Patent Application
20150349491
1. Field of Invention
Various embodiments of the present invention relate to a distributed bragg reflector ridge laser diode and fabricating method thereof, and more particularly, to a distributed bragg reflector ridge laser diode that is capable of easily embodying a diffraction grating and that minimizes an optical absorption effect on a DBR area, and a fabricating method thereof.
2. Description of Related Art
In general, a red color semiconductor single mode laser diode having a working wavelength of 650 nm has a peripheral layer made of a material having a high specific gravity of aluminum. Therefore, in the case of reclaiming a diffraction grating near an active zone through a regrowing process, the element transference number becomes extremely low due to oxidization of the aluminum. Furthermore, since it is difficult to regrow material layers on gain areas and DBR (Distributed Bragg Reflector) areas, it is difficult to embody them in different material groups, which is a problem. Recently, cases have been reported where a diffraction grating layer is embodied on a surface of an element, where a DBR active zone and a gain area are embodied with a same material, where the cycle of a diffraction grating relates to a working wavelength based on bragg conditions, and where a diffraction grating of a high order mode is used to embody a smooth diffraction grating cycle.
Such a conventional distributed bragg reflector laser diode aforementioned has several problems in terms of fabricating and structure thereof.
First of all, it requires a process of etching the cap layer (p-GaAs) 70, upper clad layer (p-AlGaAs) 60, and upper wave guide (p-AlGaInP) 50 in order to form a diffraction grating A on a DBR area, but it is difficult to embody a diffraction grating of good quality due to differences in etching rates and changes in etching forms for heteromaterials. Furthermore, in the case of etching the upper clad layer 60, due to reduction of layer thickness, the form of the wave guide may be severely distorted, which is a problem. Furthermore, in the case of embodying a diffraction grating A of a high order mode, radiation modes of low orders are mainly formed in y-z direction, and thus reflecting of the radiation modes may increase noise output and reduce the diffraction grating efficiency.
Secondly, an active zone refractive index of the DBR area must be changed for adjustment of single mode characteristics and for wavelength conversion, and just as in a general gain area, an oscillating wavelength may be changed by injecting current into the cap layer 70. In a conventional structure, since it is difficult to sufficiently planarize a diffraction grating formed by deep etching with an insulating film, a portion of the wave guide light may contact a pad metal surface, which would increase light loss, and due to the reflecting on the metal surface, it would become difficult to obtain smooth wave guide characteristics and good spectrum characteristics. Furthermore, due to the increase of resistance caused by p-GaAs material partially formed on the cap layer 70, it is difficult to obtain smooth wavelength conversion characteristics, and further, optical output would change according to wavelength conversion due to additional light created by injection of current.
Thirdly, since in a conventional structure, a wave guide core layer on a DBR area uses an active zone as it is, the optical absorption that occurs on the active zone would increase the loss of DBR area.
Due to the aforementioned problems, in the case of a conventional red DBR-LD, the high loss rate of the DBR area would make oscillation at room temperature difficult, and cause a low side mode suppression ratio at the oscillation spectrum.
Various embodiments of the present invention are directed to a distributed bragg reflector laser diode that is capable of easily embodying a diffraction grating without the problems that used to be caused by etching a clad layer.
Furthermore, various embodiments of the present invention are also directed to minimize an optical absorption effect that occurs when a light created on a gain area penetrates a DBR area.
Furthermore, various embodiments of the present invention are also directed to embody a laser diode capable of causing small loss and a high diffraction efficiency based on no significant change in a wave guide mode, and to embody a laser diode having a room temperature oscillation, low oscillation inception current, and high optical output characteristics.
One embodiment of the present invention provides a distributed bragg reflector ridge laser diode including: a lower clad layer formed on top of a substrate; an active core zone formed on top of the lower clad layer; a plurality of ridge wave guides formed on top of the active core zone such that they are spaced from one another and extend in an axial direction; and a diffraction grating formed on top of the active core zone and between the plurality of ridge wave guides.
Herein, an etching stopping layer may be formed on top of the active core zone, and the plurality of ridge wave guides and diffraction grating may be formed on top of the etching stopping layer.
Herein, a middle clad layer may be formed between the active core zone and etching stopping layer.
Herein, the distributed bragg reflector ridge laser diode may further include a contact layer formed on top of the plurality of ridge wave guides.
Herein, the contact layer may include a grating on a location corresponding to a location of the diffraction grating.
Herein, the active core zone may include a first core layer, active zone, and second core layer formed successively in the axial direction, the first core layer and second core layer being made of a material having a greater band gap than the active zone.
Herein, a COD (Catastrophic Optical Damage) area may be formed on top of at least one of the plurality of ridge wave guides corresponding to the location of the second core layer.
Herein, an anti-reflector coating film may be formed on a side of an axial direction of where the first core layer is formed.
Herein, a coating film having a predetermined reflectivity may be formed on a side of an axial direction of where the second core layer is formed.
Herein, an electrode may be formed on top of the plurality of ridge wave guides and below the substrate.
Another embodiment of the present invention provides a method for fabricating a distributed bragg reflector ridge laser diode, the method including forming a lower clad layer on top of a substrate, and forming an active core zone on top of the lower clad layer to form a multilayer structure; forming a plurality of ridge wave guides on top of the active core zone such that they are spaced from one another and extend in an axial direction; and forming a diffraction grating between the plurality of ridge wave guides on top of the active core zone.
Herein, the active core zone may include a first core layer, active zone and second core layer formed successively in the axial direction, and the first core layer and second core layer may be formed as a material having a greater band gap than the active zone is injected after the forming of the ridge wave guide and forming of the diffraction grating.
Herein, a COD (Catastrophic Optical Damage) area may be formed on top of at least one of the plurality of ridge wave guides corresponding to the location of the second core layer.
Herein, the method may further include forming an anti-reflector coating film on a side of an axial direction of where the first core layer is formed.
Herein, the method may further include forming a coating film having a predetermined reflectivity on a side of an axial direction of where the second core layer is formed.
Herein, the forming of a ridge wave guide and the forming of the diffraction grating may be performed at the same time.
Herein, the forming of a ridge wave guide and the forming of a diffraction grating may include forming an etching stopping layer on top of the active core zone; forming an upper clad layer on top of the etching stopping layer; forming a contact layer on top of the upper clad layer; forming a grating of a grating shape on top of the contact layer; and forming the ridge wave guide and diffraction grating by etching the grating, contact layer, and upper clad layer.
Herein, the method may further include forming a middle clad layer on top of the active core zone prior to the forming of an etching stopping layer.
Herein, the method may further include forming a passivation layer on top of the ridge wave guide and diffraction grating.
Herein, the method may further include forming an electrode on top of the plurality of ridge wave guides and below the substrate.
According to various embodiments of the present invention, it is possible to embody a distributed bragg reflector laser diode that is capable of easily embodying a diffraction grating without the problems that used to be caused by etching a clad layer (distortion of wave guide light on a DBR area, reflecting of radiation mode when embodying a diffraction grating of a high order mode, loss and reflecting due to a metal-pad on top of the DBR area, and increase of resistance).
Furthermore, according to various embodiments of the present invention, it is possible minimize an optical absorption effect that occurs when light created on a gain area penetrates a DBR area by changing the material of the active zone of the DBR area into a material having a greater band gap than the core layer of the gain area.
Furthermore, according to various embodiments of the present invention, it is possible to embody a laser diode capable of causing small loss and a high diffraction efficiency based on no significant change in a wave guide mode, and to embody a laser diode having a room temperature oscillation, low oscillation inception current, and high optical output characteristics.
The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings in which:
Hereinafter, exemplary embodiments will be described in greater detail with reference to the accompanying drawings. Exemplary embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of exemplary embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, exemplary embodiments should not be construed as limited to the particular shapes of regions illustrated herein but may include deviations in shapes that result, for example, from manufacturing. In the drawings, lengths and sizes of layers and regions may be exaggerated for clarity. Like reference numerals in the drawings denote like elements. It is also understood that when a layer is referred to as being “on top of” another layer or substrate, it can be directly on the other or substrate, or intervening layers may also be present.
In this specification, a singular form may include a plural form as long as it is not specifically mentioned in a sentence. Furthermore, ‘include/comprise’ or ‘including/comprising’ used in the specification represents that one or more components, steps, operations, and elements exist or are added.
Hereinbelow, a structure of a distributed bragg reflector ridge laser diode according to an embodiment of the present invention will be explained.
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The substrate 110 may be forms as an n-GaAs layer.
The lower clad layer 120 is formed on top of the substrate 110. The lower clad layer may be a buffer and n-clad layer that includes AlGaInP.
The active core zone 130 is formed on top of the lower clad layer 120.
The active core zone 130 includes a first core layer 131, active zone 132, and second core layer 133. Herein, in an axial direction (z axis), the second core layer 133 is formed first, then followed by the active zone 132, then followed by the first core layer 131.
The middle clad layer 140 is formed on top of the active core zone 130. Herein, the middle clad layer 140 may include AlGaInP.
The etching stopping layer 150 is formed on top of the active core zone 130 and the middle clad layer 140. Herein, the etching stopping layer 150 may include InGaP.
A plurality of ridge wave guides 161, 162, 163, that is a first ridge wave guide 161, second ridge wave guide 162, and third ridge wave guide 163 are formed on top of the active core zone 130. More particularly, the first ridge wave guide 11, second ridge wave guide 162, and third ridge wave guide 163 are formed on top of the etching stopping layer 150 such that they are spaced from one another and extend in an axial direction. Herein, the plurality of ridge wave guides 161, 162, 163 may include AlGaInP or AlGaAs.
Furthermore, on top of at least one of the plurality of ridge wave guides 161, 162, 163, there may be formed a COD (Catastrophic Optical Damage) area where the plurality of contact layers 171, 172, 173 and plurality of electrodes 191, 192, 193 that will be explained hereinafter are not formed on an area corresponding to the location of the second core layer 131. The width of each of the plurality of ridge wave guides 161, 162, 163 determine x axis mode characteristics, and may embody a lateral direction single mode in or below 7 μm.
A plurality of diffraction gratings 164, 165, that is a first diffraction grating 164 and second diffraction grating 165 are formed on top of the active core zone. More specifically, the first diffraction grating 164 and second diffraction grating 165 are formed on top of the etching stopping layer 150, and may be formed between the plurality of ridge wave guides 161, 162, 163. By these plurality of diffraction gratings 164, 165, the thickness of the clad layer near the plurality of ridge wave guides 161, 162, 163 is modulated. The plurality of diffraction gratings 164, 165 may be made of a same material as the plurality of ridge wave guides 161, 162, 163.
Each of the plurality of contact layers 171, 172, 173, that is the first contact layer 171, second contact 172, and third contact layer 173 are formed on top of the first ridge wave guide 161, second ridge wave guide 162, and third ridge wave guide 163, respectively. Furthermore, on top of each of the first contact layer 171, second contact layer 172, and third contact layer 173, a first diffraction grating 171a, second diffraction grating 172a, and third diffraction grating 173a are formed on corresponding locations of the plurality of diffraction gratings 164, 165, respectively.
The passivation layer 180 is formed on top of the plurality of ridge wave guides 161, 162, 163, plurality of diffraction gratings 164, 165, and plurality of contact layers 171, 172, 173.
Of the plurality of electrodes 191, 192, 193, the first electrode 191 and second electrode 192 are formed on top of the plurality of ridge wave guides 161, 162, 163. Furthermore, the first electrode 191 is formed on top of the second ridge wave guide 162 such that it extends to the top of the third ridge wave guide 163, and the second electrode 192 is formed on top of the first ridge wave guide 161 such that it extends to the top of the second ridge wave guide 162. Herein, the first electrode 191 and second electrode 192 are formed such that they are spaced from each other. The third electrode 193 is formed on top of the substrate 110.
On a distributed bragg reflector ridge laser diode according to an embodiment of the present invention, light may be output to both directions, and for embodiment of smooth oscillation characteristics, on a side of an axial direction (z axis) of where the first core layer 131 is formed, an anti-reflector coating film (not illustrated) may be further formed.
Furthermore, on a side of an axial direction (z axis) of where the second core layer 133 is formed, a coating film having a predetermined reflectivity may be formed. Herein, the reflectivity of the coating film may be 30%.
Hereinbelow, a method for fabricating a distributed bragg reflector ridge laser diode according to an embodiment of the present invention will be explained.
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Furthermore, there may be further included a step of forming a coating layer (not illustrated) having a predetermined reflectivity on a side of an axial direction of where the second core layer 133 is formed. Herein, the reflectivity of the coating film may be 30%.
Furthermore, there may be further included a step of forming an anti-reflector coating layer (not illustrated) on a side of an axial direction of where the first core layer 131 is formed.
In the drawings and specification, there have been disclosed typical exemplary embodiments of the invention, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation. As for the scope of the invention, it is to be set forth in the following claims. Therefore, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2014-0067632 | Jun 2014 | KR | national |
The present application claims priority to Korean patent application number 10-2014-0067632, filed on Jun. 3, 2014, the entire disclosure of which is incorporated herein in its entirety by reference.
