JP2012019165A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser device capable of stably performing a self-excited oscillation operation.SOLUTION: The semiconductor laser device comprises: a substrate 110; a ground layer 114 of a first conductive type formed on the substrate 110; a laminate structure composed of a nitride semiconductor including an n-type cladding layer 115, an n-type guide layer 116, an active layer 117, a p-type guide layer 118, a p-type cladding layer 120, and a p-type contact layer 122 that are sequentially formed on the ground layer 114; a p-side electrode 123 electrically connected to the p-type contact layer 122; and an n-side electrode 124 electrically connected to the n-type cladding layer 115. The laminate structure includes a first dislocation region that is located under the p-side electrode 123 and is configured to have a first dislocation density, and a second dislocation region configured to have a second dislocation density different from the first dislocation density. The second dislocation density is larger than the first dislocation density.

Description

  The present invention relates to a semiconductor laser device used for an optical disk light source or a display light source, and more particularly to a self-pulsation operation type semiconductor laser device using a nitride semiconductor.

  2. Description of the Related Art Semiconductor laser devices using nitride semiconductors are actively being used to improve characteristics and reduce costs as light sources for optical pickup devices for BD (Blu-ray Disc (registered trademark)). In recent years, a semiconductor laser device that oscillates a laser beam from blue to green using a nitride semiconductor has been developed, and is expected as a small light source for a display such as a projector. In semiconductor laser devices used for such optical discs and displays, it is important to reduce the noise of the semiconductor laser devices.

  For example, in a BD optical pickup device, laser light emitted from a semiconductor laser device is reflected by an optical disk (BD) and then incident on the end face of the semiconductor laser device again, thereby generating return light noise. This return light noise causes an optical disk reading error. For this reason, at the time of BD signal reproduction, a high-frequency current is superimposed on the semiconductor laser device by using a high-frequency superimposing circuit to make the oscillation spectrum multi-mode, thereby reducing the coherence of the laser light and reducing the return light noise. The method of reducing is used.

  Further, in a semiconductor laser device for display, due to the high coherence of the laser, the intensity of interference is locally generated within the screen, and so-called spec noise is generated in which the screen appears to be glaring. In order to reduce such spec noise, semiconductor laser devices used for displays have been studied, for example, by attaching a vibrator to the semiconductor laser device and vibrating it to smooth the intensity of interference within the screen. Has been made.

  However, it is not preferable to newly attach a high-frequency superposition circuit or a vibrator to the light source as a countermeasure against such noise, which increases the cost of the light source. Therefore, it is required to reduce the noise of the semiconductor laser device itself.

  As a method for reducing the noise of the semiconductor laser device, it is conceivable to reduce the coherence of the emitted light. Conventionally, as a method of reducing the coherence of emitted light, a self-excited oscillation type semiconductor laser device capable of self-excited oscillation operation has been proposed.

  Patent Document 1 discloses a conventional self-excited oscillation type semiconductor laser device. Patent Document 1 discloses that a self-oscillation operation is caused by forming a light absorption region called a saturable absorption region around a current injection region into which current is injected in an active layer. In such a self-excited oscillation operation, since the effective refractive index in the optical waveguide changes, the oscillation wavelength fluctuates and the coherence is reduced, thereby making it possible to reduce noise.

  Hereinafter, a conventional self-excited oscillation type semiconductor laser device disclosed in Patent Document 1 will be described with reference to FIG. FIG. 11 is a sectional view of a conventional self-excited oscillation type semiconductor laser device.

  As shown in FIG. 11, a conventional self-pulsation type semiconductor laser device includes an n-type contact layer 402, an n-type cladding layer 403, an active layer 404, and a p-type cladding layer 405 on a sapphire substrate 401. The n-type current constricting layers 406 and 407 and the p-type contact layer 408 are laminated.

  The p-type cladding layer 405 includes a flat portion 405a formed so as to cover the surface of the active layer 404, a lower stripe portion 405b having a width W2 protruding upward at the center of the flat portion 405a, and a lower stripe portion 405b. The upper stripe portion 405c having a width W1 further protruded from the center portion. The lower stripe portion 405b and the upper stripe portion 405c are configured such that the width W1 is narrower than the width W2.

  An n-side electrode 409 is provided on the opening of the n-type contact layer 402, and a p-side electrode 410 is provided on the p-type contact layer 408.

  According to the semiconductor laser device having such a configuration, the current flowing from the p-type cladding layer 405 to the active layer 404 flows to the active layer 404 in a state where the lateral spread is restricted by the upper stripe portion 405c of the width W1. . Therefore, a current injection region having a size corresponding to the width W1 of the upper stripe portion 405c is formed in the center of the active layer 404. Further, since the width W2 of the lower stripe portion 405b is wider than the width W1 of the upper stripe portion 405c, the light emission spot width becomes a size corresponding to the width W2 of the lower stripe portion 405b, and the light emission spot width is equal to the current injection region. It becomes larger than the width. As a result, a saturable absorption region is formed around the current injection region, and in the active layer 404, the current injection region and the saturable absorption region interact to perform self-oscillation operation, thereby generating a pulsed light output. Obtainable.

JP 2000-286504 A

  However, the conventional self-excited oscillation type semiconductor laser device has a problem that it is difficult to perform a stable self-excited oscillation operation.

  By the way, in a self-excited oscillation type semiconductor laser device, an optical gain region (its width is G) in the active layer caused by current spreading is made as narrow as possible, and conversely, an optical waveguide spot size (its width is S). Is set to be relatively large and the relationship of S> G is satisfied, this difference functions as a saturable absorption region and self-oscillation operation occurs. Therefore, the self-excited oscillation type semiconductor laser device constitutes an intermediate waveguide between the refractive index waveguide (Index Guide) type semiconductor laser device and the gain waveguide (Gain Guide) type semiconductor laser device. .

  Here, in a self-excited oscillation type semiconductor laser device, it is important to maintain a sufficient saturable absorption effect in order to maintain a stable self-excited oscillation operation. The saturable absorption effect has a small differential gain (∂G / ∂n: G is an optical gain, n is an injected carrier concentration) in the optical gain region (light emitting region) in the center of the active layer (saturation during laser oscillation), and It is effective that the differential gain in the saturable absorption region is large and that the difference between the two is large. That is, the self-excited oscillation condition is important for the differential gain and its magnitude in the optical gain region and the saturable absorption region. In general, as the active layer structure, a multiple quantum well (MQW) structure is often employed.

  Thus, in order to stably generate the self-excited oscillation operation, the following two things are considered necessary. First, (1) a structure in which the difference between the differential gain in the light emitting region of the active layer and the differential gain in the saturable absorption region is large, and the differential gain in the light emitting region is likely to be saturated; (2) The light absorption effect in the saturable absorption region is large. The conditions (1) and (2) will be discussed below with reference to FIGS.

  FIG. 12 is a diagram showing a general relationship between the optical gain G and the injected carrier concentration n in a semiconductor laser device in which the active layer has a bulk structure. As described above, in order to cause a stable self-excited oscillation operation, it is necessary to satisfy the above conditions. However, in a semiconductor laser device having an active layer in a bulk structure, as shown in FIG. 12, the differential gain in the light emitting region is difficult to saturate, so that self-oscillation operation is difficult.

  FIG. 13 is a diagram qualitatively showing the relationship between the number N of quantum wells and the injected carrier concentration of optical gain in a semiconductor laser device having an MQW structure as an active layer. As shown in FIG. 13, in the semiconductor laser device having an MQW structure in the active layer, as the number of quantum wells N increases, the optical gain is less likely to be saturated and the self-excited oscillation operation is difficult. Conversely, the smaller the quantum well number N, the easier the optical gain G in the light emitting region is saturated. In other words, an active layer having an MQW structure with a smaller number of quantum wells than an active layer in which optical gain is difficult to saturate, such as a bulk structure, is more likely to saturate optical gain and enhances the saturation effect, thereby allowing self-oscillation operation. Can be strong.

  On the other hand, with respect to the light absorption coefficient in the light absorption region, referring to FIGS. 12 and 13, the absorption coefficient of the active layer of the quantum well structure is smaller, and the light absorption coefficient of the active layer of the bulk structure is more active in the quantum well structure. Greater than the light absorption coefficient of the layer. This point has also been demonstrated from the fact that when a quantum well structure is used for an optical waveguide, good waveguide characteristics can be obtained with little waveguide loss.

  However, since the light absorption coefficient is small and the amount of light absorption is small, it is contrary to the condition (2) that “the light absorption effect in the saturable absorption region is large”, so that it is difficult to realize a stable self-excited operation. It becomes. In order to increase the amount of light absorption, it is effective to introduce an active layer having a bulk structure or to increase the number of quantum wells in an active layer having a multiple quantum well structure. The condition that “the differential gain difference in the light emitting region of the active layer and the differential gain in the saturable absorption region is large and the differential gain in the light emitting region is easily saturated” cannot be satisfied.

  Thus, at present, a semiconductor laser device that achieves (1) and (2) and performs stable self-excited oscillation has not been realized.

  The present invention has been made to solve such a problem, and an object thereof is to provide a semiconductor laser device that performs a stable self-oscillation operation.

  In order to achieve the above object, the inventors of the present application greatly change the current distribution narrowed by the current constricting structure and the light distribution in the optical waveguide in the optical waveguide including the active layer current injection region. investigated. In the optical waveguide region, low dislocations are formed in the active layer current injection region where the current distribution in the active layer is widened, and dislocations are banded in the saturable absorption region where the current distribution in the active layer is not widened. As a result, it was found that the stable lifetime can be realized by shortening the carrier lifetime and promoting the time-saturated absorption recovery.

  The present invention has been obtained based on such knowledge, and is realized by the following solution means.

  One aspect of a semiconductor laser device according to the present invention is a semiconductor laser device that performs a self-excited oscillation operation. The semiconductor laser device includes a substrate, a first conductivity type ground layer formed on the substrate, and the ground layer. The first conductivity type cladding layer, the first conductivity type guide layer, the active layer, the second conductivity type guide layer having a conductivity type different from the first conductivity type, and the second conductivity type clad are sequentially formed. A laminated structure made of a nitride semiconductor composed of a layer and a second conductivity type contact layer, a first electrode electrically connected to the first conductivity type cladding layer, and the second conductivity type contact A second electrode electrically connected to the layer, and the stacked structure includes a first dislocation region which is a region below the second electrode and has a first dislocation density, and the first A second dislocation region which is a region having a second dislocation density different from the dislocation density of Seen, the second dislocation density is configured to be larger than the first dislocation density.

  According to one aspect of the semiconductor laser of the present invention, the second dislocation density is relatively high in a part of the saturable absorption region that is the active layer region in the optical waveguide region that does not include the active layer current injection region. Since the second dislocation region having the dislocation density can be present, the amount of light absorption in the saturable absorption region can be increased. As a result, a semiconductor laser device that performs a stable self-oscillation operation can be realized.

  Furthermore, in one aspect of the semiconductor laser device according to the present invention, the optical waveguide region in the stacked structure includes an active layer current injection region, which is a region into which the current injected from the second electrode flows into the active layer, and An active layer current non-injection region that is a region different from the active layer current injection region, the active layer current injection region includes the first dislocation region, and the active layer current non-injection region includes the second dislocation. It is preferable to include a region.

  According to this aspect, the optical waveguide region includes the first dislocation region present in the active layer current injection region and the second dislocation region present in the saturable absorption region that is the active layer current non-injection region. become. As a result, a semiconductor laser device that performs a stable self-oscillation operation can be realized.

  Furthermore, in one aspect of the semiconductor laser device according to the present invention, it is preferable that the second dislocation region exists only in one place in the optical waveguide region.

  If there are a plurality of dislocation regions in which dislocations are concentrated in the saturable absorption region, the amount of light absorption is greatly increased, which may increase the threshold current. According to this aspect, a necessary minimum amount of light absorption can be ensured. For example, by disposing the second dislocation region on either the left or right side of the active layer current injection region, it is possible to realize a semiconductor laser device that prevents a significant increase in threshold current and performs stable self-oscillation operation. it can.

  Furthermore, in one aspect of the semiconductor laser device according to the present invention, it is preferable that the second dislocation region exists in a range within 5 μm from the center of the first dislocation region.

  The stable self-oscillation operation is maintained by the balance between the active layer current injection region and the current non-injection region functioning as the saturable absorption region in the optical waveguide region. This balance can be realized by increasing the lateral spread distance of light with respect to the lateral diffusion distance (region where the optical gain is positive) from the current injection region. That is, it depends on the balance between the region where the optical gain is positive and the active layer region where the current in the optical waveguide is not injected, that is, the region where the optical gain is negative.

  Since the leakage of light in the lateral direction as guided light is several μm or less, if the current injection region width is too wide, the proportion of the saturable absorption region is too small relative to the proportion of the positive region. Stable self-oscillation operation cannot be obtained.

  Therefore, as in this embodiment, the distance to the second dislocation region in the current non-injection region in the optical waveguide region is within 5 μm from the center of the first dislocation region, so that Wave light can be absorbed efficiently. As a result, a semiconductor laser device that performs a stable self-oscillation operation can be realized.

Furthermore, in one embodiment of the semiconductor laser device according to the present invention, the second dislocation density is preferably 1 × 10 ⁷ / cm ² or more.

As in this embodiment, the amount of light absorption in the saturable absorption region can be increased by setting the dislocation density in the second dislocation region to 1 × 10 ⁷ / cm ² or more. As a result, carriers generated by light absorption due to an increase in dislocation density are predominantly eliminated by non-radiative recombination. Therefore, it is possible to realize a semiconductor laser device that performs a stable self-oscillation operation. Note that a stable self-oscillation operation is determined by the balance between the light leakage from the current injection region in the lateral direction and the light absorption amount. Further, since the current injection density in the current injection region reaches several kA / cm ² level, it is required that the current injection region has a low dislocation, and the dislocation density is 1 × 10 ⁶ / cm ² or less. It is preferable.

  Furthermore, in one aspect of the semiconductor laser device according to the present invention, the active layer preferably contains indium.

  As in this embodiment, by configuring the active layer to contain In, an emission wavelength from the ultraviolet region to the visible region can be realized. Therefore, the emission wavelength can be freely changed according to the application. Furthermore, since the nitride material containing In is a material that easily segregates In, the In segregated portion has a small band gap energy and efficiently absorbs the light of the guided light in the saturable absorption region. It becomes possible to make it. As a result, a semiconductor laser device that performs a stable self-oscillation operation can be realized.

  Furthermore, in one aspect of the semiconductor laser device according to the present invention, a dislocation control layer is provided between the substrate and the base layer, and the dislocation control layer has a dislocation control layer formed on the dislocation control layer. It is preferable to have a dislocation-concentrating region that can be concentrated.

  According to this aspect, the position of the dislocation concentrated region can be controlled by the dislocation control layer. Thereby, the position of the dislocation region (second dislocation region) in the layer stacked on the dislocation-concentrated region can be freely adjusted laterally with respect to the current injection region. Therefore, the position of the light distribution in the optical waveguide region can be freely controlled, so that the amount of light absorption can be adjusted freely. Therefore, a semiconductor laser device that performs a stable self-oscillation operation can be realized.

  Furthermore, in one aspect of the semiconductor laser device according to the present invention, the dislocation control layer preferably includes a lateral growth layer in which a nitride semiconductor is grown in a direction parallel to the main surface of the substrate.

Thereby, a dislocation concentration possible region can be easily constituted by the lateral growth layer.
Furthermore, in one aspect of the semiconductor laser device according to the present invention, it is preferable that the laterally grown layer is made of Al _x Ga _1-x N (0 ≦ x ≦ 1).

As a result, a part of the dislocation control layer can be made of Al _x Ga _1-x N having a refractive index lower than that of GaN. As a result, the longitudinal light confinement (Γv) in the optical waveguide region is increased. It is possible to reduce the threshold current density by reducing the waveguide loss. Therefore, it is possible to realize a semiconductor laser device that performs a stable self-oscillation operation.

  Furthermore, in one aspect of the semiconductor laser device according to the present invention, the dislocation control layer includes an underlayer seed crystal layer having a plurality of protrusions and a growth layer formed between the protrusions of the plurality of protrusions. The growth layer is formed by joining a first growth layer and a second growth layer grown from the side surfaces of the convex portions facing each other, and the dislocation-concentrated region is formed by the first growth layer and the second growth layer. It is preferable that the region be joined.

  As in this embodiment, by forming the growth layer by joining the first growth layer and the second growth layer grown from the side surface of the convex portion of the base seed crystal layer, the junction region is made a dislocation-concentrated region. be able to. Thereby, the 2nd dislocation area | region which concentrated the dislocation | rearrangement can be formed easily.

  Furthermore, in one aspect of the semiconductor laser device according to the present invention, the dislocation control layer includes an underlayer seed crystal layer having a plurality of protrusions, and a selective growth film formed between the protrusions of the plurality of protrusions. A growth layer formed on the underlayer seed crystal layer and the selective growth film, and the growth layer includes a first growth layer and a second growth layer grown from the top surfaces of the plurality of protrusions. Preferably, the dislocation-concentrated region is a region where the first growth layer and the second growth layer are bonded.

  As in this embodiment, by forming the growth layer by bonding the first growth layer and the second growth layer grown from the upper surface of the convex portion of the base seed crystal layer, the junction region is made a dislocation concentrated region. be able to. Thereby, the 2nd dislocation area | region which concentrated the dislocation | rearrangement can be formed easily.

  Furthermore, in one aspect of the semiconductor laser device according to the present invention, a plurality of convex portions are formed on the substrate, and the dislocation control layer is formed on one side surface of the convex portion for each of the plurality of convex portions. Formed on the underside seed crystal layer, the selective growth film formed on the other side surface of the convex portion for each of the plurality of convex portions, and the underlying seed crystal layer and the selective growth film. A first growth layer grown from one of the plurality of base seed crystal layers and another base different from the one base seed crystal film. It is preferable that the second growth layer grown from the seed crystal layer is joined and formed, and the dislocation concentrated region is a region where the first growth layer and the second growth layer are joined.

  As in this embodiment, by forming the growth layer by bonding the first growth layer and the second growth layer grown from the base seed crystal layer formed on the side surface of the convex portion of the substrate, the junction region is dislocated. It can be set as a concentration possible area. Thereby, the 2nd dislocation area | region which concentrated the dislocation | rearrangement can be formed easily.

Furthermore, in one embodiment of the semiconductor laser device according to the present invention, a part or all of the underlayer is formed of Al _x Ga _1-x N (0 ≦ x ≦ 1) and Al _y Ga _1-y N (0 ≦ y It is preferable to have a laminated structure of ≦ 1, x ≠ y).

  Thereby, it is possible to control the number of dislocations in the dislocation region (second dislocation region) in the layer stacked above the dislocation-concentrated region.

  Furthermore, in one aspect of the semiconductor laser device according to the present invention, the substrate is preferably a sapphire substrate, a Si substrate, or a SiC substrate.

  Low dislocation substrates for laser light sources are very expensive at present, but by using a low-cost sapphire substrate, Si substrate, or SiC substrate as in this embodiment, the cost per element is greatly increased. Can be reduced. As a result, a semiconductor laser device capable of self-oscillation operation at low cost can be realized.

  Furthermore, in one aspect of the semiconductor laser device according to the present invention, it is preferable that a main surface of the multilayer structure is semipolar or nonpolar.

  Conventionally, a semiconductor laser device that performs self-excited oscillation operation on the c-plane (polar plane) has been realized. However, in this case, electrons and holes in the active layer are spatially separated due to the piezo effect, so that the annihilation time of carriers generated by light absorption in the saturable absorption region becomes long. .

  By making the main surface of the semiconductor layer of the stacked structure semi-polar or non-polar as in this embodiment, the piezo effect can be reduced, and electrons and holes are not spatially separated. As a result, the disappearance time of carriers generated by light absorption is accelerated, the time until light absorption is possible can be shortened, and the amount of light absorption per unit time can be increased. Therefore, it is possible to realize a semiconductor laser device that performs a more stable self-excited oscillation operation.

  According to the semiconductor laser device of the present invention, it is possible to shorten the carrier life and promote the time-saturated absorption, thereby realizing a stable self-oscillation operation.

1 is a cross-sectional view showing a structure of a semiconductor laser device according to a first embodiment of the present invention. 1 is a partially enlarged cross-sectional view schematically showing the vicinity of an optical waveguide in a semiconductor laser device according to a first embodiment of the present invention. It is a figure which shows the relationship between a dislocation density and PL light emission intensity. It is sectional drawing of each process in the manufacturing method of the semiconductor laser apparatus concerning the 1st Embodiment of this invention. (A) is a schematic diagram of the base substrate which concerns on 1st Embodiment. (B) is the cross-sectional TEM image which produced the base substrate which concerns on 1st Embodiment, and observed the said base substrate from the m-axis direction. (C) is a cathodoluminescence image obtained by observing the base substrate of (b) from above. It is sectional drawing which shows the structure of the semiconductor laser apparatus which concerns on the 2nd Embodiment of this invention. It is sectional drawing of each process in the manufacturing method of the semiconductor laser apparatus concerning the 2nd Embodiment of this invention. (A) is the cross-sectional TEM image which produced the base substrate which concerns on 2nd Embodiment, and observed the said base substrate from the m-axis direction. (B) is the cathode luminescence image which observed the base substrate of (a) from the upper surface. It is sectional drawing which shows the structure of the semiconductor laser apparatus which concerns on the 3rd Embodiment of this invention. It is sectional drawing of each process in the manufacturing method of the semiconductor laser apparatus concerning the 3rd Embodiment of this invention. It is sectional drawing of the conventional self-oscillation type semiconductor laser apparatus. It is a figure which shows the general relationship between the optical gain G and the injection | pouring carrier density | concentration n in the semiconductor laser apparatus whose active layer is a bulk structure. It is the figure which showed qualitatively the relationship between the number N of quantum wells and the injection carrier density | concentration of an optical gain in the semiconductor laser apparatus whose active layer is MQW structure.

  Hereinafter, a semiconductor laser device according to an embodiment of the present invention will be described in detail with reference to the drawings. Each figure is a schematic diagram for explanation, and the film thickness, the ratio of the size of each part, and the like are not necessarily strict, and the figures may not match each other.

(First embodiment)
First, a semiconductor laser device according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing the structure of a semiconductor laser device according to the first embodiment of the present invention.

  As shown in FIG. 1, a semiconductor laser device 1 according to a first embodiment of the present invention is a self-excited oscillation type semiconductor laser device that performs a self-excited oscillation operation, and is formed on a substrate 110 and a substrate 110. And a first conductivity type (n-type) base layer 114 formed on the base seed crystal layer 111 and the lateral growth layer 112.

  As the substrate 110, for example, a sapphire substrate whose principal surface has a (001) plane orientation can be used.

  The base seed crystal layer 111 is a nitride semiconductor layer made of GaN (gallium nitride) or the like having a concavo-convex structure in which a plurality of stripe-shaped concave portions are formed. The base seed crystal layer 111 includes a plurality of convex portions 111a configured by forming a plurality of concave portions.

  The laterally grown layer 112 is a nitride semiconductor layer made of GaN or the like formed so as to fill the recesses between the protrusions 111 a of the base seed crystal layer 111. The laterally grown layer 112 is obtained by crystal growth in the lateral direction (direction substantially parallel to the main surface of the substrate) from the side surface of the convex portion 111a of the base seed crystal layer 111, and is grown laterally from the side surface of the convex portion 111a facing each other. The direction growth layers 112a and 112b are joined and integrated. A portion where adjacent lateral growth layers 112a and 112b are joined is a joint portion 113a, and a peripheral region including the joint portion 113a is a joint region 113. The junction region 113 functions as a dislocation concentration capable region in which dislocations of a layer formed on the junction region 113 can be concentrated, and the layer formed on the junction region 113 concentrates dislocations and increases the dislocation density. . Further, dislocations are concentrated in the layer formed on the convex portion 111a of the base crystal layer 111, and the dislocation density is increased. In the present embodiment, the laterally grown layer 112 functions as a dislocation control layer having a dislocation concentrated region together with the base seed crystal layer 111.

  The foundation layer 114 is an n-type nitride semiconductor layer formed on the entire surface of the foundation seed crystal layer 111 and the lateral growth layer 112. In the present embodiment, the base layer 114 is composed of n-type GaN doped with Si (silicon) as an impurity.

  Further, as shown in FIG. 1, the semiconductor laser device 1 according to the first embodiment of the present invention has an n-type cladding layer 115, an n-type guide layer 116, an active layer 117, a first layer on a base layer 114. A p-type guide layer 118, a carrier overflow suppression layer 119, and a p-type cladding layer 120, which are second conductivity types (p-type) different from the conductivity type, are sequentially stacked. These layers are a laminated structure made of a nitride semiconductor.

The n-type cladding layer 115 is an n-type nitride semiconductor layer formed on the base layer 114, and can be made of, for example, Al _0.05 Ga _0.95 N doped with an n-type impurity such as Si.

  The n-type guide layer 116 is an n-type nitride semiconductor layer formed on the n-type cladding layer 115, and can be composed of, for example, GaN doped with an n-type impurity such as Si.

The active layer 117 is formed on the n-type guide layer 116 and is, for example, an active layer having a multiple quantum well structure including a barrier layer made of In _0.02 Ga _0.98 N and a well layer made of In _0.06 Ga _0.94 N.

  The p-type guide layer 118 is a p-type nitride semiconductor layer formed on the active layer 117, and can be composed of, for example, GaN doped with a p-type impurity such as Mg (magnesium).

The carrier overflow suppression layer 119 is a nitride semiconductor layer formed on the p-type guide layer 118 and can be composed of, for example, Al _0.20 Ga _0.80 N.

The p-type cladding layer 120 is a p-type nitride semiconductor layer formed on the carrier overflow suppression layer 119. For example, p-type Al _0.10 Ga _0.90 N and p-type GaN are laminated repeatedly several times. The nitride semiconductor layer can be formed of a formed strained superlattice structure. The p-type cladding layer 120 has a ridge portion 120a having a stripe shape in a top view and a convex cross section.

  Further, a p-type contact layer 122 and a p-side electrode 123 (second electrode) are formed on the ridge portion 120 a of the p-type cladding layer 120, and the p-side electrode 123 is electrically connected to the p-type contact layer 122. It is connected. A dielectric film 121 is formed on the region of the p-type cladding layer 120 where the ridge portion 120a is not formed. In addition, the base layer 114 is exposed in the opening from which the stacked structure is removed, and an n-side electrode 124 (first electrode) is formed on the base layer 114. The n-side electrode 124 is electrically connected to the n-type cladding layer 115 through the base layer 114.

  The ridge portion 120a in which the p-type contact layer 122 and the p-side electrode 123 are formed is a region for injecting current into the active layer 117, and the region below the p-side electrode 123 and the ridge portion 120a and its peripheral region are currents. This is an implantation region 130.

In the present embodiment, the p-type contact layer 122 can be composed of GaN doped with a p-type impurity such as Mg (magnesium), for example. The dielectric film 121 can be made of SiO ₂ . The p-side electrode 123 can be composed of a laminated metal film of palladium (Pd) and platinum (Pt), and the n-side electrode 124 is a laminated film of Ti (titanium), platinum (Pt), and gold (Au). It can be constituted by a metal film.

  In the semiconductor laser device 1 according to the first embodiment of the present invention, as described above, the laterally grown layers 112a and 112b adjacent to each other in the concave portion of the base seed crystal layer 111 are joined to form the junction region 113. . In the stacked structure formed on the junction region 113, a strip-shaped dislocation region 141 is formed from the dielectric film 121 to the junction region 113. That is, a layer that grows on the junction region 113 in the lateral growth layer 112 is formed so that dislocations are concentrated by the junction portion 113 a of the junction region 113.

  On the other hand, the layer grown on the laterally grown layer 112 where the junction region 113 is not formed is formed without concentration of dislocations, and a region with low dislocations is formed on this portion.

  In addition, dislocations are concentrated on a region where the base layer 114 is formed directly on the convex portion 111 a of the base seed crystal layer 111, and a band-shaped dislocation region extends from the dielectric film 121 to the base seed crystal layer 111. 151 is formed. That is, the convex portion 111a of the base seed crystal layer 111 also functions as a dislocation concentration region. As described above, in the semiconductor laser device 1 according to the present embodiment, the strip-shaped dislocation regions 141 and 151 having a dislocation density larger than that of other portions are formed.

  Next, the operation of the semiconductor laser device 1 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 2 is a partially enlarged cross-sectional view schematically showing the vicinity of the optical waveguide in the semiconductor laser device according to the first embodiment of the present invention.

  In FIG. 2, an elliptical area indicated by a broken line indicates the optical waveguide area 160 of the semiconductor laser device 1. The optical waveguide region 160 includes an active layer current injection region where the current injected from the p-side electrode 123 flows into the active layer 117 and an active layer current non-injection region which is a region different from the active layer current injection region. Contains.

  As shown in FIG. 2, in the present embodiment, in the region below the p-side electrode 123, that is, the region below the ridge 120a of the p-type cladding layer 120 and the current injection region 130 that is the peripheral region thereof, the optical waveguide region The current is squeezed by the current squeezing structure in 160 to greatly change the current distribution 170 and the light distribution in the optical waveguide region 160.

  That is, a region where the current distribution 170 in the active layer 117 is wide is a low dislocation region having a low dislocation density. A neighboring region 140 that is a peripheral region of the current injection region 130 and includes the band-shaped dislocation region 141 is a region where the current distribution 170 is not expanded in the optical waveguide region 160 and functions as a saturable absorption region. . That is, the optical waveguide region 160 in the current injection region 130 is an active layer current injection region, and the optical waveguide region 160 in the vicinity region 140 is an active layer non-current injection region.

  The neighboring region 140 is a region on the bonding region 113 in FIG. In the belt-like dislocation region 141 (second dislocation region) in the neighboring region 140, the belt-like dislocations are formed in a band shape parallel to the optical waveguide (perpendicular to the paper surface) and perpendicular to the substrate. Since the light in the optical waveguide region 160 is absorbed by the band-shaped dislocation region 141, the non-radiative recombination component can be increased with respect to the generated carriers to shorten the lifetime of the carriers. As a result, the amount of light absorption that promotes the temporal recovery of saturable absorption can be increased, and a stable self-oscillation operation can be realized.

  In the semiconductor laser device 1 according to the present embodiment configured as described above, the dislocation density in the current injection region 130, particularly, the dislocation density in the active layer injection region is the first dislocation density a, and the dislocation in the neighboring region 140 is If the density, in particular, the dislocation density in the band-shaped dislocation region 141 in the active layer non-current injection region is the second dislocation density b, the relationship between the first dislocation density a and the second dislocation density b is a <b. The second dislocation density is larger than the first dislocation density. Note that the neighboring region 150 including the strip-shaped dislocation region 151 is similar to the neighboring region 140, and the strip-shaped dislocation region 151 functions as a saturable absorption region that increases the amount of light absorption.

  Here, the relationship between dislocations and non-radiative recombination components of carriers will be described with reference to FIG. FIG. 3 is a diagram showing the relationship between dislocation density and PL (Photo Luminescence) emission intensity. Note that FIG. 3 has already been investigated and reported in the literature (Appl. Phys. Lett., 76, p, 2000). In FIG. 3, the horizontal axis represents dislocation density, and the vertical axis represents PL emission intensity.

As shown in FIG. 3, it can be seen that when the dislocation density is 10 ⁷ / cm ⁻² or more, the PL emission intensity rapidly decreases. This is because the emission recombination component in the excited carrier was dominant at the beginning, but by increasing the dislocation density, the carrier disappears through the dislocation and the non-light emission recombination component increases, and PL emission It shows that the strength has decreased.

  Therefore, according to the semiconductor laser device 1 according to the first embodiment of the present invention, dislocations are concentrated in the optical waveguide region 160 and arranged in the vicinity region 140 that is the peripheral region of the current injection region 130. That is, the amount of light absorption can be increased efficiently by disposing the dislocation region in the saturable absorption region.

  In the present embodiment, two dislocation regions 141 and 151 are formed in the optical waveguide region 160 (in the saturable absorption region) of the neighboring region 140 as the band-shaped dislocation region (second dislocation region). It is not limited to. If there are a plurality of dislocation regions in which dislocations are concentrated in the saturable absorption region, the amount of light absorption increases significantly, which may increase the threshold current. In this case, the band-shaped dislocation region may be configured to exist only in one place in the optical waveguide region 160, for example, only in the vicinity region 140 or 150. That is, the number of dislocation regions and the dislocation density may be set so that a desired light absorption amount is obtained.

  Next, a method for manufacturing the semiconductor laser device 1 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 4 is a cross-sectional view of each step in the method of manufacturing the semiconductor laser device according to the first embodiment of the present invention.

First, as shown in FIG. 4A, a base seed crystal made of GaN having a film thickness of 3.0 μm is formed on the main surface of a substrate 110 made of a sapphire substrate whose plane orientation is (001). Layer 111 is formed. The crystal growth of the base seed crystal layer 111 was performed by a metal organic chemical vapor deposition (MOCVD) method. More specifically, trimethylgallium (TMG) was used as a gallium (Ga) raw material, and ammonia (NH ₃ ) was used as a nitrogen (N) raw material. The growth temperature was about 1000 ° C.

Thereafter, a 600 nm-thick silicon oxide (SiO ₂ ) film is formed on the underlying seed crystal layer 111 by a thermal chemical vapor deposition (TCVD) method using silane (SiH ₄ ) as a raw material. To do.

  Thereafter, by patterning silicon oxide by lithography and etching, a plurality of stripe-shaped mask films M10 having a width of 5 μm in the a-axis direction and parallel to the m-axis are formed as shown in FIG. 4B. To do. A stripe-shaped opening having a width of, for example, 6 μm in the a-axis direction is formed between the adjacent mask films M10. That is, silicon oxide is not formed in the opening, and the GaN of the seed crystal layer 111 is exposed. If the crystal orientations of the substrate 110 and the laminated structure are c, a, and m, the c-axis is a normal vector with a (0001) plane and the a-axis has a (11-20) plane. It is a normal vector, and the m-axis is a normal vector whose plane orientation is (1-100) plane.

Next, as shown in FIG. 4C, the mask film M10 is etched by etching with an inductively coupled plasma (ICP) etching apparatus using carbon tetrafluoride (CF ₄ ) as an etching gas. A plurality of recesses having a depth of 1.8 μm are formed in the base seed crystal layer 111 through the plurality of openings. Thereby, a plurality of convex portions 111 a can be formed in the base seed crystal layer 111.

  Thereafter, by removing the mask film M10 using hydrofluoric acid (HF), as shown in FIG. 4D, the base substrate on which the base seed crystal layer 111 having the concavo-convex structure is formed can be formed. it can. In addition, the convex part 111a (concave part) of the base seed crystal layer 111 has a stripe shape extending in the m-axis direction.

Next, using this base substrate, GaN crystal growth is performed by MOCVD. In this case, the substrate 110 on which the base seed crystal layer 111 having the concavo-convex structure is formed is put into a MOCVD apparatus reactor, and the temperature is raised to 800 ° C. in an ammonia gas atmosphere which is a nitrogen raw material of N ₂ gas and GaN crystal. carry out. Thereafter, the nitrogen raw material is changed from ammonia (NH ₃ ) to dimethylhydrazine (DMHy), and GaN is grown as a growth layer. At this time, the growth layer of GaN selectively grows from each side surface of the convex portion 111 a of the base seed crystal layer 111. At this time, the crystal growth temperature is about 800 ° C., and the supply of ammonia is stopped.

  The growth of GaN by DMHy can realize a special growth mode as compared with the growth of GaN by ammonia. In this embodiment, the growth of GaN is started only from the side surface of the convex portion 111a which is a seed crystal, and GaN can be crystal-grown only in the lateral direction (substantially parallel to the substrate main surface). Note that the semiconductor layer grown only in the lateral direction is called a lateral epitaxial growth layer, and in this embodiment, the semiconductor layer is referred to as the lateral growth layer 112. The lateral growth layer 112 can be grown at a high crystal growth rate of about 10 μm / h by setting a large flow rate of DMHy, and in spite of such a high crystal growth rate. High quality crystallinity is maintained. The crystal plane orientation of the lateral growth layer 112 is the same as the plane orientation of the side surface of the convex portion 111a of the base seed crystal layer 111 which is a seed crystal. Thus, since the laterally grown layer 112 grown by DMHy grows only in the lateral direction, all the dislocations at the interface between the convex side surface of the base seed crystal layer 111 and GaN are laterally (substantially with respect to the main surface of the substrate). Bend in the parallel direction).

  The lateral growth layer 112 that has started growing in the lateral direction from the convex side surface of the base seed crystal layer 111 is grown until the lateral growth layers 112a and 112b grown from the opposing convex side surface are connected. Thereby, as shown in FIG. 4E, the space between the convex portions 111 a (concave portions) of the base seed crystal layer 111 is filled with the lateral growth layer 112. At this time, the adjacent laterally grown layers 112a and 112b are connected and united.

In the present embodiment, as described above, a large flow rate of DMHy is set as the growth condition of the lateral growth layer 112 made of GaN. Thereby, carbon (C) contained in DMHy is intentionally (positively) taken into the lateral growth layer 112. The carbon actively taken into the laterally grown layer 112 has a function of increasing the lattice constant of the layer formed thereon. Here, the carbon concentration of the laterally grown layer 112 is, for example, about 1 × 10 ¹⁹ cm ⁻³ to 5 × 10 ²⁰ cm ⁻³ .

Furthermore, by using DMHy as the nitrogen source of the lateral growth layer 112, the hydrogen (H) concentration in the lateral growth region can be reduced. This is because an unstable methyl (CH ₃ ) group can be liberated in the thermal decomposition process of DMHy, and this is stabilized as methane (CH ₄ ), so that it can be efficiently combined with hydrogen on the surface. It is. As a result, the hydrogen concentration in the lateral growth layer 112 can be further reduced as compared with other nitride semiconductor layers such as the foundation layer 114 grown on the lateral growth layer 112. Thereby, since the diffusion of hydrogen in the active layer 117 can be efficiently suppressed, the operating voltage of the semiconductor laser device 1 can be stabilized.

Next, the nitrogen raw material of GaN is returned from dimethylhydrazine (DMHy) to ammonia (NH ₃ ), and the temperature is raised to 1100 ° C., so that the group III raw material TMG and the n-type doping material monosilane (SiH ₄ ) 4 (f), an n-type underlayer made of n-GaN having a thickness of 2 μm is formed on the upper surface of the convex portion 111a of the underlayer seed crystal layer 111 and the upper surface of the lateral growth layer 112, as shown in FIG. 114 crystals are grown. At this time, the base layer 114 grows in the c-axis direction.

  Further, in this case, dislocations concentrate in the base layer 114 immediately above the protrusions 111a of the base seed crystal layer 111 and immediately above the junction region 113 where the adjacent lateral growth layers 112a and 211b are joined. The direction of the dislocation is a direction perpendicular to the upper surface of the convex portion 111 a of the base seed crystal layer 111 and the upper surface of the bonding region 113. As described above, a region having a high dislocation density is formed on the convex portion 111 a and the bonding region 113 of the base seed crystal layer 111. On the other hand, a low-dislocation region is formed on the lateral growth layer 112 other than the convex portion 111 a of the base seed crystal layer 111 and the junction region 113.

  Next, as shown in FIG. 4G, a layered structure is formed on the base layer 114 by sequentially crystal-growing each layer of the layered structure made of a nitride semiconductor layer by MOCVD.

Specifically, an n-type cladding layer 115 made of n-type Al _0.05 Ga _0.95 N having a thickness of 1.5 μm is grown on the base layer 114, and then made of n-type GaN having a thickness of 0.1 μm. An n-type guide layer 116 is grown. Thereafter, a quantum well structure consisting of a barrier layer made of In _0.02 Ga _0.98 N having a thickness of 7.5 nm and a well layer made of In _0.06 Ga _0.94 N having a thickness of 3 nm is formed on the n-type guide layer 116 for five periods. A split active layer 117 is grown.

Next, a p-type guide layer 118 made of p-type GaN having a thickness of 0.1 μm is grown on the active layer 117. Thereafter, a carrier overflow suppression layer 119 made of Al _0.20 Ga _0.80 N having a thickness of 10 nm is grown, and then p-type Al _0.10 Ga _0.90 N having a thickness of 1.5 nm and p-type GaN having a thickness of 1.5 nm. Are repeated for 160 cycles to grow a p-type cladding layer 120 having a strained superlattice structure. Thereafter, a p-type contact layer 122 made of p-type GaN having a thickness of 0.05 μm is grown.

In addition, as a III group material at the time of using said MOCVD method, trimethyl gallium (TMG) was used as Ga material, trimethyl aluminum (TMA) was used as Al material, and trimethyl indium was used as In material. . In addition, ammonia (NH ₃ ) was used as the Group V raw material. Further, Si is used as the n-type impurity material, monosilane (SiH ₄ ) gas is used as the material, Mg is used as the p-type impurity material, and biscyclopentadienyl magnesium (Cp ₂ ) is used as the material. Mg) was used.

Next, as shown in FIG. 4G, a stripe shape parallel to the m-axis direction having a film thickness of 0.3 μm and a width of 1.5 μm is formed on the p-type contact layer 122 by thermal CVD. A mask M11 made of silicon oxide (SiO ₂ ) is selectively formed. The silicon oxide is formed in the m-axis direction so as to be within a range of, for example, about 3 μm from the junction portion 113a of the lateral growth layer 112 in the lateral direction and not directly above the junction region 113. .

  As described above, the layer formed on the base layer 114 including the region where the dislocations are concentrated inherits the crystallinity of the underlying layer. Therefore, the portion of the base layer 114 on the region where the dislocations are concentrated is A region where dislocations are concentrated is formed, and a band-like dislocation region is formed in the stacked structure.

Next, as shown in FIG. 4 (h), the upper part of the p-type cladding layer 120 is etched to a depth of, for example, 0.35 μm by the ICP method using the silicon oxide as a mask. 120a is formed. Thereafter, the silicon oxide mask M11 is removed using hydrofluoric acid, and the SiO 2 film having a thickness of 200 nm is formed on the entire surface including the ridge portion 120a on the p-type cladding layer 120 exposed again by the thermal CVD method. _A dielectric film 121 made of 2 is formed. Next, a resist pattern having an opening having a width of 1.3 μm is formed along the stripe shape of the ridge 120a on the dielectric film 121 on the upper surface of the ridge 120a by lithography. Thereafter, the reactive ion etching (RIE) using trifluoromethane (CHF ₃ ) gas is used to etch away the dielectric film 121 on the ridge portion 120a using the resist pattern as a mask. The p-type contact layer 122 is exposed from the upper surface.

  Next, a metal laminated film made of palladium (Pd) having a thickness of 40 nm and platinum (Pt) having a thickness of 35 nm is formed on at least the p-type contact layer 122 exposed from the upper surface of the ridge 120a by vapor deposition. Form. Thereafter, the resist pattern is removed by a lift-off method, and a p-side electrode 123 is formed as shown in FIG.

  Next, a wiring electrode having a width of 150 μm is formed on the dielectric film 121 so as to cover the p-side electrode 123 on the upper portion of the ridge portion 120a and in a direction parallel to the stripe direction of the ridge portion 120a by lithography and lift-off methods. Are selectively formed. The wiring electrode is formed of a laminated metal film made of titanium (Ti) / platinum (Pt) / gold (Au) having a thickness of 50 nm, 200 nm, or 100 nm. Thereafter, the thickness of the Au layer is increased to about 10 μm by electrolytic plating to form a pad electrode. Thereafter, adjacent chips are separated. At this time, if the pad electrode is continuously connected to the adjacent chip, electrode separation occurs when the chip is separated. Therefore, the pad electrode is separated for each chip. It is preferable.

Next, the n-side electrode 124 is formed. First, a mask made of SiO ₂ is formed by a thermal CVD method in the region where the pad electrode is formed. Thereafter, a resist having an opening in the vicinity of the ridge portion 120a and in parallel with the stripe direction of the ridge portion 120a, and further in a region without the pad electrode, is formed by a lithography method and a lift-off method. Thereafter, the underlying structure 114 is exposed by etching the laminated structure at the opening to a depth of about 2.5 μm from above by ICP. Thereafter, the n-side electrode 124 is formed on the base layer 114. The n-side electrode 124 is manufactured by forming and patterning a metal laminated film made of Ti / Pt / Au having thicknesses of 5 nm, 10 nm, and 1000 nm, respectively.

  Thereafter, the resist and dielectric film 121 on the pad electrode are removed. Next, the back surface of the substrate 110 is polished, and the substrate 110 is thinned until the thickness becomes about 100 μm. Next, primary cleavage of the substrate is performed along the m-plane direction so that the length in the m-axis direction is 400 μm. Thereafter, the substrate that has been primarily cleaved is cleaved along the a-plane direction so that the length in the a-axis direction becomes 200 μm and separated into chips.

  As described above, the semiconductor laser device 1 according to the first embodiment of the present invention can be manufactured.

  Next, an example of the semiconductor laser device 1 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 5A corresponds to FIG. 4F, and shows a state of the base substrate in which the base seed crystal layer 111 and the lateral growth layer 112 are formed on the substrate 110 and the base layer 114 is formed thereon. It is a schematic diagram. FIG. 5B is a cross-sectional TEM image in which the base substrate shown in FIG. 5A is manufactured and the base substrate is observed from the m-axis direction. FIG. 5C is a cathode luminescence image (CL image) obtained by observing the base substrate of FIG. 5B from the upper surface. In the experiment of the present embodiment, the width of the stripe-shaped opening is 20 μm, but the width of the opening can be freely changed according to the pattern of the mask film M10, and the same result is obtained even in the width of different openings. Is obtained. In this embodiment, the base layer 114 having a thickness of 1.5 μm is formed on the substrate 110 by the method described with reference to FIG.

  As shown in FIG. 5B, it can be seen that the dislocation direction of the base seed crystal layer 111 extends in the (0001) plane direction. On the other hand, the lateral growth layer 112 grown by DMHy grows only in the lateral direction, and all dislocations at the interface with the convex side surface of the base seed crystal layer 111 are lateral (direction parallel to the substrate main surface). It can be seen that it is bent in the (11-20) direction.

  Further, as shown in FIG. 5B, it can be seen that the dislocations in the base layer 114 are concentrated immediately above the convex portions 111 a of the base seed crystal layer 111. It can also be seen that the dislocations of the underlying layer 114 in the portion immediately above the laterally grown layer 112 are regions with a low dislocation.

  Further, as shown in FIG. 5C, dislocations are band-like in the region 111b immediately above the convex portion 111a of the base seed crystal layer 111 and the junction region 113 in which the adjacent lateral growth layers 112a and 112b are combined. It can be seen that the dislocations are controlled by being concentrated as dark spots. It can also be seen that dislocations are not concentrated in the region between the region 111b immediately above the convex portion 111a and the junction region 113 in the base seed crystal layer 111, and a region with reduced dislocations is formed.

  As described above, by using the dislocation control technique according to this embodiment, dislocations can be concentrated in a band shape, a low dislocation region can be formed, and the dislocation arrangement can be freely controlled.

  As described above, according to the semiconductor laser device 1 according to the first embodiment of the present invention, by utilizing the difference between the current diffusion length and the light distribution in the optical waveguide and disposing the dislocations as desired, the saturable absorption amount can be reduced. Can be increased. By disposing the band-shaped dislocation region in the optical waveguide and in the region where current is not diffused, only the amount of light absorption can be easily increased, and a self-oscillation type that performs stable self-oscillation operation. A semiconductor laser device can be realized. As a result, it is possible to reduce the return light noise and the speckle noise. In addition, the cost of the semiconductor laser device can be reduced by using a sapphire substrate having a large area at a low cost instead of an expensive GaN substrate conventionally used.

  In the present embodiment, a sapphire substrate is used as the substrate 110, but is not limited thereto. For example, even if it is a low-cost SiC substrate or a Si substrate, a semiconductor laser device having the same effect can be manufactured by the same process. By using these substrates, the cost can be reduced by further increasing the area. Is possible.

In the present embodiment, as the active layer 117, the n-type guide layer 116, and the p-type guide layer 118, a barrier layer made of In _0.02 Ga _0.98 N and In _0.06 Ga _0.94 N are used so as to be suitable for an optical disk light source. An active layer having a multiple quantum well structure with a well layer made of, n-type GaN and p-type GaN, and an emission wavelength of around 405 nm are not limited thereto. For example, the semiconductor laser device according to this embodiment can be used as a semiconductor laser device for display. In the semiconductor laser device for display, the emission wavelength is preferably blue (wavelength 450 nm) to green (wavelength 530 nm). In order to realize this emission wavelength, the well layer of the active layer 117 has an In composition. An InGaN layer having a composition of 10% to 20% or more is preferable. The n-type guide layer 116 and / or the p-type guide layer 118 are preferably n-type or p-type InGaN layers, respectively, in order to increase optical confinement.

  In addition to the n-type GaN, the underlayer 114 may be an n-type AlGaN layer, an n-type AlGaN, or an AlN / GaN superlattice growth layer.

  In the present embodiment, the carrier overflow suppression layer 119 is formed on the p-type guide layer 118. However, a carrier overflow suppression layer is formed on the active layer 117, and the p-type is further formed thereon. You may make it the structure of forming a guide layer.

(Second Embodiment)
Next, a semiconductor laser device 2 according to a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a cross-sectional view showing the structure of a semiconductor laser device according to the second embodiment of the present invention.

  The semiconductor laser device 2 according to the second embodiment of the present invention is a self-excited oscillation type semiconductor laser device, as in the first embodiment. The semiconductor laser device 2 according to the second embodiment of the present invention differs from the semiconductor laser device 1 according to the first embodiment of the present invention in the structure of the base substrate. Other components are basically the same.

  As shown in FIG. 6, the semiconductor laser device 2 according to the second embodiment of the present invention includes a substrate 210, a base seed crystal layer 211 and a selective growth dielectric film 225 formed on the substrate 210, A direction growth layer 212 and an n-type underlayer 214 are provided.

  As the substrate 210, for example, a sapphire substrate whose principal surface has a (001) plane orientation can be used.

  The base seed crystal layer 211 is a nitride semiconductor layer made of GaN (gallium nitride) or the like having a concavo-convex structure in which a plurality of stripe-shaped concave portions are formed. The base seed crystal layer 211 includes a plurality of convex portions 211a configured by forming a plurality of concave portions.

The selective growth dielectric film 225 is a selective growth film for selecting the growth direction of the lateral growth layer 212 and is formed so as to fill the concave portion of the base seed crystal layer 211. In this embodiment, a dielectric film made of SiO ₂ is used as the selective growth dielectric film 225.

  The lateral growth layer 212 is a nitride semiconductor layer made of GaN or the like formed on the entire surface of the base seed crystal layer 211 and the selective growth dielectric film 225. The lateral growth layer 212 is grown from the upper surface of the convex portion 211a of the base seed crystal layer 211 by the selective growth dielectric film 225, and is grown in the lateral direction (direction substantially parallel to the substrate main surface). Is. The lateral growth layer 212 is formed by joining and integrating the lateral growth layers 212a and 212b grown from adjacent convex portions 211a. A portion where the adjacent lateral growth layer 212a and lateral growth layer 212b are combined is a joint portion 213a, and a peripheral region including the joint portion 213a is a joint region 213. The junction region 213 functions as a dislocation concentration capable region in which dislocations of the layer formed on the junction region 213 can be concentrated, and the layer formed on the junction region 213 concentrates dislocations and increases the dislocation density. . Further, dislocations are concentrated in the layer formed on the convex portion 211a of the base crystal layer 211, and the dislocation density is increased. In the present embodiment, the lateral growth layer 212 functions as a dislocation control layer having a dislocation concentration region together with the base seed crystal layer 211 and the selective growth dielectric film 225.

  The underlayer 214 is an n-type nitride semiconductor layer formed on the entire surface of the lateral growth layer 212. In the present embodiment, the base layer 214 is composed of n-type GaN doped with Si (silicon) as an impurity.

  Further, as shown in FIG. 6, the semiconductor laser device 2 according to the second embodiment of the present invention has an n-type cladding layer 215, an n-type guide layer 216, an active layer 217, a p-type on the base layer 214. A guide layer 218, a carrier overflow suppression layer 219, and a p-type cladding layer 220 are sequentially stacked. These layers are a laminated structure made of a nitride semiconductor. Each layer of the underlayer 214, the n-type cladding layer 215, the n-type guide layer 216, the active layer 217, the p-type guide layer 218, the carrier overflow suppression layer 219, and the p-type cladding layer 220 is the underlayer in the first embodiment. 114, the n-type cladding layer 115, the n-type guide layer 116, the active layer 117, the p-type guide layer 118, the carrier overflow suppression layer 119, and the p-type cladding layer 120.

  The p-type cladding layer 220 has a ridge portion 220a having a stripe shape in a top view and a convex section, and a p-type contact layer 222 and a p-side electrode 223 (second electrode) are formed on the ridge portion 220a. Yes. As a result, the p-side electrode 223 is electrically connected to the p-type contact layer 222.

  A dielectric film 221 is formed on the region of the p-type cladding layer 220 where the ridge 220a is not formed. In addition, the base layer 214 is exposed in the opening from which the stacked structure is removed, and an n-side electrode 224 (first electrode) is formed on the base layer 214. The n-side electrode 224 is electrically connected to the n-type cladding layer 215 through the base layer 214.

  The ridge portion 220a in which the p-type contact layer 222 and the p-side electrode 223 are formed is a region for injecting current into the active layer 217, and the region below the p-side electrode 223 and the ridge portion 220a and its peripheral region are currents. This is an implantation region 230.

  The dielectric film 221, the p-type contact layer 222, the p-side electrode 223, and the n-side electrode 224 are the dielectric film 121, the p-type contact layer 122, the p-side electrode 123, and the n-side electrode in the first embodiment. It can be configured in the same manner as 124.

  In the semiconductor laser device 2 according to the second embodiment of the present invention, as described above, the selective growth dielectric film 225 is formed in the recess of the base seed crystal layer 211, and the surface is convex of the base seed crystal layer 211. A base substrate composed of the upper surface of the portion 211a and the selective growth dielectric film 225 is used. As a result, the laterally grown layer 212 formed thereon is formed by joining the laterally grown layers 212a and 212b grown from the upper surface of the adjacent convex portion 211a of the base seed crystal layer 211. In the stacked structure formed on the junction region 213, a band-shaped dislocation region 241 is formed from the dielectric film 221 to the junction region 213. That is, a layer that grows on the junction region 213 in the lateral growth layer 212 is formed such that dislocations are concentrated by the junction portion 213a of the junction region 213.

  On the other hand, the laterally grown layer 212 in which the junction region 213 is not formed and grown on the selective growth dielectric film 225 is formed without concentration of dislocations, and the dislocations are lowered on this portion. Areas are formed.

  In addition, a region where dislocations are concentrated is formed also in the lateral growth layer 212 formed on the convex portion 211a of the base seed crystal layer 211 and the base layer 214 thereabove, and the band-like dislocation region 251 is the base seed crystal. A laterally grown layer 212 and an underlayer 214 are formed on the convex portion 211 a of the layer 211.

  As described above, also in the semiconductor laser device 2 according to the present embodiment, as in the first embodiment, the band-shaped dislocation region 241 having a dislocation density larger than that of other portions is formed. Similarly to the first embodiment, in the semiconductor laser device 2 according to the present embodiment, the dislocation density in the current injection region 230, in particular, the dislocation density in the active layer injection region is the first dislocation density a, If the dislocation density in the region near the current injection region 230, particularly the dislocation density in the band-shaped dislocation region 241 in the non-current injection region of the active layer is the second dislocation density b, the first dislocation density a and the second dislocation. The relationship of density b is a <b, and the second dislocation density is larger than the first dislocation density.

  Therefore, the semiconductor laser device 2 according to the present embodiment also exhibits the same operational effects as those of the semiconductor laser device 1 according to the first embodiment of the present invention described above.

  In this embodiment, unlike the first embodiment, the dislocation region 241 is formed only in one of the vicinity of the ridge portion 220a, but this is not restrictive. Similar to the first embodiment, dislocation regions may be arranged on both sides of the ridge 220a.

  Next, a method for manufacturing the semiconductor laser device 2 according to the second embodiment of the present invention will be described with reference to FIG. FIG. 7 is a cross-sectional view of each step in the method of manufacturing a semiconductor laser device according to the second embodiment of the present invention.

First, as shown in FIG. 7A, an underlying seed crystal made of GaN having a film thickness of 3.0 μm is formed on a main surface of a substrate 210 made of a sapphire substrate whose plane orientation is (001). Layer 211 is formed. Note that the crystal growth of the base seed crystal layer 211 was performed by the MOCVD method. More specifically, as in the first embodiment, TMG and NH ₃ were used as raw materials for Ga and N, respectively. The growth temperature was about 1000 ° C.

Thereafter, silicon oxide (SiO ₂ ) having a thickness of 600 nm is formed on the base seed crystal layer 211 by TCVD using silane (SiH ₄ ) as a raw material.

  Thereafter, silicon oxide is patterned by lithography and etching, thereby forming a plurality of stripe-shaped mask films M20 having a width of 3 μm parallel to the m-axis and 3 μm in the a-axis direction, as shown in FIG. 7B. To do. A stripe-shaped opening having a width of, for example, 2 to 10 μm in the a-axis direction is formed between the adjacent mask films M20. That is, no silicon oxide is formed in the opening, and the GaN of the seed crystal layer 211 is exposed.

Next, as shown in FIG. 7C, by etching with an ICP etching apparatus using carbon tetrafluoride (CF ₄ ) as an etching gas, the underlying seed crystal layer is passed through a plurality of openings of the mask film M20. A plurality of recesses having a depth of, for example, 1.8 μm are formed in 211. Thereby, a plurality of convex portions 211 a can be formed in the base seed crystal layer 211.

  Thereafter, by removing the mask film M20 using hydrofluoric acid (HF), as shown in FIG. 7D, a base substrate on which the base seed crystal layer 211 having a concavo-convex structure is formed can be formed. it can. In addition, the recessed part (convex part) of the base seed crystal layer 211 has a stripe shape extending in the m-axis direction.

Next, SiO ₂ is formed on the surface of the concavo-convex structure of the base seed crystal layer 211 by a thermal CVD method, and then the SiO ₂ is patterned by a lithography method and an etching method. As a result, as shown in FIG. 7E, a selective growth dielectric film 225 made of SiO ₂ formed so as to be embedded in the concave portion of the base seed crystal layer 211 can be obtained. At this time, SiO ₂ is not formed on the convex portion 211a of the base seed crystal layer 211, and the upper surface of the convex portion 211a is exposed.

Next, using the base substrate thus formed, GaN crystal growth is performed by MOCVD. In this case, the base substrate is put into a MOCVD apparatus reactor, and the temperature is raised to 1100 ° C. in an ammonia gas atmosphere which is a nitrogen raw material of N ₂ gas and GaN crystal. Thereafter, TMG which is a group III raw material is flown to grow a crystal made of GaN.

  At this time, the upper surface of the convex portion 211a of the base seed crystal layer 211 is the (0001) plane, and GaN starts crystal growth selectively from the upper surface of the convex portion 211a. Then, by adjusting the growth rate, the group V flow rate, and the V / III ratio, which is the molar concentration ratio of the group V raw material and the group III raw material, which are the epi conditions, The growth rate and the growth rate in the (11-20) plane direction which is the lateral direction (the direction parallel to the main surface of the substrate) are controlled. Thereby, the growth in the (11-20) plane direction is promoted, and the growth is performed until the adjacent lateral growth layers 212a and 212b are in contact with each other. As a result, as shown in FIG. 7F, the adjacent lateral growth layers 212a and 212b are joined together to form a joint portion 213a, and the lateral growth layer 212 having the joint region 213 can be formed.

Next, the growth temperature is maintained as it is, the growth rate which is an epi condition is increased, the V group flow rate is decreased, and the V / III ratio which is the molar concentration ratio of the V group raw material and the III group raw material is decreased. By adjusting, it is changed to the condition that the growth of GaN is promoted in the (0001) plane direction which is the substrate main surface direction. Then, TMG as a group III material and monosilane (SiH ₄ ) as an n-type doping material are introduced, and as shown in FIG. 7G, an n-type underlayer 214 made of n-GaN having a thickness of 2 μm. Crystal growth.

  In this case, dislocations concentrate on the base layer 214 immediately above the protrusions 211a of the base seed crystal layer 211 and immediately above the junction region 213 where the adjacent lateral growth layers 212a and 212b are joined. The direction of the dislocation is a direction perpendicular to the upper surface of the convex portion 211 a of the base seed crystal layer 211 and the upper surface of the bonding region 213. As described above, a region having a high dislocation density is formed on the convex portion 211 a and the junction region 213 of the base seed crystal layer 211. On the other hand, a low-dislocation region is formed on the lateral growth layer 212 other than the convex portion 211 a and the junction region 213 of the base seed crystal layer 211. Note that the base layer 214 is formed on the entire surface of the substrate 210.

  Next, as shown in FIG. 7 (h), the stacked structure is formed on the base layer 214 by sequentially crystal-growing each layer of the stacked structure made of nitride semiconductor layers by MOCVD.

Specifically, an n-type cladding layer 215 made of n-type Al _0.05 Ga _0.95 N having a thickness of 1.5 μm is grown on the base layer 214, and then made of n-type GaN having a thickness of 0.1 μm. An n-type guide layer 216 is grown. Thereafter, a quantum well structure composed of a barrier layer made of In _0.02 Ga _0.98 N having a thickness of 7.5 nm and a well layer made of In _0.06 Ga _0.94 N having a thickness of 3 nm is formed on the n-type guide layer 216 for five periods. A split active layer 217 is grown.

Next, a p-type guide layer 218 made of p-type GaN having a thickness of 0.1 μm is grown on the active layer 217. Thereafter, a carrier overflow suppression layer 219 made of Al _0.20 Ga _0.80 N having a thickness of 10 nm is grown, and then p-type Al _0.10 Ga _0.90 N having a thickness of 1.5 nm and p-type GaN having a thickness of 1.5 nm. Are repeated for 160 periods to grow a p-type cladding layer 220 having a strained superlattice structure. Thereafter, a p-type contact layer 222 made of p-type GaN having a thickness of 0.05 μm is grown.

In addition, as a III group material at the time of using said MOCVD method, trimethyl gallium (TMG) was used as Ga material, trimethyl aluminum (TMA) was used as Al material, and trimethyl indium was used as In material. . In addition, ammonia (NH ₃ ) was used as the Group V raw material. Further, Si is used as the n-type impurity material, monosilane (SiH ₄ ) gas is used as the material, Mg is used as the p-type impurity material, and biscyclopentadienyl magnesium (Cp ₂ ) is used as the material. Mg) was used.

Next, as shown in FIG. 7 (h), stripe-shaped oxidation parallel to the m-axis direction having a film thickness of 0.3 μm and a width of 1.5 μm is formed on the p-type contact layer 222 by thermal CVD. A mask M21 made of silicon (SiO ₂ ) is selectively formed. The silicon oxide is formed in the m-axis direction so as not to be positioned immediately above the bonding region 213 within a range within about 5 μm from the bonding portion 213a of the lateral growth layer 212 in the horizontal direction.

  As described above, the layer formed on the base layer 214 including the region where the dislocations are concentrated inherits the crystallinity of the underlying layer. A region where dislocations are concentrated is formed, and a band-like dislocation region is formed in the stacked structure.

Next, as shown in FIG. 7 (i), the upper part of the p-type cladding layer 220 is etched to a depth of 0.35 μm by the ICP method using the silicon oxide as a mask, thereby forming a striped ridge portion 220a. Form. Thereafter, the silicon oxide mask M21 is removed using hydrofluoric acid, and the SiO 2 film having a thickness of 200 nm is formed on the entire surface including the ridge 220a on the p-type cladding layer 220 exposed again by the thermal CVD method. _A dielectric film 221 made of 2 is formed. Next, a resist pattern having an opening having a width of 1.3 μm is formed along the stripe shape of the ridge 220a on the dielectric film 221 on the upper surface of the ridge 220a by lithography. Thereafter, the dielectric film 221 on the ridge 220a is etched away by reactive ion etching (RIE) using trifluoromethane (CHF ₃ ) gas using the resist pattern as a mask. The mold contact layer 222 is exposed.

  Next, a metal laminated film made of palladium (Pd) having a thickness of 40 nm and platinum (Pt) having a thickness of 35 nm is formed on at least the p-type contact layer 222 exposed from the upper surface of the ridge 220a by vapor deposition. Form. Thereafter, the resist pattern is removed by a lift-off method, and a p-side electrode 223 is formed as shown in FIG.

  Next, a wiring electrode having a width of 150 μm is formed on the dielectric film 221 in a direction parallel to the stripe direction of the ridge 220a so as to cover the p-side electrode 223 above the ridge 220a by lithography and lift-off. Are selectively formed. The wiring electrode is formed of a laminated metal film made of titanium (Ti) / platinum (Pt) / gold (Au) having a thickness of 50 nm, 200 nm, or 100 nm. Thereafter, the thickness of the Au layer is increased to about 10 μm by electrolytic plating to form a pad electrode. Thereafter, adjacent chips are separated. At this time, if the pad electrode is continuously connected to the adjacent chip, electrode separation occurs when the chip is separated. Therefore, the pad electrode is separated for each chip. It is preferable.

Next, the n-side electrode 224 is formed. First, a mask made of SiO ₂ is formed by a thermal CVD method in the region where the pad electrode is formed. Thereafter, a resist having an opening is formed by a lithography method and a lift-off method in the vicinity of the ridge portion 220a and in parallel with the stripe direction of the ridge portion 220a, and in a region where there is no pad electrode. Thereafter, the underlying structure 214 is exposed by etching the laminated structure at the opening to a depth of about 2.5 μm from above by ICP. Thereafter, an n-side electrode 224 is formed on the base layer 214. The n-type n-side electrode 224 is produced by forming and patterning a metal laminated film made of Ti / Pt / Au having thicknesses of 5 nm, 10 nm, and 1000 nm, respectively.

  Thereafter, the resist and dielectric film 221 on the pad electrode are removed. Next, the back surface of the substrate 210 is polished, and the substrate 210 is thinned until the thickness becomes about 100 μm. Next, primary cleavage of the substrate is performed along the m-plane direction so that the length in the m-axis direction is 400 μm. Thereafter, the substrate that has been primarily cleaved is cleaved along the a-plane direction so that the length in the a-axis direction becomes 200 μm and separated into chips.

  As described above, the semiconductor laser device 2 according to the second embodiment of the present invention can be manufactured.

  Next, an example of the semiconductor laser device 2 according to the second embodiment of the present invention will be described with reference to FIG. In FIG. 8A, the base seed crystal layer 211 and the selective growth dielectric film 225 are formed on the substrate 210, and the base substrate on which the lateral growth layer 212 and the base layer 214 are formed is formed in the m-axis direction. It is the cross-sectional TEM image observed from. FIG. 8B is a cathodoluminescence image (CL image) obtained by observing the base substrate of FIG. In this example, the base layer 214 having a thickness of 1 μm was formed on the substrate 210 by the method described in FIG.

  As shown in FIG. 8A, it can be seen that the dislocation direction of the base seed crystal layer 211 extends in the (0001) plane direction. On the other hand, the laterally grown layer 212 grows laterally, and all the dislocations at the interface with the side surface of the convex portion of the base seed crystal layer 211 are laterally (direction parallel to the substrate main surface) (11 -20) It turns out that it is bent in the direction.

  Further, as shown in FIG. 8A, it can be seen that the dislocations in the base layer 214 are concentrated immediately above the convex portions 211a of the base seed crystal layer 211. It can also be seen that the dislocations of the underlying layer 214 in the portion immediately above the laterally grown layer 212 are regions with a low dislocation.

  Further, as shown in FIG. 8B, dislocations are band-like in the region 211b immediately above the convex portion 211a of the base seed crystal layer 211 and the junction region 213 in which the adjacent lateral growth layers 212a and 212b are combined. It can be seen that the dislocations are controlled by being concentrated as dark spots. It can also be seen that dislocations are not concentrated in the region between the region 211b immediately above the convex portion 211a and the junction region 213 in the base seed crystal layer 211, and a region with low dislocations is formed.

  As described above, by using the dislocation control technique according to this embodiment, dislocations can be concentrated in a band shape, a low dislocation region can be formed, and the dislocation arrangement can be freely controlled.

  As described above, according to the semiconductor laser device 2 according to the second embodiment of the present invention, by utilizing the difference between the current diffusion length and the light distribution in the optical waveguide and disposing the dislocations as desired, the saturable absorption amount is reduced. Can be increased. By disposing the band-shaped dislocation region in the optical waveguide and in the region where current is not diffused, only the amount of light absorption can be easily increased, and a self-oscillation type that performs stable self-oscillation operation. A semiconductor laser device can be realized. As a result, it is possible to reduce the return light noise and the speckle noise. In addition, the cost of the semiconductor laser device can be reduced by using a sapphire substrate having a large area at a low cost instead of an expensive GaN substrate conventionally used.

  In FIG. 8A, a gap is opened between the laterally grown layers 212a and 212b and the selective growth dielectric film 225. This gap reduces the thickness of the underlying seed crystal layer 211, for example. By adjusting the crystal growth conditions of the lateral crystal layers 212a and 212b, it can be made small or negligible.

  In this embodiment, a sapphire substrate is used as the substrate 210, but the present invention is not limited to this. For example, even if it is a low-cost SiC substrate or a Si substrate, a semiconductor laser device having the same effect can be manufactured by the same process. By using these substrates, the cost can be reduced by further increasing the area. Is possible.

  Also in this embodiment, as in the first embodiment, the well layer of the active layer 117 is an InGaN layer having an In composition of 10% to 20% or more, or the n-type guide layer 116 and Alternatively, the p-type guide layer 118 may be an n-type or p-type InGaN layer, and may have a configuration suitable for a semiconductor laser device for display.

  In addition to the n-type GaN, the underlayer 114 may be an n-type AlGaN layer, an n-type AlGaN, or an AlN / GaN superlattice growth layer.

  In the present embodiment, the carrier overflow suppression layer 119 is formed on the p-type guide layer 118. However, a carrier overflow suppression layer is formed on the active layer 117, and the p-type is further formed thereon. You may make it the structure of forming a guide layer.

(Third embodiment)
Next, a semiconductor laser device 3 according to a third embodiment of the present invention will be described with reference to FIG. FIG. 9 is a sectional view showing the structure of a semiconductor laser device according to the third embodiment of the present invention.

  The semiconductor laser device 3 according to the third embodiment of the present invention is a self-excited oscillation type semiconductor laser device, as in the first embodiment. The semiconductor laser device 3 according to the third embodiment of the present invention differs from the semiconductor laser device 1 according to the first embodiment of the present invention in the structure of the base substrate. Further, the present embodiment is characterized in that a stacked body such as an active layer or a cladding layer is stacked on the (1-101) plane which is a semipolar plane of a nitride semiconductor. Note that the configuration of the laminated body, the electrode, and the like and the manufacturing conditions in the manufacturing process are slightly different from those in the first embodiment or the second embodiment, but are basically the same.

  As shown in FIG. 9, in the semiconductor laser device 3 according to the third embodiment of the present invention, a concavo-convex portion having a plurality of convex portions 310a having a triangular cross-sectional shape is formed, and the surface crystal plane is from (100). A substrate 310 made of Si having a crystal plane inclined by about 7 degrees, a base seed crystal layer 311 formed on one side surface of each of the plurality of projections 310a of the substrate 310, and a plurality of projections Each of 310a includes a selective growth dielectric film 325 which is a selective growth film formed on the other side surface of the convex portion 310a. The side surface of the convex portion 310a is made of Si (111), and the inclination angle is about 62 degrees on one side and about 48 degrees on the other side in the horizontal direction. A base seed crystal layer 311 is formed on a side surface having an inclination angle of about 62 degrees, and a selective growth dielectric film 325 is formed on a side surface having an inclination angle of about 48 degrees. The base seed crystal layer 311 can be composed of, for example, an AlN film. The selective growth dielectric film 325 can be formed of, for example, a silicon oxide film or a silicon nitride film.

  Further, a base GaN growth layer 312 is formed on the surface of the base seed crystal layer 311 so as to fill in the space between the adjacent convex portions 310 a (recesses) of the substrate 310. An n-type underlayer 314 made of GaN is formed on the underlayer GaN growth layer 312, and an n-type cladding layer 315, an n-type guide layer 316, an active layer 317, a p-type are formed on the underlayer 314. A guide layer 318, a carrier overflow suppression layer 319, and a p-type cladding layer 320 are sequentially stacked.

  At this time, the (1-101) plane of the underlying GaN growth layer 312 has an angle of about 62 degrees with respect to the (1000) plane where crystal growth is performed from the (111) plane of Si. The surface of the base GaN growth layer 312 is a horizontal plane. For this reason, since the laminated body formed on the upper part of the underlying GaN growth layer 312 is laminated in a direction perpendicular to the main surface of the substrate plate 310, a process for forming electrodes and the like described later can be easily performed. .

  The p-type cladding layer 320 has a ridge part 320a having a stripe shape in a top view and a convex section, and a p-type contact layer 322 and a p-side electrode 323 (second electrode) are formed on the ridge part 320a. Yes. Thereby, the p-side electrode 323 is electrically connected to the p-type contact layer 322.

  A dielectric film 321 is formed on the region of the p-type cladding layer 320 where the ridge 320a is not formed. In addition, the base layer 314 is exposed in the opening from which the stacked structure is removed, and an n-side electrode 324 (first electrode) is formed on the base layer 314. The n-side electrode 324 is electrically connected to the n-type cladding layer 315 through the base layer 314.

  The ridge portion 320a in which the p-type contact layer 322 and the p-side electrode 323 are formed is a region for injecting current into the active layer 317, and the region below the p-side electrode 323 and the ridge portion 320a and its peripheral region are currents. This is an injection region 330.

  In the semiconductor laser device 3 according to the third embodiment of the present invention, as described above, the base seed crystal layer 311 is formed on one side surface of the convex portion 310a of the substrate 310, and the dielectric for selective growth is formed on the other side surface. A body film 325 is formed. Thereby, the underlying GaN growth layer 312 formed thereon starts growing from the underlying seed crystal layer 311 and grows in the direction indicated by the arrow in FIG. Adjacent underlying GaN growth layers 312 are bonded to each other to form a bonded portion 313a, and a bonded region 313 is formed. At this time, dislocations generated from the interface between the side surface of the convex portion and the seed crystal layer 311 do not extend linearly, whereas one (dislocation generated near the bottom of the concave portion) bends to the dielectric film 325 for selective growth. It reaches the surface of the dielectric film 325. The other (dislocations generated near the surface of the concave portion) bends to the surface, and the laminated structure formed on the junction region 313 and the base seed crystal layer 311 includes the dielectric film 321 and the base seed crystal layer. A band-shaped dislocation region 341 is formed over 311. That is, the layer that grows in the vicinity of the junction portion 313 a in the underlying GaN growth layer 312 is formed so that dislocations are concentrated by the junction portion 313 a in the junction region 313.

  On the other hand, the layer grown on the underlying GaN growth layer 312 on the selective growth dielectric film 325 in which the junction region 313 is not formed is formed without concentration of dislocations, and the dislocations are lowered on this portion. A region is formed.

  As described above, in this embodiment, the underlying GaN growth layer 312 is formed by joining and bonding the adjacent underlying GaN growth layers 312 grown from each of the underlying seed crystal layers 311 of the adjacent convex portions 310a. . The junction region 313 in the underlying GaN growth layer 312 functions as a dislocation-concentrated region capable of concentrating the dislocations of the layer formed on the junction region 313, and the dislocation density of the layer formed on the junction region 313. Will grow. The underlying GaN growth layer 312 functions together with the underlying seed crystal layer 311 and the selective growth dielectric film 325 as a dislocation control layer having a dislocation concentrated region.

  As described above, also in the semiconductor laser device 3 according to the present embodiment, as in the first and second embodiments, the band-shaped dislocation region 341 having a dislocation density larger than that of other portions is formed. Similarly to the first and second embodiments, also in the semiconductor laser device 3 according to the present embodiment, the dislocation density in the current injection region 330, particularly, the dislocation density in the active layer injection region is set to the first dislocation density. If the dislocation density in the vicinity of the current injection region 330, in particular, the dislocation density in the band-like dislocation region 341 in the active layer non-current injection region is the second dislocation density b, the first dislocation density a and the second dislocation density The relationship of the dislocation density b is a <b, and the second dislocation density is larger than the first dislocation density.

  Therefore, the semiconductor laser device 3 according to the present embodiment also has the same operational effects as those of the semiconductor laser devices 1 and 2 according to the first and second embodiments of the present invention described above.

  Next, a method for manufacturing a semiconductor laser device according to the third embodiment of the present invention will be described with reference to FIG. FIG. 10 is a cross-sectional view of each step in the method for manufacturing a semiconductor laser device according to the third embodiment of the present invention.

  First, a Si (100) 7 ° off substrate having a silicon oxide film or a silicon nitride insulating film is prepared as the substrate 310, and the substrate 310 is striped by using a photolithography method or dry etching. A mask made of the insulating film having an opening is manufactured.

  Next, the Si (100) 7 ° off substrate on which the mask is formed is subjected to wet etching using, for example, potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH), so that the opening of the mask is cross-sectioned. A plurality of triangular recesses are formed. As a result, as shown in FIG. 10A, a plurality of convex portions 310 a having a triangular cross section can be formed on the substrate 310. At this time, the side surface of each convex portion 310a is an inclined surface, and the side surface is a (111) facet surface of silicon.

  Next, as shown in FIG. 10B, one of the tilted silicon (111) facets of the protrusion 310a is selectively grown of a silicon oxide film or a silicon nitride film by sputtering or vacuum deposition. It is covered with a dielectric film 325 for use.

  Next, as shown in FIG. 10C, an underlying seed crystal layer 311 made of an AlN film is formed on the side surface of the convex portion 310a that is not covered with the selective growth dielectric film 325. To do.

  Thereafter, when a nitride semiconductor crystal made of GaN is grown on the selective growth dielectric film 325 and the underlying seed crystal layer 311 by MOCVD, the nitride semiconductor crystal starts to grow only on the underlying seed crystal layer 311. It grows in the direction indicated by the arrow in FIG. At this time, the underlying GaN growth layer 312 on the (1-101) facet surface of the nitride semiconductor appears in the growth direction of the nitride semiconductor crystal.

  Thereafter, when the crystal growth is further continued, the (1-101) facet plane of the nitride semiconductor grown from the base seed crystal layer 311 of one convex portion 310a is the base seed crystal layer 311 of the other convex portion 310a adjacent thereto. As shown in FIG. 10D, the nitride semiconductor is bonded to the nitride semiconductor grown from the above, and becomes a (1-101) plane of the nitride semiconductor in a continuous film state.

Next, a group III raw material TMG and an n-type doping material monosilane (SiH ₄ ) are introduced on the underlying GaN growth layer 312 thus obtained, and as shown in FIG. An n-type underlayer 314 made of n-GaN having a thickness of 2 μm is crystal-grown. In this case, dislocations are concentrated immediately above the convex portion 310a that becomes the seed crystal and immediately above the junction region 313 where the adjacent underlying GaN growth layer 312 is joined. In this manner, a region having a high dislocation density is formed on the junction region 313 including the junction portion 313a, while a region having a low dislocation is formed on the underlying GaN growth layer 312 other than the junction region 313. Is done. Note that the base layer 314 is formed over the entire surface of the substrate 310.

  Next, as shown in FIG. 10F, a layered structure is formed on the base layer 314 by sequentially growing each layer of the layered structure made of the nitride semiconductor layer by MOCVD.

Specifically, an n-type cladding layer 315 made of n-type Al _0.05 Ga _0.95 N having a film thickness of 1.5 μm is grown on the base layer 314, and then made of n-type GaN having a film thickness of 0.1 μm. An n-type guide layer 316 is grown. Thereafter, a quantum well structure including a barrier layer made of In _0.02 Ga _0.98 N having a thickness of 7.5 μm and a well layer made of In _0.06 Ga _0.94 N having a thickness of 3 nm is formed on the n-type guide layer 316 in five cycles. A split active layer 317 is grown.

Next, a p-type guide layer 318 made of p-type GaN having a thickness of 0.1 μm is grown on the active layer 317. Thereafter, a carrier overflow suppression layer 319 made of Al _0.20 Ga _0.80 N having a thickness of 10 nm is grown, and then p-type Al _0.10 Ga _0.90 N having a thickness of 1.5 μm and p-type GaN having a thickness of 1.5 μm. Are repeated for 160 periods to grow a p-type cladding layer 320 having a strained superlattice structure. Thereafter, a p-type contact layer 322 made of p-type GaN having a thickness of 0.05 μm is grown.

In addition, as a III group material at the time of using said MOCVD method, trimethyl gallium (TMG) was used as Ga material, trimethyl aluminum (TMA) was used as Al material, and trimethyl indium was used as In material. . In addition, ammonia (NH ₃ ) was used as the Group V raw material. Further, Si is used as the n-type impurity material, monosilane (SiH ₄ ) gas is used as the material, Mg is used as the p-type impurity material, and biscyclopentadienyl magnesium (Cp ₂ Mg) is used as the material. ) Was used.

Next, as shown in FIG. 10 (f), stripe-shaped oxidation parallel to the m-axis direction having a film thickness of 0.3 μm and a width of 1.5 μm is formed on the p-type contact layer 322 by thermal CVD. A mask M31 made of silicon (SiO ₂ ) is selectively formed. The silicon oxide is formed in the m-axis direction so as not to be positioned directly above the junction region 313 within a range within about 5 μm in the lateral direction from the junction portion 313a of the underlying GaN growth layer 312.

  As described above, the layer formed on the base layer 314 including the region where the dislocations are concentrated inherits the crystallinity of the underlying layer. A region where dislocations are concentrated is formed, and a band-like dislocation region is formed in the stacked structure.

Next, as shown in FIG. 10G, the upper part of the p-type cladding layer 320 is etched to a depth of 0.35 μm by the ICP method using the silicon oxide as a mask, thereby forming a striped ridge portion 320a. Form. Thereafter, the silicon oxide mask M31 is removed using hydrofluoric acid, and the SiO film having a film thickness of 200 nm is formed on the entire surface including the ridge 320a on the p-type cladding layer 320 exposed again by the thermal CVD method. _A dielectric film 321 made of 2 is formed. Next, a resist pattern having an opening having a width of 1.3 μm is formed along the stripe shape of the ridge 320 a on the dielectric film 321 on the upper surface of the ridge 320 a by lithography. Thereafter, the reactive ion etching (RIE) using trifluoromethane (CHF ₃ ) gas is used to remove the dielectric film 321 on the ridge 320a by etching using the resist pattern as a mask, and p from the upper surface of the ridge 320a. The mold contact layer 322 is exposed.

  Next, a metal laminated film made of palladium (Pd) having a thickness of 40 nm and platinum (Pt) having a thickness of 35 nm is formed on at least the p-type contact layer 322 exposed from the upper surface of the ridge portion 320a by vapor deposition. Form. Thereafter, the resist pattern is removed by a lift-off method, and a p-side electrode 323 is formed as shown in FIG.

  Next, a wiring electrode having a width of 150 μm is formed on the dielectric film 321 in a direction parallel to the stripe direction of the ridge portion 320a so as to cover the p-side electrode 323 above the ridge portion 320a by lithography and lift-off methods. Are selectively formed. The wiring electrode is formed of a laminated metal film made of titanium (Ti) / platinum (Pt) / gold (Au) having a thickness of 50 nm, 200 nm, or 100 nm. Thereafter, the thickness of the Au layer is increased to about 10 μm by electrolytic plating to form a pad electrode. Then, the adjacent chips are separated. At this time, if the pad electrode is continuously connected to the adjacent chip, electrode separation occurs when the chip is separated, so the pad electrode is separated for each chip. It is preferable to keep it.

Next, the n-side electrode 324 is formed. First, a mask made of SiO ₂ is formed by a thermal CVD method in the region where the pad electrode is formed. Thereafter, a resist having an opening in the vicinity of the ridge portion 320a and in parallel with the stripe direction of the ridge portion 320a, and further in a region without a pad electrode, is formed by a lithography method and a lift-off method. Thereafter, the underlying structure 314 is exposed by etching the laminated structure in the opening to a depth of about 2.5 μm from above by ICP. Thereafter, an n-side electrode 324 is formed on the base layer 314. Note that the n-side electrode 324 is manufactured by forming and patterning a metal laminated film made of Ti / Pt / Au having thicknesses of 5 nm, 10 nm, and 1000 nm, respectively.

  Thereafter, the resist and dielectric film 321 on the pad electrode are removed. Next, the back surface of the substrate 310 is polished, and the substrate 310 is thinned until the thickness becomes about 100 μm. Next, primary cleavage of the substrate is performed along the m-plane direction so that the length in the m-axis direction is 400 μm with respect to the crystal axis of the nitride semiconductor material of the stacked body. At this time, since the m-plane direction of the laminate is the (100) plane of the substrate 310, the laminate and the substrate 310 can be easily separated by cleavage. Thereafter, the substrate that has been primarily cleaved is cleaved along the a-plane direction so that the length in the a-axis direction becomes 200 μm and separated into chips.

  As described above, the semiconductor laser device 3 according to the third embodiment of the present invention can be manufactured.

  As described above, by using the dislocation control technique according to this embodiment, dislocations can be concentrated in a band shape, a low dislocation region can be formed, and the dislocation arrangement can be freely controlled.

  As described above, according to the semiconductor laser device 3 according to the third embodiment of the present invention, by utilizing the difference between the current diffusion length and the light distribution in the optical waveguide and disposing the dislocations as desired, the saturable absorption amount can be reduced. Can be increased. By disposing the band-shaped dislocation region in the optical waveguide and in the region where current is not diffused, only the amount of light absorption can be easily increased, and a self-oscillation type that performs stable self-oscillation operation. A semiconductor laser device can be realized. As a result, it is possible to reduce the return light noise and the speckle noise. In addition, the cost of the semiconductor laser device can be reduced by using a sapphire substrate having a large area at a low cost instead of an expensive GaN substrate conventionally used.

In this embodiment, a Si substrate is used as the substrate 310, but the present invention is not limited to this.
Next, modified examples of the semiconductor laser device according to each embodiment of the present invention, particularly preferable examples will be described.

  First, in each embodiment, it is preferable that the band-like dislocation region (second dislocation region) where dislocations are concentrated exists in a range within 5 μm from the center of the current injection region.

  As a result, it is possible to efficiently absorb the guided light leaking into the current non-injection region, and to realize a semiconductor laser device that performs a more stable self-excited oscillation operation.

Moreover, in each embodiment, it is preferable that the dislocation density of the band-shaped dislocation region where dislocations are concentrated is 1 × 10 ⁷ / cm ² or more.

  As a result, the amount of light absorption in the saturable absorption region can be increased, so that a semiconductor laser device that performs a more stable self-oscillation operation can be realized.

  In each embodiment, the material of the active layer is not limited to that in each embodiment, but the active layer preferably contains indium.

  Thereby, since the light emission wavelength from the ultraviolet region to the visible region can be realized, the light emission wavelength can be freely changed according to the application. Furthermore, since the nitride material containing In is a material that easily segregates In, the In segregated portion has a small band gap energy and efficiently absorbs the light of the guided light in the saturable absorption region. It becomes possible to make it. As a result, a semiconductor laser device that performs a more stable self-excited oscillation operation can be realized.

In the first and second embodiments, the laterally grown layers 112 and 113 are preferably made of Al _x Ga _1-x N (0 ≦ x ≦ 1).

  As a result, the vertical optical confinement (Γv) in the optical waveguide region can be increased, and the threshold current density can be reduced by reducing the waveguide loss. Therefore, it is possible to realize a semiconductor laser device that performs a more stable self-excited oscillation operation.

In each embodiment, the underlying layer is partially or entirely made of Al _x Ga _1-x N (0 ≦ x ≦ 1) and Al _y Ga _1-y N (0 ≦ y ≦ 1, x ≠ y). And a laminated structure.

  As a result, the average refractive index can be reduced, and the vertical optical confinement (Γv) in the optical waveguide can be increased. Therefore, the waveguide loss can be reduced, and the threshold current density can be reduced. Therefore, a semiconductor laser device that performs a more stable self-oscillation operation can be realized.

  Moreover, in each embodiment, it is preferable that the main surface of the semiconductor layer in a laminated structure is semipolar or nonpolar.

  Thereby, since the piezo effect in the laminated structure can be reduced, the spatial separation between electrons and holes can be eliminated. Therefore, the disappearance time of carriers generated by light absorption is accelerated, the time until light absorption is possible can be shortened, and the amount of light absorption per unit time can be increased. Therefore, it is possible to realize a semiconductor laser device that performs a more stable self-excited oscillation operation.

  As described above, the semiconductor laser device according to the present invention has been described based on each embodiment, but the present invention is not limited to the above-described embodiment. For example, embodiments obtained by subjecting each embodiment to various modifications conceived by those skilled in the art, and embodiments realized by arbitrarily combining the components and functions in each embodiment without departing from the spirit of the present invention Are also included in the present invention.

  The present invention is useful as a light source for an optical disk, a display, or an illumination.

1, 2, 3 Semiconductor laser device 110, 210, 310 Substrate 111, 211 Underlying seed crystal layer 111a, 211a, 310a Protruding portion 111b, 211b Immediately above region 112, 112a, 112b, 212, 212a, 212b Lateral growth layer 113, 213, 313 Junction region 113a, 213a, 313a Junction portion 114, 214, 314 Underlayer 115, 215, 315 N-type cladding layer 116, 216, 316 N-type guide layer 117, 217, 317 Active layer 118, 218, 318 p Type guide layer 119, 219, 319 Carrier overflow suppression layer 120, 220, 320 p-type cladding layer 120a, 220a, 320a Ridge part 121, 221, 321 Dielectric film 122, 222, 322 p-type contact layer 123, 223, 323 p Side electrode 124, 224, 324 n-side electrode 130, 230, 330 Current injection region 140, 150 Neighborhood region 141, 151, 241, 251, 341 Dislocation region 160 Optical waveguide region 170 Current distribution 225, 325 Dielectric film for selective growth 311 Underlying seed crystal layer 312 Underlying GaN growth layer

Claims (15)

A semiconductor laser device that performs self-oscillation operation,
A substrate,
A base layer of a first conductivity type formed on the substrate;
A first conductivity type cladding layer, a first conductivity type guide layer, an active layer, a second conductivity type guide layer having a conductivity type different from the first conductivity type, sequentially formed on the underlayer, A laminated structure made of a nitride semiconductor composed of a two-conductivity-type cladding layer and a second-conductivity-type contact layer;
A first electrode electrically connected to the cladding layer of the first conductivity type;
A second electrode electrically connected to the contact layer of the second conductivity type,
The stacked structure includes a first dislocation area which is a region below the second electrode and has a first dislocation density, and a region having a second dislocation density different from the first dislocation density. Including a second dislocation region,
A semiconductor laser device configured such that the second dislocation density is larger than the first dislocation density. The optical waveguide region in the stacked structure includes an active layer current injection region where the current injected from the second electrode flows into the active layer, and an active layer current which is a region different from the active layer current injection region. A non-injection region,
The active layer current injection region includes the first dislocation region,
The semiconductor laser device according to claim 1, wherein the active layer current non-injection region includes the second dislocation region. The semiconductor laser device according to claim 2, wherein the second dislocation region exists only in one place in the optical waveguide region. The semiconductor laser device according to claim 1, wherein the second dislocation region is present within a range of 5 μm from the center of the first dislocation region. The semiconductor laser device according to claim 1, wherein the second dislocation density is 1 × 10 ⁷ / cm ² or more. The semiconductor laser device according to claim 1, wherein the active layer contains indium. A dislocation control layer is provided between the substrate and the base layer,
7. The semiconductor laser device according to claim 1, wherein the dislocation control layer has a dislocation concentration region in which dislocations of a layer formed on the dislocation control layer can be concentrated. The semiconductor laser device according to claim 7, wherein the dislocation control layer includes a laterally grown layer in which a nitride semiconductor is grown in a direction parallel to a main surface of the substrate. The semiconductor laser device according to claim 8, wherein the laterally grown layer is made of Al _x Ga _1-x N (0 ≦ x ≦ 1). The dislocation control layer includes an underlayer seed crystal layer having a plurality of protrusions, and a growth layer formed between the protrusions of the plurality of protrusions,
The growth layer is formed by joining a first growth layer and a second growth layer grown from the side surfaces of the convex portions facing each other,
The semiconductor laser device according to claim 7, wherein the dislocation-concentrated region is a region where the first growth layer and the second growth layer are joined. The dislocation control layer includes a base seed crystal layer having a plurality of convex portions, a selective growth film formed between the convex portions of the plurality of convex portions, and the base seed crystal layer and the selective growth film. A growth layer formed thereon,
The growth layer is formed by bonding a first growth layer and a second growth layer grown from the upper surfaces of the plurality of convex portions,
The semiconductor laser device according to claim 7, wherein the dislocation-concentrated region is a region where the first growth layer and the second growth layer are joined. A plurality of convex portions are formed on the substrate,
The dislocation control layer is formed on the other side surface of the convex portion with respect to each of the plurality of convex portions, and the base seed crystal layer formed on one side surface of the convex portion with respect to each of the plurality of convex portions. A selective growth film, and a growth layer formed on the underlayer seed crystal layer and the selective growth film,
The growth layer includes a first growth layer grown from one base seed crystal layer of the plurality of base seed crystal layers, and a first growth layer grown from another base seed crystal layer different from the one base seed crystal film. 2 grown layers are joined together,
The semiconductor laser device according to claim 7, wherein the dislocation-concentrated region is a region where the first growth layer and the second growth layer are joined. A part or all of the underlayer has a laminated structure of Al _x Ga _1-x N (0 ≦ x ≦ 1) and Al _y Ga _1-y N (0 ≦ y ≦ 1, x ≠ y). Item 13. The semiconductor laser device according to any one of Items 1 to 12. The semiconductor laser device according to claim 1, wherein the substrate is a sapphire substrate, a Si substrate, or a SiC substrate. The semiconductor laser device according to claim 1, wherein a main surface of the multilayer structure is semipolar or nonpolar.