JP2003303954A - n-TYPE DIAMOND SEMICONDUCTOR - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an n-type diamond semiconductor, in which the change in carrier concentration and resistivity is small over a wide temperature range, starting from room temperature to a high temperature. <P>SOLUTION: In the n-type diamond semiconductor, doped and undoped layers are laminated alternately. The n-type diamond semiconductor comprises a single- crystal diamond substrate 100 (a), the thin undoped layers 110<SB>1</SB>to 110<SB>n+1</SB>(n is the number of cycles) made of a diamond semiconductor material, where impurities are not substantially added (b), and the extremely thin doped layers 120<SB>1</SB>to 120<SB>n</SB>, that are formed so that they are sandwiched by the undoped layers 110<SB>1</SB>to 110<SB>n+1</SB>and are made of the diamond semiconductor material, where at least two kinds of impurities are added so that they form the n-type diamond semiconductor (c). <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a diode, LE.
The present invention relates to an n-type diamond semiconductor used for an electronic device such as a D, a transistor, an electron-emitting device, etc., and relates to an n-type diamond semiconductor having a small change in carrier concentration and resistivity in a wide temperature range from room temperature to high temperature. More specifically, the present invention relates to an n-type diamond semiconductor having a small change in carrier concentration and resistivity in a wide temperature range from room temperature to high temperature as compared with an n-type diamond semiconductor having a deep impurity level obtained by ordinary doping. .

[0002]

2. Description of the Related Art Diamond semiconductors are devices that operate stably under harsh environments such as high temperatures and radiation.
Also, its application is drawing attention as a device that can withstand operation at high speed and high output. The reason why the diamond semiconductor can operate even at high temperatures is that the band gap is as large as about 5.5 eV. This value is much larger than those of silicon (about 1.1 eV) and gallium arsenide (about 1.4 eV) which are widely used at present. Due to this wide band gap, the temperature range (intrinsic region) in which carriers of the semiconductor are not controlled does not exist below 1400 ° C.

Diamond without impurities is an insulator, but it can be made into a p-type semiconductor or an n-type semiconductor by doping impurities into the crystal. For example, if boron is doped, it becomes a p-type semiconductor, and if it is doped with nitrogen, phosphorus, or sulfur, it becomes an n-type semiconductor.

However, even if diamond is doped with the above impurities, the impurity levels of these impurities are deep, and a large amount of energy is required to excite electrons and holes into the conduction band and the valence band. For this reason, the concentration of the excited carriers varies greatly depending on the temperature, and the carrier saturation region is a very high temperature region. For example, the activation energy of an n-type diamond semiconductor doped with phosphorus is about 0.6 eV, and the activation energy is 300 K (room temperature) to 80
In the temperature range of 0K, the carrier concentration changes by four digits or more, and the saturation region is a temperature of 800K or more. That is, in the temperature range from room temperature to high temperature, the characteristics of the device largely change depending on the ambient temperature, so that the advantage that the diamond semiconductor device can be used even at high temperature cannot be utilized.

As a method for suppressing such temperature dependence of carrier concentration and obtaining a diamond semiconductor with a small change in carrier concentration in the temperature range from room temperature to high temperature, a large amount of impurities are doped to reduce the impurity level. There is a degenerate method. However, if a large amount of impurities are doped, the number of carriers will increase. As a result, it exhibits electric conductivity similar to that of metal, and the semiconductor characteristics are lost.

Therefore, for example, Japanese Patent Laid-Open No. 4-280622.
As disclosed in the publication, a doped layer having a thickness of several nm, which is heavily doped with impurities, and a non-doped layer having a thickness of tens to several hundreds nm, which is not substantially doped with impurities, are alternately arranged. A diamond semiconductor has been proposed which is laminated and has a multilayer structure.

As described above, in a structure in which a very thin doped layer is sandwiched between thin non-doped layers, the depth profile of the impurity concentration changes in a delta (delta) function, so that it occurs in the doped layer. The carriers diffuse into the non-doped layer. As a result, the average carrier concentration is reduced to such an extent that semiconductor characteristics can be obtained, and the carrier supply source is a doped layer with little temperature dependency of the carrier concentration, so that the temperature dependency of the average carrier concentration is almost entirely low. Not a diamond semiconductor.

In order to obtain a diamond semiconductor having the semiconductor characteristics in the operating temperature region and having almost no temperature dependence of carrier concentration with the above structure, a doped layer doped with a high concentration of impurities is required. The high-concentration doped layer can be relatively easily obtained if the p-type diamond semiconductor is used, since boron can be doped at a high concentration while maintaining the crystallinity of diamond. However, in the case of an n-type diamond semiconductor, it is not easy to dope a single impurity stably at a high concentration until it degenerates while maintaining good crystallinity. For this reason, it has heretofore been difficult to obtain an n-type diamond semiconductor that exhibits semiconductor characteristics in an operating temperature range from room temperature to high temperature and has almost no temperature dependence of carrier concentration.

[0009]

[Patent Document 1] Japanese Patent Application Laid-Open No. 4-280622

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide an n-type diamond which can be used for a semiconductor device and which exhibits semiconductor characteristics in a wide temperature range from room temperature to high temperature and has almost no temperature dependence of carrier concentration. It is to provide a semiconductor.

[0011]

The n-type diamond semiconductor of the present invention comprises a diamond semiconductor material, and
A first non-doped layer which is substantially not doped with impurities, and (b) a doping which is doped with two or more kinds of impurities so as to be an n-type semiconductor formed on one surface of the first non-doped layer. A layer and (c) a second non-doped layer which is formed on the surface of the doped layer and is substantially not doped with impurities. The dope layer is characterized by being doped with two or more kinds of impurities in order to dope the impurities that become the n-type semiconductor to such a concentration that the impurity level degenerates while maintaining the crystallinity of diamond.

In this diamond semiconductor, a non-doped layer and a doped layer are alternately laminated, and both layers can be formed as non-doped layers.

The two or more kinds of impurities added to the doped layer are nitrogen (N), phosphorus (P), sulfur (S),
At least one atom selected from the group A consisting of arsenic (As), selenium (Se), and chlorine (Cl), and hydrogen (H), boron (B), lithium (Li), aluminum (Al).
It can be one or more atoms selected from the group B consisting of. Further, it is desirable that the impurity concentration of at least one kind of atoms among the added impurities is 10 ¹⁹ cm ⁻³ or more.

Further, the impurities added to the doped layer are
In the case of nitrogen (N) and boron (B), the nitrogen atom concentration (C _n ) and the boron atom concentration (C _b ) are C _b <C _n ≦.
In the range of 100C _b, and _{C n} ≧ ¹⁰ 19 ^{cm -3}
Is desirable.

The impurities added to the doped layer are
In the case of sulfur (S) and boron (B), the sulfur atom concentration (C _s ) and the boron atom concentration (C _b ) are 0.5C.
_b <C _s ≦ 100C _b , and C _s ≧ 10
It is preferably ¹⁹ cm ⁻³ .

The impurities added to the dope layer are lithium
In the case of aluminum (Li) and nitrogen (N), lithium atom concentration
Degree (C_Li) And nitrogen atom concentration (C_n) And C_Li≤1
0C _n, And C_Li≧ 10¹⁹cm^-3so
Is desirable. In this case, the lithium atom is
Interstitials of carbon atoms composing the diamond in the doped layer
Where the nitrogen atom is at the substitution position of the carbon atom,
And the lithium and nitrogen atoms are
It is desirable that the structures are adjacent to each other, and the lithium atom is
And the distance between the centers of nitrogen atoms are 0.145 nm or more, 0.
It is preferably 155 nm or less.

The activation energy of the n-type diamond semiconductor having the above structure can be less than 0.1 eV.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The n-type diamond semiconductor of the present invention is made of a diamond semiconductor material, and a very thin doped layer containing two or more kinds of impurities forming the n-type semiconductor is substantially added with impurities. It is a structure sandwiched between thin non-doped diamond layers. Alternatively, it has a multi-layer structure in which a very thin doped layer and a thin non-doped layer are alternately stacked, and has a non-doped layer at both ends. With such a so-called δ (delta) -doped structure, the carrier concentration, that is, the electron concentration can be adjusted to the extent that semiconductor characteristics can be obtained as a whole. Moreover, as a whole, an n-type diamond semiconductor having almost no temperature dependence of electron concentration can be obtained.

At this time, if the thickness of the doped layer is made extremely thin on the order of nanometers, the ratio of the carriers (electrons) generated in the doped layer to the carriers diffused in the non-doped layer is increased, resulting in a more uniform carrier throughout the structure. A high concentration of n-type diamond semiconductor can be obtained.

In order to make the doped layer have n-type metallic electrical conductivity, one kind of impurity for bringing out n-type characteristics is doped, and it is degenerated while maintaining the crystallinity of diamond. In order to perform stable doping up to the above concentration, another one or more kinds of impurities are further doped.

Here, when the thickness of the doped layer is d, the thickness of the non-doped layer is D, and the electron concentration of the doped layer is n ⁺ , the average electron concentration n is n = n ⁺ * d / (d + D). Becomes

The shape of the dope layer is easily a thin film having a relatively simple two-dimensional spread, but even a one-dimensional linear film is a zero-dimensional dot film. Even so,
As long as the structure is surrounded by non-doped layers, the effect obtained is the same.

When the thin film doped layers and the non-doped layers having a two-dimensional spread are alternately laminated, the thickness of the doped layer is less than 50 nm and the thickness of the non-doped layer is 500.
It is preferably less than nm. When the thickness of the doped layer is 50 nm or more, carriers near the center of the doped layer are less likely to diffuse, and semiconductor characteristics cannot be obtained. When the thickness of the non-doped layer is 500 nm or more, carrier diffusion does not reach near the center of the non-doped layer, and the depth profile of carrier concentration is interrupted near the center of the non-doped layer, so that semiconductor characteristics cannot be obtained as a whole. Also, the lower the impurity concentration of the non-doped layer, the better,
To facilitate the diffusion of carriers from the doped layer,
It is preferably 10 ¹⁷ cm ⁻³ or less.

The doped layer of the n-type diamond semiconductor of the present invention has a group A consisting of nitrogen (N), phosphorus (P), sulfur (S), arsenic (As), selenium (Se) and chlorine (Cl). It is preferable to dope one or more selected atoms and one or more selected from the group B consisting of hydrogen (H), boron (B), lithium (Li), and aluminum (Al). This makes it possible to dope the impurities that realize the n-type semiconductor characteristics with a large amount of impurities that degenerate the impurity levels.

At least one of the impurities added is
The impurity concentration of the types of atoms ^is preferably at ¹⁰ 1 9 ^{cm -3} or more. By doping such a large amount, the doped layer has little temperature dependence of the carrier concentration and is likely to be a stable carrier supply source with respect to ambient temperature changes. It is more preferable that the impurity concentration is 10 ²⁰ cm ⁻³ or more.

As a preferable combination of the above impurities, nitrogen is used.
And boron, sulfur and boron, lithium and nitrogen
There are kinds. In the case of nitrogen and boron, the nitrogen atom concentration (C_n)
And boron atom concentration (C_b) Is C_b<C_n≤100C_b
Is the range of C_nIs 10^{1 9}cm^-3Be above
Is preferred. In the case of sulfur and boron, sulfur atom concentration
(C_s) And boron atom concentration (C_b) Is 0.5C_b<C
_s≤100C_bIs the range of C_sIs 10¹⁹cm^-3
The above is preferable. For lithium and nitrogen,
Lithium atomic concentration (C_Li) And nitrogen atom concentration (C_n)
Is C_Li≤10C _nIs the range of C_LiIs 10¹⁹
cm^-3The above is preferable. More preferably,
The C_n, C_s, C_LiIs 10²⁰cm^-3And above
It

By setting the concentration range as described above,
The doped layer has almost no temperature dependence of carrier concentration and can be used as a more stable carrier supply source.
However, in the case of nitrogen and boron, when C _b <0.01 C _n and the concentration of boron are extremely low, C _n is 10 ¹⁹ cm.
It becomes difficult to set ^-3 or more. Further, also in the case of sulfur and boron, if C _b <0.01 C _s and the concentration of boron are extremely low, it becomes difficult to set C _s to 10 ¹⁹ cm ⁻³ or more.

Further, in the case of lithium and nitrogen, lithium enters interstitial positions of carbon atoms constituting diamond. The other atom enters the substitution position of the carbon atom. Then, the lithium atom and the nitrogen atom exist close to each other to some extent and serve to fix lithium. However, C _n <
When the concentration of nitrogen is 0.1 C _Li and is low, the number of nitrogen atoms is small and the ability to fix lithium atoms is small, so that the carrier concentration of the doped layer becomes unstable.

In the interstitial doping of the lithium atom and the substitutional doping of the nitrogen atom, the formation energy was calculated by the first principle calculation to predict the optimum structure. As a result, it was found that the closer the lithium atom and the nitrogen atom are to each other, the lower the formation energy is, and that the structure close to each other is the most stable and optimal structure. In this case, the center distance between the lithium atom and the nitrogen atom is 0.1494 nm.
, The activation energy was calculated to be 0.10 eV. Further, by repeating such calculation a plurality of times, it was found that the center distance between the lithium atom and the nitrogen atom that can have the optimum structure is 0.145 nm or more and 0.155 nm or less.

Since the activation energy of the n-type diamond semiconductor having the above structure can be set to less than 0.1 eV, it can be set in a wide temperature range from room temperature to high temperature.
There is little temperature dependence of carrier concentration.

The n-type diamond semiconductor of the present invention may be a natural or artificial (high pressure synthetic) bulk single crystal,
Even if it is a thin film polycrystal by vapor phase synthesis or a thin film single crystal (epitaxial film), the effect is not changed.

The vapor-phase synthetic diamond film can be formed by the following methods: (1) activating a source gas by causing a discharge by a direct current or an alternating electric field; (2) heating a thermoelectron emitting material to generate the source gas. A method of activating, (3) a method of bombarding the surface on which diamond is grown with ions,
There are various methods such as (4) a method of exciting the raw material gas with light such as laser or ultraviolet rays, and (5) a method of burning the raw material gas, and any of these methods can be used in the present invention Does not change.

As described above, according to the present invention, it is possible to obtain an n-type diamond semiconductor which exhibits semiconductor characteristics in a wide temperature range from room temperature to high temperature and has a small temperature dependence of carrier concentration.

[0034]

EXAMPLES Example 1 FIG. 1 is an example of a cross-sectional configuration diagram of an n-type diamond semiconductor of the present invention. As shown in the figure, this n-type diamond semiconductor is formed on the artificial single crystal diamond substrate 100 with {10
0} plane, by microwave plasma CVD, under the following conditions, a non-doped layer _{110 1 ~110 n +} 1
(N is the number of cycles) and doped layers 120 _{1 to} 120 _n doped with nitrogen and boron were alternately formed.

(1) The film forming conditions for the non-doped layer are as follows. H ₂ (hydrogen) gas flow rate: 2000 sccm (cm ³ /
Min) CH ₄ (methane) gas flow rate: 1 sccm (cm ³ / min) pressure: 100 torr (13.3 KPa) microwave power: 300 W substrate temperature: 850 ° C.

(2) The film forming conditions for the doped layer doped with nitrogen and boron are as follows. H ₂ (hydrogen) gas flow rate: 2000 sccm CH ₄ (methane) gas flow rate: 1 sccm B ₂ H ₆ (diborane) (hydrogen dilution 1000 ppm) gas flow rate: 1 sccm NH ₃ (ammonia) (hydrogen dilution 1%) gas flow rate: 3 s
ccm Pressure: 100 torr (13.3 KPa) Microwave power: 300 W Substrate temperature: 850 ° C.

A non-doped layer and a doped layer doped with nitrogen and boron are alternately laminated on the {100} plane of a single crystal diamond. Two types of samples were prepared. Sample (a): non-doped layer 30 nm, doped layer 3 nm,
Number of cycles n = 10 Sample (b): non-doped layer 300 nm, doped layer 3n
m, number of cycles n = 5

Each sample was measured by electron diffraction to
Confirm epitaxial growth in 100> direction
did. Also, on the {100} plane of artificial single crystal diamond
Under the same conditions as the above condition (2) in which nitrogen and boron are doped.
And 100 nm thick epitaxial diamond film
Film is formed, and the film is measured by secondary ion mass spectrometry (SIMS).
Of nitrogen and boron in the diamond film
The quantity was measured. As a result, the nitrogen atom concentration (C_n) Is 8x
10²⁰cm^-3And the boron atom concentration (C _b) Is 1
x10¹⁹cm^-3Met. Under the above condition (2),
Elemental concentration and boron concentration are C_b<C_n≤100C_bRange of
Inside, there are 10 nitrogen atoms¹⁹cm^-3Be above
Was confirmed.

Regarding the prepared samples (a) and (b),
Temperature dependence measurement of carrier concentration by Hall effect measurement,
And the temperature dependence of the resistivity was measured. Before the measurement, each sample was heated in the air (400 ° C., 40 ° C., 40 ° C.) in order to remove the surface conductive layer accompanying the hydrogen termination on the surface of each sample.
Then, the surface was terminated with oxygen. Further, the electrodes were ion-implanted (ion species: Ar ⁺ , energy: 30 keV, dose amount: 5 × 10 ¹⁵ c into the electrode formation portion on the sample surface.
m ⁻² ) to form a graphitized layer, and a thin film of Ti, Pt, and Au was sequentially formed thereon with a thickness of 300 nm to form an ohmic electrode.

FIG. 2 shows the measurement results of the temperature dependence of the carrier concentration by the Hall effect measurement of each sample. The horizontal axis is the reciprocal of absolute temperature 1 / T (K ⁻¹ ), and the vertical axis is the carrier concentration (cm ⁻³ ). From these results, it was found that both the sample (a) and the sample (b) were n-type conductivity type,
800K-300K (room temperature) (horizontal axis 0.0013-0.
It was found that the carrier concentration hardly changed with temperature in the range of 0033). The activation energies of the sample (a) were 0.03 eV and those of the sample (b) were 0.
It was 05 eV. From this, the existence of a saturation region independent of temperature was confirmed in the range of 800 K to room temperature.

It was also found that samples (a) and (b) could be prepared with different carrier concentrations. Sample (a) is a non-doped layer having a thickness of 30 nm and a doped layer having a thickness of 3 nm, and sample (b) has a non-doped layer of 3 nm.
The average carrier concentration of sample (b) should be about 1/10 of that of sample (a) because it is a stack of 00 nm and doped layers of 3 nm each. I was able to confirm that

FIG. 3 shows the measurement results of the temperature dependence of the resistivity. The horizontal axis is the reciprocal of absolute temperature 1 / T as in FIG.
(K ⁻¹ ) and the vertical axis represents the resistivity (Ω · cm). From this result, the sample (a) and the sample (b) are 800
It was confirmed that there was almost no temperature dependence of the resistivity in the temperature range of K to 300K (room temperature).

From the above, the δ-doped structure having the doped layer containing nitrogen and boron makes it possible to adjust the average carrier concentration, that is, the average electron concentration to the extent that semiconductor characteristics are obtained as a whole, and is a carrier supply source n. Since the electron concentration of the type-doped layer has little temperature dependence, the electron concentration and the resistivity have almost no temperature dependence as a whole.
It was confirmed that a diamond semiconductor of the type could be produced.

Comparative Example 1 Among the film forming conditions for the non-doped layer and the film forming condition for the doped layer in Example 1, the gas flow rate of diborane (hydrogen diluted 10 ppm) was 10 sccm, and ammonia (hydrogen diluted 1000 pp).
The non-doped layers and the doped layers were alternately formed on the {100} plane of the artificial single crystal diamond substrate under the film forming conditions of the doped layer of Example 1 except that the gas flow rate of m) was 1 sccm. However, the film thickness and the number of cycles were as follows. Comparative sample: non-doped layer 30 nm, doped layer 1
00 nm, cycle number n = 5

It was confirmed by electron beam diffraction measurement that the prepared comparative sample was epitaxially grown in the <100> direction. Moreover, when the amounts of nitrogen and boron in the doped layer were measured by SIMS measurement in the same manner as in Example 1, it was found that C
_n is ^6x10 18 ^cm -3, _{C b} is ^5x10 17 cm
It was ^-3 .

When an electrode was formed in the same manner as in Example 1 and the temperature dependence of carrier concentration was measured by Hall effect measurement, the conductivity type was n-type, but the temperature dependence of carrier concentration was large. It was Further, when the activation energy of the comparative sample was obtained from the temperature dependence of the carrier concentration, the activation energy was as large as 1.7 eV. In this way, when the impurity concentration of the doped layer is low and is not thick, the activation energy is
It was found to be 0.1 eV or more.

Example 2 As in Example 1, the microwave plasma C was formed on the {100} plane of the artificial single crystal diamond substrate 100 with the structure shown in FIG.
The non-doped layer 11 is formed by the VD method under the following conditions.
0 _{1 to} 110 _{n + 1} (n is the number of cycles) and doped layers 120 _{1 to} 120 _n doped with sulfur and boron were alternately formed.

(1) The film forming conditions for the non-doped layer are as follows. H ₂ (hydrogen) gas flow rate: 2000 sccm CH ₄ (methane) gas flow rate: 1 sccm Pressure: 100 torr (13.3 KPa) Microwave power: 300 W Substrate temperature: 850 ° C.

(2) The film forming conditions for the doped layer doped with sulfur and boron are as follows. H ₂ (hydrogen) gas flow rate: 2000 sccm CH ₄ (methane) gas flow rate: 1 sccm B ₂ H ₆ (diborane) (hydrogen dilution 1000 ppm) gas flow rate: 1 sccm H ₂ S (hydrogen sulfide) (hydrogen dilution 1000 ppm) gas flow rate: 5 sccm Pressure: 100 torr (13.3 KPa) Microwave power: 300 W Substrate temperature: 850 ° C.

A non-doped layer and a doped layer doped with sulfur and boron are alternately laminated on the {100} face of a single crystal diamond. The following two kinds of samples having different film thickness and cycle number n are used. It was created. Sample (c): non-doped layer 30 nm, doped layer 3 nm,
Number of cycles n = 10 Sample (d): non-doped layer 300 nm, doped layer 3n
m, number of cycles n = 5

By electron beam diffraction measurement, all samples were
Confirm epitaxial growth in 100> direction
did. Also, as in Example 1, adding sulfur and boron
A sample with a thickness of 100 nm was prepared, and the ion was measured by SIMS.
C atomic concentration (C_s) And boron atom concentration (C_b) Is measured
As a result, the sulfur atom concentration (C_s) Is 7x10²⁰cm
^-3, Boron atom concentration (C_b) Is 9x10¹⁸cm^-3
Met. That is, the doped layer is 0.5C_b<C_s≤1
00C_bAnd the sulfur atom is 10¹⁹cm
^-3It was confirmed that the above was done.

Regarding the prepared samples (c) and (d),
Similarly to Example 1, the temperature dependence of carrier concentration and resistivity was measured. The pretreatment before the measurement was the same as in Example 1.

FIG. 4 shows the measurement results of the temperature dependence of the carrier concentration by the Hall effect measurement of each sample. This measurement revealed that the conductivity type was n-type. Further, from this result, the sample (c) and the sample (d) are 800K to 300K.
It was found that the carrier concentration hardly changed with temperature in the range of (room temperature) (horizontal axis 0.0013 to 0.0033). Moreover, the activation energy was 0.01 eV in both samples. From this, the existence of a saturation region independent of temperature was confirmed in the range of 800 K to room temperature. It was also found that samples having different carrier concentrations could be prepared as in Example 1.

FIG. 5 shows the measurement results of the temperature dependence of the resistivity. The horizontal axis is the reciprocal of absolute temperature 1 / T (K
⁻¹ ), and the vertical axis represents the resistivity (Ω · cm). From this result, it was confirmed that there was almost no temperature dependence of the resistivity in the temperature range of 800K to 300K (room temperature).

From the above, it was confirmed that an δ-doped structure having a doped layer containing sulfur and boron could produce an n-type diamond semiconductor having the same characteristics as in Example 1 as a whole.

Example 3 As in Example 1, the non-doped layers 110 _{1 to} 110 _{n + 1} (n is the number of cycles) were formed on the {100} plane of the artificial single crystal diamond substrate 100 with the structure shown in FIG. 1 under the following conditions. )
And doped layers 120 ₁ to ₁ 1 doped with lithium and nitrogen
Films of 20 _n were formed alternately. For film formation, a photoexcited vapor phase synthesis method using vacuum ultraviolet light was used.

(1) The film forming conditions for the non-doped layer are as follows. H ₂ (hydrogen) gas flow rate: 4000 sccm CH ₄ (methane) gas flow rate: 1 sccm Pressure: 30 torr (4 KPa) Substrate temperature (heater heating): 300 ° C. Light source: synchrotron radiation (wavelength: 70 nm, accumulated current: 200 mA)

(2) The film forming conditions for the doped layer doped with lithium and nitrogen are as follows. H ₂ (hydrogen) gas flow rate: 4000 sccm CH ₄ (methane) gas flow rate: 1 sccm NH ₃ (ammonia) (hydrogen dilution 1%) gas flow rate: 10
sccm Pressure: 30 torr (4 KPa) Substrate temperature (heater heating): 300 ° C. Light source: Synchrotron radiation (wavelength: 70 nm, accumulated current: 200 mA)

The lithium was supplied by a laser ablation method using an ArF excimer laser having an intensity of 5 J / cm ² with Li ₂ O (lithium oxide) as a target.

A non-doped layer and a doped layer doped with lithium and nitrogen are alternately laminated on the {100} plane of single crystal diamond. The following two kinds of samples with different film thickness and cycle number n are used. It was created. Sample (e): non-doped layer 30 nm, doped layer 3 nm,
Number of cycles n = 10 Sample (f): non-doped layer 300 nm, doped layer 3n
m, number of cycles n = 5

By electron diffraction measurement, all samples were
Confirm epitaxial growth in 100> direction
did. Also, as in Example 1, lithium and nitrogen were added.
A sample with a thickness of 100 nm was prepared and re-measured by SIMS measurement.
Titanium atom concentration (C_Li) And nitrogen atom concentration (C_n)
As a result, the lithium atom concentration (C_Li) Is 3x10
²⁰cm^-3, Nitrogen atom concentration (C_n) Is 4x10²⁰c
m^-3Met. That is, the doped layer is C_Li≤10C
_nAnd the lithium atom is 10¹⁹cm ^-3Since
It was confirmed to be above.

Further, in order to identify the doping positions of lithium atoms and nitrogen atoms, a combination of Rutherford backscattering analysis, particle beam excited X-ray emission analysis, nuclear reaction analysis and electron spin resonance analysis was conducted. As a result, it was found that most of the lithium atoms were at the interstitial positions of the carbon atoms constituting diamond and the nitrogen atoms were at the substitution positions of the carbon atoms. It was also found that a lithium atom exists adjacent to most of the nitrogen atoms. From these results, the center distance between the lithium atom and the nitrogen atom was estimated to be about 0.15 nm of the optimum structure calculated by the first principle calculation.

Regarding the prepared samples (e) and (f),
Similarly to Example 1, the temperature dependence of carrier concentration and resistivity was measured. The pretreatment before the measurement was the same as in Example 1.

FIG. 6 shows the measurement result of the temperature dependence of the carrier concentration by the Hall effect measurement of each sample. This measurement revealed that the conductivity type was n-type. Further, from this result, the sample (e) and the sample (f) are 800K to 300K.
It was found that the carrier concentration hardly changed with temperature in the range of (room temperature) (horizontal axis 0.0013 to 0.0033). The activation energy of the sample (e) was 0.01 eV and that of the sample (f) was 0.02 eV. From this, the existence of a saturation region independent of temperature was confirmed in the range of 800 K to room temperature. In addition, Example 1
It was found that samples with different carrier concentrations could be prepared in the same manner as in.

FIG. 7 shows the measurement result of the temperature dependence of the resistivity. The horizontal axis is the reciprocal of absolute temperature 1 / T (K ⁻¹ ), and the vertical axis is the resistivity (Ω · cm). From this result, it was confirmed that there was almost no temperature dependence of the resistivity in the temperature range of 800K to 300K (room temperature).

From the above, it was confirmed that an δ-doped structure having a doped layer containing lithium and nitrogen could produce an n-type diamond semiconductor having the same characteristics as in Example 1 as a whole.

[0067]

The n-type diamond semiconductor of the present invention has almost no temperature dependence of carrier concentration, that is, electron concentration and resistivity in the temperature range of room temperature to 800K. Moreover, the electron concentration can be freely controlled. Therefore, n of the present invention
The type diamond semiconductor can be used for devices such as diodes, LEDs, transistors, and electron-emitting devices that operate stably in a wide temperature range from room temperature to high temperature.

[Brief description of drawings]

FIG. 1 is an example of a configuration diagram of an n-type diamond semiconductor according to an embodiment of the present invention.

FIG. 2 is a sample of an n-type diamond semiconductor of the present invention (a).
3 is a graph in which the Hall effect measurement is performed on Sample (b) and the temperature dependence of carrier concentration is obtained.

FIG. 3 is a sample of an n-type diamond semiconductor of the present invention (a).
3 is a graph in which the temperature dependence of the resistivity of the sample (b) is calculated.

FIG. 4 is a sample (c) of an n-type diamond semiconductor of the present invention.
3 is a graph in which the Hall effect measurement is performed on Sample (d) and the temperature dependence of carrier concentration is obtained.

FIG. 5 is an n-type diamond semiconductor sample (c) of the present invention.
3 is a graph in which the temperature dependence of the resistivity of the sample (d) is calculated.

FIG. 6 is a sample of an n-type diamond semiconductor of the present invention (e)
3 is a graph in which the Hall effect measurement is performed on Sample (f) and the temperature dependence of carrier concentration is obtained.

FIG. 7 is a sample (e) of the n-type diamond semiconductor of the present invention.
3 is a graph in which the temperature dependence of the resistivity of the sample (f) is calculated.

[Explanation of symbols]

100 substrates 110 Non-doped layer 120 doped layer

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Claims (10)

[Claims] 1. A diamond semiconductor material,
Two or more kinds of impurities are added so that (a) a first non-doped layer not substantially added with impurities and (b) an n-type semiconductor formed on one surface of the first non-doped layer. N-type diamond semiconductor, comprising: a doped non-doped layer formed on a surface of the doped layer; and (c) a second non-doped layer formed on a surface of the doped layer. 2. The n-type diamond semiconductor according to claim 1, wherein the non-doped layers and the doped layers are alternately laminated, and the layers at both ends are non-doped layers. 3. The two or more kinds of impurities added to the doped layer are nitrogen (N), phosphorus (P), sulfur (S), arsenic (As), selenium (Se), chlorine (Cl) A One or more kinds of atoms selected from the group and one or more kinds of atoms selected from the group B consisting of hydrogen (H), boron (B), lithium (Li), and aluminum (Al). The n-type diamond semiconductor according to claim 1 or 2. 4. At least one of the impurities added.
The n-type diamond semiconductor according to claim 3, wherein the impurity concentration of each type of atom is 10 ¹⁹ cm ^-3 or more. 5. The impurities added to the doped layer are nitrogen (N) and boron (B), and have a nitrogen atom concentration (C _n ).
And the boron atom concentration (C _b ) are C _b <C _n ≦ 100C
The n-type diamond semiconductor according to claim 1 or 2, wherein the range is _b and C _n ≧ 10 ¹⁹ cm ⁻³ . 6. The impurities added to the doped layer are sulfur (S) and boron (B), and the sulfur atom concentration (C)
_s ) and the boron atom concentration (C _b ) are 0.5 C _b <C _s
≦ 100 C _b , and C _s ≧ 10 ¹⁹ cm
It is ^-3 , The n-type diamond semiconductor of Claim 1 or 2 characterized by the above-mentioned. 7. The impurities added to the doped layer are lithium (Li) and nitrogen (N), and the lithium atom concentration (C _Li ) and the nitrogen atom concentration (C _n ) are C _Li ≦ 10.
The n-type diamond semiconductor according to claim 1 or 2, wherein C _{n is in} the range and C _Li ≧ 10 ¹⁹ cm ⁻³ . 8. The lithium atom is mixed in the interstitial positions of the carbon atoms constituting the diamond of the doped layer, the nitrogen atom is mixed in the substitution position of the carbon atom, and the lithium atom and the nitrogen atom are mixed. The n-type diamond semiconductor according to claim 7, wherein the n-type diamond semiconductors are structures adjacent to each other. 9. The n-type diamond semiconductor according to claim 8, wherein the center distance between the lithium atom and the nitrogen atom is 0.145 nm or more and 0.155 nm or less. 10. The n according to claim 1, wherein the activation energy is less than 0.1 eV.
Type diamond semiconductor.