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

Abstract

The mechanical and electronic properties of two GaN crystals, wurtzite and zinc-blende GaN, under various hydrostatic pressures were investigated using first principles calculations. The results show that the lattice constants of the two GaN crystals calculated in this study are close to previous experimental results, and the two GaN crystals are stable under hydrostatic pressures up to 40 GPa. The pressure presents extremely similar trend effect on the volumes of unit cells and average Ga-N bond lengths of the two GaN crystals. The bulk modulus increases while the shear modulus decreases with the increase in pressure, resulting in the significant increase of the ratios of bulk moduli to shear moduli for the two GaN polycrystals. Different with the monotonic changes of bulk and shear moduli, the elastic moduli of the two GaN polycrystals may increase at first and then decrease with increasing pressure. The two GaN crystals are brittle materials at zero pressure, while they may exhibit ductile behaviour under high pressures. Moreover, the increase in pressure raises the elastic anisotropy of GaN crystals, and the anisotropy factors of the two GaN single crystals are quite different. Different with the obvious directional dependences of elastic modulus, shear modulus and Poisson’s ratio of the two GaN single crystals, there is no anisotropy for bulk modulus, especially for that of zinc-blende GaN. Furthermore, the band gaps of GaN crystals increase with increasing pressure, and zinc-blende GaN has a larger pressure coefficient. To further understand the pressure effect on the band gap, the band structure and density of states (DOSs) of GaN crystals were also analysed in this study.

Polarity reversal and strain modulation of Janus MoSSe/GaN polar semiconductor heterostructures

“…First of all, the lattice constants of the fully optimized monolayer Janus MoSSe and GaN unit cells were 3.25 and 3.22 Å, respectively, indicating a good agreement with the previous reports. 44,45 There was only a 0.9% lattice mismatch between Janus MoSSe and GaN, which was favorable for the heterostructure formation with negligible internal strain. In intrinsic MoSSe (GaN), the spontaneous polarization direction came from S (N) to Se (Ga) along the c -axis, respectively.…”

The Evolution of Manufacturing Technology for GaN Electronic Devices

“…On the other hand, the piezoelectric polarization effect (P PE ) is induced because of the stack of two lattice-mismatched wurtzite III-nitride materials. Polarization charges are formed due to the mismatch strain at the heterogeneous junction, as shown in Figure 2 [ 18 ].…”