弱光触发下GaAs光电导开关的工作机理研究

发布时间：2018-09-06 07:25

【摘要】：砷化镓(Gallium arsenide,GaAs)光电导开关非线性工作模式的发现,使所需的触发光能量比线性工作模式低3到5个数量级,使激光二极管等小型光源替代大型激光器触发光电导开关产生强电流成为可能。本论文使用单个脉冲激光二极管作为光源触发GaAs光电导开关,研究了偏置电场、储能电容、触发光斑位置和开关温度对开关输出脉冲的影响;同时开发了蒙特卡罗模拟软件,研究了开关非线性工作模式下丝状电流、锁定效应、倍增效应、存在光电阈值等特性的形成机理。具体完成了以下工作:(1)研究了弱光触发下偏置电场和储能电容对GaAs光电导开关的影响。在激光二极管单脉冲能量为1.6μJ的情况下,逐步增加偏置电场至24 kV/cm,在光电导开关由线性模式逐步过渡到非线性模式的过程中,分析对比了超快光电导过程对应的倍增效应。考察了储能电容对输出电脉冲宽度的影响,结果表明电容越小脉宽越窄。特别是,当储能电容为10 pF时,获得了纳秒级输出电脉冲,该现象与电容器中电荷的快速耗尽有关。(2)研究了弱光触发下触发光斑方向、位置及开关温度对光电导开关进入非线性模式电场阈值的影响。当光斑平行电极触发时,光斑中心到阴极距离等间隔从0.2 mm到2.8mm时,电场阈值按线性规律由15 k V/cm增加到22 kV/cm;当光斑垂直电极时,随着光斑中心到阴极距离等间隔从0.0 mm增加到2.2 mm,电场阈值先由27 kV/cm左右减少到16 kV/cm,然后再升高到27 kV/cm,呈现出类抛物线型规律。其中,触发光斑贯穿阴阳电极时电场阈值最小。激光二极管单脉冲能量为1.6μJ时,考察了温度对开关电场阈值的影响。光斑垂直于电极时,随着温度从-12°C增加到24°C,电场阈值线性减小;对于同样的温度变化范围,在光斑平行于电极的情况下,电场阈值与温度之间不再满足线性关系。开关内部的Franz-Keldysh效应和热效应能够解释温度对电场阈值的影响。(3)基于已有光激发电荷畴理论,结合蒙特卡罗方法开发了针对GaAs光电导开关非线性工作模式的仿真软件。在具体的仿真设计中,充分考虑了光激发电荷畴理论的两种核心机制,对碰撞电离和载流子辐射复合再吸收进行了建模。其中,碰撞电离是载流子倍增的基础,载流子辐射复合再吸收是电荷畴形成和快速传播根本原因。通过对电子碰撞电离和空穴碰撞电离两种机制的考察,给出了GaAs材料的负微分特性、电子在各能谷的布居率及速场关系,考察了GaAs光电导开关线性和非线性工作模式中的主要机制。(4)结合对光激发电荷畴形成、输运过程的模拟,研究了弱光(微焦量级)触发下GaAs光电导开关进入非线性工作模式的物理过程。结果表明,弱光触发下Ga As光电导开关中光生载流子的聚束输运特性形成需具备两个条件:(a)负微分电场,即偏置电场大于4.0 kV/cm;(b)能够让自建电场与偏置电场具有可比性的光生载流子浓度,大约为1.0×1013 cm-3,处于弱光光源触发范围。验证了GaAs光电导开关非线性工作模式的基本过程,包含电子稠密区域形成、电荷畴形成、丝状电流形成、丝状电流生长和丝状电流吸收5个阶段;丝状电流传播速度的模拟结果为2.0×108 cm/s,整体形态呈树状形式发展,与用红外荧光拍摄的结果相符;解释了开关输出具有超快上升沿的原因是高浓度丝状电流头部被电极快速吸收的直接结果。基于空穴碰撞电离和电子碰撞电离两种机制,分析了载流子倍增效应和锁定效应。通过对载流子浓度和偏置电场对光电导开关内部输运特性的影响,给出了GaAs光电导开关非线性工作模式存在光电阈值的原因。
[Abstract]:The discovery of Gallium arsenide (GaAs) photoconductive switch (PCS) nonlinear mode of operation makes the required trigger light energy three to five orders of magnitude lower than the linear mode of operation, which makes it possible for small light sources such as laser diodes to replace large laser triggered photoconductive switches to generate strong current. The effects of bias electric field, energy storage capacitance, spot position and switching temperature on the output pulse of GaAs photoconductive switch triggered by light source are studied. The Monte Carlo simulation software is developed to study the formation mechanism of filamentary current, lock-in effect, multiplication effect and photoelectric threshold under switching nonlinear operation mode. The following work has been accomplished: (1) The influence of bias electric field and energy storage capacitance on GaAs photoconductive switch triggered by weak light is studied. The bias electric field is gradually increased to 24 kV/cm when the single pulse energy of laser diode is 1.6 uJ. The ultrafast light is analyzed and compared during the transition from linear mode to nonlinear mode of photoconductive switch. The results show that the smaller the capacitance is, the narrower the pulse width is. Especially, when the capacitance is 10 pF, the nanosecond output pulse is obtained, which is related to the rapid depletion of charge in the capacitor. (2) The direction of the trigger spot under weak light triggering is studied. The influence of switching temperature on the threshold value of electric field for a photoconductive switch entering a nonlinear mode is discussed. When the spot parallel electrode is triggered, the distance between the spot center and the cathode increases from 0.2 m m to 2.8 m m, the threshold value of electric field increases linearly from 15 kV/cm to 22 kV/cm; when the spot is perpendicular to the electrode, the distance between the spot center and the cathode increases from 0.0 m with the distance between the spot center and the cathode. The threshold value of electric field decreases from 27 kV/cm to 16 kV/cm, and then increases to 27 kV/cm. The threshold value of electric field is the smallest when the trigger spot penetrates the anode and cathode electrodes. The electric field threshold decreases linearly as the temperature increases from - 12 C to 24 C. For the same temperature range, the relationship between the electric field threshold and temperature no longer satisfies the linear relationship when the facula is parallel to the electrode. Based on the charge domain theory and Monte Carlo method, a simulation software for the nonlinear operation mode of GaAs photoconductive switch is developed. In the specific simulation design, two core mechanisms of photoexcited charge domain theory are fully considered, and collision ionization and recombination of carrier radiation are modeled. On the basis of the increase, the recombination and reabsorption of carrier radiation is the fundamental reason for the formation and rapid propagation of charge domains. The negative differential properties of GaAs materials, the population rate of electrons in various energy valleys and the relationship between velocity fields are given by investigating the mechanisms of electron collision ionization and hole collision ionization. The nonlinear and nonlinear working modes of GaAs photoconductive switches are investigated. (4) Combining with the simulation of photoexcited charge domain formation and transport process, the physical process of GaAs photoconductive switch entering the nonlinear mode of operation triggered by weak light is studied. The negative differential electric field, i.e. the bias electric field is greater than 4.0 kV/cm; (b) the photogenerated carrier concentration, about 1.0 *1013 cm-3, which is comparable to the self-built electric field and the bias electric field, is in the triggering range of the weak light source. The simulation result of filamentary current propagation velocity is 2.0 *108 cm/s, and the whole morphology develops in a dendritic form, which is consistent with the result of infrared fluorescence photography. Direct results. Carrier multiplication and locking effects are analyzed based on the two mechanisms of hole collision ionization and electron collision ionization.
【学位授予单位】：西安理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN36

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