Localized strain effects on photoluminescence of quantum dots induced by nanoprobe indentation

We report localized strain effects on the low temperature (10 K) photoluminescence (PL) of self-assembled InGaAs/GaAs quantum dots (QDs), measured through an optical fiber nanoprobe (metal coated, aperture approximately 850 nm, flat apex). The localized strain is generated by the indentation of the nanoprobe onto the sample surface within elastic limit. The simultaneous measurement of the indentation force (typically<3 mN) and PL spectra enables us to perform the quantitative analysis of the strain effects through numerical model calculations. The energy-band shift calculated with 6×6 strain Hamiltonian for QDs and GaAs matrix figures out the accumulation of photoexcited holes at the edge region of the nanoprobe-indented area, which should be the mechanism of PL enhancement evoked by the nanoprobe indentation. The hole accumulation is caused by the shear strain components and thus not realized by the conventional hydrostatic experiments. The mechanism must be related closely to the emission enhancement reported for a p-type modulation doped laser.