Terahertz emission from lateral
photo-Dember currents

Abstract

The photo-Dember effect is a source of impulsive THz emission following femtosecond pulsed optical excitation. This emission results from the ultrafast spatial separation of electron-hole pairs in strong carrier gradients due to their different diffusion coefficients. The associated time dependent polarization is oriented perpendicular to the excited surface which is inaptly for efficient out coupling of THz radiation. We propose a scheme for generating strong carrier gradients parallel to the excited surface. The resulting photo-Dember currents are oriented in the same direction and emit THz radiation into the favorable direction perpendicular to the surface. This effect is demonstrated for GaAs and In(0.53)Ga(0.47)As. Surprisingly the photo-Dember THz emitters provide higher bandwidth than photoconductive emitters. Multiplexing of phase coherent photo-Dember currents by periodically tailoring the photoexcited spatial carrier distribution gives rise to a strongly enhanced THz emission, which reaches electric field amplitudes comparable to a high-efficiency externally biased photoconductive emitter.

Photo-Dember terahertz emitter excited with an Er:fiber laser

“…This effect may be enhanced by multiplexing the opaque edges through parallel stripes and breaking the symmetry of the diffusion currents. 15 Here we show that a terahertz emitter based on the lateral photo-Dember effect excited at the fundamental wavelength of an Er:fiber laser of 0.78 m is an efficient source for terahertz radiation. Conventional In 0.53 Ga 0.47 As grown by molecular beam epitaxy or metal-organic chemical vapor deposition may be used because the photo-Dember effect does not rely on external bias or high resistivity of the substrate.…”

“…Recently we demonstrated the efficient generation of terahertz radiation by lateral photoDember currents induced in GaAs and InGaAs based emitters pumped with a Ti:sapphire laser. 15 The lateral photoDember effect is based on ultrafast diffusion currents of electrons when exciting the edge of an opaque material covering the semiconductor. The fast diffusion of electrons into the nonexcited area compared to the slower hole diffusion builds up a space-charge field, i.e., the lateral photo-Dember field.…”

Генерация терагерцового излучения при облучении фемтосекундными лазерными импульсами In-=SUB=-0.38-=/SUB=-Ga-=SUB=-0.62-=/SUB=-As, выращенного на подложке GaAs с метаморфным буферным слоем

“…Для In x Ga 1−x As (x > 0.4) соотношение подвижностей электронов и дырок в Г-долине составляет ∼ 40, в то время как для LT GaAs этот показатель < 20 [20]. По этой причине In x Ga 1−x As с x > 0.4 является отличным кандидатом для создания источника ТГц генерации на основе фотоэффекта Дембера.…”

“…Важно отметить, что в та-ком случае не требуется, чтобы фотопроводник InGaAs обладал высоким сопротивлением, что является обяза-тельным условием при изготовлении материала для ФА, а скейлинг ТГц излучения возможен за счет изменения области фотовозбуждения. В работе [20] также было показано, что источники генерации ТГц излучения на основе фотоэффекта Дембера имеют широкий спектр излучения до 5 ТГц.…”

Mapping the distribution of photo-currents responsible for generation of terahertz pulses at semiconductor surfaces

“…While the photocarrier dynamics normal to the surface-plane have been regarded as the THz radiation origin 1 , recent studies also took into account in-plane carrier dynamics 2,3 . Both photo-currentsin the surface plane and normal to it -can play a role in the generation of THz pulses, however, their individual contributions have not been evaluated yet.…”