Abstract:We present experimental results concerning optical transitions and carrier dynamics (capture and relaxation) in self assembled InAs/GaAs quantum dot structures grown by metalorganic vapor phase epitaxy. Photoluminescence (PL) measurements at high excitation level reveal optical transitions above the ground state emission. These transitions are found to originate from occupied hole states by solving the quantum dot eigenvalue problem. Time-resolved studies after non-resonant pulse excitation exhibit a relaxatio… Show more
“…We find that the effective gaps range from 0.954 to 1.2 eV as the height changes from 85 to 55 A. The preferred size has a peak energy of-1.04 eV, which agrees well with the experimental PL results [14]. The electronic spectrum for different dot sizes is shown in figure 4.…”
The past few years have seen considerable efforts in growth and device application of selfassembled quantum dots. However, the photoluminescence (PL) linewidth, which represents structural fluctuations in dot sizes, is still in the range of 30-50 meV. This large linewidth has deleterious effects on devices such as lasers based on self-assembled dots. In this paper we will examine the configuration-energy diagram of self-assembled dots. Our formalism is based on: (1) an atomistic Monte Carlo method which allows us to find the minimum energy configuration and strain tensors as well as intermediate configurations of dots; (2) an 8-band k -p method to calculate the electronic spectra. We present results on the strain energy per unit cell for various distributions of InAs/GaAs quantum dots and relate them to published experimental results. In particular we examine uncovered InAs/GaAs dots and show that in the uncovered state a welldefined minimum exists in the configuration energy plot. The minimum corresponds to the size that agrees well with experiments.
“…We find that the effective gaps range from 0.954 to 1.2 eV as the height changes from 85 to 55 A. The preferred size has a peak energy of-1.04 eV, which agrees well with the experimental PL results [14]. The electronic spectrum for different dot sizes is shown in figure 4.…”
The past few years have seen considerable efforts in growth and device application of selfassembled quantum dots. However, the photoluminescence (PL) linewidth, which represents structural fluctuations in dot sizes, is still in the range of 30-50 meV. This large linewidth has deleterious effects on devices such as lasers based on self-assembled dots. In this paper we will examine the configuration-energy diagram of self-assembled dots. Our formalism is based on: (1) an atomistic Monte Carlo method which allows us to find the minimum energy configuration and strain tensors as well as intermediate configurations of dots; (2) an 8-band k -p method to calculate the electronic spectra. We present results on the strain energy per unit cell for various distributions of InAs/GaAs quantum dots and relate them to published experimental results. In particular we examine uncovered InAs/GaAs dots and show that in the uncovered state a welldefined minimum exists in the configuration energy plot. The minimum corresponds to the size that agrees well with experiments.
“…Photoluminescence recombination measurements www.lpr-journal.org indicate a shorter recombination time from the excited states (ES) as compared to the GS. Non-radiative relaxation processes that result from the Auger effect [25] and step-wise ("intra-dot") relaxation of excitons through subsequent QD energy states are dependent on both the available intraband relaxation channels and phonon interactions [26]. The difference between carrier capture and carrier relaxation in this case is defined by whether photocarriers are considered as mobile or not mobile.…”
Compact and tunable semiconductor terahertz sources providing direct electrical control, efficient operation at room temperatures and device integration opportunities are of great interest at the present time. One of the most well-established techniques for terahertz generation utilises photoconductive antennas driven by ultrafast pulsed or dualwavelength continuous wave laser systems, though some limitations, such as confined optical wavelength pumping range and thermal breakdown, still exist. The use of quantum dotbased semiconductor materials, having unique carrier dynamics and material properties, can help to overcome limitations and enable efficient optical-to-terahertz signal conversion at room temperatures. Here we discuss the construction of novel and versatile terahertz transceiver systems based on quantum dot semiconductor devices. Configurable, energy-dependent optical and electronic characteristics of quantum-dot-based semiconductors are described, and the resonant response to optical pump wavelength is revealed. Terahertz signal generation and detection at energies that resonantly excite only the implanted quantum dots opens the potential for using compact quantum dot-based semiconductor lasers as pump sources. Proof-ofconcept experiments are demonstrated here that show quantum dot-based samples to have higher optical pump damage thresholds and reduced carrier lifetime with increasing pump power.
“…Therefore, the excited carriers in the WLs and the spacer layers lead to the transfer of an impaired hole into the QDs (Adler et al, 1996). In the lower temperature region, lateral coupling-like behaviour arises from the hole injection from the spacer layers.…”
Section: Temperature Dependence Of Excitons In Qd Ensemblesmentioning
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