Er-related Luminescence Research Articles

Enhancement of Er luminescence in microdisk resonators made of Er,O-codoped GaAs

We report on the fabrication and optical characteristics of microdisk (MD) resonators with Er,O-codoped GaAs (GaAs:Er,O) as an active component. MD resonators based on GaAs:Er,O with different sidewall angles are fabricated by electron beam lithography followed by two different processes: dry and wet etching. Numerical simulations using a finite-difference time-domain method demonstrate an increase in the cavity quality (Q) factor of the MDs when sharpening the taper angle of the MDs. Micro-photoluminescence characterization of the MD resonators with excitation by a He–Ne laser reveals an 11.4-fold enhancement of Er-related luminescence and a cavity Q factor of 4.2 × 103. For the MD resonators with tapered sidewalls, further enhancement of Er luminescence and increased Q factor (>9.0 × 103) are observed.

The influence of cation additives on the NIR luminescence intensity of Er3+-doped borate glasses

Er3+-doped 25BaO-(25-x)SiO2-xAl2O3-25B2O3 transparent glasses are prepared with x = 0, 12.5 and 25 by a solid-state reaction. The Er-related NIR luminescence intensity, which corresponds to the transition of 4I15/2-4I13/2, is obviously altered with different silicon/aluminum ratios. The Judd-Ofelt parameters of the Er3+ ions are adopted to explain the intensity change in the NIR fluorescence, and the Raman scattering intensity versus the amount of Al and/or Si components are discussed. The spectra of the three samples are quite similar in the peak positions, but different in intensity. The maximal phonon density of state for the samples is calculated from the Raman spectra and is correlated to the NIR luminescence efficiency.

Suppression of concentration quenching of Er-related luminescence in Er-doped GaN

Erbium-doped GaN with different doping concentrations were grown by ammonia-source molecular beam epitaxy. The intra-4f-shell transitions related green luminescence were observed by both photoluminescence (PL) and cathodoluminescence (CL) measurements. It was found that concentration quenching of Er-related luminescence was observed in PL measurements while not in CL measurements. The different excitation and relaxation processes are suggested as the cause of the concentration quenching characteristics between PL and CL. The strong Er-related CL intensity in highly doped GaN demonstrates that high energy excitation is a promising approach to suppress the concentration quenching in Er-doped GaN.

Effect of V/III flux ratio on luminescence properties and defect formation of Er-doped GaN

Erbium-doped GaN samples grown with different V/III ratios through gas source molecular beam epitaxy were prepared to investigate the influence of the V/III ratio on the defect formation and the optical activity of the Er-related luminescence center. Obvious V/III ratio dependence was observed in photoluminescence measurement. Positron annihilation spectroscopy measurements suggested that VGa-VN vacancy-complexes formed in these samples and that the VN/VGa ratio depended on the V/III ratio. The generation of Er-VN defect complexes, which act as high optical active luminescence centers, is suggested as the cause of improved optical properties of Er-doped GaN grown with a lower V/III ratio.

Relationship between defects and optical properties in Er-doped GaN

The density of the vacancy-type defect in Er doped GaN was measured by positron annihilation spectrometry (PAS) and the correlation between the intensity of the Er-related luminescence was studied. A luminescence peak at 558 nm originating from 4 S 3/2 to 4 I 15/2 transition of Er 3+ was observed in Er-doped GaN. The intensity of the luminescence increased with increasing Er concentration and showed the maximum with the Er concentration of around 4.0 at%. The PAS measurements showed that the vacancy-type defect density increased with increasing Er concentration up to 4 at%, and around 4 at% of Er, the formation of defect complex such as V Ga– V N was suggested. The contribution of the defect to the radiative recombination of intra-4 f transition of Er is discussed.

Incorporation sites and luminescence characterizations of Er-doped GaN grown by molecular beam epitaxy

The relationship between optical and structural properties of Er-doped GaN grown by molecular beam epitaxy on sapphire (0 0 0 1) substrates was studied. The Er-related luminescence with wavelength at around 558 nm originated from 4S 3/2 to 4I 15/2 transition was observed. The intensity of the Er-related luminescence increased abruptly with the Er concentration of about 2 at% and showed a maximum at about 4 at%. X-ray diffraction analyses and Rutherford backscattering measurements suggested that most of the Er ions are incorporated into substitutional lattice site with the Er concentration of up to 2 at%, and then begin to occupy interstitial sites. The incorporation site of Er was found to be dependent on the Er concentration. Based on these results, the optically active center of Er in GaN is discussed.

1.54 μ m photoluminescence of Er-doped GeOx thin films

Amorphous Er-doped GeOx alloys were prepared by evaporation on substrates maintained at 100°C. Photoluminescence experiments were carried out in the visible and near-infrared ranges. The Er-related peak was observed at 1.54μm at room temperature in the as deposited samples. The PL of erbium is characterized by a weak temperature quenching and by a decay time in the millisecond range. The luminescence of Er is a decreasing function of the annealing temperature. Undoped GeOx layers showed a PL band at 800nm, attributed to defects states, which disappeared when Er is introduced. The intense Er-related luminescence was assigned to an indirect excitation process from defects states to Er ions.

Population Dynamics of Excitons in Silicon Nanocrystals Structures under Strong Optical Excitation

We report on the experimental and theoretical studies of population/depopulation dynamics of excitons in the structures with Si nanocrystals in SiO2 matrix (nc-Si/SiO2) under strong optical excitation. The experimental results are explained using a phenomenological model based on rate equations for coupled system of energy donors (excitons) and energy acceptors (erbium ions). Exciton luminescence is found to exhibit superlinear dependence for Er-doped samples. At the same time the Er-related luminescence at 1.5 μm shows a saturation of the intensity and shortening of the lifetime, which are attributed to the population inversion of the Er ions states. The obtained results demonstrate that nc-Si/SiO2:Er systems can be used for applications in Si-based optical amplifiers and lasers, compatible with planar Si-technology.

Influence of the annealing temperature on the photoluminescence of Er-doped SiO thin films

Er-doped amorphous silicon suboxide thin films were prepared by the coevaporation method. The Er concentration was varied from 0.4to6at.% and the samples were annealed at different temperatures up to 900°C. The samples exhibit a broad photoluminescence band in the visible range. Both energy and intensity of this band were dependent on the annealing temperature. For as-deposited films and samples annealed below 500°C, this band was assigned to defects in the oxide films. For higher annealing temperatures, this photoluminescence band shifted to higher wavelengths and was correlated to the appearance of amorphous silicon clusters. Two narrow bands in the near-infrared range at 0.98 and 1.54μm were also observed for the annealed samples. The intensity of these Er-related luminescence was maximal for an annealing temperature equal to around 700°C. The effective absorption cross section of Er was dependent on the annealing temperature and was equal to 6.6×10−16cm2 for the sample annealed at 700°C. The strong Er-related photoluminescence is discussed in terms of a coupling phenomenon between Er3+ ions and spatially confined amorphous silicon clusters which act as sensitizers. The existence of a low annealing temperature to obtain the best Er-related photoluminescence is also discussed.

Donor-State-Enabling Er-Related Luminescence in Silicon: Direct Identification and Resonant Excitation

We conclusively establish a direct link between formation of an Er-related donor gap state and the 1.5 microm emission of Er in Si. The experiment is performed on Si/Si:Er nanolayers where a single type of Er optical center dominates. We show that the Er emission can be resonantly induced by direct pumping into the bound exciton state of the identified donor. Using two-color spectroscopy with a free-electron laser we determine the ionization energy of the donor-state-enabling Er excitation as E(D) approximately 218 meV. We demonstrate quenching of the Er-related emission upon ionization of the donor.

Effect of Space Charge Region Width on Er-Related Luminescence in Reverse Biased Si:Er-Based Light Emitting Diodes

In this paper, an effect of space charge region (SCR) width on Er-related electroluminescence (EL) in reverse biased Si:Er-based light-emitting diodes (LEDs) is under investigation. It is concluded that a trivial widening of the SCR in the examined LEDs with triangular and trapezoidal electric field profiles through SCR does not result in a desirable increase in the Er-related EL intensity. The tunnel transit-time diode structure with a complicated electric field profile through SCR is offered to increase the Er-related EL intensity. The difficulties hampering this process in erbium EL from reverse biased LEDs are under discussion

Enhancement of photoluminescence at 1.54 μm from Er in strained Si and SiGe

We studied on the photoluminescence (PL) properties of Er in tensile-strained Si on a SiGe layer (Si:Er:O/SiGe) and compressively strained SiGe on a Si layer (SiGe:Er:O/Si) grown by molecular beam epitaxy (MBE). Er-related luminescence was observed around 1.54 μm in both tensile- and compressively strained samples. The PL intensities of strained Si:Er:O/SiGe and SiGe:Er:O/Si samples were much stronger than those of unstrained Si:Er:O/Si samples. Moreover, intensive luminescence was observed in strained samples with low Er concentrations far below 10 18 cm −3. The PL spectra of Si:Er:O/SiGe samples were broader than those of unstrained Si:Er:O/Si samples. On the other hand, no significant differences in the width between SiGe:Er:O/Si and unstrained samples were observed. These differences in the PL intensity between strained and unstrained samples strongly suggest that the optical activation of Er in Si and SiGe can be enhanced by the presence of strain.

Comparative study of photoluminescence of undoped and erbium-doped size-controlled nanocrystalline Si∕SiO2 multilayered structures

Spectra and transients of the photoluminescence (PL) of undoped and Er-doped size-controlled nanocrystalline Si∕SiO2 multilayered structures with mean nanocrystal size of 1.5–4.5nm have been comparatively investigated. The Er-doped structures exhibit a strong Er-related PL band at 0.81eV, while the efficiency of the intrinsic PL band of Si nanocrystals at 1.2–1.7eV decreases by several orders of magnitude in comparison with the undoped structures. At low temperature the PL spectra of the Er-doped structures show several dips separated by the energy of Si TO-phonon and bound to the transition energies between the second and third excited states to the ground state of Er3+. The Er-related PL is characterized by lifetimes of around 3–5ms, a weak temperature quenching, and a high efficiency, which is comparable or even stronger than that of the intrinsic PL in the corresponding undoped samples. This efficient sensitizing of the Er-related luminescence is explained by the structural properties of the samples, which favor a strong coupling between the excitons confined in Si nanocrystals and upper excited states of the Er3+ ions in the SiO2 matrix.

Electrical properties of GaSe doped with Er

Measurements of the Hall effect and Er-related luminescence were made on Er-doped GaSe. Deep-level transient spectroscopy (DLTS) was also performed. Hall measurements show that hole concentrations of 0.2%, 0.5%, and 1% Er-doped GaSe samples are 1.5×1017–6×1017 cm−3 at room temperature, and that the mobility of these holes is in the range 22–34 cm2/V s. The temperature dependence of the hole concentration is explained using the two-acceptor model, in which one acceptor level is at around 65 meV above the valence band and the other one is at ∼158 meV. The DLTS measurements yield similar results. Furthermore, the shallow acceptor impurities contribute free hole carriers and act as radiative centers; the deep acceptor impurities are nonradiative centers, which are responsible for the quenching behavior of Er-related luminescence. The temperature dependence of the hole mobility can be understood as the combined scatterings of homopolar optical phonons and ionized impurities.

Rare-earth doped Si nanostructures for Microphotonics

AbstractIn the present paper, we will review our work on rare-earth doped Si nanoclusters. The samples have been obtained by implanting the rare-earth (e.g. Er) in a film containing preformed Si nanocrystals. After the implant, samples have been treated at 900°C for 1h. This annealing temperature is not enough to re-crystallize all of the amorphized Si clusters. However, even if the Si nanoclusters are in the amorphous phase, they can still efficiently transfer the energy to nearby rare-earth ions. We developed a model for the Si nanoclusters-Er system, based on an energy level scheme taking into account the coupling between each Si nanocluster and the neighboring Er ions. By fitting the data, we were able to determine a value of 3×10−15cm3s−1for the Si nanocluster-Er coupling coefficient. Moreover, a strong cooperative up-conversion mechanism between two excited Er ions and characterized by a coefficient of 7×10−17cm3s−1, is shown to be active in the system, demonstrating that more than one Er ion can be excited by the same nanocluster. We show that the overall light emission yield of the Er related luminescence can be enhanced by using higher concentrations of very small nanoaggregates. Eventually, electroluminescent devices based on rare-earth doped Si nanoclusters will be demonstrated.

Enhancing effect of tensile strain on photoluminescence of Er in Si on a SiGe layer

We studied on the effect of the strain on photoluminescence (PL) properties of Er-doped Si on a SiGe layer (Si:Er:O/SiGe) and Er-doped SiGe on a Si layer (SiGe:Er:O/Si) grown by molecular beam epitaxy. Er-related luminescence was observed around 1.54μm in all the samples. The PL spectra of the Si:Er:O/SiGe samples are much broader and stronger than those of the Si:Er:O/Si samples prepared as reference. Moreover, the intensive luminescence was observed in the Si:Er:O/SiGe sample that had much lower Er concentration of about 2.5×1016cm−3. On the other hand, the significant differences in the PL spectra between the SiGe:Er:O/Si and Si:Er:O/Si samples were not observed. These indicate that the tensile strained Si enhances the optical activation of Er.

Fabrication and photoluminescence properties of erbium doped size-controlled silicon nanocrystals

Er doping of dense arrays of nearly monodisperse Si nanocrystals produced by a new SiO/SiO 2 superlattice approach is presented. This synthesis method is fully compatible with standard Si technology. The prepared samples show a strong increase of Er-related luminescence by a factor of up to 5000 in comparison with Er-doped bulk SiO 2. Photoluminescence (PL) spectra and transients of the undoped and Er-doped size-controlled nanocrystalline Si/SiO 2 superlattices have been comparatively investigated as a function of implantation dose and Si nanocrystal size. It is shown that the energy of the optically excited Si nanocrystals can almost be completely transferred to the Er 3+ ions, resulting in a very strong emission at 1.54 μm. The efficiency of the energy transfer increases for smaller crystal sizes and an increasing overlap between the emission energy of the Si-related luminescence and the absorbing Er 3+ energy levels. For superlattices with nanocrystal sizes of 2 nm a transfer efficiency to the Er 3+ ions is found to be nearly one at room temperature under an excitation with photons of 3.7 eV. This properties of a highly efficient excitation of the Er ions via the Si nanocrystals is in agreement with the Förster mechanism.

Compositional changes in erbium-implanted GaN films due to annealing

We have conducted a study of the material and infrared-luminescence properties of Er-implanted GaN thin films as a function of annealing. The GaN films, grown by metal-organic chemical-vapor deposition, were coimplanted with Er and O ions. After implantation, the films were furnace annealed at temperatures up to 1,100°C. Following each annealing stage, the samples were examined by photoluminescence (PL) measurements and secondary ion-mass spectrometry (SIMS) analysis. In the as-implanted samples, no PL signal near 1,540 nm could be detected with either above-bandgap or below-bandgap excitation. Only after annealing at temperatures above 900°C was the 1,540-nm luminescence detectable. Annealing at higher temperatures resulted first in an increase and then a decrease in the PL-signal intensities. The SIMS data showed that large concentrations of Al, O, and C atoms entered into the GaN films with high-temperature annealing. The stoichiometric changes in the GaN appear responsible for the changes in the Er-related luminescence.

Optical characterization of Er-implanted ZnO films formed by sol–gel method

In this paper, we report on the 1.54 μm photoluminescence (PL) of Er-implanted ZnO thin films formed by a sol–gel method on Si substrates. In spite of the polycrystalline structure of the sol–gel ZnO thin films, they showed strong PL emissions due to the near band edge recombination at 375 nm as well as the Er-related luminescence at 1.54 μm. The Er-related luminescence showed no decrease (quench) in the intensity up to the Er concentration of 1.5 × 10 21 cm −3. The PL intensity of Er-implanted ZnO at 1.54 μm was found to be as strong as Er-doped PS (porous Si) at 20 K, and the intensity reduced to 1/3 at room temperature.

Er-related luminescence in Er,O-codoped InGaAs/GaAs multiple-quantum-well structures grown by organometallic vapor phase epitaxy

We have grown Er,O-codoped InGaAs/GaAs multiple-quantum-well (MQW:Er,O) structures by low-pressure organometallic vapor phase epitaxy (OMVPE), and investigated their luminescence properties. The MQW structures are designed to emit light at 0.98 μm for direct excitation of Er ions. Degradation of the structures due to introduction of Er and oxygen is not observed in x-ray diffraction patterns. Er ions doped with oxygen exhibit a sharp and well-ordered photoluminescence spectrum predominantly from one kind of Er center (Er-2O center). Photoluminescence excitation measurements on MQW:Er,O and Er,O-codoped GaAs samples reveal that under below-GaAs-band-gap excitation (830–940 nm), the Er-related luminescence is observed only in the MQW:Er,O sample. It indicates that the luminescence originates from Er ions in InGaAs QWs by means of trap-mediated excitation process.