Electrical and photo-electrical properties of MoS(2) nanosheets with and without an Al(2)O(3) capping layer under various environmental conditions

The electrical and photo-electrical properties of exfoliated MoS(2) were investigated in the dark and in the presence of deep ultraviolet (DUV) light under various environmental conditions (vacuum, N(2) gas, air, and O(2) gas). We examined the effects of environmental gases on MoS(2) flakes in the dark and after DUV illumination through Raman spectroscopy and found that DUV light induced red and blue shifts of peaks (E(1) (2 g) and A(1 g)) position in the presence of N(2) and O(2) gases, respectively. In the dark, the threshold voltage in the transfer characteristics of few-layer (FL) MoS(2) field-effect transistors (FETs) remained almost the same in vacuum and N(2) gas but shifted toward positive gate voltages in air or O(2) gas because of the adsorption of oxygen atoms/molecules on the MoS(2) surface. We analyzed light detection parameters such as responsivity, detectivity, external quantum efficiency, linear dynamic range, and relaxation time to characterize the photoresponse behavior of FL-MoS(2) FETs under various environmental conditions. All parameters were improved in their performances in N(2) gas, but deteriorated in O(2) gas environment. The photocurrent decayed with a large time constant in N(2) gas, but decayed with a small time constant in O(2) gas. We also investigated the characteristics of the devices after passivating by Al(2)O(3) film on the MoS(2) surface. The devices became almost hysteresis-free in the transfer characteristics and stable with improved mobility. Given its outstanding performance under DUV light, the passivated device may be potentially used for applications in MoS(2)-based integrated optoelectronic circuits, light sensing devices, and solar cells.