Selective wet etching of InGaAs∕InGaAsP in HCl∕HF∕CrO3 solution: Application to vertical taper structures in integrated optoelectronic devices

The etching characteristics of In0.53Ga0.47As and In0.72Ga0.28As0.6P0.4, which are lattice matched to the InP substrate, in HCl∕HF∕CrO3 solution were studied by using the dynamic etch mask technique. For the solution with HCl∕HF∕CrO3 volume ratio of x: 0.5: 1, the etching selectivity decreases from 42.4 to 1.5 for In0.53Ga0.47As∕In0.72Ga0.28As0.6P0.4 with HCl∕CrO3 volume ratio x increasing from 0 to 1.0. The selective etching was experimentally applied to the fabrication of vertical taper structures with angles ranging from 1.35° to 33.7° on the In0.72Ga0.28As0.6P0.4 epitaxial layer, and surface roughness of the etched taper was <1.6nm. The etching behavior can be explained in a combined electroless and chemical etching mechanism.