Design Of In-situ Stress Monitoring System During MOCVD Growth And Fabrication Of SiO₂/Si₃N₄Distributed Bragg Reflectors

Heteroepitaxy plays a fundamental role in compound semiconductor materials and devices. It has become one of the hottest scientific topics on heteroepitaxally grown GaN, ZnO, SiC, and other compound semiconductor thin films on silicon or sapphire substrates. However, the stress between substrate and epitaxial layer is inevitable during growth, because of the mismatches of thermal expansion coefficient and lattice constants between the epitaxial layer and the substrate. The excessively large tensile stress or compressive stress will cause cracking, curling, shedding and breakage in the surface of the film, and those cannot be ignored. So in-situ monitoring of the stress in the epitaxial layer is important.Distributed Bragg reflectors (DBR) are one of the crucial components in the field of resonance photonic devices. They are widely used in vertical external cavity surface emitter laser (VECSEL), Fabry-Perot Cavity Photomodulator, Fabry-Perot filter, resonant cavity detector as well as light-emitting diodes (LED). The SiO2/Si3N4dielectric multi-layers are suitable for using as the DBR structures. Because it is cost efficient, easy to get, high optical performance.Firstly this thesis proposes an optical system for epitaxial film stress in-situ measurement; secondly investigates on fabrications of DBR as well as the properties of DBR, and main achievements include:1. In order to measuring micro-press in thin film during semiconductor hetero epitaxy, an interferometer with two laser beams injecting through two quartz optical ports vertically to a sample is designed. The parameters of curvature and stress are in-situ measured by optical path difference, and the impact caused by sample lean is avoided. With beams vertical injection, comparatively large optical window and CCD are not necessary, and measurement accuracy of the system is improved greatly. With interference intensity and phase probed by a lock-in amplifier, the system can measure accurately the stress evolution of semiconductor epitaxial files, and it provides the basis for growing the high quality epilayers.2. Optimize the process of fabrications of SiO2and Si3N4, and obtain their deposition rates and refractive indexes; It is found that there are some oxygen impurities in Si3N4, due to the unintentional doping of oxygen element in PECVD reaction.3. The reflectivity of single DBR structure reaches as high as97%, and whose reflection spectra are fit well with simulations. With two combined DBRs with different center wavelengths to form a vertical double DBR structure, one broad reflection and one wavelength filter are obtained. However, the deep interference phenomenon occurs in high-reflection region, which origins that the reflectance spectra of long wavelength band are affected by the upper DBR in the vertical structure.