A preparation method and structure of a high-reliability and low-noise vertical laser

Abstract

The present application relates to the technical field of semiconductor lasers, and in particular to a method and structure for preparing a high-reliability, low-noise vertical laser. A substrate with a lattice direction of [1 0 0]2-15° offset from [1 1 0] is selected; two arc-shaped grooves are etched on the layer structure of the substrate, an opening is formed between the ends of the two arc-shaped grooves, and the opening direction is along the crystal direction [0 0 1]; the oxidation restriction layer is oxidized, and a circular oxidation hole is formed between the two arc-shaped grooves; a passivation protective film is covered at the opening and the surface of the device; the opening is filled, and a metal ring is connected through the opening position to lead the P-pole current injection point to the peripheral area; an elliptical relief with a short-to-long axis ratio of 1:1-1:2 is etched from the surface passivation layer at the top of the light-emitting area. The opening is designed to face the [0 0 1] lattice direction, and the final oxidation shape of the device is circular, which improves reliability. The surface passivation film is etched into an elliptical relief to reduce relative intensity noise and effectively improve transmission quality.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor lasers, and in particular to a preparation method and structure of a high-reliability and low-noise vertical laser. Background Art

[0002] High-speed vertical cavity surface emitting laser (VCSEL) plays an important role in the development of large data centers and supercomputer technology due to its small size, low power consumption, low cost, high speed, etc. The data throughput increases year by year, which leads to the need for higher speed and lower noise VCSEL in data centers and supercomputer systems.

[0003] Oxidation-restricted VCSELs have the advantages of low cost, low power consumption, and low threshold, and are used for mass production of VCSELs. The main process steps of the oxidation holes of existing VCSELs include: wafer epitaxial growth, during which a groove is etched in the layer structure formed by the epitaxial growth to form a columnar (usually cylindrical) active area platform, and it is necessary to ensure that the oxidation restriction layer is exposed to the sidewall of the active area platform. The etched grooves usually have two forms, one is a closed groove and the other is a non-closed groove. Both methods are common methods of current VCSEL etching processes.

[0004] The sidewalls of the active area platform are oxidized, and the oxidation is carried out laterally along the oxidation restriction layer. The unoxidized area in the middle forms an oxidation hole, which is the light output hole and current injection area of ​​the VCSEL; then the surface is passivated.

[0005] The shape of the oxide aperture of the traditional oxide-limited VCSEL is designed to be as close to a circle as possible, so that the current is injected evenly and the device failure caused by cracking of the oxide layer is reduced. However, the quasi-circular oxide aperture leads to non-selective competition between the two orthogonal polarization states of the transverse mode, which deteriorates the relative intensity noise and greatly affects the high-speed transmission performance. Summary of the invention

[0006] In order to reduce noise and improve transmission performance, the present application provides a preparation method and structure of a high-reliability and low-noise vertical laser.

[0007] One of the purposes of this application is to provide a method for preparing a high-reliability, low-noise vertical laser, using the following technical solution:

[0008] A method for preparing a high-reliability and low-noise vertical laser, comprising:

[0009] S1, select a substrate with a lattice direction of [1 0 0] 2-15° offset from [1 1 0];

[0010] S2, etching two opposite arc-shaped grooves on the layer structure of the substrate, forming an opening between the ends of the two arc-shaped grooves, and the opening direction is along the crystal direction [0 0 1];

[0011] S3, oxidizing the oxidation restriction layer in the layer structure, and forming a circular oxidation hole between the two arc-shaped grooves;

[0012] S4, covering the opening and the device surface with a passivation protective film to form a surface passivation layer;

[0013] S5, filling the opening to form a dielectric filling layer, and connecting a metal ring through the opening position to lead the P-pole current injection point to the peripheral area to form a P-side ohmic contact layer;

[0014] S6. Etching the surface passivation layer on the top of the light-emitting area into an elliptical relief with a short-to-long axis ratio of 1:1-1:2 to form a polarization control layer.

[0015] By adopting the above technical solutions, in order to ensure structural stability and prevent the coating stress from causing the oxide layer to crack and affect reliability, non-closed grooves are mostly used. The non-closed groove structure causes the oxidation aperture to be non-circular, resulting in uneven current injection and excessive local current density, leading to device failure. Conventionally, the non-closed groove structure is made into a quasi-circular oxidation aperture, and a barrier layer needs to be set in some areas of the groove sidewall to actively correct the difference in oxidation rate in each direction. This process is extremely complex and unstable.

[0016] The present invention retains the non-closed groove and designs the arc groove opening toward the [0 0 1] lattice direction. The final oxidation shape of the device is quasi-circular, which effectively improves reliability compared with the non-circular oxidation shape. At the same time, the surface passivation film is etched into an elliptical relief pattern with a short-to-long axis ratio of 1:1-1:2, which regulates the polarization characteristics of the emitted light, reduces the relative intensity noise, and effectively improves the transmission quality.

[0017] Preferably, the relief in step S6 is etched along the crystal direction [0 1 1] [0 -1 1].

[0018] Preferably, the method further includes step S7, using an evaporation process to form a metal ring on the top of the light-emitting area of ​​the device as a current injection area.

[0019] Preferably, the distances between the two openings in S2 are different.

[0020] Preferably, in S5, the opening is filled with phenylcyclobutene as a filling medium through an electroplating process.

[0021] By adopting the above technical solution, external parasitic capacitance is reduced.

[0022] Preferably, the material of the surface passivation layer in S4 is SiNx.

[0023] By adopting the above technical solution, the stress of SiNx is lowered, thereby reducing the internal stress.

[0024] Another object of the present application is to provide a high-reliability, low-noise vertical laser structure, using the following technical solution:

[0025] A structure of a high-reliability, low-noise vertical laser is manufactured by the above-mentioned method for preparing a high-reliability, low-noise vertical laser, comprising a substrate, a layer structure is provided on the substrate, the layer structure comprises a light-emitting area, a circular-shaped oxidation hole is provided in the center of the light-emitting area, the layer structure comprises a surface passivation layer located at the top, and an elliptical surface relief is etched on the surface passivation layer located in the light-emitting area.

[0026] By adopting the above technical solution, high-reliability quasi-circular oxidation aperture technology can be taken into account while polarization state control can be achieved, so that high-reliability, low-noise vertical cavity surface emitting laser manufacturing can be achieved at extremely low cost and price.

[0027] Preferably, the layer structure includes an N-side DBR layer, an N-type restriction layer, an active area, a P-type restriction layer, an oxidation restriction layer, a P-type DBR layer, an ion implantation layer, a dielectric filling layer and a surface passivation layer, which are arranged in sequence from bottom to top. An N-side electrode is also provided on the substrate. The ion implantation layer is located on the outside of the P-type DBR layer in the light-emitting area, and a P-side ohmic contact layer is provided on the top of the light-emitting area.

[0028] By adopting the above technical solution, the effective thickness of the non-conductive area on the oxide layer is increased, the parasitic capacitance of the device is reduced, and the high-speed characteristics of the device are improved.

[0029] In summary, this application includes the following beneficial technical effects:

[0030] The high-reliability quasi-circular oxide aperture technology can achieve polarization state control at the same time, and can realize high-reliability, low-noise vertical cavity surface emitting laser manufacturing at extremely low cost and price. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a cross-sectional view of the laser in Example 1;

[0032] Figure 2 FIG. 1 is a top view of the laser in the first embodiment.

[0033] Description of reference numerals:

[0034] 1. Substrate; 2. N-side electrode; 3. N-type DBR layer; 4. N-type confinement layer; 5. Active region; 6. P-type confinement layer; 7. Oxidation confinement layer; 8. P-type DBR layer; 9. Ion implantation layer; 10. Dielectric filling layer; 11. Surface passivation layer; 12. P-side ohmic contact layer; 13. Polarization control layer; 14. Arc groove; 15. Opening; 16. Oxidation hole. DETAILED DESCRIPTION

[0035] The present application is further described in detail below in conjunction with all the accompanying drawings.

[0036] Example 1: This application example discloses a method for preparing a high-reliability, low-noise vertical laser. Figure 1 and Figure 2 , including the following steps:

[0037] S1, selecting a substrate 1 with a lattice direction of [1 0 0] 2-15° offset from [1 1 0]; wherein the material of the substrate 1 is GaAs;

[0038] S2, etching two opposite arc-shaped grooves 14 on the layer structure of the substrate 1 by dry etching process, forming an opening 15 between the ends of the two arc-shaped grooves 14, and the direction of the opening 15 is along the crystal direction [0 0 1]; and the two openings 15 are different in size, that is, the width of one opening 15 is greater than the width of the other opening 15;

[0039] S3, through the wet oxidation process, the oxidation restriction layer 7 in the layer structure is oxidized, and the high Al layer exposed in the arc-shaped groove 14 reacts, so that a circular oxidation hole 16 is formed between the two arc-shaped grooves 14; the opening 15 is along the crystal direction [00 1], and since the chemical bond properties of the crystal directions [0 0 1] and [0 -1 0] are consistent, a circular oxidation hole 16 can be stably obtained;

[0040] S4, through a dielectric thin film deposition process, a low stress SiNx passivation protective film is covered on the opening 15 of the arc-shaped groove 14 and the surface of the device to form a surface passivation layer 11;

[0041] S5. Fill the opening 15 with styrene cyclobutene material through an electroplating process to form a dielectric filling layer 10 to improve heat dissipation capability. Meanwhile, connect a metal ring through the opening 15 to lead the P-pole current injection point to the peripheral area.

[0042] S6, etching the passivation film on the top of the light-emitting area along the crystal direction [0 1 1] [0 -1 1] to form an elliptical relief with a short-to-long axis ratio of 1:1-1:2 to form a polarization control layer 13 by a dry etching process;

[0043] S7, using an evaporation process, making a metal ring on the top of the light-emitting area of ​​the device as a current injection area;

[0044] S8, through the dry etching process, leak out the N-side electrode 2, and use the evaporation process to form the N-pole current injection area. The above steps S1-S8 only represent the content and number of steps, and do not represent the order of the steps.

[0045] The opening 15 of the arc groove 14 is designed to face the [0 0 1] lattice direction, and the final oxidation shape of the oxidation hole 16 is quasi-circular, which effectively improves reliability compared with the non-circular oxidation shape. The surface passivation film is etched into an elliptical relief pattern with a short and long axis ratio of 1:1-1:2 using the SiNx dry etching process to adjust the polarization characteristics of the output light, reduce the relative intensity noise, and effectively improve the transmission quality.

[0046] Embodiment 2: This embodiment of the present application discloses a structure of a high-reliability, low-noise vertical laser, which is prepared by the above embodiment, referring to Figure 1 and Figure 2 , including a substrate 1, the substrate 1 is made of GaAs, and the lattice direction of the commercial substrate 1 is [1 0 0]2-15° offset from [1 1 0]. A layer structure is provided on the substrate 1, and the layer structure includes a light-emitting area, and a circular oxide hole 16 is provided in the center of the light-emitting area.

[0047] An N-side electrode 2 is provided on the substrate 1 and the material of the electrode is Au, Ge, Ni or Au.

[0048] The layer structure includes the following, arranged from bottom to top:

[0049] N-type DBR layer 3, made of GaAs or AlAs, using AlAs as a heat dissipation layer to improve reliability;

[0050] N-type confinement layer 4, made of AlGaAs

[0051] Active region 5, material is InGaAs or AlGaAs strained quantum well structure

[0052] P-type confinement layer 6, made of AlGaAs

[0053] P-type DBR layer 8, made of GaAs or AlGaAs

[0054] Oxidation restriction layer 7, made of AlGaAs;

[0055] The ion implantation layer 9 is located outside the P-type DBR layer 8 in the light emitting area and does not exceed the active area 5. The effective thickness of the non-conductive area on the oxide layer is increased, the parasitic capacitance of the device is reduced, and the high-speed characteristics of the device are improved.

[0056] The dielectric filling layer 10 is made of styrene to reduce external parasitic capacitance;

[0057] The surface passivation layer 11 is made of SiNx and has a passivation protection function. An elliptical relief with a short-to-long axis ratio of 1:1-1:2 is etched along the crystal direction [0 1 1] [0 -1 1] on the surface passivation layer 11 located in the light-emitting area to form a polarization control layer 13. A P-face ohmic contact layer 12 is provided on the top of the light-emitting area.

[0058] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a high-reliability, low-noise vertical laser, characterized in that: include, S1, select a substrate (1) with a lattice direction of [1 0 0] 2-15° offset from [1 1 0]; S2, etching two opposite arc-shaped grooves (14) on the layer structure of the substrate (1), forming two openings (15) between the ends of the two arc-shaped grooves (14), and the directions of the two openings (15) are along the crystal direction [0 0 1]; S3, oxidizing the oxidation restriction layer (7) in the layer structure, causing the high Al layer exposed in the arc-shaped groove (14) to react, so that a circular oxidation hole (16) is formed between the two arc-shaped grooves (14); S4, covering the opening and the device surface with a passivation protective film to form a surface passivation layer (11); S5, filling the opening (15) to form a dielectric filling layer (10), and at the same time connecting a metal ring through the position of the opening (15) to lead the P-pole current injection point to the peripheral area to form a P-side ohmic contact layer (12); S6, etching the surface passivation layer (11) on the top of the light-emitting area to form an elliptical relief with a short-to-long axis ratio of 1:1-1:2 to form a polarization control layer (13).

2. The method for preparing a high-reliability, low-noise vertical laser according to claim 1, characterized in that: The relief in step S6 is etched along the crystal direction [0 1 1] [0 -1 1].

3. The method for preparing a high-reliability, low-noise vertical laser according to claim 1, characterized in that: The method also includes step S7, using an evaporation process to form a metal ring on the top of the light-emitting area of ​​the device as a current injection area.

4. The method for preparing a high-reliability, low-noise vertical laser according to claim 1, characterized in that: The distances between the two openings (15) in S2 are different.

5. The method for preparing a high-reliability, low-noise vertical laser according to claim 1, characterized in that: In S5, the opening (15) is filled by electroplating process using phenylcyclobutene as a filling medium.

6. The method for preparing a high-reliability, low-noise vertical laser according to claim 1, characterized in that: The material of the surface passivation layer (11) in S4 is SiNx.

7. A structure of a high reliability and low noise vertical laser, characterized in that: A method for preparing a high-reliability, low-noise vertical laser according to any one of claims 1 to 6 is used, comprising a substrate (1), a layer structure being provided on the substrate (1), the layer structure comprising a light-emitting area, a circular-shaped oxidation hole (16) being provided at the center of the light-emitting area, the layer structure comprising a surface passivation layer (11) located on the top, an elliptical surface relief being etched on the surface passivation layer (11) located in the light-emitting area.

8. The structure of a high reliability and low noise vertical laser according to claim 7, characterized in that: The layer structure comprises, arranged in order from bottom to top, an N-side DBR layer (3), an N-type restriction layer (4), an active region (5), a P-type restriction layer (6), an oxidation restriction layer (7), a P-type DBR layer (8), an ion implantation layer (9), a dielectric filling layer (10) and a surface passivation layer (11); an N-side electrode (2) is also provided on the substrate (1); the ion implantation layer (9) is located outside the P-type DBR layer (8) in the light-emitting region; and a P-side ohmic contact layer (12) is provided on the top of the light-emitting region.

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