Monolithic integration of InGaAs/InP uni-traveling-carrier photodiode with series-fed microstrip patch array on SiC substrate for on-chip 0.6 THz fan-beam generation

A monolithically integrated on-chip THz emitter is demonstrated by directly bonding an InGaAs/InP uni-traveling-carrier photodiode (UTC-PD) onto a silicon carbide (SiC) substrate and coupling it to a series-fed microstrip patch array (MPA) antenna. The device is fabricated using an adhesive-free flip-wafer bonding technique that transfers the InGaAs/InP epitaxial layers of the UTC-PD onto the SiC platform, overcoming the lattice and thermal mismatch limitations. The SiC substrate provides both C-band optical transparency and high thermal conductivity, allowing efficient backside illumination and stable high-power operation of the UTC-PD. The UTC-PD performs optical heterodyne mixing of two laser tones to generate a tunable signal in the 0.6 THz band, which is guided and radiated through a weakly leaky traveling-wave MPA array. The eight-element MPA array produces a directional fan-beam with a mainlobe angle of 14°, exhibiting a passive beam squint of about 10° as the beat frequency varies from 0.60 to 0.62 THz. The total radiated power at 0.6 THz is estimated to be 22 µW at a photocurrent of 15 mA under a −1 V bias. This monolithic SiC-based integration enables on-chip optical-to-THz conversion and free-space THz radiation, offering a compact platform for beam-scannable THz transmitters in next-generation photonic THz wireless systems.