In-plane magnetophotoluminescence studies of modulation-doped GaAs/AlGaAs coupled double quantum wells

Abstract

In-plane magnetic field photoluminescence spectra from a series of GaAs/AlGaAs coupled double quantum wells show distinctive doublet structures related to the symmetric and antisymmetric states. The magnetic field behavior of the upper transition from the antisymmetric state strongly depends on sample mobility. In lower mobility samples, the transition energy shows an N -type kink with fields (namely a maximum followed by a minimum), whereas higher mobility samples have a linear dependence. The former is due to a homogeneous broadening of electron and hole states and the results are in good agreement with theoretical calculations.The electrical and optical properties of quantum well heterostructures have been the subject of considerable investigation for a number of years. Coupled double quantum well (CDQW) structures, where the two wells are separated by a thin barrier, are of interest due to an enhanced quantum Stark effect and provide an ideal system for studying tunneling dynamics. 1-5 Modulation-doping of a CDQW creates two parallel two-dimensional electron gas (2DEG) layers. [6][7][8][9][10] This additional electronic degree of freedom in the growth (z) direction can be controlled by varying the barrier thickness, external gate voltages, and magnetic fields. For a strong tunneling structure, wherein two quantum wells are separated by a very thin barrier (typically < 40Å), a tunnel split bandgap (∆ SAS ) is formed such that the symmetric and antisymmetric states are nearly degenerate in energy. For electronic applications, a gated CDQW has a function similar to a double barrier resonant tunneling device (RTD). However, an RTD has a side gate structure, whereas a gated CDQW device is an entirely planar configuration which has many advantages. Moon et. al. recently demonstrated that these double layer systems could be used as compact digital logic devices constituting a great reduction in circuit complexity due to their planar geometry. 11In the presence of magnetic fields parallel to the growth direction (B⊥), the tunnel-split band gap (∆ SAS ) collapses and the structure acts as a single quantum well due to Coulomb interactions at certain odd integer Landau filling factors. 10 By contrast, in a purely in-plane field, single particle dynamics dominate the interactions between the 2DEGs and there is a linear shift in the canonical momentumhk in one quantum well with respect to another. The primary effect is to produce a partial energy gap and a strong modulation of the in-plane conductance due to an anti-crossing of the k-dispersion curves as demonstrated by Simmons et. al.. 7,9 In a recent theoretical investigation, Huang and Lyo 12 describe many different phenomena related to the inplane magnetic field dependence of the photoluminescence (PL) spectra. Their calculations show that, as the magnetic field increases, transition energy between the antisymmetric and symmetric states displays an Ntype kink, namely a maximum followed by a minimum. In the presence of in-plane magnetic fields the degenerate k-dispers...

Luminescence of double quantum wells subject to in-plane magnetic fields

“…Therefore, our model is different in this particular way. The disordered potential as a necessary condition for a N-type kink observation was also suggested by Kim et al 15 They have identified this effect in the PL from only one particular sample that had the lowest mobility in the studied set of structures. Samples that allowed the observation of the N-type kink are thus similar to those, where the Fermi edge singularity was studied.…”

“…Similar measurements on wide QWs and heterojunctions have very recently been carried out by Ashkinadze et al 13 Other in-plane magneto-optical measurements, in this case already on symmetric DQW structures, were published by Kim and co-workers. 14,15 In a parallel field, they observed two resolved peaks and their shift to the higher energy with increasing magnetic field. The peaks were related to the recombination of electrons from an upper ͑an-tibonding͒ subband-created by an antisymmetric linear combination of wave functions of a single QW, and from a lower ͑bonding͒ subband formed by a symmetric combination of electron states of a single well.…”