Two-dimensional NbOI2/TaOI2 van der Waals heterostructures with promoted carrier lifetime and mobility

The lifetime and mobility of photogenerated carriers are crucial factors influencing the stability and sensitivity of optoelectronic devices. In this work, we constructed a van der Waals heterostructure with a type-II band alignment by combining monolayer NbOI2 and TaOI2. Through first-principles calculations and nonadiabatic molecular dynamics simulations, the electronic property and the dynamics of excited electron/hole in this composite system were systematically investigated. The study reveals that these two monolayers exhibit carrier lifetimes of approximately 13 nanosecond (ns) and mobilities greater than 103 cm2 V−1 s−1. Upon constructing the heterostructure, the photogenerated electron and hole are rapidly spatially separated, resulting in a carrier lifetime approximately twice that of the monolayer structure. Additionally, tensile strain is found to enhance the hole mobility in TaOI2 to more than 3 × 103 cm2 V−1 s−1, thus further optimizing the overall transport properties of the heterostructure. This work elucidates the underlying physical mechanisms governing the carrier-related properties in the two-dimensional NbOI2/TaOI2 van der Waals heterostructure, and is beneficial for the development of high-performance optoelectronic devices.