Sic Thin Films Of Ssmbe Epitaxial Growth And Structural Characterization

Silicon Carbide(SiC) is one of the most important wide-band gap semiconductor material with excellent physics and chemical properties, which is a promising material for many applications in electronic and optoelectronic devices working in very extreme conditions such as high temperature, high frequency, high voltage, high power density. SiC material will play an important role in modern semiconductor device technology. Comparing with the other method, solid-source molecular beam epitaxy(SSMBE) has unique advantage in the field of SiC films growth. In this thesis, high quality 3C-SiC films on Si single crystal substrates and quantum wells structure based on SiC polytype on 6H-SiC single crystal substrates are first grown by using SSMBE in China. In situ RHEED, conventional analysis methods and synchrotron radiation(SR) experimental techniques are employed to investigate the structure, composition, morphology, and optical property of the samples. The main work and results are listed as following.1. Building up of SSMBE system and developing of its key componentsA sample holder with the heater of high temperature up to 1400℃which can work under the condition of ultra high vacuum(UHV) stably and two electron beam evaporators(EBE) for Si and C sources are designed and developed successfully. The EBE has many advantages, such as simple structure, low price, easy maintenance, and stable flux, etc. Based on the development of such key components, the first high temperature SSMBE system in China for SiC films growth has been built up, which provide the necessary condition for SiC film growth. 2. Hetero epitaxy of SiC films on Si substrate and investigation of their structure and optical propertiesDuring the process of hetero epitaxy of 3C-SiC films on Si substrate, the effects of growth parameters, such as carbonization of Si surface, carbonization temperature, growth temperature, Si/C flux ratio, and flux rate on the quality of SiC films are investigated systematically. The parameters are optimized and the high quality 3C-SiC films have been obtained. The FWHM of XRD rocking curve of 3C-SiC(111) diffraction of the sample which was grown at the optimized growth parameters is only 1.1°. With higher substrate temperature(1250℃), the hetero epitaxy of 6H-SiC films on Si substrate are performed successfully. The adsorption of C₆₀ on Si surface and the process of annealing to form SiC are investigated by in situ RHEED and SRPES in detail. SR X-ray grazing incidence diffraction(GID) experiments are employed to investigate the information of structure and strain of SiC films grown on Si substrate with different depth. The results indicate that the strain of the SiC film decreases and the crystalline quality of the SiC film becomes better with the depth from the SiC/Si interface to the internal of the film. This phenomena indicates that the influences of misfits of lattice and thermal expand coefficient between SiC film and Si substrate upon the film quality become smaller with the depth departing from SiC/Si interface. The results of GID and XRD show that the SiC films are under biaxial tensile strain which is caused by misfit of the thermal expand coefficient between SiC film and Si substrate. The film has different tilt mosaic and twist mosaic. The angle distribution of the former is larger than that of the latter. We attribute it to the misfit dislocation. Photoluminescence excited by vacuum ultra violet light of SR is used to investigate the optical properties of the samples. The results indicate the luminescence becomes more intense when the crystalline quality of the films becomes better. 3. Homoepitaxy and research on the growth, structure and optical properties of SiC polytype quantum wells on 6H-SiC(0001) substrateA new approach to obtain the reconstruction of SiC(0001) surface is developed. The 3×3 and 3^1/2×3^1/2 reconstruction can be obtained and transform reversely by maintaining or cutting Si flux. The 3×3 reconstruction obtained by this approach is at high-temperature. Comparing with the 3^1/2×3^1/2 reconstruction surface at the same temperature, the diffusion of the atoms on the 3×3 reconstruction surface are more active, which is convenient for the film growth. During the homoepitaxial growth on 6H-SiC(001), the surface reconstructions, the growth mode and the polytype of film can be influenced by varying the Si/C flux ratio. The pre-nucleation followed by step flow growth mode can be performed by changing the Si/C flux ratio and the 6H-SiC/3C-SiC/6H-SiC quantum wells structure is obtained with this growth mode. XRD results indicate that there are a tilt angle 0.3°between the film and the substrate. The FWHM of the rocking curve of SiC(111) diffraction is 0.09°. The results of GID confirm the 6H-SiC/3C-SiC/6H-SiC quantum wells structure of the homoepitaxial film and indicate that because of the defects introduced by the random nucleation of 3C-SiC, the crystalline quality degrade during the nucleation of 3C-SiC on the 6H-SiC surface. While the defects are eliminated gradually and the crystalline quality is improved during the process of following step flow growth. PL excited by He-Cd laser with 325nm at room temperature is used to investigate the optical properties of the sample. The results show that there are intense emissions in the range of 480-600nm. We attribute it to the luminescence of the 6H-SiC/3C-SiC/6H-SiC quantum wells. The calculated results show that the wide range of spectrum is probably caused by the different width of quantum wells.