JP2012069970A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device having high reliability.SOLUTION: A semiconductor device comprises: an n-type cladding layer 13 provided above a substrate 11; an n-type guide layer 14 provided on the n-type cladding layer 13; an active layer 15 provided on the n-type guide layer 14; a first p-type guide layer 16 provided on the active layer 15; an overflow prevention layer 17 provided on the first p-type guide layer 16; a second p-type guide layer 18 provided on the overflow prevention layer 17; and a p-type cladding layer 19 provided on the second p-type guide layer 18. Each of the layers includes a laser diode composed of a Group III-V nitride-based compound semiconductor, a first protective layer 51 of aluminum-containing nitride provided on the emission surface of the laser diode, and a second protective layer 52 of silicon-containing nitride that is provided on the first protective layer 51 and has a different refractive index from the first protective layer 51. The film thickness of the first protective layer and the second protective layer ranges from 0.25 nm or more to 50 nm or less respectively.

Description

  The present invention relates to a semiconductor device, and more particularly to a gallium nitride based semiconductor device.

  Nitride III-V compound semiconductors such as gallium nitride (GaN) are semiconductors with a wide band gap, and high-intensity ultraviolet to blue / green light-emitting diodes and blue-violet laser diodes have been studied and utilized. Has been developed. In addition, high-frequency and high-power field-effect transistors using nitride-based III-V group compound semiconductors have been produced.

The device layer structure of the III-V compound semiconductor is formed by crystal growth. In general, the surface of a semiconductor crystal is not directly exposed to the atmosphere or the like, but is covered with an electrode such as a metal or a protective film such as Al ₂ O ₃ or SiO ₂ , and these protective films prevent deterioration of element characteristics. . Considering a laser diode as an example, the reflecting mirror is formed by a cleaved end face. Usually, if the cleaved end face is not provided with any protective film, the refractive index changes due to contamination by moisture, organic matter, inorganic matter, etc., and the reflectance changes. If the reflectance fluctuates, the characteristics of the laser diode will change, degrading device reliability. From the knowledge of laser diodes using GaAs-based or InGaAlP-based materials, Al ₂ O ₃ films have often been used as cleaved end face protective films (see Non-Patent Document 1).

However, when the present inventors manufactured a blue-violet laser diode using a nitride-based III-V group compound semiconductor, when Al ₂ O ₃ was used for the cleaved end face protective film, it was necessary for writing at a high speed disk. The device life was about 700 hours in a continuous oscillation state with an optical output of 60 mW (optical output of 120 mW in the pulse oscillation state). Observation of the end face of this device with an electron microscope revealed that the end face was altered. This is because the blue-violet laser has a shorter photon wavelength than the GaAs near-infrared laser or InGaAlP-based red laser, resulting in higher photon energy, resulting in damage to the Al ₂ O ₃ protective film. It is considered a thing.

On the other hand, the cavity end face of the laser diode made of a nitride semiconductor, a SiN film is formed to a thickness of about 1 nm, a low reflection _coating, a highly reflective coating of SiO 2 / TiO ₂ subjected consisting SiO _2, the light output 1 mW, the operating temperature A technique for improving the lifetime to several hundred hours at 50 ° C. has been devised (see Patent Document 1). However, with this method, the lifetime was not improved at a high light output of 60 mW in the continuous oscillation state (120 mW in the pulse oscillation state).

In addition, a technique is known in which an end face film made of single crystal Al _x Ga _1-x N (0 ≦ x ≦ 1) is formed on a resonator end face of a laser element made of a nitride semiconductor (for example, Patent Document 2). reference). However, since the temperature is raised in the single crystal manufacturing apparatus before the single crystal film is formed on the end face of the element, oxygen remaining in the manufacturing apparatus reacts with the end face of the semiconductor element and is oxidized. As a result, the end face of the nitride semiconductor element deteriorates, and there is a problem that the reliability of the semiconductor element cannot be increased even if an end face film is formed on the end face.
K. Itaya et al., “Effect of facet coating on the reliability of InGaAlP visible light laser diodes”, Applied Physics Letters, Oct. 10, 1988, Vol. 1363-1365. JP 2002-237648 A International Publication No. 03/036731 Pamphlet

  As described above, conventionally, it has been difficult to obtain a semiconductor element including a highly reliable nitride III-V compound semiconductor layer.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor element including a highly reliable nitride III-V compound semiconductor layer.

  A semiconductor device according to a first aspect of the present invention includes a substrate, an n-type cladding layer provided on the substrate, an n-type guide layer provided on the n-type cladding layer, and the n-type guide layer. An active layer provided on the active layer, a first p-type guide layer provided on the active layer, an overflow prevention layer provided on the first p-type guide layer, and provided on the overflow prevention layer A laser having a second p-type guide layer formed and a p-type clad layer provided on the second p-type guide layer, each of which is made of a nitride III-V compound semiconductor A diode, a first protective layer of nitride containing aluminum provided on the emission surface of the laser diode, and silicon having a refractive index different from that of the first protective layer provided on the first protective layer. A second protective layer of nitride comprising Said first protective layer, the thickness of the second protective layer, respectively, characterized in that at 50nm or less than 0.25 nm.

  ADVANTAGE OF THE INVENTION According to this invention, the semiconductor element provided with the nitride type III-V group compound semiconductor layer with high reliability can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
A cross section of the semiconductor device according to the first embodiment of the present invention is shown in FIG. The semiconductor element of this embodiment is formed as follows.

  First, an n-type semiconductor layer (n-type GaN buffer layer) 12 doped with an n-type impurity is crystal-grown on an n-type GaN {0001} substrate 11. For crystal growth, metal organic chemical vapor deposition (MOCVD) is used, but molecular beam epitaxy (MBE) may be used. Si, Ge, or the like may be used as the n-type impurity, and Si is used in this embodiment. The parentheses {} represent a plane, and the {1-100} plane will be described as an example. The {1-100} plane means the (1-100) plane, and the (1-100) plane (10 −10), (−1100), (−1010), (01-10), and (0-110) are equivalent to planes, and {1-100} for convenience in order to comprehensively define these planes Use notation. Here,-(bar) is a symbol used in association with the immediately following number. This symbol also means the same for the direction described later.

An n-type cladding layer 13 is grown on the n-type GaN buffer layer 12. The n-type cladding layer 13 is a superlattice composed of an undoped Ga _0.9 Al _0.1 N layer and a GaN layer doped with n-type impurities at about 1 × 10 ¹⁸ cm ⁻³ . The n-type cladding layer 13 is not limited to this, and may be a thick film (thickness of about 1.5 μm) doped with an n-type impurity made of Ga _0.95 Al _0.05 N, for example. Moreover, although a superlattice composed of an undoped Ga _0.9 Al _0.1 N layer and a GaN layer doped with n-type impurities of about 1 × 10 ¹⁸ cm ⁻³ was used, Ga _0.9 Al _0.1 Both the N layer and the GaN layer may be doped with n-type impurities.

On the n-type cladding layer 13, an n-type guide layer 14 made of GaN having a thickness of about 0.1 μm doped with n-type impurities of about 1 × 10 ¹⁸ cm ⁻³ is grown. Further, In _0.01 Ga _0.99 N having a film thickness of about 0.1 μm may be used as the n-type guide layer 14.

An active layer 15 is grown on the n-type guide layer 14. This active layer 15 includes three quantum well layers composed of an undoped In _0.1 Ga _0.9 N layer having a thickness of about 3.5 nm, and an undoped In _0. A multiple quantum well (MQW) structure in which barrier layers made of ₀₁ Ga _0.99 N layers are alternately stacked is used.

  A first guide layer 16 made of p-type GaN is grown on the active layer 15. The first guide layer 16 may have a thickness of 0.03 μm.

Overflow prevention layer 17 is grown on first guide layer 16. The overflow prevention layer 17 is composed of a Ga _0.8 Al _0.2 N layer having a thickness of about 10 nm doped with a p-type impurity element to about 5 × 10 ¹⁸ cm ⁻³ , and is a layer that prevents an overflow of electrons. is there. As the p-type impurity, Mg, Zn or the like may be used. In this case, Mg is used.

A second guide layer 18 made of p-type GaN is grown on the overflow prevention layer 17. In the present embodiment, the second guide layer 18 is a GaN layer having a thickness of about 0.1 μm doped with a p-type impurity element of about 5 × 10 ¹⁸ cm ⁻³ to 10 × 10 ¹⁸ cm ⁻³ . More generally, however, a p-type nitride-based III-V group compound semiconductor layer such as In _x Ga _1-xy Al _y N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) may be used. Is possible.

A p-type cladding layer 19 is grown on the second guide layer 18. In this embodiment, the p-type cladding layer 19 is a superlattice composed of an undoped Ga _0.9 Al _0.1 N layer and GaN doped with a p-type impurity. However, the present invention is not limited to this, and a thick film (thickness of about 0.6 μm) doped with a p-type impurity made of Ga _0.95 Al _0.05 N, for example, may be used. In addition, although a superlattice composed of undoped Ga _0.9 Al _0.1 N and GaN doped with a p-type impurity is used, p-type impurities are present in both Ga _0.9 Al _0.1 N and GaN. May be doped.

A contact layer 20 made of p-type GaN is grown on the p-type cladding layer 19. In the present embodiment, the contact layer 20 is a GaN layer having a thickness of about 0.1 μm doped with p-type impurities, but In _x Ga _1-xy Al _y N (0 ≦ x ≦ 1, 0 ≦). A layer doped with a p-type impurity such as y ≦ 1) may be used.

  A laser diode is manufactured through the device process for the wafer thus crystal-grown.

  As shown in FIG. 1, the stacked structure of the p-type cladding layer 19 and the p-type contact layer 20 has a convex portion including the p-type cladding layer 19 and the p-type contact layer 20 at the center. The flat portion in the periphery of the p-type cladding layer 19 is configured. That is, a step structure (ridge structure) composed of a convex portion and a flat portion is formed. The convex laminated structure formed by the p-type cladding layer 19 and the p-type GaN contact layer 20 extends in the direction perpendicular to the paper surface, and becomes a resonator.

In addition, as shown in FIG. 1, a convex laminated structure is not limited to the rectangle which a cross section has a perpendicular | vertical side wall, You may have a mesa-shaped slope and may make a trapezoid convex part. The p-type contact layer 20 has a width (ridge width) of about 2 μm. Here, the resonator direction (perpendicular to the paper surface) is aligned with the <1-100> direction of the nitride III-V compound semiconductor. Here, the <1-100> direction means the direction [1-100], and the [1-100] direction means [10-10], [-1100], [-1010], [01]. −10] and [0-110], and in order to comprehensively define these directions, the notation <1-100> is used for convenience.

A current blocking layer 41 made of an insulating film is formed on the p-type cladding layer 19 serving as a flat portion around the side surface of the protruding portion and the periphery of the protruding portion. The mode is controlled. The thickness of the current blocking layer 41 can be arbitrarily selected depending on the design, but may be set to a value of about 0.3 μm to 0.6 μm, for example, about 0.5 μm. The current blocking layer 41 may be a high specific resistance semiconductor film such as an AlN film or a Ga _0.8 Al _0.2 N film. A semiconductor film irradiated with protons, a silicon oxide film (SiO ₂ film), an oxidation film, etc. A zirconium film (ZrO ₂ film) or the like can be used. Furthermore, for example, a multilayer film made of a SiO ₂ film and a ZrO ₂ film may be used. That is, as the current blocking layer 41, various materials can be adopted as long as the refractive index is lower than that of the nitride-based III-V compound semiconductor used for the active layer 15. In addition to the ridge waveguide laser structure of the present embodiment, an n-type semiconductor layer such as n-type GaN or n-type GaAlN is used instead of the insulating film, and the pn junction is separated to function as a current blocking layer. An embedded laser structure may be used.

  On the p-type GaN contact layer 20, a p-side electrode 32 made of, for example, a composite film (laminated film) of palladium / platinum / gold (Pd / Pt / Au) is disposed. For example, the Pd film has a thickness of 0.05 μm, the Pt film has a thickness of 0.05 μm, and the Au film has a thickness of 1.0 μm. On the back surface of the n-type GaN substrate 11, an n-side electrode 31 made of a composite film (laminated film) of titanium / platinum / gold (Ti / Pt / Au) or the like is provided. The n-side electrode 31 can be composed of, for example, a Ti film having a thickness of 0.05 μm, a Pt film having a thickness of 0.05 μm, and an Au film having a thickness of 1.0 μm.

  The resonator is formed using cleavage. That is, the cleaved end faces are on both sides of the resonator end, and function as a laser reflecting mirror. Here, the cleavage plane is the {1-100} plane of the nitride III-V compound semiconductor. For example, the resonator length may be 600 μm.

If the cleaved end face is left as it is, it is contaminated by the atmosphere, organic matter, and inorganic matter. Even if it can be sealed in a package with little influence of contamination on the end face, when the laser diode is energized and begins to emit laser light, it is induced by the laser light and organic and inorganic substances gather on the end face. come. Therefore, some kind of protective film is necessary on the cleavage end face of the nitride III-V compound semiconductor. In the present embodiment, as shown in FIG. 2, as the protective film 50, an AlN layer 51 is formed on the {1-100} plane of a nitride III-V compound semiconductor, and then Si ₃ N having a refractive index different from that of AlN. ₄ (silicon nitride) layer 52 was formed. Here, ECR (Electron Cyclotron Resonance) sputtering was used to form AlN and Si ₃ N ₄ . However, the method for forming the protective film made of nitride is not limited to the ECR sputtering method, and other film forming methods can be selected.

  The cleaved end face usually has a laser light extraction face (exit face) and a reflection face. The protective film made of nitride may be formed on one or both of the emission surface and the reflection surface. Preferably, a protective film made of nitride is formed on the emission surface.

  The oscillation wavelength of the blue-violet laser diode in this embodiment is designed to be 405 nm.

Refractive index _{n AlN} of AlN at a wavelength of 405nm is 2.16, the refractive index _{n Si3 N4} of _Si 3 _{N 4} is 2.06. When the AlN film thickness is fixed at 0.25 nm and the Si ₃ N ₄ film thickness is changed, the reflectance at the exit surface is calculated as shown in FIG. For example, the reflectance is designed to be 10% on the emission surface. For this purpose, as shown in FIG. 3, when the film thickness of AlN is 0.25 nm, the film thickness of Si ₃ N ₄ may be 32 nm. When AlN is formed on the reflecting surface, the reflectance is about 95% on the reflecting surface. Therefore, AlN and Si ₃ N ₄ are formed at a thickness of about 0.25 nm, and SiO ₂ and ZrO ₂ , SiO ₂ and Si are formed. _A dielectric film having a different refractive index, such as ₃ N _4, may be formed into a multilayer.

The threshold current of the semiconductor device (laser diode) according to the present embodiment was 30 mA on average. At this time, the reflectance at the exit surface was 10%, the thickness of the AlN layer 51 was 0.25 nm, and the thickness of the Si ₃ N ₄ layer 52 was 32 nm.

As a first comparative example, a laser diode having the same configuration as that of this embodiment except for the material of the end face protective film was manufactured. The end face protective film of the laser diode of the first comparative example is made of Al ₂ O ₃ formed so that the reflectance is 10%. In the laser diode of this comparative example, the average threshold current was 30 mA. As long as the initial characteristics are observed in this way, neither the first comparative example nor the present embodiment has changed.

Therefore, a life test of the laser diode at a constant light output was performed. The change in operating current in an optical output of 60 mW, an operating temperature of 60 ° C., and a continuous oscillation state was examined, and the point where the operating current increased by 20% was defined as the lifetime. The laser diode of the first comparative example had an average lifetime of 700 hours. However, as in this embodiment, in the laser diode in which the end face protective film 50 is composed of the AlN layer 51 and the Si ₃ N ₄ layer 52, the lifetime is greatly improved to an average of 4000 hours or more.

  Since AlN is a single crystal and has a very large band gap energy of 6.2 eV (200 nm in terms of wavelength), it is considered that deterioration due to light absorption is unlikely to occur in the end face protective film with a laser beam having a wavelength of 405 nm. AlN is a material having a very high thermal conductivity. By forming the AlN protective film on the end face of the semiconductor element, heat generated in the semiconductor element can be efficiently released. On the other hand, in a semiconductor element made of a nitride semiconductor, since the AlN formed on the end face is also a nitride semiconductor, the stoichiometry (composition ratio) of the end face is not easily broken. Further, in the film formation in ECR sputtering, when the film formation temperature of AlN is lowered from room temperature to room temperature, a semiconductor element made of a nitride-based III-V compound semiconductor single crystal, and an AlN end face protective film on the {1-100} plane From the difference in the linear expansion coefficient, the {1-100} plane of the semiconductor element is distorted, and the band gap energy at the end face is changed, thereby suppressing the light absorption at the end face.

Further, by forming Si ₃ N ₄ on the end face protective film AlN, it is more effective than SiN against contaminants such as organic matter and inorganic matter that are present in the package and are gathered at the end face induced by laser light. ₃ N ₄ is stronger in preventing the adsorption of these contaminants, and the deterioration of the end face is dramatically suppressed.

Further, Si ₃ N ₄ is one of nitride films having strong oxidation resistance, and the Si ₃ N ₄ protective film is not altered by O (oxygen) remaining in the package in the packaged semiconductor element. . Since AlN is a nitride film that easily oxidizes to some extent, when only AlN is used as the protective film on the semiconductor element end face, oxygen remaining in the package generates AlNO _x and reacts with the end face of the laser diode. As a result, it is considered that the reflectance of the end face varies and the light absorption layer is formed, and the reliability of the laser diode is impaired. Therefore, also in the meaning of realizing the reliability of the semiconductor element in the medium and long term, it is necessary to use the end face protective film 50 having a multilayer structure using AlN as the first protective layer and Si ₃ N ₄ as the second protective layer. preferable.

On the other hand, as a second comparative example, an end face protective film having a first protective layer made of AlN formed so as to be in contact with the nitride semiconductor and having a reflectance of 10%, and a _second protective layer made of SiO ₂ Was formed. The laser diode of the second comparative example has the same configuration as that of this embodiment except for the material of the end face protective film. Also in the laser diode of the second comparative example, the average threshold current was about 30 mA. However, the light output is 60 mW, the operating temperature is 60 ° C., and the lifetime in the continuous oscillation state is about 900 hours, which is a slight improvement over the laser diode of the first comparative example in which the end face protective film is a single layer film made of Al ₂ O _3. It was seen. It is considered that heat generated in the semiconductor element could be efficiently released by using AlN as the first protective layer. However, oxygen, which is a constituent element of SiO _{2 serving} as the second protective layer, reacts with AlN to generate AlNO _x and reacts with the end face of the laser diode. As a result, it is considered that the reflectance of the end face varies and the light absorption layer is formed, and the reliability of the laser diode is impaired.

  As described above, according to the present embodiment, in a semiconductor device made of a nitride-based III-V compound semiconductor on a GaN substrate, a plurality of nitrides having different refractive indexes are formed on the {1-100} plane. By forming the protective film, it is possible to prevent the {1-100} plane from being deteriorated, and a highly reliable semiconductor element can be provided.

(Modification)
Further, as a modification of the present embodiment, when forming the laser diode of the present embodiment, a laser in which an end surface is subjected to nitrogen plasma treatment in an ECR sputtering apparatus before forming a protective film made of nitride on the end surface. A diode was fabricated. The laser diode of this modified example has a lifetime of 5000 hours or more under the same conditions as in the above test, that is, the conditions of continuous oscillation at an optical output of 60 mW and an operating temperature of 60 ° C., which is a much improved improvement over the case of this embodiment. . This is considered to be due to the function of recovering the N stoichiometry separated from the {1-100} plane.

  Note that it is not preferable to raise the temperature to a temperature exceeding 400 ° C. when the end face is subjected to nitrogen plasma treatment. This is because, by raising the temperature before forming the protective film in the nitrogen plasma processing apparatus, oxygen remaining in the apparatus reacts with the end face and is oxidized. As a result, the end face of the nitride semiconductor element is deteriorated, so that even if a protective film is formed thereon, it becomes difficult to achieve high reliability of the semiconductor element.

(Second Embodiment)
Next, FIG. 4 shows a semiconductor device according to the second embodiment of the present invention.

  The semiconductor element of this embodiment is manufactured as follows.

  First, an n-type semiconductor layer (n-type GaN buffer layer) 112 doped with an n-type impurity is first grown on a {0001} substrate 111 made of n-type GaN. For the crystal growth, metal organic chemical vapor deposition (MOCVD) was used, but molecular beam epitaxy (MBE) may be used. For the n-type impurity, Si, Ge, or the like may be used. In this case, Si is used.

An n-type guide layer 113 is grown on the buffer layer 112. The n-type guide layer 13 is made of GaN having a film thickness of about 0.1 μm doped with n-type impurities of about 1 × 10 ¹⁸ cm ⁻³ . Further, In _0.01 Ga _0.99 N having a thickness of about 0.1 μm may be used as the n-type guide layer 113. Note that an n-type cladding layer made of, for example, Ga _0.95 Al _0.05 N and having a thickness of about 1 μm may be grown between the buffer layer 112 and the n-type guide layer 113.

An active layer 114 is grown on the n-type guide layer 113. This active layer includes three quantum well layers composed of an undoped In _0.1 Ga _0.9 N layer having a thickness of about 3.5 nm and an undoped In _{0.01 having a} thickness of about 7 nm sandwiching the quantum well. It has a multiple quantum well (MQW) structure in which barrier layers made of Ga _0.99 N layers are alternately stacked. In the present embodiment, the light emission wavelength of the multiple quantum well structure is designed to be 405 nm, but it can be changed between 380 nm and 550 nm by changing the In composition and film thickness of the quantum well layer and the barrier layer. Is possible.

  A first guide layer 115 made of p-type GaN is grown on the active layer 114. The first guide layer 115 may be formed to a thickness of 0.03 μm.

Overflow prevention layer 116 is grown on first guide layer 115. This overflow prevention layer 116 is made of a Ga _0.8 Al _0.2 N layer having a thickness of about 10 nm doped with a p-type impurity element to about 5 × 10 ¹⁸ cm ⁻³ and prevents overflow of electrons. Is a layer. As the p-type impurity, Mg, Zn or the like may be used, and Mg is used in this embodiment.

A second guide layer 117 made of p-type GaN was grown on the overflow prevention layer 116. In the present embodiment, the second guide layer 117 is a GaN layer having a thickness of about 0.1 μm doped with a p-type impurity element of about 5 × 10 ¹⁸ cm ⁻³ to 10 × 10 ¹⁸ cm ⁻³ . More generally, a p-type nitride III-V group compound semiconductor layer such as In _x Ga _1-xy Al _y N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) can be formed. is there.

A p-type cladding layer 118 is grown on the second guide layer 117. The p-type cladding layer 118 is a superlattice composed of an undoped Ga _0.9 Al _0.1 N layer and GaN doped with a p-type impurity, but is not limited to this. For example, Ga _0.95 Al A thick film (thickness of about 0.3 μm) doped with _0.05 N p-type impurities may be used. In the present embodiment, a superlattice made of undoped Ga _0.9 Al _0.1 N and GaN doped with p-type impurities is used, but both Ga _0.9 Al _0.1 N and GaN are used. A p-type impurity may be doped. Furthermore, GaN having a thickness of about 0.3 μm doped with p-type impurities may be used. Note that the p-type cladding layer 118 may be omitted as necessary.

A contact layer 119 made of p-type GaN is grown on the p-type cladding layer 118. The contact layer 119 is a GaN layer having a thickness of about 0.1 μm doped with a p-type impurity, but In _x Ga _1-xy Al _y N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). A layer doped with a p-type impurity such as may be used.

  A light-emitting diode is manufactured through the device process for the wafer thus crystal-grown.

  As shown in FIG. 4, on the p-type GaN contact layer 119, for example, a p-side electrode 132 made of a composite film of palladium / platinum / gold (Pd / Pt / Au) is disposed. For example, the Pd film has a thickness of 0.05 μm, the Pt film has a thickness of 0.05 μm, and the Au film has a thickness of 1.0 μm.

  An n-side electrode 131 made of a titanium / platinum / gold (Ti / Pt / Au) composite film or the like is formed on the back surface of the n-type GaN substrate 111. The n-side electrode can be composed of, for example, a Ti film having a thickness of 0.05 μm, a Pt film having a thickness of 0.05 μm, and an Au film having a thickness of 1.0 μm.

  By cleaving or dicing, {1-100} end faces and {11-20} end faces of the semiconductor elements are formed, and the elements are separated. If the end face is left as it is, it is contaminated by the atmosphere, organic matter, and inorganic matter. Even if the package can be sealed with little influence of contamination on the end face, if light is applied to the light emitting diode and laser light starts to be emitted, the light is induced to collect organic or inorganic substances on the end face. . Therefore, some kind of protective film is necessary on the end face of the nitride III-V compound semiconductor.

Therefore, similarly to the first embodiment, the first protective layer made of AlN is formed on the {1-100} plane of the nitride-based III-V compound semiconductor, and then Si ₃ N ₄ having a refractive index different from that of AlN. The 2nd protective layer which consists of was formed. Here, ECR (Electron Cyclotron Resonance) sputtering was used to form AlN and Si ₃ N ₄ . However, the method for forming the protective film made of nitride is not limited to the ECR sputtering method, and other film forming methods can be selected.

Regarding the film thickness of the protective film formed on the end face, various film thicknesses can be selected according to the desired reflectance as shown in FIG. 3, for example. For example, when the film thickness of AlN is 0.25 nm and the film thickness of Si ₃ N ₄ is 50 nm, the reflectance can be reduced to the minimum and the light extraction efficiency can be improved. Further, after forming a film thickness of AlN of 0.25 nm and a film thickness of Si ₃ N ₄ of 0.25 nm, a dielectric film having different refractive indexes, such as SiO ₂ and ZrO ₂ , SiO ₂ and Si ₃ N _4, etc. is made into a multilayer. Thus, the reflectance of the end face may be improved to 90% or more so that light is not emitted from the end face, and the light may be extracted from the front surface or the back surface on which the electrode is formed.

As in the present embodiment, the lifetime of the light emitting diode having the protective film including the first protective layer made of AlN and the second protective layer made of Si ₃ N ₄ was 3000 hours or longer. Here, the lifetime was constant at an operating current of 350 mA, and was defined as the time until the light output decreased to 90% of the initial value.

As a comparative example, a light emitting diode having the same configuration as that of the present embodiment was manufactured except that the end face protective film was Al ₂ O ₃ . The life of the light emitting diode of this comparative example was about 1500 hours.

As in the first embodiment, the first protective layer is made of AlN and the second protective layer is made of Si ₃ N ₄ , so that heat generated inside the semiconductor element can be efficiently released to the submount and protected. This is probably because the film itself is highly resistant to oxidation and contamination with organic and inorganic substances.

  As described above, this embodiment can also provide a highly reliable semiconductor element as in the first embodiment.

  Although a protective film made of nitride is formed on the {1-100} end face in the above, a similar protective film may be formed on the {11-20} end face that appears in element isolation.

  In the first and second embodiments, the GaN substrate is used. However, a substrate made of an insulating material such as a sapphire substrate, a substrate made of another semiconductor material such as an SiC substrate, or the like may be used. Note that when a substrate made of an insulating material such as a sapphire substrate is used, an n-type semiconductor layer formed over the substrate can be used as the n-type contact layer.

In the first and second embodiments, AlN is used for the first protective layer and Si ₃ N ₄ is used for the second protective layer. However, the first protective layer has a thermal conductivity higher than that of the second protective layer. It is preferable to use a material having high resistance and use an oxidation-resistant material for the second protective layer. For example, when AlN is used for the first protective layer, Si _x Al _1-x N _y (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is used for the second protective layer instead of Si ₃ N _4. Also good. Further, instead of AlN, Si _x Al _1-x N _y (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) may be used for the first protective layer.

  The present invention is not limited to the above embodiments, and can be applied to optical devices such as photodetectors, and electronic devices such as field effect transistors and heterojunction transistors in addition to laser diodes and light emitting diodes.

The schematic diagram which shows the cross-section of the semiconductor element (laser diode) by 1st Embodiment of this invention. The perspective view which shows the edge part of the semiconductor element (laser diode) by 1st Embodiment of this invention. The reflectance of an emission end surface of the blue-violet laser diode of the first embodiment, AlN was formed to a thickness of 0.25 nm, it shows the film thickness dependence the Si ₃ N ₄ formed thereon. The schematic diagram which shows the cross-section of the semiconductor element (light emitting diode) by 2nd Embodiment of this invention.

11 {0001} substrate made of n-type GaN 12 n-type GaN layer 13 n-type cladding layer 14 guide layer 15 made of n-type GaN active layer 16 p-type first guide layer 17 overflow prevention layer 18 second made of p-type GaN Guide layer 19 P-type cladding layer 20 Contact layer 31 made of p-type GaN n-side electrode 32 p-side electrode 41 Insulating film (current blocking layer)
50 End face protective film 51 First protective layer 52 Second protective layer 111 ... n-type GaN {0001} substrate 112 ... n-type GaN layer 113 ... n-type GaN guide layer 114 ... active layer 115 ... p-type first guide layer 116 ... Overflow prevention layer 117 ... p-type GaN second guide layer 118 ... p-type cladding layer 119 ... p-type GaN contact layer 131 ... n-side electrode 132 ... p-side electrode

Claims (6)

A substrate, an n-type cladding layer provided on the substrate, an n-type guide layer provided on the n-type cladding layer, an active layer provided on the n-type guide layer, and the active layer A first p-type guide layer provided on the first p-type guide layer, an overflow prevention layer provided on the first p-type guide layer, a second p-type guide layer provided on the overflow prevention layer, A p-type cladding layer provided on the second p-type guide layer, and each of the layers is made of a nitride III-V compound semiconductor;
A first protective layer of nitride comprising aluminum provided on the emission surface of the laser diode;
A second protective layer made of nitride containing silicon and provided on the first protective layer and having a refractive index different from that of the first protective layer;
And a film thickness of each of the first protective layer and the second protective layer is 0.25 nm to 50 nm.   The first protective layer has a higher thermal conductivity than the second protective layer, and the second protective layer is a material having higher oxidation resistance than the first protective layer. The semiconductor device according to claim 1.   3. The semiconductor device according to claim 1, wherein the first protective layer is made of aluminum nitride or silicon aluminum nitride.   The second protective layer is silicon nitride or silicon aluminum nitride when the first protective layer is aluminum nitride, and silicon nitride when the first protective layer is silicon aluminum nitride. The semiconductor device according to claim 3.   5. The semiconductor element according to claim 1, wherein a surface on which the first protective layer is provided is a {1-100} surface.   The semiconductor element according to claim 1, wherein the substrate is a GaN substrate.

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