Nanoscale cathodoluminescence probing of neutral and charged excitons with tunable photo-capacitance in RIE-thinned WSe2

This study presents the thickness-dependent excitonic physics of WSe2 achieved through a precisely controlled reactive ion etching (RIE) process, enabling deterministic thinning from 40 layers down to ten layers on SiO2/Si substrate. This deterministic thickness engineering facilitates a systematic exploration of layer-dependent electronic and optical properties. Detailed Comprehensive characterization confirms the structural integrity, surface uniformity, and stable work-function profile of the etched films. Cathodoluminescence (CL) spectroscopy reveals pronounced band-edge emission features, including neutral and charged excitons, in the ultra-thin regions of the film. Possible transitions from the calculated band structures for varying thin layered WSe2 are estimated by performing density functional theory with correlation of emissions via CL spectroscopy. To evaluate device characteristics, a metal–oxide–semiconductor structure fabricated on the RIE-thinned WSe2 exhibits strong thickness-dependent photo-capacitance, where thicker sections show enhanced photo-response and improved electron inversion even at high frequencies. Low-temperature C–V measurements further highlight robust photoinduced inversion behavior with wide range of probe frequency ∼ 10 kHz to 10 MHz. Overall, this work establishes RIE as a reliable approach for achieving thickness-tailored, high-quality WSe2 suitable for device integration. The combined excitonic physics and tunable photo-capacitance underline its potential for next-generation optoelectronic platforms, including quantum emitters, spin-selective excitonic devices, and quantum photonic architectures.