Bandgap Energies of Cubic Al x Ga 1-x N y As 1-y Calculated by Means of the Dielectric Method
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MRS Advances © 2016 Materials Research Society DOI: 10.1557/adv.2016.107
Bandgap Energies of Cubic AlxGa1−xNyAs1−y Calculated by Means of the Dielectric Method Hiroyuki Naoi1 and Takeyuki Matsumoto1 1 Department of Electrical and Computer Engineering, National Institute of Technology, Wakayama College, 77 Nojima, Nada-Cho, Gobo, Wakayama 644−0023, Japan ABSTRACT Bandgap energies of the group III-V quaternary alloy semiconductor, cubic AlxGa1−xNyAs1−y, were calculated by means of the dielectric method. While only GaN and GaAs are considered to be direct transition type among the four constituent binary compounds of this quaternary alloy system, the calculation results show that the bandgap energy range covered in the direct transition regime of this alloy system was further extended to the higher energy side of GaN as well as to the lower energy sides of GaAs. The extension to the higher energy side was attributed to the larger direct bandgap of AlN. On the other hand, the extension to the lower energy side was caused by the large bowing in the bandgap energy between group III nitrides and arsenides. Calculations under lattice matching to Si and GaAs are also presented. INTRODUCTION Group III-V quaternary alloy semiconductors are attractive materials due to their capability of covering a relatively wide wavelength range (at least between those values of the four constituent binary compounds). These alloy systems are also attractive due to their capability of changing their bandgap energies even under a fixed lattice constant [1]. The latter furthermore opens a possibility of fabricating high-quality layers of these alloys lattice-matched to an underlying layer with a low density of crystal defects. Among a number of group III-V quaternary alloys, this study is focused on cubic AlxGa1−xNyAs1−y in terms of not only a wide range of its usable light wavelengths spanning from the ultraviolet to infrared regions but also its lattice matching ability to both Si and GaAs substrates. Furthermore, this alloy system can be grown in the cubic phase over the entire composition range, since each of the four constituent binaries of this alloy system can be grown in the cubic phase [2, 3]. The large difference in the atomic radius between N and As should cause large energy gap bowing. This may lower the minimum bandgap energy value of this alloy system to below the bandgap energies of the any constituent binary compounds [4, 5]. Thus the bandgap energy range of this alloy system may extend even to the lower energy side of GaAs, which has the lowest bandgap energy value among the four constituent binary compounds. While cubic AlxGa1−xNyAs1−y is an attractive alloy system, neither experimental nor theoretical studies on bandgap energies of this alloy system have been reported to the best of the authors’ knowledge. In this study, direct and indirect bandgap energies of cubic AlxGa1−xNyAs1−y were calculated by means of the dielectric method [6-10]. The transition types and the energy range in the direct transition regime of this alloy
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