Two-dimensional phase-engineered 1T′– and 2H–MoTe2-based near-infrared photodetectors with ultra-fast response

Abstract

Two-dimensional (2D) crystal growth allows wafer-scale van der Waals epitaxial integration of transition metal dichalcogenides (TMDs) semiconductors onto a Si substrate. 2D MoTe2 and WTe2 among TMDs are considered as possible candidates for high-performance near-infrared photodetector, due to its relatively low band gap energy (0.8–1.1 eV). Herein, 2D MoTe2 was selected for the development of high-performance visible–near-infrared (0.5–1.1 μm) photodetectors. Phase-engineered MoTe2 films of four atomic layers were grown by metal–organic chemical vapor deposition on an 8-inch SiO2/Si substrate. 1T′ and 2H phase MoTe2 films were verified by Raman spectra and scanning transmission electron microscopy. A fabricated 2H-MoTe2-based field-effect transistor (FET) was found to have p-type electrical transport with a mobility of 22.8 cm2/V·s—the fastest among all currently reported 2H phase films synthesized by bottom-up methods—and an on/off ratio of 1.3 × 104. Moreover, a photodetector based on the 1T′ phase (semimetal) film exhibited excellent performance, including photoresponsivity as high as 62–109 mA/W at 500–1000 nm—a 900% enhancement over that with a 2H phase (p-type semiconductor) film—and extremely fast response (a rise time of 0.82 μs and a fall time of 7.29 μs at a wavelength of 1000 nm).