Ge Growth On Patterned Si Substrates And Si-based Ge Waveguide Photodetector

It is well known that microelectronics technology dominated by silicon have made remarkable achievements in the past half century. It greatly promoted the development of information technology. However, due to the indirect-band-gap and no response on above1.1μm bands, Silicon is difficult to apply in some active optical communication devices. Ge have been extensively applied in optoelectronic devices such as photodetectors, optical modulator and MOSFET due to their higher electron and hole mobility, high absorption coefficient in the infrared wavelengths and in compatibility with Si microelectronic processing. Si based Ge waveguide photodetectors which combine the advantages of Ge and waveguide-coupled structure, can improve the quantum efficiency and bandwidth. But it is a great challenge to directly deposit high-quality Ge films on Si substrates due to the large lattice mismatch and thermal mismatch between Si and Ge. Therefore, the fabrication of high quality Si-based Ge films and the Ge photodetector with well optical responsivity are very meaningful. In this thesis, we carried out a series of work about the epitaxy of Ge on patterned Si substrate. Moreover, we fabricated the Si-based Ge waveguide photodector and measured its photoelectric properties. The main works are summarized as follows:1. Finite element method is used to simulate thermal mismatch strain in epitaxial film on patterned Si substrate. Strain distribution is analyzed which is from the inside out of the film and the strain against film thickness and substrate size are obtained. The results indicate that maximal thermal mismatch appears in the interface of film/substrate heterostructure, and the thermal mismatch is smaller from the interface to the epitaxial film surface; strain decreases gradually from center to edge and suddenly drops on the edge; strain distribution of the film is in the same rule with different thickness and thin film means small strain; size of the substrate has great influence on film strain, strain release of the epitaxial film can be accepted when the substrate width are10μm respectively. 2. In order to obtain a patterned Si substrate with a good surface smoothness and high selection ratio, we studied the process of dry etching and anisotropic wet etching of silicon and compared the advantages and disadvantages of two solutions of KOH and TMAH to etch silicon. During the process of dry etching of silicon, we compared the effect of two different etching models of RIE and ICP. Finally, we concluded that a silicon mesa with a high surface smoothness and steep sidewall could be achieved by using ICP etching model.3. We studied the surface topography, discrepancy of crystalline FWHM and strain in epitaxial Ge grown on patterned and plane substrate. The thickness of Ge film is1.2μm.Ge{311}facet occurs on the patterned substrate. The dislocation density of Ge mesa is smaller than that around the mesa. X-ray diffraction and Raman spectroscopy indicated that Ge grown on patterned silicon substrate had better crystal quality with a smaller value of FWHM and a smaller strain.4. The properties of the propagating field in the mixed-coupled structure pohotodetector were simulated by Rsoft. It revealed that about85%of the light is absorbed by Ge with0.99μm thicknesses,20μm Ge legth, unincluding the coupling loss form the optical fiber to the waveguide.5. SOI-based Ge waveguide photodectors were fabricated. The dark current density is0.2mA/cm2at-1V reverse bias. At wavelength1.3μm, the responsivity is64mA/W at-1V reverse bias, and the corresponding external quantum efficiency is6.06%.