Effects of Zn doping on intermixing in InGaAs/AlGaAs laser diode structures

Impurity-free intermixing using spin-on-glass (SOG) capping layers was studied in undoped and Zn-doped laser diode structures using photoluminescence and C-V profiling. The doped laser structure was further processed into devices and the intermixed structures were characterized. Considerable Zn migration after annealing with Ga-doped SOG (cap layer that prevents intermixing in undoped samples) was observed, leading to degradation of device performance. The "thermal" intermixing is considerably larger in doped structures than in undoped structures. The device performance is not significantly affected only if the annealing step is made with no cap. Differential intermixing can still be achieved by etching the highly doped layers and afterward capping with an undoped SOG layer that injects vacancies. A laser-waveguide device was demonstrated using undoped SOG layers.