Superlattices and Microstructures, Vol. 22, No. 1, 1997 Theory of electron transport in a THz-field irradiated semiconductor superlattice: occurrence of quantized DC voltages and current responsivity A. A. Ignatov, E. Schomburg, J. Grenzer, S. Winnerl, K. F. Renk Institut f ¨ ur Angewandte Physik, Universit¨ at Regensburg 93040 Regensburg, Germany E. P. Dodin Institute for Physics of Microstructures, RAS, N. Novgorod, Russia (Received 15 July 1996) We use a semiclassical description for an analysis of the detection of THz-photons by electrons performing Bloch oscillations in a semiconductor superlattice. We show that the current responsivity of the superlattice detector can nearly reach the quantum efficiency e/¯ h ω at room temperature if the superlattice is matched to the THz radiation. c  1997 Academic Press Limited Key words: semiconductor superlattices, terahertz radiation, Bloch oscillations. 1. Introduction In several papers [1] it has been proposed to probe Bloch oscillations performed by electrons in a superlattice (SL) miniband [2] in a strong electric field E 0 by applying an additional strong AC field E ω cos ωt . Self-induced transparency and absolute negative conductance have been predicted to occur in condition of dynamical (or ac) localization of electrons, J 0 ( eE ω d ¯ hω ) → 0 [1] (where J 0 (x ) is the Bessel’s function, d the SL period) if the AC field frequency ω is higher than electron’s collision frequency ν , i.e. in the THz-frequency band. It was shown [3] that for a strong AC field, similar to the inverse AC Josephson effect, quantized DC voltages (‘Shapiro steps’) should occur in the irradiated SLs due to multiphoton resonances  B = nω (where  B = eE 0 d /¯ h is the Bloch frequency, n the integer). Recently, a strong DC current suppression by THz radiation indicating the onset of dynamical localization of electrons [4] , absolute negative conductance [5] and ‘Shapiro steps’ [6] on the DC current–voltage curve of the THz-field irradiated SL have been observed experimentally, that may contribute to development of novel THz solid state detectors. In this paper we calculate the current responsivity of the superlattice detector and show that it can be quite comparable to the quantum efficiency e/¯ h ω in the THz-frequency band if a superlattice is matched to electromagnetic radiation. 2. Basic equations We start from the equation for time-dependent drift velocity v(t ) describing the current flow in a SL, with 0749–6036/97/050015 + 04 $25.00/0 sm960336 c  1997 Academic Press Limited