Photoluminescence studies on pseudomorphic delta-doped AlGaAs/InGaAs/GaAs quantum wells

Photoluminescence (PL) measurements were performed on several series of single-side Si-doped pseudomorphic high electron mobility transistors (p-HEMTs) quantum well (QW) samples, with different spacer layer widths, well widths and Si delta -doped concentrations , under different temperatures and excitation power densities. The dynamic competitive luminescence mechanism between the radiations of e2-hh1 and e1-hh1 was discussed in detail. The confining potential, subband energies, corresponding envelope functions, subband occupations and transferring efficiency etc., were calculated by self-consistent finite differential method at different temperatures in comparison with the present experiment results. The relative variation of the integrated luminescence intensity of the two transitions (e1-hh1 and e2-hh1) was found to be dependent on the temperature and the structure's properties, e. g. spacer layer width, dopant concentration and well width.

Photoluminescence of InAs quantum dots grown on GaAs surface

InAs quantum dots (QDs) grown on GaAs surface are investigated. The observed abnormal photoluminescence (PL) properties, including extremely sharp high-energy peaks, almost temperature-independent linewidth, and fast thermal quenching, are discussed in terms of the strong quantum confinement effects due to the absence of a cap layer and the lack of carrier redistribution channel caused by the small number of QDs capable of contributing to PL and the high-density surface defects. (C) 2000 American Institute of Physics. [S0003-6951(00)01244-4].

Formation of InAs quantum dots on low-temperature GaAs epi-layer

InAs self-organized quantum dots (QDs) grown on annealed low-temperature GaAs (LT-GaAs) epi-layers and on normal temperature GaAs buffer layers have been compared by transmission electron microscopy (TEM) and photoluminescence (PL) measurements. TEM evidences that self-organized QDs were formed with a smaller size and larger density than that on normal GaAs buffer layers. It is discussed that local tensile surface strain regions that are preferred sites for InAs islands nucleation are increased in the case of the LT-GaAs buffer layers due to exhibiting As precipitates. The PL spectra show a blue-shifted peak energy with narrower linewidth revealing the improvement of optical properties of the QDs grown on LT-GaAs epi-layers. It suggests us a new way to improve the uniformity and change the energy band structure of the InAs self-organized QDs by carefully controlling the surface stress states of the LT-GaAs buffers on which the QDs are formed. (C) 2000 Elsevier Science B.V. All rights reserved.

1.5 mu m luminescence characteristic of erbium in B, P doped a-SiO : H films

Hydrogenated amorphous silicon films co-doped with oxygen (O), boron (B) and phosphorus (P) were fabricated using PECVD technique. The erbium (Er) implanted samples were annealed in a N-2 ambient by rapid thermal annealing. Strong photoluminescence (PL) spectra of these samples were observed at room temperature. The incorporation of O, B and P could not only enhance the PL intensity but also the thermal annealing temperature of the strongest PL intensity. It seems that the incorporation of B or P can decrease the grain boundary potential barriers thus leading to an easier movement of carriers and a stronger PL intensity. Temperature dependence of PL indicated the thermal quenching of Er-doped hydrogenated amorphous silicon is very weak.

Structural and optical characterization of InAs nanostructures grown on (001) and high index InP substrates

The effects of InP substrate orientations on self-assembled InAs quantum dots (QDs) have been investigated by molecular beam epitaxy (MBE). A comparison between atomic force microscopy (AFM) and photoluminescence (PL) spectra shows that a high density of smaller InAs islands can be obtained by using such high index substrates. On the other hand, by introducing a lattice-matched underlying In0.52Al0.24Ga0.24As layer, the InAs QDs can be much more uniform in size and have a great improvement in PL properties. More importantly, 1.55-mu m luminescence at room temperature (RT) can be realized in InAs QDs deposited on (001) InP substrate with underlying In0.52Al0.24Ga0.24As layer. (C) 2000 Elsevier Science B.V. All rights reserved.

Temperature dependence of photoluminescence of an n-i-p-i GaAs superlattice

Both the photoluminescence peaks corresponding to the vertical transitions and the nonvertical transitions in an n-i-p-i GaAs superlattice are clearly observed. The redshifts of the two peaks with increasing temperature are: discussed in terms of the temperature-dependent carrier separation effect.

Photoluminescence of Eu2+ doped ZnS nanocrystals

Eu2+ doped ZnS nanocrystals exhibit new luminescence properties because of the enlarged energy gap of nanocrystalline ZnS host due to quantum confinement effects. Photoluminescence emission at about 520 nm from Eu2+ doped ZnS nanocrystals at room temperature is investigated by using photoluminescence emission and excitation spectroscopy. Such green emission with long lifetime (ms) is proposed to be a result of excitation, ionization, carriers recapture and recombination via Eu2+ centers in nanocrystalline ZnS host.

Anomalous temperature dependence of photoluminescence from InAs quantum dots

Self-assembled InAs quantum dots are fabricated on a GaAs substrate by molecular beam epitaxy. The dots are covered by several monolayers of In0.2Ga0.8As before a GaAs cap layer and an in situ postgrowth annealing is performed to tune the emission to higher energy. The temperature dependence of photoluminescence from this structure demonstrates a slower redshift rate of the peak position, a gradual broadening of the linewidth and an abnormal enhancement of integrated intensity as the temperature is increased from 15 to 300 K. These phenomena are closely related to the introduction of an InGaAs layer and to the intermixing of In and Ga atoms during annealing. We propose a model to explain the unusual increase in PL intensity, which fits the experimental data well. (C) 2000 American Institute of Physics. [S0021-8979(00)04618-1].

Photoluminescence and electroluminescence of (Gd2O3-Ga2O3): Ce thin film

A novel electroluminescence oxide phosphor (Gd2O3-Ga2O3):Ce has been prepared by electron beam evaporation. The emission peaks of photoluminescence lie at 390nm and a shoulder at 440nm. However, the electroluminescence of the (Gd2O3-Ga2O3):Ce thin film have four emission peaks at 358nm, 390nm, 439nm and 510nm, respectively. The optical absorption of (Gd2O3-Ga2O3):Ce thin film and the photoluminescence of composite materials with various ratios of Ga2O3/(Gd2O3+Ga2O3) have also been described to investigate the origin of emission of photoluminescence and electroluminescence.

Surface states induced photoluminescence from Mn2+ doped CdS nanoparticles

Manganese doped CdS nanoparticles were synthesized in basic aqueous solution by using mercapto acetate as capping reagents. The nanoparticles were characterized by HRTEM, EPR, photoluminescence and optical absorption measurements. Out of our expectation, doping of Mn2+ ions altered the recombination paths in CdS nanoparticles markedly. The surface stares facilitated PL from Mn2+ doped CdS nanoparticles is reported. A complete suppression of the emission from surface states at room temperature when doping with Mn2+ ions has been observed for the first time. (C) 2000 Elsevier Science Ltd. All rights reserved.

Optical properties of self-assembled ternary In(GA/Al)As quantum dots on (100) and (N 1 1)B InP substrates

In this paper, we investigated the self-assembled quantum dots formed on (100) and (N11)B (N = 2, 3, 4, 5) InP substrates by molecular beam epitaxy (MBE). Two kinds of ternary QDs (In0.9Ga0.1As and In0.9Al0.1As QDs) are grown on the above substrates; Transmission electron microscopy (TEM) and photoluminescence (PL) results confirm QDs formation for all samples. The PL spectra reveal obvious differences in integral luminescence, peak position, full-width at half-maximum and peak shape between different oriented surfaces. Highest PL integral intensity is observed from QDs on (411)B surfaces, which shows a potential for improving the optical properties of QDs by using high-index surface. (C) 2000 Elsevier Science B.V. All rights reserved.

Photoluminescence and optical quenching of photoconductivity studies on undoped GaN grown by molecular beam epitaxy

Deep levels in undoped GaN materials grown by modified molecular beam epitaxy (MBE) are investigated by photoluminescence (PL) and optical quenching of photoconductivity measurements. A broad band which extends from 2.1 to 3.0 eV with a maximum at about 2.7 eV is observed, and four prominent quenching bands were found located at 2.18, 2.40, 2.71, and 2.78 eV above the valence band, respectively. These levels are attributed to four holes trap levels existence in the material. The defects cannot be firmly identified at present. (C) 2000 Elsevier Science B.V, All rights reserved.

Photoluminescence of erbium-doped hydrogenated amorphous SiOx(0 < x < 2)

Hydrogenated amorphous SiOx films are fabricated via plasma enhanced chemical vapor deposition technique. After erbium implantation and rapid thermal annealing, photoluminescence (PL) are measured at 77 K and room temperature (RT), respectively. We observed the strong PL at 1.54 mu m at RT. The 1.54 mu m PL intensity changes with the variation of concentration of oxygen. The most intense PL at 77 K in a-SiOx:H (Er) corresponds to O/Si = 1.0 and at RT to O/Si = 1.76. Based on our results, we propose that Er ions contributed to PL come from O-rich region in the film. Er ions in Si-rich region have no relation with FL. Temperature dependence of the intensity of the 1.54 mu m line of the Er3+ transition displays a very weak temperature quenching in Er-doped hydrogenated amorphous Si. The PL intensity at 250 K is a little more one half of that at 15 K.

Blue-violet photoluminescence from large-scale highly aligned boron carbonitride nanofibers

We report on the strong blue-violet photoluminescence (PL) at room temperature from the large-scale highly aligned boron carbonitride (BCN) nanofibers synthesized by bias-assisted hot filament chemical vapor deposition. The photoluminescence peak wavelength shifts in the range of 470-390 nm by changing the chemical composition of the BCN nanofibers, which shows an interesting blue and violet-light-emitting material with adjustable optical properties. The mechanism for the shift of the PL peaks at room temperature is also discussed. (C) 2000 American Institute of Physics. [S0003-6951(00)04427-2].

Study of self-assembled InAs quantum dots grown on low temperature GaAs epi-layer

InAs self-organized quantum dots (QDs) grown on annealed low temperature GaAs (LT-GaAs) epi-layer were investigated by transmission electron microscopy (TEM) and photoluminescence (PL) measurement. TEM showed that QDs formed on annealed LT-GaAs epi-layer have a smaller size and a higher density than QDs formed on normal GaAs buffer layer. In addition, the PL spectra analysis showed that the LT-GaAs epi-layer resulted in a blue shift in peak energy, and a narrower linewidth in the PL peak. The differences were attributed to the point defects and As precipitates in annealed LT-GaAs epi-layer for the point defects and As precipitates change the strain field of the surface. The results provide a method to improve the uniformity and change the energy band structure of the QDs by controlling the defects in the LT-GaAs epi-layer.