Transistor device, semiconductor epitaxial structure and method for manufacturing the same

Abstract

The application discloses a transistor device, a semiconductor epitaxial structure and a preparation method thereof. The transistor device comprises a substrate, a compound semiconductor composite structure generating a two-dimensional electron gas, which is arranged on the substrate; a first cap layer arranged on the compound semiconductor composite structure; an insertion layer arranged on the first cap layer; a second cap layer arranged on the insertion layer; the band gap of the material of the insertion layer is greater than the band gap of the material of the first cap layer and the second cap layer; along the direction from the first cap layer to the second cap layer, the band gap of the material of the insertion layer first increases and then decreases; and a gate metal arranged on the second cap layer. In this way, the on-state gate leakage is reduced, the gate voltage resistance and the voltage swing of the device are increased, and the gate reliability of the device is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor technology, in particular to a transistor device, a semiconductor epitaxial structure and a preparation method thereof. BACKGROUND

[0002] The transistor device comprises an epitaxial layer and a gate metal arranged on the surface of the epitaxial layer, and an ohmic contact or a Schottky contact is formed between the gate metal and the surface of the epitaxial layer; when the device is turned on, there is a large gate leakage. SUMMARY

[0003] The transistor device, the semiconductor epitaxial structure and the preparation method thereof provided by the present application can reduce the on-state gate leakage.

[0004] To solve the above technical problems, the first technical solution provided by the present application is to provide a transistor device, comprising a substrate, a compound semiconductor composite structure generating two-dimensional electron gas arranged on the substrate, a first cap layer arranged on the compound semiconductor composite structure, an insertion layer arranged on the first cap layer, a second cap layer arranged on the insertion layer, the band gap of the material of the insertion layer is greater than the band gap of the material of the first cap layer and the second cap layer respectively, along the direction from the first cap layer to the second cap layer, the band gap of the material of the insertion layer first increases and then decreases, and the gate metal is arranged on the second cap layer.

[0005] To solve the above technical problems, the second technical solution provided by the present application is to provide a semiconductor epitaxial structure, comprising a substrate, a compound semiconductor composite structure generating two-dimensional electron gas arranged on the substrate, a cap layer arranged on the compound semiconductor composite structure, the cap layer comprising a first cap layer arranged on the compound semiconductor composite structure, an insertion layer arranged on the first cap layer, and a second cap layer arranged on the insertion layer, the band gap of the material of the insertion layer is greater than the band gap of the material of the first cap layer and the second cap layer respectively, along the direction from the first cap layer to the second cap layer, the band gap of the material of the insertion layer first increases and then decreases.

[0006] To solve the above technical problems, the third technical solution provided by the application is to provide a preparation method of a semiconductor epitaxial structure, which comprises the following steps: providing a substrate; forming a compound semiconductor composite structure generating two-dimensional electron gas on the substrate; forming a cap layer on the compound semiconductor composite structure, wherein the cap layer comprises a first cap layer arranged on the compound semiconductor composite structure, an insertion layer arranged on the first cap layer, and a second cap layer arranged on the insertion layer; the band gap of the material of the insertion layer is greater than the band gap of the material of the first cap layer and the second cap layer respectively; and along the direction from the first cap layer to the second cap layer, the band gap of the material of the insertion layer first increases and then decreases.

[0007] The application has the following beneficial effects: Different from the prior art, the application discloses a transistor device, a semiconductor epitaxial structure, and a preparation method thereof. The transistor device comprises a substrate, a compound semiconductor composite structure generating two-dimensional electron gas arranged on the substrate, a first cap layer arranged on the compound semiconductor composite structure, an insertion layer arranged on the first cap layer, a second cap layer arranged on the insertion layer, and a gate metal arranged on the second cap layer. The band gap of the material of the insertion layer is greater than the band gap of the material of the first cap layer and the second cap layer respectively. Along the direction from the first cap layer to the second cap layer, the band gap of the material of the insertion layer first increases and then decreases. By arranging the insertion layer between the first cap layer and the second cap layer, and by making the band gap of the material of the insertion layer greater than the band gap of the material of the second cap layer, a sharp peak is generated in the energy band of the cap layer, thereby reducing the on-state gate leakage current, increasing the gate withstand voltage and voltage swing of the device, and improving the gate reliability of the device. By making the band gap of the material of the insertion layer first increase and then decrease, the insertion layer is polarized with the first cap layer and the second cap layer, so that the sharp peak generated in the energy band of the cap layer is more obvious, thereby reducing the on-state gate leakage current. BRIEF DESCRIPTION OF DRAWINGS

[0008] In order to more clearly illustrate the technical solutions in the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0009] Figure 1 FIG. 1 is a structural schematic diagram of a transistor device provided by an embodiment of the application;

[0010] Figure 2 FIG. 2 is a structural schematic diagram of a cap layer of the transistor device shown in FIG. 1; Figure 1

[0011] Figure 3 FIG. 3 is a structural schematic diagram of another cap layer of the transistor device shown in FIG. 1; and​Figure 2 A schematic diagram of a variation of the band gap of the material in the cap layer is shown.

[0012] Figure 4 A schematic diagram of the band structure of the structure is shown. Figure 3 A schematic diagram of the band structure of the structure is shown.

[0013] Figure 5 A schematic diagram of the band structure of the structure is shown. Figure 1 A schematic diagram of the structure of another embodiment of the cap layer of the transistor device is shown.

[0014] Figure 6 A schematic diagram of the band structure of the structure is shown. Figure 5 A schematic diagram of a variation of the band gap of the material in the cap layer is shown.

[0015] Figure 7 A schematic diagram of a variation of the band gap of the material in the cap layer is shown. Figure 5 A schematic diagram of a variation of the band gap of the material in the cap layer is shown.

[0016] Figure 8 A schematic diagram of a variation of the band gap of the material in the cap layer is shown. x In y Ga 1-x-y A diagram of the relationship between the band gap of AlN and the composition is shown.

[0017] Figure 9 A schematic diagram of a comparison of the band structure of the insertion layer of the transistor device in different doping cases is shown.

[0018] Figure 10 A schematic diagram of a comparison of the gate leakage current of the insertion layer of the transistor device in different doping cases is shown.

[0019] Figure 11 A comparison diagram of the ID-VG experiment of the transistor device provided by the embodiment of the present application and the existing transistor device is shown.

[0020] Figure 12 A comparison diagram of the IG-VG experiment of the transistor device provided by the embodiment of the present application and the existing transistor device is shown.

[0021] Figure 13 A schematic diagram of a semiconductor epitaxial structure is shown. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0023] In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the application.

[0024] The terms "first", "second", "third", etc. are used herein only to describe different instances, and cannot be construed to refer to a relative importance or a specific number of the technical features indicated. Thus, the features defined with "first", "second", "third" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise explicitly and specifically limited. All directional indications (such as upper, lower, left, right, front, rear, etc.) in the embodiments of the present application are only used to explain the relative position relationship, movement condition, etc. between the components, and if the specific posture (as shown in the drawings) changes, the directional indications also change accordingly. The terms "comprise" and "have" and any variations thereof in the embodiments of the present application are intended to cover the inclusions without exclusivity. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units not listed, or can optionally include other steps or components inherent to the process, method, product or device.

[0025] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase that the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. As will be apparent to those of ordinary skill in the art, embodiments described herein can be combined with other embodiments.

[0026] The application will be described in detail below with reference to the drawings and embodiments.

[0027] Based on the spontaneous polarization and piezoelectric polarization effect of wide bandgap semiconductor gallium nitride based material (GaN, AlGaN, InGaN, etc.), high density and high mobility two-dimensional electron gas (2-DEG) is generated in the AlGaN / GaN heterojunction channel, so that the GaN-based HEMT (High Electron Mobility Transistor) device becomes a solution for high-efficiency and high-power-density power devices, which can provide greater breakdown voltage and power density. Under zero bias of the gate, the 2-DEG existing in the channel makes the device conductive, and the threshold voltage of the device is negative (depletion mode device). In order to simplify the gate drive circuit and for safety purposes, the channel needs to be turned off under zero bias in GaN power devices, and the threshold voltage needs to be positive (enhancement mode device). At present, the P-GaN gate structure is used in GaN HEMT devices to realize enhancement. The gate metal of the P-GaN gate HEMT device is usually in ohmic or Schottky contact with the underlying PGaN. When the device is turned on, there will be a large gate leakage, which results in weak gate voltage resistance of the device, small gate voltage swing, and poor gate reliability of the device.

[0028] In view of this, the embodiment of the present application provides a transistor device.

[0029] Please refer to Figures 1 to 7 , Figure 1 is a structure schematic diagram of the transistor device provided by the embodiment of the present application, Figure 2 is Figure 1 a structure schematic diagram of an embodiment of the cap layer of the transistor device shown in Figure 3 is Figure 2 a schematic diagram of one change mode of the band gap width of the material in the cap layer, Figure 4 is Figure 3 a schematic diagram of the energy band of the structure shown in Figure 5 is Figure 1 a structure schematic diagram of another embodiment of the cap layer of the transistor device shown in Figure 6 is Figure 5 a schematic diagram of one change mode of the band gap width of the material in the cap layer, Figure 7 is Figure 5 a schematic diagram of another change mode of the band gap width of the material in the cap layer.

[0030] The transistor device provided by the embodiment of the present application comprises a substrate 11, a compound semiconductor composite structure 12 generating two-dimensional electron gas, a cap layer 121 arranged on the compound semiconductor composite structure 12, the cap layer 121 comprising a first cap layer 1211 arranged on the compound semiconductor composite structure 12, an interposed layer 1212 arranged on the first cap layer 1211, and a second cap layer 1213 arranged on the interposed layer 1212. The band gap of the material of the interposed layer 1212 is greater than the band gap of the material of the first cap layer 1211 and the second cap layer 1213. A gate metal 13 is arranged on the second cap layer 1213.

[0031] In some embodiments, the gate metal 13 forms a Schottky contact or an ohmic contact with the second cap layer 1213.

[0032] In the prior art, the material of the entire cap layer is the same, there is almost no difference in the band gap, the gate metal forms a Schottky contact or an ohmic contact with the cap layer, and the device has a large gate leakage current when it is turned on, i.e., the on-state gate leakage current. In the embodiment of the present application, the interposed layer 1212 is arranged between the first cap layer 1211 and the second cap layer 1213, and the band gap of the material of the interposed layer 1212 is greater than the band gap of the material of the second cap layer 1213, so that a sharp peak is generated in the energy band of the cap layer 121, and there are sharp peaks in the conduction band and the valence band, which hinders the flow of electrons and holes, reduces the current size in the cap layer 121, and thus reduces the on-state gate leakage current, increases the gate withstand voltage capability and voltage swing of the device, and is beneficial to improving the gate reliability of the device.

[0033] In an embodiment, the transistor device is a GaN-based HEMT device. It can be understood that the present application is not limited to the GaN-based HEMT device, and can be applied to other devices with on-state gate leakage current.

[0034] In an embodiment, along the direction from the first cap layer 1211 to the second cap layer 1213, the band gap of the material of the interposed layer 1212 first increases and then decreases. The band gap of the material of the interposed layer 1212 is arranged to be variable, and the interposed layer 1212 is polarized with the first cap layer 1211 and the second cap layer 1213, so that the sharp peak generated in the energy band of the cap layer 121 is more obvious, and the on-state gate leakage current is further reduced.

[0035] In an embodiment, as shown in FIG. 1B, the interposed layer 1212 is a film layer structure. Optionally, as shown in FIG. 1C, the interposed layer 1212 is a plurality of film layers. Figure 2 Figure 3 ​As shown, along the direction from the first cap layer 1211 to the second cap layer 1213, the band gap of the material of the insertion layer 1212 first gradually increases and then gradually decreases, that is, the band gap of the middle part of the insertion layer 1212 is the largest, and gradually decreases to both sides. The band gap of the material of the surface of the insertion layer 1212 in contact with the first cap layer 1211 can be the same as or different from the band gap of the material of the surface of the insertion layer 1212 in contact with the second cap layer 1213, and is specifically designed according to requirements. For example, the insertion layer 1212 can be grown by MOCVD, in which the insertion layer 1212 with a variable band gap of the material is formed by adjusting the gas ratio. For example, the material of the insertion layer 1212 is AlGaN, the Al component of the surface of the insertion layer 1212 in contact with the first cap layer 1211 is 0 (that is, the band gap is 0), the Al component of the surface of the insertion layer 1212 in contact with the second cap layer 1213 is 0 (that is, the band gap is 0), and the Al component in the highest part of the insertion layer 1212 is 0.05-0.4, so as to achieve a better effect of reducing the on-state gate leakage current. For AlGaN, the Al component and the Ga component add up to 1, the higher the Al component, the lower the Ga component, and the larger the band gap.

[0036] According to Figure 4 As shown in the band diagram, by setting the insertion layer 1212 with a variable band gap of the material, a sharp peak is generated in the middle of the band of the cap layer 121, and the conduction band and the valence band both have sharp peaks, which hinders the flow of electrons and holes, thereby reducing the current size in the cap layer 121.

[0037] In addition, by setting the band gap of the material of the insertion layer 1212 to gradually increase first and then gradually decrease along the direction from the first cap layer 1211 to the second cap layer 1213, the stress mismatch introduced by the sudden change of the band gap of the material can be reduced, the polarization of the insertion layer 1212 with the first cap layer 1211 and the second cap layer 1213 is weakened, and the growth quality of the insertion layer 1212, the first cap layer 1211 and the second cap layer 1213 is improved, thereby reducing the interface charge and the interface state of the insertion layer 1212 with the first cap layer 1211 and the insertion layer 1212 with the second cap layer 1213, and facilitating the reduction of the gate leakage current and avoiding problems such as dynamic threshold voltage drift.

[0038] In some other embodiments, along the direction from the first cap layer to the second cap layer, the band gap of the material of the insertion layer 1212 first increases in steps and then decreases in steps.

[0039] In an embodiment, as shown in Figure 5As shown, the insertion layer 1212 is a multi-layer film layer structure, and the insertion layer 1212 includes 2n+1 sub-insertion layers 1212a, where n is greater than or equal to 1, and the thickness of each sub-insertion layer is the same, where the thickness direction is the direction from the first cap layer to the second cap layer. The band gap of the material of the n+1th sub-insertion layer 1212a is greater than the band gap of the material of the nth sub-insertion layer 1212a, and the band gap of the material of the n+1th sub-insertion layer 1212a is greater than the band gap of the material of the n+2th sub-insertion layer 1212a, so as to achieve the band gap of the material of the insertion layer 1212 first increasing and then decreasing along the direction from the first cap layer 1211 to the second cap layer 1213. The material of each sub-insertion layer 1212a is the same. For example, n=1, and the insertion layer 1212 includes three sub-insertion layers 1212a.

[0040] By inserting a plurality of sub-insertion layers 1212a with different band gaps of materials between the first cap layer 1211 and the second cap layer 1213, the band gap of the insertion layer 1212 is variable, and the insertion layer 1212 is polarized with the first cap layer 1211 and the second cap layer 1213, so that the peak generated in the energy band of the cap layer 121 is more obvious, and the on-state gate leakage is further reduced.

[0041] Optionally, the band gap of the material of each sub-insertion layer 1212a is the same. For example, as shown in FIG. 12B, Figure 6 As shown, n=1, and the insertion layer 1212 includes three sub-insertion layers 1212a, which are defined as a first sub-insertion layer 1212a-1, a second sub-insertion layer 1212a-2, and a third sub-insertion layer 1212a-3. The first sub-insertion layer 1212a-1 is located on one side of the second sub-insertion layer 1212a-2 close to the first cap layer 1211, and the third sub-insertion layer 1212a-3 is located on one side of the second sub-insertion layer 1212a-2 close to the second cap layer 1213. The band gap of the material of the first sub-insertion layer 1212a-1 is the same everywhere; the band gap of the material of the second sub-insertion layer 1212a-2 is the same everywhere; the band gap of the material of the third sub-insertion layer 1212a-3 is the same everywhere; the band gap of the material of the second sub-insertion layer 1212a-2 is greater than the band gap of the material of the first sub-insertion layer 1212a-1, and the band gap of the material of the second sub-insertion layer 1212a-2 is greater than the band gap of the material of the third sub-insertion layer 1212a-3; and the band gap of the material of the first sub-insertion layer 1212a-1 is the same as the band gap of the material of the third sub-insertion layer 1212a-3.

[0042] Optionally, the band gap of the material of each sub-insertion layer 1212a is set to be variable. For example, as shown in FIG. 12C, Figure 7As shown, n = 1, the insertion layer 1212 includes three sub-insertion layers 1212a, respectively defined as a first sub-insertion layer 1212a-1, a second sub-insertion layer 1212a-2 and a third sub-insertion layer 1212a-3, the first sub-insertion layer 1212a-1 is located on one side of the second sub-insertion layer 1212a-2 close to the first cap layer 1211, and the third sub-insertion layer 1212a-3 is located on one side of the second sub-insertion layer 1212a-2 close to the second cap layer 1213. In the direction from the first cap layer 1211 to the second cap layer 1213, the material band gap of the first sub-insertion layer 1212a-1 gradually increases, the material band gap of the second sub-insertion layer 1212a-2 gradually increases first and then gradually decreases, and the material band gap of the third sub-insertion layer 1212a-3 gradually decreases; the material band gap of the surface of the second sub-insertion layer 1212a-2 close to the first sub-insertion layer 1212a-1 is greater than the material band gap of the surface of the first sub-insertion layer 1212a-1 close to the second sub-insertion layer 1212a-2, and the material band gap of the surface of the second sub-insertion layer 1212a-2 close to the third sub-insertion layer 1212a-3 is greater than the material band gap of the surface of the third sub-insertion layer 1212a-3 close to the second sub-insertion layer 1212a-2. Through the above setting, the material band gap of the insertion layer 1212 changes approximately continuously and gradually, which can reduce the stress mismatch introduced by the sudden change of the material band gap.

[0043] It should be noted that the material band gap of the first sub-insertion layer 1212a-1, the second sub-insertion layer 1212a-2 and the third sub-insertion layer 1212a-3 can be grown by gas phase epitaxy (MOCVD) to grow the sub-insertion layer 1212a, wherein the sub-insertion layer 1212a with varying material band gap is formed by adjusting the gas ratio.

[0044] In an embodiment, the first cap layer 1211 and the second cap layer are both PGaN layers, and the materials thereof can both be P-type GaN materials.

[0045] In an embodiment, the material of the insertion layer 1212 is Al x In y Ga 1-x-y N, where 0 < x ≤ 1, 0 ≤ y ≤ 1, and 0 < x + y ≤ 1. The components of Al, In and Ga are 1. Please refer to Figure 8 , Figure 8 The relationship between the band gap of Al x In y Ga 1-x-y N and the component.

[0046] Al x In y Ga 1-x-yThe bandgap width of N satisfies the following formula:

[0047] Eg=xEg(AlN)+(1-xy)Eg(GaN)+yEg(InN)-b Al x(1-x)-b In y(1-y)

[0048] At room temperature, Eg(AlN) = 6.026 eV, Eg(GaN) = 3.39 eV, and Eg(InN) = 1.9 or 0.7 eV. Al b In It is related to the growth process. Figure 8 In the diagram, x represents the Al component, y represents the In component, curve 1 represents AlGaN, curve 2 represents InGaN, and curve 3 represents AlInN. (The remaining text appears to be a fragment and doesn't translate directly.) Figure 8 As can be seen, since both the first cap layer 1211 and the second cap layer 1213 are made of PGaN, the bandgap of the insertion layer 1212 only needs to be greater than the bandgap of GaN; AlInN without Ga composition is also acceptable. The bandgap of AlGaN is always greater than that of GaN. The bandgap of InGaN is always less than that of GaN. The bandgap of AlInN has a wide range, with some parts greater than that of GaN and some parts less than that of GaN. The bandgap of the material in the insertion layer 1212 is continuously varied; at the maximum bandgap Eg, it is also feasible to use AlN material, gradually transitioning to AlGaN, AlInN, or AlInGaN.

[0049] Optionally, when y = 0 and 0 < x ≤ 1, the Al component in the insert layer 1212 first increases and then decreases along the direction from the first cap layer 1211 to the second cap layer 1213. The bandgap width of the insert layer 1212 in this case is:

[0050] Eg=xEg(AlN)+(1-x)Eg(GaN)-b Al x(1-x), where b Al =1.3.

[0051] In the insertion layer 1212, the Al content first increases and then decreases, while the Ga content first decreases and then increases. The bandgap of the insertion layer 1212 also first increases and then decreases. For example, x = 0.5, and the material of the insertion layer 1212 is AlGaN.

[0052] In the insertion layer 1212, the In content first decreases and then increases, the Ga content first increases and then decreases, and the bandgap of the insertion layer 1212 first increases and then decreases. For example, y = 0.5, and the material of the insertion layer 1212 is InGaN.

[0053] Optionally, when x = 1 / 3 and y = 1 / 3, the material of the insertion layer 1212 is AlInGaN, and the composition of In, Al and Ga determines the band gap width together.

[0054] In some embodiments, when y is constant, the composition of Al in the insertion layer 1212 first increases and then decreases along the direction from the first cap layer 1211 to the second cap layer 1213, and the band gap width of the insertion layer 1212 first increases and then decreases.

[0055] In other embodiments, when x is constant, the composition of In in the insertion layer 1212 first decreases and then increases along the direction from the first cap layer 1211 to the second cap layer 1213, and the band gap width of the insertion layer 1212 first increases and then decreases.

[0056] It should be understood that when both x and y change, the change of the band gap width of Al x In y Ga 1-x-y N depends on the change direction and change amplitude of x, and the change direction and change amplitude of y. For example, when both x and y increase, if the increase amplitude of x is greater than that of y, the band gap width of Al x In y Ga 1-x-y N depends on the change of x, and if the increase amplitude of x is less than that of y, the band gap width of Al x In y Ga 1-x-y N depends on the change of y.

[0057] For example, along the direction from the first cap layer 1211 to the second cap layer 1213, the composition of Al in the insertion layer 1212 first increases from x1 to x2 and then decreases to x3, and the composition of In in the insertion layer 1212 first increases from y1 to y2 and then decreases to y3; the difference between x2 and x1 is greater than the difference between y2 and y1, and in this stage, the change trend of the band gap width of the insertion layer 1212 mainly depends on the composition of Al, and the band gap width increases along the direction from the first cap layer 1211 to the second cap layer 1213; and the difference between x2 and x3 is also greater than the difference between y2 and y3, and in this stage, the change trend of the band gap width of the insertion layer 1212 mainly depends on the composition of Al, and the band gap width decreases along the direction from the first cap layer 1211 to the second cap layer 1213.

[0058] Exemplarily, along the direction from the first cap layer 1211 to the second cap layer 1213, the Al component in the interposed layer 1212 first increases from x4 to x5 and then decreases to x6, and the In component in the interposed layer 1212 first increases from y4 to y5 and then increases to y6; the difference between x5 and x4 is greater than the difference between y5 and y4, at this stage, the change trend of the band gap width of the interposed layer 1212 mainly depends on the Al component, and the band gap width increases along the direction from the first cap layer 1211 to the second cap layer 1213; at the stage of the Al component x5 to x6 and the In component y5 to y6, the change trend of the band gap width of the interposed layer 1212 is affected by the Al component and the In component, the change trends of the band gap widths of the Al component and the In component are consistent, and the band gap width decreases along the direction from the first cap layer 1211 to the second cap layer 1213.

[0059] Exemplarily, along the direction from the first cap layer 1211 to the second cap layer 1213, the Al component in the interposed layer 1212 first increases from x7 to x8 and then decreases to x9, and the In component in the interposed layer 1212 first decreases from y7 to y8 and then increases to y9; at the stage of the Al component x7 to x8 and the In component y7 to y8, the change trend of the band gap width of the interposed layer 1212 is affected by the Al component and the In component, the change trends of the band gap widths of the Al component and the In component are consistent, and the band gap width increases along the direction from the first cap layer 1211 to the second cap layer 1213; at the stage of the Al component x8 to x9 and the In component y8 to y9, the change trend of the band gap width of the interposed layer 1212 is affected by the Al component and the In component, the change trends of the band gap widths of the Al component and the In component are consistent, and the band gap width decreases along the direction from the first cap layer 1211 to the second cap layer 1213.

[0060] Exemplarily, along the direction from the first cap layer 1211 to the second cap layer 1213, the Al component in the interposed layer 1212 first increases from x10 to x11 and then increases to x12, and the In component in the interposed layer 1212 first increases from y10 to y11 and then increases to y12; the difference between x11 and x10 is greater than the difference between y11 and y10, at this stage, the change trend of the band gap width of the interposed layer 1212 mainly depends on the Al component, and the band gap width increases along the direction from the first cap layer 1211 to the second cap layer 1213; the difference between y12 and y11 is greater than the difference between x12 and x11, at this stage, the change trend of the band gap width of the interposed layer 1212 mainly depends on the In component, and the band gap width decreases along the direction from the first cap layer 1211 to the second cap layer 1213.

[0061] Exemplarily, along the direction from the first cap layer 1211 to the second cap layer 1213, the Al component in the interposition layer 1212 first increases from x13 to x14 and then increases to x15, and the In component in the interposition layer 1212 first decreases from y13 to y14 and then increases to y15; in the stage of the Al component from x13 to x14 and the In component from y13 to y14, the change trend of the band gap width of the interposition layer 1212 is affected by the Al component and the In component, the change trends of the band gap widths of the Al component and the In component are consistent, and the band gap width increases along the direction from the first cap layer 1211 to the second cap layer 1213; the difference between y15 and y14 is greater than the difference between x15 and x14, and in this stage, the change trend of the band gap width of the interposition layer 1212 mainly depends on the In component, and the band gap width decreases along the direction from the first cap layer 1211 to the second cap layer 1213.

[0062] Exemplarily, along the direction from the first cap layer 1211 to the second cap layer 1213, the Al component in the interposition layer 1212 first decreases from x16 to x17 and then increases to x18, and the In component in the interposition layer 1212 first decreases from y16 to y17 and then increases to y18; the difference between x16 and x17 is less than the difference between y16 and y17, in this stage, the change trend of the band gap width of the interposition layer 1212 mainly depends on the In component, and the band gap width increases along the direction from the first cap layer 1211 to the second cap layer 1213; and the difference between x18 and x17 is less than the difference between y18 and y17, in this stage, the change trend of the band gap width of the interposition layer 1212 mainly depends on the In component, and the band gap width decreases along the direction from the first cap layer 1211 to the second cap layer 1213.

[0063] Exemplarily, along the direction from the first cap layer 1211 to the second cap layer 1213, the Al component in the interposition layer 1212 first decreases from x19 to x20 and then decreases to x21, and the In component in the interposition layer 1212 first decreases from y19 to y20 and then increases to y21; the difference between y19 and y20 is greater than the difference between x19 and x20, in this stage, the change trend of the band gap width of the interposition layer 1212 mainly depends on the In component, and the band gap width increases along the direction from the first cap layer 1211 to the second cap layer 1213; in the stage of the Al component from x20 to x21 and the In component from y20 to y21, the change trend of the band gap width of the interposition layer 1212 is affected by the Al component and the In component, the change trends of the band gap widths of the Al component and the In component are consistent, and the band gap width decreases along the direction from the first cap layer 1211 to the second cap layer 1213.

[0064] For example, along the direction from the first cap layer 1211 to the second cap layer 1213, the Al component in the insertion layer 1212 first decreases from x22 to x23 and then to x24, and the In component in the insertion layer 1212 first decreases from y22 to y23 and then to y24; the difference between y22 and y23 is greater than the difference between x22 and x23. In this stage, the bandgap width of the insertion layer 1212 mainly depends on the In component, and the bandgap width increases along the direction from the first cap layer 1211 to the second cap layer 1213; the difference between x23 and x24 is greater than the difference between y23 and y24. In this stage, the bandgap width of the insertion layer 1212 mainly depends on the Al component, and the bandgap width decreases along the direction from the first cap layer 1211 to the second cap layer 1213.

[0065] In one embodiment, the thickness of the first cap layer 1211 is 2nm-100nm; and / or the thickness of the insertion layer 1212 is 2nm-100nm; and / or the thickness of the second cap layer 1213 is 2nm-100nm. By designing the thicknesses of the first cap layer 1211, the insertion layer 1212, and the second cap layer 1213 as described above, the energy band is adjusted, the current is controlled, and thus the on-state gate leakage current is reduced.

[0066] For example, the thickness of the first cap layer 1211 is 50nm-100nm.

[0067] For example, the thickness of the insertion layer 1212 is 5nm-50nm.

[0068] For example, the thickness of the second cap layer 1213 is 5nm-50nm.

[0069] In one embodiment, the insertion layer 1212 is undoped.

[0070] In one embodiment, the insertion layer 1212 is P-doped.

[0071] In one embodiment, the insertion layer 1212 is N-doped.

[0072] It should be noted that, as Figure 9 As shown, Figure 9 This is a schematic diagram comparing the band structure of the transistor device with different doping conditions of the insertion layer according to the embodiments of this application; for the degree of band bending, the order is: P-doped insertion layer 1212 < undoped insertion layer 1212 < N-doped insertion layer 1212. Figure 10 As shown, Figure 10FIG. 3 is a comparison diagram of gate leakage current of the transistor device provided by the embodiment of the present application in different doping conditions of the insertion layer, for the gate leakage current, P-doped insertion layer 1212 > non-doped insertion layer 1212 > N-doped insertion layer 1212. The N-doped insertion layer 1212 can achieve a better effect of reducing the on-state gate leakage.

[0073] With reference to Figure 1 , along the direction from the first cap layer 1211 to the second cap layer 1213, the compound semiconductor composite structure 12 generating two-dimensional electrons includes the buffer layer 122, the first semiconductor layer 123 and the second semiconductor layer 124 arranged in layers, and the two-dimensional electron gas 2-DEG is formed between the first semiconductor layer 123 and the second semiconductor layer 124. The cap layer 121 is arranged on the surface of the second semiconductor layer 124 away from the first semiconductor layer 123.

[0074] In an embodiment, the material of the buffer layer 122 includes at least one of AlGaN, GaN and InAlGaN. For example, the material of the buffer layer 122 is AlGaN. For example, the buffer layer 122 is a superlattice of AlGaN and GaN materials.

[0075] In an embodiment, the material of the first semiconductor layer 123 includes one of GaN, AlGaN and InAlGaN.

[0076] In an embodiment, the material of the second semiconductor layer 124 includes one of AlGaN, InGaN and InAlGaN. It can be understood that when the material of the second semiconductor layer 124 includes AlGaN, the first cap layer 1211 in the cap layer 121 is in contact with the second semiconductor layer 124, and when the material of the first cap layer 1211 includes PGaN, it is beneficial to deplete the two-dimensional electron gas between the first semiconductor layer 123 and the second semiconductor layer 124, thereby forming an enhancement device.

[0077] With reference to Figure 1 , the transistor device further includes a source electrode 14 and a drain electrode 15, and the source electrode 14 and the drain electrode 15 are arranged on the side of the second semiconductor layer 124 away from the substrate 11 and above the two-dimensional electron gas. The cap layer 121 is laterally located between the source electrode 14 and the drain electrode 15.

[0078] With reference to Figure 11 and Figure 12 , Figure 11 is an ID-VG experimental comparison diagram of the transistor device provided by the embodiment of the present application and the existing transistor device, Figure 12 is an IG-VG experimental comparison diagram of the transistor device provided by the embodiment of the present application and the existing transistor device.

[0079] This application also provides an experimental comparison between the transistor device provided in the embodiments of this application and existing transistor devices. Figure 11 In the diagram, the horizontal axis represents the applied gate voltage VG, the vertical axis represents the current, ID represents the device's on-state current, and IG represents the device's gate leakage current. In this experiment, the only difference between the existing transistor device and the transistor device of this embodiment is the structure of the cap layer. The cap layer of the existing transistor device is a monolithic film structure, and the material includes PGaN. The cap layer 121 of the transistor device used in the experiment is... Figure 2 The cap layer 121 is shown.

[0080] like Figure 11 As shown, the ID of the transistor device provided in this embodiment is basically the same as that of existing transistor devices, indicating that the insertion layer 1212 between the first cap layer 1211 and the second cap layer 1213 will not affect the on-resistance. Figure 12 As shown, when VG is greater than 0V, the IG of the transistor device provided in this application embodiment is less than that of existing transistor devices. This indicates that the transistor device provided in this application embodiment can reduce on-state gate leakage current. Lower on-state gate leakage current indicates improved gate withstand voltage and gate voltage swing, while also improving gate reliability.

[0081] Transistor devices typically operate with a gate voltage of 6V, such as Figure 12 As shown, when the horizontal axis is 6V, the IG of the transistor device provided in this application embodiment is less than that of the existing transistor device, that is, the transistor device provided in this application embodiment reduces the leakage current.

[0082] Please see Figure 13 This application also provides a semiconductor epitaxial structure, which includes a substrate 11, a compound semiconductor composite structure 12 generating a two-dimensional electron gas, and a cap layer 121 disposed on the compound semiconductor composite structure 12. The cap layer 121 includes a first cap layer 1211 disposed on the compound semiconductor composite structure 12, an insertion layer 1212 disposed on the first cap layer 1211, and a second cap layer 1213 disposed on the insertion layer 1212. The bandgap of the material of the insertion layer 1212 is greater than the bandgap of the materials of the first cap layer 1211 and the second cap layer 1213. A gate metal 13 is disposed on the second cap layer 1213.

[0083] In the prior art, the material of the whole cap layer is the same, there is little band gap difference, the gate metal forms a Schottky contact or an ohmic contact with the cap layer, and the device has large gate leakage when it is turned on, that is, the on-state gate leakage. The embodiments of the present application set the insertion layer 1212 between the first cap layer 1211 and the second cap layer 1213, and the band gap of the material of the insertion layer 1212 is greater than the band gap of the material of the second cap layer 1213, so that a sharp peak is generated in the energy band of the cap layer 121, and there are sharp peaks in the conduction band and the valence band, which hinders the flow of electrons and holes, reduces the current size in the cap layer 121, thereby reducing the on-state gate leakage, increasing the gate withstand voltage capability and voltage swing of the device, and improving the gate reliability of the device.

[0084] In some embodiments, along the direction from the first cap layer 1211 to the second cap layer 1213, the band gap of the material of the insertion layer 1212 first increases and then decreases. The band gap of the material of the insertion layer 1212 is set to vary, and the insertion layer 1212 is polarized with the first cap layer 1211 and the second cap layer 1213, so that the sharp peak generated in the energy band of the cap layer 121 is more obvious, further reducing the on-state gate leakage.

[0085] It should be noted that the specific setting mode, material selection and technical effects that can be achieved of the insertion layer of the semiconductor epitaxial structure in the present embodiment can be referred to the related introduction of the insertion layer 1212 in the semiconductor device described above, and will not be repeated here.

[0086] The embodiments of the present application also provide a preparation method of a semiconductor epitaxial structure, which comprises:

[0087] providing a substrate;

[0088] forming a compound semiconductor composite structure generating two-dimensional electron gas on the substrate;

[0089] forming a cap layer on the compound semiconductor composite structure, the cap layer comprising a first cap layer arranged on the compound semiconductor composite structure, an insertion layer arranged on the first cap layer, and a second cap layer arranged on the insertion layer; the band gap of the material of the insertion layer is greater than the band gap of the material of the first cap layer and the second cap layer respectively; along the direction from the first cap layer to the second cap layer, the band gap of the material of the insertion layer first increases and then decreases.

[0090] Exemplarily, the compound semiconductor composite structure can be a III-V compound semiconductor composite structure.

[0091] Exemplarily, the compound semiconductor composite structure generating a two-dimensional electron gas can be grown on the substrate by a known semiconductor epitaxial growth method such as chemical vapor deposition.

[0092] The technical effects that can be achieved by the insertion layer in the semiconductor epitaxial structure prepared by the method can be referred to the above description of the insertion layer 1212 in the semiconductor device, and will not be repeated here.

[0093] The above is only an embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation using the content of the specification and drawings, or direct or indirect application in other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. A transistor device, characterized by, The method comprises: providing a substrate; forming a compound semiconductor composite structure generating two-dimensional electron gas on the substrate; forming a cap layer on the compound semiconductor composite structure, the cap layer comprising a first cap layer disposed on the compound semiconductor composite structure, an interposition layer disposed on the first cap layer, and a second cap layer disposed on the interposition layer; the material of the interposition layer has a band gap width greater than the band gap width of the material of the first cap layer and the second cap layer respectively; along the direction from the first cap layer to the second cap layer, the band gap width of the material of the interposition layer first increases and then decreases. The method comprises: providing a substrate; forming a compound semiconductor composite structure generating two-dimensional electron gas on the substrate; forming a cap layer on the compound semiconductor composite structure, the cap layer comprising a first cap layer disposed on the compound semiconductor composite structure, an interposition layer disposed on the first cap layer, and a second cap layer disposed on the interposition layer; the material of the interposition layer has a band gap width greater than the band gap width of the material of the first cap layer and the second cap layer respectively; along the direction from the first cap layer to the second cap layer, the band gap width of the material of the interposition layer first increases and then decreases.

2. The transistor device of claim 1, wherein, The method comprises:

3. The transistor device of claim 1, wherein, providing a substrate; 4. The transistor device of claim 3, wherein, forming a compound semiconductor composite structure generating two-dimensional electron gas on the substrate; forming a cap layer on the compound semiconductor composite structure, the cap layer comprising a first cap layer disposed on the compound semiconductor composite structure, an interposition layer disposed on the first cap layer, and a second cap layer disposed on the interposition layer; the material of the interposition layer has a band gap width greater than the band gap width of the material of the first cap layer and the second cap layer respectively; along the direction from the first cap layer to the second cap layer, the band gap width of the material of the interposition layer first increases and then decreases.

5. The transistor device of claim 1, wherein, The method comprises:

6. The transistor device of claim 1, wherein, The material of the insertion layer is Al x In y Ga 1-x-y N, 0 < x < 1, 0 < y < 1, and 0 < x + y < 1.

7. The transistor device of claim 6, wherein, providing a substrate; 8. The transistor device of claim 6, wherein, forming a compound semiconductor composite structure generating two-dimensional electron gas on the substrate; 9. A semiconductor epitaxial structure, characterized by, forming a cap layer on the compound semiconductor composite structure, the cap layer comprising a first cap layer disposed on the compound semiconductor composite structure, an interposition layer disposed on the first cap layer, and a second cap layer disposed on the interposition layer; the material of the interposition layer has a band gap width greater than the band gap width of the material of the first cap layer and the second cap layer respectively; along the direction from the first cap layer to the second cap layer, the band gap width of the material of the interposition layer first increases and then decreases. ​ ​ ​ 10. The epitaxial structure of claim 9, wherein, ​ 11. A method of producing a semiconductor epitaxial structure, characterized by, ​ ​ ​ ​

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