JP2007258230A - Semiconductor substrate and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor substrate free from an increase in man-hours necessary for manufacture and improved in crystallinity of a GaN layer. <P>SOLUTION: A semiconductor device formed on a substrate 1 includes: a first Al<SB>a</SB>Ga<SB>b</SB>In<SB>1-a-b</SB>N<SB>v</SB>(where 0≤a≤1, 0≤b≤1 and 0≤a+b≤1) layer 2, a second Al<SB>c</SB>Ga<SB>d</SB>In<SB>1-c-d</SB>N<SB>w</SB>layer 3 formed on the first layer 2, a multilayered film 4 located on the second layer 3 and consisting of a third Al<SB>e</SB>Ga<SB>f</SB>In<SB>1-e-f</SB>N<SB>x</SB>(where 0≤e≤1, 0≤f≤1 and 0≤e+f≤1) layer and a fourth Al<SB>g</SB>Ga<SB>h</SB>In<SB>1-g-h</SB>N<SB>y</SB>(where 0≤g≤1, 0≤h≤1 and 0≤g+h≤1) layer alternately laminated on the multilayered film 4, and a fifth Al<SB>i</SB>Ga<SB>j</SB>In<SB>1-i-j</SB>N<SB>z</SB>(where 0≤i≤1, 0≤j≤1 and 0≤i+j≤1) layer 5. The number of the laminated third Al<SB>e</SB>Ga<SB>f</SB>In<SB>1-e-f</SB>N<SB>x</SB>layers and fourth Al<SB>g</SB>Ga<SB>h</SB>In<SB>1-g-h</SB>N<SB>y</SB>layers is 160 or less. In the above formulas, v, w, x, y and z are integers. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor substrate having a group III nitride layer formed on a silicon substrate and a semiconductor device using the same. In particular, the present invention relates to a semiconductor substrate in which the crystallinity of a group III nitride formed on a Si substrate is improved and a semiconductor device using the same.

  Group III nitride semiconductors, such as gallium nitride semiconductors, have a wider band gap than silicon and GaAs. For this reason, when a group III nitride layer is used as a substrate of a semiconductor device, a semiconductor device having excellent characteristics can be formed.

  A conventional group III nitride substrate has a structure in which a group III nitride layer is formed on a sapphire substrate via a buffer film. However, since the sapphire substrate is an insulator, the electrode structure is complicated. Moreover, the sapphire substrate has low productivity, high price, and poor heat dissipation. Therefore, a technique for forming a group III nitride layer using Si (silicon) as a base material having high productivity, low cost and good heat dissipation is desired.

  However, there is a large lattice mismatch (for example, about 14% in the case of GaN) between the Si crystal and the group III nitride layer, and the coefficient of thermal expansion is also different. For this reason, it is difficult to form a high-quality group III nitride layer directly on the Si substrate. One technique for solving this is a technique in which a plurality of AlN / GaN multilayer buffer layers starting from an AlN layer are inserted between a Si substrate and a GaN layer. Thereby, a relatively thick GaN layer can be formed on the Si substrate. However, even with this technique, if the GaN layer has a required thickness, cracks occur in the GaN layer.

As one of techniques for solving this, there is a technique described in Patent Document 1. In this technology, BP (boron phosphide) is formed as a buffer layer on a Si substrate, 10 superlattice buffer crystal layers made of AlN / GaN are formed thereon, and a GaN layer is formed thereon. is there.
JP 2005-5657 A

  However, in the technique described in Patent Document 1, stress is generated at the interface between the Si base and the BP layer, and as a result, the GaN substrate is warped. When the GaN substrate warps, defects are introduced into the GaN layer in order to relieve the stress, and the quality of the substrate deteriorates (for example, the 10th paragraph of Patent Document 1). As a technique for solving this, the 11th and 12th paragraphs of Patent Document 1 disclose a technique for growing a GaN layer only in a portion necessary as an operation layer of a semiconductor element. However, the number of processes increases when such a method is adopted.

  The present invention has been made in consideration of the above circumstances, and its purpose is to provide a semiconductor substrate having improved group III nitride layer crystallinity without increasing the number of steps required for production, and a semiconductor substrate thereof. It is to provide a semiconductor device used.

The inventors of the present inventors have intensive studies to form the appropriate buffer layer on a Si _{substrate, Al e Ga f In 1-} ef N x (0 ≦ e ≦ 1,0 ≦ f ≦ 1 thereon, And 0 ≦ e + f ≦ 1) layers and Al _g Ga _h In _1-gh N _y (0 ≦ g ≦ 1, 0 ≦ h ≦ 1 and 0 ≦ g + h ≦ 1) layers alternately in an appropriate number of layers. A compound semiconductor substrate is formed by stacking and further forming an Al _i Ga _j In _1-ij N _z (0 ≦ i ≦ 1, 0 ≦ j ≦ 1, and 0 ≦ i + j ≦ 1) layer thereon as a substrate. Thus, it has been found that the crystallinity of the compound semiconductor layer can be improved without increasing the number of steps required for production.

That is, the semiconductor substrate according to the present invention includes a first Al _a Ga _b In _1-ab N _v (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, and 0 ≦ a + b ≦ 1) formed on a Si base. Layers,
Second Al _c Ga _d In _1-cd N _w (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, and 0 ≦ c + d) formed on the first Al _a Ga _b In _{1-ab Nv} layer ≦ 1) layer,
Located on the second _{Al c Ga d In 1-cd} N w layer, the third _{Al e Ga f In 1-ef} N x (0 ≦ e ≦ 1,0 ≦ f ≦ 1, and 0 ≦ e + f ≦ 1) a multilayer film in which layers and fourth Al _g Ga _h In _1-gh N _y (0 ≦ g ≦ 1, 0 ≦ h ≦ 1, and 0 ≦ g + h ≦ 1) layers are alternately stacked;
A fifth Al _i Ga _j In _1-ij N _z (0 ≦ i ≦ 1, 0 ≦ j ≦ 1, and 0 ≦ i + j ≦ 1) layer formed on the multilayer film;
Comprising a, the number of laminations of the third _{Al e Ga f In 1-ef} N x layer and the fourth _{Al g Ga h In 1-gh} N y layer in the multilayer film is less than 160 layers Features. However, v, w, x, y, and z are positive numbers.

In the said third _{Al e Ga f In 1-ef} N x layer and the fourth Al _g Ga _h In _1-gh number of stacked N _y layer is 40 or more layers multilayer film has preferably 60 or more layers Preferably there is. In the present invention, the half width of the rocking curve of the diffraction peak of the (0004) plane of the fifth Al _i Ga _j In _1-ij N _x layer in the double crystal X-ray diffraction method may be 800 arcsec or less. it can.

A semiconductor device according to the present invention includes a first Al _a Ga _b In _1-ab N _v (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, and 0 ≦ a + b ≦ 1) layer formed on a Si substrate. When,
Second Al _c Ga _d In _1-cd N _w (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, and 0 ≦ c + d) formed on the first Al _a Ga _b In _{1-ab Nv} layer ≦ 1) layer,
Located on the second _{Al c Ga d In 1-cd} N w layer, the third _{Al e Ga f In 1-ef} N x (0 ≦ e ≦ 1,0 ≦ f ≦ 1, and 0 ≦ e + f ≦ 1) and the layer, and the multilayer film and the fourth _{Al g Ga h in 1-gh} N y (0 ≦ g ≦ 1,0 ≦ h ≦ 1, and 0 ≦ g + h ≦ 1) layer are alternately stacked,
A fifth Al _i Ga _j In _1-ij N _z (0 ≦ i ≦ 1, 0 ≦ j ≦ 1, and 0 ≦ i + j ≦ 1) layer formed on the multilayer film;
A semiconductor element formed using the fifth Al _i Ga _j In _1-ij N _z layer;
Comprising a number of stacked lamination number of the third _{Al e Ga f In 1-ef} N x layer and the fourth _{Al g Ga h In 1-gh} N y layer in the multilayer film is below 160 layers It is characterized by being.
In this case, the pit density on the surface of the semiconductor element can be 1.3 × 10 ¹⁰ cm ⁻² .

  According to the present invention, in the semiconductor substrate and the semiconductor device, the crystallinity of the group III nitride layer formed on the Si base can be improved without increasing the number of steps required for manufacturing.

A semiconductor device according to an embodiment of the present invention will be described below with reference to FIG. In this semiconductor device, an undoped fifth Al _i Ga _j In _1-ij N _z (0 ≦ i ≦ 1, with a first conductivity type (for example, n-type) Si substrate 1 having a (111) surface on the surface. (0 ≦ j ≦ 1 and 0 ≦ i + j ≦ 1) The layer 5 is used as the base layer. Si substrate 1 and between the fifth _{Al i Ga j In 1-ij} N z layer 5, the first as a buffer layer _{Al a Ga b In 1-ab} N v (0 ≦ a ≦ 1,0 ≦ b ≦ 1 and 0 ≦ a + b ≦ 1) Layer 2 (may be an AlN layer), second Al _c Ga _d In _1-cd N _w (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, and 0 ≦ c + d ≦ 1) layer 3, and, in the third _{Al e Ga f in 1-ef} N x (0 ≦ e ≦ 1,0 ≦ f ≦ 1, and 0 ≦ e + f ≦ 1) layer (AlN layer And a fourth Al _g Ga _h In _{1 -gh} N _y (0 ≦ g ≦ 1, 0 ≦ h ≦ 1, and 0 ≦ g + h ≦ 1) layer (may be a GaN layer) Are stacked in this order. Note that v, w, x, y, and z are positive numbers.

The thickness of the first Al _a Ga _b In _{1-ab Nv} layer 2 is preferably 200 nm or more and 500 nm or less. If it is less than 200 nm, the function as a buffer layer is insufficient, and if it exceeds 500 nm, cracks occur in the film and the crystallinity of the film grown on the upper layer is deteriorated. The thickness of the second Al _c Ga _d In _{1 -cd} N _w layer 3 is preferably 2 μm or less from the viewpoint of suppressing cracks. Further, in the multilayer film 4, the third _{Al e Ga f In 1-ef} N x layer and the fourth _{Al g Ga h In 1-gh} N y layer each having a thickness of, from the viewpoint of suppressing cracks, It is preferable to set it as 5-40 nm and 2.5-20 nm. The third _{Al e Ga f In 1-ef} N x layer and the fourth Al _g Ga _h In _1-gh when the number of stacked N _y layer increases fifth _{Al i Ga j In 1-ij} N z Since the crystallinity of the layer 5 is improved, the lower limit of the number of stacked layers is 40 or more in total, preferably 60 or more in total. Meanwhile, the stress generated in the multilayer film 4 as the number of stacked third _{Al e Ga f In 1-ef} N x layer and the fourth _{Al g Ga h In 1-gh} N y layer increases is increased, as a result Since the fifth Al _i Ga _j In _{1-ij Nz} layer 5 cracks and falls below the state where crystallinity is required, the upper limit is 160 layers in total.

By making the structure of the buffer layer as described above, the crystallinity of the fifth Al _i Ga _j In _1-ij N _z layer 5 and the layers above it can be increased without increasing the number of steps required for manufacturing. Can be improved.
Moreover, since the crystallinity of the fifth _{Al i Ga j In 1-ij} N z layer 5 and the layer above the this is improved, when used as a substrate of a light emitting element, a light reflector, such as a vertical cavity structure It is also possible to produce a structure having

An element formed using this substrate (that is, a layer below the fifth Al _i Ga _j In _{1-ij Nz} layer 5) will be described by taking HEMT as an example. A semiconductor layer 10 is formed on the fifth Al _i Ga _j In _{1-ij Nz} layer 5 via an AlN layer 6. The semiconductor layer 10 includes a barrier layer 7 (for example, Al _t Ga _1-t N (0 <t <1) layer), a first conductivity type (for example, n-type) carrier supply layer 8 (for example, Al _t Ga _1-t N). Layer), and a cap layer 9 (for example, an Al _t Ga _1-t N layer) are stacked in this order. The component of the semiconductor layer 10 is set so that the band gap is larger than that of the fifth Al _i Ga _j In _{1-ij Nz} layer 5. For this reason, the carriers supplied from the carrier supply layer 8 of the semiconductor layer 10 are accumulated at the interface between the fifth Al _i Ga _j In _1-ij N _z layer 5 and the AlN layer 6, and thereby two-dimensional electron gas is generated. Formed and can exhibit high mobility.

Next, a method for manufacturing the semiconductor device shown in FIG. 1 will be described. First, the first Al _a Ga _b In _1-ab N _v layer 2, the second Al 2 Ga 2 In 2 _-ab N _v layer 2 are formed by MOCVD using trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMI), and NH ₃ as source gases. An Al _c Ga _d In _{1 -cd} N _w layer 3, a multilayer film 4, and a fifth Al _i Ga _j In _{1 -ij} N _z layer 5 are formed.

When the buffer layer between the Si base material 1 and the multilayer film 4 is likely to be thermally decomposed, the buffer layer is thermally decomposed and reacts with the Si base material 1 in the formation process of the multilayer film 4, resulting in a large number of upper semiconductor layers. It becomes a crystal structure (see, for example, paragraphs 6 and 7 of JP-A-2000-277441). On the other hand, in the present invention, the melting points of the first Al _a Ga _b In _{1 -ab Nv} layer 2 and the second Al _c Ga _d In _{1 -cd} N _w layer 3 which are buffer layers are high. Therefore, the crystallinity of the multilayer film 4 and the fifth Al _i Ga _j In _{1-ij Nz} layer 5 is improved. When the first Al _a Ga _b In _{1 -ab Nv} layer 2 is an AlN layer, the effect of suppressing thermal decomposition is further increased. Here, the growth temperature of the AlN layer is preferably set to 1100 ° C. or higher. By doing so, the AlN layer becomes a high melting point semiconductor layer, heat treatment for crystallization is unnecessary, and the production efficiency is increased.

Thereafter, the AlN layer 6 is formed by MOCVD using TMA and NH ₃ as source gases, and further the semiconductor layer 10 is formed by MOCVD using TMG, TMA, and NH ₃ as source gases. These steps can be performed continuously in the same semiconductor manufacturing apparatus.

In the above-described steps, it is preferable that the temperature of the Si base material 1 is 900 ° C. or higher.
Even when the temperature of the Si substrate 1 is 900 ° C. or higher, the first Al _a Ga _b In _{1 -ab Nv} layer 2 and the second Al _c Ga are formed on the Si substrate 1 as described above. _{Since the d} In _{1 -cd} N _w layer 3 is formed, it is possible to prevent the Si base material 1 from reacting with each layer positioned above these layers. For this reason, the crystallinity and flatness of the fifth Al _i Ga _j In _1-ij N _z layer 5 are improved.

By the method described above, five semiconductor devices having the structure shown in FIG. 1 and different in the number of stacked multilayer films 4 were formed. In each semiconductor device, the first Al _a Ga _b In _{1 -ab Nv} layer 2 is an AlN layer, and its growth temperature and thickness are 1000 ° C. and 100 nm. The Al _c Ga _d In _{1 -cd} N _w layer 3 is an Al _0.26 Ga _0.74 N layer having a thickness of 40 nm, and the multilayer film 4 is formed by alternately laminating GaN (20 nm) layers and AlN (5 nm) layers at 900 ° C. . The number of stacked GaN layers and AlN layers in the multilayer film 4 is 40 layers, 60 layers, 100 layers, 140 layers, or 200 layers. The fifth Al _i Ga _j In _{1-ij Nz} layer 5 is a GaN layer of 1 μm, and the AlN layer 6 is 1 nm. The barrier layer 7, the carrier supply layer 8, and the cap layer 9 of the semiconductor layer 10 are respectively 7 nm Al _0.26 Ga _0.74 N layer, 15 nm n-type Al _0.26 Ga _0.74 N layer, and 3 nm. Al _0.26 Ga _0.74 N layer.

  Each drawing in FIG. 2 is a surface SEM photograph of the GaN layer 5 in each sample. When the number of stacked layers in the multilayer film 4 is 140 or less, the GaN layer 5 is not cracked. However, when the number of stacked layers is 200, the GaN layer 5 was cracked. Was impossible. Further, when the number of laminated multilayer films 4 was 60 or more, the number of pits in the GaN layer 5 was reduced, and the flatness was sufficiently improved. For this reason, it can be judged that the number of laminated multilayer films 4 is preferably 60 or more.

FIG. 3 is a graph showing the relationship between the number of stacked multilayer films 4 and the warpage of the substrate (the difference between the height of the substrate center and the edge: μm). As the number of laminated multilayer films 4 increased, the warpage of the substrate increased linearly from 73 μm to 148 μm.
From the results described with reference to FIGS. 2 and 2, it can be determined that if the number of stacked layers in the multilayer film 4 is 160 or more, the GaN layer 5 is cracked and does not have the necessary characteristics.

FIG. 4 is a graph showing the relationship between the full width at half maximum of the rocking curve of the diffraction peak from each of the (0004) plane and the (2024) plane of the GaN layer 5 and the number of stacked multilayer films 4 in the double crystal X-ray diffraction method. is there. The half width of the diffraction peak from each of the (0004) plane and the (2024) plane is 770 arcsec and 1589 arcsec when the number of stacked multilayer films 4 is 40 layers, whereas it is 688 arcsec when the number of stacked layers is 140 layers. 1118 arcsec. From this, it was found that the crystallinity of the fifth Al _i Ga _j In _{1-ij Nz} layer 5 improved as the number of multilayer films 4 stacked increased. In particular, when the number of stacked layers is 60 or more, the half-value widths of the diffraction peaks from the (0004) plane and the (2024) plane are 715 arcsec or less and 1490 arcsec or less, respectively, and it has been found that the crystallinity can be sufficiently increased.

5A to 5E respectively show an atomic force microscope (AFM) on the surface of the GaN layer 5 when the number of stacked multilayer films 4 is 40, 60, 100, 140, and 200. FIG. 6 is a chart showing the pit density on the surface of the GaN layer 5 according to the number of stacked multilayer films 4. From these photographs and diagrams, the pit density on the surface of the fifth Al _i Ga _j In _1-ij N _z layer 5 is 1.3 × 10 ¹⁰ (cm ⁻² ) as the number of stacked multilayer films 4 increases. 1 × 10 ¹⁰ (cm ⁻² ), 7.3 × 10 ⁹ (cm ⁻² ), 3.8 × 10 ⁹ (cm ⁻² ), and 3.1 × 10 ⁹ (cm ⁻² ) I found out. However, cracks occurred when the number of laminated layers was 200 as described above.

  FIG. 7 is a graph showing the temperature dependence of carrier (electron) mobility and carrier density due to a two-dimensional electron gas in a semiconductor device in which the number of stacked multilayer films 4 is 40 layers, 100 layers, and 140 layers. The carriers are accumulated at the interface between the GaN layer 5 and the AlN layer 6. In this graph, the horizontal axis is temperature. FIG. 8 is a graph showing the relationship between the number of stacked multilayer films 4 and the sheet resistance of the semiconductor device.

The carrier mobility increased at any temperature as the number of stacked multilayer films 4 increased. When showing a specific value, the mobility of carriers in the 77K and room temperature, 6227cm ² / Vs when the number of laminated multi-layer film 4 is 40 layers, but was 1414cm ² / Vs, the number of laminated multi-layer film 4 Of 140 layers were 10958 cm ² / Vs and 1524 cm ² / Vs. The electron mobility showed this tendency because the crystallinity of each layer above the multilayer film 4 was improved and the scattering due to crystal defects was reduced by increasing the number of multilayer films 4 stacked. It is thought to be caused.

From the above results, when the number of stacked multilayer films 4 is 40 layers or more (preferably 60 layers or more) and 160 layers or less, the fifth Al _i Ga _j In _1-ij N _z layer 5 and each layer on the fifth Al _i Ga _j In _1-ij N _z layer 5 It has been found that the crystallinity is improved and the characteristics of the semiconductor device formed using the fifth Al _i Ga _j In _{1-ij Nz} layer 5 are also improved.

  Note that the present invention is not limited to the above-described embodiments or examples, and various modifications can be made without departing from the spirit of the present invention.

Sectional drawing which shows the semiconductor device which concerns on embodiment of this invention. Each figure is an SEM photograph of the surface of the GaN layer 5. The graph which shows the relationship between the lamination | stacking number of the multilayer film 4, and the curvature of a board | substrate. The graph which shows the relationship between the half value width of the rocking curve of the diffraction peak and the number of lamination | stacking of the multilayer film 4 in a double-crystal X-ray diffraction method. Each figure is an AFM photograph of the surface of the GaN layer 5. The chart which shows the pit density on the surface of a GaN film according to the lamination | stacking number of the multilayer film. The graph which shows the temperature dependence of the mobility of a carrier (hole) and carrier density in it.

Explanation of symbols

1 ... Si substrate, 2 ... first _{Al a Ga b In 1-ab} N v layer, 3 ... second _{Al c Ga d In 1-cd} N w layer, 4 ... multilayer film, 5 ... fifth _{al i Ga j In 1-ij} N z layer, 6 ... AlN layer, 7 ... barrier layer, 8 ... carrier supply layer, 9 ... cap layer, 10 ... semiconductor layer

Claims (5)

A first Al _a Ga _b In _1-ab N _v (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, and 0 ≦ a + b ≦ 1) layer formed on a Si substrate;
Second Al _c Ga _d In _1-cd N _w (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, and 0 ≦ c + d) formed on the first Al _a Ga _b In _{1-ab Nv} layer ≦ 1) layer,
Located on the second _{Al c Ga d In 1-cd} N w layer, the third _{Al e Ga f In 1-ef} N x (0 ≦ e ≦ 1,0 ≦ f ≦ 1, and 0 ≦ e + f ≦ 1) a multilayer film in which layers and fourth Al _g Ga _h In _1-gh N _y (0 ≦ g ≦ 1, 0 ≦ h ≦ 1, and 0 ≦ g + h ≦ 1) layers are alternately stacked;
A fifth Al _i Ga _j In _1-ij N _z (0 ≦ i ≦ 1, 0 ≦ j ≦ 1, and 0 ≦ i + j ≦ 1) layer formed on the multilayer film;
Comprising a, the number of laminations of the third _{Al e Ga f In 1-ef} N x layer and the fourth _{Al g Ga h In 1-gh} N y layer in the multilayer film is less than 160 layers A characteristic semiconductor substrate.
However, v, w, x, y, and z are positive numbers. Said third _{Al e Ga f In 1-ef} N x layer in the multilayer film, the number of stacked fourth _{Al g Ga h In 1-gh} N x layer and characterized in that a total of 40 layers or more The semiconductor substrate according to claim 1. The half width of the rocking curve of the diffraction peak of the (0004) plane of the fifth Al _i Ga _j In _1-ij N _x layer in the double crystal X-ray diffraction method is 800 arcsec or less. Or the semiconductor substrate of 2. A first Al _a Ga _b In _1-ab N _v (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, and 0 ≦ a + b ≦ 1) layer formed on a Si substrate;
Second Al _c Ga _d In _1-cd N _w (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, and 0 ≦ c + d) formed on the first Al _a Ga _b In _{1-ab Nv} layer ≦ 1) layer,
Located on the second _{Al c Ga d In 1-cd} N w layer, the third _{Al e Ga f In 1-ef} N x (0 ≦ e ≦ 1,0 ≦ f ≦ 1, and 0 ≦ e + f ≦ 1) a multilayer film in which layers and fourth Al _g Ga _h In _1-gh N _y (0 ≦ g ≦ 1, 0 ≦ h ≦ 1, and 0 ≦ g + h ≦ 1) layers are alternately stacked;
A fifth Al _i Ga _j In _1-ij N _z (0 ≦ i ≦ 1, 0 ≦ j ≦ 1, and 0 ≦ i + j ≦ 1) layer formed on the multilayer film;
A semiconductor element formed using the fifth Al _i Ga _j In _1-ij N _z layer;
Comprising a number of stacked lamination number of the third _{Al e Ga f In 1-ef} N x layer and the fourth _{Al g Ga h In 1-gh} N y layer in the multilayer film is below 160 layers There is a semiconductor device. The semiconductor device according to claim 4, wherein a pit density on the surface of the semiconductor element is 1.3 × 10 ¹⁰ cm ⁻² or less.