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Regensburg 2019 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 12: HL Poster I

HL 12.25: Poster

Montag, 1. April 2019, 17:30–20:00, Poster E

High frequency impact ionization and nonlinearity of photocurrent induced by intense terahertz radiation in HgTe-based quantum well structures — •Stefan Hubmann1, Sebastian Gebert1, Grigory Budkin2, Vasily Belkov2, Eugenius Ivchenko2, Alexandr Dmitriev2, Susanne Baumann1, Maximilian Otteneder1, Dimitry Kozlov3, Nikolay Mikhailov3, Sergey Dvoretsky3, Ze-Don Kvon3, and Sergey Ganichev11Terahertz Center, University of Regensburg, 93040 Regensburg, Germany — 2Ioffe Institute, 194021 St. Petersburg, Russia — 3Rzhanov Institute of Semiconductor Physics, 630090 Novosibirsk, Russia

We report on a strong nonlinear behavior of photogalvanics and photoconductivity under excitation of HgTe quantum wells by intense terahertz radiation. The increasing radiation intensity causes an inversion of sign of the photocurrent and transition to its superlinear dependence on the intensity. The photoconductivity also shows a superlinear raise with the intensity. We show that the observed nonlinearities are caused by light impact ionization with a photon energy less than the band gap. The signature of this kind of impact ionization is that the angular radiation frequency ω=2π f is much higher than the reciprocal momentum relaxation time. Thus, the impact ionization takes place solely because of collisions in the presence of a high-frequency electric field. The effect has been measured applying polarized radiation with f from 0.6 to 1.07 THz and intensities up to hundreds of kW/cm2. We demonstrate that the impact ionization probability W ∝ exp(−E02/E2), with the radiation electric field amplitude E and the field parameter E0.

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