JP4929776B2 - Nitride semiconductor laser device - Google Patents

Description

  The present invention relates to a nitride semiconductor laser device, and more particularly to a nitride semiconductor laser device that exhibits high reliability even in continuous driving in a high output state.

Nitride semiconductor, for example, is formed formula is the compound semiconductor represented by _{In x Al y Ga 1-xy} N (0 ≦ x, 0 ≦ y, 0 ≦ x + y ≦ 1), the semiconductor using the same The use of laser elements for optical disk systems capable of recording / reproducing large-capacity and high-density information such as next-generation DVDs, and applications for electronic devices such as personal computers is being studied. Further, since it is considered that oscillation in a wide wavelength range from ultraviolet to red is possible, there is an increasing demand for light sources such as laser printers and optical networks. For this reason, research on semiconductor laser elements using nitride semiconductors has been actively conducted.

  Such a nitride semiconductor laser can be driven stably for a longer period of time by preventing deterioration of the cavity facet on the light emitting side and appropriately oscillating light generated in the active layer at the cavity facet. It is being considered.

  Therefore, for example, in order to suppress light absorption caused by oxidation of the resonator end surface, it is proposed to form the resonator end surface in an ultrahigh vacuum and immediately form a dielectric film on the resonator end surface. Has been. In addition, in order to suppress the deterioration of the semiconductor layer near the cavity end face due to the diffusion of oxygen due to the laser driving operation, oxygen-bonded aluminum oxide is formed on the cavity end face to prevent natural oxidation of the end face. In addition, it has been proposed to prevent diffusion of oxygen into the semiconductor layer (for example, Patent Document 1).

In addition, the output light is absorbed at the resonator end face and heat is generated, the temperature of the resonator end face rises, the band gap at the resonator end face becomes narrow, and the absorption of the output light may further increase. As a result, end face optical damage (COD) may occur. On the other hand, by forming ions in the contact layer of the optical semiconductor device to form a current non-injection region, a light non-absorption region is formed on the cavity end face, and the active layer other than the light absorption region is selected. A method has been proposed in which the effective forbidden band width of the active layer is narrowed by performing impurity doping (for example, Patent Document 2).
JP 2005-175111 A JP 2002-261379 A

  However, even if a dielectric film is formed on the end face of the resonator as described above and oxidation of the end face of the resonator is prevented, stress is generated between the nitride semiconductor and the dielectric film on the end face of the resonator, causing resonance. There are cases where the dielectric film formed on the end face of the vessel peels off or breaks without being able to withstand the stress. With this, not only the stable continuous operation of the nitride semiconductor laser element cannot be realized, but also the laser oscillation cannot be sufficiently performed. This is the same when the current non-injection region is formed.

  The present invention has been made in view of the circumstances as described above. In particular, in a nitride semiconductor laser element, the stress between the nitride semiconductor and the dielectric film on the cavity end face is relaxed, and the cavity end face, particularly the optical An object of the present invention is to provide a nitride semiconductor laser device that stabilizes the adhesion between a nitride semiconductor and a dielectric film in the emission region and exhibits high reliability even in continuous driving in a high output state.

The nitride semiconductor laser device of the present invention is
A substrate, a nitride semiconductor layer in which a first nitride semiconductor layer, an active layer, and a second nitride semiconductor layer are stacked in this order on the substrate, and resonator end faces facing each other formed in the nitride semiconductor layer A nitride semiconductor laser device comprising:
At least one selected from the group consisting of Al ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ , AlN, GaN, InN, AlON, GaON, and InON so as to cover the resonator end face on the light output side . A dielectric film is formed,
At least one element constituting the nitride semiconductor layer and one element constituting the dielectric film are the same,
A cavity end face of the optical output side, the upper and / or below the light emitting region, and wherein the impurity-containing region containing an impurity to increase the lattice constant of the nitride semiconductor layer is formed To do.

In this nitride semiconductor laser element, it is preferable that the same element constituting the nitride semiconductor layer and the dielectric film is nitrogen.
Further, it is preferable that the same element constituting the nitride semiconductor layer and the dielectric film further includes at least one selected from the group consisting of aluminum, indium, and gallium.

Furthermore, the impurity concentration peak is preferably located in the first nitride semiconductor layer and / or the second nitride semiconductor layer.
The first nitride semiconductor layer and / or the second nitride semiconductor layer is preferably composed of a plurality of layers, and the impurity-containing region is preferably formed over a plurality of layers.

The impurity-containing region preferably includes at least one selected from the group consisting of indium, arsenic, phosphorus, antimony, zinc, thallium, and bismuth.
The impurity-containing region may be formed only in the first nitride semiconductor layer or only in the second nitride semiconductor layer.
The dielectric film is preferably made of aluminum nitride, oxide or oxynitride.

  According to the present invention, the stress between the nitride semiconductor and the dielectric film on the resonator end face can be relieved, and the adhesion between the nitride semiconductor and the dielectric film in the resonator end face, particularly the light emitting region, can be stabilized. In addition, it is possible to provide a nitride semiconductor laser element that exhibits high reliability even in continuous driving in a high output state.

  The nitride semiconductor laser device of the present invention mainly includes a nitride semiconductor layer in which a first nitride semiconductor layer, an active layer, and a second nitride semiconductor layer are stacked in this order on a substrate. Resonator end faces facing each other are formed in the layer.

  For example, as shown in FIG. 1A, a first (for example, n-type) nitride is formed as a nitride semiconductor layer on a first main surface of a substrate 10 having a first main surface and a second main surface. A semiconductor layer 11, an active layer 12, and a second (eg, p-type) nitride semiconductor layer 13 are formed in this order. A ridge 14 is formed on the surface of the second nitride semiconductor layer 13, and a p-electrode (not shown) is formed on the upper surface of the ridge 14. An n electrode 20 is formed on the second main surface of the substrate 10. The nitride semiconductor laser device of the present invention may have a structure without a ridge, or may have a structure in which both a p-electrode and an n-electrode are formed on the first main surface side of the substrate.

  In addition, as shown in FIG. 1A, such a nitride semiconductor laser element is formed on the resonator end face 30 on the light output side of the first nitride semiconductor layer 11 and / or the second nitride semiconductor layer 13. A first impurity-containing region 31 and / or a second impurity-containing region 32 containing impurities that increase the lattice constant of the nitride semiconductor layer are formed. By such an impurity-containing region, stress generated at the interface between the nitride semiconductor layer and a dielectric film 44 described later can be further relaxed, and the nitride semiconductor layer, more specifically, the resonator end face on the light output side In combination with the improvement in the adhesion between the dielectric film 44 and the optical waveguide region 30 including the active layer 30 or the laser light emission layer, continuous driving of the nitride semiconductor laser device can be realized. In addition, it is possible to obtain a single-mode semiconductor laser device that absorbs stray light leaking from the optical waveguide region in the impurity-containing region and has a good Gaussian shape without ripple on the FFP of the main laser light.

  The impurities contained in this manner may be those that increase the lattice constant of the nitride semiconductor layer, in other words, those that narrow the band gap of the nitride semiconductor layer. It is an element except aluminum and gallium among elements from the third period to the sixth period, and is an element starting from silicon to bismuth. Preferably, at least one atom selected from the group consisting of indium, arsenic, phosphorus, antimony, zinc, thallium, and bismuth is used. More preferred is at least one atom selected from the group consisting of indium, arsenic, and phosphorus.

  The first impurity-containing region 31 may be formed substantially only in the first nitride semiconductor layer 11, may be formed in the first nitride semiconductor layer 11 and the substrate 10, or may be formed in the substrate 10. It may be formed only inside. When the thickness of the first nitride semiconductor layer 11 is increased as shown in FIG. 3, the proportion of the first nitride semiconductor layer in the thickness direction of the laser element increases, so that a large impurity-containing region is provided. Can do. As a result, a region where the lattice constant of the nitride semiconductor is increased can be increased, so that the contact area between the nitride semiconductor layer and the dielectric film is reduced on the first nitride semiconductor layer and the substrate side. The stress can be relieved at the portion, and the adhesion in the light emitting region can be improved more effectively. In addition, even if a large impurity-containing region is provided, the distance between the impurity-containing region and the active layer can be secured, so that the influence of impurities on the active layer can be suppressed. In the case where a large impurity-containing region is provided in the substrate, the effect can be obtained more remarkably.

The first impurity-containing region has a ratio (H / T ₁ ) of the height H of the region containing no impurities from the active layer to the end of the impurity-containing region with respect to the thickness T ₁ of the first nitride semiconductor layer. Is preferably 1/10 or more, more preferably 1/2 or more. Specifically, it is preferable that the active layer 12 is formed at a distance of about 2000 mm or more, more preferably 1 μm or more. This is because impurities that change the lattice constant reach the active layer and do not inhibit the original function of the active layer.
In the impurity-containing region provided in the substrate, the ratio of the height Y _1b of the impurity-containing region in the substrate to the thickness T ₂ of the substrate (Y _1b / T ₂ ) is 1/8 or more), and 1 / 4 or more). Specifically, it is 10 μm or more, preferably 20 μm or more. By providing the impurity-containing region in this way, the stress between the nitride semiconductor and the dielectric film on the resonator end face can be more effectively relaxed.

When the impurity-containing region is provided in the substrate and the first nitride semiconductor layer, the impurity-containing region is provided in the first nitride semiconductor layer with respect to the height Y ₁ of the impurity-containing region provided in the substrate and the first nitride semiconductor layer. If the ratio of the height Y _1a of the impurity-containing region (Y _1a / Y ₁ ) is 1/5 or less, preferably 1/20 or less, the stress between the nitride semiconductor and the dielectric film on the resonator end face is reduced. It is preferable that the laser element having good characteristics can be obtained without causing the impurities to reach the active layer and inhibiting the original function of the active layer at the same time as the effective relaxation.

  The shape of this region is not particularly limited, and can be appropriately adjusted depending on the composition of the active layer, the first and second nitride semiconductor layers, the performance of the laser element, and the like. For example, a quadrangle, a rhombus, an inverted triangle (31a in FIG. 4 (a)), a downwardly convex pan lid shape (31b in FIG. 4 (b)), or a shape close to these. Furthermore, when an impurity-containing region that is convex upward or downward is formed, the width of the impurity-containing region in the substrate may be widened or narrowed. In the case where the convex impurity-containing region is provided on the upper side, the impurity-containing region is largely provided at a position away from the light emitting region, so that the adhesion between the nitride semiconductor layer and the dielectric film is improved at the same time in the light emitting region. Since the large impurity-containing region is separated from the light emitting region, the influence on the element characteristics can be reduced.

  The size is not particularly limited and can be appropriately adjusted depending on the composition of the active layer, the first and second nitride semiconductor layers, the performance of the laser element, and the like. The height (see Y1 in FIG. 1B) is, for example, about 1/200 to about 1 times the film thickness of the first nitride semiconductor layer, specifically, 100 to 2 μm. The width (refer to X1 in FIG. 1A) can be, for example, about the same as the ridge width to about the same as the element width, and in particular, about 1.0 to 20 times the ridge width, 1.5 About 6 times is appropriate. Specifically, 1-50 micrometers is mentioned. The depth Z1 (Z1 in FIG. 1B) from the resonator end face to the inside of the element is, for example, within a range of at least about 1.0 μm from the resonator end face, or 0.1 to 3% of the resonator length. It is appropriate that they are arranged in a degree. Specifically, 1-20 micrometers is mentioned.

  The second impurity-containing region 32 is preferably formed only in the second nitride semiconductor layer 13, and is preferably formed at a distance of about 2000 mm or more from the active layer 12. This is because impurities that change the lattice constant reach the active layer and do not inhibit the original function of the active layer.

The shape and size of this region can be substantially the same as those of the first impurity region 31. In particular, the height Y ₂ in the stacking direction is about 100 μm to 1 μm, and the width X ₂ is about ₁ to 50 μm. The depth Z ₂ from the resonator end face to the inside of the element is preferably in the range of about 1 to 20 μm. The second impurity-containing region 32 may reach the surface of the second nitride semiconductor layer 13 or may be disposed at a position separated from the surface of the second nitride semiconductor layer 13. When this region is formed on the surface of second nitride semiconductor layer 13, it is possible to effectively prevent a short circuit with the nitride semiconductor layer at the end face of the p-electrode, and from the surface of the nitride semiconductor layer. It is possible to reliably prevent the flow of current to the resonator end face.

  In the first and / or second impurity-containing regions 31 and 32, it is preferable that the peak position of the impurity concentration exists in the first nitride semiconductor layer and / or the second nitride semiconductor layer. By forming the peak position of the impurity concentration, in other words, the region where the lattice constant is changed most in the first nitride semiconductor layer and / or the second nitride semiconductor layer, the lattice constant of the active layer is substantially changed. First, while maintaining the adhesion between the active layer and the dielectric film as shown in FIG. 2, by reducing the adhesion between the first nitride semiconductor layer or the second nitride semiconductor layer and the dielectric film, This is because the stress between the nitride semiconductor layer and the dielectric film can be relaxed relatively. In this case, the peak position of the impurity concentration in the horizontal direction (in-plane direction of each semiconductor layer) is preferably at or near the resonator end face. Therefore, the impurity concentration constituting the impurity-containing region is maximized on the resonator end face side, gradually decreases toward the inside of the element, and almost disappears on the inside of the distance from the predetermined end face described above. Further, in the width direction of the element, it is preferably present on the light emitting region or on the stacking direction line in the vicinity thereof.

  The impurity concentration preferably has an asymmetric concentration distribution with respect to the peak position in the nitride semiconductor layer stacking direction. In particular, on the first nitride semiconductor layer side, it is preferable that the attenuation rate toward the active layer side is higher than the attenuation rate toward the substrate side with respect to the peak position. This effectively suppresses diffusion of unintended impurities to the active layer.

  The first and / or second impurity-containing region is a region into which an impurity is introduced, and the lattice constant of the region is changed. That is, in the in-plane direction of each nitride semiconductor layer, this is a region having a larger lattice constant than a region that is not the impurity-containing region. In the first and / or second impurity-containing region, the crystal system may be partially destroyed or further partially recovered by introducing impurities (for example, by ion implantation). Also good. Further, in the case where the first nitride semiconductor layer and / or the second nitride semiconductor layer are each formed in a stacked structure, each configuration in the stacked structure in the first and / or second impurity-containing region. In the complete crystal system of the other region in the in-plane direction immediately after the first nitride semiconductor layer and / or the second nitride semiconductor layer is formed or in which no impurities are contained There may be a region having a composition different from the composition. For example, in the same layer of the first nitride semiconductor layer, the difference in lattice constant between the region containing no impurities and the first impurity containing region 31 is about 0.0002 mm or more, more preferably about 0.001 mm or more. It is. Further, in the same layer of the second nitride semiconductor layer, the difference in lattice constant between the impurity-free region and the second impurity-containing region 32 is about 0.0002 mm or more, more preferably about 0.001 mm or more. It is.

The first and / or second impurity-containing region can be formed by ion implantation or diffusion. In this case, the impurities are distributed at a concentration of, for example, about 1 × 10 ¹⁵ to 1 × 10 ²³ / cm ³ , preferably 10 ¹⁸ / cm ³ to 10 ²¹ / cm ³ . As described above, an appropriate change in lattice constant (crystal system) can be given depending on the type and concentration of these impurities. In the case where the impurity-containing region is formed in both the first nitride semiconductor layer and the second nitride semiconductor layer, the concentration peaks of both impurities may be equal, or one of them may be large. For example, when the first impurity-containing region is formed in the first nitride semiconductor layer by ion implantation, it is preferable to perform ion implantation before forming the active layer. In addition, when the second impurity-containing region is formed in the second nitride semiconductor layer, it is preferable to perform ion implantation so as not to reach the active layer. That is, in the case where the same element as the element constituting the semiconductor layer is ion-implanted over the entire face of the resonator and contains impurities, the dielectric film containing the same element on the face of the resonator When the film is coated, the stress is too strong and the dielectric film may be peeled off or destroyed. On the other hand, in the case where impurities are not included in the entire surface as in the present invention, the dielectric film and the first and / or second are formed at the resonator end face in order not to perform ion implantation in the active layer which is the light emission region and in the vicinity thereof. The nitride semiconductor layer in the light emitting region and the dielectric film according to the position of the impurity containing region, the positional relationship of the first and / or second impurity containing regions in the nitride semiconductor layer, the peak position, the symmetric / asymmetric relationship, etc. Thus, it is possible to adjust both the improvement of the adhesiveness and the stress relaxation at the interface between the dielectric film and the nitride semiconductor layer in the impurity-containing region.

  Note that, in the impurity-containing region, as will be described later, the first nitride semiconductor layer and the second nitride semiconductor layer usually contain impurities that originally exhibit n-type or p-type conductivity in order to perform a predetermined function. However, the impurities forming the impurity-containing region are functionally different from the impurities for imparting conductivity as described above.

  Further, as shown in FIG. 1B, in this nitride semiconductor laser element, a dielectric film 44 is formed so as to cover the resonator end face 30 on the light output side of the resonator end faces 30 facing each other. It is preferable that The dielectric film 44 may cover the end face of the resonator on the monitor side opposite to the end face on the light emission side.

In the dielectric film 44, at least one element constituting the dielectric film 44 is the same as one element constituting a nitride semiconductor layer described later. The constituent element contained in both the dielectric film 44 and the nitride semiconductor layer is preferably nitrogen. When the dielectric film 44 contains nitrogen which is a main constituent element of the nitride semiconductor layer, the adhesion between the nitride semiconductor layer and the dielectric film can be improved. Furthermore, both preferably include at least one selected from the group consisting of aluminum, indium, and gallium. Thereby, the adhesion between the nitride semiconductor layer and the dielectric film can be further improved. Specifically, the dielectric film 41 includes an oxide film such as Al ₂ O ₃ , Ga ₂ O ₃ and In ₂ O ₃ , a nitride film such as AlN, GaN and InN, and an oxynitride film such as AlON, GaON and InON. Etc. Among these, an aluminum oxide film, a nitride film, and an oxynitride film are preferable.

The dielectric film 44 does not necessarily have a single layer structure, and may be configured by laminating at least two kinds of films having different refractive indexes with respect to the laser beam in a predetermined number of pairs. For example, a first film having a first refractive index with respect to laser light and a second film having a second refractive index relatively lower than that are stacked in order from the light emission region side. can do. In this case, it is appropriate that one pair or 1.5 to 10.5 pairs of the first film and the second film are laminated depending on the material of the translucent film to be used. In the case of using a laminated structure, reflection and transmission of laser light are repeated at the interface of each film, so that the reflectance approaches 100% as the number of laminated layers increases. For example, the dielectric film 41 is preferably configured to have a reflectance of 75% or less, further 60% or less, or 20% or less on the light emitting side. Further, on the monitor side, it is preferable that the reflectance be 75% or more, further 85% or more, 90% or more. It is appropriate that each film has a thickness of m / 4n (n: refractive index, m: odd number) of the laser light wavelength inside each film. Thereby, the optical damage of the resonator end face on the light emitting side can be protected, and the deterioration and life of the light emission output can be improved. In the case of the laminated structure, it is preferable that at least the film in contact with the nitride semiconductor layer is formed of the above-described material, and other films are, for example, Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ , oxide film such as Nb ₂ O ₅ , Ta ₂ O ₅ , Ga ₂ O ₃ , In ₂ O ₃ , HfO _x , nitride film such as AlN, SiN, InN, AlON, SiON, ZrON, TiON, NbON, TaON Any of oxynitride films such as GaON, InON, and HfON may be used.

  In particular, when the nitride semiconductor layer is GaN, even if a film made of AlN is covered as a thin film as a dielectric film, it is usually easy to crack due to stress. However, in the present invention, since the impurity-containing region is formed above and / or below the light emitting region, the lattice constant of the nitride semiconductor layer increases in the impurity-containing region, and the resonator end face and the dielectric film The dielectric film can be formed without cracking even with a thick film, and a film with good adhesion can be formed in the light emitting region. In addition, GaN has high light energy and tends to accumulate heat. Generally, it is difficult to sufficiently stabilize the interface with the dielectric film, but the light output region above the resonator end face and / or Since an ion-containing region is formed below and the lattice constant of the nitride semiconductor layer is large in the impurity-containing region, the dielectric film in the light output region is relatively closely attached to the resonator end face as shown in FIG. It is possible to suppress heat generation by suppressing light absorption in the light output region of the resonator end face.

  In order to realize continuous driving of the nitride semiconductor laser element, not only the adhesion between the nitride semiconductor layer and the dielectric film is improved, but also, as described above, the nitride semiconductor layer and the dielectric film It is also important to further relax the stress generated at the interface.

The nitride semiconductor laser device of the present invention will be described below.
The substrate constituting the nitride semiconductor laser element of the present invention may be an insulating substrate or a conductive substrate. In the case of an insulating substrate, a part of the nitride semiconductor layer may be removed in the thickness direction, and an n-electrode may be formed so as to contact the n-type semiconductor layer.

As the nitride semiconductor layer, can be used of the general formula _{In x Al y Ga 1-xy} N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y ≦ 1). In addition to this, a group III element partially substituted with B may be used, or a group V element partially substituted with P and As may be used. The n-type semiconductor layer contains at least one of group IV elements such as Si, Ge, Sn, S, O, Ti, Zr, and Cd, group VI elements, and the like as n-type impurities. The p-type semiconductor layer contains Mg, Zn, Be, Mn, Ca, Sr, etc. as p-type impurities. The impurities are preferably contained in a concentration range of about 1 × 10 ¹⁶ to 1 × 10 ²¹ / cm ³ , for example.

The active layer may have either a multiple quantum well structure or a single quantum well structure.
The nitride semiconductor layer has a light guide layer that constitutes an optical waveguide in an n-type semiconductor layer and a p-type semiconductor layer, and thus has an SCH (Separate Confinement Heterostructure) structure that is a separated light confinement structure with an active layer interposed therebetween. It is preferable that However, the present invention is not limited to these structures.

  In the present application, the light emitting region is a region where laser light is output, and the nitride semiconductor layer is a region including at least a well layer and may be a region including an active layer. In the case of a nitride semiconductor laser element having an SCH structure, the region includes an optical guide layer.

  The growth method of the nitride semiconductor layer is not particularly limited, but MOVPE (metal organic chemical vapor deposition), MOCVD (metal organic chemical vapor deposition), HVPE (hydride vapor deposition), MBE (molecular beam epitaxy). Any method known as a method for growing a nitride semiconductor can be suitably used. In particular, MOCVD is preferable because it can be grown with good crystallinity.

  A ridge is formed on the surface of the nitride semiconductor layer, for example, a p-type semiconductor layer. The ridge functions as a waveguide region, and the width is preferably about 1.0 μm to 30.0 μm, and more preferably about 1.0 μm to 3.0 μm. The height (etching depth) can be appropriately adjusted depending on the film thickness, material, and the like of the layer constituting the p-type semiconductor layer, and examples thereof include 0.1 to 2 μm. The ridge is preferably set so that the length in the resonator direction is about 100 μm to 1000 μm. Further, they may not all have the same width in the resonator direction, and the side surfaces thereof may be vertical or tapered. The taper angle in this case is suitably about 45 ° to 90 °.

  The electrode formed on the surface of the second nitride semiconductor layer is suitably a p-electrode, for example. This electrode and optionally an electrode (n electrode) formed on the first nitride semiconductor layer are palladium, platinum, nickel, gold, titanium, tungsten, copper, silver, zinc, tin, indium, aluminum, iridium, rhodium, It can be formed of a single layer film or a laminated film of a metal such as ITO or an alloy. The film thickness of the electrode can be appropriately adjusted depending on the material used, and for example, about 500 to 5000 mm is appropriate. The electrode may be formed so as to be electrically connected to at least the p-type and n-type semiconductor layers or the substrate. Further, one or a plurality of conductive layers such as a pad electrode may be formed on this electrode.

  In particular, if the p-electrode is electrically connected to the ridge, and the end face of the p-electrode on the light output region side is arranged inside the element with respect to the resonator end face on the light output region side, the shape is Although not particularly limited, it is usually wider than the width of the ridge and formed along the extending direction of the ridge. The electrode is generally formed in the same shape as long as the nitride semiconductor layer is formed in a square shape or the like. That is, the electrode end faces are arranged in parallel or substantially in parallel (including the same plane) with each of the resonator end faces (however, the electrode end faces are not necessarily arranged in parallel or substantially in parallel with the resonator end faces). Good). Therefore, it is suitable that all end faces of the electrode are disposed inside the element. The distance between the electrode end face and the resonator end face on the light output region side depends on the size of the nitride semiconductor laser element, but is, for example, 0.1 μm or more, further 1.0 μm or more, preferably about 2.0 to 3.0 μm. Is suitable. As a result, current injection into the vicinity of the resonator end face on the light emission region side can be reduced and light absorption by the electrode in the vicinity of the resonator end face can be prevented. Can be reduced. The electrode is preferably narrower than the inside of the element, particularly in the vicinity of the resonator end face on the light emission region side. Thereby, the effect mentioned above can be exhibited more efficiently. For example, the electrode may be about 10 to 90% of the inner width on the resonator end face side.

  In the nitride semiconductor laser device of the present invention, it is preferable that the first protective film is formed from the ridge side surface to the second nitride semiconductor layer surface. For example, the first protective film is preferably formed of an insulating material having a refractive index smaller than that of the nitride semiconductor layer. Specifically, a single layer or a plurality of layers such as oxides and nitrides such as Zr, Si, V, Nb, Hf, Ta, and Al can be given. Thus, by forming the first protective film from the side surface of the ridge to the nitride semiconductor surface on both sides of the ridge, a refractive index difference with respect to the nitride semiconductor layer, particularly the p-type semiconductor layer, is ensured. Light leakage from the active layer can be controlled, light can be confined efficiently in the ridge, insulation in the vicinity of the ridge base can be further secured, and generation of leakage current can be avoided. it can. The film thickness of the first protective film is not particularly limited, but for example, it is appropriate to set the thickness to about 100 to 20000 mm, preferably 100 to 5000 mm.

  A second protective film is preferably formed on the first protective film. The second protective film only needs to be disposed on the first protective film at least on the surface of the nitride semiconductor layer, and the side surface of the nitride semiconductor layer and / or the substrate is not interposed through or through the first protective film. It is preferable that the side surface or the surface is further coated. The second protective film can be formed using the same material as the first protective film. As a result, not only the insulating properties but also the exposed side surfaces or surfaces can be reliably protected.

  In the nitride semiconductor laser device of the present invention, it is preferable that an insulating film is formed on the second nitride semiconductor layer from the cavity end face to the electrode end face. As the insulating film, the same materials as those exemplified as the first and second protective films described above can be used. The film thickness is not particularly limited and can be appropriately adjusted depending on the type of insulating film, the characteristics of the laser element, and the like. It is preferable that the end portion of the insulating film coincides with the end face of the resonator, and the end portion inside the element may coincide with the electrode end portion or may wrap around below the electrode. Thereby, a short circuit with the second nitride semiconductor layer at the electrode end can be prevented.

  The nitride semiconductor laser device of the present invention is not limited to a ridge structure laser device, and is a layer having a current confinement function in a semiconductor layer (for example, an opening in an optical waveguide region and made of AlN or the like). A laser element having a current confinement structure in which a current is confined by providing a layer may be used.

The nitride semiconductor laser device of the present invention can be manufactured, for example, by the following manufacturing method.
First, a nitride semiconductor layer is formed on a substrate. As the substrate, for example, a nitride semiconductor substrate having an off angle of about 0 ° to 10 ° on the first main surface and / or the second main surface can be used. The film thickness is about 50 μm to 10 mm, preferably about 100 to 1000 μm. The nitride semiconductor substrate can be formed by vapor phase growth methods such as MOCVD method, HVPE method, MBE method, hydrothermal synthesis method for crystal growth in a supercritical fluid, high pressure method, flux method, melting method and the like. A commercially available product may be used.

A nitride semiconductor layer is grown on the first main surface of the nitride semiconductor substrate.
As the nitride semiconductor layer, for example, an n-type semiconductor layer, an active layer, and a p-type semiconductor layer are grown in this order under a reduced pressure to atmospheric pressure condition, for example, by MOCVD. The n-type semiconductor layer and the p-type semiconductor layer may have a single film structure, a multilayer film structure, or a superlattice structure including two layers having different composition ratios. Also, the order may be reversed.

The n-type semiconductor layer is preferably formed of a multilayer film. For example, the first n-type semiconductor layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5), preferably Al _x Ga _1-x N (0 <x ≦ 0.3). As specific growth conditions, the growth temperature in the reactor is set to 1000 ° C. or higher and the pressure is set to 600 Torr or lower. The first n-type semiconductor layer can function as a cladding layer. A film thickness of about 0.5 to 5 μm is appropriate.

The second n-type semiconductor layer can function as a light guide layer and can be formed of Al _x Ga _1-x N (0 ≦ x ≦ 0.3). The film thickness is suitably 0.5-5 μm.
After forming the n-type semiconductor layer, a protective layer for ion implantation is formed. The protective layer here is not particularly limited as long as it is a material that can be completely removed from the n-type semiconductor layer after ion implantation, and is not limited to an insulator layer, a conductor layer, a metal layer, and a semiconductor layer. Etc. can be formed. Among these, a silicon oxide layer is preferable. This is because it can be completely and easily removed without damaging the n-type semiconductor layer or the like by applying etching that is normally used. The film thickness of the protective layer is not particularly limited, and can be appropriately adjusted depending on the ion species used, the dose, and the like. For example, about 100 to 10 μm can be mentioned.

  For example, as shown in FIG. 5 (a), the protective layer 26 has a thin film region 21 that allows ions 27 to penetrate into the nitride semiconductor layer only in a desired region. Examples of the region include those having a thick film region 22 that does not allow ions to penetrate. Further, as shown in FIG. 6 (a) or (b), the protective layers 23 and 24 may change in thickness in a stepwise or stepwise manner, or as shown in FIG. The protective layer 25 may change in thickness. Corresponding to the shape of the protective layer, the shape of the impurity-containing region viewed from the resonator surface side can be changed (31c in FIG. 5B, 31a in FIG. 4A, FIG. 4B). ) 31b and FIG. 7B 31d).

After forming the protective layer, ion implantation is performed on the n-type semiconductor layer through the protective layer. Ion implantation can be performed by any method known in the art. The implantation energy and dose can be appropriately adjusted depending on the ion species used, the thickness of the protective layer, and the like. For example, when ions are implanted into a semiconductor laser device manufactured under the above conditions, the implantation energy is 10 to 5000 keV, in particular, indium is 10 to 3000 keV, arsenic is 10 to 2000 keV, and phosphorus is 10 to 1000 keV. preferable. The dose amount is about 1 × 10 ¹⁵ to 1 × 10 ¹⁷ ions / cm ² . The present invention is not limited to this range, and the implantation energy can be appropriately adjusted according to the implantation region and depth, such as about 10 keV to 10 MeV, and the dose amount about 1 × 10 ¹⁵ to 1 × 10 ²⁰ ions / cm ^2. is there.

In addition, ion implantation can be performed a plurality of times, and the impurity-containing region may be formed by repeating ion implantation and regrowth.
After ion implantation, it is preferable to perform a heat treatment for crystal recovery of the n-type semiconductor layer. Any known method may be used for the heat treatment. For example, it is appropriate to carry out for about 5 to 200 minutes in a temperature range of about 700 to 1100 ° C. in an ammonia and / or nitrogen atmosphere.

Thereafter, the protective layer is removed, and an active layer and a p-type semiconductor layer are stacked on the n-type semiconductor layer.
The active layer preferably has a general formula In _x Al _y Ga _1-xy N (0 <x ≦ 1, 0 ≦ y <1, 0 <x + y ≦ 1) containing at least In. Increasing the Al content enables emission in the ultraviolet region. Further, light emission on the long wavelength side is possible, and light emission from 360 nm to 580 nm can be performed. Luminous efficiency can be improved by forming the active layer with a quantum well structure.

Subsequently, a p-type semiconductor layer is formed. The p-type semiconductor layer is preferably formed of a multilayer film. For example, Al _x Ga _1-x N (0 ≦ x ≦ 0.5) containing a p-type impurity is formed as the first p-type semiconductor layer. The first p-type semiconductor layer 161 functions as a p-side electron confinement layer. The second p-type semiconductor layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.3), and the third p-type semiconductor layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5). The third p-type semiconductor layer preferably has a superlattice structure made of GaN and AlGaN, and functions as a cladding layer. The fourth p-type semiconductor layer can be formed of Al _x Ga _1-x N (0 ≦ x ≦ 1) containing p-type impurities. In these semiconductor layers, In may be mixed. Note that the first p-type semiconductor layer and the second p-type semiconductor layer can be omitted. The thickness of each layer is suitably about 30 mm to 5 μm.

After forming the p-type semiconductor layer, a protective layer is formed and ion implantation is performed in the same manner as described above.
Note that the ion implantation is not necessarily performed after the n-type semiconductor layer is completely formed, before the active layer is formed, or after the p-type semiconductor layer is completely formed, and may optionally be an n-type or p-type semiconductor. It may be performed after any layer forming the layer is formed.

  Thus, after forming the n-type or p-type semiconductor layer or forming only a part of the n-type or p-type semiconductor layer, ion species are implanted through the protective layer as will be described later. Since ion species can be intensively implanted at a desired depth (site), and unnecessary ion species can be eliminated from the nitride semiconductor layer by removing the protective layer. Sufficient crystal recovery in the nitride semiconductor layer can be achieved.

  As the heat treatment for crystal recovery, heat treatment during the formation of the layers constituting the n-type or p-type semiconductor layer may be used, or after any semiconductor layer is formed, a separate heat treatment is performed. Also good.

Subsequently, optionally, the nitride semiconductor layer is preferably etched to expose the n-type semiconductor layer (for example, the first n-type semiconductor layer). The exposure can be performed using, for example, Cl ₂ , CCl ₄ , BCl ₃ , SiCl ₄ gas or the like by the RIE method. Thereby, stress can be relieved. In addition, when the n-type semiconductor layer is exposed, the resonator surface can be formed simultaneously by etching so as to expose the end face perpendicular to the striped waveguide region. However, the formation of the resonator surface may be performed in a separate process by cleavage.

Next, a first mask pattern is formed on the nitride semiconductor layer, and ridges are formed by etching using the mask pattern.
The mask pattern can be formed in a desired shape by using a known method such as photolithography and an etching process using an oxide film such as SiO _{2 and} a nitride such as SiN. The film thickness of the mask pattern is suitably such that the first mask pattern remaining on the ridge after the ridge is formed can be removed by a lift-off method in a later step. For example, about 0.1-5.0 micrometers is mentioned.

  Subsequently, a first protective film is formed on the nitride semiconductor layer exposed after forming the mask pattern and the ridge. The first protective film can be formed by a method known in the art. As the film thickness of the first protective film, a film formed with a film thickness of about 100 to 5000 mm is preferable. Thereafter, annealing may be performed to lower the resistance of the p-type semiconductor layer. In this case, the annealing temperature is preferably 500 ° C. or higher.

Next, the first protective film existing on the mask pattern and the mask pattern are removed. These removals can be performed by known dry or wet etching.
Thereafter, a p-electrode having a desired shape is formed on the surface of the ridge. It is preferable to perform ohmic annealing after the p-electrode is formed. For example, annealing conditions of 300 ° C. or higher, preferably 500 ° C. or higher in a nitrogen and / or oxygen-containing atmosphere are appropriate.

  Next, a second protective film may be formed on the first protective film. The second protective film can be formed by a method known in the art. Optionally, a pad electrode may be formed on the p-electrode. The pad electrode is preferably a laminate made of a metal such as Ni, Ti, Au, Pt, Pd, or W.

  Moreover, it is preferable to form an n-electrode on the second main surface of the nitride semiconductor substrate partially or entirely. For example, V (film thickness 100 mm), Pt (film thickness 2000 mm), and Au (film thickness 3000 mm) are formed from the substrate side. The n electrode can be formed by, for example, sputtering, CVD, vapor deposition, or the like. For forming the n-electrode, it is preferable to use a lift-off method, and after forming the n-electrode, it is preferable to anneal at 500 ° C. or higher. Further, a metallized electrode may be formed on the n electrode. The metallized electrodes are, for example, Ti—Pt—Au— (Au / Sn), Ti—Pt—Au— (Au / Si), Ti—Pt—Au— (Au / Ge), Ti—Pt—Au—In, It can be formed of Au / Sn, In, Au / Si, Au / Ge, or the like.

  After forming the n-electrode, it is preferable to divide the wafer into bars in order to form a resonator end face of the nitride semiconductor layer in a direction perpendicular to the striped p-electrode. Here, the resonator end face is the M plane (1-100) or the A plane (11-20). The resonator end face can be formed using a known method such as cleavage or etching.

For example, when the resonator end surface is formed by cleavage, the resonator end surface can be a relatively clean surface, and the film quality of the dielectric film formed thereon can be improved.
In addition, when the resonator end face is formed by etching, a dielectric film is formed on the obtained resonator end face, and then the substrate is divided in a separate process, compared to the case where the dielectric film is formed on the entire surface. Thus, since the area of the dielectric film is small and the stress applied to the dielectric film is small, the impurity-containing region is formed only in the first nitride semiconductor layer, and the impurity-containing region is relatively small, or the lattice constant is changed. Even if the impurity-containing region is formed using a small impurity, the effect of the present invention can be easily obtained.

  The wafer dividing process may be performed in two stages. By this method, the resonator end face can be formed with high yield. First, a cleavage assist groove is formed in advance by etching or the like from the first main surface side or the second main surface side of the substrate. The cleavage assist grooves are formed at the four corners of the element to be chipped. Thereby, bending of the cleavage direction can be suppressed. Next, the wafer is divided into bars by a breaker. As a method for dividing the wafer into bars, there is a blade break, a roller break or a press break.

  After forming the resonator end face, a dielectric film is formed. However, the dielectric film may be formed after being formed into a chip. The dielectric film can be formed by a known method such as sputtering or CVD.

The nitride semiconductor substrate having a bar shape can be divided into chips in parallel with the stripe direction of the ridge.
In such a manufacturing method, impurities may be introduced into a predetermined region in the resonator end face by a diffusion method such as solid phase diffusion instead of the above-described ion implantation. In this case, after forming the n-type semiconductor layer 11 as the first nitride semiconductor layer or the p-type semiconductor layer 13 on the substrate 10, the impurity to be introduced is contained at a predetermined position. By forming a film (for example, an oxide film such as a SiO ₂ film when the impurity is an oxygen atom) and performing a heat treatment under the above-described conditions, an impurity-containing region can be formed by diffusion. .

Alternatively, after forming the resonator end face, a mask may be formed on the end face, and an impurity may be implanted into a desired region from above to form an impurity-containing region.
Hereinafter, embodiments of the nitride semiconductor laser device of the present invention will be described in detail with reference to the drawings.

Example 1
As shown in FIG. 1A, the nitride semiconductor laser device of the present invention has a first n-type semiconductor layer (Si: 8 × 10 ¹⁷ / cm) as an n-type semiconductor layer 11 on a GaN substrate 10. ^{3 to} 3 × 10 ¹⁸ / cm ³ doped, Al _0.02 Ga _0.98 N, film thickness 3.5 μm), second n-type semiconductor layer (Si: 2 × 10 ¹⁸ / cm ³ to 1 × 10 ¹⁹ / cm ³ doped , In _0.06 Ga _0.94 N, film thickness: 0.15 μm), third n-type semiconductor layer (undoped Al _0.038 Ga _0.962 N (25Å) and Si: 8 × 10 ¹⁷ / cm ^{3 to} 3 × 10 ¹⁸ / cm ³ A superlattice layer having a total film thickness of 1.2 μm with doped GaN (25 μm) and a fourth n-type semiconductor layer (undoped GaN, film thickness: 0.17 μm) are formed.

On top of that, a barrier layer (140 Å) made of Si-doped In _0.02 Ga _0.98 N and a well layer (70 Å) made of undoped In _0.07 Ga _0.93 N are alternately laminated twice, and a barrier layer is formed thereon. An active layer 12 having a total quantum film thickness of 560 mm and having a multiple quantum well structure (MQW) is formed.

Furthermore, as the p-type semiconductor layer 13 thereon, a first p-type semiconductor layer (Mg: 1 × 10 ¹⁹ / cm ³ to 1 × 10 ²⁰ / cm ³ doped, Al _0.25 Ga _0.75 N, 100 と), Second p-side nitride semiconductor layer (undoped GaN, 0.15 μm), third p-type semiconductor layer (undoped Al _0.10 Ga _0.90 N (25 （) and Mg: 1.25 × 10 ¹⁹ / cm ³ doped GaN And a fourth p-type semiconductor layer (Mg: 1 × 10 ²⁰ / cm ³ doped, GaN, 150 Å).

A first impurity-containing region 31 and a second impurity-containing region 32 are formed on the cavity facet on the light emitting side of the nitride semiconductor laser element. As shown in FIGS. 1A and 1B, the first impurity-containing region 31 has a width X1 of about 80% of the entire width of the n-type semiconductor layer 11 with the depth below the ridge as the center. Z ₁ is arranged at about 2.5 μm from the resonator end face, and its height Y ₁ is 0.3 μm. The second impurity-containing region 32 has a width X ₂ of about 60% of the entire width of the p-type semiconductor layer 13 around the lower side of the ridge, and a depth Z 2 of about 2.5 μm from the resonator end face. The height Y ₂ is arranged at 0.3 μm.

A ridge is formed on the surface of the p-type semiconductor layer. A first protective film 15 made of ZrO _{2 having} a thickness of 550 mm is formed from the side surface of the ridge to the surface of the p-type semiconductor layer.
A p-electrode (not shown) made of Ni (100）)-Au (1500Å) is formed on the first protective film 15. The end portion of the end surface on the resonator surface side of the p-electrode is disposed on the inner side of D = 2.5 μm away from the resonator surface. Further, a p-pad electrode (not shown) made of Ni (1000 Å) -Ti (1000 Å) -Au (8000 形成) is formed through a second protective film (not shown).

On the back side of the GaN substrate 10, an n-electrode 20 made of Ti (100Å) -Al (5000Å) is formed.
Further, as shown in FIG. 1B, a dielectric film 44 is formed on the resonator end face 30 on the light emitting side. The dielectric film 44 is formed of Al ₂ O ₃ with a film thickness of 120 nm, for example.

This nitride semiconductor laser device was formed by the following manufacturing method.
According to the method described above, first, an n-type semiconductor layer 11 composed of first to fourth n-type semiconductor layers is formed on a GaN substrate.

Thereafter, a resist layer (film thickness: 2 μm) is formed on the entire surface of the n-type semiconductor layer 11, and the resist layer in a predetermined region is removed in a rectangular shape by photolithography and etching processes. A SiO ₂ film (film thickness: 0.1 μm) is formed on the entire surface of the obtained resist layer. Thus, as shown in FIG. 5A, a protective layer 26 having a thin film region 21 into which ions can be implanted and a thick film region 22 that does not allow ions to penetrate in other regions can be formed. . For example, phosphorus ions are implanted from above the protective layer 26 at an acceleration energy of 300 keV and a dose of 1 × 10 ¹⁶ / cm ² .

Next, as shown in FIG. 5B, the protective layer 26 is removed by wet etching.
Subsequently, an active layer having a multiple quantum well structure and first to fourth p-type semiconductor layers are formed on the n-type semiconductor layer 11.

Thereafter, a protective layer is formed on the entire surface of the p-type semiconductor layer 13 in the same manner as described above, and phosphorus ions are implanted from above the protective layer, for example, at an acceleration energy of 300 keV and a dose of 1 × 10 ¹⁶ / cm ² .

  Next, in the reaction vessel, the wafer is annealed at a temperature of 700 ° C. or higher in a nitrogen atmosphere to reduce the resistance of the p-type semiconductor layer. This heat treatment simultaneously recovers the crystals of the two impurity-containing regions formed in the n-type and p-type semiconductor layers, and improves the transparency of the ion-implanted portion.

A ridge is formed by forming a first mask pattern made of SiO ₂ on the p-type semiconductor layer and etching the first mask pattern.
Subsequently, a first protective film is formed on the nitride semiconductor layer exposed after forming the first mask pattern and the ridge. The first protective film is formed by a method known in the art.

Next, the first protective film and the first mask pattern existing on the first mask pattern are removed, and a p-electrode is formed on the surface of the ridge and an n-electrode is formed on the second main surface of the nitride semiconductor substrate. To do.
Thereafter, the nitride semiconductor layer is divided by using blade breakage in a direction perpendicular to the ridge and overlapping with the ion-containing region, and further, a resonator end surface on the light emitting side is formed by sputtering. A dielectric film made of aluminum oxide is formed on the entire surface.

Next, a chip-shaped semiconductor laser element is formed.
In the nitride semiconductor laser element formed by such a manufacturing method, the impurity-containing region has a larger lattice constant than other regions.
Further, since the first and second impurity-containing regions are formed, the stress between the semiconductor layer and the dielectric film is relieved in the impurity-containing region on the resonator end face, and the resonance of the dielectric film in the light output region. The adhesion to the vessel end surface can be improved.

Example 2
The semiconductor laser device of this example was formed in substantially the same manner as in Example 1 except that no impurity-containing region was formed in the p-type semiconductor layer in Example 1.
Also in the semiconductor laser device thus obtained, the adhesion of the dielectric film in the light output region to the resonator end face can be improved.

Example 3
The semiconductor laser device of this example was formed in substantially the same manner as in Example 1 except that no impurity-containing region was formed in the n-type semiconductor layer in Example 1.
Also in the semiconductor laser device thus obtained, the adhesion of the dielectric film in the light output region to the resonator end face can be improved.

  The nitride semiconductor laser device of the present invention can be used for optical disc applications, optical communication systems, printing machines, exposure applications, measurements, and the like. Further, it can be used as a bio-related excitation light source that can detect the presence or position of a substance by irradiating a substance having sensitivity at a specific wavelength with light obtained from a nitride semiconductor laser.

FIG. 3 is a schematic perspective view and a cross-sectional view of a main part for explaining the structure of the nitride semiconductor laser device of the present invention. It is the schematic sectional drawing of the principal part for demonstrating the adhesiveness of the dielectric film in the nitride semiconductor laser element of this invention. It is the schematic sectional drawing of another principal part for demonstrating the adhesiveness of the dielectric film in the nitride semiconductor laser element of this invention. It is sectional drawing for demonstrating the shape of the impurity containing area | region of the resonator surface in the nitride semiconductor laser element of this invention. It is a schematic manufacturing process diagram of the principal part for demonstrating the shape of the protective layer for forming the nitride semiconductor laser element of this invention. It is a schematic manufacturing process figure of the principal part for demonstrating the shape of the protective layer for forming another nitride semiconductor laser element of this invention. It is a schematic manufacturing process figure of the principal part for demonstrating the shape of the protective layer for forming another nitride semiconductor laser element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 11 N-type semiconductor layer 12 Active layer 13 P-type semiconductor layer 14 Ridge 15 First protective film 21 Thin film region 22 Thick film region 23, 24, 25, 26 Protective layer 27 Ion 30 Resonator end faces 31, 31a, 31b 31c, 31d First impurity-containing region 32 Second impurity-containing region 44 Dielectric film

Claims (4)

A substrate, a nitride semiconductor layer in which a first nitride semiconductor layer, an active layer, and a second nitride semiconductor layer are stacked in this order on the substrate, and resonator end faces facing each other formed in the nitride semiconductor layer A nitride semiconductor laser device comprising:
At least one selected from the group consisting of Al ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ , AlN, GaN, InN, AlON, GaON, and InON so as to cover the resonator end face on the light output side . A dielectric film is formed,
At least one element constituting the nitride semiconductor layer and one element constituting the dielectric film are the same,
A cavity end face of the optical output side, the upper and / or below the light emitting region, and wherein the impurity-containing region containing an impurity to increase the lattice constant of the nitride semiconductor layer is formed Nitride semiconductor laser device. The first nitride semiconductor layer and / or the second nitride semiconductor layer is formed of a plurality of layers, the impurity-containing region, the nitride semiconductor according to claim 1 comprising formed over a plurality of layers Laser element. The impurity-containing region, indium, arsenic, phosphorus, antimony, zinc, thallium, nitride semiconductor laser device according to claim 1 or 2 comprising at least one selected from the group consisting of bismuth. Said dielectric film, a nitride of aluminum, a nitride semiconductor laser device according to any one of claims 1 to 3 made of an oxide or oxynitride.

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