Ross P. Stanley

Toward ultrahigh-efficiency aluminum oxide microcavity light-emitting diodes: guided mode extraction by photonic crystals

In this paper, we present an improved version of microcavity light-emitting diodes, relying on the use of a low-index material, aluminum oxide. Our work addresses in particular the injection scheme required by the insulating nature of this oxide. The device we fabricated demonstrated efficiencies up to 28% in air, using only planar technology. In these structures, most of the emission is guided. We further propose to include photonic crystals to extract this guided light. The design of the photonic crystals are discussed and substantiated by photoluminescence-based experiments.

Continuous-wave dual-wavelength lasing in a two-section vertical-cavity laser

A vertical-cavity surface-emitting laser with two monolithically grown cavities is presented. The three-terminal device allows current injection into the active regions of both cavities. Under various injection conditions, the device lases continuous wave on either one of the two longitudinal modes supported by the cavity, or on both wavelengths simultaneously. By using a constant injection current in the bottom cavity, and adjusting the current in the top cavity, the device shows all four possible emission states. These are the off states, lasing at the short wavelength /spl lambda//sub S/, at the long wavelength /spl lambda//sub L/, and at both /spl lambda//sub S/ and /spl lambda//sub L/ at the same time.

Parametric Polariton Amplification in Semiconductor Microcavities

We present novel experimental results demonstrating the coherence properties of the nonlinear emission from semiconductor microcavities in the strong coupling regime, recently interpreted by parametric polariton four-wave mixing. We use a geometry corresponding to degenerate four-wave mixing. In addition to the predicted threshold dependence of the emission on the pump power and spectral blueshift, we observe a phase dependence of the amplification which is a signature of a coherent polariton wave mixing process.

Quantitative Cerebral Blood Flow Measurements in the Rat Using a Beta-Probe and H215O

Beta-probes are a relatively new tool for tracer kinetic studies in animals. They are highly suited to evaluate new positron emission tomography tracers or measure physiologic parameters at rest and after some kind of stimulation or intervention. In many of these experiments, the knowledge of CBF is highly important. Thus, the purpose of this study was to evaluate the method of CBF measurements using a beta-probe and H215O. CBF was measured in the barrel cortex of eight rats at baseline and after acetazolamide challenge. Trigeminal nerve stimulation was additionally performed in five animals. In each category, three injections of 250 to 300 MBq H215O were performed at 10-minute intervals. Data were analyzed using a standard one-tissue compartment model (K1 = CBF, k2 = CBF/p, where p is the partition coefficient). Values for K1 were 0.35 ± 0.09, 0.58 ± 0.16, and 0.49 ± 0.03 mL · min−1 · mL−1 at rest, after acetazolamide challenge, and during trigeminal nerve stimulation, respectively. The corresponding values for k2 were 0.55 ± 0.12, 0.94 ± 0.16, and 0.85 ± 0.12 min−7, and for p were 0.64 ± 0.05, 0.61 ± 0.07, and 0.59 ± 0.06. The standard deviation of the difference between two successive experiments, a measure for the reproducibility of the method, was 10.1%, 13.0%, and 5.7% for K1, k2, and p, respectively. In summary, beta-probes in conjunction with H215O allow the reproducible quantitative measurement of CBF, although some systematic underestimation seems to occur, probably because of partial volume effects.

Observation of enhanced transmission for s-polarized light through a subwavelength slit

Enhanced optical transmission (EOT) through a single aperture is usually achieved by exciting surface plasmon polaritons with periodic grooves. Surface plasmon polaritons are only excited by p-polarized incident light, i.e. with the electric field perpendicular to the direction of the grooves. The present study experimentally investigates EOT for s-polarized light. A subwavelength slit surrounded on each side by periodic grooves has been fabricated in a gold film and covered by a thin dielectric layer. The excitation of s-polarized dielectric waveguide modes inside the dielectric film strongly increases the s-polarized transmission. A 25 fold increase is measured as compared to the case without the dielectric film. Transmission measurements are compared with a coupled mode method and show good qualitative agreement. Adding a waveguide can improve light transmission through subwavelength apertures, as both s and p-polarization can be efficiently transmitted.

Structural and electrooptical characteristics of quantum dots emitting at 1.3 /spl mu/m on gallium arsenide

We present a comprehensive study of the structural and emission properties of self-assembled InAs quantum dots emitting at 1.3 /spl mu/m. The dots are grown by molecular beam epitaxy on gallium arsenide substrates. Room-temperature emission at 1.3 /spl mu/m is obtained by embedding the dots in an InGaAs layer. Depending on the growth structure, dot densities of 1-6/spl times/10/sup 10/ cm/sup -2/ are obtained. High dot densities are associated with large inhomogeneous broadenings, while narrow photoluminescence (PL) linewidths are obtained in low-density samples. From time-resolved PL experiments, a long carrier lifetime of /spl ap/1.8 ns is measured at room temperature, which confirms the excellent structural quality. A fast PL rise (/spl tau//sub rise/=10/spl plusmn/2 ps) is observed at all temperatures, indicating the potential for high-speed modulation. High-efficiency light-emitting diodes (LEDs) based on these dots are demonstrated, with external quantum efficiency of 1% at room temperature. This corresponds to an estimated 13% radiative efficiency. Electroluminescence spectra under high injection allow us to determine the transition energies of excited states in the dots and bidimensional states in the adjacent InGaAs quantum well.

High-efficiency light-emitting diodes at /spl ap/1.3 /spl mu/m using InAs-InGaAs quantum dots

Light-emitting diodes (LEDs) based on long-wavelength, self-assembled InAs-InGaAs quantum dots (QDs) are demonstrated and characterized. The LEDs consist of a single layer of QDs positioned at /spl lambda//2 from a top gold mirror to enhance the extraction efficiency. The external quantum efficiency at room temperature is 1%, which corresponds to an estimated 13% radiative efficiency. High-injection electroluminescence and photovoltage spectra under reverse bias allow us to determine the transition energies of excited states in the QDs and bidimensional states in the adjacent InGaAs quantum well.

Enhanced transmission from a single subwavelength slit aperture surrounded by grooves on a standard detector

An enhanced transmission is detected through a single slit of subwavelength width surrounded by grooves in a gold layer that is added as a postprocess to a standard complementary metal oxide semiconductor (CMOS) fabricated detector. The enhanced transmission results from constructive interference of surface waves, which interact with the incident light. The measured enhanced transmission shows strong qualitative agreement with that predicted by the modal expansion method. With the decreasing dimensions available in standard CMOS process, such nanostructures in metals could be used to replace current optical systems or to improve performance by increasing the signal to noise ratio and/or allowing polarization selection.

High extraction efficiency, laterally injected, light emitting diodes combining microcavities and photonic crystals

The use of photonic crystals (PCs) for realistic light emitting diodes (LEDs) is discussed, given the constraints of planar semiconductor technology. A viable route for the fabrication of high-efficiency high-brightness electrically injected LEDs is presented. The starting point is a top-emitting microcavity using a single Alox Bragg mirror. The active area is surrounded by two-dimensional PCs, namely arrays of air rods etched through the top layers; injection of the electrons is achieved through the crystals. Design rules for PCs as efficient out-couplers are detailed. The building blocks are assessed experimentally, and we show that promising results are at hand.

Experimental determination of the internal quantum efficiency of AlGaInP microcavity light-emitting diodes

Detailed study of external quantum efficiency ηQE is reported for AlGaInP-based microcavity light-emitting diodes (MCLEDs). Unlike conventional light-emitting diodes (LEDs) the extraction efficiency γext and far field profile depend on the linewidth of the intrinsic spontaneous emission and wavelength detuning between cavity mode and peak electroluminescence. This dependence makes it difficult to estimate the intrinsic spectrum, hence the performances of MCLEDs. By using a nondestructive deconvolution technique, the intrinsic spectra of a MCLED and a reference LED (with the same active regions) could be determined at different current densities. This allowed precise calculation of γext for both devices (values close to 11% were found for the MCLED), and hence of their apparent internal quantum efficiencies ηintapp. At 55 A/cm2, values of 90% and 40% were determined for the LED and MCLED, respectively. In order to explain this difference, we measured ηQE for devices with different sizes. From a fitting pro...