Semiconductor laser element and method for manufacturing the same
The introduction of a seamless Al-based getter layer in semiconductor lasers prevents residue diffusion, stabilizing device characteristics and improving reliability by encapsulating the diffraction grating.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- MITSUBISHI ELECTRIC CORP
- Filing Date
- 2024-03-28
- Publication Date
- 2026-06-23
AI Technical Summary
Conventional diffusion suppression layers fail to prevent the diffusion of residues from manufacturing processes into the active layer of semiconductor lasers, leading to fluctuations in device characteristics and reduced reliability.
A semiconductor laser device with a seamless getter layer made of an Al-based material is introduced to prevent the diffusion of residues, formed on the second cladding layer to encapsulate the diffraction grating, ensuring residues do not reach the active layer.
Prevents fluctuations in semiconductor laser characteristics and enhances reliability by blocking the diffusion of manufacturing residues, maintaining consistent performance.
Smart Images
Figure 0007878617000001 
Figure 0007878617000002 
Figure 0007878617000003
Abstract
Description
Technical Field
[0001] The present disclosure relates to a semiconductor laser device and a method for manufacturing the same.
Background Art
[0002] It has been proposed to provide a diffusion suppression layer for suppressing the propagation of crystal defects or metal diffusion from the chip surface to the active layer in a semiconductor laser (see, for example, Patent Document 1).
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] A semiconductor layer such as an upper cladding layer and a diffraction grating layer is formed on the active layer. When an insulating film is formed on this semiconductor layer using plasma CVD or the like, fluorine or hydrogen is introduced into the semiconductor layer. Further, fluorine or hydrogen is introduced onto the surface of the semiconductor layer by methane or a halogen compound used when processing the diffraction grating layer. In the manufacturing process of such a semiconductor laser device, the diffusion of residues of the materials used cannot be stopped by a conventional diffusion suppression layer. When the residues diffuse to the active layer, there is a problem that the characteristics of the semiconductor laser device fluctuate and the reliability decreases.
[0005] The present disclosure has been made to solve the above-described problems, and an object thereof is to obtain a semiconductor laser device and a method for manufacturing the same that can prevent fluctuations in characteristics and a decrease in reliability.
Means for Solving the Problems
[0006] The semiconductor laser device according to the present disclosure is The device comprises a semiconductor substrate of a first conductivity type, a first cladding layer of the first conductivity type, an active layer, and a second cladding layer of the second conductivity type formed sequentially on the semiconductor substrate, a getter layer made of an Al-based material formed without gaps on the second cladding layer, a diffraction grating formed on the getter layer, and a third cladding layer of the second conductivity type formed on the getter layer, wherein the diffraction grating is formed on the third cladding layer. characterized in that. [Effects of the Invention]
[0007] In this disclosure, a getter layer made of an Al-based material is formed seamlessly on the second cladding layer. This prevents material residues used in the manufacturing process from diffusing into the active layer. Consequently, it is possible to prevent fluctuations in the characteristics and a decrease in reliability of the semiconductor laser device. [Brief explanation of the drawing]
[0008] [Figure 1] This is a cross-sectional view showing a semiconductor laser element according to Embodiment 1. [Figure 2] This is a cross-sectional view showing the manufacturing process of a semiconductor laser element according to Embodiment 1. [Figure 3] This is a cross-sectional view showing the manufacturing process of a semiconductor laser element according to Embodiment 1. [Figure 4] This is a cross-sectional view showing the manufacturing process of a semiconductor laser element according to Embodiment 1. [Figure 5] This is a cross-sectional view showing the manufacturing process of a semiconductor laser element according to Embodiment 1. [Figure 6] This is a cross-sectional view showing the manufacturing process of a semiconductor laser element according to Embodiment 1. [Figure 7] This is a cross-sectional view showing a semiconductor laser element according to Embodiment 2. [Figure 8] This is a cross-sectional view showing the manufacturing process of a semiconductor laser element according to Embodiment 2. [Figure 9] This is a cross-sectional view showing a semiconductor laser element according to Embodiment 3. [Figure 10] This is a cross-sectional view showing the manufacturing process of a semiconductor laser element according to Embodiment 3. [Figure 11] This is a cross-sectional view showing a semiconductor laser element according to Embodiment 4. [Modes for carrying out the invention]
[0009] A semiconductor laser element according to an embodiment and its manufacturing method will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repetition of the description may be omitted.
[0010] Embodiment 1. Figure 1 is a cross-sectional view showing a semiconductor laser element according to Embodiment 1. This semiconductor laser element is a DFB laser (distributed feedback semiconductor laser) that performs single-mode oscillation. Although not shown, an optical waveguide structure and a resonator structure using reflective mirrors are formed to enable it to function as a semiconductor laser.
[0011] A first-conductivity semiconductor substrate 1 has a first cladding layer 2 of the first conductivity type, an active layer 3, and a second cladding layer 4 of the second conductivity type formed in sequence. A second-conductivity getter layer 5 made of an Al-based material is formed on the second cladding layer 4. A third cladding layer 6 of the second conductivity type is formed on the getter layer 5. A second-conductivity diffraction grating 7 is formed on the third cladding layer 6. A second-conductivity semiconductor layer 8 embeds the diffraction grating 7. An upper electrode 9 is formed on the semiconductor layer 8. A lower electrode 10 is formed on the lower surface of the semiconductor substrate 1. The diffraction grating 7 consists of multiple patterns formed periodically with gaps between them. On the other hand, the getter layer 5 is formed without gaps across the entire upper surface of the second cladding layer 4.
[0012] One of the n-type and p-type materials is the first conductivity type, and the other is the second conductivity type. The semiconductor substrate 1, the first cladding layer 2, the second cladding layer 4, the third cladding layer 6, and the semiconductor layer 8 are made of, for example, InP. The getter layer 5 is made of a mixed crystal layer containing Al, such as AlGaInAs or AlAs. The diffraction grating 7 is made of a material that can obtain a refractive index difference from InP, such as a mixed crystal of InGaAsP or AlGaInAs. An InP buffer layer may be provided between the semiconductor substrate 1 and the first cladding layer 2.
[0013] Next, a method for manufacturing a semiconductor laser element according to this embodiment will be described. Figures 2 to 6 are cross-sectional views showing the manufacturing process of a semiconductor laser element according to Embodiment 1.
[0014] First, as shown in FIG. 2, a first cladding layer 2, an active layer 3, a second cladding layer 4, a getter layer 5, a third cladding layer 6, and a diffraction grating layer 11 are sequentially epitaxially grown on a semiconductor substrate 1. An insulating film 12 is formed on the diffraction grating layer 11 by plasma CVD or the like. A photoresist 13 is applied on the insulating film 12. Next, as shown in FIG. 3, a periodic pattern is formed on the photoresist 13 by photolithography.
[0015] The insulating film 12 is SiO2 (silicon oxide) or SiN (silicon nitride) or the like. Fluorine or hydrogen is introduced onto the surface of the diffraction grating layer 11 by a fluorine compound gas used when cleaning the film deposition chamber of the CVD apparatus, or by a material gas for the insulating film 12 such as silane or ammonia.
[0016] Next, as shown in FIG. 4, using the photoresist 13 as a mask and using fluorocarbon (fluorinated hydrocarbon compound) as a processing gas, the insulating film 12 is patterned. Fluorine or hydrogen is introduced onto the surface of the diffraction grating layer 11 from this fluorocarbon. Thereafter, the photoresist 13 is removed with an organic solvent or the like.
[0017] Next, as shown in FIG. 5, using the patterned insulating film 12 as a mask and using methane or a halogen compound as a processing gas, the diffraction grating layer 11 is dry-etched to form a diffraction grating 7. Fluorine or hydrogen is introduced onto the surface of the third cladding layer 6 from this methane or halogen compound. Thereafter, the insulating film 12 is removed using hydrofluoric acid or buffered hydrofluoric acid or the like.
[0018] Next, as shown in FIG. 6, a semiconductor layer 8 is epitaxially grown to embed the diffraction grating 7. Thereafter, a ridge formation step and a step of forming an upper electrode 9 and a lower electrode 10 are performed, and a semiconductor laser device is manufactured.
[0019] As described above, residues of materials used in the manufacturing process are introduced onto the surface of the semiconductor layer. When these residues diffuse and reach the active layer 3, they form non-luminescent recombination centers within the active layer 3, affecting the charge state within the active layer 3 and causing variations in the properties of the semiconductor laser element.
[0020] In contrast, in this embodiment, a getter layer 5 made of Al-based material is formed seamlessly on the second cladding layer 4. This prevents material residues used in the manufacturing process from diffusing into the active layer 3. Consequently, fluctuations in the characteristics of the semiconductor laser element and a decrease in reliability can be prevented.
[0021] It has been experimentally confirmed that this effect can be obtained if the thickness of the getter layer 5 is 20 nm or more. Furthermore, the getter layer 5 can also prevent point defects introduced to the surface of the semiconductor layer during process processing from diffusing into the active layer 3. The composition of the getter layer 5 preferably has a high mixed crystal ratio of Al, which has high reactivity with other elements.
[0022] When the getter layer 5 is epitaxially grown on an uneven surface, its crystallinity decreases in the uneven areas. Fluorine or hydrogen may diffuse into the active layer 3 from the areas where the crystallinity of the getter layer 5 has decreased. Therefore, it is preferable that the upper surface of the second cladding layer 4 forming the getter layer 5 is flat.
[0023] Embodiment 2 Figure 7 is a cross-sectional view showing a semiconductor laser element according to Embodiment 2. The difference from Embodiment 1 is that there is no third cladding layer 6, and the getter layer 5 and the diffraction grating 7 are in contact.
[0024] Figure 8 is a cross-sectional view showing the manufacturing process of a semiconductor laser element according to Embodiment 2. Using a patterned insulating film 12 as a mask, the diffraction grating layer 11 is dry-etched using methane or a halogen compound as a processing gas to form a diffraction grating 7. Fluorine or hydrogen is introduced to the surface of the getter layer 5 from this methane or halogen compound. However, the getter layer 5 can prevent these residues from diffusing into the active layer 3. Therefore, fluctuations in the characteristics of the semiconductor laser element and a decrease in reliability can be prevented.
[0025] Embodiment 3 Figure 9 is a cross-sectional view showing a semiconductor laser element according to Embodiment 3. A difference from Embodiment 1 is that the getter layer 5 is formed in multiple layers, vertically within the third cladding layer 6. The total thickness of the multiple getter layers 5 is 20 nm or more, but the thickness of each layer may differ.
[0026] Figure 10 is a cross-sectional view showing the manufacturing process of a semiconductor laser element according to Embodiment 3. The multiple getter layers 5 prevent residual materials used in the manufacturing process from diffusing into the active layer 3. Therefore, it is possible to prevent fluctuations in the characteristics of the semiconductor laser element and a decrease in reliability.
[0027] The multiple getter layers 5 are compound semiconductors composed of three or more elements, and the composition and film thickness of each of the multiple getter layers 5 may differ. The refractive index of a compound semiconductor composed of three or more elements changes when its composition is altered. Since the laser light is guided near the active layer 3, placing a portion of the multiple getter layers 5 near the active layer 3 allows the optical distribution of the laser light to be altered due to the influence of the refractive index of the getter layers 5. By altering the optical distribution, laser characteristics can be improved, or coupling with the optical fiber core can be facilitated. For example, by altering the optical distribution, it is possible to achieve low-power optical output or increase optical output.
[0028] Embodiment 4 Figure 11 is a cross-sectional view showing a semiconductor laser element according to Embodiment 4. A difference from Embodiment 1 is that the getter layer 5 has a superlattice structure in which two layers with different compositions are alternately stacked. Note that some of the multiple getter layers 5 in Embodiment 3 may also have a superlattice structure.
[0029] For example, a superlattice structure is constructed by stacking 10 layers each of AlAs and AlInAs layers, each less than 10 nm in size, alternately. That is, both types of layers in the superlattice structure contain Al and have different compositions. However, it is not necessary for one layer of the superlattice structure to contain Al while the other layer does not.
[0030] At the interface where materials of different compositions are joined, a band discontinuity occurs, generating a localized electric field due to band bending. Since impurities are often charged particles, this localized electric field enhances their ability to trap. The superlattice-structured getter layer 5 has numerous bonding interfaces where band discontinuities occur, and therefore has a higher effect in trapping charged particles such as hydrogen ions or fluoride ions than a single-layer getter layer 5.
[0031] Furthermore, if the material composition of the getter layer 5 differs in lattice multiplier from that of the semiconductor substrate 1, growing a single-layer getter layer 5 beyond the critical thickness will cause lattice relaxation and a significant deterioration in crystallinity. On the other hand, a superlattice structure getter layer 5 can be grown beyond the critical thickness by keeping each layer below the critical thickness. Therefore, the thickness of the getter layer 5 can be increased to improve its ability to trap impurities.
[0032] Furthermore, epitaxial growth of a material with a larger lattice constant than the substrate introduces inherent compressive strain, while growth of a material with a smaller lattice constant introduces inherent tensile strain. Therefore, by alternately growing two types of layers in the superlattice structure—one with a larger lattice constant and the other with a smaller lattice constant than the semiconductor substrate 1—the overall strain of the getter layer 5 can be averaged (compensated). This also allows the getter layer 5 to be grown to a thickness exceeding the critical thickness. Moreover, even if both types of layers in the superlattice structure contain Al, a quaternary mixed crystal containing Ga can be formed to match the InP of the semiconductor substrate 1. [Explanation of symbols]
[0033] 1 Semiconductor substrate, 2 First cladding layer, 3 Active layer, 4 Second cladding layer, 5 Getter layer, 6 Third cladding layer, 7 Diffraction grating, 11 Diffraction grating layer, 12 Insulating film
Claims
1. A first-type conductive semiconductor substrate and A first cladding layer of first conductivity type, an active layer, and a second cladding layer of second conductivity type are formed in order on the semiconductor substrate. A getter layer made of an Al-based material is formed without gaps on the second cladding layer, A diffraction grating formed on the getter layer, The getter layer comprises a second conductive third cladding layer formed on top of the getter layer, A semiconductor laser element characterized in that the diffraction grating is formed on the third cladding layer.
2. The semiconductor laser element according to claim 1, characterized in that the getter layer is formed in multiple layers, one above the other.
3. A first-type conductive semiconductor substrate and A first cladding layer of first conductivity type, an active layer, and a second cladding layer of second conductivity type are formed in order on the semiconductor substrate. The device comprises a getter layer made of an Al-based material formed seamlessly on the second cladding layer, A semiconductor laser element characterized in that the getter layer has a superlattice structure.
4. The semiconductor laser element according to any one of claims 1 to 3, characterized in that the thickness of the getter layer is 20 nm or more.
5. A process of epitaxially growing a first cladding layer of the first conductivity type, an active layer, a second cladding layer of the second conductivity type, a getter layer, and a diffraction grating layer in sequence on a semiconductor substrate of the first conductivity type, A step of forming an insulating film on the diffraction grating layer, A process of patterning the insulating film using fluorocarbon as a processing gas, The process includes using the patterned insulating film as a mask and dry etching the diffraction grating layer using methane or a halogen compound as a processing gas to form a diffraction grating, A method for manufacturing a semiconductor laser element, characterized in that the getter layer is formed without gaps on the second cladding layer and is made of an Al-based material.