Invited: III-Nitride Semiconductor Nanowire Resonant Tunneling Diodes

Resonant tunneling devices (RTDs) have attracted considerable interests because of their extremely high switching speeds and potential applications in multi-logic circuits. Due to the large conduction band offset, strong piezoelectric and spontaneous polarization, III-nitride wide band gap semiconductors are promising materials for resonant tunneling devices. However, III-nitride thin film structures always suffer from a large density of threading dislocations due to the large lattice matches between themselves and also substrates. Therefore negative differential resistances (NDR) reported in thin film III-nitride devices are a result of trap-assisted tunneling. III-nitride heterojunction nanowires have the potential to address this issue because that the large surface-to-volume ratio and small cross sections allows semiconductor nanowires accommodate much higher lattice mismatch with an efficient elastic strain relaxation thereby inhibiting the formation of dislocations. In this work, we demonstrate III-nitride nanowire RTDs with high tunneling current density and peak-to-valley current ratio. We started with growth of n-GaN/AlN/i-GaN/AlN/n-GaN double barrier heterojunction nanowres by plasma assisted molecular beam epitaxy. The I-V characteristics show clear NDR features at both room temperature and cryogenic temperatures. Significantly, NDR happens in both forward and backward voltage sweeps at the same bias, which is a strong evidence that NDR is a result of tunneling resonance as designed rather trap-assisted tunneling reported in III-N thin film heterostructures. A maximum peak to valley current ratio (PVCR) of 41 and a maximum resonant peak current density of 10⁶ A/cm² have been demonstrated. To our best knowledge, this is higher than any reported PVCR values in AlN/GaN RTDs. The details of the design, simulation, growth, and fabrication of such III-nitride heterojunction nanowire RTDs will be discussed in this talk.