Density Functional Theory Investigation of Thermal Conductivity in α-CN and α-CP Monolayers: Implications for Thermal Management of Electronic Devices

Abstract

This work presents the density functional theory based investigations of two-dimensional carbon pnictides α-CX (X = N and P). Despite being from the group of the pnictide family, there are significant differences in the trends of the electronic and vibrational properties of both systems. The calculated electronic band gaps are 3.77 eV and 1.79 eV for α-CN and α-CP, respectively. The direct nature and moderate gap magnitude of α-CP indicate its applicability in the field of optoelectronic and photovoltaic device applications, which is confirmed by the calculated absorption spectra of the system. Distinguished phonon dispersion curves of both systems show a highly anisotropic trend. The diverse and steep nature of the acoustic phonon modes together with high phonon group velocity, low phonon anharmonicity, and high phonon mean free path (MFP) leads to a pronounced magnitude of thermal conductivity in the case of α-CN. In contrast to α-CN, α-CP owing to the lower gap between the optoacoustic phonon modes, lower MFP, and high anharmonicity possesses a remarkably lower thermal conductivity of 292 W m–1 K–1. The thermoelectric performance of the system is assessed by calculating the figure-of-merit ZT in the case of α-CP, which is 0.36 at 300 K that further attains > 0.7 at higher temperatures; whereas, for α-CN, the ZT value remains < 0.1 due to its ultra-high thermal conductivity. The present study paves the pathway toward exploration of carbon-based low-dimensional materials for high mobility and high thermal conductivity-based nanoelectronic device applications.