AVS 49th International Symposium
    Nanometer Structures Tuesday Sessions
       Session NS+EL-TuA

Invited Paper NS+EL-TuA3
Strain Effects and Inter-Dot Coupling in Self-Assembled Quantum Dot Arrays

Tuesday, November 5, 2002, 2:40 pm, Room C-207

Session: Quantum Dots
Presenter: H.T. Johnson, University of Illinois at Urbana-Champaign
Authors: H.T. Johnson, University of Illinois at Urbana-Champaign
R. Bose, University of Illinois at Urbana-Champaign
B.B. Goldberg, Boston University
H.D. Robinson, University of California at Los Angeles
Correspondent: Click to Email
A computational model is used to simulate optical properties of self-assembled InAlAs/AlGaAs quantum dot arrays. Array sections containing up to 30 dots of varying size, shape, and spacing are considered. Comparisons are made to experimental results for arrays characterized using near-field scanning optical microscopy (NSOM). The experimental and computational studies both measure emission/absorption spectra with energy resolution that shows the effects of individual dots in the array. In the computational approach, the optical properties are computed from the spectrum of electron and hole states found for the ensemble. The energies and wave functions in the spectrum are first computed using a strain-modified k-p Hamiltonian approach; the spectrum includes confined electron and hole states associated with individual dots in addition to some delocalized states associated with coupled dots as well as the wetting layer. By modeling the entire ensemble of dots simultaneously, it is possible to consider effects related to long range field interactions between dots, such as linear elastic fields and extended quantum mechanical states. Two key results are of interest. First, it is found that even minor contact between the optical fiber tip and the sample surface leads to indentation strain large enough to substantially shift emission wavelengths of individual dots in the array. Second, extended states in groups of neighboring quantum dots lead to sharp, well-defined resonances in the emission spectra for the arrays. Results of the simulations clearly show these effects that are also observed in the experimental data.