Study Of Transienttransfers Characteristics And Injuring Mechanism Of High-power Semi-insulation GaAs Photoconductance Switch

The Photoconductive Semiconductor Switch (PCSS's) is a new type of super-fast photoelectric device made through combination of the super-fast pulse laser and the semi-conducting GaAs material. Compared with the traditional switch, PCSS is free of jitter in its ignition, small in its parasitic inductance and capacitance, fast in its pulse increase, short in its turn-off delay, and high in its GHz repetition rate. And particularly remarkable are its good resistance to high voltage and its high-powered capacity that enable it to find its wide use in such fields as super-speed electronics, and the technology of generating and reshaping high-powered pulse. The study of the jitter-proof ultra-short pulse by using the GaAs photoconductive switch to generate high-powered voltage, therefore, has become the key problem that calls for prompt solution within the fields like the building of national defense, super-wideband communication, super-wideband radar, and reality of electromagnetic weapon. In this dissertation, through the research into the properties of chip material, an analysis is conducted of the effect of scattering mechanism on the output characteristics of electric pulses. A summary is made of the experimental law under the linear and non-linear modes. Then, by means of optically activated charge domain model, an analysis is" conducted of the transmission characteristics of the switch under the non-linear mode. And an experimental research and a theoretical analysis are pursued with regard to the life-span of the switch under the non-linear mode.This dissertation focuses its discussion mainly upon the properties of semi-insulating (SI) GaAs material, in which a fuller analysis is made of its mass resistivity, impurities and defects, and carrier mobility. A study is conducted on the scattering mechanism in the semi-insulating GaAs material. Based on the scattering theory, a general expression is worked out for both the scattering rate and final status of scattering mechanism, thus seeking out the scattering mechanism that produces a major effect on the output electric-pulse of semi-insulating GaAs photoconductive switches; and then a specific discussion is directed toward the effect of scattering mechanism on the output performance of the switch when there is change in such parameters as temperature, maximum power of triggering light, and the gap between switches. A theoretical analysis is made of such experimental phenomena as photo-electric delay under the linear mode, and spreading breadth of electric pulse, the results of which show that the main cause for the spreading breadth of output electric pulse is the capturing effect of anti-site As_Ga defect energy level. And a sound explanation is presented for the results of the experiment.The theory of optically activated charge domain is adopted to analyze both the output characteristics and the photoelectric threshold condition of the semi-insulating GaAs photoconductive switch under the non-linear operational mode. Based on the conclusion of experimental law, the photoelectric threshold condition is obtained for the semi-insulating GaAs photoconductive switch under the non-linear mode, pointing it out that, when the optic-energy triggers off the switch to meet the prerequisite that n₀L is greater than or equal to 10¹²cm^-2, the necessary condition is achieved for high field domain and meanwhile the threshold electric field serves to produce charge transmission effect within the material. The cooperation of optic field and electric field helps create a high-field domain within the switch. The transfer of high-field domain determines the characteristics of the photoconductive switch's output electric pulse. The working characteristics of the photoconductive switch are discussed, from the viewpoint of optically activated charge domain theory, respectively within the linear zone, non-linear zone and threshold zone; and an analysis is conducted of the causes for the photo-electric delay of the semi-insulating GaAs photoconductive switch under high voltage. What is concluded herein matches well with the results of experiments.A detailed theoretical analysis is made of the switch electrodes as well as of the deterioration and damage of chip material under both high voltage and powerful current. As pointed out in the dissertation, the deterioration and damage of electrode are the effects of such factors as respective scattering between the switch's electrode metal and semi-conducting material, and the electric transfer of metal electrode when the powerful electric field is triggered off. In such a process, the damage to the anode, due to potential barrier around, is heavier than that to the cathode. The main reason for the puncture of chip material is that there exists energy level EL2. Through the mechanism analysis of the role of energy level EL2 in the switch, it is suggested that the defect of deep energy level and heat effect are the main causes for the puncture of the switch. Through the mechanism analysis of the puncture of the photoconductive switch, therefore, the service life of the switch can be extended in the following ways: (1) Select appropriate trigger light source; (2) Choose the optimum interval between the two electrodes of the switch chip; (3) Redesign the shape and location of electrodes; (4) Select new electrode materials; (5) Improve contact interfaces. The project has been sponsored by The National Natural Science Foundation of China. (No. 10376025, 50477011)...