KR20020004275A - Fabricating Method for Nitride Semiconductor Laser Diode - Google Patents

Abstract

PURPOSE: A method for fabricating a nitride semiconductor laser diode is provided to form a laser diode used as a light source of a DVD(Digital Video Disk) system by reducing a damage of an active layer and a contact resistance between a p-type semiconductor and a metal. CONSTITUTION: The first contact layer(12) is formed on a substrate(11). A projection portion is formed by removing a predetermined region of the first contact layer(12). A current limit layer is formed on the projection portion except for an upper portion of the projection portion. The first clad layer(18), the first waveguide layer(19), an active layer(20), the second waveguide layer(21), the second clad layer(22), and the second contact layer(23) are formed sequentially on the current limit layer and the projection portion. A predetermined region of the first contact layer(12) is exposed by removing the second contact layer(23), the second clad layer(22), the second waveguide layer(21), the active layer(20), the first waveguide layer(19), the first clad layer(18), and the current limit layer, selectively. A metal(24,25) is formed on the exposed portion of the first contact layer(12) and the second contact layer(23).

Description

Fabrication Method for Nitride Semiconductor Laser Diode

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a structure for satisfying a specification required for using a nitride semiconductor laser as a light source of a DVD (Digital Versatile Disc) system, and more particularly, to a method for manufacturing a nitride semiconductor laser diode.

In recent years, nitride semiconductors have attracted great attention as materials for short wavelength light emitting diodes or semiconductor lasers that can emit blue violet colors, and many studies have been conducted on them. In particular, it is believed that a blue violet semiconductor laser using this material can be applied as a light source of a high density information storage medium.

In order to operate a semiconductor laser at a low threshold current, current supply to the active layer and side light confinement must be efficiently performed. In particular, the side limitations of the light make the shape of the beam emitted from the laser a good form for DVD systems.

Conventional nitride semiconductor lasers have a p-n diode structure that guides light by forming a waveguide layer and a cladding layer around the active layer.

The current limit and the light limit in the vertical direction use a double heterojunction structure with a band gap difference and a method of introducing a waveguide layer and a cladding layer to make use of the dielectric constant difference.

In general, in order to limit the lateral diffusion of the current in the horizontal direction, a ridge is formed on the p-type semiconductor side to reduce the asymmetry of the active region. This can limit the larger lateral diffusion by reducing the ridge width, but when the ridge width is reduced, the contact resistance between the p-type semiconductor and the metal increases the overall resistance of the device and degrades the device's performance.

Therefore, there is a limit in forming a ridge to reduce the lateral diffusion of the current, so the problem of astigmatism due to the asymmetry of the active region in the form of light emitted through the diode is serious.

In general, the problem of astigmatism is known to be worse with shorter wavelengths. Therefore, in the case of a nitride semiconductor laser, since the center wavelength is around 410 nm, the astigmatism problem is more serious than that of devices (650 nm, 780 nm, 808 nm) using InGaAsP or AlGaAs. The shape of the light is represented by a vertical emission angle and a horizontal emission angle. Generally, the horizontal emission angle is significantly smaller than the vertical emission angle. Therefore, increasing the horizontal radiation angle by reducing the horizontal length of the active area is necessary in terms of increasing the utility of the DVD system as a light source.

In order to limit the light side, a buried ridge form may be introduced in which the ridge is sandwiched from side to side by the Al _X Ga _1-X N cladding layer.

Since the buried ridge structure requires a process of cooling after the active layer is grown and growing an upper layer such as an Al _X Ga _1-X N layer, thermal shock is not prevented from being applied to the active layer. Optical loss occurs at the interface between the already grown active layer structure and the newly grown Al _X Ga _1-X N layer, and the active layer is thermally impacted while the Al _X Ga _1-X N layer is newly grown. In addition, even if the metal is deposited on the entire surface of the p-type semiconductor in order to reduce the contact resistance between the p-type semiconductor and the metal, the high resistance of the Al _X Ga _1-X N layer does not show a great effect.

1 is a view showing a ridge structure nitride semiconductor laser for limiting the side diffusion of the current according to the prior art.

In general, the GaN waveguides (4, 6) and the In _x Ga _1-x N / GaN active layer (5: multi-well structure or double heterojunction structure) are mainly used for emitting pn diodes. It is surrounded by Al _1-X Ga _X N (3) and p-Al _X Ga _1-X N (7) to guide the generated light while keeping electrons and holes from leaving the active layer 5 as much as possible. You will.

A p-GaN contact layer 8 is formed on the p-Al _X Ga _1-X N (7) to prevent the contact resistance with the metal 9 from being too high, and an n-GaN contact layer serving as the base material below. (2) is formed on the sapphire substrate 1 which is generally used.

The nitride semiconductor laser diode manufacturing method according to the related art described above has the following problems.

First, since the laser diode using the pn diode structure that guides light by forming a waveguide layer and a clad layer around the active layer has a limit in forming a ridge to reduce side diffusion of current, the shape of light emitted through the diode is in the active region. The problem of astigmatism due to the asymmetry of is severe.

Second, in the buried ridge type laser diode, optical loss and thermal shock of the active layer occur at the interface between the already grown active layer and the newly grown clad layer.

It is difficult to reduce the contact resistance between the semiconductor and the metal.

Therefore, the present invention has been made to solve the above problems, to obtain a current limiting effect without introducing a ridge in increasing the horizontal emission angle of the light while suppressing damage to the active layer, reducing the contact resistance between the p-type semiconductor and the metal To provide a method for producing a nitride semiconductor laser diode suitable as a light source of the DVD system.

1 is a cross-sectional view of a structure of a nitride semiconductor laser diode according to the prior art

2A to 2G are sectional views of the manufacturing process of the nitride semiconductor laser diode according to the present invention.

* Explanation of symbols for main parts of the drawings

1: sapphire substrate 2: n-GaN contact layer

3: Al _X Ga _1-X N 4: n-GaN waveguide

5: In _x Ga _1-x N / GaN active layer 6: p-GaN waveguide layer

7: p-Al _X Ga _1-X N 8: p-GaN contact layer

9: p electrode 10: n electrode

11 sapphire substrate 12 n-GaN contact layer

13: dielectric mask 14: n-GaN buffer layer

15: p-Al _X Ga _1-X N layer 16: p-GaN layer

17: n-GaN buffer layer 18: n-Al _X Ga _1-X N cladding layer

19: n-GaN waveguide layer 20: In _x Ga _1-x N / GaN active layer

21: p-GaN waveguide layer 22: p-Al _X Ga _1-X N clad layer

23: p-GaN contact layer 24: p electrode

25: n electrode

A feature of the method for manufacturing a nitride semiconductor laser diode according to the present invention for achieving the above object is to form a first contact layer on the substrate, and to remove the predetermined region of the first contact layer by a predetermined depth to form a protrusion A first step, a second step of forming a current limiting layer so as to cover the first contact layer except the upper surface of the protrusion, a first cladding layer, a first waveguide layer in the current limiting layer and the protrusion, A third step of sequentially forming an active layer, a second waveguide layer, a second cladding layer, and a second contacting layer; the second contacting layer and the second cladding layer to expose a predetermined region of the first contacting layer; And, a fourth step of selectively removing the second waveguide layer, the active layer, the first waveguide layer, the first cladding layer, and the current limiting layer, the predetermined region of the exposed first contact layer and the second To form a metal on the contact layer It includes a fifth step.

A buffer layer may be further formed below the first cladding layer, and a buffer layer may be further formed below the current limiting layer.

The current limiting layer is formed with a plurality of inclinations, and the current limiting layer formed with the least inclination among the inclinations of the multistage is formed by 100 nm to 1 μm lower than the upper surface of the protrusion.

The action according to the characteristics of the present invention solves the astigmatism problem by increasing the horizontal radiation angle by limiting the current in the lateral direction by introducing a current limiting layer, and forming a metal on the entire surface of the p-type semiconductor to form a p-type The high resistance between the semiconductor and the metal can be reduced, and the optical loss and thermal shock of the active layer can be reduced.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

A preferred embodiment of the nitride semiconductor laser diode manufacturing method according to the present invention will be described with reference to the accompanying drawings.

2A to 2G are cross-sectional views of a manufacturing process of a nitride semiconductor laser diode according to the present invention.

First, as shown in FIG. 2A, an n-GaN contact layer 12 is formed on the sapphire substrate 11. Subsequently, as shown in FIG. 2B, a dielectric mask 13 such as SiO ₂ or Si ₃ N ₄ is used only on a portion of the n-GaN contact layer 12 to be a current path region using PECVD deposition and photolithography. To form.

Subsequently, as illustrated in FIG. 2C, the n-GaN contact layer 12 in the region where the dielectric mask 13 is not formed is etched using the dielectric mask 13 by a predetermined depth. That is, the remaining portions are etched except for the portion through which the current passes (current path width: W).

Next, as shown in FIG. 2D, an n-GaN buffer layer 14, a p-Al _X Ga _1-X N layer 15, and a p-GaN layer are formed on the side of the etched n-GaN contact layer 12. 16 is formed by performing selective epitaxial growth.

Then, as shown in FIG. 2E, the dielectric mask mask 13 is removed.

Next, as shown in FIG. 2F, the n-GaN buffer layer 17, the n-Al _X Ga _1-X N clad layer 18, the n-GaN waveguide layer 19, and In _x Ga _{1- The x} N / GaN active layer 20, the p-GaN waveguide layer 21, the p-Al _X Ga _1-X N clad layer 22, and the p-GaN contact layer 23 are grown. The n-GaN buffer layer 14 serves as a buffer for the growth of the n-Al _X Ga _1-X N layer 15, and the p-GaN layer 16 and the n-GaN buffer layer 17 are subsequently grown. It acts as a buffer for

Next, as shown in FIG. 2G, dry etching is performed to expose the n-GaN contact layer 12 to form a mesa, and then to the n-GaN contact layer 12 and the p-GaN contact layer 23. P and n metals 24 and 25 are formed, respectively. The p metal 24 is deposited using the upper portion of the mesa. The p-GaN contact layer 23 has a higher doping concentration than the p-GaN waveguide layer 21 in order to lower the contact resistance with the p metal 24.

The current cannot flow to the portion of the p-Al _X Ga _1-X N layer 15 and the p-GaN layer 16 except the current path width W. The current limiting effect can be obtained in the left and right directions without using a ridge. As a result, the p-metal 24 may be deposited on the p-GaN contact layer 23 to be formed on the front surface, thereby having a low contact resistance between the p-GaN contact layer 23 and the p-metal 24.

In addition, looking at the active layer 20 above the current path width W, the p-GaN waveguide layer 21 and the p-Al _X Ga _1-X N cladding layer 22 can be seen to the left and right. As a result, the side in which the light is guided in the lateral direction, that is, the lateral index guiding effect occurs.

In addition, since the In _x Ga _1-x N / GaN active layer 20 is grown in the fabrication process, it is cooled and then subjected to a process of growing the upper layer again, so that an additional thermal shock is applied to the active layer 20. It brings excellent light guiding effect.

Therefore, by introducing current blocking layers such as p-Al _X Ga _1-X N layer 15 and p-GaN layer 16 without forming a ridge on the p-type semiconductor side, current limiting effect in the left and right directions is obtained. The p metal 24 can be formed on the entire surface of the p-type semiconductor, thereby reducing the high resistance between the p-type semiconductor and the metal, and leading to excellent light guiding effects in the lateral direction without thermally impacting the active layer 20. Introduce the structure.

Here, the height of the current path formed in the n-GaN contact layer 12, the thickness of the n-GaN buffer layer 14, the p-Al _X Ga _1-X N layer 15, and the p-GaN layer 16 If not properly adjusted, the side index guiding effect by the p-GaN waveguide layer 21 and the p-Al _X Ga _1-X N cladding layer 22 cannot be made large. That is, when the inclination is too gentle, the thickness of the p-GaN waveguide layer 21 and the p-Al _X Ga _1-X N cladding layer 22, which the light senses to the side, becomes too thick, resulting in p-Al _X Ga _{1 Because the -X} N cladding layer 22 is far away, no suitable light limiting effect can be expected. On the other hand, if the step is too large, growth is unlikely to occur to cover the side and bottom. This step difference range is 100 nm to 1 m.

The nitride semiconductor laser diode manufacturing method according to the present invention as described above has the following effects.

First, it solves the astigmatism problem caused by the asymmetry of the active region because the horizontal radiation angle is increased by limiting the current in the lateral direction by introducing a current blocking layer without forming a ridge on the p-type semiconductor side. It can be formed on the entire surface of the p-type semiconductor has the effect of reducing the high resistance between the p-type semiconductor and the metal.

Second, since the cooling process after the active layer is grown in the manufacturing process, and does not undergo the process of growing the upper layer again, it has excellent optical properties by reducing the thermal shock on the active layer.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (5)

A first step of forming a first contact layer on the substrate and removing a predetermined region of the first contact layer by a predetermined depth to form a protrusion; Forming a current limiting layer to cover the first contact layer except for the upper surface of the protrusion; A third step of sequentially forming a first cladding layer, a first waveguide layer, an active layer, a second waveguide layer, a second cladding layer, and a second contact layer on the current limiting layer and the protruding portion; The second contact layer, the second cladding layer, the second waveguide layer, the active layer, the first waveguide layer, the first cladding layer, and the current limiting layer are selectively exposed so that a predetermined region of the first contact layer is exposed. With the fourth step to remove, And a fifth step of forming a metal on the predetermined region of the exposed first contact layer and the second contact layer. The method of claim 1, wherein a buffer film is further formed under the first cladding layer. The method of claim 1, wherein a buffer film is further formed below the current limiting layer. The method of claim 1, wherein the current limiting layer is formed with a slope of multiple stages. The method of claim 4, wherein The current limiting layer formed with the least slope of the multi-stage inclination of the nitride semiconductor laser diode manufacturing method, characterized in that formed by 100nm ~ 1㎛ lower than the upper surface of the protrusion.