JP2008166639A - Rectifier element and power converter using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rectifier element that has a small ON voltage and a small inverse leak current, and to provide a power converter that has low loss and can operate efficiently by the rectifier element. <P>SOLUTION: The rectifier element has a first nitride semiconductor layer 3. A second nitride semiconductor layer 4 having a forbidden bandwidth wider than that of the first nitride semiconductor layer 3 is formed on the first nitride semiconductor layer 3. A first anode electrode 6 is formed on the second nitride semiconductor layer 4. Further, a fluorine introduction region 9 is formed on the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4 below the first anode electrode 6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rectifier element and a power converter using the same, and more particularly to a rectifier element using a nitride semiconductor suitable for high power applications with a low on-voltage and a high breakdown voltage, and a power converter using the same. It is.

  A semiconductor element using a nitride semiconductor material has attracted attention as a power element capable of operating with a high breakdown voltage and a large current because of its essential characteristics. Among them, a rectifying element using a Schottky junction is promising as an element for a power converter because it can achieve both a low on-voltage and a high breakdown voltage.

  FIG. 5 is a cross-sectional view for explaining the main part of a conventional rectifying element using a nitride semiconductor. As shown in FIG. 5, the conventional rectifying device includes a substrate 101, a buffer layer 102, a first nitride semiconductor layer 103, and a second nitride having a forbidden band width larger than that of the first nitride semiconductor layer 103. A physical semiconductor layer 104, a contact layer 105, a first anode electrode 106, a second anode electrode 107, and a cathode electrode 108 are provided.

  A two-dimensional electron gas is present on the first nitride semiconductor layer 103 side of the heterojunction interface between the first nitride semiconductor layer 103 and the second nitride semiconductor layer 104, and a channel layer (not shown) Is formed. The first anode electrode 106 and the second anode electrode 107 are electrically connected to each other and jointly form a composite anode electrode. Each of the first anode electrode 106 and the second anode electrode 107 and the second nitride semiconductor layer 104 form a Schottky junction, and the Schottky barrier of the first anode electrode 106 is the second It is higher than the Schottky barrier of the anode electrode 107. On the other hand, the cathode electrode 108 is in ohmic contact with the channel layer in the first nitride semiconductor layer 103 through the contact layer 105.

  In this configuration, when a forward voltage is applied to the composite anode electrode, first, a current flows through the second anode electrode 107 having a low Schottky barrier. Thereafter, when the forward voltage is further increased, the current flows through both the first anode electrode 106 and the second anode electrode 107 having a high Schottky barrier. As described above, according to the conventional rectifying element, forward operation is performed as compared with the rectifying element including only the first anode electrode 106 having a high Schottky barrier due to the presence of the second anode electrode 107. Since the rise voltage at the time is lowered, the on-voltage can be lowered.

  On the other hand, when the voltage is applied in the reverse direction, the first Schottky barrier is high before the depletion layer spreads in the second nitride semiconductor layer 104 immediately below the second anode electrode 107 having the low Schottky barrier. A depletion layer spreads in the second nitride semiconductor layer 104 immediately below the anode electrode 106. Therefore, the current path is pinched off and the current is interrupted.

  As described above, according to the conventional rectifying element, due to the presence of the first anode electrode 106, the reverse leakage is compared with the rectifying element configured only by the second anode electrode 107 having a low Schottky barrier. The current can be reduced and the withstand voltage can be increased.

Therefore, according to the conventional rectifier, a rectifier having a low on-voltage and a high withstand voltage is realized. Technologies relating to such a rectifying element including a nitride semiconductor are disclosed in, for example, Patent Document 1 and Non-Patent Document 1 shown below.
JP 2005-317843 A Seikoh Yoshida et al., “A New GaN Based Field Effect Schottky Barrier Diode with a Very Low On-Voltage Operation”, Proceedings of 2004 International Symposium on Power Semiconductor Devices & ICs, Kitakyushu, pp. 323-326. Ikeda, N. et al., "Development of GaN power devices for power supplies using thin AlGaN structures", Furukawa Electric Times, No. 117, January 2006, pp.1-5.

  However, the on-voltage and breakdown voltage of the conventional rectifying element may not satisfy the conditions of the rectifying element required for the next generation rectifying element. That is, in the future, it is expected that a rectifying element having a lower ON voltage and a higher breakdown voltage will be required.

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a rectifying element having a lower on-voltage and a higher withstand voltage, and a power converter using the same.

  The rectifying device of the present invention is provided on the first nitride semiconductor layer having the channel layer and the first nitride semiconductor layer, and the width of the forbidden band is the width of the forbidden band of the first nitride semiconductor layer. A layer that functions as a barrier layer for the first nitride semiconductor layer, and is provided on the second nitride semiconductor layer, the second nitride semiconductor layer including one or more layers, and the second nitride semiconductor layer An anode electrode. At least one of the first nitride semiconductor layer and the second nitride semiconductor layer includes a fluorine introduction region at a position below the anode layer.

  According to the above configuration, the on-voltage is lowered and the breakdown voltage is increased due to the presence of the fluorine introduction region.

  Further, at least a part of the anode electrode may be Schottky joined to the second nitride semiconductor layer, and the cathode electrode may be in ohmic contact with the channel layer.

  The anode electrode may include a first anode electrode and a second anode electrode made of a material different from that of the first anode electrode and electrically connected to the first anode electrode. The first anode electrode and the second anode electrode may be Schottky bonded to the second nitride semiconductor layer. In this case, the height of the Schottky barrier in the first anode electrode and the second nitride semiconductor layer is preferably higher than the height of the Schottky barrier in the second anode electrode and the second nitride semiconductor layer. .

  According to this configuration, when two types of anode electrodes forming a Schottky junction are used, it is possible to obtain a rectifying element that can further reduce the reverse leakage current while reducing the on-voltage.

  The anode electrode may include a first anode electrode and a second anode electrode made of a material different from that of the first anode electrode and electrically connected to the first anode electrode. In this case, the first anode electrode may be Schottky joined to the second nitride semiconductor layer, and the second anode electrode may be in ohmic contact with the channel layer.

  According to this configuration, by using two types of anode electrodes that form a Schottky junction and an ohmic contact, it is possible to obtain a rectifying element that can further reduce the on-voltage while reducing the reverse leakage current. .

  Further, it is desirable that the thickness of the second nitride semiconductor layer located below the portion of the anode electrode forming a Schottky junction with the second nitride semiconductor layer is 5 nm or more. According to this, it is possible to reduce a leakage current generated when a voltage is applied to the rectifying element in the reverse direction.

  The power converter of the present invention uses the rectifying element as described above. Therefore, since the potential drop at the rectifying element when the rectifying element is operated in the forward direction can be reduced, a power conversion device that can operate with low loss and high efficiency can be obtained.

  According to the present invention, it is possible to obtain a rectifying element having a lower on-voltage and a higher withstand voltage, and a power converter using the same.

  Hereinafter, a rectifying element and a power converter according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the part with the same or corresponding function is attached | subjected with the same referential mark, and the description is not repeated.

(Embodiment 1)
First, a rectifying device according to an embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the rectifying element of the present embodiment includes a substrate 1 and a buffer layer 2 formed on the substrate 1. A first nitride semiconductor layer 3 is formed on the buffer layer 2. A second nitride semiconductor layer 4 having a wider forbidden band than that of the first nitride semiconductor layer 3 is formed on the first nitride semiconductor layer 3. A first anode electrode 6 and a protective film 10 are formed on the second nitride semiconductor layer 4.

  Cathode electrode 8 is formed so as to be in contact with both first nitride semiconductor layer 3 and second nitride semiconductor layer 4. Further, below the first anode electrode 6, it extends from the lower surface of the first anode electrode 6 through the second nitride semiconductor layer 4 to a position at a predetermined depth of the first nitride semiconductor layer 3. A fluorine introduction region 9 is formed in the substrate. It is not essential for the present invention that the fluorine introduction region 9 is in contact with the first anode electrode 6.

  In the present embodiment, the substrate 1 is made of Si, the buffer layer 2 is made of AlN, the first nitride semiconductor layer 3 is made of undoped GaN, and the second nitride semiconductor layer 4 is undoped with a thickness of 25 nm. Each of the first anode electrode 6 and the cathode electrode 8 is made of Ti / Al, and the protective film 10 is made of SiN.

  A two-dimensional electron gas exists on the first nitride semiconductor layer 3 side of the heterojunction interface between the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4, and a channel layer (not shown) Is formed. The first anode electrode 6 and the second nitride semiconductor layer 4 form a Schottky junction. On the other hand, the cathode electrode 8 is provided in a region where a part of the second nitride semiconductor layer 4 and the first nitride semiconductor layer 3 is removed, and the first nitride semiconductor layer 3 has a first side on the side. The channel layer formed in the nitride semiconductor layer 3 is in ohmic contact.

  Fluorine is introduced into a part of the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4 on the side near the cathode electrode 8 in the region below the first anode electrode 6, thereby A fluorine introduction region 9 is formed. Fluorine acts as a negative charge because of its high electronegativity. Therefore, in the fluorine introduction region 9, the concentration of the two-dimensional electron gas in the channel layer is lower than that in the region where no fluorine is introduced.

  Therefore, the Schottky barrier in the portion having the fluorine introduction region 9 at the position below the anode electrode 6 is higher than the Schottky barrier in the portion not having the fluorine introduction region 9 at the position below the anode electrode 6. As a result, two types of Schottky junctions having different current-voltage characteristics are formed in one type of anode electrode 6.

  In the above-described configuration, a forward voltage is applied to the Schottky barrier between the anode electrode 6 and the second nitride semiconductor layer 4. As a result, since the fluorine introduction region 9 exists at a position below the anode electrode 6, the fluorine introduction region 9 does not exist at a position below the anode electrode 6 before the portion where the Schottky barrier is high. In order to flow to the lower part of the Schottky barrier. Therefore, the ON voltage of the rectifying element is lowered.

  On the other hand, when a voltage is applied in the opposite direction to the Schottky barrier between the anode electrode 6 and the second nitride semiconductor layer 4, the fluorine introduction region exists at a position below the anode electrode 6, so that the Schottky barrier is present. In the nitride semiconductor layer at a position below the high barrier portion, the depletion layer expands more greatly. Therefore, the current is interrupted. As a result, the leakage current generated in the reverse direction is reduced. That is, the breakdown voltage of the rectifying element is increased.

  As described above, according to the rectifying element according to the present embodiment, the anode electrode made of one material functions as a rectifying element having a low Schottky barrier during forward operation, and has a high Schottky barrier during reverse operation. Functions as an element. As a result, when the anode electrode is made of one type of material, the reverse leakage current can be reduced while lowering the ON voltage of the rectifying element.

  In the present embodiment, an example in which the fluorine introduction region 9 is provided from the lower surface of the anode electrode 6 to the position of a predetermined depth from the upper surface of the first nitride semiconductor layer 3 is shown. It suffices that at least one of the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4 includes the fluorine introduction region 9 at a position below the anode layer.

  More specifically, if the fluorine introduction region 9 exists in at least one of the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4, the reverse leakage current is reduced while the on-voltage is lowered. The effect that it can be done can be obtained. Even if the fluorine introduction region 9 is biased in any position in the first nitride semiconductor layer 3 and / or the second nitride semiconductor layer 4, the on-voltage is lowered and the reverse direction is maintained. An effect that the leakage current can be reduced can be obtained. In short, as long as the fluorine introduction region 9 exists at a position below the anode electrode 6 and at any position in the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4, It may be present in any manner and at any position. For example, the fluorine introduction region 9 may be divided into a plurality of regions, may exist so as to straddle the interface between layers, and may exist without contacting the interface between layers at all. May be.

  Note that, in the above-described conventional nitride semiconductor rectifier, a technique for further reducing the reverse leakage current by reducing the thickness of the second nitride semiconductor layer 104 to about 5 nm is disclosed in, for example, Seikoh Yoshida et al. al., “A New GaN Based Field Effect Schottky Barrier Diode with a Very Low On-Voltage Operation”, Proceedings of 2004 International Symposium on Power Semiconductor Devices & ICs, Kitakyushu, pp. 323-326. Naraaki et al., “Development of GaN Power Device for Power Supply Using Thin AlGaN Structure”, Furukawa Electric Time Report, No. 117, January 2006, pp.1-5. ing.

  According to the above-described conventional rectifying element, since it is necessary to use two types of anode electrodes forming a Schottky junction, there is a problem that the manufacturing cost increases.

  Further, according to the conventional rectifying element, the thickness of the second nitride semiconductor layer 104 needs to be reduced to about 5 nm in order to reduce the leakage current generated when a voltage is applied to the rectifying element in the reverse direction. There is. For this reason, in a thin nitride semiconductor layer having a film thickness of 5 nm, the characteristics of the rectifying element greatly vary due to slight variations in film thickness. Therefore, it is difficult to obtain a rectifying element having uniform operating characteristics in the in-plane direction on the substrate.

  Furthermore, according to the conventional rectifying element, when the second nitride semiconductor layer 104 is thin, it is necessary to form a protective film such as an insulating film in order to protect the rectifying element. Therefore, an adverse effect such as damage caused by the protective film formation process may be exerted on the first nitride semiconductor layer 103. As a result, the concentration of the two-dimensional electron gas is reduced, the resistance of the channel layer is increased, and there is a problem that the potential drop at the rectifying element is increased when the rectifying element is operated in the forward direction.

  Even if the rectifying element of the present embodiment as described above does not reduce the film thickness to 5 nm, since the fluorine introduction region 9 exists, the above-described problems in the conventional rectifying element do not occur. The on-voltage can be lowered and the reverse leakage current can be reduced. In addition, according to the rectifying element of the present embodiment, since one type of anode electrode 6 can be used to reduce the on-voltage and the reverse leakage current, the manufacturing process of the rectifying element is simplified. .

(Embodiment 2)
Next, a rectifying element according to Embodiment 2 of the present invention will be described with reference to FIG. The rectifying element according to the present embodiment is different from the rectifying element according to the first embodiment in that a contact layer 5 and a second anode electrode 7 are further provided. The configuration of the rectifying element of the present embodiment other than the above-described configuration is substantially the same as the configuration of the rectifying element of the first embodiment. Hereinafter, differences between the rectifying device of the present embodiment and the rectifying device of the first embodiment will be described.

In the rectifying device of the present embodiment, the substrate 1 is made of Si, the buffer layer 2 is made of AlN, the first nitride semiconductor layer 3 is made of undoped GaN, and the second nitride semiconductor layer 4 is made of a film thickness. Is a multilayer film of undoped AlGaN / n-AlGaN / undoped AlGaN with a thickness of 30 nm, the contact layer 5 is composed of an n ⁺ AlGaN / n ⁺ GaN layer doped at a high concentration by ion implantation or the like, and the first anode electrode 6 is Each of the second anode electrode 7 and the cathode electrode 8 is made of Ti / Al, and the protective film 10 is made of SiN.

  The first anode electrode 6 is formed so as to cover the upper surface of the second anode electrode 7. Thereby, the first anode electrode 6 and the second anode electrode 7 are electrically connected to each other, and jointly form a composite anode electrode. Even if another substance exists between the first anode electrode 6 and the second anode electrode 7, the first anode electrode 6 and the second anode electrode 7 are electrically connected to each other. Then, the effect obtained by the rectifying element of the present embodiment can be obtained. Each of the first anode electrode 6 and the second anode electrode 7 and the second nitride semiconductor layer 4 form a Schottky junction, and at the height of the Schottky barrier, the first anode electrode 6 Is higher than the second anode electrode 7. On the other hand, the cathode electrode 8 is in ohmic contact with the channel layer formed in the first nitride semiconductor layer 3 through the contact layer 5.

  A fluorine introduction region 9 is formed in the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4 below the first anode electrode 6. The fluorine introduction region 9 penetrates the second nitride semiconductor layer 4 from the lower surface of the first anode electrode 6 below the first anode electrode 6, and has a predetermined depth of the second nitride semiconductor layer 4. It is formed to extend to the position of.

  Thereby, the density | concentration of the two-dimensional electron gas in the 1st anode electrode 6 falls. Therefore, a structure in which the barrier of the Schottky junction is high and the depletion layer is widened is formed as compared with the conventional rectifying element in which fluorine is not introduced into the nitride semiconductor layer. As a result, according to the rectifier according to the present embodiment, even if a thick layer of 30 nm is used for the second nitride semiconductor layer 4, the leakage current in the reverse direction can be reduced while maintaining the on-voltage low. Can do.

  As described above, according to the rectifying element according to the present embodiment, even when two types of anode electrodes forming different Schottky junctions are used, the leakage current in the reverse direction is further reduced while the on-voltage is reduced. can do.

(Embodiment 3)
Next, a rectifying element according to Embodiment 3 of the present invention will be described with reference to FIG. The rectifying element of the present embodiment is different from the rectifying element of the first embodiment in the shapes of the second anode electrode 7 and the cathode electrode 8. The configuration of the rectifying element of the present embodiment other than the above-described configuration is substantially the same as the configuration of the rectifying element of the first embodiment. Hereinafter, differences between the rectifying device of the present embodiment and the rectifying device of the first embodiment will be described.

  In the present embodiment, the substrate 1 is made of Si, the buffer layer 2 is made of AlN, the first nitride semiconductor layer 3 is made of undoped GaN, and the second nitride semiconductor layer 4 is undoped with a thickness of 15 nm. The first anode electrode 6 is made of Ni / Au, each of the second anode electrode 7 and the cathode electrode 8 is made of Ti / Al, and the protective film 10 is made of SiN.

  The first anode electrode 6 is formed so as to cover the second anode electrode 7. The first anode electrode 6 and the second anode electrode 7 are electrically connected to each other and jointly form a composite anode electrode. The first anode electrode 6 and the second nitride semiconductor layer 4 form a Schottky junction. On the other hand, each of the second anode electrode 7 and the cathode electrode 8 is ohmically formed in the channel layer in the first nitride semiconductor layer 3 so as to generate a tunnel current through the second nitride semiconductor layer 4. Sexual contact.

  Further, the difference between the rectifying device of the present embodiment and the rectifying device of the second embodiment is that the second anode electrode 7 is Schottky joined to the nitride semiconductor layer 4 or the channel layer is ohmic. It ’s about sexual contact.

  In the rectifying element of the present embodiment, the second anode electrode 7 is in ohmic contact with the channel layer. However, when the voltage of the anode electrode is 0 V, fluorine below the first anode electrode 6 is used. The channel region below the first anode electrode 6 is depleted by the introduction region 9. As a result, the current path is pinched off and the current is interrupted. When a forward voltage is applied to the anode electrode, a two-dimensional electron gas is generated in the channel layer below the first anode electrode 6 and a current flows. For this reason, according to the rectifying element of the present embodiment, the rising voltage during forward operation can be brought close to 0 V in comparison with the rectifying element of the above-described second embodiment, and the on-voltage of the rectifying element can be reduced. Can be lowered.

  Thus, according to the rectifying element of the present embodiment, by using two kinds of anode electrodes that form a Schottky junction and an ohmic contact, the on-voltage can be further reduced while reducing the reverse leakage current. Can do.

(Embodiment 4)
The power conversion device according to the fourth embodiment of the present invention will be described with reference to FIG. In the present embodiment, the configuration of the main part of the circuit for power factor improvement will be described. As shown in FIG. 4, an AC power supply 21, diodes 22 to 26 that are rectifier elements, an inductor 27, a field effect transistor 28, a capacitor 29, and a load resistor 30, and rectifier elements 22, 23, 24, 25, And 26, the rectifying element described in any one of the first to third embodiments is used.

  When any of the rectifying elements of the first to third embodiments is applied to a diode used in a power factor improving circuit that is a power conversion device, it occurs at both ends of the diode when the diode operates in the forward direction. Potential drop can be reduced. Therefore, the loss inside the circuit is reduced. Therefore, the efficiency of the power conversion device is improved.

  As described above, according to the power conversion device of the present embodiment, the rectifying element of the present invention is applied to the diode that is a component thereof, so that the potential drop that occurs at both ends of the diode when the diode operates in the forward direction. Can be reduced. Therefore, a power conversion device that can operate with low loss and high efficiency is obtained.

  As described above, the rectifying element and the power conversion device according to the present invention have been specifically described based on the rectifying element and the power conversion device according to the above-described embodiment, but the rectifying element and the power conversion device according to the present invention are described above. The present invention is not limited to the rectifying element and the power conversion device of the form, and the following changes are allowed within the scope of the present invention.

  For example, in the rectifying device of the present embodiment, Si is used as the composition of the substrate, but a substrate made of a composition such as SiC, sapphire, GaN, or GaAs may be used.

  In the rectifying device of the above embodiment, GaN is used as the composition of the buffer layer, but a buffer layer made of other materials such as AlN, AlGaN, or AlN / GaN may be used.

  In the rectifying device of the above embodiment, a single layer of undoped GaN is used as the first nitride semiconductor layer 3, but a nitride semiconductor layer doped with n-GaN or p-GaN or the like. May be used. Further, other nitride semiconductor layers made of one or more layers of undoped or doped layers other than GaN such as AlGaN, InGaN, GaN / AlGaN, or InGaN / GaN may be used.

  In the rectifying device of the above embodiment, the thickness of the second nitride semiconductor layer 4 below the anode electrode is 15 nm to 30 nm, but may be any value as long as it is 5 nm or more.

  Further, as the configuration of the second nitride semiconductor layer, a single layer film made of undoped AlGaN or a multilayer film made of undoped AlGaN / n-AlGaN / undoped AlGaN is used, but the composition of doped AlGaN, Al or A multilayer AlGaN layer including a plurality of AlGaN layers having different doping concentrations, a multilayer nitride semiconductor layer including a nitride semiconductor layer other than an AlGaN layer such as GaN / AlGaN or InGaN / AlGaN, or one or more layers An undoped or doped nitride semiconductor layer may be used.

In the first embodiment, Ti / Al is used as the composition of the anode electrode and the cathode electrode. However, the anode electrode and the cathode electrode do not need to be made of a material having the same composition. Therefore, other materials such as Pt / Au, Ni / Au, W, WN _x , or WSi _x may be used as the composition of the anode electrode and the cathode electrode.

In Embodiments 2 and 3, Ni / Au is used as the composition of the anode electrode, but other materials such as Pt / Au, Ni / Au, W, WN _x , or WSi _x are used. May be used.

  In the second and third embodiments, the first anode electrode 6 and the second anode electrode 7 are electrically connected to each other when the first anode electrode 6 covers the upper surface of the second anode electrode 7. Connected. However, the first anode electrode 6 and the second anode electrode 7 may be electrically connected to each other by the second anode electrode 7 covering the upper surface of the first anode electrode 6. The first anode electrode 6 and the second anode electrode 7 are not in direct contact with each other on the second nitride semiconductor layer 4 and are mediated by another conductive layer such as a wiring electrode formed thereon. They may be electrically connected to each other. That is, the first anode electrode 6 and the second anode electrode 7 may be electrically connected in any form.

  In each of the above embodiments, the ohmic contact is formed on the side surface of the first nitride semiconductor layer 3 in order to form the ohmic contact between the cathode electrode and the channel layer. The ohmic contact is formed by forming a contact layer highly doped by ion implantation or the like on the nitride semiconductor layer 4 and the first nitride semiconductor layer 3 and forming a cathode electrode on the contact layer. In addition, a configuration in which an ohmic contact is formed using a tunnel current through the second nitride semiconductor layer 4 is used.

  However, a part of the second nitride semiconductor layer 4 and the first nitride semiconductor layer 3 is removed, and GaN or InGaN doped at a high concentration is regrown on the exposed surface formed by the removal. Etc., and a cathode electrode may be formed on the contact layer. This also realizes ohmic contact.

  Further, a part of the second nitride semiconductor layer 4 is removed, a cathode electrode is formed on the exposed surface formed by the removal, and a tunnel current is utilized through the second nitride semiconductor layer 4 as a medium. Ohmic contact may be formed. Also, the cathode electrode is formed on the second nitride semiconductor layer without removing the second nitride semiconductor layer 4 and the first nitride semiconductor layer 3, and the cathode electrode and the second nitride semiconductor layer are formed by heat treatment. The nitride semiconductor layer may be alloyed. This also realizes ohmic contact. That is, as long as ohmic contact is realized, any connection method between the cathode electrode and the second nitride semiconductor layer may be used.

  In the above embodiment, the cathode electrode and the channel layer form an ohmic contact, but the cathode electrode and the channel layer may form a Schottky junction having a low barrier height. However, since it is desirable that the potential drop at the rectifying element when the rectifying element is operated in the forward direction is small, it is desirable to realize ohmic contact between the cathode electrode and the channel layer.

In the above embodiment, SiN is used as the protective film. Instead, SiO ₂ and Al ₂ O ₃ , HfO ₂ , TiO ₂ , TaO _x , MgO, Ga ₂ O ₃ , or Other protective films such as a SiN / SiO ₂ laminated film may be used.

  In this embodiment, the rectifying element of the present invention is applied to a circuit for power factor improvement, but may be applied to other power conversion devices such as an inverter or a converter.

  Further, not only in the first embodiment but also in other embodiments, the fluorine introduction region 9 is present in at least one of the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4. For example, the effect of reducing the reverse leakage current while lowering the on-voltage can be obtained. That is, as long as the fluorine introduction region 9 exists at a position below the anode electrode 6 and at any position in the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4, It may be present in any manner and at any position.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

FIG. 3 is a diagram illustrating a rectifying element according to the first embodiment. 6 is a diagram illustrating a rectifying element according to Embodiment 2. FIG. 6 is a diagram illustrating a rectifying element according to Embodiment 3. FIG. FIG. 10 is a circuit diagram illustrating a configuration of a main part of a power conversion device according to a fourth embodiment. It is a figure which shows the conventional rectifier.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,101 Substrate, 2,102 Buffer layer, 3,103 First nitride semiconductor layer, 4,104 Second nitride semiconductor layer, 5,105 Contact layer, 6,106 First anode electrode, 7, 107 Second anode electrode, 8, 108 Cathode electrode, 9 Fluorine introduction region, 10 Protective film, 21 AC power source, 22, 23, 24, 25, 26 Rectifier element, 27 Inductor, 28 Field effect transistor, 29 Capacitor, 30 Load resistor.

Claims (6)

A first nitride semiconductor layer having a channel layer;
The first nitride semiconductor layer is provided on the first nitride semiconductor layer and has a forbidden band width larger than a forbidden band width of the first nitride semiconductor layer, and thus functions as a barrier layer for the first nitride semiconductor layer. A second nitride semiconductor layer comprising one or more layers,
An anode electrode provided on the second nitride semiconductor layer,
At least one of the first nitride semiconductor layer and the second nitride semiconductor layer includes a fluorine introduction region at a position below the anode layer. At least a portion of the anode electrode is Schottky joined to the second nitride semiconductor layer;
The rectifying device according to claim 1, further comprising a cathode electrode in ohmic contact with the channel layer. The anode electrode includes a first anode electrode and a second anode electrode made of a material different from that of the first anode electrode and electrically connected to the first anode electrode,
The first anode electrode and the second anode electrode are Schottky joined to the second nitride semiconductor layer,
The height of the Schottky barrier in the first anode electrode and the second nitride semiconductor layer is higher than the height of the Schottky barrier in the second anode electrode and the second nitride semiconductor layer. Item 3. The rectifying device according to Item 1 or 2. The anode electrode includes a first anode electrode and a second anode electrode made of a material different from the first anode electrode and electrically connected to the first anode electrode,
The first anode electrode is Schottky joined to the second nitride semiconductor layer,
The rectifying device according to claim 1, wherein the second anode electrode is in ohmic contact with the channel layer.   5. The film thickness of the second nitride semiconductor layer located immediately below a portion of the anode electrode forming a Schottky junction with the second nitride semiconductor layer is 5 nm or more. The rectifier according to any one of the above.   The power converter device formed using the rectifier in any one of Claims 1-5.

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