The Microstructural Study of Aluminum Nitride Thin Films: Epitaxy on the Two Orientations of Sapphire and Texturing on S
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for coating applications in aggressive environment with extreme thermal, chemical and physical conditions. Many of these important properties are related to the crystal structure of the films, their orientation with the substrate. Epitaxial single crystal films with low defects density (such as dislocations, stacking faults, grain boundaries) are required for possible future device applications. The most prospective substrates for AIN and GaN films growth are considered to be 6H-SiC and, in spite of large lattice mismatch, at-A12 03 (sapphire). The crystal quality of the film is determined by the growth conditions and substrate variables such as temperature, lattice misfit and interfacial chemical free energy [1]. The epitaxial growth of aluminum nitride has been already demonstrated in some papers ([2 - 8], for example). In this paper the details of epitaxial growth of AIN on different substrates as well as microstructural defects, interfaces in the AIN films are discussed. EXPERIMENT Aluminum nitride films of 300 nm thickness were grown in a horizontal, atmospheric pressure metalorganic chemical vapor deposition (MOCVD) reactor at a substrate temperature of 1050 0 C. Films were deposited on sapphire (0001) and (1012) and on Si (111) and (100) substrates. All the films were deposited under similar conditions to investigate crystalline quality as a function of processing and substrate parameters. Details of the MOCVD growth procedure are published elsewhere [2]. Samples for transmission electron microscopy (TEM) were prepared by a conventional planar and cross-sectional sample preparation technique with the Ar+ ion-milling at
387 Mat. Res. Soc. Symp. Proc. Vol. 395 01996 Materials Research Society
the final stage. TEM investigations have been carried out using a Topcon 002B electron microscope operated at 200 kV with point-to point resolution of 0.18 nm.
RESULTS AND DISCUSSION TEM investigations of the AIN films grown on the two different orientations of sapphire have shown that in both cases the films are epitaxial. Plan-view TEM images and corresponding selected area diffraction patterns (SADPs) for the AIN films on basal and rhombic r-plane of sapphire are shown in Figs. 1 a, b and 2 a, b respectively. Dislocations are visible in the image of AMN film grown on (0001) sapphire (Fig. a), and both dislocations and planar defects of high
Fig. 1 a) Plan-view TEM
micrograph of AIN thin film grown on (0001) sapphire showing the upper part of the film without the substrate; b) [0001] zone axis SADP of overlapping AIN and sapphire regions of the sample.
Fig. 2 a) Plan-view TEM micrograph of AIN thin film grown on
(10 T2) a-Al203;
b) corresponding SADP in [1120] AIN zone (arrows indicate the reflections of sapphire).
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concentration present in the film grown on (10T2) a-A1203 (Fig.2 a). Long arrows show the dislocations, short arrows - planar defects. The following epitaxial relationships were obtained from the SADPs: (0001)AIN II(0 001)sap with the 300 in-plane rotation - [01 T0]AI II[ T210]sap for AIN film
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