Growth-induced trade-off between polarity, electrical isolation, and structural quality in AlN grown on Si(111) by plasma-assisted molecular beam epitaxy

Abstract

We investigate the effects of substrate temperature and Al flux, at a fixed N flux, on the polarity, electrical properties, and structural quality of AlN films grown on high-resistivity Si(111) by plasma-assisted molecular beam epitaxy. N-rich conditions result in relatively highly resistive Al-polar AlN/Si, whereas Al-rich conditions promote N-polarity and improved structural quality but simultaneously lead to increased p-type conductivity of AlN/Si stacks, consistent with unintentional Al doping of the Si substrate during AlN growth. Increasing the substrate temperature further improves the structural quality while enhancing the unwanted conductivity, revealing a growth-induced trade-off among polarity, electrical isolation, and structural quality. By reducing the substrate temperature to 575°C while maintaining slightly Al-rich conditions, an N-polar AlN/Si stack with a sheet resistance of 276 kΩ/sq is achieved. These results provide guidelines for optimizing AlN/Si templates for various nitride device heterostructures.