Bandgap Engineering of Ternary ε-InSe_1−xS_x and ε-InSe_1−yTe_y Single Crystals for High-Performance Electronics and Optoelectronics

Alloying offers an efficient strategy to tune the bandgap of two-dimensional (2D) layered materials, enabling them to tailor the optical and electronic attributes without compromising the structural integrity. Here the authors report the synthesis of a series of ternary InSe_1−xS_x and InSe_1−yTe_y alloys possessing ε-polymorph and single crystalline structure. Both the photoluminescence and Raman spectra of multilayer InSe_1−xS_x and InSe_1−yTe_y demonstrate that an effective modulation of bandgap and concomitant optical properties is achieved by tuning the alloy compositions, consistent with density functional theory calculations. Field-effect transistors fabricated from the multilayer alloys on SiO₂ dielectric substrates display electron field-effect mobilities of up to ≈127 cm² V⁻¹ s⁻¹. All the multilayer alloy devices show a high current on/off ratio of ≈10⁸. When fabricated into photodetectors, multilayer InSe_0.9S_0.1 and InSe_0.9Te_0.1 exhibit maximum photoresponsivities of 5.4 × 10⁵ and 7.7 × 10⁴ A W⁻¹, respectively. Moreover, the InSe_1−yTe_y alloys are able to expand the photoresponse range into 1250 nm due to the bandgap narrowing upon Te alloying. This work sheds light on rationally designing 2D layered InSe with tunable bandgaps via alloying, and demonstrates their promising applications in electronics and optoelectronics.