JP2009016798A - Nitride semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser element with which there is minimized stress load on the active layer, which prevents the degradation that would result in the laser element during drive, and with which good adhesion of the protective film to the surface of a resonator is ensured owing to the reduction in stress, and the performance of the laser element itself can be enhanced. <P>SOLUTION: The nitride semiconductor laser element includes: a nitride semiconductor layer that includes a first nitride semiconductor layer, an active layer, and a second nitride semiconductor layer; and a protective film that is in contact with the surface of a resonator formed on nitride semiconductor layers. In the protective film, the crystallinity at a portion adjacent to the active layer is different from that at portions adjacent to the first and second nitride semiconductor layers. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor laser device, and more particularly to a nitride semiconductor laser device having a protective film on a resonator surface formed in a nitride semiconductor layer.

  In a nitride semiconductor laser device, the resonator surface formed by RIE (reactive ion etching) or cleavage has a small band gap energy, so that absorption of emitted light occurs at the end surface, and heat is generated at the end surface due to this absorption. In order to realize a high output semiconductor laser, there was a problem in life characteristics. For this reason, for example, a method of manufacturing a high-power semiconductor laser in which an Si oxide film or a nitride film is formed as a protective film for the resonator end face has been proposed (for example, Patent Document 1).

On the other hand, conventionally, in a nitride semiconductor laser element, a method of changing the thickness of a protective film formed on the resonator surface in accordance with the emitted light density in order to suppress variations in device characteristics between chips (for example, Patent Document 2), adopting a stripe structure inside the resonator and using a SiO ₂ film as the protective film in order to realize FFP monomodality, and changing the thickness of the protective film for each stripe (for example, Patent document 3) etc. are adopted.
In order to suppress end face deterioration, a method of forming an end face coat film on a resonator end face via an adhesion layer has been proposed (for example, Patent Document 4).
JP-A-9-283443 JP 2006-228892 A JP 2002-329926 A JP 2002-335053 A

However, with the realization of a semiconductor laser with higher output, it is required to further improve the structure related to light emission at the resonator surface. In other words, depending on its performance, for example, it is necessary to have a structure that can prevent degradation of the protective film during driving of the laser element while ensuring maximum adhesion of the protective film without applying stress to the active layer. It is.
In addition, there is an increasing demand for a small-sized and low-power nitride semiconductor laser device used for reproducing next-generation optical disks. When the reflectance of the resonator surface of the nitride semiconductor laser element is increased, the load on the resonator surface is large even at a low output. Therefore, it is necessary to improve the structure related to the light emission of the resonator surface as in the case of a high-power semiconductor laser.

  The present invention has been made in view of the above problems, and reduces the load of stress on the active layer, thereby preventing deterioration during driving of the laser element, and also due to stress relaxation, An object of the present invention is to provide a nitride semiconductor laser device capable of ensuring adhesion to the resonator surface and improving the performance of the laser device itself.

  The nitride semiconductor laser device of the present invention includes a first nitride semiconductor layer, an active layer, and a second nitride semiconductor layer, and is in contact with at least one end surface of the nitride semiconductor layer having a resonator having an end surface. A nitride semiconductor laser element having a first protective film, wherein the first protective film has a brightness and darkness determined by a scanning transmission electron microscope in a region in contact with the active layer and a region in contact with the first and second nitride semiconductor layers. It is characterized by having an observed film structure.

Another nitride semiconductor laser device of the present invention includes a nitride semiconductor layer including a first nitride semiconductor layer, an active layer, and a second nitride semiconductor layer, and having a resonator having an end face, and at least one of the nitride semiconductor laser elements. A nitride semiconductor laser device having a first protective film in contact with an end face,
The first protective film has a film structure in which crystallinity is different between a part adjacent to the active layer and a part adjacent to the first and second nitride semiconductor layers.

In such a nitride semiconductor laser device, the bright part or dark part of the region in contact with the active layer is continuously arranged in the film thickness direction of the first protective film, or is wider on the outside of the element than the resonator surface side. Preferably there is.
The first protective film has a thickness of 3 nm to 1000 nm, is formed of a material having a hexagonal crystal structure, or is in a region in contact with the first and second nitride semiconductor layers. It is preferable to have a crystal structure coaxial with the surface or to be covered with a second protective film.
Further, the second protective film, the region in contact with the active layer, and the region in contact with the first and second nitride semiconductor layers may be observed with high or low brightness by a scanning transmission electron microscope in this order. preferable.
The second protective film preferably has a thickness of 10 nm to 1500 nm.

Further, the portion adjacent to the active layer has substantially the same crystallinity over the thickness direction of the first protective film, or the portion adjacent to the active layer having substantially the same crystallinity is the resonator surface. It is preferable that the width is wider outside the element than at the side.
The site adjacent to the first and second nitride semiconductor layers, the site adjacent to the active layer, and the second protective film preferably have good crystallinity in this order.

  According to the present invention, the first protective film is observed by the scanning transmission electron microscope, and brightness and darkness are observed in the region in contact with the active layer and the region in contact with the first and second nitride semiconductor layers. It is considered that the crystallinity of the region of the protective film in contact with the active layer and the region of the first protective film in contact with the first nitride semiconductor layer and the second nitride semiconductor layer are different. As described above, the light and darkness is observed in the first protective film, that is, the crystallinity is varied for each of the above-described regions, thereby relieving the stress caused by the first protective film around the active layer on the resonance surface. Can be made. As a result, it is possible to secure the adhesion of the first protective film to the resonator surface and to prevent the laser element from deteriorating during driving. As a result, it is possible to provide a nitride semiconductor laser device that can ensure a stable operation, has high reliability, and has an improved COD level.

  The nitride semiconductor laser device of the present invention is mainly composed of a first nitride semiconductor layer 11, an active layer 12, and a second nitride semiconductor layer 13, as typically shown in FIGS. 1, 2A, and 2B, for example. And a resonator surface is provided on the opposing end face of the nitride semiconductor layer to form a resonator.

  In such a nitride semiconductor laser element, a nitride semiconductor layer is usually formed on the substrate 10, a ridge 14 is formed on the surface of the second nitride semiconductor layer 13, and the resonator is formed on the entire surface of the resonator. The first protective film 25 is in contact with the surface, and the second protective film 26 is formed on the first protective film 25. In addition, a buried film 15, a p electrode 16, a third protective film 17, a p pad electrode 18, an n electrode 19 and the like are appropriately formed. In this specification, the protective film formed on the resonator surface, such as the first protective film and the second protective film, may be described as a “protective film”.

The first protective film is made of, for example, an oxide such as Si, Mg, Al, Hf, Nb, Zr, Sc, Ta, Ga, Zn, Y, B, or Ti (in particular, Al ₂ O ₃ , SiO ₂ , Nb ₂ O _{5, TiO} 2, ZrO _2, etc.), nitrides (in particular, AlN, AlGaN, BN and the like) or fluoride, and may be formed by a combination of two or more thereof. Among these, an oxide is preferable. From another point of view, it is preferably formed of a material that does not absorb the oscillation wavelength of the laser element.

The film thickness of the first protective film is not particularly limited, and for example, it is suitable that it is about 3 nm to nm, and further about 5 nm to 700 nm, 10 nm to 400 nm.
The first protective film covers the resonator surface formed on the nitride semiconductor layer, but does not necessarily cover the entire surface of the resonator surface, and at least the optical waveguide region (active layer) on the resonator surface. And covering a part of the upper and lower layers thereof). The first protective film may partially cover the surface other than the resonator surface.

  The first protective film of the present invention is preferably in a crystalline state composed of single crystal, polycrystal, or the like. Examples of the crystal structure of the first protective film include a hexagonal system, a cubic system, and an orthorhombic system. The material, crystallinity, and orientation of the first protective film can be selected according to the material, crystallinity, orientation, and the like of the resonator end face that forms the first protective film. When the first protective film has a hexagonal crystal structure, the M-axis <1-100>, the A-axis <11-20>, the C-axis <0001>, the R-axis <1-102> orientation, etc. It is preferable that the film be oriented coaxially with the end face of the resonator. The reason is that by forming a first protective film having a crystal structure coaxial with the resonator end face, the band gap energy of the resonator end face is widened and a window structure is formed, so that the resonator end face is deteriorated. It is because it is thought that it can prevent.

  Note that the crystal structure in the present invention does not necessarily have to be strictly single crystal or polycrystal, and has a crystal structure close to these or a crystal structure exhibiting characteristics of these crystal structures. It may be. In addition, if the lattice constant is close to that of the nitride semiconductor (for example, the difference in lattice constant from the nitride semiconductor is 15% or less), the first protective film with good crystallinity can be formed. As a result, the film quality of the first protective film becomes better, and even when the semiconductor laser device is driven, stress can be relaxed to prevent cracks in the nitride semiconductor layer, and the COD level is reliably improved. be able to. In other words, when it is in a polycrystalline state or contains a polycrystal, the difference in the lattice constant from the resonator surface does not appear strictly, and the difference can be mitigated.

  Among these, a film made of a material having a hexagonal crystal structure is preferable. Further, it has a hexagonal crystal structure and is more preferably M-axis oriented. Here, the M-axis orientation is a single crystal and not only a state strictly aligned with the M axis (single crystal) but also a mixture of polycrystals, but a state uniformly including a portion aligned with the M axis, It may be in a state of being distributed uniformly.

  In general, the state of a film is classified into single crystal, polycrystalline, and amorphous depending on the degree of crystal of the material constituting the film. A single crystal has almost no change in lattice constant in the material, and has almost no lattice plane inclination. In other words, the atomic arrangement is regularly arranged in the material, and the long-range order is maintained. The polycrystal is composed of a large number of minute single crystals, that is, microcrystals. Amorphous means one that does not have a periodic structure as in crystals, that is, one that has an irregular atomic arrangement and no long-range order.

The state of such a film (in the case of being crystalline, its crystallinity or crystal state) can be easily determined from a diffraction image by an electron beam. That is, when an electron beam is incident on the film, an electron beam diffraction image appears corresponding to the size of the lattice constant and the surface direction. For example, in the case of a single crystal, since the crystal planes are substantially aligned, diffraction points are regularly observed side by side. In the case of a polycrystal, since it is composed of microcrystals, the directions of the respective lattice planes are not aligned, and the diffraction points can be seen in a complicated state or Debye ring can be seen. On the other hand, in the case of amorphous, the atomic arrangement does not have a periodic structure over a long distance, so that electron beam diffraction does not occur. Therefore, the diffraction image is observed in a state where there is no diffraction point.
Note that the observation of the electron beam diffraction image can be performed by cutting the end surface on which the protective film is formed so that a cross section of the protective film is exposed and applying an electron beam. Observation of an electron beam diffraction image can be performed using, for example, JEM-2010F type manufactured by JEOL Ltd.

  Such a first protective film 25 includes a region 25a substantially in contact with the active layer 12 (arbitrarily in the vicinity thereof) and other layers, that is, the first nitride semiconductor layer 11 and the second nitride. Brightness and darkness are observed with a scanning transmission electron microscope between the region in contact with the physical semiconductor layer 13. Here, “substantially contact” means that the first protective film is not directly in contact with the resonator surface of the nitride semiconductor, but a thin film is formed on the resonator surface to the extent that the effect of the present invention is obtained. In addition, a first protective film may be formed. For example, a thin film formed by pretreatment or an atmosphere at the start of film formation may exist on the resonator surface.

In the present specification, a portion extending in the entire film thickness direction including a region in contact with the active layer of the first protective film may be referred to as a portion adjacent to the active layer.
Further, the region 25a in contact with the active layer 12 (arbitrarily in the vicinity thereof) and the region in contact with the first nitride semiconductor layer 11 and the second nitride semiconductor layer 13 are formed of substantially the same material. A slight difference may occur between the compositions of the two depending on the manufacturing method and the like.

  The light and darkness observed in the first protective film formed of the same material is considered to appear based on the difference in crystal state in the first protective film 25. This difference in crystal state can be confirmed not only by observation of light and darkness with a scanning transmission electron microscope but also by a method such as electron beam diffraction as described later. That is, “difference in crystallinity” means that a difference appears in observation by observation with a scanning transmission electron microscope, electron beam diffraction, or the like.

  Therefore, the thickness of the first protective film adjacent to the active layer 12 between the region 25a in contact with the active layer 12 and the region in contact with the first nitride semiconductor layer 11 and the second nitride semiconductor layer 13 is further increased. In other words, the crystallinity is different between the region extending in the direction and the region extending in the film thickness direction of the first protective film adjacent to the first nitride semiconductor layer 11 and the second nitride semiconductor layer 13. However, there may be a region where the crystallinity changes gently above and below the region in contact with the active layer or in the region in contact with the active layer. In the region 25a in contact with the active layer, regions having different crystallinity (bright or dark portions) may be discontinuous, or regions having different crystallinity may be divided.

  As described above, the first protective film is observed to be bright and dark by a scanning transmission electron microscope or has different crystallinity in the vicinity of the active layer, so that the first protective film is in contact with almost the entire resonator surface of the nitride semiconductor layer. In the first protective film formed in this manner, the stress generated inside the first protective film due to the difference in the lattice constant, thermal expansion coefficient, etc. from the resonator surface can be effectively relaxed, and the first protective film in contact with the active layer It is presumed that the adhesion of the film to the resonator surface can be improved.

  The bright part or dark part of the region in contact with the active layer is preferably formed continuously in the film thickness direction of the first protective film. Thereby, the adhesiveness between the first protective film and a film (for example, a second protective film described later) formed on the first protective film is improved, and the peeling between the protective films can be suppressed.

  Further, the width of the region in contact with the active layer (the region with high brightness in FIG. 3) may change in the thickness direction of the first protective film. For example, as shown in FIGS. 2A and 3, the element outer side may be formed wider than the resonance surface side. By forming in this way, a region in contact with the active layer (region having different crystallinity) comes into contact with a second protective film described later in a larger area. Thereby, the adhesion between the first protective film and the second protective film is improved, and peeling between the protective films can be suppressed. As a result, adhesion can be improved at the interface between the resonator surface and the first protective film, and between the first protective film and the second protective film. As shown in FIG. 5A, it may be formed substantially parallel to the film thickness of the active layer, or as shown in FIG. 5B, the width may be narrower outside the element than on the resonance surface side. The first protective film formed on the resonator surface has a region in contact with the first nitride semiconductor layer and a region in contact with the second nitride semiconductor layer so as to sandwich the region in contact with the active layer. Therefore, the width of the region in contact with the first nitride semiconductor layer also changes in accordance with the width of the region in contact with the active layer of the first protective film. The same applies to the region in contact with the second nitride semiconductor layer.

  In the region in contact with the active layer and the region in contact with the other layers, any crystallinity may be good or bad. The active layer, the first nitride semiconductor layer, and the second nitride semiconductor layer, In general, it is suitable that the crystallinity is poor in a region in contact with the active layer, for example, from the composition of the semiconductor layer constituting the. As a result, the adhesion between the active layer and the region of the first protective film in contact with the active layer can be improved, and stress on the resonator surface of the first nitride semiconductor layer and the second nitride semiconductor layer can be relieved. be able to. Also, the difference in lattice constant between the material used for the first protective film and the material used for the active layer is usually used for the material used for the first protective film, the first nitride semiconductor layer, and the second nitride semiconductor layer. It becomes larger than the lattice constant difference of the material. For this reason, it is considered that the crystalline state of the first protective film in the region in contact with the active layer changes, and a region having different crystallinity is likely to be formed.

  Here, “good crystallinity” refers to a state close to a single crystal, that is, a material in which there is almost no change in lattice constant in the material and there is almost no lattice plane inclination. “Poor crystallinity” refers to a state that is closer to polycrystalline or amorphous than the film to be compared, and is composed of microcrystals, and also has no periodic structure as in crystals. Point to.

  The degree of difference in crystallinity is not particularly limited. For example, in the first protective film, the crystal structure of the region in contact with the first nitride semiconductor layer 11 and the second nitride semiconductor layer 13 is substantially single crystal or While it has a crystal structure close to a single crystal, the crystal structure in the region in contact with the active layer is a crystal structure partially including polycrystal or amorphous, a crystal structure close to polycrystal, or a crystal structure closer to an amorphous structure It means that. Alternatively, the crystallinity of the active layer, the first nitride semiconductor layer, and the second nitride semiconductor layer may be reversed.

The difference in crystallinity is, for example, in cross-sectional observation with a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), a scanning electron microscope (SEM), or the like. Not only is it recognized, but it can also be confirmed from the difference in electron beam diffraction and the etching rate as described above.
That is, in the observation of the first protective film with a microscope, due to the difference in crystallinity, both the region in contact with the active layer and the region in contact with the first nitride semiconductor layer and the second nitride semiconductor layer Visual differences are observed.
In particular, in observation with STEM, TEM, etc., light and darkness (contrast) is observed due to the difference in the state of the film (in the case of being crystalline, its crystallinity or crystal state).

  For example, according to STEM observation as shown in FIG. 3, the lightness is observed in the order of single crystal, polycrystal, and amorphous (brighter). It should be noted that single crystal, polycrystal, and amorphous may not be clearly distinguished as bright and dark even by observation with these microscopes. For example, when a film in which a single crystal and a polycrystal are mixed is observed, the lightness is observed between the single crystal and the polycrystal. In addition, the brightness may change gradually. In the present invention, if the brightness of the Munsell system has a difference of one or more steps, the crystallinity or the crystal state is different. If the difference is within one step, the crystallinity or the crystal state is substantially the same. More preferably, it is assumed that the crystallinity or crystal state is different when there is a difference of two or more steps, and further a difference of three or more steps.

Even when the same film is observed, the light and darkness may be reversed and observed by changing the observation conditions (display setting of STEM image and TEM image).
Specifically, as shown in FIG. 3, light and dark (light portions and dark portions) in a region of the first protective film in contact with the first nitride semiconductor layer 11 and the second nitride semiconductor layer 13 and a region in contact with the active layer. ) Is observed. A region in contact with the first nitride semiconductor layer 11 and the second nitride semiconductor layer 13 is dark (low brightness), and a region in contact with the active layer is observed bright (high brightness).

  STEM observation can be performed using, for example, JEM-2010F type manufactured by JEOL Ltd. As an observation procedure, first, a sample is cut out by microprobing using a focused ion beam (FIB) processing apparatus (for example, SMI3050MS2 manufactured by Seiko Instruments Inc.), and the sample is about 50 nm or less. The thin film is processed into FIB. Next, STEM observation as shown in FIG. 3 can be obtained by performing STEM observation in an acceleration voltage of 200 kV and a dark field.

  For example, as shown in FIG. 6, an electron beam diffraction image can be measured by making an electron beam incident on a nitride semiconductor laser element from the GaN (11-20) plane direction. The state of arrangement of elements constituting the crystal of the protective film can be visually grasped from the obtained electron beam diffraction image. In addition, when observing a film in contact with the resonator surface and / or a film near the resonator surface, a diffraction point of GaN constituting the nitride semiconductor layer may be observed. In this case, the GaN diffraction points may be separated and analyzed.

Further, by immersing the obtained protective film in an appropriate etchant, for example, an acid (for example, buffered hydrofluoric acid) or an alkali (for example, KOH) solution, the difference in solubility (difference in etching rate). ) Shows a difference in crystallinity. In this etching, those with poor crystallinity are quickly dissolved or removed, and those with good crystallinity remain or are maintained.
Without being limited to these methods, the crystallinity of the protective film can be evaluated using a known method.

  As described above, the nitride semiconductor laser element can suppress deterioration of the end face by forming the first protective film coaxially aligned with the resonator face on the resonator face. However, in general, in a nitride semiconductor laser element, it is difficult to form the first protective film coaxially with the resonator surface with good crystallinity. Even when the first protective film with good crystallinity is formed, cracks are likely to occur in the first protective film due to the difference in lattice constant between the first protective film and the nitride semiconductor layer. Alternatively, the first protective film tends to float or peel off due to the stress. Furthermore, in a laser element using a nitride semiconductor, the light density on the resonator surface is higher than in a laser element using another material. Therefore, a thin first protective film that does not cause problems such as cracks cannot sufficiently dissipate heat by being in close contact with the resonator surface. On the other hand, as described above, the first protective film in the region in contact with the first nitride semiconductor layer and the second nitride semiconductor layer is further increased due to the different crystallinity of the first protective film in the first protective film. Since the crystallinity of this is better than the crystallinity of the first protective film in the region in contact with the active layer, the stress due to the heat can be relaxed even when the laser element is driven. As a result, the occurrence of cracks in the first protective film can be suppressed, and the adhesion of the first protective film on the resonator surface can be ensured, and heat dissipation can be achieved while maintaining the COD level high. Can be improved.

  When a film having good adhesion (for example, an amorphous film) is formed on the resonator end face, the above-described problems can be avoided, but the first protective film is formed at the interface between the first protective film and the resonator end face. Reacts with the end face of the resonator, light absorption occurs at the end face of the resonator, and the COD level decreases. However, since the crystallinity is different in the first protective film as in the present invention, it is possible to prevent the COD level from being lowered. In addition, when the stress caused by the heat can be relaxed during driving, the generation of cracks in the first protective film can be suppressed, and the adhesion of the first protective film on the resonator surface can be suppressed. The heat dissipation can be improved while maintaining the COD level high.

The first protective film can be formed by a method known in the art. For example, evaporation method, sputtering method, reactive sputtering method, ECR plasma sputtering method, magnetron sputtering method, ion beam assisted evaporation method, ion plating method, laser ablation method, CVD method, spray method, spin coating method, dip method or A method combining two or more of these methods, or these methods and whole or partial pretreatment, inert gas (Ar, He, Xe, etc.) or plasma irradiation, oxygen or ozone gas or plasma irradiation, oxidation Various methods such as a method of combining one or more of treatment (heat treatment) and exposure treatment can be used. Note that in the combination method, the film formation and / or treatment may not necessarily be performed simultaneously or continuously, and the treatment may be performed after the film formation, or vice versa.
Of these, a combination of pretreatment and ECR plasma sputtering is preferable.
In particular, when an oxide film is formed as the first protective film, it is preferable to use oxygen or ozone for the pretreatment, and when forming a nitride film, nitrogen is used for the pretreatment.

  In particular, as described above, in order to obtain a film having a coaxial orientation with the resonator surface as the first protective film, depending on the film forming method, the surface of the resonator surface is oxygen plasma before the film formation. Process, adjust the film formation rate to a relatively slow rate, control the atmosphere during film formation to, for example, an oxygen atmosphere, or adjust the film formation pressure relatively low, or a combination of two or more It is preferable to control the film formation.

In addition, conditions such as oxygen partial pressure and film formation pressure may be varied during film formation by each method.
In order to improve the adhesion in the region in contact with the active layer, the crystallinity can be varied by adjusting various conditions during pretreatment or film formation. For example, it can be realized by methods such as shortening the pretreatment time, lowering the gas pressure during pretreatment, and reducing the microwave / RF power. The conditions for film formation can be realized by adjusting the gas pressure and microwave / RF power during film formation.

In order to vary the crystallinity so that light and darkness can be observed in a region in contact with the active layer with a scanning transmission electron microscope, the following method can also be used.
Only the active layer portion on the resonator surface is pretreated. The pretreatment method and / or pretreatment conditions are changed between the active layer portion of the resonator surface and the first nitride semiconductor layer and the second nitride semiconductor layer portion. A mask is provided on the active layer portion, a first protective film is formed on the first nitride semiconductor layer and the second nitride semiconductor layer portion, and then a first protective film is formed on the active layer portion. Or the method of forming a 1st protective film in the reverse order is mentioned.

  The formation of the oxide film as the first protective film is not limited to the case where an oxide target is used. A sputtering method may be used while irradiating oxygen gas or plasma using a non-oxide target or in an oxygen atmosphere. In the case of forming a nitride film, a method of sputtering with a non-nitride target while irradiating nitrogen gas or nitrogen plasma or the like in a nitrogen atmosphere may be used.

As the nitride semiconductor layers constituting the laser element of the present invention, the use of those of the general formula _{In x Al y Ga 1-xy} N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y ≦ 1) Can do. In addition to this, an element in which B is partially substituted as a group III element may be used, or an element in which a part of N is substituted with P or As may be used as a group V element. The n-side semiconductor layer may contain any one or more of IV group elements or VI group elements such as Si, Ge, Sn, S, O, Ti, Zr, and Cd as n-type impurities. The p-side semiconductor layer may contain Mg, Zn, Be, Mn, Ca, Sr, etc. as p-type impurities. The impurities are preferably contained in a concentration range of, for example, about 5 × 10 ¹⁶ / cm ³ to 1 × 10 ²¹ / cm ³ .

  The nitride semiconductor layer is not limited. For example, the nitride semiconductor layer has a light guide layer that constitutes an optical waveguide of light in the n-side semiconductor layer and the p-side semiconductor layer, thereby having a separated light confinement structure with an active layer interposed therebetween. A certain SCH (Separate Confinement Heterostructure) structure is preferable.

  The active layer may have either a multiple quantum well structure or a single quantum well structure. The active layer preferably has a smaller band gap energy than the first protective film. In the present invention, the band gap energy of the first protective film is made larger than that of the active layer, so that the band gap energy of the end face is widened, in other words, the impurity level near the resonator surface is widened to form the window structure. By doing so, the COD level can be further improved.

Well layer and the barrier 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). Preferably, at least the well layer contains In, and more preferably, both the well layer and the barrier layer contain In. This tends to facilitate the formation of the above-described regions having different crystallinity. Furthermore, the adhesiveness with the first protective film of the present invention can be improved, and the COD level can be kept high, which is preferable.
When the active layer is formed with a multiple quantum well structure including a layer containing In, regions having different crystallinity may be discontinuous or divided due to the difference in composition ratio or In mixed crystal ratio. There is.
In the present invention, particularly when the oscillation wavelength is 220 nm to 580 nm, peeling of the first protective film can be effectively prevented, and the COD level can be improved.

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

  In the nitride semiconductor layer, for example, a resonator is formed in a direction in which a ridge described later extends, and a pair of resonator surfaces are formed orthogonal to the direction. Examples of the resonator surface include M-axis, A-axis, C-axis, and R-axis orientation, that is, M-plane (1-100), A-plane (11-20), C-plane (0001), or R-plane ( It is preferable that the surface is selected from the group consisting of 1-102), particularly M-axis orientation. The resonator surface here usually means a region including an optical waveguide region or a region corresponding to NFP, but may include a region other than the optical waveguide region or NFP. Such an optical waveguide region or a region corresponding to NFP may not exhibit the above-described orientation.

A ridge is formed on the surface of the nitride semiconductor layer, that is, the p-side semiconductor layer. The ridge functions as an optical waveguide region and has a width of about 1.0 μm to 30.0 μm. Furthermore, when the laser beam is used as a light source having a single transverse mode, it is preferably about 1.0 μm to 3.0 μm. The height (etching depth) is, for example, 0.1 to 2 μm. The degree of light confinement can be appropriately adjusted by adjusting the film thickness, material, and the like of the layers constituting the p-side semiconductor layer. The ridge is preferably set so that the length in the resonator direction is about 200 μm to 5000 μm. The widths may not all be the same in the direction of the resonator, and the side surfaces may be vertical or tapered. The taper angle in this case is suitably about 45 ° to 90 °.
In the laser device of the present invention, it is not always necessary to form a ridge. For example, a semiconductor laser device in which a current confinement layer is formed in a nitride semiconductor layer may be used.

The nitride semiconductor layer is usually formed on a substrate. Such a substrate may be an insulating substrate or a conductive substrate. The substrate is preferably a nitride semiconductor substrate having an off angle of 0 ° to 10 ° on the first main surface and / or the second main surface, for example. The film thickness is, for example, about 50 μm to 10 mm.
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. Further, for example, known substrates such as various substrates exemplified in JP-A-2006-24703, commercially available substrates, and the like may be used.

In the nitride semiconductor laser device of the present invention, it is preferable that a second protective film (for example, refer to 26 in FIG. 2) having a different film quality, material or composition is further laminated on the first protective film. Examples of the second protective film include oxides such as Si, Mg, Al, Hf, Nb, Zr, Sc, Ta, Ga, Zn, Y, B, and Ti. Among them, an Al ₂ O ₃ or SiO ₂ film is used. preferable. More preferably, it is the same material as the first protective film. Thereby, since the thermal expansion coefficient of a 1st protective film and a 2nd protective film corresponds, it can suppress that a crack generate | occur | produces in a 1st protective film and a 2nd protective film.

  The second protective film may have either a single layer structure or a laminated structure. For example, a single layer of Si oxide, a single layer of Al oxide, a stacked structure of Si oxide and Al oxide, or the like can be given. By forming such a film, the first protective film can be more firmly adhered to the resonator surface. As a result, stable operation can be ensured and the COD level can be improved.

  The second protective film is preferably formed as an amorphous film. By forming such a film, a change in the composition of the first protective film can be prevented, and the first protective film can be more firmly adhered to the resonator surface. By forming the second protective film on the first protective film formed in a different state in the film, the stress relaxation state is reinforced, and the first protective film has good adhesion. can do. Thereby, peeling of the first protective film as a whole can be prevented.

When the first protective film and the second protective film were observed with an acceleration voltage of 200 kV and a dark field, a STEM image as shown in FIG. 3 was obtained. According to this, the brightness was observed to be higher (brighter) in the order of the second protective film 26, the region 25a in contact with the active layer, and the region 25 in contact with the first and second nitride semiconductor layers.
Further, when an electron beam was incident from the GaN (11-20) plane direction and an electron beam diffraction image of the second protective film was observed, as shown in FIG. 6C, the diffraction image was observed without a diffraction point. From these observations, it was confirmed that the second protective film was amorphous.

  The film thickness of the second protective film is not particularly limited, and is suitably a film thickness that can function as a protective film. The film thickness is preferably about 10 nm to 1500 nm. The total thickness of the first protective film and the second protective film is preferably about 2 μm or less.

  The second protective film can be formed by using the known method illustrated as in the case of the first protective film described above. In particular, the second protective film is preferably formed as an amorphous film. Therefore, depending on the film formation method, the film formation atmosphere is adjusted to a higher film formation rate, for example, It is preferable to control the film formation by any one or a combination of two or more of controlling the oxygen atmosphere and adjusting the film formation pressure higher. When controlling to an oxygen atmosphere, it is preferable to introduce oxygen to such an extent that it does not absorb.

  Both the first protective film and the second protective film may be formed not only on the emission side of the resonator surface but also on the reflection side, and the materials, film thicknesses, and the like may be different between the two. As the second protective film on the reflection side, a stacked structure of Si oxide and Zr oxide, a stacked structure of Al oxide and Zr oxide, a stacked structure of Si oxide and Ti oxide Examples thereof include a structure, a laminated structure of Al oxide, Si oxide, and Zr oxide, and a laminated structure of Si oxide, Ta oxide, and Al oxide. The stacking period and the like can be adjusted as appropriate according to the desired reflectance.

  It is preferable to form a film having transparency with respect to the oscillation wavelength of the laser element as the outermost layer of the end surface protective film such as the first protective film and the second protective film formed on the resonator end surface. By forming such an outermost layer, it is possible to provide a protection effect against moisture and the outside air, and it is possible to suppress peeling of the first protective film and the second protective film, in particular, peeling of the outer film. it can. The term “transmitting to the oscillation wavelength of the laser element” means that the film thickness is λ / 2n (λ: oscillation wavelength, n: refractive index) or an integral multiple thereof, depending on the material that does not absorb the oscillation wavelength of the laser element. This means that a film is formed.

  Specific examples of the material for forming the outermost layer include an oxide of Al or Si. By using an oxide on the outermost surface, surface oxidation can be suppressed. For example, when a protective film is provided as a second protective film with a laminated structure of an oxide of Al and an oxide of Zr, if a highly reflective Zr oxide is formed on the outermost layer, the Zr oxide film is peeled off. It tends to be easier. However, when the outermost layer is formed of a permeable film made of an Al or Si oxide film having the thickness as described above, peeling of the protective film can be suppressed.

  The second protective film may partially cover a surface other than the resonator surface, similarly to the first protective film. For example, when the second protective film is arbitrarily formed from the resonator surface to the semiconductor layer surface together with the first protective film, the second protective film is formed to have a crystal plane different from the resonator surface and the semiconductor layer surface at the corners. It is preferable to do. As a result, it is possible to suppress the local application of stress at corners where the protective film easily peels off and to prevent the protective film from peeling off by relaxing the stress between the resonator surface and the protective film. it can. The second protective film may optionally be formed together with the first protective film so as to extend from the resonator surface to the back surface of the substrate (the surface opposite to the surface on which the nitride semiconductor layer is formed). In this case, similarly to the case described above, a different crystal plane may be provided between the resonator surface and the back surface of the substrate.

  In the semiconductor laser device of the present invention, a buried film is usually formed over the surface of the nitride semiconductor layer and the side surface of the ridge. That is, the buried film is formed on the nitride semiconductor layer in a region other than the region in which the nitride semiconductor layer and an electrode described later are in direct contact and electrically connected. The connection region between the nitride semiconductor layer and the electrode is not particularly limited in position, size, shape, etc., and is formed on a part of the surface of the nitride semiconductor layer, for example, on the surface of the nitride semiconductor layer. A substantially entire upper surface of the striped ridge is illustrated.

  The buried film is generally formed of an insulating material having a refractive index smaller than that of the nitride semiconductor layer. The refractive index is a spectroscopic ellipsometer using ellipsometry. A. It can be measured using HS-190 manufactured by WOOLLAM. For example, the buried film is a single layer of an insulating film or a dielectric film such as an oxide such as Zr, Si, V, Nb, Hf, Ta, Al, Ce, In, Sb, Zn, nitride, oxynitride, etc. Or a laminated structure is mentioned. Further, the embedded film may be single crystal, polycrystalline or amorphous. As described above, since the buried film is formed from the side surface of the ridge to the nitride semiconductor surface on both sides of the ridge, the refractive index difference with respect to the nitride semiconductor layer, particularly the p-side semiconductor layer, is secured, and the active layer The light leakage from the ridge can be controlled, the light can be efficiently confined in the ridge, the insulation in the vicinity of the ridge base portion can be further secured, and the occurrence of a leakage current can be avoided.

  The buried film can be formed by a method known in the art. For example, evaporation method, sputtering method, reactive sputtering method, ECR plasma sputtering method, magnetron sputtering method, ion beam assisted evaporation method, ion plating method, laser ablation method, CVD method, spray method, spin coating method, dip method or Various methods such as a method of combining two or more of these methods or a method of combining these methods and oxidation treatment (heat treatment) can be used.

  In the present invention, the pair of electrodes are electrically connected to the p-side and n-side nitride semiconductor layers. In particular, the p-electrode is preferably formed on the nitride semiconductor layer and the buried film. Since the p-electrode is continuously formed on the uppermost nitride semiconductor layer and the buried film, peeling of the buried film can be prevented. In particular, by forming the p-electrode up to the ridge side surface, the embedded film formed on the ridge side surface can be effectively prevented from peeling off.

The p electrode and the n electrode are, for example, a single layer film or a multilayer film of a metal or an alloy such as palladium, platinum, nickel, gold, titanium, tungsten, copper, silver, zinc, tin, indium, aluminum, iridium, rhodium, ITO, etc. Can be formed. The film thickness of the electrode can be appropriately adjusted depending on the material used, and for example, about 50 nm to 500 nm is appropriate. The electrodes only need to be formed on at least the first and second semiconductor layers or the substrate, respectively, and one or more conductive layers such as pad electrodes may be formed on the electrodes.
The p electrode and the n electrode may be formed on the same surface side with respect to the substrate.

A third protective film 17 is preferably formed on the buried film. The third protective film may be disposed on the buried film at least on the surface of the nitride semiconductor layer, and may be disposed on the side surface of the nitride semiconductor layer and / or on the substrate without or through the buried film. It is preferable that the side surface or the surface is further coated. The third protective film can be formed of the same material as that exemplified for the buried film. Thereby, not only the insulating property but also the exposed side surface or surface of the nitride semiconductor layer can be reliably protected.
A p-pad electrode 18 is preferably formed on the top surface of the buried film 15, the p-electrode 16 and the third protective film 17 from the side surface of the nitride semiconductor layer.

  The first protective film and the second protective film may be formed continuously from the resonator surface to the second nitride semiconductor layer surface. The first protective film and / or the second protective film formed on the surface of the nitride semiconductor layer may be separated from, in contact with, or in contact with the p-electrode, the buried film, and the p-side pad electrode. You may do it. Preferably, the first protective film and / or the second protective film covers the buried film and the p-electrode. Thereby, peeling of the buried film and the p-electrode can be prevented.

The thickness of the protective film formed on the surface of the second nitride semiconductor layer is preferably thinner than the thickness of the first protective film and the second protective film formed on the resonator surface. Thereby, it can prevent that a crack generate | occur | produces in a protective film.
The protective film formed on the surface of the second nitride semiconductor layer is preferably coaxial with the crystal plane of the nitride semiconductor layer, and particularly preferably C-axis oriented. Thereby, the adhesiveness between the semiconductor layer surface and the protective film can be improved.

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 FIGS. 1, 2A, and 2B, the nitride semiconductor laser device of this embodiment has a first nitride semiconductor layer (for example, n-side) 11 on a GaN substrate 10 having a C plane as a growth surface. The active layer 12 and a second nitride semiconductor layer (for example, p side) 13 having a ridge 14 formed on the surface are stacked in this order, and a resonator having the M plane as a resonator plane is formed. ing.
Such a nitride semiconductor laser device has a first protective film 25 and a second protective film 26 on the resonator surface, a buried film 15, a p-electrode 16, an n-electrode 19, a third protective film 17, and a p-pad electrode. 18 etc. are formed.
The resonator surface is mainly formed of a nitride semiconductor layer having M-axis orientation. As shown in FIGS. 2A and 2B, the first protective film 25 is formed on at least one of the resonator surfaces. The second protective film 26 is formed thereon.

The first protective film 25 is made of Al ₂ O ₃ and has a thickness of about 20 nm. In the first protective film 25, a region 25 a in contact with the active layer is formed in a region extending from the active layer 12 and the first nitride semiconductor layer 11 and the second nitride semiconductor layer 14 above and below the active layer 12.
When this first protective film 25 was observed with an accelerating voltage of 200 kV and a dark field, a cross-sectional STEM image as shown in FIG. 3 was obtained. In the region 25a in contact with the active layer, it was observed brighter (higher brightness) than in the other regions, and it was recognized that the crystallinity was visually different.

  The first protective film 25 was measured by entering an electron beam from the direction of the GaN (11-20) plane with a camera length of 50 cm, and analyzed from the protective film surface side by electron beam diffraction. As shown in FIG. An electron diffraction image was obtained. In the region 25a in contact with the active layer, as shown in FIG. 6B, the point indicating the presence of atoms was unclear. On the other hand, when the other region of the first protective film 25 is analyzed, as shown in FIG. 6A, the points indicating the presence of atoms are clearly represented, and the arrangement is more orderly than the region 25a in contact with the active layer. I found out that

The second protective layer 26 is made of _Al 2 _{O 3,} thickness of about 100 nm. When the second protective film 26 was analyzed from the surface side of the second protective film by electron beam diffraction, as shown in FIG. 6C, the point indicating the presence of atoms was almost unclear and not recognized.

This nitride semiconductor laser device is manufactured as follows.
First, a gallium nitride substrate is prepared. In a reactor, Al _0.03 Ga ₀ doped with Si at 4 × 10 ¹⁸ / cm ³ on this gallium nitride substrate at 1160 ° C. using TMA (trimethylaluminum), TMG (trimethylgallium), ammonia, and silane gas. _A layer made of _.97 N is grown to a thickness of 2 μm. Note that the n-side cladding layer may have a superlattice structure.
Subsequently, the silane gas is stopped, and an n-side light guide layer made of undoped GaN is grown to a thickness of 0.175 μm at 1000 ° C. The n-side light guide layer may be doped with n-type impurities.

Next, the temperature is set to 900 ° C., a barrier layer made of Si-doped In _0.02 Ga _0.98 N is grown to a thickness of 14 nm, and then at the same temperature, undoped In _0.07 Ga _0.93 N A well layer made of this is grown to a thickness of 7 nm. A barrier layer and a well layer are alternately stacked twice, and finally an active layer having a multi-quantum well structure (MQW) having a total thickness of 56 nm is grown by ending with the barrier layer.

The temperature was raised to 1000 ° C., TMG, TMA, ammonia, Cp ₂ Mg (cyclopentadienyl magnesium) was used, and the band gap energy was larger than that of the p-side light guide layer, and Mg was doped at 1 × 10 ²⁰ / cm ³ . A p-side cap layer made of p-type Al _0.25 Ga _0.75 N is grown to a thickness of 10 nm.
Subsequently, Cp ₂ Mg and TMA are stopped, and a p-side light guide layer made of undoped GaN having a band gap energy smaller than that of the p-side cap layer 10 is grown to a thickness of 0.145 μm at 1000 ° C.

Next, a layer made of undoped Al _0.10 Ga _0.90 N is grown at a film thickness of 2.5 nm at 1000 ° C., and then the TMA is stopped and a layer made of p-type GaN using Cp ₂ Mg. A p-side cladding layer made of a superlattice layer with a total film thickness of 0.45 μm is grown with a film thickness of 2.5 nm.
Finally, a p-side contact layer made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown on the p-side cladding layer at 1000 ° C. to a thickness of 15 nm.

The wafer on which the nitride semiconductor is grown in this way is taken out of the reaction vessel, a protective film made of SiO ₂ is formed on the surface of the uppermost p-side contact layer, and the width in the direction parallel to the resonator surface is 800 μm. A stripe structure is formed. This part becomes the resonator body of the laser element. The resonator length is preferably in the range of about 200 μm to 5000 μm.

Next, a protective film made of striped SiO ₂ is formed on the surface of the p-side contact layer, and etched with SiCl ₄ gas using RIE (reactive ion etching) to form a ridge which is a striped optical waveguide region. Forming part.
The side surface of the ridge portion is protected with a buried film made of ZrO ₂ .

Next, a p-electrode made of Ni (10 nm) / Au (100 nm) / Pt (100 nm) is formed on the surface above the p-side contact layer and the buried film. After forming the p-electrode, ohmic annealing is performed at 600 ° C. After ohmic annealing, a third protective film made of a Si oxide film (SiO ₂ ) is formed on the p electrode, the buried film, and the side surface of the semiconductor layer by sputtering to a thickness of 0.5 μm.
Next, a p-pad electrode is formed continuously with Ni (8 nm) / Pd (200 nm) / Au (800 nm) on the exposed p-electrode not covered with the third protective film.
Thereafter, polishing is performed from the surface opposite to the growth surface of the nitride semiconductor layer so that the substrate thickness becomes 80 μm.

An n electrode made of Ti (15 nm) or V (10 nm) / Pt (200 nm) / Au (300 nm) is formed on the polished surface.
A concave groove is formed by scribing on the first main surface side of the wafer-like nitride semiconductor substrate on which the n electrode, the p electrode, and the p pad electrode are formed. For example, the recess groove has a depth of 10 μm. Also, the width is 50 μm from the side surface in the direction parallel to the resonator surface and 15 μm in the vertical direction. Next, this concave groove is used as a cleavage assist line to cleave in a bar shape from the n-electrode formation surface side of the nitride semiconductor substrate, and the cleavage plane ((1-100) plane, the plane corresponding to the hexagonal columnar crystal surface = M plane) is the resonator plane. The cavity length is set to 800 μm, and then a bar is formed into chips in a direction parallel to the p-electrode to obtain a semiconductor laser element.

Subsequently, surface treatment is performed by exposing the resonator surface of the obtained element to oxygen plasma using a plasma processing apparatus. At this time, for example, the treatment is performed at a flow rate of O ₂ of 20 sccm and a microwave / RF power of 500 W for 10 minutes. Then transferred element ECR sputtering apparatus, using Al target, the flow rate of Ar is 30 sccm, the flow rate of oxygen is 10 sccm, a microwave / RF power 500 W, forming a first protective film composed of _Al 2 _{O 3} (20nm) To do.
On the first protective film made of Al ₂ O ₃ on the emission side end surface, an Al target is used with an ECR sputtering apparatus, the flow rate of Ar is 30 sccm, the flow rate of oxygen is 4 sccm, and the microwave / RF power is 500 W. _{A second} protective film made of ₂ O _{3 is formed} to a thickness of 100 nm.
The reflective side, the same film forming conditions and the exit side, after forming a first protective film composed of _Al 2 _{O 3} (20nm), to form a second protective film made of _Al 2 _{O 3} (40nm). On top of that, (SiO ₂ / ZrO ₂ ) may be formed at (67 nm / 44 nm) for 6 cycles.

For comparison, a single-layer protective film made of Al ₂ O ₃ is substantially the same as described above except that the surface treatment with oxygen plasma is not performed and the film thickness is 120 nm without changing other conditions. A laser element was formed by the same manufacturing method as the semiconductor laser element.

With respect to the obtained semiconductor laser element, the current-light output characteristics after continuous oscillation were measured, and the COD level was evaluated.
The measurement results are shown in FIG.
The data indicated by the solid line indicates the current-light output characteristics of the laser element of the present invention having the first protective film having different crystallinity in the plane, and the data indicated by the dotted line indicates that the crystallinity as a comparative example is in the plane. The current-light output characteristics of a laser element having the same thick protective film are shown. In the current-light output characteristic curve, the light output increases as the injection current increases. When the light output reaches the COD level, the end face is destroyed and laser oscillation stops.
According to FIG. 4, in the laser element provided with the protective film of the present invention, it was found that the COD level was significantly higher than that of the comparative example.

  In this way, by forming a protective film having a different crystallinity from the other regions in contact with the active layer, without causing stress on the light emitting portion of the nitride semiconductor layer constituting the resonator surface, Cracks do not occur in the nitride semiconductor, the adhesion to the resonator surface is good, peeling is prevented, and as a result, the COD level can be improved.

  In order to verify the protective film of the obtained nitride semiconductor laser device, the chip on which the protective film was formed by the same method as described above was immersed in buffered hydrofluoric acid composed of ammonium fluoride and 15.7% hydrofluoric acid. Then, dissolution of the protective film was observed. As a result, the protective film in the region in contact with the active layer 5 minutes after immersion was completely dissolved in the film thickness direction, whereas the protective film in the region in contact with the first and second nitride semiconductor layers was on the surface. Some dissolution or swelling was noted but not removed.

Examples 2-9
In this embodiment, the materials and thicknesses of the first protective film and the second protective film are changed, and oxygen plasma is used when the first protective film is an oxide film, and nitrogen plasma is used when the first protective film is a nitride film. A laser element is manufactured in the same manner as in Example 1 except that the surface treatment is performed.
The first protective film and the second protective film have the compositions and film thicknesses shown in Table 2. In Examples 2 to 5, Ni-based p electrodes and Ti-based n electrodes were used, and in Examples 6 to 9, Ni-based p electrodes and V-based n electrodes were used.

In these laser elements, when the same evaluation as in Example 1 is performed, the COD level is improved as in Example 1, and the life characteristics are improved.

Example 10
In this embodiment, on the first protective film made of _Al 2 _{O 3} of the end face on the exit side (20 nm), a _{for Al} 2 _O 3 second protective layer (40 nm) was deposited, thereon, Al ₂ Two cycles of O ₃ / ZrO ₂ (60 nm / 43 nm) are formed, and finally Al ₂ O ₃ (120 nm) is formed.
On the reflection side, six periods of Al ₂ O ₃ / ZrO ₂ (60 nm / 43 nm) are formed.
Except for these conditions, a laser element is fabricated in the same manner as in Example 1.
In such a laser device, but ZrO ₂ of a high reflectivity formed on the exit side is likely to peel off tendency, by forming an Al ₂ O ₃ as an outermost layer thereon, ZrO ₂ is less likely to peel Thus, a laser element with stable element operation can be obtained, and the COD level is improved and the life characteristics are improved as in the first embodiment.

  The present invention provides not only a laser diode element (LD) but also a light emitting diode element (LED), a light emitting element such as a super photoluminescence diode, a light receiving element such as a solar cell or a photosensor, or an electronic device such as a transistor or a power device. It can be widely applied to nitride semiconductor elements that need to ensure the adhesion between the protective film and the semiconductor layer as used in the above. In particular, it can be used for nitride semiconductor laser elements in optical disc applications, optical communication systems, printing presses, exposure applications, measurements, bio-related excitation light sources, and the like.

It is a schematic sectional drawing of the principal part for demonstrating the structure of the nitride semiconductor laser element of this invention. It is sectional drawing in the resonator direction for demonstrating the protective film of the nitride semiconductor laser element of this invention. FIG. 2B is a schematic perspective view of the nitride semiconductor laser element in FIG. 2A. It is a STEM image of the protective film of the nitride semiconductor laser element of this invention. It is a graph which shows the current-light output characteristic of the nitride semiconductor laser element of this invention, and the nitride semiconductor laser element of a comparative example. It is sectional drawing in the resonator direction for demonstrating the structure of another nitride semiconductor laser element of this invention. FIG. 6 is a cross-sectional view in the cavity direction for explaining the structure of still another nitride semiconductor laser element of the present invention. 2 is an electron diffraction image of a protective film in contact with a first nitride semiconductor layer and a second nitride semiconductor layer of the nitride semiconductor laser device of the present invention. 3 is an electron beam diffraction image of a protective film in contact with an active layer of the nitride semiconductor laser device of the present invention. It is an electron beam diffraction image of the 2nd protective film of the nitride semiconductor laser element of this invention.

Explanation of symbols

10 substrate 11 first nitride semiconductor layer 12 active layer 13 second nitride semiconductor layer 14 ridge 15 buried film 16 p electrode 17 third protective film 18 p-side pad electrode 19 n electrode 25 protective film 25a region in contact with the active layer 26 Second protective film

Claims (18)

A nitride semiconductor including a nitride semiconductor layer including a first nitride semiconductor layer, an active layer, and a second nitride semiconductor layer and having a resonator having an end face, and a first protective film in contact with at least one end face A laser element,
The first protective film has a film structure in which brightness and darkness are observed by a scanning transmission electron microscope in a region in contact with the active layer and a region in contact with the first and second nitride semiconductor layers. element.   2. The nitride semiconductor laser device according to claim 1, wherein a bright part or a dark part of a region in contact with the active layer is continuously arranged in a film thickness direction of the first protective film.   3. The nitride semiconductor laser element according to claim 1, wherein a bright part or a dark part of a region in contact with the active layer is wider outside the element than on the resonator surface side.   The nitride semiconductor laser element according to claim 1, wherein the first protective film has a thickness of 3 nm to 1000 nm.   The nitride semiconductor laser element according to claim 1, wherein the first protective film is formed of a material having a hexagonal crystal structure.   6. The nitride semiconductor laser element according to claim 1, wherein the first protective film has a crystal structure coaxial with a resonator surface in a region in contact with the first and second nitride semiconductor layers. .   The nitride semiconductor laser element according to claim 1, wherein the first protective film is covered with a second protective film.   The brightness of the second protective film, the region in contact with the active layer, and the region in contact with the first and second nitride semiconductor layers are observed in this order by a scanning transmission electron microscope with high or low brightness. The nitride semiconductor laser device described in 1.   The nitride semiconductor laser element according to claim 7 or 8, wherein the second protective film has a thickness of 10 nm to 1500 nm. A nitride semiconductor including a nitride semiconductor layer including a first nitride semiconductor layer, an active layer, and a second nitride semiconductor layer and having a resonator having an end face, and a first protective film in contact with at least one end face A laser element,
The nitride semiconductor laser device, wherein the first protective film has a film structure in which crystallinity is different between a portion adjacent to the active layer and a portion adjacent to the first and second nitride semiconductor layers.   The nitride semiconductor laser device according to claim 10, wherein a portion adjacent to the first and second nitride semiconductor layers has better crystallinity than a portion adjacent to the active layer.   12. The nitride semiconductor laser element according to claim 10, wherein a portion adjacent to the active layer has substantially the same crystallinity over the thickness direction of the first protective film.   The nitride semiconductor laser device according to claim 12, wherein a portion adjacent to the active layer having substantially the same crystallinity is wider on the outside of the device than on the resonator surface side.   The nitride semiconductor laser element according to claim 10, wherein the first protective film has a thickness of 3 nm to 1000 nm.   The nitride semiconductor laser element according to claim 10, wherein the first protective film is formed of a material having a hexagonal crystal structure.   The nitride semiconductor laser device according to claim 10, wherein the first protective film is covered with a second protective film.   The nitride semiconductor laser according to claim 16, wherein a portion adjacent to the first and second nitride semiconductor layers, a portion adjacent to the active layer, and the second protective film have good crystallinity in this order. element.   The nitride semiconductor laser element according to claim 16 or 17, wherein the second protective film has a thickness of 10 nm to 1500 nm.

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