Acoustoelectric amplification of Rayleigh waves in low sheet density AlGaN/GaN heterostructures on sapphire

This letter demonstrates amplification of surface acoustic waves through the application of dc electric fields in low sheet density heterostructures of AlxGa1−xN barrier layers over GaN grown by metal organic chemical vapor deposition on a sapphire substrate. The use of the GaN material offers a convenient platform to study acoustoelectric (AE) effects, due to its piezoelectricity and the ability to support a two-dimensional electron gas at the interface with the barrier. In this work, low Al molar fractions (between 6% and 10%) in the barrier layer are investigated to tune the sheet resistivity, which is a key aspect to realizing appreciable AE gains. Rayleigh waves in GaN at 920 MHz exhibit non-reciprocity (defined as the contrast in the peak amplitude of the amplified forward traveling wave and the attenuated reverse traveling wave) of up to 6.5 dB/mm under the influence of dc bias fields applied to a 24 nm Al0.07Ga0.93N barrier over GaN on sapphire. Gain dependence on the sheet resistance is also observed, consistent with the AE effect. This work demonstrates an approach to counteract acoustic propagation losses in GaN, which can be implemented in long delay lines for RF signal processing, in addition to other applications.This letter demonstrates amplification of surface acoustic waves through the application of dc electric fields in low sheet density heterostructures of AlxGa1−xN barrier layers over GaN grown by metal organic chemical vapor deposition on a sapphire substrate. The use of the GaN material offers a convenient platform to study acoustoelectric (AE) effects, due to its piezoelectricity and the ability to support a two-dimensional electron gas at the interface with the barrier. In this work, low Al molar fractions (between 6% and 10%) in the barrier layer are investigated to tune the sheet resistivity, which is a key aspect to realizing appreciable AE gains. Rayleigh waves in GaN at 920 MHz exhibit non-reciprocity (defined as the contrast in the peak amplitude of the amplified forward traveling wave and the attenuated reverse traveling wave) of up to 6.5 dB/mm under the influence of dc bias fields applied to a 24 nm Al0.07Ga0.93N barrier over GaN on sapphire. Gain dependence on the sheet resistance is also obse...