【作者】 屈光辉；

【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， 2009， 博士

【摘要】 半导体光电导开关(Photoconductive semiconductor switches)是利用超短脉冲激光器与光电导体(如：Si,GaAs,InP等)相结合形成的一类新型开关器件,具有快速响应(皮秒上升、下降时间),GHz的重复率,无触发晃动,寄生电感电容小等优点。在THz技术、超高速电子学、超宽带雷达、脉冲功率技术等高科技领域具有广阔的应用前景。光电导开关中光生载流子的输运及输运引起的瞬态电磁过程决定开关的输出特性。本文以光电导开关载流子输运规律为研究目标,利用理论和数值方法,分别对线性和非线性工作模式下的载流子输运规律及其对输出的影响进行了研究,完成以下工作：一、提出光电导开关线性模式下的全电流导通模型利用电磁学理论研究了横向光电导开关光生载流子输运引起的瞬态电磁过程。在低电场偏置,均匀弱光触发条件下的线性工作模式中,将光电导开关内瞬态电磁过程形成的位移电流分为两类：1.由光生载流子输运在光电导体内形成的瞬变内建电场所引起的位移电流；2.由测试电路中负载与光电导开关瞬态分压引起的位移电流。分析了两者对横向光电导开关的激活条件。建立了基于载流子输运过程与瞬态电磁过程的全电流模型。与仅考虑载流子输运的电导率模型相比,全电流模型能够更精确的描述载流子输运与输出电流之间的时域关系,并描绘出光电导开关输出电流清晰的形成机理。二、提出光激发电荷畴限制流效应在强电场偏置,非均匀触发弱光触发条件下的线性GaAs光电导开关中,利用数值方法研究了光生电子在负微分迁移率作用下的非线性输运规律。分析了线性工作模式下光激发电荷畴形成的物理过程,提出光激发电荷畴限制流效应,认为线性模式下光电导开关的输出电流受光激发电荷畴限制流的限制。三、提出了二次光子激励下的雪崩畴模型来解释GaAs光电导开关非线性模式。首先,利用数值方法,研究了光生载流子输运规律及内建电场瞬态分布规律。在此基础上结合GaAs材料光学特性,研究了非线性模式下光电导体内的瞬态光学特性。结果表明非线性模式下的光电导体内不但存在电学非均匀性,同时还存在强光学非均匀特性。其次,研究了强光学非均匀特性的作用下,光生载流子通过二次光子的发射和再吸收过程重新分布的规律。结果表明：二次光子的再吸收能够对已经达到稳态的光激发电荷畴进行二次激励。在足够的激励强度下,光激发电荷畴成长为雪崩畴。最后,提出了二次光子激励下的雪崩畴模型来解释光电导开关非线性模式,该模型能够较全面解释GaAs光电导开关非线性模式下的各项特征。四、实验验证了光激发电荷畴限制流效应。在对GaAs光电导开关电极制作、绝缘保护、传输电路设计等制作技术研究的基础上,制作了SI-GaAs光电导开关,对光激发电荷畴限制流效应进行了实验验证。利用光电导开关和超宽带天线,产生了带宽达覆盖650MHz-2GHz的电磁辐射。更多还原

【Abstract】 As a new class of switching devices, Photoconductive semiconductor switches (PCSS’s) are a combination of ultra-fast pulsed laser and photoconductor. PCSS bears such advantages as high power, fast switching speed, small parasitic capacitance, high repetition frequency, and jitterfree, Therefore it possesses a broad application prospect in the fields of superspeed electronics, generation of high power electrical pulses, fine-synchronization control and terahertz technology.PCSS’s output characteristic depended on the transportation of the photogenerated carriers and the transient electromagnetism process caused by the transportation of the photogenerated carriers. The transportation of the photogenerated carriers and the output characteristic under the linear mode and the nonlinear mode are studied individually, and the major points are summarized as below:1. A total current mode for linear mode of PCSS’s is proposed.The transient electromagnetism process is studied under the condition of low biased field, the study shows that there are two types displacement current in the PCSS’s generated by the transient electromagnetism process:1. Displacement current created by the built-in field in the photoconductor, which is formed by the transportation of the photogenerated carriers; 2. Displacement current created by the electric voltage shifting from the PCSS’s to the load in the test circuit. Then, activation conditions of the two types of displacements are analyzed, and a Total Current mode is built based on the transportation of the photogenerated carriers and the transient electromagnetism process. In contrast with conductivity mode, the relationship of the transportation of the photogenerated carriers and the output current are described accurately by the new mode. 2. The current limiting effect of photoactivated charge domain is proposed.Under the condition of high bias electric field and nonuniform weak trigger laser, the nonlinear transportation process of photogenerated carriers in the linear GaAs PCSS’s is studied by simulation method. The formation and transporting process of photoactivated charge domain (PACD) in linear mode are discussed. The current limiting effect of PACD is proposed, and the max output current is limited by the PACD.3. The secondary photo excited avalanche charge domain mode is proposed.First, the transient built-in field in the photoconductor of the nonlingear GaAs PCSS’s is studied by simulation method. According to the GaAs optical characteristic, the transient optical characteristics are explored based on the transient built-in field and the transient photogenerated carries distribution. The result shows that there are not only an intense nonuniform electrical characteristic but also an intense nonuniform optical characteristic. Next, the redistribution law of photogenerated carriers through emitting and absorbing secondary photo is explored. The result shows that the PACD reached steady state can be excited once again by the secondary photo. Under adequate exciting by the secondary photo, the PACD grow into avalanche charge domain. Finally, the secondary photo excited avalanche charge domain mode is proposed for nonlinear mode of GaAs PCSS’s, this mode is more comprehensive and more accurate.4. An experiment is performed to proof current limiting effect of PACD.Based on study on the electrode making、insulation protection、transmission line design, A series of GaAs PCSS’s are made. A confirmatory experiment is successful performed and the results confirmed the current limiting effect of PACD. Then, an ultra-broadband electromagnetic wave is radiated by a horn antenna connected to the PCSS, and the spectrum covers from 650MHz to 2GHz.更多还原