JP2003115641A - Nitride semiconductor layer element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor layer element in which the crystallinity of a guide layer, an active layer or the like is improved and a laser beam having a long wavelength can be obtained. SOLUTION: The nitride semiconductor laser element comprises an n-type clad layer 4 and/or a p-type clad layer 9 containing a first nitride semiconductor having a quantum well structure containing Ala Ga1-a N (0<=a<1), in which a composition is inclined so that an Al component is reduced as the semiconductor approaches the active layer 6. The active layer 6 contains Inb Ga1-b N (0<=b<1), and n-type guide layer 5 and/or a p-type guide layer 8 in which the composition is inclined so that the composition of In is increased when the layer 8 approaches the active layer 6, but contains a second nitride semiconductor having Ind Ga1-d N (0<=d<1) in which the composition of In is reduced as compared with the composition of In of the well layer of the active layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element such as an LED (light emitting diode), an SLD (super luminescent diode), an LD (laser diode), a light receiving element such as a solar cell or an optical sensor, or a transistor.
Nitride semiconductors used in electronic devices such as power devices (InXAlYGa1-X-YN, 0≤X, 0≤Y, X + Y≤
1) The present invention relates to a device, and more particularly, to a nitride semiconductor laser device capable of obtaining laser light having a longer wavelength than blue (about 400 nm), which has good light confinement.

[0002]

2. Description of the Related Art Recently, the present inventors have proposed a practical nitride semiconductor laser device. For example, Japanese J
ournal of Aplide Physics. Vol.37 (1998) pp.L309-L312
Discloses a nitride semiconductor laser device capable of obtaining laser light having an oscillation wavelength near 400 nm. In this device, a protective film made of SiO2 is partially formed on a GaN layer grown on sapphire, and GaN is again selected by a vapor phase growth method such as metal organic vapor phase epitaxy (MOVPE). A nitride semiconductor having a small number of crystal defects (hereinafter also referred to as dislocations) obtained by growing and growing thick GaN is used as a substrate (hereinafter sometimes referred to as ELOG substrate), and is formed on this ELOG substrate. An active layer having a multiple quantum well structure is provided at least between the n-type clad layer of the multilayer film layer (superlattice layer) and the p-type clad layer of the multilayer film layer (superlattice layer). A laser device having such a device structure can achieve continuous oscillation for 10,000 hours or more.

Further, the present inventors have conducted research on the practical use of a nitride semiconductor laser device using a nitride semiconductor and capable of obtaining a laser beam having a long wavelength of, for example, about 450 nm. As a method of obtaining a laser beam having a long wavelength, for example, the method described in J. J. A. P. In the device structure described in (1), theoretically, light having a long wavelength can be obtained by increasing the In composition ratio of the active layer.

[0004]

However, when the In mixed crystal ratio of the active layer is increased, light emitted from the active layer can be satisfactorily guided between the n-type guide layer and the p-type guide layer. It is necessary to adjust the refractive index of the guide layer with respect to the active layer by including In also in the guide layer.
J. A. P. Compared with the case where the guide layer is formed of GaN described in (3), the crystallinity of the In-containing guide layer is significantly reduced. When the crystallinity of the n-type guide layer decreases, the crystallinity of the active layer also decreases, and it becomes difficult to obtain good light emission. Also,
The decrease in crystallinity of the guide layer causes light loss, absorption, and scattering in the guide layer. Further, if the In mixed crystal ratio of the active layer is increased, the crystallinity is lowered, so that the half-value width of the wavelength at the time of spontaneous light emission is widened, and it becomes difficult to use the peak wavelength as the laser light. Furthermore, in the case of a long-wavelength laser element, in order to grow an n-type guide layer containing In, which easily deteriorates in crystallinity, on the n-type clad layer containing Al, which easily cracks, the n-type clad layer It is quite difficult to improve the crystallinity.

The applicant of the present invention has also filed Japanese Patent Application Laid-Open No. 10-3357.
Japanese Laid-Open Patent Publication No. 57-57 discloses that the guide layer or the clad layer is formed into a superlattice in order to improve the crystallinity of the clad layer or the guide layer. However, in the technique described in the above publication,
This is effective for an element that can obtain a laser beam near 400 nm, but if the wavelength is further increased, the I
The amount of n composition must be increased, and even if the guide layer is a superlattice, sufficient crystallinity cannot be obtained.

As described above, in order to obtain a laser beam having a long wavelength, the crystallinity of the guide layer containing In or the active layer having a high In mixed crystal ratio is improved, and the half-width of the wavelength during spontaneous emission is narrowed. However, it is desirable to prevent light loss, absorption, and scattering in the guide layer and the like.

Therefore, an object of the present invention is to provide a nitride semiconductor laser device which can improve the crystallinity of a guide layer, an active layer and the like and can obtain a laser beam having a long wavelength.

[0008]

That is, the present invention can achieve the object of the present invention by the following constitutions (1) to (3). (1) In a nitride semiconductor laser device having at least an n-type clad layer, an n-type guide layer, an active layer, a p-type guide layer and a p-type clad layer on a substrate, the n-type and /
Or, as the p-type cladding layer approaches the active layer, A
AlaG whose composition is graded so that the composition is reduced
a1-aN (0 ≦ a <1) is contained in the active layer, and the active layer is InbGa1-bN (0 ≦ b <
1) is a quantum well structure including the n-type and / or
Alternatively, as the p-type guide layer approaches the active layer, In
Of IndGa1-dN (0≤d <1) whose composition is graded so that the composition of In becomes smaller than that of In of the well layer of the active layer. A nitride semiconductor laser device comprising: (2) The n-type and / or p-type clad layer is formed by stacking a first nitride semiconductor having a composition gradient and a third nitride semiconductor having a composition different from that of the first nitride semiconductor. The nitride semiconductor laser device according to claim 1, wherein the nitride semiconductor laser device is a multilayer film layer. (3) The n-type and / or p-type guide layer is formed by stacking the composition-graded second nitride semiconductor and a fourth nitride semiconductor having a composition different from that of the second nitride semiconductor. 3. The nitride semiconductor laser device according to claim 1, wherein the nitride semiconductor laser device is a multi-layered film.

That is, according to the present invention, the composition of In in the n-type and / or p-type guide layer and the composition of Al in the n-type and / or p-type cladding layer are gradually changed, that is, the composition is changed as they approach the active layer. By tilting, the cladding layer,
By improving the crystallinity of the guide layer, the active layer, etc., it is possible to obtain a nitride semiconductor laser device that can obtain laser light of a long wavelength.

As a result of various studies for improving the crystallinity, the inventors of the present invention tend to lower the crystallinity when GaN contains In or Al, and further
It is considered that the crystallinity is significantly reduced due to the large crystal strain at the junction surface between the clad layer and the guide layer due to the large difference in the lattice constant between GaN and InGaN. Based on this consideration, the inventors of the present invention gradually change the lattice constant difference in the cladding layer and the guide layer by gradient composition, and form a crystal in each layer and at the interface between the guide layer and the cladding layer. An improvement in crystallinity was achieved by reducing the strain that occurs.

Conventionally, in a GaAs-based semiconductor, the composition is graded to form a GRIN-SCH structure.
It is known that the threshold becomes low, but in this case,
For example, even if GaAs contains Al, the difference in lattice constant is small, and crystal distortion does not occur much.

In contrast, the present invention results in a GRI.
Although it has a compositional gradient capable of forming an N-SCH structure, it is a peculiar problem in the nitride semiconductor that the crystallinity is remarkably lowered when an oscillation of long wavelength laser light is to be achieved using the nitride semiconductor. This is solved by grading the composition of the clad layer and the guide layer to gradually change the difference in lattice constant and alleviating the strain applied to the crystal. In the present invention, as the compositionally graded layer, at least one of the n-type and p-type cladding layers and at least one of the n-type and p-type guide layers may be compositionally graded, but preferably n The composition of the n-type or p-type clad layer and the n-type and p-type guide layers, and more preferably the n-type clad layer, the n-type guide layer, the p-type clad layer and the p-type guide layer are compositionally graded, It is preferable in terms of improving crystallinity.

Furthermore, according to the present invention, when the n-type and p-type cladding layers and the n-type and p-type guide layers are compositionally graded, the refractive index is increased symmetrically with respect to the active layer as it approaches the active layer. The GRIN-SCH structure has a structure in which the ratio gradually increases, and in addition to improving the crystallinity, light can be effectively confined and the threshold value decreases. As the crystallinity is improved and the threshold value is lowered in this way, laser oscillation at a longer wavelength is facilitated. Further, as described above, when the refractive index is symmetric with respect to the active layer, the portion where the carrier concentration having the population inversion is high coincides with the portion where the gain is generated, and the light emission efficiency is improved. With such a composition gradient, that is, in the cladding layer, the Al composition is gradually decreased as it approaches the active layer, and in the guide layer, the In composition is gradually increased as it approaches the active layer. Since the difference in the crystal lattice constants at the interface between the layer and the guide layer becomes small, for example, an In-containing n-type guide layer with unstable crystallinity is formed on an Al-containing n-type clad layer with unstable crystallinity. Or In
Even if an Al-containing p-type clad layer is laminated on the contained p-type guide layer, good crystallinity can be achieved.

Still further, according to the present invention, the first nitride semiconductor in which the composition of the n-type and / or p-type cladding layer is graded and the third nitride having a composition different from that of the first nitride semiconductor are provided. A multilayer film layer formed by laminating a semiconductor is preferable in terms of improving crystallinity. Still further, the present invention provides n-type and / or
Alternatively, the p-type guide layer has a fourth composition having a composition different from that of the second nitride semiconductor in which the composition is graded, and the second nitride semiconductor.
A multilayer film layer formed by stacking the nitride semiconductor of 1) is preferable from the viewpoint of improving the crystallinity.

In the present invention, when the n-type and p-type clad layers and the n-type and p-type guide layers are compositionally graded and are multilayer films, it is more preferable for improving the crystallinity and lowering the threshold value. In addition to continuous oscillation of long wavelength laser light, continuous oscillation can be performed for a longer time.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be further described with reference to FIG. FIG. 1 is a schematic sectional view of a nitride semiconductor laser device which is an embodiment of the present invention. In Figure 1,
On a nitride semiconductor substrate (ELOG substrate) 1 selectively grown on sapphire, an undoped n-type contact layer 2, an impurity-doped n-type contact layer 3, a crack prevention layer 4, an n-type cladding layer 5, an n-type guide. Layer 6, active layer 7,
A nitride semiconductor laser device having a ridge-shaped stripe formed by sequentially stacking a p-type electron confinement layer 8, a p-type guide layer 9, a p-type cladding layer 10, and a p-type contact layer 11 is shown. In this device, at least one of the n-type and the p-type of the cladding layer and the guide layer is compositionally graded. The p-electrode is formed on the uppermost layer of the ridge-shaped stripe, and the n-electrode is formed on the n-type contact layer.

First, the n-type clad layer and the p-type clad layer of the present invention are nitride semiconductors containing at least an Al composition, and at least one of the n-type and p-type clad layers has an Al composition close to that of the active layer. Any nitride semiconductor may be used as long as the composition is graded so as to decrease. Specifically, at least one of the n-type and p-type cladding layers,
Preferably, both are AlaGa1-a whose composition is graded so that the Al composition decreases as the active layer is approached.
It comprises a first nitride semiconductor having N (0 ≦ a <1, preferably 0 ≦ a <0.7). In the first nitride semiconductor, the value of a in the formula represented by AlaGa1-aN is gradually decreased so that the Al composition becomes smaller as it approaches the active layer. , GaN containing no Al is preferable in terms of crystallinity and light confinement. In this way, by decreasing the Al composition as it approaches the active layer, the lattice constant can be gradually changed, the strain of the crystal in the clad layer can be reduced, and the occurrence of cracks in the clad layer can be reduced. Can be prevented and the crystallinity can be improved. Furthermore, by minimizing the Al composition in the clad layer at the interface between the clad layer and the guide layer, the difference in the lattice constant between the clad layer and the guide layer is reduced, and the strain generated in the crystal at the interface can be reduced. The crystallinity can be improved.

In the first nitride semiconductor, the method of grading the composition so that the Al composition decreases as it approaches the active layer is not particularly limited.
When the clad layer represented by aGa1-aN is grown, the valve is opened and closed so that the supply amount of the raw material gas that becomes the Al composition is gradually decreased in the n-type clad layer and gradually increased in the p-type clad layer. By adjusting or laminating a plurality of first nitride semiconductors having different Al compositions, A
l A plurality of first nitride semiconductors having different mixed crystal ratios are stacked to make the Al composition of the cladding layer graded.

Furthermore, when the composition is graded as described above, the refractive index gradually increases toward the active layer, which makes it easier to trap light. Preferably, the n-type and p-type cladding layers have composition gradients. By doing so, it becomes symmetrical with the active layer in between, effectively confining light.

Further, in the present invention, at least one of the n-type clad layer and the p-type clad layer, preferably both of them, has a composition different from that of the first nitride semiconductor in which the composition is graded. It is preferably a multilayer film layer formed by stacking a third nitride semiconductor. In the present invention, the third nitride semiconductor is not particularly limited as long as it has a different composition from the first nitride semiconductor, but is preferably a nitride semiconductor having a bandgap energy smaller than that of the first nitride semiconductor, Specifically, IneGa1-eN
A nitride semiconductor composed of (0 ≦ e ≦ 1, a <e) is exemplified, and GaN in which e is 0 is preferable. When the multilayer film layer is formed as described above, the Al compositions of the plurality of first nitride semiconductors in the multilayer film layer are made smaller as they approach the active layer. When the clad layer is a multilayer film, the thickness of the single layer is not particularly limited, but is preferably 100 angstroms or less, more preferably 70 angstroms or less.
It is angstrom or less, more preferably 50 angstrom or less, and preferably 10 angstrom or more. When the clad layer is a multilayer film layer including the first nitride semiconductor having a composition gradient, in addition to improving the crystallinity due to the composition gradient, the single film thickness of each layer forming the multilayer film layer is reduced, By preferably having the above single film thickness,
The thickness is less than the elastic critical film thickness of the nitride semiconductor, it is easy to prevent cracks from being generated, and it is possible to grow a clad layer having better crystallinity and good film quality. In addition, the third nitride semiconductor,
a nitride semiconductor in which e is close to 0, that is, an In composition is small,
For example, when the third nitride semiconductor is GaN, the third nitride semiconductor of GaN having particularly good crystallinity acts as a buffer layer to grow the first nitride semiconductor of AlGaN with good crystallinity. And the crystallinity of the entire cladding layer is improved. InAlN is used as the third nitride semiconductor.
Alternatively, InGaAlN or the like may be used.

In the present invention, the thickness of the n-type cladding layer is not particularly limited, but is preferably 3 μm or less, more preferably 2 μm or less, still more preferably 1.5 to 0.
It is 1 μm. When the film thickness is in the above range, the forward voltage (V
It is preferable in terms of reduction of f) and prevention of crack generation. In the present invention, the film thickness of the p-type cladding layer is not particularly limited, but is preferably 2 μm or less, more preferably 1.
It is 5 μm or less, more preferably 1 to 0.05 μm. When the film thickness is in the above range, the surface condition is good, and it is preferable from the viewpoint of preventing the occurrence of cracks.

In the present invention, the n-type cladding layer and the p-type cladding layer are preferably doped with impurities in order to lower the bulk resistance and reduce the forward voltage. Impurities may be doped in any of the layers forming the clad layer. For example, when the clad layer is made of the first nitride semiconductor in which the Al composition is graded, a certain amount of impurities is irrespective of changes in the Al composition. Even if doped, the Al composition may be adjusted so that the Al composition becomes smaller as it approaches the active layer and becomes smaller as it approaches the active layer. As a preferable method of doping impurities, it is preferable to dope so that the impurity becomes smaller as it gets closer to the active layer, which reduces light absorption in the vicinity of the active layer by the cladding layer, lowers optical loss and lowers the threshold value. Tend. Further, it is preferable that the amount of impurities in the clad layer decreases as it approaches the active layer, because the amount of impurities at the interface between the clad layer and the guide layer is small, and strain generated in the crystal is reduced.

In the case where the cladding layer is a multilayer film layer formed by laminating a first nitride semiconductor having a composition gradient and a third nitride semiconductor, impurities are contained in either one layer or both layers. Layer, preferably one or the other, more preferably the third nitride semiconductor. If the cladding layer is doped with impurities, the third
It is preferable that the nitride semiconductor is made of GaN and the third nitride semiconductor is doped with impurities because the bulk resistance can be lowered without lowering the crystallinity. When impurities are doped in both nitride semiconductors, the doping amount of the impurities may be different or the same, and the impurities of a single nitride semiconductor layer adjacent to each other in a plurality of layers forming the multilayer film layer. Different concentrations are preferred.

Examples of the n-type impurities used in the present invention include Si, Ge, Sn, S, O and the like, and Si and Sn are preferable. Examples of p-type impurities used in the present invention include Mg, Zn, Be, and Ca.
Mg is preferred.

The n-type impurity concentration of the n-type cladding layer is 1 ×
It is 1020 / cm3 or less, preferably 5 × 1019 / cm3 or less, more preferably 5 × 1017 to 5 × 1019 / cm3. The impurity concentration within this range is preferable from the viewpoint of Vf and crystallinity. When the n-type impurity changes with the gradient of the Al composition, it is appropriately adjusted within the above-mentioned impurity concentration range. The p-type impurity concentration of the p-type cladding layer is similar to the value of the n-type impurity concentration. When the p-type impurity concentration changes with the gradient of the Al composition, it is appropriately adjusted within the above-mentioned impurity concentration range.

Next, the n-type guide layer and the p-type guide layer of the present invention are nitride semiconductors containing at least In composition, and at least one of the n-type and p-type guide layers has an In composition as an active layer. Any nitride semiconductor may be used as long as it has a composition gradient so as to increase as it approaches. Specifically, at least one of the n-type and p-type guide layers, preferably both, is IndGa1-dN (0) whose composition is graded so that the In composition increases as it approaches the active layer.
Comprising a second nitride semiconductor layer having ≦ d <1, preferably 0 ≦ d <0.6). I of the second nitride semiconductor
The amount of n composition may be smaller or larger than the amount of In composition of the well layer of the active layer, and is preferably adjusted to the same amount or less.

In the second nitride semiconductor, the In composition decreases so that the In composition decreases as it approaches the active layer.
The value of d in the formula represented by -dN is gradually increased to form the guide layer having the highest In composition in the portion closest to the active layer. By grading the In composition in this way, the difference between the lattice constant of the cladding layer and the lattice constant of the guide layer at the interface with the cladding layer is minimized, and the strain applied to the crystal is relaxed to reduce the n-type conductivity. N grown on clad layer
The crystallinity of the type guide layer and the p-type clad layer grown on the p-type guide layer can be improved. Furthermore, since the In composition in the guide layer that is closest to the active layer is set to be the highest in the guide layer,
The crystallinity of the active layer containing a large amount of composition can be improved. When the crystallinity of the guide layer is improved, when the light emitted from the active layer is guided through the guide layer, light loss, absorption, or scattering is prevented, and light confinement is improved.

In the second nitride semiconductor, the method of grading the composition so that the In composition increases as it approaches the active layer is not particularly limited. However, as in the case of the above cladding layer, for example, IndGa1-dN is used. The opening / closing of the valve is adjusted so that the supply amount of the source gas having an In composition during the growth of the guide layer shown in the figure is gradually increased in the n-type guide layer and gradually decreased in the p-type guide layer, or By stacking a plurality of second nitride semiconductors having different compositions, a plurality of second nitride semiconductors having different In mixed crystal ratios are stacked so that the In composition of the guide layer is graded.

Furthermore, when the composition is graded as described above, the refractive index gradually increases toward the active layer, which makes it easier to trap light, and preferably the n-type and p-type guide layers have a composition gradient. By doing so, it becomes symmetrical with the active layer in between, and it becomes better to effectively confine light. Furthermore, when the n-type and p-type guide layers are compositionally graded and the n-type and p-type clad layers are compositionally graded, the refractive index gradually increases from the clad layer toward the active layer, and the crystallinity In addition to the improvement, it is possible to effectively confine the light, which is preferable.

Further, in the present invention, at least one of the n-type guide layer and the p-type guide layer, preferably both, has a composition different from that of the second nitride semiconductor in which the composition is graded. It is preferably a multilayer film layer formed by stacking a fourth nitride semiconductor. In the present invention,
The fourth nitride semiconductor is not particularly limited as long as it has a composition different from that of the first nitride semiconductor. For example, InfGa1-f
It may also be made of N (0 ≦ f <1) or AlgGa1-gN (0 ≦ g <1). It is preferable that the fourth nitride semiconductor is GaN in order to improve the crystallinity of the guide layer. When the multilayer film layer is formed as described above, the In composition of the plurality of second nitride semiconductors in the multilayer film layer is increased as the second nitride semiconductor is closer to the active layer. When the guide layer is a multilayer film, the thickness of the single layer is not particularly limited, but is preferably 100 angstroms or less, more preferably 70 angstroms or less, further preferably 50 angstroms or less, and preferably 10 angstroms or more. is there. When the guide layer is a multilayer film layer including a second nitride semiconductor having a composition gradient, in addition to improving the crystallinity due to the composition gradient, the single film thickness of each layer forming the multilayer film layer is reduced, The single film thickness is preferably the elastic critical film thickness of the nitride semiconductor or less, and a guide layer having better crystallinity and good film quality can be grown. In addition, when the fourth nitride semiconductor is GaN, when the multilayer film layer is formed, GaN with good crystallinity acts as a buffer layer, and the second nitride semiconductor InGaN is added. It becomes easy to grow with good crystallinity, and the crystallinity of the entire guide layer is improved.

In the present invention, the thickness of the n-type and p-type guide layers is not particularly limited, but is preferably 5 μm or less,
More preferably 3 μm or less, further preferably 2.5 to
It is 0.05 μm. Crystallinity when the film thickness is in the above range,
It is preferable in terms of Vf and light confinement.

In the present invention, the n-type guide layer is
It may be doped with an n-type impurity, and is preferably undoped. Since the second nitride semiconductor contains an In composition, it exhibits n-type even if it is not doped with impurities. Therefore, undoped with good crystallinity is preferable because the crystallinity of the n-type guide layer is good. Further, in the present invention, the p-type guide layer may be doped with p-type impurities, and is preferably doped with p-type impurities. In
Since the guide layer containing the composition exhibits n-type when undoped, it is preferable in that the p-type guide layer is doped with p-type impurities to lower the bulk resistance.

Impurities may be doped in any of the layers forming the guide layer. For example, when the guide layer is composed of the first nitride semiconductor having a composition gradient of In composition, it is related to the change of In composition. Alternatively, even if a certain amount is doped, the In composition may be adjusted so that the In composition decreases as it approaches the active layer and increases as it approaches the active layer.

In addition, the guide layer has a second composition gradient.
In the case of a multilayer film layer formed by stacking the nitride semiconductor of and the fourth nitride semiconductor, the impurity may be doped in either one layer or both layers, but preferably either One is doped, and more preferably the fourth nitride semiconductor is doped from the viewpoint of crystallinity. When the guide layer is doped with impurities, the fourth nitride semiconductor is made of GaN, and when the fourth nitride semiconductor is doped with impurities, the bulk resistance is lowered without lowering the crystallinity. Is preferred and is preferable. When the impurities are doped into both the second nitride semiconductor and the fourth nitride semiconductor, the doping amount of the impurities may be different or the same,
In a plurality of layers forming the multilayer film layer, it is preferable that adjacent single nitride semiconductor layers have different impurity concentrations.

As the n-type impurities and p-type impurities used in the guide layer of the present invention, the same impurities as those which can be doped into the clad layer can be mentioned. When the n-type guide layer is doped with n-type impurities, the n-type impurity concentration is 1 × 10 20 / cm 3 or less, preferably 5 × 10 19 /
cm 3 or less, more preferably 1 × 10 19 / cm 3 or less, most preferably undoped with good crystallinity. When the n-type impurity changes with the gradient of the In composition, it is appropriately adjusted within the above-mentioned impurity concentration range. The p-type impurity concentration of the p-type guide layer is 1 × 10 20 / cm 3 or less, preferably 5
X1019 / cm3 or less, more preferably 1 x 1019-1
× 10 16 / cm 3. When the p-type impurity concentration is within this range, it is preferable in terms of resistance and crystallinity. Impurity concentration is I
When it changes with the gradient of n composition, it is appropriately adjusted within the range of the above impurity concentration.

Next, as the active layer of the present invention, InbG
A single quantum well structure or a multiple quantum well structure containing a1-bN (0 ≦ b <1) is preferable, and a multiple quantum well structure is preferable. The multi-quantum well structure is preferable because the light emission output is improved as compared with the single quantum well structure.

The active layer of the present invention is not particularly limited, but the In composition ratio of the well layer is adjusted so that the oscillation wavelength is longer than 400 nm, preferably 420 nm or longer. Is mentioned. Furthermore,
As a specific example of the active layer of the present invention, when the active layer has a multi-quantum well structure, for example, approximately, a preferable well layer is InbGa1-bN in which b is 0.1 to 0.6,
A preferable barrier layer is InbGa1 in which b is 0 to 0.1.
-bN is mentioned. Further, one or both of the well layer and the barrier layer forming the active layer may be doped with impurities. It is preferable to dope the barrier layer with impurities because the threshold value is lowered. As an impurity, even if it is n-type, p
It can be a mold. The film thickness of the well layer is 100 angstroms or less, preferably 70 angstroms or less, preferably 10 angstroms or more, and more preferably 30 to 60 angstroms. The thickness of the barrier layer is 150 angstroms or less, preferably 100 angstroms or less, preferably 10 angstroms or more, and more preferably 90 to 150.
Angstrom.

When the active layer has a multiple quantum well structure, the stacking order of the barrier layer and the well layer forming the active layer may start from the barrier layer and end with the well layer or end with the barrier layer. May start with a well layer and end with a barrier layer, or may start with a well layer and end with a well layer. It is preferable to start from the barrier layer and repeat the pair of the well layer and the barrier layer 2 to 5 times, and preferably repeat the pair of the well layer and the barrier layer 3 times to lower the threshold value and shorten the life. It is preferable for improving the characteristics.

The In composition ratio of the well layer of the active layer may be adjusted by adjusting the In composition ratio so as to obtain a desired oscillation wavelength. However, a value obtained from the following theoretical value calculation formula can be used as an approximate value. However, in the oscillation wavelength obtained by actually operating the laser element, since the quantum level having the quantum well structure is formed, the energy of the oscillation wavelength (Eλ) is higher than that of the band gap energy (Eg) of InGaN. , And the oscillation wavelength obtained from the calculation formula tends to shift to the shorter wavelength side.

[Calculation formula of theoretical value] Eg = (1-χ) 3.40 + 1.95χ-Bχ (1-
χ) Wavelength (nm) = 1240 / Eg Eg: Band gap energy of InGaN well layer χ: In composition ratio 3.40 (eV): GaN band gap energy 1.95 (eV): InN band gap energy B : Boeing parameter is shown and is 1 to 6 eV. This variation of the Boeing parameter is due to
In recent research, SIMS analysis and the like have traditionally assumed that the crystal has no strain, but it was set to 1 eV. However, the degree of strain varies depending on the In composition ratio or when the film thickness is thin. It is becoming clear that

Although there is a slight difference between the oscillation wavelength considered from the specific In composition ratio obtained from SIMS analysis of the well layer and the oscillation wavelength when actually oscillated as described above, the actual The oscillation wavelength is adjusted to a desired wavelength.

In the present invention, the layer structure other than the above, which constitutes the laser element, is not particularly limited, and examples thereof include the layer structure shown in FIG. 1, and one embodiment thereof will be described below.

The selective growth ELOG substrate will be described below. The selective growth for obtaining the ELOG substrate is a growth method capable of temporarily stopping the vertical growth of the nitride semiconductor at least partially and suppressing the dislocation by utilizing the lateral growth of the nitride semiconductor. There is no particular limitation as long as it exists.
For example, specifically, a protective film made of a material in which the nitride semiconductor does not grow or is hard to grow is partially formed on a heterogeneous substrate made of a material different from the nitride semiconductor, and the nitride semiconductor grows on the protective film. As a result, the nitride semiconductor grows from the portion where the protective film is not formed, and by continuing the growth, the nitride semiconductor grows laterally toward the protective film to obtain a thick nitride semiconductor.

The heterogeneous substrate is not particularly limited as long as it is a substrate made of a material different from the nitride nitride semiconductor, and for example, sapphire or spinel (main surface having C-plane, R-plane, and A-plane shown in FIG. 2) is used. Insulating substrate such as MgA1 2 O4), S
iC (including 6H, 4H, 3C), ZnS, ZnO, G
Substrate materials different from conventionally known nitride semiconductors can be used, such as aAs, Si, and oxide substrates that lattice match with nitride semiconductors. Of the above, the different type of substrate is preferably sapphire, and more preferably the C plane of sapphire. Furthermore, from the viewpoint of preventing the generation of fine cracks inside the ELOG substrate, the C of sapphire is used.
The surface is off-angled in steps, and the off-angle angle θ
It is preferable that (θ shown in FIG. 3) is in the range of 0.1 ° to 0.3 °. If the off-angle angle θ is less than 0.1 °, the characteristics of the laser device are likely to be stable, and fine cracks are likely to occur inside the ELOG substrate, while the off-angle is 0.3 °. If it exceeds, the surface state of the ELOG-grown nitride semiconductor becomes step-like, and if an element structure is grown on the step, the step is slightly emphasized, and the element tends to be short-circuited and the threshold value tends to increase.
Here, the fine cracks are finer than dislocations due to the difference in crystal lattice constants of the crystals, and tend to be generated from the inside of the ELOG substrate.

A protective film is formed directly or after a nitride semiconductor is once grown on a heterogeneous substrate such as sapphire which is off-angled stepwise as described above. The protective film is not particularly limited as long as it is a material having a property that a nitride semiconductor does not grow on the surface of the protective film or does not easily grow, but for example, silicon oxide (SiOX), silicon nitride (SiXNY), titanium oxide (TiOX). In addition to oxides and nitrides such as zirconium oxide (ZrOx) and multilayer films of these, metals having a melting point of 1200 ° C. or higher can be used. As a preferred protective film material, SiO
2 and SiN. To form a protective film material on the surface of a nitride semiconductor, for example, vapor deposition, sputtering, CV
Vapor deposition techniques such as D can be used. Further, in order to partially (selectively) form, by using a photolithography technique, a photomask having a predetermined shape is produced, and the material is vapor-phase film-formed through the photomask. A protective film having a predetermined shape can be formed. The shape of the protective film is not particularly limited, but it can be formed, for example, in the shape of dots, stripes, or a checkerboard shape, preferably in the shape of a stripe so that the stripes are perpendicular to the orientation flat surface (A surface of sapphire). To be done. When the surface area where the protective film is formed is larger than the surface area of the portion where the protective film is not formed, dislocations can be prevented and a nitride semiconductor substrate having excellent crystallinity can be obtained.

When the protective film has a stripe shape, the relationship between the stripe width of the protective film and the width of the portion (window portion) where the protective film is not formed is 10: 3 or more, preferably 16 to 18 :. It is 3. When the stripe width of the protective film and the width of the window have the above relationship, the nitride semiconductor can easily cover the favorable protective film, and dislocations can be favorably prevented. The stripe width of the protective film is, for example, 6 to 27 μm.
m, preferably 11 to 24 μm, and the width of the window is, for example, 2 to 5 μm, preferably 2 to 4 μm.
Further, when the device structure is formed on the ELOG substrate and the ridge-shaped stripe is formed on the uppermost layer of the p-type nitride semiconductor layer, the ridge-shaped stripe is the upper portion of the protective film,
In addition, it is preferable that the protective film is formed so as to avoid the central portion of the protective film so that the threshold value can be lowered and the reliability of the device is improved. This is because the crystallinity of the nitride semiconductor in the upper portion of the protective film is better than that in the upper portion of the window portion, which is preferable for lowering the threshold value. Further, the vicinity of the center of the protective film is a portion where adjacent nitride semiconductors grown from the window are joined by lateral growth, and a void may be generated at such a joined portion. When the stripes are formed, dislocations are likely to propagate from the voids during the operation of the laser device, so that the reliability of the device tends to deteriorate.

The protective film may be formed directly on a different substrate, but it is necessary to form a buffer layer grown at a low temperature and then a buffer layer grown at a high temperature and then to form a protective layer to prevent dislocation. preferable. Examples of the low-temperature grown buffer layer include AlN, GaN, AlGaN, and InGa.
N or the like at a temperature of 900 ° C or lower and 200 ° C or higher,
It is grown at a film thickness of several tens of angstroms to several hundreds of angstroms. This low-temperature grown buffer layer is preferable for alleviating irregularities in the lattice constant between the heterogeneous substrate and the high-temperature grown buffer layer and preventing dislocation from occurring. For the high temperature growth buffer layer, undoped GaN, n-type impurity-doped GaN, or Si-doped GaN can be used, and undoped GaN is preferable. Further, these nitride semiconductors have high temperatures, specifically, 9
It is grown on the buffer layer at 00 ° C to 1100 ° C, preferably 1050 ° C. The film thickness is not particularly limited, but is, for example, 1 to 20 μm, preferably 2 to 10 μm.

Next, a nitride semiconductor is selectively grown on the protective film to obtain an ELOG substrate. In this case, as the nitride semiconductor to be grown, undoped GaN or impurities (for example, Si, Ge, Sn, Be, Zn, Mn,
GaN doped with Cr and Mg) may be mentioned. The growth temperature is, for example, 900 ° C. to 1100 ° C., and more specifically, the temperature is around 1050 ° C. It is preferable that impurities are doped to suppress dislocations. In the initial stage of growth on the protective film, it is grown by MOCVD (Metal Organic Chemical Vapor Deposition) or the like, which makes it easy to control the growth rate, and the growth after the protective film is covered with the nitride semiconductor of ELOG growth is carried out by HVPE (halide). It may be grown by a vapor phase growth method) or the like.

As the GaN substrate, in addition to the above method, a nitride semiconductor once grown on a heterogeneous substrate is formed with irregularities, and a protective film is formed on the concave non-bottom portion and / or the convex portion. It is possible to use a material obtained by growing a nitride semiconductor again from above. Further, a nitride semiconductor is formed again to form a concavo-convex structure on the nitride semiconductor without a protective film (a protective film is not formed on the bottom and top of the recess). You can

A device structure is grown on the above ELOG substrate. First, the n-type contact layer 2 is grown on the ELOG substrate 1. As the n-type contact layer, AlhGa1-hN (0) doped with an n-type impurity (preferably Si) is used.
<H <1), preferably h is 0.01 to 0.
05 AlhGa1-hN is grown. When the n-type contact layer is formed of a ternary mixed crystal containing Al, the ELOG substrate 1
Even if fine cracks occur in the surface, it is possible to prevent the propagation of the fine cracks, and further, due to the difference in the lattice constant and the thermal expansion coefficient between the ELOG substrate 1 and the n-type contact layer, which are the conventional problems. This is preferable because it can prevent the generation of fine cracks in the n-type contact layer. The doping amount of n-type impurities is 1 × 10 18 / cm 3 to 5 × 10 18
/ Cm3. An n electrode is formed on this n type contact layer 2. The thickness of the n-type contact layer 2 is 1 to 1
It is 0 μm. Further, between the ELOG substrate 1 and the n-type contact layer 2, undoped AlhGa1-hN (0 <h <
1) may be grown. If this undoped layer is grown, the crystallinity becomes good, which is preferable for improving the life characteristics. The thickness of the undoped n-type contact layer is several μ
m.

Next, the crack prevention layer 3 is grown on the n-type contact layer 2. As the crack prevention layer 3, Si is used.
Doped InjGa1-jN (0.05 ≦ j ≦ 0.2) is grown, and preferably j is 0.05 to 0.08.
Grow a1-jN. The crack prevention layer 3 can be omitted, but it is preferable to form the crack prevention layer 3 on the n-type contact layer 2 in order to prevent the occurrence of cracks in the device. The doping amount of Si is 5 × 10
18 / cm3. Further, if the In mixed crystal ratio is increased (j ≧ 0.1) when the crack prevention layer 3 is grown,
The crack prevention layer 3 is preferable because it can absorb the light emitted from the active layer 6 and leaked from the n-type cladding layer 4, and can prevent the disturbance of the far field pattern of the laser light. The film thickness of the crack prevention layer is a thickness that does not impair the crystallinity, and is specifically 0.0
It is 5 to 0.3 μm.

Next, the n-type cladding layer 4 is grown on the crack prevention layer 3. The n-type clad layer 4 is as described above.

Next, the n-type guide layer 5 and the n-type clad layer 4 are formed.
Grow up. The n-type guide layer 5 is as described above.

Next, the active layer 6 is grown on the n-type guide layer 5. The active layer is as described above.

Next, the p-type electron confinement layer 7 is grown on the active layer 6. As the p-type electron confinement layer 7, at least one layer of Mg-doped AldGa1-dN (0 <d≤1) is grown. Preferably d
Is 0.1 to 0.5 of Mg-doped AldGa1-dN. The film thickness of the p-type electron confinement layer 7 is 10 to 1000 angstroms, preferably 50 to 200 angstroms. When the film thickness is in the above range, electrons in the active layer 6 can be favorably confined, and the bulk resistance can be suppressed low, which is preferable. The doping amount of Mg in the p-type electron confinement layer 7 is 1 × 10 19 / cm 3 to 1 × 10 2.
It is 1 / cm3. When the doping amount is in this range, in addition to lowering the bulk resistance, Mg is well diffused into the p-type guide layer to be grown by undoping described later, and Mg is added to the p-type guide layer 8 which is a thin film layer. × 10 16 / cm 3-1
It can be contained in the range of × 10 18 / cm 3. The p-type electron confinement layer 7 has a low temperature, for example, 850 to 95.
It is preferable to grow the active layer at about 0 ° C. at a temperature similar to that for growing the active layer because decomposition of the active layer can be prevented.
The p-type electron confinement layer 7 has a low temperature growth layer, a high temperature,
For example, it may be composed of two layers including a layer grown at a temperature of about 100 ° C. higher than the growth temperature of the active layer. As described above, when it is composed of two layers, the layer grown at low temperature prevents decomposition of the active layer, and the layer grown at high temperature lowers the bulk resistance, which is favorable overall. In addition, the p-type electron confinement layer 7
The thickness of each layer is not particularly limited when it is composed of two layers, but the low temperature growth layer has a thickness of 10 to 50 angstroms,
The high temperature growth layer preferably has a thickness of 50 to 150 angstroms.

Next, the p-type guide layer 8 is grown on the p-type electron confinement layer 7. The p-type guide layer 8 is as described above.

Next, the p-type cladding layer 9 is replaced with the p-type guide layer 8
Grow to. The p-type clad layer is as described above.

Next, the p-type contact layer 10 is grown on the p-type cladding layer 9. As the p-type contact layer, M
It is formed by growing a nitride semiconductor layer made of g-doped GaN. The film thickness is 10 to 200 angstrom. The doping amount of Mg is 1 × 10 19 / cm 3 to 1 × 1
It is 022 / cm3. By adjusting the film thickness and the doping amount of Mg in this way, the carrier concentration of the p-type contact layer is increased, and the ohmic contact of the p-electrode is facilitated.

In the element of the present invention, the ridge-shaped stripe is formed by etching from the p-type contact layer to the lower side (substrate side) of the p-type contact layer. For example, a stripe formed by etching from the p-type contact layer 10 to the middle of the p-type cladding layer 9 as shown in FIG. 1, or the p-type contact layer 10
From the n-type contact layer 2 to the stripes.

On the side surface of the ridge-shaped stripe formed by etching and on the plane of the nitride semiconductor layer continuous to the side surface, insulation having a value smaller than the refractive index of the laser waveguide region, for example, as shown in FIG. A film is formed.
The insulating film formed on the side surface of the stripe or the like has, for example, a refractive index of about 1.6 to 2.3, S
An oxide containing at least one element selected from the group consisting of i, V, Zr, Nb, Hf, and Ta, BN, and Al
N or the like is preferable, and one or more elements of oxides of Zr and Hf and BN are preferable. Further, a p-electrode is formed on the surface of the p-type contact layer 10 which is the uppermost layer of the stripe via this insulating film. The width of the ridge-shaped stripe formed by etching is 0.5
-4 μm, preferably 1-3 μm. When the width of the stripe is in this range, the horizontal transverse mode is likely to be a single mode, which is preferable. Further, the etching is performed on the p-type cladding layer 9
It is preferable to make the aspect ratio closer to 1 when the area is closer to the substrate than the interface between the laser waveguide region and the laser waveguide region. As described above, when the etching amount of the ridge-shaped stripe, the stripe width, and the refractive index of the insulating film on the side surface of the stripe are specified, single mode laser light can be obtained, and the aspect ratio can be made closer to a circle. A laser beam and a lens are easy to design, which is preferable. Further, in the device of the present invention, various conventionally known ones can be appropriately selected and used as the p electrode, the n electrode and the like.

In the present invention, the growth of the nitride semiconductor is performed by MOVPE (metal organic chemical vapor deposition), MOCVD.
(Metal organic chemical vapor deposition), HVPE (halide vapor deposition), MBE (molecular beam epitaxy), or any other known method for growing a nitride semiconductor can be applied.

[0062]

The following is an example of an embodiment of the present invention. However, the present invention is not limited to this.

Example 1 As Example 1, the nitride semiconductor laser device according to the embodiment of the present invention shown in FIG. 1 is manufactured. Further, as described in the detailed description of the invention, the value of the calculation formula of the theoretical value of the In composition ratio is different from the actual oscillation wavelength due to the shift to the short wavelength due to the formation of the quantum level having the quantum well structure. Therefore, the In composition ratio of the active layer of the example is an approximate value.

As a heterogeneous substrate, as shown in FIG. 3, the C-plane which is off-angled stepwise is used as the main surface, the off-angle is θ = 0.15 °, the step difference is about 20 Å, and the terrace width W is about 800 Å. A sapphire substrate is prepared in which the orientation flat surface is the A surface and the steps are perpendicular to the A surface. This sapphire substrate was set in a reaction vessel, the temperature was set to 510 ° C., hydrogen was used as a carrier gas, ammonia and TMG (trimethylgallium) were used as source gases, and a low-temperature grown buffer layer made of GaN was formed on the sapphire substrate. It is grown to a film thickness of 200 Å. After the growth of the buffer layer, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C., TMG, ammonia, and silane gas are used as source gases, and a high-temperature grown buffer layer made of undoped GaN is formed to a thickness of 5 μm. Grow with. Next, a stripe-shaped photomask is formed on the wafer on which the high-temperature-grown buffer layer is laminated, and the stripe width is 18 μm by a CVD apparatus.
m, the protective film made of SiO2 with a window width of 3 μm is 0.1
It is formed with a film thickness of μm. The stripe direction of the protective film is perpendicular to the sapphire A surface. After forming the protective film,
The wafer is transferred to a reaction container, TMG and ammonia are used as source gases at 1050 ° C., and a nitride semiconductor layer made of undoped GaN is grown to a thickness of 15 μm to form ELO.
The G substrate 1 is used. The following element structure is grown on the obtained ELOG substrate 1.

(Undoped n-type contact layer) [not shown in FIG. 1] TMA was used as a source gas at 1050 ° C. on the ELOG substrate 1.
An n-type contact layer of undoped Al0.05Ga0.95N is grown to a thickness of 1 μm using (trimethylaluminum), TMG, and ammonia gas. (N-type contact layer 2) Next, at the same temperature, TMA, TMG, and ammonia gas are used as source gases, silane gas (SiH4) is used as impurity gas, and Si is 3 × 10 18
The n-type contact layer 2 made of Al0.05Ga0.95N doped with / cm3 is grown to a thickness of 3 μm. No fine cracks are generated in the grown n-type contact layer 2, and the generation of fine cracks is well prevented.
Further, even if minute cracks are generated in the ELOG substrate 1, by propagating the n-type contact layer 2, propagation of the minute cracks can be prevented and an element structure having good crystallinity can be grown. The crystallinity is improved by the n-type contact layer 2
It becomes better by growing the undoped n-type contact layer as described above than in the case of only the case.

(Crack prevention layer 3) Next, the temperature is set to 800.
C., TMG, TMI (trimethylindium), and ammonia are used as source gases, silane gas is used as an impurity gas, and In0.0 is doped with Si at 5 × 10 18 / cm 3
The crack prevention layer 3 made of 8 Ga 0.92 N is 0.15 μm
To grow.

(N-type clad layer 4) Next, the temperature is set to 105.
The temperature is set to 0 ° C., TMA, TMG, and ammonia are used as source gases, and the first layer is made of undoped Al0.15Ga0.86N.
Nitride semiconductor of 25 angstroms is grown to a film thickness of 25 angstroms, then TMA is stopped, silane gas is used as an impurity gas, and Si is 5 × 10 18 / cm 3 -doped GaN.
A third nitride semiconductor is grown to a film thickness of 25 Å. And this operation is 140
The first nitride semiconductor and the third nitride semiconductor are layered repeatedly to grow the n-type cladding layer 4 made of a multilayer film (superlattice structure) having a total film thickness of 7,000 angstroms. However, the Al composition of the first nitride semiconductor after the second time is adjusted so that the TMA flow rate of the raw material gas is gradually reduced, and the Al composition of the 140th first nitride semiconductor is
The Al composition is graded so that GaN does not contain the composition.

(N-type guide layer 5) Next, the temperature is set to 850 ° C.
Then, using TMI, TMG, and ammonia as source gases, a second nitride semiconductor made of undoped IndGa1-dN is grown to a film thickness of 25 angstroms, and then TMI is stopped to make a second nitride semiconductor made of undoped GaN. 4 nitride semiconductor is grown to a film thickness of 25 Å. Then, repeat this operation 40 times each
And the fourth nitride semiconductor are laminated to grow an n-type guide layer composed of a multilayer film layer having a total film thickness of 2000 angstrom. However, the value of d indicating the In composition ratio of the second nitride semiconductor is set to 0 at the first time and is gradually increased after the second time, and the second nitride that is closest to the active layer is obtained. In such that the d value of the semiconductor is 0.1.
The composition is compositionally graded.

(Active layer 6) Next, the temperature is set to 800 ° C., and TMI, TMG, and ammonia are used as source gases,
Silane gas is used as an impurity gas, and Si is 5 × 10 18
/ Cm3 doped In0.01Ga0.99N barrier layer is grown to a thickness of 100 angstroms. Subsequently, the silane gas was stopped, and undoped In0.3Ga0.7N
Is grown to a film thickness of 30 Å. This operation is repeated four times, and finally the active layer 6 having a multiple quantum well structure (MQW) having a total film thickness of 620 angstroms in which barrier layers are laminated is grown.

(P-type electron confinement layer 7) Next, at the same temperature, TMA, TMG and ammonia were used as source gases, Cp2Mg (cyclopentadienylmagnesium) was used as an impurity gas, and Mg was 1 × 10 19 / A p-type electron confinement layer 7 of cm0.4-doped Al0.4Ga0.6N is grown to a film thickness of 100 angstrom.

(P-type guide layer 8) Next, the temperature is set to 850 ° C.
Then, TMI, TMG, and ammonia are used as source gases, and a second nitride semiconductor made of undoped IndGa1-dN is grown to a film thickness of 25 angstroms. Then, TMI is stopped and Cp2Mg is used as an impurity gas. , A fourth nitride semiconductor made of GaN doped with 5 × 10 18 / cm 3 of Mg is grown to a film thickness of 25 Å. Then, this operation is repeated 40 times to stack the second nitride semiconductor and the fourth nitride semiconductor to grow a p-type guide layer composed of a multilayer film having a total film thickness of 2000 angstrom. However, the value of d indicating the In composition ratio of the second nitride semiconductor is set to 0.1 at the first time,
After the second time, the value is gradually decreased so that the value of d of the second nitride semiconductor farthest from the active layer becomes 0.
The n composition is compositionally graded.

(P-type clad layer 9) Next, the temperature is set to 900.
C., using TMA, TMG, and ammonia as source gases, a first nitride semiconductor made of undoped AlaGa1-aN is grown to a film thickness of 25 Å, then TMA is stopped, and Cp2Mg is used as an impurity gas. A second nitride semiconductor made of GaN doped with 5 × 10 18 / cm 3 of Mg is grown to a film thickness of 25 Å. Then, this operation is repeated 140 times to stack the first nitride semiconductor and the third nitride semiconductor to grow the p-type cladding layer 9 made of a multilayer film (superlattice structure) having a total film thickness of 7,000 angstroms. . However,
The value of a indicating the Al composition ratio of the first nitride semiconductor is set to 0 for the first time, and the value of a is gradually increased for the second time and thereafter, and the value of a for the first nitride semiconductor farthest from the active layer is increased. The Al composition is compositionally graded so that the value of a becomes 0.15.

(P-type contact layer 10) Next, at the same temperature, TMG and ammonia were used as source gases, Cp2Mg was used as an impurity gas, and Mg was 1 × 10 20 / cm3.
The p-type contact layer 10 made of doped GaN 15
It is grown to a film thickness of 0 angstrom.

After completion of the reaction, the wafer is annealed at 700 ° C. in a nitrogen atmosphere in the reaction vessel to further reduce the resistance of the p-type layer. After annealing, the wafer is taken out of the reaction container, a protective film made of SiO2 is formed on the surface of the uppermost p-side contact layer, and etched by SiCl4 gas using RIE (reactive ion etching), as shown in FIG. Then, the surface of the n-side contact layer 2 on which the n-electrode is to be formed is exposed. Next, as shown in FIG. 4A, almost the entire surface of the uppermost p-side contact layer 10 is
Si oxide (mainly SiO2) by PVD equipment
After forming the first protective film 61 of 0.5 μm in thickness, a mask having a predetermined shape is applied on the first protective film 61, and the third protective film 63 of photoresist is formed into stripes. The width is 1.8 μm and the thickness is 1 μm. Next, as shown in FIG. 4B, after forming the third protective film 63, RIE is performed.
With a (reactive ion etching) device, CF4 gas is used to etch the first protective film using the third protective film 63 as a mask to form stripes. After that, by treating with an etching solution to remove only the photoresist, as shown in FIG.
A first protective film 61 having a stripe width of 1.8 μm can be formed on the 0.

Further, as shown in FIG. 4D, after the stripe-shaped first protective film 61 is formed, S is again formed by RIE.
The p-side contact layer 10 and the p-side clad layer 9 are etched by using iCl4 gas to obtain a stripe width of 1.
A 8 μm ridge-shaped stripe is formed. However, the ridge-shaped stripe has an ELOG pattern as shown in FIG.
It is formed on the protective film formed during growth so as to avoid the central portion of the protective film. After forming the ridge stripe, the wafer is transferred to a PVD apparatus, and as shown in FIG. 4E, a second protective film 62 made of Zr oxide (mainly ZrO2) is formed on the first protective film 61, 0.5 μm on the p-side clad layer 9 exposed by etching
The film thickness is continuously formed. When the Zr oxide is formed in this manner, it is preferable because the pn plane is insulated and the transverse mode is stabilized. Next, the wafer is dipped in hydrofluoric acid, and as shown in FIG.
Are removed by the lift-off method.

Next, as shown in FIG. 4G, the surface of the p-side contact layer exposed by removing the first protective film 61 on the p-side contact layer 10 is made of Ni / Au.
The electrode 20 is formed. However, the p electrode 20 has a stripe width of 100 μm and is formed over the second protective film 62 as shown in this figure. After forming the second protective film 62,
As shown in FIG. 1, on the exposed surface of the n-side contact layer 2, an n electrode 21 made of Ti / Al is formed in a direction parallel to the stripe.

As described above, the sapphire substrate of the wafer on which the n electrode and the p electrode were formed was polished to 70 μm, and then cleaved in a bar shape from the substrate side in the direction perpendicular to the striped electrodes, A resonator is formed on the cleavage plane (11-00 plane, plane corresponding to side surface of hexagonal columnar crystal = M plane).
A dielectric multilayer film made of SiO2 and TiO2 is formed on the resonator surface, and finally the bar is cut in a direction parallel to the p-electrode to obtain a laser device as shown in FIG. The resonator length is 30
It is desirable to set it to 0 to 500 μm. The obtained laser device was placed on a heat sink, and each electrode was wire-bonded, and laser oscillation was attempted at room temperature. As a result, continuous oscillation with an oscillation wavelength of about 455 nm was confirmed at room temperature with a threshold value of 2.5 kA / cm 2 and a threshold voltage of 5 V, and a life of 1000 hours or more was shown at room temperature.

Example 2 A laser device is manufactured in the same manner as in Example 1, except that the p-type guide layer and the p-type clad layer are formed as follows.

(P-type guide layer 8) The temperature was set to 850 ° C., and TMI, TMG, and ammonia were used as source gases,
Cp2Mg is used as the impurity gas, and Mg is 1 × 10 18
/ Cm 3 -doped In 0.1 Ga 0.9 N first-time second nitride semiconductor was grown to a film thickness of 50 angstroms, and then the first second nitride semiconductor
Indium doped with 1 × 10 18 / cm 3 of In was similarly used except that the flow rate of the source gas was adjusted so that the composition was reduced.
A second second nitride semiconductor made of GaN is grown to a film thickness of 50 Å. In this way, the operation is repeated so that the In composition of the second nitride semiconductor gradually decreases, and the second nitride semiconductor farthest from the active layer does not contain the In composition. And the second nitride semiconductor is laminated to grow a p-type guide layer having a total film thickness of 750 angstroms and having an In composition gradient.

(P-type clad layer 9) Next, the temperature is set to 900.
℃, TMG and ammonia are used as source gas, Cp2Mg is used as impurity gas, and Mg is 5 × 10 18 /
In the same manner except that the first first nitride semiconductor made of cm 3 -doped GaN is grown to a film thickness of 25 Å, and then TMA is added as a source gas.
A second first nitride semiconductor made of AlaGa1-aN doped with g of 5.times.10@18 / cm @ 3 is grown to a film thickness of 25 angstroms. In this way, the operation is repeated so that the Al composition of the first nitride semiconductor gradually increases, and the first nitride semiconductor farthest from the active layer is Al0.2Ga0.8.
A plurality of first nitride semiconductors having different Al compositions are laminated so as to have N, and a p-type clad layer 9 having a total film thickness of 5000 angstroms and having an Al composition gradient is grown. The obtained laser device oscillated a good laser almost in the same manner as in Example 1.

[Embodiment 3] A laser device is manufactured in the same manner as in Embodiment 1 except that the n-type and p-type guide layers and the n-type and p-type cladding layers are formed as follows.

(N-type cladding layer 4) The temperature is set to 1050 ° C., TMA, TMG and ammonia are used as source gases, silane gas is used as an impurity gas, and Si is 5 × 1.
Except that the first nitride semiconductor having a film thickness of 25 angstroms made of Al0.2Ga0.86N doped with 018 / cm3 was grown to a thickness of 25 angstroms, and then the Al composition was smaller than that of the first nitride semiconductor. Similarly, Si is 5 × 10 18 /
A second cm 3 -doped first nitride semiconductor is grown. In this way, the operation is repeated so that the Al composition is gradually decreased, and the first nitride semiconductor closest to the active layer is GaN containing no Al composition, and the plurality of first nitrides having different Al compositions are used. Semiconductors are laminated to form a total film thickness of 70
A compositionally graded n-type cladding layer of Al having a composition of 00 angstrom is grown.

(N-type guide layer 5) The temperature is set to 850 ° C., TMG and ammonia are used as the source gas, and the first second nitride semiconductor made of undoped GaN is made 30 times.
Second growth of undoped InGaN containing a small amount of In composition is performed in the same manner except that the film is grown to a film thickness of angstrom and then TMI is added as a source gas.
Is grown to a film thickness of 30 Å. In this way, the operation is repeated so that the In composition of the second nitride semiconductor is gradually increased, and the second nitride semiconductor that is closest to the active layer has the second nitride of In0.1Ga0.9N. Then, a plurality of second nitride semiconductors having different In compositions are stacked, and an n-type guide layer having a total film thickness of 750 angstroms and having an In composition gradient is grown.

(P-Type Guide Layer 8) As the p-type guide layer, the same one as in Example 2 is grown.

(P-type clad layer 9) As the p-type clad layer, the same one as in Example 2 is grown.

The obtained laser device had a slightly deteriorated life characteristic as compared with Example 1, but lased as good as almost in Example 1. Further, since the multilayer film layer is not formed, the growth time can be shortened as compared with the first embodiment.

Example 4 A laser device is manufactured in the same manner as in Example 3, except that the p-type cladding layer is formed as follows.

(P-type clad layer 9) Next, at the same temperature, using TMA, TMG and ammonia as source gases,
An A layer made of undoped Al0.1Ga0.9N is grown to a film thickness of 25 angstrom, TMA is stopped, Cp2Mg is used as an impurity gas, and Mg is 5 × 1.
A B layer of 018 / cm3 doped GaN is grown to a film thickness of 25 Å. Then, this operation is repeated 100 times to stack the A layer and the B layer to form a multilayer film having a total film thickness of 5000 Å (superlattice structure).
The p-type clad layer 9 is grown.

The obtained laser device can perform excellent laser oscillation almost in the same manner as in the third embodiment.

[Embodiment 5] A laser device is manufactured in the same manner as in Embodiment 3, except that the n-type guide layer and the p-type cladding layer are formed as follows.

(N-type guide layer 5) Next, at the same temperature,
Using TMG and ammonia as a source gas, an n-type guide layer made of undoped GaN is grown to a thickness of 0.075 μm.

(P-Type Clad Layer) As the p-type clad layer, the same one as in Example 4 is grown.

The obtained laser device can perform good laser oscillation almost in the same manner as in the third embodiment.

[Embodiment 6] A laser device is manufactured in the same manner as in Embodiment 3, except that the p-type guide layer and the p-type cladding layer are formed as follows.

(P-type guide layer 8) Next, the temperature is set to 800 ° C.
Then, using TMI, TMG, and ammonia as source gases, a second nitride semiconductor made of undoped In0.2Ga0.8N is grown to a film thickness of 50 Å, and then TMI is stopped and Cp2Mg is used as an impurity gas. Is used to grow a fourth nitride semiconductor of GaN doped with Mg of 5 × 10 18 / cm 3 to a film thickness of 50 Å. Then, this operation is repeated 20 times to stack the second nitride semiconductor and the fourth nitride semiconductor to grow a p-type guide layer made of a multilayer film layer having a total film thickness of 2000 angstroms. However, the In composition of the second nitride semiconductor is not compositionally graded.

(P-type clad layer) As the p-type clad layer, the same one as in Example 4 is grown.

Although the obtained laser device has a slightly deteriorated life characteristic as compared with the third embodiment, it can perform good laser oscillation almost in the same manner as the third embodiment.

[Embodiment 7] A nitride semiconductor laser device is manufactured in the same manner as in Embodiment 1, except that the p-type electron confinement layer 7 is composed of two layers as follows. (P-type electron confinement layer 7) The temperature was set to 800 ° C., TMA, TMG, and ammonia were used as source gases, Cp 2 Mg (cyclopentadienyl magnesium) was used as an impurity gas, and 5 × 10 18 / cm 3 Mg-doped Al was used.
A low-temperature-grown A layer of 0.4 Ga0.6 N was grown to a film thickness of 30 Å, and then the temperature was set to 900 ° C., and Mg was 5 × 10 18 / cm 3 -doped Al 0.4 Ga 0.
A p-type electron confinement layer 7 consisting of two layers, a low temperature grown A layer formed by growing a high temperature grown B layer of 6N to a film thickness of 70 angstroms, and a high temperature grown B layer is grown.
The obtained laser device oscillates a long-wavelength laser beam as in the case of Example 1 and has good life characteristics.

[Embodiment 8] In the embodiment 1, when the crack prevention layer 3 is grown, the composition ratio of In is set to 0.2, and In0.2Ga0.
A laser device is manufactured in the same manner except that the crack prevention layer 3 made of 8N is grown to a film thickness of 0.15 μm. The obtained laser device oscillates a long-wavelength laser light and has a good life characteristic as in the case of Example 1, and further the light emitted from the active layer 6 and leaking from the n-type cladding layer is excellent. It is absorbed inside (clad prevention layer 3), and the far field pattern becomes better than that of Example 1.

[0100]

As described above, the present invention relaxes the strain applied to the crystal by improving the composition of the guide layer and the clad layer, and improves the crystallinity of the guide layer and the active layer. It is possible to provide a nitride semiconductor laser device that can obtain laser light of a wavelength.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a nitride semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a unit cell diagram showing a plane orientation of sapphire.

FIG. 3 is a schematic cross-sectional view showing a partial shape of an off-angled heterogeneous substrate.

FIG. 4 is a schematic cross-sectional view showing a partial structure of a wafer in each step of the method which is an embodiment of forming a ridge-shaped stripe.

[Explanation of symbols]

1. Nitride semiconductor substrate 2 ... n-type contact layer 3 ... Crack prevention layer 4 ... n-type clad layer 5: n-type guide layer 6 ... Active layer 7: p-type electron confinement layer 8: p-type guide layer 9 ... p-type clad layer 10 ... p-type contact layer

Claims (3)

[Claims] 1. A substrate having at least an n-type cladding layer,
In a nitride semiconductor laser device having an n-type guide layer, an active layer, a p-type guide layer and a p-type clad layer, the Al composition decreases as the n-type and / or p-type clad layer approaches the active layer. The composition is graded like
la1-GaN (0≤a <1), the active layer comprises InbGa1-bN (0≤a≤1).
a quantum well structure including b <1), wherein the n-type and / or p-type guide layer is closer to the active layer,
A second nitride having IndGa1-dN (0 ≦ d <1) which is compositionally graded so that the In content is high, but the In content is lower than the In content of the well layer of the active layer. A nitride semiconductor laser device comprising a semiconductor. 2. The n-type and / or p-type cladding layer,
2. A multilayer film layer formed by stacking the first nitride semiconductor having a composition gradient and a third nitride semiconductor having a composition different from that of the first nitride semiconductor. The nitride semiconductor laser device according to claim 1. 3. The n-type and / or p-type guide layer stacks a second nitride semiconductor having a composition gradient and a fourth nitride semiconductor having a composition different from that of the second nitride semiconductor. 3. The nitride semiconductor laser device according to claim 1, wherein the nitride semiconductor laser device is a multi-layered film.