{M3}}=4.1\) eV and keeping \(\Phi_{\text{M2}}=4.4\) eV. As can be seen clearly from Figure 7a, the ON-state current of the DMGE-HJLTFET increased and the OFF-state current of the DMGE-HJLTFET stayed at the order of \(10^{-17}\) A/\(\mu\)m with the increase of \(\Phi_{\text{PG}}\), so an appropriate choice for \(\Phi_{\text{PG}}\) was very important to achieve higher ON-state current and lower OFF-state current simultaneously. The reason for this was that \(\Phi_{\text{PG}}\) had a large influence on the polarization charge formation in the source region, the amount of polarization charge increased with the polar gate workfunction, resulting in the variation of energy band, as illustrated in Figure 7b. Figure 7b shows the variation of energy band with different \(\Phi_{\text{PG}}\), the position of conduction band and valance band in source region became higher and higher when \(\Phi_{\text{PG}}\) went up, which boosted the effective tunneling area of the channel-source interface, and the ON-state current of the DMGE-HJLTFET increased with the increase of \(\Phi_{\text{PG}}\). Therefore, Figure 7b further demonstrated the conclusion of Figure 7a. Figure 6: (**a**) Transfer characteristics of the DMGE-HJLTFET with different source doping concentration; (**b**) variation of ON-state current, OFF-state current and Ion/Ioff with different source doping concentration. Figure 8a-d indicate the impact of the control gate workfunction (\(\Phi_{\rm M2}\)) on transfer characteristics, electric field distribution and band diagram with keeping \(\Phi_{\rm M1}\) = \(\Phi_{\rm M3}\) = 4.1 eV and keeping \(\Phi_{\rm PG}\) = 5.9 eV. Selection of \(\Phi_{\rm M2}\) was critical for obtaining higher ratio of Ion/Ioff and prominent SSave, as depicted in Figure 8a.