Improved Channel Electron Mobility Through Electric Field Reduction in GaN Quantum-Well Double-Heterostructures

To improve the electron mobility of quantum well (QW) gallium nitride (GaN) high electron mobility transistors (HEMT), we investigated QW and conventional AlGaN/GaN heterostructures grown by metal organic vapor phase epitaxy. Using calculation and experimental results, we revealed that the primary reason for the reduced electron mobility of the QW GaN-HEMT is the increase in intrasubband scattering events because of excessive electron confinement, which is caused by a strong polarization electric field. A strained Al0.30Ga0.70N/Al0.86Ga0.14N buffer structure was applied to alleviate the electric field in the GaN channel while maintaining a strong electron confinement. It enables to increase the piezo polarization of Al0.30Ga0.70N and thus, reduces that of the GaN channel. Consequently, the electron mobility improved to 1420 cm2/Vs for the QW GaN-HEMT structure with the Al0.30Ga0.70N/Al0.86Ga0.14N buffer from 1100 cm2/Vs for the common QW GaN-HEMT structure. To the best of our knowledge, 1420 cm2/Vs at a two-dimensional electron gas density of1.5× 10^13cm−2is the highest electron mobility in the QW double heterostructure.