A gallium nitride Schottky diode and its preparation method

Abstract

The present invention discloses a gallium nitride Schottky diode and a method for fabricating the same. The diode comprises a substrate, a gallium nitride channel layer, a gallium oxide barrier layer, and a capping layer. A two-dimensional electron gas layer is formed between the gallium nitride channel layer and the gallium oxide barrier layer. Electrode grooves are provided at both ends of the gallium nitride channel layer to intercept the two-dimensional electron gas layer. The sides of the electrode grooves that contact the two-dimensional electron gas layer are filled with metal electrodes to form a cathode and an anode, respectively, while the other sides are hollowed out to form an air bridge. Both the cathode and the anode are Schottky electrodes. The Schottky diode fabricated by the present invention has the advantages of low parasitic effects, a large nonlinear capacitance range, and a high cutoff frequency.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices, and in particular relates to a gallium nitride Schottky diode and a preparation method thereof. Background Art

[0002] Compared to millimeter waves, terahertz (THz) has a higher frequency and shorter wavelength, resulting in higher resolution, stronger directionality, and greater information capacity. Compared to lasers, it has greater penetration, making it suitable for detection in extremely harsh environments, while also having lower energy and improved safety. These characteristics make THz technology of great significance in numerous national security and socioeconomic areas, including security imaging, high-speed communications, radar detection, and rapid spectral detection. However, limited THz sources have hindered the development of THz technology. An effective approach to realizing THz sources is to exploit the nonlinear properties of semiconductor devices to generate higher-order harmonics for frequency multiplication. This approach has advantages such as small size, ease of integration, and low operating voltage. The mainstream technology is to fabricate frequency multipliers based on Schottky barrier diodes (SBDs). Their low parasitic parameters enable cutoff frequencies exceeding 1 THz, making them ideal for THz source development. THz frequency multiplication technology based on SBDs has also become a hot topic in THz source research.

[0003] Traditional THz frequency multipliers use gallium arsenide (GaAs) SBDs. However, GaAs has a narrow bandgap, resulting in low device withstand voltage and limited input power. Furthermore, high losses and low conversion efficiency result in very low output power. Furthermore, the use of body doping results in low channel on-resistance and a low cutoff frequency. Wide-bandgap semiconductor gallium nitride (GaN), on the other hand, has a large bandgap, and SBDs fabricated from it offer advantages such as high breakdown voltage, high output power, and high cutoff frequency. However, current GaN SBDs still present significant challenges, including high series resistance, significant parasitic effects, and a low capacitance nonlinearity switching ratio. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide a gallium nitride Schottky diode with small parasitic effect, large nonlinear capacitance range and high cutoff frequency, and a preparation method thereof.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions.

[0006] The present invention provides a gallium nitride Schottky diode, comprising: a substrate, a gallium nitride channel layer, a gallium oxide barrier layer, and a cap layer; a two-dimensional electron gas layer is formed between the gallium nitride channel layer and the gallium oxide barrier layer; electrode grooves are respectively provided at both ends of the gallium nitride channel layer for intercepting the two-dimensional electron gas layer; metal electrodes are filled on one side of the electrode groove that contacts the two-dimensional electron gas layer to form a cathode and an anode, respectively, and an air bridge is provided on the other side; the cathode and the anode are both Schottky electrodes.

[0007] Furthermore, the substrate is one of a silicon substrate, a sapphire substrate, and a silicon carbide substrate.

[0008] Furthermore, the gallium nitride channel layer adopts m-plane gallium nitride.

[0009] Furthermore, the gallium oxide barrier layer is made of ε-Ga2O3.

[0010] Furthermore, the capping layer is made of gallium nitride or silicon nitride.

[0011] Furthermore, the metal electrode filled in the electrode groove is a Ni / Au composite electrode.

[0012] Furthermore, the air bridge is made of electroplated gold.

[0013] Furthermore, the thickness of the gallium nitride channel layer is 10 to 500 nm, the thickness of the gallium oxide barrier layer is 2 to 30 nm, the thickness of the cap layer is 2 to 50 nm, the depth of the electrode groove is 30 to 100 nm, the distance between the cathode and the anode is 500 nm to 10 μm, the width of the cathode and the anode is 2 to 40 μm, the length is 2 to 40 μm, and the thickness of the air bridge is 2 to 5 μm.

[0014] The present invention also provides a method for preparing the above-mentioned gallium nitride Schottky diode, comprising the following steps:

[0015] S1. epitaxially growing a gallium nitride channel layer, a gallium oxide barrier layer, and a cap layer on a substrate;

[0016] S2. Etching to form two electrode grooves that truncate the two-dimensional electron gas layer. After etching, fill the grooves with metal electrodes to form a cathode and an anode, respectively.

[0017] S3. Make an air bridge.

[0018] Furthermore, the specific steps of step S3 are:

[0019] P1. Use photolithography to define the shape of the bridge piers, using negative resist. After the piers are completed, surface treatment is performed and a seed layer is electroplated.

[0020] P2. Use photolithography to define the metal deposition pattern, use positive photoresist, electroplating to deposit gold, then use wet etching to etch the seed layer, and finally wet remove the photoresist and bridge piers.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention uses ε-Ga2O3 and m-plane gallium nitride to form a heterojunction. Due to the high spontaneous polarization intensity of ε-Ga2O3, the 2DEG concentration at the interface is high, the current density is high, and the device series resistance is low. The electrode directly contacts the 2DEG, and the parasitic capacitance between the electrode and the channel is small. At the same time, the electrode is led out using an air bridge, further reducing the parasitic effect of the electrode lead-out and improving the cutoff frequency. The electrode adopts a double Schottky contact method, with Schottky junctions on both sides of the channel, which improves the nonlinear effect of the junction capacitance. Compared with the traditional method of using Schottky contact for the anode and ohmic contact for the cathode, the nonlinear range of the capacitance is larger. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of the gallium nitride Schottky diode of the present invention;

[0024] Figure 2 The figure is a schematic diagram of the process flow of preparing the gallium nitride Schottky diode of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below with reference to specific examples so that those skilled in the art can more clearly understand the present invention. The examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In the examples of the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art; unless otherwise specified, the technical means used are conventional means well known to those skilled in the art.

[0026] An embodiment of the present invention provides a gallium nitride Schottky diode having a structure as follows Figure 1 As shown, it includes: a substrate 1, a gallium nitride channel layer 2, a gallium oxide barrier layer 3, and a cap layer 4; a two-dimensional electron gas layer 5 is formed between the gallium nitride channel layer 2 and the gallium oxide barrier layer 3; electrode grooves for cutting off the two-dimensional electron gas layer 5 are respectively provided at both ends of the gallium nitride channel layer 2, and metal electrodes are filled on one side of the electrode groove that contacts the two-dimensional electron gas layer 5 to form a cathode 6 and an anode 7 respectively, and an air bridge 8 is provided on the other side; the cathode 6 and the anode 7 are both Schottky electrodes.

[0027] In some preferred embodiments, the substrate 1 is a silicon substrate, a sapphire substrate, or a silicon carbide substrate. The crystal orientation of the silicon substrate can be (100), (111), or etc., the sapphire substrate crystal orientation can be Or (0001), etc., the crystal orientation of silicon carbide substrate includes or wait.

[0028] In some preferred embodiments, the gallium nitride channel layer 2 is made of m-plane gallium nitride.

[0029] In some preferred embodiments, the gallium oxide barrier layer 3 is made of ε-Ga2O3.

[0030] In some preferred embodiments, the capping layer 4 is made of gallium nitride or silicon nitride.

[0031] In some preferred embodiments, the metal electrode filled in the electrode groove is a Ni / Au composite electrode.

[0032] In some preferred embodiments, the air bridge 8 is made of electroplated gold.

[0033] In some preferred embodiments, the thickness of the gallium nitride channel layer 2 is 10 to 500 nm, the thickness of the gallium oxide barrier layer 3 is 2 to 30 nm, the thickness of the cap layer 4 is 2 to 50 nm, the depth of the electrode groove is 30 to 100 nm, the distance between the cathode 6 and the anode 7 is 500 nm to 10 μm, the width of the cathode 6 and the anode 7 is 2 to 40 μm, the length is 2 to 40 μm, and the thickness of the air bridge 8 is 2 to 5 μm.

[0034] In some preferred embodiments, the thickness of Ni in the Ni / Au composite electrode is 2 to 20 nm, and the thickness of Au is 20 to 400 nm.

[0035] The present invention provides a method for preparing a gallium nitride Schottky diode, such as Figure 2 As shown, the following steps are included:

[0036] S1. epitaxially growing a gallium nitride channel layer 2, a gallium oxide barrier layer 3, and a cap layer 4 on a substrate 1;

[0037] S2. Etching to form two electrode grooves that cut off the two-dimensional electron gas layer 5. After etching, fill the grooves with metal electrodes to form a cathode 6 and an anode 7, respectively.

[0038] S3. Make the air bridge 8.

[0039] In some preferred embodiments, dry etching is used in step S2, and the etching gases are BCl3 and Cl2.

[0040] In some preferred embodiments, the specific steps of step S3 are:

[0041] P1. The shape of the bridge pier is defined using photolithography, using a negative resist with a thickness of 1-3 μm. After the pier is completed, O2 plasma treatment is used to remove surface oxides using hydrochloric acid cleaning (HCl:O2 = 1:10). A seed layer is then electroplated, followed by sputtering of Ti / Au with a Ti thickness of 10-50 nm and an Au thickness of 50-100 nm.

[0042] P2. Use photolithography to define the metal deposition pattern, using positive photoresist with a thickness of 1 to 5 μm. Electroplating deposits gold with a thickness of 2 to 5 μm, then wet-etches the seed layer. Finally, wet-remove the photoresist and bridge piers.

[0043] The cutoff frequency formula of the Schottky diode is f = 1 / 2πRC, where R is the series resistance and C is the junction capacitance at zero bias. Due to the large spontaneous polarization intensity of ε-Ga2O3, the 2DEG concentration at the interface of the ε-Ga2O3 / m-GaN heterojunction can reach 10 14 cm -2 The device exhibits a low series resistance. At the same time, the electrodes adopt a double Schottky contact method, with Schottky junctions on both sides of the channel, which improves the nonlinear effect of the junction capacitance; and the Schottky junction is directly formed by metal and 2DEG, which reduces the parasitic capacitance between the electrode and the channel and further improves the cutoff frequency; in addition, the electrode is led out using an air bridge, which reduces the parasitic effect of the lead-out electrode and also achieves the purpose of improving the cutoff frequency. Therefore, the Schottky diode prepared by the present invention has the advantages of small parasitic effect, large nonlinear capacitance range, and high cutoff frequency.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A gallium nitride Schottky diode, characterized in that: include: Substrate, gallium nitride channel layer, gallium oxide barrier layer, cap layer; A two-dimensional electron gas layer is formed between the gallium nitride channel layer and the gallium oxide barrier layer; electrode grooves are provided at both ends of the gallium nitride channel layer to cut off the two-dimensional electron gas layer; metal electrodes are filled on one side of the electrode groove that contacts the two-dimensional electron gas layer to form a cathode and an anode, respectively, and an air bridge is provided on the other side; the cathode and the anode are both Schottky electrodes; The gallium nitride channel layer adopts m-plane gallium nitride; The gallium oxide barrier layer is made of ε-Ga2O3.

2. The gallium nitride Schottky diode according to claim 1, characterized in that: The substrate is one of a silicon substrate, a sapphire substrate and a silicon carbide substrate.

3. The gallium nitride Schottky diode according to claim 1, characterized in that: The capping layer is made of gallium nitride or silicon nitride.

4. The gallium nitride Schottky diode according to claim 1, characterized in that: The metal electrode filled in the electrode groove is a Ni / Au composite electrode.

5. The gallium nitride Schottky diode according to claim 1, characterized in that: The air bridge is electroplated with gold.

6. The gallium nitride Schottky diode according to claim 1, characterized in that: The thickness of the gallium nitride channel layer is 10~500nm, the thickness of the gallium oxide barrier layer is 2~30nm, the thickness of the cap layer is 2~50nm, the depth of the electrode groove is 30~100nm, the distance between the cathode and the anode is 500nm~10μm, the width of the cathode and the anode is 2~40μm, the length is 2~40μm, and the thickness of the air bridge is 2~5μm.

7. The method for preparing a gallium nitride Schottky diode according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. epitaxially growing a gallium nitride channel layer, a gallium oxide barrier layer, and a cap layer on the substrate; S2. Etching to form two electrode grooves that truncate the two-dimensional electron gas layer. After etching, metal electrodes are filled in to form the cathode and anode, respectively. S3. Make an air bridge.

8. The method for preparing a gallium nitride Schottky diode according to claim 7, wherein: The specific steps of step S3 are: P1. Use photolithography to define the shape of the bridge piers, using a negative resist. After the piers are completed, surface treatment is performed and a seed layer is electroplated. P2. Use photolithography to define the metal deposition pattern, use positive photoresist, electroplating to deposit gold, then wet etch the seed layer, and finally wet remove the photoresist and bridge piers.

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