Photodiode and method of fabrication

A method of fabricating a photodiode comprising steps of:

• a) providing a substrate of semiconductor material;
• b) epitaxially growing a layer stack on a top surface of the substrate, wherein epitaxially growing the layer stack includes epitaxially growing a buffer layer of extrinsic semiconductor material of a first conductivity type, for accommodating lattice mismatch;
• c) epitaxially growing an absorption layer of intrinsic semiconductor material, for absorbing light to generate current carriers, on a top surface of the layer stack;
• d) epitaxially growing a grading layer of intrinsic semiconductor material, for facilitating current flow, on a top surface of the absorption layer;
• e) epitaxially growing a blocking layer of extrinsic semiconductor material of the first conductivity type, for inhibiting current flow, on a top surface of the grading layer;
• f) etching the blocking layer to expose a window region of the top surface of the grading layer, wherein the window region of the top surface of the grading layer is smaller in area than the top surface of the grading layer;
• g) epitaxially regrowing a window layer of extrinsic semiconductor material of a second conductivity type on a top surface of the blocking layer and on the window region of the top surface of the grading layer;
• and
• h) etching the window layer to form a window mesa, for transmitting light to the absorption layer, and to expose the top surface of the blocking layer with exception of a window region of the top surface of the blocking layer, wherein the window region of the top surface of the blocking layer is smaller in area than the top surface of the blocking layer, such that the window mesa is disposed only on the window region of the top surface of the blocking layer and on the window region of the top surface of the grading layer.