Study On MBE Growth Of GeSn Film And GaAs-Based Integrated Photovoltaic Devices

In the past few decades,Group IV semiconductor optoelectronic devices have been widely used in optoelectronic integration,high-speed optical communication and high-speed signal processing.Germanium is considered to be the best candidate for Silicon-based photodetectors.The breakthrough of Ge film epitaxial growth technology has led to the advancement of Ge film photodetectors on Si.Since the indirect bandgap of Ge is smaller than its direct bandgap,Ge is an indirect bandgap semiconductor and is relatively limited in optical applications.In order to overcome this difficulty,synthesizing GeSn alloys with high quality has attracted great interest.The participation of Sn can reduce the direct band gap.People can adjust the wavelength of infrared absorption by controlling the proportion of Sn in GeSn film.Therefore,GeSn material has a good application prospect in infrared photodetection.In the study of how to prepare higher quality GeSn films,this thesis has improved the experiment in two aspects.First,GaAs is selected as the substrate.The lattice constant of GaAs and the cell size of Ge differ only by 0.1%,which results in that the density of threading dislocations in the Ge buffer layer on GaAs is much smaller than that on Si.This feature not only greatly reduce the extension structure defect when the Ge buffer layer infiltrate into the GeSn film but also reduce the surface segregation and plastic relaxation of Sn.Secondly,we attempt to fabricate three-dimensional epitaxial GeSn films.Most of GeSn film photodetectors are two-dimensional planar structures.Fabricating three-dimensional epitaxial GeSn films can improve the performance of two-dimensional film photodetectors.In this thesis,a two-dimensional GaAs-GeSn thin film PIN photodetector is fabricated.The surface topography,X-ray diffraction,X-ray photoelectron spectroscopy,Raman spectroscopy,infrared absorption and photoelectric properties are studied.This thesis has done a detailed study on the optimal growth conditions,the influence of Sn,the longitudinal structure design and fabrication of PIN junction.A detector is fabricated by semiconductor lithography,etching and other processes.Then the volt-ampere characteristic curve and On-Off curve of the device were derived by the detector.We also studied the effect of Sn composition on the performance of photodetectors.Finally,a GaAs-GeSn thin film PIN photodetector with three-dimensional epitaxial structure was fabricated.The scanning electron micrograph,Raman spectroscopy,infrared absorption and photoelectric properties of the film are studied.This thesis explores the effect of array depth for three-dimensional epitaxial GaAsGeSn thin films and their photodetectors performance.