Time Dependence of Photocurrent in Chemical Vapor Deposition MoS₂ Monolayer—Intrinsic Properties and Environmental Effects

Abstract

We report a model for the description of a room temperature photocurrent temporal response in devices made of a chemical vapor deposition grown molybdenum disulfide monolayer. The proposed model distinguishes three components of a photoresponse that may be attributed to photoconductance and a photogating effect, where photogating involves environmental and intrinsic material contribution. We showed that each time constant obtained from the model differed by an order of magnitude and remained unaffected by changes of the environment, whereas the amplitudes behaved according to the attributed effects. Notably, the rising photocurrent signal was a useful source of information regarding the persistent photoconductivity effect. Finally, we demonstrated the versatility of our model by applying it to some previous reports on time-resolved photocurrent. Our results help to determine the optoelectronic properties of MoS 2 monolayers and future photosensitive devices operating at ambient room temperature.

Gate‐Controlled Field Emission Current from MoS2 Nanosheets

“…Their presence on the MoS 2 surface affects the channel current because they decrease the carrier (electron) mobility and density. [ 62,68–71 ]…”

“…Their presence on the MoS 2 surface affects the channel current because they decrease the carrier (electron) mobility and density. [62,[68][69][70][71] The intrinsic and gate-controllable n-type doping, the low electron affinity (χ = 4.2 eV), [72] and the nanosheets' sharp edges make 2D MoS 2 appealing for FE applications. [73,74] To perform FE measurements, we used a tip as the anode and contact C2 as the cathode (Figure 3a).…”

“…[55][56][57] The degradation of conductance with increasing pressure, in some cases resulting in the dramatic transformation from n-type to p-type conduction, has been mainly attributed to adsorbed oxygen and water that act as interface traps and scattering centers with a density in the order of 10 12 cm −2 eV −1 and reduce the n-type doping of the channel. [56][57][58][59][60] The intrinsic and gate-controllable n-type doping, the low electron affinity (4.2 eV), [61] and the nanosheets' sharp edges make 2D MoS2 appealing for FE applications. [62,63] To perform field emission measurements, we used a tip as the anode and contact C2 as the cathode (Figure 3(a)).…”

Local photocurrents in two dimensional materials measured by conductive atomic force microscopy

“…This is usually observed in I/V measurements done at ambient conditions, mainly due to various adsorbed molecules which act as trapping centers [59,60]. At the same time, the photogating effect can also contribute to the observed hysteresis [55][56][57][58]60]. Although the hysteresis and its origin are outside the scope of this manuscript, their influence on measured dark and photocurrents can not be neglected.…”

“…2(b), where the current was fitted by an exponential function 𝐼 2 + (𝐼 1 − 𝐼 2 )exp(−(𝑡 −𝑡 0 )/𝜏), where 𝑡 0 corresponds to the moment (around 34 s) when the laser was switched off, whereas 𝜏 is a time constant. 𝜏 was determined by the fitting and it was in the range 150 − 200 ms. Usually, the fall time is explained as a result of the photogating effect [55][56][57][58]. Namely, charge carriers in 2D materials are trapped by molecules adsorbed on or beneath 2D layers.…”