Light emission from PbS quantum dots (QDs) is an intriguing topic from application perspectives, and even after myriad of articles, still has open questions. The paper highlights the optical characterization of PbS QDs deposited via solvent deposition on semi-insulating GaAs substrates. The QD thin films were characterized by two-photon excited photoluminescence (TPL) measurements, exciting the samples with increasing pulsed laser (1064 nm, 10 Hz, 26 ps) intensities. The work reveals alterations of the optical properties of GaAs when hetero-paired with PbS QDs, as demonstrated by the trend of the TPL peak increase, the energy where the TPL peak takes place, and the overall dynamics of the peak shift. We also report that the TPL intensity increase of PbS QDs shows the same trend as the single-photon excited emission, and observed photo-induced doping of the QDs, i.e., the dynamic Burstein-Moss blue shift. The work stresses the possibility to modify the optical properties of semiconductor hosts by means of heteropairing with QDs. Through this work, we further attempt to reconcile observations, which are much different from reported classical models in semiconductor heterostructures.
In this work we investigate carrier dynamics of narrow gap ferromagnetic alloys grown by MOVPE. We determine the intraband and interband relaxation times in these material systems where the samples are excited with photon energies above the band gap of InMnAs and InMnSb films. Our results are important for understanding the electronic states and the relaxation mechanisms in these ferromagnetic materials.
In light of the growing interest in spin-related phenomena and devices, there is now renewed interest in the
science and engineering of narrow gap semiconductors. In this work, time resolved spectroscopy of InSb-based parabolic
multi-quantum wells and narrow gap ferromagnetic alloys grown by MOVPE, have been pursued. In addition, in this
study, we report on CR experiments carried out on the ferromagnetic InMnAs film, on which clear resonance signals
have been successfully observed in high magnetic fields. Investigation of the electronic structure of III-Mn-V alloys by
techniques such as the cyclotron resonance can shed important light on the origin of ferromagnetism and the p-d
exchange interaction in III-Mn-V systems. Our results are important for understanding the electronic and magnetic states
in these material systems.
In light of the growing interest in spin-related phenomena and devices, there is now a renewed interest in the
science and engineering of narrow gap semiconductors. They offer several scientifically unique electronic features such
as a small effective mass, a large g-factor, a high intrinsic mobility, and large spin-orbit coupling effects. Our studies
have been focused on probing and controlling the coherent and quantum states in InSb quantum wells and InMnAs
ferromagnetic semiconductors. Our observations are providing new information regarding the optical control of carriers
and spins in these material systems. We demonstrated the generation of spin polarized photo-current in an InSb QW
where a non-equilibrium spin population has been achieved by using circularly polarized radiation. In addition, the
differential transmission measurements in InSb QWs demonstrated that the initial distribution function strongly
influences the carrier relaxation dynamics. We employed the polarization-resolved differential transmission as well as
the MOKE measurements to provide information on the spin relaxation dynamics in MOVPE grown InMnAs. Our
measured T1 is comparable to the reported measurements in MBE grown InMnAs and several time resolved
measurements on InAs.