Optimizing HBr-Br2-H2O etchants to form low defect regrowth interfaces for highly reliable InGaAsP/InP buried-heterostructure lasers

We have obtained a tenfold improvement in the reliability of InGaAsP/InP buried heterostructure laser diodes having a dry-etched mesa structure by optimizing the composition of a HBr-Br2-H2O etchant to produce smooth mesa sidewalls, thus reducing the number of defects at regrowth interfaces. The optimal etchant, which has a composition in the range from 0.30 M HBr/0.022 M Br2 to 0.50 M HBr/0.020 M Br2, etches both the InP(110) cladding layers and the TnGaAsP(110) multi-quantum-well active layer at the same rate. We propose a simple model of the HBr-Br2-H2O etching process that is consistent with the observed etching characteristics. We found that the etching rate was controlled by the diffusion of Br2 molecules, which act as oxidizing agents.