Generation of mW Level in the 300-GHz Band Using Resonant-Cavity-Enhanced Unitraveling Carrier Photodiodes

We present a resonant-cavity-enhanced broadband unitraveling carrier photodiode optimized for terahertz (THz) generation. It uses a novel semitransparent top-contact utilizing subwavelength apertures for enhanced optical transmission. The contact allows front-side illumination of the photodiode using 1.55-μm-wavelength light, while still retaining a small contact resistance suitable for photomixing at THz frequencies. The responsivity of the device is improved by introducing a metallic mirror below the diode mesa through wafer bonding, producing an optical resonant cavity. A record continuous-wave output power of 750 μW is measured for a single photodiode at 300 GHz. Record values of efficiency are also demonstrated.