| Zinc oxide(ZnO)is a third-generation semiconductor material with wide band gap coefficient(3.37eV)and high exciton binding energy(60meV),belonging to Group II-VI compounds,Because ZnO has good gas sensing properties,piezoelectric properties,optical properties and transparent conductive,and the material itself is non-toxic and easy to obtain raw materials for the preparation of zinc oxide,ZnO has a wide range of applications.At present,it is widely used in solar cells,surface acoustic wave devices,piezoelectric devices,gas sensors,ultraviolet detectors and other fields.The low dielectric coefficient of ZnO thin film materials is helpful to reduce the hysteresis of signals,and has great prospects in the field of optoelectronic communication and microelectronics.As a result,researchers at home and abroad have paid much attention to the ZnO thin films.The conventional preparation methods of ZnO thin films include magnetron sputtering,metal organic chemical vapor deposition,laser pulse deposition,molecular beam epitaxy and sol-gel.However,these technologies can not simultaneously achieve the requirements of low cost,high efficiency and large scale preparation of high-quality films.large scale fabrication and high quality film.Ultrasonic spray pyrolysis has the advantages of low cost and large scale preparation of thin films.Therefore,the main purpose of this paper is to design a tubular furnace assisted chemical vapor deposition(CVD)system based on ultrasonic spray pyrolysis,and explore a cheap method for preparing high-quality ZnO films.The main research work of this paper is as follows:(1)Improved the traditional ultrasonic spray pyrolysis device,and designed and built a tube furnace assisted chemical vapor deposition(CVD)system suitable for the preparation of ZnO thin films.We built the ultrasonic atomization source independently,and designed and simulated the circuit of the atomization source.In order to obtain a smooth and wide vapor laminar flow on the surface of the substrate,the boundary layer model of the tube furnace-assisted CVD system was studied,and the deposition boat was designed and manufactured as substrate carrier.At the same time,the air flow control system was fabricated and constructed.In order to optimize technique of the tube furnace assisted CVD system,an experimental platform was designed and built to study the relationship between the liquid level heights and atomization efficiency.The results show that differentliquid level heights have different atomization results.The atomizer used in this paper can achieve the best atomization results at 3.5 cm liquid level.At the same time,the liquid level maintenance device is designed and manufactured.In order to obtain an accurate substrate surface temperature,the difference in substrate temperature and tube furnace set temperature was investigated,and it was found that the temperatures differed by about 100 C.(2)High crystal quality ZnO thin films were successfully prepared on single crystal Si and sapphire substrates by using the tube furnace-assisted CVD system designed and built by us.ZnO thin films were prepared on Si and sapphire substrates by tube furnace-assisted CVD.The film samples were characterized by AFM and XRD.The effects of substrate temperature,substrate type and placement of substrates on ZnO thin films were studied.The experimental results show that with the increase of substrate temperature,the surface crystal density of ZnO films decreases,the grain size increases,the quality of ZnO thin films has been improved.However,when the temperature is too high,the quality of the ZnO thin film is also lowered.The experimental results show that high-quality ZnO films with high C-axis preferred orientation are prepared on sapphire substrates.By comparing other literatures,we designed a system that can inexpensively produce high crystalline quality ZnO thin films in low temperature environments. |
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