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Self-assembled InAs/InAlGaAs quantum dots (QDs) in an InAlGaAs matrix on InP (001) substrates were grown by the alternate growth method (AGQD), where an InAs layer with a thickness of 1 monolayer (ML) and an InAlGaAs layer with a thickness of 1 ML were alternately deposited. Cross-sectional transmission electron microscopy images indicated that the aspect ratio (height/width) for the AGQDs was ∼0.25, which was higher than ∼0.10 of conventionally grown InAs QDs. The photoluminescence (PL) peak position for the ground states of the AGQDs was 1.485 μm with a linewidth broadening of 42 meV at room temperature, while the PL linewidth for the conventionally grown QDs was 85 meV. And the peaks for the excited-state transitions were also clearly observed from the excitation-power dependent PL. This is the first observation on the well-defined excited-state transitions from the InP-based InAs QDs, even though there were several reports on the features of the excited states. [ABSTRACT FROM AUTHOR]

We have investigated the optical properties and carrier dynamics of the two-dimensional electron gas (2DEG) in Al0.4Ga0.6N/GaN single heterostructures grown by metalorganic chemical vapor deposition by means of photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy. Shubnikov-de Haas oscillations were clearly observed at 1.5 K, confirming the existence of a 2DEG. An additional 2DEG PL emission appeared at about 40 meV below the GaN band-edge emission and persisted up to about 100 K, while this peak disappeared when the top Al0.4Ga0.6N layer was removed by reactive ion etching. We observed abrupt PLE absorption at GaN band edge energy and approximately 50-ps delayed risetime compared to GaN and AlGaN emissions, indicating effective carrier transfer from the GaN flatband and AlGaN regions to the heterointerface. Even though the 2DEG emission is a spatially-indirect (slow) recombination, a fast decay component of ∼0.2 ns is found to be dominant in 2DEG emission because of the fast exhaustion of photogenerated holes in GaN flatband region via spatially-direct (fast) GaN recombination. From the results, we explain the carrier generation, transfer, and recombination dynamics and the relationships between 2DEG, GaN, and Al0.4Ga0.6N emissions in undoped Al0.4Ga0.6N/GaN single heterostructures. [ABSTRACT FROM AUTHOR]

A ridge waveguide quantum dot (QD) laser with a stripe width of 15 μm was fabricated by using the seven-stacked InAs QD layers based on the InAlGaAs-InAlAs material system on InP [001] substrate. Room-temperature lasing operation was observed at 1.501 μm, which is the first observation from the InAs QDs with the InAlGaAs-InAlAs structure. The characteristic temperature of the InAs QD laser calculated from the temperature dependence of threshold current density was 135 K in the temperature range from 200 K to room temperature. [ABSTRACT FROM PUBLISHER]

We have investigated optical properties of amorphous silicon quantum dots (a-Si QDs) embedded in a silicon nitride grown on (100) silicon substrates by plasma-enhanced chemical vapor deposition. The photoluminescence (PL) emission colors of red, orange, and blue were shown for the a-Si QDs with average dot sizes of 5.8, 2.4, and 1.3 nm, respectively. The increase in the PL peak energy with decreasing QD size was attributed to the quantum confinement effect in a-Si QDs. An anomalous temperature dependence of the PL intensity and PL peak energy was observed for a-Si QDs. The visible-light PL emission from a-Si QDs is most efficient at near room temperature, and the PL spectral shape and peak energy are almost independent of temperature, which are most favorable for light-emitting device applications. From time-resolved PL experiments, an enhancement of phonon-assisted indirect radiative recombination was proposed to explain the anomalous temperature dependence. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]