用半绝缘GaAs光电导开关产生超短电磁脉冲若干问题研究
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摘要
超短电磁脉冲在超宽带雷达，超宽带通信，以及THz成像等方面有广泛的应用前景。在兼顾功率容量和带宽两方面，用光电导体结合超短脉冲激光技术形成的超快光电导开关产生超短电磁脉冲有很大优势。本文研究了用半绝缘GaAs光电导开关产生超短电磁脉冲的有关问题。
光电导开关产生超短电磁脉冲是将光电导体和超短激光脉冲技术相结合的崭新技术。其基本工作原理是利用超短激光脉冲对加有偏置电压的半绝缘GaAs的电导率进行调制，最终在开关的输出端产生ns～亚ns量级的电脉冲。作者在研究中对不同间隙的开关用不同波长的激光脉冲进行了触发实验。论文从半导体光电子学基本理论出发，对半绝缘GaAs材料的光吸收机制进行了讨论。在实验中可以用大于半绝缘GaAs本征吸收限波长(876nm)的激光脉冲来触发开关，这表明半绝缘GaAs开关中存在非本征吸收机制。论文从半绝缘GaAs内部的EL2缺陷能级以及双光子吸收角度分析了这种非本征吸收机制。在不同的触发光能以及不同的偏置电压下，半绝缘GaAs光电导开关可以表现为：线性、非线性、复合工作模式。论文在实验基础上提出SI-GaAs光导开关复合工作模式的概念，并首次对该工作模式进行分析。实验表明，复合工作模式是在用1064nm激光脉冲触发开关时特有的工作模式。论文分析了EL2缺陷能级
西安理工大学硕士学位论文
和三种工作模式的关系。论文中利用建立的物理模型对开关输出电脉冲的上时间，以
及开关线性波形和非线性波形之间的延迟时间进行计算，结果与实验测量数据相吻
合。论文还从产主超短电磁脉冲的角度，对触发光源的选择、开关的结构形式、开关
材料、电极结构形式等进行了分析。论文给出了用半绝缘GGs光电导开关产生的超
短电脉冲通过宽带无线发射、接受后的实验结果。实验表明得到的超短电脉冲宽度在
亚us量级，带宽达到6．SGHz，这个结果在国内同类实验中处于领先水平。
The ultrashort electromagnetic pulses have a broad applied foreground in ultra-wideband randar, ultra-wideband communication and THz imaging systems. As far as the power and band width of the electromagnetic pulses are concerned, the generation of electronic pulses by photoconductive switches is more effective. Some problems about generation ultrashort electronic pulses using SI-GaAs photoconductive switches are investigated in this paper.
It is a new technology that combine the photoconductive switch with the ultra-short pulse laser to generate the ultrashort electromagnetic pulse. The base principle that generate the nanosecond^ electromagnetic pulse is changing the conductance of Semi-insulating(SI) GaAs, which the DC voltage accrose the switch ,by using the ultrashort laser pulse. The experiments of various gap switches being triggered by difference wavelength laser were performed. Based the semiconductor optoelectroniccs theory , the author discussed the GaAs material's absorption mechanism in the paper. In experiments, the phenomena were observed that the semi-insulating GaAs photoconductive switches can absorb 1064nm laser obviously, which is out of the switch absorbing range. The experiments indicate there exists non-intrinsic absorption mechanism, which is different with intrinsic absorption mechanism. The paper discussed this non-intrinsic absorption mechanism based on the theories of EL2 energy level and double-photon absorption. Th
e experiments show the switch can also enter linear mode, nonlinear model and complex model when the switches are triggered at different electrical field and different energy irradiation. The complex model is a specific
III
phenomena proper for triggering by 1064nm laser pulse. The paper discussed the relation about EL2 energy level and these three modes. The risetime of electrical pulse and the delay-time between the linear model and nonlinear model are calculated in this paper, and the results match the experimental measure. The paper also discussed the trigger laser, structure of switch, material of switch, and the structure of electrode. The experiments of generating electromagnetic pulse by photoconductive switch were performed, and the electromagnetic pulses were emitted and received through wide-band antennal. The experiments indicated that the wide of electrical pulse is less than Ins, and its bandwidth is 6.5GHz. These experimental results reached a top level in china.
光电导开关产生超短电磁脉冲是将光电导体和超短激光脉冲技术相结合的崭新技术。其基本工作原理是利用超短激光脉冲对加有偏置电压的半绝缘GaAs的电导率进行调制，最终在开关的输出端产生ns～亚ns量级的电脉冲。作者在研究中对不同间隙的开关用不同波长的激光脉冲进行了触发实验。论文从半导体光电子学基本理论出发，对半绝缘GaAs材料的光吸收机制进行了讨论。在实验中可以用大于半绝缘GaAs本征吸收限波长(876nm)的激光脉冲来触发开关，这表明半绝缘GaAs开关中存在非本征吸收机制。论文从半绝缘GaAs内部的EL2缺陷能级以及双光子吸收角度分析了这种非本征吸收机制。在不同的触发光能以及不同的偏置电压下，半绝缘GaAs光电导开关可以表现为：线性、非线性、复合工作模式。论文在实验基础上提出SI-GaAs光导开关复合工作模式的概念，并首次对该工作模式进行分析。实验表明，复合工作模式是在用1064nm激光脉冲触发开关时特有的工作模式。论文分析了EL2缺陷能级
西安理工大学硕士学位论文
和三种工作模式的关系。论文中利用建立的物理模型对开关输出电脉冲的上时间，以
及开关线性波形和非线性波形之间的延迟时间进行计算，结果与实验测量数据相吻
合。论文还从产主超短电磁脉冲的角度，对触发光源的选择、开关的结构形式、开关
材料、电极结构形式等进行了分析。论文给出了用半绝缘GGs光电导开关产生的超
短电脉冲通过宽带无线发射、接受后的实验结果。实验表明得到的超短电脉冲宽度在
亚us量级，带宽达到6．SGHz，这个结果在国内同类实验中处于领先水平。
The ultrashort electromagnetic pulses have a broad applied foreground in ultra-wideband randar, ultra-wideband communication and THz imaging systems. As far as the power and band width of the electromagnetic pulses are concerned, the generation of electronic pulses by photoconductive switches is more effective. Some problems about generation ultrashort electronic pulses using SI-GaAs photoconductive switches are investigated in this paper.
It is a new technology that combine the photoconductive switch with the ultra-short pulse laser to generate the ultrashort electromagnetic pulse. The base principle that generate the nanosecond^ electromagnetic pulse is changing the conductance of Semi-insulating(SI) GaAs, which the DC voltage accrose the switch ,by using the ultrashort laser pulse. The experiments of various gap switches being triggered by difference wavelength laser were performed. Based the semiconductor optoelectroniccs theory , the author discussed the GaAs material's absorption mechanism in the paper. In experiments, the phenomena were observed that the semi-insulating GaAs photoconductive switches can absorb 1064nm laser obviously, which is out of the switch absorbing range. The experiments indicate there exists non-intrinsic absorption mechanism, which is different with intrinsic absorption mechanism. The paper discussed this non-intrinsic absorption mechanism based on the theories of EL2 energy level and double-photon absorption. Th
e experiments show the switch can also enter linear mode, nonlinear model and complex model when the switches are triggered at different electrical field and different energy irradiation. The complex model is a specific
III
phenomena proper for triggering by 1064nm laser pulse. The paper discussed the relation about EL2 energy level and these three modes. The risetime of electrical pulse and the delay-time between the linear model and nonlinear model are calculated in this paper, and the results match the experimental measure. The paper also discussed the trigger laser, structure of switch, material of switch, and the structure of electrode. The experiments of generating electromagnetic pulse by photoconductive switch were performed, and the electromagnetic pulses were emitted and received through wide-band antennal. The experiments indicated that the wide of electrical pulse is less than Ins, and its bandwidth is 6.5GHz. These experimental results reached a top level in china.
引文
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【2】 G.M.Loubriel, F.J.Zutavern. Photoconductive semiconductor switch experiment for pulse application. IEEE Tran.on electron device. Vo1(37), No:12, 1990:2472-2477.
【3】 G.M.Loubriel, F.J.Zutavern and A.G.Baca et al. Photoconductive semiconductor switches. IEEE Trans. Plasma. Sci., Vol(25),No2, 1997:124-130.
【4】 G.M.Loubriel, F.J.Zutavern. Trigering GaAs Lock-on Switches with laser diode arrays.IEEE.Trans. Elect.device, Vol(38), 1991:692.
【5】 G.M.Loubriel, F.J.Zutavern. Measurement of the velocity of current filment in optically triggered high gain GaAs switches. APPl. Phys. Lett, Vol(64),No:24,1994:3323-3325.
【6】 G.M.Loubriel, F.J.Zutavern. Surface flashover threshold and switches field of photoconductive semiconductive switches. In the 1998 Annual Report on the Conf. On Electrical insulation and Dielectric phenomena, Ottawa,Canada, 1998:430-441.
【7】 Mazzola M S, Roush R A, Stoudt D C, et al. Evaluation of Transport Effects on the Performance of a Laser-controlled GaAs Switch. IEEE Pulse Power Conf., Vl(87), No:1,1991:114～117.
【8】 陈治明，王建农．半导体器件的材料物理学基础．科学出版社，1999：187～200．
【9】 SHI Wei. Optically Activated Charge Domain Model for High- Gain GaAs Photoconductive Switche. Chinese journal of semiconductors, Vol(22), No: 12, 2001:1481～1485.
【10】 Islam N E, Schamiloglu E, Fleddermann C B. Characterization of a semi-insulating GaAs photoconductive semiconductor switch for ultrawide band high power microwave application. Applied Physics Letters, Vol(73),No:14, 1998: 1988～1990.
【11】 Siders C W, Siders J L, Taylor A J, et al. Generation and characterization of tearhertz pulse trains from biased large-aperture photoconductors. Optics Letters, Vol(24), No: 4,1999:241～243.
【12】 孟凡宝，杨周炳．100MW重复频率超宽带脉冲辐射源的实验研究．强激光与粒子束，Vol(10)，No：2，1998：279～291．
【13】 赵卫，杨鸿儒等．光系统的自锁模飞秒激光器．光学学报．Vol(20)，No：7，2000：947～950．
【14】 SHI Wei, LIANG Zhen-xian. Fabrication and Characterization of High-Voltage Ultra-Fast GaAs Photoconductive Switch. Chinese Journal of Semiconductor, Vol(19), No: 6,1998:437～441.
【15】 Taylor T D. Introduction to ultra-wideband Radar Systtem. USA:CRC Press, 1995:120～150.
【16】 Immoreev lgov, Vovshin Boris. Feature of Ultrawide bind Radar projecting. Int Radar Conf Alexandra Virginia, 1995:720～725.
【17】 阮成礼，林为干．电磁导弹与反隐身技术．现代雷达，Vol(10)，No：3，1992：36～40．
【18】 S. Wang, S. Coffa, R. Carius, Ch. Buchal. Efficient Electroluminescence from Rare Earth Doped MOS Diodes. Materials Science & Engineering, Vol(81), No:1-3, 2000:102～105.
【19】 W R Buehwald, A Balek djian Fabrication and Design issues of Bulk Photoconductive switches used for Ultra-Wideband. High-power Microwave Generation, in Dig.Tech,paper, proc. Of IEEE 22th Pulse power conference. 1997: 970～974.
【20】 Rose A, Zutavern F J. Hight Power Optical Activated Solid-State Switches. lst ed, Boston:Artech House, Vol(22), No: 5, 1993: 252～257.
【21】 汪力．Terahertz电磁脉冲辐射的超快电光和磁光检测．量子电子学学报．Vol(15)，No：6，2000：581～584．
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