Origin of indirect optical transitions in few-layer MoS2, WS2, and WSe2.

摘要: It has been well-established that single layer MX2 (M = Mo, W and X S, Se) are direct gap semiconductors with band edges coinciding at the K point in contrast to their indirect multilayer counterparts. In few-layer MX2, there two valleys along Γ–K line similar energy. There is little understanding on which of forms conduction minimum (CBM) this thickness regime. We investigate valley structure by examining temperature-dependent shift exciton photoluminescence peak. Highly anisotropic thermal expansion lattice corresponding evolution result a distinct peak for transitions involving Λ (midpoint Γ-K) valleys. identify origin emission concurrently determine relative energy these