CN107507858B

CN107507858B - A current limiting diode

Info

Publication number: CN107507858B
Application number: CN201710749716.5A
Authority: CN
Inventors: 周琦; 胡凯; 董长旭; 朱厉阳; 张波
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2017-08-28
Filing date: 2017-08-28
Publication date: 2021-04-20
Anticipated expiration: 2037-08-28
Also published as: CN107507858A

Abstract

The invention belongs to the technical field of semiconductors, and relates to a current limiting diode. The invention proposes a new type of current-limiting diode, which uses the technology of growing a charge recovery layer on a thin potential barrier AlGaN/GaN heterojunction to modulate two-dimensional electron gas. Under the premise of withstand voltage, the advantage of this structure is that the fluorine-based gas used in the etching of the charge recovery layer will hardly cause any etching effect on the barrier layer under the charge recovery layer, and finally self-termination can be realized at the AlGaN interface to achieve the opposite effect. The purpose of precise control of the barrier layer. The invention avoids etching the AlGaN layer and does not cause damage to the AlGaN layer, so the device has larger current density, higher electron mobility and lower on-resistance.

Description

Current-limiting diode

Technical Field

The invention belongs to the technical field of power semiconductors, and relates to a current-limiting diode.

Background

Due to the high reverse breakdown voltage, the carrier concentration formed by the high piezoelectric polarization effect and the large electron mobility, the gallium nitride power device has become one of the best choices for the next generation of high-frequency high-power devices. In recent years, AlGaN/GaN heterojunction enhancement type HEMT devices have been widely studied. However, gallium nitride heterojunction material power diodes have not received sufficient attention, especially gallium nitride current limiting diodes.

As the LED lighting industry has unprecedentedly developed, the demand for current limiting diodes (rectifiers) has also increased. The current limiting diode is not only used for brightness control of LED illumination, but also can be used for protecting a power device from possible damage caused by overcurrent and overload.

Research on current limiters has led to relatively mature research in silicon carbide, silicon power devices, such as vertical depletion MOSFETs, SiC vertical JFETs, etc. However, there are few reports of GaN power diodes, which combine the advantages of GaN power devices and InGaN/GaN LEDs to further improve the reliability of the system and reduce the parasitic effect caused by interconnection.

Disclosure of Invention

In view of the above problems, the present invention provides a novel current limiting diode (as shown in fig. 5), in which a thin barrier AlGaN/GaN heterojunction (as shown in fig. 2) replaces a conventional heterojunction material (as shown in fig. 1), and a technique of growing a charge recovery layer (as shown in fig. 3) on the thin barrier material to modulate a two-dimensional electron channel is used, so as to avoid lattice damage caused by etching a barrier layer, ensure that electron mobility of two-dimensional electron gas is not reduced due to defect scattering after etching, and simultaneously achieve the purpose of accurately controlling the thickness of the barrier layer. The etched cathode charge recovery layer is used for forming a step (8), an effective modulation effect is formed on an electric field near the cathode, the length, the width and the depth of the step are changed, the regulation and control effect on the two-dimensional electron gas below the cathode is further realized, and the rectification capability of the diode is further realized.

The working principle of the novel current-limiting diode provided by the invention is as follows: ohmic contacts are formed on the source electrode, the drain electrode and the surface of the active region of the device to be used as a current input port and a current output port. And forming a gate groove between the source electrode and the drain electrode and close to the source electrode by partially and fully etching the charge recovery layer, and shorting the source electrode on the structure through Schottky metal to obtain the anode of the device. And etching the cathode charge recovery layer to form a ladder shape, and shorting the drain electrode on the ladder shape by Schottky metal to form the cathode of the device. When no voltage is applied to the grid electrode (anode), because the local depletion of the local 2-DEG below the grid electrode forms a higher potential barrier, electrons cannot pass through, the source electrode and the drain electrode cannot be conducted, and the device is in an off state. When a positive voltage with enough high voltage is applied to the grid electrode (anode), the potential barrier is lowered, the two-dimensional electron gas channel under the grid electrode is restored to be communicated, the source electrode and the drain electrode can be conducted, and the device is in an opening state. Meanwhile, the length, the width and the depth of the ladder are adjusted by the ladder-shaped field plate structure of the cathode, an obvious modulation effect is achieved on an electric field below the cathode, and the current is quickly saturated without changing the starting voltage of a device.

In the device with the conventional trench gate structure (as shown in fig. 4), electrons under the whole gate are completely depleted, and the full etching or partial etching of the barrier layer is involved, so that the process is difficult to control accurately. When the device is prepared by adopting the structure of the thin barrier material, the depletion effect on the two-dimensional electron gas can be realized by etching the charge recovery layer, the method has the advantages that fluorine-based gas used for etching the charge recovery layer hardly causes any etching effect on the barrier layer below the charge recovery layer, and finally, the self-termination at the AlGaN interface can be realized to realize the purpose of accurately controlling the barrier layer, so that the lattice damage caused by etching the barrier layer is avoided, the adverse effect of defect scattering on the electron mobility in the two-dimensional electron gas (3) is reduced, and the forward conduction characteristic of the device is improved.

In order to achieve the purpose, the invention adopts the following technical scheme:

a novel current-limiting diode is disclosed, which comprises a substrate 1, a heterojunction above the substrate, a charge recovery layer 7 above the heterojunction, a grid electrode, a source electrode and a drain electrode 5, wherein the heterojunction is formed by a GaN layer and an AlGaN layer above the GaN layer, the grid electrode is positioned above the heterojunction and forms Schottky contact with the heterojunction, the source electrode and the drain electrode are positioned on two sides of the upper surface of the charge recovery layer 7, and the upper surface of the source electrode is provided with source electrode metal; the upper surface of the drain electrode is provided with drain electrode metal; the method is characterized in that: the AlGaN layer is a thin barrier layer and has the thickness of 3-10 nm; the grid is a groove grid 9 structure formed by partially and fully etching the charge recovery layer 7, the grid is adjacent to the source electrode, and the grid metal extends to the upper surface of part of the source electrode metal; the drain metal extends along the upper surface of the charge recovery layer 7 towards the direction close to the source electrode, the drain metal of the part connected with the side surface of the drain electrode extends downwards into the charge recovery layer 7, the drain metal of the part extending into the charge recovery layer 7 is of a step-shaped structure, and the drain metal is of a laminated structure formed by Ni/Pt/Au. Preferably, the AlGaN barrier has a thickness of 5 nm.

Preferably, a dielectric layer is interposed between the gate electrode and the trench gate structure.

Preferably, the dielectric layer is one or a composite of more of Al2O3, SiO2, Si3N4, Ta2O5, MgO, Sc2O3, LaLuO3 and TiO 2.

Compared With ZHou C, Chen W, Piner E L, et al, "AlGaN/GaN double-Channel laser Field-efficiency Rectifier With drift down Immunity and Low On-Resistance [ J ]" IEEE Electron Device Letters,2010,31(1):5-7. the invention has the advantages that the enhancement purpose is realized without adopting ion implantation, because annealing and other materials are grown by high-temperature processes such as LPCVD (700 ℃ -800 ℃), PECVD (250-. Comparing Lee J G, Park B R, Cho C H, et al, "Low Turn-On Voltage AlGaN/GaN-On-Si Rectifier With Gated Ohmic Anode [ J ]" IEEE Electron devices Letters,2013,34(2):214 and 216. realizing enhancement by partially etching the gate trench; according to the invention, a heterojunction with a thin barrier is adopted to replace a traditional heterojunction structure, and a 10-200nm charge recovery layer is grown to recover two-dimensional electron gas in the heterojunction with the thin barrier; in addition, the special stepped field plate structure of the hybrid cathode has a regulating and controlling effect on two-dimensional electron distribution below the cathode through the stepped charge recovery layer; on the other hand, the special stepped metal plate of the mixed cathode can also regulate and control the electric field distribution below the cathode, and under the action of the two aspects, the diode can realize the function of quickly saturating to reach constant current by conducting current. The constant current, the current saturation point, the constant current range and the like can be regulated and controlled by regulating the step depth and the length of the mixed cathode.

The invention has the beneficial effects that: the invention provides a novel current-limiting diode, which utilizes the technology of growing a charge recovery layer on a thin potential barrier AlGaN/GaN heterojunction to modulate two-dimensional electron gas, and has the advantages that fluorine-based gas used for etching the charge recovery layer hardly causes any etching effect on the potential barrier layer below the charge recovery layer on the premise of realizing device enhancement, lower starting voltage and larger reverse withstand voltage, and finally the purpose of self-termination at an AlGaN interface to realize the accurate control of a barrier layer can be realized. The invention avoids etching the AlGaN layer and cannot damage the AlGaN layer, so that the device has higher current density, higher electron mobility and lower on-resistance. Meanwhile, the special stepped field plate structure of the cathode plays a role in regulating and controlling two-dimensional electron distribution below the cathode through the stepped charge recovery layer; on the other hand, the stepped metal field plate has obvious regulation and control capability on the electric field distribution below the cathode, and under the action of the two aspects, the current of the diode can be quickly saturated without obvious change of the starting voltage, so that the electric energy and power loss of the diode are reduced, and the current limiting range of the diode is enhanced.

Drawings

FIG. 1 is a schematic diagram of a cross-sectional structure of a source-drain wiring direction of a conventional barrier material;

FIG. 2 is a cross-sectional view of a thin barrier material source drain interconnect;

FIG. 3 is a schematic cross-sectional view of the source/drain connection after a 10-200nm charge recovery layer is grown on the surface of the thin barrier material;

FIG. 4 is a schematic diagram of a cross-sectional structure of a conventional barrier material for fabricating a source-drain wiring of a current limiter;

FIG. 5 is a cross-sectional view taken along the direction of the source/drain line of the present invention;

FIG. 6 is a schematic diagram of a three-dimensional structure of the Schottky metal prior to growing the same according to the present invention;

the device comprises a substrate 1, a GaN layer 2, a 2-DEG layer 3, an AlGaN layer 4, an ohmic metal 5, a Schottky metal 6, a charge recovery layer 7, a stepped field plate groove 8 and a groove gate formed by a charge recovery layer 9 all-time etching.

Detailed Description

The present invention has been described in detail in the summary of the invention section and will not be described in detail herein.

Claims

1. A current-limiting diode comprises a substrate (1), a heterojunction above the substrate, a charge recovery layer (7) above the heterojunction, a grid electrode, a source electrode and a drain electrode (5), wherein the heterojunction is formed by a GaN layer and an AlGaN layer above the GaN layer; the grid is Schottky metal and is positioned above the heterojunction and contacted with the AlGaN layer to form Schottky contact; the source electrode and the drain electrode are positioned on two sides of the upper surface of the charge recovery layer (7); the source electrode is an ohmic metal; the drain electrode is a stepped laminated structure consisting of ohmic metal and Schottky metal; the method is characterized in that: the AlGaN layer is a thin barrier layer and has the thickness of 3-10 nm; the grid is a groove grid (9) structure formed by partially and fully etching the charge recovery layer (7); the grid electrode is adjacent to the source electrode and extends to the upper surface of the source electrode; the Schottky metal part of the drain electrode is positioned above the ohmic metal, the rest part of the Schottky metal part extends to the direction close to the source electrode along the upper surface of the charge recovery layer (7), and the Schottky metal part of the part connected with the side surface of the ohmic metal part of the drain electrode forms a step-shaped structure (8) through partial incomplete etching of the charge recovery layer (7).

2. A current limiting diode according to claim 1 wherein: the thickness of the charge recovery layer (7) is 10-200 nm.

3. The current-limiting diode of claim 1, wherein: a dielectric layer is between the gate and the heterojunction.

4. A current limiting diode according to claim 3 wherein: the dielectric layer is made of Al₂O₃、SiO₂、Si₃N₄、Ta₂O₅、MgO、Sc₂O₃、LaLuO₃、TiO₂One or more of them are compounded.