KR20040021863A - Method of producing a semiconductor laser diode - Google Patents

Abstract

PURPOSE: A method for fabricating a semiconductor laser diode is provided to form a ridge of a symmetrical structure or a vertical structure by using an ion implantation process. CONSTITUTION: The first conductive type clad layer(215), an active layer(220), the second conductive type clad layer(222), and a cap layer are sequentially formed on the first conductive type substrate. A mask is formed on the cap layer corresponding to a current implantation region of the second conductive type clad layer(222). An ion implantation process is performed on a removal region of the second conductive type clad layer in order to form a ridge structure. The ion-implanted region is removed from the second conductive type clad layer(222) in order to form the ridge structure. A current limit layer(227) is formed around the ridge structure. The mask is removed. A contact layer(228) is formed on the cap layer formed on the ridge structure and the current limit layer(227).

Description

METHODS OF PRODUCING A SEMICONDUCTOR LASER DIODE

The present invention relates to a method for manufacturing a semiconductor laser, and more particularly, to form a ridge-type symmetry and to have a vertical cross section, thereby increasing the efficiency of current distribution injected into the active layer and distributing light due to refractive index waveguide. It relates to a method for manufacturing a semiconductor laser to stabilize the waveguide by uniformly.

In recent years, semiconductor laser diodes have been widely applied not only as light sources for optical pickup devices of optical disc systems such as CDs and DVDs, but also in various fields such as optical communication, multiple communication, and space communication. The reason for the spotlight in various fields as described above is that the laser light oscillated from the semiconductor laser diode has a narrow frequency width (short wavelength characteristic), high directivity, and high output.

In general, semiconductor laser diodes are manufactured by forming a ridge structure for forming a p-type electrode after crystal growth of a multilayer laser die structure on a substrate such as sapphire.

Specifically, FIGS. 1A and 1B illustrate a typical semiconductor laser diode structure.

As shown in FIGS. 1A and 1B, the semiconductor laser diode may include a first cladding layer 15 and a multi-quantum well structure on a substrate 13 having a first electrode 11 formed on a lower surface thereof. The active layer 20 having the (), the second cladding layer 20 having a ridge structure, and the cap layer 24 formed on the ridge top surface are sequentially formed. In addition, a current limiting layer 27 is formed on the upper surface of the second cladding layer 20 around the ridge, and the contact layer 28 and the second electrode 31 are formed on the cap layer 24 and the current limiting layer 27. It is formed in turn. A buffer layer (not shown) suitable for lattice matching is additionally formed between some layers of the crystal structure (for example, the substrate 13 and the first cladding layer 15).

In the case of a semiconductor laser diode that emits a 650 nm wavelength laser light mainly used for DVD playback or the like, an n-type GaAs substrate is used as the substrate 11, and the first cladding layer 13 and the second cladding layer 22 are used. ) Is formed of an n-type AlGaInP layer and a p-type AlGaInP layer, respectively. In addition, the active layer 20 is formed to have a multi-quantum well structure having an oscillation wavelength of 650 nm, and the cap layer 16 is formed of a p-type GaAs layer. After forming a dielectric mask (not shown) such as SiO ₂ on the current injection region of the cap layer 16, a wet etching process is performed on the cap layer 16 and the second cladding layer 22 to form a ridge as shown in FIG. 1A. The structure can be formed. In this case, in order to prevent the active layer 16 from being damaged in the wet etching process, an etching stop layer is additionally provided at a predetermined depth of the second cladding layer 22. Subsequently, after the mask is removed, an n-GaAs layer doped with a second cladding layer and another conductivity type impurity is formed as the current limiting layer 27, and a p-type GaAs contact layer and a second electrode are sequentially formed, as shown in Fig. 1A. Such a semiconductor laser diode can be completed.

The substrate used here is mainly an off substrate that is inclined by about 15 ° in the (001) direction. The use of the off substrate in this way is because the (001) plane has a rough surface, which is difficult to dope the impurities, and there is a problem in that a long wavelength phenomena caused by a natural superlattice is generated.

However, in the case of using such an off substrate, the ridge structure causes the left and right asymmetric structure due to the etching characteristic of the off substrate. That is, in the process of forming the ridge structure in the second cladding layer, after the wet etching is performed according to the inclination angle of the crystal structure of the off substrate, the ridge structure has a left-right asymmetric structure as shown in FIG. 1B.

When driving the semiconductor laser diode, a current distribution injected from the second electrode 31 into the active layer 20 is formed along the ridge structure of the second cladding layer, wherein the injected current is region A due to the asymmetric structure of the ridge. Will be partially lost. This not only makes it difficult to implement high power laser diodes, but also poses a problem of ensuring long-term device reliability.

In addition, the asymmetric ridge structure causes a problem in that the distribution of light due to the refractive index waveguide cannot be uniformed in addition to the problem of injection current loss. This is a big constraint in stabilizing waveguides.

As such, there is a need in the art for a new semiconductor laser diode manufacturing method capable of improving the ridge structure of the second clad layer to increase the efficiency of the injection current and to stabilize the light waveguide.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and its object is to improve the process so as not to be affected by the crystal orientation of the substrate in the etching process for the second cladding layer, thereby providing a semiconductor laser having a ridge shape having a symmetrical structure. The present invention provides a method for manufacturing a diode.

1A and 1B are respectively a perspective view and a cross-sectional view showing the structure of a general semiconductor laser diode.

2A to 2D are cross-sectional views of respective processes for explaining the method for manufacturing a semiconductor laser diode of the present invention.

<Code Description of Main Parts of Drawing>

213: first conductive substrate 215: first conductive clad layer

220: active layer 222: second conductivity type clad layer

224: cap layer 225: mask

227: current limiting layer 228: contact layer

In order to achieve the above technical problem, the present invention comprises the steps of sequentially forming at least a first conductive cladding layer, an active layer, a second conductive cladding layer and a cap layer on the first conductive type substrate, and the second conductive Disposing a mask on the cap layer corresponding to the current injection region of the clad cladding layer, performing ion implantation on a region of the second conductive clad layer to be removed to form a ridge structure; Removing the ion implanted region to form a ridge structure in the second conductive cladding layer, forming a current limiting layer around the ridge of the second conductive cladding layer, and after removing the mask, It provides a method for manufacturing a semiconductor laser diode comprising forming a contact layer on the cap layer and the current limiting layer of the upper surface of the ridge structure.

In a preferred embodiment of the present invention, the ion implanted region can be removed by a wet etching process. It is also preferable that the ridge structure formed after removing the ion implanted region is formed to have a substantially vertical side surface.

The element used in the ion implantation step according to the present invention may be selected from the group consisting of silicon (Si), zinc (Zn), magnesium (Mg), boron (B) and carbon (C).

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2A through 2D are cross-sectional views illustrating a method of manufacturing a semiconductor laser diode of the present invention.

As illustrated in FIG. 2A, the method of manufacturing a semiconductor laser diode of the present invention includes at least a first conductive cladding layer 215, an active layer 220, a second conductive cladding layer 222, and a first conductive cladding layer 212. The step of sequentially forming the second conductivity type cap layer 225 is started. For example, in the case of an AlGaInP-based semiconductor laser diode, the first conductivity type substrate 212 is an n-type GaAs substrate, and the first conductivity type cladding layer 213 and the second conductivity type cladding layer 220 are each n. It is composed of AlGaInP material of type and p type. In addition, the active layer is composed of a multi-quantum well structure having a predetermined oscillation wavelength, and the second conductivity type cap layer is made of a p-type GaAs material. Each such layer is formed in a continuous process in the order presented above. This is called the primary growth process. In addition, the first electrode 211 is provided on the rear surface of the first conductivity type substrate, but is not limited thereto. Although not shown in FIG. 2A, a buffer layer made of n-type GaAs or n-type InGaP may be added between the substrate and the first conductive type (eg, n-type) cladding layer.

As such, when the first growth process is completed, a mask 225 is formed on the cap layer 222 corresponding to the current injection region of the second conductive clad layer 222. The region where the mask 225 is disposed is a ridge forming region of the second conductive cladding layer 222 for current injection. As the mask 225, a dielectric film such as an oxide film such as an SiO ₂ film or a nitride film such as a SiN film may be used.

Next, as shown in FIG. 2B, ion implantation is performed in the region B to be removed to form the ridge structure of the second conductive clad layer 222. Region B, indicated by the dotted line in FIG. 2B, represents the region to be implanted, which will be removed to form a ridge. As described above, according to the crystal orientation of the off substrate (here, the first conductivity type substrate), the crystal orientation of the second conductivity type cladding layer 222 is also defined. The ridge structure obtained from the conductive cladding layer 222 is formed to have a right and left asymmetric structure. For this reason, the current injection efficiency due to the ridge structure is lowered, and there is a problem that it is difficult to uniformly guarantee the distribution of the laser light due to the refractive index waveguide.

In this step, in order to solve this problem, the crystallinity is lowered by destroying or damaging the crystallinity of the region B to be removed to form the ridge structure using ion implantation. As a result, the influence of the crystal orientation of the off substrate on the subsequent etching process can be reduced or prevented.

The element used in such an ion implantation step preferably has an ion radius suitable for breaking the crystal lattice into the implanted ions. As such elements, silicon (Si), zinc (Zn), magnesium (Mg) and boron (B) are preferred, and silicon (Si) is most preferred. Of course, the carbon (C) ion is relatively small in radius, but can be effectively applied in lowering the crystal order.

Next, as shown in FIG. 2C, the second conductivity-type cladding layer 222 ′ having a ridge structure is formed by removing the ion implanted region. In this step, a general wet etching process may be used. Conventionally, a dry etching process using plasma has been used to obtain a symmetrical structure, but this is not preferable because the etching site is damaged due to plasma and thus adversely affects device characteristics, and thus has been used in combination with a wet etching process. However, in this way it is still difficult to improve the asymmetry problem, and there is a problem that the process is complicated.

However, in the present invention, since the ion implantation region is removed through wet etching after the crystal is damaged except for the symmetrical structure by ion implantation, an accurate symmetry structure can be obtained only by the wet etching process. In this step, it is preferable that the region to be removed during etching includes or is at least nearly coincident with the implanted region. This is because when the ion implanted region remains, the crystal of the remaining region is damaged.

Finally, after the secondary crystallization process of forming the current limiting layer 227 around the ridge of the second conductive cladding layer 222 ', the mask 225 is removed and the second conductive cladding layer is removed. A tertiary crystal growth process of forming a contact layer 228 on the cap layer 224 of the ridge upper surface portion 222 'and the current limiting layer 227 is performed. As a result, a semiconductor laser diode as shown in Fig. 2D can be obtained.

First, the current limiting layer 227 formed in the secondary crystal growth process is made of a material having a conductive impurity opposite to the second conductive cladding layer 222 ′. For example, in the case of an AlGaInP-based semiconductor laser diode, a compound semiconductor material including an n-type GaAs material may be used.

After the current limiting layer 227 is formed, a tertiary crystal growth process is performed in which the contact layer 228 is formed on the current limiting layer 227 and the cap layer 224 of the ridge upper surface after removing the mask 225. Is executed. As the contact layer 228, a material having the same conductivity type as that of the second cladding layer 222 ′ is used. For example, it may be formed of a p-type GaAs material. In addition, as shown in FIG. 2D, the second electrode 230 is formed.

As described above, the feature of the present invention is that the ion implantation process is applied before the etching process for forming the ridge structure in order to prevent the ridge shape from being formed into an asymmetrical structure due to the crystal orientation of the off substrate. Such an ion implantation process lowers the crystal order that causes the asymmetric structure in the ridge shape, thereby obtaining a ridge shape having almost left and right symmetry structures in a subsequent etching process. This ridge structure not only improves the current injection efficiency, but also stabilizes the waveguide of the laser light by making the waveguide by the refractive index uniform.

Further, as shown in FIG. 2B, the region damaged by the ion implantation process is formed such that the side surface of the ridge forming region can be formed almost vertically by the straightness of the ion implantation. Using this, the ridge structure obtained in the etching process may be formed to have a vertical side surface as shown in FIG. 2C. As a result, by reducing the injection current consumed through the inclined portion by the vertical side, a ridge structure for more efficient current injection can be obtained.

The present invention described above is not limited by the above-described embodiment and the accompanying drawings, but by the appended claims. Therefore, it will be apparent to those skilled in the art that various forms of substitution, modification, and alteration are possible without departing from the technical spirit of the present invention described in the claims.

As described above, according to the method of manufacturing a semiconductor laser diode of the present invention, by applying the ion implantation process to the problem of crystal orientation of the off-substrate causing the asymmetrical ridge structure, the ridge shape having a left-right symmetrical structure and even a vertical structure You can get it. Thereby, not only can the injection current loss caused by the asymmetrical portion (particularly, the ridge side having a gentle inclination) can be reduced, but the distribution of the light due to the refractive index waveguide is uniform, which has a great effect to stabilize the waveguide of the laser beam.

Claims (4)

Sequentially forming at least a first conductive clad layer, an active layer, a second conductive clad layer, and a cap layer on the first conductive type substrate; Disposing a mask on the cap layer corresponding to the current injection region of the second conductive clad layer; Performing ion implantation into a region of the second conductive clad layer to be removed to form a ridge structure; Removing the ion implanted region to form a ridge structure in the second conductive clad layer; Forming a current limiting layer around a ridge of the second conductive cladding layer; and After removing the mask, forming a contact layer on the cap layer of the ridge upper surface portion of the second conductive clad layer and the current limiting layer. The method of claim 1, Removing the ion implanted region, the semiconductor laser diode manufacturing method, characterized in that performed by a wet etching process. The method of claim 1, And a ridge structure formed after removing the ion implanted region has a substantially vertical side surface. The method of claim 1, The element used in the ion implantation step is a semiconductor laser diode manufacturing method, characterized in that selected from the group consisting of silicon (Si), zinc (Zn), magnesium (Mg), boron (B) and carbon (C).