摘要
本文讨论在GaAs n^+-n-n^+夹层结构的Cunn器件中畴的静止-渡越-静止模式,进行了实验观察和计算机模拟,指出在超过阈值的偏置电压下,当畴的耗尽层进入阳极附近的高掺杂区后,会逐渐停止下来形成准静态畴,这时畴外电场达到最大值.如果这时阴极凹口仍不能形成新畴,则准静态畴将进一步调整成为真正的静止畴,而畴外电场也将由最大值下降到一个与偏压无关的固定值.经过理论分析,得到了静止畴所固有的与外加偏压无关的畴外电场与有源区掺杂浓度的关系式,并和计算机模拟的结果相比较,得到很好的符合.如果偏压的增加使准静态畴所对应的畴外电场最大值已经足够使阴极凹口形成新的畴,则静止畴将转变为渡越畴.如果偏压继续增加,使积累层尾部覆盖了阴极凹口,则畴会再次静止下来,直到偏压增加到畴发生雪崩为止.计算和实验表明,后一个静止区的电压变化范围要比前一个大得多.本文还讨论了两个转变电压和温度的关系及扩散系数对静止畴的影响.
The transformations between stationary and transit domains in a Gunn device whichhas a n^+-n-n^+ sandwich structure with a doping gradient near the anode are investigated.Experimental observation and computer simulation are carried out.When the domainreaches the anode,it will stop and become a quasi-stationary domain.By this time thefield outside the domain reaches its maximum value.If the bias voltage is not highenough so that this maximum value of field outside the domain does not cause a newdomain to be created at the notch near the cathod, the quasi-stationary domain willthen readjust itself to become a real stationary domain,while the field outside the do-main will decrease to a fixed value,which is independent of the bias voltage.Theoret-ical analysis has been carried out and an analytical relationship between the field out-side the domain for real stationary domains and the doping density in the active regionof the device is obtained.If the bias voltage increases,the maximum value of the fieldoutside the domain,which is accompanied by the quasi-stationary domain,increases too.As soon as this maximum value becomes high enough to cause a new domain to be createdat the notch,the stationary domain mode will transform into transit domain mode.Itis noticed that the maximum value of the field outside the domain depends not only onthe instantaneous value but also on the increasing rate of the bias voltage.If the biasvoltage increases further,the rear part of the quasi-stationary domain will extend overthe notch near the cathode, and a new stationary domain will occur again.This state willbe maintained until the avalanche takes place.The influence of diffusion coefficient onstationary domain and the temperature dependence of the threshold voltages of the twokinds of transformation between stationary and transit domains are also discussed.
