Appl. Phys. A56, 4042 (1993) Applied so,,.. PhysicsA "" Su#ace6 © Springer-Verlag 1993 Dynamics of Resonant and Non-Resonant Tunneling in Asymmetric Coupled Quantum Wells H. Cruz and A. Mufioz Departamento de Fisica Fundamental y Experimental, Universidad de La Laguna, E-38204 La Laguna, Tenerife, Spain Received 6 July 1992/Accepted 31 August 1992 Abstract. Within the framework of the effective mass ap- proximation, coherent oscillations of a photoexcited electron wave packet in an asymmetric coupled quantum well struc- ture have been studied using a time-dependent Schrtidinger equation. In the method of calculation, the continuity of the current across a semiconductor heterojunction is considered. The amplitude and period of the electronic is obtained and in the case of high bias, it is found the existence of electric field-induced tunelling to semiconductor bulk. PACS: 73.40.Gk, 72.80.Ey, 73.20.Dx Tunneling phenomena in semiconductor nanostructures is at present an important research subject because of its possible application to ultrahigh-speed electronic devices [1]. In such structures, there is considerable current interest in the processes of coherent electron tunneling in asymmetric coupled quantum wells (ACQW) [2] due to its potential optical device applications since tuning of the eigenvalues can be achieved by means of an external electric field [3]. The possibility of observing electron oscillations in coupled quantum wells was first theoretically discussed by Luryi [4] and, experimentally, various techniques such as time-resolved photoluminescence [5] and time-integrated photoluminescence [3] has been implemented to observe these effects. The main advantage of an asymmetric structure is the ability to discriminate between optical transitions in the two wells by their spectral position. In this way, ACQW have been used to study the possible tunneling mechamisms from one well to the other [6]. Leo et al. [7] have recently studied the dynamics of an electron wave packet in a semiconductor double quantum well structure by means of ultrashort pulse excitation observing oscillatory motion of the electron wave function between both quantum wells. Since such experiments have already access to time scales of femtoseconds, providing information on dynamics and mechanism in the time domain, there is clearly a need to understand and model the nonstationary evolution of electron states in heterostructures [8-10]. The ACQW structure used in the experiments of [7] consists of a 170 A GaAs well, a 17 • Ga0.65A10.35As barrier, and a 120 A GaAs well. Such heterostructure is sandwiched between two Ga0.65A10.35As semi-infinite electrodes. The energy band diagram of the semiconductor heterostructure in absence of external fields is shown in the inset of Fig. l. This structure offers the possibility of tuning the eigenstates by means of an external applied electric field. Increasing the electric field, the energy splitting between the two first conduction electronic levels decreases, takes a minimum value at resonance due to the existence of an anticrossing (Fig. 1), and then increases again. The wave function of the electronic eigenstate that is initially localized in one well at zero bias, becomes strongly delocalized at resonance, and localized again with further increase of the applied electric field. We can also notice that the lowest optical transition energies in the two quantum wells F valence band conduction band 170,~ 17~, 1201 hqh i ' hgR i F=OKV/cm Fig. 1. Schematic illustration of the asymmetric double quantum well structure at resonance condition. Electron energy levels and first light hole levels for both quantum wells are shown. In the inset of the caption: conduction band in absence of applied electric field