Highly efficient phosphorescent organic light-emitting diode with a nanometer-thick Ni silicide/polycrystalline p-Si composite anode.

A phosphorescent organic light-emitting diode (PhOLED) with a nanometer-thick (approximately 10 nm) Ni silicide/ polycrystalline p-Si composite anode is reported. The structure of the PhOLED is Al mirror/ glass substrate / Si isolation layer / Ni silicide / polycrystalline p-Si/ V(2)O(5)/ NPB/ CBP: (ppy)(2)Ir(acac)/ Bphen/ Bphen: Cs(2)CO(3)/ Sm/ Au/ BCP. In the composite anode, the Ni-induced polycrystalline p-Si layer injects holes into the V(2)O(5)/ NPB, and the Ni silicide layer reduces the sheet resistance of the composite anode and thus the series resistance of the PhOLED. By adopting various measures for specially optimizing the thickness of the Ni layer, which induces Si crystallization and forms a Ni silicide layer of appropriate thickness, the highest external quantum efficiency and power conversion efficiency have been raised to 26% and 11%, respectively.

1.54 microm electroluminescence from p-Si anode organic light emitting diode with Bphen: Er(DBM)(3)phen as emitter and Bphen as electron transport material.

1.54 microm Si-anode organic light emitting devices with Er(DBM)(3)phen: Bphen and Bphen/Bphen:Cs(2)CO(3) as the emissive and electron transport layers (the devices are referred to as the Bphen-based devices) have been investigated. In comparison with the AlQ-based devices with the same structure but with AlQ:Er(DBM)(3)Phen and AlQ as the emissive and electron transport layers, the maximum EL intensity and maximum power efficiency from the Bphen-based devices increase by a factor of 3 and 2.2, respectively. The optimized p-Si anode resistivity of the Bphen-based device of 10 Omega.cm is significantly lower than that of the AlQ-based device. The NIR EL improvement can be attributed to the energy transfer from Bphen to the Er complex and equilibrium of electron injection from the Sm/Au cathode and hole injection from the p-Si anode at a higher level.

Light emission from nanoscale Si/Si oxide materials.

Most porous Si materials studied have been oxidized in various degrees. The oxidized porous Si comprises of a great quantity of nanoscale Si particles (NSPs) and each of them is covered by a Si oxide layer. The structure and luminescence properties of the NSPs embedded Si oxide and the nanoscale Si/nanoscale SiO2 multilayers are similar to those of the oxidized porous Si. All the three kinds of materials mentioned are called nanoscale Si/Si oxide materials and their photoluminescence and electroluminescence properties especially light emission mechanisms are reviewed in this article. Nanoscale Si/Si oxide materials have been well studied and are believed to be very promising Si based light emitting materials. The very distinct roles of the NSPs and the luminescence centers in Si oxide in the photoluminescence and electroluminescence from the nanoscale Si/Si oxide materials are highlighted.

Enhanced electroluminescence from nanoscale silicon p+ -n junctions made with an anodic aluminum oxide pattern.

An enhancement of the electroluminescence (EL) from nanoscale silicon p(+)-n junctions made with an anodic aluminum oxide (AAO) pattern was demonstrated. The nanoporous AAO pattern with a pore density of 1.4 x 10(10) cm(-2) and a pore diameter of 50 +/- 10 nm was fabricated by the two-step anodic oxidation method on a n-type silicon wafer. The nanoscale AAO patterned Si p(+)-n junctions achieved an EL enhancement factor up to about 5 compared to the unpatterned Si p(+)-n junctions. The enhancement may originate from a reduction of nonradiative recombination due to partial passivation of the Si surface by the AAO pattern and improvement of the light extraction due to surface nanotextures.

1.53 µm photo- and electroluminescence from Er(3+) in erbium silicate.

Si-rich silicon oxide (SRO)/Er-Si-O/SRO multilayers were prepared on p-Si substrates using magnetron sputtering. X-ray diffraction measurements indicate that a mixture of silicates Er(2)Si(2)O(7) and Er(2)SiO(5) was formed after the multilayers were annealed at 1000 and 1150 °C. Strong Er(3+) 1.53 µm photoluminescence (PL) at room temperature has been observed from these multilayers and the full width at half-maximum of the 1.53 µm peak is less than 1.8 nm for the multilayers annealed at 1150 °C. Er(3+) 1.53 µm electroluminescence has been observed from erbium silicate films for the first time.

Combination of passivated Si anode with phosphor doped organic to realize highly efficient Si-based electroluminescence.

Silicon light source plays a key role in silicon optoelectronics, but its realization is an extremely challenging task. Although there are longterm intensive efforts to this topic, the power conversion efficiency (PCE) of the silicon-based electroluminescence is still no more than 1%. In this present report, a highly efficient silicon light source has been achieved. The device structure is p-Si (5 Omegacm)/ SiO2(approximately 2 nm)/ NPB / CBP: (ppy)(2)Ir(acac) / Bphen /Bphen: Cs2CO3 / Sm / Au. The SiO2 passivated Si is the anode having a suitably high hole-injection ability, and CBP: (ppy)(2)Ir(acac) is a highly efficient phosphor doped organic material. The device turn-on voltage is 3.2 V. The maximum luminance efficiency and maximum luminous power efficiency reach 69 cd/A and 62 lm/W, respectively, corresponding to a maximum PCE of 12% and an external quantum efficiency of 17%.

Strong enhancement of Er(3+) 1.54 µm electroluminescence through amorphous Si nanoparticles.

The roles of amorphous Si nanoparticles in light-emitting diodes (LEDs) based on Er-doped Si(1+x)O(2) films (x representing the degree of Si content, and varying widely from 0 to 4.50) have been investigated. In the aspect of the LEDs' electrical performance, it was found that the incorporation of Si nanoparticles facilitates the electrical conductivity of the films by improving the carrier mobility. With x increasing from 0 to 4.50, the mobility increases monotonically up to 5 times. The efficiency of Er(3+) electroluminescence (EL) at 1.54 µm can be enhanced by as much as 160 times when the degree of Si content x is 2.00, coincident with the value at which the rate of mobility increasing versus x slows down. The fact that the maximum of EL efficiency and the slowing down of the rate of increase of mobility occur at the same x value can be explained by coalescence of Si nanoparticles starting at x = 2.

Light extraction efficiency of a top-emission organic light-emitting diode with an Yb/Au double-layer cathode and an opaque Si anode.

We have computed the transmittances of four types of cathode--Yb/Au, Al/Au, Yb/Ag, and Al/Ag double layers--and the light extraction efficiencies of the top-emission organic light-emitting diodes with these cathodes, respectively, based on the characteristic matrix method and the dissipation spectrum model. Computations show that the Yb/Au cathode has a markedly higher transmittance than the other three types of cathode when the Yb and Au thicknesses in the Yb/Au cathode are, respectively, equal to the Al (or Yb) and Au (or Ag) thicknesses in the other three types of cathode. The power lost to the Yb/Au cathode due to the surface plasmon polaritons is the lowest, and hence the device with the Yb/Au cathode has the highest extraction efficiency. The transmittances for the four cathodes are also measured experimentally.

Synthesis and optical properties of ZnTe single-crystalline nanowires.

Single-crystalline ZnTe nanowires with the zincblende structure have been synthesized on silicon (Si) substrates via a vapor phase transport method. The ZnTe (99.99%) powders were used as the source, and 10 nm-thick thermal evaporated gold (Au) film was used as the catalyst. The as-prepared ZnTe nanowires have diameters of 30-80 nm and lengths of more than 10 microm. The products were analyzed by X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. Optical properties of these nanowires were investigated by room-temperature Raman scattering spectrum and temperature-dependent photoluminescence measurements. The results show that the as-prepared ZnTe nanowires are of high crystal quality.

[Photoluminescence from Er-doped silicon-rich silicon oxide film and Er-doped silicon-rich silicon nitride film and its annealing behavior].

Room temperature photoluminescence (PL) with a peak at 1.54 microns was observed from silicon oxide, silicon-rich silicon oxide, silicon nitride and silicon-rich silicon nitride films, all doped with Er and grown by the magnetron sputtering technique. To determine the optimum annealing temperature for the 1.54 microns PL, these films were annealed in the range of 600-1,100 degrees C with an interval of 100 degrees C. Among these four types of films annealed at an identical temperature, the intensity of 1.54 microns PL peak of the Er-doped silicon-rich silicon oxide film was always the strongest one, which arrived at a maximum in 800 degrees C annealing. A 1.38 microns PL band was also observed in each of these four types of films, and which in the silicon-rich silicon oxide or silicon-rich silicon nitride films was found to be correlated with the 1.54 microns PL band in intensity.