JP2004152821A - Gan based iii-v nitride semiconductor diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diode utilizing the reverse characteristics and exhibiting excellent high temperature characteristics and a high reverse breakdown voltage. <P>SOLUTION: In the GaN based III-V nitride semiconductor diode comprising a pn junction 4 of a p-type GaN based III-V nitride semiconductor layer 5 and an n-type GaN based III-V nitride semiconductor layer 3, a p-side electrode 7 touching the p-type GaN based III-V nitride semiconductor layer 5, and an n-side electrode 6 touching the n-type GaN based III-V nitride semiconductor layer 3, its reverse characteristics are utilized. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a GaN-based III-V nitride semiconductor diode that utilizes the characteristics of a diode in the reverse direction. More specifically, the present invention relates to a GaN-based III-V nitride semiconductor diode having a high reverse breakdown voltage and excellent high-temperature characteristics. More specifically, the present invention provides a GaN-based III-V nitride semiconductor variable capacitance diode having these characteristics and a large change in capacitance, and a GaN-based III-V nitride semiconductor constant voltage having a high output voltage. It relates to a diode.
[0002]
[Prior art]
The diode has, for example, a pn junction 4 composed of an n-type semiconductor layer 3 and a p-type semiconductor layer 5 as shown in FIG. 5, an n-side electrode 6 on the n-type semiconductor layer 3, and a p-type junction on the p-type semiconductor layer 5. The side electrode 7 is formed. FIG. 6 shows the voltage-current characteristics of the diode. The voltage axis is the horizontal axis.
As can be seen from FIG. 6, when a voltage is applied in the forward direction, a large current flows because electrons in the n-type semiconductor layer 3 and holes in the p-type semiconductor layer 5 rapidly recombine near the pn junction 4. When a voltage is applied in the reverse direction, the depletion layer expands from the pn junction 4 and almost no current flows. Since the depletion layer becomes wider as the reverse voltage increases, no current flows even when the reverse voltage is applied. However, when the reverse voltage reaches the breakdown voltage _Vb , the Zener phenomenon and the avalanche of electrons occur. Due to the phenomenon, the current suddenly flows (reverse current).
[0003]
Variable capacitance diodes and constant voltage diodes are generally known as devices utilizing the reverse characteristics of diodes. A variable capacitance diode is a diode that uses a change in the thickness of a depletion layer as a change in capacitance. Further, the constant voltage diode is a diode utilizing the property that _Vb hardly depends on the reverse current.
[0004]
The variable capacitance diode is represented by the circuit diagram of FIG. 7, and is widely used in electronic circuits such as parametric amplification, frequency multiplication, frequency conversion, frequency modulation, automatic frequency control, and electronic tuning of a resonance circuit. A constant voltage diode is represented by a circuit diagram in FIG. 8 and is widely used in a circuit requiring a reference voltage such as a constant voltage circuit.
[0005]
Conventionally, as a material of a variable capacitance diode and a constant voltage diode, a material based on Si, GaAs, or Ge has been used. When a Si substrate is used, a p-type semiconductor layer and an n-type semiconductor layer are formed by a diffusion method to form a pn junction, thereby forming a diode.
[0006]
[Non-patent document 1]
Tetsuro Ishida, "Semiconductor Device", Corona, 1978, p146
[0007]
[Problems to be solved by the invention]
However, since the semiconductor based on Si, GaAs, or Ge has a relatively small band gap of 0.5 to 1.5 eV, the following problem arises when the reverse characteristics of the diode are used as a device.
[0008]
In FIG. 6 showing the voltage-current characteristics of the diode, the value of the breakdown voltage _Vb decreases as the band gap decreases. Therefore, when a variable capacitance diode is manufactured using Si or the like, since _Vb is small, a change in the thickness of a depletion layer cannot be increased, and a problem that a large capacitance change cannot be manufactured occurs.
[0009]
Further, even when a constant voltage diode is manufactured, _Vb cannot be increased, so that there is a problem in that a diode exhibiting a high voltage constant voltage characteristic cannot be manufactured. Such a problem can be solved to some extent by increasing the area of the pn junction, but another problem of increasing the area of the element occurs. Even if this method is used, the limit of _Vb is about 100 V.
[0010]
Furthermore, since the band gap is small and the intrinsic density is large, the region becomes an intrinsic region at a high temperature of 150 ° C. or higher, and a normal voltage-current characteristic as shown in FIG. 6 cannot be obtained. was there.
[0011]
The present invention has been made in view of the above-described drawbacks of the related art, and has as its object to provide a diode utilizing reverse characteristics, which has excellent high-temperature characteristics and high withstand voltage in the reverse direction. I do. It is another object of the present invention to provide a variable capacitance diode having a large capacitance change and a constant voltage diode capable of obtaining a high voltage.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention is a pn junction comprising a p-type GaN-based III-V nitride semiconductor layer and an n-type GaN-based III-V nitride semiconductor layer, as described in claim 1. A GaN-based III-V group comprising a p-side electrode in contact with the p-type GaN-based III-V nitride semiconductor layer and an n-side electrode in contact with the n-type GaN-based III-V nitride semiconductor layer A nitride semiconductor diode, characterized by utilizing characteristics in the reverse direction.
[0013]
In the first aspect of the present invention, since the diode is formed using a GaN-based group III-V nitride semiconductor having a relatively large band gap, _Vb can be increased, and the withstand voltage in the reverse direction is improved. Therefore, a high withstand voltage characteristic can be utilized when utilizing the characteristics in the reverse direction. Further, the characteristics at high temperatures are also improved.
[0014]
Here, utilizing the characteristics in the reverse direction means that the semiconductor diode according to the present invention is used by applying a voltage in the direction opposite to the arrow in FIG.
[0015]
A second aspect of the present invention is characterized in that the p-side electrode and the n-side electrode are made of a metal silicide alloy.
[0016]
In the second aspect of the present invention, since the metal silicide alloy is used as the electrode, the contact resistance can be reduced.
[0017]
According to a third aspect of the present invention, between the p-type GaN-based III-V nitride semiconductor layer and the p-side electrode, and the n-type GaN-based III-V nitride semiconductor layer, GaN-based III-V nitride having a smaller band gap than the p-type GaN-based III-V nitride semiconductor layer and the n-type GaN-based III-V nitride semiconductor layer between the n-side electrodes Characterized in that an object semiconductor layer is inserted.
[0018]
In the third aspect of the present invention, a semiconductor layer having a small band gap is sandwiched between the electrode and the semiconductor layer forming the pn junction. Therefore, it is possible to reduce the contact resistance of the p-side electrode and the n-side electrode.
[0019]
According to a fourth aspect of the present invention, an undoped GaN-based III-V semiconductor layer is provided between the p-type GaN-based III-V nitride semiconductor layer and the n-type GaN-based III-V nitride semiconductor layer. A GaN-based III-V nitride semiconductor diode, wherein a V-nitride semiconductor layer is inserted.
[0020]
According to the fourth aspect of the present invention, the undoped GaN-based group III-V nitride semiconductor layer is sandwiched between the p-type semiconductor layer and the n-type semiconductor layer, so that the reverse breakdown voltage is further improved.
[0021]
A fifth aspect of the present invention is characterized in that the reverse characteristic of the GaN-based III-V nitride semiconductor diode is used as a change in capacitance.
[0022]
The fifth aspect of the present invention is, in other words, to use as a variable capacitance diode. In the fifth aspect of the present invention, since a GaN-based III-V nitride semiconductor diode having a large reverse breakdown voltage is used as a variable capacitance diode, it is possible to increase the change in capacitance.
[0023]
A sixth aspect of the present invention is characterized in that an output of a breakdown voltage in a reverse direction is used as the reverse characteristic of the GaN-based III-V nitride semiconductor diode.
[0024]
In the sixth aspect of the present invention, in other words, the present invention is used as a constant voltage diode. In the sixth aspect of the present invention, the output voltage can be increased because a GaN-based III-V nitride semiconductor diode having a high reverse breakdown voltage is used as a constant voltage diode.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a GaN-based III-V nitride semiconductor diode according to the present invention will be described with reference to the drawings. In the drawings, the same or similar parts are denoted by the same or similar reference numerals and names. It should be noted that the drawings are schematic and different from actual ones. Needless to say, the drawings include portions having different dimensional relationships and ratios.
[0026]
First, a GaN-based III-V nitride semiconductor diode according to an embodiment will be described.
On a sapphire substrate 1 as shown in FIG. 2, a buffer layer ₂ made of _{GaN, n-Al x Ga 1} -x N (0 ≦ x ≦ 1) n -type semiconductor layer 3 made of, pn junction 4, p-Al _A p-type semiconductor layer 5 made of yGa1 _-yN (0≤y≤1) is formed. This structure constitutes a diode. An n-side electrode 6 that contacts the n-type semiconductor layer 3 and a p-side electrode 7 that contacts the p-type semiconductor layer 5 are formed.
[0027]
The method of manufacturing the GaN-based III-V nitride semiconductor diode described above is as follows.
First, the layer 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) is used as an N source, metal Ga (5 × 10 ⁻⁷ Torr) is used as a Ga source, and a GaN buffer layer having a growth temperature of 640 ° C. and a thickness of 50 nm is used. 2 was formed. Furthermore, ammonia (5 × 10 ⁻⁶ Torr) as an N source, metal Ga (5 × 10 ⁻⁷ Torr) as a Ga source, Al (1 × 10 ⁻⁷ Torr), and metal Si as an n-type dopant Using (5 × 10 ⁻⁹ Torr), an n-type semiconductor layer 3 (doping concentration of 5 × 10 ¹⁸ cm ⁻³ ) made of n-Al _x Ga _1-x N and having a thickness of 2 μm is formed at a growth temperature of 850 ° C. .
[0028]
Next, Al (1 × 10 ⁻⁷ Torr) and metal Mg (5 × 10 ⁻⁹ Torr) as a p-type dopant are added to the N source and the Ga source, and GSMBE is grown at a growth temperature of 850 ° C. forming a p-type semiconductor layer 5 made of a thickness _{2μm p-Al y Ga 1-} y N ( doping concentration 5 × ¹⁰ 18 ^{cm -3).} Thereby, a pn junction 4 is formed, and the layer structure of FIG. 1 is completed.
[0029]
In the layer structure of FIG. 1, a diode is completed through a process of forming an n-side electrode 6 and a p-side electrode 7. That is, as shown in FIG. _2, after forming a SiO ₂ film with _{p-Al y Ga 1-y} N layer plasma CVD method on the surface of the (p-type semiconductor layer 5), and patterned with photoresist Then, wet etching is performed using the SiO ₂ film as a mask, and a part of the layer structure is removed by etching halfway through the n-Al _x Ga _1-x N layer (n-type semiconductor layer 3). Part of the surface was exposed.
[0030]
Then after removing the SiO ₂ film was formed again SiO ₂ film on the entire surface, there is formed an electrode _opening, on the _{p-Al x Ga 1-x} N layer (p-type semiconductor layer 5) the p-side electrode 7 is formed by depositing a Ti / Pt, an n-side electrode 6 and further sequentially depositing Al / Ti / Au on the n-type semiconductor layer 3 of _{n-Al x Ga 1-x} n Thus, the diode shown in FIG. 2 is completed.
[0031]
When the diode of FIG. 2 was used as a variable capacitance diode, the following characteristics were obtained. At this time, x = 0.5 and y = 0.5.
That is, when the area of the pn junction 4 is 200 × 200 μm ² , a voltage in the reverse direction can be applied up to 400 V, and a change in capacitance in the range of 0.1 pF to 1000 pF can be obtained. This is a change width of 3 to 6 times as compared with that of Si, GaAs, and Ge having the same pn junction area.
[0032]
When the diode in FIG. 2 was used as a constant voltage diode, the following characteristics were obtained. At this time, x = 0.5 and y = 0.5.
That is, when the area of the pn junction 4 is 500 × 500 μm ² , a reverse voltage of 400 V or more can be applied, and a constant voltage characteristic of 400 V was obtained. This is an order of magnitude or more in consideration of the fact that the constant voltage characteristic of a Si-based constant voltage diode having the same pn junction area is about 10 V.
[0033]
Furthermore, while the upper limit of the ambient temperature at which the Si-based diode can normally operate is 150 ° C., the variable capacitance diode and the constant voltage diode described above operate normally even at a high temperature of 600 ° C. .
[0034]
The values of x and y of the variable capacitance diode and the constant voltage diode described above are 0.5, but are not limited thereto. _{Further, p-Al y Ga 1-} y N layer (p-type semiconductor layer _5), the doping concentration of the _{n-Al x Ga 1-x} N layer (n-type semiconductor layer 3) is met 5 × ¹⁰ 18 ^{cm -3} However, the present invention is not limited to this, and can be changed to 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ depending on the required element resistance.
[0035]
In particular, when the diode according to the present invention is used as a variable capacitance diode, since the cutoff frequency can be increased as the element resistance decreases, it is effective to decrease the element resistance by increasing the doping concentration. Further, in a Si-based variable capacitance diode, a change in capacitance is reduced by performing high-concentration doping in order to increase a cutoff frequency. However, in the variable-capacitance diode according to the present invention, the breakdown voltage V _b Does not affect the capacitance change.
[0036]
In the present embodiment, Ti / Pt is used for the p-side electrode 7 and Al / Ti / Au is used for the n-side electrode 6. However, if a metal silicide alloy is used instead of these, the electrode resistance can be significantly reduced. 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.
[0037]
In this embodiment, the p-side electrode 7 and the n-side electrode 6 are formed directly on the surfaces of the p-type semiconductor layer 5 and the n-type semiconductor layer 3, but as shown in FIG. 5, ap ⁺ -type contact layer 8 and an n ⁺ -type contact layer 9 may be formed between the n-side electrode 6 and the n-type semiconductor layer 3.
[0038]
In particular, by making the band gaps of the contact layers 8 and 9 smaller than the band gaps of the p-type semiconductor layer 5 and the n-type semiconductor layer 3, the contact resistance of the electrode / contact layer can be reduced. In particular, the effect can be further enhanced by combining with the metal silicide alloy electrode described above. In FIG. 3, InGaN is used for the contact layers 8 and 9. Here, it is appropriate that the thickness of the contact layer is 50 to 500 nm and the doping concentration is 1 × 10 ^{19 to} 5 × 10 ²⁰ cm ⁻³ .
[0039]
In this embodiment, the pn junction 4 is formed only by the n-type semiconductor layer 3 and the p-type semiconductor layer 5, but as shown in FIG. It is also possible to insert an undoped layer 10 made of a -V nitride semiconductor.
[0040]
When the n-type semiconductor layer 3 and the p-type semiconductor layer 5 are directly joined, the withstand voltage may slightly decrease because the impurities of the two layers diffuse into each other. Spread out. Therefore, it is possible to increase the reverse breakdown voltage V _b. In particular, when used as a variable capacitance diode, the depletion layer can be made substantially thicker by inserting the undoped layer 10, so that the change in capacitance can be increased.
[0041]
Further, in the present embodiment, the diode is formed on the substrate 1, but the substrate 1 may be removed as shown in FIG. Removal of the substrate 1 is performed by irradiating a laser from the back surface of the substrate after forming the surface electrode. Since the heat dissipation is improved by removing the substrate 1, the performance is improved when used as a constant voltage diode for flowing a large current.
[0042]
In the present embodiment, a sapphire substrate is used as the substrate 1, but it is also possible to use Si, SiC, GaAs, and GaP instead of the sapphire substrate. Since these substrates are cheaper than sapphire substrates, they are advantageous in cost.
[0043]
In the present embodiment, AlGaN is used as the semiconductor material of the p-type semiconductor layer 5 and the n-type semiconductor layer 3. However, the present invention is not limited to this, and all GaN group III-V nitride semiconductors may be used. Can be. This holds true for the contact layers 8 and 9 as long as the condition that the band gap is smaller than that of the p-type semiconductor layer 5 and the n-type semiconductor layer 3 is satisfied. Examples of the GaN group III-V nitride semiconductor include AlInGaN, AlGaNP, AlGaNAs, AlGaNP, AlGaNAs, and AlInGaNAsP.
[0044]
【The invention's effect】
As described above, according to the present invention, there is an effect that a diode using excellent reverse temperature characteristics and high reverse breakdown voltage can be manufactured. Furthermore, when the present invention is applied to a variable capacitance diode, the change in capacitance can be increased, and when applied to a constant voltage diode, a high voltage output can be obtained.
[Brief description of the drawings]
FIG. 1 shows a semiconductor laminated structure used for manufacturing an embodiment of the present invention.
FIG. 2 shows a semiconductor multilayer structure according to an embodiment of the present invention.
FIG. 3 shows a semiconductor laminated structure according to another embodiment of the present invention.
FIG. 4 shows a semiconductor multilayer structure according to still another embodiment of the present invention.
FIG. 5 is a schematic diagram of a layer structure of a diode.
FIG. 6 shows a voltage-current characteristic of a diode.
FIG. 7 is a circuit diagram of a variable capacitance diode.
FIG. 8 is a circuit diagram of a constant voltage diode.
Reference Signs List 1 substrate 2 buffer layer 3 n-type semiconductor layer 4 pn junction 5 p-type semiconductor layer 6 n-side electrode 7 p-side electrode 8 n ⁺ -type contact layer 9 p ⁺ -type contact layer 10 undoped layer

Claims (8)

a pn junction composed of a p-type GaN-based III-V nitride semiconductor layer and an n-type GaN-based III-V nitride semiconductor layer, and a p-side contacting the p-type GaN-based III-V nitride semiconductor layer An GaN-based III-V nitride semiconductor diode comprising an electrode and an n-side electrode in contact with the n-type GaN-based III-V nitride semiconductor layer, wherein characteristics in the reverse direction are used. GaN-based III-V nitride semiconductor diode. 2. The GaN group III-V nitride semiconductor diode according to claim 1, wherein the p-side electrode and the n-side electrode are made of a metal silicide alloy. The GaN according to claim 2, wherein the metal of the metal silicide is any one of Ta, Al, Ti, Cu, Pt, Pd, Ag, Ni, W, Mo, Cr, In, Sn and Mn. III-V group nitride semiconductor diode. The p-type GaN-based III-V nitride semiconductor layer and the GaN-based III-V nitride semiconductor layer having a smaller band gap than the n-type GaN-based III-V nitride semiconductor layer are formed of the p-type GaN-based III-V nitride semiconductor layer. The semiconductor device is inserted between a III-V nitride semiconductor layer and the p-side electrode and between the n-type GaN-based III-V nitride semiconductor layer and the n-side electrode. 4. A GaN-based III-V nitride semiconductor diode according to 1, 2, or 3. An undoped GaN-based III-V nitride semiconductor layer is inserted between the p-type GaN-based III-V nitride semiconductor layer and the n-type GaN-based III-V nitride semiconductor layer. The GaN-based III-V nitride semiconductor diode according to claim 1, 2, 3, or 4. The GaN-based III-V according to claim 1, 2, 3, 4, or 5, wherein the GaN-based III-V nitride semiconductor layer is AlGaN, AlInGaN, AlGaNP, AlGaNAs, AlGaNP, AlGaNAs, or AlInGaNAsP. Group nitride semiconductor diode. 7. The GaN-based III- diode according to claim 1, wherein the reverse characteristic of the GaN-based III-V nitride semiconductor diode is used as a change in capacitance. Group V nitride semiconductor diode. The GaN according to claim 1, 2, 3, 4, 5, or 6, wherein an output of a breakdown voltage in a reverse direction is used as the characteristic in the reverse direction of the GaN-based III-V nitride semiconductor diode. III-V group nitride semiconductor diode.

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