Modulation doping of transition metal dichalcogenide/oxide heterostructures

Abstract

Control of carrier type and carrier density provides a way to tune the physical properties of two-dimensional (2D) semiconductors. Modulation doping of heterostructures can effectively inject carriers into or extract carriers from the 2D semiconductors, and eliminate the adverse effect from the ionized dopants. Here we first investigate the layer-dependent negative trion PL of 2D MoS₂, and further construct heterostructures with transition metal dichalcogenides (TMDs) and transition metal oxides (TMOs). By choosing the oxide with different charge neutrality levels (CNLs), we demonstrate effective electron injection into MoS₂ by TiO₂ doping, and electron extraction from MoS₂ by MoO₃ doping. Photoluminescence (PL) spectra and electrical characterization show that thicker MoS₂ flakes are more easily n-doped by TiO₂, while thinner MoS₂ flakes are more easily p-doped by MoO₃. Our experimental results are in good agreement with theoretical calculations. The modulation doping with TMO is compatible with conventional Si processing and highly air-stable. This method can also be extended for the controllable doping of other 2D materials.