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Thickness dependence of electrical properties of c- and a-plane InN films
|Adebowale O. Ajagunna , Eleftherios Iliopoulos , George Tsiakatouras , Katerina Tsagaraki , Maria G. Androulidaki , Alexandros Georgakilas
Microelectronics Research Group, Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, and University of Crete, Physics Department (MRG), Heraklion 71110, Greece
The structural and electrical properties of c-plane and a-plane InN thin films, as a function of thickness, are investigated and compared in this work. All samples were grown under same conditions on c- and r-plane Al2O3 substrates with RF-MBE, using GaN buffer layers. The epitaxial growth of a-plane InN proceeded through the nucleation, growth and coalescence of 3D islands, resulting to increased surface roughness with increasing film thickness. Step-flow growth mode was maintained during the growth of c-plane films. The rms roughness determined for AFM 2 x 2 μm2 scans was 0.3 nm and 5.9 nm for 500 nm thick c- and a-plane films, respectively. However, the a-plane InN films did not exhibit any structural or surface morphology anisotropy, which is typical for a-plane GaN. The lowest to date XRD (11-20) rocking curve (RC) FWHM of 1440 arcsec is reported for a-plane InN. The sheet electron density (Ns) and mobility were determined by single magnetic field Hall-effect measurements and exhibited a similar dependence on thickness for both c- and a-plane InN films. The measured Ns exhibited a minimum of ~ 2 x 1014 cm-2 for 100 nm thickness. It increased linearly with increasing thickness above 100 nm but it also increased with decreasing thickness below 100 nm. The analysis of the Hall-effect measurements, by considering the contribution of two conducting layers, indicates a similar accumulation of low mobility electrons with Ns > 1014 cm-2 at the films’ surface/interfacial region for both the a- and c-plane InN films. The actual electron mobility of the InN bulk increases with thickness for both orientations as a result of improving structural quality.
Acknowledgement: Work supported under MRTN-CT-2004-005583 (PARSEM) and the Greek State Scholarships Foundation (IKY).
Presentation: Poster at E-MRS Fall Meeting 2009, Symposium A, by Adebowale O. Ajagunna
See On-line Journal of E-MRS Fall Meeting 2009
Submitted: 2009-05-25 21:44 Revised: 2009-07-27 12:17