Opto-electronic responses of large area WSe2 layers synthesized by chemical conversion of WO3 thin films

Abstract

Atomically thin tungsten diselenide (WSe₂) has drawn much interest due to its remarkable optical properties and potential applications in next-generation optoelectronics and energy harvesting devices. High-quality, wafer-scale synthesis of such two-dimensional (2D) semiconductors is necessary for their practical applications. Chemical vapor deposition (CVD) is a promising method for synthesizing large-area thin films of 2D materials where the constituent elements are of widely different vapor pressure. Herein, we demonstrate large-area synthesis of the 2H phase of WSe₂ with a precise control over the 2D film thickness. The first step of this process is the deposition of tungsten trioxide (WO₃) films of a well-defined thickness by thermal evaporation over large areas. The subsequent selenization of these films in an atmospheric pressure CVD reactor, yields high-quality uniform films of WSe₂. The quality of these films is ascertained by measuring their characteristic Raman active vibrational modes and layer thickness dependent optical absorption and photoluminescence. The photoconductivity (PC) of these films has been measured with 405, 532 and 915 nm laser excitation. We note an increase in the PC of the films with their thickness. The best photoresponsivity and detectivity obtained are 11.3 mA/W and 1.42 × 10⁸ Jones respectively. These results are promising to create photo-transistor arrays over large areas using such WO₃ processed films.