No abstract

In InGaAsP/InP buried heterostructure lasers, a failure mode connected to the active region, not to the burying region, is observed. The degradation is related to a decrease in the carrier lifetime or a decrease in nonradiative lifetime due to degradations at the edges of the active region. Practically, the bad devices may be screened out by the hard screening method, however, the failure mode could determine the reliability of the devices under high-temperature or high-power operation, so care should be taken during forming the mesa and a regrowth of the burying layer.

Numerical analyses of the three dimensional thermal problem of double-heterostructure lasers were carried out. In particular, a multi-layered structure composed of nonuniform materials was treated, and the local heating arising at the tiny solder voids was investigated in detail. The allowable void size at which the local heating is suppressed below 10% of the uniform temperature rise was determined to be less than 4 µm × 4 µm. The complicated temperature distribution on the mirror facet obtained numerically was compared with the experimental result, showing good agreement. The observed nonuniform temperature distribution along the stripe was correlated with the lasing characteristics, e.g., a large threshold current increase at cw operation and the rapid degradation.

The buried-heterostructure, in which the quaternary active layer is completely surrounded by InP crystal, has been realized in 1.5 µm region by low temperature liquid phase epitaxial growth. Low threshold current of 25 mA under CW operation was achieved at 26°C. This is the lowest value so far reported on the InP/GaInAsP laser in 1.5 µm wavelength region.

Degradation modes due to dark defects under accelerated aging for InGaAsP/InP double heterostructure lasers are investigated by monitoring pulse threshold current, leak current, absorption coefficient, gain factor, and electroluminescence topograph. Most of the dark defects are dark spot defects (DSD’s) and there are only few 〈100〉 dark line defects. At the initial stage of the degradation, these dark defects scarcely absorb the emitted light, and the reduction of gain factor causes the increase of pulse threshold current. After this stage, dark defects begin to act as absorber of the emitted light. The generation time of such DSD’s strongly depends on the injected current density but only weakly on the junction temperature in the range of 25 ° to 250 °C. The activation energies for the generation time of the first dark spot defect and the growing speed of 〈100〉 dark line defects are estimated to be 0.16 and 0.2 eV, respectively.