G. Beister

Novel passivation process for the mirror facets of Al-free active-region high-power semiconductor diode lasers

A novel process for the passivation of mirror facets of Al-free active-region high-power semiconductor diode lasers is presented. Designed for technological simplicity and minimum damage generated within the facet region, it combines laser bar cleaving in air with a two-step process consisting of 1) removal of thermodynamically unstable species and 2) facet sealing with a passivation layer. Impurity removal is achieved by irradiation with beams of atomic hydrogen, while zinc selenide is used as the passivating medium. The effectiveness of the process is demonstrated by operation of 808-nm GaAsP-active ridge-waveguide diode lasers at record optical powers of 500 mW for several thousand hours limited only by bulk degradation.

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.

Effect of growth interruption on performance of AlGaAs/InGaAs/GaAs quantum well lasers

Abstract The effect of a growth interruption at the interfaces of the AlGaAs/InGaAs/GaAs quantum well (QW) in the active region of metalorganic vapour phase epitaxy (MOVPE) grown 980 nm laser diodes has been studied. Characterization of the layer structures by photoluminescence, photoluminescence decay and cathodoluminescence shows the necessity for a growth interruption of 10–20 s. This is consistent with the results obtained on broad area lasers that show very low threshold current densities and internal losses for such interruption times.

Stability of sulfur-passivated facets of InGaAs-AlGaAs laser diodes

The facets of GaAs-AlGaAs ridge waveguide (RW) laser diodes were passivated using (NH/sub 4/)/sub 2/S/sub x/. The effectiveness of this procedure was checked by electroluminescence power-voltage-current (P-V-I) measurements that provide information on the changes in the density of surface states. Using this nondestructive method, the degradation of the passivation under ambient atmosphere has been studied. Capping with silicon nitride is found to stabilize the sulfur passivation and avoid degradation.

Reliable 1-W CW operation of high-brightness tapered diode lasers at 735 nm

The long-term stability of high-brightness diode lasers at 735 nm was investigated. The diodes consist of an index-guided straight section and a gain-guided tapered section. A 1-W continuous-wave operation for 2-mm-long tapered lasers over 3200 h is reported. The experiments demonstrate high reliability with degradation rates below 3.2/spl times/10/sup -5/ h/sup -1/.

Beam quality of high power 800 nm broad-area laser diodes with 1 and 2 μm large optical cavity structures

Abstract The beam quality of 800 nm AlGaAs/GaAsP broad-area (BA) laser diodes with large optical cavity (LOC) waveguide structures was studied under high power conditions. The LOC structures consist of a tensile-strained GaAsP single quantum well embedded in AlGaAs layers forming 1 and 2 μm thick waveguide cores. A low beam divergence of 51° respectively 46° (full width at 1/ e 2 maximum) is obtained in fast axis direction. BA diode lasers with 2 mm cavity length and stripe widths of 60, 100 and 200 μm show beam quality factors M 2 along the slow axis of about 12, 16 and 35 at 2 W output power, respectively. M 2 also weakly depends upon the waveguide width and is slightly smaller for the 2 μm waveguide core if the stripe width is less than 100 μm .

Tensile-strained GaAsP-AlGaAs laser diodes for reliable 1.2-W continuous-wave operation at 735 nm

Tensile-strained GaAsP quantum wells embedded in AlGaAs large optical cavity structure were investigated at an emission wavelength of 735 nm. 1.2-W continuous-wave operation for 100-/spl mu/m stripe width diode lasers over 1000 h is reported. Experiments with different stripe widths showed a high stability at an output power of 12-mW//spl mu/m stripe widths with degradation rates below 5/spl middot/10/sup -5/ h/sup -1/, i.e., lifetimes larger than 5000 h could be expected.

Interface reactions in LPE grown InGaAsP/InP ridge waveguide laser diodes during aging ?

Aging experiments on ridge waveguide (RW) InGaAsP/InP laser diodes at elevated temperatures have been combined with observations of the injected carrier balance inside the laser structure. Measurements of the spontaneous emission intensity (P) and a.c. cut-off frequency (ƒc) as a function of the injection level (current and applied voltage) indicate a minority carrier lifetime decrease after the stress tests. Additionally, the spectral analysis of P provides information on barrier leakage current enhancement. Probably the degradation of P is caused by interface reactions.