Abstract
Aluminum Nitrides (AlN) thin films have been deposited on glass substrates using DC-magnetron sputtering technique for different back pressure. The piezoelectric and related properties of highly c-axis oriented AlN films fabricated by dc planar magnetron sputtering have been calculated. Experimental results show that highly c-axis oriented AlN films can be fabricated by dc planar magnetron sputtering. X-ray powder diffraction (XRD) technique shows that AlN thin films exhibit a hexagonal structure. Vienna Ab initio Simulation Package (VASP) within the framework of density functional theory (DFT) and generalized gradient approximation (GGA) was used to investigate the structural and electronic properties of hexagonal AlN structures. The experimental lattice parameters of the as prepared thin films are found to be in good agreement with ab-initio calculated parameters. UV–Vis spectrophotometer measurements are performed to investigate the optical properties of AlN thin films. We found that the refractive index of AlN thin films exhibits values ranging between 2.1 and 2.2. Furthermore, the elastic, piezoelectric and dielectric tensors of AlN crystal are calculated using VASP. The dynamical Born effective charge tensor is reported for all atoms in the unit cell of AlN. The value of the principle component of electronic contribution to the static dielectric tensor of AlN is found to be ≈ 4.68 that is in good agreement with the experimental static dielectric constant. In addition, clamped-ion piezoelectric tensor is calculated. The diagonal components of the piezoelectric tensor are found to be e_33=1.784 C/m^2 and e_31=-0.8 C/m^2. The large values of the piezoelectric coefficients show that polar AlN crystal exhibits a strong microwave piezoelectric effect. Furthermore, the components of the elastic moduli tensor are calculated. The extraordinary electronic, optical, piezoelectric and elastic properties make AlN thin films potential candidates for several opto-electronic, elastic, dielectric and piezoelectric applications.
Highlights
Aluminum nitride (AlN), in its ground state, crystallizes in a hexagonal close-packed wurtzite structure [1]
We report our results on highly textured aluminum nitride (AlN) thin films deposited on glass substrates, oriented along the c-axis, using DC-magnetron sputtering technique for different values of back pressure
We investigated the structural properties of AlN thin films computationally and experimentally
Summary
Aluminum nitride (AlN), in its ground state, crystallizes in a hexagonal close-packed wurtzite structure [1]. AlN thin films have attracted much interest owing to the fact that they have unique features and a wide range of technological applications in various fields such as pressure sensors [2], energy harvesters [3], surface acoustic wave devices [4], and light-emitting devices [5] due to their noticeable large piezoelectric coefficients, d31 and d33 [6, 7], good electrical isolation [8, 9], wide band gap [10, 11], and high acoustic wave velocity [12, 13]. AlN exhibits extraordinary optical properties such as large optical band gap energy, ∼6.2 eV, and large refractive index, ∼2.0. It has interesting electronic, thermal, dielectric, and electronic properties such as extremely high electric resistivity (1014 ), high thermal conductivity (320 W/m K), large stiffness [14], and high dielectric constant. The abovementioned interesting properties attracted the attention of several research groups to explore AlN for the fabrication of piezoelectric and optoelectronic devices
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