U.S. patent application number 15/486810 was filed with the patent office on 2018-10-18 for rapid melt growth photodetector.
The applicant listed for this patent is International Business Machines Corporation. Invention is credited to John J. Ellis-Monaghan, Edward W. Kiewra, Jason S. Orcutt.
Application Number | 20180301568 15/486810 |
Document ID | / |
Family ID | 63761684 |
Filed Date | 2018-10-18 |
United States Patent
Application |
20180301568 |
Kind Code |
A1 |
Ellis-Monaghan; John J. ; et
al. |
October 18, 2018 |
RAPID MELT GROWTH PHOTODETECTOR
Abstract
Photodetector including: a waveguide of a waveguide material
extending over a substrate; an insulating layer formed over the
waveguide and having an opening exposing the waveguide; a
photodetector layer formed over the insulating layer and into the
opening so as to make contact with the waveguide, the photodetector
layer having a first end at the opening and a second end distal
from the opening, the photodetector layer being a gradient material
of the waveguide material and germanium wherein a waveguide
material portion of the gradient material varies from a maximum at
the first end to a minimum at the second end and wherein a
germanium portion of the gradient material varies from a minimum at
the first end to a maximum at the second end; a photodetector
region at the second end; and a photodetector layer extension
extending at an angle from the photodetector layer at the second
end.
Inventors: |
Ellis-Monaghan; John J.;
(Grand Isle, VT) ; Kiewra; Edward W.; (South
Burlington, VT) ; Orcutt; Jason S.; (Katonah,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation |
Armonk |
NY |
US |
|
|
Family ID: |
63761684 |
Appl. No.: |
15/486810 |
Filed: |
April 13, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 27/144 20130101;
G02B 2006/12061 20130101; H01L 31/02327 20130101; H01L 27/146
20130101; H01L 31/03529 20130101; G02B 6/4295 20130101; H01L 31/102
20130101 |
International
Class: |
H01L 31/0232 20060101
H01L031/0232; G02B 6/42 20060101 G02B006/42 |
Claims
1. A photodetector comprising: a waveguide extending over a
substrate, the waveguide comprising a waveguide material; an
insulating layer formed over the waveguide, the insulating layer
having an opening exposing the waveguide; a photodetector layer
formed over the insulating layer and into the opening so as to make
contact with the waveguide, the photodetector layer having a first
end at the opening and a second end distal from the opening, the
photodetector layer being a gradient material of the waveguide
material and germanium wherein a waveguide material portion of the
gradient material varies from a maximum at the first end to a
minimum at the second end and wherein a germanium portion of the
gradient material varies from a minimum at the first end to a
maximum at the second end; a photodetector region at the second
end; and a photodetector layer extension extends at an angle from
the photodetector layer at the second end.
2. The photodetector of claim 1 wherein the photodetector layer
extension does not contain any portion of the photodetector
region.
3. The photodetector of claim 1 wherein the photodetector layer
extension is L shaped.
4. The photodetector of claim 1 wherein the photodetector layer
extension is curved.
5. The photodetector of claim 1 wherein the photodetector layer and
the photodetector layer extension are coplanar.
6. The photodetector of claim 1 wherein the waveguide material
comprises silicon.
7. The photodetector of claim 1 wherein the photodetector layer has
a width at the first end that is wider than a width of the
photodetector layer at the second end.
8. The photodetector of claim 1 wherein the photodetector layer
extension extends at an angle from the photodetector layer in only
one direction.
9. A photodetector comprising: a waveguide extending over a
substrate, the waveguide comprising silicon; an insulating layer
formed over the waveguide, the insulating layer having an opening
exposing the waveguide; a linear photodetector layer formed over
the insulating layer and into the opening so as to make contact
with the waveguide, the linear photodetector layer having a first
end at the opening and a second end at the terminus of the linear
photodetector layer, the photodetector layer being a gradient
material of the silicon and germanium wherein a silicon portion of
the gradient material varies from a maximum at the first end to a
minimum at the second end and wherein a germanium portion of the
gradient material varies from a minimum at the first end to a
maximum at the second end; a photodetector at the terminus of the
linear photodetector layer; and a photodetector layer extension
extends at an angle from the terminus of the linear photodetector
layer.
10. The photodetector of claim 9 wherein the photodetector layer
extension extends at an angle from the linear photodetector layer
in only one direction.
11. The photodetector of claim 9 wherein the photodetector layer
extension extends at an angle from the linear photodetector layer
in two directions.
12. The photodetector of claim 9 wherein the photodetector layer
extension comprises a portion parallel and spaced from the linear
photodetector layer.
13. The photodetector of claim 9 wherein the photodetector layer
extension is curved.
14. The photodetector of claim 9 wherein the photodetector layer
and the photodetector layer extension are coplanar.
15. The photodetector of claim 9 wherein the photodetector layer
has a width at the first end that is wider than a width of the
photodetector layer at the second end.
16. A photodetector comprising: a waveguide extending over a
substrate, the waveguide comprising silicon; an insulating layer
formed over the waveguide, the insulating layer having an opening
exposing the waveguide; a photodetector layer formed over the
insulating layer and into the opening so as to make contact with
the waveguide, the photodetector layer having a first end at the
opening and a second end at a photodetector region formed in the
photodetector layer, the photodetector layer being a gradient
material of the silicon and germanium wherein a silicon portion of
the gradient material varies from a maximum at the first end to a
minimum at the second end and wherein a germanium portion of the
gradient material varies from a minimum at the first end to a
maximum at the second end; a photodetector layer extension extends
at an angle from the photodetector layer such that the
photodetector layer and the photodetector layer extension are
coplanar.
17. The photodetector of claim 16 wherein the photodetector layer
extension does not contain any portion of the photodetector
region.
18. The photodetector of claim 16 wherein the photodetector layer
extension extends at an angle from the linear photodetector layer
in only one direction.
19. The photodetector of claim 16 wherein the photodetector layer
extension extends at an angle from the linear photodetector layer
in two directions.
20. The photodetector of claim 16 wherein the photodetector layer
extension comprises a portion parallel and spaced from the linear
photodetector layer.
21. The photodetector of claim 16 wherein the photodetector layer
has a width at the first end that is wider than a width of the
photodetector layer at the second end.
22. A photodetector comprising: a waveguide extending over a
substrate, the waveguide has an incoming portion that joins with a
main portion, the incoming portion being at an angle with respect
to the main portion; an insulating layer formed over the waveguide,
the insulating layer having an opening exposing the main portion of
the waveguide; a photodetector layer formed over the insulating
layer and into the opening so as to make contact with the main
portion of the waveguide, the photodetector layer having a first
end at the opening and a second end spaced from the first end, the
photodetector layer being a gradient material of the silicon and
germanium wherein a silicon portion of the gradient material varies
from a maximum at the first end to a minimum at the second end and
wherein a germanium portion of the gradient material varies from a
minimum at the first end to a maximum at the second end; the main
portion of the waveguide extends underneath the photodetector layer
from where the main portion of the waveguide joins with the
incoming portion of the waveguide to and past the opening, the
incoming portion juts outward from underneath the photodetector
layer, an extension portion of the photodetector layer extends past
where the main portion of the waveguide joins with the incoming
portion of the waveguide to the second end; and a photodetector
region formed in the photodetector layer that begins where the
incoming portion of the waveguide joins with the main portion of
the waveguide and extends towards the first end.
23. The photodetector of claim 22 wherein the extension portion of
the photodetector layer does not contain any portion of the
photodetector.
24. A photodetector comprising: a silicon waveguide extending over
a substrate, the waveguide has an incoming portion that joins with
a main portion, the incoming portion being at an angle with respect
to the main portion; an insulating layer formed over the waveguide,
the insulating layer having an opening exposing a silicon seed; a
photodetector layer formed over the insulating layer and into the
opening so as to make contact with the silicon seed, the
photodetector layer having a first end at the opening and a second
end spaced from the first end, the photodetector layer being a
gradient material of the silicon and germanium wherein a silicon
portion of the gradient material varies from a maximum at the first
end to a minimum at the second end and wherein a germanium portion
of the gradient material varies from a minimum at the first end to
a maximum at the second end; the main portion of the waveguide
extends underneath the photodetector layer from where the main
portion of the waveguide joins with the incoming portion of the
waveguide to and past the second end, the incoming portion juts
outward from underneath the photodetector layer, a portion of the
photodetector layer extends past where the main portion of the
waveguide joins with the incoming portion of the waveguide to the
first end; and a photodetector region formed in the photodetector
layer at the second end and over the main portion of the
waveguide.
25. The photodetector of claim 24 wherein the silicon seed is
decoupled from the waveguide.
Description
BACKGROUND
[0001] The present exemplary embodiments pertain to optoelectronic
devices and, more particularly, to waveguide photodetectors that
convert optical signals into electrical signals.
[0002] In optical communication systems, optical waveguides provide
a transmission channel for guiding an optical signal produced by a
light source, e.g., a laser, at one end of the system to a
detector, e.g., a photodetector, at the other end of the system.
The photodetector material, an active region, absorbs energy from
the photons of the transmitted optical signal, which, in response,
excites charge carriers, e.g., electrons and holes. With the
application of a reverse bias voltage, the excited charge carriers
are attracted to contacts on the photodetector, thereby creating an
electrical current that corresponds to the optical signal. In this
manner, the photodetector converts an optical signal into an
electrical signal.
[0003] Due to its potential for being grown on top of silicon,
germanium is an appropriate choice for a photodetector.
[0004] A lattice constant refers to the distance between unit cells
in a crystal lattice. The lattice constant of germanium is not
perfectly matched with the lattice constant of silicon; the lattice
constant of germanium is slightly larger than that of silicon. The
mismatch between the lattice constants of germanium and silicon
presents problems for using a regular epitaxial growth ("EPI")
technique for growing crystals. Currently, two main methods have
been heavily studied to make single crystal germanium film on top
of silicon substrates. One method is using a buffer layer and
post-process after selective epitaxial growth ("SEG"). The second
method is using a rapid melt growth ("RMG") technique. Between
these two methods, RMG has better process compatibility but has a
limitation on the structures that can be constructed.
[0005] In the RMG technique, single crystal germanium is not grown
directly on top of the silicon. Rather, poly-germanium or amorphous
germanium is deposited on an insulator that has an opening ("seed
window") to an underlying silicon layer. An insulator, such as a
nitride, is deposited to surround the poly-germanium or amorphous
germanium. The RMG method requires a micro-crucible formed by the
insulator surrounding the deposited poly-germanium or amorphous
germanium which causes melting and recrystallization of the
germanium when subjected to anneal.
[0006] Optical detectors in a CMOS compatible process sequence can
be accomplished inexpensively with an RMG germanium photodetector.
RMG photodetectors have been built in silicon compatible processes
but suffer from a couple of difficulties.
[0007] One difficulty is that the silicon seed region contaminates
the germanium photodetector resulting in a silicon germanium
detector rather than a pure crystalline germanium photodetector.
This can result in poor responsivity of the photodetector.
[0008] Another difficulty is that the melting and subsequent
recrystallization of the germanium photodetector can result in the
formation of defects near the end of the photodetector affecting
the yield and responsivity of the photodetector.
BRIEF SUMMARY
[0009] The various advantages and purposes of the exemplary
embodiments as described above and hereafter are achieved by
providing, according to an aspect of the exemplary embodiments, a
photodetector comprising: a waveguide extending over a substrate,
the waveguide comprising a waveguide material; an insulating layer
formed over the waveguide, the insulating layer having an opening
exposing the waveguide; a photodetector layer formed over the
insulating layer and into the opening so as to make contact with
the waveguide, the photodetector layer having a first end at the
opening and a second end distal from the opening, the photodetector
layer being a gradient material of the waveguide material and
germanium wherein a waveguide material portion of the gradient
material varies from a maximum at the first end to a minimum at the
second end and wherein a germanium portion of the gradient material
varies from a minimum at the first end to a maximum at the second
end; a photodetector region at the second end; and a photodetector
layer extension extends at an angle from the photodetector layer at
the second end.
[0010] According to another aspect of the exemplary embodiments,
there is provided a photodetector comprising: a waveguide extending
over a substrate, the waveguide comprising silicon; an insulating
layer formed over the waveguide, the insulating layer having an
opening exposing the waveguide; a linear photodetector layer formed
over the insulating layer and into the opening so as to make
contact with the waveguide, the linear photodetector layer having a
first end at the opening and a second end at the terminus of the
linear photodetector layer, the photodetector layer being a
gradient material of the silicon and germanium wherein a silicon
portion of the gradient material varies from a maximum at the first
end to a minimum at the second end and wherein a germanium portion
of the gradient material varies from a minimum at the first end to
a maximum at the second end; a photodetector at the terminus of the
linear photodetector layer; and a photodetector layer extension
extends at an angle from the terminus of the linear photodetector
layer.
[0011] According to a further aspect of the exemplary embodiments,
there is provided a photodetector comprising: a waveguide extending
over a substrate, the waveguide comprising silicon; an insulating
layer formed over the waveguide, the insulating layer having an
opening exposing the waveguide; a photodetector layer formed over
the insulating layer and into the opening so as to make contact
with the waveguide, the photodetector layer having a first end at
the opening and a second end at a photodetector region formed in
the photodetector layer, the photodetector layer being a gradient
material of the silicon and germanium wherein a silicon portion of
the gradient material varies from a maximum at the first end to a
minimum at the second end and wherein a germanium portion of the
gradient material varies from a minimum at the first end to a
maximum at the second end; a photodetector layer extension extends
at an angle from the linear photodetector layer such that the
photodetector layer and the photodetector layer extension are
coplanar.
[0012] According to another aspect of the exemplary embodiments,
there is provided a photodetector comprising: a waveguide extending
over a substrate, the waveguide has an incoming portion that joins
with a main portion, the incoming portion being at an angle with
respect to the main portion; an insulating layer formed over the
waveguide, the insulating layer having an opening exposing the main
portion of the waveguide; a photodetector layer formed over the
insulating layer and into the opening so as to make contact with
the main portion of the waveguide, the photodetector layer having a
first end at the opening and a second end spaced from the first
end, the photodetector layer being a gradient material of the
silicon and germanium wherein a silicon portion of the gradient
material varies from a maximum at the first end to a minimum at the
second end and wherein a germanium portion of the gradient material
varies from a minimum at the first end to a maximum at the second
end; the main portion of the waveguide extends underneath the
photodetector layer from where the main portion of the waveguide
joins with the incoming portion of the waveguide to and past the
opening, the incoming portion juts outward from underneath the
photodetector layer, an extension portion of the photodetector
layer extends past where the main portion of the waveguide joins
with the incoming portion of the waveguide to the second end; and a
photodetector region formed in the photodetector layer that begins
where the incoming portion of the waveguide joins with the main
portion of the waveguide and extends towards the first end.
[0013] According to yet another aspect of the exemplary
embodiments, there is provided a photodetector comprising: a
silicon waveguide extending over a substrate, the waveguide has an
incoming portion that joins with a main portion, the incoming
portion being at an angle with respect to the main portion; an
insulating layer formed over the waveguide, the insulating layer
having an opening exposing a silicon seed; a photodetector layer
formed over the insulating layer and into the opening so as to make
contact with the silicon seed, the photodetector layer having a
first end at the opening and a second end spaced from the first
end, the photodetector layer being a gradient material of the
silicon and germanium wherein a silicon portion of the gradient
material varies from a maximum at the first end to a minimum at the
second end and wherein a germanium portion of the gradient material
varies from a minimum at the first end to a maximum at the second
end; the main portion of the waveguide extends underneath the
photodetector layer from where the main portion of the waveguide
joins with the incoming portion of the waveguide to and past the
second end, the incoming portion juts outward from underneath the
photodetector layer, a portion of the photodetector layer extends
past where the main portion of the waveguide joins with the
incoming portion of the waveguide to the first end; and a
photodetector region formed in the photodetector layer at the
second end and over the main portion of the waveguide.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
[0014] The features of the exemplary embodiments believed to be
novel and the elements characteristic of the exemplary embodiments
are set forth with particularity in the appended claims. The
Figures are for illustration purposes only and are not drawn to
scale. The exemplary embodiments, both as to organization and
method of operation, may best be understood by reference to the
detailed description which follows taken in conjunction with the
accompanying drawings in which:
[0015] FIG. 1 is a plan view of an embodiment of a germanium
photodetector.
[0016] FIG. 2 is a cross sectional view of the germanium
photodetector of FIG. 1 in the direction of arrows 2-2.
[0017] FIG. 3 is an enlarged plan view of a section of the
germanium photodetector of FIG. 1 circumscribed by the dashed
rectangle in FIG. 1.
[0018] FIG. 4A is a plan view of another embodiment of a germanium
photodetector and FIG. 4B is a plan view of a modified version of
the germanium photodetector of FIG. 4A.
[0019] FIG. 5 is a plan view of another embodiment of a germanium
photodetector.
[0020] FIG. 6 is a plan view of another embodiment of a germanium
photodetector.
[0021] FIG. 7 is a plan view of another embodiment of a germanium
photodetector.
[0022] FIG. 8 is a plan view of another embodiment of a germanium
photodetector.
[0023] FIG. 9 is a plan view of another embodiment of a germanium
photodetector.
[0024] FIG. 10 is a plan view of another embodiment of a germanium
photodetector
[0025] FIG. 11 is a plan view of another embodiment of a germanium
photodetector.
DETAILED DESCRIPTION
[0026] There are several advantages of the exemplary embodiments.
One advantage is the creation of a photodetector with a
silicon-rich region away from the incident light. Another advantage
is a germanium-rich region near the incidence of the optical
signal. A further advantage is a defect gettering region out of the
path of the optical signal.
[0027] Referring to the Figures in more detail, and particularly
referring to FIG. 1, there is a plan view of an exemplary
embodiment of a germanium photodetector 10. The germanium
photodetector 10 includes a waveguide 12, usually silicon, with the
incoming signal, indicated by arrow 14, as coming in to the
germanium photodetector 10 from the right. The photodetector layer
16 makes contact with the underlying waveguide 12 through seed
window 18. The right side of the photodetector layer 16, indicated
by dashed oval 16A, contains a photodetector diode. Surrounding the
photodetector layer 16 is an insulator 20, such as nitride.
Surrounding the germanium photodetector 10 may be an oxide (not
shown).
[0028] The formation of the germanium photodetector 10 (or any of
the subsequent embodiments) may be accomplished in a CMOS
(Complementary Metal Oxide Semiconductor) manufacturing line. It
has been found that the exemplary embodiments formed by a CMOS
process minimize the difficulties of the prior art with respect to
contamination of the germanium and the formation of defects.
[0029] Referring now to FIG. 2, there is a cross sectional view of
germanium photodetector 10 taken in the direction of arrows 2-2 in
FIG. 1. The germanium photodetector 10 may be formed on a
semiconductor base 22, such as silicon, followed by a buried oxide
layer 24, the waveguide 12, an insulator layer 26, such as a
nitride, the photodetector layer 16 and insulator 20. The
photodetector layer 16 has a portion 28 which extends through seed
window 18 to contact the waveguide 12.
[0030] The germanium photodetector 10 may be formed by a process
that includes forming the waveguide 12 on the buried oxide layer 24
followed by the insulator 26. The seed window 18 may be formed in
the insulator 26. Thereafter, poly-germanium or amorphous germanium
may be deposited, including in the seed window 18, followed by
patterning to form the photodetector layer 16. For purposes of
illustration and not limitation, the photodetector layer 16 may
have a width 40 as indicated in FIG. 1 in the range of 1 to 5
.mu.m, for example a width of 2.5 .mu.m. The germanium
photodetector layer 16 may be encapsulated with the insulator 20
followed by heating to at least the melting point of germanium
according to the RMG process.
[0031] As a result of the RMG process, a gradient of silicon
germanium is formed. The mole fraction of silicon is highest at the
seed window 18 and gradually decreases to zero or near zero at the
photodetector diode 16A. Conversely, the mole fraction of germanium
is lowest at the seed window and gradually increases to 100% or
nearly 100% at the photodetector diode 16A. Preferably, the mole
fraction of germanium at the left edge 16B of the photodetector
diode 16A should be at least 95%.
[0032] The photodetector layer 16 further includes one or more
photodetector layer extensions 30. For purposes of illustration and
not limitation, the photodetector layer extensions may have a
length 42 indicated in FIGS. 1 of 1 to 10 .mu.m, for example a
length of 3 .mu.m. An advantage of the photodetector extensions 30
is that defects that may ordinarily form at the end 16C of the
photodetector layer 16 are now pushed into the photodetector layer
extensions 30. Thus, the photodetector layer 16 within
photodetector diode 16A is now free of these defects so that the
yield and responsivity of the photodetector diode 16A is
improved.
[0033] Referring now to FIG. 3, the photodetector diode 16A within
rectangle 21 of FIG. 1 is shown in more detail. One portion 32 of
the photodetector diode 16A may be n doped and metal contacts 34
formed while a second portion 36 may be p doped and metal contacts
38 formed. The insulator 20 may be optionally removed for doping of
the photodetector diode 16A after the RMG process to minimize
doping implant energy. If the insulator 20 remains in place, the
metal contacts 34 may be formed by locally etching through the
insulator 20 and then depositing metal for the metal contacts
34.
[0034] Also shown in more detail are photodetector layer extensions
30 which angle off to the side of the photodetector layer 16. The
photodetector layer extensions 30 are shown as being perpendicular
to photodetector layer 16 but lesser or greater angular extensions
may also be formed. The dashed lines indicate where the
photodetector layer 16 ends and the photodetector layer extensions
30 begin.
[0035] Referring now to FIG. 4A, another exemplary embodiment of a
germanium photodetector 400 is illustrated which is similar to
germanium photodetector 10 except that germanium photodetector 400
has different photodetector layer extensions 402. The photodetector
layer extensions 402 include photodetector layer extension portions
404 which angle off to the side of photodetector layer 16 and
photodetector layer extension portions 406 which angle off to the
side of photodetector layer extension portions 404. In one
embodiment, photodetector layer extension portions 406 may be
parallel to photodetector layer 16.
[0036] Referring now to FIG. 4B, the germanium photodetector 400
has been modified, now germanium photodetector 400', in that the
photodetector layer extension portions 406 have been increased in
length and now shown as photodetector layer extension portions
406'.
[0037] An advantage of germanium photodetectors 400, 400' is that
any defects during the recrystallization of the germanium are
pushed further past the end 16C of the germanium photodetector
layer 16 into the photodetector layer extensions 402.
[0038] Referring now to FIG. 5, another exemplary embodiment of a
germanium photodetector 500 is illustrated which is similar to
germanium photodetector 10 except that germanium photodetector 500
has different photodetector layer extensions 502. The photodetector
layer extensions 502 include photodetector layer extension portions
504 which angle off to the side of photodetector layer 16 and
photodetector layer extension portions 506 which angle off to the
side of photodetector layer extension portions 504. In one
embodiment, photodetector layer extension portions 506 may be
parallel to photodetector layer 16. Germanium photodetector 500 may
include additional photodetector layer extensions 508 which may
angle off to the side of photodetector layer extensions 506.
[0039] An advantage of germanium photodetector 500 is that any
defects during the recrystallization of the germanium are pushed
further past the end 16C of the germanium photodetector layer 16
into the photodetector layer extensions 502.
[0040] Referring now to FIG. 6, another exemplary embodiment of a
germanium photodetector 600 is illustrated which is similar to
germanium photodetector 10 except that germanium photodetector 600
has a different photodetector layer extension 602. The
photodetector layer extension 602 curves off to one side of
photodetector layer 16. For purposes of illustration and not
limitation, the photodetector layer extension 602 may deviate to
one side 44 as indicated in FIG. 6 by 1 to 10 .mu.m, for example 5
.mu.m.
[0041] An advantage of germanium photodetector 600 is that any
defects during the recrystallization of the germanium are pushed
further past the end 16C of the germanium photodetector layer 16
into the photodetector layer extensions 602.
[0042] The previous germanium photodetectors 10, 400, 400', 500 all
had photodetector layer extensions 30, 402, 402', 502 that angled
off to both sides of the germanium photodetector layer 16. It is
within the scope of the exemplary embodiments for the photodetector
layer extensions 30, 402, 402', 502 to angle off to only one side
as is the case with the photodetector layer extensions 602 of the
germanium photodetector 600. Germanium photodetector 700 in FIG. 7
is one such example where the photodetector layer extension 702
angles off to only one side of the germanium photodetector layer 16
as compared to germanium photodetector 500 where the photodetector
layer extensions 502 angle off to both sides of the germanium
photodetector layer 16.
[0043] Referring now to FIG. 8, another exemplary embodiment of a
germanium photodetector 800 is illustrated which is similar to
germanium photodetector 10 except that germanium photodetector 800
has a wider portion 16D of the photodetector layer 16 near the seed
window 18. For purposes of illustration and not limitation, the
photodetector layer 16 may have a width 40 as indicated in FIG. 8
in the range of 0.5 to 3 .mu.m, for example a width of 1.0 .mu.m.
Further, for purposes of illustration and not limitation, the wider
portion 16D may have a maximum width 46 as indicated in FIGS. 8 of
1.5 to 5 times, for example 3 times, the width 40 of the
photodetector layer 16. It is noted that the wider portion 16D
gradually tapers from the seed window 18 to where the wider portion
16 meets the remaining photodetector layer 16.
[0044] An advantage of germanium photodetector 800 is that any
defects during the recrystallization of the germanium are pushed
further past the end 16C of the germanium photodetector layer 16
into the photodetector layer extensions 30. Another advantage of
germanium photodetector 800 is that the wider portion 16D of the
photodetector layer 16 helps to increase the mole fraction of
germanium in the photodetector diode 16A.
[0045] Referring now to FIG. 9, another exemplary embodiment of a
germanium photodetector 900 is illustrated which is similar to
germanium photodetector 800 except that germanium photodetector 900
has a different wider portion 16E of the photodetector layer 16
near the seed window 18. For purposes of illustration and not
limitation, the photodetector layer 16 may have a width 40 as
indicated in FIG. 9 in the range of 0.5 to 3 .mu.m, for example a
width of 1.0 .mu.m. Further, for purposes of illustration and not
limitation, the wider portion 16E may have a maximum width 48 as
indicated in FIGS. 9 of 1.5 to 5 times, for example 3 times, the
width 40 of the photodetector layer 16. It is noted that the wider
portion 16E of germanium photodetector 900 has a uniform width near
the seed window and then gradually tapers to the main portion of
the photodetector layer 16.
[0046] An advantage of germanium photodetector 900 is that any
defects during the recrystallization of the germanium are pushed
further past the end 16C of the germanium photodetector layer 16
into the photodetector layer extensions 30. Another advantage of
germanium photodetector 900 is that the wider portion 16D of the
photodetector layer 16 helps to increase the mole fraction of
germanium in the photodetector diode 16A.
[0047] Referring now to FIG. 10, another exemplary embodiment of a
germanium photodetector 1000 is illustrated which is similar to
germanium photodetector 10 but differs in some respects. It is
noted that germanium photodetector 1000 does not have the
photodetector layer extensions previously described with respect to
germanium photodetector 10. It is further noted that the waveguide
12 having incoming light 14 of germanium photodetector 1000 angles
underneath the photodetector layer 16 from the side and thereafter
proceeds underneath the photodetector layer 16 past the seed window
18. The waveguide 12 proceeds underneath the photodetector layer 16
at a point to the left of the end 16C of the photodetector layer
16. The distance between where the waveguide 12 angles underneath
the photodetector layer 16 and the end 16C of the photodetector
layer 16 may be empirically determined as to be in the region 16A
where defects are minimized. This distance depends on the defect
formation details of the process used to form the germanium
photodetector 10.
[0048] The advantage of germanium photodetector 1000 is that the
defects are present at the end 16C of the photodetector layer 16
and not in the portion of the photodetector layer 16 that comprises
the photodetector diode 16A. The result is that the photodetector
diode 16A is in the high responsivity and low defect region.
[0049] Referring now to FIG. 11, another exemplary embodiment of a
germanium photodetector 1100 is illustrated which is similar to
germanium photodetector 10 but differs in some respects. It is
noted that germanium photodetector 1100 does not have the
photodetector layer extensions previously described with respect to
germanium photodetector 10. It is further noted that the waveguide
12 having incoming light 14 of germanium photodetector 1000 angles
underneath the photodetector layer 16 from the side and thereafter
proceeds underneath the photodetector layer 16. The path of the
light from the waveguide 12 is from where the waveguide 12 angles
underneath the photodetector layer 16 through the end 16C of the
photodetector layer 16. The light from the waveguide 12 never
passes by the seed window 18. In this regard, the waveguide 12 is
decoupled from another waveguide 1102 that is underneath the seed
window 18. During the RMG process, the photodetector layer 16
recrystallizes from the waveguide 1102 and not waveguide 12 as in
the previous embodiments. Further, the photodetector diode 16A is
chosen at a location before the end 16C so that the photodetector
diode 16A is at a high germanium mole fraction region but before
the end 16C of the photodetector layer 16 where defects might
accumulate. The distance between the end 16C and the location of
the photodetector diode 16A may be empirically determined as to be
in the region 16A where defects are minimized.
[0050] The advantage of germanium photodetector 1100 is that the
defects are present at the end 16C of the photodetector layer 16
and not in the photodetector diode 16A. The result is that the
photodetector diode 16A is in the high responsivity and low defect
region.
[0051] It will be apparent to those skilled in the art having
regard to this disclosure that other modifications of the exemplary
embodiments beyond those embodiments specifically described here
may be made without departing from the spirit of the invention.
Accordingly, such modifications are considered within the scope of
the invention as limited solely by the appended claims.
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