Transmission electron microscopy characterization of Au/Pt/Ti/Pt/GaAs ohmic contacts for high power GaAs/InGaAs semiconductor lasers

摘要

We report on transmission electron microscopy studies of Au/Pt/Ti/Pt( 10-30 nm) contact structures for high power GaAs/InGaAs semiconductor lasers. The studies showed that annealing at 450degC of contact structures causes the reaction of whole Pt with substrate components (Ga and As) and the formation of Pt-GaAs interlayers with smooth interfaces as required for such structures. Annealing of the structures at 470 and 490degC unfavourably affects the contact structure. At this condition, the strong downward diffusion of Au and Pt from the top layers causes a formation of Au-Pt pits, which break the Ti barrier. Transmission electron microscopy observation revealed that Au/Pt/Ti/Pt( 10-30 nm) system annealed at 450degC is appropriate for practical applications. The EDS technique used to identify the phase composition in the Pt(30nm)/GaAs structure (specially produced for the EDS analysis) annealed at 450degC showed that two layers were formed as a result of the reaction of the whole Pt layer with GaAs, and they consist of Ga, Pt and As. The top layer has the highest concentration of Ga. However, the bottom layer, which is close to the substrate, has the highest concentration of As.