Preferential Etching of InGaAsP/InP Using Low Temperature Bromine/Methanol for Planar Buried Heterostructure Lasers.

We have developed a novel low temperature etching process using bromine/methanol solution to fabricate mesa structures in InGaAsP/InP for planar buried heterostructure laser applications. We have studied the effect of etching temperature on geometry and mask undercutting. In particular, we have achieved a zero mask undercutting by reducing the etching temperature to below - 57C. Our new low temperature bromine/methanol etching technique permits the fabrications of mesas having a precise dimensional control to within +- 0.3microns. We have analyzed the etching process in terms of the diffusion and chemical reaction rates. AT high etching temperatures (above 25C), the etching process is isotropic because it is determined by diffusion; and this results in a rounded etching profile. As the etching solution temperature decreases, the chemical reaction rate becomes the rate limiting step and the etching profile has straight side walls with a planar bottom.