Observation of Asymmetric Nanoscale Optical Cavity in GaAs Nanosheets

GaAs nanosheets with no twin defects, stacking faults, or dislocations are excellent candidates for optoelectrical applications. Their outstanding optical behavior and twin free structure make them superior to traditionally studied GaAs nanowires. While many research groups have reported optically resonant cavities (i.e., Fabry−Perot) in 1D nanowires, here, we report an optical cavity resonance in GaAs nanosheets consisting of complex 2D asymmetric modes, which are fundamentally different from one-dimensional cavities. These resonant modes are detected experimentally using photoluminescence (PL) spectroscopy, which exhibits a series of peaks or “fringes” superimposed on the bulk GaAs photoluminescence spectrum. Finite-difference time-domain (FDTD) simulations confirm these experimental findings and provide a detailed picture of these complex resonant modes. Here, the complex modes of this cavity are formed by the three nonparallel edges of the GaAs nanosheets. Due to the asymmetrical nature of the nanosheets, the mode profiles are largely unintuitive. We also find that by changing the substrate from Si/SiO2 to Au, we enhance the resonance fringes as well as the overall optical emission by 5× at room temperature. Our FDTD simulation results confirm that this enhancement is caused by the local field enhancement of the Au substrate and indicate that the thickness of the nanosheets plays an important role in the formation and enhancement of fringes.