Semiconductor laser high-reflection film structure and preparation method thereof

Abstract

The application discloses a high-reflection film structure of a semiconductor laser and a preparation method thereof. The high-reflection film structure is deposited on a high-reflection end face of the semiconductor laser and sequentially comprises a blocking layer, a transition layer, and alternately arranged low-refractive-index medium film layers and high-refractive-index medium film layers in a direction away from the high-reflection end face. The blocking layer is a metal M layer deposited under vacuum evaporation of the metal M. The transition layer is a metal oxide MO layer deposited under vacuum evaporation of the metal oxide MO. The metal layer of the high-reflection film and the end face semiconductor material of the laser have good adhesion and compactness, which can prevent compound atoms in the end face semiconductor material of the laser from being combined with oxygen atoms to generate defect states during the film plating process, and thus can prevent the performance of the laser from being degraded and the laser from failing under high current. Therefore, the working reliability of the laser can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser manufacturing technology, specifically relating to a high-reflectivity film structure for semiconductor lasers and its preparation method. Background Technology

[0002] Semiconductor lasers, due to their ability to achieve photoelectric conversion through simple current injection and their compatibility with integrated circuits in terms of operating current and voltage, can be monolithically integrated. Furthermore, they can be directly current-modulated at frequencies up to GHz to obtain high-speed modulated laser signal output. Because of these advantages, semiconductor lasers have been widely used in fiber optic communication.

[0003] Semiconductor lasers consist of a resonant cavity and end faces made of III-V group semiconductor materials, generating laser beams of specific wavelengths. Due to the application requirements of fiber optic communication technology in various communication environments, lasers need to be able to operate stably under different ambient temperatures. AlInGaAs multi-quantum-well III-V group semiconductor materials, in particular, are widely used in the active region materials of the resonant cavities of optical communication semiconductor lasers due to their excellent temperature and modulation characteristics. For the end faces of AlInGaAs multi-quantum-well active region lasers, it is necessary to deposit dielectric films with different reflectivities on the two end faces to achieve the required output optical power and protect the laser end faces. The front-end light-emitting end face of the laser is a low-reflectivity dielectric film system, while the rear-end light-emitting end face is a high-reflectivity dielectric film system. The high-reflectivity film layer on the rear-end face reflects a larger optical power density to the laser end face, making it susceptible to damage to the semiconductor material and leading to performance degradation. Therefore, improving the characteristics of the high-reflectivity film layer is a key factor in improving the stability of laser performance.

[0004] Currently, the high-reflectivity dielectric film system used on the laser end face consists of multiple dielectric films. High reflectivity is achieved by utilizing the refractive index difference and optical thickness of the different dielectric films. The first dielectric film on the laser end face is typically a low-refractive-index oxide film, followed by alternating deposition of high-refractive-index and low-refractive-index oxide films. The reflectivity of the dielectric film system is highest when the optical thickness of each dielectric film is one-quarter of the laser emission wavelength. For example, when using a conventional high-reflectivity film system on the end face of an AlInGaAs multi-quantum-well active region laser, the oxygen atoms in the first oxide dielectric film combine with the Al atoms in the AlInGaAs semiconductor material during the evaporation deposition process, forming defect states at the laser end face. As the laser is used and the operating temperature increases, these defect states, influenced by the laser's output light, continuously extend and penetrate into the active region of the laser, causing laser decay or even complete degradation, rendering the laser inoperable. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a high-reflectivity film structure for semiconductor lasers, which improves the operating stability and extends the operating range of the laser. Furthermore, this invention also provides a method for fabricating the high-reflectivity film structure for lasers.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a high-reflectivity film structure for a semiconductor laser. The high-reflectivity film structure is deposited on the high-reflectivity end face of the laser and includes, in sequence along the direction away from the high-reflectivity end face, a blocking layer, a transition layer, and alternating low-refractive-index dielectric film layers and high-refractive-index dielectric film layers. The blocking layer is a metal M layer deposited under vacuum evaporation conditions, and the transition layer is a metal oxide MO layer deposited under vacuum evaporation conditions.

[0008] As a preferred technical solution, the metal M is one of Ag, Au, Al, Cu, In, Zn, Fe, Pt, and Ti.

[0009] As a preferred technical solution, the laser is an AlInGaAl multi-quantum-well laser, the metal M is Al, and the metal oxide MO is Al2O3.

[0010] As a preferred technical solution, the thickness of the metal M layer is less than 20 nm, and the thickness of the metal oxide MO layer is αλ / 4(n_MO), where λ is the emission wavelength of the laser, n_MO is the refractive index of the metal oxide MO, and α ranges from 0.1 to 0.5.

[0011] As a preferred technical solution, when depositing the metal M layer, the oxygen feed path in the evaporation deposition equipment is turned off to prevent the feed oxygen from oxidizing the first metal M layer.

[0012] As a preferred technical solution, the low refractive index dielectric film is one of Al2O3, SiO2, MgF2, NaF, Ca2F, and LiF; the high refractive index dielectric film is one of Ta2O5, Ti2O5, HFO2, ZrO2, AlN, and SiN.

[0013] As a preferred technical solution, the thickness of each layer of the low-refractive-index dielectric film is λ / (4n_L), where λ is the emission wavelength of the laser and n_L is the refractive index of the low-refractive-index dielectric film; the thickness of each layer of the high-refractive-index dielectric film is λ / (4n_H), where n_H is the refractive index of the high-refractive-index dielectric film.

[0014] As a preferred technical solution, the low-refractive-index dielectric film and the high-refractive-index dielectric film are deposited in an oxygen-permeable environment.

[0015] As a preferred technical solution, the number of alternations between the low-refractive-index dielectric film layer and the high-refractive-index dielectric film layer is 2-6.

[0016] A second aspect of the present invention provides a method for preparing a high-reflectivity film structure for a semiconductor laser, comprising the following steps:

[0017] Step S1: Cleave the laser wafer into laser strips and clamp the laser strips onto the strip fixture; then quickly load the laser strip fixture into the electron beam evaporation device and evacuate it to prepare for laser end face coating.

[0018] Step S2: Deposit the metal M layer on the emitting end face of the laser by electron beam evaporation. At the same time as electron beam evaporation, turn off the oxygen feed gas path in the electron beam evaporation equipment.

[0019] Step S3: Evaporate and deposit the metal oxide MO layer using electron beam evaporation. Simultaneously with electron beam evaporation, shut off the oxygen feed path in the electron beam evaporation equipment.

[0020] Step S4: Evaporate the low refractive index dielectric film using electron beam evaporation. Simultaneously with electron beam evaporation, open the oxygen feed path in the electron beam evaporation equipment.

[0021] Step S5: Evaporate the high refractive index dielectric film using electron beam evaporation. While evaporating the electron beam, open the oxygen feed path in the electron beam evaporation equipment.

[0022] Step S6: Steps S4 and S5 are completed alternately by electron beam evaporation to form alternating low-refractive-index dielectric film layers and high-refractive-index dielectric film layers.

[0023] Compared with the prior art, the present invention has the following technical effects:

[0024] (1) In this invention, a blocking layer, namely a metal layer, is first deposited at the emitting end of the laser. The metal layer can prevent the end face of the laser from being exposed to an oxygen-containing environment. The metal layer and the semiconductor material at the end face of the laser have good adhesion and compactness, which can prevent the compound atoms in the semiconductor material at the end face of the laser from bonding with oxygen atoms to generate defect states, thereby causing performance degradation and failure at high current. This improves the working stability of the semiconductor laser.

[0025] (2) The present invention includes a transition layer, wherein the transition layer MO and the metal M layer preferably use the same metal atoms, which can provide a good ideal deposition interface between the metal M layer and the transition layer MO, and between the transition layer MO and the subsequent oxide dielectric film layer. This can prevent stress defects between the metal M layer and the ordinary oxide dielectric film layer.

[0026] (3) The present invention limits the thickness of the metal layer and the metal oxide layer. If the thickness of the metal layer is too low, it will affect its manufacturing precision and thickness repeatability. If the thickness is too high, it will form a conductive channel and cause current leakage. If the thickness of the metal oxide layer is too low, it will affect its transition effect. If the thickness is too high, it will easily adsorb water molecules and oxygen in the environment, causing oxidation of the adjacent metal layer, and water molecules and oxygen will penetrate into the laser semiconductor material, causing the laser performance to decay.

[0027] (4) The high reflectivity film structure of the present invention can improve the reflectivity of the laser end face and improve the adhesion between the high reflectivity film layer and the laser end face, thereby reducing the laser end face loss at high temperature, thus reducing the laser operating current at high temperature, increasing the laser output power at high temperature, and effectively improving the laser operating temperature range. Attached Figure Description

[0028] 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.

[0029] Figure 1 This is a schematic diagram of the stacked structure of the high-reflectivity film structure of the present invention on the laser end face.

[0030] Figure 2 The results show the reflectivity test results after the high-reflectivity film structure of the present invention is deposited on the surface of a silicon monitoring chip.

[0031] Figure 3 The results of 85C aging tests are for eight 1310nm AlInGaAs multi-quantum-well DFB lasers employing the high-reflectivity film structure of this invention.

[0032] Figure 4 The results are from 85C aging tests of eight 1310nm AlInGaAs multi-quantum-well DFB lasers with conventional high-reflectivity film structures.

[0033] The specific reference numerals in the attached figures are explained as follows: N-INP substrate 1; N-side capping layer 2; AlInGaAs multi-quantum-well active layer 3; P-side capping layer 4; P-side electrode 5; N-side electrode 6; laser output light 7; laser rear end face 8; metal Al layer 8A; Al2O3 film layer 8B; low refractive index dielectric film layer 8C; high refractive index dielectric film layer 8D; laser front end face 9; front end face coating layer 9A. Detailed Implementation

[0034] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0035] like Figure 1 As shown, this embodiment provides a high-reflectivity film structure for a semiconductor laser. The high-reflectivity film structure is deposited on the high-reflectivity end face of the laser, i.e., the laser rear end face 8. Along the direction away from the high-reflectivity end face, it sequentially includes a blocking layer, a transition layer, and alternating low-refractive-index dielectric film layers 8C and high-refractive-index dielectric film layers 8D. The blocking layer is a metal M layer deposited under vacuum evaporation conditions, and the transition layer is a metal oxide MO layer deposited under vacuum evaporation conditions. The metal oxide MO layer and the metal M layer use the same metal atoms.

[0036] The metal M is one of Ag, Au, Al, Cu, In, Zn, Fe, Pt, and Ti. The thickness of the metal M layer is less than 20 nm, and the thickness of the metal oxide MO layer is αλ / 4(n_MO), where λ is the emission wavelength of the laser, n_MO is the refractive index of the metal oxide MO, and α ranges from 0.1 to 0.5. Most metal oxides readily absorb water vapor from the environment. In this invention, α is taken between 0.1 and 0.5, instead of the conventional high-reflectivity film system where the dielectric film thickness is one-quarter of the optical thickness (i.e., λ is 1.0). The α value between 0.1 and 0.5 effectively reduces the adsorption of environmental water vapor by the MO dielectric film system, thus reducing the degradation of the film system's performance.

[0037] The low-refractive-index dielectric film 8C is one of Al2O3, SiO2, MgF2, NaF, Ca2F, and LiF; the high-refractive-index dielectric film 8D is one of Ta2O5, Ti2O5, HFO2, ZrO2, AlN, and SiN. When depositing oxide dielectric materials using electron beam evaporation, the oxygen feed path in the electron beam evaporation equipment is opened. This prevents the oxide dielectric from decomposing during evaporation and reducing the oxygen content, thus avoiding compositional inhomogeneity. In this invention, the thickness of each layer of the low-refractive-index dielectric film 8C is λ / (4n_L), where λ is the emission wavelength of the laser and n_L is the refractive index of the low-refractive-index dielectric film 8C; the thickness of each layer of the high-refractive-index dielectric film 8D is λ / (4n_H), where n_H is the refractive index of the high-refractive-index dielectric film 8D. The number of alternations between the low-refractive-index dielectric film layer 8C and the high-refractive-index dielectric film layer 8D is 2-6. When set to 3 groups, a refractive index of 90% can be achieved. More film layers will generate unnecessarily high adhesion stress between the high-reflectivity film system and the laser end face, which will destroy the tight adhesion between the high-reflectivity film system and the laser end face, thus reducing the stability of laser operation.

[0038] In one case, such as Figure 1 As shown, the laser referred to in this embodiment is an AlInGaAs multi-quantum-well laser. The laser includes an N-INP substrate 1, an N-side capping layer 2, an AlInGaAs multi-quantum-well active layer 3, and a P-side capping layer 4. An N-side electrode 6 is located on one side of the N-INP substrate 1, and a P-side electrode 5 is located on one side of the P-side capping layer 4. The rear end face 8 of the laser is a high-reflectivity end, and the front end face 9 of the laser is the output end, used to emit laser output light 7. A front end coating layer 9A is provided on the front end face 9 of the laser. The specific structure of the laser is not the focus of this invention and will not be described in detail here.

[0039] A metallic Al layer 8A is deposited on the high-reflectivity end face of the laser. During deposition, the oxygen feed path in the evaporation deposition equipment is shut off to prevent oxidation of the first metallic Al layer 8A by the introduced oxygen. An Al₂O₃ film 8B is deposited outside the metallic Al layer 8A. Similarly, the oxygen feed path in the evaporation deposition equipment is shut off to prevent oxidation of the first metallic Al layer 8A by the introduced oxygen. The metallic Al layer 8A and the AlInGaAs semiconductor material on the laser end face exhibit excellent adhesion, effectively preventing the formation of interface defect states by the combination of Al atoms in the semiconductor and oxygen atoms in the environment. The subsequent second layer, the Al₂O₃ film 8B, chemically bonds well with the metallic Al layer 8A at the interface, providing an ideal deposition surface for the subsequent dielectric film and improving the adhesion of the dielectric film on the laser end face. The thickness of the metallic Al layer 8A is controlled to be less than 20 nm, with a preferred thickness of 10 nm. The thickness of the Al2O3 film 8B is αλ / (4n-Al2O3), the emission wavelength of the laser is λ, the refractive index of Al2O3 is n-Al2O3, and the value of α is between 0.1 and 0.5, preferably 0.25.

[0040] This embodiment also provides a method for preparing a high-reflectivity film for an AlInGaAs multi-quantum-well laser, comprising the following steps:

[0041] Step S1: The AlInGaAs multi-quantum-well laser wafer is end-face cleaved into laser beam strips. The laser beam strips are then clamped onto a beam strip fixture. This process should minimize contact between the exposed laser beam strip end-faces and air or water vapor. Preferably, this is performed in an inert gas environment, such as an N2 atmosphere. Then, the laser beam strip fixture is quickly placed into an electron beam evaporation apparatus, and a vacuum is drawn in preparation for laser end-face coating.

[0042] Step S2: A metallic Al layer 8A is deposited on the back end face of the laser by electron beam evaporation. The thickness of the metallic Al layer 8A is 10 nm. During electron beam evaporation, the oxygen feed path in the electron beam evaporation equipment is turned off to prevent the feed oxygen from oxidizing the first metallic Al layer 8A.

[0043] Step S3: Evaporate and deposit an Al2O3 film 8B using electron beam evaporation. The laser emission wavelength is λ, the refractive index of Al2O3 is N_Al2O3, and the thickness of the Al2O3 film 8B is αλ / (4n_Al2O3), where α is 0.25. For example, with an emission wavelength of 1310 nm, a refractive index of Al2O3 of 1.65, and a film thickness of 49.6 nm, the oxygen feed path in the electron beam evaporation equipment is shut off simultaneously to prevent the oxygen feed into the first metallic Al layer 8A from oxidizing.

[0044] Step S4: Evaporate the low-refractive-index dielectric film 8C using electron beam evaporation. The low-refractive-index dielectric film 8C can be one of Al2O3, SiO2, MgF2, NaF, Ca2F, or LiF. The emission wavelength of the laser is λ, the refractive index of the low-refractive-index dielectric film 8C is n_L, and the thickness of the film is λ / (4n_L). For example, if the low-refractive-index material is SiO2, the refractive index of SiO2 is 1.44, the emission wavelength is 1310 nm, and the thickness of the SiO2 film is 227.4 nm. Simultaneously with electron beam evaporation, the oxygen feed path in the electron beam evaporation equipment is opened. This prevents the oxide medium from decomposing during evaporation and reducing the oxygen content, thus avoiding compositional inhomogeneity.

[0045] Step S5: Evaporate a high-refractive-index dielectric film 8D using electron beam evaporation. The high-refractive-index dielectric film 8D can be one of Ta2O5, Ti2O5, HFO2, ZrO2, AlN, or SiN. The emission wavelength of the laser is λ, the refractive index of the high-refractive-index dielectric film 8D is n_H, and the thickness of the film is λ / (4n_H). For example, the high-refractive-index material is Ta2O5, which has a refractive index of 2.08, an emission wavelength of 1310 nm, and a film thickness of 157.5 nm. Simultaneously with electron beam evaporation, the oxygen feed path in the electron beam evaporation equipment is opened. This prevents the oxide dielectric from decomposing during evaporation and reducing the oxygen content, thus avoiding compositional inhomogeneity.

[0046] Step S6: The low-refractive-index dielectric film layer 8C and the high-refractive-index dielectric film layer 8D of steps 4 and 5 are alternately evaporated by electron beam, forming a total of 3 pairs of low / high refractive-index dielectric layers.

[0047] Figure 2 The test measured the reflectance spectrum of the high-reflectivity film deposited on the silicon wafer surface using the steps described above. Since the silicon wafer and the AlInGaAs multi-quantum-well structure have similar refractive indices, the measured reflectance is very close to the reflectance value of the laser end face. The test curve shows a reflectance of 92.3% at a wavelength of 1310 nm.

[0048] Figure 3 The results of aging tests at 85°C are shown for AlInGaAs multi-quantum-well lasers fabricated using the above method with high-reflectivity end-face coating. Eight AlInGaAs multi-quantum-well DFB lasers with a wavelength of 1310 nm, a cavity length of 150 μm, and a modulation rate of 25 Gbps were tested for 5000 hours at 85°C and 50 mA. The output power of all laser chips remained stable within a range of + / - 3% output power variation. This indicates that AlInGaAs multi-quantum-well lasers fabricated using this high-reflectivity end-face coating structure can operate stably in a high-temperature environment of 85°C.

[0049] In contrast, for the same batch of AlInGaAs multi-quantum-well DFB lasers with a 1310nm process, a cavity length of 150µm, and a modulation rate of 25Gbps, the low-refractive-index dielectric layer and the high-refractive-index dielectric layer in steps 4 and 5 above were alternately completed by electron beam evaporation, forming a total of 3 pairs of low / high-refractive-index dielectric layer pairs, thus constituting a conventional high-reflectivity film. Figure 4 These are the aging test results of eight AlInGaAs multi-quantum-well lasers after this process at 85°C. (The text then repeats itself, so the translation stops.) Figure 3 The same aging test conditions of 85°C and 50mA were used. Figure 4 The test results showed that as the aging process progressed, the laser performance continued to decline. After 750 hours, the power attenuation of 7 out of 8 lasers exceeded 25%, and the power attenuation of 1 exceeded 15%.

[0050] from Figure 3 , Figure 4 The comparison shows that the high reflectivity film for lasers proposed in this invention can very effectively improve the operating stability of AlInGaAs multi-quantum-well lasers and extend the operating temperature of lasers to a high-temperature environment of 85°C.

[0051] Although the above embodiments have provided a detailed description of the present invention, it should be understood by those skilled in the art that modifications or improvements can be made based on the disclosure of the present invention without departing from the spirit and scope of the invention, and such modifications and improvements are all within the spirit and scope of the present invention.

Claims

1. A high-reflectivity film structure for a semiconductor laser, characterized in that, The high-reflectivity film structure is deposited on the high-reflectivity end face of the semiconductor laser. Along the direction away from the high-reflectivity end face, it sequentially includes a blocking layer, a transition layer, and alternating low-refractive-index dielectric film layers and high-refractive-index dielectric film layers. The blocking layer is a metal M layer deposited under vacuum evaporation conditions. The transition layer is a metal oxide MO layer deposited under vacuum evaporation conditions. The thickness of the metal oxide MO layer is αλ / 4(n_MO), where λ is the emission wavelength of the laser, n_MO is the refractive index of the metal oxide MO, and α ranges from 0.1 to 0.

5.

2. The high-reflectivity film structure for a semiconductor laser as described in claim 1, characterized in that, The metal M is one of Ag, Au, Al, Cu, In, Zn, Fe, Pt, and Ti.

3. The high-reflectivity film structure for a semiconductor laser as described in claim 1, characterized in that, The laser is an AlInGaAl multi-quantum-well laser, the metal M is Al, and the metal oxide MO is Al2O3.

4. The high-reflectivity film structure for a semiconductor laser as described in claim 1, characterized in that, The thickness of the metal M layer is less than 20 nm.

5. The high-reflectivity film structure for a semiconductor laser as described in claim 1, characterized in that, When depositing the metal M layer, shut off the oxygen feed path in the evaporation deposition equipment.

6. The high-reflectivity film structure for a semiconductor laser as described in claim 1, characterized in that, The low-refractive-index dielectric film is one of Al2O3, SiO2, MgF2, NaF, Ca2F, and LiF; the high-refractive-index dielectric film is one of Ta2O5, Ti2O5, HFO2, ZrO2, AlN, and SiN.

7. The high-reflectivity film structure for a semiconductor laser as described in claim 6, characterized in that, The thickness of each layer of the low-refractive-index dielectric film is λ / (4n_L), where λ is the emission wavelength of the laser and n_L is the refractive index of the low-refractive-index dielectric film; the thickness of each layer of the high-refractive-index dielectric film is λ / (4n_H), where n_H is the refractive index of the high-refractive-index dielectric film.

8. The high-reflectivity film structure for a semiconductor laser as described in claim 6, characterized in that, The low-refractive-index dielectric film and the high-refractive-index dielectric film are deposited in an oxygen-feeding environment in an evaporation deposition apparatus.

9. The high-reflectivity film structure for a semiconductor laser as described in claim 1, characterized in that, The number of alternations between the low-refractive-index dielectric film and the high-refractive-index dielectric film is 2-6.

10. A method for fabricating a high-reflectivity film structure for a semiconductor laser, used to fabricate the high-reflectivity film structure for a laser according to any one of claims 1-9, characterized in that, Includes the following steps: Step S1: Cleave the laser wafer into laser strips and clamp the laser strips onto the strip fixture; then quickly load the laser strip fixture into the electron beam evaporation device and evacuate it to prepare for laser end face coating. Step S2: Deposit the metal M layer on the emitting end face of the laser by electron beam evaporation. At the same time as electron beam evaporation, turn off the oxygen feed gas path in the electron beam evaporation equipment. Step S3: Evaporate and deposit the metal oxide MO layer using electron beam evaporation. Simultaneously with electron beam evaporation, shut off the oxygen feed path in the electron beam evaporation equipment. Step S4: Evaporate the low refractive index dielectric film using electron beam evaporation. Simultaneously with electron beam evaporation, open the oxygen feed path in the electron beam evaporation equipment. Step S5: Evaporate the high refractive index dielectric film using electron beam evaporation. Simultaneously with electron beam evaporation, open the oxygen feed path in the electron beam evaporation equipment. Step S6: Steps S4 and S5 are performed alternately by electron beam evaporation to form alternating low-refractive-index dielectric films and high-refractive-index dielectric films.

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