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The structural and optical properties of an In x Ga 1Àx N/GaN multi-quantum well (MQW) were investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE) and photoluminescence (PL). The MQW structure was grown on c-plane (0 0 0 1)-faced sapphire substrates in a low pressure metalorganic chemical vapor deposition (MOCVD) reactor. The room temperature photoluminescence spectrum exhibited a blue emission at 2.84 eV and a much weaker and broader yellow emission band with a maximum at about 2.30 eV. In addition, the optical gaps and the In concentration of the structure were estimated by direct interpretation of the pseudo-dielectric function spectrum. It was found that the crystal quality of the InGaN epilayer is strongly related with the Si doped GaN layer grown at a high temperature of 1090°C. The experimental results show that the growth MQW on the high-temperature (HT) GaN buffer layer on the GaN nucleation layer (NL) can be designated as a method that provides a high performance InGaN blue light-emitting diode (LED) structure.

The important structural characteristics of hexagonal GaN in an InGaN/GaN multi quantum well, which was aimed to make a light emitted diode and was grown by metalorganic chemical vapor deposition on c-plain sapphire, are determined by using nondestructive high-resolution X-ray diffraction in detail. The distorted GaN layers were described as mosaic crystals characterized by vertical and lateral coherence lengths, a mean tilt, twist, screw and edge type threading dislocation densities. The rocking curves of symmetric (00.l) reflections were used to determine the tilt angle, while the twist angle was an extrapolated grown ω-scan for an asymmetric (hk.l) Bragg reflection with an h or k nonzero. Moreover, it is an important result that the mosaic structure was analyzed from a different (10.l) crystal direction that was the angular inclined plane to the z-axis. The mosaic structure parameters were obtained in an approximately defined ratio depending on the inclination or polar angle of the sample. © 2009 Springer Science+Business Media, LLC

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Bu çalışmada binalarda ısıtma için kullanılan kalorifer borularının yalıtımlı ve yalıtımsız durumları için iki ayrı yapay sinir ağı (YSA) modeli ve bina duvarlarının yalıtımlı ve yalıtımsız durumları için iki ayrı YSA modeli olmak üzere toplamda 4 ayrı model kullanılmıştır. Bu durumlar için tasarlanan YSA modellerinde 3 katmanlı ileri beslemeli ve geri yayılımlı bir model şekli tercih edilmiştir. Gizli katmanda sigmoid transfer fonksiyonu, çıkış katmanında ise doğrusal transfer fonksiyonu kullanılmıştır. YSA ağ topolojisi olarak geri yayılımlı YSA topolojisi tercih edilmiş ve veriler normalize edilerek ağa sunulmuştur. Ağdan elde edilen sıcaklık değerleri gerçekte ölçülen sıcaklık değerleri ile mukayese edilmiş ve sonuçların birbirlerine çok yakın ve yeterli hassasiyette olduğu görülmüştür. Bu şekilde 4 farklı iç model için YSA metodunun kullanımı, modellerin açıklayıcılık ve tahmin etme gücünü artırmıştır.