Starved source diffusion for avalanche photodiode

Abstract

Starved source diffusion methods for forming avalanche photodiodes (APDs) are provided for controlling the edge effect. The edge effect is controlled by reducing edge gain near the edges of an APD active region. This is accomplished by creating a sloped diffusion front near the edges of the active region. The sloped diffusion front is advantageously formed in a single doping step by using a patterned mask during doping. The patterned mask reduces the depth to which dopants diffuse in areas where it only partly covers the underlying layer. By covering more of the underlying layer nearer the edge and progressively less towards the center, the sloped diffusion front is formed. The shallower diffusion depth near the edge reduces the edge gain, and therefore the edge effect. As a result, an APD to fiber misalignment is less likely, and possibility of edge breakdown is greatly reduced.

Description

BACKGROUND OF THE INVENTION [0001] 1. The Field of the Invention [0002] The present invention relates to the field of optical communications. More particularly, the present invention relates to the field of avalanche photodiodes. [0003] 2. The Relevant Technology [0004] Computer and data communications networks continue to develop and expand due to declining costs, improved performance of computer and networking equipment, the remarkable growth of the internet, and the resulting increased demand for communication bandwidth. Such increased demand occurs within and between metropolitan areas as well as within communications networks. Moreover, as organizations have recognized the economic benefits of using communications networks, network applications such as electronic mail, voice and data transfer, host access, and shared and distributed databases are increasingly used as a means to increase user productivity. This increased demand, together with the growing number of distributed co...

AI Technical Summary

Benefits of technology

[0016] The present invention offers an improvement over the prior art by providing a simpler, more reliable method for controlling the edge effect in avalanche photodiodes (APDs). According to the invention, the edge effect is controlled by reducing edge gain near the edges of the active region. This is accomplished by creating a sloped diffusion front near the edges of the active region such that the distance between a diffusion region and the absorber layer below it is increased. This reduces the responsivity of the edge.

[0017] The sloped diffusion front is advantageously formed in a single doping step by using a patterned mask. The patterned mask only partly covers regions of the underlying avalanche region, which results in a lesser dopant diffusion in partly covered areas than in uncovered areas. As a result, the diffusion depth can be controlled as desired through pattern design, and a sloped diffusion front can thereby be formed in the region underlying the pattern.

[0018] Accordingly, a first example embodiment of the invention is a method for forming an avalanche photodiode. The method generally includes: forming at least an absorber layer and an avalanche layer over a substrate; forming a mask over a surface of the avalanche layer, the mask comprising a pattern; and depositing a dopant over the mask and the avalanche layer, wherein the dopant is blocked by the mask but diffuses into the avalanche layer in areas wherein the mask is not present, wherein the mask pattern gradually reduces the depth to which the dopant diffuses into the avalanche layer such that a sloped diffusion front is formed.

Problems solved by technology

This reduces the responsivity of the edge.

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