Piezoelectricity of Graphene-like Monolayer ZnO and GaN

doi:10.15541/jim20200346

Abstract

Abstract:

By employing density functional theory calculations, the mechanical, electronic and piezoelectric properties of graphene-like monolayers ZnO (g-ZnO) and GaN (g-GaN) were investigated. Elastic stiffness constants and piezoelectric tensors of monolayers g-ZnO and g-GaN using their Clamped-ion and Relaxed-ion components were mainly studied. Results indicate that these two graphene-like structures are semiconductors with excellent elasticity. The piezoelectric coefficient of monolayers g-ZnO and g-GaN are about 9.4 and 2.2 pm·V^-1, respectively, implying their piezoelectric effect in extremely thin film devices, especially the g-ZnO. The remarkable piezoelectricity of monolayer g-ZnO enables it a wide range of applications, such as mechanical stress sensors, actuators, transducer and energy harvesting devices.

Key words: piezoelectricity, elasticity, electronic structure, ZnO, GaN, graphene-like monolayer

CLC Number:

O482

XIANG Hui, QUAN Hui, HU Yiyuan, ZHAO Weiqian, XU Bo, YIN Jiang. Piezoelectricity of Graphene-like Monolayer ZnO and GaN[J]. Journal of Inorganic Materials, 2021, 36(5): 492-496.

Figures/Tables 6

Fig. 1 Crystal structure and phonon spectra of monolayer g-ZnO and g-GaN The top view (a) and side view (b) of monolayers g-ZnO and g-GaN, where oxygen and nitrogen atoms are blue, while zinc and gallium atoms are gray. The axes and direction of piezoelectric polarization are labeled as P. The phonon dispersion calculations for monolayers g-ZnO (c) and g-GaN (d) are also depicted, respectivelyColorful figures are available on website

Fig. 2 Band structures of monolayers g-ZnO (a) and g-GaN (b) The Fermi level is set at zeroColorful figures are available on website

Table 1 Elastic stiffness constants C11 and C12 (N·m-1) of Clamped-ion and Relaxed-ion components for monolayers g-ZnO and g-GaN) against that of h-BN and graphene (Δ= C11 - C12)

Material	Clamped-ion			Relaxed-ion
Material	C₁₁	C₁₂	Δ	C₁₁	C₁₂	Δ
g-ZnO	109	35	75	86	57	29
g-GaN	157	37	120	135	58	77
h-BN^[6]	300	53	247	291	62	229
Graphene^[26]	-	-	-	358	60	298

Fig. 3 Monolayers g-ZnO (a) and g-GaN (b) polarization as a function of strain strength when applied uniaxial strain along the armchair direction

Table 2 Calculated Clamped- and Relaxed-ion e11 (×10-10, C·m-1) and d11 (pm·V-1) of g-ZnO and g-GaN against piezoelectric coefficients of wurtzite bulk and graphene-like monolayer BN (h-BN)

Material	Clamped-ion		Relaxed-ion
Material	e₁₁	d₁₁	e₁₁	d₁₁
g-ZnO	1.7	2.3	2.7	9.4
g-GaN	2.4	2.0	1.7	2.2
Bulk ZnO^[2]	-	-	-	9.9 (d₃₃)
Bulk GaN^[27]	-	-	-	3.1 (d₃₃)
h-BN^[6]	3.7	1.5	1.4	0.6

Fig. 4 Total densities of states (TDOS) and partial DOS (PDOS) of monolayers g-ZnO (a) and g-GaN (b) under the conditions of 1% tensile strain along the armchair direction Colorful figures are available on website

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