Figure 4: EL from vertically stacked GaN–Al₂O₃–MoS₂–Al₂O₃-graphene heterostructures.

(a) A schematic illustration of the cross-sectional view of the GaN–Al₂O₃–MoS₂–Al₂O₃-graphene vertical heterostructure. (b) Current versus bias voltage characteristic of the GaN–Al₂O₃–MoS₂–Al₂O₃-graphene vertical device. (c) The optical image, EL mapping (under an injection current of 8 μA) and PL mapping ( excited by a 514-nm Ar ion laser) of a multilayer device. The MoS₂ flake is composed of two parts with different thicknesses: the 36-nm-thick lower part and the 92-nm-thick upper part. Scale bar, 3 μm. (d) EL spectra from the thick part and thin part of the MoS₂ flake under an injection current of 174 μA. The GaN emission has been subtracted based on a Gaussian fitting. (e) PL spectra from the thick part and thin part of the same MoS₂ flake. (f) EL spectra of the thick part at different injection currents. The GaN emission has been subtracted based on the Gaussian fitting. The corresponding applied voltages are 6, 13, 17 and 18 V. (g) The integrated EL intensity and EL efficiency as a function of the injection current for the thick part. (h) The EL efficiency as a function of the electric field. The discrete points are experimental results and the solid line is the theoretical calculation.