JP2006332125A - Semiconductor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor element for improving the crystallinity of a nitride semiconductor layer 8 formed on an Si substrate 1, and further, to provide a semiconductor element for improving the conductivity. <P>SOLUTION: The semiconductor element has the nitride semiconductor layer 8 on the Si substrate 1. The semiconductor element 1 has a first multilayered film structure 2, in which at least a first layer 4 and a second layer 5 are alternately laminated on the side of the Si substrate 1, and a second multilayer film structure 3, in which at least a third layer 6 and a fourth layer 7 are alternately laminated on the first multilayer film structure 2. The first layer 4 and the third layer 6 are nitride semiconductors, having a composition in which the difference in a lattice constant to the Si substrate 1, is smaller than that of the second layer 5 and the fourth layer 7, the film thickness is larger than that of the second layer 5 and the fourth layer 7, and the first layer 4 has a larger film thickness than that of the third layer 6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor device, and more particularly to a nitride-based semiconductor device.

When a nitride semiconductor layer is formed on a substrate different from the nitride semiconductor to obtain a nitride semiconductor element, there is a difference in lattice constant between the nitride semiconductor layer and the substrate. A buffer layer is formed between the semiconductor layer and the substrate. For example, in Patent Document 1, a first layer and a second layer are alternately provided on a substrate such as Si (silicon), SiC (silicon carbide), or Ai ₂ O ₃ (sapphire). An invention has been proposed in which a superlattice structure is formed by stacking several layers.
JP 2002-170776 A

However, particularly when a nitride semiconductor layer is formed on a Si substrate, a nitride semiconductor layer with good crystallinity tends to be difficult to obtain. Therefore, in the conventional superlattice structure, a nitride semiconductor layer with good crystallinity still cannot be obtained particularly when a nitride semiconductor layer is formed using a Si substrate as a substrate.
Accordingly, an object of the present invention is to provide a semiconductor element in which the crystallinity of a nitride semiconductor layer formed on a Si substrate is improved, and further a semiconductor element capable of improving conductivity. .

  According to the present invention, the above problem is solved by the following means.

A first invention is a semiconductor device comprising a nitride semiconductor layer on a Si substrate, wherein the nitride semiconductor layer includes at least a first layer and a second layer on the Si substrate side. A first multilayer film structure alternately laminated, and a second multilayer film structure in which at least a third layer and a fourth layer are alternately laminated on the first multilayer film structure, The first layer and the third layer are nitride semiconductors having a composition having a smaller lattice constant difference from the Si substrate than any of the second layer and the fourth layer, and the second layer The semiconductor element is characterized in that the film thickness is larger than any of the layer and the fourth layer, and the first layer is thicker than the third layer.
According to the first invention, a layer having a large lattice constant difference from the Si substrate (second layer, fourth layer) is a layer having a small lattice constant difference from the Si substrate (first layer, third layer). Layer). The first layer and the second layer will be described. Since the first layer and the second layer are both nitride semiconductors, the lattice constant is smaller than that of the Si substrate. That is, when a nitride semiconductor layer is formed on a Si substrate, there is a difference in lattice constant, so that compressive stress and tensile stress act on the interface between the Si substrate and the nitride semiconductor layer, respectively. Specifically, when a first layer made of a nitride semiconductor is formed on a Si substrate, compressive stress acts on a Si substrate having a large lattice constant, whereas tensile stress acts on a first layer having a small lattice constant. . Since tensile stress acts on the first layer, if the first layer continues to grow, cracks will occur on the growth surface. Further, the occurrence of this crack makes it difficult to further grow the nitride semiconductor layer. Here, when the second layer made of a nitride semiconductor having a larger lattice constant difference than the first layer is formed as a thin film, the second layer is formed at the interface between the first layer and the second layer. A tensile stress acts on the layer, and a compressive stress acts on the first layer. That is, since compressive stress acts on the growth surface of the first layer that continues to have tensile stress, the occurrence of cracks can be suppressed. In other words, the first layer can be formed while suppressing the occurrence of cracks, and is made of a nitride semiconductor that suppresses cracks by forming a multilayer film structure in which the first layers and the second layers are alternately laminated. A multilayer film structure can be obtained. The relationship between the first layer and the second layer is the same for the third and fourth layers.
Furthermore, on the Si substrate, a multilayer film structure in which the third layer and the fourth layer are alternately stacked on the multilayer film structure in which the occurrence of cracks between the first layer and the second layer is suppressed. By forming, a nitride semiconductor layer with good crystallinity can be formed. Here, according to the first invention, the first layer is thicker than the third layer. That is, the third layer is thinner than the first layer. Thereby, a nitride semiconductor layer with good crystallinity can be obtained. The multilayer film structure of the third layer and the fourth layer exhibits its function by being on the multilayer film structure of the first layer and the second layer. For example, a nitride semiconductor layer with good crystallinity cannot be obtained even if a multilayer film structure of the third layer and the fourth layer having the same thickness is directly formed on the Si substrate. That is, the multilayer film structure of the third layer and the fourth layer can exhibit its effect by being formed on the Si substrate and on the film in which the generation of cracks is suppressed.
As described above, according to the first invention, it is possible to obtain a nitride semiconductor layer having good crystallinity.

A second invention is a semiconductor element according to the first invention, wherein a total film thickness of the first multilayer film structure is smaller than a total film thickness of the second multilayer film structure.
If the total film thickness of the first multilayer structure is smaller than the total film thickness of the second multilayer structure, the crystallinity of the nitride semiconductor layer can be further improved.

A third invention is the semiconductor element according to the first invention or the second invention, wherein the second layer and the fourth layer have substantially the same film thickness.
According to the third aspect, since the thicknesses of the second layer and the fourth layer are substantially the same, it is easy to design the periodicity and thickness ratio change of the multilayer film.

In a fourth aspect of the invention, the second layer and the fourth layer contain Al, and the first layer and the third layer contain Ga. This is a semiconductor device according to any one of the inventions.
According to the fourth invention, since the second layer and the fourth layer are nitride semiconductors containing Al, and the first layer and the third layer are nitride semiconductors containing Ga, Furthermore, a multilayer film structure that effectively utilizes the properties of a nitride semiconductor containing Al and the properties of a nitride semiconductor containing Ga can be obtained.

According to a fifth aspect of the invention, the first layer and the third layer contain Al, and the Al mixed crystal ratio is smaller than that of the second layer and the fourth layer. A semiconductor device according to any one of the inventions to the fourth invention.
According to the fifth aspect of the invention, layers having different lattice constants are provided with a mixed crystal ratio of Al, and a multilayer film structure that effectively utilizes the properties of a nitride semiconductor containing Al can be obtained.

According to a sixth aspect of the invention, the second layer and the fourth layer contain Ga, and the Ga mixed crystal ratio is smaller than that of the first layer and the third layer. It is a semiconductor element which concerns on any one of invention-5th invention.
According to the sixth aspect of the present invention, layers having different lattice constants are provided with a Ga mixed crystal ratio, and a multilayer film structure that effectively utilizes the properties of a nitride semiconductor containing Ga can be obtained.

In a seventh aspect of the invention, the first layer and the third layer are Al _x Ga _1-x N (0 ≦ x ≦ 0.5), and the second layer and the fourth layer are A semiconductor element according to any one of the first to sixth inventions, characterized in that Al _y Ga _1-y N (0.5 <y ≦ 1).
In the multilayer film, unless the difference in the composition ratio between the two layers constituting this is taken large, the difference in crystal properties and mechanical properties peculiar to each composition becomes small, and the first layer and the second layer According to the seventh aspect, according to the seventh aspect, the first layer and the third layer are made of AlGaN (0 ≦ 0) where it is difficult to achieve the purpose of crystal growth by extracting the compositional properties of the (third layer and fourth layer). x <0.5) and the second layer and the fourth layer are AlGaN (0.5 <y ≦ 1), so that the first layer and the second layer (the third layer and the second layer) The crystal growth can be achieved by taking out the properties of both of the four layers.

In an eighth aspect of the invention, the first layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5), and the second layer is Al _y Ga _1-y N (0.5 <Y ≦ 1) and (y−x)> 0.5. The semiconductor element according to any one of the first to seventh inventions.
According to the eighth invention, the first layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5), and the second layer is Al _y Ga _1-y N (0.5 <y Since ≦ 1) and (y−x)> 0.5, the difference in composition ratio between the two layers can be increased, and the layer sufficiently functions as a layer for suppressing cracks.

According to a ninth aspect of the invention, in the semiconductor element according to any one of the first to eighth aspects, the first layer and the third layer contain an n-type impurity of a nitride semiconductor. It is.
According to the ninth aspect of the invention, the n-type impurity of the nitride semiconductor is contained in the first layer and the third layer, so that the multilayer structure can be a suitable charge transfer layer. In addition, band discontinuity due to the difference in band structure occurs at the interface between the Si substrate and the multilayer structure, so that a potential barrier is formed at the interface. Therefore, by including an n-type impurity of a nitride semiconductor in the first layer and the third layer of the multilayer structure, the thickness of the potential barrier is reduced, and V _f can be reduced. In particular, since the first layer includes an n-type impurity, it is effective to reduce V _f .

According to a tenth invention, in any one of the first to ninth inventions, the first layer contains more n-type impurities of a nitride semiconductor than the third layer. This is a semiconductor element.
In the tenth invention, Vf is reduced because the first layer of the multilayer structure contains an n-type impurity. This effect is due to a potential barrier generated at the interface between the Si substrate and the multilayer film. Therefore, the layer containing the n-type impurity is preferably the first layer on the Si substrate side, and conversely, it is difficult to obtain a remarkable effect on the nitride semiconductor layer side opposite to the Si substrate side. From the viewpoint of crystallinity, the inclusion of n-type impurities reduces the crystallinity of the nitride semiconductor layer on the multilayer structure. Therefore, according to the tenth invention, by reducing the n-type impurity on the nitride semiconductor layer side relative to the Si substrate side, a nitride semiconductor layer with good crystallinity can be obtained in addition to the reduction of Vf. . Further, the first layer closest to the Si substrate side contains a larger amount of n-type impurities than the other first layers, thereby reducing the thickness of the potential barrier between the Si substrate and the multilayer structure. In addition, the crystallinity can be suppressed and a suitable charge transfer layer can be obtained.

In an eleventh invention, the first multilayer film structure and the second multilayer film structure are of a first conductivity type, and the nitride semiconductor layer includes at least an active layer and a second conductivity type layer in order from the substrate side. A semiconductor device according to any one of the first to tenth inventions.
According to the eleventh aspect of the invention, since the nitride semiconductor layer is improved in crystallinity by the first multilayer structure and the second multilayer structure, the active layer and the second conductivity type layer are formed. The function of each layer can be suitably exhibited. In addition, according to the eleventh aspect, since the first multilayer film structure and the second multilayer film structure are accommodated in one conductivity type region, synergistic problem deterioration due to the change in crystallinity and the change in conductivity is avoided. It becomes possible to do.

A twelfth aspect of the invention is a semiconductor device including a nitride semiconductor layer on a Si substrate, and a buffer region between the Si substrate and the nitride semiconductor layer, wherein the buffer region is formed on the substrate side. A first region and a second region farther from the Si substrate than the first region, wherein the first region and the second region are a first layer made of a nitride semiconductor; Each having a multilayer structure in which a second layer made of a nitride semiconductor having a film thickness smaller than that of the first layer and having a composition different from that of the first layer is laminated. The semiconductor element is characterized in that the thickness of the first layer included in the region is larger than the thickness of the first layer included in the second region.
According to the twelfth aspect, the layer (second layer) having a large lattice constant difference from the Si substrate is formed as a thin film than the layer (first layer) having a small lattice constant difference from the Si substrate. Since the first layer is a nitride semiconductor, it has a smaller lattice constant than the Si substrate. That is, when a nitride semiconductor layer is formed on a Si substrate, there is a difference in lattice constant, so that compressive stress and tensile stress act on the interface between the Si substrate and the nitride semiconductor layer, respectively. Specifically, when a first layer made of a nitride semiconductor is formed on a Si substrate, compressive stress acts on a Si substrate having a large lattice constant, whereas tensile stress acts on a first layer having a small lattice constant. . Since tensile stress acts on the first layer, if the first layer continues to grow, cracks will occur on the growth surface. Further, the occurrence of this crack makes it difficult to further grow the nitride semiconductor layer. Here, when the second layer made of a nitride semiconductor having a larger lattice constant difference than the first layer is formed as a thin film, the second layer is formed at the interface between the first layer and the second layer. A tensile stress acts on the layer, and a compressive stress acts on the first layer. That is, since compressive stress acts on the growth surface of the first layer that continues to have tensile stress, the occurrence of cracks can be suppressed. In other words, the first layer can be formed while suppressing the occurrence of cracks, and is made of a nitride semiconductor that suppresses cracks by forming a multilayer film structure in which the first layers and the second layers are alternately laminated. A buffer region can be obtained.
Further, a second layer in which the first layer and the second layer are alternately stacked on the first region where the occurrence of cracks between the first layer and the second layer is suppressed on the Si substrate. By forming the region, a nitride semiconductor layer with good crystallinity can be formed. Here, according to the twelfth aspect, the film thickness of the first layer included in the first region is larger than the film thickness of the first layer included in the second region, that is, the second region has. The thickness of the first layer is a layer thinner than the thickness of the first layer included in the first region. Thereby, a nitride semiconductor layer with good crystallinity can be obtained. The second region exhibits its function by being on the first region. For example, a nitride semiconductor layer with good crystallinity cannot be obtained even if the second region having the same thickness is directly formed on the Si substrate. That is, the effect can be exhibited by forming the second region on the Si substrate and on the film in which the generation of cracks is suppressed.
As described above, according to the twelfth invention, a nitride semiconductor layer with good crystallinity can be obtained.

A thirteenth invention is a semiconductor device comprising a nitride semiconductor layer on a Si substrate and a buffer region between the Si substrate and the nitride semiconductor layer, wherein the buffer region is a nitride semiconductor The first layer and the second layer having different compositions are periodically provided, and the length of one cycle in the film thickness direction (one cycle length) is shorter on the nitride semiconductor layer side than on the Si substrate side. Alternatively, in the semiconductor element, the number of periods in a desired length in the film thickness direction (at least two periods or more) is larger on the nitride semiconductor layer side than on the Si substrate.
According to the thirteenth aspect, the layer (second layer) having a large lattice constant difference from the Si substrate is formed as a thin film than the layer (first layer) having a small lattice constant difference from the Si substrate. Since the first layer is a nitride semiconductor, it has a smaller lattice constant than the Si substrate. That is, when a nitride semiconductor layer is formed on a Si substrate, there is a difference in lattice constant, so that compressive stress and tensile stress act on the interface between the Si substrate and the nitride semiconductor layer, respectively. Specifically, when a first layer made of a nitride semiconductor is formed on a Si substrate, compressive stress acts on a Si substrate having a large lattice constant, whereas tensile stress acts on a first layer having a small lattice constant. . Since tensile stress acts on the first layer, if the first layer continues to grow, cracks will occur on the growth surface. Further, the occurrence of this crack makes it difficult to further grow the nitride semiconductor layer. Here, when the second layer made of a nitride semiconductor having a larger lattice constant difference than the first layer is formed as a thin film, the second layer is formed at the interface between the first layer and the second layer. A tensile stress acts on the layer, and a compressive stress acts on the first layer. That is, since compressive stress acts on the growth surface of the first layer that continues to have tensile stress, the occurrence of cracks can be suppressed. In other words, the first layer can be formed while suppressing the occurrence of cracks, and is made of a nitride semiconductor that suppresses cracks by forming a multilayer film structure in which the first layers and the second layers are alternately laminated. A buffer region can be obtained.
Further, a second layer in which the first layer and the second layer are alternately stacked on the first region where the occurrence of cracks between the first layer and the second layer is suppressed on the Si substrate. By forming the region, a nitride semiconductor layer with good crystallinity can be formed. Here, according to the thirteenth aspect, the thickness of the first layer included in the first region is larger than the thickness of the first layer included in the second region, that is, the second region has. The thickness of the first layer is a layer thinner than the thickness of the first layer included in the first region. Thereby, a nitride semiconductor layer with good crystallinity can be obtained. The second region exhibits its function by being on the first region. For example, a nitride semiconductor layer with good crystallinity cannot be obtained even if the second region having the same thickness is directly formed on the Si substrate. That is, the effect can be exhibited by forming the second region on the Si substrate and on the film in which the generation of cracks is suppressed.
As described above, according to the thirteenth invention, it is possible to obtain a nitride semiconductor layer with good crystallinity.

A fourteenth aspect of the invention is a semiconductor device comprising a nitride semiconductor layer on a Si substrate and a buffer region between the Si substrate and the nitride semiconductor layer, wherein the buffer region is at least nitrided A first layer made of a nitride semiconductor, and a second layer made of a nitride semiconductor having a smaller lattice constant difference than the first substrate and having a composition larger than that of the first layer. The film thickness difference between the first layer and the second layer ([first layer]-[second layer]) is more than that on the Si substrate side. The nitride semiconductor layer side is small, or the film thickness ratio ([first layer] / [second layer]) between the first layer and the second layer is higher than that of the Si substrate side. The semiconductor element is characterized in that the semiconductor layer side is small.
In the fourteenth invention, the same effect as in the thirteenth invention can be obtained.

A fifteenth aspect of the present invention is the semiconductor element according to any one of the twelfth to fourteenth aspects, wherein the second layer in the buffer region has substantially the same film thickness.
According to the fifteenth aspect, since the thickness of the second layer is substantially the same, it is easy to design the periodicity of the multilayer film and the change in the film thickness ratio.

According to a sixteenth aspect of the invention, in the semiconductor element according to any one of the twelfth to fifteenth aspects, the second layer contains Al, and the first layer contains Ga. It is.
According to the sixteenth aspect, since the second layer is a nitride semiconductor containing Al and the first layer is a nitride semiconductor containing Ga, the properties of the nitride semiconductor further containing Al, and Ga It is possible to provide a buffer region that effectively utilizes the properties of nitride semiconductors including

According to a seventeenth aspect of the invention, in any one of the twelfth to sixteenth aspects, the first layer contains Al and has an Al mixed crystal ratio smaller than that of the second layer. This is a semiconductor element.
In a multilayer film, unless the difference in the composition ratio of the two layers constituting this is taken large, the difference in crystal properties and mechanical properties peculiar to each composition will be small, and the properties of both compositions will be extracted and crystallized. Where the purpose of achieving growth is difficult to achieve, according to the seventeenth aspect, since the Al mixed crystal ratio of the first layer is smaller than that of the second layer, both the first layer and the second layer It is possible to achieve crystal growth by extracting the properties of.

According to an eighteenth aspect of the invention, in any one of the twelfth aspect to the seventeenth aspect, the second layer contains Ga and has a Ga mixed crystal ratio smaller than that of the first layer. This is a semiconductor element.
According to the eighteenth aspect of the present invention, layers having different lattice constants are provided with a Ga mixed crystal ratio, and a buffer region that effectively utilizes the properties of a nitride semiconductor containing Ga can be obtained.

In a nineteenth aspect of the invention, the first layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5), and the second layer is Al _y Ga _1-y N (0.5 <Y ≦ 1). A semiconductor element according to any one of the twelfth to eighteenth inventions.
In a multilayer film, unless the difference in the composition ratio of the two layers constituting this is taken large, the difference in crystal properties and mechanical properties peculiar to each composition will be small, and the properties of both compositions will be extracted and crystallized. Where the purpose of achieving growth is difficult to achieve, according to the nineteenth invention, the first layer is made of AlGaN (0 ≦ x <0.5), and the second layer is made of AlGaN (0.5 <y ≦ 1). Therefore, the crystal growth can be achieved by extracting the properties of both the first layer and the second layer.

In a twentieth aspect, the first layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5), and the second layer is Al _y Ga _1-y N (0.5 <Y ≦ 1) and (y−x)> 0.5. The semiconductor element according to any one of the twelfth to nineteenth inventions.
According to the twentieth invention, the first layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5), and the second layer is Al _y Ga _1-y N (0.5 <y Since ≦ 1) and (y−x)> 0.5, the difference in composition ratio between the two layers can be increased, and the layer sufficiently functions as a layer for suppressing cracks.

A twenty-first invention is the semiconductor element according to any one of the twelfth to twentieth inventions, wherein the first layer contains an n-type impurity of a nitride semiconductor.
According to the twenty-first aspect, the buffer layer can be a suitable charge transfer layer by including the n-type impurity of the nitride semiconductor in the first layer. In addition, since a band discontinuity occurs due to a difference in band structure at the interface between the Si substrate and the multilayer film, a potential barrier is formed at the interface. Therefore, by including the n-type impurity of the nitride semiconductor in the first layer of the buffer region, the thickness of the potential barrier can be reduced and V _f can be reduced. In particular, since the first layer includes an n-type impurity, it is effective to reduce V _f .

In a twenty-second aspect of the invention, any one of the twelfth to twenty-first aspects, wherein the buffer region contains more n-type impurities of the nitride semiconductor on the Si substrate side than on the nitride semiconductor layer side. This is a semiconductor device according to one.
In the twenty-second aspect, Vf is reduced because the first layer of the multilayer structure contains an n-type impurity. This effect is due to a potential barrier generated at the interface between the Si substrate and the multilayer film. Therefore, the layer containing the n-type impurity is preferably the first layer on the Si substrate side, and conversely, it is difficult to obtain a remarkable effect on the nitride semiconductor layer side opposite to the Si substrate side. From the viewpoint of crystallinity, the inclusion of n-type impurities reduces the crystallinity of the nitride semiconductor layer on the multilayer structure. Accordingly, in the twenty-second aspect, by reducing the n-type impurity on the nitride semiconductor layer side relative to the Si substrate side, a nitride semiconductor layer with good crystallinity can be obtained in addition to the reduction in Vf. Further, the first layer closest to the Si substrate side contains a larger amount of n-type impurities than the other first layers, thereby reducing the thickness of the potential barrier between the Si substrate and the multilayer structure. In addition, the crystallinity can be suppressed and a suitable charge transfer layer can be obtained.

According to a twenty-third aspect, in the semiconductor element according to any one of the twelfth to twenty-second aspects, the buffer region is a first conductivity type layer, and an active layer is formed on the buffer region, A semiconductor element comprising a second conductivity type layer having a conductivity type opposite to that of the buffer region.
According to the twenty-third aspect, since the active layer and the second conductivity type layer are formed after the crystallinity of the nitride semiconductor layer is improved by the buffer region, the functions of these layers can be suitably exhibited. According to the twenty-third aspect, since the buffer region is accommodated in one conductivity type region, it becomes possible to avoid synergistic problem deterioration due to the change in crystallinity and the change in conductivity.

  According to the present invention, in the semiconductor element, both the crystallinity and conductivity of the nitride semiconductor layer formed on the Si substrate can be improved.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing a part of a semiconductor element according to the first embodiment of the present invention.
As shown in FIG. 1, the semiconductor device according to the first embodiment of the present invention includes a Si substrate 1, on which a first multilayer film structure 2 and a second multilayer film structure 3 are provided. And. In the first multilayer film structure 2, the first layers 4 and the second layers 5 are alternately stacked. In the second multilayer film structure 3, the third layers 6 and the fourth layers are stacked. 7 are alternately stacked. Here, the first layer 4 is a nitride semiconductor having a smaller lattice constant difference from the Si substrate 1 than the second layer 5 and the fourth layer 7. The third layer 6 is also a nitride semiconductor having a smaller lattice constant difference from the Si substrate 1 than the second layer 5 and the fourth layer 7. Further, the first layer 4 is thicker than the third layer 6. Further, in the semiconductor element according to the first embodiment, the layer having the large lattice constant difference from the Si substrate 1 (the second layer 5 and the fourth layer 7) has a lattice constant difference from the Si substrate 1. Is formed of a thin film than the smaller layers (the first layer 4 and the third layer 6).
In the semiconductor element according to the first embodiment, since the first layer 4 and the second layer 5 are both nitride semiconductors, the lattice constant is smaller than that of the Si substrate 1. For this reason, when a nitride semiconductor is formed on the Si substrate 1, there is a difference in lattice constant, so that compressive stress and tensile stress act on the interface between the Si substrate 1 and the nitride semiconductor, respectively. Specifically, when the first layer 4 made of a nitride semiconductor is formed on the Si substrate 1, compressive stress is applied to the Si substrate 1 having a large lattice constant, whereas the first layer 4 having a small lattice constant is applied to the first layer 4 having a small lattice constant. Tensile stress works. Since tensile stress acts on the first layer 4, if the first layer 4 continues to grow, cracks will occur on the growth surface. In addition, the occurrence of cracks makes it difficult to grow a nitride semiconductor. When the second layer 5 made of a nitride semiconductor having a lattice constant difference larger than that of the first layer is formed as a thin film, at the interface between the first layer 4 and the second layer 5, A tensile stress acts on the second layer 5 and a compressive stress acts on the first layer 4. That is, since compressive stress acts on the growth surface of the first layer 4 that continues to have tensile stress, the occurrence of cracks can be suppressed. In other words, the first layer 4 can be formed while suppressing the occurrence of cracks, and the nitridation with reduced cracks can be achieved by forming the multilayer film structure 2 in which the first layers 4 and the second layers 5 are alternately stacked. It is possible to obtain a multilayer film structure made of a physical semiconductor. The same holds true for the third layer 6 and the fourth layer 7 regarding the relationship between the first layer 4 and the second layer 5.
Further, in the semiconductor element according to the first embodiment, on the first multilayer film structure 2 in which the occurrence of cracks between the first layer 4 and the second layer 5 is suppressed on the Si substrate 1, Since the second multilayer structure 3 in which the third layers 6 and the fourth layers 7 are alternately stacked is formed, the nitride semiconductor layer 8 with good crystallinity can be formed. In the semiconductor element according to the first embodiment, the first layer 4 is thicker than the third layer 6. That is, the third layer 6 is thinner than the first layer 4. Thereby, the nitride semiconductor layer 8 with good crystallinity can be obtained. The second multilayer structure 3 of the third layer 6 and the fourth layer 7 is on the first multilayer structure 2 of the first layer 4 and the second layer 5, so that its function is achieved. Demonstrate. For example, even if the second multilayer structure 3 of the third layer 6 and the fourth layer 7 having the same film thickness is directly formed on the Si substrate 1, the nitride semiconductor layer 8 with good crystallinity can be obtained. Absent. In other words, the second multilayer film structure 3 of the third layer 6 and the fourth layer 7 exhibits its effect by being formed on the Si substrate 1 and a film in which the generation of cracks is suppressed. Can do. In the first embodiment, the second multilayer film structure 3 is formed immediately above the first multilayer film structure 2. However, in the present invention, the second multilayer film structure 3 is replaced with the first multilayer film structure. If it is formed above 2, the effect of improving crystallinity and conductivity can be obtained even if it is not formed directly above. However, when the second multilayer film structure 3 is formed immediately above the first multilayer film structure 2, the crystallinity and conductivity can be further improved as compared with the case where the second multilayer film structure 3 is not formed immediately above. .
From the above, according to the first embodiment, it is possible to obtain the nitride semiconductor layer 8 with good crystallinity.

As shown in FIG. 1, when the total film thickness of the first multilayer film structure 2 is smaller than the total film thickness of the second multilayer film structure 3, the crystallinity of the nitride semiconductor layer 8 is further improved. Can do.
Further, if the film thicknesses of the second layer 5 and the fourth layer 7 are substantially the same, it is easy to design the periodicity of the multilayer film and the film thickness ratio change. In the present invention, “substantially the same” means not only strictly the same, but also includes a case where they are not strictly the same.
In addition, if the second layer 5 and the fourth layer 7 are nitride semiconductors containing Al, and the first layer 4 and the third layer 6 are nitride semiconductors containing Ga, then Al is further added. A multilayer film structure that effectively utilizes the properties of the nitride semiconductor containing Ga and the properties of the nitride semiconductor containing Ga can be obtained.
Further, when the first layer 4 and the third layer 6 contain Al and the Al mixed crystal ratio is smaller than that of the second layer 5 and the fourth layer 7, the lattice is formed with the mixed crystal ratio of Al. Layers having different constants are provided, and a multilayer film structure that effectively utilizes the properties of a nitride semiconductor containing Al can be obtained.
Further, when the second layer 5 and the fourth layer 7 contain Ga and the Ga mixed crystal ratio is smaller than that of the first layer 4 and the third layer 6, the lattice is formed with the Ga mixed crystal ratio. Layers having different constants are provided, and a multilayer film structure that effectively utilizes the properties of a nitride semiconductor containing Ga can be obtained.
Also, in the multilayer film, unless the difference in composition ratio between the two types of layers constituting this is taken large, the difference in crystal properties and mechanical properties peculiar to each composition becomes small, and the first layer and the second layer. It is difficult to achieve the purpose of crystal growth by extracting the compositional properties of the layers (third layer and fourth layer). Therefore, the first layer 4 and the third layer 6 are AlGaN (0 ≦ x <0.5), and the second layer 5 and the fourth layer 7 are AlGaN (0.5 <y ≦ 1). In such a case, the properties of both the first layer 4 and the second layer 5 (the third layer 6 and the fourth layer 7) can be brought out to achieve crystal growth. Further, when (y−x)> 0.5, the difference in composition ratio between the two layers can be increased, and the layer sufficiently functions as a layer for suppressing cracks.
When the first layer 4 and the third layer 6 contain an n-type impurity of a nitride semiconductor, a multilayer structure is a suitable charge transfer layer. At the interface between the Si substrate 1 and the multilayer structure, band discontinuity occurs due to the difference in the band structure, so that a potential barrier is formed at the interface. Therefore, by adding the n-type impurity of the nitride semiconductor to the first layer 4 and the third layer 6 having a multilayer structure, the thickness of the potential barrier is reduced, and V _f can be reduced. In particular, since the first layer 4 contains an n-type impurity, V _f can be effectively reduced.
Further, when the first layer of the multilayer structure contains an n-type impurity, Vf is reduced, but this effect is due to a potential barrier generated at the interface between the Si substrate 1 and the multilayer film. The layer containing n-type impurities is preferably the first layer 4 on the Si substrate 1 side, and conversely, a remarkable effect is hardly obtained on the nitride semiconductor layer 8 side opposite to the Si substrate 1 side. From the viewpoint of crystallinity, the inclusion of n-type impurities reduces the crystallinity of the nitride semiconductor layer 8 on the multilayer structure. Therefore, by reducing the n-type impurities on the nitride semiconductor layer 8 side with respect to the Si substrate 1 side, the nitride semiconductor layer 8 with good crystallinity can be obtained in addition to the reduction of Vf. Further, the first layer 4 closest to the Si substrate 1 side contains a larger amount of n-type impurities than the other first layers 4, so that the potential barrier between the Si substrate 1 and the multilayer structure is present. By reducing the thickness of the substrate and suppressing the decrease in crystallinity, a suitable charge transfer layer can be obtained.

As described above, according to the first embodiment, the semiconductor element includes the buffer region 9 between the Si substrate 1 and the nitride semiconductor layer 8 as in the semiconductor element shown in FIG. It will be. The buffer region 9 includes a first region 10 on the substrate side, and a first layer 12 made of a nitride semiconductor in a second region 11 farther from the Si substrate 1 than the first region 10; Each has a multilayer structure in which the second layer 13 made of a nitride semiconductor having a thickness smaller than that of the first layer 12 and having a composition different from that of the first layer 12 is alternately laminated. The film thickness of the first layer 12 included in the first region 10 is larger than the film thickness of the first layer 12 included in the second region 11. Therefore, in the first embodiment, the first layer 12 made of a nitride semiconductor and the first layer 12 are smaller in thickness than the first layer 12 in a region near and far from the substrate side. Since a multilayer structure is formed by alternately laminating second layers 13 made of nitride semiconductors having different compositions, the characteristics (crystallographic and mechanical) of each layer (first layer 12 and second layer 13) are formed. Can be suitably extracted. Further, according to the first embodiment, since the film thickness of the first layer 12 included in the first region 10 is larger than the film thickness of the first layer 12 included in the second region 11, the substrate The problem of crystallinity (lattice mismatch) and mechanical (stress) depending on the distance can be made into a multilayer film structure adapted thereto, and a suitable crystal can be obtained.
Further, when the active layer and the second conductivity type layer are formed after the crystallinity of the nitride semiconductor layer 8 is improved by the first multilayer film structure and the second multilayer film structure, the functions of these layers are formed. Can be suitably exhibited. Further, since the first multilayer film structure 2 and the second multilayer film structure 3 are accommodated in one conductivity type region, it becomes possible to avoid synergistic problem deterioration due to the change in crystallinity and the change in conductivity. .

In the first embodiment, the first multilayer film structure 2 includes the first layer 4 and the second layer 5, but the first multilayer film structure 2 includes the first layer 4 and the second layer 5. A layer other than the second layer 5 may be included. Similarly, in the first embodiment, the second multilayer film structure 3 includes the third layer 6 and the fourth layer 7. However, the second multilayer film structure 3 includes the third layer 6. In addition, layers other than the fourth layer 7 may be included.
Moreover, the preferable film thickness of the 1st layer-4th layer which implement | achieves these 1st Embodiments is as follows. The first layer is 5 nm to 100 nm, more preferably 10 nm to 40 nm, the second layer and the fourth layer are thinner than the first layer, and 1 nm to 10 nm, more preferably 1 nm to 5 nm. The third layer is thicker than the second layer and thinner than the first layer. Preferably, the first layer is about twice as large as the third layer.

FIG. 2 is a diagram showing a part of a semiconductor element according to the second embodiment of the present invention.
As shown in FIG. 2, the semiconductor device according to the second embodiment includes a nitride semiconductor layer 8 on a Si substrate 1, and a buffer region between the Si substrate 1 and the nitride semiconductor layer 8. 9 is provided. The buffer region 9 periodically includes a first layer 12 and a second layer 13 having different nitride semiconductor compositions, and the length of one cycle (one cycle length) in the film thickness direction is the Si substrate 1. The nitride semiconductor layer 8 side is shorter than the side.
According to the semiconductor element of the second embodiment, a layer having a large lattice constant difference from the Si substrate 1 (second layer 13) is a layer having a small lattice constant difference from the Si substrate 1 (the first layer). It is formed of a thinner film than layer 12). Since the first layer 12 is a nitride semiconductor, it has a smaller lattice constant than the Si substrate 1. That is, when the nitride semiconductor layer 8 is formed on the Si substrate 1, there is a difference in lattice constant, so that compressive stress and tensile stress act on the interface between the Si substrate 1 and the nitride semiconductor layer 8, respectively. Specifically, when the first layer 12 made of a nitride semiconductor is formed on the Si substrate 1, compressive stress is applied to the Si substrate 1 having a large lattice constant, whereas the first layer 12 having a small lattice constant is applied to the first layer 12 having a small lattice constant. Tensile stress works. Since tensile stress acts on the first layer 12, if the first layer 12 continues to grow, cracks will occur on the growth surface. Further, the occurrence of this crack makes it difficult to further grow the nitride semiconductor layer 8. When the second layer 13 made of a nitride semiconductor having a lattice constant difference larger than that of the first layer 12 is formed as a thin film, the interface between the first layer 12 and the second layer 13 is formed. 2, tensile stress is applied to the second layer 13, and compressive stress is applied to the first layer 12. That is, since compressive stress acts on the growth surface of the first layer 12 that continues to have tensile stress, the occurrence of cracks can be suppressed. In other words, the first layer 12 can be formed while suppressing the occurrence of cracks, and a nitride film in which cracks are suppressed by forming a multilayer film structure in which the first layers 12 and the second layers 13 are alternately stacked. A buffer region 9 made of a semiconductor can be obtained.
Furthermore, the first layer 12 and the second layer 13 are alternately formed on the Si region 1 on the first region 10 in which the occurrence of cracks between the first layer 12 and the second layer 13 is suppressed. By forming the second region 11 stacked on the nitride semiconductor layer 8, it is possible to form the nitride semiconductor layer 8 with good crystallinity. Here, according to the second embodiment, the film thickness of the first layer 12 included in the first region 10 is larger than the film thickness of the first layer 12 included in the second region 11. The film thickness of the first layer 12 included in the second region 11 is smaller than the film thickness of the first layer 12 included in the first region 10. Thereby, the nitride semiconductor layer 8 with good crystallinity can be obtained. The second region 11 exhibits its function by being on the first region 10. For example, even if the second region 11 having the same thickness is directly formed on the Si substrate 1, the nitride semiconductor layer 8 with good crystallinity cannot be obtained. That is, the effect can be exhibited by forming the second region 11 on the Si substrate 1 and a film in which the occurrence of cracks is suppressed.
From the above, according to the second embodiment, it is possible to obtain the nitride semiconductor layer 8 with good crystallinity.
According to the second embodiment, the semiconductor element includes the buffer region 9 between the Si substrate 1 and the nitride semiconductor layer 8. The buffer region 9 includes a first region 10 on the substrate side, and a first layer 12 made of a nitride semiconductor in a second region 11 farther from the Si substrate 1 than the first region 10; Each has a multilayer structure in which the second layer 13 made of a nitride semiconductor having a thickness smaller than that of the first layer 12 and having a composition different from that of the first layer 12 is alternately laminated. The film thickness of the first layer 12 included in the first region 10 is larger than the film thickness of the first layer 12 included in the second region 11. Therefore, in the second embodiment, the first layer 12 made of a nitride semiconductor and the first layer 12 are smaller in thickness than the first layer 12 in a region near and far from the substrate side. Since a multilayer structure is formed by alternately laminating second layers 13 made of nitride semiconductors having different compositions, the characteristics (crystallographic and mechanical) of each layer (first layer 12 and second layer 13) are formed. Can be suitably extracted. Further, according to the first embodiment, since the film thickness of the first layer 12 included in the first region 10 is larger than the film thickness of the first layer 12 included in the second region 11, the substrate The problem of crystallinity (lattice mismatch) and mechanical (stress) depending on the distance can be made into a multilayer film structure adapted thereto, and a suitable crystal can be obtained.

In the second embodiment, the buffer region 9 periodically includes the first layer 12 and the second layer 13 having different nitride semiconductor compositions, and has a length of one cycle in the film thickness direction. Although the (one cycle length) is shorter on the nitride semiconductor layer 8 side than the Si substrate 1 side, the present invention has a cycle in a desired length (at least two cycles or more) in the film thickness direction. When the number of the nitride semiconductor layer 8 is larger than that of the Si substrate 1, or the difference in film thickness between the first layer 12 and the second layer 13 ([first layer 12]-[second layer 13]) is smaller on the nitride semiconductor layer 8 side than on the Si substrate 1, or the film thickness ratio between the first layer 12 and the second layer 13 ([first layer 12] / [second layer] 13]) is included when the nitride semiconductor layer 8 side is smaller than the Si substrate 1 side.
In the semiconductor element according to the second embodiment, if the thickness of the second layer 13 is substantially the same, it is easy to design the periodicity of the multilayer film and the change in the film thickness ratio.
Further, if the second layer 13 is a nitride semiconductor containing Al and the first layer 12 is a nitride semiconductor containing Ga, the characteristics of the nitride semiconductor further containing Al and the nitride semiconductor containing Ga Thus, the buffer region 9 can be effectively used.
In addition, in a multilayer film, unless the difference in composition ratio between the two types of layers constituting it is taken large, the difference in crystal properties and mechanical properties peculiar to each composition is reduced, and the properties of both compositions are extracted. It is difficult to achieve the purpose of crystal growth. Therefore, when the Al mixed crystal ratio of the first layer 12 is smaller than that of the second layer 13, the properties of both the first layer 12 and the second layer 13 can be extracted to achieve crystal growth. it can.
Further, when the second layer 13 contains Ga and has a Ga mixed crystal ratio smaller than that of the first layer 12, a layer having a different lattice constant is provided with the Ga mixed crystal ratio and contains Ga. The buffer region 9 that effectively utilizes the properties of the nitride semiconductor can be obtained.
In addition, in a multilayer film, unless the difference in composition ratio between the two types of layers constituting it is taken large, the difference in crystal properties and mechanical properties peculiar to each composition is reduced, and the properties of both compositions are extracted. If the first layer 12 is AlGaN (0 ≦ x <0.5) and the second layer 13 is AlGaN (0.5 <y ≦ 1), the purpose of achieving crystal growth is difficult to achieve. The crystal growth can be achieved by extracting the properties of both the first layer 12 and the second layer 13. Furthermore, if (y−x)> 0.5, the difference in composition ratio between the two layers can be increased, and the function can be sufficiently exerted as a layer for suppressing cracks.
Further, when the first layer 12 contains an n-type impurity of a nitride semiconductor, the buffer region 9 becomes a suitable charge transfer layer. Band discontinuity due to the difference in band structure occurs at the interface between the Si substrate 1 and the multilayer film, so that a potential barrier is formed at the interface. However, a nitride semiconductor is formed in the first layer 12 of the buffer region 9. By including the n-type impurity, the thickness of the potential barrier is reduced, and V _f can be reduced. In particular, since the first layer 12 contains an n-type impurity, it is effective to reduce V _f .
Further, Vf is reduced when the first layer 12 of the buffer region 9 contains n-type impurities, but this effect is due to a potential barrier generated at the interface between the Si substrate 1 and the multilayer film. The layer containing n-type impurities is preferably the first layer 12 on the Si substrate 1 side, and conversely, a remarkable effect is hardly obtained on the nitride semiconductor layer 8 side opposite to the Si substrate 1 side. From the viewpoint of crystallinity, the inclusion of n-type impurities reduces the crystallinity of the nitride semiconductor layer 8 on the buffer region 9. Therefore, by reducing the n-type impurities on the nitride semiconductor layer 8 side with respect to the Si substrate 1 side, the nitride semiconductor layer 8 with good crystallinity can be obtained in addition to the reduction of Vf. Furthermore, the first layer 12 closest to the Si substrate 1 side contains a larger amount of n-type impurities than the other first layers 12, so that the potential barrier between the Si substrate 1 and the buffer region 9 is increased. By reducing the thickness of the substrate and suppressing the decrease in crystallinity, a suitable charge transfer layer can be obtained.
Further, if the buffer region 9 is a first conductivity type layer, and an active layer and a second conductivity type layer having a conductivity type opposite to the buffer region 9 are provided on the buffer region 9, After the crystallinity of the nitride semiconductor layer 8 is improved by the buffer region 9, the active layer and the second conductivity type layer are formed. Therefore, the functions of these layers can be suitably exhibited. In this way, since the buffer region 9 is accommodated in one conductivity type region, it becomes possible to avoid synergistic problem deterioration due to the change in crystallinity and the change in conductivity.
In the second embodiment, the buffer region 9 includes the first layer 12 and the second layer 13, but the buffer region 9 is other than the first layer 12 and the second layer 13. You may have a layer of.
Moreover, the preferable film thickness of the 1st layer and 2nd layer which implement | achieve these 2nd Embodiment is as follows. The first layer is 5 nm to 100 nm, more preferably 10 nm to 40 nm, and the second layer is thinner than the first layer and is 1 nm to 10 nm, more preferably 1 nm to 5 nm.

  In the present invention, the conductivity type of the Si substrate 1 is not particularly limited, and can be either n-type or p-type. However, if the conductivity type of at least the surface of the Si substrate 1 is p-type, carriers can be injected more favorably between the Si substrate 1 and the first multilayer structure 2 or the buffer region 9, and n This is preferable because carriers are injected into the first multilayer structure 2 or the buffer region 9 more efficiently than the Si substrate 1 of the type. The reason for this is not clear, but the following is a hypothesis. If the conductivity type of the active region in the Si substrate 1 is p-type, the Fermi level in the active region of the Si substrate 1 approaches the valence band, and further, due to high-concentration doping, all or part of it degenerates and Fermi The level exists in the valence band. Further, when many electrons are present in the active region of the first multilayer structure 2 or the buffer region 9, the Fermi level in the active region of the first multilayer structure 2 or the buffer region 9 approaches the conduction band, and further increases. By concentration doping, degeneration occurs and Fermi levels exist in the conduction band. In such a state, when a forward voltage (Vf) is applied to the semiconductor element, a reverse bias is applied to the bonding surface between the Si substrate 1 and the first multilayer film structure 2 or the buffer region 9. The valence band in the active region becomes higher than the conduction band in the active region of the first multilayer film structure 2 or the buffer region 9, and the depletion layer formed at the junction becomes clogged. Thereby, it is considered that many electrons in the valence band of the Si substrate 1 are injected into the conduction band of the first multilayer structure 2 or the buffer region 9 through the narrow depletion layer. Therefore, it is considered that carriers are injected into the first multilayer film structure 2 or the buffer region 9 more efficiently than the n-type Si substrate 1. When Si is used for the substrate, an n electrode can be provided on the back surface of the Si substrate 1 so that the p electrode and the n electrode can be opposed to each other, and the semiconductor element can be miniaturized. Here, the active region is a region that determines the basic structure of the semiconductor element, and refers to a region through which a current passes when a voltage is applied between the positive electrode and the negative electrode in the element.

FIG. 3 is a diagram illustrating a semiconductor device according to an embodiment of the present invention.
Hereinafter, semiconductor devices according to examples of the present invention will be described.
[Si substrate 1]
The substrate 1 is Si. Since the present invention does not limit the conductivity type of the substrate 1, the substrate 1 can be either n-type or p-type.
[Buffer layer 14]
The buffer layer 14 has the first multilayer structure 2 and the second multilayer structure 3 described in the first embodiment, or the buffer region 9 described in the second embodiment. Yes.
[Nitride semiconductor layer 8]
The nitride semiconductor layer 8 includes an n-type nitride semiconductor layer 15, an active layer 16, and a p-type nitride semiconductor layer 17.
(N-type nitride semiconductor layer 15)
The n-type nitride semiconductor layer 15 can be made of, for example, a material represented by the general formula In _e Al _f Ga _1-ef N (0 ≦ e, 0 ≦ f, e + f ≦ 1). In order to obtain a small number of nitride semiconductor layers, GaN or Al _f Ga _1-f N having an f value of 0.2 or less is preferable. The thickness of the n-type nitride semiconductor layer 15 is preferably 0.1 to 5 μm in order to reduce the resistance value and the forward voltage (Vf) of the semiconductor element while preventing the occurrence of cracks. More preferably, it is 0.3-2 μm.
(Active layer 16)
The active layer 16 can use a single quantum well structure or a multiple quantum well structure, and is a nitride semiconductor containing In and Ga, preferably In _a Ga _1-a N (0 ≦ a <1). It is formed. When the multiple quantum well structure is used, the active layer 16 has a barrier layer and a well layer. The barrier layer is, for example, undoped GaN, and the well layer is, for example, undoped In _0.35 Ga _0.65 N. be able to. The thickness of the well layer is adjusted to 100 angstroms or less, preferably 70 angstroms or less, more preferably 50 angstroms or less. The lower limit of the thickness of the well layer is not particularly limited, but it is 1 atomic layer or more, preferably 10 Å or more. If the well layer is thicker than 100 angstroms, the output tends to be difficult to improve. In order to lower the forward voltage (Vf), a part of the active layer 5 may be doped with Si. The thickness of the barrier layer is adjusted to 2000 angstroms or less, preferably 500 angstroms or less, more preferably 200 angstroms or less. The lower limit of the thickness of the barrier layer is not particularly limited, but it is 1 atomic layer or more, preferably 10 Å or more. When the thickness of the barrier layer is within the above range, the output can be improved. The total thickness of the active layer 16 is not particularly limited, and the total thickness of the active layer 16 is set by adjusting the number and order of the barrier layers and well layers in consideration of the emission wavelength and the like. can do.
(P-type nitride semiconductor layer 17)
The p-type nitride semiconductor layer 17 has a p-type cladding layer (not shown) and a p-type contact layer (not shown) in order from the Si substrate 1 side.
The p-type cladding layer has a multilayer film structure (superlattice structure) or a single film structure. When the p-type cladding layer has a superlattice structure, the crystallinity can be improved and the resistivity can be lowered, so that the forward voltage (Vf) can be lowered. As the p-type impurity doped in the p-type cladding layer, elements of Group IIA and IIB of the periodic table such as Mg, Zn, Ca and Be are selected, and Mg, Ca and the like are preferably used as p-type impurities. In addition, when the p-type cladding layer doped with p-type impurities is composed of a single layer made of Al _t Ga _1-t N (0 ≦ t ≦ 1) containing p-type impurities, the light emission output is slightly reduced, but static The withstand voltage can be as good as that of the superlattice.
The p-type contact layer may be formed using a nitride semiconductor represented by the general formula In _r Al _s Ga _1-rs N (0 ≦ r <1, 0 ≦ s <1, r + s <1). However, in order to form a layer with good crystallinity, it is preferably a ternary mixed crystal nitride semiconductor, more preferably a nitride semiconductor composed of binary mixed crystal GaN containing no In or Al. Furthermore, when the p-type contact layer is a binary mixed crystal containing no In or Al, ohmic contact with the positive electrode can be made better, and luminous efficiency can be improved. As the p-type impurity of the p-type contact layer, various p-type impurities similar to the p-type cladding layer can be used, but Mg is preferable. When the p-type impurity doped in the p-type contact layer is Mg, p-type characteristics can be easily obtained, and ohmic contact can be easily formed.
In the present invention, the method for measuring the impurity concentration is not limited, but the impurity concentration can be measured by, for example, secondary ion mass spectrometry (SIMS).
The nitride semiconductor device obtained in this example was excellent in the crystallinity and conductivity of the nitride semiconductor layer on the Si substrate, and a semiconductor device having a low Vf could be obtained.
Further, as a comparative example of Example 1, a multilayer film structure in which the first layer and the second layer have the same film thickness was formed, and the others were obtained in the same manner as in Example 1 to obtain a semiconductor element. Vf was higher than Example 1. In particular, when the thickness of the first layer is approximately the same as that of the second layer, Vf is higher than that of Example 1 by about 1 V, and it is considered that carriers are not sufficiently supplied to the nitride semiconductor layer. . When the thickness of the second layer was set to the same level as that of the first layer, Vf was 10 V or more, which was not measurable and hardly conducted electricity.
As yet another comparative example, when the multilayer structure of the first layer and the second layer is formed on the Si substrate, the film thickness of the first layer is the same until the n-type nitride semiconductor layer is formed. When the semiconductor element was obtained in the same manner as in Example 1 except that the first layer was relatively thick, cracks occurred in the multilayer film structure. When only a partial light emitting region was obtained and the first layer was relatively thin, the device was hardly conducting electricity.

The semiconductor element according to Example 1 can be manufactured, for example, as follows.
First, the Si substrate 1 is set in a reaction vessel, the temperature of the Si substrate 1 is raised while flowing hydrogen, and the Si substrate 1 is cleaned.
Next, the buffer layer 14 according to the first embodiment or the buffer layer 14 according to the second embodiment is grown on the Si substrate 1.
Next, the n-type nitride semiconductor layer 15 is grown at a predetermined temperature.
Next, five barrier layers and four well layers are alternately stacked in the order of barrier + well + barrier + well... + Barrier to grow an active layer 16 having a multiple quantum well structure.
Next, a p-type multilayer clad layer made of a multilayer film having a superlattice structure is grown.
Next, a p-type contact layer is grown.
Next, the Si substrate 1 is annealed in a reaction vessel in a nitrogen atmosphere, and the resistance of the p-type nitride semiconductor layer 17 is further reduced.
Here, when the positive electrode 18 and the negative electrode 19 are provided on the same surface side, the Si substrate 1 is taken out of the reaction container, and a predetermined shape is formed at the position where the positive electrode 18 is formed in the uppermost p-type contact layer. An SiO ₂ mask is formed with a thickness of 1 μm, and etching is performed from the p-type contact layer side with an RIE (reactive ion etching) apparatus. Then, a resist film is formed on the formed SiO ₂ mask while leaving a part, and a part of the surface of the Si substrate 11 or the n-type nitride semiconductor layer 15 is exposed by RIE.
Next, a translucent positive electrode 18 containing Ni and Au with a film thickness of 200 angstroms is formed on almost the entire surface of the p-type contact layer as the uppermost layer, and a pad electrode made of Au for bonding on the positive electrode 18 ( (Not shown) with a film thickness of 0.5 μm. On the other hand, a negative electrode 19 containing W and Al is formed on the anti-nitride semiconductor layer side of the Si substrate 1 (or the surface of the Si substrate 1 or the n-type nitride semiconductor layer 15 exposed by etching).
If the Si substrate 1 formed as described above is made into a chip, the semiconductor element according to Example 1 can be obtained.
The semiconductor element thus obtained is mounted on a lead frame (not shown) or the like and bonded, and then sealed with a sealing member (not shown). Here, as the sealing member, a translucent resin that transmits light having a desired wavelength is used. For example, epoxy resin, Si resin, acrylic resin, or the like is suitable. Note that the sealing member may be mixed with a light diffusing material that diffuses light, a fluorescent material that is excited by light from a semiconductor element and can emit light having a wavelength longer than that wavelength. The shape of the sealing member can be arbitrarily designed, and can be, for example, a semi-cylindrical shape or a linear shape.

  The present invention can be applied to all semiconductor elements, but is particularly suitable for nitride-based semiconductor elements.

It is a figure which shows a part of semiconductor element based on the 1st Embodiment of this invention. It is a figure which shows a part of semiconductor element based on the 2nd Embodiment of this invention. It is a figure which shows the semiconductor element which concerns on the Example of this invention.

Explanation of symbols

1 Si substrate,
2 first multilayer structure,
3 Second multilayer structure,
4 First layer,
5 Second layer,
6 Third layer,
7 Fourth layer,
8 Nitride semiconductor layer,
9 Buffer area,
10 first region,
11 second region,
12 first layer,
13 Second layer 14 Buffer layer,
15 n-type nitride semiconductor layer,
16 active layer,
17 p-type nitride semiconductor layer,
18 positive electrode,
19 Negative electrode.

Claims (23)

A semiconductor device comprising a nitride semiconductor layer on a Si substrate,
The nitride semiconductor layer is
A first multilayer structure in which at least a first layer and a second layer are alternately stacked on the Si substrate side;
A second multilayer structure in which at least a third layer and a fourth layer are alternately stacked on the first multilayer structure;
Have
The first layer and the third layer are nitride semiconductors having a composition having a smaller lattice constant difference from the Si substrate than any of the second layer and the fourth layer, and The film thickness is larger than any of the second layer and the fourth layer,
The first layer is thicker than the third layer.
The semiconductor element characterized by the above-mentioned.   The semiconductor device according to claim 2, wherein a total film thickness of the first multilayer film structure is smaller than a total film thickness of the second multilayer film structure.   The semiconductor element according to claim 1, wherein the second layer and the fourth layer have substantially the same film thickness.   4. The method according to claim 1, wherein the second layer and the fourth layer contain Al, and the first layer and the third layer contain Ga. 5. The semiconductor element as described.   The said 1st layer and the said 3rd layer contain Al, and Al mixed crystal ratio is smaller than the said 2nd layer and the said 4th layer, Any one of Claims 1-4 characterized by the above-mentioned. 2. The semiconductor element according to item 1.   The said 2nd layer and the said 4th layer contain Ga, Ga mixed crystal ratio is smaller than the said 1st layer and the said 3rd layer, Any one of Claims 1-5 2. The semiconductor element according to item 1. The first layer and the third layer are Al _x Ga _1-x N (0 ≦ x ≦ 0.5),
The second layer and the fourth layer are Al _y Ga _1-y N (0.5 <y ≦ 1).
The semiconductor element according to claim 1, wherein: The first layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5),
The second layer is Al _y Ga _1-y N (0.5 <y ≦ 1),
(Y−x)> 0.5,
The semiconductor element according to claim 1, wherein the semiconductor element is a semiconductor element.   9. The semiconductor device according to claim 1, wherein the first layer and the third layer include an n-type impurity of a nitride semiconductor.   10. The semiconductor device according to claim 1, wherein the first layer includes a larger amount of an n-type impurity of a nitride semiconductor than the third layer. The first multilayer structure and the second multilayer structure are of a first conductivity type;
The nitride semiconductor layer includes at least an active layer and a second conductivity type layer in order from the substrate side.
The semiconductor element according to claim 1, wherein the semiconductor element is a semiconductor element. A semiconductor device comprising a nitride semiconductor layer on a Si substrate, and comprising a buffer region between the Si substrate and the nitride semiconductor layer,
The buffer region has a first region on the substrate side and a second region farther from the Si substrate than the first region,
The first region and the second region are formed of a first layer made of a nitride semiconductor and a nitride semiconductor having a film thickness smaller than that of the first layer and having a composition different from that of the first layer. Each has a multilayer structure in which the second layers are alternately laminated,
The film thickness of the first layer in the first region is larger than the film thickness of the first layer in the second region.
The semiconductor element characterized by the above-mentioned. A semiconductor device comprising a nitride semiconductor layer on a Si substrate, and comprising a buffer region between the Si substrate and the nitride semiconductor layer,
The buffer region periodically includes a first layer and a second layer having different nitride semiconductor compositions,
The length of one cycle in the film thickness direction (one cycle length) is shorter on the nitride semiconductor layer side than the Si substrate side, or at a desired length in the film thickness direction (at least two cycles or more) The number of periods becomes larger on the nitride semiconductor layer side than the Si substrate,
The semiconductor element characterized by the above-mentioned. A semiconductor device comprising a nitride semiconductor layer on a Si substrate, and comprising a buffer region between the Si substrate and the nitride semiconductor layer,
The buffer region includes at least a nitride semiconductor having a composition in which the difference in lattice constant between the first layer made of a nitride semiconductor and the Si substrate is smaller than the first layer and having a smaller film thickness than the first layer. A multilayer film structure in which second layers made of
The film thickness difference between the first layer and the second layer ([first layer]-[second layer]) is smaller on the nitride semiconductor layer side than on the Si substrate side, or The thickness ratio of the first layer to the second layer ([first layer] / [second layer]) is smaller on the nitride semiconductor layer side than on the Si substrate side,
The semiconductor element characterized by the above-mentioned.   The semiconductor element according to claim 12, wherein the second layer in the buffer region has substantially the same film thickness.   The semiconductor element according to claim 12, wherein the second layer includes Al, and the first layer includes Ga.   17. The semiconductor device according to claim 12, wherein the first layer contains Al and has an Al mixed crystal ratio smaller than that of the second layer.   The semiconductor element according to claim 12, wherein the second layer contains Ga and has a Ga mixed crystal ratio smaller than that of the first layer. The first layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5),
The second layer is Al _y Ga _1-y N (0.5 <y ≦ 1).
The semiconductor device according to claim 12, wherein the semiconductor device is a semiconductor device. The first layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5),
The second layer is Al _y Ga _1-y N (0.5 <y ≦ 1),
(Y−x)> 0.5,
The semiconductor device according to claim 12, wherein the semiconductor device is a semiconductor device.   21. The semiconductor device according to claim 12, wherein the first layer includes an n-type impurity of a nitride semiconductor.   The semiconductor element according to any one of claims 12 to 21, wherein the buffer region contains more n-type impurities of a nitride semiconductor on the Si substrate side than on the nitride semiconductor layer side. The semiconductor device according to any one of claims 12 to 22,
The buffer region is a first conductivity type layer;
An active layer and a second conductivity type layer having a conductivity type opposite to that of the buffer region are provided on the buffer region.
The semiconductor element characterized by the above-mentioned.