JP2002261393A - Nitride semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a threshold current in a nitride semiconductor device where an active layer having a nitride semiconductor containing In is held between p- and n-type cladding layers, and, especially, light emission is made at a wavelength of at least 440 nm. SOLUTION: The nitride semiconductor device has first and second nitride semiconductor layers 31 and 32 between the n- and p-type cladding layers 25 and 30 and the active layer 12, the first semiconductor layer 31 is made of the nitride semiconductor containing In, and the second one 32 is made of that without any In, thus achieving asymmetric waveguide structure, avoiding deterioration in crystallizability caused by providing the nitride semiconductor containing In at the side of a p-type layer 13 and loss of light due to In by using the second semiconductor layer 32, increasing a refractive index in the waveguide by the first nitride semiconductor layer 31, and hence reducing the density of the threshold current.

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 device (LED) and a laser diode device (LD), a light receiving device such as a super photoluminescent diode, a solar cell, an optical sensor, a transistor, and a power device. Nitride semiconductors (In _x Al _Y Ga _{1 -XYN} , 0 ≦ X, 0 ≦ Y, X + Y ≦
In particular, the present invention relates to a nitride semiconductor device using 1), in particular, a nitride semiconductor device having an active layer containing a nitride semiconductor layer containing In having an optical wavelength of 440 nm or more, and a semiconductor device sandwiched between optical confinement cladding layers. The present invention relates to an edge emitting device and a laser device having a waveguide structure.

[0002]

2. Description of the Related Art At present, 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 high-capacity and high-density information, such as a DVD. For this reason, semiconductor laser devices using nitride semiconductors have been actively studied. In addition, a semiconductor laser device using a nitride semiconductor is considered to be capable of oscillating in a wide range of visible light from ultraviolet to red. It is expected to be a wide variety of light sources, such as optical networks. 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.

A light emitting element, a light receiving element, and the like using a nitride semiconductor have a structure in which an active layer is formed using a nitride semiconductor containing In. Is important in improving the device characteristics.

In order to obtain long-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, increasing the In mixed crystal ratio can increase the emission wavelength. In the case of an edge emitting device or a 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, and the inside of the waveguide sandwiched between the upper and lower cladding layers is reduced. By increasing the refractive index of the laser, light is efficiently confined in the waveguide, and as a result, contributes to a reduction in threshold current density in the laser element.

Conventionally, in a nitride semiconductor device having such a cladding layer, as a structure for obtaining long-wavelength light emission of 440 nm or more, for example, in a laser device, SGaN using InGaN for the guide layer and AlGaN for the cladding layer is used.
A CH structure has been proposed.

However, as the long wave lengthens, A
The difference in the refractive index between lGaN and InGaN becomes smaller, that is, a loss occurs due to light absorption in the guide layer in the waveguide, and the threshold current increases. Further, when the upper cladding layer is made of a p-type nitride semiconductor and the lower cladding layer is made of an n-type nitride semiconductor, p-type InGaN is used for the upper guide layer. worse compared to, adversely affect the device characteristics, even worse still crystallinity of the upper cladding layer of AlGaN formed thereon, according to this, shortening of element characteristics becomes a problem.

[0007]

According to the present invention, there is provided a nitride semiconductor device having a structure in which an active layer is sandwiched between an upper cladding layer and a lower cladding layer, wherein the light wavelength is 440 nm or more. In the waveguide sandwiched between the cladding layers, it is necessary to suppress the light absorption, efficiently confine the light in the waveguide including the active layer, and form a device structure with better crystallinity. It is.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a nitride semiconductor device having excellent device characteristics such as threshold current density and good crystallinity.

That is, the semiconductor device of the present invention can achieve the object of the present invention by the following constitution.

[0010] The active layer has a structure sandwiching between p-type layer and the n-type layer, p-type layer has a p-type cladding layer, an n-type layer n
In the nitride semiconductor device having the n-type cladding layer, the active layer has a nitride semiconductor containing In, and the n-type cladding layer and the active layer have an In mixed crystal ratio of z> 0. A second nitride semiconductor layer having a first nitride semiconductor layer and an In mixed crystal ratio u of z> u between the p-type cladding layer and the active layer.
Characterized by having a nitride semiconductor layer. With this configuration, the n-type layer is provided with the first nitride semiconductor layer having a large In mixed crystal ratio z (z> u), and the p-type layer is more mixed with the In nitride crystal than the first nitride semiconductor layer. becomes the ratio u (u = 0 included) the second nitride semiconductor layer is smaller structure provided in the waveguide structure described below, asymmetric structure sandwiching the active layer of the waveguide is formed. According to another aspect of the present invention, there is provided a nitride semiconductor device having a structure in which an active layer is sandwiched between a p-type clad layer and an n-type clad layer, wherein the active layer includes a nitride semiconductor containing In. the first has a nitride semiconductor layer, a second nitride in mixed crystal ratio of 0 between the p-type cladding layer and the active layer made of a nitride semiconductor containing in between the active layer It has a semiconductor layer. With this configuration, by using a nitride semiconductor containing no In or having a low In mixed crystal ratio (second nitride semiconductor layer) between the active layer and the p-type cladding layer,
By suppressing the deterioration of crystallinity and using a nitride semiconductor containing In (a first nitride semiconductor layer) between the active layer and the n-type cladding layer, a waveguide sandwiched between both cladding layers can be formed. An appropriate refractive index difference can be provided between the clad layer and the clad layer. Particularly in the nitride semiconductor device with a light emission over a long wavelength 440nm in the active layer, such as a low laser device having a threshold current can be obtained, an excellent nitride semiconductor device in the element characteristics. This is because, in a waveguide sandwiched between p-type and n-type cladding layers, in order to guide light having a long wavelength of 440 nm or more with an appropriate spread, an In layer used for an active layer is used.
It has been considered that it is preferable to provide a nitride semiconductor containing In less than or equal to the In mixed crystal ratio of the nitride semiconductor containing, for example, an optical guide layer, which will be described later, in the waveguide, but doped with Mg which is a p-type impurity. The nitride semiconductor containing In described above has a problem of deteriorating device characteristics because crystallinity is greatly deteriorated. That is, in the present invention, the waveguide sandwiched between the p-type clad layer and the n-type clad layer has the first nitride semiconductor layer and the second nitride semiconductor layer having different compositions and sandwiching the active layer. it is, then an asymmetrical waveguide structure, a nitride semiconductor device having excellent device characteristics in the long wavelength is obtained. In addition, as the n-type and p-type cladding layers, a cladding layer for light confinement is provided so as to form such a waveguide structure, and in an element having no waveguide, as a carrier confinement layer. A functioned structure can also be used.
For such a cladding layer, the band gap energy should be larger than that of the active layer. If the active layer has a quantum well structure, the band gap energy should be larger than that of the well layer. Increase the gap energy.

Further, in the element structure in which an active layer is provided between the first nitride semiconductor layer in the n-type layer and the second nitride semiconductor layer in the p-type layer, Among the barrier layers in the active layer, an n-side barrier layer (2a) disposed closest to the n-type layer side, a p-side barrier layer (2c) disposed closest to the p-type layer side, At least one well layer made of a nitride semiconductor containing In is provided between the barrier layer (2a) and the p-side barrier layer (2b), and the n-type impurity concentration of the p-side barrier layer (2c) is n. N of the side barrier layer (2a)
It is preferable to make the configuration smaller than the type impurity concentration. This is because, as described later, when the p-side barrier layer (2c) serves as a carrier injection port and the p-side barrier layer (2c) is heavily doped with n-type impurities, holes are injected into the active layer. It tends to be inhibited the, n than n side barrier layer (2a)
The function of the n-side and p-side barrier layers can be made different by reducing the type impurity concentration, and the carrier injection can be made good. On the other hand, the n-side barrier layer (2a) can have a structure in which carrier injection from the n-type layer is promoted by making the n-type impurity concentration higher than that of the p-side barrier layer. Also, the n-type impurity concentration of the p-side barrier layer (2c) may be close to or in contact with the p-type layer, so that diffusion of the p-type impurity may occur. 2c) to n
When formed by impurity doping, n-type, since a barrier layer having a p-type impurity, carrier injection function of the p-side barrier layer (2c) tends to decrease. Therefore, in such a case, if the n-type impurity concentration of the p-side barrier layer (2c) is preferably lower than the p-type impurity concentration, such a decrease in function can be avoided. In any case, the p-side barrier layer preferably has a low n-type impurity concentration.
Specifically, by setting it to less than 5 × 10 ¹⁶ / cm ³ ,
The function of the p-side barrier layer (2c) can be improved.

In the nitride semiconductor device according to the present invention, the p-type layer may include a nitride containing Al between an active layer and a second nitride semiconductor layer or between an active layer and a p-type cladding layer. it is preferred that the p-side electron confinement layer made of a semiconductor. The p-side electron confinement layer functions as a layer for confining carriers from the n-type layer in the active layer, and when the p-type cladding layer is a light confinement layer, the p-type cladding layer is more active than the p-type cladding layer. A structure in which the p-side electron confinement layer disposed nearby functions mainly as a carrier confinement and the cladding layer functions mainly as a light confinement can be used for an edge emitting device and a laser device. In an element in which the p-type cladding layer does not need to function as light confinement, for example, in a light-emitting element, the structure is such that the p-type cladding layer and the p-side carrier confinement layer confine carriers.
As the p-side electron confinement layer, the band gap energy is made larger than that of the active layer as in the case of the cladding layer. It is also preferable to increase the band gap energy. When the p-type cladding layer is a light confinement layer, the barrier can be increased by increasing the bandgap energy as compared with the p-type cladding layer as shown in the embodiment, thereby enabling efficient electron confinement. On the other hand, when the Al mixed crystal ratio increases, the resistance value of the p-side electron confinement layer described later tends to increase. In such a case, the Al mixed crystal ratio and the band gap energy are reduced. This is preferable because the structure can be made smaller than the p-type cladding layer to suppress the heat generated by the high-resistance layer and enhance the function of the active layer.

Preferably, the p-side electron confinement layer is provided in contact with the active layer or with a buffer layer interposed therebetween, so that a structure having an enhanced electron confinement function can be obtained. For the buffer layer, as described later, a large piezoelectric field due to a nitride semiconductor containing Al and a nitride semiconductor further containing Al are provided near the nitride semiconductor containing In used for the active layer and the well layer. The active layer is formed so as to suppress an adverse effect on the active layer due to internal stress caused by the internal stress, and to obtain suitable crystallinity as an underlayer during growth. As a specific composition of the buffer layer, as described later, it is preferable that the buffer layer be composed of GaN or a nitride semiconductor containing Al having an Al mixed crystal ratio smaller than that of the p-side electron confinement layer. Further, it has been shown that the adverse effect of such a p-side electron confinement layer on the active layer, particularly on the well layer, can be avoided by increasing the distance between them, but the buffer layer also has
Similar to the p-side barrier layer (2c), such a function as a spacer can be provided. That is, a well layer (1b) provided between the n-side barrier layer (2a) and the p-side barrier layer (2b) is provided closest to the p-side electron confinement layer in the active layer. With a configuration in which the distance between the well layer (1b) and the p-side barrier layer is 100 ° or more, a device having excellent element characteristics can be obtained. What determines the distance of the well layer and (1b) and p-side barrier layer, which is determined by a layer interposed between them, in particular p-side barrier layer, active layer and p-side electron This is a buffer layer interposed between the confinement layer and the device. By adjusting the thickness of these layers, the element characteristics can be improved. The upper limit of this distance is, as described later, 400 degrees or less. Further, when the p-side barrier layer (2c) is made of a nitride semiconductor containing In,
Similarly to the first nitride semiconductor layer, the refractive index in the vicinity of the waveguide, particularly the active layer, is increased to increase the refractive index difference between the waveguide and the cladding layer for confining light. An element structure excellent in a light-emitting element can be formed. The second nitride semiconductor layer, the buffer layer, and the p-side barrier layer (2c)
The difference between the p-side electron confinement layer and the layer interposed between the well layer (1b) is that the p-side electron confinement layer provided near the active layer and the p-side electron confinement layer provided near the active layer when the element is biased. Due to the formation of the n-junction, the buffer layer and the p-side barrier layer (2c) arranged closer to the active layer than the pn junction are
This is because the adverse effect of providing a nitride semiconductor containing In on the p-type layer side tends to be avoided.

It is preferable that the n-side barrier layer (2a) and / or the p-side barrier layer (2c) have the outermost structure in the active layer. 2
a) It is preferable because the function of the p-side barrier layer (2c) can be enhanced.

The p-type clad layer and the n-type clad layer are
It is characterized by having a nitride semiconductor containing Al. With this configuration, it is possible to provide a large difference in the refractive index between the waveguide sandwiched between the two cladding layers and each cladding layer. Thus, a nitride semiconductor device having excellent characteristics can be obtained. Where A
The preferred nitride semiconductor containing l, by using the nitride semiconductor In mixed crystal ratio containing no In in 0, excellent crystallinity can be provided a larger refractive index difference, further Al _x Ga ₁ It is more preferable to use a nitride semiconductor represented by _-xN (0 <x ≦ 1).

The active layer has a quantum well structure having a well layer composed of a nitride semiconductor containing In, and the In nitride crystal ratio of the first nitride semiconductor layer is smaller than the In alloy crystal ratio of the well layer. the features. With this configuration, by forming an active layer having a quantum well structure, a light emitting recombination is promoted, a threshold current is reduced, an output is improved, and a nitride semiconductor having excellent device characteristics is provided, as compared with a case without a quantum well structure. An element is obtained. Further, by making the In mixed crystal ratio of the nitride semiconductor used for the first nitride semiconductor layer smaller than that of the well layer, the band gap energy difference between the well layer and the well layer can be increased, and the injection of carriers can be improved. This leads to improvement in device characteristics. In addition, since In has an effect of absorbing and scattering light in light guiding, a first nitride semiconductor layer of a nitride semiconductor having a low In mixed crystal ratio and a second nitride not containing In are included. By using the nitride semiconductor layer, a nitride semiconductor element in which loss of light is suppressed and threshold current and drive current are reduced is obtained. Here, even when the active layer does not have a quantum well structure, the same effect can be obtained by reducing the In mixed crystal ratio of the first nitride semiconductor layer from the In mixed crystal ratio of the nitride semiconductor used for the active layer. can get.

[0017] The semiconductor device is characterized in that the first nitride semiconductor layer is provided in contact with an active layer. With this configuration, as shown in FIGS. 5 and 6, the band gap energy difference is reduced stepwise from the n-type cladding layer to connect to the active layer, and carriers are efficiently injected into the active layer and the well layer. Thus, a nitride semiconductor device having excellent device characteristics can be obtained. Further, as described above, since light is lost due to In, by providing the first nitride semiconductor layer in contact with the active layer, the light distribution in the waveguide overlaps with the active layer. It is considered that the structure has a peak, and a large amount of light is distributed in the active layer, functions as a layer almost similar to the active layer, and can reduce light loss in the waveguide. . On the other hand, as shown in FIG. 8 and FIG. 10, the In mixed crystal ratio z of the first nitride semiconductor layer is set to
Is substantially equal to or smaller than the In mixed crystal ratio v, that is, when z ≦ v, the In mixed crystal ratio can be made larger than that of the n-side barrier layer, thereby increasing the refractive index of the waveguide. possible to the structure. In this case, carrier confinement from the p-type layer is mainly performed by the n-side barrier layer (2b). However, in a nitride semiconductor in which the diffusion length of holes is smaller than that of electrons, the p-side electron confinement layer It is possible to confine carriers in the active layer without providing a large barrier as in the above. That is, in confining carriers from the p-type layer, the n-side barrier layer (2
a) plays the role of minimizing the simplification and realizing a structure, while the first nitride semiconductor layer has a large In mixed crystal ratio, so that the active layer and the center of the waveguide can be formed. by increasing the refractive index, the formation of excellent device structure waveguiding of light becomes possible.

Between the p-type cladding layer and the active layer, the second
And a p-type electron confinement layer made of a nitride semiconductor containing Al between the p-type light guide layer and the active layer. With this configuration, the p-type light guide layer including the p-side electron confinement layer and the second nitride semiconductor layer is provided between the active layer and the p-type cladding layer in the waveguide, so that the crystallinity is improved. Deterioration and loss of light due to In are suppressed, and the device characteristics are improved. At this time, by having the p-side electron confinement layer, the electrons are efficiently confined in the active layer, and the device characteristics are improved. It is necessary to use it for the side electron confinement layer. In particular, in order to keep light loss low, it is preferable to use a nitride semiconductor containing no In, and more preferably Al _z Ga _{1 -z} N That is, a nitride semiconductor represented by <z ≦ 1) is used.

An n-type light guide layer made of a nitride semiconductor having an In mixed crystal ratio of 0 is provided between the active layer and the first nitride semiconductor layer. With this configuration,
In the waveguide, the n-type optical guide layer does not contain In and thus becomes a guide layer without light loss, and the first nitride semiconductor layer increases the refractive index difference between the waveguide and the cladding layer. Function as a layer to be formed, and the element characteristics are improved.

The film thickness of the first nitride semiconductor layer is 300
Å or more. With this configuration, the effect of having the first nitride semiconductor layer described above to increase the refractive index in the waveguide increases, and the difference in refractive index from the cladding layer can be increased, thereby improving device characteristics.

In the active layer, the layer closest to the n-type layer is n
And a sum of film thicknesses of the n-side barrier layer and the first nitride semiconductor layer is 300 ° or more.

In another embodiment of the present invention, the p
A first cladding layer and an n-type cladding layer are light-confining cladding layers, and at least one of the p-type cladding layer and the n-type cladding layer has a nitride semiconductor containing at least Al. A multilayer clad layer in which layers and second layers having different band gap energies from the first layer are alternately stacked is to be a light confinement layer. When the clad 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, a first layer and a second layer having a different composition from the first layer are stacked as a multilayer film, and a plurality of layers having different refractive indices and band gap energies are provided. For example, Al composition ratio x
1 and a second layer having an Al composition ratio x2 (x1 ≠ x2).
A multilayer film having a structure in which the Al layer and the Al layer are stacked may be used. At this time, if the Al composition ratio is set to x1> x2 (0 ≦ x2, x1 ≦ 1), the refractive index of the first layer having a large Al composition ratio is increased. The second layer, which is small, has a large band gap energy, and has a small Al composition ratio, can suppress deterioration of crystallinity due to the formation of the first layer. Further, a plurality of layers having different compositions may be further stacked by stacking the first layer and the second layer, and stacking a fifth layer having a different composition from the second layer. Further, a structure in which a plurality of first layers and second layers are alternately stacked may be employed, and a structure in which a plurality of pairs including at least the first layer and the second layer are formed may be employed. 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.

It is preferable that the clad layer having a multilayer structure has a superlattice structure so that the crystallinity can be further improved and the clad layer can be formed. Here, the superlattice structure is provided on at least a part of the clad layer. Preferably, the superlattice structure is provided on all of the clad layers so that the clad layer can be formed with good crystallinity. At this time, as the superlattice structure, as in the case of the light guide layer, at least the first layer and the second layer are alternately laminated in a plurality, or at least the first layer and the second layer are formed. A structure having a plurality of pairs is provided. The thickness of each layer constituting the superlattice structure varies depending on the composition and the combination of each layer, but is specifically 10 nm or less, preferably 7.5 nm or less. sex and can be kept good, and more preferably may be that a better crystallinity and 5nm or less. At this time,
By setting at least one of the first and second layers within the above-described thickness range, and preferably setting both of the thicknesses within the above-described thickness range, the formation of a thick clad layer becomes favorable in crystallinity.

The cladding layer is preferably doped with at least impurities of each conductivity type. Like the light guide layer, the cladding layer may be doped entirely or partially.
In the case of a multilayer film, similarly to the light guide layer, for example, the multilayer film having the first layer and the second layer may be doped with both, or the first layer and the second layer may be doped. Alternatively, the modulation doping may be different from that described above, or one may be doped and the other may be undoped. For example, the first layer / the second layer is composed of Al _x1 Ga _1-x1 N (0 <x1 ≦ 1) /
Al _x2 Ga _1-x2 N (0 ≦ x2 ≦ 1, x1> x2)
In the case of the superlattice multilayer film structure, the second layer having a small Al composition ratio is doped with impurities and the first layer is undoped, whereby the crystallinity can be improved similarly to the light guide layer. it can.

The thickness of the cladding layer is not particularly limited, but is formed in the range of 10 nm or more and 2 μm or less and 50 nm or more and 1 μm or less. When the thickness is 10 nm or more, the confinement of carriers is possible. When the thickness is 2 μm or less, the deterioration of crystallinity is suppressed. For example, when the thickness is 1 μm or less, the cladding layer can be formed with good crystallinity.

Further, in addition to the light confining cladding layer, a light guiding layer is provided between at least one of the p-type cladding layer and the n-type cladding layer and the active layer. A multilayer light guide layer in which a third layer having a nitride semiconductor containing at least In and a fourth layer having a band gap energy different from that of the third layer are alternately stacked. Can be. The composition of the multilayer film optical guide layer, like the multilayer film cladding layer, it is preferable that the multilayer film of super lattice structure. In particular,
A plurality of nitride semiconductors having different In composition ratios are stacked. When formed with a multilayer film in this way, as shown in FIG. 10, the first nitride semiconductor layer arranged near the active layer and the multilayer light guide arranged near the cladding layer are provided on the n-type layer side. And a structure in which the refractive index of the waveguide can be reduced, and it is possible to suppress the deterioration of crystallinity in the case where a light guide layer made of a nitride semiconductor containing In as a single film is provided. Becomes Specifically, as the multilayer film, the sixth layer
And a fourth layer having a composition different therefrom are stacked, and a plurality of layers having different refractive indices and band gap energies are provided. For example, a multilayer film having a structure in which a third layer having an In composition ratio y1 and a fourth layer having an In composition ratio y2 (y1 ≠ y2) may be stacked. At this time, the In composition ratio is set to y1> y2 (0 ≦ 0). y
2, y1 ≦ 1) and the when the structure, increasing the refractive index with a large third layer of the In composition ratio, increasing the band gap energy, a small fourth layer In composition ratio, the third layer Deterioration of crystallinity due to formation can be suppressed. Further, a plurality of layers having different compositions may be further stacked by stacking a third layer and a fourth layer, and stacking a sixth layer having a different composition from the fourth layer. Further, a structure in which a plurality of third layers and fourth layers are alternately stacked may be employed, or a structure in which a plurality of pairs including at least the third layer and the fourth layer are formed may be employed. In such a multilayer structure, I
It is possible to suppress the deterioration of the crystallinity of the nitride semiconductor containing n, to increase the refractive index of the waveguide, and to increase the refractive index difference from the cladding layer.

It is preferable that the light guide layer having a multilayer structure has a superlattice structure so that crystallinity can be further improved and the light guide layer can be formed. Here, the superlattice structure is provided in at least a part of the light guide layer, and preferably, the light guide layer can be formed with good crystallinity by providing the superlattice structure in all the light guide layers. At this time, as in the case of the cladding layer, the superlattice structure has at least a third layer and a fourth layer alternately stacked in a plurality, or has at least a third layer and a fourth layer. The structure is such that a plurality of pairs are provided. The thickness of each layer constituting the superlattice structure varies depending on the composition and the combination of each layer, but is specifically 10 nm or less, preferably 7.5 nm or less. sex and can be kept good, and more preferably may be that a better crystallinity and 5nm or less. At this time,
By setting at least one of the first and second layers within the above-mentioned thickness range, and preferably setting both of the thicknesses within the above-described thickness range, favorable crystallinity of the formation of the light guide layer is achieved.

The cladding layer is preferably doped with at least impurities of each conductivity type. Like the light guide layer, it may be doped entirely or partially.
In the case of a multilayer film, similarly to the light guide layer, for example, a multilayer film having the third layer and the fourth layer may be doped in both, or the third layer and the fourth layer may be doped. It is also possible to use a different doping amount depending on the above or a modulation doping in which one is doped and the other is undoped. For example, the third layer / fourth layer is composed of In _y1 Ga _1-y1 N (0 <y1 ≦ 1) /
_{In y2 Ga 1-y2 N (} 0 ≦ y2 ≦ 1, y1> y2)
In the case of the superlattice multilayer structure of the above, the fourth layer having a small In composition ratio is doped with impurities and the third layer is undoped, whereby the crystallinity can be improved similarly to the cladding layer. .

The thickness of the light guide layer is not particularly limited, but may be 10 nm or more and 1 μm or less, preferably 50 nm or more and 500 nm or less. , A superior waveguide structure is formed. More preferably, when the thickness is 100 nm or more and 300 nm or less, a suitable optical waveguide is formed in a configuration in which the first nitride semiconductor layer, the second nitride semiconductor layer, and the optical guide layer are used in combination, and the efficiency is improved. Light is confined, and the threshold current can be reduced.

A good waveguide structure is formed by the n-type layer having a light guide layer and the first nitride semiconductor layer between the light guide layer of the n-type layer and the active layer. Is done. The p
The mold layer has a light guide layer, and the light guide layer of the p-type layer is
By having the second nitride semiconductor layer, it is possible to suppress the crystallinity deterioration due to the nitride semiconductor containing In and to increase the refractive index of the waveguide.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION The nitride semiconductor used in the nitride semiconductor device of the present invention is GaN, AlN, or IN.
nN or a gallium nitride-based compound semiconductor which is a mixed crystal thereof (In _x Al _y Ga _1-xy N, 0 ≦ x, 0 ≦ y, x +
y ≦ 1). In addition, a mixed crystal in which a part of the gallium nitride-based compound semiconductor is substituted with B and P may be used. In addition, a nitride semiconductor containing In used for an active layer, a well layer, a barrier layer, or the like is specifically In _x Al _y Ga _1-xy
In other words, a nitride semiconductor represented by N (0 <x, 0 ≦ y, x + y ≦ 1) is used. Further, as a nitride semiconductor including Al, _{specifically, In x Al y Ga 1-} xy N (0 ≦
x, 0 <y, x + y ≦ 1).

(Active Layer) The active layer according to the present invention has a nitride semiconductor containing at least In, and emits light having a wavelength of 440 nm or more. Where I
Although the composition of the nitride semiconductor containing n is not particularly limited, a nitride semiconductor represented by In _x Ga ₁ -xN (0 <x ≦ 1) is preferably used. At this time,
The nitride semiconductor containing In may be non-doped, n-type doped, or p-type doped, but preferably a non-doped or undoped or n-type doped nitride semiconductor containing In is provided in the active layer. Thus, high output can be achieved in a nitride semiconductor device such as a laser device and a light emitting device. When the active layer has a quantum well structure, the nitride semiconductor containing In is used for at least the well layer. 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, output can be improved, oscillation threshold can be reduced, and the like. As the quantum well structure of the active layer, a structure in which a well layer and a barrier layer described later are stacked can be used. At this time, in the case of a quantum well structure, the number of well layers is 1
By setting the number to 4 or less, for example, in a laser device, it is possible to reduce the threshold current, and it is more preferable. Laser elements and light emitting elements tend to be obtained.

In the multiple quantum well structure, the number of barrier layers sandwiched between the well layers is not limited to one (well layer / barrier layer / well layer), but may be two or more layers. The barrier layer of "well layer / barrier layer (1) / barrier layer (2)
/ Barrier layer (3) /.../ well layer "
A plurality of barrier layers having different impurity amounts may be provided. For example, there is a structure in which an upper barrier layer made of a nitride semiconductor containing Al is provided on a well layer, and a lower barrier layer having a smaller energy band gap than the upper barrier layer is provided thereon. Specifically, by providing an upper barrier layer made of a nitride semiconductor containing Al disposed on the well layer, segregation of In and in-plane distribution of In concentration are induced in the well layer, and quantum dots, Since the quantum wire effect tends to be obtained, this may be used. At this time, as the nitride semiconductor containing Al, specifically, In _x Al _y Ga _1-xy N (0 ≦
x, 0 <y, x + y ≦ 1), preferably a ternary mixed crystal Al _z Ga _{1 -zN.}
The use of (0 <z ≦ 1) is preferable because the crystal can be grown with good crystallinity and controllability. Further, the nitride semiconductor containing Al is not limited to the upper barrier layer, and may be a lower barrier layer disposed below the well layer.
And (3) may be provided as a barrier layer (2). It is preferable to use a layer other than the lower barrier layer provided in contact with the lower part of the well layer because the well layer tends to be formed with good crystallinity and the above-described quantum effect tends to be easily obtained. Because there is. The lower barrier layer in contact with the bottom of the well layer, it is preferable to use a nitride semiconductor not containing _{Al, In x Ga 1 -x N} (0 ≦ x ≦ 1)
Is preferable from the viewpoint of the crystallinity of the well layer.
GaN is preferred because the effect of the underlayer on the well layer can be obtained.

Examples of the well layer in the (well layer) the present invention, it is preferable to use a nitride semiconductor layer containing In, as the case concrete composition, In α Ga _1-α N
(0 <α ≦ 1) can be preferably used. This results in a well layer that enables good light emission and oscillation. At this time, the emission wavelength can be determined by the In mixed crystal ratio.

The thickness of the well layer and the number of the well layers can be arbitrarily determined. When the specific film thickness is in the range of 10 ° to 300 °, preferably in the range of 20 ° to 200 °, Vf and the threshold current density can be reduced. Further, from the viewpoint of crystal growth, if the thickness is 20 ° or more, a layer having a relatively uniform film quality without large unevenness in film thickness can be obtained. It becomes possible. 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, the active layer becomes The overall film thickness increases, and Vf
Is increased, the thickness of the well layer is reduced to 100 Å.
It is preferable to keep the thickness of the active layer low within the following range.

In the well layer of the present invention, In in the active layer
Similarly to the nitride semiconductor containing, the n-type impurity may or may not be doped. However, the well layer is I
Nitride semiconductor is used containing n, the crystallinity and the n-type impurity concentration is increased tends to deteriorate, it is preferable that the n-type impurity concentration kept low in the good crystallinity well layer. Specifically, in order to maximize the crystallinity, the well layer is grown undoped. At this time, the n-type impurity concentration is 5 × 10 ¹⁶ / cm ³ or less, which is substantially n-type. That is, the well layer contains no impurities.
Further, when the well layer is doped with an n-type impurity, if the n-type impurity concentration is in the range of 1 × 10 ¹⁸ or less and 5 × 10 ¹⁶ or more, deterioration of crystallinity is suppressed and carrier concentration is reduced. Can be increased, and the threshold current density and Vf 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 particular, when the element is driven by a large current (such as a high-output LD, a high-power LED, or a superphotoluminescence diode), the well layer is undoped.
By not substantially containing an n-type impurity, recombination of carriers in the well layer is promoted, and light-emitting recombination with high efficiency is realized. Conversely, when the n-type impurity is doped into the well layer,
Since the carrier concentration in the well layer is high, the probability of radiative recombination is rather reduced, and a vicious cycle occurs, which causes an increase in drive current and drive current under a constant output, and reliability of the device (device life).
Tend to decrease significantly. For this reason, in such a high-output device, the n-type impurity concentration of the well layer is set to at least 1 × 10 ¹⁸ / cm ³ or less, and preferably, the undoped or substantially n-type impurity-free concentration. By doing so, a nitride semiconductor device capable of high-output and stable driving can be obtained. Also, in the case of a laser element in which an n-type impurity is doped in a well layer, the spectral width of the peak wavelength of laser light tends to be widened, so that it is not preferable that the 1 × 1
0 ¹⁸ / cm ³ , preferably 1 × 10 ¹⁷ / cm ³ or less.

(Barrier Layer) In the present invention, the composition of the barrier layer is not particularly limited. , A nitride semiconductor containing In having a lower In mixed crystal ratio than the well layer or G
A nitride semiconductor containing aN or Al can be used. As a specific composition, In _β Ga _1-β N (0 ≦ β
<1, α> β), GaN, Al γ Ga 1-γ N (0 <γ ≦
1) can be used. Here, in the case of a barrier layer (lower barrier layer) serving as an underlayer in contact with the well layer, Al
It is preferable to use a nitride semiconductor containing no. This is because a well layer made of a nitride semiconductor containing In is formed of AlGa.
This is because, when grown directly on a nitride semiconductor containing Al such as N, the crystallinity tends to decrease, and the function of the well layer tends to deteriorate.

The barrier layer has p-type impurities and n-type impurities.
May be doped or non-doped
Is preferably doped with n-type impurities or non-doped.
Or undoped. this
When doping n-type impurities in the barrier layer,
At least 5 × 10¹⁶/cm^ThreeDoped over
That is. Specifically, for example, in the case of an LED
5 × 10¹⁶/cm ^ThreeMore than 2 × 10¹⁸/cm^ThreeThe following range
Having an n-type impurity in the surrounding area, and a higher output
LED and high power LD, 5 × 10¹⁷/cm^Threethat's all
1 × 10²⁰/cm^ThreeThe following range, preferably 1 × 10¹⁸/ C
m^Three5 × 10 or more¹⁹/cm^ThreeDoped in the following range
It is preferable to dope at such a high concentration.
Means that the well layer contains substantially no n-type impurity,
It is preferred to grow in a loop.

On the other hand, as shown in FIGS. 3 and 5, the barrier layer 2c located on the outermost side and the p-type layer 13 side in the active layer preferably contains substantially n-type impurities. By avoiding this, the carrier injection from the p-type layer 13 becomes good, and the device life tends to be improved. This is because the p-side barrier layer 2c is provided in contact with the p-type layer, serves as an injection port for carriers from the p-type layer, and impedes the injection of carriers when it has an n-type impurity. And n
It is considered that by substantially not including the type impurity, the carriers from the p-type layer 13 are stably and efficiently injected deeper into the well layer far from the p-type layer. . In particular, there is a tendency that a remarkable effect of improving the element life is obtained in a large-current driven high-output LD, LED, or the like in which a large amount of carriers are injected with a large current. At this time, when the n-type impurity does not substantially include the n-type impurity, the n-type impurity concentration of the p-side barrier layer 2c is 5 × 1
0 ¹⁶ / cm ³ . The p-side barrier layer 2c is preferably formed on the outermost side in the active layer. However, when the effect is reduced but not on the outermost side, for example, the well layer / barrier is formed. Even if the structure is stacked in the order of layer / well layer / p-type layer 13, the effect can be expected. The position of the most p-side barrier layer 2c is preferably arranged at the outermost position in the active layer.
By being provided in contact with the side electron confinement layer, confinement of electrons and injection of carriers from the p-type layer become more efficient. Furthermore, since the p-side barrier layer 2c has a p-type impurity, carriers from the p-type layer 13 can also be transmitted to the well layer at a deeper portion and the well layer located far from the p-type layer 13. Since it is efficiently implanted and the device lifetime tends to be improved, n-type impurities are substantially not contained and p
It is preferable that the barrier layer contains a type impurity. At this time,
The amount of p-type impurities is 5 × 10 ¹⁶ / cm ³ or more and 1 × 10
The range is ²⁰ / cm ³ or less, preferably 5 × 10 ¹⁶ / cm ³ or more and 1 × 10 ¹⁸ / cm ³ or less. This is 1 × 10
^{Even if the} p-type impurity is increased to ²⁰ / cm ³ or more, the carrier concentration hardly changes, so that the crystallinity is deteriorated due to the inclusion of the impurity, and the loss due to the light scattering action due to the impurity is increased. Decreases luminous efficiency. Further, when the concentration is 1 × 10 ¹⁸ / cm ³ or less, it is possible to suppress the decrease in the luminous efficiency due to the increase in the impurity and to keep the carrier concentration from the p-type layer in the active layer stably high. Become. In addition, as a lower limit of the p-type impurity, it is preferable that the p-type impurity has a small amount of p-type impurity. This is because impurities tend to function as carriers.

The thickness of the barrier layer is not particularly limited, and may be 5
A range of 10 ° or more and 300 ° or less can be applied, similarly to the well layer.

(Waveguide Structure) In the nitride semiconductor device of the present invention, the active layer is made of a p-type nitride semiconductor layer, an n-type clad layer and a p-type clad layer in the n-type nitride semiconductor layer. And at least a structure sandwiched between them. At this time, it is preferable to use a nitride semiconductor containing In for the active layer.
It is preferable to set the In mixed crystal ratio so that light emission of 40 nm or more can be obtained. Further, a light guide layer may be provided between the cladding layer and the active layer so as to sandwich the active layer. Here, a region sandwiched between the p-type cladding layer and the n-type cladding layer is called a waveguide.

Here, as the n-type cladding layer and the p-type cladding layer, a nitride semiconductor containing Al is preferably used.
The refractive index difference can be made large. At this time, it is preferable that the nitride semiconductor of the cladding layer does not contain In, because the nitride semiconductor containing In tends to have lower crystallinity than the case not containing In, and in particular, In a structure having a p-type cladding layer on an active layer, when a nitride semiconductor containing In is used for the p-type cladding layer, crystallinity is greatly deteriorated and device characteristics are greatly deteriorated. At this time, specifically, as a nitride semiconductor used for the cladding layer, Al _b Ga ₁ -bN (0 <b <1)
Is preferably used.

In the present invention, a layer between the cladding layer and the active layer, such as the light guide layer shown in FIG. 2, is important in forming a waveguide. This is because, in order to confine light in the waveguide, the refractive index of the cladding layer is lowered relatively to the waveguide and the refractive index difference is increased, or the refractive index in the waveguide is increased. However, when the wavelength of light from the active layer is long, a difficult problem occurs. The reason is that the refractive index difference between AlGaN and InGaN has a large refractive index difference in a short wavelength region, for example, around 400 nm, but the refractive index difference becomes smaller as the wavelength becomes longer. For this reason, the Al alloy crystal ratio of the nitride semiconductor used for the cladding layer is increased to reduce the refractive index of the cladding layer, or to reduce the refractive index of the optical guide layer.
It is necessary to use a nitride semiconductor containing n to reduce the refractive index in the waveguide and increase the difference in the refractive index between the waveguide and the cladding layer. However, the cladding layer Al
When the mixed crystal ratio is increased, the crystallinity is greatly deteriorated, and cracks are generated, which causes a leak current.
It is difficult to provide a thick film and a nitride semiconductor having a high Al mixed crystal ratio in the element structure. Furthermore, in a structure in which a nitride semiconductor containing In is used for a nitride semiconductor layer in a waveguide except an active layer, for example, an optical guide layer, and the refractive index of the waveguide is increased, the nitride semiconductor containing In is used. Light absorption occurs, which results in loss of light in the waveguide and deterioration of device characteristics such as an increase in threshold current. Further, as described above, as a p-type nitride semiconductor, for example, the p-type nitride semiconductor shown in FIG.
When a nitride semiconductor containing In is used for the mold light guide layer,
Inclusion of Mg, which is preferably used as a p-type impurity, greatly deteriorates crystallinity, and consequently deteriorates device characteristics.

According to the present invention, by providing a first nitride semiconductor layer and a second nitride semiconductor layer sandwiching an active layer as a waveguide sandwiched between both clad layers, a waveguide at a long wavelength and a crystal can be obtained. Sexual problems are solved. That is, by providing the first nitride semiconductor layer made of a nitride semiconductor containing In between the n-type cladding layer and the active layer, the refractive index in the waveguide is relatively lower than that of the cladding layer. To
On the other hand, between the p-type cladding layer and the active layer, a second nitride semiconductor layer made of a nitride semiconductor containing no In (the In mixed crystal ratio is 0) is provided, and a crystal on the p-type layer side is provided. It has a structure that solves the problem of sex deterioration. Therefore, the waveguide has a structure in which the active layer is sandwiched between the first nitride semiconductor layer containing In and the second nitride semiconductor layer not containing In, and the composition is asymmetric.

Conventionally, as a waveguide structure in which the emission wavelength of the active layer is long, InGa in the long wavelength region described above is used.
Due to the problem of a decrease in the refractive index difference between N and AlGaN and the problem of deterioration in crystallinity due to a high Al mixed crystal, InGa
A structure using a nitride semiconductor containing In such as N as an optical guide layer, for example, an InGaN single film, an InGaN / GaN multilayer film (superlattice layer), and the like have been considered. However, even if the p-type optical guide layer is formed of an InGaN / GaN superlattice multilayer film to suppress the deterioration of crystallinity, it is difficult to obtain crystallinity to such an extent that the element characteristics are not affected yet. The loss of light due to In also becomes a major cause of deterioration of device characteristics. This is because, as the emission wavelength of the active layer becomes longer, the refractive index difference between InGaN and AlGaN becomes smaller, and the In mixed crystal ratio of the nitride semiconductor used for the optical guide layer or the like to increase the refractive index in the waveguide. Must be increased, but if the In mixed crystal ratio becomes large, the deterioration of device characteristics due to crystallinity, light loss, and the like also increases.

However, according to the present invention, the refractive index of the entire waveguide is increased by using the first nitride semiconductor layer containing In on the n-type cladding layer side in the waveguide, and the cladding layer is formed. By increasing the refractive index difference between the first and second layers and providing the second nitride semiconductor layer on the p-type cladding layer side,
It is possible to obtain a nitride semiconductor device having excellent device characteristics while avoiding deterioration of crystallinity and light loss due to a nitride semiconductor containing n. Hereinafter, each layer will be described.

(First Nitride Semiconductor Layer) The first nitride semiconductor layer in the present invention is disposed between the active layer and the n-type cladding layer in the waveguide, and is made of a nitride semiconductor containing In. It becomes. Here, the composition of the first nitride semiconductor layer is preferably a nitride semiconductor containing no Al, whereby the difference in the refractive index from the cladding layer using the nitride semiconductor containing Al is obtained. In other words, it is possible to relatively increase the refractive index in the waveguide between the cladding layer and the waveguide sandwiched between the cladding layer and In _z Ga _{1 -z} N (0 <z ≦ 1). By forming a nitride semiconductor represented by
Can be obtained. In addition, another layer may or may not be provided between the first nitride semiconductor layer and the active layer or the n-type clad layer, that is, the first nitride semiconductor layer may be formed as an active layer or an n-type clad layer. It may be provided in contact with the n-type cladding layer or both, or may be provided separately on one or both of them. Further, a multilayer film structure in which a plurality of first nitride semiconductor layers are stacked alternately with layers different in composition from the first nitride semiconductor layer may be used. Since the first nitride semiconductor layer of the present invention is located between the active layer and the n-type cladding layer and is in the waveguide, the first nitride semiconductor layer functions as an optical guide layer. By increasing the rate and contributing to confinement of light in the waveguide, it also functions as a second light confinement layer as compared with the second nitride semiconductor layer on the p-type layer side. It is thought that there is.

Further, the In mixed crystal ratio z of the first nitride semiconductor layer is the In mixed crystal ratio of the nitride semiconductor containing In in the active layer, or in the case of an active layer having a quantum well structure, the well layer. When the In mixed crystal ratio is w, it is preferable that z ≦ w, and it is more preferable that z <w. For example, as shown in FIGS. 5 and 6, the In compound crystal ratio z of the first nitride semiconductor layer 31 satisfies z ≦ w as compared with the compound crystal ratio w of the well layer 1 in the active layer 12. By doing so, as shown in the figure, a stepwise band gap energy structure can be formed, and efficient injection of carriers into the active layer in the waveguide, particularly injection of carriers from the n-type layer 11 side can be achieved. Will contribute. At this time, when z <w, a large bad gap energy difference can be provided between the first nitride semiconductor layer and the nitride semiconductor layer containing In in the well layer, or between the well layer and the first nitride semiconductor layer. In addition, the carrier injection efficiency can be improved. Further, a first nitride semiconductor layer 31 is provided adjacent to the active layer 12, is disposed on the outermost side of the active layer and closest to the n-type layer 11, and is adjacent to the first nitride semiconductor layer 31. When the barrier layer 2a is provided, it is more preferable that the In mixed crystal ratio z of the first nitride semiconductor layer 31 is set to satisfy z ≦ v as compared with the In mixed crystal ratio v of the barrier layer 2a. , And z <v. This is because, as shown in FIGS. 5 and 6, when z ≦ v, the band gap gradually increases near the junction between the active layer 12 and the n-type layer 11 from the n-type layer 11 to the active layer 12. Energy can be reduced and the n-type layer 1
This is because carriers can be efficiently injected from 1 into the active layer, and a more stepwise bandgap structure can be obtained as shown in FIG. 5, which is more effective.

On the other hand, as shown in FIG.
When the In mixed crystal ratio z of the nitride semiconductor layer of the above is substantially equal to or larger than the In mixed crystal ratio v of the barrier layer (z ≧
v), preferably larger (z> v), and the bandgap energy is smaller than that of the barrier layer.
The refractive index of the waveguide is increased by the first nitride semiconductor layer formed with a large In mixed crystal ratio and a larger film thickness than the barrier layer (n-side barrier layer), so that the first nitride semiconductor layer can be formed with the light confinement clad layer. The difference in refractive index can be increased. In this case, a barrier is provided between the first nitride semiconductor layer and the n-side barrier layer when carriers are injected from the n-type layer.
In a biased area, the barrier is smaller and its effect is less. On the other hand, the n-side barrier layer 2a mainly serves as a confinement layer for carriers from the p-type layer. However, since the diffusion length of holes is small in a nitride semiconductor, the barrier is small and the thickness is reduced. Is relatively low. As for the In mixed crystal ratio between the light guide layer and the first nitride semiconductor layer, as shown in FIG. 8, the band gap energy is made smaller and the In mixed crystal ratio is made larger than that of the light guide layer. Is preferred. This is because the first nitride semiconductor layer is provided to increase the refractive index, and it is preferable to increase the refractive index in the vicinity of the active layer corresponding to the center of the waveguide structure. By providing the enlarged first nitride semiconductor layer closer to the active layer than to the optical guide layer, a more excellent waveguide structure can be formed. Here, in the present invention, when the cladding layer and the light guide layer are formed of a multilayer film, particularly when the layers are formed of a superlattice multilayer film, the In mixed crystal ratio, Al mixed crystal ratio, and band gap energy of each layer are , The average composition and the average energy are compared with those of the other layers, and the average composition and the average energy are the first layer (third layer) constituting the multilayer film,
At each film thickness of the second layer (fourth layer), the Al, In composition and energy are weighted average values. For example, the light guide layer, a In composition ratio y1, a third layer of thickness d _3, the superlattice structure In mixed crystal ratio y2, and a fourth layer of thickness d ₄ are alternately stacked Te is the average mole fraction _{y m} of _{in, y} m =
[(D ₃ × y 1) + (d ₄ × y 2)] / (d ₃ + d ₄ )
Is required.

As shown in FIGS. 5, 6, and 10, between the cladding layers 25, 30 and the active layer 12, the light guide layer 2 is provided.
6, 29 are provided, and on the n-type layer 11 side,
In the case of having the first nitride semiconductor layer of the light guide layer 26 and the active layer, as shown in FIG. 10, the light guide layer is disposed outside the In mixed crystal ratio or the average composition in the active layer. It is preferable to increase the In composition z of the n-side barrier layer 2a. This suitably brings out the function of increasing the refractive index by the first nitride semiconductor layer described above. Specifically, the first nitride semiconductor layer provided closer to the active layer than the light guide layer 26 By increasing the In mixed crystal ratio and increasing the refractive index in the vicinity of the active layer, a layer having a large refractive index is provided around the active layer located near the center of the waveguide, so that good light distribution can be realized. . On the other hand, on the p-type layer side, p
The side barrier layer plays this role, that is, the p-side barrier layer 2c
The same function as the first nitride semiconductor layer can be obtained by making the In composition ratio of the first nitride semiconductor layer larger than the In composition ratio of the light guide layer 29 of the p-type layer.

Here, referring to the above-described embodiments at the position of the first nitride semiconductor layer, in the embodiment in which the first nitride semiconductor layer is provided in contact with the active layer and the n-type cladding layer, the nitride containing In Since it tends to be difficult to form a semiconductor in a thick film with good crystallinity, if the film is formed with a sufficient thickness as a waveguide, the device characteristics will deteriorate due to the deterioration of crystallinity. If the film is formed to a thickness that does not deteriorate, the film thickness becomes insufficient to function as a waveguide, and the device characteristics tend to deteriorate due to loss due to light leakage outside the cladding layer. When the first nitride semiconductor layer is a multilayer film in which a plurality of layers are stacked between the active layer and the n-type cladding layer, for example, as a superlattice structure, a large number of layers are stacked together with a nitride semiconductor not containing In. A thick film can be formed while suppressing deterioration in crystallinity. For example, In
A structure in which the composition is graded so that the In mixed crystal ratio increases from the GaN / GaN multilayer film layer or the n-type cladding layer toward the active layer. On the other hand,
In order to make the refractive index of the waveguide equal to that of a single film, the thickness of the multilayer film is increased, and the first film containing In in the multilayer film is formed.
Since the nitride semiconductor layer has a structure in which the nitride semiconductor layers are scattered, light loss due to In occurs in a multilayer film thicker than a single film, and the loss tends to be larger than that in a single film. . Further, the position of the first nitride semiconductor layer is specifically between the n-type cladding layer and the active layer,
When a light guide layer is provided between the n-type cladding layer and the active layer, the light guide layer is provided between the light guide layer and the active layer as shown in FIGS. The first nitride semiconductor layer can be provided inside the light guide layer or inside the light guide layer. In the present invention, the above-described various forms can be applied. However, it is preferable that the above-mentioned various forms are preferably disposed close to the active layer, more preferably in contact with the active layer.
Although this is not known in detail, as shown in FIGS. 5 and 6 and the like, the band gap structure is made stepwise in the region from the n-type cladding layer to the active layer, and It is considered that promoting the injection of the carrier has an effect.

The thickness of the first nitride semiconductor layer is not particularly limited, but is at least 1500 ° or less in consideration of the occurrence of light loss due to In as described above. By setting the angle to preferably 300 ° or more, the refractive index of the entire waveguide can be increased, and a large refractive index difference can be formed between the waveguide and the n-type cladding layer. A wave path is formed. At this time, as described later, the function as a waveguide is
Since the first nitride semiconductor is affected by the total thickness of the region sandwiched between the clad layer and the active layer, the first nitride semiconductor It is good to decide the layer. Also, as shown in FIGS.
When the first nitride semiconductor layer is disposed adjacent to the barrier layer 2a closest to the n-type layer, the first nitride semiconductor layer is
Since the first nitride semiconductor layer in this case is considered to contribute as a barrier layer, the total thickness of the first nitride semiconductor layer and the barrier layer 2a is set to be 300 ° or more, so that the barrier layer and the light The film preferably contributes well to confinement, and the upper limit of the film thickness at this time is preferably 1500 ° or less.

The first nitride semiconductor layer may or may not be doped with an n-type impurity.
Preferably, it is doped with an n-type impurity to have good n-type conductivity. At this time, since the first nitride semiconductor layer is a nitride semiconductor containing In, although not as large as a p-type impurity as described above, there is a deterioration in crystallinity due to doping with an n-type impurity. Preferably, the doping amount is in the range of 1 × 10 ¹⁹ / cm ³ or less,
Deterioration of crystallinity in a nitride semiconductor containing In can be suppressed.

(Second Nitride Semiconductor Layer) In the present invention, a nitride semiconductor having an In mixed crystal ratio of 0 is used as the second nitride semiconductor layer. Is provided between the p-type cladding layer and the active layer, the layer has excellent crystallinity and functions as a waveguide. This is to provide a structure in which an active layer is sandwiched between the first nitride semiconductor layer and the second nitride semiconductor layer in the waveguide;
In other words, the first nitride semiconductor layer on the n-type layer side and the second nitride semiconductor layer on the p-type layer side are arranged opposite each other with the active layer interposed therebetween. This is an asymmetric waveguide structure having different functions in the wave path. By setting the In mixed crystal ratio u of the nitride semiconductor used for the second nitride semiconductor layer to u = 0, a layer excellent in crystallinity can be formed, and Vf and threshold current increase due to crystallinity deterioration can be reduced. Can be avoided. This is because the nitride semiconductor containing In is
This is because the crystallinity tends to be worse than that containing no n. Further, unlike the first nitride semiconductor layer, the second nitride semiconductor layer needs to be doped with a p-type impurity to have p-type conductivity, and the impurity doping causes deterioration in crystallinity. Mg, which is preferably used as a p-type impurity, causes a significant deterioration in crystallinity.
In a nitride semiconductor containing In, the deterioration of crystallinity is more remarkable than that of a nitride semiconductor not containing In.

In addition, as shown in FIGS.
In nitride semiconductor devices such as D and LD, a structure in which an n-type layer 11 / an active layer 12 / a p-type layer 13 is laminated on a substrate in many cases is adopted. The n-type layer 11 disposed below the active layer 12 using a nitride semiconductor including: and the p-type layer 13 disposed above the
Normally, the growth conditions are different, and the p-type layer 13 disposed above the active layer usually needs to be grown under such temperature conditions that crystallinity is not deteriorated due to decomposition of In in the active layer. The mold layer 11 does not have such a limitation. For this reason, it may be difficult to grow the p-type layer 13 grown at a low temperature under good crystal growth conditions.

More specifically, as shown in FIG.
A structure in which an active layer 11 is provided between the active layer 11 and the p-type layer 13 is provided on a substrate (not shown) or the like. There is a structure in which a mold clad layer 26 is provided, and a p-type clad layer 30 is provided in the p-type layer 13. Furthermore, an n-type contact layer 25 and a p-type contact layer may be formed on the respective conductive type layers at positions farther from the active layer than the cladding layers 26 and 30. Electrodes may be provided on the surfaces thereof. On which an n-type layer 11, an active layer 12, and a p-type layer 13 are sequentially stacked,
An electrode is provided on the surface of the substrate facing the n-type layer, and the n-type contact layer 25 is used as a charge injection layer, and the n-type cladding layer 26 is used.
A layer doped with an n-type impurity at a higher concentration can also be provided. Further, the configuration may be such that these cladding layers also serve as contact layers. In such a basic structure, as shown in FIG. 3, a first nitride semiconductor layer 31 and a second nitride semiconductor layer 32 are respectively formed by an n-type cladding layer 26, a p-type cladding layer 30, and an active layer. 12 between them. Also, as shown in FIGS.
When the light guide layers 26 and 29 are provided between the active layer and the clad layer, first and second nitride semiconductor layers may be provided between the light guide layer and the active layer. The light guide layer may have a structure including the first nitride semiconductor layer or the second nitride semiconductor layer. Therefore, when the light guide layer has a multilayer film structure, a multilayer film structure including the first nitride semiconductor layer or the second nitride semiconductor layer can be obtained.

The composition of the second nitride semiconductor layer is I
A nitride semiconductor containing no n is used, and a nitride semiconductor represented by Al _t Ga _{1 -tN} (0 ≦ t <1) is preferably used. At this time, in order to provide a refractive index difference from the p-type cladding layer, the p-type cladding layer
It is preferable to make the Al mixed crystal ratio t of the second nitride semiconductor smaller than the mixed crystal ratio. Furthermore, in consideration of the refractive index difference between the cladding layer and the waveguide, t ≦ 0.5, to form with a low Al mixed crystal ratio, or to maximize the refractive index in the waveguide, Most preferably, GaN with t = 0 is used. In addition, the second nitride semiconductor layer preferably has a p-type impurity. The second nitride semiconductor layer contains a p-type impurity and has p-type conductivity, so that the second nitride semiconductor layer can function as a p-type layer having good conductivity. . At this time, the doping amount of the p-type impurity is not particularly limited. Even if the nitride semiconductor does not contain In, the deterioration of the crystallinity is small as compared with the case where In is included. Since it tends to be good, the second nitride semiconductor layer having good crystallinity can be obtained by preferably setting the range to 1 × 10 ¹⁸ / cm ³ or less. In the examples described later, the second nitride semiconductor layer is grown undoped, and the p-type impurity is doped by diffusion from an adjacent layer. However, the present invention is not particularly limited to this method, and the same applies to other layers. However, either diffusion after growth or a method of growing while doping may be used.

The second nitride semiconductor layer may be formed of a single film or a multilayer film. The multilayer film may be a multilayer film in which a plurality of AlGaN / GaN layers are stacked, or a layer having a composition gradient such that the Al mixed crystal ratio increases as the distance from the active layer increases.

When the second nitride semiconductor layer is used for the p-type light guide layer, the p-type light guide layer may be constituted only by the second nitride semiconductor layer. May be combined with a layer having a different composition. At this time,
Preferably, it is preferable to use only the second nitride semiconductor layer containing no In because light loss due to In in the waveguide can be avoided. At this time, the thickness of the p-type light guide layer is not particularly limited, but by forming the film with a thickness of at least 200 ° or more, a good waveguide as a waveguide and light guiding with little loss is realized. This leads to a decrease in the threshold current. At this time, by setting the upper limit of the film thickness to 4000 ° or less, it is possible to suppress the increase in the threshold current and Vf. By lowering Vf, a waveguide having a thickness suitable for guiding light can be formed. This film thickness can be applied to the n-type layer side of the region sandwiched between the cladding layer and the active layer, that is, the film thickness of the region sandwiched between the n-type cladding layer and the active layer. Specifically, when a first nitride semiconductor layer is provided between the n-type cladding layer and the active layer, the thickness of the first nitride semiconductor layer and another thickness such as the first nitride semiconductor layer and the n-type light guide layer are different. In the case of having layers, the present invention can be applied to the total thickness of those layers. As described above, the thickness of the region sandwiched between the cladding layer and the active layer is made substantially the same on both the p-type layer side and the n-type layer side, so that a waveguide structure having a symmetrical thickness via the active layer can be obtained. It is good that the thicknesses of the two layers are different from each other, and a waveguide structure having an asymmetrical film thickness may be used. The waveguide structure may be appropriately selected in consideration of the characteristics of the obtained nitride semiconductor device.

According to another aspect of the present invention, the second
In the configuration (u <z) in which the In mixed crystal ratio u of the nitride semiconductor layer is smaller than the In mixed crystal ratio z of the first nitride semiconductor layer, the nitride semiconductor including In is provided on the p-type layer side. A layer that increases the refractive index of the waveguide can also be formed on the p-type layer side by suppressing a decrease in crystallinity due to being provided.
A structure in which the shift to the n-type layer side is suppressed can be achieved.

(P-side electron confinement layer)
As the type nitride semiconductor layer, it is preferable to provide a p-side electron confinement layer particularly in a laser device and an edge emitting device. As the p-side electron confinement layer, a nitride semiconductor containing Al is used, and specifically, Al _γ Ga _{1- γ}
N (0 <γ <1) is used. At this time, the Al mixed crystal ratio γ needs to have a band gap energy (offset) sufficiently larger than that of the active layer so as to function as an electron confinement layer, and at least 0.1 ≦ γ <1.
And preferably 0.2 ≦ a <0.
5 range. If γ is 0.1 or less, the laser element does not function as a sufficient electron confinement layer, and if γ is 0.2 or more, sufficient electron confinement (carrier confinement) is performed and carrier overflow occurs. In addition, when it is 0.5 or less, it is possible to grow while suppressing the occurrence of cracks. More preferably, when γ is 0.35 or less, it is possible to grow with good crystallinity.
At this time, it is preferable that the Al mixed crystal ratio is larger than that of the p-type clad layer, and this requires a nitride semiconductor having a mixed crystal ratio higher than that of the clad layer for confining carriers to confine carriers. Because. This p-side electron confinement layer can be used for 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, as in 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 p-side electron confinement layer of the present invention is at least 1000 ° or less, preferably 400 ° 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. Therefore, if it is provided in the element exceeding 1000 °, it becomes an extremely high resistance layer, which causes a large increase in the forward voltage Vf. If it is 400 ° or less, the rise of Vf is suppressed to a low level. It is possible to further suppress the temperature by setting the angle to 200 ° or less. Here, when the lower limit of the film thickness of the p-side electron confinement layer is at least 10 ° or more, preferably 50 ° or more, it functions well as electron confinement.

In the laser device, the p-side electron confinement layer is provided between the active layer and the cladding layer in order to function as an electron confinement layer as shown in FIGS. Further, it is provided between the second nitride semiconductor layer and the active layer. When the nitride semiconductor device has a waveguide structure and has an optical guide layer between the cladding layer and the active layer, the p-side electron confinement layer is between the optical guide layer 29 and the active layer 27. In this case, a structure in which a p-side electron confinement layer is provided close to the active layer can be achieved, so that a suitable carrier confinement structure can be realized. A configuration in which a confinement layer is provided can also be employed, whereby a structure in which the p-side electron confinement layer and the active layer are separated from each other can be provided. This is preferable because the heat generation effect can be avoided. At this time, when the distance between the active layer and the p-side electron confinement layer is at least 1000 ° or less, it functions as carrier confinement, and preferably at 500 ° or less, good carrier confinement becomes possible. . In other words, the closer to the active layer, the more effectively the p-side electron confinement layer functions to confine carriers. In addition, most of the laser element and the light-emitting element have a gap between the active layer and the p-side electron confinement layer. In this case, it is most preferable that a p-side electron confinement layer can be usually provided in contact with the active layer because no other layer is required. At this time, when the layer located closest to the p-type nitride semiconductor layer in the active layer having the quantum well structure and the p-side electron confinement layer are provided in contact with each other, the crystallinity is deteriorated. It is also possible to provide a buffer layer in crystal growth between them. For example, a buffer layer made of GaN may be provided between the most p-side layer of the active layer and the p-side electron confinement layer of InGaN or AlGaN. And a buffer layer made of a nitride semiconductor containing Al.

Here, as the p-side electron confinement layer, specifically, the threshold current density decreases as the p-side electron confinement layer is closer to the active layer, but the element life decreases as the p-side electron confinement layer is closer to the active layer. Become. As described above, since the p-side electron confinement layer is a layer having an extremely high resistance as compared with the other layers, a large amount of heat is generated when the element is driven, that is, a high temperature is exhibited in the element. It is considered that this has an adverse effect on the heat-sensitive active layer and well layer and greatly reduces the element life.
On the other hand, as described above, the p-side electron confinement layer responsible for confinement of carriers is more effective in confining carriers closer to the active layer, particularly to the well layer. Weakens. Therefore, the p-side electron confinement layer has a larger bandgap energy than the active layer, and preferably has a bandgap energy larger than at least one barrier layer in the active layer so as to suitably function as carrier confinement. More preferably, a composition is selected such that the band gap energy becomes larger than that of all the barrier layers in the active layer. In an edge emitting device and a laser device having a waveguide structure, it is necessary to increase the band gap energy of the p-side electron confinement layer more than a part, preferably all of the light guide layer, so that carrier confinement by the guide layer is achieved. Is insufficient, it is preferable that the p-side electron confinement layer disposed closer to the active layer than the guide layer can realize a suitable carrier confinement in the active layer. When the bandgap energy is made larger than a part or all of the above, a large barrier is arranged near the active layer to realize suitable carrier confinement, and the thickness of the p-side electron confinement layer is reduced. However, this function can be maintained, which is preferable.

Therefore, in order to suppress a reduction in the element life,
5 and 6, the distance between the well layer 1b closest to the p-side electron confinement layer in the active layer and the p-side electron confinement layer 28 is set to at least 100 ° or more, preferably 12 ° or more.
0 ° or more, and more preferably 140 ° or more. The reason for this is that if the distance between the well layer and the p-side electron confinement layer is shorter than 100 °, the device life tends to be sharply reduced. , 150 ° or more, the device life tends to be further improved, but the threshold current density tends to gradually increase. Further, when the distance is larger than 200 °, a clear tendency of increase in the threshold current density is observed, and when the distance is larger than 400 °, the threshold current density tends to sharply increase. It is 400 ° or less, preferably 200 ° or less. This is because the p-side electron confinement layer moves away from the well layer, which lowers the efficiency of carrier confinement. This is mainly attributable to an increase in threshold current density and a decrease in luminous efficiency. it is conceivable that.

The p-side electron confinement layer of the present invention usually has a p-type
Doped with impurities, such as laser devices and high power LEDs
When driving with which large current, the carrier mobility
In order to increase the concentration, doping is performed at a high concentration. Specific doping amount and
At least 5 × 10 ¹⁶/cm^ThreeDope
And preferably 1 × 10¹⁸/cm^ThreeDoping
In the element driven by the large current, 1 × 10¹⁸
/cm^ThreeAbove, preferably 1 × 10¹⁹/cm^ThreeDope more
That is. The upper limit of the amount of the p-type impurity is not particularly limited.
But 1 × 10^{twenty one}/cm^ThreeIt is as follows. Where p
Increased bulk impurity tends to increase bulk resistance
And as a result, Vf rises,
Preferably avoids the required carrier mobility
The minimum p-type impurity concentration that can ensure
You. Also, the p-side electron confinement layer may be doped at a low concentration.
And, for example, p-side electron confinement of guide layers, cladding layers, etc.
Can be doped at a lower concentration than the layer near the
Alternatively, it may be a non-doped layer.

In the nitride semiconductor device of the present invention,
As shown, a ridge was set up as a striped waveguide.
After the beam is formed, an insulating film to be a buried layer is formed on the side surface of the ridge.
At this time, as the buried layer, the material of the second protective film is used here.
As SiO_TwoOther materials, preferably Ti, V, Z
at least one selected from the group consisting of r, Nb, Hf, Ta
Oxide containing one kind of element, SiN, BN, SiC,
It is desirable to form at least one of AlN.
Of which, oxides of Zr and Hf, BN and SiC are used
Is particularly preferred. In addition, as a buried layer, semi-insulating
, I-type nitride semiconductor, conductivity type opposite to ridge,
In the embodiment, an n-type nitride semiconductor and a current confinement layer are used.
For nitride semiconductors containing Al such as AlGaN
Can be. In addition, ridge by etching etc.
Without implanting ions such as B, Al, etc.
The region is formed in a stripe shape so that a current flows therethrough.
It can also be made. Nitride semiconductor used at this time
As In_xAl_1-yGa _1-xyN (0 ≦ x ≦ 1, 0
≦ y ≦ 1, x + y = 1)
It can be used properly.

The ridge width is 1 μm or more and 3 μm or more.
m, preferably 1.5 μm or more and 2 μm or less, laser light having an excellent spot shape and beam shape can be obtained as a light source for an optical disk system.

Here, each figure will be described below. 2 and 3 are schematic cross-sectional views according to an embodiment of the present invention, and particularly show a structure in which an active layer 12 is sandwiched between an n-type layer 11 and a p-type layer 13 in a laser element structure and a light-emitting element structure. Things. FIG. 2 shows an element structure in which the active layer 12 is sandwiched between an upper clad layer 30 and a lower clad layer 25 and a p-side electron confinement layer 28 as an electron confinement layer is provided between the active layer 12 and the upper clad layer 30. It is to explain.
FIGS. 3 and 4 show that as a feature of the present invention, the first nitride semiconductor layer and the second nitride semiconductor layer are provided in a waveguide in a region sandwiched between upper and lower cladding layers. Of the nitride semiconductor layer are formed in the n-type cladding layer (not shown), between the n-type light guide layer 26 and the active layer 12 (shown in FIGS. 3 and 4),
The second nitride semiconductor layer is provided between the n-type light guide layer 26 and the n-type clad layer 25 (not shown), and the second nitride semiconductor layer is used for the p-type light guide layer 29. FIG. 3 illustrates a quantum well structure of the active layer 12, which has a structure in which a barrier layer 2a / well layer 1a is repeatedly stacked as a pair, and a barrier layer 2c is provided last. 5 to 8 show a waveguide structure in a region sandwiched between the active layer 12, the upper and lower cladding layers 26 and 30, a laminated structure 20 around the active layer, and the laminated structure 20 in one embodiment of the present invention. Below, the corresponding energy band gap 21 is shown. 10 also shows the laminated structure 20 and the energy band diagram 21 corresponding to the laminated structure similarly to FIGS. 5 to 8, and shows one embodiment of the Al composition ratio 41 and the In composition ratio 42 in each layer in addition to them. A schematic diagram is shown.

The doping amount of each layer in the nitride semiconductor device of the present invention will be described below with reference to FIG. Regarding the impurity doping of the light guide layer of the present invention, as shown in FIG. If the area is smaller or the doping amount in the region near the active layer is smaller than that in the region farther from the active layer, the waveguide, particularly in the light guide layer,
Light loss can be further reduced, and good light guiding 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, as described above, the waveguide has at least a structure in which the first light guide layer 226 and the second light guide layer 229 sandwich the active layer 227. The waveguide is divided into upper and lower cladding layers 22 having a smaller refractive index than the guide layer.
5, 230, the light is confined in the waveguide, and a large amount of light is distributed in the active layer 27 and in the vicinity of the active layer in the waveguide. By reducing the amount, a loss of light in a region where a large amount of light is distributed is reduced, and a waveguide having a small loss of light is obtained. Specifically, in the first light guide layer 226 and the second light guide layer 229, when a region is divided by half the thickness of each layer and a region close to the active layer and a region far from the active layer are considered, a region close to the active layer is considered. Is to be lower than the impurity concentration in a region far from the active layer. The impurity concentration of the light guide layer is not particularly limited, but specifically, 5 × in the region near the active layer.
Is that it 10 ^{1 7} / cm ³ or less. Here, the impurity doping means that the first light guide layer is doped with a first conductivity type impurity, and the second light guide layer is doped with a second conductivity type impurity.

As a form of changing the doping amount in the light guide layer, as a specific example, in each light guide layer, the doping amount is gradually and gradually reduced as approaching the active layer (43a). Either a mode in which the doping amount is reduced continuously and stepwise (43b), or a mode in which the stepwise change in the doping amount is reduced and the doping amount is partially changed in the optical guide layer (43c) may be used. Or a combination of these. Preferably, in the light guide layer, a region whose distance from the active layer side is 50 nm or less is a lightly doped region (226b, 229a),
Preferably, light loss can be reduced by undoping, and preferably, light-loss loss, threshold current density, and drive current can be reduced satisfactorily by setting the regions of 100 nm or less as low-concentration doped regions (226b, 229a). Becomes possible. At this time, the thickness of the light guide layer is 50 nm or more when the low-concentration doped regions (226b and 229a) are 50 nm or less, and 100 nm or more when the light-concentration doped region (226b, 229a) is 100 nm or less. Needless to say, the film thickness is set as follows. At this time, the lightly doped region (22)
6b, 229a) is preferably used in combination with the above-described light guide layer having a composition gradient structure when the light guide layer is provided in the light guide layer. This is because the light guide layer with reduced carrier injection efficiency is formed even when a region not doped with impurities is provided near the active layer due to the band structure that becomes smaller as approaching. At this time, the light guide layer having a composition gradient is preferably a GRIN structure as described above, and even if the multilayer film structure has a structure in which the band gap energy becomes smaller as approaching the active layer, a lightly doped region is formed. Is effective. Here, in each light guide layer, even if the impurity is not doped at the time of growth, that is, even if the light guide layer is grown with low concentration doping, the impurity may diffuse from the adjacent layer. The above-described region grown by doping also becomes doped with impurities. Specifically, Mg which is preferably used as a p-type impurity easily causes such a diffusion phenomenon, and 43a schematically shows a mode in which the impurity is diffused from the p-side electron confinement layer 228 to an adjacent layer by diffusion. In the light guide layer (region 229a) adjacent to the heavily doped p-side electron confinement layer 229 and the active layer (near the p-side barrier layer), a concentration gradient is generated and diffusion is observed. Is done. Further, as shown in Example 1, even if the p-side light guide layer is formed with low concentration doping, p-type impurities are doped by diffusion from the electron confinement layer and the cladding layer of the adjacent layers. As described above, when impurity doping is performed by diffusion, as described above, the impurity concentration in a region near the active layer is to be smaller than that in a region far from the active layer. Such a doped region is preferably provided in at least one of the light guide layers, and more preferably provided in both of the light guide layers to provide a waveguide with reduced light loss. In addition, 51 and 52 in the figure show the change of the doping amount in each light guide layer.

The layer structure, the form of impurity doping, the composition, the film thickness, etc. of the light guide layer may be the same as those of the first light guide layer and the second light guide layer. May be. For example, there is a mode in which the first light guide layer is a single film, the second light guide layer is a multilayer film, and the two light guide layers have different layer configurations. In the present invention, between the cladding layers 225, 230 and the active layer 227, the high-concentration doped regions (226a, 229b) disposed on the cladding layer side are doped at a lower concentration than the heavily-doped regions. By providing the lightly doped regions (226b, 229a) disposed on the active layer side, a structure in which light loss in the waveguide is reduced can be obtained. More preferably, the lightly doped region (226b, 2
It is preferable to provide the high-concentration doped layers (231, 228) between the active layer 29a) and the active layer side of the light guide layer. Here, the heavily doped layer can be provided as part or all of the p-side electron confinement layer 228 and the first nitride semiconductor layer 231 located near the active layer. The doping amount of
Each of them is doped at a higher concentration than the lightly doped regions 226b and 229a located on the respective cladding layer sides. Preferably, the doping amount of the heavily doped layer 228 in the p-type layer is By making the p-type layer larger than the heavily doped region 229b in the p-type layer, a pn junction is formed in the heavily doped layer, so that the carrier injection from the p-type layer is excellent, the impurity doping amount changes, and the carrier concentration changes. Can be provided, which is preferable. Here, 225 in FIG.
230 correspond to the respective layers 25 to 30 in the laminated structure 20 in FIG.

[0074]

【Example】

Example 1 Hereinafter, as examples, the laser device structure shown in FIG. 1 and the waveguide structure shown in FIG.
explain.

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 can be performed with good 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 nitride semiconductor single substrate. The element structure may be formed as
A method of removing different kinds of substrates may be used.

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 improved. It will be. In addition, as an underlayer (growth substrate) provided on a heterogeneous substrate, ELOG (E
When a nitride semiconductor grown pitaxially Laterally Overgrowth is used, a growth substrate having good crystallinity can be obtained. EL
As a specific example of the OG 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. A non-mask region to be formed is provided in a stripe shape, and a nitride semiconductor is grown from the non-mask region. In addition to the growth in the film thickness direction, the growth in the lateral direction is performed. Also, there is a layer formed by growing a nitride semiconductor. 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, in this embodiment, GaN was grown as a thick film (100 μm), and then the heterogeneous substrate was removed.
A nitride semiconductor substrate made of 80 μm GaN 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
_{Using 3} ), a buffer layer made of GaN is grown to a thickness of 200 °, and then the temperature is increased to increase the undoped G layer.
aN is grown to a thickness of 1.5 μm to form an underlayer.
Next, a plurality of stripe-shaped masks are formed on the surface of the underlying layer, and a nitride semiconductor, in this embodiment, GaN is selectively grown from the mask opening (window), and growth accompanied by lateral growth (ELOG) The nitride semiconductor layer formed by the method described in (1) is further grown as a thick film, and the heterogeneous substrate, the buffer layer, and the underlayer are removed to obtain a nitride semiconductor substrate. At this time, the mask at the time of selective growth is made of SiO ₂ and has a mask width of 15 μm.
m, and the opening (window) width is 5 μm.

(Buffer Layer 102) A buffer layer 102 of Al _0.05 Ga _0.95 N is formed on a nitride semiconductor substrate at a temperature of 1050 ° C. using TMG (trimethylgallium), TMA (trimethylaluminum) and ammonia. It is grown to a thickness of 4 μm. This layer is made of AlG
It functions as a buffer layer between the aN n-type contact layer and the nitride semiconductor substrate made of GaN. Next, the respective layers forming the element structure are stacked on the base layer made of the nitride semiconductor.

(N-type contact layer 103)
On the buffer layer 102, TMG, TMA, ammonia,
Silane gas at 1050 ° C using silane gas as pure gas
Al_0.05Ga_0.95N-type contact layer made of N
103 is grown to a thickness of 4 μm. n-type contact
Layer or a base layer such as a buffer layer
Compound semiconductor, specifically Al _xGa_1-xN (0 <x ≦
1), the use of Al-free nitride such as GaN
Crystal by using ELOG compared to nitride semiconductor
Deterioration of properties, especially generation of pits
Surface tends to provide a nitride semiconductor containing Al
Preferably, it is used.

(Crack Prevention Layer 104) Next, the TM
Using G, TMI (trimethylindium), and ammonia at a temperature of 800 ° C., a crack prevention layer 104 of In _0.06 Ga _0.94 N is grown to a thickness of 0.15 μm. The crack prevention layer can be omitted.

(N-type clad layer 105) Next, the temperature is raised to 1050 ° C., and an A layer made of undoped Al _0.05 Ga _0.95 N is grown to a thickness of 25 ° using TMA, TMG and ammonia as the source gas. Then, TMA is stopped, and silane gas is used as an impurity gas, and Si
A B layer of GaN doped with 0 ¹⁸ / cm ³ is grown to a thickness of 25 °. This operation is repeated 200 times to stack the A layer and the B layer, and grow the n-type cladding layer 106 composed of a multilayer film (superlattice structure) having a total film thickness of 1 μm. At this time, if the Al mixed crystal ratio of the undoped AlGaN is in the range of 0.05 or more and 0.3 or less, it is possible to provide a refractive index difference that sufficiently functions as a cladding layer.

(N-type light guide layer 106) Next, at the same temperature, using TMG and ammonia as source gases, the n-type light guide layer
It is grown to a thickness of μm. Further, an n-type impurity may be doped.

(First Nitride Semiconductor 131) Next, as shown in FIG.
Using MI (trimethylindium) and TMG, a first layer made of Si-doped In _0.05 Ga _0.95 N and having a thickness of 500 °
Is formed.

(Active Layer 107) Next, the temperature is set to 800 ° C.
Then, as shown in FIG.
Chillindium), undoped In using TMG
_0.05Ga _0.95N barrier layer, undoped on it
In_0.32Ga_0.68The N-well layer is formed as a barrier layer 2a /
Well layer 1a / barrier layer 2b / well layer 1b / barrier layer 2c
To be laminated. At this time, as shown in FIG.
2b and 2c have a thickness of 130 °, and the well layers 1a and 1b have a thickness of 2 °.
It is formed with a thickness of 5 °. The active layer 107 has a total thickness of about 44
It becomes a multiple quantum well structure (MQW) of 0 °.

(P-side electron confinement layer 108) Next, at the same temperature, TMA, TMG and ammonia are used as source gases, Cp ₂ Mg (cyclopentadienyl magnesium) is used as impurity gas, and Mg is reduced to 1%. A p-type electron confinement layer 10 of × 10 ¹⁹ / cm ³ doped Al _0.3 Ga _0.7 N
8 is grown to a thickness of 100 °. This layer is not necessarily provided, but when provided, it functions as electron confinement and contributes to lowering of the threshold.

(P-Type Light Guide Layer 109: Second Nitride Semiconductor Layer) Next, the temperature is set to 1050 ° C., and TMG and ammonia are used as source gases to form a p-type light guide layer 109 made of undoped GaN. It is grown to a thickness of 0.15 μm.

The p-type light guide layer 109 is grown as an undoped layer. However, Mg is diffused from adjacent layers such as the p-side electron confinement layer 108 and the p-type cladding layer 109 so that M
The g concentration was 5 × 10 ¹⁶ / cm ³ , indicating p-type. This layer may be intentionally doped with Mg during growth.

(P-type cladding layer 110)
At 50 ° C., two layers of undoped Al _0.05 Ga _0.95 N
Grown at a thickness of 5 °, followed by stopping TMA, Cp ₂ M
g, a layer made of Mg-doped GaN is grown to a thickness of 25 °, and this is repeated 90 times to obtain a total thickness of 0.45.
A p-type cladding layer 110 consisting of a superlattice layer of μm is grown. When the p-type cladding layer is made of a superlattice in which at least one includes a nitride semiconductor layer containing Al and has different band gap energies from each other, the impurity is doped into one of the layers in a large amount. When so-called modulation doping is performed, the crystallinity tends to be improved, but both may be doped in the same manner. Clad layer 1
10 is a nitride semiconductor layer containing Al, preferably Al _x
It is desirable to have a superlattice structure containing Ga ₁ -XN (0 <X ≦ 1), and more preferably a superlattice structure in which GaN and AlGaN are stacked. Since the p-side cladding layer 110 has a superlattice structure, the Al mixed crystal ratio of the entire cladding layer can be increased, so that the refractive index of the cladding layer itself decreases and the band gap energy increases. It is very effective in lowering.
Further, the use of the superlattice reduces the number of pits generated in the cladding layer itself as compared with the non-superlattice, thereby reducing the occurrence of short circuits.

(P-type contact layer 111) Finally, 1
At 050 ° C., 1 × of Mg was deposited on the p-type cladding layer 110.
A p-type contact layer 111 made of p-type GaN doped with 10 ²⁰ / cm ³ is grown to a thickness of 150 °. The p-type contact layer 111 is made of p-type In _x Al _Y Ga _{1 -XYN} (0 ≦
X, 0 ≦ Y, X + Y ≦ 1), and preferably Mg-doped GaN provides the most preferable ohmic contact with the p-electrode 120. Contact layer 1
11 is a layer for forming an electrode, so that 1 × 10 ¹⁷ / cm ³
It is desirable that the carrier concentration be as high as above. 1 × 10
^If it is lower than 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, the wafer is annealed in a nitrogen atmosphere at 700 ° C. in a reaction vessel.
The resistance of the p-type layer is further reduced.

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-type contact layer, and RIE ( Etching is performed with SiCl ₄ gas using reactive ion etching (RIE) to expose the surface of the n-type contact layer 103 where the n-electrode is to be formed, as shown in FIG. In order to deeply etch the nitride semiconductor in this way, 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 layer p
Almost all of the 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 of the ridge stripe (etching depth) is such that the p-type contact layer 111, the p-type cladding layer 109, and a part of the p-type light guide layer 110 are etched so that the thickness of the p-type light guide layer 109 becomes zero. Etching is performed to a depth of 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 made of
A film having a thickness of 0.5 μm is continuously formed on the p-type 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 way, after forming the second protective film, at a temperature of 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-type contact layer 111 is removed, and the p-type contact layer is exposed. As described above, as shown in FIG. 1, the second protective film 162 is formed on the side surface of the ridge stripe and the plane continuous therewith (the exposed surface of the p-type light guide layer 109).

After the first protective film 161 provided on the p-type contact layer 112 is removed, the exposed p-type contact layer 111 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 exposed n
On the surface of the mold contact layer 103, a striped n-electrode 121 made of Ti / Al is formed in a direction parallel to the stripe.

Next, a mask is formed on the p and n electrodes on the surface exposed by etching to form the n-electrode, and on a desired region for providing an extraction electrode, and a dielectric multilayer film 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, (11-00), etc.) ), 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.
The laser device obtained in this way has a laminated structure 20 and a band gap energy diagram shown in FIG.

The obtained laser device is a nitride semiconductor device having a threshold current density of 2.8 kA / cm ² and a wavelength of 448 nm, and has a longer wavelength than the light guide layer of Reference Example 1 made of InGaN. In this region, a laser having a low threshold current density can be obtained.

FIG. 8 is a graph showing the relationship between I and I of the well layer 1 in the first embodiment.
A laser device having a wavelength of 425 to 450 nm is manufactured by changing the n-crystal ratio, and the threshold current density Jth is measured to show the wavelength dependence of the threshold current density. As is apparent from FIG. 8, in the short wavelength region of 430 nm or less, it is preferable to use the structure in which the active layer is sandwiched between the upper and lower optical guide layers having the nitride semiconductor containing In as in Reference Example 1 for the waveguide structure. The threshold current density tends to be low, and the threshold current densities of Reference Example 1 and Example 1 are reversed around 440 nm (435 nm to 445 nm). While showing a trend,
In Reference Example 1, it can be seen that a sharp upward trend is observed.
As described in the first embodiment, the structure in which the active layer is sandwiched between the first nitride semiconductor layer and the second nitride semiconductor layer, which is a feature of the present invention, is provided in the waveguide, so that the above-described In It can be understood that the problem of light loss due to the above and the problem of crystallinity of the p-type light guide layer can be improved, and a nitride semiconductor device having excellent device characteristics in a long wavelength region can be obtained.

Example 2 In Example 1, as shown in FIG. 5, a first nitride semiconductor layer made of undoped In _0.025 Ga _0.975 N having a mixed crystal ratio lower than the In mixed crystal ratio of the barrier layer 2 was used. It is formed with a thickness of 500 °. In the obtained laser device, the In nitride crystal ratio of the first nitride semiconductor layer 31 was equal to that of Example 1.
Is smaller than that of the waveguide sandwiched between the upper and lower clad layers, in this embodiment, the region sandwiched by the n-type light guide layer and the p-type light guide layer, and the refractive index difference between the clad layer and the waveguide. Since the threshold current is larger than that of the laser diode of 1, the laser diode having a longer wavelength region has excellent characteristics.

Embodiment 3 In Embodiment 2, as shown in FIG. 8, the first nitride semiconductor layer 31 is
Provided at a distance of 00 mm. At this time, the laminated structure sandwiched between the n-side cladding layer and the active layer is the n-type cladding layer 2.
5 / the first n-type light guide layer 26a / the first nitride semiconductor layer 31 / the second n-type light guide layer 26b / the active layer 12 are stacked in this order. 26a
Is set to 800 ° with undoped GaN, and the second n-type light guide layer 26b is set to 200 ° with undoped GaN. In the obtained laser device, the effect of confining light and injecting carriers by the first nitride semiconductor layer is weakened because the first nitride semiconductor layer is farther from the active layer than in Example 2, and The light distribution in the waveguide is more distributed on the n-type cladding layer side than in the first embodiment, the stimulated emission in the active layer is reduced, and the light loss due to the first nitride semiconductor occurs. , The threshold current tends to be larger than in the second embodiment.

[Embodiment 4] In Embodiment 1, as shown in FIG.
Undoped In as the n-type light guide layer, _0.05G
a_0.95N, the first nitride semiconductor having a thickness of 0.15 μm
Using the body, a laser element is obtained in the same manner as in Example 1. Profit
The laser element to be used is InGaN or
Between the waveguide and the cladding layer
The difference in the refractive index increases, but due to the thick n-type light guide layer
The absorption of light increases, and the light distribution in the waveguide also increases.
To the region from the conductive layer to the n-type cladding layer.
And stimulated emission in the active layer is reduced.
The threshold current is slightly larger than in the first embodiment. this
At this time, the n-type light guide layer (first nitride semiconductor layer) is
Even when formed by a superlattice multilayer film composed of aN / GaN,
Crystallinity of the film is better than that of a film
The problem of the light distribution, the refractive index of the waveguide,
And the obtained laser element has the same tendency.
It becomes characteristic.

Reference Example 1 In Example 4, the p-side light guide layer was replaced by the same undoped In _0.05 G as the n-side light guide layer.
A laser element is obtained in the same manner as in Example 4 _{except that} a _0.95 N is used. The obtained laser device is different from the waveguide structure of Example 1 in that the first nitride semiconductor is not provided and n
The light guide layer has the same thickness as the p-type light guide layer, and both light guide layers have a structure using a nitride semiconductor containing In. In the laser device obtained in this manner, crystallinity is greatly deteriorated by using a nitride semiconductor containing In for the p-type light guide layer, and further, light is absorbed by the light guide layer. The threshold current is larger than in Example 1. FIG. 9 shows a reference example 1 in which a laser element having a wavelength of 425 nm to 450 nm was manufactured by changing the In mixed crystal ratio of the well layer, and the threshold current density Jth was measured. It shows the nature. As is clear from FIG. 9, in the structure using the nitride semiconductor containing In for the upper and lower light guide layers, the threshold current density tends to increase sharply as the wavelength increases from around 430 nm.
It can be seen that in the long wavelength region of 40 nm or more, the threshold current density is higher than in Example 1, and the difference becomes larger as the wavelength becomes longer.

[Embodiment 5] In Embodiment 1, the n-type layer,
A p-type clad layer, a guide layer, and an active layer are formed as follows, and a laser device having a structure shown in FIG. 10 is manufactured.

(N-type cladding layer 105) On the n-type contact layer 103 and the crack preventing layer 104 (omissible),
Undoped Al _0.1 Ga as an n-type cladding layer
Growing a first layer of _0.9 N to a thickness of 25 °;
Subsequently, TMA was stopped, and silane gas was used as an impurity gas, and Al doped with 5 × 10 18 / cm 3 was used.
A second layer consisting of _{0.0 5} Ga _0.95 N is grown to the thickness of 25 Å. This operation is repeated 200 times, and the first layer and the second layer are alternately laminated to grow the n-type cladding layer 106 composed of a multilayer film (superlattice structure) having a total film thickness of 1 μm. When this n-type cladding layer is to be a lower cladding layer provided below the active layer, it is not necessary to constitute a superlattice multilayer film, but a single film or a film having a thickness of 100 Å.
A clad layer can be formed even with a multilayer film having the above layers.

(N-type light guide layer 106) A third layer made of Si-doped GaN is grown to a thickness of 15 °, and then a fourth layer made of undoped In _0.05 Ga _0.95 N is formed. It is grown to a thickness of 15 °. Then, this operation is repeated 60 times, and the third layer and the fourth layer are alternately laminated to form an n-type light guide layer 106 composed of a multilayer film (superlattice structure) having a total film thickness of 0.18 μm. It grows on an n-type cladding layer.

(First Nitride Semiconductor 131) Next, S
i-doped In _0.05 Ga _0.95 N, thickness 530 °
A first nitride semiconductor layer is formed on the n-type light guide layer.

(Active Layer 107) As shown in FIG.
130 ° -thick n-side barrier layer 2a made of undoped GaN, 25 ° -thick undoped In _0.25 Ga
_A well layer 1a made of _0.75 N, a barrier layer 2b made of undoped GaN having a thickness of 100 °, and a well layer 1a
Well layer 1b, undoped In with a thickness of 530 °
_A p-side barrier layer 2c made of _0.05 Ga _0.95 N is laminated in the order of barrier layer 2a / well layer 1a / barrier layer 2b / well layer 1b / barrier layer 2c. The active layer 107 has a total thickness of about 81
It has a multiple quantum well structure (MQW) of 0 ° and is formed on the first nitride semiconductor layer. When the n-side barrier layer 2a is in contact with the first nitride semiconductor layer, the first nitride semiconductor layer can also serve as the n-side barrier layer 2a. In this case, the n-side barrier layer 2a Can be omitted, and the first nitride semiconductor layer in contact with the active layer also functions as the n-side barrier layer 2a.

(P-side electron confinement layer 108) Next, at the same temperature, TMA, TMG and ammonia are used as source gases, Cp2Mg (cyclopentadienyl magnesium) is used as an impurity gas, and Mg is 1 × 1019. / Cm
A p-type electron confinement layer 108 of 3-doped Al _0.3 Ga _0.7 N is grown to a thickness of 100 °. This layer is not necessarily provided, but when provided, it functions as electron confinement and contributes to lowering of the threshold.

(P-Type Light Guide Layer 109) A third layer made of Mg-doped GaN is grown to a thickness of 15 °, and then a fourth layer made of undoped In _0.05 Ga _0.95 N is formed. It is grown to a thickness of 5 °. This operation is repeated 90 times, and the third layer and the fourth layer are alternately laminated to form a multilayer film (superlattice structure) having a total film thickness of 0.18 μm.
A p-type light guide layer 109 is grown on the p-side electron confinement layer. At this time, the second nitride semiconductor layer of the present invention is formed as a third layer.

(P-type cladding layer 110) A first layer made of undoped Al _0.1 Ga _0.9 N is grown to a thickness of 25 °, followed by Mg-doped Al _0.05
Ga _{0 . A} second layer of 95N is grown to a thickness of 25 °. This operation is repeated 90 times, and the first layer and the second layer are alternately laminated, and the total film thickness is 0.45.
p-type cladding layer 1 consisting of a multilayer film (superlattice structure) of μm
10 is grown on the p-type light guide layer.

As described above, the n-type clad layer 25, the n-type light guide layer 27, the first nitride semiconductor layer 31, the active layer 2
7, a structure in which the p-side electron confinement layer 28, the p-type light guide layer 29, and the p-type cladding layer 30 are stacked as shown in FIG.
The structure as shown in 41 and 42 is obtained. In this embodiment, in the light guide layer, the fourth layer constituting the multilayer n-type light guide layer is formed to be thicker than the fourth layer of the p-type light guide layer. Since the In-crystal ratio (average composition) of the n-type light guide layer is larger than that of the p-type light guide layer, a nitride semiconductor layer containing In is provided on the p-type layer side. Has a structure in which deterioration of crystallinity is reduced. Further, in order to reduce the thickness of the p-type light guide layer from that of the n-type light guide layer, the In mixed crystal ratio of the third and fourth layers constituting the multilayer film may be reduced. It is also possible to reduce the ratio. The laser device thus obtained has a threshold current density of 1.
Continuous oscillation at 9 kA / cm ² , wavelength 453 nm, room temperature is possible, and element lifetime 1 at 60 ° C. and 5 mW continuous oscillation.
A nitride semiconductor laser device that lasts up to 10,000 hours is obtained.

[Embodiment 6] In Embodiment 5, the first layer constituting the multilayer film of the n-type cladding layer and the p-type cladding layer is made of undoped Al _0.05 Ga _0.95 N,
, Except that the layers of
A laser device is obtained in the same manner as in the fifth embodiment.

In the device structures of Examples 1, 5, and 6, the change in threshold current when the wavelength is changed by changing the In crystal ratio of the well layer is shown in FIG. Example 5 is an open triangle, and Example 6 is an open square.
Indicated by As can be seen from FIG. 12, in the long wavelength region of the wavelength of 440 nm or more, Examples 5 and 6 provide a laser device with a reduced threshold current, and Example 5 is superior to Examples 5 and 6 in comparison. It can be seen that a laser element having the following characteristics can be obtained. The thickness of the p-side barrier layer and the thickness of the n-side barrier layer are largely different between the first embodiment and the fifth and sixth embodiments, and both barrier layers have a thickness of 200 ° or more, preferably 300 ° or more, more preferably 400 ° or more. As a result, the threshold current tends to decrease. In particular, increasing the distance between the p-side barrier layer or the p-side electron confinement layer and the well layer 1b closest to the p-type layer in the active layer, that is, 200 ° As described above, it is considered that a good waveguide structure in a long wavelength region is formed by setting the angle to preferably 300 ° or more, more preferably 400 ° or more, and the threshold current characteristics as shown in FIG. 12 are obtained. Another difference in the configuration is that the light guide layer has a multilayer structure including a nitride semiconductor layer containing In.
In Examples 5 and 6, it is considered that the refractive index in the waveguide was improved by this, which led to an improvement in element characteristics.
Further, Example 5 and Example 6 have a structure in which the Al mixed crystal ratio (average composition) of the clad layer is different.
It is considered that by setting the l-mixed crystal ratio (average composition) to 0.05 or more, an excellent waveguide structure was formed in a long wavelength region, thereby improving the characteristics. The upper limit of the crystal ratio (average composition) is set to 0.5 or less in consideration of crystallinity. In the case of forming a clad layer of a multilayer film, the nitride semiconductor layer containing Al (first
) And a nitride semiconductor layer (second layer) containing Al having a lower Al composition ratio than the first layer are preferably stacked at least alternately. The Al mixed crystal ratio x1 of the layer is larger than the Al mixed crystal ratio x2 of the second layer, and it is preferable that x1> x2 (x2> 0). It can be seen that it can be obtained. Further, in the fifth embodiment, a laser device having a device life at the oscillation wavelengths 465 and 470 reaching 10,000 hours and 3000 hours under the same conditions as in the fifth embodiment can be obtained.

[0116]

According to the nitride semiconductor device of the present invention, a laser device having a low threshold current in a long wavelength region and an edge emitting device having excellent device characteristics can be obtained. In particular, as shown in FIG. 9, the structure in the waveguide is asymmetrical as in the present invention as compared with the structure of the reference example using a nitride semiconductor containing In for the guide layer, so that A nitride semiconductor device having excellent device characteristics in a long wavelength region can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating one embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating one embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view illustrating one embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating an embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating a laminated structure 20 according to an embodiment of the present invention and a band structure 21 corresponding to the laminated structure.

FIG. 6 is a schematic diagram illustrating a laminated structure 20 according to an embodiment of the present invention and a band structure 21 corresponding to the laminated structure.

FIG. 7 is a schematic diagram illustrating a laminated structure 20 according to an embodiment of the present invention and a band structure 21 corresponding to the laminated structure.

FIG. 8 is a schematic diagram illustrating a laminated structure 20 according to an embodiment of the present invention and a band structure 21 corresponding to the laminated structure.

FIG. 9 is a graph showing wavelength dependence of a threshold current density in one embodiment of the present invention and the embodiment of Reference Example 1.

FIG. 10 shows a laminated structure 20 according to an embodiment of the present invention;
Band structure 21 corresponding to the laminated structure, Al composition ratio 4
FIG. 1 is a schematic diagram illustrating an In composition ratio of 42.

FIG. 11 is a schematic diagram illustrating an impurity concentration change (51, 52) corresponding to the laminated structure 20 of FIG. 10 according to an embodiment of the present invention.

FIG. 12 is a diagram showing the wavelength dependence of the threshold current in each embodiment (Examples 1, 5, and 6) of the present invention.

[Brief description of reference numerals]

1 ... well layer 2 (2b) ... barrier layer 2
a ... n-side barrier layer, 2c ... p-side barrier layer, 11
... n-type nitride semiconductor layer 12 ... active layer
13: p-type nitride semiconductor layer, 20: laminated structure, 101: substrate (GaN substrate) 102
... buffer layer, 103 ... n-type contact layer, 104 ... crack prevention layer, 105,2
5,225... N-type cladding layer (lower cladding layer),
106, 26, 226 ... n-type light guide layer (lower light guide layer), 107, 27, 227 ... active layer, 108, 28, 228 ... p-side electron confinement layer,
109, 29, 229 ... p-type light guide layer (upper light guide layer), 110, 30, 230 ... p-type clad layer (upper clad layer), 111 ... p-type contact layer, 120 ...・ P electrode, 121 ・ ・ ・
n electrode, 122 ... p pad electrode, 123 ...
n-pad electrode 131,311,231 ... first nitride semiconductor layer 32,232 ... second nitride semiconductor layer 163 ... third protective film 164
... Insulating film

Claims (23)

[Claims] 1. A nitride semiconductor having a structure in which an active layer is sandwiched between a p-type layer and an n-type layer, wherein the p-type layer has a p-type cladding layer and the n-type layer has an n-type cladding layer. In the device, the active layer includes a nitride semiconductor including In, and a first nitride semiconductor layer including a nitride semiconductor having an In mixed crystal ratio of z> 0 between an n-type cladding layer and the active layer. And a second nitride semiconductor layer having an In mixed crystal ratio u of z> u between the p-type cladding layer and the active layer. 2. A nitride semiconductor having a structure in which an active layer is sandwiched between a p-type layer and an n-type layer, wherein the p-type layer has a p-type cladding layer and the n-type layer has an n-type cladding layer. In the device, the active layer has a nitride semiconductor containing In, and has a first nitride semiconductor layer made of a nitride semiconductor containing In between the n-type clad layer and the active layer, and has a p-type clad layer. A nitride semiconductor device comprising a second nitride semiconductor layer having an In mixed crystal ratio of 0 between a layer and an active layer. 3. An n-side barrier layer (2a) disposed closest to the n-type layer among the barrier layers in the active layer.
And a p-side barrier layer (2c) disposed closest to the p-type layer.
And at least one well layer made of a nitride semiconductor containing In between the n-side barrier layer (2a) and the p-side barrier layer (2b), and an n-type impurity of the p-side barrier layer (2c). 3. The nitride semiconductor device according to claim 1, wherein the concentration is lower than the n-type impurity concentration of the n-side barrier layer (2a). 4. The semiconductor device according to claim 1, wherein the p-type layer is formed between the active layer and the second nitride semiconductor layer or between the active layer and the p-type cladding layer. 4. The nitride semiconductor device according to claim 1, further comprising a confining layer. 5. The p-type layer has a p-side electron confinement layer made of a nitride semiconductor containing Al, and the p-side electron confinement layer is in contact with an active layer or via a buffer layer. The nitride semiconductor device according to claim 1, wherein the nitride semiconductor device is provided. 6. The nitride according to claim 5, wherein the buffer layer is made of a nitride semiconductor containing Al having an Al composition ratio lower than that of the p-side electron confinement layer, or is GaN. Semiconductor device. 7. The well layer provided between the n-side barrier layer (2a) and the p-side barrier layer (2b), wherein the active layer is closest to the p-side electron confinement layer in the active layer. (1b),
7. The nitride semiconductor device according to claim 4, wherein a distance between the well layer (1b) and the p-side barrier layer is 100 ° or more. 8. The n-side barrier layer (2a) and / or
7. The nitride semiconductor device according to claim 1, wherein the p-side barrier layer is disposed on the outermost side in the active layer. 9. The nitride semiconductor device according to claim 1, wherein said first nitride semiconductor layer is provided in contact with an active layer. 10. The first nitride semiconductor layer having a thickness of 3
The nitride semiconductor device according to claim 1, wherein the thickness is at least 00 °. 11. The well layer (1b) and a p-side barrier layer (2)
11. The nitride semiconductor device according to claim 7, wherein a distance from c) is 400 ° or less. 12. An n-side barrier layer (2a) as a layer disposed closest to the n-type layer in the active layer, wherein the n-side barrier layer (2a) and the first nitride semiconductor layer are Of the film thickness of
The angle is not less than 300 °.
The nitride semiconductor device as described in the above. 13. The In-crystal ratio z of the first nitride semiconductor layer and the In-crystal ratio v of the n-side barrier layer (2a) are as follows:
10. The nitride semiconductor device according to claim 1, wherein z ≦ v. 14. The nitride semiconductor device according to claim 1, wherein the p-side barrier layer has a p-type impurity. 15. The nitride semiconductor device according to claim 1, wherein the n-type impurity concentration of the p-side barrier layer is lower than the p-type impurity concentration. 16. n-type impurity concentration of the p-side barrier layer (2c) is, 5 × ^{10 1} 6 / to wherein the cm less than ³ claims 1 to 15 nitride semiconductor device according. 17. The nitride semiconductor device according to claim 1, wherein the p-type cladding layer and the n-type cladding layer are light-confining cladding layers and include a nitride semiconductor containing Al. . 18. The semiconductor device according to claim 1, wherein the active layer has a quantum well structure having a well layer made of a nitride semiconductor containing In.
15. The nitride semiconductor device according to claim 1, wherein the In compound crystal ratio of the nitride semiconductor layer is smaller than the In compound crystal ratio of the well layer. 19. An n layer made of a nitride semiconductor having an In mixed crystal ratio of 0 is provided between the active layer and the first nitride semiconductor layer.
2. A light guide layer comprising: a light guide layer;
10. The nitride semiconductor device according to item 9. 20. The p-type cladding layer and the n-type cladding layer are light-confining cladding layers, and at least one of the p-type cladding layer and the n-type cladding layer includes a nitride containing at least Al. A first layer having an oxide semiconductor;
18. The nitride semiconductor device according to claim 17, wherein the first layer is a multilayer clad layer in which second layers having different band gap energies are alternately stacked. 21. A light guide layer between at least one of the p-type clad layer and the n-type clad layer and the active layer, wherein the light guide layer includes a nitride semiconductor containing at least In. 18. The light guide layer according to claim 16, wherein the third layer and the third layer are multilayer light guide layers in which fourth layers having different band gap energies are alternately stacked.
The nitride semiconductor device as described in the above. 22. The n-type layer has a light guide layer, and has a first nitride semiconductor layer between the light guide layer and the active layer of the n-type layer. 23. The nitride semiconductor device according to 22. 23. The method according to claim 22, wherein the p-type layer has a light guide layer, and the light guide layer of the p-type layer has the second nitride semiconductor layer. Nitride semiconductor device.