KR100590567B1 - Laser diode and manufacturing method thereof - Google Patents

Abstract

A laser diode and a method of manufacturing the same are disclosed. The disclosed laser diode includes a substrate; A first cladding layer formed on the substrate and having a ridge formed at a center thereof; An active layer formed on an upper surface of the first clad layer and including an upper flat portion and an inclined portion disposed on upper and inclined surfaces of the ridge and lower flat portions disposed on both sides of the ridge; A second clad layer formed on a top surface of the active layer in a shape corresponding to the ridge of the first clad layer; And a current blocking layer having a window corresponding to the upper flat portion of the upper ridge of the second cladding layer and including an oxide layer.

Description

Laser diode and method of manufacturing the same

1 is a schematic cross-sectional view of a conventional laser diode.

2A is a schematic cross-sectional view of a laser diode according to a first embodiment of the present invention.

2B is a schematic cross-sectional view of a laser diode according to a second embodiment of the present invention.

3A to 3F are views for explaining a method of manufacturing a laser diode according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

100 ... n-type electrode 110 ... substrate

120 ... buffer layer 130 ... lower clad layer

140 ... active layer 150 ... upper cladding layer

171, 172,173 ... Lamination included in current blocking layer

200 ... p-type electrode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode and a method of manufacturing the same. Specifically, the step of providing a step to the active layer can improve the light confinement effect in the lateral mode direction. The present invention relates to a laser diode and a method of manufacturing the same.

In general, semiconductor laser diodes are relatively small, and the threshold current for laser oscillation is smaller than that of general laser devices, so that high-speed data transfer or high-speed data recording in a communication field or a player using an optical disk is common. And widely used as an element for reading.

The most important performance for using a laser diode as a light source in the field of optical information processing such as an optical disk is stable basic transverse mode oscillation. That is, it is necessary that the light emission spot becomes single, and furthermore, the position of the light intensity peak does not move in accordance with the light output level. The next important performance is the low threshold current. The stripe type laser diode was developed to satisfy these two performances.

The stripe laser diode is roughly classified into a gain waveguide laser diode in which an optical waveguide is determined by a gain distribution by current injection and a refractive index distribution in which a refractive index distribution is designed in a bonding direction. Refractive-waveguided laser diodes are far superior in the stability, threshold current, and non-point difference in the lateral mode, and currently used laser diodes have an effective refractive index waveguide laser diode that confines light in the junction width by providing an effective refractive index difference in the junction parallel direction. Is most of them. An example of such an effective refractive index waveguide laser diode is a V-channeled substrate inner stripe laser diode. The VSIS laser diode has a light absorbing layer formed close to the active layers on both sides of the stripe, which serves as current blocking and forms an internal stripe structure.

Figure 1 shows a schematic cross section of a conventional laser diode of a typical selectively buried ridge (SBR) structure in the 670 nm wavelength range. Referring to FIG. 1, the buffer layer 20, the first cladding layer 30, the undoped (u−) active layer 40 and the second cladding layer 50 are first grown on the substrate 10. A ridge stripe having a predetermined width and height is formed at the center of the second cladding layer 50 by a photolithography process and an etching process. Next, the bandgap reducing layer 60 and the current limiting layer 70 are grown by second, and then the contact layer 80 is formed by growing the third.

However, during the second to third growth, impurities such as zinc (Zn) are diffused into the active layer 40 to cause non-light emission or to deteriorate the reliability of the device. In addition, it is difficult to accurately control the width and depth of the ridge by wet chemical etching.

The present invention provides a laser diode having an improved structure and a method of manufacturing the same, which can improve the light confinement effect in the lateral direction by giving a step to the active layer, and can reduce the oscillation starting current by providing a current blocking region made of oxide. The purpose is to provide.

In order to achieve the above object,

Laser diode according to the present invention,

Board;

A first cladding layer formed on the substrate and having a ridge formed at a center thereof;

An active layer formed on an upper surface of the first clad layer and including an upper flat portion and an inclined portion disposed on an upper surface and an inclined surface of the ridge and lower flat portions positioned on both sides of the ridge;

A second clad layer formed on a top surface of the active layer in a shape corresponding to the ridge of the first clad layer; And

And a current blocking layer including an oxide layer and having a window corresponding to an upper flat portion of the ridge on the upper portion of the second clad layer.

In the laser diode of the present invention, the inclined portion of the active layer is preferably thinner than the upper and lower flat portions of the active layer.

The current blocking layer includes an undoped Al _X Ga _1-X As layer or an n-Al _X Ga _1-X As layer, and an undoped GaAn or n-GaAs layer according to an embodiment of the present invention.

According to a preferred embodiment of the present invention, the current blocking layer includes an n-type or undoped Al _X Ga _1-X As layer and an n-GaAs layer sequentially stacked on a p ⁺ -GaAs layer, wherein n A-type or undoped Al _X Ga _1-X As layer and n-GaAs layer are repeatedly stacked in multiple layers. This current blocking layer is thinner than other portions on the inclined surfaces on both sides of the ridge.

On the other hand, the manufacturing method of the laser diode according to the present invention

Forming a first clad layer on the substrate;

Forming a ridge in a center portion of the first clad layer;

Sequentially forming an active layer and a second cladding layer in a shape corresponding to the ridge on the first cladding layer;

Forming a current blocking layer including at least one semiconductor material layer on the second clad layer;

Forming a window for current passing through a portion of the current blocking layer corresponding to the upper surface of the ridge; And

And oxidizing both sides of the semiconductor material layer selected from the current blocking layer.

In the manufacturing method of the present invention, the forming of the ridge;

Forming an etch mask in a center portion of the first clad layer; And

And etching the first clad layer disposed at both sides of the etching mask to a predetermined depth.

According to an embodiment of the manufacturing method of the present invention, the current blocking layer is an undoped Al _X Ga _1-X As layer or an n-Al _X Ga _1-X As layer, and is not doped according to an embodiment of the present invention. A GaAn or n-GaAs layer.

The current blocking layer includes a window corresponding to the ridge of the second clad layer, an inclined portion on both sides of the ridge, and a lower flat portion corresponding to both sides of the ridge.

On the other hand, according to a preferred embodiment of the present invention, the step of forming the window;

Forming an etching mask on a portion of the current blocking layer to form a window; And

And etching the current blocking layer of the window portion of the etching mask by a selective wet method up to the p ⁺ -GaAs layer. In the selective wet etching step,

The GaAs layer is wet etched with citric acid / H ₂ O ₂ solution and the AlGaAs layer with H ₂ O / Buffered HF solution.

Oxidation of one material layer of the current blocking layer is according to a wet oxidation method.

In the preferred method of the present invention, an n-type or undoped Al _X Ga _1-X As layer, an n-type or undoped GaAs layer is sequentially laminated as the current blocking layer, and the n-type or doped A plurality of multi-layer stacks of non-Al _X Ga _1-X As layers, n-type or undoped GaAs layers.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

2A is a schematic cross-sectional view illustrating a laser diode according to an embodiment of the present invention.

Referring to FIG. 2A, a laser diode according to an embodiment of the present invention includes a substrate 110 and a laser oscillation layer formed on the substrate 110, and shoulder portions at both sides of the ridge structure of the laser oscillation layer. And a current blocking layer having a multilayer structure formed thereon. The current blocking layer is open at the central ridge 150a of the laser oscillation layer, and thus current injection is allowed only to the ridge 150a portion of the second cladding layer 150. The laser generation layer includes an active layer 140 and first and second cladding layers 130 and 150 formed under and over the active layer 140, respectively. The ridge structure starts from the protruding ridge 130a at the center of the first cladding layer 130.

The substrate 110 may be made of n-GaAs. In addition, a buffer layer 120 made of n-GaAs may be formed on an upper surface of the substrate 110.

A first cladding layer 130 having a ridge formed in a center portion thereof is formed on an upper surface of the buffer layer 120. Here, the first cladding layer 130 may be made of n-InGaAlP. In addition, an active layer 140 is formed on the upper surface of the first cladding layer 130 to have a predetermined thickness. The active layer 140 may be made of InGaP. The active layer 140 includes an upper flat portion and an inclined portion respectively positioned on an upper surface and an inclined surface of the ridge 130a of the first cladding layer 130 and lower flat portions positioned on both sides of the ridge. Here, the thickness of the active layer 140 is formed thinner than the thickness of the upper and lower flat portion. As such, when the thickness of the inclined portion is formed by giving a step to the active layer 140, an energy band gap is increased in the inclined portion of the active layer 140, thereby improving light confinement effect. Will be. The second cladding layer 150 is formed in a shape corresponding to the ridge of the first cladding layer 130 on the upper surface of the active layer 140. The second clad layer 150 may be made of p-InGaAlP.

The current blocking layer is formed in the lower p ⁺ -GaAs layer 171, n-GaAs layer 172 and n-Al _x Ga _1-x As (0.5 ?? X ?? 1, where Al is 0.98 ) Oxide 173. Here, as shown in FIG. 2, the n-GaAs / n-Al _x Ga _1-x As stack has a double repetitive multilayer structure, that is, n-GaAs / n-Al _x Ga _1-x As / n-GaAs / It may have a lamination structure of n-Al _x Ga _1-x As / p-GaAs. According to another embodiment, the current blocking layer may simply have a stacked structure of n-GaAs / n-Al _x Ga _1-x As / p-GaAs. Each material layer 171, 172, 173 of the current blocking layer may have a thickness of approximately 20 nm to 1000 nm.

According to other embodiments, the n-GaAs / n-Al _x Ga _1-x As stack of the current blocking layer has a u-GaAs / n-Al _x Ga _1-x As stack structure or n-GaAs / u-Al _It is replaced by a stacked structure of _x Ga _1-x As. In FIG. 2A and FIG. 2B, "u-" means an undoped state.

As described above, each material layer of the current blocking layer is formed to have a smaller thickness at the inclined portion of the ridge 150a than at the lower flat portions at both sides of the ridge. The u-Al _X Ga _1-X As or n-Al _X Ga _1-X As layer 172 of the material layer may be formed of an oxide. The Al _X Ga _1-X As layer is oxidized in a selective wet oxidation method for a predetermined time from both sides of the laser diode.

In the drawings, reference numerals 100 and 200 denote n-type electrodes 100 and p-type electrodes 200 formed on the bottom surface of the substrate 110 and on the current blocking layer, respectively.

In the laser diode having the structure as described above, the light restraining effect can be improved by providing a step in the active layer 140 to form a thin thickness at the inclined portion, and oscillating by providing a current blocking layer including an oxide layer. It is possible to reduce the starting current.

FIG. 2B has a structure in which only one pair of the (u- or n-) Al _X Ga _1-X As layer 172 and the n-GaAs layer 173 of the current blocking layer are formed in the embodiment shown in FIG. 2A. . That is, according to the present invention, the n-Al _X Ga _1-X As layer 172 is a pair of n-GaAs layer 173, and only one pair may be used as shown in FIG. Two tones can be used as shown in FIG. 2A. Meanwhile, according to another exemplary embodiment, three or more n-GaAs layers 173 may be provided in the Al _X Ga _1-X As layer 172. In addition to the modification, the doped or undoped Al _X Ga _1-X As and n-GaAs are selectively applied to the stack structure as described above.

Hereinafter, a method of manufacturing a laser diode according to an embodiment of the present invention will be described with reference to FIGS. 3A to 3E.

First, referring to FIG. 3A, an n-GaAs buffer layer 120 is formed on a substrate 110 made of n-GaAs, and a first cladding layer 130 made of n-InGaAlP is formed on an upper surface of the buffer layer 120. To form a predetermined thickness. Next, referring to FIG. 3B, an etch mask 250 is formed on a center portion of the upper surface of the first cladding layer 130. Here, the etching mask 250 may be made of SiO ₂ . The etching mask 250 may be formed by forming a SiO ₂ layer on an upper surface of the first cladding layer 130 and patterning the SiO ₂ layer into a predetermined shape by a photolithography process. In addition, when the first cladding layer 130 on both sides of the etching mask 250 is inclinedly etched to a predetermined depth and the etching mask 250 is removed, a ridge is formed at the center of the first cladding layer 130. Is formed.

Subsequently, referring to FIG. 3C, an active layer 140 made of InGaP is formed on the upper surface of the first cladding layer 130 on which the ridges are formed. The active layer 140 includes an upper flat portion and an inclined portion respectively positioned on an upper surface and an inclined surface of the ridge formed on the first cladding layer 130 and lower flat portions positioned on both sides of the ridge. Here, since the active layer 140 is formed to grow on the upper surface of the first cladding layer 130, the thickness in the inclined portion is generally formed thinner than the thickness in the upper and lower flat portion. Next, a second cladding layer 150 made of p-InGaAlP is formed on the top surface of the active layer 140 to correspond to the ridges of the first cladding layer 130, and the upper portion of the second cladding layer 150 is formed. P-GaAs 171 is formed in the current blocking layers 172 and 173 thereon.

The current blocking layer includes at least one n- or u-Al _X Ga _1-X As (0.5 ?? X ?? 1) layer 172 and at least one n- or u- GaAs layer 173. . Here, although FIG. 3C illustrates that the Al _X Ga _1-X As layer 172 and the GaAs are two pieces, the present invention is not limited thereto and may be formed of one stack or two or more stacks as described above. The current blocking layer is formed on both sides of the ridge of the first cladding layer 130 and on both sides of the ridge of the first cladding layer 130. Each of the material layers 172 and 173 of the current blocking layer is formed to have a smaller thickness at the inclined portion than at the upper and lower flat portions.

As shown in FIG. 3D, a window W for current passing over the ridge is formed in the current blocking layer by patterning and selective wet etching. Here, the GaAs layer is etched using a citric acid / H ₂ O ₂ , and the AlGaAs layer using a H ₂ O / Buffered HF mixture.

Referring to FIG. 3E, the n-Al _X Ga _1-X As layer 172 of the current blocking layer is oxidized. To this end, it may be formed by oxidizing for a predetermined time by a selective wet oxidation method from both sides of the p-Al _X Ga _1-X As layer 172. Here, the thinner the p-Al _X Ga _1-X As layer, the slower the oxidation rate becomes, so that the oxidation rate at the inclined portion of the ridge is lower than the oxidation rate at the lower flat portion. Finally, referring to FIG. 3F, when the n-type electrode 100 and the p-type electrode 200 are formed on the bottom surface of the n-GaAs substrate 110 and the current blocking layer, respectively, according to the embodiment of the present invention. The laser diode according to this is completed.

As such, since the laser diode according to the embodiment of the present invention can be manufactured in one regrowth, the manufacturing process is simple, and the current blocking region can be easily formed by the oxidation rate difference of the material layer thickness.

Although the preferred embodiment according to the present invention has been described above, this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

As described above, according to the present invention, it is possible to improve the light restraining effect by providing a step in the active layer to form a thin thickness at the inclined portion, and to reduce the oscillation starting current by providing a current blocking region made of oxide. do. In addition, since the laser diode according to the embodiment of the present invention can be manufactured by one regrowth, the manufacturing process is simple, and the current blocking region can be easily formed by the oxidation rate difference of the thickness of the material layer.

Claims (17)

Board; A first cladding layer formed on the substrate and having a ridge formed at a center thereof; An active layer formed on an upper surface of the first clad layer and including an upper flat portion and an inclined portion disposed on an upper surface and an inclined surface of the ridge and lower flat portions positioned on both sides of the ridge; A second clad layer formed on a top surface of the active layer in a shape corresponding to the ridge of the first clad layer; And And a current blocking layer including an oxide layer and having a window corresponding to an upper flat portion of the ridge above the second cladding layer. The method of claim 1, And the inclined portion of the active layer is thinner than the upper and lower flat portions of the active layer. The method according to claim 1 or 2, The current blocking layer is a laser diode, characterized in that it comprises an n-Al _X Ga _1-X As layer, n-GaAs layer. The method according to claim 1 or 2, The current blocking layer is a laser diode, characterized in that it comprises an undoped Al _X Ga _1-X As layer, n-GaAs layer. The method according to claim 1 or 2, Wherein the current blocking layer comprises an undoped Al _X Ga _1-X As layer and an undoped GaAs layer. The method according to claim 1 or 2, The current blocking layer is p ⁺ -GaAs n- type or non-doped layer being sequentially stacked on the _X Ga _1-X As layer Al, n-GaAs having a layer, the n- type or undoped Al _X Ga _1-X As layer, n-GaAs layer is a laser diode, characterized in that a plurality of layers are repeatedly stacked. The method of claim 3, wherein The current blocking layer is a laser diode, characterized in that thinner than other portions on the inclined surfaces on both sides of the ridge. Forming a first clad layer on the substrate; Forming a ridge in a center portion of the first clad layer; Sequentially forming an active layer and a second cladding layer in a shape corresponding to the ridge on the first cladding layer; Forming a current blocking layer including at least one semiconductor material layer on the second clad layer; Forming a window for current passing through a portion of the current blocking layer corresponding to the upper surface of the ridge; And Oxidizing both sides of the semiconductor material layer selected from the current blocking layer. The method of claim 8, Forming the ridge; Forming an etch mask in a center portion of the first clad layer; And And etching the first cladding layers positioned at both sides of the etching mask to a predetermined depth. The method of claim 8, The current blocking layer is a laser diode manufacturing method, characterized in that it comprises an n-Al _X Ga _1-X As layer, n-GaAs layer. The method of claim 8, The current blocking layer is a laser diode manufacturing method, characterized in that it comprises an undoped Al _X Ga _1-X As layer, n-GaAs layer. The method of claim 8, Wherein the current blocking layer comprises an undoped Al _X Ga _1-X As layer and an undoped GaAs layer. The method of claim 10, The current blocking layer includes a window corresponding to the ridge of the second cladding layer, an inclined portion on both sides of the ridge, and a lower flat portion corresponding to both sides of the ridge. The method of claim 8 or 13, Forming the window; Forming an etching mask on a portion of the current blocking layer to form a window; And And etching the current blocking layer of the window portion of the etching mask by a selective wet method up to a p ⁺ -GaAs layer. The method of claim 14, Selective wet etching, A method of manufacturing a laser diode, characterized in that the GaAs layer is wet etched with citric acid / H ₂ O ₂ solution and the AlGaAs layer is H ₂ O / Buffered HF solution. The method of claim 13, And the material layer is oxidized by a selective wet oxidation method. The method of claim 8, N- type or non-doped layer as the current blocking layer Al _X Ga _1-X As, n- type or are undoped and stacking a GaAs layer, it is not doped with the n- type or Al _X Ga _1-X A method of fabricating a laser diode, characterized in that multiple layers of multiple layers of an As layer, n-type or undoped GaAs layer are laminated.

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