Structural, electronic, and photocatalytic water splitting in two-dimensional monolayer MNXY(M/N=Al,Ga,X/Y=N,P,As) semiconductors: A first-principles perspective

The exploration of novel and stable two-dimensional (2D) materials holds considerable significance in the development of optoelectronic devices and photocatalytic water splitting. Herein, $\mathit{MNXY}(M\text{/}N=\mathrm{Al},\mathrm{Ga},X\text{/}Y=\mathrm{N},\mathrm{P},\text{As})$ monolayers are constructed based on 2D double-layer honeycomb structures. Six stable semiconductor types were screened through first-principles calculations, and their mechanical, electrical, optical, and transport properties as well as their applications in photocatalytic water splitting were investigated. We found that the six stabilized MNXY monolayers had band gaps of 0.846--3.806 eV. The mechanical properties indicate that ${\mathrm{AlGaN}}_{2}$ has a Young's modulus exceeding 100 N/m, whereas the remaining five monolayers exhibit values below this threshold. The hole carrier mobility of the ${\mathrm{AlGaN}}_{2}$ monolayer along the armchair direction reaches an ultrahigh value of 3649.21 ${\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$; thus it has the potential for application in optoelectronic devices. Furthermore, we observed that ${\mathrm{AlGaP}}_{2}$ monolayers exhibit band-edge potentials spanning the redox potential of water, a considerable difference in electron-hole carrier mobility, strong visible light absorption, and a high solar to hydrogen efficiency (17.51%) in the absence of strain, making them suitable for photocatalytic water splitting. We expect that our results will pave the way forward for material selection for next-generation optoelectronic devices and photocatalysts.