JP3707947B2 - Semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device such as a semiconductor laser. The present invention is suitably used as a semiconductor laser that is required to have a high output and a long life, such as an excitation light source for an optical fiber amplifier and a light source for optical information processing. The present invention is also used for LEDs such as superluminescent diodes whose light exit ends are formed by end faces, surface emitting lasers, and the like.
[0002]
[Prior art]
Recent progress in optical information processing technology and optical communication technology is remarkable. For example, there is no spare time for high-density recording using a magneto-optical disk and bi-directional communication using an optical fiber network.
[0003]
For example, in the communications field, a rare earth such as Er ³⁺ is doped as a signal amplifying amplifier that has flexibility for its transmission system, along with a large-capacity optical fiber transmission line that will fully support the future multimedia age. Research on optical fiber amplifiers (EDFA) has been actively conducted in various fields. Development of a semiconductor laser for a high-efficiency excitation light source, which is an indispensable element as an EDFA component, is awaited.
[0004]
In principle, there are three types of oscillation wavelengths of excitation light sources that can be used for EDFA applications: 800 nm, 980 nm, and 1480 nm. Of these, it is known that excitation at 980 nm is most desirable in view of the characteristics of the amplifier in consideration of gain, noise, and the like. Such a laser having an oscillation wavelength of 980 nm is required to satisfy the conflicting requirement that it has a high output and a long life as an excitation light source. Further, in the vicinity of wavelengths, for example, 890 to 1150 nm, there is a demand as a heat source for an SHG light source and a laser printer, and development of a high output and highly reliable laser is awaited in various other applications. In the field of information processing, semiconductor lasers have been increased in output and wavelength for the purpose of high-density recording, high-speed writing and reading. High output is strongly desired for conventional LDs with an oscillation wavelength of 780 nm, and development of LDs in the 630 to 680 nm band has been vigorously conducted in various fields.
[0005]
So far, semiconductor lasers having a wavelength of about 980 nm and semiconductor lasers that can withstand continuous use for about two years at an optical output of about 50 to 100 mW have been developed. However, operation at higher light output results in rapid degradation and insufficient reliability. The same applies to the LDs in the 780 nm band and the 630 to 680 nm band, and ensuring the reliability at the time of high output is a problem for the entire semiconductor laser using a GaAs substrate.
[0006]
One of the causes of insufficient reliability is deterioration of the emission end face of the laser light exposed to a very high light density. As is well known for GaAs / AlGaAs semiconductor lasers, there are many surface levels in the vicinity of the end face. Since these levels absorb the laser light, the temperature near the end face is generally the laser. It is described that the temperature rises higher than the internal temperature, and that this temperature rise further narrows the band gap in the vicinity of the end face and further facilitates the absorption of laser light. This phenomenon is known as end-of-face destruction (COD), which is observed when a large current is applied instantaneously. In addition, many semiconductors have abrupt deterioration due to a decrease in COD level during a long-term current test. This is a common problem in laser elements.
[0007]
In order to solve these problems, various proposals have been made so far. For example, various methods have been proposed so far in which the band gap of the active layer region in the vicinity of the end face is made transparent with respect to the oscillation wavelength, and the light absorption in the vicinity of the end face is suppressed. The lasers having these structures are generally called window structure lasers or NAM (Non Absorbing Mirror) structure lasers, and are effective when a high output is required. However, in the method of epitaxially growing a semiconductor material transparent to the oscillation wavelength on the laser end face, the subsequent electrode process is very complicated because the laser is epitaxially grown on the end face in a bar state. End up.
[0008]
Various methods for disordering the active layer by intentionally thermal diffusion or ion implantation of Zn or Si or the like as impurities into the active layer near the end face of the laser have also been proposed (Japanese Patent Laid-Open No. 2-45992). JP-A-3-31083, JP-A-6-302906). However, since impurity diffusion generally performed in the LD manufacturing process is performed from the epitaxial direction of the laser element to the substrate direction, there is a problem in controlling the diffusion depth and in the lateral direction with respect to the resonator direction, and stable fabrication is not possible. difficult. Further, in the case of ion implantation, since high energy ions are introduced from the end face, even if annealing is performed, damage tends to remain on the LD end face. In addition, an increase in reactive current accompanying a decrease in resistance in a region where impurities are introduced has a problem such as an increase in laser threshold current and drive current.
[0009]
On the other hand, Japanese Patent Application Laid-Open No. 3-101183 describes a manufacturing method in which an end surface free from contamination is formed, and an oxygen-free material that does not cause diffusion or reaction with the semiconductor end surface is formed as a passivation layer. Yes.
In general, in the atmosphere (for example, in a clean room), generation of non-radiative recombination centers such as Ga—O and As—O generated at the end face during cleavage cannot be suppressed. Therefore, as described in this publication, in order to “form a contamination-free end face”, it is indispensable to form a passivation layer in the cleaved spot, but this can be realized by using a vacuum. It is only cleavage within. However, cleavage in a vacuum requires a very complicated apparatus and operation compared to general cleavage in the atmosphere. This publication also describes a method of forming an end face by dry etching. However, since many non-radiative recombination centers are formed as compared with an end face formed by cleavage, an LD that requires a long lifetime is also described. It is not suitable for the manufacturing method.
[0010]
Although this publication describes that Si or amorphous Si is optimal as a passivation material, there is generally no substance that does not cause any diffusion. In particular, in a semiconductor laser premised on driving at high output and high temperature for a long time, there is a concern about the diffusion of these passivation materials.
As similar to this publication, LWTu et al., (In-vacuum cleaving and coating of semiconductor laser facets using silicon and a dielectric, J. Appl. Phys. 80 (11) 1 DEC. 1996) It is described that when the / AlOx structure is coated on the laser end face, if the cleavage is performed in a vacuum, the carrier recombination speed at the cleavage plane is slowed and the initial COD level is increased. However, there is no description of long-term reliability in this paper, nor is there any mention of the relationship between coating and LD structure.
[0011]
Further, in order to reduce the electric field strength at the light emitting end face of the semiconductor laser, Si is added to the interface between the coating film and the semiconductor so that the antinode part of the standing wave existing in the cavity direction does not coincide with the end face part. It has also been proposed to insert / 4 wavelengths. However, in a wavelength band where a general semiconductor laser is realized, particularly in a range of 400 to 1600 nm where a high output LD is desired, since Si itself acts as a light absorber, the temperature rise at the end face is a device. May accelerate the degradation of
[0012]
In addition, US Pat. No. 4,563,368 discloses that a passivation layer containing Al, Si, Ta, V, Sb, Mn, Cr or Ti is necessary and sufficient to remove only oxygen on the cleavage plane. It is described that it is formed on a cleaved surface by adjusting the thickness. However, according to the study by the present inventors, this US patent does not clearly show how to give energy that is considered necessary for the passivation layer to hold oxygen. In addition, it is necessary to oxidize all of the passivation layer and to produce a thickness with sufficient controllability so that the oxide remaining on the end face can be removed sufficiently, but this requires complicated monitoring in production. The question remains in reproducibility. Furthermore, since the passivation layer reacts with oxygen to become all oxides, in the long term, the oxygen trapped in the passivation layer during the process causes the end face again when the laser is driven for a long time. It is feared that it reacts with the elements constituting the structure, and its reliability remains a question.
As described above, none of the semiconductor light emitting devices proposed so far has been technically satisfactory.
[0013]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems of the prior art.
Specifically, the present invention provides a semiconductor light emitting device that stably suppresses the interface state density at the end face for a long period of time and operates stably even if diffusion occurs during LD driving of the passivation layer. It was an issue to be solved. That is, an object of the present invention is to provide a high-performance semiconductor light emitting device that suppresses deterioration at the end face and achieves both high output and long life.
[0014]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have selected the elements constituting the first and second passivation layers of the semiconductor light emitting device according to specific conditions. The present inventors have found that the interface state density of the end face can be stably controlled for a long period of time, and have completed the present invention.
[0015]
That is, the present invention provides a semiconductor light emitting device having a resonator structure having a compound semiconductor layer including a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer on a substrate. The surfaces of the first conductivity type cladding layer, the active layer, and the second conductivity type cladding layer to be formed are covered with the first passivation layer, and the first passivation layer is covered with the second passivation layer. And the deactivation layer comprising the first deactivation layer and the second deactivation layer has a portion composed of a single element, and at least one element constituting the second deactivation layer It is intended to provide a semiconductor light emitting device characterized in that the absolute value of the enthalpy of formation of the oxide is larger than the absolute value of the enthalpy of formation of the oxide of at least one element constituting the first passivation layer. .
In the semiconductor light emitting device of the present invention, the absolute value of the enthalpy of formation of the oxide of at least one element constituting the first passivation layer is greater than the absolute value of the enthalpy of formation of the oxide of at least one element constituting the end face. Is also preferably large. Further, it is preferable that at least one of the elements constituting the end surface does not have a bond with oxygen. Furthermore, it further includes at least one passivation layer covering the second passivation layer, and a coating layer made of a dielectric or a combination of a dielectric and a semiconductor is formed on the surface of the passivation layer that is the outermost layer. It is preferable to have.
[0016]
In a preferred embodiment of the present invention, the first passivation layer thickness T _{p (1)} , the second passivation layer thickness T _{p (2)} and the sum of the thicknesses of these two passivation layers. T _{p (1 + 2)} is set within the range represented by the following equation.
[Expression 4]
0.2 (nm) <T _{p (1)} <λ / 8n ₁ (nm) (Formula 1)
0.2 (nm) <T _{p (2)} <λ / 4n ₂ (nm) (Formula 2)
0.4 (nm) <T _{p (1 + 2)} <3λ / 8n ₁₂ (nm) (Formula 3)
(Where λ is the oscillation wavelength of the semiconductor light emitting device, n ₁ is the real part of the refractive index at the wavelength λ of the first passivation layer, and n ₂ is the real part of the refractive index at the wavelength λ of the second passivation layer. , N ₁₂ represents the real part of the average refractive index at the wavelength λ of the two passivation layers.)
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the semiconductor light emitting device of the present invention will be described in detail.
[0018]
The semiconductor light emitting device of the present invention uses a semiconductor wafer produced by sequentially growing a compound semiconductor layer on a substrate. The semiconductor wafer used in the present invention has a compound semiconductor layer including a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer on a substrate, and can be used for manufacturing a semiconductor light emitting device. If it is a thing, the kind in particular will not be restrict | limited. Therefore, layers other than those described above may exist in the semiconductor wafer, and the type and amount of material used for each layer and the layer structure thereof are not particularly limited.
[0019]
Below, the preferable structural example of the semiconductor wafer used by this invention and its manufacturing method are demonstrated concretely. The semiconductor wafer to be described has a refractive index waveguide structure, the second conductivity type cladding layer is divided into two layers, a current injection region is formed by the second conductivity type second cladding layer and the current blocking layer, and the electrode And a contact layer for lowering the contact resistance (FIG. 2). For example, Japanese Patent Application Laid-Open No. 8-130344 can be referred to for various basic laser manufacturing methods including this example. This type of laser is used as a light source for optical fiber amplifiers used in optical communications and as a pick-up light source for large-scale magneto-optical memory for information processing, and can be used in various applications by appropriately selecting the layer configuration and materials used. It can also be applied.
[0020]
FIG. 2 is a schematic cross-sectional view showing the configuration of a groove type semiconductor laser as an example of the epitaxial structure in the semiconductor light emitting device of the present invention.
As the substrate (1), a single crystal substrate such as InP, GaAs, GaN, InGaAs, or Al ₂ O ₃ is used in terms of desired oscillation wavelength, lattice matching, and strain that is intentionally introduced into the active layer. Is done. In some cases, a dielectric substrate such as Al ₂ O ₃ can also be used. As an embodiment of the present invention, it is desirable to use an InP substrate or a GaAs substrate from the viewpoint of lattice matching with a III-V semiconductor light emitting device containing As, P, etc. as the V group. When As is included as the V group, it is most preferable to use a GaAs substrate.
[0021]
A dielectric substrate such as Al ₂ O ₃ may be used for a material containing nitrogen or the like as a group V among group III-V semiconductor light emitting devices.
As the substrate, not only a so-called just substrate but also a so-called off-substrate can be used from the viewpoint of improving crystallinity during epitaxial growth. Off-substrates have the effect of promoting good crystal growth in step flow mode and are widely used. The off-substrate having a tilt of about 0.5 to 2 degrees is widely used, but the tilt may be set to about 10 degrees depending on the material system constituting the quantum well structure.
The substrate may be subjected to chemical etching, heat treatment, or the like in advance as a preparation for manufacturing a light emitting element using a crystal growth technique such as MBE or MOCVD.
[0022]
The buffer layer (2) is preferably grown on the substrate to alleviate imperfections in the substrate bulk crystal and facilitate the formation of an epitaxial thin film having the same crystal axis. The buffer layer (2) is preferably composed of the same compound as the substrate (1). When the substrate is GaAs, GaAs is usually used. However, the use of a superlattice layer as a buffer layer is also widely performed and may not be formed of the same compound. On the other hand, when a dielectric substrate is used, the material is not necessarily the same as the substrate, and a material different from the substrate may be selected as appropriate from the desired emission wavelength and the structure of the entire device.
[0023]
The first conductivity type cladding layer (3) is generally made of a material having a refractive index smaller than the average refractive index of the active layer (4), and is a substrate (1) prepared to realize a desired oscillation wavelength. The material is appropriately defined by the buffer layer (2), the active layer (4), and the like. For example, GaAs is used as the substrate (1), and when the buffer layer (2) is also GaAs, an AlGaAs-based material, an InGaAs-based material, an AlGaInP-based material, an InGaP-based material, or the like is used. In some cases, the entire cladding layer can have a superlattice structure.
[0024]
The effect of the present invention is recognized regardless of the conductivity type, material, structure, etc. of the active layer (4), but the conductivity type is preferably P-type. In general, as described in, for example, Heterostructure Lasers (HCCasey, Jr. MBPanish, Academic Press 1978 P.157), the band gap of a semiconductor tends to decrease as the hole concentration increases. For example, the band gap Eg (eV) of GaAs is expressed as follows, where the P-type carrier concentration is P (cm ⁻³ ):
Eg = 1.424-1.6 × 10 ⁻⁸ × P ^1/3
It is shown that. One feature of the present invention is that the material inserted as the passivation layer (14), particularly the first passivation layer (14-1), into the laser end face and the dielectric interface is particularly high during long-term laser driving. When diffusion occurs during the output operation, it is gradually introduced as an n-type impurity into the active layer (4) and the like, and the effective hole concentration is lowered by the compensation effect. This means that in the vicinity of the semiconductor end face, in other words, the passivation layer (14) increases the band gap of the part where the constituent elements are diffused together with the LD driving, and absorbs light at the end face. It is expected to act to suppress. In this respect, a P-type active layer is desirable.
[0025]
From the viewpoint of material selection, the active layer (4) is preferably a system containing In and / or Ga. This is a material system in which so-called ordering is likely to occur during crystal growth, and is inserted into the interface between the laser facet and the dielectric as an inactivation layer (14), in particular, a first inactivation layer (14-1). This is because, when the material to be diffused as described above during long-term laser driving, it is expected to cause disorder in the vicinity of the end face. In general, disordering of the material leads to an increase in the band gap, and this, in combination with the carrier compensation effect, suppresses light absorption at the end face for a long period of time.
[0026]
From these viewpoints, the material of the active layer (4) is preferably an AlGaAs-based material, an InGaAs-based material, an InGaP-based material, an AlGaInP-based material, or the like, and specifically, Al _x Ga _1-x As (0 ≦ x ≦ 1). In _x Ga _1-x As (0 ≦ x ≦ 1) or (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x, y ≦ 1) is desirable. A quantum well structure is particularly desirable for disordering. The selection of these materials is generally defined by the desired oscillation wavelength.
[0027]
The structure of the active layer (4) may be a normal bulk active layer composed of a single layer, but a single quantum well (SQW) structure, a double quantum well (DQW) structure, or a multiple quantum (MQW) structure. A quantum well structure such as the above can also be adopted depending on the purpose. In the quantum well structure, an optical guide layer is usually used in combination, and a barrier layer is used in combination as needed to separate the quantum well. The structure of the active layer includes a structure in which light guide layers are provided on both sides of the quantum well (SCH structure), and a structure in which the refractive index is continuously changed by gradually changing the composition of the light guide layer (GRIN-SCH). Structure) etc. can be adopted. As the material of the light guide layer, an AlGaAs-based material, an InGaAs-based material, an InGaP-based material, an AlGaInP-based material, or the like can be selected according to the active layer.
[0028]
On the other hand, Si is desirable as a material for the passivation layer (14). This is because, in general, it can become an n-type dopant by diffusion from the (110) plane that forms the resonator in an edge-emitting device or from the (100) plane that becomes the exit end of a surface-emitting laser or the like. Furthermore, this is because it is possible to disorder AlGaAs-based materials, InGaAs-based materials, InGaP-based materials, and AlGaInP-based materials that are preferably used as the material of the active layer (4).
[0029]
The second conductivity type first clad layer (5) and the second conductivity type second clad layer (8) are generally the same as the first conductivity type clad layer (3) and generally have an average refractive index of the active layer (4). It is made of a material having a smaller refractive index, and the material is appropriately defined by the substrate (1), the buffer layer (2), the active layer (4), and the like. For example, when GaAs is used for the substrate (1) and GaAs is also used for the buffer layer (2), an AlGaAs-based material, an InGaAs-based material, an AlGaInP-based material, an InGaP-based material, or the like is used.
[0030]
In FIG. 2, two types of etch stop layers (6), (7) and a cap layer (10) are described. These layers are employed in a preferred embodiment of the present invention to create a current injection region. It is effective to perform accurately and easily.
[0031]
In the case where the second etching stop layer (6) is made of, for example, an Al _a Ga _1-a As (0 ≦ a ≦ 1) material, usually GaAs is preferably used. This is because the second conductivity type second clad layer (8) and the like can be laminated with good crystallinity, particularly when regrown in an AlGaAs system by MOCVD or the like. The thickness of the second etching stop layer (6) is usually preferably 2 nm or more.
[0032]
The first etching blocking layer (7) is preferably a layer represented by In _b Ga _1-b P (0 ≦ b ≦ 1). When GaAs is used as a substrate, a normal strain-free system is used. Set to 0.5. The thickness of the first etching blocking layer (7) is usually 5 nm or more, preferably 10 nm or more. If it is less than 5 nm, there is a risk that etching cannot be prevented due to film thickness disturbance or the like. On the other hand, depending on the film thickness, a strain system can be used, and a composition such as b = 0, b = 1, etc. can be adopted.
[0033]
The cap layer (10) is used as a protective layer for the current blocking layer (9) in the first growth and is used to facilitate the growth of the second conductivity type second cladding layer (8). Before obtaining the structure, some or all are removed.
[0034]
Since the current blocking layer (9) is literally required to block the current so that it does not flow substantially, its conductivity type should be the same as that of the first conductivity type cladding layer (3) or undoped. Is preferred. For example, when the current blocking layer (9) is formed of AlGaAs, the refractive index is higher than the second conductivity type second cladding layer (8) made of Al _y Ga _1-y As (0 <y ≦ 1). Is preferably small. That is, if the current blocking layer (9) is Al _z Ga _1-z As (0 ≦ z ≦ 1), the mixed crystal ratio is preferably z> y.
[0035]
The refractive index of the second conductivity type second cladding layer (8) is usually not more than the refractive index of the active layer (4). The second conductivity type second cladding layer (8) is usually the same as the first conductivity type cladding layer (3) and the second conductivity type first cladding layer (5). Further, as one of preferred embodiments of the present invention, the second conductive type first cladding layer (5), the second conductive type second cladding layer (8) and the current blocking layer (9) are all made of the same material system having the same composition. The case where it comprises is mentioned. In that case, an effective refractive index difference is formed by the first etching stop layer (7), and when the cap layer (10) is not completely removed, the cap layer (7) is added in addition to the first etching layer (7). 10) also forms an effective refractive index difference. By adopting such a layer structure, it is possible to avoid problems caused by the mismatch of materials or compositions at the respective interfaces of the second conductivity type second cladding layer (8) and the current blocking layer (9). Highly preferred.
[0036]
A contact layer (11) is preferably provided on the second conductivity type second cladding layer (8) for the purpose of, for example, reducing the contact resistivity with the electrode (12). The contact layer (11) is usually made of a GaAs material. This layer usually has a higher carrier concentration than the other layers in order to reduce the contact resistivity with the electrode.
[0037]
In general, the buffer layer (2) has a thickness of 0.1 to 3 [mu] m, the first conductivity type cladding layer (3) has a thickness of 0.5 to 3 [mu] m, and the active layer (4) has a quantum well structure. In this case, 0.0005 to 0.02 μm per layer, the thickness of the second conductivity type first cladding layer (5) is 0.05 to 0.3 μm, and the thickness of the second conductivity type second cladding layer (8) is The thickness of the cap layer (10) is selected from the range of 0.5 to 3 μm, and the thickness of the current blocking layer (9) is selected from the range of 0.3 to 2 μm.
[0038]
The semiconductor light emitting device shown in FIG. 2 is configured by further forming electrodes (12) and (13). In the case of the p-type, the electrode (12) is formed by, for example, sequentially depositing Ti / Pt / Au on the surface of the contact layer (11) and then alloying it. On the other hand, the electrode (13) is formed on the surface of the substrate (1). In the case of an n-type electrode, for example, AuGe / Ni / Au is sequentially deposited and then formed by alloying.
As mentioned above, although the example of a structure and manufacture example of the preferable semiconductor wafer were demonstrated, the semiconductor wafer which has a structure other than the above can also be used in this invention.
[0039]
A resonator end face is formed on the manufactured semiconductor wafer. The resonator end face can be prepared by a method usually used in the manufacturing process of the semiconductor light emitting device, and the specific method is not particularly limited.
A method of forming an end face by cleavage is preferred. Cleavage is widely used in the case of edge emitting lasers, and the end face formed by cleavage differs depending on the orientation of the substrate used. For example, when an element such as an edge-emitting laser is formed using a substrate having a surface crystallographically equivalent to the suitably used nominally (100), (110) or crystallographically The equivalent surface is the surface that forms the resonator. On the other hand, when using an off substrate (miss oriented substrate), the end face may not be 90 degrees with respect to the resonator direction depending on the relationship between the tilted direction and the resonator direction. For example, when a substrate having an angle of 2 degrees toward the (1-10) direction from the (100) substrate is used, the end face is also inclined by 2 degrees. In some cases, a resonator is manufactured in the crystal growth process like a surface emitting laser, but the material manufactured in this way is also an object of use of the present invention.
[0040]
When manufacturing the semiconductor light emitting device of the present invention, it is not always necessary to perform a complicated cleavage step in a vacuum. Since it may be cleaved in atmospheric air or nitrogen atmosphere, the semiconductor light emitting device of the present invention can simplify the whole manufacturing process as compared with the conventional case. Cleaving in a vacuum is not an essential process because part or all of oxides and / or nitrides that are non-radiative recombination centers on the end face are irradiated with plasma on the end face and / or first This is because the first passivation layer can be removed by plasma irradiation after the passivation layer is formed. That is, the first conductivity type cladding layer (3), the active layer (4), the second conductivity type cladding layer (5) (8), the substrate (1) exposed at the end face, the current blocking layer (9), Oxide and / or nitride located near the resonator mirror such as the contact layer (11) can be effectively removed by plasma irradiation.
[0041]
Plasma irradiation is preferably performed on the formed resonator end face. The plasma irradiation is preferably plasma irradiation in which a rare gas is ionized, and group 18 elements, particularly Ar plasma irradiation is particularly effective. The irradiation energy of Ar plasma is preferably in the low energy range of about 25 eV to 300 eV, more preferably 25 eV to 100 eV. This makes it possible to remove a part of the oxide, nitride, or the like that is a non-radiative recombination center without excessively damaging the semiconductor end face. Since the plasma treatment can be performed with much lower energy than conventional techniques such as ion implantation of impurities, it is excellent in that damage to the end face can be suppressed. When the plasma treatment is performed, for example, in the case of a GaAs-based material, As—O can be effectively removed among oxides. In some cases, oxygen or the like bonded to an element constituting another semiconductor end face can be removed in the same manner.
In this specification, the element group names are expressed in Arabic numerals in accordance with the latest IUPAC notation, but in Roman numerals such as “Group III” and “Group V”. When a family name is written, it is assumed that the normal notation in the semiconductor field is followed. For example, “Group III” means Group 13 made of elements such as Al and Ga, and “Group V” means Group 15 made of N, P, As and the like.
[0042]
The irradiation effect of this low energy Ar plasma is not limited to the removal of oxides and nitrides. The active layer of the semiconductor wafer forms a quantum well. In particular, the material system is preferably an AlGaAs material, InGaAs material, InGaP material, AlGaInP material, etc. It is possible to form an end face in which the vicinity of the end face is disordered and the resistance is increased during the laser manufacturing process, instead of diffusion of the passivation layer. This means an increase in the band gap near the end face and an increase in resistance near the end face at the initial stage of laser fabrication, that is, the effect of suppressing light absorption at the end face and suppressing the current injection into the end face that is likely to break down, and further extending the life of the laser. Can be expected.
[0043]
In addition, this plasma irradiation also has the effect of widening the band gap near the end face in the LD manufacturing process as described above, and the deactivation layer, particularly the first deactivation layer, diffuses while driving the LD and further near the end face. Combined with the effect of widening the band gap, achieves high output and long life.
[0044]
A first passivation layer is formed on the resonator end face. The element deposited on the end face as the first passivation layer is preferably an n-type impurity when diffused into the active layer. As an element attached to the end face as the first passivation layer, it is preferable to select an element having a larger absolute value of oxide enthalpy of formation than at least one element constituting the cavity end face. It is desirable that an element satisfying such a condition is contained in at least a part of the element attached to the end face as the first passivation layer. As elements constituting the semiconductor material, for example, the formation enthalpy of Ga ₂ O ₃ is −5.64 eV / metal atom, the formation enthalpy of In ₂ O ₃ is −4.80 eV / metal atom, and the formation enthalpy of MgO is −6.24 eV. / metal atom. Examples of the element having an absolute value of the enthalpy of formation of the oxide larger than the absolute value of these enthalpies of formation include Sc (Sc ₂ O ₃ : −9.89), Y (Y ₂ O ₃ : −9.46), Ti (TiO ₂ : −9.74), Zr (ZrO ₂ : −11.41), V (V ₂ O ₅ : −8.04), Ta (Ta ₂ O ₃ : −10.60), Mo ( Examples include MoO ₃ : −7.72), W (WO ₃ : −8.74), Al (Al ₂ O ₃ : −8.68), Si (SiO ₂ : −9.44) and lanthanoids. Yes (in parentheses the enthalpy of oxide formation in units of eV / metal atom).
[0045]
Of these, Si is preferably used. Although the structure and characteristics of Si differ crystallographically depending on the production method, the effect is recognized in any case of single crystal, polycrystal, and amorphous. Particularly suitable is amorphous Si formed at a low film formation rate in a high vacuum. In general, the absorption edge of Si varies depending on the film quality, but it is transparent for wavelengths of about 2 μm or more, and it is considered that there is no absorption. Conversely, for wavelengths shorter than about 2 μm, the refractive index N of Si is N = n + ik (n is the real part of the refractive index, k is the extinction coefficient, and n is about 3.5).
[0046]
Generally, it is desirable that the thickness of the first passivation layer is greater than 0.2 nm. However, an extremely thick film thickness (for example, 100 nm) may not be suitable. The desired thickness of the first passivation layer is defined by the requirement for the lower limit to exist as a film itself. On the other hand, the upper limit is to promote the chemical reaction between the semiconductor end face and the interface of the first passivation layer by the effect that light emitted from the active layer is absorbed by Si and the subsequent plasma irradiation to the first passivation layer. It is determined within a range where the effect to be fully exhibited.
[0047]
In general, absorption of light having an oscillation wavelength by Si causes an increase in temperature at the end face, and in an extreme case, deterioration of the laser is accelerated. Moreover, since it will also prevent oxygen uptake | capture to the 2nd passivation layer mentioned later, the passivation layer which is too thick is not effective. Further, the thickness of the first passivation layer is preferably set to such an extent that the effect of the irradiated plasma can sufficiently reach the interface and cause a chemical reaction there. Whether or not the effect of plasma irradiation reaches the interface can be determined by the penetration depth determined from the plasma energy or the like. If the effect of plasma irradiation reaches the interface sufficiently, even if oxides with high binding energy such as Ga-O remain at the time of first ion irradiation to the end face, oxygen from the residual oxides will remain. The effect of separating the first passivation layer can be expected. From such a viewpoint, it has been experimentally confirmed that a desirable thickness when the first passivation layer is deposited on the end face is within the range represented by the following formula.
[Formula 6]
0.2 (nm) <T _{p (1)} <λ / 8n ₁ (nm) (1)
(Where T _{p (1)} is the thickness of the first passivation layer, λ is the oscillation wavelength of the semiconductor light emitting device, and n ₁ is the real part of the refractive index at the wavelength λ of the first passivation layer. )
However, the effect has been confirmed even when the thickness is 0.2 nm or less.
[0048]
Plasma irradiation is preferably performed after the formation of the first passivation layer. As described above, the irradiation of the first passivation layer is performed for the purpose of separating oxygen and / or nitrogen from the oxides and / or nitrides of the constituent elements of the semiconductor end surface that have remained by ion irradiation to the initial laser end surface. In this case, a part of the first passivation layer is reversely oxidized and / or nitrided. This step is important for removing the oxides and / or nitrides of the constituent elements of the semiconductor end face that act as non-radiative recombination centers when the laser is driven, and improving the reliability of the laser.
As described above, the irradiation of the first passivation layer with plasma is particularly preferably performed with a rare gas. Furthermore, irradiation with Ar ions has a great effect among rare gases. The irradiation energy of Ar ions is preferably in the low energy range of about 25 eV to 300 eV, more preferably about 50 eV to 200 eV. Thereby, the residual oxide can be removed without damaging the semiconductor end face. In this case, for example, when Si is used as the first passivation layer, Si separates oxygen from Ga—O and becomes Si—O, so that light absorption near the semiconductor end face may be reduced. Be expected.
[0049]
A second passivation layer is further formed on the plasma-irradiated first passivation layer.
Since there is an upper limit to the thickness of the first passivation layer due to requirements in the manufacturing process, the second passivation layer is formed to supplement the thickness of the first passivation layer. That is, in order to reduce damage to the semiconductor end face, plasma irradiation to the first passivation layer is performed with low energy, and accordingly, the thickness of the first passivation layer may be near the lower limit of the optimum range. Many. At this time, if the second passivation layer is not formed, the oxide or nitride coating film formed on the passivation layer easily becomes a supply source of oxygen or nitrogen. The second passivation layer is formed to solve this problem and to completely separate the oxide or nitride coating film from the semiconductor laser end face.
[0050]
The element deposited as the second passivation layer is preferably selected from those having a refractive index close to that of the first passivation layer and not containing oxygen. As an element attached as the second passivation layer, an element having an absolute value of the enthalpy of formation of oxide larger than that of the element constituting the first passivation layer is used. It is desirable that an element satisfying such a condition is included in at least a part of the element deposited as the second passivation layer. For example, when Si (SiO ₂ : −9.44) is deposited as the first passivation layer, Sc (Sc ₂ O ₃ : −9.89) and Y (Y ₂ ) are deposited as the second passivation layer. Group 3 elements such as O ₃ : −9.46), Group 4 elements such as Ti (TiO ₂ : −9.74), Zr (ZrO ₂ : −11.41), Ta (Ta ₂ O ₃ : It is possible to preferably deposit a group 5 element such as -10.60) (in parentheses indicate the enthalpy of formation of oxides in units of eV / metal atoms).
[0051]
Generally, it is desirable that the thickness of the second passivation layer is 0.2 nm or more. On the other hand, an extremely thick film thickness (for example, 100 nm) may not be suitable. Similarly to the first passivation layer, the lower limit of the second passivation layer is defined by the requirement for the film itself to exist as a film. On the other hand, the upper limit is defined by the degree to which light emitted from the active layer is absorbed by the second passivation layer when the second passivation layer is not transparent to the laser oscillation wavelength. Considering these, it has been experimentally confirmed that the desired thickness of the second passivation layer is within the range represented by the following formula.
[Expression 7]
0.2 (nm) <T _{p (2)} <λ / 4n ₂ (nm) (Formula 2)
(Where T _{p (2)} is the thickness of the second passivation layer, λ is the oscillation wavelength of the semiconductor light emitting device, and n ₂ is the real part of the refractive index at the wavelength λ of the second passivation layer). )
Furthermore, the sum of the thicknesses of the first passivation layer and the second passivation layer is preferably within the range represented by the following formula.
[Equation 8]
0.4 (nm) <T _{p (1 + 2)} <3λ / 8n ₁₂ (nm) (3)
_Where T _{p (1 + 2)} is the sum of the thicknesses of the two passivation layers, λ is the oscillation wavelength of the semiconductor light emitting device, and n ₁₂ is the average refractive index at the wavelength λ of the two passivation layers. Represents the real part of
[0052]
The second passivation layer may be further subjected to a step of forming a passivation layer by irradiating with plasma. This step can be repeated a plurality of times, and three or more passivation layers can be formed. The elements used in the third and subsequent passivation layers can be selected according to the first passivation layer and the second passivation layer, but the oxide is selected from the elements in the adjacent passivation layer. Either a large or small absolute value of the enthalpy of formation can be preferably used. In addition, ZnS, Ge, or the like may be used for the third and subsequent passivation layers from the viewpoint that the refractive index is close to GaAs, Si, or the like. Furthermore, fluorides such as AlF and MgF ₂ can also be used because of their physical stability.
[0053]
In the present invention, a dielectric or dielectric further laminated on the first passivation layer (14-1) and the second passivation layer (14-2) configured on the exposed semiconductor end face, and It is preferable to form the coating layers (15) and (16) made of a combination of semiconductors (FIG. 1). In particular, plasma irradiation to the end face, formation of the first passivation layer (14-1), plasma irradiation to the first passivation layer, formation of the second passivation layer (14-2), coating layer ( 15) The formation of (16) is desirably carried out continuously under a negative pressure, more preferably in a vacuum. The coating layer is formed mainly for the two purposes of increasing the light extraction efficiency from the semiconductor laser and enhancing the protection of the end face. In order to achieve a particularly high output, it is common to apply an asymmetric coating with a coating having a low reflectance with respect to the oscillation wavelength on the front end surface and a coating having a high reflectance with respect to the oscillation wavelength on the rear end surface. Is.
[0054]
Various materials can be used for this coating. For example, it is preferable to use one or a combination of two or more selected from the group consisting of AlOx, TiOx, SiOx, SiN, Si, and ZnS. As the low reflection coating, AlOx, TiOx, SiOx or the like is used, and as the high reflection coating, an AlOx / Si multilayer film, a TiOx / SiOx multilayer film, or the like is used. Each film thickness is adjusted to achieve a desired reflectance. However, in general, as a low-reflection coating, AlOx, TiOx, SiOx, etc. are generally adjusted to have a film thickness in the vicinity of λ / 4n, where n is the real part of the bending rate at the wavelength λ. It is. In addition, it is preferable to adjust the highly reflective multilayer film so that each material constituting the highly reflective multilayer film is in the vicinity of λ / 4n, and further laminate this pair according to the purpose.
[0055]
A so-called IAD (Ion Assisted Deposition) method is preferably used in the method of manufacturing the coating layers (15) and (16). This is a method of irradiating ions having a certain energy simultaneously with vacuum deposition of a coating material, and ion irradiation with a rare gas is particularly suitable. Furthermore, among rare gases, IAD using Ar ions has a great effect on improving the film quality of the coating material. In particular, the irradiation energy of Ar ions is preferably in a low energy range of about 25 eV to 300 eV, more preferably about 50 eV to 200 eV. As a result, coating can be performed without damaging the semiconductor end face.
[0056]
If oxide remains on the semiconductor end face due to the energy of the plasma irradiated simultaneously with the formation of this coating film or the energy of the plasma or heat rays irradiated after the formation of each passivation layer, at least part of the oxide is oxidized. It takes no form of things. That is, the reaction in which the constituent elements present in the passivation layer and particularly adjacent to the semiconductor end face are combined with oxygen remaining on the semiconductor end face is promoted. As a result, it is possible to greatly reduce or eliminate the bond between the elements constituting the semiconductor end face and oxygen. Therefore, these plasma irradiations are also effective for suppressing the above-mentioned extrinsic surface levels. The plasma irradiation accompanying the formation of the coating film is most preferably performed simultaneously with the formation of the coating film, but can also be performed before and after the coating film.
[0057]
In order to effectively promote such a reaction, in the semiconductor light emitting device of the present invention, the absolute value of the enthalpy of formation between oxygen and at least one element constituting the second passivation layer is the first value. It is larger than the absolute value of the enthalpy of formation between oxygen and at least one element constituting the passivation layer. Further, the absolute value of the enthalpy of formation between oxygen and at least one element constituting the first passivation layer is the absolute value of the enthalpy of formation between oxygen and at least one element constituting the semiconductor end face. Is preferably larger. In manufacturing the semiconductor light emitting device of the present invention, plasma energy, thermal energy, or the like that is large enough to cause the above reaction is supplied. However, it is desirable to select these energies within a range that does not cause excessive damage to the semiconductor end face.
[0058]
For example, when Ga—O remains on the semiconductor end face, each passivation layer is formed and irradiated with plasma, or after irradiation of argon plasma while supplying AlOx raw material after the passivation layer is formed, The metal element on the semiconductor end face side of the activation layer is promoted to bond with oxygen derived from Ga—O, and as a result, a part thereof takes the form of a metal oxide. For this reason, Ga constituting a part of the semiconductor end face is not in the form of an oxide, but is bonded to metal Ga or another element constituting the semiconductor end face, for example, Ga-As. As a result, the non-radiative recombination centers existing on the semiconductor end face derived from the Ga—O bond are greatly reduced, which greatly contributes to the provision of a desirable semiconductor light emitting device that has a high output and a long lifetime. it can.
Such a reaction is most effective in the IAD method in which the raw material is supplied simultaneously. However, when ion irradiation is performed on the passivation layer alone after the passivation layer is formed, heat radiation is irradiated after the passivation layer is formed. In the case where it is carried out, the same effect is also obtained when the heat ray is irradiated simultaneously with the plasma irradiation.
[0059]
In particular, when the above reaction is induced by the IAD method, the semiconductor end face side is defined by some elements constituting the coating film on the coating film side of the passivation layer or nitrogen plasma supplied in the form of plasma at the time of film formation. Another reaction may occur. That is, when the coating film is an oxide, the passivation layer may be oxidized by this. When the coating film is a nitride, the nitriding reaction may be promoted.
As a result of these reactions, the passivation layer may be composed of an oxide or the like in the portion adjacent to the end face of the compound semiconductor layer, and the other portion may be the constituent element itself of the passivation layer formed in the initial stage. In addition, in the passivation layer, the portion adjacent to the end face of the compound semiconductor layer is made of an oxide or the like, and the intermediate portion is made of a constituent element or compound of the passivation layer formed in the initial stage, and the portion adjacent to the coating layer is oxidized. In some cases, it may be made of a material, nitride, sulfide or the like. In the semiconductor light emitting device of the present invention, the absolute value of the enthalpy of formation of the oxide of the element constituting the second passivation layer is greater than the absolute value of the enthalpy of formation of the oxide of the element constituting the first passivation layer. Due to the large size, the second passivation layer takes in part of the oxygen present in the first passivation layer and becomes a metal oxide. The thickness of these oxide layers depends on the thickness of the passivation layer to be formed. Usually, an oxide layer or a nitride layer of about 1 to 10 mm is formed on the semiconductor end face side and the coating film side, and at the center and / or the adjacent part to the semiconductor end face, it is several tens to several tens that does not further deteriorate. The thickness of the passivated layer is adjusted so that the passivated passivated layer remains.
[0060]
This is because it is desirable that the passivation layer has a thickness and structural characteristics that do not oxidize all the passivation layer constituent elements. If the entire passivation layer is oxidized or nitrided by oxygen derived from the end surface of the compound semiconductor layer and / or oxygen or nitrogen derived from the coating layer, oxygen taken into the passivation layer This is because there is a concern that the end face is oxidized again while the laser is driven for a long time. In addition, it is preferable that all the elements constituting the semiconductor end face have no bond with oxygen, but if the entire passivation layer is oxidized, the bond between the element constituting the semiconductor end face and oxygen is completely achieved. There is a concern that it cannot be eliminated, and these are not preferable because the effect of improving the life is reduced. In the semiconductor light emitting device of the present invention, the absolute value of the enthalpy of formation of the oxide of the element constituting the second passivation layer is greater than the absolute value of the enthalpy of formation of the oxide of the element constituting the first passivation layer. Largely, since the second passivation layer takes in a part of oxygen in the first passivation layer and becomes a metal oxide, oxidation of the semiconductor end face can be more effectively prevented.
[0061]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. The materials, concentrations, thicknesses, operating procedures, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown in the following examples.
[0062]
(Example 1)
The groove type laser element shown in FIG. 2 was manufactured according to the following procedure.
An n-type GaAs layer having a thickness of 1 μm and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ as a buffer layer (2) on an n-type GaAs substrate (1) having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ by MBE; N-type Al _0.35 Ga _0.65 As layer having a thickness of 1.5 μm and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ as a first conductivity type cladding layer (3); then, a thickness of 24 nm thick on an undoped GaAs optical guide layer 6 nm thick undoped In _0.2 Ga _0.8 As single quantum well (SQW), and active layer (4) having an undoped GaAs light guide layer having a thickness of 24 nm thereon; second conductivity type first cladding layer (5) A p-type Al _0.35 Ga _0.65 As layer having a thickness of 0.1 μm and a carrier concentration of 1 × 10 ¹⁸ cm ^−3; a p-type Al _0.35 Ga _0.65 As layer having a thickness of 10 nm and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ as the second etching stop layer (6) Type GaAs layer; An n-type In _0.49 Ga _0.51 P layer having a thickness of 20 nm and a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ as a chewing blocking layer (7); a carrier concentration of 5 × 10 ¹⁷ cm and a thickness of 0.5 μm as a current blocking layer (9) ^-3 n-type Al _0.39 Ga _0.61 As layer; an n-type GaAs layer having a thickness of 10 nm and a carrier concentration of 1 × 10 ¹⁸ cm ^-3 was sequentially laminated as a cap layer (10).
[0063]
A silicon nitride mask was provided in a portion other than the uppermost current injection region portion. At this time, the width of the opening of the silicon nitride mask was 1.5 μm. Etching was performed at 25 ° C. for 30 seconds using the first etching stop layer (7) as an etching stop layer, and the cap layer (10) and the current blocking layer (9) in the current injection region portion were removed. As the etching agent, a mixed solution in which sulfuric acid (98 wt%), hydrogen peroxide (30 wt% aqueous solution) and water were mixed at a volume ratio of 1: 1: 5 was used.
[0064]
Next, the silicon nitride layer was removed by immersing in a mixed solution in which HF (49%) and NH ₄ F (40%) were mixed at 1: 6 for 2 minutes and 30 seconds. Thereafter, etching was performed at 25 ° C. for 2 minutes using the second etching stopper layer (6) as an etching stop layer, and the first etching stopper layer in the current injection region portion was removed by etching. As the etching agent, a mixed solution in which hydrochloric acid (35 wt%) and water were mixed at a ratio of 2: 1 was used.
[0065]
Thereafter, a p-type Al _0.35 Ga _0.65 As layer with a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ is embedded as the second conductivity type second cladding layer (8) by MOCVD, and the thickness of the buried portion (current injection region portion) is 1. It was grown to 5 μm. Further, a p-type GaAs layer having a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ was grown to a thickness of 7 μm as a contact layer (11) for maintaining good contact with the electrode. The width W of the current injection region (the width of the second conductivity type second cladding layer at the interface with the second etching stop layer) was 2.2 μm. Further, AuGe / Ni / Au was deposited on the substrate side as an n-type electrode, and Ti / Pt / Au was deposited on a p-type electrode and alloyed at 400 ° C. for 5 minutes to complete a semiconductor wafer.
[0066]
Subsequently, the substrate was cleaved into a laser bar having a cavity length of 700 μm in a nitrogen atmosphere and placed in a vacuum chamber having an Ar plasma generator. In the vacuum chamber, Ar plasma was irradiated for 1 minute with Ar plasma having an average energy of 60 eV and a current density of 150 μA / cm ² . Continuously, amorphous Si was deposited on the end face of 2 nm using a normal electron beam evaporation method to form a first passivation layer (14-1). Further, Ar plasma with an average energy of 120 eV and a current density of 150 μA / cm ^{2 was} continuously irradiated to the first passivation layer for 30 seconds. Furthermore, Ti was deposited on the end face of 2 nm using a normal electron beam evaporation method to form a second passivation layer (14-2). Here, the formation enthalpy of SiO ₂ is −9.44 eV / metal atom, and the formation enthalpy of TiO ₂ is −9.74 eV / metal atom. Subsequently, an AlOx film was formed at 165 nm so that the reflectance of the front end face was 2.5% at an oscillation wavelength of 980 nm, and a coating layer (15) was formed. The AlOx film was formed by the IAD method, and simultaneously with supply to the end face of AlOx, Ar plasma with an average energy of 110 eV and a current density of 200 μA / cm ² was irradiated.
[0067]
Further, the laser bar was once taken out from the vacuum layer in order to perform the processing on the rear end face side. The Ar plasma irradiation, the formation of the first passivation layer (14-1), the plasma irradiation of the first passivation layer, the second passivation layer (14) are performed on the rear edge surface side in the same manner as the front edge surface side. -2) was formed. Further, a coating layer (16) comprising four layers of an AlOx layer having a thickness of 170 nm / an amorphous Si layer having a thickness of 60 nm / an AlOx layer having a thickness of 170 nm / an amorphous Si layer having a thickness of 60 nm was formed, and the reflectance A rear end face of 92% was produced. The AlOx film was formed by the IAD method similarly to the front end face side.
[0068]
The manufactured semiconductor light emitting device 5 device was placed on a heat dissipating submount and packaged in a nitrogen atmosphere. Regarding the average initial characteristics of this semiconductor light emitting device, the threshold current was 23 mA at 25 ° C., and kinks were observed at 350 mA and 250 mW. A life test was performed on this population. As a result of an accelerated test at 225 mW and 70 ° C., stable operation was confirmed with no malfunction at all even after 1000 hours had passed.
[0069]
(Example 2)
A semiconductor wafer was manufactured by the same method as in Example 1, and then cleaved into a laser bar having a resonator length of 700 μm in a nitrogen atmosphere and placed in a vacuum chamber having an Ar plasma generator. In the vacuum chamber, Ar plasma was irradiated for 1 minute with Ar plasma having an average energy of 60 eV and a current density of 150 μA / cm ² . Continuously, amorphous Si was deposited on the end face of 2 nm using a normal electron beam evaporation method to form a first passivation layer (14-1). Further, Ar plasma with an average energy of 120 eV and a current density of 150 μA / cm ^{2 was} continuously irradiated to the first passivation layer for 30 seconds. Furthermore, Ti was deposited on the end face of 2 nm using a normal electron beam evaporation method to form a second passivation layer (14-2). Subsequently, the second passivation layer was irradiated with Ar plasma having an average energy of 120 eV and a current density of 150 μA / cm ² for 30 seconds. Further, a third passivation layer (not shown) was formed by depositing amorphous Si on the end face of 2 nm using a normal electron beam evaporation method. Here, the formation enthalpy of SiO ₂ is −9.44 eV / metal atom, and the formation enthalpy of TiO ₂ is −9.74 eV / metal atom. Further, an AlOx film was formed to a thickness of 165 nm so that the reflectance of the front end face was 2.5% at an oscillation wavelength of 980 nm to form a coating layer (15). The AlOx film was formed by the IAD method, and simultaneously with the supply to the end face of AlOx, Ar plasma with an average energy of 90 eV and a current density of 200 μA / cm ² was irradiated.
[0070]
Further, the laser bar was once taken out from the vacuum layer in order to perform the processing on the rear end face side. Ar plasma irradiation, formation of the first passivation layer, plasma irradiation to the first passivation layer, formation of the second passivation layer, second passivation in the same manner as the front edge side on the rear edge side Plasma irradiation to the activated layer and formation of the third passivation layer were performed. Further, a coating layer (16) comprising four layers of an AlOx layer having a thickness of 170 nm / an amorphous Si layer having a thickness of 60 nm / an AlOx layer having a thickness of 170 nm / an amorphous Si layer having a thickness of 60 nm was formed, and the reflectance A rear end face of 92% was produced. The AlOx film was formed by the IAD method similarly to the front end face side.
[0071]
The manufactured semiconductor light emitting device 5 device was placed on a heat dissipating submount and packaged in a nitrogen atmosphere. Regarding the average initial characteristics of this semiconductor light emitting device, the threshold current was 23 mA at 25 ° C., and kinks were observed at 350 mA and 250 mW. A life test was performed on this population. As a result of an accelerated test at 225 mW and 70 ° C., stable operation was confirmed with no malfunction at all even after 1000 hours had passed.
[0072]
(Example 3)
A semiconductor wafer was manufactured by the same method as in Example 1, and then cleaved into a laser bar having a resonator length of 700 μm in a nitrogen atmosphere and placed in a vacuum chamber having an Ar plasma generator. In the vacuum chamber, Ar plasma was irradiated for 1 minute with Ar plasma having an average energy of 60 eV and a current density of 150 μA / cm ² . Continuously, amorphous Si was deposited on the end face of 2 nm using a normal electron beam evaporation method to form a first passivation layer (14-1). Further, Ar plasma with an average energy of 120 eV and a current density of 150 μA / cm ^{2 was} continuously irradiated to the first passivation layer for 30 seconds. Furthermore, Ti was deposited on the end face of 2 nm using a normal electron beam evaporation method to form a second passivation layer (14-2). Subsequently, the second passivation layer was irradiated with Ar plasma having an average energy of 120 eV and a current density of 150 μA / cm ² for 30 seconds. Further, a third passivation layer (not shown) is formed by depositing Ta on the end face of 2 nm by using an ordinary electron beam evaporation method, and the average energy of 120 eV and current are formed with respect to the formed third passivation layer. Ar plasma with a density of 150 μA / cm ² was irradiated for 30 seconds. Here, the formation enthalpy of SiO ₂ is −9.44 eV / metal atom, the formation enthalpy of TiO ₂ is −9.74 eV / metal atom, and the formation enthalpy of Ta ₂ O ₃ is −10.60 eV / metal atom. Further, an AlOx film was formed to a thickness of 165 nm so that the reflectance of the front end face was 2.5% at an oscillation wavelength of 980 nm to form a coating layer (15). The AlOx film was formed by an electron beam evaporation method.
[0073]
Further, the laser bar was once taken out from the vacuum layer in order to perform the processing on the rear end face side. Ar plasma irradiation, formation of the first passivation layer, plasma irradiation to the first passivation layer, formation of the second passivation layer, second passivation in the same manner as the front edge side on the rear edge side Plasma irradiation to the activated layer, formation of the third passivation layer, and plasma irradiation to the third passivation layer were performed. Further, a coating layer (16) comprising four layers of an AlOx layer having a thickness of 170 nm / an amorphous Si layer having a thickness of 60 nm / an AlOx layer having a thickness of 170 nm / an amorphous Si layer having a thickness of 60 nm was formed, and the reflectance A rear end face of 92% was produced. The AlOx film was formed by the electron beam evaporation method in the same manner as the front end face side.
[0074]
The manufactured semiconductor light emitting device 5 device was placed on a heat dissipating submount and packaged in a nitrogen atmosphere. Regarding the average initial characteristics of this semiconductor light emitting device, the threshold current was 23 mA at 25 ° C., and kinks were observed at 350 mA and 250 mW. A life test was performed on this population. As a result of an accelerated test at 225 mW and 70 ° C., stable operation was confirmed with no malfunction at all even after 1000 hours had passed.
[0075]
(Comparative Example 1)
A comparative semiconductor light emitting device was manufactured and tested in the same procedure as in Example 1 with the following changes.
That is, both the front end face and the rear end face are irradiated with Ar plasma on the laser end face, formed with the first passivation layer (14-1), irradiated with Ar plasma on the first passivation layer, and with the second passivation layer. No formation was made. Further, the coating layers (15) and (16) were formed using a normal electron beam evaporation method without using the IAD method. Except for these, a semiconductor light emitting device was manufactured in exactly the same procedure as in Example 1.
The average initial characteristics of the manufactured semiconductor light emitting device were a threshold current of 23 mA at 25 ° C. as in the example, and kinks were observed at 350 mA and 250 mW. However, as a result of an accelerated test at 225 mW and 70 ° C., all 10 devices used in the experiment suddenly became inoperable by the end of 100 hours.
[0076]
(Comparative Example 2)
A semiconductor light emitting device was manufactured in the same procedure as in Example 1 except that both the front end face and the rear end face were not subjected to Ar plasma irradiation to the first passivation layer and formation of the second passivation layer.
As for the average initial characteristics of the manufactured semiconductor light emitting device, the threshold current was 23 mA at 25 ° C. as in Example 1, and kinks were observed at 350 mA and 250 mW. As a result of an accelerated test at 225 mW and 70 ° C., all three devices used in the experiment suddenly became inoperable by the end of 200 hours.
[0077]
(Comparative Example 3)
Both the front end face and the rear end face were not irradiated with Ar plasma on the laser end face, and the coating layers (15) and (16) were formed using a normal electron beam evaporation method without using the IAD method. A semiconductor light emitting device was manufactured in the same procedure as in Example 1 except that.
As for the average initial characteristics of the manufactured semiconductor light emitting device, the threshold current was 23 mA at 25 ° C. as in Example 1, and kinks were observed at 350 mA and 250 mW. However, as a result of an accelerated test at 225 mW and 70 ° C., all 10 devices used in the experiment suddenly became inoperable by the end of 150 hours.
[0078]
【The invention's effect】
According to the present invention, it is possible to provide a semiconductor light emitting device such as a semiconductor laser capable of stably suppressing the interface state density at the end face over a long period of time. Moreover, since the semiconductor light emitting device of the present invention can be manufactured very simply, the industrial applicability is extremely high.
[Brief description of the drawings]
FIG. 1 is a perspective view showing one embodiment of a semiconductor light emitting device of the present invention.
FIG. 2 is a cross-sectional view showing one embodiment of a semiconductor light emitting device of the present invention.
[Explanation of symbols]
1: Substrate 2: Buffer layer 3: First conductivity type cladding layer 4: Active layer 5: Second conductivity type first cladding layer 6: Second etching prevention layer 7: First etching prevention layer 8: Second conductivity type first Bi-cladding layer 9: Current blocking layer 10: Cap layer 11: Contact layer 12: Electrode 13: Electrode 14-1: First deactivation layer 14-2: Second deactivation layer 15: Coating layer 16: Coating layer

Claims (8)

In a semiconductor light emitting device having a resonator structure having a compound semiconductor layer including a first conductivity type cladding layer, an active layer and a second conductivity type cladding layer on a substrate,
The surfaces of the first conductivity type cladding layer, the active layer, and the second conductivity type cladding layer forming the end face of the compound semiconductor layer are covered with the first passivation layer, and the first passivation layer is the second passivation layer. The second deactivation layer is covered with a deactivation layer, and the deactivation layer comprising the first deactivation layer and the second deactivation layer has a portion composed of a single element, and the second deactivation layer Semiconductor light emission characterized in that the absolute value of the enthalpy of formation of the oxide of at least one element constituting the oxide is larger than the absolute value of the enthalpy of formation of the oxide of at least one element constituting the first passivation layer element.   The absolute value of the formation enthalpy of the oxide of at least one element constituting the first passivation layer is larger than the absolute value of the formation enthalpy of the oxide of at least one element constituting the end face, The semiconductor light emitting device according to claim 1.   3. The semiconductor light emitting device according to claim 1, wherein at least one of the elements constituting the end face does not have a bond with oxygen. The second semiconductor light emitting device according to claim 1, further comprising a passivation layer at least one layer covering the passivation layer. On the surface of the passivation layer is the outermost layer, the semiconductor light-emitting device according to any one of claims 1 to 4, characterized in that a coating layer made of a dielectric or a dielectric and semiconductor combinations. The semiconductor light-emitting device according to any one of claims 1 to 5, characterized in that forming the first passivation layer to a thickness within the range represented by the following (Equation 1).

(Wherein, T _{p (1)} is the thickness of the first passivation layer, λ is the oscillation wavelength of the semiconductor light emitting device, and n ₁ is the real part of the refractive index at the wavelength λ of the passivation layer.) The second semiconductor light-emitting device according to any one of claims 1 to 6, a passivation layer and forming a thickness within the range represented by the following (Equation 2).

(Where T _{p (2)} is the thickness of the second passivation layer, λ is the oscillation wavelength of the semiconductor light emitting device, and n ₂ is the real part of the refractive index at the wavelength λ of the second passivation layer). ) The first deactivation layer and the second deactivation layer are formed so that a sum of thicknesses is within a range represented by (Formula 3). the device according to one paragraph or.

(Where T _{p (1 + 2)} is the sum of the thicknesses of the first and second passivation layers, λ is the oscillation wavelength of the semiconductor light emitting device, and n ₁₂ is the first passivation layer) (Represents the real part of the average refractive index at the wavelength λ of the second passivation layer.)

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