We report an extreme-bandgap (EBG) AlGaN HEMT employing an undoped AlN barrier over a digital-alloy (DA) channel formed by AlN/GaN short-period superlattice (SPSL) and metalorganic chemical vapor deposition (MOCVD) regrown n(++)-GaN contacts on sapphire. The coupling of carrier wave functions through thin AlN barriers in DA leads to the formation of minibands in the transverse direction, due to which the DA channel acts as an Al (0.62) Ga (0.38) N layer. In lateral direction, regrown n++-GaN is in direct contact with GaN layers of DA, thus removing severe interface barriers existing in most known EBG HEMTs, showing a low contact resistance of R (C)=6.5 Omega & sdot; mm. With a peak drain current of 333 mA/mm, the DA-channel HEMT achieved an on-resistance R (ON)=28 Omega & sdot; mm at 6 mu m source-drain spacing, a subthreshold swing (SS) of 77 mV/dec, an ON/OFF ratio >10(7) , negligible gate hysteresis, and a critical breakdown field E (C)approximate to 2.3 MV/cm without field-plating. These results establish DA-channel as a promising new design for EBG HEMT with insulating AlN barriers for high-power and high-voltage electronics.

This article reports on the temperature dependent performance of a HEMT with an Al0.62Ga0.38N channel layer and an Al0.84Ga0.16N barrier layer grown by metal–organic chemical vapor deposition. The device in this report was measured at room temperature and elevated temperatures of 100–150 °C. The sheet resistance increased from 3.5 kΩ/sq (25 °C) to 5.4 kΩ/sq (150 °C), while the contact resistance remained nominally similar. For a device with 160 nm gate length and 2 μm source-to-drain length, excellent electrical characteristics have been achieved when the device was operated at 150 °C with a fT of 17 GHz and a fmax of 25.6 GHz. The reported device also exhibited outstanding gate leakage control, where 60% Al composition AlGaN channel HEMT, which suggests the great potential of AlGaN channel devices for high frequency, high power, high temperature applications.

AlGaN/GaN multi-channel Super Lattice Castellated Field Effect Transistors (SLCFETs) have shown great potential for next generation RF applications. We demonstrate a 2.44 & times; reduction in thermal resistance reduction in AlGaN/GaN multi-channel SLCFETs by replacing the standard AlGaN buffer with a high thermal conductivity AlN buffer layer and adding a poly-crystalline diamond overcoat layer. The thermal conductivity of each material in the device stack was measured using time-domain and frequency-domain thermoreflectance techniques, including 223(-18)(+21) W/m & sdot; K for 2.2 mu m-thick AlN buffer versus 38(-5)(+5.5) W/m & sdot; K for the reference 1.8 mu m AlGaN buffer. Device thermal resistance was reduced from 29 mm degrees C/W to 11.9 mm degrees C/W by combining the AlN buffer and poly-crystalline diamond overcoat layer, determined using Raman thermography together with 3-D thermal simulation. The corresponding 2.44 & times; increase RF power density capability enabled by improved thermal management can unlock the next-generation ultra-high-power RF devices.

In this paper we report a novel ohmic contact formation scheme for Extreme Bandgap (EBG) AlxGa1-xN (x>0.6) channel HEMTs with undoped barrier layers. Our approach consists of using a new low temperature (LT) pulsed metal-organic chemical vapor deposition (PMOCVD) doping scheme for the n++-GaN regrown contacts and an AlxGa1-xN digital alloy (DA) channel layer comprising short period super lattices (SPSL) of AlN and GaN. Pulsed growth and doping yield a sheet resistivity which is a factor of 3-5 lower than that of conventional doped n++-GaN layers grown under identical conditions. Moreover, the regrown n++-GaN layer has no hetero-barrier with the GaN layers of the AlxGa1-xN DA channel. These innovations led to MOCVD regrown linear ohmic contacts and a record-low contact resistance Rc 6.5 Ω-mm to the Al0.62Ga0.38N DA channel layer of a HEMT with AlN barrier layer.

High Al-content AlxGa1-xN (0.7 < x < 1) quasi-vertical Schottky barrier diodes (SBDs) with distributed polarization doping were grown on the bulk AlN substrate. They exhibit excellent rectification behavior with a large forward current density (similar to 14 kA/cm2) and a high breakdown field of similar to 8.3 MV/cm. The SBDs also exhibited low ideality factors of (eta similar to 1.2) with a high Schottky barrier height ( Phi(b) similar to 1.7 eV). Thus, this study demonstrates the feasibility of the distributed polarization doping approach for high current-high voltage devices.

In this paper we present a study of distribution polarization doped AlxGa1-xN layers and their use in quasi-vertical configuration pn-diodes which exhibited a high breakdown field of similar to 8.5 MV cm-1 and a large forward current density (similar to 23 kA cm-2). We also establish their potential use in UVC light emitters by studying the optical emission from a quantum well inserted at the distribution polarization doped pn-junction interface.

In this letter, we report a heterostructure field effect transistor (HFET) with Al0.87Ga0.13N barrier and Al0.64Ga0.36N channel grown by metalorganic chemical vapor deposition (MOCVD). TLM measurements of the structure showed a sheet resistance of similar to 2000 Omega/sq and linear ohmic contact resistance of 4.54 Omega. mm. A HFET with a gate length of similar to 200 nm, source-drain spacing of 4 mu m showed a peak transconductance of similar to 40 mS/mm and a high peak drain current of similar to 0.6 A/mm. A current gain cutoff frequency (f(T)) of 15.7 GHz and a power gain cutoff frequency of 20.4 GHz was observed. The breakdown voltage of this device is 390 V, yielding a high Johnson's figure of merit (JFOM) of 6.1 THz. V. This JFOM value is one of the highest reported JFOM values for AlxGa1-xN channel HFET (x > 0.4) and also for other ultra-wide bandgap (UWBG) transistors.

Herein, the first demonstration of hybrid high‐ k oxide (ZrO 2 ‐Al 2 O 3 ) incorporation into extreme bandgap (EBG) Al 0.87 Ga 0.13 N/Al 0.64 Ga 0.36 N metal‐oxide‐semiconductor heterostructure field‐effect transistors (MOSHFETs) is presented, with both planar and recessed‐gate designs on the same AlN/sapphire template with a state‐of‐the‐art low contact resistance of 1.4 Ω mm (contact resistivity, ρ c ≈ 5.7 × 10 −6 Ω cm 2 ). The recessed‐gate MOSHFETs achieve a threshold voltage shift of Δ V TH = 5.8 V, highlighting improved channel control. Static output measurements reveal a peak drain current ( I DS ) of 340 mA mm −1 for the planar gate and 280 mA mm −1 for the recessed gate at V GS = +8 V, with corresponding on–off current ratios of ≈10 6 and ≈10 8 . The recessed‐gate structure demonstrates reduced gate leakage and minimal hysteresis, indicating robust fabrication processes with negligible impact on interface states. Transfer characteristics further show a peak transconductance ( g m ) of 31 and 45 mS mm −1 for the plain and recessed structures, respectively. These findings establish EBG recessed‐gate MOSHFETs as a promising solution for advanced power devices requiring precise threshold voltage control, enhanced on‐state current, and reduced leakage currents.

In this letter, we report an heterostructure field effect transistor (HFET) with Al0.87Ga0.13N barrier and Al0.64Ga0.36N channel grown by metalorganic chemical vapor deposition (MOCVD). TLM measurements of the structure showed a sheet resistance of ~ 2000 Ω/sq and linear ohmic contact resistance of 4.54 Ω∙mm. A HFET with a gate length of ~ 200 nm, source-drain spacing of 4 μm showed a peak transconductance of ~40 mS/mm and a high peak drain current of ~0.6 A/mm. A current gain cutoff frequency (fT) of 15.7 GHz and a power gain cutoff frequency of 20.4 GHz was observed. The breakdown voltage of this device is 390 V, yielding a high Johnson’s figure of merit (JFOM) of 6.1 THz∙V. This JFOM value is one of the highest reported JFOM values for AlxGa1-xN channel HFET (x > 0.4) and also for other ultra-wide bandgap (UWBG) transistors.

We report on an exceptional thermal droop of 3.3% for a 272 nm ultraviolet C-band (UVC) light-emitting diode (LED) at 300 mA (39.4 A/cm2) and 102 °C junction temperature. To understand the superior thermal droop, we developed a method to determine the contributions of Shockley–Read–Hall (SRH) non-radiative, bimolecular radiative, and Auger non-radiative recombinations. Our analysis shows that the small thermal droop of the LED is due to a low SRH non-radiative recombination efficiency and a high defect thermal activation energy of 456.3 meV. At room temperature, the deciphered recombination efficiencies for the 272 nm LED, across a driving current range of 50–300 mA, are 1.0%–0.3% for SRH non-radiative recombination, 74.5%–60.2% for bimolecular radiative recombination, and 24.4%–39.5% Auger non-radiative recombination. We also compared a 268 nm LED that showed a significant thermal droop of 33% (at 350 mA and 105 °C) but a minimal injection-dependent efficiency droop of 2.2% (at 350 mA). Our method produced a defect thermal activation energy of 308.4 meV for this LED. The room-temperature recombination efficiencies for the 268 nm LED (50–350 mA) are 11.4%–14.3% for SRH non-radiative recombination, 80.0%–81.8% for bimolecular radiative recombination, and 5.7%–6.9% for Auger non-radiative recombination. This study suggests that thermal droop is primarily caused by SRH non-radiative recombination, while injection-dependent efficiency droop is mainly due to Auger recombination. These factors are linked to the material quality and the polarization electric field within the light-emitting quantum wells. Optimal UVC LED performance, with minimal thermal and injection-dependent droop, requires both excellent material quality and a low polarization field.

A digital alloy is a superlattice-like nanostructure formed by stacking ultra-thin (<= 4 monolayers) AlN and GaN layers periodically. Digital alloys allow for the tunability of the bandgap and electrical transport behavior. However, for them to be explored for electronic device applications, it is crucial that we determine their thermal properties, as this greatly impacts the thermal resistance and heat spreading within a device. Here we investigate the thermal properties of various AlN/AlGaN and AlxGa1-xN/AlyGa1-yN digital alloys (where x and y are the associated alloy composition) are investigated using the combined techniques of time-domain thermoreflectance and steady-state thermoreflectance. A highly anisotropic thermal conductivity of 9.6 W/m-K (cross-plane) and 39.8 W/m-K (in-plane) was measured for an AlN/AlGaN digital alloy (0.86/5.93 nm period thickness), while all measured AlxGa1-xN/AlyGa1-yN digital alloys measured a thermal conductivity of 2.9-3.3 W/m-K (cross-plane) and 8.6 W/m-K (in-plane). To investigate the influence of these thermal properties have on in-planedevice thermal transport, a number of die-level thermal management approaches are investigated on an AlGaN metal-semiconductor field-effect transistor using numerical simulations. The effects of the various cooling approaches on the device channel temperature were comprehensively investigated, along with guidance for material selection to enable the most effective thermal solutions. Specifically, we investigate the influence of substrate material, top-side heat spreader thickness/thermal conductivity, digital alloy thickness, and flip-chip design. Overall, this numerical study shows that it is possible to achieve high power digital alloy device operation with appropriate die-level thermal management solutions.

"Extreme bandgap n-Al0.63Ga0.37N quasi-vertical Schottky barrier diodes (SBDs) with doping densities of approximate to 8 x 1017 cm-3 (Sample A) and approximate to 2 x 1017 cm-3 (Sample B) are grown on an AlN/sapphire substrate using metalorganic-chemical vapor deposition (MOCVD). Sample A achieves a high forward current density of approximate to 59.5 kA cm-2 at 10 V with an ION/IOFF ratio of approximate to 108 (calculated from the forward current at + 3.8 V and the reverse current at -1 V) and an ideality factor of 2.8. Sample B has a forward current density of approximate to 6.25 kA cm-2 and a much better ideality factor of 1.9. For Sample B, a breakdown voltage of 389 V is measured, which translates into a breakdown field of approximate to 7.8 MV cm-1 and a Baliga figure of merit of 630 MW cm-2, which are the highest values ever reported for quasi-vertical Schottky barrier diodes with a similar AlxGa1-xN composition.

This article reports on the performances of a high-electron-mobility transistor (HEMT) with Al0.62Ga0.38N channel layer and Al0.84Ga0.16N barrier layer grown by metalorganic chemical vapor deposition (MOCVD). The device in this report demonstrated a contact resistance (R-C) of 3.7 Omega & sdot;mm and a sheet resistance (R-sh) of similar to 3.3 k Omega/sq. For a device with 180-nm gate length and 3-mu m source-to-drain length, excellent electrical characteristics have been achieved with a high f(T) of 30.5 GHz and f(max) of 55.3 GHz. The device also exhibited high drain current (0.46 A/mm) while maintaining low gate and drain leakage. A high breakdown voltage (up to 315 V) was also obtained, indicating excellent high-power capabilities with a high Johnson's figure of merit (JFOM) of 9.6 THz center dot V. This JFOM value is the highest among other ultra wide bandgap (UWBG) transistors. In this report, the barrier design of the devices is further discussed to obtain a better understanding of relationships between the barrier thickness and high-frequency performances. Furthermore, the intrinsic electron velocity is extracted from the small-signal parameters to be >1 x 10(7) cm/s using the drain delay method, demonstrating good carrier transport properties.

High voltage (similar to 2 kV) Al0.64Ga0.36N-channel high electron mobility transistors were fabricated with an on-resistance of similar to 75 Omega. mm (similar to 21 m Omega. cm(2)). Two field plates of variable dimensions were utilized to optimize the breakdown voltage. The breakdown voltage reached >3 kV (tool limit) before passivation however it reduced to similar to 2 kV after Si3N4 surface passivation and field plate deposition. The breakdown voltage and on-resistance demonstrated a strong linear correlation in a scattered plot of similar to 50 measured transistors. The fabricated transistors were electrically characterized and benchmarked against the state-of-the-art high-voltage (> 1 kV) Al-rich (>40%) AlGaN-channel transistors in breakdown voltage and on-resistance, indicating significant progress.

In this paper we describe a pulsed metalorganic chemical vapor deposition (MOCVD) Si-doping approach for AlN epilayers over bulk AlN. The Al-rich growth/doping conditions in the pulsed MOCVD process resulted in n-AlN layers with transmission line model currents that were an order higher than for structures on layers that were grown/doped at identical temperatures using the conventional MOCVD process. Our work demonstrated that like the other reported approaches such as UV exposure during growth, the pulsed MOCVD process is also very effective in reducing point defects by the defect quasi-Fermi level-chemical potential control.

Ultra-wide bandgap (AlN, diamond, Ga 2 O 3 ) have attracted significant research interest for high power and high frequency applications. Al rich (> 60%) AlGaN channel heterojunction field effect transistor (HFET) is a promising candidate for high power RF devices due to the large bandgap, high breakdown field and compatible saturation velocity with GaN. Consequently, Al rich (>60%) AlGaN channel transistors have been explored [ 1 – 8 ] . The AlGaN channel (Al > 60%) transistors have demonstrated good unity gain frequency (f T ) performance (~40 GHz) and decent breakdown voltage (~45 V) [6] . However, short channel effects in Al rich (Al > 60%) transistors due to a reduced gate length between 80nm–150nm limited the high breakdown voltage performance demonstration with >10 GHz f T for Al rich (Al > 60%) AlGaN channels [6 , 7] . In this work, we demonstrate high frequency (fT > 17 GHz) and high breakdown voltage (>360 V, >150 V/μm) simultaneously for 64% AlGaN channel transistors.

State-of-the-art semiconducting aluminum nitride (AlN) films were characterized by cathodoluminescence (CL) spectroscopy in the range of 200–500 nm in an attempt to identify the energy levels within the bandgap and their associated defects. Near-band edge emission (around 206 nm) and high-intensity peaks centered in the near UV range (around 325 nm) are observed for both n- and p-type AlN films. The near UV peaks are potentially associated with oxygen contamination in the films. The p-type AlN films contain at least two unidentified peaks above 400 nm. Assuming that the dopant concentration is independent of compensation (i.e., in the perfect doping limit), three effective donor states are found from Fermi–Dirac statistics for Si-doped AlN, at ∼0.035, ∼0.05, and ∼0.11 eV. Similarly, a single effective acceptor energy of ∼0.03–0.05 eV (depending on the degeneracy factory considered) was found for Be doped AlN. CL investigation of doped AlN films supports claims that AlN may be a promising optoelectronic material, but also points to contaminant mitigation and defect theory as major areas for future study.

An extreme bandgap Al0.64Ga0.36N quantum channel HEMT with Al0.87Ga0.13N top and back barriers, grown by MOCVD on a bulk AlN substrate, demonstrated a critical breakdown field of 11.37 MV/cm—higher than the 9.8 MV/cm expected for the channel’s Al0.64Ga0.36N material. We show that the fraction of this increase is due to the quantization of the 2D electron gas. The polarization field maintains electron quantization in the quantum channel even at low sheet densities, in contrast to conventional HEMT designs. An additional increase in the breakdown field is due to quantum-enabled real space transfer of energetic electrons into high-Al barrier layers in high electric fields. These results show the advantages of the quantum channel design for achieving record-high breakdown voltages and allowing for superior power HEMT devices.