Degradation study in SCH-SQW GaAs/AlGaAs lasers

GaAs/AlGaAs SCH-SQW laser diode structures grown by MBE were investigated. The structures had waveguide and cladding bulk layers replaced with GaAs/AlGaAs superlattices (SLs). Accelerated ageing tests were applied to the laser diodes. Some lasers showed stable operation during 3000h, others demonstrated fast degradation as observed by measuring the output optical power. The degradation of lasers was also studied by I–V curve analysis. The presence of defects was examined by means of DLTS. DX and other defects have been revealed by the DLTS spectra. In lasers which showed rapid degradation a deep trap at EC−0.63 eV was observed in much higher concentration comparing with the concentration of the trap in the reference samples. On the basis of its emission characteristics the trap is interpreted as a complex involving point defect and oxygen. Its enhanced concentration can be due to trapping of oxygen at the ‘inverted interface’. For comparison, the trap concentration in GRIN-SCH-SQW GaAs/AlGaAs lasers studied was lower an order of magnitude. In the latter case the SLs were not embedded in the layers and lasers did not exhibit the rapid degradation. In spite that the mechanism for degradation is not clear, a marked correlation between an increase in the concentration of the deep level at EC−0.63 eV and degradation of lasers suggests that this level can limit the performance of the optoelectronic devices.