Photoluminescence of CdSe quantum dots with Zn_0.38Cd_0.23Mg_0.39Se barriers under hydrostatic pressure

Abstract

We have investigated the pressure dependence of the room-temperature photoluminescence (PL) of selfassembled CdSe quantum dots (QDs) with quaternary ZnCdMgSe barriers. Four samples with different CdSe deposition times, i.e. different average dot size, were studied. Samples exhibit a very distinct emission energy covering the visible spectrum from the red to the blue. We found, however, a similar pressure coefficient of around 47 meV/GPa for the PL emission of all samples. This value is close to that of bulk CdSe, which gives evidence that dot and quaternary barrier material have a similar compressibility. In contrast, the PL linewidth displays a clear trend with respect to the emission energy, the PL line being broader for the smaller dots emitting in the blue. This is explained by taking into account the huge bandgap offset of ≈ 1 eV between dot and barrier and considering quantum confinement effects within a very simplistic infinitely deep square-well model.

Size-dependent strain effects in self-assembled CdSe quantum dots with Zn0.38Cd0.23Mg0.39Se barriers

“…This is due to the strong increase with pressure of the energy of the fundamental optical transition of the dots with a slope of about 47 meV/ GPa. 6 The only Raman peaks which resonate with the PL emission from the CdSe dots are the two ones previously assigned to the LO CdSe mode at around 220 cm −1 and the Mg-local mode near 300 cm −1 . Their Raman intensity is not only comparable to that of the dot PL but it also increases as these modes become more in outgoing resonance with the PL band, as the applied pressure increases.…”