Substrate Effect on Thin Layer MoSe$_{2}$ Field-Effect Transistors with Photo-Response

The discovery of graphene has opened the gates for the study of layered semiconducting materials such as the transition metal dichalcogenides (TMDs), i.e. MoS$_{2}$, MoSe$_{2}$, WS$_{2}$, WSe$_{2}$. In addition, recent works have shown that hexagonal boron nitride (hBN) can act as an ideal substrate with electrical performance enhancement for graphene and possibly for other materials as well. In this study, we examine this substrate effect for MoSe$_{2}$ by comparing various material properties on both SiO$_{2}$ and hBN. Field-effect transistors (FETs) were fabricated on both substrates using mechanically exfoliated MoSe$_{2}$. Our FETs show n-type doping and strong gate modulation yielding I$_{on}$/I$_{off}$ ratios larger than 10$^{6}$ for both substrates. Using a 4-probe measurement we found a relatively high mobility on SiO$_{2}$ that was larger than previous reports, with a slight variation between substrates. Under illumination, devices on both substrates showed ``photo-doping'' effects that in some cases were very large and persistent, thought to be the persistent photoconductivity (PPC) effect. These initial results have shown promising characteristics in MoSe$_{2}$ for applications in electronics and optoelectronics as well as shown the effects that a substrate can play in device performance and material properties.