KR102183019B1 - Highly efficient oxidation-type VCSEL comprising an anti-reflection layer and method for manufacturing thereof - Google Patents

Abstract

The present invention relates to a vertical resonance surface emission laser (VCSEL) and a method of manufacturing the same, and more particularly, to a highly efficient oxidation type vertical resonance surface emission laser emitting a laser having a peak wavelength of 860 nm, and a method of manufacturing the same.
The oxidation-type VCSEL according to the present invention has an antireflection layer on top of the upper dispersed Bragg reflector (DBR), and the antireflection layer transmits laser light emitted from the active layer, and has a refractive index lower than that of the upper dispersed Bragg reflector and higher than air. It has an upper rough surface and a lower rough surface, characterized in that the anti-reflection layer is located. .

Description

Highly efficient oxidation-type VCSEL comprising an anti-reflection layer and method for manufacturing thereof

The present invention relates to a vertical resonance surface emission laser (VCSEL) and a manufacturing method thereof, and more particularly, to a highly efficient oxidation type vertical resonance surface emission laser that emits a laser with high efficiency due to improved light extraction, and a manufacturing method thereof. will be.

The oxidation-type VSCEL 100, which is one of the vertical resonance surface emission lasers (VCSEL), is a device in which electrodes are applied to the upper and lower portions to emit a laser to the upper surface, and has the advantage of a wide application field.

In general, as shown in FIG. 1, laser light is emitted in a direction above the substrate 120, and a lower electrode 110 is provided under the substrate 120. A lower n-DBR 130 is provided on the upper side of the substrate 110, and an active layer 140 is provided on the lower DBR 130. The active layer 140 includes a quantum well structure for light generation. An oxide layer 180 is provided on the active layer 140, and an upper p-DBR 150 is provided on the oxide layer 180. An upper electrode 170 is provided on the upper p-DBR 150 in a ring shape.

The oxide layer 180 includes an oxidized ring-shaped peripheral portion 181 and a non-oxidized circular window-shaped central portion 182. The peripheral portion 181 is a region in which the same material as the central portion 182 is converted to non-conductive by oxidation, and the central portion forms a circular current window having a predetermined diameter.

In such an oxidation-type VCSEL, as current flows from the ring-shaped upper electrode 170 to the circular current window in the center, an uneven flow of current is formed, thereby reducing efficiency.

KR 10-2018-0015630 publication (WO 2016/198282) discloses a method of forming a plurality of oxide layers inside an upper DBR in order to improve the efficiency of an oxidation-type VCSEL having a peak wavelength of 850 nm.

There is a method of forming a transparent ITO layer on the upper DBR as a whole so that the current emitted from the ring-shaped upper electrode 170 is uniformly supplied to the center through the ITO layer, but in this case, an expensive transparent ITO electrode is required. In addition, it is difficult to avoid a sharp drop in yield during the formation of ITO.

The problem to be solved in the present invention is to provide a method of preventing the efficiency of the oxidized VCSEL from deteriorating due to loss in the process of emitting a light source generated inside the oxidized VCSEL to the outside.

Another problem to be solved in the present invention is to provide a highly efficient oxidized VCSEL with improved external emission of a light source generated inside the oxidized VCSEL.

Another problem to be solved in the present invention is to provide a highly efficient oxidation-type VCSEL with improved external emission of a laser light source generated inside of an oxidation-type VCSEL that emits a laser having a center wavelength of 860 nm.

Another problem to be solved in the present invention is to provide a method of manufacturing a highly efficient oxidized VCSEL with improved external emission of a light source generated inside the oxidized VCSEL.

In order to solve the above problems, in the present invention

Oxidation, characterized in that an anti-reflection layer having an upper roughened surface and a lower roughened surface is disposed on the upper part of the upper dispersed Bragg reflector, and has a lower refractive index than the upper distributed Bragg reflector and higher than the air. Type vertical cavity surface radiation laser (VCSEL).

'Upper rough surface' refers to the roughened upper surface.

'Lower rough surface' refers to the roughened lower surface.

'Transmission' means to transmit 95% or more, more preferably 99% or more, and even more preferably 99.9% or more of the laser of a specific wavelength emitted from the oxidized VCSEL.

'Laser' is understood to mean a wavelength with an FHWM half width of less than 5 nm.

In the present invention, the lower rough surface of the antireflection layer may contact the upper surface of the upper DBR layer, and preferably, may form an interface with the upper rough surface of the upper DBR.

In the present invention, the upper rough surface of the antireflection layer may form an interface with air.

In the present invention, the refractive index of the antireflection layer may be 0.5 or more, preferably 0.6 or more, more preferably 0.7 or more, and even more preferably 1.0 or more lower than the refractive index of the upper DBR.

In the present invention, the anti-reflection layer may be SiN, SiO, GaN, AlN, AlGaN, ITO, ZnO, AzO, preferably SiN or SiO.

In the present invention, the anti-reflection layer may be grown to a thickness of about 100 to 500 nm, preferably 200 to 400 nm. If the thickness of the anti-reflection layer is less than the above range, the anti-reflection layer is removed or only a part of the anti-reflection layer is left when the rough surface is formed, and if the thickness is too thick, a problem of partially absorbing light in a translucent state may occur.

In the present invention, the antireflection layer and the rough surface of the upper DBR may be prepared by etching the antireflection layer and the upper surface of the upper DBR. The etching may use wet etching or dry etching, and the roughness of the etched surface may be >±50 nm. In the implementation of the present invention, in the case of wet etching, it is made by mixing an acid-based such as hydrochloric acid and sulfuric acid, and in the case of dry etching, it is processed with an etching equipment using a mixed gas such as BCl-based gas and Ar gas and a plasma applied with RF power. I can.

In the implementation of the present invention, when the anti-reflection layer is non-conductive, such as SiN, it is preferable that the anti-reflection layer is formed in a central portion of the upper surface of the upper DBR layer, that is, in a central region not in contact with the ring-shaped upper electrode. In another embodiment of the present invention, when the antireflection layer is conductive, such as ITO, it may be formed entirely on the upper surface of the upper DBR layer. In the practice of the present invention, the upper or lower rough surface of the anti-reflection layer may be formed on all or part of the upper surface of the anti-reflection layer.

In the present invention, the oxidized vertical cavity surface-emitting laser (VCSEL) may include a lower electrode, a substrate, a lower Distributed Bragg Reflector, an active layer, an upper distributed Bragg reflector, an upper electrode, and an oxide layer.

In the present invention, the active layer of the VCSEL is an active layer capable of emitting light having a peak wavelength of 850±10 nm (hereinafter, 850 nm peak wavelength). In one embodiment of the invention, the active layer may include a GaAs quantum well and an AlGaAs quantum barrier layer.

In the present invention, the upper dispersed Bragg reflector and the lower dispersed Bragg reflector are used to reflect the light emitted from the active layer up and down to resonate.

In the present invention, the upper and lower DBRs may be DBRs in which a pair of reflective layers composed of a high refractive layer and a low refractive layer are repeatedly stacked so as to reflect light emitted from the active layer and light reflected from the opposite reflector.

In the practice of the present invention, 30 or more, preferably 40 pairs of n-DBRs may be used so that the lower DBR can substantially completely reflect the light reflected from the active layer and the upper DBR, and the upper DBR is In order to increase the likelihood of release, it may have 5 to 10 pairs less than the lower DBR, and preferably p-DBR consisting of 20 to 25 pairs.

In one embodiment of the invention, the upper distributed Bragg reflector and lower distributed Bragg reflector and Al _x Ga ₁ having a refractive index _{- x} As layer, 0.8 <x <1, and Al _y Ga _1-y As layer having a low refractive index , 0<y<0.2 may be a distributed Bragg reflector (DBR) having a structure in which alternately and repeatedly stacked.

In the present invention, the oxide layer is made of an oxidizing material, and may mean a layer in which an oxidized region and a non-oxidized region coexist for resonance. It may be a _z As, 0.95 <z≤1 _- the oxidation layer is to be easily oxidized by the high-temperature water vapor, Al _z Ga _1. The oxide layer may be formed of a ring-shaped oxide layer and a current window in the form of an inner central circle while being oxidized from the outer side to the center.

In the present invention, the diameter of the central circle forming the current window in the oxide layer must be narrow enough to emit laser light, and may preferably be 10 μm or less.

In the present invention, the oxide layer may be located above the active layer, and preferably may be located inside the upper p-DBR, preferably between layers constituting p-DBR so as not to affect the active layer. More preferably, it may be located between the lower first pair and the second pair in the lower end of the upper p-BDR, for example, the upper DBR, and may be applied in a thickness of 30 to 100 nm.

In the practice of the present invention, the oxidation-type VCSEL may operate at a current of 15 to 150 mA, preferably in the range of 20 to 120 mA, and most preferably at 30 to 100 mA. When the current is less than 15 mA, the laser is not generated, and when the current exceeds 150 mA, the laser with a peak wavelength of 860 may not be generated due to the effect of heat generation.

In the present invention, the upper electrode may be formed in a ring shape so as not to shield the emitted light, and preferably may be a multilayer electrode made of Au/Pt/Ti. In one embodiment, the electrode may be about 2 micrometers or less.

In the present invention, the antireflection layer may be a single layer or multiple layers. When the antireflection layer is a multilayer, preferably, the refractive index decreases as the antireflection layer rises upward.

The present invention in one aspect,

Providing an oxidized VCSEL;

Roughening the surface of the upper DBR of the oxidized VCSEL;

Forming an antireflection layer on the surface of the roughened upper DBR layer; And

It provides a high-efficiency oxidation-type VCSEL manufacturing method comprising the step of roughening the upper surface of the anti-reflection layer.

According to the present invention, a new method capable of improving the light extraction characteristics of an oxidized VCSEL has been provided.

The oxidation-type VCSEL according to the present invention prevents total internal reflection of the emitted light at the interface between DBR and air, thereby exhibiting a great improvement in light efficiency.

1 is a cross-sectional view of a conventional oxidized VCSEL.
2 is a photograph of the surface of a conventional oxidized VCSEL.
3 is a cross-sectional view of an acid-substituted VCSEL according to the present invention.
4 is a graph showing the (a) an oxidized VCSEL chip surface image and (b) DBR characteristics (inverse peak is cavity peak) and wavelength characteristics of an active layer of a 860nm VCSEL according to the present invention.
5 is a schematic diagram of light extraction of (a) Comparative Example 1, (b) Example 2, and (c) Example 1. FIG.
6 is a comparison of light intensity at 20 mA of Comparative Example 1, Example 2, and Example 1. FIG.

Hereinafter, the present invention will be described in detail through examples. The following examples are not intended to limit the present invention, but to illustrate the present invention.

Example 1

3 shows a structure of a VCSEL layer emitting a laser having a peak wavelength of 860 nm to which a roughened SiN antireflection layer manufactured by an MOCVD system is applied. As shown in FIG. 3, the oxidized VSCEL 100 having a 860 nm peak wavelength to which the roughened SiN antireflection layer according to the present invention is applied is an oxidized VCSEL that emits laser light in the upper direction of the substrate 120 ( 100). The substrate 120 is an n-type GaAs substrate. On the lower side of the substrate 120, a lower electrode 110 is provided.

On the upper side of the substrate 110, a lower n-DBR 130 in which pairs of a high refractive index AlGaAs layer and a low refractive index AlGaAs layer are repeatedly stacked is provided. The refractive index (n) of 3.0, a Ga0 _.15 Al _0.85 As layer with a refractive index of 3.8 of Al _0.15 Ga _0.85 As layer is a laminate of 40 replications.

An active layer 140 is provided on the lower DBR 130. The active layer 140 includes a quantum well structure for light generation. The active layer 140 is a GaAs/AlGaAs active layer (QW) emitting a central wavelength of 850 nm.

An upper p-DBR 150 including an oxide layer 180 is provided on the active layer 140. The oxide layer 180 is inserted between the pairs of the p-DBR 150 to avoid damage to the active layer during the oxidation process, so that direct contact with the active layer 140 may be avoided. The oxide layer 140 is stacked on one or two pairs of upper DBRs among 20 pairs, and the remaining pairs of upper DBRs are stacked on the oxide layer 180.

Accordingly, the upper DBR 150 includes a first upper DBR 151 positioned under the oxide layer 180 and a second upper DBR 142 positioned above the oxide layer 180.

In the upper p-DBR 150, a pair of a high refractive index AlGaAs layer and a low refractive index AlGaAs layer are repeatedly stacked in the same manner as the lower n-DBR, and Al _{0 . 85} Ga0 _{. 15} As layer and Al _{0 . 15} Ga _{0 . It} consists of 20 pairs of ₈₅ As layers.

In the upper p-DBR 150, in order to reduce the difference in refractive index from the antireflection layer, the low refractive index layer is located on the top surface.

The oxide layer 180 has a thickness of about 30 nm Al _{0 . 98} Ga _{0 . It} consists of a circular current window (oxidation aperture) 181 in the center made of ₀₂ As and an oxidation ring 182 in the periphery where they are oxidized to water vapor.

An upper electrode 170 is formed in a ring shape on an edge of the upper surface of the upper p-DBR 150. On the upper surface of the upper p-DBR 150, a central portion where the upper electrode 170 is not located was formed through a PR-litho and etching process. The roughness of the upper DBR 150 rough surface was Ra = 10.3 nm.

An antireflection layer 190 made of SiN was deposited to a thickness of 250 nm on the top surface of the roughened p-DBR 150. The upper surface of the SiN antireflection layer 190 was formed through a PR-litho and etching process in the same manner as the upper DBR. The roughness Ra of the upper rough surface of the SiN antireflection layer 190 was 35 nm.

FIG. 4 shows (a) an image of the surface of the oxidized VCSEL chip and (b) DBR characteristics (inverse peak is cavity peak) and wavelength characteristics of the active layer of the 860nm VCSEL. When checking the fabricated oxidized VCSEL image, 7 light emitting poles were identified. From FIG. 4(b), it was confirmed that the important peak wavelength of the QW active layer was about 850 nm, and the cavity (resonant) peak from DBR reflection was about 860 nm. In addition, the DBR reflectance showed excellent characteristics in the form of stop-band at almost 98%.

Comparative Example 1

As shown in Fig. 5A, the lower structure is the same as the embodiment, and the upper structure is different. In Comparative Example 1, the upper electrode was formed around the upper surface of the upper p-DBR, the smooth surface of the center was exposed to air, and the SiN antireflection layer was not formed on the upper surface of the upper DBR.

Example 2

As shown in FIG. 5B, the lower structure is the same as the embodiment, and the upper structure is different. In Example 2, an upper electrode was formed around the upper surface of the upper p-DBR, and a rough surface was formed in the center by etching. A SiN antireflection layer was laminated on the upper surface of the roughened upper DBR, and the upper surface of the SiN antireflection layer did not undergo a roughening process to form a smooth surface.

Light emission schematic diagram

5 is a schematic diagram of light emission of an oxidized VCSEL chip of Comparative Example 1 without an anti-reflection layer (a), a schematic diagram of light emission of an oxidized VCSEL chip of Example 2 with an anti-reflection layer (b), and a rough reflection A schematic diagram (c) of light emission of the oxidation-type VCSEL chip of Example 1 with a blocking layer is shown.

As shown in FIG. 5A, in the case of general VCSEL chips without an anti-reflection layer, the uppermost portion is an AlGaAs-based upper DBR and has a refractive index of about 3.5, so that the light generated in the emission region of the active layer and moved to the surface is external (air n ( When applying a narrow emission intensity of 16.6° according to snell's raw at the interface with refractive index) = 1), most of the light is totally internally reflected.

In order to more effectively emit such total internal reflection light to the outside, in the case of Example 2, SiN, which is a textured lower portion of the antireflection layer, was applied, and as shown in FIG. 5B, the intermediate refractive index of SiN is 2.5 when applied. When applied, it exhibits a higher light extraction effect due to the increased light emission angle of about 45.6° and the lower texture shape. The light emitted from the limited emission area of the active layer was extracted by the lower textured SiN antireflection layer, but eventually some disappeared at the interface between the SiN layer and the air, due to the difference in refractive index between the SiN and air layers. This is because some total reflection occurs at the interface.

In order to completely solve this problem, it can be seen from FIG. 5C that, as in the present invention, when the upper and lower portions are all textured (roughened) SiN anti-reflection layers are applied, a considerably high light extraction efficiency can be finally obtained. have.

Performance test

6 is a general VCSEL (indicated as No SiN) without an anti-reflection layer, as in Comparative Example 1 measured on application of 20 mA current, and as in Example 2, the upper surface of the upper DBR is a rough surface, but the upper surface of the anti-reflection layer is a non-rough surface, That is, SiN VCSEL (bottom textured SiN) having a rough surface only on the lower surface of the anti-reflection layer, and, as in the embodiment, a SiN VCSEL (top and bottom textured VCSEL) having a rough surface on the upper surface of the upper DBR and the upper surface of the SiN anti-reflection layer. It shows emission intensity.

In the case of a general VCSEL (No SiN) without an anti-reflection layer, most of the emitted light is totally reflected, showing a fairly low characteristic of about 14.5 mW. On the other hand, in the case of bottom textured SiN with a rough surface formed on the lower surface of the anti-reflection layer, the light efficiency of about 24.6 mW is increased by about 70% due to the light emission threshold that is increased by more than 2 times and the texturing surface structure advantageous for light extraction.

In addition, in the case of a VCSEL having top and bottom textured SiN, light extraction efficiency is additionally applied by an additional uppermost texture structure, showing a high optical characteristic of 30mW, which is increased by about 20%.

As a result, it was confirmed that in the case of the VCSEL to which the top and bottom textured SiN anti-reflection layer according to the present invention was applied, a considerably high characteristic, which was increased by about 100% compared to the general VCSEL characteristic, can be obtained.

Although the present invention has been shown and described in detail in the drawings and the above description, it is contemplated that such illustrations and descriptions are illustrative, illustrative and not limiting. From the present invention, other modifications will become apparent to the average technician. These modifications may involve other features that are already known in the art and may be used instead of or in addition to the features described herein. Variations to the disclosed embodiments may be understood and influenced by those skilled in the art, from learning of the drawings, the invention and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article does not exclude a plurality of elements or steps. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to benefit. Any reference signs in the claims should not be construed as limiting their scope.

100: oxidized VCSEL
110: lower electrode
120: substrate
130: lower DBR
140: active layer
150: upper DBR
160: anti-reflection layer
170: upper electrode
180: oxide layer

Claims (13)

Lower electrode;
A substrate positioned above the lower electrode;
A lower dispersion Bragg reflector positioned on the substrate;
An active layer positioned on the lower dispersion Bragg reflector;
An upper dispersion Bragg reflector (DBR) positioned on the active layer, including an oxide layer comprising an outer oxide layer in a ring shape and an inner current window in a central circle shape, and having a roughened upper surface;
It has an anti-reflection layer having a roughened lower surface forming an interface with the roughened upper surface of the upper dispersed Bragg reflector on the upper surface of the upper dispersed Bragg reflector,
Here, the anti-reflection layer transmits laser light emitted from the active layer, is lower than the upper dispersion Bragg reflector, has a higher refractive index than air, and an upper rough surface; And
Upper electrode;
Oxidized vertical resonance surface radiation laser (VCSEL) comprising a. delete The method of claim 1,
An oxidation-type vertical resonance surface radiation laser (VCSEL), characterized in that the refractive index of the antireflection layer is 0.5 or more lower than that of the upper DBR. The method of claim 1,
The anti-reflection layer is an oxidation-type vertical resonance surface radiation laser (VCSEL), characterized in that one or more selected from the group consisting of SiN, SiO, GaN, AlN, AlGaN, ITO, ZnO, and AzO. The method of claim 1,
The anti-reflection layer is an oxidation-type vertical resonance surface radiation laser (VCSEL), characterized in that having a thickness of 100 ~ 500nm. The method of claim 1,
Oxidation type vertical resonance surface radiation laser (VCSEL), characterized in that the roughness of the surface of the anti-reflection layer is roughness>±50 nm. The method of claim 1,
The anti-reflection layer is an oxidation type vertical resonance surface radiation laser (VCSEL), characterized in that the non-conductive material formed in the center of the upper surface of the upper DBR layer. delete The method of claim 1,
The active layer includes a GaAs quantum well and an AlGaAs quantum barrier layer, and is an active layer emitting light having a peak wavelength of 850 nm,
The upper DBR and the lower DBR are an Al _x Ga _1-x As layer having a high refractive index, where 0.8<x<1 and an Al _y Ga _1-y As layer having a low refractive index, where 0<y<0.2 alternately It is a DBR having a structure that is repeatedly stacked with, and,
The oxide layer is an oxidation-type vertical resonance surface emission laser (VCSEL), characterized in that the Al _z Ga _1-z As, 0.95 < _z &lt; 1, and an oxide thereof is formed of a ring-shaped peripheral portion. The method of claim 1,
The oxide layer is an oxidation-type vertical resonance surface radiation laser (VCSEL), characterized in that located between the layers of the upper DBR. In the method of manufacturing an oxidized vertical resonance surface radiation laser (VCSEL) comprising a lower electrode, a substrate, a lower dispersed Bragg reflector, an active layer, an oxide layer, an upper dispersed Bragg reflector, an antireflection layer, and an upper electrode,
Roughening the surface of the upper DBR of the oxidized VCSEL;
Forming an antireflection layer on the surface of the roughened upper DBR layer; And
Including the step of roughening the upper surface of the anti-reflection layer,
In the VCSEL, an upper dispersion Bragg reflector (DBR) includes an oxide layer consisting of an outer oxide layer in a ring shape and an inner current window in a central circle shape, and the antireflection layer transmits laser light emitted from the active layer, and the upper dispersion Bragg reflector High-efficiency oxidation-type VCSEL manufacturing method, characterized in that it has a lower, higher refractive index than air. The method of claim 11,
The method of manufacturing a highly oxidized VCSEL, characterized in that the roughening is performed by etching.
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