U.S. patent number 3,847,758 [Application Number 05/331,993] was granted by the patent office on 1974-11-12 for method of manufacturing an electrode system.
This patent grant is currently assigned to U.S. Phillips Corporation. Invention is credited to Ties Siebolt Te Velde.
United States Patent |
3,847,758 |
Te Velde |
November 12, 1974 |
METHOD OF MANUFACTURING AN ELECTRODE SYSTEM
Abstract
The invention relates to a method of manufacturing an electrode
system having a monograin layer. On free grain surfaces of the
monograin layer a first electrode layer is deposited. After a
material-removing treatment, a deposition step is applied in which
parts of enveloping layers of the grains and edges of cores of the
grains adjoining pn-junctions are selectively covered with an
insulating material and a second eletrode layer is deposited on
parts of the cores of the grains not covered.
Inventors: |
Te Velde; Ties Siebolt
(Emmasingel, Eindhoven, NL) |
Assignee: |
U.S. Phillips Corporation (New
York, NY)
|
Family
ID: |
19815410 |
Appl.
No.: |
05/331,993 |
Filed: |
February 12, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Feb 19, 1972 [NL] |
|
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7202215 |
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Current U.S.
Class: |
438/107; 136/250;
205/223; 205/318; 438/63; 438/633; 204/485; 205/118; 148/DIG.120;
205/316; 257/E31.051 |
Current CPC
Class: |
H01L
33/00 (20130101); H01L 31/0384 (20130101); Y10S
148/12 (20130101) |
Current International
Class: |
H01L
31/0384 (20060101); H01L 31/036 (20060101); H01L
33/00 (20060101); C23b 005/48 (); C23b 011/00 ();
B01k 005/02 () |
Field of
Search: |
;29/572
;204/181,56R,15 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mack; John H.
Assistant Examiner: Andrews; R. L.
Attorney, Agent or Firm: Trifari; Frank R.
Claims
What is claimed is:
1. A method of manufacturing an electrode system having a monograin
layer, in which grains of a semiconductor material with enveloping
layers and cores of opposite conductivity types are embedded in a
layer of binder in a substantially monograin layer over a part of
the layer thickness, a first electrode layer for contacting the
enveloping layers of the grains is deposited on one side of the
monograin layer with free grain surfaces, a material-removing
treatment is used in which parts of the cores of the grains and
parts of the enveloping layers of the grains are exposed, after
which in a succeeding process step insulating material is provided
on the exposed parts and a second electrode layer for contacting
the cores of the grains is deposited, characterized in that in said
process step the insulating material is selectively provided on the
exposed parts of the enveloping layers of the grains and on edges
of the exposed parts of the cores of the grains adjoining the
junctions and parts of the cores of the grains not covered during
the provision of the insulating material are then contacted by
depositing the second electrode layer.
2. A method as claimed in claim 1, characterized in that an
insulating layer is provided on the first electrode layer, the
material-removing treatment is applied to both last-mentioned
layers, parts of the first electrode layer being exposed, said
latter parts being covered during the selective provision of
insulating material.
3. A method as claimed in claim 1, characterized in that the
insulating material is provided by electrophoresis in that the
exposed parts are contacted with a bath containing an insulating
material suitable for electrophoretic coating and electrophoresis
is carried out by giving the first electrode layer a voltage
relative to the bath at which the junctions between the cores of
the grains and the enveloping layers of the grains are biased in
the reverse direction.
4. A method as claimed in claim 1, characterized in that the
insulating material is provided by electrochemical polymerisation
in that the exposed parts are contacted with a bath containing a
material which is converted into the insulating material by
electrochemical polymerisation and polymerisation is carried out by
giving the first electrode layer a voltage relative to the bath at
which the junctions between the cores of the grains and the
enveloping layers of the grains are biased in the reverse
direction.
5. A method as claimed in claim 1, characterized in that the
insulating material is provided on the monograin layer prior to the
material-removing treatment and after the treatment the insulating
material is caused to swell so that the exposed parts of the
enveloping layers of the grains and the edges of the exposed parts
of the cores of the grains adjoining the junctions are covered.
6. A method as claimed in claim 1, characterized in that a grinding
process or a polishing process is chosen as a material-removing
treatment.
7. A method as claimed in claim 1, characterized in that prior to
depositing the first electrode layer the monograin layer is
obtained in that the grains are provided as a substantially
monograin layer in an adhesive layer on a substantially plane
substrate and embedded in the layer of binder, after which the
monograin layer is separated from the substrate to obtain the side
with the free grain surfaces.
8. A method as claimed in claim 7, characterized in that the side
with the free grain surfaces is then treated with a specific
solvent for the binder so as to enlarge the free grain surface.
Description
The invention relates to a method of manufacturing an electrode
system having a monograin layer, in which grains of a semiconductor
material with enveloping layers and cores of opposite conductivity
types are embedded in a layer of binder in a substantially
monograin layer over a part of the layer thickness, a first
electrode layer for contacting the enveloping layers of the grains
is deposited on one side of the monograin layer with free grain
surfaces, a material-removing treatment is used in which parts of
the cores of the grains and parts of the enveloping layers of the
grains are exposed, after which in a succeeding process step
insulating material is provided on the exposed part and a second
electrode layer for contacting the cores of the grains is
deposited.
The invention furthermore relates to an electrode system
manufactured by means of the method.
The said electrode systems may comprise monograin layers with
grains operating as diodes, in which the first and the second
electrode layer are deposited on oppositely located sides of the
monograin layer.
One side of other electrode systems manufactured by means of the
above-mentioned method is often free from electrode layers to
facilitate the entrance and/or emanation of light. These electrode
systems ar used, for example, in solar cells and in injection
luminescent light sources.
In manufacturing the said electrode systems, the enveloping layers
of the grains must be connected together and the cores of the
grains must be connected together by electrode layers which may not
contact each other.
It is often difficult to fulfil this requirement since in the
material-removing treatment both the cores of the grains and the
enveloping layers of the grains are exposed; this holds good in
particular if one of the sides of the electrode system must be free
from contact layers. For example, in a method of the type mentioned
in the preamble (see U.S. Pat. No. 3,040,416) an insulating layer
is provided on the first electrode layer and the material-removing
treatment is applied on the side of said layers and the material of
the grains and the material of the first insulating layer must be
matched to each other in such manner and the material-removing
treatment should be such that of the grains a part of the first
electrode layer and a part of the enveloping layer of the grains is
removed and between the grains the first insulating layer is
removed over a greater part of the layer thickness without,
however, entirely removing the first electrode layer from and
between the grains.
After providing insulating material in the form of a second
insulating layer on the exposed parts, a second material-removing
treatment is carried out in which the material of the grain and the
material of the second insulating layer are to be removed to an
equal extent so as to be able to deposit the second electrode layer
which contacts the cores of the grains and is separated from the
first electrode layer.
The materials of the two insulating layers and of the grains must
be accurately matched to each other and in addition very high
requirements are imposed upon the material-removing treatment so
that the above-described method is difficult and cumbersome and
often does not produce the desired result but results, for example,
in shortcircuit.
One of the objects of the invention is to provide a novel method of
contacting the cores of the grains and the enveloping layers of the
grains in an insulated manner and furthermore to provide an
improvement of the method described in the U.S. patent
specification, as a result of which the manufacture becomes easier
and can be carried out in fewer steps. The invention is inter alia
based on the recognition of the fact that the second
material-removing treatment may be omitted when no more insulating
material is used than is necessary for the insulation of the second
electrode layer relative to the enveloping layers of grains.
Therefore, according to the invention, the method is characterized
in that in said process step the insulating material is selectively
provided on the exposed parts of the enveloping layers of the
grains and on edges of the exposed parts of the cores of the grains
adjoining the junctions and parts of the cores of the grains not
covered during the provision of the insulating material are then
contacted by depositing the second electrode layer.
One of the advantages obtained is that a second material-removing
treatment may be omitted and it is achieved that the
material-removing treatment to be used can be particularly simple
since no relief need be provided in the monograin layer. A grinding
or polishing process is preferably chosen as the material-removing
treatment.
By means of the method according to the invention, good results can
be obtained in providing mutually insulated electrode layers on the
cores of the grains and on the enveloping layers of the grains, for
example, in manufacturing the already stated electrode system the
electrode layers of which are deposited on either side of the
monograin layer.
An insulating layer is preferably provided on the first electrode
layer and the material-removing treatment is applied to both
last-mentioned layers, parts of the first electrode layer being
exposed, said last-mentioned parts being covered during the
selective provision of the insulating material.
In a preferred embodiment of the method according to the invention,
the insulating material is provided by electrophoresis in that the
exposed parts are contacted with a bath containing an insulating
material suitable for electrophoretic coating and electrophoresis
is carried out by giving the first electrode layer a voltage
relative to the bath at which the junctions between the cores of
the grains and the enveloping layers of the grains are biased in
the reverse direction.
In another preferred embodiment of the method according to the
invention the insulating material is provided by electrochemical
polymerization in that the exposed parts are contacted with a bath
containing a material which is converted into the insulating
material by electrochemical polymerization and polymerization is
carried by giving the first electrode layer a voltage relative to
the bath at which the junctions between the cores of the grains and
the enveloping layers of the grains are biased in the reverse
direction.
In the above preferred embodiments, the provision of the insulating
material proceeds more slowly according as more material is
provided and is finally discontinued automatically.
The insulating material is preferably provided on the monograin
layer prior to the material-removing treatment and after the
treatment the insulating material is caused to swell so that the
exposed parts of the enveloping layers of the grains and the edges
of the exposed parts of the cores of the grains adjoining the
junctions are covered.
Swelling may be carried out, for example, by a treatment with
vapour or a solution with a swelling agent suitable for the
insulating material.
The swelling agent may be removed, for example, by evaporation or
extraction, in which insulating material remains in the place
covered due to the swelling.
When a grinding process is used as a material-removing treatment,
it is advantageous when the grains project approximately equally
far from the layer of binder with their free grain surfaces.
Therefore, the monograin layer is preferably obtained prior to
depositing the first electrode layer in that the grains are
provided as a substantially monograin layer in an adhesive layer on
a substantially plane substrate and embedded in the layer of
binder, after which the monograin layer is separated from the
substrate to obtain the side with the free grain surfaces.
Preferably the side with the free grain surfaces is then treated
with a specific solvent for the binder so as to enlarge the free
grain surface.
It is achieved that the grains project approximately equally far
from the layer of binder also in the case in which all the grains
are not accurately equally large.
The invention furthermore relates to an electrode system
manufactured by means of the method according to the invention.
The invention will now be described in greater detail with
reference to a drawing and a few examples.
In the drawing:
FIGS. 1 to 5 are diagrammatic sectional views of parts of an
electrode system in successive stages of manufacture by means of
preferred embodiments of the method according to the invention
and
FIG. 6 is a diagrammatic sectional view of a part of an electrode
system in a stage of manufacture by means of a variation of the
method according to the invention.
The manufacture will now be described of an electrode system having
both layers on one side of the monograin layer, which systems are
used in solar cells an injection luminescent light sources. An
electrode system 51 (see FIG. 5) with a monograin layer (11, 21) is
manufactured, in which grains 11 having a size of approximately 50
.mu.m and consisting of semiconductor material, for example gallium
phosphide, having approximately 5 .mu.m thick enveloping layers 12
and cores 13 of opposite conductivity types are embedded in a layer
21 of binder (see FIG. 3) in a substantially monograin layer over
part of the layer thickness.
After implantation in the usual manner in the gallium phosphide
grain of ions of an element which can cause the same conductivity
type in the gallium phosphide as the enveloping layers of the
grains have, a first electrode layer 41 (see FIG. 4) for contacting
the enveloping layers of the grains is deposited on one side 31 of
the monograin layer (11, 21) with free grain surfaces, for example,
by means of vapour deposition of gold. An insulating layer 42, for
example of polyurethane, is provided on the first electrode layer
41. By using a material-removing treatment, for which a grinding
process is preferably chosen, parts 43 of the cores 13 of the
grains, cores 44 of the enveloping layers 12 of the grains and
parts 45 of the first electrode layer 41 are exposed.
Insulating material 52 of materials to be described hereinafter is
selectively provided in the form of a pattern of grains on the
exposed parts 44 of the enveloping layers 12 of the grains, on the
exposed parts 45 of the first electrode layer 41 and on edges 54 of
the exposed parts 43 of the cores 13 of the grains adjoining the
junctions 14.
Parts of the cores 13 of the grains not covered during the
provision of the insulating material 52 are then contacted by
depositing the second electrode layer 53. For that purpose, ions
are implanted in a usual manner in the gallium phosphide grains of
an element which can cause the same conductivity type in the
gallium phosphide as the cores of the grain have, and a second
electrode layer 53 is deposited, for example, by vapour-depositing
gold.
The first electrode layer 41 and the second electrode layer 53 can
be provided with current conductors in a usual manner.
When a grinding process is used as a material-removing treatment,
it is advantageous when the grains project approximately equally
far from the layer of binder with the free grain surfaces.
Therefore, the monograin layer (11, 21) is obtained prior to
depositing the first electrode layer 41 by providing the grains 11
as a layer which has a thickness substantially of one grain in an
adhesive layer 15 on a substantially plane substrate 6 (see FIG.
1).
The adhesive layer 15 consists, for example, of a usual rubber glue
and the substrate 16 of glass. The grains 11 are embedded in the
layer 21 of binder (see FIG. 2) which consists of an electrically
insulating material, for example, polyurethane.
The monograin layer (11, 21) is then separated from the substrate
16 and the side 31 with the free grain surfaces is obtained (see
FIG. 3).
The free grain surface may still be enlarged by a treatment with a
specific solvent for a binder. In the case of polyurethane this can
be carried out in a usual manner by a treatment with an alcoholic
potassium hydroxide solution.
EXAMPLE 1
In the first example the insulating material 52 is provided by
electrophoresis in that the exposed parts 43, 44, 45 are contacted
with a bath containing an insulating material suitable for
electrophoretic coating.
Electrophoresis is carried out by giving the first electrode layer
41 a voltage relative to the bath at which the junctions 14 between
the cores 13 of the grains and the enveloping layers 12 of the
grains are biased in the reverse direction.
The grains consist, for example, of the semiconductor material
gallium phosphide. By doping with zinc the cores 13 have been made
p-type conductive and by doping with sulfur the enveloping layers
12 have been made n-type conductive.
In a manner conventionally used in electrophoretic coating, a bath
is used of a solution of a synthetic resin containing carboxyl
groups and/or hydroxyl groups and of an organic amine or ammonia in
water. The weight concentration of solid of the solution is 10 to
15 percent. Conventional materials such as epoxy-, acrylate- or
alkyl resins may be used as a synthetic resin. A positive voltage
of, for example, approximately +100 volt relative to the bath is
given to the first electrode layer 41. During the passage of
current through the bath, the current rapidly decreases to a
fraction, for example, 1 to 10 percent of the original value, and
the exposed parts 44, 45 and at most edges 54 of the exposed parts
43 of the cores 13 of the grains are covered. The insulating
material reaches, for example, a layer thickness of 5 .mu.m. The
insulating material is finally subjected to a baking treatment for
5 to 20 minutes 120.degree. to 180.degree.C. During providing the
insulating material there may also be proceeded so that a certain
current density is adjusted (in the order of magnitude of 0.1
mA/cm.sup. 2) and the process is discontinued when the voltage has
reached a certain high value.
EXAMPLE 2
The second example differs from the first example in that in this
case the insulating material 53 is provided by electrochemical
polymerisation in that the exposed parts 43, 44, 45 are contacted
with a bath containing a material which is converted into the
insulating material by electrochemical polymerisation. The
polymerisation is carried out by giving the first electrode layer
41 a voltage relative to the bath at which the junctions 14 between
the cores 13 of the grains and the enveloping layers 12 of the
grains are biased in the reverse direction.
In a manner conventionally used in electrochemical polymerisation a
bath is used having a mixture of orthoisopropylphenol and
triethylamine in a molecular ratio of 10 : 1. At a positive voltage
of +200 V of the first electrode layer 41 relative to the bath,
insulating material 52 is provided in a thickness of 0.6 .mu.m. The
current density decreases during the process from approximately
10.sup.-.sup.3 A/cm.sup.2 to approximately 10.sup.-.sup.6
A/cm.sup.2.
EXAMPLE 3
The third example differs from the preceding examples in that the
insulating material is provided on the monograin layer (11, 21)
prior to the material-removing treatment and the insulating
material after the treatment is allowed to swell so that the
exposed parts 45 of the first electrode layer 41, the exposed parts
44 of the enveloping layers 12 of the grains and the edges 54 of
the exposed parts 43 of the cores 13 of the grains adjoining the
junctions 14 are covered (see FIG. 6). The insulating material is
provided, for example, as an insulating layer 42. As a material for
the insulating layer 42 is used, for example, polyurethane which
swells by a treatment with vapour of ethyl acetate.
After removing the ethyl acetate by evaporation at 80.degree.C,
insulating material 52 remains in the places covered by the
swelling.
The invention is not restricted to the examples described.
For example, instead of gallium phosphide another suitable
semiconductor material, for example zinc selenide, mixed crystals
of gallium arsenide and gallium phosphide or mixed crystals of
gallium arsenide and aluminium arsenide may be used. The cores of
the grains may also show n-type conductivity and the enveloping
layers of the grains may show p-type conductivity. In the latter
case, of course, the insulating material used in the
electrophoretic coating and the material used in the
electrochemical polymerisation must be adapted to the polarity of
the first electrode layer varying relative to the bath. In the case
of electrophoretic coating, for example, synthetic resins on the
basis of melamine are to be considered. Upon providing insulating
material by means of swelling it makes no difference whether the
enveloping layers of the grains have p-type or n-type
conductivity.
The method according to the invention may also be used in
manufacturing electrode systems in which the electrode layers are
present on oppositely located sides of the monograin layer.
* * * * *