KR100269384B1 - Laser diode and method for fabricating the same - Google Patents

Abstract

The present invention relates to a laser diode having a buried tapered ridge (BTR) structure and a method of manufacturing the same, the method comprising: a first conductive cladding layer, an active layer, a second conductive first cladding layer, and an etching method on a first conductive substrate; After the stop layer, the second conductivity type second clad layer, the second conductivity type InGaP layer, and the second conductivity type GaAs layer are sequentially formed, a first insulating film is formed on the second conductivity type GaAs layer and patterned to form a predetermined region. The second conductivity type GaAs layer is exposed. The second conductive type GaAs layer, the second conductive type InGaP layer, and the second conductive type second clad layer are removed to a predetermined depth by reactive ion etching using the patterned first insulating layer as a mask. Exposing the etch stop layer by removing the second conductive second clad layer remaining in the wet etching while leaving a portion of the clad layer, a current blocking layer is formed on the exposed etch stop layer, and the current on the front surface including the current blocking layer. By forming the conductive layer and forming the electrodes on the upper side of the current conducting layer and the lower side of the substrate, the optical system can maintain the characteristics of the index guiding laser itself and at the same time obtain the improvement of the optical characteristics obtained from the tapered ridge structure. Can be applied more efficiently.

Description

Laser diode and manufacturing method thereof

The present invention relates to a laser diode, and more particularly, to a laser diode having a buried tapered ridge structure (BTR) and a method of manufacturing the same.

Currently, the 635nm, 650nm and 670nm bands of visible light semiconductor laser diodes that are commonly manufactured are index waveguide-type using InGap / AlGaInP heterostructures.

Epi structures for the fabrication of such semiconductor laser diodes generally avoid several superlattice structures that occur naturally during crystal growth and generally require a few degrees of wavelength to obtain shorter wavelengths in relation to optical recording densities. For example, 9 degrees and 15 degrees) are fabricated on a misoriented substrate.

Therefore, when the ridge is formed by using wet etching during device fabrication, the ridge is shaped asymmetrically by the influence of the substrate.

As a result, the horizontal radiation angle is reduced and the stability of the mode is reduced.

In addition, it has a considerable effect on the increase in mass productivity and yield due to the instability of the wet etching.

Referring to the drawings in more detail a conventional laser diode having the above problems as follows.

FIG. 1 is an index guided AlGaInP laser structure which is widely used as a SBR (Selectively Buried Ridge) waveguide laser diode fabricated using wet etching.

In order to maintain a uniform thickness t, as shown in FIG.

The thickness t is an important factor that affects the mode, optical and current characteristics of the laser. It is essential to maintain the thickness t.

SBR structure as shown in Figure 2 is a big advantage in the simplicity of manufacturing, but basically has a structural problem in manufacturing.

That is, since the ridge is formed through wet etching using the insulating film as a mask, the ridge is formed between the top ridge width W _T and the bottom ridge width W _B as shown in FIG. 2. Differences occur and asymmetrical shapes such as angle a and angle b occur due to substrate characteristics.

Here, the size of W _T is related to the oscillation start current (I _th ) among the current characteristics, and the size of W _B is closely related to the characteristics of the parallel far-field angle among optical characteristics.

In the SBR structure, the size of the insulating film is controlled and the size of W _T and W _B is controlled. Since the trade off between the oscillation start current and the horizontal radiation occurs between W _T and W _B , the two characteristics are simultaneously improved. It is necessary to make a ridge structure to make it.

That is, in order to increase the number m square is W _B should be less, which W _T also more reduced eventually W _T is surface reduces below one size oscillation start current is rapidly increased is limited to the size of W _B occurs because .

On the contrary, in order to reduce the oscillation starting current, W _T must be large, which results in increasing the size of W _B , thereby reducing the horizontal radiation angle.

Initially, in a gain guiding laser structure, a tapered ridge structure for freely adjusting the spot size of the beam and the radius of curvature of the phase front, respectively. Was introduced.

In other words, the center portion of the ridge is formed in a straight portion like conventional lasers, and the structure of the ridge width is reduced toward the facet (light) gradually.

This resulted in the improvement of the optical characteristics mentioned above, but due to the fundamental structure of the gain guiding laser, there is a problem when applied to the optical system due to bad single mode operation and high astigmatism.

Therefore, an index guiding laser structure is required for stable single mode operation, low astigmatism, and high mode stability.

In order to implement this, a structure for making a current blocking layer on the ridge side like the SBR structure described above is appropriate.

However, various problems occur when the tapered ridge is formed by using wet etching.

That is to say, the problem related to the structural formation of the ridge.

And, in order to improve the problems caused when forming the ridge of the SBR structure by the aforementioned wet etching and the structural problems occurring in forming the tapered ridge by the wet etching, as shown in Figure 3 using a reactive ion etching Much research has been done to create vertical ridge structures.

Reactive ion etching is anisotropic etching, which can easily realize symmetrical and vertical ridge structure even in epi structure grown on misoriented wafer. Because.

As shown in FIG. 3, the difference between W _T and W _B is small compared to the ridge structure using wet etching shown in FIG. 2, thereby satisfying the aforementioned characteristics.

However, the method using the reactive ion etching cannot use the etch stop layer as shown in FIG. 2 to maintain the thickness of t mentioned above. Therefore, it is necessary to rely solely on the uniformity and the etching thickness control ability of the reactive ion etching. Many problems are pointed out compared to the structure.

In addition, since the surface is damaged by reactive ion etching, there may be a problem in growing a current blocking layer.

The laser diode according to the prior art has the following problems.

Gain guiding laser structures present several problems when applied to optical systems due to poor single mode operation and astigmatism.

The index guiding laser structure fabricated using wet etching has a symmetrical ridge shape, which reduces the size of the horizontal emission angle and reduces the stability of the mode.

In addition, since the index guiding laser structure manufactured by using reactive ion etching cannot use an etch stop layer, it is necessary to rely on the uniformity of reactive ion etching and the ability to adjust the etching thickness.

The present invention is to solve this problem by introducing a reactive ion etching process by applying a tapered ridge structure to the laser of the index guiding type, excellent characteristics of the index guiding structure itself It is an object of the present invention to provide a laser diode and a method of manufacturing the same having excellent characteristics of a tapered ridge structure.

1 to 3 is a structural cross-sectional view showing a laser diode according to the prior art

Figures 4a to 4i is a cross-sectional view showing a manufacturing process of a laser diode according to the present invention

Explanation of symbols for main parts of the drawings

11: n-type GaAs substrate 12: n-type GaAs buffer layer

13: n-type AlGaInP clad layer 14: active layer

15: p-type primary AlGaInP clad layer 16: p-type InGaP etch stop layer

17: p-type secondary AlGaInP clad layer 18: p-type InGaP layer

19 p-type GaAs layer 20 insulating film

21 n-type GaAs current blocking layer 22 photoresist

23: p-type GaAs current conducting layer 24: p-type electrode

25: n-type electrode

The main feature of the laser diode according to the present invention is to form a tapered ridge in the index guiding structure whose width is narrower than that of other portions.

Another feature of the laser diode of the present invention is a laser diode having an active layer between epi layers formed on a substrate, the ridge being formed in a predetermined area on the epi layer and having a front width narrower than the width of the other portion, and formed on both sides of the ridge. The current blocking layer, the current conducting layer formed on the ridge and the current blocking layer, and the electrode formed on the upper portion of the current conducting layer and the lower substrate.

The laser diode manufacturing method according to the present invention is characterized in that the first conductivity type cladding layer, the active layer, the second conductivity type first cladding layer, the etch stop layer, the second conductivity type second cladding layer, A step of sequentially forming a second conductivity type InGaP layer and a second conductivity type GaAs layer, forming and patterning a first insulating film on the second conductivity type GaAs layer to expose a second conductivity type GaAs layer in a predetermined region; The second conductive type GaAs layer, the second conductive type InGaP layer, and the second conductive type second clad layer are removed to a predetermined depth by reactive ion etching using the patterned first insulating layer as a mask, and the second conductive type second clad layer is removed. Exposing the etch stop layer by removing the second conductive second cladding layer remaining in the wet etch, leaving a portion of the etch stop; forming a current blocking layer on the exposed etch stop layer and conducting a current through the entire surface including the current blocking layer. Forming a layer There makin made to a step of forming a tab on each electrode, a current-conductive layer and the upper substrate lower.

A laser diode and a method of manufacturing the same according to the present invention having the above characteristics will be described with reference to the accompanying drawings.

The inventive concept provides stable single mode operation, low astigmatism, high mode by applying a tapered ridge structure to an index guiding type laser using reactive ion etching and wet etching processes. It is to ensure the excellent characteristics of the stability of the index guiding structure and the tapered structure having a large horizontal radiation angle.

4A to 4I are process cross-sectional views showing a manufacturing process of a laser diode according to the present invention. As shown in FIG. 4A, an n-type GaAs buffer layer 12 and an n-type AlGaInP clad layer on an n-type GaAs substrate 11 are shown. (13), active layer 14, p-type primary AlGaInP cladding layer 15, p-type InGaP etch stop layer 16, p-type secondary AlGaInP cladding layer 17, p-type InGaP layer 18, p The GaAs layer 19 is grown sequentially.

Subsequently, as shown in FIG. 4B, an insulating film 20 is formed on the p-type GaAs layer 19, and as shown in FIG. 4C, an insulating film is formed to fabricate a tapered type ridge structure. The p-type GaAs layer 19 in the predetermined region is exposed by patterning the 20 in a shape where the width of the front surface is narrower than that of the other portions.

Here, the insulating film 20 is formed of SiO ₂ or SiN _X.

4D, the p-type GaAs layer 19, the p-type InGaP layer 18, and the p-type secondary AlGaInP clad layer 17 exposed by reactive ion etching the patterned insulating layer 20 using a mask are exposed. Remove part of).

Here, the thickness t of the p-type secondary AlGaInP cladding layer 17 on the p-type InGaP etch stop layer 16 is appropriately adjusted so that the thickness t is about 500 to 1500 mW.

This is related to the removal of damage layer on the surface resulting from reactive ion etching and the wet etching process which is a post process.

Subsequently, as shown in FIG. 4E, the p-type secondary AlGaInP clad layer 17 remaining by the thickness t by wet etching is removed, and the remaining insulating layer 20 is removed.

After the etching process, the overall ridge shape maintains a vertical structure, and the width of the front surface of the ridge is narrower than that of other parts, thereby increasing the horizontal radial angle.

As shown in FIG. 4F, an n-type GaAs current blocking layer 21 is formed on the entire surface including the ridge, and as shown in FIG. 4G, a photoresist is formed on the n-type GaAs current blocking layer 21. After forming 22, the photoresist 22 is patterned to expose the n-type GaAs current blocking layer 21 on the ridge.

Subsequently, as shown in FIG. 4H, the exposed n-type GaAs current blocking layer 21 is wet etched to expose the p-type GaAs layer 19, the remaining photoresist 22 is removed, and then the n-type GaAs The p-type GaAs current conducting layer 23 is formed on the entire surface including the current blocking layer 21.

4I, a p-type electrode 24 is formed on the p-type GaAs current conducting layer 23, and an n-type electrode 25 is formed below the n-type GaAs substrate 11 to form a laser diode. To produce.

The laser diode and the method of manufacturing the same according to the present invention have the following effects.

The present invention applies the tapered ridge structure to the index guiding laser by using reactive ion etching and wet etching, thereby maintaining the characteristics of the index guiding laser itself and improving the optical properties that can be obtained from the tapered ridge structure. You can get it.

Therefore, it can be applied more efficiently in the optical system.

In addition, since uniformity and reproducibility are better than a process using only wet etching, mass productivity and yield can be improved.

Claims (3)

In a laser diode having an active layer between epi layers formed on a substrate, A ridge formed in a predetermined area on the epi layer, the width of the front surface being narrower than the width of the other portion; Current blocking layers formed on both sides of the ridge; A current conducting layer formed on the ridge and the current blocking layer; And a electrode formed above the current conducting layer and below the substrate. In a laser diode having an active layer between a first conductive cladding layer formed on a substrate and a second conductive first cladding layer, An etch stop layer formed in a predetermined region of the second conductive first clad layer; A second conductivity type second cladding layer, a second conductivity type InGaP layer, and a second conductivity type GaAs layer are sequentially formed on the etch stop layer, and the width of the front surface is smaller than that of the other portions; Current blocking layers formed on both sides of the ridge; A current conducting layer formed on the ridge and the current blocking layer; And a electrode formed above the current conducting layer and below the substrate. On the first conductive substrate, the first conductive cladding layer, the active layer, the second conductive first cladding layer, the etch stop layer, the second conductive second cladding layer, the second conductive InGaP layer, and the second conductive GaAs Sequentially forming the layers; Forming and patterning an insulating film on the second conductivity type GaAs layer to expose the second conductivity type GaAs layer in a predetermined region; Reactive ion etching of the patterned insulating layer using a mask removes the exposed second conductive GaAs layer, the second conductive InGaP layer, and the second conductive second clad layer to a predetermined depth, thereby removing the second conductive second clad layer. Removing the second conductive type cladding layer remaining in the wet etching, leaving a portion of the exposed portion to expose the etch stop layer; Removing the remaining insulating film, forming a current blocking layer on the exposed etch stop layer, and then forming a current conducting layer on the entire surface including the current blocking layer; And a step of forming an electrode on the upper portion of the current conducting layer and the lower portion of the substrate, respectively.