JP4177048B2 - Power converter and GaN-based semiconductor device used therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power conversion device having a power conversion circuit and a GaN-based semiconductor device used for the power conversion circuit.
[0002]
[Prior art]
Since a switching element incorporated in a power conversion circuit of a power conversion device needs to handle power of several watts or more, conventionally, a bipolar transistor has been mainly used. However, FETs (Field Effect Transistors) that handle high power have been developed since then, and power MOSFETs (Metal Oxide Semiconductor FETs) have come to be widely used. Alternatively, an IGBT (Insulated Gate Bipolar Transistor) that is a composite of a bipolar transistor and a MOSFET can operate at a high voltage at a high speed like a bipolar transistor, and has a low on-resistance like a MOSFET. Therefore, it is used as a switching element.
[0003]
By the way, in such a power MOSFET or the like, it is necessary to incorporate a protective element in order to remove the parasitic bipolar transistor effect or to prevent element destruction due to application of an instantaneous rush current or surge voltage. For example, in the most common Si-based MOSFET, a Zener diode using a pn junction is usually incorporated as a protection element.
[0004]
[Problems to be solved by the invention]
However, the Zener diode having the pn junction structure used as the conventional protection element described above has an on-resistance of 10 mΩcm.²Since the on-voltage at the rising in the forward direction is as high as about 1.2 to 1.5V, the breakdown voltage is as low as about 100V.
For this reason, when a MOSFET having a low on-voltage is used as a switching element constituting the power conversion circuit of the power conversion device, the following problems occur when the Zener diode having the pn junction structure described above is incorporated as the protection element. It was.
[0005]
In other words, since the protection device has a low withstand voltage and a high on-voltage, it cannot sufficiently withstand the inrush current or surge voltage of the MOSFET, or heat is generated when a surge voltage is applied, and the protection device The MOSFET was destroyed before it worked, so that the stable operation of the power conversion device could not be guaranteed, and the reliability was lowered. Further, the low on-voltage operation of the MOSFET cannot be performed, resulting in a high loss, and the efficiency of the power converter is lowered.
[0006]
On the other hand, GaN-based FETs are known to have a high withstand voltage and are capable of high-temperature operation and large-current operation, and research and development of various devices using GaN-based semiconductor materials are underway. However, up to now, there has been no known case where a power conversion device is configured by incorporating a GaN-based semiconductor device.
The present invention has been made in consideration of the above-described conventional problems, and by utilizing the characteristics of a GaN-based semiconductor material, a power converter having high reliability and high efficiency that guarantees stable operation, and the same An object of the present invention is to provide a GaN-based semiconductor device as a component used for realizing the above.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, a power conversion device having a power conversion circuit, wherein a GaN-based Schottky diode or a GaN-based FET is used as a protective element of a switching element constituting the power conversion circuit. The power converter characterized by being provided is provided.
[0008]
In the present invention, the GaN-based Schottky diode is used as a protective element of a switching element constituting a power conversion circuit of a power conversion device, and has an on-voltage of 1 V or less and a withstand voltage of 300 V or more. A GaN-based semiconductor device is provided.
In the present invention, the GaN-based FET is used as a protective element of a switching element constituting a power conversion circuit of a power conversion device, and is a GaN-based FET having an on-voltage of 1 V or less and a withstand voltage of 300 V or more. A semiconductor device is provided.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the component which is common in each embodiment, and description is abbreviate | omitted. (First embodiment)
In the present embodiment, as shown in FIG. 1A, a power FET 10 is used as a switching element constituting a power conversion circuit of a power conversion device, and a GaN-based Schottky diode 20 is used as a protection element for the power FET 10. It is what was used. Specifically, a GaN-based Schottky diode 20 is connected between the source and drain of the power FET 10.
[0010]
Here, the power FET 10 may be a Si-based MOSFET, a GaN-based MISFET (Metal Insulator Semiconductor FET), or a GaN-based MESFET (Metal Semiconductor FET).
The GaN-based Schottky diode 20 has a horizontal structure as shown in FIG. That is, for example, an undoped GaN layer 23 that is a group III-V nitride semiconductor layer is formed on an insulating or semi-insulating sapphire substrate 21 via a GaN buffer layer 22. An undoped AlGaN layer 24 which is a group III-V nitride semiconductor layer having a wider band gap than the GaN layer 23 is formed. Further, an n-type GaN layer 26 is formed on the GaN layer 23 so as to be connected to the heterojunction between the GaN layer 23 and the AlGaN layer 24. In the vicinity of the heterojunction surface between the GaN layer 23 and the AlGaN layer 24, a two-dimensional electron gas is generated. A cathode electrode 27 is formed in ohmic contact with the n-type GaN layer 26. An anode electrode 28 is formed on the AlGaN layer 24 in Schottky contact.
[0011]
Next, an example of a method for manufacturing the GaN-based Schottky diode 20 in FIG. 1B will be described with reference to FIGS.
First, a series of crystal growth is performed on the sapphire substrate 21 at a growth temperature of 640 ° C. by a gas source MBE (Molecular Beam Epitaxy) method using, for example, an ultra-vacuum growth apparatus.
[0012]
That is, a partial pressure of 6.65 × 10 as a source gas^-FivePa Ga (gallium) and radicalized partial pressure 4.0 × 10^-FourThe GaN buffer layer 22 is grown to a thickness of 5 nm using Pa (N). Continuously, for example, partial pressure 1.33 × 10^-FourPa Ga and partial pressure 6.65 × 10^-FourNH of Pa_Three(Ammonia) is used to grow an undoped GaN layer 23 to a thickness of 3000 nm. Further continuously, for example, a partial pressure of 6.65 × 10^-FivePa Ga and partial pressure 2.66 × 10^-FiveAl of Pa and partial pressure 6.65 × 10^-FourNH of Pa_ThreeThen, an undoped AlGaN layer 24 is grown to a thickness of 30 nm. Thus, a first intermediate having a heterojunction structure between the GaN layer 23 and the AlGaN layer 24 is formed (see FIG. 2A).
[0013]
In this series of crystal growth, a MOCVD (Metal Organic Chemical Vapor Deposition) method, a halide vapor phase growth method, or the like may be used instead of the gas source MBE method.
Next, the first intermediate is once taken out from the ultra-vacuum growth apparatus, and is then formed on the AlGaN layer 24 using, for example, a plasma CVD (Chemical Vapor Deposition) apparatus.₂A film is formed. This SiO₂SiN instead of film_XA film or an AlN film may be formed. Subsequently, for example, a wet etching method using BHF or CF_FourBy dry etching using₂The film is selectively etched away to form a predetermined shape of SiO.₂A pattern 25 is formed.
[0014]
Subsequently, for example, an ECR (Electron Cyclotron Resonance) plasma etching method using a methane-based gas or a reactive ion beam etching (RIBE) method is used to form SiO.₂Using the pattern 25 as a mask, the AlGaN layer 24 and a part of the GaN layer 23 are selectively etched away in order. In this way, a second intermediate with the surface of the GaN layer 23 exposed is formed (see FIG. 2B).
[0015]
The second intermediate is then loaded again into the ultra-vacuum growth apparatus and then SiO 2₂Using the pattern 25 as a mask, for example, a partial pressure of 6.65 × 10^-FivePa Ga and partial pressure 6.65 × 10^-FourNH of Pa_ThreeAnd partial pressure 1.33 × 10^-6Using Si as a dopant for Pa, 5 × 10¹⁹cm^-3An n-type GaN layer 26 doped with Si at a high concentration is selectively grown on the exposed GaN layer 23. Thus, a third intermediate is formed by selectively growing the n-type GaN layer 26 adjacent to the AlGaN layer 24 on the GaN layer 23 (see FIG. 2C).
[0016]
Next, after removing the third intermediate from the ultra-vacuum growth apparatus, SiO 3₂The pattern 25 is removed. Subsequently, on the entire surface of the third intermediate,₂After a film (not shown) is formed, a contact hole that exposes the n-type GaN layer 26 is opened by selective etching using a photolithography technique and an etching technique. Then, TaSi and Au are sequentially deposited by, for example, a sputtering deposition method using Ar plasma. In this way, the cathode electrode 27 having a TaSi / Au laminated structure in ohmic contact with the n-type GaN layer 26 is formed.
[0017]
Similarly, SiO₂After selectively removing the film by etching and opening a contact hole exposing the AlGaN layer 24, Ti, WSi and Au are sequentially deposited. In this way, an anode electrode 28 having a Ti / WSi / Au laminated structure in Schottky contact with the AlGaN layer 24 is formed (see FIG. 2D).
Through such a series of steps, the GaN-based Schottky diode 20 shown in FIG.
[0018]
Incidentally, when the inventors made a prototype of a GaN-based Schottky diode as shown in FIG. 1B according to the above manufacturing method and measured its characteristics, the following results were obtained. That is, the breakdown voltage of the GaN-based Schottky diode exceeded 600V. The on-resistance is 24 mΩcm²The forward voltage rose from around 0.3V. Moreover, the electric current was able to flow up to 100A.
[0019]
Next, a power conversion device having a power conversion circuit using the power FET 10 as the switching element and the GaN-based Schottky diode 20 as the protection element shown in FIGS. 1A and 1B will be described.
In general, an inverter circuit or a converter circuit is used as the power conversion circuit of the power conversion device. And the inverter circuit or converter circuit actually used as a power converter circuit has a very versatile circuit configuration due to various requirements for its control function. Therefore, here, an example of a power converter having an inverter circuit is shown using FIG. 3, and several examples of the power converter having a converter circuit are shown using FIGS. 4 (a) to 4 (d).
[0020]
As shown in FIG. 3, the power conversion device 30 includes an AC power supply 31 having a frequency of 50 Hz or 60 Hz and a voltage of 100 V, a rectifier circuit 32 that rectifies the AC supplied from the AC power supply 31 to DC, and the rectifier circuit 32. And a DC-AC inverter circuit 33 that converts the direct current from the converter into an alternating current having a frequency of 1 k to 24 kHz. The alternating current from the DC-AC inverter circuit 33 is supplied to the load M. A power FET 10 is used as a switching element constituting the DC-AC inverter circuit 33, and a GaN Schottky diode 20 is used as a protection element.
[0021]
As shown in FIGS. 4A to 4D, the power conversion device includes (a) Buck circuit (step-down type), (b) Boost circuit (step-up type), and (c) Boost-Buck circuit (step-up / step-down type). And (d) DC-DC converter circuits 34a to 34d called Cuk circuits (buck-boost type), respectively. And power FET10 is used as a switching element which comprises each DC-DC converter circuit 34a-34d, and the GaN-type Schottky diode 20 is used as the protection element.
[0022]
As described above, in the present embodiment, the GaN-based Schottky diode 20 is used as a protection element for the power FET 10 (switching element) in the DC-AC inverter circuit 33 or the DC-DC converter circuits 34a to 34d that are power conversion circuits of the power conversion device. Since the on-voltage of the GaN-based Schottky diode 20 is about 0.3 V, the power FET 10 can easily operate at a low on-voltage of at least 1 V or less. For this reason, it becomes possible to reduce a loss and to achieve high inverter efficiency or converter efficiency, and to realize high efficiency of a power converter.
[0023]
Further, even when an instantaneous rush current or surge voltage is applied, the GaN-based Schottky diode 20 functions as a protective element having a withstand voltage of 600 V or more, thereby preventing the power FET 10 from being destroyed by heat generation. It becomes possible. For this reason, the stable operation | movement of power FET10 is ensured and the reliability of a power converter device can be improved.
[0024]
Note that the GaN-based Schottky diode 20 in the present embodiment includes, for example, SiO 2 between the AlGaN layer 24 and the gate electrode 28a, or between the AlGaN layer 24 and the anode electrode 28b.₂Alternatively, it is preferable to provide an extremely thin insulating film made of SiN or the like and having a thickness of 10 to 24 nm. In this case, an increase in leakage current can be suppressed even when a large current operation is performed under a high breakdown voltage.
[0025]
(Second Embodiment)
In the present embodiment, a lateral GaN-based Schottky diode 40 shown in FIG. 5 is used in place of the GaN-based Schottky diode 20 in the first embodiment.
In the GaN-based Schottky diode 40, for example, a thickness of 2000 nm and 5 × 10 5 are formed on an insulating or semi-insulating sapphire substrate 41 via a GaN buffer layer 42 having a thickness of 50 nm.¹⁹cm^-3N of high impurity concentration⁺A type GaN layer 43 is laminated. n⁺On the type GaN layer 43, an n-type GaN layer 44 having a part of the surface protruding in a convex shape is formed. The impurity concentration of the n-type GaN layer 44 is 2 × 10¹⁷cm^-3The flat portion has a thickness of 500 nm, and the convex portion has a width and a height of 2000 nm and 2000 nm, respectively. The impurity concentration of the n-type GaN layer 44 is 2 × 10.¹⁷cm^-3It is not necessary to limit the degree, preferably 2 × 10¹⁷cm^-3The following is sufficient.
[0026]
Further, the surface of the flat portion and the side surface of the convex portion of the n-type GaN layer 44 are undoped Al having a thickness of 30 nm, which has a larger band gap energy than the n-type GaN layer 44._0.2Ga_0.8Covered by an N layer 46. Here, the n-type GaN layer 44 and Al_0.2Ga_0.8Since the contact portion with the N layer 46 forms a heterojunction, a two-dimensional electron gas schematically represented by a broken line in the figure is generated in the vicinity of the heterojunction surface.
[0027]
Further, a Ti (titanium) electrode 48 as a first anode electrode is formed in Schottky contact with the upper surface of the convex portion of the n-type GaN layer 44. On the contact surface between the Ti electrode 48 and the n-type GaN layer 44, a Schottky barrier of 0.3 eV is generated. Note that the material forming the first anode electrode is not limited to Ti. For example, any metal that produces a Schottky barrier lower than 0.8 eV with respect to the n-type GaN layer 8 such as W (tungsten) or Ag (silver) may be used.
[0028]
Also, Ti electrode 48 and Al_0.2Ga_0.8A Pt (platinum) electrode 49 as a second anode electrode is formed on the N layer 46. The Pt electrode 49 is electrically connected to the Ti electrode 48, and Al is formed on the side surface of the convex portion of the n-type GaN layer 44._0.2Ga_0.8Schottky contact is made through the N layer 46. Therefore, here, the Pt electrode 49 is not in direct Schottky contact with the n-type GaN layer 44. However, when the Pt electrode 49 is in direct Schottky contact with the n-type GaN layer 44, a 1.0 eV Schottky barrier is generated on the contact surface. Note that the material forming the second anode electrode is not limited to Pt. For example, any metal that produces a Schottky barrier higher than 0.8 eV with respect to the n-type GaN layer 44, such as Ni (nickel), Pd (palladium), or Au (gold), may be used.
[0029]
Then, the Ti electrode 48 that is in Schottky contact with the upper surface of the convex portion of the n-type GaN layer 44, and the Al surface of the convex portion of the n-type GaN layer 44_0.2Ga_0.8A composite anode electrode 50 is composed of a Pt electrode 49 in Schottky contact via the N layer 46.
Also, Pt electrode 49, Al_0.2Ga_0.8Each side surface of the N layer 46 and the n-type GaN layer 44, and n⁺The surface of the type GaN layer 43 is SiO₂Covered by the film 51. SiO₂N through the opening formed in the film 51.⁺A cathode electrode 52 made of a Ta—Si layer in ohmic contact is formed on the type GaN layer 43.
[0030]
Next, the current-voltage characteristics of the GaN-based Schottky diode 40 in FIG. 5 will be described.
When a forward bias was applied between the composite anode electrode 50 and the cathode electrode 52, a good rise in which the forward current rapidly increased was observed at an ON voltage of 0.1 to 0.3V. The reason why this good rise characteristic is obtained is considered as follows.
[0031]
The on-voltage required for rising when a forward bias is applied between the Schottky-contacted Ti electrode and the n-type GaN layer is generally about 0.3 to 0.5V. In addition, the on-voltage required for rising when a forward bias is applied between the Pt electrode and the n-type GaN layer in Schottky contact is generally about 1.0 to 1.5V.
[0032]
In the GaN-based Schottky diode 40, the Ti electrode 48 of the composite anode electrode 50 mainly functions as an anode electrode at the first stage of rising in the forward direction. For this reason, the ON voltage is a value closer to about 0.3 to 0.5 V than about 1.0 to 1.5 V. Further, the n-type GaN layer 44 and Al_0.2Ga_0.8Two-dimensional electron gas is generated in the vicinity of the heterojunction surface with the N layer 46, and this two-dimensional electron gas serves as a carrier and contributes to an increase in forward current. Therefore, the ON voltage is further smaller than about 0.3 to 0.5 V, and a good rising characteristic of 0.1 to 0.3 V is obtained. When the forward bias becomes about 1.0 to 1.5 V or more, both the Ti electrode 48 and the Pt electrode 49 function as anode electrodes.
[0033]
When a reverse bias was applied between the composite anode electrode 50 and the cathode electrode 52, a large breakdown voltage of about 500V was observed. The reason why this good breakdown voltage characteristic is obtained is considered as follows.
When a reverse bias is applied between the Schottky contact Ti electrode and the n-type GaN layer, it is generally 10 V at −10V.^-6-10^-FiveA reverse leakage current of about A is generated. Further, when a reverse bias is applied between the Schottky contact Pt electrode and the n-type GaN layer, the reverse leakage current is much smaller than in the above case, and a breakdown voltage of about 500 V is obtained.
[0034]
When a reverse bias is applied to the GaN-based Schottky diode 40, a depletion layer spreads on the upper surface of the convex portion of the n-type GaN layer 44 that is in Schottky contact with the Ti electrode 48, and the Pt electrode 49 and Al_0.2Ga_0.8A depletion layer also extends on the side surface of the convex portion of the n-type GaN layer 44 that is in Schottky contact via the N layer 46.
At the stage where the reverse bias is smaller than −10 V, there is almost no reverse leakage current passing through the depletion layer formed on the side surface of the convex portion of the GaN layer 44, but it is formed on the upper surface of the convex portion of the n-type GaN layer 44. The reverse leakage current passing through the depletion layer increases gradually as the reverse bias increases. However, comparing the extent of the spread of the two depletion layers formed on the top and side surfaces of these protrusions, the depletion layer due to the Schottky contact with the Ti electrode 48 is larger than that due to the Schottky contact with the Pt electrode 49. The spread of the depletion layer becomes larger. Between the Pt electrode 49 and the side surface of the convex portion of the n-type GaN layer 44, Al having a larger band gap energy than the n-type GaN layer 44_0.2Ga_0.8Since the N layer 46 is interposed, the depletion layer is further expanded.
[0035]
As a result, when the reverse bias increases and reaches about −10 V, the depletion layers extending from both side surfaces of the convex portion of the GaN layer 44 come into contact with each other, and a pinch-off state is obtained. For this reason, the reverse leakage current passing through the depletion layer on the upper surface of the convex portion of the n-type GaN layer 44 is prevented. At a stage where the reverse bias further increases, only the Pt electrode 49 of the composite anode electrode 50 functions as an anode electrode. Therefore, a good breakdown voltage characteristic of about 500V can be obtained.
[0036]
Next, an example of a manufacturing method of the GaN-based Schottky diode 40 in FIG. 5 will be described with reference to FIGS. 6 (a) to 6 (e) and FIGS. 7 (a) to 7 (d).
First, a series of crystal growth is performed on the sapphire substrate 41 at a growth temperature of 640 ° C., for example, by a gas source MBE method using an ultra-vacuum growth apparatus.
That is, a partial pressure of 6.65 × 10 as a source gas^-FivePartial pressure 4.0 × 10 radicalized with Pa Ga^-FourUsing N of Pa, the GaN buffer layer 42 is grown to a thickness of 50 nm. Continuously, for example, partial pressure 1.33 × 10^-FourPa Ga and partial pressure 6.65 × 10^-FourNH of Pa_ThreeAnd partial pressure 1.33 × 10^-6Using Si as a dopant for Pa, 5 × 10¹⁹cm^-3N of high impurity concentration⁺The type GaN layer 43 is grown to a thickness of 2000 nm.
[0037]
Further continuously, for example, a partial pressure of 1.33 × 10^-FourPa Ga and partial pressure 6 × 10^-FourNH of Pa_ThreeAnd partial pressure 2 × 10^-7Using Si as a dopant for Pa, 2 × 10¹⁷cm^-3An n-type GaN layer 44 having a low impurity concentration is grown to a thickness of 2500 nm. Thus, on the sapphire substrate 41, the GaN buffer layer 42, n⁺A first intermediate body in which the n-type GaN layer 43 and the n-type GaN layer 44 are sequentially stacked is formed (see FIG. 6A).
[0038]
Next, after the first intermediate is once taken out from the ultra-vacuum growth apparatus, the SiO 2 is deposited on the n-type GaN layer 44 by, eg, plasma CVD.₂A film is formed. This SiO₂Instead of a film, for example SiN_XA film or an AlN film may be formed. Subsequently, for example, a wet etching method using BHF or CF_FourBy dry etching using₂Pattern the film, eg SiO 2 having a width of 2 μm₂A pattern 45 is formed (see FIG. 6B).
[0039]
Next, for example, by an ECR plasma etching method or a RIBE method using a methane-based gas, SiO 2 is used.₂Using the pattern 45 as a mask, the n-type GaN layer 44 is selectively removed by etching by the n-type GaN layer to form a convex portion having a height of 2000 nm from which a part of the surface of the n-type GaN layer 44 protrudes. Thus, a second intermediate body is formed in which a part of the surface of the GaN layer 44 protrudes into a convex shape (see FIG. 6C).
[0040]
The second intermediate is then loaded again into the ultra vacuum growth apparatus. And SiO₂Using the pattern 45 as a mask, for example, a partial pressure of 6.65 × 10^-FivePa Ga and partial pressure 2.66 × 10^-FiveAl of Pa and partial pressure 6.65 × 10^-FourNH of Pa_ThreeAs raw material gas, undoped Al with a thickness of 30 nm_0.2Ga_0.8An N layer 46 is selectively grown on the n-type GaN layer 44. Thus, the surface of the flat part and the side surface of the convex part of the n-type GaN layer 44 are Al._0.2Ga_0.8A third intermediate body covered with the N layer 46 is formed (see FIG. 6D).
[0041]
Next, after removing the third intermediate from the ultra-vacuum growth apparatus, SiO 3₂The pattern 45 is removed. Subsequently, SiO 3 is deposited on the entire surface of the third intermediate.₂After forming a film (not shown), patterning is performed using a photolithography technique and an etching technique, and the upper surface of the convex portion of the n-type GaN layer 44 and its surrounding Al_0.2Ga_0.8SiO covering a part of the surface of the N layer 46₂A pattern 47 is formed (see FIG. 6E).
[0042]
Next, for example, by an ECR plasma etching method or a RIBE method using a methane-based gas, SiO 2 is used.₂Al with pattern 47 as mask_0.2Ga_0.8The N layer 46 and the n-type GaN layer 44 are selectively removed by etching, and n⁺The surface of the type GaN layer 43 is exposed (see FIG. 7A).
Then SiO₂The pattern 45 is removed. Subsequently, a Ti electrode 48 as a first anode electrode that is in Schottky contact with the upper surface of the convex portion of the n-type GaN layer 44 is formed by a lift-off method. Specifically, using the photolithography technique, the upper surface of the convex portion of the n-type GaN layer 44 and Al_0.2Ga_0.8N layer 46 and n⁺After applying a resist film (not shown) that covers the entire surface of the n-type GaN layer 43, patterning is performed to form an opening through which the upper surface of the convex portion of the n-type GaN layer 44 is exposed. Subsequently, a Ti film is deposited on the resist film and in the opening by vapor deposition. Thereafter, the Ti film on the resist film is removed together with the resist film. Thus, the Ti film is left on the upper surface of the convex portion of the n-type GaN layer 44 to form the Ti electrode 48 (see FIG. 7B).
[0043]
Next, similarly to the process shown in FIG. 7B, the lift-off method is performed on the Ti electrode 48 and Al._0.2Ga_0.8A Pt layer is selectively formed on the N layer 46. Thus, the Ti electrode 48 is electrically connected, and the side surface of the convex portion of the n-type GaN layer 44 is Al._0.2Ga_0.8A Pt electrode 49 is formed as a second anode electrode in Schottky contact through the N layer 46. The Ti electrode 48 and the Pt electrode 49 constitute a composite anode electrode 50 (see FIG. 7C).
[0044]
Next, the surface and side surfaces of the Pt electrode 49, Al_0.2Ga_0.8Each side surface of the N layer 46 and the n-type GaN layer 44, and n⁺SiO that covers the entire surface of the GaN layer 43₂A film 51 is formed. Then, using photolithography and etching techniques, SiO₂The film 51 is selectively etched away to expose the surface of the Pt electrode 49 and n⁺A part of the surface of the type GaN layer 43 is exposed. Subsequently, a part of the surface is exposed by a lift-off method.⁺A Ta—Si layer is selectively formed on the type GaN layer 43. Thus, n⁺A cathode electrode 52 made of a Ta—Si layer in ohmic contact is formed on the type GaN layer 43 (see FIG. 7D).
[0045]
Through such a series of steps, the GaN-based Schottky diode 40 shown in FIG. 5 is manufactured.
Next, another example of the manufacturing method of the GaN-based Schottky diode 40 in FIG. 5 will be described with reference to FIGS.
First, in substantially the same manner as the process shown in FIG. 6A, the GaN buffer layer 42 and n are formed on the sapphire substrate 41.⁺After sequentially laminating the type GaN layers 43, n⁺On the n-type GaN layer 43, the n-type GaN layer 44a is laminated to a thickness of 500 nm under the same film formation conditions as the n-type GaN layer 44 of FIG. (See FIG. 8 (a)).
[0046]
Next, SiO 2 is deposited on the n-type GaN layer 44a by, for example, plasma CVD.₂A film 53 is formed. This SiO₂Instead of the film 53, SiN_XA film or an AlN film may be formed. Subsequently, for example, a wet etching method using BHF or CF_FourBy dry etching using₂The film 53 is selectively etched to form an opening having a width of 2 μm (see FIG. 8B).
[0047]
Then SiO₂Using the film 53 as a mask, an n-type GaN layer 44b having a thickness of 2000 nm is selectively grown on the n-type GaN layer 44a in the opening under the same film formation conditions as the n-type GaN layer 44a. In this way, the n-type GaN layer 44 having a part of the surface protruding into a convex shape having a height of 2000 nm is formed from the n-type GaN layer 44a and the n-type GaN layer 44b on the n-type GaN layer 44a (see FIG. 8C). ).
[0048]
Next, through the same processes as the processes shown in FIGS. 6D to 6E and FIGS. 7A to 7D, the GaN-based Schottky diode 40 shown in FIG. d)).
As described above, in the embodiment, the GaN-based Schottky diode 40 includes the Ti electrode 48 in Schottky contact with the upper surface of the convex portion of the n-type GaN layer 44 and the Pt electrode 49 in Schottky contact with the side surface of the convex portion. By having the composite anode electrode 50 as described above, a low on-voltage and a high breakdown voltage can be realized simultaneously.
[0049]
Further, undoped Al having a large band gap energy between the side surface of the convex portion of the n-type GaN layer 44 and the Pt electrode 49._0.2Ga_0.8Since it has the N layer 46, the n-type GaN layer 44 and Al_0.2Ga_0.8The two-dimensional electron gas generated in the vicinity of the heterojunction surface with the N layer 46 contributes to the increase of the forward current, and the good rise characteristics can be further improved. In addition, the depletion layer spreads further due to the Schottky contact with the Pt electrode 49, and the favorable breakdown voltage characteristics can be further improved.
[0050]
Therefore, by using the GaN-based Schottky diode 40 as a protection element for the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, loss is reduced and high inverter efficiency or converter is achieved. Efficiency can be achieved, and high efficiency of the power conversion device can be realized. Further, even when an instantaneous rush current or surge voltage is applied, the GaN-based Schottky diode 40 functions as a high breakdown voltage protection element, so that the stable operation of the power FET 10 is guaranteed, and Reliability can be increased.
[0051]
In the GaN-based Schottky diode 40 of this embodiment, the width of the convex portion of the n-type GaN layer 44 is 2000 nm, but this value varies depending on the characteristics required for the GaN-based Schottky diode 40. That is, the width of the convex portion of the n-type GaN layer 44 is preferably wide in order to increase the forward current. On the other hand, the depletion layer spreading from both sides of the convex portion of the GaN layer 44 is pinched off with the smallest possible reverse bias to prevent reverse leakage current passing through the depletion layer on the upper surface of the convex portion of the n-type GaN layer 44. Therefore, the narrower one is preferable. Therefore, in the actual case, the width of the convex portion of the n-type GaN layer 44 is determined in consideration of two characteristic requirements that are in a trade-off relationship. The same applies to GaN-based Schottky diodes as protective elements in the fourth, sixth, eighth, tenth and twelfth embodiments described later.
[0052]
(Third embodiment)
In the present embodiment, a lateral GaN-based Schottky diode 40A shown in FIG. 9 is used instead of the GaN-based Schottky diode 40 in the second embodiment.
In this GaN-based Schottky diode 40 </ b> A, convex portions are formed at two locations on the surface of the n-type GaN layer 44. Compared with the GaN-based Schottky diode 40 of FIG. 5, the number of convex portions of the n-type GaN layer 44 is increased from one to two. Then, on the surface of the flat portion of the n-type GaN layer 44 and the side surfaces of the two convex portions, Al_0.2Ga_0.8An N layer 46 is formed. Further, Ti electrodes 48 are formed on the upper surfaces of the two convex portions of the n-type GaN layer 44, respectively. Furthermore, on these two Ti electrodes 48 and Al_0.2Ga_0.8A Pt electrode 49 is formed on the N layer 46.
[0053]
Therefore, when a forward bias is applied between the composite anode electrode 50 and the cathode electrode 52, the number of protrusions of the n-type GaN layer 44a serving as a current path is increased by the amount of the second embodiment. The forward current increases compared to the case.
The manufacturing method of the GaN-based Schottky diode 40A in FIG. 9 is basically the same as that of the GaN-based Schottky diode 40 in the second embodiment, and thus the description thereof is omitted.
[0054]
As described above, in the embodiment, the GaN-based Schottky diode 40A has the same basic structure as that of the GaN-based Schottky diode 40 in the second embodiment, and can realize the same characteristics. In addition, the n-type GaN The forward current can be increased by the increase in the number of convex portions of the layer 44. Therefore, by using this GaN-based Schottky diode 40A as a protection element for the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the same as in the case of the second embodiment or More effects can be achieved.
[0055]
In the GaN-based Schottky diode 40A of the present embodiment, the width of the convex portion of the n-type GaN layer 44 is narrower than that of the second embodiment, and the n-type GaN layer 44 is made with a smaller reverse bias. It is possible to prevent reverse leakage current passing through the depletion layer formed on the upper surface of the protrusions and improve the breakdown voltage characteristics. That is, by combining the increase in the number of protrusions of the n-type GaN layer 44 and the reduction in the width of the protrusions, two characteristic requirements that are in the trade-off relationship described in the second embodiment are satisfied. It becomes possible to achieve both. Therefore, the number of convex portions of the n-type GaN layer 44 need not be limited to two, and may be three or more. The same applies to GaN-based Schottky diodes as protective elements in fifth, seventh, ninth, eleventh and thirteenth embodiments described later.
[0056]
(Fourth embodiment)
In the present embodiment, a lateral GaN-based Schottky diode 40B shown in FIG. 10 is used instead of the GaN-based Schottky diode 40 in the second embodiment.
In this GaN-based Schottky diode 40B, Al in the GaN-based Schottky diode 40 of FIG._0.2Ga_0.8Instead of the N layer 46, an undoped GaN layer 54 having a thickness of 50 nm is provided. That is, the GaN layer 54 is interposed between the side surface of the convex portion of the n-type GaN layer 44 and the Pt electrode 49. Therefore, when a reverse bias is applied between the composite anode electrode 50 and the cathode electrode 52, the depletion layer formed on the side surface of the convex portion of the n-type GaN layer 44 has a presence of the GaN layer 54. Will be bigger.
[0057]
Note that the GaN-based Schottky diode 40B shown in FIG._0.2Ga_0.8Except for the point that the GaN layer 54 is formed instead of the N layer 46, this is basically the same as the case of the GaN-based Schottky diode 40 in the second embodiment, and a description thereof will be omitted.
As described above, in the embodiment, the GaN-based Schottky diode 40B has the same basic structure as that of the GaN-based Schottky diode 40 in the second embodiment, and can realize the same characteristics. Since the undoped GaN layer 54 is provided between the side surface of the convex portion of the layer 44 and the Pt electrode 49, the depletion layer spreads more due to the Schottky contact with the Pt electrode 49, and the favorable breakdown voltage characteristics are further improved. it can. Therefore, by using this GaN-based Schottky diode 40B as a protective element of the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the same as in the case of the second embodiment or More effects can be achieved.
[0058]
(Fifth embodiment)
In the present embodiment, a lateral GaN-based Schottky diode 40C shown in FIG. 11 is used instead of the GaN-based Schottky diode 40 in the second embodiment.
In this GaN-based Schottky diode 40C, convex portions are formed at two locations on the surface of the n-type GaN layer 44, like the GaN-based Schottky diode 40A in the third embodiment. Further, similarly to the GaN-based Schottky diode 40B in the fourth embodiment, a GaN layer 54 is formed between the side surface of the convex portion of the n-type GaN layer 44 and the Pt electrode 49. That is, the GaN-based Schottky diode 40C is configured by combining the GaN-based Schottky diodes 40A and 40B shown in FIGS.
[0059]
The manufacturing method of the GaN-based Schottky diode 40C in FIG. 11 is basically the same as that of the GaN-based Schottky diodes 40A and 40B in the third and fourth embodiments, and thus the description thereof is omitted.
As described above, in the embodiment, since the GaN-based Schottky diode 40C is configured by combining the GaN-based Schottky diodes 40A and 40B in the third and fourth embodiments, the GaN-based Schottky diode 40A. , 40B have the same basic structure and can realize the same characteristics. Therefore, in the case of the third or fourth embodiment, the GaN-based Schottky diode 40C is used as a protective element for the power FET 10 (switching element) in the inverter circuit or the converter circuit that is the power conversion circuit of the power conversion device. The same or more effects can be achieved.
[0060]
(Sixth embodiment)
In this embodiment, a lateral GaN-based Schottky diode 40D shown in FIG. 12 is used instead of the GaN-based Schottky diode 40 in the second embodiment.
In this GaN-based Schottky diode 40D, Al in the GaN-based Schottky diode 40 of FIG._0.2Ga_0.8The N layer 46 is not formed, and the Pt electrode 49 is in direct Schottky contact with the side surface of the convex portion of the n-type GaN layer 44.
The manufacturing method of the GaN-based Schottky diode 40D in FIG._{0. 2}Ga_0.8If the step of forming the N layer 46 is omitted, it is basically the same as the case of the GaN-based Schottky diode 40 in the second embodiment, and a description thereof will be omitted.
[0061]
As described above, in the embodiment, the GaN-based Schottky diode 40D has the same basic structure as the GaN-based Schottky diode 40 in the second embodiment, and can realize the same characteristics._0.2Ga_0.8The structure and the manufacturing process thereof can be simplified by the absence of the N layer. Therefore, by using this GaN-based Schottky diode 40D as a protective element for the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the same as in the case of the second embodiment or More effects can be achieved.
[0062]
(Seventh embodiment)
In this embodiment, a lateral GaN-based Schottky diode 40E shown in FIG. 13 is used instead of the GaN-based Schottky diode 40 in the second embodiment.
In the GaN-based Schottky diode 40E, convex portions are formed at two locations on the surface of the n-type GaN layer 44, like the GaN-based Schottky diode 40A in the third embodiment. Further, like the GaN-based Schottky diode 40D in the sixth embodiment, the Pt electrode 49 is in direct Schottky contact with the side surface of the convex portion of the n-type GaN layer 44. That is, the GaN-based Schottky diode 40E is configured by combining the GaN-based Schottky diodes 40A and 40E shown in FIGS.
[0063]
The manufacturing method of the GaN-based Schottky diode 40E shown in FIG. 13 is basically the same as that of the GaN-based Schottky diodes 40A and 40E shown in FIGS.
As described above, in the embodiment, since the GaN-based Schottky diode 40E is configured by combining the GaN-based Schottky diodes 40A and 40E in the third and sixth embodiments, the GaN-based Schottky diode 40A. , 40B have the same basic structure and can realize the same characteristics. Therefore, in the case of the third or sixth embodiment, the GaN-based Schottky diode 40E is used as a protection element for the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device. The same or more effects can be achieved.
[0064]
(Eighth embodiment)
In this embodiment, a vertical GaN-based Schottky diode 60 shown in FIG. 14 is used instead of the GaN-based Schottky diode 40 in the second embodiment.
In this GaN-based Schottky diode 60, for example, an n-type GaN layer 62 whose surface partially protrudes into a convex shape is formed on a conductive n-type SiC substrate 61. The impurity concentration of the n-type GaN layer 62 is 2 × 10¹⁷cm^-3The flat portion has a thickness of 500 nm, and the convex portion has a width and a height of 2000 nm and 2000 nm, respectively. The impurity concentration of the n-type GaN layer 62 is 2 × 10.¹⁷cm^-3There is no need to limit the degree to 2x10¹⁷cm^-3The following is sufficient.
[0065]
Further, the surface of the flat portion of the n-type GaN layer 62 and both side surfaces of the convex portions are undoped Al having a thickness of 30 nm, which has a larger band gap energy than the n-type GaN layer 62._0.2Ga_0.8Covered by the N layer 63. Here, the n-type GaN layer 62 and Al_0.2Ga_0.8Since the contact portion with the N layer 63 forms a heterojunction, a two-dimensional electron gas schematically represented by a broken line in the drawing is generated in the vicinity of the heterojunction surface.
[0066]
A Ti electrode 64 is formed as a first anode electrode in Schottky contact with the upper surface of the convex portion of the n-type GaN layer 62. Note that the material forming the first anode electrode is not limited to Ti. For example, any material that generates a Schottky barrier lower than 0.8 eV with respect to the 1n-type GaN layer 8 such as W or Ag may be used.
Further, on the Ti electrode 64 and Al_0.2Ga_0.8A Pt electrode 65 as a second anode electrode is formed on the N layer 63. The Pt electrode 65 is electrically connected to the Ti electrode 64 and Al on the side surface of the convex portion of the n-type GaN layer 62._0.2Ga_0.8Schottky contact is made through the N layer 63. Note that the material forming the second anode electrode is not limited to Pt. For example, any material that produces a Schottky barrier higher than 0.8 eV with respect to the n-type GaN layer 62 such as Ni, Pd, or Au may be used.
[0067]
Then, the Ti electrode 64 that is in Schottky contact with the upper surface of the convex portion of the n-type GaN layer 62, and Al on the side surface of the convex portion of the n-type GaN layer 62_0.2Ga_0.8A Pt electrode 65 that is in Schottky contact via the N layer 63 is electrically connected to each other to form a composite anode electrode 66.
Also, Pt electrode 65, Al_0.2Ga_0.8SiO covering each side surface of the N layer 63 and the n-type GaN layer 62 and the surface of the n-type SiC substrate 61₂A film 67 is formed. A cathode electrode 68 made of a Ta—Si layer that is in ohmic contact with the back surface of the n-type SiC substrate 61 is formed.
[0068]
As described above, the GaN-based Schottky diode 60 includes a conductive n-type SiC substrate 61 instead of the insulating or semi-insulating sapphire substrate 41 of the lateral GaN-based Schottky diode 40 according to the second embodiment. The cathode electrode 68 is formed on the back surface of the n-type SiC substrate 61 to have a vertical structure. Then, although there is a difference between the horizontal structure and the vertical structure, the Ti electrode 64 is in Schottky contact with the upper surface of the convex portion of the n-type GaN layer 62 and Al is formed on the side surface of the convex portion._0.2Ga_0.8The basic structure in which the Pt electrode 65 is in Schottky contact via the N layer 63 and the composite anode electrode 66 is composed of the Ti electrode 64 and the Pt electrode 65 is the GaN-based Schottky in the second embodiment. The same as the diode 60.
[0069]
Next, the current-voltage characteristics of the GaN-based Schottky diode 60 in FIG. 14 will be described.
When a forward bias was applied between the composite anode electrode 66 and the cathode electrode 68, the forward current suddenly increased with an ON voltage of 0.1 to 0.3 V, as in the case of the second embodiment. An increasing good rise was observed. When a reverse bias was applied between the composite anode electrode 66 and the cathode electrode 68, a large breakdown voltage of about 500 V was observed. The reason why such a good rise characteristic and breakdown voltage characteristic are obtained is considered to be the same as the reason described for the GaN-based Schottky diode 60 in the second embodiment.
[0070]
Next, an example of a manufacturing method of the GaN-based Schottky diode 60 in FIG. 14 will be described with reference to FIGS.
First, a series of crystal growth is performed on the conductive n-type SiC substrate 61 by, for example, a gas source MBE method using an ultra-vacuum growth apparatus.
That is, as the source gas, for example, a partial pressure of 6.65 × 10^-FivePa Ga and partial pressure 6.65 × 10^-FourNH of Pa_ThreeAnd partial pressure 2 × 10^-7Using Si as a dopant for Pa, 2 × 10¹⁷cm^-3An n-type GaN layer 62 having a low impurity concentration is grown to a thickness of 2500 nm (see FIG. 15A).
[0071]
Next, steps similar to those shown in FIGS. 6D to 6E and FIGS. 7A to 7D in the second embodiment are performed. That is, the n-type GaN layer 62 is selectively etched away to form a convex portion having a height of 2000 nm with a part of the surface protruding, and undoped Al_0.2Ga_0.8The N layer 63 is selectively grown to a thickness of 30 nm. Subsequently, a Ti electrode 64 that is in Schottky contact is formed on the upper surface of the convex portion of the n-type GaN layer 62, and Al is formed on the side surface of the convex portion of the n-type GaN layer 62._0.2Ga_0.8A Pt electrode 65 in Schottky contact is formed via the N layer 63, and the composite anode electrode 66 is constituted by the Ti electrode 64 and the Pt electrode 65. Subsequently, SiO₂A film 67 is formed (see FIG. 15B).
[0072]
Next, a cathode electrode 68 made of a Ta—Si layer in ohmic contact with the back surface of the n-type SiC substrate 61 is formed (see FIG. 15C).
Through such a series of steps, the GaN-based Schottky diode 60 shown in FIG. 14 is manufactured.
In addition, it is also possible to apply the other manufacturing method demonstrated using FIG. 8 (a)-(d) in 2nd Embodiment instead of said manufacturing method.
[0073]
As described above, in the embodiment, the GaN-based Schottky diode 60 has the same basic structure as the GaN-based Schottky diode 40 in the second embodiment, regardless of the difference between the horizontal structure and the vertical structure. Similar characteristics can be realized. Therefore, by using this GaN-based Schottky diode 60 as a protection element for the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the same as in the case of the second embodiment. There is an effect.
[0074]
(Ninth embodiment)
In this embodiment, a vertical GaN-based Schottky diode 60A shown in FIG. 16 is used instead of the GaN-based Schottky diode 60 in the eighth embodiment.
In the GaN-based Schottky diode 60A, the number of convex portions of the n-type GaN layer 62 in the GaN-based Schottky diode 60 of FIG. 14 is increased from one to two. From another viewpoint, in the GaN-based Schottky diode 40A of the third embodiment, an n-type SiC substrate 61 is used instead of the sapphire substrate 41, and a cathode electrode 68 is formed on the back surface of the n-type SiC substrate 61. Thus, it has a vertical structure.
[0075]
The manufacturing method of the GaN-based Schottky diode 60A shown in FIG. 16 is basically the same as that of the GaN-based Schottky diode 60 in the third embodiment, and a description thereof will be omitted.
As described above, in the embodiment, the GaN-based Schottky diode 60A has the same basic structure as the horizontal GaN-based Schottky diode 40A in the third embodiment, and has the same basic structure. The characteristics can be realized. Accordingly, by using this GaN-based Schottky diode 60A as a protective element for the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the same as in the case of the third embodiment. There is an effect.
[0076]
(Tenth embodiment)
In the present embodiment, a vertical GaN-based Schottky diode 60B shown in FIG. 17 is used instead of the GaN-based Schottky diode 60 in the eighth embodiment.
In this GaN-based Schottky diode 60B, Al in the GaN-based Schottky diode 60 of FIG._0.2Ga_0.8Instead of the N layer 63, an undoped GaN layer 69 having a thickness of 50 nm is used. From another viewpoint, in the GaN-based Schottky diode 40B of the fourth embodiment, an n-type SiC substrate 61 is used instead of the sapphire substrate 41, and a cathode electrode 68 is formed on the back surface of the n-type SiC substrate 61. Thus, it has a vertical structure.
[0077]
The manufacturing method of the GaN-based Schottky diode 60B shown in FIG._0.2Ga_0.8Except for the point that the GaN layer 69 is formed instead of the N layer 63, this is basically the same as the case of the GaN-based Schottky diode 60 in the eighth embodiment, and the description thereof is omitted.
As described above, in the embodiment, the GaN-based Schottky diode 60B has the same basic structure as the horizontal GaN-based Schottky diode 40B in the fourth embodiment, and has the same basic structure. The characteristics can be realized. Therefore, by using this GaN-based Schottky diode 60B as a protective element of the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the same as in the case of the fourth embodiment. There is an effect.
[0078]
(Eleventh embodiment)
In this embodiment, a vertical GaN-based Schottky diode 60C shown in FIG. 18 is used instead of the GaN-based Schottky diode 60B in the tenth embodiment.
In the GaN-based Schottky diode 60C, the number of convex portions of the n-type GaN layer 62 in the GaN-based Schottky diode 60B in FIG. 17 is increased from one to two. From another viewpoint, in the GaN-based Schottky diode 40C of the fifth embodiment, an n-type SiC substrate 61 is used instead of the sapphire substrate 41, and a cathode electrode 68 is formed on the back surface of the n-type SiC substrate 61. Thus, it has a vertical structure.
[0079]
The manufacturing method of the GaN-based Schottky diode 60C in FIG. 18 is basically the same as that in the case of the GaN-based Schottky diode 60B in the tenth embodiment, and a description thereof will be omitted.
As described above, in the embodiment, the GaN-based Schottky diode 60C has the same basic structure because the horizontal GaN-based Schottky diode 40C in the fifth embodiment has a vertical structure. The characteristics can be realized. Therefore, by using this GaN-based Schottky diode 60C as a protection element for the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the same as in the case of the fifth embodiment. There is an effect.
[0080]
(Twelfth embodiment)
In this embodiment, a vertical GaN-based Schottky diode 60D shown in FIG. 19 is used instead of the GaN-based Schottky diode 60 in the eighth embodiment.
In this GaN-based Schottky diode 60D, Al in the GaN-based Schottky diode 60 of FIG._0.2Ga_0.8The N layer 63 is not formed, and the Pt electrode 65 is in direct Schottky contact with the side surface of the convex portion of the n-type GaN layer 62. From another viewpoint, in the GaN-based Schottky diode 40D of the sixth embodiment, an n-type SiC substrate 61 is used instead of the sapphire substrate 41, and a cathode electrode 68 is formed on the back surface of the n-type SiC substrate 61. Thus, it has a vertical structure.
[0081]
The manufacturing method of the GaN-based Schottky diode 60D shown in FIG._0.2Ga_0.8If the step of forming the N layer 63 is omitted, it is basically the same as the case of the GaN-based Schottky diode 60 in the eighth embodiment, and thus description thereof is omitted.
As described above, in the embodiment, the GaN-based Schottky diode 60D has the same basic structure as the horizontal GaN-based Schottky diode 40D in the sixth embodiment, and has the same basic structure. The characteristics can be realized. Therefore, by using this GaN-based Schottky diode 60D as a protective element for the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the same as in the case of the sixth embodiment. There is an effect.
[0082]
(13th Embodiment)
In this embodiment, a vertical GaN-based Schottky diode 60E shown in FIG. 20 is used instead of the GaN-based Schottky diode 60D in the twelfth embodiment.
In the GaN-based Schottky diode 60E, the number of convex portions of the n-type GaN layer 62 in the GaN-based Schottky diode 60D in FIG. 19 is increased from one to two. From another viewpoint, in the GaN-based Schottky diode 40E of FIG. 13 of the seventh embodiment, an n-type SiC substrate 61 is used instead of the sapphire substrate 41, and a cathode electrode 68 is formed on the back surface of the n-type SiC substrate 61. To form a vertical structure.
[0083]
The manufacturing method of the GaN-based Schottky diode 60E shown in FIG. 20 is basically the same as that of the GaN-based Schottky diode 60D in the twelfth embodiment, and a description thereof will be omitted.
As described above, in the embodiment, the GaN-based Schottky diode 60E has the same basic structure as the horizontal GaN-based Schottky diode 40E in the seventh embodiment, and has the same basic structure. The characteristics can be realized. Therefore, by using this GaN-based Schottky diode 60E as a protection element for the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the same as in the case of the seventh embodiment. There is an effect.
[0084]
(Fourteenth embodiment)
In this embodiment, a vertical GaN-based Schottky gate FET 70 shown in FIG. 21 is used instead of the GaN-based Schottky diode 40 in the second embodiment.
In this GaN-based Schottky gate FET 70, for example, an n-type GaN layer 72 having a part of the surface protruding in a convex shape is formed on a conductive n-type SiC substrate 71. The impurity concentration of the n-type GaN layer 72 is 2 × 10¹⁷cm^-3The flat portion has a thickness of 500 nm, and the convex portion has a width and a height of 2000 nm and 2000 nm, respectively. The impurity concentration of the n-type GaN layer 72 is 2 × 10.¹⁷cm^-3There is no need to limit the degree to 2x10¹⁷cm^-3The following is sufficient. On the top surface of the convex portion of the n-type GaN layer 72, a thickness of 50 nm, 5 × 10¹⁹cm^-3N of high impurity concentration⁺A type GaN layer 73 is laminated.
[0085]
Further, the surface of the flat part of the n-type GaN layer 72 and the both side surfaces of the convex part n⁺The side surface of the n-type GaN layer 73 is 30 nm thick undoped Al having a band gap energy larger than that of the n-type GaN layer 72._0.2Ga_0.8It is covered with an N layer 75. Here, the n-type GaN layer 72 and Al_0.2Ga_0.8Since the contact portion with the N layer 75 forms a heterojunction, a two-dimensional electron gas schematically represented by a broken line in the figure is generated in the vicinity of the heterojunction surface.
[0086]
As will be described later, the convex portion of the n-type GaN layer 72 has a drain current I of the GaN-based Schottky gate FET 70._DIs a channel region that flows vertically. Therefore, this channel region is connected to the drain current I_DWhen this flows, this two-dimensional electron gas contributes as a carrier. That is, it has a kind of vertical HEMT (High Electron Mobility Transistor) structure.
[0087]
N⁺A source electrode 76 made of a Ta—Si layer is formed on the type GaN layer 73. That is, the source electrode 76 is n⁺The n-type GaN layer 72 is in ohmic contact with the upper surface of the projection of the n-type GaN layer 72 through the n-type GaN layer 73. Further, the side surface of the convex portion of the n-type GaN layer 72 is Al._0.2Ga_0.8A Schottky gate electrode 77 made of a Pt layer in Schottky contact through the N layer 75 is formed. Note that the material forming the Schottky gate electrode 77 is not limited to Pt. For example, Ti, Ni, W, Ag, Pd, Au, or the like may be used as long as it generates a Schottky barrier for the n-type GaN layer 72, but a metal that generates a higher Schottky barrier is suitable. A drain electrode 78 made of a Ta—Si layer that is in ohmic contact with the back surface of the n-type SiC substrate 71 is formed.
[0088]
Next, the current-voltage characteristics of the GaN-based Schottky gate FET 70 in FIG. 21 will be described.
On the side surface of the convex portion of the n-type GaN layer 72, Al_0.2Ga_0.8Since the Schottky gate electrode 77 is formed via the N layer 75, the gate voltage V applied to the Schottky gate electrode 77._GBut V_GEven when = 0, depletion layers are formed on both side surfaces of the convex portion of the n-type GaN layer 72. In this state, a predetermined drain voltage V between the source electrode 76 and the drain electrode 78 is obtained._DIs applied, the drain current I_DFlows in the vertical direction using a region sandwiched between depletion layers on both sides of the convex portion of the n-type GaN layer 72 as a channel. Drain voltage V_DIncreases the channel width and the drain current I_DWill also increase.
[0089]
The gate voltage V_GWhen the size of the depletion layer is increased or decreased, the spread of the depletion layer on both sides of the convex portion of the n-type GaN layer 72 increases or decreases, and the width of the channel sandwiched between the depletion layers extending from two directions changes. For this reason, the gate voltage V_GControls the width of the channel and the drain current I flowing therethrough_DIs controlled.
At this time, the n-type GaN layer 72 and Al_0.2Ga_0.8A two-dimensional electron gas generated in the vicinity of the heterojunction surface with the N layer 75 becomes a drain current I as a carrier._DTo reduce the drain voltage V_DDrain current I_DGood start-up characteristics can be obtained.
[0090]
Further, between the Schottky gate electrode 77 and the side surface of the projection of the n-type GaN layer 72, undoped Al having a larger band gap energy than the n-type GaN layer 72._0.2Ga_0.8Since the N layer 75 is interposed, a small gate voltage V_GBut the depletion layer expands greatly. As a result, the gate voltage V_GDrain current I due to_DControllability is improved.
[0091]
Next, an example of a method for manufacturing the GaN-based Schottky gate FET 70 in FIG. 21 will be described with reference to FIGS. 22 (a) to 22 (d) and FIGS. 23 (a) to 23 (c).
First, a series of crystal growth is performed on the conductive n-type SiC substrate 71 by, for example, the gas source MBE method using an ultra-vacuum growth apparatus.
That is, as a raw material gas, for example, partial pressure 1.33 × 10^-FivePa Ga and partial pressure 6.65 × 10^-FourNH of Pa_ThreeAnd partial pressure 2 × 10^-7Using Si as a dopant for Pa, 2 × 10¹⁷cm^-3An n-type GaN layer 72 having a low impurity concentration is grown to a thickness of 2500 nm. Continuously, for example, partial pressure 1.33 × 10^-FivePa Ga and partial pressure 6.65 × 10^-FourNH of Pa_ThreeAnd partial pressure 1.33 × 10^-6Using Si as a dopant for Pa, 5 × 10¹⁹cm^-3N of high impurity concentration⁺The type GaN layer 73 is grown to a thickness of 50 nm (see FIG. 22A).
[0092]
Next, for example, by plasma CVD, n⁺On the type GaN layer 73₂A film is formed. Subsequently, for example, a wet etching method using BHF or CF_FourBy dry etching using₂Patterning the film, for example SiO having a width of 2 μm₂A pattern 74 is formed (see FIG. 22B).
Next, for example, by an ECR plasma etching method or a RIBE method using a methane-based gas, SiO 2 is used.₂N using pattern 74 as a mask⁺The type GaN layer 73 and the n-type GaN layer 72 are selectively removed by etching. In this way, a convex portion having a height of 2000 nm and a width of 2000 nm from which a part of the surface of the n-type GaN layer 44 protrudes is formed, and n is formed on the upper surface of the convex portion.⁺The type GaN layer 73 is left (see FIG. 22C).
[0093]
Then SiO₂Using the pattern 74 as a mask, for example, a partial pressure of 6.65 × 10^-FivePa Ga and partial pressure 2.66 × 10^-FiveAl of Pa and partial pressure 6.65 × 10^-FourNH of Pa_ThreeAs raw material gas, undoped Al_0.2Ga_0.8The N layer 75 is selectively grown to a thickness of 30 nm. Thus, the surface of the flat portion and the side surface of the convex portion of the n-type GaN layer 72 and n⁺The side surface of the GaN layer 73 is Al_0.2Ga_0.8Covered with an N layer 75 (see FIG. 22D).
[0094]
Then SiO₂The pattern 74 is removed. Subsequently, n is lifted off by the lift-off method.⁺A Ta—Si layer is selectively formed on the upper surface of the type GaN layer 73. Thus, the n-type GaN layer 44 has n on the upper surface of the convex portion.⁺A source electrode 76 made of a Ta—Si layer that is in ohmic contact with the p-type GaN layer 73 is formed (see FIG. 23A).
Next, in the same manner as in the step shown in FIG._0.2Ga_0.8A Pt layer is selectively formed on the N layer 75. Thus, Al is formed on the side surface of the convex portion of the n-type GaN layer 72._0.2Ga_0.8A Schottky gate electrode 77 made of a Pt layer that is in Schottky contact is formed through the N layer 75 (see FIG. 23B).
[0095]
Next, a drain electrode 78 made of a Ta—Si layer that is in ohmic contact with the back surface of the n-type SiC substrate 71 is formed (see FIG. 23C).
Through such a series of steps, the GaN-based Schottky gate FET 70 shown in FIG. 21 is manufactured.
As described above, in the embodiment, in the GaN-based Schottky gate FET 70, the source electrode 76 is in ohmic contact with the upper surface of the convex portion of the n-type GaN layer 72 forming the channel region, and the Schottky gate electrode 77 is disposed on the side surface of the convex portion. Has a basic structure in which the drain electrode 78 is in ohmic contact with the back surface of the n-type SiC substrate 71, and the gap between the side surface of the convex portion of the n-type GaN layer 72 and the Schottky gate electrode 77. Undoped Al with large band gap energy_0.2Ga_0.8Since the N layer 75 is included, the n-type GaN layer 72 and Al_0.2Ga_0.8The two-dimensional electron gas generated near the heterojunction surface with the N layer 75 is the drain current I_DThe drain current I_DCan be obtained. Further, the spread of the depletion layer due to the Schottky contact with the Schottky gate electrode 77 is further increased, and the gate voltage V_GDrain current I due to_DControllability can be improved.
[0096]
Therefore, by using the GaN-based Schottky gate FET 70 as a protection element for the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the loss is reduced, and high inverter efficiency or converter is achieved. Efficiency can be achieved, and high efficiency of the power conversion device can be realized.
[0097]
(Fifteenth embodiment)
In this embodiment, a vertical GaN-based Schottky gate FET 70A shown in FIG. 24 is used instead of the GaN-based Schottky gate FET 70 in the fourteenth embodiment.
[0098]
In this GaN-based Schottky gate FET 70A, Al in the GaN-based Schottky gate FET 70 of FIG._0.2Ga_0.8Instead of the N layer 75, an undoped GaN layer 79 having a thickness of 50 nm is provided. That is, the GaN layer 79 is interposed between the side surface of the convex portion of the n-type GaN layer 72 and the Schottky gate electrode 77.
[0099]
Note that the GaN-based Schottky gate FET 70A shown in FIG._0.2Ga_0.8Except for the point that the GaN layer 79 is formed instead of the N layer 75, this is basically the same as the case of the GaN-based Schottky gate FET 70 in the fourteenth embodiment, and the description thereof is omitted.
As described above, in the embodiment, the GaN-based Schottky gate FET 70A has the same basic structure as the GaN-based Schottky gate FET 70 in the fourteenth embodiment, and can realize the same characteristics. Since the undoped GaN layer 79 is provided between the side surface of the convex portion of the layer 72 and the Schottky gate electrode 77, the depletion layer expands further due to Schottky contact with the Schottky gate electrode 77, and the gate voltage V_GDrain current I due to_DControllability can be improved. Therefore, by using this GaN-based Schottky gate FET 70A as a protection element of the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the same as in the case of the fourteenth embodiment or More effects can be achieved.
[0100]
(Sixteenth embodiment)
In this embodiment, a vertical GaN-based Schottky gate FET 70B shown in FIG. 25 is used instead of the GaN-based Schottky gate FET 70 in the fourteenth embodiment.
In this GaN-based Schottky gate FET 70B, Al in the GaN-based Schottky gate FET 70 of FIG._0.2Ga_0.8The N layer 75 is not formed, and the Schottky gate electrode 77 is in direct Schottky contact with the side surface of the convex portion of the n-type GaN layer 72.
Note that the GaN-based Schottky gate FET 70B shown in FIG._0.2Ga_0.8If the step of forming the N layer 75 is omitted, it is basically the same as the case of the GaN-based Schottky gate FET 70 in the fourteenth embodiment, and the description thereof is omitted.
[0101]
As described above, in the embodiment, the GaN-based Schottky gate FET 70B has the same basic structure as the GaN-based Schottky gate FET 70 in the fourteenth embodiment, and can realize the same characteristics. Therefore, by using this GaN-based Schottky gate FET 70B as a protection element for the power FET 10 (switching element) in the inverter circuit or converter circuit that is the power conversion circuit of the power conversion device, the same as in the case of the fourteenth embodiment. There is an effect.
[0102]
In the second to sixteenth embodiments, the width of the protrusions of the n-type GaN layers 44, 62, 72 is 2000 nm, but is not limited to the exemplified values. The width of the convex portion may be, for example, in the range of 5 nm to 10 μm, preferably in the range of 10 nm to 5 μm, and more preferably in the range of 50 nm to 3 μm.
[0103]
In the second to sixteenth embodiments, the gas source MBE method is used for crystal growth of the GaN-based III-V group nitride semiconductor layer, but the manufacturing method is limited to the gas source MBE method. For example, a MOCVD (Metal Organic Chemical Vapor Deposition) method, a hydride vapor deposition method, or the like may be used instead.
[0104]
In the eighth to sixteenth embodiments, the conductive n-type SiC substrates 61 and 71 are used, but instead of a conductive semiconductor substrate made of, for example, SiC, Si, GaN, AlN, GaAs, GaP or the like. You may use for.
In the first to third, eighth, ninth, and fourteenth embodiments, the GaN 23 layer and the AlGaN layer 24, the n-type GaN layer 44 and the AlGaN layer 46, as heterojunction structures that generate a two-dimensional electron gas, A GaN / AlGaN junction using a combination of an n-type GaN layer 62 and an AlGaN layer 63 and an n-type GaN layer 72 and an AlGaN layer 75 is used. A heterojunction combining semiconductor layers may be used instead. Further, instead of using the heterojunction, an n-type GaN layer doped with Si may be used instead of the AlGaN layer.
[0105]
(Seventeenth embodiment)
In this embodiment, as shown in FIG. 26 (a), a GaN-based MESFET 10A is used as the power FET 10 which is a switching element in the first embodiment, and a GaN-based Schottky as a protective element is used in the GaN-based MESFET 10A. The diode 20A is built-in. Specifically, a lateral GaN-based Schottky diode 20A is connected between the source and drain of the GaN-based MESFET 10A.
[0106]
In addition, as shown in FIG. 26B, the GaN-based MESFET 10A and the GaN-based Schottky diode 20A are integrated on the same substrate. That is, for example, a GaN buffer layer 22, an undoped GaN layer 23, and an undoped AlGaN layer 24 are sequentially stacked on the sapphire substrate 21. Further, two n-type GaN layers 26 are formed on the GaN layer 23 so as to be connected to the heterojunction between the GaN layer 23 and the AlGaN layer 24.
[0107]
Furthermore, an electrode (hereinafter, simply referred to as “source / cathode combined electrode”) 27 a and a drain electrode 27 b that are used as both a source electrode and a cathode electrode are formed in ohmic contact with each other on the two n-type GaN layers 26. . A gate electrode 28a is formed on the AlGaN layer 24 sandwiched between the two n-type GaN layers 26 in Schottky contact. An anode electrode 28b is formed in Schottky contact with the AlGaN layer 24 on the opposite side of the gate electrode 28a with the source / cathode electrode 27a interposed therebetween.
[0108]
That is, in this embodiment, a GaN-based MESFET 10A as a switching element (power FET 10) and a GaN-based Schottky diode 20 as a protection element thereof are integrated on the same substrate.
Next, an example of a method for manufacturing the GaN-based MESFET 10A and the GaN-based Schottky diode 20A in FIG. 26B will be described with reference to FIGS.
[0109]
First, a GaN buffer layer 22 having a thickness of 5 nm, an undoped GaN layer 23 having a thickness of 3000 nm, and an undoped AlGaN layer 24 having a thickness of 30 nm are sequentially grown on the semi-insulating sapphire substrate 21. Thus, a heterojunction structure of the GaN layer 23 and the AlGaN layer 24 is formed (see FIG. 27A).
Next, SiO formed on the AlGaN layer 24.₂The film is selectively etched away and SiO having openings at two locations₂After forming the pattern 25, this SiO 2₂Using the pattern 25 as a mask, the AlGaN layer 24 and a part of the GaN layer 23 are selectively etched away in order to expose the surface of the GaN layer 23 (see FIG. 27B).
[0110]
Then, on these two exposed GaN layers 23, 5 × 10 5 respectively.¹⁹cm^-3An n-type GaN layer 26 doped with Si at a high concentration is selectively grown (see FIG. 27C).
Next, a source / cathode combined electrode 27a and a drain electrode 27b having a TaSi / Au laminated structure in ohmic contact with the two n-type GaN layers 26 are formed. Further, a gate electrode 28a having a Ti / WSi / Au laminated structure in Schottky contact is formed on the AlGaN layer 24 sandwiched between the two n-type GaN layers 26, and the source / cathode combined electrode 27a is sandwiched therebetween. An anode electrode 28b having a Ti / WSi / Au laminated structure in Schottky contact is formed on the AlGaN layer 24 on the opposite side of the gate electrode 28a (see FIG. 27C).
[0111]
Through such a series of steps, a GaN-based semiconductor device in which the GaN-based MESFET 10A and the GaN-based Schottky diode 20A shown in FIG. 26B are integrated on the same substrate is manufactured.
As described above, in this embodiment, the GaN-based MESFET 10A and the GaN-based Schottky diode 20A are formed simultaneously by a common process using a common material. That is, in the process of manufacturing the GaN-based MESFET 10A, it is not necessary to complicate or increase the process by merely modifying the mask pattern for selective etching or selective crystal growth. Therefore, as compared with the case where the switching element and the GaN-based Schottky diode are manufactured as separate electronic components and connected, not only the manufacturing cost is reduced, but also the miniaturization of the component by integration is achieved. As a result, the power converter can be downsized.
[0112]
The GaN-based Schottky diode 20A functions as a protective element for the GaN-based MESFET 10A formed on the same substrate. When this GaN-based semiconductor device is used as a switching element of an inverter circuit or a converter circuit that is a power conversion circuit of a power conversion device, the configuration is the same as that of the first embodiment shown in FIG. 3 or FIGS. The operation and effects are the same as those described in the first embodiment.
[0113]
However, in the case of this power conversion device, with the achievement of the high inverter efficiency or converter efficiency described above, the GaN-based MESFET 10A including the GaN-based Schottky diode 20A includes a conventional pn junction structure Zener diode having the same performance. Compared to Si-based MOSFETs, the chip area can be reduced. Moreover, the number used for the power converter circuit which consists of an inverter circuit or a converter circuit can also be reduced significantly. Therefore, significant downsizing for the power conversion device can be realized.
[0114]
Incidentally, when a prototype GaN-based MESFET 10A having a built-in GaN-based Schottky diode 20A as shown in FIGS. 26A and 26B is manufactured as a switching element for a power converter, a conventional pn junction structure having the same performance is obtained. Compared to the case of a Si-based MOSFET with a built-in zener diode, the chip area is, for example, 1 cm.²From 16mm²Was able to be reduced. In addition, when the above-described prototype switching element is incorporated in an inverter circuit as a power conversion circuit of a power conversion device, the number of chips required can be reduced to less than half of the conventional case. In addition, when incorporated in a converter circuit as a power conversion circuit, the number of chips required can be reduced from 32 in the conventional case to 8, for example.
[0115]
In the present embodiment, the case where the GaN-based MESFET 10A as the switching element (power FET 10) and the GaN-based Schottky diode 20 as the protection element in the first embodiment are integrated on the same substrate has been described. Integration with the protective element is not limited to this combination. For example, the GaN-based MESFET 10A and any one of the GaN-based Schottky diodes 40 and 40A to 40E as the protection elements in the second to seventh embodiments can be integrated on the same substrate.
[0116]
(Eighteenth embodiment)
In this embodiment, as shown in FIG. 28A, an IGBT 80 is used instead of the power FET 10 in the first embodiment. Specifically, a GaN Schottky diode 20 as a protection element is connected between the emitter and collector of an IGBT 80 as a switching element.
[0117]
Here, the GaN-based Schottky diode 20 shown in FIG. 28B is the same as that shown in FIG. 1B of the first embodiment, and the description of the structure and the manufacturing method thereof is omitted. To do.
In addition, when the IGBT 80 and the GaN-based Schottky diode 20 shown in FIG. 28A are used in an inverter circuit or a converter circuit that is a power conversion circuit of a power conversion device, FIG. 3 or 4 of the first embodiment. In the circuit diagrams illustrated in (a) to (d), the power FET 10 may be replaced by the IGBT 80, and the basic circuit configuration is the same. For this reason, illustration of the inverter circuit or converter circuit which is a power converter circuit of the power converter in this case is omitted.
[0118]
As described above, in the present embodiment, since the GaN-based Schottky diode 20 used as a protection element of the IGBT 80 that is a switching element has a breakdown voltage exceeding 600 V, the IGBT 80 has a high breakdown voltage of at least 500 V or more. For example, a large current operation of 100 A or more can be easily performed. Similarly to the case of the first embodiment, the IGBT 80 is destroyed by heat generation before the GaN-based Schottky diode 20 functions as a protection element even when an instantaneous rush current or surge voltage is applied. Therefore, stable operation is ensured, and the reliability of the power conversion device can be improved.
[0119]
In this embodiment, the case where the IGBT 80 as a switching element is combined with the GaN-based Schottky diode 20 as the protection element in the first embodiment has been described. For example, the IGBT 80 in the second to sixteenth embodiments is combined. It is also possible to combine any of GaN-based Schottky diodes 40, 40A to 40E, 60, 60A to 60E or GaN-based Schottky gate FETs 70, 70A, and 70B as protective elements.
[0120]
【The invention's effect】
As described above in detail, according to the present invention, a GaN-based Schottky diode having a low on-voltage of 1 V or less and a high withstand voltage of 300 V or more is used as a protective element of a switching element constituting a power conversion circuit of a power conversion device. Alternatively, by using a GaN-based FET, the switching element can be easily operated at a low on-voltage. For this reason, when, for example, an inverter circuit or a converter circuit is used as the power conversion circuit, it is possible to reduce loss and achieve high inverter efficiency or converter efficiency, thereby realizing high efficiency of the power conversion device. it can. In addition, even when an instantaneous rush current or surge voltage is applied, the high breakdown voltage GaN-based Schottky diode functions as a protection element, ensuring stable operation of the switching element and reliability of the power converter. Can be increased. Furthermore, a large current operation at a high breakdown voltage of the switching element can be easily performed.
[0121]
In addition, since a GaN-based FET as a switching element and a GaN-based Schottky diode as a protection element constituting a power conversion circuit of a power conversion device are integrated on the same substrate, a conventional pn junction structure is obtained. Compared to a Si-based MOSFET incorporating a Zener diode, the chip area can be reduced, and the number used in the power conversion circuit can be greatly reduced. For this reason, the significant downsizing for the power conversion device can be realized.
[Brief description of the drawings]
FIG. 1A is a circuit diagram showing a power FET as a switching element and a GaN Schottky diode as a protection element thereof according to the first embodiment of the present invention, and FIG. It is a schematic sectional drawing which shows a key diode.
FIGS. 2A to 2D are process cross-sectional views for explaining a method of manufacturing the GaN-based Schottky diode shown in FIG.
3 is a circuit diagram showing a power conversion device having an inverter circuit using the power FET and GaN-based Schottky diode shown in FIGS. 1 (a) and 1 (b). FIG.
FIGS. 4A to 4D are circuit diagrams showing power converters having converter circuits using power FETs and GaN-based Schottky diodes shown in FIGS. 1A and 1B, respectively.
FIG. 5 is a schematic cross-sectional view showing a lateral GaN-based Schottky diode according to a second embodiment of the present invention.
6 is a process cross-sectional view (No. 1) for explaining an example of the manufacturing method of the GaN-based Schottky diode of FIG. 5; FIG.
7 is a process cross-sectional view (No. 2) for explaining an example of the manufacturing method of the GaN-based Schottky diode of FIG. 5; FIG.
8 is a process cross-sectional view for explaining another example of the manufacturing method of the GaN-based Schottky diode of FIG.
FIG. 9 is a schematic cross-sectional view showing a lateral GaN-based Schottky diode according to a third embodiment of the present invention.
FIG. 10 is a schematic cross-sectional view showing a lateral GaN-based Schottky diode according to a fourth embodiment of the present invention.
FIG. 11 is a schematic cross-sectional view showing a lateral GaN-based Schottky diode according to a fifth embodiment of the present invention.
FIG. 12 is a schematic cross-sectional view showing a lateral GaN-based Schottky diode according to a sixth embodiment of the present invention.
FIG. 13 is a schematic cross-sectional view showing a lateral GaN-based Schottky diode according to a seventh embodiment of the present invention.
FIG. 14 is a schematic sectional view showing a vertical GaN-based Schottky diode according to an eighth embodiment of the present invention.
15 is a process cross-sectional view for explaining an example of a manufacturing method of the GaN-based Schottky diode of FIG.
FIG. 16 is a schematic sectional view showing a vertical GaN-based Schottky diode according to a ninth embodiment of the present invention.
FIG. 17 is a schematic sectional view showing a vertical GaN-based Schottky diode according to a tenth embodiment of the present invention.
FIG. 18 is a schematic sectional view showing a vertical GaN-based Schottky diode according to an eleventh embodiment of the present invention.
FIG. 19 is a schematic sectional view showing a vertical GaN-based Schottky diode according to a twelfth embodiment of the present invention.
FIG. 20 is a schematic sectional view showing a vertical GaN-based Schottky diode according to a thirteenth embodiment of the present invention.
FIG. 21 is a schematic sectional view showing a vertical GaN-based Schottky gate FET according to a fourteenth embodiment of the present invention.
22 is a process cross-sectional view (No. 1) for describing an example of the manufacturing method of the GaN-based Schottky gate FET of FIG. 21;
FIG. 23 is a process cross-sectional view (part 2) for explaining the example of the method for manufacturing the GaN-based Schottky gate FET of FIG. 21;
FIG. 24 is a schematic sectional view showing a vertical GaN-based Schottky gate FET according to a fifteenth embodiment of the present invention.
FIG. 25 is a schematic sectional view showing a vertical GaN-based Schottky gate FET according to a sixteenth embodiment of the present invention.
FIG. 26A is a circuit diagram showing a GaN-based MESFET as a switching element and a GaN-based Schottky diode as its protection element according to a seventeenth embodiment of the present invention, and FIG. 1 is a schematic cross-sectional view showing a GaN-based MESFET having a Schottky diode built therein.
FIGS. 27A to 27D are process cross-sectional views for explaining a method of manufacturing a GaN-based MESFET having a built-in GaN-based Schottky diode shown in FIG.
FIG. 28A is a circuit diagram showing an IGBT as a switching element and a GaN-based Schottky diode as its protection element according to an eighteenth embodiment of the present invention, and FIG. It is a schematic sectional drawing which shows a diode.
[Explanation of symbols]
10 Power FET as a switching element
10A GaN-based MESFET as a switching element
20, 20A, 40, 40A to 40E, 60, 60A to 60E GaN-based Schottky diode as protective element
21, 41 Insulating or semi-insulating sapphire substrate
22, 42 GaN buffer layer
23, 54, 69, 79 Undoped GaN layer
24 Undoped AlGaN layer
26, 44, 72 n-type GaN layer
27, 52 Cathode electrode
27a Electrode for both source and cathode
27b, 78 Drain electrode
28, 28b Anode electrode
28a Gate electrode
30 Power converter
31 AC power supply
32 Rectifier circuit
34 DC-AC inverter circuit
34a, 34b, ..., 34d DC-DC converter circuit
43, 73 n⁺Type GaN layer
46, 63, 75 Undoped Al_0.2Ga_0.8N layers
48 Ti electrode as first anode electrode
49 Pt electrode as second anode electrode
50 Composite anode electrode
61 Conductive n-type SiC substrate
62 n-type GaN layer
64 Ti electrode as the first anode electrode
65 Pt electrode as second anode electrode
66 Composite anode electrode
68 Cathode electrode
70, 70A, 70B GaN Schottky gate FET as protective element
71 Conductive n-type SiC substrate
76 Source electrode
77 Schottky gate electrode
80 IGBT as a switching element

Claims (10)

A GaN-based Schottky diode used as a protective element of a switching element that constitutes a power conversion circuit of a power conversion device,
The GaN-based Schottky diode includes a substrate, a group III-V nitride semiconductor layer formed on the substrate, and a part of the surface having a convex shape, and a convex portion of the group III-V nitride semiconductor layer. A first anode electrode that is in Schottky contact with the upper surface of the first electrode and a second electrode that is in Schottky contact with the side surface of the convex portion of the group III-V nitride semiconductor layer and electrically connected to the first anode electrode. A Schottky barrier formed between the first anode electrode and the group III-V nitride semiconductor layer, the second anode electrode and the group III-V nitride semiconductor layer. A GaN-based semiconductor device that is smaller than the Schottky barrier generated between the two. The GaN-based semiconductor device according to claim 1, wherein a carrier concentration of the group III-V nitride semiconductor layer is 2 × 10 ¹⁷ cm ⁻³ or less. A Schottky barrier generated between the first anode electrode and the group III-V nitride semiconductor layer is lower than 0.8 eV, and the second anode electrode and the group III-V nitride semiconductor layer are The GaN-based semiconductor device according to claim 1, wherein a Schottky barrier generated therebetween is higher than 0.8 eV. A group III-V nitride semiconductor layer having a band gap energy larger than that of the group III-V nitride semiconductor layer between the side surface of the convex portion of the group III-V nitride semiconductor layer and the second anode electrode The GaN-based semiconductor device according to claim 1, wherein: 2. The GaN-based semiconductor according to claim 1, wherein an undoped group III-V nitride semiconductor layer is formed between a side surface of the convex portion of the group III-V nitride semiconductor layer and the second anode electrode. apparatus. The GaN-based semiconductor device according to claim 1, wherein the substrate is an insulating or semi-insulating substrate, and a cathode electrode is formed in ohmic contact with the group III-V nitride semiconductor layer. The group III-V nitride semiconductor layer having higher conductivity than the group III-V nitride semiconductor layer is formed between the group III-V nitride semiconductor layer and the cathode electrode. The GaN-based semiconductor device described. The GaN-based semiconductor device according to claim 1, wherein the substrate is a conductive substrate, and a cathode electrode is formed in ohmic contact with the back surface of the substrate. A plurality of locations on the surface of the III-V nitride semiconductor layer have a convex shape, and the first anode electrode is Schottky on the upper surface of each of the plurality of convex portions of the III-V nitride semiconductor layer. 2. The GaN-based material according to claim 1, wherein the GaN-based material is formed in contact with each other, and the second anode electrode is formed in Schottky contact with each side surface of the plurality of convex portions of the group III-V nitride semiconductor layer. Semiconductor device. 2. The GaN-based semiconductor device according to claim 1, wherein the width of the convex portion of the group III-V nitride semiconductor layer is 5 nm or more and 10 μm or less.

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