Novel III-V Nitride Polymorphs in the P42/mnm and Pbca Phases

Abstract

In this work, the elastic anisotropy, mechanical stability, and electronic properties for P42/mnm XN (XN = BN, AlN, GaN, and InN) and Pbca XN are researched based on density functional theory. Here, the XN in the P42/mnm and Pbca phases have a mechanic stability and dynamic stability. Compared with the Pnma phase and Pm-3n phase, the P42/mnm and Pbca phases have greater values of bulk modulus and shear modulus. The ratio of the bulk modulus (B), shear modulus (G), and Poisson's ratio (v) of XN in the P42/mnm and Pbca phases are smaller than those for Pnma XN and Pm-3n XN, and larger than those for c-XN, indicating that Pnma XN and Pm-3n XN are more ductile than P42/mnm XN and Pbca XN, and that c-XN is more brittle than P42/mnm XN and Pbca XN. In addition, in the Pbca phases, XN can be considered a semiconductor material, while in the P42/mnm phase, GaN and InN have direct band-gap, and BN and AlN are indirect wide band gap materials. The novel III-V nitride polymorphs in the P42/mnm and Pbca phases may have great potential for application in visible light detectors, ultraviolet detectors, infrared detectors, and light-emitting diodes.

Theoretical Investigations of a BN Polymorph with sp2 + sp3 Hybridizations

“…In Figure 3a, different colors represent different value ranges: the minimum value and maximum value of E in P4/m BN are indicated by the curved surface of the solid cyan line and the solid purple line, respectively. The ratio between the maximum value and the minimum value (Emax/Emin = 514.72/193.57 = 2.66) of E is greater than that of the Pbca phase [22], P42/mnm phase [50] and Pm-3m phase [56], while it is much weaker than that of P4/mbm BN, B7N7, B11N11 and B15N15 [57]. The anisotropy in E of P4/mbm BN, B7N7, B11N11 and B15N15 is approximately 4, 6, 8 and 24 times that of P4/m BN, respectively.…”

“…In Figure 3a, different colors represent different value ranges: the minimum value and maximum value of E in P4/m BN are indicated by the curved surface of the solid cyan line and the solid purple line, respectively. The ratio between the maximum value and the minimum value (E max /E min = 514.72/193.57 = 2.66) of E is greater than that of the Pbca phase [22], P4 2 /mnm phase [50] and Pm-3m phase [56], while it is much weaker than that of P4/mbm BN, B 7 N 7 , B 11 N 11 and B 15 N 15 [57] For P4/m BN in distinct directions, the variations of E of P4/m BN in different planes were plotted, as shown in Figure 3a. In Figure 3a, different colors represent different value ranges: the minimum value and maximum value of E in P4/m BN are indicated by the curved surface of the solid cyan line and the solid purple line, respectively.…”

“…The two-dimensional (2D) extreme values of E in the (001), ( 101), ( 100), ( 110), ( 010) and ( 111 The variations of the Gmax and Gmin of P4/m BN in different directions are displayed in Figure 4a,b, which indicate the mechanical anisotropy properties of G for P4/m BN in distinct directions. The shape of the 3D-structured surface of G for P4/m BN is a very close sphere; the Gmax/Gmin for P4/m BN is 2.08, while it is larger than that for the Pbca phase [22], P42/mnm phase [50] and Pm-3m phase [56]. Regarding the Young's modulus, the anisotropy of the shear modulus of P4/m BN is still weaker than that of P4/mbm BN, B7N7, B11N11 and B15N15.…”

“…The mechanical anisotropy of crystals is very important in the study of their physical characteristics [50]. A directional dependence can visually show the anisotropic characteristics due to the varying Young's moduli generated in different planes.…”

“…As demonstrated in Figure 4c,d The variations of the extremum value of v for P4/m BN in different directions are demonstrated in Figure 5a,b, and the 2D representations of the Poisson's ratio in the (001), (101), (100), (110), (010) and (111) planes for P4/m BN are displayed in Figure 5c,d, respectively. The shape of the three-dimensional (3D) contour map of the P4/m BN shear modulus deviates far from the sphere; the vmax/vmin for P4/m BN is 7.00, while it is larger than that of the Pbca phase [22], P42/mnm phase [50] and Pm-3m phase [56]. Since all these materials are BN polymorphs, the reason for the differences in their anisotropy is not the different constituent elements.…”