Epitaxial Growth of Aluminum Nitride on Sapphire and Silicon
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demonstrated with a dislocation density of about 2*10 0cm . The films on Si(lll) and Si(100) substrates were textured with the c-axis of AIN being perpendicular to the substrate surface. INTRODUCTION Aluminum nitride is a direct band gap semiconductor with a band gap energy of 6.2eV and is a highly attractive material for optoelectronic devices operating in the ultraviolet spectral region. AIN is also a material with good resistance to oxidation and high thermal conductivity. These properties make AIN suitable as coatings for application in aggressive environment with extreme thermal, chemical and physical conditions. Many of these properties are related to the crystal structure of the films, their orientation and epitaxial relations with the substrate. That is why the epitaxial growth of metal nitride thin films is currently under intensive investigation. The epitaxial growth of aluminum nitride has been already demonstrated in some papers ([I - 5], for example). All commonly used substrates have rather large lattice mismatch with aluminum nitride (except SiC), and it is very important to know the interfacial structure which has not been properly characterized in case of a-A1203 substrate so far. Here we present a structural investigation of high-quality A1N thin films grown by MOCVD on sapphire and silicon as well as a study of the A1N/(0001)cz-AI203 interface. EXPERIMENTAL Aluminum nitride films of 0.3 gtm thickness were grown in a horizontal, atmospheric pressure metal-organic chemical vapor deposition (MOCVD) 0 reactor at a substrate temperature of 1050 C. Films were deposited on 1023
Mat. Res. Soc. Symp. Proc. Vol. 358 01995 Materials Research Society
a-A1203 (0001) and (10T2), Si (111), Si (100) substrates. Experimental deposition parameters were kept at the same level for all the four cases to study the influence of the substrate on the crystallinity and texturing of the film. Details of the MOCVD growth procedure are published in [2]. Samples for transmission electron microscopy were prepared by a conventional planar and cross-sectional sample preparation technique with low-angle ion milling at the final stages of thinning. TEM investigations have been carried out using a "Topcon" 002B electron microscope operated at 200 kV. RESULTS AND DISCUSSION
The AIN films were characterized by x-ray diffraction techniques [2]. The 0-20 scans showed that the AIN films deposited on (0001) a-A1203 were single-crystal with the (0001)AIN face parallel to the (0001) face of a-A1203. The FWHM of the x-ray rocking curve of the (0002) AIN peak on the (0001) aA1203 was 97.2 arcsec. The films on (IlI)Si substrates were found to be perfectly textured with the c-axis normal to the substrate surface with a small fraction of other orientations. However, the AIN films grown on (10T2) az-A1203 substrates showed [1120] orientation. The rocking curve of the (I 120) peak of AIN on the (10T2) orientation of sapphire was found to show FWHM of about 3200 arcsec. TEM investigations of the AIN film showed a variety of microstructural
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