Structural and optical properties of MOCVD InAlN epilayers

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0892-FF23-04.1

Structural and optical properties of MOCVD InAlN epilayers S. Hern´andez,1,2 K. Wang,1 D. Amabile,1 E. Nogales,1 D. Pastor,2 R. Cusc´o,2 L. Art´us,2 R.W. Martin,1 K.P. O’Donnell,1 I.M. Watson 3 and the RENiBEl Network.1 1 Department of Physics, University of Strathclyde, Glasgow, G4 0NG, Scotland, United Kingdom. 2 Institut Jaume Almera (CSIC), C. Llu´ıs Sol´ e i Sabar´ıs s.n., 08028 Barcelona, Spain. 3 Institute of Photonics, University of Strathclyde, Glasgow G4 0NW, United Kingdom. ABSTRACT We have studied the structural and optical properties of Inx Al1−x N alloys with compositions nearly lattice-matched to GaN. Scanning electron microscopy measurements reveals a good overall surface quality, with some defect structures distributed across the surface whose density increases with the InN concentration. On the other hand, Raman scattering experiments show three peaks in the frequency range between 500 and 900 cm −1 , which have been assigned to InN-like and AlN-like E2 modes and A1 (LO) mode of the Inx Al1−x N. These results agree with theoretical calculations previously reported where two-mode and one-mode behavior was predicted for the E2 and A1 (LO) modes, respectively. Photoluminescence and photoluminescence excitation allowed us to determine the emission and absorption energies of the In x Al1−x N epilayers. Both energies display a redshift as the InN fraction increases. We find a roughly linear increase of the Stokes shift with InN fraction, with Stokes shift values of ≈ 0.5 eV in the composition range close to the lattice-matched condition. INTRODUCTION In the last few years, nitride based materials have generated a growing interest due to their applications in optoelectronics. In particular, the Inx Al1−x N alloys can be used to cover the emission energy range from 0.6 eV to 6.2 eV by varying the InN fraction. Nearly lattice-matched conditions to GaN have been estimated to be in the 16–18% InN fraction range [1]. Alloy compositions in this range have attracted much interest since they can provide a large enough energy band gap to be used as insulating barriers in GaN-based electronic devices and, by the same token, they can be used to fabricate strain-free structures on free standing GaN [1] or as a facilitation layer in homoepitaxy [2]. The Inx Al1−x N alloys are unexplored compared to other nitrides mainly because the growth of these alloys is still difficult due to large differences in the chemical and physical properties of AlN and InN. The large difference in the growth temperature for AlN (TG ≈ 1100 o C) and InN (TG ≈ 600 o C) makes it difficult to incorporate of In atoms in the alloy and crystal quality worsens as the InN fraction increases. Raman scattering is a powerful technique for assessing the crystalline quality in a non-destructive way, and provides information about defects and strain fields in the structure. In contrast to the Inx Ga1−x N alloys, whose phonons show a one-mode behavior for both, the E2 and the A1 (LO) modes [3], the only Raman scattering study reported so fa

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