  One of the key problems in valleytronics is to realize valley polarization.
Ferrovalley (FV) semiconductor and half-valley-metal (HVM) have been proposed,
which possess intrinsic spontaneous valley polarization. Here, we propose the
concept of quasi-half-valley-metal (QHVM), including electron and hole carriers
with only a type of carriers being valley polarized. The QHVM may realize
separation function of electron and hole. A concrete example of
$\mathrm{VGe_2P_4}$ monolayer is used to illustrate our proposal through the
first-principle calculations. To better realize QHVM, the electric field is
applied to tune related valley properties of $\mathrm{VGe_2P_4}$. Within
considered electric field range, $\mathrm{VGe_2P_4}$ is always ferromagnetic
(FM) ground state, which possesses out-of-plane magnetization by calculating
magnetic anisotropy energy (MAE) including magnetic shape anisotropy (MSA) and
magnetocrystalline anisotropy (MCA) energies. These out-of-plane FM properties
guarantee intrinsic spontaneous valley polarization in $\mathrm{VGe_2P_4}$.
Within a certain range of electric field, the QHVM can be maintained, and the
related polarization properties can be effectively tuned. Our works pave the
way toward two-dimensional (2D) functional materials design of valleytronics.
