JP2011124258A - Nitride-based diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride-based diode with a high withstanding voltage, operable at a low ON-voltage. <P>SOLUTION: The nitride-based diode 10 includes a buffer layer 12 formed on a (111) plane of a silicon substrate 11, a channel layer 13 made of undoped GaN, an electron supply layer 14 formed on the channel layer 13 and made of undoped AlGaN, and a cathode electrode 15 and an anode electrode 16 formed on the electron supply layer 14. The nitride-based diode 10 also includes a mesa 18 formed by partially removing the electron supply layer 14 down to the depth of the channel layer 13 and the anode electrode 16 is in contact with one side surface part 18a of the mesa 18. The anode electrode 16 is electrically connected with a two-dimensional electron gas layer 17 owing to contact of the anode electrode 16 with the side surface part 18a of the mesa 18. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nitride-based diode such as a nitride-based Schottky barrier diode.

Wide band gap semiconductors typified by Group III nitride compound semiconductors have high dielectric breakdown voltage, good electron transport properties, and good thermal conductivity, so they can be used as semiconductor devices for high temperature, high power, or high frequency applications. Very attractive.
For example, gallium nitride (GaN), which is a group III nitride compound semiconductor, has a higher bandgap energy than a GaAs material, and therefore has a high dielectric breakdown voltage, a high heat resistance temperature, and high temperature operation. Therefore, development of field effect transistors (FETs) and power switching diodes using these materials, particularly GaN / AlGaN-based semiconductors, is in progress.

  As an example, a Schottky barrier diode (SBD) is shown in FIG. In the SBD 100 shown in FIG. 14, a channel layer 101 made of a conductive GaN-based semiconductor in which carriers drift and an electron supply layer 102 made of an AlGaN-based semiconductor are formed on a substrate (not shown). A GaN-based diode in which an ohmic electrode 103 and a Schottky electrode 104 are arranged with an insulating film 105 interposed therebetween. The Schottky electrode 104 has a laminated structure containing a metal such as Ni or Pt, and the ohmic electrode 103 has a laminated structure containing a metal such as Ti and Al. The SBD 100 uses the channel layer 101 in which the two-dimensional electron gas layer 106 is formed at the heterojunction interface with the electron supply layer 102, and uses the Schottky electrode 104 as an anode electrode and the ohmic electrode 103 as a cathode electrode.

In a nitride-based diode having an AlGaN / GaN heterostructure like the SBD 100 shown in FIG. 14, a two-dimensional electron gas layer 106 is formed on the channel layer 101 side at the interface between the channel layer 101 and the electron supply layer 102 by the piezoelectric effect. Has been. Since the two-dimensional electron gas layer 106 has high electron mobility and carrier density, the heterojunction nitride-based diode using the AlGaN / GaN heterostructure operates with low on-resistance and high switching speed. Is possible. These features are very suitable for power switching applications.
As the Schottky barrier diode having the AlGaN / GaN heterostructure described above, for example, those disclosed in Patent Document 1, Non-Patent Document 1, and the like are known.

JP 2006-147951 A

K. Kmada, K. Matsubayashi, A. Nakagawa, Y. Terada and T. Egawa, “High-Voltage AlGaN / GaN Schottky Barrier Diodes on Si Substrate With Low-Temperature GaN Cap Layer for Edge Termination” Proc. ISPSD'08, pp 225-228, 2008.

In recent years, a structure in which a high electron mobility transistor (HEMT) structure is effectively used to operate as a diode has been considered. However, although the above-described conventional SBD 100 shown in FIG. 14 has good on-characteristics, the reverse leakage current increases essentially up to the pinch-off voltage, resulting in a large leak. For this reason, there is also a problem that a sufficient breakdown voltage cannot be secured.
Therefore, the problem to be solved by the present invention is to provide a nitride-based diode capable of operating at a high breakdown voltage and a low on-voltage.

  In order to solve the above-described problem, a nitride-based diode according to the invention described in claim 1 is formed on a channel layer made of a first nitride-based compound semiconductor formed on a substrate, and on the channel layer. , An electron supply layer made of a second nitride-based compound semiconductor, a cathode electrode and an anode electrode formed on the electron supply layer, and a part of the electron supply layer partially to a depth reaching the channel layer And at least the anode electrode of the cathode electrode and the anode electrode is in contact with the side surface of the mesa.

  The nitride-based diode according to claim 2 is characterized in that an insulating film is formed on an upper surface of the mesa, and the anode electrode is formed over the side surface of the mesa from the insulating film. .

  In the nitride-based diode according to the third aspect of the present invention, the cathode electrode and the anode electrode have finger portions, and the mesa is intermittently formed along the longitudinal direction of the finger portions. It is characterized by.

  In the nitride-based diode according to claim 4, the mesa has an area where the cathode electrode or the anode electrode and each side surface of the mesa contact each other gradually toward the tip side of the finger portion. It is characterized by being formed so as to be larger.

  The nitride diode according to the invention of claim 5 is characterized in that the first GaN-based semiconductor material is GaN and the second GaN-based semiconductor material is AlGaN.

  The nitride-based diode according to the invention of claim 6 is characterized in that the first GaN-based semiconductor material is InGaN or GaN, and the second GaN-based semiconductor material is InAlGaN.

  The nitride-based diode according to the invention described in claim 7 is characterized in that Ni, Pt, Pd, W, Ta and Al, or an alloy of these metals is used for the anode electrode.

  The nitride-based diode according to an eighth aspect of the invention is characterized in that Ti, Al, Si, Ta, W, Mo, or an alloy thereof is used for the cathode electrode.

  In the nitride-based diode according to claim 9, the substrate is a conductive substrate, and the cathode electrode or the anode electrode is electrically connected to a back electrode formed on the back surface of the substrate. It is characterized by.

  According to the first aspect of the present invention, at least the anode electrode of the cathode electrode and the anode electrode is in contact with the channel layer (two-dimensional electron gas layer) at the side surface of the mesa. Thereby, since no tunnel current is generated in the electron supply layer, the reverse leakage current is reduced. As a result, it is possible to realize a nitride-based diode that can operate at a high breakdown voltage and a low on-voltage.

  According to the second aspect of the present invention, the anode electrode is in contact with the side surface of the mesa by reducing the area where the anode electrode is in contact with the mesa upper surface of the electron supply layer as much as possible. Is further reduced, whereby the breakdown voltage is further improved.

  According to the fourth aspect of the present invention, the electric field concentration at the end of the anode electrode having the finger portion is alleviated, and a diode having a higher breakdown voltage can be realized.

It is sectional drawing which shows schematic structure of the nitride-type diode which concerns on the 1st Embodiment of this invention. It is the perspective view which looked at the nitride type diode shown in FIG. 1 from diagonally upward. It is the figure which looked at the nitride type diode shown in Drawing 1 from the upper part, and is a mimetic diagram for explaining arrangement of each electrode. It is sectional drawing along the AA line of FIG. It is a graph which shows the electrical property of the nitride-type diode which concerns on 1st Embodiment, and the electrical property of a prior art example. (A)-(c) is process drawing for demonstrating the manufacturing method of the nitride-type diode which concerns on 1st Embodiment. (A)-(c) is process drawing for demonstrating the manufacturing method of the nitride-type diode which concerns on 1st Embodiment. It is sectional drawing which shows schematic structure of the nitride-type diode which concerns on the 2nd Embodiment of this invention. (A)-(c) is process drawing for demonstrating the manufacturing method of the nitride-type diode which concerns on 2nd Embodiment. (A)-(c) is process drawing for demonstrating the manufacturing method of the nitride-type diode which concerns on 2nd Embodiment. It is a figure which shows the nitride-type diode which concerns on the 3rd Embodiment of this invention, and is a perspective view similar to FIG. It is the figure which looked at the nitride-type diode which concerns on the 3rd Embodiment of this invention from upper direction, and is a schematic diagram similar to FIG. It is sectional drawing along BB of FIG. It is sectional drawing which shows the conventional Schottky barrier diode.

  Embodiments of a nitride diode according to the present invention will be described below with reference to the drawings. In the description of each embodiment, the same parts are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
FIG. 1 shows a schematic configuration of a nitride-based diode according to the first embodiment of the present invention.
The nitride diode according to the present embodiment is configured as a nitride Schottky barrier diode having an AlGaN / GaN heterojunction structure as an example. As shown in FIG. 1, the nitride-based diode 10 includes a silicon (111) substrate 11, a buffer layer 12 formed on the (111) surface of the silicon substrate 11, and an undoped layer formed on the buffer layer 12. Channel layer 13 made of GaN (first nitride compound semiconductor), an electron supply layer 14 made of undoped AlGaN (second nitride compound semiconductor) formed on the channel 13 layer, and an electron supply A cathode electrode 15 and an anode electrode 16 formed on the layer 14 are provided.

  In the nitride-based diode 10 having such an AlGaN / GaN heterojunction structure, two-dimensional electrons are formed on the channel layer 13 side by the piezoelectric effect at the interface between the channel layer 13 and the electron supply layer 14, that is, the AlGaN / GaN heterojunction interface. A gas layer 17 is generated. In the nitride-based diode 10, the cathode electrode 15 is an ohmic electrode and the anode electrode 16 is a Schottky electrode using the channel layer 13 in which the two-dimensional electron gas layer 17 having a high carrier concentration is formed.

  As shown in FIGS. 1 and 2, the nitride-based diode 10 further includes a mesa 18 in which a part of the electron supply layer 14 is partially removed to a depth reaching the channel layer 13. The anode electrode 16 is in contact with the side surface portion 18a. That is, a part of the surface of the channel layer 13 exposed by partially removing the region where the anode electrode is formed in the electron supply layer 14 to the depth reaching the channel layer 13 by etching (the side surface portion 18a of the mesa 18). An anode electrode 16 is formed on a part of the upper surface of the mesa 18. The anode electrode 16 and the two-dimensional electron gas layer 17 are electrically connected by the anode electrode 16 being in contact with the side surface portion 18 a of the mesa 18.

The cathode electrode 15 is in contact with the other side surface 18 b of the mesa 18. That is, a part of the surface of the channel layer 13 exposed by partially removing the region where the cathode electrode 15 is formed in the electron supply layer 14 to the depth reaching the channel layer 13 by etching (the side surface portion of the mesa 18). A cathode electrode 15 is formed on a part of the upper surface of 18b and mesa 18. Further, the nitride-based diode 10 includes an insulating film 19 made of SiO ₂ or the like formed on the surface of the channel layer 13 and the electron supply layer 14 so as to insulate the cathode electrode 15 and the anode electrode 16.

FIG. 3 is a view of the nitride-based diode 10 as viewed from above, and is a schematic diagram for explaining the arrangement of each electrode. 4 is a cross-sectional view taken along line AA in FIG.
In the nitride-based diode 10 described in FIG. 1, as shown in FIGS. 2 and 3, it is necessary to increase the length in order to obtain a large current performance. Is formed in a finger shape that is long in a direction b (see FIG. 3) perpendicular to a direction a (see FIG. 4) in which current flows, and becomes a comb-like electrode in which cathode electrodes 15 and anode electrodes 16 are alternately arranged. ing. That is, the cathode electrode 15 and the anode electrode 16 have finger portions 15a and 16a, respectively (see FIG. 3). Corresponding to such a comb-like electrode configuration, the side portions 18a and 18b of the mesa 18 are elongated in the direction b as shown by the broken lines in FIGS. The entire center portion of the finger-shaped anode electrode 16 (the entire center portion of the finger portion 16a) is in contact with the side surface portion 18a of the mesa 18 (see FIGS. 2 and 3). On the other hand, the entire center portion of the finger-shaped cathode electrode 15 (the entire center portion of the finger portion 15a) is in contact with the side surface portion 18b of the mesa 18 (see FIGS. 2 and 3).

  The nitride-based diode 10 shown in FIG. 1 can be manufactured as follows. That is, the growth apparatus was a MOCVD (Metal Organic Chemical Deposition) apparatus, and the substrate was a silicon (111) substrate 11.

(Process 1)
A buffer layer 12 is formed on the (111) plane of the silicon substrate 11. In (Step 1), first, the silicon substrate 11 is introduced into the MOCVD apparatus, and the vacuum degree in the MOCVD apparatus is reduced to 1 × 10 ⁻⁶ hPa or less with a turbo pump, and then the vacuum degree is set to 100 hPa. The substrate 11 was heated to 1000 ° C. When the temperature is stabilized, the silicon substrate 11 is rotated at 900 rpm, trimethylaluminum (TMA) as a raw material is introduced into the surface of the silicon substrate 11 at a flow rate of 100 cm ³ / min, and ammonia is 12 liters / min. Layer growth was performed. The growth time is 4 min and the film thickness is about 50 nm. Next, about 160 multilayers of AlN (5 nm) and GaN (20 nm) are stacked. The GaN layer was grown at a flow rate of 300 cm ³ / min for trimethylgallium (TMG) and 12 liter / min for ammonia. Thereby, the buffer layer 12 is formed.

(Process 2)
Next, a channel layer 13 made of undoped GaN is formed on the buffer layer 12. In (Step 2), the temperature is increased while flowing ammonia at a flow rate of 12 liters / min, and the temperature is maintained at 1050 ° C., then TMG is 300 cm ³ / min and ammonia is flowed on the buffer layer 12 at a flow rate of 12 liters / min. Then, the channel layer 13 made of undoped GaN was grown. The growth time was 2000 sec and the thickness of the channel layer 13 was 1000 nm.

(Process 3)
Next, an electron supply layer 14 made of undoped AlGaN is formed on the channel layer 13. In (Step 3), TMA was introduced at a flow rate of 50 cm ³ / min, TMG was introduced at a flow rate of 100 cm ³ / min, and ammonia was introduced at a flow rate of 12 liter / min, and an electron supply layer 14 made of undoped Al _0.2 Ga _0.75 N was grown. . The growth time is 40 sec, and the thickness of the electron supply layer 14 is 20 nm. In this way, the epitaxial layer structure shown in FIG. 6A is completed.

(Process 4)
Next, part of the channel layer 13 and the electron supply layer 14 is removed by etching using chlorine gas (Cl ₂ gas) or the like to perform element isolation.

(Process 5)
Next, the region where the cathode electrode and the anode electrode of the electron supply layer 14 are formed is dry-etched using a chlorine-based gas and partially removed to a depth reaching the channel layer 13 to form a mesa 18 (FIG. 6 ( b)).

(Step 6)
Next, the cathode electrode 15 is formed so as to be in contact with the side surface portion 18 b of the mesa 18. In (Step 6), a cathode electrode is formed on a part of the surface of the channel layer 13 exposed by removing by etching in the above (Step 5), a surface of the side surface portion 18b of the mesa 18 and a part of the surface of the electron supply layer 14. 15 is formed by a lift-off method (see FIG. 6C).
That is, a photoresist (not shown) is applied to the exposed surface of the channel layer 13 and the entire surface of the electron supply layer 14, and this photoresist is exposed and developed to form an opening in the formation region of the cathode electrode 15. Further, after forming a metal film in the opening and on the photoresist by sputtering, vacuum deposition or the like, the metal film remaining by removing the photoresist is used as the cathode electrode 15. The cathode electrode 15 is a metal film containing a metal such as Ti, Al, Si, Ta, Mo, or W, or an alloy thereof (especially a silicide alloy is preferable). Further, the formed cathode electrode 15 is subjected to heat treatment for making ohmic contact.

(Step 7)
Next, an insulating film 19 made of SiO ₂ or the like is formed on the entire surface of the channel layer 13 and the electron supply layer 14 so as to cover the cathode electrode 15, and the anode electrode forming region is etched to form an opening 19a. (See FIG. 7 (a)).

(Process 8)
Next, the anode electrode 16 is formed by a lift-off method so as to be in contact with the side surface portion 18a of the mesa 18. In (Step 8), first, a photoresist 21 is applied to the entire surface of the insulating film 19, and the photoresist 21 is exposed and developed, so that the area where the anode electrode 16 is formed is larger than the opening 19a of the insulating film 19. Opening 21a is formed (see FIG. 7B).

  Thereafter, a metal film is formed in the openings 19a and 21a and on the photoresist 21 by sputtering, vacuum evaporation, or the like, and the metal film remaining by removing the photoresist 21 is used as the anode electrode 16 (FIG. 7 (c)). The anode electrode is a metal film containing a metal such as Ni, Pt, Pd, W, Ta and Al, or an alloy of these metals. As a result, the nitride-based diode 10 shown in FIG.

  In the nitride-based diode 10 configured as described above, when a predetermined voltage (forward bias) is applied to the anode electrode 16 that is a Schottky electrode, the anode passes through the two-dimensional electron gas layer 17 from the cathode electrode 15. Electrons flow to the electrode 16, and current flows from the anode electrode 16 to the cathode electrode 15.

According to the nitride-based diode 10 according to the first embodiment having the above configuration, the following operational effects can be obtained.
The anode electrode 16 is in direct contact with the channel layer 13 at the side surface portion 18a of the mesa 18, and the anode electrode 16 and the two-dimensional electron gas layer 17 are electrically connected. As a result, no tunnel current is generated in the electron supply layer 14, thereby reducing the reverse leakage current. As a result, the breakdown voltage is improved, and a low on-voltage can be realized.

FIG. 5 is a graph showing the electrical characteristics of the nitride-based diode 10 which is a Schottky diode and the electrical characteristics of the conventional Schottky diode (conventional example) as described in FIG. The horizontal axis represents the applied voltage (Vac) to the anode electrode, and the vertical axis represents the current (Iac) flowing from the anode electrode to the cathode electrode. In FIG. 5, the electrical characteristics of the nitride-based diode 10 are indicated by a curve 23, and the electrical characteristics of the conventional example are indicated by a curve 24. As shown in the graph of FIG. 5, in the case of the conventional example, the reverse leakage current I ₁ was very large, about several hundred μA / mm to mA / mm. the leakage current I ₂ lower 4 digits or more than the conventional example, it has become possible to reduce to a few nA / mm to several tens of nA / mm. Further, in the case of the conventional example, the on-voltage was as high as about 1V, but according to the present embodiment, the on-voltage could be reduced to about 0.6V.

  A region of the electron supply layer 14 where the anode electrode is formed is removed to a depth reaching the channel layer 13 so that the anode electrode 16 is in direct contact with the channel layer 13 at the side surface portion 18 a of the mesa 18. For this reason, it is easy to manufacture the diode and it is possible to suppress variations such as an on-voltage.

  By contacting the entire central portion of the finger-shaped anode electrode 16 long in the direction b (see FIG. 3) with the side surface portion 18a of the mesa 18 having an elongated shape in the same direction b, the anode electrode 16 and the two-dimensional electron gas layer 17 is in line contact, and a good electrical connection between the anode electrode 16 and the two-dimensional electron gas layer 17 can be obtained.

(Second Embodiment)
FIG. 8 shows a schematic configuration of a nitride-based diode 10A according to the second embodiment of the present invention.
The nitride-based diode 10A is characterized in that an insulating film 30 such as SiO ₂ is formed on the entire top surface of the mesa 18 in the nitride-based diode 10 according to the first embodiment shown in FIG. A part of the anode electrode 16 in contact with the portion 18 a extends on the insulating film 30. That is, the anode electrode 16 is formed from the insulating film 30 to the side surface portion 18 a of the mesa 18. This nitride-based diode 10A has a structure in which the area where the anode electrode 16 that is in direct contact with the channel layer 13 on the side surface portion 18a of the mesa 18 is in contact with the upper surface of the mesa 18 of the electron supply layer 14 is reduced as much as possible. . The other configuration of the nitride-based diode 10A is the same as that of the nitride-based diode 10 according to the first embodiment.

As described above, in the nitride-based diode 10A, the anode electrode 16 is brought into contact with the two-dimensional electron gas layer 17 generated at the AlGaN / GaN interface to be conductive, while the electron supply layer 14 (the upper surface of the mesa 18). ) Is formed with an insulating film 30 (surface protective film) such as SiO ₂ and has a structure in which the area where the anode electrode 16 contacts the electron supply layer 14 is reduced as much as possible. In other words, the insulating film 30 is disposed on the surface of the electron supply layer 14 and at least the contact with the anode electrode 16 is limited to the channel layer 13 as much as possible so that the reverse leakage current and withstand voltage can be improved.

The nitride diode 10A shown in FIG. 8 can be manufactured as follows. That is, a MOCVD apparatus was used as a growth apparatus, and a silicon (111) substrate 11 having a (111) plane as a main surface was used as a substrate.
First, the epitaxial layer structure shown in FIG. 9A is manufactured in the same manner as the above-described manufacturing method of the nitride-based diode 10.

Next, a part of the channel layer 13 and the electron supply layer 14 is removed by etching using Cl ₂ gas or the like to perform element isolation.
Next, the region where the cathode electrode and the anode electrode of the electron supply layer 14 are formed is dry-etched using a chlorine-based gas and partially removed to a depth reaching the channel layer 13 to form a mesa 18 (FIG. 9 ( b)).
Next, an insulating film 30 such as SiO ₂ is formed on the upper surface of the mesa 18 (see FIG. 9C).

Next, the cathode electrode 15 is formed by a lift-off method so as to be in contact with the side surface portion 18 b of the mesa 18.
That is, a photoresist 31 is applied to the exposed surface of the channel layer 13 and the entire surface of the electron supply layer 14 so as to cover the insulating film 30 (see FIG. 10A), and the photoresist 31 is exposed and developed. Then, an opening 31a is formed in the formation region of the cathode electrode 15, and a metal film is formed in the opening 31a and on the photoresist 31 by a sputtering method, a vacuum evaporation method, or the like, and then the photoresist is removed. The metal film is used as the cathode electrode 15 (see FIG. 10B). The cathode electrode 15 is a metal film containing a metal such as Ti, Al, Si, Ta, Mo, or W, or an alloy thereof (especially a silicide alloy is preferable). Further, the formed cathode electrode 15 is subjected to heat treatment for making ohmic contact.

Next, the anode electrode 16 is formed by a lift-off method so as to be in contact with the side surface portion 18a of the mesa 18.
That is, a photoresist (not shown) is applied to the exposed surface of the channel layer 13 and the entire surface of the electron supply layer 14 so as to cover the cathode electrode 15 and the insulating film 30, and the photoresist is exposed and developed to form an anode. An opening is formed in the formation region of the electrode 16, and a metal film is formed in the opening and on the photoresist by a sputtering method, a vacuum evaporation method or the like, and then the remaining metal film is removed by removing the photoresist. 16 (see FIG. 10C). The anode electrode is a metal film containing a metal such as Ni, Pt, Pd, W, Ta, Al or an alloy of these metals.
As a result, the nitride diode 10A shown in FIG. 8 was fabricated.

According to the nitride-based diode 10A according to the second embodiment having the above-described configuration, the following operational effects can be obtained in addition to the operational effects exhibited by the first embodiment. If the surface state of the electron supply layer 14 is incomplete, that is, the surface roughness is large, a tunnel current is partially generated in the electron supply layer 14 in the mesa 18 portion. When the area where the mesa 18 of the electron supply layer 14 and the anode electrode 16 are in contact with each other is large, the probability that the tunnel current is generated increases, and the reverse leakage current increases. Therefore, it is preferable that the anode electrode 16 is not in contact with the upper surface of the mesa 18 of the electron supply layer 14 as much as possible, but is directly in contact with the channel layer 13 at the side surface portion 18a of the mesa 18.
According to the second embodiment, the area in which the anode electrode 16 in direct contact with the channel layer 13 in the side surface portion 18a of the mesa 18 is in contact with the upper surface of the mesa 18 of the electron supply layer 14 is reduced as much as possible. Therefore, the reverse leakage current is further reduced, thereby further improving the breakdown voltage.

(Third embodiment)
FIG. 11 is a perspective view showing a main part of a nitride-based diode 10B according to the third embodiment of the present invention. 12 is a view of the nitride-based diode 10B as viewed from above, and is a schematic view similar to FIG. 13 is a cross-sectional view taken along line BB in FIG. The feature of this nitride-based diode 10B is that, in the nitride-based diode 10A according to the first embodiment shown in FIG. 1, the electric field tends to concentrate on the end portions of the finger-shaped cathode electrode 15 and anode electrode 16. In order to alleviate the electric field concentration, the following configuration is adopted.

In the nitride diode 10B, as shown in FIG. 11 to FIG. 13, the electron supply layer 14 and the channel layer 13 have the mesa 18 in the longitudinal direction of the finger portions 15a and 16a (the direction a current flows through the channel layer 13). Are partially removed so as to be intermittently formed along the vertical direction b).
That is, a plurality of side surface portions 18a are formed on one slope of the mesa 18 (see FIG. 11). The mesa 18 is formed so that the area where the finger-shaped anode electrode 16 and each side surface portion 18a of the mesa 18 come into contact gradually increases toward the tip end side (left side in FIG. 12) of the finger portion 16a. (See FIGS. 11 and 12).

Further, a plurality of side surface portions 18b are formed on the other slope of the mesa 18 (see FIG. 11). The mesa 18 is formed so that the area where the finger-shaped cathode electrode 15 and each side surface portion 18b of the mesa 18 come into contact gradually increases toward the distal end side (right side in FIG. 12) of the finger portion 15a. (See FIGS. 11 and 12).
Other configurations of the nitride-based diode 10B are the same as those of the nitride-based diode 10A according to the second embodiment.

According to the nitride-based diode 10B according to the third embodiment having the above configuration, the following operational effects can be obtained in addition to the operational effects exhibited by the first embodiment.
The area where the finger-shaped anode electrode 16 and each side surface portion 18a of the mesa 18 are in contact with each other gradually increases toward the tip side (left side in FIG. 12) of the finger portion 16a. The electric field concentration at the end of the anode electrode 16 is easily relaxed, and a structure strong against the electric field concentration can be realized.

  In each of the above embodiments, the description has been given of the nitride-based diode in which the anode electrode 16 is in contact with the side surface portion 18a of the mesa 18 and the cathode electrode 15 is in contact with the side surface portion 18b. The present invention is applicable to a nitride-based diode that is in contact with the side surface portion 18 a of the mesa 18.

  In the nitride diodes described in the above embodiments, it is preferable to insert a thin AlN layer in order to increase the carrier concentration of the two-dimensional electron gas layer 17 and increase the mobility of carriers. In the nitride-based diode having such a configuration, as described in the above embodiments, the anode electrode 16 and the cathode electrode 15 are brought into contact with the side surface portions 18a and 18b of the mesa 18, respectively. Good ohmic contact is obtained between the layers (electron supply layer 14 and channel layer 13).

  In each of the above embodiments, an example of a lateral nitride-based diode has been described, but it goes without saying that it can also be applied to a vertical nitride-based diode. That is, in each of the above embodiments, a vertical nitride diode having a configuration in which the substrate is a conductive substrate and the cathode electrode 15 or the anode electrode 16 is electrically connected to the back electrode formed on the back surface of the substrate. In addition, the present invention is applicable.

  In each of the above-described embodiments, the nitride-based diode configured as a nitride-based Schottky barrier diode having an AlGaN / GaN heterojunction structure has been described as an example. The present invention is widely applicable to nitride-based diodes having a / GaN heterojunction structure and having an anode electrode and a cathode electrode.

In each of the above embodiments, the nitride diode in which the channel layer 13 is made of InGaN (first GaN-based compound semiconductor) and the electron supply layer 14 is made of InAlGaN (second GaN-based compound semiconductor) is also used. The present invention is applicable. In this nitride-based diode, a high-concentration two-dimensional electron gas layer is formed on the GaN side by spontaneous polarization at the InAlGaN / GaN heterojunction interface.
Further, it goes without saying that elements on all substrates on which GaN can grow crystals, such as SiC substrates other than silicon substrates, sapphire substrates, GaN substrates, MgO substrates, ZnO substrates, and the like are also valid.

10, 10A, 10B: Nitride diode 11: Silicon substrate 12: Buffer layer 13: Channel layer 14: Electron supply layer 15: Cathode electrode 15a: Finger part 16: Anode electrode 16a: Finger part 17: Two-dimensional electron gas layer 18: Mesa 18a, 18b: Side surface 30: Insulating film

Claims (9)

A channel layer made of a first nitride-based compound semiconductor formed on a substrate;
An electron supply layer formed on the channel layer and made of a second nitride compound semiconductor;
A cathode electrode and an anode electrode formed on the electron supply layer;
A mesa partially removed to a depth reaching the channel layer, a part of the electron supply layer,
A nitride-based diode, wherein at least the anode electrode of the cathode electrode and the anode electrode is in contact with a side surface portion of the mesa.   2. The nitride-based diode according to claim 1, wherein an insulating film is formed on an upper surface of the mesa, and the anode electrode is formed from the insulating film to a side surface portion of the mesa. The cathode electrode and the anode electrode have finger portions,
The nitride diode according to claim 1 or 2, wherein the mesa is intermittently formed along a longitudinal direction of the finger portion.   The mesa is formed so that an area in which the cathode electrode or the anode electrode and each side surface of the mesa contact each other gradually increases toward a tip end side of the finger portion. 4. The nitride diode according to item 3.   The nitride-based diode according to any one of claims 1 to 4, wherein the first GaN-based semiconductor material is GaN, and the second GaN-based semiconductor material is AlGaN.   The nitride system according to any one of claims 1 to 4, wherein the first GaN-based semiconductor material is InGaN or GaN, and the second GaN-based semiconductor material is InAlGaN. diode.   The nitride diode according to any one of claims 1 to 6, wherein Ni, Pt, Pd, W, Ta and Al, or an alloy of these metals is used for the anode electrode.   The nitride diode according to any one of claims 1 to 7, wherein Ti, Al, Si, Ta, Mo, W, or an alloy thereof is used for the cathode electrode.   9. The substrate according to claim 1, wherein the substrate is a conductive substrate, and the cathode electrode or the anode electrode is electrically connected to a back electrode formed on the back surface of the substrate. The nitride-based diode described in 1.

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