Nonequilibrium Acoustic Phonon-Assisted Tunneling in GaAs/(AlGa)As Double Barrier Devices

Abstract

We report the first observations of nonequilibrium phonon-assisted tunneling in a double barrier resonant tunneling device in GaAs. The change in tunnel current produced by the phonons occurs at a bias voltage, which depends on the phonon energy showing that the device has potential as a phonon spectrometer.PACS numbers: 73.40.Gk There has been considerable progress in the understanding of resonant tunneling structures including double barrier structures and an increasing interest in their potential as devices [1]. Somewhat less attention, however, has been given to the component of the tunnel current arising from inelastic phonon-assisted tunneling. It is known that the broad satellite peak in tunnel current above the resonant peak is attributable to phonon-assisted tunneling involving the emission of longitudinal optic (LO) phonons [2], and this has been confirmed by theoretical analysis [3] and further studied experimentally by a number of other authors [4]. Assisted tunneling associated with acoustic phonons is also assumed to take place [5,6], and the current will also be affected by changes in electron distribution caused by a rise in electron temperature.In this Letter, we report the first measurements of assisted tunneling caused by nonequilibrium acoustic phonons.The sample is a GaAs/(A1Q4Gap6)A1 double barrier resonant tunneling device (DBRTD) in which barriers of (A1Ga)As are located on either side of a GaAs layer, which acts as a quantum well. The results provide information on the potential variation across the DBRTD and demonstrate this type of device could have value as a phonon spectrometer. The sample used (NU165) was grown by molecular beam epitaxy on a (100) semi-insulating substrate at a temperature of 630 'C.The substrate was Cr free and grown by the liquidencapsulated Czochralski method. The structure consists of two 5.5 nm thick Alo4Ga06As barriers, separated by a 5 nm thick GaAs well. The barriers are separated from the doped n+ GaAs contact regions by a 2.5 nm thick GaAs spacer layer. The doping on each side varies from -1 X 10' cm at the edge of the spacer layer to 2 X 10' cm 50 nm away from the edge. When a bias voltage is applied, accumulation occurs on one side resulting in a two-dimensional emitter, while the collector remains three dimensional as shown schematically in the inset to Fig. 1. The layers were etched down to a 3 && 80 p, m mesa, and contacts were made to emitter and collector. The back face of the 400 p, m substrate was polished, and a 600 X 60 p, m 600 400 200 0' I 0.2 0.4 0.6 v(v) 0.8 FIG. 1. The current-voltage characteristics I(V) and dI/dV of the DBRTD at 4.2 K. The arrow shows the satellite peak attributed to LO phonon-assisted tunneling. The inset gives the energy band diagram of the DBRTD showing a phonon-assisted transition. constantan heater evaporated opposite the mesa using back-to-front alignment. The current-voltage characteristics of the DBRTD, I(V) and dI/dV, are shown in Fig. 1. Since both energy and in-plane wave vector k~~a re conserved, the resonan...

Nonequilibrium linked cluster expansion for steady-state quantum transport

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Tunnelling of Direct and Indirect Excitons in Slightly Asymmetric Double Quantum Wells

“…A theoretical analysis of these processes has been carried out [2,3] and a direct observation of acoustic phonon-assisted tunnelling in double barrier resonant tunnelling stuctures has been recently obtained using phonon pulses [4]. Detailed information on all these relaxation and tunnelling processes would be of value in the development of semiconductor nanostuctures as phonon spectrometers and generation at frequencies up to 1 ΤHz and above [2][3][4][5].In the present paper we are studying the cw photoluminescence from slightly asymmetric DQWs, in which the widths of the coupled QWs differ by only 1 or 2 monolayers (MLs). The paper is aimed particularly at extracting information on (895) …”

“…For simplicity therefore we refer to the observed process as phonon-assisted tunnelling in the expectation that in our high quality samples this will turn out to be the stronger of the two. A theoretical analysis of these processes has been carried out [2,3] and a direct observation of acoustic phonon-assisted tunnelling in double barrier resonant tunnelling stuctures has been recently obtained using phonon pulses [4]. Detailed information on all these relaxation and tunnelling processes would be of value in the development of semiconductor nanostuctures as phonon spectrometers and generation at frequencies up to 1 ΤHz and above [2][3][4][5].…”