Photoluminescence Line Intensity Research Articles

W and X Photoluminescence Centers in Crystalline Si: Chasing Candidates at Atomic Level Through Multiscale Simulations

Several atomistic techniques have been combined to identify the structure of defects responsible for X and W photoluminescence lines in crystalline Si. We used kinetic Monte Carlo simulations to reproduce irradiation and annealing conditions used in photoluminescence experiments. We found that W and X radiative centers are related to small Si self-interstitial clusters but coexist with larger Si self-interstitials clusters that can act as nonradiative centers. We used molecular dynamics simulations to explore the many different configurations of small Si self-interstitial clusters, and selected those having symmetry compatible with W and X photoluminescence centers. Using ab initio simulations, we calculated their formation energy, donor levels, and energy of local vibrational modes. On the basis of photoluminescence experiments and our multiscale theoretical calculations, we discuss the possible atomic configurations responsible for W and X photoluminescence centers in Si. Our simulations also reveal that the intensity of photoluminescence lines is the result of competition between radiative centers and nonradiative competitors, which can explain the experimental quenching of W and X lines even in the presence of the photoluminescence centers.

Optically detected cyclotron resonance in heavily boron-doped silicon nanostructures on n-Si (100)

Electron and hole cyclotron resonance at a frequency of 94 GHz is detected by a change in the intensity of photoluminescence lines whose positions are identical to those of dislocation luminescence lines D1 and D2 in single-crystal silicon and in heavily boron-doped silicon nanostructures on the Si (100) surface. The angular dependence of the spectrum of the optically detected cyclotron resonance corresponds to the tensor of the electron and hole effective mass in single-crystal silicon, and the resonance-line width indicates long carrier free-path times close to 100 ps. The results obtained are discussed within the framework of the interrelation of the electron-vibration coupling to charge and spin correlations in quasi-one-dimensional chains of dangling bonds in silicon.

Temperature and concentration dependences of the photoluminescence of MEH-PPV polymer composite films with ZnO nanoparticles

The absorption and photoluminescence (PL) spectra of MEH-PPV: ZnO composite films have been investigated at different concentrations of ZnO nanoparticles and at different temperatures (in the case of PL). It has been shown that, at 297 K, with increasing concentration of ZnO nanoparticles in the composite, the intensity of the PL lines of MEH-PPV decreases, whereas the intensity of the PL lines of ZnO increases. At a relatively low concentration of ZnO nanoparticles, a decrease in the temperature leads to an increase in the intensity of PL lines associated with MEH-PPV and ZnO, whereas at higher concentrations of ZnO nanoparticles, the intensity of these lines decreases. This is accompanied by a slight shift in the maximum of the PL toward the infrared (IR) region and a narrowing of the PL line of MEH-PPV with a decrease in the temperature and with an increase in the ZnO concentration. The mechanism of energy transfer in composite systems consisting of a polymer and inorganic nanoparticles that can be responsible for the observed effects has been discussed.

Giant fluctuations in the radiation intensity of two-dimensional electrons under quantum hall effect conditions

Giant fluctuations in the 2D-electron recombination radiation were studied in structures with a single or double GaAs quantum well under quantum Hall effect conditions. It is established that, if these conditions are exactly satisfied, the amplitude of the 2D-electron photoluminescence (PL) intensity is several orders of magnitude higher than the noise level, with the noise having a normal (Poisson) distribution. The fluctuations in the PL line intensity are accompanied by a jumpwise change in the line positions. Analogous jumps were also observed in the spectra of inelastic light scattering by 2D electrons in structures with a single GaAs quantum well. The fluctuation processes are correlated over macroscopic distances. The characteristic correlation length is 1–2 mm. The spectral density of giant fluctuations was found to exhibit narrow peaks. The ratios of the frequencies of these peaks are equal to those of Fibonacci numbers. The appearance of such frequencies in the fluctuation spectrum indicates that the fluctuations studied bear a resemblance to processes occurring in open dissipative dynamic systems. The methods developed in the theory of these systems can, in principle, be used to study giant fluctuations.

Photoluminescence characteristics of rare earth ion-implanted SiO 2/Si

The photoluminescence (PL) characteristics were studied for the ion-implanted Tb, Eu and Dy ions with the accelerated voltage 180 kV into SiO 2/Si, changing the annealing temperatures every 100 °C up to 1200 °C for an hour. Then, the thickness of thermally oxidized SiO 2 film was determined as 400 nm from TRIM simulation and SIMS atom analysis. At first from PL spectra, we found that the ion-implanted rare earth ions as mass-filtered monovalent states actually were both embedded as the trivalent states: Tb 3+ and Eu 3+, respectively. This suggested that accelerated RE ions had lost their own electrons generating lattice defects through colliding with SiO 2 atoms. With increasing annealing temperatures, the intensities of PL lines at 544 nm of Tb 3+ ion increased more, reaching the maximum at 600 °C to disappear at 1000 °C. A peak at 280 nm observed commonly through all the specimens was identified as a hole-trapped O-vacancy defect or E′ center created in SiO 2 because the PL intensity decreased in response to the intensity of electron spin resonance (ESR) spectrum measured in parallel with the increasing annealing temperatures.

Studies of physical phenomena in semiconductor nanostructures using samples with laterally nonuniform layers: Photoluminescence of tunneling-coupled quantum wells

The previously suggested spectral-correlative method for studying nanostructures is applied to an analysis of photoluminescence of tunneling-coupled and isolated quantum wells in structures with laterally nonuniform layers. This method made it possible to use a single wafer to study the dependences of intensities of photoluminescence lines and their energy positions on the tunneling-barrier width for a system of tunneling-coupled GaAs-InGaAs-GaAs wells and on the quantum-well widths in a system of isolated AlGaAs-GaAs-AlGaAs quantum wells. Good agreement between the results of calculations and experimental data can be attained if it is assumed that a constant transverse electric field affecting the processes of trapping of charge carriers by quantum wells exists in a structure with tunneling-coupled quantum wells. The dependence of photoluminescence parameters on the width of isolated quantum wells is sensitive to the profile of heterointerfaces and to the processes of trapping the charge carriers by quantum wells.

The photoluminescence investigation of Zn xMn 1− xTe films

We have measured photoluminescence spectra of Zn 1− x Mn x Te films grown on a GaAs substrate with ZnSe buffer layer at the low temperature (10 K) . These spectra were taken with the use of an Ar ion laser excitation (=488.8 nm) . The value x equals 0, 0.045, 0.117, 0.152, 0.1811 and 0.268. For the pure ZnTe, we observed the well-resolved five exciton lines that can be attributed to free and bound excitons. The integral (total) intensity of photoluminescence lines from the sample with x=0.045 is approximately in five times higher than from the sample ZnTe. The photoluminescence from the samples is associated with excitons bounded on Mn. With the increasing of the Mn, the line width of the main peak increases essentially. The FWHL for the ZnTe film is about 3 meV and for the Zn 0.74Mn 0.26Te film is 35 meV . The essential increase of the line width indicates an increase of an inhomogeneous structure.

Extremely narrow photoluminescence from the ensemble of InAsP/InP quantum dots

We report a photoluminescence (PL) study of self-assembled InAsP quantum dots (QDs) formed on InP by As/P exchange reaction in the reactor of low-pressure metalorganic chemical vapor deposition. By varying the buffer surface morphology, we succeeded to resolve earlier observed broad emission between 1.2 and 1.35 μm. As a result, a double-peak feature with extremely narrow line at about 1.2 μm was observed in the PL from QDs formed on the undoped InP buffer layer. The temperature and excitation intensity dependence has been measured. We found that the PL line intensity does not depend on the temperature, when PL spectra exhibit state filling as the excitation is increased.

Thermal stability of GaN investigated by low-temperature photoluminescence spectroscopy

We have studied the thermal behavior of 1-μm-thick GaN films grown by plasma-enhanced molecular beam epitaxy. Samples were annealed at elevated temperatures in a nitrogen environment and were characterized by low-temperature photoluminescence (PL). After GaN samples were annealed at up to 700 °C, the free-exciton transition PL line intensity improved. This PL line intensity degraded when annealing temperatures reached 900 °C. After annealing at 900 °C, GaN samples with inferior crystalline quality exhibited a line at 2.3 eV attributed to point defects and antisite defects.

Photoluminescence characterization of ultrahigh purity silicon

When photoluminescence (PL) measurements on silicon are calibrated against an established measurement technique, they become a powerful characterization tool capable of quantitatively identifying impurities. PL is particularly useful for characterizing ultrahigh purity silicon, due to its ability to determine the concentrations of the shallow impurities down to ≈5 × 1010 atoms-cm−3. We have utilized variable temperature Halleffect measurements to calibrate PL measurements made at 4.2 K on ultrahigh purity float-zone silicon, establishing calibration relationships to determine boron, phosphorus, and gallium concentrations. The concentrations range from the low −1012 atoms-cm-3 for phosphorus and boron, to 1 × 1014 atoms-cm−3 for boron and 1 × 1016 atoms-cm−3 for phosphorus. The preliminary gallium calibration concentration range is from the high-1012 to the mid-1010 atoms-cm3. Previous PL calibrations based on variable temperature Hall-effect measurements have not produced the theoretically expected proportionality between the impurity concentration and the PL line intensities of the transverse-optical phonon-assisted replicas of the impurity bound exciton normalized to the PL line intensity of the free-exciton. By performing the PL measurements at a fixed free-exciton density, we have achieved the theoretically expected proportionality. The experimental methods and an overview of the theory concerning fixed free-exciton con-ditions, the associated Hall-effect analyses, and the PL calibrations are presented.