光猝灭/电场调控下非线性光电导开关的工作机理和稳定性研究

In this proposal, we plan to investigate the mechanism and stability of operation of non-linear (high gain) GaAs photoconductive semiconductor swithes (GaAs PCSS) affected by laser quenching and electric field modulation,in order to improve the lifetime of high power, high current GaAs PCSS operated at repetition rate, with lower excitation and high electric field bias. In order to restrain the process of photo-activated carriers within a special suppressed state and quench the non-linear mode,it is used with excitation of two laser pulses delayed each other and influence of external periodic discharge. The conduction time of PCSS is controlled and the approximate uniformity of momentary electric field is obtained. Then, the transportion of photo-activated carriers, in the form of photo-activated charge domain (PACD) which is resulted from photo-activated impact ionization, is restrained in a special state. Consequently, the linear waveform featured by the mechanism of high gain avalanche is achieved. Based on the optical pump and THz probe system which has already been built, the critical restrain conditions of process from the generation of photo-activated charge domain (PACD) to quench is determined. The proven techique, using the PACD's quenching mode to switch pulses at a certain repetition rate, is achieved. In addition, the assessment system of non-linear operation of PCSS under low optical excition and high electric field,including the semiconductor process,fabrication of PCSS, design of electrodes' structure and isolated encapsulation is built. Finally, the GaAs PCSS devices with the advantages of non-linear mode are developed, which can operate at bias voltage above 50 kV, current as high as 1kA, repetition frequency in the range of kilohertz,pulsewidth of the order of magnitude from hundreds picoseconds to tens nanoseconds.

围绕弱光/强电场下高功率大电流砷化镓光电导开关（GaAs PCSS）重复频率的工作寿命问题，对GaAs PCSS非线性工作模式在光猝灭/电场调控作用下的工作机理和稳定性进行深入研究。采用双光束级联触发和外部负载放电周期性作用的组合方式，控制导通时间、均匀瞬态电场，将因光致碰撞电离引起的、以光激发电荷畴(PACD)为表现形式的载流子约束在特殊的输运状态下，实现猝灭畴诱发具有瞬态载流子雪崩倍增机制的线性波形输出。基于光泵浦-THz探测平台和模拟分析，确定光生载流子从产生到畴猝灭的瞬态约束条件，利用成熟的PACD猝灭模式来实现超快电脉冲的重复频率输出。建立包括半导体材料处理、光电导开关制备、电极结构设计、绝缘封装等方面在内的弱光/强电场下光电导开关非线性模式调控综合评价体系。研制工作电压>50kV,输出电流～1kA,重复频率kHz量级,电流脉冲宽度百ps到几十ns量级的GaAs PCSS器件。

本项目针对高功率、大电流的超快光电导器件在弱光/强电场、重复频率工作条件下所涉及到的基本物理问题进行实验设计与理论研究，以光猝灭/电场调控作用下的非线性光电导开关的工作机理和稳定性为主要研究目标。在具体执行过程中完成研究目标情况如下：获得了非线性工作模式电场阈随温度变化的规律，给出了GaAs PCSS禁带宽度和电离率的温度变化特性对载流子浓度的影响规律。在改善GaAs 芯片材料性能的基础上，有针对性地通过光触发方式、电极结构、绝缘处理等方面的优化设计，完成了不同波长下，nJ量级弱光/强电场条件下具有载流子倍增机制的稳定输出。采用了电场调控的方法来抑制高倍增工作模式中的电荷成畴机制，通过外部负载放电来加强对GaAs PCSS 内瞬态电场分布的影响作用，进而缩短了光电导开关导通时间（最小为脉宽可猝灭为1.23ns）、均匀触发导通瞬态过程中电场的分布（最大偏置电场为71.8kV/cm），最终实现具有高倍增效应的线性波形输出。在kHz条件下，结合THz 时域光谱技术、使用微米量级电极阵列PCSS的瞬态输出特性来分析光猝灭/电场调制过程中光生载流子的倍增机制。进行了不同偏置电压和触发光能条件下GaAs PCSS的同步性输出实验测试，分析了同步性的计算方法，讨论了影响同步性的主要因素。项目研究的系列结果为超快光电导器件的高功率大电流重复频率应用技术奠定了实验和理论基础。