Hongta Yang

AlGaN/AlN/GaN high-electron-mobility transistors (HEMTs) and metal–semiconductor–metal photodetectors (MSM-PDs) were integrated on Al2O3 and 4H-SiC substrates to quantify the impact of substrate selection on cryogenic electrical stability and ultraviolet (UV) optoelectronic performance. The HEMT/SiC structure exhibited a higher peak transconductance (gm) of 1.56 mS/2.34 mS at 300 K/130 K compared to the HEMT/Al2O3 structure (1.27 mS/1.83 mS). At 300 K, the gate-source voltage corresponding to peak gm was −0.3 V for the HEMT/SiC compared to −2.1 V for the HEMT/Al2O3, indicating different strain-induced polarization effects. For integrated sensing, the peak relative spectral response wavelengths were observed at 300 nm (on Al2O3) and 370 nm (on SiC). High-resolution characterization confirms that improved crystal quality and carrier transport in SiC-based heterostructures result from reduced lattice mismatch at the GaN/SiC interface. These findings establish the AlGaN/AlN/GaN-on-SiC platform as a compelling architecture for high-efficiency, switching GaN electronics and integrated cryogenic optoelectronic applications.

Cyan-blue resonant-cavity light-emitting diodes (RC-LEDs) have been designed and fabricated to enhance directional emission by using a monolithic porous-AlGaN distributed Bragg reflector (DBR), integrating a 13-spot multiaperture array (20 μm diameter) via nitrogen ion implantation for current confinement. The RC-LED structure incorporates a 25-pair bottom porous-AlGaN DBR and a top TiO2/SiO2 dielectric DBR to form a resonant cavity. The RC-LED achieves a 5.41-fold increase in electroluminescence (EL) intensity in the normal direction compared to standard LED structures. Furthermore, the resonant cavity effect significantly narrows the EL emission linewidth from 27.9 to 14.7 nm and reduces the far-field divergence angle from 128° to 62°. The spectral purity and beam directionality were demonstrated in the RC-LEDs with a multiaperture emitting array, making them ideal candidates for short-distance plastic optical fiber communication in artificial intelligence data centers and high-resolution micro-LED displays.

This study investigates the critical impact of channel scaling on the performance of AlGaN/AlN/GaN high-electron-mobility transistors (HEMTs) by comparing a 4-channel stack structure and a 5-channel double-sided channel structure. While multi-channel designs are intended to enhance current density, the results reveal a complex trade-off between carrier volume and gate electrostatic control. The 4-channel HEMT, with a periodic AlGaN/AlN/GaN stack, achieved the drain current (IDS) of 1.35 × 10–2 A and a peak transconductance (gm) of 2.2 × 10–3 S at VGS = 0 V. In contrast, the 5-channel HEMT, with a novel 2-pair double-sided GaN/AlN/AlGaN/AlN/GaN configuration, exhibited a slightly lower IDS of 1.05 × 10–2 A and a gm value of 1.4 × 10–3 S, attributed to increased series resistance and inter-channel scattering in the deeper layers. A significant highlight of this work is the observation of sequential channel activation: the transfer characteristics exhibit exactly four and five distinct gm peaks for the HEMT devices, providing direct evidence of independent channel modulation and pinch-off. Despite the increased complexity, both structures maintained high crystalline quality, as confirmed by X-ray satellite peaks and sharp heterostructure interfaces observed in TEM micrographs. These multiple-channel AlGaN-based HEMT structures with an AlGaN/AlN/GaN stack and a double-sided channel were fabricated for high-current-density, short-channel-width AlGaN-based HEMT device applications.

Shortfin mako sharks are armored with riblet-like scales, measuring tens to hundreds of micrometers and oriented toward their caudal fins. These well-organized features are known to reduce hydrodynamic drag by regulating boundary layer flow, thereby enabling rapid locomotion and facilitating the removal of attached microorganisms in marine environments. Interestingly, the scales located in the caudal peduncle are superimposed with oriented microwrinkles that promote antifouling performance under low-velocity flow regimes, which guide the design of the antifouling coatings. Bioinspired by shark scales, a self-assembly methodology is developed to engineer hierarchical wrinkle arrays with tunable structural geometries. These architectures induce pronounced anisotropic antiwetting behavior and provide weak microbial anchoring sites, thereby enhancing the efficiency of microbial removal. The influence of structural geometries on the antifouling performance has also been systematically evaluated in this research. It is anticipated that such hierarchically wrinkled structures will provide an environmentally sustainable strategy for manufacturing advanced antifouling coatings applicable to biomedical, marine, and fluid transport applications.

Green InGaN-based resonant-cavity light-emitting diodes (RC-LEDs) with integrated nanoporous (NP) GaN distributed Bragg reflectors (DBRs) were fabricated by using a selective electrochemical (EC) etching technique. The epitaxial structure comprised 25 alternating Si-doped GaN layers, forming a periodic high- and low-refractive-index stack after the EC etching process. The resulting porous-GaN DBR exhibited an effective refractive index of 2.02 and a stopband centered at 566 nm, achieving 98% reflectivity. By integrating a top-3-pairs dielectric mirror, the electroluminescence (EL) spectra showed a narrower full width at half-maximum (fwhm) from 41 nm (nontreated LED) to 12.8 nm (RC-LED). Polarization analysis revealed two spectral peaks at 536.7 and 544.7 nm, with one suppressed by a polarizer. The fwhm varied with the polarization direction, being 5.2 nm at 0° and 6.4 nm at 90°. These results demonstrate that integrating bottom porous GaN and top dielectric DBRs yields a high-reflectivity, low-loss RC structure suitable for high light coupling in fiber interconnection and high-color-purity micro-LED display applications.

Antireflective structures have been widely used to suppress the light reflection occurring on optical lenses, optical devices, and photovoltaic cells. Nevertheless, most of the structures are highly susceptible to mechanical damage, which significantly diminishes their antireflection performance. Bioinspired by the impact-resistant structures found on the Taiwan rhinoceros beetle forewings, shape memory polymer-based sandwich structures are engineered to serve as an antireflection coating. These sandwich structures, templated from self-assembled monolayer silica colloidal crystals, establish a refractive index transition at the air/substrate interface and hence exhibit broadband antireflective characteristics. Moreover, the presence of porous structures facilitates the dissipation of impact energies to protect the substrate underneath. Once the structures are damaged, the stimuli-responsive structures can even recover their original configurations under ambient conditions. Furthermore, the dependence of the structural geometry of the sandwich structure on the antireflective functionality and impact resistance is systematically studied in this research.

Taiwan rhinoceros beetle (Trypoxylus dichotomus tsunobosonis) forewings, covered with micrometer-scale sandwich structures, can dissipate impact energies to protect the membranous hindwings underneath. Bioinspired by the forewings, monolayer silica colloidal crystals are self-assembled and utilized as structural templates to engineer sandwich structures, which are supported by nonclose-packed shape memory polymer-based structure arrays. These sandwich structures provide sufficient space for the structural supports to be contorted under external stresses, facilitating the dissipating of impact energies. Importantly, the deformed structures, accompanied by diminished impact resistances, can restore their original states through manipulating the corresponding stimuli-responsive structural transitions under ambient conditions. To gain a better comprehension, the dependences of the structure arrangement, structure size, and structure shape of structural supports on the recoverable impact-resistant capabilities are systematically investigated in this research.

Since the advent of formamidinium (FA)-based perovskite photovoltaics (PVs), significant performance enhancements have been achieved. However, a critical challenge persists: the propensity for void formation in the perovskite film at the buried perovskite-interlayer interface has a deleterious effect on device performance. With most emerging perovskite PVs adopting the p-i-n architecture, the specific challenge lies at the perovskite-hole transport layer (HTL) interface, with previous strategies to overcome this limitation being limited to specific perovskite-HTL combinations; thus, the lack of universal approaches represents a bottleneck. Here, we present a novel strategy that overcomes the formation of such voids (microstructural defects) through a film treatment with methylammonium chloride (MACl). Specifically, our work introduces MACl via a sequential deposition method, having a profound impact on the microstructural defect density at the critical buried interface. Our technique is independent of both the HTL and the perovskite film thickness, highlighting the universal nature of this approach. By employing device photoluminescence measurements and conductive atomic force microscopy, we reveal that when present, such voids impede charge extraction, thereby diminishing device short-circuit current. Through comprehensive steady-state and transient photoluminescence spectroscopy analysis, we demonstrate that by implementing our MACl treatment to remedy these voids, devices with reduced defect states, suppressed nonradiative recombination, and extended carrier lifetimes of up to 2.3 μs can be prepared. Furthermore, our novel treatment reduces the stringent constraints around antisolvent choice and dripping time, significantly extending the processing window for the perovskite absorber layer and offering significantly greater flexibility for device fabrication.