JP5777437B2 - Single crystal substrate and semiconductor device using the same - Google Patents

Description

  The present invention relates to a single crystal substrate composed of a semiconductor made of silicon carbide and a semiconductor element using the same.

  There is silicon carbide (SiC) which is a compound of carbon and silicon. Silicon carbide has a wider band gap than silicon, a high electric field strength that leads to dielectric breakdown (good withstand voltage characteristics), high thermal conductivity, high heat resistance, excellent chemical resistance, In addition, it attracts attention because of various advantages such as excellent radiation resistance. Fields of interest for silicon carbide are broad, for example, heavy electricity including nuclear power, transportation including automobiles and aviation, home appliances, and space. A single crystal of silicon carbide is manufactured by a manufacturing method as described in Patent Document 1, for example.

JP 2000-264790 A

  In the research and development of such a single crystal made of silicon carbide, one of the challenges is to further improve the withstand voltage characteristics. The present invention has been devised in view of such circumstances, and an object of the present invention is to provide a single crystal substrate made of a single crystal of silicon carbide capable of improving withstand voltage characteristics.

Single crystal substrate of the present invention consists of a single crystal of silicon carbide, seen contains yttrium, zirconium, at least one of magnesium and calcium as dopants, the concentration of the dopants is near the first main surface The vicinity of the second main surface opposite to the first main surface is higher than the first main surface .

The semiconductor element of the present invention is provided on the single crystal substrate, the p-type semiconductor layer made of silicon carbide provided on the first main surface of the single crystal substrate, and the single crystal substrate. A first electrode; and a second electrode provided on the p-type semiconductor layer.

  According to the single crystal substrate of the present invention, since it is silicon carbide containing at least one of yttrium, zirconium, magnesium, and calcium as a trace additive, it is possible to improve withstand voltage characteristics.

  Further, according to the semiconductor element of the present invention, since the p-type semiconductor layer, the first electrode on the single crystal substrate, and the second electrode on the p-type semiconductor layer are provided on the single crystal substrate, the withstand voltage characteristics. Can be improved.

It is a perspective view which shows an example of embodiment of the single crystal substrate which concerns on this invention. It is a figure which shows typically the relationship between a lattice constant and a band gap. It is a figure which shows the modification of embodiment of the single crystal substrate of FIG. 1, and has shown the density | concentration distribution of the trace additive. It is a figure which shows an example of embodiment of the semiconductor element which concerns on this invention, (a) is equivalent to the perspective view which shows schematic structure, (b) is a cross section when cut | disconnected by the AA 'line | wire of (a) It corresponds to the figure. 2 is a single crystal growth apparatus for manufacturing the ingot of the single crystal substrate shown in FIG.

<Single crystal substrate and semiconductor element>
(Single crystal substrate)
An example of an embodiment of a single crystal substrate according to the present invention will be described with reference to the drawings as appropriate. Single crystal substrate 1 is made of a single crystal of silicon carbide.

  The single crystal substrate 1 is set to have a thickness of, for example, 0.5 μm or more and 50 mm or less. Here, the thickness h of the single crystal substrate 1 indicates the distance from the first main surface 1A to the second main surface 1B opposite to the first main surface 1A. The single crystal substrate 1 is set to have a diameter of, for example, 1 inch or more and 10 inches or less.

  The single crystal substrate 1 can be set so that the shape in plan view is, for example, a polygonal shape such as a square shape or a hexagonal shape, or a circular shape. As will be described later, the single crystal substrate 1 of the present embodiment may be manufactured by cutting out an ingot manufactured by a solution method, or the ingot may be used as the single crystal substrate 1.

  The single crystal substrate 1 has a crystal plane such as 3C, 4H, 6H, 2H, or 15R. In the present embodiment, the single crystal substrate 1 is configured such that the thickness direction is mainly a 4H crystal plane. The single crystal substrate 1 may have dislocations or micropipes extending in the thickness direction.

A small amount of a material having an atomic radius larger than that of carbon is added to the silicon carbide single crystal of the single crystal substrate 1 according to the present embodiment. Examples of such trace additives include yttrium, zirconium, magnesium, and calcium. The concentration of the trace additive may be set to such an extent that does not affect the carrier mobility, and can be set to be, for example, 1 × 10 ¹⁵ cm ⁻³ or less.

  As described above, the single crystal substrate 1 of the present embodiment contains at least one trace additive of yttrium, zirconium, magnesium, and calcium having an atomic radius larger than that of carbon. The lattice constant of the silicon carbide single crystal is small. The trace additive may be contained between the crystal lattices constituting the single crystal of silicon carbide, or may be replaced with any of carbon and silicon constituting the crystal lattice.

  Thus, when the trace additive is contained in the single crystal of silicon carbide, the trace additive distorts the crystal lattice existing around. For this reason, in the distorted crystal lattice, the distance between the crystal lattices becomes close, and the lattice constant becomes small. As a result, the lattice constant of the entire single crystal substrate 1 can be made smaller than that of silicon carbide.

  Here, the relationship between the lattice constant of the single crystal made of silicon carbide and the band gap is shown in FIG. In FIG. 2, a two-dot chain line schematically shows a lattice constant and a band gap in a state where a trace additive is not added, and a dotted line schematically shows a lattice constant and a band gap in a state where a trace additive is added.

Here, the band gap of silicon carbide is set to be, for example, 2.2 eV or more and 3.3 eV or less depending on the crystal structure. When silicon carbide is constituted by a 4H crystal plane, for example, the lattice constant in the a-axis direction is 0.307 nm and the band gap is 3.26 eV.

  Since the single crystal substrate 1 of the present embodiment contains a trace amount additive in the silicon carbide single crystal, the lattice spacing of the crystal lattice located in the periphery thereof is shortened, and the lattice constant is locally reduced. . The local change in lattice constant is set to be smaller than, for example, 0.307 nm because the lattice spacing of the crystal lattice of silicon and carbon in a 4H crystal is 0.307 nm.

  Single crystal substrate 1 has a change region where the lattice constant is locally reduced and a normal region where the lattice constant hardly changes. As a result, the single crystal substrate 1 has a lattice constant that averages the change region and the normal region. Therefore, the single crystal substrate 1 containing a trace additive has a lattice constant smaller than that of silicon carbide not containing the trace additive. Specifically, the lattice constant of the single crystal substrate 1 is reduced by, for example, about 0.01 nm.

  Therefore, as shown in FIG. 2, the single crystal substrate 1 has a wider band gap than a silicon carbide single crystal containing no trace additive. When the lattice constant of the single crystal substrate 1 is decreased by, for example, 0.0125 nm, the band gap is increased by about 0.14 eV.

  Since the band gap can be widened in this way, the withstand voltage characteristics of the single crystal substrate 1 can be enhanced. Here, as a value indicating the relationship between the electrical characteristics of the single-crystal substrate 1 and the band gap, there is a Baliga index. By using this Variger index, it is possible to confirm improvement in the withstand voltage characteristics of the single crystal substrate 1 from the change in the band gap. The Variger index is a value proportional to the cube of the change in the band gap.

(Modification 1 of single crystal substrate)
The trace additive may be substituted with a part of elements of carbon or silicon of the single crystal constituting the single crystal substrate 1. By replacing the trace additive with a part of carbon or silicon constituting the single crystal substrate 1, the trace additive can be firmly fixed. Since the trace additive is fixed in this way, it is difficult to move the trace additive within the crystal lattice even when a high thermal load such as heating of 500 ° C. or more is applied to the single crystal substrate 1. And the fluctuation of the withstand voltage characteristic of the single crystal substrate 1 can be suppressed.

(Modification 2 of single crystal substrate)
As shown in FIG. 3, the concentration of the trace additive may increase from the first main surface 1A toward the second main surface 1B opposite to the first main surface 1A. FIG. 3 is a diagram showing the concentration distribution of the trace additive in the thickness direction (direction toward the second main surface 1B) of the single crystal substrate 1 from the surface of the first main surface 1A. The concentration of the trace additive in the vicinity of the first main surface 1A and the concentration of the trace additive in the vicinity of the second main surface 1A can be set so as to have a concentration difference of 10 times or less, for example.

  Since single crystal substrate 1 has such a concentration distribution, the concentration of the trace additive contained in the vicinity of second main surface 1B is higher than that of first main surface 1A. Therefore, when the semiconductor layer made of carbon and silicon constituting the single crystal substrate 1 is epitaxially grown on the first main surface 1A of the single crystal substrate 1, the concentration of the trace additive is lower than that of the second main surface 1B. For this reason, the shift of the lattice constant can be suppressed. As a result, the withstand voltage characteristic of the single crystal substrate 1 can be improved, and a semiconductor layer made of silicon carbide can be favorably grown on the first main surface 1A.

(Modification 3 of single crystal substrate)
Single crystal substrate 1 may be an n-type semiconductor including a dopant in the single crystal. As the dopant contained in the single crystal, for example, nitrogen or the like can be used. Such a dopant concentration can be set to be 1 × 10 ¹⁸ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less, for example.

  As will be described later, the single crystal substrate 1 made of silicon carbide of the present embodiment may be manufactured using a crucible made of at least one oxide of yttrium, zirconium, magnesium and calcium by a solution growth method. In this case, the amount of aluminum functioning as a p-type dopant in the single crystal is smaller than in the prior art. As a result, it is possible to provide a single crystal substrate 1 made of silicon carbide that exhibits high-quality n-type semiconductor properties with a dopant concentration lower than usual.

(Semiconductor element)
Next, an embodiment of the semiconductor element 2 will be described with reference to FIG. The semiconductor element 2 according to this embodiment mainly includes a single crystal substrate 1, a p-type semiconductor layer 3 provided on the single crystal substrate 1, a first electrode 4 provided on the single crystal substrate 1, and a p-type semiconductor. The second electrode 5 is provided on the layer 3.

The p-type semiconductor layer 3 is provided on the first main surface 1 </ b> A of the single crystal substrate 1. The single crystal substrate 1 is an n-type semiconductor by including a dopant in the single crystal. The p-type semiconductor layer 3 is set to have a thickness of, for example, 100 nm or more and 50 μm or less. The p-type semiconductor layer 3 is composed of a single crystal of silicon carbide, and is doped with a dopant such as boron, aluminum, or vanadium. The dopant is set so that the concentration is, for example, 1 × 10 ¹⁸ cm ⁻³ or more.

  In the semiconductor element 2, the p-type semiconductor layer 3 is provided on the single crystal substrate 1 exhibiting the properties of an n-type semiconductor, so that both are pn-junctioned. Such a semiconductor element 2 can be used for a power device such as a high breakdown voltage diode. The semiconductor element 2 of the present embodiment has a good pn junction with the p-type semiconductor layer 3 because the single crystal substrate 1 exhibiting the properties of an n-type semiconductor can be produced with a dopant concentration lower than that of the prior art. It will be. As a result, it is possible to provide the semiconductor element 2 capable of obtaining good diode characteristics.

In the present embodiment, the semiconductor element 2 in which the p-type semiconductor layer 3 is formed on the single crystal substrate 1 has been described, but an n ⁻ -type semiconductor layer may be formed instead of the p-type semiconductor layer 3. Thus, the semiconductor element 2 in which the n ⁻ type semiconductor layer is formed can be used as a Schottky barrier diode. As such a semiconductor element 2, a single crystal substrate 1 to which a dopant having a concentration of, for example, 1 × 10 ¹⁸ cm ^{−3 to} 1 × 10 ²⁰ cm ⁻³ is added can be used. As the n ⁻ type semiconductor layer, for example, a layer to which a dopant having a concentration of about 1 × 10 ¹⁶ is added can be used.

In this case, since the n-type dopant concentration contained in the single crystal substrate 1 is smaller than the conventional one, the n ⁻ type semiconductor layer can be grown on the single crystal substrate 1 with good crystallinity.

  Alternatively, the first electrode 4 and the second electrode 5 may be formed directly on the single crystal substrate 1 and used as a Schottky barrier diode. In that case, the first electrode 4 and the second electrode 5 may be made of a material that makes ohmic contact with the single crystal substrate 1 and a material that makes Schottky contact. An example of a material that is brought into ohmic contact with the single crystal substrate 1 made of silicon carbide is nickel. An example of a material that forms a Schottky contact with the single crystal substrate 1 made of silicon carbide is titanium.

<Manufacturing method of single crystal substrate and semiconductor element>
(Manufacturing method of single crystal substrate)
An example of a method for manufacturing the single crystal substrate 1 will be described with reference to FIG. A single crystal made of silicon carbide constituting the single crystal substrate 1 can be manufactured by a solution growth method as follows.

  A single crystal made of silicon carbide can be manufactured by the single crystal growing apparatus 6. The single crystal growing apparatus 6 includes a crucible 7, a crucible container 8, a heating mechanism 9, a transport mechanism 10, and a control unit 11. In this single crystal growing apparatus 6, a single crystal is grown using a solution growth method.

  The crucible 7 has a function as a vessel for melting the raw material of the single crystal (carbon or silicon) to be grown. In this embodiment, the single crystal raw material is melted in the crucible 7 and stored as the raw material melt 12. In the present embodiment employing the solution growth method, a thermal equilibrium state is created inside the crucible 7 to grow a single crystal.

  The crucible 7 is composed of oxides such as yttrium oxide, zirconium oxide, magnesium oxide and calcium oxide. The crucible 7 may be formed from one of such oxides, or may be formed by mixing a plurality of oxides. Alternatively, a crucible 7 made of carbon coated with at least one oxide such as yttrium oxide, zirconium oxide, magnesium oxide and calcium oxide may be used as the crucible 7. Note that the surface of the crucible that coats the oxide includes at least the surface in contact with the raw material melt 12.

  The crucible 7 is arranged inside the crucible container 8. The crucible container 8 has a function of holding the crucible 7. A heating member 13 and a heat insulating material 14 are disposed between the crucible container 8 and the crucible 7. This heat insulating material 14 surrounds the crucible 7. The heat insulating material 14 suppresses heat radiation from the crucible 7 and contributes to keeping the temperature of the crucible 7 stable.

  The crucible 7 is heated by the heating member 13 heated by the heating mechanism 9. That is, the heating mechanism 9 has a function of indirectly heating the crucible 7. The heating mechanism 9 of the present embodiment employs an electromagnetic heating method in which the heating member 13 is heated by electromagnetic waves, and includes a coil 15 and an AC power supply 16. The coil 15 is formed of a conductor and is wound so as to surround the periphery of the crucible 7. The AC power supply 16 is for flowing an AC current through the coil 15, and the heating time up to the set temperature in the crucible 7 can be shortened by using an AC current having a high frequency.

  For the heating member 13, for example, a metal material such as copper, platinum, gold, nickel, or zinc can be used. By using the heating member 13, even if the crucible 7 is made of the above-described oxide, the heating member 13 can be heated with electromagnetic waves to heat the crucible 7 satisfactorily.

  In this embodiment, the crucible 7 is indirectly heated as follows. First, an electric current is passed through the coil 15 using the AC power source 16 to generate an electromagnetic field in the space including the heating member 13. Next, an induced current flows through the heating member 13 made of a metal material by this electromagnetic field. The induced current flowing through the heating member 13 is converted into thermal energy by various losses such as Joule heat generation due to electric resistance and heat generation due to hysteresis loss. That is, the heating member 13 is heated by the heat loss of the induced current.

In the present embodiment, an electromagnetic heating method is employed as the heating mechanism 9, but the crucible 7 may be heated using another method. Instead of the heating mechanism 9 and the heating member 13, for example, other methods such as a method of transferring heat generated by a heating resistor such as carbon can be adopted. When this heat transfer type heating mechanism is employed, a heating resistor is disposed in place of the heating member 13 (between the crucible 7 and the heat insulating material 14).

  A single crystal seed crystal 17 is supplied to the raw material melt 12 of the crucible 7 by the transport mechanism 10. That is, the transport mechanism 10 has a function of carrying the seed crystal into the raw material melt 12. The transport mechanism 10 also has a function of transporting a single crystal grown from the raw material melt 12.

  The transport mechanism 10 includes a pulling shaft 10a and a power source 10b. The pulling shaft 10a carries in and out the seed crystal 17 and the grown single crystal. The seed crystal 17 is attached to the tip of the pulling shaft 10a, and the movement of the pulling shaft 10a in the vertical directions D1 and D2 is controlled by the power source 10b. In the present embodiment, the D1 direction means a downward direction on the physical space, and the D2 direction means an upward direction on the physical space.

  In the single crystal growing apparatus 6, the AC power source 16 of the heating mechanism 9 and the power source 10 b of the transport mechanism 10 are connected to the control unit 11 and controlled. That is, in the single crystal growing apparatus 6, the control unit 11 controls the heating and temperature control of the raw material melt 12 and the loading and unloading of the seed crystal 17 and the seed crystal. The control unit 11 includes a central processing unit and a storage device such as a memory, and includes, for example, a known computer.

  In the raw material melt 12, an element constituting a single crystal to be grown is melted as a solvent. In the raw material melt 12, an element constituting a single crystal grown in this solvent is dissolved as a solute. The solubility of the solute element increases as the temperature of the solvent element increases. For this reason, when the raw material melt 12 in which many solutes are dissolved in a solvent at a high temperature is cooled, the solutes are deposited with thermal equilibrium as a boundary. In the solution growth method employed in this embodiment, single crystals are grown by utilizing precipitation due to this thermal equilibrium.

  Since the heating mechanism 9 of the present embodiment suitably causes precipitation on the D1 direction side to which the seed crystal 17 is supplied, the temperature on the D2 direction side around the seed crystal 17 is lower than the temperature on the D1 direction side. So that it is heated. Specifically, the number of turns of the coil 15 is smaller on the D2 direction side than on the D1 direction side. By configuring the coil 15 in this way, the induced current generated on the D1 direction side can be increased, and the D1 direction side can be relatively heated.

  By such a single crystal growing apparatus 6, a single crystal ingot made of silicon carbide is manufactured. The single crystal ingot (lump) can be produced, for example, by cutting it in a direction perpendicular to the pulled-up direction. As a method for cutting the ingot, for example, there is a method of physically cutting using a wire saw, a dicing saw, a blade blade or the like.

  In the present embodiment, the crucible 7 is made of an oxide such as yttrium oxide, zirconium oxide, magnesium oxide, and calcium oxide. The crucible 7 made of such an oxide is less likely to contain a material imparted with p-type conductivity as an impurity. Therefore, the concentration of the material imparted with p-type conductivity contained in the single crystal is lower than that of a single crystal grown using a conventional carbonization crucible. As a result, a single crystal made of intrinsic or n-type silicon carbide having a low concentration of material imparted with p-type conductivity can be manufactured. That is, aluminum which is a p-type dopant is less likely to be contained in a single crystal made of silicon carbide.

Further, since an oxide that does not contain a material imparting p-type conductivity is used as the crucible 7, even when a silicon carbide single crystal is grown over a long period of time so as to be thick. The concentration of the material imparted with p-type conductivity contained in the raw material melt can be reduced. Therefore, it is possible to easily increase the thickness of the single crystal and improve the productivity.

In the conventional solution growth method, carbon is used as a crucible when producing a single crystal made of silicon carbide. Since the crucible made of carbon contains aluminum as an impurity, the grown silicon carbide single crystal contains aluminum having a concentration of 1 × 10 ¹⁴ cm ⁻³ or more. Therefore, aluminum functions as a p-type dopant with respect to silicon carbide, and it is difficult to produce an intrinsic or n-type silicon carbide single crystal. In particular, when the thickness of the single crystal is thick, in the production of the conventional single crystal, the concentration of aluminum contained in the raw material melt is increased by heating the crucible for a long time, so it is difficult to increase the thickness of the single crystal. Productivity was low.

  On the other hand, in this embodiment, yttrium, zirconium, magnesium, and calcium, which are constituent elements of the oxide that constitutes the crucible 7, are partly dissolved and easily mixed into the raw material melt 12. As a result, elements constituting the crucible 7 such as yttrium, zirconium, magnesium and calcium are contained in the grown single crystal. Therefore, when such an element is contained in the single crystal substrate 1, the withstand voltage characteristic of the single crystal substrate 1 can be improved.

  Crystal growth may be performed by adding elements such as yttrium, zirconium, magnesium, and calcium to the raw material melt 12. Thus, the withstand voltage characteristic of the single crystal substrate 1 can be improved more reliably by growing the crystal while adding elements such as yttrium, zirconium, magnesium and calcium to the raw material melt 12. Further, the concentration of elements such as yttrium, zirconium, magnesium and calcium contained in the single crystal substrate 1 can be easily adjusted while adjusting the concentrations of these elements.

(Modification of manufacturing method of single crystal substrate)
The concentration of an element such as yttrium, zirconium, magnesium, and calcium contained in the single crystal substrate may be adjusted by adjusting the magnitude of the frequency of the alternating current flowing through the coil 15 or the current density of the alternating current. Specifically, by increasing the frequency of the alternating current flowing through the coil 15 as the single crystal is pulled up, the amount of the element dissolved from the crucible 7 into the raw material melt 12 is increased, and the crucible 7 contained in the single crystal. The concentration of the elements constituting can be increased.

  Alternatively, elements such as yttrium, zirconium, magnesium, and calcium may be introduced into the raw material melt 12 to adjust the concentration of the element contained in the single crystal to be grown. Specifically, as the single crystal is pulled up, the concentration of the input element contained in the raw material melt 12 is increased by increasing the input amount of the element (referred to as input element) input into the raw material melt 12. The concentration of the input element contained therein may be increased.

  Thus, the single crystal substrate 1 in which the concentration of elements such as yttrium, zirconium, magnesium and calcium is increased from the first main surface 1A toward the second main surface 1B opposite to the first main surface 1A. Can be manufactured.

(Semiconductor element manufacturing method)
Next, an embodiment of a method for manufacturing the semiconductor element 2 will be described below. As shown in FIG. 4, the semiconductor element 2 is mainly composed of a single crystal substrate 1, a p-type semiconductor layer 3, a first electrode 4, and a second electrode 5.

  The p-type semiconductor layer 3 is provided by crystal growth on the first main surface 1A of the single crystal substrate 1. As a method for growing the p-type semiconductor layer 3, for example, a molecular beam epitaxy method, a hydride vapor phase growth method, a pulse laser deposition method, or the like can be used. In addition, when the conductivity type is imparted to the semiconductor, an additive may be mixed while the optical semiconductor layer 3 is crystal-grown.

  Next, the first electrode 4 and the second electrode 5 are formed. As a method of forming the first electrode 4 and the second electrode 5, for example, when using a metal, a sputtering method or a vapor deposition method can be used. In addition, after laminating | stacking the metal used as the 1st electrode 4 and the 2nd electrode 5, you may make ohmic contact, respectively by performing annealing. In this way, the semiconductor element 2 can be manufactured.

  As described above, in the conventional semiconductor element, aluminum is contained in the single crystal, and it is difficult to manufacture a single crystal substrate to which an n-type conductivity type is imparted by suppressing the amount of dopant added. . Therefore, for example, when a p-type semiconductor layer is crystal-grown on an n-type single crystal substrate to which a large amount of dopant is added, the lattice constants of both are shifted and a p-type semiconductor layer having good crystallinity is formed. It was not possible to improve the diode characteristics.

In the semiconductor element 2 of the present embodiment, a p-type semiconductor layer is formed on an n-type single crystal substrate 1 in which aluminum in a single crystal of silicon carbide is set to be lower than, for example, 1 × 10 ¹⁴ cm ^−3. 3 is grown. Therefore, the crystallinity of the p-type semiconductor layer 3 can be improved, and since the lattice constants of the single crystal substrate 1 and the p-type semiconductor layer 3 are close, a good pn junction surface is formed near the interface between the two. be able to. As a result, it is possible to provide a semiconductor element capable of improving the diode characteristics as compared with the conventional one.

  The present invention is not limited to the above-described embodiment, and various improvements and modifications may be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Single crystal substrate 1A 1st main surface 1B 2nd main surface 2 Semiconductor element 3 P-type semiconductor layer 4 1st electrode 5 2nd electrode 6 Single crystal growth apparatus 7 Crucible 8 Crucible container 9 Heating mechanism
10 Transport mechanism
10a Lifting shaft
10b Power source
11 Control unit
12 Raw material melt
13 Heating material
14 Thermal insulation
15 coils
16 AC power supply
17 seed crystals

Claims (5)

Made of single crystal of silicon carbide, seen contains yttrium, zirconium, at least one of magnesium and calcium as dopants,
A concentration of the trace additive is higher in the vicinity of the second main surface opposite to the first main surface than in the vicinity of the first main surface .   The single crystal substrate according to claim 1, wherein the trace additive is substituted with a part of elements of carbon or silicon of the single crystal.   3. The single crystal substrate according to claim 1, wherein the concentration of the trace additive increases from the first main surface toward the second main surface opposite to the first main surface.   The single crystal substrate according to claim 1, wherein the single crystal is an n-type semiconductor containing a dopant. The single crystal substrate according to claim 4, a p-type semiconductor layer made of silicon carbide provided on the first main surface of the single crystal substrate, a first electrode provided on the single crystal substrate, A semiconductor element having a second electrode provided on the p-type semiconductor layer.

Images