U.S. patent application number 14/961963 was filed with the patent office on 2017-06-08 for method of making photonic crystal.
The applicant listed for this patent is NATIONAL CHUNG SHAN INSTITUTE OF SCIENCE AND TECHNOLOGY. Invention is credited to TA-CHING LI, BO-CHENG LIN, DAI-LIANG MA, BANG-YING YU.
Application Number | 20170159206 14/961963 |
Document ID | / |
Family ID | 58800192 |
Filed Date | 2017-06-08 |
United States Patent
Application |
20170159206 |
Kind Code |
A1 |
LI; TA-CHING ; et
al. |
June 8, 2017 |
METHOD OF MAKING PHOTONIC CRYSTAL
Abstract
A method of making a photonic crystal includes step 1 providing
a seed, followed by etching a surface of the seed to form thereon
submicron voids; step 2 providing a graphite disk, followed by
coating a side of the graphite disk with a graphite adhesive
whereby the void-formed surface of the seed is attached to the
graphite disk to form a seed holder; step 3 placing the seed holder
above a growth chamber, followed by placing a raw material below
the growth chamber; step 4 forming a thermal field in the growth
chamber with a heating device to sublime the raw material; and step
5 controlling temperature, thermal field, atmosphere and pressure
in the growth chamber to allow the gaseous raw material to be
conveyed and deposited on the seed, thereby forming a photonic
crystal.
Inventors: |
LI; TA-CHING; (TAOYUAN CITY,
TW) ; MA; DAI-LIANG; (TAOYUAN CITY, TW) ; YU;
BANG-YING; (TAOYUAN CITY, TW) ; LIN; BO-CHENG;
(TAOYUAN CITY, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL CHUNG SHAN INSTITUTE OF SCIENCE AND TECHNOLOGY |
Taoyuan City |
|
TW |
|
|
Family ID: |
58800192 |
Appl. No.: |
14/961963 |
Filed: |
December 8, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C30B 23/025 20130101;
C30B 29/36 20130101 |
International
Class: |
C30B 23/02 20060101
C30B023/02; C30B 29/36 20060101 C30B029/36; C30B 23/00 20060101
C30B023/00 |
Claims
1. A method of making a photonic crystal, the method comprising:
step 1: providing a seed, followed by etching a surface of the seed
to form thereon submicron voids; step 2: providing a graphite disk,
followed by coating a side of the graphite disk with a graphite
adhesive whereby the void-formed surface of the seed is attached to
the graphite disk to form a seed holder; step 3: placing the seed
holder above a growth chamber, followed by placing a raw material
below the growth chamber; step 4: forming a thermal field in the
growth chamber with a heating device to sublime the raw material by
controlling the thermal field in a manner to position the seed
holder at a relatively cool end of the thermal field and position
the raw material at a relatively hot end of the thermal field; and
step 5: controlling temperature, thermal field, atmosphere and
pressure in the growth chamber to allow the gaseous raw material to
be conveyed and deposited on the seed, thereby forming a photonic
crystal, wherein, in step 5, the submicron voids are subjected to a
locally high temperature such that crystals at the bottom of the
submicron voids sublime, thereby increasing a depth of the
submicron voids, and then gas molecules in the submicron voids
crystallize on a surface of the graphite adhesive to seal the
submicron voids hermetically, thereby finalizing formation of the
submicron voids.
2. The method of claim 1, wherein steps 1-5 are repeated to use the
photonic crystal made in preceding steps 1-5 as a seed and thus
form a photonic crystal having multiple layers of submicron
voids.
3. The method of claim 1, wherein the seed and the raw material are
wide-bandgap materials.
4. The method of claim 3, wherein the wide-bandgap material is one
of silicon carbide, gallium nitride and aluminum nitride.
5. The method of claim 4, wherein the wide-bandgap material is
silicon carbide.
6. The method of claim 5, wherein the silicon carbide has a silicon
surface.
7. The method of claim 1, wherein the submicron voids formed by
etching performed in step 1 have a depth of at least 500 .mu.m.
8. The method of claim 1, wherein the graphite adhesive further
comprises a doping element which, in step 5, evaporates and spreads
to the submicron voids to deposit in the submicron voids such that
the doping element is eventually enclosed in the submicron
voids.
9. The method of claim 8, wherein the doping element is carbon.
10. The method of claim 8, wherein the doping element is a metallic
element.
Description
FIELD TECHNOLOGY
[0001] The present invention relates to methods of making a
photonic crystal and more particularly to a method of making a
photonic crystal having submicron voids.
BACKGROUND
[0002] Conventional growth of crystals from silicon carbide is
achieved by Physical Vapor Transport (PVT) and Physical Vapor
Deposition (PVD) which are also applicable to mass production of
chips. For example, U.S. Pat. No. 5,746,827 discloses a method of
growing large-size crystals from silicon carbide by PVT.
[0003] Furthermore, a photonic crystal exhibits periodic changes in
material refractive index or dielectric constant in two-dimensional
or three-dimensional space to simulate arrangement of atoms in a
solid-state crystal. Hence, as regards related prior art, Taiwan
patents 1318418 and U.S. Pat. No. 8,384,988 disclose growing a
crystal in a two-dimensional manner to build a three-dimensional
structure at the expense of restricting the photonic crystal to
two-dimensional transmission. Due to the difficulty in a
manufacturing process, three-dimensional photonic crystals lag
behind two-dimensional photonic crystals in terms of technological
advancement. There are few research conducted on three-dimensional
crystal manufacturing techniques in Taiwan and the United States,
because the prior art renders it difficult to deposit different
types of atoms alternately to form multilayer structure. For
instance, U.S. Pat. No. 8,384,988 discloses controlling the
deposition of atoms in electrochemical and voltage-driven manner.
Both U.S. Pat. No. 8,309,113 and U.S. Pat. No. 7,799,378 disclose
that substance or polymeric material microparticles, which can be
etched and removed, serve as the fillers between different media to
undergo a multilayer stacking process and eventually form a
three-dimensional structure. Both U.S. Pat. No. 7,990,611 and U.S.
Pat. No. 7,919,216 disclose making photonic crystals by an optical
means. U.S. Pat. No. 7,990,611 discloses bringing about an
interference pattern by laser-based optical diffraction to thereby
produce a periodic structure required for photonic crystals. U.S.
Pat. No. 7,919,216 discloses effectuating a periodic structure
having the same photonic crystal as a mask. As indicated above,
photonic crystal materials are manufactured by an electrochemical
means, etching, optical exposure and development, and a
semiconductor process, that is, a simple process characterized by
easy processing and etching, thereby imposing limitations upon the
choice of materials which photonic crystals are made from.
SUMMARY
[0004] A photonic crystal contains therein different media
periodically arranged. For example, assuming that a photonic
crystal contains therein a first medium and a second medium which
are periodically arranged, wherein the first medium has a high
refractive index n1, and the second medium has a high refractive
index n2, with the two media having a refractive index ratio of
n1/n2, the larger the ratio, the larger the refractive index
difference between the two media, and in consequence the larger the
photonic band gap of the photonic crystal.
[0005] Photonic crystals are commonly made from materials as
follows: silicon dioxide, with a refractive index (n) of 1.45; and
zinc oxide, with a refractive index (n) of 2.0, Compared with
silicon dioxide and zinc oxide, wide-bandgap materials has a high
refractive index. For example, silicon carbide has a refractive
index (n) of 2.65, aluminum nitride has a refractive index (n) of
2.15, and gallium nitride has a refractive index (n) of 2.4.
[0006] In the situation where air, whose refractive index (n) also
approximates to 1, serves as the second medium with a low
refractive index, the larger the refractive index of the first
medium, the larger the refractive index difference of the photonic
crystal, and thus the larger the photonic band gap. Using a
wide-bandgap material with a high refractive index as the first
medium is effective in increasing the refractive index difference
between two media to thereby obtain a photonic crystal with a large
photonic band gap.
[0007] Hence, it is necessary to provide a method of making a
photonic crystal from a wide-bandgap material to increase the
refractive index difference between two media of a photonic
crystal.
[0008] To overcome the aforesaid drawback of the prior art, the
present invention provides a method of making a photonic crystal.
The method comprises:
[0009] step 1: providing a seed, followed by etching a surface of
the seed to form thereon submicron voids;
[0010] step 2: providing a graphite disk, followed by coating a
side of the graphite disk with a graphite adhesive whereby the
void-formed surface of the seed is attached to the graphite disk to
form a seed holder;
[0011] step 3: placing the seed holder above a growth chamber,
followed by placing a raw material below the growth chamber;
[0012] step 4: forming a thermal field in the growth chamber with a
heating device to sublime the raw material by controlling the
thermal field in a manner to position the seed holder at a
relatively cool end of the thermal field and position the raw
material at a relatively hot end of the thermal field; and
[0013] step 5: controlling temperature, thermal field, atmosphere
and pressure in the growth chamber to allow the gaseous raw
material to be conveyed and deposited on the seed, thereby forming
a photonic crystal.
[0014] In step 5, the submicron voids are subjected to a locally
high temperature such that crystals at the bottom of the submicron
voids sublime to thereby produce gas molecules, thereby increasing
the depth of the submicron voids; afterward, the gas molecules in
the submicron voids crystallizes on the surface of the graphite
adhesive to thereby seal the submicron voids hermetically, thereby
finalizing the formation of the submicron voids.
[0015] Regarding the method, steps 1-5 are repeated to use the
photonic crystal made in preceding steps 1-5 as a seed and thus
form a photonic crystal having multiple layers of submicron
voids.
[0016] Regarding the method, the seed and the raw material are
wide-bandgap materials.
[0017] Regarding the method, the wide-bandgap material is silicon
carbide, gallium nitride or aluminum nitride.
[0018] Regarding the method, wherein the wide-bandgap material is
silicon carbide.
[0019] Regarding the method, wherein the silicon carbide has a
silicon surface.
[0020] Regarding the method, the submicron voids formed by etching
performed in step 1 have a depth of at least 500 .mu.m.
[0021] Regarding the method, wherein the graphite adhesive further
comprises a doping element which, in step 5, evaporates and spreads
to the submicron voids to deposit in the submicron voids such that
the doping element is eventually enclosed in the submicron
voids.
[0022] Regarding the method, wherein the doping element is
carbon.
[0023] Regarding the method, wherein the doping element is a
metallic element.
[0024] The present invention is characterized in that a
wide-bandgap monocrystalline crystal is grown from a seed with a
surface having submicron voids by a Physical Vapor Transport (PVT)
system such that air or a specific metallic element is periodically
enclosed in the wide-bandgap crystal to form a photonic
crystal.
[0025] A method of making a photonic crystal according to the
present invention is characterized in that: the photonic crystal is
made from a seed with a surface having submicron voids to create a
temperature gradient difference such that crystals at the bottom of
the submicron voids sublime, thereby increasing the depth of the
submicron voids; afterward, the gaseous molecules in the submicron
voids crystallize on the surface of the graphite adhesive such that
the seed encloses a doping element or forms voids gradually in the
course of crystal growth, thereby finalizing the formation of a
two-dimensional or even three-dimensional photonic crystal.
[0026] Compared with the prior art, the present invention provides
a method of making a photonic crystal so as to make the photonic
crystal from a wide-bandgap material. With the wide-bandgap
material having a high refractive index, the photonic crystal thus
made has a large photonic band gap.
BRIEF DESCRIPTION
[0027] Objectives, features, and advantages of the present
invention are hereunder illustrated with specific embodiments in
conjunction with the accompanying drawings, in which:
[0028] FIG. 1 is a schematic view of a seed holder according to
embodiment 1 of the present invention;
[0029] FIG. 2 is a schematic view of a growth chamber according to
embodiment 1 of the present invention;
[0030] FIG. 3 is a schematic view of how to perform step 5 on a
photonic crystal according to embodiment 1 of the present
invention;
[0031] FIG. 4 is a schematic view of how to perform step 5 on a
photonic crystal according to embodiment 1 of the present
invention;
[0032] FIG. 5 is a schematic view of a seed holder according to
embodiment 2 of the present invention;
[0033] FIG. 6 is a schematic view of how to perform step 5 on a
photonic crystal according to embodiment 2 of the present
invention;
[0034] FIG. 7 is a schematic view of how to perform step 5 on a
photonic crystal according to embodiment 2 of the present
invention;
[0035] FIG. 8 is a schematic view of a seed holder according to
embodiment 3 of the present invention;
[0036] FIG. 9 is a schematic view of how to perform step 5 on a
photonic crystal according to embodiment 3 of the present
invention;
[0037] FIG. 10 is a schematic view of how to perform step 5 on a
photonic crystal according to embodiment 3 of the present
invention;
[0038] FIG. 11 is a diagram of isotherms on the surface of a seed
having submicron voids according to the present invention; and
[0039] FIG. 12 is a diagram of isotherms on the surface of a seed
lacking submicron voids according to the present invention.
DETAILED DESCRIPTION
Embodiment 1
[0040] Embodiment 1 is implemented by following the steps below to
make a photonic crystal having a single layer of submicron
voids.
[0041] Step 1: providing a seed, followed by etching a surface of
the seed to form thereon submicron voids.
[0042] In embodiment 1, the seed is silicon carbide, but the
present invention is not limited thereto. The seed can also be any
other wide-bandgap material, such as aluminum nitride or gallium
nitride. Preferably, the seed has a silicon surface whenever
silicon carbide serves as the seed.
[0043] In step 1, a surface of the seed is etched to thereby take
on a submicron pattern formed from submicron voids.
[0044] In step 1, the submicron voids have a depth of 500 .mu.m,
but the present invention is not limited thereto. Preferably, the
submicron voids have a depth of 500 .mu.m or more.
[0045] Step 2: providing a graphite disk, followed by coating one
side of the graphite disk with a graphite adhesive whereby the
void-formed surface of the seed is attached to the graphite disk to
form a seed holder.
[0046] Referring to FIG. 1, a seed holder 110 made with step 2
comprises: a graphite disk 111; a graphite adhesive 112 coated on
one surface of the graphite disk 111; and a seed 114 with one
surface having submicron voids 113, wherein the submicron voids 113
are disposed between the graphite adhesive 112 and the seed
114.
[0047] Step 3: placing the seed holder above a growth chamber,
followed by placing a raw material below the growth chamber.
[0048] Referring to FIG. 2, the seed holder 110 is disposed above a
growth chamber 120, and the raw material 121 is disposed below the
growth chamber 120. A heating device 122 is positioned in the
vicinity of the growth chamber 120. In the subsequent steps, the
heating device 122 creates a thermal field inside the growth
chamber 120.
[0049] In embodiment 1, the raw material is silicon carbide, but
the present invention is not limited thereto. The raw material can
also be any other wide-bandgap material, such as aluminum nitride
or gallium nitride.
[0050] Step 4: forming a thermal field in the growth chamber with a
heating device to sublime the raw material by controlling the
thermal field in a manner to position the seed holder at a
relatively cool end of the thermal field and position the raw
material at a relatively hot end of the thermal field.
[0051] Step 5: controlling temperature, thermal field, atmosphere
and pressure in the growth chamber to allow the gaseous raw
material to be conveyed and deposited on the seed, thereby forming
a photonic crystal. In step 5, the submicron voids are subjected to
a locally high temperature such that crystals at the bottom of the
submicron voids sublime, thereby increasing the depth of the
submicron voids; afterward, the gaseous molecules in the submicron
voids crystallize on the surface of the graphite adhesive to
thereby seal the submicron voids hermetically, thereby finalizing
the formation of the submicron voids.
[0052] Referring to FIG. 3, in step 5, the submicron voids 113 are
subjected to a locally high temperature such that crystals at the
bottom of the submicron voids sublime, thereby increasing the depth
of the submicron voids 113.
[0053] Referring to FIG. 4, the gaseous molecules in the submicron
voids crystallize on the surface of the graphite adhesive 112 to
seal the submicron voids hermetically, thereby finalizing the
formation of the submicron voids 141.
[0054] In embodiment 1, the growth chamber has a temperature of
2100-2200.degree. C., atmosphere of Ar/N.sub.2, and pressure of 1-5
torr, but the present invention is not limited thereto. Persons
skilled in the art understand that the temperature, thermal field,
atmosphere and pressure in the growth chamber can be kept within an
appropriate range according to the seed in use, the raw materials
which the seed is made from, and the intended deposition rate.
Embodiment 2
[0055] In embodiment 2, a photonic crystal with two layers of
submicron voids is made by following the steps below.
[0056] Step 1: a photonic crystal made in embodiment 1 is provided
to serve as a seed, and then one surface of the seed is etched to
form a seed with a surface having submicron voids.
[0057] In embodiment 2, the seed is silicon carbide, but the
present invention is not limited thereto. The seed can also be any
other wide-bandgap material, such as aluminum nitride or gallium
nitride. In the situation where silicon carbide is used as a seed,
the seed has a silicon surface, preferably.
[0058] In step 1, a surface of the seed is etched to thereby take
on a submicron pattern formed from submicron voids.
[0059] In step 1, the submicron voids have a depth of 500 .mu.m,
but the present invention is not limited thereto. Preferably, the
submicron voids have a depth of 500 .mu.m or more.
[0060] Step 2: providing a graphite disk, followed by coating one
side of the graphite disk with a graphite adhesive whereby the
void-formed surface of the seed is attached to the graphite disk by
the graphite adhesive to form a seed holder.
[0061] Referring to FIG. 5, the seed holder 210 made in step 2
comprises: a graphite disk 211; a graphite adhesive 212 coated on
one side of the graphite disk 211; and a seed 214 with a surface
having submicron voids 213 and having therein first layer submicron
voids 241, wherein the submicron voids 213 are disposed between the
graphite adhesive 212 and the seed 214.
[0062] Step 3: placing the seed holder above a growth chamber,
followed by placing a raw material below the growth chamber.
[0063] Embodiment 2 has the same growth chamber, seed holder in the
growth chamber, and raw materials as embodiment 1.
[0064] In embodiment 2, the raw material is silicon carbide, but
the present invention is not limited thereto. The raw material can
also be any other wide-bandgap material, such as aluminum nitride
or gallium nitride.
[0065] Step 4: forming a thermal field in the growth chamber with a
heating device to sublime the raw material by controlling the
thermal field in a manner to position the seed holder at a
relatively cool end of the thermal field and position the raw
material at a relatively hot end of the thermal field.
[0066] Step 5: controlling temperature, thermal field, atmosphere
and pressure in the growth chamber to allow the gaseous raw
material to be conveyed and deposited on the seed, thereby forming
a photonic crystal. In step 5, the submicron voids are subjected to
a locally high temperature such that crystals at the bottom of the
submicron voids sublime, thereby increasing the depth of the
submicron voids; afterward, the gaseous molecules in the submicron
voids crystallize on the surface of the graphite adhesive to
thereby seal the submicron voids hermetically, thereby finalizing
the formation of second layer submicron voids.
[0067] Referring to FIG. 6, in step 5, the submicron voids 213 are
subjected to a locally high temperature such that crystals at the
bottom of the submicron voids sublime, thereby increasing the depth
of the submicron voids 213.
[0068] Referring to FIG. 7, afterward, the gaseous molecules in the
submicron voids crystallize on the surface of the graphite adhesive
212 to thereby seal the submicron voids hermetically, thereby
forming second layer submicron voids 242.
[0069] In embodiment 2, the growth chamber has a temperature of
2100-2200.degree. C., atmosphere of Ar/N.sub.2, and pressure of 1-5
torr, but the present invention is not limited thereto. Persons
skilled in the art understand that the temperature, thermal field,
atmosphere and pressure in the growth chamber can be kept within an
appropriate range according to the seed in use, the raw materials
which the seed is made from, and the intended deposition rate.
[0070] In embodiment 2, the photonic crystal made in embodiment 1
is used as a seed, and then steps 1-5 described in embodiment 1 are
repeated to thereby make a photonic crystal having two layers of
submicron voids, but the present invention is not limited thereto.
Instead, embodiment 2 can further involve repeating steps 1-5 in
multiple instances such that the photonic crystal made in the
preceding steps 1-5 is used as a seed to form a photonic crystal
having multiple layers of submicron voids, thereby attaining a
two-dimensional or even three-dimensional photonic crystal
structure.
Embodiment 3
[0071] In embodiment 3, a photonic crystal with one layer of
submicron voids each enclosing a doping element is made by
following the steps below.
[0072] Step 1: providing a seed, followed by etching a surface of
the seed to form thereon submicron voids.
[0073] In embodiment 3, the seed is silicon carbide, but the
present invention is not limited thereto. The seed can also be made
from any other wide-bandgap material, such as aluminum nitride or
gallium nitride. In the situation where the seed is made from
silicon carbide, the seed has a silicon surface, preferably.
[0074] In step 1, a surface of the seed is etched to thereby take
on a submicron pattern formed from submicron voids.
[0075] In step 1, the submicron voids have a depth of 500 .mu.m,
but the present invention is not limited thereto. Preferably, the
submicron voids have a depth of 500 .mu.m or more.
[0076] Step 2: providing a graphite disk, followed by coating one
side of the graphite disk with a graphite adhesive whereby the
void-formed surface of the seed is attached to the graphite disk to
form a seed holder, wherein the graphite adhesive contains a doping
element. Unlike embodiment 1, embodiment 3 is characterized in that
the graphite adhesive contains a doping element.
[0077] In embodiment 3, the doping element is carbon, but the
present invention is not limited thereto. For example, the doping
element can also be a metallic element.
[0078] Referring to FIG. 8, wherein the seed holder 310 made in
step 2 comprises: a graphite disk 311; a graphite adhesive 312
coated on one surface of the graphite disk 311 and comprising a
doping element 343; and a seed 314 with a surface having submicron
voids 313, wherein the submicron voids 313 are disposed between the
graphite adhesive 312 and the seed 314.
[0079] Step 3: placing the seed holder above a growth chamber,
followed by placing a raw material below the growth chamber.
[0080] Embodiment 3 has the same growth chamber, seed holder in the
growth chamber, and raw materials as embodiment 1.
[0081] In embodiment 3, the raw material is silicon carbide, but
the present invention is not limited thereto. The raw material can
also be any other wide-bandgap material, such as aluminum nitride
or gallium nitride.
[0082] Step 4: forming a thermal field in the growth chamber with a
heating device to sublime the raw material by controlling the
thermal field in a manner to position the seed holder at a
relatively cool end of the thermal field and position the raw
material at a relatively hot end of the thermal field.
[0083] Step 5: controlling temperature, thermal field, atmosphere
and pressure in the growth chamber to allow the gaseous raw
material to be conveyed and deposited on the seed, thereby forming
a photonic crystal. In step 5, the submicron voids are subjected to
a locally high temperature such that crystals at the bottom of the
submicron voids sublime, thereby increasing the depth of the
submicron voids. Then, gaseous molecules in the submicron voids
crystallize on the surface of the graphite adhesive to seal the
submicron voids hermetically, thereby finalizing the formation of
the submicron voids. In step 5, the doping element evaporates and
spreads to the submicron voids so as to deposit in the submicron
voids such that the doping element is eventually enclosed in the
submicron voids.
[0084] Referring to FIG. 9, in step 5, the submicron voids 313 are
subjected to a locally high temperature such that crystals at the
bottom of the submicron voids sublime, thereby increasing the depth
of the submicron voids 313. The doping element 343 evaporates and
spreads to the submicron voids 313.
[0085] Referring to FIG. 10, the gaseous molecules in the submicron
voids crystallize on the surface of the graphite adhesive 312 to
seal the submicron voids hermetically, thereby finalizing the
formation of the submicron voids 341, wherein the doping element
343 deposits in the submicron voids and thus is eventually enclosed
in the submicron voids 341.
[0086] In embodiment 3, the growth chamber has a temperature of
2100-2200.degree. C., atmosphere of Ar/N.sub.2 and pressure of 1-5
torr, but the present invention is not limited thereto. Persons
skilled in the art understand that the temperature, thermal field,
atmosphere and pressure in the growth chamber can be kept within an
appropriate range according to the seed in use, the raw materials
which the seed is made from, and the intended deposition rate.
[0087] In step 5 of the method of making a photonic crystal
according to the present invention, with the submicron voids having
a lower thermal conductivity than the nearby crystal material, the
thermal conductivity of the submicron void-formed surface of the
seed varies with the submicron pattern formed from the submicron
voids. The submicron voids exhibits unsatisfactory thermal
conductivity and thus has a high temperature. In step 5, due to the
locally high temperature at the submicron voids, the crystals at
the bottoms of submicron voids sublime and thus turn into gaseous
molecules, thereby increasing the depth of the submicron voids.
Afterward, in the submicron voids, the gas molecules near the
graphite adhesive crystallize on the surface of the graphite
adhesive as the temperature drops gradually, so as to seal the
submicron voids hermetically, thereby finalizing the formation of
the submicron voids.
[0088] According to the present invention, temperature changes
caused by heating the seed with one surface having submicron voids
by the thermal field in the growth chamber are analyzed by thermal
simulation, and temperature changes caused by heating the seed with
one surface lacking submicron voids by the thermal field in the
growth chamber are analyzed by thermal simulation as well, so as to
provide contrast data for reference.
[0089] FIG. 11 is a diagram of isotherms on the surface of a seed
having submicron voids according to the present invention. FIG. 11
shows that the temperature in the vicinity of the submicron voids
is slightly higher than the temperature of the nearby crystal after
the seed has been heated up by the thermal field in the growth
chamber. Referring to FIG. 11, the higher the isotherms, the more
uneven is the distribution of the temperature within the region.
This indicates that, in even of periodic submicron voids,
significant temperature changes will occur at the junction of the
seed and the graphite adhesive. Referring to FIG. 11, in step 5,
there is a temperature difference between the submicron void region
and the nearby crystal region. The present invention is
characterized in that, due to the aforesaid temperature difference,
submicron voids can be formed inside the seed in step 5 such that a
doping element is enclosed in the submicron voids.
[0090] FIG. 12 is a diagram of isotherms on the surface of a seed
lacking submicron voids according to the present invention. FIG. 12
differs from FIG. 11 in that the isotherms in the vicinity of the
seed surface shown in FIG. 12 are more gradual than those shown in
FIG. 11, thereby indicating no significant changes in the
temperature of the surface of the seed whose surface lacks
submicron voids.
[0091] The present invention is disclosed above by preferred
embodiments. However, persons skilled in the art should understand
that the preferred embodiments are illustrative of the present
invention only, but should not be interpreted as restrictive of the
scope of the present invention.
[0092] Hence, all equivalent modifications and replacements made to
the aforesaid embodiments should fall within the scope of the
present invention. Accordingly, the legal protection for the
present invention should be defined by the appended claims.
* * * * *