In this work, the leakage current properties of semi-insulating GaN (SI-GaN) grown on Si(1 1 1) substrate with a low-temperature (LT) AlN interlayer were studied. Two terminal lateral current–voltage measurements revealed an early conduction phenomenon via buffer layers with an LT-AlN interlayer, in which both p- and n-type conduction phenomena were observed from Hall-effect measurement during temperature changing. It is suggested that the p-type conduction existed in the Si substrate due to the diffusion of Al atoms into the Si substrate during the epitaxial growth. The origin of n-type conduction was two-dimensional electron gas (2DEG) in the LT-AlN/GaN interface, which acted as a conduction channel in SI-GaN. Furthermore, the vertical leakage current measurement and the space charge limited current model were used to analyse the impact of the 2DEG conduction channel on the leakage current properties. It is revealed that leakage current properties are very sensitive to the thickness of the GaN layer above the LT-AlN interlayer (Top-GaN). Increasing the thickness of Top-GaN becomes an effective way to suppress leakage current. Therefore, both strain engineering and leakage current properties are essential factors to be considered in the selection of strain compensation interlayer in the growth of SI-GaN on Si substrate for power switching applications.
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