Microelectronic Engineering 47 (1999) 59-63 Current Spectroscopy of Superlattice Bandstructure and Transport C. Rauch, G. Strasser, E. Gornik Institut fur Festkiirperelektronik und Mikrostrukturzentrum der TU Wien, Technische Universitat Wien, Floragasse 7, A-1040 Wien, Austria A systematic study of electron transport in undoped GaAs/GaAlAs superlattices is presented. Hot electron spectroscopy is used to measure the superlattice transmisstance at different bias conditions. At zero bias the measured transfer ratio a=&& is used to determine the miniband positions and the miniband widths. The transmittance of a five period superlattice is found to be independent of the direction of the electric field, while for a superlattice larger than ten periods, a dependence of the transmission on the electric field direction is observed. The onset of scattering induced miniband transport is clearly evident. From the experimental data a coherence length of 150 nm is derived. The limiting mechanism is found to be interface roughness scattering. INTRODUCTION Decreasing the barrier thickness of multiple quantum well structures leads to a stronger coupling between the degenerate eigenstates in the wells and thus to the formation of superlattice minibands. The application of an external electric field parallel to the growth axis quantizes the energy continuum associated with the miniband dispersion into a Stark ladder’ of discrete energy levels, and transforms the extended Bloch waves into strongly localized wave functions. Under strong localization coherence will be reduced to a few periods and in the limit, to a single quantum well. Transport and optical properties of superlattices have been the object of intense investigations in the last three decades. Numerous studies of the formation of superlattice minibands by optical techniques*, magnetotransport3, and by current voltage characterization of two terminal device structures have been reported including transport measurements of biased n-i-n superlattice structures4. The observed experimental I-V characteristics can be fitted with a self consistent solution of Poisson and Bolzmann equation using semiclassical field velocity relations in accordance with the original work by E&i and TsuS. However, it turns out that the experimental study of electronic properties of a biased superlattice is hindered by the interdependence of the intensity of the current injected and the field present in the superlattice”. At high electric fields the large current densities make the field in the superlattice nonuniform and causes the formation of high field domains and leads to thermal saturation of miniband transport7. 0167-9317/99/$ - see front matter 0 1999 Elsevier Science B.V. All rights reserved. PII: SO167-9317(99)00148-3