The Physical Mechanisms In Gaas Photoconductive Semiconductor Switches (pcss)

In this dissertation the physical mechanisms in gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS) have been explored. This original research has given emphasis to the physical mechanisms of the high gain GaAs PCSS. The lock-on effect observed in high power, light-activated GaAs bulk switches is very important in determining the GaAs power device performance and in applying the GaAs PCSS to engineering. In this thesis, much attention is paid to the relation between the theoretical analyses and experimental results, and the action of a connecting link between the preceding and the following. Based on the analysis of the reported experimental results: S-shaped current-voltage (I-V) characteristic curve of the high gain GaAs PCSS, photoionization, the relations between the domainlike structures and current filaments, the characteristics of the current filaments, and the relations between the current filaments and lock-on, fast current rise times, etc., in high gain GaAs PCSS, the"domain electron avalanche (DEA)"concept and the"ionizing wave (IW)"processes are first introduced to understand the mechanisms of lock-on. The basic theory of the"streamer model"is therefore established. The impact ionization in the DEA and IW processes describe the mechanisms of the"local high-field impact ionization (HFII)"avalanche carrier generation. They can explain the streamer formation and propagation, and"low-field avalanche carrier generation"in the high gain GaAs PCSS. The theoretical framework of a full understanding of the physical mechanisms of lock-on effect has been systematically established. The main contents in this thesis are as follows:1. The physical mechanisms of the high gain GaAs PCSS are analyzed with the semiconductor physics and the gas discharge theory. The model of the streamer on the basis of"domain electron avalanche (DEA)"is presented. The model describes the development of the multistage streamers. The discharge of the current filament across the gap of PCSS leads to lock-on. The development of each stage streamer consists of three processes: photo-ionization, the DEA associated with the carrier injection and avalanche carrier growth. Photo-ionization effects include the laser trigger and recombination radiation originating from streamer. The space threshold for illumination region in the direction of initial electric field is presented. Radiation effect in a streamer of semi-insulating (SI) GaAs PCSS is analyzed. It is revealed that the upper limit of the local excess carrier density created by photo-ionization from the streamer. The necessary conditions and basic characteristics of the DEA are presented. The physical processes of the evolution of the S-shaped I-V characteristic of the device are described. The general processes of a streamer formation and propagation is elucidated. The streamer is maintained by the IW processes. After the first"return ionizing wave (RIW)"crosses the current filament, the transition from the space-charge-limited (SCL) current to double injection current at high injection level is completed and the lock-on occurs. The model is successfully used to explain the experimental results of the high gain GaAs PCSS.2. According to the result of the experiment of linear electrical pulse generated by PCSS, and combining the external circuit, the numerical simulation was performed by computer.In Chapter 1, a historical overview of the developments of the PCSS is given and shows that no satisfying theory is currently available for the high gain GaAs PCSS. In Chapter 2, the basic theories for analyzing the high gain GaAs PCSS is elucidated. In Chapter 3, the ideal model for high gain intrinsic GaAs PCSS are established. In Chapter 4, the physical mechanisms in high gain semi-insulating (SI) GaAs PCSS are explored. In Chapter 5, this model is further used to analyze the experimental results of high gain SI GaAs PCSS, and this indicates that this model is reasonable. In Chapter 6, the physical mechanisms of linear PCSS are validated. In Chapter 7, the summary of the whole dissertation and the outlook for the future works are given.