JP2007288030A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device by which a deterioration in characteristics at the time of movement in a forward direction can be easily improved. <P>SOLUTION: A first electrode 4 in contact with a hetero semiconductor region 3 is formed of a metal material which is so selected that the difference in work function between the first electrode 4 and a drift region 2 is larger than at least the difference in work function between the hetero semiconductor region 3 and the drift region 2. Consequently, since the junction is higher than the barrier of the hetero-junction part between the hetero semiconductor region 3 and the drift region 2, no leakage current arises and a IV waveform shown by the original hetero junction can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor device, and more particularly to a technique for improving characteristic degradation during forward operation.

Conventionally, a P ⁺ -type polycrystalline silicon region is formed in contact with one main surface of a semiconductor substrate in which an N ^-- type epitaxial region is formed on an N ⁺ -type silicon carbide substrate. A semiconductor device in which a heterojunction is formed between regions is known (see Patent Document 1). In such a semiconductor device, a surface metal electrode made of aluminum is formed on the polycrystalline silicon region, and a back metal electrode made of titanium or nickel is formed on the back surface of the silicon carbide substrate. Then, by applying a voltage between the electrodes using the front surface metal electrode and the back surface metal electrode as an anode and a cathode, respectively, a rectifying action is produced at the heterojunction interface, and diode characteristics can be obtained.

Specifically, when a positive potential is applied to the anode with the cathode grounded, a conduction characteristic corresponding to the forward characteristic of the diode is obtained, and conversely, when a negative potential is applied to the anode, the reverse of the diode is obtained. A blocking characteristic corresponding to the directional characteristic is obtained. These forward and reverse characteristics can be adjusted arbitrarily as well as exhibiting characteristics such as a Schottky junction composed of a metal electrode and a semiconductor material, compared with a diode using a Schottky junction. This has the advantage that it can be adjusted to the optimum pressure resistance system as required. Furthermore, by adjusting the impurity density and conductivity type of the polycrystalline silicon region to predetermined conditions, a very small leakage current characteristic can be obtained by an operation mechanism that is essentially different from that of the Schottky junction.
JP 2005-259797 A

  However, according to the structure of the semiconductor device described above, the deterioration of characteristics during forward operation occurs due to the influence of the diffusion of metal atoms forming the crystal grain boundaries and electrodes existing in the polycrystalline silicon region. There was a limit.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a semiconductor device capable of easily improving characteristic deterioration during forward operation.

  In order to solve the above-described problems, a semiconductor device according to the present invention is characterized by a first-conductivity-type semiconductor substrate and a band gap width that is in contact with one main surface of the semiconductor substrate and different from the band gap width of the semiconductor substrate. A semiconductor device having a hetero semiconductor region having a first electrode in contact with the hetero semiconductor region, and a second electrode in contact with the semiconductor substrate, wherein the first electrode is a work of the first electrode and the semiconductor substrate. The difference is that the functional difference is made of a metal material that is at least larger than the work function difference between the hetero semiconductor region and the semiconductor substrate.

  According to the semiconductor device of the present invention, the metal material constituting the first electrode diffuses to the junction between the hetero semiconductor region and the drift region, thereby forming a Schottky junction between the metal material and the drift region material. Even so, the barrier height of the Schottky junction is higher than the barrier height of the heterojunction between the hetero semiconductor region and the drift region, so that leakage current does not occur and an IV waveform indicated by the original hetero junction is obtained. Can do. Therefore, according to the semiconductor device according to the present invention, stable device characteristics in which current does not concentrate on a specific portion can be obtained, so that the original device characteristics of the heterojunction diode can be obtained with a high yield.

  Hereinafter, a configuration of a semiconductor device according to an embodiment of the present invention will be described in detail with reference to the drawings.

[Example 1]
First, the configuration of the semiconductor device according to the first embodiment of the present invention will be described with reference to FIG.

[Configuration of semiconductor device]
As shown in FIG. 1, the semiconductor device of this embodiment has an N − type drift region (N μm) on a substrate region (N + SiC) 1 made of N ⁺ type silicon carbide having a polytype of 4H. In this embodiment, the impurity density of the drift region 2 is 10 ¹⁶ [cm ⁻³ ] and the film thickness is 10 [μm] In this embodiment, the first semiconductor region 100 is used. However, the first semiconductor region 100 may be formed of only the substrate region 1 regardless of the resistivity.

In the semiconductor device of the present embodiment, the hetero semiconductor region 3 made of polycrystalline silicon (Si) having a band gap width smaller than that of silicon carbide is used as the second semiconductor region between the drift region 2 and the substrate region 1. It is formed so as to be in contact with the main surface facing the bonding surface. That is, in this semiconductor device, a heterojunction diode is formed at the junction between the drift region 2 and the hetero semiconductor region 3 because the band gap width of silicon carbide and the band gap width of polycrystalline silicon are different, and energy is generated at the hetero junction interface. There are barriers. In the present embodiment, the hetero semiconductor region 3 is made of a P-type material having an impurity density of 10 ¹⁹ [cm ⁻³ ] and a film thickness of 0.5 [μm].

  The semiconductor device of this embodiment includes a first electrode 4 and a second electrode 5 formed so as to be in contact with the hetero semiconductor region 3 and the substrate region 1, respectively. The first electrode 4 has a work function difference between the first electrode 4 and the drift region 2 that is at least larger than the work function difference between the hetero semiconductor region 3 and the drift region 2, for example, a material in which Ni (nickel) is deposited. It is formed of a metal material selected as described above. The second electrode 5 is made of a metal material, such as Ni deposited on Ti (titanium).

[Operation of semiconductor device]
Next, the operation of the semiconductor device when operating as a vertical diode by using the first electrode 4 and the second electrode 5 as an anode and a cathode, respectively, will be described separately for a forward operation and a reverse operation.

[Forward operation]
First, the forward operation of the semiconductor device will be described.

  When the second electrode 5 is set to the ground potential and a positive potential is applied to the first electrode 4, the heterojunction diode between the drift region 2 and the hetero semiconductor region 3 exhibits forward characteristics, such as a Schottky junction diode. Shows conduction characteristics. That is, in this case, a forward current flows due to a voltage drop determined by the sum of the built-in potentials spreading from the heterojunction portion to the drift region 2 side and the hetero semiconductor region 3 side. For example, in this embodiment, the sum of the built-in potentials extending from the heterojunction portion to the drift region 2 and the hetero semiconductor region 3 is about 1.3 [V], and a forward current flows due to a voltage drop corresponding to this sum. .

  By the way, in the conventional semiconductor device, there is a limit to improvement in yield because characteristic deterioration during forward operation occurs due to diffusion of metal atoms forming crystal grain boundaries and electrodes existing in the polycrystalline silicon region. That is, as shown by the dotted line in FIG. 2, the IV waveform of the conventional semiconductor device includes, in addition to the IV waveform obtained at the original heterojunction, aluminum used for the surface electrode and silicon carbide which is the material of the epitaxial region. The IV waveform obtained by the Schottky junction is a waveform combined as a leakage current. This is because there are crystal grain boundaries at a predetermined density in the polycrystalline silicon region, and the aluminum constituting the surface metal electrode formed on the polycrystalline silicon region passes through the polycrystalline silicon region and the epitaxial region. It can be estimated that a Schottky junction between aluminum and silicon carbide which is a material of the epitaxial region is also formed. This phenomenon may occur due to the presence of crystal defects or a predetermined heat treatment process even when single crystal silicon or another material is used for the polycrystalline silicon region.

  On the other hand, in the semiconductor device of this embodiment, an IV waveform indicated by the original heterojunction can be obtained without depending on the material or process of the hetero semiconductor region 3. That is, in the present embodiment, the first electrode 4 in contact with the hetero semiconductor region 3 has a work function difference between the first electrode 4 and the drift region 2 such as Ni, which is at least a work between the hetero semiconductor region 3 and the drift region 2. Ni that is formed of a metal material selected so as to be larger than the functional difference and forms the first electrode 4 diffuses to the junction between the hetero semiconductor region 3 and the drift region 2 as in the conventional semiconductor device, and Ni Even when a Schottky junction is formed between silicon carbide, which is the material of the drift region 2, and the barrier height of the heterojunction portion of the hetero semiconductor region 3 and the drift region 2, a leakage occurs. No current is generated, and an IV waveform exhibited by the original heterojunction can be obtained. Therefore, according to the semiconductor device of the present embodiment, stable device characteristics in which current does not concentrate on a specific portion can be obtained, so that the original device characteristics of the heterojunction diode can be obtained with a higher yield than conventional semiconductor devices. Obtainable.

In order to obtain such a technical effect, at least the first electrode 4 in contact with the hetero semiconductor region 3 has a work function difference between the first electrode 4 and the drift region 2 of at least the hetero semiconductor region 3 and the drift region. Any metal material selected so as to be larger than the work function difference of 2 may be used. Examples of materials generally used for semiconductor metal materials include Au, Pt, and the like. Further, if the material used for the hetero semiconductor region 3 and the conductivity type and density of the impurity change, the metal material that can be used also changes. For example, when the hetero semiconductor region 3 is N type and the impurity density is 10 ¹⁹ [cm ⁻³ ]. Can also use materials such as Ti and Mo. In any case, the metal material forming the first electrode 4 is such that the work function difference between the first electrode 4 and the drift region 2 is at least larger than the work function difference between the hetero semiconductor region 3 and the drift region 2. It suffices if it is selected to be.

[Reverse operation]
Next, the reverse operation of the semiconductor device will be described.

  When the first electrode 4 is set to the ground potential and a positive potential is applied to the second electrode 5, the heterojunction diode exhibits reverse characteristics and enters a cut-off state. Note that the leakage current characteristics of the heterojunction diode also affect the Schottky junction formed between the metal diffused at the junction between the hetero semiconductor region 3 and the drift region 2 and the drift region 2. According to the semiconductor device of the present embodiment, since a metal that forms a higher junction barrier is used as compared with the conventional semiconductor device, the generated leakage current can be greatly reduced.

In general, the outer peripheral end portion of the semiconductor device has a change point in potential distribution or electric field distribution as compared with other flat portions. Therefore, in the above embodiment, as shown in FIG. 3, the electric field relaxation region 6 may be formed at the end of the junction between the drift region 2 and the hetero semiconductor region 3. According to such a configuration, the amount of change in potential distribution or electric field distribution can be relaxed. The material for forming the electric field relaxation region 6 is a P-type 4H—SiC having a conductivity type opposite to the conductivity type of the drift region 2, an inactive region having a high resistance value, a highly insulating material such as SiO _2. Can be illustrated. Further, a breakdown voltage structure such as a guard ring may be provided further outside the electric field relaxation region 6.

Further, as shown in FIG. 4, the end portion of the hetero semiconductor region 3 may be formed on an interlayer insulating film 7 made of SiO ₂ . According to such a configuration, the effect of electric field relaxation can be obtained, and etching damage can be prevented from entering the drift region 2 when the hetero semiconductor region 3 is patterned by a process such as a dry etching process. The example shown in FIG. 4 is a case where the interlayer insulating film 7 is formed together with the electric field relaxation region 6, but it is needless to say that only the interlayer insulating film 7 may be formed. Further, in order to relax the electric field at the junction end, a mesa structure 8 in which the ends of the hetero semiconductor region 3 and the drift region 2 are dug may be formed as shown in FIG.

  In the semiconductor device shown in FIGS. 3 to 5, the end of the first electrode 4 is in contact with the hetero semiconductor region 3, but the end of the first electrode 4 runs over the insulating film or the like. Also good. In the semiconductor device shown in FIGS. 1 to 5, the second semiconductor region is formed only by the hetero semiconductor region 3 having a single conductivity type and impurity density. However, as shown in FIGS. In addition, the second semiconductor region may have a second hetero semiconductor region 9 having a conductivity type or impurity density different from that of the hetero semiconductor region 3. The second hetero semiconductor region 9 may be either P-type or N-type conductivity type, and the impurity density may be larger or smaller than the impurity density of the hetero semiconductor region 3.

  1 to 7 has a structure in which only a heterojunction diode is formed between the first electrode 4 and the second electrode 5, the Schottky junction shown in FIGS. A structure combined with a diode or a PN junction diode shown in FIGS. 8 shows an example in which the first electrode 4 and the Schottky electrode region 10 are formed in different regions, and FIG. 9 shows an example in which the Schottky electrode region 10 also serves as the first electrode 4. . 8 and 9, the metal material of the first electrode 4 has a work function difference between the first electrode 4 and the drift region 2 of at least the hetero semiconductor region 3 and the drift region 2. It is only necessary to be selected so as to be larger than the work function difference.

  FIG. 10 shows an example in which the first electrode 4 and the P-type region 11 are directly connected. FIG. 11 shows the case where the first electrode 4 and the P-type region 11 are connected via the hetero semiconductor region 3. An example is shown. The P-type region 11 shown in FIGS. 10 and 11 is, for example, a P-type that is the conductivity type opposite to the conductivity type of the drift region 2, and the metal material forming the first electrode 4 is the same as that of the first electrode 4. The work function difference of the drift region 2 may be selected so as to be at least larger than the work function difference between the hetero semiconductor region 3 and the drift region 2. 10 and 11 show examples in which the P-type region 11 and the electric field relaxation region 6 have different depths, but the same impurity density and the same depth may be used. Further, the end portion of the hetero semiconductor region 3 may not necessarily be in contact with the electric field relaxation region 6. 8 to 11, the metal material forming the first electrode 4 is such that the work function difference between the first electrode 4 and the drift region 2 is at least between the hetero semiconductor region 3 and the drift region 2. As long as it is selected so as to be larger than the work function difference, the technical effect of the semiconductor device according to the present invention can be obtained. Further, as shown in FIG. 12, a high electric field region 12 having an impurity density higher than that of the drift region 2 may be formed in the drift region 2 in contact with the hetero semiconductor region 3.

[Example 2]
Next, the configuration of the semiconductor device according to the second embodiment of the present invention will be described with reference to FIG.

[Configuration of semiconductor device]
In the semiconductor device of the present embodiment, an N ⁻ type drift region 22 is formed on a substrate region 21 made of silicon carbide having a polytype of 4H type and N ⁺ , and the drift region 22, the substrate region 21, A hetero semiconductor region 23 made of P-type polycrystalline silicon and a second hetero semiconductor region 24 made of N-type polycrystalline silicon are formed so as to be in contact with the main surface opposite to the junction surface. In other words, in this semiconductor device, the junction between the drift region 22 and the hetero semiconductor region 23 and the second hetero semiconductor flow region 24 is formed of a hetero junction made of materials having different band gap widths of silicon carbide and polycrystalline silicon, and the junction interface. There are energy barriers. Further, the gate electrode 26 is connected to the second hetero semiconductor region 24 through the gate insulating film 25 made of a silicon oxide film so as to be in contact with the junction surface of the second hetero semiconductor region 24 and the drift region 22 together. A drain electrode 28 is formed so that the source electrode 27 is connected to the substrate region 21. A P-type electric field relaxation region 29 is formed at the outer peripheral end of the active region. Further, the source electrode 27 is selected such that the work function difference between the source electrode 27 and the drift region 22 is at least larger than the work function difference between the hetero semiconductor region 23 and the drift region 22, for example, Ni deposited. It is made of a metal material.

  In the present embodiment, the groove is formed in the drift region 22, but a so-called planar type configuration in which no groove is formed may be used. In addition, the hetero semiconductor region 23 and the second hetero semiconductor region 24 are formed on the drift region 22. A groove is formed in a predetermined region of the drift region 22, and the hetero semiconductor region 23 and the second hetero semiconductor region 23 are formed in the groove. The hetero semiconductor region 24 may be formed so as to be embedded. Further, although the gate electrode 26 and the second hetero semiconductor region 24 are in contact with each other through the gate insulating film 25, the gate electrode 26 and the hetero semiconductor region 23 are in contact with each other through the gate insulating film 25 as shown in FIG. The second hetero semiconductor region 24 may not be provided.

[Operation of semiconductor device]
Next, the operation of the semiconductor device will be described.

  First, when the gate electrode 26 is set to the ground potential or the negative potential, the cut-off state is maintained. This is because energy barriers for conduction electrons are formed at the heterojunction interfaces between the hetero semiconductor region 23 and the second hetero semiconductor region 24 and the drift region 22. In addition, since the semiconductor device of this embodiment is comprised so that a leakage current may become smaller than the conventional semiconductor device, it can hold | maintain higher interruption | blocking property.

  Next, when a positive potential is applied to the gate electrode 26 so as to shift from the cut-off state to the conductive state, the gate electric field is supplied through the gate insulating film 25 to the heterojunction interface where the second hetero semiconductor region 24 and the drift region 22 are in contact. Therefore, a conduction electron accumulation layer is formed in the second hetero semiconductor region 24 and the drift region 22 in the vicinity of the gate electrode 26. That is, the potential on the second hetero semiconductor region 24 side at the junction interface between the second hetero semiconductor region 24 and the drift region 22 in the vicinity of the gate electrode 26 is pushed down, and the energy barrier on the drift region 22 side becomes steep. Thus, conduction electrons can be conducted through the energy barrier.

  Next, when the gate electrode 26 is set to the ground potential again to shift from the conductive state to the cut-off state, the inversion state of the conduction electrons formed at the heterojunction interface in the second hetero semiconductor region 24 and the drift region 22 is released. , Tunneling in the energy barrier stops. Then, when the conduction electrons flow from the second hetero semiconductor region 23 to the drift region 22 stops and the conduction electrons existing in the drift region 22 flow to the substrate region 21 and are exhausted, a heterojunction portion is formed on the drift region 22 side. The depletion layer spreads out and becomes a cutoff state.

  The above description is the operation of the semiconductor device when the semiconductor device is operated in the forward direction by grounding the source electrode 27 and applying a positive potential to the drain electrode 28. However, the source electrode 27 is grounded, It is also possible to operate the semiconductor device in the reverse direction by applying a negative potential to the drain electrode 28. For example, when a predetermined negative potential is applied to the drain electrode 28 in a state where the source electrode 27 and the gate electrode 26 are at the ground potential, the energy barrier against the conduction electrons disappears, and the hetero semiconductor region 23 and the second semiconductor layer 23 from the drift region 22 side. Conduction electrons flow to the hetero semiconductor region 24 side, and a reverse conduction state is established. At this time, since there is no injection of holes and conduction is performed only with conduction electrons, loss due to reverse recovery current when shifting from the reverse conduction state to the cutoff state is small. The gate electrode 26 can be used as a control electrode without being grounded.

  In the above-described embodiment, the heterojunction diode structure that can reduce the leakage current described in the first embodiment is applied to a part of the switch element that drives the heterojunction at the gate. As shown in FIG. 4, the same effect can be obtained even when the circuit is used as a freewheeling diode built in a part of the switch element. That is, FIG. 15 shows an example in which a heterodiode is built in a MOSFET made of silicon carbide, and the first conductive type source region is formed in the first semiconductor region made of the first conductive type substrate region 41 and the drift region 42. 43 and a second conductivity type base region 44 are formed. A gate electrode 46 is formed through a gate insulating film 45 so as to be in contact with the drift region 42, the base region 44, and the source region 43. The base region 44 and the source region 43 are connected to the source electrode 47, and the substrate region 41 is connected to the drain electrode 48. Further, the band gap width is different from that of the drift region 42, and the hetero semiconductor region 49 made of polycrystalline silicon is arranged so as to form a hetero junction with the drift region 42. The hetero semiconductor region 49 is connected to the source electrode 43. An electric field relaxation region 50 is formed at the outer peripheral end of the active region where the MOSFET is formed. Thus, even when used as a built-in free-wheeling diode of a MOSFET, leakage current caused by a heterojunction diode can be reduced.

  Similarly, in FIG. 16, the same effect can be obtained even when a hetero diode is built in a JFET made of silicon carbide. In FIG. 16, a first conductivity type source region 53 and a second conductivity type gate region 54 are formed in a first semiconductor region including a first conductivity type substrate region 51 and a drift region 52. 54 is connected to the gate electrode 55. The source region 53 is connected to the source electrode 56, and the substrate region 51 is connected to the drain electrode 57. Further, the bandwidth is different from that of the drift region 52, and the hetero semiconductor region 58 made of polycrystalline silicon is arranged so as to form a hetero junction with the drift region 52. In the present embodiment, the source regions 53 and the hetero semiconductor regions 58 are alternately formed in the depth direction, and the hetero semiconductor regions 49 are connected to the source electrode 56. An electric field relaxation region 59 is formed at the outer peripheral end of the active region where the JFET is formed. Thus, even when used as a built-in free-wheeling diode of JFET, the leakage current caused by the heterojunction diode can be reduced. As described above, in any case, if at least a part of each part of the transistor has a heterojunction diode that can reduce the leakage current, which is a feature of the present invention, the interrupting performance is greatly improved. Can be improved.

  As mentioned above, although embodiment which applied the invention made by the present inventors was described, this invention is not limited by the description and drawing which make a part of indication of this invention by this embodiment. For example, in the above embodiment, the substrate material is silicon carbide, but the substrate material may be other semiconductor materials such as silicon, silicon germanium, gallium nitride, and diamond. In addition, although the polytype of silicon carbide is the 4H type, other polytypes such as 6H and 3C may be used. In the semiconductor device, the second electrode 5 (drain electrodes 28, 48, 57) and the first electrode 4 (source electrodes 27, 47, 56) are opposed to each other with the drift regions 2, 22, 42, 52 interposed therebetween. Although it has been described as a so-called vertical structure diode or transistor in which the current flowing between both electrodes flows in a standing direction, the second electrode 5 (drain electrodes 28, 48, 57) and the first electrode It may be a so-called lateral structure diode or transistor in which the electrode 4 (source electrodes 27, 47, and 56) is disposed on the same main surface and a current flows in the lateral direction. Further, although polycrystalline silicon is used as the material used for the hetero semiconductor regions 3, 23, 49, 58 and the second hetero semiconductor regions 9, 24, single crystal silicon can be used as long as the material forms a heterojunction with silicon carbide. Other silicon materials such as amorphous silicon, other semiconductor materials such as germanium and silicon germanium, and other polytypes of silicon carbide such as 6H and 3C may be used. N-type silicon carbide is used for drift regions 2, 22, 42, and 52, and P-type polycrystalline silicon is used for hetero semiconductor regions 3, 23, 49, and 58. N-type silicon carbide and P-type silicon are used. Other combinations such as polycrystalline silicon, P-type silicon carbide and P-type polycrystalline silicon, and P-type silicon carbide and N-type polycrystalline silicon may be used. As described above, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

It is sectional drawing which shows the structure of the semiconductor device used as the 1st Embodiment of this invention. It is a current-voltage characteristic figure which shows the forward direction characteristic of the semiconductor device of the past and this invention. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the semiconductor device used as the 2nd Embodiment of this invention. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG. It is sectional drawing which shows the structure of the application example of the semiconductor device shown in FIG.

Explanation of symbols

1: substrate region 2: drift region 3: hetero semiconductor region 4: first electrode 5: second electrode 100: first semiconductor region

Claims (5)

A semiconductor substrate of a first conductivity type; a hetero semiconductor region in contact with one main surface of the semiconductor substrate and having a band gap width different from the band gap width of the semiconductor substrate; and a first electrode in contact with the hetero semiconductor region A semiconductor device having a second electrode in contact with the semiconductor substrate,
The first electrode is formed of a metal material in which a work function difference between the first electrode and the semiconductor substrate is at least larger than a work function difference between the hetero semiconductor region and the semiconductor substrate. .   The semiconductor device according to claim 1, further comprising a gate electrode in contact with a part of a junction between the hetero semiconductor region and the semiconductor substrate through a gate insulating film.   3. The semiconductor device according to claim 1, wherein a conductivity type of at least a part of the hetero semiconductor region is a second conductivity type different from the first conductivity type.   4. The semiconductor device according to claim 1, wherein the semiconductor substrate is formed of any one of silicon carbide, gallium nitride, and diamond. Semiconductor device.   5. The semiconductor device according to claim 1, wherein the hetero semiconductor region is any one of single crystal silicon, polycrystalline silicon, amorphous silicon, germanium, and silicon germanium. A semiconductor device formed by the method described above.

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