A method of inhibiting end face failure of a laser

Abstract

The application provides a method for inhibiting end face failure of a laser, and belongs to the technical field of semiconductor lasers, and aims at solving the technical problem of excessive electric field intensity at the junction of laser epitaxial material and optical coating material.The method comprises the following steps: (1) cleaving a semiconductor laser wafer into bars, and evaporating a first film layer on the front cavity surface and the rear cavity surface of the bar respectively; (2) evaporating an anti-reflection film on the front cavity surface of the bar, and evaporating 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 junction of the laser epitaxial material and the optical coating material is reduced to zero.The electric field intensity at the junction of the laser epitaxial material and the optical coating material is reduced to zero, and the zero electric field intensity design reduces the non-radiation recombination caused by the electric field, so that the end face damage threshold is improved, and the reliability is improved.

Description

Technical Field

[0001] This invention belongs to the technical field of semiconductor lasers, and particularly relates to a method for suppressing laser end-face failure. Background Technology

[0002] In 1962, semiconductor lasers were successfully emitted using semiconductor materials as the working medium. After numerous upgrades in technology and design, semiconductor lasers have gradually developed into laser sources that are small in size, lightweight, highly efficient, and inexpensive. Currently, semiconductor lasers are widely used in fields such as fiber optic communication, data centers, lidar, medical aesthetics, laser ranging, and laser printers.

[0003] Reliability is a key indicator for the application of lasers and a decisive factor in their successful market entry. For edge-emitting lasers (such as DFB and FP), the manufacturing process is complex, and each process can potentially become a point of failure for reliability. During the fabrication process, the bar-scraping process can damage the crystal structure of the semiconductor, creating numerous dangling bonds, defect centers, and recombination centers on the end face. During bar removal, the end face is exposed to air, leading to oxidation and contamination. These problems are among the main reasons for the reduced COD (Catastrophic Optical Damage) threshold and reliability failure in edge-emitting lasers. Patent publication number CN115051238A discloses a reliability-optimized laser chip and its fabrication method. This patent has an insulating dielectric layer on the upper surface of the waveguide region near the end face of the laser. The absence of carrier injection and reduced photon density in this region near the end face improves the COD level and enhances reliability. However, this method is relatively complex, and the fabrication process is not simple enough.

[0004] Patent publication number CN109193338A discloses a method for depositing a passivation film on the cavity surface of a semiconductor laser. The steps are as follows: S1: The semiconductor laser chip is cleaved in air into bars with a cavity length of 500μm-2000μm; S2: The cleaved bars are fixed onto a special chip coating fixture and placed in a vacuum coating machine, and the vacuum coating machine is evacuated until the pressure inside the vacuum coating machine is lower than 1×10-4 Pa; S4: GaSe material is vapor-deposited on the cavity surface of the bars as a passivation film layer; S5: An antireflection cavity film is deposited on the front cavity surface of the bars, and a high-reflection cavity film is deposited on the rear cavity surface of the bars; S6: The coated device is then cleaved into a single tube and welded to an oxygen-free copper heat sink. This patent uses GaSe as the material for vapor-deposited passivation film. GaSe has a large band gap, reaching 2.2 eV. This effectively prevents electrons and holes from diffusing to the surface and recombinizing, eliminates absorption at 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 some extent. However, the applicant found that an excessively large electric field intensity at the interface between the laser epitaxial material and the optical coating material can also lead to an increase in nonradiative recombination excited by the electric field, which reduces the luminous efficiency and stability of the laser. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for suppressing laser end-face failure. This method reduces the electric field intensity at the interface between the laser epitaxial material and the optical coating material to zero. The zero electric field intensity design reduces non-radiative recombination excited by the electric field, thereby increasing the end-face damage threshold and improving reliability.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

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

[0008] (1) The semiconductor laser wafer is cleaved into bar strips, and the first film layer is deposited on the front cavity surface and the rear cavity surface of the bar strips respectively;

[0009] (2) An antireflective film is deposited on the front cavity surface of the bar and a high reflective film is deposited on the rear cavity surface of the bar.

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

[0011] In step (1), the semiconductor laser wafer is cleaved and stripped in air, and the front and back cavity surfaces of the strips are cleaned with plasma before the first film layer is deposited.

[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 first film layer is made of silicon. When the dielectric constants of the two layers are close, their refractive index difference decreases, thereby reducing reflection at the interface. This is similar to using a transition layer with a gradually changing refractive index to alleviate severe reflection of incident light at the interface. For materials like InP, which have a high dielectric constant (typically around 12.5), if the dielectric constant of the first film is also high and close to that of InP, the reflection at the interface will be significantly reduced. This reduces the electric field strength at the interface, allowing the electric field to transition as smoothly as possible between the first film and the substrate. Computer simulations show that the optimal dielectric constant for the first film is within 12.5 ± 1. The closer the dielectric constant is to that of the substrate, the better the effect. Common coating materials have dielectric constants such as... Figure 1 As shown, considering the limited availability of materials for optical coatings, as well as the refractive index, film quality, and coating process, silicon was chosen as the material for the first layer.

[0015] The thickness of the first film layer was determined by computer simulation. The simulation steps are as follows:

[0016] S1 uses membrane system design software to input the material and thickness information of other membrane layers besides the first membrane layer, and views the electric field intensity distribution between each layer of the membrane 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 interface between the epitaxial material and the first film layer is the minimum.

[0018] Preferably, this is done using membrane system design software. The electric field intensity distribution between each layer of the membrane system can be viewed through the Coupute EFI function in the Run section of the software analysis. The thickness of the first membrane layer can be interactively analyzed through the Interactive Analysis function in the Run toolbar. After determining the optimal thickness of the first membrane layer, this thickness is locked. By optimizing the thickness of other layers, the spectrum can be optimized to the required level.

[0019] Both the antireflective coating and the high-reflective coating are composed of several alternating layers of high refractive index and low refractive index.

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

[0021] The thickness of the antireflective coating is 200-300 nm, and the thickness of the high reflective coating is 500-800 nm.

[0022] The beneficial effects of this invention are as follows: Excessive electric field strength at the interface between the laser epitaxial material and the optical coating material leads to increased non-radiative recombination excited by the electric field, reducing the laser's luminous efficiency and stability. This invention optimizes the electric field distribution inside the laser by modifying the optical coating design, selecting materials that match the epitaxial material, and precisely controlling the film structure and thickness. This reduces 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 non-radiative recombination excited by the electric field, thereby increasing the end-face damage threshold and improving reliability. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

[0025] Figure 2 The diagram shows the electric field distribution of the semiconductor laser fabricated 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 The image shows the spectrum of the semiconductor laser prepared in Example 1.

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

[0029] Figure 6 The image shows the spectrum of the semiconductor laser prepared in Example 2. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

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

[0033] (1) Using optical film system design software, the materials and thicknesses of other film layers except the first film layer are confirmed. The electric field intensity 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. 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 when the electric field intensity at the junction of the epitaxial material and the first film layer is the minimum is observed. Finally, it is determined to be 95nm.

[0034] (2) The semiconductor laser wafer is cleaved in air into bar strips with a cavity length of 1000 μm.

[0035] (3) Fix the cleaved bar strips on the special fixture for coating and put them together with the K9 test glass sheet and the InP plate sheet to be coated into the vacuum evaporation coating machine (Leybold ARES1100). Evacuate the vacuum to a pressure of 2.0E-6 Torr, set the temperature to 150℃, and bake for 30 minutes.

[0036] (4) Next, turn on the Hall ion source to perform ion cleaning on the product. Select Ar as the gas, set the gas flow rate to 30 SCCM, select 90V as the voltage, set the current to 4A, and set the time to 2min to perform ion cleaning 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 as 95 nm, the coating temperature is 150 °C, and the deposition rate is [missing value]. The electron gun current is adjusted between 100-165mA according to the coating rate feedback via PID, where P (proportional adjustment) is set to 100, I (integral adjustment) is set to 0.6, and D (derivative adjustment) is set to 0.5 to ensure a stable coating rate.

[0038] (6) Repeat steps (4) and (5) to plate the other side, using the same process parameters;

[0039] (7) Next, the Bar bar is coated with an antireflective film on the front cavity surface in an evaporation coating machine. The film structure and thickness are as follows: Al2O3-16nm / Si-56nm / Al2O3-207nm; then, a high reflective film is coated on the back cavity surface. The film structure and thickness are as follows: Al2O3-133nm / Si-76nm / Al2O3-246nm / Si-80nm / Al2O3-117nm.

[0040] A semiconductor laser is fabricated by cleaving a coated Bar strip. The light-emitting surface of the semiconductor laser includes a Si layer and an anti-reflection coating from the inside out, and the back surface of the semiconductor laser includes a Si layer and a high-reflection coating from the inside out.

[0041] Before optimizing the optical coating thickness, the electric field distribution and film system design are as follows: Figure 2 As shown; after the optical coating thickness 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 spectral fluctuation is not large. Using a Cary 7000 spectrophotometer, the reflection spectrum of the InP substrate (without the first film layer in step (5)) can be measured. The measurement band is 1100nm-1500nm, the spectral bandwidth is 4nm, and the step size of the measurement result is 1nm. Since the laser 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 its substrate spectrum at the working wavelength of the laser is greater than 92%, which can effectively reflect the laser, thereby improving the light output effect of the emitting surface and meeting the requirements of the laser product. The new design and electric field distribution are as follows Figure 3 As shown, the spectral comparison before and after membrane system optimization is as follows: Figure 4 As shown.

[0042] Example 2

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

[0044] (1) Using optical film system design software, the materials and thicknesses of other film layers except the first film layer are confirmed. The electric field intensity distribution between each layer of the film system can be viewed through Coupute EFI in Run. The first film layer material 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 when the electric field intensity at the junction of the epitaxial material and the first film layer is the minimum is observed. Finally, it is determined to be 85nm.

[0045] (2) The semiconductor laser wafer is cleaved in air into bar strips with a cavity length of 1000 μm.

[0046] (3) Fix the cleaved bar strips on the special fixture for coating and put them together with the K9 test glass sheet and the InP plate sheet to be coated into the vacuum evaporation coating machine (Leybold ARES1100). Evacuate the vacuum to a pressure of 2.0E-6 Torr, set the temperature to 150℃, and bake for 30 minutes.

[0047] (4) Next, turn on the Hall ion source to perform ion cleaning on the product. Select Ar as the gas, set the gas flow rate to 30 SCCM, select 90V as the voltage, set the current to 4A, and set the time to 2min to perform ion cleaning 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 as 85 nm, the coating temperature is 150 °C, and the deposition rate is [missing value]. The electron gun current is adjusted between 100-165mA according to the coating rate feedback via PID, where P (proportional adjustment) is set to 100, I (integral adjustment) is set to 0.6, and D (derivative adjustment) is set to 0.5 to ensure a stable coating rate.

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

[0050] (7) Next, the Bar bar is coated with an antireflective film layer on the front cavity surface in an evaporation coating machine. The film structure and thickness are as follows: Al2O3-16nm / Si-56nm / Al2O3-207nm; then, the high reflective film layer on the back cavity surface is coated with an antireflective film layer. The film structure and thickness are as follows: SiO2-223nm / Si-82nm / SiO2-221nm / Si-82nm / SiO2-220nm.

[0051] A semiconductor laser is fabricated by cleaving a coated Bar strip. The light-emitting surface of the semiconductor laser includes a Si layer and an anti-reflection coating from the inside out, and the back surface of the semiconductor laser includes a Si layer and a high-reflection coating from the inside out.

[0052] After optimizing the optical coating thickness, the electric field intensity at the interface between the laser epitaxial material and the optical coating material is reduced to zero, while the spectral fluctuation is also small. Using a Cary 7000 spectrophotometer, the reflection spectrum of the co-coated InP wafer can be measured in the 1100nm-1500nm wavelength range, with a spectral bandwidth of 4nm and a measurement step size of 1nm. Since the laser emitting surface material is also InP, its reflection spectrum is almost identical to the actual reflection at the laser end face. This indicates that the co-coated wafer's spectrum reflects more than 94% of the laser at its operating wavelength, effectively reflecting the laser and thus improving the light output effect of the emitting surface, meeting the requirements of laser products. The new design and electric field distribution are as follows: Figure 5 As shown, the spectral comparison before and after membrane system optimization is as follows: Figure 6 As shown.

[0053] Example 3

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

[0055] (1) Using optical film system design software, the materials and thicknesses of other film layers except the first film layer are confirmed. The electric field intensity 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. 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 when the electric field intensity at the junction of the epitaxial material and the first film layer is the minimum is observed. Finally, it is determined to be 60nm.

[0056] (2) The semiconductor laser wafer is cleaved in air into bar strips with a cavity length of 1000 μm.

[0057] (3) Fix the cleaved bar strips on the special fixture for coating and put them together with the K9 test glass sheet and the InP plate sheet to be coated into the vacuum evaporation coating machine (Leybold ARES1100). Evacuate the vacuum to a pressure of 2.0E-6 Torr, set the temperature to 150℃, and bake for 30 minutes.

[0058] (4) Next, turn on the Hall ion source to perform ion cleaning on the product. Select Ar as the gas, set the gas flow rate to 30 SCCM, select 90V as the voltage, set the current to 4A, and set the time to 2min to perform ion cleaning 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 as 60 nm, the coating temperature is 150 °C, and the deposition rate is [missing value]. The electron gun current is adjusted between 100-165mA according to the coating rate feedback via PID, where P (proportional adjustment) is set to 100, I (integral adjustment) is set to 0.6, and D (derivative adjustment) is set to 0.5 to ensure a stable coating rate.

[0060] (6) Repeat steps (4) and (5) to plate the other side, using the same process parameters;

[0061] (7) Next, the Bar bar is coated with an antireflective film on the front cavity surface in an evaporation coating machine. The film structure and thickness are as follows: Al2O3-16nm / Si-56nm / Al2O3-207nm; then, a high reflective film is coated on the back cavity surface. The film structure and thickness are as follows: Al2O3-133nm / Si-76nm / Al2O3-246nm / Si-80nm / Al2O3-117nm.

[0062] A semiconductor laser is fabricated by cleaving a coated Bar strip. The light-emitting surface of the semiconductor laser includes a Si layer and an anti-reflection coating from the inside out, and the back surface of the semiconductor laser includes a Si layer and a high-reflection coating from the inside out.

[0063] Example 4

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

[0065] (1) Using optical film system design software, the materials and thicknesses of other film layers except the first film layer are confirmed. The electric field intensity 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. 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 when the electric field intensity at the junction of the epitaxial material and the first film layer is the minimum is observed. Finally, it is determined to be 100nm.

[0066] (2) The semiconductor laser wafer is cleaved in air into bar strips with a cavity length of 1000 μm.

[0067] (3) Fix the cleaved bar strips on the special fixture for coating and put them together with the K9 test glass sheet and the InP plate sheet to be coated into the vacuum evaporation coating machine (Leybold ARES1100). Evacuate the vacuum to a pressure of 2.0E-6 Torr, set the temperature to 150℃, and bake for 30 minutes.

[0068] (4) Next, turn on the Hall ion source to perform ion cleaning on the product. Select Ar as the gas, set the gas flow rate to 30 SCCM, select 90V as the voltage, set the current to 4A, and set the time to 2min to perform ion cleaning 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 as 100 nm, the coating temperature is 150 °C, and the deposition rate is [missing value]. The electron gun current is adjusted between 100-165mA according to the coating rate feedback via PID, where P (proportional adjustment) is set to 100, I (integral adjustment) is set to 0.6, and D (derivative adjustment) is set to 0.5 to ensure a stable coating rate.

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

[0071] (7) Next, the Bar bar is coated with an antireflective film layer on the front cavity surface in an evaporation coating machine. The film structure and thickness are as follows: Al2O3-16nm / Si-56nm / Al2O3-207nm; then, the high reflective film layer on the back cavity surface is coated with an antireflective film layer. The film structure and thickness are as follows: SiO2-223nm / Si-82nm / SiO2-221nm / Si-82nm / SiO2-220nm.

[0072] A semiconductor laser is fabricated by cleaving a coated Bar strip. The light-emitting surface of the semiconductor laser includes a Si layer and an anti-reflection coating from the inside out, and the back surface of the semiconductor laser includes a Si layer and a high-reflection coating from the inside out.

[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 principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for suppressing laser end-face failure, characterized in that, Includes the following steps: (1) The semiconductor laser wafer is cleaved into bars, and the first film layer is deposited on the front cavity surface and the back cavity surface of the bar respectively; (2) An antireflective film is deposited on the front cavity surface of the bar, and a high reflective film is deposited on the rear cavity surface of the bar; The thickness of the first film layer was determined by computer simulation. The simulation steps were as follows: S1 uses membrane system design software to input the material and thickness information of other membrane layers besides the first membrane layer, and views the electric field intensity distribution between each layer of the membrane system. S2 inputs the material information of the first film layer. By changing the thickness of the first film layer, the thickness of the first film layer is taken when the electric field strength at the interface between the epitaxial material and the first film layer is the minimum. 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.

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

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 claim 3, characterized in that, The epitaxial material of the laser is InP, and the material of the first film layer is silicon.

5. 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.

6. The method for suppressing laser end-face failure according to claim 1, characterized in that, Both the antireflective coating and the high-reflective coating are composed of several alternating layers of high refractive index and low refractive index.

7. The method for suppressing laser end-face failure according to claim 6, characterized in that, The high refractive index layer is made of any one of TiO2, Ta2O5, HfO2, or Si; the low refractive index layer is made of SiO2 or Al2O3.

8. The method for suppressing laser end-face failure according to claim 7, characterized in that, The thickness of the antireflective coating is 200-300 nm, and the thickness of the high reflective coating is 500-800 nm.

9. A laser prepared by the method according to any one of claims 1-8.

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