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Lateral GaN-based p-n junction gated field effect transistor (LJFET) power transistors on large area substrates were fabricated as a proof-of-concept to evaluate candidate power switching devices that could be designed with avalanche breakdown capability. The devices performed to design specifications aimed at demonstrating a device suitable for operation in cascode with a normally-off low-voltage Si based transistor companion. The maximum current density was 200 mA/mm and threshold voltage was [?]30V. Large gate width devices (40mm) exhibited >1A current. The devices have blocking capability to 800V. Initial testing of the switching dynamics indicates low dynamic RON even with an un-optimized buffer.

The material and device performance of GaN layers on large diameter (150mm-200mm) engineered substrates was assessed. Vertical Schottky diode structures and lateral P-N junction gated field effect transistors were used as the device test vehicles. Vertical devices formed by substrate removal exhibited rectifying behavior and reasonable blocking performance, while lateral transistors exhibited excellent gate control and high current density.

Homoepitaxial growth of GaN yields significantly higher quality material and, thus, expands the application space for commercially competitive III-nitride based devices. A critical aspect in controlling homoepitaxial growth consists of understanding impurity incorporation at the interface of GaN grown on GaN. This paper investigates the source of impurity incorporation at the regrowth interface for a MOCVD process and the associated effects on lateral high-electron mobility transistor device structures.

High-yield wafer bonding with minimal bonding imperfections and high-aspect etch process of 4H-SiC/SiO2/4H-SiC stacks is presented. The top 4H-SiC layer is thinned, patterned, etched, and is then ready to be released to form the MEMS device layer. An anti-bosch process is used to etch high aspect ratio trenches within the 4H-SiC device layer in the presence of buried oxide; the oxide serves both as a sacrificial layer and as an etch stop. The etch yields an aspect ratio of 10.5 (42.9 um etch depth : 4.1 um mask opening) within the 4H-SiC device layer. The handle wafer is 4H-SiC, as opposed to Si, which allows for all SiC-based MEMS devices for high shock resistant and temperature applications.

Quantum technology is a field of significant interest that will benefit many applications including communications and sensing. SiC is a promising material for quantum applications such as quantum memories, due to point defects, specifically VSi, in the material, which result in long spin coherence times. We have found that no VSi are present in our epitaxially grown unintentionally and nitrogen-doped 4H-SiC with electron concentrations ranging from 1014 to 1018 cm-3. We create these vacancies using electron irradiation, in concentrations from single defects to ensembles. To utilize the defect luminescence for realistic applications, we have fabricated the SiC into photonic crystal arrays. We present the processing steps required to create photonic crystal cavities in SiC and subsequent challenges.

The atomic-level resolution of scanning transmission electron microscopy (TEM) is used for structural characterization of nanomaterials, but the resolution afforded by TEM also enables electronic characterization of defects in these materials through electron energy-loss spectroscopy (EELS). Here, the power of EELS is harnessed to characterize the local band gap of inclusion defects in hexagonal silicon carbide nanowires with a high density of stacking faults. The band gaps we extract from the EELS data align within 0.1 eV of expected values for hexagonal silicon carbide and stacking faults within hexagonal silicon carbide. These experiments show that individual cubic phase inclusions in hexagonal silicon carbide significantly alter the local electronic structure, in particular, the band gap, in contrast to the polarizability tensor that retains the characteristic signature of the global hexagonal crystal structure.

Copper Oxide and Nickel Oxide were deposited and investigated for their electrical and optical properties as a wide bandgap p-type oxide semiconductor. Heterojunctions of CuxOy/b-Ga2O3 were fabricated with a rectification ratio of 2.5x104 at +-2 V. NiO films were deposited using both RF sputtering and atomic layer deposition methods, resulting in rectifying heterojunctions in both cases. A 3.6 eV bandgap was measured upon a 500 degC post-deposition anneal for the sputtered films.

A hierarchical cobalt oxide (Co3O4)-functionalized silicon carbide nanowire (SiC NW) array electrode is synthesized on 4H–SiC(0001) substrates and investigated for use in the oxygen evolution reaction (OER) of water splitting. Ni-catalyzed chemical vapor deposition is employed to obtain vertically-aligned SiC NWs, and electrodeposition is used to functionalize the nanowires with hierarchical Co3O4nano-clusters and a thin Co3O4layer on the top side and the side-walls of the NWs, respectively. By using the Co3O4-functionalized SiC NW electrode for OER, the overpotential required to drive an anodic current density (Janodic) of 10 mA cm−2is 0.22 V, a value much lower than those of Co3O4nano-clusters (0.42 V), of bare SiC NWs (1.27 V) electrodes and of Pt foil (0.56 V). The overpotential value of 0.22 V is among the most active for the noble metal-free electro-catalytic electrode to produce Janodicof 10 mA cm−2. The deposition of Co3O4on the SiC NW substrate produces an extremely hydrophilic surface, which improves the charge transfer characteristics at the interface between the electrode and the aqueous electrolyte. Moreover, the vertically-aligned SiC NWs provide a directional charge transport route along the nanowire length, as seen from a lower charge transfer resistance (Rct) in the Co3O4-functionalized SiC NW electrode compared to the Co3O4-functionalized SiC electrode under the same OER operating conditions. Finally, the Co3O4-functionalized SiC NW electrode maintains stable performance in an alkaline electrolyte (i.e., 1 M KOH aqueous solution) during continuous electrolysis testing over 16 h. The outstanding electro-catalytic performance and stability make the Co3O4-functionalized SiC NW electrode a promising noble metal-free electro-catalytic electrode for the OER and other renewable energy applications.

Deep reactive-ion etching (DRIE) of high aspect ratio structures in 4H-SiC is demonstrated. Electroplated nickel is used as the etch mask and patterned with openings ranging from 2-10 um. Etch depths of 51 to 57 um are obtained after a 2 hour reactive ion etch with SF6/O2 inductively coupled plasma for 2-6 um mask openings. Thus, aspect ratios (depth: mask opening) of 25.5 to 9.5 are achieved. Sidewall morphology is shown as a function of helium back side cooling with close to vertical sidewalls obtained with less cooling.

We demonstrate a symmetric supercapacitor by using yttria-stabilized zirconia (YSZ) as the electrolyte and silicon carbide nanowires (SiC NWs) as the electrode. The stacked symmetric SiC NWs/YSZ/SiC NWs supercapacitors exhibit excellent thermal stability and high areal capacitance at temperatures above 300 °C. The supercapacitor functions well at a record high temperature of 450 °C, yielding an areal capacitance of 92 μF cm–2at a voltage scan rate of 100 mV s–1. At this temperature, it is also capable of withstanding current densities up to 50 μA cm–2, yielding a maximum areal power density of 100 μW cm–2. Good cycling stability is demonstrated with a capacitance retention of over 60% after 10 000 cycles at the operation temperature of 450 °C and a scan rate of 200 mV s–1.

Three-dimensional ultrathin graphitic foams are grown via chemical vapor deposition on templated Ni scaffolds, which are electrodeposited on a close-packed array of polystyrene microspheres. After removal of the Ni, free-standing foams composed of conjoined hollow ultrathin graphite spheres are obtained. Control over the pore size and foam thickness is demonstrated. The graphitic foam is tested as a supercapacitor electrode, exhibiting electrochemical double-layer capacitance values that compare well to those obtained with the state-of-the-art 3D graphene materials.

Recognition of the proper start codon on mRNAs is essential for protein synthesis, which requires scanning and involves eukaryotic initiation factors (eIFs) eIF1, eIF1A, eIF2, and eIF5. The carboxyl terminal domain (CTD) of eIF5 stimulates 43S preinitiation complex (PIC) assembly; however, its precise role in scanning and start codon selection has remained unknown. Using nuclear magnetic resonance (NMR) spectroscopy, we identified the binding sites of eIF1 and eIF2β on eIF5-CTD and found that they partially overlapped. Mutating select eIF5 residues in the common interface specifically disrupts interaction with both factors. Genetic and biochemical evidence indicates that these eIF5-CTD mutations impair start codon recognition and impede eIF1 release from the PIC by abrogating eIF5-CTD binding to eIF2β. This study provides mechanistic insight into the role of eIF5-CTD's dynamic interplay with eIF1 and eIF2β in switching PICs from an open to a closed state at start codons.

We have demonstrated the utility of hollow silica nanoparticles in fabricating conformal thin film nanoporous antireflection (AR) coatings on both poly(methyl methacrylate) (PMMA) and glass substrates. Layer-by-layer (LbL) assembly was successfully used to produce ultrathin AR coatings on planar and textured surfaces. Hollow silica nanoparticles were synthesized to extend the range of apparent refractive indices possible in an AR coating, enabling the design of both single index and graded index AR coatings on PMMA substrates. The diameter and shell thickness of the silica nanoparticles are the two independent, controllable parameters that we manipulated to tune the refractive index of the coating. The AR coatings reduced the minimum reflection of PMMA from 7% to 0.5%, while the maximum transmission increased from 92% to 98% at the optimized wavelength region that could be adjusted from the near UV into the visible. Cross sectional SEM showed that conformal coatings can be achieved on grooved PMMA Fresnel lenses. AFM was used to study surface topography on flat substrates.

Ion implantation of magnesium for p‐type GaN presents many opportunities; however, activation has proven difficult due to the decomposition of GaN at relevant annealing temperatures. Herein, testing the efficacy of multiple in situ and ex situ caps based on aluminum nitride and silicon nitride for GaN protection during annealing is presented. Photoluminescence shows better activation for in situ metal organic chemical vapor deposition (MOCVD)‐grown aluminum nitride caps compared with ex situ sputtered aluminum nitride and the best performance by ex situ plasma‐enhanced chemical vapor deposition (PECVD) silicon nitride. Furthermore, only samples annealed at the highest temperatures tested show preferential growth of UV luminescence to yellow‐green luminescence reinforcing the need for better capping solutions and higher temperature annealing. Herein, direct comparison of in situ and ex situ caps including aluminum and silicon nitrides for stabilization of GaN during implanted dopant activation is described. Caps seen here evaluate on macroscopic integrity after annealing, whereas dopant activation and structural quality are also determined.

Here we present a direct comparison between the activation of implanted Mg ions in N-polar and Ga-polar substrates to produce p-type GaN via symmetric multicycle rapid thermal annealing (SMRTA). Physical dopant activation was achieved by annealing in moderate nitrogen pressures (3.3 MPa) in conjunction with a bi-layer cap. Photoluminescence shows activation was more readily achieved for N-polar films with measured UV luminescence up to [?]15x as intense as yellow/green luminescence compared to [?]2.4x for Ga-polar films. The greater activation of N-polar material was primarily due to a higher thermal stability compared to Ga-polar films. This demonstration of implanted Mg activation by SMRTA enables a facile route toward next generation vertical devices.

Lateral GaN-based p-n junction gated field effect transistor (LJFET) power transistors on large area substrates were fabricated as a proof-of-concept to evaluate candidate power switching devices that could be designed with avalanche breakdown capability. The devices performed to design specifications aimed at demonstrating a device suitable for operation in cascode with a normally-off low-voltage Si based transistor companion. The maximum current density was 200 mA/mm and threshold voltage was −30V. Large gate width devices (40mm) exhibited >1A current. The devices have blocking capability to 800V. Initial testing of the switching dynamics indicates low dynamic RONeven with an un-optimized buffer.

The material and device performance of GaN layers on large diameter (150mm-200mm) engineered substrates was assessed. Vertical Schottky diode structures and lateral P-N junction gated field effect transistors were used as the device test vehicles. Vertical devices formed by substrate removal exhibited rectifying behavior and reasonable blocking performance, while lateral transistors exhibited excellent gate control and high current density.

Homoepitaxial growth of GaN yields significantly higher quality material and, thus, expands the application space for commercially competitive III-nitride based devices. A critical aspect in controlling homoepitaxial growth consists of understanding impurity incorporation at the interface of GaN grown on GaN. This paper investigates the source of impurity incorporation at the regrowth interface for a MOCVD process and the associated effects on lateral high-electron mobility transistor device structures.

High-yield wafer bonding with minimal bonding imperfections and high-aspect etch process of 4H-SiC/SiO2/4H-SiC stacks is presented. The top 4H-SiC layer is thinned, patterned, etched, and is then ready to be released to form the MEMS device layer. An anti-bosch process is used to etch high aspect ratio trenches within the 4H-SiC device layer in the presence of buried oxide; the oxide serves both as a sacrificial layer and as an etch stop. The etch yields an aspect ratio of 10.5 (42.9 μm etch depth : 4.1 μm mask opening) within the 4H-SiC device layer. The handle wafer is 4H-SiC, as opposed to Si, which allows for all SiC-based MEMS devices for high shock resistant and temperature applications.

Copper Oxide and Nickel Oxide were deposited and investigated for their electrical and optical properties as a wide bandgap p-type oxide semiconductor. Heterojunctions of CuxOy/β-Ga2O3were fabricated with a rectification ratio of 2.5x104at ±2 V. NiO films were deposited using both RF sputtering and atomic layer deposition methods, resulting in rectifying heterojunctions in both cases. A 3.6 eV bandgap was measured upon a 500 °C post-deposition anneal for the sputtered films.

Deep reactive-ion etching (DRIE) of high aspect ratio structures in 4H-SiC is demonstrated. Electroplated nickel is used as the etch mask and patterned with openings ranging from 2–10 μm. Etch depths of 51 to 57 μm are obtained after a 2 hour reactive ion etch with SF6/O2inductively coupled plasma for 2–6 μm mask openings. Thus, aspect ratios (depth: mask opening) of 25.5 to 9.5 are achieved. Sidewall morphology is shown as a function of helium back side cooling with close to vertical sidewalls obtained with less cooling.