Chemical vapor deposition growth of crystalline monolayer MoSe₂

Recently, two-dimensional layers of transition metal dichalcogenides, such as MoS₂, WS₂, MoSe₂, and WSe₂, have attracted much attention for their potential applications in electronic and optoelectronic devices. The selenide analogues of MoS₂ and WS ₂ have smaller band gaps and higher electron mobilities, making them more appropriate for practical devices. However, reports on scalable growth of high quality transition metal diselenide layers and studies of their properties have been limited. Here, we demonstrate the chemical vapor deposition (CVD) growth of uniform MoSe₂ monolayers under ambient pressure, resulting in large single crystalline islands. The photoluminescence intensity and peak position indicates a direct band gap of 1.5 eV for the MoSe₂ monolayers. A back-gated field effect transistor based on MoSe₂ monolayer shows n-type channel behavior with average mobility of 50 cm ² V^-1 s^-1, a value much higher than the 4-20 cm² V^-1 s^-1 reported for vapor phase grown MoS₂.