An oxidation type VCSEL for eliminating table edge stress and a manufacturing method thereof

Abstract

The present invention discloses a method for manufacturing an oxidized VCSEL that eliminates the edge stress of a table. By designing the diameter and height of a light-emitting column and an initial column, the initial column is first etched out of the epitaxial structure of the VCSEL, so that the diameter of the initial column is larger than the diameter of the light-emitting column and the height is smaller than the height of the light-emitting column; then the initial column is oxidized by a wet oxidation process until the limiting layer reaches a preset central hole aperture, and an edge oxidation zone is generated at the same time; then the initial column is subjected to a second etching to obtain a light-emitting column, and the second etching separates the edge oxidation zone from the light-emitting column. The present invention avoids the problem of reliability failure of the oxidized VCSEL caused by the accumulated stress of the edge oxidation zone, such as the movement of delamination, cracks or dislocations to the light-emitting column, and makes the device performance more stable.

Description

Technical Field

[0001] The invention belongs to the technical field of lasers, and in particular relates to an oxidized VCSEL capable of eliminating the stress on the edge of a table and a manufacturing method thereof. Background Art

[0002] Vertical Cavity Surface Emitting Laser (VCSEL) is widely used in data communication and other fields because of its advantages such as low cost, low threshold, high speed and low power consumption. For the VCSEL semiconductor lasers currently used in a large number of commercial applications, an oxidized structure with GaAs as the substrate is usually used. The oxide layer can effectively limit the current and light field, thereby effectively reducing the threshold current and light loss, improving the power conversion efficiency of VCSEL, and greatly improving the performance of VCSEL.

[0003] In the oxidized VCSEL, the oxide layer (aluminum oxide) is made of AlAs or Al containing a very small amount of Ga. 0.98 Ga 0.02 The As layer is completed by mesa water vapor oxidation. In the selective wet oxidation process, a mesa columnar structure needs to be etched out, and then the oxidation process is carried out. This structural design is relatively dangerous for the reliability of the device. Most failures are caused by the mirror oxidation (mirror oxide) of this structure. The Bragg reflector (DBR) is made of AlGaAs materials with low Al content and high Al content grown alternately, so it will be partially oxidized during the actual oxidation process. In addition, the DBR has many layers, so the accumulated stress is very high. When the stress is high enough, it will cause delamination or cracks, and dislocations will move from the edge of the oxide to the active area, causing reliability problems. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides an oxidized VCSEL capable of eliminating the edge stress of a mesa and a manufacturing method thereof.

[0005] In order to achieve the above purpose, the technical solution of the present invention is:

[0006] A method for manufacturing an oxidized VCSEL for eliminating mesa edge stress comprises the following steps:

[0007] 1) providing or growing an epitaxial structure, wherein the epitaxial structure comprises a substrate, a buffer layer, a first DBR, a resonant cavity and a second DBR arranged in sequence, wherein the resonant cavity comprises a quantum well active region and a confinement layer;

[0008] 2) Designing the diameter and height of the light-emitting pillar, performing a first etching on the epitaxial structure, and etching out an initial pillar, wherein the diameter of the initial pillar is larger than the diameter of the light-emitting pillar, and the height is smaller than the height of the light-emitting pillar;

[0009] 3) using a wet oxidation process to oxidize the initial pillar until the limiting layer reaches a preset central hole diameter and an edge oxidation zone is generated;

[0010] 4) Performing a second etching on the initial pillar to obtain a light-emitting pillar, wherein the second etching separates the edge oxidation region from the light-emitting pillar.

[0011] Optionally, in step 4), the second etching is to remove the edge oxidation area, and the etching is stopped until the remaining part is the designed light-emitting column.

[0012] Optionally, in step 4), the second etching is to etch an annular groove on the periphery of the designed light-emitting column, and the annular groove separates the light-emitting column and the edge oxidation area.

[0013] Optionally, the etching width of the annular groove is 3 μm to 6 μm, and the depth is not less than the height of the initial pillar.

[0014] Optionally, in step 1), the material of the restriction layer is Al x Ga 1-x As, wherein 1≥x≥0.98; the first DBR and the second DBR are respectively composed of Al y Ga 1-y As layer and Al z Ga 1-z As layers grow alternately, where 0.95≥y≥0.80 and 0.20≥z≥0.10.

[0015] Optionally, the width of the edge oxidation zone is estimated based on x and y, and the diameter of the initial pillar is designed to be larger than the sum of the diameter of the light-emitting pillar and the width of the edge oxidation zone.

[0016] Optionally, the thickness of the restriction layer is 20-30 nm.

[0017] Optionally, the wet oxidation process is: the oxidation furnace is heated to 380-420°C, the water temperature is set to 92-98°C, a trace amount of nitrogen is passed to remove excess air in the oxidation furnace, the flow rate is 0.5-1.5L / min, stabilize for 15-30min, and then start to pass water vapor + nitrogen, the flow rate is 3-8L / min.

[0018] The oxidation-type VCSEL that eliminates the edge stress of the mesa manufactured by the above manufacturing method has an epitaxial structure from bottom to top including a substrate, a buffer layer, a first DBR, a resonant cavity and a second DBR, wherein the resonant cavity includes a quantum well active region and a confinement layer; the epitaxial structure is etched downward to the second DBR to form a mesa, and the epitaxial structure above the mesa is separated to form a light-emitting column located in the center and an edge oxidation region surrounding the periphery of the light-emitting column, wherein the confinement layer of the light-emitting column defines a central hole by oxidation, and the confinement layer of the edge oxidation region and parts of the first DBR and the second DBR are oxidized.

[0019] Optionally, the light-emitting column and the edge oxidation area are separated by an annular groove, and the annular groove is filled with an insulating material.

[0020] The beneficial effects of the present invention are:

[0021] The edge oxidation zone is reserved by table etching, and the second etching step is performed after the limiting layer is oxidized to separate the edge oxidation zone from the light-emitting column. This avoids the problem of reliability failure of the oxidation-type VCSEL caused by the accumulated stress in the edge oxidation zone, such as delamination, cracks or dislocations moving toward the light-emitting column, making the device performance more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 to Figure 4 They are schematic diagrams of the structures obtained in steps 1 to 4 of Example 1;

[0023] Figure 5 This is a schematic diagram of the structure obtained in Example 2;

[0024] Figure 6 for Figure 5 Top view of the . DETAILED DESCRIPTION

[0025] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. The various drawings of the present invention are only for illustration to make it easier to understand the present invention, and the specific proportions can be adjusted according to design requirements. The upper and lower relationships of the relative elements and the definitions of the front / back in the figures described in the text should be understood by those skilled in the art to refer to the relative positions of the components, so they can all be flipped to present the same components, which should all fall within the scope disclosed in this specification.

[0026] Example 1

[0027] refer to Figure 1 to Figure 4 , a method for manufacturing an oxidized VCSEL for eliminating mesa edge stress in Example 1, the steps are as follows.

[0028] Step 1, reference Figure 1, providing or growing an epitaxial structure, the epitaxial structure comprising a substrate 1, a buffer layer 2, a first DBR 3, a resonant cavity 4, and a second DBR 5 arranged in sequence, the material of the substrate 1 is n GaAs, the material of the buffer layer 2 is GaAs, the first DBR 3 and the second DBR 4 are respectively composed of multiple groups of Al with high Al content 0.92 Ga 0.08 As layer and Al with low Al content 0.18 Ga 0.82 As layers grow alternately, Al 0.92 Ga 0.08 The optical thickness of the As layer is one quarter of the wavelength of the emitted laser (optical thickness = physical thickness * refractive index of the material), 0.18 Ga 0.82 The optical thickness of the As layer is one quarter of the wavelength of the emitted laser. The first DBR 3 is an N DBR, and the second DBR 5 is a P DBR. The resonant cavity 4 includes a quantum well active region 41 and a confinement layer 42. The quantum well active region 41 is, for example, a GaAs / AlGaAs multi-quantum well, and its structural design refers to the conventional structure. The material of the confinement layer 42 is Al 0.98 Ga 0.02 As, the thickness is 20-30nm. The resonant cavity 4 may also optionally include other structures such as a cladding layer.

[0029] Step 2, reference Figure 2 , design the diameter and height of the light-emitting column, perform the first etching on the epitaxial structure, etch from top to bottom to the first DBR3, and etch out the initial column a, the diameter of the initial column a is larger than the diameter of the light-emitting column, and the height is smaller than the height of the light-emitting column. It is known that the oxidation rate is a strongly related function of the Al content, and the Al content of the confinement layer 42 is higher than the Al content in the DBR. 0.92 Ga 0.08 As layer, so the oxidation rate of the limiting layer 42 is much greater than that of the DBR. According to the difference in Al content and other factors, the possible oxidation width of the DBR is estimated when the limiting layer 42 completes the designed oxidation requirements, and the etching edge of the initial pillar a needs to leave a range larger than the oxidation width relative to the edge of the designed light-emitting pillar. For example, the diameter of the desired light-emitting pillar is 30μm, the table depth is 8μm, and the estimated width of the DBR to be oxidized is about 2-4μm, then the diameter of the initial pillar a is designed to be 40μm, and the table depth is 5μm.

[0030] Step 3: Reference Figure 3, the initial pillar a is wet oxidized by a wet oxidation process. The wet oxidation process is as follows: the oxidation furnace is heated to 400°C, the water temperature is set to 95°C, and a small amount of nitrogen is passed to remove excess air in the oxidation furnace. The flow rate is 1L / min and the process is stable for 20 minutes. Then water vapor + nitrogen is passed at a flow rate of 5L / min. The oxidation time depends on the oxidation pore size to be oxidized. The limiting layer 42 is oxidized from the outside to the inside to form an insulating Al oxide. When oxidized to a preset width, the central unoxidized section forms a central hole 421. The central hole 421 is used to define the range of the active area. During the oxidation process, the edge of the DBR, especially Al 0.92 Ga 0.08 The As layer is also significantly oxidized, and the oxidized width area is defined as the edge oxidation region b.

[0031] Step 4: Reference Figure 4 The initial pillar a is subjected to a second etching to remove the edge oxidation region b, and the etching is stopped until the designed diameter of the light-emitting pillar is reached, thereby obtaining the light-emitting pillar c.

[0032] The obtained light-emitting column c has a smooth edge, and there is no problem of DBR edge oxidation. When the AlGaAs material is oxidized to form Al oxide, the volume will shrink to a certain extent, which will form a large stress in the oxidation area. At the same time, the aluminum oxide formed after oxidation does not match the DBR semiconductor lattice, the bonding force is weak, and the CTE mismatch and other reasons lead to the easy formation of stratification or cracks between the two interfaces in the DBR, which is the main source of defects. This embodiment removes the edge oxidation area of ​​the DBR, making the performance of the light-emitting column more stable.

[0033] The subsequent processes can all refer to the traditional oxidation-type VCSEL process flow and will not be elaborated on.

[0034] Example 2

[0035] The steps of manufacturing an oxidized VCSEL for eliminating mesa edge stress in Example 2 are as follows.

[0036] Step 1, reference example 1 and Figure 1 .

[0037] Step 2: The difference from Example 1 is that the desired diameter of the light-emitting column is 30 μm, so the diameter of the initial column is designed to be 50 μm.

[0038] Step 3, reference example 1 and Figure 3 .

[0039] Step 4: Reference Figure 5 and Figure 6 , the light-emitting pillar c and the edge oxidation area b are separated by etching an annular groove d, the width of the annular groove is 5 μm, and the depth is not less than the depth of the initial pillar.

[0040] The obtained oxidized VCSEL has an epitaxial structure including a substrate 1, a buffer layer 2, a first DBR 3, a resonant cavity 4 and a second DBR 5 from bottom to top, wherein the resonant cavity 4 includes a quantum well active region 41 and a confinement layer 42; the epitaxial structure is etched downward to the second DBR to form a table, and the epitaxial structure above the table is separated by an annular groove d to form a light-emitting column c located in the center and an edge oxidation region b surrounding the periphery of the light-emitting column, wherein the confinement layer 42 of the light-emitting column c has a central hole 421, and the confinement layer of the edge oxidation region b and partial regions of the first DBR and the second DBR are oxidized to form Al oxide.

[0041] In this embodiment, an annular groove is used to separate the light-emitting column and the edge oxidation zone, thereby blocking the transmission of defects in the edge oxidation zone to the active area; on the other hand, the edge oxidation zone is arranged outside the light-emitting column to provide protection for the VCSEL light-emitting cavity, avoiding possible edge mechanical damage to the VCSEL light-emitting cavity during subsequent processing, manufacturing and use, and further improving reliability.

[0042] In the subsequent manufacturing process, the annular groove d will be filled with insulating materials, such as BCB (benzocyclobutene) or PI (polyimide) or silicon nitride, silicon oxide materials, etc.

[0043] The above embodiments are only used to further illustrate an oxidized VCSEL for eliminating mesa edge stress and a method for manufacturing the same of the present invention, but the present invention is not limited to the embodiments. Any simple modification, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for manufacturing an oxidized VCSEL for eliminating mesa edge stress, characterized in that: The following steps are involved: 1) providing or growing an epitaxial structure, wherein the epitaxial structure comprises a substrate, a buffer layer, a first DBR, a resonant cavity and a second DBR arranged in sequence, wherein the resonant cavity comprises a quantum well active region and a confinement layer; 2) Design the diameter and height of the light-emitting pillar, perform the first etching on the epitaxial structure, and etch out the initial pillar. The material of the restriction layer is Al x Ga 1-x As, wherein 1≥x≥0.98; the first DBR and the second DBR are respectively composed of Al y Ga 1-y As layer and Al z Ga 1-z As layers are grown alternately, wherein 0.95≥y≥0.80, 0.20≥z≥0.10; when the limiting layer reaches the preset central hole diameter in the wet oxidation process, the width of the edge oxidation zone generated by the first DBR and the second DBR is estimated according to x and y, and the diameter of the initial pillar is designed to be larger than the sum of the diameter of the light-emitting pillar and the width of the edge oxidation zone, and the height is smaller than the height of the light-emitting pillar; 3) The initial pillar is oxidized by a wet oxidation process until the limiting layer reaches the preset central hole diameter and an edge oxidation zone is generated at the same time; the wet oxidation process is: the oxidation furnace is heated to 380-420°C, the water temperature is set to 92-98°C, a trace amount of nitrogen is passed to remove excess air in the oxidation furnace, the flow rate is 0.5-1.5L / min, and it is stabilized for 15-30min, and then water vapor + nitrogen is started to pass at a flow rate of 3-8L / min; 4) Performing a second etching on the initial pillar to obtain a light-emitting pillar, wherein the second etching is to etch an annular groove on the periphery of the designed light-emitting pillar, wherein the annular groove separates the light-emitting pillar and the edge oxidation area.

2. The method for manufacturing an oxidized VCSEL for eliminating mesa edge stress according to claim 1, characterized in that: The etching width of the annular groove is 3 μm to 6 μm, and the depth is not less than the height of the initial pillar.

3. The method for manufacturing an oxidized VCSEL for eliminating mesa edge stress according to claim 1, characterized in that: The thickness of the restriction layer is 20-30 nm.

4. An oxidized VCSEL with table edge stress eliminated manufactured according to the manufacturing method of claim 1, characterized in that: The epitaxial structure includes a substrate, a buffer layer, a first DBR, a resonant cavity and a second DBR from bottom to top, and the resonant cavity includes a quantum well active region and a confinement layer; the epitaxial structure is etched downward to the second DBR to form a table top, and the epitaxial structure above the table top is separated to form a light-emitting column located in the center and an edge oxidation region surrounding the periphery of the light-emitting column, wherein the confinement layer of the light-emitting column is defined by oxidation to define a central hole, and the confinement layer of the edge oxidation region and parts of the first DBR and the second DBR are oxidized, and the light-emitting column and the edge oxidation region are separated by an annular groove, and the annular groove is filled with insulating material.

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