Seppo Orsila

Annealing of the deep recombination center in GaInP/AlGaInP quantum wells grown by solid-source molecular beam epitaxy

Time resolved photoluminescence and deep level transient spectroscopy have been used to monitor the effect of rapid thermal annealing on bulk GaInP and GaInP/AlGaInP quantum wells grown by solid source molecular beam epitaxy similar to those used in 650 nm range lasers. Following rapid thermal annealing at temperatures up to 875 °C, reductions in the concentration of several deep level traps are observed. Correlation of these data with photoluminescent intensity and lifetime measurements indicate that the defect labeled N3, 0.83 eV below the conduction band, is the dominant recombination center. The combination of these two transient spectroscopy measurement techniques is therefore not only able to measure the change in deep level concentration, but also to correlate this change with improved carrier lifetimes and, ultimately, reduced threshold current densities in quantum well lasers. There is also evidence to suggest that this same defect, possibly a phosphorous vacancy or a related complex, plays an im...

Influence of deep level impurities on modulation response of InGaP light emitting diodes

The effect of deep level impurities on static and dynamic properties of InGaP-based light emitters grown by all-solid-source molecular-beam epitaxy is analyzed. The improvement of the output power and the decrease in modulation bandwidth induced by the burn-in process are explained by the recombination enhanced annealing of one deep level trap. This assumption is experimentally proven through comparison of small-signal analysis for resonant cavity light-emitting diodes operating at 650 nm and deep level transient spectroscopy results. Finally, the concentration of the midgap recombination center N3 in the active region is shown to play an important role in the performance of the InGaP devices.

High-power 600-nm-range lasers grown by solid-source molecular beam epitaxy

This paper presents the performance characteristics and reliability data of AlGaInP-based VISIBLE laser diodes emitting at the wavelengths from 630 to 670 nm. The lasers are grown by toxic gas free solid source molecular beam epitaxy.

Resonant cavity light-emitting diodes at 660 and 880 nm

Abstract Resonant cavity light-emitting diodes (RCLEDs) operating at λ≅660 nm and λ≅880 nm have been fabricated and studied. The RCLED layer structures consisted of 1−λ thick cavities sandwiched between AlGaAs distributed Bragg reflectors. The cavities were detuned to improve temperature stability and light extraction. The temperature induced red-shifts in the peak emission wavelength were found to be 0.14 and 0.22 nm °C−1 for the 660- and 880-nm devices, respectively.

Modeling and optimization of resonant cavity light-emitting diodes grown by solid source molecular beam epitaxy

Abstract Monolithic top emitting resonant cavity light-emitting diodes (RC-LEDs) operating at 660 and 880 nm have been prepared using solid-source molecular beam epitaxy (SSMBE) growth. Transfer matrix based modelling together with a self-consistent model have been used to optimise the devices’ performances. Intermediate-composition barrier-reduction layers were introduced in the distributed Bragg reflector (DBR) mirrors for improving the I – V characteristics and the cavity and mirrors were detuned aiming at maximum extraction efficiency. The fabricated devices showed line widths below 15 nm, CW light power output of 8 and 22.5 mW, and wall-plug efficiencies of 3% and 14.1% in the 660 nm and 880 nm ranges, respectively, while the simulations indicate significant performance improvement possibilities.

HIGH-POWER EDGE EMITTING RED LASER DIODE OPTIMISATION USING OPTICAL SIMULATION

The laser diode structures reported up to now in literature for the red wavelength range are still far from optimal – mostly because many of the desired characteristics are contradictory coupled. Some of the contradictory coupled laser diode characteristics are investigated and a novel transverse layer structure is proposed. Both optical simulation and a fully self-consistent model are used in a design optimization methodology and simple evaluation and optimization criteria are derived. A number of the analyzed high-power edge-emitting GazIn1−zP/(AlxGa1−x)yIn1−yP/GaAs quantum well laser structures were prepared using all-solid-source molecular beam epitaxy for layer growth and remarkable performances were obtained (continuous wave output powers of 3 W at 670 nm, 2 W at 650 nm, and 1 W at 630 nm; threshold current densities of 350–450 A/cm2 for 670 nm, 500–540 A/cm2 for 650 nm, and less than 700 A/cm2 for 630 nm). The good agreement between measurements and simulations for the prepared structures indicate that significant performance improvements – predicted by the simulations – are still possible. The presented novel structure and design optimisation procedure can also be applied to laser diode structure optimisation in other emission ranges – like, for example, in the case of 800 nm-range edge emitting AlxGa1−xAsyP1−y/GazIn1−zAswP1−w/GaAs laser diodes.

Resonant-cavity LEDs at 655- and 880-nm wavelengths

Monolithic top-emitting resonant cavity light-emitting diodes (RCLEDs) have been fabricated by solid-source MBE. The RCLEDs in the 650-nm range, with modulation bandwidths exceeding 180 MHz, are possible low-cost transmitter candidates for systems using plastic optical fibers (POFs), such as IEEE-1394 at 100 Mb/s and 200 Mb/s and ATM at 155 Mb/s. Modulation bandwidth of greater than 120 MHz and light power of 2 mW (cw) have been achieved for (phi )84-micrometer devices driven at a 40 mA current. Accelerated aging tests for 27,500 device-hours indicate no degradation in output power. A variation in device temperature significantly modifies the far-field pattern and thus the fiber coupling efficiency, due to a cavity detuning effect. The effects of detuning and the temperature and bias dependencies of the devices are investigated. The 880-nm RCLEDs have a maximum output power of 25 mW. Applications include open-air optical communication systems, collision avoidance and measurement systems.

Transparent Perfect Mirror

A mirror that reflects light fully and yet is transparent appears paradoxical. Current so-called transparent or “one-way” mirrors are not perfectly reflective and thus can be distinguished from a standard mirror. Constructing a transparent “perfect” mirror has profound implications for security, privacy, and camouflage. However, such a hypothetical device cannot be implemented in a passive structure. We demonstrate here a transparent perfect mirror in a non-Hermitian configuration: an active optical cavity where a certain prelasing gain extinguishes Poynting’s vector at the device entrance. At this threshold, all vestiges of the cavity’s structural resonances are eliminated and the device presents spectrally flat unity-reflectivity, thus, becoming indistinguishable from a perfect mirror when probed optically across the gain bandwidth. Nevertheless, the device is rendered transparent by virtue of persisting amplified transmission resonances. We confirm these predictions in two photonic realizations: a comp...

Subthreshold carrier losses from GaInP quantum wells measured by time resolved photoluminescence

We report here on measurements of carrier loss processes in GaInP quantum wells made using time resolved photoluminescence spectroscopy. Measurements were made as a function of temperature and excitation intensity on quantum wells with different confinement barrier heights. The measurements reveal three distinct lifetime components identifiable by their activation energy and excitation intensity dependence. The lifetime components are assigned to thermionic emission of holes from the quantum well, nonradiative recombination at deep level defects, and radiative band-to-band recombination. The valence band offsets between GaInP and AlGaInP have been determined from the activation energy for thermionic emission of holes and are found to increase from 0.096 to 0.147 eV as the Al content in the waveguide layer increased from 50% to 70%. The relative contributions of the different carrier loss mechanisms to the subthreshold current of GaInP quantum well lasers is also discussed.

MBE growth of monolithic MgZnSSe/ZnSSE/CdZnSE microcavity led structures

The molecular beam epitaxy growth of green, monolithic, microcavity light-emitting diode structures is presented. The uniformity and controllability of the growth of vertical cavity structures is found to improve by using in situ reflectivity measurements and a rotating substrate. An electrical injection study for a microcavity light-emitting diode shows a narrow spectral width of 6 nm from a device at resonance.