Persistent photoconductivity in single-layer MoS2: The role of impurities and doping

Persistent photoconductivity is often observed in single-layer MoS2 devices and has a bearing on device applications because it alters device conductivity and characteristics. It originates in the trapping and detrapping of photo-generated charges and may be useful in devices serving neuromorphic computing. The dependence of persistent photoconductivity on the nature of the substrate, traps, and working parameters including doping, gate voltage, and temperature is the subject of debate. Here, we measure transport characteristics in single-layer MoS2 on SiO2/Si substrates as a function of temperature and gating, following illumination. Analysis of the multiexponential decay of the photocurrent shows that extrinsic impurities at the device–substrate interface act as traps when ionized. For shallow traps probably formed from Na impurities, we deduce an activation energy of about 80 meV, while deep traps are estimated to have activation energies of a few hundred meV. We give a coherent and self-consistent explanation of the microscopic mechanisms governing the phenomenon.