Aluminum-nitrogen HEMT device and preparation method thereof

Abstract

The invention discloses an aluminum-nitrogen HEMT (High Electron Mobility Transistor) device and a preparation method thereof, the aluminum-nitrogen HEMT device comprises an n-type contact improvement layer arranged between an aluminum-nitrogen barrier layer and a source and a drain, and the n-type contact improvement layer is obtained by performing n-type doping in a gallium-nitrogen material. According to the invention, the n-type contact improvement layer is arranged between the aluminum-nitrogen barrier layer and the source electrode and between the aluminum-nitrogen barrier layer and the drain electrode, and the n-type contact improvement layer is obtained by carrying out n-type doping in the gallium-nitrogen material layer, so that an energy band step structure can be constructed, and the effect of reducing the injection barrier and the contact resistance is achieved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and specifically to an aluminum nitride-based HEMT device and its fabrication method. Background Technology

[0002] Aluminum-nitrogen materials, such as AlN (aluminum nitride) and high-aluminum AlGaN (aluminum gallium nitride), have become important basic materials for deep ultraviolet optoelectronic devices, high-frequency and high-power HEMT (High electron mobility transistor) devices due to their ultra-wide bandgap, high breakdown field strength and excellent thermal stability.

[0003] However, the fabrication of HEMT devices on AlN or high-Al content AlGaN is consistently limited by excessively high metal-semiconductor contact resistance. This is because the conduction band of AlN and high-Al content AlGaN materials is much higher than the metal Fermi level, resulting in a large Schottky barrier between the metal and the semiconductor, making electron injection difficult. Even after annealing, traditional metal systems such as Ti / Al or Ti / Al / Ni / Au still struggle to form low-resistance ohmic contacts in high-Al materials. Furthermore, the high Al content increases the activation energy of n-type impurities such as Si, significantly reducing the effective electron concentration and resulting in a wider depletion layer in the contact region, further increasing contact resistance. Simultaneously, the electron freezing effect is significant in the high-Al barrier layer, leading to insufficient available electron concentration and affecting source / drain injection capabilities, thus limiting the on-current, transconductance, and frequency performance of AlN-based HEMTs. Summary of the Invention

[0004] To address at least one of the aforementioned problems, the inventors conducted extensive research and experiments, and serendipitously discovered that introducing an n-type gallium nitride (GaN) contact improvement layer between the aluminum nitride barrier layer and the source and drain electrodes in an aluminum nitride-based HEMT device could construct a bandgap structure, thereby reducing the injection barrier. Based on this discovery, the inventors proposed an aluminum nitride-based HEMT device.

[0005] The aluminum nitride HEMT device includes an n-type contact improvement layer disposed between the aluminum nitride barrier layer and the source and drain electrodes. The n-type contact improvement layer is obtained by n-type doping of gallium nitride material.

[0006] Because the present invention provides an n-type contact improvement layer between the aluminum nitride barrier layer and the source and drain, the n-type contact improvement layer is obtained by n-type doping in the gallium nitride material layer, which can construct a band ladder structure, thereby reducing the injection barrier and contact resistance.

[0007] In some embodiments, the aluminum-nitrogen HEMT device further includes an aluminum-nitrogen barrier layer, on which an n-type contact improvement layer is epitaxially grown. This results in an aluminum-nitrogen HEMT device with a low implantation barrier.

[0008] In some embodiments, the gallium nitride (GaN) material includes at least one of GaN (gallium nitride) and InGaN (indium gallium nitride). The GaN material used in the n-type contact improvement layer, employing at least one of GaN and InGaN, can construct a bandgap structure, effectively reducing the barrier height between the metal and aluminum nitride barrier layers in the source and drain, thereby lowering the injection barrier and improving electron injection efficiency.

[0009] During their research and experiments, the inventors also discovered that common wide-bandgap nitrides such as GaN have relatively small exciton Bohr radii (approximately 3 nm). When the size of the nanoislands is ≤6 nm, the quantum confinement effect is very significant; however, when the size ranges from nanometers to >10 nm, they are closer to "quasi-nanoislands," and the quantum effect weakens. Furthermore, the inventors found that common wide-bandgap nitrides can reduce the donor activation energy by lowering the conduction band edge energy level, thereby increasing the electron concentration of the system.

[0010] Based on the above findings, the inventors proposed setting GaN nanoislands in an aluminum nitride barrier layer. This is because the material in the aluminum nitride barrier layer is an ultrawide bandgap nitride, while GaN is a common wide bandgap nitride. This invention embeds narrow-bandgap nitride semiconductor nanoislands within a wide-bandgap n-type doped nitride layer. Since the conduction band bottom of ordinary wide-bandgap nitride nanoislands is typically lower than that of the ultra-wide-bandgap nitride matrix and closer to the donor level, the distance between the donor impurity (such as an n-type dopant) level and the conduction band bottom at the interface decreases. This improves the ionization behavior of the donor impurities, thereby reducing the activation energy. The lower activation energy facilitates ionization of the donor under lower thermal conditions, releasing more free electrons, increasing the electron concentration of the n-type doped nitride, and ultimately improving the overall carrier concentration of the material. This results in excellent n-type conductivity in the ultra-wide-bandgap n-type doped nitride. Furthermore, GaN nanoislands can form localized barriers in high Al barriers, trapping and releasing electrons, thus increasing the effective activation rate. Simultaneously, due to the localized quantum confinement effect of GaN nanoislands, the overall composition of the material does not change, meaning it does not reduce the material's breakdown voltage or other properties.

[0011] In some embodiments, the aluminum nitride barrier layer is made of AlN or high-Al content AlGaN. This allows for the creation of aluminum nitride HEMT devices with ultra-wide bandgap, high breakdown field strength, and excellent thermal stability.

[0012] In some implementations, the thickness of the n-type contact improvement layer ranges from 3 nm to 80 nm. This avoids both a decrease in device breakdown voltage due to an excessively thick n-type contact improvement layer and an inability to provide a sufficient number of electrons due to an excessively thin n-type contact improvement layer.

[0013] In some embodiments, the element used for n-type doping in gallium nitride (GaN) materials is at least one of Si and Ge (germanium); the region surrounding the GaN nanoislands in the aluminum nitride barrier layer is n-type doped, for example, by using delta doping or heavy doping of at least one of Si and Ge. Doping the region surrounding the GaN nanoislands in the aluminum nitride barrier layer can increase the effective electron concentration of the aluminum nitride barrier layer through the quantum potential well, giving the aluminum nitride barrier layer a higher carrier supply capability, thereby achieving low contact resistance and excellent electrical performance; moreover, this doping method can enhance electron accumulation in the potential well, thereby increasing the effective electron concentration of the barrier layer and mitigating the electron freezing effect.

[0014] In some implementations, the size of the GaN nanoislands ranges from 3 nm to 20 nm laterally and from 1 nm to 5 nm vertically. Since the inventors discovered that the quantum confinement effect is very significant when the nanoisland size is ≤ 6 nm, controlling the size of the GaN nanoislands within this range ensures the effectiveness of the quantum confinement effect.

[0015] In some embodiments, the thickness of the aluminum-nitrogen barrier layer ranges from 10 nm to 100 nm. GaN nanoislands are embedded in the aluminum-nitrogen barrier layer, and the GaN nanoislands divide the aluminum-nitrogen barrier layer into aluminum-nitrogen barrier sublayers with a thickness ranging from 2 nm to 10 nm (preferably 3 nm to 6 nm) along the growth direction of the aluminum-nitrogen barrier layer. Controlling the thickness of the aluminum-nitrogen barrier layer within the range of 10 to 100 nm ensures sufficient polarization charge to form a stable two-dimensional electron gas, while also providing structural space for the embedding of multiple GaN nanoislands. Simultaneously, it avoids the problems of stress accumulation and excessively long electron injection paths caused by an excessively thick aluminum-nitrogen barrier layer, thus achieving comprehensive optimization between two-dimensional electron gas density, contact injection efficiency, and structural reliability. Furthermore, by controlling the thickness of the aluminum-nitrogen barrier sublayers, while ensuring the isolation and structural stability of each GaN nanoisland layer, effective synergy of multiple quantum wells in the vertical direction can be achieved. This results in a high-density, stepwise release electron storage structure within the barrier layer, thereby improving the activation rate of embedded doped electrons and enhancing source and drain injection capabilities.

[0016] In some implementations, the high-Al composition AlGaN is AlGaN with an Al content of not less than 60%. Therefore, a high breakdown voltage can be ensured by maintaining a high Al content.

[0017] In some embodiments, the aluminum nitride HEMT device further includes source and drain electrodes deposited on an n-type contact improvement layer, and a gate electrode deposited on an aluminum nitride barrier layer. This improves the ohmic contact between the source and drain.

[0018] According to another aspect of the present invention, a method for fabricating the aforementioned aluminum nitride HEMT device is provided, comprising the following steps: S30: An n-type contact improvement layer is epitaxially grown on an aluminum nitride barrier layer. The n-type contact improvement layer is obtained by n-type doping of a gallium nitride material.

[0019] Because the present invention provides an n-type contact improvement layer between the aluminum nitride barrier layer and the source and drain, the n-type contact improvement layer is obtained by n-type doping in the gallium nitride material layer, which can construct a band ladder structure, thereby reducing the injection barrier.

[0020] In some embodiments, step S30, epitaxially growing an n-type contact improvement layer on the aluminum nitride barrier layer, includes: epitaxially growing a gallium nitride layer on the aluminum nitride barrier layer, and performing n-type doping on the gallium nitride layer to form the n-type contact improvement layer. The n-type contact improvement layer formed by n-type doping in the gallium nitride layer can construct a bandgap structure, thereby reducing the implantation barrier.

[0021] Before step S30, the following step S20 is also included: preparing an n-type doped aluminum-nitrogen barrier layer on the channel layer, surrounding the GaN nanoislands. This allows for an increase in the effective electron concentration of the aluminum-nitrogen barrier layer via a quantum potential well, resulting in a higher carrier supply capability, thus achieving low contact resistance and excellent electrical performance.

[0022] In some embodiments, step S20, preparing an aluminum-nitrogen barrier layer with n-type doped regions around the GaN nanoislands on the channel layer, includes: epitaxially growing an aluminum-nitrogen barrier layer on the channel layer, intermittently preparing GaN nanoislands during the growth of the aluminum-nitrogen barrier layer, and performing n-type doping in the regions surrounding each GaN nanoisland after the growth of each GaN nanoisland layer, to form an aluminum-nitrogen barrier layer with n-type doped regions around the GaN nanoislands. Generally, the GaN nanoislands are periodically arranged in the growth direction of the aluminum-nitrogen barrier layer.

[0023] In some embodiments, during step S30, when growing the gallium nitride-based material layer, the carrier concentration is increased to (0.8~3)×10⁻⁶ by introducing at least one of Si and Ge. 19 cm -3 To obtain an n-type contact improvement layer.

[0024] In some embodiments, step S20, preparing GaN nanoislands includes: after preparing 0.6 to 1.6 times the size of a single atomic layer (one GaN hexagonal cell) of GaN, interrupting the growth for 5 to 30 seconds to allow the GaN to form island-shaped nanoislands. By controlling the size of the GaN nanoislands, the growth of GaN nanoislands on the surface of the aluminum nitride barrier layer can be transformed from a two-dimensional layered growth mode to a stable three-dimensional island growth mode, thereby forming GaN nanoislands with controlled size and uniform distribution. This deposition amount range can avoid the problem of insufficient deposition amount leading to difficulty in GaN nanoisland nucleation, and can also prevent excessive deposition amount from causing GaN nanoislands to merge and form a continuous thin layer, which is beneficial for obtaining discrete GaN nanoislands with obvious quantum confinement effects. Combined with the subsequent growth interruption step, atomic rearrangement and island stability can be further promoted, making the formed GaN nanoislands an effective local quantum potential well in the aluminum nitride barrier layer, improving the activation rate of embedded doped electrons, and enhancing the electron supply capability of the aluminum nitride barrier layer.

[0025] In some embodiments, in step S20, after the growth of each GaN nanoisland layer, n-type doping in the region surrounding the GaN nanoisland includes: after the growth of each nanoisland layer, introducing at least one of Si and Ge as a δ-doping source within a 2nm range above and below the nanoisland layer, and controlling the equivalent areal density of the doping to be (1~8)×10⁻⁶. 13 cm -2 This can improve the electron transport capability between GaN nanoislands and aluminum nitride barrier layers. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of an aluminum nitride HEMT device according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the process structure for fabricating an aluminum nitride HEMT device according to the first embodiment of the present invention. Figure 3 This is a schematic diagram of the process structure for fabricating an aluminum nitride HEMT device according to the second embodiment of the present invention. Figure 4 This is a schematic diagram of the process structure for fabricating an aluminum nitride HEMT device according to the third embodiment of the present invention. Figure 5 This is a schematic diagram of the process structure for fabricating an aluminum nitride HEMT device according to the fourth embodiment of the present invention. Figure 6 This is a schematic diagram of the process structure for fabricating an aluminum nitride HEMT device according to the fifth embodiment of the present invention. Figure 7The diagram shows the CBM (Conduction Band Minimum) and its difference, and the VBM (Valence Band Maximum) of AlN, GaN, and InN. Figure 8 Schematic diagram of CBM before and after embedding GaN nanoislands into AlN; Figure reference numerals: 21, substrate; 22, template layer; 23, channel layer; 24, aluminum nitride barrier layer; 241, aluminum nitride barrier sublayer; 25, GaN nanoisland; 26, n-type contact improvement layer; 27, source; 28, drain; 29, gate. Detailed Implementation

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0028] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising" or "including" include not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. The terminology used herein is generally that commonly used by those skilled in the art; in case of any discrepancy with commonly used terminology, the terminology used herein shall prevail.

[0029] Furthermore, for ease of description, spatial relative terms such as “below,” “under,” “lower,” “above,” and “upper” may be used herein to describe the relationship between one element or component and another (or other) element or component as shown in the figure. In addition to the orientation shown in the figure, spatial relative terms are intended to include different orientations of the device during use or operation. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptors used herein can be interpreted accordingly.

[0030] In this invention, the term "δ-doping" refers to a precise doping technique at the atomic level. It involves introducing an extremely high concentration of dopant gas during semiconductor crystal growth for a very short time (or even pausing growth), thereby forming a very thin (only 1-2 atomic layers thick) doped plane with an extremely high doping concentration. This plane resembles a two-dimensional "sheet," hence the name δ-doping. The concentration of this doping is extremely steep in the vertical direction, approximating a δ function (pulse), with extremely high spatial precision. The dopant is confined within an atomic layer, resulting in very low impurity scattering and spatial separation of charge carriers and dopant impurities.

[0031] In this invention, the term "heavy doping" refers to the process of artificially introducing a very high concentration of impurity atoms (donors or acceptors) into a semiconductor material, thereby significantly altering the material's electrical properties (such as carrier concentration, Fermi level position, band gap, etc.). It is relative to light doping. The direct result of heavy doping is an extremely high concentration of free electrons (n-type) or holes (p-type) in the material, typically reaching 10¹⁸ cm⁻³ to 10²¹ cm⁻³ or even higher. This results in extremely low resistivity, approaching that of a metal. When the doping concentration reaches a certain level, the Fermi level will penetrate into the conduction band (n-type) or valence band (p-type), a phenomenon known as "degeneracy." At this point, the semiconductor behaves more like a metal, and its conductivity becomes less sensitive to temperature changes. Moreover, heavy doping can reduce contact resistance through the tunneling effect.

[0032] In this invention, the term "nano island" refers to an artificial semiconductor nanostructure whose dimensions are extremely small in all three dimensions [typically 1 nm to 10 nm (nanometers), approximately 10 to 50 atomic diameters], such that charge carriers (electrons and holes) are severely confined in all three spatial directions and cannot move freely. This leads to a fundamental change in its physical properties, exhibiting a significant quantum confinement effect.

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] To address at least one of the aforementioned problems, the inventors conducted extensive research and experiments, and accidentally discovered that introducing an n-type gallium nitride (GaN) contact improvement layer between the aluminum nitride barrier layer 24 and the source 27 and drain 28 in an aluminum nitride HEMT device could construct a bandgap structure, thereby reducing the injection barrier. Based on this discovery, the inventors proposed an aluminum nitride HEMT device.

[0035] Figure 1 An aluminum nitride HEMT device according to an embodiment of the present invention is shown as an example.

[0036] like Figure 1 As shown, the aluminum nitride HEMT device includes an n-type contact improvement layer 26 disposed between the aluminum nitride barrier layer 24 and the source 27 and drain 28. The n-type contact improvement layer 26 is obtained by n-type doping of gallium nitride material.

[0037] Since the present invention provides an n-type contact improvement layer 26 between the aluminum nitride barrier layer 24 and the source 27 and drain 28, the n-type contact improvement layer 26 is obtained by n-type doping in the gallium nitride material layer, which can construct a band ladder structure, thereby reducing the injection barrier and contact resistance.

[0038] In some embodiments, the gallium nitride material includes at least one of GaN and InGaN. The gallium nitride material of the n-type contact improvement layer 26 is at least one of GaN and InGaN, which can construct a band ladder structure and effectively reduce the barrier height between the metal and the aluminum nitride barrier layer 24 in the source 27 and drain 28, thereby reducing the injection barrier and improving the electron injection efficiency.

[0039] In order to avoid the breakdown voltage of the device being too low due to the thickness of the n-type contact improvement layer 26 being too thick, and to avoid the insufficient number of electrons being insufficient due to the thickness of the n-type contact improvement layer 26 being too thin, in some embodiments, the thickness of the n-type contact improvement layer 26 is in the range of 3nm to 80nm.

[0040] In some embodiments, the element used for n-type doping in gallium nitride materials is at least one of Si and Ge.

[0041] In some preferred embodiments, such as Figure 1 As shown, the aluminum-nitrogen HEMT device further includes an aluminum-nitrogen barrier layer 24, and an n-type contact improvement layer 26 is epitaxially grown on the aluminum-nitrogen barrier layer 24 to obtain an aluminum-nitrogen HEMT device with a low implantation barrier. In some embodiments, the material of the aluminum-nitrogen barrier layer 24 includes AlN or high-Al content AlGaN to obtain an aluminum-nitrogen HEMT device with an ultra-wide bandgap, high breakdown field strength, and excellent thermal stability. In some embodiments, the high-Al content AlGaN is AlGaN with an Al content of not less than 60% to ensure a high breakdown voltage by ensuring a high Al content.

[0042] During their research and experiments, the inventors also discovered that common wide-bandgap nitrides such as GaN have relatively small exciton Bohr radii (approximately 3 nm). When the size of the nanoislands is ≤6 nm, the quantum confinement effect is very significant; while when the size ranges from nanometers to >10 nm, they are closer to "quasi-nanoislands," and the quantum effect weakens. Furthermore, the inventors found that common wide-bandgap nitrides can reduce the donor activation energy by lowering the conduction band edge energy level, thereby increasing the electron concentration of the system. Moreover, due to the quantum confinement effect, the introduced nanoislands do not cause changes in the system's composition and do not significantly affect the overall device performance, meaning they do not reduce the material's breakdown voltage or other properties.

[0043] Based on the above findings, the inventors proposed setting GaN nanoislands 25 (such as...) in the aluminum nitride barrier layer 24. Figure 1(As shown). Since the material in the aluminum nitride barrier layer 24 is an ultra-wide bandgap nitride, and GaN is a common wide bandgap nitride, this invention embeds narrow bandgap nitride semiconductor nanoislands within a wide-bandgap n-type doped nitride layer. Because the conduction band bottom of a common bandgap nitride nanoisland is typically lower than the conduction band bottom of the ultra-wide bandgap nitride substrate and closer to the donor level, the distance between the donor impurity (such as an n-type dopant) level and the conduction band bottom at the interface decreases. This improves the ionization behavior of the donor impurity, thereby reducing the activation energy. The reduced activation energy facilitates ionization of the donor under lower thermal conditions, releasing more free electrons, increasing the electron concentration of the n-type doped nitride, and ultimately improving the overall carrier concentration of the material, resulting in good n-type conductivity of the n-type doped ultra-wide bandgap nitride. In some embodiments, the region surrounding the GaN nanoisland 25 in the aluminum nitride barrier layer 24 is n-type doped, for example, by δ-doping or heavy doping of at least one of Si and Ge. The area surrounding the GaN nanoislands 25 in the aluminum-nitrogen barrier layer 24 is doped, which can increase the effective electron concentration of the aluminum-nitrogen barrier layer 24 through the quantum potential well, giving the aluminum-nitrogen barrier layer a higher carrier supply capability, thereby achieving low contact resistance and excellent electrical performance. In some embodiments, the size of the GaN nanoislands 25 ranges from 3 nm to 20 nm laterally and from 1 nm to 5 nm vertically to ensure the effect of quantum confinement. In some embodiments, the thickness of the aluminum-nitrogen barrier layer 24 ranges from 10 nm to 100 nm, and the GaN nanoislands 25 are embedded in the aluminum-nitrogen barrier layer 24. The GaN nanoislands 25 divide the aluminum-nitrogen barrier layer 24 into aluminum-nitrogen barrier sublayers 241 with a thickness ranging from 2 nm to 10 nm (preferably 3 nm to 6 nm) along the growth direction of the aluminum-nitrogen barrier layer 24. By controlling the thickness of the aluminum nitride barrier layer 24 within the range of 10~100 nm, sufficient polarization charge can be ensured to form a stable two-dimensional electron gas, while providing structural space for the embedding of multilayer GaN nanoislands 25. At the same time, the problems of stress accumulation and excessively long electron injection paths caused by excessive thickness of the aluminum nitride barrier layer 24 are avoided, thus achieving comprehensive optimization between two-dimensional electron gas density, contact injection efficiency and structural reliability. In addition, by controlling the thickness of the aluminum nitride barrier sublayer 241, while ensuring that each layer of GaN nanoisland 25 is isolated from each other and structurally stable, effective synergy of multilayer quantum potential wells in the vertical direction can be achieved, so that a high-density, stepwise release electron storage structure is formed in the aluminum nitride barrier layer 24, thereby improving the activation rate of embedded doped electrons and enhancing the source and drain injection capabilities.

[0044] In some further preferred embodiments, the aluminum nitride HEMT device further includes a source 27 and a drain 28 deposited on an n-type contact improvement layer 26, and a gate 29 deposited on an aluminum nitride barrier layer 24 to improve the ohmic contact of the source 27 and the drain 28.

[0045] Figure 2 The method for preparing the aforementioned aluminum nitride HEMT device according to the first embodiment of the present invention is illustrated by way of example.

[0046] like Figure 2 As shown, the fabrication method of this aluminum-nitrogen HEMT device includes the following steps: S30: An n-type contact improvement layer 26 is epitaxially grown on an aluminum nitride barrier layer 24. The n-type contact improvement layer 26 is obtained by n-type doping of a gallium nitride material.

[0047] Since the present invention provides an n-type contact improvement layer 26 between the aluminum nitride barrier layer 24 and the source 27 and drain 28, the n-type contact improvement layer 26 is obtained by n-type doping in the gallium nitride material layer, which can construct a metal-semiconductor band ladder structure, thereby reducing the injection barrier.

[0048] In some embodiments, step S30, epitaxially growing an n-type contact improvement layer 26 on the aluminum nitride barrier layer 24, includes: epitaxially growing a gallium nitride layer on the aluminum nitride barrier layer 24, and performing n-type doping on the gallium nitride layer to form the n-type contact improvement layer 26. The n-type contact improvement layer 26 formed by n-type doping in the gallium nitride layer can construct a bandgap structure, thereby reducing the implantation barrier.

[0049] In some embodiments, in step S30, a gallium nitride-based material layer is grown at 980°C~1050°C (MOCVD) or 680°C~850°C (MBE), and the carrier concentration is increased to (0.8~3)×10⁻⁶ by introducing at least one of Si and Ge. 19 cm -3 An n-type contact improvement layer 26 was fabricated. Due to the high concentration of n-type doping in the gallium nitride-based material layer, the carrier concentration in the contact region can be increased, further reducing the contact resistance.

[0050] Figure 3 The method for preparing the aforementioned aluminum nitride HEMT device according to the second embodiment of the present invention is illustrated by way of example.

[0051] like Figure 3 As shown, the main difference between the fabrication method of the aluminum-nitrogen HEMT device in this embodiment and the fabrication method of the aluminum-nitrogen HEMT device in the first embodiment is that, based on the fabrication method of the aluminum-nitrogen HEMT device in the first embodiment, the following step S20 is included before step S30: an n-type doped aluminum-nitrogen barrier layer 24 is fabricated in the channel layer 23 around the GaN nano-islands 25, so as to increase the effective electron concentration of the aluminum-nitrogen barrier layer 24 through the quantum potential well, so that the aluminum-nitrogen barrier layer has a higher carrier supply capability, thereby achieving low contact resistance and excellent electrical performance.

[0052] In some embodiments, in step S20, preparing an aluminum-nitrogen barrier layer 24 with n-type doped regions surrounding the GaN nanoislands 25 on the channel layer 23 includes: epitaxially growing an aluminum-nitrogen barrier layer 24 on the channel layer 23, and intermittently preparing GaN nanoislands 25 during the growth of the aluminum-nitrogen barrier layer 24, and performing n-type doping in the regions surrounding each GaN nanoisland 25 after the growth of each GaN nanoisland 25, to form an aluminum-nitrogen barrier layer 24 with n-type doped regions surrounding the GaN nanoislands 25. Generally, the GaN nanoislands 25 are periodically arranged in the growth direction of the aluminum-nitrogen barrier layer 24.

[0053] In some embodiments, step S20, preparing GaN nanoislands 25 includes: after preparing 0.6 to 1.6 times the number of single-atom layers of GaN, interrupting the process for 5 to 30 seconds to allow the GaN to form island-shaped nanoislands. By controlling the size of the GaN nanoislands 25, the GaN nanoislands 25 on the surface of the aluminum-nitrogen barrier layer 24 can be transformed from a two-dimensional layered growth mode to a stable three-dimensional island growth mode, thereby forming GaN nanoislands 25 with controlled size and uniform distribution. This deposition amount range can avoid the problem of insufficient deposition amount leading to difficulty in nucleation of GaN nanoislands 25, and can also prevent excessive deposition amount from causing the GaN nanoislands 25 to merge and form a continuous thin layer, which is beneficial for obtaining discrete GaN nanoislands 25 with obvious quantum confinement effect. Combined with the subsequent growth interruption step, atomic rearrangement and island stability can be further promoted, so that the formed GaN nanoislands 25 can act as effective local quantum potential wells in the aluminum-nitrogen barrier layer 24, improve the activation rate of embedded doped electrons, and enhance the electron supply capability of the aluminum-nitrogen barrier layer 24.

[0054] In some embodiments, in step S20, after the growth of each GaN nanoisland 25, n-type doping in the region surrounding the GaN nanoisland 25 includes: after the growth of each nanoisland layer, introducing at least one of Si and Ge as a δ-doping source within a 2nm range above and below the nanoisland layer, and controlling the equivalent areal density of the doping to be (1~8)×10⁻⁶. 13 cm -2 To improve the electron transport capability between GaN nanoislands 25 and aluminum nitride barrier layer 24.

[0055] Figure 4 The method for preparing the aforementioned aluminum nitride HEMT device according to the third embodiment of the present invention is illustrated by way of example.

[0056] like Figure 4As shown, the main difference between the fabrication method of the aluminum nitride HEMT device in this embodiment and the fabrication method of the aluminum nitride HEMT device in the second embodiment is that, based on the fabrication method of the aluminum nitride HEMT device in the second embodiment, the following step S40 is added after step S30: fabricating the source 27 and the drain 28 on the n-type contact improvement layer 26.

[0057] In step S40, fabricating the source 27 and drain 28 on the n-type contact improvement layer 26 includes: first removing the n-type contact improvement layer 26 in the non-source / drain regions, then removing the native oxide layer on the n-type contact improvement layer 26 in the source / drain regions, and then fabricating a metal layer on the n-type contact improvement layer 26 in the source / drain regions. The material of the metal layer is Ti / Al, Ti / Al / Ni / Au, or Ti / Al / TiN (titanium nitride). Finally, the aluminum nitride HEMT device with the metal layer is subjected to rapid thermal annealing so that the metal layer forms the source 27 and drain 28 with low resistance ohmic contact with the n-type contact improvement layer 26.

[0058] Figure 5 The preparation method of the aforementioned aluminum nitride HEMT device according to the fourth embodiment of the present invention is illustrated by way of example.

[0059] like Figure 5 As shown, the main difference between the fabrication method of the aluminum nitride HEMT device in this embodiment and the fabrication method of the aluminum nitride HEMT device in the third embodiment is that, based on the fabrication method of the aluminum nitride HEMT device in the third embodiment, the following step S10 is included before step S20: fabricating a channel layer 23 on the substrate 21.

[0060] In step S10, the substrate 21 is selected from sapphire, SiC (silicon carbide, for example, 4H-SiC [4H-SiC is a crystal structure type (polymorph) of silicon carbide, 4H describes the stacking period and symmetry of its unit cells. "4" represents a complete stacking period containing 4 layers of Si-C atomic pairs, and "H" represents the hexagonal crystal system]), or AlN substrate. The channel layer 23 can be epitaxially grown directly on the substrate 21, or a template layer 22 can be set between the channel layer 23 and the substrate 21. The material of the channel layer 23 is AlN; the thickness of the channel layer 23 ranges from 100 nm to 2 μm; the channel layer 23 can be prepared by MOCVD (Metal-organic Chemical Vapor Deposition) or MBE (Molecular Beam Epitaxy). The material of the template layer 22 is AlN.

[0061] Figure 6 The fifth embodiment of the present invention illustrates a method for preparing the aforementioned aluminum nitride HEMT device.

[0062] like Figure 6 As shown, the main difference between the fabrication method of the aluminum nitride HEMT device in this embodiment and the fabrication method of the aluminum nitride HEMT device in the fourth embodiment is that, based on the fabrication method of the aluminum nitride HEMT device in the fourth embodiment, the following step S50 is added after step S40: a gate 29 is fabricated on an n-type doped aluminum nitride barrier layer 24 in the region surrounding the GaN nanoisland 25.

[0063] In step S50, the material of the gate 29 is Ni / Au, Pt (platinum) / Au, or TiN.

[0064] This invention significantly improves the electron concentration of the aluminum-nitrogen barrier layer 24 by introducing GaN nano-islands 25 and performing localized n-type doping in the layer 24 above the channel layer 23, thus alleviating the problems of electron freezing and low doping activation rate in high-Al materials. Simultaneously, an n-type contact improvement layer 26 is epitaxially formed above the aluminum-nitrogen barrier layer 24, creating a stepped band structure that effectively reduces the metal-semiconductor barrier height and improves electron injection efficiency. The synergistic effect of these two elements enables the contact region to achieve higher electron density and a smaller potential barrier. Furthermore, the composite structure of "source and drain + n-type contact improvement layer + aluminum-nitrogen barrier layer with n-type doping around the GaN nano-islands" achieves lower contact resistance, significantly improving the conduction, transconductance, power density, and high-frequency performance of HEMTs. This invention is compatible with traditional MOCVD / MBE processes, offers strong structural controllability, and is suitable for large-scale manufacturing, providing a new industrializable path for high-performance aluminum-nitrogen HEMT devices and polarization-induced channel (PIC-HEMT) devices.

[0065] The following specific embodiments illustrate the fabrication method of the aluminum nitride HEMT device of the present invention.

[0066] Example 1: AlN-based HEMT device with multilayer GaN nanoislands and n-type GaN contact improvement layer Step 1: Substrate 21 processing and epitaxial fabrication of AlN template layer 22 and channel layer 23.

[0067] First, a sapphire substrate was selected, and hydrogen gas was introduced into the MOCVD reaction chamber to heat-treat the substrate 21 at 1100℃~1200℃. Then, using trimethylaluminum (TMAl) and ammonia (NH3) as precursors, an AlN template layer was epitaxially grown at 1250℃~1350℃ and 50mbar~150mbar, with a thickness controlled at 1.5μm~3.0μm. After the template layer 22 was grown, the temperature was lowered to 1150℃~1250℃, and epitaxial growth of Al2N with a thickness of 150nm~250nm was continued. 0.8 Ga0.2 N-channel layer.

[0068] Step 2: Preparation of n-type doped aluminum nitride barrier layer 24 containing GaN nanoislands 25.

[0069] After the channel layer 23 is grown, an AlGaN barrier layer is epitaxially grown at 1250℃~1350℃ and 50mbar~150mbar. The total thickness of the barrier layer is controlled at 25nm~35nm, and GaN nanoislands 25 are periodically introduced during the growth process: TMAl is turned off, and GaN equivalent to a single atom layer of 0.8~1.6 is deposited while maintaining the supply of NH3 and TMGa (trimethylgallium). After deposition, the introduction of TMGa is stopped, and the process is maintained for 5 to 20 seconds with only NH3 introduced to promote the formation of island-shaped GaN nanoislands 25. The above process is repeated three times to form a three-layer nested GaN nanoisland structure in the barrier layer. Each nanoisland is separated by an AlGaN barrier sublayer (i.e., aluminum nitride barrier sublayer 241) with a thickness of 2nm~10nm (preferably 3nm~6nm).

[0070] Step 3: Embedded n-type doping near GaN nanoislands 25.

[0071] After each GaN nanoisland 25 layer is grown, silane (SiH4) is introduced into a region of approximately 1 nm to 2 nm above and below the nanoisland for pulsed doping, so that the doped electrons are concentrated near the quantum potential well; the equivalent areal density of the embedded doping is controlled at (2~8)×10. 13 cm -2 Within this range, the effective electron concentration in the high-Al composition barrier layer is significantly increased, and the electron freezing effect is suppressed.

[0072] Step 4: Growth of n-type contact improvement layer 26.

[0073] After the growth of the multilayer nano-island aluminum-nitrogen barrier layer 24, an n-type GaN contact improvement layer was epitaxially grown on top of the aluminum-nitrogen barrier layer 24. The thickness of this n-type GaN contact improvement layer was controlled at 3 nm to 8 nm, and it was grown at 980 °C to 1050 °C. The carrier concentration was increased to (0.8 to 3) × 10⁻⁶ by introducing Si doping. 19 cm -3 This is to form a stepped band structure between the source 27 and drain 28 and the AlGaN barrier layer, thereby reducing the electron injection barrier.

[0074] Step 5: Preparation of the source 27 and drain 28 ohmic contacts.

[0075] The n-type GaN contact improvement layer in the non-source / drain regions was removed using photolithography and ICP (inductively coupled plasma etching) dry etching processes, exposing the source / drain regions. Subsequently, the source / drain regions were surface-cleaned to remove the native oxide layer, and Ti / Al / Ni / Au metal layers were sequentially deposited using electron beam evaporation. After metal deposition, rapid thermal annealing was performed at 850℃~900℃ for 20~40 seconds in a nitrogen atmosphere to form a low-resistance ohmic contact between the metal and the n-type GaN contact improvement layer.

[0076] Step 6: Gate 29 and device completed.

[0077] After the source 27 and drain 28 ohmic contacts are fabricated, Ni / Au or Pt / Au gate metal is deposited on top of the aluminum nitride barrier layer 24. If necessary, a SiNx passivation layer is deposited on the device surface and a gate window is opened, thereby completing the fabrication of the AlN-based HEMT device.

[0078] according to Figure 7 As shown, the conduction band depth of GaN material is 1.9 eV lower than that of AlN.

[0079] according to Figure 8 The CBM before and after GaN embedding into AlN shows that the conduction band bottom energy level of GaN nanoislands 25 is lower than that of the donor energy level in AlN material. By embedding GaN nanoislands 25 into n-type doped AlN, zero activation energy or even negative activation energy can be achieved, thereby significantly increasing the electron concentration of the system.

[0080] Example 2: High Al composition AlGaN HEMT device with bilayer GaN nanoislands + n-type GaN contact improvement layer Step 1: Substrate 21 processing and epitaxial fabrication of AlN template layer 22 and channel layer 23.

[0081] Al2N template substrates with a thickness of 120nm~200nm were epitaxially grown using MBE. 0.7 Ga 0.3 During the growth of the N-channel layer, the temperature of the substrate 21 is controlled at 700℃~820℃, preferably 740℃~780℃. Active nitrogen is provided by an RF plasma source with a nitrogen flow rate of 0.6~1.2 sccm and an RF power of 300~450W, corresponding to an equivalent working pressure of (5×10⁻⁶)W. -7 ~5×10 -6 The Al and Ga metal sources were provided by high-purity metal evaporation, with the beam flux ratio Al / (Al+Ga) controlled between 0.65 and 0.75 to obtain Al. 0.7 Ga 0.3The target component of N was obtained. The material growth rate was maintained at 0.20–0.40 μm / h by adjusting the group III total flux, thereby achieving Al thicknesses of 120–200 nm. 0.7 Ga 0.3 N-channel layer.

[0082] Step 2: Preparation of n-type doped aluminum nitride barrier layer 24 containing GaN nanoislands 25.

[0083] Epitaxial growth of Al at 760℃~780℃ 0.9 Ga 0.1 The N-type barrier layer has a total thickness controlled between 18 nm and 30 nm. During the growth of the barrier layer, GaN equivalent to 0.6 to 1.4 single-atom layers is deposited at two predetermined locations, and the growth is interrupted for 10 to 30 seconds after each deposition to induce the spontaneous formation of nano-islands by GaN. The two nano-islands are separated by an AlGaN barrier sublayer spacer layer (i.e., aluminum nitride barrier sublayer 241) with a thickness of 2 nm to 10 nm (preferably 3 nm to 5 nm).

[0084] Step 3: Delta doping near the nanoislands.

[0085] Si or Ge is introduced as a δ-doping source within approximately 1 nm above each nanoisland layer, with the equivalent areal density controlled at (1~6)×10⁻⁶. 13 cm -2 This increases the concentration of free electrons within the high-Al component barrier layer.

[0086] Step 4: Growth of n-type contact improvement layer 26.

[0087] An n-type GaN contact improvement layer of 5 nm to 10 nm is epitaxially grown on top of the barrier layer. The thickness of this n-type GaN contact improvement layer is controlled at 3 nm to 8 nm. It is grown at 680 °C to 720 °C, and the carrier concentration is increased to (0.8 to 3) × 10⁻⁶ by introducing Si doping. 19 cm -3 This is to form a stepped band structure between the source 27 and drain 28 and the high-Al composition AlGaN barrier layer, thereby reducing the electron injection barrier.

[0088] Step 5: Preparation of the source 27 and drain 28 ohmic contacts.

[0089] The n-type GaN contact improvement layer in the non-source / drain regions was removed using photolithography and ICP (inductively coupled plasma etching) dry etching processes, exposing the source / drain regions. Subsequently, the source / drain regions were surface-cleaned to remove the native oxide layer, and Ti / Al / Ni / Au metal layers were sequentially deposited using electron beam evaporation. After metal deposition, rapid thermal annealing was performed at 850℃~900℃ for 20~40 seconds in a nitrogen atmosphere to form a low-resistance ohmic contact between the metal and the n-type GaN contact improvement layer.

[0090] Step 6: Gate 29 and device completed.

[0091] After the source 27 and drain 28 ohmic contacts are fabricated, Ni / Au or Pt / Au gate metal is deposited on top of the aluminum nitride barrier layer 24. If necessary, a SiNx passivation layer is deposited on the device surface and a gate window is opened, thereby completing the fabrication of the high Al composition AlGaN-based HEMT device.

[0092] This embodiment significantly improves the electron concentration of the barrier layer by introducing GaN nanoislands 25 and performing localized doping in the high-Al composition AlGaN barrier layer above the AlN channel, thus alleviating the problems of electron freezing and low doping activation rate in high-Al materials. Simultaneously, an epitaxial n-type GaN layer is added above the barrier layer as a contact improvement layer, forming a stepped band structure that effectively reduces the metal-semiconductor barrier height and improves electron injection efficiency. The synergy of these two elements results in higher electron density and a smaller barrier in the contact region. Furthermore, the composite structure of "source and drain + n-GaN + AlGaN barrier layer with n-type doping around the nanoislands" achieves lower contact resistance, significantly improving the conduction, transconductance, power density, and high-frequency performance of the HEMT.

[0093] Example 3: AlN-based HEMT device with a three-layer GaN nanoisland barrier and an n-type InGaN contact improvement layer Step 1: Substrate 21 processing and epitaxial fabrication of AlN template layer 22 and channel layer 23.

[0094] AlN substrate was selected, and Al was epitaxially grown on the AlN substrate. 0.75 Ga 0.25 The N-channel layer has a thickness of 150nm~200nm, and the process parameters of the template layer 22 and the channel layer 23 are the same as in Example 1.

[0095] Step 2: Preparation of n-type doped aluminum nitride barrier layer 24 containing GaN nanoislands 25.

[0096] An AlN barrier layer with a thickness of 22 nm to 32 nm is epitaxially grown on the channel layer 23. The process conditions are the same as those for the AlN template layer 22. Simultaneously, 5 to 10 sccm of SiH4 is continuously introduced during the growth process for n-type doping. During the growth of the barrier layer, a three-layer GaN nanoisland 25 nested structure is formed by multiple short-time GaN depositions and growth interruptions. Each nanoisland is separated by an AlN barrier sublayer (i.e., an aluminum nitride barrier sublayer 241) with a thickness of 2 nm to 10 nm (preferably 3 nm to 6 nm).

[0097] Step 3: GaN nanoislands 25-enhanced n-type doping.

[0098] Introducing Siδ doping into the upper and lower interface regions of each nanoisland layer concentrates electrons near the quantum potential well, thereby increasing the overall electron concentration of the barrier layer.

[0099] Step 4: Growth of the n-type InGaN contact improvement layer.

[0100] n-type In epitaxial layer 4nm~10nm was formed on top of aluminum nitride barrier layer 24. 0.03 Ga 0.97 A thin layer of N is formed and highly doped with Si to serve as a low-conductivity n-type contact improvement layer 26. During growth, TMI (Group III source), TMI (Group III source), and NH3 (Group V source) are used as the In, Ga, and N sources, respectively, with N2 being the preferred carrier gas. The reaction temperature is controlled at 720℃~820℃, preferably 750℃~800℃; the reaction pressure is controlled at 80~200 mbar, preferably 100~160 mbar. By adjusting the supply ratio of TMI to TMI, the In / (In+Ga) ratio is controlled at 0.03±0.01, while the V / III (Group III source / Group V source) ratio is controlled at 3000~20000, preferably 6000~12000, thereby obtaining an In layer with a thickness of 4~10 nm. 0.03 Ga 0.97 N-type thin layer. During growth, SiH4 or Si2H6 is introduced as a dopant source to achieve high-concentration n-type doping, resulting in a Si doping concentration of 1×10⁻⁶ in the thin layer. 19 ~5×10 19 cm -3 Preferably about 2×10 19 cm -3 This allows the InGaN thin layer to serve as a low conduction band n-type contact improvement layer 26 to reduce the metal-semiconductor contact barrier and decrease contact resistance.

[0101] Step 5: Preparation of the source 27 and drain 28 ohmic contacts.

[0102] The n-type GaN contact improvement layer in the non-source / drain regions was removed using photolithography and ICP (inductively coupled plasma etching) dry etching processes, exposing the source / drain regions. Subsequently, the source / drain regions were surface-cleaned to remove the native oxide layer, and Ti / Al / Ni / Au metal layers were sequentially deposited using electron beam evaporation. After metal deposition, rapid thermal annealing was performed at 820℃~880℃ for 20~40 seconds in a nitrogen atmosphere to form a low-resistance ohmic contact between the metal and the n-type GaN contact improvement layer.

[0103] Step 6: Gate 29 and device completed.

[0104] After the source 27 and drain 28 ohmic contacts are fabricated, Ni / Au or Pt / Au gate metal is deposited on top of the aluminum nitride barrier layer 24. If necessary, a SiNx passivation layer is deposited on the device surface and a gate window is opened, thereby completing the fabrication of the AlN-based HEMT device.

[0105] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. An aluminum nitride HEMT device, characterized in that, It includes an n-type contact improvement layer disposed between an aluminum nitride barrier layer and the source and drain electrodes, wherein the n-type contact improvement layer is obtained by n-type doping of a gallium nitride material.

2. The aluminum-nitrogen HEMT device according to claim 1, characterized in that, It also includes an aluminum-nitrogen barrier layer, on which the n-type contact improvement layer is epitaxially grown; and / or The gallium nitride materials include at least one of GaN and InGaN.

3. The aluminum-nitrogen HEMT device according to claim 2, characterized in that, The aluminum-nitrogen barrier layer contains GaN nanoislands; and / or The material of the aluminum nitride barrier layer includes AlN or high-Al AlGaN.

4. The aluminum-nitrogen HEMT device according to claim 2, characterized in that, The thickness of the n-type contact improvement layer ranges from 3 nm to 80 nm; and / or The element used for n-type doping in the gallium nitride material is at least one of Si and Ge, and the region surrounding the GaN nanoislands in the aluminum nitride barrier layer is n-type doped.

5. The aluminum-nitrogen HEMT device according to claim 3, characterized in that, The GaN nanoislands have a size range of 3nm~20nm laterally and 1nm~5nm vertically; and / or The thickness of the aluminum-nitrogen barrier layer ranges from 10 nm to 100 nm. The GaN nanoislands are embedded in the aluminum-nitrogen barrier layer. The GaN nanoislands divide the aluminum-nitrogen barrier layer into aluminum-nitrogen barrier sublayers with a thickness range of 2 nm to 10 nm along the growth direction of the aluminum-nitrogen barrier layer.

6. The aluminum-nitrogen HEMT device according to claim 3, characterized in that, The high-Al component AlGaN is AlGaN with an Al content of not less than 60%; and / or It also includes the source and drain electrodes deposited on the n-type contact improvement layer, and the gate electrode deposited on the aluminum nitride barrier layer.

7. The method for fabricating an aluminum nitride HEMT device according to any one of claims 1 to 6, characterized in that, Includes the following steps: S30: An n-type contact improvement layer is epitaxially grown on an aluminum nitride barrier layer, wherein the n-type contact improvement layer is obtained by n-type doping of a gallium nitride material.

8. The method for fabricating an aluminum nitride-based HEMT device according to claim 7, characterized in that, In step S30, epitaxially growing an n-type contact improvement layer on the aluminum nitride barrier layer includes: epitaxially growing a gallium nitride layer on the aluminum nitride barrier layer, and performing n-type doping on the gallium nitride layer to form an n-type contact improvement layer; and / or The following steps are included before step S30. S20: An n-type doped aluminum nitride barrier layer is prepared on the channel layer, with the GaN nanoislands surrounded by the channel layer.

9. The method for fabricating an aluminum nitride HEMT device according to claim 8, characterized in that, In step S20, the fabrication of an aluminum-nitrogen barrier layer with n-type doped regions around the GaN nanoislands on the channel layer includes: epitaxially growing an aluminum-nitrogen barrier layer on the channel layer, and intermittently fabricating GaN nanoislands during the growth of the aluminum-nitrogen barrier layer, and performing n-type doping in the regions surrounding each GaN nanoisland after the growth of each GaN nanoisland, to form an aluminum-nitrogen barrier layer with n-type doped regions around the GaN nanoislands; and / or In step S30, during the growth of the gallium nitride material layer, the carrier concentration is increased to (0.8~3)×10⁻⁶ by introducing at least one of Si and Ge. 19 cm -3 To obtain an n-type contact improvement layer.

10. The method for fabricating an aluminum nitride-based HEMT device according to claim 9, characterized in that, In step S20, the preparation of GaN nanoislands includes: after preparing 0.6 to 1.6 times the number of single-atom layers of GaN, interrupting the process for 5 to 30 seconds to allow the GaN to form island-like nanoislands; and / or In step S20, after the growth of each GaN nanoisland layer is completed, n-type doping is performed in the region surrounding the GaN nanoisland layer, which includes: after the growth of each nanoisland layer is completed, introducing at least one of Si and Ge as a δ-doping source within a 2nm range above and below the nanoisland layer, and controlling the equivalent areal density of the doping to be (1~8)×10. 13 cm -2 .

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