First Principles Calculations of Nb1-xGaxM (M = N, P and As)
S. Ramesha, b* and S. Marutheeswaranb aDepartment
of Chemistry, Saveetha School of Engineering, Saveetha University, Chennai-602105. bDepartment of Chemistry, Pondicherry University, Pondicherry 605014 * rameshsiva_chem@yahoo.com
Abstract The electronic structural calculations of NbxGa1-xM (M = N, P and As) were studied by first principles calculations based on spin-polarized density functional theory using the local spin density approximation, as implemented in the fullpotential linearized augmented plane wave method. We examine energy band structures, densities of states, and anticipate the properties of these promising systems for applications in spin electronic devices.
Results and Discussions The Structure The structural optimization is first performed for GaN. The optimized lattice parameters are 3626 Å and α, β and γ = 90 with FM-3M space group. The unit cell volume is 380.92 Å. After Ga atom substituted by Nb and N with P or As substitution has no lattice distortion is observed in the supercell.
Introduction 100
The III–V semiconductors have been the focus of a major research effort in the recent In te n s ity
Nb1-xGaxM (M = N, P and As)
years. The trivalent Ga is the most stable state of 3d impurities in III–V semiconductors.
AB= Ga, Nb M= N, P, As
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The GaN, GaP and GaAs alloys are having more interest for their capability to produce light in a infrared to ultraviolet wavelength region. The III–V compound semiconductors provide the materials basis for a number of well-established commercial technologies, as well as new cutting-edge classes of electronic and optoelectronic devices. Just a few examples include high-electron-mobility and heterostructure bipolar transistors, diode lasers, light-emitting
diodes, photodetectors, electro-optic
modulators, and frequency-mixing components. In consequence, theoretical investigation on the inorganic crystal is the key for finding the good candidates for fabricating application. In this report, we investigated the electronic structure of Nb doped GaN, GaP and GaAs.
Computational Methods The structural optimizations and electronic structure calculations are performed using Accelrys package with CASTEP code19, which is based on density functional theory (DFT) and plane-wave pseudo potential method.
FIGURE. Schematic primitive face centered unit cell crystal structures of NbxGa1-xM (M = N, P and As)
FIGURE. The simulated powder X-ray diffraction pattern of NbxGa1-xM (M = N, P and As)
Electronic structure The density of states in the band gap generally arises from surface atoms, for which the surroundings are unlike from the bulk. We can identify the peak arises and analyze its orbital character by partial density of states. The band structure and density of states arises mainly consist of Ga and Nb hybridized bond mixed with M (M=N, P and As) surface states. The Band structure and density of states of Nb0.5Ga0.5N and Nb0.5Ga0.5As shows metallic in nature. When the P introduced in the system the Nb0.5Ga0.5P in shows slight changes in the bond structure. After introducing the P into the Nb-Ga system the band structure slightly opened and the value of band gap is estimated to 0.338 eV. In the system, p and d orbital electrons are considerably involved in the fermi level. Therefore, the atom change induces the transformation from a metallic character to a semiconducting character.
The generalized gradient approximation (GGA) 20 in the Perdew-Burke-Ernzerhof (PBE)21 form was adopted in the calculations. The cutoff energy for the plane wave basis was set to be 310 eV. All geometry optimizations and electronic structure calculations such as band structure and density of states were performed using periodic boundary conditions, and Brillouin zone integrations are performed using a 1x1x1 Monkhorst-Pack (MP) grid22. Criterion of convergence for the residual forces is set to be less than 0.01 eV/Å and the change of total energy less than 5x10-6eV.
Ga0.5Nb0.5N
Ga0.5Nb0.5P
Ga0.5Nb0.5As
FIGURE. Band structure and density of states of NbxGa1-xM (M = N, P and As)
Conclusion R EF ERENCES 1. I. Vurgaftman, J. R. Meyer, and L. R. R. Mohan, J. Appl. Phys. 89, 5815-5875 (2001). 2. M. Ishikawa, T. Nakayama, J. Microelectronics. 40 824-826 (2009). 3. Y. Li, X. Pengshou, P. Haibin X. Faqiang, J. Elect. Spectra. Related Phenomena. 144, 597–600 (2005)
Acknowledgements The author thanks to Dr. M. M. Balakrishnarajan, Associate professor, Pondicherry University, Pondicherry, India. For the Materials Studio software package.
The electronic structural calculations of NbxGa1-xM (M = N, P and As) were studied by first principles calculations. Substitution no effect on lattice distortion in supercell. The P in Nb-Ga system has slightly opened band structure slightly. In the system, p and d orbital electrons are considerably involved in the fermi level.