Direct nanoscale characterization of polarization-dependent diffusion in non-polar GaN via scanning diffusion microscopy

Abstract

Non-polar GaN planes (e.g., a-plane and m-plane) present a promising path to mitigate the quantum-confined Stark effect inherent to polar orientations, thereby enhancing the efficiency of optoelectronic devices. Their inherent optical polarization anisotropy is also advantageous for applications requiring polarized light without using a polaroid. However, the polarization-dependent carrier diffusion behavior in non-polar GaN, which is governed by different valence bands and critically influences device performance, remains inadequately characterized. Here, we employ scanning diffusion microscopy based on photo-assisted Kelvin probe force microscopy to quantitatively map the polarization-dependent carrier diffusion coefficients in non-polar a-plane and m-plane GaN. By comparing the diffusion behavior under light polarized perpendicular and parallel to the c-axis, we reveal a clear polarization dependence that aligns with the effective mass. Our study provides the first direct nanoscale mapping of polarization-dependent diffusion coefficients in non-polar GaN, bridging a critical gap between macroscopic transport properties and microscopic band structure parameters. In future, the polarization-dependent diffusion in non-polar GaN-based devices would provide information for better design of the transverse-electric or transverse-magnetic modes via band control.