GaAs光电导开关非线性模式的雪崩畴输运机理

Mechanism of avalanche charge domain transport for nonlinear mode of GaAs photoconductive semiconductor switches

光电导开关非线性模式的产生机理研究是该领域热点问题之一.本文采用波长1064 nm、脉宽5 ns的激光脉冲触发半绝缘GaAs光电导开关,在触发光能1 mJ、偏置电压2750 V时获得稳定的非线性波形.基于双光子吸收模型,计算了开关体内光生载流子浓度,计算结果表明光生载流子弥补了材料本征载流子的不足,在开关体内形成由光生载流子参与的电荷畴.依据转移电子效应原理,对畴内的峰值电场进行了计算,结果表明高浓度载流子可使畴内峰值电场远高于材料的本征击穿场强,致使畴内发生强烈的雪崩电离.基于光激发雪崩畴模型,对非线性模式的典型实验规律进行了解释,理论与实验一致.基于漂移扩散模型和负微分电导率效应,对触发瞬态开关体内电场进行仿真,结果表明开关体内存在有峰值电场达GaAs本征击穿场强的多畴输运现象.该研究为非线性光电导开关的产生机理及光激发电荷畴理论的完善提供实验依据和理论支撑.

Photoconductive semiconductor switch is of significance in the fields of ultafast electronics,high-repetition rate and high-power pulse power system,and THz radiation.The mechanism of the nonlinear mode of the switch is an important area of study.In this work,stable nonlinear wave forms are obtained by a semi-insulating GaAs photoconductive semiconductor switch triggered by a 5-ns laser pulse with pulsed energy of 1 mJ at a wavelength of 1064 nm under a bias of 2750 V.Based on two-photon absorption model,the photogenerated carrier concentration is calculated.The theory analysis and calculation result show that the photogenerated carrier can compensate for the lack of intrinsic carrier,and lead to the nucleation of photo-activated charge domain.According to transferred-electron effect principium,the electric field inside and outside the domain are calculated,indicating that the electric field within the domain can reach the electric field which is much larger than intrinsic breakdown electric field of GaAs material,and results in strong impact avalanche ionization in the bulk of the GaAs switch.According to the avalanche space charge domain,the typical experimental phenomena of nonlinear mode for GaAs switch are analyzed and calculated,the analysis and calculations are in excellent agreement with the experimental results.Based on drift-diffusion model and negative differential conductivity effect,the transient electric field in the bulk of the switch is simulated numerically under the optical triggering condition.The simulation results show that there are moving multiple charge domains with a peak electric filed as high as the intrinsic breakdown electric field of GaAs within the switch.This work provides the experimental evidence and theoretical support for studying the generation mechanism of the nonlinear photoconductive semiconductor switch and the improvement of the photo-activated charge domain theory.