F. Kohler

Low-resistance InGa(Al)As Tunnel Junctions for Long Wavelength Vertical-cavity Surface-emitting Lasers

A new method is proposed for a significant reduction of series resistance and device heating in long wavelength vertical-cavity surface-emitting lasers (VCSELs) based on InP. Our technique involves a twofold epitaxial growth with a buried low-resistance (3×10-6 Ωcm2) tunnel junction. The substitution of high-resistive p-type confining layers by low-resistive n-type material results in total resistances smaller 100 Ω even for the case of non-conducting dielectric mirrors. With the application of buried tunnel junctions in a VCSEL-structure, we could demonstrate small electrical series resistance (U < 1 V at 3 kAcm-2) and effective current confinement simultaneously. Furthermore, because of the laterally varying cavity length, an effective lateral waveguiding effect occurs.

Laser hygrometer using a vertical-cavity surface-emitting laser (VCSEL) with an emission wavelength of 1.84 /spl mu/m

This paper presents a hygrometer setup for measuring the concentration of water vapor in air by means of infrared absorption spectroscopy. Recently developed vertical-cavity surface-emitting lasers (VCSELs) emitting near 1.84 /spl mu/m are used as source of the infrared light. The laser hygrometer is able to calculate the density of water molecules from the measurement of one single light-current characteristic, without any additional reference measurement. The absolute and relative humidity are calculated from the water molecule density and the temperature of the ambient air.

80/spl deg/C continuous-wave operation of 2.01-/spl mu/m wavelength InGaAlAs-InP vertical-cavity surface-emitting lasers

Electrically pumped buried tunnel junction InGaAlAs-InP vertical-cavity surface-emitting lasers (VCSELs) with self-adjusted lateral current and optical confinement and record emission wavelengths beyond 2 /spl mu/m are presented. Front and back side mirrors are realized using 31.5 epitaxial layer pairs of alternating InGaAs-InAlAs and a dielectric 2.5 pair CaF/sub 2/-a-Si layer stack. The devices show single-mode continuous-wave operation up to heat sink temperatures over 80/spl deg/C. The maximum output power at 20/spl deg/C reaches 0.43 mW, threshold current and voltage are as low as 0.66 mA and 0.73 V, respectively. To reach the long emission wavelength, we use an optimized active region comprising heavily strained quantum wells. High-resolution X-ray diffraction and photoluminescence measurements reveal excellent material quality without relaxation in the quantum wells.

Long-Wavelength Buried-Tunnel-Junction Vertical-Cavity Surface-Emitting Lasers

High-performance InP-based Vertical-Cavity Surface-Emitting Lasers for the 1.45–1.85 μm wavelength range have been fabricated applying the buried-tunnel-junction structure on the InGaAlAs-InP material system. With this technique very small thermal and electrical resistances can be achieved enabling the continuous-wave operation up to 90° C. Record stationary parameters have been demonstrated, such as sub-mA threshold currents, low electrical resistances of 30–60 Ω for 5–10 μm diameter, 0.9 V threshold voltage at 1.55 μm wavelength and stably polarized single-mode operation with side-mode suppression of the order of 50 dB.

Thermal Conductivity Analysis and Device Performance of 1.55 μm InGaAlAs/InP Buried Tunnel Junction VCSELs

The thermal resistance of InGaAlAs/InP long-wavelength VCSELs with buried tunnel junctions is investigated by means of a heat flow finite element analysis. Because of the low thermal conductivity of InP based compound layers, a significant improvement is obtained for a top-down mounted structure with a hybrid dielectric-metal back mirror and an InP heat spreading layer. Experimental results for such lasers show cw operation up to 75 °C with a maximum power exceeding 2 mW at room temperature for 17 μm diameter. The temperature behavior of the threshold current indicates a substantial improvement for laser operation at values even far beyond room temperature by adjusting cavity mode and spectral gain.