[Paper Review] A DFT Study on the Mechanical, Electronic, Thermodynamic, and Optical Properties of GaN and AlN Counterparts of Biphenylene Network

K. A. L. Lima, Luiz Antônio Ribeiro|arXiv (Cornell University)|Jun 20, 2023

Boron and Carbon Nanomaterials ResearchMaterials Science69 references3 citations

TL;DR

This DFT study investigates the mechanical, electronic, thermodynamic, and optical properties of two group-III nitride counterparts of the biphenylene network: GaN-BPN and AlN-BPN. Using HSE06 functional, the authors find indirect bandgaps of 2.3 eV (GaN) and 3.2 eV (AlN), with BPN-AlN showing dynamic stability and strong UV optical activity, indicating strong potential for ultraviolet optoelectronic applications.

ABSTRACT

The biphenylene network (BPN) is a notable achievement in recent fabrication endeavors for conceiving new 2D materials. The stability of its boron nitride counterpart, BN-BPN, has been confirmed through numerical investigations. In this study, we conducted a density functional theory (DFT) analysis to examine the mechanical, electronic, thermodynamic, and optical properties of two other group-III counterparts of BPN: gallium nitride (BPN-GaN) and aluminum nitride (BPN-AlN). Our findings reveal that the band gap values for BPN-GaN and BPN-AlN are 2.3 eV and 3.2 eV, respectively, at the HSE06 level. At the GGA/PBE level, we found band gap values of 1.8 eV and 2.3 eV for BPN-GaN and BPN-AlN, respectively. Phonon calculations and ab initio molecular dynamics (AIMD) simulations suggest that BPN-AlN has good structural and dynamic stabilities. On the other hand, BPN-GaN displayed negative phonon frequencies, suggesting potential instability. Nevertheless, results from AIMD simulations point to its structural integrity with no bond reconstructions at 1000 K. These materials exhibit noteworthy UV activity, presenting promising prospects as UV collectors. The thermodynamic properties reveal that the heat capacity of both BPN-AlN and BPN-GaN increases with temperature, eventually reaching the Dulong-Petit limit at around 800 K. We also performed calculations to determine the elastic stiffness constants, Young's modulus, and Poisson ratio for both BPN-GaN and BPN-AlN, providing valuable insights into their mechanical properties.

Motivation & Objective

• To evaluate the structural, electronic, mechanical, and thermodynamic stability of GaN and AlN variants of the biphenylene network (BPN).
• To assess the dynamic stability of BPN-GaN and BPN-AlN under thermal conditions using phonon dispersion and ab initio molecular dynamics (AIMD).
• To determine the electronic band structure and effective mass of charge carriers for both materials.
• To analyze the optical response and UV activity of BPN-GaN and BPN-AlN for potential optoelectronic applications.
• To compare the mechanical properties, including Young’s modulus and Poisson’s ratio, of the two materials.

Proposed method

• Employed density functional theory (DFT) with the HSE06 hybrid functional for accurate electronic structure calculations.
• Conducted phonon dispersion calculations along high-symmetry directions to assess dynamical stability.
• Performed ab initio molecular dynamics (AIMD) simulations at 1000 K to evaluate thermal stability and structural integrity.
• Calculated formation energies to evaluate thermodynamic stability of the BPN-(Ga,Al)N monolayers.
• Used linear and quadratic fitting of total energy and band edge positions under strain to determine carrier effective mass, in-plane stiffness (C2D), and DP constant (E1).
• Computed charge carrier mobility from effective mass using the standard formula for mobility in 2D materials.

Experimental results

Research questions

• RQ1 Is BPN-GaN dynamically stable, and does it maintain structural integrity at high temperatures?
• RQ2 What are the electronic band structures and bandgap values of BPN-GaN and BPN-AlN at the HSE06 level?
• RQ3 How do the mechanical properties such as Young’s modulus and Poisson’s ratio differ between BPN-GaN and BPN-AlN?
• RQ4 What is the optical response of BPN-GaN and BPN-AlN in the ultraviolet region?
• RQ5 How does the charge carrier mobility in BPN-(Ga,Al)N compare to that of conventional hexagonal (h-) GaN and AlN monolayers?

Key findings

• BPN-AlN exhibits dynamic stability with all real phonon frequencies and no bond reconstruction in AIMD simulations at 1000 K.
• BPN-GaN shows imaginary phonon frequencies but maintains structural integrity in AIMD simulations at 1000 K, indicating thermal resilience.
• The HSE06-calculated indirect bandgap is 2.3 eV for BPN-GaN and 3.2 eV for BPN-AlN, with BPN-AlN behaving as an insulator.
• BPN-GaN and BPN-AlN display strong optical activity in the ultraviolet region, indicating potential as UV collectors.
• Electron mobility in BPN-(Ga,Al)N is higher than in conventional h-(Ga,Al)N, with values up to 0.32 × 10³ cm² V⁻¹ s⁻¹ in the x-direction for BPN-AlN.
• The materials exhibit anisotropic carrier mobility, with higher values along the x-direction due to lower effective mass in that direction.