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Article comprising a Si-based photodetector
| Details |
Inventors: Levine, Barry F.;
Assignee: Lucent Technologies Inc. (Murray Hill, NJ)
Primary Examiner: Tran; Minhloan
Assistant Examiner:
Attorney, Agent or Firm: Pacher; Eugen E.
Si-based photodetectors according to the invention can have high speed (e.g.,.gtoreq.1 Gb/s) and high efficiency (e.g.,>20%). The detectors include a relatively thin (e.g.,<0.5.alpha..sup.-1, where .alpha..sup.-1 is the absorption length in Si of the relevant radiation) crystalline Si layer on a dielectric (typically SiO.sub.2) layer, with appropriate contacts on the Si layer. Significantly, the surface of the Si layer is textured such that the radiation that is incident on the surface and transmitted into the Si layer has substantially random direction. The randomization of the propagation direction results in substantial trapping of the radiation in the Si layer, with attendant increased effective propagation length in the Si. Detectors according to the invention advantageously are integrated with the associated circuitry on a Si chip, typically forming an array of detectors. |
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DETAILED DESCRIPTION In a general aspect the invention is embodied in an article comprising an improved Si-based photodetector.
More specifically, the photodetector comprises a crystalline Si (silicon) layer disposed on a dielectric material, and spaced apart first and second contacts to the Si layer.
The article also comprises a voltage source for applying a bias voltage between said first and second contacts, and apparatus (typically intergrated receiver circuitry) that is responsive to the current between said first and second contacts.
The Si layer has a major surface, and the current is responsive to electromagnetic radiation of wavelength .
lambda.
that is incident on the major surface and transmitted therethrough.
Significantly, the thickness t of the crystalline Si layer is less (typically substantially less) than the absorption length .
alpha.
.
sup.
-1 in crystalline Si of the radiation of wavelength .
lambda.
, the dielectric material has a refractive index that is less than the refractive index of crystalline Si at .
lambda.
, and at least a portion of the major surface is textured such that the propagation direction of radiation of wavelength .
lambda.
that is incident on the textured surface is substantially randomized.
In an exemplary embodiment the photodetector is a MSM photodetector, and the first and second contacts are disposed on the major surface of the Si layer.
In another exemplary embodiment the photodetector is a p-n junction device, with a first portion of the Si layer being n-type and a second portion being p-type, with the first and second contacts contacting the first and second portions, respectively.
In articles according to the invention, the substantially randomized radiation that results from transmission through the textured surface is substantially confined in the Si layer, resulting in an effective path length in the Si layer that can be substantially longer than the thickness of the Si layer.
Consequently, detectors according to the invention can at the same time have relatively high (e
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MEMS 
