This work demonstrates high-performance AlN/GaN double-barrier resonant tunneling diodes (RTDs) with high peak current density grown by plasma-assisted molecular beam epitaxy on c-plane free-standing GaN substrates, featuring stable and repeatable negative differential resistance (NDR) characteristics at room temperature. By scaling down the barrier thickness of AlN barrier and the lateral mesa size of collector, the record peak current density of 1551 kA/cm2 is achieved along with a peak-to-valley current ratio (PVCR) of 1.24, which is attributed to the reduced resonant tunneling time under thinner AlN barrier and the suppressed external incoherent valley current by reducing the dislocation number contained in the RTD device with the smaller size of collector. By statistically analyzing the NDR performance of RTD devices with different thicknesses of AlN barrier, the average peak current density increases from 145.7 to 1215.1 kA/cm2, while the average PVCR decreases from 1.45 to 1.1, correspondingly, accompanying with a decreased peak voltage from 6.89 to 5.49 V, with downscaling the AlN barrier thickness from 1.5 to 1.25 nm. The peak current density obtained in this work is the highest value among all the reported nitride-based RTDs up until now while maintaining high PVCR value simultaneously, which illustrates that ultra-scaled RTD based on vertical quantum-well structure and lateral collector size is a valuable approach for the development of nitride-based RTDs with excellent NDR characteristics and reveals their great potential applications in high-frequency oscillation sources and high-speed switch circuits.

An effect of the position of notch-doping layer in 1-μm GaN Gunn diode on threading dislocations (TDs) distribution is investigated by transmission electron microscopy. Compared with the top-notching-layer (TNL) structure, the bottom-notching-layer (BNL) structure can efficiently reduce the TDs density and improve the crystal quality in the transit region of GaN Gunn diode because it exhibits twice-transition of growth mode from atomic step flow to layer-by-layer nucleation and leads to a significant annihilation of TDs before penetrating into the transit region. X-ray diffraction and Raman spectroscopy reveal that the BNL structure has less compressive stress than the TNL structure.

Semiconductor devices based on quantum tunneling hold immense promise for developing multi‐valued logic, memory, and oscillators. Recently, two‐terminal gallium nitride (GaN) resonant tunneling diodes (RTDs) have been extensively studied due to their inherent negative differential resistance (NDR) and superior properties of wide bandgap materials. However, conventional GaN RTDs lack current gain, limiting functional modulation and performance improvement. Here, we demonstrate three‐terminal GaN resonant tunneling transistors (RTTs), which comprise an AlN/GaN double‐barrier RTD integrated with a GaN high‐electron‐mobility transistor (HEMT) through epitaxial growth. The GaN RTTs exhibit gate‐tunable NDR behavior through precise control of carrier concentration in the HEMT channel. Remarkably, the series‐connected RTT achieves an NDR voltage span of 4.1 V compared to the 0.41 V span in conventional RTDs, and the parallel‐configured RTT achieves 10 times amplification of peak current by regulating gate voltage. This work provides a feasible approach to tune NDR performance and offers a new opportunity for engineering the functionality of nitride‐based electronics, which is highly expected to alleviate the challenge posed by the saturation of Moore's law and motivate the development of beyond binary logic systems.

In this work, we demonstrate N-polar AlN/GaN heterostructures grown on free-standing GaN substrates by plasma-assisted molecular beam epitaxy, featuring an ultra-low sheet resistance at room temperature. An AlN/GaN digital-alloy barrier with high heterointerface quality is used to improve electron mobility by suppressing interface roughness and alloy disorder scatterings. Meanwhile, a Si-doped GaN layer is incorporated under the barrier to compensate hole traps and enhance the two-dimensional electron gas (2DEG) density. The homoepitaxial N-polar GaN heterostructure exhibits an atomically smooth surface with a root mean square roughness of 0.21 nm over a 5 × 5 μm2 scan area and an abrupt heterointerface in digital-alloy barrier, resolved by atomic force microscopy and scanning transmission electron microscopy, respectively. High electron mobility of 1729 cm2/(V s) and 2DEG carrier density of 1.95 × 1013 cm−2 are obtained with 10 periods of 0.5 nm AlN/1.5 nm GaN digital-alloy barrier, yielding a record low sheet resistance of 184 Ω/□ among all the reported homoepitaxial N-polar GaN heterostructures to date. This work establishes a promising platform for high-performance N-polar GaN-based electronic devices with low access region resistance.

In this work, we demonstrate fully strained GaN channel high electron mobility transistors (HEMTs) with superlattice barriers on AlN-on-sapphire templates by plasma-assisted molecular beam epitaxy. Here, ferroelectric Sc0.18Al0.82N epilayers are introduced into the heterostructure to engineer the device performance. Instead of the conventionally thick AlN buffer, an ultrathin Sc0.18Al0.82N layer is positioned between the AlN template and the GaN channel to effectively suppress the leakage at the interface between the secondary epilayers and the AlN template, realizing fully strained epitaxial structures less than 60 nm. Besides, a Sc0.18Al0.82N layer serves as a part of the superlattice barrier with well-defined interfaces, which results in a stronger polarization effect and larger conduction band offset and thus a high carrier density of 3.12 × 1013 cm−2. The processed GaN HEMT engineered by Sc0.18Al0.82N epilayers exhibits direct-current transfer characteristics with an on/off current ratio of ∼106 and distinct counterclockwise ferroelectric hysteresis windows, with a widely tunable threshold voltage ranging from −6.3 to −2.7 V. The fabricated device with a 180-nm T-shaped gate and gate-drain space of 1.5 μm achieves a breakdown voltage of 80 V, a cutoff frequency of 32 GHz, and a maximum oscillation frequency of 70 GHz, respectively. This work provides a new approach for developing next-generation multifunctional transistors on an ultrawide bandgap AlN platform through synergistically integrating ferroelectric gate modulation with a superlattice barrier, offering a promising candidate for highly reliable microwave power electronics with tunable switching characteristics.