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Two-color InGaN/GaN micro-facet multiple-quantum well (MQW) samples grown on 4 in. Si (111) substrate were systematically characterized. The micro-facet structure was achieved by epitaxial lateral overgrowth on SiO2 masked GaN surfaces with stripes along the <[formula]> direction and composed of (0001) and ([formula]) facets. Two different emission peaks stemming from (0001) and ([formula]) oriented MQWs are observed by photoluminescence. The relative intensities of the two peaks can be tuned by controlling the structure's geometry and the experimentally derived growth rates on the different facets. For each facet, we have also determined the MQWs' optical properties, the polarization, the internal quantum efficiency, and the light extraction efficiency. In addition, we analyzed the blue shift for differently oriented MQWs as function of temperature and excitation power. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the growth, structural, electrical and optical characterization of strained triple-quantum-well light emitting diodes. Use of molecular beam epitaxy to grow the heterostructures; Optical performance of the diodes.

The design of an all-electrical spin-injection-detection device is discussed. It is shown that the use and the design of tunnel barriers cannot simply be copied from the spin light-emitting diodes, where they have already been demonstrated. Using one-dimensional and two-dimensional self-consistent simulations, the doping levels of the tunnel contacts and the spin-transport region are engineered to obtain an optimal tunnel barrier resistance and an optimal current distribution in the spin-transport region. [ABSTRACT FROM AUTHOR]

Presents a study that detailed the growth of In[subx]Ga[sub1-x]As/In[suby]Al[sub1-y]As biased light-emitting diodes emitting in the wavelength range 1.7-1.9 µm nonlattice matched on gallium arsenide. Area where the electroluminescence spectra are measured; Manner that the position of the band gap and the electron temperature are derived; Function of the injected carrier density.

We present a detailed quantitative analysis of the light extraction and loss mechanisms in high-efficiency GaAs-AlGaAs surface-textured thin-film light-emitting diodes (LEDs). The analysis is based on a Monte Carlo simulation. Most input parameters, including scattering of photons at the textured surface, sub-bandgap absorption, and absorption at the metal mirror are obtained from experiments or from literature. The simulation also takes into account the effect of photon recycling and the realistic geometry of the diodes. The only remaining fitting parameter is the internal quantum efficiency, which is deduced to be about 80% at room temperature for the experimentally realized 850-nm LEDs with an external quantum efficiency of 44%. The analysis shows further that the most important loss mechanism is reabsorption in the active layer, and in particular in those parts of the active layer that are not electrically pumped. This conclusion is also valid for other types of high-efficiency LEDs. We could furthermore verify the validity of the Monte-Carlo simulation results by conducting experiments at low temperatures, where nonradiative recombination processes are reduced, resulting in the internal quantum efficiency approaching unity. The measured external quantum efficiency at 90 K is 68%, which is close to the theoretically predicted efficiency for a perfect active layer. The results demonstrate that the light extraction from surface-textured LEDs is fully understood and can be quantitatively modeled by a simple raytracing algorithm [ABSTRACT FROM PUBLISHER]

We report on nonresonant cavity light-emitting diodes (NRC-LED) with large quantum efficiencies and high speed. A maximum quantum efficiency of 31% is measured for a device with an active layer thickness of 120 nm, and 18.7% for a device having an active layer of 30 nm. Further, we report on optical rise and fall times of NRC-LEDs. Even when switched to current levels below 4 mA, at which the external quantum efficiency exceeds 17%, our NRC-LEDs have 10%-90% rise and fall times of less than 2 ns. As a result, eye diagrams taken at this current level at 622 Mb/s are wide open. This demonstrates the suitability of high-efficiency NRC-LEDs for optical interconnects. Finally, from a system's viewpoint it is important to note that the optical output power of NRC-LEDs decreases by only 0.36%/°C [ABSTRACT FROM PUBLISHER]

We demonstrate experimentally the electrical electron spin injection from a ferromagnetic metal/ tunnel barrier contact into a III-V semiconductor light emitting diode (LED). The injected electrons have in-plane spin orientation. By applying a relatively small oblique external magnetic field this spin orientation within the semiconductor can be manipulated to have a nonzero out-of-plane component. By measuring the resulting circular polarization of the emitted light, we observe injected spin polarization in excess of 9% at 80 K in a CoFe/AlO[sub x]/(Al,Ga)As/GaAs surface-emitting spin-LED. [ABSTRACT FROM AUTHOR]

The transmission properties of semiconductor surfaces can be changed by surface texturing. We investigate these changes experimentally and find that an enhancement of the angle-averaged transmission by a factor of 2 can be achieved with optimum texturing parameters. This enhanced transmission provides an additional light extraction mechanism for high-efficiency surface-textured light-emitting diodes. External quantum efficiencies of 46% and 54% are demonstrated before and after encapsulation, respectively. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates light-emitting diodes (LED) with 31 percent external quantum efficiency. Impact of the outcoupling of lateral waveguide modes; Combination of light scattering at a textured top surface and reflection on a backside mirror; Partial extraction of the confined light.

Investigates the bistable optical switching behavior of resonant tunneling light-emitting diode using triple barrier structures. Suppression of the resonant electron current; Luminescence effects of a sudden increase in electron population in a high current state; Applications of the triple-barrier structures.

Abstract: Spin-LED''s have been used as a powerful tool to demonstrate the electrical injection of spin-polarized carriers into a semiconductor. We first give a review of some of the injector strategies that have been used (oxide-based tunnel injectors, highly doped Schottky tunnel injectors and magnetic semiconductors) with focus on the obtained spin polarizations and the bias dependence of these polarizations. We then move to the electrical aspects of the contacts and show that these should not be overlooked. The oxide-based tunnel injectors suffer from a large parasitic hole current when they are used in a spin-LED, and may become incapable of injecting any electrons in an all-electrical (unipolar) injection-detection device. We discuss the origin of this effect and point out possible solutions both for III–V semiconductors and for Si. [Copyright &y& Elsevier]

A novel compound 2,6-diphenyl-1,5-diaza-1,5-dihydro-s-indacene (Indacene) was synthesized by means of the Madelung reaction starting from 2,5-dimethyl-1,4-phenylenediamine. The structure was characterised by NMR, IR, MS, and elemental analysis. The UV/Vis absorption and photoluminescence spectra were investigated. The electroluminescent behaviour of the new compound was studied in ITO/PEDOT-PSS/Indacene-CNPPP/Mg–Ag(10:1)/Ag devices. The electroluminescent maximum was recorded at 504 nm corresponding to a greenish blue emission. The results demonstrate the potential application of Indacene in OLEDs. [Copyright &y& Elsevier]