Implantation isolation in AlGaAs/GaAs structures

Abstract: In this work the effect of implantation isolation in vertical cavity surface emitting laser (VCSEL) samples have been investigated cross sectional measurements using scanning spreading resistance microscopy (SSRM). The samples consist of two AlGaAs/GaAs Distributed Bragg Reflectors (DBR) structures with a GaAs quantum well region sandwiched in between them. The samples were implanted with 330 and 660 keV helium ions using doses from 7'1013 cm-2 to 1'1016 cm-2. Due to variations and uncertainties in the SSRM output quantitative values of resistivity in the highly resistive regions created by ion implantations were not attained. Relative differences, however, were notable for the different doses. It was found that the resistive regions were not located as deep inside the samples for the 660 keV implantations as for the 330 keV. This does not agree with the simulations performed. A correlation between implantation dose and the depth of the resistive region created was also found - higher doses caused resistive regions deeper inside the samples. Furthermore, as the implantation dose is increased the resistive region is confined to only about one AlGaAs/GaAs period of width at the same depth as the wide resistive region for lower doses, i.e. the structure is somehow regaining its conductive properties in the shallow areas only leaving a thin stripe of the resistive region at the deepest end for higher implantation doses. Samples implanted with low He doses were heated in a vacuum furnace at 300, 350 and 380 ˚C. The heated samples showed a tendency to regain the conductivity in the resistive region, similar to the samples implanted with high doses. This suggests that there may be some kind of annealing effect for higher doses, possibly due to the increased flux for higher doses.