The Investigation Of Epitaxial-growth And Doping For SiC And ZnO

As third era wide gap semiconductors,Silicon carbide and Zinc oxide have attracted great attention due to themselves' excellent properties.Silicon carbide exhibits great potential applications in high frequency,high power,high temperature and high radiation conditions,because it has high electron saturated drift velocity,excellent thermal and chemical stability.While,the SiC single crystal is too expensive, which spur people to keep on study the heteroepitaxial growth of SiC film on silicon substrate.Zinc oxide has a high excition binding energy of 60meV at room temperature,and it is considered to be a new photo-electric material in shortwave length as GaN.However,the applications of higher-efficiency laser diode and light emission diode devices have been limited by the lack of reliable p-type ZnO.On the other hand,to realize the EL on the bases of ZnO,hunting for other wide bind gap p-type materials and hetero-epitaxy ZnO films on them has attracted people's attentions.Based on the research background,the major works and conclusion are listed as follows:Firstly,there has been a great deal of interest in heteroepitaxial growth of SiC films on silicon substrates."Two steps method" is the basic technics for the hetero-epitaxy growth of SiC films on silicon substrates.However,the interface holes which were induced by the diffuse of Si atom from silicon substrates during the high temperature carbonization processes will cause serious damage to electronic devices.Under this conditions,"Three steps method" was promoted which is consist of carbonization, little flux buffer layer and SiC film growth for the hetero-epitaxy growth of SiC films. The introducing of Silane during carbonization could restrain the out-diffusition of Si atom and reduce the interface holes effectively,and then increase the crystal quality of SiC films.This improvement will facilitate the development of devices which based on the hetero-junction of SiC/Si and ZnO/SiC/Si.Secondly,during the growth of p-type SiC films,it is found that the introducing of TMA could improve the crystal quality of SiC films and increase the growth rate, which will lead to the relaxation of strain stress in SiC films.Moreover,the growth process varies from three-dimensional island-growth mode to step-flow growth mode after introducing TMA during SiC films growth.The influence of TMA on the growth of SiC films on the Si(100)and Si(111)substrates varied,this is because the surface free energy of Si(100)and Si(111)is different.The Al:SiC/n-Si hetero-junction was fabricated successfully,and then its electrical properties and deep level transient spectroscopy were analysised.According to deep level transient spectroscopy,The acceptor energy level was calculated which is 220meV.Based on p-type SiC films,the n-ZnO/p-SiC could be prepared and its EL properties could be investigated in the following work.Thirdly,the electrical and optical properties of Al-doped ZnO films have been studied.Based on the results of N-doped ZnO film by the plasma-assisted metal-organic chemical vapor deposition,p-type ZnO films were prepared by N-Al codoping.The change of optical and electrical properties of ZnO films were studied by varied the RF power and the flux of TMA.To investigate the luminescence mechanism of N-Al doped ZnO films,low temperature photoluminescence spectra was measured.The peak near 3.312meV was existed both in undoped and N-Al doped ZnO films.We classified this peak as the transition of the acceptor-bound excition (A⁰X)related to No acceptor.Compared with the position of A⁰X in undoped ZnO films,the peak of A⁰X shifted to lower energies,and this phenomenon was induced by the incorporation of Al.A photoluminescence recombination possibly due to the free-electron-to-acceptor(FA)transition was observed at temperatures higher than 40K in N-Al doped ZnO films.The acceptor ionization energy was estimated from the energy position of the FA luminescence to be 183.7meV.Moreover,the excitation intensity-dependent PL spectra which taken at 80K in N-Al doped ZnO film was measured.The luminescence band labeled DAP shifts to higher energies with increase excitation intensity.Lastly,using DEZ and H₂O as source materials,the growth of high crystal quality ZnO films under lower growth temperature by MOCVD was investigated.Compared with the ZnO films which were grown by using CO₂ as oxygen source material,the ZnO films which were grown by using H₂O as oxygen source material have excellent photoluminescence properties.The total N₂ flow rate,the ratio of Zn/O and the growth temperature were optimized to improve the crystalline quality of ZnO films on silicon substrates.Then by using the buffer layer technique,the ZnO films with high crystal quality and excellent photoluminescence properties were got.The luminescence band in visible range for the annealed ZnO films varied with the annealed temperature and the annealed ambience.The green band is shown to consist of several components,such as V_O,V_Zn,O_Znand so on.The surface morphology shown that the growth of ZnO films proceed three-dimensional island growth mode. So it is still need to take deeper study to realize step-flow growth mode.