Optical properties of CdSe MgS monolayer quantum wells and self-assembled quantum dots

The optical properties of CdSe MgS monolayer (ML) quantum wells (QW's) and self-assembled quantum dots (QD's) grown by molecular beam epitaxy are investigated by continuous-wave (cw) and time-resolved (TR) photoluminescence (PL) spectroscopy. The cw-PL spectra clearly show the growth development from ML-QW to QD's as the CdSe thickness increases from 1 to beyond 3 ML. The carrier dynamics are characterized chiefly by TRPL. For ML-QW's, it is determined that carrier localization in the potential fluctuations and scattering by phonons significantly influence the optical properties. On the other hand, TRPL reveals the carrier dynamics for QD's and a wetting layer (WL); some of the carriers photogenerated in the WL radiatively emit, while others are captured by QD's via a carrier-carrier scattering on a ~5 ps time scale. Within the next 10-50 ps, the carriers relax to the ground level via a carrier-LO-phonon scattering. Finally, the carriers radiatively recombine with a recombination lifetime of 100-300 ps, depending on the emission energy. © 2006 The American Physical Society.