JP5149093B2 - GaN substrate and manufacturing method thereof, nitride semiconductor device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a GaN substrate and a manufacturing method thereof, and a nitride semiconductor device and a manufacturing method thereof.

  In recent years, gallium nitride (GaN) has attracted attention as a substrate material for light-emitting devices. The GaN substrate is formed, for example, by growing a GaN single crystal layer on a semiconductor single crystal substrate such as a gallium arsenide (GaAs) substrate and then removing the GaAs substrate. Then, an GaN substrate is completed by growing an epitaxial layer on the substrate.

Conventionally, a homoepitaxial layer made of GaN having the same composition as the substrate has been grown as such an epitaxial layer. This is because by growing such a homoepitaxial layer, defects such as threading dislocations can be reduced. In particular, in a laser element made of a GaN-based semiconductor, a threading dislocation affects the lifetime of the element, and thus a homoepitaxial layer is required. In addition, as a well-known technique of a GaN substrate, there exist the following patent documents 1 and 2.
JP 2001-102307 A JP 2000-340509 A

  However, the conventional GaN substrate manufactured in this way has the following problems. That is, there is a problem that the GaN homoepitaxial layer does not grow normally on the substrate while the surface of the substrate is contaminated. This will be described with reference to FIG. 13. When a GaN homoepitaxial layer 42 is grown on a GaN single crystal substrate 40 to produce a GaN substrate 44, in a partial region 40 b of the surface 40 a of the substrate 40, The GaN homoepitaxial layer 42 does not grow normally, and a recess is formed in that portion. As a result, the flatness of the surface of the GaN substrate 44 is significantly impaired. One reason for the occurrence of such a situation is that the contaminants adhering to the substrate surface 40a remained on the substrate 40 until the GaN homoepitaxial layer 42 was grown when the substrate 40 was manufactured. I thought it was.

  Further, the inventors have found that as another cause, the crystal quality of the surface of the defect concentration region formed when the substrate 40 is manufactured is not sufficient. This will be described with reference to FIGS. 14 (a) to 14 (d). As shown in FIG. 14A, the substrate 40 made of GaN single crystal often includes a plurality of defect concentration regions 40c having a defect density higher than that of the surrounding low defect regions and extending in the thickness direction. When the GaN homoepitaxial layer 42 is grown on the surface 40a of the substrate 40, as shown in FIG. 14B, the GaN homoepitaxial layer 42 grows mainly in a portion other than the surface of the defect concentration region 40c. Then, as shown in FIG. 14C, as a result of incomplete growth of the GaN homoepitaxial layer 42 on the defect concentration region 40c, as shown in FIG. 14D, the GaN homoepitaxial region on the defect concentration region 40c. A depression (pit 42a) is formed on the surface of the epitaxial layer 42. Therefore, the flatness of the surface of the GaN substrate 44 is significantly impaired. The inventors found a technique capable of avoiding the above-described situation after intensive research.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a GaN substrate whose surface is flattened, a manufacturing method thereof, a nitride semiconductor device, and a manufacturing method thereof.

The GaN substrate according to the present invention has a defect concentration region in which the defect density is higher than that of the surrounding low defect region and is distributed in the form of dots on the main surface, and a substrate made of GaN and Al epitaxially grown on the main surface of the substrate. It is characterized by comprising an intermediate layer made of _x Ga _1-x N (0 <x ≦ 1) and an upper layer made of GaN epitaxially grown on the intermediate layer. Alternatively, the GaN substrate according to the present invention includes a substrate made of a GaN single crystal, an intermediate layer made of Al _x Ga _1-x N (0 <x ≦ 1) and epitaxially grown on the intermediate layer. And an upper layer made of GaN.

  In the GaN substrate, an intermediate layer is interposed between the substrate and the upper layer. The intermediate layer is made of AlGaN, and it has been found by the inventors that the AlGaN grows over the entire surface of the substrate including a region to which contaminants adhere and a defect concentration region. Therefore, the intermediate layer is normally grown on the substrate, and the growth surface (that is, the upper surface) is flat. Thus, since the growth surface of the intermediate layer is flat, the growth surface of the upper layer epitaxially grown on the intermediate layer is also flat.

In the GaN substrate, the density of defect concentration regions on the main surface of the substrate may be 100 [pieces / cm ² ] or more. Thus, even when the density of defect concentration regions is relatively high, the growth surface of the intermediate layer and the upper layer can be flattened according to the GaN substrate.

  The intermediate layer preferably has n-type or p-type conductivity by adding a dopant. In this case, since the specific resistance of the intermediate layer is reduced, when a vertical device such as a light emitting diode (LED) or a heterojunction bipolar transistor (HBT) is manufactured using a GaN substrate, the device characteristics are improved. .

The intermediate layer has a superlattice structure including a second intermediate layer made of Al _y Ga _1-y N (0 ≦ y ≦ 1, y ≠ x) having a composition different from that of Al _x Ga _1-x N. Preferably there is. In this case, since the propagation of threading dislocations in the GaN substrate is prevented by the superlattice structure, the GaN substrate has good crystallinity.

The GaN substrate preferably further includes an In _z Ga _1-z N (0 <z ≦ 1) epitaxial layer sandwiched between the intermediate layers. In this case, the GaN substrate can be further planarized by the In _z Ga _1-z N (0 <z ≦ 1) epitaxial layer sandwiched between the intermediate layers.

The intermediate layer preferably having a thickness of (-5x + 1.2) μm of less than _{Al x Ga 1-x N (} 0 <x <0.24). By forming the intermediate layer with such a thickness, generation of defects such as cracks in the intermediate layer can be suppressed.

The method for manufacturing a GaN substrate according to the present invention has a defect concentration region having a defect density higher than that of the surrounding low defect region and distributed in a dotted manner on the main surface, and Al _x Ga _{1 is formed} on the main surface of the substrate made of GaN. An intermediate layer forming step of epitaxially growing an intermediate layer made of _-xN (0 <x≤1) and an upper layer forming step of epitaxially growing an upper layer made of GaN on the intermediate layer are characterized. Alternatively, the method for manufacturing a GaN substrate according to the present invention includes an intermediate layer forming step of epitaxially growing an intermediate layer made of Al _x Ga _1-x N (0 <x ≦ 1) on a substrate made of a GaN single crystal, And an upper layer forming step of epitaxially growing an upper layer made of GaN on the layer.

  In the method of manufacturing the GaN substrate, an intermediate layer made of AlGaN is laminated on the substrate before the upper layer made of GaN is laminated on the substrate. It has been found by the inventors that AlGaN constituting the intermediate layer grows over the entire surface of the substrate including a region to which contaminants adhere and a defect concentration region. Therefore, the growth surface (that is, the upper surface) of the intermediate layer laminated on the substrate is flat. The upper growth surface on which the growth surface is epitaxially grown on the flat intermediate layer is also flat.

In the GaN substrate manufacturing method, the density of defect concentration regions on the main surface of the substrate may be 100 [pieces / cm ² ] or more. Thus, even when the density of the defect concentration region is relatively high, the growth surface of the intermediate layer and the upper layer can be flattened according to the method of manufacturing the GaN substrate.

  Further, it is preferable to add a dopant during the intermediate layer forming step to make the intermediate layer n-type or p-type. In this case, since the specific resistance of the intermediate layer is reduced, when a vertical device such as a light emitting diode (LED) or a heterojunction bipolar transistor (HBT) is manufactured using a GaN substrate, the device characteristics are improved. .

Further, it is made of Al _y Ga _1-y N (0 ≦ y ≦ 1, y ≠ x) having a composition different from that of Al _x Ga _1-x N, which interrupts the intermediate layer forming step and is sandwiched between the intermediate layers. It is preferable to further include a second intermediate layer forming step for forming a second intermediate layer, and to form a superlattice structure with the intermediate layer and the second intermediate layer. In this case, since the formed superlattice structure prevents the propagation of threading dislocations in the GaN substrate, a GaN substrate having good crystallinity is produced.

It is preferable to further include an InGaN epitaxial layer forming step of interrupting the intermediate layer forming step and forming an In _z Ga _1-z N (0 <z ≦ 1) epitaxial layer so as to be sandwiched between the intermediate layers. In this case, the GaN substrate can be further planarized by the In _z Ga _1-z N (0 <z ≦ 1) epitaxial layer sandwiched between the intermediate layers.

Further, in the method for manufacturing a GaN substrate, the intermediate layer made of Al _x Ga _1-x N (0 <x <0.24) is made less than (−5x + 1.2) μm in the intermediate layer forming step. It is preferable to grow it. By forming the intermediate layer with such a thickness, generation of defects such as cracks in the intermediate layer can be suppressed.

  Moreover, in the manufacturing method of a GaN substrate, it is preferable to grow an intermediate | middle layer and an upper layer under the pressure of 80 kPa or more. Since AlGaN grows over the entire surface of the substrate including the area where the contaminant is attached and the surface of the defect concentration area, even if the intermediate layer is grown under a relatively high pressure of 80 kPa or more, the growth surface of the intermediate layer (that is, , The upper surface) can be made flat. Therefore, the intermediate layer and the upper layer having good crystallinity can be obtained by growing the intermediate layer and the upper layer under a relatively high pressure.

The nitride semiconductor device according to the present invention has a defect concentration region in which the defect density is higher than that of the surrounding low defect region and is distributed in the form of dots on the main surface, and is epitaxially grown on the substrate made of GaN and the main surface of the substrate. , Al _x Ga _1-x N (0 <x ≦ 1), and an n-type nitride semiconductor region and a p-type nitride semiconductor region provided on the intermediate layer.

  In the nitride semiconductor device, an intermediate layer is provided on the substrate. The inventors have found that AlGaN can grow over the entire surface of the substrate including the area where contaminants are attached and the defect concentration area. Since the intermediate layer includes an AlGaN layer epitaxially grown on the substrate, the intermediate layer normally grows on the substrate, and its growth surface (that is, the upper surface) becomes flat. Since the growth surface of the intermediate layer is flat in this way, the flatness of the interface between the n-type nitride semiconductor region and the p-type nitride semiconductor region formed on the intermediate layer is improved, and the device of the nitride semiconductor element Characteristics (for example, light emission amount) are improved.

In the nitride semiconductor device, the density of defect concentration regions on the main surface of the substrate may be 100 [pieces / cm ² ] or more. Thus, even when the density of the defect concentration region is relatively high, according to the nitride semiconductor, the growth surface of the intermediate layer, the n-type nitride semiconductor region, and the p-type nitride semiconductor region can be flattened. it can.

  In the nitride semiconductor device, the n-type nitride semiconductor region or the p-type nitride semiconductor region preferably includes an upper layer made of GaN epitaxially grown on the intermediate layer. In this case, even if there are minute irregularities due to processing etc. on the surface of the substrate and these irregularities appear on the surface of the intermediate layer, the growth surface is flattened by epitaxially growing the upper layer on the intermediate layer. it can. Accordingly, the crystallinity of the n-type nitride semiconductor region and the p-type nitride semiconductor region excluding the upper layer is improved, so that the device characteristics are further improved.

  The nitride semiconductor device further includes a light emitting layer between the n-type nitride semiconductor region and the p-type nitride semiconductor region, and each of the n-type nitride semiconductor region and the p-type nitride semiconductor region is a cladding layer. It is preferable to contain. In this case, since the flatness of the interface between the n-type and p-type clad layers and the light emitting layer laminated on the substrate having a flat growth surface is improved, the light emitting characteristics of the device are improved.

  In the nitride semiconductor, the light emitting region in the light emitting layer preferably extends over at least a part of the defect concentration region. According to the nitride semiconductor, since the interface of the light emitting layer can be flat regardless of the position of the defect concentration region, the crystallinity in the light emission region can be improved even when the light emission region extends over the defect concentration region. .

  In the nitride semiconductor device, the intermediate layer preferably has n-type or p-type conductivity by adding a dopant. In this case, since the specific resistance of the intermediate layer is reduced, the device characteristics of the nitride semiconductor element are further improved.

In the nitride semiconductor device, the intermediate layer may be Al _y Ga _1-y N (0 ≦ y ≦ 1, different in composition from the Al _x Ga _1-x N layer and the Al _x Ga _1-x N layer. It is preferable to have a superlattice structure in which y ≠ x) layers are alternately stacked. In this case, since the propagation of threading dislocations in the intermediate layer is prevented by the superlattice structure, an n-type nitride semiconductor region and a p-type nitride semiconductor region having good crystallinity are formed.

The nitride semiconductor element preferably further includes an In _z Ga _1-z N (0 <z ≦ 1) epitaxial layer sandwiched between the intermediate layers. In this case, the intermediate layer can be further planarized by the In _z Ga _1-z N (0 <z ≦ 1) epitaxial layer sandwiched between the intermediate layers.

In the nitride semiconductor device, the intermediate layer is preferably made of Al _x Ga _1-x N (0 <x <0.24) having a thickness of less than (−5x + 1.2) μm. By forming the intermediate layer with such a thickness, generation of defects such as cracks in the intermediate layer can be suppressed.

The method for manufacturing a nitride semiconductor device according to the present invention has a defect concentration region having a defect density higher than that of a surrounding low defect region and distributed in a dotted manner on the main surface, and Al _{x is formed} on the main surface of the substrate made of GaN. An intermediate layer forming step of epitaxially growing an intermediate layer made of Ga _1-x N (0 <x ≦ 1), and a semiconductor region forming step of forming an n-type nitride semiconductor region and a p-type nitride semiconductor region on the intermediate layer Each of the intermediate layer, the n-type nitride semiconductor region, and the p-type nitride semiconductor region is grown under a pressure of 80 kPa or more.

  In the nitride semiconductor device manufacturing method, an intermediate layer including an AlGaN layer is stacked on a substrate. Since AlGaN grows over the entire surface of the substrate including the area where the contaminant is attached and the defect concentration area, even if the intermediate layer is grown under a relatively high pressure of 80 kPa or more, the growth surface of the intermediate layer (that is, , The upper surface) can be made flat. Therefore, by growing each layer under such a relatively high pressure, an intermediate layer, an n-type nitride semiconductor region, and a p-type nitride semiconductor region with good crystallinity are obtained, and the device characteristics of the nitride semiconductor device Will improve.

In the method for manufacturing a nitride semiconductor device, the density of defect concentration regions on the main surface of the substrate may be 100 [pieces / cm ² ] or more. Thus, even when the density of the defect concentration region is relatively high, according to the nitride semiconductor device manufacturing method, the growth surface of the intermediate layer, the n-type nitride semiconductor region, and the p-type nitride semiconductor region is flat. Can be.

In the method for manufacturing a nitride semiconductor device, the intermediate layer made of Al _x Ga _1-x N (0 <x <0.24) has a thickness (−5x + 1.2) during the intermediate layer forming step. It is preferable to grow to less than μm. By forming the intermediate layer with such a thickness, generation of defects such as cracks in the intermediate layer can be suppressed.

  According to the present invention, there are provided a GaN substrate having a planarized surface and a manufacturing method thereof, and a nitride semiconductor device and a manufacturing method thereof.

  Hereinafter, embodiments of a GaN substrate and a manufacturing method thereof, and a nitride semiconductor device and a manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
FIG. 1 is a view showing a vapor phase growth apparatus used for producing a GaN substrate according to the first embodiment of the present invention. The vapor phase growth apparatus 10 is a so-called horizontal MOCVD apparatus having a flow channel 12 made of quartz in which gas flow paths are formed in a horizontal direction. The substrate 14 used for producing the GaN substrate is installed in a tray 20 on a susceptor 18 having a heater 16, and the susceptor 18 supports the substrate 14 rotatably.

  The flow channel 12 includes an upstream flow channel 12A, an intermediate flow channel 12B, and a downstream flow channel 12C. The gas necessary for manufacturing the GaN crystal is introduced from the three-layer nozzle 22 of the upstream flow channel 12A and mixed immediately before the substrate 14 in the intermediate flow channel 12B. Residual gas generated by the reaction on the substrate 14 is exhausted from the downstream flow channel 12C.

A gas containing trimethylgallium (TMG), trimethylaluminum (TMA), or trimethylindium (TMI) as a group III source gas and a gas containing NH ₃ as a group V source gas are appropriately supplied from the nozzle 22 onto the substrate 14. In addition, a gas containing monosilane (SiH ₄ ) is supplied as the n-type doping gas, and a gas containing cyclopentadienyl magnesium (Cp ₂ Mg) is supplied as the p-type doping gas. As the carrier gas, hydrogen gas (H ₂ gas), nitrogen gas (N ₂ gas), a mixed gas of H ₂ gas and N ₂ gas, or the like is used. A switching valve (not shown) is arranged between the nozzle 22 and a plurality of lines for supplying each group III source gas to the nozzle 22, and each flow rate of the group III source gas is controlled by this switching valve. Is adjusted. Specifically, the switching valve appropriately distributes the group III source gas sent from the line to a main line that is sent to the nozzle 22 and a dummy line for exhaust, and shuts off each group III source gas and stabilizes the flow rate. Plan

  Next, the substrate 14 used in this embodiment will be described. FIG. 2A is a plan view showing a part of the substrate 14. FIG. 2B is a cross-sectional view showing a II cross section of the substrate 14 shown in FIG. The substrate 14 is formed by a known technique in which a mask layer having a plurality of opening windows is formed on a GaAs substrate and GaN is laterally grown from the opening windows. In addition, after the lateral growth, the GaAs substrate is etched away in aqua regia, and the front and back surfaces 14a and 14b of the substrate 14 are mechanically polished.

The substrate 14 has a plurality of defect concentration regions 14c extending in the thickness direction. The defect concentration region 14 c has a defect density that is 10 times or more higher than that of the surrounding low defect region 14 d, for example, and is distributed in the form of dots on the main surface 14 a of the substrate 14. The defect concentration region 14c is a portion formed by gathering defects such as dislocations inside the GaN by forming concave portions (pits) made of, for example, a plurality of facets on the GaN surface when the GaN is laterally grown. In the present embodiment, the defect concentration regions 14 c may be irregularly (randomly) arranged on the substrate 14. The density of the defect concentration region 14c in the main surface 14a of the substrate 14 is, for example, 100 [pieces / cm ² ] or more and 1 × 10 ⁵ [pieces / cm ² ] or less. Further, the ratio of the surface area of the defect concentration region 14c to the area of the main surface 14a of the substrate 14 is, for example, 1% or less. The dislocation density in the defect concentration region 14c is, for example, 3 × 10 ⁷ cm ⁻² or less, and the dislocation density in the low defect region 14d is, for example, 5 × 10 ⁶ cm ⁻² or less.

  Next, a procedure for producing the GaN substrate according to the present embodiment will be described with reference to FIG. 3A to 3C are diagrams showing a procedure for manufacturing a GaN substrate.

First, the wafer-like substrate 14 made of GaN single crystal is placed on the tray 20 on the susceptor 18 in the flow channel 12 so that the upper surface (main surface) 14a becomes the (0001) surface (FIG. 3A). reference). Prior to this epitaxial growth on the substrate 14, a mixed gas containing NH ₃ gas is introduced from the nozzle 22 to make the inside of the flow channel 12 a mixed gas atmosphere containing NH ₃ gas. And the susceptor 18 and the board | substrate 12 are heated to about 1100 degreeC with the heater 16, and the cleaning process (thermal cleaning) of the main surface 14a of the board | substrate 14 is performed. Specifically, NH ₃ was flowed at 5 slm and H ₂ was flowed at 6 slm. By performing thermal cleaning under such appropriate conditions, contaminants on the substrate surface (main surface) 14a are removed and the flatness of the substrate surface 14a is improved.

Next, in a state where the temperature of the substrate 14 (substrate temperature) is maintained at 1100 ° C. and the pressure in the intermediate flow channel is maintained at 80 kPa or more, the group III source gas, the group V source gas, and the doping gas are combined with the above carrier gas. , And supplied onto the substrate 14 from the nozzle 22. More specifically, TMG is supplied at a condition of 24.42 μmol / min and TMA at a condition of 2.02 μmol / min for 23 minutes, and NH ₃ is supplied at 6 slm and H ₂ is supplied at 8 slm. Thereby, the intermediate layer 24 made of Al _x Ga _1-x N (x = 0.08) having a film thickness of 200 nm is grown on the substrate 14 (see the intermediate layer forming step, FIG. 3B). The Al composition ratio x may be in the range of 0 <x ≦ 1. The thickness of the intermediate layer 24 can be appropriately selected from a thickness of 10 nm or more and 500 nm or less by changing the growth conditions of the intermediate layer, but if it is thicker than this, there is a high possibility that defects such as cracks will occur. As shown in Examples described later, the present inventors have a thickness of the intermediate layer 24 of less than (−5x + 1.2) μm when the Al composition ratio is in the range of 0 <x <0.24. It has been found that defects such as cracks can be suppressed if present.

  Thus, the intermediate layer 24 made of AlGaN grows on the substrate 14 made of GaN single crystal, and the growth occurs over the entire substrate surface 14a including the surface of the defect concentration region 14c (see FIG. 2). On the other hand, when a layer made of GaN is directly grown on the substrate 14, in some regions of the substrate surface 14a such as the surface of the defect concentration region 14c, a recess is generated without normal epitaxial growth (see FIGS. 13 and 14). ), The flatness of the surface of the GaN substrate is significantly impaired.

The inventors found that such a situation occurs because contaminants are attached to the substrate surface 14a during the production of the substrate 14, or because the crystal quality of the surface of the defect concentration region 14c is not sufficient. As a result of intensive research, it was found that it is effective to stack a layer made of AlGaN (intermediate layer 24) on the substrate 14. That is, the intermediate layer 24 grows over the entire region including the substrate surface region to which the contaminant is attached and the surface region of the defect concentration region 14c, and the surface 24a becomes flat and has a good morphology. The intermediate layer 24 contains carbon during the formation process, but the carbon concentration is low, which is about 1 × 10 ¹⁸ cm ⁻³ or less.

  After forming the intermediate layer 24 on the substrate 14, the substrate temperature is raised to 1150 ° C., and the upper layer 26 made of GaN is epitaxially grown under a pressure of 80 kPa or more (upper layer forming step) to form a GaN epitaxial wafer. The production of a certain GaN substrate 28 is completed (see FIG. 3C). As described above, since the surface 24a of the intermediate layer 24 is flat, the surface 26a of the upper layer 26 that is epitaxially grown with good crystallinity on the intermediate layer 24 (that is, the surface of the GaN substrate 28) is also flat. Yes.

  When manufacturing a light emitting device using the GaN substrate 28, an electrode 30 is further formed on the lower surface (back surface) 14 b of the substrate 14 and the upper surface 26 a of the upper layer 26.

As described above, in the GaN substrate 28, the intermediate layer 24 is interposed between the substrate 14 and the upper layer 26. The intermediate layer 24 is made of Al _x Ga _1-x N (0 <x ≦ 1, in this embodiment, x = 0.08), and this AlGaN covers the surface where the contaminant is attached and the surface of the defect concentration region 14c. The substrate is epitaxially grown over the entire area of the substrate surface 14a. Therefore, the intermediate layer 24 grows normally on the substrate 14 and its growth surface 24a is flat. Since the growth surface 24a of the intermediate layer 24 is thus flat, the growth surface 26a of the upper layer 26 epitaxially grown on the intermediate layer 24 is also flat.

When the intermediate layer 24 is made conductive to reduce the specific resistance of the intermediate layer 24, 2.5 sccm of SiH ₄ diluted to 10 ppm with H ₂ is used as a dopant during the formation process of the intermediate layer 24. By flowing under the conditions, an n-type intermediate layer having a carrier concentration of 5 × 10 ¹⁸ cm ⁻³ can be obtained. Further, in the process of forming the intermediate layer 24, a p-type intermediate layer having a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ is formed by supplying Cp ₂ Mg as a dopant at a condition of 0.0539 μmol / min. Can do. In this case, it is necessary to separately activate the intermediate layer 24 in order to increase the p-type carrier concentration. When the GaN substrate 28 has such an intermediate layer 24 in which the specific resistance is reduced, when a vertical device such as an LED or an HBT is manufactured using the GaN substrate 28, the device characteristics thereof are improves.

  The intermediate layer 24 and the upper layer 26 are preferably grown under a pressure of 80 kPa or more as in the present embodiment. Since AlGaN can grow over the entire surface 14a of the substrate 14 including the region where the contaminant is attached, even if the intermediate layer 24 is grown under a relatively high pressure of 80 kPa or more, the growth surface 24a of the intermediate layer 24 can be formed. Can be flat. Therefore, the intermediate layer 24 and the upper layer 26 with good crystallinity can be obtained by growing the intermediate layer 24 and the upper layer 26 under such a relatively high pressure.

Further, as described above, the density of the defect concentration region 14c on the main surface 14a of the substrate 14 may be 100 [pieces / cm ² ] or more. Thus, even when the density of the defect concentration region 14c is relatively high, the growth surfaces of the intermediate layer 24 and the upper layer 26 can be flattened according to the GaN substrate 28 and the manufacturing method thereof of the present embodiment.

  Next, a GaN substrate having a mode different from the above-described GaN substrate and a manufacturing method thereof will be described with reference to FIG. FIGS. 4A to 4E are diagrams showing a procedure for manufacturing a GaN substrate.

First, the intermediate layer 24 is laminated on the substrate 14 by the same method as the method for manufacturing the GaN substrate 28 described above. That is, after the substrate 14 is installed on the tray 20 of the apparatus 10 so that the upper surface (main surface) 14a becomes the (0001) surface and subjected to a cleaning process (see FIG. 4A), the above-described conditions are satisfied. TMG and TMA are supplied and NH ₃ and H ₂ are supplied under the same or equivalent predetermined conditions. Thereby, an intermediate layer 24A made of Al _x Ga _1-x N (x = 0.16) having a thickness of about several nm is grown on the substrate 14 (see FIG. 4B).

Next, the switching valve located upstream of the nozzle 22 is operated to cut off only the supply of TMA onto the substrate 14 without changing other conditions. Thus, an epitaxial thin film (second intermediate layer) 32 made of GaN (that is, Al _y Ga _1-y N (y = 0)) and having a film thickness of about several nm is stacked on the intermediate layer 24A ( (Refer FIG.4 (c)). Then, by operating such a switching valve, the intermediate layer 24A and the epitaxial thin film 32 are alternately stacked on the epitaxial thin film 32 to form a five-layer superlattice structure (see FIG. 4D). Finally, the upper layer 26 is epitaxially grown on the uppermost intermediate layer 24A, thereby completing the production of the GaN substrate 28A having a mode different from the GaN substrate 28 described above (see FIG. 4E).

Between the intermediate layer 24A, an epitaxial thin film 32 made of Al _y Ga _1-y N (0 ≦ y ≦ 1) having a composition different from that of the intermediate layer 24A is provided, and the intermediate layer 24A and the epitaxial thin film 32 have a superlattice structure. In the GaN substrate 28A on which the (strained superlattice structure) is formed, the propagation of threading dislocations from the substrate 14 is prevented by the superlattice structure. Thereby, the dislocation density in the GaN substrate 28A is reduced and the crystallinity of the GaN substrate 28A is improved, so that it can be used for manufacturing a high-quality device. The material of the epitaxial thin film 32 is not limited to GaN, and a composition of Al _y Ga _1-y N (0 ≦ y ≦ 1) different from the composition of the intermediate layer 24A can be selected as appropriate. Further, the superlattice structure composed of the intermediate layer 24A and the epitaxial thin film 32 is not limited to five layers, and the number of layers may be appropriately increased or decreased.

  Next, a GaN substrate having a mode different from the above-described GaN substrate and a manufacturing method thereof will be described with reference to FIG. FIGS. 5A to 5E are views showing a procedure for producing a GaN substrate.

First, the intermediate layer 24 is laminated on the substrate 14 by the same method as the method for manufacturing the GaN substrate 28 described above. That is, after the substrate 14 is placed on the tray 20 of the apparatus 10 so that the upper surface 14a becomes the (0001) surface and subjected to a cleaning process (see FIG. 5A), TMG is 24.42 μmol / min. , TMA is supplied at a condition of 2.02 μmol / min, a substrate temperature of 1100 ° C. and a pressure of 80 kPa or higher for 11.5 minutes, and NH ₃ is supplied at 6 slm and H ₂ is supplied at 8 slm. Thereby, an intermediate layer 24B made of Al _x Ga _1-x N (X = 0.08) having a film thickness of 100 nm is grown on the substrate 14 (see FIG. 5B).

Here, the epitaxial growth on the substrate 14 may result in abnormal growth as shown in FIG. 5B due to various factors even when the material of the layer to be stacked is AlGaN. is there. Therefore, on the intermediate layer 24B, TMG is supplied at 24.42 μmol / min, TMI at 11.16 μmol / min, a substrate temperature of 830 ° C. and a pressure of 80 kPa or more for 5 minutes, NH ₃ is 6 slm, and H ₂ is 8 slm. Then, an InGaN epitaxial layer 34 made of In _z Ga _1-z N (z = 0.10) having a film thickness of 50 nm is grown on the intermediate layer 24B (see FIG. 5C). In this case, the substrate surface 14a is heavily contaminated, or the crystal quality on the surface of the defect concentration region 14c (see FIG. 2) is extremely low, so that the intermediate layer 24B grows abnormally and cannot be sufficiently flattened. Even if it exists, the inventors newly discovered that the planarization of the growth surface 34a is complemented by growing the layer which consists of InGaN on the intermediate | middle layer 24B.

  After the InGaN epitaxial layer 34 having a flat upper surface 34a is grown, an intermediate layer 24C is grown thereon under the same conditions as the intermediate layer 24B (see FIG. 5D), and under the same conditions as the upper layer described above. The upper layer 26 is epitaxially grown to complete the production of the GaN substrate 28B (see FIG. 5E). In addition, by laminating the intermediate layer 24C on the InGaN epitaxial layer 34, it is possible to avoid a situation where the InGaN constituting the InGaN epitaxial layer 34 is decomposed when the substrate temperature is increased to form the upper layer 26.

  As described above, in this GaN substrate 28B having the InGaN epitaxial layer 34 between the intermediate layers 24B and 24C, even if the intermediate layer 24B grows abnormally and sufficient surface flattening cannot be achieved, The upper surface 26a of the GaN substrate 28B becomes flat. Note that the above-described superlattice structure can be formed by modulating the Al concentration of the intermediate layers 24B and 24C and the In concentration of the InGaN epitaxial layer 34 at the time of layer formation. If necessary, a GaN thin film may be interposed between the intermediate layers 24B and 24C and the InGaN epitaxial layer 34.

(Second Embodiment)
Next, a nitride semiconductor device and a method for manufacturing the same according to a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a side cross-sectional view showing the configuration of the light emitting element 1A as the nitride semiconductor element according to this embodiment. In the present embodiment, a blue LED is exemplified as the light emitting element 1A.

  The light emitting element 1A includes a conductive substrate 46 made of a GaN single crystal and having a main surface 46a and a back surface 46b. The substrate 46 has a defect concentration region 14c having a defect density 10 times or more higher than that of the surrounding low defect region 14d and distributed in the form of dots on the main surface 46a of the substrate 46. The defect concentration region 14 c extends in the thickness direction of the substrate 14. The defect concentration region 14 c may be irregularly arranged on the substrate 46. The density of the defect concentration region 14c in the substrate 46, the defect density in the defect concentration region 14c and the low defect region 14d, and the ratio of the surface area of the defect concentration region 14c to the area of the main surface 14a are the same as those of the substrate 14 described above. is there. The light-emitting element 1A includes an intermediate layer 48, an n-type nitride semiconductor region 53, a light-emitting layer 52, and a p-type nitride semiconductor region 55 that are epitaxially grown in order on the main surface 46a of the substrate 46. The light emitting element 1 </ b> A includes a cathode electrode 58 </ b> A on the back surface 46 b of the substrate 46 and an anode electrode 58 </ b> B on the p-type nitride semiconductor region 55.

The intermediate layer 48 includes an Al _x Ga _1-x N (0 <x ≦ 1) layer epitaxially grown on the main surface 46a (for example, (0001) plane) of the substrate 46 including the surface of the defect concentration region 14c. The Further, an n-type dopant is added to the intermediate layer 48. The thickness of the intermediate layer 48 is 50 nm in this embodiment. The thickness of the intermediate layer 48 can be appropriately selected from a thickness of 10 nm or more and 500 nm or less by changing the growth conditions of the intermediate layer 48, but if it is thicker than this, there is a high possibility that defects such as cracks will occur. As shown in the examples described later, if the thickness of the intermediate layer 48 is less than (−5x + 1.2) μm when the Al composition ratio is 0 <x <0.24, defects such as cracks are preferable. Can be suppressed. The intermediate layer 48 contains carbon during the formation process, but the carbon concentration is such that there is no problem with the electrical characteristics of the light-emitting element 1A (1 × 10 ¹⁸ cm ⁻³ or less).

  The n-type nitride semiconductor region 53 includes an n-type nitride semiconductor such as an n-type buffer layer 50, for example. The n-type buffer layer 50 is an upper layer in the present embodiment. That is, in the present embodiment, the substrate 46, the intermediate layer 48, and the n-type buffer layer 50 can be formed by cutting the GaN substrate 28 of the first embodiment into a chip shape. The n-type buffer layer 50 is formed by epitaxially growing GaN on the intermediate layer 48, and has an n-type conductivity by adding an n-type dopant such as Si. The n-type buffer layer 50 has a composition such that the refractive index is smaller than that of the light emitting layer 52 and the band gap is large, and serves as a lower cladding for the light emitting layer 52. In the present embodiment, the thickness of the n-type buffer layer 50 is 2 μm.

  The light emitting layer 52 is formed on the n-type nitride semiconductor region 53 (on the n-type buffer layer 50 in this embodiment), and the carriers (from the n-type nitride semiconductor region 53 and the p-type nitride semiconductor region 55 ( Light is generated in the light emitting region 52a by recombination of electrons and holes. The light emitting layer 52 of this embodiment has a multiple quantum well structure in which a barrier layer having a thickness of 15 nm and a well layer having a thickness of 3 nm are alternately stacked over three periods. Each of the barrier layer and the well layer is made of InGaN, and the band gap of the barrier layer is configured to be larger than the band gap of the well layer by appropriately selecting the composition of indium (In). In addition, the light emitting region 52 a is generated in a region where carriers are injected in the light emitting layer 52. In the present embodiment, the light emitting region 52 a is generated in the entire light emitting layer 52. Therefore, the light emitting region 52 a is formed over at least a part of the defect concentration region 14 c of the defect concentration region 14 c of the substrate 46.

  The p-type nitride semiconductor region 55 includes a p-type nitride semiconductor such as a p-type cladding layer 54 and a p-type contact layer 56, for example. The p-type cladding layer 54 is formed by epitaxially growing AlGaN on the light emitting layer 52, and has a p-type conductivity by adding a p-type dopant such as Mg. Further, the p-type cladding layer 54 has a composition such that the refractive index is smaller and the band gap is larger than that of the light emitting layer 52, and serves as an upper cladding for the light emitting layer 52. In the present embodiment, the thickness of the p-type cladding layer 54 is 20 nm.

  The p-type contact layer 56 is a layer for electrically connecting the p-type cladding layer 54 and the anode electrode 58B. The p-type contact layer 56 is formed by epitaxially growing GaN on the p-type cladding layer 54, and has p-type conductivity by adding a p-type dopant such as Mg. In the present embodiment, the thickness of the p-type contact layer 56 is 150 nm.

  The cathode electrode 58 </ b> A is made of a conductive material, and ohmic contact is realized with the substrate 46. The anode electrode 58B is made of a conductive material that transmits light generated in the light emitting layer 52, and between the at least part thereof and the p-type nitride semiconductor region 55 (p-type contact layer 56 in this embodiment). Ohmic contact is realized.

  Next, a procedure for manufacturing the light emitting element 1A according to the present embodiment will be described with reference to FIG. 7A to 7E are diagrams showing a procedure for manufacturing the light emitting element 1A.

  First, the GaN substrate 28 of the first embodiment is created. That is, the wafer-like substrate 14 made of GaN single crystal is placed on the tray 20 on the susceptor 18 in the flow channel 12 shown in FIG. 1 with the (0001) plane facing upward (see FIG. 7A). . Next, the cleaning process (thermal cleaning) of the main surface 14a of the substrate 14 is performed in the same manner as in the first embodiment.

Subsequently, in a state where the temperature of the substrate 14 (substrate temperature) is maintained at 1050 ° C. and the pressure in the intermediate flow channel is maintained at 101 kPa, the group III source gas, the group V source gas, and the doping gas together with the carrier gas described above, Supply from the nozzle 22 onto the substrate 14. Specifically, TMG, TMA, NH ₃ , and SiH ₄ are supplied onto the substrate 14, and an intermediate layer 24 made of n-type AlGaN is grown on the main surface 14a of the substrate 14 (intermediate layer formation step, FIG. 7 (b)). At this time, it is preferable to adjust the growth conditions so that the composition of the intermediate layer 24 is Al _x Ga _1-x N (0 <x <0.24). At this time, it is preferable to set the growth time so that the thickness of the intermediate layer 24 is less than (−5x + 1.2) μm.

Subsequently, TMG, NH ₃ , and SiH ₄ are supplied onto the intermediate layer 24 while maintaining the substrate temperature at 1050 ° C. and the pressure in the intermediate flow channel at 101 kPa, respectively. An upper layer 26 serving as a mold buffer layer is epitaxially grown on the intermediate layer 24 (see FIG. 7C). Thus, the GaN substrate 28 including the substrate 14, the intermediate layer 24, and the upper layer 26 is formed.

Subsequently, the substrate temperature is lowered to 800 ° C., and TMG, TMI, and NH ₃ are supplied onto the upper layer 26, whereby the light emitting layer 66 made of InGaN is epitaxially grown on the upper layer 26. At this time, a quantum well structure including a barrier layer and a well layer is formed by periodically changing the flow rates of TMG, TMI, and NH ₃ . Subsequently, the substrate temperature is raised to 1000 ° C., and TMG, TMA, NH ₃ , and Cp ₂ Mg are supplied onto the light emitting layer 66, whereby the p-type cladding layer 68 made of p-type AlGaN is formed on the light emitting layer 66. Epitaxially grow. Subsequently, while maintaining the substrate temperature at 1000 ° C., TMG, NH ₃ , and Cp ₂ Mg are supplied onto the p-type cladding layer 68, thereby forming the p-type contact layer 70 made of p-type GaN into the p-type cladding. Epitaxial growth is performed on the layer 68 (semiconductor region forming step, see FIG. 7D).

  Subsequently, the GaN substrate 28 on which the light emitting layer 66, the p-type cladding layer 68, and the p-type contact layer 70 are formed is taken out from the flow channel 12, and the cathode electrode 58A is formed on the back surface of the GaN substrate 28 with the p-type contact layer. An anode electrode 58B is formed on each 70 by vapor deposition or the like. Then, by dividing the GaN substrate 28 into chips in element units, a light emitting device including a substrate 46, an intermediate layer 48, an n-type buffer layer 50, a light emitting layer 52, a p-type cladding layer 54, and a p-type contact layer 56. 1A is completed (see FIG. 7E).

  The effects of the light emitting device 1A according to the present embodiment described above and the manufacturing method thereof will be described. As described in the description of the first embodiment, when a layer made of GaN is directly grown on a substrate made of GaN single crystal, in some regions of the substrate surface, normal epitaxial growth does not occur and depressions occur ( The flatness of the surface of the intermediate layer is significantly impaired. On the other hand, in the light emitting device 1A of this embodiment and the manufacturing method thereof, the intermediate layer 24 (48) made of AlGaN is grown on the substrate 14 (46). Since AlGaN grows over the entire surface of the substrate 46 including the region where the contaminant is attached or the surface region of the defect concentration region 14c, the surface 48a of the intermediate layer 48 can be formed flat. Therefore, since the interface (growth surface) of each layer stacked on the intermediate layer 48 can be flattened, device characteristics such as the light emission amount of the light emitting element 1A can be improved.

  Further, since AlGaN grows over the entire surface of the substrate 14 (46) including the area where the contaminant is attached or the surface of the defect concentration area 14c, the intermediate layer 24 (48) is grown under a relatively high pressure of 80 kPa or more. Even in this case, the surface 48a of the intermediate layer 48 can be flattened. Therefore, even if the n-type buffer layer 50, the light-emitting layer 52, the p-type cladding layer 54, and the p-type contact layer 56 stacked on the intermediate layer 48 are grown under such a relatively high pressure, the interface between the layers is maintained. Since it can be formed flat, these layers can be grown under relatively high pressure, thereby improving the crystallinity of each layer. Therefore, the device characteristics of the light emitting element 1A are improved.

  Further, as in the present embodiment, the n-type nitride semiconductor region 53 preferably includes an n-type buffer layer 50 made of GaN epitaxially grown on the intermediate layer 48. Since the n-type nitride semiconductor region 53 includes the n-type buffer layer 50, for example, minute irregularities due to processing or the like exist on the main surface 46a of the substrate 46, and the irregularities appear on the surface 48a of the intermediate layer 48. Even in such a case, the growth surface (the surface of the n-type buffer layer 50) can be flattened by epitaxially growing the n-type buffer layer 50 on the intermediate layer 48. Therefore, since the crystallinity of each layer epitaxially grown on the n-type buffer layer 50 is improved, the device characteristics such as the light emission amount in the light emitting element 1A are further improved.

  Further, as in the present embodiment, the intermediate layer 48 preferably has n-type conductivity. In this case, since the specific resistance of the intermediate layer 48 is reduced, in the light emitting element 1A which is a vertical device in which the cathode electrode 58A and the anode electrode 58B are formed on both sides of the substrate 46, the device characteristics such as the light emission amount are further improved. . In the present embodiment, the intermediate layer 48 is doped n-type, but may be doped p-type depending on the structure of the device.

Further, the density of the defect concentration region 14 c on the main surface 46 a of the substrate 46 may be 100 [pieces / cm ² ] or more as in the substrate 14. As described above, even when the density of the defect concentration region 14c is relatively high, according to the light emitting device 1A of the present embodiment and the manufacturing method thereof, the interface between the intermediate layer 48 and each layer stacked on the intermediate layer 48 is flattened. can do.

  In the present embodiment, the light emitting region 52a in the light emitting layer 52 extends over at least a part of the defect concentration region 14c. In a light emitting device such as the light emitting device 1A, it is preferable to grow the light emitting layer 52 (particularly, the light emitting region 52a) with better crystallinity. However, in the conventional light-emitting element, it is difficult to form a light-emitting layer on a crystal defect region with good crystallinity, which is one factor that hinders high luminance. On the other hand, according to the light emitting element 1A of the present embodiment, the interface of the light emitting layer 52 can be made flat regardless of the arrangement of the defect concentration region 14c of the substrate 46, so that the crystallinity in the light emitting region 52a of the light emitting layer 52 is further improved. Can be better.

  It should be noted that the intermediate layer 48 in the present embodiment is different from a so-called cladding layer. In an LED such as the light emitting element 1A of the present embodiment, the cladding layer needs to be formed relatively thick in order to confine light in the vicinity of the light emitting layer. For example, the thickness of the n-type buffer layer 50 of this embodiment is 2 μm. On the other hand, the thickness of the intermediate layer 48 of this embodiment is 50 nm. Even if the intermediate layer 48 has such a relatively thin film thickness, the above-described effects can be suitably achieved.

  Next, a light-emitting element 1B having a mode different from the above-described light-emitting element 1A will be described with reference to FIG. FIG. 8 is a side sectional view showing the configuration of the light emitting element 1B. The light emitting element 1B is different from the light emitting element 1A in the structure of the intermediate layer 49. Since the configuration of the light emitting element 1B other than the intermediate layer 49 is the same as that of the light emitting element 1A, detailed description thereof is omitted.

The light emitting element 1 </ b> B includes an intermediate layer 49 on the main surface 46 a of the substrate 46. The intermediate layer 49 includes first layers 49A and second layers 49B that are alternately stacked. The first layer 49A is made of n-type doped Al _x Ga _1-x N (0 <x ≦ 1), and the second layer 49B is n-type doped Al _y Ga _1-y N (0 ≦ y ≦ 1, y ≠ x). In the present embodiment, the first layer 49A and the second layer 49B are alternately stacked over the main surface 46a of the substrate 46 over 10 periods to form a superlattice structure (strained superlattice structure). The thicknesses of the first layer 49A and the second layer 49B are each 10 nm, for example.

The manufacturing method of such a light emitting element 1B is the same as that of the light emitting element 1A except for the following points. That is, when manufacturing the light emitting element 1B, in the step of forming the intermediate layer 49, after forming the first layer 49A, for example, the switching valve located upstream of the nozzle 22 (see FIG. 1) is operated to operate the TMA. Shut off the supply. As a result, the second layer 49B made of GaN (that is, Al _y Ga _1-y N (y = 0)) is stacked on the first layer 49A. Then, by operating such a switching valve, the first layer 49A and the second layer 49B are alternately stacked to form a 10-layer superlattice structure.

  In the light-emitting element 1B including the intermediate layer 49 in which the superlattice structure (strained superlattice structure) is formed by the first layer 49A and the second layer 49B, propagation of threading dislocations from the substrate 46 is caused by the superlattice structure. Be blocked. As a result, the dislocation density of the n-type nitride semiconductor region 53, the light-emitting layer 52, and the p-type nitride semiconductor region 55 is reduced and the crystallinity is improved, so that the device characteristics can be improved, for example, the emission luminance is increased. Note that the superlattice structure including the first layer 49A and the second layer 49B is not limited to ten layers, and the number of layers may be increased or decreased as appropriate.

  Next, a light-emitting element 1C having a mode different from the above-described light-emitting elements 1A and 1B will be described with reference to FIG. FIG. 9 is a side sectional view showing the configuration of the light emitting element 1C. The light emitting element 1C is different from the light emitting elements 1A and 1B in that an InGaN epitaxial layer 57 is provided between the intermediate layers 51. Since the configuration other than the InGaN epitaxial layer 57 in the light emitting element 1C is the same as that of the light emitting elements 1A and 1B, detailed description thereof is omitted.

The light emitting element 1 </ b> C includes an intermediate layer 51 on the main surface 46 a of the substrate 46. The intermediate layer 51 includes a first layer 51A and a second layer 51B. The light emitting element 1C includes an InGaN epitaxial layer 57 sandwiched between the first layer 51A and the second layer 51B of the intermediate layer 51. The first layer 51A and the second layer 51B are each made of n-type doped Al _x Ga _1-x N (0 <x ≦ 1), and the InGaN epitaxial layer 57 is n-type doped In _z Ga. _1-zN (0 <z ≦ 1).

The manufacturing method of such a light emitting element 1C is the same as that of the light emitting element 1A except for the following points. That is, when manufacturing the light emitting element 1C, in the step of forming the intermediate layer 51, the first layer 51A made of n-type AlGaN is formed, and then TMG, TMI, NH ₃ , and SiH ₄ are used as the first layer. By supplying on the layer 51A, the InGaN epitaxial layer 57 made of n-type In _z Ga _1-z N (0 <z ≦ 1) is grown. Then, the second layer 51 </ b> B is formed by growing n-type AlGaN on the InGaN epitaxial layer 57.

Even if the material of the layer to be stacked is AlGaN, the epitaxial growth on the substrate 46 may be abnormally grown as in the first layer 51A shown in FIG. 9 due to various factors. Therefore, an InGaN epitaxial layer 57 made of In _z Ga _1-z N (0 <z ≦ 1) is grown on the first layer 51A as in the light emitting element 1C. In this case, the main surface 46a of the substrate 46 is heavily contaminated, or the crystal quality on the surface of the defect concentration region 14c is extremely low, so that the first layer 51A of the intermediate layer 51 grows abnormally and is sufficiently flattened. Even if it cannot be achieved, the planarization of the growth surface 57a is complemented by growing a layer made of InGaN on the first layer 51A.

(First embodiment)
Next, examples for the second embodiment will be described. First, as 1st Example, 1 A of light emitting elements which light-emit blue light were created.

First, a wafer-like substrate 14 made of a GaN single crystal is placed on a tray 20 on a susceptor 18, and NH ₃ and H ₂ are introduced into the flow channel 12 while maintaining the pressure in the flow channel 12 (in-furnace pressure) at 101 kPa. Then, the temperature of the substrate 14 was kept at 1050 ° C. for 10 minutes to clean the main surface 60a. Next, while maintaining the substrate temperature at 1050 ° C. and the furnace pressure at 101 kPa, TMA, TMG, NH ₃ , and SiH ₄ were introduced into the flow channel 12 to form an n-type Al _0.07 having a thickness of 50 nm. An intermediate layer 24 made of Ga _0.93 N was grown. Thereafter, while maintaining the substrate temperature and the pressure in the furnace, an upper layer 26 made of n-type GaN having a thickness of 2 μm and serving as the n-type buffer layer 50 was grown to produce a GaN substrate 28.

Next, the substrate temperature was lowered to 800 ° C., and a barrier layer made of InGaN having a thickness of 15 nm and a well layer made of InGaN having a thickness of 3 nm were alternately grown over three periods to form a light emitting layer 66. Thereafter, the substrate temperature is raised again to 1000 ° C., TMA, TMG, NH ₃ , and Cp ₂ Mg are introduced into the flow channel 12, and p composed of p-type Al _0.12 Ga _0.88 N having a thickness of 20 nm. A mold cladding layer 68 was grown. Then, TMG, NH ₃ and Cp ₂ Mg were introduced to grow a p-type contact layer 70 made of p-type GaN having a thickness of 50 nm.

  FIG. 10 is a photograph of the surface of the p-type contact layer 70 of the light-emitting element 1A produced according to this example, taken with a differential interference microscope. As shown in FIG. 10, it can be seen that the surface of the p-type contact layer 70 is a flat surface with little unevenness. The state of the surface of the p-type contact layer 70 that is the uppermost layer reflects the state of the interface (growth surface) of the p-type cladding layer 68, the light emitting layer 66, and the upper layer 26 that are the lower layers. From the photograph shown in FIG. 10, it can also be inferred that the interface of the p-type cladding layer 68, the light emitting layer 66, and the upper layer 26 is flat.

  Thereafter, a cathode electrode 58A was formed on the back surface of the GaN substrate 28, and an anode electrode 58B was formed on the p-type contact layer 70. Then, the GaN substrate 28 was divided into elements to complete the light emitting element 1A. When a current was continuously applied to the light-emitting element 1A thus prepared, the emission value was 450 nm at a current value of 20 mA, and a light emission amount of 3 mW was obtained in the state of a bare chip (element before packaging).

Furthermore, the present inventors tried to produce the light emitting element 1A by setting various thicknesses and Al composition ratios of the intermediate layer 48 in this example. Table 1 below is a table showing the results of examining the presence or absence of cracks in the intermediate layer 48 created with 13 different thicknesses and Al composition ratios. Table 1 also shows the film thickness of the intermediate layer 48 and the Al composition ratio x derived from the PL wavelength.

  FIG. 11 is a graph showing the correlation between the thickness and Al composition ratio and the presence or absence of cracks for the 13 intermediate layers 48 shown in Table 1. Referring to FIG. 11, it can be seen that the presence or absence of cracks in the intermediate layer 48 is clearly different from the straight line A (thickness = −5x + 1.2, 0 <x <0.24). That is, when the Al composition ratio x is in the range of 0 <x <0.24, if the thickness of the intermediate layer 48 is less than (−5x + 1.2) μm, the intermediate layer 48 is not cracked. Has been found to grow favorably.

(Second embodiment)
Subsequently, as a second example, a light emitting element 1B that emits blue light was produced. First, the substrate 14 was placed on the tray 20, and the main surface 14a was cleaned in the same manner as in the first example. Next, while maintaining the substrate temperature at 1050 ° C. and the furnace pressure at 101 kPa, TMA, TMG, NH ₃ , and SiH ₄ were introduced into the flow channel 12 to form an n-type Al _0.14 having a thickness of 10 nm. An intermediate layer was grown by alternately stacking 10 cycles of Ga _0.86 N and 10 nm thick n-type GaN. Thereafter, an n-type buffer layer, a light emitting layer, a p-type cladding layer, and a p-type contact layer were grown in the same manner as in the first example. When the surface of the p-type contact layer thus grown was observed with a differential interference microscope, the surface was formed flat as in the first example.

  Thereafter, a cathode electrode 58A was formed on the back surface of the substrate 14, and an anode electrode 58B was formed on the p-type contact layer. And the board | substrate 14 was divided | segmented into the element, and the light emitting element 1B was completed. When a current was continuously applied to the light emitting device 1B thus produced, an emission wavelength of 450 nm was obtained at a current value of 20 mA, and a light emission amount of 5 mW was obtained in a bare chip state.

(Comparative example)
Subsequently, comparative examples for verifying the effects of the above-described embodiments will be described. Here, as a comparative example, a light-emitting element without an intermediate layer was created.

First, a substrate made of a GaN single crystal was placed on the tray 20 on the susceptor 18 and the main surface was cleaned in the same manner as in the first example. Next, while maintaining the substrate temperature at 1050 ° C. and the furnace pressure at 101 kPa, TMG, NH ₃ , and SiH ₄ were introduced into the flow channel 12 to grow n-type GaN having a thickness of 2 μm. Thereafter, a light emitting layer, a p-type cladding layer, and a p-type contact layer were sequentially grown in the same manner as in the first example.

  FIG. 12 is a photograph obtained by photographing the surface of the p-type contact layer of the light emitting device produced according to this comparative example with a differential interference microscope. As shown in FIG. 12, the surface of the p-type contact layer in this comparative example had many irregularities and the flatness was not very good. Therefore, it can be estimated that the interface of the p-type cladding layer, the light emitting layer, and the n-type buffer layer is also not flat.

  Thereafter, a cathode electrode was formed on the back surface of the substrate, and an anode electrode was formed on the p-type contact layer. And the board | substrate was divided | segmented into the element and the light emitting element was completed. When a current was continuously applied to the thus produced light emitting device, an emission wavelength of 450 nm was obtained at a current value of 20 mA, and only a light emission amount of 1 mW was obtained in a bare chip state. Thus, in each of the above examples, it was proved that the device characteristics of the light emitting element were improved by providing the intermediate layer on the substrate.

The present invention is not limited to the above-described embodiments and examples, and various modifications are possible. For example, the composition of Al _x Ga _1-x N (0 <x ≦ 1) and Al _y Ga _1-y N (0 ≦ y ≦ 1) constituting the intermediate layer is x = 0.08 or x = 0. 16, y is not limited to 0 and can be appropriately increased or decreased. Further, the composition of In _z Ga _1-z N constituting the InGaN epitaxial layer is not limited to z = 0.10, but can be appropriately increased or decreased within the range of 0 <z ≦ 1. Moreover, the effect of the present invention can be suitably obtained even when polycrystalline GaN is used in addition to the above-described single crystal GaN as the material of the substrate.

  In the second embodiment, the n-type semiconductor region is formed on the intermediate layer, and the p-type semiconductor region is formed on the active layer. The p-type semiconductor region is formed on the intermediate layer. An n-type semiconductor region may be formed on the active layer with the active layer interposed therebetween.

  In the second embodiment, the light emitting device is exemplified as the nitride semiconductor device of the present invention. However, the present invention is not limited to this, and the present invention is not limited to this, and also includes a transistor having an n-type region and a p-type region made of group III nitride. Preferably used.

It is the figure which showed the vapor phase growth apparatus used for preparation of the GaN substrate which concerns on 1st Embodiment of this invention. (A) is a top view which shows a part of board | substrate. (B) is sectional drawing which shows the II cross section of the board | substrate shown to (a). (A)-(c) It is the figure which showed the procedure which produces a GaN substrate. (A)-(e) It is the figure which showed the procedure which produces a GaN substrate. (A)-(e) It is the figure which showed the procedure which produces a GaN substrate. It is side surface sectional drawing which shows the structure of a light emitting element as the nitride semiconductor element which concerns on 2nd Embodiment of this invention. It is the figure which showed the procedure which produces (a)-(e) light emitting element. It is side surface sectional drawing which shows the structure of a light emitting element. It is side surface sectional drawing which shows the structure of a light emitting element. It is the photograph which image | photographed the surface of the p-type contact layer of the light emitting element produced by 1st Example with the differential interference microscope. It is a graph which shows correlation with thickness and Al composition ratio, and the presence or absence of a crack about 13 types of intermediate | middle layers shown in Table 1. FIG. It is the photograph which image | photographed the surface of the p-type contact layer of the light emitting element produced by the comparative example with the differential interference microscope. It is the schematic sectional drawing which showed the surface state of the conventional GaN substrate. It is a figure which shows the surface state of a GaN board | substrate at the time of growing a GaN homoepitaxial layer on the board | substrate which has (a)-(d) defect concentration area | regions.

Explanation of symbols

  1A to 1C: Light emitting element, 14, 46: Substrate, 24, 24a, 24B, 24C, 48, 49, 51 ... Intermediate layer, 24a, 26a, 34a ... Surface, 26 ... Upper layer, 28, 28A, 28B ... GaN substrate 32 ... Epitaxial thin film, 34, 57 ... InGaN epitaxial layer, 49A, 51A ... first layer, 49B, 51B ... second layer, 50 ... n-type buffer layer, 52 ... light emitting layer, 53 ... n-type nitride Semiconductor region 54 ... p-type cladding layer 55 ... p-type nitride semiconductor region 56 ... p-type contact layer 58A ... cathode electrode 58B ... anode electrode

Claims (4)

A substrate having a defect concentration region in which the defect density is more than 10 times higher than that of the surrounding low defect region and distributed in the form of dots on the main surface, made of GaN, and having a cathode electrode on the back surface;
An intermediate layer made of Al _x Ga _1-x N (0 <x <0.24) having a thickness of less than (−5x + 1.2) μm and epitaxially grown on the main surface of the substrate;
An n-type nitride semiconductor region and a p-type nitride semiconductor region provided on the intermediate layer,
The intermediate layer is doped with a dopant and has n-type conductivity,
The n-type nitride semiconductor region includes an n-type buffer layer;
The p-type nitride semiconductor region includes a p-type cladding layer and a p-type contact layer provided on the p-type cladding layer and in contact with the anode electrode,
Der density 100 pieces / cm ^2] or more of the defect concentration regions in the main surface of the substrate is,
The substrate is formed by forming a mask layer having a plurality of opening windows on another substrate and laterally growing GaN from within the opening window, and after the lateral growth, the other substrate is etched away, The main surface and the back surface are subjected to mechanical polishing,
2. The nitride semiconductor device according to claim 1, wherein the defect concentration region is a region formed by collecting defects inside GaN when GaN is grown . A light emitting layer is further provided between the n-type nitride semiconductor region and the p-type nitride semiconductor region;
The nitride semiconductor device according to claim 1, wherein the n-type nitride semiconductor region includes a cladding layer.   The nitride semiconductor device according to claim 2, wherein a light emitting region in the light emitting layer extends over at least a part of the defect concentration region. On the main surface of the substrate having a defect concentration region in which the defect density is more than 10 times higher than the surrounding low defect region and distributed in the form of dots on the main surface, made of GaN, and having a back surface for contacting the cathode electrode, An intermediate layer forming step of epitaxially growing an intermediate layer made of Al _x Ga _1-x N (0 <x <0.24) to a thickness of less than (−5x + 1.2) μm;
On the intermediate layer, an n-type nitride semiconductor region including an n-type buffer layer, a p-type cladding layer, and a p-type nitride layer including a p-type contact layer provided on the p-type cladding layer and in contact with the anode electrode A semiconductor region forming step for forming a physical semiconductor region,
A dopant is added during the intermediate layer forming step to make the intermediate layer n-type,
Growing each of the intermediate layer, the n-type nitride semiconductor region, and the p-type nitride semiconductor region under a pressure of 80 kPa or more;
Der density 100 pieces / cm ^2] or more of the defect concentration regions in the main surface of the substrate is,
The substrate is formed by forming a mask layer having a plurality of opening windows on another substrate and laterally growing GaN from within the opening windows, and after the lateral growth, the other substrate is etched away, The main surface and the back surface are subjected to mechanical polishing,
The method for manufacturing a nitride semiconductor device, wherein the defect concentration region is a region formed by gathering defects inside GaN during GaN growth .