A nitrogen-polar gallium nitride high electron mobility transistor and a preparation method thereof

Abstract

The present invention provides a nitrogen-polar nitride high electron mobility transistor and a preparation method thereof, belonging to the technical field of semiconductor devices. The transistor sequentially includes a substrate, a nucleation layer, a semi-insulating layer, a buffer layer, a doping layer, and a ridge mesa structure from bottom to top, as well as a source electrode, a drain electrode, and a gate electrode; the ridge mesa structure includes a back barrier layer and a channel layer from bottom to top. On one side of the ridge mesa structure, the source electrode extends from the upper surface of the channel layer along the side wall of the ridge mesa structure to the upper surface of the doping layer; on the other side of the ridge mesa structure, the drain electrode extends from the upper surface of the channel layer along the side wall of the ridge mesa structure to the upper surface of the doping layer. The gate electrode is located between the source electrode and the drain electrode. The direction from the substrate to the channel layer is the nitrogen-polar crystal orientation. This device structure can suppress the current collapse phenomenon caused by the back barrier-like donor state trap charges, improve the confinement effect of the back barrier on the channel electrons and reduce the on-resistance, thereby improving the device performance and reliability.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices, and particularly relates to a nitrogen-polarity gallium nitride high electron mobility transistor and a preparation method thereof. Background Art

[0002] Gallium nitride high electron mobility transistors (GaN HEMTs) have the characteristics of high power, high operating frequency, and high breakdown voltage. Radio frequency power amplifier devices fabricated using GaN HEMTs have been applied in fields such as 5G base stations and radar detection. Gallium nitride (GaN) is a polar material, having the characteristics of gallium (Ga) polarity and nitrogen (N) polarity along the c-axis crystal direction. Conventional GaN HEMT radio frequency power amplifier devices are all fabricated on the Ga-polarity surface. However, it has been found that GaN HEMT radio frequency power amplifier devices fabricated on the N-polarity surface have a power density 2-3 times that of Ga-polarity HEMT devices and a higher power added efficiency at the same operating frequency. Since the manufacturing process of N-polarity GaN devices is different from that of Ga-polarity HEMTs, and the preparation of high-quality N-polarity GaN materials has always faced great challenges, therefore, only a few research institutions can realize high-performance N-polarity GaN HEMT power amplifier devices, and commercialization has not been achieved yet. In addition, the reliability of N-polarity GaN power amplifier devices is also an important factor restricting their commercialization. The reliability problems are mainly manifested as gate leakage and threshold drift problems caused by interface states between the metal gate and the dielectric, and current collapse problems caused by deep-level traps existing in the back barrier interface.

[0003] As Figure 1 shown Figure 1 Figure (a) in Figure 1 is an epitaxial structure of an N-polarity GaN HEMT device, and Figure 2 Figure (b) in

[0004] is the energy band diagram corresponding to the structure in Figure (a). Due to the polarization electric field effect, there is a two-dimensional electron gas at the interface between the surface GaN channel layer 106 and the AlGaN (aluminum gallium nitride) back barrier layer; while at the interface between the AlGaN back barrier layer 105 and the GaN layer 102, there are donor-like interface traps near the valence band. Due to polarization-induced band bending, some of the donor-like interface traps at this interface are ionized, thereby inducing more two-dimensional electron gas in the channel. Therefore, the two-dimensional electron gas concentration is regulated by the donor-like states at the back barrier interface. When the device operates dynamically, the ionization speed of the donor-like states may not be able to keep up with the change of the input signal frequency, resulting in the two-dimensional electron gas concentration not being able to be replenished by the electrons contributed by the donor-like states in time, and finally resulting in the dynamic output current being less than the static output current (as Figure 3As shown in Figure (a), in order to eliminate the current collapse phenomenon caused by the trap charges of the back-barrier-like donor states, the most direct technical solution is to replace the GaN layer under the AlGaN back-barrier layer 105 with an aluminum nitride (AlN) layer having a larger bandgap than the AlGaN back-barrier layer 105, that is, to completely use an AlN substrate 101 to grow an N-polar GaN HEMT device structure. Figure 3 Figure (b) in Figure 3 is the energy band diagram corresponding to the structure in Figure (a) in Figure 3 It can be seen from

[0005] that since there is no AlGaN / GaN interface under the back-barrier, this method can completely eliminate the influence caused by the donor-like trap charges. Moreover, since the substrate is AlN, the thermal conductivity and high-voltage resistance performance of the device can be further improved. However, since high-quality single-crystal AlN substrates are still difficult to obtain, their crystal growth is relatively difficult, resulting in a very high substrate cost, a relatively high impurity content in the substrate, and a relatively small size (not exceeding 2 inches). In addition, it is difficult to grow an N-polar AlGaN layer with a high Al content on an AlN substrate, and a very high growth temperature is required to reduce the impurity content and obtain a smooth surface morphology, which also leads to a very high production cost and is not conducive to the commercialization of N-polar GaN RF power amplifier devices.

[0005] Another method to suppress the influence of the back-barrier interface donor-like trap charges is to perform n-type doping on the back-barrier layer and the GaN thin layer under the back-barrier layer. As Figure 4 shown in Figure (a), below the AlGaN back-barrier layer 105, there is also an n-type doped AlGaN back-barrier layer 104 and an n-type doped GaN thin layer 103, and the Al content in the n-type doped AlGaN back-barrier layer 104 decreases gradually from the surface to the inside. As Figure 4 shown in Figure (b), through such a structural design, the Fermi level near the back-barrier interface is modulated away from the valence band level, thereby reducing the ionization degree of the interface donor-like trap charges, and thus reducing the influence of the donor-like trap charges on the two-dimensional electron gas in the channel. Figure 5 The output current of the N-polar GaN HEMT device with the structure in Figure 4 Figure (a) during dynamic and static operations is shown. It can be seen from the figure that the current collapse effect has been significantly suppressed. However, the Fermi level is more sensitive to the doping concentration and the thickness of the doped region of the back-barrier layer, and there is a certain threshold value. Only when it is higher than this threshold value, the Fermi level may be modulated away from the valence band position. In the actual epitaxial growth process, the existing process instability and non-uniformity have a greater impact on the performance of the device. As Figure 6 shown, when the doping concentration of the back-barrier layer is <8×10 18 / cm 3When the doping concentration is at a certain level, the Fermi level is still very close to the valence band top at the AlGaN / GaN interface of the back barrier. Only when the doping concentration exceeds this value can the Fermi level be modulated to be close to the conduction band bottom. When the doping concentration is around 8.5×10 18 / cm 3 , a doping concentration fluctuation of ±3% will cause a large range of changes in the Fermi level position from 0.5 - 0.7 eV. In addition, this method also reduces the AlGaN back barrier height (as shown in Figure 6 ). When the Fermi level is modulated to be close to the conduction band, its barrier height decreases from 4.15 eV to 2.1 eV. Therefore, the confinement and blocking effects on the two-dimensional electron gas in the channel become weaker. SUMMARY OF THE INVENTION

[0006] In order to solve the deficiencies in the prior art, the present invention provides a nitrogen-polarity gallium nitride high electron mobility transistor. This gallium nitride high electron mobility transistor can suppress the current collapse phenomenon caused by the donor-like trap charges in the back barrier, and at the same time can improve the confinement effect of the back barrier on the channel electrons and reduce the on-resistance of the device, thereby improving the device performance and reliability.

[0007] Specifically, in order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A nitrogen-polarity nitride high electron mobility transistor includes a substrate, a nucleation layer, a semi-insulating layer, a buffer layer, a doping layer, a ridge mesa structure, as well as a source electrode, a drain electrode, and a gate electrode from bottom to top in sequence; the ridge mesa structure includes a back barrier layer and a channel layer from bottom to top, the bottom surface of the back barrier layer is the bottom surface of the ridge mesa structure, and the upper surface of the channel layer is the upper surface of the ridge mesa structure; there is a two-dimensional electron gas at the interface between the channel layer and the back barrier layer; on one side of the ridge mesa structure, the source electrode extends from the upper surface of the channel layer along the side wall of the ridge mesa structure to the upper surface of the doping layer; on the other side of the ridge mesa structure, the drain electrode extends from the upper surface of the channel layer along the side wall of the ridge mesa structure to the upper surface of the doping layer; the gate electrode is located on the channel layer between the source electrode and the drain electrode; the materials of the semi-insulating layer, the buffer layer, the doping layer, the back barrier layer, and the channel layer are all nitride semiconductor materials of group IIIA elements; the doping type of the doping layer is n-type; the direction from the substrate to the channel layer is the nitrogen-polarity crystal orientation.

[0009] As a preferred embodiment of the present invention, the nitride semiconductor material of group IIIA elements is any one of AlN, GaN, AlGaN, InN, and InGaN.

[0010] As a preferred embodiment of the present invention, the width of the upper surface of the ridge mesa structure ≤ the width of the bottom surface of the ridge mesa structure.

[0011] As a further preferred embodiment of the present invention, the included angle between the side wall and the bottom surface of the ridge mesa structure is 50° - 60°.

[0012] As a preferred embodiment of the present invention, the material of the nucleation layer is at least one of GaN, AlN, and AlGaN.

[0013] As a preferred embodiment of the present invention, the band gap widths of the materials of the semi-insulating layer, the buffer layer, the doped layer, and the channel layer are smaller than the band gap width of the material of the back barrier layer.

[0014] As a preferred embodiment of the present invention, the doping element of the doped layer is any one of Si, Ge, and Sn, and the doping concentration is 1×10 18 / cm 3 ~1×10 20 / cm 3 .

[0015] As a preferred embodiment of the present invention, the material of the back barrier layer is an aluminum-containing nitride semiconductor material, and along the direction from the channel layer to the doped layer, the aluminum content in the back barrier layer decreases.

[0016] As a preferred embodiment of the present invention, the doping type of the back barrier layer is n-type, and the doping concentration ≤ 5×10 18 / cm 3 .

[0017] As a preferred embodiment of the present invention, ohmic contact layers are provided on the side walls of the ridge mesa structure and the upper surface of the doped layer that is not in contact with the back barrier layer. The material of the ohmic contact layer is an indium-containing nitride semiconductor material, and both the source electrode and the drain electrode form ohmic contacts with the ohmic contact layer.

[0018] As a further preferred embodiment of the present invention, the material of the ohmic contact layer is an indium-containing nitride semiconductor material.

[0019] As a preferred embodiment of the present invention, the substrate is any one of a silicon substrate, a silicon carbide substrate, a sapphire substrate, a gallium nitride substrate, or an aluminum nitride single crystal substrate.

[0020] The present invention also provides a method for manufacturing a nitrogen-polar nitride high electron mobility transistor according to any one of the above-described solutions, including the following steps:

[0021] A nucleation layer, a semi-insulating layer, a buffer layer, a doping layer, a back barrier layer, and a channel layer are sequentially epitaxially grown on a substrate;

[0022] A gate electrode is fabricated on the surface of the channel layer away from the back barrier layer;

[0023] A ridge mesa structure is fabricated by etching both sides of the back barrier layer and the channel layer;

[0024] On one side of the gate electrode, a source electrode is fabricated from the surface of the ridge mesa structure along the sidewall of the ridge mesa structure to the surface of the doping layer away from the buffer layer; on the other side of the gate electrode, a drain electrode is fabricated from the surface of the ridge mesa structure along the sidewall of the ridge mesa structure to the surface of the doping layer away from the buffer layer.

[0025] As a preferred embodiment of the present invention, the preparation method further includes the following steps: after the ridge mesa structure is fabricated, a secondary epitaxy method is used to grow an ohmic contact layer on the sidewall of the ridge mesa structure and the upper surface of the doping layer not in contact with the back barrier layer. The material of the ohmic contact layer is an indium-containing nitride semiconductor material.

[0026] Compared with the prior art, the present invention has the following beneficial effects: (1) In the device structure of the present invention, since the source electrode extends from the upper surface of one side of the channel layer along the sidewall of the ridge mesa structure on the same side to the upper surface of the doping layer on the same side, and the drain electrode extends from the upper surface of the other side of the channel layer along the sidewall of the ridge mesa structure on that side to the upper surface of the doping layer, both the source electrode and the drain electrode are in direct contact with the two-dimensional electron gas in the channel, not only forming a good ohmic contact, but also reducing the contact resistance to a certain extent; thus, compared with the prior art, the device structure of the present invention has a higher output current and output transconductance. (2) In the device structure of the present invention, the back barrier layer is further doped at a low concentration, which is more conducive to forming an ohmic contact on the sidewall of the ridge mesa structure while still maintaining a high back barrier height, so compared with the prior art, the blocking effect on electrons is more effective. (3) The device structure of the present invention can effectively suppress the current collapse effect of the nitrogen-polarity device during high-frequency dynamic operation. Description of the Drawings

[0027] Figure 1 It is an epitaxial structure and energy band diagram of an N-polarity GaN HEMT device in the prior art;

[0028] Figure 2 It is for having Figure 1 The output current curve diagram of the N-polarity GaN HEMT device with the epitaxial structure in

[0029] Figure 3The epitaxial structure (using AlN as the substrate) and energy band diagram of another N-polarity GaN HEMT device in the prior art;

[0030] Figure 4 The epitaxial structure (with doping in the back barrier layer) and energy band diagram of another N-polarity GaN HEMT device in the prior art;

[0031] Figure 5 For having Figure 4 The output current curve diagram of the N-polarity GaN HEMT device with the epitaxial structure in

[0032] Figure 6 For having Figure 4 The change relationship between the energy difference (Ef - Ev) between the Fermi level and the valence band top position at the back barrier AlGaN / GaN interface and the back barrier height and the doping concentration of the back barrier layer of the N-polarity GaN HEMT device with the epitaxial structure in

[0033] Figure 7 The structural schematic diagram of a nitrogen-polarity gallium nitride high electron mobility transistor provided in the embodiment of the present invention;

[0034] Figure 8 The structural schematic diagram of another nitrogen-polarity gallium nitride high electron mobility transistor provided in the embodiment of the present invention;

[0035] Figure 9 The process schematic diagram of a preparation method of a nitrogen-polarity gallium nitride high electron mobility transistor provided in the embodiment of the present invention;

[0036] Figure 10 The structural schematic diagram of the nitrogen-polarity gallium nitride high electron mobility transistor provided in the comparative example;

[0037] Figure 11 The test result diagram of the high voltage stress of the drain electrode of the HEMT in the embodiment and the HEMT in the comparative example;

[0038] Figure 12 The energy band diagram from the channel layer to the semi-insulating layer of the HEMT in the embodiment;

[0039] Figure 13 The comparison diagram of the output current (Id) and transconductance (Gm) curves of the HEMT in the embodiment and the HEMT in the comparative example.

[0040] In the figure: 1. Substrate; 2. Nucleation layer; 3. Semi-insulating layer; 4. Buffer layer; 5. Doping layer; 6. Back barrier layer; 7. Channel layer; 8. Source electrode; 9. Drain electrode; 10. Gate electrode; 11. Two-dimensional electron gas; 12. Ohmic contact layer; 101. AlN substrate; 102. GaN layer; 103. n-type doped GaN thin layer; 104. n-type doped AlGaN back barrier layer; 105. AlGaN back barrier layer; 106. GaN channel layer; α. Included angle. Detailed implementation manners

[0041] The following content describes the technical solutions of the present invention clearly and completely in conjunction with embodiments, so that those skilled in the art can fully understand the present invention. Obviously, the described embodiments are only some preferred embodiments of the present invention, rather than all embodiments. Any equivalent transformation or substitution made by those of ordinary skill in the art without creative efforts to the following implementation manners shall fall within the protection scope of the present invention.

[0042] Directional terms mentioned in this article, such as "from bottom to top", "upward", "upper surface", "bottom surface", and the like, refer to the directions in the drawings. Therefore, the directional terms are only for illustration and not for limiting the present invention. The methods not described in detail in the following embodiments are all conventional methods well known to those skilled in the art.

[0043] Embodiment

[0044] As Figure 7 shown, an embodiment of the present invention provides a nitrogen-polar nitride high electron mobility transistor (HEMT), which sequentially includes a substrate 1, a nucleation layer 2, a semi-insulating layer 3, a buffer layer 4, a doping layer 5, and a ridge mesa structure from bottom to top, as well as a source electrode 8, a drain electrode 9, and a gate electrode 10. The ridge mesa structure includes a back barrier layer 6 and a channel layer 7 from bottom to top. The bottom surface of the back barrier layer 6 is the bottom surface of the ridge mesa structure, and the upper surface of the channel layer 7 is the upper surface of the ridge mesa structure. There is a two-dimensional electron gas 11 at the interface between the channel layer 7 and the back barrier layer 6. On one side of the ridge mesa structure, the source electrode 8 extends from the upper surface of the channel layer 7 along the side wall of the ridge mesa structure to the upper surface of the doping layer 5. On the other side of the ridge mesa structure, the drain electrode 9 extends from the upper surface of the channel layer 7 along the side wall of the ridge mesa structure to the upper surface of the doping layer 5. The gate electrode 10 is located on the channel layer 7 between the source electrode 8 and the drain electrode 9. Among them, the materials of the semi-insulating layer 3, the buffer layer 4, the doping layer 5, the back barrier layer 6, and the channel layer 7 are all nitride semiconductor materials of group IIIA elements. The doping type of the doping layer 5 is n-type. The direction from the substrate 1 to the channel layer 7 is the nitrogen-polar crystal orientation.

[0045] Further, the included angle α between the side wall and the bottom surface of the ridge-shaped mesa structure satisfies α ≤ 90°, that is, the width of the upper surface of the ridge-shaped mesa structure ≤ the width of the bottom surface of the ridge-shaped mesa structure. For example, α is 90°, 80°, 70°, 65°, 60°, 55°, 50°, 45°...

[0046] Furthermore, the included angle α between the side wall and the bottom surface of the ridge-shaped mesa structure is 50° - 60°.

[0047] Further, the nitride semiconductor material of the Group IIIA element is any one of AlN, GaN, AlGaN, InN, and InGaN. For example, the material of the semi-insulating layer 3 is GaN, the material of the buffer layer 4 is GaN, the material of the doping layer 5 is GaN, the material of the back barrier layer 6 is AlGaN, and the material of the channel layer 7 is GaN.

[0048] Further, the material of the nucleation layer 2 is at least one of GaN, AlN, and AlGaN.

[0049] Further, the doping element of the doping layer 5 is any one of Si, Ge, and Sn, and the doping concentration is 1×10 18 / cm 3 ~1×10 20 / cm 3 . For example, the doping element of the doping layer 5 is Si, and the doping concentration is 1×10 18 / cm 3 、2×10 18 / cm 3 、3×10 18 / cm 3 、4×10 18 / cm 3 ……4×10 19 / cm 3 ……1×10 20 / cm 3 .

[0050] Further, the doping type of the back barrier layer 6 is n-type, and the doping concentration ≤ 5×10 18 / cm 3 . For example, the doping concentration is 5×10 18 / cm 3 、4×10 18 / cm 3 、3×10 18 / cm 3 ……5×10 17 / cm 3 ……5×10 16 / cm 3 、3×10 16 / cm3 ……

[0051] Further, the material of the back barrier layer 6 is an aluminum-containing nitride semiconductor material, and along the direction from the channel layer 7 to the doping layer 5, the aluminum content in the back barrier layer 6 decreases. For example, the material of the back barrier layer 6 close to the channel layer 7 (i.e., the upper layer of the back barrier layer 6) is AlN, and the material of the back barrier layer 6 close to the doping layer 5 (i.e., the bottom layer of the back barrier layer 6) is Al 0.1 Ga 0.9 N.

[0052] Further, as Figure 8 shown, ohmic contact layers 12 are provided on the sidewalls of the ridge mesa structure and the upper surfaces of the doping layer 5 that are not in contact with the back barrier layer 6. The source electrode 8 and the drain electrode 9 both form ohmic contacts with the ohmic contact layer 12. The material of the ohmic contact layer 12 is an indium-containing nitride semiconductor material. For example, the material of the ohmic contact layer 12 is In 0.1 Ga 0.9 N.

[0053] Further, the substrate 1 is any one of a silicon substrate, a silicon carbide substrate, a sapphire substrate, and a gallium nitride substrate. For example, the substrate 1 is a silicon substrate.

[0054] As Figure 9 shown, an embodiment of the present invention further provides a method for manufacturing a nitrogen-polar nitride high electron mobility transistor, including the following steps:

[0055] Epitaxially grow a nucleation layer 2, a semi-insulating layer 3, a buffer layer 4, a doping layer 5, a back barrier layer 6, and a channel layer 7 on the substrate 1 in sequence;

[0056] Deposit gate metal on the upper surface of the obtained structure and etch it to obtain a gate electrode 10;

[0057] Use plasma dry etching on both sides of the back barrier layer 6 and the channel layer 7 to fabricate a ridge mesa structure; deposit source metal on the upper surface of the obtained device structure and etch it, retaining the source metal on one side of the gate electrode 10 from the surface of the ridge mesa structure along the sidewalls of the ridge mesa structure to the surface of the doping layer 5 far from the buffer layer 4 to obtain a source electrode;

[0058] Deposit drain metal on the upper surface of the obtained device structure and etch it, retaining the drain metal on the other side of the gate electrode 10 from the surface of the ridge mesa structure along the sidewalls of the ridge mesa structure to the surface of the doping layer 5 far from the buffer layer 4 to obtain a drain electrode.

[0059] Further, after fabricating the ridge mesa structure, use the secondary epitaxy method to grow the ohmic contact layer 12 on the sidewalls of the ridge mesa structure and the upper surfaces of the doping layer 5 that are not in contact with the back barrier layer 6.

[0060] Comparative Example

[0061] As Figure 10 shown, this comparative example provides a nitrogen-polar nitride high electron mobility transistor, which sequentially includes a substrate 1, a semi-insulating layer 3, a buffer layer 4, a back barrier layer 6, and a channel layer 7 from bottom to top, as well as a source electrode 8, a drain electrode 9, and a gate electrode 10. There is a two-dimensional electron gas 11 at the interface between the channel layer 7 and the back barrier layer 6. The source electrode 8 and the drain electrode 9 are respectively located on both sides of the upper surface of the channel layer 7, and the gate electrode 10 is located on the channel layer 7 between the source electrode 8 and the drain electrode 9.

[0062] Performance Test

[0063] In the structure of the HEMT provided by the embodiment, the substrate is a silicon substrate; the material of the nucleation layer is GaN; the material of the semi-insulating layer is GaN; the material of the buffer layer is GaN; the material of the doping layer is GaN, the doping element is Si, and the doping concentration is 1×10 19 / cm 3 ; the material of the back barrier layer is undoped AlGaN; the material of the channel layer is GaN; the material of the drain electrode is a four-layer metal layer of Ti / Al / Ni / Au, the material of the gate electrode is a two-layer metal layer of Ni / Au, and the material of the source electrode is a four-layer metal layer of Ti / Al / Ni / Au. The materials of the respective elements in the structure of the HEMT provided by the comparative example are the same as those of the corresponding elements in the HEMT structure provided by the foregoing embodiment.

[0064] Figure 11 It is a test result diagram of the high-voltage stress of the drain electrode of the HEMT (without ohmic contact layer) provided in the embodiment and the HEMT provided in the comparative example. From Figure 11 it can be seen that before and after the test, the output current of the HEMT in the comparative example decreased by 14%, while the output current of the HEMT in the embodiment hardly changed. This shows that the HEMT in the present invention can effectively suppress the current collapse effect caused by the donor-like trap charges at the back barrier interface during the high-frequency dynamic operation of the nitrogen-polar devices.

[0065] Figure 12 It is the energy band diagram from the channel layer to the semi-insulating layer of the HEMT in the embodiment. From the figure, it can be seen that the energy band height of the undoped back barrier layer can maintain a very high level, and the blocking effect on the channel electrons is better. Therefore, even under a high electric field strength, the electrons in the channel layer are not easily driven into the buffer layer or the semi-insulating layer and trapped by the deep-level traps therein, which is beneficial to improving the reliability of the HEMT device.

[0066] Figure 13Comparison graph of output current (Id) and transconductance (Gm) curves of HEMT of the embodiment and HEMT of the comparative example. As can be seen from the figure, the HEMT of the embodiment has a larger output current and transconductance than the HEMT of the comparative example. This is because, in the structure of the comparative example, the source and drain electrodes of the device are electrically connected to the two-dimensional electron gas in the channel through the surface of the channel layer; while in the structure of the embodiment, in addition to a part of the source electrode and the drain electrode contacting the surface of the channel layer on the upper surface of the ridge mesa structure, there is also a part directly contacting the two-dimensional electron gas channel on the side wall of the ridge mesa structure. Therefore, it has a smaller contact resistance. When the back barrier layer is doped with n-type at a certain concentration, or / and an indium-containing nitride semiconductor layer is regrown on the side wall of the ridge mesa structure as an ohmic contact layer, it is more conducive to reducing the contact resistance between the source electrode and the drain electrode.

[0067] The above are only the preferred embodiments of the present invention and are not used to limit the protection scope of the present invention. For any person skilled in the art, various changes and modifications can be made to the present invention. Any simple equivalent changes and modifications made according to the protection scope of the present invention application and the content of the specification shall be included in the protection scope of the present invention.

Claims

1. A nitrogen-polar nitride high electron mobility transistor, characterized in that, It includes a substrate, a nucleation layer, a semi-insulating layer, a buffer layer, a doping layer, a ridge mesa structure, a source electrode, a drain electrode, and a gate electrode in sequence from bottom to top; the ridge mesa structure includes a back barrier layer and a channel layer from bottom to top, the bottom surface of the back barrier layer is the bottom surface of the ridge mesa structure, and the upper surface of the channel layer is the upper surface of the ridge mesa structure; there is a two-dimensional electron gas at the interface between the channel layer and the back barrier layer; on one side of the ridge mesa structure, the source electrode extends from the upper surface of the channel layer along the side wall of the ridge mesa structure to the upper surface of the doping layer; on the other side of the ridge mesa structure, the drain electrode extends from the upper surface of the channel layer along the side wall of the ridge mesa structure to the upper surface of the doping layer; the gate electrode is located on the channel layer between the source electrode and the drain electrode; the materials of the semi-insulating layer, the buffer layer, the doping layer, the back barrier layer, and the channel layer are all nitride semiconductor materials of group IIIA elements; the doping type of the doping layer is n-type; the direction from the substrate to the channel layer is the nitrogen-polar crystal orientation.

2. The nitrogen-polar nitride high electron mobility transistor according to claim 1, characterized in that, The width of the upper surface of the ridge mesa structure ≤ the width of the bottom surface of the ridge mesa structure.

3. The nitride polar nitride high electron mobility transistor according to claim 1, characterized in that, The material of the nucleation layer is at least one of GaN, AlN, and AlGaN.

4. The nitrogen-polar nitride high electron mobility transistor according to claim 1, characterized in that The band gap widths of the materials of the semi-insulating layer, the buffer layer, the doping layer, and the channel layer are smaller than the band gap width of the material of the back barrier layer.

5. The nitrogen-polar nitride high electron mobility transistor according to claim 1, wherein The doping element of the doping layer is any one of Si, Ge, and Sn, and the doping concentration is 1×10 18 / cm 3 ~1×10 20 / cm 3 .

6. The nitrogen-polar nitride high electron mobility transistor according to claim 1, characterized in that, The material of the back barrier layer is an aluminum-containing nitride semiconductor material, and along the direction from the channel layer to the doping layer, the aluminum content in the back barrier layer decreases.

7. The nitride polar nitride high electron mobility transistor according to claim 1, wherein The doping type of the back barrier layer is n-type, and the doping concentration ≤ 5×10 18 / cm 3 .

8. The nitrogen-polar nitride high electron mobility transistor according to claim 1, wherein Ohmic contact layers are provided on the side walls of the ridge mesa structure and the upper surfaces of the doping layer that are not in contact with the back barrier layer. The materials of the ohmic contact layers are indium-containing nitride semiconductor materials, and the source electrode and the drain electrode both form ohmic contacts with the ohmic contact layers.

9. The method for preparing a nitrogen-polar nitride high electron mobility transistor according to any one of claims 1 to 8, characterized in that, It includes the following steps: Epitaxially grow a nucleation layer, a semi-insulating layer, a buffer layer, a doping layer, a back barrier layer, and a channel layer on the substrate in sequence. Fabricate a gate electrode on the surface of the channel layer away from the back barrier layer. Etch both sides of the back barrier layer and the channel layer to fabricate a ridge mesa structure. On one side of the gate electrode, fabricate a source electrode from the surface of the ridge mesa structure along the side wall of the ridge mesa structure to the surface of the doping layer away from the buffer layer; on the other side of the gate electrode, fabricate a drain electrode from the surface of the ridge mesa structure along the side wall of the ridge mesa structure to the surface of the doping layer away from the buffer layer.

10. The manufacturing method of the nitrogen-polar nitride high electron mobility transistor according to claim 9, wherein, It includes the following steps: After fabricating the ridge mesa structure, grow ohmic contact layers on the side walls of the ridge mesa structure and the upper surfaces of the doping layer that are not in contact with the back barrier layer by using the secondary epitaxy method.

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