Revealing the electronic, optical and photocatalytic properties of PN-MCO (P = Al, Ga; M = Ti, Zr, Hf) heterostructures.

Using DFT, the electronic structure, optical, and photocatalytic properties of PN (P = Ga, Al) and MCO (M = Ti, Zr, Hf) monolayers and their PN-MCO van der Waals heterostructures (vdWHs) are investigated. Optimized lattice parameters, bond length, bandgap, conduction and valence band edges show the potential of PN (P = Ga, Al) and MCO (M = Ti, Zr, Hf) monolayers in photocatalytic applications, and the application of the present approach to combine these monolayers and form vdWHs for efficient electronic, optoelectronic and photocatalytic applications is shown. Based on the same hexagonal symmetry and experimentally achievable lattice mismatch of PN (P = Ga, Al) with MCO (M = Ti, Zr, Hf) monolayers, we have fabricated PN-MCO vdWHs. Binding energies, interlayer distance and AIMD calculations show the stability of PN-MCO vdWHs and demonstrate that these materials can be easily fabricated experimentally. The calculated electronic band structures show that all the PN-MCO vdWHs are indirect bandgap semiconductors. Type-II[-I] band alignment is obtained for GaN(AlN)-TiCO[GaN(AlN)-ZrCO and GaN(AlN)-HfCO] vdWHs. PN-TiCO (PN-ZrCO) vdWHs with a PN(ZrCO) monolayer have greater potential than a TiCO(PN) monolayer, indicating that charge is transfer from the TiCO(PN) to PN(ZrCO) monolayer, while the potential drop separates charge carriers (electron and holes) at the interface. The work function and effective mass of the carriers of PN-MCO vdWHs are also calculated and presented. A red (blue) shift is observed in the position of excitonic peaks from AlN to GaN in PN-TiCO and PN-HfCO (PN-ZrCO) vdWHs, while significant absorption for photon energies above 2 eV for AlN-ZrCO, GaN-TiCO and PN-HfCO, give them good optical profiles. The calculated photocatalytic properties demonstrate that PN-MCO (P = Al, Ga; M = Ti, Zr, Hf) vdWHs are the best candidates for photocatalytic water splitting.