Two-dimensional piezoelectric AlSiX2 (X = N, P, As) semiconductors with Raman activity, favorable band-gap, and high carrier mobility based on first-principles calculations

Abstract

In the present work, we attempt to construct two-dimensional AlSiX₂ (X = N, P, As) monolayers and examine their stabilities, Raman activity, piezoelectricity, as well as electronic/transport properties for various applications, using first-principles calculations. All three – AlSiN₂, AlSiP₂ and AlSiAs₂ – configurations are confirmed to have good dynamic, thermal, and mechanical stabilities from their phonon spectra, ab initio molecular dynamics investigations, and attained elastic constants/cohesive energy results. The Raman spectra of the AlSiX₂ monolayers are performed using the finite displacement technique to assess their vibrational properties and Raman activities. The calculated electronic band structures of the studied monolayers reveal their semiconductor behaviors. The AlSiN₂ monolayer shows a direct band-gap meanwhile the AlSiP₂ and AlSiAs₂ monolayers exhibit an indirect band-gap. The AlSiX₂ monolayers are found as piezoelectric materials with the in-plane piezoelectric effects. The AlSiN₂ has the in-plane piezoelectric coefficient d₁₁ value of 0.43 pm V⁻¹, whereas the AlSiP₂ and AlSiAs₂ monolayers have the higher absolute d₁₁ values of −0.76 and −0.71 pm V⁻¹, respectively. Moreover, we also examine the carrier mobilities of the AlSiX₂ monolayers for their transport properties by utilizing the deformation potential approach. The AlSiN₂, AlSiP₂, and AlSiAs₂ monolayers exhibit high and anisotropic electron mobilities. The achieved mobility of electrons are 1096.01 and 1765.43 cm² V⁻¹ s⁻¹ in the x direction for the AlSiN₂ and AlSiP₂ monolayers, respectively. AlSiAs₂ shows the highest electron mobility of 2027.28 cm² V⁻¹ s⁻¹ in the x direction and 1120.49 cm² V⁻¹ s⁻¹ in the y direction. The findings in our study demonstrate that the AlSiX₂ monolayers are potential piezoelectric semiconductors with impressive anisotropic electron mobilities and favorable band-gaps for applications in electronic, photovoltaic, optic, and piezoelectric fields.