Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals

Abstract

For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and <111>, respectively, while they are in the orientations <111> and <100> for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson’s ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson’s ratios at planes (100) and (111) are isotropic, while the Poisson’s ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol−1 K−1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap. Densities of states in the orbital hybridization between Ga and N atoms of wurtzite GaN are much higher, indicating more electrons participate in forming Ga-N ionic bonds in the wurtzite GaN.

The Mechanical Properties and Elastic Anisotropies of Cubic Ni3Al from First Principles Calculations

“…H v = 0.92(B/G) 1.3137 G 0.708 (10) It is reported that materials with Vickers hardness larger than 40 GPa can be classified as superhard materials [45]. For the calculated value of H v of Ni 3 Al is 54.004 GPa, it is supposed that N 3 Al and N 3 Al-based materials have an excellent ability to resist being scratched or dented.…”

“…For example, the bulk modulus of L1 2 -ordered Ni 3 Al explored by Pearson et al is 229.2 GPa [8] while the value obtained by Yasuda et al is 171.0 GPa [9]. In order to break through the limitation derived from experimental methods, in recent years, first principles calculations have been successfully conducted to calculate the elastic properties of alloys and intermetallics [10][11][12][13][14]. Based on first principles, Wen et al [1] calculated the bulk modulus and Young's modulus of Ni 3 Al, as well as the effects of pressure on the mechanical properties.…”

Influence of Pressure on the Mechanical and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals

“…Generally, GGA overestimates the lattice parameters while LDA underestimates them, and the lattice parameters obtained from LDA are much closer to experimental data. Our previous work revealed that, compared to GGA, LDA is more accurate in predicting elastic properties [38]. Therefore, LDA was applied in the following study.…”

Упругость И Неупругость Объемных Кристаллов Нитрида Галлия

“…Нитрид галлия (GaN) в настоящее время широко применяется для производства устройств силовой и оптоэлектроники и вызывает огромный интерес у исследователей. Несмотря на большой объем накопленных сведений о свойствах GaN [1,2], все еще остаются недостаточно изученными его упругие и пластические свойства. Это связано с тем, что для достоверности таких исследований требуются достаточно крупные образцы, которые в силу ряда причин были ранее недоступны.…”