{"references": ["Sung-Nam Lee, H.S. Paek, H. Kim, K.K. Kim, Y.H. Cho, T. Jang, Y-Park,\n\"Growth and characterization of the AlInGaN quaternary protective layer\nto suppress the thermal damage of InGaN multiple quantum wells,\"\nJournal of Crystal Growth, vol. 310, pp. 3881-3883, 2008.", "D.B. Li, X. Dong, J. Huang, X. Liu, Z. Xu, and Z. Wang, \"Growth and\nphotoluminescence of InAlGaN films,\" Phys. Stat. Solidi C, vol. 0, No.7,\npp. 2001-2005, 2003.", "D.B. Li, X. Dong, J. Huang, X. Liu, Z. Xu, Z. Zhang, Z. Wang, \"Alloy\ncompositional fluctuation in InAlGaN epitaxial films,\" Appl. Phys. A, vol\n80, pp. 649-652, 2005.", "B.Z. Wang, X. L. Wang, X.Y. Wang, X.H. Wang, L.C. Guo, H.L. Xiao,\nJ.X. Wang, H.X. Liu, Y.P. Zeng, J.M. Li, Z.G. Wang, \"Growth and\nstructural properties of InAlGaN quaternary alloys on sapphire substrates\nby RF-MBE,- IEEE, 2006.", "J. Li, K.B. Nam, K.H. Kim, J.Y. Lin, and H.X. Jiang, \"Growth and optical\nproperties of InxAlyGa1-x-yN quaternary alloys,\" Appl. Phys. Lett, vol. 78,\nNo.1, pp. 61-63, 2001.", "E. Dimakis, A. Georgakilas, G. Kittler, M. Androulidaki, K. Tsagaraki,\nE.B. Amalric D. Jalabert, and N.T. Pelekanos, \"High quality quaternary\nalloys grown by plasma-assisted molecular beam epitaxy,\" IEEE, 2002.", "M. Androulidaki, N.T. Pelekanos, K. Tsagaraki, E.Dimakis, E. Ilipoulus,\nA. Adikimenakis, E.B. Amalric, D. Jalabert, and A. Georgakilas, \"Energy\ngaps and bowing parameters of InAlGaN ternary and quaternary alloys,\"\nPhys. Stat. Sol. C, vol. 3, No. 6, pp. 1866-1869, 2006.", "J. Han, J.J.F, G.A. Petersen, S.M. Meyers, M.H. Crawford, and M.A.\nBanas, \"Metal-organic vapor-phase epitaxial growth and characterization\nof quaternary AlGaInN,\" Jpn. J. Appl. Phys., vol. 39, pp. 2372-2375,\n2000.", "E. Monroy, N.G, F. Enjalbert, F. Fossard, D. Jalabert, and E.B-Amalric,\n\"Molecular-beam epitaxial growth and characterization of quaternary III-nitride compounds,\" J. Appl.Phys., vol. 94, No. 5, pp. 3121-3127,\n2003.\n[10] S.W. Feng, Y.C. Cheng, Y.Y. Chung,C.C. Yang, K.J. Ma, C.C. Yan, C.\nHsu, J.Y. Lin and H.X. Jiang, \"Strong green luminescence in quaternary\nInAlGaN thin films,\" Appl. Phys. Lett, vol. 82, No. 9, pp. 1377-1379,\n2003."]}

Quaternary InxAlyGa1-x-yN semiconductors have attracted much research interest because the use of this quaternary offer the great flexibility in tailoring their band gap profile while maintaining their lattice-matching and structural integrity. The structural and optical properties of InxAlyGa1-x-yN alloys grown by molecular beam epitaxy (MBE) is presented. The structural quality of InxAlyGa1-x-yN layers was characterized using high-resolution X-ray diffraction (HRXRD). The results confirm that the InxAlyGa1-x-yN films had wurtzite structure and without phase separation. As the In composition increases, the Bragg angle of the (0002) InxAlyGa1-x-yN peak gradually decreases, indicating the increase in the lattice constant c of the alloys. FWHM of (0002) InxAlyGa1-x-yN decreases with increasing In composition from 0 to 0.04, that could indicate the decrease of quality of the samples due to point defects leading to non-uniformity of the epilayers. UV-VIS spectroscopy have been used to study the energy band gap of InxAlyGa1-x-yN. As the indium (In) compositions increases, the energy band gap decreases. However, for InxAlyGa1-x-yN with In composition of 0.1, the band gap shows a sudden increase in energy. This is probably due to local alloy compositional fluctuations in the epilayer. The bowing parameter which appears also to be very sensitive on In content is investigated and obtained b = 50.08 for quaternary InxAlyGa1-x-yN alloys. From photoluminescence (PL) measurement, green luminescence (GL) appears at PL spectrum of InxAlyGa1-x-yN, emitted for all x at ~530 nm and it become more pronounced as the In composition (x) increased, which is believed cause by gallium vacancies and related to isolated native defects.