U.S. patent application number 14/472241 was filed with the patent office on 2014-12-18 for germanium/silicon avalanche photodetector with separate absorption and multiplication regions.
The applicant listed for this patent is Olufemi I. Dosunmu, Ansheng Liu, Micheal T. Morse, Mario J. Paniccia. Invention is credited to Olufemi I. Dosunmu, Ansheng Liu, Micheal T. Morse, Mario J. Paniccia.
Application Number | 20140367740 14/472241 |
Document ID | / |
Family ID | 37499586 |
Filed Date | 2014-12-18 |
United States Patent
Application |
20140367740 |
Kind Code |
A1 |
Morse; Micheal T. ; et
al. |
December 18, 2014 |
GERMANIUM/SILICON AVALANCHE PHOTODETECTOR WITH SEPARATE ABSORPTION
AND MULTIPLICATION REGIONS
Abstract
A semiconductor waveguide based optical receiver is disclosed.
An apparatus according to aspects of the present invention includes
an absorption region including a first type of semiconductor region
proximate to a second type of semiconductor region. The first type
of semiconductor is to absorb light in a first range of wavelengths
and the second type of semiconductor to absorb light in a second
range of wavelengths. A multiplication region is defined proximate
to and separate from the absorption region. The multiplication
region includes an intrinsic semiconductor region in which there is
an electric field to multiply the electrons created in the
absorption region.
Inventors: |
Morse; Micheal T.; (San
Jose, CA) ; Dosunmu; Olufemi I.; (Santa Clara,
CA) ; Liu; Ansheng; (Cupertino, CA) ;
Paniccia; Mario J.; (Santa Clara, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Morse; Micheal T.
Dosunmu; Olufemi I.
Liu; Ansheng
Paniccia; Mario J. |
San Jose
Santa Clara
Cupertino
Santa Clara |
CA
CA
CA
CA |
US
US
US
US |
|
|
Family ID: |
37499586 |
Appl. No.: |
14/472241 |
Filed: |
August 28, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11724805 |
Mar 15, 2007 |
8829566 |
|
|
14472241 |
|
|
|
|
11170556 |
Jun 28, 2005 |
7233051 |
|
|
11724805 |
|
|
|
|
Current U.S.
Class: |
257/186 |
Current CPC
Class: |
H01L 27/14629 20130101;
H01L 31/0312 20130101; H01L 31/028 20130101; H01L 31/1075 20130101;
Y02E 10/547 20130101; H01L 31/1812 20130101 |
Class at
Publication: |
257/186 |
International
Class: |
H01L 31/107 20060101
H01L031/107; H01L 27/146 20060101 H01L027/146 |
Claims
1. An apparatus, comprising: an absorption region including a
germanium layer and a different, second type of semiconductor layer
disposed above the germanium layer, wherein the germanium layer is
to absorb light in a first range of wavelengths and the different,
second type of semiconductor layer is to absorb light in a second
range of wavelengths, wherein the first range of wavelengths
includes wavelengths longer than any wavelength of the second range
of wavelengths; and a multiplication region disposed below the
absorption region, the multiplication region including an intrinsic
semiconductor material to multiply electrons from the absorption
region in response to an electric field.
2. The apparatus of claim 1, further comprising a buried oxide
layer below the multiplication region.
3. The apparatus of claim 2, wherein the buried oxide layer
comprises a buried oxide layer of a silicon-on-insulator (SOI)
wafer.
4. The apparatus of claim 1, wherein the multiplication region is
adjacent to and disposed between a layer of p-doped silicon and a
layer of n+doped silicon.
5. The apparatus of claim 1, wherein the different, second type of
semiconductor layer includes a silicon based layer.
6. The apparatus of claim 1 further comprising a doped contact
layer disposed proximate to the absorption region.
7. The apparatus of claim 6 further comprising guard rings defined
in the absorption region proximate to the doped contact layer.
8. The apparatus of claim 1 wherein the different, second type of
semiconductor layer comprises silicon.
9. The apparatus of claim 1 wherein the apparatus is a
photodetector, wherein the photodetector is one of a plurality of
photodetectors arranged in an array to collectively detect an image
focused on the array.
10. The apparatus of claim 1 further comprising a reflective layer
disposed proximate to the multiplication region, wherein the
multiplication region is disposed between the absorption region and
the reflective layer such that a resonant cavity including the
absorption region and the multiplication region is defined between
the reflective layer and a surface of the apparatus onto which
light is incident.
11. A system, comprising: a photodetector array including a
plurality of photodetectors each comprising: an absorption region
including a germanium layer and a different, second type of
semiconductor layer disposed above the germanium layer, wherein the
germanium layer is to absorb light in a first range of wavelengths
and the different, second type of semiconductor layer is to absorb
light in a second range of wavelengths, wherein the first range of
wavelengths includes wavelengths longer than any wavelength of the
second range of wavelengths; and a multiplication region disposed
below the absorption region, the multiplication region including an
intrinsic semiconductor material to multiply electrons from the
absorption region in response to an electric field; and an optical
focusing element to focus an optical image onto the photodetector
array.
12. The system of claim 11, the plurality of photodetectors each
further comprising a buried oxide layer below the multiplication
region.
13. The system of claim 12, wherein the buried oxide layer
comprises a buried oxide layer of a silicon-on-insulator (SOI)
wafer.
14. The system of claim 11, wherein the multiplication region is
adjacent to and disposed between a layer of p-doped silicon and a
layer of n+doped silicon.
15. The system of claim 11, wherein the different, second type of
semiconductor layer includes a silicon based layer.
16. The system of claim 11 the plurality of photodetectors each
further comprising a doped contact layer disposed proximate to the
absorption region.
17. The system of claim 16, the plurality of photodetectors each
further comprising guard rings defined in the absorption region
proximate to the doped contact layer.
18. The system of claim 11 wherein the different, second type of
semiconductor layer comprises silicon.
19. The apparatus of claim 11, the plurality of photodetectors each
further comprising a reflective layer disposed proximate to the
multiplication region, wherein the multiplication region is
disposed between the absorption region and the reflective layer
such that a resonant cavity including the absorption region and the
multiplication region is defined between the reflective layer and a
surface of the apparatus onto which light is incident.
Description
REFERENCE TO PRIOR APPLICATION
[0001] This application is a continuation of, and claims priority
to, U.S. application Ser. No. 11/724,805, filed Mar. 15, 2007,
which is to issue on Sep. 9, 2014 as U.S. Pat. No. 8,829,566, which
is a continuation of and claims priority to U.S. application Ser.
No. 11/170,556, filed Jun. 28, 2005, which issued as U.S. Pat. No.
7,233,051 on Jun. 19, 2007.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of invention relate generally to optical devices
and, more specifically but not exclusively relate to
photodetectors.
[0004] 2. Background Information
[0005] The need for fast and efficient optical-based technologies
is increasing as Internet data traffic growth rate is overtaking
voice traffic pushing the need for fiber optical communications.
Transmission of multiple optical channels over the same fiber in
the dense wavelength-division multiplexing (DWDM) system provides a
simple way to use the unprecedented capacity (signal bandwidth)
offered by fiber optics. Commonly used optical components in the
system include wavelength division multiplexed (WDM) transmitters
and receivers, optical filter such as diffraction gratings,
thin-film filters, fiber Bragg gratings, arrayed-waveguide
gratings, optical add/drop multiplexers, lasers, optical switches
and photodetectors. Photodiodes may be used as photodetectors to
detect light by converting incident light into an electrical
signal. An electrical circuit may be coupled to the photodetector
to receive the electrical signal representing the incident light.
The electrical circuit may then process the electrical signal in
accordance with the desired application.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Non-limiting and non-exhaustive embodiments of the present
invention are described with reference to the following figures,
wherein like reference numerals refer to like parts throughout the
various views unless otherwise specified.
[0007] FIG. 1A is a diagram illustrating a cross-section view of a
plurality of germanium/silicon avalanche photodetectors with
separate absorption and multiplication regions in a system for an
embodiment of the present invention.
[0008] FIG. 1B is a diagram illustrating a top view of a plurality
of germanium/silicon avalanche photodetectors with separate
absorption and multiplication regions arranged in a two-dimensional
array for an embodiment of the present invention.
[0009] FIG. 2 is a diagram illustrating responsivity versus
wavelength relationships with respect to the silicon and germanium
layers of an absorption region of an avalanche photodetector for an
embodiment of the present invention.
[0010] FIG. 3 is a diagram illustrating an improvement in
sensitivity with the use of silicon in the multiplication region of
a germanium/silicon avalanche photodetector with separate
absorption and multiplication regions for an embodiment of the
present invention.
[0011] FIG. 4A is a diagram illustrating a cross-section view of a
germanium/silicon avalanche photodetector with a resonant cavity
for an embodiment of the present invention.
[0012] FIG. 4B is another diagram illustrating a cross-section view
of a germanium/silicon avalanche photodetector with a resonant
cavity that shows electron-hole pairs being generated for an
embodiment of the present invention.
DETAILED DESCRIPTION
[0013] Methods and apparatuses for germanium/silicon avalanche
photodetectors (APDs) with separate absorption and multiplication
(SAM) regions are disclosed. In the following description numerous
specific details are set forth in order to provide a thorough
understanding of the present invention. It will be apparent,
however, to one having ordinary skill in the art that the specific
detail need not be employed to practice the present invention. In
other instances, well-known materials or methods have not been
described in detail in order to avoid obscuring the present
invention.
[0014] Reference throughout this specification to "one embodiment"
or "an embodiment" means that a particular feature, structure or
characteristic described in connection with the embodiment is
included in at least one embodiment of the present invention. Thus,
appearances of the phrases "in one embodiment" or "in an
embodiment" in various places throughout this specification are not
necessarily all referring to the same embodiment. Furthermore, the
particular features, structures or characteristics may be combined
in any suitable manner in one or more embodiments. In addition, it
is appreciated that the figures provided herewith are for
explanation purposes to persons ordinarily skilled in the art and
that the drawings are not necessarily drawn to scale.
[0015] FIG. 1A is a diagram illustrating a cross-section view of a
system 100 including plurality of avalanche photodetectors 103A,
103B, . . . 103N arranged in a grid or an array 101 having one or
more dimensions for an embodiment of the present invention.
Illumination 117 is incident upon one or more of the plurality of
avalanche photodetectors 103A, 103B, . . . 103N of the array 101.
In the illustrated example, an image of an object 116 may be
focused onto the array 101 through an optical element 130 with
illumination 117. Thus, array 101 may function to sense images,
similar to for example a complementary metal oxide semiconductor
(CMOS) sensor array or the like.
[0016] To illustrate, FIG. 1B shows a top view of array 101 with
the plurality of avalanche photodetectors 103A, 103B, . . . 103N
arranged in a two dimensional grid such that each of the plurality
of avalanche photodetectors 103A, 103B, . . . 103N function as
pixels or the like for an embodiment of the present invention. The
example illustrated in FIG. 1B shows an image 118 of object 116
using the pixels of array 101 within illumination 117.
[0017] It is noted that although FIGS. 1A and 1B illustrate an
example application of the avalanche photodetectors being employed
in a imaging system for explanation purposes, the avalanche
photodetectors may be employed in other types of applications in
which for example the detection of light having any of a variety of
wavelengths including visible through infrared wavelengths is
realized in accordance with the teachings of the presenting
invention.
[0018] Referring back to FIG. 1A, optical element 131 may be a lens
or other type of refractive or diffractive optical element such
that the image is focused on array 101 with illumination 117.
Illumination 117 may include visible light, infrared light and/or a
combination of wavelengths across the visible through infrared
spectrum for an embodiment of the present invention.
[0019] In the example illustrated in FIG. 1A, each of the plurality
of avalanche photodetectors 103A, 103B, . . . 103N includes
semiconductor material layers, 105, 107, 109, 111, 113 and 115. A
contact 131 is coupled to layer 105 and a contact 133 is coupled to
layer 115. For one embodiment, layer 105 is a p+doped layer of
silicon having a doping concentration of for example 5e19 cm.sup.-3
and a thickness of for example 100 nanometers. For one embodiment,
layer 105 has a doping concentration that provides an improved
electrical coupling between a contact 131 and layer 105. For one
embodiment, layers 107 and 109 are intrinsic semiconductor material
regions that form an absorption region 135 of the avalanche
photodetector 103A. Layer 107 is a layer of intrinsic silicon and
layer 109 is a layer of intrinsic germanium for one embodiment.
Proximate to the absorption region 135 is a separate multiplication
region 137, which includes a layer 113 of intrinsic semiconductor
material such as silicon. As shown in the illustrated example,
layer 113 is disposed between a layer 111 of p-doped silicon and a
layer 115 of n+doped silicon. For one embodiment, layer 111 has a
thickness of for example 100 nanometers and a doping concentration
of for example 1-2e17 cm.sup.-3. For one embodiment, layer 115 has
a doping concentration of for example 5e19 cm.sup.-3. In the
illustrated example, each of the plurality of avalanche
photodetectors 103A, 103B, . . . 103N is coupled between ground and
a voltage V.sub.1, V.sub.2, . . . V.sub.n such that each avalanche
photodetector is biased resulting in an electric field between
layers 105 and 115 as shown.
[0020] It is appreciated of course that the specific example doping
concentrations, thicknesses and materials or the like that are
described in this disclosure are provided for explanation purposes
and that other doping concentrations, thicknesses and materials or
the like may also be utilized in accordance with the teachings of
the present invention.
[0021] In operation, illumination 117 is incident upon layer 105 of
one or more of each of the plurality of avalanche photodetectors
103A, 103B, . . . 103N. Layer 105 is relatively thin such that
substantially all of illumination 117 is propagated through layer
105 to layer 107 of the absorption region 135. For one embodiment,
the intrinsic silicon of layer 107 absorbs the light having
wavelengths in the range of approximately 420 nanometers to
approximately .about.1100 nanometers. Most of the light having
wavelengths greater than approximately .about.1100 nanometers is
propagated through the intrinsic silicon layer 107 into the
intrinsic germanium layer 109 of the absorption region 135. The
intrinsic germanium of layer 109 absorbs that remaining light that
propagates through layer 107 up to wavelengths of approximately
1600 nanometers.
[0022] To illustrate, FIG. 2 is a diagram 201 that shows example
responsivity versus wavelength relationships of silicon and
germanium for an embodiment of the present invention. In
particular, diagram 201 shows plot 207, which shows the
responsivity of silicon with respect to wavelength, and plot 209,
which shows the responsivity of germanium with respect to
wavelength. For one embodiment, plot 207 may correspond to the
responsivity of the intrinsic silicon of layer 107 and plot 209 may
correspond to the responsivity of the intrinsic germanium of FIG.
1A. As shown in plot 207, the silicon absorbs light having
wavelengths as short as approximately 420 nanometers. As the
wavelengths get longer, the responsivity of silicon begins to drop
off due to the lower absorption of silicon at infrared wavelengths.
Indeed, as the wavelength of light increases at this point, the
silicon becomes increasingly transparent as the light becomes more
infrared. Thus, with respect to FIG. 1A, the longer wavelengths of
illumination 117 are not absorbed in layer 107 and are instead
propagate through to layer 109. However, plot 209 shows that the
germanium absorbs the longer wavelength light in layer 109 that is
propagated through layer 107 up to wavelengths of approximately
1600 nanometers for an embodiment of the present invention. The
silicon in layer 107 absorbs the shorter wavelengths of light less
than approximately 1000 nanometers, while at the same wavelength
range the germanium has a much larger absorption coefficient and
would otherwise not generate significant photocurrent due to
surface recombination in accordance with the teachings of the
present invention.
[0023] Therefore, referring back to FIG. 1A, with the combination
of the intrinsic silicon of layer 107 and the intrinsic germanium
of layer 109 in absorption region 135, illumination 117 is absorbed
in the absorption regions 135 of the avalanche photodetectors from
visible light having a wavelength of approximately 420 nanometers
all the way up to longer infrared wavelengths having wavelengths up
to approximately 1600 nanometers in accordance with the teachings
of the present invention. This absorption of the light of
illumination 117 in semiconductor layers 107 and 109 results in the
generation of photocarriers or electron-hole pairs in the
absorption region 135.
[0024] Due to the biasing and electric fields present in the
avalanche photodetector, the holes of the electron-hole pairs
generated in the absorption region 135 drift towards layer 105 and
the electrons drift towards layer 115. As the electrons drift into
the multiplication region 137, the electrons are subjected to a
relatively high electric field in intrinsic silicon layer 113
resulting from the doping levels of the neighboring layers of
p-doped silicon in layer 111 and n+ doped silicon in layer 115. As
a result of the high electric field in layer 113, impact ionization
occurs to the electrons that drift into the multiplication region
137 from the absorption region 135 in accordance with the teachings
of the present invention. Therefore, the photocurrent created from
the absorption of illumination 117 in absorption region 135 is
multiplied or amplified in multiplication region 137 for an
embodiment of the present invention. The photocarriers are then
collected at contacts 131 and 133. For instance holes may be
collected at contact 131 and electrons are collected at contact
133. Contacts 131 and 133 may be coupled to electrical circuitry to
process the signals present at each of the contacts 131 and 133
according to embodiments of the present invention.
[0025] As mentioned above, multiplication region 137 includes
intrinsic silicon in layer 113 as will as silicon in neighboring
p-doped and n+ doped layers 111 and 115, respectively. FIG. 3 is a
diagram 301 illustrating an improvement in sensitivity that is
realized for an embodiment of an avalanche photodetector utilizing
silicon in the multiplication region 137 instead of another
material, such as for example indium phosphide (InP). In
particular, diagram 301 shows a relationship between a receiver
sensitivity dBm versus photomultiplication gain M for various
embodiments of an avalanche photodectector. In particular, plot 333
shows a receiver sensitivity versus photomultiplication gain
relationship for an indium phosphide based avalanche photodetector
while plot 335 shows a receiver sensitivity versus
photomultiplication gain relationship for silicon based avalanche
photodetector. As can be observed in FIG. 3 by comparing plots 333
and 335, receiver sensitivity is improved by approximately 4-5 dB
by using a silicon based avalanched photodetector instead of an
indium phosphide based avalanche photodetector for an embodiment of
the present invention. This shows that less power is therefore
needed using silicon instead of indium phosphide in multiplication
region 137 to accurately detect a signal encoded in an optical
signal received by an avalanche photodetector for an embodiment of
the present invention.
[0026] The utilization of silicon in the multiplication region 137
for an embodiment of the present invention improves sensitivity of
the avalanche photodetectors 103A, 103B, . . . 103N as shown in
FIGS. 1A and 1B because of the impact ionization properties of the
electrons and holes in the material. For an embodiment of the
present invention, substantially only one type of carrier, in
particular electrons, are able to achieve impact ionization because
of the use of silicon in multiplication region 137. This can be
seen quantitatively with the k-factor, which is the ratio of impact
ionization coefficients of holes to electrons. Silicon has a
k-factor about one order of magnitude lower than, for example,
indium phosphide. A result of the use of silicon is that
substantially only electrons are selectively multiplied or
amplified in multiplication region 137 instead of holes. Thus,
noise and instability in the avalanche photodetectors 103A, 103B, .
. . 103N is reduced for an embodiment of the present invention
compared to a material with a higher k-factor. An equation showing
the excess noise tied to the k-factor (k) is:
F.sub.A(M)=kM+(1-k)(2-(1/M)) (Equation 1)
where F.sub.A is the excess noise factor and M is the gain of the
avalanche photodetector.
[0027] The chances of runaway resulting from the generation more
than one type of carrier in multiplication region 137 is
substantially reduced because substantially only electrons are able
to achieve impact ionization by using silicon of multiplication
region 137 for an embodiment of the present invention. To
illustrate, the k-factor value of silicon for an embodiment of the
present invention is less than 0.05 or approximately 0.02-0.05. In
comparison, the k-factor value for other materials such as for
example indium gallium arsenide (InGaAs) is approximately 0.5-0.7
while the k-factor value for germanium is approximately 0.7-1.0.
Thus, the k-factor value using silicon for an embodiment of the
present invention is less than other materials. Therefore, using
silicon for an embodiment of an avalanche photodetector in
multiplication region 137 results in improved sensitivity over
avalanche photodetectors using other materials such as indium
gallium arsenide or germanium or the like.
[0028] FIG. 4A is a diagram illustrating a cross-section view of a
germanium/silicon avalanche photodetector 403 with a resonant
cavity for an embodiment of the present invention. It is
appreciated that avalanche photodetector 403 shares similarities
with the examples avalanche photodetectors 103A, 103B, . . . 103N
shown in FIGS. 1A and 1B and that avalanche photodetector 403 may
be used in place of any one or more of the avalanche photodetectors
103A, 103B, . . . 103N in accordance with the teachings of the
present invention. Referring back to the example shown in FIG. 4A,
avalanche photodetector 403 includes layers, 405, 407, 409, 411,
413 and 415. In the example illustrated in FIG. 4A, avalanche
photodetector 403 is disposed on a silicon-on-insulator (SOI)
wafer, and therefore, avalanche photodetector also includes a
silicon substrate layer 419 and a reflective layer, which is
illustrated in FIG. 4A as a buried oxide layer 425. For one
embodiment, avalanche photodetector 403 also includes guard rings
421, which are disposed at the surface and into layer 407 on
opposing sides of layer 405 at the surface of layer 407 as shown in
FIG. 4A.
[0029] For one embodiment, layer 405 and guard rings 421 are p+
doped silicon having a doping concentration that provides an
improved electrical coupling between a contact coupled to layer 405
and layer 407. For one embodiment, guard rings 421 are disposed
proximate to layer 405 as shown in FIG. 4A to help prevent or
reduce electric field from extending to or past the edges of
avalanche photodetector 403. By helping to isolate or confine the
electric field within the structure of avalanche photodetector 403,
guard rings 431 help to reduce leakage current from the avalanche
photodetector 403 structure in accordance with the teachings of the
present invention.
[0030] For one embodiment, layers 407 and 409 form an absorption
region 435 of the avalanche photodetector 403. Layer 407 is a layer
of intrinsic silicon and layer 409 is a layer of intrinsic
germanium for one embodiment. Proximate to the absorption region
435 is a separate multiplication region 437, which includes a layer
413 of intrinsic silicon. As shown in the depicted example, layer
413 is disposed between a layer 411 of p- doped silicon and a layer
415 of n+doped silicon. For one embodiment, layers 411 and 415
having doping concentrations that result in a high electric field
in layer 413 of multiplication region 437. For example, layer 411
has doping concentration of for example 1-2e17 cm.sup.-3 and layer
415 has a doping concentration of for example 5e19 cm.sup.-3 for
one embodiment. In addition, a lower electric field is also present
between layer 405 and layer 415 for an embodiment of the present
invention.
[0031] In operation, as shown in FIG. 4A, illumination 417 is
directed to avalanche photodetector 403 and is incident upon a
surface of avalanche photodetector 403. In the example illustrated
in FIG. 4A, illumination 417 is directed through free space and is
incident upon a surface of layer 405. The light from illumination
417 is absorbed in absorption region 435 and electrons from the
photocurrent or electron-hole pairs generated in absorption region
435 are multiplied in multiplication region 437 as a result of
impact ionization in accordance with the teachings of the present
invention. For one embodiment, a resonant cavity is also defined in
avalanche photodetector 403 between buried oxide layer 425 and the
surface of avalanche photodetector 403 on which the light of
illumination 417 is incident. As a result, the light illumination
417 circulates in the resonant cavity between buried oxide layer
425 and the surface of the avalanche photodetector as shown in FIG.
4A as shown.
[0032] FIG. 4B is another diagram illustrating increased detail of
a cross-section view of avalanche photodetector 403 with a resonant
cavity that shows electron-hole pairs being generated for an
embodiment of the present invention. In particular, FIG. 4B shows
illumination 417 incident on the surface of layer 405 of avalanche
photodetector 403. As illumination propagates through layers 407
and 409 of the absorption region 435, the light is absorbed, which
generates photocurrent or electron-hole pairs including electron
427 and hole 429. With the electric field between p+ doped layer
405 and n+ doped layer 415, electrons 427 drift from absorption
region 435 into multiplication region 437. With the high electric
field present in layer 413 of multiplication region 437, impact
ionization occurs with the electrons 427, which generates
additional electron-hole pairs and therefore results in the
multiplication or amplification of the photocurrent generated in
absorption region 435. The holes 429 and electrons 427 are then
collected by contacts that are coupled to layers 405 and 415 for an
embodiment of the present invention.
[0033] As further illustrated, light from illumination 417 that is
not absorbed in the first pass through avalanche photodetector 403
is reflected from buried oxide layer 425, illustrated as SiO.sub.2
in FIG. 4B, and is recirculated back and forth through avalanche
photodetector 403 as shown. As a result, the light from
illumination 417 is recycled within the absorption region 435 and
multiplication region 437, thereby increasing the probability of
absorption of illumination 417 and improving the performance of
avalanche photodetector 403 in accordance with the teachings of the
present invention.
[0034] The above description of illustrated embodiments of the
invention, including what is described in the Abstract, is not
intended to be exhaustive or to be limitation to the precise forms
disclosed. While specific embodiments of, and examples for, the
invention are described herein for illustrative purposes, various
equivalent refinements and modifications are possible, as those
skilled in the relevant art will recognize. Indeed, it is
appreciated that the specific wavelengths, dimensions, materials,
times, voltages, power range values, etc., are provided for
explanation purposes and that other values may also be employed in
other embodiments in accordance with the teachings of the present
invention.
[0035] These modifications can be made to embodiments of the
invention in light of the above detailed description. The terms
used in the following claims should not be construed to limit the
invention to the specific embodiments disclosed in the
specification and the claims. Rather, the scope is to be determined
entirely by the following claims, which are to be construed in
accordance with established doctrines of claim interpretation.
* * * * *