Jun 14, 2019

Efficient textured colour conversion layer of a down-converted white organic light-emitting diode by transfer imprinting

In this paper, we demonstrated an efficient textured colour conversion layer (CCL) of a down-converted white organic light-emitting diode (WOLED), which was fabricated by a very simple transfer imprinting method based on silicon wafer. The textured CCL not only helped to extract wave-guided light in the device, but also had an outstanding performance in enhancing the colour conversion rate, which was 1.75 times greater than that of flat CCL. Compared to flat CCL, the lower-doped textured CCL produced better white emission and higher efficiency simultaneously. Moreover, the WOLED with textured CCL also exhibited good colour stability at various voltages.



Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

Jun 5, 2019

The 310–340 nm ultraviolet light emitting diodes grown using a thin GaN interlayer on a high temperature AlN buffer

Previously, we reported that a thin GaN interlayer approach has been developed for growth of 340 nm ultraviolet light emitting diodes (UV-LEDs) with significantly improved performance. In this paper, more recent results on the further development of UV-LEDs with shorter wavelengths are reported, and the limitation of the wavelength of the UV-LEDs that can be pushed to, while retaining high device performance using the approach has been investigated. Transmission electron microscopy and device-performance data, including electrical and optical characteristics, indicated that the thin GaN interlayer approach can be effectively employed for growth of UV-LEDs to an emission wavelength approaching at least 300 nm. The approach should be taken into account in growth of UV-LEDs on sapphire substrates, as it provides a simple but effective growth method to achieve UV-LEDs with high performance. This paper also reports that a micro-LED array using the UV-LED wafer has been successfully fabricated, offering versatile micro-structured UV light sources for a wide range of applications.



Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

May 28, 2019

High-Brightness GaN-Based Light-Emitting Diodes on Si Using Wafer Bonding Technology

GaN-based light-emitting diodes (LEDs) grown on Si(111) substrates were fabricated with a vertical electrode method by using wafer bonding technology. The fabricated vertical LEDs showed a lower operating voltage and larger light output power than conventional LEDs due to enhancement in current spreading and reduction in tensile strain. The light output power of the vertical structured LEDs was 2.6 times higher than that of conventional LEDs, with an operating voltage at 20 mA reduced from 3.5 to 3.2 V.


Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

May 23, 2019

Characterization of Large-Area AlGaInP/Mirror/Si Light-Emitting Diodes Fabricated by Wafer Bonding

High-brightness AlGaInP/mirror/barrier/Si light-emitting diodes (LEDs) with vertical electrodes were fabricated using a wafer bonding technique. The high-thermal-conductivity Si substrate provides a better heat sink (compared with GaP or GaAs), which is a particularly important characteristic for high-power, large-area emitter applications. It allows for saturation of the small-area LED (300×300 µm2) after 150 mA injection and for the large-area LED (1200×1200 µm2) to increase output power even at 300 mA injection. The light output of the large-area vertical-conducting LED is mainly affected by the top-side (i.e., n-AlGaInP cladding) electrode design, where an interdigitated-finger electrode provides the better current spreading performance and prevents the current crowding problem. The extent of junction heating on LED samples (300×300–1200×1200 µm2) can also be evaluated from the corresponding electroluminescence spectra and emission-peak-wavelength driven by different injection current values. Finally, using a natural lithography technique, the mirror-substrate (MS) LEDs with textured surfaces present a brightness of 10 cd, which is about 4 cd brighter than that of the MS LED without a textured surface. With a combination of the MS wafer bonding and surface texturing techniques, thermal management in packaging becomes the key factor in further enhancing the external quantum efficiency of large-area LEDs under high flux operation.


Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

May 10, 2019

Hexagonal Truncated Pyramidal Light Emitting Diodes through Wafer Bonding of ZnO to GaN, Laser Lift-off, and Photo Chemical Etching

We report on a hexagonal pyramidal light emitting diodes (LEDs) produced by direct wafer bonding of a metal organic chemical vapor deposition (MOCVD) grown GaN LED on sapphire to a n-type ZnO wafer, laser lift off, and photochemical etching of the nitrogen face of the GaN LED. Laser lift off was used to remove the sapphire of the GaN wafer, exposing the Nitrogen face for roughening, in the form of microcones, as well as allowing deposition of metal contacts to the nitrogen face of the GaN LED. Contacts to the ZnO allow for the creation of a vertical current path. Selective etching was used to form truncated hexagonal pyramids of the ZnO.


Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

Apr 30, 2019

The fabrication and characterization of organic light-emitting diodes using transparent single-crystal Si membranes

For applications such as solar cells and displays, transparent single-crystal Si membranes were fabricated on a silicon-on-insulator (SOI) wafer. The SOI wafer included a buried layer of SiO2 and Si3N4 as an etch-stop layer. The etch-stop layer enabled fabrication of transparent single-crystal Si membranes with various thicknesses, and the thinning technology is described. For membranes with thicknesses of 18, 72 and 5000 nm, the respective optical transparent were 96.9%, 93.7% and 9% for R (red, λ = 660 nm), 96.9%, 91.4% and 1% for G (green, λ = 525 nm), and 97.0%, 93.2% and 0% for B (blue, λ = 470 nm). Organic light-emitting diodes (OLEDs) were then fabricated on transparent single-crystal Si membranes with various top Si thicknesses. OLEDs fabricated on 18, 72 and 5000 nm thick membranes and operated at 6 V demonstrated a luminance of 1350, 443 and 27 cd m−2 at the current densities of 148, 131 and 1.5 mA cm−2, respectively.


Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

Apr 25, 2019

Light-Emitting Diode Based on ZnO and GaN Direct Wafer Bonding

We report on direct wafer bonding of an n-type ZnO wafer to a III–nitride light-emitting diode (LED) structure. Wafers were successfully bonded in nitrogen at 600 °C. ZnO was then selectively etched to form a p-type electrode having a truncated hexagonal pyramid shape. This wafer bonded LED was evaluated with transmission, reflectivity, current–voltage (I–V), and electroluminescence (EL) measurements. This electrode revealed to be highly transparent and suitable for improving light extraction.


Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,