【作者】 裴涛；

【导师】 施卫；

【作者基本信息】 西安理工大学 ， 物理电子学， 2009， 硕士

【摘要】 GaAs光电导开关(Photoconductive Semiconductor Switches简称PCSS’s)具有触发无晃动、寄生电感电容小、上升时间快、重复频率高等特点,特别是耐高压及大功率容量使其在超高速电子学和大功率脉冲产生与整形技术领域具有广泛的应用前景。然而高增益模式下存在丝状电流现象且锁定时间长达几到几十微秒,极易造成开关电极和芯片材料的损伤,极大的缩短了开关的使用寿命,限制了这类器件在高电压大功率领域的应用。寿命问题已经成为制约开关发展的关键因素。分析了开关电极和芯片材料的退化和损伤机制。指出芯片材料的损伤主要是由于EL2能级的存在；深能级缺陷及热效应是导致开关击穿的主要原因。电极的退化和损伤主要是由于强电场触发时,开关电极金属-半导体材料互扩散、金属电极的电迁移等效应。在高压强流下分别进行了开关的寿命实验和耐压实验。基于光电导开关中丝状电流的流注理论解释了开关芯片上损伤的深沟道现象。认为电流流注首先出现于载流子高密度区,由于辐射复合和再吸收,会触发材料产生新的电子-空穴对,导致载流子雪崩倍增。随着电流的增加,容易在熔融材料的流注通道上产生二次流注,这样流注通道不断积累,最终造成了很深的损伤沟渠。通过两种组合开关可以抑制锁定效应,提高高压强流下开关的寿命。GaAs PCSS’s与气体开关的组合开关：既可以获得更大的电流脉冲；又可以获得超快的下降沿,后者可以避免由锁定效应引起的开关的持续损伤,同时,气体间隙的存在使得光电导开关不会长时间承受高电压,有利于提高开关寿命。双层GaAs PCSS’s的组合开关：两层GaAs开关既能先后发生高增益过程,又能相互抑制对方进入锁定状态,因此在高于非线性触发光电阈值的条件下,既具有非线性模式特有的所需光能小的优点,又具有线性模式特有的使用寿命长的优点。更多还原

【Abstract】 GaAs Photoconductive Semiconductor Switches (PCSS’s) are free of fitter in their ignition, small in their parasitic inductance and capacitance, fast in their pulse increase, short in their turn-off delay, and high in their GHz repetition rate. And particularly remarkable are their high withstand voltage and their high-powered capacity that enable whom to find their wide use in such fields as ultrahigh-speed electronics, and the technology of generating and reshaping high-powered pulse. However, because of the existence of the filament currents in the non linear mode of PCSS’s, the switch electrodes as well as chip material are easily damaged, which greatly reduces the lifetime of PCSS’s and limits the application of these devices in high-voltage and high-power fields. The longevity problem has become the key factor in restricting the development of PCSS’s.The degradation and damage of the switch electrodes as well as chip material is analyzed. It is shown that the main reason for the puncture of chip material is that there exists the deep level trap EL2; The defect of deep level trap and Joule heat effect are the main causes for the puncture of the switch. The degradation and damage of electrode are caused by the effects such as diffusion effect between the switch’s electrode alloy and semiconductor material, and the electromigration metal electrode when the switch is triggered under high electric field.Voltage withstand test and lifetime test of the PCSS’s are performed under high voltage and strong current. The phenomenon of deeply melted groove in chip material is analyzed based on the streamer theory of the current filaments in the PCSS’s. The current streamer appears in the regions with high carrier density initially, and then chip material is excited by the recombination and reabsorption, which generats new electron-hole pairs and causes avalanche multiplication of carriers. As the increase of current, a second streamer grow in the molten material with streamers easily. In terms of this property, the current streamer accumulates continually, and a deeply melted groove forms ultimately.The lock-on effect can be suppressed through two kinds of combined switches, which can improve the longevity of PCSS’s under high voltage and strong current. The combined switch of GaAs PCSS’s and gas switch:This combined switch not only gains larger current but also shorter falling edge. The latter can help preventing the lock-on effect from destroying GaAs PCSS’s continually. Further-more, GaAs PCSS’s can be avoid supporting high-voltage for a very long time due to the existence of gas gap, which is propitious to improve its longevity. High-gain double-layer GaAs PCSS’s:The double GaAs layers can go into the high-gain state one after the other but prevent each other from entering the lock-on state. This operating mode not only has the strong points of far less laser energy required under the nonlinear mode, but also has the merits of longer lifetime under the linear mode.更多还原