The vertical integration of a ferromagnetic monolayer and a ferroelectric monolayer into van der Waals heterostructures offers a promising route to achieve two-dimensional multiferroic semiconductor due to the lack of the intrinsic single-phase multiferroic materials in nature. Here, we propose a VN2H2/Al2O3 van der Waals magnetoelectric multiferroic heterostructure, and investigate the electronic, magnetic, and transport properties by using density-functional theory combined with Boltzmann transport theory. The VN2H2 monolayer is a room-temperature ferromagnetic semiconductor with a band gap of 0.24 eV and a Curie temperature of 411 K, while the monolayer Al2O3 is a ferroelectric semiconductor with a polarization value of 0.11 C/m2. In the VN2H2/Al2O3 van der Waals heterostructures, the conversion between metal and semiconductor can be controlled by altering the polarization of the Al2O3 layer. The VN2H2/Al2O3 van der Waals heterostructure retains room-temperature ferromagnetism, and reverse of polarization is accompanied by a change of direction of the easy magnetization axis. In addition, electrostatic doping can significantly improve the conductivity of the downward polarization state, and transform the upward polarization state from a metal to a half-metal, achieving 100% spin polarization. Our results thus pave the way for achieving highly tunable electromagnetic and transport properties in van der Waals magnetoelectric heterostructure, which have potential applications in next-generation low-power logic and memory devices.

VN2H2 monolayer; Al2O3 monolayer; Room-temperature ferromagnetic semiconductor; Conductivity; van der Waals magnetoelectric heterostructures