Improvement in electrostatic characteristics of doped TFETs by hole layer formation

摘要

We present a distinct approach to enhance the performance of physically doped tunnel field-effect transistors (TFETs) based on creation of a layer of positive charge at the semiconductor-insulator interface in the source region. Formation of such a hole layer resolves the issue related to material solubility and improves direct-current (DC) as well as high-frequency figures of merit. To implement this approach, a typical P+-I-N+-type physically doped TFET structure is considered. Furthermore, a metal electrode with workfunction of 4.53 eV is placed over the heavily doped P+ source region with a negative supply voltage. The negative voltage at the source electrode attracts holes from the source region and creates a hole layer just below the semiconductor-insulator interface. This phenomenon makes the source-channel junction abrupt and reduces the tunneling barrier width, resulting in higher tunneling generation rate of charge carriers at the source-channel junction. Thus, the proposed device shows 100-fold increased ON-state current and a threshold voltage reduction of 300 mV. Analog/radiofrequency (RF) parameters are also greatly improved compared with the conventional device. Furthermore, optimization of the spacer length (L-SG), i.e., the gap between the source and gate electrode, and application of a negative voltage (-V-SE) at the source electrode (SE), were applied to achieve the optimum performance. Moreover, device linearity was also analyzed in a comparative manner.