Nitride semiconductor equipment

Abstract

To obtain a nitride-based semiconductor device with high voltage resistance and low on-resistance. [Solution] A nitride semiconductor device comprising: a first nitride semiconductor layer having a two-dimensional electron gas layer on its upper part; a second nitride semiconductor layer having a band gap larger than the band gap of the first nitride semiconductor layer; a third nitride semiconductor layer having a band gap energy smaller than that of the second nitride semiconductor layer and having a two-dimensional hole gas layer formed near the interface with the second nitride semiconductor layer; a P-type semiconductor layer on the third nitride semiconductor layer; a first main electrode on the high-potential side electrically connected to the two-dimensional electron gas layer; a second main electrode on the low-potential side electrically connected to the two-dimensional electron gas layer; a control electrode located on the first nitride semiconductor layer between the first and second main electrodes and electrically connected to the P-type semiconductor layer; a recess provided in the third nitride semiconductor layer; and a field plate electrically connected to the second main electrode and having an end on the first main electrode side above the region of the recess.

Description

Technical Field

[0001] The present disclosure relates to the structure of a nitride semiconductor device using a heterojunction of nitride semiconductors.

Background Art

[0002] As a semiconductor device using a heterojunction of nitride semiconductors (GaN and its mixed crystal semiconductors), for example, a HEMT (High Electron Mobility Transistor) is known. Such a semiconductor device is required to have a breakdown voltage between the source and the drain when it is off. Further, although a current collapse phenomenon is known as a problem in a HEMT using a nitride semiconductor, it is said that it is effective to relax the local electric field concentration between the drain and the gate in order to reduce the current collapse phenomenon.

[0003] As an example of a HEMT structure using a nitride semiconductor, for example, a HEMT structure using a PSJ (Polarization Super Junction) structure as described in Patent Document 1 is known. FIG. 14 is a cross-sectional view schematically showing a HEMT structure having a PSJ structure, and FIG. 15 is a plan view schematically showing a HEMT structure having a PSJ structure. In the nitride semiconductor device 100 shown in FIG. 14, for example, on a nitride semiconductor layer (first nitride semiconductor layer 3) made of undoped GaN, an undoped AlGaN (exactly Al 1-x Ga x N: 0 <x <1) is formed. As a result, a two-dimensional electron gas layer is generated in the first nitride semiconductor layer 3 near the interface between the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4.

[0004] On the second nitride semiconductor layer 4, a nitride semiconductor layer (third nitride semiconductor layer 8) is formed, similar to the first nitride semiconductor layer 3, and composed of, for example, undoped GaN. A two-dimensional hole gas, in which holes are accumulated in a planar manner, is generated within the third nitride semiconductor layer 8 near the interface between the second nitride semiconductor layer 4 and the third nitride semiconductor layer 8.

[0005] By setting the gate electrode 7, which is provided on the third nitride semiconductor layer 8 via a P-type semiconductor layer 9, to a negative potential, the two-dimensional electron gas directly beneath the gate electrode 7 disappears, and the nitride semiconductor device 100 enters an off state. During turn-off, electrons constituting the two-dimensional electron gas move towards the drain electrode 6, and holes constituting the two-dimensional hole gas move towards the gate electrode 7. As a result, the electric field strength within the third nitride semiconductor layer 8 extending from the gate electrode 7 towards the drain electrode 6 is made nearly uniform, and the localized increase in electric field strength in the second nitride semiconductor layer 4 directly beneath the gate electrode 7 is reduced. This enables higher breakdown voltage of the nitride semiconductor device 100 and reduces the current collapse phenomenon. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-123161 [Overview of the project] [Problems that the invention aims to solve]

[0007] The region with the PSJ structure can have its electric field strength nearly uniform, thereby increasing its breakdown voltage. However, when the nitride semiconductor device is turned on, the concentration of the two-dimensional electron gas in the first nitride semiconductor layer 3 decreases, which increases the operating resistance and reduces the allowable current.

[0008] This disclosure has been made in view of the aforementioned problems and aims to provide a nitride-based semiconductor device that solves the above problems. [Means for solving the problem]

[0009] This disclosure has the following structure in order to solve the above-mentioned problems. This disclosure provides a first nitride-based semiconductor layer having a two-dimensional electron gas layer on top; a second nitride-based semiconductor layer provided on the first nitride-based semiconductor layer and having a band gap larger than the band gap of the first nitride-based semiconductor layer; a third nitride-based semiconductor layer provided on the second nitride-based semiconductor layer and made of a nitride-based semiconductor material having a band gap energy smaller than that of the second nitride-based semiconductor layer, the third nitride-based semiconductor layer having a two-dimensional hole gas layer formed near the interface with the second nitride-based semiconductor layer; and the third The present invention is characterized by comprising: a P-type semiconductor layer on a nitride-based semiconductor layer; a first main electrode on the high-potential side electrically connected to a two-dimensional electron gas layer; a second main electrode on the low-potential side electrically connected to the two-dimensional electron gas layer; a control electrode located on the first nitride-based semiconductor layer between the first main electrode and the second main electrode and electrically connected to the P-type semiconductor layer; a recess provided in the third nitride-based semiconductor layer; and a field plate electrically connected to the second main electrode and having an end on the first main electrode side above the region of the recess.

[0010] Furthermore, this disclosure includes a first nitride-based semiconductor layer having a two-dimensional electron gas layer on top; a second nitride-based semiconductor layer provided on the first nitride-based semiconductor layer and having a band gap larger than the band gap of the first nitride-based semiconductor layer; a third nitride-based semiconductor layer provided on the second nitride-based semiconductor layer and made of a nitride-based semiconductor material having a band gap energy smaller than that of the second nitride-based semiconductor layer, the third nitride-based semiconductor layer having a two-dimensional hole gas layer formed near the interface with the second nitride-based semiconductor layer; a first P-type semiconductor layer on the third nitride-based semiconductor layer; a first main electrode on the high-potential side electrically connected to the two-dimensional electron gas layer; a second main electrode on the low-potential side electrically connected to the two-dimensional electron gas layer; and between the first main electrode and the second main electrode. The invention is characterized by comprising: a control electrode electrically connected to a first P-type semiconductor layer on a first nitride-based semiconductor layer; a fourth nitride-based semiconductor layer provided on a second nitride-based semiconductor layer spaced apart from a third nitride-based semiconductor layer and made of a nitride-based semiconductor material having a smaller bandgap energy than the second nitride-based semiconductor layer, and having a two-dimensional hole gas layer formed near the interface with the second nitride-based semiconductor layer; a second P-type semiconductor layer on the fourth nitride-based semiconductor layer; an auxiliary electrode electrically connected to the control electrode on the second P-type semiconductor layer; and a field plate electrically connected to a second main electrode and having an end on the first main electrode side above the region between the third nitride-based semiconductor layer and the fourth nitride-based semiconductor layer.

[0011] Furthermore, this disclosure provides a first nitride-based semiconductor layer having a two-dimensional electron gas layer on top; a second nitride-based semiconductor layer provided on the first nitride-based semiconductor layer and having a band gap larger than the band gap of the first nitride-based semiconductor layer; and a third nitride-based semiconductor layer provided on the second nitride-based semiconductor layer and made of a nitride-based semiconductor material having a band gap energy smaller than that of the second nitride-based semiconductor layer, wherein the third nitride-based semiconductor layer has a two-dimensional hole gas layer formed near the interface with the second nitride-based semiconductor layer. The device is characterized by comprising: a conductor layer; a P-type semiconductor layer on a third nitride-based semiconductor layer; a first main electrode on the high-potential side electrically connected to a two-dimensional electron gas layer; a second main electrode on the low-potential side electrically connected to a two-dimensional electron gas layer; a control electrode located on the first nitride-based semiconductor layer between the first main electrode and the second main electrode and electrically connected to a P-type semiconductor layer; and a recess provided in the third nitride-based semiconductor layer on the control electrode side, when the region of the third nitride-based semiconductor layer between the first main electrode and the control electrode is viewed in plan view. [Effects of the Invention]

[0012] As described above, this disclosure provides a nitride-based semiconductor device that reduces operating resistance while achieving high voltage resistance by making the electric field strength substantially uniform. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view taken at FF in Figure 3, showing the structure of the first embodiment of the nitride-based semiconductor device according to the embodiments of this disclosure. [Figure 2] This is a cross-sectional view taken at GG in Figure 3, showing the structure of the first embodiment of the nitride-based semiconductor device according to the embodiments of this disclosure. [Figure 3] This is a plan view showing the structure of a first embodiment of a nitride-based semiconductor device according to an embodiment of the present disclosure. [Figure 4] This is a plan view showing a modified example 1 of the structure of the first embodiment of the nitride-based semiconductor device according to the embodiments of this disclosure. [Figure 5]It is a cross-sectional view showing a modified example 2 structure of a first embodiment of a nitride semiconductor device according to an embodiment of the present disclosure. [Figure 6] It is a cross-sectional view showing a structure of a second embodiment of a nitride semiconductor device according to an embodiment of the present disclosure. [Figure 7] It is a plan view showing a structure of a second embodiment of a nitride semiconductor device according to an embodiment of the present disclosure. [Figure 8] It is a cross-sectional view showing a structure of a third embodiment of a nitride semiconductor device according to an embodiment of the present disclosure. [Figure 9] It is a plan view showing a structure of a third embodiment of a nitride semiconductor device according to an embodiment of the present disclosure. [Figure 10] It is a cross-sectional view showing a structure of a fourth embodiment of a nitride semiconductor device according to an embodiment of the present disclosure. [Figure 11] It is a plan view showing a structure of a fourth embodiment of a nitride semiconductor device according to an embodiment of the present disclosure. [Figure 12] It is a cross-sectional view showing a structure of a modified example of a third embodiment of a nitride semiconductor device according to an embodiment of the present disclosure. [Figure 13] It is a cross-sectional view showing a structure of a modified example 2 of a first embodiment of a nitride semiconductor device according to an embodiment of the present disclosure. [Figure 14] It is a cross-sectional view showing a structure of a conventional nitride semiconductor device with a PSJ structure. [Figure 15] It is a plan view showing a structure of a conventional nitride semiconductor device with a PSJ structure.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, a nitride-based semiconductor device, which is an embodiment of the present disclosure, will be described with reference to the drawings. In the following drawings, identical or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between thickness and planar dimensions, the ratio of lengths of each part, etc., may differ from those of reality. Therefore, specific dimensions should be determined by referring to the following explanation. Furthermore, it should be noted that there are parts where the relationships and ratios of dimensions differ between drawings. Furthermore, the embodiments described below illustrate nitride-based semiconductor devices for embodying the technical concept of this disclosure, and the technical concept of this disclosure does not limit the shape, structure, arrangement, etc. of the components to those described below. Various modifications can be made to the embodiments of this disclosure within the scope of the claims. In this disclosure, terms such as "top" and "bottom" are used for convenience of description, and even if they are provided on the side, they fall within the scope of the present invention if they are substantially identical to the constituent elements of this disclosure. Furthermore, "above" includes not only cases where it is formed in contact with the object, but also cases where it is formed through another layer. Also, in this disclosure, "connection" is not limited to direct connection; even if something such as a resistor is interposed between the two, if it is substantially the same as the constituent elements of this disclosure, it falls within the scope of the rights of the present invention.

[0015] <First Embodiment> The nitride-based semiconductor device 50, which is the first embodiment of the present disclosure, is shown in the cross-sectional view of the nitride-based semiconductor device 50 in Figure 2, and comprises a substrate 1 made of sapphire, GaN, silicon, or silicon carbide, and a substrate provided on the substrate 1, made of AlN or Al X Ga 1-X N and Al Y Ga 1-Y A multilayer buffer structure in which N is repeatedly stacked, or Al with a gradient in composition X Ga 1-XA buffer layer 2 having an N structure, a first nitride semiconductor layer 3 provided on the buffer layer 2 and composed of undoped GaN, and an undoped Al having a larger bandgap energy than the first nitride semiconductor layer 3 and containing, for example, Al Z Ga 1-Z A second nitride semiconductor layer 4 composed of GaN (where Z>0), and a third nitride semiconductor layer 8 provided on the second nitride semiconductor layer 4 and composed of, for example, undoped GaN having a smaller bandgap energy than the second nitride semiconductor layer 4. In the first nitride semiconductor layer 3 near the interface between the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4, a two-dimensional electron gas layer is generated by spontaneous polarization or piezoelectric polarization or both. Also, in the third nitride semiconductor layer 8 near the interface between the second nitride semiconductor layer 4 and the third nitride semiconductor layer 8, a two-dimensional hole gas layer (two-dimensional positive hole gas layer) is generated by spontaneous polarization or piezoelectric polarization or both. The third nitride semiconductor layer 8 may be composed of P-type GaN or P-type AlGaN so that a two-dimensional hole gas layer is generated. W Ga 1-W N (where Z>W>0).

[0016] The source electrode 5 and the drain electrode 6 are formed on the first nitride semiconductor layer 3 or the second nitride semiconductor layer 4, and are composed of a material that makes an ohmic contact with the two-dimensional electron gas layer in the first nitride semiconductor layer 3, and are composed of, for example, a stacked structure of Ti / Au. Note that the drain electrode 6 and the source electrode 5 do not contact the third nitride semiconductor layer 8 and are not connected to the two-dimensional hole gas layer in the third nitride semiconductor layer 8.

[0017] A gate electrode 7 is provided on a second nitride-based semiconductor layer 4 between the source electrode 5 and the drain electrode 6, and is electrically connected to a third nitride-based semiconductor layer 8. In Figure 1, the second nitride-based semiconductor layer 4 contains a third nitride-based semiconductor layer 8, a P-type semiconductor layer 9 made of a P-type nitride semiconductor such as P-GaN or P-InGaN, or NiO, and a gate electrode 7 on the P-type semiconductor layer 9. The gate electrode 7 is made of a material that makes relatively ohmic contact with the P-type semiconductor layer 9, such as a Ni / Au stacked structure. The P-type semiconductor layer 9 and the gate electrode 7 are provided on the second nitride-based semiconductor layer 4 on the source electrode 5 side of the third nitride-based semiconductor layer 8, and the P-type semiconductor layer 9 and the third nitride-based semiconductor layer 8 may be electrically connected. Alternatively, as shown in Figure 2, the P-type semiconductor layer 9 and the gate electrode 7 may be stacked on the third nitride-based semiconductor layer 8. The portion of the third nitride semiconductor layer 8 that extends towards the drain electrode 6 side from the gate electrode 7 or the P-type semiconductor layer 9, combined with the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4 directly beneath it (the portion of length B in Figure 2), is sometimes called a PSJ structure (Polarization Super Junction).

[0018] Here, in Figure 1, a recess 10 is provided in the third nitride semiconductor layer 8. Figure 3 is a plan view of the nitride semiconductor device 50 viewed from above, with Figure 1 being a cross-sectional view taken along F-F including the recess 10 in Figure 3, and Figure 2 being a cross-sectional view taken along G-G including the recess 10 in Figure 3. As shown in Figure 3, the source electrode 5 and drain electrode 6, the third nitride semiconductor layer 8 which is part of the PSJ structure, the P-type semiconductor layer 9 and the gate electrode 7 each extend in the direction in which the gate electrode 7 extends (the Y direction in Figure 3). Multiple recesses 10 are provided spaced apart from each other in the direction in which the gate electrode 7 extends (the Y direction in Figure 3). The length of the recess 10 in the Y direction (length C) and the length between adjacent recesses 10 in the Y direction (length D) may be equal, or length C may be longer than length D. Also, length D may be longer than length C. The length (L) in the X direction of region A where the recess 10 is provided is shorter than the length B of the PSJ structure, and is preferably half or less of the length B of the PSJ structure. In other words, it is preferable that the recess 10 is provided on the gate electrode 7 side within a region of the third nitride-based semiconductor layer 8 that is half or less of the length B of the PSJ structure. Furthermore, the recess 10 may not be provided on the drain electrode 6 side of the PSJ structure. For example, the region where the recess 10 is not provided may be at least 1 / 3, preferably at least 1 / 2, of the length B of the PSJ structure from the edge of the third nitride-based semiconductor layer 8 on the drain electrode 6 side within the region of the third nitride-based semiconductor layer 8. This increases the concentration of the two-dimensional electron gas on the gate electrode 7 side, allowing the PSJ structure on the drain electrode 6 side to equalize the electric field, suppress the breakdown voltage peak, reduce leakage current at low voltages, and improve on-resistance. Furthermore, the recessed portion 10 may be sandwiched by a third nitride-based semiconductor layer 8 that constitutes part of the PSJ structure, or, when viewed in plan, surrounded by the third nitride-based semiconductor layer 8. Also, when viewed in plan, the total area of ​​the recessed portion 10 on the gate electrode 7 side may be larger than the total area of ​​the recessed portion 10 on the drain electrode 6 side. In addition, as shown in the cross-sectional view of the nitride-based semiconductor device 50 in Figure 1, the recessed portion 10 penetrates the third nitride-based semiconductor layer 8, and the bottom of the recessed portion 10 may be the second nitride-based semiconductor layer 4.

[0019] The recessed portion 10 does not necessarily have to be a through-hole penetrating the third nitride semiconductor layer 8. As shown in the nitride semiconductor device 51 of Modification 2 of the first embodiment in Figure 5, it may be a recessed portion 10a in which a portion of the third nitride semiconductor layer 8 remains on the bottom side in the thickness direction. The recessed portions 10 and 10a are regions in which at least a portion of the third nitride semiconductor layer 8 is not provided, and are regions in which a two-dimensional hole gas layer does not form within the third nitride semiconductor layer 8 or regions in which the concentration of the two-dimensional hole gas is less than in other regions of length B of the third nitride semiconductor layer 8. The recessed portions 10 and 10a are, for example, portions in which grooves or holes are formed that do not penetrate the third nitride semiconductor layer 8, or portions in which grooves or holes that penetrate the third nitride semiconductor layer 8 are provided. By leaving a portion of the third nitride semiconductor layer 8, it is possible to suppress the occurrence of crystal defects etc. on the upper part of the second nitride semiconductor layer 4 directly below the recessed portion 10a, and characteristics such as current collapse and on-resistance can be improved. It is clear that in subsequent descriptions of recessed portion 10, it may be replaced with recessed portion 10a.

[0020] A field plate 11 may be provided above the second nitride-based semiconductor layer 4 between the gate electrode 7 and the drain electrode 6. An insulating film 12, such as a silicon oxide film or silicon nitride film, is provided between the field plate 11 and the third nitride-based semiconductor layer 8 and the recess 10. A similar insulating film 12 may also be provided inside the recess 10. As shown in Figures 1 and 2, the field plate 11 is electrically connected to the source electrode 5, and the wiring 13 of the field plate 11 that is electrically connected to the source electrode 5 is provided so as to straddle the gate electrode 7 or to bypass the side of the gate electrode 7. The field plate 11 and the wiring 13 are made of metal or conductive polysilicon, etc. In the plan view of Figure 3, the range in the x direction in which the field plate 11 is provided is shown, but the field plate 11, insulating film 12 and wiring 13 are omitted. The field plate 11 extends in the direction in which the gate electrode 7 extends (the Y direction in Figure 3). In other words, the field plate 11 is provided above the recessed portion 10 in Figure 1 and above the space between the recessed portions 10 in Figure 2. Multiple field plates 11 may be configured in the Y direction in Figure 3. For example, as shown in the plan view of Figure 4, the field plates 11 are provided above each of the recessed portions 10, and the field plates 11 on adjacent recessed portions 10 may be spaced apart from each other. Incidentally, Figure 4 shows a modified example, illustrating the field plate 11 of Modification 1 of the First Embodiment relative to the plan view of Figure 3. For Modification 1 of the First Embodiment, the cross-sectional structure cut along FF in Figure 4 is the same as in Figure 1, but the cross-sectional structure cut along G-G in Figure 4 differs from the cross-sectional structure in Figure 2, as no field plate 11 is provided. Furthermore, while we have described a structure in which the field plate 11 is wider in the Y direction than the recessed portion 10 in a plan view, the field plate 11 may also be narrower than the recessed portion 10 and provided only in the upper part of the recessed portion 10.

[0021] As shown in Figure 1, the field plate 11 is provided above the recess 10 in the X direction, from the gate electrode 7 side of the gate electrode 7 side of the recess 10, and the gate electrode 7 side end of the field plate 11 may be above the third nitride semiconductor layer 8 which has a PSJ structure. In other words, in a planar view, the region directly below the field plate 11 may be provided so as to include the gate electrode 7 side end of the recess 10. Furthermore, the drain electrode 6 side end or corner of the field plate 11 above the recess 10 is located above the region of the recess 10, and the field plate 11 above the recess 10 does not have to extend to the drain electrode 6 side end of the recess 10. Note that in the X direction, the field plate 11 may be provided only above the region of the recess 10.

[0022] When a potential above a threshold is applied to the gate electrode 7, the depletion layer directly beneath the gate electrode 7 decreases, the two-dimensional electron gas layer becomes conductive, and the nitride semiconductor device 50 turns on. At this time, a two-dimensional hole gas layer is formed within the third nitride semiconductor layer 8, canceling out electrons trapped on the surface of the second nitride semiconductor layer 4 directly beneath and near the PSJ structure of the third nitride semiconductor layer 8. This reduces the current collapse phenomenon of the nitride semiconductor device 50. Here, the concentration of the two-dimensional electron gas layer directly beneath the third nitride-based semiconductor layer 8, which is part of the PSJ structure, decreases to some extent. However, the nitride-based semiconductor device 50 has a recess 10, and there is no two-dimensional hole gas in the recess 10, or less than the surrounding two-dimensional hole gas. Therefore, the concentration of the two-dimensional electron gas layer directly beneath the recess 10 can be increased compared to the concentration of the two-dimensional electron gas layer directly beneath the third nitride-based semiconductor layer 8, which is part of the PSJ structure surrounding the recess 10. This allows for a further reduction in the on-resistance of the nitride-based semiconductor device 50. Furthermore, when viewed in plan view, it is preferable that the recess 10 be provided on the gate electrode 7 side of the PSJ structure rather than the drain electrode 6 side. This would increase the concentration of the two-dimensional electron gas on the gate electrode 7 side of the nitride-based semiconductor device 50, thereby improving the on-resistance.

[0023] On the other hand, when an off signal (for example, a negative potential compared to the source electrode 5) is applied to the gate electrode 7, the carriers in the two-dimensional electron gas layer directly beneath the gate electrode 7 are depleted, and the nitride semiconductor device 50 is turned off. Holes in the two-dimensional hole gas layer within the third nitride semiconductor layer 8 move to the gate electrode 7 and are discharged, reducing the concentration of the two-dimensional hole gas layer within the third nitride semiconductor layer 8. As a result, the electric field strength in the second nitride semiconductor layer 4 beneath the third nitride semiconductor layer 8 in the direction from the gate electrode 7 to the drain electrode 6 (X direction in Figure 2) is made nearly uniform. Therefore, localized increases in electric field strength near the gate electrode 7 are suppressed, and the breakdown voltage of the nitride semiconductor device 50 can be increased. Furthermore, the recessed portion 10 is sandwiched between the third nitride-based semiconductor layer 8, which is part of the PSJ structure, for example in the Y direction in Figure 3. The electric field strength on the surface of the recessed portion 10 is a valley, but due to the influence of the electric field of the third nitride-based semiconductor layer 8, which is part of the PSJ structure, the electric field strength on the surface of the recessed portion 10 rises and becomes relatively smooth. Therefore, the nitride-based semiconductor device 50 can suppress electrons trapped on the surface of the second nitride-based semiconductor layer 4, etc., and reduce the current collapse phenomenon. On the other hand, the electric field strength tends to be high near the drain electrode 6 end of the PSJ structure. Therefore, it is possible to reduce the number of recesses 10 in the drain electrode 6 region, which is the high-electric-field side, and provide more recesses 10 on the gate electrode 7 side of the PSJ structure. Alternatively, the drain electrode 6 side of the PSJ structure may not have recesses 10, and a uniform third nitride semiconductor layer 8 with a thickness in the Y direction may be provided. Furthermore, when viewed in plan, it is preferable that the total area of ​​the recesses 10 is larger on the gate electrode 7 side than on the drain electrode 6 side of the PSJ structure. This makes the electric field distribution in the Y direction on the drain electrode 6 side of the PSJ structure more uniform, reduces leakage current at low voltages, and reduces localized electric field concentration. Furthermore, the end of the field plate 11 on the drain electrode 6 side is positioned above the area of ​​the recess 10, and does not need to extend beyond the recess 10 to the drain electrode 6 side of the third nitride semiconductor layer 8. Since there is a valley in the electric field strength in the area directly below the recess 10, the breakdown voltage of the nitride semiconductor device 50 can be increased by having the area directly below the drain electrode 6 side end of the field plate 11 locally contribute to the electric field.

[0024] From the above, it is possible to provide a nitride-based semiconductor device 50 that reduces on-resistance while achieving high voltage resistance by making the electric field strength nearly uniform.

[0025] For example, in the direction in which the PSJ structure extends (the X direction in Figure 2), if the maximum length of the PSJ structure is Bmax and the length of region A where the recessed portion 10 is provided is L, then L / Bmax may be greater than 1 / 3, less than 1, and less than 1 / 2. Also, if the length of the recessed portion 10 (the length in the Y direction in Figure 2) is C and the length between the recessed portions 10 (the length in the Y direction in Figure 2) is D, then length D may be greater than length C. This makes it possible to provide a nitride-based semiconductor device 50 that reduces on-resistance while achieving high breakdown voltage by making the electric field strength approximately uniform.

[0026] <Second Embodiment> Figure 6 is a cross-sectional view showing a second embodiment of the nitride-based semiconductor device 52 of the present disclosure, and Figure 7 is a plan view showing a second embodiment of the nitride-based semiconductor device 52 of the present disclosure. Figure 6 is a cross-section taken in Figure 7 at a cross-section including the recessed portion 10. Although not particularly limited, as shown in Figures 6 and 7, the gate electrode 7 side end of the recessed portion 10 is provided directly below the drain electrode 6 side end of the P-type semiconductor layer 9. The recessed portion 10 in the X direction is positioned closer to the gate electrode 7 than to the drain electrode 6 side, the length L of the recessed portion 10 in the X direction is shorter than the length B of the PSJ structure, and the recessed portion 10 is provided closer to the gate electrode 7 than to the drain electrode 6 side. Also, in plan view, the total area of ​​the recessed portion 10 on the gate electrode 7 side may be larger than the total area of ​​the recessed portion 10 on the drain electrode 6 side. The end or corner of the field plate 11 on the drain electrode 6 side is located above the area of ​​the recess 10. The end or corner of the field plate 11 on the gate electrode 7 side may be located on the gate electrode 7, and in a plan view, a portion of the field plate 11 on the gate electrode 7 side may overlap with a portion of the gate electrode 7 on the drain electrode 6 side. Here, within the range of the maximum length Bmax of the PSJ structure, it is desirable that there is a region in the third nitride semiconductor layer 8 where the area of ​​the two-dimensional hole gas layer is smaller or where the hole concentration of the two-dimensional hole gas layer is lower than the area (E × Bmax) of the range enclosed and defined by the length of the gate electrode 7 (finger length of the gate electrode 7) E in the direction in which the gate electrode 7 extends (Y direction in Figure 3). As in the modified example of the first embodiment, a field plate 11 may also be provided in each of the multiple recesses 10 in the nitride semiconductor device 52 of the second embodiment. Alternatively, the recess 10 may be a recess 10a in which a portion of the third nitride semiconductor layer 8 remains on the bottom side in the thickness direction.

[0027] The concentration of the two-dimensional electron gas directly below the drain electrode 6 side of the gate electrode 7 is increased compared to the semiconductor device 50 of the first embodiment. The field plate 11 suppresses the electric field concentration on the drain electrode 6 side of the gate electrode 7, and causes a localized portion of the electric field peak to be carried out in the vicinity directly below the drain electrode 6 side of the field plate 11, which is spaced apart from the gate electrode 7. The gate electrode 7 side of the field plate 11 may be closer to the gate electrode 7 than the gate electrode 7 side of the recess 10, and may be above the third nitride semiconductor layer 8. Furthermore, a PSJ structure is provided on the drain electrode 6 side of the field plate 11 to substantially homogenize the electric field strength. Therefore, even in the nitride-based semiconductor device 52 of the second embodiment, it is possible to provide a nitride-based semiconductor device 52 that reduces on-resistance while making the electric field strength substantially uniform and increasing the breakdown voltage.

[0028] <Third Embodiment> FIG. 8 is a cross-sectional view showing a third embodiment of the nitride semiconductor device 53 of the present disclosure, and FIG. 9 is a plan view showing the third embodiment of the nitride semiconductor device 53 of the present disclosure. Although not particularly limited, as shown in FIGS. 8 and 9, a plurality of recessed portions 10b and 10c are provided in the direction from the gate electrode 7 side to the drain electrode 6 side (X direction). Although there are two recessed portions 10b and 10c adjacent to each other in the X direction in FIG. 8, the present invention is not limited to this, and a large number of recessed portions may be formed. Further, in the X direction of FIG. 8, the recessed portion 10b and the recessed portion 10c are arranged alternately like a stagger, but the recessed portion 10b and the recessed portion 10c may be aligned linearly in the X direction. Further, although a plurality of recessed portions 10b and 10c are formed in the direction (Y direction) in which the gate electrode 7 extends, one large recessed portion 10b and 10c may be provided. Further, the recessed portion 10b on the gate electrode 7 side may be formed longer in the X direction than the recessed portion 10c on the drain electrode 6 side (L1>L2), or may be the same (L1 = L2). The recessed portion 10b on the gate electrode 7 side may be shorter in the X direction than the recessed portion 10c on the drain electrode 6 side (L1<L2). The region A in the X direction where the recessed portions 10b and 10c are provided is provided on the gate electrode 7 side rather than on the drain electrode 6 side of the PSJ structure, and when viewed planar, the total area of the recessed portions on the gate electrode 7 side may be wider than the total area of the recessed portions on the drain electrode 6 side.

[0029] The ends or corners of the field plates 11b and 11c on the drain electrode 6 side are located above the respective regions of the recesses 10b and 10c. The field plates 11b and 11c may be formed continuously, in which case the corners that form on the field plate 11b are included as ends. In Figure 8, the field plate 11 corresponding to the upper part of each region of the recesses 10b and 10c has a corner (end) on the drain electrode 6 side. Here, the height h of the field plate is higher for the field plate 11c that is closer to the drain electrode 6 than the field plate 11b, such that the height h1 of the field plate 11b < the height h2 of the field plate 11c. However, the height h of the corners (ends) on the drain electrode 6 side of the field plates 11b and 11c may be the same (h1=h2), or the height h of the field plate may be lower for the field plate 11c that is closer to the drain electrode 6 than the field plate 11b (h1>h2). For example, as shown in the cross-sectional view of Figure 8, the source electrode 5 and each field plate 11b, 11c can be easily adjusted by connecting them with the electrode wiring and the wiring 13 including the through-holes in the insulating film 12 and the wiring inside the through-holes.

[0030] From the above, it is possible to provide a nitride-based semiconductor device 53 that reduces on-resistance while achieving higher voltage resistance by making the electric field strength nearly uniform.

[0031] Furthermore, as in the modified example of the first embodiment, field plates 11b, 11c may be provided in each of the multiple recesses 10b, 10c. Also, at least one of the recesses 10b, 10c may be a recess 10a with a portion of the third nitride-based semiconductor layer 8 remaining on the bottom side in the thickness direction. The depth of the recess 10b may be greater than the depth of the recess 10c.

[0032] <Fourth Embodiment> Figure 10 is a cross-sectional view showing a fourth embodiment of the nitride semiconductor device 54 of the present disclosure, and Figure 11 is a plan view showing a fourth embodiment of the nitride semiconductor device 54 of the present disclosure. Although not particularly limited, as shown in Figures 10 and 11, a fourth nitride semiconductor layer 8b, 8c is provided on the second nitride semiconductor layer 4 on the drain electrode 6 side, spaced apart from the third nitride semiconductor layer 8, and a two-dimensional hole gas layer (two-dimensional hole gas layer) is generated in the fourth nitride semiconductor layer 8b, 8c near the interface between the second nitride semiconductor layer 4 and the fourth nitride semiconductor layer by spontaneous polarization, piezoelectric polarization, or both. For example, the fourth nitride semiconductor layer 8b, 8c is made of undoped GaN, the same as the third nitride semiconductor layer 8. The length Bmax in the X direction of the portion of nitride semiconductor device 54 that includes the third nitride semiconductor layer 8 and the fourth nitride semiconductor layers 8b and 8c corresponds to the length B in the X direction of the third nitride semiconductor layer 8 of nitride semiconductor device 50. As shown in Figures 10 and 11, the divided portions 10d and 10e function like depressions 10, and the concentration of the two-dimensional electron gas directly beneath the divided portions 10d and 10e is relatively higher than that directly beneath the third nitride semiconductor layer 8.

[0033] On the fourth nitride semiconductor layers 8b and 8c, there are second p-type semiconductor layers 9a and 9b, which, like the p-type semiconductor layer 9, are made of a p-type nitride semiconductor such as p-GaN or p-InGaN, or NiO, and auxiliary electrodes 7a and 7b are located on the second p-type semiconductor layer. The auxiliary electrodes 7a and 7b are electrically connected to the gate electrode 7. It is preferable that the length of the fourth nitride semiconductor layer 8c directly beneath the auxiliary electrode 7b extending toward the drain electrode 6 side (X direction) is longer than the length of the third nitride semiconductor layer 8 directly beneath the gate electrode 7 extending toward the drain electrode 6 side (X direction). The length of the fourth nitride semiconductor layer 8c directly beneath the auxiliary electrode 7b extending toward the drain electrode 6 side (X direction) may be 1 / 3 or more, preferably 1 / 2 or more, of the maximum length Bmax of the PSJ structure. The length of the fourth nitride-based semiconductor layer 8b directly beneath the auxiliary electrode 7a extending toward the drain electrode 6 side (X direction) may be longer than the length of the third nitride-based semiconductor layer 8 directly beneath the gate electrode 7 extending toward the drain electrode 6 side (X direction). The drain electrode 6 side end of the field plate 11c is located above the space between the third nitride semiconductor layer 8 and the fourth nitride semiconductor layer, and it is preferable that the field plate 11c extends above the third nitride semiconductor layer 8. In other words, the gate electrode 7 side end of the field plate 11c is located on the third nitride semiconductor layer 8. The drain electrode 6 side end of the field plate 11d is located above the space between the fourth nitride semiconductor layer 8b and the fourth nitride semiconductor layer 8c, and it is preferable that the field plate 11d extends above the fourth nitride semiconductor layer 8b. In other words, the gate electrode 7 side end of the field plate 11d is located on the fourth nitride semiconductor layer 8b.

[0034] From the above, it is possible to provide a nitride-based semiconductor device 54 that reduces on-resistance while achieving higher voltage resistance by making the electric field strength nearly uniform.

[0035] Furthermore, as in the modified example of the first embodiment, at least one of the spaces between the third nitride-based semiconductor layer 8 and the fourth nitride-based semiconductor layer 8b, or between the fourth nitride-based semiconductor layers 8b and 8c, may be a recessed portion 10a, or they may be connected to each other by a thin third nitride-based semiconductor layer 8. Furthermore, in the nitride-based semiconductor devices of the first to third embodiments, the recessed portion 10 may be circular instead of rectangular, as shown in the plan view of Figure 12, or it may be a polygonal recessed portion 10. Also, as shown in the plan view of Figure 13, it is clear that in the nitride-based semiconductor devices of the first to third embodiments, the width of the recessed portion 10 in the Y direction may be formed to be narrower on the drain electrode 6 side compared to the gate electrode 7 side. [Explanation of symbols]

[0036] 1 circuit board 2 buffer layers 3. First Nitride Semiconductor Layer 4. Second Nitride Semiconductor Layer 5. Source electrode (second main electrode) 6. Second drain electrode (first main electrode) 7 Airports 8. Third Nitride Semiconductor Layer 9 P-type semiconductor layer 10 Recessed area 11 Field Plate 12 Insulating layer 13 Wiring 50, 51, 52, 53, 54 Nitride-based semiconductor equipment

Claims

1. A first nitride-based semiconductor layer having a two-dimensional electron gas layer on top, A second nitride-based semiconductor layer is provided on the first nitride-based semiconductor layer and has a band gap larger than the band gap of the first nitride-based semiconductor layer, A third nitride-based semiconductor layer is provided on the second nitride-based semiconductor layer and is made of a nitride-based semiconductor material having a smaller bandgap energy than the second nitride-based semiconductor layer, and the third nitride-based semiconductor layer has a two-dimensional hole gas layer formed near the interface with the second nitride-based semiconductor layer, The P-type semiconductor layer on the third nitride-based semiconductor layer, The first main electrode on the high-potential side is electrically connected to the two-dimensional electron gas layer, A second main electrode on the low-potential side, electrically connected to the two-dimensional electron gas layer, A control electrode is located on the first nitride-based semiconductor layer between the first main electrode and the second main electrode, and is electrically connected to the P-type semiconductor layer. A recess provided in the third nitride-based semiconductor layer, A field plate electrically connected to the second main electrode and having the end on the first main electrode side above the region of the recess, A nitride-based semiconductor device characterized by containing [the specified material].

2. Viewed in two dimensions, The nitride-based semiconductor device according to claim 1, characterized in that the total area of ​​the recessed region is wider on the control electrode side than on the first main electrode side.

3. Viewed in two dimensions, The nitride-based semiconductor device according to claim 1, characterized in that a plurality of recesses in the third nitride-based semiconductor layer are arranged spaced apart from each other in the direction of extension of the control electrode.

4. The field plates are provided in each of the recessed portions, The nitride-based semiconductor device according to claim 3, characterized in that the field plates on adjacent recesses are spaced apart from each other.

5. The nitride semiconductor device according to claim 1, characterized in that the recess is provided directly below the first main electrode side end of the P-type semiconductor layer.

6. The nitride-based semiconductor device according to claim 1, characterized in that a plurality of recesses are provided, each at a different distance from the first main electrode side.

7. Multiple recesses are provided, each at a different distance from the first main electrode side. The nitride semiconductor device according to claim 1, characterized in that the field plate has the first main electrode side end provided at the upper part of the recessed area.

8. A first nitride-based semiconductor layer having a two-dimensional electron gas layer on top, A second nitride-based semiconductor layer is provided on the first nitride-based semiconductor layer and has a band gap larger than the band gap of the first nitride-based semiconductor layer, A third nitride-based semiconductor layer is provided on the second nitride-based semiconductor layer and is made of a nitride-based semiconductor material having a smaller bandgap energy than the second nitride-based semiconductor layer, and the third nitride-based semiconductor layer has a two-dimensional hole gas layer formed near the interface with the second nitride-based semiconductor layer, The first P-type semiconductor layer on the third nitride-based semiconductor layer, The first main electrode on the high-potential side is electrically connected to the two-dimensional electron gas layer, A second main electrode on the low-potential side, electrically connected to the two-dimensional electron gas layer, A control electrode is located on the first nitride-based semiconductor layer between the first main electrode and the second main electrode, and is electrically connected to the first P-type semiconductor layer. A fourth nitride-based semiconductor layer is provided on the second nitride-based semiconductor layer, spaced apart from the third nitride-based semiconductor layer, and is made of a nitride-based semiconductor material having a smaller bandgap energy than the second nitride-based semiconductor layer, and the fourth nitride-based semiconductor layer has a two-dimensional hole gas layer formed near the interface with the second nitride-based semiconductor layer, The second P-type semiconductor layer on the fourth nitride-based semiconductor layer, On the second P-type semiconductor layer, an auxiliary electrode electrically connected to the control electrode, A field plate electrically connected to the second main electrode and having the first main electrode side end located above the region between the third nitride-based semiconductor layer and the fourth nitride-based semiconductor layer, A nitride-based semiconductor device characterized by containing [the specified material].

9. A first nitride-based semiconductor layer having a two-dimensional electron gas layer on top, A second nitride-based semiconductor layer is provided on the first nitride-based semiconductor layer and has a band gap larger than the band gap of the first nitride-based semiconductor layer, A third nitride-based semiconductor layer is provided on the second nitride-based semiconductor layer and is made of a nitride-based semiconductor material having a smaller bandgap energy than the second nitride-based semiconductor layer, and the third nitride-based semiconductor layer has a two-dimensional hole gas layer formed near the interface with the second nitride-based semiconductor layer, The P-type semiconductor layer on the third nitride-based semiconductor layer, The first main electrode on the high-potential side is electrically connected to the two-dimensional electron gas layer, A second main electrode on the low-potential side, electrically connected to the two-dimensional electron gas layer, A control electrode is located on the first nitride-based semiconductor layer between the first main electrode and the second main electrode, and is electrically connected to the P-type semiconductor layer. Viewing the region of the third nitride-based semiconductor layer between the first main electrode and the control electrode in a plan view, a recess is provided in the third nitride-based semiconductor layer on the control electrode side, A nitride-based semiconductor device characterized by containing [the specified material].

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