Diamond electronic device and process for producing the same

A diamond electronic device constituted of a diamond crystal formed on a substrate comprises a diamond crystal having the ratio (h/L) of length (h) of the diamond crystal in direction substantially perpendicular to the face of the substrate to length (L) of the diamond crystal in direction parallel to the face of the substrate ranging from 1/4 to 1/1000 and an upper face of the diamond crystal making an angle of from substantially 0.degree. to 10.degree. to the face of the substrate, and a semiconductor layer and an electrode layer provided on the diamond crystal, wherein the diamond crystal serves as a heat-radiating layer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a semiconductor electronic device, in 
particular to an electronic device which employs a diamond crystal at 
least for a heat-radiating layer. 
The present invention also relates to a process for producing the above 
electronic device. 
2. Related Background Art 
The formation of a semiconductor crystal on a heat radiation layer of an 
insulator is an important technique to achieve higher response speed of 
electronic elements. Various materials are being investigated for the 
insulator. Of the materials, diamond is attracting attention because of 
its excellent characteristics, which are not achieved by other materials, 
such as larger band gap (5.5 eV), larger carrier mobility (1800 cm.sup.2 
/V.multidot.S for electrons, and 1600 cm.sup.2 /V.multidot.S for positive 
holes), suitability for a heat sink (or heat-releasing material) owing to 
higher thermal conductivity (2000 W/(m.multidot.K)), excellent insulation 
properties (not less than 10.sup.16 .OMEGA..multidot.cm), high hardness, 
high abrasion resistance, and so forth. 
Accordingly, synthesis of diamond from a vapor phase is being developed, in 
particular, by chemical vapor deposition (CVD). Japanese Patent 
Application Laid-Open No. 2-110968 discloses formation of a silicon 
semiconductor layer on a diamond insulator. 
Hitherto, diamond crystals shown below have been formed on a substrate by a 
CVD process. 
(1) A diamond crystal is formed by homoepitaxial growth on a natural or 
artificial diamond base or by heteroepitaxial growth on a cubic boron 
nitride (c-BN) base having a crystal structure close to that of the 
diamond crystal. Both of thus obtained diamond crystal films are in 
epitaxial relation to the underlying base material and are a 
monocrystalline film having an excellent surface smoothness. 
(2) A diamond crystal is formed under ordinary synthesis conditions on a 
silicon substrate, a high melting-point substrate such as molybdenum, 
tungsten and tantalum, or a quartz substrate. In the synthesis of such a 
diamond crystal, the substrate is usually subjected preliminarily to 
scratching treatment with abrasive diamond grains in order to increase 
nucleation density. The scratching treatment by use of diamond grains was 
reported by Iijima et al. (Preprint of 4th Diamond Symposium, p. 115 
(1991). According to this report, the scratching treatment causes 
embedding of fine diamond particles on the surface of the substrate, and 
these particles serve as nuclei in diamond crystal formation. On the fine 
diamond particles as the nuclei, the diamond crystals deposit in vapor 
phase synthesis as below depending on the nucleation density: (i) at a low 
nucleation density, diamond crystals deposit in a grain form or in random 
orientation, and (ii) at a high nucleation density, diamond crystals 
deposit in a polycrystal form having a rough surface. It is known that the 
diamond polycrystalline film is not oriented generally, but can be made 
oriented in {100} or {110} direction by selecting the synthesis 
conditions. 
(3) A diamond crystal is formed on a monocrystalline copper plate as the 
substrate. The crystal has the same crystal orientation as that of the 
substrate according to Japanese Patent Application Laid-Open No. 2-160695. 
The diamond crystals formed by the above conventional processes have 
disadvantages below. 
(1) The monocrystalline film which is formed by heteroepitaxial growth on 
diamond crystal or on cubic boron nitride is not suitable for practical 
uses because of extreme expensiveness although it has excellent surface 
smoothness and high crystallinity. 
(2) In the formation of diamond crystal under ordinary synthesis conditions 
on a silicon substrate, a high melting-point metal substrate, or a quartz 
substrate, (i) at a low nucleation density, a monocrystal is formed but it 
is deposited in random orientation directions or (ii) at a high nucleation 
density, a crystal is obtained usually in a form of a non-oriented 
polycrystalline film having remarkable surface roughness. If an oriented 
crystalline film is obtained, the resulting {110}-oriented film has 
remarkable surface roughness or the resulting {100}-oriented film has 
inevitably a large thickness (several ten .mu.m or more) for orientation 
although its surface is parallel to the substrate and has good surface 
smoothness. 
(3) The diamond crystals which are formed on a monocrystalline copper 
substrate are in a particle shape, and further grow and come contact into 
each other to become a film with roughness although the film is deposited 
in epitaxial relation to the substrate. 
When a semiconductor electronic device is formed on the diamond crystal or 
the diamond crystal film of the above item (2) or (3), the surface 
roughness of the diamond may adversely affect the yield of the device 
formation, or the crystal grain boundary may give an adverse effect of 
lowering the performance of the device. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a diamond electronic 
device which is free from the above technical disadvantages. 
Another object of the present invention is to provide a process for 
producing the electronic device. 
A still another object of the present invention is to provide a diamond 
electronic device prepared by forming a semiconductor layer and a metal 
layer on a diamond crystal film. 
A further object of the present invention is to provide an electronic 
device which has high durability and excellent semiconductor 
characteristics, and is useful for various application fields. 
A further object of the present invention is to provede a diamond 
electronic device constituted of a diamond crystal formed on a substrate, 
which comprises a diamond crystal, and a semiconductor layer and an 
electrode layer provided on the diamond crystal, wherein the diamond 
crystal has a ratio (h/L) of length (h) of the diamond crystal in 
direction substantially perpendicular to the substrate face provided with 
the diamond crystal to length (L) of the diamond crystal in direction 
parallel to the substrate face ranging from 1/4 to 1/1000 and an upper 
face of the diamond crystal making an angle of from substantially 
0.degree. to 10.degree. to the substrate face, and the diamond crystal 
serves as a heat-radiating layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention have been accomplished after comprehensive studies to 
obtain a diamond electronic device having excellent semiconductor 
characteristics and having no disadvantage of prior art. 
The diamond electronic device of the present invention which is constituted 
of a diamond crystal formed on a substrate comprises a diamond crystal, 
and a semiconductor layer and an electrode layer provided on the diamond 
crystal, wherein the ratio (h/L) of length (h) of the diamond crystal in 
direction substantially perpendicular to the substrate face to length (L) 
thereof in direction parallel to the substrate face is in a range from 1/4 
to 1/1000, an upper face of the diamond crystal makes an angle of from 
substantially 0.degree. to 10.degree. to the substrate face, and the 
diamond crystal serves as a heat-radiating layer. 
The present invention relates also to a process for producing a diamond 
electronic device having a diamond crystal formed on a substrate. The 
process comprises forming a diamond crystal by vapor phase synthesis (1) 
at a controlled position wherein the diamond crystal is selectively 
deposited on a substrate and at a controlled crystal nucleation density 
and (2) at a substrate temperature in a range of from 400.degree. to 
900.degree. C. such that the ratio (h/L) of length (h) of the diamond 
crystal in direction substantially perpendicular to the substrate face to 
length (L) thereof in direction parallel to the substrate face is in a 
range from 1/4 to 1/1000, and an upper face of the diamond crystal makes 
an angle of from substantially 0.degree. to 10.degree. to the substrate 
face; and forming a semiconductor layer and an electrode layer on the 
diamond crystal. 
The present invention is more specifically explained together with the 
inventor's findings. 
The facts as described below were found by the inventor of the present 
invention as the results of comprehensive investigation of electric 
characteristics of electronic devices employing diamond crystal particles 
and diamond polycrystalline film formed by techniques of prior art: 
(1) The grain boundary of diamond polycrystal causes deterioration of 
electric characteristics of the device. 
(2) The surface roughness of diamond polycrystal is liable to cause 
non-uniformity of the electric field application. 
(3) The diamond formed by a method of forming diamond of low crystallinity 
has poor electric characteristics. 
Presumably, the phenomena are caused mainly by the presence of an amorphous 
carbon phase or a graphite phase in the grain boundary of the 
light-emitting diamond layer. Such a non-diamond phase exists mainly in 
grain boundaries of the diamond crystals. The non-diamond phase is 
inferior significantly to crystalline diamond in semiconductor and thermal 
characteristics. Therefore the non-diamond phase, if it is included in 
diamond crystal, will impair greatly the electric characteristics of the 
diamond crystal. Further, the surface roughness of a diamond polycrystal 
film makes voltage application non-uniform, causing concentration of an 
electric field, which may lead to dielectric breakdown. 
The effects of the shape of a diamond crystal were investigated by the 
inventor of the present invention for solving the above problems and 
providing a diamond electronic device having satisfactory electric 
characteristics. As the results, it was found that excellent semiconductor 
and excellent thermal characteristics of the diamond electronic device can 
be achieved by use of a plate-shaped diamond crystal and thereby the 
present invention has been accomplished. 
FIG. 1 is a schematic sectional view of a plate-shaped diamond crystal 
employed in the present invention. FIG. 2 is a schematic sectional view of 
an ordinary granular diamond crystal. In FIG. 1, a plate-shaped diamond 
crystal 2 is formed on a substrate 1. This plate-shaped diamond crystal 
has the ratio (h/L) of the length (height) h in direction perpendicular to 
the substrate face to the length (breadth) L in direction parallel to the 
substrate face is 1/4 or less, preferably 1/4.5, more preferably from 1/5 
to 1/1000. The upper face 2a of the crystal is a {111} plane, and makes an 
angle (.THETA.) of from 0.degree. to 10.degree. to the face 1a of the 
substrate, the both faces being substantially parallel. 
On the contrary, granular diamond crystal 22 formed by a conventional 
method as shown in FIG. 2 has the ratio h/L of not less than 1/3, 
generally 1/2 or more, and the angle .THETA. varies at random. 
The plate-shaped diamond crystal is obtainable only through a process for 
producing a high-quality diamond crystal such as a CVD process and a 
burning flame method. The CVD process includes hot-filament CVD, microwave 
CVD, magneto-microwave CVD, DC plasma CVD, and RF plasma CVD. The carbon 
source gas in the starting gases employed in the CVD process includes 
hydrocarbon gases such as methane, ethane, ethylene, and acetylene; 
organic compounds which are liquid at ordinary temperature such as alcohol 
and acetone; carbon monoxide, and carbon halides. The gas may contain 
hydrogen, oxygen, chlorine, fluorine, or the like, if necessary. 
(1) Formation of Oriented Diamond Crystal by CVD 
The starting material gas needs to contain at least hydrogen, carbon, and 
oxygen in the compositional formula of the gas. One starting gas may 
contain all the these elements, or a plurality of gases containing any of 
the elements may be combinedly used. The concentration of the carbon 
source in the starting gas is required to be not more than 10%. The carbon 
source concentration herein means the value derived by calculation: 
[(carbon source gas flow rate).times.(carbon number in compositional 
formula of carbon source gas)/(total starting gas flow rate)].times.100. 
The "carbon number in compositional formula of carbon source" is, for 
example, 1 for methane (CH.sub.4), 3 for propane (C.sub.3 H.sub.8), and 3 
for acetone (CH.sub.3 COCH.sub.3). The carbon source concentration is 
required to be not higher than 10% in order to suppress the 
supersaturation degree of diamond crystal to prevent growth of amorphous 
carbon. The minimum of the carbon source concentration is not specially 
limited, but at the concentration of 0.01% or lower, the diamond crystal 
cannot always be formed at a practical formation rate. 
Additionally, in the CVD process, the ratio of the number of oxygen atoms 
to the number of carbon atoms (O/C) in the starting gas is in a range of 
0.5.ltoreq.O/C.ltoreq.1.2, preferably 0.7.ltoreq.O/C.ltoreq.1.1. At the 
O/C ratio of lower than 0.5, the effect of oxygen addition is not 
achievable, and a plate-shaped diamond crystal is not formed. At the ratio 
of higher than 1.2, practical rate of diamond formation is not achievable 
owing to etching effect of oxygen. An oxygen addition gas such as O.sub.2, 
H.sub.2 O, and N.sub.2 O may be added to the starting gas to adjust the 
above O/C value. 
In the case where an oxygen-containing organic compound such as an alcohol 
is employed as the carbon source, a plate-shaped diamond crystal can be 
formed even at a relatively low O/C value. For example, in the case where 
hydrogen and ethanol (C.sub.2 H.sub.5 OH) are used as the starting gases, 
a satisfactory plate-shaped diamond crystal can be obtained at the O/C 
value of 0.5. The reason therefor is not known. Probably, it is because 
that the oxygen-containing compound easily generates an active species of 
oxygen (OH radical). 
The plate-shaped diamond crystal employed in the present invention is 
formed at a relatively low nucleation density. For example, in crystal 
formation by a CVD process such as plasma CVD and filament CVD, a 
plate-shaped diamond crystal is formed only at the nucleation density of 
not higher than 2.times.10.sup.6 nuclei/mm.sup.2. The reason therefor is 
not clear. Probably, it is because that the sufficient amount of etching 
gas (hydrogen radicals or OH radicals) is required in order to control the 
crystal growth in height direction and the sufficient amount of active 
species (CH.sub.x radicals, or the like) reaching the lateral face for 
diamond formation in order to promote the growth in lateral direction. 
(2) Formation of Oriented Diamond Crystal by Burning Flame Process 
Oxygen-acetylene flame is employed in a burning flame process. The molar 
ratio of oxygen to acetylene in the main starting gas is in a range of 
0.9.ltoreq.O.sub.2 /C.sub.2 H.sub.2 .ltoreq.1.0, preferably 
0.95.ltoreq.O.sub.2 /C.sub.2 H.sub.2 .ltoreq.0.99 for forming the oriented 
diamond with high reproducibility at a relatively high growth rate (growth 
rate in lateral direction: several ten .mu.m/hr) 
In the burning flame process, the nucleation density of the diamond crystal 
is controlled to be not higher than 1.times.10.sup.5 nuclei/mm.sup.2, 
preferably in a range of from 1.times.10.sup.2 nuclei/mm.sup.2 to 
1.times.10.sup.5 nuclei/mm.sup.2. In the burning flame process, the 
nucleation density is controlled to be lower than that in the CVD process. 
This is because, in the burning flame process, the growth rate of a 
plate-shaped diamond crystal in lateral direction (several ten .mu.m/hr) 
is ten times or more the growth rate in hot-filament CVD or microwave CVD. 
To obtain a plate-shaped crystalline diamond, the intervals between the 
centers of crystals need to be sufficiently large. The necessary interval 
depends on the crystal formation conditions, but is usually equal 
approximately to the width of the plate-shaped diamond crystal to be 
formed (10 .mu.m if the width is 10 .mu.m). 
The upper face of the plate-shaped diamond crystal is a {111} plane having 
morphology of a triangle or a hexagon. 
The plate-shaped diamond crystal is monocrystal, or a twin crystal having a 
twinning plane in the plate. The most of the plate-shaped diamond crystal 
has a twinning plane parallel to the upper face of the crystal. This is 
considered to be due to the fact that a recessed incident angle is made by 
the formation of the twinning plane, and the effect thereof, so-called 
recessed incident angle effect, tends to promote the growth of the crystal 
in the direction of the recessed incident angle to form diamond crystal in 
a plate shape. The plane is not limited to one, but two or more twinning 
planes are sometimes formed. 
The plate-shaped diamond crystal employed in the present invention can be 
grown into a film shape and brought into contact with each other to form a 
crystalline diamond film. The resulting diamond crystal film formed from 
plate-shaped diamond crystals has small surface roughness as the results 
of formation by growth and coalescence of plate-shaped diamond crystals 
having relatively uniform crystal particle height. The film is a film with 
high smothness, that is, a small surface roughness, for example, the 
maximum surface roughness of not higher than 100 nm. 
The electronic device of the present invention is prepared by forming 
plate-shaped diamond crystal through a selective deposition method on a 
predetermined site. The selective deposition of diamond crystal can be 
conducted, for example, by the method disclosed in Japanese Patent 
Application Laid-Open No. 2-30697 by the inventor of the present 
invention. 
According to the method disclosed by this application, a diamond crystal 
can be formed from a single nucleus by controlling a sufficiently small 
size of the nucleation site of 10 .mu.m or less. When diamond crystal is 
formed from a single nucleus by the burning flame process, the nucleation 
density is lower than that in other synthesis method. If the nucleation 
site is in a size of 10 .mu.m.sup.2, deposition defect is liable to occur. 
Therefore, in order to grow a diamond crystal from a single nucleus in the 
burning flame process, the size of the nucleation site is made to be in a 
range of from 10 .mu.m.sup.2 to 100 .mu.m.sup.2, preferably in a range of 
from 25 .mu.m.sup.2 to 80 .mu.m.sup.2. 
In the selective deposition of diamond according to the process disclosed 
in the above Japanese Patent Application Laid-Open No. 2-30697, but the 
deposition process is not limited thereto, a substrate is subjected to a 
scratching treatment, a patterned mask is formed on the substrate, the 
substrate is subjected to etching treatment, and then the mask is removed 
to obtain a scratching-treated site in a pattern. Otherwise, the 
scratching-treated site can be formed in a pattern by forming a patterned 
mask on the substrate and removing the mask. In another method, the 
substrate is subjected to a scratching treatment, and a patterned mask is 
formed on the scratched substrate with a heat resistant material to form a 
scratched portion in a pattern on the substrate surface. The scratching 
treatment with diamond abrasive grain is not limited to a special method, 
and includes grinding, ultrasonic treatment, sand-blasting, and the like 
by use of diamond abrasive grain. 
An example of selective deposition of diamond on a substrate by utilizing 
the pattern of scratched portion formed by use of diamond abrasive grains 
is explained below by reference to the schematic drawings of FIG. 9A to 
FIG. 9F. 
Firstly, the surface of the substrate 91 is treated for scratching with 
diamond abrasive grains (FIG. 9A). A mask 92 is formed on the substrate 
surface (FIG. 9B). The material of the mask is not specially limited. An 
example of the mask is a resist formed in a pattern by photolithography. 
Then the substrate having the mask 92 thereon is etched to form a pattern 
of the scratched portion (FIG. 9C). 
The etching may be conducted either by dry etching or by wet etching. The 
wet etching is conducted, for example, by use of a hydrofluoric 
acid-nitric acid mixture. The dry etching is conducted, for example, by 
plasma etching method, or ion beam etching. The etching gas for plasma 
etching includes rare gases such as argon, helium, and neon; oxygen, 
fluorine, hydrogen, CF.sub.4, and the like. The etching depth is not less 
than 10 nm, preferably in a range of from about 50 to about 1000 nm, more 
preferably from 80 to 200 nm. 
Subsequently, the mask 92 is removed (FIG. 9D). A plate-shaped diamond 
crystal is formed thereon by a vapor-phase synthesis method, whereby a 
plate-shaped diamond crystals 93 are formed selectively only on the 
scratch-treated sites (FIG. 9E). The crystals are grown and allowed to 
coalesce into a film of a diamond crystal (FIG. 9F). 
The thickness of the formed diamond film depends on the synthesis 
conditions, particularly on the nucleation density, and cannot be simply 
predicted. Generally, the crystals become a film when the thickness of the 
deposited crystals is 10 .mu.m or more. 
On the diamond crystal formed above, a semiconductor layer and an electrode 
layer are formed. The electrode layer is formed from a metal, a 
semiconductor, or a transparent electroconductive film. It is formed in a 
thickness ranging from about 50 nm to about 200 nm using these materials 
through a process such as vacuum vapor deposition, ion-plating, 
sputtering, spraying, and CVD. 
The electrode may be either a Schottky junction electrode or an ohmic 
junction electrode. The material for these electrodes is selected 
depending on the surface state of the diamond crystal (cleanness of the 
surface, and adsorbed species). Generally, in the case of p-type diamond 
crystal, a material exhibiting higher work function is employed as an 
ohmic junction electrode, and a material exhibiting a lower work function 
is employed for a Schottky junction electrode. 
The semiconductor layer may be made from silicon, diamond, gallium 
arsenide, silicon carbide, indium, germanium, or the like. Of these, 
silicon and diamond are preferred. The silicon semiconductor is formed by 
a known method such as vacuum deposition, sputtering, and CVD. By such a 
method, a p-type silicon layer or an n-type silicon layer, or a pn 
junction, a pnp junction, or an npn junction of a silicon semiconductor, 
or the like is formed. 
The method for forming the diamond semiconductor layer need not be the same 
as that for forming the aforementioned plate-shaped diamond crystal. In 
formation of the p-type semiconductor, boron may be incorporated into the 
diamond crystal by addition of diborane (B.sub.2 H.sub.6), boron 
trifluoride (BF.sub.3), or the like as a boron source into the starting 
gas, or otherwise by addition of boric acid (H.sub.3 BO.sub.3) or the like 
into the organic compound which is liquid at ordinary temperature 
(alcohol, acetone, ether, etc.) when such an organic compound is used as a 
carbon source. 
In formation of the n-type semiconductor, phosphorus, lithium, or the like 
may be incorporated into the diamond crystal by addition of phosphine 
(PH.sub.3) to a starting gas, by addition of solid or liquid lithium or a 
lithium compound by heating and evaporation at a suitable temperature, or 
by a like method. In the case where an organic compound which is liquid at 
ordinary temperature (alcohol, acetone, ether, etc.) is used as a carbon 
source, the above elements may be incorporated into the diamond crystal by 
addition of phosphoric acid, lithium, or lithium compound to the organic 
compound. 
The p-type diamond layer or the n-type diamond layer, or a pn junction, an 
np junction or an npn junction of a diamond semiconductor or the like is 
formed by the diamond crystal growth and the impurity addition as 
described above. 
In the electronic device of the present invention, the semiconductor layer 
may be a hetero junction (junction between different materials): e.g., 
junction between a diamond semiconductor and silicon semiconductor, 
junction between a diamond semiconductor and gallium arsenide, and 
junction between silicon and gallium arsenide. 
The present invention is described more specifically by reference to 
Examples. 
EXAMPLE 1 
A pn junction device of a silicon crystal as shown in FIG. 3 was formed by 
deposition of a diamond crystal through a burning flame method shown in 
FIG. 10. 
FIG. 10 illustrates a burning flame method with an oxygen-acetylene flame 
burner. In the drawing, the numeral 101 denotes a burner; 102, a 
substrate; 103, inner flame; 104, outer flame; and 105, a substrate 
holder. The substrate is cooled by cooling the substrate holder with 
water. 
A silicon monocrystal plate (25 mm in diameter, 0.5 mm thick) was used as 
the substrate. This substrate was put into an alcohol in which diamond 
particles of 15 .mu.m in average diameter were dispersed, and ultrasonic 
wave vibration was applied thereto for scratching treatment. Thereafter, 
on the substrate, a PMMA based resist pattern was formed in 2 .mu.m 
diameter at a 30 .mu.m pitch by means of an aligner. The substrate was 
etched to a depth of about 100 nm by means of an argon ion beam etching 
apparatus under the etching conditions of acceleration voltage of 1 kV and 
etching time of 8 minutes. 
Then the resist was removed from the substrate by an organic solvent, and 
the substrate was placed on a burning flame treatment apparatus as shown 
in FIG. 10. The burning flame treatment was practiced under the 
conditions: acetylene gas flow rate: 1.5 l/min, oxygen gas flow rate: 1.4 
l/min, substrate temperature: 650.degree. C., and synthesis time: 4 hours. 
The resulting diamond crystal was a diamond polycrystal film (denoted by 
the numeral 32 in FIG. 3) having a thickness of about 18 .mu.m and of 
excellent flatness. 
Another sample was synthesized under the same conditions as above except 
that the synthesis time was one hour. With regard to this sample, it was 
observed that plate-shaped diamond grains of 15 .mu.m in average diameter 
having hexagonal {111} plane orienting in a direction parallel to the 
substrate were formed selectively on the remaining scratched portions 
(portions which had been protected by the resist). 
On the diamond film, a p-type silicon polycrystal film 33 was formed by a 
known thermal CVD process. Thereon, an n-type silicon polycrystal film 34 
was formed. On the n-type silicon polycrystal film, a resist was formed on 
a predetermined area by a known light exposure method, and it was removed 
by plasma dry etching. An electrode 35 was formed respectively on the 
p-type silicon layer, and on the n-type silicon layer. Thus a pn junction 
diode was completed. 
This pn junction diode had stable rectification characteristics with stable 
heat release even at a large electric current flow for a long time, 
because the diamond polycrystal film 32 is used as the heat-radiating 
layer. 
EXAMPLE 2 
A pn hereto junction diode was prepared by depositing a diamond crystal by 
hot filament CVD as shown in FIG. 11 and forming a p-type diamond crystal 
and an n-type silicon crystal as shown in FIG. 4. 
FIG. 11 illustrates schematically a hot filament CVD method employing 
hydrogen-ethyl alcohol as a starting gas. In the drawing, the numeral 111 
denotes a quartz reaction tube; 112, an electric furnace; 113, a filament 
made of tantalum; 114, a substrate; 115, a starting gas inlet connected to 
a gas cylinder, an alcohol vaporizer, a flow controller, a valve, etc. 
which are not shown; and 116, a gas outlet connected to a pressure control 
valve, and an evacuation system (combination of a mechanical booster pump 
and a rotary pump) which are not shown in the drawing. 
The substrate 114 employed was a silicon monocrystal which had been 
preliminarily treated in the same manner as in Example 1. The diamond was 
synthesized under the conditions: starting gases and flow rates: hydrogen 
200 ml/min, and ethyl alcohol 2 ml/min, filament temperature: 2050.degree. 
C., substrate temperature: 680.degree. C., pressure: 1.3.times.10.sup.4 
Pa, synthesis time: 12 hours. The resulting diamond crystal was a diamond 
polycrystal (42 in FIG. 4) having a thickness of about 18 .mu.m with 
excellent flatness. 
Another sample was synthesized under the same conditions as above except 
that the synthesis time was one hour. With regard to this sample, it was 
observed that plate-shaped diamond grains of 8 .mu.m in average diameter 
having hexagonal {111} plane orienting in a direction parallel to the 
substrate were formed selectively on the remaining scratched portions 
(portions which had been protected by the resist). 
On the diamond crystal film, a p-type diamond crystal film 43 in the same 
manner as in the above diamond synthesis except that a starting gas and 
its flow rate were boric acid-containing ethyl alcohol (B/C=100 ppm and 2 
ml/min, and the synthesis time was one hour. Thereon, an n-type silicon 
polycrystal film 44 was formed. Further thereon, a resist was formed on a 
predetermined area on the n-type silicon film by a known light exposing 
method, and it was removed by dry etching by plasma. An electrode 45 was 
formed respectively on the p-type diamond layer 43 and on the n-type 
silicon layer 44. Thus a pn junction diode was completed. 
This pn-junction diode exhibited excellent rectification characteristics. 
EXAMPLE 3 
A Schottky diode device was prepared as shown in FIG. 5A. 
Plate-shaped diamond crystals 52 were formed in the same manner as in 
Example 2 except that the diamond formation was conducted for 4 hours. 
Then p-type diamond layers 54 were formed under the same conditions as in 
Example 2. On the diamond layers, an aluminum electrode as a Schottky 
junction electrode 55 and a gold electrode as an ohmic junction electrode 
56 were formed by vacuum deposition, each having thickness of about 150 nm 
such that the electrodes do not overlap with each other. Thus a Schottky 
diode was completed. This Schottky diode exhibited excellent rectification 
characteristics. 
EXAMPLE 4 
A Schottky diode device as shown in FIG. 5B was prepared. 
On a substrate 51, a diamond film 53 was formed by growth and coalescence 
of plate-shaped diamond crystals and a p-type diamond layer 54 was formed 
in the same manner as in Example 2. Thereon, an aluminum electrode as a 
Schottky junction electrode 55 and a gold electrode as an ohmic junction 
electrode 56 were formed by vacuum deposition, each having thickness of 
about 150 nm such that the electrodes do not overlap with each other. Thus 
a Schottky diode was completed. This Schottky diode exhibited excellent 
rectification characteristics. 
EXAMPLE 5 
A pn junction type light-emitting diode device was prepared as shown in 
FIG. 6A. 
Firstly, a silicon substrate 61 was subjected to preliminary treatment 
(i.e., patterning, etching, and washing) under the same conditions as in 
Example 1. Thereon, plate-shaped diamond crystal 62 and p-type diamond 
crystal 64 were formed in the same manner as in Example 3. On half of the 
areas of the p-type diamond crystals, an SiO.sub.2 film (thicness: 100 nm) 
was formed as a mask. Further, on this plate-shaped diamond crystal, an 
n-type diamond semiconductor layer was formed in a manner as described 
below. 
Ethyl alcohol was used as the carbon source in which lithium metal was 
dissolved in a lithium-carbon ratio (Li/C) of 50 ppm. The above substrate 
was placed in a hot-filament CVD apparatus other than the one used in 
Example 2 for n-type semiconductor layer formation. An n-type 
semiconductor layer was formed under the following conditions: starting 
gases and flow rate: hydrogen (200 ml/min) and ethyl alcohol (2 ml/min), 
filament temperature: 2050.degree. C., substrate temperature: 680.degree. 
C., pressure 6.65.times.10.sup.3 Pa, and synthesis time: one hour. 
Thereby, an n-type diamond semiconductor layer 65 which serve as pn 
junction was formed on the area of the diamond crystal other than that of 
the above SiO.sub.2 film. 
The SiO.sub.2 film was removed by hydrofluoric acid, and platinum electrode 
66 was formed on the p-type diamond layer, and aluminum electrodes 67 was 
formed on the n-type diamond layer, each in thickness of 100 nm, such that 
the electrodes do not overlap with each other. 
DC current was applied by using the platinum electrode on the p-type 
diamond crystal as the anode and the aluminum electrode on the n-type 
diamond crystal as the cathode by means of a power source not shown in the 
drawing. Thereby light emission was observed at the pn junction portion at 
voltage application of several to several ten volts with light emission 
peak wavelength of about 430 nm. This sample was tested for durability for 
200 hours, and was found to have good durability without deterioration 
such as decrease of luminance and element breakdown. 
EXAMPLE 6 
A pn junction type light-emitting diode device was prepared as shown in 
FIG. 6B. 
Firstly, a silicon substrate 61 was subjected to preliminary treatment 
(i.e., patterning, etching, and washing) under the same conditions as in 
Example 1. A diamond film 63 was formed by growth and coalescence of 
plate-shaped diamond crystals and a p-type diamond layer 64 was formed in 
the same manner as in Example 4. On half of the area of the p-type diamond 
crystal, an SiO.sub.2 film (thickness: 100 nm) was formed as a mask. 
Further, on the plate-shaped crystal, an n-type diamond semiconductor 
layer 65 was formed in the same manner as in Example 5. 
A platinum electrode 66 and an aluminum electrode 67 were formed in the 
same manner as in Example 5 such that the electrodes do not overlap with 
each other. DC current was applied by using the platinum electrode on the 
p-type diamond crystal as the anode and the aluminum electrode on the 
n-type diamond crystal as the cathode by means of a power source not shown 
in the drawing. Thereby light emission was observed at the pn junction 
portion at voltage application of several to several ten volts with light 
emission peak wavelength of about 430 nm. This sample was tested for 
durability for 200 hours, and was found to have good durability without 
deterioration such as decrease of luminance and element breakdown. 
COMATIVE EXAMPLE 1 
A silicon monocrystal plate (25 mm in diameter, 0.5 mm thick) was put into 
an alcohol in which diamond particles of 15 .mu.m in average diameter were 
dispersed, and ultrasonic wave vibration was applied thereto for 
scratching treatment. By this scratching treatment, the nucleation density 
of the diamond was raised to not less than 5.times.10.sup.6 
nuclei/mm.sup.2. Then a diamond film 63, a p-type diamond crystal 64, and 
an n-type diamond semiconductor layer 65 were formed on the substrate in 
the same manner as in Example 6 except that the substrate temperature was 
950.degree. C. Electrodes 66 and 67 were formed in the same manner as in 
Example 4 to form a pn junction type light-emission diode. 
DC current was applied by using the platinum electrode on the p-type 
diamond crystal as the anode and the aluminum electrode on the n-type 
diamond crystal as the cathode by means of a power source not shown in the 
drawing. Thereby light emission was observed at the pn junction portion at 
voltage application of several to several ten volts with light emission 
peak wavelength of about 430 nm. This sample was tested for durability in 
the same manner as in Example 6. As the results, the luminance decreased 
and the element failure (presumed to be element breakdown) occurred for 
about 150 hours. 
EXAMPLE 7 
A transistor as shown in FIG. 7 was prepared. 
A silicon monocrystal plate 71 (25 mm in diameter, 0.5 mm thick) was used 
as the substrate. This substrate was put into an alcohol in which diamond 
particles of 15 .mu.m in average diameter were dispersed, and ultrasonic 
wave vibration was applied thereto for scratching treatment. On the 
substrate, a PMMA based resist pattern was formed in 2 .mu.m diameter at a 
25 .mu.m pitch by means of an aligner. The substrate was etched to a depth 
of about 100 nm by means of an argon ion beam etching apparatus under the 
etching conditions of acceleration voltage of 1 kV and etching time of 8 
minutes. Then the resist was removed from the substrate by an organic 
solvent, and the substrate was placed on a known microwave plasma CVD 
apparatus. 
A diamond crystal was synthesized under the conditions: starting gas and 
flow rate: hydrogen (150 ml/min) and carbon monoxide (10 ml/min), 
microwave power: 500 W, substrate temperature: 640.degree. C., pressure: 
6.65.times.10.sup.3 Pa, and synthesis time: 12 hours. Thereby, a smooth 
diamond film 72 was formed. 
Another sample was synthesized under the same conditions as above except 
that the synthesis time was 4 hours. With this sample, it was observed 
that plate-shaped diamond grains having hexagonal {111} plane orienting in 
a direction parallel to the substrate deposited on the substrate. 
A p-type diamond film 73 was formed in the same manner as in synthesis of 
the aforementioned diamond film, except that diborane gas (100 ppm 
diborane in diluent hydrogen) was added in the starting gas at a flow rate 
of 5 ml/min and synthesis time was one hour. A insulating diamond film 74 
was formed in the same manner as in formation of the above diamond film 72 
except that an SiO.sub.2 film was employed as the selective deposition 
mask and the synthesis time was one hour. After removal of the SiO.sub.2 
film, a source electrode 75 and a drain electrode 77 were formed from 
titanium, and a gate electrode 76 was formed from aluminum. 
The resulting transistor was found to have excellent voltage-current 
characteristics with little leak current (not more than 5 nA at 40 V) 
between the gate and the source. 
EXAMPLE 8 
An ultraviolet light detection device as shown in FIG. 8A was prepared. 
A silicon monocrystal plate 81 (25 mm in diameter, 0.5 mm thick) was used 
as the substrate. This substrate was put into an alcohol in which diamond 
particles of 15 .mu.m in average diameter were dispersed, and ultrasonic 
wave vibration was applied thereto for scratching treatment. On the 
substrate, a PMMA based resist pattern was formed in 2 .mu.m diameter at a 
25 .mu.m pitch by means of an aligner. The substrate was etched to a depth 
of about 100 nm by means of an argon ion beam etching apparatus under the 
etching conditions of acceleration voltage of 1 kV and etching time of 8 
minutes. Then the resist was removed from the substrate by an organic 
solvent, and the substrate was placed on a known microwave plasma CVD 
apparatus. 
Diamond crystal was synthesized under the conditions: starting gas and flow 
rate: hydrogen (150 ml/min) and carbon monoxide (10 ml/min), microwave 
power: 550 W, substrate temperature: 670.degree. C., pressure: 
4.0.times.10.sup.3 Pa, and synthesis time: 8 hours. Thereby, a 
plate-shaped diamond particle was observed to deposit which have a 
hexagonal {111} plane in direction parallel to the substrate face. 
A p-type diamond film 84 was formed in the same manner as in synthesis of 
the above diamond film, except that diborane gas (100 ppm diborane in 
diluent hydrogen) was added in the starting gas at a flow rate of 5 ml/min 
and the synthesis time was one hour. 
On the p-type diamond film, gold electrode 85 was formed. Thereto, voltage 
was applied by power sources 86, and the change of the resistance of the 
diamond film was observed with irradiation of ultraviolet light (mercury 
lamp). The ultraviolet light detection device was found to be excellent in 
detection sensitivity and optical responsiveness. 
EXAMPLE 9 
An ultraviolet light detection device as shown in FIG. 8B was prepared. 
Firstly, an alumina substrate 81 was subjected to preliminarily treatment 
(patterning, etching, and washing). Then diamond was formed in the same 
manner as in Example 8 except that the synthesis time was 15 hours. 
Thereby a diamond film 83 was formed by growth and coalescence of 
plate-shaped diamond crystals. Further a p-type diamond crystal 84 was 
formed in the same manner as in Example 8. 
Gold electrode 85 was formed on the p-type diamond film. Thereto voltage 
was applied by means of a power source 86, and change of the resistance of 
the diamond film during irradiation of ultraviolet light (with a mercury 
pump). As the results, the ultraviolet detection device was excellent in 
detection sensitivity and optical responsiveness. 
As described above, the electronic device of the present invention releases 
heat stably and effectively to give stable working characteristics even in 
severe environment for a long term, owing to the use of a heat-radiation 
layer which is constituted of a diamond crystal film formed from growth 
and coalescence of plate-shaped crystals.