# Improvement of Electrical Performance in Heterostructure Junctions TFET Based on Dual Material Gate
## 1 Introduction  
The mechanism of conventional metal oxide semiconductor field effect transistors (MOSFETs) is thermal electron emission, so the continuous scaling of conventional MOS device is extremely difficult in nanoscale circuit because of a great many reasons, such as, VDD scaling of MOSFETs is no longer viable, OFF-state current dramatically increases and short channel effects (SCE) is severely aggravated, and a limitation of 60 mV/Dec subthreshold swing (SS) can't be broken [1; 2]. In order to overcome these issues, different types of structure have been investigated in recent years, among them, tunnel field effect transistor (TFET) [3; 4] is a selective candidate for future low power applications due to its complementary MOS (CMOS) process compatibility and scalability, which employs band-to-band tunneling (BTBTBT) mechanism and is not influenced by the short channel effect, moreover, it can break the SS limit of 60 mV/Dec, and the leakage current is small under the OFF-state condition [5; 6; 7]. However, there are also inherent disadvantages in TFETs, the most serious problems are small ON-state current and large miller capacitance. To address these issues, a lot of novel structures of TFETs are proposed [8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19]. As a whole, most of TFETs reported in recent years adopt different doping concentration in channel and active regions to form heavily doped abrupt junction at tunneling interface, which leads to a complex fabrication processes and a high thermal budget, what's more,introduction of high-density layer at source/channel junction and Gaussian doping in drain region also find difficultly during fabrication process and it's easy to be influenced by random dopant fluctuations (RDFs) [20; 21; 22; 23]. To avoid the above issues in TFETs, the junctionless tunneling field effect transistor (JLTFET) [24; 25; 26; 27; 28; 29; 30] is proposed, which uses a uniformly high-doping concentration in source, channel, and drain region, wherein the doping concentration and type of channel are consistent with source and drain. Therefore, junctionless tunnel field-effect transistor (JLTFET) is immune to random dopant fluctuations (RDFs) [31], while complex fabrication processes and high thermal budgets in JLTFET manufacturing can be effectively avoided by the charge plasma concept. Still, low ON-state current remains the problem in junctionless TFETs due to the presence of a barrier between source and channel. As we know, TFETs use a heavily doped source and a lightly doped channel to make the distance between the source valance band and the channel conduction band as short as possible, so that band to band tunneling from source valance band to channel conduction band will occur at source/channel interface, that is to say, a heavily doped degenerate source is required in TFETs to make the working mechanism of this structure change from hot electron emission to band to band tunneling. In this paper, different doping regions in the uniform doping device are achieved via the charge plasma concept. In this paper, a dual material gate heterostructure junctionless TFET (DMMG-HJLTFET) is proposed and investigated, in which we adopt a uniform doping concentration and a corresponding P\({}^{+}\)-N\({}^{+}\)-I-N\({}^{+}\) structure can be realized via the charge plasma concept with appropriate work function for polar gate (PG) and control gate (CG). The PG is located at the source region and has a larger work function than CG for inducing a P\({}^{+}\) source while CG is located at the middle for inducing intrinsic channel. We use Si/SiGe heterostructure at the source/channel interface to improve band to band tunneling (BTBT) rate. Meanwhile, a sandwich stack structure (GaAs/Si/GaAs) at the drain region is introduced to suppress the OFF-state current and ambipolar current. Moreover, based on the gate-engineered concept, the gate electrode is divided into three parts in DMMG-HJLTFET so that the ON-state current and the OFF-state current can be further improved.