Enhancement of photocurrent on few-layered $p$-WSe$_{\mathrm{2}}$ FET by multi-terminal measurement

Recently, two dimensional materials particularly transition metal dichalcogenides (TMDs) have been extensively studied because of their strong light-matter interactions and extraordinary electrical and optical properties in field-effect transistors (FETs). We investigated the photocurrent response on few-layered $p$-WSe$_{\mathrm{2}}$ and MoSe$_{\mathrm{2}}$ FETs in a multi-terminal configuration using a 532 nm laser. Photogenerated current $I_{\mathrm{ph}}$ ($=I_{\mathrm{light}}$-$I_{\mathrm{dark}})$ was measured as a function of optical power incident on the sample with varying source-drain bias, $V_{\mathrm{ds}}$, and back gate voltage, $V_{\mathrm{bg}}$. We observed a large enhancement of photocurrent in a four-terminal configuration compared to a two-terminal configuration. The measured two-terminal photoresponsivity ($R)$ and external quantum efficiency (\textit{EQE}) from our \textasciitilde 10 layers $p$-WSe$_{\mathrm{2}}$ at applied $V_{\mathrm{ds}}=$1V and $V_{\mathrm{bg}}=$10V were \textasciitilde 18A/W and \textasciitilde 4000{\%}, respectively. The $R$ and \textit{EQE} values increased to \textasciitilde 85 A/W and \textasciitilde 20000{\%} respectively using a four-terminal configuration. Thus by using a multi-terminal configuration, one can observe an enhanced photocurrent response on few-layered TMDs for potential applications in photo-detection and optoelectronic circuits.