Resonant-cavity Light-emitting Diodes Research Articles

High-Performance 650 nm Resonant-Cavity Light-Emitting Diodes for Plastic Optical-Fiber Application

AlGaInP-based resonant-cavity light-emitting diodes (RCLEDs) with high power and high speed have been fabricated. In this study, the RCLEDs were designed with different light-output aperture sizes 84, 60, and 40 µm, for different applications on plastic optical fibers. Small-signal modulation bandwidths as high as 310 MHz at a forward current of 20 mA and an output power as high as 1.5 mW can be achieved for devices with 40 µm apertures. The devices with 84 µm apertures had an output power of more than 3.5 mW at a driving current of 20 mA and a maximum efficiency of over 12% with an epoxy-encapsulated package. The devices with 40 µm apertures satisfied with the IEEE 1394b s400 standard. Furthermore, the devices showed stable coupling efficiency for various currents and output powers at different ambience temperatures. In addition, the lifetime of devices is over 1300 h, and the power decay is less than 0.5 dB at 85 °C for a 40 mA driving current.

Fabrication and Characterization of InGaN-Based Green Resonant Cavity Light-Emitting Diodes by Using H+ Ion-Implantation

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High-sensitivity detection of narrowband light in a more intense broadband background using coherence interferogram phase

This paper describes an optical interferometric detection technique, known as the interferogram phase step shift, which detects narrowband, coherent, and partially coherent light in more intense broadband incoherent background light using changes in the phase gradient with the optical path difference of the coherence interferogram to distinguish the bandwidth or coherence of the signal from that of the background. The detection sensitivity is assessed experimentally by measuring the smallest signal-to-background ratio or signal-to-clutter ratio (SCR), which causes a detectable change in the self-coherence interferogram phase. This minimum detectable SCR (MDSCR) is measured for the multimode He-Ne laser, resonant-cavity light-emitting diode (LED), narrowband-filtered white light, and LED signal sources in a more intense tungsten-halogen-lamp white-light background. The highest MDSCRs to date, to the authors' knowledge, are -46.42 dB for coherent light and -31.96 dB for partially coherent light, which exceed those of existing automatic single-domain techniques by 18.97 and 4.51 dB with system input dynamic ranges of 19.24 and 11.39 dB, respectively. The sensitivity dependence on the signal-to-system bandwidth ratio and on the relative offset of their central wavelengths is also assessed, and optimum values are identified

Surface plasmon mediated emission in resonant-cavity light-emitting diodes

In this letter the authors describe a particular method to outcouple in air, via surface plasmons (SPs), optical radiation trapped in leaky waveguide modes of a resonant-cavity light-emitting diode. The deposition of a thin metal layer on the device surface creates SP modes at both the metal-dielectric interfaces. The successive overcoating of the metal layer with a thin polymer film and the roughening of its surface produce outcoupling of radiation trapped in leaky modes via SP modes. Experimental results for polarization resolved reflectivity and emission spectra are in excellent agreement with theoretical predictions.

Temperature Characteristics of High Modulation Rate Platinum-Diffused AlGaInP Resonant-Cavity Light-Emitting Diodes

This study is focused on the temperature characteristics of platinum-diffused AlGaInP resonant-cavity light-emitting diodes (RCLED). The shape of the platinum-diffused AlGaInP RCLED emission spectra and the full width at half maximum (FWHM) of the main electroluminescent (EL) spectra are almost uninfluenced over the measured temperature range of 20 to 100 °C. Therefore, the platinum-diffused devices show a high characteristic temperature, and a small temperature shift in the peak emission wavelength.

Design and fabrication of temperature-insensitive InGaP-InGaAlP resonant-cavity light-emitting diodes

Visible InGaP-InGaAlP resonant-cavity light-emitting diodes with low-temperature sensitivity output characteristics were demonstrated. By means of widening the resonant cavity to a thickness of three wavelength (3lambda), the degree of power variation between 25 degC and 95 degC for the devices biased at 20 mA was apparently reduced from -2.1 dB for the standard structure design (1-lambda cavity) to -0.6 dB. An output power of 2.4 mW was achieved at 70 mA. The external quantum efficiency achieved a maximum of 3% at 13 mA and dropped slowly with increased current for the device. The external quantum efficiency at 20mA dropped only 14% with elevated temperature from 25 degC to 95degC. The current dependent far-field patterns also showed that the emission always took place perfectly in the normal direction, which was suitable for plastic fiber data transmission

Analysis of reflectance and modulation spectroscopic lineshapes in optoelectronic device structures

We discuss the spectral lineshapes of reflectance and modulated reflectance (MR) measurements on optoelectronic device structures such as epi-layers, quantum wells (QWs), vertical-cavity surface emitting-lasers (VCSELs) and resonant-cavity light-emitting diodes (RCLEDs). We consider the various methods for the extraction of built-in electric fields and band-gap energies from Franz-Keldysh oscillations (FKO), using the example of a tensilely strained InGaAs QW system, whose InGaAsP barriers yield strong FKO. We describe how critical point transition energies can be easily obtained by eye from Kramers-Kronig (KK) transforms of low field or QW modulation spectra, using the example of the modulated transmittance spectra of dilute-nitrogen InGaAsN p-i-n structures. We also discuss how the ordinary reflectivity spectrum, usually acquired at the same time as the MR signal, may also be exploited to extract layer thicknesses and compositions, and information about the active QW absorption spectrum in VCSEL and RCLED structures.

1.32 μ m InAs∕GaAs quantum-dot resonant-cavity light-emitting diodes grown by metalorganic chemical vapor deposition

The first demonstration of InAs∕GaAs quantum-dot (QD) resonant-cavity light-emitting diode (RCLED) operating at 1.32μm at room temperature is reported. A single-layer InAs QDs inserted in GaAs matrix as the active medium was grown by metalorganic chemical vapor deposition. The bottom and top mirrors of QD RCLEDs were fabricated by employing epitaxial AlGaAs∕GaAs pairs and one dielectric SiO2∕Si3N4 pair as distributed Bragg reflectors (DBRs), respectively. As compared to the nonresonant QD LEDs, the RCLEDs exhibit a forward voltage of 1.13V at 20mA, a peak wavelength of 1.318μm, a narrower full width at half maximum in the electroluminescent spectrum of 14meV at 20mA, a high Q factor of 73.9, a low redshift rate with injection current of 0.033nm∕mA, and a higher light-output power of 28μW at 100mA.

Fabrication and characterization of InGaN resonant‐cavity light‐emitting diodes on silicon substrates

AbstractGaN‐based resonant‐cavity light‐emitting diodes (RCLEDs) have been fabricated on Si substrates by a combination of laser lift‐off and wafer bonding techniques. The RCLED structure consisted of an InGaN/GaN multiple‐quantum‐well active layer between the top (5‐pairs) and bottom (7.5‐pairs) dielectric TiO2/SiO2 distributed Bragg reflector (DBR) with an optical reflectance of 85 and 99.9%, respectively. The cavity mode of the RCLED shows a linewidth of 5.5 nm at a main emission peak at 525 nm. The emission full width at half maximum can decrease from 48 to 35 nm, indicating the effect of the DBR microcavity. The quality factor for this resonant cavity structure was estimated to be approximately 100. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Far-field radiation pattern of red emitting thin-film resonant cavity LEDs

AlGaInP thin-film resonant cavity light-emitting diodes (RCLEDs) show an improved performance compared to standard red emitting RCLEDs. External quantum efficiencies at 650 nm of 23% and 18% with and without encapsulation, respectively, have been obtained for devices showing a maximum emission in the normal direction. Thanks to the high angle-averaged reflectivity of the bottom hybrid mirror, a strong photon recycling effect occurs in these structures. The decrease of the absorption with increasing injection level reduces photon recycling and increases extraction of lateral guided modes. The redirection of part of the emission from the vertical to the lateral direction with increasing current density is reflected in the evolution of the far-field radiation pattern.

GaN-Based Green Resonant Cavity Light-Emitting Diodes

GaN-based resonant cavity light-emitting diodes (RCLEDs) have been successfully fabricated on Si substrate by laser lift-off and wafer bonding techniques. A five-pair TiO2/SiO2 dielectric distributed Bragg reflector (DBR) (with 85% reflectivity) and an Ag layer (with 99% reflectivity) were employed as top and bottom mirrors, respectively, for front emission RCLEDs. The room temperature light output power of the RCLED was 1.5 times that of similar LED structures without a top DBR mirror under 20 mA injection current. The cavity modes exhibit a linewidth of 5.5 nm at 525 nm wavelength, which corresponds to a quality factor about 100. Moreover, the full width at half maximum of the emission can be reduced to 35 nm, as a result of the effect of the resonant cavity.

Experimental characterization of integrated optical wireless components

Line of sight optical links can provide extremely high bandwidth communications between terminals, but in order to maintain alignment between transmitter and receiver, tracking is required. In this letter, we report results from a solid-state tracking transmitter and receiver. The transmitter consists of a custom complementary metal-oxide-semiconductor (CMOS) integrated circuit that is flip-chip bonded to a seven-element resonant cavity light-emitting diode. The receiver uses a custom seven-element InGaAs detector array that is flip-chip bonded to a CMOS integrated circuit. Results from an initial link demonstration show overall system operation at 100 Mb/s/channel, for Manchester coded data.

Improving the light extraction efficiency of red-emitting conjugated polymer light emitting diodes

We demonstrate a significant improvement in the external electroluminescence efficiency of red-emitting polymer light emitting diodes (LEDs) by modifying the optical structure of the device. By using a cathode composed of a thin (5nm) film of calcium backed with an optically thick film of silver, we measured improvements in the external efficiency of polymer LEDs by a factor of 1.6 times compared to a device using a cathode composed of calcium backed with lower reflectivity aluminum. By incorporating the LED into a microcavity structure (to form a resonant cavity LED) it is possible to obtain additional (but rather smaller) improvements in external efficiency of the order of 1.15 times, compared to a standard LED utilizing the same cathode. By combining high reflectivity cathode∕mirror materials with a low finesse cavity structure, we show that the external efficiency of a LED can be improved by as much as 1.8 times compared to a standard (noncavity) LED. Our results are in good agreement with those of theoretical calculations and demonstrate the real improvements in device external efficiency that can be achieved by reducing optical losses within the LED structure.

Effect of resonant cavity in wafer-bonded Green InGaN LED with dielectric and silver mirrors

The green InGaN-based resonant cavity light-emitting diodes (RCLEDs) on Si substrates were fabricated using laser liftoff and wafer bonding techniques. Five-pair TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> --SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> distributed Bragg reflectors (reflectivity: 85%) and an Ag metal layer (reflectivity: 99%) were employed as the top and bottom mirrors, respectively. The light output power of the RCLED at room temperature is 1.5 times the magnitude of a similar structure without a resonant cavity at an injecting current density of 600A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The mode spectrum exhibits a line width of approximately 5.5 nm at the dominant peak wavelength of 525 nm, which indicates a quality factor of 100. Under various injection current densities, a low thermally induced red shift in the 525-nm emission peak was observed. This indicates that the resonant microcavity effect contributes to the stability of electroluminescence emission wavelength

Enhanced modulation rate in platinum-diffused resonant-cavity light-emitting diodes

This study is focused on the modulation response of resonant-cavity light-emitting diodes (RCLEDs). Platinum (Pt) atoms are diffused into the 660nm RCLED epitaxial layers to increase the concentration of recombination centers and to improve the modulation speed. The RCLED has an AlInGaP multi-quantum-well active layer which was embedded into AlGaAs-distributed Bragg reflectors to form a one-wavelength (1-λ) optical resonator. Afterwards, the deep-level Pt impurity was diffused into the RCLED and an improved average rise time, from 18.07to12.21ns, was obtained. The corresponding modulation frequency can be increased from 19.54to30.21MHz.

Electrical control of the uncertainty in the time of single photon emission events

We report that with appropriate voltage biasing it is possible to reduce the uncertainty in the time at which photons are emitted from a single quantum dot by an arbitrary factor. Using a resonant cavity light-emitting diode, we reduce the photon emission time jitter to one-fifth of the radiative lifetime. This enables us to demonstrate single-photon emission at a repetition rate of $1.07\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$ from both the exciton and biexciton states. This idea may lead to a new method by which pairs of indistinguishable photons can be generated for photonic quantum logic experiments.

Cubic InGaN/GaN multi-quantum wells and AlGaN/GaN distributed Bragg reflectors for application in resonant cavity LEDs

In this contribution, we present results on the growth and characterization of c-InGaN/GaN MQWs and c-AlGaN/GaN DBRs, which may be used as building blocks of green (510nm) resonant cavity light emitting diodes, which have a high potential as light sources for local area networks using plastic optical fibers. First, the impact of the indium and gallium flux on the growth of cubic-InGaN by plasma assisted molecular beam epitaxy has been studied. Indium is observed to incorporate into the c-GaInN films only when the gallium flux is reduced significantly below the value needed for stoichiometric c-GaN growth. A decrease of the surface roughness of the InGaN layers and an increase of their photoluminescence intensity per unit thickness at the transition from metal-flux limited to active nitrogen-limited growth is observed. High quality c-InGaN/GaN multi-quantum wells were grown with superlattice peaks clearly resolved in high resolution X-ray diffraction and a strong room temperature photoluminescence with a full width at half maximum of 240meV. Cubic-AlGaN/GaN distributed Bragg reflectors with a maximum reflectivity of about 50% at 515nm and a stop bandwidth of 33nm have been realized. Enhanced 526nm room temperature photoluminescence has been observed from a combined structure of a c-InGaN/GaN multi-quantum well and a c-AlGaN/GaN distributed Bragg reflector.

Optical coherence of planar microcavity emission

An analytical expression for the self-coherence function of a microcavity and a partially coherent source is derived. Excellent agreement is found between the model and the experimental measurements from two resonant-cavity light-emitting diodes. The variation of coherence length as a function of numerical aperture is examined and indicates that the variable coherence properties of planar microcavities are determined by the underlying coherences of the microcavity and the source. Furthermore, coherence-length variations approaching a factor of five can be achieved by engineering the cavity finesse.

Efficient light emitting diodes based on nanoscale silicon

After giving an overview about various approaches for silicon based light emitters, we will present our results on Si light emitting diodes prepared by high-dose boron implantation. The electroluminescence (EL) increases with temperature, resulting in a wall-plug efficiency of 0.1% at room temperature. Extensive low-temperature EL measurements allow us to put forward a model, which is based on the interplay between free excitons/carriers and excitons localized at nanoscale boron doping spikes. Finally, we demonstrate an electrically driven resonant-cavity LED based on silicon. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and properties of AlGaInP resonant cavity light emitting diodes on Ge∕SiGe∕Si substrates

Visible AlGaInP resonant cavity light emitting diodes (RCLEDs) were grown by molecular beam epitaxy and fabricated on low-dislocation density, SiGe∕Si metamorphic substrates. A comparison with identical devices grown on GaAs and Ge substrates shows that not only did the RCLED device structure successfully transfer to the SiGe∕Si substrate, but also a higher optical output power was obtained. This result is attributed to enhanced lateral current spreading by the low residual dislocation density (∼1×106cm−2) network within the virtual Ge substrate and the superior thermal conductivity of the underlying Si wafer. In addition, the growth of an AlGaAs current spreading layer and a modified top metal contact were incorporated in the RCLED on SiGe to optimize device performance. The measured electroluminescent output power was 166μW at a 665nm peak wavelength under 500mA current injection. Extremely narrow electroluminescence linewidths were achieved with a full width half maximum value of 3.63nm under 50mA current injection. These results demonstrate great promise for the monolithic integration of visible band optical sources with Si-based electronic circuitry.