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 d(11) 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 cm(2) 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.