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We have successfully grown InGaN self assembled quantum dots (QD's) on a GaN layer, using atmospheric-pressure metalorganic chemical vapor deposition (MOCVD). The average diameter of the QD's was as small as 8.4 nm, and strong emission from the QD's was observed at room temperature. Next, we have investigated a structure in which InGaN QD's were stacked to increase the total QD density. InGaN QD's were formed even when the number of stacked layers was ten. As the number of layers increased, the photoluminescence (PL) intensity increased drastically. Moreover, we have fabricated a laser structure with InGaN QD's embedded into the active layer. A clear threshold of 6.0 mJ/cm2 was observed in the dependence of the emission intensity on the excitation energy at room temperature under optical excitation. Above the threshold, the emission was strongly polarized in the transverse electric (TE) mode, and the linewidth of the emission spectra was reduced to below 0.1 nm (resolution limit). The peak wavelength was around 405 nm. These results indicate lasing action at room temperature [ABSTRACT FROM PUBLISHER]

We described the photoluminescence (PL) properties of individual micelle-encapsulated single-walled carbon nanotubes (SWNTs) at room temperature. Single PL peak from isolated individual SWNT with a chiral index of (6, 5) showed a linear increase and saturation behavior of the PL intensity. Unusual PL intensity fluctuation in the temporal evolutions of the PL intensity, referred to as PL intermittency, was seen with some SWNTs, while the PL intensity with most SWNTs remained at a constant amplitude. The mechanism of the PL intermittency was discussed. [ABSTRACT FROM AUTHOR]

Presents a correction to the article "Photoluminescence intermittency in an individual single-walled carbon nanotube at room temperature" published in a 2005 issue of "Applied Physics Letters".

High-quality GaN with smooth surface morphology has been grown on vicinal a-plane sapphire substrates by metalorganic chemical vapor deposition. The misorientation angles of vicinal a-plane sapphire substrates were changed systematically and the results were compared with the growth on exact a- and c-plane sapphire substrates. Surface morphology and crystalline qualities are found to be very sensitive to misorientation angles of a-plane sapphire substrates and the misorientation angle was optimized to be 0.25°. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) spectra were measured for sub-nanometer-thick GaN quantum wells (QWs) with Al[sub 0.8]Ga[sub 0.2]N barriers, which were grown by atmospheric-pressure metal-organic chemical-vapor deposition. The thickness of the GaN QW layers was systematically varied from 1 to 4 ML. We clearly observed a PL peak at room temperature at a wavelength as short as 247 nm (5.03 eV) from 1-ML-thick QWs. The effective confinement energy, or difference between this recombination energy and the band gap of bulk GaN, is as large as 1.63 eV. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report photoluminescence (PL) and time-resolved PL measurements of GaN/Al[sub x]Ga[sub 1-x]N multiple quantum wells with barriers of high aluminum content, x=0.5. In wells of width 1-2 nm, low temperature recombination appears to be dominated by radiative processes with lifetimes ∼0.5 ns. Dependence of lifetime on emission energy is very small compared to InGaN quantum wells, indicating that carrier localization is very slight and interface quality is high. In 4 nm wells, PL emission at an energy below the bulk GaN band gap and long recombination lifetimes result from the polarization field across the wells. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) of modulation-doped Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures was investigated. The PL peak related to recombination between the two-dimensional electron gases (2DEG) and photoexcited holes is located at 3.448 eV at 40 K, which is 45 meV below the free excitons (FE) emission in GaN. The peak can be observed at temperatures as high as 80 K. The intensity of the 2DEG PL peak is enhanced significantly by incorporating a thin Al[sub 0.12]Ga[sub 0.88]N layer into the GaN layer near the heterointerface to suppress the diffusion of photoexcited holes. The energy separation of the 2DEG peak and the GaN FE emission decreases with increasing temperature. Meanwhile, the 2DEG peak energy increases with increasing excitation intensity. These results are attributed to the screening effect of electrons on the bending of the conduction band at the heterointerface, which becomes stronger when temperature or excitation intensity is increased. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In continuation to the steady state detection of below-gap states by combining a below-gap excitation (BGE) light with an above-gap excitation (AGE) light, we have studied the time-response of both donor-acceptor pair luminescence (DAP) and yellow luminescence (YL) in undoped GaN after switching off the BGE light. An extremely slow recovery of YL with a time constant of up to 28 s was observed, which is interpreted as a relaxation process of electrons from a below-gap state chosen by a BGE energy of 1.17 eV. Trap parameters were quantitatively determined by studying the intensity change and subsequent recovery time of DAP as a function of AGE and BGE power densities. The BGE energy dependence of the intensity change and subsequent recovery time of DAP and YL implies an energy distribution of traps in the band-gap of GaN. The combination of time-resolved PL measurement under two-wavelength excitation scheme was shown to be powerful for understanding the carrier recombination dynamics including YL among below-gap states. [Copyright &y& Elsevier]