半绝缘GaAs光电导开关的瞬态热效应

实验用波长1064 nm,触发光能为1.0 mJ的激光脉冲触发电极间隙为4 mm的半绝缘GaAs光电导开关,当光电导开关的偏置电压达到3800 V时,开关进入非线性(lock-on)工作模式,在偏置电场和触发光能不变的条件下,开关输出稳定的非线性电脉冲,1500次触发后GaAs开关表面出现因丝状电流引起损伤的痕迹.分析认为:在一定触发光能和电场阈值条件下,开关芯片内存在两种瞬态热效应:热弛豫效应和光激发电荷畴-声子曳引效应.热弛豫时间很短,在皮秒甚至亚皮秒量级,热弛豫过程导致了热传导的弛豫行为;当光激发电荷畴以10⁷ cm/s的速度从阴极向阳极渡越时,在这两种效应的作用下使得开关芯片瞬态温度变化发生了弛豫振荡现象.光激发电荷畴-声子曳引效应在位错运动方向上传播,声子流携带的热能集中在移动的平面内,使得移动区域温度升高,移动轨迹经多次叠加累积呈现出丝状的损伤痕迹. 关键词： 半绝缘GaAs光电导开关 热弛豫效应 光激发电荷畴-声子曳引效应 丝状电流

Transient thermal effect of semi-insulating GaAs photoconductive switch

Results of experiments of the 4 mm gap semi-insulating(SI) GaAs photoconductive switch triggered by 1064 nm, 1.0 mJ pulse laser showed the nonlinear mode when the bias field was 3800 V. Under the same bias electric field and trigger light energy conditions, the switch outputs stably nonlinear electrical pulses, and the switch surface injury mark is caused by filamentation after 1500 times triggering. Analysis shows that under given conditions of trigger energy and electric field, two transient thermal effects occur in the switch chip, namely the thermal relaxation and photoactivated charge domain-phonon drag, respectively. Thermal relaxation time is shortened to the order of picoseconds or subpicoseconds, thermal relaxation process leads to the thermal conduction relaxation. When photoactivated charge domain moves at 10⁷cm/s speed from cathode to anode, switch chip transient temperature makes relaxation oscillations owing to these effects, and the rapid increase of temperature in the chip is constrained. Photoactivated charge domain-phonon drag effect transmits in the direction of the dislocation movement, the temperature in mobile region increases when the flow of thermal energy carried by the phonons was concentrated in the movement plane, the injury of filamentation is produced by superposition and cumulation of mobile tracks.