JP4629955B2 - GaN-based III-V nitride semiconductor switching device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a GaN-based group III-V nitride semiconductor switching element. More specifically, the present invention relates to a GaN-based III-V nitride semiconductor switching element, which relates to a thyristor and the like.
[0002]
[Prior art]
A thyristor is known as a switching element. As shown in FIG. 5, a typical thyristor has a p ₁ n ₁ p ₂ n ₂ structure and has junctions J ₁ , J ₂ , and J ₃ . The anode electrode A is connected to the p ₁ layer, the cathode electrode C is connected to the n ₂ layer, and the gate electrode G is connected to the p ₂ layer. Note that Si is mainly used as the material of the semiconductor layers constituting the p layer and the n layer.
[0003]
FIG. 6 shows the relationship between the current and voltage flowing between the anode electrode and the cathode electrode when a voltage is applied between the anode electrode and the cathode electrode. When a positive voltage V is applied to the anode electrode A, a reverse bias is applied to J ₂ and a forward bias is applied to J ₁ and J ₃ . Therefore, almost no current flows. However, when the voltage exceeds V _BO , the electric field in the depletion layer of J ₂ becomes strong, an electron avalanche occurs, and a current flows rapidly (turn-on phenomenon).
[0004]
Here, if a positive voltage is applied to the gate electrode G to inject holes, the gate electrode G can be turned on even when V <V _BO . That is, by controlling the voltage applied to the gate electrode G, a switching element that controls the current flowing between the anode electrode and the cathode electrode is realized. On the other hand, when applying a negative voltage to the anode electrode, forward bias to J _2, applied reverse bias to J _1, J _3, when a negative voltage exceeds the breakdown voltage V _BR with the J _1, J _3, 6 So that the current flows rapidly.
[0005]
[Non-Patent Document 1]
Furukawa Shizujiro “Semiconductor Device” Corona 14th Print p189-192
[0006]
[Problems to be solved by the invention]
When a thyristor is formed of a Si-based semiconductor, the breakdown voltage cannot be increased because the band gap is as small as about 1 eV. Therefore, there is a problem that V _BO and V _BR cannot be increased. Further, since the band gap is small, the high temperature operation cannot be performed, and there is a problem that a thyristor generates heat when high power is controlled, and a means for cooling it must be provided.
[0007]
In the conventional thyristor as shown in FIG. 5, the doping concentration of the p ₂ layer to which the gate electrode G is connected must be higher than the doping concentration of the n ₁ layer in order to generate holes. Therefore, when a positive voltage is applied to the anode electrode A, the depletion layer spreads to the n ₁ layer side. Therefore, in order not to reduce V _BO , the n ₁ layer must be made sufficiently thick. For this reason, there is a problem that the traveling time of electrons in the n ₁ layer increases, the turn-on time becomes long, and the switching speed becomes slow.
[0008]
The present invention has been made in view of the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a switching element such as a thyristor that has a high withstand voltage and can operate at a high temperature. Furthermore, it aims at improving the switching speed of a switching element.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, an anode electrode, a cathode electrode, a gate electrode, an n-type GaN-based III-V nitride semiconductor layer, and a p-type GaN-based III- In a GaN-based III-V nitride semiconductor switching device having three or more pn junctions made of a group V nitride semiconductor layer, a pn junction to which a reverse bias is applied when a positive or negative voltage is applied to the anode electrode. One of the p-type semiconductor layer and the n-type semiconductor layer that is present and constitutes the pn junction is connected to the gate electrode, and the pn junction is connected to the anode electrode among the pn junctions And an i-type GaN-based III-V layer between an n-type GaN-based III-V group nitride semiconductor layer and a p-type GaN-based group III-V nitride semiconductor layer constituting a pn junction connected to the cathode electrode. Group nitride semiconductor Characterized in that the insertion of the layers.
[0010]
In the first aspect of the present invention, the switching element has an anode electrode, a cathode electrode, a gate electrode, and three or more pn junctions, and has a pn junction to which a reverse bias is applied when a positive or negative voltage is applied to the anode electrode. In the present invention, a GaN-based III-V group nitride semiconductor having a larger band gap than Si or the like is used as a semiconductor material constituting the pn junction.
[0011]
Therefore, the breakdown voltage of the pn junction that is reverse-biased when a positive voltage is applied to the anode electrode can be increased, and when the negative voltage is applied to the anode electrode, the remaining pn junction is reverse-biased. The breakdown voltage can also be increased. Therefore, the voltage that can be applied between the anode electrode and the cathode electrode can be increased. Furthermore, since a GaN-based III-V group nitride semiconductor is used, high-temperature operation is possible, and a cooling mechanism is not required even when the device is used for high power. In addition, an i-type GaN-based III III is interposed between an n-type GaN-based III-V group nitride semiconductor layer and a p-type GaN-based III-V group nitride semiconductor layer constituting a pn junction connected to the anode electrode and the cathode electrode. Since the −V group nitride semiconductor layer is inserted, the reverse breakdown voltage can be further improved.
[0012]
According to a second aspect of the present invention, the cathode electrode and the anode electrode are made of metal silicide as described in claim 4 .
[0013]
In the second aspect of the present invention, since a metal silicide alloy is used as the electrode, the contact resistance of the electrode can be reduced. Therefore, heat generation is suppressed and the effect of the first invention can be further improved.
[0014]
Third, as according to claim 3 of the present invention, and the anode electrode, between the anode electrode side of the semiconductor layer constituting the connected pn junction to the anode electrode, and said cathode electrode, said cathode Between the semiconductor layer on the cathode electrode side constituting the pn junction connected to the electrode, the semiconductor layer on the anode electrode side constituting the pn junction connected to the anode electrode, and the pn connected to the cathode electrode A GaN-based group III-V nitride semiconductor layer having a smaller band gap than the semiconductor band gap constituting the semiconductor layer on the cathode electrode side constituting the junction is inserted.
[0015]
According to the third aspect of the present invention, the p-type semiconductor connected to the anode electrode is connected between the anode electrode and the p-type semiconductor layer connected to the anode electrode, and between the cathode electrode and the n-type semiconductor layer connected to the cathode electrode. Since the GaN-based III-V nitride semiconductor layer having a band gap smaller than the band gap of the semiconductor constituting the n-type semiconductor layer connected to the layer and the cathode electrode is inserted, the contact resistance of the electrode should be reduced Can do. Therefore, heat generation is suppressed and the effects of the first or second invention can be improved.
[0018]
Fifth, as according to claim 5 of the present invention, the GaN-based III-V nitride semiconductor GaN-based III-V constituting the switching element nitride semiconductor layer is AlGaN, AlInGaN, AlGaNP, AlGaNAs, AlGaNP, They are AlGaNAs and AlInGaNAsP.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of a GaN-based III-V group nitride semiconductor switching element according to the present invention will be described below with reference to the drawings. In the description of the drawings, the same or similar parts are given the same or similar reference numerals and names. Also, it should be noted that the drawings are schematic and are different from actual ones. Of course, the drawings include portions having different dimensional relationships and ratios.
[0021]
First, a GaN-based III-V group nitride semiconductor switching element according to an embodiment will be described.
As shown in FIG. 2, a p-type semiconductor layer 3 made of p-Al _w Ga _1-w N (0 ≦ w ≦ 1) and an n-type made of n-Al _z Ga _1-z N (0 ≦ x ≦ 1). semiconductor layer _{4, p-Al y Ga 1} -y n (0 ≦ y ≦ 1) p -type semiconductor layer _{5, n-Al z Ga 1-} z n n -type semiconductor layer made of (0 ≦ z ≦ 1) consisting of 6 is formed. With this structure, _three pn junctions J ₁ , J ₂ and J ₃ are formed. An anode electrode 7 connected to the p-type semiconductor layer 3, a cathode electrode 8 connected to the n-type semiconductor layer 6, and a gate electrode 9 connected to the n-type semiconductor layer 4 are formed. These structures form an npnp type structure.
[0022]
The manufacturing method of the above-described GaN-based III-V group nitride semiconductor switching element is as follows.
First, the laminated structure shown in FIG. 1 was manufactured by a gas source molecular beam epitaxial growth method (GSMBE method).
That is, on the sapphire substrate 1, dimethylhydrazine (5 × 10 ⁻⁵ Torr) as an N source, metal Ga (5 × 10 ⁻⁷ Torr) as a Ga source, and metal Mg (5 × 10 ⁻⁹ Torr) as a p-type dopant. ) Was used to form a GaN buffer layer 2 having a growth temperature of 640 ° C. and a thickness of 50 nm. Further, ammonia (5 × 10 ⁻⁶ Torr) as the N source, metal Ga (5 × 10 ⁻⁷ Torr) as the Ga source, Al (1 × 10 ⁻⁷ Torr) as the Al source, and a p-type dopant. Metal Mg (5 × 10 ⁻⁹ Torr) is added to form a p-type semiconductor layer 3 (doping concentration 5 × 10 ¹⁸ cm ⁻³ ) made of p-Al _w Ga _1-w N with a growth temperature of 850 ° C. and a thickness of 2 μm. Filmed.
[0023]
Then, using the metal Si (5 × 10 ⁻⁹ Torr) as an n-type dopant for the N source, Ga source, and Al source described above, the growth temperature is 850 ° C., and the thickness is 2 μm from n-Al _x Ga _1-x N. A layer (n-type semiconductor layer 4) (doping concentration 5 × 10 ¹⁸ m ⁻³ ) to be formed was formed.
[0024]
Then, N sources described above, the Ga source and the Al source, added metal Mg (5 × 10 ^-9 Torr) is a p-type dopant, carried out growth GSMBE at a growth temperature of 850 ° C., the thickness 2 [mu] m p-Al _y A p-type semiconductor layer 5 (doping concentration 5 × 10 ¹⁸ cm ⁻³ ) made of Ga _1-y N is formed. Finally, N source as described above, the Ga source and the Al source, n-type dopant using a metal Si (5 × 10 ^-9 Torr) is, the thickness of 2μm at a growth temperature of _{850 ℃ n-Al z Ga 1-} z N A layer (n-type semiconductor layer 6) made of (doping concentration 5 × 10 ¹⁸ cm ⁻³ ) was formed. As a result, _three pn junctions J ₁ , J ₂ , and J ₃ are formed, and the stacked structure in FIG. 1 is completed.
[0025]
In the laminated structure of FIG. 1, the switching element is completed through a process of forming the anode electrode 7, the cathode electrode 8, and the gate electrode 9. That is, after forming a SiO ₂ film on the surface of n-Al _z Ga _{1 -z} N (n-type semiconductor layer 6) by plasma CVD, patterning is performed with a photoresist, and wet etching is performed using this SiO ₂ film as a mask. Then, a part of the layer structure is removed by etching until the surface of the n-Al _x Ga _{1 -x} N layer (n-type semiconductor layer 4) is exposed, and the n-Al _x Ga _{1 -x} N layer (n-type semiconductor) A partial surface of layer 4) was exposed.
[0026]
Then after removing the SiO ₂ film was formed again SiO ₂ film on the entire _{surface, n-Al x Ga 1-} x N layer (n-type semiconductor layer 4) to form an opening of the gate electrode 9 on the surface _{, n-Al x Ga 1-} x n layer to form a gate electrode 9 by depositing Al / Ti / Au on the (n-type semiconductor layer 4), further _{n-Al z Ga 1- z n} (n -type A cathode electrode 8 is formed by evaporating Al / Ti / Au on the semiconductor layer 6). Then, laser is irradiated from the back surface of the sapphire substrate 1 to remove the sapphire substrate 1 and the buffer layer 2. Finally, Ti / Pt is vapor-deposited on the back surface of the p-Al _w Ga _1-w layer (p-type semiconductor layer 3) to form the anode electrode 7, thereby completing the switching element shown in FIG.
[0027]
When the switching element of FIG. 2 was used as a thyristor, the following characteristics were obtained. At this time, w = 0.3, x = 0.5, y = 0.3, and z = 0.3.
A voltage was applied between the anode electrode 7 and the cathode electrode 8, and the flowing current was measured. The measurement result was the same as in FIG.
[0028]
That is, when a positive voltage is applied to the anode electrode 7, a forward bias is applied to the pn junctions J ₁ and J ₃ and a reverse bias is applied to the pn junction J ₂ . Since the n-type semiconductor layer 4 and the p-type semiconductor layer 5 constituting the pn junction J ₂ are made of a GaN-based III-V group nitride semiconductor, the breakdown voltage of the pn junction J ₂ is that of a Si-based semiconductor. It can be significantly higher than As a result of the measurement, it was possible to obtain V _BO of 600V or more.
[0029]
Further, when a negative voltage is applied to the anode electrode 7, a reverse bias is applied to the pn junctions J ₁ and J ₃ and a forward bias is applied to the pn junction J ₂ . Since the p-type semiconductor layer 3, the n-type semiconductor layer 4, the p-type semiconductor layer 5, and the n-type semiconductor layer 6 constituting the pn junctions J ₁ and J ₃ use a GaN-based III-V group nitride semiconductor, pn As with the junction J ₂ , the breakdown voltage of the pn junctions J ₁ and J ₃ can be significantly increased. As a result of the measurement, a V _BR of 600 V or more was obtained.
[0030]
Further, the switching element of FIG. 2 has the characteristics shown in FIG. 6 as in the conventional Si thyristor by controlling the voltage applied to the gate electrode 9. This is because the switching element has a function as a thyristor.
[0031]
Furthermore, while the upper limit of the ambient temperature at which a Si-based thyristor can operate normally is 200 ° C., it has been found that the switching element described above operates normally even at a high temperature of 600 ° C.
[0032]
The values of w, x, y, and z of the switching element described above were w = 0.3, x = 0.5, y = 0.3, and z = 0.3. However, the present invention is not limited to this. Absent. Therefore, it is possible to manufacture a thyristor suitable for the application. Moreover, although the switching element according to the present embodiment has an npnp structure, a pnpn structure is also possible.
[0033]
The doping concentration of the p-AlGaN layer (p-type semiconductor layers 3 and 5) and the n-AlGaN layer (n-type semiconductor layers 4 and 6) was 5 × 10 ¹⁸ cm ⁻³ , but is not limited thereto. It not, can be varied in a range of ^{1 × 10 17 cm -3 ~1 ×} 10 19 cm -3. A thyristor made of a Si-based semiconductor has a problem that V _BO and V _BR are remarkably reduced when high concentration doping is performed. However, in the switching element according to the present invention, V _BO can lower the element resistance without lowering V _BR even at high concentration doping.
[0034]
In the embodiment of the present invention, Ti / Pt and Al / Ti / Au are used as the material of the anode electrode 7 and the cathode electrode 8, but if a metal silicide alloy is used instead of these, the contact resistance of the electrode is greatly increased. Can be lowered. Examples of the metal material of the metal silicide alloy include Ta, Al, Ti, Cu, Pt, Pd, Ag, Ni, W, Mo, Cr, In, Sn, and Mn.
[0035]
In the embodiment of the present invention, the anode electrode 7 and the cathode electrode 8 are directly formed on the surface of the p-type semiconductor layer 3 and the surface of the n-type semiconductor layer 6, but the anode electrode 7 and the p-type semiconductor layer are formed as shown in FIG. 3. A p ⁺ -type contact layer 11 and an n ⁺ -type contact layer 10 may be formed between the cathode electrode 8 and the n-type semiconductor layer 6. Here, the thickness of the contact layer is 50 to 500 nm, and the doping concentration is suitably 1 × 10 ^{19 to} 5 × 10 ²⁰ cm ⁻³ .
[0036]
In particular, the contact resistance of the electrode can be reduced by making the band gaps of the p ⁺ -type contact layer 11 and the n ⁺ -type contact layer 10 smaller than the band gaps of the p-type semiconductor layer 3 and the n-type semiconductor layer 6. The effect can be further enhanced by combining with the metal silicide alloy electrode described above. In FIG. 3, InGaN is used as the p ⁺ -type contact layer 11 and the n ⁺ -type contact layer 10.
[0037]
Further, as shown in FIG. 3, i-type GaN-based III-V group nitride semiconductor layers 12, 13 are disposed between the n-type semiconductor layer 4 and the p-type semiconductor layer 3 and between the n-type semiconductor layer 6 and the p-type semiconductor layer 5. It is also possible to insert When the n-type semiconductor layer and the p-type semiconductor layer are directly joined, the impurities in the two layers diffuse to each other, so that V _BO and V _BR may be slightly reduced. By inserting, mutual diffusion can be prevented. As a method for forming an i-type semiconductor layer having a particularly high insulating property, there is a method of doping any one of C, Mg, and Zn as described in JP-A-2001-247399.
[0038]
In the embodiment of the present invention, the thickness of the p-type semiconductor layer 5 is 2 μm, but this thickness can be reduced to 500 nm or less. In the Si-based thyristor of FIG. 5, the doping concentration of the p ₂ layer to which the gate electrode G is connected must be higher than the doping concentration of the n ₁ layer in order to generate holes, and V _BO is maintained. In order to do so, the n ₁ layer had to be made sufficiently thick. However, in the present invention, the layer corresponding to the n ₁ layer can be made thin without lowering V _BO . Therefore, the turn-on time can be shortened and the switching speed can be improved.
[0039]
In the embodiment of the present invention, the thyristor has been described as the switching element, but the present invention is not limited to this. That is, a GaN-based III-V group nitride semiconductor switching element having an anode electrode, a cathode electrode, a gate electrode, and three or more pn junctions, and when a positive or negative voltage is applied to the anode electrode, a reverse bias is generated. There is an added pn junction, and the current flowing between the anode electrode and the cathode electrode is controlled by controlling the carrier concentration of one of the two layers constituting the junction with the voltage applied to the gate electrode. It can be applied to anything you do. For example, a gate turn-off thyristor in which an insulating film 14 is inserted between semiconductor layers in contact with the gate electrode 9 as shown in FIG.
[0040]
In the embodiment of the present invention, AlGaN is used as the semiconductor material of the p-type semiconductor layer, the n-type semiconductor layer, and the i-type semiconductor layer. However, the present invention is not limited to these, and all GaN-based III-V groups are used. A nitride semiconductor can be used. This also applies to the p ⁺ -type contact layer 11 and the n ⁺ -type contact layer 10 as long as the condition that the band gap is smaller than that of the p-type semiconductor layer 3 and the n-type semiconductor layer 6 is satisfied. Examples of the GaN-based III-V group nitride semiconductor include AlInGaN, AlGaNP, AlGaNAs, AlGaNP, AlGaNAs, and AlInGaNAsP.
[0041]
【The invention's effect】
As described above, according to the switching element of the present invention, it is possible to realize a high breakdown voltage and capable of high temperature operation. Further, the switching speed of the switching element can be increased.
[0042]
[Brief description of the drawings]
FIG. 1 shows a semiconductor multilayer structure used in an embodiment of the present invention.
FIG. 2 shows a laminated structure according to an embodiment of the present invention.
FIG. 3 shows a laminated structure according to another embodiment of the present invention.
FIG. 4 shows a laminated structure of still another embodiment of the present invention.
FIG. 5 is a schematic diagram of a laminated structure of thyristors.
FIG. 6 shows voltage-current characteristics of a thyristor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 Buffer layer 3 p-type semiconductor layer 4 n-type semiconductor layer 5 p-type semiconductor layer 6 n-type semiconductor layer 7 Anode electrode 8 Cathode electrode 9 Gate electrode 10 n ⁺ type contact layer 11 p ⁺ type contact layer 12 i type Semiconductor layer 13 i-type semiconductor layer 14 Insulating film

Claims (6)

GaN-based III-V group having three or more pn junctions composed of an anode electrode, a cathode electrode, a gate electrode, an n-type GaN-based group III-V nitride semiconductor layer and a p-type GaN-based group III-V nitride semiconductor layer In the nitride semiconductor switching element,
When a positive or negative voltage is applied to the anode electrode, there is a pn junction to which a reverse bias is applied, and any one of the p-type semiconductor layer and the n-type semiconductor layer constituting the pn junction is Connected to the gate electrode,
Among the pn junctions, an n-type GaN-based III-V nitride semiconductor layer and a p-type GaN-based III-V group constituting a pn junction connected to the anode electrode and a pn junction connected to the cathode electrode A GaN-based group III-V nitride semiconductor switching element, wherein an i-type GaN-based group III-V nitride semiconductor layer is inserted between the nitride semiconductor layers . The i-type GaN-based III-V nitride semiconductor layer, a GaN-based Group III-V nitride semiconductor switching element according to claim 1, wherein that it has been insulated by doping C. And the anode electrode, between the anode electrode side of the semiconductor layer constituting the connected pn junction to the anode electrode, and the cathode electrode side constituting said cathode electrode, the connected pn junction to the cathode electrode Between the semiconductor layers of
The semiconductor layer on the anode electrode side constituting the pn junction connected to the anode electrode and the band gap of the semiconductor constituting the semiconductor layer on the cathode electrode side constituting the pn junction connected to the cathode electrode The GaN-based III-V group nitride semiconductor switching device according to claim 1 or 2, wherein a GaN-based III-V group nitride semiconductor layer having a small gap is inserted. 4. The GaN-based III-V nitride semiconductor switching element according to claim 1 , wherein the cathode electrode and the anode electrode are made of metal silicide . 5. Claim 1 GaN-based III-V nitride semiconductor layer forming the GaN-based III-V nitride semiconductor switching element is characterized AlGaN, AlInGaN, AlGaNP, AlGaNAs, AlGaNP, AlGaNAs, the AlInGaNAsP der Rukoto 5. The GaN-based III-V nitride semiconductor switching element according to any one of items 1 to 4 . The GaN-based III-V group nitride semiconductor switching device according to any one of claims 1 to 5, wherein the GaN-based III-V group nitride semiconductor switching device is a thyristor or a gate turn-off transistor .

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