Superlinear Composition-Dependent Photocurrent in CVD-Grown Monolayer MoS_2(1–x)Se_2x Alloy Devices

Abstract

Transition metal dichalcogenides (TMDs) have emerged as a new class of two-dimensional materials that are promising for electronics and photonics. To date, optoelectronic measurements in these materials have shown the conventional behavior expected from photoconductors such as a linear or sublinear dependence of the photocurrent on light intensity. Here, we report the observation of a new regime of operation where the photocurrent depends superlinearly on light intensity. We use spatially resolved photocurrent measurements on devices consisting of CVD-grown monolayers of TMD alloys spanning MoS2 to MoSe2 to show the photoconductive nature of the photoresponse, with the photocurrent dominated by recombination and field-induced carrier separation in the channel. Time-dependent photoconductivity measurements show the presence of persistent photoconductivity for the S-rich alloys, while photocurrent measurements at fixed wavelength for devices of different alloy compositions show a systematic decrease of the responsivity with increasing Se content associated with increased linearity of the current-voltage characteristics. A model based on the presence of different types of recombination centers is presented to explain the origin of the superlinear dependence on light intensity, which emerges when the nonequilibrium occupancy of initially empty fast recombination centers becomes comparable to that of slow recombination centers.

Highly Efficient Infrared Photodetection in a Gate‐Controllable Van der Waals Heterojunction with Staggered Bandgap Alignment

“…Here, the selenium vacancies serving as traps in ReSe 2 seem to possess considerably shorter recombination and generation times for carriers than the sulfur vacancies in ReS 2 . This result agrees well with previous studies on vdW photodetectors, in which considerably shorter photoresponses were confirmed in selenide‐based devices compared to sulfide‐based devices 7, 31. Additionally, we investigated the stability of the photodetectors with respect to the repetitive photoswitching cycle (Figure S4, Supporting Information).…”

Anisotropic photocurrent response at black phosphorus–MoS2p–n heterojunctions

“…15 As shown in Figure 2b, I pc has a superlinear relationship with increasing laser power at a reverse drain bias, which is possibly due to nonequilibrium occupancy of intragap recombination centers at low laser powers. 29 Moreover, scanning photocurrent microscopy was utilized to obtain spatially-resolved photocurrent mapping of the BP-MoS 2 device to investigate the photocurrent generation process. In our experiments, a diffraction-limited 785 nm laser spot was scanned over the sample by a piezo-controlled mirror with nanometer-scale spatial resolution.…”

Two-dimensional transition metal dichalcogenide alloys: preparation, characterization and applications

“…As the composition changes, the positions of VB and CB change 41 . So far, one work on photon detection using MoS 2(1-x) Se 2x monolayer alloys 78 has revealed superlinear photocurrent generation with increasing the illumination power. At the composition of around 0.3 for MoS 2(1-x) Se 2x monolayers, ambipolar transport has been observed ( Figure 12c).…”