First-principles Study On P-type Doping Modification Of SnO₂ Optoelectronic Semiconductors

The electronic devices fabricated from wide bandgap semiconductor metal oxide materials are widely used in solar cells,flat panel displays,lasers,etc.,and also are one of the current research hotspots.In general,metal oxide materials can be converted from insulators to semiconductors or conductors by doping elements.Most undoped metal oxides exhibit n-type conductivity due to intrinsic defects,and unintentionally doped p-type TCO thin film materials are so small that it is difficult to achieve a true"full transparency device."In addition,it is very important to form a good ohmic contact to improve the device performance for an optoelectronic device with a p-type work area.Therefore,the p-type material with excellent photoelectric properties is the focus and difficulty in the research of metal oxide semiconductors.Compared with GaN and ZnO,SnO₂ has wider bandgap and higher exciton binding energy at room temperature,and is a shorter wavelength UV luminescence materials with important potential application prospects,especially in the field of short wave light emitting devices.Therefore,based on SnO₂,the photoelectric properties of different p-type doping models are analyzed,and expects to provide meaningful theoretical guidance for the preparation of optoelectronic devices with excellent photoelectric properties.In this paper,the CASTEP code,the first-principles based on density functional theory,was used for the simulation calculation.By comparing the p-type doping of SnO₂ with Ag and Al elements,finds that two impurity levels appeare in the bandgap of the Ag-doped SnO₂system and its minimum ionization accountes for about 45%of the forbidden band width and belonge to the deep energy level recombination center.But obvious impurity level is not observed in the Al-doped SnO₂ system,even though the doping concentration of Al increases from 4.17 at.%to 8.33 at.%,and obvious impurity level is still not observed,however it will significantly enhance the absorption coefficient in the visible region and improve the utilization of visible light.Subsequently,Ag-Al co-doped method is performed and find that Al element not only reduces the ionization energy of the single acceptor Ag impurity level by about 53%,but also significantly reduces the formation energy of the composite defect under O-rich conditions,even lower than the formation energy of defect Al _Sn in Al-doped SnO₂system.In addition,Al element will lead to red shift of the absorption edge,further increases the absorption coefficient in the visible and infrared regions,and broadens the optical response range.On the other hand,the Al-N co-doped SnO₂ models with different N concentrations of2.08 at.%,4.67 at.%,and 6.25 at.%were also studied.The result is that the N 2p state electrons introduce significant defect levels in the forbidden band,and as the N doping concentration increases,the number of defect levels also increases,but the minimum depth of defect energy level tend to decrease.In terms of optical properties,the appeared impurity levels induced by N element lead to the more transitions from the other levels in the valence band to these impurity levels,resulting in the red shift of the absorption edge and the consequent increment of the first peak of?₂???,absorption coefficient and reflectivity in the infrared region and visible region.But the Sn₂₃Al₁O₄₆N₁N₅ model is very specially,two defect energy levels are induced by the Al 3p states and N 2p states hybridization,and the absorption coefficient in the visible region approaches zero,and the long-wave ultraviolet region between 2.6eV and 6eV,very similar to the undoped SnO₂ spectrum,has lower light absorption coefficient,indicating that it exhibits higher light transmittance in the energy range of 0eV-6eV?visible light region,infrared region,and some ultraviolet regions?and relatively excellent transparency conductive film material.