Electronic properties and tunability in graphene/3D-InP mixed-dimensional van der Waals heterostructure

InP solar cell is promising for space application due to its strong space radiation resistance and high power conversion efficient(PCE).Graphene/InP heterostructure solar cell is expected to have a higher PCE because strong near-infrared light can also be absorbed and converted additionally by graphene in this heterostructure.However,a low PCE was reported experimentally for Graphene/InP heterostructures.In this paper,electronic properties of graphene/InP heterostructures are calculated using density functional theory to understand the origin of the low PCE and propose possible improving ways.Our calculation results reveal that graphene contact with InP form a p-type Schottky heterostructure with a low Schottky barrier height(SBH).It is the low SBH that leads to the low PCE of graphene/InP heterostructure solar cells.A new heterostructure,graphene/insulating layer/InP solar cells,is proposed to raise SBH and PCE.Moreover,we also find that the opened bandgap of graphene and SBH in graphene/InP heterostructures can be tuned by exerting an electric field,which is useful for photodetector of graphene/InP heterostructures.

Dynamic nuclear self-polarization of Ⅲ–Ⅴsemiconductors

Ⅲ–Ⅴ semiconductors exhibit dynamic nuclear self-polarization(DYNASP) owing to the contact hyperfine interaction(HFI) between optically excited conduction electrons and lattice nuclei. In the self-polarization process at a low temperature, electron spin state and the nuclear polarization(magnetization) exchange a positive feedback, increasing energy splitting of the conduction electron states, thereby a large nuclear polarization. This phenomenon was theoretically predicted previously for conduction electrons excited linearly and elliptically polarized light. The polarization of the conduction electrons was represented by a parameter α in a formula for nuclear polarization(Eq.(9) in Ref. [1]); however, the effect of external magnetic fields on the nuclear polarization was not considered. Therefore, this study introduces this effect by further extending the previous studies. Herein, α′represents the combination of the effects of elliptically polarized electrons and an external magnetic field, which is used in the equations presented in previous studies. When α′ = 0, a large nuclear polarization is obtained below critical temperature Tc, but no polarization occurs above Tc. When α′ > 0, the nuclear polarization is enhanced above Tc. Below Tc, the nuclear polarization follows a hysteresis curve when α′ is partially manipulated by adjusting the degree of the polarization of the exciting laser.