Vision loss, among the most feared complications of diabetes, is primarily caused by diabetic retinopathy, a disease that manifests in well-recognized, characteristic microvascular lesions. The reasons for retinal susceptibility to damage in diabetes are unclear, especially considering that microvascular networks are found in all tissues. However, the unique metabolic demands of retinal neurons could account for their vulnerability in diabetes. Photoreceptors are the first neurons in the visual circuit and are also the most energy-demanding cells of the retina. Here, we review experimental and clinical evidence linking photoreceptors to the development of diabetic retinopathy. We then describe the influence of retinal illumination on photoreceptor metabolism, effects of light modulation on the severity of diabetic retinopathy, and recent clinical trials testing the treatment of diabetic retinopathy with interventions that impact photoreceptor metabolism. Finally, we introduce several possible mechanisms that could link photoreceptor responses to light and the development of retinal vascular disease in diabetes. Collectively, these concepts form the basis for a growing body of investigative efforts aimed at developing novel pharmacologic and nonpharmacologic tools that target photoreceptor physiology to treat a very common cause of blindness across the world.

Measurements of oxygen consumption by a series of single pupae of Glossina morsitans orientalis Vanderplank maintained at 30°C. showed that the time course of respiration during this stage follows a U-shaped curve and thus resembles that of other holometabolous insects. The rate of pupal respiration was found to be directly proportional to wet weight at all temperatures investigated, and did not appear to be affected by the temperature to which females were subjected during pregnancy. The relation between temperature and the logarithm of metabolic rate was found to be curvilinear, tending to a relatively stable level between 35 and 40°C., the highest part of the range investigated.

Chloride ion concentration can be used as a biomarker for the level of pollen exposure in allergic asthma, chronic cough and airway acidification related to respiratory disease. AlGaN/GaN high electron mobility transistor (HEMT) with an InN thin film in the gate region was used for real time detection of chloride ion detection. The InN thin film provided surface sites for reversible anion coordination. The sensor exhibited significant changes in channel conductance upon exposure to various concentrations of NaCl solutions. The sensor was tested over the range of 100 nM to 100 μM NaCl solutions. The effect of cations on the chloride ion detection was also studied.

Layers of GaN deposited on Si substrates have been studied using Thermal Admittance Spectroscopy (TAS) and Optical Admittance Spectroscopy (OAS). Transparent front-side contacts were used to facilitate the optical measurements. Six specimens were cut from the same location in two different wafers, and three samples were randomly chosen from other growths. A shallow level at EC − 0.051 eV was found in all the specimens using TAS. In some specimens this peak was asymmetric, indicating more than one level near this energy. Deeper levels were also seen in the high-temperature portion of the spectra, but were poorly resolved in most specimens. Illuminating the specimen with UV light at 25 K resulted in the thermal position of the peak shifting to a lower temperature, and hence, the calculated energy, of the peak shifting lower. The amplitude of the peak also decreased. Transient OAS measurements revealed the interesting phenomenon of negative persistent photo conductance at room temperature in some of the specimens when the illumination photon energy was less than the bandgap. The negative response time was very short. At lower temperatures, below 100 K, the negative response diminished, but the response time was still short. At wavelengths above the bandgap energy, normal transient response was seen, with a longer time constant.

Au-gated AlGaN/GaN High Electron Mobility Transistor (HEMT) structures were functionalized in the gate region with label free 3′-thiol modified oligonucleotides. This serves as a binding layer to the AlGaN surface for hybridization of matched target Deoxyribonucleic Acid (DNA). X-ray photoelectron spectroscopy (XPS) shows that immobilization of thiol modified DNA covalently bonded with gold on the gated region. Hybridization between probe DNA and matched or mismatched target DNA on the Au-gated HEMT was detected by electrical measurements. The HEMT drain-source current showed a clear decrease of 115 μA as this matched target DNA was introduced to the probe DNA on the surface, showing the promise of the DNA sequence detection approach for biological sensing.

One of the principle problems of high power electronic devices is the extraction of heat from the active region of the device. The thermal conductivity of the substrate is a crucial parameter affecting the thermal dissipation capability of a device. In this study we investigated the thermal conductivity at room temperature of five GaN samples grown on silicon, employing the 3 omega thermal conductivity method. The thickness of the GaN layers varied from 0 to 700 nm. The effective thermal conductivity for the GaN layers was found to range from 130 to 140 W/m·K which is comparable to thermal conductivity of the silicon substrate. This result indicates that the heat transfer of GaN on silicon is as good as either GaN or silicon alone, and that no substantial thermal degradation attributable to the GaN/Silicon interface is observed.

Discrete and coalesced monocrystalline GaN and AlxGa1−xN layers grown via pendeo-epitaxy (PE) originated from side walls of GaN seed stripes with and without SiNx top masks have been grown via organometallic vapor phase deposition on GaN/AlN/6H-SiC(0001) and GaN(0001)/AlN(0001)/3C-SiC(111)/Si(111) substrates. Scanning and transmission electron microscopies were used to evaluate the external microstructures and the distribution of dislocations, respectively. The dislocation density in the laterally grown sidewall regions and in the regions grown over the SiNx masks was reduced by at least five orders of magnitude relative to the initial GaN seed layers. Tilting of 0.2° in the coalesced GaN epilayers grown over the SiNx masks was determined via X-ray and selected area diffraction; however, tilting was not observed in the material suspended above the SiC substrate and that grown on unmasked stripes. A strong, low-temperature photoluminescence band-edge peak at ~3.45 eV with a FWHM of <300 µeV was determined on the overgrowth material grown on the silicon carbide substrates. The band-edge in the GaN grown on silicon substrates was shifted to a lower energy by 10 meV, indicative of a greater tensile stress.

Single crystalline (0001) gallium nitride layers, capped with a thin epitaxial aluminum nitride layer, were implanted with magnesium and subsequently annealed in vacuum to 1150-1300 °C for 10-60 minutes. Photoluminescence (PL) measurements showed the typical donor acceptor pair (DAP) transition at 3.25 eV after annealing at high temperatures, which is related to optically active Mg acceptors in GaN. After annealing at 1300 °C a high degree of optical activation of the implanted Mg atoms was reached in the case of low implantation doses. Electrical measurements, performed after removing the AlN-cap and the deposition of Pd/Au contacts, showed no p-type behavior of the GaN samples due to the compensation of the Mg acceptors with native n-type defects.

Discrete and coalesced monocrystalline GaN and AlxGa1−xN layers grown via Pendeoepitaxy (PE) [1] originated from side walls of GaN seed structures containing SiNx top masks have been grown via organometallic vapor phase deposition on GaN/AlN/6HSiC(0001) and GaN(0001)/AlN(0001)/3C-SiC(111)/Si(111) substrates. Scanning and transmission electron microscopies were used to evaluate the external microstructures and the distribution of dislocations, respectively. The dislocation densities in the PE grown films was reduced by at least five orders of magnitude relative to the initial GaN seed layers. Tilting in the coalesced GaN epilayers was observed via X-ray diffraction. A tilt of 0.2° was confined to areas of mask overgrowth; however, no tilting was observed in the material suspended above the SiC substrate. The strong, low-temperature PL band-edge peak at 3.45 eV with a FWHM of 17 meV was comparable to that observed in PE GaN films grown on 6H-SiC(0001). The band-edge in the GaN grown on AlN(0001)/SiC(111)Si(111) substrates was shifted to a lower energy by 10 meV, indicative of a greater tensile stress.

Growth of GaN and AlxGa1−xN thin films on 6H-SiC(0001) and Si(111) substrates with low densities of defects using the PENDEO™ process and the characterization of the resulting materials are reported. The application of a mask on the GaN seed structures hinders the vertical propagation of threading dislocations of the seed material during regrowth, but introduces a misregistry in the overgrowing material resulting in low quality crystal growth. This misregistry has been eliminated due to advanced processing and the exclusion of the masking layer. The new generation of samples do not show any misregistry, as shown by transmission electron microscopy.

Pendeo-epitaxy of individual GaN and AlxGa12−xN films and single- and multi-layer heterostructures of these materials have been achieved on a columnar GaN seed layer using metallorganic vapor phase epitaxy. These structures have been characterized using scanning electron microscopy and atomic force microscopy. The RMS roughness value of the grown side wall plane (110) of these structures was 0.099 nm.

Single crystalline (0001) gallium nitride layers, capped with a thin epitaxial aluminum nitride layer, were implanted with magnesium and subsequently annealed in vacuum to 1150-1300 oC for 10-60 minutes. Photoluminescence (PL) measurements showed the typical donor acceptor pair (DAP) transition at 3.25 eV after annealing at high temperatures, which is related to optically active Mg acceptors in GaN. After annealing at 1300 °C a high degree of optical activation of the implanted Mg atoms was reached in the case of low implantation doses. Electrical measurements, performed after removing the AlN-cap and the deposition of Pd/Au contacts, showed no p-type behavior of the GaN samples due to the compensation of the Mg acceptors with native n-type defects.

Discrete and coalesced monocrystalline GaN and AlxGa1−xN layers grown via Pendeoepitaxy (PE) [1] originated from side walls of GaN seed structures containing SiNx top masks have been grown via organometallic vapor phase deposition on GaN/AlN/6HSiC(0001) and GaN(0001)/AlN(0001)/3C-SiC(111)/Si(111) substrates. Scanning and transmission electron microscopies were used to evaluate the external microstructures and the distribution of dislocations, respectively. The dislocation densities in the PE grown films was reduced by at least five orders of magnitude relative to the initial GaN seed layers. Tilting in the coalesced GaN epilayers was observed via X-ray diffraction. A tilt of 0.2° was confined to areas of mask overgrowth; however, no tilting was observed in the material suspended above the SiC substrate. The strong, low-temperature PL band-edge peak at 3.45 eV with a FWHM of 17 meV was comparable to that observed in PE GaN films grown on 6H-SiC(0001). The band-edge in the GaN grown on AlN(0001)/SiC(111)Si(111) substrates was shifted to a lower energy by 10 meV, indicative of a greater tensile stress.

Pendeo-epitaxy is a type of selective growth of thin films from the sidewalls of etched forms. The resulting films are suspended from the sidewalls and do not interface with the substrate. This process route has advantages over conventional lateral epitaxial overgrowth (LEO) techniques. In this research, pendeo-epitaxial growth of GaN films has been achieved on elongated GaN seed columns. The seed columns were etched from GaN grown on 6H-SiC (0001) substrates via metalorganic vapor phase epitaxy (MOVPE). Silicon nitride mask layers atop the GaN seed columns forced growth from the sidewalls. Pendeo-epitaxial growth of GaN was investigated using several growth temperatures. Higher growth temperatures resulted in improved coalescence due to greater lateral to vertical growth ratios.

Growth of GaN and AlxGa1−xN thin films on 6H-SiC(0001) and Si(111) substrates with low densities of defects using the PENDEO™ process and the characterization of the resulting materials are reported. The application of a mask on the GaN seed structures hinders the vertical propagation of threading dislocations of the seed material during regrowth, but introduces a misregistry in the overgrowing material resulting in low quality crystal growth. This misregistry has been eliminated due to advanced processing and the exclusion of the masking layer. The new generation of samples do not show any misregistry, as shown by transmission electron microscopy.

Pendeo-epitaxy is a type of selective growth of thin films from the sidewalls of etched forms. The resulting films are suspended from the sidewalls and do not interface with the substrate. This process route has advantages over conventional lateral epitaxial overgrowth (LEO) techniques. In this research, pendeo-epitaxial growth of GaN films has been achieved on elongated GaN seed columns. The seed columns were etched from GaN grown on 6H-SiC (0001) substrates via metalorganic vapor phase epitaxy (MOVPE). Silicon nitride mask layers atop the GaN seed columns forced growth from the sidewalls. Pendeo-epitaxial growth of GaN was investigated using several growth temperatures. Higher growth temperatures resulted in improved coalescence due to greater lateral to vertical growth ratios.