Lateral trench optical detectors

Details Lateral trench optical detectors Lateral trench optical detectors

1998-12-04

2001-01-23

Niebling, John F. (Department: 2812)

Semiconductor device manufacturing: process

With measuring or testing

Optical characteristic sensed

C438S243000, C438S244000, C438S245000, C438S386000, C438S387000, C438S388000

Reexamination Certificate

active

06177289

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to optical detectors, and more particularly, to high bandwidth monolithic optical detectors formed on a semiconductor opto-electronic integrated circuit.
2. Description of the Related Art
The increasing use of fiber optic computer communications has created a need for inexpensive high speed optical receivers. In particular, receivers using opto-electronic integrated circuit (OEIC) techniques in which the photo diodes are fabricated on the same chip as the electronic circuitry are desirable because of the resulting reduction in packaging and testing costs. At wavelengths less than about 870 nanometers (nm) metal-semiconductor-metal photo detectors can be formed on a substrate along with GaAs MESFET circuitry.
It is also desirable to form such detectors on a silicon substrate in order to take advantage of the lower manufacturing costs associated with silicon fabrication. However, the long optical absorption length for silicon at wavelengths of about 850 nm is prohibitive. This absorption length, which is about 12 &mgr;m, requires relatively thick layers of high resistivity silicon to absorb an appreciable amount of incident light. Unfortunately, such thick layers are not available in the device portion of standard silicon integrated circuit processes. Further, the long absorption length also leads to long transit times for electrons and holes to move through these layers, thereby limiting the frequency response of prior art silicon detectors.
Accordingly, there remains a need for an optical detector design which is compatible with current silicon manufacturing technology and offers sufficient bandwidth to be useful in high speed optical communications applications.
SUMMARY OF THE INVENTION
In accordance with one form of the present invention, a monolithic semiconductor optical detector is formed on a semiconductor substrate having a plurality of trenches etched therein. The trenches are formed as a plurality of alternating N-type and P-type trench regions separated by a pillar region of the substrate. A first contact connects the N-type trench regions and a second contact connects the P-type trench regions.
To establish the N-type and P-type trench regions, a layer of amorphous silicon is deposited in the trenches of the substrate. The N-type trench regions are then formed by infusing N-type semiconductor impurities into the amorphous silicon and the P-type trench regions are formed by infusing P-type semiconductor impurities into the amorphous silicon.
The trenches preferably have a depth which is comparable to an optical extinction length of optical radiation to which the detector is responsive to. Preferably, the monolithic semiconductor optical detector is responsive to radiation of about 850 nanometers (nm) and the depth of the trenches is in the range of about 10-15 micrometers (&mgr;m).
In accordance with a method of the present invention, an optical detector is formed on a semiconductor substrate by the steps of: forming a plurality of trenches on the substrate; forming alternating N-type and P-type regions in alternate trenches, respectively; forming a contact layer over said regions; forming a first contact connecting the N-type regions; and forming a second contact connecting the P-type regions.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.


REFERENCES:
patent: 5627092 (1997-05-01), Alsmeier et al.
Rong-Heng Yuang et al., “Overall Performance Improvement in GaAs MSM Photodetectors by Using Recessed-Cathode Structure”, IEEE Photonics Technology Letters, vol. 9, No. 2, Feb. 1997.
Jacob Y.L. Ho and K.S. Wong, “Bandwidth Enhancement in Silicon Metal-Semiconductor-Metal Photodetector by Trench Formation”, IEEE Photonics Technology Letters, vol. 8, No. 8, Aug. 1996.

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