JPH11121877A - Compd. semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably suppress an interface level density at the semiconductor light emitting element end face for a long time, and stably operate in the event of diffusion in an inactive layer during LD driving, by covering with an inactive layer the surfaces of a first conductivity type clad layer, active layer and second conductivity type clad layer which form end faces. SOLUTION: An inactive layer 14 covers the surfaces of a first conductivity type clad layer 3, active layer 4 and second conductivity type clad layer 5 which form end faces. The active layer 4 near the end face is permeable to an oscillation wavelength. A window structure is adopted to stably suppress the optical absorption at the semiconductor light emitting element end faces for a long time, and an inactive layer 14 is inserted between coating layers 15, 16 made of a dielectric or dielectric combined with a semiconductor to realize long stable end faces, and also to realize by a simple method a semiconductor light emitting element stably operable even in the event of diffusion in the inactive layer 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor laser. The device of the present invention requires both high output and long life of a pump light source for an optical fiber amplifier and a light source for optical information processing. It is suitably used for the intended use. In addition, LEDs such as spear luminescent diodes having a light emitting end formed by an end face, and applications to surface emitting lasers and the like are also possible.

[0002]

2. Description of the Related Art In recent years, progress in optical information processing technology and optical communication technology has been remarkable. For example, there is no shortage of high-density recording using a magneto-optical disk and two-way communication using an optical fiber network. For example, in the telecommunications field, Er ^{3+ is used} as an amplifier for signal amplification that has flexibility in the transmission system, as well as a large-capacity optical fiber transmission line corresponding to the future of the multimedia age.
Optical fiber amplifier (EDF) doped with rare earth such as
The research of A) is being actively conducted in various fields. And
It is an essential element as a component of EDFA,
Development of a semiconductor laser for a highly efficient excitation light source is awaited.

[0003] In principle, there are three types of oscillation wavelengths of an excitation light source that can be used for EDFA applications.
80 nm and 1480 nm. From the characteristics of the amplifier, it is known that pumping at 980 nm is most desirable in consideration of gain, noise, and the like. It is desired that such a laser having an oscillation wavelength of 980 nm satisfies the contradictory characteristics of a high output and a long life as an excitation light source. Wavelengths in the vicinity,
For example, at 890-1150 nm, an SHG light source,
There is also a demand as a heat source for a laser printer, and development of a laser with high output and high reliability is also straddled in various other applications.

In the field of information processing, the output and wavelength of semiconductor lasers have been increasing for the purpose of high-density recording, short-time writing and reading, and the output of conventional LDs having an emission wavelength of 780 nm has been increased. There is a strong demand, and the development of LDs in the 630-680 nm band is also being vigorously conducted in various fields. As an approach for achieving both high power and high reliability indispensable for realizing the laser, for example, the band gap of the active layer region near the end face is made transparent to the oscillation wavelength, and Various methods have been proposed to reduce the light absorption in the light. Lasers with these structures are generally window-structured lasers or NAMs (non Ab
This laser is called a sorbing mirror (structured laser) and is very effective when high power is required.

On the other hand, a solution to the problem as disclosed in Japanese Patent Application Laid-Open No. 3-101183 has been proposed. According to this, an end face without contamination is formed, and a substance which does not cause a reaction with the semiconductor end face or diffusion itself and does not contain oxygen is formed as a passivation layer or a part thereof. The manufacturing method is said to be effective. Further, as a known document similar to the above-mentioned JP-A-3-101183,
LWTuet al., (In-vacuum cleaving and coating
of semiconductor laser facets using silicon
and a dielectric, J. Appl. Phys. 80 (11) 1 DEC. 19
96). According to this, when the Si / AlO _x structure is coated on the laser end face and cleaved in a vacuum, the recombination rate of carriers at the cleaved face is reduced, and the initial CO 2
It is described that the D level rises.

Further, in order to reduce the electric field intensity at the light emitting end face of the semiconductor laser, Si is coated between the coating film and the semiconductor so that the antinode of the standing wave existing in the cavity direction does not coincide with the end face part. A technique of inserting a quarter wavelength into the interface is also known.

[0007]

For example, for a semiconductor laser having a wavelength of about 980 nm, a semiconductor laser capable of withstanding continuous use for about two years at an optical output of about 50 to 100 mW has already been developed. In this case, rapid deterioration occurs and the reliability is insufficient. The same is true for the laser diode (hereinafter, referred to as “LD”) in the 780 nm band and the 630-680 nm band, and ensuring the reliability at the time of high output is a problem especially for the whole semiconductor laser using a GaAs substrate. It is.

[0008] One of the causes is caused by deterioration of an emission end face of a laser beam exposed to a very high light density. As is well known in GaAs / AlGaAs-based semiconductor lasers, there are many surface levels near the end face, but these levels absorb laser light.
In general, it is described that the temperature near the end face becomes higher than the temperature inside the laser, and this temperature rise further narrows the band gap near the end face, and further causes positive feedback such that laser light is more easily absorbed. This phenomenon is called end-face destruction, so-called COD (c
Known as atastrophic optical damage), sudden deterioration of the device due to a decrease in the COD level during a long-term energization test is a common problem in many semiconductor laser devices. Attempts to solve these problems have been made vigorously as described above, but are still technically insufficient.

Considering the case of an LD having a window structure, for example, there is a method of epitaxially growing a semiconductor material transparent to an emission wavelength on a laser end face. In this method, since the laser is grown in a so-called bar state and epitaxial growth is performed on the end face, an electrode process performed thereafter becomes very complicated. Also, Zn or Si
Various methods have been proposed for intentionally causing thermal diffusion or ion implantation as impurities into an active layer near the end face of a laser to make the active layer disorder. Examples of these known documents include JP-A-2-45992, JP-A-3-31083, and 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 toward the substrate, there is a problem in controllability of the diffusion depth and controllability of lateral diffusion with respect to the cavity direction. It is difficult to make stable production. Further, in the case of ion implantation, high-energy ions are introduced from the end face, so that damage tends to remain on the LD end face even after annealing. In addition, an increase in reactive current due to a decrease in resistance in a region into which impurities are introduced has a problem that a threshold current and a drive current of a laser increase.

On the other hand, for example, Japanese Patent Laid-Open Publication No.
No. 3 discloses a non-contaminated end face, on which a reaction with the semiconductor end face or a substance which does not itself diffuse and does not contain oxygen is formed as a passivation layer or a part thereof. The technical problems of the manufacturing method are as follows. Generally, by working in a clean room, for example, in the atmosphere, there is no effect of suppressing the generation of non-radiative recombination centers such as Ga-O and As-O, which are generated on the end face at the time of cleavage. As described in the first claim, the specific <method of forming an end face without contamination> disclosed in the above patent requires the formation of a passivation layer on the cleaved site, and this specific realization is possible. The environment is only cleavage in a vacuum as stated in the tenth claim. However, compared to general cleavage in the atmosphere,
Very complicated equipment and work are required. In addition, the end face formed by dry etching disclosed in the eleventh to fourteenth claims generally forms more non-radiative recombination centers than the end face formed by cleavage, and has a long life. It is not suitable as a required LD manufacturing method.

Further, Si or amorphous Si is preferably used as a passivation layer, that is, an inactive layer.
However, in general, there is no substance that does not cause any diffusion at all, and in particular, in a semiconductor laser that is supposed to be driven for a long time under high power and high temperature, the passivation material disclosed in the above-mentioned patent is used. Concern about proliferation. Also,
Above, LWTu et al., (In-vacuum cleaving and c
oating of semiconductor laser facets using s
ilicon and a dielectric, J. Appl. Phys. 80 (11) 1
According to DEC. 1996), when the Si / AlO _x structure is coated on the laser end face, cleaving in a vacuum slows the recombination rate of carriers at the cleavage face and increases the initial COD level. There is no statement about the reliability of
No mention is made of the connection between the coating and the LD structure.

Further, in order to reduce the electric field strength at the light emitting end face of the semiconductor laser, Si is coated between the coating film and the semiconductor so that the antinode of the standing wave existing in the cavity direction does not coincide with the end face part. In the technology of inserting a quarter wavelength into the interface, a wavelength band in which a general semiconductor laser is realized, particularly a high output LD is desired to be 400-1600n.
In m, since Si itself acts as a light absorber, a temperature rise at the end face may accelerate the deterioration of the device.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to stably suppress the interface state density at the end face of a semiconductor laser for a long period of time, and to further improve the LD of the passivation layer. This is to make it possible to realize a semiconductor laser that operates stably even when diffusion occurs during driving by a simple method, that is, it achieves both high output and long life while suppressing degradation at the end face. It is nothing but to provide a high performance semiconductor laser.

[0015]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, at least a first conductive type clad layer, an active layer, and a second conductive type clad layer are laminated on a substrate. A compound semiconductor light emitting device having an oscillation wavelength λ (nm) in which two opposing end faces form a resonator structure, wherein the first conductivity type cladding layer, the active layer, and the second conductivity type forming the end faces are formed. The surface of the cladding layer is covered with a passivation layer made of silicon or the like, and preferably, the surface of the passivation layer is covered with a coating layer made of a dielectric or a combination of a dielectric and a semiconductor, and an active layer near the end face thereof. In the case of a compound semiconductor light emitting device which is transparent to the oscillation wavelength λ, it has been found that both high output and long life can be achieved at a level far exceeding that of the prior art, and the present invention has been achieved.

That is, the gist of the present invention resides in that at least a first conductive type clad layer, an active layer and a second conductive type clad layer are laminated on a substrate, and two opposing end faces form a resonator structure. A compound semiconductor light emitting device having a wavelength of λ (nm), wherein the surfaces of the first conductivity type cladding layer, the active layer and the second conductivity type cladding layer forming the end face are covered with a passivation layer; An active layer near an end face is transparent to an oscillation wavelength λ.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The semiconductor light emitting device of the present invention has an oscillation wavelength λ in which at least a first conductivity type clad layer, an active layer and a second conductivity type clad layer are laminated on a substrate, and two opposing end faces form a resonator structure. (Nm), wherein the surfaces of the first conductivity type cladding layer, the active layer, and the second conductivity type cladding layer forming the end face are covered with a passivation layer and are near the end face. The structure is not particularly limited as long as the active layer is a compound semiconductor light emitting device that is transparent to the oscillation wavelength λ. The conductive cladding layer is divided into two layers, a first one and a second one, to form a current injection region with the second conductive type second cladding layer and the current blocking layer, and to further lower the contact resistance with the electrode. Semiconductor with structure with contact layer The laser will be described.

A method for manufacturing a basic epitaxial structure of such a laser is described in, for example, Japanese Patent Application Laid-Open No. Hei 8-130344 by Horie et al.
This type of laser is used as a light source for an optical fiber amplifier used for optical communication and as a pickup light source for a large-scale magneto-optical memory for information processing, and includes an active layer and a cladding layer. Depending on the layer configuration such as the above and the material configuration, it can be further applied to various uses.

FIG. 2 is a schematic example in which a groove type semiconductor laser is formed as an example of the epitaxial structure in the semiconductor laser of the present invention. The substrate (1) may be made of InP, GaAs, GaN, InGa in view of a desired oscillation wavelength, lattice matching, distortion intentionally introduced into the active layer and the like.
A single crystal substrate such as As or Al ₂ O ₃ is used. Al ₂ O ₃
In some cases, a dielectric substrate can be used. As an embodiment of the present invention, an InP substrate or a GaAs substrate is preferable from the viewpoint of lattice matching with a III-V semiconductor light emitting device containing As, P, or the like as a V group, and includes As as a V group. Most preferably, a GaAs substrate is used.

A dielectric substrate such as Al ₂ O ₃ is made of III-V
Among group V semiconductor light emitting devices, a material containing nitrogen or the like as V group may be used. The substrate is not only a so-called just substrate, but also a so-called off-substrate (miss oriented) from the viewpoint of improving crystallinity during epitaxial growth.
substrate) can also be used. This is widely used with the effect of promoting good crystal growth in a so-called step flow mode. The off-substrate is generally used from about 0.5 degrees to about 2 degrees off, but a substrate having an inclination of about 10 degrees may be used depending on the material system constituting the quantum well structure.

In some cases, the substrate is subjected to chemical etching, heat treatment, etc., in preparation for the fabrication of a light emitting device, utilizing a crystal growth technique such as MBE or MOCVD. The buffer layer (2) is preferably provided to alleviate incompleteness of the substrate bulk crystal and facilitate formation of an epitaxial thin film having the same crystal axis. The buffer layer (2) is preferably made of the same compound as the substrate (1). When the substrate is GaAs, GaAs is usually used. However, a superlattice layer is widely used as a buffer layer, and may not be formed of the same compound. On the other hand, when a dielectric substrate is used, a material different from that of the substrate may be appropriately selected depending on the desired emission wavelength and the structure of the entire device, instead of the same material as the substrate.

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 prepared to realize a desired oscillation wavelength. The material is appropriately defined by the substrate (1), 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 GaAs, an AlGaAs-based material, an InGaAs-based material,
aInP-based materials, InGaP-based materials, and the like are used. In some cases, the entire cladding layer may have a superlattice structure.

Although the present invention is effective irrespective of the conductivity type, material, structure, etc. of the active layer (4), from the viewpoint of material selection,
The active layer (4) is preferably a system containing In and / or Ga, more preferably a system containing In, and most preferably a system containing In and Ga. This is a material system in which so-called ordering is likely to occur during crystal growth, and the passivation layer (14)
Si inserted at the interface between the laser end face and the dielectric as
This is because when diffusing as described above during long-term laser driving, disordering near the end face may be expected. Generally, disordering of the material causes an increase in the band gap, which, in combination with the compensation effect of the carrier, further suppresses the light absorption at the end face in the long term.

From these viewpoints, as the material of the active layer (4), specifically, an AlGaAs-based material, InGaAs
s-based material, InGaP-based material, AlGaInP-based material, etc., and among them, In _x Ga _1-x As (0 <x <1) or (Al _x G
a _1−x ) _y In _1−y P (0 <x, y <1) is desirable, and it is particularly desirable to have a quantum well structure from the viewpoint of disordering. The choice of these materials is usually dictated by the desired oscillation wavelength. By selecting the material of the active layer, the oscillation wavelength λ (n
m) is substantially determined, and the oscillation wavelength λ (nm) is S
The wavelength is preferably shorter than the i-absorption edge.

The active layer (4) may be a normal bulk active layer consisting of a single layer, but may have a single quantum well (SQW) structure, a double quantum well (DQW) structure, or a multiple quantum well (DQW) structure. A quantum well structure such as an MQW structure is adopted according to the purpose. In the quantum well structure, an optical guide layer is usually used in combination, and if necessary, a barrier layer is also used for separating 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) can be adopted. The material of the light guide layer is AlGa
As-based material, InGaAs-based material, InGaP-based material A
Selection can be made according to the active layer, such as an lGaInP-based material. Also, the light guide layer can be a superlattice combining the above materials.

A second conductivity type first and second cladding layer (5),
(8), like the first conductivity type clad layer (3), is generally made of a material having a refractive index smaller than the average refractive index of the active layer (4), and the substrate (1) and the buffer layer (2). The material is appropriately defined by the active layer (4) and the like. For example, GaAs is used as the substrate (1), and when the buffer layer (2) is GaAs, an AlGaAs-based material, an InGaAs-based material, an AlGaInP-based material, an InGaP-based material, or the like is used.

FIG. 2 illustrates two types of etch stop layers (6) and (7) and a cap layer (10), which are employed in a preferred embodiment of the present invention and provide for current injection. This is effective for accurately and easily creating a region. When the second etching stop layer (6) is made of, for example, _a material of Al _a Ga _1-a As (0 ≦ a ≦ 1), usually, GaAs is preferably used. This is because the second conductive type second cladding layer (8) and the like can be laminated with good crystallinity when regrowth is performed by the MOCVD method or the like, particularly, in the case of AlGaAs. The thickness of the second etching stop layer (6) is usually preferably 2 nm or more.

The first etching stop layer (7) is made of In _b G
A layer represented by a _1-b P (0 ≦ b ≦ 1) is preferable, and when GaAs is used as the substrate as in the present invention, b = 0.5 is usually used in a strain-free system. . The thickness of the first etching stop layer (7) is usually 5 nm or more, preferably 10 nm or more. If the thickness is less than 5 nm, etching may not be able to be prevented due to disorder of the film thickness or the like. On the other hand, depending on the film thickness, a strain system can be used, and b = 0, b = 1, and the like can be used.

The cap layer (10) is used as a protective layer for the current blocking layer (9) in the first growth and at the same time to facilitate the growth of the second conductive type second clad layer (8). Before the element structure is obtained, some or all of the elements are removed. Since it is necessary for the current blocking layer (9) to literally block the current and not substantially flow, the conductivity type is preferably the same as that of the first conductivity type cladding layer (3) or undoped. ,Also,
For example, when the current blocking layer (9) is formed of an AlGaAs-based material, it is preferable that the refractive index is smaller than that of the second conductivity type second cladding layer (8) made of AlyGa1-yAs (0 <y ≦ 1). That is, the current block layer is made of Al
_{If z} Ga _{1 -z} As (0 ≦ z ≦ 1), it is preferable that the mixed crystal ratio be z> y.

The refractive index of the second-conductivity-type second cladding layer (8) is usually lower than the refractive index of the active layer (4). The second conductive type second clad layer (8) is usually the same as the first conductive type clad layer (3) and the second conductive type first clad layer (5). Further, as one preferred embodiment of the present invention, the second conductive type first clad layer (5), the second conductive type second clad layer (8) and the current blocking layer (9) are all made of the same material of the same composition. It is constituted by. 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, in addition to the first etching layer (7), the cap layer ( An effective refractive index difference is also formed by (10). By adopting such a layer configuration, it is possible to avoid various problems caused by mismatching of materials or compositions at respective interfaces of the second conductivity type second cladding layer (8) and the current blocking layer (9), Very preferred.

It is preferable to provide a contact layer (11) on the second conductive type second clad layer (8) for the purpose of lowering the contact resistivity with the electrode (12). The contact layer (11) is usually made of a GaAs material. In this layer, the carrier concentration is usually made higher than the other layers in order to lower the contact resistivity with the electrode (12). Usually, the thickness of the buffer layer (2) is 0.1 to 3 μm,
The thickness of the first conductivity type cladding layer (3) is 0.5 to 3 μm,
In the case of a quantum well structure, the thickness of the active layer (4) is 0.0005 to 0.02 μm per layer, and the thickness of the second conductive type first cladding layer (5) is 0.05 to 0.3 μm. The thickness of the second cladding layer (8) is 0.5 to 3 μm, the thickness of the cap layer (10) is 0.005 to 0.5 μm, and the thickness of the current blocking layer (9) is 0.3 to 2 μm. Selected from a range.

The semiconductor light emitting device shown in FIG. 2 is constituted by further forming electrodes (12) and (13). Electrode (1
In the case of p-type, 2) is formed by sequentially depositing, for example, Ti / Pt / Au on the surface of the contact layer (11), followed by alloying. 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 on the surface of the substrate (1) and then formed by alloying. You.

The semiconductor wafer thus formed is cleaved to form a so-called laser bar. The present invention does not necessarily require generally complicated cleavage in a vacuum. This is because, for example, the band gap near the end face can be widened and made transparent to the oscillation wavelength λ stably and with good reproducibility by using the following two methods.

One is the first conductivity type clad layer (3), the active layer (4), the second conductivity type clad layer (5),
(8) Further, the substrate (1), buffer layer (2), first etching stop layer (7), second etching stop layer (6), current blocking layer (9), cap layer ( 10) irradiating the constituent elements such as the contact layer (11) with charged particles having a low energy of about 25 eV to about 300 eV, that is, a plasma that is ions, electrons, or a combination thereof, preferably argon plasma;
This can be realized by forming a disordered region near the active layer. Irradiation with plasma is preferably performed by exposing the first conductive type clad layer, active layer and second clad layer which are exposed to the end face to at least the plasma, usually the end face including other layers. The whole surface is irradiated with plasma. About 10 ⁻³ Torr or less, preferably 10 ⁻⁴ Torr
Hereinafter, it is most preferably performed in a vacuum of about 10 ⁻⁵ Torr or less.

At this time, as described above, a system in which the active layer contains In and / or Ga, more preferably a system containing In,
Most preferably, in the case of a system containing In and Ga, a disordered region is exposed to the low-energy argon plasma irradiation as described above because of a material system in which ordering is likely to occur during crystal growth. Is a desirable mode because the energy difference from the band gap of the active layer portion which is not disordered becomes large. Also from these viewpoints, specific materials for the active layer include the above-mentioned AlGaAs-based material and In
GaAs-based material, InGaP-based material, AlGaInP-based material or the like, among _{others, In X Ga 1-x As} (0 <x <1) or _{(Al x Ga 1-x)} y In 1-y P (0 <x, y It is desirable to include <1), and particularly to have a quantum well structure from the viewpoint of disordering.

On the other hand, another example of the means for widening the band gap near the end face to make it transparent to the oscillation wavelength λ is to irradiate a light beam, a heat ray and / or an electron beam, or the like.
It is to thermally or optically desorb some of the elements constituting the active layer near the end face that have a high vapor pressure. Generally, the vapor pressure involved in the re-evaporation of a group III element As compound in vacuum is InAs> GaAs.
> AlAs, and by selecting a heat treatment temperature, an element having a low vapor pressure can be selectively removed. For example, to realize a lasing wavelength of 980 nm, In _x Ga _{1 -x} As (x = about 0.2) having a strained quantum well structure is used as an active layer.
In this case, the vicinity of the end face is selectively heated, and 500 ° C. to 6 ° C.
When the temperature is set to 50 ° C., InAs selectively re-evaporates, and a region having a low In concentration can be formed only near the end face. This means that the band gap near the end face is widened. By such processing, it is possible to stably realize that the active layer near the end face is transparent to the laser oscillation wavelength λ. Rays, heat rays and / or
Alternatively, the irradiation amount of the electron beam may be appropriately adjusted so that the surface of the laser bar rises to a target temperature. In order to reduce the thermal load on the entire laser bar, the irradiation time is preferably as short as possible, usually 10 minutes or less, and more preferably 5 minutes or less. This process is performed in a vacuum, and the degree of vacuum is about 10 ^-3 Torr or less, preferably 10 ^-4 Torr or less, and most preferably 1 ^-4 Torr or less.
It is preferably about 0 ^-7 Torr or less.

These two methods are examples of means for widening the band gap near the end face in the LD fabrication process. The passivation layer diffuses during driving of the LD and further widens the band gap near the end face. In combination with the above-mentioned effect, a high-output and long-life element can be realized. In particular, the method of irradiating low-energy argon plasma of about 25 eV to about 300 eV to form a disordered high-resistance region near the active layer, which is the method described above, is based on the method in which elements located near the resonator mirror are used. It is also possible to remove, in particular, oxides, such as at least one oxide and / or nitride. For example, it is particularly effective for removing As-O,
The irradiation effect of low-energy argon plasma is enormous. This is a treatment with very low energy as compared with ion implantation of impurities or the like, and it can be said that it is excellent in that the process can be performed with less damage to the end face. Ga-O and the like have the same effect.

As a method of analyzing whether at least one of the constituent elements does not exist in the form of an oxide, for example, XPS (X-ray Photo-electron Spectr
oscopy X-ray photoelectron spectroscopy). This is a very useful tool for knowing the chemical bonding state of each element.
By irradiating the laser end face with X-rays having a size of about μm × 100 μm, and photo-electrons generated as a result of the energy spectroscopy, the chemical bonding state of each element constituting the laser end face can be confirmed. At this time, by changing the angle between the photoelectron detector and the sample surface, it is possible to easily obtain only information near the surface. In addition, since a general laser is coated on its end face with a dielectric or a dielectric and semiconductor pair as described later, various etching methods are used before the XPS measurement to a thickness suitable for analysis. Usually, the coating film is thinned. Further, with respect to a laser on which a thin coating film of about 2 nm is formed, it is possible to analyze the end face of the semiconductor laser without performing such processing as etching.

Cleavage is preferably used for forming the end face. This is widely used in the case of an edge-emitting laser, but there are also cases where a resonator is formed during the crystal growth process like a surface-emitting laser. The end face formed by cleavage varies depending on the orientation of the substrate used. For example, when forming an element such as an edge emitting laser using a substrate having a crystallographically equivalent surface to the nominally (100) (nominally (100)) preferably used, (110) or The plane crystallographically equivalent to this is the plane that forms the resonator, but when using the aforementioned off-substrate (miss oriented substrate),
Depending on the relationship between the inclined direction and the resonator direction, the end face may not form 90 ° with the resonator direction. For example, when a substrate whose angle is inclined by 2 ° from the (100) substrate toward the (1-10) direction is used, the end face is also inclined by 2 degrees.

In the present invention, the passivation layer is formed on the end face of the compound semiconductor light-emitting device, and forms a non-radiative recombination center when the elements constituting the end face are combined. This layer prevents chemical reactions. The passivation layer is formed so as to cover at least the first conductivity type clad layer, the active layer and the second conductivity type clad layer which form the end face, but is usually formed so as to cover the entire end face. . In the present invention, the passivation layer is formed by irradiating the end face with plasma in a vacuum and subsequently in a vacuum, that is, 10 ^-3 To ³
in a vacuum of about rr or less, preferably about 10 ^-6 Torr or less,
Most preferably, it is formed in a high vacuum of about 10 ⁻⁷ Torr or less. As the material of the passivation layer, Si, Ge, S, S
e, etc., among which Si is preferable, and it is preferable that 50 atomic% or more of Si is included in the passivation layer.

The Si deposited as a passivation layer (14) on the semiconductor end face has a crystallographically different structure and characteristics depending on the manufacturing method, but an effect is recognized in any of single crystal, polycrystal and amorphous. . Particularly preferably, amorphous Si formed at a low film formation rate in a high vacuum is used. In general, the absorption edge of Si differs depending on the film quality, but it is considered that the absorption edge is transparent for a wavelength of about 2 μm or more and does not absorb. Conversely, for wavelengths shorter than about 2 μm, the refractive index N of Si is N = n + ik, where n is the real part of the refractive index, k is the extinction coefficient, and n is about 3.5.

Generally, the thickness T of the passivation layer (14)
It is desirable that _p (nm) is thicker than 0.2 (nm).
However, on the other hand, an extremely thick film thickness, for example, 100 nm may not be suitable. The desirable thickness of the passivation layer (14) is defined by the lower limit based on the requirement that the passivation layer itself exists as a film, and the upper limit is defined by the fact that light emitted from the active layer is Si.
It is determined by the balance with the effect absorbed by. That is, the requirement that the end face be entirely covered with the passivation film and the effect of both sides such as the temperature rise of the end face due to the absorption of Si can be considered when Si is deposited on the end face. According to these experimental results, 0.2 (nm) <T _p (nm) <λ / 8n (nm) (I) (where, in the formula (I), n is the wavelength λ of the silicon layer) Represents the real part of the refractive index in the above.). However, the effect has been confirmed even when the thickness is 0.2 nm or less.

Further, on the passivation layer (14) formed on the exposed semiconductor end face, a coating layer (1) made of a laminated dielectric or a combination of a dielectric and a semiconductor is formed.
5) It is important to have (16). Particularly preferably, the ion irradiation on the end face, the formation of the passivation layer (14), and the formation of the coating layers (15) and (16) are continuously performed in a vacuum. This is mainly performed for the two purposes of increasing the efficiency of extracting light from the semiconductor laser and further protecting the end face. Particularly, in order to obtain a high output, an asymmetric coating is widely used, in which a coating having a low reflectance with respect to the oscillation wavelength is applied to the front end face, and a coating having a high reflectance is applied to the rear end face.

Various materials are used for this coating.
AlO_x, TiO_x, SiO_x, SiN,
One or more selected from the group consisting of Si and ZnS
The above combination is preferred, but as a low reflection coating
Is AlO_x, TiO_x, SiO _xEtc., also a high reflection coating
AlO_x/ Si multilayer, TiO_x/ Si
O_xIs used. Each film thickness is desired
Adjusted to achieve reflectivity. But in general
Is AlO for low reflection coating_x, TiO_x, Si
O_xAnd so on, where n is the real part of the bending ratio at the wavelength λ.
In general, the thickness is adjusted so as to be in the vicinity of / 4n.
is there. In addition, each material constituting the high-reflection multilayer film is λ
/ 4n is adjusted so that it is close to
The method of laminating according to is suitable.

In the method for producing the coating layers (15) and (16), a so-called IAD (Ion Assisted Depositio) is used.
The n) method is preferably used. This is a method in which ions having a certain energy are irradiated simultaneously with the vacuum deposition of the coating material, and ion irradiation with a rare gas is particularly preferable. Further, among rare gases, IAD by Ar ions has a great effect on improving the film quality of the coating material. In particular, the optimal condition for Ar ion irradiation is 25 e
V to about 300 eV, more preferably 50 eV to 2
This is to be used in a low energy range of about 00 eV, whereby coating can be performed without damaging the semiconductor end face. In addition, it is preferable to perform the treatment in a vacuum of about 10 ⁻³ Torr or less, more preferably about 10 ⁻⁴ Torr or less, and most preferably about 10 ⁻⁵ Torr or less.

[0046]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. Example 1 A groove type laser device shown in FIG. 2 was manufactured as follows.

Carrier concentration 1 × 10¹⁸cm^-3N-type Ga
On the (100) plane of the As substrate (1),
Carrier concentration 1 × 1 μm thick as buffer layer (2)
10 ¹⁸cm^-3N-type GaAs layer, first conductivity type cladding layer
(3) Carrier concentration of 1 × 10 with a thickness of 1.5 μm
¹⁸cm^-3N-type Al_0.35Ga_0.65As layer, then thickness 2
6n thickness on 4nm undoped GaAs light guide layer
m undoped In_{0. Two}Ga_0.8As single quantum well (S
QW), and further undoped Ga having a thickness of 24 nm
Active layer (4) having As light guide layer, second conductivity type first
0.1 μm thick clad layer (5), carrier concentration
1 × 10¹⁸cm^-3P-type Al_0.35Ga_{0. 65}As layer, second
10 nm-thick carrier as etching stop layer (6)
Concentration 1 × 10¹⁸cm^-3P-type GaAs layer, first etchin
20 nm thick and a carrier concentration of 5 × as a blocking layer (7).
10¹⁷cm^-3N-type In_0.49Ga_0.51P layer, current block
0.5 μm thick as carrier layer (9), carrier concentration 5 × 1
0¹⁷cm^-3N-type Al_0.39Ga_0.61As layer, cap layer
(10) thickness 10 nm, carrier concentration 1 × 10¹⁸
cm^-3N-type GaAs layers were sequentially laminated.

Next, a mask of silicon nitride was provided in a portion other than the uppermost current injection region. In this case, the width of the opening of the silicon nitride mask was 1.5 μm. First
Etching was performed using the etching stopper layer as an etching stop layer, and the cap layer (10) and the current block layer (9) in the current injection region were removed. The etchant used at this time was sulfuric acid (98 wt%), hydrogen peroxide (30 wt%).
% Aqueous solution) and water mixed at a volume ratio of 1: 1: 5, and performed at 25 ° C. for 30 seconds.

Next, HF (49%) and NH ₄ F (40
%) In an etching solution mixed at a ratio of 1: 6 to remove the silicon nitride layer by removing the silicon nitride layer for 2 minutes and 30 seconds, and further using the second etching stop layer (6) as an etching stop layer to stop the first etching in the current injection region. Layer (7) was etched away. The etchant used at this time was hydrochloric acid (35 wt.
%) And water at a ratio of 2: 1 at a temperature of 25%.
C. and the time was 2 minutes.

Thereafter, a carrier concentration of 1 × 10 ¹⁸ cm ^{−3 is formed} as the second conductive type second clad layer (8) by MOCVD.
The p-type Al _0.35 Ga _0.65 As layer is grown to a thickness of 1.5 μm at the buried portion (current injection region),
Finally, as a contact layer (11) for maintaining good contact with the electrode, a thickness of 7 μm and a carrier concentration of 1 × 10 ¹⁹
A p-type GaAs layer of cm ⁻³ was grown to form a laser device. The width W of the current injection region of this laser element, that is, the width of the second conductive type second cladding layer at the interface with the second etching stop layer was 2.2 μm.

On this wafer, AuGeNi / Au is deposited as an n-type electrode (13) on the substrate side, and Ti / Pt / Au is deposited on the p-side electrode (12), and an alloy is formed at 400 ° C. for 5 minutes. The wafer was completed. Subsequently, the substrate was cleaved in the atmosphere into a laser bar having a cavity length of 700 μm to expose the (110) plane, and the laser bar was placed in a vacuum chamber having an Ar plasma generator. 3x1
The end face (cleavage face) was irradiated with Ar plasma having an average energy of 60 eV and a current density of 150 μA / cm ² for 1 minute in a vacuum of 0 ⁻⁵ Torr. Continuously, 2 nm of amorphous Si is deposited on the end face in a vacuum of 2 × 10 ⁻⁷ Torr or less using a normal electron beam evaporation method to form a Si passivation layer (14).
Was formed. Further, the AlO _x film is continuously oscillated at an oscillation wavelength of 98
A 165 nm film was formed so that the reflectance of the front end face became 2.5% at 0 nm to form a coating layer (15). At the time of AlO _x film formation, I was formed in a vacuum of 4 × 10 ⁻⁵ Torr.
Average energy 120 eV, current density 2 using AD method
An Ar plasma of 00 μA / cm ² was irradiated simultaneously with the supply of AlO _{x to} the end face.

It has been confirmed that the real part of the refractive index of amorphous Si at 980 nm is about 3.4. Further, the laser bar was once taken out of the vacuum layer in order to perform the processing on the rear end face side. Ar plasma irradiation and the formation of the Si passivation layer (14) were performed on the rear end face in exactly the same manner as on the front end face, and further, the AlO _x film was continuously 170 nm / amorphous Si 60 nm / AlO _x film 170 nm / A coating layer (16) was formed by forming four continuous layers of amorphous Si with a thickness of 60 nm, and a rear end face having a reflectance of 92% was formed. Note that the AlO _x film is formed by the same IAD method as that for the front end face side.
The formation of i was performed by the same electron beam evaporation method as that on the front end face side.

One sample of this laser bar was subjected to XPS measurement for end face analysis. At this time, the take-out angle of the photoelectrons was set to 75 degrees, and the state of the end face of the semiconductor laser was observed. As a result, GaAs normally exposed once to the atmosphere
Neither Ga-O nor As-O existing on the s (110) plane was detected at all. Also, one device was taken out from this laser bar as a sample for analysis, and Al on the front end face was
The O _x layer and the Si layer placed in a vacuum analyzer after removing an etchant of hydrofluoric acid was measured band gap of the front end surface near the active layer using electron energy loss spectroscopy.
Since electron energy loss spectroscopy is an analysis method that obtains information only near the sample surface (maximum analysis depth of about 1.5 nm), it is a powerful method for measuring the band gap of the laser end face without being affected by the physical properties of the bulk region. It is an effective method. 1
When an electron beam of 1000 eV focused on about 00 nmφ is irradiated near the active layer on the laser end face, the energy of the loss electron diffracted from a region 1 nm deep from the end face of the semiconductor itself behind the surface oxide layer was analyzed. From the loss peak due to the inter-transition, the band gap near the end face of the InGaAs quantum well layer was measured to be 1.5 eV, and the band gap near the end face of the GaAs light guide layer was measured to be 1.65 eV. Room temperature InG determined from photoluminescence measurements
Since the energy gap between the quantum levels of the aAs quantum well active layer is 1.29 eV, and the band gap of GaAs is 1.41 eV, the band gap near the end face is widened by Ar plasma irradiation, and the end face has an oscillation wavelength. It was confirmed that it was transparent.

Further, 10 devices were placed on the heat-dissipating submount from the laser bar and packaged in a nitrogen atmosphere. As the average initial characteristics of the device, the threshold current was 23 mA at 25 ° C., and kink was observed at 350 mA and 250 mW. A life test was performed on this population. As a result of an acceleration test at 200 mW and 50 ° C., FIG.
As shown in the figure, there was no sudden death at the time of lapse of 2000 hours, and stable operation was confirmed. One of the fabricated devices was processed into a sample for observation with a transmission electron microscope (TEM), and the state of the bulk near the active layer near the end face was compared with that of the sample. As a result, it was confirmed that in the vicinity of the end face irradiated with the Ar plasma, the crystallinity in the vicinity of the active layer was broken and disorder occurred.

(Example 2) The coating layer on the rear end face was
SiO formed by the same IAD method as the front end side _xMembrane
200nm / TiO_xIs 120 nm / SiO_x200 membranes
nm / TiO_xIs 120 nm / SiO_x200 nm /
TiO_xIs a continuous layer of 120 nm, and has a reflectance of 88.
% In the same manner as in Example 1 except that
A laser bar was prepared. One sample of this laser bar
XPS for end face analysis exactly as in Example 1
As a result of measurement, both Ga-O and As-O
Not detected.

Further, one device was taken out from this laser bar as an analysis sample, and the energy of the lost electrons was analyzed in the same manner as in Example 1. From the loss peak due to the interband transition, the energy near the edge of the InGaAs quantum well layer was found. The band gap was measured to be 1.5 eV, and the band gap near the end face of the GaAs light guide layer was measured to be 1.65 eV. Room temperature InG determined from photoluminescence measurements
Since the energy gap between the quantum levels of the aAs quantum well active layer is 1.29 eV and the band gap of GaAs is 1.41 eV, the band gap near the end face is widened by the Ar plasma irradiation, and the end face has an oscillation wavelength. It was confirmed that it was transparent.

Further, 5 devices were taken out of the laser bar as life test samples separately from the analysis samples, mounted on a heat radiating submount, and packaged in a nitrogen atmosphere. The average initial characteristics of the device are that the threshold current is 25 mA at 25 ° C., 359 mA, 2
Kink was observed at 40 mW. As a result of a life test at 200 mW and 50 ° C. performed on this group, as shown in FIG. 4, there was no sudden death when 2000 hrs had elapsed, and stable operation was confirmed. When one of the fabricated devices was observed with a TEM in exactly the same manner as in Example 1, Ar
In the vicinity of the end face irradiated with the plasma, it was confirmed that the crystallinity in the vicinity of the active layer was broken and disorder occurred.

(Comparative Example 1) Both the front end face and the rear end face
Example 1 was the same as Example 1 except that the formation of the passivation layer and the Ar plasma irradiation prior to it were not performed, and the formation of the coating layer was performed not by the IAD method but by a normal electron beam evaporation method in all layers. When completely the same, the average initial characteristics of the device were 25 ° C. as in the example.
And the threshold current is 23 mA, 350 mA, 250 mW
Kink was observed in the test, but the life test (200 mW, 50
C), all 10 devices died suddenly by 100 hrs as shown in FIG. In addition, XPS analysis, electron energy loss spectroscopy analysis, and TEM observation were performed in exactly the same manner as in Example 1 to confirm that Ga—O was present at the end face, and that the band gaps of the quantum well layer and the optical guide layer were bulky even near the end face. It was confirmed that the crystal was similar to the region, and that the appearance of the crystal near the end face was similar to that of the single crystal in the bulk region.

(Comparative Example 2) Both the front end face and the rear end face
Except that the passivation layer was not formed, the same procedure as in Example 1 was carried out. The average initial characteristics of the device were that the threshold current was 23 mA at 25 ° C., 350 mA,
A kink was observed at 250 mW. This was the same result as in Example 1. However, a life test (200 mW, 50 ° C.) performed on a group of 10
Sudden death at the time when 000 hrs passed, as shown in FIG.
Six devices were confirmed. In addition, the deterioration rate was higher than that of the first embodiment.

(Comparative Example 3) Both the front end face and the rear end face
Except that the Ar plasma irradiation prior to the formation of the passivation layer was not performed, the same procedure as in Example 1 was performed. The average initial characteristics of the device were as follows.
3 mA, and kink was observed at 350 mA and 250 mW. This was the same result as in Example 1. However, a life test (200 mW, 50 ° C.) performed on a group of 10 devices of the same number as in Example 1, as shown in FIG.
All devices died suddenly after 250 hrs. In addition, XPS analysis, electron energy loss spectroscopy analysis, and TEM observation were performed in exactly the same manner as in Example 1 to confirm that Ga—O was present at the end face, and that the band gaps of the quantum well layer and the optical guide layer were bulky even near the end face. It was confirmed that the crystal was similar to the region, and that the appearance of the crystal near the end face was similar to that of the single crystal in the bulk region.

(Comparative Example 4) Both the front end face and the rear end face
Except that the formation of the passivation layer and the prior Ar plasma irradiation were not performed, the procedure was the same as in Example 2 except that InGa measured by electron energy loss spectroscopy was used.
The band gap at the end face of the As quantum well active layer is 1.28 e.
V was almost the same as the value of the bulk region measured by photoluminescence. As shown in FIG. 8, the results of the life test showed that all of the five devices died suddenly after 100 hours. In addition, the XP
S analysis and TEM observation confirmed that Ga—O was present on the end face and that the appearance of the crystal near the end face was the same as that of the single crystal in the bulk region.

[0062]

According to the present invention, light absorption at the end face of a semiconductor light emitting element such as a semiconductor laser is stably suppressed for a long period of time by employing a window structure, and the passivation layer is made of a dielectric material or a semiconductor material. A semiconductor light-emitting element that realizes a stable end face for a long period of time and that operates stably even when diffusion of a passivation layer occurs can be realized by a simple method And provide a great industrial benefit.

[Brief description of the drawings]

FIG. 1 is a perspective view of a semiconductor light emitting device of the present invention.

FIG. 2 is an explanatory cross-sectional view of the semiconductor laser according to the first embodiment of the present invention as viewed from the direction of the resonator.

FIG. 3 shows a life test (2) of the semiconductor laser according to the first embodiment of the present invention.
00mW constant output, 50 ° C.).

FIG. 4 shows a life test (2) of a semiconductor laser according to a second embodiment of the present invention.
00mW constant output, 50 ° C.).

FIG. 5 shows a life test (2) of a semiconductor laser of Comparative Example 1 of the present invention.
00mW constant output, 50 ° C.).

FIG. 6 shows a life test (2) of a semiconductor laser of Comparative Example 2 of the present invention.
00mW constant output, 50 ° C.).

FIG. 7 shows a life test (2) of a semiconductor laser of Comparative Example 3 of the present invention.
00mW constant output, 50 ° C.).

FIG. 8 shows a life test (2) of a semiconductor laser of Comparative Example 4 of the present invention.
00mW constant output, 50 ° C.).

[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 stop layer 7: first etching stop layer 8: second conductivity type Nicladding layer 9: Current blocking layer
10: Cap layer 11: Contact layer 12: Electrode
13: electrode 14: passivation layer 15: coating layer 16: coating layer

Claims (12)

[Claims] 1. An oscillation wavelength λ (nm) in which at least a first conductivity type clad layer, an active layer, and a second conductivity type clad layer are laminated on a substrate, and two opposing end faces form a resonator structure. Wherein the surfaces of the first conductivity type cladding layer, the active layer and the second conductivity type cladding layer forming the end face are covered with a passivation layer and the active layer near the end face. Is a compound semiconductor light-emitting device, which is transparent to an oscillation wavelength λ. 2. The method according to claim 1, wherein the passivation layer has a thickness T _p (nm)
2. The compound semiconductor light emitting device according to claim 1, wherein the following formula (I) is satisfied, where n is a real part of the refractive index at a wavelength λ (nm) of the passivation layer. 0.2 (nm) <T _p (nm) <λ / 8n (nm) (I) 3. The compound semiconductor light emitting device according to claim 1, wherein said passivation layer surface is covered with a coating layer comprising a dielectric or a combination of a dielectric and a semiconductor. 4. The method according to claim 1, wherein the coating layer is made of AlO _x , Ti
O _x, SiO _x, SiN, alone is selected from the group consisting of Si and ZnS or a compound semiconductor light-emitting device according to any one of claims 1 to 3, characterized in that it consists of a combination thereof. 5. The compound semiconductor light emitting device according to claim 1, wherein said coating layer includes a low reflection coating layer and a high reflection coating layer. 6. The compound semiconductor light emitting device according to claim 5, wherein said low reflection coating layer contains AlO _x , and said high reflection layer contains AlO _x and Si. 7. The compound semiconductor light emitting device according to claim 1, wherein said active layer contains In. 8. The method according to claim 1, wherein the active layer is formed of In._xGa_1-xAs (0 <
x <1) or (Al _xGa_1-x)_yIn_1-yP (0 <x, y
The compound according to claim 7, which comprises <1).
Conductive light emitting element. 9. The compound semiconductor light emitting device according to claim 1, wherein the vicinity of the cavity end face is disordered. 10. The compound semiconductor light emitting device according to claim 1, wherein said active layer has a quantum well structure. 11. The resonator formed by the end face is (110).
The compound semiconductor light-emitting device according to claim 1, wherein the compound semiconductor light-emitting device is a plane or a plane crystallographically equivalent to the plane. 12. The compound semiconductor light emitting device according to claim 1, wherein said passivation layer contains Si.