Anomalous Sharp Dip of Large Field-Induced Refractive Index Change in GaAs/AlGaAs Five-Layer Asymmetric Coupled Quantum Well

Abstract

The five-layer asymmetric coupled quantum well (FACQW) is a new potential-tailored quantum well for ultrafast and low-voltage optical modulators and switches. Almost linear and large electrorefractive index change can be obtained in the transparency wavelength regions. In the GaAs/AlGaAs FACQW, an abrupt change in refractive index change n due to an applied electric field F occurs at a certain electric field range, which results in an anomalous sharp dip of n versus F. The physical origin and the elimination of the dip are discussed in detail. The abrupt change of refractive index is caused by significant changes of the wavefunction overlap integrals (and exciton binding energies) of transitions between the ground states for an electron (e1) and a heavy hole (hh1), and transitions between e1 and the first excited state for a heavy hole (hh2). The overlap changes are mainly due to shifts of the wavefunction distribution of hh1 and hh2, respectively. The dip can be eliminated by changing the position or Al content of the AlGaAs barrier layer in the FACQW. In addition, the larger negative index change in a modified FACQW structure is demonstrated.KEYWORDS: five-layer asymmetric coupled quantum well (FACQW), quantum well, optical modulator, optical switch, quantum confined Stark effect, electrorefractive effect, electroabsorptive effect, binding energy, wavefunction overlap, dip of refractive index change 6329

Proposal of ultra-low voltage quantum well optical modulator for optical interconnection in superconducting integrated circuit systems

“…The effective mass of the heavy hole is larger than that of an electron, the change in wavefunction distribution is more sensitive to that in the applied electric field, exhibiting the large absorption change by a small change in the electric field. 23) Figure 6 shows the wavefunction distributions for an electron and a hole at applied electric fields of (a) −11 kV cm −1 and (b) −12 kV cm −1 in the case where the wavevector in the well plane k t is equal to 0.02k 0 where k 0 is equal to 2π/a 0 . a 0 is the lattice constant of InP (0.587 nm).…”

Robust Coupled-Quantum-Well Structure for Use in Electrorefraction Modulators

“…The Lorentzian broadening function used in the model is described in [9], and the refractive-index changes are obtained using the Kramers-Kronig relation [1]. Our model is very similar to that used in [3] and [10] except that, in our model, the refractive-index changes are obtained for a whole period of a CQW structure and not only for the quantum-well layers. Fig.…”

“…The dip is due to the anticrossing of Ψ HH1 and Ψ HH2 at F HH ≈ 4.5 kV/cm, and it does not appear in ∆n TM1 as the heavy-hole momentum matrix element is zero for TM light. The dip is very sharp because of the large effective masses of Ψ HH1 and Ψ HH2 and the relatively large thickness of the middle barrier [10].…”

Suppressing nonradiative recombination in crown-shaped quantum wells

“…To minimize any change in wavelength, it is necessary to tailor well width; however, in practice the well width can be varied only within a very limited range owing to physical limitations such as the material choice corresponding to the target emission wavelength, lattice parameters, strain, and critical layer thickness. To alleviate the physical limitations of RQWs, coupled QWs with a multilayered structure have been studied theoretically [6][7][8][9][10] and experimentally. [11][12][13][14][15][16] The coupled QW is a distinctive structure that can be used to control the spatial distribution of carriers directly by tailoring the bandgap energy profiles.…”