Temperature-dependent photoconductivity in two-dimensional MoS2 transistors

The photoconductivity in monolayer MoS2 back-gate transistors is studied as a function of temperature and pressure. The photocurrent increases linearly with the light intensity up to a maximum responsivity of ∼30 A/W in air. Time-resolved photocurrent measurements confirm that the photoresponse is dominated by the photogating effect. The device shows slow photoresponse with two-time constants that are attributed to the photobolometric effect and the desorption of adsorbates, respectively. An enhancement of the photocurrent is observed above room temperature and below the atmospheric pressure, that is, when the photoinduced desorption of adsorbates such as O2 and H2O molecules is facilitated. Indeed, the light-induced removal of adsorbates from the surface of MoS2 enhances the n-doping level and the current of the channel. Moreover, at lower pressures, the reverse mechanism of re-adsorption in dark conditions is suppressed and results in a persistent photocurrent. The study clarifies the photocurrent relaxation dynamics and unveils the key role of surface adsorbates in the optoelectronic properties of monolayer MoS2 and other similar 2D materials.