An ultraviolet (UV) photodetector employing the twodimensional electron gas (2DEG) formed at the AlGaN/GaN interface as an interdigitated transducer (IDT) is characterized under optical stimulus. The 2DEG-IDT photodetector exhibits a record high normalized photocurrent-to-dark current ratio of 6 × 10 14 . We also observe a high responsivity (7800 A/W) and ultraviolet−visible rejection ratio (10 6 ), among the highest reported values for any GaN photodetector architecture. We argue that the valence band offset in the AlGaN/GaN heterostructure is essential in achieving this high responsivity, allowing for large gains without necessitating the presence of trap states. Our proposed gain mechanism is consistent with measurements of the scaling of gain with device channel width and incident power. The photodetector architecture has a simple two-step fabrication process, compatible with AlGaN/GaN high electron mobility transistor (HEMT) processing. This unique combination of low dark current, high responsivity, and simple fabrication is attractive for a variety of UV sensing applications.

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Over the past decade, solid‐state thermal control devices have emerged as potential candidates for enhanced thermal management and storage. They distinguish themselves from traditional passive thermal management devices in that their thermal properties have sharp, nonlinear dependencies on direction and operating temperature, and can lead to more efficient circuits and energy conversion systems than what is possible today. They also distinguish themselves from traditional active thermal management devices (e.g., fans) in that they have no moving parts and are compact and reliable. In this article, the recent progress in the four broad categories of solid‐state thermal control devices that are under active research is reviewed: diodes, switches, regulators, and transistors. For each class of device, the operation principle, material choices, as well as metrics to compare and contrast performance are discussed. New architectures that are explored theoretically, but not experimentally demonstrated, are also discussed.

Monolithic strong magnetic induction at the mtesla to tesla level provides essential functionalities to physical, chemical, and medical systems. Current design options are constrained by existing capabilities in three-dimensional (3D) structure construction, current handling, and magnetic material integration. We report here geometric transformation of large-area and relatively thick (~100 to 250 nm) 2D nanomembranes into multiturn 3D air-core microtubes by a vapor-phase self-rolled-up membrane (S-RuM) nanotechnology, combined with postrolling integration of ferrofluid magnetic materials by capillary force. Hundreds of S-RuM power inductors on sapphire are designed and tested, with maximum operating frequency exceeding 500 MHz. An inductance of 1.24 μH at 10 kHz has been achieved for a single microtube inductor, with corresponding areal and volumetric inductance densities of 3 μH/mm2 and 23 μH/mm3, respectively. The simulated intensity of the magnetic induction reaches tens of mtesla in fabricated devices at 10 MHz.

Over the last decade, progress in wide bandgap, III-V materials systems based on gallium nitride (GaN) has been a major driver in the realization of high power and high frequency electronic devices. Since the highly conductive, two-dimensional electron gas (2DEG) at the AlGaN/GaN interface is based on built-in polarization fields (not doping) and is confined to very small thicknesses, its charge carriers exhibit much higher mobilities in comparison to their doped counterparts. In this study, we show that this heterostructured material also offers the unique ability to manipulate electrical transport separately from thermal transport through the examination of fully-suspended AlGaN/GaN diaphragms of varied GaN buffer layer thicknesses. Notably, we show that ~100 nm thin GaN layers can considerably impede heat flow without electrical transport degradation, and that a significant improvement (~4x) in the thermoelectric figure of merit (zT) over externally doped GaN is observed in 2DEG based heterostructures. We also observe state-of-the art thermoelectric power factors (4-7×10 -3 Wm -1 K -2 at room temperature) in the 2DEG of this material system. This remarkable tuning behavior and thermoelectric enhancement, elucidated here for the first time in a polarization-based heterostructure, is achieved since the electrons are at the heterostructured interface, while the Tuning Electrical and Thermal Transport in AlGaN/GaN Heterostructures via Buffer Layer Engineering