JP5834495B2 - Nitride semiconductor device - Google Patents

Description

  The present invention relates to a nitride semiconductor device.

Nitride semiconductors have been put to practical use in various light sources such as full-color LED displays, traffic signal lights, and image scanner light sources as materials for high-brightness blue LEDs and pure green LEDs, for example. Various structures of LEDs are known. For example, there is a structure in which an n-side nitride semiconductor layer and a p-side nitride semiconductor layer are formed of multilayer films having different compositions (for example, Patent Document 1).
In the nitride semiconductor device described herein, an n-type multilayer film layer and a p-type multilayer film layer having different compositions or the like are formed in contact with or in proximity to the active layer, whereby Vf (forward voltage of the element) is formed. ) And the electrostatic withstand voltage can be improved.

  However, since the n-type multilayer layer in contact with or close to the active layer is doped with n-type impurities, there still remains a problem that leakage current is more likely to occur when a reverse bias is applied than in the case of undoped. To do.

JP 2000-232237 A

  The present invention has been made in view of the above problems, and can reliably prevent a leakage current when a reverse bias is applied while reducing Vf, and has high luminance and high luminous flux and a highly reliable nitride. An object is to provide a semiconductor device.

The nitride semiconductor device of the present invention is
A nitride semiconductor device in which an n-side nitride semiconductor layer, an active layer, and a p-side nitride semiconductor layer are stacked in this order,
The n-side nitride semiconductor is formed by laminating an n-type contact layer, an undoped semiconductor layer, and an n-type multilayer film layer in this order,
The n-type multilayer film layer is composed of 20 or more layers and has a total film thickness of 50 nm to 500 nm.
The nitride semiconductor element preferably includes one or more of the following.
The active layer has a total film thickness of 90 nm to 200 nm.
A first nitride semiconductor layer having a substrate on the n-side nitride semiconductor layer side and having a dislocation density of 1 × 10 ^{7 to} 5 × 10 ⁹ cm ⁻² between the substrate and the n-type contact layer; And the first nitride semiconductor layer has a thickness of 1 μm to 10 μm.
The first nitride semiconductor layer has a dislocation density lower on the n-type contact layer side than on the substrate side.
The first nitride semiconductor layer has at least two layers formed at different film formation temperatures.
The first nitride semiconductor layer has at least two layers formed under different conditions in which the ratio of the NH ₃ flow rate to the total gas flow rate is different.
The undoped semiconductor layer is an undoped GaN layer.
The undoped semiconductor layer is formed by alternately laminating undoped layers and Si doped layers.

  ADVANTAGE OF THE INVENTION According to this invention, the leakage current at the time of reverse bias application can be prevented reliably, aiming at low Vf, and the reliable nitride semiconductor device which has a high brightness | luminance and a high luminous flux can be provided. .

It is a schematic sectional drawing for demonstrating the structure of the semiconductor light-emitting device concerning one embodiment of this invention. It is a graph which shows the result regarding the forward voltage (Vf) and output of the semiconductor light-emitting device of Example 1 of this invention. It is a graph which shows the result regarding Vf of the semiconductor light-emitting device of Example 1 of this invention. It is a graph which shows the result regarding Ir of the semiconductor light-emitting device of Example 1 of this invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a nitride semiconductor element for embodying the technical idea of the present invention, and the present invention does not specify the nitride semiconductor element as follows. Furthermore, in the following description, the same name and symbol indicate the same or the same members, and detailed description thereof will be omitted as appropriate.

The nitride semiconductor device of the present invention is a so-called LED. As shown in FIG. 1, the n-side nitride semiconductor layer 14, the active layer 8, and the p-side nitride semiconductor are mainly formed on the substrate 1. The layer 15 is formed by stacking in this order. The substrate 1 may not exist in the final form.
Further, the p-side nitride semiconductor layer 15 has a full-surface electrode 11 connected to substantially the entire upper surface and a p-electrode 12 connected to a part of the full-surface electrode. The n-type contact layer 5 is exposed by removing a part of the n-side nitride semiconductor layer, the active layer 8 and the p-side nitride semiconductor layer 15 laminated thereon, and on the exposed surface. An n-electrode 13 is connected.
Although not shown, a protective film is formed on a part of the side surface and upper surface of the substrate 1 and the semiconductor layer, and optionally on a part of the side surface and upper surface of the electrode.
Here, “part” includes both part in the plane (part of the region) and part in the film thickness direction.

The n-side and p-side nitride semiconductor layers 14 and 15 and the active layer 8 are, for example, represented by the formula (A)
_{In x Al y Ga 1-x} -y N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y ≦ 1) (A)
It can form with the compound semiconductor shown by these. In addition to this, an element in which B is partially substituted as a group III element may be used, or an element in which a part of N is substituted with P or As may be used as a group V element.
The n-side nitride semiconductor layer contains at least one group IV element or group VI element such as Si, Ge, Sn, S, O, Ti, Zr, and Cd as an n-type impurity with respect to the active layer. It is a general term for the laminated layer on the side where the layer is disposed. Of these, Si and Sn are preferable as the n-type impurity.
The p-side nitride semiconductor layer is a general term for a stacked layer on the side where Mg, Zn, Be, Mn, Ca, Sr and the like are disposed as p-type impurities with respect to the active layer.
These n-type and p-type impurities are preferably contained in a concentration range of, for example, about 5 × 10 ¹⁶ / cm ³ to 1 × 10 ²¹ / cm ³ . However, all of the n-side and p-side nitride semiconductor layers do not necessarily contain n-type or p-type impurities.

[N-side nitride semiconductor layer 14]
In the n-side nitride semiconductor layer 14, the n-type contact layer 5, the undoped semiconductor layer 6, and the n-type multilayer film layer 7 are laminated in this order from the substrate 1 side.

(N-type contact layer 5)
The composition of the n-type contact layer 5 is not particularly limited. For example, a layer made of AlGaN or GaN having an Al ratio of 0.2 or less is preferable, and a layer made of a single layer is more preferable. With such a composition, it is easy to obtain a nitride semiconductor layer with few crystal defects.
The film thickness of the n-type contact layer 5 is not particularly limited, and can be, for example, about 1 μm or more, preferably about 3 μm or more.
N-type contact layer 5 contains an n-type impurity, and its concentration is preferably high enough not to deteriorate the crystallinity of the nitride semiconductor. For example, it is 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less.

(Undoped semiconductor layer 6)
As the undoped semiconductor layer 6, for example, a layer composed of the above-described formula (A) can be given. Among these, the undoped semiconductor layer 6 is preferably Al _y Ga _1-xy N or In _x Ga _1-xy N having GaN, x and / or y of 0.2 or less, and further, a layer made of GaN. It is preferable to contain. With such a composition, a nitride semiconductor layer with few crystal defects can be easily obtained. The undoped semiconductor layer 6 may be formed of a single layer, but is preferably formed of a multilayer film.
When the undoped semiconductor layer 6 is formed of a multilayer film, the composition of all the layers may not be the same, and the composition may change partially, in a gradient, stepwise, or alternately.
Further, when the undoped semiconductor layer 6 is formed of a multilayer film, it is not necessary for all the layers to be undoped layers that do not contain n-type impurities, and at least one layer may be an undoped layer.
When two or more layers containing impurities are included, the impurity concentration is not necessarily the same, and at least one layer may be different from each other. For example, the impurity concentration is 3 × 10 ¹⁸ / cm ³ or more, and preferably 5 × 10 ¹⁸ / cm ³ or more. The upper limit of the n-type impurity concentration is not particularly limited, but is preferably such that the crystallinity does not deteriorate too much, for example, 5 × 10 ²¹ / cm ³ or less. By setting such an impurity concentration, it is possible to improve both the light emission output and the decrease in Vf.
In particular, when the undoped semiconductor layer 6 is formed of a multilayer film, it is preferable that undoped layers and doped layers having the same composition are alternately stacked. These alternate laminated layers are, for example, preferably 3 layers or more, and preferably 5 layers or less, and any of the undoped layer and the doped layer is the lowermost layer and / or the uppermost layer. Also good.

In this specification, “undoped” refers to a layer formed without introducing the above-described p-type or n-type impurities at the time of film formation, and after the film formation and / or by heat treatment or the like in the manufacturing process. It does not mean a layer diffused from the upper and lower layers and mixed with impurities. In other words, a layer having an impurity concentration of about 1 × 10 ¹⁷ / cm ³ or less is substantially referred to as an “undoped” layer.

  By disposing the undoped semiconductor layer 6 on the n-type contact layer 5 doped with a relatively high concentration of impurities, the underlying crystallinity is improved, so that the n-type multilayer layer 7 to be grown next grows. In addition, the active layer 8 having good crystallinity can be grown on the n-type multilayer film layer 7. Thereby, Vf can be reduced as a nitride semiconductor device.

For example, the undoped semiconductor layer 6 preferably has a thickness of about 5 nm or more. Thereby, the electrostatic withstand voltage can be improved. Preferably, it is about 100 nm or more, more preferably about 300 nm or more. In consideration of the balance between the production efficiency and the electrostatic withstand voltage, the thickness is preferably about 500 nm or less.
When the undoped semiconductor layer 6 is formed of a multilayer film, for example, the thicknesses of the undoped layer and the n-type impurity doped layer may be the same, or at least one layer may be different. Although the film thickness of each layer which comprises a multilayer film is not specifically limited, For example, 5-500 nm is suitable, Preferably it is 5-300 nm, More preferably, it is 5-200 nm. By setting the film thickness of the multilayer film within this range, it is possible to satisfactorily balance both optimization of Vf and improvement of electrostatic withstand voltage.

  Depending on the composition, the film thickness, and / or the impurity concentration, the multilayer film may have different effects on the characteristics of the device depending on the position where it is stacked. Therefore, in consideration of these factors and element characteristics that each layer will be greatly involved in, the composition and / or film thickness and / or impurity concentration of the undoped layer or doped layer are changed stepwise, etc. It is preferable to adjust to good characteristics. By performing such adjustment, it is possible to remarkably improve the light emission output and electrostatic withstand voltage in particular while maintaining various element characteristics as a whole (see, for example, Japanese Patent Laid-Open No. 2000-232237). .

(N-type multilayer film layer 7)
Examples of the n-type multilayer film layer 7 include nitride semiconductors composed of at least two kinds of elements having different compositions, for example, a layer composed of the above-described formula (A). In particular, the n-type multilayer film layer 7 is preferably formed of a superlattice multilayer film, and Al _z Ga _1-z N (0 ≦ z <1) (first layer) and In _p Ga _1-p N. A superlattice layer in which layers having two kinds of compositions of (0 <p <1) (second layer) are alternately stacked is more preferable. Any of the first layer and the second layer may be the lowermost layer and / or the uppermost layer. However, the composition of all the layers of the first layer, the second layer, the first layer and the second layer may not necessarily be the same, and the composition may be partially, in a gradient, stepwise or alternately. It may change. Especially, it is preferable that 1st layers and 2nd layers are layers of the same composition.

The first layer is preferably a layer made of GaN with z = 0 because the smaller z, that is, the smaller the aluminum content, the better the crystallinity.
The second layer is preferably a layer having p of 0.5 or less, and more preferably a layer having p of 0.2 or less.
Among these, as the n-type multilayer film layer 7, a superlattice multilayer film in which the first layer is GaN and p is 0.2 or less In _p Ga _1-p N in the second layer is preferable.

The n-type multilayer film layer 7 is suitably a laminated film having a total of 20 or more layers in which 10 or more layers having different compositions (preferably the first layer and the second layer described above) are respectively laminated. A laminated film of at least layers (total of 40 layers or more) is preferable. Although the upper limit of the number of laminated layers of the first layer and the second layer is not particularly limited, for example, 500 layers or less is suitable, and 200 layers or less and 100 layers or less are preferable. By disposing such an n-type multilayer film layer, it is possible to effectively reduce Vf.
The film thickness of the single layer (that is, the first layer or the second layer) constituting the n-type multilayer film layer 7 is not particularly limited, but it is suitable that the film thickness of at least one single layer is 10 nm or less. 7 nm or less is preferable, and 5 nm or less is more preferable. By reducing the film thickness of the single layer in this way, the multilayer film layer has a superlattice structure and is equal to or less than the critical elastic film thickness, and the crystallinity of each single layer in the multilayer film layer is improved. Therefore, as the stacking progresses, crystallinity can be further improved, and further improvement in light output can be realized.
Further, all the single layers constituting the n-type multilayer film layer 7, preferably the first layer and the second layer described above are both preferably 10 nm or less, more preferably 7 nm or less, and further preferably 5 nm or less. preferable. The crystallinity mentioned above can be improved more by making the film thickness of the layer which comprises the n-type multilayer film layer 6 into this range.

  The n-type multilayer film layer 7 is not particularly limited, but the total film thickness is suitably about 50 nm or more, preferably about 65 nm or more, more preferably about 75 nm or more, more preferably about 80 nm or more, and further about 90 nm. The above is even more preferable. Although the upper limit of the total film thickness is not particularly limited, in consideration of improvement in manufacturing efficiency and characteristics, about 500 nm or less can be mentioned, and about 400 nm or less is preferable. By setting the total film thickness within this range, the crystallinity is improved and the output of the element can be improved.

The n-type multilayer film layer 7 does not have to contain n-type impurities in all layers, and it is sufficient that at least one layer contains n-type impurities. For example, only one of the first layer and the second layer described above may not contain n-type impurities, or all layers may contain n-type impurities. In this case, the types and concentrations of impurities may not be the same in all layers, and may be different from each other or at least one layer. For example, both the first layer and the second layer described above are doped with n-type impurities, and by adopting a modulation dope having different concentrations between adjacent nitride semiconductor layers, the light output tends to be further improved. There is.
Examples of the impurity concentration include 5 × 10 ¹⁶ / cm ³ or more and 3 × 10 ¹⁸ / cm ³ or more, and 5 × 10 ¹⁸ / cm ³ or more is preferable. The upper limit of the n-type impurity concentration is not particularly limited, but is preferably such that the crystallinity is not deteriorated too much, for example, 5 × 10 ²¹ / cm ³ or less or 1 × 10 ²⁰ / cm ³ or less. By setting such an impurity concentration, Vf can be further reduced.

  The film formation method of the n-type multilayer film layer 7 is not particularly limited, and known film formation methods such as MOVPE, metal organic chemical vapor deposition (MOCVD), hydride vapor deposition (HVPE), molecular beam epitaxial growth Any of (MBE) etc. may be used. The film formation temperature is not particularly limited, but is preferably 850 ° C. or higher, more preferably 900 ° C. or higher. Thereby, crystallinity can be made more favorable.

[Active layer 8]
The active layer 8 has a single quantum well structure or multiple layers including a nitride semiconductor containing at least In, preferably a well layer containing In _j Ga _1-j N (0 ≦ j <1), and a barrier layer. The thing of a quantum well structure is mentioned. In particular, i is preferably about 0.1 to 0.2 for the well layer, and j is preferably 0 for the barrier layer. In the active layer 8, the well layer and the barrier layer may be either the lowermost layer and / or the uppermost layer.
For example, the active layer 8 is suitably about 90 nm or more in total thickness, and preferably about 100 to 200 nm. Within this thickness range, the leakage current when applying reverse bias is effectively controlled by adjusting the number of barrier layers and well layers, the order of stacking, etc., taking into account the desired wavelength of the nitride semiconductor device. Can be reduced.

[P-side nitride semiconductor layer 15]
The p-side nitride semiconductor layer 15 preferably includes, for example, the p-side cladding layer 9 and the p-type contact layer 10 in order from the active layer side.
(P-side cladding layer 9)
Examples of the p-side cladding layer 9 include a single layer composed of the above-mentioned formula (A) containing p-type impurities, or at least two laminated layers having different band gap energies or a superlattice multilayer film. Among these, a single layer made of Al _b Ga _1-b N (0 ≦ b ≦ 1) or a stacked layer of at least two semiconductor layers having different band gap energies is preferable.
The p-side cladding layer 9 has a p-type impurity concentration of, for example, preferably about 1 × 10 ²² / cm ³ or less, and more preferably about 5 × 10 ²⁰ / cm ³ or less. The lower limit of the p-type impurity concentration is not particularly limited, but about 5 × 10 ¹⁶ / cm ³ or more is suitable.
In the laminated layer or the superlattice multilayer film, the p-type impurity may not be contained in all the layers. Further, the p-type impurity concentration in each layer or a part of the layers may be different or the same.
The film thickness of the p-side cladding layer 9 is not particularly limited, and may be about 10 nm or more. In the laminated layer or the superlattice multilayer film, the thickness of the single nitride semiconductor layer is preferably about 10 nm or less, more preferably about 7 nm or less and about 5 nm or less. By forming the thin film, the multilayer film layer has a superlattice structure, and the crystallinity of the multilayer film layer can be improved. As a result, when a p-type impurity is added, a layer having a high carrier concentration and a low resistivity is obtained, and the Vf, threshold value, etc. of the device tend to decrease. Thereby, a favorable light emission output can be obtained with low power consumption.

(P-type contact layer 10)
Examples of the p-type contact layer 10 include a layer made of a nitride semiconductor represented by the above-described formula (A). Among them, GaN, AlGaN having an Al ratio of 0.2 or less, and In ratio of 0.2 or less. A layer made of InGaN is preferred, and a layer made of GaN is more preferred. These compositions can provide good ohmic contact with the electrode material.
The film thickness of the p-type contact layer 10 is not particularly limited, and is preferably about 50 nm or more, and more preferably about 60 nm or more.
Examples of the impurity concentration include 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less.

[Substrate 1]
The nitride semiconductor layer described above is usually formed on the substrate 1.
As the substrate 1, sapphire whose principal surface is the C-plane, R-plane or A-plane, other insulating substrates such as spinel (MgA ₁₂ O ₄ ), SiC (including 6H, 4H, 3C), A semiconductor substrate such as Si, ZnO, GaAs, or GaN can be used.

A buffer layer 2 is preferably formed on the substrate 1.
Examples of the buffer layer 2 include a nitride semiconductor made of Ga _d Al _1-d N (0 <d ≦ 1). The Al mixed crystal ratio is preferably 0.3 or less, and the Al mixed crystal ratio is 0.1. Two or less layers are more preferred. The smaller the Al content, the more remarkable the improvement in crystallinity. More preferred is a buffer layer 2 made of GaN. Further, the buffer layer 2 can be finally removed, or can be omitted by itself.
The buffer layer 2 preferably has a thickness of about 0.002 to 0.5 μm, preferably about 0.05 to 0.2 μm, and more preferably about 0.01 to 0.02 μm. By setting it within this range, the crystal morphology of the nitride semiconductor is improved, and the crystallinity of the nitride semiconductor grown on the buffer layer 2 is improved. The temperature for growing the buffer layer 2 is suitably 200 to 900 ° C., and preferably adjusted to a range of 400 to 800 ° C. Thereby, a good polycrystal can be formed, and the crystallinity of the nitride semiconductor grown on the buffer layer 2 can be made good by using this polycrystal as a seed crystal.

[First Nitride Semiconductor Layer 16]
When the buffer layer 2 described above is formed between the substrate 1 and the n-type contact layer 5, the dislocation density is 1 × 10 ^{7 to} 5 × between the buffer layer 2 and the n-type contact layer 5. It is suitable to include the first nitride semiconductor layer 16 having a ^density of 10 ⁹ cm ⁻² . The first nitride semiconductor layer 16 is preferably a GaN layer, but may be an Al _1-x Ga _x N layer (0 <x <1).
The first nitride semiconductor layer 16 may not be a single layer, and may be a laminated structure of two or more layers, for example. Examples of the laminated structure include a laminated structure in which a low dislocation layer 3 having a reduced dislocation density and a layer called a pit buried layer 4 for reducing pits are laminated from the substrate side. Further, an arbitrary intermediate layer may be disposed above or below the laminated structure. Regardless of the layer structure of the first nitride semiconductor layer 16, the crystallinity becomes better as the film formation proceeds, and the dislocation on the side (or layer) formed at the end of film formation from the initial stage of film formation is improved. The density is low. Therefore, generally, the pit buried layer 4 has a lower dislocation density than the low dislocation layer 3, the dislocation density is lower on the pit buried layer 4 side in the low dislocation layer 3, and lower in the pit buried layer 4. The dislocation density is higher on the dislocation layer 3 side.

When the first nitride semiconductor layer 16 is formed as a laminated structure, both have the same composition. However, the first nitride semiconductor layer 16 can be distinguished by, for example, a difference in film formation method. For example, in the known film formation method as described above, a layer in which the low dislocation layer 3 and the pit buried layer 4 are further formed at different film formation temperatures can be cited. It is suitable that the film formation temperature is higher at the end of film formation than at the initial stage of film formation. Therefore, it is preferable to set the deposition temperature of the pit buried layer 4 higher than the deposition temperature of the low dislocation layer 3.
The ratio of NH ₃ flow rate be mentioned layers formed under different conditions to the total gas flow rate during deposition. It is suitable that the ratio of the NH ₃ flow rate to the total gas flow rate is higher at the end of film formation than at the initial stage of film formation. Therefore, it is preferable that the NH ₃ flow rate of the pit buried layer 4 is higher than the NH ₃ flow rate of the low dislocation layer 3.
The first nitride semiconductor layer 16 does not substantially contain impurities.

  The thickness of the first nitride semiconductor layer 16 is, for example, preferably about 1 μm or more, more preferably about 2 μm or more, about 3 μm or more, preferably about 10 μm or less, preferably about 5 μm or less. It is more preferable.

For example, the low dislocation layer 3 has a thickness of about 500 to 5000 nm, and preferably about 1000 to 3000 nm. In particular, the dislocation density at the end (active layer side) of the low dislocation layer is preferably 1 × 10 ^{7 to} 5 × 10 ⁸ cm ⁻² , and preferably 5 × 10 to 3 × 10 ⁸ cm ^−2. Is more preferable.
As a method for forming this low dislocation layer, any method known in the art may be used. For example, a method of controlling the ratio of NH ₃ gas to the total supply gas flow rate during growth to about 30% or less and / or controlling the growth rate to about 200 nm / min or less can be mentioned. Furthermore, it is preferable to set the temperature during film formation to a temperature range of about 800 to 1400 ° C.

The pit embedding layer 4 has, for example, a film thickness of about 500 to 5000 nm, and preferably about 1000 to 3000 nm. In particular, the pit buried layer is a layer having a dislocation density lower than that of the low dislocation layer and the generation of pits being reduced as much as possible.
As a method for forming the pit buried layer, any method known in the art may be used. Furthermore, the temperature during film formation is preferably higher than the film formation temperature of the low dislocation layer, for example, in a temperature range of about 850 to 1450 ° C.

[Electrodes 11, 12, 13]
The entire surface electrode, p electrode and n electrode used in the nitride semiconductor device of the present invention are not particularly limited, such as the composition of the single layer, the composition and order of the laminated structure, and the film thickness. Can also be adopted.
In particular, the entire surface electrode is preferably formed of a material that does not absorb light emitted from the active layer in consideration of light extraction efficiency, and examples thereof include a conductive oxide (ITO or the like).
〔Protective film〕
The material and film thickness of the protective film are not particularly limited, but for example, a single layer film or a multilayer film made of SiO ₂ , ZrO ₂ , TiO ₂ , Al ₂ O ₃ , Nb ₂ O ₅ , AlN, AlGaN, or the like Is mentioned. The film thickness is preferably adjusted as appropriate.

Examples of the nitride semiconductor device of the present invention will be described below, but the present invention is not limited to the following examples.
Example 1
The nitride semiconductor device of this example is formed on a substrate 1 made of sapphire.
Buffer layer 2 made of undoped AlGaN (film thickness: about 15 nm),
Low dislocation layer 3 (film thickness: about 1.5 μm) made of undoped GaN,
Pit buried layer 4 made of undoped GaN (film thickness: about 2.0 μm),
From the bottom, an n-type contact layer (film thickness: 4.2 μm) made of GaN doped with 9 × 10 ¹⁸ / cm ^{3 of} Si, an undoped GaN layer (film thickness: 145 nm), and Si of 2 × 10 ¹⁸ / cm ³ Doped GaN layer (film thickness: 10 nm), undoped GaN layer (film thickness: 145 nm), GaN layer doped with 1.5 × 10 ¹⁹ / cm ^{3 of} Si (film thickness: 30 nm), undoped GaN layer (film thickness: 5 nm) are sequentially stacked, an undoped semiconductor layer 6;
A GaN layer p (film thickness: 4 nm) doped with 2.5 × 10 ¹⁸ / cm ^{3 of} Si was stacked, an undoped In _0.02 Ga _0.98 N layer q (film thickness: 2 nm), and Si 2 .5 × 10 ¹⁸ / cm ³ doped GaN layer p (film thickness: 4 nm) in this order, an n-type multilayer film layer having a superlattice structure with a total of 121 layers in which the GaN layer q and the GaN layer p are stacked 7 (film thickness: 364 nm),
A barrier layer e (film thickness: about 4 nm) made of GaN doped with Si of 5 × 10 ¹⁸ / cm ³ and a barrier layer f (film thickness: about 3.5 nm) made of undoped GaN are stacked, and then undoped In _{0. .2 In} the stacked structure of the well layer g (thickness: about 3.3 nm) made of Ga _0.8 N and the barrier layer h (thickness: about 4.4 nm) made of undoped GaN, 15 well layers f and barriers are formed. Active layer 8 (film thickness: film thickness: 123 nm) having a multiple quantum well structure in which 15 layers h are alternately stacked;
P-side cladding layer 9 (film thickness: about 25 nm) made of p-type Al _0.2 Ga _0.8 N doped with 1 × 10 ²⁰ / cm ^{3 of} Mg, and a layer made of undoped GaN (film thickness: about 50 nm) in order from the bottom, A layer made of p-type GaN doped with 1 × 10 ²⁰ / cm ³ Mg (film thickness: about 50 nm) and a layer made of p-type GaN doped with 5 × 10 ²⁰ / cm ³ Mg (film thickness: about 15 nm) The p-type contact layers 10 stacked in this order are stacked in this order, and a part of the p-side nitride semiconductor layer, the active layer, and the n-side nitride semiconductor layer are removed, and the n-type contact layer 5 The surface is exposed.
On almost the entire surface of the p-type contact layer 10, a light-transmitting full-surface electrode 11 made of ITO and a p-electrode 12 containing Ti, Rh, and Au formed thereon are formed, and the exposed n-type is exposed. An n electrode 13 made of the same laminated material as that of the p electrode 12 is formed on the surface of the contact layer 5.

Such a nitride semiconductor device can be manufactured by the following method.
(Substrate 1)
The substrate 1 made of sapphire (C surface) is set in a MOCVD reaction vessel, and the temperature of the substrate 1 is raised to about 900 ° C. to 1200 ° C. while flowing hydrogen to clean the substrate.
(Buffer layer 2)
Subsequently, the temperature is lowered to 400 ° C. to 800 ° C., hydrogen is used as the carrier gas, ammonia, TMG (trimethylgallium) and TMA (trimethylaluminum) are used as the carrier gas, and a buffer layer 2 made of undoped AlGaN is formed on the substrate at about 15 nm. Growing with a film thickness of

(First Nitride Semiconductor Layer 16)
As described below, the first nitride semiconductor layer 16 including the low dislocation layer 3 and the pit buried layer 4 is formed.
(Low dislocation layer 3)
After the growth of the buffer layer 2, only TMG is stopped and the temperature is raised to about 800 ° C to 1400 ° C. Using TMG and ammonia gas as source gas, a low dislocation layer 3 made of undoped GaN is grown to a thickness of about 1.5 μm. At this time, the ratio of the ammonia gas flow rate to the total gas flow rate is set to about 30%.
(Pit embedded layer 4)
Subsequently, at a temperature of about 850 ° C. to 1450 ° C., TMG and ammonia gas are used as the source gas, and the pit buried layer 4 made of undoped GaN is grown to a thickness of about 2.0 μm. At this time, the ratio of the ammonia gas flow rate to the total gas flow rate is set to about 60%.

(N contact layer 5)
Next, the n-type contact layer 5 made of GaN doped with 9 × 10 ¹⁸ / cm ^{3 of} Si is similarly grown to a thickness of about 4.2 μm using TMG, ammonia gas as the source gas, and silane gas as the impurity gas.

(Undoped semiconductor layer 6)
Next, at about 800 ° C. to 1400 ° C., the presence or absence of TMG, ammonia gas, and impurity gas in the source gas is controlled by the presence or absence of silane gas, and an undoped GaN layer (film thickness: 145 nm), Si is 2.5 × 10 ¹⁸ / cm ³ doped GaN layer (film thickness: 10 nm), undoped GaN layer (film thickness: 145 nm), Si 1.5 × 10 ¹⁹ / cm ³ doped GaN layer (film thickness: 30 nm), undoped GaN layer (film) (Thickness: 5 nm) is grown in order.

(N-type multilayer film layer 7)
Subsequently, a GaN layer p (film thickness: 4 nm) doped with 2.5 × 10 ¹⁸ / cm ^{3 of} Si using TMG, TMI (trimethylindium), and ammonia at a temperature of about 800 ° C. to 1000 ° C. In addition, an undoped In _0.02 Ga _0.98 N layer q (film thickness: 2 nm), and a GaN layer p (film thickness: 4 nm) doped with 2.5 × 10 ¹⁸ / cm ^{3 of} Si are arranged in this order. An n-type multilayer film layer 7 (film thickness: 364 nm) having a superlattice structure with a total of 121 layers in which the p and GaN layers q are stacked is grown.

(Active layer 8)
Next, a barrier layer e made of GaN containing Si is grown about 4 nm, and a barrier layer f made of undoped GaN is grown to a thickness of about 3.5 nm. After that, using TMG, TMI, and ammonia, the well layer g made of undoped In _0.2 Ga _0.8 N is alternately formed in a thickness of about 3.3 nm, and the barrier layer h made of undoped GaN is formed in an alternating thickness of about 4.4 nm. Then, an active layer 8 having a multiple quantum well structure with a total film thickness of 123 nm is grown.

(P-side cladding layer 9)
Next, the p-side cladding layer 9 made of p-type Al _0.2 Ga _0.8 N doped with 1 × 10 ²⁰ / cm ^{3 of} Mg using TMG, TMA, ammonia, Cp ₂ Mg (cyclopentadienyl magnesium) is about 25 nm. Growing with a film thickness of
(P-type contact layer 10)
Subsequently, TMG, TMA, and ammonia are used at a temperature of about 900 ° C. to 1000 ° C., and a layer made of undoped GaN is grown to a thickness of about 50 nm. On top of this, TMG, ammonia, and Cp ₂ Mg are used. A layer of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is about 50 nm thick, and a layer of p-type GaN doped with 5 × 10 ²⁰ / cm ³ of Mg is further about 15 nm in thickness. Grow with film thickness.

After the completion of the reaction, the temperature is lowered to room temperature, and the wafer is annealed in a reaction vessel at 300 ° C. to 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-side layer.
Thereafter, the wafer is taken out from the reaction vessel, a mask having a predetermined shape is formed on the surface of the uppermost p-type contact layer 10, and etching is performed from the p-type contact layer side 10 with an RIE (reactive ion etching) apparatus. As shown in FIG. 1, the surface of the n-type contact layer 5 is exposed.
Subsequently, a light-transmitting full-surface electrode 11 made of ITO is formed on almost the entire surface of the p-type contact layer 10 as the uppermost layer.
A laminated film containing Ti, Rh, and Au is formed on the n-type contact layer exposed by p-etching on the entire surface electrode 11, and patterned to form a p-electrode 12 and an n-electrode 13, respectively.
The obtained laminated structure is cut into each chip to obtain a nitride semiconductor element.

About the obtained nitride semiconductor element, the forward voltage and the output were measured. The evaluation was performed in a state where a forward current of 60 mA was applied as a pulse to a 500 × 290 μm size chip.
Further, the leakage current was evaluated when leakage was easily generated by applying 100 mA to the nitride semiconductor element and operating the nitride semiconductor element in a 120 ° C. environment. The transition between Ir and Vf is shown as an indicator of the presence or absence of leakage current. If Ir rises and Vf drop increases, it can be considered that leakage current is generated.
In the above-described embodiment, the n-type multilayer film layer is not doped with Si, and the n-type multilayer film layer 7 having a total of 41 superlattice structures (film thickness: 124 nm) is used. Similarly, a nitride semiconductor device was manufactured and used as a comparative example.
These results are shown in FIGS.

As shown in FIG. 2, in the device of the example (n = 5), an average decrease in Vf of about 2.3% was observed with respect to the comparative example, and an increase in output of an average of 4.2% was further observed. Admitted. Note that these Vf decreases and output increases tend to be confirmed in all n = 5 elements.
Further, as shown in FIGS. 3 and 4, even if the n-type multilayer film layer is doped with Si, even after the device is operated for 1000 hours under harsh conditions, as in the case of the element in which the same layer is not doped with Si, Ir As a result, it was confirmed that the leakage current was effectively prevented.

  The nitride semiconductor device of the present invention can be used as various light sources such as a full-color LED display, a traffic signal light, and an image scanner light source, for example, as a high-intensity blue LED, a pure green LED, or the like.

DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 Buffer layer 3 Low dislocation GaN layer 4 Pit reduction GaN layer 5 N-type contact layer 6 Undoped semiconductor layer 7 N-type multilayer film layer 8 Active layer 9 p-type single layer 10 p-type contact layer 11 Whole surface electrode 12 P electrode 13 n-electrode 14 n-side nitride semiconductor layer 15 p-side nitride semiconductor layer 16 first nitride semiconductor layer

Claims (6)

A nitride semiconductor device in which an n-side nitride semiconductor layer, an active layer, and a p-side nitride semiconductor layer are stacked in this order,
The n-side nitride semiconductor layer is formed by laminating an n-type contact layer, an undoped semiconductor layer, and an n-type multilayer film layer in this order,
The n-type multilayer film layer is formed by alternately laminating layers having an n-type impurity concentration of 5 × 10 ¹⁶ / cm ³ or more and undoped layers, and comprising 121 or more layers, and having a total thickness of 364 nm or more and 500 nm or less. A nitride semiconductor device having a film thickness.   The nitride semiconductor device according to claim 1, wherein the active layer has a total film thickness of 90 nm to 200 nm. A first nitride semiconductor layer having a substrate on the n-side nitride semiconductor layer side and having a dislocation density of 1 × 10 ^{7 to} 5 × 10 ⁹ cm ⁻² between the substrate and the n-type contact layer; The nitride semiconductor device according to claim 1, wherein the first nitride semiconductor layer has a thickness of 1 μm or more and 10 μm or less.   The nitride semiconductor element according to claim 3, wherein the first nitride semiconductor layer has a dislocation density lower on the n-type contact layer side than on the substrate side.   The nitride semiconductor device according to claim 1, wherein the undoped semiconductor layer is an undoped GaN layer. The nitride semiconductor device according to claim 1, wherein the undoped semiconductor layer is formed by alternately laminating undoped layers and Si doped layers.

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