An N-polar GaN-based planar Gunn diode and a preparation method thereof

Abstract

The application discloses an N-polarity GaN-based planar Gunn diode and a preparation method thereof. The N-polarity GaN-based planar Gunn diode comprises a substrate layer, an n-AlGaN back barrier layer grown on the substrate layer, a GaN channel layer, a left ohmic contact layer and a right ohmic contact layer grown on the n-AlGaN back barrier layer, the left ohmic contact layer and the right ohmic contact layer are respectively located on two sides of the GaN channel layer, and a left ohmic contact electrode and a right ohmic contact electrode are respectively grown on the left ohmic contact layer and the right ohmic contact layer. The GaN channel layer is provided with a left Schottky contact electrode, a right Schottky contact electrode and a passivation layer, and the left Schottky contact electrode and the right Schottky contact electrode are respectively located on two sides of the passivation layer. A two-dimensional electron gas thin layer is formed between the GaN channel layer and the n-AlGaN back barrier layer. When electricity is conducted, the current direction is transverse along the n-AlGaN back barrier layer. A drifting Gunn domain is formed at the bottom of the channel layer. The drifting process of the Gunn domain is limited in the GaN channel layer, so that the alternating current-direct current conversion efficiency and the output power of the device are improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically an N-polar GaN-based planar Gunn diode and its fabrication method. Background Technology

[0002] A planar Gunn diode utilizes the negative differential mobility characteristic of semiconductors. When direct current passes through the device, Gunn domains are generated. These domains drift in the channel, creating a semiconductor negative resistance device with a certain frequency, forming a relaxation oscillator. This is because the formation of electron domains causes a decrease in the anode output current, and the disappearance of electron domains causes an increase in the anode output current, thus forming a periodic current oscillation in the circuit. From the perspective of the overall circuit, the negative differential resistance in the Gunn diode cancels out part of the real positive resistance, thus effectively creating a "zero-resistance" circuit, theoretically resulting in an infinite oscillation circuit effect. Compared to the traditional Ga-polar planar Gunn diode, the N-polar planar Gunn diode has stronger quantum confinement of the two-dimensional electron gas, resulting in a significant improvement in device performance. The oscillation frequency generated by the Gunn diode is affected by the channel layer of the Gunn diode, and the oscillation frequency and AC / DC conversion efficiency can also be changed by altering other external factors. Gunn diodes are used in a variety of circuits, such as rectangular waveguide cavities, coaxial waveguide cavities, non-radiating dielectric (NRD) waveguides, substrate integrated waveguides (SIWs), microstrip circuits, coplanar waveguides (CPWs), and other different applications as oscillators.

[0003] In a planar Gunn diode, current flows parallel to the electrode plane. Its operation is as follows: when energized, a two-dimensional electron gas forms Gunn domains within the device channel, which drift from the cathode to the anode over time. Externally, this manifests as a continuously oscillating current output from the anode. Figure 1 In the traditional Ga-polar planar Gunn diode shown, the electrodes need to be connected to the device channel through the AlGaN back barrier layer. The device has high ohmic contact resistance loss, small current delivery, and large operating voltage, resulting in low AC / DC conversion efficiency and output power, poor heat dissipation, and is not conducive to large-scale integration. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide an N-polar GaN-based planar Gunn diode and its fabrication method, which not only improves the AC / DC conversion efficiency and output power of the device, but also enhances circuit compatibility and facilitates large-scale integration.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] An N-polar GaN-based planar Gunn diode includes a substrate layer, an n-AlGaN back barrier layer grown on the substrate layer, a GaN channel layer, a left ohmic contact layer and a right ohmic contact layer grown on the n-AlGaN back barrier layer, the left ohmic contact layer and the right ohmic contact layer being located on opposite sides of the GaN channel layer, and left ohmic contact electrodes and right ohmic contact electrodes being grown on the left ohmic contact layer and the right ohmic contact layer, respectively.

[0007] A left Schottky contact electrode, a right Schottky contact electrode, and a passivation layer are grown on the GaN channel layer, with the left Schottky contact electrode and the right Schottky contact electrode located on both sides of the passivation layer, respectively.

[0008] A two-dimensional electron gas thin layer is formed between the GaN channel layer and the n-AlGaN back barrier layer. When energized, the current direction is along the transverse direction of the n-AlGaN back barrier layer. Drifting Gunn domains are formed at the bottom of the channel layer, and the drifting process of the Gunn domains is confined inside the GaN channel layer.

[0009] Furthermore, the n-AlGaN back barrier layer has a thickness of 250–300 nm, and the molar percentage of Al is 20%–60%, with a doping concentration of 1 × 10⁻⁶. 15 ~2×10 16 cm -3 n-AlGaN.

[0010] Furthermore, the GaN channel layer has a thickness of 25–300 nm and a doping concentration of 1 × 10⁻⁶. 15 ~2×10 16 cm -3 n+-GaN.

[0011] Furthermore, the channel length of the GaN channel layer is 1000–1500 nm, and the two-dimensional electron gas thin layer is located at the bottom of the GaN channel layer.

[0012] Furthermore, both the left and right ohmic contact layers have a thickness of 250–300 nm and a doping concentration of 1 × 10⁻⁶. 20 ~3×10 20 cm -3 n+-GaN.

[0013] Furthermore, the left ohmic contact electrode and the right ohmic contact electrode include Ti, Al, Pt and Au metal layers with thicknesses of 15 nm, 50 nm, 30 nm and 30 nm, respectively.

[0014] Furthermore, the left Schottky contact electrode and the right Schottky contact electrode comprise Ni and Au metal layers with thicknesses of 95 nm and 30 nm, respectively.

[0015] Furthermore, the relative permittivity of the passivation layer is 10 to 200, and its thickness is equal to the thickness of the left ohmic contact electrode and the right ohmic contact electrode.

[0016] A method for fabricating an N-polar GaN-based planar Gunn diode includes the following steps:

[0017] S1. Select sapphire material as the initial material to form the substrate layer;

[0018] S2. An n-AlGaN back barrier layer is formed on the upper layer of the substrate;

[0019] S3. A GaN channel layer is formed on top of the n-AlGaN back barrier layer;

[0020] S4. Etch the n-GaN channel layer down to the upper surface of the n-AlGaN back barrier layer to form left and right mesa surfaces;

[0021] S5. A left ohmic contact layer and a right ohmic contact layer are grown on the mesa on both sides of the GaN channel layer.

[0022] S6. Left ohmic contact electrode and right ohmic contact electrode are formed on the upper layers of the left ohmic contact layer and the right ohmic contact layer, respectively.

[0023] S7. A left Schottky contact electrode is formed on the right side of the left ohmic contact electrode, and a right Schottky contact electrode is formed on the left side of the right ohmic contact electrode.

[0024] S8. A passivation layer is formed between the left Schottky contact electrode and the right Schottky contact electrode, and the passivation layer is located on top of the GaN channel layer;

[0025] S9. When energized, drifting Gunther domains are formed at the bottom of the channel layer.

[0026] Compared with the prior art, the present invention has the following technical effects:

[0027] 1) Compared with traditional Ga-polar GaN-based planar Gunn diodes, the N-polar GaN-based planar Gunn diode of this invention has an ohmic contact layer directly connected to the GaN channel layer with a low surface barrier, resulting in lower ohmic contact resistance loss and thus enabling the delivery of larger currents. In addition, the reduced resistance means a smaller voltage drop under the same current conditions, which can reduce the operating voltage of the Gunn diode, thereby improving the AC / DC conversion efficiency and output power of the Gunn diode. Since heat generation mainly comes from contact resistance loss, this invention innovates at the device structure level, breaking through the bottleneck of difficulty in obtaining low contact resistance in the AlGaN back barrier layer of existing Ga-polar planar Gunn diodes. The low contact resistance of the obtained N-polar GaN / AlGaN planar Gunn diode greatly reduces the heat generation of the Gunn device, improves the heat dissipation conditions of the device, and effectively prevents thermal damage to the device.

[0028] 2) The short-channel effect mainly originates from the distribution of the two-dimensional electron gas in the channel of the Gunn device and the space charge-confined current through the buffer layer. Because the anode and cathode of the N-polar planar Gunn diode have stronger control over the GaN channel, the discontinuous conduction band at the GaN / AlGaN interface forms a back barrier structure. This structural characteristic prevents the static electron misalignment from lowering the barrier height; electrons require higher energy to enter the AlGaN back barrier layer. Due to the depletion effect and the strong confinement of the heterojunction, the two-dimensional electron gas can achieve stricter channel confinement, resulting in lower impurity scattering. The narrower two-dimensional electron gas in the channel layer of the N-polar GaN / AlGaN heterojunction promotes Gunn domain formation. The high concentration of two-dimensional electron gas in the channel not only significantly increases the device power but also allows for a significant reduction in device size, contributing to breakthrough performance. Breaking the bottleneck of Moore's Law, thanks to this, under the same size and channel layer thickness, N-polarized Gunn diodes can significantly suppress the short-channel effect of devices compared to traditional Ga-polarized Gunn diodes, thereby greatly reducing the size of the devices. This makes them suitable for large-scale production and application as microwave oscillators. As microwave oscillators, N-polarized planar Gunn diodes can be seamlessly connected with monolithic microwave integrated circuits (MMICs) to form RF output systems in the millimeter-wave and even terahertz frequency bands, significantly improving productivity and reproducibility. In addition, N-polarized planar Gunn diodes can be combined with high-capacity devices to improve power output performance, and they also have excellent compatibility with planar circuits. For example, based on coplanar waveguide (CPW) components, qualified chips can be manufactured on a separate wafer using photolithography technology.

[0029] 3) The N-polar planar Gunn diode of the present invention employs an Ohm-Schottky composite electrode. By extending the Schottky electrode, the concentration of two-dimensional electron gas (2DEG) in the channel directly below it is reduced, forming a depletion layer at the cathode. This modulates the electric field distribution in the channel below the device electrode, effectively reducing the dead zone of the Gunn diode and thus increasing the AC / DC conversion efficiency of the device. At the same time, the composite electrode suppresses impurity scattering inside the device, making it easier for electrons to be heated by the external electric field and thus gain sufficient energy to jump to higher energy valleys. The reduction in ionized impurity scattering also enhances the low-field mobility of electrons, thereby improving the peak-to-valley ratio in the velocity-field relationship of the semiconductor device, making the negative differential mobility effect of the N-polar heterojunction Gunn diode more significant. Moreover, the composite electrode is more conducive to heat dissipation of the device, further improving the heat dissipation conditions of the device and effectively preventing thermal damage to the device. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of a traditional Ga-polar planar Gunn diode;

[0031] Figure 2 This is a schematic diagram of the structure of the N-polar GaN-based planar Gunn diode of the present invention;

[0032] Figure 3 This is a flowchart illustrating the fabrication method of the N-polar GaN-based planar Gunn diode of the present invention.

[0033] Figure 4 This is a flowchart illustrating the specific process for fabricating an N-polar GaN-based planar Gunn diode according to the present invention.

[0034] In the figure: 1. Substrate layer; 2. n-AlGaN back barrier layer; 3. GaN channel layer; 4. Left ohmic contact layer; 5. Right ohmic contact layer; 6. Left ohmic contact electrode; 7. Right ohmic contact electrode; 8. Left Schottky contact electrode; 9. Right Schottky contact electrode; 10. Passivation layer. Detailed Implementation

[0035] The specific content of the present invention will be further explained in detail below with reference to the embodiments.

[0036] like Figure 2 As shown, an N-polar GaN-based planar Gunn diode includes a substrate layer 1, an n-AlGaN back barrier layer 2, a GaN channel layer 3, a left ohmic contact layer 4, a right ohmic contact layer 5, a left ohmic contact electrode 6, a right ohmic contact electrode 7, a left Schottky contact electrode 8, a right Schottky contact electrode 9, and a passivation layer 10.

[0037] The n-AlGaN back barrier layer 2 is located on the substrate layer 1. The GaN channel layer 3, the left ohmic contact layer 4, and the right ohmic contact layer 5 are located on the n-AlGaN back barrier layer 2. The left ohmic contact layer 4 and the right ohmic contact layer 5 are located on both sides of the GaN channel layer 3. The left ohmic contact electrode 6 and the right ohmic contact electrode 7 are located on the left ohmic contact layer 4 and the right ohmic contact layer 5, respectively. The left Schottky contact electrode 8, the right Schottky contact electrode 9, and the passivation layer 10 are all located on the GaN channel layer 3. The left Schottky contact electrode 8 and the right Schottky contact electrode 9 are located on both sides of the passivation layer 10.

[0038] The polarization between the GaN channel layer 3 and the n-AlGaN back barrier layer 2 produces, as... Figure 2 The electron trap shown by the dashed line forms a two-dimensional electron gas thin layer 2DEG. When energized, the current direction is transverse along the n-AlGaN back barrier layer 2. Drifting Gunn domains are formed at the bottom of the channel layer 3, and the drifting process of the Gunn domains is confined inside the GaN channel layer 3.

[0039] Preferably, both the left ohmic contact layer 4 and the right ohmic contact layer 5 are made of n+-GaN, with a thickness of 250-300 nm and a doping concentration of 1×10⁻⁶. 20 ~3×10 20 cm -3 .

[0040] Preferably, the n-AlGaN back barrier layer 2 is made of n-AlGaN with a thickness of 250–300 nm, an Al molar percentage of 20%–60%, and a doping concentration of 1 × 10⁻⁶. 15 cm -3 ~2×10 16 cm -3 .

[0041] Preferably, the left ohmic contact electrode 6 and the right ohmic contact electrode 7 comprise Ti, Al, Pt, and Au metal layers with thicknesses of 15 nm, 50 nm, 30 nm, and 30 nm, respectively.

[0042] Preferably, the left Schottky contact electrode 8 and the right Schottky contact electrode 9 comprise Ni and Au metal layers with thicknesses of 95 nm and 30 nm, respectively.

[0043] Preferably, the relative permittivity of the passivation layer 10 is in the range of 10 to 200, and its thickness is equal to the thickness of the left ohmic contact electrode (6) and the right ohmic contact electrode (7).

[0044] Preferably, the GaN channel layer 3 has a thickness of 250–300 nm and a doping concentration of 1 × 10⁻⁶. 15 ~2×10 16 cm-3 The n+-GaN has a channel length of 1000-1500 nm in the GaN channel layer 3, and a two-dimensional electron gas thin layer is located at the bottom of the GaN channel layer 3.

[0045] The N-polar planar Gunn diode proposed in this embodiment has a barrier layer grown from bottom to top, with current flowing in a direction parallel to the electrode plane. When the channel layer 3 is working, the drift process of electron domains (i.e., Gunn domains) is confined within the two-dimensional electron gas thin layer by utilizing a two-dimensional electron gas, thereby optimizing the electron domain drift process. The high concentration of two-dimensional electron gas in the channel layer greatly improves the power of the device. Moreover, the ohmic contact region of the N-polar planar Gunn diode is directly connected to the GaN channel layer, eliminating the need to connect the wide bandgap material AlGaN. This reduces the ohmic contact resistance of the device, decreases the device size, and allows the device to operate at higher oscillation frequencies and high frequencies. At the same time, the composite electrode formed by the left ohmic contact electrode and the left Schottky electrode reduces the dead zone of the Gunn diode by modulating the electric field distribution at the left cathode end, and the composite electrode formed by the right ohmic contact electrode and the right Schottky electrode suppresses ionization scattering at the anode end, further improving the device's operating efficiency. This has important reference value for the application of Gunn diodes.

[0046] like Figure 3 As shown, a method for fabricating an N-polar GaN-based planar Gunn diode includes the following steps:

[0047] S1. Select sapphire material as the initial material to form substrate layer 1;

[0048] S2. An n-AlGaN back barrier layer 2 is formed on the substrate layer 1;

[0049] S3. A GaN channel layer 3 is formed on the n-AlGaN back barrier layer 2;

[0050] S4. Etch the n-GaN channel layer 3 up to the upper surface of the n-AlGaN back barrier layer 2 to form left and right mesa.

[0051] S5. A left ohmic contact layer 4 and a right ohmic contact layer 5 are grown on the n-AlGaN back barrier layer 2, and the left ohmic contact layer 4 and the right ohmic contact layer 5 are located on the terraces on both sides of the GaN channel layer 3.

[0052] S6. A left ohmic contact layer 4 and a right ohmic contact layer 5 are grown on the mesa on both sides of the GaN channel layer 3.

[0053] S7. A left Schottky contact electrode 8 is formed on the right side of the left ohmic contact electrode 6, and a right Schottky contact electrode 9 is formed on the left side of the right ohmic contact electrode 7.

[0054] S8. A passivation layer 10 is formed between the left Schottky contact electrode 8 and the right Schottky contact electrode 9. The passivation layer 10 is located on the GaN channel layer 3.

[0055] S9. When energized, drifting Gunther domains are formed at the bottom of channel layer 3.

[0056] like Figure 4 As shown, the specific fabrication process of the N-polar GaN-based planar Gunn diode is as follows:

[0057] Step 1: Select sapphire material as substrate layer 1 and clean substrate layer 1: Etch in a solution with a molar ratio of H2So4:H2Po4 = 3:1 for 20 min, then rinse with deionized water and dry with NH3;

[0058] Step 2, Preheating of substrate 1: Ammoniation of substrate 1 is completed at 800℃ in an ammonia stream for 5-15 minutes;

[0059] Step 3: Deposit n-AlGaN back barrier layer 2: The temperature of substrate 1 is 800℃, the aluminum source temperature is 1070℃, the nitrogen source ammonia flow rate is 16 SCCM, and metal-organic chemical vapor deposition (MOCVD) is used. The reaction chamber temperature is 1050℃, the reaction chamber pressure is set to 100 Torr, and trimethylgallium, nitrogen, and trimethylaluminum are simultaneously introduced into the reaction chamber. A thickness of 250–300 nm is grown on substrate 1, with a doping concentration of 1 × 10⁻⁶. 15 ~2×10 16 cm -3 The n-AlGaN molar composition is 20% to 60%, forming an n-AlGaN back barrier layer 2;

[0060] Step 4: Growth of GaN channel layer 3: Triethylgallium and high-purity nitrogen are used as the gallium source and nitrogen source, respectively. The temperature of substrate layer 1 is reduced to 700℃, the gallium source temperature is 970℃, and the ammonia flow rate is 35 SCCM (5 × 10⁻⁶). 16 cm -3 ), and continue to use the metal-organic chemical vapor deposition (MOCVD) method, under the condition that the reaction chamber pressure is reduced to 40 Torr, grow 250-300 n+-GaN on the n-AlGaN back barrier layer 2 to form GaN channel layer 3.

[0061] Step 5: Using reactive ion etching (RIE), the GaN channel layer 3 is etched with a BCl3 / Cl2 gas etching source to the upper surface of the AlGaN back barrier layer 2, forming left and right mesa.

[0062] Step 6: Doping is performed by ion implantation to grow n+-GaN left ohmic contact layer 4 and n+-GaN right ohmic contact layer 5 with a thickness of 250-300 nm on the left and right mesa surfaces of GaN channel layer 3, with a doping concentration of 1×10⁻⁶ for both layers. 20 ~3×10 20 cm -3 ;

[0063] Step 7: Ti, Al, Pt and Au metal layers are sequentially evaporated on the left ohmic contact layer 4 and the right ohmic contact layer 5 using a vacuum electron beam evaporation device, with thicknesses of 15nm, 50nm, 30nm and 30nm respectively. After metal peeling, annular left ohmic contact electrode 6 and right ohmic contact electrode 7 are formed. Then, Ni and Au metal layers are sequentially evaporated on the GaN channel layer 3, with thicknesses of 95nm and 30nm respectively. After metal peeling, annular left Schottky contact electrode 8 and right Schottky contact electrode 9 are formed. Then, the entire device is subjected to rapid thermal annealing at 750℃ for 3 minutes using nitrogen gas to form ohmic contacts.

[0064] Step 8: Using an RF magnetron sputtering device, a Si3N4 layer with a thickness of 80 nm and a width of 15 nm is sputtered on the GaN channel layer 3 to form a passivation layer 10. The RF magnetron sputtering process conditions are: RF power of 100 W, target spacing of 20 cm, and argon and nitrogen gas introduced when the reaction chamber pressure is 0.4 Pa, with a nitrogen flow rate ratio of 20%.

Claims

1. An N-polar GaN-based planar Gunn diode, characterized in that, The system includes a substrate layer (1), an n-AlGaN back barrier layer (2) grown on the substrate layer (1), a GaN channel layer (3), a left ohmic contact layer (4) and a right ohmic contact layer (5) grown on the n-AlGaN back barrier layer (2), the left ohmic contact layer (4) and the right ohmic contact layer (5) being located on both sides of the GaN channel layer (3), and a left ohmic contact electrode (6) and a right ohmic contact electrode (7) being grown on the left ohmic contact layer (4) and the right ohmic contact layer (5) respectively. A left Schottky contact electrode (8), a right Schottky contact electrode (9), and a passivation layer (10) are grown on the GaN channel layer (3), with the left Schottky contact electrode (8) and the right Schottky contact electrode (9) located on both sides of the passivation layer (10). A two-dimensional electron gas thin layer is formed between the GaN channel layer (3) and the n-AlGaN back barrier layer (2). When energized, the current direction is along the transverse direction of the n-AlGaN back barrier layer (2). Drifting Gunn domains are formed at the bottom of the channel layer (3), and the drifting process of the Gunn domains is confined inside the GaN channel layer (3).

2. The N-polar GaN-based planar Gunn diode according to claim 1, characterized in that, The n-AlGaN back barrier layer (2) has a thickness of 250–300 nm, and the molar percentage of Al is 20%–60%, with a doping concentration of 1 × 10⁻⁶. 15 ~2×10 16 cm -3 n-AlGaN.

3. The N-polar GaN-based planar Gunn diode according to claim 1, characterized in that, The GaN channel layer (3) has a thickness of 250–300 nm and a doping concentration of 1 × 10⁻⁶. 15 ~2×10 16 cm -3 n+-GaN.

4. The N-polar GaN-based planar Gunn diode according to claim 1, characterized in that, The channel length of the GaN channel layer (3) is 1000-1500 nm, and the two-dimensional electron gas thin layer is located at the bottom of the GaN channel layer (3).

5. The N-polar GaN-based planar Gunn diode according to claim 1, characterized in that, Both the left ohmic contact layer (4) and the right ohmic contact layer (5) have a thickness of 250–300 nm and a doping concentration of 1 × 10⁻⁶. 20 ~3×10 20 cm -3 n+-GaN.

6. The N-polar GaN-based planar Gunn diode according to claim 1, characterized in that, The left ohmic contact electrode (6) and the right ohmic contact electrode (7) include Ti, Al, Pt and Au metal layers with thicknesses of 15 nm, 50 nm, 30 nm and 30 nm, respectively.

7. The N-polar GaN-based planar Gunn diode according to claim 1, characterized in that, The left Schottky contact electrode (8) and the right Schottky contact electrode (9) include Ni and Au metal layers with thicknesses of 95 nm and 30 nm, respectively.

8. The N-polar GaN-based planar Gunn diode according to claim 1, characterized in that, The passivation layer (10) has a relative permittivity of 10 to 200 and its thickness is equal to the thickness of the left ohmic contact electrode (6) and the right ohmic contact electrode (7).

9. A method for fabricating an N-polar GaN-based planar Gunn diode as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Select sapphire material as the initial material to form a substrate layer (1); S2. An n-AlGaN back barrier layer (2) is formed on the substrate layer (1); S3. A GaN channel layer (3) is formed on the n-AlGaN back barrier layer (2); S4. Etch the n-GaN channel layer (3) until the upper surface of the n-AlGaN back barrier layer (2) to form the left and right mesa. S5. A left ohmic contact layer (4) and a right ohmic contact layer (5) are grown on the mesa on both sides of the GaN channel layer (3). S6. Left ohmic contact electrode (6) and right ohmic contact electrode (7) are formed on the upper layers of the left ohmic contact layer (4) and the right ohmic contact layer (5), respectively. S7. A left Schottky contact electrode (8) is formed on the right side of the left ohmic contact electrode (6), and a right Schottky contact electrode (9) is formed on the left side of the right ohmic contact electrode (7). S8. A passivation layer (10) is formed between the left Schottky contact electrode (8) and the right Schottky contact electrode (9), and the passivation layer (10) is located on the GaN channel layer (3); S9. When energized, drifting Gunther domains are formed at the bottom of the channel layer (3).

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