Aluminum Nitride (AlN) is an important material for ultraviolet emitters and detectors. AlN has wide band gap (6.2 eV), high thermal conductivity (3.2 W cm^-1 K^-1), high breakdown voltage (12 MV cm^-1) and excellent lattice match with Gallium Nitride (GaN). However, growth of AlN always has many challenges due to the lack of native (AlN) substrates, high sticking coefficient of Aluminum (Al) that restricts the migration of Al atoms and unwanted parasitic reactions between Al and ammonia (NH3). Sapphire (Al₂O₃) and Silicon carbide (SiC) substrates have been used to grow AlN heteroepitaxially. Among these substrates c-plane sapphire is often used for AlN growth due to its affordability, despite the large lattice mismatch and large difference in thermal expansion.

In the present investigation, AlN epilayers were grown on 2” sapphire c-plane substrate by metal organic chemical vapor deposition system. High purity (7N) trimethyl aluminum and ammonia were used as the precursors for aluminum and nitrogen respectively. Hydrogen was used as a carrier gas. The effect of AlN nucleation layer (NL) deposition temperature on the surface morphology and structural quality of AlN epilayers has been studied using atomic force microscopy (AFM), high resolution X-ray diffraction and Raman spectroscopy. Figure 1(a) and 1(b) show the AFM images and X-ray rocking curve FWHM of AlN epilayers grown using the NLs deposited in the temperature range of 850 -1250 °C. It has been found that coalescence and size of nucleation island (NI) plays the vital role in determining the quality of AlN layer. The uniform size NIs of 80-100 nm range formed at a nucleation temperature of 950 °C tend to coalesce for a two dimensional specular AlN layer and resulted in the good crystalline quality.

Figure 1 (a) AlN AFM images in the scan area of 10μm×10μm. (b) X-ray rocking curve FWHM of (002) and (102) reflections of AlN layers grown using the NLs in the  temperature range of 850 - 1250 °C

1. PRESENTATION: Effect of nucleation islands coalescence on determining the quality of AlN layers grown by MOCVD, Zip archive data, at least v2.0 to extract, 0.1MB

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