Fabrication And Properties Of Transparent Electrode Vertical Photo-conductive Switch Device Based On SiC Crystal

In this thesis,the development history of semiconductor photo-conductive switch devices is briefly reviewed.In recent years,the developments of photo-conductive switches based on SiC crystals and their applications in the field of pulsed power technology have attracted more and more attention due to their physical properties such as wide band gap,high critical breakdown field strength,high electron mobility,high thermal conductivity and good chemical stability.In this thesis,the basic types,working principles,micro-mechanisms and application directions of semiconductor photo-conductive switches are briefly introduced.It is pointed out that how to improve the on-state performance and how to increase the working power of the switches are two emphases in current researches of this kind of switch.In this thesis,V-doped semi-insulated 4H-SiC wafers were selected as the substrates.Meanwhile,a circular metal electrode vertical switch device was selected as the basic structure to improve the on-state performance of photo-conductive switch devices.The effects of different film layers on improving the performance of switch devices were systematically studied by adding AZO anti-reflection film in the anode region,adding Ag reflective film in the cathode region and inserting AZO sub-contact layer between 4H-SiC wafer and Ag reflective film.The optimal structure of this kind of switch device was determined.For the switch device with AZO anti-reflection film,metal Ag reflective film and AZO sub-contact layer,the on-state performance has been improved to a certain extent.It is confirmed that the crystal quality of SiC crystal substrate is closely related to the on-state performance of the switch device.The important criterion for selecting SiC wafer as the substrate of switch device is that the SiC wafer must have the consistency of multi-type structure.Even better,there are few micro-channels,dislocations and other micro-defects extending parallel to the crystal c-axis direction.In 4H-SiC wafers,some point defects composed of impurity particles can introduce impurity level into the band gap,which plays a positive role on the on-state performance of switch devices.In this thesis,the possibility of introducing SGO film layer into transparent electrode vertical photo-conductive switch based on SiC crystal is explored to improve the working power of the photo-conductive switch device.SGO film has a better absorption of light-triggered pulse in ultraviolet band.As an anti-reflection film in the anode area of the switch device,it can effectively improve the laser energy inputted into the substrate and the saturation value of photo-generated carrier concentration in the substrate,thus improving the working power of the switch device.The experimental results show that the conductive properties of the SGO poly-crystalline film prepared on 4H-SiC wafer substrate by magnetron sputtering and high temperature treatment are balanced between its conductivity and transmittance properties in UV-visible light band.