JP3315378B2 - Semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for outputting a short-wavelength laser beam which is expected to be applied to the field of optical information processing.
The present invention relates to an IV nitride semiconductor laser device.

[0002]

2. Description of the Related Art In recent years, large-capacity optical disk devices such as digital video disk devices have been put to practical use, and disk capacities have been increased. As is well known for increasing the capacity of an optical disk device, it is one of the most effective means to shorten the wavelength of a laser beam serving as a light source for recording or reproducing information. The semiconductor laser device incorporated in the current digital video disk device mainly uses a semiconductor material made of AlGaInP among III-V group semiconductor materials, and its oscillation wavelength is 650 nm. Therefore, in order to cope with a high-density digital video disk device currently under development, a shorter wavelength laser device using a III-V nitride semiconductor material is indispensable.

Hereinafter, a conventional III-V nitride semiconductor laser device will be described with reference to the drawings.

FIG. 10 shows a sectional structure of a conventional III-V nitride semiconductor laser device.

[0005] As shown in FIG. 10, a GaN buffer layer 102 for alleviating the lattice constant mismatch between the substrate 101 and a nitride semiconductor crystal grown on the substrate 101 is formed on a sapphire substrate 101. , Low-resistance n-type Ga
An n-type contact layer 103 made of N is sequentially formed. In the element formation region on the n-type contact layer 103,
N-type Al for confining electrons and generated light in the active layer described later
An n-type cladding layer 104 made of GaN, an n-type light guide layer 105 made of n-type GaN for facilitating confinement of generated light in the active layer, a well layer made of Ga _1-x In _x N, and Ga
_1-y In _y N barrier layer (where x and y are 0 <y
<X <1. ) Are alternately stacked, and a multiple quantum well active layer 106 for generating generated light by recombining the confined electrons and holes, and a p-type GaN made of p-type GaN for easily confining the generated light in the active layer 106. Mold light guide layer 107
And a p-type cladding layer 108 made of p-type AlGaN having a ridge-shaped ridge stripe portion 108 a having a width of about 3 μm to 10 μm on the upper surface and confining holes and generated light in the active layer 106. .

On the p-type cladding layer 108, a low-resistance p-type
P-type contact layer 109 made of n-type GaN is formed,
Ridge stripe part 1 on p-type cladding layer 108
08a and the side surfaces of the element forming region
Covered by 0.

The p-type contact layer 10 is formed on the insulating film 110.
For example, a stripe-shaped p-side electrode 111 formed by stacking Ni and Au is formed so as to be in contact with No. 9.
An n-side electrode 112 formed by laminating Ti and Al is formed.

When the n-side electrode 112 is grounded and a predetermined voltage is applied to the p-side electrode 111 with respect to the semiconductor laser device formed as described above, the oscillation wavelength becomes 370 nm to 430 nm.
nm laser oscillation. This oscillation wavelength depends on Ga _1-x In _x N and Ga constituting the multiple quantum well active layer 106.
_It varies depending on the composition and film thickness of _1-y In _y N. At present, continuous oscillation has been achieved in a temperature environment equal to or higher than room temperature, and the time for practical use is near.

[0009]

However, the conventional nitride semiconductor laser device has an oscillation wavelength of 370 nm.
It cannot be smaller than about nm, and further shortening of the wavelength is difficult in principle.

In order to shorten the wavelength of a semiconductor laser, a so-called wide-gap semiconductor having a large forbidden band (energy gap) may be used as an active layer. Taking the above-mentioned multiple quantum well active layer 106 as an example, as a well layer,
The composition ratio x of In in Ga _1-x In _x N is 0, that is, Ga _1-x In _x N
This can be realized by using N, or by using AlGaN containing Al, which has a larger energy gap.

By the way, in a laser device having a double hetero structure in which carriers and generated light are confined in an active layer,
It is necessary to use a semiconductor material having a larger energy gap than the active layer as the cladding layer.

In general, a cladding layer having an energy gap at least about 0.4 eV larger than that of an active layer is required to obtain a semiconductor laser device having a practical level of operating characteristics capable of operating at room temperature or higher. Since the energy gap of the AlGaN semiconductor can be largely changed in the range of 3.4 eV to 6.2 eV, it is possible to form a clad layer having a large energy gap. However, if a semiconductor made of AlGaN has a composition having a large energy gap, it is particularly difficult to dope p-type impurities to obtain a p-type semiconductor because the thermal activation rate of holes is reduced. Therefore, at present, only a p-type semiconductor having an Al composition of at most 0.2 (Al _0.2 Ga _0.8 N as a mixed crystal) and an energy gap of at most 4.0 eV has been obtained.

As described above, the conventional III-V nitride semiconductor laser device has a first problem that the energy gap of the p-type semiconductor layer can be obtained only up to about 4.0 eV.

Further, when a crystal having a large Al composition and a crystal having a small Al composition are stacked, a stress is exerted on the stacked crystals due to a difference in their lattice constants. For this reason, when a semiconductor crystal having a large Al composition is grown to a thickness of 1 μm or more required as a cladding layer, cracks occur in the semiconductor crystal, which deteriorates laser characteristics and lowers the reliability of the laser element. There is a second problem.

SUMMARY OF THE INVENTION It is a first object of the present invention to solve the above-mentioned conventional problems and to realize a semiconductor laser device capable of oscillating even in the ultraviolet region, and to improve the reliability of the semiconductor laser device. As a second object.

[0016]

Means for Solving the Problems The present inventors have proposed a p-type.
As a result of various studies on the reason why the energy gap of a III-V nitride semiconductor, particularly a semiconductor made of p-type AlGaN, is only about 4.0 eV, the following conclusions are obtained.

FIG. 11 shows p-type gallium nitride (GaN) and p-type gallium nitride.
Energy level with the aluminum nitride (AlN), and the vertical axis indicates the energy of electrons. FIG.
As shown in FIG. 5, an acceptor level Ea is formed above the valence band Ev of GaN and AlN by magnesium (Mg) which is a p-type dopant. This Mg is
It is generally recognized as the shallowest nitride semiconductor, that is, the acceptor having the smallest energy gap and being easily activated, and is widely used as a p-type dopant.

However, even with Mg, since the acceptor level from the upper end of the valence band Ev of GaN is relatively large at 0.15 eV, the thermal activation rate at room temperature is only about 1%. . Therefore, in order to obtain a carrier concentration of 1 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ required for the p-type cladding layer, the doping concentration of Mg should be 1 × 10 ¹⁹ to 1 × 10 ²⁰ c.
It needs to be about m ^-3 . Mg doping concentration of 1
The value of × 10 ²⁰ cm ^-3 is close to the limit value at which a good-quality semiconductor crystal can be obtained. If Mg is further doped, the crystallinity is significantly reduced. Therefore, the impurity concentration is 1 × 10 ²⁰ cm
^Assuming that the value of ^-3 is the limit of the doping concentration, 1 × 10
^In order to obtain a carrier concentration of ¹⁷ cm ^-3 or more, the thermal activation rate of the acceptor needs to be 0.1% or more.

On the other hand, as shown in FIG. 11, in AlN, the acceptor level Ea of Mg further deepens and reaches almost 0.6 eV. For example, Al _y Ga _1-y
In the case of N, it changes from 0.15 eV to 0.6 eV almost linearly when the composition y of Al is changed. In order for the thermal activation rate of the acceptor to be 0.1% or more, the difference between the acceptor level Ea and the energy Ev at the upper end of the valence band must be relatively small.
Cannot be made large.

From the above, it is extremely difficult to shorten the oscillation wavelength of the conventional nitride semiconductor laser device to the ultraviolet region, and it is considered that the oscillation wavelength is limited to about 360 nm.

Therefore, in order to achieve the first object, the present invention increases the energy gap of the p-type semiconductor layer by adding phosphorus or arsenic to the composition of the p-type semiconductor layer of the nitride semiconductor laser device. While keeping the difference, the difference between the acceptor level and the energy at the upper end of the valence band is made small, that is, the so-called acceptor level is made shallow. Further, the present invention provides a method for achieving the second object,
In the nitride semiconductor laser device containing gallium, the lattice constant of the semiconductor layer sandwiching the active layer is made substantially equal to the lattice constant of gallium nitride.

A first semiconductor laser device according to the present invention comprises:
A first semiconductor layer made of a first conductivity type first nitride semiconductor formed on a substrate to achieve the first object,
A second semiconductor layer formed on the semiconductor layer and including a second nitride semiconductor having a forbidden band width smaller than the first nitride semiconductor; and a forbidden band width formed on the second semiconductor layer. And a third semiconductor layer made of a third nitride semiconductor of a second conductivity type that is larger than the second nitride semiconductor. The first nitride semiconductor or the third nitride semiconductor contains phosphorus.

According to the first semiconductor laser device, the second semiconductor layer has a first conductivity type first semiconductor layer and a second conductivity type third semiconductor layer whose forbidden band has a larger width than the second semiconductor layer. Since the second semiconductor layer is formed so as to be sandwiched from above and below by the layers, the second semiconductor layer corresponds to an active layer that generates recombination light of carriers supplied from the first semiconductor layer and the second semiconductor layer, respectively. The first semiconductor layer and the third semiconductor layer correspond to a cladding layer or an optical guide layer for confining carriers and recombination light in the active layer. Therefore, since the first semiconductor layer or the third semiconductor layer contains phosphorus (P), the upper end of the valence band and the lower end of the conduction band are shifted to the higher energy side (upward) while maintaining the width of the forbidden band large. Can be done.

In the first semiconductor laser device, the first conductivity type is n-type, the second conductivity type is p-type, the composition of the first nitride semiconductor is AlGaN _1-x P _x , Preferably, the composition of the nitride semiconductor of _No. 3 is AlGaN _1-y P _y (where x and y are 0 ≦ x ≦ y). By doing so, the composition of phosphorus in the p-type third semiconductor layer becomes n
Since the composition is larger than the phosphorus composition of the first semiconductor layer of the mold, the upward shift of the upper end of the valence band is larger. Therefore, the energy gap between the acceptor level and the upper end of the valence band can be further reduced.

In this case, the composition of the n-type first nitride semiconductor is preferably AlGaN. In this case, the energy gap between the donor level and the lower end of the conduction band can be prevented from increasing, so that the oscillation wavelength in the ultraviolet region can be output reliably.

A second semiconductor laser device according to the present invention comprises:
A first semiconductor layer made of a first conductivity type first nitride semiconductor formed on a substrate to achieve the first object,
A second semiconductor layer formed on the semiconductor layer and including a second nitride semiconductor having a forbidden band width smaller than the first nitride semiconductor; and a forbidden band width formed on the second semiconductor layer. And a third semiconductor layer made of a third nitride semiconductor of the second conductivity type that is larger than the second nitride semiconductor. The first nitride semiconductor or the third nitride semiconductor contains arsenic.

According to the second semiconductor laser device, as in the first semiconductor laser device, the first semiconductor layer or the third semiconductor layer contains arsenic (As). The upper end of the electronic band and the lower end of the conduction band can be shifted to the higher energy side.

[0028] In the second semiconductor laser device, the first conductivity type is n-type, the second conductivity type is p-type, the composition of the first nitride semiconductor is AlGaN _1-x As _x, the 3
The composition of the nitride semiconductor AlGaN _1-y As y (where the,
x and y are 0 ≦ x ≦ y. ) Is preferable. With this configuration, the arsenic composition of the p-type third semiconductor layer is larger than the arsenic composition of the n-type first semiconductor layer, so that the upward shift of the upper end of the valence band becomes larger. Therefore, the energy gap between the acceptor level and the upper end of the valence band can be further reduced.

In this case, the composition of the n-type first nitride semiconductor is preferably AlGaN. In this case, the energy gap between the donor level and the lower end of the conduction band can be prevented from increasing, so that the oscillation wavelength in the ultraviolet region can be output reliably.

A third semiconductor laser device according to the present invention is:
A first semiconductor layer formed of a first conductivity type first nitride semiconductor and formed on a substrate to achieve the second object;
A second semiconductor layer formed on the semiconductor layer and including a second nitride semiconductor including gallium and having a forbidden band width smaller than the first nitride semiconductor; and a second semiconductor layer formed on the second semiconductor layer; The second bandgap having a larger forbidden band width than the second nitride semiconductor
A third semiconductor layer made of a conductive third nitride semiconductor, wherein the first nitride semiconductor and the third nitride semiconductor are:
It has a composition such that its lattice constant substantially matches the lattice constant of gallium nitride.

According to the third semiconductor laser device, the second semiconductor layer made of the second nitride semiconductor containing gallium and having a narrower forbidden band than the first nitride semiconductor becomes substantially an active layer. . Therefore, the first semiconductor layer and the third semiconductor layer corresponding to the cladding layer or the guide layer have compositions such that their lattice constants substantially match the lattice constant of gallium nitride. No stress due to the difference occurs.

In the first to third semiconductor laser devices, the width of the forbidden band of the first nitride semiconductor or the third nitride semiconductor is preferably 4 eV or more.

[0033]

(First Embodiment) A first embodiment of the present invention.
An embodiment will be described with reference to the drawings.

FIG. 1 shows a sectional structure of a multiple quantum well type nitride semiconductor laser device according to the first embodiment of the present invention. Here, the configuration of the laser element will be described as a method of manufacturing each semiconductor layer for forming a double hetero junction.

As shown in FIG. 1, first, for example, when the plane orientation is (00
01) surface of the substrate 11 made of sapphire
And a buffer layer 12 made of GaN for relaxing a lattice constant mismatch between the nitride semiconductor crystal grown on the substrate 11 and a semiconductor layer having few crystal defects, and a low resistance using Si as an n-type dopant. N-type contact layer 13 made of n-type GaN, an n-type clad layer 14 made of n-type Al _0.3 Ga _0.7 N for confining electrons and generated light in an active layer described later, and n for facilitating confinement of generated light in the active layer. Type Al
_An n-type light guide layer 15 made of _0.25 Ga _0.75 N is sequentially grown.

Subsequently, on the n-type light guide layer 15, Al
_0.2Ga_0.8N well layer and Al_0.25Ga_0.75With N
By alternately stacking barrier layers consisting of
The generated electrons and holes recombine to generate light.
Multiple quantum well active layer 16 and Mg as a p-type dopant.
And p-type Al for facilitating confinement of generated light in the active layer 16.
_0.25Ga_0.75N-type p-type light guide layer 17 and active layer
P-type Al confining holes and generated light_0.4Ga
_0.6N_0.98P_0.02A p-type cladding layer 18 made of
Sequentially with a p-type contact layer 19 made of p-type GaN
Let it grow. As a result, the active layer 16 is
An n-type semiconductor having an energy gap larger than that of the active layer 16.
Between the lad layer 14 and the p-type cladding layer 18.
Of epitaxial layer with double heterojunction
I do.

After the epitaxial layer is formed, the element forming region in the p-type contact layer 19 and the p-type cladding layer 18 is selectively subjected to dry etching, whereby the width is about 5 μm and the upper part is the p-type contact layer 19. A ridge-shaped ridge stripe portion 18a is formed.

Next, on the p-type contact layer 19 of the ridge stripe portion 18a, a p-layer made of a laminate of Ni and Au is formed.
The side electrode 20 is selectively formed, and then the element forming region of the epitaxial layer is masked to form the n-type contact layer 13.
By performing dry etching until is exposed,
An n-side electrode formation region is formed on the upper surface of the n-type contact layer 13, and then an n-side electrode 21 made of a laminate of Ti and Al is selectively formed on the n-side electrode formation region on the n-type contact layer 13. Form.

Next, a protective insulating film 22 made of a silicon oxide film or the like is formed on both sides of the ridge stripe portion 18a on the p-type cladding layer 18 and on side surfaces of the element formation region.

Next, a wiring electrode 23 electrically connected to the p-side electrode 20 is formed in a region including the p-side electrode 20 on the protective insulating film 22, so that the nitride semiconductor laser device shown in FIG. Get.

The operation of the semiconductor laser device constructed as described above and its operation characteristics will be described below with reference to the drawings.

The effective energy gap of the multiple quantum well active layer 16 of the semiconductor laser device according to this embodiment is about 4 eV. Therefore, when the n-side electrode 21 is grounded and a predetermined voltage is applied to the p-side electrode 20, the active layer 16
Holes are injected from the p-side electrode 20, and electrons are injected from the n-side electrode 21, and an optical gain is generated in the active layer 16. As a result, laser oscillation having an oscillation wavelength of about 310 nm occurs.

FIG. 2 shows the relationship between the respective composition ratios of Al and P and the energy gap in the AlGaNP nitride semiconductor constituting the semiconductor laser device according to the present embodiment. As shown in FIG.
3, the n-type cladding layer 14 having a P composition ratio of 0 and the p-type cladding layer 18 having an Al composition ratio of 0.4 and a P composition ratio of 0.02 both have an energy gap of about 4. 4e
V, and electrons and holes can be reliably confined in the active layer 16.

FIG. 3 shows the respective composition ratios of Al and P and the energy E at the upper end of the valence band in the nitride semiconductor composed of AlGaNP constituting the semiconductor laser device according to the present embodiment.
7 shows the result of calculating the relationship with v based on the Vegard rule. In FIG. 3, 0 eV on the vertical axis represents a case where both the composition ratio x of Al and the composition ratio y of P are 0, and
It represents the energy Ev at the upper end of the valence band in the crystal.

As shown in FIG. 3, the Al composition ratio was 0.4
When the composition ratio of P is 0, the energy Ev at the upper end of the valence band is reduced by 0.17 eV as compared with the GaN mixed crystal. Thereby, the acceptor level is deepened by 0.17 eV. However, in the present embodiment, Al _0.4 Ga _0.6 N _0.98 P _0.02 having a composition ratio of Al of 0.4 and a composition ratio of P of _0.02 is used as the p-type cladding layer 18. Energy Ev at the top of the valence band
And the acceptor level is even slightly shallower.

Here, the impurity doping of the n-type cladding layer 14 and the p-type cladding layer 18 which is a feature of this embodiment will be described.

The n-type cladding layer 14 can realize a carrier concentration of about 1 × 10 ¹⁸ cm ⁻³ by using Si as an n-type dopant.

As shown in FIG. 3, the p-type cladding layer 18 made of a group III-V nitride semiconductor is obtained by adding phosphorus (P) of group V to the p-type cladding layer 18 in its composition. As a result, the acceptor level Ea generated by Mg as a p-type dopant is changed to 0.15e, which is almost equal to GaN.
V.

As can be seen from FIG. 3, when the composition of Al in the group III-V nitride semiconductor increases, the energy Ev at the upper end of the valence band shifts to the lower energy side (downward). However, in the present embodiment, as shown in FIGS. 2 and 3, by adding phosphorus, the energy Ev at the upper end of the valence band is increased to the higher energy side (upward) while maintaining the energy gap of 4 eV or more. ), Thereby improving the activation rate of the acceptor.

In general, the thermal activation rate p of holes can be simply expressed as p = exp {-(Ea-Ev) / kT}. Here, Ea represents the acceptor level, Ev represents the energy at the upper end of the valence band, k represents the Boltzmann constant, and T represents the absolute temperature. Actually, although not so simple, when the difference between the acceptor level Ea and the valence band Ev increases, the activation rate p of the p-type dopant still decreases sharply.

As shown in FIG. 3, since the energy Ev at the upper end of the valence band decreases as the composition x of Al increases, the impurity depth, which is the difference between the acceptor level Ea and the energy Ev at the upper end of the valence band, is obtained. Increase, and the activation rate p decreases.

Therefore, as described above, in the present embodiment, phosphorus is added to the group V element of the group III-V nitride semiconductor, and the composition ratio y of phosphorus is optimized to thereby increase the upper end of the valence band. Is shifted to the higher energy side. Thereby, the difference (Ea−Ev) between the acceptor level Ea and the valence band Ev is reduced.

By the way, as shown in FIG.
When P is added to a nitride semiconductor made of, the energy gap is also reduced, so that it is necessary to increase the Al composition ratio in order to obtain a predetermined energy gap.

As described above, according to this embodiment, by increasing the composition ratio of Al to the group III-V nitride semiconductor containing Al, a predetermined energy gap is maintained and P is added to the composition. Gives the acceptor level E
The difference between a and the valence band Ev can be reduced. This allows
The thermal activation rate of the acceptor increases, and the active layer 16 has an energy gap corresponding to the oscillation wavelength in the ultraviolet region.
Can be obtained.

In order to obtain an oscillation wavelength in the ultraviolet region, when P is added to the n-type cladding layer 14, the donor level becomes conversely deep, and the activation rate of the donor is slightly lowered.
In the n-type cladding layer 14, the composition of P is preferably reduced, and more preferably, AlGaN to which P is not added is used.

However, when the oscillation wavelength is about blue and the oscillation wavelength is relatively long, the n-type cladding layer 14 is made of the same quaternary mixed crystal as the p-type cladding layer 18, and the reason for the operation of the crystal growth apparatus is considered. Therefore, the manufacture of the laser element becomes easy. Therefore,
According to the oscillation wavelength of the laser beam, that is, n
The composition of the mold cladding layer 14 may be determined.

As described above, aluminum (A)
By adding phosphorus (P) to the composition of the group III-V nitride semiconductor including 1), a shallow acceptor level can be generated while maintaining a predetermined energy gap. as a result,
When a mixed crystal composed of p-type AlGaNP is used for the p-type cladding layer of a double hetero-type semiconductor laser device, a semiconductor laser device capable of oscillating in a short wavelength region extending to an ultraviolet region can be realized.

Incidentally, the n-type light guide layer 15 and the p-type light guide layer 17 having an energy gap larger than that of the active layer 16.
On the other hand, phosphorus (P) may be added to the composition of the p-type light guide layer 17, particularly. (Second Embodiment) Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 4 shows a cross-sectional structure of a multiple quantum well type nitride semiconductor laser device according to a second embodiment of the present invention. In FIG. 4, the same components as those shown in FIG.

As shown in FIG. 4, in the present embodiment, the p-type cladding layer 28 is made of p-type A doped with Mg.
It is formed of a semiconductor layer made of l _0.4 Ga _0.6 N _0.98 As _0.02 .

FIG. 5 shows the relationship between each composition ratio of Al and As and the energy gap in the nitride semiconductor made of AlGaNAs constituting the semiconductor laser device according to the present embodiment. FIG. 6 shows the relationship between the respective composition ratios of Al and As and the energy Ev at the upper end of the valence band calculated based on the Vegard rule in the nitride semiconductor made of AlGaNAs constituting the semiconductor laser device according to the present embodiment. The results are shown.

As shown in FIG. 5, in the p-type cladding layer 28, since the composition ratio of Al is 0.4 and the composition ratio of As is 0.02, the magnitude of the energy gap is about 4.3 eV. As a result, electrons and holes can be confined in the active layer 16.

Further, as shown in FIG. 6, the difference between the acceptor level Ea and the energy Ev at the upper end of the valence band (Ea
-Ev) is smaller than when the composition ratio of As is 0.

Therefore, as in the first embodiment, arsenic (As) is added to the composition of the group III-V nitride semiconductor containing aluminum (Al), and the Al composition ratio is increased to about 0.4. By setting, an acceptor level shallower than that in the case where As is not included can be generated while maintaining a predetermined energy gap. As a result, p-type AlGaN
When a mixed crystal of As is used for the p-type cladding layer of a double hetero semiconductor laser device, a semiconductor laser device capable of oscillating in a short wavelength region extending to an ultraviolet region can be realized.

In order to obtain an oscillation wavelength in the ultraviolet region, when As is added to the n-type cladding layer 14, the activation rate of the donor is slightly reduced. Therefore, the composition of As in the n-type cladding layer 14 should be reduced. Is preferable, and it is more preferable not to add As.

However, in the case where the oscillation wavelength is about blue and the oscillation wavelength is relatively long, if the n-type cladding layer 14 is made of the same quaternary mixed crystal as the p-type cladding layer 28, the manufacture of the laser element becomes easy. . Therefore, the n-type cladding layer 14 is
May be determined.

Further, the n-type light guide layer 15 and the p-type light guide layer 17 having an energy gap larger than that of the active layer 16.
In particular, arsenic (As) may be added to the composition of the p-type light guide layer 17. (Third Embodiment) Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.

FIG. 7 shows a sectional structure of a multiple quantum well type nitride semiconductor laser device according to a third embodiment of the present invention. In FIG. 7, the same components as those shown in FIG.

As shown in FIG. 7, in this embodiment,
Means that the n-type cladding layer 34 is made of n-type A doped with Si.
l_0.4Ga_0.6N_0.98P_0.02Shaped by a semiconductor layer consisting of
And the p-type cladding layer 38 is made of Mg-doped p-type.
Type Al_0.4Ga_0.6N_0.98P_{0. 02}Semiconductor layer consisting of
Is formed.

Here, as in the first embodiment, the effective energy gap of the multiple quantum well active layer 16 is about 4 eV. Therefore, the oscillation wavelength of the laser light output from the active layer 16 is about 310 nm.

As shown in FIG. 2, the energy gaps of the n-type cladding layer 34 and the p-type cladding layer 38 are both about 4.4 eV, so that electrons and holes can be reliably confined in the active layer 16. Can be.

In the first and second embodiments, the structure for improving the activation rate of the acceptor of the p-type semiconductor layer in the group III-V nitride semiconductor laser device containing Al has been described. In this embodiment, a configuration for improving the crystal quality of a semiconductor crystal in a group III-V nitride semiconductor laser device containing Al will be described.

As described above, in a group III-V nitride semiconductor containing Al, for example, if the cladding layer requiring a relatively thick film contains a large amount of Al for increasing the energy gap, the cladding layer Cracks are likely to occur. Therefore, the thickness of the cladding layer itself is limited to such an extent that cracks do not occur as the Al composition ratio increases.

The reason for the occurrence of cracks is that, when the composition ratio of Al is increased, the lattice constant of a group III-V nitride semiconductor containing Al and the gallium nitride (GaN) which is a main semiconductor of the group III-V nitride semiconductor are increased. This is because the lattice constant and the difference of are enlarged.

FIG. 8 shows the relationship between the respective composition ratios of Al and P and the lattice constant in the AlGaNP nitride semiconductor constituting the semiconductor laser device according to the present embodiment. In FIG. 8, white circles on the vertical axis indicate the case where both the Al composition ratio x and the P composition ratio y are 0, and represent the lattice constant of the GaN crystal.

As shown in FIG. 8, the cladding layers 34 and 38 of the present semiconductor laser device have a composition ratio of Al of 0.4 and a composition ratio of P of 0.02. The constant substantially matches the lattice constant of GaN crystal, 3.19 °. Therefore, during the crystal growth, between the n-type contact layer 13 and the n-type
Since no stress is generated between the mold contact layer 19 and the p-type cladding layer 38, lattice defects such as cracks can be suppressed, and a high-quality semiconductor crystal can be obtained.

As described above, according to the present embodiment, in the nitride semiconductor laser device composed of a wide gap semiconductor, the cladding layer for which the energy gap needs to be increased is composed of a high quality semiconductor crystal having very few lattice defects. In addition, the semiconductor laser device has a long life and operates at a low threshold current, and a high-performance short-wavelength semiconductor laser device can be realized.

FIG. 9 shows the relationship between the respective composition ratios of Al and As and the lattice constant in a nitride semiconductor made of AlGaNAs. Therefore, as the n-type cladding layer 34 shown in FIG. 7, n-type Al _0.4 Ga _0.6 N _0.98 As _0.02
And a p-type cladding layer 38
Even when a semiconductor layer made of p-type Al _0.4 Ga _0.6 N _0.98 As _0.02 is used, each cladding layer 34,
The lattice constant of 38 can be made to substantially match the lattice constant of the GaN crystal.

[0079]

According to the first semiconductor laser device of the present invention, since the first semiconductor layer or the third semiconductor layer contains phosphorus (P), the upper end of the valence band is maintained while keeping the width of the forbidden band large. Since the portion and the lower end of the conduction band can be shifted to the higher energy side, the acceptor level can be reduced in the acceptor-doped semiconductor layer of the first semiconductor layer and the third semiconductor layer. Accordingly, the activation rate of holes in the first semiconductor layer or the third semiconductor layer can be increased, so that the first semiconductor layer (active layer) having an energy gap corresponding to a wavelength extending to the ultraviolet region can be used. Since carriers can be reliably confined by the layer or the third semiconductor layer, short-wavelength laser light extending to the ultraviolet region can be reliably oscillated.

In the first semiconductor laser device, the first conductivity type is n-type, the second conductivity type is p-type, the composition of the first nitride semiconductor is AlGaN _1-x P _x , When the composition of the nitride semiconductor of No. 3 is AlGaN _1-y P _y (where x and y are 0 ≦ x ≦ y), the composition of phosphorus in the p-type third semiconductor layer is n-type. Since the composition is larger than the composition of phosphorus in one semiconductor layer, the upward shift of the upper end of the valence band is further increased, so that the energy gap between the acceptor level and the upper end of the valence band can be reduced. Further, since the n-type first semiconductor layer is formed on the substrate side with respect to the second semiconductor layer, and the p-type semiconductor layer is formed on the side opposite to the substrate with respect to the second semiconductor layer, the formed semiconductor is formed. The quality of the crystal is improved.

According to the second semiconductor laser device of the present invention, like the first semiconductor laser device of the present invention, the first
Since the semiconductor layer or the third semiconductor layer contains arsenic (As),
Since the upper end of the valence band and the lower end of the conduction band can be shifted to the higher energy side while maintaining the width of the forbidden band large, the semiconductor doped with the acceptor in the first semiconductor layer and the third semiconductor layer can be used. The acceptor level can be reduced in the layer. This makes it possible to increase the activation rate of holes in the first semiconductor layer or the third semiconductor layer, so that short-wavelength laser light down to the ultraviolet region can be reliably oscillated.

According to the third semiconductor laser device of the present invention, since a stress due to a difference in lattice constant does not occur during crystal growth, a relatively large film thickness is required for the first semiconductor layer or the third semiconductor layer. Even when it is used for a simple cladding layer, cracks hardly occur in the first semiconductor layer or the third semiconductor layer, and the quality of the semiconductor crystal is improved, so that long-term reliability can be improved.

In the first to third semiconductor laser devices, when the width of the forbidden band of the first nitride semiconductor and the third nitride semiconductor is 4 eV or more, laser light whose oscillation wavelength extends to the ultraviolet region is output. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a multiple quantum well nitride semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between each composition ratio of Al and P and an energy gap in a nitride semiconductor made of AlGaNP constituting the semiconductor laser device according to the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the respective composition ratios of Al and P and the energy Ev at the upper end of the valence band in the nitride semiconductor made of AlGaNP constituting the semiconductor laser device according to the first embodiment of the present invention. is there.

FIG. 4 is a sectional view showing a configuration of a multiple quantum well type nitride semiconductor laser device according to a second embodiment of the present invention.

FIG. 5 is a graph showing a relationship between each composition ratio of Al and As and an energy gap in a nitride semiconductor made of AlGaNAs constituting a semiconductor laser device according to a second embodiment of the present invention.

FIG. 6 is a graph showing the relationship between the respective composition ratios of Al and As and the energy Ev at the upper end of a valence band in a nitride semiconductor made of AlGaNAs constituting a semiconductor laser device according to a second embodiment of the present invention. is there.

FIG. 7 is a sectional view showing a configuration of a multiple quantum well type nitride semiconductor laser device according to a third embodiment of the present invention.

FIG. 8 is a graph showing a relationship between each composition ratio of Al and P and a lattice constant in a nitride semiconductor made of AlGaNP constituting a semiconductor laser device according to a third embodiment of the present invention.

FIG. 9 is a graph showing a relationship between each composition ratio of Al and As and a lattice constant in a nitride semiconductor made of AlGaNAs constituting a semiconductor laser device according to a third embodiment of the present invention.

FIG. 10 is a configuration sectional view showing a conventional multiple quantum well type nitride semiconductor laser device.

FIG. 11 is a diagram showing energy levels of p-type gallium nitride and p-type aluminum nitride.

[Explanation of symbols]

 Reference Signs List 11 substrate 12 buffer layer 13 n-type contact layer 14 n-type cladding layer 15 n-type light guide layer 16 multiple quantum well active layer 17 p-type light guide layer 18 p-type clad layer 18a ridge stripe portion 19 p-type contact layer 20 p side Electrode 21 n-side electrode 22 protective insulating film 23 wiring electrode 28 p-type cladding layer 34 n-type cladding layer 38 p-type cladding layer

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yusaburo Ban 1006 Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Yoshiaki Hasegawa 1006 Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Satoshi Ueyama 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-8-56054 (JP, A) JP-A 8-64870 (JP, A) (58) (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 33/00

Claims (3)

(57) [Claims] A first semiconductor layer formed of a first conductivity type first nitride semiconductor formed on a substrate; and a first forbidden band formed on the first semiconductor layer and having a forbidden band width of the first semiconductor layer. A second semiconductor layer made of a second nitride semiconductor smaller than the nitride semiconductor; and a second conductivity type formed on the second semiconductor layer and having a forbidden band width larger than that of the second nitride semiconductor. third and a third semiconductor layer made of a nitride semiconductor, the first nitride semiconductor or the third nitride semiconductor seen containing phosphorus, the first conductivity type is n-type, the The second conductivity type is p-type
There, the composition of the first nitride semiconductor is AlGaN _1-x P _x
And the composition of the third nitride semiconductor is AlGaN _1-y
P _y (where x and y are 0 ≦ x <y) . 2. A first semiconductor layer made of a first conductivity type first nitride semiconductor formed on a substrate; and a forbidden band formed on the first semiconductor layer and having a width of the first bandgap. A second semiconductor layer made of a second nitride semiconductor smaller than the nitride semiconductor; and a second conductivity type formed on the second semiconductor layer and having a forbidden band width larger than that of the second nitride semiconductor. includes third and the third semiconductor layer made of a nitride semiconductor, the first nitride semiconductor or the third nitride semiconductor see contains arsenic, the first conductivity type is n-type, the The second conductivity type is p-type
And the composition of the first nitride semiconductor is AlGaN _1-x As _x
And the composition of the third nitride semiconductor is AlGaN
_1-y As _y (here, x and y are 0 ≦ x <y) der
The semiconductor laser device characterized by that. 3. The semiconductor laser device according to claim 1 , wherein a width of a forbidden band of the first nitride semiconductor or the third nitride semiconductor is 4 eV or more.