Ultrahigh electron mobility induced by strain engineering in direct semiconductor monolayer Bi2TeSe2.

The successful commercial applications as thermoelectric devices and, due to their exotic electronic properties, as topological insulators of bismuth telluride (Bi2Te3) and bismuth selenide (Bi2Se3) have stimulated research interest on Bi2Se3/Bi2Te3-based chemical compounds. Based on the first-principles calculations, we investigate the electronic, optical, vibrational and transport properties of new monolayer Bi2TeSe2 obtained by transmuting one Se atom into its neighboring Te atom in the same group from Bi2Se3. We find that the monolayer Bi2TeSe2 maintains a stable hexagonal structure up to 700 K. Monolayer Bi2TeSe2 possesses a direct bandgap of 0.29 eV due to the strong spin-orbit coupling effects, and it remains a direct semiconductor for strains in a moderate range. The optical absorption covers a wide range from the green region to the ultraviolet region, which may lead to applications in optoelectronic devices like saturable absorbers. An extremely high electron mobility of 20 678 cm2 V-1 s-1 along the zigzag direction can be achieved by strain engineering with -6% compressive strain, which is nearly ten times larger than the intrinsic mobility. These indicate that monolayer Bi2TeSe2 is a promising candidate for future high-speed (opto)electronic devices.