Browsing by Subject "Optical qualities"

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    Characterization of an AlN buffer layer and a thick-GaN layer grown on sapphire substrate by MOCVD
    (Springer, 2010-10-23) Çörekçi, S.; Öztürk, M. K.; Bengi, A.; Çakmak, M.; Özçelik, S.; Özbay, Ekmel
    An AlN buffer layer and a thick-GaN layer for high-electron-mobility transistors (HEMTs) were grown on sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The structural and morphological properties of the layers were investigated by high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) techniques. The optical quality of the thick-GaN layer was also evaluated in detail by a photoluminescence (PL) measurement. It was found that the AlN buffer layer possesses high crystal quality and an atomically flat surface with a root-mean-square (rms) roughness of 0.16 nm. The screw-and edge-type dislocation densities of the thick-GaN layer were determined as 5.4 9 107 and 5.0 9 109 cm-2 by means of the mosaic crystal model, respectively. It was observed that the GaN layer has a smooth surface with an rms of 0.84 nm. Furthermore, the dark spot density of the GaN surface was estimated as 6.5 9 108 cm-2 over a scan area of 4 μm2. © Springer Science+Business Media, LLC 2010.
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    Large-area (> 50 cm × 50 cm), freestanding, flexible, optical membranes of Cd-free nanocrystal quantum dots
    (IEEE, 2012) Mutlugün, Evren; Hernandez Martinez, Pedro L.; Eroğlu, Cüneyt; Coşkun, Yasemin; Erdem, Talha; Sharma, Vijay K.; Ünal, Emre; Panda, S. K.; Hickey, S. G.; Gaponik, N.; Eychmuller, A.; Demir, Hilmi Volkan
    Colloidal semiconductor quantum dots (QDs) have been extensively explored for numerous applications ranging from optoelectronics to biotechnology. This strong demand for the colloidal QDs arises because of their favorable optical and electronic properties. From the application points of view, QDs typically need to be used in their solid form, as opposed to their as-synthesized dispersion form. For immobilization of QDs and homogeneity of their films, various polymers have been used to host QDs within solid media. However, the integration of QDs into a polymeric medium is commonly complex, which requires a high level of understanding to provide optical quality. © 2012 IEEE.