Application of external tensile and compressive strain on a single layer InAs/GaAs quantum dot via epitaxial lift-off

摘要

Tensile and compressive strains via epitaxial lift-off (ELO) techniques were applied on single-layer InAs/GaAs quantum dots (QDs). At low temperatures, due to the difference in thermal expansion coefficients of the ELO film and host substrate, the ELO QDs film bonded to Si and MgO substrates experienced tensile and compressive strain, respectively. At 13K, we observed that the photoluminescence (PL) spectra of the ELO film bonded to MgO blueshifts by 10meV while the ELO film bonded to Si redshifts by 8.5meV with respect to the ground state of the as-grown sample. The estimated tensile and compressive strains at this temperature were determined by monitoring the valence-band splitting of the GaAs PL peak. The film bonded to Si has a light hole (lh) to heavy hole (hh) energy separation of 4.6meV, resulting to values of strain, ε{lunate}=6.049×10~(-4) and stress, X=0.746×10~(-3)kbar or 74.6MPa. On the other hand, the film bonded on MgO has an lh-hh energy separation of 3.7meV, giving ε{lunate}=4.8×10~(-4) and X=0.24×10~(-3)kbar or 24MPa. Furthermore, we also observed a reversal of the PL intensity peak between the ground and excited-state transition of the film bonded on silicon only. A plateau-like feature between the two peaks also emerged, indicating the presence of another optical transition, which is enhanced due to application of tensile strain. We associated this peak to the 1LO-phonon replica of the PL transition resulting from the excited state. Based on these observations, this reversal is most likely attributed to the reduction of the carrier-relaxation mechanism from excited states to the ground-state transition upon the application of tensile strain. Finally, the result of this study showed the efficacy of the ELO technique as an alternative way of introducing variable tensile and compressive strain in the InAs/GaAs QD's heterostructure.