Characterization of an AlN buffer layer and a thick-GaN layer grown on sapphire substrate by MOCVD
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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 × 107 and 5.0 × 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 × 108 cm−2 over a scan area of 4 μm2.
KeywordsSapphire Substrate Thread Dislocation Density Yellow Luminescence Terrace Width Blue Luminescence Band
This work was supported by the Turkish State Planning Organization (Project No. 2001K120590). This work is also supported by TUBITAK under Project Nos. 105E066, 105A005, 106E198, and 106A017. One of the authors (E. O.) also acknowledges partial support from the Turkish Academy of Sciences.
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