U.S. patent application number 10/045356 was filed with the patent office on 2003-04-24 for high sensitivity polarized-light discriminator device.
This patent application is currently assigned to MCNC. Invention is credited to Dausch, David E., Lannon, John M. JR., Temple, Dorota.
Application Number | 20030075767 10/045356 |
Document ID | / |
Family ID | 21937414 |
Filed Date | 2003-04-24 |
United States Patent
Application |
20030075767 |
Kind Code |
A1 |
Lannon, John M. JR. ; et
al. |
April 24, 2003 |
HIGH SENSITIVITY POLARIZED-LIGHT DISCRIMINATOR DEVICE
Abstract
The present invention provides for an improved polarized-light
detector device. The device comprises a photodiode having a first
contact disposed on the backside of a light-sensing medium and a
second contact disposed on the frontside of the light-sensing
medium. A spin filter medium is disposed between the backside of
the light-sensing medium and the first contact. The application of
a magnetic field aligns the magnetic moments in the spin-filter
medium to cause the device to discriminate between different
polarizations of an optical signal. The polarization discrimination
is affected by introducing a net magnetization into the spin filter
medium, thereby allowing selected spin-polarized electrons to
either be transmitted through the spin filter medium to the point
of detection or deflected from further transmission. Additionally,
the invention is embodied in a polarization-selective-light
detector array and methods for discriminating a polarized optical
signal and selective optical wavelength detection.
Inventors: |
Lannon, John M. JR.;
(Raleigh, NC) ; Dausch, David E.; (Raleigh,
NC) ; Temple, Dorota; (Cary, NC) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
MCNC
Research Triangle Park
NC
|
Family ID: |
21937414 |
Appl. No.: |
10/045356 |
Filed: |
October 23, 2001 |
Current U.S.
Class: |
257/414 ;
257/E31.119; 257/E31.127 |
Current CPC
Class: |
H01F 10/3254 20130101;
H01L 31/02327 20130101; H01F 41/325 20130101; B82Y 25/00 20130101;
G01J 4/00 20130101; H01L 31/0216 20130101 |
Class at
Publication: |
257/414 |
International
Class: |
H01L 027/14; H01L
029/82; H01L 029/84 |
Claims
That which is claimed:
1. A high-sensitivity, polarized-light discriminator device
comprising: a photodiode having a first contact disposed on the
backside of a light-sensing medium and a second contact disposed on
the frontside of the light-sensing medium; and a spin filter medium
disposed between the backside of the light-sensing medium and the
first contact, wherein applying a magnetic field to the device
aligns the magnetic moments in the spin filter medium to cause the
device to discriminate between different polarizations of an
optical signal.
2. The device of claim 1, further comprising a magnetic field
proximate to the spin filter medium that induces a net
magnetization in the spin filter medium.
3. The device of claim 2, wherein the magnetic field is an external
magnetic field.
4. The device of claim 2, wherein the magnetic field is a local
magnetic field.
5. The device of claim 1, further comprising an anti-reflective
coating layer disposed on the frontside of the light-sensing medium
and generally surrounding the second contact.
6. The device of claim 1, wherein the light-sensing medium further
comprises a semiconductor material that can be optically
stimulated.
7. The device of claim 1, wherein the spin filter medium further
comprises alternating layers of magnetic material and non-magnetic
material.
8. The device of claim 1, wherein the spin filter medium further
comprises a Giant Magnetoresistance (GMR) multilayer stack.
9. The device of claim 1, wherein the spin filter medium further
comprises a Dilute Magnetic Semiconductor (DMS) layer.
10. The device of claim 1, wherein the spin filter medium further
comprises a ferromagnetic layer.
11. The device of claim 1, wherein the second contact disposed on
the frontside of the light-sensing medium further comprises a
transparent conductive material layer.
12. A high-sensitivity, polarized-light discriminator device,
comprising: a light-sensing substrate having semiconductor
characteristics; a spin filter layer disposed on the backside of
the light-sensing substrate; a contact layer disposed on the spin
filter layer; an anti-reflective coating layer disposed on the
frontside of the light-sensing substrate; and one or more contacts
disposed on the frontside of the light-sensing substrate, wherein
applying a magnetic field to the device aligns the magnetic moments
in the spin filter medium to cause the device to discriminate
between different polarizations of an optical signal.
13. The device of claim 12, further comprising an anti-reflective
coating layer disposed on the frontside of the light-sensing
substrate.
14. The device of claim 12, further comprising a magnetic field
proximate to the spin filter layer that induces a net magnetization
in the spin filter layer.
15. The device of claim 14, wherein the magnetic field is an
external magnetic field.
16. The device of claim 14, wherein the magnetic field is a local
magnetic field.
17. The device of claim 12, wherein the light-sensing substrate
further comprises a semiconductor material that can be optically
stimulated.
18. The device of claim 12, wherein the spin filter layer further
comprises alternating layers of magnetic material and non-magnetic
material.
19. The device of claim 12, wherein the spin filter layer further
comprises a Giant Magnetoresistance (GMR) multilayer stack.
20. The device of claim 12, wherein the spin filter layer further
comprises a semiconductor material doped with metal ions so as to
exhibit ferromagnetic behavior.
21. The device of claim 12, wherein the spin filter layer further
comprises a Dilute Magnetic Semiconductor (DMS) layer.
22. The device of claim 12, wherein the spin filter layer further
comprises a ferromagnetic layer.
23. The device of claim 12, wherein the one or more contacts
further comprises a grid-like array of contacts disposed on the
frontside of the light-sensing medium.
24. The device of claim 12, wherein the one or more contacts
further comprises a transparent conductive material layer.
25 A polarization-selective-light detector array, comprising: a
plurality of photodiodes, each photodiode having a first contact
disposed on the backside of a light-sensing medium and a second
contact disposed on the frontside of the light-sensing medium a
spin filter medium incorporated in each of the plurality of
photodiodes such that the spin filter medium is disposed between
the backside of the light-sensing medium and the first contact, and
a variable wavelength splitter proximate the plurality of
photodiodes that segments an optical signal into individual
wavelengths, wherein applying a magnetic field to the device aligns
the magnetic moments in the spin filter medium to cause the device
to discriminate between different polarizations of an optical
signal.
26. The array of claim 25, further comprising a magnetic field
proximate to the array that induces a net magnetization in the spin
filter medium of the plurality of photodiodes.
27. The array of claim 26, wherein the magnetic field is an
external magnetic field.
28. The array of claim 26, wherein the magnetic field is a local
magnetic field.
29. The array of claim 25, wherein the plurality of photodiodes
further comprise an anti-reflective coating layer disposed on the
frontside of the light-sensing medium and generally surrounding the
second contact.
30. The array of claim 25, wherein the light-sensing medium further
comprises a semiconductor material that is capable of being
optically stimulated.
31. The array of claim 25, wherein the spin filter medium further
comprises an alternating stack of magnetic material and
non-magnetic material.
32. The array of claim 25, wherein the spin filter medium further
comprises a Giant Magnetoresistance (GMR) multilayer stack.
33. The array of claim 25, wherein the spin filter medium further
comprises a semiconductor material doped with metal ions so as to
exhibit ferromagnetic behavior.
34. The array of claim 25, wherein the spin filter medium further
comprises a Dilute Magnetic Semiconductor (DMS) layer.
35. The array of claim 25, wherein the spin filter medium further
comprises a ferromagnetic layer.
36. The array of claim 25, wherein the optical signal is generated
by an array of Vertical Cavity Surface Emitting Lasers
(VCSELs).
37. The array of claim 25, wherein the plurality of photodiodes are
electrically addressable concurrently to detect polarization state
of all wavelengths.
38. The array of claim 25, wherein the plurality of photodiodes are
independently electrically addressable to detect polarization state
of individual wavelengths.
39. A method for discriminating a polarized optical signal, the
method comprising: transmitting a polarized optical signal into a
polarized-light detector having a spin filter medium disposed on
the backside of a light-sensing medium, a first contact disposed on
the spin filter medium and a second contact disposed on the
frontside of the light-sensing medium; exciting electrons to the
conduction band of the light-sensing medium into a spin-polarized
state; applying a reverse bias current to the first and second
contacts to move the excited spin-polarized electrons toward the
spin filter medium and the first contact; applying a magnetic field
to induce net magnetization in the spin filter medium; and
transmitting selected electrons through the spin filter medium
based upon the spin orientation of the electrons.
40. The method of claim 39, further comprising the steps of
detecting the selected electrons that have been transmitted through
the spin filter medium and measuring the output current of the
detected electrons.
41. A method for selective optical wavelength detection; the method
comprising: splitting a multiple wavelength optical signal into
individual wavelength segments; transmitting the individual
wavelength segments into an array of polarized-light detectors,
each of the detectors having a spin filter medium disposed on the
backside of a light-sensing medium, a first contact disposed on the
spin filter medium and a second contact disposed on the frontside
of the light-sensing medium; exciting electrons to the conduction
band of the light-sensing medium into a spin-polarized state;
applying a reverse bias current to the first and second contacts of
at least one polarized light detector to move the excited
spin-polarized electrons toward the spin filter medium and the
first contact; applying a magnetic field to induce net
magnetization in the spin filter medium; transmitting selected
electrons through the spin filter medium based upon the spin
orientation of the electrons; and detecting the selected electrons
at the first contact to measure output current.
42. The method of claim 41, wherein applying a reverse bias current
to the first and second contacts of at least one polarized light
detector to move the excited spin-polarized electrons toward the
spin filter medium and the first contact further comprises applying
a reverse bias current to the first and second contacts of all the
polarized light detectors in the array to detect polarization state
of all wavelengths segments transmitted into the array.
43. The method of claim 41, wherein applying a reverse bias current
to the first and second contacts of at least one polarized light
detector to move the excited spin-polarized electrons toward the
spin filter medium and the first contact further comprises applying
a reverse bias current to the first and second contacts of a
selected group of polarized light detectors in the array to detect
polarization state of selected wavelength segments transmitted into
the array.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to optical detectors, and more
particularly to an integrated solid state light-sensing device that
discriminates between different polarizations of optical signals,
arrays incorporating such light sensing devices and the
corresponding methods for using such devices.
BACKGROUND OF THE INVENTION
[0002] Conventional polarized-light detectors will typically
require the use of polarizing filters/lenses that are positioned
proximate the photodetector to achieve detection of the selected
polarization. In this manner, a discrete filter and/or lens is
required for each particular polarization detection scheme. As
such, these detectors tend to add bulk and size to the overall
light detection systems. Additionally, filtered optical signals
tend to decrease the degree of sensitivity of the detection process
because less of the optical signal ultimately reaches the
light-sensing medium in the photodetector.
[0003] The need exists to develop a polarized-light detector that
will eliminate the need to incorporate external filters and/or
lenses, thereby, decreasing the size of such optical detection
systems and allowing a greater degree of sensitivity and
polarization discrimination capability. Such a device would have
widespread application in optical spectrometry, for example, gas
sensing or characterization. Additionally, enhancements in data
encryption for optical telecommunications could be realized if the
polarized-light detector allows for the detection of optical
signals transmitted on a selected polarization of light.
[0004] Recent advancements in optical communication technology have
led to the development of solid state polarized light emitters that
incorporate the use of magnetic materials in conjunction with light
emitting media. By incorporating these magnetic materials, such as
Giant Magnetoresistance (GMR) materials or Dilute Magnetic
Semiconductor (DMS) materials, the emitters eliminate the need for
optical filters and/or lenses that would typically be used to
convert the emitted light to the desired polarization (i.e., right
circularly polarized, left circularly polarized, etc.). In
addition, by changing the direction of the applied magnetic field,
it is possible to alter the type of polarized light emitted. The
resulting emitters occupy less space, are generally more efficient
and typically provide for devices that can be manufactured at a
lower cost.
[0005] A GMR multilayer stack operates under the principle that
very large changes in resistance can be realized in materials
comprised of alternating very thin layers of various metallic
elements. The general structure of GMR multilayer stacks is
alternating ferromagnetic and non-ferromagnetic spacer layers, each
a few atomic layers thick. The thickness of the spacer layer is
such that the magnetic moments of successive ferromagnetic layers
are aligned anti-parallel to each other in the absence of an
applied magnetic field. It is observed that the resistance of the
structure is much higher when the magnetic moments of the adjacent
magnetic layers are aligned antiparallel than when they are
parallel. Switching from the antiparallel to the parallel
configuration can be achieved by an applied magnetic field. This
effect is referred to as giant magnetoresistance (GMR).
[0006] Dilute magnetic semiconductors (DMSs), based on manganese
doped II-VI and III-V host materials, for example, have recently
received a large amount of attention for their unique combination
of magnetic and electronic properties. DMSs are formed by
substituting a fraction of cations with a magnetic ion. These
alloys exhibit a variety of novel magneto-optical properties coming
from the exchange interaction between the magnetic ions and the
conduction or valence electrons (s.+-.p exchange interaction).
[0007] By incorporating a spin filter layer in a polarized-light
detector it is possible to eliminate the need to incorporate
external filters and/or lenses in the detector construct. This
improvement would decrease the size of such optical detection
systems and allow a greater degree of sensitivity and polarization
discrimination capability.
SUMMARY OF THE INVENTION
[0008] The present invention provides for an improved integrated
solid state light-sensing device that discriminates between
different polarizations of light. The device incorporates a spin
filter layer between the light-sensing medium and the backside
contact of a conventional photodiode structure. Standard
polarized-light detectors require the use of polarizing filters
and/or lenses that are typically placed in front of the
photodetector. The present invention eliminates the need for
polarizing lenses and/or filters, thereby decreasing the overall
size and complexity of a light detection system. Additionally, by
providing for the capability to change the magnetization direction
in the spin filter layer, the device's sensitivity can be altered
from a first polarization to a second polarization. The degree of
sensitivity of the device should be heightened due to the device's
capability to allow the entire incident optical signal to reach the
light-sensing medium unfiltered.
[0009] A polarized-light discriminator device according to the
present invention comprises a conventional photodiode having a
first contact disposed on the backside of a light-sensing medium
and a second contact disposed on the frontside of the light-sensing
medium. A spin filter medium, typically a Giant Magnetoresistance
(GMR) multilayer stack, a Dilute Magnetic Semiconductor (DMS), or a
ferromagnetic layer is disposed between the backside of the
light-sensing medium and the first contact.
[0010] Polarized light incident on the light sensing medium excites
electrons with a preferred spin polarization into the conduction
band of the light-sensing medium. The spin polarization preference
is governed by selection rules for the light sensing medium and the
type of light polarization. The application of a reverse bias
voltage to the first and second contact causes the optically
excited, spin polarized electrons in the light-sensing medium to
move toward the spin filter medium and the first contact. In the
presence of a magnetic field, typically proximate to the spin
filter medium, a net magnetization will be induced in the spin
filter medium. The magnetic field may be an external magnetic
field, a local magnetic field, or any other magnetic field suitable
for inducing a net magnetization in the spin filter medium. The
direction of induced magnetization determines the type of spin
polarized electrons transmitted (or reflected) by the spin filter
medium.
[0011] The device typically incorporates an anti-reflective coating
layer disposed on the frontside of the light-sensing medium (i.e.,
the optical signal receiving side of the photodiode) that serves to
increase the amount of the incident optical signal that reaches the
light-sensing medium. In embodiments in which the second contact is
a grid-like array of one or more contact pads the anti-reflective
coating layer generally surrounds the one or more contact pads. In
embodiments in which the second contact is a transparent conductive
layer, such as Indium Tin Oxide or the like, the anti-reflective
coating layer may be formed directly on the frontside of the
light-sensing medium followed by the transparent conductive layer
or the transparent conductive layer may be formed directly on the
frontside of the light-sensing medium followed by the
anti-reflective coating layer.
[0012] In an alternate embodiment, the polarized-light
discriminator device of the present invention comprises a
light-sensing substrate having semiconductor characteristics, a
spin filter layer, typically a GMR multilayer stack, a DMS material
or a ferromagnetic material, disposed on the backside of the
light-sensing substrate and a contact layer disposed on the spin
filter layer. The frontside of the light-sensing substrate has
disposed thereon an anti-reflective coating layer and one or more
contacts. The application of a magnetic field to the spin filter
layer causes the device to discriminate between different
polarizations of light. The magnetic field may be external, local
or the like, typically proximate to the spin filter layer and is
applied to induce a net magnetization in the spin filter layer.
[0013] The invention is also embodied in a
polarization-selective-light detector array that includes a
plurality of photodiodes, each photodiode having a first contact
disposed on the backside of a light-sensing medium and a second
contact disposed on the frontside of the light-sensing medium. A
spin filter medium is incorporated in each of the plurality of
photodiodes such that the spin filter medium is disposed between
the backside of the light-sensing medium and the first contact.
Additionally, a variable wavelength splitter is positioned
proximate the plurality of photodiodes for the purpose of
segmenting an optical signal into individual wavelengths. In
operation, a reverse bias potential difference is applied to the
first and second contacts and a magnetic field is applied to the
spin filter layer of the plurality of photodiodes to allow the
device to determine the polarization states of the individual
wavelength or, alternatively, a reverse bias potential difference
is applied to select photodiodes within the array to independently
address selected elements (i.e., passive matrix addressing). In a
typical array, a magnetic field is positioned proximate to the
array to induce a net magnetization in the spin filter medium of
the plurality of photodiodes, thus allowing only spin compatible
electrons to be transmitted to the first contact. Additionally, an
anti-reflective coating layer will typically be disposed on the
frontside of the light-sensing medium of each photodiode construct.
The antireflective layer may be formed to surround the second
contact of the photodiode in those embodiments in which the second
contact comprises a grid-like array of contact. Conversely, in
those embodiments in which the second contact comprises a layer of
transparent conductive material, the anti-reflective layer will
typically be formed directly on either the light-sensing medium or
the transparent conductive material.
[0014] Further, the invention is embodied in a method for using the
polarized-light discriminator device of the present invention. The
method comprises the steps of transmitting a polarized optical
signal into a polarized-light detector having a spin filter medium
disposed on the backside of a light-sensing medium, a first contact
disposed on the spin filter medium and a second contact disposed on
the frontside of the light-sensing medium. The polarized optical
signal excites spin-polarized electrons into the conduction band of
the light-sensing medium. The application of a reverse bias current
to the first and second contacts moves the spin-polarized electrons
toward the spin filter medium and the first contact. A magnetic
field is applied to induce net magnetization in the spin filter
medium. The electrical field in conjunction with the magnetic field
causes transmission of select electrons through the spin filter
medium based upon the spin orientation of the electrons. In one
embodiment of the invention the output current of the transmitted
selected electrons is detected at the first contact.
[0015] In accordance with yet another embodiment of the invention,
a method for selective optical wavelength detection comprises
splitting a multiple wavelength optical signal into individual
wavelength segments and transmitting the individual wavelength
segments into an array of photodiodes. Each photodiode having a
spin filter medium disposed on the backside of a light-sensing
medium, a first contact disposed on the spin filter medium and a
second contact disposed on the frontside of the light-sensing
medium. Spin-polarized electrons are then excited within the
light-sensing medium into the conduction band of the medium by the
transmitted polarized optical signal. The application of a reverse
bias current to the first and second contacts moves the excited
spin-polarized electrons toward the spin filter medium and the
first contact. A magnetic field is applied to induce net
magnetization in the spin filter medium. The electrical field in
conjunction with the magnetic field causes transmission of select
electrons through the spin filter medium based upon the spin
orientation of the electrons. The select electrons are then
detected at the first contact by measuring the current output.
[0016] The light-sensing device of the present invention provides
for the capability to discriminate between different polarizations
of optical signals. In doing so it eliminates the need to provide
for extraneous polarizing filters and/or lenses, thereby decreasing
the size of known devices. Additionally, the present invention
provides for a light polarization sensitive device that can be
switched from one polarization to another by switching the electron
spin that is transmitted through the spin filter layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a cross-sectional view of a highly sensitive,
polarized-light discriminator device, in accordance with an
embodiment of the present invention.
[0018] FIG. 2 is a perspective view of a highly sensitive,
polarized-light discriminator device, in accordance with an
embodiment of the present invention.
[0019] FIG. 3 is a cross-sectional view of an alternate embodiment
highly sensitive, polarized-light discriminator, in accordance with
an alternate embodiment of the present invention.
[0020] FIG. 4 is a cross-sectional view of a polarization
selective-light detector array, in accordance with an embodiment of
the present invention.
[0021] FIG. 5 is a flow diagram of a method for discriminating a
polarized optical signal, in accordance with an embodiment of the
present invention.
[0022] FIG. 6 is a flow diagram of a method for selective optical
wavelength detection, in accordance with an embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention now will be described more filly
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout.
[0024] Referring to FIG. 1, in accordance with the present
invention a highly sensitive, polarized-light discriminator device
10 is depicted in cross-section. The device typically incorporates
the structure of a conventional photodiode, such as a Schottky
barrier diode or the like, with a spin filter layer 20 being
disposed between the light-sensing medium 30 and the backside
contact 40. The frontside of the light-sensing medium has disposed
thereon one or more frontside contacts 50 and, in most embodiments,
an anti-reflective layer 60 generally surrounds the frontside
contact(s).
[0025] In operation, an optical source is directed toward the
light-sensing medium 30 and incident photons in the optical beam
excite electron-hole pairs in the n-type region 32 of the
light-sensing medium. The polarization of the incident photons
(i.e., left circularly or right circularly polarized), in
conjunction with the allowed energy states of the light-sensing
medium, will determine the preferred spin orientation of the
excited electrons. An applied electric field causes the excited
electrons to migrate toward the spin filter layer 20. A magnetic
field, either external or local, is applied to the device to induce
a net magnetization in the spin filter layer. Depending on the
orientation of the magnetization in the spin filter medium, only
electrons with a compatible spin polarization (i.e., parallel to
the magnetization) are transmitted through the spin filter medium
to the backside contact 40. In this manner, the electrons reaching
the spin filter medium that have spin polarizations not aligned
with the magnetization of the layer will be filtered (scattered)
out. The transmitted electrons that reach the backside contact are
then detected by an ammeter or other similar device.
[0026] The light-sensing medium 30 typically comprises an organic
or inorganic semiconductor layer or multi-layer stack that is
optically stimulated to act as an electrical conductor. For
example, the light-sensing medium may be formed of a traditional
semiconductor substrate (such as gallium arsenide (GaAs), gallium
nitride (GaN), silicon carbide (SiC) or the like), a polymer or
semiconductor superlattice structure. As shown in FIG. 1, the
light-sensing medium may comprise a region 32, adjacent to the
frontside contacts 50 that has n-type semiconductor
characteristics. The dotted line 34 indicates the transition point
at which the light-sensing medium transitions from the n-type
region to an intrinsic region 36 of the semiconductor. This
embodiment is illustrative of a conventional avalanche photodiode
structure that may be implemented in the present invention. It
should be noted that FIG. 1 illustrates one embodiment of the
invention and that other embodiments utilizing other photodiode
structures, such as p-n diodes, p-i-n diodes and the like, are also
within the inventive concepts herein disclosed. The light-sensing
medium typically has a thickness in the range of about 0.001
millimeters (mm) to about 0.01 mm.
[0027] The spin filter layer 20 is disposed on the backside of the
light-sensing medium 30. It will be understood by those having
ordinary skill in the art that when a layer or medium is described
herein as being "on" another layer or medium, it may be formed
directly on the layer, at the top, bottom or side surface area, or
one or more intervening layers may be provided between the layers.
The spin filter layer may comprise a Giant Magnetoresistance (GMR)
multilayer stack, a Dilute Magnetic Semiconductor (DMS) layer or a
ferromagnetic material.
[0028] In the embodiments in which the spin filter layer 20
comprises a GMR multilayer stack, the stack may comprise
alternating magnetic and non-magnetic layers, for example,
iron/chromium/iron (Fe/Cr/Fe), cobalt/copper/cobalt (Co/Cu/Co),
permalloy/copper/permalloy (FeNiCo/Cu/FeNiCo), etc. As typified by
GMR stacks, the intermediate layer of the stack is a non-magnetic
spacer (Cr, Cu, etc.) that isolates the two magnetic layers. In a
typical embodiment of the present invention the GMR multilayer
stack will have a thickness in the range of about 20 angstroms to
about 200 angstroms, typically about 100 angstroms. The layers of
the GMR stack are typically disposed using conventional
semiconductor processing techniques, such as RF sputtering, ion
beam sputtering or the like.
[0029] In the embodiments in which the spin filter layer 20
comprises a DMS layer, the layer comprises a semiconductor material
doped with a metal ion such that the material exhibits
ferromagnetic behavior. Examples of such semiconductor materials
include gallium arsenide (GaAs), zinc selenide (ZnSe), cadmium
telluride (CdTe) and the like and a suitable metal ion would be
manganese (Mn) or the like. In a typical embodiment of the present
invention the DMS layer will have a thickness of about 200
nanometers (nm) to about 400 nm. The DMS layer is generally
disposed using conventional semiconductor deposition techniques,
such as chemical vapor deposition (CVD) or the like.
[0030] In the embodiments in which the spin filter layer 20
comprises a ferromagnetic material, the layer may be formed of a
single layer or a multilayer stack of ferromagnetic materials, such
as iron (Fe) or the like.
[0031] The backside contact layer 40 is disposed on the spin filter
layer 20. The backside contact layer will typically comprise a
conductive material that is suitable to optical semiconductor
devices. For example, gold may be used to form the contact layer.
In a typical embodiment of the present invention the backside
contact layer will have a thickness in the range of about 0.05
microns to about 0.5 microns. The backside contact layer is
generally disposed using standard semiconductor deposition
techniques, such as evaporation or sputtering.
[0032] The anti-reflective layer 60 is typically disposed on the
frontside of the light-sensing medium 30 prior to providing for the
one or more frontside contacts 50. The anti-reflective layer may
comprise cerium oxide (CeO.sub.2), magnesium fluoride (MgF.sub.2),
tantalum pentoxide (Ta.sub.2O.sub.5), silicon oxide (SiO.sub.2),
silicon nitride (Si.sub.3N.sub.4) or any other optical coating
material that provides anti-reflective properties. The
anti-reflective coating serves to reduce optical signal loss due to
scattering of the signal at the light-sensing medium interface. The
anti reflective coating layer can be deposited on the frontside of
the light-sensing medium using an evaporation process or any other
suitable semiconductor deposition process can be used to form the
anti-reflective layer. Once the anti-reflective layer is formed a
standard photolithography process is typically performed to define
the regions where the one or more frontside contacts will be
disposed. The photolithography process will entail applying
photoresist, masking a predefined contact pattern and etching away
those areas of the anti-reflective layer to define the frontside
contact regions.
[0033] The one or more frontside contacts 50 are then disposed on
the frontside of the light-sensing medium 30 within the openings in
the anti-reflective layer 60 defined by the photolithography
processing. A perspective view of the FIG. 1 embodiment is shown in
FIG. 2. The FIG. 2 view illustrates an embodiment in which the
frontside contacts are disposed in a grid-like array with the
anti-reflective layer generally surrounding the frontside contacts.
The frontside contacts will typically comprise a conductive
material that is suitable to optical semiconductor devices. For
example, gold may be used to form the frontside contacts. In a
typical embodiment of the present invention the frontside contact
layer will have a thickness in the range of about 100 angstroms to
about 5000 angstroms. The one or more frontside contacts are
generally disposed using standard semiconductor deposition
techniques, such as evaporation or sputtering.
[0034] It should be noted that while the embodiment described
herein appears to provide for a specific order of layering; i.e.,
constructing the backside layers prior to disposing the frontside
layers, it is possible to process the layering of the device in any
order that makes for efficient and reliable manufacturing. In other
words, it is possible and within the inventive concepts herein
disclosed to fabricate the device with the frontside layering
preceding the backside layering or for processing of the backside
and frontside layering to be alternated. In same regard, while the
described processing provides for the anti-reflective layer 60 to
be disposed prior to the formation of the frontside contacts 50, it
may also be possible to fabricate the device by initially forming
the frontside contacts followed by the deposition of the
antireflective layer.
[0035] Referring to FIG. 3, an alternate embodiment of the highly
sensitive polarized-light discriminator device 10 is illustrated in
cross-section. In the embodiment shown the frontside contacts have
been replaced with a transparent conducting material layer 70. The
transparent conducting material layer may comprise Indium Tin Oxide
(ITO) or any other suitable transparent conductive material. The
transparent conducting material layer provides the same general
purpose as the frontside contact(s) in the FIG. 1; i.e. electrical
contact points for providing a reverse bias current to the
light-sensing medium of the photodiode. However unlike the
conventional contacts in the FIG. 1 embodiment, the transparent
nature of the transparent conducting material makes it is possible
to form a layer on the frontside of the light-sensing medium that
covers the frontside in its entirety. As shown in FIG. 3, the
transparent conductive material may be disposed directly on the
light-sensing medium 30 with the anti-reflective layer 60
subsequently formed on the transparent conductive material layer.
Additionally, it is possible and within the inventive concepts
herein disclosed to form the anti-reflective layer directly on the
light-sensing medium with the transparent conductive material layer
subsequently formed on the anti-reflective material layer. The
transparent conducting material layer will typically have a
thickness in the range of about 100 angstroms to about 5000
angstroms. The transparent conducting material layer may be
deposited using a conventional sputtering technique or other
suitable methods, depending on the material of choice.
[0036] FIG. 4 is a cross-sectional view of a polarization
selective-light detector array 100, in accordance with an
embodiment of the present invention. The light detector array
provides for the polarization detection of each wavelength in a
multiple wavelength signal. Such an array has potential application
within the field of optical light telecommunication data
encryption. In this regard, the array would allow information to be
encoded based upon the wavelength of the optical signal and the
polarization of the optical signal.
[0037] The array comprises a series of polarized-light
discriminator devices 10 disposed in array formation. Each
polarized-light discriminator device will define a photodiode
having a first contact 40 disposed on the backside of a
light-sensing medium 30 and a second contact 50 disposed on the
frontside of the light-sensing medium. Additionally, each
discriminator device in the array will incorporate a spin filter
layer 20 that is disposed between the light sensing medium and the
backside contact. In the embodiment shown, the array is formed on
substrate 110.
[0038] In order to segment the input optical signal 120 into
wavelength specific segments 130, the light detector array will
comprise a variable wavelength beam splitter 140 that is located
proximate the plurality of polarized-light discriminator devices.
Conventional diffraction gratings or prism structures may be
implemented as wavelength beam splitters.
[0039] In operation, the array of the present invention would
receive an optical signal at the variable wavelength splitter. The
splitter would parse the optical signal into wavelength specific
segments. In turn, the polarization of each of the wavelength
specific segments would be determined by an individual light
discriminator device within the array. In one embodiment of the
present invention, each element in the array is individually
electrically addressable such that each element can independently
detect the polarization state of a given wavelength. In an
alternate embodiment of the present invention, all elements in the
array can be electrically addressable concurrently such that the
array can detect the polarization state of all wavelengths to
determine which wavelengths are "on" or "off" for a given
polarization.
[0040] In accordance with another embodiment of the present
invention, a method for discriminating a polarized optical signal
is defined in the flow diagram of FIG. 5. At step 200, a polarized
optical signal is transmitted from an optical signal source to a
polarized-light detector. The polarized-light detector is in
accordance with the polarized-light detector described in detail
above and will incorporate a spin filter medium between the
backside of a light-sensing medium and the backside electrical
contact. At step 210, the polarized light excites electrons to the
conduction band of the light-sensing medium into a spin-polarized
state. An electrical field in the form of a reverse bias current is
applied to the polarized-light detector, at step 220, to move the
excited spin-polarized electrons toward the spin filter medium and
the backside electrical contact. At step 230, a magnetic field is
applied to induce a net magnetization in the spin filter medium and
based on the magnetization in the spin filter layer, at step 240,
selected electrons are transmitted through the spin filter medium
based upon the spin orientation of the electrons aligning with the
magnetization in the spin filter medium; only electrons with spin
orientations parallel with the magnetization in the spin filter
medium are transmitted. In addition, optional step 250 may be
performed in which the selected electrons that have been
transmitted through the spin filter medium are detected at the
backside contact and output current is measured.
[0041] The invention is also defined in accordance with a method
for selective optical wavelength detection. The method is detailed
in the flow diagram of FIG. 6. At step 300, a multiple wavelength
optical signal is split into individual wavelength components. The
individual wavelength components are then, at step 310, transmitted
into an array of polarized-light detectors. In this regard, one
wavelength component is transmitted into one individual
polarized-light detector. Each polarized-light detector will be in
accordance with the polarized-light detector described in detail
above and will incorporate a spin filter medium disposed between
the light sensing medium and the backside electrical contact. At
step 320, the polarized light excites electrons to the conduction
band of the light-sensing medium into a spin-polarized state. An
electrical field, in the form of a reverse bias current, is applied
to the array of polarized-light detectors, at step 330, to move the
excited spin-polarized electrons toward the spin filter medium and
the backside contact. At step 340, a magnetic field is applied to
induce a net magnetization in the spin filter medium and based on
the magnetization in the spin filter layer, at step 350, selected
electrons are transmitted through the spin filter medium based upon
the spin orientation of the electrons aligning with the
magnetization in the spin filter medium; only electrons with spin
orientations parallel to the magnetization in the spin filter
medium are transmitted. At step 360, the selected electrons that
have been transmitted through the spin filter medium are detected
at the backside contact and output current is measured.
[0042] Accordingly, the present invention provides for an improved
light-sensing device that provides for the capability to
discriminate between different polarizations of optical signals. In
doing so it eliminates the need to provide for extraneous
polarizing filters and/or lenses, thereby decreasing the size of
known devices. Additionally, the present invention provides for a
sensitive device that can be switched from one polarization to
another by switching the electron spin that is transmitted through
the spin filter layer.
[0043] Many modifications and other embodiments of the invention
will come to mind to one skilled in the art to which this invention
pertains having the benefit of the teachings presented in the
foregoing descriptions and the associated drawings. Therefore, it
is to be understood that the invention is not to be limited to the
specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are employed herein, they
are used in a generic and descriptive sense only and not for
purposes of limiting the scope of the present invention in any
way.
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