Li-Wen Laih

The carrier blocking effect on 850 nm InAlGaAs/AlGaAs vertical-cavity surface-emitting lasers

In this study, the carrier blocking effect on 850 nm InAlGaAs/AlGaAs vertical-cavity surface-emitting layers (VCSELs) was theoretically and experimentally investigated. By means of inserting a high-bandgap electron blocking layer, which was either 10 nm thick Al0.75Ga0.25As or 13 nm thick Al0.9Ga0.1As, on the p-side of a quantum-well active region, the laser output performance was theoretically found to be improved. VCSELs with and without an electron blocking layer were also experimentally demonstrated. It was found that the threshold current was reduced from 1.47 to 1.33 mA and the slope efficiency was increased from 0.37 to 0.53 mW mA −1 by inserting a 10 nm thick Al0.75Ga0.25As electron blocking layer. Also, the device became less sensitive to the device temperature, where the amount of increase in the threshold current at an elevated temperature of 95 ◦ Cw as only 0.27 mA and the slope efficiency dropped by only 24.5%. A peak frequency response of nearly 9 GHz at 5 mA, measured from relative intensity noise (RIN), was obtained in these VCSEL devices.

Fabrication and Characteristics of high-speed oxide-confined VCSELs using InGaAsP-InGaP strain-compensated MQWs

This paper presents the fabrication and characteristics of high-performance 850-nm InGaAsP-InGaP strain-compensated multiple-quantum-well (MQW) vertical-cavity surface-emitting lasers (VCSELs). The InGaAsP-InGaP MQWs composition was optimized through theoretical calculations, and the growth condition was optimized using photoluminescence. These VCSELs exhibit superior performance with characteristics threshold currents /spl sim/0.4 mA and slope efficiencies /spl sim/0.6 mW/mA. The threshold current change with temperature is less than 0.2 mA, and the slope efficiency drops less than /spl sim/30% when the substrate temperature is raised from room temperature to 85/spl deg/C. A high modulation bandwidth of 14.5 GHz and a modulation current efficiency factor of 11.6 GHz/(mA)/sup 1/2/ are demonstrated. The authors have accumulated life test data up to 1000 h at 70/spl deg/C/8 mA.

Efficiency Improvement of Single-Junction In0.5Ga0.5P Solar Cell with Compositional Grading p-Emitter/Window Capping Configuration

In this study a novel p-emitter/window capping configuration design applied to a p+–n In0.5Ga0.5P solar cell is developed. By grading the Ga and Al compositions in the interface between the p-In0.5Ga0.5P emitter and p-In0.5Al0.5P window layers, the output characteristics of the p+–n In0.5Ga0.5P solar cell are improved. It is found that the photoluminescence (PL) intensity is increased and the minority carrier lifetime obtained from room-temperature time-resolved (TR) PL measurement can be increased from 5.3 ns of the typical design to 7.0 ns, indicating that the application of compositional grading can improve crystal quality and the interface becomes smoother, thus reducing the nonradiative recombination losses. Both the short-circuit current and open-circuit voltage are increased correspondingly and the conversion efficiency is improved from 14.57% of the typical design to 15.32% of the new p-emitter/window configuration under one-sun air-mass 1.5 global illumination.

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

Fabrication and Characterization of Temperature Insensitive 660-nm Resonant-Cavity LEDs

InGaP/AlGaInP 660-nm resonant-cavity light-emitting diodes (RCLEDs) with stable temperature characteristics have been achieved by extending the resonant cavity length from one optical wavelength (1 lambda) to three optical wavelengths (3 lambda) and tripling the number of quantum wells. When the operation temperature increases from 25degC to 95degC, the degree of power variation at 20 mA is reduced from -2.1 dB to -0.6 dB for the conventional 1- lambda cavity RCLEDs and 3- lambda cavity RCLEDs, respectively. In order to interpret the temperature-dependent experimental results, advanced device simulation is applied to model the RCLEDs with different cavity designs. According to the numerical simulation results, we deduce that the stable temperature-dependent output performance should originate from the reduction of electron leakage current and thermally enhanced hole transport for the 3- lambda cavity AlGaInP RCLEDs.

High temperature stability 850-nm In0.15Al0.08Ga0.77As/Al0.3Ga0.7As vertical-cavity surface-emitting laser with single Al0.75Ga0.25As current blocking layer

In this paper, we employed a high bandgap Al0.75Ga0.25As layer acting as an electronic blocking layer in the upper In0.15Al0.08Ga0.77As/Al0.3Ga0.7As active region before the growth of p-type layers of 850-nm vertical-cavity surface-emitting lasers (VCSELs). A threshold current of 1.33 mA and slope efficiency of 0.53 W/A at 25°C were obtained, and the temperature dependent light output and voltage versus current (L–I–V) characteristics showed that the VCSELs with a high bandgap Al0.75Ga0.25As layer were more stable when the substrate temperature was in a range of 25–95°C. The threshold current increased with temperature up to 95°C was less than 21% and the slope efficiency dropped only 24.5%.

Fabrication of high speed and reliable 850nm oxide-confined VCSELs for 10Gb/s data communication

In this paper, we demonstrate high performance 850 nm InGaAsP/InGaP strain-compensated MQWs vertical-cavity surface-emitting lasers (VCSELs). These VCSELs exhibit superior performance with threshold currents of ~0.4 mA, and slope efficiencies of ~ 0.6 mW/mA. High modulation bandwidth of 14.5 GHz and modulation current efficiency factor of 11.6 GHz/(mA)1/2 are demonstrated. We have accumulated life test data up to 1000 hours at 70°C/8mA. In addition, we also report a high speed planarized 850nm oxide-implanted VCSELs process that does not require semi-insulating substrates, polyimide planarization process, or very small pad areas, therefore very promising in mass manufacture.

Growth and characterization of 850 nm InGaAsP/InGaP strain-compensated VCSELs by MOCVD

In this paper, we demonstrate the growth and characterization of 850 nm oxide-confined VCSELs utilizing In/sub 0.18/Ga/sub 0.82/P/sub 0.2//ln/sub 0.4/Ga/sub 0.6/P strain-compensated SC-MQWs by MOCVD. The VCSELs show very low threshold current good temperature performance, and high modulation response up to 12.5 Gb/s from 25C to 85C.

Enhancement of proton-implanted GaAs VCSEL performance by transparent overcoating

Deposition of thin metal film and ITO as transparent overcoating on proton-implanted GaAs VCSEL increases the laser output power by two-fold and the slope efficiency by five-fold, and also improves the kinks in L-I characteristics.