A first-principles theoretical study of the electronic and optical properties of twisted bilayer GaN structures

Xiang Cai,Lijie Li,Shuo Deng,Ling Hao

doi:10.1007/s10825-020-01512-7

Abstract

Gallium nitride (GaN) is a well-investigated material that is applied in many advanced power electronic and optoelectronic devices due to its wide bandgap. However, derivatives of its monolayer form, such as bilayer structures, have rarely been reported. We study herein the electronic and optical properties of GaN bilayer structures that are rotated in the plane at several optimized angles by using the density functional theory method. To maintain the structural stability and use a small cell size, the twisting angles of the GaN bilayer structures are optimized to be 27.8°, 38.2°, and 46.8° using the crystal matching theory. The band-structure analysis reveals that the bandgap is wider for the twisted structures compared with the nontwisted case. The simulation results provide the absorption coefficient, extinction coefficient, reflectivity, and refractive index at these angles. The spectra of all these optical properties match with the bandgap values. The simulated refractive index of the bilayer structures at all the twisting angles including 0° is smaller than that of bulk GaN, indicating a reduced scattering loss for optoelectronics applications. Considering the results of this analysis, the possible applications may include low-loss integrated electronic and optical devices and systems.

Highlights

Gallium nitride (GaN) is a typical group III–V compound semiconductor material and has been widely applied in power semiconductor and optoelectronic devices
The bilayer GaN models are simulated to determine several key optical properties such as the absorption coefficient and refractive index using the general mathematical procedure described in our previous work [35]
According to the results of these first-principles simulations, the bandgap, absorption coefficient, extinction coefficient, reflectivity, and refractive index vary with the rotation angle

Summary

Introduction

GaN is a typical group III–V compound semiconductor material and has been widely applied in power semiconductor and optoelectronic devices. It was reported in past studies that devices with a suspended bilayer structure offer advantages in terms of enhanced electronic performance Such two-dimensional (2D) material forms are deemed to have much thinner thickness than the bulk form, resulting in different electronic, mechanical, and optical performance characteristics [5,6,7,8,9,10,11,12,13,14,15]. The twisted GaN bilayer model is built and subsequently analyzed to reveal its electronic and optical properties These results will lead to wider and deeper explorations of single-layer GaN in the hope its application in practical electronic and optoelectronic devices

Computational methods

Optical properties

Conclusions