TW202414936A - A semiconductor laser diode including multiple junctions and grating layer - Google Patents

Abstract

Provided is a semiconductor laser diode including multiple active layers and a grating layer. The semiconductor laser diode includes two (or more than two) active layers, a grating layer and a tunnel junction. The grating layer and the tunnel junction are provided between two active layers. The tunnel junction is used to connectthe two active layers in series, and the two active layers share the grating layer and are optically coupled to the grating layer, thereby improving the external quantum efficiency and slope efficiency of the semiconductor laser diode.

Description

Semiconductor laser diode including multiple active layers and grating layers

A semiconductor laser diode, in particular a semiconductor laser diode comprising multiple active layers and grating layers, wherein the grating layer is disposed between two active layers, and the two active layers are shared and optically coupled to the grating layer, thereby improving the external quantum efficiency and slope efficiency of the semiconductor laser diode.

Semiconductor lasers or laser diodes have the advantages of small size, low power consumption, fast response, shock resistance, long life, high efficiency and low price, so they are widely used in optoelectronic system products, such as light wave communication, information system, household appliances, precision measurement and optical fiber communication, etc. Among them, distributed feedback lasers (DFB lasers) have the characteristics of simple process, single-mode output and suitability for long-distance transmission. The laser light signal generated by the distributed feedback laser can still maintain a good signal-to-noise ratio after long-distance transmission, so it has become a widely used light source in today's light wave communication and optical fiber communication systems.

However, in distance sensing applications such as LiDAR (Light Detection And Ranging) or 3D sensing, the light output power of semiconductor laser diodes with a single active layer and grating layer is obviously insufficient. Therefore, distance sensing applications such as LIDAR require a semiconductor laser diode with high light output power.

The embodiments of this invention are semiconductor laser diodes with high light output power, and their external quantum efficiency and slope efficiency are better than those of existing semiconductor laser diodes. Compared with the prior art, the semiconductor laser epitaxial structure of the embodiments of this invention has more active layers (regions) and in some embodiments, a horizontal resonant cavity (instead of a vertical resonant cavity) is used to generate laser light, but the laser light is emitted perpendicular to the epitaxial plane.

In addition, as the number of active layers (regions) increases, the number of grating layers may increase accordingly or the grating structure may need to be changed accordingly, but this will prolong the manufacturing time and increase the manufacturing difficulty.

In the embodiment of this invention, the grating layer is disposed between two active layers so that the two active layers can share the grating layer. In this way, there is no need to increase the number of grating layers, and even the structural design of the grating layer may not need to be changed. Therefore, not only can the number of grating layers be reduced, but also the manufacturing process of the semiconductor laser epitaxial structure can be simplified.

In addition, when the laser light field distribution of the two active layers can be optically coupled to the grating layer, the slope efficiency and external quantum efficiency of the semiconductor laser element can be significantly improved. In summary, the optical output power of the semiconductor laser element made with the epitaxial structure of the embodiment of this article is not only significantly improved, but the epitaxial structure is also easier to make, in other words, the manufacturing cost will not increase significantly.

In one embodiment, a semiconductor laser diode includes two active layers, a grating layer and a tunneling junction layer; the grating layer and the tunneling junction layer are disposed between the two active layers, and the tunneling junction layer is used to electrically connect the two active layers in series. The two active layers are shared and optically coupled to the grating layer.

In one embodiment, a semiconductor laser diode including multiple active layers and grating layers is provided, including: a substrate; a first epitaxial stacking structure formed on the substrate, including a first active layer, the first active layer including one or more first quantum well layers, the first active layer generates a first light field distribution; a grating layer formed on the first epitaxial stacking structure; a second epitaxial stacking structure formed on the grating layer, including a second active layer, the The second active layer includes one or more second quantum well layers, and the second active layer generates a second light field distribution; a tunneling junction layer is arranged between the first active layer and the second active layer to electrically connect the first active layer and the second active layer; wherein the grating layer is located between the first active layer and the second active layer, and is within the range of the first light field distribution and the second light field distribution, so that the first light field distribution and the second light field distribution are optically coupled to the grating layer.

In ranging applications such as optical radar systems , it has been studied in various ways how to extract more light through grating pattern design . The present invention is the first to disclose a semiconductor laser diode that uses multiple junctions (active regions) optically coupled to a grating layer and electrically connects the multiple junctions through a tunneling junction layer, thereby improving the external quantum efficiency and slope efficiency of the semiconductor laser diode.

The following is a more detailed description of the implementation of the present invention with the aid of drawings and component symbols, so that those skilled in the art can implement the invention accordingly after studying this manual. The thickness ratio between the film layers in the drawings is not the actual ratio, and the thickness of each film layer should be adjusted according to actual needs.

The following describes specific examples of components and their arrangement to simplify the present invention. Of course, these are only examples and should not be used to limit the scope of the present invention. For example, when a layer is mentioned in the description as being on top of another layer, it may include embodiments in which the layer is in direct contact with the other layer, and it may also include embodiments in which there are other components or epitaxial layers formed between the two layers without direct contact. In addition, repeated numbers and/or symbols may be used in different embodiments. These repetitions are only for the purpose of simply and clearly describing some embodiments, and do not represent a specific relationship between the different embodiments and/or structures discussed.

In addition, spatially relative terms such as "below," "below," "lower," "above," "higher," and similar terms may be used to facilitate describing the relationship between one (or some) elements or features and another (or some) elements or features in the drawings. These spatially relative terms include different orientations of the device in use or operation, as well as the orientations described in the drawings.

This specification provides different embodiments to illustrate the technical features of different embodiments. For example, "some embodiments" referred to in the entire specification means that the specific features, structures, or characteristics described in the embodiments are included in at least one embodiment. Therefore, the phrase "in some embodiments" appearing in different places in the entire specification does not necessarily refer to the same embodiment.

In addition, specific features, structures, or characteristics can be combined in one or more embodiments by any suitable method. Further, for the terms "including", "having", "having", "wherein" or the aforementioned changes used herein, these meanings are similar to the term "comprising" to include corresponding features.

In addition, a “layer” may be a single layer or may include multiple layers; and a “part” of an epitaxial layer may be one layer of the epitaxial layer or multiple layers adjacent to each other.

Referring to FIG. 1 , FIG. 1 is a schematic diagram of a semiconductor laser diode according to an embodiment of the present invention. As shown in FIG. 1 , the semiconductor laser 100 includes a substrate 10, a first epitaxial stacking structure 11, a first interlayer 13, a grating layer 15, a second interlayer 17, and a second epitaxial stacking structure 19. The first epitaxial stacking structure 11 and the second epitaxial stacking structure 19 include a first active layer 11A and a second active layer 19A, respectively. The first active layer 11A generates a first light field distribution, and the second active layer 19A generates a second light field distribution.

The grating layer 15 is between the first active layer 11A and the second active layer 19A. The first active layer 11A and the second active layer 19A are shared and "optically coupled" to the grating layer 15, thereby providing in-plane optical feedback of the semiconductor laser diode and improving the slope efficiency of the semiconductor laser diode. The semiconductor laser diode 100 further includes a tunneling junction layer TD. The tunneling junction layer TD is between the first active layer 11A and the second active layer 19A to form a series electrical connection relationship with the first active layer 11A and the second active layer 19A. The tunnel junction layer TD includes a highly doped P-type layer and a highly doped N-type layer.

The above-mentioned "optical coupling" means that the first active layer 11A and the second active layer 19A respectively generate a (laser) light field distribution, and a portion of the laser light field of the first active layer 11A and the second active layer 19A will be distributed in the grating layer to provide in-plane optical feedback for the semiconductor laser diode. For example, a portion of the first light field distribution will be distributed to the portion of the grating layer close to the first active layer, such as the lower side of the grating layer, and a portion of the second light field distribution will be distributed to the portion of the grating layer close to the second active layer, such as the upper side of the grating layer. The two active layers can emit laser light of the same or different wavelengths and/or the same or different polarizations to meet different design requirements.

The grating structure design of the grating layer 15 can be a first order grating or a second order grating according to actual needs. Using a second order grating (i.e., L=l/ _Neff ), light emission can be diffracted perpendicular to the surface through the grating, which provides another solution for surface emitting lasers. Compared with edge emitting lasers, surface emitting lasers have the advantage of on-wafer testing, without the need to cut the wafer and coat the cleaved surface of the wafer, so they are more cost-effective and more efficient to manufacture. Further use of a two-dimensional grating or so-called photonic crystal can produce a laser with a small far field angle and good beam quality, and can even be used in a lensless system.

In one embodiment, the grating layer 15 includes a plurality of high refractive index dielectric layers 151 and a plurality of low refractive index dielectric layers 153. Preferably (see FIG. 1 ), the tunneling junction layer TD is a portion of the high refractive index dielectric layer 151, such as the middle portion of the high refractive index dielectric layer 151, and a semiconductor layer may be disposed above and/or below the tunneling junction layer TD. Preferably, the tunneling junction layer TD is disposed at or near the point where the light field intensity of the (laser) light field distribution is minimum. Therefore, if the position of the point where the light field intensity of the (laser) light field distribution is minimum changes, the setting position of the tunneling junction layer TD may also change accordingly, such as being disposed in the high refractive index dielectric layer 151 of the grating layer or above or below the grating layer.

The low refractive index medium layer 153 can be a void, a semiconductor material, a dielectric material, or a photonic crystal, etc. When the low refractive index medium layer is a void, a semiconductor material, or a dielectric material, the grating layer 15 is a one-dimensional periodic structure, that is, as shown in FIG. 2 , the high refractive index medium layer 151 and the low refractive index medium layer 153 are arranged periodically in a one-dimensional shape along a first horizontal direction X (not limited to the X direction shown in the figure, and can be along the Y direction in another embodiment), and the first horizontal direction is perpendicular to the thickness direction Z (Z direction) of the grating layer.

As shown in FIG3 , the grating layer 15 may be a photonic crystal layer having a plurality of micro-photonic crystal structures distributed along a first horizontal direction (X direction) and a second horizontal direction (Y direction), wherein the second horizontal direction (X direction) is perpendicular to the first horizontal direction (Y direction).

In principle, the material of the substrate 10 can be InP or GaAs; the material of each epitaxial layer formed on the substrate 10 can be _{InxGayAl1 -xyAs} , where _0≤x≤1 , 0≤y≤1, according to different practical needs. Alternatively, the material of each epitaxial layer formed on the substrate 10 can be _{InxGa1 -xAsyP1 - y} , where 0≤x≤1, 0≤y≤1. Preferably, the tunneling junction layer can be InGaAsSb.

FIG4 is a schematic diagram showing that an etching stop layer 131 is further disposed between the first interlayer and the grating layer according to an embodiment of the present invention. As shown in the epitaxial structure 200 of FIG4 , the etching stop layer 131 is formed on the first interlayer 13, and the grating layer 15 is then fabricated on the etching stop layer 131, so that the grating layer 15 can be easily fabricated. Alternatively, the etching stop layer 131 is formed on the portion of the first interlayer 13 close to the grating layer 15.

Refer to FIG5, which is a schematic diagram of the first epitaxial stacking structure of an embodiment of the present invention. As shown in FIG5, the first epitaxial stacking structure 11 on the substrate 10 sequentially forms a first cladding layer 111, a first optical confinement layer (Separate Confinement Heterostructure) 113, a first active layer (including a quantum well layer or multiple quantum well layers) 11A, and a second optical confinement layer 115 from bottom to top. The substrate 10 can be an InP substrate, the material of the first cladding layer 111 can be InP, the material of the first optical confinement layer 113 can be InAlAs, the material of the first active layer 11A can be InAlGaAs, and the material of the second optical confinement layer 115 can be InAlAs. The material of the first interlayer 13 on the first epitaxial stack structure 11 may be InP. If an etching stop layer 131 is disposed on or on a portion of the first interlayer 13 ( FIG. 4 or 6 ), the material of the etching stop layer may be InGaAsP.

Refer to FIG6 , which is a schematic diagram of a grating layer of an embodiment of the present invention. As shown in FIG6 , the high refractive index medium layer 151 of the grating layer 15 sequentially forms a second cladding layer 1511 and a first resistance reduction layer 1513 (resistance reduction layer), a tunneling junction layer TD, a third cladding layer 1515, an optical field adjustment layer 1517 (optical extending layer) and a cover layer 1519 from bottom to top, wherein the optical field adjustment layer 1517 is used to expand or compress the optical field distribution (shape). A second epitaxial stacking structure is formed on the cover layer (not shown in this figure).

The material of the second cladding layer 1511 may be InP; the material of the first resistance reducing layer 1513 may be InGaAsP; the material of the tunneling junction layer TD may be InGaAs or InGaAsP, wherein the P-type layer of the tunneling junction layer TD may be doped with carbon (C), and the N-type layer of the tunneling junction layer TD may be doped with tellurium (Te); the material of the third cladding layer 1515 may be InP; the material of the light field adjustment layer 1517 may be InGaAsP; the material of the cover layer 1519 may be InP. In principle, the epitaxial layer or semiconductor layer directly or adjacent to the grating layer can also have the function of expanding or compressing the light field distribution (shape). For example, the covering layer 1519 can have the function of light field adjustment, or the covering layer 1519 can be replaced by forming a whole layer of light field adjustment layer on the light field adjustment layer 1519.

Referring to FIG. 7 , FIG. 7 is a schematic diagram of a second epitaxial stack structure of an embodiment of the present invention. As shown in FIG. 7 , the second epitaxial stack structure 19 sequentially forms a fourth cladding layer 191, a third optical confinement layer 192, a second active layer (including a quantum well layer or multiple quantum well layers) 19A, a fourth optical confinement layer 193 and a fifth cladding layer 194, a second resistance reduction layer 195 and an ohmic contact layer 196 from bottom to top. The material of the fourth cladding layer 191 may be InP; the material of the third optical confinement layer 192 may be InAlAs; the material of the second active layer 19A may be InAlGaAs; the material of the fourth optical confinement layer 193 may be InAlAs; the material of the fifth cladding layer 194 may be InP; the material of the second resistance reducing layer 195 may be InGaAsP; and the material of the ohmic contact layer 196 may be InGaAs.

FIG8 is a schematic diagram of a low refractive index medium layer of a grating layer according to an embodiment of the present invention being a dielectric material. The low refractive index medium layer 153 in the grating layer 15 of FIG8 is a dielectric material or a semiconductor material. Although FIG8 is substantially the same as FIG1 , the grating layer contains a dielectric material, and therefore the manufacturing method is different, so there is a slight difference in structure. As shown in the epitaxial structure of FIG8 , an etch stop layer 131 is epitaxially grown on the first interlayer 13, and a capping layer 1519 is further formed on the etch stop layer 131. In addition, in the epitaxial structure of FIG. 8 , the second epitaxial stacking structure 19 is directly formed on the grating layer 15 , so there is no need to provide a second interlayer between the grating layer 15 and the second epitaxial stacking structure 19 , but this is not limited thereto and can be changed according to actual needs.

In one embodiment, the first cladding layer 111 and the first optical confinement layer 113 have the same conductivity type as the substrate 10, such as N-type. The second optical confinement layer 115, the first interlayer 13, the first etching stop layer 131, the second cladding layer 1511 and the first resistance reducing layer 1513 have the opposite conductivity type as the substrate 10, such as P-type. The third cladding layer 1515, the optical field adjustment layer 1517, the cover layer 1519, the fourth cladding layer 191 and the third optical confinement layer 192 have the same conductivity type as the substrate 10, such as N-type. The fourth photoconfinement layer 193, the fifth cladding layer 194, the second resistance reduction layer 195 and the ohmic contact layer 196 have a conductivity type opposite to that of the substrate 10, such as a P type.

The first active layer 11A and the second active layer 19A are multiple quantum well (MQWs) structures composed of InAlGaAs, and the number of periods of the quantum wells can be 7, but is not limited thereto.

In an embodiment of FIG. 9a, FIG. 9a shows a semiconductor laser diode with a ridge structure, and the grating layer is a second-order grating. The light field distribution of the first active layer and the second active layer of FIG. 9a is shown in FIG. 9b. The first active layer and the second active layer are both optically coupled to the grating layer (thickness is about 720 nm). When the first active layer and the second active layer are both optically coupled to the grating layer, the slope efficiency of the semiconductor laser diode will be significantly improved. By arranging the active layer above or below the grating layer and optically coupling the two active layers, the slope efficiency and/or external quantum efficiency of the semiconductor laser diode are improved.

In one embodiment, the semiconductor laser diode is a VCSEL, a horizontal cavity surface emitting laser (HCSELs), an edge emitting laser diode (EEL), or a DFB laser.

Please refer to FIG. 10A , which shows a semiconductor laser diode 400 of the front light emitting type. When the semiconductor laser diode 400 of the front light emitting type is further provided with a DBR layer 20 , and the DBR layer 20 is provided below the grating layer 15 of the second-order grating and the first active layer 11A, the light output power of the semiconductor laser diode of the front light emitting type can be increased. FIG. 10B shows a semiconductor laser diode 500 of the back light emitting type, in which the DBR layer 20 must be provided above the grating layer 15 of the second-order grating and the second active layer 19A, so that the light output power of the semiconductor laser diode of the back light emitting type can be increased. A front-emitting type semiconductor laser diode refers to a semiconductor laser diode in which light is emitted from the epitaxial surface of the epitaxial structure, while a back-emitting type semiconductor laser diode refers to a semiconductor laser diode in which light is emitted from the substrate or from the side of the epitaxial structure facing the substrate.

When the grating layer is arranged in a one-dimensional periodic manner and the semiconductor laser diode is a semiconductor laser diode with a ridge structure, a DBR layer is respectively disposed on the front and rear sides of the semiconductor laser diode (horizontally resonating between the front and rear sides), thereby increasing the light output power of the semiconductor laser diode side and reducing the critical current.

The epitaxial layers in the first epitaxial stack structure and the second epitaxial stack structure are manufactured by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE) or other epitaxial growth methods.

The above is only used to explain the preferred embodiments of the present invention, and is not intended to limit the present invention in any form. Therefore, any modifications or changes made to the present invention under the same spirit of the invention should still be included in the scope of protection of the present invention.

100, 200, 300, 400, 500: semiconductor laser 10: substrate 11: first epitaxial stacking structure 111: first cladding layer 113: first optical confinement layer 115: second optical confinement layer 13: first interlayer 15: grating layer 17: second interlayer 131: etching stop layer 151: high refractive index dielectric layer 1511: second cladding layer 1513: first resistance reduction layer 1515: third cladding layer 1517: optical field adjustment layer 1519: cover layer 153: low refractive index dielectric layer 19: Second epitaxial stacking structure 191: Fourth cladding layer 192: Third optical confinement layer 193: Fourth optical confinement layer 194: Fifth cladding layer 195: Second resistance reduction layer 196: Ohmic contact layer 20: DBR layer 11A: First active layer 19A: Second active layer TD: Tunneling junction layer

FIG. 1 is a schematic diagram of a semiconductor laser diode according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a grating layer according to an embodiment of the present invention being a one-dimensional periodic structure. FIG. 3 is a schematic diagram of a grating layer according to an embodiment of the present invention being a photonic crystal layer. FIG. 4 is a schematic diagram of an etching stop layer disposed between a first interlayer and a grating layer according to an embodiment of the present invention. FIG. 5 is a schematic diagram of a first epitaxial stacking structure according to an embodiment of the present invention. FIG. 6 is a schematic diagram of a grating layer according to an embodiment of the present invention. FIG. 7 is a schematic diagram of a second epitaxial stacking structure according to an embodiment of the present invention. FIG. 8 is a schematic diagram of a low refractive index medium layer in a grating layer according to an embodiment of the present invention being a dielectric material. FIG9a is a schematic diagram of a semiconductor laser diode with a ridge structure according to an embodiment of the present invention. FIG9b is a light field distribution diagram of the first active layer and the second active layer according to an embodiment of the present invention shown in FIG9a. FIG10a is a schematic diagram of the position of the DBR layer in a front-emitting semiconductor laser diode according to an embodiment of the present invention. FIG10b is a schematic diagram of the position of the DBR layer in a back-emitting semiconductor laser diode according to an embodiment of the present invention.

100:Semiconductor laser

10: Substrate

11: The first epitaxial stacking structure

11A: First active layer

13: First interlayer

15: Grating layer

151: High refractive index dielectric layer

153: Low refractive index dielectric layer

TD: Tunneling junction layer

17: Second interlayer

19: Second epitaxial stacking structure

19A: Second active layer

Claims (11)

A semiconductor laser diode including multiple active layers and grating layers, comprising: a substrate; a first epitaxial stacking structure formed on the substrate, comprising a first active layer, the first active layer comprising one or more first quantum well layers, the first active layer generating a first light field distribution; a grating layer formed on the first epitaxial stacking structure; a second epitaxial stacking structure formed on the grating layer, comprising a second active layer, the second active layer comprising one or more second quantum well layers, the second active layer generating a second light field distribution; and A tunneling junction layer is disposed between the first active layer and the second active layer to electrically connect the first active layer and the second active layer; Wherein, the grating layer is located between the first active layer and the second active layer, and the grating layer is within the range of the first light field distribution and the second light field distribution, and the first light field distribution and the second light field distribution are optically coupled to the grating layer. A semiconductor laser diode comprising multiple active layers and grating layers as described in claim 1, wherein the tunneling junction layer is disposed above or below the grating layer. A semiconductor laser diode comprising multiple active layers and grating layers as described in claim 1, wherein the grating layer comprises a plurality of high refractive index medium layers and a plurality of low refractive index medium layers, and the high refractive index medium layers are interposed with the tunnel junction layer. A semiconductor laser diode comprising multiple active layers and grating layers as described in claim 1, wherein the grating layer comprises a plurality of high-refractive-index medium layers and a plurality of low-refractive-index medium layers, and the low-refractive-index medium layers are voids, dielectric materials or semiconductor materials. A semiconductor laser diode comprising multiple active layers and a grating layer as described in claim 3, wherein the grating layer is a one-dimensional periodic structure or a two-dimensional periodic structure. A semiconductor laser diode comprising multiple active layers and grating layers as described in claim 1, wherein the grating layer is a photonic crystal layer having a plurality of micro-photonic crystal structures distributed along a first horizontal direction and a second horizontal direction, and the second horizontal direction is perpendicular to the first horizontal direction. A semiconductor laser diode comprising multiple active layers and a grating layer as described in claim 1, wherein the grating layer is a first-order grating or a second-order grating. A semiconductor laser diode comprising multiple active layers and grating layers as described in claim 1, wherein the semiconductor laser diode is a surface emitting laser diode, a horizontal cavity surface emitting laser diode or an edge emitting laser diode. A semiconductor laser diode comprising multiple active layers and grating layers as described in claim 1, further comprising a DBR layer. When the semiconductor laser diode is a front-emitting semiconductor laser diode, the DBR layer is formed under the grating layer and the first active layer. A semiconductor laser diode comprising multiple active layers and grating layers as described in claim 1, further comprising a DBR layer. When the semiconductor laser diode is a back-emitting semiconductor laser diode, the DBR layer is formed on the grating layer and the second active layer. A semiconductor laser diode comprising multiple active layers and grating layers as described in claim 1, wherein when the grating layer is arranged in a one-dimensional periodic manner and the semiconductor laser diode is a semiconductor laser diode with a ridge structure, a DBR layer is respectively provided on two opposite side surfaces of the semiconductor laser diode.

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