JP2002359436A - Nitride semiconductor laser diode and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser diode, having a ridge shape in which ripples are not generated, regardless of low output or high output. SOLUTION: This method for manufacturing a nitride semiconductor laser diode is provided with a ridge, and formed with embedded films at the both sides of the ridge; the embedded films are formed by a process for forming the ridge, and for forming a first insulation film, whose absorption coefficient is high on the exposed face of a p-side nitride semiconductor layer of a region from which the upper part and sidewalls of the ridge are excluded; and a process for forming a second insulating film, whose absorption coefficient is low on the first insulation film and at the sidewalls of the ridge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor laser diode and a method of manufacturing the same, and more particularly, to a ridge-shaped nitride semiconductor laser diode having a buried layer.

[0002]

2. Description of the Related Art A nitride semiconductor laser diode, which is a semiconductor light emitting element, is expected to be used for a medium such as a DVD for storing a large amount of information, a light source for communication, or a printing apparatus. In addition, the gallium-containing nitride semiconductor has a light emission wavelength in a short wavelength region of a 400 nm band, and thus can be used as a light source from ultraviolet to green. for that reason,
When used as a gallium-containing nitride semiconductor laser diode, it can be used as a reproducing device or a storage device for a large-capacity medium several times larger than a conventional red laser diode. Further field effect transistors (FETs)
Applications to such electronic devices are also expected.

Some of such nitride semiconductor laser diodes have a ridge formed by etching a nitride semiconductor in order to form an optical waveguide and realize lateral light confinement. This nitride semiconductor laser diode has an insulating buried layer on the exposed surface of the p-side nitride semiconductor layer on both sides of the ridge from the side wall of the ridge exposed after forming the ridge. This is because the ridge is formed on both sides of the ridge by having a buried layer having a different refractive index from the nitride semiconductor, for example, a low refractive index, on the exposed surface of the p-side nitride semiconductor layer on both sides of the ridge which has become an exposed surface. This is to make the refractive index of a certain nitride semiconductor lower than the refractive index of the nitride semiconductor serving as the core region. Thus, light is confined in the core region, thereby enabling lateral light confinement. Such a laser diode is called an effective refractive index type laser diode. Further, in the nitride semiconductor laser diode, current confinement can be achieved by using the buried layers on both sides of the ridge as insulators. This effective refractive index type laser diode is, for example, Jpn.J.Appl.Phys.vol.37
(1988) pp. L309-L312, Part 2, No. cB, 15 March 1998.

[0004] For example, SiO ₂ and ZrO ₂ have been reported as buried layers satisfying the property of having insulating properties.
With a nitride semiconductor laser diode having a buried layer made of ZrO ₂ , when the output is about 5 mW, a good nitride semiconductor laser diode whose life characteristics have achieved continuous oscillation of 10,000 hours or more is possible.

[0005]

SUMMARY OF THE INVENTION However, SiO
_{When 2} or ZrO ₂ is used as the buried film, ripple occurs regardless of the low output or high output.
This is because the active refractive index type laser diode has active layers not only on the core region but also on both lateral sides of the core region. The light emission from the active layers on both sides of the core region causes uneven output. Also, light emission from the core region may be considered. If a ripple occurs, the FFP (far field pattern) has a non-Gaussian distribution. A nitride semiconductor laser diode exhibiting such a non-Gaussian distribution as a characteristic is difficult to use for writing to an optical disk or the like. In other words, if ripples occur, the FFP will be such that a plurality of peaks will occur, and there will be a problem of lowering the yield due to erroneous reading of the peaks.
Accordingly, an object of the present invention is to provide a nitride semiconductor laser diode that does not generate ripples regardless of low output or high output.

[0006] The ripple indicates the meaning of ripples. FIG. 3A shows an FFP-X having no ripple.
FIG. 3B shows an FFP-X in which a ripple has occurred. The core region indicates a light confinement region.
The light confinement in the vertical direction utilizes the difference in the refractive index between the guide layer and the cladding layer. For the light confinement in the lateral direction, buried films formed on both sides of the ridge have a low refractive index. Thereby, the refractive index of the nitride semiconductor below the buried film is reduced to form an effective refractive index. Therefore, lateral light confinement becomes possible.

[0007]

In order to achieve the above object, a nitride semiconductor laser diode according to the present invention has a ridge, and a buried film is formed on both sides of the ridge. The buried film has a two-layer structure in which a first insulating film and a second insulating film having different absorption coefficients are sequentially formed.

In the nitride semiconductor laser diode according to the present invention, the first insulating film has a higher absorption coefficient than the second insulating film.

A nitride semiconductor laser diode according to the present invention comprises an n-side nitride semiconductor layer, an active layer, and a p-side nitride semiconductor layer formed on a substrate, and the p-side nitride semiconductor layer is an active layer. And a p-side cap layer, a p-side guide layer, a p-side clad layer, and a p-side contact layer on the nitride semiconductor laser diode.
The ridge is formed by etching the side cladding layer.

In the nitride semiconductor laser diode according to the present invention, the first insulating film is formed on an exposed surface of the p-side nitride semiconductor layer after the ridge is formed, and is not in contact with a sidewall of the ridge. It is characterized by.

The nitride semiconductor laser diode according to the present invention is an effective refractive index type laser diode having a ridge shape, and has a buried layer having a two-layer structure of a first insulating film and a second insulating film having different absorption coefficients. Having. The first insulating film has a high absorption coefficient. Thus, the first insulating film has an effect as a light absorbing film, and can eliminate ripple by absorbing light leakage from the core region and light emitted from regions other than the core region. Here, as the buried layer having a high absorption coefficient, Ti
O ₂ (titanium oxide), Nb ₂ O ₃ (niobium oxide), Rh
O and the like. Further, the first insulating film Ti
O _{2 and the} like have higher thermal conductivity than SiO ₂ and ZrO ₂ ,
It is excellent in heat dissipation and is preferable as a buried film used for continuous oscillation at high output. Further, according to the present invention, the reverse breakdown voltage is increased by using a buried film having a two-layer structure. This is because insulation between the electrode for forming the nitride semiconductor laser diode and the nitride semiconductor becomes stronger. Therefore, even if a voltage is applied in the reverse direction, it is hard to break, and an improvement in quality can be expected.

Further, the nitride semiconductor laser diode forms a ridge by etching at least up to the p-side cladding layer. In addition, if the active layer is etched, the active layer is damaged, so that the life characteristics are reduced. Further, a first ridge formed after the ridge is formed.
Is not in contact with the side wall of the ridge. This is because if the first insulating film is in contact with the ridge,
This is because the threshold value increases and the life characteristics are reduced. This is because, although the first insulating film has an effect as a light absorbing film, the first insulating film absorbs laser light required for laser oscillation.

[0013] The method for manufacturing a nitride semiconductor laser diode has a ridge, and a buried layer is formed on both sides of the ridge. Forming a first insulating film on the exposed surface of the p-side nitride semiconductor layer in a region excluding the side wall, and then forming a second insulating film on the first insulating film and on the side wall of the ridge. Forming a film. The method for forming the first insulating film and the second insulating film is not particularly limited, but sputtering, ECR sputtering, or vapor deposition can be used.

In the method for manufacturing a nitride semiconductor laser diode, a wet etching method is used for forming the first insulating film. For this wet etching, hot sulfuric acid, BHF, or hydrofluoric acid is used.
By forming the first insulating film by wet etching, the distance between the sidewalls on both sides of the ridge and the first insulating film can be uniformly controlled. In addition, etching can be performed in a narrow range of 1/10 of several microns from the edge of the ridge. Therefore, confinement on both sides of the ridge can be made uniform, and the peak shift of the FFP can be suppressed.

If the buried film of the present invention is made of the above-mentioned material, it has a low electric conductivity of 10 ⁶ to 10 ¹² Ωc.
Since m is an insulator, there is no leakage of current from the buried layer. Furthermore, it has high thermal conductivity and excellent heat dissipation. Therefore, even in a nitride semiconductor laser diode that continuously oscillates at a high output of 30 mW or more, the heat generated in the core can be released from the buried layer to the outside to suppress deterioration of the element due to heat generation, thereby improving the life characteristics. Can be expected. Further, in the nitride semiconductor laser diode having a face-down structure, the junction area between the nitride semiconductor laser diode and the stem is large, so that heat can be efficiently released, which is preferable. In addition, if the first insulating film is formed only in the range on both sides of the ridge, not only the insulating film but also a metal can be used.

As described above, the nitride semiconductor laser diode of the present invention is an effective refractive index type laser diode having a ridge shape, and uses a buried layer having a two-layer structure. Thus, it is possible to provide a nitride semiconductor laser diode having no ripple regardless of low output or high output.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor laser diode according to an embodiment of the present invention has a ridge, and a nitride semiconductor laser diode in which a buried film is formed continuously from the side wall of the ridge to both side surfaces of the ridge. Wherein the buried film has a two-layer structure in which a first insulating film and a second insulating film having different absorption coefficients are sequentially formed.
The first insulating film has a higher absorption coefficient than the second insulating film. For the measurement of the absorption coefficient, a first insulating film in the range of 0.005 to 0.1 is formed using an ellipsometer.

The nitride semiconductor laser diode has an n-side nitride semiconductor layer, an active layer, and a p-side nitride semiconductor layer formed on a substrate. This substrate may be a heterogeneous substrate such as sapphire different from the nitride semiconductor substrate.
The n-side nitride semiconductor layer has an n-side contact layer, a crack prevention layer, an n-side cladding layer, and an n-side guide layer on the substrate. Further, the active layer formed on the n-side nitride semiconductor layer has a multiple quantum well structure. The p-side nitride semiconductor layer formed on the active layer includes a p-side cap layer, a p-side guide layer, a p-side clad layer,
In this embodiment, the ridge is formed by etching at least up to the p-side cladding layer.

In the nitride semiconductor laser diode, the first insulating film is formed on an exposed surface of the p-side nitride semiconductor layer after the ridge is formed, and is not in contact with a side wall of the ridge. .

The buried layer in the nitride semiconductor laser diode according to the embodiment of the present invention has a two-layer structure in which a first insulating film and a second insulating film having different absorption coefficients are sequentially formed. In addition, the first insulating film has the following effects in order to have a higher absorption coefficient than the second insulating film.

Effect 1 As described above, the use of the first insulating film having a high absorption coefficient as the buried film makes it possible to eliminate the occurrence of ripple in the FFP-X. As the first insulating film, an insulating film such as TiO ₂ is used. The reason for eliminating the occurrence of the ripple is that light can be absorbed due to the high absorption coefficient of these insulating films. Specific numerical values are 0.005 to 0.1. With the insulating film having a high absorption coefficient, leakage light from the core region or light emission from regions other than the core region can be removed, and a single laser beam can be obtained. Therefore, ripples can be eliminated by forming the buried film. In addition, TiO ₂
As a film forming method, a sputtering method or the like can be considered.

Effect 2 In the present invention, since the buried film has a two-layer structure,
Reverse breakdown voltage is increased. The reason is that when the nitride semiconductor laser diode is formed, the insulation between the electrode and the nitride semiconductor is increased by forming a two-layer structure.

The etching depth when forming the ridge is as follows:
If the active layer is not etched, the p-side cap layer may be etched, and preferably, the p-side guide layer and the p-side clad layer are also etched. This is because it is considered that the etching surface of the nitride semiconductor formed by etching is deteriorated. This is because it is preferable that the influence of the deterioration due to the etching be in a range not affecting the active layer.

As described above, according to the present invention, when etching is performed up to the p-side guide layer, current can be confined without flowing current except in the core region. As a result, the nitride semiconductor laser diode has a buried film formed in a two-layer structure on the p-side guide layer which becomes an exposed surface after the formation of the ridge, and has not only a low output of about 5 mW but also 30 mW or more, preferably 50 mW.
It is possible to provide a ridge-shaped nitride semiconductor laser diode capable of performing continuous oscillation for 3000 hours or more without generating a ripple or kink even at a high output of about W.

A method for forming a buried film in a semiconductor laser diode according to an embodiment of the present invention will be described below. First, a ridge is formed on a nitride semiconductor laser diode to form a buried film. As shown in FIG. 2A, after a resist or SiO ₂ or the like is formed as a protective mask on the uppermost surface of the ridge, the upper portion of the resist, the side wall of the ridge, and the exposed surface of the p-side nitride semiconductor layer are formed by sputtering or the like. Next, a first insulating film is formed. Next, as shown in FIG. 2B, first resists formed on the upper portion of the resist and on the side walls of the ridge are formed.
Is removed by wet etching or the like using hot sulfuric acid or BHF (buffered hydrofluoric acid). Here, it is preferable that the side walls on both sides of the ridge and the first insulating film are not in contact with each other. Thereafter, as shown in FIG. 2C, a second insulating film is formed on the resist, on the side wall of the ridge, and on the first insulating film. Further, as shown in FIG. 2D, a resist or Si formed on the upper surface of the ridge is formed.
O ₂ and the second insulating film are removed to expose the top surface of the ridge. A p-side electrode is formed on this exposed surface in a later step.

Here, the film forming conditions of TiO ₂ are shown below. As a film forming apparatus, a sputtering apparatus is used. A Ti target is used as a raw material, and the film forming temperature is 600 ° C. or less, which is a temperature that does not damage the nitride semiconductor.
0 ° C. If the film formation temperature is higher than 600 ° C.,
There is a risk of damaging the nitride semiconductor during film formation.
As described above, the film forming conditions of the buried film in the present invention are 100 ° C. or more, preferably 200 ° C. or more and 500 ° C. or less. Since the buried film has a two-layer structure, the refractive index of the buried film can be formed in a wide range of 2.0 to 2.65 depending on the combination. Therefore, the nitride semiconductor layer of the nitride semiconductor laser diode is formed of GaN (refractive index =
About 2.3) as well as the general formula _In x _Al y Ga
_1-xy N (0 ≦ X <1, 0 ≦ Y <1, 0 ≦ X + Y <
Also in the case of 1), it is possible to maintain a difference in the refractive index with respect to the refractive index in this composition formula, and it is possible to stably confine light in the nitride semiconductor having the above composition. Further, the thickness of the buried film is 100Å to 25 が for the first insulating film.
00 °, and the second insulating film has a thickness of 100 ° to 6000 °.

The first insulating film and the second insulating film which are buried films are formed by a sputtering method such as a sputtering method or an ECR sputtering method, or an electron beam evaporation method or an ion beam evaporation method. Evaporation method, plasma CVD method such as microwave plasma CVD method and DC plasma CVD method, hot filament CVD method, EACVD
An apparatus using an ion plating method, an arc ion plating method, or an electronic excitation type ion plating method can be used.

Hereinafter, an example of the manufacturing process of the semiconductor laser diode according to the embodiment of the present invention will be described in more detail, but the present invention is not limited to this. The substrate in the present invention may be any substrate on which a nitride semiconductor layer can be epitaxially grown, and the size and thickness of the substrate are not particularly limited. As specific examples of this substrate, an insulating substrate such as sapphire or spinel having any one of the C plane, the R plane, and the A plane as a main surface, silicon carbide (6H, 4H, 3C), silicon, ZnS, ZnO, G
oxide substrates that lattice-attach with aAs, diamond, and nitride semiconductors. When sapphire is used as a substrate, the sapphire substrate has an A-plane as an orientation flat and a C-plane as a growth surface. In addition, an R-plane or an A-plane can be used as a growth plane, but it is preferable to grow a nitride semiconductor layer having a C-axis orientation. This substrate may be one whose outer periphery is chamfered or whose back surface is ground.

Next, the nitride semiconductor layer to be grown on the substrate is a nitride semiconductor and has a general formula of In.
_{x Al y Ga 1-x-} y N (0 ≦ X <1,0 ≦ Y <1,
0 ≦ X + Y <1). In the present invention, the nitride semiconductor layer is grown by using a metal organic chemical vapor deposition (MOCVD) method, a halide vapor phase epitaxial growth (HVPE) method, a molecular beam epitaxy (MBE) method, or another vapor phase growth method.

[0030] First, growing the base layer made of nitride semiconductor _{Al x Ga 1-x N (} 0 ≦ X ≦ 1) at a low temperature on the substrate. Thereby, defects and cracks caused by a lattice constant difference between the substrate and the nitride semiconductor can be suppressed.
Here, the low temperature is a temperature range of 300 to 800 ° C.
Further, Al _x Ga _1-x N (0 ≦
When X ≦ 1) is grown by metal organic chemical vapor deposition, TMG (trimethyl gallium), TMA
(Trimethylaluminum) and ammonia are used to grow about 1 to 20 μm at a growth temperature of 1150 ° C. or lower to make the surface of the nitride semiconductor a flat mirror surface.

An ELO (Epitaxial) is formed on the underlayer.
Lateral Overgrowth) _xGa_1-xN (0
≦ X ≦ 1) A layer may be grown. This ELO (Epitax
What is the ialLateral Overgrowth method?
Bending and converging threading dislocations by growing
This is to reduce dislocations. Semi-nitride on heterogeneous substrate
When growing a conductor, the substrate and nitride semiconductor
Stress is generated at the growth interface due to the difference in the element constants. This stress
Causes threading dislocations and the like, and threading dislocations are nitrided.
The crystallinity of the semiconductor is reduced. So this E
In the LO method, threading dislocations having the property of extending in the vertical direction
To reduce threading dislocations on the surface of nitride semiconductor
It is to let. First, a protective film is formed on the underlayer,
An opening is provided in this protective film. The properties of this protective film
Indicates that the nitride semiconductor does not grow on the protective film.
You. Furthermore, the underlying layer is exposed at the opening of the protective film.
Also, a nitride semiconductor is grown using this underlayer as a nucleus.
It is. The nitride semiconductor grown from the nucleus lays on the protective film.
Grow in the direction. Same as this laterally grown nitride semiconductor
In addition, threading dislocations also extend laterally. This laterally extending penetration
The dislocation bonds on the protective film and converges. Also from the opening
There are threading dislocations extending in the longitudinal direction. From the above, the protective film
The nitride semiconductor grown on the protective film from the opening protects
The contact between the laterally grown layers on the opening of the film and on the protective film
Low dislocation regions can be formed in areas other than the joint
You.

Further, the present inventors can provide a nitride semiconductor laser diode formed on the nitride semiconductor substrate shown in FIGS. In the nitride semiconductor substrate shown in FIG. 4, the nitride semiconductor grown laterally on the substrate has a T-shape, and the nitride semiconductor is regrown. In this nitride semiconductor substrate, although dislocations extend on the T-shaped pillars, the dislocations are significantly reduced on the upper portions of the T-shaped wings and on the openings of the adjacent T-shaped wings, so that the nitride semiconductors have good crystallinity. A substrate can be obtained. Since this nitride semiconductor substrate has a wide range of low defect areas on the wafer, the nitride semiconductor laser diode formed thereon can be expected to have good life characteristics. In addition, as shown in FIG. 6, a nitride semiconductor substrate can be formed by a method in which a nitride semiconductor is grown on a substrate, partially etched, and then the nitride semiconductor is regrown. The etching depth is not particularly limited, but may be any as long as it does not expose the substrate and has a cavity on the bottom surface. When the substrate is exposed, the growth interface between the substrate and the nitride semiconductor is exposed. At the growth interface, the crystallinity of the nitride semiconductor is not good because the lattice constant of the substrate is different from that of the nitride semiconductor.
If the nitride semiconductor having poor crystallinity is exposed, damage to the nitride semiconductor on the substrate is large, and dislocations extend to the upper nitride semiconductor. Therefore, it is preferable not to expose the substrate. However, if the etching depth is small, regrowth of the nitride semiconductor from the bottom of the concave portion occurs, and the dislocation lengthens. Therefore, the nitride semiconductor substrate shown in FIG. 6 which does not expose the substrate and has a cavity is preferable.

In order to reduce threading dislocations generated in the nitride semiconductor, in addition to the above-mentioned ELO method, a method of growing a thick film by HVPE and converging threading dislocations during the growth of the thick film to reduce dislocations. Is mentioned.

When a nitride semiconductor is grown by the HVPE method, for example, in the case of GaN, HCl gas reacts with Ga metal to form GaCl or GaCl ₃ , and this Ga chloride reacts with ammonia. With GaN
Is deposited on a substrate. By changing the growth rate during the growth of the nitride semiconductor by the HVPE method and performing two-stage growth, crystal defects can be significantly reduced. Thus, it is not necessary to perform lateral growth using the protective film, and a nitride semiconductor substrate can be obtained efficiently. This two-stage growth substrate is shown in FIG.

In the case where a nitride semiconductor is grown in a thick film on a heterogeneous substrate different from the nitride semiconductor by the HVPE method, only the nitride semiconductor is removed by removing the heterogeneous substrate from the thick nitride semiconductor substrate. Can be formed. As a method for removing a heterogeneous substrate from a thick nitride semiconductor substrate, a method for removing the heterogeneous substrate by polishing, or, alternatively, removing the heterogeneous substrate by irradiating an excimer laser to an interface between the heterogeneous substrate and the nitride semiconductor Method. Therefore, even if a nitride semiconductor substrate is grown on an insulating substrate such as a sapphire substrate, the sapphire substrate can be removed to form a single substrate made of a nitride semiconductor and a back electrode structure. A nitride semiconductor grown on the substrate obtained in the steps so far, a nitride semiconductor grown by the ELO method, and HV
Hereinafter, the substrate including the substrate grown by the PE method is referred to as a nitride semiconductor substrate.

Next, a nitride semiconductor device is formed on the nitride semiconductor substrate. Al _x Ga doped with an n-type impurity on the nitride semiconductor substrate as an n-side contact layer 3
_{1- xN} (0 ≦ X <1) is grown to about 5 μm. On this n-side contact layer, an n-type impurity-doped In _x Ga _1-x N (0
≦ X <1) is grown at about 0.2 μm. The crack prevention layer can be omitted. Subsequently, the n-side cladding layer 4 is grown on the crack prevention layer. As the n-side cladding layer is preferably a superlattice structure, a layer of undoped _{Al x Ga 1-x N (} 0 ≦ X <1), a layer of n-type GaN doped with n-type impurity Are alternately stacked to grow an n-side cladding layer having a superlattice structure with a total film thickness of about 1.2 μm. Subsequently, an n-side optical guide layer 5 made of undoped GaN is grown to a thickness of about 0.1 μm. This n-side light guide layer may be doped with an n-type impurity.

Next, the non-doped In _x Ga is applied to the barrier layer.
_1-x N (0 ≦ X ≦ 1) and n-type impurity doped I in the well layer
_{n x Ga 1-x N (} 0 ≦ X ≦ 1) consisting of a single quantum well structure, or growing the active layer 6 is multi-quantum well structure. In the case of a multiple quantum well structure, the barrier layers and the well layers are alternately stacked at the same temperature about 2 to 5 times, and finally the barrier layer is formed to have a total thickness of 200 to 500 °.

Next, a p-type Al _x doped with a p-type impurity is formed on the active layer as a p-side cap layer (not shown).
Ga _1-x N (0 ≦ X <1) is grown. This p-side cap layer is grown with a thickness of about 300 °. continue,
0.1 μm p-side light guide layer made of undoped GaN
It is grown with a film thickness of the order. This p-side light guide layer 7 is
Type impurities may be doped. Next, the p-side cladding layer 8 is grown on the p-side light guide layer. The p-side cladding layer preferably has a superlattice structure similarly to the n-side cladding layer, and is undoped Al _x Ga _1-x N (0 ≦ X <
1) layer and p-type GaN doped with p-type impurities
And a p-side cladding layer having a superlattice structure having a total film thickness of about 0.6 μm is grown alternately. Finally, a p-type impurity-doped A
_{l x Ga 1-x N (} 0 ≦ X ≦ 1) growing a p-side contact layer 9 made of.

Here, the impurity concentration is not particularly limited, but it is preferable that the n-type impurity and the p-type impurity are 1 × 10 ¹⁸ / cm ³ to 1 × 10 ²⁰ / cm ³ . Further, as the n-type impurity, Si, Ge, Sn,
Examples include S, O, Ti, Zr, and Cd, and examples of the p-type impurity include Be, Zn, Mn, Mg, Ca, and Sr.

Next, when a p-electrode and an n-electrode are formed on the same surface after forming a nitride semiconductor device on the nitride semiconductor substrate, an n-side contact layer is formed to form the n-electrode. It is exposed by etching. Next, a ridge is formed by etching to form a striped optical waveguide region. Here, the etching is preferably anisotropic etching in order to form a ridge. For example, an RIE (reactive ion etching) device or the like is used. Although the ridge width formed here depends on the buried layer and the output formed in a later step in the present invention, the ridge width can be as wide as 1.0 to 3.0 μm. The etching depth is such that at least the p-side cladding layer in the nitride semiconductor device is etched.
Further, the ridge shape includes a forward mesa type, an inverted mesa type, and a vertical type, and these shapes are preferable because light can be confined in a lateral direction.

After the formation of the ridge, a buried film as an insulator is formed in a two-layer structure from the exposed side wall of the ridge on the nitride semiconductor layers on both sides of the ridge by a sputtering method or the like. The method of forming the buried film and the film forming conditions have been described above, and will not be described here.

The effect of this buried film is that the first insulating film 11 absorbs light. The effects of the second insulating film 12 are current confinement and lateral light confinement.
In order to confine light in the lateral direction, it is necessary to provide a difference in the refractive index between the nitride semiconductor layer and the nitride semiconductor layer. Used for In the vertical light confinement, light is confined in the core by providing a refractive index difference between the core region having a high refractive index and the p and n-side cladding layers having a low refractive index.

Thereafter, the buried layer formed on the uppermost surface of the ridge for forming the p-side electrode 13 is removed by lift-off or the like. Next, after the removal, a p-side electrode made of Ni / Au is formed in a stripe shape on the exposed surface of the p-side contact layer. After the p-side electrode is formed, an n-side made of Ti / Al is formed on the surface of the n-side contact layer. The side electrode 10 is formed in parallel with the ridge stripe. Next, the pad electrode 1 which is an extraction electrode
4 is formed on the p-electrode and the n-electrode.

The p-side electrode is made of Ni / Au / RhO.
And the p-side pad electrode is RhO / Pt / Au
It can also be done. Before forming the pad electrode,
SiO ₂, TiO₂Dielectric multilayer film consisting of
(Light emitting end face side). This dielectric multilayer film
The end face of the light emitting end face at the time of high output by having
Deterioration can be suppressed.

Further, the substrate is cleaved in a bar shape in the direction perpendicular to the stripe-shaped electrodes, and the cleaved surface ((1
A resonator is formed on the (1-00) plane, a plane corresponding to a hexagonal side surface = M plane). A dielectric multilayer film is formed on the surface of the resonator, and a bar is cut in a direction parallel to the electrodes to obtain a nitride semiconductor laser device. This nitride semiconductor laser device is placed on a heat sink, wire-bonded, and sealed with a cap to obtain a nitride semiconductor laser diode.

The nitride semiconductor laser diode obtained as described above
When laser oscillation was attempted at room temperature using an
Oscillation wavelength 400 to 420 nm, threshold current density 2.9 kA /
cm ²Shows continuous oscillation at low output of about 5mW
Not only light of 30 mW or more, preferably about 50 mW
Ripple does not occur even at the time of output and the life is over 3000 hours
Shows life characteristics.

[0047]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 First, a sapphire substrate of 2 inches in diameter and 2 mm in thickness having a C surface as a main surface and an orientation flat surface as an A surface was set as a substrate 1 and set in a MOCVD apparatus at a temperature of 1050 ° C.
For 10 minutes to remove moisture and deposits on the surface.

Next, at a temperature of 510 ° C., an underlayer made of GaN is grown to a thickness of 200 Å using hydrogen as a carrier gas, ammonia and TMG (trimethylgallium) as a source gas.

Thereafter, GaN as a second underlayer is grown at a growth temperature of 1050 ° C. and a thickness of 2.5 μm. This second
The underlayer is grown by using hydrogen as a carrier gas and ammonia as a source gas, similarly to the above-described underlayer.

After the second underlayer is grown, SiO _{2 is}
A protective film made of a film having a thickness of 0.5 μm is formed. further,
A stripe pattern having an opening is formed in the protective film. The stripe pattern of the protective film is formed in a direction perpendicular to the orientation flat surface of the substrate. The protective film has a stripe width of 14 μm and an opening width of 6 μm. This opening exposes the underlying layer of GaN. Next, GaN is laterally grown with the GaN exposed from the opening as a nucleus, and the growth is stopped before the GaNs are joined. At this time, the GaN has a T-shaped cross section.
After that, the protective film was removed, and both sides of the T-shaped GaN,
And by growing GaN again from the upper surface of the T-shape,
A GaN layer 2 of 5 μm is formed. This GaN substrate is a nitride semiconductor substrate having a flat mirror shape, and a region grown laterally on the protective film has a low defect in which threading dislocations per unit area is 1 × 10 ⁷ / cm ² or less. A certain nitride semiconductor substrate can be obtained.

Next, a nitride semiconductor device is formed on the nitride semiconductor substrate. [Undoped n-type contact layer (not shown)]
MOCVD is performed on the wafer on which the nitride semiconductor substrate is formed.
It was set in a reaction vessel of the apparatus, and TMG (trimethylgallium), TMA (trimethylaluminum) and ammonia were used as the nitride semiconductor at 1050 ° C., and Al _0.05
An undoped n-type contact layer made of Ga _0.95 N is grown to a thickness of 1 μm. This layer has a function as a buffer layer between a nitride semiconductor substrate made of GaN and a semiconductor element such as an n-type contact layer.

[N-type contact layer 3] Next, undoped n
Using TMG, TMA, ammonia, and silane gas as impurity gas, Al _0.05 Ga _{0. An} n-type contact layer 3 of ₉₅ N is grown to a thickness of 4 μm.

[Crack prevention layer] Next, TMG, TMI
Using (trimethylindium) and ammonia at a temperature of 900 ° C., a crack prevention layer made of In _0.07 Ga _0.93 N is grown to a thickness of 0.15 μm. The crack prevention layer can be omitted.

[N-type cladding layer 4] Next, the temperature was set to 105
At 0 ° C., an A layer made of undoped Al _0.05 Ga _0.95 N is grown to a thickness of 25 ° using TMA, TMG and ammonia as source gases. 5x Si using silane gas
A B layer made of GaN doped with 10 ¹⁸ / cm ³ is 25
It grows with the film thickness of Å. Repeat this operation 200 times A
An n-type clad layer having a multilayer structure (superlattice structure) having a total thickness of 1 μm and having a layered structure of the layer and the B layer is grown.

[N-Type Light Guide Layer 5] Next, the silane gas was stopped, and at the same temperature, an N-type guide layer 5 of undoped GaN was formed to a thickness of 0.15 μm using TMG and ammonia as source gases. Let it grow. The n-type light guide layer 5 may be doped with an n-type impurity.

[Active Layer 6] Next, the temperature is set to 900 ° C.
Indium doped with 5 × 10 ¹⁸ / cm ³ using TMI (trimethyl indium), TMG and ammonia as source gas, silane gas as impurity gas, and Si
_A barrier layer of _0.05 Ga _0.95 N is grown to a thickness of 140 °, silane gas is stopped, and undoped In
By growing a well layer made of _0.13 Ga _{0.8 7} N with a thickness of 25 Å, stacked in this order of the barrier layer / well layer / barrier layer / well layer, as the last barrier layer, TMI, TM
Undoped In _0.05 G using G and ammonia
a _0.95 N is grown. The active layer 6 has a total thickness of 500
多重 is a multiple quantum well structure (MQW).

[P-type cap layer (not shown)]
Next, at the same temperature as the active layer, TMA, TMG
And ammonia, and Cp ₂ Mg as an impurity gas.
(Cyclopentadienylmagnesium), Al _0.3 Ga _0.7 doped with Mg at 1 × 10 ¹⁹ / cm ³
A p-type electron confinement layer made of N is grown to a thickness of 100 °.

[P-type light guide layer 7] Next, Cp ₂ Mg,
Stop TMA, raise temperature to 1050 ° C, and add T
Using MG and ammonia, a p-type guide layer 7 made of undoped GaN is grown to a thickness of 0.15 μm.

[P-type cladding layer 8] Next, an A layer made of undoped Al _0.05 Ga _0.95 N is grown at a temperature of 1050 ° C. to a thickness of 25 °, then TMA is stopped and Cp ₂
Using Mg, a B layer made of GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown to a thickness of 25 °, and this is repeated 90 times to form a p-type made of a superlattice layer having a total thickness of 0.45 μm. The cladding layer 8 is grown. The p-type cladding layer
It has a super lattice structure in which GaN and AlGaN are stacked. p
When the mold cladding layer 8 has a superlattice structure, the Al mixed crystal ratio of the entire cladding layer can be increased, so that the refractive index of the cladding layer itself decreases and the bandgap energy increases. Is very effective in lowering

[P-type contact layer 9] Finally, 1050
At 10 ° C., a p-type contact layer 9 made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg using TMG, ammonia, and Cp ₂ Mg was formed on the p-type cladding layer 109 by 15 μm.
It is grown to a thickness of 0 °. After the reaction, the wafer is annealed at 700 ° C. in a nitrogen atmosphere in a reaction vessel to further reduce the resistance of the p-type layer.

After annealing, the wafer on which the nitride semiconductor was laminated was taken out of the reaction vessel, and a protective film made of SiO ₂ was formed on the surface of the uppermost p-type contact layer.
The surface of the n-type contact layer 3 on which the n-electrode is to be formed is exposed by etching with a Cl ₂ gas using an IE (reactive ion etching) method.

Next, a resist is formed as a mask, and R
The ridge stripe is formed into a stripe-shaped waveguide region by using the IE and etching with a Cl ₂ gas and a SiCl ₄ gas to have a ridge stripe width of 1.8.
Formed in μm. This etching is performed up to the p-side guide layer to form a ridge serving as a stripe-shaped optical waveguide region. Thereafter, TiO ₂ as a first insulating film is formed to a thickness of 500 ° using a sputtering apparatus. Thereafter, the first insulating film on the ridge side wall and on the resist is removed, and ZrO ₂ as a _second insulating film is formed to a thickness of 550 ° as shown in FIG. Then, using a stripper,
The upper part of the ridge is exposed as shown in FIG.

Next, a p-side electrode is formed of Ni / Au with a stripe width of 100 μm on the exposed p-type contact layer on the uppermost surface of the ridge, and the n-side exposed by etching is formed.
An n-type electrode made of Ti / Al is formed on the mold contact layer. The p-side electrode is formed in stripes on the ridge, and is formed in a direction parallel to the n-side electrodes also formed in stripes.

Next, after a dielectric multilayer film made of SiO ₂ and TiO ₂ is provided on the light reflection end face, Ni-Ti-Au (1000Å-1000Å-8) is formed on the p-side electrode and the n-side electrode.
000 °) are formed.

The nitride semiconductor laser device obtained as described above is placed on a heat sink, and each pad electrode is wire-bonded to obtain a nitride semiconductor laser diode. FIG. 7 shows the FFP-X according to the present embodiment. FIG. 8 shows an FFP-X of a nitride semiconductor laser diode formed in the same manner as in Example 1 except that only the buried film is ZrO ₂ . As described above, using this nitride semiconductor laser diode, no ripple occurs at an output of 5 to 30 mW at a threshold value of 2.8 kA / cm ² at room temperature, and a continuous oscillation wavelength of 405 nm having a life characteristic of 3000 hours or more is obtained. An oscillating nitride semiconductor laser diode was obtained.

Example 2 After a base layer 2 was grown on a sapphire substrate 1 in the same manner as in Example 1, it was set in a hydride vapor phase epitaxial growth apparatus, Ga metal was prepared in a quartz boat, and HCl was used as a halogen gas. GaCl ₃ is generated by using a gas, and then reacted with ammonia gas, which is an N gas, to grow a nitride semiconductor 2a made of undoped GaN. The growth temperature of the nitride semiconductor 2a is 1000 ° C., and the growth rate is 1 mm / ho.
The film is grown as a ur with a film thickness of 100 μm. Next, nitride semiconductor 2b is grown on nitride semiconductor 2a using a hydride vapor phase epitaxial growth apparatus. As growth conditions at this time, the growth temperature is the same as that of the nitride semiconductor 2a, and the growth rate of the nitride semiconductor 2b is 50 μm / h.
Our film was grown at a thickness of 50 μm. The surface of the obtained nitride semiconductor substrate is flat and mirror-finished. According to CL observation, the threading dislocation density is about 1 × 10 ⁶ cm ⁻² , and the nitride semiconductor substrate shown in FIG. Can be provided.

A nitride semiconductor laser diode was formed in the same manner as in Example 1 except that the nitride semiconductor substrate obtained as described above was used, and a buried film was formed under the same conditions as in Example 1 with the first insulating film and the second insulating film. It is formed in a two-layer structure with an insulating film. The nitride semiconductor laser diode obtained here can be expected to have a life characteristic of 3000 hours or more of continuous oscillation without generation of ripples, similarly to the first embodiment.

[Example 3] A sapphire substrate of 2 inches in diameter and 2 mm in thickness having the C surface as the main surface and the orientation flat surface as the A surface was used as the substrate 1, and was set in a MOCVD apparatus.
Thermal cleaning is performed at 0 ° C. for 10 minutes to remove moisture and attached substances on the surface. Next, the temperature was increased to 510 ° C., and hydrogen was used as the carrier gas, and ammonia and TM were used as the source gas.
Using G (trimethylgallium), an underlayer made of GaN is grown to a thickness of 200 angstroms.

Thereafter, GaN is grown as nitride semiconductor 2a at a growth temperature of 1050 ° C. and a film thickness of 10 μm. This nitride semiconductor 2a is grown using hydrogen as a carrier gas and ammonia as a source gas, as in the case of the underlayer.

Next, a nitride semiconductor 2a having a depth of 8.5 μm
Is formed. The width of this groove is 14 μm, and 14:
The grooves are formed at regular intervals at a ratio of 6. Further, the nitride semiconductor 2b is grown from the side surface and the upper surface of the nitride semiconductor 2a to obtain a nitride semiconductor substrate with a reduced total defect thickness of 15 μm. The growth condition of the nitride semiconductor 2b is the same as that of the nitride semiconductor 2a.

A nitride semiconductor laser diode was formed in the same manner as in Example 1 except that the nitride semiconductor substrate obtained as described above was used, and the buried film was formed by using the first insulating film and the second insulating film under the same conditions as in Example 1. It is formed in a two-layer structure with an insulating film. The nitride semiconductor laser diode obtained here can expect the same effect as that of the first embodiment.

[0072]

As described above, if the buried film of the present invention is formed on a nitride semiconductor laser diode,
It is possible to provide a nitride semiconductor laser diode in which ripple does not occur regardless of low output and high output, and has stable life characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating an embodiment of the present invention.

FIG. 2 is a process chart illustrating an embodiment of the present invention.

FIG. 3 is a diagram showing FFP-X.

FIG. 4 is a schematic cross-sectional view of a nitride semiconductor substrate illustrating one embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view of a nitride semiconductor substrate illustrating one embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view of a nitride semiconductor substrate illustrating one embodiment of the present invention.

FIG. 7 is a diagram showing FFP-X in one embodiment of the present invention.

FIG. 8 is a diagram showing FFP-X in a comparative example.

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Underlayer 3 ... n-side contact layer 4 ... n-side cladding layer 5 ... n-side light guide layer 6 ... Active layer 7 ... p-side light guide Layer 8: p-side cladding layer 9: p-side contact layer 10: n-side electrode 11: embedded film (first insulating film) 12: embedded film (second insulating film) 13 ... p-side electrode 14 ... pad electrode

Claims (6)

[Claims] In a nitride semiconductor laser diode having a ridge and buried films formed on both sides of the ridge, the buried film is formed by forming a first insulating film and a second insulating film having different absorption coefficients in order. A nitride semiconductor laser diode having a two-layer structure. 2. The nitride semiconductor laser diode according to claim 1, wherein said first insulating film has a higher absorption coefficient than said second insulating film. 3. The nitride semiconductor laser diode according to claim 1,
An n-side nitride semiconductor layer, an active layer, and a p-side nitride semiconductor layer are formed on a substrate. The p-side nitride semiconductor layer has a p-side cap layer, a p-side guide layer, 2. The ridge according to claim 1, further comprising a side cladding layer and a p-side contact layer, wherein the nitride semiconductor laser diode forms a ridge by etching at least up to the p-side cladding layer. Nitride semiconductor laser diode. 4. In the nitride semiconductor laser diode, the first insulating film is formed on an exposed surface of the p-side nitride semiconductor layer after the formation of the ridge, and does not contact a sidewall of the ridge. The nitride semiconductor laser diode according to claim 1, wherein: 5. A method for manufacturing a nitride semiconductor laser diode having a ridge and having a buried film formed on both sides of the ridge, wherein the ridge is formed after removing the ridge and excluding a sidewall of the ridge. forming a first insulating film on the exposed surface of the p-side nitride semiconductor layer;
Forming a buried film by the step of forming a second insulating film on the first insulating film and on the side wall of the ridge. 6. The method for manufacturing a nitride semiconductor laser diode according to claim 5, wherein the first insulating film is formed using a wet etching method. Production method.