Infrared and Ultraviolet Raman Spectra of AlN Thin Films Grown on Si(111)
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Infrared and Ultraviolet Raman Spectra of AlN Thin Films Grown on Si(111) V. M. Naik, D. Haddad1, Y. V. Danylyuk2, R. Naik1, G. W. Auner2, L. Rimai2, W. H. Weber3 and D. Uy3 Department of Natural Sciences, University of Michigan-Dearborn, Dearborn, MI 1 Dept. of Physics, Wayne State University, Detroit, MI 2 Dept. of Electrical and Computer Engineering, Wayne State University, Detroit, MI 3 Scientific Research Laboratory, Ford Motor Company, Dearborn, MI
ABSTRACT Infrared (IR) spectroscopy and ultraviolet near-resonance enhanced Raman scattering have been used as alternative techniques to characterize the AlN films grown on Si(111). Epitaxial AlN films have been prepared by plasma source molecular beam epitaxy (PSMBE) at growth temperatures of 400 and 650 oC. The AlN/Si grown at 650 °C shows distinct reflection highenergy electron diffraction (RHEED) patterns with the following epitaxial relations: AlN [0001] || Si [111], and AlN < 01 1 0 > || Si < 11 2 > . This is in sharp contrast with the observation of a spotty RHEED pattern for AlN/Si sample grown at 400 °C, which appeared the same when viewed along any Si azimuth. Furthermore, the X-ray diffraction (XRD) rocking curve width showed a significant reduction from 5.7o for sample grown at 400 oC to 2o for the one grown at 650 °C. The observation of Raman active A1(LO) and E2, and IR active E1(TO) zone center phonons, in both the films, is in accordance with the c-axis orientation of the films. However, the observed phonon mode frequencies and line widths indicate that the AlN samples grown at 400 o C have less strain but more disorder compared to the ones grown at 650 °C in agreement with RHEED and XRD data.
INTRODUCTION AlN films have been grown on silicon substrates using different growth techniques such as chemical vapor deposition (CVD) [1,2], reactive sputtering [3,4], plasma assisted molecular beam epitaxy [5,6], and pulsed laser deposition [7]. Good epitaxial AlN films have been grown with substrate temperatures maintained at > 800 οC. However, for developing new hybridized devices with Si, it is important to grow AlN films on Si substrates at low temperatures to avoid thermal damage to Si devices. Therefore, an investigation of the microstructure of the low temperature grown AlN films on Si substrates is of interest. Recently, we have studied the microstructure of AlN thin films grown on Si(111) by PSMBE deposition using cross-sectional transmission electron microscopy (TEM) studies [8]. The TEM studies showed that the AlN film grown at 400 oC forms an initial amorphous region (~50 Å) at the interface, followed by a c-axis oriented columnar grains (~ 200 Å) with slightly different tilts and twists. On the other hand, the AlN film grown at 600 oC showed a significantly reduced amorphous region near the AlN/Si interface promoting an epitaxial growth of AlN[0001]||Si[111] with AlN< 01 1 0 >||Si. However, both the films showed numerous I6.7.1
defects such as stacking faults, dislocations and grain boundaries. This is consistent with the observed large XRD r
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