Solid State Communications, Vol. 86, No. 2, pp. 113-117, 1993. Printed in Great Britain. 0038-1098/93 $6.00 + .00 Pergamon Press Ltd DOUBLE BARRIER RESONANT TUNNELING DEVICE WITH SELECTIVELY APPLIED FIELD IN THE WELL A.M. Kan'an and A. Puff Physics Department, University of New Orleans, LA 70148, USA and T. Odagaki Physics Department, Kyoto Institute of Technology, Kyoto 606, Japan (Received 27 August 1992 by J. Tauc) Resonant tunneling of an electron through a model Alo.sGao.sAs- AlyGal _:,A.s-Al0.sGa0.sAs structure is investigated numerically using a transmlsslon matrix approach. Our model considers the electricfield, in the well region only. This model isphysicallyrealizedby changing Al-concentration continuously in the well region. Transmission coefficientis obtained as a function of incident electron energy for various a values. Tunneling characteristics(transmission coefficient vs voltage) are examined as a function of a. The effect of change in temperature is discussed. 1. INTRODUCTION TUNNELING of electrons through potential barriers in one of the most important problems in quantum mechanics. The problem of resonant tunneling through double and multiple barriers has been investigated extensively. It has been more than two decades since Esaki and Tsui [1] proposed that "the study of superlattices and observation of quantum mechanical effects on a new physical scale may provide a valuable area of investigation in the field of semiconductor physics". Tsui and Esaki [2] computed the transport properties from tunneling view point leading to current-voltage characteristics of electrons. The technique of molecular-beam- epitaxy and metal-organic-vapor deposition has made it possible to grow high quality heterostruc- tures by controlling barrier and well parameters at the atomic scale. The best fabricated heterostructure is GaAs-AlxGal_xAs where GaAs has a narrower band gap than AlxGal _xAs. In recent years several new devices have been proposed. Resonant tunneling in AIGaAs-InGaAs- AIGaAs [3], AISb-InAs~AISb [4], GaSb-AISb- GaSb-AlSb-InAs [5], and AlAs-In0.53Ga0.47As- AlAs [6] have been investigated. GaAs-ZnSe and InAs-ZnTe [7] tunnel structures provide a novel way to mix III-V/II-VI materials, the other structures investigated are sawtoothed GaAs-AlxGal_xAs [8] superlattices. It is found that these structures exhibit resonant tunneling similar to the step superlattice. Much attention has been focussed on device application of multibarrier structures. Resonant tunneling diodes for optoelectronic applications [9, 10] have bean proposed. The device is referred to as a bistable-optical-negative resistance device. In this paper we investigate the current-voltage characteristics of a new device, Al0.5Ga0.5As-AlyGal_yAs-Al0.sGao.sAs, in which Al-concentration is changed uniformly in the well region only. Varying AI-concentration in the well region is equivalent to applying static electricfield selectivelyin the well region only. Purl et al. [II] have studied the polarization of the electron in such a quantum well, recently. They demonstrate that an electron in the excited state shows an anomalous polarization, which in turn may affect various transport properties. Recently, a new transmission matrix approach has been developed to study the resonant tunneling phenomena [12]. It has been shown that well developed theory of transmission lines can be effectivelyused to numerically calculate the quantum mechanical transmission probability across an arbi- trary shaped barrier [13]. In the numerical solution, any continuous variation of potential energy is approximated by a multistep function of N seg- ments. Each one of these segments represents a single barrier with constant potential and effectivemass. A 113