Semiconductor laser device

Abstract

On the first conductive type semiconductor substrate (2), layers of c1 a first conductive type cladding layer (3), a first conductive type side light guiding layer (56), an active layer (7), a second conductive type side light guiding layer (89), and a refractive index n c2 The second conductive type cladding layer (11) has an oscillation wavelength of λ, and has a thickness of d1 and a refractive index of n between the first conductive type side light guide layer (56) and the first conductive type cladding layer (3), or in the first conductive type cladding layer (3). c1 The invention relates to a first conductive type low refractive index layer (4) having a refractive index n1 lower than nc2, and a second conductive type low refractive index layer (10) having a thickness d2 and a refractive index n2 lower than nc2 between the second conductive type side light guiding layer (89) and the second conductive type cladding layer (11), or within the second conductive type cladding layer (11), and satisfying the standardized frequency v2>standardized frequency v1.

Description

Technical Field

[0001] The present application relates to a semiconductor laser device. Background Art

[0002] In semiconductor laser devices, especially high-output semiconductor laser devices, in order to reduce heat dissipation and simplify the cooler, it is required to improve the oscillation efficiency as much as possible. For example, Patent Document 1 discloses a semiconductor laser device that improves slope efficiency and achieves high power conversion efficiency at high output. FIG. 27 of Patent Document 1 shows a ridge-type semiconductor laser device, which has a light guiding layer thick enough to allow a high-order mode of one order or more in the stacking direction of the crystal, an active layer arranged at a position closer to the p-type cladding layer than the center of the light guiding layer, and a refractive index n c The n-type cladding layer and the n-side optical guiding layer have a refractive index n lower than that of the n-type cladding layer. 11 And the layer thickness d 11 The n-type low refractive index layer has a refractive index of n c The p-type cladding layer and the p-side optical guide layer have a refractive index n lower than that of the p-type cladding layer. 12 And the layer thickness d 12 A p-type low refractive index layer is provided, and satisfies the following formula (1).

[0003] Number 1

[0004] Patent Document 1: Japanese Patent Application Publication No. 2017-84845

[0005] Non-patent document 1: Kawakami, "Optical Waveguide," pp. 21, September 20, 1982 (Asakura Bookstore)

[0006] Non-patent document 2: Iga, ed., "Semiconductor Lasers," pp. 35-38, October 25, 1997 (Ohmsha)

[0007] Non-patent document 3: GBHocker and WKBurns, "Mode dispersion in diffusedchannel waveguides by the effective index method," Appl.Opt., Vol.16, No.1, pp.113-118, 1977

[0008] A study was conducted on the case where the structure of the semiconductor laser device described in Patent Document 1 is applied to a large-area semiconductor laser device having a ridge shape that allows higher-order modes of the first order or higher in a direction perpendicular to the stacking direction of the crystal and the length direction of the resonator (horizontal direction). It was found that there are problems such as a widening of the beam divergence angle in the horizontal direction, a reduction in brightness, and a low coupling efficiency with optical components. Summary of the invention

[0009] The present application discloses a technology for solving the above-mentioned problems, and its object is to provide a large-area semiconductor laser device having a ridge shape that narrows the divergence angle in the horizontal direction and improves the coupling efficiency with optical components.

[0010] The semiconductor laser device disclosed in the present application has a plurality of layers of semiconductor substrates having a refractive index of n stacked in sequence on a semiconductor substrate of a first conductivity type. c1 A first conductive type cladding layer, a first conductive type side light guiding layer, an active layer, a second conductive type side light guiding layer, and a refractive index of n c2 The second conductive type cladding layer is provided on the first conductive type side light guiding layer and the first conductive type cladding layer, and constitutes a resonator that reciprocates the laser, and becomes a structure that allows a high-order mode of the first order or more in the direction of the stacking in the cross section perpendicular to the optical axis direction of the resonator, and becomes a large-area structure that allows a high-order mode of the first order or more in the direction perpendicular to the optical axis direction of the resonator and the stacking direction, and has a ridge shape having a cladding region on both sides of the ridge region and a ridge region, and allows a high-order mode of the first order or more, and has a thickness of d1 and a refractive index greater than the above n between the first conductive type side light guiding layer and the first conductive type cladding layer, or in the first conductive type cladding layer. c1 The first conductive type low refractive index layer has a lower n1, and between the second conductive type side light guiding layer and the second conductive type cladding layer, or in the second conductive type cladding layer, has a thickness of d2 and a refractive index lower than the n1. c2 The second conductivity type low refractive index layer has a low n2 and satisfies the following formula:

[0011] Number 2

[0012] According to the semiconductor laser device disclosed in the present application, it is possible to obtain a semiconductor laser device that reduces the number of modes allowed in the horizontal direction, can narrow the divergence angle in the horizontal direction, and has high coupling efficiency with optical components. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic perspective view showing a stacked structure of the semiconductor laser device according to the first embodiment.

[0014] Figure 2 This is a schematic perspective view showing a stacked structure of a semiconductor laser device according to a second embodiment.

[0015] Figure 3 This is a schematic perspective view showing a stacked structure of a semiconductor laser device according to a third embodiment.

[0016] Figure 4 This is a schematic perspective view showing a stacked structure of a semiconductor laser device according to a fourth embodiment.

[0017] Figure 5 This is a schematic perspective view showing a stacked structure of a semiconductor laser device according to a fifth embodiment.

[0018] Figure 6 This is a schematic perspective view showing a stacked structure of a semiconductor laser device according to a sixth embodiment.

[0019] Figure 7 It is a diagram showing a schematic refractive index distribution of an optical waveguide.

[0020] Figure 8 It is a schematic perspective view showing a stacked structure of a semiconductor laser device according to a comparative example.

[0021] Fig. 9 It is used to illustrate Figure 8 Figure 2 is a graph of the refractive index distribution in the stacking direction in the ridge region of the structure.

[0022] Fig.10 It is used to illustrate Figure 8 A diagram of the refractive index distribution in the stacking direction in the outer area of ​​the ridge region of the structure. DETAILED DESCRIPTION

[0023] A detailed examination of the phenomenon that the beam divergence angle in the horizontal direction widens when the structure of Patent Document 1 is applied to a large-area semiconductor laser device reveals that the cause is multi-mode oscillation in the horizontal direction. Figure 7 : is a diagram showing a schematic refractive index distribution of an optical waveguide for explaining the normalized frequency v. Figure 7 The refractive index of the core region 101 is n a , the width is t, and the refractive index of the cladding region 102 and the cladding region 102a is n b , and n a >n b The normalized frequency v is defined by equation (2) using the oscillation wavelength λ (see Non-Patent Document 1).

[0024] Number 3

[0025] If we compare equation (2) with equation (1), we can see that equation (1) is based on the normalized frequency v. Therefore, at the refractive index n cInsert a refractive index n between the cladding layer and the guiding layer i And the layer thickness d i The magnitude relationship shown in formula (1) when the low refractive index layer is obtained by formula (3) i In other words, if the definition of formula (3) is used, formula (1) as the condition disclosed in Patent Document 1 represents v1>v2.

[0026] Number 4

[0027] i=1 or 2

[0028] Figure 8 This is a schematic perspective view showing a stacked structure of an example in which the technology described in Patent Document 1 is applied to a large-area semiconductor laser device having a ridge shape and an oscillation wavelength of 975 nm as a comparative example of the present application. Figure 8 The layers in the Figure 8 From the bottom, there are, in order, an n-type electrode 103, an n-type GaAs substrate 104, an n-type AlGaAs cladding layer 105 with an Al composition ratio of 0.20 and a layer thickness of 1.5 μm, an n-type AlGaAs low refractive index layer 106 with an Al composition ratio of 0.25 and a layer thickness of d1 (also referred to as an n-type low refractive index layer, with a refractive index of n1), an n-side AlGaAs second optical guiding layer 107 with an Al composition ratio of 0.16 and a layer thickness of 1100nm, an n-side AlGaAs first optical guiding layer 108 with an Al composition ratio of 0.14 and a layer thickness of 100nm (107 and 108 are also collectively referred to as an n-side optical guiding layer), an InGaAs layer with an In composition ratio of 0.119 and a layer thickness of 8nm As quantum well active layer 109, p-side AlGaAs first optical guiding layer 110 with an Al composition ratio of 0.14 and a layer thickness of 300nm, p-side AlGaAs second optical guiding layer 111 with an Al composition ratio of 0.16 and a layer thickness of 300nm (110 and 111 are also collectively referred to as p-side optical guiding layer), p-type AlGaAs low refractive index layer 112 with an Al composition ratio of 0.55 and a layer thickness of d2 (also referred to as p-type low refractive index layer, refractive index n2), p-type AlGaAs cladding layer 113 with an Al composition ratio of 0.20 and a layer thickness of 1.5μm, p-type GaAs contact layer 114, SiN film 115 with a film thickness of 0.2μm, and p-type electrode 116. The In composition ratio of the InGaAs quantum well active layer is set to 0.119 and the layer thickness is set to 8nm in order to make the oscillation wavelength approximately 975nm. Region I is a ridge region having a width of W, and regions II and IIa are cladding regions outside the ridge region.

[0029] In addition, the surfaces constituting the resonator for reciprocating the laser light at both ends are provided by, for example, cleavage. Figure 8As shown, the direction of reciprocation of the laser, i.e., the optical axis direction of the laser, is set to the z direction, the stacking direction of each layer is set to the y direction, and the direction perpendicular to the z direction and the y direction, i.e., the width direction of the ridge is set to the x direction. The same is true for the x, y, and z directions in other drawings of the present application.

[0030] If the refractive index calculation described in Non-Patent Document 2 is used, for example, the refractive index of the AlGaAs layer with Al composition ratios of 0.14, 0.16, 0.20, 0.25, and 0.55 at a wavelength of 975 nm is 3.432173, 3.419578, 3.394762, 3.364330, and 3.191285, respectively. In addition, based on experience, the refractive indexes of InGaAs and SiN with an In composition ratio of 0.119 are 3.542393 and 2.00, respectively. Fig. 9 The refractive index distribution in the y direction of the ridge region is shown. Fig.10 The refractive index distribution in the y direction of the cladding region outside the ridge region is shown.

[0031] The layer thickness d of the n-type low refractive index layer n When the wavelength is 200 nm, the wavelength is 975 nm and v1 in the formula (3) is 0.292273. p When the thickness is 40 nm, v2 in the formula (3) is 0.149202, v1>v2 holds, and the above formula (1) as the condition disclosed in Patent Document 1 is satisfied.

[0032] for Figure 8 For the semiconductor laser device described in , if the effective refractive index of region I and region II and IIa is known, it can be regarded as a three-layer planar waveguide with a width W in the x direction. In this case, v is calculated according to formula (2), and the number of modes allowed in the x direction can be known according to how many times this value is π / 2. The effective refractive index can be calculated, for example, according to the equivalent refractive index method described in non-patent document 3. Figure 8 In the case of a semiconductor laser device, the effective refractive indexes of region I and region II and IIa are calculated to be 3.41738 and 3.41600, respectively. Assuming that the ridge width W is 100 μm, the v value is 31.28979, allowing 20 modes from the 0th order (basic mode) to the 19th order. The larger the order of the mode, the wider the divergence angle, so if the number of allowed modes increases, the divergence angle will also be wider.

[0033] As described above, it is clear that the following problem exists: the conventional large-area semiconductor laser device having a ridge shape satisfying the condition v1>v2 equivalent to that disclosed in Patent Document 1 has a large number of modes allowed in the horizontal direction, so the divergence angle in the horizontal direction is wide and the coupling efficiency with optical components is low.

[0034] Based on the above research results, the results of considering a structure in which the number of modes allowed in the horizontal direction is small will be described as each embodiment.

[0035] Implementation method 1.

[0036] Figure 1 1 is a schematic perspective view showing a stacked structure of a semiconductor laser device of Embodiment 1, i.e., a large-area semiconductor laser device having a ridge shape. The semiconductor laser device of this embodiment is a semiconductor laser device that reduces the number of carriers retained in the guide layer during operation by shifting the position of the active layer in the guide layer from the center of the guide layer to the p-cladding layer side, thereby improving the slope efficiency.

[0037] exist Figure 1 In the embodiment, each layer is composed of the following parts: from the bottom, an n-type electrode 1, an n-type GaAs substrate (also referred to as a semiconductor substrate) 2, an n-type AlGaAs cladding layer with an Al composition ratio of 0.20 and a layer thickness of 1.5 μm (also referred to as an n-type cladding layer or a first conductive cladding layer, with a refractive index of n c1 ) 3. n-side AlGaAs low refractive index layer with an Al composition ratio of 0.25 and a layer thickness of d1 (also called n-side low refractive index layer, or first conductivity type low refractive index layer 4, refractive index n1) 4. n-side AlGaAs second optical guiding layer with an Al composition ratio of 0.16 and a layer thickness of 1100nm (also called n-side second optical guiding layer, or first conductivity type side second optical guiding layer) 5. n-side AlGaAs first optical guiding layer with an Al composition ratio of 0.14 and a layer thickness of 100nm (also called n-side first optical guiding layer, or first conductivity type side first optical guiding layer) 6. InGaAs quantum well active layer with an In composition ratio of 0.119 and a layer thickness of 8nm 7. Al composition ratio of 0 .14 ​​and a p-side AlGaAs first optical guiding layer with a layer thickness of 300nm (also called p-side first optical guiding layer or second conductivity type side first optical guiding layer) 8. A p-side AlGaAs second optical guiding layer with an Al composition ratio of 0.16 and a layer thickness of 300nm (also called p-side second optical guiding layer or second conductivity type side second optical guiding layer) 9. A p-type AlGaAs low refractive index layer with an Al composition ratio of 0.55 and a layer thickness of d2 (also called p-type low refractive index layer or second conductivity type low refractive index layer, with a refractive index of n2) 10. A p-type AlGaAs cladding layer with an Al composition ratio of 0.20 and a layer thickness of 1.5μm (also called p-type cladding layer or second conductivity type cladding layer, with a refractive index of n c2)11, a p-type GaAs contact layer 12, a SiN film 13 with a film thickness of 0.2μm, and a p-type electrode 14. In addition, the n-side second optical guiding layer 5 and the n-side first optical guiding layer 6 are collectively referred to as the n-side optical guiding layer 56 or the first conductive type side optical guiding layer 56, and the p-side first optical guiding layer 8 and the p-side second optical guiding layer 9 are collectively referred to as the p-side optical guiding layer 89 or the second conductive type side optical guiding layer 89. Since these optical guiding layers are usually undoped layers, "side" is added to distinguish which side of the active layer 7 the layer is on. The In composition ratio of the InGaAs quantum well active layer 7 is set to 0.119, and the layer thickness is set to 8nm in order to make the oscillation wavelength approximately 975nm. Region I is a ridge region with a width of W, and regions II and IIa are cladding regions outside the ridge region.

[0038] In the description of the present application, although the structure in which a ridge structure is formed on the p-type contact layer side using an n-type semiconductor substrate 2 is described, the same effect can be obtained by using a p-type semiconductor substrate 2 to form a ridge on the n-type contact layer side. Sometimes the conductivity type of the semiconductor substrate 2 is referred to as the first conductivity type, and the conductivity type opposite to the conductivity type of the semiconductor substrate 2 is referred to as the second conductivity type. That is, if the first conductivity type is n-type, the second conductivity type is p-type, and if the first conductivity type is p-type, the second conductivity type is n-type. In each embodiment, although the structure in which the first conductivity type is set to n-type and the second conductivity type is set to p-type is described as an example, it can also be a structure in which the first conductivity type is set to p-type and the second conductivity type is set to n-type. In the present application, the first conductivity type is described as n-type, and the parameters related to the first conductivity type are marked with subscript 1, the second conductivity type is described as p-type, and the parameters related to the second conductivity type are marked with subscript 2. As described above, since the optical guiding layer is generally an undoped layer, “side” is added to distinguish on which side of the active layer 7 the optical guiding layer is located.

[0039] Although Figure 1 The main structures of the semiconductor laser device are shown in FIG. Figure 8 The structure shown is the same, but as described below, v2>v1, that is:

[0040] Number 5

[0041] The thickness and refractive index of the first conductivity type low refractive index layer 4 and the second conductivity type low refractive index layer 10, and the refractive index of the first conductivity type cladding layer 3 and the second conductivity type cladding layer 11 are set in a certain manner.

[0042] First, the number of modes in the y direction is examined. The refractive index of the first conductive side light guiding layer 56 and the active layer 7 is higher than that of the second conductive side light guiding layer 89, and the refractive index of each low refractive index layer is lower than that of the cladding layer to which it is in contact. Therefore, when the refractive index of the first conductive side light guiding layer 56 and the active layer 7 is replaced by the refractive index of the second conductive side light guiding layer 89, and the refractive index of the low refractive index layer is replaced by the refractive index of the cladding layer, v is less than Figure 1 Therefore, if the permuted structure v allows higher-order modes of order 1 or higher, then Figure 1 The configuration of the present application shown also necessarily allows higher order modes above the first order. Figure 7 From equation (2), it can be seen that the v of the replaced structure is 2.39564, which is a structure that allows the 0th order (fundamental mode) and the 1st order.

[0043] More precisely, the number of allowed modes can be found by calculating the average refractive index of the optical guiding layer as follows. Assuming that the refractive index and layer thickness of the first optical guiding layer 6 on the n side are n g11 and g11 , the refractive index and layer thickness of the second optical guide layer 5 on the n side are n g12 and g12 , the refractive index and layer thickness of the first optical guide layer 8 on the p side are n g21 and g21 , the refractive index and layer thickness of the second optical guiding layer 9 on the p side are n g22 and g22 , then the average refractive index n of the light guiding layer is gm It is formula (5).

[0044] Number 6

[0045] The above n gm Substitute n into formula (2) a , Substitute the refractive index of the cladding into n b , d g11 +d g12 +d g21 +d g22 Substitute t to calculate v and find the number of modes allowed. The same can be found when there are more guide layers. In addition, since the active layer 7 is thin, it is omitted, but the average refractive index can also be taken into account. For the y direction, even when high-order modes are allowed, the light confinement rate of the fundamental (0th order) mode is the largest, that is, the gain of the fundamental (0th order) mode is the largest, so generally the y direction becomes the fundamental (0th order) mode oscillation.

[0046] Next, the number of modes in the x direction is examined. In the semiconductor laser device disclosed in the present application, the condition is that higher-order modes of the first order or higher are also allowed in the x direction. That is, when satisfying Figure 1 The effective refractive index of the ridge region with width w shown, that is, region I, is n r , the effective refractive index of the cladding regions II and IIa outside the ridge region is set to n b When , the following formula is satisfied, namely:

[0047] Number 7

[0048] A structure that satisfies this condition is sometimes referred to as a large-area structure.

[0049] Thus, when the thickness d1 of the first conductive type low refractive index layer 4 is 200nm, the wavelength is 975nm and v1 is 0.292273. At this time, when the thickness d2 of the second conductive type low refractive index layer 10 is 140nm, v2 is 0.522208, and v2>v1 holds. The effective refractive indexes of region I and region II and IIa are respectively calculated to be 3.41665 and 3.41637. When the ridge width W satisfying the above formula (6) is 100μm, v is 14.09388. As a result, only 9 modes from the 0th order (basic mode) to the 8th order are allowed, and modes above the 9th order are not allowed.

[0050] As described above, when d2=40nm satisfies the condition v2<v1 disclosed in Patent Document 1, 20 modes are allowed as modes in the x direction. On the other hand, when d2=140nm satisfies the condition v2>v1 disclosed in the present application, 9 modes are allowed as modes in the x direction, and the number of modes allowed in the x direction can be reduced to less than half. That is, by setting the layer thickness of d2 and d1 to v2>v1, the number of modes allowed in the x direction is reduced compared to setting the layer thickness of each layer to v2<v1, and the divergence angle in the horizontal direction can be narrowed.

[0051] In addition, in the present embodiment 1, the thickness of the first conductive type side light guiding layer 56 is made thicker than the thickness of the second conductive type side light guiding layer 89, and the position of the active layer is shifted from the center of the light guiding layer to the second conductive type cladding layer side, similar to the structure of Patent Document 1. According to this structure, it is also possible to reduce light absorption caused by carriers retained in the light guiding layer during operation, and improve slope efficiency.

[0052] Implementation method 2.

[0053] Figure 21 is a schematic perspective view showing a stacked structure of a semiconductor laser device according to Embodiment 2. Embodiment 2 is an embodiment of a symmetrical structure in which the active layer is arranged at the center of the optical guiding layer. Figure 2 In the embodiment, the first conductive type side optical guiding layer 56 is composed of an n-side AlGaAs second optical guiding layer 5a with an Al composition ratio of 0.16 and a layer thickness of 700nm, and an n-side AlGaAs first optical guiding layer 6a with an Al composition ratio of 0.14 and a layer thickness of 200nm, and the second conductive type side optical guiding layer 89 is composed of a p-side AlGaAs first optical guiding layer 8a with an Al composition ratio of 0.14 and a layer thickness of 200nm, and a p-side AlGaAs second optical guiding layer 9a with an Al composition ratio of 0.16 and a layer thickness of 700nm. The other layers are the same as Figure 1 same.

[0054] In the above structure, when the layer thickness d1 of the first conductive type low refractive index layer 4 is 200nm, v1 is 0.292273, and when the layer thickness d2 of the second conductive type low refractive index layer 10 is set to 40nm, v2 is 0.149202, and v2<v1 as the condition disclosed in Patent Document 1 is established. At this time, the effective refractive indexes of region I and region II and IIa are respectively calculated to be 3.41873 and 3.41810, and when the ridge width W is 100μm, v is 21.14672. As a result, 14 modes from the 0th order (basic mode) to the 13th order are allowed.

[0055] On the other hand, in the second embodiment, the parameters of each layer are set so that v2>v1 holds. As an example of v2>v1, consider the case of d2=140nm. When d2=140nm, v2 is 0.522208, so v2>v1 holds. At this time, the effective refractive indexes of region I and region II and IIa are calculated to be 3.41840 and 3.41828, respectively, and when the ridge width W is 100μm, v is 9.229082. As a result, only six modes from the 0th order (basic mode) to the 5th order are allowed. By making v2>v1, the number of modes allowed in the horizontal direction can be reduced compared to the case of v2<v1, and the divergence angle in the horizontal direction can be narrowed.

[0056] Implementation method 3.

[0057] Figure 3 is a schematic perspective view showing a stacked structure of a semiconductor laser device according to Embodiment 3. Embodiment 3 is a combination of Embodiment 2 and Embodiment 3. Figure 2The p-type cladding layer 11 in the embodiment is a p-type AlGaAs cladding layer 11a having an Al composition ratio of 0.25 and a layer thickness of 1.5 μm. According to this structure, the refractive index n of the n-type cladding layer (first conductivity type cladding layer) 3 can be made c1 The refractive index n of the p-type cladding layer (second conductivity type cladding layer) 11a is c2 High. Other layers are the same as those in Implementation 2 Figure 2 By setting the refractive index n of the first conductivity type cladding layer 3 to c1 The refractive index n of the second conductivity type cladding layer 11a is c2 The highly asymmetric structure can reduce light absorption caused by carriers in the second conductivity type cladding layer 11 a , thereby improving the slope efficiency.

[0058] When the thickness d1 of the first conductive type low refractive index layer 4 is 200 nm, v1 is 0.292273, and when the thickness d2 of the second conductive type low refractive index layer 10 is 40 nm, v2 is 0.13727, and v2<v1, which is the condition disclosed in Patent Document 1, holds. At this time, the effective refractive indexes of region I and region II and IIa are respectively calculated to be 3.41858 and 3.41810, and assuming that the ridge width W is set to 100 μm, v is 18.45816. As a result, 12 modes from the 0th order (basic mode) to the 11th order are allowed.

[0059] On the other hand, in the third embodiment, the parameters of each layer are set so that v2>v1 holds. As an example of v2>v1, consider the case of d2=140nm. When d2=140nm, v2 is 0.480463, so v2>v1 holds. At this time, the effective refractive indexes of region I and region II and IIa are calculated to be 3.41837 and 3.41828, respectively, and when the ridge width W is 100μm, v is 7.992602. As a result, only six modes from the 0th order (basic mode) to the 5th order are allowed. By making v2>v1, the number of modes allowed in the horizontal direction can be reduced compared to the case of v2<v1, and the divergence angle in the horizontal direction can be narrowed.

[0060] Implementation method 4.

[0061] Figure 4 is a schematic perspective view showing a stacked structure of a semiconductor laser device according to a fourth embodiment. Figure 1 The p-type cladding layer 11 in the embodiment is a p-type AlGaAs cladding layer 11a having an Al composition ratio of 0.25 and a layer thickness of 1.5 μm. The other layers are the same as those in the embodiment 1. As in the embodiment 3, the refractive index n of the first conductivity type cladding layer 3 is c1The refractive index n of the second conductivity type cladding layer 11a is c2 The first conductive type side optical guide layer 56 is thicker than the second conductive type side optical guide layer 89, so that the active layer position can be shifted from the center of the optical guide layer to the second conductive type cladding layer side, and the optical absorption caused by the carriers retained in the optical guide layer during operation can be reduced, thereby improving the slope efficiency.

[0062] When the thickness d1 of the first conductive type low refractive index layer 4 is 200 nm, v1 is 0.292273, and when the thickness d2 of the second conductive type low refractive index layer 10 is 40 nm, v2 is 0.137275, and v2<v1 as the condition disclosed in Patent Document 1 is established. At this time, the effective refractive indexes of region I and region II and IIa are respectively calculated to be 3.41704 and 3.41600, and assuming that the ridge width W is set to 100 μm, v is 27.16245. As a result, 18 modes from the 0th order (basic mode) to the 17th order are allowed.

[0063] On the other hand, in the present embodiment 4, the parameters of each layer are set so that v2>v1 holds. As an example of v2>v1, consider the case of d2=140nm. When d2=140nm, v2 is 0.480463, so v2>v1 holds. At this time, the effective refractive indexes of region I and regions II and IIa are calculated to be 3.41659 and 3.41637 respectively, and when the ridge width W is 100μm, v is 12.49284. As a result, only 8 modes from the 0th order (basic mode) to the 7th order are allowed. By making v2>v1, the number of modes allowed in the horizontal direction can be reduced compared to the case of v2<v1, and the divergence angle in the horizontal direction can be narrowed.

[0064] Implementation method 5.

[0065] Figure 51 is a schematic perspective view showing a stacked structure of a semiconductor laser device according to Embodiment 5. Embodiment 5 is an example in which the second conductive type low refractive index layer 10 and the first conductive type low refractive index layer 4 are respectively arranged in the second conductive type cladding layer 11 and the first conductive type cladding layer 3. In the figure, the n-type AlGaAs cladding layer 3 having an Al composition ratio of 0.20 is composed of an n-type AlGaAs second cladding layer 3b having a layer thickness of 1.4 μm and an n-type AlGaAs first cladding layer 3a having a layer thickness of 0.1 μm, and the n-type low refractive index layer 4 is arranged between the n-type AlGaAs second cladding layer 3b and the n-type AlGaAs first cladding layer 3a. In addition, the p-type AlGaAs cladding layer 11 having an Al composition ratio of 0.20 is formed by a p-type AlGaAs first cladding layer 11b having a layer thickness of 0.1 μm and a p-type AlGaAs second cladding layer 11c having a layer thickness of 1.4 μm, and the second conductive type low refractive index layer 10 is disposed between the p-type AlGaAs first cladding layer 11b and the p-type AlGaAs second cladding layer 11c. The rest is the same as in the second embodiment.

[0066] When the thickness d1 of the first conductive type low refractive index layer 4 is 200 nm, v1 is 0.292273, and when the thickness d2 of the second conductive type low refractive index layer 10 is 40 nm, v2 is 0.149202, and v2<v1, which is the condition disclosed in Patent Document 1, holds. At this time, the effective refractive indexes of region I and region II and IIa are respectively calculated to be 3.41906 and 3.41867, and when the ridge width W is 100 μm, v is 16.63924. As a result, 11 modes from the 0th order (basic mode) to the 10th order are allowed.

[0067] On the other hand, in the fifth embodiment, the parameters of each layer are set so that v2>v1 holds. As an example of v2>v1, consider the case of d2=140nm. When d2=140nm, v2 is 0.522208, so v2>v1 holds. At this time, the effective refractive indexes of region I and regions II and IIa are calculated to be 3.41886 and 3.41878, respectively, and when the ridge width W is 100μm, v is 7.536043. As a result, only five modes from the 0th order (basic mode) to the 4th order are allowed. By making v2>v1, the number of modes allowed in the horizontal direction can be reduced compared to the case of v2<v1, and the divergence angle in the horizontal direction can be narrowed.

[0068] Implementation method 6.

[0069] Figure 61 is a schematic perspective view showing the stacked structure of a semiconductor laser device according to Embodiment 6. Embodiment 6 is an embodiment in which the p-type AlGaAs low refractive index layer 10 outside the ridge region I is removed when forming the ridge, and the etching is stopped at the p-type AlGaAs first cladding layer 11b. That is, the p-type low refractive index layer (second conductive type low refractive index layer) 10 is formed only in the ridge region I. Other features are similar to those of Embodiment 5. Figure 5 same.

[0070] When the thickness d1 of the first conductive type low refractive index layer 4 is 200 nm, v1 is 0.292273, and when the thickness d2 of the second conductive type low refractive index layer 10 is 40 nm, v2 is 0.149202, and v2<v1, which is the condition disclosed in Patent Document 1, holds. At this time, the effective refractive indexes of region I and region II and IIa are respectively calculated to be 3.41906 and 3.41857, and when the ridge width W is 100 μm, v is 18.65074. As a result, 12 modes from the 0th order (basic mode) to the 11th order are allowed.

[0071] On the other hand, in the sixth embodiment, the parameters of each layer are set so that v2>v1 holds. As an example of v2>v1, consider the case of d2=140nm. When d2=140nm, v2 is 0.522208, so v2>v1 holds. At this time, the effective refractive indexes of region I and regions II and IIa are calculated to be 3.41886 and 3.41857, respectively, and when the ridge width W is 100μm, v is 14.34798. As a result, only 10 modes from the 0th order (basic mode) to the 9th order are allowed. By making v2>v1, the number of modes allowed in the horizontal direction can be reduced compared to the case of v2<v1, and the divergence angle in the horizontal direction can be narrowed.

[0072] In the above-mentioned embodiments, the example of changing the thickness of the p-type low refractive index layer, i.e., the second conductive type low refractive index layer, so that v2>v1 is established is described, but not only changing the thickness but also changing the refractive index, or changing both the thickness and the refractive index, can make v2>v1 established, and the effects described in the embodiments can be achieved. That is, the thickness and refractive index of the n-type low refractive index layer and the p-type low refractive index layer, i.e., the first conductive type low refractive index layer and the second conductive type low refractive index layer, and the refractive index of the first conductive type cladding layer and the second conductive type cladding layer can be set in a manner that satisfies formula (4).

[0073] In the above embodiments, a semiconductor laser with an oscillation wavelength of 975 nm is used as an example, but it is not limited to this wavelength. For example, GaN series with a wavelength of 400 nm, GaInP series with a wavelength of 600 nm, and InGaAsP series with a wavelength of 1550 nm can all achieve the same effect.

[0074] Although various illustrative embodiments and examples are described in this application, the various features, forms, and functions described in one or more embodiments are not limited to the application of a specific embodiment, and can be applied to the embodiment alone or in various combinations. Therefore, countless unillustrated variations can be imagined within the technical scope disclosed in the specification of this application. For example, it includes the case where at least one constituent element is deformed, added, or omitted, and also includes the case where at least one constituent element is extracted and combined with constituent elements of other embodiments.

[0075] Description of Reference Numerals

[0076] 2...semiconductor substrate; 3...first conductive type cladding layer; 4...first conductive type low refractive index layer; 56...first conductive type side light guiding layer; 7...active layer; 89...second conductive type side light guiding layer; 10...second conductive type low refractive index layer; 11...second conductive type cladding layer; I...ridge region; II, IIa...cladding region.

Claims

1. A semiconductor laser device, characterized in that: On the first conductivity type semiconductor substrate, layers having a refractive index of n are sequentially stacked c1 a first conductive type cladding layer, an undoped first conductive type side light guiding layer, an active layer, an undoped second conductive type side light guiding layer, and a refractive index of n c2 The second conductive type cladding layer is formed to form a resonator that reciprocates the laser light, and the oscillation wavelength is λ. A structure that allows higher-order modes of the first order or higher in the stacking direction in a cross section perpendicular to the optical axis direction of the resonator, A ridge shape having a ridge region and cladding regions on both sides of the ridge region in a direction perpendicular to the optical axis direction of the resonator and the stacking direction, and a large-area structure that allows high-order modes of the first order or higher, Between the first conductive type side light guiding layer and the first conductive type cladding layer, or in the first conductive type cladding layer, there is a layer with a thickness of d1 and a refractive index greater than that of the first conductive type side light guiding layer. c1 A first conductive type low refractive index layer having a lower n1, and between the second conductive type side light guiding layer and the second conductive type cladding layer, or in the second conductive type cladding layer, having a thickness d2 and a refractive index lower than the n1. c2 The second conductivity type low refractive index layer has a low n2 and satisfies the following formula:

2. The semiconductor laser device according to claim 1, wherein The layer thickness of the first conductivity type side light guiding layer is thicker than the layer thickness of the second conductivity type side light guiding layer.

3. The semiconductor laser device according to claim 1 or 2, characterized in that: The c1 Than the n c2 high.

4. The semiconductor laser device according to claim 1 or 2, characterized in that: The second conductive type low refractive index layer is formed only in the ridge region.

5. The semiconductor laser device according to claim 3, wherein: The second conductive type low refractive index layer is formed only in the ridge region.

Images