| Functional semiconductors are the basis materials in the fields of optoelectronic information and energy.However,intrinsic semiconductors usually possess some disadvantages,such as instability,toxicity,low energy conversion efficiency and so on.It is essential to optimize the optoelectronic properties in semiconductors,according to its own circumstance.Here,the optoelectronic properties of several representative semiconductors are modulated by alloying and doping,utilizing first-principles calculations combined with experiments.The innovative results are as following:(1)Tuning the physical properties of layered SnX2(X=S,Se)crystals by the formation of van der Waals SnSe2(1-x)S2x alloy.With the miniaturization of electronic devices,two-dimensional semiconductors have attracted great attention.As the layered van der Waals crystals,tin disulphide(SnS2)and tin diselenide(SnSe2)have the advantages of low-cost and nontoxic,thus it is potential to apply in electronics,optoelectronics and thermoelectrics.Single-layer and multilayer nanosheets of SnS2and SnSe2 can be isolated from their bulk counterparts by mechanical exfoliation.However,their physical properties,such as in-plane lattice constants and interlayer binding energies,are weakly dependent on the layer thickness.Here,we report a theoretical and experimental study on some important physic properties of van der Waals SnSe2(1-x)S2x alloys.The SnSe2(1-x)S2x alloys show an excellent miscibility at room temperature and a tendency to solid solution miscibility.For SnSe2(1-x)S2x alloys,their band gaps increase with increasing the S concentration and the bowing coefficient is large,deriving from the different sizes and orbital energies of S and Se atoms.The electron-phonon coupling of SnSe2(1-x)S2x alloys increases with the increasing of S concentration because the Sn-S covalent bonding is stronger than Sn-Se.For SnX2(X=S,Se),the electron effective mass is lighter in the layer plane and the hole effective mass out-of-plane is lighter,which indicates that SnSe2(1-x)S2x is a semiconductor with a quasi-1D character for holes and quasi-2D character for electrons.In addition,we find that the ordered S-vacancy in SnS2 can affect its optoelectronic properties.The SnSe2(1-x)S2x alloys combined with ordered S/Se-vacancy maybe induce some novel physical properties.(2)Doping Barium in lead-based halide perovskites to tune toxicity,thermodynamic stability and optoelectric properties.Organic-inorganic halide perovskites(ABX3;A=CH3NH3,HC(NH2)2;B=Pb;X=Cl,Br,I)are widely used in the field of photoelectric devices due to their advanced optoelectronic properties.However,the poor stability and toxicity of organic lead halogen perovskites remain the major challenge for outdoor solar cell deployment.Inorganic halide perovskites CsPbX3(X=Cl,Br,I)have similar optoelectronic properties and improved stability with their organic counterparts,whereas the toxicity remains a question.Here,we report a comprehensive study of the alloyed perovskite CsPb1-xBaxX3(X=Cl,Br,I),using disorder alloy structure search method combined with first-principles calculations.We find that it is not easy to dope barium into the perovskite lattice with low Ba concentration and stable disordered solid solutions can exist in high Ba concentration.Carrier effective masses and band gaps increase with the increases of Ba concentration and the range of bandgap is wide(1.74?5.12 eV),owing to the smaller electronegativity and larger ionic radius of Ba compared Pb.For CsPb1-xBaxX3 system,the electrons and holes locate on Pb sites that may induce the formation of local potential wells which is beneficial to improve the quantum yield.The CsPb1-xBaxX3(X=Cl,Br,I)system with high Ba concentration can be stable and less-toxic,and they can be used in short wave light-emitting diodes,radiation detectors or other fields because of their large bandgaps(>2.8 eV).(3)Realizing p-type and n-type surface charge transfer doping of diamond via transition metal oxides and organic molecules adsorption and exploring the influencing factors of doping.Diamond with a wide band gap(?5.47 eV)has attracted great interest due to its unique properties,such as high hardness,high breakdown voltage,high thermal conductivity,low dielectric constant and so on.However,the normal bulk dopants have very high activation energies or low carrier concentration,which impedes the development of diamond-based electronic devices.We study surface charge transfer doping of diamond by using first-principles calculations.Transition metal oxides can make hydrogenated diamond(diamond(100):H)generate p-type conductivity.The areal hole density shows a sharp increase and gradually saturates(6.26×1013 cm-2)with increasing areal MoO3 density.For MoO3monolayer,the MoO3molecule units are linked together and interact with each other,so that areal hole density per MoO3 molecule is very low and even final areal hole density(5.23×1013 cm-2)is lower than the saturation value induced by MoO3 molecule.Therefore,the MoO3molecule is more desirable as surface acceptor.The induced maximal areal hole density for CrO3 double chains and V2O5 monolayer are 8.00×1013 cm-2 and 5.24×1013 cm-2,respectively.The greater the energy separation between the conduction band minimum(CBM)of two-dimensional transition metal oxides monolayer and the valence band maximum of diamond(100):H,the interaction between two-dimensional transition metal oxides monolayer and diamond(100):H and layer thickness of two-dimensional transition metal oxides,the larger the areal hole density.The oxygen-and fluorine-terminated diamond can be n-type doped via organic molecules.We screen out twenty-one organic molecules as surface donor of oxygen-terminated diamond(diamond(100):O),and nine organic molecules adsoprtion makes the fluorine-terminated diamond(diamond(100):F)n-type doping.The induced maximal areal electron density for diamond(100):O and diamond(100):F are 2.60×1013 cm-2 and9.20×1012 cm-2,respectively.Taking Co Cp2(Co(C5H5)2)as an example,we explore the influence of density and thickness of organic molecule on doping.Note that the areal electron density shows a sharp increase and gradually saturates(4.06×1013 cm-2)with increasing the density and thickness of Co Cp2 molecule.The greater the energy separation between the highest occupied molecular orbital of organic molecules and the CBM of diamond(100):O/F,the interaction between organic molecules and diamond(100):O/F and density and thickness of organic molecules,the larger the electron hole density.To sum up,the dimensionality,thickness and density of surface dopant as well as the energy separation and interaction between surface dopant and diamond surface would affect the doping.We tune the optoelectronic properties of three typical semiconductors by using alloying and doping,promoting their application in practical electronic devices and providing a trajectory to the modulation of optoelectronic properties in semiconductors. |
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