JP2004207272A - Diamond electronic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diamond electronic element which has a small forward resistance, keeps a small backward leakage current, and is kept high in effective efficiency and performance. <P>SOLUTION: An undoped diamond layer 2 is formed without dopant on an n-type semiconductor substrate 1 having a dopant concentration of 1×10<SP>17</SP>cm<SP>-3</SP>or above, a high-concentration doped diamond layer 3 which has been doped with boron as high as 1×10<SP>19</SP>cm<SP>-3</SP>or above to turn to a low-resistance n-type semiconductor is formed on the undoped diamond layer 2, and furthermore an electrode 4 is formed on the high-concentration doped diamond layer 3 for the formation of the diamond electronic element. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a diamond electronic device that can be used for various electronic devices such as a rectifying and light emitting diode, an optical sensor, or a power generating device.
[0002]
[Prior art]
Diamond is the hardest among materials, has excellent heat resistance, has a large band gap of 5.47 eV, and is usually an insulator, but can be made into a semiconductor by doping with a dopant. In addition, it has excellent electrical characteristics such as a high dielectric breakdown voltage and a high saturation drift speed and a low dielectric constant. Further, it shows the highest thermal conductivity among materials at around room temperature, and has high heat dissipation. Due to these characteristics, diamond is expected as an electronic device and sensor material for high temperature, high frequency or high electric field, in addition to tools and wear-resistant coatings. In particular, a diode-type electronic element includes a rectifier diode that operates at a high withstand voltage or a high temperature (for example, see Patent Literature 1 and Non-Patent Literature 1), an ultraviolet or visible light emitting diode (for example, see Patent Literature 2), and light such as ultraviolet light. It is expected to be applied to sensors, photovoltaic elements such as solar cells that can withstand strong ultraviolet rays, radiation sensors, and the like. Further, diamond is not chemically attacked by acids and alkalis, is extremely stable chemically, and can be imparted with conductivity by doping with boron. Therefore, diamond is also promising as an electrode for a chemical reaction ( For example, see Patent Document 3).
[0003]
As a method for synthesizing a diamond film, a microwave CVD (C hemical V apor D eposition : chemical vapor deposition) method (for example, see Patent Documents 4 and 5 and Non-Patent Document 2), a high-frequency plasma CVD method, hot filament CVD Gas-phase synthesis methods such as a plasma CVD method, a DC plasma CVD method, a plasma jet method, a combustion method, and a thermal CVD method are known.
[0004]
Also, diamond becomes a p-type semiconductor when doped with boron, and becomes an n-type semiconductor when doped with phosphorus or the like. However, since the resistivity of the n-type semiconductor diamond reported at the present time is at least about 10 × 10 ⁵ Ω · cm, the n-type semiconductor diamond is considered to be unsuitable for a pn junction diode or the like. I have. On the other hand, by combining p-type semiconductor diamond with a metal such as aluminum, a Schottky junction diode can be manufactured (for example, see Non-Patent Document 3). In the Schottky junction diode, the resistance of the p-type semiconductor diamond must be reduced in order to reduce the ON resistance and the Joule loss. The resistance of a p-type semiconductor diamond can be reduced by doping an acceptor such as boron at a high concentration, but when the dopant concentration is high, the depletion layer becomes thinner at the time of reverse bias, so that the leakage current increases and the rectification ratio increases. There is a problem that becomes smaller.
[0005]
Therefore, a rectifying diode and a light emitting diode having a metal electrode / undoped diamond / p-type semiconductor diamond laminated structure without using an n-type semiconductor diamond have been proposed (for example, see Non-Patent Document 1). In Non-Patent Document 1, the undoped diamond layer, which is provided between the metal electrode layer and the p-type semiconductor diamond layer and is not doped with a dopant, functions similarly to the depletion layer. Even if the acceptor is doped at a certain concentration, an increase in leakage current can be suppressed, and a rectification ratio of 1 × 10 ^{6 to} 1 × 10 ⁷ can be obtained.
[0006]
Further, a junction with an n-type semiconductor made of a material other than diamond, that is, a so-called hetero pn junction diode has been studied. For example, a junction element with n-type hydrogenated amorphous silicon (for example, see Non-Patent Document 4) or a junction diode with p-type highly oriented diamond and silicon carbide or silicon thin film (for example, see Patent Document 6) have been proposed. ing.
[0007]
[Patent Document 1]
JP-A-04-312982 (Page 2-7, FIG. 2)
[Patent Document 2]
JP 03-222376 A (Pages 1-4, FIG. 1)
[Patent Document 3]
JP-A-09-13188 (pages 2-5, FIG. 1)
[Patent Document 4]
Japanese Patent Publication No. 59-27754 (Page 1-3, Figure 1-2)
[Patent Document 5]
JP-B-61-3320 (Pages 1-3, Fig. 1)
[Patent Document 6]
JP-A-07-94527 (pages 2-4, FIG. 2)
[Non-patent document 1]
K. Miyata and two others, "Metal-intrinsic semiconductor-semiconductor structures using polycrystalline diamond films", "Applied Physics Letters", (USA), January 27, 1992, Vol. 60, No. 4, p. 480-482
[Non-patent document 2]
T. Tachibana and two others, "Azimuthal rotation of diamond crystals epitaxially nucleated on silicon {001}", "Applied Physics Letters", (USA), January 27, 1992, Vol. 60, No. 4, p. 480-482
[Non-Patent Document 3]
Akira Otsuki, "Current state and problems of Schottky electrode in diamond semiconductor", "Materia", 1994, Vol. 33, No. 6, p. 744-749
[Non-patent document 4]
H. Kiyota and 6 others, "Polycrystalline Diamond / Hydrogenated Amorphous Silicon PN Heterojunction", "Japanese Applied Physics", 1992, Vol. 31, Part 2, No. 4A, p. L388-L391
[0008]
[Problems to be solved by the invention]
The metal electrode / undoped diamond / p-type semiconductor diamond laminated structure proposed in Non-Patent Document 1 forms a depletion layer in a pseudo manner using an undoped diamond layer to obtain rectification. However, for example, in the case of a diode sensor that detects light or particles having high energy such as ultraviolet light, a potential (diffusion potential) generated in a depletion layer is used to collect carriers generated by light irradiation with an electrode. Since the diffusion potential is generated only immediately below the electrode, even in the electronic device having the structure of Non-Patent Document 1, carriers cannot be efficiently captured in portions other than immediately below the electrode, and a large output cannot be obtained. Therefore, if the area of the electrode is increased to improve the output, the area where the electrode covers the diamond surface increases, and the effective irradiation area on the diamond decreases, so that good characteristics cannot be obtained.
[0009]
In the case of the heterojunction diode proposed in Non-Patent Document 4, as in the case of the Schottky junction diode, it is necessary to lower the resistance of the p-type semiconductor diamond in order to reduce the ON resistance and the Joule loss. As described above, p-type diamond can be made to have low resistance by doping the acceptor with a high concentration. However, since the depletion layer becomes thinner at the time of reverse bias, the leakage current increases, and the rectification ratio increases. Become smaller. Therefore, if the dopant concentration of the n-type semiconductor is reduced to obtain rectification, the depletion layer spreads to the n-type semiconductor side having a small band gap, so that the diamond blindness (visible light insensitivity) is hindered. Further, it is difficult to obtain a rectifying characteristic due to an interface state existing at the junction interface.
[0010]
The present invention has been made in view of such a problem, and an object of the present invention is to provide a high-performance diamond electronic device having a small forward resistance and a small reverse leakage current and a high effective efficiency.
[0011]
[Means for Solving the Problems]
The diamond electronic device according to the present invention includes an n-type semiconductor substrate, an undoped first diamond layer formed on the substrate in contact with the substrate, and a dopant concentration of 1 on the first diamond layer. And a second diamond layer having a size of × 10 ¹⁹ cm ⁻³ or more.
[0012]
The substrate is preferably made of n-type silicon or n-type silicon carbide having a dopant concentration of 1 × 10 ¹⁷ cm ⁻³ or more. The thickness of the first diamond layer is preferably 10 to 500 nm. Further, the dopant of the second diamond layer is preferably boron.
[0013]
A third diamond layer having a dopant concentration of 1 × 10 ¹⁸ cm ⁻³ or less may be provided between the first diamond layer and the second diamond layer. It is preferable that the thickness of the third diamond layer is 0.1 to 1.5 μm.
[0014]
By providing the first diamond layer not doped with a dopant between the n-type semiconductor substrate and the second diamond layer having a dopant concentration of 1 × 10 ¹⁹ cm ⁻³ or more, the resistance in the forward direction and the reverse direction can be improved. And the effective operating efficiency can be increased.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a diamond electronic device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view of the diamond electronic device according to the first embodiment of the present invention. As shown in FIG. 1, a diamond electronic device according to a first embodiment of the present invention comprises, on an n-type semiconductor substrate 1, an undoped diamond layer 2 doped with no dopant as a first diamond layer in contact with the substrate. Is formed. On the undoped diamond layer 2, a highly doped diamond layer 3 having a dopant concentration of 1 × 10 ¹⁹ cm ⁻³ or more is formed as a second diamond layer. An electrode 4 is formed on the heavily doped diamond layer 3.
[0016]
Next, the operation of the diamond electronic device configured as described above will be described. When a p-type semiconductor diamond is bonded to an n-type semiconductor made of a material other than diamond, a so-called heterojunction is formed, and a depletion layer is formed near the interface. Leakage current flows due to the influence of a carbonized layer containing many defects to be formed, and good rectification characteristics cannot be obtained. In the diamond electronic device of the present embodiment, the undoped diamond layer 2 formed between the n-type silicon substrate 1 and the heavily-doped diamond layer 3 which is a p-type semiconductor diamond functions as a depletion layer. Can be.
[0017]
The high-concentration doped diamond layer 3 has a dopant concentration of 1 × 10 ¹⁹ cm ⁻³ or more. If the dopant concentration is less than 1 × 10 ¹⁹ cm ⁻³ , the activation rate of the dopant is low, and a desired resistance value cannot be obtained. The dopant concentration is preferably set to 1 × 10 ²⁰ cm ⁻³ or more at which the activation rate of the dopant becomes 100%, and more preferably from the Mott dislocation concentration of diamond (2 × 10 ²⁰ cm ⁻³ ). It is more preferable to set it as high as 3 × 10 ²⁰ cm ⁻³ or more.
[0018]
As the n-type semiconductor substrate 1 of the present embodiment, it is preferable to use n-type silicon or n-type silicon carbide. Silicon and silicon carbide have a low resistance value and an n-type substrate excellent in crystallinity can be easily obtained. Further, they have a track record as substrates for diamond films and have excellent adhesion to diamond, so that they are optimal as n-type semiconductor substrates used in the diamond electronic device of the present embodiment. Further, the dopant concentration of the substrate is preferably 1 × 10 ¹⁷ cm ⁻³ or more, more preferably 1 × 10 ¹⁸ cm ⁻³ or more. If the dopant concentration is less than 1 × 10 ¹⁷ cm ⁻³ , the depletion layer spreads to the n-type semiconductor side, so that carriers are generated even on the n-type semiconductor side having a small band gap, and the characteristics are deteriorated.
[0019]
The thickness of the undoped diamond layer 2 is preferably 10 to 500 nm. If the thickness of the undoped diamond layer 2 exceeds 500 nm, the series resistance increases and a large forward current cannot be obtained. On the other hand, if the thickness of the undoped diamond layer 2 is less than 10 nm, it becomes impossible to prevent exchange of carriers through the interface state, and the effect is lost.
[0020]
The undoped layer 2 is formed on the n-type semiconductor substrate 1 using, for example, a CVD apparatus or the like. Conventionally, when diamond is formed on a silicon substrate or the like, it has been necessary to polish (scratch) the substrate surface with diamond powder or the like. However, the diamond layer formed after the scratching treatment had a particle density of about 10 ⁸ cm ⁻³ , and it was difficult to form a thin continuous film. In the diamond electronic device of the present embodiment, when the undoped diamond layer 2 is formed, the bias application method described in Non-Patent Document 2 is applied, and the film forming conditions are set, for example, the reaction gas is set to 1% by volume of methane and By exposing the substrate to plasma for 20 minutes while applying -200 V to the substrate at a hydrogen temperature of 99% by volume and a substrate temperature of 800 [deg.] C., the nucleation density can be dramatically increased and the target film thickness can be formed with good reproducibility. it can.
[0021]
Note that the dopant of the highly doped diamond layer 3 is preferably boron. By doping with boron, a p-type semiconductor diamond having lower resistance can be obtained.
[0022]
Next, a diamond electronic device according to a second embodiment of the present invention will be described. FIG. 2 is a sectional view of a diamond electronic device according to a second embodiment of the present invention. As shown in FIG. 2, the diamond electronic device of this embodiment has a low-concentration doped diamond layer 5 having a dopant concentration of 1 × 10 ¹⁸ cm ⁻³ or less between the undoped diamond layer 2 and the high-concentration doped diamond layer 3. Is formed.
[0023]
In the present embodiment, the lightly doped diamond layer 5 is formed, and the lightly doped diamond layer 5 moderately changes the concentration of the dopant existing between the undoped diamond layer 2 and the heavily doped diamond layer 3. This has the effect of gradually changing the electric field distribution.
[0024]
The dopant concentration in the low-concentration doped diamond layer 5 is set to 1 × 10 ¹⁸ cm ⁻³ or less. When the dopant concentration is higher than 1 × 10 ¹⁸ cm ⁻³ , the reverse current increases. If the dopant concentration is 1 × 10 ¹⁸ cm ⁻³ or less, the resistance does not decrease and the leak current can be suppressed low. However, if the dopant concentration is too low, charge injection from the heavily doped diamond layer 3 becomes difficult to occur, and the forward current decreases. According to experiments by the present inventors, the optimum value of the dopant concentration in the lightly doped diamond layer 5 is 1 × 10 ^{17 to} 8 × 10 ¹⁷ cm ⁻³ .
[0025]
Note that the thickness of the low-concentration doped diamond layer 5 is preferably 0.1 to 1.5 μm. If the thickness of the low-concentration doped diamond layer 5 is less than 0.1 μm, there is no effect of inserting the low-concentration doped diamond layer. If the thickness exceeds 1.5 μm, the resistance of the entire device becomes too high, and the operation of the device deteriorates. I do.
[0026]
The diamond electronic device of the present invention is different from a conventional electronic device having a structure in which an electrode of amorphous silicon or the like is laminated on diamond, and can receive high-energy light or particles from the diamond side, and has high durability. Property is obtained. Although it is possible to irradiate light or particles from the back side even with a conventional electronic element, since the substrate layer is thick, the light or particles often disappear before reaching the depletion layer, which is inefficient. In addition, the diamond electronic device of the present invention can easily control the thickness of the heavily doped diamond layer 3 and calculate the amount of absorption in the heavily doped diamond layer 3 to provide the effect of the attenuation filter. The energy of the particles can be controlled. Further, the diamond electronic device of the present invention does not require steps such as thin film formation, ion implantation and annealing, unlike the conventional electronic device, since the substrate is an n-type semiconductor, and thus the manufacturing cost is lower than that of the conventional electronic device. Can be reduced.
[0027]
INDUSTRIAL APPLICABILITY The diamond electronic device of the present invention can be applied to rectifier diodes, light-emitting diodes, optical sensors such as ultraviolet sensors, solar cells, and other various electronic devices, and can achieve high performance thereof.
[0028]
【Example】
Hereinafter, examples of the present invention will be specifically described in comparison with comparative examples that are out of the scope of the present invention.
[0029]
First Example As a first example of the present invention, a diode was manufactured using the electronic device of the present invention. FIG. 3 shows a sectional view of the diode according to the first embodiment of the present invention. The diode of the present embodiment is formed on the n-type silicon substrate 6 by using the inorganic material polishing type microwave plasma CVD apparatus described in Non-Patent Document 5 and by nucleation by a bias application method, and has a thickness of 10 nm. An undoped diamond layer 7 having a thickness of about 500 μm was formed. Next, the reaction gas was set to 0.5% by volume of methane and 99.5% by volume of hydrogen, and the addition amount of the borane gas was changed to form a highly doped diamond layer 8 having a changed dopant concentration. At that time, as Comparative Example 1, nucleation promoting treatment was performed on the n-type silicon substrate 6 by applying ultrasonic waves in an ethanol turbid solution of diamond powder having a diameter of several 10 μm. After washing away the diamond particles, an undoped diamond layer 7 and a highly-doped diamond layer 8 were formed in the same manner as in the example. Further, as Comparative Example 2, a diode without the undoped diamond layer 8 was also manufactured. After forming the high-concentration doped diamond layer 8, the boron concentration in the high-concentration doped diamond layer 8 of this embodiment was measured by secondary ion mass spectrometry, and the result was 1 × 10 ¹⁹ cm ⁻³ (boron to carbon in the reaction gas). Atomic ratio: B / C = 400 ppm) to 3 × 10 ²⁰ cm ⁻³ (B / C = 4000 ppm).
[0030]
Thereafter, the surface is cleaned by immersing in a saturated solution of chromic sulfuric acid at 200 ° C. and subsequently in aqua regia at 100 ° C. After removing the oxide film on the back surface of the n-type silicon substrate 6 with hydrofluoric acid, To form an ohmic bond 9. Next, as the upper electrode 10, aluminum was deposited on the surface of the highly-doped diamond layer 8 to a diameter of 100 μm and a thickness of 200 nm.
[0031]
The ohmic electrode 9 on the back surface of the n-type silicon substrate 6 was grounded, a voltage was applied to the aluminum upper electrode 10, and voltage-current characteristics were measured. The result is shown in FIG. As shown in FIG. 4, in the diode having the undoped diamond layer 7, good rectification characteristics were obtained. However, in the diode of Comparative Example 2 in which the undoped diamond layer 8 was not formed, the leakage current was large. No rectification was observed. The characteristics of the diode of Comparative Example 1 in which nucleation treatment was performed with diamond powder were the same as those of the diode of Comparative Example 2 in which the undoped diamond layer 7 was not formed. Then, when the electron microscope observation was performed after the undoped diamond layer 7 was formed, the diode of Comparative Example 1 showed that the undoped diamond layer 7 was not a continuous film. The doped diamond layer 8 was in contact.
[0032]
Further, in order to investigate the influence of the thickness of the undoped diamond layer, a diode having an undoped diamond layer 7 having a thickness of 10 to 1000 nm was manufactured, and its forward characteristics were measured. The result is shown in FIG. In FIG. 5, a minus is indicated in the first quadrant. As shown in FIG. 5, a good diode operation was confirmed when the thickness of the undoped diamond layer 7 was 10 nm or more. When the thickness of the undoped diamond layer 7 was 200 nm or more, a rise in the rising voltage was observed. However, until the thickness exceeded 500 nm, the diode operated as a practical diode. On the other hand, in a diode having a thickness of the undoped diamond layer 7 exceeding 500 nm which is out of the range of the present invention, a clear rise was not observed when the voltage was applied up to -40V.
[0033]
Second Example As a second example of the present invention, a diode was manufactured using the diamond element of the present invention. FIG. 6 is a sectional view of a diode according to a second embodiment of the present invention. In the diode of this embodiment, similarly to the first embodiment, after forming an undoped diamond layer 7 on an n-type silicon substrate 6, a low-concentration diamond layer 11 is formed, and diborane as a reaction gas is further formed thereon. This was added to form a high-concentration diamond layer 8. In the diode of the present embodiment, grooves having a pitch of 3 mm in length and 3 mm in width were provided on the surface of the n-type silicon substrate 6 for cutting out as individual elements. Next, as in the first embodiment, an ohmic electrode 9 was formed on the back surface of the n-type silicon substrate 6, and an upper electrode 10 was formed on the surface of the heavily doped diamond layer 8. The upper electrode 10 was 3 mm long and 3 mm wide, and one electrode was provided for each element.
[0034]
When the voltage-current characteristics of the diode manufactured by the above process were measured, the current in the forward direction (applied a negative voltage to the upper electrode) decreased by about one digit compared to the conventional diode, but decreased by three digits in the reverse direction. The rectification characteristics have been greatly improved. In addition, when the low-pressure mercury lamp was irradiated to the diode of this embodiment from a position having a height of 5 cm, the current increased by two digits or more in the range of 0 to -5 V when a negative voltage was applied. At the time of voltage application, the current increased by two digits or more in all regions. On the other hand, in the conventional MiS (M etal- i ntrinsicsemiconductor- S emicondouctor ) diode, from the fact that the increase in current is about one order of magnitude at most, an electronic device of the present embodiment is the maintenance of efficient photocurrent line Have been
[0035]
【The invention's effect】
As described above in detail, according to the present invention, an insulating material without a dopant is doped between an n-type semiconductor substrate and a diamond layer having a dopant concentration of 1 × 10 ¹⁹ cm ⁻³ or more, which is a p-type semiconductor. By providing the diamond layer, the forward resistance and the reverse leakage current can be reduced, and the effective operating efficiency can be further increased.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a diamond electronic device according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of a diamond electronic device according to a second embodiment of the present invention.
FIG. 3 is a sectional view of a diode according to the first embodiment of the present invention.
FIG. 4 is a graph showing current-voltage characteristics of the diodes of the first embodiment and the comparative example of the present invention.
FIG. 5 is a graph showing the forward characteristics of the diodes of the first embodiment and the comparative example of the present invention.
FIG. 6 is a sectional view of a diode according to a second embodiment of the present invention.
[Explanation of symbols]
1, 6; n-type semiconductor substrate 2, 7; undoped diamond layer 3, 8; high-concentration doped diamond layer 4; electrode 5, 11; low-concentration doped diamond layer 6; n-type silicon substrate 9; ohmic electrode 10;

Claims (6)

an n-type semiconductor substrate; an undoped first diamond layer formed on the substrate in contact with the substrate; and a dopant concentration of 1 × 10 ¹⁹ cm ⁻³ or more formed on the first diamond layer. And a second diamond layer. 2. The diamond electronic device according to claim 1, wherein the substrate is made of n-type silicon or n-type silicon carbide having a dopant concentration of 1 × 10 ¹⁷ cm ⁻³ or more. ³ . 3. The diamond electronic device according to claim 1, wherein the thickness of the first diamond layer is 10 to 500 nm. 4. The diamond electronic device according to claim 1, wherein the dopant of the second diamond layer is boron. 5. 5. The semiconductor device according to claim 1, further comprising a third diamond layer having a dopant concentration of 1 × 10 ¹⁸ cm ⁻³ or less between the first diamond layer and the second diamond layer. 2. The diamond electronic device according to claim 1. The diamond electronic device according to claim 5, wherein the thickness of the third diamond layer is 0.1 to 1.5 m.

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