Preparation And Research Thermoelectric Properties Of P-type ZnO:Sb Thin Films

Thermoelectric materials can convert heat to electricity through the Seebeck effect.They play a key role in solving the problem of waste heat recovery.Zinc oxide(ZnO)is an outstanding candidate because of a relatively high Seebeck coefficient(-360 ?V K-1 at 85?),a low resistance(250 ? at 300?)and good chemical stability(decomposition temperature>2000?).However,for the homojuction type TE device,there still lacks stable p-type ZnO due to the selfcompensating effect from native defects of oxygen vacancy and zinc interstitial,low solubility of acceptors,and hydrogen incorporation.This has become the limitation for the application of ZnO because it is difficult to fabricate a ZnO-based p-n junction.In addition,large-sized-mismatched Sb doped p-type ZnO(ZnO:Sb)increases much more attention because the Sbzn-2Vzn complex can be identified as a shallow acceptor instead of deep Sbo acceptor in the Sb-doped ZnO films.These p-type ZnO films are often unstable and liable to revert back to the n-type conduction behavior over time.Films are often unstable and liable to revert back to the n-type conduction behavior over time.The reproducibility and reliability of these results are still under constant debate.Thus,it is necessary to study further to search stable p-type behavior and high power factor.This paper mainly studies the preparation of stable p-type ZnO:Sb films and ways to improve their thermoelectric properties.Preparation methods(Thermal evaporation,RF sources assisted in situ growth),Deposition conditions(substrate temperature,composition),Oxidation conditions(Oxidation time,high magnetic field(HMF))were investigated.Finally,the influence mechanism of microstructure evolution of p-type ZnO:Sb thin films on thermoelectric properties.One is the preparation of ZnO:Sb film by oxidation growth,First of all,the effect of Sb content at high magnetic field(0 T/12 T)on the microstructure,conduction type and thermoelectric properties of ZnO:Sb films.Then the effects of substrate temperature,oxidation time and Sb content on the microstructure,conduction type and thermoelectric properties of ZnO:Sb films were investigated.Secondly,the RF source assisted in situ growth of ZnO:Sb thin films,reducing the Zn-Sb compound by reducing the Sb content.Then,the influence of Sb content and substrate temperature in situ on the conduction type and thermoelectric properties of ZnO:Sb thin films was investigated.The results of the study on the microstructure and thermoelectric properties of ZnO:Sb films with different Sb contents under the high magnetic field.ZnO:Sb thermoelectric films with microporous structures are fabricated by oxidizing evaporated Zn-Sb thin films in a leaf-like surface.High magnetic field and Sb are employed to tune the formation of nanowires and nanorods in the microporous films and conduction type.Nanowire is formed in the film with Sb content of 3.0%and'nanorod is formed with 4.6%Sb with the absence of HMF.P-type ZnO films with a wuterzite are formed.The resistivity of the films decreases by two orders of magnitude by increasing Sb content.The resistivity of films decreases 45%and 80%by forming nanowires and nanorods,respectively.The power factor of the nanorod structures increases by two orders of magnitude by comparison with others and reaches to 52.6 ?W/m·K2.This indicates that the nanorod structures with a higher Sb content are easy to obtain stable p-type semiconductor with a higher power factor.The results of ZnO:Sb thin films at different substrate temperatures,oxidation times and Sb contents show that,the film with a high Sb content(5.32%)is easy to form Zn4Sb3 and ZnSb compound in the wurtzite ZnO.The resistivity has a sharply reduction with the Sb content from 0.228 ?·m of 3.95%Sb to 4.68×10-5 ?·m of 5.32%Sb.The lowest resistivity is lower at least one order of magnitude than the results of others with the similar Sb content.The Seebeck coefficient indicates that the 5.32%Sb film remains stable p-type conduction.The carrier concentration is about 1020 cm-3 and is higher at least one order of magnitude than the other results.The power factor of the p-type ZnO:Sb at 427? is 46.79 ?W/m·K2.The results show that the doping content of Sb effects the surface quality and roughness of the films and the light transmittance of the film is higher(80%).In situ growth of various Sb contents of ZnO thermoelectric thin films conduction type are n-type.The conduction type of the film after increasing the substrate temperature is still n-type.The analysis of the results shows that increasing oxygen flow makes the film grow under oxygen-rich condition,which is more conducive to obtaining p-type ZnO:Sb thin films.The temperature range varies from 50 to 250? with a power factor of 1-2.5?W/m·K2.When the substrate temperature is 450?,it will improve the thermoelectric properties.