Heterogeneous integration of ultrawide bandgap semiconductors for radio frequency power devices

Ultrawide bandgap (UWBG) semiconductors offer high critical electric fields and saturation velocities ideal for radio frequency (rf) devices, but achieving both shallow-level doping and high thermal conductivity (k_T) in a single material remains difficult. We demonstrate a scalable, exfoliation-based layer-transfer process to heterogeneously integrate gallium oxide (Ga₂O₃) thin films with shallow dopants onto high-k_T aluminum nitride (AlN) substrates. This method obviates ion implantation and interfacial dielectric layers used in conventional approaches. A large conduction band offset (3.4 electron volts) at the Ga₂O₃/AlN interface improves electron confinement in the Ga₂O₃ channel. T-gate rf power transistors achieve a maximum oscillation frequency of 90 gigahertz and output power densities of 4.6 watts per millimeter at 2 gigahertz and 4.1 watts per millimeter at 6 gigahertz-among the highest for UWBG devices. A minimal noise figure of 0.48 decibels at 8 gigahertz-among the lowest reported in this frequency range-further highlights the platform's promise for next-generation rf applications.