Er Films Research Articles

Electroluminescence from silicon-based light-emitting devices with erbium-doped TiO2 films annealed at different temperatures

We have previously developed silicon-based light-emitting devices (LEDs) with luminescent erbium (Er)-doped TiO2 (TiO2:Er) films [Yang et al., Appl. Phys. Lett. 100, 031103 (2012)]. In an LED therein, the TiO2:Er film is sandwiched between the ITO film and heavily boron-doped p-type silicon (p+-Si). In this work, we have investigated the electroluminescence (EL) from two LEDs with the TiO2:Er films annealed at 650 and 850 °C, respectively. It is revealed that between the TiO2:Er film and p+-Si, there is an intermediate silicon oxide (SiOx, x ≤ 2) layer and its thickness increases from ∼4 to 8 nm with the increase of annealing temperature from 650 to 850 °C. Interestingly, the thickness of the intermediate SiOx layer is found to exhibit a profound impact on the EL from the LED with the TiO2:Er film on p+-Si. The EL from the LED with the 650 °C-annealed TiO2:Er film is activated only under the forward bias with the positive voltage connecting to the p+-Si substrate. Such EL consists of the oxygen-vacancy-related emissions from TiO2 host and the characteristic visible and ∼1540 nm emissions from the Er3+ ions, while the EL from the LED with the 850 °C-annealed TiO2:Er film can only be enabled by the reverse bias with the negative voltage applied on the p+-Si substrate. Such EL features only the visible and ∼1540 nm emissions from the Er3+ ions. The difference in the EL behaviors of the two LEDs as mentioned above is found to be ascribed to the different electrical conduction mechanisms.

On the potential of Er-doped AlN film as luminescence sensing layer for multilayer Al/AlN coating health monitoring

Luminescence sensing is an attractive approach for in-situ monitoring the health and integrity of multilayered surface protective coatings on highly active metals. In this work, we demonstrate the potential of erbium (Er) doped aluminum nitride (AlN) films to be applied as luminescence sensing layer in the Al/AlN multilayered coating system. The AlN:Er films were prepared by radio-frequency magnetron sputtering from Al targets doped with varied concentrations (from 0.5 at.% to 2.5 at.%) of Er. The chemical composition, surface morphology, crystal structure, chemical state and optical properties of the deposited AlN:Er films were investigated. We found that the crystal structure, surface roughness and optical properties of the AlN:Er films have strong correlations with the Er doping level. The as-deposited AlN:Er films showed the characteristic photoluminescence emission lines of the trivalent Er ions in the visible frequency range and quenching was observed when the Er doping level increased to 2.5 at.%. This work signifies the viability of AlN:Er film as luminescence sensing layer and the optimal Er doping concentration of the Al sputtering target is 2.0 at.% for practical applications.

Preparation and performance study of Er2O3 film selective thermal emitter

Solar thermophotovoltaic (STPV) generator is a popular energy converter due to providing low noise, low thermal mechanical stress and portability. It has the ability to exceed the efficiency of pure solar photovoltaic system. An idealized STPV generator is a reversible heat-engine, offering a theoretical efficiency of over 80%, but the actual conversion efficiency of STPV generator is still low due to the mistuned spectral property between the thermal selective emitter and the TPV cell. One key issue in developing the STPV generator with high performance is the spectral matching between the thermal radiation spectrum of radiator and the spectral response of photovoltaic cell in visible and near-infrared region, which usually lies between the visible and the near-infrared region. High-temperature spectral emissivity of rare earth oxide is of special interest, because the radiation has a narrow band of wavelengths in the near infrared and infrared region from 900 to 3000 nm. In this work, the thermal-selective film Er2O3 emitter is fabricated by post-oxidation of Er film deposited on Si substrate through using electron-beam gun evaporation. Based on the X-ray diffraction results, the Er2O3 film is of cubic phase structure and well-crystallized when the oxidation temperature is 700℃, and the Si substrate has no obvious influence on the crystal structure of Er2O3 film. According to the X-ray photoelectron spectroscopy results of the Er2O3 film after thermal oxidation at 700℃, the atomic ratio of Er/O is stoichiometric. In order to obtain the selective emission characteristic of the Er2O3 film, a measurement system is designed. The system consists of two major portions, i.e., one is a near infrared spectrometer purchased from Ocean Optics, the other is a high-temperature emission characteristic tester which can provide oxyhydrogen flame to heat the sample by using an electronic impulse ignition to torch the hydrogen-oxygen mixture. The oxyhydrogen flame passes through the nozzle and sprays vertically on the surface of the thermal-selective emitter sample. The facula of the oxyhydrogen flame convergence is very small (facula diameter:~0.8 cm), and the highest temperature achieved is about 2500℃. The measurement condition of selective emission performance of the Er2O3 film emitter coincides with the application characteristic of STPV generator. The emission performance result of the film emitter at 700℃ shows a typical gray-body emission characteristic. The measurements carried out at 900 and 1100℃ show that the Er2O3 film has a distinct emittance spectrum at 1550 nm corresponding to Er3+, and the intensity of the selective emission peak strengthens with the measuring temperature or film thickness increasing. The thermal-selective film Er2O3 emitter is found to have emission spectrum suitable for efficient matching with the infrared response of GaSb photovoltaic cell.

Crystalline phase, profile characteristics and spectroscopic properties of Er3+/Tm3+-diffusion-codoped LiNbO3 crystal

Er3+/Tm3+-codoped LiNbO3 crystal was prepared by co-diffusion of stacked Er and Tm metal films coated onto surface of off-congruent, Li-deficient LiNbO3 substrate produced by Li-poor vapor transport equilibration technique. The crystalline phase on the diffused surface was analyzed by X-ray single-crystal diffraction. The Er3+ and Tm3+ profile characteristics were studied by secondary ion mass spectrometry. The emission spectra were measured under the 980 or 795nm wavelength excitation, and the emission and absorption cross section spectra were calculated based upon McCumber theory. The lifetimes of some emissions were measured. The results show that the Er3+ and Tm3+ ions presence is in the form of LiNbO3 phase. Both ions obey to Gaussian profile with a diffusion depth 21.5μm. In the codoping case, both ions keep their respective spectroscopic features of only doping case and do not affect each other. The codoping enables to combine the wavelength emissions of both ions and the resultant emission band in the telecommunication window around 1.5 μm is as wide as 150nm, providing the possibility of S+C+L broadband amplification by employing commercial 980 and 795nm laser diodes as the pump sources. The Er3+/Tm3+-codoped LN is a promising host material for integrated optics.

Evidence of Silicon Band-Edge Emission Enhancement When Interfaced with SiO2:Er Films

Nearly two-orders of magnitude increase in room-temperature band-to-band (1.067 eV) infrared emission from crystalline silicon, coated with erbium-doped sol–gel films, have been achieved. Phonon-assisted band-to-band emission from coated and annealed p-Si is strongest for the sample annealed at 700°C. In this paper, evidence of the origin of the emission band from the band edge recombination activities is established. Enhancement of radiative recombination of free carriers is reasoned by stresses at the interface due to the annealed sol–gel-deposited silica. Comparative studies with other strained silicon samples are presented.

Electroluminescence from light-emitting devices with erbium-doped TiO2 films: Enhancement effect of yttrium codoping

We have recently reported erbium (Er)-related visible and near-infrared (∼1540 nm) electroluminescence (EL) from the light-emitting device (LED) with a structure of ITO/TiO2:Er/SiO2/Si in which TiO2:Er refers to the Er-doped TiO2 film [Zhu et al., Appl. Phys. Lett. 107, 131103 (2015)]. In this work, we codope yttrium (Y) into the TiO2:Er film in the aforementioned LED to achieve the significantly enhanced Er-related visible and ∼1540 nm EL. It is suggested that the Y-codoping leads to a less symmetric and distorted crystal field around the Er3+ ions incorporated into the TiO2 host, thus increasing the probabilities of intra-4f transitions of Er3+ ions. Moreover, the Y-codoping facilitates the dispersion of Er3+ ions into the TiO2 host, which is favorable for reducing the concentration quenching effect on the Er-related EL. For the aforementioned two reasons, the EL from the LED based on the TiO2:Er film can be enhanced by means of codoping Y into the TiO2 host.

Silicon shallow doping by erbium and oxygen recoils implantation

Abstract In order to get shallow high doping of Si with optically active complexes ErOn, Er followed by O recoils implantation was realized by means of subsequent Ar+ 250–290 keV implantation with doses 2×1015–1×1016 cm–2 through 50-nm deposited films of Er and then SiO2, accordingly. High Er concentration up to 5×1020 cm−3 to the depth of 10 nm was obtained after implantation. However, about a half of the Er implanted atoms become part of surface SiO2 during post-implantation annealing at 950 °С for 1 h in the N2 ambient under a SiO2 cap. The mechanism of Er segregation into the cap oxide following the moving amorphous–crystalline interface during recrystallization was rejected by the transmission electron microscopy (TEM) analysis. Instead, the other mechanism of immobile Er atoms and redistribution of recoil-implanted O atoms toward cap oxide was proposed. It explains the observed formation of two Er containing phases: Er–Si–O phase with a high O content adjacent to the cap oxide and deeper O depleted Er–Si phase. The correction of heat treatments is proposed in order to avoid the above-mentioned problems.

Use of aluminum oxide as a permeation barrier for producing thin films on aluminum substrates

Aluminum has desirable characteristics of good thermal properties, good electrical characteristics, good optical properties, and the characteristic of being nonmagnetic and having a low atomic weight (26.98 g atoms), but because of its low melting point (660 °C) and ability as a reactive metal to alloy with most common metals in use, it has been ignored as a substrate material for use in processing thin films. The author developed a simple solution to this problem, by putting a permeation barrier of alumina (Al2O3) onto the surface of pure Al substrates by using a standard chemical oxidation process of the surface (i.e., anodization), before additional film deposition of reactive metals at temperatures up to 500 °C for 1-h, without the formation of alloys or intermetallic compounds to affect the good properties of Al substrates. The chromic acid anodization process used (MIL-A-8625) produced a film barrier of ∼(500–1000) nm of alumina. The fact that refractory Al2O3 can inhibit the reaction of metals with Al at temperatures below 500 °C suggests that Al is a satisfactory substrate if properly oxidized prior to film deposition. To prove this concept, thin film samples of Cr, Mo, Er, Sc, Ti, and Zr were prepared on anodized Al substrates and studied by x-ray diffraction, Rutherford ion back scattering, and Auger/argon sputter surface profile analysis to determine any film substrate interactions. In addition, a major purpose of our study was to determine if ErD2 thin films could be produced on Al substrates with fully hydrided Er films. Thus, a thin film of ErD2 on an anodized Al substrate was prepared and studied, with and without the alumina permeation barrier. Films for study were prepared on 1.27 cm diameter Al substrates with ∼500 nm of the metals studied after anodization. Substrates were weighed, cleaned, and vacuum fired at 500 °C prior to use. The Al substrates were deposited using standard electron beam cold crucible evaporation techniques, and after deposition the Er film was hydrided with D2 gas using a standard nonair exposure hydriding technique. All processing was conducted in an all metal ion pumped ultrahigh vacuum system. Results showed that e-beam deposition of films studied onto Al substrates could be successfully performed, if a permeation barrier of Al2O3 from 500 to 1000 nm was made prior to thin film deposition up to temperatures of 500 °C for 1-h. Hydrides also, could be produced with full gas/metal atomic ratios of ∼2.0 as evidenced by the ErD2 films produced. Thus, the use of a simple permeation barrier of Al2O3 on Al substrates prior to additional metal film deposition was proven to be a successful method of producing both thin metal films and hydride films of various types for many applications.

Analytical interactomic potential for a molybdenum–erbium system

Analytical interatomic potentials of a molybdenum–erbium (Mo–Er) system are developed based on a Tersoff–Brenner-type form. The potentials well describes the bulk and defect properties of bcc Mo, including lattice parameter, cohesive energy, elastic constants, formation energies of point defects, surface energies and melting point. The adsorption behavior of Er on a Mo (1 1 0) surface is studied using ab initio calculations based on the density functional theory, which is used to fit the interatomic potential of a Mo–Er interaction. The growth mechanism of the Er film on a Mo substrate is investigated using the present potentials. The simulation results show that the microstructures and morphologies of Er films are sensitive to substrate temperatures. Columnar grains of hexagonal close-packed Er parallel to a Mo (1 1 0) surface are observed and the grain sizes increase with increasing substrate temperature.

Upconversion and tribological properties of β-NaYF4:Yb,Er film synthesized on silicon substrate

In this work, β-NaYF4:Yb,Er upconversion (UC) film was successfully prepared on silicon (Si) substrate via self-assemble method for the first time. The chemical composition and surface morphology of the UC film were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA), X-ray power diffraction (XRD), and scanning electron microscopy (SEM) measurements. To investigate the effects of KH-560 primer film and chemical reactions on the UC luminescence properties of β-NaYF4:Yb,Er UC film, decay profiles of the 540nm and 655nm radiations were measured. Furthermore, tribological test was applied to qualitatively evaluate the adhesion of the UC film. The results indicate that the UC film has been successfully prepared on Si substrate by covalent chemical bonds. This work provides a facile way to synthesize β-NaYF4:Yb,Er UC film with robust adhesion to the substrate, which can be applicable for other UC films.

Effects of site substitutions and concentration on the structural, optical and visible photoluminescence properties of Er doped BaTiO3 thin films prepared by RF magnetron sputtering

The structural, optical and visible photoluminescence of the Erbium (Er) doped BaTiO3 (BT:Er) thin films were studied in terms of Er3+ substitutions for Ba and Ti sites with different Er3+ doping concentrations (0, 1, 3 and 5wt%). X-ray diffraction pattern of BT:Er films with different Er3+ concentration showed tetragonal phase with preferred orientation along (101) plane. The lattice constant of BT:Er film of 1wt% Er3+ shrank and then expanded for higher concentration. This indicates that Er3+ ions are completely incorporated into the host lattice by substituting for Ba2+ sites for 1wt% Er3+ and then Ti4+ sites for higher Er3+ concentration in the BaTiO3 host. The crystallite size decreased for 1wt% and then increased for higher Er (3 and 5wt%) concentrations. The Scanning electron microscopy images revealed well patterned arrangement of larger spherical grains with neck formation. X-ray photoelectron spectroscopy analysis confirmed the presence of barium, titanium, erbium and oxygen in BT:Er films. An average transmittance >80% in visible region were observed for all the films. Optical band gap energy of BT:Er films were found to vary with increase in Er3+ concentration. The high refractive index >2 of these films can be used in optical application and anti-reflection coatings. Photoluminescence spectra of the films exhibited an increase in the emission intensity up to 3wt% of Er3+ and then a decrease, due to self quenching. The improved optical properties of BT:Er films makes suitable for optical applications.

Effect of trivalent rare-element doping on structural and optical properties of SnO2 thin films deposited by dip coating deposition technique

Erbium doped tin oxide thin films (SnO2:Er) were prepared by the sol–gel method using dip coating technique. X-ray diffraction patterns showed a decrease of crystallinity in the films with increase in erbium doping concentration (0–5 mol%). Scanning electron microscopy analysis revealed an inhibition of grain growth with increase in erbium doping concentration. The film surfaces were uniform with crack free appearance. X-ray photoelectron spectroscopy revealed the presence of erbium, oxygen, tin oxide in the SnO2:Er films. The resistivity of the SnO2:Er films decreased and then increased with the increase in erbium doping concentration. The optical properties of the films have been studied from transmission spectra. An average transmittance of 80 % in ultraviolet–visible region was observed for all the films. Optical band gap energy (Egap) of SnO2:Er films were observed to increase with the increase in doping concentration. Photoluminescence spectra of the films exhibited an increase in the emission intensity for (0–3 mol%) and decreased for 5 mol% erbium doping film. Such SnO2:Er films with wide band gap and luminescence efficiency are applicable in blue and ultraviolet optical devices, such as light-emitting diodes and laser diodes.

Energy dissipation channels affecting photoluminescence from resonantly excited Er3+ ions doped in epitaxial ZnO host films

We identified prerequisite conditions to obtain intense photoluminescence at 1.54 μm from Er3+ ions doped in ZnO host crystals. The epitaxial ZnO:Er films were grown on sapphire C-plane substrates by sputtering, and Er3+ ions were resonantly excited at a wavelength of 532 nm between energy levels of 4I15/2 and 2H11/2. There is a threshold deposition temperature between 500 and 550 °C, above which epitaxial ZnO films become free of miss-oriented domains. In this case, Er3+ ions are outside ZnO crystallites, having the same c-axis lattice parameters as those of undoped ZnO crystals. The improved crystallinity was correlated with enhanced emissions peaking at 1538 nm. Further elevating the deposition temperature up to 650 °C generated cracks in ZnO crystals to relax the lattice mismatch strains, and the emission intensities from cracked regions were three times as large as those from smooth regions. These results can be consistently explained if we assume that emission-active Er3+ ions are those existing at grain boundaries and bonded to single-crystalline ZnO crystallites. In contrast, ZnO:Er films deposited on a ZnO buffer layer exhibited very weak emissions because of their degraded crystallinity when most Er3+ ions were accommodated into ZnO crystals. Optimizing the degree of oxidization of ZnO crystals is another important factor because reduced films suffer from non-radiative decay of excited states. The optimum Er content to obtain intense emissions was between 2 and 4 at. %. When 4 at. % was exceeded, the emission intensity was severely attenuated because of concentration quenching as well as the degradation in crystallinity. Precipitation of Er2O3 crystals was clearly observed at 22 at. % for films deposited above 650 °C. Minimizing the number of defects and impurities in ZnO crystals prevents energy dissipation, thus exclusively utilizing the excitation energy to emissions from Er3+ ions.

Electroluminescence from metal-oxide-semiconductor devices with erbium-doped CeO2 films on silicon

We report on erbium (Er)-related electroluminescence (EL) in the visible and near-infrared (NIR) from metal-oxide-semiconductor (MOS) devices with Er-doped CeO2 (CeO2:Er) films on silicon. The onset voltage of such EL under either forward or reverse bias is smaller than 10 V. Moreover, the EL quenching can be avoidable for the CeO2:Er-based MOS devices. Analysis on the current-voltage characteristic of the device indicates that the electron transportation at the EL-enabling voltages under either forward or reverse bias is dominated by trap-assisted tunneling mechanism. Namely, electrons in n+-Si/ITO can tunnel into the conduction band of CeO2 host via defect states at sufficiently high forward/reverse bias voltages. Then, a fraction of such electrons are accelerated by electric field to become hot electrons, which impact-excite the Er3+ ions, thus leading to characteristic emissions. It is believed that this work has laid the foundation for developing viable silicon-based emitters using CeO2:Er films.

Properties of Sputtered-n-nc-Si:Er/p-Si Heterojunction Solar Cells

Nanocrystalline Si:Er (nc-Si:Er) films were sputtered on p-Si (100) substrates and diffused with phosphorus to form PN heterojunction diodes. The I-V properties of these diodes were characterized. And the properties of diodes without Er were compared with n-nc-Si:Er/p-Si. It was found that n-nc-Si:Er/p-Si diodes had better characteristics. Solar cells based on n-nc-Si:Er/i-nc-Si/p-Si were fabricated and characterized. The photoelectrical conversion efficiency of 18.13% for n-nc-Si:Er/i-nc-Si/p-Si solar cell was achieved.

Formation of Er‐germanosilicide films on strained Si1−xGex with different Ge contents

Er‐germanosilicide [Er(Si1−zGez)2−y] films were formed on strained Si1−xGex layers with different Ge contents (x = 0.14 and 0.28), and their dependency of formation kinetics on the Ge concentrations was investigated while minimizing the oxygen‐incorporation effect using a TaN capping layer. When a ~30 nm‐thick Er film was used, uniform Er(Si1−zGez)2−y films were obtained at an annealing temperature of around 600 °C without their agglomeration and also the strain relaxation of the remaining Si1−xGex layer. The increase in the Ge concentration of the reacting Si1−xGex layer enhanced the formation of the crystalline Er(Si1−zGez)2−y film. Furthermore, some enrichment of the Ge content within the Er(Si1−zGez)2−y film occurred in comparison with that in the initial and remaining Si1−xGex layers.

Effect of Annealing on the Photoluminescence of Er Doped AlN Thin Films Grown by PVD Magnetron Sputtering (RF)

We report on Er3+luminescence at room temperature in the near infrared regions in amorphous and columnar AlN:Er films prepared by RF magnetron sputtering. The effect of annealing on the room temperature 1.54μm infra-red photoluminescence intensity of erbium doped AlN films grown by r. f. magnetron sputtering, has been studied. The AlN:Er thin films were deposited on (001) Silicon substrates. The study presents relative photoluminescence intensities of nanocrystallized and columnar samples prepared with identical sputtering parameters for optimum erbium doping levels (1 atomic %). The luminescence due to rare earth ions in Al nitride thin layers can be increased by proper structural tailoring. In this contribution, we report on the photoluminescence of the rare earth ion Er3+ that is contained in films prepared by RF magnetron sputtering of Al targets with additional Er constant sector in a nitrogen atmosphere. These results are typical also for other rare earth ions, such as Eu3+, Sm3+, Tm3+ and Ce3+. Thermal annealing of the samples results in significant improvement of the photoluminescence by factors up to several tens in intensity. The intensity of the Er3+ luminescence at 1.54μm corresponding to the 4I13/2→ 4I15/2 transition increased after annealing at 1000°C.

Visible PL Emission from Erbium Doped BaTiO3 thin Films Deposited by RF Magnetron Sputtering

The present study reports the deposition and characterization of Er3+ (Er) doped BaTiO3 (BT: Er) thin films obtained onto quartz substrates by RF magnetron sputtering method. BT films with different Er3+ concentrations (1, 3 and 5wt %) were annealed at 1073K in air. X-ray diffraction pattern (XRD) of BT: Er thin films with different Er3+ concentration showed tetragonal phase with preferred orientation along (110) plane and the crystallinity increased with concentration. The average crystallite size increased from 12.52-15.04nm. An average transmittance of >80% in visible region were observed for all the films. Optical band gap energy of BT: Er films varied from 3.76-3.59eV. Tuning of refractive index can be done using BT: Er thin films. Photoluminescence spectra of the films exhibited an increase in the emission intensity upto 3 wt% of Er3+ and then a decrease, due to concentration quenching.

Time-resolved Spectroscopy of Er Doped AlN Thin Films with Columnar and Nanogranular Morphologies Grown by PVD Magnetron Sputtering (RF)

Er-doped III-nitride semiconductors have emerged as very attractive materials to achieve photonic devices with multiple functionalities for photonic integrated circuits (PICs). We report on Er3+ luminescence at room temperature in the near infrared regions at 1.54μm and Time-resolved spectroscopy in nanogranular and columnar AlN:Er films prepared by RF magnetron sputtering. The AlN:Er thin films were deposited on (001) Silicon substrates. The study presents relative photoluminescence intensities of nanocrystallized and columnar samples prepared with identical sputtering parameters for optimum erbium doping levels (1 atomic %). The luminescence due to rare earth ions in Al nitride thin layers can be in-creased by proper structural tailoring. In this contribution, we report on the photo-luminescence of the rare earth ion Er3+ that is contained in films prepared by RF magnetron sputtering of Al targets with additional Er constant sector in a nitrogen atmosphere.

Electronic state of Er in sputtered AlN:Er films determined by magnetic measurements

The optoelectronic and piezoelectric properties of AlN:Er thin films have been of great recent interest for potential device applications. In this work, the focus is on the electronic state of Er in AlN:Er thin films prepared by reactive magnetron sputtering on (001) p-type Si substrate. X-ray diffraction shows that Er doping expands the lattice and the AlN:Er film has preferential c-plane orientation. To determine whether Er in AlN:Er is present as Er metal, Er2O3, or Er3+ substituting for Al3+, detailed measurements and analysis of the temperature dependence (2 K–300 K) of the magnetization M at a fixed magnetic field H along with the M vs. H data at 2 K up to H = 90 kOe are presented. The presence of Er2O3 and Er metal is ruled out since their characteristic magnetic transitions are not observed in the AlN:Er sample. Instead, the observed M vs. T and M vs. H variations are consistent with Er present as Er3+ substituting for Al3+ in AlN:Er at a concentration x = 1.08% in agreement with x = 0.94% ± 0.20% determined using x-ray photoelectron spectroscopy (XPS). The larger size of Er3+ vs. Al3+explains the observed lattice expansion of AlN:Er.