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We present a compositional dependence study of electrical characteristics of AlxGa1−xN quantum well channel-based AlN/AlGaN/AlN high electron mobility transistors (HEMTs) with x=0.25,0.44, and 0.58. This ultra-wide bandgap heterostructure is a candidate for next-generation radio frequency and power electronics. The use of selectively regrown n-type GaN Ohmic contacts results in contact resistance that increases as the Al content of the channel increases. The DC HEMT device characteristics reveal that the maximum drain current densities progressively reduce from 280 to 30 to 1.7 mA/mm for x=0.25,0.44, and 0.58, respectively. This is accompanied by a simultaneous decrease (in magnitude) in threshold voltage from −5.2 to −4.9 to −2.4 V for the three HEMTs. This systematic experimental study of the effects of Al composition x on the transistor characteristics provides valuable insights for engineering AlGaN channel HEMTs on AlN for extreme electronics at high voltages and high temperatures. 

Due to its high breakdown electric field, the ultra-wide bandgap semiconductor AlGaN has garnered much attention recently as a promising channel material for next-generation high electron mobility transistors (HEMTs). A comprehensive experimental study of the effects of Al composition x on the transport and structural properties is lacking. We report the charge control and transport properties of polarization-induced 2D electron gases (2DEGs) in strained AlGaN quantum well channels in molecular-beam-epitaxy-grown AlN/AlxGa1−xN/AlN double heterostructures by systematically varying the Al content from x = 0 (GaN) to x = 0.74, spanning energy bandgaps of the conducting HEMT channels from 3.49 to 4.9 eV measured by photoluminescence. This results in a tunable 2DEG density from 0 to 3.7 × 1013 cm2. The room temperature mobilities of x ≥ 0.25 AlGaN channel HEMTs were limited by alloy disorder scattering to below 50 cm2/(V.s) for these 2DEG densities, leaving ample room for further heterostructure design improvements to boost mobilities. A characteristic alloy fluctuation energy of ≥1.8 eV for electron scattering in AlGaN alloy is estimated based on the temperature dependent electron transport experiments. 

Abstract Gallium nitride high-electron-mobility transistors (GaN HEMTs) are at a point of rapid growth in defense (radar, SATCOM) and commercial (5G and beyond) industries. This growth also comes at a point at which the standard GaN heterostructures remain unoptimized for maximum performance. For this reason, we propose the shift to the aluminum nitride (AlN) platform. AlN allows for smarter, highly-scaled heterostructure design that will improve the output power and thermal management of III-nitride amplifiers. Beyond improvements over the incumbent amplifier technology, AlN will allow for a level of integration previously unachievable with GaN electronics. State-of-the-art high-current p-channel FETs, mature filter technology, and advanced waveguides, all monolithically integrated with an AlN/GaN/AlN HEMT, is made possible with AlN. It is on this new AlN platform that nitride electronics may maximize their full high-power, high-speed potential for mm-wave communication and high-power logic applications. 

Aluminum nitride (AlN) offers novel potential for electronic integration and performance benefits for high‐power, millimeter‐wave amplification. Herein, load‐pull power performance at 30 and 94 GHz for AlN/GaN/AlN high‐electron‐mobility transistors (HEMTs) on silicon carbide (SiC) is reported. When tuned for peak power‐added efficiency (PAE), the reported AlN/GaN/AlN HEMT shows PAE of 25% and 15%, with associated output power () of 2.5 and 1.7 W mm⁻¹, at 30 and 94 GHz, respectively. At 94 GHz, the maximum generated is 2.2 W mm⁻¹, with associated PAE of 13%. 

The recent demonstration of  W mm⁻¹output power at 94 GHz in AlN/GaN/AlN high‐electron‐mobility transistors (HEMTs) has established AlN as a promising platform for millimeter‐wave electronics. The current state‐of‐art AlN HEMTs using ex situ‐deposited silicon nitride (SiN) passivation layers suffer from soft gain compression due to trapping of carriers by surface states. Reducing surface state dispersion in these devices is thus desired to access higher output powers. Herein, a potential solution using a novel in situ crystalline AlN passivation layer is provided. A thick, 30+ nm‐top AlN passivation layer moves the as‐grown surface away from the 2D electron gas (2DEG) channel and reduces its effect on the device. Through a series of metal‐polar AlN/GaN/AlN heterostructure growths, it is found that pseudomorphically strained 15 nm thin GaN channels are crucial to be able to grow thick AlN barriers without cracking. The fabricated recessed‐gate HEMTs on an optimized heterostructure with 50 nm AlN barrier layer and 15 nm GaN channel layer show reduction in dispersion down to compared with in current state‐of‐art ex situ SiN‐passivated HEMTs. These results demonstrate the efficacy of this unique in situ crystalline AlN passivation technique and should unlock higher mm‐wave powers in next‐generation AlN HEMTs.