Physica B 249 —251 (1998) 961—965 Nonlinear and oscillatory electronic transport in superlattices as a probe of structural imperfections E. Scho¨ll*, G. Schwarz, A. Wacker Institut fu ( r Theoretische Physik, Technische Universita ( t Berlin, Hardenbergstra}e 36, 10623 Berlin, Germany Abstract We present a theoretical analysis of the correlations between the macroscopic global transport properties and microscopic imperfections of a superlattice. High-field transport and domain formation is modelled using a microscopic quantum transport model which includes interface roughness and impurity scattering and describes resonant and nonresonant tunnelling processes in weakly coupled multiple quantum wells without adjustable parameters. Our analysis can be used on one hand to identify random fluctuations of the structural parameters in real samples like deviations from the perfect periodicity due to varying barrier widths, or doping densities in the individual wells. On the other hand, we demonstrate that the current—voltage characteristics can be tailored in a wide range to exhibit specific features like sharply rising steps at given voltages, arbitrarily modulated current maxima of multistable branches, or self-generated current oscillations.  1998 Elsevier Science B.V. All rights reserved. Keywords: Superlattice; Electric field domains Vertical transport in semiconductor superlattices (SL) has drawn much attention since the pioneering work of Esaki and Tsu in 1970 [1]. An important feature in the current—field characteristic is the oc- currence of a peak at low fields F followed by a regime of negative differential conductivity (NDC) for higher fields and another pronounced peak due to resonant tunnelling. If the sample is biased with an average electric field in the NDC regime, the homogeneous field distribution be- comes unstable leading to the formation of stable stationary electric field domains or causing self- * Corresponding author. Fax: #49 30 314 21130; e-mail: schoell@physik.tu-berlin.de. sustained oscillations. The domain-type instability has been already discussed in the seventies [2,3]. During the last decade, it has been shown that the current—voltage characteristic of medium or highly doped weakly coupled superlattices consists of a se- quence of branches where each branch corresponds to the location of the domain boundary in a differ- ent quantum well (see, e.g., Ref. [4]). First theoret- ical approaches [5—7] exhibited a regular sequence of current branches. In contrast, experimental data showed irregular branches of varying lengths, which could be attributed to deviations of the per- fect superlattices structures [8]. Furthermore, it could be shown that the current—voltage character- istics could be manipulated in a predictable way by 0921-4526/98/$19.00  1998 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 8 ) 0 0 3 5 4 - 8