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

In the present work, we attempt to construct two-dimensional AlSiX (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 - AlSiN, AlSiP and AlSiAs - configurations are confirmed to have good dynamic, thermal, and mechanical stabilities from their phonon spectra, molecular dynamics investigations, and attained elastic constants/cohesive energy results. The Raman spectra of the AlSiX 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 AlSiN monolayer shows a direct band-gap meanwhile the AlSiP and AlSiAs monolayers exhibit an indirect band-gap. The AlSiX monolayers are found as piezoelectric materials with the in-plane piezoelectric effects. The AlSiN has the in-plane piezoelectric coefficient value of 0.43 pm V, whereas the AlSiP and AlSiAs monolayers have the higher absolute values of -0.76 and -0.71 pm V, respectively. Moreover, we also examine the carrier mobilities of the AlSiX monolayers for their transport properties by utilizing the deformation potential approach. The AlSiN, AlSiP, and AlSiAs monolayers exhibit high and anisotropic electron mobilities. The achieved mobility of electrons are 1096.01 and 1765.43 cm V s in the direction for the AlSiN and AlSiP monolayers, respectively. AlSiAs shows the highest electron mobility of 2027.28 cm V s in the direction and 1120.49 cm V s in the direction. The findings in our study demonstrate that the AlSiX monolayers are potential piezoelectric semiconductors with impressive anisotropic electron mobilities and favorable band-gaps for applications in electronic, photovoltaic, optic, and piezoelectric fields.