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First-principles calculations have been carried out to explore the effect of atom surface adsorption on the electronic, magnetic, and optical properties of the germanium phosphide (GeP) monolayer. It is shown that the GeP monolayer exhibits good adsorption capability to all the selected adatoms and can preserve the structural integrity upon the adsorption of most adatoms. The adatoms can bring out diverse electronic properties to the GeP monolayer. The H, Li, Na, K, and Al adatoms donate electrons to the GeP monolayer and result in its metallization. The other adatoms do not change the semiconducting nature of the GeP monolayer and will induce midgap states (Mg, Ca, Si, Ge, Ag, and Au) or reduce the bandgaps (Ni, Pd, and Pt). The B, N, P, As, V, Cr, Mn, Fe, and Co adatoms induce spin magnetic moments into the GeP monolayer. Especially, the spin magnetic moments are mainly located on the adatoms for the GeP decorated with the V, Cr, Mn, Fe, and Co atoms. As a result, the dilute magnetic semiconductor can be obtained. In addition, all the adatoms decrease the work function, except O. Thus, some effects on the optical properties are highly expected. The GeP monolayer exhibits a wide range of light absorption and the Mg, Si, Ge, Cu, Ag, Au, and Pt adatoms can further redshift the absorption edge of the GeP monolayer along the x and y directions. Our calculations provide an effective method to modulate the electronic, magnetic, and optical properties of the GeP monolayer for device applications.

First-principles calculations have been performed to study the modulation of the electronic and optical properties of the black phosphorous carbide monolayer (b-PC) by the adsorption of O2, H2O, NO2, and NH3 molecules. All the molecules are weakly physisorbed on the surface of the b-PC, which act as electron acceptors except NH3. Especially, O2 and NO2 molecules can introduce deep acceptor states in the bandgap of the b-PC. The effects of the external electric field and the in-plane strain were further studied. For the b-PC with the adsorbed O2, the typical p-type doping can be achieved under an appropriate external electric field. However, the b-PC with the adsorbed NO2 is the most susceptible to the in-plane strain, as evidenced by the significant changes in the adsorption energy and the charge transfer under the compressive strain. In addition, the optical absorption of the b-PC can be significantly enhanced upon the adsorption of O2 and NO2 molecules, which can be further modulated by the external electric field and the in-plane strain. Our calculations predict an effective method to modulate the electronic and optical properties of the b-PC, which may widen its applications in the future electronics and optoelectronics.