Pekko Sipilä

Uncooled 2.5 Gb/s operation of 1.3 μm GaInNAs DQW lasers over a wide temperature range

Ridge waveguide 1.3 mum GaInNAs lasers were fabricated from high quality double quantum well material grown by molecular beam epitaxy. Short cavity (250 mum) lasers have low threshold currents and small temperature dependencies of threshold current and slope efficiency, with a characteristic temperature of the threshold current as high as 200 K. The temperature stability allows for uncooled 2.5 Gb/s operation up to temperatures as high as 110 degrees C with a constant modulation voltage and only the bias current adjusted for constant average output power. Under these conditions, an extinction ratio larger than 6 dB and a spectral rms-width smaller than 2 nm are obtained.

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.

Temperature behaviour of resonant cavity light-emitting diodes at 650 nm

Performance characteristics of resonant cavity light-emitting diodes operating at the wavelength of 650 nm have been studied. It has been shown that a variation in device temperature significantly modifies the far-field pattern and thus the fibre coupling efficiency, due to a cavity detuning effect. Temperature dependences of output power and emission wavelength are also studied. Modulation bandwidth of >120 MHz and light power of 2 mW (cw) have been achieved for 84 µm devices driven at a 40 mA current. Accelerated ageing tests for 36 000 device hours indicate no degradation in output power.

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.

Reliability assessment and degradation analysis of 1.3 μm GaInNAs lasers

The degradation of 1.3 mu m GaInNAs lasers was investigated using accelerated aging tests. This was followed by comprehensive characterization, including standard light-current-voltage (L-I-V) characterization, capacitance measurements, photoluminescence microscopy (PLM), on-axis amplified spontaneous emission (ASE) spectra measurements, and photocurrent (PC) and electroluminescence (EL) spectroscopies. The slope efficiency of the device dropped by 50% with a 300% increase in the threshold current after the accelerated aging test. The ideality factors of the aged devices are higher than those of the unaged devices. PLM images showed no evidence of catastrophic optical mirror damage. The measured capacitances of the aged devices are all similar to those of the unaged devices, indicating that there was no significant dopant diffusion in the junction region. Fourier transforms of the ASE spectra showed that no intracavity defects were present in the aged lasers, suggesting that intracavity defects are not responsible for the rapid degradation of the aged devices. Although the PC measurements showed defects at 0.88-0.95 eV and at similar to 0.76 eV, these defect signatures did not increase with aging. On the other hand, EL measurements revealed that radiative deep level defects were generated during the aging tests. which may be related to the degradation of the devices. Based on the above measurement results, we identify, the generation Of radiative deep level defects as the main causes of degradation of these devices.

Growth of resonant cavity quantum well light emitting diodes and two-junction solar cells by solid source molecular beam epitaxy

Abstract Monolithic resonant cavity light emitting diodes (RCLEDs) for room temperature operation at 650–670 nm and 850–880 nm wavelengths and double-junction GaInP/GaAs solar cells have been designed and grown using a toxic-gas-free solid-source molecular beam epitaxy method. The presence of the microcavity in RCLEDs causes strong cavity enhancement, which can be utilized to modify natural spontaneous emission. These devices are shown to exhibit performance characteristics that are better than those of conventional LEDs in many ways. They may be suitable for optical fibre communications and interconnects where a relatively high speed, good fibre coupling efficiency, nearly monochromatic spectrum, and long-term reliability are desirable. The GaInP/GaAs cascade cells also reported in this paper are state-of-the-art, exhibiting conversion efficiencies up to 23.2% at one-sun air-mass-zero illumination. With so high efficiency and good radiation resistance, the cascade solar cells are potential candidates for solar power generation of satellites.

Uncooled 2.5 Gb/s Operation of 1.3 μm GaInNAs double quantum well lasers up to 110 °C

We demonstrate uncooled 2.5 Gb/s operation up to 110degC of 1.3 mum GaInNAs double quantum well lasers with low threshold current and excellent temperature stability.