Normally-off high electron mobility transistor integrated with gallium nitride thyristor and method for manufacturing the same

Abstract

The present invention provides a normally closed high electron mobility transistor integrated with a gallium nitride thyristor and a manufacturing method thereof, wherein the method uses a p-GaN / n-GaN / p-GaN three-layer structure to replace a traditional p-GaN capping layer, so that the three-layer structure can form a GaN-based thyristor structure with the n-AlGaN barrier layer below it. Since the turn-on voltage of the GaN-based thyristor is large, the normally closed HEMT device integrated with the GaN thyristor can have a larger positive threshold voltage. When the external bias reaches the threshold voltage, the HEMT device is turned on. At this time, the maintenance voltage required by the GaN-based thyristor is low and a large current can be generated, and the HEMTs will have a large operating leakage current. After the gate voltage of the HEMTs is cut off, under the action of the forward leakage voltage, the GaN-based thyristor will be in a reverse blocking state, and the HEMTs will be instantly turned off. At the same time, the device preparation process is a pure gallium nitride process, and the process is simple.

Description

Technical Field

[0001] The invention relates to the field of third-generation wide bandgap semiconductor devices, and in particular to a normally-off high electron mobility transistor with a large threshold voltage and a preparation method thereof. Background Art

[0002] With the rapid development of the semiconductor industry, generations of semiconductor materials have emerged. In the 1950s, the first generation of semiconductor devices represented by silicon and germanium were widely used; in the 1990s, the second generation of semiconductor materials came into being, and materials such as gallium arsenide and indium phosphide continued to challenge traditional silicon materials; but due to their high prices and toxicity, which have certain environmental pollution, the third generation of semiconductor materials, silicon carbide and gallium nitride (GaN), have attracted a lot of attention since their appearance.

[0003] In recent years, people have conducted a lot of research on GaN materials. GaN material is a new type of composite semiconductor material with many excellent properties, such as wide bandgap, high critical breakdown electric field, low on-resistance, high electron saturation velocity, good thermal conductivity, etc. Due to the excellent properties of GaN, AlGaN / GaN High-Electron Mobility Transistor (AlGaN / GaN HEMT) has great application prospects in many fields and has become a new research hotspot in the past two decades. The piezoelectric polarization effect of the AlGaN / GaN interface and the spontaneous polarization effect of the GaN layer and the AlGaN layer form a high concentration (>10 13 cm -2 ) and high mobility (>2000cm 2 / Vs) two-dimensional electron gas (2DEG), so that AlGaN / GaN HEMT devices can have both high breakdown voltage and low on-resistance. However, due to the presence of a large amount of 2DEG in the channel under the gate, the conventional AlGaN / GaN HEMT structure is in the on state without gate voltage. Although it can be used in low-voltage and high-frequency environments, in electronic power applications, the realization of normally-off HEMTs is necessary for safety reasons and the need to simplify the drive circuit.

[0004] At present, the main methods for realizing normally-off AlGaN / GaN HEMTs include p-GaN capping layer, thin barrier layer, trench gate structure, fluorine ion implantation and other technologies. The most popular method nowadays is to use a p-GaN capping layer, so that in the absence of an external gate voltage, the energy band of the AlGaN barrier layer will also be raised. When the barrier layer contacts the channel, the conduction band in the GaN channel layer below the capping layer will be raised above the Fermi level, and the 2DEG channel in this area will be depleted, so that the device will be normally closed. When there is an external gate bias, the p-GaN capping layer is depleted to share part of the applied gate voltage, so that the device can withstand a higher gate voltage without excessive gate current. However, the threshold voltage (V th ) is still low and cannot meet the 3V or above required in practical applications; and has a gate current (I g ) and large on-resistance. Therefore, the idea is to use a p-GaN / n-GaN / p-GaN three-layer structure to replace the traditional p-GaN cap layer. This three-layer structure and the n-AlGaN barrier layer below it form a GaN-based thyristor structure (GaN Thyristor), such as Figure 2 , thus optimizing the HEMT device characteristics.

[0005] Thyristor is a traditional high-power device in electronic power technology, mainly used for high voltage and high current control, so that the device can be converted from the closed or blocked state to the open or conducting state, and vice versa. Since the advent of silicon thyristors in the 1950s, researchers of power semiconductor devices have made unremitting efforts to achieve the goal of ideal devices and have achieved remarkable achievements. The so-called thyristor is essentially a pnpn structure semiconductor device that can realize the conversion of bistable positive feedback switching characteristics. Normally, a transistor requires a continuous base drive or gate voltage to turn on the device; for thyristors, the device can remain in the blocking state until a control signal causes it to switch to a low-resistance state, and this signal does not have to be maintained all the time.

[0006] Figure 3 The diagram is a basic structural diagram of a thyristor. The top p-type region is called the anode, and the bottom n-type region is called the cathode. If a positive voltage is applied to the anode, the J2 junction in the device is in a reverse bias state, and the blocking state of the thyristor will be maintained until the J2 junction begins to enter a breakdown state; if a negative voltage is applied to the anode, the J1 and J3 junctions in the device are in a reverse bias state, and the device also has only a very small current. Figure 4 is the current-voltage characteristic curve of the traditional thyristor, V pIt is the breakdown voltage of the J2 junction and also the turn-on voltage of the device. From the figure, we can see that the turn-on voltage of the thyristor is relatively large. After replacing the traditional p-GaN cover layer with a p-GaN / n-GaN / p-GaN three-layer structure, the normally closed HEMT device (GaN-Thyristor HEMTs) with integrated GaN thyristors can have a larger positive threshold voltage. When the applied bias reaches the threshold voltage, the GaN-based thyristor is turned on and the GaN-Thyristor HEMTs are turned on. Thereafter, the total voltage of the GaN-based thyristor will be reduced to almost a diode drop value, not only the required maintenance voltage is low, but also a very large current will be generated in the thyristor, so that the GaN-Thyristor HEMTs will have a large operating leakage current. When the gate voltage of the GaN-Thyristor HEMTs is cut off, there is still a forward leakage voltage in the HEMT device; under its action, the GaN-based thyristor will be in a reverse blocking state, and the GaN-Thyristor HEMTs will be instantly turned off, ensuring the safety of use. Summary of the invention

[0007] The present invention aims to provide a normally-off high electron mobility transistor integrated with a gallium nitride thyristor and a method for manufacturing the same, which provides a feasible solution for improving the threshold voltage and operating current of normally-off HEMTs and promotes the development of power switching devices to a certain extent.

[0008] The present invention adopts the following technical solutions:

[0009] A normally closed high electron mobility transistor with integrated gallium nitride thyristor, comprising a substrate, a nucleation layer, an aluminum gallium nitride (AlGaN) buffer layer, a gallium nitride (GaN) channel, an AlGaN barrier layer, a p-GaN1 layer, an n-GaN2 layer, a p-GaN3 layer, a source electrode, a drain electrode, a gate electrode, and a passivation layer;

[0010] The nucleation layer, the AlGaN buffer layer, the GaN channel, and the AlGaN barrier layer are grown from bottom to top on the substrate;

[0011] A p-GaN / n-GaN / p-GaN three-layer structure is arranged from bottom to top above the middle of the AlGaN barrier layer, including a p-GaN1 layer, an n-GaN2 layer, and a p-GaN3 layer;

[0012] The two ends of the AlGaN barrier layer are respectively provided with a source electrode and a drain electrode;

[0013] A gate is provided above the p-GaN3 layer;

[0014] A passivation layer is symmetrically arranged between the p-GaN / n-GaN / p-GaN three-layer structure and the source electrode and the drain electrode.

[0015] Further: the AlGaN barrier layer is thin and is made of unintentionally doped i-AlGaN or Si-doped n-AlGaN material. If it is n-AlGaN, its doping concentration is about 10 19 cm -3 .

[0016] Further: The Mg doping concentration in the p-GaN1 layer is about 10 17 ~10 18 cm -3 , and the thickness of this layer cannot be too large; the Si doping concentration in the n-GaN2 layer is about 10 14 cm -3 , and the thickness is thick; the Mg doping concentration in the p-GaN3 layer is about 10 19 cm -3 , and the thickness is thin.

[0017] Furthermore: the substrate may be any one of SiC, Si, GaN, and Al2O3; the nucleation layer may be one of GaN, AlN, and AlGaN; and the passivation layer may be SiN or Al2O3 or AlN.

[0018] Furthermore: the contact formed between the source and drain and the AlGaN barrier layer is an ohmic contact; the contact formed between the gate and the p-GaN3 layer is a Schottky contact; the electrode materials used for the source, drain and gate are one or more of metals Ni, Al, Au, Pt or Ti.

[0019] Furthermore, the AlGaN barrier layer, the p-GaN1 layer, the n-GaN2 layer and the p-GaN3 layer form a GaN-based thyristor structure. By utilizing the basic characteristics of the GaN-based thyristor structure, a normally-off HEMT device with a large forward threshold voltage, high operating current, fast closing speed and simple process can be obtained.

[0020] The method for preparing the normally-off high electron mobility transistor integrated with the gallium nitride thyristor comprises the following steps:

[0021] Step 1, growing a nucleation layer, an AlGaN buffer layer, a GaN channel, an AlGaN barrier layer, a p-GaN1 layer, an n-GaN2 layer, and a p-GaN3 layer from bottom to top on a substrate by metal organic chemical vapor deposition;

[0022] Step 2, dry etching the p-GaN1 layer, the n-GaN2 layer and the p-GaN3 layer to leave areas for growing the source electrode, the drain electrode and the passivation layer;

[0023] Step 3, using plasma enhanced chemical vapor deposition to form a passivation layer, and dry etching it to leave areas for growing source and drain electrodes;

[0024] Step 4, depositing a metal layer in the region where the source and drain are grown and reserved on the AlGaN barrier layer to form ohmic contact electrodes of the source and drain;

[0025] Step 5: deposit a metal layer on the p-GaN3 layer to form a Schottky gate.

[0026] Preferably, the source and drain growing regions are located at both ends of the AlGaN barrier layer; the passivation layer growing regions are located on the AlGaN barrier layer between the p-GaN / n-GaN / p-GaN three-layer structure and the source and drain.

[0027] The principle of the above-mentioned normally-off HEMT device with integrated GaN thyristor is:

[0028] When the p-GaN / n-GaN / p-GaN three-layer structure is used to replace the traditional p-GaN cap layer, the three-layer structure can form a GaN-based thyristor structure with the n-AlGaN barrier layer below it. Due to the large turn-on voltage of the GaN-based thyristor, the normally-off HEMT device (GaN-Thyristor HEMTs) with integrated GaN thyristors can have a larger positive threshold voltage. When the external bias reaches the threshold voltage, the GaN-based thyristor is turned on and the GaN-Thyristor HEMTs are turned on. Thereafter, the total voltage of the GaN-based thyristor will be reduced to almost a diode drop value, which not only requires a low maintenance voltage but also generates a large current, so that the GaN-Thyristor HEMTs will have a large operating leakage current. When the gate voltage of the GaN-Thyristor HEMTs is cut off, there is still a forward leakage voltage in the HEMT device; under its action, the GaN-based thyristor will be in a reverse blocking state, and the GaN-Thyristor HEMTs will be turned off instantly. At the same time, the three-layer structure used is all GaN material, and the device preparation process is pure gallium nitride technology, which is simple.

[0029] Beneficial Effects

[0030] (1) The present invention uses a p-GaN / n-GaN / p-GaN three-layer structure to replace the traditional p-GaN cap layer, providing another effective method for preparing a normally-off HEMT device. The three-layer structure used forms a GaN-based thyristor structure with the n-AlGaN barrier layer below it, thereby utilizing the basic characteristics of the GaN-based thyristor to prepare a normally-off HEMT device with a larger threshold voltage and a higher operating current.

[0031] (2) After the GaN-Thyristor HEMT device is turned on, the GaN-based thyristor only needs a very small voltage to maintain conduction, and a large current is generated in the thyristor, so the HEMT device will have a larger operating leakage current.

[0032] (3) After the gate voltage of GaN-Thyristor HEMTs is cut off, there is still a forward leakage voltage in the HEMT device. Under its action, the GaN-based thyristor will be in a reverse blocking state, and the GaN-Thyristor HEMTs will be turned off instantly, ensuring the safety of use.

[0033] (4) Since the GaN-based thyristor structure is p-GaN / n-GaN / p-GaN / n-AlGaN layers, the device preparation process is a pure gallium nitride process, which is simple.

[0034] (5) The present invention provides a feasible exploration idea for the research of normally-off HEMT devices, and opens up new application prospects of GaN-based thyristors in normally-off GaN-based HEMT devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The schematic diagram of the structure of the normally closed high electron mobility transistor integrated with the gallium nitride thyristor of the present invention is shown.

[0036] Figure 2 Schematic diagram of the structure of GaN-based thyristor.

[0037] Figure 3 Schematic diagram of the structure of a traditional pnpn thyristor.

[0038] Figure 4 is the current-voltage characteristic curve of the traditional pnpn thyristor.

[0039] Figure 5 It is a schematic diagram of the transfer characteristic curve of the normally-off high electron mobility transistor integrated with the gallium nitride thyristor of the present invention.

[0040] Figure 6 It is a schematic diagram of the output characteristic curve of the normally-off high electron mobility transistor integrated with the gallium nitride thyristor of the present invention. DETAILED DESCRIPTION

[0041] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0042] Example 1

[0043] See Figure 1A normally-off high electron mobility transistor with integrated gallium nitride thyristor of the present embodiment includes a SiC substrate 1, and an AlN nucleation layer 2, an AlGaN buffer layer 3, a GaN channel 4, and an i-AlGaN barrier layer 5 are grown from bottom to top on the SiC substrate 1; a source 9 and a drain 10 are provided at both ends of the i-AlGaN barrier layer 5, and a p-GaN / n-GaN / p-GaN three-layer structure and a gate 11 are provided from bottom to top in the middle; a SiN passivation layer 12 is symmetrically provided between the p-GaN / n-GaN / p-GaN three-layer structure and the source 9 and the drain 10.

[0044] The p-GaN / n-GaN / p-GaN three-layer structure includes a p-GaN1 layer 6 , an n-GaN2 layer 7 , and a p-GaN3 layer 8 .

[0045] The i-AlGaN barrier layer 5, p-GaN1 layer 6, n-GaN2 layer 7 and p-GaN3 layer 8 form a GaN-based thyristor structure. By utilizing the basic characteristics of the GaN-based thyristor structure, a normally-off HEMT device with a large forward threshold voltage, high operating current, fast closing speed and simple process can be obtained.

[0046] The present embodiment provides a method for manufacturing a normally-off high electron mobility transistor integrated with a gallium nitride thyristor, comprising the following steps:

[0047] Step 1, prepare a 2 μm thick SiC substrate 1 (can be homemade or purchased commercially), place the SiC substrate 1 in a reaction chamber of a metal organic chemical vapor deposition system, and anneal at about 970° C. in an atmosphere of H 2 and NH 3 .

[0048] Step 2: On the SiC substrate 1, Al source, Ga source, N source, Si source, hydrogen (H2) and nitrogen (N2) are used as carrier gases. A 5 nm thick AlN nucleation layer 2, a 1.25 μm thick AlGaN buffer layer 3, a 0.2 μm thick Mg doped layer with a thickness of 1e16 cm are grown from bottom to top by metal organic chemical vapor deposition. -3 GaN channel 4, 14nm thick i-AlGaN barrier layer 5, 30nm thick Mg doping with a density of 5e17 cm -3 The p-GaN1 layer is 60nm thick and Si doped with 1e14 cm -3 The Mg doped n-GaN2 layer of 7,35nm thickness is 1e19cm -3 p-GaN3 layer 8.

[0049] Step 3, using reactive ion etching technology, dry-etching the p-GaN1 layer, the n-GaN2 layer and the p-GaN3 layer to leave areas for growing the source, the drain and the passivation layer.

[0050] Step 4, using plasma enhanced chemical vapor deposition, using SiH4 and N2 as chemical reaction sources, selecting 200W RF power, 350°C growth temperature, and 18nm / min deposition rate to grow a 130nm thick Si3N4 passivation layer 12.

[0051] Step 5: using reactive ion etching technology, dry-etching the Si3N4 passivation layer 12 to leave areas for growing the source electrode 9 and the drain electrode 10.

[0052] Step 6: Use a magnetron sputtering coating machine to deposit a Ti / Al / Ti / Au multilayer metal structure on the surface of the i-AlGaN barrier layer 5, and then peel off and anneal at 870°C for 50s in a N2 atmosphere to form an ohmic contact source 9 and drain 10. The thickness is 11 / 70 / 30 / 25nm.

[0053] Step 7: Use a magnetron sputtering coating machine to sputter Ni / Au metal, grow a Schottky gate 11 with a thickness of 5 / 30 nm through a lift-off process, and then undergo a high temperature annealing at 700-900° C.

[0054] In step 1, a SiC substrate is used because many key physical properties of GaN materials are similar to those of SiC materials, and SiC materials have high resistivity and thermal conductivity, and are very suitable for high-power devices.

[0055] In step 6, in the source 9 and the drain 10, the first layer of Ti reacts with Al, GaN or AlGaN diffused to the interface to generate a multi-product containing Ti, Al, Ga and N, forming N vacancies in the surface layer of the semiconductor material, which is equivalent to n-type heavy doping; the second layer of Ti acts as a diffusion barrier layer to prevent Au from diffusing downward and reduce the reaction between Au and Al. The outermost layer of Au is to prevent Ti and Al from being oxidized and improve the thermal stability of the ohmic contact.

[0056] In step 7, Ni is selected as the metal for preparing the Schottky gate because its work function is greatly different from that of the AlGaN material and Ni has good adhesion. The introduction of Au is to prevent metal oxidation and reduce gate resistance.

[0057] The principle of a normally-off high electron mobility transistor integrated with a gallium nitride thyristor in this embodiment is:

[0058] When the p-GaN / n-GaN / p-GaN three-layer structure (p-GaN1 layer 6, n-GaN2 layer 7 and p-GaN3 layer 8) is used to replace the traditional p-GaN cap layer, the three-layer structure can form a GaN-based thyristor structure with the n-AlGaN barrier layer below it. Due to the large turn-on voltage of GaN-based thyristors, normally closed HEMT devices (GaN-Thyristor HEMTs) with integrated GaN thyristors can have a larger positive threshold voltage. It is estimated that the threshold voltage of the device at this time can reach more than 5V (such as Figure 5 ). When the applied bias reaches the threshold voltage, the GaN-based thyristor is turned on and the GaN-Thyristor HEMTs are turned on. After that, the total voltage of the GaN-based thyristor will be reduced to almost a diode voltage drop value, which not only requires a low maintenance voltage but also generates a large current, so that the GaN-Thyristor HEMTs will have a large operating leakage current (such as Figure 6 ). When the gate voltage of GaN-Thyristor HEMTs is cut off, there is still a forward drain voltage in the HEMT device; under its action, the GaN-based thyristor will be in a reverse blocking state, and the GaN-Thyristor HEMTs will be turned off instantly. At the same time, the three-layer structure used is all GaN material, and the device preparation process is a pure gallium nitride process with a simple process. If the doping and process parameters of the p-GaN / n-GaN / p-GaN three-layer structure are further optimized, the key performance indicators of the device can continue to improve.

[0059] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific 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 protection scope of the present invention.

Claims

1. A normally-off high electron mobility transistor integrated with a gallium nitride thyristor, characterized in that: It comprises a substrate (1), a nucleation layer (2), an AlGaN buffer layer (3), a GaN channel (4), an AlGaN barrier layer (5), a p-GaN1 layer (6), an n-GaN2 layer (7), a p-GaN3 layer (8), a source electrode (9), a drain electrode (10), a gate electrode (11), and a passivation layer (12); The nucleation layer (2), the AlGaN buffer layer (3), the GaN channel (4), and the AlGaN barrier layer (5) are grown from bottom to top on the substrate; A p-GaN / n-GaN / p-GaN three-layer structure is arranged from bottom to top above the middle of the AlGaN barrier layer (5), including a p-GaN1 layer (6), an n-GaN2 layer (7), and a p-GaN3 layer (8); A source electrode (9) and a drain electrode (10) are respectively provided at two ends of the AlGaN barrier layer (5); A gate (11) is provided above the p-GaN3 layer (8); A passivation layer (12) is symmetrically arranged between the p-GaN / n-GaN / p-GaN three-layer structure and the source electrode (9) and the drain electrode (10).

2. The normally-off high electron mobility transistor integrated with a gallium nitride thyristor according to claim 1, characterized in that: The AlGaN barrier layer (5) is thin and is made of unintentionally doped i-AlGaN or Si-doped n-AlGaN material. If it is n-AlGaN, its doping concentration is about 10 19 cm -3 .

3. The normally-off high electron mobility transistor integrated with a gallium nitride thyristor according to claim 1, characterized in that: The Mg doping concentration in the p-GaN1 layer (6) is 10 17 ~10 18 cm -3 ; The Si doping concentration in the n-GaN2 layer (7) is 10 14 cm -3 ; The Mg doping concentration in the p-GaN3 layer (8) is about 10 19 cm -3 .

4. The normally-off high electron mobility transistor integrated with a gallium nitride thyristor according to claim 1, characterized in that: The substrate (1) may be any one of SiC, Si, GaN, and Al2O3; the nucleation layer (2) may be any one of GaN, AlN, and AlGaN; and the passivation layer (12) may be SiN, Al2O3, or AlN.

5. The normally-off high electron mobility transistor integrated with a gallium nitride thyristor according to claim 1, characterized in that: The contact formed between the source electrode (9) and the drain electrode (10) and the AlGaN barrier layer (5) is an ohmic contact; the contact formed between the gate electrode (11) and the p-GaN3 layer (8) is a Schottky contact; the electrode materials used for the source electrode (9), the drain electrode (10) and the gate electrode (11) are one or more of the metals Ni, Al, Au, Pt or Ti.

6. The normally-off high electron mobility transistor integrated with a gallium nitride thyristor according to claim 1, characterized in that: The AlGaN barrier layer (5), the p-GaN1 layer (6), the n-GaN2 layer (7) and the p-GaN3 layer (8) form a GaN-based thyristor structure.

7. The method for preparing a normally-off high electron mobility transistor integrated with a gallium nitride thyristor according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1, growing a nucleation layer (2), an AlGaN buffer layer (3), a GaN channel (4), an AlGaN barrier layer (5), a p-GaN1 layer (6), an n-GaN2 layer (7), and a p-GaN3 layer (8) from bottom to top on a substrate (1) by metal organic chemical vapor deposition; Step 2, dry etching the p-GaN1 layer (6), the n-GaN2 layer (7) and the p-GaN3 layer (8) to leave areas for growing a source electrode (9), a drain electrode (10) and a passivation layer (12); Step 3, using plasma enhanced chemical vapor deposition to form a passivation layer (12), and dry etching it to leave areas for growing the source electrode (9) and the drain electrode (10); Step 4, depositing a metal layer in the region of the AlGaN barrier layer (5) reserved for growing the source electrode (9) and the drain electrode (10), so as to form an ohmic contact electrode between the source electrode (9) and the drain electrode (10); Step 5: depositing a metal layer on the p-GaN3 layer (8) to form a Schottky gate (11).

8. The method for preparing a normally-off high electron mobility transistor integrated with a gallium nitride thyristor according to claim 7, characterized in that: The regions for growing the source electrode (9) and the drain electrode (10) are located at two end positions on the AlGaN barrier layer (5); and the regions for generating the passivation layer (12) are located respectively on the AlGaN barrier layer (5) between the p-GaN / n-GaN / p-GaN three-layer structure and the source electrode (9) and the drain electrode (10).

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