Patent Application
20230290742
This application relates to the field of semiconductor technologies, and in particular, to a nitride epitaxial structure and a semiconductor device.
Gallium nitride (GaN) materials have advantages such as a large band gap and high mobility, and therefore are widely used in electronic power devices, radio frequency devices, and photoelectric devices. A high electron mobility transistor (HEMT) is the most widely used. A gallium nitride material is usually obtained through epitaxial growth on a silicon substrate. However, a large lattice mismatch and a thermal expansion coefficient mismatch of more than 17% occur between GaN and silicon. Therefore, a large stress is generated in a silicon-based gallium nitride, and the stress causes warpage in epitaxy, affecting uniformity and reliability of a GaN epitaxial wafer. In addition, with an increase of a size of the substrate, the impact of warpage is increasingly significant. Currently, in conventional technology, stress is mainly adjusted by using a gradient AlGaN structure and a superlattice structure. However, the gradient AlGaN structure has poor dynamic performance and poor crystal quality. Although stress control capability and crystal quality of the superlattice structure are both better than those of the gradient AlGaN structures, it is difficult to balance voltage resilience versus and crystal quality.
In view of this, an embodiment of this disclosure provide a nitride epitaxial structure and a semiconductor device. A buffer layer of a specific structure is disposed between a substrate and an epitaxial layer, to effectively alleviate and release stress generated between the substrate and the epitaxial layer due to a lattice mismatch and a thermal mismatch, reduce warpage during epitaxy and after epitaxy, and improve uniformity and reliability of the nitride epitaxial structure. Further, crystal quality and voltage withstand performance of the epitaxial layer can be improved, thereby effectively improving performance of the semiconductor device.
Generally, a first aspect of the an embodiment of this disclosure provides a nitride epitaxial structure, including:
The nucleation layer may provide a nucleation center for subsequent growth of the nitride epitaxial layer, to alleviate a lattice mismatch between the substrate and the epitaxial layer, and may further effectively prevent impurities brought by the substrate from affecting subsequent growth of the nitride epitaxial layer, thereby improving crystal quality of the epitaxial layer. The buffer layer is disposed between the substrate and the epitaxial layer, to effectively alleviate and release stress generated between the substrate and the epitaxial layer due to a lattice mismatch and a thermal mismatch, reduce warpage during epitaxy and after epitaxy, and improve uniformity and reliability of the nitride epitaxial structure. In addition, the buffer layer is disposed by stacking a plurality of group-III nitride double-layer structures with gradient band gap differences, so that dynamic performance is good, crystal quality and voltage withstand performance can be effectively balanced, and an electric leakage risk can be reduced, thereby effectively improving performance of a semiconductor device. In addition, double-layer structures with different band gap differences are adaptively used at different locations, so that advantages of filtering dislocations and improving voltage withstand performance can be both achieved, and a balance between the two aspects of performance can be achieved according to an actual requirement. The dynamic performance usually refers to a recovery capability of a transistor after electrical stress is increased, and may be measured by using an indicator such as dynamic resistance (Dron).
In an implementation of this application, in each double-layer structure, the material of the upper layer and the material of the lower layer each are selected from one of GaN, AlN, InN, or a combination thereof: AlGaN, InGaN, InAlN, or InAlGaN. Generally, a combination of the materials of the upper layer and the lower layer of the double-layer structure may be AlN/GaN, AlGaN/GaN, AlN/AlGaN, or AlGaN/AlGaN.
In an implementation of this application, a thickness of the lower layer is greater than twice a thickness of the upper layer. A thick lower layer and a thick upper layer are disposed, so that lattice relaxation can be effectively avoided. For heteroepitaxy, when the thickness of the upper layer is smaller, the material is in a strained state, to be specific, a lattice constant of the material of the upper layer is the same as that of the material of the lower layer after the material of the upper layer is stretched or compressed by the material of the lower layer, so that a superlattice can effectively function; or when the thickness of the upper layer is greater, the material is restored to a lattice constant of the material, causing lattice relaxation.
In an implementation of this application, the band gap differences of the K double-layer structures gradually decrease from one side of the nucleation layer to one side of the epitaxial layer. When the band gap difference is large, a difference between lattice constants of the materials of the double-layer structure is large, thereby helping filter dislocations. However, because a polarization effect is also strong, electric leakage is likely to occur. On the contrary, when the band gap difference is small, this helps reduce a leakage current, but is not conducive to dislocation filtering. A double-layer structure with a large band gap difference is disposed on a side close to the nucleation layer, thereby helping eliminate dislocations at an early stage of epitaxy and reduce impact of electric leakage. A double-layer structure with a small band gap difference is disposed on a side close to the epitaxial layer, thereby helping reduce a leakage current and improve voltage withstand performance.
In an implementation of oneembodiment, a difference between a largest band gap difference and a smallest band gap difference in the K double-layer structures is greater than 20% of a band gap difference between a group-III nitride with a largest band gap and a group-III nitride with a smallest band gap that constitute the double-layer structure. The difference between the largest band gap difference and the smallest band gap difference of the K double-layer structures of the entire buffer layer is controlled within an appropriate range, so that crystal quality and voltage withstand performance can be better balanced and adjusted.
In an implementation of an embodiment, the K double-layer structures include two types of group-III nitrides: GaN and AlN, and an average Al component content in each double-layer structure is 5% to 50%. The average Al component content is an average molar percentage of an Al element in group-III metal elements in each double-layer structure. An Al component content of each double-layer structure is controlled within an appropriate range, to ensure that the buffer layer has good crystal quality.
In an implementation of an embodiment, the average Al component content in each double-layer structure is the same. An Al component remains unchanged. Therefore, when pre-compensation is designed for high-temperature warpage, only impact of a thickness of a film layer needs to be considered, and impact of a change of the Al component does not need to be considered, thereby simplifying a parameter design.
In an implementation of an embodiment, average Al component contents of the K double-layer structures present a gradient trend along the thickness direction of the buffer layer. Average Al component contents of a plurality of double-layer structures are designed to be gradient, thereby facilitating stress adjustment.
In an implementation of an embodiment, in the K double-layer structures, any two adjacent double-layer structures may have different band gap differences, or some adjacent double-layer structures may have a same band gap difference. A repetition periodicity of double-layer structures that are adjacently stacked and that have a same band gap difference may be 1 to 10.
In an implementation of an embodiment, to avoid relaxation, a thickness of each double-layer structure is set to be less than 100 nm.
In an implementation of an embodiment, a material of the epitaxial layer includes one or more of GaN, AlN, InN, AlGaN, InGaN, InAlN, and InAlGaN.
In an implementation of an embodiment, a thickness of the epitaxial layer is greater than or equal to 300 nm. A thickness of a conventional gallium nitride epitaxial layer is usually small due to a limitation of stress. However, a nitride epitaxial wafer in an embodiment of this disclosure can well eliminate stress, and therefore theoretically may have an infinite thickness. In some implementations of an embodiment, a thickness of the epitaxial layer may be greater than or equal to 5 µm, or may be greater than or equal to 10 µm.
In an implementation of an embodiment, the substrate includes a silicon substrate, a sapphire substrate, a silicon-on-insulator substrate (SOI substrate), a gallium nitride substrate, a gallium arsenide substrate, an indium phosphide substrate, an aluminum nitride substrate, a silicon carbide substrate, a quartz substrate, or a diamond substrate.
In an implementation of an embodiment, a thickness of the nucleation layer is 10 nm to 300 nm.
In an implementation of an embodiment, the nitride epitaxial structure further includes a transition layer disposed between the nucleation layer and the epitaxial layer, and a material of the transition layer is AlGaN. In an implementation of an embodiment, a material of the transition layer is the same as that of the nucleation layer. In an implementation of an embodiment, a thickness of the transition layer is 10 nm to 300 nm.
In an implementation of an embodiment, the nitride epitaxial structure further includes other functional layers disposed on the epitaxial layer. The other functional layers may be disposed according to an actual application requirement, and may generally include an AlN insertion layer, an AlGaN barrier layer, a P-type GaN layer, and the like.
According to a second aspect, an embodiment of this disclosure further provides a semiconductor device, including the nitride epitaxial structure according to the first aspect of an embodiment of this disclosure. The semiconductor device may be a power device, a radio frequency device, or a photoelectric device. Generally, for example, the semiconductor device is a field-effect transistor, a light emitting diode, or a laser diode.
In the nitride epitaxial structure provided in an embodiment of this disclosure, the nucleation layer is disposed on the substrate, and the buffer layer is disposed on the nucleation layer, thereby effectively alleviating and releasing stress generated between the substrate and the epitaxial layer due to a lattice mismatch and a thermal mismatch, reducing warpage during epitaxy and after epitaxy, improving uniformity and reliability of the nitride epitaxial structure, and further improving performance of the semiconductor device. In the semiconductor device provided in an embodiment of this disclosure, because the nitride epitaxial structure provided in an embodiment of this disclosure is used, a large-size thick nitride epitaxial layer device can be obtained, thereby effectively reducing device costs and improving device performance.
The following describes an embodiment of this disclosure with reference to accompanying drawings in this disclosure.
As shown in
It should be noted that, for the upper layer and the lower layer of the double-structure in an embodiment, the “upper” and the “lower” do not represent specific orientations. In the art, for a superlattice double-layer structure, usually, a layer with a larger band gap is written as an upper layer, and a layer with a smaller band gap is written as a lower layer. Even if the two layers are exchanged in order during actual growth, the writing is not changed.
In an implementation of an embodiment, the substrate 10 may be a silicon substrate, a sapphire substrate, a silicon-on-insulator substrate (SOI substrate), a gallium nitride substrate, a gallium arsenide substrate, an indium phosphide substrate, an aluminum nitride substrate, a silicon carbide substrate, a quartz substrate, or a diamond substrate, or may be any known conventional substrate that can be used to prepare a group-III nitride film. A crystal orientation of the silicon substrate is not limited, for example, may be a silicon substrate with a crystal facet index of (111), or may be a silicon substrate with a crystal facet index of (100), or may be a silicon substrate with another crystal facet index.
In an implementation of an embodiment, the nucleation layer 20 is a layer of aluminum nitride or gallium nitride film, and the nucleation layer 20 fully covers the substrate 10. The nucleation layer 20 may provide a nucleation center for subsequent growth of the nitride epitaxial layer, may alleviate stress generated between the substrate 10 and the epitaxial layer 40 due to a lattice mismatch, and may further effectively prevent impurities brought by the substrate 10 from affecting subsequent growth of the nitride epitaxial layer, to reduce lattice defects, reduce dislocation density, and improve crystal quality of the nitride epitaxial layer. In addition, the nucleation layer 20 is thin, and is monocrystalline or quasi-monocrystalline. Therefore, stress generated between the substrate 10 and the epitaxial layer 40 due to a lattice mismatch can be alleviated, without affecting subsequent crystal quality of the nitride epitaxial layer, and costs can also be effectively controlled. In some implementations of this disclosure, a thickness of the nucleation layer 20 may be 10 nm to 300 nm. In some other implementations of this disclosure, a thickness of the nucleation layer 20 may be 20 nm to 200 nm. In some other implementations of this disclosure, a thickness of the nucleation layer 20 may be alternatively 50 nm to 150 nm.
In an implementation of an embodiment, the nucleation layer 20 may be prepared in a manner of metal-organic chemical vapor deposition or molecular beam epitaxy. The metal-organic chemical vapor deposition (MOCVD) is a chemical vapor deposition technology for growing a film through vapor phase epitaxy by using a thermal decomposition reaction of an organic metal compound. Generally, an organic compound of group-III or group-II elements, a hydride of group-V or group-VI elements, and the like may be used as source materials for crystal growth of a metal organic compound, to grow a group-III-V or group II-VI compound film on a substrate by using a thermal decomposition reaction. The manner of metal-organic chemical vapor deposition can improve subsequent crystal quality of the nitride epitaxial layer.
In an implementation of an embodiment, the buffer layer 30 includes K stacked group-III nitride double-layer structures 300. In some implementations, a value of K may be 3 to 100. In some other implementations, a value of K may be 10 to 60. In some other implementations, a value of K may be alternatively 20 to 50. In each double-layer structure, the material of the upper layer 301 and the material of the lower layer 302 each may be selected from one of GaN, AlN, InN, or a combination thereof: AlGaN, InGaN, InAlN, or InAlGaN. AlGaN is a combination of two types of group-III nitrides: GaN and AlN. InGaN is a combination of two types of group-III nitrides: GaN and InN. InAlN is a combination of two types of group-III nitrides: AlN and InN. InAlGaN is a combination of three types of group-III nitrides: GaN, AlN, and InN. A band gap of GaN is 3.4 eV, a band gap of AlN is 6.2 eV, and a band gap of InN is 0.7 eV. Generally, a combination of the materials of the upper layer and the lower layer of the double-layer structure 300 may be AlN/GaN, AlGaN/GaN, AlN/AlGaN, or AlGaN/AlGaN.
In an implementation of an embodiment, a thickness of the buffer layer 30 may be set based on a withstand voltage level. For example, if the withstand voltage level is 100 V, the buffer layer usually needs to be disposed to be 2 µm to 3 µm; or if the withstand voltage level is 600 V, the buffer layer needs to be disposed to be greater than 5 µm. In some implementations of this disclosure, a thickness of the buffer layer 30 is greater than 300 nm. A thickness of each double-layer structure is less than 100 nm. Generally, the thickness of each double-layer structure may be 10 nm to 80 nm, or 20 nm to 60 nm. An appropriate thickness of the double-layer structure helps avoid relaxation. In each double-layer structure 300, a thickness of the lower layer 302 is greater than twice a thickness of the upper layer 301. A thick lower layer and a thick upper layer are disposed, so that lattice relaxation can be effectively avoided. For heteroepitaxy, when the thickness of the upper layer is smaller, the material is in a strained state, to be specific, a lattice constant of the material of the upper layer is the same as that of the material of the lower layer after the material of the upper layer is stretched or compressed by the material of the lower layer, so that a superlattice can effectively function; or when the thickness of the upper layer is greater, the material is restored to a lattice constant of the material, causing lattice relaxation. In the K double-layer structures 300, thicknesses of all upper layers may be the same, and thicknesses of all lower layers may be the same.
In some implementations of this disclosure, band gap differences of the K double-layer structures 300 gradually decrease from one side of the nucleation layer 200 to one side of the epitaxial layer 400. When the band gap difference is large, a difference between lattice constants of the materials of the double-layer structure is large, thereby helping filter dislocations. However, because a polarization effect is also strong, electric leakage is likely to occur. On the contrary, when the band gap difference is small, this helps reduce a leakage current, but is not conducive to dislocation filtering. A double-layer structure with a large band gap difference is disposed on a side close to the nucleation layer, thereby helping filter dislocations. In addition, because the double-layer structure is far away from an AlGaN barrier layer and a channel layer, adverse impact caused by electric leakage is small. A double-layer structure with a small band gap difference is disposed on a side close to the epitaxial layer, thereby helping reduce a polarization effect and improve voltage withstand performance. In some other implementations, alternatively, the K double-layer structures 300 may be arranged, according to a requirement, in a manner that band gap differences gradually increase from one side of the nucleation layer 200 to one side of the epitaxial layer 400.
In an embodiment, a difference between a largest band gap difference and a smallest band gap difference in the K double-layer structures is greater than 20% of a band gap difference between a group-III nitride with a largest band gap and a group-III nitride with a smallest band gap that constitute the double-layer structure. For example, in K AlGaN/AlGaN double-layer structures, group-III nitrides that constitute the double-layer structure include GaN and AlN, where a band gap of GaN is 3.4 eV, and a band gap of AlN is 6.2 eV. In this case, 20% of a band gap difference between a group-III nitride with a largest band gap and a group-III nitride with a smallest band gap that constitute the double-layer structure is 20% × (6.2 - 3.4) eV. For another example, in K InAlGaN/InAlGaN double-layer structures, group-III nitrides that constitute the double-layer structure include InN, GaN, and AlN, where a band gap of InN is 0.7 eV, a band gap of GaN is 3.4 eV, and a band gap of AlN is 6.2 eV. In this case, 20% of a band gap difference between a group-III nitride with a largest band gap and a group-III nitride with a smallest band gap that constitute the double-layer structure is 20% × (6.2 - 0.7) eV.
In some implementations of this disclosure, the K double-layer structures 200 include two types of group-III nitrides: GaN and AlN, and a combination of the upper layer and the lower layer of the double-layer structure may be expressed as AlxGa1-xN/AlyGa1-yN (0 < x ≤ 1, y > 0). In the double-layer structures, a gradient trend of band gap differences may be equivalent to a gradient trend of Al component content differences. A change trend of band gaps and a change trend of an Al component content in AlGaN are approximately in a linear relationship. To be specific, a higher Al component content in AlGaN indicates a larger band gap. Therefore, a gradient trend of band gap differences of the double-layer structures may be equivalent to a gradient trend of Al component content differences of the double-layer structures. It should be noted that the Al component content in an embodiment is a molar percentage of an Al element in group-III metal elements. A band gap of AlxGa1-xN may be approximately equal to [6.2x + (1 - x) 3.4] eV. Therefore, Al component contents in an upper layer and a lower layer of each double-layer structure are controlled, so that the Al component content differences of the double-layer structures are in a gradient trend, and therefore the band gap differences of the K double-layer structures can be gradient. For example, as shown in
In an implementation of this application, the K double-layer structures include two types of group-III nitrides: GaN and AlN, and an average Al component content in each double-layer structure may be 5% to 50%. In some implementations, an average Al component content in each double-layer structure is 8% to 38%. In some other implementations, an average Al component content in each double-layer structure is 15% to 30%. In some other implementations, an average Al component content in each group-III nitride double-layer structure is 20% to 25%. The average Al component content is an average molar percentage of an Al element in group-III metal elements in each double-layer structure. The average Al component content of each double-layer structure is controlled within an appropriate range, to ensure that the buffer layer has good crystal quality. For the AlxGa1-xN/AlyGa1-yN double-layer structure, an average Al component content in each double-layer structure may be expressed as [(Tupper × x + Tlower × y)/(Tupper + Tlower)] × 100%, where Tupper and Tlower indicate thicknesses of an upper layer and a lower layer of the double-layer structure respectively, and x and y indicate Al component contents of the upper layer and the lower layer respectively. In some implementations of this disclosure, the average Al component content in each double-layer structure is the same. An Al component remains unchanged. Therefore, when pre-compensation is designed for high-temperature warpage, only impact of a thickness of a film layer needs to be considered, and impact of a change of the Al component does not need to be considered, thereby simplifying a parameter design. In some other implementations of this disclosure, average Al component contents of the K double-layer structures present a gradient trend along the thickness direction of the buffer layer. Average Al component contents of a plurality of double-layer structures are designed to be gradient, thereby facilitating stress adjustment.
In addition, in this application, that the band gap differences of the K double-layer structures generally present a gradual tend along the thickness direction of the buffer layer may be that the band gap differences strictly present a change of gradually increasing or gradually decreasing along the thickness direction of the buffer layer, or may be that the band gap differences generally present a change of gradually increasing or gradually decreasing, but there are a few special cases in which a change is opposite to the overall gradient trend, for example, in a buffer layer in which band gap differences generally gradually increase, there are a few double-layer structures whose band gap differences gradually decrease.
In an implementation of this application, a material of the epitaxial layer includes one or more of GaN, AlN, InN, AlGaN, InGaN, InAlN, and InAlGaN. In an implementation of this application, a material of the epitaxial layer 40 includes a group-III nitride, and may be generally, for example, one or more of GaN, AlN, InN, AlGaN, InGaN, InAlN, and InAlGaN. A thickness of the epitaxial layer 40 is greater than or equal to 300 nm. A thickness of a conventional gallium nitride epitaxial layer is usually small due to a limitation of stress. However, the nitride epitaxial structure in an embodiment of this disclosure can well eliminate stress, and therefore is applicable to preparation of a thick-film epitaxial layer, and theoretically may have an infinite thickness. In some implementations of this disclosure, a thickness of the epitaxial layer may be greater than or equal to 5 µm, or may be greater than or equal to 10 µm, for example, 15 µm to 100 µm. The epitaxial layer 40 may fully cover the nucleation layer 20, or may partially cover the nucleation layer 20.
In an implementation of this application, different nitride epitaxial layers are applicable to different semiconductor devices. For example, GaN, AlGaN, and AlN are applicable to power devices, and a nitride epitaxial layer including In is applicable to photoelectric devices.
In this implementation of this application, to meet a usability requirement, another element may be alternatively added to the epitaxial layer 40. For example, to improve insulation, carbon may be added to achieve a high resistance and improve voltage withstand performance.
As shown in
In an implementation of this application, as shown in
As shown in
S01: Form a nucleation layer on a substrate, where the nucleation layer is an AlN layer or a GaN layer.
Generally, the nucleation layer 20 may be prepared on the substrate 10 in a manner of metal-organic chemical vapor deposition or molecular beam epitaxy. Before preparation of the nucleation layer 20, conventional cleaning may be performed on the substrate 10.
In a specific implementation of this application, the nucleation layer 20 is prepared on the substrate 10 in a manner of metal-organic chemical vapor deposition. Details may be as follows: The substrate 10 is placed in a metal-organic chemical vapor deposition reaction chamber, and hydrogen and ammonia are injected for 3 min to 5 min at a temperature of 900° C. to 1100° C. and under a pressure of 30 to 60 Torr, to obtain a processed substrate 10. Then hydrogen, ammonia, and an aluminum source or a gallium source are injected, and an aluminum nitride or a gallium nitride is deposited on the processed substrate 10, to obtain the nucleation layer 20. In this implementation of this application, the parameters in the deposition process are not limited to the foregoing ranges. The gallium source includes but is not limited to trimethyl gallium and triethyl gallium. The aluminum source includes but is not limited to trimethyl aluminum and triethyl aluminum.
S02: Form a buffer layer on the nucleation layer.
In an implementation of this application, the buffer layer 30 may be prepared in a manner of metal-organic chemical vapor deposition. Generally, the substrate with the nucleation layer that is obtained in step SOI is placed in a metal-organic chemical vapor deposition reaction chamber. Then hydrogen, ammonia, and a group-III metal source are injected at a temperature of 900° C. to 1100° C. and under a pressure of 30 to 60 Torr, and a group-III nitride is obtained through epitaxial growth on the buffer layer 30, to obtain the buffer layer 30. The group-III metal source is an organic compound including a group-III metal element, for example, trimethyl gallium, triethyl gallium, trimethyl aluminum, or triethyl aluminum. A flux of the group-III metal source may be changed to change a content of each group-III nitride in the buffer layer, and deposition time may be controlled to obtain nitride layers of different thicknesses.
S03: Epitaxially grow a group-III nitride on the buffer layer to form an epitaxial layer.
In an implementation of this application, the epitaxial layer 40 may be prepared in a manner of metal-organic chemical vapor deposition. Generally, the substrate 10 obtained in step S02 is placed in a metal-organic chemical vapor deposition reaction chamber, and hydrogen and ammonia are injected for 3 min to 5 min at a temperature of 900° C. to 1100° C. and under a pressure of 30 to 60 Torr, to obtain a processed substrate 10. Then hydrogen, ammonia, and a group-III metal source are injected, and a group-III nitride is obtained through epitaxial growth on the buffer layer 30, to form the epitaxial layer 40. The group-III nitride may be generally, for example, one or more of GaN, AlN, InN, AlGaN, InGaN, InAlN, and InAlGaN. The group-III metal source is an organic compound including a group-III metal element, for example, trimethyl gallium, triethyl gallium, trimethyl aluminum, or triethyl aluminum.
In an implementation of this application, the preparation method may further include: forming a transition layer 50 between the buffer layer 30 and the epitaxial layer 40. To be specific, before step S03, the transition layer 50 is first prepared on the buffer layer 30, and then the epitaxial layer 40 is grown on the transition layer 50. A material of the transition layer 50 may be an AlGaN layer.
One embodiment of this disclosure further provides a semiconductor device, including the foregoing nitride epitaxial structure described here in this disclosure. The nitride epitaxial structure in may be directly used as a part of the semiconductor device, or it may be separately used in the semiconductor device. The semiconductor device includes but is not limited to a power device (namely, an electronic power device), a radio frequency device, or a photoelectric device. The power device or the radio frequency device may be a transistor, and may be generally a field-effect transistor, for example, a high electron mobility transistor (HEMT). The photoelectric device is, for example, a light emitting diode (LED) or a laser diode (LD), and may be generally a nitride-based light emitting diode or a nitride-based quantum well laser diode.
The following further describes an embodiment of this disclosure by illustrating a plurality of embodiments.
A nitride epitaxial structure includes a substrate, and a nucleation layer, a buffer layer, an epitaxial layer, and other functional layers that are sequentially disposed on the substrate. A material of the substrate is Si, sapphire, GaN, SiC, diamond, SOI, or the like. The nucleation layer is an AlN nucleation layer with a thickness of 50 nm to 400 nm. The buffer layer is a structural layer with gradient band gap differences, and includes 11 double-layer structures with an upper layer and a lower layer of AlxGa1-xN/AlyGa1-yN. An average Al component content of each double-layer structure is 20%. Table 1 shows values of x and y and thicknesses Tupper and Tlower in each double-layer structure. The epitaxial layer is a GaN layer, may include a carbon-doped structure such as GaN or AlGaN, and has a thickness of 100 nm to 3 µm. The other functional layers may include the following layers that are sequentially disposed on the epitaxial layer: an AlN insertion layer with a thickness of 1 nm; an AlGaN barrier layer with an Al component range of 10% to 30% and a thickness of 10 nm to 30 nm; and a p-GaN layer, where a P-type impurity is implemented through Mg doping, and a thickness range is 30 nm to 120 nm.
Double-layer structures whose sequence numbers are 1 to 11 are sequentially disposed in a stacked manner. A double-layer structure with a sequence number of 1 is disposed close to the epitaxial layer, and a double-layer structure with a sequence number of 11 is disposed close to the nucleation layer. The periodicity 5 in Table 1 means that a double-layer structure with each sequence number is repeated five times. To be specific, double-layer structures with different band gap differences have a same repetition periodicity, to form 11 groups of double-layer structures, and each group includes five same double-layer structures that are stacked. To be specific, the buffer layer includes five stacked Al0.5Ga0.5N/Al0.17Ga0.83N double-layer structures, five stacked Al0.55Ga0.45N/Al0.165Ga0.835N double-layer structures, and so on. It can be learned from Table 1 that, in the nitride epitaxial structure in Embodiment 1, Al component content differences of the 11 groups of double-layer structures of the buffer layer gradually decrease from one side of the nucleation layer to one side of the epitaxial layer, that is, band gap differences of the 11 groups of double-layer structures gradually decrease from one side of the nucleation layer to one side of the epitaxial layer. In addition, an average Al component content of each group of double-layer structures in Embodiment 1 is the same, and is 20%.
A difference from Embodiment 1 lies only in that the buffer layer includes 51 double-layer structures with an upper-layer and a lower layer of AlxGa1-xN/AlyGa1-yN. Table 2 shows values of x and y, an upper-layer thickness Tupper, and a lower-layer thickness Tlower in each double-layer structure.
Double-layer structures whose sequence numbers are 1 to 51 are sequentially disposed in a stacked manner. A double-layer structure with a sequence number of 1 is disposed close to the epitaxial layer, and a double-layer structure with a sequence number of 51 is disposed close to the nucleation layer. The periodicity 1 in Table 2 means that there is only one double-layer structure with each sequence number. It can be learned from Table 2 that, in the nitride epitaxial structure in Embodiment 2, Al component content differences of the 51 double-layer structures of the buffer layer gradually decrease from one side of the nucleation layer to one side of the epitaxial layer, that is, band gap differences of the 51 double-layer structures gradually decrease from one side of the nucleation layer to one side of the epitaxial layer. In addition, an average Al component content of each double-layer structure in Embodiment 2 is the same, and is 20%. Compared with Embodiment 1, a gradient spacing between band gap differences of the buffer layer in Embodiment 2 is smaller, so that stress between the substrate and the epitaxial layer can be better adjusted.
Note: The EDS graph includes curves for three elements: Ga, Al, and N. The N element accounts for approximately 50%. Therefore, a vertical-coordinate value of each point on a curve for the Al element multiplied by 2 is an Al component content. Due to factors such as measurement errors, a measured value may be different from a designed value.
A difference from Embodiment 1 lies in that the buffer layer includes 11 groups of double-layer structures with an upper-layer and a lower layer of AlxGa1-xN/AlyGa1-yN. Table 3 shows values of x and y, an upper-layer thickness Tupper, and a lower-layer thickness Tlower in each group of double-layer structures.
Double-layer structures whose sequence numbers are 1 to 11 are sequentially disposed in a stacked manner. A double-layer structure with a sequence number of 1 is disposed close to the epitaxial layer, and a double-layer structure with a sequence number of 11 is disposed close to the nucleation layer. The periodicity 5 in Table 1 means that a double-layer structure with each sequence number is repeated five times. To be specific, double-layer structures with different band gap differences have a same repetition periodicity, to form 11 groups of double-layer structures, and each group includes five same double-layer structures that are stacked. It can be learned from Table 3 that, in the nitride epitaxial structure in Embodiment 3, Al component content differences of the 11 groups of double-layer structures of the buffer layer gradually decrease from one side of the nucleation layer to one side of the epitaxial layer, that is, band gap differences of the 11 groups of double-layer structures gradually decrease from one side of the nucleation layer to one side of the epitaxial layer. In addition, average Al component contents of the 11 groups of double-layer structures in Embodiment 3 also gradually decrease from one side of the nucleation layer to one side of the epitaxial layer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202011025013.6 | Sep 2020 | CN | national |
This application is a continuation of International Application No. PCT/CN2021/118342, filed on Sep. 14, 2021, which claims priority to Chinese Patent Application No. 202011025013.6, filed on Sep. 25, 2020. The disclosures of the aforementioned applications are hereby incorporated by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2021/118342 | Sep 2021 | WO |
| Child | 18189581 | US |
