Spontaneous charge transfer doping of transition metal dichalcogenides via ruthenium(III) chloride

Abstract

Transition metal dichalcogenides (TMDs) materials possess intriguing optical and electrical properties, such as the formation of valley-polarised excitons and trions, offering potential for exciting applications in spintronics, valleytronics and optoelectronics. In this paper, we investigate the viability of doping TMDs, using ruthenium(III) chloride as an electron acceptor, via spontaneous charge transfer doping to study the properties of trions in TMDs. We characterized the trion response in TMD devices using reflection spectroscopy, observing the spectrum to verify whether charge transfer doping had occurred. The presence of trion resonance indicated that spontaneous charge transfer had indeed taken place. We then use electrical gating to determine the doping density in the TMDs due to the spontaneous charge transfer. Our findings revealed that hole doping in TMDs led to the formation of trions under photoexcitation, as evident from the trion response detected in the reflection contrast spectroscopy performed on molybdenum diselenide (MoSe2). However, no trion response was detected in tungsten diselenide (WSe2), contrary to theoretical predictions. This discrepancy could be attributed to inconsistencies in the layers of hBN spacer used, defects or contaminants introduced during device fabrication, or effects of lattice alignment. This study contributes to understanding doping mechanisms and trion behavior in TMDs. Further investigation into the factors influencing trion formation in different TMD materials could lead to improved control and utilization of their unique properties for future electronic and optoelectronic applications.