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Structural Investigation of GaN Nanograins Nucleated on a Sapphire Substrate
Chinkyo Kim,이현재,Meoungwhan Cho,Seogwoo Lee 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6
The structural characteristics of GaN layers nucleated by Ga-assisted nitridation on an Al2O3 (0001) substrate were investigated by using atomic force microscopy (AFM) and synchrotron X-ray scattering. The nitridation was carried out by exposing an sapphire substrate in a quartz reactor to NH3 and Ga vapor carried by N2. The AFM images of the surface morphology for the samples showed that the mean height and width of the GaN grains formed on the substrate had a strong dependence on the growth temperature. Particularly, for the sample grown at 600 C with a mean width of 50 ± 5 nm, the specular reflectivity obtained through the (002) Bragg peak revealed that the nucleated GaN layers consisted of strained and fully relaxed layers. A detailed analysis of the X-ray scattering data showed that the 4.5 ± 0.3-nm-thick GaN layers were compressively strained and highly coherent with the substrate, but that approximately 17-nm-thick fully relaxed layers were relatively disordered in orientation. From the combined results of AFM and X-ray rocking curve measurements, we could conclude that fully relaxed nanograins were grown on top of highly strained GaN layers, not directly on top of the sapphire substrate.
이현재,하준석,Hyo-Jong Lee,Seogwoo Lee,Meoungwhan Cho,T. Yao,김진교,홍순구,장지호 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.6
The effect of refined nitridation of sapphire substrates on the characteristics of GaN layers subsequently grown by using hydride vapor phase epitaxy (HVPE) was investigated. When low-temperature-grown (LTG) GaN buffer layers were grown on nitridated sapphire substrates in a refined way, the structural characteristics of the LTG GaN layers were found to be transferred to the subsequent high-temperature-grown (HTG) GaN layers. This result implies that well-controlled nitridation of sapphire substrates plays an important role and that the quality of the HTG GaN layer can be rationally controlled by monitoring the characteristics of a LTG GaN buffer layer when it is grown on a properly nitridated sapphire substrate.