S-band acoustoelectric amplifier utilizing an ultra-high thermal conductivity heterostructure for low self-heating

Here we report on an acoustoelectric slab waveguide heterostructure for phonon amplification using a thin Al$_{0.58}$Sc$_{0.42}$N film grown directly on a 4H-SiC substrate with an ultra-thin In$_{0.53}$Ga$_{0.47}$As epitaxial film heterogeneously integrated onto the surface of the Al$_{0.58}$Sc$_{0.42}$N. The aluminum scandium nitride film grown directly on silicon carbide enables a thin (1 micron thick) piezoelectric film to be deposited on a thermally conductive bulk substrate (370 W/m-K for 4H-SiC), enabling negligible self-heating when combined with the In$_{0.53}$Ga$_{0.47}$As semiconductor parameters of large mobility (~7000 cm$^2$/V-s) and low concentration of charge carriers (~5x10$^{15}$ cm$^{-3}$). A Sezawa mode with optimal overlap between the peak of its evanescent electric field and the semiconductor charge carriers is supported. The high velocity of the heterostructure materials allows us to operate the Sezawa mode amplifier at 3.05 GHz, demonstrating a gain of 500 dB/cm (40 dB in 800 microns). Additionally, a terminal end-to-end radio frequency gain of 7.7 dB and a nonreciprocal transmission of 52.6 dB are achieved with a dissipated DC power of 2.3 mW. The power added efficiency and acoustic noise figure are also characterized.