Negative differential mobility in GaAs at ultrahigh fields: Comparison between an experiment and simulations

Abstract

Direct measurement of the electron velocity vn at an extreme electric field E is problematic due to impact ionization. The dependence vn(E) obtained by a Monte Carlo method can be verified, however, by comparing simulated and experimental data on superfast switching in a GaAs bipolar transistor structure, in which the switching transient is very sensitive to this dependence at high electric fields (up to 0.6MV∕cm). Such a comparison allows the conclusion to be made that the change from negative to positive differential mobility predicted earlier at E∼0.3MV∕cm should not happen until the electric field exceeds 0.6MV∕cm.

Investigation on properties of ultrafast switching in a bulk gallium arsenide avalanche semiconductor switch

“…30) was used, that contradicts Eq. (6) in which electron velocity saturates at very moderate fields.…”

Picosecond-Range Avalanche Switching of High-Voltage Diodes: Si Versus GaAs Structures

“…For decades the lock-on effect was a puzzle. The key finding that has helped to explain such anomalous dynamics is the discovery of collapsing high-field domains that spontaneously appear in electronhole plasma due to negative differential electron mobility in GaAs [19]- [21]. These domains were originally predicted as a mechanism that explains picosecond-range switching and terahertz emission in GaAs avalanche transistors [19], [20].…”

“…These domains were originally predicted as a mechanism that explains picosecond-range switching and terahertz emission in GaAs avalanche transistors [19], [20]. The mechanism that initiates the instability of the spatially uniform current flow is essentially the same as that for the well-known Gunn effect and is related to negative differential conductivity [19]- [21]. However, the shape and spatiotemporal dynamics of collapsing domains turn out to be very different from the conventional monopolar Gunn effect [22] as well as from the early analytical description of bipolar Gunn domains [23].…”

Transmission Subterahertz Imaging Utilizing Milliwatt-Range Nanosecond Pulses from Miniature, Collapsing-Domain-Based Avalanche Source

“…Namely, NDM must take place well above the ionization threshold . We have proved this condition so far [ 31 ] only for GaAs, in which NDM takes place up to at least 600 kV/cm, while for other III-V materials the question is still open.…”

“…In contrary, in our case multiple fi eld domains are generated, which number varies from a few to ~20 during the transient; the ionization threshold is exceeded several times and causes extremely powerful impact ionization; both electrons and holes are presented forming plasma between the domains; drastic domain shrinkage causes very fast voltage reduction across the structure and even complete domain disappearance [ 27 ]. As for the fundamental physical reason, the collapsing domain effect requires not simply presence of NDM [ 30 ] (as Gunn effect), but much more hard condition must be satisfi ed [ 31 ]. Namely, NDM must take place well above the ionization threshold .…”