光电导开关工作模式的蒙特卡罗模拟

Monte Carlo simulation of operating modes of semi-insulting GaAs photoconductive switches

利用二维ensemble-MonteCarlo方法模拟了直流偏置的半绝缘GaAs(SI-GaAs)光电导开关在飞秒激光脉冲触发下的两种工作模式.结果表明:当偏置电场低于耿氏电场(GaAs为4.2kV/cm)时,开关输出电脉冲呈线性模式;偏置电场超过耿氏电场但触发光脉冲能量低于光能阈值,光电导开关仍然表现出线性工作模式;当偏置电场和触发光脉冲能量都超过非线性模式("lock-on"模式)所需阈值,开关呈现非线性模式;在光子能量较高的激光脉冲触发下,开关非线性模式所需光能阈值降低.非线性工作模式源于光生载流子发生谷间散射,并在开关体内局部区域形成高场区,电场变化大,弛豫时间长,电脉冲呈现非线性.

An ensemble Monte Carlo simulation method has been employed to study the operating modes of semi-insulated GaAs（SI-GaAs）photoconductive semiconductor switches（PCSS）excited by a femtosecond laser pulse and biased in an electrical field.The results show that,under a bias field lower than the Gunn threshold field（which is 4.2kV/cm for GaAs）,or the optical pulse energy is below the optical threshold,the time-resolved current in the switch operates in the linear mode.When the bias field and triggering optical energy are respectively greater than the electrical and optical thresholds,the PCSS operates in the nonlinear mode.The simulation shows that when triggered by laser pulse with higher photon energy,the switch has lower optical threshold in the nonlinear mode.The mechanism of the nonlinear mode for the switch is concluded to be due to the inter-valley scattering of the photo-generated carriers,leading to local high field in the switch.