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GaN-based LEDs grown on Si-implanted GaN templates form air gaps beneath the active layer to enhance light-extraction efficiency. GaN-based epitaxial layers grown on selective Si-implanted regions had lower growth rates compared with those grown on implantation-free regions, resulting in selective growth and the subsequent over the Si-implanted regions. Accordingly, air gaps were formed over the Si-implanted regions after the meeting of laterally growing GaN facet fronts. The experimental results indicate that the light-output power of the LEDs grown on the Si-implanted GaN templates was enhanced by 36% compared with conventional LEDs. This enhancement in output power was attributed mainly to the air gaps, which led to a higher escape probability for the photons. [ABSTRACT FROM AUTHOR]

An extremely high optical absorbing film made of alternating aluminum–silver layers was used as cathode in polymeric light-emitting devices (PLEDs). Physical properties of the cathodes were characterized by I–V measurement, atomic force microscopy, and x-ray photoemission spectroscopy. As a result of the slow evaporation rate, each pair of the aluminum–silver layer was shown to be in the form of aluminum–aluminum oxide nanoclusters embedded in an amorphous charge conducting network of silver. The nanoclusters helped to absorb and scatter the ambient light effectively. The use of four alternating layers structure in conventional PLEDs demonstrated 126% enhancement of contrast under 1000 lx ambient illumination. The I–V characteristics of the black cathode PLEDs remained intact when compared with reference PLEDs. This technology offers precise control of the cathode quality in terms of its reflectivity and conductivity. [ABSTRACT FROM AUTHOR]

A "fuzzy-junction" organic light-emitting device (OLED) containing a graded organic-organic interface is reported. Such graded junction is effectively produced utilizing interdiffusion through an ultrathin interfacial fusing layer sandwiched between two functional layers. With a glass transition temperature (T[sub g]) lower than remaining layers, this fusing layer permits smooth interdiffusion and mixing of neighboring layers by annealing above its T[sub g]. With appropriate material combinations, fuzzy-junction OLEDs thus prepared exhibit both reduced voltage and enhanced emission efficiency in comparison with conventional abrupt-junction devices. As an instance, a green fluorescent OLED with such fuzzy junction shows a high peak power efficiency of ∼20 lm/W, substantially higher than ∼14 lm/W of a corresponding abrupt-junction device. A "fuzzy-junction" organic light-emitting device (OLED) containing a graded organic-organic interface is reported. Such graded junction is effectively produced utilizing interdiffusion through an ultrathin interfacial fusing layer sandwiched between two functional layers. With a glass transition temperature (T[sub g]) lower than remaining layers, this fusing layer permits smooth interdiffusion and mixing of neighboring layers by annealing above its T[sub g]. With appropriate material combinations, fuzzy-junction OLEDs thus prepared exhibit both reduced voltage and enhanced emission efficiency in comparison with conventional abrupt-junction devices. As an instance, a green fluorescent OLED with such fuzzy junction shows a high peak power efficiency of ∼20 lm/W, substantially higher than ∼14 lm/W of a corresponding abrupt-junction device. [ABSTRACT FROM AUTHOR]

An efficient and morphologically stable pyrimidine-containing spirobifluorene-cored oligoaryl, 2,7-bis[2-(4-tert-butylphenyl)pyrimidine-5-y1]-9,9'-spirobifluorene (TBPSF), as an emitter or a host for blue organic light-emitting devices (OLEDs), is reported. The steric hindrance inherent with the molecular structure renders the material a record-high neat-film photoluminescence (PL) quantum yield of 80% as a pure blue emitter (PL peak at 430 nm) of low molecular weight, and a very high glass-transition temperature (T[sub g]) of 195°C. Blue OLEDs employing this compound as the emitter or the emitting host exhibit unusual endurance for high currents over 5000 mA/cm². When TBPSF is used as a host for perylene in a blue OLED, maximal brightness of ∼80 000 cd/m² had been achieved, representing the highest values reported for blue OLEDs under dc driving. [ABSTRACT FROM AUTHOR]

In this letter, we report a promising type of electrically programmable, i.e., reconfigurable, organic light-emitting devices (OLEDs) incorporating a thin carrier-blocking layer as the sacrificial fusing layer. In such devices, the carrier-blocking layer has a lower glass transition temperature than neighboring layers. By raising the internal temperature of the device above the transition temperature of the carrier-blocking layer with a large enough current, interdiffusion between organic layers could occur through such a layer. As a consequence, neighboring layers are fused and a new path for carrier transport is formed, bypassing the carrier-blocking property and altering the device characteristics. A device that emits blue light as fabricated but can be transformed into a green-emitting one is demonstrated. Such a type of device may be used for color pixels in OLED displays, user-programmable OLED applications, and nonvolatile memory devices.© 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]