Nitride-based semiconductor device

Abstract

To provide a nitride-based semiconductor device capable of further suppressing the occurrence of a current collapse phenomenon.SOLUTION: A first nitride semiconductor layer having a two-dimensional electron gas layer in an upper portion thereof, a second nitride semiconductor layer having a band gap energy larger than that of the first nitride semiconductor layer on the first nitride semiconductor layer, first and second main electrodes connected to the two-dimensional electron gas layer, a control electrode on the second nitride semiconductor layer between the first and second main electrodes, and a third nitride semiconductor layer having a band gap energy smaller than that of the second nitride semiconductor layer between the first main electrode and the control electrode and having a first two-dimensional hole gas layer generated in the vicinity of an interface with the second nitride semiconductor layer; A nitride-based semiconductor device, comprising: a first P-type semiconductor layer on and electrically connected to a first main electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to nitride-based semiconductor devices. [Background technology]

[0002] FETs, which are typical nitride-based semiconductor devices that use nitride semiconductors, are prone to a phenomenon called current collapse. Current collapse is a phenomenon in which the resistance (on-resistance) increases (current becomes difficult to flow) when a device is turned on again after being turned off. Poor current collapse characteristics make high-speed switching difficult, causing serious problems in the operation of the device.

[0003] Therefore, Patent Document 1 discloses a nitride-based semiconductor device (FET) having a configuration as shown in Fig. 7. In this configuration, a hole injection part 141 is provided on a nitride semiconductor layer 123, the hole injection part 141 being formed closer to a drain electrode 132 than a gate electrode 133, the hole injection part 141 having a p-type nitride semiconductor layer 142 and a hole injection electrode 143 formed on the p-type nitride semiconductor layer 142, and the drain electrode 132 and the hole injection electrode 143 are substantially connected (at a position different from that in the cross section of Fig. 7).

[0004] When the semiconductor element is turned on, holes are injected from the hole injection portion 141. The injected holes recombine with electrons trapped in the surface states and the like of the nitride semiconductor layer 123. Therefore, it is possible to eliminate electrons trapped in the surface states and the like that cause current collapse, making it possible to suppress the occurrence of current collapse. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5739564 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 shows an example of Mg-doped p-type GaN as the p-type nitride semiconductor layer 142, but the activation rate of Mg is low and the effective acceptor concentration cannot be increased. As a result, hole injection is insufficient and the occurrence of the current collapse phenomenon cannot be sufficiently suppressed.

[0007] The present disclosure has been made in view of the above problems, and has an object to provide a nitride-based semiconductor device that can further suppress the occurrence of the current collapse phenomenon. [Means for solving the problem]

[0008] In order to achieve the above object, the present disclosure provides a semiconductor device comprising: a first nitride semiconductor layer having a two-dimensional electron gas layer (also referred to as a 2DEG layer) formed thereon; a second nitride semiconductor layer on the first nitride semiconductor layer, the second nitride semiconductor layer being made of a nitride semiconductor material having a band gap energy larger than that of the first nitride semiconductor layer; a first main electrode on a high potential side electrically connected to the two-dimensional electron gas layer; a second main electrode on a low potential side electrically connected to the two-dimensional electron gas layer; and a gate electrode provided on the second nitride semiconductor layer between the first main electrode and the second main electrode. a control electrode connected to the first main electrode; a third nitride semiconductor layer provided on the second nitride semiconductor layer between the first main electrode and the control electrode and made of a nitride semiconductor material having a band gap energy smaller than that of the second nitride semiconductor layer, the third nitride semiconductor layer having a first two-dimensional hole gas layer (also referred to as a 2DHG layer) generated in the vicinity of the interface with the second nitride semiconductor layer; and a first P-type semiconductor layer on the third nitride semiconductor layer and electrically connected to the first main electrode.

[0009] In such a nitride-based semiconductor device, the third nitride semiconductor layer includes an auxiliary electrode electrically connected to the first main electrode via the first P-type semiconductor layer. When a positive potential is applied to the first main electrode, electrons trapped in the surface states of the second nitride semiconductor layer can be eliminated not only by holes in the first P-type semiconductor layer but also by holes in the first two-dimensional hole gas layer in the third nitride semiconductor layer, thereby further suppressing the occurrence of the current collapse phenomenon.

[0010] Furthermore, it is preferable to include a fourth nitride semiconductor layer that is provided on the second nitride semiconductor layer between the control electrode and the third nitride semiconductor layer and spaced apart from the third nitride semiconductor layer, the fourth nitride semiconductor layer being made of a nitride semiconductor material having a band gap energy smaller than that of the second nitride semiconductor layer, the fourth nitride semiconductor layer having a second two-dimensional hole gas layer generated near the interface with the second nitride semiconductor layer, and a second P-type semiconductor layer that is electrically connected to the control electrode on the fourth nitride semiconductor layer.

[0011] In this way, the fourth nitride semiconductor layer has a second two-dimensional hole gas layer generated near the interface with the second nitride semiconductor layer. Electrons trapped in the surface states and the like of the second nitride semiconductor layer directly below and in the vicinity of the fourth nitride semiconductor layer are also annihilated by holes in the second two-dimensional hole gas layer in the fourth nitride semiconductor layer. With such a nitride-based semiconductor device, electrons trapped in the surface states and the like of the third nitride semiconductor layer and the second nitride semiconductor layer directly below and in the vicinity of the fourth nitride semiconductor layer can be annihilated, further suppressing the occurrence of the current collapse phenomenon.

[0012] Preferably, the fourth nitride semiconductor layer extends further toward the first main electrode than the second P-type semiconductor layer.

[0013] If the fourth nitride semiconductor layer is extended in this manner, the area of ​​the fourth nitride semiconductor layer with a high effective acceptor concentration increases. This allows electrons trapped at the surface of the second nitride semiconductor layer and other locations to be eliminated when the nitride-based semiconductor device is in the on-state. Furthermore, when the nitride-based semiconductor device is turned off, the holes in the second two-dimensional hole gas layer in the fourth nitride semiconductor layer are reduced, alleviating localized electric field concentrations and making the electric field at the surface of the second nitride semiconductor layer under the PSJ structure relatively uniform. This reduces the local electric field peak near the gate electrode, making it difficult for electrons to be trapped at the surface of the second nitride semiconductor layer and other locations near the gate electrode. These factors further suppress the occurrence of the current collapse phenomenon.

[0014] Furthermore, it is preferable that the third nitride semiconductor layer extends further toward the control electrode than the first P-type semiconductor layer, and that the length by which the fourth nitride semiconductor layer extends toward the first main electrode is longer than the length by which the third nitride semiconductor layer extends toward the control electrode.

[0015] In this way, if the third nitride semiconductor layer extends further than the first P-type semiconductor layer, holes are reduced in the extended portion when the device is off, and current collapse can be further reduced without increasing the distance between the control electrode and the first main electrode to ensure the breakdown voltage.

[0016] Furthermore, it is preferable to include a fifth nitride semiconductor layer that is provided in a region on the second nitride semiconductor layer between a region immediately below the second P-type semiconductor layer and the third nitride semiconductor layer, and that is spaced apart from the second P-type semiconductor layer and the third nitride semiconductor layer, and that is made of a nitride semiconductor material having a band gap energy smaller than that of the second nitride semiconductor layer, and that has a third two-dimensional hole gas layer generated in the vicinity of the interface with the second nitride semiconductor layer.

[0017] Providing the first P-type semiconductor layer, the second P-type semiconductor layer, the third nitride semiconductor layer, and the fourth nitride semiconductor layer reduces the electron concentration in the two-dimensional electron gas layer directly below them, thereby increasing the on-resistance of the nitride semiconductor device by a considerable amount. By providing the fifth nitride semiconductor layer between the second P-type semiconductor layer and the fourth nitride semiconductor layer and in a region spaced apart from the second P-type semiconductor layer and the fourth nitride semiconductor layer, the increase in on-resistance can be relatively suppressed, while further suppressing the occurrence of the current collapse phenomenon.

[0018] Preferably, the third nitride semiconductor layer extends closer to the control electrode than the first P-type semiconductor layer.

[0019] If the third nitride semiconductor layer is extended in this manner, the area of ​​the fourth nitride semiconductor layer having a high effective acceptor concentration increases, which allows electrons trapped at the surface of the second nitride semiconductor layer and the like to be more efficiently eliminated when the nitride-based semiconductor device is in the on-state. [Effects of the Invention]

[0020] As described above, in the nitride-based semiconductor device of the present disclosure, the third nitride semiconductor layer has a first two-dimensional hole gas layer near the interface with the second nitride semiconductor layer. Since the third nitride semiconductor layer is connected to the first main electrode to which a high potential is applied via the first P-type semiconductor layer, electrons trapped in the surface states of the second nitride semiconductor layer and holes in the third nitride semiconductor layer cancel each other out, thereby suppressing the occurrence of the current collapse phenomenon. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view showing a first embodiment of a nitride-based semiconductor device according to the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view showing a second embodiment of a nitride-based semiconductor device according to the present disclosure. [Figure 3] FIG. 2 is a cross-sectional view showing a third embodiment of a nitride-based semiconductor device according to the present disclosure. [Figure 4] FIG. 2 is a top view showing a third embodiment of a nitride-based semiconductor device according to the present disclosure. [Figure 5] FIG. 10 is a cross-sectional view showing a fourth embodiment of a nitride-based semiconductor device according to the present disclosure. [Figure 6] FIG. 10 is a cross-sectional view showing a fifth embodiment of a nitride-based semiconductor device according to the present disclosure. [Figure 7] FIG. 1 is a cross-sectional view of a conventional nitride-based semiconductor device (FET). DETAILED DESCRIPTION OF THE INVENTION

[0022] As described above, there has been a demand for a nitride-based semiconductor device that can suppress the occurrence of the current collapse phenomenon.

[0023] Therefore, the present inventors conducted extensive research and found that the occurrence of the current collapse phenomenon can be suppressed by providing a nitride semiconductor layer in which a two-dimensional hole gas layer is formed and a first P-type semiconductor layer on a second nitride semiconductor layer, and electrically connecting the first main electrode and the first P-type semiconductor layer, and thus completed the present disclosure.

[0024] That is, the present disclosure provides a nitride-based semiconductor device comprising: a first nitride semiconductor layer having a two-dimensional electron gas layer generated thereon; a second nitride semiconductor layer on the first nitride semiconductor layer, the second nitride semiconductor layer being made of a nitride semiconductor material having a band gap energy larger than that of the first nitride semiconductor layer; a first main electrode electrically connected to the two-dimensional electron gas layer; a second main electrode electrically connected to the two-dimensional electron gas layer; a control electrode provided on the second nitride semiconductor layer between the first main electrode and the second main electrode; a third nitride semiconductor layer provided on the second nitride semiconductor layer between the first main electrode and the control electrode, the third nitride semiconductor layer being made of a nitride semiconductor material having a band gap energy smaller than that of the second nitride semiconductor layer, the third nitride semiconductor layer having a first two-dimensional hole gas layer generated near the interface with the second nitride semiconductor layer; and a first P-type semiconductor layer on the third nitride semiconductor layer, electrically connected to the first main electrode.

[0025] The present disclosure will be described in detail below with reference to the drawings, but the present disclosure is not limited thereto.

[0026] First Embodiment FIG. 1 is a cross-sectional view showing a first embodiment of a nitride-based semiconductor device according to the present disclosure.

[0027] First, the nitride-based semiconductor device of this embodiment includes a first nitride semiconductor layer 12 having a two-dimensional electron gas layer (also referred to as a 2DEG layer) 14 formed thereon, a second nitride semiconductor layer 13 formed on the first nitride semiconductor layer 12 and made of a nitride semiconductor material having a band gap energy larger than that of the first nitride semiconductor layer 12, a first main electrode 19 electrically connected to the two-dimensional electron gas layer 14, a second main electrode 23 electrically connected to the two-dimensional electron gas layer 14, a control electrode 21 provided on the second nitride semiconductor layer 13 between the first main electrode 19 and the second main electrode 23, and a first The nitride-based semiconductor device includes: a third nitride semiconductor layer 15 provided on the second nitride semiconductor layer 13 between a main electrode 19 and a control electrode 21, the third nitride semiconductor layer 15 being made of a nitride semiconductor material having a band gap energy smaller than that of the second nitride semiconductor layer 13; the third nitride semiconductor layer 15 having a first two-dimensional hole gas layer (also referred to as a 2DHG layer) 16 generated near the interface with the second nitride semiconductor layer 13; a first P-type semiconductor layer 17 on the third nitride semiconductor layer 15; an auxiliary electrode 18 on the first P-type semiconductor layer 17; and wiring 20 connecting the first main electrode 19 and the auxiliary electrode 18.

[0028] In such a nitride-based semiconductor device, third nitride semiconductor layer 15 has a first two-dimensional hole gas layer (2DHG layer) 16 near the interface with second nitride semiconductor layer 13. Here, third nitride semiconductor layer 15 is provided with auxiliary electrode 18 connected to first main electrode 19 via first P-type semiconductor layer 17. When a positive potential is applied to first main electrode 19, electrons trapped in the surface states, etc. of the second nitride semiconductor layer are annihilated not only by holes in first P-type semiconductor layer 17 but also by holes in the first two-dimensional hole gas layer in third nitride semiconductor layer 15, and therefore the nitride-based semiconductor device of this embodiment can further suppress the occurrence of the current collapse phenomenon.

[0029] This embodiment will be described in more detail below.

[0030] First, the nitride-based semiconductor device of the present disclosure may include a substrate 10. The substrate 10 is not particularly limited, but may be made of silicon, silicon carbide, sapphire, GaN, or the like.

[0031] Next, a buffer layer 11 may be provided on the substrate 10. Although not particularly limited, it is possible to use AlN or Al x Ga 1-x N and Al y Ga 1-Y Multilayer buffers with repeated stacking of N and Al with gradient Al composition x Ga 1-x It can be an N structure.

[0032] Next, a first nitride semiconductor layer 12 is provided on the buffer layer 11. Although not particularly limited, the first nitride semiconductor layer 12 can be a channel layer made of undoped GaN.

[0033] Next, a second nitride semiconductor layer 13 made of a nitride semiconductor material having a band gap energy larger than that of the first nitride semiconductor layer 12 is provided on the first nitride semiconductor layer 12. Although not particularly limited, the second nitride semiconductor layer 13 can be a barrier layer made of AlGaN. When the second nitride semiconductor layer 13 is heterojunctioned with the first nitride semiconductor layer 12, either or both of spontaneous polarization and piezoelectric polarization are generated, and a two-dimensional electron gas layer (2DEG layer) 14 is generated in the upper part of the first nitride semiconductor layer 12 near the heterojunction interface.

[0034] Next, a third nitride semiconductor layer 15 made of a nitride semiconductor material having a band gap energy smaller than that of the second nitride semiconductor layer 13 is provided on the second nitride semiconductor layer 13. Although not particularly limited, the third nitride semiconductor layer 15 can be a non-doped GaN layer. When a heterojunction is formed with the second nitride semiconductor layer 13, either spontaneous polarization or piezoelectric polarization or both are generated, and a first two-dimensional hole gas layer (2DHG layer) 16 is generated in the lower part of the third nitride semiconductor layer 15 near the heterojunction interface. The thickness of the third nitride semiconductor layer 15 is set to, for example, several tens to 100 nm.

[0035] Next, a first P-type semiconductor layer 17 is provided on the third nitride semiconductor layer 15 in which the first two-dimensional hole gas layer 16 is generated. Although not particularly limited, the first P-type semiconductor layer 17 may be a metal oxide semiconductor that functions as a P-type, such as NiO, in addition to P-type GaN, P-type AlGaN, P-type InGaN, etc.

[0036] Furthermore, a hole injection electrode 18 serving as an auxiliary electrode is provided on the first P-type semiconductor layer 17, and the hole injection electrode 18 and a drain electrode 19 serving as a first main electrode are electrically connected by wiring 20 or the like. The hole injection electrode 18 may be made of, for example, Ni / Au. A higher potential (positive potential) than that of the source electrode (second main electrode) 23 is applied to the drain electrode (first main electrode) 19, and therefore a first two-dimensional hole gas layer (2DHG layer) 16 is generated in the third nitride semiconductor layer 15 whether the nitride-based semiconductor device is on or off.

[0037] The first two-dimensional hole gas layer 16 has a high hole concentration, and the concentration is high near the heterointerface between the second nitride semiconductor layer 13 and the third nitride semiconductor layer 15, so that the holes are more likely to cancel out electrons trapped on the surface of the second nitride semiconductor layer 13, etc. As a result, the occurrence of the current collapse phenomenon can be suppressed more effectively than in the conventional example.

[0038] The drain electrode 19 and the source electrode 23 are each electrically connected to the two-dimensional electron gas layer 14 .

[0039] A second P-type semiconductor layer 22 is provided on the second nitride semiconductor layer 13 between the drain electrode 19 and the source electrode 23, and a gate electrode (control electrode) 21 is provided on the second P-type semiconductor layer 22. In Fig. 1, the second P-type semiconductor layer 22 is formed on the second nitride semiconductor layer 13, but a hole may be formed in the second nitride semiconductor layer 13 directly below the second P-type semiconductor layer 22 to reduce the thickness of at least a portion of the second nitride semiconductor layer 13, and the second P-type semiconductor layer 22 and the gate electrode 21 may be provided on the hole.

[0040] In addition, although FIG. 1 shows the drain electrode 19 in direct contact with the third nitride semiconductor layer 15 and the first P-type semiconductor layer 17, this is not limitative and they may be connected to each other via the hole injection electrode (auxiliary electrode) 18, and the drain electrode 19 may be separated from at least one of the third nitride semiconductor layer 15 and the first P-type semiconductor layer 17.

[0041] Furthermore, the second P-type semiconductor layer 22 below the gate electrode 21 is separated from the third nitride semiconductor layer 15 and the first P-type semiconductor layer 17 below the hole injection electrode 18.

[0042] <Second embodiment> FIG. 2 is a cross-sectional view showing a second embodiment of the nitride-based semiconductor device of the present disclosure.

[0043] Although not particularly limited, as shown in FIG. 2, the fourth nitride semiconductor layer 24 is electrically connected to the gate electrode 21, and is provided on the second nitride semiconductor layer 13 between the gate electrode 21 and the drain electrode 19, spaced apart from the third nitride semiconductor layer 15, and is made of a nitride semiconductor material having a smaller band gap energy than the second nitride semiconductor layer 13, and the fourth nitride semiconductor layer 24 has a second two-dimensional hole gas layer 25 generated near the interface with the second nitride semiconductor layer 13.

[0044] Thus, in addition to the first two-dimensional hole gas layer 16, the fourth nitride semiconductor layer 24 has a second two-dimensional hole gas layer 25 in the vicinity of the interface with the second nitride semiconductor layer 13. Electrons trapped in the surface states and the like of the second nitride semiconductor layer 13 immediately below and in the vicinity of the fourth nitride semiconductor layer 24 are annihilated not only by the first two-dimensional hole gas layer 16 but also by the holes in the second two-dimensional hole gas layer 25 in the fourth nitride semiconductor layer 24. As a result, it is possible to further suppress a decrease in the concentration of the two-dimensional electron gas layer 14 due to electrons trapped in the surface states and the like of the second nitride semiconductor layer 13 immediately below and in the vicinity of the third nitride semiconductor layer 15 and the fourth nitride semiconductor layer 24, and further suppress the occurrence of the current collapse phenomenon.

[0045] This embodiment will be described in more detail below.

[0046] The present embodiment is an example in which a fourth nitride semiconductor layer 24 in which a second two-dimensional hole gas layer 25 is generated is also provided below a second P-type semiconductor layer 22 (which is not particularly limited and may be, for example, P-GaN) below the gate electrode 21. The fourth nitride semiconductor layer 24 below the gate electrode 21 and the third nitride semiconductor layer 15 below the hole injection electrode 18 are spaced apart.

[0047] When a zero or positive potential is applied to the gate electrode 21, no depletion layer is formed directly below the gate electrode 21, and the two-dimensional electron gas layer 14 between the drain electrode 19 and the source electrode 23 is continuous, thereby turning the nitride-based semiconductor device into an on-state. At this time, a second two-dimensional hole gas layer 25 is formed in the fourth nitride semiconductor layer 24 near the interface with the second nitride semiconductor layer 13. Electrons trapped in the surface states of the second nitride semiconductor layer 13 directly below and in the vicinity of the fourth nitride semiconductor layer 24 are canceled out by holes in the second two-dimensional hole gas layer 25 in the fourth nitride semiconductor layer 24 in addition to the first two-dimensional hole gas layer 16. As a result, it is possible to suppress a decrease in the concentration of the two-dimensional electron gas layer due to electrons trapped in the surface states of the second nitride semiconductor layer directly below and in the vicinity of the third nitride semiconductor layer and the fourth nitride semiconductor layer, and to further suppress the occurrence of the current collapse phenomenon.

[0048] When an off signal (negative potential) is applied to gate electrode 21 of the nitride-based semiconductor device to turn it off, a depletion layer is generated in two-dimensional electron gas layer 14 directly below gate electrode 21 (or two-dimensional electron gas layer 14 is disconnected). Here, the hole concentration in second two-dimensional hole gas layer 25 of fourth nitride semiconductor layer 24 decreases, thereby reducing leakage current.

[0049] Although FIG. 2 shows an example in which the second P-type semiconductor layer 22 is provided under the gate electrode 21, the second P-type semiconductor layer 22 may be electrically connected to the gate electrode 21, and for example, the gate electrode 21 may be formed on the second nitride semiconductor layer 13 between the fourth nitride semiconductor layer 24 and the source electrode 23.

[0050] <Third embodiment> 3 and 4 are a cross-sectional view and a top view showing a third embodiment of the nitride-based semiconductor device of the present disclosure. To make the arrangement easier to understand, Fig. 4 shows only the electrodes 18, 19, 21, and 23, the third nitride semiconductor layer 15, the first P-type semiconductor layer 17, the second P-type semiconductor layer 22, and the fourth nitride semiconductor layer 24.

[0051] Although not particularly limited, as shown in FIGS. 3 and 4, in a plan view from above, the drain electrode 19 is surrounded by the hole injection electrode 18, the third nitride semiconductor layer 15, and the first P-type semiconductor layer 17, and the fourth nitride semiconductor layer 24 extends closer to the drain electrode 19 than the second P-type semiconductor layer 22.

[0052] Increasing the third nitride semiconductor layer 15 and the fourth nitride semiconductor layer 24 between the gate electrode 21 and the drain electrode 19 on the second nitride semiconductor layer 13 also increases the areas of the first two-dimensional hole gas layer 16 and the second two-dimensional hole gas layer 25, thereby reducing current collapse.

[0053] When the nitride-based semiconductor device is turned off, the concentration of the first two-dimensional hole gas layer 16 in the third nitride semiconductor layer 15 does not decrease, but the concentration of the second two-dimensional hole gas layer 25 in the fourth nitride semiconductor layer 24 decreases. Because the third nitride semiconductor layer 15 is electrically connected to the drain electrode 19 via the first P-type semiconductor layer 17, the first two-dimensional hole gas layer 16 has a relatively high potential. On the other hand, the concentration of the second two-dimensional hole gas layer 25 decreases, and the fourth nitride semiconductor layer 24 exhibits characteristics close to insulation. Therefore, by making the length (A) of the fourth nitride semiconductor layer 24 extending toward the drain electrode 19 from the second P-type semiconductor layer 22 longer than the length of the third nitride semiconductor layer 15 extending toward the gate electrode 21 from the first P-type semiconductor layer 17, current collapse can be further reduced without significantly increasing the distance between the gate electrode 21 and the drain electrode 19 to ensure a sufficient breakdown voltage.

[0054] 3 and 4, the side surface of the third nitride semiconductor layer 15 on the gate electrode 21 side and the side surface of the first P-type semiconductor layer 17 on the gate electrode 21 side are aligned and flush with each other. Therefore, current collapse can be further reduced without increasing the chip size too much.

[0055] This embodiment will be described in more detail below.

[0056] The present embodiment is an example in which a fourth nitride semiconductor layer 24 below a second P-type semiconductor layer 22 (which is not particularly limited and may be, for example, P-GaN) below a gate electrode (control electrode) 21 extends further toward the drain electrode (first main electrode) 19 than the second P-type semiconductor layer 22. The portions extending further toward the drain electrode 19 than the second P-type semiconductor layer 22 (three fourth nitride semiconductor layers 24 in FIG. 4 ) are sometimes called a PSJ structure (Polarization Super Junction).

[0057] When the nitride-based semiconductor device is in the on state, a first two-dimensional hole gas layer 16 is generated in the third nitride semiconductor layer 15. A second two-dimensional hole gas layer 25 is also generated in the fourth nitride semiconductor layer 24 of the PSJ structure. Because the effective acceptor concentration of the second two-dimensional hole gas layer 25 is higher than that of the second P-type semiconductor layer 22, a decrease in the concentration of the two-dimensional electron gas layer 14 due to electrons trapped under the third nitride semiconductor layer 15, under the second P-type semiconductor layer 22, and on the surface of the second nitride semiconductor layer 13 under the PSJ structure, etc., can be suppressed, thereby reducing the current collapse phenomenon.

[0058] On the other hand, when the nitride-based semiconductor device is turned off, the holes in second two-dimensional hole gas layer 25 in fourth nitride semiconductor layer 24 decrease, making it insulating layer-like, alleviating local electric field concentrations and making the electric field on the surface of second nitride semiconductor layer 13 under the PSJ structure relatively uniform. This reduces the local electric field peak near gate electrode 24, making it difficult for electrons to be trapped on the surface of second nitride semiconductor layer 13 near gate electrode 24.

[0059] Since the third nitride semiconductor layer 15 is electrically connected to the drain electrode 19 via the first P-type semiconductor layer 17, the first two-dimensional hole gas layer 16 has a relatively high potential. Therefore, by making the length (A) of the fourth nitride semiconductor layer 24 extending toward the drain electrode 19 longer than the length (B) of the third nitride semiconductor layer 15 extending toward the gate electrode 21, it is possible to further reduce current collapse without increasing the distance between the gate electrode 21 and the drain electrode 19 to ensure the breakdown voltage.

[0060] 3 and 4, the boundary between the side surface of third nitride semiconductor layer 15 on the gate electrode 21 side and the side surface of first P-type semiconductor layer 17 on the gate electrode 21 side is flush with no irregularities. In other words, the length (B) by which third nitride semiconductor layer 15 extends toward gate electrode 21 is set to zero. This makes it possible to further reduce current collapse without significantly increasing the chip size.

[0061] In addition, in order to prevent electrons discharged from the drain electrode 19 from being trapped on the surface of the second nitride semiconductor layer 13 toward the gate electrode 21, it is desirable to provide a third nitride semiconductor layer 15 and a first P-type semiconductor layer 17 so as to surround the drain electrode 19, as shown in FIG. 4, for example.

[0062] Furthermore, providing the third nitride semiconductor layer 15 or the first P-type semiconductor layer 17 reduces the electron concentration in the two-dimensional electron gas layer 14 directly below the third nitride semiconductor layer 15 or the first P-type semiconductor layer 17, thereby increasing the on-resistance of the nitride semiconductor device to a considerable extent. Therefore, it is preferable that the area of ​​the third nitride semiconductor layer 15 or the first P-type semiconductor layer 17 is as small as possible.

[0063] Furthermore, providing the fourth nitride semiconductor layer 24 or the second P-type semiconductor layer 22 reduces the electron concentration in the two-dimensional electron gas layer 14 directly below the fourth nitride semiconductor layer 24 or the second P-type semiconductor layer 22, thereby significantly increasing the on-resistance of the nitride semiconductor device. Although not particularly limited, it is preferable to alternately provide portions with a PSJ structure (portion of the fourth nitride semiconductor layer 24 extending toward the drain electrode 19) and portions without a PSJ structure in the extension direction (Y direction) of the gate electrode 21, as shown in FIG. 4 . This can further reduce current collapse while suppressing an increase in the on-resistance of the nitride semiconductor device. Furthermore, the hole injection electrode (auxiliary electrode) 18 connected to the drain electrode (first main electrode) 19, and the third nitride semiconductor layer 15 and first P-type semiconductor layer 17 below it, may be arranged to surround the drain electrode 19. It should be noted that "surrounding" here does not necessarily mean that they are completely ring-shaped, and they may be arranged at multiple locations around the drain electrode 19 at intervals.

[0064] <Fourth embodiment> FIG. 5 is a cross-sectional view showing a fourth embodiment of a nitride-based semiconductor device according to the present disclosure.

[0065] 5, the third nitride semiconductor layer 15 extends by a length (B) toward the control electrode 21 side beyond the first P-type semiconductor layer 17. Therefore, the side surface of the third nitride semiconductor layer 15 facing the control electrode 21 and the side surface of the first P-type semiconductor layer 17 facing the control electrode 21 are not aligned or flush with each other.

[0066] If the third nitride semiconductor layer 15 is extended in this way, the area of ​​the third nitride semiconductor layer 15 increases. At this time, the area of ​​the first two-dimensional hole gas layer (2DHG layer) 16 in the third nitride semiconductor layer 15 also increases. As a result, the occurrence of the current collapse phenomenon can be further suppressed.

[0067] 5, the third nitride semiconductor layer 15 extends by a length (B) toward the control electrode 21 side beyond the first P-type semiconductor layer 17, and the fourth nitride semiconductor layer 24 extends by a length (A) toward the first main electrode 19 side beyond the second P-type semiconductor layer 22. In this case, it is preferable that the length (A) by which the fourth nitride semiconductor layer 24 extends toward the first main electrode 19 side beyond the second P-type semiconductor layer 22 is longer than the length (B) by which the third nitride semiconductor layer 15 extends toward the control electrode 21 side beyond the first P-type semiconductor layer 17.

[0068] As shown in the third embodiment of the nitride-based semiconductor device of the present disclosure, even if the side surface of the third nitride semiconductor layer 15 facing the control electrode 21 and the side surface of the first P-type semiconductor layer 17 facing the control electrode 21 are not aligned, a first two-dimensional hole gas layer 16 is generated in the portion of the third nitride semiconductor layer 15 extending closer to the control electrode 21 than the first P-type semiconductor layer 17. Since the third nitride semiconductor layer 15 can accommodate more holes than the first P-type semiconductor layer 17, it is possible to further reduce electrons trapped in the surface states, etc., of the second nitride semiconductor layer 13. As a result, it is possible to further suppress the occurrence of the current collapse phenomenon.

[0069] <Fifth embodiment> FIG. 6 is a cross-sectional view showing a fifth embodiment of a nitride-based semiconductor device according to the present disclosure.

[0070] 6, it is preferable to provide fifth nitride semiconductor layers 26, 27 made of a nitride semiconductor material having a band gap energy smaller than that of the second nitride semiconductor layer 13, which are provided in a region between a fourth nitride semiconductor layer 24 on the second nitride semiconductor layer 13 or the second P-type semiconductor layer 22 and the third nitride semiconductor layer 15, and which have third two-dimensional hole gas layers (2DHG layers) 28, 29 generated near the interface with the second nitride semiconductor layer 13. Note that, in this embodiment, two examples are shown for the fifth nitride semiconductor layers 26, 27 and the third two-dimensional hole gas layers 28, 29, but the present invention is not limited to this. One, or three or more, may be provided.

[0071] In this way, by having a third two-dimensional hole gas layer 28, 29 in addition to the first two-dimensional hole gas layer 16, the occurrence of the current collapse phenomenon can be further suppressed while relatively suppressing the increase in on-resistance.

[0072] This embodiment will be described in more detail below.

[0073] The present embodiment (FIG. 6) is an example in which a plurality (not limited to a plurality, but may be a single layer) of mutually separated fifth nitride semiconductor layers 26, 27 are further arranged in an island shape between the fourth nitride semiconductor layer 24 below the gate electrode (control electrode) 21 and the third nitride semiconductor layer 15 below the hole injection electrode (auxiliary electrode) 18 in the third embodiment (FIG. 3). The fifth nitride semiconductor layers 26, 27 arranged in an island shape may be at a floating potential, i.e., not connected to the gate electrode 21 or the drain electrode 19, or may be connected to the gate electrode 21 or the drain electrode 19. FIG. 6 shows an example in which one (the fifth nitride semiconductor layer 26) is electrically connected to the gate electrode 21 and the other (the fifth nitride semiconductor layer 27) is electrically connected to the drain electrode 19. The connection may be, but is not particularly limited to, a P-type semiconductor layer such as P-GaN and an electrode provided thereon on the fifth nitride semiconductor layers 26 and 27, and the gate electrode 21 and the drain electrode 19 may be connected via the electrode. Although a two-dimensional hole gas layer increases the on-resistance of a nitride semiconductor device, providing the fifth nitride semiconductor layers 26 and 27 spaced apart from each other suppresses the increase in on-resistance, and providing the fifth nitride semiconductor layers 26 and 27 further suppresses the occurrence of the current collapse phenomenon. Note that, when providing the fifth nitride semiconductor layers 26 and 27, it is preferable to divide a portion of the fourth nitride semiconductor layer 24 and the third nitride semiconductor layer 15 in FIG. 5 into the fourth nitride semiconductor layer 24 and the fifth nitride semiconductor layer 26, and the third nitride semiconductor layer 15 and the fifth nitride semiconductor layer 27 in FIG. 6, respectively.

[0074] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Explanation of symbols]

[0075] 10...substrate, 11...buffer layer, 12...GaN channel layer (first nitride semiconductor layer), 13...AlGaN barrier layer (second nitride semiconductor layer), 14...Two-dimensional electron gas layer (2DEG layer), 15...GaN layer (third nitride semiconductor layer), 16...first two-dimensional hole gas layer (2DHG layer), 17...first P-type semiconductor layer, 18... hole injection electrode (auxiliary electrode), 19... drain electrode (first main electrode), 20...wiring, 21...gate electrode (control electrode), 22...second P-type semiconductor layer, 23...source electrode (second main electrode), 24...fourth nitride semiconductor layer, 25...second two-dimensional hole gas layer (2DHG layer), 26, 27...fifth nitride semiconductor layer, 28, 29...Third two-dimensional hole gas layer (2DHG layer), 122...Channel layer (nitride semiconductor layer), 123...Nitride semiconductor layer, 132... drain electrode; 133... gate electrode; 141... hole injection portion; 142: p-type nitride semiconductor layer; 143: hole injection electrode. A, B...length, X, Y...direction.

Claims

1. a first nitride semiconductor layer having a two-dimensional electron gas layer formed thereon; a second nitride semiconductor layer on the first nitride semiconductor layer, the second nitride semiconductor layer being made of a nitride semiconductor material having a band gap energy larger than that of the first nitride semiconductor layer; a first main electrode on a high potential side electrically connected to the two-dimensional electron gas layer; a second main electrode on a low potential side electrically connected to the two-dimensional electron gas layer; a control electrode provided on the second nitride semiconductor layer between the first main electrode and the second main electrode; a third nitride semiconductor layer provided on the second nitride semiconductor layer between the first main electrode and the control electrode, the third nitride semiconductor layer being made of a nitride semiconductor material having a band gap energy smaller than that of the second nitride semiconductor layer, the third nitride semiconductor layer having a first two-dimensional hole gas layer generated near an interface with the second nitride semiconductor layer; a first P-type semiconductor layer on the third nitride semiconductor layer, the first P-type semiconductor layer being electrically connected to the first main electrode.

2. a fourth nitride semiconductor layer provided on the second nitride semiconductor layer between the control electrode and the third nitride semiconductor layer and spaced apart from the third nitride semiconductor layer, the fourth nitride semiconductor layer being made of a nitride semiconductor material having a band gap energy smaller than that of the second nitride semiconductor layer, the fourth nitride semiconductor layer having a second two-dimensional hole gas layer generated in the vicinity of the interface with the second nitride semiconductor layer; 2. The nitride-based semiconductor device according to claim 1, further comprising a second P-type semiconductor layer on said fourth nitride semiconductor layer, said second P-type semiconductor layer being electrically connected to said control electrode.

3. 3. The nitride-based semiconductor device according to claim 2, wherein the fourth nitride semiconductor layer extends further toward the first main electrode than the second P-type semiconductor layer.

4. the third nitride semiconductor layer extends closer to the control electrode than the first P-type semiconductor layer, 4. The nitride-based semiconductor device according to claim 3, wherein the length by which the fourth nitride semiconductor layer extends toward the first main electrode is longer than the length by which the third nitride semiconductor layer extends toward the control electrode.

5. 5. The nitride-based semiconductor device according to claim 2, further comprising: a fifth nitride semiconductor layer provided in a region on the second nitride semiconductor layer from a region immediately below the second P-type semiconductor layer to the third nitride semiconductor layer, the fifth nitride semiconductor layer being spaced apart from the second P-type semiconductor layer and the third nitride semiconductor layer, the fifth nitride semiconductor layer being made of a nitride semiconductor material having a band gap energy smaller than that of the second nitride semiconductor layer, the fifth nitride semiconductor layer having a third two-dimensional hole gas layer generated in the vicinity of an interface with the second nitride semiconductor layer.

6. 4. The nitride-based semiconductor device according to claim 1, wherein the third nitride semiconductor layer extends closer to the control electrode than the first P-type semiconductor layer.

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