Large Area Growth and Electrical Properties of p-Type WSe2 Atomic Layers

Transition metal dichacogenides represent a unique class of two-dimensional layered materials that can be exfoliated into single or few atomic layers. Tungsten diselenide (WSe2) is one typical example with p-type semiconductor characteristics. Bulk WSe2 has an indirect band gap (similar to 1.2 eV), which transits into a direct band gap (similar to 1.65 eV) in monolayers. Monolayer WSe2, therefore, is of considerable interest as a new electronic material for functional electronics and optoelectronics. However, the controllable synthesis of large-area WSe2 atomic layers remains a challenge. The studies on WSe2 are largely limited by relatively small lateral size of exfoliated flakes and poor yield, which has significantly restricted the large-scale applications of the WSe2 atomic layers. Here, we report a systematic study of chemical vapor deposition approach for large area growth of atomically thin WSe2 film with the lateral dimensions up to similar to 1 cm(2). Microphotoluminescence mapping indicates distinct layer dependent efficiency. The monolayer area exhibits much stronger light emission than bilayer or multilayers, consistent with the expected transition to direct band gap in the monolayer limit. The transmission electron microscopy studies demonstrate excellent crystalline quality of the atomically thin WSe2. Electrical transport studies further show that the p-type WSe2 field-effect transistors exhibit excellent electronic characteristics with effective hole carrier mobility up to 100 cm(2) V-1 s(-1) for monolayer and up to 350 cm(2) V-1 s(-1) for few-layer materials at room temperature, comparable or well above that of previously reported mobility values for the synthetic WSe2 and comparable to the best exfoliated materials.