Silicon-based Light-emitting Diodes Research Articles

Tunable Ag Nanocavity Enhanced Green Electroluminescence from SiNx:O Light-Emitting Diode.

As the driving source, highly efficient silicon-based light emission is urgently needed for the realization of optoelectronic integrated chips. Here, we report that enhanced green electroluminescence (EL) can be obtained from oxygen-doped silicon nitride (SiNx:O) films based on an ordered and tunable Ag nanocavity array with a high density by nanosphere lithography and laser irradiation. Compared with that of a pure SiNxO device, the green electroluminescence (EL) from the SiNx:O/Ag nanocavity array device can be increased by 7.1-fold. Moreover, the external quantum efficiency of the green electroluminescence (EL) is enhanced 3-fold for SiNx:O/Ag nanocavity arrays with diameters of 300 nm. The analysis of absorption spectra and the FDTD calculation reveal that the localized surface plasmon (LSP) resonance of size-controllable Ag nanocavity arrays and SiNx:O films play a key role in the strong green EL. Our discovery demonstrates that SiNx:O films coupled with tunable Ag nanocavity arrays are promising for silicon-based light-emitting diode devices of the AI period in the future.

Stimulated emission at 1.54 μm from erbium/oxygen-doped silicon-based light-emitting diodes

Silicon-based light sources, including light-emitting diodes (LEDs) and laser diodes (LDs) for information transmission, are urgently needed for developing monolithic integrated silicon photonics. Silicon with erbium ions ( Er 3 + ) doped by ion implantation is considered a promising approach, but it suffers from an extremely low quantum efficiency. Here we report an electrically pumped superlinear emission at 1.54 μm from Er/O-doped silicon planar LEDs, which are produced by applying a new deep cooling process. Stimulated emission at room temperature is realized with a low threshold current of ∼ 6 mA ( ∼ 0.8 A / cm 2 ). Time-resolved photoluminescence and photocurrent results have revealed the complex carrier transfer dynamics by relaxing electrons from the Si conduction band to the Er 3 + ion. This picture differs from the frequently assumed energy transfer via electron–hole pair recombination of the silicon host. Moreover, the amplified emission from the LEDs is likely due to a quasi-continuous Er/O-related donor band created by the deep cooling technique. This work paves the way for fabricating superluminescent diodes or efficient LEDs at communication wavelengths based on rare-earth-doped silicon.

Cesium-lead-bromide perovskites with balanced stoichiometry enabled by sodium-bromide doping for all-vacuum deposited silicon-based light-emitting diodes

A more balanced stoichiometry is realized in vacuum vapor deposited cesium-lead-bromide perovskite films through the introduction of NaBr.

Van der Waals Integrated Silicon/Graphene/AlGaN Based Vertical Heterostructured Hot Electron Light Emitting Diodes.

Silicon-based light emitting diodes (LED) are indispensable elements for the rapidly growing field of silicon compatible photonic integration platforms. In the present study, graphene has been utilized as an interfacial layer to realize a unique illumination mechanism for the silicon-based LEDs. We designed a Si/thick dielectric layer/graphene/AlGaN heterostructured LED via the van der Waals integration method. In forward bias, the Si/thick dielectric (HfO2-50 nm or SiO2-90 nm) heterostructure accumulates numerous hot electrons at the interface. At sufficient operational voltages, the hot electrons from the interface of the Si/dielectric can cross the thick dielectric barrier via the electron-impact ionization mechanism, which results in the emission of more electrons that can be injected into graphene. The injected hot electrons in graphene can ignite the multiplication exciton effect, and the created electrons can transfer into p-type AlGaN and recombine with holes resulting a broadband yellow-color electroluminescence (EL) with a center peak at 580 nm. In comparison, the n-Si/thick dielectric/p-AlGaN LED without graphene result in a negligible blue color EL at 430 nm in forward bias. This work demonstrates the key role of graphene as a hot electron active layer that enables the intense EL from silicon-based compound semiconductor LEDs. Such a simple LED structure may find applications in silicon compatible electronics and optoelectronics.

Detection of chalk in single kernels of long‐grain milled rice using imaging and visible/near‐infrared instruments

AbstractBackground and objectivesTo maintain the competitiveness of U.S. long‐grain rice in U.S. and foreign markets, having translucent whole milled grain is critical. An objective technique to detect grain chalk, opaque areas in the grain, will provide breeders and industry with an effective tool for developing low‐chalk varieties or agronomic practices that reduce chalk occurrence. Two instruments developed at the Center for Grain and Animal Health Research, U.S. Department of Agriculture‐Agricultural Research Service (USDA‐ARS), a single‐kernel near‐infrared (SKNIR) tube instrument and a silicon‐based light‐emitting diode (SiLED) high‐speed sorter, were compared with two commercially available imaging instruments, WinSEEDLE and SeedCount used for chalk quantification. Three 2‐way chalk classifications were defined for single kernels based on visual inspection: (a) <50% or ≥50% opacity or chalk (modified Grain Inspection, Packers & Stockyards Administration [GIPSA]), (b) <10% or ≥10% opacity (10% cutoff), and (c) 100% opacity or 100% translucent (MaxLevel).FindingsThe SKNIR method provided the best classification for the modified GIPSA definition with an 82.4% average correct classification (CC), that is, 89% and 76% for nonchalky and chalky kernels, respectively. The WinSEEDLE had the best classification for the 10% cutoff definition, with an 84% CC for nonchalky kernels and a 96% CC for chalky kernels. For the MaxLevel definition, average CCs of both the SKNIR and SiLED methods were similar, at 93% and 95%, respectively. The average CCs were lower for both the WinSEEDLE method and the SeedCount method at 14% and 58%, respectively. These low CC values are a result of using a threshold of 100% for chalky or nonchalky kernels, where a single misclassified pixel within the image will cause misclassification. Calibration models developed for both the SKNIR and SiLED methods indicate that their classifications were based mainly on spectral differences near the adsorption bands for starch, protein, and water content.ConclusionsAll of the instruments can be used to classify chalk, but their level of accuracy depends on how chalk is defined.Significance and noveltyThe SiLED has the capability to process seeds at a high rate, and the SKNIR has the potential to measure compositional traits in addition to chalk measurements.

Fabrication method of the patterned mask for controllable growth of low-dimensional semiconductor nanostructures

One of the important problems on the way to development of highly efficient optoelectronic devices such as silicon-based light-emitting diodes, hybrid solar cells as well as semiconductor lasers based on quantum dots is to obtain nanostructures with high crystalline perfection and small size dispersion. In this paper, we studied the method of thegrowth mask fabrication using photolithography through a close-packed array of microspherical lenses to obtain monodisperse nanostructures on a silicon growth substrate for the subsequent epitaxy of ordered GaP nanowires (NWs) array with a controllable morphology. Theoretical modeling of UV wave propagation demonstrated the possibility of the light focusing under a microspherical lenses array in the photoresist. With the method use the growth masks made of silicon oxide on Si (111) substrates were fabricated. Molecular-beam epitaxy was used to synthesize GaP NW ordered arrays.

Si:Si LEDs with room-temperature dislocation-related luminescence

Silicon-based light-emitting diodes (LEDs) fabricated by the Si-ion implantation and chemical-vapor deposition methods are studied. Room-temperature dislocation-related electroluminescence (EL) is observed in LEDs based on n-Si. In LEDs based on p-Si, the EL is quenched at temperatures higher than 220 K. The EL-excitation efficiencies are measured for the D1 line at room temperature and the D1 and D4 lines at liquid-nitrogen temperature.

Light-Emitting Diodes Fabricated From Carbon Ions Implanted Into p-Type Silicon

Silicon-based light-emitting diodes (LEDs) are fabricated using p-type silicon implanted with C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ions and postannealed at 1000 °C in flowing nitrogen. The ion implantation is carried out at ambient temperature (AT) and 400 °C to investigate the influence of high-temperature implantation on the luminescence of LEDs. Transmission electron microscopy shows a near-surface layer of amorphous silicon (a-Si) with nanoscale carbon-rich inclusions in both ambient and heated targets while an additional polycrystalline Si layer is observed in the heated target only. A Schottky diode is constructed from C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -implanted Si (C:Si) with a semitransparent gold layer on the implanted surface and aluminum on the back of the target. Contact firing at 400 °C in flowing nitrogen is used to optimize diode performance. Turn-ON voltage is determined to be about 3 V for all devices. Electroluminescence (EL) spectra show visible orange-red emission indicating luminescence primarily due to a-Si and Si nanoparticles in the LEDs fabricated from C:Si implanted at AT. The high-temperature samples produced EL attributed to a-Si and porous silicon carbide.

Silicon-Based White LED Packaging Module With an Integrated RGB Color Sensor

This letter presents a silicon-based light-emitting diode (LED) packaging module with integrated red, green, and blue (RGB) color sensors, which can detect the variations in the brightness and specified wavelength intensity of white LEDs to evaluate the chromaticity and color temperature of emitting light in real time. The carrier substrate with color sensors was fabricated by semiconductor manufacturing technology and a deep silicon etching process was used to complete electrical division and thermal isolation. By integrating blue LED and silicone phosphor, a monolithic packaging module with miniaturization and low cost was achieved. A typical experimental result shows the output currents of the RGB color sensors as 0.082, 0.086, and 0.068 mA, respectively, when the input current to the LED is 0.2 A. The calculated chromaticity coordinates of x and y are 0.35 and 0.36, respectively, and the corresponding color temperature is 4852 K. These experimental results are consistent with the measurements of a commercial luminous meter.

A Novel Silicon-Based LED Packaging Module With an Integrated Temperature Sensor

The thermal management of light-emitting diode (LED) packaging modules has become more important in the past decade, especially for high-powered LED chips, which produce high temperatures during lighting, resulting in luminance decay and color temperature drift. For this issue, this paper proposes a novel silicon-based LED packaging module with an integrated temperature sensor. The LED die is mounted directly on a silicon substrate with a resistive nickel/titanium bilayer temperature sensor, which monitors the temperature variations in the LED inside the package, in real time. The thermal conductivity characteristics and the sensor performance for the specified packaging modules are evaluated using finite element analysis and by experiment. The experimental results shows that when the thickness of the bilayer sensing film and its equivalent length, within a sensing area of 1.4 $\,\times\,$ 1.4 ${\rm mm}^{2}$ , are 0.2 $\mu{\rm m}$ and 72.3 mm, respectively, a high sensitivity measurement of 30.4 $\Omega/^{\circ}{\rm C}$ is obtained and good linear output is achieved, at a working temperature for the LED of less than 120 $^{\circ}{\rm C}$ . A miniaturized, integrated, low-cost smart LED packaging module is implemented using this co-packaging method.

Novel Silicon-Based LED Packaging Module With an Integrated Photosensing Element

This letter presents a novel design for a silicon-based light emitting diodes (LEDs) packaging module with an integrated photosensor. The carrier substrate for the LED submount and a photosensitive element are directly fabricated on a silicon wafer, using ion doping and inductively coupled plasma etching, thereby achieving a smart LED packaging module featuring miniaturization, integration and low cost. The subsequent assembly, with a specific heat sink and a shelled optical cap, results in a decrease in thermal effects and improves measurement sensitivity. The typical experiment result shows that the operating temperatures of the LED die and the photosensing element remain below 70°C and 45°C, respectively, when the input current to the LED is 0.3 A. The sensitivity of the photosensing module is 8.2 μA/nt for a chip size of 1×1 × 0.15 cm3. The working temperature and photosensitivity of this packaging module can be improved by using a system with high heat dissipation efficiency.

An electric-field-active 1377-nm narrow-line Si light-emitting diode at 150 K

A new class of silicon-based light-emitting diode is demonstrated using InSb-quantum-dot-embedded Si containing the emissive {311} rod-like defects (RLDs). A narrow peak centered at 1377 nm (900 meV) characteristic of the {311} RLDs was found to develop out of an otherwise broad background electroluminescence (EL) upon the application of electric fields in the growth direction. Such electric-field-active EL was observed up to 150 K with a slight downward shift of the peak energies, accompanied by an anomaly in the thermal roll-off of the EL intensity. Spectral variations with temperature and electric field indicate a switching of dominance between the closely correlated defect states that are responsible for the EL emission.

Dislocation engineered silicon light emitting devices

The influence of boron-induced dislocation loops on the luminescence efficiency of silicon-based light-emitting diodes is investigated. Luminescence measurements and transmission-electron-microscopy images from devices fabricated by boron implantation into crystalline silicon, and subsequently processed under different conditions to form dislocation loops of different size and densities, were compared. Light emitting devices were also fabricated in an otherwise identical but a pre-amorphized substrate, to prevent boron-induced loop formation. The results demonstrate a strong correlation between the dislocation loop density and areal coverage, and the light emission efficiency. The devices produced in the pre-amorphized substrate, without dislocation loops, show strongly quenched light emission.

On the role of dislocation loops in silicon light emitting diodes

The role of boron-induced dislocation loops on the suppression of the luminescence thermal quenching in silicon-based light-emitting diodes is investigated here. Luminescence measurements and cross-sectional transmission-electron-microscopy images from devices fabricated by boron implantation into crystalline silicon, and into a pre-amorphized substrate, to prevent the boron-induced loops formation, were compared. The results show that, in the devices incorporating dislocation loops between the depletion region and sample surface (the boron induced loops), the thermal quenching has been completely eliminated, in contrast with devices fabricated from the pre-amorphized substrate where strong thermal quenching is still observed.

A Silicon-Silica Nanocomposite Material

The synthesis and characterization of a novel silicon–silica nanocomposite material are reported. A self-assembly method allows the encapsulation of silicon nanoclusters within the channels of a periodic mesoporous silica thin film. The result is the formation of a silicon–silica nanocomposite film with bright, room-temperature photoluminescence in the visible range, and a nanosecond luminescence lifetime. The properties of the nanocomposite material have been studied by several analytical techniques, which collectively show the existence within the channels of non-diamondoid-structure-type silicon nanoclusters with various hydrogenated silicon sites. It is estimated that the silicon nanoclusters in the silica mesoporous films occupy up to 39 % of the accessible pore volume. The nanocomposite film shows improved resistance to air oxidation compared to crystalline silicon. The high loading and chemical stability to oxidation under ambient conditions are important advantages in terms of the development of silicon-based light-emitting diodes from this class of materials.

Oxygen-Induced Modification of Dislocation Luminescence Centers in Silicon

Prospects for using the long-wavelength dislocation luminescence line D1 in silicon-based light-emitting diodes are considered. The standard spectral position of this line at 807 meV, rather than being canonic, depends on the morphology of the dislocation structure and the impurity environment of an individual dislocation. Data on the spectral distribution of luminescence intensity in the region of the D1 line have been analyzed in terms of the concentration of interstitial oxygen in a sample, plastic deformation parameters, and thermal treatment. The results obtained suggest that oxygen exerts a dominant effect on the spectral position of line D1 and luminescence intensity in its vicinity. It is shown that the probable structure of recombination centers can be described in terms of the donor-acceptor pair model, in which oxygen complexes serve as donors and the acceptors are structural defects in the dislocation core.

Solar cell technology for fabrication of silicon light‐emitting diodes

Application of solar cell technology is considered for fabrication of silicon-based light-emitting diodes, which are especially interesting as optoelectronic devices compatible with the conventional silicon technology. First experimental results obtained with non-optimized amorphous silicon-crystalline silicon heterostructure demonstrate an external quantum efficiency of 0.013% (the internal quantum efficiency being 0.3%). The measures directed to a further development of such light-emitting diodes are discussed. They indicate a possibility to increase the quantum efficiency up to several percent. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Near-field optical investigation of porous silicon samples

Abstract Near-field optical spectroscopy has been used to study the photoluminescence features of a porous silicon device at room temperature, with a subwavelength space resolution of about 50-100nm. In particular, a prototype of a porous silicon-based light-emitting diode has been characterized by imaging morphology, near-field scattering intensity and emission maps of the same portion of the sample with a space resolution of better than 60 nm. Structured emitting centres are found on the porous regions with size ranging from 200 nm to 1 μm. Emission features, acquired as near-field spectra as well as emission maps at fixed wavelengths, provide crucial information on the prototype structure at the nanometric level, exploitable for improvement in production steps as well as for the study of the dominant working mechanisms of the device.