Analyzing the interface properties of cubic GaN/AlN heterostructures using impedance spectroscopy

Cubic gallium nitride (c-GaN) is an attractive material system for various electronic and optoelectronic device applications, as it lacks internal piezoelectric polarization fields unlike its hexagonal counterpart. Yet, the fabrication of high-performing device structures depends on the growth of high-quality c-GaN thin films, which remains a challenging task. Here, we present a systematic characterization of the electrical properties of cubic GaN/AlN heterostructures with varying thicknesses grown by molecular beam epitaxy on 3C-SiC/Si templates. Impedance spectroscopy is used as a powerful tool for characterizing transport through the sample structure as well as the defect density at the existing interfaces. While the bare template exhibits a single feature in the impedance spectrum associated with the 3C-SiC/Si interface, a second low-frequency process arises under forward bias in samples with cubic GaN/AlN layers on top. Quantitative analysis of the impedance response reveals a reduction in the impurity density with increasing c-GaN film thickness. This improvement in structural quality with extended growth time is accompanied by a decrease in defect density at the interfaces. These results establish a direct link between optimized growth conditions and structural quality in cubic nitride heterostructures, providing a pathway toward the reliable design of next-generation electronic and optoelectronic devices.