Maximizing output power and efficiency in resonant-tunneling-diode oscillators: Role of high current density

A direct experimental comparison of two resonant-tunneling-diode (RTD) layer designs with 1.6 and 1.0 nm barriers demonstrates that thinner-barrier RTDs with higher current density yield a 30% increase in the output power of an RTD oscillator at 200 GHz and a 2.2× higher power at 425 GHz. Output powers of 370 μW at 199 GHz, 215 μW at 422 GHz, and 73 μW at 863 GHz were achieved with the thin-barrier RTDs, which are the highest for simple symmetrical-slot-antenna RTD oscillators so far. We measured dc-to-THz conversion efficiencies of 11% at 221 GHz, 8% at 434 GHz, and 2% at 764 GHz, which are the highest reported at these frequencies. The RTD-oscillator parameters showing maximum conversion efficiency differ from those exhibiting maximum power: the two quantities cannot be maximized simultaneously. Good agreement between the simulations and experiment for both types of RTD layer designs confirms the validity and accuracy of the modeling and optimization approach. The data also illustrate the significant impact of a relatively small stray capacitance of 1.7 fF, which reduces the output power by a factor of ∼5 at 1 THz and lowers the oscillator cut-off frequency from 1.75 THz to 1.35 THz. Although the study has been performed for the simplest type of RTD oscillators, the main conclusions are expected to have broader validity: RTDs with thin barriers and high current density should significantly increase the output power and conversion efficiency of RTD oscillators across all frequencies, including the sub-THz range.