Figure 2.
Comparison of the photocurrent measured in vacuum for treated and untreated samples. (a) Photocurrent increase calculated as a maximum photocurrent obtained after the same amount of time for each gate voltage and normalized by the maximum photocurrent of the pristine sample on WS2. The results show that the devices treated with a single plasma process respond stronger to illumination, and their response is the highest for low gate voltages. (b) The photocurrent signal of the samples before (pristine—blue lines) and after plasma treatment (first plasma—beige lines, second plasma—red lines) measured in vacuum. The graphs show the gate voltage dependence of the photocurrent for −20, 0, 20, and 60 V. Large enhancement of the photocurrent was observed after the first plasma treatment. The second plasma treatment also increased the signal compared to the pristine sample, but the effect was not as pronounced as for the first treatment. Although the point at −40 V results from a random unexpected event, the trend is visible.