| Summary: | 碩士 === 明志科技大學 === 材料工程系碩士班 === 103 === This study adopted density functional theory and the Hubbard U (DFT + U) method based on CASTEP 5.5 mod to investigate the formation energies, electronic structures, and optical properties of Al/Ga-co-doped ZnO. 3 × 3 × 2 72-atom ZnO supercell model considered in Al location and concentration doped ZnO. 3 × 3 × 3 108-atom ZnO supercell model considered in Al/Ga-co-doped ZnO.
In this wok, Al location and concentration doped ZnO. For all of doping models, the fermi level shifts upward into the conduction band with n-type conductive characteristics, where as the optical energy gaps exceed those of pure ZnO. The total density of states (TDOS) shows Als(O) and Ali shallow donor levels produce carrier concentration are more than Als(Zn), but Als(O) and Ali also have deep donor levels. To investigate the imaginary part of the dielectric function. Due to transition of shallow donor levels is reduced visible light (400 - 800 nm) wavelength transmittance. From 89.5 %(pure) respectively decrease to 70.8 %(Als(O))、73.4 %(Ali(tet))and 68.3 %(Ali(oct)), The deep donor levels is also reduced UV light (200 - 400 nm) wavelength transmittance. But Als(Zn) did not have deep donor levels, Besides shallow donor levels have low carrier concentration. But increased visible light 91.1 % and UV light 75.7 %.
When Als(Zn) concentration from 2.77% to 8.31 at%. while the band gap Al concentration will increase to increase in the optical band gap. When Al concentration increase, which can increase two wave crest in band gap, That cause the near-infrared transmittance decreased.
The formation energies calculated at various AGZO position in ZnO are summarized, It is well known that Als(Zn)+Gas(Zn) is lower formation energies other position. Due to AGZO the fermi level shifts upward into the conduction band with n-type conductive characteristics, where as the optical energy gaps exceed those of pure ZnO, while (Ga、Al)s(O) also have deep donor levels in valence band maximum, and (Ga、Al)i have shallow donor levels in conduction band maximum. The total density of states (TDOS) shows Al-Ga contributions will be Ga is the main contribution in donor energy level. To investigate the imaginary part of the dielectric function. Only Als(Zn)+Gas(Zn) doesn't have deep donor levels. From the transmittance can keep visible light 90.78% and UV light 72.79%, the other Al-Ga combination transmittance is lower than pure ZnO because of deep donor levels.
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