B. Wittmann, S.N. Danilov, V.V. Bel’kov, S.A. Tarasenko, E.G. Novik, H. Buhmann, C. Brüne, L.W. Molenkamp, Z.D. Kvon, N.N. Mikhailov, S.A. Dvoretsky, N.Q.Vinh, A.F.G. van der Meer, B. Murdin, and S.D. Ganichev Terahertz Center, University of Regensburg, 93040 Regensburg, Germany A.F. Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 194021 St. Petersburg, Russia 3 Physical Institute (EP3), University of Würzburg, 97074 Würzburg, Germany 4 Institute of Semiconductor Physics, 630900 Novosibirsk, Russia 5 FOM Institute for Plasma Physics “Rijnhuizen”, P.O. Box 1207, NL-3430 BE Nieuwegein, The Netherlands and University of Surrey, Guildford, GU2 7XH, UK

We describe the observation of the circular and linear photogalvanic effects in HgTe/CdHgTe quantum wells. The interband absorption of mid-infrared radiation as well as the intrasubband absorption of terahertz radiation in the quantun well structures is shown to cause a dc electric current due to these effects. The photocurrent magnitude and direction varies with the radiation polarization state and crystallographic orientation of the substrate in a simple way that can be understood from a phenomenological theory. The observed dependences of the photocurrent on the radiation wavelength and temperature are discussed in terms of a microscopic model.

This paper presents the results of growing quantum wells based on HgTe (HgTe/Cd(0.735)Hg(0.265)Te) 16.2 and 21 nm thick on substrates of (013) CdTe/ZnTe/GaAs by molecular-beam epitaxy. The composition and thickness of the spacer and of the quantum well were monitored by an ellipsometric technique during growth. Galvanomagnetic studies in a wide range of magnetic fields (1-12 T) at temperatures close to that of liquid helium (4.2 K) showed that a two-dimensional electron gas is present in the nanostructures and that the levels are quantized. High mobilities were obtained for the two-dimensional electron gas: mu(e)=2 x 10(5) cm(2)/(V.sec) for an electron density of N(s)=1.5 x 10(11) cm(-2) and mu(e)=5 x 10(5) cm(2)/(V.sec) for N(s)=3.5 x 10(11) cm(-2). The circular and linear photogalvanic effects were studied in the quantum wells at room temperature in a wide wavelength interval: from the mid-IR (6-16 mu m) to the terahertz range (100-500 mu m). (C) 2009 Optical Society of America.

A fast room temperature pure photoelectrical detection scheme for obtaining the information about polarization ellipticity of laser radiation (described by the Stokes parameters) with a bandwidth from the infrared to the terahertz range is reported. The device consists of two elements, back-to-back, which detect the polarization ellipticity and the ellipse azimuthal angle. The first element utilizes the circular photogalvanic effect in a narrow gap semiconductor and the second the linear photogalvanic effect in a bulk piezoelectric semiconductor. In contrast to optical methods we propose an all-electric approach, which is demonstrated by applying a large number of different laser sources.

We report a fast, room temperature detection scheme for the polarization ellipticity of laser radiation, with a bandwidth that stretches from the infrared to the terahertz range. The device consists of two elements, one in front of the other, that detect the polarization ellipticity and the azimuthal angle of the ellipse. The elements, respectively, utilize the circular photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic effect in a bulk piezoelectric semiconductor. For the former we characterized both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In contrast with optical methods we propose is an easy to handle all-electric approach, which is demonstrated by applying a large number of different lasers from low power, continuous wave systems to high power, pulsed sources.

The resonant circular photogalvanic effect is observed in wurtzite (0001)-oriented GaN low-dimensional structures excited by infrared radiation. The current is induced by angular-momentum transfer of photons to the photoexcited electrons at resonant intersubband optical transitions in a GaN/AlGaN heterojunction. The signal reverses upon the reversal of the radiation helicity or, at fixed helicity, when the propagation direction of the photons is reversed. Making use of the tunability of the free-electron laser FELIX, we demonstrate that the current direction changes by sweeping the photon energy through the intersubband resonance condition, in agreement with theoretical considerations.

Photogalvanic effects are observed and investigated in wurtzite (0001)-oriented GaN/AlGaN low-dimensional structures excited by terahertz radiation. The structures are shown to represent linear quantum ratchets. Experimental and theoretical analysis exhibits that the observed photocurrents are related to the lack of an inversion center in the GaN-based heterojunctions.

We report on the observation of the terahertz radiation induced circular (CPGE) and linear (LPGE) photogalvanic effects in HgTe quantum wells. The current response is well described by the phenomenological theory of CPGE and LPGE.