Interface effect on emission properties of Er-doped Si nanoclusters embedded in SiO2 prepared by magnetron sputtering

Er-doped Si nanoclusters embedded in SiO2 (NCSO) films were prepared by radio frequency magnetron sputtering on either silicon or quartz substrates. A 1.16 mu m (1.08 eV) photoluminescence (PL) peak was observed from an Er-doped NCSO film deposited on a Si substrate. This 1.16 mu m peak is attributed to misfit dislocations at the NCSO/Si interface. The emission properties of the 1.16 mu m peak and its correlation with the Er3+ emission (1.54 mu m) have been studied in detail. The observed behavior suggests that the excitation mechanism of the 1.16 mu m PL is in a fashion similar to that shown for Er-doped Si nanoclusters embedded in a SiO2 matrix. (C) 2006 American Institute of Physics.

Dependence of bimodal size distribution on temperature and optical properties of InAs quantum dots grown on vicinal GaAs (1-00) substrates by using MOCVD

Self-assembled InAs quantum dots (QDs) are grown on vicinal GaAs (100) substrates by using metal-organic chemical vapour deposition (MOCVD). An abnormal temperature dependence of bimodal size distribution of InAs quantum dots is found. As the temperature increases, the density of the small dots grows larger while the density of the large dots turns smaller, which is contrary to the evolution of QDs on exact GaAs (100) substrates. This trend is explained by taking into account the presence of multiatomic steps on the substrates. The optical properties of InAs QDs on vicinal GaAs(100) substrates are also studied by photoluminescence (PL). It is found that dots on a vicinal substrate have a longer emission wavelength, a narrower PL line width and a much larger PL intensity.

The role of Sb in the molecular beam epitaxy growth of 1.30-1.55 mu m wavelength GaInNAs/GaAs quantum well with high indium content

Sb-assisted GaInNAs/GaAs quantum wells (QWs) with high (42.5%) indium content were investigated systematically. Transmission electron microscopy, reflection high-energy electron diffraction and photoluminescence (PL) measurements reveal that Sb acts as a surfactant to suppress three-dimensional growth. The improvement in the 1.55 mu m range is much more apparent than that in the 1.3 mu m range.. which can be attributed to the difference in N composition. The PL intensity and the full-width at half maximum of the 1.55 mu m single-QW were comparable with that of the 1.3 Am QWs. (c) 2006 Elsevier B.V. All rights reserved.

Influence of growth parameters of frequency-radio plasma nitrogen source on extending emission wavelengths from 1.31 mu m to 1.55 mu m GaInNAs/GaAs quantum wells grown by molecular-beam epitaxy

High (42.5%) indium content GaInNAs/GaAs quantum wells with room temperature emission wavelength from 1.3 mu m to 1.5 mu m range were successfully grown by Radio Frequency Plasma Nitrogen source assisted Molecular Beam Epitaxy. The growth parameters of plasma power and N-2 How rate were optimized systematically to improve the material quality. Photoluminescence and transmission electron microscopy measurements showed that the optical and crystal quality of the 1.54 mu m GaInNAs/GaAs QWs was kept as comparable as that in 1.31 mu m.

Growth of InAs quantum dots on vicinal GaAs (100) substrates by metalorganic chemical vapor deposition and their optical properties

The growth of InAs quantum dots on vicinal GaAs (100) Substrates was systematically studied using low-pressure metalorganic chemical vapor deposition (MOCVD). The dots showed a clear bimodal size distribution on vicinal substrates. The way of evolution of this bimodal size distribution was studied as a function of growth temperature, InAs layer thickness and InAs deposition rate. The optical properties of dots grown on vicinal substrates were also studied by photoluminescence (PL). It was found that, compared with dots on exact substrates, dots on vicinal substrates had better optical properties such as a narrower PL line width, a longer emission wavelength, and a larger PL intensity. (c) 2006 Elsevier B.V. All rights reserved.

Enhancement of 1.53 mu m photoluminescence from spin-coated Er-Si-O (Er2SiO5) crystalline films by nitrogen plasma treatment

Er-Si-O (Er2SiO5) crystalline films are fabricated by the spin-coating and subsequent annealing process. The fraction of erbium is estimated to be 21.5 at% based on Rutherford backscattering measurement. X-ray diffraction pattern indicates that the Er-Si-O films are similar to Er2SiO5 compound in the crystal structure. The fine structure of room-temperature photoluminescence of Er3+-related transitions suggests that Er has a local environment similar to the Er-O-6 octahedron. Our preliminary results show that the intensity of 1.53 mu m emission is enhanced by a factor of seven after nitrogen plasma treatment by NH3 gas with subsequent post-annealing. The full-width at half-maximum of 1.53 pm emission peak increases from 7.5 to 12.9 nm compared with that of the untreated one. Nitrogen plasma treatment is assumed to tailor Er3+ local environment, increasing the oscillator strength of transitions and thus the excitation/emission cross-section. (c) 2005 Elsevier B.V. All rights reserved.

Synthesis and temperature-dependent near-band-edge emission of chain-like Mg-doped ZnO nanoparticles

Chain-like Mg-doped ZnO nanoparticles were prepared using a wet chemical method combined with subsequent heat treatment. The blueshifted near-band-edge emission of the doped ZnO sample with respect to the undoped one was investigated by temperature-dependent photoluminescence. Based on the energy shift of the free-exciton transition, a band gap enlargement of similar to 83 meV was estimated, which seems to result in the equivalent shift of the bound-exciton transition. At 50 K, the transformation from the donor-acceptor-pair to free-to-acceptor emissions was observed for both the undoped and doped samples. The results show that Mg doping leads to the decrease of the acceptor binding energy. (c) 2006 American Institute of Physics.

Dual-wavelength distributed feedback laser for CWDM based on non-identical quantum well

Using non-identical quantum wells as the active material, a new distributed-feed back laser is fabricated with period varied Bragg grating. The full width at half maximum of 115 nm is observed in the amplified spontaneous emission spectrum of this material, which is flatter and wider than that of the identical quantum wells. Two wavelengths of 1.51 mu m and 1.53 mu m are realized under different work conditions. The side-mode suppression ratios of both wavelengths reach 40 dB. This device can be used as the light source of coarse wavelength division multiplexer communication systems.

Study on Er3+ emission from the erbium-doped hydrogenated amorphous silicon suboxide film

The erbium-doped hydrogenated amorphous silicon suboxide films containing amorphous silicon clusters were prepared. The samples exhibited photoluminescence peaks at around 750 nm and 1.54 mum, which could be assigned to the electron-hole recombination in amorphous silicon clusters and the intra-4f transition in Er3+, respectively. Correlations between the intensities of these two photoluminescence peaks and oxidation and dehydrogenation of the films during annealing were studied. It was found that the oxidation is triggered by dehydrogenation of the films even at low annealing temperatures, which decisively changes the intensities of the two photoluminescence peaks. On the other hand, the increase of Er content in the erbium-doped hydrogenated amorphous silicon suboxide film will enhance Er3+ emission at 1.54 mum, while quench amorphous silicon cluster emission at 750 nm, such a competitive relationship, was also observed in the erbium-doped silicon nanocrystals embedded in SiO2 matrix. Moreover, we found that Er3+ emission is not sensitive to whether silicon clusters are crystalline or amorphous. The amorphous silicon clusters can be as sensitizer on Er3+ emission as that of silicon nanocrystals. (C) 2003 American Institute of Physics.

Measurement of gain spectrum for semiconductor lasers utilizing integrations of product of emission spectrum and a phase function over one mode interval

A technique based on the integrations of the product of amplified spontaneous emission spectrum and a phase function over one mode interval is proposed for measuring gain spectrum for Fabry-Perot semiconductor lasers, and a gain correction factor related to the response function of the optical spectrum analyzer (OSA) is obtained for improving the accuracy of measured gain spectrum. The gain spectra with a difference less than 1.3 cm(-1) from 1500 to 1600 nm are obtained for a 250-mum-long semiconductor laser at the OSA resolution of 0.06, 0.1, 0.2, and 0.5 nm. The corresponding gain correction factor is about 9 cm(-1) at the resolution of 0.5 nm. The gain spectrum measured at the resolution of 0.5 nm has the same accuracy as that obtained by the Hakki-Paoli method at the resolution of 0.06 nm for the laser with the mode interval of 1.3 nm.

Photoluminescence behaviors from stoichiometric gadolinium oxide films

Stoichiometric gadolinium oxide thin films have been grown on silicon (100) substrates with a low-energy dual ion-beam epitaxial technique. Gadolinium oxide shares Gd2O3 structures although the ratio of gadolinium and oxygen in the film is about 2:1 and a lot of oxygen deficiencies exist. Photoluminescence (PL) measurements have been carried out within a temperature range of 5-300 K. The detailed characters of the PL emission integrated intensity, peak position, and peak width at different temperature were reported and an anomalous photoluminescence behavior was observed. The character of PL emission integrated intensity is similar to that of some other materials such as porous silicon and silicon nanocrystals in silicon dioxide. Four peaks relative to alpha band and beta band were observed also. Therefore we suggest that the nanoclusters with the oxygen deficiencies contribute to the PL emission and the model of singlet-triplet exchange splitting of exciton was employed for discussion. (C) 2003 American Institute of Physics.

Hydrogen related defects in neutron-irradiated silicon grown in hydrogen ambient

Isochronal thermal-annealing behavior of NTD floating-zone silicon grown in hydrogen ambient (called NTD FZ(H) Si) is presented. The dependencies of resistivity and carrier mobility on annealing temperature are determined by room-temperature Hall electrical measurements. Using infrared absorption spectroscopy, hydrogen-related infrared absorption bands evolution for NTD FZ(H) Si were measured in detail. It is demonstrated that compared with NTD FZ(Ar) Si, NTD FZ(H) Si exhibits the striking features upon isochronal annealing in temperature range of 150 similar to 650 degreesC: there appears the formation of an excessive shallow donor at annealing temperature of 500 degreesC. It is shown that the annealing behavior is directly related to the reaction of hydrogen and irradiation-induced defects. The evolution of infrared absorption bands upon temperature reflects a series of complex reaction process: irradiation-induced defects decomposition, breaking of Si-H bonds, migration and aggregation of atomic hydrogen, and formation of the secondary defects. (C) 2002 Elsevier Science B.V. All rights reserved.

Role of amorphous silicon domains on Er3+ emission in the Er-doped hydrogenated amorphous silicon suboxide film

An investigation on the correlation between amorphous Si (a-Si) domains and Er3+ emission in the Er-doped hydrogenated amorphous silicon suboxide (a-Si:O:H) film is presented. On one hand, a-Si domains provide sufficient carriers for Er3+ carrier-mediated excitation which has been proved to be the highest excitation path for Er3+ ion; on the other hand, hydrogen diffusion from a-Si domains to amorphous silicon oxide (a-SiOx) matrix during annealing has been found and this possibly decreases the number of nonradiative centres around Er3+ ions. This study provides a better understanding of the role of a-Si domains on Er3+ emission in a-Si:O:H films.

Optimization of cubic GaN growth by metalorganic chemical vapor deposition based on residual strain relaxation

The reduction of residual strain in cubic GaN growth by inserting a thermoannealing process is investigated. It is found that the epilayer with smaller tensile strain is subject to a wider optimal "growth window." Based on this process, we obtain the high-quality GaN film of pure cubic phase with the thickness of 4 mum by metalorganic chemical vapor deposition. The photoluminescence spectrum at room temperature shows the thick GaN layer has a near-band emission peak with a full width at half maximum of 42 meV which confirms its high crystal quality, further supported by the x-ray (002) diffraction measurement. A simplified model is demonstrated to interpret this strain effect on the growth process. (C) 2003 American Institute of Physics.

Correlation between Er3+ emission and the microstructure of a-SiOx : H < Er > films

Photoluminescence (PL) from Er-implanted hydrogenated amorphous silicon suboxide (a-SiOX:H(x<2.0)) films was measured. Two luminescence bands with maxima at lambda congruent to 750 nm and lambda congruent to 1.54mum, ascribed to the a-SiOX:H intrinsic emission and Er3+ emission, were observed. Peak intensities of the two bands follow the same trend as a function of annealing temperature from 300 to 1000degreesC. Micro-Raman results indicate that the a-SiOX:H films are a mixture of two phases, an amorphous SiOX matrix and amorphous silicon (a-Si) domains embedded there in. FTIR spectra confirm that hydrogen effusion from a-SiOX:H films occurs during annealing. Hydrogen effusion leads to a reconstruction of the microstructure of a-Si domains, thus having a strong influence on Er3+ emission. Our study emphasizes the role of a-Si domains on Er3+ emission in a-SiOX:H films.