Evaluation of the etch depth dependence of three-dimensional confinement in strain-induced quantum well dot structures

Abstract

Strain-induced quantum well dots (SIQWDs) 120 nm in diameter have been fabricated by laser holography and wet etching. Lateral confinement was generated in the GaAs quantum well (QW) by etching a doubly exposed grating pattern into a strained layer of InGaAs which overlies the QW. Atomic force microscopy was used to examine the surface morphology of the SIQWDs. Photoluminescence spectra of quantum wells located at different distances below the InGaAs stressor probe the etch depth dependence of the strength of the strain modulation. The extent of the strain modulation in the vertical direction falls off within a distance comparable to the lateral dimension of the dot. A maximum redshift of 12 meV is observed for the uppermost QW located 22 nm away from the InGaAs stressor, implying carrier confinement in the SIQWD region. The dots were etched for varying amounts of time, changing the distance between the etched surface and the uppermost QW from 18 to 0 nm. Although the spatial distribution of strain modulation did not change significantly, the luminescence intensities from the uppermost QW decreased by about a factor of 50. This observation suggests that extrinsic causes, such as surface states formed on the etched surfaces are the major cause of diminished luminescence in these SIQWDs, rather than intrinsic causes such as slower electron–phonon interaction rate.