JP3574093B2 - Semiconductor element and method of forming semiconductor layer - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor element and a method for forming a semiconductor layer, and more particularly, to a semiconductor element and a method for forming a semiconductor layer in which a semiconductor layer is formed on a base.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there has been known a technique of hetero-growing a nitride-based semiconductor made of a material different from that of a base on the base. For example, in the crystal growth of GaN, which is one of the nitride-based semiconductors, hetero-growth is performed on a heterogeneous substrate such as a sapphire substrate because there are few lattice-matched substrates. In this case, in order to grow GaN having few crystal defects and good crystallinity, a technique of inserting a buffer layer by low-temperature growth between a substrate and a GaN layer is conventionally known.
[0003]
However, even when a low-temperature buffer layer as described above is used, the density of defects that can be reduced is limited, and it is difficult to further reduce dislocations. Therefore, conventionally, a technique has been proposed in which, when GaN is grown, a base layer in which dislocations are reduced by an Epitaxial Lateral Overgrowth (ELOG) method is used. This selective lateral growth is disclosed in, for example, pages 53 to 58 and pages 210 to 215 of the Journal of Applied Electronic Properties, Vol. 4, (1998).
[0004]
34 to 37 are cross-sectional views illustrating an example of a conventional method for forming a nitride-based semiconductor layer using selective lateral growth. Next, an example of a conventional method of forming a nitride-based semiconductor layer using selective lateral growth will be described with reference to FIGS.
[0005]
First, as shown in FIG. 34, after forming a low-temperature buffer layer 202 on a sapphire substrate 201, a GaN layer 203 serving as a base is grown on the low-temperature buffer layer 202.
[0006]
Next, as shown in FIG. 35, the SiO 2₂A striped (elongated) mask layer 204 made of, for example, is formed. When regrowth is performed using the mask layer 204 as a selective growth mask and the GaN layer 203 as a base layer, a GaN layer 205 having a facet structure with a triangular cross section is first formed on an exposed portion of the GaN layer 203.
[0007]
Further, as the growth proceeds, the GaN layer 205 having the facet structure is bonded as shown in FIG. 36, and the lateral growth becomes dominant. For this reason, the dislocations extending in the c-axis direction (vertical direction) are bent at the facet joints and do not reach the upper part. However, dislocations remain on the facet joint.
[0008]
Further, as the growth proceeds, as shown in FIG. 37, the GaN layers 205 having the facet structure are united to form a continuous film. Thus, a GaN layer 205 having a flat upper surface is formed. The number of dislocations reaching the surface of the flattened GaN layer 205 is significantly reduced as compared with the underlayer.
[0009]
[Problems to be solved by the invention]
According to the conventional method for forming a nitride-based semiconductor layer shown in FIGS. 34 to 37, when the GaN layer 205 is formed by selective lateral growth, dislocations remain concentrated on the mask layer 204 to which facets are coupled. Therefore, in order to reduce dislocations, the width of the mask layer 204 is preferably small. However, when the width of the mask layer 204 is reduced to reduce dislocations, the width of the exposed portion of the underlying GaN layer 203 is increased, so that the GaN facet formed on the exposed portion of the GaN layer 203 is also large. (High). Therefore, in order to combine and flatten the large facet, it was necessary to form the GaN layer 205 thick. As described above, conventionally, it has been difficult to obtain the GaN layer 205 having a small thickness and few dislocations.
[0010]
Conventionally, there has also been proposed a method of forming a mask layer directly on a substrate and growing a GaN layer using selective lateral growth. FIG. 38 is a cross-sectional view for explaining the conventional method of forming a nitride-based semiconductor layer. Referring to FIG. 38, in this conventional proposed method, SiO 2 is directly formed on sapphire substrate 211.₂After forming a mask layer 212 made of GaN, a low-temperature buffer layer 213 made of GaN and a high-temperature grown GaN layer 214 are formed thereon, thereby forming a GaN layer 214 in which dislocations are reduced by one growth. In this conventional proposed method, since the mask layer 212 is formed directly on the sapphire substrate 211, the total film thickness is reduced because there is no underlying layer.
[0011]
However, the conventional proposed method shown in FIG. 38 has the same problem as the conventional example shown in FIGS. That is, even when the mask layer 212 is formed directly on the sapphire substrate 211 and the selective lateral growth is performed, it is necessary to reduce the width of the mask layer 212 in order to reduce dislocations. However, when the width of the mask layer 212 is reduced, the exposed area of the sapphire substrate 211 is increased, and the facet made of GaN formed on the low-temperature buffer layer 213 in the exposed portion is increased (increased). Therefore, in order to flatten the GaN layer 214 by combining the large facets, it is necessary to form the GaN layer 214 with a large thickness of about 5 μm or more. As a result, it was difficult to obtain a GaN layer 214 having a small thickness and few dislocations even in the conventional proposed method shown in FIG.
[0012]
Conventionally, when growing a mixed crystal of AlGaN, InN, InGaN, BGaN, BAlGaN, BInGaN, AlGaInN or the like thickly, it is more difficult to find a substrate that is lattice-matched. For example, when InGaN is directly grown on a sapphire substrate, it is difficult to grow the InGaN layer thickly because of a large difference in lattice constant. Therefore, conventionally, as shown in FIG. 39, first, a GaN layer 223 is grown on a sapphire substrate 221 via a buffer layer 222. Then, after forming a mask layer 224 on the GaN layer 223, a low dislocation GaN layer 225 is formed by performing selective lateral growth using the mask layer 224 as a growth mask. Then, an InGaN layer 226 was grown on the low dislocation GaN layer 225. As described above, by growing the InGaN layer 226 on the low dislocation GaN layer 225 formed by using the selective lateral growth, the low dislocation InGaN layer 226 can be grown to a certain thickness.
[0013]
In the conventional method for forming a nitride-based semiconductor layer made of a mixed crystal shown in FIG. 39, as described above, in order to obtain an InGaN layer 226 with a small number of dislocations, a low lateral dislocation is formed using selective lateral growth as an underlayer. The GaN layer 225 needs to be formed. For this reason, in the conventional example shown in FIG. 39, the entire thickness becomes large, and as a result, it is difficult to obtain the InGaN layer 226 having a small thickness and few dislocations as a whole. In the conventional method for forming a nitride-based semiconductor layer made of a mixed crystal shown in FIG. 39, the GaN layer 225 formed using selective lateral growth is used as an underlayer, and the InGaN layer 226 is further grown. There was also a problem that it became complicated.
[0014]
The present invention has been made to solve the above problems,
An object of the present invention is to provide a method for forming a semiconductor layer capable of easily growing a semiconductor layer having a small thickness and a low dislocation.
[0015]
Another object of the present invention is to provide a semiconductor element having a structure capable of forming a semiconductor layer having a small thickness and few dislocations.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, a method of forming a semiconductor layer according to a first aspect of the present invention includes a method of forming a plurality of masks at predetermined intervals so as to contact an upper surface of a base and expose a part of the base. Forming a layer, and forming a trapezoidal first semiconductor layer having a width on the upper surface smaller than the lower surface at a position lower than the upper surface of the mask layer on the upper surface of the base exposed between the mask layers; Growing a second semiconductor layer on the first semiconductor layer and the mask layer.
[0017]
In the method of forming a semiconductor layer according to the first aspect, as described above, the trapezoidal shape having the width of the upper surface smaller than the lower surface is formed on the upper surface of the base exposed between the mask layers at a position lower than the upper surface of the mask layer. By forming the first semiconductor layer, when the second semiconductor layer is grown on the first semiconductor layer, the side surfaces of the trapezoidal first semiconductor layer gradually grow in the lateral direction. Thereby, lateral growth is promoted from the initial growth stage of the semiconductor layer including the first semiconductor layer and the second semiconductor layer, so that dislocations are generated in the horizontal direction from the initial growth stage of the semiconductor layer including the first and second semiconductor layers. Can be bent. As a result, dislocations that propagate in the vertical direction from the initial growth stage of the semiconductor layer including the first and second semiconductor layers can be reduced, so that a low-dislocation semiconductor layer can be grown with a small thickness on the base. it can.
[0018]
In the method of forming a semiconductor layer according to the first aspect, preferably, the trapezoidal first semiconductor layer whose upper surface is smaller in width than the lower surface is formed with a thickness smaller than the thickness of the mask layer. According to this structure, the side surfaces of the trapezoidal first semiconductor layer can be easily laterally grown from the initial growth stage of the semiconductor layer including the first and second semiconductor layers. Dislocations can be easily bent laterally from the initial growth stage of a semiconductor layer including two semiconductor layers.
[0019]
In the above-described method for forming a semiconductor layer, preferably, the step of growing the second semiconductor layer includes substantially growing the trapezoidal first semiconductor layer, thereby substantially forming the trapezoidal first semiconductor layer and the mask layer. Forming a second semiconductor layer having a flat upper surface. According to this structure, a low-dislocation second semiconductor layer having a substantially flat upper surface over the base can be formed with a small thickness.
[0020]
In the above-described method for forming a semiconductor layer, preferably, the third semiconductor layer including at least one layer having a different composition from the first semiconductor layer is formed on the first semiconductor layer prior to the step of growing the second semiconductor layer. The method further comprises the step of forming With this configuration, distortion can be generated between the third semiconductor layer and the first semiconductor layer. The dislocation reduced by the first semiconductor layer can be further reduced by the interface stress due to the distortion. In this case, prior to the step of growing the second semiconductor layer, a step of forming, as the third semiconductor layer, a superlattice layer having a periodic structure in which layers having different lattice constants are alternately stacked on the first semiconductor layer. It is preferable to further include According to this structure, since a larger strain is generated due to lattice mismatch of the superlattice layer having the periodic structure, the dislocation bent in the lateral direction by the trapezoidal first semiconductor layer due to a large interfacial stress due to the strain. Are more easily bent in a direction parallel to the direction in which the superlattice layer extends. Accordingly, dislocations that are bent in a direction parallel to the direction in which the superlattice layer extends may collide with each other due to collision with each other, so that lateral dislocations can be further reduced. As a result, dislocations can be more easily reduced from the initial stage of the growth of the semiconductor layer including the first and second semiconductor layers.
[0021]
In the above-described method for forming a semiconductor layer, preferably, the dislocation density of the first semiconductor layer near the upper surface of the mask layer is lower than the dislocation density of the first semiconductor layer near the upper surface of the base. According to this structure, since the dislocation density is already low near the upper surface of the mask layer, dislocations can be easily reduced from the initial growth stage of the semiconductor layer including the first and second semiconductor layers. In this case, the dislocation density of the first semiconductor layer in the vicinity of the upper surface of the mask layer is preferably not more than 以下 of the dislocation density of the first semiconductor layer in the vicinity of the upper surface of the base.
[0022]
In the above-described method for forming a semiconductor layer, the first semiconductor layer and the second semiconductor layer may include a nitride-based semiconductor layer. With such a configuration, lateral growth is promoted from the initial growth stage of the nitride-based semiconductor layer, so that the nitride-based semiconductor layer with low dislocation can be grown with a small thickness on the base.
[0023]
Preferably, the method for forming a semiconductor layer further includes, prior to the step of forming the first semiconductor layer, a step of forming a buffer layer on an upper surface of a base exposed between the mask layers. The thickness of the buffer layer located near the mask layer on the upper surface of the underlayer is smaller than the thickness of the buffer layer located at the central portion on the exposed upper surface of the underlayer. According to this structure, the growth of the first semiconductor layer becomes faster in the central portion where the thickness of the buffer layer is large, and the growth of the first semiconductor layer becomes slow in the vicinity of the mask layer where the thickness of the buffer layer is small. In addition, the first semiconductor layer is more likely to grow into a trapezoidal shape from the initial growth stage. As a result, the lateral growth is further promoted from the initial growth stage of the first semiconductor layer, so that the semiconductor layer with low dislocation can be grown with a smaller thickness on the base.
[0024]
Preferably, the method for forming a semiconductor layer further includes, before the step of forming the first semiconductor layer, a step of forming a buffer layer on the upper surface of the base exposed between the mask layers. Are formed at substantially the same thickness in the central portion on the upper surface of the base exposed between the mask layers, and are not formed near the mask layer on the upper surface of the exposed base. With this configuration, the growth of the first semiconductor layer is accelerated in the central portion where the thickness of the buffer layer is large, and the growth of the first semiconductor layer is slow in the vicinity of the mask layer without the buffer layer. One semiconductor layer is more likely to grow into a trapezoidal shape from the initial growth stage. As a result, the lateral growth is further promoted from the initial growth stage of the first semiconductor layer, so that the semiconductor layer with low dislocation can be grown with a smaller thickness on the base.
[0025]
In the above-described method for forming a semiconductor layer, preferably, the shortest distance between the adjacent mask layers is smaller than the width of the exposed portion of the base located between the adjacent mask layers. According to this structure, when the first semiconductor layer is formed on the base using the mask layer as a mask, the material does not easily reach a portion of the exposed portion of the base where the mask layer is formed above, The first semiconductor layer easily grows in a trapezoidal shape. This makes it possible to easily form the trapezoidal first semiconductor layer. In this case, preferably, the mask layer has an overhang portion projecting above the exposed portion of the base. According to this structure, the material of the first semiconductor layer hardly reaches the upper surface of the base located below the overhang portion, so that the first semiconductor layer is less likely to be formed on the upper surface of the base located below the overhang portion. This makes it possible to easily form the trapezoidal first semiconductor layer in which the thickness of the portion formed on the upper surface of the base located below the overhang portion is smaller than that of the other portions.
[0026]
In the configuration having the overhang portion, the thickness of the buffer layer located below the overhang portion of the mask layer may be smaller than the thickness of the buffer layer located below the shortest distance portion between adjacent mask layers. Further, in this case, preferably, the thickness of the buffer layer located below the overhang portion of the mask layer decreases at substantially the same rate as the distance from the shortest distance portion between adjacent mask layers increases.
[0027]
In the configuration having the overhang portion, the buffer layer is formed with substantially the same thickness on the central portion of the upper surface of the base exposed between the mask layers, and is located below the overhang portion of the mask layer. It may not be formed on the upper surface of the base.
[0028]
In the configuration having the overhang portion, at least a part of the mask layer preferably has an inverted trapezoidal shape.
[0029]
In the above method for forming a semiconductor layer, preferably, the base includes the substrate, and the mask layer is formed to be in contact with the upper surface of the substrate. According to this structure, a semiconductor layer having a small thickness and a low dislocation can be directly grown on the base. In this case, the substrate preferably includes one substrate selected from the group consisting of a Group 3-5 semiconductor substrate, a Group 4 semiconductor substrate, a sapphire substrate, a spinel substrate, a SiC substrate, and a quartz substrate. With such a substrate, a semiconductor layer can be easily grown directly on the substrate.
[0030]
The above-described method for forming a semiconductor layer preferably further includes a step of growing a semiconductor element layer having an element region on the second semiconductor layer. According to this structure, a semiconductor element layer having an element region can be grown on a low-dislocation semiconductor layer formed with a small thickness on a base, so that a semiconductor element layer having good element characteristics can be formed. It can be easily formed. As a result, a semiconductor element having a small thickness and excellent element characteristics can be obtained.
[0031]
A semiconductor device according to a second aspect of the present invention includes a plurality of mask layers formed at a predetermined interval so as to contact an upper surface of a base and expose a part of the base, and is exposed between the mask layers. A dislocation density of the semiconductor layer near the upper surface of the mask layer is smaller than a dislocation density of the semiconductor layer near the upper surface of the base layer.
[0032]
In the semiconductor device according to the second aspect, the dislocation density of the semiconductor layer in the vicinity of the upper surface of the mask layer is configured to be smaller than the dislocation density of the semiconductor layer in the vicinity of the upper surface of the base, so that the dislocation density is near the upper surface of the mask layer In addition, since the dislocation density of the semiconductor layer is low, the dislocation of the semiconductor layer can be easily reduced from the initial growth stage. In this case, the dislocation density of the semiconductor layer near the upper surface of the mask layer is preferably equal to or less than １ ／ of the dislocation density of the semiconductor layer near the upper surface of the base.
[0033]
A semiconductor device according to a third aspect of the present invention includes a plurality of mask layers formed at predetermined intervals so as to be in contact with the upper surface of a base and to expose a part of the base, and exposed between the mask layers. A trapezoidal first semiconductor layer formed at a position lower than the upper surface of the mask layer and having a smaller upper surface width than the lower surface, on the upper surface of the base, and a first semiconductor layer formed on the surface of the first semiconductor layer. The layer includes a third semiconductor layer including at least one layer having a different composition, and a second semiconductor layer formed on the third semiconductor layer and the mask layer.
[0034]
In the semiconductor device according to the third aspect, a trapezoidal first semiconductor layer having a width of the upper surface smaller than the lower surface is provided at a position lower than the upper surface of the mask layer on the upper surface of the base exposed between the mask layers. Accordingly, when the second semiconductor layer is grown on the first semiconductor layer, the side surfaces of the trapezoidal first semiconductor layer gradually grow in the lateral direction. Thereby, lateral growth is promoted from the initial growth stage of the semiconductor layer including the first semiconductor layer and the second semiconductor layer, so that dislocations are generated in the horizontal direction from the initial growth stage of the semiconductor layer including the first and second semiconductor layers. Can be bent. As a result, dislocations that propagate in the vertical direction from the initial growth stage of the semiconductor layer including the first and second semiconductor layers can be reduced, so that a low-dislocation semiconductor layer can be grown with a small thickness on the base. it can.
[0035]
In the semiconductor device according to the third aspect, the third semiconductor layer including at least one layer having a composition different from that of the first semiconductor layer is provided on the trapezoidal first semiconductor layer. Distortion can be generated between the first semiconductor layer and the first semiconductor layer. The dislocation reduced by the first semiconductor layer can be further reduced by the interface stress due to the distortion. In this case, the third semiconductor layer preferably includes a superlattice layer having a periodic structure in which layers having different lattice constants are alternately stacked. According to this structure, since a larger strain is generated due to lattice mismatch of the superlattice layer having the periodic structure, the dislocation bent in the lateral direction by the trapezoidal first semiconductor layer due to a large interfacial stress due to the strain. Are more easily bent in a direction parallel to the direction in which the superlattice layer extends. Accordingly, dislocations that are bent in a direction parallel to the direction in which the superlattice layer extends may collide with each other due to collision with each other, so that lateral dislocations can be further reduced. As a result, dislocations can be more easily reduced from the initial stage of the growth of the semiconductor layer including the first and second semiconductor layers.
[0036]
BEST MODE FOR CARRYING OUT THE INVENTION
Before describing the embodiments of the present invention, the concept of the method for forming a semiconductor layer of the present invention will be described first. 1 to 5 are cross-sectional views for explaining the concept of the method for forming a semiconductor layer according to the present invention.
[0037]
First, in the present invention, as shown in FIG. 1, an inverted trapezoidal mask layer 2 having an overhang portion 2a is formed on an undersubstrate 1 composed of an undersubstrate or an underlayer formed on the substrate. In the mask layer 2, the shortest distance between the adjacent mask layers 2 is smaller than the width of the exposed portion of the base 1 located between the adjacent mask layers 2. Using such a mask layer 2 as a selective growth mask, the semiconductor layer 3a is selectively grown in the lateral direction on the base 1.
[0038]
In this case, of the exposed portion of the base 1, there is a difference in the raw material supply amount between a region located below the overhang portion 2a and a region not located below the overhang portion 2a. That is, at the center of the exposed portion of the base 1, which is not located below the overhang portion 2a, the thickness of the semiconductor layer 3a is formed to be substantially uniform due to the large amount of raw material supplied. On the other hand, since it is difficult for the raw material to reach under the overhang portion 2a, the thickness of the semiconductor layer 3a decreases as the distance from the central portion increases. Thus, a trapezoidal semiconductor layer 3a as shown in FIG. 2 is formed.
[0039]
When the semiconductor layer 3a is further grown from the state shown in FIG. 2, the side surface of the trapezoidal semiconductor layer 3a gradually grows in the lateral direction as shown in FIG. Promotes lateral growth. Thereby, the dislocation of the semiconductor layer 3a is bent in the lateral direction with the lateral growth. As a result, dislocations that propagate in the vertical direction from the initial growth stage of the semiconductor layer 3a can be reduced. In this case, the dislocation is reduced to １ ／ or less in the vicinity of the upper surface of the semiconductor layer 3a in the state of FIG. 3 as compared with the vicinity of the lower surface of the semiconductor layer 3a. The semiconductor layer 3a in the state shown in FIGS. 2 and 3 is an example of the “first semiconductor layer” of the present invention.
[0040]
When the semiconductor layer 3a is further grown from the state shown in FIG. 3, the trapezoidal semiconductor layer 3a is united into a continuous film through the state shown in FIG. 4, as shown in FIG. Thereby, the semiconductor layer 3 having a flat upper surface is formed. The semiconductor layer 3 in the state shown in FIG. 5 is an example of the “second semiconductor layer” of the present invention.
[0041]
As described above, in the present invention, the lateral growth becomes dominant in the early stage of the growth, so that the semiconductor layer 3 with low dislocation can be grown on the base 1 with a small thickness.
[0042]
Next, an embodiment embodying the above-described concept of the present invention will be described.
[0043]
(1st Embodiment)
FIG. 6 is a cross-sectional view illustrating the method for forming the nitride-based semiconductor layer according to the first embodiment of the present invention. FIG. 7 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a nitride-based semiconductor layer of the first embodiment shown in FIG.
[0044]
First, a method for forming a nitride-based semiconductor layer according to the first embodiment will be described with reference to FIG. In the first embodiment, first, a mask layer 12 made of SiN is formed directly on the upper surface of a sapphire substrate 11 as a base. This mask layer 12 is formed in an inverted mesa shape (an inverted trapezoidal shape) having an overhang portion 12a. In the mask layer 12, the shortest distance between the adjacent mask layers 12 is smaller than the width of the exposed portion of the sapphire substrate 11 located between the adjacent mask layers 12.
[0045]
As a method of forming such a mask layer 12, first, an SiN layer (not shown) is formed on the entire surface of the sapphire substrate 11, and then a resist (not shown) is formed on a predetermined region on the SiN layer. . Then, the SiN layer is wet-etched using the resist as a mask, so that the inverted trapezoidal mask layer 12 having the overhang portion 12a can be easily formed. The mask layer 12 has a stripe shape (elongated shape) having a period of about 7 μm and a thickness of about 10 nm to about 1000 nm. The opening of the mask layer 12 is preferably formed, for example, in the [11-20] direction of sapphire or in the [1-100] direction of sapphire.
[0046]
Thereafter, a low-temperature buffer layer 13 made of AlGaN or GaN having a thickness of about 10 nm to about 50 nm is grown on the sapphire substrate 11 at a temperature of about 500 ° C. to about 700 ° C. The low-temperature buffer layer 13 is an example of the “buffer layer” of the present invention. Then, an undoped GaN layer 14 is formed on the low-temperature buffer layer 13 by using the mask layer 12 as a selective growth mask by MOCVD or HVPE. This undoped GaN layer 14 is formed to have a thickness of about 2 μm under a temperature condition of about 950 ° C. to about 1200 ° C. The undoped GaN layer 14 is an example of the “nitride-based semiconductor layer” of the present invention.
[0047]
Here, when growing the low-temperature buffer layer 13, since the mask layer 12 has the overhang portion 12a, the material does not easily reach below the overhang portion 12a. Therefore, the thickness of the buffer layer 13 below the overhang portion 12a is reduced. This makes it difficult for the undoped GaN layer 14 to grow on the thin low-temperature buffer layer 13 below the overhang portion 12a, and also makes it difficult for the raw material of the undoped GaN layer 14 to reach below the overhang portion 12a. As in the conceptual diagram shown in FIG. 2, a trapezoidal undoped GaN layer 14 is easily formed from the initial stage of growth. Thereby, the lateral surface of the undoped GaN layer 14 having the trapezoidal shape gradually grows in the lateral direction, so that the lateral growth of the undoped GaN layer 14 is promoted from the initial growth stage. For this reason, the dislocations are bent in the horizontal direction from the initial growth stage of the undoped GaN layer 14, so that the dislocations that propagate in the vertical direction from the initial growth stage of the undoped GaN layer 14 can be reduced. As a result, a low dislocation undoped GaN layer 14 can be hetero-grown on the sapphire substrate 11 with a small thickness.
[0048]
Next, the structure of a semiconductor laser device manufactured by using the method for forming a nitride-based semiconductor layer of the first embodiment will be described with reference to FIG.
[0049]
In the semiconductor laser device of the first embodiment, as shown in FIG. 7, a first conductivity type contact layer 105 made of n-type GaN having a thickness of about 4 μm is formed on the undoped GaN layer 14 shown in FIG. ing. On the first conductivity type contact layer 105, a first conductivity type cladding layer 106 made of n-type AlGaN having a thickness of about 0.45 μm is formed. On the first conductivity type cladding layer 106, a multiple quantum well (MQW) light emitting layer 107 made of InGaN is formed. On the MQW light emitting layer 107, a second conductivity type cladding layer 108 of p-type AlGaN having a thickness of about 0.45 μm is formed. On the second conductivity type cladding layer 108, a second conductivity type contact layer 109 made of p-type GaN having a thickness of about 0.15 μm is formed. An n-type first conductivity type electrode 110 is formed on the exposed upper surface of the first conductivity type contact layer 105. On the upper surface of the second conductivity type contact layer 109, a p-type second conductivity type electrode 111 is formed.
[0050]
The first conductivity type contact layer 105, the first conductivity type clad layer 106, the MQW light emitting layer 107, the second conductivity type clad layer 108, and the second conductivity type contact layer 109 are examples of the “semiconductor element layer” of the present invention. It is.
[0051]
In the semiconductor laser device of the first embodiment described above, since the layers 105 to 109 are formed on the undoped GaN layer 14 having a reduced thickness and reduced dislocations formed by using the formation method shown in FIG. In 105 to 109, good crystallinity can be realized. Therefore, in the first embodiment, a semiconductor laser device having a small thickness and excellent device characteristics can be obtained.
[0052]
(2nd Embodiment)
FIG. 8 is a cross-sectional view for explaining a method for forming a nitride-based semiconductor layer according to the second embodiment of the present invention. FIG. 9 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a nitride-based semiconductor layer of the second embodiment shown in FIG.
[0053]
First, a method for forming the nitride-based semiconductor layer according to the second embodiment will be described with reference to FIG. In the second embodiment, a mask layer 22 is formed on the surface of an n-type SiC substrate 21 as a base. This mask layer 22 is composed of a SiN layer 22a,₂It has a three-layer structure including the layer 22b and the SiN layer 22c, and has a thickness of about 10 nm to about 1000 nm. Further, the mask layer 22 is made of an intermediate SiO 2 layer.₂The film 22b has a shape (overhang shape) projecting to both sides. In this mask layer 22, the adjacent mask layer 22 (SiO₂The shortest distance between the layers 22b) is smaller than the width of the exposed portion of the n-type SiC substrate 21 located between the adjacent mask layers 22.
[0054]
As a method of forming such a mask layer 22, a SiN layer 22a, an SiO₂After sequentially forming the layer 22b and the SiN layer 22c, a resist (not shown) is formed in a predetermined region on the SiN layer 22c. Then, using the resist as a mask, wet etching is performed using a hydrofluoric acid-based etchant to obtain SiO 2.₂The mask layer 22 having the overhang shape as shown in FIG. 8 is formed by utilizing the difference in the etching rate between the layer 22b and the SiN layers 22a and 22c.
[0055]
Thereafter, a low-temperature buffer layer 23 made of AlGaN or GaN having a thickness of about 10 nm to about 50 nm is formed on the n-type SiC substrate 21 at a temperature of about 500 ° C. to about 700 ° C. The low-temperature buffer layer 23 is an example of the “buffer layer” of the present invention. Then, the n-type GaN layer 24 is grown on the low-temperature buffer layer 23 by using the mask layer 22 as a selective growth mask by MOCVD or HVPE. This n-type GaN layer 24 is formed with a thickness of about 2 μm under a temperature condition of about 950 ° C. to about 1200 ° C. The n-type GaN layer 24 is an example of the “nitride-based semiconductor layer” of the present invention.
[0056]
When growing the low-temperature buffer layer 23, since the mask layer 22 has an overhang shape, the material does not easily reach under the overhang portion. For this reason, the thickness of the low-temperature buffer layer 23 below the overhang portion is reduced. This makes it difficult for the n-type GaN layer 24 to grow on the low-temperature buffer layer 23 having a small thickness below the overhang portion, and also makes it difficult for the raw material of the n-type GaN layer 24 to reach below the overhang portion 12a. Therefore, as shown in the conceptual diagram of FIG. 2, the n-type GaN layer 24 is easily formed in a trapezoidal shape from the initial growth stage. As a result, the side surface of the trapezoidal n-type GaN layer 24 gradually grows in the lateral direction, so that the lateral growth is promoted from the initial growth stage of the n-type GaN layer 24. For this reason, dislocations are bent in the horizontal direction from the initial growth stage of the n-type GaN layer 24, so that dislocations that propagate in the vertical direction from the initial growth stage of the n-type GaN layer 24 can be reduced. As a result, the n-type GaN layer 24 having a small thickness and reduced dislocations can be hetero-grown on the n-type SiC substrate 21.
[0057]
Next, a structure of a semiconductor laser device manufactured by using the formation method of the second embodiment shown in FIG. 8 will be described with reference to FIG. In the semiconductor laser device according to the second embodiment, as shown in FIG. 9, the first conductivity type layer 115 made of n-type GaN having a thickness of about 4 μm is formed on the n-type GaN layer 24 shown in FIG. Is formed. On the first conductivity type layer 115, a first conductivity type cladding layer 116 of n-type AlGaN having a thickness of about 0.45 μm is formed. On the first conductivity type cladding layer 116, a multiple quantum well (MQW) light emitting layer 117 made of InGaN is formed. A second conductivity type cladding layer 118 made of p-type AlGaN and having a thickness of about 0.45 μm is formed on the MQW light emitting layer 117. On the second conductivity type cladding layer 118, a second conductivity type contact layer 119 made of p-type GaN having a thickness of about 0.15 μm is formed. An n-type first conductivity type electrode 120 is formed on the back surface of the n-type SiC substrate 21. On the upper surface of the second conductivity type contact layer 119, a p-type second conductivity type electrode 121 is formed.
[0058]
The first conductive type layer 115, the first conductive type clad layer 116, the MQW light emitting layer 117, the second conductive type clad layer 118, and the second conductive type contact layer 119 are examples of the “semiconductor element layer” of the present invention. is there.
[0059]
In the semiconductor laser device according to the second embodiment, after forming the n-type GaN layer 24 having a small thickness and reduced dislocations, the layers 115 to 119 are formed on the n-type GaN layer 24. , Excellent crystallinity can be realized. Thus, in the second embodiment, a semiconductor laser device having a small thickness and excellent device characteristics can be obtained.
[0060]
In the second embodiment, the intermediate layer SiO 2₂The mask layer 22 having the overhang shape as shown in FIG. 8 is formed by utilizing the difference in the etching rate between the layer 22b and the lower SiN layer 22a and the upper SiN layer 22c. Other combinations are possible as long as the upper and lower layers are easily etched. For example, the upper or lower layer is made of a metal such as tungsten, and the intermediate layer is made of SiO 2.₂, SiN, TiO₂, TiN or the like.
[0061]
(Third embodiment)
FIG. 10 is a cross-sectional view illustrating the method for forming the nitride-based semiconductor layer according to the third embodiment of the present invention. FIG. 11 is a cross-sectional view showing a semiconductor laser device manufactured by using the method of forming a nitride-based semiconductor layer shown in FIG.
[0062]
First, a method for forming a nitride-based semiconductor layer according to the third embodiment will be described with reference to FIG. In the third embodiment, first, a mask layer 32 having an overhang portion is directly formed on a sapphire substrate 31 as a base. The mask layer 32 has a two-layer structure including a lower SiN layer 32a formed at a RF power of 150 W using a plasma CVD method and an upper SiN layer 32b formed at a RF power of 250 W using a plasma CVD method. And has a thickness of about 50 nm to about 1000 nm. In this case, the upper SiN layer 32b formed as described above is less likely to be etched than the lower SiN layer 32a.
[0063]
As a specific method of forming the mask layer 32, first, a lower SiN layer 32a and an upper SiN layer 32b are sequentially formed on the entire surface of the sapphire substrate 31 under the above conditions, and then the upper SiN layer 32b is formed. A resist (not shown) is formed in a predetermined area of the substrate. Then, using the resist as a mask, the upper SiN layer 32b and the lower SiN layer 32a are wet-etched using buffered hydrofluoric acid to form a two-layer structure having an overhang shape as shown in FIG. A mask layer 32 is formed. In the mask layer 32, the shortest distance between the adjacent mask layers 32 (SiN layers 32b) is smaller than the width of the exposed portion of the sapphire substrate 31 located between the adjacent mask layers 32.
[0064]
Thereafter, an undoped GaN layer 33 of high-temperature growth is selectively laterally grown on the sapphire substrate 31 by using the mask layer 32 as a selective growth mask by MOCVD or HVPE. Also in the third embodiment, since the mask layer 32 has an overhang shape, it is difficult for the raw material to reach under the overhang portion. As a result, an undoped GaN layer 33 having a small thickness is formed below the overhang portion, and an undoped GaN layer 33 having a uniform thickness is formed at the center of the exposed portion of the sapphire substrate 31. Similarly to the above, a trapezoidal undoped GaN layer 33 is formed from the initial stage of growth. For this reason, since the side surface of the trapezoidal undoped GaN layer 33 gradually grows in the lateral direction, the lateral growth of the undoped GaN layer 33 is promoted from the initial growth stage.
[0065]
Thereby, the dislocations are bent in the horizontal direction from the initial growth stage of the undoped GaN layer 33, so that the dislocations propagating in the vertical direction from the initial growth stage of the undoped GaN layer 33 can be reduced. As a result, the undoped GaN layer 33 having a small thickness and low dislocation can be hetero-grown on the sapphire substrate 31. The undoped GaN layer 33 is an example of the “nitride-based semiconductor layer” of the present invention.
[0066]
Next, a semiconductor laser device manufactured by using the nitride-based semiconductor layer forming method of the third embodiment will be described with reference to FIG. In this semiconductor laser device, as shown in FIG. 11, a first conductivity type contact layer 105, a first conductivity type cladding layer 106, an MQW light emitting layer 107, and a second conductivity type are formed on the undoped GaN layer 33 shown in FIG. A cladding layer 108, a second conductivity type contact layer 109, an n-type first conductivity type electrode 110, and a p-type second conductivity type electrode 111 are formed. The composition and thickness of each of the layers 105 to 109 are the same as those of the semiconductor laser device of the first embodiment shown in FIG.
[0067]
In the third embodiment, by forming the layers 105 to 109 on the low-dislocation undoped GaN layer 33 formed in such a small thickness, good crystallinity can be realized in each of the layers 105 to 109. Can be. As a result, in the third embodiment, as in the first embodiment, a semiconductor laser device having a small thickness and good characteristics can be obtained.
[0068]
(Fourth embodiment)
FIG. 12 is a cross-sectional view for explaining the method for forming the nitride-based semiconductor layer according to the fourth embodiment of the present invention. FIG. 13 is a cross-sectional view showing a semiconductor laser device manufactured by using the nitride-based semiconductor layer forming method of the fourth embodiment shown in FIG.
[0069]
First, a method for forming a nitride-based semiconductor layer according to the fourth embodiment will be described with reference to FIG. In the fourth embodiment, an inverted mesa (inverted trapezoidal) mask layer 42 having an overhang portion 42a made of tungsten (W) is formed on an n-type SiC substrate 41 as a base. The mask layer 42 is formed in a stripe shape having a thickness of about 10 nm to about 1000 nm and a period of about 5 μm. In the mask layer 42, the shortest distance between the adjacent mask layers 42 is smaller than the width of the exposed portion of the n-type SiC substrate 41 located between the adjacent mask layers 42.
[0070]
As a method of forming the mask layer 42 having the overhang portion 42a made of W, first, a W layer (not shown) is formed on the entire surface of the n-type SiC substrate 41, and then a predetermined region on the W layer is formed. A resist (not shown) is formed. Then, when the W layer is etched using the resist as a mask, the etching conditions are adjusted so as to be over-etched. Thus, a mask layer 42 having an overhang portion 42a made of W is formed.
[0071]
Thereafter, an n-type AlC is formed on the n-type SiC substrate 41 by using the mask layer 42 as a selective growth mask by MOCVD or HVPE._WB_XGa_YIn_ZTl_1-WXYZThe N layer 43 is selectively grown. Al_WB_XGa_YIn_ZTl_1-WXYZThe composition of N is a composition excluding Y = Z = 0 and the composition of Al_WB_XGa_YIn_ZTl_1-WXYZThe lattice constant of N is larger than that of GaN. In the present embodiment, for example, the n-type InGaN layer 43 is selectively grown. The n-type InGaN layer 43 is formed with a thickness of about 2 μm under a temperature condition of about 650 ° C. to about 900 ° C.
[0072]
If the n-type InGaN layer 43 is grown directly on the n-type SiC substrate 41, it becomes difficult for the raw material to reach below the overhang portion 42a of the mask layer 42. Thus, the n-type InGaN layer 43 having a small thickness is formed below the overhang portion 42a, and the n-type InGaN layer 43 having a uniform thickness is formed at the center of the exposed portion of the n-type SiC substrate 41. 2, a trapezoidal n-type InGaN layer 43 is formed from the initial stage of growth. For this reason, since the side surface of the trapezoidal n-type InGaN layer 43 gradually grows in the lateral direction, lateral growth is promoted from the initial growth stage of the n-type InGaN layer 43. Accordingly, a low dislocation n-type InGaN layer 43 can be grown thickly on the n-type SiC substrate 41 without providing a GaN layer as a base layer as in the conventional example shown in FIG. In this case, since there is no need to provide a GaN layer as an underlayer, the overall thickness can be reduced as compared with the conventional example shown in FIG. The n-type InGaN layer 43 is an example of the “nitride-based semiconductor layer” of the present invention.
[0073]
Next, the structure of a semiconductor laser device formed by using the nitride-based semiconductor layer forming method of the fourth embodiment will be described with reference to FIG. In the semiconductor laser device of the fourth embodiment, a first conductivity type layer 115 made of an n-type InGaN layer and a first conductivity type clad layer 116 made of an n-type GaN layer are formed on the n-type InGaN layer 43 shown in FIG. , An MQW light emitting layer 117 made of InGaN, a second conductivity type cladding layer 118 made of a p-type GaN layer, and a second conductivity type contact layer 119 made of a p-type InGaN layer. On the back surface of the n-type SiC substrate 41, an n-type first conductivity type electrode 120 is formed. On the upper surface of the second conductivity type contact layer 119, a p-type second conductivity type electrode 121 is formed. The thickness of each of the layers 115 to 119 is the same as that of the semiconductor laser of the second embodiment shown in FIG.
[0074]
In the semiconductor laser device according to the fourth embodiment, the layers 115 to 119 are formed on the low dislocation n-type InGaN layer 43 formed by using the formation method shown in FIG. Crystallinity can be realized. Further, in the method of forming the nitride-based semiconductor layer shown in FIG. 12, since the entire thickness is formed thin, when each of the layers 115 to 119 is formed thereon, the thickness of the semiconductor laser element becomes thin. Thus, in the fourth embodiment, as in the second embodiment, a semiconductor laser device having a small thickness and good device characteristics can be obtained.
[0075]
In the semiconductor laser device according to the fourth embodiment, the MQW light emitting layer 117 is formed on the low dislocation n-type InGaN layer 43 formed by using the forming method shown in FIG. Even if the In composition of the MQW light emitting layer 117 is increased to increase the lattice constant, good crystallinity can be realized. Therefore, it is possible to realize a semiconductor laser having a longer wavelength such as green than a conventional nitride semiconductor laser.
[0076]
(Fifth embodiment)
FIG. 14 is a cross-sectional view for explaining the method for forming the nitride-based semiconductor layer according to the fifth embodiment of the present invention. FIG. 15 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a nitride-based semiconductor layer shown in FIG. First, a method for forming a nitride-based semiconductor layer according to the fifth embodiment will be described with reference to FIG.
[0077]
First, in the fifth embodiment, a mask layer 52 made of SiN is formed on the surface of an n-type GaAs (111) A substrate 51 as a base with a thickness of about 10 nm to about 1000 nm at a period of 5 μm. Then, using the mask layer 52 as a mask, the n-type GaAs substrate 51 is etched. At this time, over-etching is performed to form an inverted mesa-shaped projection 51a on the n-type GaAs substrate 51. The etching of the n-type GaAs substrate 51 is performed by H₂SO₄+ H₂O₂+ H₂O (4: 1: 1) or H₃PO₄+ H₂O₂+ H₂O (3: 1: 1).
[0078]
Thereafter, a low-temperature buffer layer 53 made of AlGaN or GaN having a thickness of about 10 nm to about 50 nm is formed on the exposed surface of the n-type GaAs substrate 51 at a temperature of about 500 ° C. to about 700 ° C. In the portion below the convex portion (overhang portion) 51a of the inverted mesa shape, the thickness of the low-temperature buffer layer 53 becomes small because the raw material is difficult to be supplied.
[0079]
Next, an n-type GaN layer 54 is selectively laterally grown on the low-temperature buffer layer 53 by using the mask layer 52 as a selective growth mask by MOCVD or HVPE. In this case, since the protrusions 51a under the mask layer 52 have an inverted mesa shape, both ends of the mask layer 52 have a structure having an overhang shape protruding above the exposed portion of the n-type GaAs substrate 51. Become. That is, in the mask layer 52, the shortest distance W1 between the adjacent mask layers 52 is smaller than the width W2 of the exposed portion of the n-type GaAs substrate 51 located between the adjacent mask layers 52.
[0080]
Here, the n-type GaN layer 54 is unlikely to grow on the thin low-temperature buffer layer 53 below the overhang portion 51a, and the material of the n-type GaN layer 54 is formed below the overhang portion 51a. 2, it is easy to form the trapezoidal n-type GaN layer 54 from the initial stage of growth, as in the conceptual diagram shown in FIG. Thereby, the lateral surface of the trapezoidal n-type GaN layer 54 gradually grows in the lateral direction, so that the lateral growth of the n-type GaN layer 54 is promoted from the initial growth stage. For this reason, dislocations are bent in the horizontal direction from the initial growth stage of the n-type GaN layer 54, so that dislocations propagating in the vertical direction from the initial growth stage of the n-type GaN layer 54 can be reduced. As a result, the n-type GaN layer 54 can be hetero-grown on the n-type GaAs substrate 51 with a small thickness. The n-type GaN layer 54 is an example of the “nitride-based semiconductor layer” of the present invention.
[0081]
Next, a semiconductor laser device manufactured by using the nitride-based semiconductor layer forming method of the fifth embodiment shown in FIG. 14 will be described with reference to FIG. In the semiconductor laser device of the fifth embodiment, a first conductivity type layer 115, a first conductivity type cladding layer 116, an MQW light emitting layer 117, and a second conductivity type cladding layer are formed on the n-type GaN layer 54 shown in FIG. 118 and a second conductivity type contact layer 119 are formed. On the back surface of the n-type GaAs substrate 51, an n-type first conductivity type electrode 120 is formed. On the upper surface of the second conductivity type contact layer 119, a p-type second conductivity type electrode 121 is formed. The composition and thickness of each of the layers 115 to 119 are the same as those of the semiconductor laser of the second embodiment shown in FIG.
[0082]
In the semiconductor laser device according to the fifth embodiment, since the layers 115 to 119 are formed on the thin dislocation n-type GaN layer 54 having a small thickness formed by using the forming method shown in FIG. , Excellent crystallinity can be realized. Thus, in the fifth embodiment, as in the second and fourth embodiments, a semiconductor laser device having a small thickness and excellent device characteristics can be obtained.
[0083]
(Sixth embodiment)
FIG. 16 is a cross-sectional view for explaining the method for forming the nitride-based semiconductor layer according to the sixth embodiment of the present invention. FIG. 17 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a nitride-based semiconductor layer of the sixth embodiment shown in FIG.
[0084]
First, a method for forming a nitride-based semiconductor layer according to the sixth embodiment will be described with reference to FIG. In the sixth embodiment, after a tungsten (W) layer is formed with a thickness of about 10 nm to about 1000 nm on the surface of an n-type Si (111) substrate 61 as a base, patterning is performed using photolithography. As a result, a mask layer 62 made of stripe-shaped W having a period of about 10 μm is formed. Then, using the mask layer 62 as a mask, HF: HNO₃: CH₃By etching the n-type Si substrate 61 using COOH (1: 5: 1), a region of the n-type Si substrate 61 located under both ends of the mask layer 62 as shown in FIG. The shape is formed. That is, both ends of the mask layer 62 have an overhang shape protruding above the end of the exposed portion of the n-type Si substrate 61. In the mask layer 62, the shortest distance W1 between the adjacent mask layers 62 is smaller than the width W2 of the exposed portion of the n-type Si substrate 61 located between the adjacent mask layers 62.
[0085]
Using this mask layer 62 as a selective growth mask, AlGaN having a thickness of about 10 nm to about 50 nm at a temperature of about 1100 ° C. is formed on the exposed surface of n-type Si substrate 61 by MOCVD or HVPE. Is formed. Thereafter, an n-type GaN layer 64 is selectively grown in the lateral direction on the exposed n-type Si substrate 61 and the buffer layer 63.
[0086]
In this case, it is difficult for the raw material to reach the surface of the n-type Si substrate 61 located under the overhang portions at both ends of the mask layer 62. Therefore, an n-type GaN layer 64 having a small thickness is formed below the overhang portion, and an n-type GaN layer 64 having a uniform thickness is formed at the center of the exposed portion of the n-type Si substrate 61. As in the conceptual diagram shown, a trapezoidal n-type GaN layer 64 is formed from an early stage of growth. Thereby, the lateral surface of the trapezoidal n-type GaN layer 64 gradually grows in the lateral direction, so that the lateral growth from the initial growth stage of the n-type GaN layer 64 is promoted. For this reason, the dislocations are bent in the horizontal direction from the initial growth stage of the n-type GaN layer 64, so that the dislocations propagating in the vertical direction from the initial growth stage of the n-type GaN layer 64 can be reduced. As a result, the n-type GaN layer 64 having a small thickness and low dislocation can be hetero-grown on the n-type Si substrate 61. The n-type GaN layer 64 is an example of the “nitride-based semiconductor layer” of the present invention.
[0087]
Next, the structure of a semiconductor laser device formed by using the method for forming a nitride-based semiconductor layer of the sixth embodiment shown in FIG. 16 will be described with reference to FIG. In the semiconductor laser device according to the sixth embodiment, the first conductivity type layer 115, the first conductivity type cladding layer 116, the MQW light emitting layer 117, and the second conductivity type cladding layer are formed on the n-type GaN layer 64 shown in FIG. 118 and a second conductivity type contact layer 119 are formed. Further, on the back surface of the n-type Si substrate 61, an n-type first conductivity type electrode 120 is formed. On the upper surface of the second conductivity type contact layer 119, a p-type second conductivity type electrode 121 is formed. The composition and thickness of each of the layers 115 to 119 are the same as those of the semiconductor laser of the second embodiment shown in FIG.
[0088]
In the semiconductor laser device according to the sixth embodiment, since the layers 115 to 119 are formed on the thin dislocation n-type GaN layer 64 having a small thickness formed by using the forming method shown in FIG. , Excellent crystallinity can be realized. Thus, in the sixth embodiment, as in the second, fourth, and fifth embodiments, a semiconductor laser device having a small thickness and good device characteristics can be obtained.
[0089]
In the above-described first to sixth embodiments, a sapphire substrate, a Si substrate, a SiC substrate, and a GaAs substrate are used as substrates. In addition to these substrates, a spinel substrate, a GaP substrate, an InP substrate, and a quartz substrate are used. A substrate or the like may be used, and when a substrate other than these nitride semiconductors is used, the effect of reducing dislocations is particularly large.
[0090]
(Seventh embodiment)
FIG. 18 is a cross-sectional view for explaining the method for forming the nitride-based semiconductor layer according to the seventh embodiment of the present invention. FIG. 19 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a nitride-based semiconductor layer of the seventh embodiment shown in FIG.
[0091]
First, a method for forming a nitride-based semiconductor layer according to the seventh embodiment will be described with reference to FIG. In the seventh embodiment, a mask layer 72 made of inverted mesa SiN having an overhang portion 72a is formed on an n-type GaN substrate 71 as a base. The mask layer 72 made of SiN has a film thickness of about 10 nm to about 1000 nm and is formed in a stripe shape at a period of about 10 μm. As a method of forming the mask layer 72, first, an SiN layer (not shown) is formed on the entire surface of the n-type GaN substrate 71, and then a resist (not shown) is formed on a predetermined region on the SiN layer. . Then, using the resist as a mask, overetching is performed when etching the SiN layer. As a result, an inverted mesa-shaped mask layer 72 having an overhang portion 72a is formed. In this mask layer 72, the shortest distance between adjacent mask layers 72 is smaller than the width of the exposed portion of n-type GaN substrate 71 located between adjacent mask layers 72.
[0092]
Thereafter, the n-type Al substrate is formed on the n-type GaN substrate 71 by using the mask layer 72 as a selective growth mask by MOCVD or HVPE._WB_XGa_YIn_ZTl_1-WXYZThe N layer 73 is selectively grown in the lateral direction. Where Al_WB_XGa_YIn_ZTl_1-WXYZThe composition of N is a composition excluding X = Y = 0 and the composition of Al_WB_XGa_YIn_ZTl_1-WXYZThe lattice constant of N is smaller than that of GaN. For example, Al_WGa_1-WN (0 <W ≦ 1) or B_XGa_1-XN (0 <X ≦ 1). In the present embodiment, for example, B_0.05Ga_0.95The N layer 73 is formed to have a thickness of about 2 μm under a temperature condition of about 850 ° C. to about 1400 ° C.
[0093]
In this case, it is difficult for the raw material to reach below the overhang portion 72a of the mask layer 72. Therefore, the n-type BGaN layer 73 having a small thickness is formed below the overhang portion 72a, and the n-type BGaN layer 73 having a uniform thickness is formed at the center of the exposed portion of the n-type GaN substrate 71. 2, a trapezoidal n-type BGaN layer 73 is formed from the initial stage of growth. Thereby, the lateral surface of the trapezoidal n-type BGaN layer 73 gradually grows in the lateral direction, so that the lateral growth of the n-type BGaN layer 73 is promoted from the initial growth stage. As a result, the n-type BGaN layer 73 of low dislocation can be formed thick on the n-type GaN substrate 71 even without the underlying GaN layer. In this case, since there is no need to provide a GaN layer as an underlayer, the overall thickness can be reduced as compared with the conventional example shown in FIG. The n-type BGaN layer 73 is an example of the “nitride-based semiconductor layer” of the present invention.
[0094]
Next, a semiconductor laser device formed by using the method for forming a nitride-based semiconductor layer according to the seventh embodiment will be described with reference to FIG. In this semiconductor laser device, a first conductivity type layer 115 made of an n-type BGaN layer, a first conductivity type clad layer 116 made of an n-type BGaN layer, and an MQW made of AlGaN are formed on the n-type BGaN layer 73 shown in FIG. A light emitting layer 117, a second conductivity type cladding layer 118 made of a p-type BGaN layer, and a second conductivity type contact layer 119 made of a p-type GaN layer are formed. On the back surface of the n-type GaN substrate 71, an n-type first conductivity type electrode 120 is formed. On the upper surface of the second conductivity type contact layer 119, a p-type second conductivity type electrode 121 is formed. The thickness of each of the layers 115 to 119 is the same as that of the semiconductor laser of the second embodiment shown in FIG.
[0095]
In the semiconductor laser device according to the seventh embodiment, since the layers 115 to 119 are formed on the n-type BGaN layer 73 having low dislocation, good crystallinity can be realized in the layers 115 to 119. Further, in the formation method of FIG. 19, since the entire thickness is formed thin, when the layers 115 to 119 are formed thereon, the thickness of the semiconductor laser element becomes thin. Thus, also in the seventh embodiment, as in the second, fourth, fifth, and sixth embodiments, a semiconductor laser device having a small thickness and excellent device characteristics can be obtained.
[0096]
In the semiconductor laser device according to the seventh embodiment, the MQW light emitting layer 117 is formed on the thick low dislocation n-type BGaN layer 73, so that the MQW light emitting layer 117 has a small lattice constant. Good crystallinity can be realized even when the Al composition of the layer 117 is increased. Therefore, a semiconductor laser having a shorter wavelength than a conventional nitride-based semiconductor laser can be realized.
[0097]
In the seventh embodiment, the example in which the n-type BGaN layer 73 is formed as the nitride-based semiconductor layer has been described. However, in the present embodiment, the material formed as the nitride-based semiconductor layer is formed in the n-type BGaN layer 73. It is not limited. For example, a mixed crystal of a nitride-based semiconductor layer such as InN, GaInN, AlGaN, AlGaInN, or AlN, or a mixed crystal of a nitride-based semiconductor layer containing at least one of B, In, and Tl can be formed. .
[0098]
In the seventh embodiment, the n-type GaN substrate 71 is used as the substrate. Instead of the n-type GaN substrate 71, a sapphire substrate, a Si substrate, a SiC substrate, a GaAs substrate, a spinel substrate, a GaP substrate, an InP A substrate, a quartz substrate, or the like may be used.
[0099]
(Eighth embodiment)
FIG. 20 is a sectional view illustrating the method of forming the nitride-based semiconductor layer according to the eighth embodiment of the present invention. FIG. 21 is a sectional view showing a semiconductor laser device manufactured by using the nitride-based semiconductor layer forming method according to the eighth embodiment shown in FIG.
[0100]
First, a method for forming a nitride-based semiconductor layer according to the eighth embodiment will be described with reference to FIG. In the eighth embodiment, a low-temperature buffer layer 82 of AlGaN or GaN having a thickness of about 10 nm to about 50 nm is formed on a sapphire substrate 81 at a temperature of about 500 ° C. to about 700 ° C. On the low-temperature buffer layer 82, a GaN layer 83 serving as a base is formed with a thickness of about 2 μm by using the MOCVD method or the HVPE method. On the GaN layer 83, a mask layer 84 made of inverted mesa SiN having an overhang portion 84a is formed. In the mask layer 84, the shortest distance between the adjacent mask layers 84 is smaller than the width of the exposed portion of the GaN layer 83 located between the adjacent mask layers 84.
[0101]
Then, using such a mask layer 84 as a mask, MOCVD or HVPE is used to form an Al layer on the GaN layer 83._1-WXYZB_WGa_XIn_YTl_ZAn N layer 85 is selectively grown in the lateral direction. Al_1-WXYZB_WGa_XIn_YTl_ZThe composition of N is a composition excluding Y = Z = 0 and the composition of Al_1-WXYZB_WGa_XIn_YTl_ZThe lattice constant of N is larger than that of GaN. For example, Ga_1-YIn_YN (0 <Y ≦ 1) or Ga_1-ZTl_ZN (0 <Z ≦ 1). In the present embodiment, for example, the AlGaInN layer 85 is grown in the selective lateral direction. The AlGaInN layer 85 is formed to have a thickness of about 1 μm under a temperature condition of about 600 ° C. to about 1200 ° C.
[0102]
In this case, it is difficult for the raw material to reach below the overhang portion 84a of the mask layer 84. Therefore, the AlGaInN layer 85 having a small thickness is formed under the overhang portion 84a, and the AlGaInN layer 85 having a uniform thickness is formed at the center of the exposed portion of the GaN layer 83, as shown in FIG. As in the conceptual diagram, a trapezoidal AlGaInN layer 85 is formed from the initial stage of growth. Thereby, the side surface of the trapezoidal AlGaInN layer 85 gradually grows in the lateral direction, so that the lateral growth of the AlGaInN layer 85 is promoted from the initial growth stage. For this reason, the dislocations are bent in the horizontal direction from the initial growth stage of the AlGaInN layer 85, so that the dislocations propagating in the vertical direction from the initial growth stage of the AlGaInN layer 85 can be reduced. As a result, the AlGaInN layer 85 having a small thickness and a low dislocation can be formed. The AlGaInN layer 85 is an example of the “nitride-based semiconductor layer” of the present invention.
[0103]
Next, the structure of a semiconductor laser device formed by using the nitride-based semiconductor layer forming method shown in FIG. 20 will be described with reference to FIG. In the semiconductor laser device according to the eighth embodiment, as shown in FIG. 21, a first conductivity type contact layer 105, a first conductivity type cladding layer 106, an MQW light emitting layer 107, and an AlGaInN layer 85 shown in FIG. A second conductivity type cladding layer 108, a second conductivity type contact layer 109, an n-type first conductivity type electrode 110, and a p-type second conductivity type electrode 111 are formed. The composition and thickness of each of the layers 105 to 109 are the same as those of the semiconductor laser device of the first embodiment shown in FIG.
[0104]
In the eighth embodiment, by forming the layers 105 to 109 on the AlInGaN layer 85 of low dislocation formed in such a thin film thickness, it is possible to realize good crystallinity in the layers 105 to 109. it can. As a result, in the eighth embodiment, a semiconductor laser device having a small thickness and excellent characteristics can be obtained.
[0105]
(Ninth embodiment)
FIG. 22 is a cross-sectional view for explaining the method for forming the nitride-based semiconductor layer according to the ninth embodiment of the present invention. FIG. 23 is a sectional view showing a semiconductor laser device manufactured by using the nitride-based semiconductor layer forming method according to the ninth embodiment shown in FIG.
[0106]
First, a method for forming a nitride-based semiconductor layer according to the ninth embodiment will be described with reference to FIG. In the ninth embodiment, after a low-temperature buffer layer 92 of AlGaN is formed on a sapphire substrate 91, a GaN layer 93 serving as a base is formed to a thickness of about 2 μm by MOCVD or HVPE. On the GaN layer 93, a mask layer 94 made of inverted mesa SiN having an overhang portion 94a is formed. In the mask layer 94, the shortest distance between the adjacent mask layers 94 is smaller than the width of the exposed portion of the GaN layer 93 located between the adjacent mask layers 94.
[0107]
Then, using such a mask layer 94 as a mask, a GaN layer 95 is selectively grown in a lateral direction on the GaN layer 93 by MOCVD or HVPE. In this embodiment, the GaN layer 95 is formed to have a thickness of about 1 μm under a temperature condition of about 1150 ° C.
[0108]
In this case, it is difficult for the raw material to reach below the overhang portion 94a of the mask layer 94. For this reason, the GaN layer 95 having a small thickness is formed below the overhang portion 94a, and the GaN layer 95 having a uniform thickness is formed at the center of the exposed portion of the GaN layer 93, as shown in FIG. As in the conceptual diagram, a trapezoidal GaN layer 95 is formed from an early stage of growth. Thereby, the lateral surface of the trapezoidal GaN layer 95 gradually grows in the lateral direction, so that the lateral growth of the GaN layer 95 is promoted from the initial growth stage. For this reason, dislocations are bent in the horizontal direction from the initial growth stage of the GaN layer 95, so that dislocations that propagate in the vertical direction from the initial growth stage of the GaN layer 95 can be reduced. As a result, a GaN layer 95 having a small thickness and reduced dislocations can be grown. The GaN layer 95 is an example of the “nitride-based semiconductor layer” of the present invention.
[0109]
Next, a structure of a semiconductor laser device formed by using the method for forming a nitride-based semiconductor layer shown in FIG. 22 will be described with reference to FIG. In the semiconductor laser device according to the ninth embodiment, as shown in FIG. 23, a first conductivity type contact layer 105, a first conductivity type cladding layer 106, an MQW light emitting layer 107, and a GaN layer 95 shown in FIG. A second conductivity type cladding layer 108, a second conductivity type contact layer 109, an n-type first conductivity type electrode 110, and a p-type second conductivity type electrode 111 are formed. The composition and thickness of each of the layers 105 to 109 are the same as those of the semiconductor laser device of the first embodiment shown in FIG.
[0110]
In the ninth embodiment, by forming the layers 105 to 109 on the low dislocation GaN layer 95 formed in such a thin film thickness, it is possible to realize good crystallinity in each of the layers 105 to 109. it can. As a result, in the ninth embodiment, a semiconductor laser device having a small thickness and excellent characteristics can be obtained.
[0111]
(Tenth embodiment)
FIG. 24 is a cross-sectional view for explaining the method for forming the semiconductor layer according to the tenth embodiment of the present invention. FIG. 25 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a semiconductor layer of the tenth embodiment shown in FIG.
[0112]
First, a method for forming a semiconductor layer according to the tenth embodiment will be described with reference to FIG. In the tenth embodiment, an inverted mesa (inverted trapezoidal) mask layer 132 having an overhang portion 132a made of tungsten (W) is formed on an n-type Si (111) substrate 131 as a base. This mask layer 132 is formed in a stripe shape having a thickness of about 10 nm to about 1000 nm and a period of about 5 μm. In the mask layer 132, the shortest distance between the adjacent mask layers 132 is smaller than the width of the exposed portion of the n-type Si substrate 131 located between the adjacent mask layers 132.
[0113]
As a method of forming the mask layer 132 having the overhang portion 132a made of W, first, a W layer (not shown) is formed on the entire surface of the n-type Si substrate 131, and then a predetermined region on the W layer is formed. A resist (not shown) is formed. Then, when the W layer is etched using the resist as a mask, the etching conditions are adjusted so as to be over-etched. As a result, a mask layer 132 having an overhang portion 132a made of W is formed.
[0114]
Thereafter, the n-type GaAs layer 133 is selectively grown on the n-type Si substrate 131 by using the mask layer 132 as a selective growth mask by MOCVD or MBE. Note that the n-type GaAs layer 133 is grown with the (111) B plane as a growth surface. The GaAs layer 133 is formed with a thickness of about 2 μm under a temperature condition of about 600 ° C., for example.
[0115]
Also in the tenth embodiment, it is difficult for the raw material to reach below the overhang portion 132a of the mask layer 132. Therefore, the n-type GaAs layer 133 having a small thickness is formed below the overhang portion 132a of the mask layer 132, and the n-type GaAs layer 133 having a uniform thickness is formed at the center of the exposed portion of the n-type Si substrate 131. As a result, the trapezoidal n-type GaAs layer 133 can be formed from the initial stage of growth, as in the conceptual diagram shown in FIG. Thereby, the lateral surface of the trapezoidal n-type GaAs layer 133 gradually grows in the lateral direction, so that the lateral growth is promoted from the initial growth stage of the n-type GaAs layer 133. For this reason, dislocations are bent in the horizontal direction from the initial growth stage of the n-type GaAs layer 133, so that dislocations that propagate in the vertical direction from the initial growth stage of the n-type GaAs layer 133 can be reduced. As a result, when growing the n-type GaAs layer 133 directly on the n-type Si substrate 131, the low-dislocation n-type GaAs layer 133 can be grown thick on the n-type Si substrate 131. In this case, the entire thickness can be reduced because there is no need to provide an underlayer.
[0116]
Next, the structure of a semiconductor laser device formed by using the method for forming a semiconductor layer according to the tenth embodiment will be described with reference to FIG. In the semiconductor laser device of the tenth embodiment, the first conductivity type layer 115a made of n-type GaAs, the first conductivity type cladding layer 116a made of n-type AlGaAs, and the GaAs are formed on the n-type GaAs layer 133 shown in FIG. An MQW light emitting layer 117a made of AlGaAs and AlGaAs, a second conductivity type cladding layer 118a made of p-type AlGaAs, and a second conductivity type contact layer 119a made of p-type GaAs are formed. Further, on the back surface of the n-type Si substrate 131, an n-type first conductivity type electrode 120 is formed. A p-type second conductivity type electrode 121 is formed on the upper surface of the second conductivity type contact layer 119a.
[0117]
The first conductive type layer 115a, the first conductive type clad layer 116a, the MQW light emitting layer 117a, the second conductive type clad layer 118a, and the second conductive type contact layer 119a are examples of the "semiconductor element layer" of the present invention. is there.
[0118]
In the semiconductor laser device according to the tenth embodiment, the layers 115a to 119a are formed on the low dislocation n-type GaAs layer 133 formed by using the forming method shown in FIG. Crystallinity can be realized.
[0119]
(Eleventh embodiment)
FIG. 26 is a cross-sectional view for explaining the method for forming a semiconductor layer according to the eleventh embodiment of the present invention. FIG. 27 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a semiconductor layer of the eleventh embodiment shown in FIG.
[0120]
First, a method for forming a semiconductor layer according to the eleventh embodiment will be described with reference to FIG. In the eleventh embodiment, an n-type GaAs layer 143 is grown on an n-type Si (111) substrate 141 as a base. The n-type GaAs layer 143 is grown with the (111) A plane as a growth surface. On the (111) A surface of the n-type GaAs layer 143, an inverted mesa (inverted trapezoidal) mask layer 142 having an overhang portion 142a made of tungsten (W) is formed. This mask layer 142 is formed in a stripe shape having a thickness of about 10 nm to 1000 nm and a period of about 5 μm. In the mask layer 142, the shortest distance between the adjacent mask layers 142 is smaller than the width of the exposed portion of the n-type GaAs layer 143 located between the adjacent mask layers 142.
[0121]
As a method of forming the mask layer 142 having the overhang portion 142a made of W, first, a W layer (not shown) is formed on the entire surface of the n-type GaAs layer 143, and then a predetermined region on the W layer is formed. A resist (not shown) is formed. Then, when the W layer is etched using the resist as a mask, the etching conditions are adjusted so as to be over-etched. As a result, a mask layer 142 having an overhang portion 142a made of W is formed.
[0122]
Thereafter, the n-type GaAs layer 144 is selectively grown on the n-type GaAs layer 143 by using the mask layer 142 as a selective growth mask by MOCVD. The n-type GaAs layer 144 is grown with the (111) A plane as the growth surface. This n-type GaAs layer 144 is formed with a thickness of about 2 μm under a temperature condition of about 600 ° C.
[0123]
Also in the eleventh embodiment, it is difficult for the raw material to reach below the overhang portion 142a of the mask layer 142. Therefore, the n-type GaAs layer 144 having a small thickness is formed under the overhang portion 142a, and the n-type GaAs layer 144 having a uniform thickness is formed at the center of the exposed portion of the n-type GaAs layer 143 as a base. Therefore, a trapezoidal n-type GaAs layer 144 is formed from the initial stage of growth, as in the conceptual diagram shown in FIG. Accordingly, the lateral surface of the trapezoidal n-type GaAs layer 144 gradually grows in the lateral direction, and thus the lateral growth is promoted from the initial growth stage of the n-type GaAs layer 144. For this reason, dislocations are bent in the horizontal direction from the initial growth stage of the n-type GaAs layer 144, so that dislocations that propagate in the vertical direction from the initial growth stage of the n-type GaAs layer 144 can be reduced. As a result, a low dislocation n-type GaAs layer 144 can be grown on the n-type GaAs layer 143.
[0124]
Next, the structure of a semiconductor laser device formed by using the method for forming a semiconductor layer of the eleventh embodiment will be described with reference to FIG. In the semiconductor laser device of the eleventh embodiment, the first conductivity type layer 115a made of n-type GaAs, the first conductivity type cladding layer 116a made of n-type AlGaAs, and the GaAs are formed on the n-type GaAs layer 144 shown in FIG. An MQW light emitting layer 127a made of AlGaAs and AlGaAs, a second conductivity type cladding layer 118a made of p-type AlGaAs, and a second conductivity type contact layer 119a made of p-type GaAs are formed. On the back surface of the n-type Si substrate 141, an n-type first conductivity type electrode 120 is formed. In addition, a p-type second conductivity type electrode 121 is formed on the upper surface of the p-type second conductivity type contact layer 119a.
[0125]
In the semiconductor laser device according to the eleventh embodiment, the layers 115a to 119a and 127a are formed on the low dislocation n-type GaAs layer 144 formed by using the forming method shown in FIG. In 127a, good crystallinity can be realized.
[0126]
(Twelfth embodiment)
FIG. 28 is a cross-sectional view for explaining the method for forming the nitride-based semiconductor layer according to the twelfth embodiment of the present invention. FIG. 29 is a cross-sectional view showing a semiconductor laser device manufactured by using the method for forming a nitride-based semiconductor layer shown in FIG. In the twelfth embodiment, an example using a super lattice layer will be described.
[0127]
First, in the twelfth embodiment, a mask layer 152 made of SiN is formed directly on the upper surface of a sapphire substrate 151 as a base. This mask layer 152 is formed in an inverted mesa shape (an inverted trapezoidal shape) having an overhang portion 152a. In the mask layer 152, the shortest distance between the adjacent mask layers 152 is smaller than the width of the exposed portion of the sapphire substrate 151 located between the adjacent mask layers 152.
[0128]
As a method for forming such a mask layer 152, first, an SiN layer (not shown) is formed on the entire surface of the sapphire substrate 151, and then a resist (not shown) is formed on a predetermined region on the SiN layer. . Then, by using the resist as a mask, the SiN layer is wet-etched, so that an inverted trapezoidal mask layer 152 having an overhang portion 152a can be easily formed. The mask layer 152 is formed in a stripe shape (elongated shape) having a period of about 7 μm and a thickness of about 1 μm. It is preferable that the opening of the mask layer 152 be formed, for example, in the [11-20] direction of sapphire or in the [1-100] direction of sapphire.
[0129]
Thereafter, a low-temperature buffer layer 153 made of AlGaN or GaN having a thickness of about 10 nm to about 50 nm is grown on the sapphire substrate 151 at a temperature of about 500 ° C. to about 700 ° C. Then, an undoped GaN layer 154 is formed on the low-temperature buffer layer 153 by using the mask layer 152 as a selective growth mask by MOCVD or HVPE. The undoped GaN layer 154 is formed to have a thickness of about 0.5 μm under a temperature condition of about 950 ° C. to about 1200 ° C.
[0130]
Here, when growing the low-temperature buffer layer 153, since the mask layer 152 has the overhang portion 152a, it is difficult for the raw material to reach below the overhang portion 152a. For this reason, the thickness of the buffer layer below the overhang portion 152a becomes thin. This makes it difficult for the undoped GaN layer 154 to grow on the thin low-temperature buffer layer 153 below the overhang portion 152a, and that the raw material of the undoped GaN layer 154 does not easily reach below the overhang portion 152a. As in the conceptual diagram shown in FIG. 2, a trapezoidal undoped GaN layer 154 is easily formed. The trapezoidal undoped GaN layer 154 is an example of the “first semiconductor layer” of the present invention.
[0131]
Thereafter, a superlattice layer 155 made of a layer having a composition different from that of GaN is formed on the surface of the trapezoidal undoped GaN layer 154 with a thickness of about 0.1 μm. Here, the superlattice layer refers to a layer having a periodic structure in which layers having different lattice constants are alternately stacked. An example of the superlattice layer 155 is Al having a thickness of about 10 nm._XGa_1-XA superlattice layer having a periodic structure of N (0 <X ≦ 1) and GaN having a thickness of about 10 nm;_1-XIn_XA superlattice layer having a periodic structure of GaN having N (0 <X ≦ 1) and a thickness of about 10 nm can be considered. The superlattice layer 155 is an example of the “third semiconductor layer” of the present invention.
[0132]
After forming the superlattice layer 155 as described above, an undoped GaN layer 156 is formed on the superlattice layer 155 so as to have a thickness of about 1.5 μm, and the surface is flattened. The undoped GaN layer 156 is an example of the “second semiconductor layer” of the present invention.
[0133]
In the twelfth embodiment, the superlattice layer 155 is formed on the undoped GaN layer 154 formed in the trapezoidal shape, and then the undoped GaN layer 156 is formed again. The dislocation bent in the direction L is more easily bent in a direction parallel to the direction in which the superlattice layer 155 extends due to the interface stress generated by the lattice mismatch of the superlattice layer 155. Thereby, the dislocations that are bent in a direction parallel to the direction in which the superlattice layer 155 extends collide with each other, so that the dislocations are likely to be coupled and annihilated, so that the lateral dislocations can be further reduced. As a result, dislocations can be more easily reduced from the initial growth stage.
[0134]
Next, the structure of a semiconductor laser device manufactured by using the forming method of the twelfth embodiment shown in FIG. 28 will be described with reference to FIG. In the semiconductor laser device according to the twelfth embodiment, as shown in FIG. 29, the first conductivity type contact layer 105, the first conductivity type cladding layer 106, and the MQW light emitting layer 107 are formed on the undoped GaN layer 156 shown in FIG. , A second conductivity type cladding layer 108, a second conductivity type contact layer 109, an n-type first conductivity type electrode 110, and a p-type second conductivity type electrode 111. The composition and thickness of each of the layers 105 to 109 are the same as those of the semiconductor laser device of the first embodiment shown in FIG.
[0135]
In the twelfth embodiment, better crystallinity is realized in each of the layers 105 to 109 by forming the layers 105 to 109 on the undoped GaN layer 156 with a lower dislocation formed in such a thin film thickness. be able to. As a result, in the twelfth embodiment, a semiconductor laser device having a small thickness and better characteristics can be obtained.
[0136]
(1st referenceForm)
FIG. 30 to FIG.First reference formFIG. 4 is a cross-sectional view for describing a method of forming a semiconductor layer according to the first embodiment. FIG. 33 is shown in FIGS.1st referenceFIG. 4 is a cross-sectional view showing a semiconductor laser device manufactured by using the method of forming a semiconductor layer according to the embodiment.
[0137]
First, referring to FIGS.1st referenceThe method for forming the semiconductor layer according to the embodiment will be described. this1st referenceIn the embodiment, first, an n-type GaAs layer 163a is grown on the entire surface of an n-type Si (111) substrate 161 as a base. Note that the n-type GaAs layer 163a is grown with the (111) B plane as a growth surface. A periodic etching mask is formed on the surface of the n-type GaAs layer 163a using a photolithography technique. Then, the n-type GaAs layer 163a is changed to H_ThreePO_Four: H_TwoO_Two: H_TwoA trapezoidal n-type GaAs layer 163a as shown in FIG. 31 is formed by wet etching using an etching solution of 0 = 8: 1: 1.I do.
[0138]
After that, the SiO₂Is formed in a predetermined region on the exposed portion of the n-type Si substrate 161. This mask layer 162 is formed in a stripe shape having a thickness of about 10 nm to about 1000 nm and a period of about 5 μm. Note that the trapezoidal GaAs layer 163a is formed so as to be thinner than the mask layer 162.
[0139]
Thereafter, the n-type GaAs layer 163 is selectively grown on the trapezoidal n-type GaAs layer 163 and the mask layer 162 by using the mask layer 162 as a selective growth mask by MOCVD. BookreferenceIn the embodiment, the n-type GaAs layer 163 is formed with a thickness of about 2 μm under a temperature condition of about 600 ° C., for example. Thereby, an n-type GaAs layer 163 having a flat upper surface as shown in FIG. 32 is formed.Is done.
[0140]
Note that this1st referenceAlso in the embodiment, by forming the trapezoidal GaAs layer 163a, the side surface of the trapezoidal GaAs layer 163a gradually grows in the lateral direction from the initial growth stage, so that the lateral growth is promoted from the initial growth stage. This makes it easy for the vertical dislocations to be bent in the horizontal direction from the initial growth stage, so that the n-type GaAs layer 163 having a small thickness and reduced dislocations can be formed.
[0141]
Next, referring to FIG.1st referenceThe structure of a semiconductor laser device formed using the method for forming a semiconductor layer according to the embodiment will be described. this1st referenceIn the semiconductor laser device of the embodiment, a first conductive type layer 115a made of n-type GaAs, a first conductive type clad layer 116a made of n-type AlGaAs, and GaAs and AlGaAs are formed on the n-type GaAs layer 163 shown in FIG. An MQW light emitting layer 117a, a second conductivity type cladding layer 118a made of p-type AlGaAs, and a second conductivity type contact layer 119a made of p-type GaAs are formed. An n-type first conductivity type electrode 120 is formed on the back surface of the n-type Si substrate 161. A p-type second conductivity type electrode 121 is formed on the upper surface of the second conductivity type contact layer 119a.
[0142]
1st referenceIn the semiconductor laser device according to the embodiment, the layers 115a to 119a are formed on the low dislocation n-type GaAs layer 163 formed by using the forming method shown in FIGS. Crystallinity can be realized.
[0143]
It should be noted that the embodiments disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description of the embodiments, and includes all modifications within the scope and meaning equivalent to the terms of the claims.
[0144]
For example, in the above embodiments, the mask layers having various overhang shapes are shown, but the present invention is not limited to this, and the distance between the adjacent mask layers is larger than the width of the exposed portion of the base located between the adjacent mask layers. Any structure other than the above-described embodiment may be used as long as the shape also becomes smaller.
[0145]
In addition, the above first to firstTwelfth embodiment and first reference formAlthough an example in which a stripe-shaped mask layer is formed has been described, the present invention is not limited to this. For example, a hexagonal mask layer, a triangular mask layer, a mask layer having a hexagonal opening, a triangular mask layer, A mask layer having an opening may be used.
[0146]
In addition, the above first to firstTwelfth embodiment and first reference formThe material of the mask layer in is not limited to the above embodiment, and another material may be used. For example, SiO_x, TiO_x, ZrO_xAlternatively, a high melting point metal or the like can be considered.
[0147]
In addition, the above first to firstTwelfth embodiment and first reference formIn the above, the case where a semiconductor laser element is manufactured has been described. However, the present invention is not limited to this, and can be applied to a case where another semiconductor element such as a light emitting diode, a field effect transistor, a photodiode, or a solar cell is manufactured. .
[0148]
In addition, the tenth and eleventhEmbodiment and first referenceIn the embodiment, the case where the n-type GaAs layer (arsenide-based semiconductor layer) is grown has been described.Embodiment and first referenceThe formation method of the form includes a material other than the GaAs layer (a Group 2-6 semiconductor, a Group 3-5 semiconductor (including a system composed of nitrogen and a material other than nitrogen as Group 5), a Group 4-4 semiconductor, and a Group 4 semiconductor. The present invention is also applicable to the case where a semiconductor layer made of a semiconductor or the like is grown.
[0149]
Further, in the twelfth embodiment, the example in which the superlattice layer is formed as a layer having a composition different from that of GaN has been described. However, the present invention is not limited to this._XGa_1-XN (0 <X ≦ 1) or Ga having a thickness of about 0.1 μm_1-XIn_XA layer other than the superlattice layer such as N (0 <X ≦ 1) may be formed. Since the layers other than the superlattice layer have different lattice constants and elastic coefficients from GaN, strain can be generated between these layers and the GaN layer. Dislocation can be reduced by the interfacial stress due to this distortion. However, since the superlattice layer having a periodic structure has a greater effect of generating a strain than the above-described single-layered layer, the superlattice layer has a greater dislocation reduction effect.
[0150]
Further, in the twelfth embodiment, the case where the undoped GaN layer (nitride-based semiconductor layer) is grown has been described. However, the present invention is not limited to this. Materials other than nitride-based semiconductors (Group 2-6 semiconductors, Group 3-5 semiconductors (including systems made of nitrogen and materials other than nitrogen as Group 5), Group 4-4 semiconductors, Group 4 semiconductors, etc.); The present invention is also applicable to the case where a semiconductor layer made of a group 4-4 semiconductor, a group 4 semiconductor, etc.) is grown. For example, when a group III-V semiconductor other than a nitride-based semiconductor (GaAs-based semiconductor) is formed on a Si substrate, as a layer having a different composition, a group III-V semiconductor other than a nitride-based semiconductor (AlGaAs or GaInAs) is used. ) And their superlattices may be formed.
[0151]
【The invention's effect】
As described above, according to the present invention, a low dislocation semiconductor layer can be grown with a small thickness on a base.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining the concept of a method for forming a semiconductor layer according to the present invention.
FIG. 2 is a cross-sectional view for explaining the concept of the method for forming a semiconductor layer according to the present invention.
FIG. 3 is a cross-sectional view for explaining the concept of the method for forming a semiconductor layer according to the present invention.
FIG. 4 is a cross-sectional view for explaining the concept of the method for forming a semiconductor layer according to the present invention.
FIG. 5 is a cross-sectional view for explaining the concept of the method for forming a semiconductor layer of the present invention.
FIG. 6 is a sectional view illustrating the method for forming the nitride-based semiconductor layer according to the first embodiment of the present invention.
FIG. 7 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a nitride-based semiconductor layer according to the first embodiment shown in FIG. 6;
FIG. 8 is a cross-sectional view for explaining a method of forming a nitride-based semiconductor layer according to a second embodiment of the present invention.
FIG. 9 is a cross-sectional view showing a semiconductor laser device manufactured by using the nitride-based semiconductor layer forming method according to the second embodiment shown in FIG.
FIG. 10 is a sectional view for explaining a method for forming a nitride-based semiconductor layer according to a third embodiment of the present invention.
FIG.
FIG. 11 is a sectional view showing a semiconductor laser device manufactured by using the nitride-based semiconductor layer forming method according to the third embodiment shown in FIG. 10;
FIG. 12 is a cross-sectional view for explaining a method of forming a nitride-based semiconductor layer according to a fourth embodiment of the present invention.
FIG. 13 is a cross-sectional view showing a semiconductor laser device manufactured by using the nitride-based semiconductor layer forming method of the fourth embodiment shown in FIG.
FIG. 14 is a cross-sectional view for explaining a method of forming a nitride-based semiconductor layer according to a fifth embodiment of the present invention.
FIG. 15 is a cross-sectional view showing a semiconductor laser device manufactured by using the nitride-based semiconductor layer forming method of the fifth embodiment shown in FIG.
FIG. 16 is a cross-sectional view for explaining a method for forming a nitride-based semiconductor layer according to a sixth embodiment of the present invention.
FIG. 17 is a cross-sectional view of a semiconductor laser device manufactured by using the nitride-based semiconductor layer forming method of the sixth embodiment shown in FIG.
FIG. 18 is a cross-sectional view for explaining a method for forming a nitride-based semiconductor layer according to a seventh embodiment of the present invention.
FIG. 19 is a sectional view showing a semiconductor laser device manufactured by using the nitride-based semiconductor layer forming method according to the seventh embodiment shown in FIG. 18;
FIG. 20 is a sectional view illustrating the method of forming the nitride-based semiconductor layer according to the eighth embodiment of the present invention.
21 is manufactured by using the method for forming a nitride-based semiconductor layer according to the eighth embodiment shown in FIG. 20;
It is sectional drawing which showed the semiconductor laser element.
FIG. 22 is a sectional view illustrating the method of forming the nitride-based semiconductor layer according to the ninth embodiment of the present invention.
FIG. 23 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a nitride-based semiconductor layer of the ninth embodiment shown in FIG. 22;
FIG. 24 is a sectional view illustrating the method for forming the semiconductor layer according to the tenth embodiment of the present invention.
FIG. 25 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a semiconductor layer according to the tenth embodiment shown in FIG. 24;
FIG. 26 is a sectional view illustrating the method for forming the semiconductor layer according to the eleventh embodiment of the present invention.
FIG. 27 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a semiconductor layer of the eleventh embodiment shown in FIG. 26;
FIG. 28 is a cross-sectional view for explaining the method for forming the nitride-based semiconductor layer according to the twelfth embodiment of the present invention.
FIG. 29 is a sectional view showing a semiconductor laser device manufactured by using the method for forming a nitride-based semiconductor layer of the twelfth embodiment shown in FIG. 28;
FIG. 30 of the present invention.1st referenceFIG. 4 is a cross-sectional view for describing a method of forming a semiconductor layer according to an embodiment.
FIG. 31 of the present invention.1st referenceFIG. 4 is a cross-sectional view for describing a method of forming a semiconductor layer according to an embodiment.
FIG. 32 of the present invention.1st referenceFIG. 4 is a cross-sectional view for describing a method of forming a semiconductor layer according to an embodiment.
FIG. 331st referenceFIG. 4 is a cross-sectional view showing a semiconductor laser device manufactured by using the method of forming a semiconductor layer according to the embodiment.
FIG. 34 is a cross-sectional view illustrating an example of a conventional method for forming a nitride-based semiconductor layer using selective lateral growth.
FIG. 35 is a cross-sectional view illustrating an example of a conventional method for forming a nitride-based semiconductor layer using selective lateral growth.
FIG. 36 is a cross-sectional view illustrating an example of a conventional method for forming a nitride-based semiconductor layer using selective lateral growth.
FIG. 37 is a cross-sectional view illustrating an example of a conventional method for forming a nitride-based semiconductor layer using selective lateral growth.
FIG. 38 is a cross-sectional view for explaining a method of forming a nitride-based semiconductor layer directly on a substrate by using conventional selective lateral growth.
FIG. 39 is a cross-sectional view for describing a conventional method of forming a nitride-based semiconductor layer made of a mixed crystal.

Claims (20)

A step of forming a plurality of mask layers at predetermined intervals so as to contact the upper surface of the base and expose a part of the base,
Forming a trapezoidal first semiconductor layer on the upper surface of the base exposed between the mask layers at a position lower than the upper surface of the mask layer and having a width of the upper surface smaller than the lower surface;
Growing a second semiconductor layer on the first semiconductor layer and the mask layer,
Prior to the step of growing the second semiconductor layer, a step of forming a third semiconductor layer including at least one layer having a different composition from the first semiconductor layer on the first semiconductor layer . A method for forming a semiconductor layer. Forming a superlattice layer having a periodic structure in which layers having different lattice constants are alternately stacked as the third semiconductor layer on the first semiconductor layer prior to the step of growing the second semiconductor layer. The method for forming a semiconductor layer according to claim 1, further comprising : Prior to the step of forming the first semiconductor layer, the method further includes the step of forming a buffer layer on an upper surface of a base exposed between the mask layers,
The thickness of the buffer layer located in the vicinity of the mask layer on the upper surface of the exposed base is smaller than the thickness of the buffer layer located in the center on the upper surface of the exposed base. Or the method for forming a semiconductor layer according to 2 . A step of forming a plurality of mask layers at predetermined intervals so as to contact the upper surface of the base and expose a part of the base,
Forming a trapezoidal first semiconductor layer on the upper surface of the base exposed between the mask layers at a position lower than the upper surface of the mask layer and having a width of the upper surface smaller than the lower surface;
Growing a second semiconductor layer on the first semiconductor layer and on the mask layer;
Prior to the step of forming the first semiconductor layer, a step of forming a buffer layer on an upper surface of a base exposed between the mask layers,
A semiconductor layer that is formed at substantially the same thickness in a central portion on the upper surface of the underlayer exposed between the mask layers and that is not formed near the mask layer on the exposed upper surface of the underlayer; Formation method. A step of forming a plurality of mask layers at predetermined intervals so as to contact the upper surface of the base and expose a part of the base,
Forming a trapezoidal first semiconductor layer on the upper surface of the base exposed between the mask layers at a position lower than the upper surface of the mask layer and having a width of the upper surface smaller than the lower surface;
Growing a second semiconductor layer on the first semiconductor layer and on the mask layer;
Forming a third semiconductor layer including at least one layer having a different composition from the first semiconductor layer on the first semiconductor layer, prior to the step of growing the second semiconductor layer,
A method for forming a semiconductor layer , wherein a shortest distance between the adjacent mask layers is smaller than a width of an exposed portion of the base located between the adjacent mask layers . The method for forming a semiconductor layer according to claim 5, wherein the mask layer has an overhang portion protruding above the exposed portion of the base . The method of claim 6, wherein a thickness of the buffer layer located below the overhang portion of the mask layer is smaller than a thickness of the buffer layer located below a shortest distance portion between the adjacent mask layers . 8. The semiconductor layer according to claim 7, wherein the thickness of the buffer layer located below the overhang portion of the mask layer decreases at substantially the same rate as the distance from the shortest distance portion between the adjacent mask layers increases. Forming method. The buffer layer is formed with substantially the same thickness on the center of the upper surface of the base exposed between the mask layers, and is not formed on the upper surface of the base located below the overhang portion of the mask layer. A method for forming a semiconductor layer according to claim 8 . The method for forming a semiconductor layer according to claim 6, wherein at least a part of the mask layer has an inverted trapezoidal shape . It said first semiconductor layer width of the upper surface is smaller trapezoidal than the lower surface is formed with a thickness smaller than the thickness of the mask layer, forming a semiconductor layer according to any one of claims 1 to 10 . The step of growing the second semiconductor layer includes:
Forming a second semiconductor layer having a substantially planar upper surface on said first semiconductor layer and said mask layer by further growing said trapezoidal first semiconductor layer. 12. The method for forming a semiconductor layer according to any one of 1 to 11 . The semiconductor layer according to claim 1, wherein a dislocation density of the first semiconductor layer near an upper surface of the mask layer is lower than a dislocation density of the first semiconductor layer near an upper surface of the underlayer. Formation method. 14. The method of forming a semiconductor layer according to claim 13, wherein a dislocation density of the first semiconductor layer near an upper surface of the mask layer is equal to or less than a half of a dislocation density of the first semiconductor layer near an upper surface of the base. . The method of forming a semiconductor layer according to claim 1, wherein the first semiconductor layer and the second semiconductor layer include a nitride-based semiconductor layer . The underlayer includes a substrate,
The method for forming a semiconductor layer according to claim 1, wherein the mask layer is formed so as to contact an upper surface of the substrate . 17. The formation of a semiconductor layer according to claim 16, wherein the substrate includes one substrate selected from the group consisting of a group III-V semiconductor substrate, a group IV semiconductor substrate, a sapphire substrate, a spinel substrate, a SiC substrate, and a quartz substrate. Method. The method of forming a semiconductor layer according to claim 1, further comprising a semiconductor element layer formed on the second semiconductor layer and having an element region . A plurality of mask layers formed at predetermined intervals so as to contact the upper surface of the base and to expose a part of the base,
A trapezoidal first semiconductor layer formed at a position lower than the upper surface of the mask layer and having a smaller upper surface width than the lower surface, on the upper surface of the base exposed between the mask layers;
A third semiconductor layer formed on a surface of the first semiconductor layer and including at least one layer having a composition different from that of the first semiconductor layer;
A semiconductor device comprising: a third semiconductor layer formed on the third semiconductor layer and the mask layer. 20. The semiconductor device according to claim 19, wherein the third semiconductor layer includes a superlattice layer having a periodic structure in which layers having different lattice constants are alternately stacked .

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