Reliability of InGaAsP/InP buried heterostructure 1.3 micron lasers

The sudden degradation of 1.3-micron InGaAsP/InP buried-heterostructure laser chips after long stable operation is investigated, and improved manufacturing techniques are evaluated. The lasers manufactured and tested had CW threshold current = 30 mA at 25 C, differential quantum efficiency = 0.18 W/A, series resistance = 6 ohms, characteristic temperature 70 C between 20 and 70 C, cavity length 300 microns, and active-layer width and thickness 1.5-2.5 and 0.2-0.3 microns, respectively. Au-Sn or Pb-Sn (40 wt percent Pb) eutectic alloys were used to bond the lasers either p-side-up or p-side down to Cu, Si, or SiC submounts. Degradation is found to be associated with metallurgical reactions and Sn-whisker growth in the p-down, Au-Sn-soldered lasers, while p-up, Pb-Sn-soldered lasers are free of these problems, as confirmed in aging tests at 40, 50, and 60 C, 5 or 7 mW/facet output power, and up to 8000 h. The degradation rate of these improved lasers was about 3 percent/kh at 60 C. The mechanisms of the degradation are discussed in detail.