Submillimeter-Wave InN Gunn Diodes Featuring a GaInN Graded-Gap Injector

Developing efficient submillimeter-wave solid-state sources is a key challenge for semiconductor electronics. This study presents a theoretical investigation into high-frequency oscillations in submicron InN-based Gunn diodes featuring a graded GaInN injector near the cathode. The research employs a three-valley hydrodynamic electron transport model adapted for graded-gap III-nitride structures, accounting for coordinate-dependent parameters. This model is integrated into a self-consistent framework that couple’s device equations with an equivalent resonant circuit and Poisson's equation. Unlike short-term simulations, this approach analyzes stable generation over thousands of cycles, providing realistic estimations of RF power, efficiency, and transients. Results show that the graded-gap GaInN injector significantly modifies space-charge wave dynamics, facilitating a transition from accumulation layer drift to dipole domain instability. Simulations demonstrate that optimizing the GaInN region length and composition substantially reduces the threshold electron concentration for current instability. An "incomplete domain drift" regime is identified, where space-charge layers dissipate within the active region before reaching the anode. This enables frequencies up to 391 GHz in a 1.0 m device, surpassing frequencies of homogeneous InN structures. A diode with a 0.2 m GaInN layer provides a peak power of 116.8 mW at 300.7 GHz, exceeding existing InGaAs and InP-based devices by orders of magnitude. The paper also addresses technological implementation challenges, including thermal management and the risk of impact ionization. It is demonstrated that InN-based diodes with a GaInN injector are potentially feasible and can be used to achieve oscillation in the sub-THz range.