Mesa-type photodetectors with lateral diffusion junctions
View Patent ↗The present invention relates to a stable mesa-type photodetector with lateral diffusion junctions. The invention has found that without resorting to the complicated regrowth approach, a simple Zn diffusion process can be used to create high-quality semiconductor junction interfaces at the exposed critical surface or to terminate the narrow-bandgap photon absorption layers. The invention converts the epi material layers near or at the vicinity of the etched mesa trench or etched mesa steps into a different dopant type through impurity diffusion process. Preferably the diffused surfaces are treated with a subsequent surface passivation. This invention can be applied to both top-illuminating and bottom-illuminating configurations.
1. A mesa-type PIN photodiode comprising:
an epitaxial semiconductor layer structure including the following layers over a substrate: a buffer layer; an absorption layer; a grading layer; and a window layer;
a mesa structure, including a light input window to a diffused p-n junction in the window layer, the mesa defined by a trench through the epitaxial layers, the mesa having sidewalls in the trench, and the side walls including a diffusion margin of p-type material terminating the lateral extent of the epitaxial layers of the mesa wherein the diffused margin comprises a diffused lateral p-n junction for terminating the epitaxial layers;
a p-contact disposed for electrical contact to the p-n junction; and
an n-contact disposed for electrical contact to the p-n junction.
2. A mesa-type PIN photodiode as defined in claim 1 , wherein the diffused margin fully terminates the absorption layer, grading layer and window layer.
3. A mesa-type PIN photodiode as defined in claim 2 , wherein the diffused margin penetrates into the buffer layer.
4. A mesa-type PIN photodiode as defined in claim 1 , wherein the diffusion margin has a depth sufficient to eliminate the effects of sidewall defects caused by etching.
5. A mesa-type PIN photodiode as defined in claim 4 , wherein the diffusion margin is at least 0.2 microns to about 1 micron in depth.
6. A mesa-type PIN photodiode as defined in claim 1 further including a reflector for increasing the responsivity of the photodiode.
7. A mesa-type PIN photodiode as defined in claim 6 , wherein the photodiode is a top illuminated mesa-type PIN photodiode, and the reflector comprises a distributed Bragg reflector over the substrate.
8. A mesa-type PIN photodiode as defined in claim 6 , wherein the photodiode is a bottom illuminated mesa-type PIN photodiode, and the reflector comprises a metal or dielectric reflector on the window layer surface.
9. A mesa-type PIN photodiode as defined in claim 8 , wherein the bottom illuminated mesa-type PIN photodiode further includes a lens etched in the substrate to facilitate light coupling to the diffused p-n junction.
10. A mesa-type PIN photodiode as defined in claim 1 , wherein the epitaxial semiconductor layer structure is selected from the group consisting of the following materials:
the substrate comprises n+InP or Semi-Insulating InP; the buffer layer comprises n+InP or InGaAsP; the absorption layer comprises intrinsic InGaAs or InGaAsP; the grading layer comprises intrinsic InGaAsP and the window layer comprises n- or intrinsic InGaAsP or InP.
11. A mesa-type PIN photodiode as defined in claim 10 , wherein a dopant selected from the group consisting of: zinc, cadmium, carbon, magnesium, beryllium forms the diffused p-n junction and the diffusion margin.