Nitrogen polarity GaN HEMT device based on diamond substrate and preparation method

Abstract

The invention discloses a nitrogen polarity GaN HEMT (High Electron Mobility Transistor) device based on a diamond substrate and a manufacturing method of the nitrogen polarity GaN HEMT device. The SiNx layer is located on the diamond substrate; the inverted T-shaped gate electrode comprises a transverse structure and a longitudinal structure, and the transverse structure is located in the SiNx layer; the AlGaN barrier layer is located on the SiNx layer, and the longitudinal structure is located in the AlGaN barrier layer; the AlN insertion layer is located on the AlGaN barrier layer; the GaN channel layer is located on the AlN insertion layer, and the gallium polar surface of the GaN channel layer is in contact with the AlN insertion layer; the source electrode and the drain electrode are located at the two ends of the device, embedded into the GaN channel layer and not in contact with the AlN insertion layer, and the nitrogen polar face of the GaN channel layer is exposed. According to the invention, the gate electrode in the nitrogen polarity GaN-based HEMT device is arranged on the back surface, so that the gate control capability is improved, and the frequency characteristic of the device is further improved.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and in particular relates to a nitrogen-polar GaN HEMT device based on a diamond substrate and a preparation method thereof. Background Art

[0002] Gallium nitride (GaN), as a third-generation wide bandgap semiconductor material, has the advantages of high breakdown electric field, high electron mobility and high electron saturation velocity. Thanks to these advantages, GaN high electron mobility transistors (HEMT) have obvious advantages in fields such as radio frequency and microwave that require high power and high frequency.

[0003] Compared with traditional gallium-polar (Ga-polar) GaN-based HEMT devices, nitrogen-polar (N-polar) GaN-based HEMT devices have the following unique advantages: (1) greater device size scaling capability and RF application potential; (2) easier to form low-resistance ohmic contact; (3) stronger gate control capability; (4) effective suppression of short channel effect. It has great application potential in high-power microwave power transistors, CMOS logic gate circuits, ultra-high-speed digital signal integrated circuits and systems. However, in nitrogen-polar GaN / AlGaN / GaN heterostructures, 2DEG is easily formed at the GaN / AlGaN interface due to its opposite polarization direction to gallium polarity, so that in nitrogen-polar GaN-based HEMT devices, the contact between the electrode metal and the channel layer does not need to pass through the AlGaN barrier layer, which greatly reduces the ohmic contact resistance. However, the gate electrode metal will form a leakage channel with the GaN channel, and the ion bombardment during the etching process will damage the nitrogen-polar GaN channel. Therefore, a gate dielectric is usually required to reduce the leakage between the GaN channel and the gate electrode and reduce the damage to the GaN channel during the etching process.

[0004] However, doing so increases the distance between the gate electrode and the GaN channel, which will weaken the gate control capability and thus affect the frequency characteristics of the device. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a nitrogen-polar GaN HEMT device based on a diamond substrate and a preparation method. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0006] In a first aspect, an embodiment of the present invention provides a nitrogen-polar GaN HEMT device based on a diamond substrate, the device comprising:

[0007] Diamond substrate;

[0008] S Nx A layer located on the diamond substrate;

[0009] The inverted "T" type gate electrode comprises a lateral structure and a vertical structure, wherein the lateral structure is located at the SiN x In-layer;

[0010] AlGaN barrier layer, located on the SiN x layer, and the vertical structure is located in the AlGaN barrier layer;

[0011] An AlN insertion layer, located on the AlGaN barrier layer;

[0012] A GaN channel layer is located on the AlN insertion layer; wherein a gallium polarity surface of the GaN channel layer is in contact with the AlN insertion layer;

[0013] The source electrode and the drain electrode are located at two ends of the device, embedded in the GaN channel layer and not in contact with the AlN insertion layer; wherein the nitrogen polarity surface of the GaN channel layer is exposed.

[0014] In one embodiment of the present invention, the lateral structure of the inverted “T” type gate electrode is x The depth of the layer is less than that of the SiN x Half the thickness of the layer.

[0015] In one embodiment of the present invention, the depth of the vertical structure of the inverted “T” type gate electrode in the AlGaN barrier layer is greater than half of the thickness of the AlGaN barrier layer.

[0016] In one embodiment of the present invention, the SiN x The thickness of the layer is 20 nm to 50 nm.

[0017] In one embodiment of the present invention, the thickness of the AlGaN barrier layer is 15 nm to 50 nm.

[0018] In one embodiment of the present invention, the thickness of the GaN channel layer is 100 nm to 300 nm.

[0019] In a second aspect, an embodiment of the present invention provides a method for preparing a nitrogen-polar GaN HEMT device based on a diamond substrate, the preparation method comprising:

[0020] Obtaining a Si substrate;

[0021] Growing a GaN buffer layer on the Si substrate;

[0022] Growing a GaN channel layer on the GaN buffer layer; wherein the gallium polarity surface of the GaN channel layer is exposed;

[0023] growing an AlN insertion layer on the gallium polar surface of the GaN channel layer;

[0024] growing an AlGaN barrier layer on the AlN insertion layer;

[0025] Etching a middle region of the AlGaN barrier layer to form a gate groove, and depositing a gate metal in the gate groove and on the AlGaN barrier layer on both sides to form a “T”-shaped gate electrode;

[0026] Growing SiN on the “T” type gate electrode and the AlGaN barrier layer x layer;

[0027] In the SiN x A diamond substrate is grown on the layer;

[0028] Flipping the device, and etching away the Si substrate and the GaN buffer layer; wherein after flipping, the “T”-shaped gate electrode becomes an inverted “T”-shaped gate electrode, and after etching, the nitrogen polarity surface of the GaN channel layer is exposed;

[0029] Part of the nitrogen polarity surface of the GaN channel layer at both ends of the device is etched, and a source electrode and a drain electrode are formed on the remaining nitrogen polarity surface of the GaN channel layer at both ends of the device, and the source electrode and the drain electrode are not in contact with the AlN insertion layer.

[0030] In one embodiment of the present invention, growing a GaN channel layer on the GaN buffer layer comprises:

[0031] A GaN channel layer with a thickness of 100nm to 300nm is grown on the GaN buffer layer.

[0032] In one embodiment of the present invention, the depth of the gate groove formed by etching is greater than half the thickness of the AlGaN barrier layer.

[0033] In one embodiment of the present invention, the thickness of the gate metal deposited on the AlGaN barrier layer is less than that of the SiN x Half the thickness of the layer.

[0034] Beneficial effects of the present invention:

[0035] The nitrogen-polar GaN HEMT device based on diamond substrate proposed in the present invention innovatively places the gate electrode in the nitrogen-polar GaN-based HEMT device on the back side. The advantage of this is that the conventional nitrogen-polar GaN-based HEMT device avoids the problem that the leakage between the GaN channel and the gate electrode is reduced by the gate dielectric, but the distance between the gate electrode and the GaN channel is increased, resulting in a weakened gate control capability. Moreover, by growing the source-drain electrode and the gate electrode on both sides of the heterojunction, the ohmic contact resistance is reduced, and the contact between the gate electrode metal and the GaN channel layer is avoided. At the same time, there is no need to grow a gate dielectric layer, which improves the gate control capability and further improves the frequency characteristics of the device. At the same time, since the diamond substrate has good thermal conductivity and mechanical stability, it can effectively reduce the device temperature and provide good thermal management, which will improve the reliability and tolerance of the device and reduce the influence of thermal effects on the device performance. In general, the device structure proposed in the present invention has more application potential in high-power microwave power transistors, CMOS logic gate circuits, ultra-high-speed digital signal integrated circuits and systems.

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of a process of a nitrogen-polar GaN HEMT device based on a diamond substrate provided by an embodiment of the present invention;

[0038] Figure 2 It is a schematic flow chart of a method for preparing a nitrogen-polar GaN HEMT device based on a diamond substrate provided by an embodiment of the present invention;

[0039] Figure 3a to Figure 3g It is a structural schematic diagram corresponding to the preparation process of a nitrogen-polar GaN HEMT device based on a diamond substrate provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0041] Due to the inherent properties of GaN HEMT, severe local self-heating effects may occur in the conductive channel; this effect increases with the increase of device power density, and the substrates of nitride materials currently mostly use materials such as silicon and sapphire, which have poor thermal conductivity; a large amount of heat cannot be dissipated in time, which limits the performance of GaN devices and further damages reliability. To address this problem, existing methods provide nitrogen-polar GaN-based HEMT device structures based on diamond substrates. First, diamond has the highest thermal conductivity of all bulk materials, and the integration of diamond film and GaN-based HEMT devices as substrates or packages has been proven to enhance the extraction of heat generated during device operation, thereby significantly reducing the junction temperature, so that the maximum power density that GaN-based HEMT devices can safely handle is increased. Secondly, the method of controlling the polarity by inverting the formation of nitrogen polarity after epitaxy of gallium-polar GaN materials avoids many problems caused by the direct growth of nitrogen-polar GaN, thereby improving device performance. However, for nitrogen-polar GaN-based HEMT devices, not only the self-heating effect needs to be considered, but also the gate control capability needs to be considered to better improve the frequency characteristics of the device. In response to the above requirements, an embodiment of the present invention provides a nitrogen-polar GaN HEMT device based on a diamond substrate and a preparation method thereof.

[0042] First, see Figure 1 The embodiment of the present invention provides a nitrogen-polar GaN HEMT device based on a diamond substrate, the device comprising:

[0043] Diamond substrate;

[0044] S N x layer, located on a diamond substrate;

[0045] The inverted "T" type gate electrode includes a lateral structure and a vertical structure. The lateral structure is located at the SiN x In-layer;

[0046] AlGaN barrier layer, located on SiN x layer, and the vertical structure is located in the AlGaN barrier layer;

[0047] An AlN insertion layer located on the AlGaN barrier layer;

[0048] A GaN channel layer is located on the AlN insertion layer; wherein a gallium polar surface of the GaN channel layer is in contact with the AlN insertion layer;

[0049] The source electrode and the drain electrode are located at two ends of the device, embedded in the GaN channel layer and not in contact with the AlN insertion layer; wherein the nitrogen polarity surface of the GaN channel layer is exposed.

[0050] The thickness of the diamond substrate in the embodiment of the present invention is 50 μm to 200 μm;x The thickness of the layer is 20nm~50nm, SiN x The layer can be Si3N4, for example; the thickness of the AlGaN barrier layer is 15nm to 50nm; the thickness of the AlN insertion layer is 1nm to 2nm; the thickness of the GaN channel layer is 100nm to 300nm; the material of the source electrode and the drain electrode can be Ti / Al / Ni / Au, and the source electrode and the drain electrode are made of Figure 1 The black filling inside the GaN channel layer is shown; the material of the inverted "T" gate electrode can be Ni / Au, and the lateral structure of the inverted "T" gate electrode is on the SiN x The depth within the layer is less than that of SiN x half the thickness of the layer, preferably a lateral structure in SiN x The depth in the layer is 5nm-20nm, the depth of the vertical structure of the inverted "T" type gate electrode in the AlGaN barrier layer is greater than half the thickness of the AlGaN barrier layer, and preferably the depth of the vertical structure in the AlGaN barrier layer is 10nm-40nm.

[0051] In summary, the nitrogen-polar GaN HEMT device based on diamond substrate proposed in the embodiment of the present invention innovatively makes the gate electrode in the nitrogen-polar GaN-based HEMT device on the back side. The advantage of this is that it avoids the problem that the conventional nitrogen-polar GaN-based HEMT device reduces the leakage between the GaN channel and the gate electrode through the gate dielectric, but increases the distance between the gate electrode and the GaN channel, resulting in the weakening of the gate control ability. In addition, by growing the source-drain electrode and the gate electrode on both sides of the heterojunction, the ohmic contact resistance is reduced, and the contact between the gate electrode metal and the GaN channel layer is avoided. At the same time, there is no need to grow a gate dielectric layer, which improves the gate control ability and further improves the frequency characteristics of the device. At the same time, since the diamond substrate has good thermal conductivity and mechanical stability, it can effectively reduce the device temperature and provide good thermal management, which will improve the reliability and tolerance of the device and reduce the influence of thermal effects on the device performance. In general, the device structure proposed in the embodiment of the present invention has more application potential in high-power microwave power transistors, CMOS logic gate circuits, ultra-high-speed digital signal integrated circuits and systems.

[0052] Second, see Figure 2 The embodiment of the present invention provides a method for preparing a nitrogen-polar GaN HEMT device based on a diamond substrate, the preparation method comprising:

[0053] S10, obtaining a Si substrate.

[0054] The embodiment of the present invention is not limited to a Si substrate, and the obtained substrate may also be a sapphire substrate or the like.

[0055] S20. Growing a GaN buffer layer on the Si substrate.

[0056] The embodiment of the present invention adopts a MOCVD (Metal-organic Chemical Vapor Deposition) process to grow a GaN buffer layer with a thickness of 500nm to 2000nm on a Si substrate.

[0057] S30, growing a GaN channel layer on the GaN buffer layer; wherein the gallium polarity surface of the GaN channel layer is exposed.

[0058] The embodiment of the present invention adopts the MOCVD process to grow a GaN channel layer with a thickness of 100 nm to 300 nm on the GaN buffer layer, and at this time, the nitrogen polarity surface of the GaN channel layer is exposed.

[0059] S40, growing an AlN insertion layer on the gallium polar surface of the GaN channel layer.

[0060] The embodiment of the present invention adopts the MOCVD process to grow an AlN insertion layer with a thickness of 1 nm to 2 nm on the gallium polar surface of the GaN channel layer.

[0061] S50 , growing an AlGaN barrier layer on the AlN insertion layer.

[0062] The embodiment of the present invention adopts the MOCVD process to grow an AlGaN barrier layer with a thickness of 15nm to 50nm on the AlN insertion layer.

[0063] Finally, the device structure obtained after S10 to S50 in the embodiment of the present invention is as follows: Figure 3a As shown, the existing epitaxial structure as shown in 3a can also be directly obtained.

[0064] S60, etching the middle area of ​​the AlGaN barrier layer to form a gate groove, and depositing gate metal in the gate groove and on the AlGaN barrier layer on both sides to form a "T"-shaped gate electrode.

[0065] In the embodiment of the present invention, an ICP (Inductively Couple Plasma) process is used to etch the middle region of the AlGaN barrier layer to form a gate groove. At this time, it is necessary to ensure that the depth of the longitudinal structure of the inverted "T"-shaped gate electrode in the AlGaN barrier layer is greater than half of the thickness of the AlGaN barrier layer, that is, the depth of the gate groove formed by etching is greater than half of the thickness of the AlGaN barrier layer. Preferably, the depth of the gate groove formed by etching is 10nm to 40nm, that is, preferably, the depth of the longitudinal structure in the AlGaN barrier layer is 10nm to 40nm; and an electron beam evaporation process is used to deposit a gate metal such as Ni / Au on the AlGaN barrier layer in the gate groove and on both sides to form a "T"-shaped gate electrode such as Figure 3b shown.

[0066] It should be noted that when the AlGaN barrier layer is etched to form a gate groove, the depth of the gate groove is controllable, and a conventional depletion-mode GaN-based HEMT device can be made, or a deep gate groove can be formed to deplete the two-dimensional electron gas in the GaN channel layer under the gate electrode to realize an enhancement-mode GaN-based HEMT device, thereby improving the switching performance and operating frequency.

[0067] S70, growing SiN on the "T" type gate electrode and AlGaN barrier layer x layer.

[0068] The embodiment of the present invention uses PECVD (Plasma Enhanced Chemical Vapor Deposition) process to grow SiN with a thickness of 20nm to 50nm on the "T"-shaped gate electrode and AlGaN barrier layer. x Layer Figure 3c As shown, at this time, it is necessary to ensure that the "T" type gate electrode is on the SiN x The depth within the layer is less than that of SiN x The thickness of the gate metal deposited on the AlGaN barrier layer is less than that of the SiN x The thickness of the gate metal deposited on the AlGaN barrier layer is preferably 5nm to 20nm, that is, the "T" type gate electrode is preferably deposited on the SiN x The depth of the layer is 5nm to 20nm. x The purpose of the layer growth is to prevent the hydrogen ion etching used in the subsequent diamond substrate growth from damaging the underlying epitaxial layer.

[0069] S80, in SiN x A diamond substrate is grown on the layer.

[0070] The embodiment of the present invention adopts MPCVD (Microwave Plasma Chemical Vapor Deposition) process to deposit SiN x A diamond substrate with a thickness of 50 μm to 200 μm is grown on a layer such as Si3N4. Figure 3d The diamond substrate can increase the thermal conductivity and mechanical stability of the device, helping to reduce the temperature and improve the power handling capacity of the device.

[0071] S90, flipping the device over, and etching away the Si substrate and the GaN buffer layer; wherein, after flipping, the "T"-shaped gate electrode becomes an inverted "T"-shaped gate electrode, and after etching, the nitrogen polarity surface of the GaN channel layer is exposed.

[0072] In the embodiment of the present invention, the device obtained in step S80 is first turned over. Figure 3e As shown, the Si substrate and GaN buffer layer are then etched away. Figure 3f As shown, specifically: the Si substrate can be removed by wet etching or dry etching, if the sapphire substrate is used, it can be removed by laser, and the GaN buffer layer can be precisely etched by ICP (Inductively Coupled Plasma, inductively coupled plasma etching) process. At this time, the "T" type gate electrode becomes an inverted "T" type gate electrode, and the nitrogen polarity surface of the GaN channel layer is exposed.

[0073] S100, etching the nitrogen polarity surfaces of part of the GaN channel layer at both ends of the device, and forming a source electrode and a drain electrode on the nitrogen polarity surfaces of the remaining GaN channel layer at both ends of the device, and the source electrode and the drain electrode are not in contact with the AlN insertion layer.

[0074] In the embodiment of the present invention, the nitrogen polarity surface of the GaN channel layer at both ends of the device is obtained by etching S90 using the ICP process, that is, the etching depth is less than the thickness of the GaN channel layer, and ohmic metals such as Ti / Al / Ni / Au are deposited on the nitrogen polarity surface of the remaining GaN channel layer at both ends of the device to form source electrodes and drain electrodes, and they are not in contact with the AlN insertion layer. Figure 3g shown.

[0075] In summary, the method for preparing a nitrogen-polarity GaN HEMT device based on a diamond substrate provided by an embodiment of the present invention innovatively places the gate electrode on the back side of the nitrogen-polarity GaN-based HEMT device, and first grows a Ga-polarity GaN channel layer and then flips it to form an N-polarity GaN channel layer, so that the gate electrode can be grown first and then the nitrogen-polarity GaN channel layer can be formed. The advantage of this is that the conventional nitrogen-polarity GaN-based HEMT device avoids the problem of reducing the leakage between the GaN channel layer and the gate electrode through the gate dielectric, so that the device has better gate control capability; by etching the groove gate on the gallium polarity surface of the GaN channel layer, ion bombardment during the etching process to damage the nitrogen polarity surface of the GaN channel layer is avoided, the on-resistance of the device is effectively reduced and the leakage is reduced, thereby reducing energy loss and increasing the switching speed, thereby improving the efficiency of the device; after growing the gallium-polarity GaN wafer, the diamond substrate is replaced, and the diamond substrate has good thermal conductivity and mechanical stability, can effectively reduce the device temperature, and provide good thermal management, which will improve the reliability and tolerance of the device and reduce the impact of thermal effects on performance.

[0076] As for the preparation method embodiment of the second aspect, since it is basically similar to the device structure embodiment of the first aspect, the description is relatively simple, and the relevant parts may refer to the partial description of the device structure embodiment of the first aspect.

[0077] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0078] Although the present invention is described herein in conjunction with various embodiments, in the process of implementing the claimed invention, those skilled in the art may understand and implement other variations of the disclosed embodiments by viewing the specification and its drawings. In the specification, the word "comprising" does not exclude other components or steps, and "a" or "one" does not exclude multiple situations. Certain measures are recorded in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0079] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A nitrogen-polar GaN HEMT device based on a diamond substrate, characterized in that: The device comprises: Diamond substrate; S N x A layer located on the diamond substrate; The inverted "T"-shaped gate electrode comprises a lateral structure and a vertical structure, wherein the lateral structure is located at the SiN x In-layer; The AlGaN barrier layer is located on the SiN x layer, and the vertical structure is located in the AlGaN barrier layer; An AlN insertion layer, located on the AlGaN barrier layer; A GaN channel layer is located on the AlN insertion layer; wherein a gallium polarity surface of the GaN channel layer is in contact with the AlN insertion layer; The source electrode and the drain electrode are located at two ends of the device, embedded in the GaN channel layer and not in contact with the AlN insertion layer; wherein the nitrogen polarity surface of the GaN channel layer is exposed.

2. The nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 1, characterized in that: The lateral structure of the inverted "T" gate electrode is x The depth within the layer is less than that of the SiN x Half the thickness of the layer.

3. The nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 1, characterized in that: The depth of the vertical structure of the inverted “T” type gate electrode in the AlGaN barrier layer is greater than half of the thickness of the AlGaN barrier layer.

4. The nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 1, characterized in that: The SiN x The thickness of the layer is 20 nm to 50 nm.

5. The nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 1, characterized in that: The thickness of the AlGaN barrier layer is 15 nm to 50 nm.

6. The nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 1, characterized in that: The thickness of the GaN channel layer is 100nm-300nm.

7. A method for preparing a nitrogen-polar GaN HEMT device based on a diamond substrate, characterized in that: The preparation method comprises: Obtaining a Si substrate; Growing a GaN buffer layer on the Si substrate; Growing a GaN channel layer on the GaN buffer layer; wherein the gallium polarity surface of the GaN channel layer is exposed; growing an AlN insertion layer on the gallium polar surface of the GaN channel layer; growing an AlGaN barrier layer on the AlN insertion layer; Etching the middle area of ​​the AlGaN barrier layer to form a gate groove, and depositing gate metal in the gate groove and on the AlGaN barrier layer on both sides to form a "T"-shaped gate electrode; Growing SiN on the "T" type gate electrode and the AlGaN barrier layer x layer; In the SiN x A diamond substrate is grown on the layer; The device is flipped over, and the Si substrate and the GaN buffer layer are etched away; wherein, after flipping, the "T"-shaped gate electrode becomes an inverted "T"-shaped gate electrode, and after etching, the nitrogen polarity surface of the GaN channel layer is exposed; Part of the nitrogen polarity surface of the GaN channel layer at both ends of the device is etched, and a source electrode and a drain electrode are formed on the remaining nitrogen polarity surface of the GaN channel layer at both ends of the device, and the source electrode and the drain electrode are not in contact with the AlN insertion layer.

8. The method for preparing a nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 7, characterized in that: Growing a GaN channel layer on the GaN buffer layer, comprising: A GaN channel layer with a thickness of 100nm to 300nm is grown on the GaN buffer layer.

9. The method for preparing a nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 7, characterized in that: The depth of the gate groove formed by etching is greater than half the thickness of the AlGaN barrier layer.

10. The method for preparing a nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 7, characterized in that: The thickness of the gate metal deposited on the AlGaN barrier layer is less than that of the SiN x Half the thickness of the layer.

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