Nonreciprocal acoustoelectric interaction of surface waves and fluorine plasma-treated AlGan/GaN 2DEG

This paper demonstrates acoustoelectric (AE) effects for surface acoustic waves (SAWs) propagating in an AlGaN/GaN 2DEG, where a fluorine based plasma has been used to tune the carrier concentration. Incorporation of fluorine ions in the AlGaN barrier is shown to reduce sheet carrier density in the 2D layer, which is required to prevent screening of piezoelectric fields. Tuning of the 2DEG channel is also observed with a progressive shift of the threshold voltage for co-fabricated HEMT structures. The monolithic gain devices exhibit nonreciprocal insertion losses under applied DC bias for higher-order Rayleigh modes in GaN on sapphire at 728 MHz and 1.48 GHz. This constitutes a first step in implementing the carrier control required for AE gain in 2D semiconductors with intrinsically high sheet density.