The Study On Preparation And Thermal Stability Of Hydrogen-doped AZO Thin Films

Transparent conductive films are widely used in solar cell front electrodes,flat panel displays,organic light emitting diodes and other fields due to high transmittance and high conductivity characteristics.Tin doped indium oxide?ITO?thin film is one of the more mature transparent conductive oxide films.However,due to the nature of In,Sn reserves and ITO thin film in the hydrogen plasma instability and other characteristics limit its application to a certain extent.Compared with ITO thin films,aluminum-doped zinc oxide?AZO?films have the advantages of low cost,non-toxic and hydrogen plasma stability,and are considered to be the most likely alternatives for ITO films.However,the electrical conductivity of AZO films has a certain gap with ITO films.Recent theoretical and experimental studies have shown that incorporation of H into AZO films can improve the electrical conductivity of films.At present,the preparation of H-AZO thin films is mainly focused on the RF magnetron sputtering method,and the research on H-AZO films prepared by DC magnetron sputtering method is less.Therefore,H-AZO thin films were prepared by DC magnetron sputtering in this paper.In addition,the stability of the photoelectric properties of H-AZO thin films is also worthy of study in the applications of optoelectronic devices.??In this paper,H-AZO thin films were prepared by DC magnetron sputtering coating,the effect of H₂ flow rate and substrate temperature on the properties of the films were investigated.The results are as follows:H₂ flow on the properties of H-AZO films,?1?The intensity of?103?diffraction peak of H-AZO thin films increases with the appropriate amount of H₂,and the average grain size increases,and the crystallization rate of the films increases.?2?The introduction of H₂,thin film grain together,the film is more dense and the surface appeared obvious pits.?3?The effect of H₂ on the light transmittance of H-AZO in the visible area is relatively small,the average transmittance is maintained over 90%,and the optical bandgap value of the H-AZO film increases.?4?The incorporation of H has a significant increase in the electrical conductivity of AZO thin films,the resistivity is reduced from 1.5×10-3?cm to 4.69×10-4?cm,the main reason is attributed to the increase of carrier concentration,from 2.83×1020cm-3 increased to 7.68×1020cm-3.The mechanism of the increase in carrier concentration is that?i?H is incorporated into AZO in the form of Hi and HO in AZO to increase the concentration of carriers and play the role of donor.?ii?The introduction of H₂ promotes the doping of Al.The effect of substrate temperature on the properties of H-AZO thin films,in the range of the substrate temperature of 100 to 200°C,as the substrate temperature increases:?1?The?103?diffraction peak of H-AZO film is enhanced,the average grain size is the largest,and the crystallinity of the film is improved.?2?The resistivity of the film is lowered,the lowest is at the substrate temperature of 200°C,the resistivity is 5.0×10-4 ?cm,the reason is that as the substrate temperature increases,the crystallinity of the film increases and the carrier mobility increases.?3?The transmittance of the film in the visible region is improved and has no effect on the optical band gap of the film,the optical bandgap is about 3.8eV.??The effects of different annealing temperatures on the thermal stability of H-AZO thin films were investigated by annealing the prepared H-AZO films in a vacuum atmosphere.Experimental results show that:?1?After the annealing at 200? and 300?,the resistivity of H-AZO film remained basically unchanged compared with that before annealing,When the annealing temperature is 400?,the resistivity of H-AZO film is increased from 4.69×10-4?.cm to 1.43×10-3?cm when the annealing time in the range of 0¹20min.The carrier concentration was significantly reduced from 7.7×1020 cm-3 to 3.8×1020 cm-3.The electron mobility also decreased significantly from 17.4 cm2/?V·S?to 11.4 cm2/?V·S?.It is concluded that the deterioration of the electrical properties of the films annealed at 400? is that the Hi and HO desorption,during the annealing process reduces the carrier concentration of the films.The decrease in the mobility of the H-AZO film is due to the desorption of H,resulting in a decrease in the crystallinity of the film.The results show that the electrical properties of H-AZO thin films are relatively stable when the ambient temperature is lower than 300?.?2?The different annealing temperature have no effect on the transmittance of H-AZO film in the visible region,and the transmittance of the sample was above 90% before and after annealing.After 400? annealing,the optical bandgap value of the film decreases due to the decrease of the carrier concentration.?3?After annealing at 200?,the effect on the crystallization performance of the film is small,while the crystallization performance of HAZO films has deteriorated after annealing at 300 and 400 ?.