JP3986432B2 - Diamond electronic element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diamond electronic element that can be used in various electronic devices such as a rectifier and a light emitting diode, an optical sensor, or a power generation element.
[0002]
[Prior art]
Diamond is the hardest material, 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, the dielectric breakdown voltage and saturation drift speed are high, and the electrical characteristics such as low dielectric constant are also excellent. Furthermore, it has the highest thermal conductivity among substances at around room temperature and has high heat dissipation. Due to these features, diamond is expected as an electronic device and sensor material for high temperature, high frequency or high electric field, besides tools and wear resistant coatings. In particular, a diode-type electronic element includes a rectifier diode that operates at a high withstand voltage or at a high temperature (see, for example, Patent Document 1 and Non-Patent Document 1), ultraviolet light or visible light emitting diode (see, for example, Patent Document 2), and light such as ultraviolet light. Applications to sensors, photovoltaic elements such as solar cells that can withstand strong ultraviolet rays, and radiation sensors are expected. Furthermore, since diamond is not eroded by acids and alkalis, is chemically very stable, and can be imparted with conductivity by doping with boron, it is also promising as an electrode for 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 Vapor phase synthesis methods such as a method, a direct current plasma CVD method, a plasma jet method, a combustion method, and a thermal CVD method are known.
[0004]
Diamond becomes a p-type semiconductor by doping boron, and becomes an n-type semiconductor by doping phosphorus or the like. However, since the resistivity of n-type semiconductor diamond reported at present is about 10 × 10 ⁵ Ω · cm at the lowest, n-type semiconductor diamond is considered unsuitable for pn junction diodes and the like. Yes. On the other hand, a p-type semiconductor diamond can be combined with a metal such as aluminum to produce a Schottky junction diode (see, for example, Non-Patent Document 3). In the Schottky junction diode, in order to reduce the on-resistance and reduce the Joule loss, the resistance of the p-type semiconductor diamond must be lowered. The p-type semiconductor diamond can be reduced in resistance by doping with an acceptor such as boron at a high concentration. However, when the dopant concentration is increased, the depletion layer becomes thinner at the time of reverse bias. There is a problem that becomes smaller.
[0005]
Therefore, a rectifier diode and a light emitting diode having a metal electrode / undoped diamond / p-type semiconductor diamond laminated structure without using n-type semiconductor diamond have been proposed (for example, see Non-Patent Document 1). In Non-Patent Document 1, an undoped diamond layer not doped with a dopant provided between a metal electrode layer and a p-type semiconductor diamond layer functions in the same manner as a depletion layer. Even if the acceptor of the concentration is doped, 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, 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 a silicon thin film (for example, see Patent Document 6) has been proposed. ing.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 04-312982 (page 2-7, FIG. 2)
[Patent Document 2]
JP-A-03-222376 (page 1-4, FIG. 1)
[Patent Document 3]
JP 09-13188 (page 2-5, FIG. 1)
[Patent Document 4]
Japanese Examined Patent Publication No. 59-27754 (Page 1-3, Figure 1-2)
[Patent Document 5]
Japanese Examined Patent Publication No. 61-3320 (Page 1-3, Fig. 1)
[Patent Document 6]
JP 07-94527 A (page 2-4, FIG. 2)
[Non-Patent Document 1]
K. Miyata and two others, “Metal-intrinsic semiconductor-semiconductor structures using collimating 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]
Summary, “Current Status and Problems of Schottky Electrodes in Diamond Semiconductors”, “Materia”, 1994, Vol. 33, No. 6, p. 744-749
[Non-Patent Document 4]
H. Kiyota et al., “Polycrystalline Diamond / Hydrogenated Amorphous Silicon PN Heterojunction”, “Japanese Applied Physics”, 1992, Vol. 31, Part 2, 4A, p. L388-L391
[0008]
[Problems to be solved by the invention]
The metal electrode / undoped diamond / p-type semiconductor diamond multilayer structure proposed in Non-Patent Document 1 forms a depletion layer in a pseudo manner by an undoped diamond layer, thereby obtaining rectification. However, for example, in the case of a diode sensor that detects light or particles having high energy such as ultraviolet rays, 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 directly under the electrode, even in the electronic device having the structure of Non-Patent Document 1, carriers cannot be efficiently captured in a portion other than directly under the electrode, and a large output cannot be obtained. Therefore, when 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 of the diamond decreases, and good characteristics cannot be obtained.
[0009]
In addition, in the case of the heterojunction diode proposed in Non-Patent Document 4, it is necessary to reduce the resistance of the p-type semiconductor diamond in order to reduce the on-resistance and the Joule loss, as in the Schottky junction diode. As described above, p-type diamond can be reduced in resistance by doping the acceptor at a high concentration. However, since the depletion layer becomes thin at the time of reverse bias, the leakage current is increased, and the rectification ratio is increased. Get smaller. Therefore, when the dopant concentration of the n-type semiconductor is lowered in order to obtain rectifying properties, the depletion layer spreads to the n-type semiconductor side having a small band gap, so that the solar blind property (visible light insensitivity) of diamond is hindered. Furthermore, it is difficult to obtain rectification characteristics due to the interface states existing at the junction interface.
[0010]
The present invention has been made in view of such problems, and an object of the present invention is to provide a high-performance diamond electronic device with low forward resistance and reverse leakage current and 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 formed on the first diamond layer. a second diamond layer is × ¹⁰ 19 ^{cm -3} or more, have a thickness of the first diamond layer is characterized by a 10 to 500 nm.
[0012]
Another 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 formed on the first diamond layer. a second diamond layer but is 1 × ¹⁰ 19 ^{cm -3} or higher, the dopant concentration is formed of 1 × ¹⁰ 18 ^{cm -3} or less between the first diamond layer and the second diamond layer 3 diamond layers.
[0013]
The substrate is preferably n-type silicon or n-type silicon carbide having a dopant concentration of 1 × 10 ¹⁷ cm ⁻³ or more. The dopant of the second diamond layer is preferably boron. Furthermore, 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 the dopant between the n-type semiconductor substrate and the second diamond layer having a dopant concentration of 1 × 10 ¹⁹ cm ⁻³ or more, forward resistance and reverse direction Leakage current can be reduced, and the effective operating efficiency can be increased.
[0015]
DETAILED DESCRIPTION OF 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 cross-sectional view of a diamond electronic device according to a first embodiment of the present invention. As shown in FIG. 1, the diamond electronic device according to the first embodiment of the present invention has an undoped diamond layer 2 on a n-type semiconductor substrate 1 that is in contact with the substrate and is not doped with a dopant as a first diamond layer. 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 highly 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 and an n-type semiconductor made of a material other than diamond are joined, a so-called heterojunction is formed, and a depletion layer is formed near the interface. Leakage current flows under the influence of the carbonized layer containing many defects 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 highly doped diamond layer 3 which is a p-type semiconductor diamond functions as a depletion layer, so that rectification is ensured. Can do.
[0017]
The dopant concentration of the highly doped diamond layer 3 is 1 × 10 ¹⁹ cm ⁻³ or more. When the dopant concentration is less than 1 × 10 ¹⁹ cm ⁻³ , the activation rate of the dopant is low, and a target resistance value cannot be obtained. The dopant concentration is preferably 1 × 10 ²⁰ cm ⁻³ or more at which the dopant activation rate is 100%, and moreover, from the Mott dislocation concentration of diamond (which is 2 × 10 ²⁰ cm ⁻³ ). More preferably, it is 3 × 10 ²⁰ cm ⁻³ or higher.
[0018]
As the n-type semiconductor substrate 1 of this embodiment, it is preferable to use n-type silicon or n-type silicon carbide. Silicon and silicon carbide have low resistance values, and an n-type substrate excellent in crystallinity can be easily obtained. Furthermore, since they have a track record as diamond film substrates and have excellent adhesion to diamond, they are optimal as n-type semiconductor substrates used in the diamond electronic device of this embodiment. The dopant concentration of the substrate is preferably 1 × 10 ¹⁷ cm ⁻³ or more, more preferably 1 × 10 ¹⁸ cm ⁻³ or more. When the dopant concentration is less than 1 × 10 ¹⁷ cm ⁻³ , the depletion layer spreads to the n-type semiconductor side, so that generation of carriers also occurs on the n-type semiconductor side with a small band gap, and the characteristics deteriorate.
[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 a diamond film is formed on a silicon substrate or the like, the surface of the substrate has to be polished (scratched) with diamond powder or the like. However, the diamond layer formed after the scratching treatment has a particle density of about 10 ⁸ cm ⁻³ , and it is 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 formation conditions are, for example, that the reaction gas is 1% by volume of methane and It is possible to drastically increase the nucleation density and form the desired film thickness with good reproducibility by exposing to plasma for 20 minutes while applying −200V to the substrate at a substrate temperature of 800 ° C. with hydrogen of 99 volume%. it can.
[0021]
The dopant of the highly doped diamond layer 3 is preferably boron. By doping boron, a p-type semiconductor diamond having a 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 cross-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 the present 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 this embodiment, a lightly doped diamond layer 5 is formed, and this lightly doped diamond layer 5 moderates the concentration change of the dopant existing between the undoped diamond layer 2 and the highly doped diamond layer 3. And has the effect of gradually changing the electric field distribution.
[0024]
The dopant concentration in the lightly doped diamond layer 5 is 1 × 10 ¹⁸ cm ⁻³ or less. When the dopant concentration is higher than 1 × 10 ¹⁸ cm ⁻³ , the reverse current increases. When the dopant concentration is 1 × 10 ¹⁸ cm ⁻³ or less, the resistance does not decrease and the leakage current can be kept low. However, if the dopant concentration is too low, charge injection from the heavily doped diamond layer 3 is difficult to occur, and the forward current is reduced. According to the 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]
The thickness of the lightly doped diamond layer 5 is preferably 0.1 to 1.5 μm. If the thickness of the lightly doped diamond layer 5 is less than 0.1 μm, there is no effect of inserting the lightly doped diamond layer. If the thickness of the lightly doped diamond layer 5 exceeds 1.5 μm, the resistance of the entire device becomes too high, so that the operation of the device is deteriorated. To do.
[0026]
Unlike the conventional electronic device having a structure in which an electrode such as amorphous silicon is laminated on diamond, the diamond electronic device of the present invention is capable of high energy light or particle incidence from the diamond side and has high durability. Sex is obtained. Although it is possible to irradiate light or particles from the back surface even with a conventional electronic device, 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 highly doped diamond layer 3, and can achieve the effect of an attenuation filter by calculating the amount of absorption in the highly doped diamond layer 3. The energy of the particles can be controlled. Furthermore, since the substrate of the diamond electronic device of the present invention is an n-type semiconductor, steps such as thin film formation, ion implantation, and annealing are unnecessary as in the conventional electronic device, and the manufacturing cost is lower than that of the conventional electronic device. Can be reduced.
[0027]
The diamond electronic element of the present invention can be applied to optical sensors such as rectifier diodes, light emitting diodes, and ultraviolet sensors, solar cells, and other various electronic elements, and can achieve high performance.
[0028]
【Example】
Examples of the present invention will be specifically described below 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 fabricated using the electronic device of the present invention. FIG. 3 shows a cross-sectional view of the diode according to Example 1 of the present invention. The diode of this example is formed on a n-type silicon substrate 6 by nucleation by a bias application method using an inorganic material type microwave plasma CVD apparatus described in Non-Patent Document 5, and has a thickness of 10 An undoped diamond layer 7 having a thickness of 500 μm was formed. Next, the highly doped diamond layer 8 in which the dopant concentration was changed was formed by changing the reaction gas to 0.5 volume% of methane and 99.5 volume% of hydrogen and changing the addition amount of siborane gas. At that time, as Comparative Example 1, the n-type silicon substrate 6 was subjected to nucleation promotion treatment by applying ultrasonic waves in an ethanol turbid solution of diamond powder having a diameter of several tens of 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 produced. After forming the high-concentration doped diamond layer 8, the boron concentration in the high-concentration doped diamond layer 8 of this example was measured by secondary ion mass spectrometry, and found to be 1 × 10 ¹⁹ cm ⁻³ (boron with respect to carbon in the reaction gas). The atomic ratio was: 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 chromium sulfuric acid at 200 ° C. and subsequently in aqua regia at 100 ° C. Further, after removing the oxide film on the back surface of the n-type silicon substrate 6 with hydrofluoric acid, A silver paste was applied to form an ohmic bond 9. Next, as the upper electrode 10, aluminum was vapor-deposited on the surface of the highly doped diamond layer 8 with 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, and a voltage was applied to the aluminum upper electrode 10 to measure voltage-current characteristics. The result is shown in FIG. As shown in FIG. 4, in the diode in which the undoped diamond layer 7 was formed, good rectification characteristics were obtained, but in the diode of Comparative Example 2 in which the undoped diamond layer 8 was not formed, the leakage current was large, Rectification was not observed. Further, the characteristics of the diode of Comparative Example 1 in which the 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 undoped diamond layer 7 was formed and then observed with an electron microscope, the diode of Comparative Example 1 had a high concentration of n-type silicon substrate 6 and p-type semiconductor diamond because the undoped diamond layer 7 was not a continuous film. The dope 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 fabricated, and its forward characteristics were measured. The result is shown in FIG. In FIG. 5, minus is shown in the first quadrant. As shown in FIG. 5, good diode operation was confirmed when the thickness of the undoped diamond layer 7 was 10 nm or more. In addition, although the rising voltage increased when the thickness of the undoped diamond layer 7 was 200 nm or more, it operated as a practical diode until the thickness exceeded 500 nm. On the other hand, in a diode in which the thickness of the undoped diamond layer 7 outside the scope of the present invention exceeds 500 nm, no clear rise was observed when applied up to -40V.
[0033]
Second Example As a second example of the present invention, a diode was fabricated 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, as in the first embodiment, after the undoped diamond layer 7 is formed on the n-type silicon substrate 6, the low-concentration diamond layer 11 is formed, and further, diborane is used as a reactive gas. This was added to form a high-concentration diamond layer 8. In the diode of this example, grooves with a pitch of 3 mm in length and 3 mm in width were provided on the surface of the n-type silicon substrate 6 in order to cut 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 in length and 3 mm in width, 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 (a negative voltage was applied to the upper electrode) decreased by about one digit compared to the conventional diode, but the reverse direction decreased by three digits, The rectification characteristics are greatly improved. Further, when the low-pressure mercury lamp was irradiated to the diode of this example from a position of 5 cm in height, the current increased by two orders of magnitude or more in the range of 0 to -5 V when a negative voltage was applied, compared to the case where no irradiation was performed. When voltage was applied, the current increased by two orders of magnitude 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 It has been broken.
[0035]
【The invention's effect】
As described above in detail, according to the present invention, an insulating property in which a dopant is not 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 cross-sectional view of a diode according to a first embodiment of the present invention.
FIG. 4 is a graph showing current-voltage characteristics of the diodes of the first example and the comparative example of the present invention.
FIG. 5 is a graph showing the forward characteristics of the diodes of the first example and the comparative example of the present invention.
FIG. 6 is a cross-sectional view of a diode according to a second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 6; N-type semiconductor substrate 2, 7; Undoped diamond layer 3, 8; Highly-doped diamond layer 4; Electrode 5, 11; Lightly-doped diamond layer 6; N-type silicon substrate 9;

Claims (5)

an n-type semiconductor substrate; an undoped first diamond layer formed on the substrate in contact with the substrate; and a dopant concentration formed on the first diamond layer of 1 × 10 ¹⁹ cm ⁻³ or more. diamond electronic device and the second diamond layer, was perforated, the thickness of the first diamond layer is characterized by a 10 to 500 nm. an n-type semiconductor substrate; an undoped first diamond layer formed on the substrate in contact with the substrate; and a dopant concentration formed on the first diamond layer of 1 × 10 ¹⁹ cm ⁻³ or more. A second diamond layer; and a third diamond layer formed between the first diamond layer and the second diamond layer and having a dopant concentration of 1 × 10 ¹⁸ cm ⁻³ or less. Diamond electronic element. The substrate, diamond electronic device according to claim 1 or 2, characterized in that the dopant concentration is 1 × 10 ¹⁷ cm ^-3 or more n-type silicon or n-type silicon carbide. 4. The diamond electronic device according to claim 1, wherein the dopant of the second diamond layer is boron. 5. The diamond electronic device according to claim 2 , wherein the third diamond layer has a thickness of 0.1 to 1.5 μm.

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