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Ultra-wide bandgap (UWBG) Al0.65Ga0.35N channel high electron mobility transistors (HEMTs) were deposited using a close-coupled showerhead metal-organic chemical vapor deposition reactor on AlN-on-sapphire templates to investigate the effect of transport properties of the two-dimensional electron gas (2DEG) on the epitaxial structure design. The impact of various scattering phenomena on AlGaN channel HEMTs was analyzed with respect to the channel, buffer, and AlN interlayer design, revealing that the alloy disorder and ionized impurity scattering mechanisms were predominant, limiting the mobility of 2DEG up to 180 cm2/Vs for a sheet charge density of 1.1 × 1013 cm−2. A surface roughness of <1 nm (2 μm × 2 μm atomic force microscopy scan) was achieved for the epitaxial structures demonstrating superior crystalline quality. The fabricated HEMT device showed state-of-the-art contact resistivity (ρc = 8.35 × 10^−6 Ω · cm2), low leakage current (<10^−6 A/mm), high ION/IOFF ratio (>10^5), a breakdown voltage of 2.55 kV, and a Baliga's figure of merit of 260 MW/cm2. This study demonstrates the optimization of the structural design of UWBG AlGaN channel HEMTs and its effect on transport properties to obtain state-of-the-art device performance. 

Thin Si-doped Al-rich (xAl > 0.85) regrown Al(Ga)N layers were deposited on AlN on sapphire template using metal-organic chemical vapor deposition (MOCVD) techniques. The optimization of the deposition conditions, such as temperature (1150 °C), V/III ratio (750), deposition rate (0.7 Å/s), and Si concentration (6 × 10^19/cm3), resulted in a high charge carrier concentration (> 10^15 cm−3) in the Si-doped Al-rich Al(Ga)N films. A pulsed deposition condition with pulsed triethylgallium and a continuous flow of trimethylaluminum and ammonia was employed to achieve a controllable Al composition xAl > 0.95 and to prevent unintended Ga incorporation in the AlGaN material deposited using the close-coupled showerhead reactor. Also, the effect of unintentional Si incorporation on free charge carrier concentration at the regrowth interface was studied by varying the thickness of the regrown Al(Ga)N layer from 65 to < 300 nm. A maximum charge carrier concentration of 4.8 × 10^16 and 7.5 × 10^15/cm3 was achieved for Al0.97Ga0.03N and AlN films with thickness <300 nm compared to previously reported n-Al(Ga)N films with thickness ≥400 nm deposited using MOCVD technique. 

We simulated the light extraction efficiency (LEE) of porous GaN-based InGaN/GaN micrometer-sized light-emitting diodes (μLEDs) emitting within the visible wavelength range using the finite-difference time-domain (FDTD) method. The simulations show that the embedding of a porous GaN layer with 40 % porosity reduces the bottom LEE, while the top side LEE of the μLEDs is increased. In addition, it also exhibits complex scattering properties that affect the microcavity structure of these devices. The LEE and the degree of microcavity structure disruption are related to nanopore size and location. This association weakens with increasing wavelength. Also, a decrease in nanopore size corresponds to a diminished impact on μLED optical properties. Since the porous GaN layer contributes to the deposition of high-quality InGaN, controlling pore size of the porous GaN layer will aid the development of GaN-based red μLEDs and full-color displays. 

UV‐ranged micro‐LEDs are being explored for numerous applications due to their high stability and power efficiency. However, previous reports have shown reduced external quantum efficiency (EQE) and increased leakage current due to the increase in surface‐to‐volume ratio with a decrease in the micro‐LED size. Herein, the size‐related performance for UV‐A micro‐LEDs, ranging from 8 × 8 to 100 × 100 μm², is studied. These devices exhibit reduced leakage current with the implementation of atomic layer deposition‐based sidewall passivation. A systematic EQE comparison is performed with minimal leakage current and a size‐independent on‐wafer EQE of around 5.5% is obtained. Smaller sized devices experimentally show enhanced EQE at high current density due to their improved heat dissipation capabilities. To the best of authors’ knowledge, this is the highest reported on‐wafer EQE demonstrated in <10 μm dimensioned 368 nm UV LEDs.