Yazar "Razeghi, Manijeh" seçeneğine göre listele

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    AlGaN/AlN MOVPE heteroepitaxy: pulsed co-doping SiH4 and TMIn
    (Iop Publishing Ltd, 2019) Demir, Ilkay; Kocak, Yusuf; Kasapoglu, A. Emre; Razeghi, Manijeh; Gur, Emre; Elagoz, Sezai
    We report a new growth approach pulsed co-doping growth of AlxGa1-xN (x > 0.5) epilayers on AlN/Al2O3 templates by metal organic vapor phase epitaxy (MOVPE). Using this approach SiH4 (silane) and TMIn (trimethylindium) supplied to the growth chamber alternately and pulsed during the growth of AlGaN epilayers. Structural and morphological quality of AlGaN epilayers were investigated by high resolution x-ray diffraction (HRXRD), atomic force microscopy (AFM), Raman spectroscopy, and scanning electron microscopy (SEM) techniques. It has shown that higher crystalline quality with low full width at half maximum (FWHM) and smoother surface morphology with reduced hexagonal hillock density has been obtained by the pulsed codoping growth approach. Volcano like hillock structures has been confirmed by Raman mapping.
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    Direct growth of thick AlN layers on nanopatterned Si substrates by cantilever epitaxy
    (WILEY-V C H VERLAG GMBH, 2017) Demir, Ilkay; Robin, Yoann; McClintock, Ryan; Elagoz, Sezai; Zekentes, Konstantinos; Razeghi, Manijeh
    AlN layers have been grown on 200 nm period of nano-patterned Si (111) substrates by cantilever epitaxy and compared with AlN layers grown by maskless lateral epitaxial overgrowth (LEO) on micropatterned Si (111) substrates. The material quality of 5-10 mu m thick AlN grown by LEO is comparable to that of much thinner layers (2 mu m) grown by cantilever epitaxy on the nanopatterned substrates. Indeed, the latter exhibited root mean square (RMS) roughness of 0.65 nm and X-ray diffraction full width at half-maximum (FWHM) of 710 arcsec along the (0002) reflection and 930 arcsec along the (10-15) reflection. The corresponding room temperature photoluminescence spectra was dominated by a sharp band edge peak. Back emission ultra violet light emitting diodes (UV LEDs) were fabricated by flip chip bonding to patterned AlN heat sinks followed by complete Si (111) substrate removal demonstrating a peak pulsed power of similar to 0.7mW at 344 nm peak emission wavelength. The demonstrated UV LEDs were fabricated on a cost effective epitaxial structure grown on the nanopatterned Si substrate with a total thickness of 3.3 mu m. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    High brightness ultraviolet light-emitting diodes grown on patterned silicon substrate
    (ELSEVIER SCI LTD, 2019) Robin, Yoann; Ding, Kai; Demir, Ilkay; McClintock, Ryan; Elagoz, Sezai; Razeghi, Manijeh
    We report on the fabrication of high brightness AlGaN-based ultraviolet light emitting diodes (UV-LED) on patterned silicon. Using the lateral epitaxial overgrowth approach, we demonstrate the growth of a 6 mu m thick AIN layer of high crystalline quality. X-ray diffraction characterization showed a rocking curve with a full width at half maximum of 553 and 768 '' for the (00.2) and (10.2) planes, respectively. The low dislocation density of the AIN template enabled the growth of bright AlGaN/GaN quantum wells emitting at 336 nm. By appropriate flip-chip bonding and silicon substrate removal processing steps, the patterned AIN surface was exposed and efficient bottom-emission UV-LEDs were realized. Improvement of the AIN quality and the structure design allowed the optical output power to reach the milliwatt range under pulsed current, exceeding the previously reported maximum efficiency. Further investigations of the optical power at different pulsed currents and duty cycles show that thermal management in this device structure is still challenging, especially in continuous wave mode operation. The strategy presented here is of interest, since AIN crystalline quality improvement and optimization of the light extraction are the main issues inhibiting efficient UV emitter on silicon fabrication.