Nanoindentation effect on the optical properties of self-assembled quantum dots

The optical emission spectrum of a quantum dot array is computed for a series of cases in which a nanometer scale microscope tip indenter is used to impose increasing elastic strain on the sample. The system under consideration consists of approximately 30 self-assembled In_0.55Al _0.45As quantum dots buried in a matrix material of Al _0.35Ga_0.65As; the indenter is a tapered optical fiber tip used to collect emitted light from the array while simultaneously imposing strain on the sample. A continuum analysis is used to compute the confined electron and hole energies and wave functions in the presence of the imposed elastic indentation strain field. The analysis includes the consideration of exciton binding energy effects, which are found to be small for quantum dots in the size range of interest. From the computed energy states, the optical conductivity of the system is evaluated using simple scattering rate theory. The blue-shift in light emitted by individual dots predicted by the analysis agrees well with experimental observations by Robinson et al. (Appl. Phys. Lett. 72 (1998) 2081). Finally, a simple dislocation nucleation estimate based on a Rice-Thomson-type analysis is developed for the system. The estimate supports the observation that dislocation activity in the single crystalline sample may be responsible for the experimentally observed optical emission quenching when indentation exceeds a critical depth.