【作者】 戴慧莹；

【导师】 施卫；

【作者基本信息】 西安理工大学 ， 微电子学与固体电子学， 2008， 博士

【摘要】 半绝缘GaAs光电导开关是利用脉冲激光器与半绝缘GaAs相结合组成的一类新型超快光电器件。与传统开关相比,半导体光电导开关具有触发无晃动、寄生电感电容小、上升时间快、关断时间短、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。用GaAs光电导开关产生高功率高压无晃动超短电脉冲的研究,成为国防建设、超宽带通信、超宽带雷达、电磁武器的实现等领域急需解决的关键问题。本文通过GaAs光电导开关芯片材料特性的研究,分析了散射机制对电脉冲输出特性的影响;总结了线性和非线性模式下的实验规律,用光激发电荷畴模型分析了光电导开关非线性模式下传输特性;对非线性工作模式下的使用寿命问题展开实验研究和理论分析。本文着重讨论了半绝缘GaAs的材料特性,对其电阻率、杂质和缺陷、载流子迁移率等几个方面进行了较为全面的分析。研究了半绝缘GaAs材料中的散射机制,并根据散射理论计算了各种散射机制的散射率和散射终态的一般表达式,选择出对半绝缘GaAs光电导开关输出电脉冲产生主要影响的散射机制,并具体讨论了当温度、最大触发光功率、开关缝隙长度等参数发生变化时,散射机制对光电导开关输出特性的影响。对线性模式下的光电延迟、输出电脉冲展宽等实验现象理论分析。研究表明,引起输出电脉冲展宽的主要原因是由于反位As_Ga点缺陷能级的俘获作用,并成功地解释了实验结果。用光激发电荷畴理论分析了半绝缘GaAs光电导开关在非线性工作模式下的输出特性和光电阈值条件。在总结实验规律的基础上,得到半绝缘GaAs光电导开关非线性模式的光电阈值条件,指出当光能触发使开关满足n0L≥10¹²cm^-2时,达到形成高场畴的必要条件,阈值电场的作用是使材料体内产生电子转移效应。光场、电场的共同作用使开关体内产生高场畴。高场畴的输运决定了光电导开关输出电脉冲的特性。用电荷畴的观点讨论光电导开关在线性区域、非线性区域及阈值区的工作特性。分析了高电压下引起半绝缘GaAs光电导开关的光电延迟的原因,得到与实验测试结果相吻合的结论。对开关电极和芯片材料在高电压强电流条件下的退化和损伤分别作了详细的理论分析。指出电极退化和损伤的主要原因是强电场触发时,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。其中阳极附近由于存在势垒等原因,损坏比阴极严重。芯片材料的损伤主要是由于EL2能级的存在;通过对EL2能级在开关中所起作用的机理分析,提出深能级缺陷及热效应是导致开关击穿的主要原因。通过对光电导开关击穿机理的研究,我们认为改进开关寿命的主要途径是以下几种:（1）选择适当的触发光源;（2）开关芯片两电极之间的间隙长度最优取值;（3）电极形状及位置进行重新设计;（4）选用新的电极材料;（5）改善接触界面。本研究得到国家自然科学基金（No.10376025,50477011）的资助。更多还原

【Abstract】 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）更多还原