JP5055737B2 - Field effect transistor having a two-dimensional carrier gas layer - Google Patents

Description

  The present invention relates to a field effect transistor using a two-dimensional carrier gas layer (for example, a two-dimensional electron gas layer) as a current channel.

  A field effect transistor using a two-dimensional electron gas layer, that is, a 2DEG layer, as a current channel, that is, a current path is generally known as a HEMT (High Electron Mobility Transistor). The HEMT has, for example, an electron transit layer (channel layer) made of GaN to which no impurity is added and an electron supply layer made of, for example, n-type AlGaN. A source electrode and a drain electrode are disposed on the electron supply layer, and a gate electrode made of a Schottky electrode is disposed therebetween. Since the resistance value in the thickness direction (vertical direction) of the electron supply layer is small and the resistance value in the lateral direction (horizontal direction) is large, the current between the drain electrode and the source electrode passes through the 2DEG layer generated in the electron transit layer. Flowing. As is well known, the 2DEG layer is generated based on piezo polarization and spontaneous polarization at the heterojunction surface between the electron transit layer and the electron supply layer.

By the way, the HEMT having a general configuration has a normally-on characteristic. A negative power supply is required to turn off the normally-on HEMT. Further, there is a case where a means for preventing a short circuit based on the HEMT from being formed when the electric circuit including the HEMT having the normally-on characteristic is turned on may be required. Therefore, the use of HEMT having normally-on characteristics is not good.

  Therefore, an attempt has been made to manufacture a HEMT having a normally-off characteristic. However, it has been difficult to obtain a HEMT having a small on-resistance, that is, a drain-source resistance in the on-state and a normally-off characteristic.

  The normally-off characteristic of HEMT can be obtained, for example, by forming a thin electron supply layer made of n-type AlGaN. When the electron supply layer made of AlGaN is thinly formed, the electric field due to piezoelectric polarization based on the heterojunction between the electron supply layer and the electron transit layer becomes weak. As a result, the electron concentration of the 2DEG layer is reduced. On the other hand, there is a built-in potential, that is, a potential difference in the absence of a bias voltage, between the electron supply layer and the gate electrode in Schottky contact therewith. When an electric field based on the built-in potential acts on a 2DEG layer whose electron concentration has decreased due to the thin electron supply layer, the 2DEG layer immediately below the gate electrode disappears. Therefore, the drain and source are turned off in the state where no bias voltage is applied to the gate electrode.

  As described above, a normally-off HEMT can be provided by thinning the electron supply layer. However, when the electron supply layer is thinned, the electron concentration is lowered in the 2DEG layer other than just below the gate electrode, and the on-resistance between the drain and the source is increased.

  As another problem when the electron supply layer is formed thin so as to obtain normally-off characteristics, there is a problem of current confinement, that is, collapse. For example, as disclosed in Patent Document 1, when this HEMT is used in an AC circuit, negative charge is generated on the surface of the electron supply layer, and the maximum drain that flows through the electron transit layer based on the negative charge is disclosed in Patent Document 1. A phenomenon in which the current is lower than the maximum drain current during DC operation. The decrease in the maximum drain current due to collapse is considered to be due to the relative decrease in the electron concentration of the 2DEG layer based on the negative charge on the surface of the electron supply layer. When the electron supply layer is thin, the 2DEG layer is easily affected by the surface of the electron supply layer, and the influence of the collapse phenomenon is increased.

The following two methods are conceivable as methods for obtaining a normally-off HEMT by suppressing an increase in on-resistance and suppressing the influence of the collapse phenomenon.
(1) For example, an electron supply layer made of, for example, n-type AlGaN having a thickness that enables normally-off is formed on the GaN electron transit layer by epitaxial growth, and a cap layer (auxiliary layer) made of undoped AlGaN is further formed thereon. And providing a gate electrode on the cap layer, or selectively removing the cap layer to expose the electron supply layer and providing the gate electrode on the electron supply layer.
(2) The electron supply layer is formed thick, a portion corresponding to the gate electrode of the electron supply layer is removed by etching, and a thin portion having a thickness that enables normally-off is formed in the electron supply layer, and the gate is formed on the thin portion. Provide electrodes.

  However, when the method (1) is adopted, the crystallinity of the semiconductor region including the electron transit layer and the electron supply layer is deteriorated due to an increase in the high temperature epitaxial growth process, and the HEMT characteristics are deteriorated. In addition, it is difficult to form the electron supply layer and the cap layer as intended, and it is difficult to obtain a HEMT having characteristics as intended.

  When the method (2) is adopted, when the electron supply layer is selectively etched, the electron transit layer and the semiconductor crystals of the electron supply layer are damaged, and the electrical characteristics of the HEMT are deteriorated. In addition, it has been difficult to easily and accurately achieve selective etching of the electron supply layer.

In addition to the presence or absence of normally-off characteristics, the HEMT is required to improve the electrical characteristics of the HEMT, such as reducing on-resistance. When the electron supply layer is formed thick, theoretically, the electron concentration of the 2DEG layer generated based on piezoelectric polarization increases. However, forming a thick electron supply layer inevitably increases the epitaxial growth time for this purpose, resulting in deterioration of crystallinity of the electron transit layer and diffusion of n-type impurities in the electron supply layer into the electron transit layer. The electrical characteristics of the are deteriorated.
Further, not only the HEMT having a Schottky contact gate electrode but also another field effect transistor having an insulated gate electrode and having a two-dimensional carrier layer such as a 2DEG layer is required to reduce on-resistance. A field effect transistor that uses a two-dimensional hole gas layer as a two-dimensional carrier gas layer instead of the 2DEG layer has the same problem as a field effect transistor that uses a 2DEG layer.
JP 2004-214471 A JP-A-1-29559

  Therefore, the problem to be solved by the present invention is that it is difficult to reduce the on-resistance in a field effect transistor using a two-dimensional carrier gas layer. Further, it is difficult to easily configure a field effect transistor using a two-dimensional carrier gas layer so as to have normally-off characteristics.

The present invention for solving the above problems is as follows.
First and second main surfaces facing each other, a first semiconductor layer having a first conductivity type and a crystal structure, and the first semiconductor layer for generating a two-dimensional carrier gas The semiconductor layer is made of a different semiconductor material, is disposed adjacent to the first semiconductor layer, is disposed at a position farther from the first semiconductor layer than the first main surface, and has a crystal structure. A semiconductor region comprising a second semiconductor layer;
A source electrode and a drain electrode formed on the first main surface of the semiconductor region;
A gate electrode disposed between the source electrode and the drain electrode on the first main surface of the semiconductor region;
A first organic semiconductor film disposed on at least a portion between the source electrode and the drain electrode on the first main surface of the semiconductor region and having the first conductivity type;
A second organic semiconductor film disposed on the first organic semiconductor film having the first conductivity type and having a second conductivity type opposite to the first conductivity type;
The present invention relates to a field effect transistor characterized by comprising:

According to another aspect of the present invention, the gate electrode is an electrode that is in Schottky contact with the first semiconductor layer, and the first semiconductor layer operates the field effect transistor in a normally-off state. It is desirable to have a possible thickness.
According to a third aspect of the present invention, the first conductivity type is n-type, and the first organic semiconductor film is preferably made of fullerene or metal phthalocyanine showing n-type.
According to a fourth aspect of the present invention, the semiconductor region further includes a cap layer made of a crystalline semiconductor that is disposed on the first semiconductor layer and is not doped with a conductive impurity. It is desirable.
In addition, according to a fifth aspect of the present invention, the semiconductor region is further made of a crystalline semiconductor that is disposed between the first semiconductor layer and the second semiconductor layer and is not doped with a conductive impurity. It is desirable to have a spacer layer that is formed and thinner than the first semiconductor layer.
Further, as shown in claim 6, further Ru can be arranged an insulating film between said semiconductor region first organic semiconductor film.
Also, as shown in claim 7, further an insulating film between the second organic semiconductor film having the first organic semiconductor film and the second conductivity type having the first conductivity type Can be arranged.
In addition, as described in claim 8 , it is desirable to further have a resistive field plate disposed on the one main surface of the semiconductor region and connected to the gate electrode or the drain electrode.
According to a ninth aspect of the present invention, the apparatus further includes a field plate disposed on the first organic semiconductor film having the first conductivity type and connected to the gate electrode or the drain electrode. It is desirable.
Further, as shown in claim 10, it is possible further to place the gate insulating film between said first major surface of said gate electrode said semiconductor region.

The present invention has the following effects.
(1) The amorphous first organic semiconductor film formed on the first semiconductor layer having a crystal structure according to the present invention has the same first conductivity type as that of the first semiconductor layer. . Accordingly, the first organic semiconductor film of a first conductivity type, enable the carrier in the same manner as in the first semiconductor layer (e.g., electrons) as a carrier supply layer for supplying to the second semiconductor layer (e.g., electron supply layer) To do. Therefore, when the thickness of the first semiconductor layer having the crystal structure is made the same as that of the conventional one and the first organic semiconductor film according to the present invention is provided thereon, the first semiconductor layer is made thicker than the conventional one. A similar effect can be obtained, and the carrier concentration of the two-dimensional carrier gas layer (for example, 2DEG layer) is increased, and the on-resistance of the field effect transistor is reduced.
(2) When the first semiconductor layer is thinned so that the normally-off characteristic can be obtained and the first organic semiconductor film having the same conductivity type as the first semiconductor layer according to the present invention is formed, the normally-off characteristic is obtained. However, the on-resistance can be kept at a relatively low value. That is, a field effect transistor having a small on-resistance and a normally-off characteristic can be provided.
(3) The deterioration of the characteristics of the semiconductor region having a crystal structure due to the formation of the first organic semiconductor film is less than in the conventional methods (1) and (2). Accordingly, it is possible to provide a field effect transistor with a low on-resistance or a normally-off characteristic field effect transistor with suppressed deterioration of electrical characteristics.
(4) to the onset bright Accordingly, when providing the second organic semiconductor film of a second conductivity type, it is possible to suppress the collapse.

  Next, an embodiment of the present invention will be described with reference to FIGS.

  The HEMT as a field effect transistor having a two-dimensional carrier gas layer shown in FIG. 1 is roughly divided into a main semiconductor region 1, a support substrate 2, a source electrode 3, a drain electrode 4, a gate electrode 5, a first and a first 2 organic semiconductor films 6 and 7.

The main semiconductor region 1 can also be called a semiconductor substrate or a semiconductor substrate, and is a buffer formed sequentially on a support substrate 2 made of, for example, a single crystal silicon semiconductor by a known epitaxial growth method (for example, MOCVD method). The layer 8, the electron transit layer 9, and the electron supply layer 10 are included. A source electrode 3, a drain electrode 4, and a gate electrode 5 are disposed on the first main surface 11 of the main semiconductor region 1, and the support substrate 2 is coupled to the second main surface 12. Each layer 8, 9, 10 of the main semiconductor region 1 extends parallel to the first and second main surfaces 11, 12.
Each layer 8, 9, 10 of the main semiconductor region 1 is formed of, for example, GaN, InGaN, AlGaN, AlInGaN, AlN, InAlN, AlP, GaP, AlInP, GaInP, AlGaP, AlGaAs, GaAs, AlAs, InAs, InP, InN, GaAsP, It is formed of a semiconductor material having a crystal structure such as Si, SiC, or C. In order to obtain a high breakdown voltage HEMT, it is desirable that the layers 8, 9, and 10 of the main semiconductor region 1 are made of a nitride semiconductor. Next, each part of the HEMT will be described in more detail.

  The buffer layer 8 formed on the support substrate 2 is a multilayer structure buffer in which a first sublayer made of AlN (aluminum nitride) and a second sublayer made of GaN (gallium nitride) are alternately stacked. . Since the buffer layer 8 is not directly related to the operation of the HEMT, it can be omitted. Further, the semiconductor material of the buffer layer 8 can be replaced with a material other than AlN and GaN, or a single layer structure can be used.

  The electron transit layer 9 formed on the buffer layer 8 functions as the second semiconductor layer in the present invention, and can also be called a channel layer. The electron transit layer 9 of this embodiment is made of undoped GaN (gallium nitride) to which no impurity is added, and has a thickness of 1 to 3 μm, for example. The electron transit layer 9 is disposed at a position farther from the first main surface 11 of the main semiconductor region 1 than the electron supply layer 10 thereabove.

The electron supply layer 10 as the first semiconductor layer in the present invention is disposed on the electron transit layer 9 and is obtained by adding an n-type (first conductivity type) impurity to a nitride semiconductor represented by the following formula. Become.
Al _x Ga _1-x N,
Here, x is a numerical value satisfying 0 <x <1, preferably 0.2 to 0.4, and more preferably 0.3.
Since the electron supply layer 10 is formed to be relatively thin, the resistance perpendicular to the first main surface 11 of the main semiconductor region 1 is negligibly small, and the direction parallel to the first main surface 11 (lateral direction) ) Is greater than the vertical direction. Therefore, the component of the drain-source current flowing in the lateral direction through the electron supply layer 10 can be ignored.

  The electron supply layer 10 made of n-type AlGaN has a smaller lattice constant than the electron transit layer 9 made of GaN below. Therefore, a well-known piezoelectric polarization occurs based on the heterojunction 13 between the electron supply layer 10 and the electron transit layer 9. In addition, spontaneous polarization occurs based on the electron supply layer 10 containing n-type impurities. Based on the piezo polarization and the electric field of the spontaneous electrode, a well-known 2DEG layer 14 indicated by a dotted line is formed on the electron transit layer 9. FIG. 1 shows the 2DEG layer 14 when a voltage for turning on the HEMT is applied to the gate electrode 5. The 2DEG layer 14 corresponds to the two-dimensional carrier gas layer of the present invention, and includes electrons (carriers) having a degree of freedom in a direction parallel to the first main surface 11 of the main semiconductor region 1. Functions as a current path.

  In this embodiment, the thickness T of the electron supply layer 10 is determined to a value (for example, 3 to 10 nm, more preferably 3 to 5 nm) that can obtain normally-off characteristics. As already described in the background art section, when the electron supply layer 10 is formed thin, the electron concentration of the 2DEG layer 14 is lowered. Further, a built-in potential between the gate electrode 5 and the electron supply layer 10 acts immediately below the gate electrode 5. As a result, the 2DEG layer 14 disappears from directly under the gate electrode 5, and a normally-off characteristic is obtained.

  If the electron supply layer 10 is simply formed so as to obtain a normally-off characteristic, the electron concentration also decreases in the 2DEG layer 14 other than immediately below the gate electrode 5. As a result, the ON resistance (drain-source resistance) when the HEMT is turned on by applying a bias voltage to the gate electrode 5 is increased. However, since the HEMT of this example includes the n-type first organic semiconductor film 6, an increase in on-resistance is suppressed.

In the present embodiment, the first organic semiconductor film 6 is formed between the source electrode 3 and the gate electrode 5 on the first main surface 11 of the main semiconductor region 1, between the drain electrode 4 and the gate electrode 5, and between the source electrode 3. It covers the outer part and the outer part of the drain electrode 4. However, the first organic semiconductor film 6 can also be formed so as to cover only a part of the first main surface 11 of the main semiconductor region 1 between the source electrode 3 and the drain electrode 4. Note that the outer portion of the first organic semiconductor film 6 than the source electrode 3 and the outer portion of the drain electrode 4 do not substantially contribute to the reduction of the on-resistance, but the first main semiconductor region 1 has the first main main film. It contributes to the protection of the surface 11.
The first organic semiconductor film 6 is an amorphous semiconductor having the same conductivity type (n-type) as the electron supply layer 10 made of an n-type nitride semiconductor having a crystal structure. For example, fullerene or fullerene derivatives. (Preferably C60 or C70), or metal phthalocyanine containing Cu or the like. The n-type first organic semiconductor film 6 is formed by, for example, well-known vapor deposition, sputtering, spin-on (coating), sol-gel method or the like. Preferably, the first organic semiconductor film 6 is formed to a thickness of about 200 nm by a spin-on method or vapor deposition of Cu phthalocyanine.

  Since the first organic semiconductor film 6 has the same n-type as the electron supply layer 10 and is disposed so as to cover the electron supply layer 10, the first organic semiconductor film 6 exhibits the same function as the electron supply layer 6. Therefore, the first organic semiconductor film 6 can also be called an auxiliary electron supply layer.

  Next, the function of the first organic semiconductor film 6 will be described with reference to FIG. If the electron supply layer 10 has such a thickness that the normally-off characteristic cannot be obtained and the first organic semiconductor film 6 is not provided, a HEMT having a gate-source voltage Vgs and a drain current is formed. When the relationship with Id is obtained, the characteristic line B shown by the dotted line in FIG. 2 is obtained, and the drain current Id flows when the gate-source voltage Vgs is zero. In order to turn off the HEMT having the normally-on characteristic, a voltage of −Vgs2 must be applied between the gate and the source. If the electron supply layer 10 has a thickness capable of obtaining a normally-off characteristic and the first organic semiconductor film 6 is not provided, a HEMT is formed, and the HEMT gate-source voltage Vgs and the drain current Id are When the relationship is obtained, the characteristic C indicated by the chain line in FIG. 2 is obtained. When the gate-source voltage Vgs is zero, the drain current Id does not substantially flow, and when the gate-source voltage + Vgs1 or more is applied, the drain current Id Flows. However, when the electron supply layer 10 is simply thinned in this way, even if the normally-off characteristic is obtained, the on-resistance increases due to the decrease in the electron concentration of the 2DEG layer 14, and the drain current of the characteristic line C The saturation value of Id becomes smaller than the characteristic line B.

  On the other hand, the relationship between the gate-source voltage Vgs and the drain current Id of the HEMT having the first organic semiconductor film 6 according to the present invention is the characteristic line A shown by the solid line in FIG. The characteristic line A according to the present invention has a normally-off characteristic like the characteristic line C and has a large saturation value of the drain current Id similar to the characteristic line B.

  For example, the highest processing temperature when forming the first organic semiconductor film 6 by spin-on (coating) is to form the main semiconductor region 1 made of a nitride semiconductor having a crystal structure by the MOCVD method (metal organic chemical growth method). It is lower (eg, 300 ° C.) than the highest temperature (eg, 1120 ° C.). Therefore, the crystal of the main semiconductor region 1 is hardly deteriorated by forming the first organic semiconductor film 6.

  In FIG. 1, the p-type second organic semiconductor film 7 is disposed on the first organic semiconductor film 6. The second organic semiconductor film 7 has a p-type (second conductivity type) opposite to the n-type electron supply layer 10. The p-type second organic semiconductor film 7 has an amorphous structure different from that of the main semiconductor region 1 made of an inorganic semiconductor or a crystalline semiconductor. For example, a pentacene derivative or a tetracene (tethracene) is used. ) Derivatives or anthracene derivatives, etc., acene, perylene, rubrene, phthalocyanine, Zn phthalocyanine, oligothiophene or the like.

  The second organic semiconductor film 7 is formed on the surface of the electron supply layer 10 made of, for example, n-type AlGaN by a known vapor deposition, sputtering, spin-on, or sol-gel method. The second organic semiconductor film 7 of Example 1 in FIG. 1 is formed by depositing a p-type organic semiconductor material made of Zn phthalocyanine on the electron supply layer 10 and has a thickness of about 40 nm. Further, the second organic semiconductor film 7 in FIG. 1 is formed between the drain electrode 4 and the gate electrode 5 on the first main surface 11 of the main semiconductor region 1 and between the source electrode 3 and the gate electrode 5. All of them are formed in an outer portion than the source electrode 3 and an outer portion than the drain electrode 4. The portion outside the source electrode 3 and the portion outside the drain electrode 4 of the second organic semiconductor film 7 do not substantially contribute to the improvement of the collapse, but contribute to the protection of the first main surface 11 of the main semiconductor region 1. .

If the p-type second organic semiconductor film 7 for improving the collapse is not provided, the negative half cycle of the AC voltage is applied to the HEMT so that the potential of the drain electrode 4 becomes the potential of the source electrode 3. On the other hand, when it becomes negative, a negative charge is charged on the surface of the n-type first organic semiconductor film 6. As a result, the electron concentration of the 2DEG layer 14 is reduced, and the maximum drain current when the HEMT is in an on state is reduced. On the other hand, when the p-type second organic semiconductor film 7 is provided as shown in FIG. 1, the action of the electric field based on the p-type second organic semiconductor film 7 causes the first organic semiconductor film 6. The negative charge on the surface is reduced. In other words, holes are supplied from the p-type second organic semiconductor film 7 to the first organic semiconductor film 6, and the negative charges on the surface of the first organic semiconductor film 6 are canceled by the holes. That is, it disappears.
The collapse improvement by the p-type second organic semiconductor film 7 will be described from another viewpoint. An electron composed of the p-type second organic semiconductor film 7, the n-type first organic semiconductor film 6, and the n-type AlGaN. The supply layer 10 and the 2DEG layer 14 can be considered as one capacitor. In this case, the n-type electron supply layer 10 and the n-type first organic semiconductor film 6 function as a dielectric layer of the capacitor, and the p-type second organic semiconductor film 7 functions as a positive electrode of the capacitor. The 2DEG layer 14 functions as a negative electrode of the capacitor. When the main surface of the first organic semiconductor film 6 as a dielectric layer is fixed to a positive potential by the p-type second organic semiconductor film 7, the negative charge of the heterojunction surface 13 of the electron supply layer 6 is stabilized. Is planned. As a result, the reduction in the electron concentration of the 2DEG layer 14 based on the collapse phenomenon is reduced.

  The action of reducing the negative charge on the main surface of the first organic semiconductor film 6 based on the p-type second organic semiconductor film 7 is different from the action of reducing the charge on the surface of the surface of the main semiconductor region 1 according to the related art. Yes. That is, a dangling bond (dangling bond) is generated on the surface of the main semiconductor region 1 based on blocking of bonds between atoms constituting the semiconductor, and this dangling bond is involved in charging. Therefore, in general, the main semiconductor region 1 is subjected to a charge based on the uncoupler and a process for preventing it, that is, a termination process. This conventional termination treatment is indirect antistatic, whereas the antistatic of negative charges by the p-type second organic semiconductor film 7 is based on the combination of holes and negative charges. Direct antistatic.

The n-type first organic semiconductor film 6 and the p-type second organic semiconductor film 7 have carrier mobility sufficiently smaller than the carrier (electron) mobility of the electron supply layer 10 made of a Group 3-5 compound semiconductor. (1.5 cm ² /V.s at the maximum). Accordingly, the first and second organic semiconductor films 6 and 7 are substantially insulating films, and the first and second layers between the drain electrode 4 and the gate electrode 5 and between the source electrode 3 and the gate electrode 5 are used. The current passing through the organic semiconductor films 6 and 7 is negligibly small. Accordingly, the first and second organic semiconductor films 6 and 7 have a function as a protective film on the surface of the main semiconductor region 1 in addition to the functions of improving the on-resistance and the collapse.

  Source electrode 3 is arranged on first main surface 11 of main semiconductor region 1. The drain electrode 4 is disposed on the first main surface 11 of the main semiconductor region 1 with a predetermined distance from the source electrode 3. Each of the source electrode 3 and the drain electrode 4 is composed of, for example, a laminated electrode of titanium (Ti) and aluminum (Al), and is in low resistance contact with the electron supply layer 10.

  The gate electrode 5 is disposed between the source electrode 3 and the drain electrode 4 on the first main surface 11 of the main semiconductor region 1 and is made of, for example, rhodium (Rh) and is in Schottky contact with the electron supply layer 10. .

The HEMT of Embodiment 1 in FIG. 1 has the following effects.
(1) A HEMT having normally-off characteristics can be obtained by the relatively thin electron supply layer 10. In addition, since the n-type first organic semiconductor film 6 has an effect equivalent to the thickness of the electron supply layer 10, the electron concentration in the 2 DEG layer 14 becomes relatively high, and the HEMT having a low on-resistance, that is, a high conductivity. Can be provided. Therefore, it is possible to obtain a HEMT having a small on-resistance despite having a normally-off characteristic. Since the first organic semiconductor film 6 is not disposed under the gate electrode 5, it does not interfere with the normally-off operation.
(2) Since the n-type first organic semiconductor film 6 is formed at a temperature lower than the temperature at which the main semiconductor region 1 is formed, when the electron supply layer 10 having a crystal structure is formed thick, or Compared with the case where the electron supply layer 10 is formed by stacking a plurality of layers, it is possible to prevent deterioration of the semiconductor crystal in the main semiconductor region 1 or unnecessary impurity diffusion, and to provide a HEMT with good characteristics.
(3) Compared to the conventional method of forming a recess in a thick electron supply layer to obtain normally-off characteristics and forming a gate electrode in the recess, this embodiment includes a step of forming a recess in the electron supply layer. Since there is no damage, the main semiconductor region 1 is less damaged. Therefore, it is possible not only to easily manufacture a normally-off characteristic HEMT but also to maintain good characteristics.
(4) The collapse can be improved by the action of the p-type second organic semiconductor film 7.
(5) Since the main semiconductor region 1 is made of a nitride semiconductor, a high breakdown voltage HEMT can be provided.

  Next, the HEMT of Example 2 shown in FIG. 3 will be described. However, in FIG. 3 and FIGS. 3 to 14 described later, substantially the same parts as those in FIG.

The HEMT in FIG. 3 changes the arrangement position of the first and second organic semiconductor films 6 and 7 only between the drain electrode 4 and the gate electrode 5 on the first main surface 11 of the main semiconductor region 1. Is the same as that shown in FIG. As shown in FIG. 3, even if the first and second organic semiconductor films 6 and 7 are limitedly provided, the electron concentration in the 2DEG layer 14 in the portion facing the first and second organic semiconductor films 6 and 7 is reduced. The reduction can be suppressed, and the on-resistance reduction effect by the first organic semiconductor film 6 and the collapse improvement effect by the second organic semiconductor film 7 can be obtained as in the first embodiment.
In addition, as shown with a broken line in FIG. 3, the 2nd organic semiconductor film 7 is arrange | positioned to a part or all of the part in which the 1st organic semiconductor film 6 of the 1st main surface 11 of the main semiconductor region 1 is not provided. Thus, the effect of improving the collapse can be enhanced.

In the HEMT of Example 3 shown in FIG. 4, first and second organic semiconductor films 6 and 7 are provided between the drain electrode 4 and the gate electrode 5 on the first main surface 11 of the main semiconductor region 1. 3 except that it is provided only on the drain electrode 4 side and a gap is provided between the gate electrode 5 and the first and second organic semiconductor films 6 and 7. The effect similar to that of the second embodiment shown in FIG. 3 can be obtained by the third embodiment shown in FIG.
In addition, as shown with a broken line in FIG. 4, the 2nd organic semiconductor film 7 is arrange | positioned to a part or all of the part in which the 1st organic semiconductor film 6 of the 1st main surface 11 of the main semiconductor region 1 is not provided. Thus, the effect of improving the collapse can be enhanced.

In the HEMT of Example 4 shown in FIG. 5, the first and second organic semiconductor films 6 and 7 are not provided between the drain electrode 4 and the gate electrode 5, but are provided only on the gate electrode 5 side. 3 except that a gap is provided between the electrode 4 and the first and second organic semiconductor films 6 and 7. The effect similar to that of the second embodiment shown in FIG. 3 can be obtained by the fourth embodiment shown in FIG.
In addition, as shown with a broken line in FIG. 5, the 2nd organic semiconductor film 7 is arrange | positioned to a part or all of the part in which the 1st organic semiconductor film 6 of the 1st main surface 11 of the main semiconductor region 1 is not provided. Thus, the effect of improving the collapse can be enhanced.

In the HEMT of Example 5 shown in FIG. 6, the first and second organic semiconductor films 6 and 7 are not provided between the drain electrode 4 and the gate electrode 5, but only in the intermediate region between them. Others are the same as in FIG. Also in the fifth embodiment of FIG. 5, the same effect as that of the second embodiment of FIG. 3 can be obtained.
In addition, as shown with a broken line in FIG. 6, the 2nd organic semiconductor film 7 is arrange | positioned to a part or all of the part in which the 1st organic semiconductor film 6 of the 1st main surface 11 of the main semiconductor region 1 is not provided. Thus, the effect of improving the collapse can be enhanced.

  The HEMT of Example 6 in FIG. 7 is formed in the same manner as FIG. 1 except that a deformed main semiconductor region 1a is provided. The modified main semiconductor region 1a in FIG. 7 is obtained by adding a cap layer 21 made of undoped AlGaN and a spacer layer 22 made of undoped AlGaN to which, for example, no conductive impurities are added, to the main semiconductor region 1 in FIG.

  The cap layer 21 in FIG. 7 is disposed on the electron supply layer 10 and has a thickness of 2 to 5 nm, for example. The source electrode 3 and the drain electrode 4 are in low resistance contact with the cap layer 21, and the gate electrode 5 is in Schottky contact with the cap layer 21. The cap layer 21 has an effect of increasing the Schottky barrier between the gate electrode 5 and the main semiconductor region 1a.

  The spacer layer 22 in FIG. 7 is disposed between the electron transit layer 9 and the electron supply layer 10 and has a thickness of 2 to 5 nm, for example. The spacer layer 22 has an effect of preventing impurities in the electron supply layer 10 from diffusing into the electron transit layer 9.

The effect similar to that of the HEMT of FIG. 1 can be obtained by the HEMT of FIG.
One or both of the cap layer 21 and the spacer layer 22 in FIG. 7 are also provided in the HEMTs in Examples 2 to 5 in FIGS. 3 to 6 and Examples 7 to 13 in FIGS. be able to. In FIG. 7, one of the cap layer 21 and the spacer layer 22 can be omitted, and only the remaining other can be provided.

  The HEMT of Example 7 of FIG. 8 is obtained by adding an insulating film 15 made of a solid insulating material, ie, a dielectric to the HEMT of Example 1 of FIG. .

  The insulating film 15 is disposed between the first organic semiconductor film 6 and the second organic semiconductor film 7. The insulating film 15 is formed of, for example, SiO 2 (silicon oxide) and has a function of protecting the main semiconductor region 1 and the first organic semiconductor film 6.

  Since the insulating film 15 is made of a dielectric, the insulating film 15, the first organic semiconductor film 6, and the electron supply layer 9 function equivalently as a dielectric part of the capacitor, and the same principle as that of the first embodiment of FIG. With it, the effect of improving the collapse can be obtained.

  In FIG. 8, the first and second organic semiconductor films 6 and 7 and the insulating film 15 are disposed between the source electrode 3 and the drain electrode 4, outside the source electrode 3, and outside the drain electrode 4. These can also be arranged in a limited portion between the drain electrode 4 and the gate electrode 5 as shown in FIGS. Further, in the case where the first organic semiconductor film 6 is provided in a limited manner as shown in FIGS. 3 to 6, a portion where the first organic semiconductor film 6 is not provided on the first main surface 11 of the main semiconductor region 1. The insulating film 15 or the second organic semiconductor film 7 or both of them can be disposed on a part or all of the film.

  The HEMT according to the eighth embodiment shown in FIG. 9 is obtained by adding a resistive Schottky barrier type field plate 16 to the HEMT according to the first embodiment shown in FIG.

  The resistive Schottky barrier type field plate 16 is disposed between the first organic semiconductor film 6 and the first main surface 11 of the main semiconductor region 1, is connected to the gate electrode 5, and is connected to the drain electrode 4 and the gate electrode 5. It is arrange | positioned limitedly to a part between. That is, the resistive Schottky barrier type field plate 16 is in Schottky contact with the first main surface 11 of the main semiconductor region 1 and connected to the gate electrode 5. This resistive Schottky barrier type field plate 14 is the same as that disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 1-29559), and is made of, for example, a titanium oxide having a sheet resistance of 10 kΩ / □ or more. .

  The resistive Schottky barrier type field plate 16 contributes to the improvement of the breakdown voltage of the gate electrode 5 made of a Schottky barrier electrode, as in Patent Document 2. That is, the resistive Schottky barrier type field plate 16 can prevent the occurrence of an electric field concentration between the drain electrode 4 and the gate electrode 5. Therefore, according to the embodiment of FIG. 9, the breakdown voltage between the drain electrode 4 and the gate electrode 5 is increased. 9 can obtain the effect of improving the on-resistance by the first organic semiconductor film 6 and the effect of improving the collapse by the second organic semiconductor film 7 in the same manner as in Example 1 of FIG. it can.

  Also in FIG. 9, the first and second organic semiconductor films 6 and 7 can be arranged in a limited manner as shown in FIGS. Further, when the first organic semiconductor film 6 in FIG. 9 is provided in a limited manner as shown in FIGS. 3 to 6, the first organic semiconductor film 6 on the first main surface 11 of the main semiconductor region 1 is provided. The second organic semiconductor film 7 or the insulating film or both of them can be arranged on a part or all of the portions that are not formed.

  The HEMT of Example 9 shown in FIG. 10 is formed in the same manner as FIG. 9 except that the position of the resistive Schottky barrier type field plate 16 of FIG. 9 is changed.

  The resistive Schottky barrier type field plate 16 of FIG. 10 is connected to the drain electrode 4 and extends from the drain electrode 4 toward the gate electrode 5. Even if the resistive Schottky barrier type field plate 16 is formed as shown in FIG. 10, the electric field concentration between the drain electrode 4 and the gate electrode 5 can be reduced. In addition, also in Example 9 of FIG. 10, the on-resistance improvement effect by the first organic semiconductor film 6 and the collapse improvement effect by the second organic semiconductor film 7 can be obtained similarly to Example 1 of FIG. Can do.

Also in FIG. 10, the first and second organic semiconductor films 6 and 7 can be disposed in a limited manner as shown in FIGS. 10 is provided in a limited manner as shown in FIGS. 3 to 6, the first organic semiconductor film 6 on the first main surface 11 of the main semiconductor region 1 is provided. The second organic semiconductor film 7 or the insulating film or both of them can be arranged on a part or all of the portions that are not formed.

  The HEMT according to the tenth embodiment shown in FIG. 11 has the same configuration as that shown in FIG. 8 except that a resistive field plate 16a is added to the HEMT shown in FIG. The resistive field plate 16a of FIG. 11 is disposed between the first organic semiconductor film 6 and the insulating film 15, is connected to the gate electrode 5, and is limited to a part between the drain electrode 4 and the gate electrode 5. Are arranged. That is, the resistive field plate 16a is made of, for example, a titanium oxide having a sheet resistance of 10 kΩ / □ or more, and makes a resistive contact or a Schottky contact with the first organic semiconductor film 6, thereby contributing to an improvement in the breakdown voltage of the gate electrode 5. To do. In addition, according to Example 10 shown in FIG. 11, the effect of improving the on-resistance by the first organic semiconductor film 6 and the effect of improving the collapse by the second organic semiconductor film 7 can be obtained in the same manner as in Example 1 of FIG. Can do.

Also in FIG. 11, the first and second organic semiconductor films 6 and 7 can be arranged in a limited manner as shown in FIGS. 11 is provided in a limited manner as shown in FIGS. 3 to 6, the first organic semiconductor film 6 on the first main surface 11 of the main semiconductor region 1 is provided. The second organic semiconductor film 7 or the insulating film 15 or both of them can be disposed on a part or all of the portions that are not formed.

  The HEMT of Example 11 shown in FIG. 12 is formed in the same manner as FIG. 11 except that the position of the resistive field plate 16a in FIG. 11 is changed.

  The resistive field plate 16 a in FIG. 12 is connected to the drain electrode 4 and extends from the drain electrode 4 toward the gate electrode 5. Even if the resistive field plate 16a is formed as shown in FIG. 12, the electric field concentration between the drain electrode 4 and the gate electrode 5 can be reduced. In addition, also in Example 11 shown in FIG. 12, the effect of improving the on-resistance by the first organic semiconductor film 6 and the effect of improving the collapse by the second organic semiconductor film 7 can be obtained in the same manner as in Example 1 of FIG. Can do.

Also in FIG. 12, the first and second organic semiconductor films 6 and 7 can be arranged in a limited manner as shown in FIGS. 11 is provided in a limited manner as shown in FIGS. 3 to 6, the first organic semiconductor film 6 on the first main surface 11 of the main semiconductor region 1 is provided. The second organic semiconductor film 7 or the insulating film 15 or both of them can be disposed on a part or all of the portions that are not formed.

The HEMT of Example 12 shown in FIG. 13 is the same as that shown in FIG. 8 except that the position of the insulating film 15 in FIG. 8 is changed. In FIG. 13, the thin insulating film 15 is disposed between the first organic semiconductor film 6 and the main semiconductor region 1. When the insulating film 15 is thin, the action of the n-type first organic semiconductor film 6 reaches the electron supply layer 10 and the 2DEG layer 14 via the insulating film 15. As a result, the same effects as those of the first embodiment can be obtained by the twelfth embodiment shown in FIG.
Also in FIG. 13, the first and second organic semiconductor films 6 and 7 can be arranged in a limited manner as shown in FIGS. Further, when the first organic semiconductor film 6 of FIG. 13 is provided in a limited manner as shown in FIGS. 3 to 6, the first organic semiconductor film 6 on the first main surface 11 of the main semiconductor region 1 is provided. The second organic semiconductor film 7 or the insulating film 15 or both of them can be disposed on a part or all of the portions that are not formed.

The HEMT of Example 13 shown in FIG. 14 is the same as FIG. 1 except that a gate insulating film 17 is provided below the gate electrode 5 of FIG. In the HEMT according to the thirteenth embodiment shown in FIG. 14, the depletion layer under the gate insulating film 17 is changed by the gate control voltage applied between the gate electrode 5 and the source electrode 3, and the current flowing through the 2DEG layer 14 is changed. Be controlled.
Also in Example 13 shown in FIG. 14, the effect of improving the on-resistance by the first organic semiconductor film 6 and the effect of improving the collapse by the second organic semiconductor film 7 can be obtained in the same manner as in Example 1 of FIG. .
In FIG. 14 as well, the first and second organic semiconductor films 6 and 7 can be arranged in a limited manner as shown in FIGS. Further, when the first organic semiconductor film 6 of FIG. 13 is provided in a limited manner as shown in FIGS. 3 to 6, the first organic semiconductor film 6 on the first main surface 11 of the main semiconductor region 1 is provided. The second organic semiconductor film 7 or the insulating film or both of them can be arranged on a part or all of the portions that are not formed.

The present invention is not limited to the above-described embodiments, and for example, the following modifications are possible.
(1) The electron supply layer 10 of FIGS. 1 and 3 to 14 can be replaced with a p-type semiconductor hole supply layer. In this case, a two-dimensional hole gas layer is generated as a two-dimensional carrier gas layer in a region corresponding to the 2DEG layer 11. In this way, when the two-dimensional carrier is a hole, the first organic semiconductor film 6 is changed to p-type, and the second organic semiconductor film 7 is changed to n-type.
(2) Another semiconductor layer can be added to the main semiconductor regions 1 and 1a as necessary. For example, a source contact layer can be disposed under the source electrode 3 and a drain contact layer can be disposed under the drain electrode 4. In addition, the source electrode 3 and the drain electrode 4 can be directly connected to the electron transit layer 8.
(3) The resistive Schottky barrier type field plate 14 of FIGS. 9 and 10 and the resistive field plate 14a of FIGS. 11 and 12 are formed on the first main surface 11 of the main semiconductor region 1 and the gate electrode 5 and the source electrode. 3 can also be provided.
(4) The support substrate 2 can be formed of a silicon compound other than silicon, sapphire, or a group 3-5 compound semiconductor.

It is sectional drawing which shows HEMT of Example 1 of this invention. It is a characteristic view which shows the relationship between the gate-source voltage and drain current of HEMT of Example 1 of FIG. 1, and HEMT of a prior art example. It is sectional drawing which shows HEMT of Example 2 of this invention. It is sectional drawing which shows HEMT of Example 3 of this invention. It is sectional drawing which shows HEMT of Example 4 of this invention. It is sectional drawing which shows HEMT of Example 5 of this invention. It is sectional drawing which shows HEMT of Example 6 of this invention. It is sectional drawing which shows HEMT of Example 7 of this invention. It is sectional drawing which shows HEMT of Example 8 of this invention. It is sectional drawing which shows HEMT of Example 9 of this invention. It is sectional drawing which shows HEMT of Example 10 of this invention. It is sectional drawing which shows HEMT of Example 11 of this invention. It is sectional drawing which shows HEMT of Example 12 of this invention. It is sectional drawing which shows HEMT of Example 13 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a Main semiconductor region 2 Support substrate 3 Source electrode 4 Drain electrode 5 Gate electrode 6 1st n-type organic semiconductor film 7 2nd p-type organic semiconductor film 8 Buffer layer 9 Electron travel layer 10 n-type electron Supply layer 13 Heterojunction 14 2 DEG layer

Claims (10)

First and second main surfaces facing each other, a first semiconductor layer having a first conductivity type and a crystal structure, and the first semiconductor layer for generating a two-dimensional carrier gas The semiconductor layer is made of a different semiconductor material, is disposed adjacent to the first semiconductor layer, is disposed at a position farther from the first semiconductor layer than the first main surface, and has a crystal structure. A semiconductor region comprising a second semiconductor layer;
A source electrode and a drain electrode formed on the first main surface of the semiconductor region;
A gate electrode disposed between the source electrode and the drain electrode on the first main surface of the semiconductor region;
A first organic semiconductor film disposed on at least a portion between the source electrode and the drain electrode on the first main surface of the semiconductor region and having the first conductivity type;
A second organic semiconductor film disposed on the first organic semiconductor film having the first conductivity type and having a second conductivity type opposite to the first conductivity type;
Field effect transistor, characterized in that it comprises a.   The gate electrode is an electrode that is in Schottky contact with the first semiconductor layer, and the first semiconductor layer has a thickness that allows the field effect transistor to operate normally off. The field effect transistor according to claim 1. 3. The field effect transistor according to claim 1, wherein the first conductivity type is n-type, and the first organic semiconductor film is made of fullerene or metal phthalocyanine exhibiting n-type.   4. The semiconductor region according to claim 1, further comprising a cap layer made of a crystalline semiconductor disposed on the first semiconductor layer and not doped with a conductive impurity. The field effect transistor according to any one of the above.   The semiconductor region is further composed of a crystalline semiconductor that is disposed between the first semiconductor layer and the second semiconductor layer and is not doped with a conductive impurity, and is more than the first semiconductor layer. 5. The field effect transistor according to claim 1, further comprising a spacer layer formed to be thin. The field effect transistor according to claim 1, further comprising an insulating film disposed between the semiconductor region and the first organic semiconductor film. The electric field according to claim 1, further comprising an insulating film disposed between the first organic semiconductor film and the second organic semiconductor film. Effect transistor. Furthermore, any one of claims 1 to 7, characterized in that it has the semiconductor regions the one disposed on the main surface of and the gate electrode or resistive field plate connected to said drain electrode of 1 Field effect transistor as described in one. Further, it claims 1 to 7, characterized by having the first organic semiconductor film disposed and the gate electrode or connected field plate to the drain electrode on having the first conductivity type The field effect transistor according to any one of the above.   2. The field effect transistor according to claim 1, further comprising a gate insulating film disposed between the gate electrode and the first main surface of the semiconductor region.

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