The deep-level emission at 1.0 eV is analyzed to be associated with the slow degradation of GaAlAs DH laser diodes. The intensity of this deep-level emission increases at the same rate as the increase in the threshold current during the slow degradation. The carrier lifetime does not change correspondingly to the increase in the threshold current. This deep level is considered to act as the photon-absorption center to cause the increase in the threshold current.
The mechanism of asymmetric longitudinal mode competition in InGaAsP/InP lasers is discussed. It is shown that the asymmetric mode competition is not due to the spatial hole burning. When we assume that the energy relaxation time of electrons in the conduction band is ∼0.3 ps, we find that the asymmetric longitudinal mode competition is well explained by the model of Bogatov et al. for the external cavity laser. The asymmetric mode competition can be understood on the basis of the pulsation of the electron population at the beat frequency between two longitudinal modes of ∼1012 Hz. The long energy relaxation time may have relevance to the observed low characteristic temperature of the quaternary lasers.
The catastrophic degradation of GaAlAs DH laser diodes is examined with the application of pulsed or dc current. The dependence of the pulsewidth on the degradation is measured using samples with or without facet coating. The light output PD at which the catastrophic degradation occurs decreases with an increase in the pulsewidth in the pulsewidth range 100 nsec to 10–50 μsec, and PD is constant over the pulsewidth of 10–50 μsec. The sample with an Al2O3 film coating has the highest PD. Photoluminescence patterns of the active layer in degraded samples both with and without facet coating show the growth of DLD’s in the 〈110〉 direction from the vicinity of a facet in the stripe region.
Aging characteristics of Ga1−xAlxAs DH lasers bonded with gold eutectic alloy solder and indium solder were studied. In the lasers bonded with indium solder, it was found that thermal resistance increased during the aging test and the activation energy for the increasing rate of thermal resistance was 0.6 eV. Sixteen lasers bonded with gold-tin eutectic alloy solder have been operating at 70 °C over 1800 h with no increase in thermal resistance and a slight increase in the driving current required to maintain the cw optical power constant during the aging test; and lasers bonded with gold-germanium eutectic alloy solder have been operating at 70 °C over 10 000 hours with a slight increase in driving current. The use of gold eutectic alloy solder makes possible the long-lived lasers.
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