The emission dynamics properties of self-assembled InAs quantum dots with different cap layers are investigated by steady-state and time-resolved photoluminescence (PL). The uniformity of the dots can be improved by the proper cap layer structure. It is found that the InGaAs and InAlAs combination cap layer structure could more effectively release the strain in QDs, suppress the indium segregation, enhance the confinement effect on carriers and reduce the thermally induced carrier escape from QDs. This has led to QDs with narrower emission, above 1.3 µm, and to improved temperature stability of PL intensity and has resulted in an increase of the PL decay time to 10 ns at 160 K.
Luminescence properties of blue emission InGaN/GaN multiple quantum well (MQW) have been studied by temperature dependent photoluminescence (PL), photoluminescence excitation (PLE) and time-resolved photoluminescence (TRPL) spectroscopic techniques. Two typical samples are studied, both consisting of five periods of InGaN wells with different indium compositions of 21% and 24%, respectively. According to the PL and PLE measurement results, large values of activation energy and Stokes’ shift are obtained. This indicates that higher Indium composition results in an increase of composition fluctuation in the InGaN MQW region, showing the stronger carrier localization effect. The lifetime at the low-energy side of the InGaN peaks is longer for higher indium composition, as expected from the larger Stokes shift.
Self –organized InAs quantum wires (QWRs) were fabricated on the step edges of GaAs (331)A surface by molecular beam epitaxy (MBE). The atomic force microscopy (AFM) results show that the lateral size of InAs QWRs is 90 nm while the size along the step lines increasing with the thicknesses of InAs layers, amounting to 1100nm. The height of InAs QWRs varies from 7.9nm to 13nm. Photoluminescence (PL) measurements on the two samples were explored and an obvious PL peak around 967 nm was observed at 25 K. The PL intensity decreases as the temperature increases, and it will vanish above 60 K. However, the QWR sample with thicker InAs layer emits a long emission of 1100 nm -1400 nm as the temperature rises above 50 K, and a longer emission of 1400-1600nm as the temperature approaches to 100 K. We considered that the complex photoluminescence spectra were originated from the multiple energy steps. The carrier migration among the different QWRs structures intensified with temperature, and the chance rate from the higher energy levels to the lower ones which generated a stronger emission of long wavelength. The carrier dynamics of QWR samples were measured by using time resolved PL (TRPL) spectra from 25 K to 100 K. The PL decay time in the QWR structure at longer emission was found to be independent of the temperature as T<100 K, showing a typical dynamical behavior of the localized excitons.
The evolution operator method is applied to studying the time-dependent and spin-related electron transport through a magnetic quantum dot coupled to two normal-metal leads. When the microwave field is applied on quantum dot there are additional peaks of PAT current besides the main peak of resonant tunneling current, and the energy distance between peaks relate to the frequency of microwave fields. Furthermore, owe to the spin non-degeneration in the magnetic quantum dot, the spin-up and spin-down current peaks are separated, and the separated distance depends on Zeeman energy. These effects allow us to propose a scheme to control the magnitude and spin polarization of current.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.