A review is presented of the fabrication, operation, and applications of rare-earth-doped GaN electroluminescent devices (ELDs). GaN:RE ELDs emit light due to impact excitation of the rare earth (RE) ions by hot carriers followed by radiative RE relaxation. By appropriately choosing the RE dopant, narrow linewidth emission can be obtained at selected wavelengths from the ultraviolet to the infrared. The deposition of GaN:RE layers is carried out by solid-source molecular beam epitaxy, and a plasma N 2 source. Growth mechanisms and optimization of the GaN layers for RE emission are discussed based on RE concentration, growth temperature, and V/III ratio. The fabrication processes and electrical models for both dc-and ac-biased devices are discussed, along with techniques for multicolor integration. Visible emission at red, green, and blue wavelengths from GaN doped with Eu, Er, and Tm has led to the development of flat-panel display (FPD) devices. The brightness characteristics of thick dielectric EL (TDEL) display devices are reviewed as a function of bias, frequency, and time. High contrast TDEL devices using a black dielectric are presented. The fabrication and operation of FPD prototypes are described. Infrared emission at 1.5 m from GaN:Er ELDs has been applied to optical telecommunications devices. The fabrication of GaN channel waveguides by inductively coupled plasma etching is also reviewed, along with waveguide optical characterization. Index Terms-Channel waveguides, electroluminescent devices, flat-panel displays, gallium nitride, molecular beam epitaxy, optical telecommunications, rare earths. GaN thin-film growth by CVD and MBE, focused ion beam fabrication of photonic components and circuits, rare-earth-doped luminescent devices for flat-panel displays, and communications. He has authored over 290 published articles and over 300 conference and seminar presentations.766

In this paper, we demonstrate a scalable process for the precise position-controlled selective growth of GaN nanowire arrays by metalorganic chemical vapor deposition (MOCVD) using a pulsed-mode growth technique.

[1] We investigate the chemical evolution of dust particles and examine the magnitudes of reaction probability (g) of sulfate and nitrate precursors (such as H 2 SO 4 , SO 2 , N 2 O 5 , and HNO 3 ) onto dust particles in East Asia. For this investigation, three data sets from ACE-Asia U.S. National Science Foundation (NSF) C130 flights 6, 7, and 8 and three data sets from measurements in Seoul were analyzed. During the selected dust storm periods, large amounts of CO 3 2À still remained in fine-mode dust particles (Dp < $1.3 mm). ] equivalences) for the three C130 flights were 0.87, 0.68, and 0.39, respectively, and the average CO 3 2À fractions for the three data sets in Seoul ranged from 0.43 to 0.86. The degrees of chemical evolution of mineral dust indicated by the CO 3 2À fractions were significantly smaller than those reported in previous dust chemistry transport modeling studies conducted with the assumption of aerosol internal mixing. Our analysis suggests that this could be due to the use of excessively high g values in the model simulations, as further confirmed in this study with Lagrangian photochemical model simulations conducted with both the constraints observed by ACE-Asia C130 flights and the initial concentrations obtained by U.S.-EPA Models-3/Community Multi-scale Air Quality (CMAQ) modeling over East Asia. It is also found in this study that the magnitudes of gs are closely related with aerosol mixing state. In order to confirm this we conducted Lagrangian model simulations for an example case under the assumption of aerosol external mixing. Under this assumption the formations of sulfate and nitrate on/in fine-mode mineral dust are greatly limited because of small gs onto mineral dust (g Dust ) and low precursor concentrations. However, it is also recommended that for more precise evaluations of g Dust , a more sophisticated Lagrangian type of photochemical modeling is necessary. In addition, in this study a possible dependence of the g values on relative humidity (RH) is also investigated. On the basis of our analysis we suggest that particular attention should be paid to the issue of the RH-dependent g in future dust chemistry transport modeling studies with the issue of aerosol mixing state.

No abstract

The implementation of a part-time rapid response system reduced the cardiopulmonary arrest incidence based on the reduction of cardiopulmonary arrest during rapid response system operating times. Further analysis of the cost effectiveness of part-time rapid response system is needed.

voltage, high mobility, high luminous efficiency, long service life, and tunable bandgap energy by adjusting the aluminum and indium composition covering from ultraviolet to infrared. However, there are drawbacks for GaN. For example, growing GaN on a sapphire or silicon (111) substrate generates dislocation due to lattice mismatch between the GaN epitaxial layer and the substrate. In addition, the strong chemical bond at the interface makes it difficult to separate the epitaxial layer from the substrate, which limits the ability to apply GaN with excellent properties in various fields. Recently, several studies have sought to overcome these problems by adopting 2D materials between the epitaxial layer and the substrate.Xu and co-workers reported the reduced dislocation density in GaN/graphene/GaN structure using self-organized graphene as a nanomask at high-temperature in hydrogen (H 2 ) ambient with many graphene defects. [1,2] Liu and co-workers also reported that when aluminum nitride was grown on plasma-treated graphene, the dislocation density was reduced compared to when directly grown on sapphire. [3] Hong and co-workers proved that the embedded graphene oxide could be used to improve the heat dissipation in GaN light-emitting diodes. [4,5] In addition, other researchers are making efforts to separate epitaxially grown III−V films from the substrate with the help of the 2D material making the weak chemical bond between the epitaxial layer and the substrate that is transferred to the substrate such as graphene/silicon dioxide, [6] graphene/silicon carbide, [7,8] graphene/ gallium arsenide (GaAs), [9] and boron nitride/sapphire [10] structures. Very recently, Kim and co-workers reported demonstration results using various semiconductors that showed that the polarity of 2D materials and bulk play a crucial role in remote epitaxy. The article also provides the necessary general understanding of single-crystalline growth on 2D-material-coated substrates and subsequent exfoliation. [11] However, the earlyreported graphene-loss issue, particularly in GaN growth in metal-organic chemical vapor deposition (MOCVD), remains unclear and warrants investigation to take advantages of graphene in III−V compound semiconductor growth.Here, we investigated how the decomposition of substrates that support the graphene layer affect the graphene layer by Graphene has been adopted in III−V material growth since it can reduce the threading dislocations and the III−V epilayer can easily be separated from the substrate due to the weak chemical bond. However, depending on the substrate supporting the graphene, some substrates decompose in the III−V material growth environment, which results in the problem that no graphene remains. In this study, the influence of temperature-dependent substrate decomposition on graphene through an annealing process that resembles conventional growth conditions in metal-organic chemical vapor deposition (MOCVD) is investigated. It is also confirmed that trimethylgallium, hydrogen, and ammonia gases d...

We studied GaN-based optoelectronic devices such as light-emitting diodes (LEDs) and solar cells (SCs) with graphene electrodes. A decoration of Au nanoparticles (NPs) on multi-layer graphene films improved the electrical conductivity and modified the work function of the graphene films. The Au NP-decorated graphene film enhanced the current injection and electroluminescence of GaN-based LEDs through low contact resistance and improved the power conversion efficiency of GaN-based SCs through additional light absorption and energy band alignment. Our study will enhance the understanding of the role of Au NP-decorated graphene electrodes for GaN-based optoelectronic device applications.

We investigate the mechanism of light extraction enhancement of a GaN-based light-emitting diode (LED) grown on patterned sapphire substrate (PSS), that has ZnO nanorod arrays (NRAs) fabricated on top of the device using the hydrothermal method. We found that the light output power of the LED with ZnO NRAs increases by approximately 30% compared to the conventional LED without damaging the electrical properties of the device. We argue that the gradual decrease of the effective refractive index, which is caused by the fabrication of ZnO NRAs, is the mechanism of the observed improvement. Our argument is confirmed by cross-sectional confocal scanning electroluminescence microscopy (CSEM) and the theoretical simulations, where we observed a distinct increase of the transmission at the interface between LED and air at the operation wavelength of the LED. In addition, the plane-view CSEM results indicate that ZnO NRAs, which were grown on the bare p-type GaN layer as an electrical safety margin area, also contribute to the enhanced light output power of the LED, which indicate further enhancement is manifested even in the optically ineffective sacrificial area.