The physical mechanism underpinning superfast switching of GaAs S-diode

Abstract

Recently a physical phenomenon termed “collapsing field domains” (CFDs) was discovered, which manifests itself in several avalanching gallium arsenide (GaAs) structures. The phenomenon consists of the formation of a comb of ultra-high-amplitude field domains, which generate a dense electron-hole (e-h) plasma. Each domain surrounded by the plasma shrinks down to a nanometre scale in width, followed by collapse. Those domains cause different peculiar transient features from superfast (picosecond range) high-current avalanche switching in the voltage-blocking layers to sub-THz pulsed electromagnetic emission, filaments with extreme (∼10 MA/cm2) current density, hot-photon radiation, etc. The physics of those moving domains differs drastically from the Gunn effect having in common only a requirement of negative differential mobility (NDM) of the electrons and the fact that both phenomena have so far been observed in n-type GaAs layers. Here we demonstrate the CFD phenomenon in a p-layer formed by a deep acceptor. This finding contributes to the interpretation of superfast switching in so-called S-diodes. Besides proving the CFD nature underpinning superfast switching, we show the unique parameters of a simple, S-diode-based optical transmitter that achieves high-power (∼160 W) sub-nanosecond output. This performance is relevant to automotive and flight guidance applications of lidar. A brief review of alternative solutions presenting previous state-of-the-art for miniature lidar transmitters is given for comparison.