Investigation of electrical activity at the AlN/Si interface using scanning capacitance microscopy and scanning spreading resistance microscopy

Abstract

This work aims to understand the origin of propagation losses in GaN-on-Si devices at microwave frequencies thanks to original AFM's electrical modes such as scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM). AlN films on Si substrate were grown using Metalorganic Vapor Phase Epitaxy (MOVPE) technique. SCM and SSRM measurements evidence a p-type conductive channel as well as a pn-junction beneath the AlN/Si interface. The diffusion depths of Al and Ga atoms obtained by Secondary Ion Mass Spectroscopy (SIMS) are in good agreement with those deduced from SCM and SSRM. Sample grown at lower temperature (1000°C) exhibits a conductive channel and a junction over a shallow depth explaining its lower propagation losses in comparison with those synthesized at higher temperature (1150°C). Thus, monitoring the dopant diffusion beneath the AlN/Si interface is crucial to achieve efficient GaN-on-Si microwave power devices.