Effect of the annealing temperature on erbium ion electroluminescence in Si:(Er,O) diodes with (111) substrate orientation

The influence of the temperature of secondary annealing, stimulating the formation of optically and electrically active centers, on the erbium ion electroluminescence (EL) at λ≈1.54 μm in (111) Si:(Er,O) diodes has been studied. The diodes were fabricated by the implantation of 2.0 and 1.6 MeV erbium ions at doses of 3×10¹⁴ cm⁻² and oxygen ions (0.28 and 0.22 MeV, 3×10¹⁵ cm⁻²). At room temperature, the EL intensity in the breakdown mode grows with the annealing temperature increasing from 700 to 950°C. At annealing temperatures of 975–1100°C, no erbium EL is observed in the breakdown mode owing to the formation of microplasmas. The intensity of the injection EL at 80 K decreases with the annealing temperature increasing from 700 to 1100°C. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 10, 2001, pp. 1224–1227. Original Russian Text Copyright ? 2001 by Sobolev, Emel’yanov, Nikolaev.     

Nature of the edge electroluminescence peak in the Si:(Er,O) diode breakdown mode

Electroluminescence (EL) of erbium-and oxygen-doped Si:(Er,O) diodes at λ=1.00–1.65 μm has been studied in the p-n junction breakdown and forward current modes. The EL was measured at room temperature from the front and back surfaces of the diodes. A peak corresponding to the absorption band edge of silicon was observed in the EL spectra of some diodes in the p-n junction breakdown mode. The peak is associated with the injection of minority carriers from the metal contact into silicon, with subsequent band-to-band radiative recombination. The band-to-band recombination intensity increases sharply on reaching a certain current density that depends on the fabrication technology. This threshold current density decreases with the temperature of post-implantation annealing of Si:(Er,O) diodes increasing in the range 900–1100°C. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 4, 2002, pp. 453–456. Original Russian Text Copyright ? 2002 by Emel’yanov, Nikolaev, Sobolev.     

Erbium ion electroluminescence in p ++/n +/n-Si:Er/n ++ silicon diode structures

Results of experimental studies of erbium ion electroluminescence in p ⁺⁺/n ⁺/n-Si:Er/n ⁺⁺ silicon diode structures grown by sublimation molecular-beam epitaxy are discussed. The distinctive feature of these structures is that the regions of electron flux formation of (n ⁺-Si) and impact excitation of erbium ions (n-Si:Er) are spaced. The influence of the n ⁺-Si layer thickness on electrical and electroluminescent properties of diodes was studied. It was shown that n ⁺-Si layer thinning causes the transformation of the structure breakdown mechanism from tunneling to avalanche. The dependence of the Er³⁺ ion electroluminescence on the thickness of the heavily doped n ⁺-Si region is bell-shaped. At the n ⁺-Si-layer doping level n ≈ 2 × 10¹⁸ cm^?3, the maximum electroluminescence intensity is attained at an n ⁺-Si layer thickness of ～23 nm.     

Unusual temperature dependence of electroluminescence intensity in blue InGaN single quantum well diodes

Temperature dependence of electroluminescence (EL) spectral intensity of the super-bright blue InGaN single quantum well (SQW) light emitting diodes (LEDs) has been carefully investigated over a wide temperature range (T=15-300 K) and as a function of injection current level (0.1-10 mA) in comparison with high quality GaAs SQW-LEDs. When T is slightly decreased to 180 K, the EL intensity efficiently increases in both cases due to the reduced non-radiative recombination processes. However, further decreasing T below 100 K, striking differences exist in EL intensity as well as injection current dependences between the two types of diodes. That is, the EL efficiency at lower T is found to be quite low for the blue diode in strong contrast to that of red GaAs SQW-LED where significant enhancement of the EL efficiency persists down to 15 K. These results indicate that the carrier capture efficiency of the blue SQW diode is unusually worse at lower T than at T=180-300 K, reflecting the unique radiative recombination processes under the presence of high-density dislocation (10¹⁰ cm⁻²).     

Structural and Luminescent Properties of SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>(Si) Nanocomposite Films

With a view to creating Si LEDs, the structural and luminescent properties of SiO _x N _y films containing Si nanocrystals in the SiO _x N _y matrix are studied experimentally. It is found that the film structure (nanocrystal size and concentration, the presence of an amorphous phase, etc.) and the spectrum and intensity of photoluminescence (PL) and electroluminescence (EL) are strongly dependent on the Si stoichiometric excess δ and annealing conditions. At δ≈ 10%, unannealed films are amorphous and contain Si clusters of size < 2 nm, as deduced from the TEM and microdiffraction data obtained. Annealing at 800–1000°C for 10–60 min produces Si crystals 3–5 nm in size with a concentration of ≈10¹⁸ cm^?3. The annealed films exhibit room-temperature PL and EL over the wavelength range 400–850 nm with intensity peaks located at 50–60 and 60–70 nm, respectively. The PL and EL spectra are found to be qualitatively similar. This suggests that both the PL and the EL should be associated with the formation of luminescent centers at nanocrystal–matrix interfaces and in boundary regions. However, the two phenomena should differ in the mechanism by which the centers are excited. With the EL, excitation should occur by impact processes due to carrier heating in high electric fields. It is found that as δ increases, so does the proportion of large amorphous Si clusters with a high density of dangling bonds. This enhances nonradiative recombination and suppresses luminescence.     

Luminescence and microstructure of Er/O co-doped Si structures grown by MBE using Er and SiO evaporation

Er and O co-doped Si structures have been prepared using molecular-beam epitaxy (MBE) with fluxes of Er and O obtained from Er and silicon monoxide (SiO) evaporation in high-temperature cells. The incorporation of Er and O has been studied for concentrations of up to 2×10²⁰ and 1×10²¹ cm⁻³, respectively. Surface segregation of Er can take place, but with O co-doping the segregation is suppressed and Er-doped layers without any indication of surface segregation can be prepared. Si_1−xGe_x and Si_1−yC_y layers doped with Er/O during growth at different substrate temperatures show more defects than corresponding Si layers. Strong emission at 1.54 μm associated with the intra-4f transition of Er³⁺ ions is observed in electroluminescence (EL) at room temperature in reverse-biased p–i–n-junctions. To optimize the EL intensity we have varied the Er/O ratio and the temperature during growth of the Er/O-doped layer. Using an Er-concentration of around 1×10²⁰ cm⁻³ we find that Er/O ratios of 1 : 2 or 1 : 4 give higher intensity than 1 : 1 while the stability with respect to breakdown is reduced for the highest used O concentrations. For increasing growth temperatures in the range 400–575°C there is an increase in the EL intensity. A positive effect of post-annealing on the photoluminescence intensity has also been observed.     

Enhanced pure red electroluminescence intensity of Eu(o-BBA)3(phen) by red dye co-doping and inorganic semiconductor as charge carrier function layer

There is an emission peak at 494 nm in the electroluminescence (EL) of PVK [poly(n-vinylcarbazole)]: Eu(o-BBA)₃(phen) besides PVK exciton emission and Eu³⁺ characteristic emissions. Both the peaking at 494 nm emission and PVK emission influenced the color purity of red emission from Eu(o-BBA)₃(phen). In order to restrain these emissions and obtain high intensity red emission, 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7,-tetramethyljulolidy-9-enyl)-4Hpyran (DCJTB) and Eu(o-BBA)₃(phen) were co-doped in PVK solution and used as the active emission layer. The EL intensity of co-doped devices reached to 420 cd/m² at 20 V driving voltage. The chromaticity coordinates of EL was invariable (x = 0.55, y = 0.36) with the increase of driving voltage. For further improvement of EL intensity, organic–inorganic hybrid devices (ITO/active emission layer/ZnS/Al) were fabricated. The EL intensity was increased by a factor of 2.5 [(420 cd/m²)/(168 cd/m²)] when the Eu complex was doped with an efficient dye DCJTB, and by a factor of ≈4 [(650 cd/m²)/(168 cd/m²)] when in addition ZnS layer was deposited on such an emitting layer prior to evaporation of the Al cathode.     

Effect of Yb^3＋ concentration on Er^3＋ luminescence properties of sol-gelderived silica-alumina xerogels

Er~(3 )-activated silicate glasses are recognized of tech-nological interest in several areas and,in particular ,it iswell known for their successful application in opticalamplification at the C band (1530 -1565 nm) of tele-communications[1].Inside this l…     

Luminescence properties of light-emitting diodes based on GaAs with the up-conversion Y<Subscript>2</Subscript>O<Subscript>2</Subscript>S:Er,Yb luminophor

Y₂O₂S luminophors doped with Er³⁺ and Yb³⁺ ions are produced by means of solid-phase synthesis and deposited onto standard AL123A infrared light-emitting diodes. When excited with 940 nm radiation from a light-emitting diode, the structures exhibit intense visible up-conversion luminescence. A maximal brightness of 2340 cd/m² of green and red up-conversion luminescence at corresponding wavelengths around 550 and 600 nm is observed for the Y₂O₂S compound doped with 2 at % Er³⁺ ions and 6 at % Yb³⁺ ions. The ratio of the intensity of green (or red) up-conversion luminescence to the intensity of infrared Stokes luminescence increases with increasing applied voltage. The efficiency of visible emission of the light-emitting diode structures is η = 1.2 lm/W at an applied voltage of 1.5 V.     

Electroluminescence mechanisms in SiO x N y (Si) nanocomposite films

With a view to creating the Si LED, the mechanisms of electroluminescence (EL) in SiO_xN_y(Si) nanocomposite films with Si nanocrystals embedded in the SiO_xN_y matrix are studied experimentally and theoretically. The most important results are obtained from a Au/SiO_xN_ySi)/p-Si structure having a semitransparent electrode, the oxynitride film containing Si nanocrystals with a mean size of 3–5 nm and a concentration of ～10¹⁸ cm^?3; the measurements are made on a reverse-biased structure (substrate potential negative). Room-temperature EL is observed in the visible and IR ranges; the respective peaks are located at wavelengths of 600–700 and about 1200 nm. The study examines current-voltage characteristics of the structure and the dependence of integrated EL intensity on current, voltage, film thickness, the type of substrate conductivity, etc. The following conclusions are drawn from the experimental and theoretical results: The IR branch is mainly associated with carrier heating, avalanche ionization, and formation of light-emitting microplasmas near the substrate-film interface. The visible branch is linked to (i) hot-electron injection from the substrate into the film and (ii) impact excitation of luminescent centers at nanocrystal-matrix interfaces.     

The effect of erbium and oxygen on the photoluminescence intensity of erbium and the composition of <Emphasis Type="Italic">a</Emphasis>-SiO<Subscript>x</Subscript>:(H,Er, O) films deposited by DC magnetron sputtering

The effect of the oxygen content (\(C_{O_2 } \)) in the gas mixture (20% of SiH₄ + 80% of Ar) + O₂ and the surface area of an erbium target (S_Er) on the composition and Er³⁺ photoluminescence of amorphous a-SiO_x:(H, Er, O) films prepared by dc magnetron sputtering has been investigated. Analysis of the experimental data shows that [Er-O] and [Er-O-Si-O] clusters are formed in the gas plasma due to the competing processes of oxidation and sputtering of Si and Er targets and to the interaction of [Si-O] and [Er-O] clusters with each other and with the oxygen in the gas phase. The discontinuities in the dependences of the contents of erbium-bound oxygen and erbium in a film, and N _O ^Er-O and N_Er = f(\(C_{O_2 } \), S_Er), at \(C_{O_2 } \) ≈ (5–6.5) mol % supports the hypothesis on the existence of different erbium clusters. The necessary conditions for preparing a-SiO_x:(H, Er, O) films with the highest photoluminescence intensity of erbium ions at a wavelength of 1.54 μm are determined.     

Silicon light-emitting diodes with strong near-band-edge luminescence

Electroluminescence (EL) in the region of interband transitions from silicon light-emitting diodes (LEDs) fabricated by cutting a solar cell with an area of 21 cm² and external quantum efficiency η_ext of EL up to 0.85% has been studied at room temperature. Despite the considerable decrease in η_ext because of the cutting and Auger recombination, record-breaking values of the total power emitted by a diode (up to W = 8 mW) and emitted power per unit area (up to P ₀ = 65 mW/cm²) were achieved at pulse currents of up to 10 A and structure areas in the range S = 0.1–0.9 cm². The EL decay kinetics was measured for LEDs with different areas. The emission pattern of a Si LED with a textured surface and the emission intensity distribution along different directions in the plane of the emitting area of the LED were measured.     

ErIII‐Cored Complexes Based on Dendritic PtII–Porphyrin Ligands: Synthesis,Near‐IR Emission Enhancement,and Photophysical Studies

A series of stable and inert complexes with Er^III cores and dendritic Pt^II‐porphyrin ligands exhibit strong near‐IR (NIR) emission bands via highly efficient energy transfer from the excited triplet state of the Pt^II‐porphyrin ligand to Er³⁺ ions. The NIR emission intensity of thin films of Er^III complexes at 1530 nm, originating from 4f–4f electronic transitions from the first excited state (⁴I_13/2) to the ground state (⁴I_15/2) of the Er³⁺ ion, is dramatically enhanced upon increasing the generation number (n) of the aryl ether dendrons because of site‐isolation and light‐harvesting (LH) effects. Attempts are made to distinguish the site‐isolation effect from the LH effect in these complexes. Surprisingly, the site‐isolation effect is dominant over the LH effect in the Er³⁺‐[Gn‐PtP]₃(terpy) (terpy: 2,2′:6′,2″‐terpyridine) series of complexes, even though the present dendrimer systems with Er^III cores have a proper cascade‐type energy gradient. This might be due to the low quantum yield of the aryl ether dendrons. Thus, the NIR emission intensity of Er³⁺‐[G3‐PtP]₃(terpy) is 30 times stronger than that of Er³⁺‐[G1‐PtP]₃(terpy). The energy transfer efficiency between the Pt^II‐porphyrin moiety in the dendritic Pt^II‐porphyrin ligands and the Ln³⁺ ion increases with increasing generation number of the dendrons from 12–43 %. The time‐resolved luminescence spectra in the NIR region show monoexponential decays with a luminescence lifetime of 0.98 μs for Er³⁺‐[G1‐PtP]₃(terpy), 1.64 μs for Er³⁺‐[G2‐PtP]₃(terpy), and 6.85 μs for Er³⁺‐[G3‐PtP]₃(terpy) in thin films of these complexes. All the Er^III‐cored dendrimer complexes exhibit excellent thermal stability and photostability, and possess good solubility in common organic solvents.     

Influence of the orientation of the silicon substrate on the properties of avalanche Si:Er:O light-emitting structures

The influence of the orientation of silicon on the structural and luminescence properties of avalanche light-emitting diodes fabricated by the coimplantation of erbium and oxygen followed by solid-phase epitaxial (SPE) crystallization of the amorphized layer is considered. The luminescence properties are a consequence of the formation of various structural defects during the SPE crystallization: V-shaped dislocations and erbium precipitates form in (100) Si:Er:O layers, and larger structural defects, i.e, twins, are observed in (111) Si:Er:O layers along with an increase in the dislocation density by more than four orders of magnitude in comparison with the (100) orientation. The luminescence properties of avalanche and tunnel light-emitting diodes are also compared. In contrast to tunnel diodes, in avalanche diodes erbium ions are excited in the entire space-charge layer, and the effective excitation cross section of the Er³⁺ ions and their lifetime in the excited state are 3–4 times larger. Fiz. Tekh. Poluprovodn. 33, 660–663 (June 1999)     

An analysis of the charge-transport mechanisms defining the reverse current-voltage characteristics of the metal-GaAs barriers

Reverse current-voltage characteristics of metal-GaAs contacts with a Schottky barrier were measured. Linear portions of the reverse-current dependence on the squared electric-field strength in the space-charge region of diodes were obtained. Such a dependence is related to electron interaction with the lattice vibrations. The reverse current of the Mo-GaAs:Si contacts is analyzed at different temperatures. Results of the analysis showed that measured current-voltage characteristics are controlled by the phonon-assisted electron tunneling from metal into semiconductor with the involvement of a deep center attributed to the EL2 trap. A similar mechanism governs the reverse current-voltage characteristics of the Ni-GaAs:S Schottky diodes.     

SiO_2:Er和Si_xO_2:Er薄膜室温Er~(3+)1.54μm波长的电致发光

在 n+ -Si衬底上用磁控溅射淀积掺 Er氧化硅 (Si O2 :Er)薄膜和掺 Er富硅氧化硅 (Six O2 :Er,x>1 )薄膜 ,薄膜经适当温度退火后 ,蒸上电极 ,形成发光二极管 (LED)。室温下在大于 4V反偏电压下发射了来自 Er3+的 1 .5 4μm波长的红外光。测量了由 Si O2 :Er/n+ -Si样品和 Six O2 :Er/n+ -Si样品分别制成的两种 LED,其 Er3+1 .5 4μm波长的电致发光峰强度 ,后者明显比前者强。还发现电致发光强度与 Si O2 :Er/n+ -Si样品和 Six O2 :Er/n+ -Si样品的退火温度有一定依赖关系     

1.54 μm Near-infrared photoluminescent and electroluminescent properties of a new Erbium (III) organic complex

The crystal structure of Er(PM)₃(TP)₂ [PM = 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone, TP = triphenyl phosphine oxide] was reported and its photoluminescence properties were studied by UV–vis absorption, excited, and emission spectra. The Judd–ofelt theory was introduced to calculate the radiative transition rate and the radiative decay time of 3.65 ms for the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ ion in this complex. The antenna-effect and phonon-assisted energy-transfer were introduced to discuss the intramolecular energy transfer from ligands to Er³⁺ ion. Based on this Er(III) complex as the emitter, the multilayer phosphorescent organic light emitting diode was fabricated with the structure of ITO/NPB 20 nm/Er(PM)₃(TP)₂ 50 nm/BCP 20 nm/AlQ 40 nm/LiF 1 nm/Al 120 nm, which shows the typical 1.54 μm near-infrared (NIR) emission from Er³⁺ ion with the maximum NIR irradiance of 0.21 μW/cm².     

Combined Optical and MR Bioimaging Using Rare Earth Ion Doped NaYF4 Nanocrystals

Here, novel nanoprobes for combined optical and magnetic resonance (MR) bioimaging are reported. Fluoride (NaYF₄) nanocrystals (20–30 nm size) co‐doped with the rare earth ions Gd³⁺ and Er³⁺/Yb³⁺/Eu³⁺ are synthesized and dispersed in water. An efficient up‐ and downconverted photoluminescence from the rare‐earth ions (Er³⁺ and Yb³⁺ or Eu³⁺) doped into fluoride nanomatrix allows optical imaging modality for the nanoprobes. Upconversion nanophosphors (UCNPs) show nearly quadratic dependence of the photoluminescence intensity on the excitation light power, confirming a two‐photon induced process and allowing two‐photon imaging with UCNPs with low power continuous wave laser diodes due to the sequential nature of the two‐photon process. Furthermore, both UCNPs and downconversion nanophosphors (DCNPs) are modified with biorecognition biomolecules such as anti‐claudin‐4 and anti‐mesothelin, and show in vitro targeted delivery to cancer cells using confocal microscopy. The possibility of using nanoprobes for optical imaging in vivo is also demonstrated. It is also shown that Gd³⁺ co‐doped within the nanophosphors imparts strong T1 (Spin‐lattice relaxation time) and T2 (spin‐spin relaxation time) for high contrast MR imaging. Thus, nanoprobes based on fluoride nanophosphors doped with rare earth ions are shown to provide the dual modality of optical and magnetic resonance imaging.     

Effect of electric field in the course of obtaining a-SiO x :H(Er, O) films by dc magnetron sputtering on their composition and photoluminescence intensity of erbium ions

The effect of electric field on the elemental composition and photoluminescence of films of amorphous hydrogenated silicon doped with erbium and oxygen (a-SiO _x :H(Er, O)) in the course of obtaining these films by dc magnetron sputtering is studied. Two series of films were studied in relation to the electric-field strength in the magnetron, the area of the metallic erbium target, and oxygen content in the working chamber. The first series of films was obtained using an electrically insulated substrate holder, and the second series was obtained with a positive potential at the substrate holder with respect to the cathode. It is shown that, although the character of variation in the elemental composition and photoluminescence intensity for erbium Er³⁺ ions differ appreciably in the films of the two series, both of these factors are determined, as a result, by the processes of sputtering oxidation of the Si and Er targets that represent the cathode.     

Photoluminescence of erbium-doped aluminum oxide films with embedded silicon nanoparticles

Erbium-doped aluminum oxide films with embedded Si nanoparticles have been obtained by magnetron puttering of a composite (Al + Er₂O₃ + Si) target and subsequent electrochemical anodization at room temperature. The photoluminescence (PL) spectra of these films are measured in the temperature range 4.2–300 K. Efficient PL is observed at a wavelength of 1.54 μm without preliminary annealing of the samples, which indicates the possibility of activating Er³⁺ ions without any high-temperature treatment. The aluminum oxide films with embedded Si nanoparticles were observed to show stronger PL at a wavelength of 1.54 μm than similar films without Si nanoparticles. This effect can be explained by additional pumping of Er-based luminescence centers and energy transfer from the Si nanoparticles.