Claims
- 1. An improved infrared detector comprising at least one unit comprising a thin single crystal metal silicide layer sandwiched between two single crystal silicon layers, each doped to a first doping level, each said silicon layer forming an interface with said silicide layer, the improvement comprising that portion of each said silicon layer adjacent said interface having a second doping level higher than that of said first doping level, thereby forming a reduced Schottky barrier.
- 2. The detector of claim 1 wherein said metal silicide layer is selected from the group of metal silicides that may be epitaxially grown on silicon, thereby forming a heteroepitaxial interface with said silicon.
- 3. The detector of claim 2 comprising a plurality of said units to form repeated Schottky barriers.
- 4. The detector of claim 2 wherein said metal silicide is selected from the group consisting of CoSi.sub.2 and NiSi.sub.2.
- 5. The detector of claim 1 wherein said metal silicide has a thickness ranging up to about 10 nm.
- 6. An improved infrared detector comprising a plurality of stacked metal silicide layers, each silicide layer sandwiched between two silicon layers, each doped to a first doping level, each said silicon layer forming an interface with an adjacent metal silicide layer to form repeated p-type Schottky barriers, the improvement comprising that portion of each said silicon layer adjacent said interface having a doping level higher than that of said first doping level, thereby providing a reduced effective barrier height.
- 7. The detector of claim 6 wherein said metal silicide is selected from the group consisting of metal silicides that may be epitaxially grown on silicon.
- 8. The detector of claim 7 wherein lateral contacts are provided to a plurality of layers by providing common n.sup.+ contacting regions to the metal silicides and common p.sup.+ contacting regions to the interleafing p-silicon layers.
- 9. The detector of claim 8 wherein said metal silicide is selected from the group consisting of CoSi.sub.2 and NiSi.sub.2.
- 10. The detector of claim 7 wherein said metal silicide has a thickness ranging up to about 10 nm.
ORIGIN OF INVENTION
The invention described herein was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law 96-517 (35 U.S.C. 202) in which the Contractor has elected to retain title.
This invention relates to infrared detectors, and, more particularly, to an infrared detector useful in the mid-wavelength (MWIR) to long-wavelength (LWIR) infrared region, from a few to several micrometers.
Large infrared focal plane detector arrays have been developed (by industry) using Pt-silicide/silicon Schottky barriers as detector elements. These detector structures are compatible with silicon technology, allowing large monolithic detector arrays to be fabricated with extensive on-chip data processing. This major advantage is offset, however, by the marginal performance of the Schottky barrier detector elements, which are limited by their inherently low quantum efficiency (.apprxeq.1%). In addition, these detectors are limited by their Schottky barrier heights to cut-off wavelengths of not more than a few micrometers. Because of these limitations, alternate detector materials (e.g. HgCdTe), which require the use of hybrid technology, are being developed for longer wavelengths. However, such hybrid technology involves complex interconnections, which adversely impacts on device yield.
Accordingly, it is desired to extend the range of detectors compatible with monolithic silicon technology into the mid- to long-wavelength infrared region.
U.S. Pat. No. 4,544,939 by Kosonocky and Elabd offers some extension to longer wavelength response of Schottky barrier detectors by implanting a high concentration of dopant impurities in the Schottky barrier contact region of the semiconductor. An improved doping profile is incorporated in an embodiment of this invention.
It is also known according to V.L. Dalal, J. Appl. Phys., Vol. 42, pp. 2274-2279 (1971) that enhancement of internal photoemission occurs in very thin metal films of Schottky contacts if the thickness is less than the mean-free-path of the photoexcited carriers. Unfortunately, the absorption of light is reduced in such thin layers, thus reducing the total quantum efficiency of the detector. The present invention overcomes this limitation by incorporating multiple metal layers in a stacked configuration of Schottky barriers.
In accordance with the invention, a stacked configuration of silicide/silicon Schottky-barrier-type structures is provided for infrared detector arrays which: (1) is compatible with monolithic silicon technology; (2) can be tailored for mid- to long-wavelength response (e.g., >5 .mu.m); and (3) provides high quantum efficiency (e.g., >10%).
The stack configuration comprises a plurality of stacked silicon/metal silicide layers to form repeated Schottky barriers to increase the total absorption and thus the quantum efficiency. The metal silicide layers are made very thin to achieve optimum quantum efficiency per layer. The silicon layers are selectively doped, as with a doping spike, in the vicinity of the silicon/silicide Schottky barrier to alter the Schottky barrier sufficiently to permit tunneling of holes into silicon at energies below the barrier height. This lower energy results in an increased cut-off wavelength, thus extending the wavelength response to longer wavelengths.
US Referenced Citations (6)
| Number |
Name |
Date |
Kind |
|
4137545 |
Becke et al. |
Jan 1979 |
|
|
4244750 |
Chenevas Paule et al. |
Jan 1981 |
|
|
4492971 |
Bean et al. |
Jan 1985 |
|
|
4544939 |
Kosonocky et al. |
Oct 1985 |
|
|
4742017 |
Bredthauer |
May 1988 |
|
|
4794438 |
Levinson et al. |
Dec 1988 |
|
Non-Patent Literature Citations (2)
| Entry |
| Dohler, Scientific American, Nov. 1983 pp. 144-151, "Semiconductor Superlattices". |
| Dalal, Jour. of Appl. Phys. vol. 42 No. 3 May 1971, pp. 2274-2279 "Simple Model for Internal Photoemission". |
Patent Grant
4908686
