Investigation Of Preparationand Properties For Multicomponent Metal Oxide N-type Semiconductors

Amorphous Indium Gallium Zinc oxide?IGZO?has been emerging as one kind of key materials in thin film transistors?TFTs?for the next generation flat panel displays because of its attractive features such as large carrier mobility,high optical transparency,excellent uniformity and low-temperature process.In the thesis,IGZO films were fabricated by magnetron sputtering.Systematic and detailed study on the electronic properties of IGZO films influenced by process parameters was carried out and thefunctional mechanism has been analyzed and discussed.Furthermore,the intrinsic factors controlling the electron mobility have been revealed through the investigation on carrier transport properties in IGZO films,and the amendment for percolation conduction model has been proposed.Based on the investigation of IGZO films,Nb doped IZO?INZO?films werefirstly proposed as a channel layer in TFTsin order to improve the Hall mobility and reduce the density of deep sub-gap states which relate to the working stability of TFT devices.The main research works and results are as follows:The effects of sputtering current,oxygen flow rate,substrate temperature,and annealing temperature on the carrier concentration and Hall mobility in IGZO films were intensively studied.The results indicated that the variation of carrier concentration in IGZO films originates from the change of oxygen vacancies which act as dornors in IGZO.The Hall mobility is controlled by carrier concentration as well as structural disorder.The reduction of carrier concentration or the enhancement of structural disorder will increase the effective potential barrier height and intensify the carrier scattering,leading to the decrease of Hall mobility.Under the optimized processing condition,high quality IGZO films were obtained with the carrier concentration of 6.01×10¹⁶ cm^-3,which meets the demand for the fabrication of TFT devices.And the optimal Hall mobility was 19.1 cm²·V^-1·s^-1,which is almost 20 times as large as that of a-Si.The carrier transport behaviors in IGZO films were invesgated by Hall Effect measurement at different temperatures from 87 K to room temperature.The results demonstrated that the carrier transport mechanism in IGZO films is percolation conduction.An amendment for the percolation conduction model was proposed by induce the modulation factor M which is related to the spatial distribution of potential barriers.In detail,the intrinsic mobility can be expressed by the product of modulation factor M and the mobility of the electron with high energy that exceeds the potential barrier height.Based on the amended percolation conduction model,it can be concluded that the carrier mobility is essentially subject to the width of potential wells and the average height of potential barriers.The deep sub-gap states in IGZO films were characterized by photoluminescence?PL?spectroscopy technology.The excitation and emission mechanism of each PL peak was analyzed.The 529 nmemission and 698 nm emission are related to the deep sub-gap states which are the origin of threshold voltage shift in TFTs.Those two kinds of emission results from the radiative transition from the conduction band edge to the ionized oxygen vacancy located just above the valance band.Nb doped IZO?INZO?as a new channel layer material was firstly proposed and designed based on the new idea by substitution for Ga in IGZO with Nb.Systematic and detailed studieson the influences of oxygen flow rate and substrate temperatureon the electronic properties of INZO films were carried out.The higher mobility of INZO films originates from the wider width of the potential wells and lower height of potential barriers.The lower density of deep sub-gap states originates from the suppression of oxygen vacancy formation due to strong ion field strength of element Nb.The highest mobility of 45.0 cm²·V^-1·s^-1 for the INZO films with the carrier concentration of 10¹⁹ 10²⁰ cm^-3was reached.