Few studies in literature have try to quantitatively compare the 2T model with experimental data at very short time scale and study the dependency and importance of model’s parameters. We have developed a new numerical model and fitting algorithm which combined the 2T model, thermal conduction and 3D FEM EM code to link the spatial distribution of temperature to the optical reflectivity of the sample. Using a state-of-the-art pump-probe setup allowing the acquisition of the full spectro-temporal optical response of the sample, we have compared measurements on thin gold films and array of nanostructures with our model.
This work reports on a chemical beam epitaxy growth study of InGaAs/GaAs quantum dots (QDs) engineered using an in-situ indium-flush technique. The emission energy of these structures has been selectively tuned over 225 meV by varying the dot height from 7 to 2 nm. A blueshift of the photoluminescence (PL) emission peak and a decrease of the intersublevel spacing energy are observed when the dot height is reduced. Numerical investigations of the influence of dot structural parameters on their electronic structure have been carried out by solving the single-particle one-band effective mass Schrödinger equation in cylindrical coordinates, for lens-shaped QDs. The correlation between numerical calculations and PL results is used to better describe the influence of the In-flush technique on both the dot height and the dot composition.
Improvised Explosive Devices (IEDs) are a major threat to Canadian and allies troups involved in peacekeeping and
minor conflict operations and despite their relative low technology they represent a major challenge in terms of detection
and countermeasures. In order to provide tools to detect these threats, Defence Research & Development Canada -
Valcartier initiated a research project to the feasibility of using terahertz (THz) radiations to detect and identify the
presence of commonly used explosives and concealed weapons in a standoff method. This paper presents the initial
results of the first year of the project and the future directions. A compact THz time domain spectroscopy was
developed to build a THz signature table of commonly used explosives.
In this work we show that improved performances of small-aperture terahertz antennas can be obtained using an ion implantation process. Our photoconductive materials consist of high resistivity GaAs substrates. Terahertz pulses are generated by exciting our devices with ultrashort laser pulses. Ion implantation introduces nonradiative centers which reduce the carrier lifetime in GaAs and modify the shape of our terahertz pulses. The introduction of charge defects also induces a redistribution of the electric field between the antenna electrodes. The overall process is optimized to better control the dynamical field screening effect which has a huge influence on the amplitude of the radiated terahertz field. Results obtained as a function of the laser excitation power is discussed and comparison of the performance of these devices with conventional small-aperture antennas is given.
Carrier dynamics in InAs/GaAs self-assembled quantum dots have been studied by using time-resolved photoluminescence experiment. We have studied a series of doped quantum dot structures by looking at the role of the experimental conditions, such as the laser excitation intensity, the crystal temperature and the intersublevel energy, on the carrier relaxation time. For all samples, we have found two distinct relaxation regimes. At a crystal temperature of 77K, a rise time of the quantum dot emission signal of a few tens of ps has been measured under low photocarrier densities. This rise time decreases significantly, down to few ps, as the laser intensity increases. These results show that carrier-carrier scattering processes play a significant role at high photo-excited carrier densities. Under the low-excitation regime, the dot emission rise time depends on the dopant type, on the doping level on the degree of intermixing and on the temperature. Our results obtained on structures having a relatively low density of dots indicate that transport processes (diffusion and localization at the InAs/GaAs interfaces) limit the dot capture efficiency at low temperatures. The experimental conditions and the dot structural parameters that give rise to ultrafast capture and intra-dot relaxation times are discussed.
In this paper we show that low energy ion implantation of InP based heterostructures for quantum well intermixing is a promising technique for photonic integrated devices. In order to fabricate complex optoelectronic devices with a spatial control of the bandgap profile of the heterostructure, there is a list of requirements that have to be fulfilled. We have fabricated high quality discrete blueshifted laser diodes to verify the capability of low energy ion implantation induced intermixing for integration. We also adapted this intermixing process to specific heterostructures in order to obtain submicrometer bandgap tuning spatial control.
Understanding the physics of Ini..GaAsPi multiple quantum well (MQW)
nanostructures is essential for the development of new photonic devices such as lasers,
amplifiers and modulators. In this work, optical and structural properties as well as
vertical transport of three different heterostructures grown by metalorganic vapor phase
epitaxy and emitting at 1 .33 tm and 1 .55 jim have been studied using continuous wave
and time-resolved photoluminescence (cw-PL and TRPL) and high resolution x-ray
diffraction (HRXRD). Cw-PL measurements show an anomalous PL characteristics for
the structure with a thicker active layer which is discussed in terms of electron-acceptor
transitions, donor-acceptor pairs, and constraint relaxation and related structural defects.
The overall observed red shift with increasing temperature is interpreted as resulting
from two opposite and competitive processes: band-gap shrinkage (dominant) and blue
shi:ft caused by fluctuations in the QW layer thickness across the lateral sample
direction. In the observed full width at half maximum, we identified a component of 8
meV as a contribution from longitudinal optical phonons. At high excitation densities, it
is shown that carrier spillover and Auger recombination may be the major mechanisms
limiting the quantum efficiency. For TRPL measurements, carrier cooling rates are
discussed in terms of concurrent and opposite scattering mechanisms. It is found that
the rise times of the QWs and the confinement region increase slightly (''2 ps) on
decreasing the excitation wavelength. The observed difference is attributed to a higher
initial carrier temperature associated with the shorter excitation wavelength.
Comparable times of 4 ps are observed for the carrier transport and relaxation time
within the confinement region and the carrier capture time in the quantum wells.
We investigate vertical carrier transport, carrier relaxation and capture in three In1-xGaxAsyP1-y multiple-quantum-well lasers structures emitting at 1.3 and 1.55 micrometers at room temperature using time resolved photoluminescence. In the initial regime following the excitation, high effective carrier temperatures Tc different from the lattice temperature TL equals 77 K are reported. A significant signature of transport and capture is observed with characteristic times of approximately 10 ps and approximately 12 ps respectively.
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