JP2006108641A - Semiconductor laser and semiconductor laser gyro using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser with a new structure suited for a semiconductor laser gyro, and to provide a semiconductor laser gyro capable of detecting rotations more accurately and simply than conventional gyros using the semiconductor laser by using the semiconductor laser. <P>SOLUTION: A semiconductor laser is capable of emitting a first and second laser beams, and is provided with an active layer 24 and a first and second electrodes for injecting carriers to the active layer 24. The first laser beam 35 is a part of the emitted beam (L1) rounding on a polygonal path in the active layer 24. The second laser beam 36 is a part of the emitted beam (L2) rounding on the path in the reverse direction of the laser beam (L1). The active layer 24 includes at least one layer of semiconductor layer (A). The semiconductor layer (A) comprises a plurality of quantum dots comprising a first semiconductor, and a cover layer comprising a second semiconductor different from the first semiconductor and formed in such a manner as to cover the quantum dots. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser and a semiconductor laser gyro using the same.

  Among the gyros for detecting the angular velocity of the rotating object, the optical gyro has a feature of high accuracy. In the optical gyro, the angular velocity is detected using a frequency difference between two laser beams traveling in opposite directions along an annular optical path. As such an optical gyro, an optical gyro using a rare gas laser has been proposed (see, for example, Patent Document 1). In these optical gyros, laser beams that circulate in the opposite directions on the same path are extracted to form interference fringes. A general configuration of these optical gyros is shown in FIG. In the optical gyro of FIG. 17, the interference fringes are expressed by the following formula (1).

Here, I ₀ is the light intensity of the laser light, and λ is the wavelength of the laser light. Further, ε is an angle shown in FIG. 17, and χ is a coordinate in the X direction shown in FIG. Δω is a frequency difference between a clockwise mode and a counterclockwise mode when the gyro is rotated, and t is a time. Δω is proportional to the angular velocity Ω of the gyro rotation. That is, Δω = 4 AΩ / (Lλ). Here, A is an area surrounded by a ring shape, and L is an optical path length. φ indicates the initial phase difference between the two laser beams. In this gyro, the rotational speed and direction of the gyro are detected by detecting the movement speed and direction of the interference fringes. However, an optical gyro using a rare gas laser has a problem that a high voltage is required for driving and power consumption is large, and a problem that the apparatus is large and weak against heat.

As a gyro for solving such a problem, a gyro using a semiconductor ring laser having an annular (for example, a square annular) waveguide has been proposed (see, for example, Patent Document 2). The semiconductor laser used in this gyro has an annular waveguide having a substantially constant width. Then, two laser beams that circulate in the opposite directions in the annular waveguide are extracted to detect the interference fringes. However, since the laser beam confined using a thin waveguide spreads greatly when emitted to the outside of the waveguide, it is difficult to actually detect the interference fringes with high accuracy. Therefore, in a gyro using a semiconductor laser, a gyro for detecting a beat frequency corresponding to a frequency difference between two laser beams from a voltage change between two electrodes of the semiconductor laser (see, for example, Patent Document 3), or an end face of a resonator A gyro (see, for example, Patent Document 4) that detects beat frequency using evanescent light that oozes out is generally used.
Japanese Patent Laid-Open No. 11-351881 JP 2000-230831 A JP-A-4-174317 JP 2000-121367 A

  However, a gyro that detects the beat frequency requires a special device for detecting the rotational direction. Further, since the conventional semiconductor laser generates a large amount of heat, it is necessary to cool it with a Peltier element or the like in order to stably oscillate continuously.

  In view of such circumstances, an object of the present invention is to provide a semiconductor laser having a novel structure suitable for a semiconductor laser gyro. Another object of the present invention is to provide a semiconductor laser gyro capable of detecting rotation more accurately and easily than a conventional gyro using a semiconductor laser.

  The present inventors have found that a special laser beam can be excited by a semiconductor laser having a special structure. In this semiconductor laser, two laser beams traveling in opposite directions along the rhombus path are excited. These two laser beams are emitted from the semiconductor laser to the outside in a well-collimated state, and form clear interference fringes. The present invention is based on this new knowledge. Furthermore, in the semiconductor laser of the present invention, the quantum dots are applied to the active layer to suppress heat generation.

  The semiconductor laser of the present invention is a semiconductor laser capable of emitting first and second laser beams, and includes a substrate, an active layer formed on the substrate, and a first for injecting carriers into the active layer. The first laser beam is a laser beam from which a part of the laser beam (L1) that circulates on a polygonal path in the active layer is emitted; The laser beam 2 is a laser beam emitted from a part of the laser beam (L2) that circulates in the direction opposite to the laser beam (L1) on the path, and the active layer includes at least one layer. The semiconductor layer (A) includes a plurality of quantum dots made of a first semiconductor and a second semiconductor different from the first semiconductor and is formed so as to cover the quantum dots. Cover layer.

  The semiconductor laser gyro of the present invention is a semiconductor laser gyro comprising a semiconductor laser that emits first and second laser beams and a photodetector, and the photodetector includes the first and second lasers. The semiconductor laser is disposed at a position where interference fringes are formed by laser light, and the semiconductor laser is the semiconductor laser of the present invention.

  According to the present invention, a semiconductor laser having a low threshold current and suitable for a semiconductor laser gyro can be obtained. From this semiconductor laser, two laser beams traveling in opposite directions along an annular optical path are emitted in a well-collimated state. Further, in this semiconductor laser, the deterioration of the laser beam at the emission end face is small. Therefore, in the semiconductor laser gyro of the present invention using the semiconductor laser of the present invention, clear interference fringes are formed by the two laser beams, and the rotational speed (angular speed) can be detected with high accuracy. In addition, the semiconductor laser of the present invention generates less heat because quantum dots are applied to the active layer. Therefore, the semiconductor laser gyro of the present invention can continuously oscillate without being cooled by a Peltier element or the like. In addition, since the semiconductor laser of the present invention has a small thermal expansion of the element and a constant optical path length, stable laser light without frequency fluctuation can be obtained.

  Further, according to the gyro of the present invention, the rotation speed and the rotation direction can be easily calculated by observing the movement of the interference fringes with two or more light receiving elements. For these detections, a circuit similar to a circuit used in a conventional optical gyro using a rare gas laser can be applied. Therefore, the gyro of the present invention can be easily applied to various devices.

  Hereinafter, embodiments of the present invention will be described. A semiconductor laser and a semiconductor laser gyro (semiconductor laser gyro element) described below are examples of the present invention, and the present invention is not limited to the following description. Moreover, in the following description, the same code | symbol may be attached | subjected to the same part and the overlapping description may be abbreviate | omitted.

  The semiconductor laser of the present invention is a semiconductor laser capable of emitting first and second laser beams, and includes a substrate, an active layer formed on the substrate, and first and second carriers for injecting carriers into the active layer. A second electrode. The first laser beam is a laser beam emitted from a part of the laser beam (L1) that circulates on the polygonal path in the active layer, and the second laser beam is a laser beam ( L1) is a laser beam emitted from a part of the laser beam (L2) that circulates in the opposite direction. The active layer includes at least one semiconductor layer (A), and the semiconductor layer (A) includes a plurality of quantum dots made of a first semiconductor and a quantum made of a second semiconductor different from the first semiconductor. And a cover layer formed to cover the dots.

  The planar shape of the active layer is a shape that encloses the polygon so that the corner of the polygonal path is located at the outer edge. When current is injected into the active layer, light is generated. This light is reflected by the end face of the active layer and causes stimulated emission. Then, laser light (L1 and L2) that circulates a specific path stably is excited according to the planar shape of the active layer. That is, the active layer functions as a resonator (cavity). The end face of the active layer that functions as a resonator is formed so that the generated light circulates in a predetermined path. For example, when exciting laser light that circulates a rhombus path, end faces (side surfaces) are formed in the active layer at positions corresponding to the four corners of the path (virtual rhombus). The clad layer disposed so as to sandwich the active layer is usually a uniform layer, and a waveguide having a certain width corresponding to the above path is not formed. The shape of the polygonal path can be changed according to the shape of the active layer. A preferable shape of the polygonal path is a rhombus, but may be another quadrangle or a triangle.

(Semiconductor laser)
First, the semiconductor laser of the present invention will be described.

  The quantum dots arranged in the active layer are fine particles made of the first semiconductor. The average size of the quantum dots is usually in the range of 10 nm to 100 nm in diameter and 2 nm to 20 nm in height. The active layer preferably has a structure in which 1 to 50 sets (for example, 2 to 10 sets) of a set of a semiconductor layer including quantum dots and a barrier layer are stacked. The active layer may include 10 to 20 semiconductor layers including quantum dots.

  In order to facilitate the self-formation of quantum dots, the amount of lattice mismatch (distortion) between the first semiconductor forming the quantum dots and the substrate is the underlying layer (the layer on which the quantum dots are formed) It is preferable that the amount of lattice mismatch between the substrate and the substrate is larger. For example, when the substrate and the underlayer are GaAs, InAs or InGaAs can be applied as the first semiconductor. The amount of lattice mismatch between the cover layer covering the quantum dots and the substrate is preferably smaller than the amount of lattice mismatch between the first semiconductor and the substrate.

  Usually, the band gap of the first semiconductor forming the quantum dots is smaller than the band gap of the second semiconductor forming the cover layer.

  In the semiconductor laser of the present invention, the first semiconductor is a III-V group compound semiconductor containing In and As, and the second semiconductor is a III-V group compound semiconductor containing Ga, As, and Sb. Is preferred. For example, InAs or InGaAs can be used as the first semiconductor, and InGaAsSb can be used as the second semiconductor. By adding Sb to the cover layer, the surface flatness of the cover layer can be improved, and the crystallinity of the semiconductor layer formed thereon can be improved.

  The proportion of Sb in the V-group element of the second semiconductor is preferably in the range of 0.2 atomic% to 10 atomic% (more preferably 1 atomic% to 5 atomic%). By setting the ratio of Sb in the range of 0.2 atomic% to 10 atomic%, a flat effect can be obtained. On the other hand, when the proportion of Sb exceeds 10 atomic%, dislocations are formed and crystallinity may be deteriorated.

  The semiconductor laser of the present invention may include a semiconductor layer (B) formed on the substrate side of the semiconductor layer (A) so as to be adjacent to the semiconductor layer (A). The semiconductor layer (B) is made of a III-V group compound semiconductor containing Sb. The semiconductor layer (B) is, for example, GaAsSb or InGaAsSb. The Sb content of the semiconductor layer (B) is higher than the Sb content of the first semiconductor constituting the quantum dots. The quantum dots grow on the semiconductor layer (B). By growing quantum dots on the semiconductor layer (B) having a high Sb content, a semiconductor laser that is easily oscillated can be obtained.

  In the group III-V compound semiconductor constituting the semiconductor layer (B), the proportion of Sb in the group V element is in the range of 0.2 atomic% to 100 atomic% (more preferably 1 atomic% to 10 atomic%). Preferably there is.

  The semiconductor laser of the present invention may include a semiconductor layer (C) having a thickness of 20 atomic layers or less, disposed between the semiconductor layer (A) and the semiconductor layer (B). The semiconductor layer (C) is made of a III-V group compound semiconductor containing Ga and As, for example, GaAs.

  The semiconductor laser of the present invention may usually include a semiconductor layer (D) formed on the semiconductor layer (A) so as to be adjacent to the semiconductor layer (A). The band gap of the semiconductor layer (D) is larger than the band gap of the second semiconductor. The semiconductor layer (D) functions as a barrier layer. The semiconductor layer (D) may be composed of a plurality of layers.

At least a part of the semiconductor layer (D) may be doped or p-type doped. By performing p-type modulation doping on the barrier layer, sufficient holes are supplied to the ground level on the valence band side of the quantum dot, so that the quantum dot laser easily oscillates at the ground level. That is, low threshold oscillation is possible. When p-type modulation doping is performed on the semiconductor layer (D), the doping concentration is preferably in the range of 1 × 10 ^{17 to} 5 × 10 ¹⁹ cm ⁻² .

  The active layer of the semiconductor laser preferably has a planar shape that is not annular. Since the laser light confined in the narrow waveguide formed in an annular shape spreads when emitted, clear interference fringes are not formed. For this reason, the planar shape of the active layer is preferably not substantially annular (for example, polygonal annular). In this case, carriers can be injected into the active layer, and a laser beam in a specific mode using the active layer spreading in the two-dimensional direction as a resonator, specifically, a laser beam circulating in the active layer can be obtained. Laser light emitted from such an active layer is well collimated, and the half-value width of the laser light intensity can be set to 10 ° or less (for example, 5 ° or less). Even when the through hole is formed near the center of the active layer, it may be an active layer that is not substantially annular, that is, an active layer in which a waveguide having a substantially constant width is not formed in an annular shape. In this specification, the “planar shape” means a shape shown in FIG. 3, that is, a shape perpendicular to the stacking direction of the semiconductor layers.

  The polygonal path is a rhombus path, and the active layer preferably has first to fourth end faces formed at positions corresponding to the first to fourth corners of the rhombus path. That is, the first to fourth corners of the rhombic path are located on the first to fourth end faces, respectively. In this case, by injecting carriers into the active layer, laser light that circulates on the rhombus is excited. That is, the laser beam (L1) is a laser beam that circulates on the rhombus path, and the laser beam (L2) is a laser beam that circulates on the rhombus path in a direction opposite to the laser beam (L1). It is.

  It is preferable that at least one electrode selected from the first and second electrodes and the semiconductor layer constituting the semiconductor laser are in contact with each other along the rhombic path (polygonal path). Current is injected through the contact area. According to this configuration, carriers can be injected into the rhomboid path portion of the active layer, and two laser beams (L1 and L2) that circulate on the rhombus path are easily excited. In a typical example, the at least one electrode contacts the semiconductor layer so as to substantially correspond to a diamond-shaped path (polygonal path). In these cases, the at least one electrode and the semiconductor layer may be in annular contact. In this specification, the phrase “so as to substantially correspond to the rhombus route” means 50% or more (preferably 70% or more) of the rhombus route in addition to the case of completely corresponding to the rhombus route. And more preferably 90% or more). Further, “in contact with the ring” means that the contacted region may substantially form a ring and does not have to be a completely continuous ring. In addition, the area of the region corresponding to the rhombus path is usually 50% or less, for example, 30% or less, with respect to the area of the planar shape of the active layer.

  At least one electrode selected from the first and second electrodes may include a first portion that injects a current that generates a gain, and a second portion that injects less current than the first portion. . In the first part, a current necessary for laser oscillation is injected. By injecting a weak current into the second portion so as not to generate a gain, the laser light traveling in a direction other than the rhombus optical path can be attenuated.

  The interior angles of the first and second corners facing each other in the rhombus path are smaller than the interior angles of the third and fourth corners, and both the first and second laser beams are the first corners. It is preferable that the light is emitted from the first end face formed at a position corresponding to. More specifically, the first and second laser beams are preferably emitted from one end in the longitudinal direction of the active layer functioning as a cavity. The diagonal line connecting the first corner and the second corner is not parallel to the first and second lasers.

  The active layer preferably satisfies the condition that the laser beam (L1) and the laser beam (L2) are totally reflected at the third and fourth end faces. Although the first to fourth end surfaces function as mirror surfaces, the laser oscillation threshold can be lowered by totally reflecting the laser light at the third and fourth end surfaces. In order to totally reflect the laser light on the third and fourth end faces, the angle formed by the third and fourth end faces and the laser light (L1 and L2) incident thereon is set to an angle equal to or less than a certain angle. Good. The angle required for total reflection is easily derived from the wavelength of the laser light and the refractive index of the active layer. The angle formed by the end face of the active layer and the laser beam can be adjusted by changing the shape of the rhombic path, that is, by changing the planar shape of the active layer. The preferred shape varies depending on the wavelength of the laser light and the material of the active layer, but the distance between the first corner and the second corner (the length of the longer diagonal of the rhombus), the third corner and the second corner The ratio of the distance connecting the four corners (the length of the shorter diagonal of the rhombus) is, for example, in the range of 600: 190 to 600: 30. Although the first end surface is a mirror surface, mirror coating treatment or the like is usually not performed so that a part of the laser light circulating in the active layer is emitted to the outside. Note that the first end face may be processed so that the laser light is easily emitted to the outside. Moreover, it is preferable that the end surface of the active layer in the second corner is mirror coated.

  The first end surface of the active layer is preferably a curved surface. In particular, it is preferable that each of the first and second end surfaces is an outwardly convex curved surface. According to this configuration, it is possible to stably generate the laser light that goes around the rhombus path, and to stably emit the first and second laser lights from the first end face. Each of the two outwardly convex curved surfaces is preferably a part of a cylinder having a center on a diagonal line connecting the first and second corners of the rhombus path. Note that at least one selected from the first and second end faces may be a flat surface or a curved surface convex inward.

  The radius of the cylinder, that is, the radius of curvature R1 of the first end face and the radius of curvature R2 of the second end face are both equal to or greater than the distance L between the first corner and the second corner. Also good. According to this configuration, it is possible to stably excite the laser beams (L1 and L2) that go around the rhombus optical path. The upper limit of R1 and R2 is not particularly limited, but is, for example, not more than twice the distance L.

  The active layer preferably includes a first region including a rhombic path and a second region adjacent to the first region. In this case, the planar shape of the first region is preferably a substantially rectangular shape, and more specifically, a shape in which the short side of the rectangle is a curved surface convex outward. In this configuration, laser light that travels along the rhombic optical path using the first region as a resonator is excited. Further, according to this configuration, the laser light traveling in a direction other than the rhombus path can be attenuated by the second region.

  The planar shape of the active layer constituted by the first region and the second region is preferably substantially H-shaped (more specifically, a shape obtained by extending H laterally) (see FIG. 3). In this case, four second regions are adjacent to the first region. In this case, the length Ls (μm) of the second region in the direction parallel to the diagonal line connecting the first corner and the second corner, and the distance between the first corner and the second corner L (μm) preferably satisfies L / 4 <Ls. Also, the length Ws (see FIG. 3) of the second region in the direction parallel to the diagonal line connecting the third corner and the fourth corner is, for example, the third corner and the fourth corner. 1 to 3 times the distance W connecting the two.

  There is no particular limitation on the semiconductor and the laminated structure that constitute the semiconductor laser of the present invention, and the semiconductor laser is selected according to the wavelength of the laser beam to be used. The wavelength of the laser beam emitted from the semiconductor laser of the present invention is not particularly limited, but the shorter angular wavelength can detect the angular velocity of rotation with higher accuracy. The wavelength of the laser beam is, for example, in the range of 300 to 1700 nm, preferably 1550 nm or less, and particularly preferably 900 nm or less. An example of the material of the semiconductor layer is, for example, a III-V compound semiconductor.

  Hereinafter, a preferred example of the semiconductor laser used in the present invention will be described. A perspective view of an example of a semiconductor laser is shown in FIG. 1, and a cross-sectional view taken along line II in FIG. 1 is shown in FIG. In FIG. 2, hatching other than the insulating layer 12 is omitted. Note that the drawings used for explaining the present invention are schematic, and the scale of each part is changed for easy understanding.

  1 includes a substrate 11, a semiconductor layer 20 formed on the substrate 11, an insulating layer 12 and a first electrode 13 formed on the semiconductor layer 20, and the entire back surface of the substrate 11. And a second electrode 14 formed on the substrate.

  Referring to FIG. 2, the semiconductor layer 20 is laminated in order from the substrate 11 side, and includes a buffer layer 21, a cladding layer 22, a light confinement layer 23, an active layer 24, a light confinement layer 25, a cladding layer 26, and a contact layer 27. including. On the contact layer 27, a patterned insulating layer 12 is formed. A first electrode 13 is formed on the insulating layer 12. Since the insulating layer 12 has a through hole, the first electrode 13 and the contact layer 27 are in contact with each other in the region 31 in which the through hole is formed. Laser light is confined in the active layer 24 by the clad layer 22, the optical confinement layer 23, the optical confinement layer 25, and the clad layer 26.

  3 and 4 show a planar shape when the active layer 24 of the semiconductor laser 10 is viewed from above. In FIG. 4, a region 31 where the first electrode 13 and the semiconductor layer 20 (contact layer 27) are in contact with each other is indicated by hatching. The semiconductor layer 20 has the same planar shape as the active layer 24.

  Referring to FIG. 3, the active layer 24 is a thin film formed in a planar shape including a rhombic path 32. Of the first to fourth corners 32a to 32d of the path 32, the first and second corners 32a and 32b are smaller in angle than the third and fourth corners 32c and 32d. The active layer 24 has first to fourth end surfaces (mirror surfaces) 24a to 24d arranged so as to include corner portions 32a to 32d. The first and second end faces 24a and 24b are curved surfaces that protrude outward. The third and fourth end faces 24c and 24d are flat planes.

  The active layer 24 includes a first region 24f and four second regions 24s adjacent to the first region. The planar shape of the first region 24f is a shape in which the short side of the rectangle is a curved surface protruding outward. The path 32 is formed in the first region 24f. The active layer 24 constituted by the first region 24f and the second region 24s has a substantially H-shape (more specifically, a shape obtained by horizontally extending the H-shape).

  Referring to FIG. 4, the region 31 where the first electrode 13 and the insulating layer 12 are in contact is formed in a substantially diamond shape so as to correspond to the path 32. The reason why the region 31 does not completely correspond to the path 32 is that when the through hole is formed in the insulating layer 12, there is a limitation in the manufacturing process. Although it is possible to form the region 31 in a diamond shape by a known method so as to completely correspond to the path 32, the manufacturing process becomes complicated.

  When a voltage is applied between the first electrode 13 and the second electrode 14 to inject carriers into the active layer 24, light is emitted from the active layer 24. Since this light is confined by the optical confinement layer and the clad layer, it moves in the active layer 24. Among such lights, the light traveling on the path 32 causes stimulated emission while being reflected by the end faces 24a to 24d. For this reason, the laser beam L1 which goes around the path 32 as an optical path is generated. Similarly, a laser beam L2 that circulates in a direction opposite to the laser beam L1 using the path 32 as an optical path is generated. Part of the laser beams L1 and L2 is emitted from the first corner portion 32a of the first end face 24a, and becomes the first and second laser beams 35 and 36 (see FIG. 4).

  In order to reduce the loss of the laser beams L1 and L2, the end surface 24b is mirror-coated with a dielectric multilayer film. The distance L (see FIG. 3) between the first corner 32a and the second corner 32b is 600 μm, and the distance W between the third corner 32c and the fourth corner 32d is 60 μm. It is. In the semiconductor laser 10, the laser beams (L1 and L2) are totally reflected at the end faces 24c and 24d.

  The four second regions 24s are formed in order to suppress a mode generated by the multiple reflection of the laser light generated in the first region 24f on the end surfaces 24c and 24d. In the semiconductor laser 10, the length Ls (see FIG. 3) of the second region 24s in the direction parallel to the diagonal line 32ab connecting the first corner portion 32a and the second corner portion 32b is 160 μm. On the other hand, L / 4 is 150 μm, and since L / 4 <Ls is satisfied, the above mode is particularly suppressed. The length Ws of the second region 24s in the direction of the diagonal line 32cd connecting the third corner portion 32c and the fourth corner portion 32d is 70 μm.

  The shapes of the end faces 24a and 24b are each a partial shape of a cylindrical curved surface. Specifically, it has the same shape as a part of a curved surface of a cylinder on the diagonal line 32ab and having a central axis perpendicular to the surface of the active layer 24. The radius of the cylinder, that is, the curvature radius R1 (see FIG. 3) of the end face 24a is 600 μm, and the curvature radius R2 (not shown) of the end face 24b is also 600 μm. The semiconductor laser 10 has a line-symmetric shape with respect to the diagonal line 32ab and the diagonal line 32cd, and the end face 24b is line-symmetric with the end face 24a with respect to the diagonal line 32cd connecting the third corner part 32c and the fourth corner part 32d. It is the shape. However, the semiconductor laser of the present invention does not necessarily have a line-symmetric shape. For example, the end surface 24b may be a curved surface having a different curvature from the end surface 24a, a flat surface, or a curved surface convex inward. It may be.

  The stacked structure of the active layer 24 will be described with reference to FIG. The active layer 24 includes three semiconductor layers (semiconductor layers (A)) 51 and three barrier layers (semiconductor layers (D)) 52 that are alternately stacked. The semiconductor layer 51 includes a plurality of quantum dots 51a and a cover layer 51b formed so as to cover the quantum dots. The barrier layer 52 is a layer for efficiently confining electrons, and is formed of a material having the same band gap as that of the cover layer 51b or larger than that of the cover layer 51b. Note that the cover layer 51b and the barrier layer 52 may be formed of the same material.

  In the active layer 24 of FIG. 5, the flatness of the surface of the cover layer can be improved by adding Sb to the cover layer 51b containing Ga and As (and In). Thereby, when forming a laminated film including a plurality of semiconductor layers 51, the upper semiconductor layer 51 and the barrier layer 52 can be formed without being affected by the quantum dots grown in the lower layer. As a result, the size of the quantum dots included in each semiconductor layer 51 can be made uniform.

However, when the composition ratio of Sb in the cover layer is too high, dislocation occurs, so that the crystallinity of the semiconductor layer 51 deteriorates. In order to examine the influence of the composition ratio of Sb, the relationship between the composition ratio of Sb occupying the group V elements of the cover layer and the half width of the photoluminescence (PL) peak of the active layer 24 was determined by experiments. At this time, as the active layer 24, active layers shown in Table 1 below (the ratio of Sb is different) were grown. In the experiment, in Rezaepi structure of Table 1, were compared _{Ga 0.85 In 0.15 As 1-y} Sb y cover layer is epitaxial growth six changing the Sb composition of PL. In the growth, the conditions other than the Sb flux are all the same as those of the manufacturing example described later, and the Sb flux is changed in the range of 0 to 2.0 × 10 ⁻⁴ Pa (0 to 1.5 × 10 ⁻⁶ Torr). did. The experimental results are shown in FIG. As shown in FIG. 6, the ratio of Sb in the group V element is preferably in the range of 0.2 atomic% to 10 atomic%, and more preferably in the range of 1 atomic% to 5 atomic%.

  An example of the configuration of each layer of the substrate 11 and the semiconductor layer 20 is shown in Table 1. As shown in FIG. 5, the active layer 24 has a structure in which three sets of a cover layer including quantum dots and a barrier layer are stacked. According to this configuration, 1 μm band laser light is emitted.

The insulating layer 12 can be formed of Si ₃ N ₄ or SiO ₂ . The first electrodes 13 and 14 can be formed of a known electrode material. For example, a Ni / Ge / Au laminated film or a Ti / Pt / Au laminated film can be used. In addition, each layer which comprises the 1st electrode 13 and the 2nd electrode 14 may be alloyed by heat processing. Moreover, the structure shown in Table 1 is an example, and is suitably changed according to the characteristic calculated | required by the semiconductor laser.

  The first electrode 13 of the semiconductor laser 10 may include a first portion 13a that injects a current that generates a gain, and a second portion 13b that injects a smaller current than the first portion 13a. . FIG. 7 shows the relationship between the shape of a region where such an electrode and the semiconductor layer 20 (contact layer 27) are in contact, the planar shape of the active layer 24, and the path 32. In FIG. 7, a region 31 a where the first portion 13 a is in contact with the contact layer 27 and a region 31 b where the second portion 13 b is in contact with the contact layer 27 are indicated by hatching. The region 31a is formed at a position corresponding to one side of the path 32, and the region 31b is formed at a position corresponding to the other three sides. Such an electrode can be easily formed by changing the shape of the insulating layer 12.

  In the semiconductor laser 10, single mode oscillation starts when the injected current exceeds the threshold current. As the injected current further increases from the threshold current, the oscillation mode changes in the order of single mode, twin mode, and rocking mode. In the single mode, as shown in FIG. 4, the first and second laser beams 35 and 36 are emitted. In the twin mode, two laser beams are periodically and alternately emitted. In the rocking mode, only one of the two laser beams is emitted. Therefore, when used in a semiconductor laser gyro, the semiconductor laser 10 is normally operated in a single mode. Note that the gyro of the present invention may be provided with a special function by utilizing the fact that the oscillation mode can be changed by the injected current.

When quantum dots are not used in the active layer, the threshold current density is about 500 A / cm ² . Therefore, in the case of a laser with L = 600 μm, the threshold current during the room temperature pulse operation is about 180 mA. When the thermal resistance of the device during CW driving is Rth [K / W], the injection current is I [A], the operating voltage is V [V], and the light output from the laser end face is P [W], the temperature of the active layer The increase ΔT can be described by the following equation.
ΔT = Rth (IV−P)

  Here, in the 850 nm band laser, assuming that Rth = 80 K / W and the threshold voltage is 2 V, the temperature rise of the active layer at the threshold is about 30 K. In this case, even when the element is mounted on the heat sink and the temperature of the heat sink is always kept at 25 ° C. by the Peltier element, the active layer becomes 55 ° C. When the heat sink is not cooled, heat dissipation from the active layer is not smoothly performed, so that CW oscillation becomes difficult.

On the other hand, in the semiconductor laser of the present invention, since the quantum dots are used in the active layer, the threshold current density can be reduced to about 1/10. In the active layer 24 shown in Table 1, the threshold current density can be reduced to 50 A / cm ^2, and a low value of 18 mA is obtained as the threshold current. As a result, the temperature rise of the active layer can be reduced to 3K, and CW oscillation can be sufficiently performed in a Peltier-free manner. Thus, in the semiconductor laser of the present invention, the use of quantum dots in the active layer can eliminate the need for a Peltier device, and can realize an ultra-small and inexpensive laser gyro.

(Semiconductor laser gyro)
The gyro of the present invention includes a semiconductor laser that emits first and second laser light, and a photodetector that is disposed at a position where an interference fringe is formed by the first and second laser light. The semiconductor laser of the present invention is used for the semiconductor laser. The photodetector is not particularly limited as long as it can detect the movement of interference fringes, and usually a semiconductor light receiving element such as a photodiode or a phototransistor is used. The photodetector outputs a signal corresponding to the intensity of the interference fringes. When the interference fringe moves, the amount of light input to the photodetector changes periodically, so that the movement speed of the interference fringe can be calculated.

  The photodetector may be a two-channel photodetector including a plurality of light receiving elements. By arranging two or more light receiving elements in the moving direction of the interference fringes, the moving direction of the interference fringes can be detected in addition to the moving speed of the interference fringes. By detecting the moving speed and moving direction of the interference fringes, the rotating direction and rotating speed of the semiconductor laser gyro can be calculated.

  In the gyro of the present invention, the semiconductor laser and the light receiving element (photodetector) may be formed monolithically. In this case, the semiconductor laser and the photodetector (for example, a photodiode) may have the same stacked structure. In this configuration, the semiconductor laser and the photodetector can be simultaneously formed by a series of processes for manufacturing a semiconductor element. Therefore, the manufacturing is easy, and the semiconductor laser and the photodetector can be formed in an accurate arrangement.

  The gyro of the present invention may further include a lens. In this case, the photodetector is arranged at a position where an interference fringe is formed by the first and second laser beams transmitted through the lens. The semiconductor layer and the lens of the semiconductor laser may have the same stacked structure. The lens in this case is, for example, a lens having a semicircular planar shape, and the portion functioning as the lens is made of the same semiconductor as the active layer of the semiconductor laser. Therefore, the light incident on the lens is absorbed and attenuated by the semiconductor lens. In order to suppress such attenuation, a current may be passed through the stacked semiconductor layers constituting the lens. In order to pass the current, for example, the semiconductor laser and the lens including the electrode may have the same stacked structure. It is desirable that the flowing current is smaller than the current that causes laser oscillation. By passing an electric current, attenuation of light by the lens can be suppressed. Further, in order to suppress the attenuation of light by the lens, the lens may be formed of a material that absorbs less laser light, such as silicon oxide. Even in such a case, although the number of manufacturing steps is increased, the lens and the semiconductor laser can be formed monolithically by a known method.

  The gyro of the present invention may further include a prism. In this case, the photodetector is arranged at a position where an interference fringe is formed by the first and second laser beams transmitted through the prism. By using a prism having a predetermined shape, the period length of the formed interference fringes can be increased, and the movement of the interference fringes can be measured more accurately.

  When the semiconductor laser gyro is provided with a prism, the semiconductor laser and the prism may be formed monolithically. Further, the semiconductor laser, the prism, and the photodetector may be formed monolithically. According to these configurations, each element can be accurately formed at a predetermined position and shape. Further, in this case, the semiconductor layer of the semiconductor laser and the prism may have the same stacked structure. Further, the semiconductor layer of the semiconductor laser, the semiconductor layer of the photodetector (for example, a photodiode), and the prism may have the same stacked structure. According to this configuration, the photodetector and / or the prism can be formed by a series of processes for manufacturing the semiconductor laser.

  Note that in the case where the laminated structure of the prism is the same as the semiconductor layer of the semiconductor laser, the laser light emitted from the semiconductor laser is incident on the prism made of the semiconductor and attenuates. In order to suppress such attenuation, a current may be passed through the stacked semiconductor layers constituting the prism. In order to pass the current, for example, the semiconductor laser and the prism including the electrodes may have the same stacked structure. It is desirable that the flowing current is smaller than the current that causes laser oscillation. It is possible to suppress the attenuation of light by the prism by flowing an electric current. In addition, in order to suppress attenuation of light by the prism, the prism may be formed of a material that does not absorb laser light, such as silicon oxide. Even in such a case, although the number of manufacturing steps is increased, the prism and the semiconductor laser can be formed monolithically by a known method.

  The principle of the semiconductor laser gyro of the present invention will be briefly described with reference to FIG. When the semiconductor laser 10 rotates, the time required to go around the optical path of the path 32 varies between the laser light L1 and the laser light L2. Since the speed of light is constant, when the semiconductor laser 10 rotates, a frequency difference is generated between the laser light L1 and the laser light L2, and the interference fringes move at a speed corresponding to the frequency difference. The movement direction of the interference fringes changes according to the rotation direction of the semiconductor laser 10. Therefore, the rotational speed (angular speed) of the semiconductor laser 10 can be calculated by measuring the moving speed of the interference fringes, and the rotational direction of the semiconductor laser can be detected by detecting the moving direction of the interference fringes. More specifically, the rotation direction and rotation speed in a plane parallel to the surface of the active layer 24 can be calculated. As described above, the principle of such an optical gyro is a known principle, and is used in an optical gyro using a rare gas laser. Therefore, the semiconductor laser gyro of the present invention can be driven by a known driving circuit, and information obtained by the gyro can be processed by a known method. Note that by combining three semiconductor laser gyros of the present invention, the rotation direction and rotation speed in all directions can be calculated.

  Hereinafter, the semiconductor laser gyro of the present invention will be described with examples. In the following embodiment, the case where the first electrode 13 is the electrode shown in FIG. 7 is shown. However, the first electrode 13 may be the electrode shown in FIGS. 1 and 4.

(Embodiment 1)
In the first embodiment, an example of a semiconductor laser gyro in which a semiconductor laser and a photodetector are formed monolithically will be described. FIG. 8A shows a perspective view of the gyro 101 according to the first embodiment. FIG. 8B shows a perspective view of the substrate 11 on which the semiconductor laser 10 and the photodetector 113 (light receiving elements 113a and 113b) of the semiconductor laser gyro 101 are monolithically formed. FIG. 8A shows a state in which a part of the cover 111 is cut and the inside is released (the same applies to the following drawings).

  Referring to FIG. 8A, the main part of gyro 101 is packaged by a cover 111 and a stem 112 (so-called CAN package). The gyro 101 includes a stem 112 and a substrate 11 disposed on the stem 112. The semiconductor laser 10 and the light receiving elements 113a and 113b are formed monolithically by sharing the substrate 11. The stem 112 is supported by five electrodes 114. Four of the five electrodes are connected to the first portion 13a, the second portion 13b, the light receiving element 113a, and the light receiving element 113b of the first electrode 13 of the semiconductor laser 10, respectively. The remaining one of the five electrodes is a ground electrode paired with the four electrodes. Note that the connection method of the electrode 114 is an example, and the present invention is not limited to this. The diameter of the circular stem 112 is not limited, but may be a size determined by a standard, for example, a diameter of 5.6 mm.

  The light receiving elements 113a and 113b are photodiodes and have the same stacked structure as the semiconductor laser 10. The light receiving elements 113 a and 113 b are formed together with the semiconductor laser 10 in a manufacturing process for forming the semiconductor laser 10.

  The first laser light 35 and the second laser light 36 emitted from the first end face 24a of the semiconductor laser 10 form interference fringes in the vicinity of the first end face 24a. In order to observe the moving direction and moving speed of the interference fringes, the light receiving elements 113a and 113b are arranged close to the first end face 24a. In order to detect the movement speed of the interference fringes with high accuracy, the size of the light receiving region of the photodetector is determined in consideration of the period length of the interference fringes and the light receiving sensitivity of the photodetector. Usually, the size of the light receiving region is preferably set to about one fifth or less of the periodic length of the interference fringes.

  The semiconductor laser gyro 101 according to the first embodiment has an advantage that no optical element such as a prism or a lens is required. On the other hand, in order to obtain the semiconductor laser gyro 101, it is necessary to form fine light receiving elements 113a and 113b.

(Embodiment 2)
In the second embodiment, an example of a semiconductor laser gyro provided with a lens will be described. FIG. 9A shows a perspective view of the gyroscope 102 of the second embodiment. A perspective view of the semiconductor laser 10 used in the gyro 102 is shown in FIG.

  The gyro 102 includes the semiconductor laser 10, a spherical lens 115, and a photodetector 116. The photodetector 116 is a two-channel photodetector including two light receiving elements. The gyro 102 includes five electrodes 114. The electrode 114 is connected in the same manner as the gyro 101.

  The spherical lens 115 is disposed so that the focal point thereof is positioned in the vicinity of the laser light emitting portion (end surface 24a). The photodetector 116 is disposed at a position away from the end face 24a by a certain distance (for example, several centimeters). Therefore, an example size of the gyro 102 is about 3 cm × 2 cm × 1 cm.

  The two laser beams emitted from the end face 24a become substantially parallel light by the spherical lens 115, and overlap to generate interference fringes. Since the period length of the interference fringes can be increased by using the spherical lens 115, the gyro 102 can accurately measure the movement of the interference fringes.

The spherical lens 115 is not limited to a spherical shape, but may be other shapes such as a thin film. For example, a thin film lens having a semicircular planar shape may be used. In this case, the lens may be formed monolithically on the substrate 11. As a material for the lens, a transparent material such as SiO ₂ can be used, but a semiconductor may be used. For example, the semiconductor layer and the lens of the semiconductor laser may have the same stacked structure.

(Embodiment 3)
In the third embodiment, an example of a semiconductor laser gyro in which a semiconductor laser and a prism are formed monolithically will be described. A perspective view of the gyro 103 of Embodiment 3 is shown in FIG. FIG. 10B is a perspective view of the substrate 11 on which the semiconductor laser 10 and the prism 117 are formed.

  The gyro 103 includes a stem 112, a semiconductor laser 10 disposed on the stem 112 and a two-channel photodetector 116, and a prism 117 formed on the substrate 11. The prism 117 has the same stacked structure as the semiconductor layer 20 of the semiconductor laser 10 and is formed monolithically with the semiconductor laser 10. Therefore, the prism 117 can be formed simultaneously with the formation of the semiconductor layer 20.

  The optical paths of the two laser beams in the gyro 103 are schematically shown in FIG. The two laser beams emitted from the semiconductor laser 10 are overlapped by the prism 117 to generate interference fringes. The movement of the interference fringes is observed by the two light receiving elements 116 a and 116 b of the photodetector 116. The interference fringes move in the direction of the arrow at a speed corresponding to the rotational speed of the gyro 103. The movement direction of the interference fringes changes corresponding to the rotation direction of the gyro 103.

  The shape of the prism 117 is determined according to conditions such as the angle and interval between the two incident laser beams and the distance from the photodetector 116. In order to increase the period length of the interference fringes, it is preferable that the largest angle of the triangle which is the cross-sectional shape of the prism 117 is slightly larger than 90 ° (0.5π radians). If the angle is (0.5π + ε) radians, ε is preferably 0.5 radians or less.

(Embodiment 4)
In the fourth embodiment, an example of a semiconductor laser gyro in which a semiconductor laser, a prism, and a photodetector are formed monolithically will be described. FIG. 12A shows a perspective view of the gyro 104 according to the fourth embodiment, and FIG. 12B shows a perspective view of the main part.

  The semiconductor laser 10, the prism 117, and the photodetector 113 (light receiving elements 113 a and 113 b) are monolithically formed on the substrate 11. In the gyro 104, interference fringes are formed by two laser beams traveling along the same optical path as in FIG.

The semiconductor layer 20 of the semiconductor laser 10, the semiconductor layers of the light receiving elements 113a and 113b, and the prism 117 have the same stacked structure. Since these can be formed simultaneously in the process of forming the semiconductor layer 20, they are easy to manufacture. Moreover, since these can be formed by a semiconductor process, they can be formed in an accurate position and shape. It is also possible to form only the prism 117 with another material such as SiO ₂ .

(Manufacturing method of semiconductor laser gyro)
There is no limitation on the method of manufacturing the semiconductor laser used in the gyro of the present invention, and it can be manufactured by a known technique for manufacturing a semiconductor element. The gyro of the present invention can be easily manufactured by assembling a semiconductor laser and other members by a known technique. Hereinafter, an example of a method for manufacturing the semiconductor laser 10 will be described.

  FIGS. 13A to 13H schematically show the manufacturing process. In FIGS. 13A to 13H, the surface of the insulating layer 12 is hatched for easy understanding of the formation state of the insulating layer 12.

First, as shown in FIG. 13A, a semiconductor layer 20a composed of a plurality of semiconductor layers and an insulating layer 12a are formed on a substrate 11. The semiconductor layer 20a is a layer that becomes the semiconductor layer 20 (see FIG. 2 and Table 1) by etching. Except for the active layer 24, each layer constituting the semiconductor layer 20a can be formed by a general method, for example, MBE (Molecular Beam Epitaxy) method or CVD (Chemical Vapor Deposition) method. The insulating layer 12a is made of, for example, Si ₃ N ₄ or SiO ₂ . The insulating layer 12a can be formed by a method such as sputtering or CVD.

  The active layer 24 is formed of, for example, quantum dots made of InAs and a cover layer made of GaInAsSb. Quantum dots can be formed by self-formation. Specifically, after supplying InAs, a cover layer and a barrier layer are stacked. 1 to 50 sets of the semiconductor layer and the barrier layer thus formed are stacked. The quantum dots, the cover layer, and the barrier layer can be formed by, for example, gas sources MBE, MBE, CBE, and MOCVD.

An example of forming the active layer 24 using the MBE method will be described. First, 2.5 ML (Mono-Layer) with In flux 1.1 × 10 ⁻⁵ Pa (8 × 10 ⁻⁸ Torr) and As flux 1.3 × 10 ⁻³ Pa (1 × 10 ⁻⁵ Torr). InAs is supplied to form quantum dots. Quantum dots are formed by self-formation. Next, In flux 1.1 × 10 ⁻⁵ Pa (8 × 10 ⁻⁸ Torr), Ga flux 4.7 × 10 ⁻⁵ Pa (3.5 × 10 ⁻⁷ Torr), and As flux 1.3 By supplying × 10 ⁻³ Pa (1 × 10 ⁻⁵ Torr) and Sb flux 2.7 × 10 ⁻⁵ Pa (2 × 10 ⁻⁷ Torr), a Ga _0.85 In _0.15 As _0.98 Sb _0.02 layer ( 5 nm thick). Next, by supplying Ga flux 4.7 × 10 ⁻⁵ Pa (3.5 × 10 ⁻⁷ Torr) and As flux 1.3 × 10 ⁻³ Pa (1 × 10 ⁻⁵ Torr), A GaAs barrier layer (thickness 15 nm) is formed. The active layer 24 can be formed by repeating these steps three times.

  Next, as shown in FIG. 13B, a patterned resist film 151 is formed on the insulating layer 12a. The resist film 151 is patterned into the shape of the active layer 24 shown in FIG.

  Next, as shown in FIG. 13C, the insulating film 12a, the semiconductor layer 20a, and a part of the substrate 11 are etched using the resist film 151 as a mask, and then the resist film 151 is removed. Etching is performed by the RIE (Reactive Ion Etching) method, and is performed at least to the depth of the cladding layer 22. The insulating layer 12 and the semiconductor layer 20 having a predetermined shape are formed by etching. Etching is performed under conditions such that the verticality and smoothness of the side surfaces of the semiconductor layer 20 are high. Such conditions are commonly employed in semiconductor manufacturing processes. By etching, the planar shape of all the semiconductor layers constituting the semiconductor layer 20 becomes the same as the planar shape of the active layer 24 shown in FIG. Further, the side surface of the semiconductor layer 20 functions as a mirror surface.

  Next, as shown in FIG. 13D, a substantially diamond-shaped through hole 12h is formed in the insulating layer 12 so as to correspond to the region 31 (see FIGS. 2 and 4). The through hole 12h can be formed by a general photolithography / etching process.

  Next, as illustrated in FIG. 13E, a resist film 152 is formed so as to cover the entire surface of the substrate 11. At this time, in order to fill a step between the surface of the substrate 11 and the surface of the insulating layer 12, the resist film 152 is preferably formed of two layers, a resist layer 152a and a resist layer 152b. The resist film 152 can be formed by applying the resist layer 152b after applying the resist layer 152a to the entire surface of the substrate 11 to fill the steps. According to this method, the resist film 152 having a high surface flatness can be formed.

  Next, as shown in FIG. 13F, the resist film 152 is patterned to form a through hole 152 h in the resist film 152. The through hole 152h is formed in a shape corresponding to a region where the first electrode 13 is formed. After forming the through hole 152h, the surface of the semiconductor layer 20 (contact layer 27) in the through hole 152h so that a good contact can be obtained between the semiconductor layer 20 (contact layer 27) and the first electrode 13. Is etched by about 0.01 μm to 0.02 μm.

  Next, as shown in FIG. 13G, the first electrode 13 is formed. The first electrode 13 can be formed by a lift-off method. Specifically, first, using the resist film 152 as a mask, a plurality of metal layers constituting the first electrode 13 are sequentially formed by an electron beam method. Thereafter, the resist film 152 is removed with acetone. In this way, the first electrode 13 having a predetermined shape can be formed. The first electrode 13 is in contact with the semiconductor layer 20 (contact layer 27) through the through hole 12h formed in the insulating layer 12.

  When a large number of semiconductor lasers are formed using a single substrate 11 (wafer), the back surface of the substrate 11 is polished so that the thickness of the substrate 11 becomes 100 to 150 μm in order to facilitate cleavage of the substrate 11. It is preferable.

  Next, as shown in FIG. 13H, a plurality of metal layers are sequentially formed on the back side of the substrate 11 by vapor deposition to form the second electrode 14. Then, in order to alloy the metal layer which comprises the 1st electrode 13 and the 2nd electrode 14, it heat-processes at 400-450 degreeC. Finally, the substrate 11 is cleaved for each semiconductor laser as necessary.

  In this way, the semiconductor laser 10 is formed. When a photodiode having the same stacked structure as that of the semiconductor laser 10 is formed monolithically, the resist films 151 and 152 are patterned so as to correspond to a portion where the semiconductor laser is formed and a portion where the photodiode is formed. That's fine. Similarly, in the case of forming a prism having the same stacked structure as the semiconductor layer of the semiconductor laser, the resist film 151 may be patterned so as to correspond to the portion where the semiconductor laser is formed and the portion where the prism is formed.

  Note that other optical elements and electronic components other than the photodetector and the prism may be formed on the substrate 11. For example, a driving circuit for driving the semiconductor laser or a circuit for processing a signal output from the photodetector may be formed. Moreover, you may further apply the well-known technique used for the conventional gyro to the semiconductor laser gyro of this invention.

  Another example of the semiconductor laser of the present invention is shown. The semiconductor laser described below can also be applied to the gyro of the present invention.

  Table 2 shows the layer structure of the 1.3 μm band laser. The shape of the semiconductor laser is the same as that of the laser described above.

  FIG. 14 schematically shows a part of the active layer. The active layer includes a base layer (semiconductor layer (B)) 141, a semiconductor layer (semiconductor layer (A)) 142 formed on the base layer 141, and a barrier layer (semiconductor layer (D)) 143. The structure 144 has a structure in which 12 sets are stacked. The semiconductor layer 142 includes quantum dots 142a and a cover layer 142b that covers the quantum dots.

As the underlayer 141, a non-doped GaAs _0.98 Sb _0.02 layer (thickness 7 nm) was used. The quantum dots 142a were formed by supplying 2.5 ML of non-doped InAs on the base layer 141. A non-doped Ga _0.87 In _0.13 As layer (thickness 3 nm) was used for the cover layer 142b. As the barrier layer 143, a non-doped GaAs layer (thickness: 23 nm) was used.

Each layer constituting the laser is formed by the MBE method, but may be formed by a method such as gas source MBE, CBE, or MOCVD. Quantum dots are formed by self-formation. In addition, the substrate temperature at the time of growing each layer was 530 degreeC. After each layer was formed, photolithography and mesa etching were performed to form a laser. The threshold current density (J _th ) of this laser at 25 ° C. was as low as 0.04 kA / cm ² and the threshold current was also as low as 15 mA.

By using a base layer (semiconductor layer (B)) made of GaAsSb, it is possible to increase the photoluminescence intensity as compared with the case where quantum dots are formed on GaAs. FIG. 15 shows the relationship between quantum dot density and photoluminescence intensity when quantum dots are formed on GaAsSb and when quantum dots are formed on GaAs. As shown in FIG. 15, when the dot density was 3 × 10 ¹⁰ cm ⁻² , the photoluminescence intensity was approximately tripled by using the underlayer made of GaAsSb.

  The number of repetitions of the laminated structure is not limited to 12 sets, and may be selected from a range of 1 set to 50 sets.

In addition, the semiconductor constituting the barrier layer 143 is not limited to non-doped GaAs, and p-type modulation doping may be performed in a doping concentration range of 1 × 10 ^{17 to} 5 × 10 ¹⁹ cm ⁻² . FIG. 16 schematically shows a part of an example of an active layer including a barrier layer subjected to modulation doping.

The active layer in FIG. 16 differs from the active layer in FIG. 14 only in the portion of the barrier layer. The active layer in FIG. 16 has a structure in which 12 sets of a laminated structure 164 including a non-doped GaAsSb underlayer 141, a semiconductor layer 142, and a barrier layer 163 (thickness 26 nm) are laminated. The barrier layer 163 includes a non-doped GaAs layer 163a (thickness 18 nm), a p-type GaAs layer 163b (thickness 6 nm), and a non-doped GaAs layer 163c (thickness 2 nm). The doping concentration of the p-type GaAs layer 163b is 1 × 10 ¹⁸ cm ⁻³ . Each layer can be formed by the same method as the laser described in Table 2.

The threshold current density (J _th ) at 25 ° C. of the laser using the active layer of FIG. 16 was as low as 0.04 kA / cm ² and the threshold current was also as low as 15 mA.

  The above-described underlayer and modulation doping can also be applied to a laser having a wavelength of 300 nm to 1700 nm.

  The embodiments of the present invention have been described above by way of examples, but the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention.

  The semiconductor laser of the present invention can be used for a semiconductor laser gyro. Further, the semiconductor laser gyro of the present invention can be applied to various devices that require detection of rotation of an object. As a typical example, it can be used for an attitude control device, a navigation device, and a camera shake correction device. Specifically, the gyro of the present invention can be used for moving means such as aircraft such as rockets and airplanes, automobiles and motorcycles. Further, the gyro of the present invention can be used for a portable information terminal such as a mobile phone or a small personal computer, a toy, a camera, etc. by taking advantage of being ultra-small and easy to handle.

It is a perspective view which shows typically an example of the semiconductor laser of this invention. It is sectional drawing which shows the semiconductor laser shown in FIG. 1 typically. It is a figure which shows typically the planar shape of the active layer of the semiconductor laser shown in FIG. It is a figure explaining the function of the semiconductor laser shown in FIG. It is sectional drawing which shows typically an example of the active layer of the semiconductor laser of this invention. It is a graph which shows the relationship between the ratio of Sb to the V group element which comprises the cover layer of an active layer, and the half value width of PL peak. It is a top view which shows typically an example of a 1st electrode. BRIEF DESCRIPTION OF THE DRAWINGS (a) Whole perspective view and (b) Perspective view which shows an example of the semiconductor laser gyro of this invention typically. It is the (a) whole perspective view and (b) the perspective view of the principal part which show typically another example of the semiconductor laser gyro of this invention. It is the perspective view of (a) whole and (b) principal part which show typically another example of the semiconductor laser gyro of this invention. It is a schematic diagram which shows the optical path of the laser beam in the semiconductor laser gyro shown in FIG. It is the perspective view of (a) whole and (b) principal part which show typically another example of the semiconductor laser gyro of this invention. It is a perspective view which shows typically an example of the manufacturing process of the semiconductor laser used with the semiconductor laser gyro of this invention. It is sectional drawing which shows typically a part of example of the active layer used with the semiconductor laser gyro of this invention. It is a graph which shows that photoluminescence intensity changes with the base layer which forms a quantum dot. It is sectional drawing which shows typically a part of other example of the active layer used with the semiconductor laser gyro of this invention. It is a figure which shows typically the structure of the conventional optical gyroscope.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor laser 11 Substrate 12 Insulating layer 12h Through-hole 13 1st electrode 13a 1st part 13b 2nd part 14 2nd electrode 20 Semiconductor layer 21 Buffer layer 22 Cladding layer 23 Optical confinement layer 24 Active layers 24a-24d (First to fourth) end face 25 optical confinement layer 26 clad layer 27 contact layer 31, 31a, 31b second region 32 rhombic path 32a-32d (first to fourth) corner 35 first laser Light 36 Second laser light 51, 142 Semiconductor layer (semiconductor layer (A))
51a, 142a Quantum dot 51b, 142b Cover layer 52, 143, 163 Barrier layer (semiconductor layer (D))
101-104 Semiconductor laser gyro 111 Cover 112 Stem 113, 116 Photo detector 113a, 113b, 116a, 116b Light receiving element 114 Electrode 115 Spherical lens 117 Prism 141 Underlayer (semiconductor layer (B))
151, 152 Resist film L1, L2 Laser light

Claims (13)

A semiconductor laser capable of emitting first and second laser beams,
A substrate, an active layer formed on the substrate, and first and second electrodes for injecting carriers into the active layer,
The first laser beam is a laser beam emitted from a part of the laser beam (L1) that circulates on a polygonal path in the active layer,
The second laser beam is a laser beam emitted from a part of the laser beam (L2) that circulates in the direction opposite to the laser beam (L1) on the path,
The active layer includes at least one semiconductor layer (A), and the semiconductor layer (A) includes a plurality of quantum dots made of a first semiconductor and a second semiconductor different from the first semiconductor. And a cover layer formed so as to cover the quantum dots.   2. The semiconductor according to claim 1, wherein the first semiconductor is a group III-V compound semiconductor containing In and As, and the second semiconductor is a group III-V compound semiconductor containing Ga, As, and Sb. laser.   3. The semiconductor laser according to claim 2, wherein a ratio of Sb to a group V element of the second semiconductor is in a range of 0.2 atomic% to 10 atomic%. A semiconductor layer (B) formed on the substrate side of the semiconductor layer (A) so as to be adjacent to the semiconductor layer (A);
The semiconductor layer (B) is made of a III-V group compound semiconductor containing Sb,
4. The semiconductor laser according to claim 1, wherein the Sb content of the semiconductor layer (B) is higher than the Sb content of the first semiconductor. 5.   5. The semiconductor laser according to claim 4, wherein in the group III-V compound semiconductor constituting the semiconductor layer (B), the proportion of Sb in the group V element is in the range of 0.2 atomic% to 100 atomic%.   The semiconductor laser according to claim 4 or 5, comprising a semiconductor layer (C) having a thickness of 20 atomic layers or less, disposed between the semiconductor layer (A) and the semiconductor layer (B). A semiconductor layer (D) formed on the semiconductor layer (A) so as to be adjacent to the semiconductor layer (A);
The semiconductor laser according to claim 1, wherein a band gap of the semiconductor layer (D) is larger than a band gap of the second semiconductor.   8. The semiconductor laser according to claim 7, wherein at least a part of the semiconductor layer (D) is doped.   The semiconductor laser according to claim 1, wherein a planar shape of the active layer is not annular. The polygonal path is a rhombus path;
10. The semiconductor laser according to claim 1, wherein the active layer has first to fourth end faces formed at positions corresponding to first to fourth corners of the rhombic path. 11. . A semiconductor laser gyro comprising a semiconductor laser that emits first and second laser beams and a photodetector,
The photodetector is disposed at a position where an interference fringe is formed by the first and second laser beams;
A semiconductor laser gyro, wherein the semiconductor laser is the semiconductor laser according to claim 1.   The semiconductor laser gyro according to claim 11, wherein the photodetector includes a plurality of light receiving elements.   The semiconductor laser gyro according to claim 12, wherein the semiconductor laser and the light receiving element are formed monolithically.

Images