Subnanosecond switching of high-voltage GaAs diodes initiated by a steep reverse voltage ramp (≥1 kV/ns) is investigated experimentally and numerically. The triggering occurs at the voltage U_m which exceeds stationary breakdown voltage U_b, similar to delayed impact ionization breakdown in Si picosecond-range high-voltage diodes known as silicon avalanche sharpening (SAS) diodes. Despite this similarity, we argue that the triggering mechanism of GaAs diodes is qualitatively different and is based on negative differential electron mobility in GaAs. Spatial patterns of recombination emission indicate formation of narrow conducting channels. Numerical simulations reveal the spontaneous appearance of high-field (∼400 kV/cm) bipolar Gunn domains in these channels. The agreement of experiments and simulations demonstrates that impact ionization within collapsing Gunn domains is responsible for a rapid increase of nonequilibrium carrier concentration and subnanosecond switching of the reversely biased GaAs diode to the conducting state with low (<100 V) residual voltage. In particular, the proposed mechanism explains why GaAs diodes exhibit subnanosecond switching at moderate overvoltage ratio U_m/U_b ≈ 1.5 smaller than typical overvoltage U_m/U_b ≈ 2 required for switching Si diodes, and the origin of anomalous delay of several nanoseconds that is experimentally observed in such regimes.

通过实验和数值研究了由陡峭反向电压斜坡 (≥1 kV/ns) 启动的高压 GaAs 二极管的亚纳秒开关。触发发生在电压U _m超过稳态击穿电压U _b时，类似于硅皮秒范围高压二极管（称为硅雪崩锐化 (SAS) 二极管）中的延迟碰撞电离击穿。尽管存在这种相似性，但我们认为 GaAs 二极管的触发机制在本质上是不同的，并且基于 GaAs 中的负微分电子迁移率。复合发射的空间图案表明窄传导通道的形成。数值模拟揭示了这些通道中高场（∼400 kV/cm）双极耿氏域的自发出现。实验和模拟的一致性表明，塌陷耿氏域内的碰撞电离导致非平衡载流子浓度快速增加，以及反向偏置 GaAs 二极管亚纳秒切换到低残余电压 (<100 V) 的导通状态。特别是，所提出的机制解释了为什么 GaAs 二极管在中等过压比U _m / U _b  ≈ 1.5 小于开关 Si 二极管所需的典型过压U _m / U _b  ≈ 2 时表现出亚纳秒开关，以及几纳秒异常延迟的起源这是在此类制度中通过实验观察到的。