An MoS₂-Based Piezoelectric FET: A Computational Study of Material Properties and Device Design

摘要

In this paper, we show that MoS2 multilayers have mechanical and electrical properties that qualify them as promising channel materials for an n-type piezoelectric FET (PZ-FET). We present extensive density functional theory calculations to investigate the effects of a compressive, out-of-plane stress on MoS2 monolayers and multilayers and extract the corresponding stiffness, as well as the sensitivity to stress of the conduction and valence band edge, and of the effective masses. Then, we use these material properties and a top-of-the-barrier ballistic transistor model to evaluate numerically the I-DS versus V-G characteristics of n-type PZ-FETs with an MoS2 channel material. Our results indicate that MoS2 multilayers are the best material option for n-type PZ-FETs, which can reach a subthreshold swing of about 40 mV/decade for a 5-nm-thick piezoelectric layer. This is because the weak interlayer van der Waals bonding makes the conduction band edge in MoS2 multilayers very sensitive to vertical compressive stress. The simulated MoS2 PZ-FETs exhibit large I-ON/I-OFF ratios at low voltage and have better subthreshold steepness compared with the counterpart device employing a 3-D semiconductor.