Evidence for long-living charge carriers in electrically biased low-temperature-grown GaAs photoconductive switches

Abstract

Low-temperature-grown GaAs continues to be one of the most important materials of ultrafast optoelectronics. Little is known, however, about the recombination dynamics of photogenerated charge carriers under the influence of an applied electric field, and it has remained unclear to what extent biased photoswitches exhibit field screening effects. Here, the authors investigate the screening in biased few-micrometer-sized photoconductive gaps quantitatively and find that it can amount to tens of percent of the applied field. They find that a subgroup of the photogenerated carriers recombines on an unexpectedly long excitation-density-dependent time scale of nanoseconds to tens of nanoseconds.

High speed photoswitching: from material properties to device performances

“…This long relaxation has also been observed up to the ns scale in [5] for THz emitting antennas. It has been attributed to electrical field screening because of a residual inhomogeneous spatial distribution of ionized antisites after illumination.…”

“…Both systems are based on MSM structures working as ultrafast photoswitches (PS). Under ultimate testing conditions such as high optical fluence, high biasing voltage, or high laser pulses repetition rate, some deterioration of the PS performances is observed: nonlinear electrical response and bandwidth reduction [3,4], lower THz generation efficiency [5] and so on. Here we review these effects and show how they are related to both material properties and device design.…”

Observation of Long-Lived Screening in Low-Temperature-Grown GaAs Photoconductive Switches

“…We derive effective carrier recombination times, or more correctly speaking, de-screening times τ DS , for the various excitation conditions of all data sets [8]. The main panel of Fig.…”

Tunable, continuous-wave Terahertz photomixer sources and applications

“…Trapped charge carriers are responsible for space charge screening but do not contribute to the THz current. There is evidence that the recombination takes place on a much longer time scale (i.e., 10 ps to several ns 66,68 ) than the trapping time, which is shorter than 1 ps for high-quality material. Within the fs and THz community, however, the trapping time is referred to as s rec as it is responsible for reducing carrier contributions to the current.…”

“…The space charge close to the contacts originates from trapped carriers that do not find a recombination partner of opposite sign due to the carrier separation. 66 The larger the recombination time, the further the center of mass of electrons will move apart from the center of mass of holes. This effect is well known for standard GaAs photomixers, 67 where carrier lifetimes are larger than the transit times through the gap.…”