In a one-dimensional (1-D) periodic Bragg stack of light-emitting quantum wells (QWs), the standing-wave pattern has nodes at the QW positions, which for normal (perpendicular to the Bragg-stack planes) light output leads to inefficient emission. To combat this situation, researchers at the University of Arizona (Tucson, AZ), the A. F. Ioffe Physico-Technical Institute (St. Petersburg, Russia), and the Universität Karlsruhe (Karlsruhe, Germany) are researching QW structures with active thicknesses of two values (A and B), but whose order is based on the Fibonacci sequence—in other words, a 1-D Fibonacci quasicrystal. In such a structure, not all QWs coincide with nodes.
The researchers grew a gallium arsenide/aluminum gallium arsenide—based structure with A and B values of 82 and 134 nm (optical thicknesses of 0.36λ and 0.59λ); the A:B ratio is based on the golden mean. They also grew a similar but periodic structure (optical thicknesses of λ/2). Photoluminescence experiments were carried out with 780 nm light from a continuous-wave Ti:sapphire laser. Strong photoluminescence occurred at the Bragg condition only for the Fibonacci case (even though the quasicrystal’s long-range order produces an excitonic polariton stopband similar to those in photonic crystals). Contact Joshua Hendrickson at [email protected].