Degradation mechanism of two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures

This paper finds that the two-dimensional electron gas density inhigh Al-content AlGaN/GaN heterostructures exhibits an obvioustime-dependent degradation after the epitaxial growth. Thedegradation mechanism was investigated in depth using Hall effectmeasurements, high resolution x-ray diffraction, scanning electronmicroscopy, x-ray photoelectron spectroscopy and energy dispersivex-ray spectroscopy. The results reveal that the formation of surfaceoxide is the main reason for the degradation, and the surfaceoxidation always occurs within the surface hexagonal defects forhigh Al-content AlGaN/GaN heterostructures.