JP2005045239A - Nitride semiconductor laser device and laser diode apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser device which has few malfunctions and a preferred FFP. <P>SOLUTION: The nitride semiconductor laser device comprises a nitride semiconductor substrate and a nitride semiconductor layer thereon in which an n-type semiconductor layer, an active layer, and a p-type semiconductor layer are laminated. The nitride semiconductor layer has a waveguide area for a stripe-like laser beam, and an end face protective film is provided on both end faces almost perpendicular to the waveguide area. The nitride semiconductor substrate has an excitation area which absorbs light from the active layer and emits excitation light having a wavelength longer than a luminous wavelength. The end face protective film has a high reflectivity relative to a luminous wavelength from the excitation area. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser device in which a dielectric protective film is formed on an end face of a semiconductor layer using a nitride semiconductor, and more particularly to a high-power semiconductor laser device using a nitride semiconductor substrate. Specific examples of the composition of the semiconductor element include GaN, AlN, InN, or III-V group nitride semiconductors containing AlGaN, InGaN, and AlInGaN, which are mixed crystals thereof.

Conventional

  A nitride semiconductor device has a light emission in a wide wavelength region from a relatively short wavelength ultraviolet region to a visible light region including red, and is a material constituting a semiconductor laser diode (LD) or a light emitting diode (LED). Is widely used. In recent years, miniaturization, long life, high reliability, and high output have progressed, and they are mainly used for electronic devices such as personal computers and DVDs, medical devices, processing devices, and light sources for optical fiber communication.

  Such a nitride semiconductor device mainly includes a buffer layer, an n-type contact layer, a crack prevention layer, an n-type cladding layer, an n-type light guide layer, an active layer, a p-type electron confinement layer, and a p-type light guide on a sapphire substrate. A layered structure in which a layer, a p-type cladding layer, a p-type contact layer, and the like are sequentially stacked. A stripe-shaped waveguide region is formed by forming a stripe-shaped ridge by etching or forming a current confinement layer. The n-type contact layer and the p-type contact layer are provided with an n-side electrode and a p-side electrode, respectively, and emit light from the active layer by energization. Further, a resonator surface is formed on both end faces of the waveguide region with a predetermined resonator length, and laser light is emitted from this resonator surface.

  An insulating protective film or the like is formed on such a resonator surface, thereby protecting the semiconductor layer from the outside air and providing a difference in reflectance between the emission side and the rear side. The output of the rear side protective film can be improved by using a protective film having a higher reflectance than that of the outgoing side protective film.

  In addition, in a semiconductor laser element having a protective film with a large difference in reflectance between the rear side and the emission side, light leaking from the waveguide region (stray light) is unlikely to be emitted from the rear side, and is emitted from the end surface on the emission side. become. Therefore, the stray light may cause noise (unevenness) in the far field pattern (FFP), resulting in a non-Gaussian distribution. In order to prevent these stray lights from being emitted to the outside, an opaque film made of a metal film or the like can be formed so as to cover the end face of the substrate.

JP 2002-280663 A

  However, if an opaque film is provided on a part of the emission-side resonance surface, it is necessary to increase the number of processes such as a mask formation process. In particular, when a wafer is divided into bars and an end face protective film is formed on the end face of the bar laser, it is difficult to form a mask with high positional accuracy. Is more difficult to control. In particular, when a metal material is used as the opaque film, there is a problem that a short circuit may be caused if the controllability of position accuracy is low. In addition, if an opaque film is formed over a wide area, the adhesion between the opaque film and the semiconductor layer or other protective film may decrease depending on the material due to the difference in thermal expansion coefficient between the metal material and the semiconductor layer. Problems such as easy peeling off occur.

  Therefore, the present invention suppresses the deterioration of FFP due to stray light emitted from the emission side end face, provides good beam characteristics, has few malfunctions when driving the element, and has excellent lifetime characteristics. An object is to provide a semiconductor laser element.

In order to solve the above problem, the present inventors have conducted intensive studies, and as a result, the end face film of the laser element can control the laser light and the stray light by distinguishing them. That is, it has been found that a laser element can be obtained which can simultaneously satisfy the two functions of efficiently extracting the LD light of the laser element and efficiently confining the stray light component so as not to be emitted, thereby achieving the present invention. The nitride semiconductor laser device of the present invention includes a nitride semiconductor substrate and a nitride semiconductor layer formed by laminating an n-type semiconductor layer, an active layer, and a p-type semiconductor layer thereon, and stripes are formed on the nitride semiconductor layer. The nitride semiconductor laser device has an end face protection film on both end faces substantially perpendicular to the waveguide area, and the nitride semiconductor substrate absorbs light emitted from the active layer And it has an excitation area | region which light-emits excitation light longer than the light emission wavelength, and an end surface protective film has a high reflectance with respect to the light emission wavelength from excitation light, It is characterized by the above-mentioned. Specifically, when the emission wavelength of the nitride semiconductor laser element is λ _LD and the wavelength of the excitation light is λ _ex , the reflectance of the end face protective film is larger at λ _ex than at λ _LD. It is a protective film. That is, an end face protective film in which the reflectance of the excitation light wavelength λ _ex of the substrate is higher than the reflectance of the laser light wavelength λ _LD is used. Therefore, the pumping light wavelength _λex is a high reflectance end face protective film for pumping light having a higher reflectance. Furthermore, for the laser light wavelength λ _LD , the end face protective film has a protective film transmittance higher than the excitation light wavelength λ _ex , so that the laser light can be efficiently extracted and the excitation light can be efficiently used. Both blocking can be achieved and this is preferable.

  Light emitted from the active layer is confined in a region (active layer and guide layer) sandwiched between cladding layers having a refractive index lower than that of the active layer in the vertical direction (direction substantially perpendicular to the stacking surface). Further, in the horizontal direction (the direction horizontal to the laminated surface), the stripes are confined in a stripe shape so as to correspond to the current injection region. Thus, by forming the resonator surface in the region where the light from the active layer is confined, a striped waveguide region is formed. However, light leaks from the waveguide region to other regions. In the present application, instead of providing an opaque film that does not transmit the light leaking from the waveguide region (stray light), the stray light is converted into a different wavelength, and the reflected wavelength has a high reflectivity. By forming the end face protective film, mixing of noise with the laser light is suppressed. In the present invention, specifically, the high reflectance is about 50% to 100%, preferably 70 to 100%, and the low reflectance is a protective film of a gallium nitride compound semiconductor. It can be used in the range of about 18% or less of the reflectance at the end face.

  The nitride semiconductor laser element according to claim 2 of the present invention is characterized in that the end face protective film is provided on both the emission side end face and the rear side end face.

  With such a configuration, it is possible to efficiently suppress stray light from being emitted to the outside. Specifically, the light from these laser elements is irradiated onto the PD, which is the photodetector, on a part of the optical path of the resonator direction, the outgoing light, and the reflected light (light from the rear side end face) facing it. The And the output of each light etc. are detected with this photodetector, and the drive of a laser element is controlled based on the information. For this reason, it is sufficient that the excitation light component, which is a noise component, is eliminated in the PD, and as described above, it is preferable that at least the protective film is provided on both end faces of the resonator, thereby eliminating the noise component. More preferably, the protective film is also provided on the end face of the laser element different from the end face of the resonator, for example, the side face and the bottom face in the direction of the resonator, so that the excitation light component from the element can be almost completely eliminated. There is no excitation light in the LD device, and the detection sensitivity accuracy of PD can be improved. However, as described above, in the LD device, the photodetector is arranged at a position irradiated with emitted light and reflected light (light from the rear side end face), so that this resonator end face, particularly PD, detects it. This effect is achieved by providing at least the high reflectance protective film on the end face side from which the emitted light is emitted. Furthermore, if protective films are provided on both end faces of the resonator, which is the main exit of light with high light intensity and density, most of the noise components emitted from the laser element can be removed. preferable.

  The nitride semiconductor laser element according to claim 3 of the present invention is characterized in that the end face protective film has a low reflectance with respect to the emission wavelength from the active layer.

  With such a configuration, it is possible to provide an end face protective film that can oscillate laser light and can suppress emission of excitation light excited by absorbing stray light to the outside.

  The nitride semiconductor laser element according to claim 4 of the present invention is characterized in that the end face protective film has a single layer or a multilayer structure.

  By setting it as such a structure, it can adjust so that it may become an end surface protective film of desired reflectance. For the end face protection film, it is necessary not only to consider the reflectance, refractive index, or transmittance, but also to select the material in consideration of the coefficient of thermal expansion, stress, etc. The end face protective film can be selected and has a more excellent function.

The nitride semiconductor laser device of the present invention includes a nitride semiconductor substrate and a nitride semiconductor layer formed by laminating an n-type semiconductor layer, an active layer, and a p-type semiconductor layer thereon, and the nitride semiconductor layer A nitride semiconductor laser device having a stripe-shaped laser beam waveguide region and an emission-side end surface protective film and an opposite rear-side end surface protective film on an end surface substantially perpendicular to the waveguide region, The nitride semiconductor substrate has an excitation region that absorbs light emitted from the active layer and emits excitation light having a wavelength longer than the emission wavelength, and the rear end face protective film is highly reflective to the wavelength of the excitation light. A first end face protective film having a refractive index and a second end face protective film having a high reflectance with respect to the emission wavelength from the active layer, and the emission side end face protective film is high with respect to the wavelength of the excitation light. Provided with a third end face protective film having reflectivity And it features. Specifically, it has first and third end face protective films that increase the pumping light side and a second end face protective film that increases the laser light side in the reflectance of the laser light wavelength λ _LD and the pumping light wavelength λ _ex. In other words, each end face protection film is provided with a protection film excellent in reflection of laser light and reflection of excitation light, and is a combination of end face protection films separated in function from each film.

  By adopting such a configuration, it is possible to prevent the excitation light from being emitted to the outside from the rear side. Therefore, malfunctions such as when a detector (photodiode) is provided on the rear side to control driving can be avoided. Can be suppressed. In particular, since the emission wavelength of the excitation light is longer than the emission wavelength from the active layer, it is easy to recognize even weak light. FIG. 4 shows a spectral sensitivity curve of Si, which is a general photodiode (PD). The sensitivity peak is in the infrared region, and it is easy to recognize long wavelength light emission. For this reason, when the wavelength is relatively short, such as a laser element using a nitride semiconductor, for example, having an emission wavelength of about 390 to 420 nm, the light is absorbed and excitation light having a wavelength of about 550 to 600 nm is emitted. In this case, the sensitivity of the PD increases to nearly three times. Then, even weak light that is not laser light is easily recognized. When the light emitted from the rear side is not excitation light but stray light that is weak light having the same wavelength as the laser light, the sensitivity of the PD is the same as that of the laser light, so the stray light greatly affects the sensitivity of the PD. There is nothing. In the present invention, stray light is absorbed into excitation light, and an end face protective film having high reflectivity is formed on the excitation light, thereby suppressing excitation light from being emitted from both the emission side and the rear side. Thus, excellent laser element characteristics can be obtained.

  In the nitride semiconductor laser device according to claim 6 of the present invention, the first end face protective film and / or the third end face protective film has a low reflectance with respect to the emission wavelength from the active layer. Features.

  By setting it as such a structure, it can suppress that a reflectance falls by a 1st and 3rd end surface protective film, and can reduce a threshold value.

  The nitride semiconductor laser element according to claim 7 of the present invention is characterized in that the emission-side end face protective film has a fourth end face protective film having a high reflectance with respect to the emission wavelength from the active layer. . In the nitride semiconductor laser element according to claim 8 of the present invention, the first end face protective film, the second end face protective film, the third end face protective film, and the fourth end face protective film are each a single layer. Or it is a multilayer structure.

  By setting it as such a structure, it becomes easy to adjust the reflectance of an output side and a rear side to a desired value, and the reflectance according to a use can be obtained.

  The nitride semiconductor laser element according to claim 9 of the present invention is characterized in that the first end face protective film and the second end face protective film are laminated so that at least a part thereof overlaps. The nitride semiconductor laser element according to claim 10 of the present invention is characterized in that the third end face protective film and the fourth end face protective film are laminated so that at least a part thereof overlaps.

  Since the first end face protective film and the second end face protective film have different emission wavelengths to be reflected, even if they are laminated, high reflectivity can be maintained for light of the target wavelength. The same applies to the third end face protective film and the fourth end face protective film.

  The nitride semiconductor laser element according to claim 11 of the present invention is characterized in that the second end face protective film is formed in contact with the semiconductor layer. The nitride semiconductor laser element according to claim 12 of the present invention is characterized in that the fourth end face protective film is formed in contact with the semiconductor layer.

  Since the excitation light has a longer wavelength than the emission wavelength from the active layer, it is low in energy and is excited by stray light leaking from the waveguide region. In comparison, the light density is also low. Therefore, by providing an end face protective film with high reflectivity against the light emitted from the active layer so as to be in contact with the semiconductor layer, it is possible to suppress the deterioration of the end face protective film against the excitation light and obtain a laser beam with a stable mode. Can do.

  The nitride semiconductor laser device according to claim 13 of the present invention is characterized in that the excitation region has a lower dislocation density than the peripheral region. Specifically, in the substrate surface, a nitride semiconductor substrate having a low dislocation density region and a high dislocation density, the low region functions as an excitation region, and stray light propagating through the substrate is optically converted, whereby the end face As excitation light that can be controlled by the protective film, stray light emitted from the laser element can be prevented.

  The nitride semiconductor laser device according to claim 14 of the present invention is characterized in that the excitation region has a higher impurity concentration than the peripheral region. Specifically, in the nitride semiconductor substrate having a region with a low impurity concentration and a region with a high impurity concentration in the substrate plane, the high region functions as an excitation region, whereby the above-described configurations and effects can be extracted.

  The nitride semiconductor laser element according to claim 15 of the present invention is characterized in that the impurity is at least one of H, O, C, and Si.

  The nitride semiconductor laser element according to claim 16 of the present invention is characterized in that the emission wavelength from the active layer is 390 to 420 nm.

  The nitride semiconductor laser element according to claim 17 of the present invention is characterized in that the wavelength of the excitation light is 550 to 600 nm.

  The nitride semiconductor laser device according to claim 18 of the present invention is characterized in that the excitation region is formed in a stripe shape substantially parallel to the waveguide region. Specifically, as the excitation region, the high impurity concentration region and the low dislocation density region in the substrate surface described above are formed in a stripe shape, and the stripe direction and the stripe direction of the ridge stripe as the waveguide are substantially parallel. It is to provide. As described above, since the light that oozes out in the vertical direction and the horizontal direction from the striped waveguide region becomes the light that is converted into the excitation light is provided in parallel, the waveguide region, the excitation region By making these substantially parallel to each other, the above-described light conversion and excitation light generation are suitably performed.

  The nitride semiconductor laser element according to claim 19 of the present invention is characterized in that the waveguide region is formed above the excitation region. Specifically, the waveguide region of the semiconductor layer is provided as the excitation region so that the above-described high impurity concentration region and low dislocation density region in the substrate surface overlap at least partially with the region in the substrate surface. Is. Preferably, the waveguide region is provided so that almost the entire surface of the waveguide region is covered with the excitation region. When the entire surface laser device structure is a ridge waveguide, the efficiency is improved by providing the ridge so as to overlap with the stripe-shaped ridge within the substrate surface, preferably with a wider excitation region than the ridge stripe. Excitation light generation and stray light conversion are possible.

  The nitride semiconductor laser element according to claim 20 of the present invention is characterized in that the waveguide region is formed in a region separated from the excitation region. Specifically, in the substrate plane, the excitation region and the waveguide region of the laser element structure on the substrate are separated from each other. For example, when the excitation region and the waveguide region are striped There is a structure in which the stripes are provided so that their longitudinal directions are substantially the same and are substantially parallel to each other.

The LD device according to claim 21 of the present invention includes the nitride semiconductor laser element and a PD (photodiode) which is a photodetector for detecting the laser light, and the spectral sensitivity of the PD is The pumping light wavelength λ _ex is larger than the laser light wavelength λ _LD . In other words, an LD device having a photodiode that shakes the spectral sensitivity of [λ _LD sensitivity] <[λ _ex sensitivity] as a photodetector, and an LD device using a PD that is highly sensitive to excitation light. In addition, the excitation light confinement function by the end face protective film preferably works, and even an LD device that seriously affects the LD drive even with a slight leakage of excitation light can control the LD drive with high accuracy. This is because the Si semiconductor, which is usually used as a photodiode, is not a PD with good sensitivity in the wavelength band of a wide band gap nitride semiconductor laser element. Although it has been difficult to control the semiconductor laser element with high accuracy, this can be solved. In addition, as a specific LD device, in addition to a CAN type laser element device in which a laser element chip and a PD chip are mounted on respective mounting portions and connected to each electrode terminal of the LD device with a wire or the like. There are LD devices such as a laser coupler and an integrated structure in which a laser element chip, a PD chip, and an electric circuit that drives them and supplies external terminals are mounted with high density. Laser couplers include a stack element in which a laser element chip and a PD chip are stacked and mounted, and the laser element side and the PD chip side are mounted on another mounting substrate or base. At this time, the laser element is not limited to the one on which only one type of the nitride semiconductor laser element is mounted, and may include a second laser element that emits laser light of other wavelengths, that is, A plurality of laser elements and a multi-wavelength LD device may be used.

  The nitride semiconductor laser device of the present invention suppresses the stray light from being mixed with the laser light by absorbing the stray light in the substrate, and suppresses the FFP from being deteriorated, and absorbs the stray light to generate the excitation light to generate the excitation. By forming a highly reflective end face protective film so that light is not emitted to the outside, a more stable laser beam can be obtained. Also, on the rear side, it is possible to drive with good controllability by forming a high-reflectance end face protective film so that excitation light having a wavelength longer than the emission wavelength from the active layer does not cause the detector to malfunction. A semiconductor laser element having excellent reliability can be obtained.

  Hereinafter, the present invention will be described, but the nitride semiconductor laser element of the present invention is not limited to the element structure shown in the embodiment.

  The nitride semiconductor laser element of the present invention uses a nitride semiconductor substrate having an excitation region that absorbs light emitted from the active layer and emits excitation light having a wavelength longer than the emission wavelength, thereby providing a laser light waveguide. Light that leaks from the region (stray light) is suppressed from being emitted to the outside. As a result, good element characteristics can be obtained.

  FIG. 1 shows a configuration of a nitride semiconductor device according to an embodiment of the present invention. An n-type nitride semiconductor layer 102, an active layer 104, and a p-type nitride semiconductor are formed on a nitride semiconductor substrate 101. This is a nitride semiconductor laser device in which the layer 103 is stacked and a p-type nitride semiconductor layer is provided with a striped ridge. The ridge can be formed by removing a part of the p-type nitride semiconductor layer by means such as etching, whereby an effective refractive index type waveguide can be formed. The ridge may be formed by etching a part from the p-type nitride semiconductor layer to the n-type nitride semiconductor layer to form a refractive index type waveguide, or the ridge is formed by selective growth. May be. The ridge is not limited to the forward mesa shape whose width on the bottom side is large and the stripe width decreases as it approaches the top surface. Conversely, the reverse mesa shape that the stripe width decreases as it approaches the ridge bottom surface may be used. It may be a stripe having various side surfaces or a shape in which these are combined. Also, the striped waveguides need not have the same width. Alternatively, a buried laser element in which a semiconductor layer is regrown on the ridge surface or both sides of the ridge after such a ridge is formed may be used. Further, it may be a gain waveguide type waveguide having no ridge.

  A first insulating film 109 is formed from the side surface of the ridge and the upper surface of the continuous p-type nitride semiconductor layer from the ridge. A p-side ohmic electrode 105 is provided on the top surface of the ridge and the first insulating film, and an n-side electrode 107 is provided on the back surface of the nitride semiconductor substrate. In addition, a second insulating film 108 covering the side surface of the semiconductor layer is provided so as to continue to the top of the first insulating film. A p-side pad electrode 106 in contact with the second insulating film and the p-side ohmic electrode is provided on the p-type nitride semiconductor layer.

(Nitride semiconductor substrate)
Examples of the composition of the substrate used include GaN, AlN, InN, or mixed crystals of them such as AlGaN, InGaN, and AlInGaN. These substrates can be manufactured by the following method.

  The nitride semiconductor to be a substrate is formed by growing a nitride semiconductor to a thickness of 100 μm or more on a heterogeneous substrate by, for example, halide vapor phase epitaxy (hereinafter referred to as HVPE method), and then removing the heterogeneous substrate. Here, the surface from which the heterogeneous substrate is removed is the (000-1) plane of the nitride semiconductor, and the inclined plane other than the (000-1) plane is referred to as dry etching, wet etching, or chemical mechanical polishing (hereinafter referred to as CMP). ). Furthermore, if the nitride semiconductor has a half-width of (0002) diffraction X-ray rocking curve by biaxial crystal method within 3 minutes, more preferably within 2 minutes, the step of removing the dissimilar substrate is also possible. It is difficult to damage the nitride semiconductor, and a nitride semiconductor having a thickness of 100 μm or more can be obtained while maintaining good crystallinity. Thereafter, a novel nitride semiconductor element is fabricated on the (0001) plane of the nitride semiconductor. A first electrode is formed on the back surface of the nitride semiconductor.

The nitride semiconductor is a general formula _{In X Al Y Ga 1-X} -Y N (0 ≦ X ≦ 1,0 ≦ Y ≦ 1,0 ≦ X + Y ≦ 1). The nitride semiconductor is preferably formed on a different substrate through a buffer layer represented by Al _a Ga _1-a N (0.01 ≦ a ≦ 0.5). This is for improving crystallinity. The growth temperature of the buffer layer is a low temperature growth of 800 ° C. or lower, and thereby dislocations and pits on the nitride semiconductor can be reduced. After a buffer layer is grown on the heterogeneous substrate by metal organic vapor phase epitaxy (hereinafter referred to as MOCVD), an Al _x Ga _1-x N (0 ≦ X ≦ 1) layer is further formed by lateral over-growth (ELO). It may be grown. In the ELO method, a threading dislocation is bent by laterally growing a nitride semiconductor, and further, the threading dislocations are converged to reduce threading dislocations on the surface and improve crystallinity.

As a growth substrate for growing a nitride semiconductor substrate, various substrates such as a GaAs substrate or a sapphire substrate, a SiC substrate, a Si substrate, a spinel substrate, an NdGaO ₃ substrate, a ZnO substrate, a GaP substrate, or a GaN substrate can be used.

  As described above, a nitride semiconductor layer is grown by a growth method accompanied by lateral growth and used as a substrate, so that the dislocation density (defect density) and the like are not uniform at positions corresponding to the shape of the growth starting point. It can be set as the board | substrate used. Further, it is preferably grown while doping impurities, and a non-uniform region of impurity concentration is also formed so as to correspond to the dislocation density distribution state.

  The distribution state of the low dislocation density region as described above can be selected depending on the shape of the growth starting point, but since the laser light waveguide region is formed in a stripe shape, the growth starting point is correspondingly formed in a stripe shape. Preferably formed. Then, by growing the nitride semiconductor layer from the growth starting points periodically arranged in a stripe shape, a region having low dislocation density and excellent crystallinity, and conversely, a region having many dislocations and poor crystallinity. (Dislocation bundle) can be a periodically formed nitride semiconductor substrate. This dislocation bundle is difficult to grow a nitride semiconductor layer on it, and the crystallinity of the grown layer is not good. For this reason, since it is easy to adversely affect the device driving, it is preferable to form the operation region such as the waveguide region in a region other than the dislocation bundle. For example, as shown in FIG. By adjusting so as to be, deterioration of element characteristics can be suppressed.

  Further, by making the nitride semiconductor substrate conductive by doping impurities or the like, an n-electrode can be provided on the back side of the substrate as shown in FIG. In addition, an insulating or low-conductivity substrate may be used. In that case, an n-electrode is provided on the same side as the p-electrode. Further, the film thickness of the nitride semiconductor substrate may be about 100 μm in consideration of the strength during handling.

(Excitation region)
As described above, a nitride semiconductor substrate grown on a growth substrate has a region grown by lateral growth, and the crystal characteristics are not easily uniform in the plane, and the dislocation density and impurity concentration are low. , Different regions are formed. In particular, a region with a low dislocation density is an excitation region because it easily absorbs the emission wavelength from the active layer. The excited region is formed in a different state depending on the type of growth substrate used and the growth conditions (temperature, gas flow rate, pressure, impurity type and concentration, etc.) of the nitride semiconductor layer. For this reason, there is not much boundary between the excitation region and the non-excitation region, and it can be an excitation region having weak excitation light over almost the entire surface, or it seems to have locally strong excitation light as shown in FIG. An excitation region 112 can be formed, and the shape and distribution of the excitation region of such a substrate depend on the type of substrate and the growth conditions. These can select a preferable form according to the objective and the use.

  Further, such an excitation region is formed in a stripe shape so as to correspond to the waveguide region of the laser beam, specifically, the excitation region, the waveguide region, and the ridge stripe overlap in the substrate surface. preferable.

  Further, by forming a waveguide region in the nitride semiconductor layer grown on such an excitation region, a good waveguide region for laser light can be obtained. By forming the excitation region so as to correspond to the waveguide region, the stray light absorption efficiency is improved. Therefore, the excitation region is preferably provided in the vicinity of the waveguide region. However, too much absorption may cause a decrease in the threshold value. In such a case, the excitation region, the waveguide region, and the ridge stripe are separated from the excitation region, specifically in the substrate plane. Are provided apart from each other, and a waveguide region can be formed in the grown nitride semiconductor. In addition, the excitation region only needs to absorb the emission wavelength from the active layer and thereby be able to emit excitation light. Specifically, the excitation region is stronger than the other partial regions. Since it is sufficient if excitation light can be obtained, the excitation region can be formed by a method such as ion implantation in a subsequent process, in addition to forming the nitride semiconductor substrate by adjusting the dislocation density and impurities by the method described above. It can also be formed.

(End face protection film)
In the present invention, the end face protective film has a high reflectance with respect to the emission wavelength from the excitation region. This end face protective film may have a single layer structure or a multilayer structure. Since it is excitation light generated by absorbing stray light leaking from the waveguide region, its intensity is lower than that of laser light emitted to the outside from the waveguide region. For this reason, it is preferable to set the reflectance so as not to hinder the emission of laser light. The laser beam is difficult to be reflected because of the difference in wavelength, but depending on the material, it may be absorbed, and even if transmitted, some loss occurs, so it is preferable to reduce the film thickness.

  By providing not only the end face protective film for the wavelength of the excitation light but also the end face protective film for the wavelength of the laser light as the end face protective film, the laser light can be emitted more efficiently. Of the protective films provided on the rear side end face, the protective film having high reflectivity with respect to the excitation light is used as the first end face protective film, and the protective film having high reflectivity with respect to the emission wavelength of the waveguide region is used as the second end face. A protective film is used. Of the protective films provided on the end face on the emission side, the protective film having a high reflectivity with respect to the excitation light is used as the third end face protective film, and the protective film having a high reflectivity with respect to the emission wavelength of the waveguide region 4 is an end face protective film.

  Either the first end face protective film or the second end face protective film may be in contact with the semiconductor layer, but preferably the second end face protective film is provided in contact with the semiconductor layer. Thereby, deterioration of the first end face protective film can be suppressed.

  When only the third end face protective film is provided on the end face on the emission side, the film thickness is set so as to have a high reflectivity with respect to the wavelength of the excitation light, and it is provided on the entire end face on the output side. It may be provided only in the region where the excitation light is emitted to the outside, but by providing it on the end face of the laser light emitting portion, it can function as a protective film that prevents the semiconductor layer such as the active layer from being exposed to the outside air. it can. Since the excitation light and the laser light have different wavelengths, it is difficult to block the laser light. Specifically, when the excitation region and the waveguide region correspond to each other as described above, it is more preferable that the excitation region of the substrate and the element structure thereon are covered so as to cover the excitation region of the substrate end surface. It is preferable to provide a protective film so as to cover the waveguide region on the end face of the element structure including the active layer.

  In addition to the third end face protective film, a fourth end face protective film can be provided on the end face on the emission side. In this case, by providing the fourth end surface protective film so as to be in contact with the semiconductor layer, it is possible to suppress the third end surface protective film from being deteriorated by laser light having a high light density. Further, by providing a protective film on the emission side and adjusting the reflectance, the laser beam can be emitted efficiently and the threshold value can be lowered. The excitation light is transmitted without being reflected by the fourth protective film, is reflected by the first protective film, and is not emitted to the outside.

  Specific materials for the end face protective film include Si, Mg, Al, Hf, Nb, Zr, Sc, Ta, Ga, Zn, Y, B, Ti, and oxides, nitrides thereof as conductor materials. Any one selected from compounds such as fluorinated compounds and fluorides can be used. These may be used alone, or may be used as a compound or a multilayer film in which a plurality of them are combined. Preferred materials are materials using Si, Mg, Al, Hf, Zr, Y, and Ga. Moreover, AlN, AlGaN, BN, etc. can be used as a semiconductor material. As the insulator material, compounds such as Si, Mg, Al, Hf, Nb, Zr, Sc, Ta, Ga, Zn, Y, and B oxides, nitrides, fluorides, and the like can be used.

  Examples of preferable materials for the first to fourth end face protective films include the following combinations.

A: First end face protective film (rear side end face protective film against excitation light)
1 pair to 3 pairs of GaN / ZrO ₂ + (SiO ₂ / ZrO ₂ ) 1 pair to 3 pairs of GaN / TiO ₂ + (SiO ₂ / TiO ₂ ) B: second end face protective film (light emission from active layer) Protective film on rear side against
GaN / ZrO ₂ + (SiO ₂ / ZrO ₂ ) 3 pairs to 6 pairs GaN / TiO ₂ + (SiO ₂ / TiO ₂ ) 3 pairs to 6 pairs C: Third end face protective film (exit side for excitation light) End face protection film)
1 pair of GaN / (SiO ₂ / Nb ₂ O ₅ ) to 2 pairs 1 pair of GaN / (Al ₂ O ₃ / Nb ₂ O ₅ ) 1 pair of GaN / (Al ₂ O ₃ / TiO ₂ ) ˜2 pairs GaN / Al ₂ O ₃ + (SiO ₂ / Nb ₂ O ₅ ) 1 pair to 3 pairs D: Fourth end face protective film (outgoing side end face protective film against light emission from active layer)
1 pair to 3 pairs of GaN / ZrO ₂ + (SiO ₂ / ZrO ₂ ) 1 pair to 3 pairs of GaN / TiO ₂ + (SiO ₂ / TiO ₂ ) Thus, a laser element having excellent characteristics can be obtained.

(electrode)
As an electrode material of the p-side ohmic electrode provided in the p-type nitride semiconductor layer, a material having high ohmic properties and adhesion with the p-type nitride semiconductor layer can be selected. Specifically, Ni, Co, Fe, Cr, Al, Cu, Au, W, Mo, Ta, Ag, Pt, Pd, Rh, Ir, Ru, Os and their oxides, nitrides, etc., and these single layers, alloys, or A multilayer film can be used. Preferably, at least one selected from Ni, Co, Fe, Cu, Au, and Al, and oxides, nitrides, and the like thereof.

  The p-side ohmic electrode can realize good ohmic properties by heat treatment. As heat processing temperature, it is preferable to set it as the temperature range of 350 to 1200 degreeC, More preferably, it is 400 to 750 degreeC, Most preferably, it is 500 to 650 degreeC.

  As electrode materials for the p-side pad electrode, Ni, Co, Fe, Ti, Cu, Au, W, Zr, Mo, Ta, Ag, Pt, Pd, Rh, Ir, Ru, Os and oxides thereof Nitrides, etc., and these single layers, alloys, or multilayer films can be used. Since the uppermost layer connects wires and the like, it is preferable to use Au. In order to prevent this Au from diffusing, a material having a relatively high melting point that functions as a diffusion preventing layer is preferably used for the lower layer. For example, Ti, Pt, W, Ta, Mo, TiN, etc. are mentioned, and Ti is mentioned as a particularly preferable material. As the film thickness, the total film thickness is preferably 3,000 to 20,000 mm, more preferably 7000 to 13,000 mm.

  When the nitride semiconductor substrate is conductive, the n electrode provided on the n-type nitride semiconductor layer is preferably provided on the back surface of the substrate. Alternatively, it may be formed on a surface exposed by etching or the like. It can also be provided in the n-type contact layer. When provided on the same surface side as the p-electrode, the ohmic electrode and the pad electrode may be formed in the same process or in separate processes. Further, depending on the material, the heat treatment can be omitted.

  As the n-side ohmic electrode, a material having high ohmic properties and adhesion with the n-type nitride semiconductor layer can be selected. Specifically, Ni, Co, Fe, Ti, Cu, Au, W, V, Zr, Mo, Ta, Al, Ag, Pt, Pd, Rh, Ir, Ru, Os, and the like can be used, and a single layer, an alloy, or a multilayer film can be used. A multilayer structure in which Ti and Al are sequentially laminated is preferable. After forming the n-side ohmic electrode, it may be preferable to perform heat treatment depending on the material in order to improve the ohmic property with the semiconductor layer. Further, the film thickness of the n-side ohmic electrode is preferably about 100 to 30000 mm, more preferably about 3000 to 15000 mm, and particularly preferably 5000 to 10,000 mm. Forming within this range is preferable because it can be an electrode with low contact resistance.

  Examples of the electrode material for the n-side pad electrode include Ni, Co, Fe, Ti, Cu, Au, W, Zr, Mo, Ta, Al, Ag, Pt, Pd, Rh, Ir, Ru, and Os. These single layers, alloys, or multilayer films can be used. Preferably, a multilayer film is used, and Au is preferably used because the uppermost layer connects wires and the like. In order to prevent this Au from diffusing, a material having a relatively high melting point that functions as a diffusion preventing layer is preferably used for the lower layer. For example, Ti, Pt, W, Mo, TiN, etc. are mentioned. As the film thickness, the total film thickness is preferably 3,000 to 20,000 mm, more preferably 7000 to 13,000 mm.

  The n-side electrode is not provided with an ohmic electrode and a pad electrode in separate steps as described above, but is formed continuously to serve both functions, that is, an ohmic electrode in ohmic contact with the semiconductor layer, and An n-electrode that also serves as a take-out electrode (pad electrode) for forming a wire may be used. This is relatively easy to make ohmic contact with the n-type semiconductor layer as compared with the p-side electrode, and is a region slightly separated from the waveguide region, so that it is not necessary to consider the optical characteristics so much. This is because of the large degree of freedom. The film thickness of such an n-electrode is preferably 3000 to 20000 mm as the total film thickness, more preferably 7000 to 13000 mm. Preferred combinations include Ti / Al, Hf / Al, Ti / Pt / Au, Ti / Mo / Pt / Au, Ti / Mo / Ti / Pt / Au, Ti / W / Pt / Au, Ti / W / Ti / Pt / Au, Mo / Pt / Au, Mo / Ti / Pt / Au, W / Pt / Au, V / Pt / Au, V / Mo / Pt / Au, V / W / Pt / Au, Cr / Pt / Au, Cr / Mo / Pt / Au, Cr / W / Pt / Au, and the like. When an n-electrode is formed on the back surface of the substrate, current can be passed by bonding using Au / Sn.

  The first insulating film is provided to limit the current injection region to the upper surface of the ridge. However, since the first insulating film is provided close to the waveguide region, it also acts on the light confinement efficiency. Therefore, a preferable film thickness can be selected depending on the insulating film material to be used. The first insulating film can also be formed to have substantially the same width as the nitride semiconductor layer. The first insulating film formed before the p-side ohmic electrode is heat-treated together when the ohmic electrode is heat-treated. By performing the heat treatment, the strength of the film (bonding force at the atomic level in the film) is increased as compared with the deposited film, and the bonding strength at the interface with the semiconductor layer is also improved. By forming such a first insulating film up to the end portion of the upper surface of the semiconductor layer on which the second insulating film is formed, the adhesion of the second insulating film can also be improved.

  Further, the p-side pad electrode can be formed so as not to contact the second insulating film. In particular, when used in junction down, heat is applied to the p-side pad electrode, but at that time, the volume increases due to thermal expansion, and it tends to flow out in the side surface direction of the element (end direction of the p-type semiconductor layer). Moreover, since not only heat but also pressure is applied, the electrode material easily flows out in the lateral direction. Therefore, by separating from the second insulating film, it is possible to prevent the electrode material of the p-side pad electrode from flowing out in the side surface direction and causing a short circuit.

  The material of the first insulating film is an oxide, SiN, BN, SiC, AlN, or AlGaN containing at least one element selected from the group consisting of Si, Ti, V, Zr, Nb, Hf, and Ta. It is desirable to use at least one kind, and among them, it is particularly preferable to use an oxide of Zr, Hf, Si, BN, AlN, or AlGaN.

  The film thickness of the first insulating film is specifically in the range of 10 to 10,000 mm, preferably in the range of 100 to 5,000 mm. This is because if the thickness is 10 mm or less, it is difficult to ensure sufficient insulation at the time of electrode formation. If the thickness is 10,000 mm or more, the uniformity of the protective film is lost, and a good insulating film is not obtained. . Moreover, by being in the preferred range, a uniform film having a good refractive index difference between the ridge and the ridge can be formed on the side surface of the ridge.

The second insulating film can be provided on the entire surface of the p-side ohmic electrode except for the upper portion of the ridge, and is preferably provided so as to continue to the side end faces of the p-type semiconductor layer and the active layer exposed by etching. . A preferable material is an oxide containing at least one element selected from the group consisting of Si, Ti, V, Zr, Nb, Hf, and Ta, and formed of at least one of SiN, BN, SiC, AlN, and AlGaN. Among them, particularly preferable materials include single layer films and multilayer films such as SiO ₂ , Al ₂ O ₃ , ZrO ₂ , and TiO ₂ .

  Further, in order to set the stripe direction of the ridge as the resonator direction, the pair of resonator surfaces provided on the end face can be formed by cleavage or etching. In the case of forming by cleavage, it is preferable that the substrate and the semiconductor layer have cleavage properties, and an excellent mirror surface can be easily obtained by utilizing the cleavage properties. Further, even if there is no cleavage, the resonator surface can be formed by etching, and in this case, it can be obtained with a small number of steps by carrying out simultaneously when exposing the n electrode formation surface. It can also be formed simultaneously with the ridge formation. In this way, the number of processes can be reduced by forming each process simultaneously. However, in order to obtain a more excellent resonator surface, it is preferable to provide another process.

  Specifically, when the cavity face is an etching end face, for example, after the etching end face is formed, the end faces (the emission side and the reflection side) are highly reflective for laser light (second and fourth). An end face protective film is provided, and as will be described later, the substrate is cleaved so that the wafer has a bar shape, and the excitation light high reflection film covers the exposed end face of the substrate and the etching end face (first and third). An end face protective film can be formed. In this way, the etching end face and the substrate end face can have different film structures (number of layers, end face for laser light and excitation light, and substrate end face for excitation light).

  Hereinafter, examples will be described. In the present invention, the device structure of the n-type nitride semiconductor layer, the active layer, and the p-type nitride semiconductor layer constituting the nitride semiconductor layer is not particularly limited, and various layer structures are provided. Can be used. Examples of the device structure include a laser device structure described in Examples described later, but other laser structures can also be applied. Specific examples of nitride semiconductors include nitride semiconductors such as GaN, AlN, or InN, III-V group nitride semiconductors that are mixed crystals thereof, and further include B, P, and the like. A thing etc. can be used. Nitride semiconductor growth is known to grow nitride semiconductors such as MOVPE, MOCVD (metal organic chemical vapor deposition), HVPE (halide vapor deposition), MBE (molecular beam vapor deposition). All methods are applicable.

(Nitride semiconductor substrate)
First, a 2 inch, heterogeneous substrate made of sapphire with the C-plane as the main surface is set in an MOCVD reaction vessel, the temperature is set to 500 ° C., trimethylgallium (TMG), ammonia (NH ₃ ) is used, and the substrate is made of GaN. A buffer layer is grown to a thickness of 200 mm. Further, the base layer made of GaN is grown at 2.5 μm at a temperature of 1000 ° C. or higher. Then, move to the HVPE reaction vessel. GaN as the nitride semiconductor 1 is grown at 500 μm using Ga metal, HCl gas, and ammonia as raw materials. Next, only sapphire is peeled off by excimer laser irradiation, and CMP is performed to form a nitride semiconductor having a thickness of 450 μm.

(N-type contact layer)
Subsequently, at 1050 ° C., an n-type contact layer made of Si-doped n-Al _0.02 Ga _0.98 N with a film thickness of 3.5 μm is similarly used using TMG, ammonia gas, and silane gas as the source gas. Grow. The film thickness of this n-type contact layer should just be 2-30 micrometers.

(Crack prevention layer)
Next, a crack prevention layer made of Si-doped n-In _0.05 Ga _0.95 N is grown to a thickness of 0.15 μm using TMG, TMI (trimethylindium), and ammonia at a temperature of 800 ° C. .

  When the nitride semiconductor substrate is a conductive substrate, the growth substrate is removed later, and an n-electrode is formed on the back side of the substrate, the n-type cladding layer described below is stacked on the nitride semiconductor substrate. It can also be made.

(N-type cladding layer)
Next, the temperature is set to 1050 ° C., TMA (trimethylaluminum), TMG, and ammonia are used as source gases, and an A layer made of undoped Al _0.05 Ga _0.095 N and B made of Si-doped GaN Each layer is grown to a thickness of 50 mm. Then, this operation is repeated 110 times, and the A layer and the B layer are alternately stacked to grow an n-type cladding layer made of a multilayer film (superlattice structure) having a total film thickness of 1.1 μm. At this time, if the mixed crystal ratio of Al in the undoped AlGaN is in the range of 0.02 or more and 0.3 or less, a refractive index difference that sufficiently functions as a cladding layer can be provided. It can also be formed.

(N-type light guide layer)
Next, TMG and ammonia are used as source gases at the same temperature, and an n-type light guide layer made of undoped GaN is grown to a thickness of 0.15 μm. This layer may be doped with n-type impurities.

(Active layer)
Next, the temperature is set to 800 ° C., TMI (trimethylindium), TMG, and ammonia are used as raw materials, silane gas is used as an impurity gas, and a barrier layer made of Si-doped In _0.02 Ga _0.98 N is formed at 140 ° C. Grow with film thickness. Subsequently, silane gas is stopped and a well layer made of undoped In _0.1 Ga _0.9 N is grown to a thickness of 70 mm. This operation is repeated twice. Finally, a barrier layer made of Si-doped In _0.02 Ga _0.98 N is grown to a thickness of 140 mm, and an active layer of a multiple quantum well structure (MQW) having a total thickness of 560 mm is obtained. Grow.

(P-type electron confinement layer)
At the same temperature, a p-type electron confinement layer made of Mg-doped Al _0.25 Ga _0.75 N is grown to a thickness of 30 mm in an N ₂ atmosphere. Next, a p-type electron confinement layer made of Mg-doped Al _0.25 Ga _0.75 N is grown to a thickness of 70 mm in an H ₂ atmosphere.

(P-type light guide layer)
Next, the temperature is set to 1050 ° C., TMG and ammonia are used as source gases, and a p-type light guide layer made of undoped GaN is grown to a thickness of 0.15 μm. The p-type light guide layer is grown as undoped, but may be doped with Mg.

(P-type cladding layer)
Subsequently, an A layer made of undoped Al _0.08 Ga _0.92 N is grown to a thickness of 80 mm, and a B layer made of Mg-doped GaN is grown to a thickness of 80 mm. This is repeated 28 times, and the A layer and the B layer are alternately laminated to grow a p-type cladding layer made of a multilayer film (superlattice structure) having a total film thickness of 0.45 μm. When a p-type cladding layer is made of a superlattice in which at least one nitride semiconductor layer containing Al is included and nitride semiconductor layers having different bandgap energies are stacked, impurities are both highly doped in one layer. Although so-called modulation doping tends to improve the crystallinity, both may be doped in the same manner.

(P-type contact layer)
Finally, a p-type contact layer made of Mg-doped GaN is grown on the p-type cladding layer at 1050 ° C. to a thickness of 150 mm. The p-type contact layer can be composed of p-type In _x Al _y Ga _1-xy N (x ≦ 0, y ≦ 0, x + y ≦ 1). The most favorable ohmic contact with the electrode is obtained. After the completion of the reaction, the wafer is annealed at 700 ° C. in a nitrogen atmosphere in the reaction vessel to further reduce the resistance of the p-type layer.

(N-type layer exposure)
After the nitride semiconductor is grown as described above to form a laminated structure, the wafer is taken out of the reaction vessel, a protective film made of SiO ₂ is formed on the surface of the uppermost p-type contact layer, and RIE (reaction) is performed. The surface of the n-type contact layer is exposed by etching with Cl ₂ gas using a reactive ion etching. At this time, the resonator surface may be formed by etching. Also, as shown in Example 3, when the n electrode is provided on the back surface of the substrate, the n electrode forming surface is not necessary, and this process is also performed. Can be omitted.

(Ridge formation)
Next, in order to form a striped waveguide region, a protective film made of Si oxide (mainly SiO ₂ ) is formed to a thickness of 0.5 μm on almost the entire surface of the uppermost p-type contact layer by a CVD apparatus. After the formation, a mask having a predetermined shape is formed on the protective film by a photolithography technique, and a protective film made of striped Si oxide is formed by etching using CHF ₃ gas by an RIE apparatus. Using this Si oxide protective film as a mask, the semiconductor layer is etched using SiCl ₄ gas to form a ridge stripe above the active layer. At this time, the width of the ridge is set to 1.6 μm.

(First insulating film)
With the SiO ₂ mask formed, a first insulating film made of ZrO ₂ is formed on the surface of the p-type semiconductor layer with a film thickness of about 550 mm. The first insulating film may be provided on the entire surface of the semiconductor layer by masking the n-side ohmic electrode formation surface. In addition, a portion where the insulating film is not formed can be provided so as to be easily divided later.

After forming the first insulating film, the wafer is heat-treated at 600 ° C. As described above, when a material other than SiO ₂ is formed as the first insulating film, after the first insulating film is formed, the temperature is 300 ° C. or higher, preferably 400 ° C. or higher, and below the decomposition temperature of the nitride semiconductor (1200 ° C.). The heat treatment can stabilize the insulating film material. In particular, in the step after the first insulating film formation, when device processing is performed mainly using SiO ₂ as a mask, the SiO ₂ mask is dissolved in a mask dissolving material used for later removal. Can be difficult. The heat treatment step of the first insulating film can be omitted depending on the material and process of the first insulating film, and the order of the steps can be selected as appropriate, for example, it is performed simultaneously with the heat treatment of the ohmic electrode. Can do. After the heat treatment, it is immersed in a buffered solution to dissolve and remove SiO ₂ formed on the upper surface of the ridge stripe, and ZrO ₂ on the p-type contact layer (and on the n-type contact layer) together with SiO ₂ by a lift-off method. Remove. Thereby, the upper surface of the ridge is exposed and the side surface of the ridge is covered with ZrO ₂ .

(Ohmic electrode)
Next, a p-side ohmic electrode is formed by sputtering on the ridge outermost surface on the p-type contact layer and on the first insulating film. This p-side ohmic electrode uses Ni / Au (100Å / 1500Å). An n-side ohmic electrode is also formed on the upper surface of the n-type contact layer. The n-side ohmic electrode is made of Ti / Al (200 Å / 5500 、), and is formed in a stripe shape parallel to the ridge and having the same length. After these electrodes are formed, heat treatment is performed at 600 ° C. in a mixed atmosphere of oxygen and nitrogen.

(Second insulating film)
Next, a resist covering the entire surface of the p-side ohmic electrode on the ridge and a part of the upper portion of the n-side ohmic electrode is formed. Next, a _second insulating film made of SiO ₂ is formed on almost the entire surface and lifted off to form a second protective film in which the entire upper surface of the p-side ohmic electrode and a part of the n-side ohmic electrode are exposed. Is done. The second insulating film and the p-side ohmic electrode may be formed so as to be separated from each other, or may be formed so as to partially overlap each other. In consideration of the subsequent division, the first and second insulating films and electrodes may not be formed in a stripe-shaped range having a width of about 10 μm across the division position.

The second insulating film is provided so as to cover the entire surface except the upper part of the p-side and n-side ohmic electrodes. A preferable material is an oxide containing at least one element selected from the group consisting of Si, Ti, V, Zr, Nb, Hf, and Ta, and formed of at least one of SiN, BN, SiC, AlN, and AlGaN. Among them, particularly preferable materials include single layer films and multilayer films such as SiO ₂ , Al ₂ O ₃ , ZrO ₂ , and TiO ₂ .

(Pad electrode)
Next, a pad electrode is formed so as to cover the ohmic electrode. At this time, it is preferable to form the second insulating film so as to cover it. The p-side pad electrode is laminated in the order of Ni / Ti / Au (1000 Å / 1000 Å / 8000 Å). Further, the n-side pad electrode is formed of Ni / Ti / Au (1000/1000/8000) from below. These pad electrodes are in contact with the p-side ohmic electrode and the n-side ohmic electrode in a stripe shape through the second insulating film, respectively.

(Cleavage and resonator surface formation)
Next, the substrate is polished and adjusted so as to have a film thickness of about 100 μm, and then a scribe groove is formed on the back surface of the substrate, braked from the nitride semiconductor layer side, and cleaved to obtain a bar-shaped laser. The cleavage plane of the nitride semiconductor layer is the M plane (1 −100) of the nitride semiconductor, and this plane is used as the resonator plane.

(End face protection film formation)
An end face protective film is provided on the resonator surface formed as described above using a sputtering apparatus such as an ECR sputtering apparatus. A third end face protective film composed of two pairs of (SiO ₂ (917Å) / Nb ₂ O ₅ (550Å)) is provided on the emission side end face as a third end face protective film. On the rear side end face, a second protective film composed of 6 pairs of ZrO ₂ (440 °) + (SiO ₂ (667 °) / ZrO ₂ (440 °)) is provided. A first protective film composed of six pairs of ZrO ₂ (440 °) + (SiO ₂ (917Å) / ZrO ₂ (605Å)) is further provided thereon. The film thickness is such that the emission wavelength from the active layer is 400 nm, the excitation light emitted by absorbing the wavelength is 550 nm, and λ / 4n (n is the refractive index) with respect to the wavelength (λ). It is set. The transmittance of the end face protective film provided with such setting is shown in the graph. FIG. 3 shows the transmittance on the emission side, and FIG. 2 shows the transmittance on the rear side. The transmittance in the wavelength region of the excitation light is low on both the emission side and the rear side, making it difficult to emit to the outside.

  Finally, a groove is formed by scribing so as to be substantially parallel to the ridge stripe, and a bar is cut at the groove portion to obtain the semiconductor laser device of the present invention. As a scribing method, mechanical or physical scribing using a blade such as a cutter, optical or thermal scribing using a YAG laser, or the like can be used. The scribe direction may be from the semiconductor layer side or from the substrate side, and various optimum methods can be selected depending on the shape of the element, the type of the substrate, and the like.

The nitride semiconductor laser device obtained as described above has an excitation region on almost the entire surface of the nitride semiconductor substrate. This is because the growth is performed so that the difference in the dislocation density becomes extremely large. Therefore, there is no region where the excitation light intensity is locally high. Further, it can continuously oscillate at an oscillation wavelength of 405 nm at a room temperature and a threshold current density of 2.5 kA / cm ² and a high output of 60 mW. By reducing the irradiation of the excitation light to the detector provided on the rear side, it can be driven with good control, and the laser light emitted from the end surface on the emission side has a good FFP with less noise (unevenness) Have.

In Example 2, a third end face protective film having three pairs of Al ₂ O ₃ (1800 Å) / (SiO ₂ (917 Å) / Nb ₂ O ₅ (550 Å)) is provided on the output side end face as a third end face protective film. An end face protective film is provided. On the rear side end face, a second protective film composed of 6 pairs of ZrO ₂ (440 °) + (SiO ₂ (667 °) / TiO ₂ (370 °)) is provided. A first protective film comprising 6 pairs of ZrO ₂ (440 °) + (SiO ₂ (917 °) / TiO ₂ (509)) is further provided thereon. As in Example 1, these film thicknesses are set to λ / 4n (n is the wavelength of the light (λ) with the emission wavelength from the active layer being 400 nm and the excitation light emitted by absorbing that wavelength being 550 nm. (Refractive index). An n electrode is provided on the back surface of the nitride semiconductor substrate. As a material for the n-electrode, V / Pt / Au (150Å / 2000Å / 3300Å) is provided. After the n-electrode is provided, no heat treatment is performed. Except for the above, the same procedure as in Example 1 was performed to obtain the nitride semiconductor laser device of the present invention. The nitride semiconductor laser device thus obtained has the excitation region in almost the entire region of the substrate as in Example 1, and has weak excitation light. It can continuously oscillate at an oscillation wavelength of 405 nm at a threshold current density of 2.5 kA / cm ² at room temperature and a high output of 60 mW. By reducing the irradiation of the excitation light to the detector provided on the rear side, it can be driven with good control, and the laser light emitted from the end surface on the emission side has a good FFP with less noise (unevenness) Have.

In Example 3, a substrate obtained as follows is used as the nitride semiconductor substrate. A GaAs substrate is used as the growth substrate. A protective film made of stripe-like SiO ₂ parallel to the M-plane of the nitride semiconductor is formed on the upper surface of the substrate, and this is used as a seed to grow so as to expose the facet plane. Thereby, a nitride semiconductor substrate having a thickness of about 300 μm is obtained. The nitride semiconductor substrate thus obtained is a nitride semiconductor substrate having a low dislocation density region and dislocation bundle in a stripe shape, and a ridge is formed on the low dislocation density region. The low dislocation density region is an excitation region, which absorbs the emission wavelength (405 nm) from the active layer together with conduction and has excitation light (560 nm). In Example 3, the n-electrode is formed on the back surface of the nitride semiconductor substrate, but etching is performed so as to expose the n-type semiconductor layer before forming the ridge. In particular, the growth state of the n-type semiconductor layer to the p-type semiconductor layer formed above the dislocation bundle having poor crystallinity is different from the peripheral portion. Therefore, the film thickness is also thinner than the peripheral part. In such a region, it is considered that the pn junction is not sufficiently formed. Therefore, by removing the n-type semiconductor layer to the p-type semiconductor layer in a range slightly wider than the width of the striped dislocation bundle by etching, it is possible to suppress the deterioration of the element function. Further, the nitride of the present invention was prepared in the same manner as in Example 1 except that a third end face protective film composed of two pairs of (Al ₂ O ₃ (823 Å) / TiO ₂ (509 Å)) was provided on the output side end face. A semiconductor laser element is obtained. In Example 3, the thickness of the third end face protective film is the same as in Example 1 except that the emission wavelength from the active layer is 400 nm and the excitation light emitted by absorbing the wavelength is 550 nm. The wavelength (λ) is set to be λ / 4n (n is a refractive index). The nitride semiconductor laser device thus obtained is capable of continuous oscillation with a threshold current density of 2.5 kA / cm ² at room temperature and a high output of 60 mW and an oscillation wavelength of 405 nm. By reducing the irradiation of the excitation light to the detector provided on the rear side, it can be driven with good control, and the laser light emitted from the end surface on the emission side has a good FFP with less noise (unevenness) Have.

  The present invention relates to all devices to which laser elements can be applied, for example, CD players, MD players, various game machines, DVD players, trunk lines and optical communication systems such as telephone lines and submarine cables, laser knives, and laser treatment devices. , Medical devices such as laser acupressure machines, printing machines such as laser beam printers and displays, various measuring instruments, laser levels, laser measuring instruments, laser speed guns, optical sensing devices such as laser thermometers, laser power transportation, etc. It can be used in various fields.

(A) Schematic perspective view for explaining the semiconductor laser device of the present invention (b) AA sectional view of FIG. 1 (a) (c) BB sectional view of FIG. 1 (a) The graph which shows the transmittance | permeability of the end surface protective film of embodiment of this invention The graph which shows the transmittance | permeability of the end surface protective film of embodiment of this invention Photodiode spectral sensitivity curve

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Nitride semiconductor substrate 102 ... N-type nitride semiconductor layer 103 ... P-type nitride semiconductor layer 104 ... Active layer 105 ... P-side ohmic electrode 106 ... P-side pad electrode 107 ... n-side electrode 108 ... second insulating film 109 ... first insulating film 110 ... end face protective film 111 ... dislocation bundle 112 ... low dislocation density region

Claims (21)

A nitride semiconductor substrate includes a nitride semiconductor layer formed by laminating an n-type semiconductor layer, an active layer, and a p-type semiconductor layer thereon, and the nitride semiconductor layer has a striped waveguide region of laser light And a nitride semiconductor laser element having end face protective films on both end faces substantially perpendicular to the waveguide region,
The nitride semiconductor substrate has an excitation region that absorbs light emitted from the active layer and emits excitation light having a wavelength longer than the emission wavelength;
The nitride semiconductor laser device, wherein the end face protective film has a high reflectance with respect to an emission wavelength from the excitation region. The nitride semiconductor laser element according to claim 1, wherein the end face protective film is provided on both the emission side end face and the rear side end face. The nitride semiconductor laser element according to claim 1, wherein the end face protective film has a low reflectance with respect to an emission wavelength from the active layer. 4. The nitride semiconductor laser element according to claim 1, wherein the end face protective film has a single layer or a multilayer structure. A nitride semiconductor substrate includes a nitride semiconductor layer formed by laminating an n-type semiconductor layer, an active layer, and a p-type semiconductor layer thereon, and the nitride semiconductor layer has a striped waveguide region of laser light And a nitride semiconductor laser element having an emission side end face protective film and an opposite rear side end face protective film on an end face substantially perpendicular to the waveguide region,
The nitride semiconductor substrate has an excitation region that absorbs light emitted from the active layer and emits excitation light having a wavelength longer than the emission wavelength;
The rear side end face protective film includes a first end face protective film having a high reflectance with respect to the wavelength of the excitation light, and a second end face protective film having a high reflectance with respect to the emission wavelength from the active layer. And
The emission-side end face protective film includes a third end face protective film having a high reflectivity with respect to the wavelength of the excitation light. The nitride semiconductor laser element according to claim 5, wherein the first end face protective film and / or the third end face protective film has a low reflectance with respect to an emission wavelength from the active layer. 7. The nitride semiconductor laser device according to claim 5, wherein the emission side end face protective film has a fourth end face protective film having a high reflectance with respect to an emission wavelength from the active layer. 8. The nitride semiconductor according to claim 5, wherein each of the first end face protective film, the second end face protective film, the third end face protective film, and the fourth end face protective film has a single layer or a multilayer structure. Laser element. 9. The nitride semiconductor device according to claim 5, wherein the first end face protective film and the second end face protective film are laminated so that at least a part thereof overlaps. The nitride semiconductor laser device according to claim 8, wherein the third end face protective film and the fourth end face protective film are laminated so that at least a part thereof overlaps. The nitride semiconductor laser element according to claim 5, wherein the second end face protective film is formed in contact with the semiconductor layer. 8. The nitride semiconductor laser element according to claim 7, wherein the fourth end face protective film is formed in contact with the semiconductor layer. The nitride semiconductor laser device according to claim 1, wherein the excitation region has a dislocation density lower than that of a peripheral region. The nitride semiconductor laser device according to claim 1, wherein the excitation region has a higher impurity concentration than a peripheral region thereof. The nitride semiconductor laser element according to claim 14, wherein the impurity is at least one of H, O, C, and Si. 16. The nitride semiconductor laser device according to claim 1, wherein an emission wavelength from the active layer is 390 to 420 nm. The nitride semiconductor laser device according to claim 1, wherein a wavelength of the excitation light is 550 to 600 nm. The nitride semiconductor laser device according to claim 1, wherein the excitation region is formed in a stripe shape substantially parallel to the waveguide region. The nitride semiconductor laser device according to claim 1, wherein the waveguide region is formed above the excitation region. The nitride semiconductor laser element according to claim 1, wherein the waveguide region is formed in a region separated from the excitation region. 21. An LD device equipped with the nitride semiconductor laser element according to claim 1 and a PD for detecting light emission of the nitride semiconductor laser element, wherein the spectral sensitivity of the PD is the nitride semiconductor laser. An LD device in which the excitation light λ _ex is larger than the light emission wavelength λ _{LD of the} element.

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