Transistor component, semiconductor epitaxy structure and methods for its fabrication

Abstract

The present application discloses a transistor device, a semiconductor epitaxy structure, and a method for their fabrication, wherein the transistor device comprises: a substrate; a compound semiconductor composite structure arranged on the substrate, generating a two-dimensional electron gas; a first cover layer arranged on the compound semiconductor composite structure; an intermediate layer arranged on the first cover layer; a second cover layer arranged on the intermediate layer, wherein the band gap of the intermediate layer material is larger than the band gap of the materials of the first and second cover layers, the band gap of the intermediate layer material initially increasing and then decreasing in the direction from the first cover layer to the second cover layer; and a gate metal arranged on the second cover layer.In this way, the gate leakage current in the switched-on state is reduced, the gate voltage withstand capability and gate voltage swing of the component are increased, and the gate reliability of the component is improved.

Description

Transistor device, semiconductor epitaxial structure and preparation method thereof Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a transistor device, a semiconductor epitaxial structure and a method for preparing the same. Background Art

[0002] The transistor device includes an epitaxial layer and a gate metal disposed 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 will be a large gate leakage. Summary of the Invention

[0003] The present application provides a transistor device, a semiconductor epitaxial structure, and a method for manufacturing the same, so as to reduce on-state gate leakage.

[0004] In order to solve the above technical problems, the first technical solution provided in the present application is: a transistor device is provided, including a substrate, a compound semiconductor composite structure that generates two-dimensional electron gas, which is arranged on the substrate; a first cap layer is arranged on the compound semiconductor composite decoupling strand; an insertion layer is arranged on the first cap layer; a second cap layer is arranged on the insertion layer; the band gap width of the material of the insertion layer is respectively greater than the band gap width of the material of the first cap layer and the second cap layer; wherein, along the direction from the first cap layer to the second cap layer, the band gap width of the material of the insertion layer first increases and then decreases; the gate metal is arranged on the second cap layer.

[0005] In order to solve the above-mentioned technical problems, the second technical solution provided in the present application is: providing a semiconductor epitaxial structure, comprising a substrate, a compound semiconductor composite structure that generates a 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 width of the material of the insertion layer is respectively greater than the band gap widths of the materials of the first cap layer and the second cap layer; wherein, along the direction from the first cap layer to the second cap layer, the band gap width of the material of the insertion layer first increases and then decreases.

[0006] In order to solve the above technical problems, the third technical solution provided in the present application is: to provide a method for preparing a semiconductor epitaxial structure, the method comprising: providing a substrate; forming a compound semiconductor composite structure that generates a 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 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 width of the material of the insertion layer is respectively greater than the band gap widths of the materials of the first cap layer and the second cap layer; wherein, along the direction from the first cap layer to the second cap layer, the band gap width of the material of the insertion layer first increases and then decreases.

[0007] The beneficial effects of this application are as follows: Different from the prior art, this application discloses a transistor device, a semiconductor epitaxial structure, and a method for preparing the same. The transistor device includes a substrate, a compound semiconductor composite structure generating a two-dimensional electron gas, disposed on the substrate; a first capping layer disposed on the compound semiconductor composite structure; an insertion layer disposed on the first capping layer; and a second capping layer disposed on the insertion layer. The bandgap width of the material of the insertion layer is greater than the bandgap widths of the materials of the first capping layer and the second capping layer, respectively. The bandgap width of the material of the insertion layer increases first and then decreases along the direction from the first capping layer to the second capping layer. A gate metal is disposed on the second capping layer. By disposing the insertion layer between the first capping layer and the second capping layer, and the bandgap width of the material of the insertion layer is greater than the bandgap width of the second capping layer, a peak is generated in the energy band of the capping layer, thereby reducing on-state gate leakage, increasing the gate withstand voltage capability and withstand voltage swing of the device, and improving the gate reliability of the device. By setting the bandgap width of the material of the insertion layer to increase first and then decrease, the insertion layer is polarized with the first and second capping layers, making the peak generated in the energy band of the capping layer more obvious, thereby reducing on-state gate leakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0009] FIG1 is a schematic structural diagram of a transistor device provided in an embodiment of the present application;

[0010] FIG2 is a schematic structural diagram of an embodiment of a cap layer of the transistor device shown in FIG1 ;

[0011] FIG3 is a schematic diagram of a method for changing the bandgap width of the material in the cap layer shown in FIG2 ;

[0012] FIG4 is a schematic diagram of the energy band of the structure shown in FIG3 ;

[0013] FIG5 is a schematic structural diagram of another embodiment of a cap layer of the transistor device shown in FIG1 ;

[0014] FIG6 is a schematic diagram showing a variation of the bandgap width of the material in the cap layer shown in FIG5 ;

[0015] FIG7 is a schematic diagram showing another variation of the bandgap width of the material in the cap layer shown in FIG5 ;

[0016] Figure 8 is Al x In y Ga 1-x-y The relationship between the band gap of N and its components;

[0017] FIG9 is a schematic diagram showing energy band comparison of different doping conditions of the insertion layer of the transistor device provided in an embodiment of the present application;

[0018] FIG10 is a schematic diagram comparing gate leakage currents of transistor devices provided in an embodiment of the present application under different doping conditions of the insertion layer;

[0019] FIG11 is a comparison diagram of ID-VG experiments of a transistor device provided in an embodiment of the present application and a conventional transistor device;

[0020] FIG12 is a comparison diagram of IG-VG experiments of the transistor device provided in an embodiment of the present application and the existing transistor device.

[0021] FIG13 is a schematic structural diagram of a semiconductor epitaxial structure provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0023] In the following description, for the purpose of explanation rather than limitation, specific details such as specific system structures, interfaces, and technologies are provided to facilitate a thorough understanding of the present application.

[0024] The terms "first," "second," and "third" in this application are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features specified as "first," "second," or "third" may explicitly or implicitly include at least one of the aforementioned features. In the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are intended only to illustrate the relative positional relationships and movement of components in a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly. The terms "including," "having," and any variations thereof in the embodiments of this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or device comprising a series of steps or units is not limited to the listed steps or units and may optionally include steps or units not listed, or may optionally include other steps or components inherent to such process, method, product, or device.

[0025] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of such phrases in various places in the specification does not necessarily refer to the same embodiment, nor do they constitute independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0026] The present application is described in detail below with reference to the accompanying drawings and embodiments.

[0027] The spontaneous polarization and piezoelectric polarization effects of wide-bandgap gallium nitride semiconductor materials (GaN, AlGaN, InGaN, etc.) generate a high-density, high-mobility two-dimensional electron gas (2-DEG) within the AlGaN / GaN heterojunction channel. This makes GaN-based HEMTs (High Electron Mobility Transistors) a highly efficient, high-power-density power device solution, offering increased breakdown voltage and power density. Under zero gate bias, the 2-DEG within the channel turns the device on, resulting in a negative threshold voltage (depletion-mode device). For safety and simplified gate drive circuitry, GaN power devices require the channel to be off at zero bias, resulting in a positive threshold voltage (enhancement-mode device). Currently, most GaN HEMTs use a P-GaN gate structure to achieve enhancement-mode operation. The gate metal of P-GaN-gate HEMT devices usually forms an ohmic or Schottky contact with the PGaN below. When the device is turned on, there will be a large gate leakage, resulting in weak gate voltage withstand capability and small gate voltage swing, which also leads to poor device gate reliability.

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

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

[0030] The transistor device provided in an embodiment of the present application includes a substrate 11, a compound semiconductor composite structure 12 that generates 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 band gap width of the material of the insertion layer 1212 is greater than the band gap width of the materials of the first cap layer 1211 and the second cap layer 1213. The gate metal 13 is disposed 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 entire cap layer is made of the same material with almost no difference in bandgap width. A Schottky contact or an Ohmic contact is formed between the gate metal and the cap layer, resulting in a large gate leakage when the device is turned on, i.e., on-state gate leakage. In the embodiment of the present application, an insertion layer 1212 is provided between the first cap layer 1211 and the second cap layer 1213, and the bandgap width of the material of the insertion layer 1212 is greater than the bandgap width of the material of the second cap layer 1213. This causes a spike to be generated in the energy band of the cap layer 121, with both the conduction band and the valence band having spikes. This simultaneously hinders the flow of electrons and holes, reduces the current in the cap layer 121, and thereby reduces on-state gate leakage, increases the gate withstand voltage capability and withstand voltage swing of the device, and helps improve the gate reliability of the device.

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

[0034] In one embodiment, the bandgap of the material of the insertion layer 1212 first increases and then decreases along the direction from the first cap layer 1211 to the second cap layer 1213. The bandgap of the material of the insertion layer 1212 is configured to vary, and the insertion layer 1212 is polarized with the first cap layer 1211 and the second cap layer 1213, making the peak in the energy band of the cap layer 121 more pronounced, further reducing on-state gate leakage.

[0035] In one embodiment, as shown in FIG2 , the insertion layer 1212 is a film layer structure. Optionally, as shown in FIG3 , along the direction from the first cap layer 1211 to the second cap layer 1213, the bandgap width of the material of the insertion layer 1212 first gradually increases and then gradually decreases, that is, the bandgap width of the middle part of the insertion layer 1212 is the largest and gradually decreases toward both sides. The bandgap width of the material on the surface of the insertion layer 1212 in contact with the first cap layer 1211 and the bandgap width of the material on the surface of the insertion layer 1212 in contact with the second cap layer 1213 may be the same or different, and may be specifically designed according to needs. For example, the insertion layer 1212 may be grown by vapor phase epitaxial growth (MOCVD), wherein the insertion layer 1212 with a material bandgap width varying is grown by adjusting the gas ratio. Exemplarily, 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 (i.e., the bandgap is 0), the Al component of the surface of the insertion layer 1212 in contact with the second cap layer 1213 is 0 (i.e., the bandgap is 0), and the highest Al component inside the insertion layer 1212 is 0.05-0.4, achieving a better effect of reducing on-state gate leakage; wherein, for AlGaN, the Al component and the Ga component add up to 1, the higher the Al component, the lower the Ga component will be, and the larger the bandgap.

[0036] According to the energy band diagram shown in Figure 4, it can be seen that by setting an insertion layer 1212 with a variable material band gap width, a peak is generated in the middle of the energy band of the cap layer 121, and both the energy band and the conduction band have peaks, which simultaneously hinders the flow of electrons and holes, thereby reducing the current in the cap layer 121.

[0037] In addition, the material band gap width of the insertion layer 1212 is set to gradually increase and then gradually decrease along the direction from the first cap layer 1211 to the second cap layer 1213, which can reduce the stress mismatch introduced by the sudden change of the material band gap width, weaken the polarization of the insertion layer 1212 and the first cap layer 1211 and the second cap layer 1213, and improve the growth quality of the insertion layer 1212, the first cap layer 1211, and the second cap layer 1213, thereby reducing the interface charge and interface state between the insertion layer 1212 and the first cap layer 1211 and the insertion layer 1212 and the second cap layer 1213. The interface state includes interface charge and interface traps, which is beneficial to reducing gate leakage 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 a step-by-step manner and then decreases in a step-by-step manner.

[0039] In one embodiment, as shown in FIG5 , the insertion layer 1212 is a multilayer film structure, and the insertion layer 1212 includes 2n+1 sub-insertion layers 1212a, where n is greater than or equal to 1, and each sub-insertion layer has the same thickness, wherein 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, thereby achieving 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. Exemplarily, n=1, and the insertion layer 1212 includes three sub-insertion layers 1212a.

[0040] By inserting several sub-insertion layers 1212a with different material band gap widths between the first cap layer 1211 and the second cap layer 1213, the band gap width of the insertion layer 1212 is varied, 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, further reducing the on-state gate leakage.

[0041] Optionally, the material band gap width of each sub-insertion layer 1212a is the same at all locations. For example, as shown in FIG6 , 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, respectively. The first sub-insertion layer 1212a-1 is located on a 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 a side of the second sub-insertion layer 1212a-2 close to the second cap layer 1213. The material bandgap width of the first sub-insertion layer 1212a-1 is the same at all locations; the material bandgap width of the second sub-insertion layer 1212a-2 is the same at all locations; the material bandgap width of the third sub-insertion layer 1212a-3 is the same at all locations; the material bandgap width of the second sub-insertion layer 1212a-2 is greater than the material bandgap width of the first sub-insertion layer 1212a-1, and the material bandgap width of the second sub-insertion layer 1212a-2 is greater than the material bandgap width of the third sub-insertion layer 1212a-3; the material bandgap width of the first sub-insertion layer 1212a-1 is the same as the material bandgap width of the third sub-insertion layer 1212a-3.

[0042] Optionally, the bandgap width of the material at each location of each sub-insertion layer 1212a is set to vary. For example, as shown in FIG7 , 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, respectively. The first sub-insertion layer 1212a-1 is located on a 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 a side of the second sub-insertion layer 1212a-2 close to the second cap layer 1213. Along the direction from the first cap layer 1211 to the second cap layer 1213, the material bandgap width of the first sub-insertion layer 1212a-1 gradually increases, the material bandgap width of the second sub-insertion layer 1212a-2 first gradually increases and then gradually decreases, and the material bandgap width of the third sub-insertion layer 1212a-3 gradually decreases; the material bandgap width of the second sub-insertion layer 1212a-2 near the first sub-insertion layer 1212a-1 is greater than the material bandgap width of the first sub-insertion layer 1212a-1 near the second sub-insertion layer 1212a-2, and the material bandgap width of the second sub-insertion layer 1212a-2 near the third sub-insertion layer 1212a-3 is greater than the material bandgap width of the third sub-insertion layer 1212a-3 near the second sub-insertion layer 1212a-2. Through the above configuration, the material bandgap width of the insertion layer 1212 changes approximately continuously and gradually, which can reduce stress mismatch introduced by sudden changes in the material bandgap width.

[0043] It should be noted that the band gaps of the materials of the above-mentioned first sub-insertion layer 1212a-1, second sub-insertion layer 1212a-2, and third sub-insertion layer 1212a-3 can be changed. The sub-insertion layer 1212a can be grown by metalorganic chemical vapor deposition (MOCVD). Among them, the sub-insertion layer 1212a with a changed band gap of the material is formed by adjusting the gas ratio during growth.

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

[0045] In one 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 sum of the components of Al, In, and Ga is 1. Please refer to FIG. 8. FIG. 8 is a graph showing the relationship between the band gap and the components of Al x In y Ga 1-x-y N.

[0046] Al x In y Ga 1-x-y The band gap of N satisfies the following formula:

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

[0048] Among them, at room temperature, Eg(AlN) = 6.026 eV, Eg(GaN) = 3.39 eV, Eg(InN) = 1.9 or 0.7 eV, and b Al 、b In are related to the growth process. In FIG. 8, x represents the Al component, y represents the In component, curve 1 represents AlGaN, curve 2 represents InGaN, and curve 3 represents AlInN. As can be seen from FIG. 8, since the materials of the first cap layer 1211 and the second cap layer 1213 both include PGaN, it is only necessary that the band gap of the insertion layer 1212 is greater than that of GaN. AlInN without the Ga component is also possible. The band gap of AlGaN is always greater than that of GaN. The band gap of InGaN is always less than that of GaN. The band gap of AlInN has a wide coverage range, some greater than that of GaN and some less than that of GaN. The band gap of the material of the insertion layer 1212 changes continuously. At the maximum of the band gap Eg, it is also feasible to be an AlN material, and it can gradually change to AlGaN or AlInN or AlInGaN.

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

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

[0051] The Al component of the insertion layer 1212 increases first and then decreases, the Ga component decreases first and then increases, and the band gap of the insertion layer 1212 increases first and then decreases. For example, x=0.5, and the material of the insertion layer 1212 is AlGaN.

[0052] The In component of the insertion layer 1212 first decreases and then increases, the Ga component first increases and then decreases, and the band gap 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 components of the three elements In, Al, and Ga jointly determine the band gap width.

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

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

[0056] It is important to understand that when both x and y are changed, Al x In y Ga 1-x-y The change of the bandgap width of N depends on the direction and magnitude of the change of x, as well as the direction and magnitude of the change of y. For example, when both x and y increase, if the increase of x is greater than the increase of y, then Al x In y Ga 1-x-y The band gap of N depends on the change of x. If the increase of x is less than the increase of y, then Al x In y Ga 1-x-y The N bandgap width 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 Al component in the insertion layer 1212 first increases from x1 to x2 and then decreases to x3, and the In component 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. At this stage, the bandgap width change trend of the insertion layer 1212 mainly depends on the Al component, and the bandgap 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. At this stage, the bandgap width change trend 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.

[0058] Exemplarily, along the direction from the first cap layer 1211 to the second cap layer 1213, the Al component in the insertion layer 1212 first increases from x4 to x5 and then decreases to x6, and the In component in the insertion 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 bandgap width change trend of the insertion layer 1212 mainly depends on the Al component, and the bandgap width increases along the direction from the first cap layer 1211 to the second cap layer 1213; in the stage from Al component x5 to x6 and In component y5 to y6, the bandgap width change trend of the insertion layer 1212 is affected by the Al component and the In component, the bandgap width change trends of the Al component and the In component are consistent, and the bandgap 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 insertion layer 1212 first increases from x7 to x8 and then decreases to x9, and the In component in the insertion layer 1212 first decreases from y7 to y8 and then increases to y9; in the stage from Al component x7 to x8 and In component y7 to y8, the bandgap width change trend of the insertion layer 1212 is affected by the Al component and the In component, and the bandgap width change trends of the Al component and the In component are consistent, and the bandgap width increases along the direction from the first cap layer 1211 to the second cap layer 1213; in the stage from Al component x8 to x9 and In component y8 to y9, the bandgap width change trend of the insertion layer 1212 is affected by the Al component and the In component, and the bandgap width change trends of the Al component and the In component are consistent, and the bandgap width decreases along the direction from the first cap layer 1211 to the second cap layer 1213.

[0060] 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 increases from x10 to x11 and then to x12, and the In component in the insertion layer 1212 first increases from y10 to y11 and then to y12; the difference between x11 and x10 is greater than the difference between y11 and y10. At this stage, the bandgap width change trend of the insertion layer 1212 mainly depends on the Al component, and the bandgap 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 bandgap width change trend of the insertion layer 1212 mainly depends on the In component, and the bandgap 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 insertion layer 1212 first increases from x13 to x14 and then to x15, and the In component in the insertion layer 1212 first decreases from y13 to y14 and then increases to y15; in the stages from the Al component x13 to x14 and from the In component y13 to y14, the changing trend of the bandgap width of the insertion layer 1212 is affected by the Al component and the In component, and the changing trends of the bandgap widths of the Al component and the In component are consistent, and the bandgap 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. At this stage, the changing trend of the bandgap width of the insertion layer 1212 mainly depends on the In component, and the bandgap 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 insertion layer 1212 first decreases from x16 to x17 and then increases to x18, and the In component in the insertion layer 1212 first decreases from y16 to y17 and then increases to y18; the difference between x16 and x17 is smaller than the difference between y16 and y17. At this stage, the bandgap width change trend 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; and the difference between x18 and x17 is smaller than the difference between y18 and y17. At this stage, the bandgap width change trend of the insertion layer 1212 mainly depends on the In component, and the bandgap 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 insertion layer 1212 first decreases from x19 to x20 and then to x21, and the In component in the insertion 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. At this stage, the bandgap width change trend 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; in the stage from Al component x20 to x21 and In component y20 to y21, the bandgap width change trend of the insertion layer 1212 is affected by the Al component and the In component, the bandgap width change trends of the Al component and the In component are consistent, and the bandgap 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. At this stage, the bandgap width change trend 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. At this stage, the bandgap width change trend 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 2 nm to 100 nm; and / or the thickness of the insertion layer 1212 is 2 nm to 100 nm; and / or the thickness of the second cap layer 1213 is 2 nm to 100 nm. By designing the thickness of the first cap layer 1211, the insertion layer 1212, and the second cap layer 1213 as described above, the energy band can be adjusted, the current can be controlled, and the on-state gate leakage can be reduced.

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

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

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

[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 shown in FIG9 , FIG9 is a schematic diagram comparing the energy bands of the transistor device provided in an embodiment of the present application under different doping conditions of the insertion layer; with respect to the degree of energy band bending, the insertion layer 1212 is P-doped < the insertion layer 1212 is undoped < the insertion layer 1212 is N-doped. As shown in FIG10 , FIG10 is a schematic diagram comparing the gate leakage current of the transistor device provided in an embodiment of the present application under different doping conditions of the insertion layer; with respect to the gate leakage current, the insertion layer 1212 is P-doped > the insertion layer 1212 is undoped > the insertion layer 1212 is N-doped. The insertion layer 1212 being N-doped can achieve a better effect in reducing on-state gate leakage.

[0073] Continuing with FIG1 , along the direction from first cap layer 1211 toward second cap layer 1213, compound semiconductor composite structure 12 generating two-dimensional electrons includes a stacked buffer layer 122, a first semiconductor layer 123, and a second semiconductor layer 124. A two-dimensional electron gas (2-DEG) is formed between first semiconductor layer 123 and second semiconductor layer 124. Cap layer 121 is disposed on a surface of second semiconductor layer 124 that is distal from first semiconductor layer 123.

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

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

[0076] In one embodiment, the material of the second semiconductor layer 124 includes one of AlGaN, InGaN, and InAlGaN. It is understood that when the material of the second semiconductor layer 124 includes AlGaN, the first cap layer 1211 in the cap layer 121 contacts the second semiconductor layer 124, and the material of the first cap layer 1211 includes PGaN, this facilitates depletion of the two-dimensional electron gas between the first semiconductor layer 123 and the second semiconductor layer 124, thereby forming an enhancement-mode device.

[0077] 1 , the transistor device further includes a source electrode 14 and a drain electrode 15 . The source electrode 14 and the drain electrode 15 are disposed on a 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 disposed between the source electrode 14 and the drain electrode 15 .

[0078] Please refer to Figures 11 and 12. Figure 11 is a comparison diagram of the ID-VG experiment of the transistor device provided in the embodiment of the present application and the existing transistor device. Figure 12 is a comparison diagram of the IG-VG experiment of the transistor device provided in the embodiment of the present application and the existing transistor device.

[0079] The present application also conducts an experimental comparison between the transistor device provided in the embodiment of the present application and the existing transistor device. In Figure 11, the horizontal axis represents the applied gate voltage VG, the vertical axis represents the current, ID represents the on-current of the device, and IG represents the gate leakage current of the device. In this experiment, the difference between the existing transistor device and the transistor device of the embodiment of the present application is only the different structure of the cap layer. The cap layer of the existing transistor device is an integral film layer structure, and the material includes PGaN. The cap layer 121 of the transistor device used in the experiment is the cap layer 121 shown in Figure 2.

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

[0081] When the transistor device is normally working, the applied voltage on the gate is 6V. As shown in FIG12 , when the horizontal axis is 6V, the IG of the transistor device provided in the embodiment of the present application is smaller than the IG of the existing transistor device, that is, the transistor device provided in the embodiment of the present application reduces the leakage current.

[0082] Referring to FIG. 13 , an embodiment of the present application further provides a semiconductor epitaxial structure comprising a substrate 11, a compound semiconductor composite structure 12 generating a two-dimensional electron gas, and a capping layer 121 disposed on the compound semiconductor composite structure 12. The capping layer 121 comprises a first capping layer 1211 disposed on the compound semiconductor composite structure 12, an insertion layer 1212 disposed on the first capping layer 1211, and a second capping layer 1213 disposed on the insertion layer 1212. The band gap of the material of the insertion layer 1212 is greater than the band gaps of the materials of the first capping layer 1211 and the second capping layer 1213. A gate metal 13 is disposed on the second capping layer 1213.

[0083] In the prior art, the entire cap layer is made of the same material with almost no difference in bandgap width. A Schottky contact or an Ohmic contact is formed between the gate metal and the cap layer, resulting in a large gate leakage when the device is turned on, i.e., on-state gate leakage. In the embodiment of the present application, an insertion layer 1212 is provided between the first cap layer 1211 and the second cap layer 1213, and the bandgap width of the material of the insertion layer 1212 is greater than the bandgap width of the material of the second cap layer 1213. This causes a spike to be generated in the energy band of the cap layer 121, with both the conduction band and the valence band having spikes. This simultaneously hinders the flow of electrons and holes, reduces the current in the cap layer 121, and thereby reduces on-state gate leakage, increases the gate withstand voltage capability and withstand voltage swing of the device, and helps improve the gate reliability of the device.

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

[0085] It should be noted that the specific configuration of the insertion layer of the semiconductor epitaxial structure of this embodiment, the material selection and the technical effects that can be achieved can be found in the relevant introduction of the insertion layer 1212 in the above-mentioned semiconductor device, and will not be repeated here.

[0086] The present invention also provides a method for preparing a semiconductor epitaxial structure, the method comprising:

[0087] providing a substrate;

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

[0089] A cap layer is formed 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 width of the material of the insertion layer is respectively greater than the band gap widths of the materials of the first cap layer and the second cap layer; wherein, along the direction from the first cap layer to the second cap layer, the band gap width of the material of the insertion layer first increases and then decreases.

[0090] Illustratively, the compound semiconductor composite structure may be a Group III-V compound semiconductor composite structure.

[0091] For example, forming a compound semiconductor composite structure generating two-dimensional electron gas on a substrate may be performed by growing the compound semiconductor composite structure generating two-dimensional electron gas on the substrate by a well-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 this method can be found in the relevant introduction of the insertion layer 1212 in the above-mentioned semiconductor device, and will not be repeated here.

[0093] The above is only an implementation method of the present application and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the description and drawings of this application, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A transistor device, wherein, comprising: a substrate; a compound semiconductor composite structure generating a two-dimensional electron gas, disposed on the substrate; a first cap layer disposed on the compound semiconductor composite structure; an insertion layer disposed on the first cap layer; a second cap layer disposed on the insertion layer; the bandgap of the material of the insertion layer is greater than the bandgaps of the materials of the first cap layer and the second cap layer respectively; wherein, along the direction from the first cap layer to the second cap layer, the bandgap of the material of the insertion layer first increases and then decreases; a gate metal, disposed on the second cap layer.

2. The transistor device according to claim 1, wherein, along the direction from the first cap layer to the second cap layer, the bandgap of the material of the insertion layer first gradually increases and then gradually decreases.

3. The transistor device according to claim 1, wherein, along the direction from the first cap layer to the second cap layer, the bandgap of the material of the insertion layer first increases stepwise and then decreases stepwise.

4. The transistor device according to claim 3, wherein, the insertion layer includes 2n + 1 sub-insertion layers, n is greater than or equal to 1, and the thicknesses of the respective sub-insertion layers are the same, wherein the thickness direction is the direction from the first cap layer to the second cap layer; the bandgap of the material of the (n + 1)-th sub-insertion layer is greater than the bandgap of the material of the n-th sub-insertion layer, and the bandgap of the material of the (n + 1)-th sub-insertion layer is greater than the bandgap of the material of the (n + 2)-th sub-insertion layer.

5. The transistor device according to claim 1, wherein, both the first cap layer and the second cap layer are PGaN layers.

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

7. The transistor device according to claim 6, wherein, when y is constant, along the direction from the first cap layer to the second cap layer, the Al component in the insertion layer first increases and then decreases.

8. The transistor device according to claim 6, wherein, when x is constant, along the direction from the first cap layer to the second cap layer, the In component in the insertion layer first decreases and then increases.

9. A semiconductor epitaxial structure, wherein, comprising: a substrate; a compound semiconductor composite structure generating a two-dimensional electron gas, disposed on the substrate; a cap layer disposed on the compound semiconductor composite structure, the cap layer including a first cap layer disposed on the compound semiconductor composite structure, an insertion layer disposed on the first cap layer, and a second cap layer disposed on the insertion layer; the bandgap of the material of the insertion layer is greater than the bandgaps of the materials of the first cap layer and the second cap layer respectively; wherein, along the direction from the first cap layer to the second cap layer, the bandgap of the material of the insertion layer first increases and then decreases.

10. The epitaxial structure according to claim 9, wherein, along the direction from the first cap layer to the second cap layer, the bandgap of the material of the insertion layer first gradually increases and then gradually decreases.

11. A method for preparing a semiconductor epitaxial structure, wherein, The method includes: providing a substrate; forming a compound semiconductor composite structure that generates a two-dimensional electron gas on the substrate; forming a cap layer on the compound semiconductor composite structure, the cap layer including a first cap layer disposed on the compound semiconductor composite structure, an insertion layer disposed on the first cap layer, and a second cap layer disposed on the insertion layer; the bandgap width of the material of the insertion layer is greater than the bandgap widths of the materials of the first cap layer and the second cap layer respectively; wherein, along the direction from the first cap layer to the second cap layer, the bandgap width of the material of the insertion layer first increases and then decreases.

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