Semiconductor laser element and method for manufacturing the same

Abstract

To provide a semiconductor laser element and a manufacturing method thereof capable of evaluating the thickness of a semiconductor layer.SOLUTION: A semiconductor laser element includes a first semiconductor layer and an active layer provided on the first semiconductor layer, and the first semiconductor layer is a superlattice layer and includes a plurality of first layers and a plurality of second layers, the plurality of first layers and the plurality of second layers are alternately stacked, and the plurality of first layers have mutually equal thicknesses, and the plurality of second layers have mutually equal thicknesses.SELECTED DRAWING: Figure 2A

Description

Technical Field

[0001] The present disclosure relates to a semiconductor laser device and a method for manufacturing the same.

Background Art

[0002] A high optical output is required for a light source used in optical communication or the like. As the light source, a semiconductor laser device is used. Patent Document 1 discloses a semiconductor laser device having a semiconductor layer, an active layer, and a p-type semiconductor layer for controlling the distribution of light. By distributing light to the semiconductor layer below the active layer, light is kept away from the active layer and the p-type semiconductor layer with a large light absorption, and the light absorption is suppressed. As a result, the output becomes high.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the thickness of the semiconductor layer affects the optical characteristics, it is important to evaluate the thickness. Therefore, an object is to provide a semiconductor laser device capable of evaluating the thickness of the semiconductor layer and a method for manufacturing the same.

Means for Solving the Problems

[0005] The semiconductor laser device according to the present disclosure includes a first semiconductor layer and an active layer provided on the first semiconductor layer, the first semiconductor layer is a superlattice layer, includes a plurality of first layers and a plurality of second layers, the plurality of first layers and the plurality of second layers are alternately stacked, the plurality of first layers have equal thicknesses with each other, and the plurality of second layers have equal thicknesses with each other.

[0006] A method for manufacturing a semiconductor laser element according to this disclosure comprises the steps of: providing a first semiconductor layer; measuring the thickness of the first semiconductor layer by X-ray diffraction; and, after the step of measuring the thickness, providing an active layer on the first semiconductor layer, wherein the first semiconductor layer is a superlattice layer and includes a plurality of first layers and a plurality of second layers, the plurality of first layers and the plurality of second layers are stacked alternately, the plurality of first layers have equal thickness to each other, and the plurality of second layers have equal thickness to each other. [Effects of the Invention]

[0007] This disclosure makes it possible to provide a semiconductor laser element capable of evaluating the thickness of a semiconductor layer and a method for manufacturing the same. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a plan view illustrating a semiconductor laser element. [Figure 2A] Figure 2A is a cross-sectional view illustrating a semiconductor laser element. [Figure 2B] Figure 2B is a magnified view of the core layer. [Figure 3] Figure 3 is a flowchart illustrating a method for manufacturing a semiconductor laser device. [Figure 4A] Figure 4A is a cross-sectional view illustrating a method for manufacturing a semiconductor laser device. [Figure 4B] Figure 4B is a cross-sectional view illustrating a method for manufacturing a semiconductor laser device. [Figure 5A] Figure 5A is a cross-sectional view illustrating a method for manufacturing a semiconductor laser element. [Figure 5B] Figure 5B is a cross-sectional view illustrating a method for manufacturing a semiconductor laser element. [Figure 6A] Figure 6A is a cross-sectional view illustrating a method for manufacturing a semiconductor laser device. [Figure 6B] Figure 6B is a cross-sectional view illustrating a method for manufacturing a semiconductor laser element. [Figure 7A] Figure 7A is a schematic diagram illustrating the rocking curve of X-ray diffraction. [Figure 7B] Figure 7B illustrates the relationship between the period of the core layer and the diffraction angle of the first peak. [Modes for carrying out the invention]

[0009] [Description of Embodiments in this Disclosure] First, the contents of the embodiments of this disclosure will be listed and explained.

[0010] One embodiment of the present disclosure is a semiconductor laser element comprising (1) a first semiconductor layer and an active layer provided on the first semiconductor layer, wherein the first semiconductor layer is a superlattice layer and includes a plurality of first layers and a plurality of second layers, the plurality of first layers and the plurality of second layers are stacked alternately, the plurality of first layers have equal thickness to each other, and the plurality of second layers have equal thickness to each other. Since the first semiconductor layer has a periodic structure, the period of the first semiconductor layer can be measured by X-ray diffraction. The thickness of the first semiconductor layer can be evaluated based on the period. (2) In (1) above, the first layer may be formed of indium phosphide, and the second layer may be formed of indium gallium arsenide phosphide or aluminum indium gallium arsenide. Since the first semiconductor layer has a periodic structure, the period of the first semiconductor layer can be measured by X-ray diffraction. (3) In (1) or (2) above, a second semiconductor layer is provided on the active layer, and the refractive index of the first semiconductor layer may be higher than that of the second semiconductor layer. Since the light generated in the active layer is distributed to the first semiconductor layer, absorption by the active layer is suppressed. This makes it possible to increase the power output of the semiconductor laser element. (4) In any of (1) to (3) above, the thickness of the first layer and the thickness of the second layer may each be 10 nm or more. The physical properties of the first semiconductor layer are stable. (5) In any of (1) to (4) above, the thickness of the first semiconductor layer may be 1 μm or more. By distributing the light across the first semiconductor layer and keeping it away from the active layer, light absorption is suppressed. (6) In any one of (1) to (5) above, the active layer forms a mesa, and the first semiconductor layer may have a width larger than the width of the mesa. The effective refractive index of the first semiconductor layer becomes high, and light can be transferred to the first semiconductor layer. Light absorption is suppressed. (7) In any one of (1) to (6) above, it includes a second semiconductor layer provided on the active layer, and the first semiconductor layer may have an n-type conductivity type. Light is distributed in the first semiconductor layer and moves away from the second semiconductor layer. Light absorption by the p-type second semiconductor layer is suppressed. (8) In (6) above, it may include buried layers provided on both sides of the mesa. By blocking the current by the buried layers, current can be selectively passed through the mesa 11. (9) A method for manufacturing a semiconductor laser device having a step of providing a first semiconductor layer, a step of measuring the thickness of the first semiconductor layer by X-ray diffraction, and a step of providing an active layer on the first semiconductor layer after the step of measuring the thickness, wherein the first semiconductor layer is a superlattice layer, includes a plurality of first layers and a plurality of second layers, the plurality of first layers and the plurality of second layers are alternately stacked, the plurality of first layers have equal thicknesses to each other, and the plurality of second layers have equal thicknesses to each other. Since the first semiconductor layer has a periodic structure, the period of the first Semiconductor layer can be measured by X-ray diffraction. Based on the measurement of the period, the thickness of the first semiconductor layer can be evaluated.

[0011] [Details of Embodiments of the Present Disclosure] Specific examples of the semiconductor laser device and its manufacturing method according to the embodiments of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, and is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0012] Figure 1 is a plan view illustrating a semiconductor laser element 100. The semiconductor laser element 100 is a distributed feedback (DFB) laser element. The X-axis represents the direction of light propagation. The Y-axis represents the width direction of the mesa 11. The Z-axis represents the direction in which the semiconductor layers are stacked. The X, Y, and Z axes are orthogonal to each other. In Figure 1, the mesa 11 is shown by viewing through the electrodes and insulating film.

[0013] The length L1 in the X-axis direction of the semiconductor laser element 100 is, for example, 800 μm. A high-reflection film 7 (HR) is provided on one end face in the X-axis direction of the semiconductor laser element 100. An anti-reflection film 9 (AR) is provided on the other end face in the X-axis direction.

[0014] The semiconductor laser element 100 has a mesa 11. The mesa 11 is located in the center in the Y-axis direction. The mesa 11 extends in the X-axis direction from one end face to the opposite end face of the semiconductor laser element 100 in the X-axis direction. Light is generated in the mesa 11 and propagates in the X-axis direction. The light is reflected by the high-reflectivity film 7, passes through the anti-reflective film 9, and is emitted out of the semiconductor laser element 100. The width W1 of the mesa 11 in the Y-axis direction is, for example, 2.4 μm.

[0015] Figure 2A is a cross-sectional view illustrating a semiconductor laser element 100, showing a cross-section along line AA in Figure 1. The semiconductor laser element 100 has a substrate 10 and a core layer 12. The core layer 12 (first semiconductor layer) is stacked on the substrate 10.

[0016] The mesa 11 includes a core layer 12, a cladding layer 14, a diffraction grating layer 15, a cladding layer 16, a guide layer 17, an active layer 18, a guide layer 19, and a cladding layer 20. The cross-sectional shape of the core layer 12 is convex. The core layer 12 has a portion that protrudes from the center in the Y-axis direction. The mesa 11 is formed by stacking the cladding layer 14, the diffraction grating layer 15, the cladding layer 16, the guide layer 17, the active layer 18, the guide layer 19, and the cladding layer 20 in this order on top of the protruding portion of the core layer 12.

[0017] The upper surface of the diffraction grating layer 15 has irregularities. Multiple irregularities are arranged periodically along the X-axis. Cladding layers 16 are embedded in the recessed parts (concave portions) of the diffraction grating layer 15. The irregularities of the diffraction grating layer 15 function as a diffraction grating.

[0018] The sides of the core layer 12 facing the mesa 11 are recessed compared to the mesa 11. The embedded layers 24 and 26 are stacked on top of the sides of the core layer 12 facing the mesa 11 in this order. The embedded layers 24 and 26 are provided on both sides of the mesa 11.

[0019] Cladding layers 20 and 28 (second semiconductor layer) are provided on the active layer 18 and guide layer 19. Cladding layer 20 is contained within the mesa 11. Cladding layer 28 is laminated on the mesa 11 and the embedded layer 26. Contact layer 29 is laminated on top of cladding layer 28. Cladding layer 28 and contact layer 29 cover the mesa 11 and the embedded layer 26.

[0020] An electrode 30 is provided on the upper surface of the contact layer 29, directly above the mesa 11. An insulating film 31 is provided on the contact layer 29 and the electrode 30. The insulating film 31 has an opening above the electrode 30. The upper surface of the electrode 30 is exposed through the opening. A wiring layer 34 is provided on the upper surface of the insulating film 31, directly above the mesa 11. The wiring layer 34 contacts the upper surface of the electrode 30 through the opening in the insulating film 31 and is electrically connected to the electrode 30. The electrode 30 and the wiring layer 34 are electrically connected to the contact layer 29. The electrode 30 is made of a metal such as a titanium, platinum, and gold laminate (Ti / Pt / Au). The wiring layer 34 is made of gold (Au), for example.

[0021] A contact layer 35 is provided on the lower surface of the substrate 10 (the surface opposite to the surface on which the core layer 12 is provided). An electrode 32 is provided on the surface of the contact layer 35 opposite to the substrate 10. The electrode 32 is electrically connected to the contact layer 35. The electrode 32 is made of a metal such as an alloy of gold, germanium, and Ni (AuGeNi).

[0022] The substrate 10 and contact layer 35 are formed of, for example, n-type indium phosphide (n-InP). The cladding layer 14 and cladding layer 16 are also formed of, for example, n-InP. Silicon (Si) is used as the n-type dopant. The dopant concentration in cladding layer 14 and cladding layer 16 is, for example, 5 × 10⁻¹⁶. 17 cm -3 The refractive indices of cladding layers 14 and 16 are, for example, 3.204. The band gaps of cladding layers 14 and 16 are, for example, 0.918 eV to 1 eV. The diffraction grating layer 15 is formed of, for example, indium gallium arsenide phosphorus (InGaAsP).

[0023] Guide layers 17 and 19 are formed of, for example, undoped indium gallium arsenide phosphate (i-InGaAsP). The refractive index of guide layers 17 and 19 is, for example, 3.320. The active layer 18 has a multi-quantum well structure (MQW). The active layer 18 includes multiple well layers and multiple barrier layers. The multiple well layers and multiple barrier layers are stacked alternately. The well layers and barrier layers are formed of, for example, i-InGaAsP. The refractive index of the well layers is, for example, 3.435. The refractive index of the barrier layers is, for example, 3.280.

[0024] Cladding layers 20 and 28 are formed of, for example, p-type indium phosphide (p-InP). The refractive index of cladding layers 20 and 28 is, for example, 3.204. The contact layer 29 is formed of, for example, p+-type indium gallium arsenide ((p+)-InGaAs). Zinc (Zn) is used as the p-type dopant. The dopant concentration in cladding layer 28 is, for example, 1 × 10⁻⁶. 18 cm -3 Therefore, the dopant concentration in the contact layer 29 is higher than the dopant concentration in the cladding layer 28.

[0025] The embedded layer 24 is formed of, for example, p-InP. The embedded layer 26 has the opposite conductivity type to the embedded layer 24 and is formed of, for example, n-InP. The dopant concentrations of the embedded layers 24 and 26 are, for example, 4 × 10⁻¹⁶. 18 cm -3 The refractive indices of the embedded layer 24 and embedded layer 26 are, for example, 3.204.

[0026] Figure 2B is an enlarged view of the core layer 12. The overall thickness T of the core layer 12 is, for example, 1 μm or more and 2 μm or less. As shown in Figure 2B, the core layer 12 is a superlattice layer and contains two types of semiconductor layers. The core layer 12 includes an indium phosphide layer 40 (InP layer 40, first layer) and an indium gallium arsenide phosphide layer 42 (InGaAsP layer 42, second layer). The InP layer 40 and the InGaAsP layer 42 have n-type conductivity. The dopant concentration (Si concentration) of the InP layer 40 and the InGaAsP layer 42 is, for example, 5 × 10⁻⁶. 17 cm -3 The refractive index of the InP layer 40 is, for example, 3.204. The refractive index of the InGaAsP layer 42 is, for example, 3.320. The effective refractive index of the core layer 12 as a whole is higher than the refractive index of the cladding layers 20 and 28. The effective refractive index of the core layer 12 is calculated, for example, as follows: Calculate the product of the refractive index of the InP layer 40 and the thickness of the InP layer 40. The refractive index of the InGaAsP layer 42 and InGaAsP layer 42 The product of the thickness of the core layer is calculated. By dividing the sum of the two products by the total thickness of the core layer 12, the average refractive index is obtained. The average refractive index can be considered as the effective refractive index. The band gap of the core layer 12 is greater than the energy of the light (wavelength 1310 nm) generated in the active layer 18.

[0027] Multiple InP layers 40 and multiple InGaAsP layers 42 are stacked alternately. That is, one InGaAsP layer 42 is provided on the upper surface of one InP layer 40, and one InP layer 40 is provided on the upper surface of one InGaAsP layer 42.

[0028] Multiple InP layers 40 have the same thickness. The thickness T1 of an InP layer 40 is, for example, 15 nm. Multiple InGaAsP layers 42 have the same thickness. The thickness T2 of an InGaAsP layer 42 is, for example, 30 nm. The core layer 12 is formed by stacking pairs of InP layers 40 and InGaAsP layers 42 at a constant period. The thickness of one pair of InP layer 40 and one InGaAsP layer 42 is sometimes referred to as the period P of the core layer 12. The product of the number of pairs and the period P is equal to the thickness T of the core layer 12. The portion of the core layer 12 that becomes a mesa 11 contains, for example, 10 pairs. The portion of the core layer 12 below the mesa 11 contains, for example, 20 pairs.

[0029] The thickness T1 of one InP layer 40 and the thickness T2 of one InGaAsP layer 42 can be measured, for example, using a transmission electron microscope (TEM). The period P of the core layer 12 can be measured by X-ray diffraction (XRD).

[0030] Current is input to the semiconductor laser element 100 through electrodes 30 and 32. On both sides of the mesa 11, an n-type core layer 12, a p-type embedding layer 24, and an n-type embedding layer 26 are stacked. As a result, current does not easily flow outside the mesa 11, but easily flows within the mesa 11. When carriers are injected into the active layer 18, the active layer 18 generates light. The wavelength of the light is, for example, 1.31 μm. The light propagates through the mesa 11 and is reflected by the highly reflective film 7 at one end of the semiconductor laser element 100, causing laser oscillation. The light is emitted from the other end of the semiconductor laser element 100.

[0031] The active layer 18 and the p-type cladding layer 28 absorb light more readily than an n-type semiconductor layer, such as the core layer 12. In the semiconductor laser element 100, light is distributed to the core layer 12 and away from the active layer 18 and cladding layer 28. As a result, light absorption is suppressed. The semiconductor laser element 100 functions as a high-power light source.

[0032] (Manufacturing method) Figure 3 is a flowchart illustrating a method for manufacturing the semiconductor laser element 100. Figures 4A to 6B are cross-sectional views illustrating a method for manufacturing the semiconductor laser element 100.

[0033] As shown in Figure 4A, for example, a core layer 12, a cladding layer 14, a diffraction grating layer 15, and a cladding layer 16 are epitaxially grown on a substrate 10 in this order by metal-organic chemical vapor deposition (MOCVD) (step S10 in Figure 3). The InP layer 40 and the InGaAsP layer 42 are alternately stacked by supplying the source gas for the InP layer 40 and the source gas for the InGaAsP layer 42 alternately. After the growth of the diffraction grating layer 15, irregularities are formed on the diffraction grating layer 15 by, for example, electron beam lithography and etching. After the formation of the irregularities, the cladding layer 16 is grown. In this process, guide layers 17 and 19, the active layer 18, the cladding layer 20, and the cladding layer 28 are not formed. The mesa 11 is also not formed.

[0034] The thickness of the core layer 12 is measured (step S12 in Figure 3). Specifically, for example, Cu Kα X-ray diffraction is performed by irradiating the core layer 12 with characteristic X-rays (wavelength 1.541 Å). The period of the core layer 12 is measured from the rocking curve. The number of InP layers 40 and InGaAsP layers 42 contained in the core layer 12 is predetermined by the manufacturing conditions. The thickness T of the core layer 12 can be determined from the thickness (period) of one pair and the number of periods. If the thickness T is within the predetermined range, the processes after step S12 are carried out. If the thickness T is outside the predetermined range, the product is considered defective.

[0035] As shown in Figure 4B, the guide layer 17, active layer 18, guide layer 19, and cladding layer 20 are epitaxially grown on the cladding layer 16 by a method such as MOCVD (step S14 in Figure 3).

[0036] As shown in Figure 5A, the mesa 11 is formed, for example, by dry etching (step S16 in Figure 3). A mask (not shown) is placed in the central part of the upper surface of the cladding layer 20. Etching is performed on the portion exposed from the mask. Etching proceeds from the cladding layer 20 to partway up the core layer 12. The mesa 11 is formed in the central part protected by the mask. The surface of the core layer 12 is exposed on both sides of the mesa 11. After etching is complete, the mask is removed.

[0037] As shown in Figure 5B, embedded growth is performed on both sides of the mesa 11 (step S18 in Figure 3). Embedded layers 24 and 26 are epitaxially grown in this order.

[0038] As shown in Figure 6A, a cladding layer 28 is epitaxially grown on the upper surfaces of the cladding layer 20 and the embedded layer 26. A contact layer 29 is epitaxially grown on the upper surface of the cladding layer 28. A contact layer 35 is epitaxially grown on the lower surface of the substrate 10 (step S20 in Figure 3).

[0039] As shown in Figure 6B, for example, an electrode 30 is formed on the upper surface of the contact layer 29, directly above the mesa 11, by vacuum deposition and lift-off. An electrode 32 is formed on the lower surface of the contact layer 35, directly below the mesa 11. For example, an insulating film 31 is formed on the upper surface of the contact layer 29 by plasma CVD (Chemical Vapor Deposition). A wiring layer 34 is formed by plating or the like (step S22 in Figure 3). The semiconductor laser element 100 is formed by the above steps.

[0040] Figure 7A is a schematic diagram illustrating the rocking curve of X-ray diffraction. The horizontal axis represents the diffraction angle. The vertical axis represents the X-ray intensity. Cu Kα By irradiating the core layer 12 with a line, a rocking curve like the one shown in Figure 7A can be measured. P represents the period in the core layer 12. Figure 7A shows the rocking curve in the example where P=P1 and the rocking curve in the example where P=P2. P1 is smaller than P2.

[0041] The numbers (0, 1, -1) in Figure 7A represent the order of the peaks. The 0th-order peak is the peak caused by the substrate 10. The 1st-order peak is the peak caused by the core layer 12. The angle between the 0th-order peak and the 1st-order peak changes depending on the period P. As the period P increases, the 1st-order peak becomes closer to the 0th-order peak. In the example in Figure 7A, the peak spacing when period P=P2 is narrower than when period P=P1.

[0042] The angle of the satellite peak (the first-order peak in Figure 7A) is expressed by the following equation: θ0 is the diffraction angle of the 0th-order peak. θn is the diffraction angle of the nth-order peak. n is the order of the peak, and for the first-order peak, n=1. λ is the wavelength of the X-ray, for example, 1.541 Å. 2P(sinθn-sinθ0)=±nλ (1) The period P of the core layer 12 can be determined from the interval (angle) between the peaks of the rocking curve (step S12 in Figure 3). If the primary peak is too close to the zeroth peak, it becomes difficult to separate the peaks and evaluate them. Even if the period is large, evaluation is possible if the angular resolution of the X-ray diffraction is high.

[0043] Figure 7B illustrates the relationship between the period P of the core layer 12 and the diffraction angle of the first peak. The horizontal axis represents the period P. The vertical axis represents the diffraction angle of the first peak. The relationship in Figure 7B is calculated from equation (1) above. As shown in Figure 7B, the smaller the period P, the larger the diffraction angle. The larger the period P, the smaller the diffraction angle. When the angular resolution of X-ray diffraction is 0.01°, the period P can be evaluated by X-ray diffraction up to about 440 nm.

[0044] The peak position of the rocking curve is determined with an accuracy of, for example, ±0.0001°. As an example, based on the accuracy of the peak position, the period P is estimated to be in the range of 199.1 nm to 200.9 nm, centered at 200 nm, i.e., within a range of approximately ±1 nm. If the thickness T of the core layer 12 is 2000 nm, the period P can be measured with an accuracy of approximately ±0.05%. A smaller period P results in a more divergent peak, allowing for more accurate measurement of the peak position and improving the accuracy of the thickness measurement.

[0045] According to this embodiment, the core layer 12 is a superlattice layer and includes a plurality of InP layers 40 and a plurality of InGaAsP layers 42. As shown in Figure 2B, the plurality of InP layers 40 have equal thickness T1. The plurality of InGaAsP layers 42 have equal thickness T2. The period within the core layer 12 can be measured by X-ray diffraction. The thickness T1 of the InP layers 40, the thickness T2 of the InGaAsP layers 42, and the number of periods are determined by the manufacturing conditions. Based on the period, the thickness T of the core layer 12 can be calculated. In other words, the thickness of the core layer 12 can be evaluated by X-ray diffraction, which is a non-destructive inspection method.

[0046] The distribution of light in the semiconductor laser element 100 is affected by the thickness T of the core layer 12. The thickness T of the core layer 12 is evaluated by X-ray diffraction, and the thickness T is set to an appropriate size. This allows for control of the light distribution. The light is distributed in the core layer 12 and away from the active layer 18 and the p-type cladding layer 28. Light absorption by the active layer 18 and the cladding layer 28 is suppressed, and the output of the semiconductor laser element 100 increases.

[0047] For example, the thickness T1 of the InP layer 40 and the thickness T2 of the InGaAsP layer 42 can be measured using a TEM. By measuring the thicknesses T1 and T2 using a TEM, growth conditions are obtained that result in the desired thicknesses of the InP layer 40 and the InGaAsP layer 42. The core layer 12 is grown using these growth conditions. The number of pairs contained in the core layer 12 is determined by the manufacturing conditions. The period P of the core layer 12 is measured by X-ray diffraction. The thickness T of the core layer 12 can be obtained from the number of pairs and the period P. The thickness T of the core layer 12 can be evaluated using X-ray diffraction, which is a non-destructive inspection method.

[0048] X-ray diffraction is performed after the formation of the core layer 12 and before the formation of the active layer 18. The active layer 18 has a periodic structure. If X-ray diffraction is performed after the formation of the active layer 18, a rocking curve caused by the periodic structure of the active layer 18 will be observed along with the rocking curve caused by the periodic structure of the core layer 12. Because the two rocking curves overlap, it is difficult to measure the period of the core layer 12. By performing X-ray diffraction of the core layer 12 before the formation of the active layer 18, the rocking curve caused by the core layer 12 can be observed and the period P of the core layer 12 can be measured.

[0049] The refractive index of the core layer 12 is higher than that of the cladding layer 20 and the cladding layer 28. Therefore, light is more easily distributed in the core layer 12, suppressing light absorption by the active layer 18 and the cladding layer 28. The bandgap wavelength of the core layer 12 is shorter than the wavelength of light generated in the active layer 18. This suppresses light absorption by the core layer 12.

[0050] The core layer 12 includes an InP layer 40 and an InGaAsP layer 42. Multiple InP layers 40 have a constant thickness T1. Multiple InGaAsP layers 42 have a constant thickness T2. Therefore, the period of the core layer 12 can be measured by X-ray diffraction. Because the core layer 12 is formed of InP layers 40 and InGaAsP layers 42, lattice matching between the InP substrate 10 and the core layer 12 is possible. The core layer 12 is made of materials other than InP and InGaAsP. semiconductor It may be formed by, for example, an aluminum indium gallium arsenide (AlInGaAs) layer may be used instead of the InGaAsP layer 42. The lattice is matched with the substrate 10. semiconductor Then the core layer 12 should be formed.

[0051] The thickness T1 of the InP layer 40 and the thickness T2 of the InGaAsP layer 42 should each be, for example, 10 nm or more. If the thickness is less than 10 nm, the physical properties will change due to quantum effects. In order to stabilize the physical properties of the core layer 12, the thicknesses T1 and T2 should each be 10 nm or more.

[0052] The overall thickness T of the core layer 12 may be, for example, 1 μm or more, 1.5 μm or more, or 1.8 μm or more. Because the light moves away from the p-type cladding layer 28, it becomes less likely to be absorbed. The thickness T of the core layer 12 should be, for example, 2 μm or less. If the core layer 12 is too thick, the overlap of the light distribution with the active layer 18 becomes too small, and the gain of the semiconductor laser element 100 decreases. As a result, the optical output decreases.

[0053] As shown in Figure 2A, an n-type core layer 12, an active layer 18, and a p-type cladding layer 28 are stacked in this order. The central part of the core layer 12 and the active layer 18 form a mesa 11. Current flows through the mesa 11, and carriers are injected into the active layer 18. Due to the injection of carriers, the active layer 18 generates light. The semiconductor laser element 100 functions as a light-emitting element. The width W2 of the core layer 12 is greater than the width W1 of the mesa 11. The effective refractive index of the core layer 12 is increased. By transferring light to the core layer 12, light absorption can be suppressed.

[0054] Embedded layers 24 and 26 are provided on both sides of the mesa 11. By blocking the current, embedded layers 24 and 26 allow current to flow selectively through the mesa 11.

[0055] The core layer 12 contains 10 pairs in the mesa 11. 20 pairs are positioned below the mesa 11. The number of pairs positioned below the mesa 11 is greater than the number of pairs contained within the mesa 11. In other words, the portion of the core layer 12 below the mesa 11 is thicker than the portion of the core layer 12 contained within the mesa 11. Light is distributed in the core layer 12 below the mesa 11, moving away from the active layer 18 and the p-type cladding layer 28. Light absorption is suppressed. The number of pairs contained in the mesa 11 may be 5 or more. pair If the number of elements is small, the distribution of light spreads too much in the lateral direction (Y-axis direction), which reduces the gain of the semiconductor laser element 100 and decreases the light output.

[0056] The substrate 10 and core layer 12 are n-type semiconductor layers and are located beneath the active layer 18. The cladding layers 20 and 28 are p-type semiconductor layers and are located above the active layer 18. An electric current flows through the active layer 18. Light can be generated by injecting carriers into the active layer 18. The light is distributed across the n-type core layer 12, and the light is directed away from the p-type cladding layers 20 and 28. Light absorption is suppressed.

[0057] Although embodiments of this disclosure have been described in detail above, this disclosure is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of this disclosure as described in the claims. [Explanation of Symbols]

[0058] 7 Highly reflective coating 9 Anti-reflection coating 10 circuit boards 11 Mesa 12 Core layer (first semiconductor layer) 14, 16 Cladding layers 20, 28 Cladding layer (second semiconductor layer) 15 Diffraction gratings 17, 19 Guide Layer 18 Active layer 24, 26 Embedding layer 29, 35 Contact layer 30, 32 electrodes 31 Insulating Film 34 wiring layer 40. Indium phosphate layer (Layer 1) 42. Indium gallium arsenide phosphate layer (Layer 2) 100 Semiconductor laser elements

Claims

1. The first semiconductor layer, A diffraction grating layer provided on the first semiconductor layer, An active layer provided on the diffraction grating layer, It is equipped with, The aforementioned first semiconductor layer is a superlattice layer and includes a plurality of first layers and a plurality of second layers. The plurality of first layers and the plurality of second layers are stacked alternately and form pairs. The plurality of first layers have equal thickness to each other. The aforementioned plurality of second layers have equal thickness to each other. The first semiconductor layer has a first portion and a second portion that protrudes upward from the first portion. The diffraction grating layer, the active layer, and the second portion of the first semiconductor layer form a mesa. The first portion of the first semiconductor layer has a width greater than the width of the mesa, The number of pairs included in the first part is greater than the number of pairs included in the second part. A semiconductor laser element, which is a distributed feedback type laser element.

2. The first layer is formed of indium phosphide, The semiconductor laser element according to claim 1, wherein the second layer is formed of indium gallium arsenide phosphorus or aluminum indium gallium arsenide.

3. The system comprises a second semiconductor layer provided on the active layer, The semiconductor laser element according to claim 1 or claim 2, wherein the refractive index of the first semiconductor layer is higher than the refractive index of the second semiconductor layer.

4. The semiconductor laser element according to claim 1 or claim 2, wherein the thickness of the first layer and the thickness of the second layer are each 10 nm or more.

5. The semiconductor laser element according to claim 1 or claim 2, wherein the thickness of the first semiconductor layer is 1 μm or more.

6. The system comprises a second semiconductor layer provided on the active layer, The first semiconductor layer has an n-type conductivity, The semiconductor laser element according to claim 1, wherein the second semiconductor layer has a p-type conductivity.

7. The semiconductor laser element according to claim 1, further comprising embedded layers provided on both sides of the mesa.

8. The process of providing the first semiconductor layer, A step of measuring the thickness of the first semiconductor layer by X-ray diffraction, After the step of measuring the thickness, the step of providing a diffraction grating layer on the first semiconductor layer, The process includes, after the step of measuring the thickness, a step of providing an active layer on the diffraction grating layer, The aforementioned first semiconductor layer is a superlattice layer and includes a plurality of first layers and a plurality of second layers. The plurality of first layers and the plurality of second layers are stacked alternately and form pairs. The plurality of first layers have equal thickness to each other. The aforementioned plurality of second layers have equal thickness to each other. The first semiconductor layer has a first portion and a second portion that protrudes upward from the first portion. The active layer, the diffraction grating layer, and the second portion of the first semiconductor layer form a mesa. The first portion of the first semiconductor layer has a width greater than the width of the mesa, The number of pairs included in the first part is greater than the number of pairs included in the second part. A method for manufacturing semiconductor laser elements, which are distributed feedback type laser elements.

Images