Photocurrent generation mechanism in GeS nanosheet phototransistor

Photoresponsivity and photocurrent according to gate voltages and various light power of 532nm laser in Germanium sulfide (GeS) phototransistor, which is noticed for its high photoresponsivity, is observed. The experimental result of photocurrent by light power was fitted with power function, and the exponent was used as a key parameter for speculation of photocurrent generation mechanisms. When the transistor is on, the photogating effect was considered as a main mechanism of photocurrent generation. There are two causes for photogating effect; One is a gating effect from captured carriers on trap state, and the other is from keeping charge neutrality resulting from the difference of electron and hole mobilities. And when the transistor is off, even though there is also a photogating effect, photocurrent from photoconduction effect is a dominant mechanism.