JP2011199187A - Gallium nitride based semiconductor diode - Google Patents

Abstract

Disclosed is a gallium nitride based semiconductor diode capable of improving the breakdown voltage of a diode structure formed on a gallium nitride substrate having nonuniform in-plane resistivity.
A semiconductor diode 1 is provided between a gallium nitride free-standing substrate 10 whose main surface is a C-plane, a junction region including a pn junction 16a or a Schottky junction 16, and a gallium nitride free-standing substrate and the junction region. And a semiconductor layer 14 having a conductivity lower than the minimum resistivity of the surface of the gallium nitride free-standing substrate in the substrate plane and having the same conductivity type as that of the gallium nitride free-standing substrate.
[Selection] Figure 3

Description

  The present invention relates to a gallium nitride based semiconductor diode. In particular, the present invention relates to a gallium nitride based semiconductor diode with improved breakdown voltage.

  2. Description of the Related Art Conventionally, a gallium nitride substrate is a closed defect collection region that is a closed region that includes a core in which a large number of defects extending through the substrate surface are aggregated and is distinguished by a grain boundary on the substrate surface, Single-crystal gallium nitride having a single-crystal low dislocation-accompaniment region associated with a defect-gathering region and a single-crystal low-dislocation residual region existing outside the single-crystal low-dislocation accompaniment region and having the same crystal orientation A substrate is known (for example, refer to Patent Document 1).

  Also, a base layer made of a group III nitride semiconductor, a void formation blocking layer formed on the base layer, a porous group III nitride semiconductor layer formed on the void formation blocking layer, and a porous III A porous substrate for epitaxial growth having a porous metal layer formed on a group nitride semiconductor layer is known (see, for example, Patent Document 2).

  According to the single-crystal gallium nitride substrate described in Patent Document 1, it is possible to eliminate the planar defects at the dislocation gathering portion at the center of the pit composed of the facet surface. Moreover, according to the porous substrate for epitaxial growth described in Patent Document 2, epitaxial crystal growth with a low dislocation density can be realized.

JP 2003-165799 A JP 2004-319711 A

  Currently available gallium nitride substrates have a relatively high dislocation density, and in addition, the dislocation density is unevenly distributed in the substrate plane. Furthermore, although the gallium nitride substrate is a conductive substrate, the conductivity is slightly nonuniform within the substrate surface.

The inventor made a gallium nitride substrate by the chloride vapor phase epitaxy method (HVPE method) with reference to the method described in Patent Document 1. As a result, the C plane was not grown and the C plane was not grown. It was discovered that the concentration of impurities in the crystal was significantly different from the location (location growing while forming facets). In general, it is known that the impurity concentration incorporation efficiency varies greatly depending on the growth surface. In the case of gallium nitride grown by the HVPE method, a large difference was observed particularly in the efficiency of oxygen (O) incorporation. In particular, it was measured that the oxygen (O) concentration was about 0.1 to 1E19 cm ⁻³ at a location where the C-plane was not grown. When the electrical characteristics of this part were measured, this part showed n-type conductivity and the resistivity was about 0.02 to 0.003 Ω · cm.

On the other hand, the oxygen concentration at the C-plane grown location is about 1E17 cm ⁻³ or less, and when other donor impurity concentrations such as germanium (Ge) and silicon (Si) are low, the resistivity at this location is It was measured that it may reach about 0.1 Ω · cm or more. When trying to lower the resistance by increasing the concentration of donor impurities such as Ge and Si, it is difficult to control the growth mode of the facet grown part and the defect density increases, so gallium nitride while maintaining the facet surface In the method of growing a substrate, it is inevitable that the resistivity becomes non-uniform within the substrate surface.

On the other hand, in the case where the inventor fabricated a gallium nitride substrate with reference to the method described in Patent Document 2, the oxygen (O) concentration was low because it was not growth while intentionally forming a facet plane. . However, although it is only a small part, a portion where the resistivity is non-uniform is recognized in a part of the region, and a region where the resistivity is partially different is mixed in the substrate surface. According to the study by the present inventor, the oxygen (O) concentration in this partial region was about 5E18 cm ⁻³ and the resistivity was about 0.005 Ω · cm. Further, although the oxygen concentration in other regions was about 1E17 cm ⁻³ or less, the resistivity in most places was reduced by controlling the concentration of other donor impurities such as germanium (Ge) and silicon (Si). It was able to be 0.005-0.02 ohm * cm. However, when observed finely, there is a region where the resistivity is slightly non-uniform in the substrate surface, and there is room for improvement in non-uniformity of the resistivity.

  That is, as described above, it was recognized that the gallium nitride substrate having the n-type conductivity described in Patent Document 1 and Patent Document 2 has non-uniform resistivity within the substrate surface. For this reason, when a device with a diode structure driven on a gallium nitride substrate with a high voltage and a large current and a large area is manufactured, the electric field distribution inside the diode is affected by the non-uniform resistivity in the substrate surface. As a result, an unexpected bias occurs, and as a result, dielectric breakdown is induced, and sufficient device breakdown voltage may not be obtained, which is significantly lower than the expected value (several hundred volts or more) of material properties. May end up.

  Accordingly, an object of the present invention is to provide a gallium nitride based semiconductor diode capable of improving the breakdown voltage of a diode structure formed on a gallium nitride substrate having non-uniform in-plane resistivity.

  In order to achieve the above object, the present invention is provided between a gallium nitride free-standing substrate whose principal surface is a C-plane, a junction region including a pn junction or a Schottky junction, and a gallium nitride free-standing substrate and the junction region, There is provided a gallium nitride based semiconductor diode having a resistivity lower than the minimum resistivity in the substrate surface of the gallium nitride free-standing substrate surface and having a semiconductor layer having the same conductivity type as that of the gallium nitride free-standing substrate.

  In the gallium nitride semiconductor diode, the semiconductor layer preferably has a superlattice structure.

  In the gallium nitride based semiconductor diode, the gallium nitride free-standing substrate can have an ohmic electrode on the surface opposite to the main surface.

  The gallium nitride semiconductor diode according to the present invention can provide a gallium nitride semiconductor diode capable of improving the breakdown voltage of a diode structure formed on a gallium nitride substrate having non-uniform in-plane resistivity.

1 is a cross-sectional view of a semiconductor diode according to a first embodiment of the present invention. It is sectional drawing of the semiconductor diode which concerns on the 2nd Embodiment of this invention. It is sectional drawing of the semiconductor diode which concerns on the 3rd Embodiment of this invention.

[Knowledge obtained by the inventor]
As a result of intensive studies, the present inventor has found that even when a gallium nitride substrate whose resistivity is not uniform in the plane is used as a growth substrate, the resistance is lower than that of the lowest resistivity region on the gallium nitride free-standing substrate. An n-type conductivity type layer having a low rate (that is, a semiconductor layer having a resistivity lower than the minimum resistivity in the substrate surface of the gallium nitride free-standing substrate surface), a pn junction or a Schottky junction, and a gallium nitride substrate It was found that the withstand voltage of the semiconductor diode can be improved by providing it between the two.

  The breakdown voltage of a semiconductor diode is determined by the voltage (breakdown voltage) when the breakdown phenomenon starts when the reverse bias voltage is increased in the case of an ideal semiconductor diode formed of a semiconductor with uniform resistivity. Is done. However, in the case of an actual semiconductor diode, a large electric field is applied to a part of the semiconductor diode because the semiconductor layer is not completely uniform. Thereby, for example, the electric field concentrates on a path through which current easily flows, such as a region where dislocations are slightly concentrated. Then, the reverse current may suddenly increase below the breakdown voltage expected from the material properties. That is, obtaining a uniform semiconductor layer or making an element structure in which an electric field is not partially concentrated is a measure for improving the breakdown voltage of the semiconductor diode.

  The present inventor inserts a layer having a sufficiently low resistivity as compared with all portions of the gallium nitride free-standing substrate between the gallium nitride free-standing substrate and a junction region including a pn junction or a Schottky junction, thereby obtaining gallium nitride. It has been found that the electric field concentration caused by the non-uniformity of the resistivity of the free-standing substrate can be suppressed, and that the withstand voltage of the diode structure formed on the gallium nitride free-standing substrate can be increased. In the case where a pin junction or an npn junction is provided instead of the pn junction and the diode structure or the transistor structure has an n-type layer on the gallium nitride free-standing substrate side, the electric field concentration is similarly suppressed and the diode structure. It is possible to improve the breakdown voltage.

  Here, a GaN layer to which a donor impurity such as germanium or silicon is sufficiently added is considered as the simplest layer as the layer having a sufficiently low resistivity as compared with all the portions of the gallium nitride free-standing substrate. In addition, for example, it is preferable that a superlattice structure whose resistance is reduced by sufficiently adding a donor impurity be a layer having a sufficiently low resistivity as compared with all the portions of the gallium nitride free-standing substrate. The reason why the superlattice structure is preferable is that the purpose of providing the layer is to reduce the resistivity of the gallium nitride free-standing substrate by inserting a layer having a sufficiently low resistance between the gallium nitride free-standing substrate and the junction region. This is because electric field concentration caused by uniformity is suppressed.

  When a superlattice structure is formed, the superlattice structure has at least a part of threading dislocations extending from the gallium nitride substrate to the pn junction or Schottky junction side to the outside of the growth direction (that is, gallium nitride self-supporting). An effect of bending (toward a direction along a direction parallel to the surface of the substrate) and an effect of promoting current dispersion in the growth plane can be exhibited. Therefore, it is more preferable to provide a superlattice structure having a sufficiently low resistance and an appropriate number of layers.

[Summary of embodiment]
In a gallium nitride based semiconductor diode comprising a gallium nitride free-standing substrate whose main surface is a C-plane and a junction region including a pn junction or a Schottky junction, the gallium nitride-based semiconductor diode is provided between the gallium nitride free-standing substrate and the junction region, There is provided a gallium nitride based semiconductor diode having a resistivity lower than the minimum resistivity of the surface of the gallium nitride free-standing substrate in the substrate plane and having a semiconductor layer having the same conductivity type as that of the gallium nitride free-standing substrate. .

[First Embodiment]
FIG. 1 shows an outline of a cross section of a semiconductor diode according to a first embodiment of the present invention.

  A semiconductor diode 1 as a gallium nitride (GaN) semiconductor diode according to the first embodiment includes a substrate 10, a semiconductor layer 12 provided on the substrate 10, and a drift layer 14 provided on the semiconductor layer 12. Prepare. Furthermore, the semiconductor diode 1 is provided on the surface of the substrate 10 on the opposite side of the semiconductor layer 12, the ohmic electrode 20 that is in ohmic contact with the substrate 10, and the Schottky provided on the surface of the drift layer 14 on the opposite side of the semiconductor layer 12. And an electrode 22.

  The semiconductor diode 1 is manufactured as follows, for example. First, an epitaxial substrate is manufactured by epitaxially growing the semiconductor layer 12 and the drift layer 14 on the substrate 10 by a metal organic chemical vapor deposition (MOVPE) method or the like. Next, the ohmic electrode 20 is formed on one surface of the epitaxial substrate using a photolithography method, a vacuum deposition method, or the like, and the Schottky electrode 22 is formed on the other surface. Thereby, the semiconductor diode 1 can be manufactured. The semiconductor diode 1 has a vertical diode structure that allows current to flow in the growth direction of the semiconductor layer 12 and the like.

  In the present embodiment, a gallium nitride free-standing substrate whose main surface is a C-plane can be used as the substrate 10. Therefore, the semiconductor layer 12 is formed on the main surface, and the ohmic electrode 20 is formed on the surface opposite to the main surface. The substrate 10 has an n-type conductivity by containing a predetermined amount of a predetermined impurity as a donor.

  Further, the semiconductor layer 12 and the drift layer 14 are formed of a semiconductor having the same conductivity type as that of the substrate 10. The semiconductor layer 12 and the drift layer 14 are made of, for example, gallium nitride. The Schottky electrode 22 is in Schottky junction with the drift layer 14 at the interface 14 a between the drift layer 14 and the Schottky electrode 22. In the present embodiment, a region including the drift layer 14 and the Schottky junction is referred to as a junction region 16. Note that the junction region 16 can be formed to include one layer made of a semiconductor or a plurality of layers made of a semiconductor and a Schottky electrode provided on the outermost surface of the one layer or the plurality of layers. .

  Here, the semiconductor layer 12 is provided between the substrate 10 and the bonding region 16. The semiconductor layer 12 has a resistivity lower than the minimum resistivity within the substrate surface of the substrate 10 surface. Specifically, the semiconductor layer 12 has a resistivity that is lower than the resistivity of the region having the lowest resistivity on the surface of the substrate 10 (that is, the surface facing the bonding region 16) over the entire layer. That is, the resistivity of the semiconductor layer 12 is adjusted to be lower than the resistivity in any region of the surface of the substrate 10 by controlling the amount of impurities added to the semiconductor layer 12.

  In addition, by making the shape of the Schottky electrode 22 in plan view a perfect circle, electric field concentration on a partial region of the diode structure of the semiconductor diode 1 can be further suppressed. Further, by implanting ions such as hydrogen into the periphery of the Schottky electrode 22, the resistance of the periphery can be increased and the electric field concentration can be reduced. Further, by forming a field plate structure in which an insulating film is sandwiched in a region below the periphery of the Schottky electrode 22, electric field concentration can be reduced.

(Effects of the first embodiment)
In the semiconductor diode 1 according to the first embodiment of the present invention, the semiconductor layer 12 having a lower resistivity than the lowest resistivity region of the substrate 10 between the substrate 10 and the drift layer 14 (that is, the surface of the substrate 10). Since the semiconductor layer 12) having a resistivity lower than the minimum resistivity in the substrate plane is provided, electric field concentration due to the non-uniformity of the resistivity of the substrate 10 can be suppressed, and the semiconductor as a Schottky diode The breakdown voltage of the diode 1 can be improved.

[Second Embodiment]
FIG. 2 shows an outline of a cross section of a semiconductor diode according to the second embodiment of the present invention.

  The semiconductor diode 2 according to the second embodiment has the same configuration as the semiconductor diode 1 except that the semiconductor layer 12a has a superlattice structure compared to the semiconductor diode 1 according to the first embodiment. , Have function. Therefore, a detailed description is omitted except for differences.

  The semiconductor layer 12a included in the semiconductor diode 2 is formed to have a superlattice structure. Specifically, the semiconductor layer 12a is a superlattice low resistance multilayer film composed of a plurality of nitride compound semiconductor layers to which n-type conductivity type donors are added at a predetermined concentration. More specifically, the semiconductor layer 12a is formed by laminating a plurality of pair layers including pairs of a first semiconductor film and a second semiconductor film different from the first semiconductor film. In this case, a predetermined amount of a predetermined donor impurity is added to one or both of the first semiconductor film and the second semiconductor film.

(Effect of the second embodiment)
In the semiconductor diode 2 according to the second embodiment of the present invention, a semiconductor layer 12a having a superlattice structure having a resistivity lower than that of the lowest resistivity region of the substrate 10 is provided between the substrate 10 and the drift layer 14. Therefore, electric field concentration resulting from the non-uniformity of the resistivity of the substrate 10 can be suppressed, and the breakdown voltage of the semiconductor diode 1 as a Schottky diode can be improved.

[Third Embodiment]
FIG. 3 shows an outline of a cross section of a semiconductor diode according to the third embodiment of the present invention.

  The semiconductor diode 3 according to the third embodiment has substantially the same configuration as that of the semiconductor diode 1 except that the junction region 16a has a pn junction as compared to the semiconductor diode 1 according to the first embodiment. , Have function. Therefore, a detailed description is omitted except for differences.

  The semiconductor diode 3 includes a substrate 10, a semiconductor layer 12 provided on the substrate 10, a drift layer 14 provided on the semiconductor layer 12, and a conductivity different from the conductivity type of the drift layer 14 provided on the drift layer 14. And a semiconductor layer 18 of a type. Further, the semiconductor diode 3 is provided on the surface of the substrate 10 on the opposite side of the semiconductor layer 12, the ohmic electrode 20 that is in ohmic contact with the substrate 10, and the ohmic electrode provided on the surface of the semiconductor layer 18 on the opposite side of the drift layer 14. 24. The semiconductor layer 12 can also be a semiconductor layer 12a having a superlattice structure, as in the second embodiment.

(Effect of the third embodiment)
In the semiconductor diode 3 according to the third embodiment of the present invention, the semiconductor layer 12 having a lower resistivity than the lowest resistivity region of the substrate 10 is provided between the substrate 10 and the drift layer 14. The electric field concentration caused by the non-uniformity of the resistivity can be suppressed, and the breakdown voltage of the semiconductor diode 3 as the pn diode can be improved.

  As a semiconductor diode according to Example 1, a semiconductor diode having the structure of the semiconductor diode 1 according to the first embodiment was manufactured.

  Specifically, first, an n-type conductivity type GaN having a uniform resistance in the growth plane and a thickness of 1 μm on a C-plane gallium nitride (GaN) substrate by metal organic vapor phase epitaxy (MOVPE). Growing layer. The resistivity of the portion with the lowest resistivity of the GaN substrate used in Example 1 was about 0.005 Ω · cm. The growth of the GaN layer was performed with the substrate temperature set to 1100 ° C., and germanium or silicon was added as a donor impurity. Also, the amount of donor impurity added was adjusted so that the resistivity of the GaN layer was smaller than the resistivity of the GaN substrate. Specifically, the resistivity of the GaN layer was adjusted in the range of 0.001 Ω · cm to 0.004 Ω · cm by adjusting the donor concentration during the growth of the GaN layer.

In addition, it was indirectly confirmed from the intensity distribution of the luminescence light when the GaN substrate was irradiated with ultraviolet rays that the resistivity of the GaN substrate was not uniform in the plane. In addition, the measurement of the minimum resistivity within the substrate surface of the GaN substrate surface is performed by ionizing a minute region of the GaN substrate (specifically, a region of 0.005 to 0.05 mm ³ as the volume of the object to be measured). It cut out by milling, calculated | required the approximate value of the volume of the area | region where a resistivity differs from luminescence light intensity distribution, and calculated | required by correcting the volume fraction by calculation from the measured value of the resistance value of the said micro area | region. By using a plurality of GaN substrates having substantially the same quality and measuring at a number of locations, it was confirmed that the resistivity at the lowest resistivity of the GaN substrate was approximately around 0.005 Ω · cm.

  For comparison, a sample (comparative example) in which the donor concentration of the GaN layer was lowered and the resistivity of the GaN layer was 0.005 Ω · cm or more and 0.1 Ω · cm or less was also produced. Note that the resistivity of the GaN layer is the same as that of Example 1 and Comparative Example 1 for the sample (thickness is 1000 nm) grown on the sapphire substrate under the same conditions as in Example 1 or Comparative Example 1. Measurements were made using the needle method.

Subsequently, with the growth temperature set at 1100 ° C., the supply amount of the donor impurity is suppressed so that the solid phase concentration of the donor impurity is about 2E16 cm ⁻³ , and a drift layer made of n-type GaN having a thickness of 10 μm is formed. Grown on the GaN layer. Because of the operating principle of the semiconductor diode, the breakdown voltage of the semiconductor diode can be increased by increasing the thickness of the drift layer made of n-type GaN. Therefore, the thickness of the drift layer made of n-type GaN should be 10 μm or more. You can also. The growth temperature is not limited to 1100 ° C. (other growth conditions are not limited).

  On the drift layer made of n-type GaN, a Schottky electrode having a true circle in plan view and a diameter of 100 μm or more and 800 μm or less was formed. The Schottky electrode was formed from a metal containing nickel and aluminum. Note that the Schottky electrode can be made of any other material that provides good Schottky contact with the drift layer. Further, by implanting ions such as hydrogen (H) into the peripheral region of the Schottky electrode, the electric field is prevented from concentrating on the peripheral portion of the Schottky electrode when a high voltage is applied. The ohmic electrode on the back surface of the GaN substrate (that is, the -C surface) was formed from a material containing aluminum and gold. As the material of the ohmic electrode, other materials can be used as long as a good ohmic contact with the GaN substrate can be obtained.

  The current-voltage (IV) characteristics of the Schottky diode on the GaN substrate according to Example 1 manufactured as described above were measured. Then, when the voltage (withstand voltage) at which the reverse current rapidly increases was examined, the withstand voltage when the resistivity of the GaN layer was 0.1 Ω · cm was about 540 V, and the withstand voltage when the resistivity was 0.01 Ω · cm. Was about 540V.

  On the other hand, the withstand voltage when the resistivity was 0.004 Ω · cm was about 720 V, and the withstand voltage when the resistivity was 0.002 Ω · cm was about 760 V. Therefore, it was confirmed that the breakdown voltage increases when the resistivity of the GaN layer is smaller than the lowest resistivity portion of the GaN substrate. Even when the substrate having the lowest resistivity of the GaN substrate of 0.01 Ω · cm was used, no change was observed in the tendency.

  In other words, by inserting a layer having a sufficiently low resistivity compared to all locations on the GaN substrate, electric field concentration due to the non-uniformity of the resistivity of the substrate can be suppressed and formed on the GaN substrate. It was shown that the breakdown voltage of the Schottky diode can be increased.

  As the semiconductor diode according to Example 2, a semiconductor diode having the structure of the semiconductor diode 2 according to the second embodiment was manufactured.

  In Example 2, instead of the GaN layer of the semiconductor diode according to Example 1, a superlattice low resistance multilayer film having n-type conductivity was formed on a GaN substrate. Specifically, a superlattice low-resistance multilayer is formed by forming a pair of AlGaN layers and GaN layers having an aluminum composition of about 10% as a pair layer and forming a multilayer film including 20 to 100 pair layers on a GaN substrate. A film was formed. Other configurations are the same as those of the semiconductor diode according to the first embodiment.

  The film thickness of each of the AlGaN layer and the GaN layer was 2.0 nm to 3.5 nm. In Example 2, the resistivity of the superlattice low resistance multilayer film was controlled by adding a donor impurity to the GaN layer. Note that the donor addition method is not limited to the example in Example 2, and donor impurities can be added to the AlGaN layer, or donor impurities can be uniformly added to both the GaN layer and the AlGaN layer.

  When the breakdown voltage of the semiconductor diode according to Example 2 was measured, the breakdown voltage when the resistivity of the superlattice low resistance multilayer film was 0.1 Ω · cm was about 580 V, and when the resistivity was 0.01 Ω · cm. The breakdown voltage was about 590V. On the other hand, the breakdown voltage when the resistivity of the superlattice low resistance multilayer film was 0.004 Ω · cm was about 810 V, and the breakdown voltage when the resistivity was 0.002 Ω · cm was about 820 V. From the above, it was shown that when a superlattice low resistance multilayer film having a resistivity lower than that of the lowest resistivity of the GaN substrate is used, the breakdown voltage of the semiconductor diode is increased. Even when the GaN substrate having the lowest resistivity of 0.01 Ω · cm was used, this tendency was not changed.

  In other words, by inserting a layer having a sufficiently low resistivity as compared to all locations on the GaN substrate, electric field concentration due to the non-uniformity of the resistivity of the substrate can be suppressed and formed on the GaN substrate. It was shown that the breakdown voltage of the Schottky diode can be increased.

  As the semiconductor diode according to Example 3, a semiconductor diode having the structure of the semiconductor diode 3 according to the third embodiment was manufactured.

  In Example 3, a p-type conductivity type GaN layer having a thickness of 500 nm and added with an acceptor such as Mg is grown on the drift layer made of n-type GaN in Example 1 and Example 2. did. An ohmic electrode made of a palladium-based material was formed on the p-type GaN layer. Thus, the semiconductor diode according to Example 3 was manufactured.

  Then, similarly to Example 1 and Example 2, the voltage (withstand voltage) at which the reverse current suddenly increased was measured from the current-voltage (IV) characteristics. As a result, when the resistivity of the GaN layer or the superlattice low-resistance multilayer film is larger than the portion with the lowest resistivity of the GaN substrate, the breakdown voltage is 720 to 790 V, which is lower than the portion with the lowest resistivity of the GaN substrate. When it was small, the withstand voltage was 830 to 1040V. That is, even in the case of the pn diode structure, it is shown that the breakdown voltage of the semiconductor diode increases when the resistivity of the GaN layer or the superlattice low-resistance multilayer film is smaller than the lowest resistivity portion of the GaN substrate. It was.

  In other words, by inserting a layer having a sufficiently low resistivity as compared to all locations on the GaN substrate, electric field concentration due to the non-uniformity of the resistivity of the substrate can be suppressed and formed on the GaN substrate. It was shown that the breakdown voltage of the pn diode can be increased.

  While the embodiments and examples of the present invention have been described above, the embodiments and examples described above do not limit the invention according to the claims. It should be noted that not all combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention.

1, 2, 3 Semiconductor diode 10 Substrate 12, 12a Semiconductor layer 14 Drift layer 14a Interface 16, 16a Junction region 18 Semiconductor layer 20, 24 Ohmic electrode 22 Schottky electrode

Claims (3)

A gallium nitride free-standing substrate whose main surface is a C-plane;
a junction region including a pn junction or a Schottky junction;
The gallium nitride free-standing substrate is provided between the junction region and the gallium nitride free-standing substrate, and has a resistivity lower than the minimum resistivity in the substrate surface of the gallium nitride free-standing substrate, and has the same conductivity type as the gallium nitride free-standing substrate A gallium nitride based semiconductor diode comprising a conductive semiconductor layer.   The gallium nitride based semiconductor diode according to claim 1, wherein the semiconductor layer has a superlattice structure.   The gallium nitride based semiconductor diode according to claim 2, wherein the gallium nitride free-standing substrate has an ohmic electrode on a surface opposite to the main surface.

Images