Low Temperature Epitaxial Growth of AlN & GaN Thin Films by the Method of Ion Beam Assisted Deposition
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313 Mat. Res. Soc. Symp. Proc. Vol. 395 01996 Materials Research Society
tried by controlling the energy and flux of ion beam. In addition, the interface structure and crystallographical properties of A1N and GaN epitaxial layers grown on Si and sapphire substrates were investigated by XRD (X-Ray Diffraction) and TEM (Transmission Electron Microscopy) analysis. EXPERIMENTS Figure 1 shows a schematic diagram of the experimental apparatus. Metal vapor was supplied by magnetron sputtering or thermal evaporation through the lab-made effusion cell. In case of Al, both methods were employed. Ga flux was supplied solely by thermal evaporation due to it's low melting point(271C) 6 . The flux of metal vapor was precisely measured through a quartz oscillator and controlled in a range of 3 X 104 - 8 X 10 atoms/cm -sec. Reactive nitrogen ions were provided by a Kaufmnan-type ion source with a beam diameter of 3 cm. The beam energy was controlled under the value of 100 eV and the flux of ions varied over the range of 5X 10"' - 3 X 10" ions/cm2- sec., which was measured by ball type ion probe. The reaction chamber was evacuated with a turbomolecular pump down to a base pressure of 2 x 10-7 Torr. The operating pressure for thermal evaporation and sputtering were maintained at 2> 10-4 and 6 X 10_ Torr, respectively. A substrate was generally pretreated using acetone, deionized water, and alcohol and then pre-sputtered with Ar ions. In case of the Si substrate, the deoxidazing process with 10 % HF solution was included. The composition and bonding characteristics of films were investigated by X-ray photoelectron spectroscopy and Auger electron spectroscopy. To characterize the epitaxial structure of AIN and GaN films, high resolution TEM and XRD analyses including grazing-incidence X-ray diffraction (GID) 78' were carried out. For the analysis of GID, a rotating anode-type X-ray generator with 10 KW and 4-circle goniometer were used. RESULTS AND DISCUSSION The AIN films synthesized by ion-assisted deposition show various crystallographical properties from amorphous to single-crystalline epitaxial structure according to the ion beam conditions and substrate temperatures. The optimum conditions of ion beam energy and arrival ratio of nitrogen to Al atoms for epitaxi.1l growth of AIN were found to .e 50 eV and 1.5 (current density of 0.25 mA - cm-, deposition rate of 1.2 A -s-) respectively. Figure 2 shows high resolution cross-sectional TEM micrograph and
AIN 2.50A 01*12
0002
00112
o
amorphous
1
0 Si 1119
0
0110
* A1N
0
Si
2nm
*220 0
* 0002
Figure 2. (a) Cross-sectional view high-resolution TEM micrograph and (b) diffraction patterns for AIN epitaxial layer grown on Si(l 11) substrate. 314
diffraction patterns of AIN epitaxial layer grown on Si(lll) plane at a temperature of 450 *C. As shown in the micrograph, the AIN film has a well-developed epitaxial structure only containing small crystallographical defects such as an anti-phase domain boundary and a very thin amorphous layer of about 30 A thickness at inte
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