Epitaxial Growth And Characterization Of Gallium Oxide Thin Films Materials

Gallium oxide?Ga₂O₃?is a wide band gap transparent conductive oxide semiconductor material with a variety excellent qualities,it has been widely used in power electronic devices,gas sensors and solar blind detectors etc in recent years.Especially in the application of the third-generation wide-bandgap semiconductor materials and devices mainly composed of gallium nitride?GaN?,Not only does the thermal stability of GaN-based semiconductor materials affect the schottky contact at high temperatures,but the surface of GaN-based semiconductor materials is prone to form oxide layers due to natural oxidation,which worsens their properties.Therefore,complex surface/interface states become one of the key factors restricting the development of GaN-based materials and devices.Considering that drain current of schottky gate is one of the main problems restricting the development of GaN based power devices,the dielectric layer material of schottky gate is a key factor affecting the performance of GaN and its multiple related semiconductor materials?AlGaN,InGaN,etc.?.Ga₂O₃ as a schottky gate dielectric layer material can effectively solve the problem of gate leakage of GaN-based power devices.Because not only the preparation of a layer of Ga₂O₃ epitaxial film on the surface or interface of GaN and its multivariate dependent materials can improve the passivation effect and greatly reduce the interface state density by replacing the naturally formed oxide layer,but epitaxial growth of Ga₂O₃ thin films on GaN epitaxial wafer,forming Ga₂O₃/GaN heterojunction structures,the regulation of the schottky barrier height,which will further expand the application of wide bandgap materials in optoelectronic devices.Therefore,it is of great significance to develop Ga₂O₃ thin film materials and Ga₂O₃/GaN heterojunction to improve the performance of GaN-based power devices.Based on the above analysis,this paper uses remote enhanced plasma atomic layer deposition?RPEALD?technology to epitaxial grow Ga₂O₃ thin film material and Ga₂O₃/GaN heterojunction,and studies the energy band structure of Ga₂O₃/GaN heterojunction.By discussing the effect of plasma on the surface structure of GaN,the influence of GaN surface structure on epitaxial Ga₂O₃ film and Ga₂O₃/GaN heterojunction is studied,and the growth mechanism is discussed.Then,Ga₂O₃ thin film is used as a gate dielectric layer in MOS devices and its electrical properties are studied.The main research contents of this paper are as follows:?1?In order to obtain controllable Ga₂O₃ thin films epitaxial growth parameters,RPEALD technique was used to study the effects of pulse time,deposition temperature,plasma RF power and substrate on RPEALD epitaxial Ga₂O₃ thin films deposition rate,surface morphology and chemical composition.Result showed that 0.1 s trimethylgallium pulse and 20 s oxygen plasma pulse time has reached the saturated state,in 100-400?deposition temperature window,the chemical state and stoichiometric ratio of Ga₂O₃ films remain unchanged,the Ga₂O₃ films surface morphology became roughen in high temperature.The deposition rate of Ga₂O₃ film increases first and then decreases with the increase of plasma RF power.Compared with Si substrate,the deposition rate of Ga₂O₃ thin film deposited on n-GaN epitaxial wafer is0.24???/cycle,which is very slow and affects the deposition efficiency of thin films.?2?Based on the efficiency of Ga₂O₃ thin film deposited on n-GaN epitaxial wafer by RPEALD,in order to improve the deposition rate of Ga₂O₃films,using NH₃ plasma treatment in situ n-GaN epitaxial wafer surface,effects of regulating n-GaN surface states on RPEALD epitaxial Ga₂O₃ thin film was studied.It was found that the deposition rate of Ga₂O₃ thin film increased to0.46???/cycle,but the surface smoothness and uniformity,chemical state and stoichiometric ratio of Ga₂O₃ thin film were not affected.It was found that the deposition rate of Ga₂O₃ thin film increased at the initial stage of growth,making the wide step of surface morphology of n-GaN epitaxial wafer become the narrow step of Ga₂O₃ thin film.In addition,NH₃ plasma acts on n-GaN epitaxial wafer,causing some surface damage,and the crystalline quality of Ga₂O₃ thin film is slightly inferior.?3?In order to verify that Ga₂O₃ dielectric layer can solve the problem of gate leakage current,Ga₂O₃ thin film was applied as a gate dielectric layer in MOS structure to regulate the interface state.A 2 nm Ga₂O₃ thin film is grown by RPEALD between the traditional Al₂O₃ dielectric layer and the GaN-based semiconductor.As a result,in the structure of Al₂O₃/Ga₂O₃ double dielectric layer,the leakage current reduced about six orders of magnitude,compared with the MOS structure of Al₂O₃ dielectric layer,explain the existence of the 2nm single-layer ultra-thin layer Ga₂O₃ layer can play a very good passivation effect the passivation effect,and the interface state density decreases significantly.Moreover,the plasma generated by in-situ H₂O treatment before deposition of Al₂O₃ dielectric layer can also reduce the interfacial state density.