JP2015119148A - Vertical cavity surface emitting laser and atomic oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vertical cavity surface emitting laser capable of reducing optical absorption in a resonator.SOLUTION: A vertical cavity surface emitting laser includes: a substrate 10; a first mirror layer 20 provided on the substrate 10; an active layer provided on the first mirror layer 20; a second mirror layer provided above the active layer; a first electrode 80 electrically connected to the first mirror layer 20; and a second electrode electrically connected to the second mirror layer. The first mirror layer 20, the active layer and the second mirror layer constitute a laminate. The first mirror layer 20 is a multilayer film formed by alternately laminating high refractive index layers 24 and low refractive index layers 26. The high refractive index layers 24 and the low refractive index layers 26 contain Al. A composition ratio of Al of each high refractive index layer 24 is less than a composition ratio of Al of each low refractive index layer 26. The first electrode 80 is brought into contact with top surfaces 24a of the plurality of high refractive index layers 24.

Description

  The present invention relates to a surface emitting laser and an atomic oscillator.

  A surface emitting laser (VCSEL) is used as a light source of an atomic oscillator using CPT (Coherent Population Trapping), which is one of the quantum interference effects, for example.

  For example, Patent Document 1 includes a substrate, a lower DBR mirror, an n-contact layer, an active layer, a p-contact layer, an upper DBR mirror, an n-side electrode, and a p-side electrode. A surface emitting laser is described. In the surface emitting laser described in Patent Document 1, an n-contact layer is provided to make ohmic contact between the n-side electrode and the n-contact layer. In Patent Document 1, the n-contact layer is formed immediately below the active layer.

JP 2008-244470 A

  Here, since the n-contact layer is made of n-type GaAs, light absorption occurs. In the surface emitting laser described in Patent Document 1, since the n-contact layer is formed immediately below the active layer having high light intensity in the resonator, the influence of light absorption is large. In the surface emitting laser, if the light absorption in the resonator is large, for example, the threshold current increases and the light emission efficiency decreases.

  One of the objects according to some embodiments of the present invention is to provide a surface emitting laser capable of reducing light absorption in a resonator. Another object of some embodiments of the present invention is to provide an atomic oscillator including the surface emitting laser.

The surface emitting laser according to the present invention is
A substrate,
A first mirror layer provided above the substrate;
An active layer provided above the first mirror layer;
A second mirror layer provided above the active layer;
A first electrode electrically connected to the first mirror layer;
A second electrode electrically connected to the second mirror layer;
Including
The first mirror layer, the active layer, and the second mirror layer constitute a laminate,
The first mirror layer is a multilayer film in which high refractive index layers and low refractive index layers are alternately stacked,
The high refractive index layer and the low refractive index layer include Al,
The Al composition ratio of the high refractive index layer is smaller than the Al composition ratio of the low refractive index layer,
The first electrode is in contact with the upper surfaces of the plurality of high refractive index layers.

In such a surface emitting laser, since the first electrode is in contact with the upper surfaces of the plurality of high refractive index layers, the resistance (contact resistance) between the first electrode and the first mirror layer can be reduced. Furthermore, since the first electrode and the first mirror layer can be electrically connected without using a contact layer, light absorption in the resonator can be reduced.

  In the description according to the present invention, the word “upper” is used, for example, “specifically” (hereinafter referred to as “A”) is formed above another specific thing (hereinafter referred to as “B”). The word “above” is used to include the case where B is formed directly on A and the case where B is formed on A via another object. Used.

  Further, in the description of the present invention, the term “electrically connected” refers to, for example, another specific member (hereinafter “electrically connected” to “specific member (hereinafter referred to as“ A member ”)”). B member "))" and the like. In the description according to the present invention, in the case of this example, the case where the A member and the B member are in direct contact and electrically connected, and the A member and the B member are the other members. The term “electrically connected” is used as a case where the case where the terminals are electrically connected to each other is included.

In the surface emitting laser according to the present invention,
The first mirror layer has a first portion provided above the substrate, and a second portion provided above the first portion and constituting a part of the stacked body,
The first electrode may be provided on a surface of the first portion.

  In such a surface emitting laser, light absorption in the resonator can be reduced.

In the surface emitting laser according to the present invention,
The surface of the first portion includes an upper surface and a side surface of the high refractive index layer,
The upper surface of the high refractive index layer is parallel to the upper surface of the substrate,
The side surface of the high refractive index layer may be inclined with respect to the upper surface of the substrate.

  In such a surface emitting laser, the first electrode and the first mirror layer can be electrically connected by a simple manufacturing process.

In the surface emitting laser according to the present invention,
The first electrode may be in contact with side surfaces of the plurality of low refractive index layers.

  In such a surface emitting laser, light absorption in the resonator can be reduced.

  The high refractive index layer and the low refractive index layer may be AlGaAs layers.

  In such a surface emitting laser, light absorption in the resonator can be reduced.

The atomic oscillator according to the present invention is
The surface emitting laser according to the present invention is included.

  Such an atomic oscillator can include a surface emitting laser capable of reducing light absorption in the resonator.

The top view which shows typically the surface emitting laser which concerns on this embodiment. Sectional drawing which shows typically the surface emitting laser which concerns on this embodiment. The top view which shows typically the surface emitting laser which concerns on this embodiment. Sectional drawing which shows typically the surface emitting laser which concerns on this embodiment. Sectional drawing which shows typically the surface emitting laser which concerns on this embodiment. Sectional drawing which shows typically the manufacturing process of the surface emitting laser which concerns on this embodiment. Sectional drawing which shows typically the manufacturing process of the surface emitting laser which concerns on this embodiment. Sectional drawing which shows typically the manufacturing process of the surface emitting laser which concerns on this embodiment. Sectional drawing which shows typically the manufacturing process of the surface emitting laser which concerns on this embodiment. Sectional drawing which shows typically the manufacturing process of the surface emitting laser which concerns on this embodiment. The functional block diagram of the atomic oscillator which concerns on this embodiment. The figure which shows the frequency spectrum of resonant light. The figure which shows the relationship of the (LAMBDA) type | mold 3 level model of an alkali metal atom, a 1st sideband, and a 2nd sideband.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, not all of the configurations described below are essential constituent requirements of the present invention.

1. Surface Emitting Laser First, a surface emitting laser according to the present embodiment will be described with reference to the drawings. FIG. 1 is a plan view schematically showing a surface emitting laser 100 according to this embodiment. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1 schematically showing the surface emitting laser 100 according to the present embodiment. FIG. 3 is a plan view schematically showing the surface emitting laser 100 according to the present embodiment. 4 is a cross-sectional view taken along line IV-IV in FIG. 3 schematically showing the surface emitting laser 100 according to the present embodiment.

  For convenience, in FIG. 2, the stacked body 2 is illustrated in a simplified manner. In FIG. 3, members other than the laminate 2 of the surface emitting laser 100 are not shown. 1 to 4 show the X axis, the Y axis, and the Z axis as three axes orthogonal to each other.

  As shown in FIGS. 1 to 4, the surface emitting laser 100 includes a substrate 10, a first mirror layer 20, an active layer 30, a second mirror layer 40, a current confinement layer 42, a contact layer 50, A first region 60, a second region 62, a resin layer (insulating layer) 70, a first electrode 80, and a second electrode 82 are included.

  The substrate 10 is, for example, a first conductivity type (for example, n-type) GaAs substrate.

The first mirror layer 20 is formed on the substrate 10. The first mirror layer 20 is a first conductivity type semiconductor layer. As shown in FIG. 4, the first mirror layer 20 is a distributed Bragg reflection (DBR) mirror in which high refractive index layers 24 and low refractive index layers 26 are alternately stacked. The high refractive index layer 24 is, for example, an n-type Al _0.12 Ga _0.88 As layer doped with silicon. The low refractive index layer 26 is, for example, an n-type Al _0.9 Ga _0.1 As layer doped with silicon. The number of stacked layers (number of pairs) of the high refractive index layer 24 and the low refractive index layer 26 is, for example, 10 pairs or more and 50 pairs or less, and specifically 40.5 pairs.

The active layer 30 is provided on the first mirror layer 20. The active layer 30 is, for example, a multiple quantum well in which three quantum well structures each composed of an i-type In _0.06 Ga _0.94 As layer and an i-type Al _0.3 Ga _0.7 As layer are stacked. (MQW) structure.

The second mirror layer 40 is formed on the active layer 30. The second mirror layer 40 is a second conductivity type (for example, p-type) semiconductor layer. The second mirror layer 40 is a distributed Bragg reflection (DBR) mirror in which high refractive index layers 44 and low refractive index layers 46 are alternately stacked. The high refractive index layer 44 is, for example, a p-type Al _0.12 Ga _0.88 As layer doped with carbon. The low refractive index layer 46 is, for example, a p-type Al _0.9 Ga _0.1 As layer doped with carbon. The number of stacked layers (number of pairs) of the high refractive index layer 44 and the low refractive index layer 46 is, for example, 3 pairs or more and 40 pairs or less, specifically 20 pairs.

  The second mirror layer 40, the active layer 30, and the first mirror layer 20 constitute a vertical resonator type pin diode. When a forward voltage of a pin diode is applied between the electrodes 80 and 82, recombination of electrons and holes occurs in the active layer 30 and light emission occurs. The light generated in the active layer 30 reciprocates between the first mirror layer 20 and the second mirror layer 40 (multiple reflection), and stimulated emission occurs at that time, and the intensity is amplified. When the optical gain exceeds the optical loss, laser oscillation occurs, and laser light is emitted from the upper surface of the contact layer 50 in the vertical direction (in the stacking direction of the first mirror layer 20 and the active layer 30).

  The current confinement layer 42 is provided between the first mirror layer 20 and the second mirror layer 40. In the illustrated example, the current confinement layer 42 is provided on the active layer 30. The current confinement layer 42 can also be provided inside the first mirror layer 20 or the second mirror layer 40. Even in this case, the oxidized constricting layer 42 is considered to be provided between the first mirror layer 20 and the second mirror layer 40. The current confinement layer 42 is an insulating layer in which an opening 43 is formed. The current confinement layer 42 can prevent the current injected into the vertical resonator by the electrodes 80 and 82 from spreading in the plane direction (direction orthogonal to the stacking direction of the first mirror layer 20 and the active layer 30).

  The contact layer 50 is provided on the second mirror layer 40. The contact layer 50 is a second conductivity type semiconductor layer. Specifically, the contact layer 50 is a p-type GaAs layer doped with carbon.

As shown in FIG. 4, the first region 60 is provided on the side of the first mirror layer 20 constituting the stacked body 2. The first region 60 includes a plurality of oxide layers 6 provided continuously with the first mirror layer 20 (in the illustrated example, a part of the first mirror layer 20). Specifically, the first region 60 includes an oxide layer 6 in which a layer continuous with the low refractive index layer (for example, Al _0.9 Ga _0.1 As layer) 26 constituting the first mirror layer 20 is oxidized. The high refractive index layer (for example, Al _0.12 Ga _0.88 As layer) 24 constituting the first mirror layer 20 and the continuous layer 4 are alternately stacked.

The second region 62 is provided on the side of the second mirror layer 40 constituting the stacked body 2. The second region 62 includes a plurality of oxide layers 16 provided continuously with the second mirror layer 40. Specifically, the second region 62 includes the oxidized layer 16 in which a layer continuous with the low refractive index layer (for example, Al _0.9 Ga _0.1 As layer) 46 constituting the second mirror layer 40 is oxidized. And a high refractive index layer (for example, Al _0.12 Ga _0.88 As layer) 44 constituting the second mirror layer 40 and a continuous layer 14 are alternately laminated. In plan view (viewed from the stacking direction of the first mirror layer 20 and the active layer 30), the oxidized region 8 is constituted by the first region 60 and the second region 62.

  The first mirror layer 20, the active layer 30, the second mirror layer 40, the current confinement layer 42, the contact layer 50, the first region 60, and the second region 62 constitute the stacked body 2. In the example shown in FIGS. 1 and 2, the laminate 2 is surrounded by a resin layer 70.

In the example illustrated in FIG. 3, the length of the stacked body 2 in the Y-axis direction is longer than the length of the stacked body 2 in the X-axis direction in plan view. That is, the longitudinal direction of the laminate 2 is the Y-axis direction. In plan view, the stacked body 2 is symmetric with respect to an imaginary straight line that passes through the center of the stacked body 2 and is parallel to the X axis, for example. Further, in plan view, the stacked body 2 is symmetric with respect to an imaginary straight line that passes through the center of the stacked body 2 and is parallel to the Y axis, for example.

  As shown in FIG. 3, the laminate 2 includes a first strain imparting portion (first portion) 2 a, a second strain imparting portion (second portion) 2 b, and a resonance portion (third portion) 2 c in plan view. ,including.

  The first strain imparting section 2a and the second strain imparting section 2b are opposed to each other in the Y-axis direction with the resonance section 2c interposed therebetween in plan view. The first strain applying part 2a protrudes in the + Y-axis direction from the resonance part 2c in plan view. The second strain applying part 2b protrudes in the −Y axis direction from the resonance part 2c in plan view. The first strain imparting section 2a and the second strain imparting section 2b are provided integrally with the resonance section 2c.

  The first strain imparting section 2a and the second strain imparting section 2b impart strain to the active layer 30 and polarize light generated in the active layer 30. Here, polarizing light means making the vibration direction of the electric field of light constant. The semiconductor layers (the first mirror layer 20, the active layer 30, the second mirror layer 40, the current confinement layer 42, the contact layer 50, the first region 60, and the first strain applying section 2a and the second strain applying section 2b) The second region 62) serves as a generation source for generating strain applied to the active layer 30. Since the first strain imparting portion 2a and the second strain imparting portion 2b include the first region 60 having the plurality of oxide layers 6 and the second region 62 having the plurality of oxide layers 16, the active layer Large distortion can be imparted to 30.

  The resonating unit 2c is provided between the first strain applying unit 2a and the second strain applying unit 2b. The length of the resonance part 2c in the X-axis direction is larger than the length of the first strain applying part 2a in the X-axis direction or the length of the second strain applying part 2b in the X-axis direction. The planar shape of the resonance part 2c (the shape seen from the stacking direction of the first mirror layer 20 and the active layer 30) is, for example, a circle.

  The resonating unit 2 c resonates the light generated in the active layer 30. That is, a vertical resonator is formed in the resonance unit 2c.

  The resin layer 70 is provided on at least the side surface of the laminate 2. In the example shown in FIG. 1, the resin layer 70 covers the first strain imparting portion 2 a and the second strain imparting portion 2 b. That is, the resin layer 70 is provided on the side surface of the first strain imparting portion 2a, the upper surface of the first strain imparting portion 2a, the side surface of the second strain imparting portion 2b, and the upper surface of the second strain imparting portion 2b. The resin layer 70 may completely cover the first strain imparting portion 2a and the second strain imparting portion 2b, or may partially cover the first strain imparting portion 2a and the second strain imparting portion 2b. . The material of the resin layer 70 is, for example, polyimide. In this embodiment, the resin layer 70 is used to apply strain to each of the strain applying portions 2a and 2b. However, since the configuration corresponding to the resin layer 70 only needs to have an insulating function, an insulating material is used. If it exists, it may not be a resin.

  In the example shown in FIG. 3, the length of the resin layer 70 in the Y-axis direction is larger than the length of the resin layer 70 in the X-axis direction in plan view. That is, the longitudinal direction of the resin layer 70 is the Y-axis direction. The longitudinal direction of the resin layer 70 coincides with the longitudinal direction of the laminate 2.

  The first electrode 80 is provided on the first mirror layer 20. The first electrode 80 is in ohmic contact with the first mirror layer 20. The first electrode 80 is electrically connected to the first mirror layer 20. As the first electrode 80, for example, a layer in which a Cr layer, an AuGe layer, a Ni layer, and an Au layer are stacked in this order from the first mirror layer 20 side is used. The first electrode 80 is one electrode for injecting a current into the active layer 30. Although not shown, the first electrode 80 may be provided on the lower surface of the substrate 10.

  The second electrode 82 is provided on the contact layer 50 (on the stacked body 2). The second electrode 82 is in ohmic contact with the contact layer 50. In the illustrated example, the second electrode 82 is further formed on the resin layer 70. The second electrode 82 is electrically connected to the second mirror layer 40 through the contact layer 50. As the second electrode 82, for example, a layer in which a Cr layer, a Pt layer, a Ti layer, a Pt layer, and an Au layer are stacked in this order from the contact layer 50 side is used. The second electrode 82 is the other electrode for injecting current into the active layer 30.

  The second electrode 82 is electrically connected to the pad 84. In the illustrated example, the second electrode 82 is electrically connected to the pad 84 via the lead wiring 86. The pad 84 is provided on the resin layer 70. The material of the pad 84 and the lead wiring 86 is the same as the material of the second electrode 82, for example.

  Here, the first mirror layer 20 and the first electrode 80 will be described in more detail. FIG. 5 is a cross-sectional view taken along line VV in FIG. 1, schematically showing the surface emitting laser 100.

As described above, the high refractive index layer (for example, Al _0.12 Ga _0.88 As layer) 24 and the low refractive index layer (for example, Al _0.9 Ga _0.1 As layer) 26 of the first mirror layer 20 are as follows. Al (aluminum) is included. The Al composition ratio of the high refractive index layer 24 is smaller than the Al composition ratio of the low refractive index layer 26. Therefore, the high refractive index layer 24 is more easily in ohmic contact with the first electrode 80 than the low refractive index layer 26. For example, the high refractive index layer 24 may be referred to as an Al low composition layer, and the low refractive index layer 26 may be referred to as an Al high composition layer.

  As shown in FIG. 5, the first electrode 80 is in contact with the upper surface 24 a and the side surface 24 b of the plurality of high refractive index layers 24. The upper surface 24 a of the high refractive index layer 24 is exposed by removing a part of the low refractive index layer 26 and is in contact with the first electrode 80. The first electrode 80 is in contact with the side surfaces 26 a of the plurality of low refractive index layers 26. Here, the upper surface 24a of the high refractive index layer 24 is, for example, a surface parallel to the upper surface of the substrate 10 among the surfaces of the high refractive index layer 24 and facing the + Z-axis direction. Further, the side surface 24b of the high refractive index layer 24 is, for example, a surface that connects the upper surface 24a of the high refractive index layer 24 and the lower surface of the high refractive index layer 24 (a surface facing away from the upper surface 24a). Further, the side surface 26a of the low refractive index layer 26 is, for example, a surface connecting the upper surface and the lower surface of the low refractive index layer 26.

  As shown in FIG. 2, the first mirror layer 20 includes a first portion 20 a provided on the substrate 10 and a second portion 20 b provided on the first portion 20 a and constituting a part of the stacked body 2. And have. In the example shown in FIG. 5, the surface 21 of the first portion 20 a of the first mirror layer 20 is composed of upper surfaces 24 a and side surfaces 24 b of the plurality of high refractive index layers 24 and side surfaces 26 a of the plurality of low refractive index layers 26. Has been.

  At least a part of the surface 21 of the first portion 20 a of the first mirror layer 20 is inclined with respect to the upper surface of the substrate 10. In the illustrated example, the side surface 24 b of the high refractive index layer 24 is inclined with respect to the upper surface of the substrate 10. Further, the upper surface 24 a of the high refractive index layer 24 is parallel to the substrate 10. The side surface 26 a of the low refractive index layer 26 is perpendicular to the upper surface of the substrate 10.

  The first electrode 80 is provided on the surface 21 of the first portion 20 a of the first mirror layer 20. That is, the first electrode 80 is provided on (in contact with) the upper surfaces 24 a and the side surfaces 24 b of the plurality of high refractive index layers 24 and the side surfaces 26 a of the plurality of low refractive index layers 26. The first electrode 80 can be in ohmic contact with the upper surfaces 24 a and the side surfaces 24 b of the plurality of high refractive index layers 24.

In the above description, the AlGaAs surface emitting laser has been described. However, the surface emitting laser according to the present invention is, for example, GaInP based, InGaN based, AlGaN based, InGaAs based, GaInNAs based, or GaAsSb based on the oscillation wavelength. The semiconductor material may be used.

  The surface emitting laser 100 has the following features, for example.

  In the surface emitting laser 100, the first mirror layer 20 is a multilayer film in which the high refractive index layer 24 and the low refractive index layer 26 are alternately laminated. The high refractive index layer 24 and the low refractive index layer 26 are made of Al. The Al composition ratio of the high refractive index layer 24 is smaller than the Al composition ratio of the low refractive index layer 26, and the first electrode 80 is in contact with the upper surfaces 24 a of the plurality of high refractive index layers 24. Since the first electrode 80 is in contact with the upper surfaces 24a of the plurality of high refractive index layers 24, the resistance (contact resistance) between the first electrode 80 and the first mirror layer 20 can be reduced. Furthermore, since the first electrode 80 and the first mirror layer 20 can be electrically connected without using a contact layer, light absorption in the resonator can be reduced.

  For example, when a contact layer (for example, an n-type GaAs layer) is provided under the active layer 30 and the first electrode 80 and the first mirror layer 20 are electrically connected, the vicinity of the active layer 30 having a high light intensity in the resonator. Since a contact layer having a large light absorption is provided on the substrate, light absorption in the resonator is increased. For example, when the contact layer is formed thin in order to reduce the influence of light absorption, high etching accuracy is required to expose the contact layer. Furthermore, the contact layer desirably has a high carrier concentration in order to reduce the resistance, but the crystal quality deteriorates when the carrier concentration is increased. If such a low crystal quality layer is provided under the active layer 30, the crystal quality of the active layer 30 and the second mirror layer 40 will also deteriorate.

  On the other hand, in the surface emitting laser 100, since the first electrode 80 is in contact with the upper surfaces 24a of the plurality of high refractive index layers 24, the first electrode 80 has a large area without the contact layer. The mirror layer 20 can be contacted, and the resistance can be reduced. Furthermore, problems such as light absorption in the resonator and deterioration of the crystal quality of the active layer and the second mirror layer due to the provision of the contact layer described above do not occur. Therefore, in the surface emitting laser 100, the resistance (contact resistance) between the first electrode 80 and the first mirror layer 20 can be reduced, and light absorption in the resonator can be reduced.

  In the surface emitting laser 100, the first mirror layer 20 includes a first portion 20a provided on the substrate 10, and a second portion 20b provided on the first portion 20a and constituting a part of the stacked body 2. The first electrode 80 is provided on the surface 21 of the first portion 20a of the first mirror layer 20, and the surface 21 of the first portion 20a includes the upper surface 24a and the side surface 24b of the high refractive index layer 24. The upper surface 24 a of the high refractive index layer 24 is parallel to the upper surface of the substrate 10, and the side surface 24 b of the high refractive index layer 24 is inclined with respect to the upper surface of the substrate 10. Therefore, the first electrode 80 and the first mirror layer 20 can be electrically connected by a simple manufacturing process. The reason will be described below.

  The first electrode 80 is formed on the exposed surface 21 of the first portion 20a of the first mirror layer 20 in the step of forming the stacked body 2 by etching.

  Here, for example, when the surface 21 of the first portion 20a of the first mirror layer 20 is a flat surface (a surface parallel to the upper surface of the substrate 10), in the step of forming the stacked body 2 by etching, a high refractive index. In order to expose the layer 24, extremely high etching accuracy is required.

On the other hand, in the surface emitting laser 100, in the step of forming the stacked body 2 by etching, first, the surface of the first portion 20a of the first mirror layer 20 is inclined, that is, the side surface 24b of the high refractive index layer 24. Then, the side surface of the low refractive index layer 26 is inclined (see FIG. 10), and then the low refractive index layer 26 is removed with hydrofluoric acid or the like to expose the upper surface 24a of the high refractive index layer 24 (see FIG. 5). . Thereby, the upper surface 24a and the side surface 24b of the plurality of high refractive index layers 24 can be easily exposed without requiring high etching accuracy. Therefore, in the surface emitting laser 100, the first electrode 80 and the first mirror layer 20 can be electrically connected by a simple manufacturing process.

2. Method for Manufacturing Surface Emitting Laser Next, a method for manufacturing a surface emitting laser according to the present embodiment will be described with reference to the drawings. 6 to 9 are cross-sectional views schematically showing the manufacturing process of the surface emitting laser 100 according to this embodiment, and correspond to FIG. FIG. 10 is a cross-sectional view schematically showing the manufacturing process of the surface emitting laser 100 according to the present embodiment, and corresponds to FIG.

  As shown in FIG. 6, on the substrate 10, the first mirror layer 20, the active layer 30, the oxidized layer 42a that is oxidized to become the current confinement layer 42, the second mirror layer 40, and the contact layer 50 are arranged in this order. Epitaxial growth. Examples of the epitaxial growth method include a MOCVD (Metal Organic Chemical Deposition) method and an MBE (Molecular Beam Epitaxy) method.

  As illustrated in FIG. 7, the contact layer 50, the second mirror layer 40, the oxidized layer 42 a, the active layer 30, and the first mirror layer 20 are patterned to form the stacked body 2. The patterning is performed by, for example, photolithography and etching. As a result, the first mirror layer 20 is formed with the first portion 20a and the second portion 20b, and the surface 21 of the first portion 20a of the first mirror layer 20 is exposed. In this step, etching is performed under the condition that the surface 21 of the first portion 20 a of the first mirror layer 20 is inclined with respect to the upper surface of the substrate 10. Accordingly, as shown in FIG. 10, the surface 21 of the first mirror layer 20 is constituted by the side surface 24 b of the high refractive index layer 24 and the side surface 26 a of the low refractive index layer 26.

As shown in FIG. 8, the oxidized layer 42a is oxidized to form a current confinement layer 42. The layer 42a to be oxidized is, for example, an Al _x Ga _1-x As (x ≧ 0.95) layer. For example, by throwing the substrate 10 on which the stacked body 2 is formed in a water vapor atmosphere at about 400 ° C., the Al _x Ga _1-x As (x ≧ 0.95) layer is oxidized from the side surface, and current confinement is achieved. Layer 42 is formed.

In the method for manufacturing the surface emitting laser 100, the first region 60 is formed by oxidizing the layer constituting the first mirror layer 20 from the side surface in the oxidation step. Further, the layer constituting the second mirror layer 40 is oxidized from the side surface to form the second region 62. Specifically, arsenic in the Al _0.9 Ga _0.1 As layer constituting the mirror layers 20 and 40 is replaced with oxygen in a water vapor atmosphere at about 400 ° C., and the regions 60 and 62 are formed. The regions 60 and 62 shrink when returning from a high temperature of about 400 ° C. to room temperature, for example, and the upper surface 63 of the second region 62 is inclined toward the substrate 10 (see FIG. 4). The first strain imparting portion 2 a and the second strain imparting portion 2 b can impart strain (stress) due to the shrinkage of the regions 60 and 62 to the active layer 30.

  Next, the surface 21 of the first portion 20a of the first mirror layer 20 is etched with hydrofluoric acid (hydrofluoric acid) or the like to remove the low refractive index layer 26, and the upper surface 24a of the high refractive index layer 24 is exposed. (See FIG. 5). Thereby, the surface 21 of the first portion 20a of the first mirror layer 20 is constituted by the upper surface 24a and the side surface 24b of the high refractive index layer 24 and the side surface 26a of the low refractive index layer 26 as shown in FIG.

As shown in FIG. 9, a resin layer 70 is formed so as to surround the laminate 2. The resin layer 70 is formed, for example, by forming a layer made of polyimide resin or the like on the surface 21 of the first mirror layer 20 and the entire surface of the laminated body 2 using a spin coating method or the like and patterning the layer. The patterning is performed by, for example, photolithography and etching. Next, the resin layer 70 is cured by heat treatment (curing). By this heat treatment, the resin layer 70 contracts. Furthermore, the resin layer 70 contracts when the temperature is returned from the heat treatment to room temperature.

  As shown in FIG. 2, the second electrode 82 is formed on the contact layer 50 and the resin layer 70, and the first electrode 80 is formed on the first mirror layer 20. The electrodes 80 and 82 are formed by, for example, a combination of a vacuum deposition method and a lift-off method. The order in which the electrodes 80 and 82 are formed is not particularly limited. Further, in the step of forming the second electrode 82, the pad 84 and the lead wiring 86 (see FIG. 1) may be formed.

  Through the above steps, the surface emitting laser 100 can be manufactured.

3. Atomic Oscillator Next, an atomic oscillator according to this embodiment will be described with reference to the drawings. FIG. 11 is a functional block diagram showing the atomic oscillator 1000 according to this embodiment.

  As shown in FIG. 11, the atomic oscillator 1000 includes an optical module 1100, a central wavelength control unit 1200, and a high frequency control unit 1300.

  The optical module 1100 includes a surface emitting laser according to the present invention (surface emitting laser 100 in the illustrated example), a gas cell 1110, and a light detection unit 1120.

FIG. 12 is a diagram illustrating a frequency spectrum of light emitted from the surface emitting laser 100. FIG. 13 is a diagram showing the relationship between the Λ-type three-level model of alkali metal atoms and the first sideband wave W1 and the second sideband wave W2. The light emitted from the surface emitting laser 100 has a fundamental wave F having a center frequency f ₀ (= c / λ ₀ : c is the speed of light and λ ₀ is the center wavelength of the laser beam), as shown in FIG. It includes a first sideband W1 having a frequency f ₁ to the upper sideband with respect to the center frequency f _0, and the second sideband wave W2 having a frequency f ₂ to the lower sideband with respect to the center frequency f _0, the. Frequency _{f 1} of the first sideband W1 _{is f 1 = f 0 + f m} , the frequency _{f 2} of the second sideband wave W2 _is f _{2 =} f 0 -f _m.

As shown in FIG. 13, the energy difference between the frequency f ₁ of the first sideband wave W1 frequency difference between the frequency f ₂ of the second sideband wave W2 is the ground level GL1 and ground level GL2 alkali metal atom ΔE _This corresponds to the frequency corresponding to ₁₂ . Therefore, the alkali metal atom is, causing the first sideband W1 having a frequency _{f 1,} a second sideband wave W2 having a frequency _{f 2,} the EIT phenomenon by.

  The gas cell 1110 is a container in which gaseous alkali metal atoms (sodium atoms, rubidium atoms, cesium atoms, etc.) are sealed. When the gas cell 1110 is irradiated with two light waves having a frequency (wavelength) corresponding to the energy difference between the two ground levels of the alkali metal atoms, the alkali metal atoms cause an EIT phenomenon. For example, if the alkali metal atom is a cesium atom, the frequency corresponding to the energy difference between the ground level GL1 and the ground level GL2 in the D1 line is 9.19263... GHz, so the frequency difference is 9.19263. When two light waves of GHz are irradiated, an EIT phenomenon occurs.

  The light detection unit 1120 detects the intensity of light transmitted through the alkali metal atoms enclosed in the gas cell 1110. The light detection unit 1120 outputs a detection signal corresponding to the amount of light transmitted through the alkali metal atom. As the light detection unit 1120, for example, a photodiode is used.

The center wavelength control unit 1200 generates a drive current having a magnitude corresponding to the detection signal output from the light detection unit 1120, supplies the drive current to the surface emitting laser 100, and sets the center wavelength λ ₀ of the light emitted from the surface emitting laser 100. Control. By the feedback loop passing through the surface emitting laser 100, the gas cell 1110, the light detection unit 1120, and the center wavelength control unit 1200, the center wavelength λ ₀ of the laser light emitted from the surface emitting laser 100 is finely adjusted and stabilized.

Based on the detection result output from the light detection unit 1120, the high-frequency control unit 1300 determines that the wavelength (frequency) difference between the first sideband W1 and the second sideband W2 is two of the alkali metal atoms enclosed in the gas cell 1110. Control is made to be equal to the frequency corresponding to the energy difference of the ground level. The high frequency control unit 1300 generates a modulation signal having a modulation frequency f _m (see FIG. 12) corresponding to the detection result output from the light detection unit 1120.

Due to the feedback loop passing through the surface emitting laser 100, the gas cell 1110, the light detection unit 1120, and the high frequency control unit 1300, the frequency difference between the first sideband wave W1 and the second sideband wave W2 is the energy of the two ground levels of alkali metal atoms. Feedback control is applied so as to match the frequency corresponding to the difference very accurately. As a result, the modulation frequency f _m is very since a stable frequency can be the output signal of the atomic oscillator 1000 a modulated signal (clock output).

  Next, the operation of the atomic oscillator 1000 will be described with reference to FIGS.

  Laser light emitted from the surface emitting laser 100 enters the gas cell 1110. The light emitted from the surface emitting laser 100 includes two light waves (first sideband wave W1 and second sideband wave W2) having a frequency (wavelength) corresponding to the energy difference between the two ground levels of alkali metal atoms. Alkali metal atoms cause the EIT phenomenon. The intensity of light transmitted through the gas cell 1110 is detected by the light detection unit 1120.

The center wavelength control unit 1200 and the high frequency control unit 1300 match the frequency difference between the first sideband wave W1 and the second sideband wave W2 very accurately with the frequency corresponding to the energy difference between the two ground levels of the alkali metal atom. Thus, feedback control is performed. In atomic oscillator 1000, utilizing the EIT phenomenon, the frequency difference _f 1 -f ₂ between the first sideband wave W1 and the second sideband wave W2 corresponds to the energy difference Delta] E ₁₂ between the ground level GL1 and ground level GL2 By detecting and controlling a steep change in light absorption behavior when deviating from the frequency, a highly accurate oscillator can be produced.

  The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 2 ... Laminated body, 2a ... 1st strain imparting part, 2b ... 2nd strain imparting part, 2c ... Resonance part, 4 ... Layer, 6 ... Oxidized layer, 8 ... Oxidized region, 10 ... Substrate, 14 ... Layer, 16 ... Oxide layer, 20 ... first mirror layer, 20a ... first portion, 20b ... second portion, 21 ... surface, 24 ... high refractive index layer, 24a ... upper surface, 24b ... side surface, 26 ... low refractive index layer, 26a ... Side surface, 30 ... active layer, 40 ... second mirror layer, 42 ... current confinement layer, 42a ... oxidized layer, 43 ... opening, 44 ... high refractive index layer, 46 ... low refractive index layer, 50 ... contact layer, 60 ... 1st area | region, 62 ... 2nd area | region, 63 ... Upper surface, 70 ... Resin layer, 80 ... 1st electrode, 82 ... 2nd electrode, 84 ... Pad, 86 ... Lead-out wiring, 100 ... Surface emitting laser, 1000 ... Atomic oscillator, 1100 ... optical module, 1110 ... gas cell, 1120 ... optical detector, 1200 Center wavelength control unit, 1300 ... high frequency control unit

Claims (6)

A substrate,
A first mirror layer provided above the substrate;
An active layer provided above the first mirror layer;
A second mirror layer provided above the active layer;
A first electrode electrically connected to the first mirror layer;
A second electrode electrically connected to the second mirror layer;
Including
The first mirror layer, the active layer, and the second mirror layer constitute a laminate,
The first mirror layer is a multilayer film in which high refractive index layers and low refractive index layers are alternately stacked,
The high refractive index layer and the low refractive index layer include Al,
The Al composition ratio of the high refractive index layer is smaller than the Al composition ratio of the low refractive index layer,
The surface emitting laser, wherein the first electrode is in contact with the upper surfaces of the plurality of high refractive index layers. In claim 1,
The first mirror layer has a first portion provided above the substrate, and a second portion provided above the first portion and constituting a part of the stacked body,
The surface emitting laser according to claim 1, wherein the first electrode is provided on a surface of the first portion. In claim 2,
The surface of the first portion includes an upper surface and a side surface of the high refractive index layer,
The upper surface of the high refractive index layer is parallel to the upper surface of the substrate,
A surface emitting laser characterized in that a side surface of the high refractive index layer is inclined with respect to an upper surface of the substrate. In any one of Claims 1 thru | or 3,
The surface emitting laser according to claim 1, wherein the first electrode is in contact with side surfaces of the plurality of low refractive index layers. In any one of Claims 1 thru | or 4,
The surface emitting laser according to claim 1, wherein the high refractive index layer and the low refractive index layer are AlGaAs layers.   An atomic oscillator comprising the surface emitting laser according to claim 1.

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