Piezoelectric GaGeX2 (X = N, P, and As) semiconductors with Raman activity and high carrier mobility for multifunctional applications: a first-principles simulation

In the present work, we propose GaGeX₂ (X = N, P, As) monolayers and explore their structural, vibrational, piezoelectric, electronic, and transport characteristics for multifunctional applications based on first-principles simulations. Our analyses of cohesive energy, phonon dispersion spectra, and ab initio molecular dynamics simulations indicate that the three proposed structures have good energetic, dynamic, and thermodynamic stabilities. The GaGeX₂ are found as piezoelectric materials with high piezoelectric coefficient d₁₁ of −1.23 pm V⁻¹ for the GaGeAs₂ monolayer. Furthermore, the results from electronic band structures show that the GaGeX₂ have semiconductor behaviours with moderate bandgap energies. At the Heyd–Scuseria–Ernzerhof level, the GaGeP₂ and GaGeAs₂ exhibit optimal bandgaps for photovoltaic applications of 1.75 and 1.15 eV, respectively. Moreover, to examine the transport features of the GaGeX₂ monolayers, we calculate their carrier mobility. All three investigated GaGeX₂ systems have anisotropic carrier mobility in the two in-plane directions for both electrons and holes. Among them, the GaGeAs₂ monolayer shows the highest electron mobilities of 2270.17 and 1788.59 cm² V⁻¹ s⁻¹ in the x and y directions, respectively. With high electron mobility, large piezoelectric coefficient, and moderate bandgap energy, the GaGeAs₂ material holds potential applicability for electronic, optoelectronic, piezoelectric, and photovoltaic applications. Thus, our findings not only predict stable GaGeX₂ structures but also provide promising materials to apply for multifunctional devices.