JP4028355B2 - GaN-based III-V nitride semiconductor diode - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a GaN-based III-V nitride semiconductor diode that utilizes the reverse characteristics of a diode. More specifically, the present invention relates to a GaN-based III-V group nitride semiconductor diode having high reverse breakdown voltage and excellent high temperature characteristics. More specifically, the present invention has a GaN-based group III-V nitride semiconductor variable capacitance diode having a large change in capacitance in addition to these features, and a GaN-based group III-V nitride semiconductor constant voltage having a high output voltage. It relates to a diode.
[0002]
[Prior art]
For example, as shown in FIG. 5, the diode has a pn junction 4 including an n-type semiconductor layer 3 and a p-type semiconductor layer 5, an n-side electrode 6 on the n-type semiconductor layer 3, and a p-type on the p-type semiconductor layer 5. A 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 recombine in the vicinity of the pn junction 4. When a voltage is applied in the reverse direction, the depletion layer spreads from the pn junction 4, so that almost no current flows. Since the depletion layer becomes wider as the reverse voltage is increased, no current flows even when the reverse voltage is applied. However, when the reverse voltage reaches the breakdown voltage V _b , the Zener phenomenon, electron avalanche The phenomenon causes the current to flow rapidly (reverse current).
[0003]
As devices utilizing the reverse characteristics of diodes, variable capacitance diodes and constant voltage diodes are generally known. A variable capacitance diode is a diode that utilizes a change in thickness of a depletion layer as a change in capacitance. The constant voltage diode is a diode utilizing the property that V _b 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. The constant voltage diode is represented by the circuit diagram of FIG. 8 and is widely used in circuits that require a reference voltage, such as a constant voltage circuit.
[0005]
Conventionally, materials based on Si, GaAs, and Ge have been used as materials for variable capacitance diodes and constant voltage diodes. When a Si substrate is used, a p-type semiconductor layer and an n-type semiconductor layer are formed using a diffusion method to form a pn junction, and a diode is formed.
[0006]
[Non-Patent Document 1]
Tetsuro Ishida, “Semiconductor Device”, Corona, 1973, p146
[0007]
[Problems to be solved by the invention]
However, since semiconductors based on Si, GaAs, and Ge have a relatively small band gap of 0.5 to 1.5 eV, the following problems arise 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 is smaller as the band gap is smaller. Therefore, when a variable capacitance diode is manufactured using Si or the like, since _Vb is small, a change in the thickness of the depletion layer cannot be increased, and there is a problem that a capacitor having a large capacitance change cannot be manufactured.
[0009]
Further, even when a constant voltage diode is manufactured, _Vb cannot be increased, so that a problem that a high voltage constant voltage characteristic cannot be manufactured occurs. 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 arises. Even if this method is used, _Vb is limited to about 100V.
[0010]
Further, 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 normal voltage-current characteristics as shown in FIG. 6 cannot be obtained. was there.
[0011]
The present invention has been made in view of the above-mentioned drawbacks of the prior art, and aims to provide a diode utilizing reverse characteristics, which has excellent high temperature characteristics and high reverse breakdown voltage. To 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]
To achieve the above object, according to a first aspect of the present invention, a pn junction comprising a p-type GaN-based III-V group nitride semiconductor layer and an n-type GaN-based III-V group nitride semiconductor layer as described in claim 1. And a p-side electrode in contact with the p-type GaN-based III-V group nitride semiconductor layer and a n-side electrode in contact with the n-type GaN-based group III-V nitride semiconductor layer. A nitride semiconductor diode is characterized by utilizing the characteristics in the opposite direction.
[0013]
In the first aspect of the present invention, since the diode is formed using a GaN-based III-V group nitride semiconductor having a relatively large band gap, V _b can be increased and the breakdown voltage in the reverse direction is improved. For this reason, a high breakdown voltage characteristic can be used when the reverse characteristic is used. In addition, characteristics at high temperatures are improved.
[0014]
Here, using 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]
According to a second aspect of the present invention, 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, the p-type GaN-based III-V group nitride semiconductor layer and the p-side electrode, and the n-type GaN-based group III-V nitride semiconductor layer as defined in claim 4 A GaN-based III-V group nitridation having a smaller band gap than the p-type GaN-based III-V group nitride semiconductor layer and the n-type GaN-based III-V group nitride semiconductor layer between the n-side electrodes. A physical 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 semiconductor layer constituting the pn junction and the previous electrode. 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, there is provided an undoped GaN-based III- layer between the p-type GaN-based III-V group nitride semiconductor layer and the n-type GaN-based group III-V nitride semiconductor layer. A GaN-based group III-V nitride semiconductor diode, wherein a group V nitride semiconductor layer is inserted.
[0020]
In the fourth aspect of the present invention, since the undoped GaN-based group III-V nitride semiconductor layer is sandwiched between the p-type semiconductor layer and the n-type semiconductor layer, the reverse breakdown voltage is further improved.
[0021]
According to a fifth aspect of the present invention, as described in claim 7, the characteristics in the reverse direction of the GaN-based III-V group nitride semiconductor diode are utilized as a change in capacitance.
[0022]
In other words, the fifth aspect of the present invention is to use as a variable capacitance diode. In the fifth aspect of the present invention, since the GaN-based III-V group nitride semiconductor diode having a large reverse breakdown voltage is used as the variable capacitance diode, the change in capacitance can be increased.
[0023]
According to a sixth aspect of the present invention, as described in claim 8, as the reverse direction characteristic of the GaN-based III-V group nitride semiconductor diode, an output of a reverse breakdown voltage is used.
[0024]
In other words, the sixth aspect of the present invention is to use as a constant voltage diode.
In the sixth aspect of the present invention, since the GaN-based III-V group nitride semiconductor diode having a high reverse breakdown voltage is used as the constant voltage diode, the output voltage can be increased.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of a GaN-based III-V nitride semiconductor diode 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.
[0026]
First, a GaN-based III-V group 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 _y Ga _1-y N (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 manufacturing method of 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, dimethyl hydrazine (5 × 10 ⁻⁵ Torr) is used as the N source, metal Ga (5 × 10 ⁻⁷ Torr) is used as the Ga source, and the growth temperature is 640 ° C. and the GaN buffer layer has a thickness of 50 nm. 2 was deposited. Furthermore, ammonia (5 × 10 ⁻⁶ Torr) as the N source, metal Ga (5 × 10 ⁻⁷ Torr) as the Ga source, and Al (1 × 10 ⁻⁷ Torr) and the metal Si which is an n-type dopant. (5 × 10 ⁻⁹ Torr) is used to form an n-type semiconductor layer 3 (doping concentration 5 × 10 ¹⁸ cm ⁻³ ) made of n-Al _x Ga _1-x N with a growth temperature of 850 ° C. and a thickness of 2 μm. .
[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 Ga source described above, 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 this SiO ₂ film as a mask, and a part of the layer structure is etched and removed partway through the n-Al _x Ga _{1 -x} N layer (n-type semiconductor layer 3). A 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 , the reverse voltage can be applied up to 400 V, and a capacitance change in the range of 0.1 pF to 1000 pF can be obtained. This is 3 to 6 times as wide as that of Si, GaAs, and Ge having the same pn junction area.
[0032]
Further, when the diode of 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 is obtained. Considering that the constant voltage characteristics of Si-based constant voltage diodes having the same pn junction area are about 10 V, this is a value of an order of magnitude or more.
[0033]
Furthermore, while the upper limit of the ambient temperature at which a Si-based diode can operate normally is 150 ° C., it has been found that the above-mentioned variable capacitance diode and constant voltage diode 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 from 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, the cut-off frequency can be increased as the element resistance decreases. Therefore, it is effective to decrease the element resistance by increasing the doping concentration. Further, in the Si-based variable capacitance diode, the capacitance change is reduced when the high concentration doping is performed in order to increase the cutoff frequency. However, in the variable capacitance diode according to the present invention, the breakdown voltage V _b is increased even in the high concentration doping. Does not decrease, it does not affect the capacity 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 greatly 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 the present embodiment, the p-side electrode 7 and the n-side electrode 6 are directly formed on the surfaces of the p-type semiconductor layer 5 and the n-type semiconductor layer 3, but the p-side electrode 7 and the p-type semiconductor layer are formed as shown in FIG. 5, a p ⁺ -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, the contact resistance of the electrode / contact layer can be reduced by making the band gap of the contact layers 8 and 9 smaller than the band gap of the p-type semiconductor layer 5 and the n-type semiconductor layer 3. In particular, the effect can be further enhanced by combining with the electrode of the metal silicide alloy described above. In FIG. 3, InGaN is used for the contact layers 8 and 9. 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 .
[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. However, as shown in FIG. 3, the GaN-based III is interposed between the n-type semiconductor layer 3 and the p-type semiconductor layer 5. It is also possible to insert an undoped layer 10 made of a −V group nitride semiconductor.
[0040]
When the n-type semiconductor layer 3 and the p-type semiconductor layer 5 are directly joined, the impurities in the two layers diffuse to each other, so that the breakdown voltage may be slightly reduced, but by inserting the undoped layer 10, There is no diffusion. Therefore, it is possible to increase the reverse breakdown voltage _Vb . In particular, when used as a variable capacitance diode, insertion of the undoped layer 10 can substantially increase the thickness of the depletion layer, so that the change in capacitance can be increased.
[0041]
In the present embodiment, the diode is formed on the substrate 1, but the substrate 1 may be removed as shown in FIG. The substrate 1 is removed 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 the substrate 1 is used as a constant voltage diode for flowing a large current.
[0042]
In this embodiment, a sapphire substrate is used as the substrate 1, but it is also possible to use Si, SiC, GaAs, or GaP instead of the sapphire substrate. Since these substrates are cheaper than sapphire substrates, they are advantageous in terms of 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, but the present invention is not limited to this, and all GaN-based III-V group nitride semiconductors are used. Can do. The same applies to 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-based III-V group 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 it is possible to manufacture a diode that uses reverse characteristics with excellent high-temperature characteristics and high reverse breakdown voltage. Further, when the present invention is applied to a variable capacitance diode, the capacitance change 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 stacked 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 multilayer 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.
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 group nitride semiconductor layer and an n-type GaN-based group III-V nitride semiconductor layer, and a p-side in contact with the p-type GaN-based group III-V nitride semiconductor layer A GaN-based group III-V nitride semiconductor diode comprising an electrode and an n-side electrode in contact with the n-type GaN-based group III-V nitride semiconductor layer, wherein the characteristics in the opposite direction are utilized. GaN group III-V nitride semiconductor diode. 2. The GaN-based 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. 3. The GaN according to claim 2, wherein the metal of the metal silicide consists of Ta, Al, Ti, Cu, Pt, Pd, Ag, Ni, W, Mo, Cr, In, Sn, or Mn. III-V nitride semiconductor diodes. The p-type GaN-based III-V group nitride semiconductor layer and the n-type GaN-based group III-V nitride semiconductor layer have a smaller band gap than the p-type GaN-based group GaN-based group III-V nitride semiconductor layer. The semiconductor device is characterized in that it is inserted between a group III-V nitride semiconductor layer and the p-side electrode and between the n-type GaN-based group III-V nitride semiconductor layer and the n-side electrode. A GaN-based group III-V nitride semiconductor diode according to 1, 2 or 3. An undoped GaN-based III-V group nitride semiconductor layer is inserted between the p-type GaN-based group III-V nitride semiconductor layer and the n-type GaN-based group III-V nitride semiconductor layer. The GaN-based III-V group nitride semiconductor diode according to claim 1, 2, 3 or 4. 6. The GaN-based III-V according to claim 1, wherein the GaN-based III-V nitride semiconductor layer is AlGaN, AlInGaN, AlGaNP, AlGaNAs, AlGaNP, AlGaNAs, or AlInGaNAsP. Group nitride semiconductor diode. The GaN-based III-III according to claim 1, 2, 3, 4, 5 or 6, wherein the reverse characteristics of the GaN-based III-V nitride semiconductor diode are utilized as a change in capacitance. Group V nitride semiconductor diode. 7. The GaN according to claim 1, wherein 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. III-V nitride semiconductor diodes.

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