Mocvd Of Heteroepitaxial Silicon-based Zno And Sic Thin Films And Characteristics Of Study

Silicon carbide is a wide gap semiconductor which exhibits outstanding electronic properties associated with chemical and thermal stability. The SiC-based devices ability to function at high temperature, high power and high radiation conditions will enable large performance enhancements to a wide variety of systems and applications. It attracted more attention for the preparation of single crystal SiC films, which makes easy for homo-epitaxy. However, the SiC crystal wafer is too expensive. Si is a powerful substrate for its low cost. But hetero-epitaxy growth of SiC film directly on Si substrate is very difficult because of the large lattice mismatch and mismatch of thermal expansion coefficients. The present paper has launched the research on the SiC/Si thin film preparation.ZnO is a II -VI compound semi-conductor material with a wide direct band gap of 3.36eV at room temperature. Recently, it has attracted great attention due to its ultraviolet luminescence. For the use of ZnO in high-efficiency light emitting devices and other optical applications, high quality single crystal ZnO films are required. But it is difficult to get high quality ZnO films on the Si substrates because of the large lattice mismatch. Using the buffer layer or substrate pretreatment is a way to get high quality ZnO films. This thesis focus on hetero-epitaxy of ZnO films by MOCVD, researching on the growth condition and using some kinds of buffer layers to grow ZnO films on Si substrates, the single crystal ZnO films on Si substrates using a 3C-SiC buffer layers. The major works and conclusions as follows:1. Single crystal SiC films were successfully prepared on Si substrates.Poly-crystal SiC films were successfully prepared on Si(111) and Si (100) substrates by low pressure metal-organic chemical vapor deposition (LP-MOCVD). The structure of the films has been investigated by X-ray diffraction (XRD) and micro-Raman spectra. 3C-SiC films were grown on Si(111) substrates. The FWHM of SiC(111) rocking curve is only 0.3 arcdegree.2. Effect on Radio Frequency Plasma Pretreatment on ZnO/Si Thin FilmZnO films have been deposited on Si (111) substrates by low-pressure MOCVD. Si (111) substrates were pretreated by RF plasma before growth. The power of RF plasma was arranged from 0W to 110W. Then ZnO thin films were grown in-situ. The great effect of RF plasma pretreatment on the structure and luminescence properties was investigated by X-ray diffraction (XRD), atomic force microscope (AFM) and photoluminescence (PL) spectrum at room temperature. The quality and surface roughness of ZnO thin films using pretreatument are better. The orientation of ZnO films was degraded when the pretreatment energy achieved the certain limiting value. The UV emission intensity decreased because the argon ion bombardment silicon surface has formed the crystal defect which makes quenching of luminescence in growth.3. Using buffer layers to grow high quality ZnO films on Si substratesDifferent buffer layers such as 3C-SiC, DC sputtered ZnO films have been employed, Buffer layers prepared on Si substrates by DC reactive sputtering system is reported in this paper. The thickness of buffer layer depends on the sputtering time. Then the high quality ZnO thin films were grown on the Si substrates by low pressure metal-organic chemical vapor deposition (LP-MOCVD) with sputtering buffer layers. The effect of sputtering buffer layer thickness on the structure and luminescence properties was investigated. The full width at half maximum (FWHM) of rocking curve of ZnO (002) peak was reduced by using sputtering buffer layer and annealing. And the intensity of luminescence was increased. High quality ZnO thin films were deposited on Si(111) substrates by LP-MOCVD with double connected, using SiC buffer layer. The effect of SiC buffer layer on the structure and luminescence properties has been investigated by X-ray diffraction (XRD), photoluminescence (PL) spectra at room temperature. The full-width at half maximum (FWHM) of rocking curve of ZnO (002) reflection is reduced by using SiC buffer layer. And the intensity of luminescence of ZnO films is also increased. In addition, with the SiC buffer layer, green luminescence is appeared which was considered to be from the electron transition from conduction band bottom to the O_Zn level formed in the band gap. With the optimized condition for the SiC buffer layer and ZnO film growth, the single crystal ZnO films were successfully prepared on Si(111) substrates.4. Nitrogen doping in ZnO films by plasma-assisted MOCVDNitrogen doped ZnO films are grown by the plasma-assisted metal-organic chemical vapor deposition(MOCVD) on Si. X-ray diffraction spectra show that they are strongly c-oriented while the N-doped sample is high crystal quality. Secondary-ion mass Spectrometry (SIMS) analysis confirmed the presence of N, The N concentration is rather high, and this means that the values are very uncertain. But p-type ZnO films were not obtained.