Читать книгу 2D Monoelements - Группа авторов - Страница 18

Pristine phosphorene is a p-type semiconductor with a direct band gap [13, 46–48]. By using polarization-resolved photoluminescence excitation spectroscopy at room temperature, the quasi-particle band gap of phosphorene is measured to be 2.2 eV [49]. The same value is observed with the typical tunneling spectra of U-shaped electronic spectra [48].

Pure phosphorene has no spin polarization, which is confirmed by symmetrical density of spin-up and -down states displayed in Figure 1.2b. Meanwhile, Figure 1.2a shows that the band dispersion is highly anisotropic around the electronic gap. Indeed, one can observe a much greater dispersion along the Γ-X direction for CBM and VBM with respect to the vertical bands in Γ-Y region. The partial density of states (p-DOS) plots clearly show that px orbital contribute mainly in the states of the unfilled C-band, while the pz orbital of phosphorus dominates the valence band states [50]. The number of layers mainly affects the gap energy [24]. For instance, it takes the values of 1.51, 0.59, and 0.3 eV for the monolayer, the five layers, and the bulk black phosphorus [51]. Furthermore, the gap energy decreases with increasing the magnitude of external electrical field, which breaks the out-of-plane symmetry. Under biaxial strain and the two possible uniaxial strains, the deformed phosphorene shows a transition from the semiconducting to metallic phase [23].

Figure 1.2 Graph of electronic features corresponding to 2D BP. (a) the band structure, (b) represents the total and partial density of states.