JP2006216731A - Nitride semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure long-term reliability and achieve improvement in characteristic yield of element in a nitride semiconductor laser element in which a far-end sight image is formed in the Gaussian shape including single peak. <P>SOLUTION: The nitride semiconductor laser element 100 has a structure that an n-type GaN contact layer 102, an n-type Al<SB>0.1</SB>Ga<SB>0.9</SB>N clad layer 103, an n-type GaN guide layer 104, a GaInN multiple quantum well active layer 105, a p-type Al<SB>0.2</SB>Ga<SB>0.8</SB>N carrier barrier layer 106, a p-type GaN guide layer 107, a p-type Al<SB>0.1</SB>Ga<SB>0.9</SB>N clad layer 108, p-type GaN contact layer 109, an insulating layer 113, and a p-type electrode 112 are laminated in this sequence on an n-type GaN substrate 101; and an impurity-added GaN layer 111 is formed to at least a part of the area other than a ridge stripe 110 of the exposed surface where the ridge stripe 110 is formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an actual refractive index type nitride semiconductor laser device having a ridge stripe.

  A semiconductor laser element made of a nitride semiconductor can be used in an information recording device as a light source for optical disk signal reading components (optical pickup). For example, when a nitride semiconductor laser element is used as a light source for an optical pickup, the required characteristics include the shape of the emitted light intensity distribution (far-field image). Is preferably unimodal and Gaussian.

However, in the conventional nitride semiconductor laser device, light generated in the ridge stripe may leak into the optical waveguide region outside the ridge stripe and be guided in that region. As a result, a small fluctuation (ripple) often occurred in the far-field image. As a technique for solving the problem, for example, Patent Document 1 is disclosed. This publication discloses a technique for forming a layer for absorbing the leaked light outside the ridge stripe so that the light leaked outside the ridge stripe does not affect the far-field image. . As a layer that absorbs the light, for example, an insulating layer such as TiO ₂ , Nb ₂ O ₅ , RhO, Cr ₂ O ₃ , Ta ₂ O ₅ , SiC, a metal layer such as Si, Zr, Nb, Ti, Ni, and a semiconductor layer of _{in z Ga 1-z N (} 0 <z <1).
JP 2002-237661 A

However, among the nitride semiconductor laser elements of Patent Document 1, as the light absorption layer, an insulating layer such as TiO ₂ , Nb ₂ O ₅ , RhO, Cr ₂ O ₃ , Ta ₂ O ₅ , SiC, Si, Zr, Nb, When a metal layer such as Ti or Ni is used, device characteristics deteriorate due to diffusion of elements constituting the light absorption layer or instability due to decomposition of the light absorption layer itself when the semiconductor laser element is operated at a high temperature for a long time. As a result, long-term reliability was not sufficient.

  Further, among the nitride semiconductor laser elements of Patent Document 1, even when an InGaN semiconductor layer is used, optical characteristics are reduced due to deterioration in element characteristic yield due to manufacturing variations in composition and the like, and deterioration of layers due to InGaN crystallinity deterioration. There has been a problem that device characteristics are unstable due to changes in absorption characteristics.

  It is an object of the present invention to ensure long-term reliability and improve device characteristic yield in a nitride semiconductor laser device having a far-field image having a single peak and a Gaussian shape.

  In order to achieve the above object, a nitride semiconductor laser device according to the present invention forms a GaN layer doped with impurities on at least a portion of a nitride semiconductor layer on which a ridge stripe is formed and other than the ridge stripe. It is characterized by this.

  The nitride semiconductor laser device of the present invention is characterized in that an impurity-added GaN layer is formed on at least a part of the exposed surface other than the ridge stripe exposed by forming the ridge stripe.

  According to these configurations, the GaN layer to which the impurity is added functions as an absorption layer for light emission leaking out of the ridge stripe.

  In the above-described nitride semiconductor laser element, when the impurity is Mg, light emitted in the nitride semiconductor laser element is efficiently absorbed.

The concentration of the impurity is preferably 1 × 10 ²⁰ cm ⁻³ or more and 5 × 10 ²¹ cm ⁻³ or less.

If the concentration is lower than 1 × 10 ²⁰ cm ⁻³ , light emission cannot be sufficiently absorbed. On the other hand, if the concentration is higher than 5 × 10 ²¹ cm ⁻³ , the crystallinity of the GaN layer is extremely deteriorated, the stability as a crystal is not sufficient, and the long-term reliability of the nitride semiconductor laser device is reduced. An adverse effect will be caused, which is not preferable.

  The layer thickness of the GaN layer is preferably about 100 nm or more. If the thickness is less than 100 nm, the leaked light cannot be absorbed sufficiently and a sufficient effect cannot be obtained. On the other hand, the thickness is not particularly limited, but about 1 μm is sufficient to obtain the effects of the present invention.

  The GaN layer is preferably formed at least apart from the side surface of the ridge stripe at a position within a range of 1 μm to 100 μm.

  If the GaN layer is formed in the vicinity of the ridge stripe, for example, in a region closer than 1 μm from the side surface of the ridge stripe, it also acts as an absorption layer for light emission contributing to laser oscillation in the stripe, and the laser element characteristics are In some cases, it may affect the situation. On the other hand, when it is formed in a region separated from 100 μm, it is not preferable because the light emitted from the stripe cannot be efficiently absorbed.

  The surface of the nitride semiconductor layer on which the ridge stripe is formed or the exposed surface is preferably AlGaN.

  In the present invention, of the light emitted from the active layer, the light leaking out of the ridge stripe is absorbed by the GaN layer, but the leaked light is absorbed from the AlGaN layer due to the refractive index. This is because it is easy to propagate to the GaN layer, and by forming a GaN layer that acts as an absorption layer in contact with the AlGaN layer, light can be efficiently absorbed by the GaN layer.

  In addition, since the GaN layer is formed after the ridge stripe is formed, the effects of the present invention can be better obtained.

  It is necessary to form the GaN layer in the vicinity of the active layer in order to absorb the light exuded from the active layer when the GaN layer is formed before the ridge stripe is formed. Since the structure includes GaN functioning as a layer, the laser characteristic itself is deteriorated, which is not preferable.

  According to the present invention, since the GaN layer doped with impurities serves as an absorption layer, the far-field image has a single peak with a Gaussian shape without ripples. Moreover, sufficient reliability can be obtained even if this element is put into a high-temperature operation reliability test. The production yield of the element is sufficiently high.

The nitride semiconductor laser device of the present invention will be described below. In this specification, the nitride semiconductor is composed of Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1). In addition, about 10% or less (but hexagonal) of the nitrogen element of the nitride semiconductor may be substituted with any element of As, P, and Sb. Further, Si, O, Cl, S, C, Ge, Zn, Cd, Mg, and Be may be doped in the nitride semiconductor.

Embodiment 1

FIG. 1 is a schematic cross-sectional view of a nitride semiconductor laser element 100 shown in the present embodiment. The nitride laser device 100 includes an n-type GaN contact layer 102, an n-type Al _0.1 Ga _0.9 N cladding layer 103, an n-type GaN guide layer 104, a GaInN multiple quantum well active layer 105, a p-type layer on an n-type GaN substrate 101 in order. A type Al _0.2 Ga _0.8 N carrier barrier layer 106, a p-type GaN guide layer 107, a p-type Al _0.1 Ga _0.9 N cladding layer 108, a p-type GaN contact layer 109, and a p-type electrode 112 are laminated.

The GaInN multiple quantum well active layer 105 includes a barrier layer made of In _0.02 Ga _0.98 N and a well layer made of In _0.15 Ga _0.85 N. The barrier layer, well layer, barrier layer, well layer, barrier layer, well layer The multi-quantum well structure including three well layers is repeated with the barrier layer. Impurities may or may not be added to these well layers and barrier layers. However, the emission intensity from the active layer 105 can be increased by adding an impurity such as Si.

  The p-type GaN guide layer 107, the p-type cladding layer 108, and the p-type contact layer 109 are partially removed to form a striped ridge 110 extending in the resonator direction. A GaN layer (hereinafter sometimes referred to as a GaN impurity added layer) 111 to which an impurity is added is formed on at least a part other than the ridge stripe 110 on the surface where the ridge stripe 110 is formed.

  Further, an insulating film 113 is provided between the p-type electrode 112, the GaN impurity added layer 111 and the ridge stripe 110 except for the top of the ridge stripe 110. Further, an n-type electrode 114 is formed on the side opposite to the side where the laminated structure of the n-type GaN substrate 101 is formed.

Below, the manufacturing process of the semiconductor laser element 100 is demonstrated. First, an n-type GaN contact layer 102, an n-type Al _0.1 Ga _0.9 N clad layer 103, an n-type GaN guide layer 104, a GaInN multiple quantum are formed on the n-type GaN substrate 101 by an MOCVD apparatus (metal organic vapor phase epitaxy). A well active layer 105, a p-type Al _0.2 Ga _0.8 N carrier barrier layer 106, a p-type GaN guide layer 107, a p-type Al _0.1 Ga _0.9 N cladding layer 108, and a p-type GaN contact layer 109 are formed. Note that when the resistance of the p-type layer is high after the growth of these semiconductor layers, the resistance may be lowered by performing heat treatment or the like.

Next, a ridge stripe 110 is formed on the formed semiconductor layer side using a dry etching technique. As an etching mask, for example, a striped SiO ₂ with a width of 2 μm is formed on the surface on which the nitride semiconductor is laminated by using a photolithography technique, and the p-type contact layer 109 and the p-type cladding layer are formed by an RIE apparatus or the like. 108 and a part of the p-type GaN guide layer 107 are removed by etching to form a stripe-shaped ridge 110 having a width of 2 μm extending in the resonator direction.

Next, SiO ₂ is formed as a mask in a region where the GaN impurity added layer 111 is not formed by using a photolithography technique. Specifically, the top and side portions of the ridge stripe 110 and the nitride semiconductor layer exposed by removing a part of the nitride semiconductor by the previous dry etching process, in this embodiment, p-type Al _0.2 SiO ₂ is formed on the surface of the Ga _0.8 N carrier barrier layer 106 and excluding a distance of 2 μm from the side surface of the ridge stripe 110.

Thereafter, for example, the GaN impurity added layer 111 is formed by an MOCVD apparatus. In this embodiment, the layer thickness is 300 nm and Mg is added as an impurity at a concentration of 1 × 10 ²¹ cm ⁻³ .

Then, after removing the GaN layer other than the necessary portion by removing the SiO ₂ layer by etching, an insulating layer 113 made of SiO ₂ and TiO ₂ is formed in a region other than the top of the ridge stripe 110, A p-electrode 112 having a laminated structure of Pd / Mo / Au is formed using a vacuum deposition apparatus or a sputtering apparatus so as to be in contact with the p-type contact layer 109 at the top of the ridge stripe 110.

  Then, an n-type electrode 114 having a laminated structure of Hf / Al / Mo / Pt / Au is formed on the surface opposite to the surface on which the semiconductor layer of the n-type GaN substrate 101 is formed. In order to form a good end face in the next chip dividing step, before forming the n-type electrode 114, the n-type GaN substrate 101 is partially removed from the back side by polishing or etching, and the layer thickness is increased. It is also possible to reduce the thickness and facilitate chip division.

  Each semiconductor laser element can be obtained by performing a chip dividing process such as scribing on the wafer having the semiconductor laser element structure formed on the substrate. In the chip dividing step, after forming the resonator end face of the semiconductor laser element, the end face may be subjected to HR coating or AR coating with a dielectric multilayer film. The nitride semiconductor laser device 100 thus obtained is bonded to the stem using solder or the like and a metal wire is connected to the electrode, so that the device can be operated by energization. .

  When the device characteristics of the nitride semiconductor laser device 100 were evaluated, the far-field image was Gaussian and unimodal without ripples. Further, even when this element was put into a high temperature operation reliability test, sufficient reliability could be obtained. The device production yield was sufficiently high.

  This is because the GaN impurity-added layer 111 can be manufactured with a stable yield and a stable characteristic as an absorption layer for light emission leaking out of the ridge stripe 110, and at the same time, it is a very stable layer in terms of long-term reliability. This is considered to indicate that

  The GaN impurity added layer 111 functions as an absorption layer for the light emitted from the nitride semiconductor laser device 100. Therefore, if the GaN impurity added layer 111 exists in the ridge stripe 110 or directly under the ridge stripe 110, the light emission necessary for laser oscillation in the stripe is reached. As a result, the characteristics of the nitride semiconductor laser device 100 are deteriorated. Therefore, the GaN impurity-added layer 111 needs to be formed in a form that does not exist in the ridge stripe 110 and immediately below the ridge stripe 110.

  As described above, the GaN impurity-added layer 111 has a characteristic of absorbing light emitted in the nitride semiconductor laser device 100, but if it exists in the vicinity of the ridge stripe 110, the laser oscillation in the stripe is similarly performed. In some cases, a part of the light emission required for the light-emitting device functions as an absorption layer, which may affect the laser characteristics. Therefore, it is preferable that the film is formed at a position 1 μm or more away from the side surface of the ridge stripe.

  On the other hand, if the GaN impurity added layer 111 is formed too far away from the ridge stripe, light emitted from the ridge stripe 110 cannot be efficiently absorbed. It is preferable to form in a region within 100 μm from the part.

Further, since the GaN impurity added layer 111 needs to have a characteristic of absorbing light emitted in the nitride semiconductor laser device 100, the impurity is desirably Mg, and its concentration is 1 × 10 ²⁰ cm ^−. It is desirable that it is ³ or more and 5 × 10 ²¹ cm ⁻³ or less. If the concentration is lower than 1 × 10 ²⁰ cm ⁻³ , light emission cannot be sufficiently absorbed. On the other hand, if the concentration is higher than 5 × 10 ²¹ cm ⁻³ , the crystallinity of the GaN layer is extremely deteriorated, the stability as a crystal is not sufficient, and the long-term reliability of the nitride semiconductor laser device 100 is reduced. Adversely affecting the operation, which is not preferable.

If the Mg concentration is 5 × 10 ²⁰ cm ⁻³ or more and 5 × 10 ²¹ cm ⁻³ or less, the resistance of the GaN impurity-added layer 111 itself is increased, and sufficient insulation can be maintained only by this layer. In addition, the insulating layer 113 can be dispensed with. In the case of 5 × 10 ²⁰ cm ⁻³ or less, the GaN impurity-added layer 111 is in a relatively low resistance state, and in order to concentrate current in the ridge stripe portion, it is better that the insulating layer 113 exists, and the element The characteristics are stable. In the case of 5 × 10 ²¹ cm ⁻³ or more, the crystallinity of the GaN impurity addition layer 111 is very deteriorated and a leak current can be generated. In this case as well, in order to stabilize device characteristics The insulating layer 113 is preferably formed.

  In addition, the layer thickness of the GaN impurity addition layer 111 is preferably approximately 100 nm or more. If the thickness is less than 100 nm, the leaked light cannot be absorbed sufficiently and a sufficient effect cannot be obtained. On the other hand, the thickness is not particularly limited, but about 1 μm is sufficient to obtain the effects of the present invention.

  Further, in the nitride semiconductor laser device 100, AlGaN is exposed on the surface of the nitride semiconductor layer removed to form the ridge stripe 110, and the GaN impurity added layer 111 is formed on the exposed surface, thereby forming A higher light absorption effect can be obtained. This is because light emitted from the active layer 105 that has leaked out of the ridge stripe 110 needs to be absorbed by the GaN impurity-added layer 111, but the leaked light is reflected by the AlGaN layer due to the refractive index. This is because light can be efficiently absorbed by the GaN impurity-added layer 111.

  In addition, since the GaN impurity added layer 111 is formed after the ridge stripe 110 is formed, the effects of the present invention can be better obtained.

  The GaN impurity added layer 111 needs to be formed in the vicinity of the active layer 105. However, when the GaN impurity added layer 111 is formed before the ridge stripe 110 is formed, the following two methods can be considered. One is the case where the GaN impurity-added layer 111 is formed as one layer in which each nitride semiconductor layer is continuously grown. In order to function as an absorption layer for light emission, the nitride semiconductor layer is formed in the vicinity of the active layer 105. Need to form. However, according to this method, the GaN impurity added layer 111 is included in or just below the ridge stripe 110 to be formed later. In this case, the GaN impurity-added layer 111 contributes to the light emission in the stripe necessary for laser oscillation, which is not preferable because the laser element characteristics deteriorate.

  As another method, in the process of forming each layer of the nitride semiconductor, when forming a layer near the active layer 105, the GaN impurity added layer 111 is formed, the growth is interrupted once, and the ridge stripe 110 is later formed. It is conceivable to remove the GaN impurity added layer 111 present at a position where the GaN impurity is to be formed and to re-grow the remaining nitride semiconductor layer. In this method, the GaN impurity added layer 111 does not exist in the vicinity of the ridge stripe 110 and there is no influence on the light emission in the ridge stripe 110 necessary for laser oscillation. However, due to the regrowth of the nitride semiconductor, Defects and the like are likely to enter the nitride semiconductor layer, making it difficult to obtain sufficient device reliability. From the above, it can be said that the effect of the present invention can be better obtained by forming the GaN impurity-added layer 111 after the ridge stripe 110 is formed.

In the present embodiment, after using SiO ₂ as a mask, the GaN impurity added layer 111 is formed, and a portion of the GaN impurity added layer 111 formed in an unnecessary portion such as immediately above the ridge stripe 110 is removed. The GaN impurity added layer 111 is produced. With respect to this step, for example, after the ridge stripe 110 is formed, the GaN impurity addition layer 111 is formed by using a technique of selective growth of a nitride semiconductor, so that the GaN impurity addition layer is formed only on the etching exposed surface outside the ridge stripe 110. 111 can also be formed. This is based on the fact that when a step is formed on the wafer surface, the nitride semiconductor is likely to grow earlier on the bottom of the step than on the top and side surfaces of the step. The GaN impurity added layer 111 can be formed more easily only at a necessary position.

Embodiment 2

  In the present embodiment, the nitride semiconductor laser device of the present invention will be described by a method different from the previous embodiment.

  FIG. 2 is a schematic cross-sectional view of the nitride semiconductor laser element 200 shown in the present embodiment. A feature of the structure of this element is that after forming the ridge stripe 110, an insulating layer 113 is formed, and a GaN impurity addition layer 111 which is a technique according to the present invention is formed so as to cover the layer. . The production will be described below.

First, similarly to the first embodiment, a nitride semiconductor stacked structure is manufactured. Then, as in the first embodiment, the ridge stripe 110 is formed on the side where the nitride semiconductor multilayer structure is formed, using a dry etching technique. As an etching mask, for example, a striped SiO ₂ with a width of 2 μm is formed on the surface on which the nitride semiconductor is laminated by using a photolithography technique, and the p-type contact layer 109 and the p-type cladding layer are formed by an RIE apparatus or the like. 108 and a part of the p-type GaN guide layer 107 are removed by etching to form a stripe-shaped ridge 110 having a width of 2 μm extending in the resonator direction.

Then, the layer 115 made of TiO _{2 is used} as a layer for improving the adhesion between the layer made of ZrO ₂ to be the insulating layer 113, the GaN impurity added layer 111 to be the absorption layer, and the p electrode 112 to be formed later. Are sequentially formed by sputtering. Thereafter, SiO ₂ is removed by etching, and the top of the ridge stripe 110 is exposed by a lift-off technique. In this case, the thickness of the insulating layer 113 made of ZrO ₂ was set to 60 nm. The GaN impurity added layer 111 serving as an absorption layer was a layer having a layer thickness of 300 nm and Mg added as an impurity at a concentration of 8 × 10 ²⁰ cm ⁻³ .

  Then, a p-electrode 112 having a Pd / Mo / Au laminated structure is formed so as to be in contact with the p-type contact layer 109 at the top of the ridge stripe 110 using a vacuum vapor deposition apparatus, a sputtering apparatus, or the like.

  After that, as in the previous embodiment, an n-electrode 114 was formed, a laser chip was manufactured through a chip forming process and a coating process, and the device characteristics were evaluated after being mounted so as to be energized. As a result, as in the previous embodiment, the far-field image was Gaussian and unimodal without ripples. Further, the high-temperature operation reliability test of this element was slightly inferior to the element shown in the first embodiment, but sufficient reliability can be obtained in use. The device production yield was sufficiently high.

  According to the structure and method shown in the present embodiment, the effects of the present invention can be obtained more easily than the structure and method shown in the first embodiment. However, in this method, the GaN impurity added layer 111 is formed so as to cover the ridge stripe 110, and as a result, it is formed in the vicinity of the ridge stripe 110. For this reason, even the light emission that contributes to the laser oscillation in the ridge stripe 110 acts as an absorption, which causes deterioration of the laser element characteristics. As a countermeasure for this, for example, a structure is required to reduce the influence by inserting the insulating layer 113 between the GaN impurity added layer 111 and the ridge stripe 110. In the structure shown in the present embodiment, since the absorption layer exists in the vicinity of the side surface of the ridge stripe 110, for example, when the stripe width becomes narrower than about 2 μm, the higher mode of laser oscillation is set. It also serves as an absorption layer, and can also be effective in improving the kink level, which is one of the laser characteristics.

  The nitride semiconductor laser device of the present invention is a single semiconductor laser device, a hologram laser device, an optoelectronic IC device packaged integrally with an IC chip for processing such as driving or signal detection, a waveguide or a micro optical element. And can be applied to a compound optical device packaged integrally. Furthermore, the present invention can be applied to an optical recording system, an optical disc system, a light source system in the ultraviolet to green region, etc. provided with these devices.

1 is a schematic cross-sectional view of a nitride semiconductor laser device of the present invention. 1 is a schematic cross-sectional view of a nitride semiconductor laser device of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Nitride semiconductor laser element 101 n-type GaN substrate 102 n-type GaN contact layer 103 n-type Al _0.1 Ga _0.9 N cladding layer 104 n-type GaN guide layer 105 GaInN multiple quantum well active layer 106 p-type Al _0.2 Ga _0.8 N carrier barrier Layer 107 p-type GaN guide layer 108 p-type Al _0.1 Ga _0.9 N cladding layer 109 p-type GaN contact layer 110 ridge stripe 111 GaN layer doped with impurities 112 p-type electrode 113 insulating film 114 n-type electrode 115 TiO ₂ layer

Claims (9)

An actual refractive index type in which a nitride semiconductor layer including an n-type cladding layer, an active layer, and a p-type cladding layer is stacked on a substrate, and a portion of the nitride semiconductor layer is removed to form a ridge stripe. In the nitride semiconductor laser device,
A nitride semiconductor laser element, wherein a GaN layer to which an impurity is added is formed on at least a part of the nitride semiconductor layer where the ridge stripe is formed and at least a part other than the ridge stripe.   2. The nitride semiconductor laser device according to claim 1, wherein a surface of the nitride semiconductor layer on which the ridge stripe is formed is AlGaN. An actual refractive index type in which a nitride semiconductor layer including an n-type cladding layer, an active layer, and a p-type cladding layer is stacked on a substrate, and a portion of the nitride semiconductor layer is removed to form a ridge stripe. In the nitride semiconductor laser device,
A nitride semiconductor laser device, wherein an impurity-added GaN layer is formed on at least a part of the exposed surface other than the ridge stripe that is exposed when the ridge stripe is formed.   The nitride semiconductor laser element according to claim 1, wherein the impurity is Mg. 5. The nitride semiconductor laser device according to claim 1, wherein the impurity concentration is 1 × 10 ²⁰ cm ⁻³ or more and 5 × 10 ²¹ cm ⁻³ or less.   6. The nitride semiconductor laser device according to claim 1, wherein the GaN layer has a thickness of 100 nm or more.   The nitride semiconductor laser element according to claim 1, wherein the GaN layer is formed at least apart from a side surface of the ridge stripe at a position within a range of 1 μm to 100 μm.   The nitride semiconductor laser element according to claim 3, wherein the exposed surface is AlGaN.   9. The nitride semiconductor laser element according to claim 1, wherein the GaN layer is formed after the ridge stripe is formed.

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