Patent ID: 7282428

Claim:
A zinc solid phase diffusion method for an InP-based photodiode, for selectively diffusing zinc on an epitaxial wafer as a p-type impurity that forms a pn junction in an absorption layer, the epitaxial wafer having an n-type InP substrate on which at least an n-type InGaAs absorption layer made of or an n-type InGaAsP absorption layer is epitaxially grown, the zinc solid phase diffusion method comprising: forming on the epitaxial wafer a selective diffusion mask that has an upper layer made of a-Si; forming a ZnO thin film, which is a zinc source, over the selective diffusion mask; forming an SiO 2 film or an SiN film over the ZnO thin film to serve as a retaining film that prevents zinc from escaping upward; heating the epitaxial wafer and allowing zinc from the ZnO thin film to diffuse with solid phase diffusion until zinc reaches the absorption layer; removing the retaining film and the ZnO thin film using hydrofluoric acid or buffered hydrofluoric acid; allowing the selective diffusion mask having an upper layer made of a-Si to remain for protecting the pn junction.