Semiconducting α′-boron sheet with high mobility and low all-boron contact resistance: a first-principles study

Two-dimensional field effect transistors (2D FETs) with high mobility semiconducting channels and low contact resistance between the semiconducting channel and the metallic electrodes are highly sought components of future electronics. Recently, 2D boron sheets (borophene) offer a great platform for realizing ideal 2D FETs but stable semiconducting phases still remain much unexplored. Herein, based on first-principles calculations and tight-binding model, we first clarify that alpha '-boron is the most stable semiconductor phase of boron sheets, while reveal the mechanism of metal-to-semiconductor transition from alpha- to alpha '-boron. Then we demonstrate that the carrier mobility in alpha '- and metastable beta(S)(3)-boron should be very high, due to small effective masses of electrons and holes, as a good candidate material for 2D FETs. Considering further the lateral contacts between semiconducting alpha ' and metallic borophene, we find that the alpha '- and beta(S)(3)-boron sheet can form Ohmic contacts with selected metallic boron sheets, without Schottky barrier. The high energetic stability and excellent mobility properties of alpha '-boron sheet together with its good contact match to metallic borophene electrodes are promising for fully boron-based FETs in the real 2D atomically thin limit.

Automated summary

This study reveals that alpha '-boron is the most stable semiconductor phase of boron sheets with high carrier mobility, making it a promising candidate material for 2D FETs. The research also shows that alpha '- and beta(S)(3)-boron sheets can form Ohmic contacts with selected metallic boron sheets, without Schottky barrier, indicating potential for fully boron-based FETs.