The influence of TMAl preflow to the AlN buffer layer and GaN thin film was studied by Optical Microscope, Atomic Force Microscope, X-ray diffraction and Transmission Electron Microscope. Different duration of TMAl preflow lead to substantially differences of the AlN buffer layer and GaN film properties in terms of surface morphology and crystal quality. It was found without TMAl preflow the crystal quality of AlN buffer layer and GaN deteriorated due to the formation of amorphous interlayer between Si and AlN. Meltback etching and cracks was observed on the surface of GaN grown on AlN without TMAl preflow. However, overlong duration of TMAl preflow degraded the properties of AlN buffer layer and the subsequent GaN layer. GaN grown with longer TMAl preflow suffer of poor crystal quality, high density cracks and rough surface morphology. With the optimum duration of TMAl preflow, crystal quality and surface roughness of GaN can be improved.
Keywords-GaN on Si(111); AlN buffer layer; TMAl preflow; MOCVDI.
We discuss the contribution of OZI-suppressed diagrams to the hyperfine splitting of charmonium in lattice QCD. We study valence quark mass regions from strange to charm quark masses. No contribution of the disconnected diagram is seen in the vector meson channel. In the pseudo-scalar channel and for valence quark masses around the strange quark, the disconnected contribution induces a considerable increase of the meson mass. This contribution quickly decreases as the quark mass increases. For charmonium the effect is very small although a decrease of the pseudoscalar mass induced by the disconnected contribution cannot be ruled out.
We present the effect of multiple AlN buffer layers on characterizations of GaN film quality, which includes a thin high-low-high- temperature (HLHT) AlN buffer layers. The study is based on two different thicknesses of the GaN films on the buffers and found that the HLHT AlN buffer layers could significantly affect on the GaN films qualities. The buffer plays a very important role for the growth of GaN film on Si (111) substrate. The GaN film with an uniformly faceted surface and very high quality has been obtained at the optimized multiple HLHT AlN buffer layers of 50-nm-thick at 1010-800-1010 0C.
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