The present invention provides a highly reliable photodiode, as well as a simple method of fabricating such a photodiode. During fabrication of the photodiode, a grading layer is epitaxially grown on a top surface of an absorption layer, and a blocking layer, for inhibiting current flow, is epitaxially grown on a top surface of the grading layer. The blocking layer is then etched to expose a window region of the top surface of the grading layer. Thus, the etched blocking layer defines an active region of the absorption layer. A window layer is epitaxially regrown on a top surface of the blocking layer and on the window region of the top surface of the grading layer, and is then etched to form a window mesa.