Fabrication Of LEDs Research Articles

Substrate Transfer for GaN based LEDs grown on Silicon

This paper focuses on the substrate transfer process which is applied after the fabrication of LEDs on 4 inch Si (111) wafers comprising p and n contact formation to the GaN layer. After applying a passivation layer, a bonding metal is deposited. The wafer is then bonded to a Si carrier substrate using metallic bonding. Next, the original Si (111) substrate is completely removed by grinding and wet etching. GaN-LEDs are thus transferred to a new carrier substrate. The last step is etching of the transferred GaN layer from the back to open the contacts. A surface roughening technique on the backside of the transferred GaN layer to improve the light extraction efficiency of GaN-LEDs is also investigated. All the issues of the substrate transfer process steps such as permanent Cu/Sn bonding, thinning by grinding and wet etching will be discussed in detailed. A typical issue occurring during processing of GaN-LEDs on Si substrates is high stress and related large wafer bow originating from the GaN layer and the thick Cu/Sn metal bonding layer. Such a large wafer bow causes problems for some automatic handling tools and processes like lithography. Solutions to manage the stress and wafer bow have been investigated.

Fabrication and Characteristics of Blue-Green and Green LEDs using ZnSSe:Te Active Layers

Blue-green and green LEDs have been successfully fabricated grown by MBE, which has introduced the ZnS y Se 1-x-y :Tex (x=0.04, y~0.11-0.14) ternary epilayer as an active layer. From the I-V characteristics, the built-in voltage (~2.1 V) is very small compared to other wide bandgap LEDs, such as commercial InGaN-based LEDs (＞3.2 V). From the C-V profiling, the effective carrier concentration in the p-type ZnMgSSe cladding layer was evaluated as ~2.8×10 16 ㎝ -3 for the present LEDs.

Dry etching characteristics of GaN using Cl 2/BCl 3 inductively coupled plasmas

ICP power/RF power, operating pressure, and Cl 2/BCl 3 gas mixing ratio are altered to investigate the effect of input process parameters on the etch characteristics of GaN films. The etch selectivity of GaN over SiO 2 and photoresist is studied. Although higher ICP/RF power can obtain higher GaN/photoresist etch selectivity, it can result in faceting of sidewall and weird sidewall profile due to photoresist mask erosion. Etch rates of GaN and SiO 2 decrease with the increase of operating pressure, and etch selectivity of GaN over SiO 2 increases with the increasing operating pressure at fixed ICP/RF power and mixture component. The highest etch selectivity of GaN over SiO 2 is 7.92, and an almost vertical etch profile having an etch rate of GaN close to 845.3 nm/min can be achieved. The surface morphology and root-mean-square roughness of the etched GaN under different etching conditions are evaluated by atomic force microscopy. The plasma-induced damage of GaN is analyzed using photoluminescence (PL) measurements. The optimized etching process, used for mesa formation during the LED fabrication, is presented. The periodic pattern can be transferred into GaN using a combination of Cl 2/BCl 3 plasma chemistry and hard mask SiO 2. Patterning of the sapphire substrate for fabricating LED with improved extraction efficiency is also possible using the same plasma chemistry.

Plasma assisted LED wafer scribing and fabrication of Ag nanoparticle‐embedded LED

AbstractTwo applications of plasma effects in fabrication of LEDs are introduced. One is scribing LED wafer by mechanical impacts of plasma, which is induced by laser ablation, to the bottom of LED wafer. The other one is the surface plasmon effect on light emission. Ag nano‐particles are formed on about 50‐nm thick p‐GaN epitaxial layer over multi‐quantum wells (MQWs) and an additional 150‐nm thick p‐GaN layer is grown again over the surface. As the result, the Ag nano‐particles are located within the overall p‐GaN epitaxial layer, very near to MQWs. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnO-GaN Hybrid Heterostructures as Potential Cost-Efficient LED Technology

Reliable and reproducible p-type doping is the main challenge for fabricating highly efficient ZnO-based light-emitting diodes. During the last few years, the lack of reliable p-type conductivity in ZnO has initiated research concerning the combination of ZnO and other semiconductors, which can then be doped p-type. One of these concepts is the combination of ZnO with GaN heterostructures aiming at the fabrication of hybrid LEDs. We discuss the problems as well as potential benefits from a combination of ZnO and GaN hybrid heterostructures in a single device. We also present our recent results on ZnO-GaN hybrid LEDs using an inverted LED concept. The hybrid LEDs have an external quantum efficiency of more than 35%.

An efficient 2-linked carbazolyl β-diketonate europium(III) complex as red phosphor applied in LED

An efficient 2-linked carbazolyl β-diketonate europium(III) complex Eu(ETFMCTFBD)3phen was designed and synthesized, where ETFMCTFBD was 1-(9-ethyl-7-(trifluoromethyl)-9H-carbazol-2-yl)-4,4,4-trifluorobutane-1,3-dione and phen was 1,10-phenanthroline. Eu(ETFMCTFBD)3phen exhibits high thermal stability and excellent photoluminescence properties. The CIE chromaticity coordinates (x=0.668, y=0.331) are close to the National Television Standard Committee (NTSC) standard values for red. The lowest triplet energy was measured and suggests the photoluminescence process as a ligand-sensitized luminescence process (antenna effect). A bright red light-emitting diode was fabricated by coating the complex phosphor onto a ∼395 nm-emitting InGaN chip. All the results indicate that Eu(ETFMCTFBD)3phen is a good candidate as a red component in the fabrication of white LEDs with a high color-rendering index.

Design and fabrication of Si LED with the N-well-P+ junction based on standard CMOS technology

A wedge shape Si LED is designed and fabricated with 0.35 μm double-grating standard CMOS technology. The device structure is based on the N-well-P+ junction. The P+ has a wedge shape and is surrounded by the N-well. The micrographs of Si LEDs’ emitting and layout are captured. The I–V characteristic and spectra of the Si LED are tested. Under room temperature and backward bias, its radiant luminosity is 12 nW at 100 mA, and the wavelength of the emitting peak is located at 764 nm.

Synthesis and luminescence of Eu 2+-doped alkaline-earth apatites for application in white LED

A series of Eu 2+-doped alkaline-earth apatites (alkaline-earth=Ca, Sr and Ba) were synthesized by a solid state reaction method with excess chlorides, and the effect of the used excess chlorides on the luminescent property of the synthesized products was discussed. Photoluminescence measurements showed that Eu 2+-doped calcium apatite exhibited intensely blue wide-band emission peaking at 457 nm under near UV excitation among the Eu 2+-doped Ca, Sr and Ba apatites. Blue and white LEDs were successfully fabricated by pre-coating the calcium apatite phosphors onto ∼395 nm-emitting InGaN chips. The CIE coordinates, color temperature, luminous efficacy and rendering index value of the fabricated white LED are (0.3432, 0.3234), 4969 K, 8 lm/W and 80, respectively. The results indicate that the Eu 2+-activated calcium apatite phosphor is a promising candidate as a blue component for fabrication of near UV-based white LEDs.

Effects of fluxes on the synthesis of Ca 3Sc 2Si 3O 12:Ce 3+ green phosphors for white light-emitting diodes

Different fluxes were added in preparation of Ca 3Sc 2Si 3O 12:0.01Ce 3+ phosphors with a solid-state method and the different influences of the fluxes on phase formation, morphology, and photoluminescence properties of the phosphors were studied. The results show that CaF 2 flux is the best flux as it can decrease single phase-forming temperature, improve morphology and enhance photoluminescence of the Ca 3Sc 2Si 3O 12:0.01Ce 3+ phosphors remarkably. White light-emitting diode was fabricated with the Ca 3Sc 2Si 3O 12:0.01Ce 3+ phosphor prepared with CaF 2 flux, and good performances of this WLED confirm that CaF 2 is a good flux for preparing Ca 3Sc 2Si 3O 12:Ce 3+, and the phosphor is an efficient green component for fabrication of white LEDs.

Manufacturing of a Nanocrystal-based LED by Layer-by-Layer Deposition

The manufacturing of nanocrystal based LEDs with the aid of the layer-by-layer deposition technique is presented and discussed. The technique is generally applicable for the fabrication of LEDs efficiently emitting in the wide spectral region from the UV-blue to the Near-Infrared.

Near UV-based LED fabricated with Ba 5SiO 4(F,Cl) 6:Eu 2+ as blue- and green-emitting phosphor

A series of halosilicate phosphor, Ba 5SiO 4(F,Cl) 6:Eu 2+, were synthesized by a solid state reaction. Excited by 370-nm light, Ba 5SiO 4Cl 6:Eu 2+ exhibits a broad emission band peaking at 440 nm. Partial substitution of Cl − with F − in the host lattice leads to red-shift in the emission band with centering wavelength from 440 nm to 503 nm. The possible mechanism for the luminescence change was discussed based on the XRD patterns. Blue and green LEDs were fabricated by combination of a 370 nm-emitting near UV chip and the optimal Ba 5SiO 4Cl 6:Eu 2+ and Ba 5SiO 4(F 3Cl 3):Eu 2+, respectively. This series of phosphors is considered as a promising blue and green component used in fabrication of near UV-based white LEDs.

Optical Simulation and Fabrication of Nitride-Based LEDs With the Inverted Pyramid Sidewalls

In this study, the numerical and experimental demonstrations for the enhancement of light-extraction efficiency in nitride-based LEDs with randomly inverted pyramid sidewalls (IPSs) by chemical etching of the chip edge are presented. With 20 mA injection current, it was found that forward voltages were 3.69 and 3.75 V while output powers were 7.07 and 8.95 mW for the conventional LED and inverted pyramid sidewall LED, respectively. The larger LED output power is attributed to the increased light-extraction efficiency by IPSs.

THE EFFECTS OF INCREASING AlN MOLE FRACTION ON THE PERFORMANCE OF AlGaN ACTIVE REGIONS CONTAINING NANOMETER SCALE COMPOSITIONALLY INHOMOGENEITIES

In this paper we report on the characterization of n - Al 0.51 Ga 0.49 N active regions and the fabrication of ultraviolet LEDs that contain self-assembled, nanometer-scale compositional inhomogeneities ( NCI - AlGaN ) with emission at ~290 nm. These active regions exhibit reduced integrated photoluminescence intensity and PL lifetime relative to 320 nm NCI - AlGaN active regions that have significantly lower AlN mole fraction, despite having more than an order of magnitude fewer threading dislocations, as measured by transmission electron microscopy. This behavior is attributed to nonradiative recombination associated with the presence of a larger density of point defects in the higher Al content samples. The point defects are ameliorated somewhat by the lower density of NCI AlGaN regions in the higher Al content samples, which leads to a larger concentration of carriers in the NCI and concomitant reduced radiative lifetime that may account for the high observed peak IQE (~ 25%). Prototype flip chip double heterostructure-NCI- ultraviolet light emitting diodes operating at 292 nm have been fabricated that employ a 50% NCI - AlGaN active region.

Corrections to “Use of Elastic Conductive Adhesive as the Bonding Agent for the Fabrication of Vertical Structure GaN-Based LEDs on Flexible Metal Substrate” [1 Apr 08 523-525

In the above titled paper (ibid., vol. 20, no. 7, pp. 523-525, 1 Apr 08), there were errors in Table I. The correct table is presented here.

Use of Elastic Conductive Adhesive as the Bonding Agent for the Fabrication of Vertical Structure GaN-Based LEDs on Flexible Metal Substrate

Through the use of elastic conductive adhesive (ECA) as the bonding agent and patterned laser lift-off technology, a flexible metal substrate technology for the fabrication of vertical structured GaN-based light-emitting diodes (flex-LEDs) was proposed and demonstrated. It showed that the flex-LEDs have negligible changes in dominant wavelength-current and light output intensity-current-voltage characteristics when subjected to an external bending stress, indicating that the ECA used in the present technology performed well as a buffer to external stresses. As compared with conventional sapphire substrate GaN-based LEDs, Flex-LEDs with a chip size of 600 x 600 mum2 showed an increase in light output intensity (power) about 216% (80%) at 120 mA with an essential decrease in forward voltage from 3.51 to 3.3 V.

Epitaxial growth of ZnMgTe with a wide composition range on ZnTe substrate by molecular beam epitaxy

Zn1-xMgxTe layers with a wide composition range of 0≥x≥0.66 were grown on ZnTe (001) substrates by molecular beam epitaxy. Zn1-xMgxTe epitaxial layers with Mg composition below 0.66 have a zincblende structure, suitable for fabrication of LED. Strained pseudomorphic epitaxial layer is obtained at the Mg composition x up to 0.05. Mg composition in epitaxial layer was controlled by the flux ratio of Mg/(Zn+Mg), but it was also affected by the flux ratio of Te/(Zn+Mg).

Ultraviolet light-emitting diodes based on group three nitrides

Light-emitting diodes with emission wavelengths less than 400 nm have been developed using the AlInGaN material system. For devices operating at shorter wavelengths, alloy compositions with a greater aluminium content are required. The material properties of these materials lie on the border between conventional semiconductors and insulators, which adds a degree of complexity to the development of efficient light-emitting devices. A number of technical developments have enabled the fabrication of LEDs based on group three nitrides (III-nitrides) that emit in the UV part of the spectrum, providing useful tools for a wealth of applications in optoelectronic systems.

Materials and Process Development for ZnMgO/ZnO Light-Emitting Diodes

We report on the fabrication of UV LEDs based on a p-n junction p-ZnMgO/n-ZnO/n-ZnMgO double heterostructure. Pulsed-laser deposition was used to grow the complete heterostructure on <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -plane sapphire templates. The LEDs were patterned by simple wet etching. Band-edge electroluminescence emission most likely associated with ZnO excitonic transitions was observed at room temperature. However, the devices show sensitivity to the presence of hydrogen in the measurement ambient due to formation of a surface conduction layer. The results show the potential of ZnO-based materials for UV emitters of potentially lower cost and with comparable or higher emission intensity than AlGaN/GaN devices provided adequate surface passivation techniques are developed.

Fabrication and property analysis of AIGaInP red light LED with high bright

The LED with DBR and enhancing transmission film was grown by MOCVD. At 20 mA DC injection current, the LED peak wavelength was 623 nm, the light intensity was 200 mcd, and the output light power was 2.14 mW. The light intensity and output light power have been improved than traditional LED.

Fabrication and Characterization of InGaN-Based Green Resonant-Cavity LEDs Using Hydrogen Ion-Implantation Techniques

The InGaN-based green resonant-cavity light-emitting diodes (RCLEDs) have been fabricated using hydrogen ion-implantation and laser liftoff techniques. The RCLEDs structure consisted of an multiple-quantum-well active layer between the top (5 pairs) and bottom (7.5 pairs) dielectric distributed Bragg reflectors with optical reflectance of 85% and 99.9%, respectively. The insulation layers of the RCLEDs with and without implantation were formed by the hydrogen ion-implantation layers of concentration and film, respectively. The corresponding forward turn-on voltage at dc current density injection were about and for the RCLEDs with and without implantation. The light output intensity of the RCLEDs with implantation is higher by a factor of 1.4 as compared to that of the similar structure without implantation at a current density of . The directionality of RCLEDs with implantation is superior to that of RCLEDs without implantation.