CN114664933B - Schottky diode - Google Patents

Abstract

The invention discloses a Schottky diode which comprises an anode region, a drift region, a substrate region, a cathode region, a field plate region and a grid structure, wherein the anode region, the drift region, the substrate region and the cathode region are sequentially arranged from top to bottom, the field plate region is arranged in the middle of the anode region and is divided into a grid structure, and the materials of the field plate region and the drift region are alpha-Ga ₂O₃. According to the invention, the field plate region of the gate structure is added in the middle of the anode region, the field plate region and the drift region are made of alpha-Ga ₂O₃ material, the field plate region of the gate structure can optimize the current crowding effect, improve the electric field distribution at the contact surface of the electrode and the drift region, improve the breakdown voltage of the device, inhibit vertical leakage current in a thickness increasing manner based on the drift region of alpha-Ga ₂O₃, and improve the withstand voltage of the device, so that the maximum breakdown field intensity of the device exceeds 10MV/cm, and the problems of high leakage current and lower withstand voltage of the current power diode are solved.

Description

A Schottky diode

Technical Field

The invention relates to a Schottky diode and belongs to the field of semiconductor devices.

Background technique

Research on Schottky diodes has found that the vertical leakage current of the device limits the device's voltage resistance and shortens its working life, resulting in a large gap between the actual parameters and theoretical expectations. Therefore, how to increase the voltage resistance range and suppress the vertical leakage current is a difficult point in current research.

Summary of the invention

The present invention provides a Schottky diode, which solves the problem disclosed in the background technology.

In order to solve the above technical problems, the technical solution adopted by the present invention is:

A Schottky diode includes an anode region, a drift region, a substrate region and a cathode region arranged from top to bottom, and also includes a field plate region, which is arranged in the middle of the anode region and is divided into a gate structure. The materials of the field plate region and the drift region are both α-Ga ₂ O ₃ .

The width of the Schottky diode is 1-2 μm.

The material of the anode region is Pt, and the thickness is 0.5 to 1 μm.

The band gap of α _{- Ga2O3} is 5.3eV.

The field plate region has a thickness of 0.5 to 1 μm, a width of 0.4 to 0.8 μm, and is n-type doped with a doping concentration of 4.4×10 ¹⁵ to 7.4×10 ¹⁵ cm ^-3 .

The drift region is n-type doped, with a doping concentration of 4.4×10 ¹⁵ to 7.4×10 ¹⁵ cm ^-3 and a thickness ranging from 1 to 8 μm.

The material of the substrate region is GaN, with a thickness of 1 to 2 μm, and n-type doping with a doping concentration of 5×10 ¹⁸ to 1×10 ¹⁹ cm ^-3 .

The material of the cathode region is Pt, and the thickness is 0.5 to 1 μm.

The beneficial effects achieved by the present invention are as follows: the present invention adds a field plate region of a gate structure in the middle of the anode region, and both the field plate region and the drift region are made of α-Ga ₂ O ₃ material. The field plate region of the gate structure can optimize the current crowding effect, improve the electric field distribution at the contact surface between the electrode and the drift region, and increase the breakdown voltage of the device. The drift region based on α-Ga ₂ O ₃ can suppress vertical leakage current by increasing the thickness, and can also improve the withstand voltage of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of a Schottky diode with a segmented field plate region;

FIG2 is a schematic diagram of the structure of a Schottky diode without segmentation of the field plate region;

Figure 3 shows the reverse I-V characteristics under different drift region thicknesses;

FIG4 is a comparison of breakdown voltage and platform width under different drift region thicknesses;

FIG5 is a graph showing the relationship between the maximum electric field and the thickness of the drift region at an anode voltage of -1000 V;

FIG6 shows the horizontal electric field of Schottky diodes with different field plate segmentation numbers;

FIG7 shows the reverse I-V characteristics of Schottky diodes with different field plate segmentation numbers;

FIG8 shows the horizontal electric field of Schottky diodes with different field plate widths;

Figure 9 shows the reverse I-V characteristics of Schottky diodes with different field plate widths.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

As shown in FIG1 , a Schottky diode includes an anode region 1, a field plate region 2, a drift region 3, a substrate region 4 and a cathode region 5; wherein the anode region 1, the drift region 3, the substrate region 4 and the cathode region 5 are arranged from top to bottom, the field plate region 2 is arranged in the middle of the anode region 1, and the field plate region 2 is divided into a gate structure, that is, the field plate region 2 is divided into a plurality of field plates, and the materials of the field plate region and the drift region are both α-Ga ₂ O ₃ . Increasing the thickness of the drift region and adding a field plate structure within a certain range can effectively suppress the vertical leakage current and increase the reverse breakdown voltage of the device, and its limiting field strength is higher than the breakdown electric field strength of the β-Ga ₂ O _3- based device reported recently.

The width of the Schottky diode is 1-2 μm, the material of the anode region 1 is Pt, and the thickness is 0.5-1 μm, the materials of the field plate region 2 and the drift region 3 are both α-Ga ₂ O ₃ with a band gap of 5.3 eV, the thickness of the field plate region 2 is 0.5-1 μm, the width of the field plate region is 0.4-0.8 μm, n-type doping, the doping concentration is 4.4×10 ¹⁵ ～7.4×10 ¹⁵ cm ^-3 , the drift region 3 is n-type doping, the doping concentration is 4.4×10 ¹⁵ ～7.4×10 ¹⁵ cm ^-3 , the total thickness range is 1-8 μm, the material of the substrate region 4 is GaN, the thickness is 1-2 μm, n-type doping, the doping concentration is 5×10 ¹⁸ ～1×10 ¹⁹ cm ^-3 , and the material of the cathode region 5 is Pt, and the thickness is 0.5-1 μm.

The Schottky diode adds a field plate region 2 of a gate structure in the middle of the anode region 1. Both the field plate region 2 and the drift region 3 are made of a new material α-Ga ₂ O _3. The field plate region 2 of the gate structure can optimize the current crowding effect, improve the electric field distribution at the contact surface between the electrode and the drift region 3, and increase the breakdown voltage of the device. The drift region 3 based on α-Ga ₂ O ₃ can suppress the vertical leakage current by increasing the thickness, and can also improve the device withstand voltage.

In order to verify the above Schottky diode, Silvaco TCAD software is used for simulation:

The band gap of gallium oxide is set to 5.3eV, the electron affinity is 4eV, the relative dielectric constant is 10, and the work function of Schottky contact is 5.65eV. The Selberrherr collision ionization model, UST model, and Pipinys model are used. For n-type Ga ₂ O ₃ materials, the electron ionization rate parameter α _n is calculated as follows:

where E is the electric field in the direction of the current at a specific location in the structure and parameters;

The contribution of electron current emitted from the local energy level of the gold-semiconductor interface is:

J＝Q·PIP.NT·W

Among them, Q is the electron charge, PIP.NT is the occupied state density near the interface, and W is the phonon-assisted tunneling probability, which can be calculated by setting the model parameters.

In order to study the relationship between the appearance of the current platform and the reverse breakdown voltage, a comparative analysis was conducted by changing the thickness of the drift region 3 and the width of the field plate, as follows:

Structure 1: The Schottky diode structure refers to Figure 2, including an anode region 1, a field plate region 2, a drift region 3, a substrate region 4, and a cathode region 5; wherein the width of the Schottky diode is 1μm; the material of the anode region 1 and the cathode region 5 is Pt, with a thickness of 1μm; the field plate region 2 is undivided, the material is α-Ga ₂ O ₃ , the thickness is 1μm, the width is 0.8μm, and n-type doping is used, and the doping concentration is 7.4×10 ¹⁵ cm ^-3 ; the material of the drift region 3 is α-Ga ₂ O, n-type doping, and the doping concentration is 7.4×10 ¹⁵ cm ^-3 ; the material of the substrate region 4 is GaN, the thickness is 1μm, n-type doping, and the doping concentration is 1×10 ¹⁹ cm ^-3 .

The relationship between the thickness of the device drift region 3 and the reverse breakdown voltage was studied. The results showed that under the optimized parameters (drift region 3 thickness 8μm), the experimental value of the breakdown voltage was much lower than the theoretical value of 1.8kV, which shows that there is still a lot of room for optimization in the withstand voltage performance of Schottky diodes.

When the doping concentration of the drift region 3 is fixed at 7.4×10 ¹⁵ cm ^-3 and the width of the field plate region 2 is fixed at 0.8 μm, it can be seen from FIG3 that the breakdown voltage gradually increases with increasing thickness of the drift region 3. This is because when the thickness increases, not only the voltage drop in the drift region 3 increases, but also the increase in the total number of carriers increases the number of charges accumulated near the Schottky barrier, thereby increasing the electric field strength at the Schottky contact surface.

The relationship between the reverse breakdown voltage and the corresponding current platform length of the 1-15μm thick Schottky diode and the thickness L of the drift region 3 is shown in reference figure 4. As the thickness of the drift region 3 increases, the reverse breakdown voltage and the length of the current platform increase approximately linearly. This is because under the breakdown condition, the drift region 3 is partially depleted, and except for the electric field peak that appears in the thin layer near the Schottky contact surface between the electrode and the drift region 3, the voltage mainly drops in the drift region 3. As the reverse bias increases, the thickness of the depletion layer in the drift region 3 gradually increases until it is completely depleted. In this process, the reverse current is basically unchanged due to the conductivity limitation of the undepleted part, so a current platform that lengthens with the increase of the thickness of the drift region 3 appears.

Referring to FIG5 , it can be seen that as the thickness of the drift region 3 increases, the maximum electric field value gradually decreases. This indicates that the increase in the thickness of the drift region 3 increases the number of electrons at the Schottky contact surface. Under the same bias voltage condition, the number of electron-hole pairs at the contact surface decreases, thereby reducing the electric field at the contact surface, making the difference between the peak and the valley in the electric field distribution smaller, and effectively delaying the occurrence of breakdown.

By adjusting the thickness of the drift region 3, it is found that the current platform that appears in the bias voltage of the gallium oxide Schottky diode is related to the depletion layer of the drift region 3. When the drift region 3 of different thicknesses begins to deplete under the action of the reverse bias voltage, the current platform begins to appear; when the depletion layer thickness increases, the length of the current platform increases accordingly. The slope of the electric field slows down with the thickness, indicating that the thicker drift region 3 has an inhibitory effect on the vertical leakage current.

The electric field distribution in the simulation experiment for structure 1 and the subsequent structure 3 is the electric field in the x and y directions in Figure 2, where the x direction refers to the horizontal electric field at 1.001 μm from the upper surface, and the y direction refers to the vertical electric field at 0.1 μm from the left boundary.

Structure 2: Based on Structure 1, the total width of the fixed field plate is 0.6μm. As shown in Figure 1, the field plate region 2 is cut into a gate structure, specifically divided into the first, second and third field plates, and compared with the traditional structure without field plate region 2; the horizontal electric field near the interface between the drift region 3 and the field plate region 2 is shown in Figure 6, and the reverse I-V characteristics of the Schottky diode are shown in Figure 7.

It can be seen from Figures 6 and 7 that the breakdown voltage of the structure without field plate region 2 is greater than the breakdown voltage with field plate region 2, but the electric field at breakdown is much lower than the peak electric field with field plate region 2. Therefore, adding field plate region 2 helps to improve the utilization of the electric field strength that the material can withstand; among them, the maximum electric field strength exceeds 10MV/cm, which is higher than the breakdown electric field size of the β- _{Ga2O3 device} (dashed line in Figure 5).

As the number of field plate region 2 divisions increases, the maximum electric field increases accordingly, and the breakdown voltage also increases. This is because adding the number of field plate region 2 divisions reduces the difference between the electric field peak and the valley, and the distribution of the electric field strength is more balanced, thereby increasing the breakdown voltage.

Therefore, by changing the number of divisions of the field plate region 2, it is found that adding a field plate region 2 domain structure can make the distribution of the electric field strength more balanced and improve the breakdown voltage.

The electric field distribution in the simulation experiment for structure 2 is the electric field in the x and y directions in Figure 1, where the x direction refers to the horizontal electric field at 1.001 μm from the upper surface, and the y direction refers to the vertical electric field at 0.1 μm from the left boundary.

Structure 3: Based on Structure 2, only the first field plate is used, and the field plate width is changed in the range of 0.1 to 0.8 μm, and the interface electric field distribution and reverse I-V characteristics are obtained as shown in Figures 8 and 9. It can be seen that as the field plate width increases, the electric field strength at the contact surface between the anode and the drift region 3 increases. However, under the condition of a single field plate, the electric field distribution is uneven, so that the reverse breakdown voltage increases with the decrease of the field plate width, as shown in Figure 9. When the field plate width is 0.1 μm, the reverse breakdown voltage reaches a maximum value of about 3.4 kV.

It can be seen that through the simulation study of the relationship between the reverse breakdown characteristics of the Schottky diode and the thickness of the drift region 3 and the width of the field plate region 2, it is found that a reverse current platform appears when the thickness of the drift region 3 is certain, and the thickness of the drift region 3 has a significant effect on the breakdown voltage and current platform. The influence mechanism can be attributed to the change in the width of the depletion layer. The addition of the field plate region 2 and the appropriate division of the field plate region 2 can optimize the electric field distribution and increase the breakdown voltage. The simulation results show that the magnitude of the reverse breakdown voltage is positively correlated with the width of the current platform within a certain range, as shown in Figure 4.

Therefore, the median value of 8μm of the thickness of the drift region 3 in Figure 4 is selected as a typical value, and the electric field distribution is optimized by dividing the field plate region 2 structure, thereby further improving the reverse breakdown voltage. In the optimized three-segment field plate structure, increasing the thickness of the drift region 3 can effectively improve the device withstand voltage according to actual process requirements.

In summary, the thickness of the drift region 3 of the α-Ga ₂ O ₃ -based Schottky diode has an important influence on the vertical leakage current mechanism and the generation of the current platform. The field plate region 2 can effectively reduce the leakage current and increase the reverse bias voltage. Its limiting field strength exceeds 10 MV/cm, which is higher than the breakdown electric field strength of the recently reported β-Ga ₂ O _3- based devices.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (8)

1. A Schottky diode, comprising an anode region, a drift region, a substrate region and a cathode region arranged in sequence from top to bottom, characterized in that it also comprises a field plate region, the field plate region is arranged in the middle of the anode region, the field plate region is divided into a gate structure, and the materials of the field plate region and the drift region are both α-Ga ₂ O ₃ . 2 . The Schottky diode according to claim 1 , wherein the width of the Schottky diode is 1 to 2 μm. 3. A Schottky diode according to claim 1, characterized in that the material of the anode region is Pt, and the thickness is 0.5-1 μm. 4 . The Schottky diode according to claim 1 , wherein the band gap of α-Ga ₂ O ₃ is 5.3 eV. 5 . The Schottky diode according to claim 1 , wherein the field plate region has a thickness of 0.5-1 μm, a width of 0.4-0.8 μm, and is n-type doped with a doping concentration of 4.4×10 ¹⁵ -7.4×10 ¹⁵ cm ⁻³ . 6 . A Schottky diode according to claim 1 , wherein the drift region is n-type doped, the doping concentration is 4.4×10 ¹⁵ to 7.4×10 ¹⁵ cm ⁻³ , and the thickness ranges from 1 to 8 μm. 7 . The Schottky diode according to claim 1 , wherein the material of the substrate region is GaN, has a thickness of 1 to 2 μm, is n-type doped, and has a doping concentration of 5×10 ¹⁸ to 1×10 ¹⁹ cm ⁻³ . 8 . The Schottky diode according to claim 1 , wherein the material of the cathode region is Pt, and the thickness is 0.5-1 μm.