Low Temperature Growth Of Polycrystalline InN Films On Non-crystalline Substrates By Atomic Layer Deposition And Fabrication Of Thin Film Transistor

In panel displays,each pixel has a thin film transistor(TFT)to switch the pixel to achieve the display effect.At present,TFTs in the market are mainly dominated by amorphous silicon and low-temperature polysilicon.Among them,amorphous silicon occupies most of the TFT market in the past few decades due to its advantages of large-scale application in flat panel displays.With the continuous development of technology,the demand for large-size,high-frame-count flat panel displays is also increasing,and the shortcomings of amorphous silicon and low-temperature polysilicon are becoming more and more obvious.Indium nitride(InN)is an important material in the third generation of semiconductor materials.Among III-V nitrides,it is very promising which has the highest carrier mobility,highest saturated driftvelocity,and minimum effective electron mass.At present,the methods of preparing InN thin films mainly include molecular beam epitaxy(MBE),metal organic chemical vapor deposition(MOCVD),magnetron sputtering and atomic layer deposition(ALD)etc..In this thesis,InN thin films was fabricated by plasma-enhanced atomic layer deposition system(PE-ALD).PE-ALD has much advantages like low deposition temperature,good uniformity,and superior step coverage.It is very suitable for the preparation of InN thin films on substrates which cannot work at high temperatures,such as glass and polyimide.The major contents of this thesis are summarized as follows:1.Polycrystalline InN thin film was prepared on a glass substrate successfully.In this research,the change of InN crystallization performance as the film thickness increases was investigated.XRD test results show that when the film thickness reaches 60 nm,the InN film grown on the glass gradually changes from amorphous to polycrystalline,and has excellent electrical conductivity.2.Polycrystalline InN film was prepared on a flexible polyimide substrate successfully.Similar to the glass substrate,the InN film on the polyimide substrate gradually crystallizes as the thickness increases.When the film thickness reaches 60 nm,the film turns into a polycrystalline form,which also has excellent conductive properties.3.Polycrystalline In-rich polycrystalline In0.8Ga0.2N thin film and Ga-rich polycrystalline In0.2Ga0.8N thin film was successfully fabricated on the glass substrate.In both groups of samples,SEM analysis showed that the grains were closely packed together,and the polycrystalline diffraction peaks were also seen in the XRD pattern.By measuring its electrical properties,it can be found that the resistivity increases significantly with the addition of Ga.4.In this research,thin film transistors with InN as the channel layer was prepared.The field effect mobility of the device is 27.8 cm2/Vs,the switching ratio is 105,and the threshold voltage is-4.25 V,which provides the possibility of preparing InN thin film transistors on flexible amorphous substrates.