Intrinsic Electronic Transport Properties and Carrier Densities in PtS2 and SnSe2: Exploration of n+‐Source for 2D Tunnel FETs

Abstract Van der Waals 2D heterostructures are the ideal platform for tunnel field‐effect transistors (TFETs) because of dangling‐bond‐free heterointerfaces. However, the limited selection of n + ‐source materials restricts 2D‐TFET research. In this study, intrinsic electron transport properties and carrier density ( n ) of bulk PtS 2 are experimentally examined by Hall measurements to explore its use as an n + ‐source material suitable for TFETs in comparison with SnSe 2 . Despite the similar maximum depletion widths ( W Dm ) and apparently metallic I D – V G curves at room temperature for both bulk samples, the Hall measurements elucidate that n ≈ 3.6 × 10 17 cm −3 in PtS 2 is much smaller than ≈4.7 × 10 18 cm −3 in SnSe 2 . They also reveal that this difference comes from the depth of the donor level below the conduction band. Therefore, although band‐to‐band tunneling current is successfully observed in the n‐PtS 2 /p‐WSe 2 TFET, V G modulates the n‐PtS 2 source as well as p‐WSe 2 channel due to the nondegenerate doping of PtS 2 , resulting in a degraded subthreshold swing. The analysis of the W Dm –donor concentration ( N D ) relation elucidates that N D is not evaluated only by W Dm but is largely affected by the energy gap. The general W Dm – N D relation for different energy gaps provides a guide to select 2D materials suitable for TFETs.