Ohmic contact structure, semiconductor laser used for ohmic contact structure and manufacturing method of ohmic contact structure

Abstract

The invention relates to the technical field of semiconductor lasers, in particular to an ohmic contact structure, a semiconductor laser used for the ohmic contact structure and a manufacturing method.The ohmic contact structure comprises an ohmic contact layer, the ohmic contact layer comprises a plurality of ohmic layers with different doping concentrations, and the ohmic layers at least comprise a jump potential weak layer and a penetration potential high layer; the doping concentration of the jump potential weak layer is smaller than or equal to 1E19cm <-3 >, and the doping concentration of the penetrating potential high layer is larger than 1E19cm <-3 >. The ohmic contact structure is provided with the ohmic layers with various doping concentrations, the ohmic layer with the low doping concentration can be arranged near the front cavity surface, due to the fact that the contact resistance of the type is large, the current injected into the front cavity surface and the position near the front cavity surface can be effectively reduced, and through the design, the current can be effectively reduced. And the reliability risk caused by overhigh density of the injected current on the front cavity surface can be solved.

Description

Technical Field

[0001] This application relates to the technical field of semiconductor lasers, and in particular to an ohmic contact structure, a semiconductor laser for use therein, and a method for manufacturing the same. Background Technology

[0002] Semiconductor lasers, due to their advantages such as compact structure, long lifespan, high reliability, high electro-optical conversion efficiency, fast modulation rate, wide wavelength range, and ease of integration, are widely used in industrial production, lidar, defense, optical communication, optical information storage, optical sensing, and medical aesthetics. In particular, in fiber optic communication systems, 980nm high-power single transverse-mode semiconductor lasers serve as ideal pump sources for erbium-doped fiber amplifiers (EDFAs), compensating for signal loss in fiber optic transmission links and playing a crucial role in long-distance optical communication transmission systems.

[0003] Because semiconductor laser chips need to be coated with composite films with reflectivity of less than 5% and greater than 95% on the front and rear cavity surfaces respectively, in order to obtain high-power laser output on the front cavity surface, the optical power density of the front cavity surface will be much higher than that of the rear cavity surface. Correspondingly, the carrier consumption rate injected into the front cavity surface region is faster, so the injection current density of the front cavity surface will be much higher than that of the rear cavity surface.

[0004] Generally, semiconductor materials are more prone to degradation at high temperatures and high current densities, ultimately becoming the starting point for COMD (Catastrophic Optical Mirror Damage) and COBD (Catastrophic Optical Bulk Damage) failures in semiconductor lasers, severely compromising their reliability. Engineering experience shows that the aging rate of COMD and COBD in semiconductor lasers is directly proportional to the fourth power of the current density J (including the effect of optical power on the aging rate). This means that if the current density of the front cavity surface is ten times that of the rear cavity surface, the aging rate of the front cavity surface will be ten times that of the rear cavity surface. 4 The difference in aging rates between the front and rear cavity surfaces is even greater if we consider the higher temperature rise at the front cavity surface due to excessive injection current density. Therefore, common failure types in semiconductor laser chips include COD (Complex Occurrence Displacement) at the front cavity surface and COBD (Coarse Occurrence Displacement) in the vicinity of the front cavity surface.

[0005] For applications requiring extremely high reliability, such as submarine fiber optic communication and satellite communication, sacrificing some performance of single-mode semiconductor lasers for high reliability is worthwhile. Traditional semiconductor lasers typically achieve fundamental transverse mode lasing by etching ridges several μm wide. This design lacks additional design for the ridge current injection region from the back cavity surface to the front cavity surface. As shown above, ideally, the current injection density in and around the front cavity surface is much higher than that in the back cavity surface, causing the probability of COMD and COBD to increase exponentially compared to the back cavity surface, thus compromising the reliability of single-mode devices. Summary of the Invention

[0006] To address the aforementioned problems, this application provides an ohmic contact structure, a semiconductor laser using the same, and a method for manufacturing it.

[0007] One objective of this application is to provide an ohmic contact structure, employing the following technical solution: An ohmic contact structure includes an ohmic contact layer comprising a plurality of ohmic layers with different doping concentrations, wherein each ohmic layer includes at least a weak potential transition layer and a high potential transition layer, and the doping concentration of the weak potential transition layer is less than or equal to 1E19cm. -3 The doping concentration of the high-level penetration layer is greater than 1E19cm. -3 .

[0008] By adopting the above technical solution, when the semiconductor doping concentration is low (≤1E19cm⁻¹), -3 When electrons are emitted thermionicly, they need to gain enough energy to overcome the potential barrier. The contact resistance per unit area can be expressed as... Where k is Boltzmann's constant, q is the electron charge, R is Richardson's constant, and T is the absolute temperature. This represents the barrier height of the gold-semiconductor contact. At this point, the contact resistance Rc decreases linearly with increasing doping concentration.

[0009] When the doping concentration of the semiconductor is further increased to the level of heavy doping (>1E19cm) -3 At this point, the depletion region width becomes sufficiently small, allowing charge carriers to tunnel directly through the potential barrier without being restricted by thermionic emission across the barrier. At this time, the contact resistance per unit area of ​​the gold semiconductor contact is... At this point, A0 and C are both constants related to the semiconductor material, and N d The doping concentration is shown. It can be seen that the contact resistance decreases rapidly with increasing doping concentration.

[0010] The ohmic contact structure in this application has ohmic layers with various doping concentrations. The ohmic layer with a lower doping concentration can be placed near the front cavity surface. Since this type of contact has a large contact resistance, the current injected into the front cavity surface and the vicinity of the front cavity surface can be effectively reduced. Through this design, the reliability risk caused by the excessive injection current density at the front cavity surface can be solved.

[0011] Another objective of this application is to provide a semiconductor laser, employing the following technical solution: A semiconductor laser includes a chip structure comprising the aforementioned ohmic contact structure and an epitaxial layer located below the ohmic contact structure. One side of the chip structure is a front cavity surface, which is located on a wide side of the vertical projection of the chip structure. The ohmic contact structure is arranged in a strip shape at the middle position of the top of the epitaxial layer, and the ohmic contact structure is parallel to the long side of the chip structure. One side of the potential-crossing weak layer is located at the top of the front cavity surface, and the potential-crossing high layer is located on the other side of the potential-crossing weak layer.

[0012] By adopting the above technical solution, the weak potential layer, since the doping concentration of this layer is between the doping concentration required for hot electron excitation and tunneling, corresponds to the simultaneous action of hot electron excitation and tunneling, resulting in a weak ohmic contact effect and relatively high contact resistance.

[0013] The tunneling high layer is heavily doped with a very high doping concentration. The carrier transport mechanism at the gold semiconductor interface is mainly tunneling, resulting in very low contact resistance and the formation of good ohmic contact.

[0014] The weak potential layer is located at the front cavity surface. Due to the relatively high contact resistance of this type, the current injected into and near the front cavity surface can be effectively reduced, resulting in a weak ohmic contact. The high potential layer b corresponds to the heavily doped semiconductor and can form a good ohmic contact. Through this design, the reliability risk caused by the excessive injection current density at the front cavity surface can be resolved.

[0015] Preferably, the weak potential layer includes multiple decreasing layers, and the doping concentration of the multiple decreasing layers gradually decreases from one side of the high potential layer to the front cavity surface.

[0016] By adopting the above technical solution, the injected current density is lower the closer to the front cavity surface, and the current density at the front cavity surface is reduced step by step, thus providing better protection for the front cavity surface.

[0017] Preferably, the decreasing layer closer to the front cavity surface of two adjacent decreasing layers is the right layer, and the decreasing layer closer to the penetration layer is the left layer. The projection length of the left layer on the long side of the chip structure is L1, and the projection length of the right layer on the long side of the chip structure is L2, where L2:L1 = 1:1~1:2.

[0018] Preferably, the length of the vertical projection of the chip structure is L, and the projection length of the weak potential layer on the long side of the chip structure is L3, where L3:L = 1:4~1:2.

[0019] Preferably, the ohmic layers are distributed sequentially from top to bottom within the chip structure, and the doping concentration of the ohmic layers decreases sequentially from top to bottom.

[0020] By adopting the above technical solution, the stacked ohmic layers facilitate production and processing. The desired ohmic layer can be etched from the top, making it convenient to use.

[0021] Preferably, a P-surface electrode is provided above the ohmic contact structure. The P-surface electrode includes a contact point that contacts each ohmic layer and a support surface that does not contact the ohmic structure. An isolation layer is provided between the support surface and the ohmic structure.

[0022] By adopting the above technical solution, the isolation layer isolates the P-side electrode, ensuring that the P-side electrode only contacts each ohmic layer through the contact point, thereby ensuring the ohmic layer's current suppression effect.

[0023] Another objective of this application is to provide a method for fabricating a semiconductor laser, employing the following technical solution: A method for fabricating a semiconductor laser, comprising the following steps: S1, Provide a substrate; S2. A buffer layer, a lower confinement layer, a lower waveguide layer, a quantum well active layer, an upper waveguide layer, an upper confinement layer, and an ohmic layer are sequentially grown on one side surface of the substrate to form an epitaxial structure; wherein the ohmic layer has multiple layers, and the doping concentration of the ohmic layer decreases from top to bottom to form an ohmic contact structure. S3. A conductive material is grown on the surface of the substrate away from the buffer layer to form a back electrode; S4. Etch the side of the epitaxial structure closest to the ohmic layer to form a first current injection window; wherein the etching endpoint of the first current injection window is the ohmic layer. S5. The etching depth of the first current injection window is set to decrease sequentially along the first direction to form multiple current injection suppression structures. The first direction is the direction from the front cavity surface to the rear cavity surface. The bottom of the different current injection suppression structures is located in different ohmic layers. S6. A conductive material is grown on the first current injection window and multiple current injection suppression structures to form a front electrode in order to fabricate a semiconductor laser.

[0024] By adopting the above technical solution, different epitaxial layer depths are etched, and the definitions and proportions of multiple segment lengths are defined to form weak ohmic contacts and normal ohmic contacts. The weak ohmic contacts are then applied to the current injection region of the front cavity surface and its vicinity to limit the current injection density, thereby protecting the front cavity surface and improving the overall reliability of the laser.

[0025] In summary, this application includes the following beneficial technical effects: Compared to traditional structures, this application can homogenize the current injection density on the front and rear cavity surfaces, which can greatly improve the reliability of single transverse mode semiconductor laser chips. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the ohmic contact structure in the embodiment; Figure 2 This is a schematic diagram of two typical carrier transport mechanisms in the metal-semiconductor contact in the embodiment; Figure 3 This is a schematic diagram of the semiconductor laser in the embodiment; Figure 4 This is a schematic diagram of the semiconductor laser in the embodiment, which has only one weak potential layer. Figure 5 This is a schematic diagram of the structure of the semiconductor laser in the embodiment, which has two decreasing layers in the potential-weak layer. Figure 6 This is a schematic diagram illustrating the improvement effect of uniform injection current density at the front and rear cavity surfaces of the semiconductor laser in this application.

[0027] Explanation of reference numerals in the attached figures: 1. Ohmic layer; 2. Weak potential layer; 3. High potential layer; 4. N-face electrode; 5. Substrate; 6. Buffer layer; 7. Lower confinement layer; 8. Lower waveguide layer; 9. Quantum well active layer; 10. Upper waveguide layer; 11. Upper confinement layer; 12. Isolation layer; 13. P-face electrode; 14. Front cavity surface; 15. Decrease layer. Detailed Implementation

[0028] The present application will be further described in detail below with reference to all the accompanying drawings.

[0029] Example

[0030] This application discloses an ohmic contact structure, referring to... Figure 1 This includes an ohmic contact layer, which comprises several ohmic layers 1 with different doping concentrations. Each ohmic layer 1 includes at least a weak potential transition layer 2 and a high potential breakthrough layer 3, wherein the doping concentration of the weak potential transition layer 2 is less than or equal to 1E19cm. -3 The doping concentration of the third high-level layer is greater than 1E19cm. -3 Reference Figure 2 When the semiconductor doping concentration is low (≤1E19cm⁻¹), -3 When electrons are emitted thermionicly, they need to gain enough energy to overcome the potential barrier. The contact resistance per unit area can be expressed as... Where k is Boltzmann's constant, q is the electron charge, R is Richardson's constant, and T is the absolute temperature. This represents the barrier height of the gold-semiconductor contact. At this point, the contact resistance Rc decreases linearly with increasing doping concentration.

[0031] Reference Figure 2 When the doping concentration of the semiconductor is further increased to the level of heavy doping (>1E19cm), -3 At this point, the depletion region width becomes sufficiently small, allowing charge carriers to tunnel directly through the potential barrier without being restricted by thermionic emission across the barrier. At this time, the contact resistance per unit area of ​​the gold semiconductor contact is... At this point, A0 and C are both constants related to the semiconductor material, and N d The doping concentration is shown. It can be seen that the contact resistance decreases rapidly with increasing doping concentration.

[0032] Reference Figure 1 Different ohmic layers 1 can suppress current in different ways, thereby adjusting the current density. Operators can freely control the desired current density and current density distribution according to their needs, thereby improving the overall reliability of the device.

[0033] Example

[0034] This application discloses a semiconductor laser, with reference to... Figures 3 to 5 The chip structure includes an ohmic contact structure and an epitaxial layer as described in the above embodiments. One side of the chip structure is a front cavity surface 14, and the vertical projection of the front cavity surface 14 lies on a wide side of the vertical projection of the chip structure.

[0035] Reference Figures 3 to 5 The chip structure, from bottom to top, includes an N-side electrode 4, a substrate 5, a buffer layer 6, a lower confinement layer 7, a lower waveguide layer 8, a quantum well active layer 9, an upper waveguide layer 10, an upper confinement layer 11, an ohmic contact structure, an isolation layer 12, and a P-side electrode 13.

[0036] Reference Figures 3 to 5 The ohmic contact structure includes several ohmic layers 1 arranged sequentially from bottom to top. The doping concentration of different ohmic layers 1 is different, and the doping concentration of ohmic layers 1 increases sequentially from bottom to top.

[0037] Reference Figures 3 to 5The P-side electrode 13 has several downwardly extending contact points, the lower surface of which contacts the ohmic layer 1. Different contact points contact different parts of the ohmic layer 1. The P-side electrode 13 also includes a support surface that does not contact the ohmic structure. An isolation layer 12 is located between the support surface and the uppermost ohmic layer 1. The material of the isolation layer 12 is silicon dioxide or silicon nitride.

[0038] Reference Figures 3 to 5 The P-side electrode 13 injects current into the ohmic layer 1 through the contact point. Different ohmic layers 1 have different resistances due to their different doping concentrations, which in turn results in different current injection densities at different contact points, thereby enabling control of the current injection density.

[0039] Reference Figures 3 to 5 The ohmic contact structure is arranged in a strip shape in the middle of the top of the epitaxial layer. The ohmic contact structure is parallel to the long side of the chip structure. One side of the weak potential layer 2 is located on the top of the front cavity surface 14, and the high potential layer 3 is located on the other side of the weak potential layer 2.

[0040] Reference Figures 3 to 5 The weak potential layer 2 may consist of only one layer or multiple decreasing layers 15, with the doping concentration of the multiple decreasing layers 15 gradually decreasing from one side of the high potential layer 3 to the front cavity surface 14. That is, the closer the decreasing layer 15 is to the front cavity surface 14, the lower its doping concentration, the higher its resistance, and the better its current suppression effect.

[0041] Reference Figures 3 to 5 The decreasing layer 15 on the side closer to the front cavity surface 14 of the two adjacent decreasing layers 15 is the right layer, and the decreasing layer 15 on the side closer to the penetration layer 3 is the left layer. The projection length of the left layer on the long side of the chip structure is L1, and the projection length of the right layer on the long side of the chip structure is L2. L2:L1=1:1~1:2.

[0042] Reference Figures 3 to 5 The length of the long side of the vertical projection of the chip structure is L, and the projection length of the weak potential layer 2 on the long side of the chip structure is L3, where L3:L = 1:4~1:2.

[0043] Since the doping concentration of the weak potential layer 2 is between that required for hot electron excitation and tunneling, hot electron excitation and tunneling work simultaneously, resulting in a weak ohmic contact effect and relatively high contact resistance.

[0044] The third high-level tunnel is heavily doped with a very high doping concentration. The carrier transport mechanism at the gold half-metal interface is mainly tunneling, resulting in very low contact resistance and the formation of good ohmic contact.

[0045] Reference Figures 3 to 6The weak potential layer 2 is located at the front cavity surface 14. Due to the relatively large contact resistance of this type, the current injected into the front cavity surface 14 and its vicinity can be effectively reduced, resulting in a weak ohmic contact. The high potential layer 3b corresponds to the heavily doped semiconductor and can form a good ohmic contact. Through this design, the reliability risk caused by the excessive injection current density at the front cavity surface 14 can be resolved.

[0046] Example

[0047] This application discloses a method for fabricating a semiconductor laser, used to fabricate the semiconductor laser described in the above embodiments, comprising the following steps: S1, Providing a substrate. Specifically, the substrate provides physical support for the epitaxial structure of the semiconductor laser and is the basis for the growth of subsequent layers. A suitable substrate enables the epitaxial layers to better maintain the integrity and consistency of the crystal during growth, reducing the generation of defects. For example, the substrate material can be gallium arsenide (GaAs) or indium phosphide (InP), etc.

[0048] In step S2, a buffer layer, a lower confinement layer, a lower waveguide layer, a quantum well active layer, an upper waveguide layer, an upper confinement layer, and an ohmic contact layer are sequentially grown on one side surface of the substrate to form an epitaxial structure.

[0049] For example, a buffer layer, a lower confinement layer, a lower waveguide layer, a quantum well active layer, an upper waveguide layer, an upper confinement layer, and an ohmic contact layer can be sequentially grown on one side surface of a substrate using molecular beam epitaxy or chemical vapor deposition.

[0050] Specifically, the buffer layer is used to alleviate the lattice mismatch stress between the substrate and the subsequent growth layer, and the confinement layers (upper and lower confinement layers) are used to confine the optical field to the waveguide layer, preventing the optical field from spreading to the highly doped confinement layer, causing free carrier absorption loss and reducing the efficiency of the semiconductor laser. At the same time, the highly doped confinement layer can reduce the series resistance of the semiconductor laser and improve the electro-optic conversion efficiency.

[0051] The quantum well active layer is the core region for laser generation in a semiconductor laser. In the quantum well structure, charge carriers (electrons and holes) are confined within a very thin space, forming a discrete energy level structure. When an injection current is applied, electrons and holes recombine within the quantum well, releasing photons and realizing stimulated emission, thus generating laser light.

[0052] The refractive index of the waveguide layer (upper waveguide layer and lower waveguide layer) is between that of the confinement layer and the quantum well active layer. The difference in refractive index forms an optical waveguide structure, which confines the light field generated by the quantum well active layer to a certain area, reduces light scattering and loss, improves light propagation efficiency, ensures that the laser can be transmitted along a specific direction, and maintains good beam quality during propagation.

[0053] Ohmic contact layers are used to provide low-resistance ohmic contacts between semiconductor lasers and external circuits, ensuring that current can be smoothly injected into the device while enabling the device to be effectively electrically connected to the external circuit.

[0054] Step S3: A conductive material is grown on the surface of the substrate away from the buffer layer to form an N-face electrode.

[0055] For example, conductive materials can be gold (Au), germanium (Ge), nickel (Ni), and their alloys.

[0056] Step S4: Etch the side of the epitaxial structure closest to the ohmic contact layer to form a first current injection window. The etching endpoint of the first current injection window is the ohmic contact layer.

[0057] Step S5: The etching depth of the first current injection window is set to decrease sequentially along the first direction to form multiple current injection suppression structures. The first direction is the direction from the front cavity surface to the rear cavity surface. The bottom of the different current injection suppression structures is located in different ohmic layers.

[0058] Step S6: A conductive material is grown on the first current injection window and multiple current injection suppression structures to form a P-side electrode in order to fabricate a semiconductor laser.

[0059] The front electrode can be made of materials such as titanium (Ti), platinum (Pt), gold (Au), and their alloys.

[0060] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. An ohmic contact structure, comprising an ohmic contact layer, characterized in that: The ohmic contact layer comprises several ohmic layers (1) with different doping concentrations, and each ohmic layer (1) includes at least a weak potential transition layer (2) and a high potential breakthrough layer (3), wherein the doping concentration of the weak potential transition layer (2) is less than or equal to 1E19cm. -3 The doping concentration of the high-level penetration layer (3) is greater than 1E19cm. -3 .

2. A semiconductor laser, comprising a chip structure, characterized in that: The chip structure includes an ohmic contact structure as described in claim 1, and also includes an epitaxial layer located below the ohmic contact structure. One side of the chip structure is a front cavity surface (14), and the front cavity surface (14) is located on a wide side of the vertical projection of the chip structure. The ohmic contact structure is arranged in a strip shape at the middle position of the top of the epitaxial layer. The ohmic contact structure is parallel to the long side of the chip structure. One side of the potential-breaking weak layer (2) is located at the top of the front cavity surface (14), and the potential-breaking high layer (3) is located on the other side of the potential-breaking weak layer (2).

3. A semiconductor laser according to claim 2, characterized in that: The weak potential layer (2) includes multiple decreasing layers (15), and the doping concentration of the multiple decreasing layers (15) gradually decreases from one side of the high potential layer (3) to the front cavity surface (14).

4. A semiconductor laser according to claim 3, characterized in that: The decreasing layer (15) on the side closer to the front cavity surface (14) of two adjacent decreasing layers (15) is the right layer, and the decreasing layer (15) on the side closer to the penetration layer (3) is the left layer. The projection length of the left layer on the long side of the chip structure is L1, and the projection length of the right layer on the long side of the chip structure is L2. L2:L1=1:1~1:

2.

5. A semiconductor laser according to any one of claims 2-4, characterized in that: The length of the vertical projection of the chip structure is L, and the projection length of the weak potential layer (2) on the long side of the chip structure is L3, where L3:L = 1:4~1:

2.

6. A semiconductor laser according to claim 2, characterized in that: The ohmic layer (1) is distributed in the chip structure from top to bottom, and the doping concentration of the ohmic layer (1) decreases from top to bottom.

7. A semiconductor laser according to claim 2, characterized in that: A P-surface electrode (13) is provided above the ohmic contact structure. The P-surface electrode (13) includes a contact point that contacts each ohmic layer (1) and a support surface that does not contact the ohmic structure. An isolation layer (12) is provided between the support surface and the ohmic structure.

8. A method for fabricating a semiconductor laser, characterized in that: The method for preparing a semiconductor laser as described in any one of claims 2-7 includes the following steps: S1, Provide a substrate; S2. A buffer layer, a lower confinement layer, a lower waveguide layer, a quantum well active layer, an upper waveguide layer, an upper confinement layer, and an ohmic layer are sequentially grown on one side surface of the substrate to form an epitaxial structure; wherein the ohmic layer has multiple layers, and the doping concentration of the ohmic layer decreases from top to bottom to form an ohmic contact structure. S3. A conductive material is grown on the surface of the substrate away from the buffer layer to form a back electrode; S4. Etch the side of the epitaxial structure closest to the ohmic layer to form a first current injection window; wherein the etching endpoint of the first current injection window is the ohmic layer. S5. The etching depth of the first current injection window is set to decrease sequentially along the first direction to form multiple current injection suppression structures. The first direction is the direction from the front cavity surface to the rear cavity surface. The bottom of the different current injection suppression structures is located in different ohmic layers. S6. A conductive material is grown on the first current injection window and multiple current injection suppression structures to form a front electrode in order to fabricate a semiconductor laser.

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