JP4646093B2 - Nitride semiconductor laser device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nitride semiconductor laser element made of a nitride semiconductor having excellent temperature characteristics at high temperatures and used as a light source for a display element, a display, an optical disk, etc., and a method for manufacturing the same.
[0002]
[Prior art]
Conventionally, nitride semiconductors have been used or studied as materials for light emitting elements and high power devices. For example, in the case of a light emitting element, it can be technically used as an element capable of emitting a wide range of light from blue to orange by adjusting the composition of the light emitting element. In recent years, blue light-emitting diodes, green light-emitting diodes, and the like have been put to practical use by utilizing such characteristics, and blue-violet semiconductor lasers have been developed as nitride semiconductor laser elements.
[0003]
Of these, for nitride semiconductor laser devices, SiO₂A technique in which the dislocation density in the crystal is reduced by applying a selective growth technique using a material such as Appl. Phys. Lett. 72 (1998) p211-p213. In this report, SiO is deposited on an n-type GaN film.₂A selective growth mask made of GaN is formed, and an n-type GaN film is regrown thereon to form SiO.₂The mask is covered to produce a flat surface and its SiO₂A laser structure is formed on the mask covering. By using this method, defects in the laser element are reduced and the laser element characteristics are improved.
[0004]
Further, in order to reduce the operating current of the semiconductor laser element and stabilize the horizontal transverse mode (direction parallel to the active layer), a semiconductor laser element having a structure as shown in FIG. 15 has been conventionally used. This semiconductor laser device includes a substrate 10, a low-temperature buffer layer 11, an n-type GaN contact layer 12, an n-type AlGaN cladding layer 13, an n-type GaN light guide layer 14, an active layer 15, an AlGaN carrier block layer 16, p-type GaN light. The guide layer 17, the p-type AlGaN cladding layer 18, the p-type GaN contact layer 19, the insulating film 20, the n-type electrode 21, and the p-type electrode 22 are configured. However, the above Appl. Phys. Lett. 72 (1998) p211-p213 reports that the n-type contact layer 12 has SiO 2₂A mask is inserted, and a cladding layer made of a GaN / AlGaN superlattice is formed instead of the n-type AlGaN cladding layer 13.
[0005]
Such a laser structure is called a ridge stripe structure. According to this ridge stripe structure, the width Wp of the stripe electrode is narrowed to about 2 μm, and the p-type cladding layer 18 is dug down to the vicinity of the p-type light guide layer 17 to narrow current injection into the active layer 15. In addition, the operating current of the laser can be reduced. Further, in the region 24 and the ridge stripe region 23 dug down to the vicinity of the p-type light guide layer 17, a difference occurs in the equivalent refractive index of the active layer 15 and the horizontal transverse mode is confined. The transverse mode can be stabilized.
[0006]
On the other hand, with respect to the vertical transverse mode (direction perpendicular to the active layer), in order to obtain a stable single (single peak) mode in a general nitride semiconductor laser element including the ridge stripe laser structure described above, the cladding layer A method is adopted in which the average Al composition ratio is increased or the thickness of the cladding layer is increased so that the vertical transverse mode light does not leak. In particular, in the latter method, when the n-type cladding layer is thin, vertical transverse mode light leaks into the n-type contact layer between the substrate and the n-type cladding layer. The leaked vertical transverse mode light is outside the cladding layer (for example, n-type AlGaN cladding layer) and has a layer having a refractive index larger than the equivalent refractive index of the cladding layer (for example, In film having a thickness of 0.3 μm or more)._xGa_1-xWhen N (0 ≦ x ≦ 1) layer) is provided, in FFP (far field pattern), a sub-peak appears on the wide angle side to impair the unimodality of the vertical transverse mode. FIGS. 16B and 17B show NFP (near field pattern) and FFP in a conventional nitride semiconductor laser device. As shown in these figures, sub-peaks are observed.
[0007]
[Problems to be solved by the invention]
However, in order to obtain a unimodal and stable vertical transverse mode, increasing the average Al composition ratio in the cladding layer or increasing the thickness of the cladding layer can lead to generation of cracks and crystal defects due to lattice mismatch. The increase in crystallinity caused by the increase and the increase in the resistance of the device caused an increase in the laser threshold current. For this reason, the growth conditions of the clad layer containing Al that can be manufactured as a laser element are limited, and a sufficiently unimodal and stable vertical transverse mode cannot be obtained.
[0008]
In contrast, Appl. Phys. Lett. 72 (1998) p211-p213, the clad layer by GaN / AlGaN superlattice suppresses the generation of cracks compared to the case where the commonly used AlGaN clad layer has the same average Al composition ratio. The clad layer thickness can be increased. However, since Al generally has a strong gas phase reaction and is a superlattice, the superlattice period varies due to valve switching, and the average Al composition ratio also changes. For this reason, crystal growth of a superlattice containing Al is difficult, and reproducibility of the cladding layer thickness and the average Al composition ratio in the cladding layer is difficult to obtain. Even in the case of a clad layer made of a GaN / AlGaN superlattice, an increase in Al composition ratio and a decrease in crystallinity and an increase in resistance of the element due to an increase in the clad layer thickness are inevitable.
[0009]
On the other hand, the stabilization of the horizontal transverse mode using the ridge stripe structure is achieved by ridge stripes in which the clad layer is dug down to the vicinity of the p-type light guide layer with a difference in refractive index that exceeds the decrease in refractive index due to the increase in the density of constricted carriers. It is necessary to build in the structure. Therefore, stabilization of the horizontal transverse mode depends on the thickness of the dug cladding layer. However, since such a ridge stripe structure is generally formed by dry etching, it is difficult to control the thickness of the cladding layer that has been dug down and the reproducibility of the layer thickness is poor, and as a result, the horizontal transverse mode has become unstable. It was. Further, since the ridge stripe structure is formed by using etching, the exposed end face is deteriorated, and the laser oscillation threshold current density is increased, thereby adversely affecting the laser element characteristics. Furthermore, stronger light confinement has been required to reduce the laser oscillation threshold current density.
[0010]
Since the instability of these transverse modes generates NFP and FFP sub-peaks as shown in FIGS. 16B and 17B, it is very problematic for a device using a laser such as an optical disk. there were. Thus, stable lateral mode controllability has been desired.
[0011]
The present invention has been made to solve such problems of the prior art, and an object of the present invention is to provide a nitride semiconductor laser device capable of obtaining a unimodal stable vertical transverse mode and a method of manufacturing the same. . It is another object of the present invention to provide a nitride semiconductor laser device capable of reducing the laser oscillation threshold current density due to light confinement in the horizontal transverse mode and obtaining a single-peak stable horizontal transverse mode and a method for manufacturing the same.
[0012]
[Means for Solving the Problems]
  A nitride semiconductor laser device according to the present invention includes a semiconductor laminated structure formed of a nitride semiconductor and formed on a substrate, including a pair of upper and lower clad layers and an active layer sandwiched between the clad layers, and an injection into the active layer A nitride semiconductor laser element having a stripe-shaped current confinement structure for confining a generated current, on a portion facing the stripe-shaped current confinement structure on the outside of the cladding layer above or below the active layer, Has light absorption functionIncluding metal filmThe light absorption mask is arranged so as to absorb the guided light leaking from the upper or lower clad layer, thereby achieving the above object.
  A nitride semiconductor laser device according to the present invention includes a semiconductor laminated structure formed of a nitride semiconductor and formed on a substrate, including a pair of upper and lower clad layers and an active layer sandwiched between the clad layers, and an injection into the active layer Nitride semiconductor laser device having a stripe-shaped current confinement structure for confining a generated current, on both sides of a portion of the upper or lower cladding layer facing the stripe-shaped current confinement structure Have light absorption functionIncluding metal filmLight absorption mask, light absorption maskAnd the active layer facing thisThe gain is increased so that the above-mentioned object can be achieved.
[0013]
  The nitride semiconductor laser device of the present invention is the light absorption mask.ConfigureThe metal film is made of a metal on which a nitride semiconductor is not directly epitaxially grown, and the semiconductor multilayer structure has an active layer sandwiched between a pair of clad layers and both clad layers, and is opposite to the substrate of the semiconductor multilayer structure A contact layer having a striped electrode on the side surface, in contact with the lower surface of the clad layer closer to the substrate, having a refractive index higher than that of the clad layer and having a refractive index different from that of the substrate; The metal film is disposed below the stripe electrode and at a position within half of the contact layer thickness from the interface between the clad layer and the contact layer toward the substrate, or closer to the substrate A contact layer that is in contact with the lower surface of the cladding layer and has a refractive index higher than that of the cladding layer and substantially the same refractive index as that of the substrate; The metal film is disposed at a position within half of the total thickness of the contact layer thickness and the substrate thickness from the interface between the cladding layer and the contact layer toward the substrate, or the cladding closer to the substrate The layer has a lower refractive index than the substrate, and there is no contact layer between the substrate and the cladding layer, below the stripe electrode, from the interface between the cladding layer and the substrate The metal film is disposed at a position within half the thickness of the substrate toward the lower surface of the substrate, or on the cladding layer or the cladding below the stripe electrode and closer to the substrate The metal film may be arranged in a layer at a position of 0.5 μm or more from the lower surface of the active layer toward the substrate.
[0014]
  The nitride semiconductor laser device of the present invention is
The light absorption maskConfigureThe metal film is made of a metal on which a nitride semiconductor is not directly epitaxially grown, and the semiconductor laminated structure has an active layer sandwiched between a pair of cladding layers and both cladding layers, and a ridge stripe portion above the active layer. A contact layer having a refractive index higher than that of the cladding layer and having a refractive index different from that of the substrate, in contact with the lower surface of the cladding layer closer to the substrate, and below the ridge stripe portion. The metal film is disposed at a position within half of the contact layer thickness from the interface between the cladding layer and the contact layer toward the substrate, or in contact with the lower surface of the cladding layer closer to the substrate, A contact layer having a refractive index higher than that of the cladding layer and having substantially the same refractive index as that of the substrate; and below the ridge stripe portion, The metal film is disposed at a position within half of the total thickness of the contact layer thickness and the substrate thickness from the interface with the tact layer toward the substrate, or the clad layer closer to the substrate is closer than the substrate. However, the refractive index is low, and no contact layer exists between the substrate and the cladding layer, and is below the ridge stripe portion and from the interface between the cladding layer and the substrate toward the lower surface of the substrate. The metal film is disposed at a position within half the thickness of the substrate, or below the ridge stripe portion and on or in the cladding layer closer to the substrate, The metal film may be arranged at a position of 0.5 μm or more from the lower surface of the active layer toward the substrate.
[0015]
  The nitride semiconductor laser device of the present invention is the light absorption mask.ConfigureA metal film is made of a metal on which a nitride semiconductor is not directly epitaxially grown, the semiconductor multilayer structure has an active layer, and a stripe electrode is provided on a surface opposite to the substrate of the semiconductor multilayer structure, The metal film is disposed at a position within 2 μm from the lower surface or the upper surface of the layer, and the mask including the metal film is disposed below the stripe-like electrode so as to have a portion not covered with the mask. It can be set as a structure.
[0016]
  The nitride semiconductor laser device of the present invention is
The light absorption maskConfigureThe metal film is made of a metal on which a nitride semiconductor is not directly epitaxially grown, and the semiconductor laminated structure has an active layer sandwiched between a pair of cladding layers and both cladding layers, and a ridge stripe portion above the active layer. The metal film is disposed at a position within 2 μm from the lower or upper surface of the active layer, and the mask including the metal film has a portion not covered with the mask below the ridge stripe portion. Can be configured.
[0017]
In the nitride semiconductor laser element of the present invention, the mask interval is preferably 1 μm or more and 15 μm or less.
[0018]
  The nitride semiconductor laser device of the present invention is the light absorption mask.ConfigureThe thickness of the metal film is preferably 0.01 μm or more, and the thickness of the entire mask including the metal film is preferably 2 μm or less.
[0019]
  The nitride semiconductor laser device of the present invention is the light absorption mask.ConfigureThe metal film is a metal material containing at least one of W, Ti, Mo, Ni, Al, Pt, Pd, Au and alloys thereof, or a plurality of layers containing at least one of those metals and alloys What consists of a composite film comprised by these can be used.
[0020]
  In the nitride semiconductor laser device of the present invention, the light absorption maskConfigureA configuration in which the metal film is directly covered with an insulating film can be employed.
[0021]
  The nitride semiconductor laser device of the present invention is the above-mentionedRimAs SiO₂Or SiN_xCan be used.
[0022]
  The nitride semiconductor laser device of the present invention is the light absorption mask.ConfigureThe metal film is preferably provided in a stripe shape in the <1-100> direction with respect to the underlying nitride semiconductor layer.
[0023]
  The nitride semiconductor laser device according to the present invention includes the light absorption mass.KThe upper nitride semiconductor layer may not be covered flat and may have a recess.
[0024]
  The method for producing a nitride semiconductor laser device according to the present invention is a method for producing the nitride semiconductor laser device according to the present invention.Light absorptionWhen the mask is covered with the nitride semiconductor layer, 10% or more of the nitrogen carrier gas is used with respect to the total carrier gas, thereby achieving the above object.
[0025]
The operation of the present invention will be described below.
[0026]
In the present invention, in a semiconductor laminated structure made of a nitride semiconductor, by providing a mask including a metal film having at least a light absorption function in a region where guided light reaches, light leakage or light from the active layer is provided. It is possible to stabilize the single horizontal transverse mode and the single vertical transverse mode and to confine the light in the horizontal transverse mode.
[0027]
The light absorption effect in the vertical transverse mode hardly depends on the position where the metal film is formed, and only depends on the thickness of the metal film. However, since the unimodal (single mode) vertical transverse mode depends on the formation position of the metal film, it is preferably as close to the active layer as possible.
[0028]
Therefore, (1) when a contact layer having a refractive index higher than that of the cladding layer and having a refractive index different from that of the substrate is in contact with the lower surface of the cladding layer closer to the substrate, the striped electrode A metal film having a light absorption function is disposed at a position within half of the thickness of the contact layer from the interface between the cladding layer and the contact layer toward the substrate. In this case, the refractive index of the substrate may be higher or lower than that of the cladding layer as long as it is different from that of the contact layer. (2) In the case of having a contact layer in contact with the lower surface of the cladding layer closer to the substrate and having a refractive index higher than that of the cladding layer and substantially the same refractive index as the substrate, A metal film having a light absorption function is disposed below the stripe-like electrode and at a position within half of the total thickness of the contact layer thickness and the substrate thickness from the interface between the cladding layer and the contact layer toward the substrate. In this case, when the substrate thickness is thicker than the contact layer, the mask is disposed in the substrate. However, the mask may be disposed when forming the substrate (for example, a GaN thick film). (3) When such a contact layer is not provided, and the clad layer closer to the substrate has a lower refractive index than the substrate, the clad layer and the substrate A mask including a metal film having a light absorption function is disposed at a position within half the thickness of the substrate from the interface toward the lower surface of the substrate. In this case as well, a mask is disposed in the substrate. However, a mask may be disposed when forming a substrate (for example, a GaN thick film) in the same manner as described above. In addition, this makes it possible to achieve unimodal vertical transverse mode. Further, by using a metal material for which the nitride semiconductor is not directly epitaxially grown as the metal film, the dislocation density can be reduced by the mask and the laser life characteristics can be improved. In the case of (1) above, since it depends on the refractive index of the contact layer in contact with the cladding layer, a metal film is disposed at a position within half the thickness of the contact layer, and in the case of (2) above, the contact layer If the refractive index of the substrate and the substrate are substantially the same, it can be considered as a single body, so a metal film is disposed at a position within half the thickness including the substrate, and in the case of (3) above, there is no contact layer. Since the substrate is in contact with the cladding layer and the substrate is the same as the contact layer, a metal film is disposed at a position within half the substrate thickness. That is, although the names of the contact layer and the substrate are different, the focus is substantially only on the refractive index of the layer called by the name.
[0029]
Here, when the metal film is provided on the clad layer closer to the substrate or in the clad layer, if the metal film is disposed at a position less than 0.5 μm from the lower surface of the active layer toward the substrate, the light absorption effect by the metal film is achieved. As a result, gain loss in laser oscillation increases, leading to an increase in laser oscillation threshold current density. Therefore, when a metal film is disposed on or in the cladding layer closer to the substrate, it is below the stripe electrode and at a position of 0.5 μm or more from the lower surface of the active layer toward the substrate. Deploy. In the present specification, the surface closer to the substrate is referred to as the lower surface, and the surface opposite to the lower surface is referred to as the upper surface.
[0030]
In the ridge stripe structure, when a contact layer having a refractive index higher than that of the clad layer and having a refractive index different from that of the substrate is in contact with the lower surface of the clad layer closer to the substrate, the ridge stripe portion A metal film having a light absorption function is disposed at a position within half of the thickness of the contact layer from the interface between the cladding layer and the contact layer toward the substrate. Further, when a contact layer having a refractive index higher than that of the cladding layer and having substantially the same refractive index as that of the substrate is in contact with the lower surface of the cladding layer closer to the substrate, the ridge stripe portion A metal film having a light absorption function is disposed at a position within half of the total thickness of the contact layer thickness and the substrate thickness from the interface between the cladding layer and the contact layer toward the substrate. Further, when such a contact layer is not provided and the clad layer closer to the substrate has a lower refractive index than the substrate, it is below the ridge stripe portion and from the interface between the clad layer and the substrate. A metal film having a light absorption function is disposed at a position within half the thickness of the substrate toward the lower surface of the substrate. Alternatively, a metal having a light absorption function below the ridge stripe portion, on or in the cladding layer closer to the substrate, and at a position of 0.5 μm or more from the lower surface of the active layer toward the substrate Place the membrane. As a result, it is possible to realize a single peak in the vertical and transverse modes. Further, by using a metal material for which the nitride semiconductor is not directly epitaxially grown as the metal film, the dislocation density can be reduced by the mask and the laser life characteristics can be improved. Furthermore, stabilization of the horizontal transverse mode and oscillation threshold current density are achieved by the ridge stripe structure.
[0031]
Further, when a portion not covered with a metal film is provided below the stripe electrode or the ridge stripe portion, a mask is provided by arranging a metal film having a light absorption function at a position exceeding 2 μm from the lower surface or the upper surface of the active layer. The difference in transmission refractive index hardly occurs between the portion where the mask is not provided and the portion where the mask is not provided, and the light confinement effect in the horizontal transverse mode is weakened. Therefore, a metal film having a light absorption function is disposed at a position within 2 μm from the lower surface or the upper surface of the active layer, and a portion not covered with the metal film is provided below the stripe-shaped electrode or ridge stripe portion, so that horizontal horizontal It becomes possible to increase the mode optical confinement and reduce the laser oscillation current density.
[0032]
In this case, according to experiments by the inventors of the present application, when the mask interval (interval between metal films) is 1 μm or more and 15 μm or less, the horizontal and transverse modes are stabilized.
[0033]
When the thickness of the metal film is 0.01 μm or more, it is possible to increase the absorption rate of laser light and stabilize the unimodal vertical transverse mode. Further, if the thickness of the entire mask including the metal film is 2 μm or less, a flat surface can be obtained when the mask is covered with a nitride semiconductor film.
[0034]
In general, since the temperature for forming the nitride semiconductor film is around 1000 ° C., it is preferable to use a metal material that can sufficiently withstand this temperature. As such a metal material, for example, W, Ti, Mo, Ni, Al, Pt, Pd, Au, or an alloy thereof, or a composite film composed of a plurality of layers including the metal or alloy may be used. it can.
[0035]
Furthermore, for example, a metallic mask made of tungsten or the like has a very strong effect of suppressing the growth of GaN and has a strong dependency on the stripe direction of the mask. Regarding the stripe direction dependency, when a mask pattern is formed in the <11-20> direction with respect to GaN, almost no lateral growth (growth in the direction parallel to the substrate) occurs, and the GaN film is covered on the mask. Is difficult. Therefore, if the metallic film is covered with an insulating film to form a metallic mask with an insulating film, such a growth suppressing effect and stripe direction dependency can be alleviated. In addition, about the position of this metallic mask with an insulating film, arrangement | positioning of a metal film is important, and it is preferable to arrange | position a metal film in the position mentioned above.
[0036]
As this insulating film, SiO₂Or SiN_xIs preferably used because the shift of the crystal orientation (crystal growth axis) of the nitride semiconductor film coated on the insulating film is suppressed.
[0037]
Furthermore, if a mask (metal film) is provided in a stripe shape in the <1-100> direction with respect to the underlying nitride semiconductor layer, the lateral growth of the nitride semiconductor layer on the mask is accelerated and the coating speed is increased. Become.
[0038]
The metallic mask or the metallic mask with an insulating film may not be flatly covered with the nitride semiconductor layer as an upper layer, and may have a depression. In this case, the crystal distortion of the regrowth nitride semiconductor layer formed thereon can be relaxed by the depression. Therefore, it is possible to prevent the crystallinity from being lowered due to strain and further increase the laser oscillation lifetime.
[0039]
In the method for manufacturing a nitride semiconductor laser device according to the present invention, when the mask is covered with a nitride semiconductor layer, a nitrogen carrier gas of 10% or more of the total carrier gas is used, and the mask is formed on the mask. Lateral growth of the nitride semiconductor layer becomes faster, and the coating speed becomes faster.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0041]
Generally, when growing a nitride semiconductor crystal, sapphire, 6H—SiC, 4H—SiC, 3C—SiC, GaN, Si, Ge, GaAs, MgAl₂O_FourEtc. are used as the substrate. Crystal growth is usually performed by metal organic vapor phase epitaxy (hereinafter referred to as MOCVD method), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (H-VPE) or the like. Among these, considering the crystallinity and mass productivity of the obtained nitride semiconductor, the most common method is to use sapphire or GaN as the substrate and the MOCVD method as the growth method.
[0042]
Accordingly, in the following embodiment, an example of a nitride semiconductor laser element in which a nitride semiconductor is grown on a sapphire substrate or a GaN substrate by MOCVD will be described. In addition, although Embodiment 1, Embodiment 2, and Embodiments 4 to 7 describe examples using a sapphire substrate, it was confirmed that the same effect can be obtained even if other substrates described above are used. ing. In particular, when a GaN substrate is used, as described in Embodiment 13 to be described later, since it is the same type of crystal, a favorable result with good lattice matching is obtained. Moreover, although Embodiment 3 and Embodiments 10 to 12 describe examples using a GaN substrate, it has been confirmed that the same effect can be obtained even if other substrates described above are used.
[0043]
(Embodiment 1)
In the present embodiment, a description will be given of a nitride semiconductor laser device in which a vertical transverse mode is stabilized (single peaked) using a metallic mask having a light absorption function.
[0044]
FIG. 1 shows the structure of the nitride semiconductor laser device of this embodiment. This nitride semiconductor laser device includes a low-temperature GaN buffer layer 101, an n-type GaN contact layer 102, an n-type Al on a sapphire substrate 100._0.1Ga_0.9N-cladding layer 103, n-type GaN light guide layer 104, active layer 105 (for example, In 2 nm thick described later)_0.15Ga_0.85N layer and 4 nm thick In_0.02Ga_0.98Multi-quantum well active layer consisting of N layer, In addition to 4 nm thick In_0.15Ga_0.85N layer and 10 nm thick In_0.01Ga_0.99N layer having three periods formed can be used), Al_0.2Ga_0.8N carrier block layer 106, p-type GaN light guide layer 107, p-type Al_0.1Ga_0.9An N clad layer 108 and a p-type GaN contact layer 109 are sequentially stacked. The p-type cladding layer 108 is dug down to the vicinity of the p-type light guide layer 107 to form a ridge stripe portion composed of the p-type contact layer 109 and the p-type cladding layer 108. On top of that, SiO₂An insulating film 110 made of is provided, and an upper portion of the ridge stripe is opened. A p-type electrode 112 is provided on the insulating film 110 and on the ridge stripe portion exposed from the opening of the insulating film 110, and the portion on the ridge stripe functions as a stripe electrode. On the other hand, the p-type contact layer 108 to the n-type contact layer 102 are partially removed so that the surface of the n-type contact layer 102 is exposed, and an n-type electrode 111 is formed on the exposed portion of the n-type contact layer 102. ing.
[0045]
The n-type contact layer 102 is composed of a lower n-type GaN film 102a and a regrown n-type GaN film 102b. The n-type contact layer 102 is reproduced on a metallic mask (tungsten mask) 113 provided on the lower film 102a below the ridge stripe portion. The growth film 102b is covered.
[0046]
FIG. 2 shows a schematic configuration of the MOCVD apparatus used in this embodiment. In the figure, 201 is a sapphire substrate having a (0001) plane, and this substrate is disposed on a susceptor 202 made of carbon. A resistance heater made of carbon is disposed in the susceptor 202, and the substrate temperature can be controlled by a thermocouple. Reference numeral 203 denotes a reaction tube made of double quartz, which is water-cooled. As group V raw material, ammonia (NH_Three) 206 and trimethylgallium (TMG) 207a, trimethylaluminum (TMA) 207b and trimethylindium (TMIn) 207c as nitrogen group (N₂) Or hydrogen gas (H₂) Was used for bubbling. As an n-type doping material, monosilane (SiH_Four209 and biscyclopentadienylmagnesium (Cp) as a p-type doping material₂Mg) 207d was used. The flow rate of each raw material is accurately controlled by a mass flow controller (MFC) 208, introduced into the reaction tube from the raw material inlet 204, and discharged from the exhaust gas outlet 205.
[0047]
The nitride semiconductor laser element of this embodiment can be manufactured as follows, for example. First, the sapphire substrate 100 is washed and placed in a crystal growth apparatus, and heat treatment is performed in a hydrogen atmosphere at a temperature of about 1100 ° C. for about 10 minutes, and then the temperature is lowered to about 500 ° C. to 600 ° C. After the temperature becomes constant, the carrier gas is changed to nitrogen, nitrogen gas is supplied at a total flow rate of 10 l / min, ammonia is supplied at 3 l / min, TMG is flowed at about 20 μmol / min, and a low temperature GaN buffer layer 101 having a thickness of 20 nm is formed. Grow.
[0048]
Next, the supply of TMG was stopped, the temperature was raised to 1050 ° C., and TMG was again reduced to about 50 μmol / min and SiH._FourA gas is supplied at about 10 nmol / min to grow a lower n-type GaN film 102 a having a thickness of 4 μm in the n-type contact layer 102. Thereafter, the substrate is once taken out from the crystal growth apparatus, and a tungsten film having a thickness of 0.1 μm is formed by EB (electron beam) evaporation. As a method for forming the tungsten film, a sputtering method may be used in addition to the EB vapor deposition method. This tungsten film is etched into a stripe shape having a mask width (M) of 3 μm using a normal photolithography technique to expose the lower n-type GaN film 102a. At this time, the tungsten mask 113 was formed in the <1-100> direction with respect to the underlying nitride semiconductor layer (GaN film 102a), and was placed below the ridge stripe portion formed in a later step. Next, the substrate was placed in the crystal growth apparatus again, and the atmosphere was replaced with nitrogen gas. Then, the temperature was raised to 1050 ° C. while flowing nitrogen at 10 l / min, hydrogen at 5 l / min, and ammonia at 3 l / min. When the temperature is stabilized, TMG is 50 μmol / min and SiH._FourThe gas is supplied at 10 nmol / min to re-grow the n-type GaN film 102b having a thickness of 4 μm. As the growth progressed, GaN began to regrow from the portion where the tungsten mask 113 was not coated, and lateral growth occurred and the tungsten mask 113 was coated. The laterally grown GaN film 102b was completely bonded, and a contact layer 102 having a flat surface was obtained.
[0049]
Subsequently, TMA was supplied at 10 μmol / min, and n-type Al having a thickness of 0.5 μm._0.1Ga_0.9An N clad layer 103 is grown. This layer was grown continuously after the lateral growth of the contact layer 102, starting the supply of TMA. Thereafter, the supply of TMA was stopped and TMG was reduced to 50 μmol / min and SiH._FourA gas is supplied at 10 nmol / min to grow an n-type GaN light guide layer 104 having a thickness of about 0.1 μm. After growth of the light guide layer 104, TMG and SiH once_FourIs stopped, the temperature is lowered to about 700 ° C. to 800 ° C., TMI and TMG are supplied, and a 2 nm thick In_0.15Ga_0.85N layer and 4 nm thick In_0.02Ga_0.98A multiple quantum well active layer 105 composed of a plurality of N layers is formed. At this time, SiH_FourMay or may not be supplied. Next, the supply of TMG and TMI was stopped again, the temperature was raised again to 1050 ° C., and TMG and TMA were supplied to form Al with a thickness of 20 nm._0.15Ga_0.85A carrier block layer 106 made of N is grown. At this time, Cp₂Mg may be supplied or may not be supplied. Note that there is no particular problem even if the carrier block layer 106 is not formed. Subsequently, the supply of TMA was stopped and the supply of TMG was adjusted to 50 μmol / min, and Cp₂A p-type GaN light guide layer 107 having a thickness of 0.1 μm is grown by supplying about 50 nmol / min of Mg. Thereafter, TMA was supplied at 10 μmol / min, and p-type Al having a thickness of 0.5 μm._0.15Ga_0.85An N clad layer 108 is grown. Finally, the supply of TMA is stopped, a p-type GaN contact layer 109 having a thickness of 0.1 μm is grown, the temperature is lowered to room temperature, and the substrate is taken out from the crystal growth apparatus.
[0050]
Thereafter, reactive ion etching is performed using a dry etching apparatus to expose the n-type GaN contact layer 102, and an Al film and a Ti film are deposited on the exposed portion to form an n-type electrode 111. At this time, the n-type contact layer 102 is exposed by reactive ion etching because the sapphire substrate 100 which is an insulating substrate is used. Therefore, when a conductive substrate such as a GaN substrate or SiC substrate is used, it is not necessary to expose the n-type contact layer 102, and an n-type electrode may be formed on the back surface of the straight substrate. On the other hand, in the p-type electrode portion, the p-type cladding layer 108 and the p-type contact layer 109 are formed in a ridge stripe by etching the p-type cladding layer 108 before the p-type GaN light guide layer 107, and SiO 2₂An insulating film 110 having a thickness of 200 nm is deposited. Thereafter, the insulating film 110 is partially removed to expose the p-type contact layer 109, and a Ni film and an Au film are deposited so as to cover the exposed portion (Wp = 2 μm width) to form the p-type electrode 112. . Finally, an end surface to be a mirror is formed by cleavage or dry etching. As described above, the nitride semiconductor laser device of the present embodiment having a blue-violet emission wavelength using a nitride semiconductor is manufactured.
[0051]
The surface of the n-type GaN contact layer 102 obtained by such a selective growth process is flat and free from cracks. When observed with a transmission electron microscope, dislocations generated from the interface between the substrate 100 and the low-temperature GaN buffer layer 101 are obtained. (Crystal defects) were hardly observed in the GaN film 102b coated on the tungsten mask 113. Further, the presence of the tangs mask 113 reduced the dislocation density by two orders of magnitude or more in each film constituting the laser structure after regrowth on the mask. Further, the lifetime characteristic of the semiconductor laser element itself was about 12000 hours.
[0052]
With respect to this nitride semiconductor laser element, the FFP in the vertical (perpendicular to the active layer) transverse mode was observed, and as shown in FIG. In the semiconductor laser device, no sub-peak as shown in FIG. 17B observed with the FFP in the vertical transverse mode was observed. Furthermore, when the nitride semiconductor laser device of this embodiment was subjected to a life test for 10,000 hours and the vertical transverse mode was observed again, a stable single vertical transverse mode similar to the above was observed.
[0053]
The following can be considered as this reason. The reason why the conventional semiconductor laser device cannot generate a sub-peak in the vertical transverse mode and cannot be unified is that the laser light emitted from the active layer leaks without being sufficiently confined in the vertical direction by the n-type AlGaN cladding layer. Because. Since the n-type GaN contact layer 102 having a thickness equal to or larger than 0.3 μm and having an equivalent refractive index larger than that of the n-type AlGaN cladding layer 103 is provided outside the n-type AlGaN cladding layer 103, the optical n-type GaN A sub-peak of vertical transverse mode light as shown in FIG. 16B is generated in the contact layer 102, and the single peak of the vertical transverse mode is inhibited.
[0054]
On the other hand, the metallic mask having the growth suppressing effect used in the present embodiment is made of tungsten, and the vertical transverse mode light generated (leaked) between the substrate 100 and the n-type AlGaN cladding layer 103 is used. Is absorbed by the tungsten mask 113. Accordingly, it is considered that the nitride semiconductor laser element of the present embodiment can stabilize the vertical transverse mode as shown in FIGS. 16 (a) and 17 (a). Hereinafter, this effect is referred to as a light absorption effect. Furthermore, with the effect of reducing the dislocation density by the selective growth, it is considered that a stable single vertical transverse mode was observed even after a life test of 10,000 hours.
[0055]
In addition, in order to obtain a single vertical transverse mode of the semiconductor laser element by the light absorption effect of the metallic mask (tungsten mask), the formation position of the metallic mask is in each of the vertical direction and the horizontal direction with respect to the substrate. It is preferable to form in the following positions.
[0056]
First, regarding the direction perpendicular to the substrate,
(1) When a contact layer having a refractive index higher than that of the clad layer and having a refractive index different from that of the substrate is in contact with the lower surface of the clad layer closer to the substrate, the clad layer and the contact layer A metallic mask is disposed at a position within half the thickness of the contact layer from the interface to the substrate. For example, when an AlGaN cladding layer and a GaN contact layer are provided on a sapphire substrate, a metallic mask is formed at a position within half the thickness of the GaN contact layer from the interface between the two. In this embodiment, a tungsten mask 113 having a thickness of 0.1 μm is formed at a position of 4 μm from the interface between the n-type AlGaN cladding layer 103 and the n-type GaN contact layer 102 (the lower surface of the n-type cladding layer 103) toward the substrate. .
[0057]
(2) When a contact layer having a refractive index higher than that of the cladding layer and having substantially the same refractive index as that of the substrate is in contact with the lower surface of the cladding layer closer to the substrate, the cladding layer and the contact layer A metallic mask is disposed at a position within half of the total thickness of the contact layer and the substrate thickness from the interface to the substrate. For example, when an AlGaN cladding layer and a GaN contact layer are provided on a GaN substrate, a metallic mask is disposed at a position within half of the combined thickness of the GaN contact layer and the GaN substrate from the interface between them.
[0058]
(3) When such a contact layer is not provided and the clad layer closer to the substrate has a lower refractive index than the substrate, the thickness of the substrate is reduced from the interface between the clad layer and the substrate toward the lower surface of the substrate. Place the metallic mask in a position within half. For example, when an AlGaN clad layer is provided on a GaN thick film (substrate), a metallic mask is disposed at a position within half the thickness of the GaN thick film from the interface between the two.
[0059]
The reason for this is that if the metallic mask is not formed within the above range, the region where the leakage light remains is wider than the region where the leakage light is absorbed by the metallic mask, and the vertical transverse mode is selected. This is because it prevents unimodalization. Further, according to the knowledge of the present inventors, it was easier to obtain a single vertical transverse mode as the distance from the interface to the metallic mask was shorter. This is because when the distance from the interface between the AlGaN cladding layer and the GaN contact layer to the metallic mask is increased, the vertical transverse mode light leaked into the GaN contact layer is reduced in the lower part of the metallic mask, but the above This is because leakage light is not sufficiently reduced from the interface to the metallic mask, so that a sub-peak due to vertical transverse mode light is observed, and the single vertical transverse mode is not obtained. Further, a metallic mask may be formed on the n-type AlGaN cladding layer 103 or in the cladding layer 103. However, if the metallic mask is formed at a position less than 0.5 μm from the interface between the active layer 105 and the n-type GaN light guide layer 104 (the lower surface of the active layer 105) toward the substrate 100, the light absorption effect of the metallic mask is achieved. For this reason, gain loss in laser oscillation increases, leading to an increase in laser oscillation threshold current density. Therefore, when the metallic mask is formed on or in the n-type AlGaN cladding layer 103, at least 0.5 μm from the interface between the active layer 105 and the n-type GaN light guide layer 104 toward the substrate 100. It is preferable to form in the above position.
[0060]
Furthermore, as will be described in detail in the ninth embodiment to be described later, when a metallic mask is provided on a nitride semiconductor film containing Al, it is more selective than when a metallic mask is provided on a GaN film not containing Al. The lateral growth rate in the growth is high, and the defect density is low. Further, a metallic mask may be formed so as to extend over either the interface between the AlGaN cladding layer and the GaN contact layer or the interface between the AlGaN cladding layer and the GaN substrate. Furthermore, when a semiconductor laser device is fabricated using a GaN substrate, the light leaked from the AlGaN cladding layer particularly strongly prevents the vertical transverse mode from being single-peaked. A very high effect can be obtained.
[0061]
On the other hand, in the direction parallel to the substrate, the metal mask is formed below the striped p-type electrode 112 (ridge stripe portion). The width (M) of the metallic mask is preferably equal to or wider than the p-type electrode width Wp. The reason for this is to sufficiently absorb the leaked vertical mode light (FFP).
[0062]
Further, the stripe direction of the metallic mask is set to the <1-100> direction with respect to the underlying nitride semiconductor layer (the lower layer GaN film 102a in this embodiment), so that the lateral direction of the nitride semiconductor layer on the mask is increased. This is preferable because the growth is accelerated, the coating speed is increased, and a flat coating film is obtained.
[0063]
In the present embodiment, tungsten (W) is used as a metallic mask having a light absorption function in addition to the growth suppressing effect, but other than that, for example, Pt, Ti, Mo, Ni, Al, Pd, Au, etc. A metal, an alloy thereof, or a composite film including a plurality of layers containing them can be used. A nitride semiconductor is not directly epitaxially grown, and a growth suppressing effect can be obtained. If the metal has a light absorption effect of absorbing the laser light leaked from the cladding layer, it is not greatly dependent on the material.
[0064]
Furthermore, in consideration of the light absorption effect, the thickness of the metallic mask is preferably about 0.01 μm or more as will be described in detail in Embodiment 8 described later. Although depending on the shape of the mask, the thickness of the metallic mask is preferably 2 μm or less in consideration of the thickness covered by the regrown nitride semiconductor film and the flatness of the coating film.
[0065]
Regarding the nitrogen carrier gas used in the selective growth, the partial pressure of nitrogen carrier gas (N₂/ (H₂+ N₂)) Is preferably 0.1 (10% or more). However, when the partial pressure of the nitrogen carrier gas exceeds 0.9, the full width at half maximum by X-ray diffraction exceeds 6 minutes, as described in detail in Embodiment 9 described later, and the crystal in the coated nitride semiconductor film The orientation of is deteriorated.
[0066]
In the present embodiment, a semiconductor laser element having a ridge stripe structure is shown, but a stripe structure as shown in Embodiments 3 to 7 described later may be used.
[0067]
Furthermore, in this embodiment, an example in which a GaN film is used as the low temperature buffer layer 101 has been described._xGa_1-xEven if N (0 ≦ x ≦ 1) is used, no problem occurs. In this embodiment, the n-type layer, the active layer, and the p-type layer are grown in order from the substrate side. However, the p-type layer, the active layer, and the n-type layer may be grown in this order. The same applies to the following embodiments.
[0068]
(Embodiment 2)
In the present embodiment, a nitride semiconductor laser element having the same configuration as that of the first embodiment except that an insulating film is provided on the metallic mask of the first embodiment will be described.
[0069]
FIG. 3 shows the structure of the nitride semiconductor laser device of this embodiment. This nitride semiconductor laser device includes a low-temperature GaN buffer layer 301, an n-type GaN contact layer 302, an n-type Al on a sapphire substrate 300._0.1Ga_0.9N clad layer 303, n-type GaN light guide layer 304, active layer 305 (for example, three periods of In_0.18Ga_0.82N layer and In_0.05Ga_0.95Multiple quantum well active layer consisting of N layers), Al_0.2Ga_0.8N carrier block layer 306, p-type GaN light guide layer 307, p-type Al_0.1Ga_0.9An N clad layer 308 and a p-type GaN contact layer 309 are sequentially stacked. The p-type cladding layer 308 is dug down to the vicinity of the p-type light guide layer 307 to form a ridge stripe portion composed of the p-type contact layer 309 and the p-type cladding layer 308. On top of that, SiO₂An insulating film 310 is provided, and an upper portion of the ridge stripe is opened. A p-type electrode 312 is provided on the insulating film 310 and on the ridge stripe portion exposed from the opening of the insulating film 310, and the portion on the ridge stripe functions as a stripe electrode. On the other hand, the p-type contact layer 308 to the n-type contact layer 302 are partially removed so that the surface of the n-type contact layer 302 is exposed, and an n-type electrode 311 is formed on the exposed portion of the n-type contact layer 302. ing.
[0070]
The n-type contact layer 302 is composed of a lower n-type GaN film 302a and a regrown n-type GaN film 302b. The n-type contact layer 302 is formed on the metal mask 315 with an insulating film provided on the lower film 302a below the ridge stripe portion. The growth film 302b is covered. This mask 315 is composed of a tungsten film 313 and SiO provided thereon.₂It is comprised from the insulating film 314 which consists of.
[0071]
The nitride semiconductor laser element of this embodiment can be manufactured as follows, for example. First, as in the first embodiment, the low-temperature GaN buffer layer 301 is grown on the sapphire substrate 300 in the crystal growth apparatus, and then the lower n-type GaN having a thickness of 3.5 μm in the n-type GaN contact layer 302. A film 302a is grown.
[0072]
Next, the substrate is once removed from the crystal growth apparatus, and a 0.1 μm thick tungsten film and a 0.05 μm thick SiO film are formed by EB vapor deposition or sputtering.₂A film is formed on the n-type GaN film 302a. This tungsten film and SiO₂The film is formed in stripes in the <1-100> direction with respect to the underlying nitride semiconductor film (GaN film 102a) by using a normal photolithography technique, the mask width (M) is 4 μm, the mask thickness is 0. At 15 μm, tungsten film 313 and SiO₂A stripe-shaped mask 315 made of the film 314 was disposed below the ridge stripe portion to be manufactured in a later step. Next, the substrate is placed in the crystal growth apparatus again, and an n-type GaN film 302b having a thickness of 1.5 μm is regrown under the same conditions as in the first embodiment to obtain an n-type GaN contact layer 302.
[0073]
Subsequently, under the same growth conditions as in Embodiment 1, n-type Al_0.1Ga_0.9N clad layer 303, n-type GaN light guide layer 304, active layer 305, Al_0.15Ga_0.85N carrier block layer 306, p-type GaN light guide layer 307, p-type Al_0.15Ga_0.85An N clad layer 308 and a p-type GaN contact layer 309 are grown. Thereafter, the substrate is taken out from the crystal growth apparatus, and the semiconductor laser device having the ridge stripe structure shown in FIG. 3 is manufactured through the same manufacturing process of the semiconductor laser device as in the first embodiment.
[0074]
The surface of the n-type GaN contact layer 302 obtained by such a selective growth process was flat and free from cracks. In the present embodiment, an insulating film (SiO 2) provided in the n-type GaN contact layer 302 is used.₂Due to the presence of the tansten mask 315 with a film), the dislocation density decreased by two orders of magnitude or more in each film constituting the laser structure after regrowth on the mask. Further, the lifetime characteristic of the semiconductor laser element itself was about 12000 hours.
[0075]
With respect to this nitride semiconductor laser device, when the FFP in the vertical transverse mode was observed, laser oscillation occurred in a single mode with a single peak. Furthermore, when the nitride semiconductor laser device of this embodiment was subjected to a life test for 10,000 hours and the vertical transverse mode was observed again, a stable single vertical transverse mode similar to the above was observed.
[0076]
This is because, as in the first embodiment, the vertical transverse mode light leaked between the substrate 300 and the n-type AlGaN cladding layer 303 is absorbed by the tungsten mask 313 in the tungsten mask 315 with an insulating film. is there. As a result, in the nitride semiconductor laser device of this embodiment, as shown in FIG. 16A and FIG. Furthermore, with the effect of reducing the dislocation density by the selective growth, it is considered that a stable single vertical transverse mode was observed even after a 10,000 hour life test.
[0077]
The difference between the second embodiment and the first embodiment is that the SiO 2 film is formed on the tungsten mask 313.₂By providing the film 314, as will be described in detail in Embodiment 9 described later, the direction dependency of the mask pattern is relaxed in the selective growth of the GaN film, and a sufficient lateral growth rate can be obtained. In general, in selective growth of a GaN film using a metallic mask such as a tungsten mask, lateral growth (growth in a direction parallel to the substrate surface) hardly occurs because the mask has a strong dependence on the stripe direction. Therefore, by improving the lateral growth rate, SiO 2 is removed from the interface between the n-type AlGaN cladding layer 303 and the n-type GaN contact layer 302.₂The distance to the tungsten mask 313 with a film is short, and SiO₂The width (M) of the tungsten mask 315 with a film can be increased. As a result, it was possible to obtain a single vertical transverse mode that was more stable than in the first embodiment.
[0078]
In addition, the metallic mask with an insulating film (SiO₂The formation positions of the masks necessary for obtaining a single vertical transverse mode of the semiconductor laser device by the light absorption effect of the film-coated tungsten mask are the same as those in the first embodiment in both the vertical direction and the horizontal direction with respect to the substrate. is there. However, the mask formation position in this case refers to the formation position of the metallic mask constituting the metallic mask with an insulating film, and in this sense, is the same as in the first embodiment.
[0079]
In the present embodiment, tungsten (W) is used as a metallic mask having a light absorption function in addition to the growth suppressing effect, but other than that, for example, Pt, Ti, Mo, Ni, Al, Pd, Au, etc. A metal, an alloy thereof, or a composite film including a plurality of layers containing them can be used. A nitride semiconductor is not directly epitaxially grown, and a growth suppressing effect can be obtained. If the metal has a light absorption effect of absorbing the laser light leaked from the cladding layer, it is not greatly dependent on the material. As an insulating film provided immediately above the metallic mask, SiO 2₂SiN besides film_xA film may be used, and if it is an insulating film, it does not depend greatly on the material. Further, the thickness of the metal film constituting the metallic mask with an insulating film is preferably about 0.01 μm or more in consideration of the light absorption effect, as in the first embodiment. In consideration of the thickness covered by the regrowth nitride semiconductor film and the flatness of the coating film, the thickness of the entire mask including the metallic film and the insulating film is preferably 2 μm or less. Furthermore, the thickness of the insulating film is preferably 1 μm or less. This is because if the thickness of the insulating film exceeds 1 μm, peeling may occur due to a difference in thermal expansion coefficient between the underlying metallic film and the insulating film.
[0080]
The nitrogen carrier gas used in the selective growth is the same as that in the first embodiment.
[0081]
Further, in the present embodiment, the semiconductor laser element having the ridge stripe structure is shown, but a stripe structure as shown in Embodiments 3 to 7 described later may be used.
[0082]
(Embodiment 3)
In the third embodiment, an example in which a metallic mask for confining light in a horizontal transverse mode is provided below the active layer will be described.
[0083]
FIG. 4 shows the structure of the nitride semiconductor laser device of this embodiment. This semiconductor laser device has an n-type Al on an n-type GaN substrate 401._0.02Ga_0.98N contact layer 402, n-type Al_0.1Ga_0.9N-cladding layer 403, n-type GaN light guide layer 404, active layer 405 (for example, 2 nm thick In_0.15Ga_0.85N layer and 4 nm thick In_0.02Ga_0.98Multiple quantum well active layer composed of N layer, 3 periods of 4 nm thick In_0.15Ga_0.85N layer and 10 nm thick In_0.01Ga_0.99Multiple quantum well active layer consisting of N layer and 3 periods of In_0.18Ga_0.82N layer and In_0.05Ga_0.95Multiple quantum well active layer consisting of N layer, etc.), Al_0.2Ga_0.8N carrier block layer 406, p-type GaN light guide layer 407, p-type Al_0.1Ga_0.9An N clad layer 408 and a p-type GaN contact layer 409 are sequentially stacked. On the p-type contact layer 409, a SiO 2 having a stripe-shaped portion opened as a current path is formed.₂The insulating film 410 is provided, and the p-type electrode 412 is provided over the opening and the insulating film 410, and the portion on the opening of the insulating film 410 functions as a stripe electrode. An n-type electrode 411 is formed so as to be in contact with the back surface of the n-type GaN substrate 401.
[0084]
n-type Al_0.1Ga_0.9The N clad layer 403 is a lower layer n-type Al_0.1Ga_0.9N film 403a and regrown n-type Al_0.1Ga_0.9A regrowth film 403b covers a metallic mask (tungsten mask) 416, which is composed of an N-clad film 403b and is provided on the lower film 403a below the striped electrode.
[0085]
This semiconductor laser element can be manufactured as follows, for example. First, a thick GaN layer is laminated while doping Si on the sapphire substrate by the HVPE method, and then the sapphire substrate is peeled off by polishing to produce an n-type GaN substrate 401 having a thickness of 250 μm. This n-type GaN substrate 401 is set in an MOCVD apparatus, and an n-type Al having a thickness of 5 μm._0.02Ga_0.98An N contact layer 402 is grown. After the growth of the n-type contact layer 402, subsequently, at a growth temperature of 1050 ° C., TMG is 50 μmol / min, SiH_FourGas is supplied at a flow rate of 10 nmol / min and TMA at a flow rate of 10 μmol / min, and the n-type cladding layer 403 has a lower n-type Al layer having a thickness of 0.2 μm._0.1Ga_0.9An N film 403a is grown.
[0086]
Next, the substrate is once taken out from the crystal growth apparatus, and a tungsten film having a thickness of about 0.1 μm is formed by EB vapor deposition. As a method for forming the tungsten film, a sputtering method may be used in addition to the EB vapor deposition method. This tungsten film is etched into a stripe shape having a mask width of 5 μm and a mask interval (S) of 3 μm by using a normal photolithography technique to form a lower layer n-type Al_0.1Ga_0.9The N film 403a is exposed. At this time, the tungsten mask 416 has a stripe direction in the lower nitride semiconductor layer (Al_0.1Ga_0.9A portion 417 that is formed in the <1-100> direction with respect to the N film 403a) and is not covered with the tungsten mask 416 is disposed below the stripe-shaped electrode formed in a later step. Next, the substrate was placed in the crystal growth apparatus again, and the atmosphere was replaced with nitrogen gas. Then, the temperature was raised to 1050 ° C. while flowing nitrogen at 10 l / min, hydrogen at 5 l / min, and ammonia at 3 l / min. When the temperature is stabilized, TMG is 50 μmol / min and SiH._FourN-type Al with a thickness of 0.3 μm by supplying 10 nmol / min of gas and 10 μmol / min of TMA_0.1Ga_0.9The N film 403b is regrown. As the growth proceeds, the portion 417 that is not covered with the tungsten mask 416 begins with Al._0.1Ga_0.9N began to regrow, lateral growth occurred and the tungsten mask 416 was coated. This laterally grown Al_0.1Ga_0.9The N film 403b was completely bonded, and a clad layer 403 having a flat surface was obtained.
[0087]
After this lateral growth, the supply of TMA is stopped, and an n-type GaN light guide layer 404 having a thickness of 0.1 μm is subsequently grown. Next, under the same conditions as in the first embodiment, the active layer 405, Al_0.15Ga_0.85N carrier block layer 406, p-type GaN light guide layer 407, p-type Al_0.15Ga_0.85An N clad layer 408 and a p-type GaN contact layer 409 are grown. Thereafter, the substrate is taken out from the crystal growth apparatus, and the nitride semiconductor laser device of this embodiment shown in FIG. 4 is manufactured through a manufacturing process of the semiconductor laser device.
[0088]
N-type Al obtained by such selective growth process_0.1Ga_0.9The surface of the N clad layer 403 was flat and had no cracks. Further, when observed with a transmission electron microscope, Al coated on the tungsten mask 416 was observed._0.1Ga_0.9Almost no dislocations (crystal defects) were observed in the N film 403b. On the other hand, in the portion 417 not covered with the tungsten mask 416, the screw dislocations and the edge dislocations were bent on the tungsten mask 416 and disappeared while canceling each other. The dislocation density observed here was extremely low compared to the case where a sapphire substrate was used. Furthermore, the n-type Al in this embodiment_0.1Ga_0.9The selective growth of the N film can speed up the lateral growth as compared with the selective growth of the GaN film, as will be described in detail in Embodiment 9 described later.
[0089]
In the nitride semiconductor laser device of this embodiment, after the GaN substrate and the AlGaN clad layer are provided with a metallic mask (tungsten mask 416) having a growth suppressing effect, the nitride semiconductor laser element is regrown on the mask. In each film constituting the laser structure, the dislocation density is about 10^Four/ Cm²It was a stand. As a result, the lifetime characteristics of the semiconductor laser element itself were improved to about 20000 hours.
[0090]
When the laser oscillation threshold current density of the nitride semiconductor laser device of this embodiment was measured, it was reduced to about 2/3 of the conventional semiconductor laser device having a ridge stripe structure shown in FIG. When the horizontal and transverse modes were observed, lasing was obtained in a single mode with a single peak. Further, when the nitride semiconductor laser device of this embodiment was subjected to a life test for 12000 hours and the horizontal transverse mode was observed again, a stable single horizontal transverse mode similar to the above was observed.
[0091]
The reason why the low-threshold current value and the laser oscillation in the horizontal and transverse modes are obtained is as follows. Since the tungsten mask 416 used in this embodiment absorbs the laser light emitted from the active layer 405, there is a difference in the equivalent refractive index of the light guide layer between where the tungsten mask 416 is provided and where it is not provided. Arise. Then, it is considered that the optical waveguide of the horizontal transverse mode becomes conspicuous above the portion 417 not covered with the tungsten mask 416 and a refractive index waveguide structure is obtained, which contributes to the reduction of the laser oscillation threshold current density. . In addition to the refractive index waveguide structure, strong light absorption by the metallic mask 416 causes a large gain loss in the upper part of the mask, and high-order transverse modes are less likely to occur. As a result, it is considered that a stable single horizontal transverse mode was observed.
[0092]
In order to obtain a refractive index waveguide structure using the metallic mask (tungsten mask), the metallic mask is formed at the following positions in the vertical and horizontal directions with respect to the substrate. preferable.
[0093]
First, with respect to the direction perpendicular to the substrate, it is preferable to form it at a position within 2 μm from the interface between the active layer 405 and the n-type light guide layer 404 (the lower surface of the active layer) toward the substrate. In this embodiment, a tungsten mask 416 having a thickness of 0.1 μm is formed at a position of 0.3 μm from the interface.
This is because when the formation position of the metallic mask exceeds 2 μm from the interface, the equivalent refractive index difference hardly occurs between where the metallic mask is provided and where the metallic mask is not provided. This is because light confinement becomes weak. Further, according to the knowledge of the present inventors, the shorter the distance from the interface to the metallic mask, the larger the refractive index difference, and the stronger the optical confinement effect in the horizontal transverse mode.
[0094]
On the other hand, in the direction parallel to the substrate, the portion 417 not covered with the metallic mask is formed below the striped p-type electrode 412. Moreover, it is preferable that the space | interval (S) between metallic masks is 15 micrometers or less. The reason for this is as follows.
[0095]
Where the tungsten mask 416 is provided, the effective refractive index of the light guide layer is n₁The effective refractive index n of the light guide layer where the tungsten mask 416 is not provided.₂, The wave number of light in vacuum₀In order to obtain a single horizontal transverse mode using the equivalent refractive index method when the circumference is π, the mask interval (S) of the metallic mask is S <π / (k₀(N_{twenty two}-N₁₂)^1/2) Is necessary. Accordingly, the mask interval (S) when a metallic mask is formed at a position 2 μm from the interface where the difference in refractive index is the smallest is 15 μm or less from the above formula. However, the upper limit value of the appropriate mask interval (S) (horizontal position) is not uniquely determined by the vertical position of the mask. This is because if the mask interval (S) becomes too narrow, gain loss occurs due to light absorption by the metallic mask, and the laser oscillation threshold current density increases. In such a case, it is preferable to set the mask interval (S) larger than the calculated value of the equivalent refractive index method. According to the experiments by the present inventors, it was preferable that the mask interval (S) be 1 μm or more and 15 μm or less.
[0096]
In the present embodiment, tungsten (W) is used as a metallic mask having a light absorption function in addition to the growth suppressing effect, but other than that, for example, Pt, Ti, Mo, Ni, Al, Pd, Au, etc. A metal, an alloy thereof, or a composite film including a plurality of layers containing them can be used. A nitride semiconductor is not directly epitaxially grown, and a growth suppressing effect can be obtained. If the metal has a light absorption effect for absorbing laser light emitted from the active layer, the material does not greatly depend on the material. Further, although the thickness of the metallic mask depends on the shape of the mask, it is preferably 0.01 μm or more in consideration of the light absorption effect. The thickness covered by the regrown nitride semiconductor film and the flatness of the coating film are preferable. Considering the properties, it is preferably 2 μm or less.
[0097]
In this embodiment, the metallic mask 416 is completely buried in the n-type AlGaN cladding layer 403. However, the metallic mask 416 may not be completely buried in the n-type AlGaN cladding layer 403. This is because the net laser element portion is composed of a whole area (column portion) below the width (Wp) of the striped p-type electrode 412. Therefore, in the n-type AlGaN cladding layer 403, it is sufficient that at least the mask interval (S) portion is crystal-grown. However, when the mask portion is not completely buried, the flatness of the p-type GaN contact layer 409 is poor, and it is difficult to form the p-type electrode, which may reduce the yield rate of the laser element structure.
[0098]
As for the nitrogen carrier gas used in the selective growth, it is preferable that the partial pressure of the nitrogen carrier gas with respect to the total carrier gas is 0.1 (10% or more) from the viewpoint of lateral growth. However, if the partial pressure of the nitrogen carrier gas exceeds 0.9, the half width by X-ray diffraction exceeds 6 minutes as shown in Embodiment 9 to be described later, and the crystal orientation in the coated nitride semiconductor film Sex worsens.
[0099]
By the way, in the conventional ridge stripe structure, in order to obtain the refractive index waveguide structure, as shown in FIG. 15, the ridge stripe portion is formed by leaving a part of the p-type cladding layer. It was difficult to control, and it was difficult to obtain horizontal / horizontal mode reproducibility. Further, the exposed end face is deteriorated due to the formation of the ridge stripe portion, and the laser element characteristics are adversely affected, such as an increase in laser oscillation threshold current density. For this reason, considering productivity, the conventional ridge stripe structure has a problem in that the yield rate is low. On the other hand, according to this embodiment, it is possible to easily manufacture a metallic mask using conventional lithography technology, there is no exposure of the end face as in the ridge stripe structure, and the thickness of the cladding layer is crystallized. Since the growth can be controlled, the yield rate can be increased compared to the ridge stripe structure.
[0100]
In the case of the ridge stripe structure, such an effect of improving the yield cannot be obtained, but by providing a metallic mask as in the present embodiment, the optical confinement effect by the metal film and the material film that does not epitaxially grow are provided. An effect of reducing the dislocation density of the growth layer thereon can be obtained. Furthermore, by providing a metallic mask with an insulating film, a current confinement effect by both the insulating film and the ridge can be obtained.
[0101]
In the present embodiment, the Al composition of the clad layer to be regrown is set to 0.1, but the same effect can be seen even in a nitride semiconductor having a composition of 0 <Al ≦ 1.
[0102]
(Embodiment 4)
In the present embodiment, a structure provided by combining the metallic mask with an insulating film of the second embodiment and the metallic mask of the third embodiment will be described.
[0103]
FIG. 5 shows the structure of the nitride semiconductor laser device of this embodiment. This semiconductor laser device includes a low-temperature GaN buffer layer 501, an n-type GaN contact layer 502, an n-type Al on a sapphire substrate 500._0.1Ga_0.9N-cladding layer 503, n-type GaN light guide layer 504, active layer 505 (for example, 2 nm thick In_0.15Ga_0.85N layer and 4 nm thick In_0.02Ga_0.98Multiple quantum well active layer composed of N layer, 3 periods of 4 nm thick In_0.15Ga_0.85N layer and 10 nm thick In_0.01Ga_0.99Multiple quantum well active layer consisting of N layer and 3 periods of In_0.18Ga_0.82N layer and In_0.05Ga_0.95Multiple quantum well active layer consisting of N layer, etc.), Al_0.2Ga_0.8N carrier block layer 506, p-type GaN light guide layer 507, p-type Al_0.1Ga_0.9An N clad layer 508 and a p-type GaN contact layer 509 are sequentially stacked. On the p-type contact layer 509, SiO having a stripe-shaped portion opened as a current path is formed.₂An insulating film 510 is provided, and a p-type electrode 512 is provided over the opening and the insulating film 510, and a portion on the opening of the insulating film 510 functions as a striped electrode. The p-type contact layer 509 to the n-type contact layer 502 are partially removed so that the surface of the n-type contact layer 502 is exposed, and an n-type electrode 511 is formed on the exposed portion of the n-type contact 502. ing.
[0104]
The n-type contact layer 502 is composed of a lower n-type GaN film 502a and a regrown n-type GaN film 502b. The n-type contact layer 502 is formed on the metallic mask 515 with an insulating film provided on the lower film 502a below the striped electrode. The growth film 502b is covered. The mask 515 includes a tungsten film 513 and SiO provided thereon.₂It is comprised from the insulating film 514 which consists of. n-type Al_0.1Ga_0.9The N clad layer 503 is formed of a lower layer n-type Al_0.1Ga_0.9N film 503a and regrown n-type Al_0.1Ga_0.9A regrowth film 503b covers a metallic mask (tungsten mask) 516, which is formed of an N clad film 503b and is provided on the lower film 503a below the striped electrode.
[0105]
The nitride semiconductor laser element of this embodiment can be manufactured as follows, for example. First, as in the second embodiment, a low-temperature GaN buffer layer 501 is grown on a sapphire substrate 500 in a crystal growth apparatus, and then, among the n-type GaN contact layers 502, a lower n-type GaN film 502a having a thickness of 10 μm. Grow.
[0106]
Next, as in the second embodiment, the metal mask 515 with an insulating film having a mask width (M) of 5 μm and a mask thickness of 0.15 μm is formed in a stripe shape in the <1-100> direction with respect to the lower GaN film 502a. Form. The mask 515 includes a tungsten film 513 having a thickness of 0.1 μm and a SiO film having a thickness of 0.05 μm.₂The film 514 is disposed below the stripe-shaped electrode that will be formed in a later step. Next, the substrate is again placed in the crystal growth apparatus, and the n-type GaN film 502b having a thickness of 2 μm is regrown in the same manner as in the second embodiment, so that the n-type GaN contact is flat and has no cracks. Layer 502 is formed.
[0107]
Subsequently, as in the third embodiment, the lower Al layer having a thickness of 0.2 μm_0.1Ga_0.9An N film 503a is grown. Next, the substrate is once taken out from the crystal growth apparatus, and in the same manner as in Embodiment 3, the lower layer Al_0.1Ga_0.9A tungsten mask 516 having a mask width of 5 μm, a mask interval (S) of 3 μm, and a thickness of about 0.1 μm is formed in stripes in the <1-100> direction with respect to the N film 503a. At this time, a portion 517 that is not covered with the tungsten mask 516 is disposed under the stripe-shaped electrode to be manufactured in a later step.
[0108]
Next, the substrate is placed again in the crystal growth apparatus, and the n-type Al having a thickness of 0.3 μm is formed as in the third embodiment._0.1Ga_0.9The N film 503b is regrown. As the growth proceeds, the portion 517 that is not covered with the tungsten mask 516 begins to Al._0.1Ga_0.9N began to regrow, lateral growth occurred and the tungsten mask 516 was coated. This laterally grown Al_0.1Ga_0.9The N film 503b was completely bonded, and a flat clad layer 503 was obtained.
[0109]
Subsequently, as in Embodiment 3, the n-type GaN light guide layer 504, the active layer 505, and Al_0.15Ga_0.85N carrier block layer 506, p-type GaN light guide layer 507, p-type Al_0.15Ga_0.85An N clad layer 508 and a p-type GaN contact layer 509 are grown. Thereafter, the substrate is taken out from the crystal growth apparatus, and the nitride semiconductor laser device of this embodiment shown in FIG. 5 is manufactured through a manufacturing process of the semiconductor laser device.
[0110]
N-type GaN contact layer 502 and n-type Al obtained by such a selective growth process_0.1Ga_0.9The surface of the N clad layer 503 was flat and had no cracks. Regarding the n-type GaN contact layer 502, dislocations (crystal defects) generated from the interface between the substrate 500 and the low-temperature GaN buffer layer 501 were reduced as in the second embodiment. On the other hand, n-type Al_0.1Ga_0.9When the N clad layer 503 was observed with a transmission electron microscope, dislocations (crystal defects) were coated on the tungsten mask 516._0.1Ga_0.9It was hardly observed in the N film 503b. Further, in the portion 517 not covered with the tungsten mask 516, the screw dislocations and the edge dislocations were bent on the tungsten mask 516 and disappeared while canceling each other. Furthermore, the n-type Al in this embodiment_0.1Ga_0.9The selective growth of the N film was faster in the lateral growth than the selective growth of the GaN film, as will be described in detail in Embodiment 9 described later.
[0111]
Furthermore, the nitride semiconductor laser device of the present embodiment is provided with a growth suppressing effect SiO provided in the GaN contact layer 502 and the AlGaN cladding layer 503.₂The presence of the film-coated tungsten mask 515 and the tungsten mask 516 reduced the dislocation density by two to three orders of magnitude in each film constituting the laser structure after regrowth on the mask. As a result, the lifetime characteristic of the semiconductor laser element itself was improved to about 17000 hours.
[0112]
When the laser oscillation threshold current density of the nitride semiconductor laser device of this embodiment was measured, it was reduced to about 2/3 of the conventional semiconductor laser device having a ridge stripe structure shown in FIG. Further, when the modes of NFP and FFP in the horizontal transverse mode and the vertical transverse mode were observed, laser oscillation was obtained in a single-peak single mode. Further, the nitride semiconductor laser device of this embodiment was subjected to a 10000 hour life test, and the horizontal transverse mode and the vertical transverse mode were observed again. As described above, a stable single horizontal transverse mode and a single vertical transverse mode were observed. Mode was observed.
[0113]
The reason why the single-peak (single) and stable vertical transverse mode laser oscillation is obtained is the same as in the first and second embodiments. Also, the formation position of the vertical transverse mode, that is, SiO₂The formation position of the film-coated tungsten mask 515 is the same as that in Embodiment 2 in each of the vertical direction and the parallel direction with respect to the substrate. Further, the reason why a single horizontal (single) and stable horizontal transverse mode laser oscillation is obtained is the same as in the third embodiment. The horizontal horizontal mode formation position, that is, the formation position of the tungsten film 516 is the same as that of the third embodiment in each of the vertical direction and the parallel direction with respect to the substrate.
[0114]
In the present embodiment, tungsten (W) is used as the metallic mask in the metallic mask 515 and the metallic mask 516 with an insulating film, but other than that, for example, Pt, Ti, Mo, Ni, Al, Pd, A metal such as Au, an alloy thereof, or a composite film including a plurality of layers containing them can be used. A nitride semiconductor is not directly epitaxially grown, and a growth suppressing effect can be obtained. If the metal has a light absorption effect for absorbing laser light emitted from the active layer, the material does not greatly depend on the material. Furthermore, in the metallic mask 515 with an insulating film, the insulating film is SiO.₂SiN besides film_xA film may be used, and if it is an insulating film, it does not depend greatly on the material. Furthermore, the thicknesses of the metal mask 515 with an insulating film and the metal mask 516 are the same as those in the second and third embodiments. However, the metallic mask 516 may not be completely embedded in the cladding layer, as in the third embodiment. The nitrogen carrier gas used in the selective growth is the same as that in the second and third embodiments.
[0115]
According to the semiconductor laser device of the present embodiment, the same effects as those of the second and third embodiments can be obtained. In this embodiment, the metallic mask with an insulating film is formed in the n-type GaN contact layer, but a metallic mask may be formed. When a metallic mask is formed, the same effect as in the first embodiment can be obtained.
[0116]
In this embodiment, an example in which a GaN film is used as the low-temperature buffer layer has been described._xGa_1-xEven if N (0 ≦ x ≦ 1) is used, no problem occurs. Furthermore, in this embodiment, the Al composition of the clad layer to be regrown is set to 0.1, but the same effect can be seen even in a nitride semiconductor having a composition of 0 <Al ≦ 1.
[0117]
(Embodiment 5)
In the present embodiment, a structure in which a metallic mask with an insulating film is provided in the AlGaN cladding layer in place of the metallic mask in the fourth embodiment will be described.
[0118]
FIG. 6 shows the structure of the nitride semiconductor laser device of this embodiment. This semiconductor laser device includes a low-temperature GaN buffer layer 601, an n-type GaN contact layer 602, an n-type Al on a sapphire substrate 600._0.1Ga_0.9N clad layer 603, n-type GaN light guide layer 604, active layer 605 (for example, In 2 nm thick In_0.15Ga_0.85N layer and 4 nm thick In_0.02Ga_0.98Multiple quantum well active layer composed of N layer, 3 periods of 4 nm thick In_0.15Ga_0.85N layer and 10 nm thick In_0.01Ga_0.99Multiple quantum well active layer consisting of N layer and 3 periods of In_0.18Ga_0.82N layer and In_0.05Ga_0.95Multiple quantum well active layer consisting of N layer, etc.), Al_0.2Ga_0.8N carrier block layer 606, p-type GaN light guide layer 607, p-type Al_0.1Ga_0.9An N clad layer 608 and a p-type GaN contact layer 609 are sequentially stacked. On the p-type contact layer 609, a stripe-shaped portion serving as a current path is opened.₂An insulating film 610 is provided, and a p-type electrode 612 is provided over the opening and the insulating film 610, and a portion on the opening of the insulating film 610 functions as a stripe electrode. The p-type contact layer 609 to the n-type contact layer 602 are partially removed so that the surface of the n-type contact layer 602 is exposed, and an n-type electrode 611 is formed on the exposed portion of the n-type contact 602. ing.
[0119]
The n-type contact layer 602 is composed of a lower layer n-type GaN film 602a and a regrown n-type GaN film 602b. The growth film 602b is covered. The mask 615 includes a tungsten film 613 and SiO provided thereon.₂It is comprised from the insulating film 614 which consists of. n-type Al_0.1Ga_0.9The N clad layer 603 is a lower layer n-type Al_0.1Ga_0.9N film 603a and regrown n-type Al_0.1Ga_0.9The regrowth film 603b covers the metal mask 618 with an insulating film formed of the N clad film 603b and provided on the lower film 603a below the striped electrode. The mask 618 includes a tungsten film 616 and SiO provided thereon.₂An insulating film 617 made of
[0120]
The nitride semiconductor laser element of this embodiment can be manufactured as follows, for example. First, as in the second embodiment, a low-temperature GaN buffer layer 601 is grown on a sapphire substrate 600 in a crystal growth apparatus, and then, among the n-type GaN contact layers 602, a lower n-type GaN film 602a having a thickness of 100 μm. Grow.
[0121]
Next, as in the second embodiment, the metal mask 615 with an insulating film having a mask width (M) of 5 μm and a mask thickness of 0.15 μm is formed in a stripe shape in the <1-100> direction with respect to the lower GaN film 602a. Form. The mask 615 includes a tungsten film 613 having a thickness of 0.1 μm and a SiO film having a thickness of 0.05 μm.₂The film 614 is formed and is disposed below a stripe electrode to be manufactured in a later step. Next, the substrate is placed in the crystal growth apparatus again, and the n-type GaN film 602b having a thickness of 10 μm is regrown in the same manner as in the second embodiment, so that the n-type GaN contact is flat and has no cracks. Layer 602 is formed. Here, an HVPE growth apparatus was used as the crystal growth apparatus.
[0122]
Subsequently, as in the third embodiment, the lower Al layer having a thickness of 0.2 μm_0.1Ga_0.9An N film 603a is grown. Thereafter, the substrate is once taken out from the crystal growth apparatus, and a tungsten film having a thickness of about 0.06 μm is formed by EB vapor deposition or sputtering, followed by EB vapor deposition, sputtering or CVD (Chemical Vapor Deposition). About 0.04μm SiO₂A film is formed. Then, using a normal photolithography technique, etching is performed in a stripe shape having a mask width of 5 μm and a mask interval (S) of 2 μm, and the lower layer Al_0.1Ga_0.9The N film 603a is exposed. At this time, SiO₂Tungsten mask 618 with a film is striped in the lower Al layer_0.1Ga_0.9A portion 619 that is formed in the <1-100> direction with respect to the N film 603a and is not covered with the tungsten mask 616 is disposed below the stripe-shaped electrode formed in a later step. Next, the substrate is placed again in the crystal growth apparatus, and the n-type Al having a thickness of 0.2 μm is formed as in the third embodiment._0.1Ga_0.9The N film 603b is regrown. As growth proceeds, SiO₂The portion 619 not covered with the film-coated tungsten mask 618 starts with Al._0.1Ga_0.9N begins to regrow, lateral growth occurs and SiO₂A filmed tungsten mask 618 was coated. This laterally grown Al_0.1Ga_0.9The N film 603b was completely bonded, and a flat clad layer 603 was obtained.
[0123]
Subsequently, as in the fourth embodiment, the n-type GaN light guide layer 604, the active layer 605, and Al_0.15Ga_0.85N carrier block layer 606, p-type GaN light guide layer 607, p-type Al_0.15Ga_0.85An N clad layer 608 and a p-type GaN contact layer 609 are grown. Thereafter, the substrate is taken out from the crystal growth apparatus, and the nitride semiconductor laser device of this embodiment shown in FIG. 6 is manufactured through a manufacturing process of the semiconductor laser device.
[0124]
N-type GaN contact layer 602 and n-type Al obtained by such a selective growth process_0.1Ga_0.9The surface of the N clad layer 603 was flat and had no cracks. Dislocations (crystal defects) related to the n-type GaN contact layer 602 and the n-type AlGaN cladding layer 603 were reduced as in the fourth embodiment. Further, the nitride semiconductor laser device of the present embodiment is provided with a growth suppressing effect SiO provided in the GaN contact layer 602 and the AlGaN cladding layer 603.₂The presence of the film-coated tungsten masks 615 and 618 reduced the dislocation density by two to three orders of magnitude in each film constituting the laser structure after regrowth on the masks. As a result, the lifetime characteristic of the semiconductor laser element itself was improved to about 17000 hours.
[0125]
When the laser oscillation threshold current density of the nitride semiconductor laser device of this embodiment was measured, it was reduced to about ½ of the conventional semiconductor laser device having a ridge stripe structure shown in FIG. Further, when the modes of NFP and FFP in the horizontal transverse mode and the vertical transverse mode were observed, laser oscillation was obtained in a single-peak single mode. Further, the nitride semiconductor laser device of this embodiment was subjected to a 10000 hour life test, and the horizontal transverse mode and the vertical transverse mode were observed again. As described above, a stable single horizontal transverse mode and a single vertical transverse mode were observed. Mode was observed.
[0126]
The reason why the laser oscillation threshold current density is thus reduced is as follows.
[0127]
The metallic mask 618 with an insulating film formed in the cladding layer 603 has a metallic mask (tungsten film 616) and an insulating film (SiO2) having a light absorption effect.₂Film 617), the refractive index waveguide structure obtained by optical confinement in the horizontal transverse mode by the former light absorption effect and the current confinement by covering the metallic mask with the latter insulating film, This is because carrier confinement has occurred. That is, SiO₂This is because by using the tungsten mask 618 with a film, in addition to the laser characteristics by the refractive index waveguide structure described in the fourth embodiment, a current confinement structure can be simultaneously formed in the element.
[0128]
Further, the reason why the single-peak (single) and stable vertical transverse mode laser oscillation is obtained is the same as in the first and second embodiments. Also, the formation position of the vertical transverse mode, that is, SiO₂The formation position of the film-coated tungsten mask 615 is the same as that in the second embodiment in each of the vertical direction and the parallel direction to the substrate. Further, the reason why a single horizontal (single) and stable horizontal transverse mode laser oscillation is obtained is the same as in the fourth embodiment. Also, the horizontal horizontal mode forming position, that is, SiO₂The formation position of the film-coated tungsten mask 618 is the same as that of the fourth embodiment in each of the vertical direction and the parallel direction to the substrate. However, in this case, the position of the metallic mask with an insulating film refers to the position of forming the metallic mask constituting the metallic mask with an insulating film, and in this sense, is the same as in the fourth embodiment. .
[0129]
In this embodiment, in addition to the current confinement effect, the following effect is also obtained. In this embodiment, the lateral growth is accelerated by the metallic mask 618 with an insulating film formed in the cladding layer 603 as compared with the fourth embodiment. The reason for this is that, as will be described in detail later in Embodiment 9, the selective growth of the AlGaN film is very fast in lateral growth compared to the selective growth of the GaN film.₂This is because the lateral growth is further accelerated by providing the film 617. As a result, the distance from the interface between the active layer 605 and the n-type light guide layer 604 to the mask 618 was shortened, and the optical confinement effect in the horizontal transverse mode could be strengthened.
[0130]
Further, as will be described in detail in Embodiment 9 to be described later, in the selective growth of a GaN film using a metallic mask (tungsten mask), the dependence on the stripe direction of the mask is generally strong and lateral growth is difficult.₂By using a tungsten mask with a film, sufficient lateral growth can be obtained without selective dependence of the mask pattern even in selective growth of a GaN film. Using this property, in order to obtain a refractive index waveguide structure in the direction perpendicular to the substrate, SiO₂Selective growth with a high lateral growth rate is possible even when a nitride semiconductor containing no Al is present within a position range where the tungsten mask 618 with a film can be formed (position within 2 μm from the upper or lower surface of the active layer). Become.
[0131]
In the present embodiment, tungsten (W) is used as the metal mask in the metal masks 615 and 618 with insulating films, but other than that, for example, Pt, Ti, Mo, Ni, Al, Pd, Au, etc. A metal, an alloy thereof, or a composite film including a plurality of layers containing them can be used. A nitride semiconductor is not directly epitaxially grown, and a growth suppressing effect can be obtained. If the metal has a light absorption effect for absorbing laser light emitted from the active layer, the material does not greatly depend on the material. Further, in the metal masks 615 and 618 with an insulating film, the insulating film is SiO.₂SiN besides film_xA film may be used, and if it is an insulating film, it does not depend greatly on the material. When the metallic mask is covered with an insulating film, the side portion 620 of the metallic mask is also preferably covered with the insulating film. Furthermore, the thicknesses of the metal masks 615 and 618 with insulating films, the nitrogen carrier gas used in the selective growth, the yield rate, and the like are the same as in the fourth embodiment.
[0132]
In this embodiment, the metallic mask with an insulating film is formed in the n-type GaN contact layer, but a metallic mask may be formed. When a metallic mask is formed, the same effect as in the first embodiment can be obtained. Furthermore, the metal mask 618 with an insulating film may not be completely embedded in the cladding layer, as in the third embodiment. However, in order to improve the yield of laser element manufacturing, it is preferable to bury the metallic mask 618 with an insulating film in the cladding layer.
[0133]
In this embodiment, an example in which a GaN film is used as the low-temperature buffer layer has been described._xGa_1-xEven if N (0 ≦ x ≦ 1) is used, no problem occurs. Furthermore, in this embodiment, the Al composition of the clad layer to be regrown is set to 0.1, but the same effect can be seen even in a nitride semiconductor having a composition of 0 <Al ≦ 1.
[0134]
(Embodiment 6)
In this embodiment, a structure in which a metallic mask is provided in a p-type cladding layer instead of forming a metallic mask in an n-type cladding layer in the fourth embodiment will be described.
[0135]
FIG. 7 shows the structure of the nitride semiconductor laser device of this embodiment. This semiconductor laser device has a low-temperature GaN buffer layer 701, an n-type GaN contact layer 702, an n-type Al on a sapphire substrate 700._0.1Ga_0.9N clad layer 703, n-type GaN light guide layer 704, active layer 705 (for example, In 2 nm thick In_0.15Ga_0.85N layer and 4 nm thick In_0.02Ga_0.98Multiple quantum well active layer composed of N layer, 3 periods of 4 nm thick In_0.15Ga_0.85N layer and 10 nm thick In_0.01Ga_0.99Multiple quantum well active layer consisting of N layer and 3 periods of In_0.18Ga_0.82N layer and In_0.05Ga_0.95Multiple quantum well active layer consisting of N layer, etc.), Al_0.2Ga_0.8N carrier block layer 706, p-type GaN light guide layer 707, p-type Al_0.1Ga_0.9An N clad layer 708 and a p-type GaN contact layer 709 are sequentially stacked. On the p-type contact layer 709, SiO having a stripe-shaped portion opened as a current path is formed.₂An insulating film 710 is provided, and a p-type electrode 712 is provided over the opening and the insulating film 710, and a portion on the opening of the insulating film 710 functions as a striped electrode. The p-type contact layer 709 to the n-type contact layer 702 are partially removed so that the surface of the n-type contact layer 702 is exposed, and an n-type electrode 711 is formed on the exposed portion of the n-type contact 702. ing.
[0136]
The n-type contact layer 702 includes a lower layer n-type GaN film 702a and a regrown n-type GaN film 702b. The growth film 702b is covered. This mask 715 is composed of a platinum film 713 and SiN provided thereon._xIt is comprised from the insulating film 714 which consists of. p-type Al_0.1Ga_0.9The N clad layer 708 is formed of a lower layer p-type Al_0.1Ga_0.9N film 708a and regrown p-type Al_0.1Ga_0.9The regrowth film 708b covers the metallic mask 716 (platinum mask), which is composed of the N clad film 708b and is provided on the lower film 708a below the stripe electrode.
[0137]
The nitride semiconductor laser element of this embodiment can be manufactured as follows, for example. First, as in the second embodiment, a low-temperature GaN buffer layer 701 is grown on a sapphire substrate 700 in a crystal growth apparatus, and then, among the n-type GaN contact layers 702, a lower n-type GaN film 702a having a thickness of 20 μm. Grow.
[0138]
Next, as in the second embodiment, the metal mask 715 with an insulating film having a mask width (M) of 5 μm and a mask thickness of 0.15 μm is formed in a stripe shape in the <1-100> direction with respect to the lower GaN film 702a. Form. The mask 715 includes a platinum film 713 having a thickness of 0.1 μm and a SiN film having a thickness of 0.05 μm._xThe film 714 is formed and disposed below the stripe-shaped electrode to be manufactured in a later step. Next, the substrate is again placed in the crystal growth apparatus, and the n-type GaN film 702b having a thickness of 20 μm is regrown in the same manner as in the second embodiment, so that the n-type GaN contact is flat and has no cracks. Layer 702 is formed.
[0139]
Subsequently, as in Embodiment 2, n-type Al_0.1Ga_0.9N clad layer 703, n-type GaN light guide layer 704, active layer 705, Al_0.2Ga_0.8An N carrier block layer 706 and a p-type GaN light guide layer 707 are grown.
[0140]
Thereafter, in the p-type contact layer 708, a lower Al layer having a thickness of 0.15 μm_0.1Ga_0.9An N film 708a is grown. Next, the substrate is once taken out from the crystal growth apparatus, and the lower layer Al_0.1Ga_0.9A platinum mask 716 having a mask width of 2.5 μm, a mask interval (S) of 2 μm, and a thickness of about 0.08 μm is formed in stripes in the <1-100> direction with respect to the N film 708a. At this time, a portion 717 that is not covered with the platinum mask 716 is disposed under the stripe-shaped electrode to be manufactured in a later step. Next, the substrate is again placed in the crystal growth apparatus, and p-type Al having a thickness of 0.4 μm_0.1Ga_0.9The N film 708b is regrown. As growth proceeds, the portion 717 that is not coated with platinum 716 begins with Al._0.1Ga_0.9N began to regrow, lateral growth occurred and the platinum mask 716 was coated. This laterally grown Al_0.1Ga_0.9The N film 708b was completely bonded, and a flat clad layer 708 was obtained.
[0141]
Subsequently, a p-type GaN contact layer 709 is grown as in the fourth embodiment. Thereafter, the substrate is taken out from the crystal growth apparatus, and the nitride semiconductor laser device of this embodiment shown in FIG. 7 is manufactured through a manufacturing process of the semiconductor laser device.
[0142]
N-type GaN contact layer 702 and p-type Al obtained by such a selective growth process_0.1Ga_0.9The surface of the N clad layer 708 was flat and had no cracks. Regarding the n-type GaN contact layer 702, dislocations (crystal defects) were reduced as in the first and second embodiments.
[0143]
The nitride semiconductor laser device of this embodiment is a SiN provided in the GaN contact layer 702 and having a growth suppressing effect._xThe presence of the film-coated platinum mask 715 reduced the dislocation density by about two orders of magnitude in each film constituting the laser structure after regrowth on the mask. As a result, the lifetime characteristic of the semiconductor laser element itself was about 12000 hours.
[0144]
When the laser oscillation threshold current density of the nitride semiconductor laser device of this embodiment was measured, it was reduced to about 2/3 of the conventional semiconductor laser device having a ridge stripe structure shown in FIG. Further, when the modes of NFP and FFP in the horizontal transverse mode and the vertical transverse mode were observed, laser oscillation was obtained in a single-peak single mode. Further, the nitride semiconductor laser device of this embodiment was subjected to a 10000 hour life test, and the horizontal transverse mode and the vertical transverse mode were observed again. As described above, a stable single horizontal transverse mode and a single vertical transverse mode were observed. Mode was observed.
[0145]
The reason why the single-peak (single) and stable vertical transverse mode laser oscillation is obtained is the same as in the first and second embodiments. In addition, the formation position of the vertical transverse mode, that is, SiN_xThe formation position of the film-coated platinum mask 715 is the same as that of the second embodiment in each of the vertical direction and the parallel direction with respect to the substrate. On the other hand, the reason why a single horizontal (single) and stable horizontal transverse mode laser oscillation is obtained is that the platinum mask 716 used in this embodiment absorbs the laser light emitted from the active layer 705, and thus the platinum mask 716 is used. There is a difference in the equivalent refractive index of the light guide layer between where it is provided and where it is not provided. Then, it is considered that the optical confinement in the horizontal transverse mode becomes remarkable above the portion 717 not covered with the platinum mask 716 and the refractive index waveguide structure is obtained, which contributes to the reduction of the laser oscillation threshold current density. . In addition to this refractive index waveguide structure, strong light absorption by the metallic mask 716 causes a large gain loss in the upper part of the mask, making it difficult for high-order transverse modes to occur. As a result, it is considered that a stable single horizontal transverse mode was observed.
[0146]
The horizontal transverse mode forming position, that is, the forming position of the platinum film 716 is preferably formed at the following positions in each of the vertical direction and the parallel direction with respect to the substrate.
[0147]
First, with respect to the direction perpendicular to the substrate, the side opposite to the substrate from the interface (upper surface of the active layer) between the active layer 705 and the carrier block layer 706 (or the p-type light guide layer 705 in the absence of the carrier block layer 706). It is preferable to form it at a position within 2 μm in the direction. In this embodiment, a platinum mask 716 having a thickness of 0.08 μm is formed at a position of 0.25 μm from the interface. This is because when the formation position of the metallic mask exceeds 2 μm from the interface, the equivalent refractive index difference hardly occurs between where the metallic mask is provided and where the metallic mask is not provided. This is because light confinement becomes weak. Further, according to the knowledge of the present inventors, the shorter the distance from the interface to the metallic mask, the larger the refractive index difference, and the stronger the optical confinement effect in the horizontal transverse mode. Furthermore, in this embodiment, the distance from the interface between the active layer 705 and the carrier block layer 706 (or the p-type light guide layer 707 in the absence of the carrier block layer 706) to the metallic mask is the crystal growth rate of the crystal growth apparatus. Can be set. Therefore, compared with the said Embodiment 4 and Embodiment 5, the distance from the said interface to a mask can be controlled with a sufficient precision, and the optical confinement effect of a horizontal transverse mode can also be controlled with a sufficient precision.
[0148]
On the other hand, in a direction parallel to the substrate, a portion 717 that is not covered with the metallic mask is formed below the striped p-type electrode 712. Further, as in the third embodiment, the interval (S) between the metallic masks is preferably 1 μm or more and 15 μm or less.
[0149]
The thicknesses of the metal mask 715 and the metal mask 716 with an insulating film, the nitrogen carrier gas used in the selective growth, the yield rate, and the like are the same as those in the fourth embodiment.
[0150]
In this embodiment, the metallic mask with an insulating film is formed in the n-type GaN contact layer, but a metallic mask may be formed. When a metallic mask is formed, the same effect as in the first embodiment can be obtained. Furthermore, the metallic mask 716 may not be completely buried in the cladding layer, as in the third embodiment. However, in order to improve the yield of laser element manufacturing, it is preferable to bury the metallic mask 716 with an insulating film in the cladding layer.
[0151]
In this embodiment, an example in which a GaN film is used as the low-temperature buffer layer has been described._xGa_1-xEven if N (0 ≦ x ≦ 1) is used, no problem occurs. Furthermore, in this embodiment, the Al composition of the clad layer to be regrown is set to 0.1, but the same effect can be seen even in a nitride semiconductor having a composition of 0 <Al ≦ 1.
[0152]
Furthermore, a synergistic effect can be obtained by combining this embodiment and the said Embodiment 4 or Embodiment 5.
[0153]
(Embodiment 7)
In the present embodiment, a structure in which a metal mask with an insulating film is provided in the AlGaN cladding layer in place of the metal mask in the sixth embodiment will be described.
[0154]
FIG. 8 shows the structure of the nitride semiconductor laser device of this embodiment. This semiconductor laser device includes a low-temperature GaN buffer layer 801, an n-type GaN contact layer 802, an n-type Al on a sapphire substrate 800._0.1Ga_0.9N clad layer 803, n-type GaN light guide layer 804, active layer 805 (for example, 2 nm thick In_0.15Ga_0.85N layer and 4 nm thick In_0.02Ga_0.98Multiple quantum well active layer composed of N layer, 3 periods of 4 nm thick In_0.15Ga_0.85N layer and 10 nm thick In_0.01Ga_0.99Multiple quantum well active layer consisting of N layer and 3 periods of In_0.18Ga_0.82N layer and In_0.05Ga_0.95Multiple quantum well active layer consisting of N layer, etc.), Al_0.2Ga_0.8N carrier block layer 806, p-type GaN light guide layer 807, p-type Al_0.1Ga_0.9An N clad layer 808 and a p-type GaN contact layer 809 are sequentially stacked. On the p-type contact layer 809, a stripe-shaped portion serving as a current path is opened.₂An insulating film 810 is provided, and a p-type electrode 812 is provided over the opening and the insulating film 810, and a portion on the opening of the insulating film 810 functions as a stripe electrode. The p-type contact layer 809 to the n-type contact layer 802 are partially removed so that the surface of the n-type contact layer 802 is exposed, and an n-type electrode 811 is formed on the exposed portion of the n-type contact 802. ing.
[0155]
The n-type contact layer 802 is composed of a lower n-type GaN film 802a and a regrown n-type GaN film 802b. The growth film 802b is covered. This mask 815 is composed of a platinum film 813 and SiN provided thereon._xInsulating film 814 made of p-type Al_0.1Ga_0.9The N-clad layer 808 is composed of a lower layer p-type Al_0.1Ga_0.9N film 808a and regrown p-type Al_0.1Ga_0.9The regrowth film 808b covers the metallic mask 818 with an insulating film, which is composed of an N clad film 808b and is provided on the lower film 808a below the stripe electrode. This mask 818 is composed of a platinum film 816 and SiN provided thereon._xThe insulating film 817 is made of.
[0156]
The nitride semiconductor laser element of this embodiment can be manufactured as follows, for example. First, as in the second embodiment, a low-temperature GaN buffer layer 801 is grown on a sapphire substrate 800 in a crystal growth apparatus, and then, a lower n-type GaN film 802a having a thickness of 20 μm in the n-type GaN contact layer 802. Grow.
[0157]
Next, as in the second embodiment, the metallic mask 815 with an insulating film having a mask width (M) of 5 μm and a mask thickness of 0.15 μm is formed in a stripe shape in the <1-100> direction with respect to the lower GaN film 802a. Form. The mask 815 includes a platinum film 813 having a thickness of 0.1 μm and a SiN film having a thickness of 0.05 μm._xA film 814 is provided below the stripe-shaped electrode that is formed in a later step. Next, the substrate is again placed in the crystal growth apparatus, and the n-type GaN film 802b having a thickness of 20 μm is regrown in the same manner as in the second embodiment, so that the n-type GaN contact is flat and has no cracks. Layer 802 is formed.
[0158]
Subsequently, as in Embodiment 6, n-type Al_0.1Ga_0.9N clad layer 803, n-type GaN light guide layer 804, active layer 805, Al_0.2Ga_0.8An N carrier block layer 806 and a p-type GaN light guide layer 807 are grown.
[0159]
Thereafter, as in Embodiment 6, p-type Al_0.1Ga_0.9Out of the N clad layer 808, the lower Al layer having a thickness of 0.1 μm_0.1Ga_0.9An N film 808a is grown. Next, the substrate is once removed from the crystal growth apparatus, and the lower layer p-type Al_0.1Ga_0.9A metallic mask 818 with an insulating film having a mask width of 3 μm, a mask interval (S) of 1.5 μm, and a mask thickness of 0.2 μm is formed in stripes in the <1-100> direction with respect to the N film 808a. The mask 818 includes a platinum film 816 having a thickness of 0.1 μm and a SiN film having a thickness of 0.1 μm._xA SiN film is formed below the stripe-shaped electrode formed of the film 817 and manufactured in a later step._xA portion 819 that is not covered with the platinum mask 818 with a film is disposed. Next, the substrate was placed again in the crystal growth apparatus, and a p-type Al having a thickness of 0.5 μm_0.1Ga_0.9The N film 808b is regrown. As growth progresses, SiN_xAl from the portion 819 not covered with the attached platinum mask 818_0.1Ga_0.9N begins to regrow, lateral growth occurs and SiN_xA platinum mask 818 with a film was coated. This laterally grown Al_0.1Ga_0.9The N film 808b was completely bonded, and a flat clad layer 808 was obtained.
[0160]
Subsequently, a p-type GaN contact layer 809 is grown as in the sixth embodiment. Thereafter, the substrate is taken out from the crystal growth apparatus, and the nitride semiconductor laser device of this embodiment shown in FIG. 8 is manufactured through a manufacturing process of the semiconductor laser device.
[0161]
N-type GaN contact layer 802 and p-type Al obtained by such a selective growth process_0.1Ga_0.9The surface of the N clad layer 808 was flat and had no cracks. Dislocations (crystal defects) related to the n-type GaN contact layer 802 were reduced as in the first and second embodiments.
[0162]
Furthermore, the nitride semiconductor laser device of the present embodiment is provided with SiN provided in the GaN contact layer 802 and having a growth suppressing effect._xThe presence of the film-coated platinum mask 815 reduced the dislocation density by about two orders of magnitude in each film constituting the laser structure after regrowth on the mask. As a result, the lifetime characteristic of the semiconductor laser element itself was about 12000 hours.
[0163]
When the laser oscillation threshold current density of the nitride semiconductor laser device of this embodiment was measured, it was reduced to about ½ of the conventional semiconductor laser device having a ridge stripe structure shown in FIG. Further, when the modes of NFP and FFP in the horizontal transverse mode and the vertical transverse mode were observed, laser oscillation was obtained in a single-peak single mode. Further, the nitride semiconductor laser device of this embodiment was subjected to a 10000 hour life test, and the horizontal transverse mode and the vertical transverse mode were observed again. As described above, a stable single horizontal transverse mode and a single vertical transverse mode were observed. Mode was observed.
[0164]
The reason why the laser oscillation threshold current density is reduced in this way is that, similarly to the fifth embodiment, in addition to the laser characteristics of the refractive index waveguide structure described in the fourth embodiment, a current confinement structure is simultaneously formed in the element. This is because of that. Further, the reason why the single-peak (single) and stable vertical transverse mode laser oscillation is obtained is the same as in the first and second embodiments. In addition, the formation position of the vertical transverse mode, that is, SiN_xThe formation position of the platinum mask 815 with a film is the same as that in the second embodiment in each of the vertical direction and the parallel direction with respect to the substrate. Further, the reason why a single horizontal (single) and stable horizontal transverse mode laser oscillation is obtained is the same as in the sixth embodiment. Also, a metallic mask (SiN with an insulating film) for obtaining a refractive index waveguide structure_xThe formation position of the film-coated platinum mask 815) is the same as in the sixth embodiment. However, the position of the metallic mask with an insulating film in this case refers to the position of forming the metallic mask constituting the metallic mask with an insulating film, and in this sense, is the same as in the sixth embodiment. .
[0165]
In the present embodiment, as in the sixth embodiment, a metallic mask with an insulating film (SiO 2) is formed from the interface between the active layer 805 and the carrier block layer 806 (or the p-type light guide layer 807 when there is no carrier block layer 806).₂The distance to the film-coated platinum mask 818) can be set by the crystal growth rate of the crystal growth apparatus. Therefore, compared with the said Embodiment 4 and Embodiment 5, the distance from the said interface to a mask can be controlled with a sufficient precision, and the optical confinement effect of a horizontal transverse mode can also be controlled with a sufficient precision.
[0166]
In addition to the current confinement effect, the present embodiment also has the following effects. As will be described in detail in Embodiment 9 to be described later, in the selective growth of a GaN film using a metallic mask, the dependence on the stripe direction of the mask is generally strong and the lateral growth is difficult, but the metallic mask with an insulating film is used. (SiN_xBy using a platinum mask with a film), sufficient lateral growth can be obtained without selective dependence of the mask pattern even in selective growth of a GaN film. By utilizing this characteristic, within a position range in which the metallic mask 818 with an insulating film can be formed in order to obtain a refractive index waveguide structure in a direction perpendicular to the substrate (within 2 μm from the upper surface or the lower surface of the active layer). Even if a nitride semiconductor containing no Al exists at the position), selective growth with a high lateral growth rate is possible.
[0167]
In this embodiment, platinum (Pt) is used as the metallic mask in the metallic masks 815 and 818 with an insulating film, but other than that, for example, W, Ti, Mo, Ni, Al, Pd, Au, etc. A metal, an alloy thereof, or a composite film including a plurality of layers containing them can be used. A nitride semiconductor is not directly epitaxially grown, and a growth suppressing effect can be obtained. If the metal has a light absorption effect for absorbing laser light emitted from the active layer, the material does not greatly depend on the material. Further, in the metal masks 815 and 818 with an insulating film, the insulating film is SiN._xIn addition to the film, SiO₂A film may be used, and if it is an insulating film, it does not depend greatly on the material. When the metallic mask is covered with an insulating film, it is preferable that the side portion 820 of the metallic mask is also covered with the insulating film. Furthermore, the thicknesses of the metal masks 815 and 818 with insulating films, the nitrogen carrier gas used in the selective growth, the yield rate, and the like are the same as those in the sixth embodiment. In this embodiment, a metallic mask (SiN with an insulating film) is formed in the n-type GaN contact layer._xAlthough a platinum mask is formed, a metallic mask may be formed. When a metallic mask is formed, the same effect as in the first embodiment can be obtained. Furthermore, the metal mask 818 with an insulating film may not be completely embedded in the cladding layer, as in the third embodiment. However, in order to improve the yield of laser element manufacturing, it is preferable to bury the metallic mask 818 with an insulating film in the cladding layer.
[0168]
In this embodiment, an example in which a GaN film is used as the low-temperature buffer layer has been described._xGa_1-xEven if N (0 ≦ x ≦ 1) is used, no problem occurs. Furthermore, in this embodiment, the Al composition of the clad layer to be regrown is set to 0.1, but the same effect can be seen even in a nitride semiconductor having a composition of 0 <Al ≦ 1.
[0169]
Furthermore, a synergistic effect can be obtained by combining this embodiment and the said Embodiment 4 or Embodiment 5.
[0170]
(Embodiment 8)
In this embodiment, the relationship between the film thickness of the metallic mask and the light absorption rate will be described.
[0171]
FIG. 9 is a diagram showing the relationship between the film thickness of the tungsten mask and the light absorption rate of the laser beam. According to this figure, when the film thickness of the mask is about 0.01 μm or more, the light absorption rate is 60% or more, and when the film thickness is about 0.05 μm or more, the light absorption rate is almost 100%. The relationship shown in FIG. 9 is not limited to tungsten (W) but is almost the same even when Pt, Ti, Mo, Ni, Al, Pd, Au, or the like is used. Therefore, in order to obtain a light absorption effect for stabilizing the vertical transverse mode with a metallic mask, the thickness of the metallic mask (in the case of a metallic mask with an insulating film, the metallic film constituting it) should be at least The thickness is preferably 0.01 μm or more, more preferably 0.05 μm or more, which shows a light absorption rate of 50% or more.
[0172]
On the other hand, when a metallic mask is covered with a nitride semiconductor film, the surface of the semiconductor film is flat so that a metallic mask (in the case of a metallic mask with an insulating film, an insulating film and a metal film) The film thickness of the entire mask is preferably 2 μm or less.
[0173]
(Embodiment 9)
In the present embodiment, the ratio (a / c) between the growth rate in the growth axis direction and the lateral growth rate when using the metallic mask and the metallic mask with an insulating film, the partial pressure of the nitrogen carrier gas, and the mask The relationship with the stripe direction will be described.
[0174]
FIG. 10A shows lateral growth (a / c) and partial pressure ratio of nitrogen carrier gas (N / N) when a GaN film is selectively grown using a tungsten mask.₂/ (H₂+ N₂)). In FIG. 10A, in the lateral growth (a / c), the growth rate in the direction perpendicular to the substrate is c, and the growth rate in the direction parallel to the substrate (lateral growth rate) is a. Expressed as a / c. Further, the partial pressure ratio of nitrogen carrier gas (N₂/ (H₂+ N₂)) Is expressed as a flow ratio of nitrogen carrier gas to the flow rate of all carrier gases (flow rate of nitrogen carrier gas + flow rate of hydrogen carrier gas). Further, in FIG. 10A, the direction indicates the stripe direction of the tungsten mask with respect to the nitride semiconductor (GaN).
[0175]
As shown in FIG. 10A, when the stripe direction of the tungsten mask is formed in the <11-20> direction, the lateral growth hardly occurs even if the partial pressure of the nitrogen carrier gas is increased. On the other hand, when it was formed in the <1-100> direction, lateral growth of about a / c = about 0.4 occurred at a nitrogen carrier gas partial pressure of 0.5. The relationship shown in FIG. 10A is not limited to tungsten (W) but is almost the same even when Pt, Ti, Mo, Ni, Al, Pd, Au, or the like is used.
[0176]
FIG. 10B shows the lateral growth (a / c) and the partial pressure ratio (N) of the nitrogen carrier gas when the AlGaN film is selectively grown using a tungsten mask.₂/ (H₂+ N₂)). In FIG. 10B, lateral growth (a / c), partial pressure ratio of nitrogen carrier gas (N₂/ (H₂+ N₂)) And orientation are the same as those in FIG.
[0177]
As shown in FIG. 10 (b), when the stripe direction of the tungsten mask is formed in the <11-20> direction, lateral growth with a nitrogen carrier gas partial pressure of 0.5 and a / c = about 1.5 is achieved. occured. On the other hand, when it was formed in the <1-100> direction, lateral growth with a / c = about 15 occurred at a nitrogen carrier gas partial pressure of 0.5. The relationship shown in FIG. 10B is not limited to tungsten (W) but is almost the same even when Pt, Ti, Mo, Ni, Al, Pd, Au, or the like is used.
[0178]
From the results shown in FIGS. 10A and 10B, when selective growth is performed using the growth suppression effect of the metallic mask, the stripe direction of the metallic mask is formed in the <1-100> direction. It is understood that a higher partial pressure of the nitrogen carrier gas is preferable. However, the selective growth film produced with the nitrogen carrier gas partial pressure larger than 0.9 had an X-ray diffraction half width of 6 minutes or more, and the crystallinity (orientation) was deteriorated. Further, the lateral growth of the metallic mask was faster in the nitride semiconductor film containing at least Al than in the GaN film.
[0179]
FIG. 11A shows SiO.₂In the case of selective growth of a GaN film using a tungsten mask with a film, the lateral growth (a / c) and the partial pressure ratio of nitrogen carrier gas (N₂/ (H₂+ N₂)). In FIG. 11A, in the lateral growth (a / c), the growth rate in the direction perpendicular to the substrate is c, and the growth rate in the direction parallel to the substrate (lateral growth rate) is a. Expressed as a / c. Further, the partial pressure ratio of nitrogen carrier gas (N₂/ (H₂+ N₂)) Is expressed as a flow ratio of nitrogen carrier gas to the flow rate of all carrier gases (flow rate of nitrogen carrier gas + flow rate of hydrogen carrier gas). Further, in FIG. 11A, the orientation is SiO with respect to the nitride semiconductor (GaN).₂The stripe direction of the film-coated tungsten mask is shown.
[0180]
As shown in FIG. 11 (a), SiO₂When the stripe direction of the film-coated tungsten mask was formed in the <11-20> direction, lateral growth of about a / c = about 0.5 occurred at a nitrogen carrier gas partial pressure of 0.5. On the other hand, when it was formed in the <1-100> direction, lateral growth with a / c = about 1.5 occurred at a nitrogen carrier gas partial pressure of 0.5. The relationship shown in FIG. 11A is not limited to tungsten (W) but is almost the same even when Pt, Ti, Mo, Ni, Al, Pd, Au, or the like is used. Also for insulating films, SiO₂Not only film but SiN_xIt was almost the same even when a film was used.
[0181]
FIG. 11B shows SiO.₂When selective growth of the AlGaN film is performed using a tungsten mask with a film, the lateral growth (a / c) and the partial pressure ratio of the nitrogen carrier gas (N₂/ (H₂+ N₂)). In FIG. 11B, lateral growth (a / c), partial pressure ratio of nitrogen carrier gas (N₂/ (H₂+ N₂)) And orientation are the same as those in FIG.
[0182]
As shown in FIG. 11B, SiO₂When the stripe direction of the tungsten mask with a film was formed in the <11-20> direction, lateral growth of about a / c = about 8 occurred at a nitrogen carrier gas partial pressure of 0.5. On the other hand, when it was formed in the <1-100> direction, lateral growth with a / c = about 28 occurred at a nitrogen carrier gas partial pressure of 0.5. The relationship shown in FIG. 11B is not limited to tungsten (W) but is almost the same even when Pt, Ti, Mo, Ni, Al, Pd, Au, or the like is used. Also for insulating films, SiO₂Not only film but SiN_xIt was almost the same even when a film was used.
[0183]
From the results shown in FIGS. 11A and 11B, when the selective growth is performed using the growth suppressing effect of the metallic mask with an insulating film, the stripe direction of the metallic mask is the <1-100> direction. It can be seen that it is preferable that the nitrogen carrier gas has a higher partial pressure. However, the selective growth film produced with the nitrogen carrier gas partial pressure larger than 0.9 had an X-ray diffraction half width of 6 minutes or more, and the crystallinity (orientation) was deteriorated. Further, the lateral growth of the metallic mask was faster in the nitride semiconductor film containing at least Al than in the GaN film. Further, the metallic mask with an insulating film has a faster lateral growth than the metallic mask, and the stripe direction dependency of the mask is relaxed.
[0184]
10A, 10B, 11A, and 11B, the lateral growth a / c greatly increases when the nitrogen carrier gas partial pressure is 0.1 or more. Therefore, the nitrogen carrier gas partial pressure is preferably 0.1 or more.
[0185]
Furthermore, from FIG. 10 and FIG. 11, the lower limit value of the laterally grown film necessary for covering the mask including the metal film can be read. This value varies depending on whether the selectively grown film (covering film) is a GaN film or an AlGaN film. Similarly, it differs also in the stripe direction of the mask, which differs depending on whether the mask is only a metal film or an insulating film is provided thereon. Furthermore, the atmospheric gas ratio (N₂/ N₂+ H₂) Also varies.
[0186]
For example, when the stripe direction of a metal mask with an insulating film is set to <1-100> and a GaN film is selectively grown thereon, an atmospheric gas (N₂/ (N₂+ H₂)) = 0.5, it can be read from FIG. 11A that lateral growth a / c = 1.5. That is, the lateral growth with respect to the laminated film thickness (coating film thickness) 1 is 1.5. In the selective growth on the mask, the growth starts from the portions on both sides of the mask which are not covered with the mask, and the mask is covered by meeting at the central portion of the mask. Therefore, the metallic mask is covered with 1.5 × 2 (for both sides) = 3 with respect to the laminated film thickness 1. If the mask width is 6 μm, the mask is covered with a laminated film thickness (lower limit) of 6/3 = 2 μm. In each of the above embodiments, N₂(10 liter / min) + H₂Selective growth is performed under the condition of (5 liters / min).
[0187]
(Embodiment 10)
In the present embodiment, an example will be described in which the metallic mask formed on the lower layer n-type AlGaN film is not flatly covered with the regrown n-type AlGaN film but has a depression. Other configurations are the same as those of the above-described embodiment.
[0188]
FIG. 12 shows the structure of the nitride semiconductor laser device of this embodiment. This semiconductor laser device has an n-type Al on an n-type GaN substrate 901._0.02Ga_0.98N contact layer 902, n-type Al_0.1Ga_0.9N clad layer 903, n-type GaN light guide layer 904, active layer 905, Al_0.2Ga_0.8N carrier block layer 906, p-type GaN light guide layer 907, p-type Al_0.1Ga_0.9An N clad layer 908 and a p-type GaN contact layer 909 are sequentially stacked. On the p-type contact layer 909, SiO having a stripe-shaped portion opened as a current path is formed.₂An insulating film 910 is provided, and a p-type electrode 912 is provided over the opening and the insulating film 910, and a portion on the opening of the insulating film 910 functions as a striped electrode. An n-type electrode 911 is formed so as to be in contact with the back surface of the n-type GaN substrate 901.
[0189]
n-type Al_0.1Ga_0.9N clad layer 903 is a lower layer n-type Al_0.1Ga_0.9N film 903a and regrown n-type Al_0.1Ga_0.9The N clad film 903b is used. Further, the metallic mask (tungsten mask or the like) 916 provided on the lower film 903a below the stripe electrode is not covered with the regrowth film 403b but has a depression.
[0190]
In this embodiment, the metallic mask 916 is introduced in accordance with the above-described embodiment in order to obtain a horizontal transverse mode light confinement effect in the semiconductor laser element. However, as a result of further detailed studies by the inventors of the present application, it has been found that in addition to the light confinement effect in the horizontal and transverse modes, the following effects can be obtained.
[0191]
In FIG. 12, there are two metallic masks 916 provided below the active layer 905, and the current injection width of the p-type stripe electrode 412 is located above the space S between the metallic masks 916 and 916. Wp is provided, and the metallic mask 916 has a recess that is not covered flat by the regrown n-type AlGaN film 903b.
[0192]
In this case, (1) by having the depression, the active layer 905 has a form close to a quantum wire structure confined in a direction perpendicular to the stripe direction of the p-type stripe electrode 912 from the quantum well structure. Thereby, the threshold current density can be further reduced. In addition, (2) by having the depression, crystal distortion of the nitride semiconductor layer formed above the regrown n-type AlGaN film 903b can be relaxed by the depression. As a result, a decrease in crystallinity due to strain can be prevented, and the laser oscillation life can be further extended. Furthermore, (3) by having the depression, it is possible to prevent the current injected from the p-type stripe electrode 912 from spreading in the lateral direction. As a result, the threshold current density can be lowered.
[0193]
This dent is N₂Carrier gas partial pressure is less than 10%, preferably H₂It can be formed by growing the regrowth layer 903b in a carrier gas atmosphere. Alternatively, the regrowth layer 903b can be formed even if the film thickness is reduced.
[0194]
In the schematic diagram of FIG. 12, the nitride semiconductor layer stacked on the side wall of the recess is exaggerated. Actually, since the thickness of each nitride semiconductor layer is thin, most of the inside of the recess is not necessarily filled with the nitride semiconductor layer as shown in FIG. The above effect according to the present embodiment is more prominent as the depth of the recess is deeper. However, if the depth is too deep, the formation of the striped electrode becomes difficult, and thus the effect is set appropriately. The position of the dent is formed above the center of the mask width with substantially reproducibility.
[0195]
(Embodiment 11)
In the present embodiment, an example will be described in which the metallic mask formed on the lower p-type AlGaN film has a depression without being covered flat by the regrowth p-type AlGaN film. Other configurations are the same as those of the above-described embodiment.
[0196]
FIG. 13 shows the structure of the nitride semiconductor laser device of this embodiment. This semiconductor laser device has an n-type Al on an n-type GaN substrate 1001._0.02Ga_0.98N contact layer 1002, n-type Al_0.1Ga_0.9N clad layer 1003, n-type GaN light guide layer 1004, active layer 1005, Al_0.2Ga_0.8N carrier block layer 1006, p-type GaN light guide layer 1007, p-type Al_0.1Ga_0.9An N clad layer 1008 and a p-type GaN contact layer 1009 are sequentially stacked. On the p-type contact layer 1009, a SiO 2 having a stripe-shaped portion opened as a current path is formed.₂An insulating film 1010 is provided, and a p-type electrode 1012 is provided over the opening and the insulating film 1010, and a portion on the opening of the insulating film 1010 functions as a striped electrode. An n-type electrode 1011 is formed so as to be in contact with the back surface of the n-type GaN substrate 1001.
[0197]
p-type Al_0.1Ga_0.9The N-clad layer 1008 is formed of a lower layer p-type Al_0.1Ga_0.9N film 1008a and regrown p-type Al_0.1Ga_0.9The N clad film 1008b is used. In addition, the metallic mask (tungsten mask or the like) 1016 provided on the lower layer film 1008a below the stripe electrode is not flatly covered with the regrowth film 1008b but has a depression.
[0198]
In the present embodiment, the metallic mask 1016 is introduced in accordance with the above-described embodiment in order to obtain a horizontal transverse mode light confinement effect in the semiconductor laser element. However, as a result of further detailed studies by the inventors of the present application, it has been found that in addition to the light confinement effect in the horizontal and transverse modes, the following effects can be obtained.
[0199]
In FIG. 13, there are two metallic masks 1016 provided above the active layer 1005, and the current injection width of the p-type stripe electrode 1012 is located above the space S between the metallic masks 1016 and 1016. Wp is provided, and the metallic mask 1016 has a recess that is not covered flat by the regrown n-type AlGaN film 1008b.
[0200]
In this case, by having the recess, the crystal distortion of the nitride semiconductor layer formed above the regrown p-type AlGaN film 1008b can be relaxed by the recess. As a result, a decrease in crystallinity due to strain can be prevented, and the laser oscillation life can be further extended.
[0201]
This dent is N₂Carrier gas partial pressure is less than 10%, preferably H₂It can be formed by growing the regrowth layer 1008b in a carrier gas atmosphere. Alternatively, the regrowth layer 1008b can be formed even if the film thickness is reduced.
[0202]
The schematic diagram of FIG. 13 exaggerates the nitride semiconductor layer stacked on the side wall of the recess. Actually, since the thickness of each nitride semiconductor layer is thin, most of the inside of the recess is not necessarily filled with the nitride semiconductor layer as shown in FIG. The above effect according to the present embodiment is more prominent as the depth of the recess is deeper. However, if the depth is too deep, the formation of the striped electrode becomes difficult, and thus the effect is set appropriately. The position of the dent is formed above the center of the mask width with substantially reproducibility.
[0203]
Embodiment 12
In the present embodiment, an example will be described in which a metallic mask formed on an n-type GaN substrate is not flatly covered with a regrown n-type AlGaN film but has depressions. Other configurations are the same as those of the above-described embodiment.
[0204]
FIG. 14 shows the structure of the nitride semiconductor laser device of this embodiment. This nitride semiconductor laser device has an n-type Al on an n-type GaN substrate 1101._0.02Ga_0.98N contact layer 1102, n-type Al_0.1Ga_0.9N clad layer 1103, n-type GaN light guide layer 1104, active layer 1105, Al_0.2Ga_0.8N carrier block layer 1106, p-type GaN light guide layer 1107, p-type Al_0.1Ga_0.9An N clad layer 1108 and a p-type GaN contact layer 1109 are sequentially stacked. The p-type cladding layer 1108 is dug down to the vicinity of the p-type light guide layer 1107 to form a ridge stripe portion composed of the p-type contact layer 1109 and the p-type cladding layer 1108. On top of that, SiO₂An insulating film 1110 is provided, and an upper portion of the ridge stripe is opened. A p-type electrode 1112 is provided on the insulating film 1110 and on the ridge stripe portion exposed from the opening of the insulating film 1110, and the portion on the ridge stripe functions as a stripe electrode. An n-type electrode 1111 is formed so as to be in contact with the back surface of the n-type GaN substrate 1101.
[0205]
Further, a metallic mask (tungsten mask or the like) 1116 provided on the upper portion of the substrate below the ridge stripe portion is not flatly covered with the contact layer 1102 but has a depression.
[0206]
In this embodiment, the metallic mask is formed at a position within half of the total thickness of the contact layer thickness and the substrate thickness from the interface between the cladding layer and the contact layer toward the substrate.
[0207]
In this embodiment, the metallic mask 1116 is introduced in accordance with the above-described embodiment in order to obtain a horizontal transverse mode light confinement effect in the semiconductor laser element. However, as a result of further detailed studies by the inventors of the present application, it has been found that in addition to the light confinement effect in the horizontal and transverse modes, the following effects can be obtained.
[0208]
In FIG. 14, a metal mask 1116 provided below the active layer 1105 is provided, and at least one of the region M1 and the region M2 in which the metal mask 1116 is covered flat by the contact layer 1102 is formed. A current injection width Wp having a ridge stripe structure is provided above.
[0209]
In this case, by having the depression, crystal distortion of the nitride semiconductor layer formed above the n-type AlGaN contact layer 1102 can be relaxed by the depression. As a result, a decrease in crystallinity due to strain can be prevented, and the laser oscillation life can be further extended.
[0210]
This dent is N₂Carrier gas partial pressure is less than 10%, preferably H₂It can be formed by growing the contact layer 1102 in a carrier gas atmosphere. Alternatively, the contact layer 1102 can be formed even when it is thin.
[0211]
The schematic diagram of FIG. 14 exaggerates the nitride semiconductor layer stacked on the side wall of the recess. Actually, since the thickness of each nitride semiconductor layer is thin, most of the inside of the recess is not necessarily filled with the nitride semiconductor layer as shown in FIG. The above effect according to the present embodiment is more prominent as the depth of the recess is deeper. However, if the depth is too deep, the formation of the striped electrode becomes difficult, and thus the effect is set appropriately. The position of the dent is formed above the center of the mask width with substantially reproducibility. In this embodiment, since the growth starts from both sides of the metallic mask, the recess is formed only on one side of the ridge stripe.
[0212]
In this embodiment, n-type Al formed on the metallic mask 1116._0.02Ga_0.08The N contact layer 1102 may have another Al composition ratio or GaN. The effect that the component of the layer formed on the metallic mask 1116 is AlGaN and the effect that the component of the layer formed on the metallic mask 1116 is GaN are the same as those in the above-described embodiment. It is the same.
[0213]
In the tenth to twelfth embodiments, the metallic mask has been described. However, a metallic mask with an insulating film may be used. The effect obtained by using the metal mask with an insulating film is the same as that of the above-described embodiment, and the formation method is also the same. However, when a metal mask with an insulating film is used, lateral growth is likely to occur, and therefore the metal mask is more likely to form a recess. Further, although the n-type electrode is formed from the back side of the GaN substrate, the n-type electrode may be formed from the same side as the p-type electrode as in the first embodiment. Furthermore, in the said Embodiment 10-Embodiment 12, although the shape of the hollow was made into V shape, you may have another shape, for example, a rectangular shape. For example, when the mask stripe direction is formed along the <1-100> direction of the nitride semiconductor crystal, a rectangular recess is likely to be formed.
[0214]
(Embodiment 13)
In this embodiment, an effect obtained by combining a metallic mask or a metallic mask with an insulating film with a GaN substrate (an example of a nitride semiconductor substrate) will be described.
[0215]
As a result of detailed studies by the inventors of the present application, when the metallic mask is formed on a nitride semiconductor layer (hereinafter referred to as an underlayer), the metal constituting the metallic mask is contained in the underlayer. Internal diffusion occurred. Such internal diffusion of the metal reduces the crystallinity and leads to a decrease in yield. In order to prevent such internal diffusion, the deposition temperature at the time of forming the metallic mask and the growth temperature of the nitride semiconductor layer covering the metallic mask can be controlled to some extent.
[0216]
However, by using a nitride semiconductor substrate (for example, a GaN substrate) as the substrate, internal diffusion of the metal can be more effectively suppressed, and the yield can be improved. The reason is as follows. According to the results of experiments conducted by the inventors of the present application, it has been found that the internal diffusion of the metal diffuses into the underlayer through threading dislocations. By using a GaN substrate, the threading dislocation density in the nitride semiconductor film grown on the GaN substrate is lower than when grown on a heterogeneous substrate other than the nitride semiconductor substrate (for example, a sapphire substrate). Thus, the internal diffusion of the metal can be suppressed more effectively.
[0217]
Although the metallic mask has been described in the present embodiment, the same effect can be obtained even when a metallic mask with an insulating film is used.
[0218]
In the first to thirteenth embodiments, examples of crystal growth by the MOCVD method have been described. However, the present invention is not limited to this, and other growth methods such as an MBE method, a hydride vapor phase growth method, a MOMBE method, and a CVD method can be used. The method may be used. The substrate is not limited to sapphire, but 6H—SiC, 4H—SiC, 3C—SiC, GaN, GaAs, Si, Ge, MgAl₂O_FourIt is also possible to use other substrates. Other nitride semiconductor substrates such as an AlGaN substrate and an InGaN substrate may be used. The mixed crystal ratio of each layer can be changed as appropriate. In addition, Al_xGa_yIn_1-xyAmong N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) nitride semiconductor constituent elements, a part of nitrogen element (about 10% or less) is replaced with at least one of P, As, and Sb The same effect can be obtained by using the prepared material.
[0219]
【The invention's effect】
As described above in detail, according to the present invention, the following effects can be obtained by applying a mask including a metal film having at least a light absorption function to a nitride semiconductor laser element.
[0220]
First, the unimodal vertical transverse mode can be stabilized by the light absorption effect of the metal film.
[0221]
Second, due to the light absorption effect by the metal film, the optical guide layer is given an equivalent refractive index difference to strengthen the horizontal transverse mode light confinement, reduce the threshold current density, and stabilize the unilateral horizontal transverse mode. Can be achieved.
[0222]
Third, by covering the metal film with an insulating film, the lateral growth rate can be improved and a current confinement structure can be realized. As a result, the first and second effects can be obtained more remarkably.
[0223]
Fourth, since the metal film has a growth suppressing effect in addition to the light absorption effect, the dislocation density in the nitride semiconductor film constituting the laser structure can be reduced together with the above effect. For this reason, the oscillation lifetime characteristic of the laser can be improved.
[0224]
The nitride semiconductor laser device of the present invention having such excellent characteristics is very useful as a light source for a display device, a display, an optical disk, or the like.
[Brief description of the drawings]
1 is a schematic cross-sectional view showing a schematic configuration of a nitride semiconductor laser element according to Embodiment 1. FIG.
FIG. 2 is a schematic diagram showing a schematic configuration of a crystal growth apparatus used in the embodiment.
3 is a schematic cross-sectional view showing a schematic configuration of a nitride semiconductor laser element according to Embodiment 2. FIG.
4 is a schematic cross-sectional view showing a schematic configuration of a nitride semiconductor laser element according to Embodiment 3. FIG.
FIG. 5 is a schematic cross-sectional view showing a schematic configuration of a nitride semiconductor laser element according to a fourth embodiment.
6 is a schematic cross-sectional view showing a schematic configuration of a nitride semiconductor laser element according to Embodiment 5. FIG.
7 is a schematic cross-sectional view showing a schematic configuration of a nitride semiconductor laser element according to Embodiment 6. FIG.
FIG. 8 is a schematic cross-sectional view showing a schematic configuration of a nitride semiconductor laser element according to a seventh embodiment.
FIG. 9 is a graph showing the relationship between the film thickness of a metallic mask (tungsten mask) and the light absorption rate.
FIG. 10A is a diagram showing the relationship between the lateral growth ratio and the partial pressure of the nitrogen carrier gas for a GaN film selectively grown using a metallic mask (tungsten mask); It is a figure which shows the relationship between the lateral growth ratio and the partial pressure of nitrogen carrier gas about the AlGaN film | membrane which performed the selective growth using the metallic mask (tungsten mask).
FIG. 11A is a metallic mask with an insulating film (SiO 2).₂It is a figure which shows the relationship between the lateral growth ratio and the partial pressure of nitrogen carrier gas about the GaN film | membrane which carried out the selective growth using the film | membrane tungsten mask, (b) is a metallic mask (SiO2 with an insulating film).₂It is a figure which shows the relationship between the lateral growth ratio and the partial pressure of nitrogen carrier gas about the AlGaN film | membrane which carried out selective growth using the film | membrane tungsten mask.
12 is a schematic cross-sectional view showing a schematic configuration of the nitride semiconductor laser element of Embodiment 10. FIG.
13 is a schematic cross-sectional view showing a schematic configuration of the nitride semiconductor laser element of Embodiment 11. FIG.
14 is a schematic cross-sectional view showing a schematic configuration of the nitride semiconductor laser element of Embodiment 12. FIG.
FIG. 15 is a diagram showing a configuration of a conventional nitride semiconductor laser element having a ridge stripe structure.
16A is a vertical transverse mode NFP in the nitride semiconductor laser device of the present invention, and FIG. 16B is a vertical transverse mode NFP in a conventional nitride semiconductor laser device.
17A is a vertical transverse mode FFP in a nitride semiconductor laser device of the present invention, and FIG. 17B is a vertical transverse mode FFP in a conventional nitride semiconductor laser device.
[Explanation of symbols]
10, 100, 300, 500, 600, 700, 800 Sapphire substrate
11, 101, 301, 501, 601, 701, 801 Low-temperature GaN buffer layer
12, 102, 302, 502, 602, 702, 802 n-type GaN contact layer
13, 103, 303, 403, 503, 603, 703, 803, 903, 1003, 1103 n-type AlGaN cladding layer
14, 104, 304, 404, 504, 604, 704, 804, 904, 1004, 1104 n-type GaN light guide layer
15, 105, 305, 405, 505, 605, 705, 805, 905, 1005, 1105 active layer
16, 106, 306, 406, 506, 606, 706, 806, 906, 1006, 1106 AlGaN carrier block layer
17, 107, 307, 407, 507, 607, 707, 807, 907, 1007, 1107 p-type GaN light guide layer
18, 108, 308, 408, 508, 608, 708, 808, 908, 1008, 1108 p-type AlGaN cladding layer
19, 109, 309, 409, 509, 609, 709, 809, 909, 1009, 1109 p-type GaN contact layer
20, 110, 310, 410, 510, 610, 710, 810, 910, 1010, 1110 SiO₂Insulation film
21, 111, 311, 411, 511, 611, 711, 811, 911, 1011, 1111 n-type electrode
22, 112, 312, 412, 512, 612, 712, 812, 912, 1012, 1112 p-type electrode
23 Near the active layer of the ridge stripe formation part
24 Near the active layer dug down by ridge stripe formation
102a, 302a, 502a, 602a, 702a, 802a Lower n-type GaN film
102b, 302b, 502b, 602b, 702b, 802b Regrown n-type GaN film
113, 416, 516 tungsten mask
201 substrate
202 Susceptor
203 reaction tube
204 Raw material entrance
205 Exhaust gas outlet
206 Ammonia
207a TMG
207b TMA
207c TMI
207d Cp₂Mg
208 Mass Flow Controller
209 SiH_Four
313, 513, 613, 616 Tungsten film
314, 514, 614, 617 SiO₂film
315, 515, 615, 618 SiO₂Tungsten mask with film
401, 901, 1001, 1101 n-type GaN substrate
402, 902, 1002, 1102 n-type AlGaN contact layer
403a, 503a, 603a, 903a Lower n-type AlGaN film
403b, 503b, 603b, 903b Regrown n-type AlGaN film
417, 517, 619, 717, 819 Parts not covered with mask
620, 820 Mask side
708a, 808a, 1008a Lower layer p-type AlGaN film
708b, 808b, 1008b Regrown p-type AlGaN film
713, 813, 816 Platinum film
714, 814, 817 SiN_xfilm
715, 815, 818 SiN_xPlatinum mask with film
716 Platinum mask
916, 1016, 1116 Metallic mask

Claims (14)

A semiconductor multilayer structure made of a nitride semiconductor, including a pair of upper and lower clad layers and an active layer sandwiched between the clad layers, and a stripe-shaped current confinement that constricts the current injected into the active layer. A nitride semiconductor laser device having a structure,
A light absorption mask including a metal film having a light absorption function is formed from the upper or lower clad layer on a portion facing the stripe current confinement structure on the outer side of the upper or lower clad layer of the active layer. A nitride semiconductor laser device arranged to absorb leaked guided light. A semiconductor multilayer structure made of a nitride semiconductor, including a pair of upper and lower clad layers and an active layer sandwiched between the clad layers, and a stripe-shaped current confinement that constricts the current injected into the active layer. A nitride semiconductor laser device having a structure,
Of the active layer upper or lower cladding layers, on either side of the portion facing to the striped current confinement structure, the light absorption mask including a metal film having a light absorbing function, light absorbing mask and to A nitride semiconductor laser device arranged to increase gain loss between the opposing active layers . The metal film constituting the light absorption mask is made of a metal on which a nitride semiconductor is not directly epitaxially grown, and the semiconductor multilayer structure has an active layer sandwiched between a pair of clad layers and both clad layers, and the semiconductor multilayer A striped electrode is provided on the surface of the structure opposite to the substrate,
A contact layer having a refractive index higher than that of the clad layer and having a refractive index different from that of the substrate, in contact with the lower surface of the clad layer closer to the substrate; Whether the metal film is disposed at a position within half of the contact layer thickness from the interface between the cladding layer and the contact layer toward the substrate;
A contact layer having a refractive index higher than that of the cladding layer and having substantially the same refractive index as that of the substrate is in contact with the lower surface of the cladding layer closer to the substrate, and is below the stripe electrode. The metal film is disposed at a position within half of the total thickness of the contact layer and the substrate thickness from the interface between the cladding layer and the contact layer toward the substrate,
The clad layer closer to the substrate has a lower refractive index than the substrate, and there is no contact layer between the substrate and the clad layer, below the stripe electrode, and the clad layer The metal film is disposed at a position within half of the substrate thickness from the interface between the substrate and the substrate toward the lower surface of the substrate,
Alternatively, the metal is located below the stripe electrode and on or in the cladding layer closer to the substrate, at a position of 0.5 μm or more from the lower surface of the active layer toward the substrate. The nitride semiconductor laser device according to claim 1, wherein a film is disposed. The metal film constituting the light absorption mask is made of a metal on which a nitride semiconductor is not directly epitaxially grown, and the semiconductor multilayer structure has an active layer sandwiched between a pair of cladding layers and both cladding layers, and the active layer With a ridge stripe above
A contact layer having a refractive index higher than that of the cladding layer and having a refractive index different from that of the substrate, in contact with the lower surface of the cladding layer closer to the substrate, and below the ridge stripe portion, Whether the metal film is disposed at a position within half of the contact layer thickness from the interface between the cladding layer and the contact layer toward the substrate;
A contact layer having a refractive index higher than that of the cladding layer and having substantially the same refractive index as that of the substrate is in contact with the lower surface of the cladding layer closer to the substrate, and is below the ridge stripe portion. The metal film is disposed at a position within half of the total thickness of the contact layer and the substrate thickness from the interface between the cladding layer and the contact layer toward the substrate,
The clad layer closer to the substrate has a lower refractive index than the substrate, and no contact layer exists between the substrate and the clad layer, and is below the ridge stripe portion, and the clad layer The metal film is disposed at a position within half of the substrate thickness from the interface between the substrate and the substrate toward the lower surface of the substrate,
Alternatively, below the ridge stripe portion and on or in the cladding layer closer to the substrate, at a position of 0.5 μm or more from the lower surface of the active layer toward the substrate, The nitride semiconductor laser device according to claim 1, wherein a metal film is disposed. The metal film constituting the light absorption mask is made of a metal on which a nitride semiconductor is not directly epitaxially grown, the semiconductor multilayer structure has an active layer, and stripes are formed on the surface of the semiconductor multilayer structure opposite to the substrate. And a portion of the active layer that is not covered with the mask under the stripe electrode, the metal film being disposed at a position within 2 μm from the lower or upper surface of the active layer. The nitride semiconductor laser device according to claim 1, wherein the nitride semiconductor laser device is disposed. The metal film constituting the light absorption mask is made of a metal on which a nitride semiconductor is not directly epitaxially grown, and the semiconductor multilayer structure has an active layer sandwiched between a pair of cladding layers and both cladding layers, and the active layer A ridge stripe portion is provided above the active layer, the metal film is disposed within 2 μm from the lower or upper surface of the active layer, and a mask including the metal film is covered with the mask below the ridge stripe portion. The nitride semiconductor laser device according to claim 1, wherein the nitride semiconductor laser device is arranged to have a portion that is not formed.   The nitride semiconductor laser element according to claim 2, wherein a distance between the masks is 1 μm or more and 15 μm or less. 8. The nitride semiconductor laser according to claim 1, wherein a thickness of the metal film constituting the light absorption mask is 0.01 μm or more, and a thickness of the entire mask including the metal film is 2 μm or less. element. The metal film constituting the light absorption mask is a metal material containing at least one of W, Ti, Mo, Ni, Al, Pt, Pd, Au, and alloys thereof, or of those metals and alloys 9. The nitride semiconductor laser element according to claim 1, comprising a composite film composed of a plurality of layers including at least one kind. The nitride semiconductor laser device according to any one of claims 1 to 9, wherein the metal film constituting the light absorption mask is covered with an insulating film. The nitride semiconductor laser element according to claim 10, wherein the insulating film is made of SiO ₂ or SiN _x . The nitride according to any one of claims 1 to 11, wherein the metal film constituting the light absorption mask is provided in a stripe shape in the <1-100> direction with respect to the underlying nitride semiconductor layer. Semiconductor laser element. The light-absorbing mask is not flat covered by the nitride semiconductor layer of the upper layer, according to claim 1 to claim 7 having a recess, a nitride semiconductor laser according to any one of claims 9 to 12 element.   13. The method for manufacturing the nitride semiconductor laser device according to claim 1, wherein the light absorption mask is covered with a nitride semiconductor layer at a rate of 10% or more with respect to the total carrier gas. For producing a nitride semiconductor laser device using a nitrogen carrier gas.

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