Experimental evidence of resonant tunneling transport in GaN-based terahertz quantum cascade heterostructures

We report the first experimental evidence of resonant tunneling transport in GaN-based terahertz (THz) quantum cascade (QCL) heterostructures. A GaN/AlGaN resonant-phonon three–quantum-well design was grown and fabricated on a c-plane free-standing GaN substrate and electrically characterized. The measured current–voltage characteristics exhibit a pronounced negative differential resistance (NDR), arising from resonant alignment and subsequent detuning of quantized states within the multi-period structure. The NDR signature persists up to ∼200 K, demonstrating coherent transport in a nitride QCL-like heterostructure at elevated temperatures. Temperature-dependent measurements reveal a progressive suppression of the NDR due to enhanced inelastic scattering and level broadening, while Arrhenius analysis indicates a transition from tunneling-dominated transport at low temperatures to thermally activated carrier injection over the contacts' barrier layers at higher temperatures. These results constitute a direct experimental validation of the fundamental transport mechanism in GaN-based THz QCL structures and establish a key step toward high-temperature THz devices based on III-nitride heterostructures.