Optical Degradation of InAs Quantum-Dot lasers on Silicon: Dependence on Temperature and on Diffusion Processes

This paper investigates the temperature dependence of the optical degradation of InAs quantum-dot (QD) lasers grown on silicon, and its relation with impurity diffusion processes. This goal was achieved by submitting a group of identical 1.3. m QD LDs on Si to a series of constant-current stress experiments at baseplate temperatures ranging from 15 degrees C to 75 degrees C. The analysis of the threshold current (I-th) kinetics revealed that the optical degradation process i) is not activated by temperature for junction temperatures (T-j) lower than 60 degrees C, ii) becomes temperature activated with E-a approximate to 0.6 eV up to 80 degrees C, iii) is further accelerated for higher operating temperatures, and iv) resembles a diffusion process, due to the squareroot dependence of the I-th variation on stress time. This peculiar temperature activation was explained in terms of a recombination-enhanced diffusion process, driven be the escape of carriers from the InAs QDs toward nearby semiconductor layers. This process, which is strongly inhibited at low/room temperature, becomes relevant only above a specific temperature threshold. In this condition escaped carriers can be captured by extended defects, where they recombine and release their excess energy non-radiatively. This energy release contributes to the generation of additional defects, and/or to the diffusion of impurities, whose physical origin could be preliminarily attributed to the p-dopant Be, or to the native defects limiting its diffusivity (V-Ga or Ga-I).