Method for inhibiting end face failure of laser

Abstract

The invention provides a method for inhibiting end face failure of a laser, belongs to the technical field of semiconductor lasers, and is used for solving the technical problem that the electric field intensity at the junction of an epitaxial material and an optical coating material of the laser is too large. The method comprises the following steps: (1) cleaving a semiconductor laser wafer into bars, and evaporating first film layers on front cavity surfaces and rear cavity surfaces of the bars respectively; (2) evaporating an antireflection film on the front cavity surface of the bar, and evaporating a high-reflection film on the rear cavity surface of the bar; and the thickness of the first film layer is the thickness when the electric field intensity at the junction of the laser epitaxial material and the optical coating material is reduced to zero. According to the invention, the electric field intensity at the junction of the laser epitaxial material and the optical coating material is reduced to zero, the design of zero electric field intensity reduces non-radiative recombination excited by the electric field, and the purposes of improving the end surface damage threshold and improving the reliability are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor lasers, and in particular relates to a method for suppressing failure of a laser end face. Background Art

[0002] In 1962, semiconductor materials were used as working materials to successfully radiate lasers. After many process and design upgrades, semiconductor lasers have gradually developed into laser light sources with small size, light weight, high efficiency and low price. Now, semiconductor lasers are widely used in optical fiber communications, data centers, laser radar, medical cosmetology, laser ranging, laser printers and other fields.

[0003] Reliability is a key indicator of whether a laser can be applied and a decisive indicator of whether a laser can be successfully introduced into the market. For edge-emitting lasers (such as DFB, FP), the process is complex and each process may become a risk point of reliability failure. During the process preparation, the bar-stripping process will destroy the crystal structure of the semiconductor, causing a large number of dangling bonds, defect centers, and composite centers on the end face; during the bar-stripping process, the end face is exposed to the air, which will cause the end face to be oxidized and dirty; the above problems are one of the main reasons for the reduction of the COD (Catastrophic Optical Damage) threshold and reliability failure of edge-emitting lasers. Patent Publication No. CN115051238A discloses a reliability-optimized laser chip and its preparation method. The patent has an insulating dielectric layer on the upper surface of the waveguide area near the end face of the laser, and there is no carrier injection and the photon density is reduced in the area near the end face, so as to achieve the purpose of improving the COD level and reliability. However, this method is relatively complicated and the preparation process is not simple enough.

[0004] Patent publication number CN109193338A discloses a method for coating a semiconductor laser cavity surface with a passivation film, the steps are S1: cleave the semiconductor laser chip in the air into bars with a cavity length of 500μm-2000μm; S2: fix the cleaved bars to a special fixture for chip coating and put them into a vacuum coating machine, and evacuate the vacuum coating machine until the pressure inside is less than 1×10-4Pa; S4: evaporate GaSe material on the cavity surface of the bars as a passivation film layer; S5: coat the front cavity surface of the bars with an anti-reflection cavity mask, and coat the rear cavity surface of the bars with a high reflection cavity mask; S6: cleave the coated device into a single tube and weld it to an oxygen-free copper heat sink. The patent uses GaSe as the material for the evaporated passivation film, and the bandgap width of GaSe is large, reaching 2.2eV. It effectively prevents electrons and holes from diffusing to the surface for recombination, eliminates the absorption of the cavity surface, improves the optical mirror damage threshold of the semiconductor laser, and extends the service life of the semiconductor laser. The above methods have improved the reliability of semiconductor lasers to a certain extent, but the applicant has found that excessive electric field strength at the interface between the laser epitaxial material and the optical coating material will also lead to an increase in non-radiative recombination stimulated by the electric field, thereby reducing the luminous efficiency and stability of the laser. Summary of the invention

[0005] In response to the above technical problems, the present invention proposes a method for suppressing the failure of the laser end face, reducing the electric field strength at the junction of the laser epitaxial material and the optical coating material to zero. The zero electric field strength design reduces the non-radiative recombination stimulated by the electric field, thereby achieving the purpose of increasing the end face damage threshold and improving reliability.

[0006] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for suppressing laser end face failure comprises the following steps:

[0008] (1) cleaving a semiconductor laser wafer into bars, and evaporating a first film layer on the front cavity surface and the back cavity surface of the bars respectively;

[0009] (2) vapor-depositing an anti-reflection film on the front cavity surface of the bar and vapor-depositing a high-reflection film on the rear cavity surface of the bar;

[0010] The thickness of the first film layer is the thickness when the electric field intensity at the interface between the laser epitaxial material and the optical coating material is reduced to zero.

[0011] In the step (1), the semiconductor laser wafer is cleaved and stripped in air, and the front cavity surface and the rear cavity surface of the strip are cleaned with plasma before the first film layer is evaporated.

[0012] The gas used in the plasma cleaning is one or more of Ar, N2, H2 or NH3.

[0013] The material of the first film layer is a material with a dielectric constant between (x-1) and (x+1), where x is the dielectric constant of the laser epitaxial material.

[0014] The laser epitaxial material is InP, and the material of the first film layer is silicon. When the dielectric constants of the two layers of material are close, their refractive index difference will also decrease, thereby weakening the reflection at the interface. This situation is similar to using a transition layer with a gradient refractive index to alleviate the violent reflection of the incident light at the interface. For materials such as InP, whose dielectric constant is relatively high (usually about 12.5), if the dielectric constant of the first film is also relatively high and close to the dielectric constant of InP, then the reflection generated at the interface will be significantly reduced, which can reduce the electric field strength at the interface and make the electric field transition as smoothly as possible between the first film and the substrate. According to computer simulation, the most suitable dielectric constant for the first film is within 12.5±1. The closer to the dielectric constant of the substrate, the better the effect. The dielectric constants of common coating materials are as follows: Figure 1 As shown, considering the limited materials available for optical coating, as well as the refractive index, film quality and coating process, silicon is selected as the first layer of film material.

[0015] The thickness of the first film layer is determined by computer simulation, and the simulation steps are:

[0016] S1 uses the film system design software to input the materials and thickness information of other film layers except the first film layer, and check the electric field intensity distribution between each layer of the film system;

[0017] S2 inputs the material information of the first film layer, and by changing the thickness of the first film layer, observes the thickness of the first film layer when the electric field strength at the junction of the epitaxial material and the first film layer is the smallest.

[0018] Preferably, the film system design software is used. The electric field intensity distribution between each layer of the film system can be viewed through Coupute EFI in Run in the software analysis. The thickness of the first film layer can be interactively analyzed through Interactive Analysis in Run in the toolbar. After determining the most suitable thickness of the first film layer, the film thickness is locked, and the spectrum can be optimized to the required level by optimizing the film thickness of other layers.

[0019] The anti-reflection film and the high-reflection film are both composed of a plurality of layers of high-refractive index layers and low-refractive index layers alternately.

[0020] The material of the high refractive index layer is any one of TiO2, Ta2O5, HfO2 or Si; the material of the low refractive index layer is SiO2 or Al2O3.

[0021] The thickness of the anti-reflection film is 200-300nm, and the thickness of the high-reflection film is 500-800nm.

[0022] The beneficial effects of the present invention are as follows: since the electric field strength at the interface between the laser epitaxial material and the optical coating material is too large, the non-radiative recombination stimulated by the electric field will increase, thereby reducing the luminous efficiency and stability of the laser. The present invention optimizes the electric field distribution inside the laser by changing the optical coating design, selecting a material that matches the epitaxial material, and precisely controlling the film structure and thickness, thereby reducing the electric field strength at the interface between the laser epitaxial material and the optical coating material to zero. The zero electric field strength design reduces the non-radiative recombination stimulated by the electric field, thereby achieving the purpose of increasing the end face damage threshold and improving reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 The dielectric constant of common coating materials

[0025] Figure 2 This is the electric field distribution diagram of the semiconductor laser prepared in Comparative Example 1.

[0026] Figure 3 This is the electric field distribution diagram of the semiconductor laser prepared in Example 1.

[0027] Figure 4 This is the spectrum diagram of the semiconductor laser prepared in Example 1.

[0028] Figure 5 This is the electric field distribution diagram of the semiconductor laser prepared in Example 2.

[0029] Figure 6 This is the spectrum diagram of the semiconductor laser prepared in Example 2. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] A method for suppressing laser end face failure comprises the following steps:

[0033] (1) Use optical film design software to confirm the materials and thicknesses of other film layers except the first film layer. The electric field strength distribution between each layer of the film system can be viewed through Coupute EFI in Run. The material of the first film layer is Si, and the thickness can be interactively analyzed through the software. By changing the thickness of the first film layer, the thickness of the first film layer is observed when the electric field strength at the junction of the epitaxial material and the first film layer is the smallest. It is finally determined to be 95nm.

[0034] (2) Cleave the semiconductor laser wafer into strips with a cavity length of 1000 μm in air.

[0035] (3) The cleaved strips are fixed on a fixture for coating and placed in a vacuum evaporation coating machine (Leybold ARES1100) together with the accompanying K9 test glass and the accompanying InP flat sheet. The vacuum is evacuated to a pressure of 2.0E-6 Torr, the temperature is set to 150°C, and the baking time is 30 minutes.

[0036] (4) Then, the Hall ion source is turned on to perform ion cleaning on the product. The gas is selected as Ar, the gas flow is set to 30 SCCM, the voltage is selected as 90 V, the current is set to 4 A, and the time is set to 2 min. Ion cleaning is performed on one side of the product;

[0037] (5) After ion cleaning, the ion source is turned off to grow the Si layer. The Si layer thickness is selected to be 95 nm, the coating temperature is 150 °C, and the deposition rate is The electron gun current is adjusted between 100-165mA by PID according to the feedback of the coating rate, where P (proportional regulation) is set to 100, I (integral regulation) is set to 0.6, and D (differential regulation) is set to 0.5 to ensure a stable coating rate;

[0038] (6) repeating steps (4) and (5) to perform plating on the other side with the same process parameters;

[0039] (7) Then, an anti-reflection film layer is evaporated on the front cavity surface of the Bar strip in an evaporation coating machine, and the film layer structure and thickness are as follows: Al2O3-16nm / Si-56nm / Al2O3-207nm; then, a high-reflection film layer is evaporated on the back cavity surface, and the film layer structure and thickness are as follows: Al2O3-133nm / Si-76nm / Al2O3-246nm / Si-80nm / Al2O3-117nm.

[0040] The coated Bar strip is split to obtain a semiconductor laser, wherein the light-emitting surface of the semiconductor laser includes a Si layer and an anti-reflection film in sequence from the inside to the outside, and the backlight surface of the semiconductor laser includes a Si layer and a high-reflection film in sequence from the inside to the outside.

[0041] Before optimizing the thickness of the optical coating layer, the electric field distribution and film system design are as follows: Figure 2 As shown; after the thickness of the optical coating layer is optimized, the electric field intensity at the junction of the laser epitaxial material and the optical coating material is reduced to zero, and the spectrum fluctuation is also small. Using the Cary7000 spectrophotometer, the reflection spectrum of the accompanying InP plate (without the coating of the first film layer in step (5)) can be measured. The measurement band is 1100nm-1500nm, the spectral bandwidth is 4nm, and the step length of the measurement result is 1nm. Since the laser light-emitting surface material is also InP, its reflection spectrum is almost consistent with the actual reflection of the laser end face. It can be seen that the reflection of the accompanying plate spectrum at the working wavelength of the laser is greater than 92%, which can effectively reflect the laser, thereby improving the light-emitting effect of the light-emitting surface and meeting the needs of laser products. The new design and electric field distribution are shown in Figure 3 As shown in the figure, the spectrum comparison before and after the film system optimization is as follows Figure 4 shown.

[0042] Example 2

[0043] A method for suppressing laser end face failure comprises the following steps:

[0044] (1) Use optical film design software to confirm the materials and thicknesses of other film layers except the first film layer. The electric field strength distribution between each layer of the film system can be viewed through Coupute EFI in Run. The material of the first film layer is Si, and the thickness can be interactively analyzed through the software. By changing the thickness of the first film layer, the thickness of the first film layer is observed when the electric field strength at the junction of the epitaxial material and the first film layer is the smallest. It is finally determined to be 85nm.

[0045] (2) Cleave the semiconductor laser wafer into strips with a cavity length of 1000 μm in air.

[0046] (3) The cleaved strips are fixed on a fixture for coating and placed in a vacuum evaporation coating machine (Leybold ARES1100) together with the accompanying K9 test glass and the accompanying InP flat sheet. The vacuum is evacuated to a pressure of 2.0E-6 Torr, the temperature is set to 150°C, and the baking time is 30 minutes.

[0047] (4) Then, the Hall ion source is turned on to perform ion cleaning on the product. The gas is selected as Ar, the gas flow is set to 30 SCCM, the voltage is selected as 90 V, the current is set to 4 A, and the time is set to 2 min. Ion cleaning is performed on one side of the product;

[0048] (5) After ion cleaning, the ion source is turned off to grow the Si layer. The Si layer thickness is selected to be 85 nm, the coating temperature is 150 °C, and the deposition rate is The electron gun current is adjusted between 100-165mA by PID according to the feedback of the coating rate, where P (proportional regulation) is set to 100, I (integral regulation) is set to 0.6, and D (differential regulation) is set to 0.5 to ensure a stable coating rate;

[0049] (6) Repeat steps 3 and 4 to passivate the other side with the same process parameters;

[0050] (7) Then, an anti-reflection film layer is evaporated on the front cavity surface of the Bar strip in an evaporation coating machine, and the film layer structure and thickness are as follows: Al2O3-16nm / Si-56nm / Al2O3-207nm; then, a high-reflection film layer is evaporated on the back cavity surface, and the film layer structure and thickness are as follows: SiO2-223nm / Si-82nm / SiO2-221nm / Si-82nm / SiO2-220nm.

[0051] The coated Bar strip is split to obtain a semiconductor laser, wherein the light-emitting surface of the semiconductor laser includes a Si layer and an anti-reflection film in sequence from the inside to the outside, and the backlight surface of the semiconductor laser includes a Si layer and a high-reflection film in sequence from the inside to the outside.

[0052] After the thickness of the optical coating layer is optimized, the electric field intensity at the junction of the laser epitaxial material and the optical coating material is reduced to zero, and the spectrum fluctuation is also small. The Cary 7000 spectrophotometer can be used to measure the reflection spectrum of the accompanying InP film. The measurement band is 1100nm-1500nm, the spectrum bandwidth is 4nm, and the step size of the measurement result is 1nm. Since the laser light-emitting surface material is also InP, its reflection spectrum is almost consistent with the actual reflection of the laser end face. It can be seen that the reflection of the accompanying coating film spectrum at the operating wavelength of the laser is greater than 94%, which can effectively reflect the laser, thereby improving the light-emitting effect of the light-emitting surface and meeting the needs of laser products. The new design and electric field distribution are as follows: Figure 5 As shown in the figure, the spectrum comparison before and after the film system optimization is as follows Figure 6 shown.

[0053] Example 3

[0054] A method for suppressing laser end face failure comprises the following steps:

[0055] (1) Use optical film design software to confirm the materials and thicknesses of other film layers except the first film layer. The electric field strength distribution between each layer of the film system can be viewed through Coupute EFI in Run. The material of the first film layer is Si, and the thickness can be interactively analyzed through the software. By changing the thickness of the first film layer, the thickness of the first film layer is observed when the electric field strength at the junction of the epitaxial material and the first film layer is the smallest. It is finally determined to be 60nm.

[0056] (2) Cleave the semiconductor laser wafer into strips with a cavity length of 1000 μm in air.

[0057] (3) The cleaved strips are fixed on a fixture for coating and placed in a vacuum evaporation coating machine (Leybold ARES1100) together with the accompanying K9 test glass and the accompanying InP flat sheet. The vacuum is evacuated to a pressure of 2.0E-6 Torr, the temperature is set to 150°C, and the baking time is 30 minutes.

[0058] (4) Then, the Hall ion source is turned on to perform ion cleaning on the product. The gas is selected as Ar, the gas flow is set to 30 SCCM, the voltage is selected as 90 V, the current is set to 4 A, and the time is set to 2 min. Ion cleaning is performed on one side of the product;

[0059] (5) After ion cleaning, the ion source is turned off to grow the Si layer. The Si layer thickness is selected to be 60 nm, the coating temperature is 150 °C, and the deposition rate is The electron gun current is adjusted between 100-165mA by PID according to the feedback of the coating rate, where P (proportional regulation) is set to 100, I (integral regulation) is set to 0.6, and D (differential regulation) is set to 0.5 to ensure a stable coating rate;

[0060] (6) repeating steps (4) and (5) to perform plating on the other side with the same process parameters;

[0061] (7) Then, an anti-reflection film layer is evaporated on the front cavity surface of the Bar strip in an evaporation coating machine, and the film layer structure and thickness are as follows: Al2O3-16nm / Si-56nm / Al2O3-207nm; then, a high-reflection film layer is evaporated on the back cavity surface, and the film layer structure and thickness are as follows: Al2O3-133nm / Si-76nm / Al2O3-246nm / Si-80nm / Al2O3-117nm.

[0062] The coated Bar strip is split to obtain a semiconductor laser, wherein the light-emitting surface of the semiconductor laser includes a Si layer and an anti-reflection film in sequence from the inside to the outside, and the backlight surface of the semiconductor laser includes a Si layer and a high-reflection film in sequence from the inside to the outside.

[0063] Example 4

[0064] A method for suppressing laser end face failure comprises the following steps:

[0065] (1) Use optical film design software to confirm the materials and thicknesses of other film layers except the first film layer. The electric field strength distribution between each layer of the film system can be viewed through Coupute EFI in Run. The material of the first film layer is Si, and the thickness can be interactively analyzed through the software. By changing the thickness of the first film layer, the thickness of the first film layer is observed when the electric field strength at the junction of the epitaxial material and the first film layer is the smallest, and it is finally determined to be 100nm.

[0066] (2) Cleave the semiconductor laser wafer into strips with a cavity length of 1000 μm in air.

[0067] (3) The cleaved strips are fixed on a fixture for coating and placed in a vacuum evaporation coating machine (Leybold ARES1100) together with the accompanying K9 test glass and the accompanying InP flat sheet. The vacuum is evacuated to a pressure of 2.0E-6 Torr, the temperature is set to 150°C, and the baking time is 30 minutes.

[0068] (4) Then, the Hall ion source is turned on to perform ion cleaning on the product. The gas is selected as Ar, the gas flow is set to 30 SCCM, the voltage is selected as 90 V, the current is set to 4 A, and the time is set to 2 min. Ion cleaning is performed on one side of the product;

[0069] (5) After ion cleaning, the ion source is turned off to grow the Si layer. The Si layer thickness is selected to be 100 nm, the coating temperature is 150 °C, and the deposition rate is The electron gun current is adjusted between 100-165mA by PID according to the feedback of the coating rate, where P (proportional regulation) is set to 100, I (integral regulation) is set to 0.6, and D (differential regulation) is set to 0.5 to ensure a stable coating rate;

[0070] (6) Repeat steps 3 and 4 to passivate the other side with the same process parameters;

[0071] (7) Then, an anti-reflection film layer is evaporated on the front cavity surface of the Bar strip in an evaporation coating machine, and the film layer structure and thickness are as follows: Al2O3-16nm / Si-56nm / Al2O3-207nm; then, a high-reflection film layer is evaporated on the back cavity surface, and the film layer structure and thickness are as follows: SiO2-223nm / Si-82nm / SiO2-221nm / Si-82nm / SiO2-220nm.

[0072] The coated Bar strip is split to obtain a semiconductor laser, wherein the light-emitting surface of the semiconductor laser includes a Si layer and an anti-reflection film in sequence from the inside to the outside, and the backlight surface of the semiconductor laser includes a Si layer and a high-reflection film in sequence from the inside to the outside.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for suppressing laser end face failure, characterized in that: The following steps are involved: (1) cleaving a semiconductor laser wafer into bars, and evaporating a first film layer on the front cavity surface and the back cavity surface of the bars respectively; (2) vapor-depositing an anti-reflection film on the front cavity surface of the bar and vapor-depositing a high-reflection film on the rear cavity surface of the bar; The thickness of the first film layer is the thickness when the electric field intensity at the interface between the laser epitaxial material and the optical coating material is reduced to zero.

2. The method for suppressing laser end face failure according to claim 1, characterized in that: In the step (1), the semiconductor laser wafer is cleaved and stripped in air, and the front cavity surface and the rear cavity surface of the strip are cleaned with plasma before the first film layer is evaporated.

3. The method for suppressing laser end face failure according to claim 2, characterized in that: The gas used in the plasma cleaning is one or more of Ar, N2, H2 or NH3.

4. The method for suppressing laser end face failure according to any one of claims 1 to 3, characterized in that: The material of the first film layer is a material with a dielectric constant between (x-1) and (x+1), where x is the dielectric constant of the laser epitaxial material.

5. The method for suppressing laser end face failure according to claim 4, characterized in that: The laser epitaxial material is InP, and the material of the first film layer is silicon.

6. The method for suppressing laser end face failure according to claim 1, characterized in that: The thickness of the first film layer is 60-120 nm. The thickness of the first film layer is determined by computer simulation, and the simulation steps are: S1 uses the film system design software to input the materials and thickness information of other film layers except the first film layer, and check the electric field intensity distribution between each layer of the film system; S2 inputs the material information of the first film layer, and by changing the thickness of the first film layer, when the electric field strength at the interface between the epitaxial material and the first film layer is the smallest, the thickness of the first film layer is taken at this time.

7. The method for suppressing laser end face failure according to claim 1, characterized in that: The anti-reflection film and the high-reflection film are both composed of a plurality of layers of high-refractive index layers and low-refractive index layers alternately.

8. The method for suppressing laser end face failure according to claim 7, characterized in that: The material of the high refractive index layer is any one of TiO2, Ta2O5, HfO2 or Si; the material of the low refractive index layer is SiO2 or Al2O3.

9. The method for suppressing laser end face failure according to claim 8, characterized in that: The thickness of the anti-reflection film is 200-300nm, and the thickness of the high-reflection film is 500-800nm.

10. A laser prepared by the method according to any one of claims 1 to 9.

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