We report on first demonstration of violet light emitting diodes (LED) based on AlGaN/GaN/AlGaN heterostructures grown by hydride vapor phase epitaxy (HVPE). The unique aspects of this technological approach are (i) growth of Al-containing epitaxial material by HVPE and (ii) use of HVPE to fabricate submicron multi-layer epitaxial structures. The LEDs provide light emission at the wavelength of 415-420 nm that did not shift with forward current. External efficiency up to 2.5% is reached at the current of 20 mA. The brightness of LED lamp is as high as 400-500 mcd. This suggests HVPE as an alternative technique for growing AlGaN-based LED structures. Results of the LED modeling and characterization are discussed.1 Introduction Group-III nitrides are the attractive materials for application in visible and UV optoelectronic and electronic devices. Significant progress in GaN-based technology has been achieved with metal organic chemical vapor deposition (MOCVD). Blue, green and white light emitting diodes (LEDs), violet laser diodes, high electron mobility transistors, and ultra-violet photodiodes have recently been developed [1,2]. Historically, HVPE is one of the first techniques employed for GaN growth [3], which has been successfully used to fabricate thick, high-purity quasi-bulk substrates [4,5]. In addition, HVPE possess other advantages such as ability to (i) combine deposition of thick low-defect layers and thin device multi-layer structures in the same growth run and (ii) easily grow high-quality AlGaN layers in the whole composition range. Moreover, HVPE can provide low-impurity films, as it is a carbon-free process producing free HCl in a reactor, which getters metallic impurities. Thus, HVPE technique can be considered as an alternative cost-effective epitaxy technique for fabrication of AlGaN-based devices.TDI has previously reported on HVPE growth of submicron multi-layer AlGaN-based epitaxial structures for optoelectronic and electronic devices [6]. This paper is aimed at demonstrating the capability of HVPE to fabricate AlGaN/GaN/AlGaN violet LED structures. Optimization of the structure design by modeling and characteristics of the violet LEDs are discussed.

PACS 68.55. Ln, 81.05.Ea, 81.15.Kk Homoepitaxial growth of GaN and AlN was under investigation. GaN homoepitaxial layers were grown by both metal organic chemical vapour deposition (MOCVD) and hydride vapor phase epitaxy (HVPE) on GaN-on-sapphire templates. AlN homoepitaxial layers were grown on AlN-on-SiC templates, AlN-onsapphire templates, and AlN bulk substrates. Both GaN and AlN templates were grown by HVPE. Crystal structure, defects, and optical properties of grown layers were studied. For GaN homoepitaxial growth processes pretreatment procedures were developed to improve materail quality and avoid layer cracking. It was observed that defect density is reduced by homoepitaxy.1 Introduction Group III nitride semiconductors are the key materials for the next generation of electronic components and systems including high power/high frequency communication electronics and blue and UV emitter/sensor optoelectronics. One of the most serious problems in the development of III-N based devices is the lack of a suitable substrate materials on which lattice-matched group IIInitride films can be grown. The most widely used substrates for III-nitride epitaxy are sapphire and SiC. The difference in crystal lattice parameters and thermal expansion coefficients between these substrates and GaN and AlN lead to the formation of defects in the epitaxial layers. These defects can cause device degradation, particularly for laser diodes (LDs) and ultra-violet light emitting diodes (LEDs) [1,2]. Epitaxial growth on foreign substrates typically requires a buffer layer to be deposited in-between the substrate and the GaN-based device structure. The buffer layer quality determines the material and device characteristics and the parameters window for the deposition of suitable buffer layers is very narrow. Homoepitaxial growth of GaN has shown its potential to achieve superior material quality resulting in noticeable reduction of the dislocation densities and extremely narrow photoluminescence (PL) linewidths [3,4].Because of its high growth rate and high material quality, hydride vapor phase epitaxy (HVPE) is an approach for fabricating GaN-on-sapphire and AlN-on-sapphire templates to be used as substrates for subsequent homoepitaxy and device fabrication. Growth of III-N device epitaxial structures on such templates does not require low temperature nucleation layer deposition, its annealing, and a thick GaN base layer growth. Use of the templates as substrates for device fabrication leads to growth time and process cost reduction. However, the initial stages of homoepitaxy on templates must be studied to ensure the high material quality of homoepitaxial material.

The structural, optical, and electrical properties of HVPE-grown GaN-on-sapphire templates were studied. The c and a lattice constants of the GaN layers were measured by x-ray diffraction. It was observed that the c and a lattice constants vary non-monotonically with Si-doping. The proper selection of Si-doping level and growth conditions resulted in controllable strain relaxation, and thus, influenced defect formation in GaN-on-sapphire templates. It was also observed that HVPE homoepitaxial GaN layers grown on the templates have better crystal quality and surface morphology than the initial templates.

Background: The study of the morphological structure and the determination of macrophagal fraction (MF) in the newly formed epidermis and dermis on the 19th day after the transplantation of auto-and heterofibroblasts and a dermal equivalent with heterofibroblasts will allow determining the optimal method for ischemic wound healing. Materials and Methods:The study was performed on 28 white mature mice of the C57/B1 line aged between 5 and 7 months. In an ischemic cutaneous wound, 0.4 ml of fibroblast suspension (1.33 million cells) and a dermal equivalent were transplanted. The biopsy material was embedded in paraffin and stained with H&E by the Weigert-Van Gieson method to visualize the elastic and collagen fibers. Macrophages were determined by monoclonal antibodies to CD68. On the 19th day of the healing of ischemic cutaneous wound, the wound healing process goes through the transition from the stage of proliferation with GT formation into the stage of differentiation or fibrosis. The most positive for regenerative histogenesis and inflammation is the introduction of autofibroblasts. The most differentiated epidermis is formed after transplantation into the wound of the dermal equivalent with heterofibroblasts due to the presence of hairpieces in the form of formed hair follicles. The favorable effect of the dermal equivalent with heterofibroblasts differs from the influence of the autofibroblast suspension only by several percent: the thickness of the epidermis by 4.29%, the area of collagen fibers by 2.66%, and the area of the blood vessels by 4.04%. The most positive treatment for regenerative histogenesis and inflammation is the introduction of autofibroblasts. The most differentiated epidermis is formed after transplantation into the wound of the dermal equivalent with heterofibroblasts, due to the presence of pieces hair in the form of formed hair follicles.Conclusion: The favorable effect of the dermal equivalent with heterofibroblasts differs from the influence of the autofibroblast suspension by only several percent: the thickness of the epidermis by 4.29%, the area of collagen fibers by 2.66%, and the area of the blood vessels by 4

No abstract