Ferroelectric domain induced giant enhancement of two-dimensional electron gas density in ultrathin-barrier AlGaN/GaN heterostructures

With high carrier mobility two-dimensional electron gas (2DEG), AlGaN/GaN heterostructures are widely used in radio frequency and power devices. While due to limited spontaneous and piezoelectric polarization in AlGaN/ GaN heterostructures, their practical 2DEG density is around 10(13) cm(-2) so far. Further enhancement of the 2DEG density is always an attractive topic with both fundamental and application importance. Theoretical studies have shown that the carrier density in the AlGaN/GaN interface can be greatly enhanced by a ferroelectric layer with large polarization. Some experimental results have already been reported, showing signatures of correlation between ferroelectric polarization and 2DEG density. However, they can only realize limited enhancement of 2DEG in AlGaN/GaN heterostructures. Recently, with a simple substrate transfer technique, the heterointegration of high-quality PbZrxTi1-xO3 (PZT) on the AlGaN/GaN was successfully fabricated by our group. A threshold voltage shifts up to 4 V was achieved by the ferroelectric polarization. Herein, we report further optimization of this structure with ultrathin-barrier layer and in-situ poled ferroelectric domain, where the 2DEG density was non-volatilely enhanced three orders of magnitude up to 2.57 x 10(14) cm(-2). This result provides good experimental support to the theoretical prediction and might help to further improve the performance GaN based electronic devices.