Juergen Maege

Mounting of high power laser diodes on boron nitride heat sinks using an optimized Au/Sn metallurgy

High power diode lasers have become more and more important to industrial and medical applications. In contrast to low power applications, long cavity lasers or laser bars are used in this field and mounting quality influences considerably laser performance and life time. In this paper we focus on the solder metallurgy and stress-induced laser behavior after mounting. The laser chips have been bonded fluxless epi-side down on translucent cubic boron nitride (T-cBN) using Au/Sn solder. The laser behavior has been tested with different chip metallizations preserving the eutectic solder composition or forming the Au rich /spl zeta/-phase during reflow. The resulting additional stress in the lasing region has been independently indicated by polarization measurements of the emitted light. A metallization scheme has been developed which forms the highly melting /spl zeta/-phase during soldering within a wide process window. This procedure yields better results then using eutectic Au/Sn which has a higher hardness than the /spl zeta/-phase. Laser diodes up to a cavity length of 2000 /spl mu/m and an aperture of 200 /spl mu/m have successfully been mounted on T-cBN. State of the art laser data, excellent thermal stability, high yield and reliability have been obtained.

Defect recognition via longitudinal mode analysis of high power fundamental mode and broad area edge emitting laser diodes

A nondestructive method is presented which allows a precise detection of defects and their positions inside the cavity of semiconductor lasers. The defect recognition is based on the measurement of the longitudinal mode spectrum below threshold and the inspection of its Fourier transformation. Using a theoretical model, it is shown that a small distortion inside the cavity leads to a peak in the Fourier transformed spectrum from which the position of the distortion relative to the facets can be determined. For a ridge waveguide laser we find a direct correlation between defects identified by the analysis of the longitudinal mode spectrum and cathodoluminescence imaging. The applicability of this method for nondestructive defect recognition will also be demonstrated for broad area laser diodes with lateral multimode emission. The investigations reveal that the presented method can be used to assess the crystal quality of manufactured laser diodes.

Simple method for examining sulphur passivation of facets in InGaAs–AlGaAs (λ=0.98 μm) laser diodes

The effect of (NH4)2Sx treatment of the facet of InGaAs/AlGaAs ridge waveguide (RW) laser diodes on the nonradiative current and catastrophic optical damage (COD) level is reported. Using the power–voltage–current (P–V–I) characteristics of the electroluminescence at low injection levels, changes in the density of surface states at the laser facets are described.

Diode lasers with Al-free quantum wells embedded in LOC AlGaAs waveguides between 715 nm and 840 nm

In this paper, we present results on diode lasers in the wavelength range between 715 nm and 840 nm with Al-free QWs which are embedded in a high-quality AlGaAs LOC broadened waveguide structure with low optical loss and a small vertical far field divergence. The laser structures were grown by LP- MOVPE. We studied tensile-strained GaAsP-QWs as well as compressively strained InGaAsP-QWs with strain compensating barriers. For lasers with GaAsP QWs, the lowest transparency current densities of about 130 A/cm2 were obtained in the wavelength range between 750 nm and 800 nm. Very low transparency current densities were achieved with InGaAsP-QWs at wavelengths above 800 nm. At 810 nm, high output powers (100 micrometer aperture) of about 7 W was achieved with both types of QWs from devices mounted epi up. However, with respect to high temperature operation and reliability tensile- strained GaAsP QWs seem to be the better choice, especially for the wavelength range below 760 nm.

Study of strained-layer InGaAs/GaAs SQW RW lasers including analysis of internal coupling of modes and antiguiding effects

Low threshold strained-layer InGaAs/GaAs single quantum well (SQW) lasers are studied experimentally and analyzed on the basis of a computer model for the ridge-waveguide structure. The transition from the index guiding to the gain guiding is occurring with power anomalies provided by the antiguiding contribution of excess carriers. The mode gain is found to have a maximum attainable in the index-guided mode and a negative slope range in the dependence on the carrier concentration. If the operation point reaches the gain maximum the laser action can be ceased in the index-guided mode with power drop to the spontaneous level (lasing collapse) or to lower level of an antiguided mode. Mechanisms of the mode gain decrease are considered caused by a breakdown of the lateral index guiding and by an internal coupling of modes inside the diode chip, particularly of laser mode to cap layer mode. Latter has resonances at a phase synchronism of both modes accompanied a strong drop of the mode gain.

Al-free 950-nm BA diode lasers with high efficiency and reliability at 50° C ambient temperature

We report device properties and results of lifetime tests for Al-free InGaAs/InGaAsP/InGaP broad-area (BA) laser diodes, emitting at 950 nm. The epitaxial layers were grown by metal organic vapor phase epitaxy (MOVPE). The mounted diode lasers have a high wallplug efficiency around 60%, for a resonator length of 2 mm, and about 50% for 4 mm long devices due to low threshold current densities of jth equals 110 . . . 140 A/cm2, high slope efficiencies of 75% and the typical low series resistance of the Al-free material. The lasers were mounted on copper heatsinks, episide-down as well as episide- up. Lifetime tests were performed with a facet load of 15 mW/micrometers at temperatures between 25 degrees Celsius and 70 degrees Celsius and with a facet load of 20 mW/micrometers at 25 degrees Celsius. All diodes survived 3000 h with degradation rates lower than 6 X 10-5h-1 at 50 degrees Celsius and 1 X 10-4h-1 at 70 degrees Celsius as well as 2000 h with a low degradation rates of 2 X 10-5h-1 at 20 mW/micrometer. As far we know, the results belong to the best ones reported until now for Al-free BA laser diodes.