JP3910043B2 - Nitride semiconductor laser device, manufacturing method thereof, and semiconductor optical device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nitride semiconductor laser element, a method for manufacturing the same, and a semiconductor optical device including the nitride semiconductor laser element as a light source, and more particularly, to a nitride semiconductor laser element using a nitride semiconductor as a substrate.
[0002]
[Prior art]
A semiconductor laser device that oscillates in the ultraviolet to visible region has been prototyped using nitride semiconductor materials typified by GaN, AlN, InN, and mixed crystals thereof. The semiconductor laser device reported in Japanese = Journal = Applied = Physics 39 No.L647-L650 (Jpn. J. Appl. Phys. Vol.39 (2000) pp.L647-650) is an example of this. SiO with periodic striped openings on the substrate₂It has been shown that a mask semiconductor is formed, a nitride semiconductor laminated structure having a striped waveguide (ridge stripe structure) is formed thereon, and a nitride semiconductor laser device is formed on the GaN layer. . It has been reported that the following method is used for manufacturing the substrate.
[0003]
SiO with periodic striped openings₂A GaN layer having a thickness of 15 μm is formed by MOCVD (Metalorganic Chemical Vapor Deposition) on the underlying GaN on which the mask pattern (period 20 μm) is formed, thereby obtaining a wafer having a flat surface. This is a technique called ELOG (Epitaxially Lateral Overgrown), which is a technique for reducing defects by utilizing lateral growth. Further, a GaN substrate having a thickness of 200 μm is formed by a normal HVPE method (Hydride Vapor Phase Epitaxy), and the base is removed to manufacture a GaN substrate. The lifetime characteristics of the semiconductor laser thus obtained were 30 mW at 60 ° C. and an estimated lifetime of 15000 hours.
[0004]
[Problems to be solved by the invention]
However, in the semiconductor laser device described in the above report, the substrate manufacturing method requires three crystal growths (base growth, MOCVD growth, and HVPE growth), which is complicated and has a problem in productivity. Further, the laser oscillation life is not yet sufficient, and the life under conditions of higher output and higher power (for example, 70 ° C., 60 mW) is not sufficient.
[0005]
The present invention has been made in view of these points, and an object of the present invention is to provide a semiconductor laser device having a further excellent laser oscillation lifetime and a simple manufacturing method thereof.
[0006]
[Means for Solving the Problems]
The nitride semiconductor substrate described in this specification means at least Al._xGa_yIn_zIt is a substrate composed of N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1). Further, in the nitride semiconductor substrate, about 20% or less of the nitrogen element which is a constituent component thereof may be substituted with at least one of the element groups of As, P and Sb.
[0007]
Most preferably, the nitride semiconductor substrate is a GaN substrate that is a binary crystal. By using a binary crystal, the composition becomes constant, and it becomes easy to obtain a substrate having stable characteristics, and the composition does not change when epitaxial growth is performed thereon. In addition, by using GaN, good conductivity can be obtained. Next is an AlGaN substrate. By using a material having a refractive index smaller than that of GaN as the substrate, such as an AlGaN substrate, when the semiconductor laser in the ultraviolet to blue region is configured with the above material system, the optical confinement of the laser light to the active layer is improved. .
[0008]
The nitride semiconductor substrate may be doped with an impurity such as an n-type or p-type dopant. As impurities, Cl, O, S, Se, Te, C, Si, Ge, Zn, Cd, Mg, and Be can be used. The total amount of impurities added is 5 × 10¹⁶/ Cm^Three5 × 10 or more²⁰/ Cm^ThreeThe following is preferred. The impurity for the nitride semiconductor substrate to have n-type conductivity is particularly preferably one of Si, Ge, O, Se, and Cl in the impurity group.
[0009]
The nitride semiconductor layer stacked on the nitride semiconductor substrate described in this specification means at least Al._xGa_yIn_zN (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1). In the nitride semiconductor layer, about 20% or less of the constituent nitrogen element may be substituted with at least one of the element groups of As, P, and Sb.
[0010]
The nitride semiconductor layer may be doped with an impurity such as an n-type or p-type dopant. As impurities, Cl, O, S, Se, Te, C, Si, Ge, Zn, Cd, Mg, and Be can be used. The total amount of impurities added is 5 × 10¹⁶/ Cm^Three5 × 10 or more²⁰/ Cm^ThreeThe following is preferred. The impurity for the nitride semiconductor layer to have n-type conductivity is particularly preferably Si, Ge, S, Se, or Te among the impurity group, and the impurity for having p-type conductivity is Mg, One of Cd and Be is particularly preferable.
[0011]
The active layer described in this specification refers to a generic name of a well layer or a layer composed of a well layer and a barrier layer. For example, an active layer having a single quantum well structure is composed of only one well layer, or is composed of a barrier layer / well layer / barrier layer. The active layer having a multiple quantum well structure includes a plurality of well layers and a plurality of barrier layers.
[0012]
In addition, when the index indicating the plane and orientation of the crystal is negative, it is a rule of crystallography that is written with a horizontal line on the absolute value, but in this specification, such a notation is not possible, A negative sign is used in front of the absolute value to indicate a negative exponent.
[0015]
  The present inventionIsNitride semiconductor substrate and nitride semiconductor layer laminated thereonWhen,WithOf the present inventionNitride semiconductor laser deviceIt is. In such a nitride semiconductor laser device,Nitride semiconductor substrateIn order to concentrate the dislocations on the bottom of the groove, the facet of the slope, which is the side of the groove with a V-shaped cross section, is used as the facet.StripedOccurred inA dislocation concentration region, and a low dislocation region that is a region excluding the dislocation concentration region;Is included, andLow dislocation regionThis is caused by the facet plane {0001} plane appearing and growing in the center ofStriped high luminescence regionThe high luminescence region and the dislocation concentration region areAlmost parallelIt has become. Also,Nitride semiconductor layerIsStriped laser light guide regionContains thatLaser beam guiding regionIsLocated on low dislocation areaAndDislocation concentration regionAgainstAlmost parallelAndThe distance d in the horizontal direction between the laser beam guiding region and the nearest dislocation concentration region is 40 μm or more,The distance t in the horizontal direction between the laser light waveguide region and the high luminescence region closest thereto is 30 μm or more. It is more desirable that the distance d is 60 μm or more.
  The high luminescence region is a region having slightly different properties from the surroundings. By shifting the laser light waveguide region by 30 μm or more from this region, a long-life semiconductor laser device is obtained.
[0016]
  Also,The distance P between adjacent dislocation concentration regions in the nitride semiconductor substrate is preferably 140 μm or more.Furthermore, it is desirable that the distance P is 300 μm or more.This is for facilitating the shifting of the laser light waveguide region from the dislocation concentration region during manufacture.
[0017]
The distance P is preferably 1000 μm or less. This is to avoid an unnecessary portion of the low dislocation region that is not located below the laser light guide region from becoming excessive.
[0018]
  In addition,A nitride semiconductor substrate having a dislocation concentration region substantially parallel to the [1-100] direction can be used.The distance t is preferably 50 μm or more.
[0021]
  In addition,The nitride semiconductor layer is made of In_xGa_1-xIt can have a quantum well active layer containing a well layer composed of N (0 <x <1).
[0022]
In addition, the nitride semiconductor layer may have a quantum well active layer including a well layer made of a nitride semiconductor containing at least one element of As, P, and Sb.
[0023]
In the present invention, the above-described nitride semiconductor laser element is provided as a light source in a semiconductor optical device.
[0026]
  Further, in the method for manufacturing a nitride semiconductor laser device of the present invention, a slope which is a side surface of a groove having a V-shaped cross section is used as a facet surface, and growth is performed while maintaining the slope of the facet surface. A plurality of dislocation concentration regions formed in stripes and substantially parallel to each other, and a low dislocation region excluding the dislocation concentration region, and a facet plane in the center of the low dislocation region { A striped laser light waveguide region is provided on a nitride semiconductor substrate that has a striped high luminescence region that is substantially parallel to the dislocation concentration region by growing while exposing the 0001} surface. Forming a nitride semiconductor layer including a nitride semiconductor stacked structure; Further, in the method of manufacturing the nitride semiconductor laser device, the laser light waveguide region is provided on the low dislocation region substantially in parallel with the dislocation concentration region, and the horizontal direction of the laser light waveguide region and the nearest dislocation concentration region to the laser light waveguide region is provided. The distance d is set to 40 μm or more, and the horizontal distance t between the laser light guide region and the high luminescence region closest thereto is set to 30 μm or more. It is more desirable that the distance d is 60 μm or more.
  In this way, the influence of the dislocation of the substrate to the laser beam guiding region can be suppressed, and not only a semiconductor laser element having a long laser oscillation lifetime can be obtained,By shifting the laser light waveguide region from the high luminescence region having slightly different properties from the surroundings, a semiconductor laser device having a longer life can be obtained.
[0027]
  Also,A nitride semiconductor substrate having a distance P of 140 μm or more between adjacent dislocation concentration regions is used.It is desirable that the distance P is 300 μm or more.It becomes easy to shift the laser light waveguide region from the dislocation concentration region.
[0028]
A nitride semiconductor substrate having a distance P of 1000 μm or less may be used. It is possible to avoid a semiconductor laser element having a large unnecessary portion that is not located below the laser light waveguide region in the low dislocation region, and the yield is improved.
[0030]
  The distance t is preferably 50 μm or more. Also,The nitride semiconductor substrate having a dislocation concentration region has a surface in which a facet surface {11-22} surface is exposed and has a serrated uneven shape, and the dislocation concentration region is below the bottom of the surface uneven shape. Those located in
[0031]
Moreover, as a nitride semiconductor substrate having a high luminescence region, the facet surface {11-22} has a surface that is exposed and has a serrated uneven shape, and the high luminescence region is a top of the uneven surface. What is located under a part can be used.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
<Embodiment 1>
FIG. 1 is a schematic cross-sectional view showing a semiconductor laser device 1 according to the first embodiment of the present invention. FIG. 1 is a view of the semiconductor laser device 1 of the present embodiment as viewed from the light emitting direction. In FIG. 1, reference numeral 10 denotes an n-type GaN substrate. A dislocation concentration region 11 exists in the substrate 10, and a portion other than the dislocation concentration region 11 is a low dislocation region. Further, in the low dislocation region, a high luminescence region 12 exists in parallel with the dislocation concentration region 11. A nitride semiconductor layer (epitaxial growth layer) 13 is formed on the substrate 10. In the nitride semiconductor layer 13, a laser light waveguide region 14 is located. Electrodes 15 and 16 are formed on the upper surface of the nitride semiconductor layer 13 and the lower surface of the substrate 10, respectively. Although not shown in the sectional view of FIG. 1, the dislocation concentration region 11, the high luminescence region 12, and the laser light waveguide region 14 extend in the depth direction of FIG. 1 and are arranged substantially parallel to each other.
[0033]
When the semiconductor laser device 1 of the present embodiment is viewed from the upper surface side (plan view), the distance between the laser light waveguide region 14 and the dislocation concentration region 11 is d, and the distance between the laser light waveguide region 14 and the high luminescence region 12 is. Where d is 80 μm and t is 120 μm. In this specification, the distances d and t are defined from the distances between the center positions of the respective striped laser beam waveguide regions, dislocation concentration regions, and high luminescence regions.
[0034]
Below, while explaining the manufacturing method of the semiconductor laser device 1 of the present embodiment, the structure thereof will be described in more detail.
[0035]
(Production method of GaN substrate)
First, the outline of the crystal growth method of the n-type GaN substrate 10 will be described. The GaN crystal is grown while maintaining the slope so that the slope formed by the facet surface is exposed. That is, the slope is gradually moved in the growth direction. As a result, dislocations generated in the middle of the slope propagate to and gather at the lower end of the slope, and the portion that was the lower end of the slope becomes the dislocation concentration region, and the portion that was in the middle of the slope becomes the low dislocation region.
[0036]
There are several states in the dislocation concentration region. For example, it may be polycrystalline. Moreover, it may become a single crystal slightly inclined with respect to the surrounding low dislocation region. Furthermore, while the growth direction of the surrounding low dislocation region is the [0001] direction, the growth direction may be the [000-1] direction. For this reason, a clear boundary is generated between the dislocation concentration region and the low dislocation region.
[0037]
In order to move the slope in the growth direction, the shape of the dislocation concentration region can be defined by the shape of the facet plane that is generated first. If facets such as the side of a pyramid that is upside down (top down and bottom up) are generated first, the dislocations gather at the apex of the pyramid and the dislocation concentration region grows in the growth direction. Pits are formed in parallel straight lines. In addition, if a facet surface such as a side surface of a groove having a V-shaped cross section is first generated, dislocations gather at a linear portion at the bottom of the groove, and the dislocation concentration region is a planar shape parallel to the growth direction. To form a stripe.
[0038]
A mask that prevents crystal growth can be used as the seed of the facet plane to be generated first. Crystal growth begins at the part where the mask is not provided, a facet surface is formed at the boundary between the part without the mask and the part, and the facet surface comes into contact with the mask due to the growth in the horizontal direction, and the contact is a dislocation concentration region. This is the starting position. After the facet surfaces come into contact with each other, crystal growth in the vertical direction (original growth direction) proceeds stably, the facet surface moves in the growth direction as it is, and the dislocation concentration region extends in the growth direction. If the mask that hinders crystal growth is made dot-like, facets like the side of a pyramid that is upside down can be generated, and if the mask is made straight, the cross-section is like the side of a V-shaped groove. Can generate a large facet surface. As the mask, an amorphous or polycrystalline layer may be provided, for example, SiO.₂The thin film is formed on the substrate surface.
[0039]
After the crystal growth, the surface is polished and mirror-finished to obtain a substrate on which semiconductor layers can be stacked. In this embodiment, a facet surface is formed in a V shape so that the dislocation concentration region has a stripe shape, or a large number of facet surfaces having a shape surrounding a dot are generated in a short period, thereby dislocation concentration. Make the region macroscopically striped.
[0040]
A specific method for manufacturing the n-type GaN substrate 10 will be described with reference to FIG. An n-type GaN layer 22 is grown on the support substrate 21 by HVPE so that the facet plane {11-22} plane 23 is mainly exposed on the growing surface. As a result, the cross-sectional figure of the surface becomes a serrated irregular shape. However, in the vicinity of the apex of the convex portion, a portion where the {0001} face 26 was exposed was slightly seen in a stripe shape. FIG. 2A is a cross-sectional view (only a part is shown) explaining this state.
[0041]
Here, the HVPE method is such that HCl gas is blown into a heated Ga melt by providing a Ga boat in the upstream portion of a hot wall type reactor, and a base is provided in the downstream portion of the reactor._ThreeThen, HCl is blown into the heated Ga metal (melt) to synthesize GaCl, which is then sent downward, and NH below._ThreeTo synthesize GaN so that GaN is deposited on the substrate.
[0042]
As the support base 21, a 2 inch (111) GaAs wafer was used. There is no particular restriction on the material of the base 21 and it is possible to use general sapphire. However, in order to cut away later, it is preferable to suppress waste by using GaAs as a material.
[0043]
The unevenness has a periodic structure with a pitch P = 400 μm and has a shape extending like a bowl in the depth direction of the drawing. As described above, in order to define the position of the unevenness, the SiO 2 corresponding to the concave portion is previously formed on the base 21.₂And the like, and crystal growth may be performed in a state where the facets are exposed using this as a seed. In other words, the masks are arranged in stripes at a pitch P = 400 μm so as to be parallel to the [1-100] direction of the GaN crystal, and the shape is a continuous stripe or a straight line at substantially constant intervals. Many dots are located.
[0044]
Japanese Patent Application No. 11-273882, filed earlier by the present applicant, discloses in detail the technique (growth conditions) for sustaining crystal growth with the facet {11-22} face exposed. In addition, the crystal to grow was made into n-type by doping O at the time of growth.
[0045]
While maintaining such a growth mode, the formation of a GaN crystal was continued to produce an ingot having a height of 30 mm on the substrate 21. FIG. 2B is a diagram showing an ingot.
[0046]
The ingot was sliced by a slicer to obtain a thin piece (n-type GaN substrate). The thin piece was polished to obtain an n-type GaN substrate 10 having a flat surface and a diameter of 2 inches (about 5 cm) and a thickness of 350 μm. The surface for epitaxial growth was mirror polished. Although this surface is almost (0001) plane, in order for the morphology of the nitride semiconductor layer 13 epitaxially grown thereon to be flat and good, 0.2 to It is desirable to have a relatively small off angle in the range of 1 °, and in order to minimize the flatness of the surface, the range of 0.4 ° to 0.8 ° is preferable. I liked it. FIG. 2C is a cross-sectional view (partially shown) of the n-type GaN substrate 10 thus obtained, and FIG. 2D is a top view (partially shown).
[0047]
Evaluation of the GaN substrate 10 thus obtained was performed as follows. First, the surface of the n-type GaN substrate 10 was observed in detail with a microscope. The polished surface was not necessarily flat, and the region corresponding to the region where the bottom of the concave portion was generated during crystal growth (portion indicated by reference numeral 24 in FIG. 2A) was slightly depressed.
[0048]
Further, the sample was immersed in a solution obtained by heating a mixed acid of sulfuric acid and phosphoric acid to 250 ° C. so that etching pits appeared on the surface. As a result, a large number of etch pits appear in the region corresponding to the region where the bottom of the concave portion has occurred during crystal growth (the portion indicated by reference numeral 24 in FIG. 2A), and this region has dislocations (or crystal defects). ) Is an extremely concentrated region (dislocation concentration region). That is, the depression corresponds to this region.
[0049]
In this way, since the dislocations are highly concentrated in the recesses, it is more likely to be eroded than the other parts in the polishing process, and it is considered that they have occurred. The width of the dislocation concentration region was about 10 to 40 μm. Other areas are EPD (etch pit density) 10^Four-10^Five/ Cm²It was a low dislocation area of the stand. The EPD in the dislocation concentration region was observed to be 3 orders of magnitude larger than this. As described above, the region represented by reference numeral 11 is a portion where the dislocation density is several orders of magnitude higher than that of the surrounding area, and is therefore referred to as a “dislocation concentration region” in this specification.
[0050]
Further, the sample was irradiated with ultraviolet rays (Hg lamp 365 nm emission line can be used), and luminescence from the surface was observed using a microscope (fluorescence microscope observation). As a result, a striped region having a relatively distinct boundary and having a contrast different from the surroundings was observed at the center of the low dislocation region sandwiched between the dislocation concentration regions 11. This region is a region where light emission (luminescence) observed with the naked eye is stronger than the surroundings, and is slightly yellowish and brightly observed.
[0051]
This region is a portion 25 where the facet plane {0001} plane has grown while being exposed at the time of crystal growth, and is a region represented by reference numeral 12 in FIGS. The reason for being observed differently from the surroundings as described above may be that the dopant is incorporated in a different manner from the surroundings. Due to the above facts, this region is referred to as a “high luminescence region” in this specification. During crystal growth, the portion 25 where the facet plane {0001} plane has been exposed does not necessarily proceed uniformly with the same width, so the width of the high luminescence region 12 has a slight fluctuation. However, it was about 30 μm in a wide area.
[0052]
Note that such a high luminescence region may be hardly formed depending on the conditions when the ingot is formed and the position (distance from the support base) in the ingot. However, the substantially central region of the portion sandwiched between the dislocation concentrated regions 11 is a portion corresponding to the region near the top of the irregularities, and this is referred to as “low dislocation region central region” in this specification. Also called. In this specification, the portion described as the high luminescence region can be replaced with the central region of the low dislocation region.
[0053]
The crystal growth for forming the GaN substrate 10 may be performed by vapor phase growth other than the HVPE method, using MOCVD (Metalorganic Chemical Vapor Deposition), MOC (Metalorganic Chloride Vapor Phase Epitaxy), sublimation method, or the like. Can also be implemented.
[0054]
As the substrate 21 used for the growth for forming the GaN substrate 10, besides GaAs, a crystal substrate having a six-fold symmetry or a three-fold symmetry around the axis can be used. That is, examples of the crystal system include crystals that are hexagonal or cubic. In the case of the cubic system, there is a three-fold symmetry if the (111) plane is used. Sapphire, SiC, quartz, NdGaO_ThreeHexagonal crystals such as ZnO, GaN, and AlN can be used. A cubic (111) plane substrate such as Si, spinel, MgO, or GaP can also be used. These grow GaN on the C plane.
[0055]
There are two types of options for providing a mask for forming the GaN substrate 10. One is a method of forming a mask directly on a substrate. In this case, it is better to devise a method such as depositing a GaN buffer layer on the substrate exposed surface inside the mask opening prior to the epi layer. The other is a method in which a GaN layer is formed relatively thin on a substrate in advance and a mask is formed thereon. The latter is more preferable because the growth proceeds smoothly.
[0056]
Here, an example in which GaN is used as the substrate 10 has been described. However, a nitride semiconductor substrate made of a material as described in the section “Means for Solving the Problems” may be substituted.
[0057]
In the method of manufacturing a nitride semiconductor substrate shown in the prior art, dislocations are reduced by using a lateral growth technique (ELOG technique) as the crystal growth of the substrate proceeds, but dislocations (defects) are not generated. The generated position is not particularly controlled, and dislocations are uniformly distributed in the plane as the crystal growth proceeds. On the other hand, in the nitride semiconductor substrate used in the present invention, the position of the dislocation concentration region is controlled to a predetermined position (pitch is on the order of several hundred μm) through the growth of the substrate crystal. There is such a difference between the conventional GaN substrate and the nitride semiconductor substrate used in the present invention.
[0058]
Therefore, when trying to obtain a substrate having a similar dislocation density, the substrate crystal manufacturing method described in this embodiment requires fewer crystal growths, and the productivity is improved. In the case where such a substrate is used, it has not been conventionally known as to where the laser light waveguide region in the semiconductor laser element should be provided. This point will be described in detail later.
[0059]
(Epitaxial growth of nitride semiconductor layer)
Next, a method of manufacturing the semiconductor laser device 1 by forming the nitride semiconductor layer 13 and the like on the n-type GaN substrate 10 will be described with reference to FIG. FIG. 3 is a schematic view showing the semiconductor laser device 1 of FIG. 1 in detail showing the layer structure of the nitride semiconductor layer 13, and the description of the structure in the substrate 10 is omitted.
[0060]
Using MOCVD equipment, Group V raw material NH_ThreeAnd SiH as dopant material to TMGa (trimethylgallium) or TEGa (triethylgallium)_FourAnd an n-type GaN layer 102 having a thickness of 3 μm was formed on the n-type GaN substrate 10 at a substrate temperature of 1050 ° C. Next, TMIn (trimethylindium) as a group III material is added to the above material at a substrate temperature of 800 ° C., and n-type In_0.07Ga_0.93The N crack prevention layer 103 was grown to 40 nm. Next, the substrate temperature was raised to 1050 ° C., and a 1.2 μm-thick n-type Al was used using a TMAl (trimethylaluminum) or TEAl (triethylaluminum) group III material._0.1Ga_0.9An N clad layer 104 was grown. Si as an n-type impurity is 5 × 10¹⁷/ Cm^Three~ 1x10¹⁹/ Cm^ThreeAdded. Subsequently, the n-type GaN light guide layer 105 (Si impurity concentration 1 × 10¹⁶~ 1x10¹⁸/ Cm^Three) Was grown to 0.1 μm.
[0061]
Thereafter, the substrate temperature is lowered to 750 ° C., and 3 cycles of 4 nm thick In_0.1Ga_0.9N well layer and 8nm thick In_0.01Ga_0.99An active layer (multiple quantum well structure) 106 composed of an N barrier layer was grown in the order of barrier layer / well layer / barrier layer / well layer / barrier layer / well layer / barrier layer. At that time, the barrier layer or both the barrier layer and the well layer is formed of SiH._Four(Si impurity concentration is 1 × 10¹⁶~ 1x10¹⁸/ Cm^Three) Was added. It is preferable to interrupt growth between the barrier layer and the well layer or between the well layer and the barrier layer for 1 second or more and 180 seconds or less because the flatness of each layer is improved and the half width of light emission is reduced.
[0062]
When adding As to the active layer, AsH_Three(Arsine) or TBAs (tertiary butyl arsine), PH when adding P to the active layer_Three(Phosphine) or TBP (tertiary butyl phosphine), and when adding Sb to the active layer, TMSb (trimethylantimony) or TESb (triethylantimony) is preferably used as a raw material. Further, when forming the active layer, as an N raw material, NH_ThreeBesides N₂H_Four(Hydrazine), C₂N₂H₈(Dimethylhydrazine) or an organic raw material containing N may be used.
[0063]
Next, the substrate temperature is increased again to 1050 ° C., and p-type Al having a thickness of 20 nm is formed._0.3Ga_0.7N carrier blocking layer 107, 0.1 μm p-type GaN light guide layer 108, 0.5 μm p-type Al_0.1Ga_0.9An N clad layer 109 and a 0.1 μm p-type GaN contact layer 110 were sequentially grown. EtCP as raw material as p-type impurity₂Mg (bisethylcyclopentadienyl magnesium) is used and Mg is 1 × 10¹⁸/ Cm^Three~ 2x10²⁰/ Cm^ThreeAdded at. The p-type impurity concentration of the p-type GaN contact layer 110 is preferably set to increase toward the p-electrode 112. Thereby, the contact resistance due to the formation of the p-electrode is reduced. Further, in order to remove residual hydrogen in the p-type layer that hinders activation of Mg, which is a p-type impurity, a trace amount of oxygen may be mixed during the growth of the p-type layer.
[0064]
After the p-type GaN contact layer 110 is grown in this way, all the inside of the reactor of the MOCVD apparatus is filled with nitrogen carrier gas and NH._ThreeInstead, the temperature was decreased at 60 ° C./min. When the substrate temperature reaches 800 ° C., NH_ThreeWas stopped at the substrate temperature for 5 minutes, and then lowered to room temperature. The substrate holding temperature here is preferably between 650 ° C. and 900 ° C., and the waiting time is preferably 3 minutes or more and 10 minutes or less. Further, the rate of temperature decrease is preferably 30 ° C./min or more.
[0065]
As a result of evaluating the growth film thus prepared by Raman measurement, the characteristics of p-type conversion have already been shown after growth without performing p-type annealing after removing the wafer from the MOCVD apparatus (Mg). Was activated). Further, the contact resistance due to the formation of the p electrode is also reduced. Combining conventional p-type annealing in addition to the above method was preferable because the Mg activation rate was further improved.
[0066]
In_0.07Ga_0.93The N crack prevention layer 103 may have an In composition ratio other than 0.07, or the InGaN crack prevention layer 103 itself may not be present. However, when the lattice mismatch between the cladding layer 104 and the GaN substrate 10 becomes large, it is more preferable in terms of preventing cracks to insert the InGaN crack prevention layer 103. In order to prevent cracks, it is also preferable to use Ge instead of Si as an n-type impurity in each n-type layer.
[0067]
The active layer 106 has a structure that starts with a barrier layer and ends with a barrier layer, but may have a structure that starts with a well layer and ends with a well layer. Further, the number of well layers is not limited to the above-described three layers, and if it is 10 layers or less, the threshold current density is low, and continuous oscillation at room temperature is possible. In particular, when the number of layers is 2 or more and 6 or less, the threshold current density is preferably low. Further, the active layer described above may contain Al.
[0068]
Further, here, a required amount of Si is added to both the well layer and the barrier layer forming the active layer 106, but the impurity may not be added. However, the emission intensity was stronger when an impurity such as Si was added to the active layer. As such an impurity, in addition to Si, any one of O, C, Ge, Zn, and Mg, or a combination of two or more thereof can be used. The total amount of impurities added is about 1 × 10¹⁷~ 8x10¹⁸/ Cm^ThreeThe degree was favorable. Furthermore, the layer to which the impurity is added is not limited to both the well layer and the barrier layer, and the impurity may be added to only one of the layers.
[0069]
p-type Al_0.3Ga_0.7The N carrier block layer 107 may have a composition other than this. AlGaN to which In is added is preferable because it becomes p-type by growth at a lower temperature, so that damage to the active layer 106 during crystal growth can be reduced. The carrier block layer 107 itself may be omitted, but the threshold current density is lower when the carrier block layer 107 is provided. This is because the carrier block layer 107 has a function of confining carriers in the active layer 106. Increasing the Al composition ratio of the carrier block layer 107 is preferable because carrier confinement is strengthened. Further, it is preferable to reduce the Al composition ratio to such an extent that carrier confinement is maintained, because the carrier mobility in the carrier block layer increases and the electrical resistance decreases.
[0070]
Here, as the p-type cladding layer 109 and the n-type cladding layer 104, Al_0.1Ga_0.9Although an N crystal is used, an AlGaN ternary crystal having an Al composition ratio other than 0.1 may be used. When the mixed crystal ratio of Al increases, the energy gap difference and the refractive index difference with the active layer 106 increase, so that carriers and light are efficiently confined in the active layer, and the laser oscillation threshold current density can be reduced. Further, if the Al composition ratio is reduced to such an extent that the confinement of carriers and light is maintained, the carrier mobility in the cladding layer increases, and the operating voltage of the device can be lowered. Considering this point, it is also preferable to set the Al composition ratio of the p-type cladding layer 109 to about 0.06 to 0.09.
[0071]
The thickness of the n-type AlGaN cladding layer 104 is preferably 0.7 μm to 1.5 μm. As a result, the unimodal vertical transverse mode and the optical confinement efficiency are increased, so that the optical characteristics of the laser can be improved and the laser threshold current density can be reduced.
[0072]
Further, although the clad layers 104 and 109 are AlGaN ternary mixed crystals in the above, they may be quaternary mixed crystals such as AlInGaN, AlGaNP, and AlGaNAs. Further, the p-type cladding layer 109 has a superlattice structure composed of a p-type AlGaN layer and a p-type GaN layer, a superlattice structure composed of a p-type AlGaN layer and a p-type AlGaN layer, or a p-type in order to reduce electrical resistance. You may have a superlattice structure which consists of an AlGaN layer and a p-type InGaN layer.
[0073]
Although the crystal growth method using the MOCVD apparatus has been described here, a molecular beam epitaxy method (MBE) or a hydride vapor phase epitaxy method (HVPE) may be used.
[0074]
Subsequently, a description will be given of a process step in which an epitaxial wafer in which each layer of the nitride semiconductor layer 13 is formed on the n-type GaN substrate 10 is taken out from the MOCVD apparatus and processed into a nitride semiconductor laser element chip.
[0075]
(Element fabrication process)
A ridge stripe portion which is the laser light waveguide region 14 is formed in the required position described with reference to FIG. 1 with respect to the n-type GaN substrate 10. This is performed by etching from the epi-wafer surface side to the middle or lower end of the p-type cladding layer 109, leaving a striped portion. Here, the stripe width was 1 to 3 μm, preferably 1.3 to 2 μm, and the distance from the p-type guide layer 108 on the etching bottom surface was 0 to 0.1 μm. Thereafter, an insulating film 113 was formed in a portion other than the ridge stripe portion. Here, AlGaN is used as the insulating film 113. Since the p-type GaN contact layer 110 remaining without being etched is exposed, a p-electrode 112 is deposited on this part and the insulating film 113 by vapor deposition in the order of Pd / Mo / Au.
[0076]
As the insulating film 113, oxides or nitrides such as silicon, titanium, zirconia, tantalum, and aluminum can be used in addition to the above, and other materials for the p-electrode 112 include Pd / Pt / Au, Pd / Au Or Ni / Au may be used.
[0077]
Further, by polishing the back side (substrate side) of the epi wafer, the thickness of the wafer was adjusted to 80 to 200 μm so that the wafer could be easily divided later. The n-electrode 111 was formed in the order of Hf / Al on the back side of the substrate. In addition to the material of the n-electrode 111, Hf / Al / Mo / Au, Hf / Al / Pt / Au, Hf / Al / W / Au, Hf / Au, Hf / Mo / Au, and Hf of these are used. You may use what replaced with Ti and Zr.
[0078]
Finally, the epi-wafer was cleaved in the direction perpendicular to the ridge stripe direction to produce a Fabry-Perot resonator having a resonator length of 600 μm. The resonator length is preferably 250 μm to 1000 μm. By this process, the wafer was formed into a bar shape in which individual laser elements were arranged side by side. The cavity end face of the nitride semiconductor laser element in which the stripe is formed along the <1-100> direction is the {1-100} plane of the nitride semiconductor crystal. Cleaving is not performed by scoring the entire surface of the wafer with a scriber. Instead, the scribing is performed on only a part of the wafer, for example, only on both ends of the wafer or on the part corresponding to both ends of the chip. Cleaved from the starting point. In addition to the method of feeding back at the end face, a DFB (Distributed Feedback) for providing feedback by providing a diffraction grating inside and a DBR (Distributed Bragg Reflector) for providing feedback by providing a diffraction grating outside may be used.
[0079]
After forming a resonator end face of a Fabry-Perot resonator, SiO having a reflectivity of about 80% is formed on this end face.₂And TiO₂The dielectric films were alternately deposited to form a dielectric multilayer reflective film. The dielectric multilayer reflective film may be formed of other dielectric materials. Further thereafter, the bar was divided into individual laser elements to obtain the semiconductor laser element 1 of FIG. A laser beam waveguide region 14 (ridge stripe) is disposed in the center of the laser chip, and the lateral width W of the laser element 1 is 400 μm.
[0080]
In the original n-type GaN substrate 10, dislocation concentration regions 11 are arranged at a pitch P = 400 μm, and a high luminescence region 12 is arranged at the center of each low dislocation region, and as described with reference to FIG. Since each region was arranged with d = 80 μm and t = 120 μm, each semiconductor laser element (chip) contained one dislocation concentration region and one high luminescence region. That is, in this embodiment, W = P and 2 (t + d) = P.
[0081]
The nitride semiconductor laser device 1 chip shown in FIGS. 1 and 3 was produced as described above.
[0082]
(Characteristics of semiconductor laser elements)
In the obtained nitride semiconductor laser device 1, the laser confinement life of 5000 hours or more was achieved under the conditions of a laser output of 60 mW and an ambient temperature of 70 ° C. due to the presence of the current confinement portion at the optimum position. In addition, when the present inventors made a semiconductor laser by the above-mentioned conventional technique and tested it under the same conditions, the lifetime was about 1000 hours.
[0083]
(Positional relationship between laser beam waveguide region and substrate)
As described above, the nitride semiconductor substrate 10 of the present embodiment has a structure such as a striped dislocation concentration region, a low dislocation region, a high luminescence region, or a central region of a low dislocation region. . Or it was produced using the above manufacturing methods. When a nitride semiconductor laser device is manufactured using such a nitride semiconductor substrate, the laser oscillation lifetime varies depending on where the laser light waveguide region of the nitride semiconductor laser device is formed on the nitride semiconductor substrate. The present inventors have found out. Hereinafter, a preferable range of the distances d and t will be examined in detail.
[0084]
FIG. 4 shows the lasers of several semiconductor laser elements manufactured on a P = 600 μm n-type GaN substrate in substantially the same manner as the semiconductor laser element 1 of the present embodiment and the position of the laser light waveguide region 14 changed. 6 is a graph in which the oscillation lifetime is plotted with respect to the distance d between the laser light waveguide region 14 and the dislocation concentrated region 11. The maximum value of the evaluated distance d is 200 μm. Evaluation was performed under conditions of a laser output of 60 mW and an ambient temperature of 70 ° C. As a result, when d ≧ 40 μm, a practical life of 3000 hours was achieved, and when d ≧ 60 μm, 5000 hours or more, sufficient characteristics were obtained. The lifetime was measured only up to 5000 hours, and the upward arrow in FIG. 4 indicates that the laser oscillation lifetime is 5000 hours or longer.
[0085]
In the case of d ≦ 10 μm, the laser beam waveguide region 14 is generally located on the dislocation concentration region 11, but in this case, the characteristics are extremely deteriorated to a life of several hours or less. When the distance d was 20 to 30 μm, a phenomenon was observed in which the drive current gradually increased with time, and laser oscillation became impossible due to thermal runaway when it reached around 200 mA. When a reverse bias was applied to the pn junction and the leakage current of the pn junction was evaluated, the leakage current of the element in which the drive current gradually increased as described above was clearly larger than that of the element with d ≧ 60 μm. This increased with time.
[0086]
In the semiconductor laser device formed near the dislocation concentration region 11 of the GaN substrate 10 manufactured by the above method, dislocations (defects) are generated in the pn junction near the laser light waveguide region 14, or due to this influence. Since the pn junction surface is not flat and disordered, it is estimated that such a leak that increases with the elapse of the driving time occurs, and the life characteristics are deteriorated. As a result, it has been found necessary to set at least d ≧ 40 μm, preferably d ≧ 60 μm.
[0087]
FIG. 5 shows a number of semiconductor laser devices manufactured on the n-type GaN substrate 10 of P = 600 μm in substantially the same manner as the semiconductor laser device 1 of the present embodiment, and the position of the laser light waveguide region 14 is changed. It is the graph which plotted the laser oscillation lifetime with respect to the distance t of the laser beam waveguide area | region 14 and the high luminescence area | region 12. FIG. The maximum value of the evaluated distance t is 200 μm. Evaluation was performed under conditions of a laser output of 60 mW and an ambient temperature of 70 ° C. As a result, a practical life of 3000 hours was achieved when t ≧ 30 μm, and sufficient characteristics of 5000 hours or more were obtained when t ≧ 50 μm. Note that the upward arrow in FIG. 5 indicates that the laser oscillation lifetime is 5000 hours or longer, as in FIG.
[0088]
In the case of t = 0 μm, the laser beam waveguide region 14 is located on the high luminescence region 12, but in this case, the characteristics deteriorated to a lifetime of about 100 hours. When the laser light guide region 14 is disposed in the vicinity of the high luminescence region 12, an increase in device voltage and an increase in drive current value are observed, which is considered to deteriorate the device life. In the substrate 10, a region having a higher resistance than the surroundings exists in the high luminescence region (or the low dislocation region central region) 12 and its vicinity, and it is considered that the device voltage is affected. When the device voltage is observed in detail, it becomes almost constant when t ≧ 50 μm, but slightly increases in a smaller region, and as a result, it is necessary to set at least t ≧ 30 μm, preferably t ≧ 50 μm. It turned out to be.
[0089]
(Preferable range of substrate)
Next, a preferable range of the pitch P at which the dislocation concentration region 11 appears in the GaN substrate 10 was examined. As described above, in manufacturing the GaN substrate 10, it is important that the cross-sectional shape of the surface becomes a serrated uneven shape while exposing the facet surface {11-22} surface. By doing so, a low dislocation region and a high luminescence region 12 can be generated, and a portion away from both the dislocation concentration region 11 and the high luminescence region 12 by a required distance is a region suitable for forming a laser waveguide region. It becomes. Therefore, if the pitch P is not more than twice the sum 70 μm of the minimum value 40 μm of the distance d for obtaining the above effect and 30 μm which is the minimum value of the distance t for obtaining the above effect, the laser waveguide region is obtained. The area to be formed is lost. Therefore, the range of the distance P is limited to P ≧ 140 μm.
[0090]
Further, the value of the distance P is also limited in terms of whether or not the growth can be continued while the position of the concavo-convex shape is kept constant in the formation of the GaN substrate 10. This is because if the position of the concavo-convex shape deviates from the initial position as the growth proceeds, the pitch P is not constant, and the laser waveguide region can be set at a predetermined position with respect to the obtained GaN substrate 10. This is because it becomes difficult. Examining the range of P from this point, it was found that such a state cannot be maintained when P <50 μm, and it is desirable that P ≧ 100 μm.
[0091]
Further, from the function of concentrating dislocations in the dislocation concentration region 11, it is better to generate a large facet surface {11-22} plane. When P ≧ 300 μm, the dislocation concentration region 11 and the low dislocation region are as described above. It was preferable that the defect density was different by 3 digits or more. The upper limit of the distance P is not stipulated from these requirements, but if it is too large, the unevenness of the ingot surface to be obtained becomes large and the number of wafers to be obtained becomes small, so about 1000 μm is appropriate. In conclusion, 140 ≦ P is necessary, and preferably 300 ≦ P, and P ≦ 1000 is preferable if an upper limit is defined.
[0092]
<Embodiment 2>
The semiconductor laser device of the second embodiment is the same as the semiconductor laser device 1 of the first embodiment, but the distances P, d, t, etc. are different. FIG. 6 is a diagram showing the positional relationship between the laser light waveguide region 14 of the semiconductor laser device of the present embodiment, the dislocation concentration region 11 of the n-type GaN substrate, and the high luminescence region 12. A region to be a semiconductor laser element (chip) is denoted by reference numerals 61 and 62. In the second embodiment and the third and fourth embodiments to be described later, the positional relationship among the laser light waveguide region 14, the dislocation concentrated region 11, and the high luminescence region 12 is different from that in the first embodiment. As in the first embodiment, reference numeral 1 denotes a semiconductor laser element.
[0093]
In the manufacturing method of the semiconductor laser device 1 of the present embodiment, the pitch P of the dislocation concentration region 11 of the n-type GaN substrate 60 is 500 μm, and two laser light waveguide regions 14 are arranged in one pitch, and the pitch Two semiconductor laser elements (chips) 1 are formed. The lateral width W of each semiconductor laser element 1 (regions 61 and 62) is 250 μm.
[0094]
For one region 61, the distance d between the laser beam waveguide region 14 and the nearest dislocation concentration region 12 is 100 μm, and the distance t between the laser beam waveguide region 14 and the nearest low dislocation region center region 12 is 150 μm. It is. For the other region 62, the distance d between the laser beam waveguide region 14 and the nearest dislocation concentration region 11 is 150 μm, and the distance t between the laser beam waveguide region 14 and the central region 12 between the nearest lower dislocation regions is 100 μm.
[0095]
The width W of the regions 61 and 62 and the pitch P of the dislocation concentration region 11 have a relationship of 2W = P, and 2 (t + d) = P. Further, when distances d and t for the region 61 are represented by d1 and t1, and distances d and t for the region 62 are represented by d2 and t2, d1 = t2 and d2 = t1.
[0096]
In one region 61, only one dislocation concentrated region 11 exists in the n-type GaN substrate 60, and the high luminescence region 12 does not exist. In the other region 62, the dislocation concentration region 11 does not exist in the n-type GaN substrate 60, and only one high luminescence region 12 exists. Also in the present embodiment, the ranges of the distances d, t, and P where the effects of the present invention appear are as described in the first embodiment, and the effects described in the first embodiment can be obtained within this range.
[0097]
<Embodiment 3>
In the method of manufacturing the semiconductor laser device according to the third embodiment, the number of semiconductor laser devices (chips) 1 manufactured per pitch P is further increased to four. FIG. 7 is a diagram showing the arrangement relationship between the laser light waveguide region 14 of the semiconductor laser element, the dislocation concentration region 11 of the n-type GaN substrate, and the high luminescence region 12 as in FIG. A region to be an individual semiconductor laser element (chip) 1 is denoted by reference numerals 71 to 74.
[0098]
In the manufacturing method of the semiconductor laser device 1 of the present embodiment, the pitch P of the dislocation concentration region 11 of the n-type GaN substrate 70 is 800 μm, and four laser light waveguide regions 14 are arranged in one pitch, and the pitch Four semiconductor laser elements (chips) 1 are formed. Each semiconductor laser element 1 (regions 71 to 74) has an equal lateral width W of 200 μm. For the regions 71, 72, 73 and 74 arranged in order, the distances d between the laser beam waveguide region 14 and the nearest dislocation concentration region 11 are 80, 280, 320, and 120 μm, respectively. The distances t from the adjacent low dislocation region central region 12 are 320, 120, 80, and 280 μm, respectively.
[0099]
As shown in the figure, the region 71 includes one dislocation concentration region 11, the region 73 includes one high luminescence region 12, and the region 72 and the region 74 include the dislocation concentration region 11 and the high luminescence region 12. None of them are included. In the method for manufacturing the semiconductor laser device 1 of the present embodiment, 4W = P, and 2 (t + d) = P for each laser light waveguide region 14.
[0100]
Also in the present embodiment, the ranges of the distances d, t, and P where the effects of the present invention appear are as described in the first embodiment, and the effects described in the first embodiment can be obtained within this range.
[0101]
<Embodiment 4>
In the fourth embodiment, the width W> pitch P, contrary to the second or third embodiment. FIG. 8 is a diagram showing the arrangement relationship between the laser light waveguide region 14 of the semiconductor laser device of the present embodiment, the dislocation concentration region 11 of the n-type GaN substrate, and the high luminescence region 12 as in FIG. A region to be the semiconductor laser element (chip) 1 in the GaN substrate 80 is denoted by reference numeral 81.
[0102]
In the manufacturing method of the semiconductor laser device 1 of the present embodiment, the pitch P of the dislocation concentration region 11 of the n-type GaN substrate 80 is 200 μm, and the lateral width W of the semiconductor laser device 1 (region 81) is 300 μm. That is, 2/3 semiconductor laser elements (chips) 1 are formed per pitch (one chip 1 is formed at 1.5 pitches). The distance d between the laser beam waveguide region 14 and the nearest dislocation concentration region 11 is 50 μm, and the distance t between the laser beam waveguide region 14 and the nearest low dislocation region center region 12 is 50 μm.
[0103]
As shown in the figure, each of the dislocation concentration regions 11 and the high luminescence regions 12 included in one semiconductor laser element (chip) 1 is one or more. In the semiconductor laser manufacturing method of the present embodiment, (2/3) W = P, and 2 (t + d) = P for each laser light waveguide region 14.
[0104]
Also in the present embodiment, the ranges of the distances d, t, and P where the effects of the present invention appear are as described in the first embodiment, and the effects described in the first embodiment can be obtained within this range.
[0105]
In the first to fourth embodiments described above, the arrangement in which one, two, four, and two thirds of semiconductor laser elements (chips) are formed per pitch has been described. However, the scope of application of the present invention is not limited to this. However, it may be arranged such as 6, 1/2, 1/3, or the like. Further, if the arrangement of some elements on the GaN substrate is allowed to deviate from the required range of t and d, it is set to a number other than an integer multiple or a value that can be expressed in a simple fraction. It is also possible to do.
[0106]
<Embodiment 5>
In the fifth embodiment, the nitride semiconductor laser element 1 having the ridge stripe structure described in the first to fourth embodiments is replaced with a nitride semiconductor laser element 2 having a current blocking layer. The nitride semiconductor laser element 2 of the present embodiment having a current blocking layer will be described with reference to FIG.
[0107]
The semiconductor laser device 2 of the present embodiment includes an n-type GaN substrate 200, an n-type GaN layer 201 formed thereon, and an n-type In._0.07Ga_0.93N crack prevention layer 203, n-type Al_0.1Ga_0.9N-clad layer 204, n-type GaN light guide layer 205, active layer 206, p-type Al_0.2Ga_0.8N carrier block layer 207, p-type GaN light guide layer 208, p-type Al_0.1Ga_0.9N first cladding layer 209a, current blocking layer 220, p-type Al_0.1Ga_0.9The N second cladding layer 209b, the p-type InGaN contact layer 210, the p-electrode 212, and the n-electrode 211 are configured.
[0108]
The current blocking layer 220 may be a layer that blocks current so that the current injected from the p-type electrode 112 can only pass through the width of the current blocking layer shown in FIG. For example, as the current blocking layer 220, n-type Al_0.25Ga_0.75An N layer may be used. The Al composition ratio of the current blocking layer 220 is not limited to 0.25, and other values may be used. In the present embodiment, the opening of the current blocking layer 220 corresponds to the laser light waveguide region 14, and also in this embodiment, the ranges of the distances d, t, and P where the effect of the present invention appears are the same as those in the embodiment. As described in the first embodiment, the effects described in the first embodiment can be obtained within this range.
[0109]
<Embodiment 6>
In the sixth embodiment, at least one element of the element group of As, P, and Sb is contained in the active layer of the nitride semiconductor laser element 1 or 2. Other configurations are as described above.
[0110]
In the present embodiment, at least one of the element groups of As, P, and Sb is contained in at least the well layer of the active layers 106 and 206 constituting the nitride semiconductor light emitting laser element 1 or 2. . Here, when the composition ratio of the sum of the elements contained in the well layer is X and the composition ratio of the N element in the well layer is Y, X is smaller than Y and X / (X + Y) is 0.3. (30%) or less, preferably 0.2 (20%) or less. In addition, the lower limit of the total sum of the element groups is 1 × 10¹⁸/ Cm^ThreeThat's it.
[0111]
When the composition ratio X is higher than 20%, concentration separation in which the composition ratio of each element is different for each region in the well layer gradually starts to occur. Further, when the composition ratio X becomes higher than 30%, this time, the concentration separation starts to shift to a crystal separation in which a hexagonal system and a cubic system are mixed, and the crystallinity of the well layer starts to deteriorate. On the other hand, the total addition amount of the above element group is 1 × 10¹⁸/ Cm^ThreeWhen it becomes smaller than this, the effect by containing the said element in a well layer becomes difficult to be acquired.
[0112]
The effect of this embodiment is that the effective mass of electrons and holes in the well layer is reduced and the mobility of electrons and holes in the well layer is increased by containing As, P or Sb in the well layer. is there. In the case of a semiconductor laser element, the former means that a carrier inversion distribution for laser oscillation can be obtained with a small amount of current injection, and the latter means that even if electrons and holes disappear in the active layer due to light emission recombination, It means that holes are injected at high speed by diffusion. That is, as compared with the InGaN-based nitride semiconductor laser element that does not contain any of As, P, and Sb in the active layer as currently reported, the nitride semiconductor laser element of this embodiment has a threshold current. Low density and excellent noise characteristics. Also in the present embodiment, the ranges of the distances d, t, and P at which the effect of the present invention appears are as described in the first embodiment.
[0113]
<Embodiment 7>
In the seventh embodiment, a selective growth technique is used when forming each nitride semiconductor layer on a substrate, and the others are the same as in any of the above-described embodiments.
[0114]
Selective growth technology uses materials that suppress growth (eg, SiO 2₂When a nitride semiconductor layer is formed on the substrate in advance by providing a mask having an opening made of an oxide such as oxide, nitride such as SiN, AlN) on the substrate, This is a technology that controls the growth in the direction. As a result, cracks that can occur with the growth of each nitride semiconductor layer are effectively prevented. The mask can be provided corresponding to the dislocation concentration region 11 and the high luminescence region 12, and can be provided regardless of these regions. Providing a mask at least directly below the laser waveguide region 14 is desirable in terms of effectively preventing cracks that may occur in the laser waveguide region.
[0115]
In each of the above-described first to seventh embodiments, an example in which GaN is used as a substrate has been described. However, a nitride semiconductor substrate made of a material as described in “Means for Solving the Problems” is used. You can also. The material of each nitride semiconductor layer grown on the nitride semiconductor substrate can also be replaced with a nitride semiconductor material as described in “Means for Solving the Problems”.
[0116]
<Eighth embodiment>
In the eighth embodiment, the nitride semiconductor laser element of the present invention is applied to a semiconductor optical device.
[0117]
The nitride semiconductor laser element (oscillation wavelength of 330 to 550 nm) of the present invention is preferable in the following points when used for a semiconductor optical device, for example, an optical pickup device. Each nitride semiconductor laser device has high output (30 mW), operates stably even in a high temperature atmosphere (60 ° C.), and has a long laser oscillation life, so that high reliability is required for high density recording / reproduction. (The shorter the oscillation wavelength, the higher the density of recording and reproduction becomes possible).
[0118]
FIG. 10 shows a schematic configuration of an optical disk apparatus (an apparatus having an optical pickup, for example, a DVD apparatus) as an example in which the nitride semiconductor laser element of the present invention is used in a semiconductor optical apparatus. The optical disc apparatus 300 includes an optical pickup 301, a control circuit 302, a motor 303 that rotates the disc D, and a motor 304 that moves the optical pickup 301. The optical pickup 301 includes a semiconductor laser element 305, a beam splitter 306, a mirror 307, an objective lens 308, and a photodetector 309. The semiconductor laser element 305 is the nitride semiconductor laser element 1 or 2 according to any one of the embodiments described above.
[0119]
When recording information, the laser light L emitted from the semiconductor laser element 305 is modulated by the control circuit 302 in accordance with the input information, and converges on the recording surface of the disk D via the beam splitter 306, the mirror 307, and the objective lens 308. , Information is recorded on the disk D. Further, while the semiconductor laser element 305 emits the unmodulated laser beam L, the information can also be obtained by modulating the magnetic field at the portion of the recording surface of the disk D where the laser beam L converges according to the input information. Can be recorded. When reproducing information, the laser light L optically changed by the pit arrangement on the disk D enters the photodetector 309 through the objective lens 308, the mirror 307, and the beam splitter 306, and is reflected by the photodetector 309. The playback signal. The power of the laser beam L output from the semiconductor laser element 305 is, for example, about 30 mW during recording and about 5 mW during reproduction.
[0120]
In addition to such an optical disk device having an optical pickup device, the semiconductor laser element of the present invention can be used for, for example, a laser printer, a barcode reader, a projector using a laser of three primary colors (blue, green, red). Yes, it is suitable as a light source with high output and long life.
[0121]
【The invention's effect】
In the present invention in which the laser beam waveguide region of the nitride semiconductor layer is shifted by 40 μm or more from the dislocation concentration region of the nitride semiconductor substrate, the influence of the substrate dislocation to the laser beam waveguide region is suppressed, and nitriding with a long laser oscillation lifetime is achieved. A semiconductor laser device can be obtained.
[0122]
Further, in the present invention in which the laser light waveguide region of the nitride semiconductor layer is shifted by 30 μm or more from the central region of the low dislocation region or the high luminescence region of the nitride semiconductor substrate, the laser light guide is formed on a portion of the substrate having a certain property. The wave region can be positioned, and a nitride semiconductor laser element having a long laser oscillation lifetime can be obtained.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view schematically showing the structure of a semiconductor laser device according to a first embodiment.
FIG. 2 is an enlarged longitudinal sectional view (a), a perspective view (b), a longitudinal sectional view (c), and a plan view (d) schematically showing a manufacturing process of a nitride semiconductor substrate in the present invention.
FIG. 3 is a longitudinal sectional view schematically showing a layer configuration of the semiconductor laser element according to the first embodiment.
FIG. 4 is a diagram showing a relationship between a laser oscillation lifetime and a distance between a laser beam waveguide region and a dislocation concentration region in a nitride semiconductor laser element.
FIG. 5 is a diagram showing a relationship between a laser oscillation lifetime and a distance between a laser beam waveguide region and a high luminescence region in a nitride semiconductor laser element.
6 is a plan view schematically showing the method for manufacturing the semiconductor laser element of the second embodiment. FIG.
7 is a plan view schematically showing the method for manufacturing the semiconductor laser element of the third embodiment. FIG.
8 is a plan view schematically showing the method for manufacturing the semiconductor laser element of the fourth embodiment. FIG.
FIG. 9 is a longitudinal sectional view schematically showing another layer configuration of the semiconductor laser elements according to the first to fourth embodiments.
10 is a block diagram showing a schematic configuration of a semiconductor optical device according to an eighth embodiment. FIG.
[Explanation of symbols]
1, 2 Nitride semiconductor laser device
10 n-type GaN substrate
11 Dislocation concentration region
12 Low dislocation region central region (high luminescence region)
13 Nitride semiconductor layer
14 Laser light guide region
15 p electrode
16 n electrode
21 Support base
22 n-type GaN layer
23 {11-22} plane
24 Uneven bottom bottom
25 Top of unevenness
26 {0001} face
60 n-type GaN substrate
61, 62 Nitride semiconductor laser element formation region
70 n-type GaN substrate
71-74 Nitride semiconductor laser element formation region
80 n-type GaN substrate
81 Nitride semiconductor laser element formation region
102 n-type GaN layer
103 n-type InGaN crack prevention layer
104 n-type AlGaN cladding layer
105 n-type GaN optical guide layer
106 InGaN active layer
107 p-type AlGaN carrier block layer
108 p-type GaN optical guide layer
109 p-type AlGaN cladding layer
110 p-type GaN contact layer
111 n electrode
112 p electrode
113 Insulating film
200 n-type GaN substrate
201 n-type GaN layer
203 n-type InGaN crack prevention layer
204 n-type AlGaN cladding layer
205 n-type GaN optical guide layer
206 Active layer
207 p-type AlGaN carrier block layer
208 p-type GaN optical guide layer
209a p-type AlGaN first cladding layer
209b p-type AlGaN second cladding layer
210 p-type InGaN contact layer
211 n electrode
212 p-electrode
220 Current blocking layer
300 Optical disk device
301 Optical pickup
302 Control circuit
303, 304 Motor
305 Nitride semiconductor laser device
306 Beam splitter
307 mirror
308 Objective lens
309 photodetector

Claims (12)

And the nitride semiconductor substrate, a nitride semiconductor laser device and a nitride semiconductor layer laminated thereon,
The nitride semiconductor substrate,
Dislocation concentration region formed in stripes by concentrating dislocations at the bottom of the groove by growing while maintaining the inclined surface that is the side surface of the groove having a V-shaped cross section as the facet surface. When,
A low dislocation region which is a region excluding a dislocation concentration region ;
Is included,
The center of the low dislocation region includes a stripe-shaped high luminescence region generated by the growth of the facet plane {0001} plane , and the high luminescence region and the dislocation concentration region are substantially parallel to each other. Yes,
In the nitride semiconductor layer ,
Includes stripe-shaped laser beam waveguide region, the laser optical waveguide region, as well as positioned on the low dislocation region has become substantially parallel to the dislocation-concentrated region,
The distance d in the horizontal direction between the laser beam guiding region and the nearest dislocation concentration region is 40 μm or more,
A nitride semiconductor laser device in which a horizontal distance t between a laser light waveguide region and a high luminescence region closest thereto is 30 μm or more. The nitride semiconductor laser element according to claim 1, wherein the distance d is 60 μm or more. The nitride semiconductor substrate has a plurality of dislocation concentration regions,
The distance P between adjacent dislocation concentration regions is 140 μm or more.
The nitride semiconductor laser device according to claim 1 or 2 . The nitride semiconductor laser device according to claim 3 , wherein the distance P is 300 μm or more. The nitride semiconductor laser element according to claim 1 , wherein the dislocation concentration region is substantially parallel to the [1-100] direction of the nitride semiconductor substrate. The nitride semiconductor laser device according to claim 1 , wherein the distance t is 50 μm or more. A semiconductor optical device comprising the nitride semiconductor laser element according to any one of claims 1 to 6 as a light source. By making the slope, which is the side of the groove having a V-shaped cross section, as a facet surface, and growing while maintaining the slope of the facet surface, the dislocations are concentrated on the bottom of the groove to form stripes and substantially parallel to each other A plurality of dislocation concentration regions,
A low dislocation region which is a region excluding the dislocation concentration region ;
And having
The center of the low-dislocation regions, by growing while expose the facets {0001} plane, on a nitride semiconductor substrate which cause substantially parallel stripes of high luminescent regions with respect to dislocation-concentrated region,
Forming a nitride semiconductor layer containing a nitride semiconductor laminated structure having a stripe-shaped laser beam waveguide region seen including,
A laser light guide region is provided on the low dislocation region substantially parallel to the dislocation concentration region,
The horizontal distance d between the laser light guide region and the nearest dislocation concentration region is set to 40 μm or more ,
A method for manufacturing a nitride semiconductor laser device, wherein a horizontal distance t between a laser beam waveguide region and a high luminescence region closest thereto is 30 μm or more. The method for manufacturing a nitride semiconductor laser device according to claim 8 , wherein the distance d is 60 μm or more. 10. The method for manufacturing a nitride semiconductor laser element according to claim 8 , wherein a nitride semiconductor substrate having a distance P between adjacent dislocation concentration regions of 140 [mu] m or more is used. The method for manufacturing a nitride semiconductor laser device according to claim 10 , wherein a nitride semiconductor substrate having a distance P of 300 μm or more is used. The method for manufacturing a nitride semiconductor laser element according to claim 8, wherein the distance t is 50 μm or more.

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