JP2002335052A - Nitride semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser element of an element structure excellent in light emitting efficiency in a short wavelength range of 375 nm. SOLUTION: In a nitride semiconductor element having an active layer between a first conductivity lower clad layer 13 and a second conductivity upper clad layer 14, first layers 25, 32 having a nitride semiconductor containing Al and In are provided for at least one of the lower clad layer and the upper clad layer. According to this constitution, crystallinity deterioration, especially a layer generating crack can be restrained in an element structure using AlGaN in each clad layer and an optical guide layer. Light confinement of the element can be improved by making a refractive index of a first layer smaller than that of second layers 26, 31 inside a clad layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device such as a light emitting diode (LED) and a laser diode (LD), a light receiving device such as a super photoluminescence diode, a solar cell, an optical sensor, a transistor, and a power device. III-V used in electronic devices such as
The present invention relates to a nitride semiconductor device using a group III nitride semiconductor, and more particularly to a nitride semiconductor light emitting device having an emission wavelength of 375 nm or less.

[0002]

2. Description of the Related Art Today, there is an increasing demand for use of a semiconductor laser using a nitride semiconductor in an optical disk system capable of recording and reproducing large-capacity and high-density information, such as a DVD. For this reason, semiconductor laser devices using nitride semiconductors have been actively studied. In addition, semiconductor laser devices and light emitting devices using nitride semiconductors are considered to be capable of oscillating in a wide range of visible light from ultraviolet to red. , Laser printers, optical networks, and other light sources are expected to be diverse. In addition, the present applicant has announced a laser that exceeds 10,000 hours under conditions of continuous oscillation of 405 nm, room temperature, and 5 mW.

Further, a laser device using a nitride semiconductor,
A light-emitting element, a light-receiving element, and the like have a structure in which an active layer is formed using a nitride semiconductor containing In, and the formation of a superior active region in the active layer is important in improving element characteristics.

In a nitride semiconductor device, particularly a laser device and a light emitting device, emission and oscillation in a wavelength range of 380 nm or less have become more important. This is because, in the optical disc system described above, the recording density can be improved by shortening the wavelength, and in the light emitting element, it becomes important as the excitation light source of the phosphor. Many applications are realized.

In order to obtain short-wavelength light emission from a nitride semiconductor laser device or a light-emitting device, the emission wavelength is changed by changing the In mixed crystal ratio of the nitride semiconductor containing In in the active layer or the light-emitting layer. Can be changed,
In particular, the emission wavelength can be shortened by reducing the In mixed crystal ratio. Further, in the edge emitting device and the laser device, when the active layer has a structure sandwiched between the upper and lower cladding layers, the refractive index of both cladding layers is reduced,
By increasing the refractive index in the waveguide sandwiched between the lower cladding layers, light is efficiently confined in the waveguide, and as a result, contributes to a reduction in threshold current density in the laser device.

However, as the wavelength becomes shorter,
It becomes difficult to use InGaN or an InGaN / InGaN quantum well structure conventionally used as a light emitting layer, and a wavelength of 36, which is the band gap of GaN, is obtained.
Below 5 nm, it is difficult to use InGaN for the light emitting layer. Further, when the wavelength becomes shorter, that is, a loss occurs due to light absorption in the guide layer in the waveguide, and the threshold current becomes higher. Further, in the light confinement by the upper clad layer and the lower clad layer, the use of GaN also requires the Al composition ratio in order to secure a loss due to light absorption and a refractive index difference for confining light in the waveguide. It is necessary to use a large nitride semiconductor, and the problem of deterioration of crystallinity becomes serious.

As an attempt to shorten the wavelength of such a nitride semiconductor device, there is a device using an AlGaN / AlGaN quantum well structure. There is no tendency.

[0008]

In the present invention, AlGa is used.
In an AlGaN-based nitride semiconductor device using N, AlInGaN, or the like, the use of a nitride semiconductor containing Al greatly deteriorates crystallinity. Become. Therefore, suppressing such deterioration of crystallinity is an indispensable subject in improving device characteristics.

In particular, in a laser device or a light emitting device having an emission wavelength of 375 nm or less, in order to confine light in a waveguide sandwiched between both clad layers, a wavelength shorter than the emission wavelength of the active layer by about 10 nm or more in terms of wavelength. It is necessary to provide a cladding layer having a band gap energy of For this reason, the wavelength region is below the absorption edge of GaN and in the vicinity thereof, and a nitride semiconductor containing Al is used. It is necessary to obtain.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and the present invention relates to a nitride semiconductor device, particularly an AlGaN-based nitride semiconductor device using AlGaN, AlInGaN, or the like. A nitride semiconductor device having excellent device characteristics is obtained by suppressing deterioration of crystallinity due to the use of a nitride semiconductor containing Al, and a nitride having excellent characteristics in a light emitting device having an emission wavelength of 375 nm or less. A semiconductor is obtained.

That is, the semiconductor device of the present invention can achieve the object of the present invention by the following constitutions (1) to (13).

(1) a lower cladding layer of the first conductivity type;
A nitride semiconductor device having an active layer between a second conductivity type upper clad layer and a nitride semiconductor containing Al and In in at least one of the lower clad layer and the upper clad layer. It is characterized in that a layer is provided. (2) The emission wavelength λ of the active layer is λ ≦ 375 nm. (3) A first layer having a nitride semiconductor containing Al and In on at least one of the lower cladding layer and the upper cladding layer, and a nitride containing Al having an In mixed crystal ratio smaller than that of the first layer. And a second layer including a semiconductor. (4) wherein the first layer _{Al x In y Ga 1-x} -y N
(0 <x <1,0 <y <1, x + y <1) having, claims wherein the second layer and having a _{Al u Ga 1-u N (} 0 <u ≦ 1) 3. The nitride semiconductor device according to 3. (5) The In composition ratio y of the first layer is 0.01 ≦ y
5. The nitride semiconductor device according to claim 3, wherein ≤0.3. (6) The second layer is provided closer to the active layer than the first layer. (7) and the refractive index _{n 1} of the first layer, the refractive index _{n 2} of the second layer, characterized in that it is a _{n 2} ≦ _{n 1.} (8) The first layer is formed of a superlattice multilayer film having a different composition. (9) A lower light guide layer and an upper light guide layer are provided between the lower clad layer and the active layer and between the upper clad layer and the active layer, respectively. (10) The lower light guide layer and the upper light guide layer are A
l α Ga _1-α N, characterized in that it consists (0 <α ≦ 1). (11) The upper cladding layer has a lower cladding layer I
It is characterized by being smaller than n composition ratio. (12) The active layer includes a nitride semiconductor containing Al and In. (13) The active layer has a quantum well structure,
Well _{layer, Al x In y Ga 1-} x-y N (0 <x <
1, 0 <y <1, x + y <1), and the barrier layer is made of _{Alu
In v Ga 1-u-v} N (0 <u ≦ 1,0 ≦ v ≦ 1, u
+ V <1).

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The nitride semiconductor used in the nitride semiconductor device of the present invention is GaN, AlN,
nN, or Group III-V nitride is of mixed crystal semiconductor _{(In α Al β Ga 1-} α-β N, 0 ≦ α, 0 ≦ β,
α + β ≦ 1). In addition, B is used as a group III element, and a part of N is P, A
It may be a mixed crystal substituted with s. The nitride semiconductor containing Al has β> 0, and the nitride semiconductor containing In has α> 0.
0.

As the n-type impurity used in the nitride semiconductor layer, a group IV or group VI element such as Si, Ge, Sn, S, O, Ti, or Zr can be used. Preferably, Si, Ge is used. , Sn, and most preferably Si
Is used. The p-type impurity is not particularly limited, but includes Be, Zn, Mn, Cr, Mg, Ca and the like, and preferably Mg is used. Thus, a nitride semiconductor layer of each conductivity type is formed, and each conductivity type layer described later is formed.

The nitride semiconductor device structure of the present invention includes:
As shown in FIG. 2, the active layer 28 is sandwiched between the upper clad layer 14 and the lower clad layer 13. Further, the active layer 28 is sandwiched between the first conductive type layer 11 and the second conductive type layer 12, and the active layer 28 is interposed between the first conductive type lower clad layer 13 and the second conductive type upper clad layer 14. Has a structure in which an active layer 28 is provided. Specifically, it has a structure in which a first conductivity type layer 11, an active layer 28, and a second conductivity type layer 12 are laminated on a substrate.
3, an active layer 28 and an upper clad layer 14 are laminated. In addition, the cladding layers of the first conductivity type and the second conductivity type may be partially or entirely made of, for example, an undoped or non-doped nitride semiconductor, and are disposed in each of the conductivity type layers. A part of the clad layer may be doped with an impurity of a different conductivity type, that is, the lower clad layer and the upper clad layer are formed on at least the first conductive type layer side and the second clad layer disposed on both sides of the active layer.
It is provided on the conductivity type layer side. Preferably, when the first conductivity type and the second conductivity type nitride semiconductor are provided in at least a part of the lower cladding layer and the upper cladding layer,
It is preferable that carriers are efficiently injected into the active layer in each conductive type layer.

In the laser device and the edge emitting device, the upper and lower cladding layers 12 and 13 are interposed, and the cladding layer serves as a light confinement layer, and the region including the active layer is a waveguide (waveguide layer). ). At this time, as shown in FIG. 2, a lower light guide layer 27 and an upper light guide layer 30 are provided between each clad layer and the active layer, that is, a light guide layer is provided in the waveguide to separate and close the light guide layer. It is good also as a confinement structure.
Hereinafter, the upper clad layer and the lower clad layer of the present invention will be described in detail.

[First Embodiment] As a first embodiment of the present invention, a lower cladding layer 13 and an upper cladding layer 14 are used.
At least has a nitride semiconductor containing In and Al. Specifically, a first layer having a nitride semiconductor containing Al and In is provided on one or both of the cladding layers. Conventionally, a cladding layer of a nitride semiconductor element has been made of Al, such as AlGaN.
Is used, and in particular, AlGaN / Ga
N multilayers have been used. This is because, when AlGaN is used, the deterioration of crystallinity, particularly the occurrence of cracks becomes a problem, and such a tendency increases as the Al composition ratio increases. Therefore, a nitride semiconductor such as GaN, which is more elastic than AlGaN, is used. The problem has been solved by using such a material to function as a buffer layer that relaxes crystallinity. For example, A
As the 1GaN / GaN superlattice multilayer structure, a clad layer in which deterioration of crystallinity is suppressed has been formed. However, in the short wavelength region where the emission wavelength is 375 nm or less, the absorption edge of GaN is 365 nm, and light absorption by GaN occurs in the region of 375 nm or less, which is approximately 10 nm near the wavelength. The use of leads to deterioration of device characteristics.

In the present invention, by providing the nitride semiconductor containing Al and In in the cladding layer, it is possible to suppress the deterioration of crystallinity due to the use of the nitride semiconductor containing Al as described above. And the occurrence of cracks can be prevented. This is because, as described above, a nitride semiconductor containing In is a material that is soft and rich in elasticity when compared with a nitride semiconductor containing Al, for example, when AlInGaN and AlGaN are compared. It functions as a buffer layer for suppressing generation of cracks due to semiconductors. Further, in the present invention, by providing a nitride semiconductor containing Al in addition to In in the cladding layer, loss due to light absorption is suppressed, and light emission efficiency, light extraction efficiency, and current-
Characteristics such as slope efficiency in light output characteristics can be improved. This depends on the material of the optical waveguide and the cladding layer, and the light confinement coefficient. Due to the wave, the loss of light in the cladding layer also greatly affects the characteristics of the light emitting element, the laser element, and the like. Light is reflected and guided at the interface between the waveguide and the cladding layer. At this time, a Goos-Henfen shift occurs, an evanescent wave exists in the cladding layer, and the light seeps into the cladding layer. It also has an effect.

As described above, conventionally, InGaN such as InGaN is used.
In a nitride semiconductor containing, there is a tendency that a large amount of loss due to light absorption occurs.
Since a nitride semiconductor containing In and Al is provided,
By including In and Al at the same time, it becomes possible to increase the energy band gap and suppress light absorption and loss. On the other hand, by appropriately adjusting the composition ratio of the nitride semiconductor containing In and Al in the cladding layer, a desired refractive index between the cladding layer and the waveguide can be obtained. It is possible to make a difference. As described above, the element having the waveguide has been described.
Reduction of light loss in the element structure contributes to improvement of characteristics such as improvement of light extraction efficiency.

The nitride semiconductor containing In and Al is as follows:
The composition is not particularly limited, but specifically, Al _x I
_ny Ga _1-xy N (0 <x <1, 0 <y <1, x +
A nitride semiconductor represented by y <1) can be preferably used. At this time, the In composition ratio y is not particularly limited, but specifically, in the range of 0 <y ≦ 0.5, deterioration of crystallinity due to the inclusion of In is suppressed. 01 ≦ y ≦ 0.3, more preferably 0.03
≦ y ≦ 0.3. This is because y ≧
When the content is in the range of 0.01, the effect of improving the crystallinity and the effect of preventing cracks by the nitride semiconductor containing In described above can be obtained, and when y ≧ 0.03, those effects can be further improved. Further, when y ≦ 0.3, it is possible to suppress deterioration of crystallinity due to the provision of the nitride semiconductor containing In and to preferably provide the first layer in the cladding layer. Here, in the nitride semiconductor containing In and Al, when the composition ratio of In is increased, the tendency of segregation of In is increased, and it is difficult to grow the semiconductor with good crystallinity. The reaction between Al and Al tends to hinder the growth of the nitride semiconductor. Therefore, by setting y ≦ 0.5, such deterioration of crystallinity is suppressed, segregation of In and precipitation of In are prevented, and furthermore, y
By setting ≦ 0.3, it is possible to grow with good crystallinity.

The thickness of the first layer of the present invention is not particularly limited, but when the thickness is 10 ° or more, the crystallinity improving effect tends to be obtained. Deterioration of crystallinity caused by providing a nitride semiconductor containing Al and Al can be suppressed. Preferably,
When the angle is 50 ° or more, the above crystallinity improving effect can be suitably obtained, and when the angle is 0.2 μm or less, the film can be formed with good crystallinity.

The first layer of the present invention may be formed of a single film made of a nitride semiconductor containing In and Al, or may be formed of a multilayer film. That is, the first
May be composed of a single film of a nitride semiconductor containing In and Al, and a nitride semiconductor containing In and Al, and a nitride semiconductor containing In and Al different in composition It may be composed of a multilayer film containing at least a semiconductor.

When the first layer is formed by a single film, the growth time can be shortened by forming the first layer by a single film as compared with the case of forming a multi-layer film. In addition, the first
When the layers are formed, the compositions are different, and the layers are composed of a nitride semiconductor containing Al and In. Therefore, each layer can have a different band gap energy, refractive index, and doping amount, and the degree of freedom in element design is improved. In addition, device characteristics suitable for the application can be obtained. Specifically, Al _x1 In _y
Ga _1-x1-y1 N (0 <x1 <1, 0 <y1 <1,
x1 + y1 <1) and an A layer composed of Al _x2 In _y2 G
_{a 1-x2-y 2 N} (0 <x2 <1,0 <y2 <1, x
2 + y2 <1), and has a structure that satisfies at least one of x1 ≠ x2 and y1 ≠ y2. In the case of forming a multilayer film, the average composition of In in the first layer is set to the above range, and preferably, each layer is set to the range of the above In composition ratio. When each layer does not have a superlattice structure, it is preferable to use each layer such as an A layer and a B layer made of a nitride semiconductor within the above range of the In composition ratio.

Provision of a first layer of a superlattice multilayer film
In that case, different from the above multilayer film, various compositions
In addition, the first layer can be formed with a layer structure. For example, including In
Alternating lamination of nitride semiconductor and nitride semiconductor containing Al
And a layer of a nitride semiconductor containing In and Al in a pseudo manner.
It is possible to Preferably, In and Al are contained.
Semiconductors and nitride semiconductors with different compositions
Are alternately stacked in one or more layers.
Thus, the light by the nitride semiconductor containing In and Al
Tends to easily obtain the loss suppressing effect. Specific composition
As Al _x1In_yGa_1-x1-y1N (0 <
A consisting of x1 <1, 0 <y1 <1, x1 + y1 <1)
Layer and Al_x2In_y2Ga_1-x2-y2N (0 <x
B layer composed of 2 <1, 0 ≦ y2 <1, x2 + y2 <1)
And a superlattice multilayer film structure having at least At this time
x1 一方 x2, y1 ≠ y2, at least one of the expressions
X1> x2, more preferably y1> y
2, at least one of the expressions is satisfied. This
At this time, specifically as a super lattice structure,
A layer and B layer are alternately laminated, and at least one is
Two or more layers, preferably each layer has two or more layers,
Or a plurality of pairs of layers A and B were periodically laminated as a pair.
Structure. Thus, the first layer in the superlattice multilayer structure is
Can be formed with good crystallinity.
Compared to the case where the first layer is formed, the thickness of the first layer is increased.
For example, the first layer of a thick film
To function well as light confinement. Ma
Further, by satisfying x1> x2 and y1> y2, the layer A is cleaned.
The layer B is made to function as an anti-rack layer, and the B layer has an In composition ratio and / or
Or, since the Al composition ratio is small, the crystallinity of the A layer, and
The effect of maintaining good crystallinity of the first layer is obtained. Super lattice
The thickness of each layer constituting the structure depends on the composition and the set of each layer.
Although the film thickness differs depending on the combination, specifically, 10
0 ° or less, preferably 75 ° or less.
By maintaining good crystallinity, it is more preferable
Is 50 ° or less, so that better crystallinity can be obtained.
Deterioration of crystallinity and cracks due to nitride semiconductor containing Al
There is a tendency that the effect of suppressing rawness is easily obtained. Also,
One layer is a superlattice multilayer film structure including the A layer and the B layer.
In this case, the In composition ratio depends on the thickness d of the A layer.₁When
And the thickness of the B layer is d₂And the average composition u_m= (D
₁× u1 + d₂× u2) / (d₁+ D₂)
Average composition u_mIn the above-mentioned range of the In composition ratio.
Is preferred. The superlattice multilayer film is other than the A layer and the B layer.
, For example, a C layer having a different composition from the A layer and the B layer.
In this case, a weighted average can be obtained by the film thickness.

In the first layer, impurities of each conductivity type may be doped, may be formed undoped, or may be provided undoped. For example, as shown in the examples, in an element structure in which the first conductivity type layer is an n-type layer and the second conductivity type layer is a p-type layer, a part or all of the lower cladding layer 13 and the upper cladding layer 14 are formed. May be doped with an n-type impurity and a p-type impurity, respectively, or may be partially undoped. It is preferable to grow by undoping because the crystallinity becomes better as compared with the case of doping. Further, a configuration in which the doping amount is inclined in the film thickness direction may be employed. Further, in the superlattice multilayer structure, it is possible to dope the A layer and make the B layer undoped for modulation doping. On the other hand, it has better carrier mobility than undoping the whole,
The resistance in the cladding layer can be reduced, and Vf in the device can be reduced. At this time, a superlattice multilayer film may be used in which the A layer and the B layer have different impurity concentrations.

As described above, the first layer is provided on at least one of the upper clad layer and the lower clad layer as a part of the clad layer. When the bandgap energy is larger than that of the layer, the bandgap energy functions as carrier confinement and light confinement, and the bandgap energy becomes larger than the emission wavelength, so that light loss due to the first layer can be avoided. Also, as in the examples described later, AlG
A nitride semiconductor containing Al such as aN is used for a carrier confinement layer, an active layer (barrier layer), a guide layer, a contact layer, or a cladding layer other than the first layer.
By providing the second layer above, below, or between the layers of the nitride semiconductor containing, it is possible to mitigate deterioration in crystallinity that seriously affects device characteristics.

[Second Embodiment] As a second embodiment of the present invention, a lower cladding layer 13 and an upper cladding layer 14 are used.
A first layer having a nitride semiconductor containing Al and In, and a second layer having a nitride semiconductor containing Al having an In mixed crystal ratio smaller than that of the first layer. It is characterized by having been done. With this configuration, different functions can be provided between the first layer and the second layer in the cladding layer. This allows the first layer having a large In composition ratio to improve the above-described crystallinity, and the second layer having a small In composition ratio to perform light confinement and carrier confinement.

Particularly, in a device such as a laser device having a waveguide between a lower cladding layer and an upper cladding layer, light seeps into the cladding layer, and light loss occurs in the cladding layer. However, in the present embodiment, by including the second layer having a small In composition ratio, compared to the first layer,
Light loss due to In can be reduced.

Here, Al used for the second layer is included.
As the nitride semiconductor, Al and I used for the first layer are used.
n than the In composition ratio y of the nitride semiconductor containing n
The composition ratio is small. Specifically, used for the second layer
Is the In composition ratio v of the nitride semiconductor containing Al
And the In composition ratio y of the nitride semiconductor in the first layer.
Thus, y> v, and v is v ≧ 0. concrete
The composition is Al_uIn_vGa_1-uvN (0 <u
<1, 0 ≦ v <1, u + v <1)
Body for the second layer, preferably the In group
Al with composition ratio v = 0 _uGa_1-uN (0 <u ≦ 1)
Is Rukoto. Al in the second layer_uGa_{1- u}N (0 <u
≦ 1) to suppress light loss
Good light confinement and carrier confinement are realized.
In a laser device having a waveguide, the loss of light
A lowered waveguide is formed, especially in the above short wavelength range.
Light emitting devices and lasers with excellent luminous efficiency and current-light output characteristics
An element is obtained.

The thickness of the nitride semiconductor containing Al used for the second layer is not particularly limited, but may be 10 °.
With the above, carriers can be confined as the cladding layer. By setting the upper limit to 2 μm or less, deterioration in crystallinity can be suppressed. Preferably, 100 °
When the thickness is in the range of 1 μm or less, a second layer having excellent crystallinity and excellently functioning as a cladding layer and as a light confinement can be obtained. Further, the second layer may be composed of a single film of a nitride semiconductor containing Al, or may be composed of a multilayer film, and in particular, may be a superlattice multilayer film in the multilayer film.

At this time, as described above, the first layer and the second layer are provided on at least one of the lower clad layer and the upper clad layer. Specifically, as shown in FIGS. 2 and 3, both the lower cladding layer 13 and the upper cladding layer 14 have the first layers 25 and 32 and the second
4, a first layer 25 and a second layer may be provided only on one side as shown in FIG. 4, and in FIG. Second layer 2
6, and the upper cladding layer 14 is composed of only the second layer.

In the clad layer having the first layer and the second layer, the first layer may have a larger band gap energy than the second layer as shown in FIGS. The size may be reduced as shown in FIG.

[Third Embodiment] The third embodiment of the present invention is characterized in that the second layer is provided closer to the active layer than the first layer. Specifically, FIG.
As shown in FIGS. 5 to 5, in each of the cladding layers 13 and 14,
The second layer is provided closer to the active layer than the first layer, that is, on the active layer side, and the second layer is provided between the first layer and the active layer. Therefore, in the device structure having an active layer between the lower cladding layer 13 and the upper cladding layer 14, the second
Is arranged on the active layer side, that is, on the inside, and the second layer has a structure arranged on the outside of the active layer. In this case, for example, on the contrary, as compared with the case where the first layer is arranged on the active layer side as shown in FIG. A light emitting element and a laser element with high efficiency can be obtained. This is because the second layer is located between the first layer and the active layer.
Is provided, that is, the first layer is spaced apart from the active layer, so that in a laser device or the like in which a waveguide is provided between cladding layers, the light intensity distributed in the first layer Can be reduced, the loss of light due to this can be reduced, and the characteristics can be improved. At this time, as shown in FIG. 3, good carrier confinement is realized by making the band gap energy of the first layer substantially equal to or larger than the band gap energy of the second layer.

[0034] As a fourth embodiment of the Fourth Embodiment The present invention includes a refractive index _{n 1} of the first layer, the refractive index _{n 2} of the second layer is the _{n 2} ≦ _{n 1} It is characterized by the following. In this configuration, as shown in FIG. 2B, the cladding layers 13, 1
4, the refractive indexes of the second layers 26 and 31 near the active layer are large, and the refractive indexes of the first layers 15 and 32 far from the active layer are small. Can be increased. Because of this, the cladding layer whose refractive index decreases as the distance from the active layer increases, the upper and lower cladding layers 1
Light is efficiently confined in the waveguide sandwiched between 4, 13 and thereby, good waveguide of light is realized.
The structure can reduce the light leaking to the outside of the cladding layer.

As described above, the first layer is made of In and Al.
By adjusting the composition ratio of Al, it is possible to obtain a layer having substantially the same refractive index as the second layer or a layer having a lower refractive index than that of the second layer. Conventionally, an InGaN layer has been used between the n-type lower cladding layer and the substrate. However, this layer allows light leaking from the cladding layer to be guided on the substrate side, thereby reducing the optical characteristics of the laser device. Has worsened. In the present invention, the refractive index of the first layer is made smaller than that of the second layer, and furthermore, the first layer is arranged farther from the active layer than the second layer, so that light can be transmitted to the substrate side. Leakage can be suppressed.

Hereinafter, the lower clad layer 13 and the upper clad layer 14 in each embodiment will be described in detail.

In the present invention, as shown in FIGS.
At least one of the lower cladding layer 13 and the upper cladding layer 14 has the second layers 25 and 32. The compositions of the lower cladding layer 13 and the upper cladding layer 14 are shown in FIGS.
As shown in the band structure 41 of FIG. 6, the bandgap energy is set to be larger than that of the active layer (well layer), and the lower light guide layer 27 is used as a waveguide such as a laser device or an edge emitting device. , Upper light guide layer 30
In the case where the light guide layer is provided, it is equal to or larger than the light guide layer. This is to make the upper and lower cladding layers function as light confinement for carrier confinement, and to function as a light confinement layer when a light guide layer is provided. Here, FIG. 3 shows a laminated structure 4 in the element structure of the present invention.
4 schematically shows a band structure 41 corresponding to 0, and FIGS. 4 to 6 show the band structure 41. FIG.

As the nitride semiconductor used for the cladding layer, a nitride semiconductor containing no Al, such as GaN, can be used. However, a nitride semiconductor containing Al is preferably used. _a Al _b Ga
_By using a nitride semiconductor represented by 1 _-abN (0 ≦ a, 0 <b, a + b ≦ 1), good carrier confinement and light confinement are realized. Preferably, the lower clad layer 13 and the upper clad layer 14 have at least the second layer, and more preferably, the In composition ratio v
= 0, the second having Al _u Ga _1-u N (0 <u ≦ 1).
Is used. This is because the In composition ratio of the second layer is made smaller than the In composition ratio of the first layer, as described in the second embodiment, and the second layer preferably does not contain In. This is because light loss due to the inclusion of In can be suppressed. In a structure in which a waveguide is sandwiched between upper and lower cladding layers, such as a laser device and an edge emitting device, the structure is sufficient between the waveguide and the cladding layer, specifically, between the active layer and / or the light guide layer. By providing a large refractive index difference, light is confined in the waveguide and light is guided. To provide such a refractive index difference, Al _u Ga
_1-u N (0 <u ≦ 1) is preferably used, and at least α between the Al composition (average composition) ratio α of the optical guide layer and
≦ u, preferably u−α ≧ 0.
By setting it to be 05, a sufficient difference in refractive index is provided. Further, since the confinement of light by the cladding layer also depends on the thickness of the cladding layer, the composition of the nitride semiconductor is determined in consideration of the thickness. Further, the upper clad layer and the lower clad layer may have substantially the same composition, layer configuration, refractive index, and film thickness, and they may be different. Further, the same applies to the second layer in each clad layer. is there.

The cladding layer of the present invention preferably has at least the second layer. At this time, as shown in FIG. 5, the second layers 26, 26 are interposed via the first layers 25, 32.
, 31, 31 'may be provided in the cladding layer.
At this time, when a plurality of second layers are provided, each of the second layers may be formed with substantially the same composition, layer configuration, and refractive index, or may be different. Further, the second layer may be formed as a single film as described above, may be formed as a multilayer film, or may have a superlattice multilayer film structure. Further, it may be a second layer having a composition-graded structure, such as a light guide layer described later, or a structure having a composition-graded inside a cladding layer.

In the case where the second layer is formed by a single film, by forming a single film made of the nitride semiconductor, the light and carrier confinement structure is reduced as compared with the case where the second layer is formed by a multilayer film. The design is easy, and the time required for growing the cladding layer can be reduced. On the other hand, it is difficult to grow an Al-containing nitride semiconductor such as AlGaN with good crystallinity. In particular, when a single film is grown with a certain thickness or more, cracks are likely to occur. Furthermore, in the above short wavelength region, the Al composition ratio of the second layer used for the cladding layer is large, so that when formed as a single film, it tends to be difficult to form a thick film. Sufficient confinement becomes difficult.

When the second layer is formed of a multilayer film, a plurality of nitride semiconductors having different compositions are stacked, and more specifically, a plurality of nitride semiconductors having different Al composition ratios are stacked. By forming a multilayer film in this way, it is possible to suppress the deterioration of crystallinity and the occurrence of cracks in the case of a single film. Specifically, as a multilayer film, an A layer and a B layer having a different composition are stacked, and a plurality of layers having different refractive indices and band gap energies are provided. For example, an A layer having an Al composition ratio u1 and a B layer having an Al composition ratio u2 (u1 ≠ u2)
A multilayer film having a structure in which layers are stacked may be used. At this time, if the Al composition ratio is set to u1 <u2 (0 ≦ u1, u2 ≦ 1), the refractive index is small in the A layer having a large Al composition ratio, The gap energy can be increased and the deterioration of crystallinity due to the formation of the B layer with the A layer having a small Al composition ratio can be suppressed. For example, by setting the A layer to GaN and the B layer to AlGaN, deterioration of crystallinity can be prevented, and in particular, in a superlattice multilayer structure described later, the second layer can be formed with excellent crystallinity. Further, a plurality of layers having different compositions may be further laminated by laminating the A layer and the B layer and laminating the C layer having a different composition from the B layer. Also, layer A,
A structure in which a plurality of B layers are alternately stacked may be employed, or a structure in which a plurality of pairs having at least the A layer and the B layer are formed. In such a multilayer structure, since the crystallinity of the nitride semiconductor containing Al can be suppressed and the film thickness can be increased, it is possible to obtain a film thickness important in light confinement.

In the second layer of the multilayer structure, the superlattice structure is used to further improve the crystallinity and improve the second layer.
And a cladding layer can be formed. Here, the superlattice structure is provided in at least a part of the second layer. Preferably, by providing the superlattice structure in all of the layers, the second layer and the cladding layer can be formed with good crystallinity. At this time, as the superlattice structure, specifically, the layer A and the layer B in the multilayer film are alternately laminated, and at least one of the layers has two or more layers, preferably each layer has two or more layers. A structure in which a plurality of layers and a layer B are stacked as one pair is adopted. Preferably, the A layer / B layer is made of Al _u1 Ga
_1-u1N (0 ≦ u1 ≦ 1) / Al _u2 Ga _1-u2 N
(0 ≦ u2 ≦ 1, u1 ≠ u2), and Al _u1 Ga _1-u1 N (0 <u1 ≦ 1) / Al _{u2 in the} short wavelength region.
By using Ga _1-u2 N (0 <u2 ≦ 1, u1 ≠ u2), light is confined well in the waveguide, light seepage is suppressed, light loss is suppressed, and the superlattice is used. The structure can suppress the deterioration of crystallinity and form the thick second layer and the clad layer. The film thickness of each layer constituting the superlattice structure varies depending on the composition and the combination of each layer. Specifically, the film thickness is set to 100 ° or less, and preferably, the crystallinity is set to 75 ° or less. It is possible to keep good, and more preferably at 50 ° or less, the crystallinity becomes better, and the second layer having a larger thickness,
It can be a clad layer.

The cladding layer and the first layer are preferably doped with at least impurities of each conductivity type, and may be doped entirely or partially. A configuration in which it is changed may be used. Also, in the case of a multilayer film, for example, in a multilayer film having the A layer and the B layer, both may be doped, or the A layer and the B layer may have different doping amounts, or one may be doped. Alternatively, modulation doping may be employed in which the other is undoped. For example, the A layer / B layer is formed of Al _u1 Ga _1-u1 N (0 ≦ u1 ≦ 1) /
Al _u2 Ga _1-u2 N (0 <u2 ≦ u1, u1 <u
In the case of the superlattice multilayer structure of 2), the B layer having a small Al composition ratio is doped with impurities and the A layer is undoped, whereby the crystallinity can be improved similarly to the light guide layer.

The thickness of the cladding layer is not particularly limited, but is formed in the range of 10 nm to 2 μm, preferably in the range of 50 nm to 1 μm. This is because carrier confinement can be achieved by setting the thickness to 10 nm or more, crystallinity deterioration is suppressed by setting the thickness to 2 μm or less, and light confinement is achieved in an element structure having a waveguide by setting the thickness to 50 nm or more. The cladding layer can be formed with good crystallinity when the thickness is 1 μm or less.

As described in the first embodiment, in the present invention, at least one of the lower clad layer 13 and the upper clad layer 14 has the first layer, for example, as shown in FIG. Things. Only one first layer may be provided in each clad layer, or a plurality of first layers may be provided with a nitride semiconductor containing no In or Al interposed therebetween. Further, the clad layer provided with the first layer may be composed of only the first layer,
As described in the embodiment, the cladding layer preferably has at least the first layer and the second layer. At this time, as shown in FIG. 4B, the first layer 32 and the second layer 31 may have a configuration having substantially the same band gap energy. As described above, by setting the band gap energy to be substantially the same as that of the second layer 31, it becomes possible to treat the element structure almost in the same manner as the conventionally used clad layer. Also, as shown in FIG.
May be configured such that the bandgap energy of the layer is smaller than that of the second layer.

The arrangement of the first layer in the cladding layer is, as shown in FIGS.
3 and 4, the structure may be arranged closer to the active layer than the second layers 25 and 32, as shown in FIGS. This makes it possible to suppress the deterioration of crystallinity and the occurrence of cracks due to AlGaN with the first layer as described above, but at this time, the first layer can be disposed either above or below the AlGaN layer. This effect can be obtained. That is, a nitride semiconductor containing Al such as AlGaN is used for the cladding layer or the second layer, or a light guide layer described later, and the first layer is arranged near these layers, so that the light guide layer 27 is formed. , 30, the structure is such that the first layer is provided between the light guide layer and the second layer, and acts on both the light guide layer and the second layer to improve the crystallinity. be able to. In particular, 375 which is the above short wavelength range
At emission wavelengths below nm, the light guide layer is made of AlGaN
Since a nitride semiconductor containing Al is preferably used, excellent device characteristics can be obtained by the above-described improvement in crystallinity.
Further, even in an element having no light guide layer, if a nitride semiconductor containing Al is used in the active layer, the first crystal located between the active layer and the second layer has the above crystal structure. The property improving effect acts on both the adjacent active layer and the second layer,
The element characteristics are improved.

In addition, as described in the third embodiment, in the cladding layer, the first layer is disposed far from the active layer, and the second layer is located near the active layer, ie, the first layer.
And a structure in which the second layer is disposed between the active layer and the active layer. In this structure, as described above, in an element structure having a waveguide sandwiched between both cladding layers, in the waveguide and each cladding layer sandwiching the waveguide, the light intensity distribution is widened to the inside of the cladding layer around the active layer. Because of the distribution, the first layer is arranged outside, so that a structure in which light loss is reduced can be obtained. In addition, as described in the third embodiment, the first layer having a lower refractive index than the second layer is arranged farther from the active layer than the second layer, so that FIG.
As shown in (b), a structure in which the refractive index increases in the cladding layers 13 and 14 as it approaches the active layer 28 and the waveguide can be achieved, and excellent light confinement in the waveguide can be realized. It becomes an element structure.

[Fifth Embodiment] As a fifth embodiment of the present invention, an upper light guide layer and a lower light guide layer are provided between the upper clad layer, the lower clad layer and the active layer, respectively. Specifically, as shown in FIG. 2, at least a lower light guide layer 27 is provided in the first conductivity type layer 11, and an upper light guide layer 30 is provided in the second conductivity type layer 13. The active layers 28 are sandwiched between the guide layers 27 and 30. A waveguide is formed by the upper and lower optical guide layers and the active layer therebetween. Further, a cladding layer is provided outside these light guiding layers, that is, a lower light guiding layer 27 is provided between the lower cladding layer 13 and the active layer 28, and the upper cladding layer 14 and the active layer 28 A structure in which the upper light guide layer 30 is provided therebetween. Further, as described later, a carrier confinement layer 29 can be provided in the light guide layer or between the light guide layer and the active layer.

In the fifth embodiment of the present invention, FIG.
As shown in (a), a structure in which an active layer 29, a lower light guide layer 27 in the first conductivity type layer 11, and an upper light guide layer 30 in the second conductivity type layer are provided as a waveguide. Has,
In particular, the device has a structure in which the above-described waveguide using the active layer having the emission wavelength of 375 nm or less is provided. The waveguide mainly guides light from the active layer, and the waveguide structure changes variously the luminous efficiency, the threshold current density, and other device characteristics in the laser device and the edge emitting device. The light guide layer is thus formed with the active layer interposed therebetween. The light guide layer is formed only on at least one of the first conductivity type layer and the second conductivity type layer, that is, the lower light guide layer or Although only the upper light guide layer may be used, preferably, by providing the light guide layers on both sides of the active layer, the threshold current density is reduced, and a high-output laser device is obtained.

The lower light guide layer 27 and the upper light guide of the present invention
For the nitride layer 30, a nitride semiconductor containing Al is used.
And as shown as band structure 41 in FIGS.
At least the well layer 1 in the active layer 28 having a quantum well structure.
Greater bandgap energy than
The difference in the refractive index between the layer 28 and the light guide layers 27 and 30 is reduced.
To form a waveguide structure. The light guide layer is shown in FIG.
The band gap energy is smaller than that of the barrier layer.
It may be large, as shown in FIGS.
No. Specifically, the composition of the light guide layer is In._βAl_α
Ga_1-α-βN (0 ≦ α, 0 ≦ β, α + β ≦ 1)
Is suitable for a wide wavelength range from ultraviolet to red.
Can be used. Preferably, In the short wavelength region, In
A nitride semiconductor containing no, ie, In composition
By using a nitride semiconductor with a ratio of 0, it is possible to include In
With a waveguide that prevents light absorption due to
Wear. In the long wavelength region of 430 nm or more, InGa
A nitride semiconductor containing In such as N can be used;
In the wavelength range between them, below 430 nm, GaN
Or In_xGa_1-xNitriding of N (0 <x <1) etc.
Semiconductors can be used, and In_xGa
_1-xN (0 ≦ x ≦ 1) multilayer film, superlattice structure
Can be. Furthermore, preferably Al_αGa_1-αN
By using (0 ≦ α ≦ 1), from the ultraviolet region to the red region
In the wavelength region of, especially 430 nm or less.
Waveguide that can be easily applied and combined with the first layer
The device structure can be formed with good crystallinity by using
You. In particular, light in the short wavelength range of 375 nm or less is guided.
To achieve this, preferably Al_αGa_1-αN (0 <α ≦
1) is used. This is because, in GaN,
Light, which is lost, and the threshold current density,
This is because the current-light output characteristics are deteriorated. Especially the light guy
Al composition ratio α of the doped layer is the photon energy of light emission of the active layer.
E_p, The band gap energy E of the light guide layer_gCompared to
In all cases, (E_g-E _p
≧ 0.05 eV). This
In the short wavelength region, light loss due to the guide layer is
This is because the waveguide is suppressed. Al_αGa_1-α
Using a light guide layer composed of N (0 <α ≦ 1),
By providing the second layer in the cladding layer, the nitride containing Al can be formed.
Of crystallinity by guide layer using nitride semiconductor
Device structure.

The lower light guide layer 27 and the upper light guide layer
30 is one or both of which are formed of a single film
Or a multilayer film. single
When forming an optical guide layer made of a nitride semiconductor film
Is a lower light guide sandwiching the active layer 28 as shown in FIG.
The layer structure 40 of the layer 27 and the upper light guide layer 30 is provided.
The band structure 41 is formed of an active layer or a well layer.
Bandgap energy is larger than that of such a light emitting layer
To be. Specifically, the above Al_αGa_{1 −α}N
(0 ≦ α ≦ 1) in the short wavelength region.
Al_αGa _1-αN (0 <α ≦ 1) is used. This
In this case, the Al composition ratio of the guide layer is appropriately adjusted according to the emission wavelength.
Change as appropriate.

The thicknesses of the lower light guide layer and the upper light guide layer are not particularly limited.
μm or less, preferably 20 nm or more and 1 μm
The range is as follows, and more preferably 50 nm or more and 300
nm or less. This tends to form a waveguide that functions as a guide layer at 10 nm or more and reduces the threshold current density at 20 nm or more.
This is because the threshold current density tends to be further reduced by setting the thickness to 0 nm or more. Further, when the thickness is 5 μm or less, it functions as a guide layer, and when it is 1 μm or less, the loss when light is guided tends to be reduced, and when it is 300 nm or less, the light loss tends to be further suppressed. Further, the lower light guide layer 27 and the upper light guide layer 30 may be formed with substantially the same film thickness, or may be formed with different film thicknesses.
In addition, the two guide layers may have different layer configurations, compositions, doping amounts, and the like, or may be substantially the same.
For example, there is a form in which the lower light guide layer is formed as a single film, the upper light guide layer is formed as a multilayer film, the two light guide layers have different layer configurations, and each light guide layer has a different composition. .

The light guide layer of the present invention may be composed of a nitride semiconductor of a multilayer film. In this case as well, it is preferable to use a nitride semiconductor containing no In particularly in a short wavelength region. the _{Al α Ga 1-α N (} 0 ≦ α ≦ 1)
It is preferable to use Al in the short wavelength region.
It is preferable to use _α Ga _1−α N (0 <α ≦ 1), and to use a multilayer film in which at least one nitride semiconductor layer having a different composition is used for each light guide layer using the nitride semiconductor. I do. Specifically, the light guide layers 27 and 30
A layer, B layer having a composition different from that of the A layer, where A layer, B layer
The layer is made of a nitride semiconductor. Thereby, the Al composition ratio may be different between the A layer and the B layer in each guide layer to form a multilayer structure having different band gap energies and different refractive indexes.

For example, in a structure in which a first conductivity type layer, an active layer, and a second conductivity type layer are laminated, one light guide layer has an A layer and a B layer, and the B layer is disposed on the active layer side. The structure in which the layer A is arranged at a position far from the active layer by arranging the layer has a structure in which the bandgap energy is reduced stepwise as it approaches the active layer. Specifically, by setting the Al composition ratio α2 of the B layer on the active layer side to be smaller than the Al composition ratio α1 of the A layer far from the active layer, and by setting α1> α2, a stepwise band structure is obtained. Since carriers are efficiently injected into the active layer in the waveguide and the refractive indexes in the active layer and the vicinity of the active layer are increased, a structure in which a large amount of light is distributed near the active layer in the waveguide can be obtained. As described above, when the light guide layer is formed into a multilayer film, the crystallinity tends to deteriorate when the Al composition ratio is increased, and it is difficult to form the light guide layer with a single film due to the deterioration in crystallinity. This is because, in the case or when the characteristics are deteriorated, it is possible to suppress deterioration of the crystallinity by forming a multilayer film. In addition, since the second layer is provided in the cladding layer, even when a nitride semiconductor including Al such as AlGaN is used for the guide layer, generation of cracks can be suppressed and an element structure can be formed. Further, contrary to the above α1> α2, α1 <α2 is satisfied, the band gap energy of the guide layer (B layer) close to the active layer is increased, the refractive index is reduced, and the distance between the guide layer (A layer and the fourth layer) is increased.
It is possible to increase the refractive index by increasing the refractive index. However, since the carrier injection and the light distribution are preferably improved, α1> α2 in the multilayer optical guide layer.
It is to be. When the light guide layer is a multilayer film, the light guide layer is not limited to the A layer and the B layer, and each light guide layer may be composed of three or more layers. That is, a guide layer may be formed by stacking a plurality of pairs with the A layer and the B layer as one pair.

Further, in the light guide layer of the present invention, FIG.
As shown in FIG. 2, a GRI composition-graded so that the band gap energy becomes smaller as approaching the active layer.
An N structure may be used. Specifically, the GRI is tilted by making the Al composition ratio α smaller, that is, by making the Al composition ratio α smaller as approaching the active layer.
An N-structure is provided, and carrier injection efficiency is improved. At this time,
In the composition gradient, the composition may be continuously gradient as shown in FIG. 4, or the composition may be discontinuously graded stepwise.
Also, for example, in a structure having a plurality of pairs in which the lower light guide layer A / B layers are alternately stacked, such as a superlattice multilayer structure, Al is made to have a composition gradient and the band becomes closer to the active layer. The gap energy may be reduced, and in this case, at least one of the layers, for example, only the A layer, may have a composition gradient, and all the layers constituting the pair, for example, the A layer and the B layer may be combined together. The composition may be gradient. Further, a composition gradient may be provided partially in the thickness direction of the light guide layer. Preferably, the composition injection gradient in all regions in the film thickness direction tends to improve carrier injection efficiency.

Further, in the light guide layer of the multilayer film, FIG.
As shown in the figure, the superlattice structure of the multilayer film may be used. By using the superlattice structure, deterioration of crystallinity due to the nitride semiconductor containing Al is suppressed, and a good crystalline waveguide is formed. be able to. Specifically, in the light guide layer, the layer A and the layer B are alternately laminated, and at least one of the layers is two or more layers, preferably each layer is two or more layers. Are a pair, and a plurality of pairs are laminated. At this time, the composition of the nitride semiconductor in each layer is the same as described above, but preferably, the A layer / B layer is made of Al _α1
Ga _1-α1 N (0 ≦ α1 ≦ 1) / Al _α2 Ga
_1-α2N (0 ≦ α2 ≦ 1, α1 ≠ α2), and in the above short wavelength region, _{Alα1Ga1 -α1N} (0 <α1 ≦ 1)
_{/ Al α2 Ga 1 -α2 N (} 0 <α2 ≦ 1, α1 ≠ α
By using 2), a waveguide is formed in which the loss of light is suppressed and the deterioration of crystallinity is also suppressed by the superlattice structure. In order for the light guide layer to have a superlattice structure, the thickness of each layer constituting the multilayer film is set to be a superlattice, and the film thickness differs depending on the composition and the combination of each layer. Is 10 nm or less, preferably 7.5 nm or less can maintain good crystallinity, more preferably 5 nm or less,
Better crystallinity can be obtained. Here, the use of the A layer and the B layer for the light guide layer has been described.
The light guide layer may be composed of a plurality of layers having different compositions such as a layer and a C layer having a different composition from the B layer.

Further, in the light guide layer of the present invention, it is preferable that impurities of each conductivity type be doped at least to improve the movement and injection of carriers. Any of a partially or partially doped form and a fully doped form may be used. In the light guide layer of the multilayer film, for example, in the lower light guide layer having the A layer and the B layer, both may be doped, or the doping amounts of the A layer and the B layer may be different. , And the other may be undoped. For example, in a superlattice multilayer structure such as a structure in which layers A and B are alternately laminated in the lower light guide layer, or a structure in which a plurality of layers are provided, preferably, modulation is performed by doping only one layer, for example, only the layer A. By doping, deterioration of crystallinity due to impurity doping can be suppressed. More preferably, by doping only a layer having a low Al composition ratio, a layer having good crystallinity can be doped, and deterioration of crystallinity due to impurity doping is suppressed, and activation by impurity doping is also good. Is preferable. This is because, for example, the A layer / B layer is made of Al _{α 1} G
a _1−α1 N (0 ≦ α1 ≦ 1) / Al _α2 Ga _1−α2
In the light guide layer having a superlattice multilayer structure of N (0 <α2 ≦ 1, α1 <α2), the B layer having a small Al composition ratio is doped with impurities, and the A layer is undoped.
The B layer having a small composition ratio has better crystallinity than the A layer. Therefore, by doping the layer having good crystallinity with impurities, good activation is realized, and an optical guide layer excellent in carrier movement / injection can be obtained. Become.

Further, with respect to the impurity doping of the light guide layer of the present invention, as shown in FIG. 6 as a change 42 of the doping amount, the doping amount of the impurity in the lower and upper light guide layers 27 and 30 is increased as approaching the active layer. Reducing the amount of doping or reducing the amount of doping in the region near the active layer compared to the region far from the active layer further reduces the loss of light in the waveguide, especially in the light guide layer, and improves the light emission. Can be realized, and the threshold current density and the drive current can be reduced. This is because, when light is guided in an impurity-doped region, light is lost due to absorption of light by the impurity. In addition to this, the waveguide has at least a structure in which the active layer 28 is sandwiched between the lower light guide layer 27 and the upper light guide layer 30 as described above. Light is confined in the waveguide by the structure sandwiched between the upper and lower cladding layers 25 and 30 having a smaller refractive index than the guide layer, and a large amount of light is distributed in the active layer and the vicinity of the active layer in the waveguide. Therefore, by reducing the amount of impurity doping in the region near the active layer, light loss in a region where a large amount of light is distributed is reduced, resulting in a waveguide with small light loss. Specifically, in the lower light guide layer and the upper light guide layer, when a region is separated by a half of the thickness of each layer and a region close to the active layer and a region far from the active layer are considered, the conductivity type impurity concentration in the region close to the active layer is determined. In other words, the impurity concentration in the region far from the active layer is made lower. Although the impurity concentration of the light guide layer is not particularly limited, it is specifically set to 5 × 10 ¹⁷ / cm ³ or less in a region near the active layer. Here, the impurity doping means
This means that the lower light guide layer is doped with a first conductivity type impurity and the upper light guide layer is doped with a second conductivity type impurity. Preferably, in the light guide layer, light loss can be reduced by undoping a region whose distance from the active layer is 50 nm or less, and more preferably undoping a region of 100 nm or less. Light loss, threshold current density, and drive current can be reduced.

[Sixth Embodiment] In a sixth embodiment of the present invention, the upper cladding layer is formed of the lower cladding layer In.
It is characterized by being smaller than the composition ratio. Specifically, when the first layer is provided on both cladding layers,
The purpose is to make the In composition ratio or the average composition of the second layer smaller in the upper cladding layer than in the lower cladding layer. At this time, the structure in which the first layer is provided in both the clad layers has been described. However, it is also possible to provide the first layer only in the lower clad layer and make the In composition ratio larger than that of the upper clad layer. This is because a nitride semiconductor containing In is mainly used for the active layer, and an upper cladding layer is provided on the active layer. Therefore, the growth conditions are limited to prevent decomposition of In, and It tends to be difficult to grow the first layer with good crystallinity as compared to the layer. Further, as shown in Examples described later, in a structure in which the first conductivity type layer is an n-type layer and the second conductivity type layer is a p-type layer,
In addition to the above reasons, since the first layer is mainly formed in an N ₂ atmosphere, it is difficult to grow the first layer with better crystallinity.
In addition, although it can be made p-type, the resistivity tends to increase, the Vf of the device tends to increase, and the use of a nitride semiconductor containing In for the upper cladding layer causes deterioration of device characteristics. easy. For this reason, it is preferable that the In composition ratio of the upper cladding layer is smaller than that of the lower cladding layer, and when the first layers are provided in both cladding layers, the first layer in the upper cladding layer is formed. The In composition ratio is set to be smaller than that of the first layer of the lower cladding layer, more preferably, the first layer is provided only in the lower cladding layer, and most preferably, the first layer is provided in the lower cladding layer. In addition, a nitride semiconductor containing In is not provided in the upper cladding layer.

Hereinafter, with respect to the element structure in each embodiment, layers other than the clad layer and the guide layer will be described. (Active Layer) As the active layer in the present invention, an active layer having a single or a plurality of light emitting layers and an active layer having a quantum well structure can be used. In these active layers or light emitting layers, nitride semiconductors containing In are preferably used, and specifically, Al _x In _y Ga _1-xy N (0 ≦
That is, a nitride semiconductor represented by x <1, 0 <y ≦ 1, 0 <x + y ≦ 1) is used. For example, at the emission wavelength from the ultraviolet region to red, In _x Ga _1-x N (0 <x
By preferably using ≦ 1), the emission wavelength can be changed by changing the In composition ratio.

In the present invention, preferably, a high output light emitting element is obtained by using an active layer having a quantum well structure. In the emission wavelength range of 375 nm or less,
A preferable quantum well structure has a well layer made of a nitride semiconductor containing at least In and Al, and has a barrier layer made of a nitride semiconductor containing Al. Specifically, the band gap energy of the well layer is 375 nm or less. At this time, the nitride semiconductor used for the active layer may be non-doped, n-type impurity-doped, or p-type impurity-doped. By providing such a structure, high output can be achieved in a nitride semiconductor device such as a laser device or a light emitting device. Preferably, by making the well layer undoped and the barrier layer being doped with n-type impurities, the laser device and the light-emitting device become devices with high output and high luminous efficiency. Here, the quantum well structure may be either a multiple quantum well structure or a single quantum well structure. Preferably, by using a multiple quantum well structure, it is possible to improve the output, lower the oscillation threshold, and the like. As the quantum well structure of the active layer, a structure in which at least one well layer and at least one barrier layer are stacked can be used. At this time, in the case of a quantum well structure, by setting the number of well layers to 1 or more and 4 or less, for example, in a laser element or a light emitting element, the threshold current can be reduced, and it is more preferable. By using a multiple quantum well structure in which the number of well layers is two or three, a high-output laser device or light-emitting device tends to be obtained.

Hereinafter, a well layer and a barrier layer which emit light in a short wavelength region of 375 nm or less in an active layer having a quantum well structure will be described.

(Well Layer) As the well layer in the present invention, it is preferable to use a nitride semiconductor containing In and Al, and the active layer has at least one well layer made of a nitride semiconductor containing In and Al. In the multiple quantum well structure, preferably, all the well layers have I
By using a well layer made of a nitride semiconductor containing n and Al, a light emitting element and a laser element having a shorter wavelength, high output, and high efficiency can be obtained. When the emission spectrum has a substantially single peak, this configuration is preferable. On the other hand, in a multicolor light-emitting element having a plurality of peaks, at least one well layer made of a nitride semiconductor containing In and Al is required. Thus, a light emission peak in a short wavelength range can be obtained, and it is possible to obtain a light emitting element of various emission colors or a light emitting device combined with a phosphor excited in the short wavelength range. At this time, when the elements of the multi-color light emission, the specific composition of the well _{layer, In α Ga 1-α N} (0 <α ≦
The use of 1) results in a well layer that enables good emission and oscillation from the ultraviolet region to the visible light region. At this time, the emission wavelength can be determined by the In mixed crystal ratio.

The well layer made of the nitride semiconductor containing In and Al according to the present invention has a wavelength range that is difficult for a conventional InGaN well layer, specifically, a wavelength around 365 nm, which is the GaN bad gap energy, or a wavelength around 365 nm. It is intended to obtain a shorter wavelength, and in particular, to emit light having a wavelength of 375 nm or less.
This is a well layer having a band gap energy capable of oscillating. This is because in a conventional InGaN well layer, Ga
When the bandgap energy of N is around 365 nm, for example, at 370 nm, it is necessary to adjust the In composition ratio to about 1% or less. It is difficult to obtain a light emitting element and a laser element with an output, and the In composition ratio is 1%.
In the following, it is also difficult to control the growth. In the present invention, by using a well layer made of a nitride semiconductor containing In and Al, the band gap can be increased by increasing the Al composition ratio x in the wavelength range of 375 nm where efficient light emission has conventionally been difficult. By increasing the energy and containing In on the other hand, it can be used for a light-emitting element and a laser element having good internal quantum efficiency and luminous efficiency.

Here, the specific composition of the nitride semiconductor containing In and Al used for the well layer is Al _x In.
_y Ga _1-xy N (0 <x <1, 0 <y <1, x + y
≦ 1). This is because, in a vapor phase growth method such as MOCVD used for growing a nitride semiconductor,
When the number of the constituent elements increases, a reaction between the constituent elements is likely to occur. For this reason, as described above, it is possible to use B, P, As, or the like to multiplex a quinary mixed crystal or more. Preferably, a quaternary mixed crystal of AlInGaN (x + y <1) is used to prevent the reaction between the elements and grow the crystal with good crystallinity. Here, the In composition ratio y is
By setting it to 0.02 or more, better luminous efficiency and internal quantum efficiency are realized as compared with the case where it is less than 0.02 as described above. Further, by setting y ≧ 0.03, the efficiency is further improved. Therefore, a light emitting element and a laser element having excellent characteristics can be obtained in a well layer having a wavelength of 375 nm or less, which is preferable. The upper limit of the In composition ratio y is not particularly limited. However, by setting y ≦ 0.1, deterioration of crystallinity due to containing In is suppressed, and more preferably, y ≦ 0.
By setting to 05, the well layer can be formed without deteriorating the crystallinity, and when a plurality of well layers are provided as in a multiple quantum well structure, the crystallinity of each well layer can be improved. Therefore, the In composition ratio y is preferably in the range of 0.02 or more and 0.1 or less, more preferably 0.03 or more and 0.05 or less.
The range is as follows, and it is preferably applied to the above quaternary mixed crystal of InAlGaN. Here, the Al composition ratio x is not particularly limited, and a desired band gap energy and a desired wavelength can be obtained by changing the Al composition ratio.

The Al _x In _y Ga _1-xy N of the present invention
FIG. 8 shows the relationship between the oscillation wavelength and the threshold current density with respect to changes in the In composition ratio y and the Al composition ratio x of the nitride semiconductor in the well layer composed of (0 <x <1, 0 <y <1, x + y <1). , 9. As shown in FIG. 8, the threshold current density J _th
Shows a downward curve from around 0.02,
It takes a local minimum value around the range of 0.05, and shows an increasing tendency in the region exceeding 0.05. Further, as shown in FIG. 8, the Al mixed crystal ratio x is within the range of x ≦ 0.1.
There is a tendency to increase due to an increase in the Al mixed crystal ratio x, and 0 <x ≦
The threshold current can be preferably reduced in the range of 0.6. Here, FIG. _{9, Al x In y Ga 1-} x-y N
(0 <x ≦ 1, 0 <y ≦ 1, x + y <1) and A
_{l u In v Ga 1-u} -v N (0 <u ≦ 1,0 ≦ v ≦
In the barrier layer of 1, u + v <1), the tendency of each characteristic is qualitatively shown, and the y-axis is an arbitrary unit. Here, the dependence of the threshold current density J _th and the wavelength λ on the In and Al mixed crystal ratios shown in FIGS. Measured for structure. As upper and lower cladding layers, Al _0.1 Ga _0.9 N having a thickness of 25 ° and Al _0.05 Ga _0.95 N having a thickness of 25 ° are alternately formed by 100.
A superlattice multilayer structure (500 °) is formed by laminating each layer. At this time, one of the superlattice layers is doped with Mg and Si as dopants in the p-side and n-side cladding layers, respectively, and undoped as upper and lower light guide layers. Al _0.04
Ga _0.96 N is formed to a thickness of _0.15 μm, and Al _0.15 In _0.01 Ga _0.84 N (200 °) is used as an active layer.
Barrier layer, well layer with a thickness of 100 °, Al _0.15 In
_0.01 Ga _{0.8 4} N and quantum well structure and barrier layer are laminated in (45 Å), Al mixed crystal ratio in FIG. 8 x (x = 0.0
3, 0.06, 0.08), the well layer is made of Al _x In _{0 . 04} Ga _0.96-x N and I in FIG.
n mixed crystal ratio y (y = 0.02, 0.03, 0.04, 0.
07), the well layer is made of Al _0.03 In _y
Ga _{0 . 97-yN} .

In the present invention, Al and In are preferably used.
Having a wavelength of 375 nm
The following band gap energy is provided. Therefore, the Al composition ratio x is set to 0.02 or more. In addition, wavelength 36, which is the band gap energy of GaN,
In the region of 5 nm or less, by setting x to 0.05 or more, good light emission and oscillation at short wavelengths can be achieved.

As the thickness of the well layer and the number of the well layers, the thickness and the number of the well layers can be arbitrarily determined. The specific film thickness is in the range of 1 nm or more and 30 nm or less. When the film thickness is less than 1 nm, it tends to be difficult to function well as a well layer. It is difficult to improve the crystallinity of the growth of the semiconductor, and the device characteristics are degraded. Preferably, the thickness is in the range of 2 nm or more and 20 nm or less, so that V
f. The threshold current density can be reduced. Further, from the viewpoint of crystal growth, when the thickness is 2 nm or more, a layer having relatively uniform film quality without large unevenness in film thickness can be obtained.
By setting the thickness to 0 nm or less, crystal growth can be performed while suppressing the generation of crystal defects. More preferably, by setting the thickness of the well layer to 3.5 nm or more, a high-output laser element or a light-emitting element tends to be obtained. It is thought that light-emitting recombination is performed with high luminous efficiency and internal quantum efficiency when a large amount of carriers are injected, as in a laser device driven by, and it is considered to be particularly effective in a multiple quantum well structure. Can be In a single quantum well structure, the film thickness is 5n.
By setting m or more, the same effect as above can be obtained. The number of well layers in the active layer is not particularly limited, and is 1 or more. At this time, when the number of well layers is 4 or more, if the thickness of each layer constituting the active layer becomes large, the active layer Since the overall film thickness becomes large and Vf is increased, it is preferable to keep the thickness of the active layer low by setting the thickness of the well layer to 10 nm or less. In the multiple quantum well structure, at least one of the plurality of well layers having a thickness in the above range is provided, and preferably, all the well layers are in the above range. Further, the thickness of each well layer may be different, or may be substantially the same.

The well layer of the present invention may be doped with a p-type impurity or an n-type impurity or may be undoped. The impurity to be doped into the well layer is preferably n
By making it a type impurity, it contributes to improvement of luminous efficiency. However, a nitride semiconductor containing In and Al is used for the well layer, and the crystallinity tends to deteriorate when the impurity concentration increases. Therefore, it is preferable that the impurity concentration be kept low to provide a well layer with good crystallinity. . Specifically, in order to maximize the crystallinity, the well layer is grown undoped. At this time, the impurity concentration is 5 × 10 ¹⁶ / cm ³ or less and substantially contains impurities. There is no well layer. When the well layer is doped with, for example, an n-type impurity, the n-type impurity concentration is 1
When doped in a range of 5 × 10 ¹⁸ / cm ³ or less and 5 × 10 ¹⁶ / cm ³ or less, deterioration in crystallinity can be suppressed and the carrier concentration can be increased, and the threshold current density and Vf can be reduced. Can be reduced. At this time, since the n-type impurity concentration of the well layer is almost the same as or smaller than the n-type impurity concentration of the barrier layer, light emission recombination in the well layer is promoted, and the light emission output tends to be improved. preferable. At this time, the well layer and the barrier layer may be grown undoped to form a part of the active layer. In a multiple quantum well structure in which a plurality of well layers are provided in the active layer, the impurity concentration of each well layer may be substantially the same or different.

In particular, when the device is driven with a large current (such as a high-output LD, high-power LED, or superluminescence diode), the well layer is undoped and contains substantially no n-type impurity. Carrier recombination in the well layer is promoted, and light emission recombination with high efficiency is realized. Conversely, when an n-type impurity is doped into the well layer, the carrier concentration in the well layer is high, so that light emission recombination is rather caused. The probability decreases, a drive current under a constant output, and a vicious cycle causing an increase in the drive current occur, and the reliability (device life) of the device tends to decrease. Therefore, in such a high-output device, the n-type impurity concentration of the well layer is set to at least 1 × 10
^By setting the concentration to ¹⁸ / cm ³ or less, and preferably to a concentration that does not substantially contain undoped or n-type impurities, a nitride semiconductor device that can be driven stably with high output can be obtained. Further, in a laser element in which a well layer is doped with an n-type impurity, the spectral width of the peak wavelength of laser light tends to be widened.
× 10 ¹⁸ / cm ³ or less, preferably 1 × 10 ¹⁷ / cm
³ or less.

(Barrier Layer) In the present invention, the composition of the barrier layer is to use a barrier layer made of a nitride semiconductor containing Al. Here, in the active layer of the present invention, at least one barrier layer in the active layer needs to be made of a nitride semiconductor containing Al, and all the barrier layers in the active layer are made of Al. Alternatively, a barrier layer made of a nitride semiconductor containing no Al may be provided in the active layer. The barrier layer needs to be a nitride semiconductor having a larger band gap energy than the well layer. In a region where the emission wavelength of the well layer is 375 nm or less, a nitride semiconductor containing Al is used for the corresponding barrier layer. Is preferred. As a barrier layer of a nitride semiconductor containing Al, preferably, Al _u In _v Ga
_1-uvN (0 <u ≦ 1, 0 ≦ v ≦ 1, u + v <1)
Is used. Specifically, for the barrier layer of a nitride semiconductor containing Al, a quaternary mixed crystal of AlInGaN and a ternary mixed crystal of AlGaN represented by the above composition formula can be used. Further, the Al composition ratio u of the barrier layer is larger than the Al composition ratio x of the well layer of the nitride semiconductor containing Al and In, and when u> x, sufficient band gap energy is provided between the well layer and the barrier layer. By providing the difference, a quantum well structure having good luminous efficiency as a laser element or a light emitting element is formed.

When the barrier layer contains In (v>
0), the In composition ratio v is preferably Al _u I
_{n v Ga 1-u-v} N (0 <u <1,0 <v <1, u +
When v <1), a favorable barrier layer can be obtained by setting the In composition ratio v ≦ 0.3. This is because, unlike the well layer, the light emitting layer is not a light emitting layer, and thus does not directly affect the light emission efficiency due to a large In composition ratio. Also, 0.
If it is larger than 3, the crystallinity of the quaternary mixed crystal is greatly deteriorated, and the crystallinity of the adjacent well layer is affected. More preferably, the content is set to 0.1 or less to suppress the deterioration of crystallinity, and more preferably, the range of 0.05 or less can be applied. This is because the In composition ratio v
Is more than 0.1, the reaction between Al and In is accelerated during the growth, the crystallinity is deteriorated, and a good film is not formed. A barrier layer can be formed with good crystallinity. In addition, I of the well layer
By setting y ≧ v for the n composition ratio y and the In composition ratio v of the barrier layer, the reaction between Al and In can be suppressed in both the well layer and the barrier layer, so that a quantum well structure with good crystallinity can be formed. You. Further, as described above, the In composition ratio of the barrier layer can be applied to a wider composition ratio than that of the well layer, and since the band gap energy difference is mainly provided by the Al composition ratio, v ≧ y can be satisfied. With such an In composition ratio, the critical film thickness of the well layer and the barrier layer can be changed, the film thickness can be set relatively freely in the quantum well structure, and the active layer having desired characteristics can be obtained. Can be designed.

In the active layer having the quantum well structure, the barrier layers may be formed alternately with the well layers, or a plurality of barrier layers may be provided for one well layer. Specifically, the number of barrier layers sandwiched between the well layers is two or more, and a structure in which barrier layers and well layers of a multilayer film are alternately stacked may be provided.

Similarly to the well layer described above, the barrier layer may be doped with a p-type impurity or an n-type impurity or may be non-doped. Preferably, the barrier layer is doped with an n-type impurity. That is, it is undoped or undoped. At this time, when the barrier layer is doped with, for example, an n-type impurity, the concentration is at least 5%.
X 10 ¹⁶ / cm ³ or more.
Specifically, for example, in the case of an LED, 5 × 10
N in the range of ¹⁶ / cm ³ or more and 2 × 10 ¹⁸ / cm ³ or less
Type impurity, and a higher output LE
5 × 10 ¹⁷ / cm ³ or more for D and high power LD
× 10 ²⁰ / cm ³ or less, preferably 1 × 10
It is preferable that the doping is performed in the range of ¹⁸ / cm ³ or more and 5 × 10 ¹⁹ / cm ³ or less. When the barrier layer is doped at such a high concentration, the well layer substantially contains an n-type impurity. Preferably, it is not grown or grown undoped. When the barrier layer is doped with an n-type impurity,
All the barrier layers in the active layer may be doped, or a part may be doped and a part may be undoped. When doping some barrier layers with n-type impurities, in the active layer,
It is preferable to dope the barrier layer disposed on the n-type layer side, specifically, the n-th barrier layer B counted from the n-type layer side.
By doping n (n = 1, 2, 3,...), electrons are efficiently injected into the active layer, and a device having excellent luminous efficiency and internal quantum efficiency is obtained. This applies not only to the barrier layer but also to the well layer. For example, when the well layer and the barrier layer are doped, the nth barrier layer B _n (n = 1, 2, 3 ...), m-th well layer W
_The above effect tends to be obtained by doping _m (m = 1, 2, 3,...), that is, by doping from the side close to the n-type layer.

Further, as shown in the examples described later, when an Mg-doped p-side electron confinement layer is provided, particularly when provided in contact with an active layer and / or a barrier layer, Mg is diffused. When an n-type impurity is doped into the p-side barrier layer disposed closest to the p-type layer in the layer, both conductive impurities are doped, and the function of the active layer tends to be deteriorated. Therefore, when the Mg-doped p-side electron confinement layer is provided, preferably, this p-side barrier layer can be avoided by substantially not including an n-type impurity.
It is set to be less than × 10 ¹⁶ / cm ³ .

The thickness of the barrier layer is not particularly limited, but is preferably 50 nm or less to constitute the quantum well structure, and preferably ranges from 1 nm to 30 nm similarly to the well layer, which is 30 nm or less. By suppressing the deterioration of crystallinity by setting the content to 1 nm or more,
This is because the film thickness can function well as a barrier layer.
More preferably, the thickness is 2 nm or more and 20 nm or less, whereby a relatively uniform film is formed by being 2 nm or more, and the function of the barrier layer is more preferably provided.
By setting the thickness to not more than nm, the crystallinity becomes good.

In the active layer having the quantum well structure of the present invention,
In a preferred embodiment, the quaternary mixed crystal Al _x In is used.
_y Ga _1-xy N (0 <x <1, 0 <y <1, x + y
<1) and a quaternary mixed crystal Al _u In _v Ga
_1-uvN (0 <u <1, 0 <v <1, u + v <1)
Or ternary mixed crystal _{Al u Ga 1-u N (} 0 <u <1)
And one or more pairs of barrier layers made of Specifically, as shown as the active layer 28 in FIG.
This is to have at least one GaN well layer 1 and at least one InAlGaN or AlGaN barrier layer 2, whereby a well layer of an In-containing nitride semiconductor has excellent internal quantum efficiency and light emission efficiency. Layer and A
By adjusting the Al composition ratio of the nitride semiconductor containing l, a well layer capable of emitting light in a short wavelength range of 375 nm or less can be obtained. In addition, by using InAlGaN or AlGaN for the barrier layer 2 having a band gap energy larger than that of the well layer 1, an excellent barrier layer can be provided even in the short wavelength region.

(Carrier Confinement Layer <P-side Electron Confinement Layer>) In the present invention, as shown in the band structure 41 of FIGS. May be provided. As shown in the figure, the light guide layers 27 and 3 are used as in the case of a laser device and an edge emitting device.
In the case of a structure having the cladding layers 13 and 14, it may be provided between the light guide layers 27 and 30 and the active layer 27 or as a part of the active layer or the light guide layer. Here, the carrier confinement layer is used to confine carriers in the active layer or the well layer.
Due to the increase in current density, it is possible to prevent carriers from overflowing the active layer, and it is possible to achieve a structure in which carriers are efficiently injected into the active layer. In particular,
As shown in FIG. 4, carriers from the first conductivity type layer are confined by the carrier confinement layer 29b disposed on the second conductivity type layer 12 side, and the carrier confinement layer 29 on the first conductivity type layer side is confined.
Due to a, carriers from the second conductivity type layer are confined. The carrier confinement layer is preferably provided on at least one side. As shown in Example 1, the first conductivity type layer is formed of n
In a device having a p-type and a second conductivity type layer, it is preferable to provide a carrier confinement layer at least on the p-type layer side. This is because, in the nitride semiconductor, since the diffusion length of electrons is longer than the diffusion length of holes, electrons easily overflow the active layer, and therefore the carrier confinement layer 29 for confining electrons is placed on the p-type layer side. With the provision, a high-power laser element or light-emitting element can be obtained. Hereinafter, an example will be described in which the p-type layer is provided as a p-side electron confinement layer as a carrier confinement layer. However, it is applicable to the n-type layer side by replacing the conductive type layer. In particular, it is preferable to provide at least a p-side electron confinement layer, because electrons have a longer carrier diffusion length than holes and easily overflow the active layer.

[0079] As the p-side electron confinement layer, which uses a nitride semiconductor including Al, specifically Al _c
Ga _1-c N (0 <c <1) is used. At this time, the Al composition ratio c needs to have a sufficiently large band gap energy (offset) than the active layer so as to function as a carrier confinement layer, and at least 0.1 ≦ c <1. And preferably in the range of 0.2 ≦ c <0.5. This is because if c is less than 0.1, the laser element does not function as a sufficient electron confinement layer, and if c is more than 0.2, electron confinement (carrier confinement) is sufficiently performed, and carrier overflow occurs. In addition, when it is 0.5 or less, the growth can be performed while suppressing the occurrence of cracks to a low level. More preferably, when c is 0.35 or less, the crystal can be grown with good crystallinity. Further, when the light guide layer is provided, it is preferable that the carrier having a band gap energy larger than the light guide layer is used as the confinement layer, and when the light guide layer has the clad layer, the carrier is substantially equal to or larger than the clad layer. The purpose is to use carriers having band gap energy as confinement layers. This is because the confinement of carriers requires a nitride semiconductor having a higher mixed crystal ratio than the cladding layer for confining light. This p-side electron confinement layer can be used in the nitride semiconductor device of the present invention. In particular, when driving with a large current and injecting a large amount of carriers into the active layer like a laser device, the p-side Compared to a case without an electron confinement layer, it enables more effective confinement of carriers and can be used not only for a laser element but also for a high-output LED.

The thickness of the carrier confinement layer of the present invention is at least 100 nm or less, preferably 40 nm or less. This is because the nitride semiconductor containing Al has a higher bulk resistance than other nitride semiconductors not containing Al, and the Al mixed crystal ratio of the p-side electron confinement layer is set higher as described above. So 1
When provided in the element exceeding 00 nm, the layer becomes extremely high-resistance, and causes a large increase in the forward voltage Vf. When it is 40 nm or less, the rise of Vf can be suppressed low, More preferably, the thickness can be further reduced to 20 nm or less, and carriers from the p-side can be efficiently injected into the active layer by a tunnel effect. Here, when the lower limit of the film thickness of the p-side electron confinement layer is at least 1 nm or more, preferably 5 nm or more, it functions well as electron confinement. here,
The carrier confinement layer may be formed by a single film or a multilayer film having different compositions.

In the nitride semiconductor device of the present invention, when only the clad layer is provided without providing the optical guide layer, the carrier is sufficiently confined between the active layer and the clad layer as described above. If there is a large band offset, it is not necessary to provide a carrier confinement layer separately from the cladding layer, but when the cladding layer is arranged away from the active layer as in a structure having an optical guide layer. It is preferable to provide a carrier confinement layer between the active layer and the cladding layer, preferably near the active layer. This is because if the carrier confinement layer is provided at a position distant from the active layer, the effect of suppressing the overflow of the carrier is lost. Specifically, the distance between the active layer and the p-side electron confinement layer (carrier confinement layer) is set to 100 nm or less to function as carrier confinement, and more preferably 500 °.
By performing the following, good carrier confinement becomes possible. When the carrier confinement layer is arranged outside the active layer, the carrier is most efficiently confined in the active layer by arranging the layer most preferably in contact with the active layer. When it is arranged inside the active layer, it can be provided as a barrier layer or a part thereof, and specifically, at the position closest to each conductivity type layer in the active layer, that is, the outermost layer in the active layer. By arranging, in the well layer inside the active layer,
Carriers are efficiently injected.

The p-side electron confinement layer (carrier confinement layer) of the present invention may be undoped or doped with a p-type impurity (impurity of each conductivity type). Preferably, impurities of each conductivity type are doped. For example, p-type impurities are doped in the p-side electron confinement layer, which increases carrier mobility and lowers Vf. That's why. Further, when driving with a large current such as a laser element or a high power LED, it is preferable to dope at a high concentration in order to increase the mobility of carriers. The specific doping amount is at least 5 × 10
^By doping ¹⁶ / cm ³ or more, preferably 1 × 1
0 ¹⁸ / cm ³ or more, and in the case of the device driven by large current, it is 1 × 10 ¹⁸ / cm ³ or more, preferably 1 × 10 ¹⁹ / cm ³ or more. Although the upper limit of the amount of p-type impurities is not particularly limited, 1 × 1
0 ²¹ / cm ³ or less. However, when the amount of the p-type impurities increases, the bulk resistance tends to increase, and as a result, Vf increases. Of the p-type impurity. Further, it is also possible to form a carrier confinement layer by undoping and to dope by impurity diffusion from an adjacent layer.

When a p-type carrier confinement layer is provided on the n-side, there is no need to provide a large band offset between the active layer and the barrier layer as in the case of the p-side electron confinement layer. This is because, when a voltage is applied to the element, the offset for confining electrons becomes small and a confinement layer of a nitride semiconductor having a large Al composition ratio is required. It is not necessary to increase the Al composition ratio as much as the confining layer. In particular,
With the n-side barrier layer disposed most n-side in the active layer,
It can function as a hole confinement layer. In particular, when the film thickness is 10 nm or more, it has an excellent hole confinement function. That is, as shown in the embodiment, by increasing the thickness of the n-side barrier layer 2a as compared with the other barrier layers, the function of confining carriers can be suitably brought out. This is because, in the multiple quantum well structure, since the other barrier layers 2b and 2c are sandwiched between the well layers, increasing the film thickness may prevent carriers from being efficiently injected into the well layers. On the other hand, since the n-side barrier layer 2a is formed without being sandwiched between the well layers, a good active layer structure is obtained by strengthening the function of confining carriers. This n-side barrier layer is preferably the outermost layer in the active layer, so that carrier confinement functions effectively. The upper limit of the film thickness is not particularly limited. Therefore, it may be formed by a multilayer film. Similarly, in a single quantum well structure,
By making the n-side barrier layer 2a function as carrier confinement, carriers can be suitably injected into the well layer.

In the nitride semiconductor laser device and the edge emitting device of the present invention, as shown in the embodiment, after forming a ridge as a striped waveguide, an insulating film serving as a buried layer is formed on the side surface of the ridge. I do. At this time, a material other than SiO 2 is used as a material of the second protective film as the buried layer,
An oxide containing at least one element selected from the group consisting of Ti, V, Zr, Nb, Hf, and Ta;
It is desirable to form at least one of SiN, BN, SiC and AlN, and among them, it is particularly preferable to use oxides of Zr and Hf, BN and SiC. Furthermore,
As the buried layer, a semi-insulating, i-type nitride semiconductor, a conductivity type opposite to that of the ridge portion, and in this embodiment, an n-type nitride semiconductor can be used, and a nitride containing Al such as AlGaN can be used. By providing a refractive index difference by a semiconductor or by functioning as a current blocking layer, lateral light confinement is realized, and by providing a light absorption coefficient difference by a nitride semiconductor containing In, the optical characteristics of the laser element are improved. Is realized. . In addition, ions such as B and Al are implanted without providing a ridge by etching or the like to form a non-implanted region in a stripe shape.
A structure in which a current flows is also possible.

The ridge width is 1 μm or more and 3 μm or more.
By setting m or less, laser light having an excellent spot shape and beam shape can be obtained as a light source of the optical disk system.

[0086]

Embodiment 1 Hereinafter, as an embodiment, a laser device structure as shown in FIG. 1 and a laser device using a nitride semiconductor with respect to the waveguide structure shown in FIG. 1 will be described. Here, an n-type nitride semiconductor is formed as the first conductivity type layer, and a p-type nitride semiconductor is formed as the second conductivity type layer. However, the present invention is not limited to this, and conversely, the first conductivity type layer is formed. The structure may be such that the layer is p-type and the second conductivity type layer is n-type.

Here, in this embodiment, a GaN substrate is used, but a heterogeneous substrate different from a nitride semiconductor may be used as the substrate. As a heterogeneous substrate, for example, C plane, R
Sapphire, spinel (insulating substrate such as MgAl ₂ O ₄ , SiC (6
H, 4H, 3C), ZnS, ZnO, GaAs,
Si, and oxide substrates lattice-matched with nitride semiconductors, etc.
A nitride semiconductor can be grown and is conventionally known, and a substrate material different from the nitride semiconductor can be used. Preferred heterosubstrates include sapphire and spinel. In addition, the heterogeneous substrate may be off-angle, and in this case, it is preferable to use a substrate that is off-angled in a step-like manner, because the growth of the underlying layer made of gallium nitride is excellent in crystallinity. Further, when a heterogeneous substrate is used, a nitride semiconductor serving as a base layer before forming an element structure is grown on the heterogeneous substrate, and then the heterogeneous substrate is removed by a method such as polishing to form a single substrate of the nitride semiconductor. The element structure may be formed as
A method of removing different kinds of substrates may be used. In addition to the GaN substrate,
A substrate of a nitride semiconductor such as AlN may be used. Also,
A nitride semiconductor substrate can be used as the substrate.

When a heterogeneous substrate is used, an element structure is formed via a buffer layer (low-temperature growth layer) and a base layer made of a nitride semiconductor (preferably GaN), and the growth of the nitride semiconductor is good. It will be. In addition, as an underlayer (growth substrate) provided on a heterogeneous substrate, ELOG (E
If a nitride semiconductor grown laterally overgrowth (pitaxially) and a laterally grown layer are used, a growth substrate having good crystallinity can be obtained. As a specific example of the ELOG layer, a mask region formed by growing a nitride semiconductor layer on a heterogeneous substrate and providing a protective film on which a nitride semiconductor is difficult to grow, and a nitride semiconductor layer are grown. The non-mask area to be
The nitride semiconductor is grown in the stripe direction, and the nitride semiconductor is grown from the non-mask region. In addition to the growth in the film thickness direction, the lateral growth is performed, so that the nitride semiconductor also grows in the mask region. And the like. In another embodiment, an opening may be provided in a nitride semiconductor layer grown on a heterogeneous substrate, and a layer may be formed by growing laterally from the side surface of the opening.

(Substrate 101) As a substrate, a nitride semiconductor grown on a heterogeneous substrate, GaN in this embodiment, was grown as a thick film (100 μm), and then the heterogeneous substrate was removed.
An 80 μm GaN nitride semiconductor substrate is used.
The detailed method of forming the substrate is as follows. A heterogeneous substrate made of sapphire whose main surface is 2 inches φ and C-plane is M
It was set in an OVPE reaction vessel, the temperature was set to 500 ° C., and trimethylgallium (TMG), ammonia (NH
₃ ), a low-temperature growth buffer layer of GaN
The substrate is grown with a thickness of 0 °, and then the temperature is increased to grow undoped GaN with a thickness of 1.5 μm to form an underlayer. Next, a plurality of stripe-shaped masks are formed on the surface of the underlayer, and a nitride semiconductor,
In this embodiment, GaN is selectively grown to form a nitride semiconductor layer (lateral growth layer) formed by growth accompanied by lateral growth (ELOG), and then 100 μm thick by HVPE. Is grown, and the heterogeneous substrate, the buffer layer, and the underlayer are removed to obtain a nitride semiconductor substrate made of GaN.

At this time, the mask at the time of selective growth is made of SiO ₂
Consisting of: mask width 15 μm, opening (window) width 5 μm
By so doing, threading dislocations can be reduced. Specifically, threading dislocations are reduced in a region grown in the lateral direction, such as the upper part of the mask, and the film is formed by film growth substantially in the mask opening, so that there is no change in threading dislocations. Is a layer in which a large area and a small area are distributed.
For the formation of a thick nitride semiconductor layer, the HVPE method is preferable because the growth rate can be increased. When a thick film is formed by HVPE, each nucleus grown from the generated nuclei grows in the film thickness direction. There is a tendency for a three-dimensional growth form in which domains are combined to form a film. In such a case,
Since threading dislocations also propagate with the nucleus growth, the threading dislocations distributed by the lateral growth layer tend to be dispersed.
As nitride semiconductors grown by HVPE, GaN,
When AlN is used, a thick film can be grown with good crystallinity.

Subsequently, on the GaN substrate, a lateral growth layer similar to the above is further formed to form an underlayer (not shown).
And

(Buffer Layer 102) On the nitride semiconductor substrate 101 and the underlayer, the temperature was set to 1050 ° C.
G (trimethyl gallium), TMA (trimethyl aluminum), with _{ammonia, Al 0.05} Ga
_A buffer layer 102 of _0.95 N is grown to a thickness of 4 μm. The Al _x Ga _1-x N (0 <x ≦ 1) layer functions as a buffer layer between the GaN nitride semiconductor substrate and the GaN nitride semiconductor substrate and can reduce pits.
The same applies to the n-side contact layer of GaN.

Specifically, when the lateral growth layer or the substrate formed using the same is GaN, the nitride semiconductor Al _a Ga _1-a N having a smaller coefficient of thermal expansion than GaN is used.
By using the buffer layer 102 composed of (0 <a ≦ 1), pits can be reduced. Preferably, it is provided on GaN, which is a lateral growth layer of a nitride semiconductor.
Further, when the Al mixed crystal ratio a of the buffer layer 102 is 0 <a <0.
With a value of 3, the buffer layer can be formed with good crystallinity. This buffer layer may be formed as an n-side contact layer. After forming the buffer layer 102, an n-side contact layer represented by the composition formula of the buffer layer is formed, and the buffer layer 102 and n The side contact layer 104 may have a buffer effect. That is, the buffer layer 102 is formed of a nitride semiconductor substrate using lateral growth, or between the lateral growth layer formed thereon and the device structure, or between the active layer in the device structure and the lateral growth layer (substrate). ) Or a lateral growth layer (substrate) formed thereon, more preferably at least one substrate side in the device structure, between the lower cladding layer and the lateral growth layer (substrate). The provision of the layers or more can reduce pits and improve element characteristics.

In the case where the n-side contact layer is used as a buffer layer, the Al mixed crystal ratio a of the n-side contact layer is set to 0.1 so as to obtain a good ohmic contact with the electrode.
It is preferably set to 1 or less. The buffer layer provided on the first nitride semiconductor layer or the lateral growth layer formed thereon is grown at a low temperature of 300 ° C. or more and 900 ° C. or less in the same manner as the buffer layer provided on the heterogeneous substrate described above. Alternatively, the crystal may be grown at a temperature of 800 ° C. or more and 1200 ° C. or less. Preferably, when a single crystal is grown at a temperature of 800 ° C. or more and 1200 ° C. or less, the above-described pit reduction effect tends to be obtained. This buffer layer may be doped with n-type or p-type impurities or may be undoped, but is preferably formed undoped in order to improve the crystallinity. When two or more buffer layers are provided, they can be provided by changing the n-type and p-type impurity concentrations and the Al mixed crystal ratio.

As described above, the AlGaN layer is used as the buffer layer,
When a contact layer or the like is provided between the substrate and the lower cladding layer, the first layer of the present invention is provided in the lower cladding layer to reduce the pits due to the AlGaN layer and to prevent cracks due to the first layer. The prevention effect is obtained.

Next, on the base layer made of a nitride semiconductor, layers forming an element structure are laminated. Here, n-side contact layers 103 to n-side light guide 1 are used as first conductivity type layers.
06, and as the second conductivity type layer, the p-side electron confinement layer 1
08 to the p-side contact layer 111 are provided.

(N-side contact layer 103) Next, an n-side contact layer made of Al _0.05 Ga _0.95 N doped with Si at 1050 ° C. using TMG, TMA, ammonia and silane gas as an impurity gas on the obtained buffer layer 102. 103 is grown to a thickness of 4 μm.

(N-side cladding layer [lower cladding layer 1
3]) Here, a first layer 104 and a second layer 105 are formed as the n-side cladding layer 13. <First Layer 104 (25)> Next, TMG, TMA,
Using TMI (trimethylindium) and ammonia,
The temperature was set to 800 ° C. and Al _0.14 In _0.06 Ga
_A first layer 104 of _0.8 N is grown to a thickness of 0.05 μm.

<Second Layer 105 (26)>
To 1050 ° C, and add TMA, TMG and
Undoped Al_0.12Ga
_0.88A layer of N is grown to a thickness of 25 °
Stop TMA and use silane gas as impurity gas
No, Si is 5 × 10¹⁸/ Cm³Doped Al
_0.02Ga _0.98B layer made of N with a thickness of 25 °
Let it grow. Then, the operation of alternately stacking the A layer and the B layer
Is repeated 120 times each to laminate the A layer and the B layer,
A second layer (superlattice structure) having a thickness of 0.6 μm
The layer 105 is grown.

(N-side light guide layer 106 [lower light guide layer 27]) Next, at the same temperature, using TMG and ammonia as source gases, Si-doped Al _0.03 Ga
_0.97 N with a film thickness of 0.15 μm and n-side light guide layer 106
Is formed, and the light guide layer is provided as a single film.

(Active Layer 107) Next, the temperature is set to 800 ° C.
And TMI (trimethyl indium) as a raw material gas,
Using TMG and TMA, Si-doped Al _0.1 Ga
_0.9 N barrier layer on which undoped In
The well layer made of _0.03 Al _0.02 Ga _{0.9 5} N, as shown in FIG. 3, stacked in this order of the barrier layer 2a / well layer 1a / barrier layer 2b / well layer 1b / barrier layer 2c. At this time, the barrier layer 2a is set at 200 ° and the barrier layers 2b and 2c are set at 40 °.
The well layers 1a and 1b are formed with a thickness of 70 °. The active layer 107 has a multiple quantum well structure (MQW) having a total thickness of about 420 °.

(P-side electron confinement layer 108 (carrier confinement layer 29)) Next, at the same temperature,
A, TMG and ammonia, C as impurity gas
Al _0.3 doped with 1 × 10 ¹⁹ / cm ^{3 of} Mg using p2Mg (cyclopentadienyl magnesium)
The p-side electron confinement layer 108 made of Ga _0.7 N is 10 nm
It grows with the film thickness of. This layer is not necessarily provided, but when provided, it functions as electron confinement and contributes to lowering of the threshold.

(P-side light guide layer 109 (upper light guide layer)
30)) Next, the temperature is raised to 1050 ° C.
Mg-doped Al using TMG and ammonia
_0.03Ga _0.97N at a film thickness of 0.15 μm
The side light guide layer 109 is formed, and the light guide layer is formed by a single film.
I can.

The p-side light guide layer 109 is doped with Mg by diffusion of Mg from adjacent layers such as the p-side electron confinement layer 108 and the p-side cladding layer 109. It can be an Mg-doped layer.

<P-side cladding layer 110 (upper cladding layer 14)> Subsequently, undoped Al at 1050 ° C.
_An A layer made of _0.12 Ga _0.88 N is grown to a thickness of 25 °, and then Mg-doped Al using Cp ₂ Mg.
An operation of growing a B layer of _0.02 Ga _0.98 N to a thickness of 25 ° and alternately stacking the A layer and the B layer 100 times is repeated to form a superlattice multilayer film having a total thickness of 0.5 μm. p
The side cladding layer 110 is grown. Here, FIG.
As shown in (a), the p-side cladding layer 14 is
Only the layer 31 is formed. (P-side contact layer 112) Finally, at 1050 ° C.,
On the p-side cladding layer 110, 1 × 10 ²⁰ / c of Mg
m ³ made of doped p-type GaN p-side contact layer 1
12 is grown to a thickness of 150 °. p-side contact layer 112 is p-type _{In x Al y Ga 1-x} -y N (0 ≦
x, 0 ≦ y, x + y ≦ 1), and preferably GaN doped with a p-type impurity or AlGaN having an Al composition ratio of 0.3 or less provides the most preferable ohmic contact with the p electrode 120. The best ohmic contact is possible, most preferably GaN. Since the contact layer 112 is a layer for forming an electrode, it is desirable that the contact layer 112 has a high carrier concentration of 1 × 10 ¹⁷ / cm ³ or more. If it is lower than 1 × 10 ¹⁷ / cm ^3, it tends to be difficult to obtain an electrode and a preferable ohmic. Further, when the composition of the contact layer is GaN, it becomes easy to obtain a preferable ohmic material with the electrode material. After the reaction is completed, the wafer is placed in a nitrogen atmosphere in a reaction vessel.
Annealing is performed at 00 ° C. to further reduce the resistance of the p-type layer.

After the nitride semiconductor is grown and the respective layers are stacked as described above, the wafer is taken out of the reaction vessel, a protective film made of SiO ₂ is formed on the surface of the uppermost p-side contact layer, and RIE ( Etching is performed by SiCl ₄ gas using reactive ion etching) to expose the surface of the n-side contact layer 103 on which the n-electrode is to be formed, as shown in FIG. In order to etch a nitride semiconductor deeply, SiO ₂ is optimal as a protective film.

Next, a ridge stripe is formed as the above-mentioned stripe-shaped waveguide region. First, the top p
Almost all of the side contact layer (upper contact layer)
After a first protective film 161 made of Si oxide (mainly SiO ₂ ) is formed to a thickness of 0.5 μm by a VD apparatus, a mask of a predetermined shape is applied on the first protective film.
CF ₄ by RIE (Reactive Ion Etching)
A first protective film 161 having a stripe width of 1.6 μm is formed by photolithography using a gas. At this time,
The height (etching depth) of the ridge stripe is such that the p-side contact layer 112, the p-side cladding layer 110, and a part of the p-side light guide layer 109 are etched, and the film thickness of the p-side light guide layer 109 becomes zero. It is formed by etching to a depth of 0.1 μm.

Next, after the formation of the ridge stripe, a Zr oxide (mainly ZrO ₂ ) is formed on the first protective film 161 from above.
A second protective film 162 formed on the first protective film,
A film having a thickness of 0.5 μm is continuously formed on the p-side light guide layer 109 exposed by the etching.

After forming the second protective film 162, the wafer is
Heat treatment at 0 ° C. When a material other than SiO ₂ is formed as the second protective film in this manner, after forming the second protective film, the temperature is set to 300 ° C. or higher, preferably 400 ° C. or higher, and lower than the decomposition temperature of the nitride semiconductor (1200 ° C.). The heat treatment makes it difficult for the second protective film to dissolve in the dissolved material (hydrofluoric acid) of the first protective film. Therefore, it is more desirable to add this step.

Next, the wafer is immersed in hydrofluoric acid, and the first protective film 161 is removed by a lift-off method. As a result, the first protective film 161 provided on the p-side contact layer 112 is removed, and the p-side contact layer is exposed. As described above, as shown in FIG. 1, the second protective film (embedded layer) 1 is formed on the side surface of the ridge stripe and the plane continuous to the ridge stripe (the exposed surface of the p-side light guide layer 109).
62 are formed.

As described above, after the first protective film 161 provided on the p-side contact layer 112 is removed, the exposed p-side contact layer 112 is removed as shown in FIG.
A p-electrode 120 made of Ni / Au is formed on the surface of the substrate.
However, the p electrode 120 has a stripe width of 100 μm,
As shown in FIG. 1, it is formed over the second protective film 162. After the formation of the second protective film 162, the n already exposed
On the surface of the side contact layer 103, a striped n-electrode 121 made of Ti / Al is formed in a direction parallel to the stripe.

Next, a desired region for providing an extraction electrode is masked on the p and n electrodes on the surface exposed by etching to form an n electrode, and a dielectric multilayer film made of SiO ₂ and TiO ₂ is formed. After providing 164, Ni and Ni are formed on the p and n electrodes.
-Ti-Au (1000-1000-8000)
Extraction (pat) electrodes 122 and 123 are provided, respectively. At this time, the width of the active layer 107 is 200 μm.
(The width in the direction perpendicular to the resonator direction), and a dielectric multilayer film made of SiO ₂ and TiO ₂ is also provided on the resonator surface (reflection surface side). After forming the n-electrode and the p-electrode as described above, the M-plane of the nitride semiconductor (M-plane of GaN, (11-100), etc.) in a direction perpendicular to the stripe-shaped electrode.
Then, the wafer is divided into bars, and the bar-shaped wafer is further divided to obtain laser devices. At this time, the resonator length is 650 μm. When forming a bar shape, cleavage is performed in the waveguide region sandwiched between the etching end surfaces, and the obtained cleavage surface may be used as a resonator surface. Alternatively, a pair of resonator faces may be formed, one of which is an etching end face and the other is a cleavage face. In addition, a reflection film made of a dielectric multilayer film is provided on the resonance surface of the etching end face, but a reflection film may be provided on the cavity surface of the cleavage surface after cleavage. Even when the bar-shaped wafer is further divided, the cleavage plane of the nitride semiconductor (single substrate) can be used, and the nitride semiconductor (GaN) perpendicular to the cleavage plane when cleaved into a bar is hexagonal. The chip may be taken out by cleavage at the M-plane and the A-plane ({1010}) approximated by the above formula, and the A-plane of the nitride semiconductor may be used when cleaving into a bar.

At this time, the reflection film is made of SiO.₂, Ti
O₂, ZrO₂, ZnO, Al₂O ₃, MgO, poly
At least one member of the group consisting of
/ 4n (λ is the wavelength, n is the refractive index of the material)
A multilayer film or a single layer may be used.
At the same time, it can be used as a surface protective film to prevent the end face of the resonator from being exposed.
May work. To function as a surface protection film, λ
/ 2n. Also, the element processing step
And without forming an etched end face, that is, an n-electrode type
Exposing only the formation surface (n-side contact layer), a pair of cleavages
A laser element having a surface as a resonator surface may be used.

As the obtained laser element, a nitride semiconductor element which continuously oscillates at a wavelength of 370 nm at room temperature can be obtained. Further, although a nitride semiconductor containing Al such as AlGaN is used for the light guide layer and the cladding layer, the device structure is formed without cracks by providing the first layer on the n-side cladding layer. Further, in the n-side cladding layer, since the first layer has a smaller refractive index than the first layer disposed on the active layer side, good light confinement is realized, and light is transmitted to the substrate side. Reduce leakage; F. P.
Is obtained. Further, n-side light guide layer of the p-side, the average composition ratio of Al is composed of 0.03 of AlGaN, and the band gap energy E _g of the upper optical guide layer and the lower light guide layer, the laser light (the active layer the difference between the photon energy _{E p} of emission _wavelength), E g -E _p is 0.
A waveguide having a voltage of 05 eV or more is formed.

In this embodiment, the contact layer below the lower cladding layer uses AlGaN, which is a nitride semiconductor containing Al, but the first layer in the lower cladding layer can improve the crystallinity. The generation of cracks can be suppressed. Further, the upper cladding layer and the contact layer thereon (p
Similarly, when a contact layer of a nitride semiconductor containing Al is used for the side contact layer, the crystallinity can be improved by providing the second layer as the upper cladding layer. That is, the upper and lower clad layers between the active layer and the contact layer of the nitride semiconductor containing Al are provided with the second
By providing such a layer, it is possible to obtain an element structure in which deterioration of crystallinity due to use of a nitride semiconductor containing Al such as AlGaN for the contact layer is suppressed. At this time, the first
Similarly to the case of reducing the In mixed crystal ratio of the second layer between the first layer and the second layer, the nitride semiconductor including Al of the contact layer is also made smaller than the In mixed crystal ratio of the first layer. It is preferable to use AlGaN that does not contain In.

[Example 2] A laser device is obtained in the same manner as in Example 1, except that the active layer is formed as follows.

(Active Layer 107) Si-doped In
_0.01 Al _0.1 Ga _0.89 N barrier layer, on which undoped In _0.03 Al _0.02 Ga
_The well layer made of _0.95 N is _divided into a barrier layer 2a and a well layer 1a.
/ Barrier layer 2b / well layer 1b / barrier layer 2c. At this time, as shown in FIG.
障壁, barrier layers 2b and 2c having a thickness of 40 ° and well layers 1a,
1b is formed with a thickness of 70 °. The active layer 107 has a multiple quantum well structure (MQW) having a total thickness of about 420 °.

As in the case of the first embodiment, a nitride semiconductor device which continuously oscillates at a wavelength of 370 nm at room temperature is obtained.

[Embodiment 3] In the embodiment 1, the active layer,
Other than forming the light guide layer and the cladding layer as follows,
A laser device is obtained in the same manner as in the first embodiment.

(N-side cladding layer (lower cladding layer 2
5)) A first layer 104 and a second layer 105 are formed as n-side cladding layers. <Second layer 105> Al _0.3 In _0.06 Ga
_A first layer 104 of _0.64 N is grown to a thickness of 0.05 μm. <First layer 104> Undoped Al having a thickness of 25 °
A layer of _0.3 Ga _0.7 N and S at a thickness of 25 °
Al _0.2 Ga doped with 5 × 10 18 / cm 3
_The operation of alternately laminating the B layer of _0.8 N is repeated 120 times each to laminate the A layer and the B layer. The layer 106 is formed.

(N-side light guide layer 106 (lower light guide layer)
27)) Si-doped Al_0.1Ga _0.9Consisting of N
A layer with a thickness of 25 °, Al_0.03Ga_0.1Consisting of N
B layers having a thickness of 25 ° are alternately and repeatedly laminated 30 times,
0.15 μm-thick n-side light guide consisting of a superlattice multilayer film
Grow in layer 106.

(Active Layer 107) Si-doped Al _0.2
A barrier layer made of Ga _0.8 N, and a well layer made of undoped In _0.03 Al _0.02 Ga _0.95 N on the barrier layer 2a / well layer 1a / barrier layer 2b / well layer 1
b / barrier layer 2c. At this time, as shown in FIG. 7, the barrier layer 2a is 200 °, and the barrier layers 2b and 2c are 40 °.
The well layers 1a and 1b are formed with a thickness of 70 °. The active layer 107 has a multiple quantum well structure (MQW) having a total thickness of about 420 °.

(P-side light guide layer 109 (upper light guide layer 30)) Mg-doped Al _0.1 Ga _{0 .} And A layer of thickness 25Å made of _{9 N,} repeatedly stacked 30 times and B layer having a thickness of 25Å made of Al 0.1 _{Ga 0.9} N, alternately,
A p-side light guide layer 109 having a superlattice multilayer structure with a thickness of 0.15 μm is grown.

(P-side cladding layer 110 (upper cladding layer 14)) Undoped Al _0.3 Ga _{0 .} A consisting of ₇ N
A layer is grown to a thickness of 25 ° and Mg doped Al _0.1 G
a _{0. A} B layer of 9N is grown to a thickness of 25 °
The operation of alternately laminating the layers and the B layers is repeated 100 times to grow the p-side cladding layer 110 composed of a superlattice multilayer film having a total thickness of 0.5 μm. Here, a second layer is provided as a p-side cladding layer as in the first embodiment.

As the obtained laser device, a nitride semiconductor device which continuously oscillates at a room temperature at a wavelength of 350 nm in a wavelength region shorter than that of Example 1 can be obtained. Further, n-side light guide layer of the p-side, the average composition ratio of Al is composed of 0.2 of AlGaN, and the band gap energy E _g of the upper optical guide layer and the lower light guide layer, the laser photon energy E
the difference between _p, E p -E _g is, waveguide becomes more 0.05eV is formed.

[Embodiment 4] In Embodiment 1, FIGS.
As shown in (1), the following second layer 31 and first layer 32 are provided as p-side cladding layers.

(P-side cladding layer [upper cladding layer 1
4]) <Second layer 110> Undoped Al _0.12 Ga
An operation of growing an A layer made of _0.88 N to a thickness of 25 ° and a B layer made of Mg-doped Al _0.02 Ga _0.98 N to a thickness of 25 °, and alternately stacking the A layer and the B layer. 10
The second layer 110 composed of a superlattice multilayer film having a total film thickness of 0.5 μm is grown by repeating 0 times. <First layer 111> Al _0.14 In _0.06 Ga
_A first layer 111 of _0.8 N is grown to a thickness of 0.05 μm.

The obtained laser device has a device structure in which cracks are suppressed in the p-side layer by providing the first layers on both clad layers, as compared with the first embodiment. The first layer 111 becomes a high-resistance layer, and Vf is larger than that of the first embodiment.

Example 5 A laser device is manufactured in the same manner as in Example 1 except that the first layer 104 in the n-side cladding layer has a superlattice multilayer structure as shown below. <First layer 104 (25)> Al _0.2 In _0.03
A layer of Ga _0.77 N with a thickness of 25 °, Al
Thickness 25 of _0.08 In _0.09 Ga _0.83 N
The layer B of Å is alternately stacked 100 times, and the first layer 104 is grown to a thickness of 0.5 μm. The first layer 104 obtained in this manner is a nitride semiconductor having an Al average composition and an In average composition substantially similar to those of the first embodiment.
With the superlattice structure, it can be formed with better crystallinity than in the first embodiment.
Is formed, the light leaking to the p-side is suppressed, and a laser device having excellent light confinement is obtained, and it becomes possible to prevent the deterioration of the far-field pattern due to the light leaking from the substrate side.

Embodiment 6 A laser device is obtained in the same manner as in the first embodiment, except that the light guide layer is formed with the following composition gradient as shown in FIG.

(N-side Light Guide Layer 106 (Lower Light Guide Layer 27)) Al _x Ga ₁ -xN is formed to a thickness of 0.15 μm.
The n-side light guide layer 106 whose composition is changed in the film thickness direction by changing from 05 to 0.01 is provided. At this time, the n-side light guide layer is formed by undoping the first region having a thickness of 50 nm and the remaining region having a thickness of 0.1 μm (the active layer side having a thickness of 0.1 μm).
(a region of μm).

(P-side light guide layer 109 (upper light guide layer 30)) Al _x Ga ₁ -xN is formed with a thickness of 0.15 μm.
The p-side light guide layer 109 having a composition gradient in the film thickness direction is provided while changing from 1 to 0.05. Here, the p-side light guide layer has an initial film thickness of 0.1 μm (active layer side 0.1 μm).
Is formed by undoping, and the remaining region having a thickness of 50 nm is formed by doping with Mg.

Although the obtained laser device has almost the same average composition of Al as that of the first embodiment, as shown in FIG. The efficiency of injection into the active layer is improved, and the internal quantum efficiency tends to be improved. Further, since the undoped region is provided on the side (active layer side) near the active layer in the light guide layer, the waveguide structure has a low light loss due to impurity doping, and the threshold current density tends to decrease. is there.

Example 7 A laser device is obtained in the same manner as in Example 1, except that the light guide layer is formed with the following composition gradient as shown in FIG.

(N-side light guide layer 106 (lower light guide layer 27)) A film made of Al _x Ga _1-x N and having a thickness of 25 °
_Layer, consisting of _{Al y Ga 1-y N (} x> y) film thickness 25Å
Layer B is alternately repeated 30 times to form a layer having a thickness of 0.15
An n-side light guide layer is formed with a superlattice multilayer structure of μm.
At this time, the Al composition ratio x is changed from 0.05 to 0.03 as the substrate grows, the Al composition ratio y is fixed at 0.015, and the n-side light guide layer 106 having a composition gradient is provided. At this time, the n-side light guide layer has an initial film thickness of 0.1 μm.
The region A is formed by undoping both the A layer and the B layer, and the remaining region having a thickness of 50 nm (the region 50 nm on the active layer side) is
Modulation doping is used in which only the layer is doped with Si and the B layer is undoped.

(P-side light guide layer 109 (upper light guide layer 30)) A film made of Al _x Ga ₁ -xN and having a thickness of 25 °
_Layer, consisting of _{Al y Ga 1-y N (} x> y) film thickness 25Å
Layer B is alternately repeated 30 times to form a layer having a thickness of 0.15
The p-side light guide layer 109 is formed with a superlattice multilayer structure of μm. Here, the p-side light guide layer has an initial thickness of 50 nm.
In the (area of 50 nm on the active layer side), both the A layer and the B layer are formed by undoping, and in the remaining area of 0.1 μm, only the A layer is formed by Mg doping and the B layer is undoped.

Although the obtained laser device has an Al average composition substantially the same as that of Example 4, the superlattice structure improves the crystallinity and the device characteristics. On the other hand, since the undoped region of the light guide layer is smaller than that of the sixth embodiment, light loss increases,
The threshold current density tends to increase slightly.

[0138]

According to the present invention, the nitride semiconductor device is formed of AlGa.
When a nitride semiconductor containing Al such as N is used for a guide layer, a cladding layer, a contact layer, and the like, it is possible to suppress deterioration of crystallinity and generation of cracks and to improve characteristics of a laser element, an edge emitting element, and the like. it can. Also,
An active layer and a waveguide structure capable of laser oscillation in a short wavelength range of 375 nm or less can be obtained. In particular, InA
In the well layer of lGaN, the In mixed crystal ratio is set to 0.03 to
By setting the Al composition ratio to be in the range of 0.05 to form a forbidden band width of a desired emission wavelength and obtaining a light-emitting element and a laser element in a short wavelength range, the internal quantum efficiency and the emission efficiency are excellent. Element.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating a laser device structure according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a layered structure of an element according to one embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a laminated structure and an energy band diagram of an element according to an embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating an energy band according to an embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating an energy band according to an embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating an energy band according to an embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view illustrating a stacked structure of an active layer according to one embodiment of the present invention.

FIG. 8 is a schematic diagram illustrating the dependence of the Al composition ratio on the threshold current density and the wavelength under pulse oscillation in the active layer according to the present invention.

FIG. 9 is a schematic diagram illustrating the dependence of the In mixed crystal ratio on the threshold current density and wavelength under pulse oscillation in the active layer according to the present invention.

[Brief description of reference numerals]

DESCRIPTION OF SYMBOLS 1 ... Well layer, 2 ... Barrier layer, 11 ... First conductivity type layer, 12 ... Second conductivity type layer, 13 ... Lower cladding layer, 14 ... Upper cladding layer, 21 ... substrate, 2
2 ... buffer layer, 23 ... underlying layer, 24, 33
Contact layer 25 first layer 26 second layer 27 lower light guide layer 28 active layer 29 carrier confinement layer 30 ..Upper light guide layer, 31 upper clad layer, 101 substrate, 102 buffer layer, 103 n-side contact layer, 104 ... n-side clad layer (first layer) ), 1
05 ... n-side cladding layer (second layer), 106 ...
n-side light guide layer, 107 ... active layer, 108 ... p
Side electron confinement layer, 109... P side light guide layer, 110
... p-side cladding layer (second layer), 111 ... p-side cladding layer (first layer), 112 ... p-side contact layer, 120 ... p electrode, 121 ... n Electrode, 122
... p pad electrode, 123 ... n pad electrode, 16
2 ... second protective film (embedded layer), 164 ... insulating film

Claims (13)

[Claims] 1. A nitride semiconductor device having an active layer between a first conductivity type lower cladding layer and a second conductivity type upper cladding layer, wherein at least one of the lower cladding layer and the upper cladding layer is provided. , A first layer having a nitride semiconductor containing Al and In is provided. 2. An emission wavelength λ of the active layer is λ ≦ 375.
2. The nitride semiconductor device according to claim 1, wherein 3. A method according to claim 1, wherein at least one of the lower cladding layer and the upper cladding layer includes a first layer having a nitride semiconductor containing Al and In, and Al having an In mixed crystal ratio smaller than that of the first layer. The nitride semiconductor device according to claim 1, further comprising: a second layer having a nitride semiconductor. 4. The method according to claim 1, wherein the first layer is Al _x In _y Ga.
_1-xy N (0 <x <1, 0 <y <1, x + y <1)
Has, the second layer is _{Al u Ga 1-u N (} 0 <u ≦
4. The nitride semiconductor device according to claim 3, wherein 1) is satisfied. 5. The method according to claim 1, wherein the In composition ratio y of the first layer is 0.0
5. The lens according to claim 3, wherein 1 ≦ y ≦ 0.3.
The nitride semiconductor device as described in the above. 6. The nitride semiconductor device according to claim 3, wherein the second layer is provided closer to the active layer than the first layer. 7. The nitride semiconductor device according to claim 6, wherein a refractive index n _{1 of} said _first layer and a refractive index n _{2 of} said _second layer are n ₂ ≦ n _1. . 8. The nitride semiconductor device according to claim 1, wherein said first layer is formed of superlattice multilayer films having different compositions. 9. The method according to claim 1, further comprising a lower light guide layer and an upper light guide layer between the lower clad layer and the active layer and between the upper clad layer and the active layer, respectively. 9. The nitride semiconductor device according to item 8. Wherein said lower optical guide layer, an upper optical guide _{layer, Al α Ga 1- α N (} 0 <α ≦ 1) nitride semiconductor device according to claim 9, wherein the consist. 11. The nitride semiconductor device according to claim 1, wherein said upper cladding layer has a smaller In composition ratio of said lower cladding layer. 12. The semiconductor device according to claim 1, wherein the active layer includes a nitride semiconductor containing Al and In.
The nitride semiconductor device as described in the above. Wherein said active layer and having a quantum well structure, the well _{layer, Al x In y Ga 1-} x-y N (0 <
x <1, 0 <y <1, x + y <1) and the barrier layer is A
_{l u In v Ga 1-u} -v N (0 <u ≦ 1,0 ≦ v ≦
13. The nitride semiconductor device according to claim 12, wherein u + v <1).