KR20070092030A - Laser diode and method of fabricating the same - Google Patents

Abstract

A laser diode and a manufacturing method thereof are provided to improve the thermal-stress resistant property of the laser diode by effectively radiating the heat from an activation layer through a metal layer and to improve the reliability of laser diode. Plural grooves are formed at a lower portion of a substrate. A metal layer fills in the plural grooves and is formed at the lower portion of the substrate. An n-contact layer(121) is formed on the substrate. A portion of the n-contact layer is etched to a predetermined depth. An n-electrode(140b) is formed on the etched portion on the n-contact layer. An n-cladding layer(122) is formed on the rest portion of the n-contact layer. A thin structure is formed on the n-cladding layer and contains an n-transport layer, an activation layer, an electron blocking layer, and a p-transport layer. A p-cladding layer(127) is formed on the p-transport layer and contains a ridge on an upper portion thereof. A p-contact layer(128) is formed on the ridge of the p-cladding layer. An insulation film(130) is formed to enclose an exposed surface of the p-cladding layer and an external surface of the p-contact layer. An insulation film includes an aperture for exposing the p-contact layer. A p-electrode(140a) fills in the aperture of the insulation film and is electrically connected to the p-contact layer.

Description

Laser diode and its manufacturing method {Laser Diode And Method Of Fabricating The Same}

1A or 1B is a cross-sectional view for schematically illustrating a conventional laser diode.

2 is a cross-sectional view illustrating a structure in which a conventional vertical electrode structure laser diode is assembled into a junction-up structure.

3 is a graph illustrating a change in active layer temperature according to a width of a lower portion of a laser diode chip when the laser diode is mounted in a junction-up structure as shown in FIG. 2.

4A or 4B are cross-sectional views for explaining the structure of a laser diode according to the present invention.

5A to 5F are horizontal cross-sectional views illustrating various groove shapes for improving heat dissipation efficiency of a trench structure substrate according to the present invention.

6A to 6G are cross-sectional views illustrating a method of manufacturing a laser diode having a vertical electrode structure according to the present invention.

<Description of main parts of drawing>

100. Substrate 120. Epi layer

121. n-Contact Layer 122. n-Clad Layer

123. n-wave layer 124. active layer

125. Electromagnetic barrier layer (EBL) 126. p-waveguide layer

127. p-clad layer 128. p-contact layer

130. The insulating film 140a. P-electrode

140b. N-electrode 110.Metal layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode (LD) and a manufacturing method thereof, and more particularly to a nitride semiconductor laser diode having a substrate having a structure capable of improving thermal and electrical characteristics of the laser diode.

Recently, as optical recording / reproducing devices such as digital versatile disks (DVDs) are widely used, demand for semiconductor laser diodes (LDs), which are core components of optical recording devices, is rapidly increasing.

Hereinafter, a general structure and a problem of a conventional semiconductor laser diode will be described with reference to the drawings.

1A or 1B illustrate a cross-sectional view of a laser diode of a general horizontal electrode structure and a vertical electrode structure, and as shown in the drawing, both laser diodes include a substrate 10, an epi layer 20, an insulating film 30, It basically has a P-electrode 40a and an N-electrode 40b.

First, in FIG. 1A, the substrate 10 forms the lowermost part of the laser diode, and is mainly made of an insulating substrate such as a sapphire (Al ₂ O ₃ ) substrate.

An epitaxial layer 20 is formed on the substrate 10. The epitaxial layer 20 includes an n-contact layer 21, an n-clad layer 22, and an n−. Waveguide 23, active layer 24, p-electron blocking layer (EBL) 25, p-waveguide 26, p-clad layer 27, p-contact layer 28 This is deposited sequentially.

The p-clad layer 27 and the p-contact layer 28 belonging to the uppermost layer of the epitaxial layer 20 are formed to have a ridge structure.

Here, the ridge structure as described above is formed by partially etching the remaining regions of the p-clad layer 27 except for the region to be formed as the ridge structure.

Meanwhile, the laser diode having a horizontal electrode structure is etched to a certain depth of the n-contact layer 21 in a portion of the p-clad layer 27.

An N-electrode 40b is formed on the n-contact layer 21 in the etched region.

In addition, the etched side portions of the upper region of the p-clad layer 27 and the epi layer 20 except the upper portion of the n-contact layer 21 except the N-electrode 40b region and the upper region of the ridge structure. The insulating film 30 is formed in this.

In this case, in the ridge structure, the insulating layer 30 exposes the upper portion of the p-contact layer 28 through an opening and is formed higher than the p-contact layer 28.

The P-electrode 40a fills an opening of the insulating layer 30 exposing the p-contact layer 28, and is formed in a portion of the upper portion of the insulating layer 30 around the ridge. .

1B is a schematic cross-sectional view for explaining a conventional vertical electrode structure laser diode.

In general, since the vertical electrode structure laser diode has the same configuration as the horizontal electrode structure laser diode, the detailed description is replaced with the foregoing description of the configuration of the horizontal electrode structure laser diode and is omitted here.

However, as shown in the drawing, the substrate 10 used in the vertical electrode structure laser diode is a conductive substrate such as a gallium nitride (GaN) substrate, not an insulating substrate such as the sapphire (Al ₂ O ₃ ) substrate mentioned above. Because of the use, there is a structural difference in which the N-electrode 40b is formed under the conductive substrate.

2 is a cross-sectional view illustrating a structure in which a conventional vertical electrode structure laser diode is assembled into a junction-up structure.

Since the laser diode does not effectively dissipate the heat generated from the active layer 25, which is a PN junction portion, the life of the device is shortened, so that a heat dissipation assembly technique is required.

One of the assembly structures for the effective heat dissipation of the laser diode, there is a junction-down structure for assembling the heat generating active layer 25 in close proximity to the heat block (Heat Block).

However, such a junction-down structure is a laser diode because the ridge, which is the center of light generation, is subjected to physical stress as it is pressed by solder and heat blocks. There is a high possibility that the optical properties of the deteriorate.

Therefore, a laser diode using a highly conductive substrate, such as gallium nitride (GaN), does not have to be assembled into a junction-down structure, but instead has a junction-up structure as shown in the drawing. Even if assembled, it can maintain excellent heat dissipation characteristics, and there is no fear of the ridge being pressed against the solder and the heat block.

FIG. 3 is a graph illustrating a change in active layer temperature according to the width of a laser diode chip when the laser diode is mounted in a junction-up structure as shown in FIG. 2.

As shown in the graph, the wider the width w of the laser diode, the lower the temperature of the active layer.

In other words, when the laser diode is assembled into the junction-up structure as described above, heat is released to the substrate. The heat is more effectively emitted as the width or area of the substrate is increased, thereby making the active layer more effective. The temperature can also be lowered and the reliability of the device can be improved.

However, in spite of this fact, the method of increasing the width or area of the device indefinitely increases production yield and unit cost per wafer, and thus it is difficult to improve the thermal and electrical characteristics of the device because it is economically inferior.

In order to solve the above problems, the present invention is to form a trench structure having a plurality of grooves in the lower portion of the substrate growing the laser diode epitaxial layer, so that the metal layer filling the plurality of grooves is provided in the lower portion of the substrate Accordingly, it is an object of the present invention to provide a laser diode and a method of manufacturing the same, in which heat generated from an active layer during laser driving is efficiently discharged to a lower portion of a device through a metal layer, thereby improving heat emission efficiency and reliability.

In addition, another object of the laser diode according to the present invention and a method for manufacturing the same is to apply the trench structure substrate and the metal layer to the laser diode of the vertical electrode structure using the conductive substrate, thereby the metal layer is not merely used for heat dissipation. It can be used as an N-electrode for supplying current to the device, and the contact resistivity at the N-electrode side is increased through the contact surface area between the substrate and the N-electrode, which is larger than the conventional structure of forming an electrode on a uniform substrate surface. It is to provide a laser diode with improved electrical characteristics by reducing the over-operation voltage.

Horizontal electrode structure laser diode according to the present invention, a substrate having a plurality of grooves formed on the bottom; A metal layer filling the plurality of grooves in the lower part of the substrate and formed in the lower part of the substrate; An n-contact layer formed on the substrate and having a portion of an upper portion etched to a predetermined depth; an N-electrode formed in the etched partial region on the n-contact layer; an n-clad layer formed in the remaining non-etched region above the n-contact layer; a thin film structure formed on the n-clad layer, in which an n-wave layer, an active layer, an electron blocking layer (EBL), and a p-wave layer are sequentially stacked; a p-clad layer formed on the p-waveguide layer and having a ridge in a portion of the upper portion; a p-contact layer formed on the ridge of the p-clad layer; An insulating film formed to surround the exposed surface of the p-clad layer including the ridge and the outer surface of the p-contact layer formed on the ridge, and having an opening exposing the upper portion of the p-contact layer; ; and an P-electrode formed over the insulating film to fill the opening of the insulating film exposing the p-contact layer so as to be electrically connected to the p-contact layer.

In addition, the vertical electrode structure laser diode according to the present invention, a conductive substrate having a plurality of grooves formed in the bottom; A metal layer filling the plurality of grooves under the conductive substrate and formed under the conductive substrate; A thin film structure formed on the conductive substrate and formed by sequentially stacking an n-contact layer, an n-clad layer, an n-wave layer, an active layer, an electron blocking layer (EBL), and a p-wave layer; a p-clad layer formed on the p-waveguide layer and having a ridge in a portion of the upper portion; a p-contact layer formed on the ridge of the p-clad layer; An insulating film formed to surround the exposed surface of the p-clad layer including the ridge and the outer surface of the p-contact layer formed on the ridge, and having an opening exposing the upper portion of the p-contact layer; ; and an P-electrode formed over the insulating film to fill the opening of the insulating film exposing the p-contact layer so as to be electrically connected to the p-contact layer.

In addition, the method for manufacturing a horizontal electrode structure laser diode according to the present invention comprises the steps of forming a plurality of grooves in the lower substrate; Filling a plurality of grooves in the lower portion of the substrate and forming a metal layer covering the lower portion of the substrate; Sequentially growing an n-contact layer, an n-clad layer, an n-wave layer, an active layer, an electron blocking layer (EBL), a p-wave layer, and a p-clad layer on the substrate; forming a ridge in a portion of the upper portion of the p-clad layer; Mesa etching other portions of the upper portion of the p-clad layer to a portion of the n-contact layer to expose the upper portion of the n-contact layer, and to form an N-electrode in some regions of the upper portion of the exposed n-contact layer ; Forming an insulating film on all regions of the p-clad layer except the upper part of the ridge; Forming a p-contact layer over the ridge; and forming a p-electrode on the p-contact layer and the insulating layer to be electrically connected to the p-contact layer.

In addition, the manufacturing method of the vertical electrode structure laser diode according to the present invention comprises the steps of forming a plurality of grooves in the lower portion of the conductive substrate; Forming a metal layer covering and filling a plurality of grooves under the conductive substrate; Sequentially growing an n-contact layer, an n-clad layer, an n-wave layer, an active layer, an electron blocking layer (EBL), a p-wave layer, and a p-clad layer on the conductive substrate; forming a ridge in a portion of the upper portion of the p-clad layer; Forming an insulating film on all regions of the p-clad layer except the upper part of the ridge; Forming a p-contact layer over the ridge; and forming a p-electrode on the p-contact layer and the insulating layer to be electrically connected to the p-contact layer.

Hereinafter, the structure of a laser diode according to the present invention will be described in detail with reference to the drawings.

4A and 4B are cross-sectional views of a horizontal electrode structure and a vertical electrode structure laser diode having a trench structure substrate, respectively, for explaining a preferred embodiment of the laser diode according to the present invention.

As shown in FIG. 4A, the laser diode of the horizontal electrode structure according to the present invention is largely divided into a substrate 100, an epi layer 120, an insulating layer 130, a P-electrode 140a, and an N-electrode 140b. ).

Here, the substrate 100 has a trench structure in which a plurality of grooves A are formed at the bottom thereof.

In addition, the substrate 100 may be a sapphire (Al ₂ O ₃ ) substrate.

The groove A is a structure for smoothly dissipating heat generated in the active layer of the substrate 100 through the lower part of the substrate, and widens the surface area for dissipating heat to act as a heat sink.

Here, only the side cross-sectional view of the groove A is schematically illustrated, but may have various horizontal cross-sectional shapes for increasing the heat dissipation surface area of the lower part of the substrate as shown in FIGS. 5A to 5F.

The metal layer 110 is formed in the lower portion of the substrate 100 to fill the groove in the lower portion of the substrate 100.

Subsequently, the epitaxial layer 120 is formed on the substrate 100.

The epi layer 120 may include an n-contact layer 121, an n-clad layer 122, an n-wave layer 123, an active layer 124, an electron blocking layer (EBL) 125, The p-waveguide layer 126, the p-clad layer 127, and the p-contact layer 128 are stacked in this order.

First, the n-contact layer 121 in which a portion of the upper portion is etched to a predetermined depth is formed at the lowermost part of the epi layer 120, and an upper portion of the region where the n-contact layer 121 is etched. An N-electrode 140b is formed on the n-clad layer 122, and an n-clad layer 122 is formed on the remaining non-etched region on the n-contact layer 121.

The n-wave layer 123, the active layer 124, the electron blocking layer (EBL) 125, and the p-wave layer 126 are sequentially formed on the n-clad layer 122. It is stacked.

The p-clad layer 127 is formed on the p-waveguide layer, in which a portion of the upper portion has a ridge region B.

The p-contact layer 128 is formed on the ridge of the p-clad layer 127.

An exposed surface of the p-clad layer including the ridge B and an outer surface of the p-contact layer 128 formed on the ridge are formed on the p-contact layer 128. An insulating layer 130 is formed to surround and has an opening exposing an upper portion of the p-contact layer.

Finally, the opening of the insulating layer exposing the p-contact layer 128 is filled to be electrically connected to the p-contact layer 128, and the P-electrode 140a is formed on the insulating layer 130. It is.

4B is a cross-sectional view illustrating a vertical electrode structure laser diode having a trench structure substrate according to the present invention.

As before, the substrate 100 has a trench structure in which a plurality of grooves A are formed thereunder.

On the other hand, the substrate 100 is preferably a conductive substrate such as gallium nitride (GaN) substrate.

Since the gallium nitride (GaN) substrate is made of the same material as the epi layer 120, the natural cleavage surface is advantageous, and since the gallium nitride (GaN) substrate is advantageous, as well as the electrical conductivity and thermal conductivity is good, the heat dissipation characteristics are good.

For reference, a laser diode having a vertical electrode structure is a structure in which electrodes are positioned at both ends of the laser diode, and as shown in the drawing, the N-electrode 140b is directly below the conductive substrate 100. It is a structure to be formed.

Therefore, unlike a laser diode having a horizontal electrode structure, an etching process such as Mesa etching for forming an N-electrode is unnecessary, and since the current flows in one direction from the top through the conductive substrate, the current It has good characteristics and is widely used for high power laser diodes.

On the other hand, the groove (A) is also a structure for smoothly dissipating heat generated in the active layer of the substrate 100 through the lower substrate, making the surface area of the heat dissipation wide to serve as a heat sink.

Here, only the side cross-sectional view of the groove A is schematically illustrated, but may have various horizontal cross-sectional shapes for increasing the heat dissipation surface area of the lower part of the substrate as shown in FIGS. 5A to 5F.

The N-electrode 140b is formed in the lower portion of the substrate 100 while filling the groove in the lower portion of the substrate 100.

Subsequently, the epitaxial layer 120 is formed on the substrate 100.

The epi layer 120 may include an n-contact layer 121, an n-clad layer 122, an n-wave layer 123, an active layer 124, an electron blocking layer (EBL) 125, The p-waveguide layer 126, the p-clad layer 127, and the p-contact layer 128 are stacked in this order.

In this case, the p-clad layer 127 has a portion of the upper portion formed of a ridge structure B, and the p-contact layer is formed on the ridge of the p-clad layer 127. Preferably, 128 is formed.

An exposed surface of the p-clad layer including the ridge B and an outer surface of the p-contact layer 128 formed on the ridge are formed on the p-contact layer 128. An insulating layer 130 is formed to surround the opening and expose the upper portion of the p-contact layer.

Finally, the opening of the insulating layer exposing the p-contact layer 128 is filled to be electrically connected to the p-contact layer 128, and the P-electrode 140a is formed on the insulating layer 130. It is.

5A to 5F are horizontal cross-sectional views illustrating various groove shapes for improving heat dissipation efficiency of a trench structure substrate according to the present invention.

As shown, the horizontal cross-section of the lower groove of the substrate 100 having the trench structure according to the present invention is a horizontal or vertical stripe (Fig. 5a, 5b) shape, curved line (Fig. 5c) shape, grid ( It can be formed in various shapes such as a grid (FIG. 5D) shape, a hexagon (FIG. 5E) shape, and a circular (FIG. 5F) shape.

6A to 6G are cross-sectional views illustrating a method of manufacturing a laser diode having a vertical electrode structure according to the present invention.

FIG. 6A illustrates a step of forming a plurality of grooves A through a lithography and etching process under the conductive substrate 100.

In this case, the conductive substrate 100 is preferably a gallium nitride (GaN) substrate.

In addition, the plurality of grooves A may be formed to have a cross-sectional shape as shown in FIGS. 5A to 5F.

FIG. 6B illustrates a step of forming a metal layer covering and filling a plurality of grooves A under the substrate 100.

Since the substrate is 100 conductive in the vertical electrode structure laser diode, the metal layer is used for the use of the N-electrode 140b. Since the surface area of the substrate and the contact surface is large, the heat dissipation efficiency is increased, as well as the contact resistivity and operation. Although the effect of reducing the voltage can be obtained, in the laser diode of the horizontal electrode structure, since the substrate is insulating, the metal layer is simply used for the purpose of further improving heat dissipation efficiency by using the high thermal conductivity of the metal itself.

FIG. 6C illustrates an n-contact layer 121, an n-clad layer 122, an n-wave layer 123, an active layer 124, and an electron blocking layer (EBL) 125 on the substrate 100. ), the p-waveguide layer 126 and the p-clad layer 127 are sequentially grown.

Such a growth process is performed through a thin film deposition method such as metal organic chemical vapor deposition (MOCVD).

6D illustrates a step of forming a ridge structure B in a portion of the upper portion of the p-clad layer 127.

As described above, the ridge structure B injects a current through a narrow region so that laser light resonating in the active layer is focused only on the ridge structure region.

FIG. 6E illustrates a step of forming the insulating layer 130 in all regions of the p-clad layer 127 except for the upper portion of the ridge structure B. Referring to FIG.

FIG. 6F illustrates a step of forming the p-contact layer 128 over the ridge structure B. Referring to FIG.

6G illustrates a step of forming the p-electrode 140a on the p-contact layer 128 and the insulating layer 130 to be electrically connected to the p-contact layer 128.

While the configuration of the invention according to the embodiment of the present invention has been described in detail, the present invention is not necessarily limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention.

According to the laser diode of the present invention and a method of manufacturing the same, the lower portion of the substrate for growing the laser diode epitaxial layer is made of a trench (Trench) structure having a plurality of grooves, the metal layer filling the plurality of grooves is the lower portion of the substrate By being provided in the, the heat generated from the active layer when driving the laser diode is efficiently discharged to the lower portion of the device through the metal layer, there is an effect that can improve the thermal characteristics and reliability of the laser diode.

Further, according to the laser diode of the present invention and a method of manufacturing the same, by applying such a trench structure substrate and a metal layer to a vertical electrode structure laser diode using a conductive substrate, the metal layer is not only used for heat dissipation, It can be used as an N-electrode for supplying and can increase the contact surface area between the substrate and the N-electrode compared to the conventional structure of forming an electrode on a uniform substrate surface, and thus the contact resistivity and operating voltage at the N-electrode side. As a result, there is an effect of improving the electrical characteristics.

Claims (10)

A substrate having a plurality of grooves formed in a lower portion thereof; A metal layer filling a plurality of grooves in the lower portion of the substrate and formed in the lower portion of the substrate; An n-contact layer formed on the substrate and having a portion of an upper portion etched to a predetermined depth; An N-electrode formed in the etched partial region on the n-contact layer; An n-clad layer formed on the non-etched remaining region above the n-contact layer; A thin film structure formed on the n-clad layer and formed by sequentially stacking an n-wave layer, an active layer, an electron blocking layer (EBL), and a p-wave layer; A p-clad layer formed on the p-waveguide layer and having a ridge in a portion of the upper portion thereof; A p-contact layer formed on the ridge of the p-clad layer; An opening formed to surround the exposed surface of the p-clad layer including the ridge and the outer surface of the p-contact layer formed on the ridge, and exposing an upper portion of the p-contact layer. An insulating film having; And a P-electrode filling the opening of the insulating film exposing the p-contact layer so as to be electrically connected to the p-contact layer and formed on the insulating film. A conductive substrate having a plurality of grooves formed in a lower portion thereof; A metal layer filling a plurality of grooves under the conductive substrate and formed under the conductive substrate; A thin film structure formed on the conductive substrate, wherein an n-contact layer, an n-clad layer, an n-wave layer, an active layer, an electron blocking layer (EBL), and a p-wave layer are sequentially stacked; A p-clad layer formed on the p-waveguide layer and having a ridge in a portion of the upper portion thereof; A p-contact layer formed on the ridge of the p-clad layer; An opening formed to surround the exposed surface of the p-clad layer including the ridge and the outer surface of the p-contact layer formed on the ridge, and exposing an upper portion of the p-contact layer. An insulating film having; And a P-electrode filling the opening of the insulating film exposing the p-contact layer so as to be electrically connected to the p-contact layer and formed on the insulating film. The method of claim 1, The substrate, A laser diode, which is an Al ₂ O ₃ substrate. The method of claim 2, The conductive substrate, A laser diode, which is a GaN substrate. The method according to claim 1 or 2, The groove is, A laser diode, characterized in that the horizontal cross section is any one of a stripe, a grid, a circle, a hexagon. Forming a plurality of grooves under the substrate; Filling a plurality of grooves in the lower portion of the substrate and forming a metal layer covering the lower portion of the substrate; Sequentially growing an n-contact layer, an n-clad layer, an n-wave layer, an active layer, an electron blocking layer (EBL), a p-wave layer, and a p-clad layer on the substrate; Forming a ridge in a portion of an upper portion of the p-clad layer; Another portion of the upper portion of the p-clad layer may be mesa-etched to a portion of the n-contact layer to expose the upper portion of the n-contact layer, and an N-electrode may be disposed on a portion of the upper portion of the n-contact layer. Forming a; Forming an insulating film on all regions of the p-clad layer except the upper portion of the ridge; Forming a p-contact layer over said ridge; And forming a p-electrode on the p-contact layer and the insulating layer so as to be electrically connected to the p-contact layer. Forming a plurality of grooves under the conductive substrate; Forming a metal layer covering and filling a plurality of grooves under the conductive substrate; Sequentially growing an n-contact layer, an n-clad layer, an n-wave layer, an active layer, an electron blocking layer (EBL), a p-wave layer, and a p-clad layer on the conductive substrate; Forming a ridge in a portion of an upper portion of the p-clad layer; Forming an insulating film on all regions of the p-clad layer except the upper portion of the ridge; Forming a p-contact layer over said ridge; And forming a p-electrode on the p-contact layer and the insulating layer so as to be electrically connected to the p-contact layer. The method of claim 6, The substrate, Laser diode manufacturing method characterized in that the Al ₂ O ₃ substrate. The method of claim 7, wherein The conductive substrate, Laser diode manufacturing method characterized in that the GaN substrate. The method according to claim 6 or 7, The groove is, A horizontal cross section is a laser diode manufacturing method, characterized in that any one of the shape of a stripe (Grid), Grid (Circle), Circle (Hexagon).

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