JP2011238852A - Surface-emitting laser element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-emitting laser element having good emission characteristics and reliability, and to provide a method of manufacturing the same.SOLUTION: A surface-emitting laser element comprises a multilayer film reflector which is grown using a growth substrate composed of ZnO, and an active layer grown on the multilayer film reflector and composed of an AlGaInN based material. The multilayer film reflector has a structure where a low refractive index layer composed of ZnMgBeO (0≤x1≤1, 0≤y1≤1) and a high refractive index layer composed of ZnO and having a refractive index higher than that of the low refractive index layer are laminated alternately, and the amount of strain for a ZnO crystal or the active layer is ±3% or less.

Description

  The present invention relates to a surface emitting laser element and a method for manufacturing the same.

  Conventionally, a semiconductor laser element using an active layer made of a GaInN-based material which is an AlGaInN-based material has been disclosed (see Patent Document 1 and Non-Patent Document 1). Patent Document 1 discloses an edge-emitting green semiconductor laser element using an active layer made of a GaInN-based material with a large In composition ratio. In this green semiconductor laser element, a ZnO substrate is used because of the similarity of the crystal structure and lattice constant to the GaInN-based material.

  On the other hand, in a semiconductor light emitting device in the ultraviolet region having a light emitting layer made of ZnO-based mixed crystal on a ZnO substrate, a DBR (Distributed) which is a multilayer film reflecting mirror made of ZnO-based mixed crystal between the ZnO substrate and the light emitting layer. A Bragg reflector is disclosed (see Patent Document 2).

JP 2008-66550 A JP 2008-78460 A

Y. Higuchi et al. “Room Temperature CW Lasing of a GaN-Based Vertical-Cavity Surface-Emitting Laser by Current Injection”, Applied Physics Express1 (2008) 121102

  An active layer made of an AlGaInN-based material has a problem that its emission characteristics and reliability are lowered when a large lattice strain (hereinafter referred to as strain) is present. In particular, when an active layer is formed on a multilayer reflector like a surface emitting laser element, the multilayer reflector may distort the active layer and reduce its emission characteristics and reliability. There's a problem.

  The present invention has been made in view of the above, and an object of the present invention is to provide a surface emitting laser element having good emission characteristics and reliability and a method for manufacturing the same.

In order to solve the above-described problems and achieve the object, a surface emitting laser device according to the present invention includes a multilayer reflector that is grown using a growth substrate made of ZnO, and an AlGaInN grown on the multilayer reflector. An active layer made of a system material, and the multilayer reflector includes a low refractive index layer made of Zn _1-x1-y1 Mg _x1 Be _y1 O (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1) and It has a structure in which high refractive index layers made of ZnO having a higher refractive index than that of the low refractive index layer are alternately stacked, and has a strain amount of ± 3% or less with respect to the ZnO crystal or the active layer.

The surface-emitting laser device according to the present invention includes a multilayer film reflecting mirror grown using a growth substrate made of ZnO, and an active layer made of an AlGaInN-based material grown on the multilayer film reflecting mirror, The multilayer mirror includes a low refractive index layer made of Zn _1-x1-y1 Mg _x1 Be _y1 O (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1) and Zn ₁ having a higher refractive index than the low refractive index layer. _-Z2 Cd _z2 O (0 ≦ z2 ≦ 1) and a structure in which high refractive index layers are alternately stacked, and a strain amount of ZnO crystal or the active layer is ± 3% or less. .

The surface-emitting laser device according to the present invention includes a multilayer film reflecting mirror grown using a growth substrate made of ZnO, and an active layer made of an AlGaInN-based material grown on the multilayer film reflecting mirror, The multilayer mirror includes a low refractive index layer made of Zn _1-x1 Mg _x1 O (0.3 ≦ x1 ≦ 0.9) and a high refractive index layer made of ZnO having a higher refractive index than the low refractive index layer. And a strain amount of the ZnO crystal or the active layer is ± 3% or less.

In the surface emitting laser element according to the present invention as set forth in the invention described above, the low refractive index layer of the multilayer reflector is Mg _x1 Be _y1 O (0.62 ≦ x1 ≦ 0.89, x1 + y1 = 1). It is characterized by that.

In the surface emitting laser element according to the present invention, the low refractive index layer of the multilayer reflector is Zn _1-y1 Be _y1 O (0.11 ≦ y2 ≦ 0.17). Features.

  The surface emitting laser element according to the present invention is characterized in that, in the above invention, the amount of distortion of the multilayer mirror is ± 2% or less.

  The surface emitting laser element according to the present invention is characterized in that, in the above invention, the amount of distortion of the multilayer reflector is ± 1% or less.

  The surface emitting laser element according to the present invention is characterized in that, in the above invention, the multilayer reflector is lattice-matched with a ZnO crystal or the active layer.

  Further, the surface emitting laser element according to the present invention is the above-described invention, wherein the low refractive index layer and the high refractive index layer of the multilayer reflector have different signs and absolute values with respect to the ZnO crystal or the active layer. Have the same amount of distortion.

In the surface emitting laser element according to the present invention, the low refractive index layer of the multilayer reflector is Mg _x1 Be _y1 O (0.62 ≦ x1 ≦ 0.73, x1 + y1 = 1). The high refractive index layer is Zn _{1-z 2} Cd _{z 2} O (0.75 ≦ 1-z2 ≦ 0.94).

In the surface emitting laser element according to the present invention, the low refractive index layer of the multilayer reflector is Mg _x1 Be _y1 O (0.70 ≦ x1 ≦ 0.82, x1 + y1 = 1). The high refractive index layer is Zn _{1 -z 2} Cd _{z 2} O (0.57 ≦ 1-z2 ≦ 0.78).

The method of manufacturing the surface emitting laser device according to the present invention includes a multilayer reflector growth process for growing a multilayer reflector on a ZnO substrate and an active layer made of an AlGaInN-based material on the multilayer reflector. A low refractive index layer made of Zn _1-x1-y1 Mg _x1 Be _y1 O (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1) in the multilayer reflector growth step. And the high refractive index layer made of ZnO having a refractive index higher than that of the low refractive index layer, the composition of each refractive index layer is adjusted so that the amount of strain with respect to the ZnO crystal or the active layer is ± 3% or less. And alternately laminating.

The method of manufacturing the surface emitting laser device according to the present invention includes a multilayer reflector growth process for growing a multilayer reflector on a ZnO substrate and an active layer made of an AlGaInN-based material on the multilayer reflector. A low refractive index layer made of Zn _1-x1-y1 Mg _x1 Be _y1 O (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1) in the multilayer reflector growth step. And a high refractive index layer made of Zn _1-z2 Cd _z2 O (0 ≦ z2 ≦ 1) having a refractive index higher than that of the low refractive index layer, the strain amount with respect to the ZnO crystal or the active layer is ± 3% or less. The composition of each refractive index layer is adjusted so as to be stacked alternately.

The method of manufacturing the surface emitting laser device according to the present invention includes a multilayer reflector growth process for growing a multilayer reflector on a ZnO substrate and an active layer made of an AlGaInN-based material on the multilayer reflector. A low-refractive index layer made of Zn _1-x1 Mg _x1 O (0.3 ≦ x1 ≦ 0.9) and the low-refractive index layer in the multilayer reflector growth step The high refractive index layers made of ZnO having a higher refractive index are alternately stacked by adjusting the composition of each refractive index layer so that the strain amount with respect to the ZnO crystal or the active layer is ± 3% or less. It is characterized by that.

  According to the present invention, since the distortion of the active layer is suppressed, there is an effect that a surface emitting laser element having good light emission characteristics and reliability can be realized.

FIG. 1 is a schematic cross-sectional view of the surface emitting laser element according to the first embodiment. FIG. 2 is a graph showing the relationship between the lattice constant (a) in the a-axis direction of the crystal lattice of the ZnMgBeCdO-based material and the band gap energy. FIG. 3 is a diagram showing the relationship between the lattice constant (a) and the refractive index of a ZnMgBeCdO-based material. Here, the refractive index changes due to a difference in crystal quality such as a carrier concentration and an impurity concentration accompanying a difference in manufacturing method and a difference in emission wavelength (wavelength dispersion of refractive index). FIG. 4 shows the refraction of the high refractive index layer and the low refractive index layer when the low refractive index layer is Mg _x1 Be _y1 O, the high refractive index layer is ZnO, and the Mg composition of the low refractive index layer is changed. It is a figure which shows the relationship between a rate difference and the reflectance of a lower DBR mirror. FIG. 5 shows the average distortion amount of the lower DBR mirror with respect to ZnO when the low refractive index layer is Mg _x1 Be _y1 O, the high refractive index layer is ZnO, and the Mg composition of the low refractive index layer is changed. It is a figure which shows the relationship between the refractive index of a low refractive index layer, thickness, and Mg composition, the refractive index difference of a high refractive index layer and a low refractive index layer, and the reflectance of a lower DBR mirror. FIG. 6 shows a case where the low refractive index layer is Mg _x1 Be _y1 O, the high refractive index layer is Zn _1-z2 Cd _z2 O, and the Mg composition of the low refractive index layer and the Zn composition of the high refractive index layer are changed. It is a figure which shows the relationship between the refractive index difference of a high refractive index layer and a low refractive index layer, and the reflectance of a lower DBR mirror. FIG. 7 shows a case where the low refractive index layer is Mg _x1 Be _y1 O, the high refractive index layer is Zn _1-z2 Cd _z2 O, and the Mg composition of the low refractive index layer and the Zn composition of the high refractive index layer are changed. The absolute value of the distortion amount of the low refractive index layer and the high refractive index layer with respect to ZnO, the Zn composition, refractive index, and thickness of the high refractive index layer, and the Mg composition, refractive index, and thickness of the low refractive index layer FIG. 4 is a diagram showing a relationship between a refractive index difference between a high refractive index layer and a low refractive index layer and a reflectance of a lower DBR mirror. FIG. 8 shows the Be composition of the low refractive index layer and the refractive index when the low refractive index layer is Zn _1-y1 Be _y1 O, the high refractive index layer is ZnO, and the Be composition of the low refractive index layer is changed. 45, the refractive index difference between the high refractive index layer and the low refractive index layer, the thickness of the low refractive index layer, the average distortion amount of the lower DBR mirror with respect to ZnO, and the number of pairs of the lower DBR mirrors It is a figure which shows the relationship with the reflectance in a case. FIG. 9 shows the Mg composition of the low refractive index layer and the refractive index when the low refractive index layer is Zn _1-x1 Mg _x1 O, the high refractive index layer is ZnO, and the Mg composition of the low refractive index layer is changed. 45, the refractive index difference between the high refractive index layer and the low refractive index layer, the thickness of the low refractive index layer, the average distortion amount of the lower DBR mirror with respect to ZnO, and the number of pairs of the lower DBR mirrors It is a figure which shows the relationship with the reflectance in a case. FIG. 10 shows the Cd composition of the high refractive index layer and the refractive index when the low refractive index layer is ZnO and the high refractive index layer is Zn _1-z1 Cd _z1 O, and the Cd composition of the high refractive index layer is changed. 45, the refractive index difference between the high refractive index layer and the low refractive index layer, the thickness of the high refractive index layer, the average strain of the lower DBR mirror with respect to ZnO, and the number of pairs of the lower DBR mirrors It is a figure which shows the relationship with the reflectance in a case. FIG. 11 shows each of the high refractive index layers and the low refractive indexes in a lower DBR mirror in which the low refractive index layer is Zn _0.64 Mg _0.36 O, the high refractive index layer is ZnO, and the number of pairs is 45 pairs. It is a figure which shows the reflection spectrum in case the deviation | shift amount with the design value in the surface of each thickness of a layer is 0%, 1%, 2%, 5%. FIG. 12 is a diagram showing the relationship between the amount of deviation and the reflectance at a wavelength of 530 nm in the reflection spectrum shown in FIG. FIG. 13 shows each of the high refractive index layers and the low refractive indexes in the lower DBR mirror in which the low refractive index layer is Mg _0.76 Be _0.24 O, the high refractive index layer is ZnO, and the number of pairs is 15 pairs. It is a figure which shows the reflection spectrum in case the deviation | shift amount with the design value in the surface of each thickness of a layer is 0%, 1%, 5%, 10%, 15%. FIG. 14 is a diagram showing the relationship between the amount of deviation and the reflectance at a wavelength of 530 nm in the reflection spectrum shown in FIG. FIG. 15 shows the low refractive index layer of the surface emitting laser element according to the second embodiment, in which the low refractive index layer of the lower DBR mirror is Mg _x1 Be _y1 O and the high refractive index layer is Zn _{1 -z2} Cd _z2 O. It is a figure which shows the relationship between the refractive index difference of a high refractive index layer and a low refractive index layer, and the reflectance of a lower DBR mirror at the time of changing Mg composition and Zn composition of a high refractive index layer. FIG. 16 shows a case where the low refractive index layer is Mg _x1 Be _y1 O, the high refractive index layer is Zn _1-z2 Cd _z2 O, and the Mg composition of the low refractive index layer and the Zn composition of the high refractive index layer are changed. The absolute value of the distortion amount of the low refractive index layer and the high refractive index layer with respect to the active layer, the Zn composition, refractive index, and thickness of the high refractive index layer, and the Mg composition, refractive index, and thickness of the low refractive index layer FIG. 6 is a diagram illustrating a relationship between a refractive index difference between a high refractive index layer and a low refractive index layer and a reflectance of a lower DBR mirror.

  Embodiments of a surface emitting laser element and a method for manufacturing the same according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
First, the surface emitting laser element according to the first embodiment of the present invention will be described. In the first embodiment, a case where the laser oscillation wavelength is 530 nm is illustrated.

  FIG. 1 is a schematic cross-sectional view of a surface emitting laser element 100 according to the first embodiment. As shown in FIG. 1, the surface-emitting laser element 100 includes a lower DBR mirror 2 that functions as a lower multilayer reflector that is laminated on a substrate 1 as a support substrate, an n-type conductivity type lower contact layer 3, n Lower electrode 4 serving as a side electrode, n-type conductivity type lower cladding layer 5, active layer 6, p-type conductivity type upper cladding layer 7, p-type conductivity type upper contact layer 8, current constriction layer 9, transparent conductive film 10, an upper electrode 11 serving as a p-side electrode, and an upper DBR mirror 12 functioning as an upper multilayer reflector. Among these, the laminated structure from the lower cladding layer 5 to the upper contact layer 8 is formed as a mesa post M formed into a columnar shape by an etching process or the like.

  The lower DBR mirror 2, the lower contact layer 3, the lower cladding layer 5, the active layer 6, the upper cladding layer 7 and the upper contact layer 8 are epitaxially grown using the substrate 1 as a growth substrate. The lower DBR mirror 2 and the upper DBR mirror 12 constitute an optical resonator with the active layer 6 interposed therebetween.

  Hereinafter, each component will be specifically described. First, the substrate 1 is made of ZnO having a wurtzite crystal structure, and the c-plane of the crystal lattice is the main surface. The main surface of the substrate 1 is particularly preferably a −c (000_1) plane which is an oxygen polar plane. In addition, the main surface of the substrate 1 is the (1_100) plane that is the m plane or the (11_20) plane that is the a plane and the plane orientation equivalent to these, or the (10_1_1) plane or the (11_22) plane that is a semipolar plane. And the plane orientation equivalent to these may be sufficient.

Lower DBR mirror 2 is stacked on the main surface of substrate 1. The lower DBR mirror 2 has a structure in which low refractive index layers 2a made of Mg _0.76 Be _0.24 O, which is a ZnMgBeCdO-based material, and high refractive index layers 2b made of ZnO are alternately stacked. If the combination of the adjacent low refractive index layer 2a and high refractive index layer 2b is one pair, the number of pairs is, for example, 15 pairs. The thicknesses of the low refractive index layer 2a and the high refractive index layer 2b are both λ / 4n (λ: laser oscillation wavelength, n: refractive index), and the reflection center wavelength of the lower DBR mirror 2 matches the laser oscillation wavelength. Is set to When the laser oscillation wavelength is 530 nm, the thickness of the low refractive index layer 2a is about 85 nm, and the thickness of the high refractive index layer 2b is about 63 nm.

  At a wavelength of 530 nm, the refractive index of the low refractive index layer 2a is 1.56, and the refractive index of the high refractive index layer 2b is 2.1. As a result, when 15 pairs of the low refractive index layer 2a and the high refractive index layer 2b are stacked, the lower DBR mirror 2 can realize a high reflectance of 99.98%.

Further, since the lattice constants of Mg _0.76 Be _0.24 O and ZnO which are constituent materials of the lower DBR mirror 2 are all 3.24 angstroms (Å, 1Å is 0.1 nm), the lower DBR mirror 2 The average lattice constant of is also 3.24Å, which matches the lattice constant of ZnO constituting the substrate 1. As a result, the lower DBR mirror 2 and the substrate 1 are lattice-matched.

  The lower contact layer 3 and the lower cladding layer 5 are sequentially stacked on the lower DBR mirror 2 and both are made of GaInN which is an AlGaInN-based material using Si as an n-type dopant. The In composition in the lower contact layer 3 and the lower cladding layer 5 is set to 10% or less.

  The lower electrode 4 has, for example, a Ti / Al structure or a Ti / Pt / Au structure, and is formed in a ring shape when viewed from above in a portion extending to the outer peripheral side of the mesa post M of the lower contact layer 3.

  The active layer 6 is laminated on the lower cladding layer 5 and has a quantum well structure in which well layers made of GaInN having a high In composition and barrier layers made of GaInN having a low In composition are alternately laminated. The thickness of the well layer and the barrier layer and the In composition are appropriately set according to the laser oscillation wavelength. For example, when the laser oscillation wavelength is 530 nm, the thickness and In composition of each layer are set such that the well layer is 4 nm, 0.35, the barrier layer is 10 nm, and 0.1.

  The upper cladding layer 7 and the upper contact layer 8 are sequentially stacked on the active layer 6, and both are made of GaInN using Mg as a p-type dopant. The In composition in the upper cladding layer 7 and the upper contact layer 8 is 10% or less, and is set to a thickness of 50 nm or less, which is a critical film thickness for the substrate 1 made of ZnO.

The current confinement layer 9 is laminated on the upper contact layer 8, and is formed in a ring shape having an opening 9a as a current injection portion. The current confinement layer 9 has an insulating property, and the current injected from the upper electrode 11 is constricted and concentrated in the opening 9a, thereby increasing the current density of the current injected into the active layer 6. ing. The current confinement layer 9 is made of an insulating material such as Si ₃ N ₄ or SiO ₂ . The current confinement layer 9 may be a layer made of GaInN that has been given high electrical resistance by implanting protons (H ⁺ ) or the like by ion implantation.

  The transparent conductive film 10 is formed so as to cover the current confinement layer 9 and the upper contact layer 8 exposed in the opening 9a. The transparent conductive film 10 is made of ITO (Indium Tin Oxide), antimony oxide or tin oxide doped with fluorine, or ZnO doped with Al or Ga. The transparent conductive film 10 transmits light emitted from the active layer 6 and spreads the current injected from the upper electrode 11 in the lateral direction (in-plane direction) from the opening 9a of the current confinement layer 9 to the upper contact layer. 8 has a function of injecting into 8.

  The upper electrode 11 has, for example, a Ni / Au structure or a Ni / Pd / Pt structure, and is formed in a ring shape on the upper contact layer 8 via the transparent conductive film 10.

  The upper DBR mirror 12 is formed on the upper contact layer 8 through the transparent conductive film 10 so as to cover the opening 9a. As the upper DBR mirror 12, for example, a mirror having the same structure as that of the lower DBR mirror 2 or a dielectric multilayer film can be used. The reflectance of the upper DBR mirror 12 is 99% or more, preferably 99.9% or more. It is preferable that the reflectance of the lower DBR mirror 2 and the upper DBR mirror 12 is increased because the threshold current density of the surface emitting laser element 100 is reduced.

When a dielectric multilayer film is used as the upper DBR mirror 12, the materials of the low-refractive index layer and the high-refractive index layer are appropriately selected and combined, and the dielectric is formed by stacking as many pairs as can achieve a desired reflectance. A multilayer film is formed. For example, as the low refractive index layer, ZrO ₂ (2.3), Ta ₂ O ₅ (2.2), HfO ₂ (2.11), MgO (1.74), Al ₂ O ₃ (1.7). ), Oxide dielectric such as SiO ₂ (1.5), nitride dielectric such as Si ₃ N ₄ (2.0), AlN (2.1), SiON (2.0-1.5), etc. Oxynitride dielectrics or fluoride dielectrics such as MgF ₂ (1.38) can be used. In addition, the inside of () represents the refractive index of each substance.

As the high refractive index layer, TiO ₂ (2.5), Nb ₂ O ₅ (2.4), ZrO ₂ (2.3), Ta ₂ O ₅ (2.2), HfO 2 (2.11). ), MgO (1.74), Al ₂ O 3 (1.7), SiO ₂ (1.5) and other oxide dielectrics, Si ₃ N ₄ (2.0), AlN (2.1), etc. Nitride dielectrics, oxynitride dielectrics such as SiON (2.0-1.5), or amorphous silicon such as α-Si: H (4.0) can be used.

  Next, the operation of the surface emitting laser element 100 will be described. When a voltage is applied between the upper electrode 11 and the lower electrode 4 and a drive current is injected, the current is concentrated from the upper electrode 11 in the opening 9a of the current confinement layer 9, and the density is increased. Implanted into the active layer 6. The active layer 6 into which the current is injected generates spontaneous emission light. The generated spontaneous emission light is laser-oscillated at a wavelength of 530 nm by the optical amplification effect of the active layer 6 and the action of the optical resonator formed by the lower DBR mirror 2 and the upper DBR mirror 12. Laser light is output upward from the upper DBR mirror 12.

  Here, in order to realize a laser oscillation wavelength longer than blue (about 420 nm or more), particularly blue to green wavelength (about 420 to 550 nm), when the active layer is made of GaInN having a high In composition, the following problems occur: Will occur. That is, phase separation occurs, the In composition in the active layer tends to be non-uniform, and the light emission efficiency may be reduced. In the case of GaInN, a piezo electric field is generated inside due to the crystal structure. However, in the case of a high In composition, the piezo electric field is increased, and the light emission recombination probability is lowered, and the light emission efficiency may be lowered. Further, when the piezo electric field is increased, there is a problem that the emission wavelength of the active layer is shifted when current is injected.

  In addition, when an active layer is formed on a substrate via a DBR mirror, as in a surface emitting laser element, strain is likely to accumulate between the substrate and the active layer, which causes a large amount of threading dislocations. There is a possibility that the light emitting efficiency and reliability of the active layer may be lowered. In particular, in the case of a DBR mirror of a surface emitting laser element, a high reflectance of, for example, 99% or more, preferably 99.9% or more is necessary. The composition must be such that the difference is as large as possible. If the difference in refractive index is small, the number of pairs of the low refractive index layer and the high refractive index layer must be increased. For this reason, threading dislocations and cracks are likely to occur in the DBR mirror, and the surface flatness is liable to be lowered. Therefore, the quality of the active layer formed thereon may be lowered, and the reliability may be lowered.

  On the other hand, in the surface emitting laser element 100 according to the first embodiment, since the average lattice constant of the lower DBR mirror 2 matches the lattice constant of the substrate 1, the lower DBR mirror 2 and the substrate 1 are Lattice matched. As a result, the influence of the strain on the active layer 6 is extremely reduced, so that the occurrence of the above-described layer separation, an increase in the piezoelectric field, and the occurrence of threading dislocations and cracks are extremely suppressed. Therefore, the active layer 6 is of high quality, and the surface emitting laser element 100 having good light emission characteristics and reliability is obtained.

  Thus, the surface emitting laser element 100 according to the first embodiment is a surface emitting laser element having good light emission characteristics and reliability.

  In the surface emitting laser element 100 according to the first embodiment, the composition of the lower DBR mirror 2 is set so as to lattice match with the substrate 1, but the composition of the lower DBR mirror 2 is not limited to this. Below, the preferable composition of the lower DBR mirror 2 will be described more specifically.

FIG. 2 is a graph showing the relationship between the lattice constant (a) in the a-axis direction of the crystal lattice of the ZnMgBeCdO-based material and the band gap energy. In FIG. 2, the unit of lattice constant is “Å”, and the unit of band gap energy is electron volt (eV, 1 eV is about 1.60 × 10 ⁻¹⁹ Joule). Small black circles are data points indicating the relationship between the lattice constant (a) of ZnO, MgO, BeO, and CdO and the band gap energy, respectively. The lattice constants (a) of ZnO, MgO, BeO and CdO are 3.24Ｏ, 3.43Å, 2.70Å and 3.66Å, respectively. In the case of a ZnMgBeCdO-based material, there are data points on or in the sides of the quadrilateral connecting the black circles according to the composition ratio of each composition.

  Point P1 represents a data point corresponding to an example of an average composition in the lower DBR mirror 2 in consideration of the thickness and composition of the high refractive index layer 2b and the low refractive index layer 2a. The broken line L1 has a band gap energy of 2.34 eV, which is 530 nm which is the laser oscillation wavelength of the surface emitting laser element 100 when converted to the wavelength of light.

  As shown in FIG. 2, if the average composition of the lower DBR mirror 2 is selected such that the band gap energy is higher than the broken line L1 as indicated by the point P1, the lower DBR mirror 2 absorbs light having a wavelength of 530 nm. This is preferable because there is no fear that the threshold value of laser oscillation is increased or the intensity of laser light is reduced.

  Next, FIG. 3 is a diagram showing the relationship between the lattice constant (a) and the refractive index of the ZnMgBeCdO-based material. Small black circles are data points indicating the relationship between the lattice constant and the refractive index of ZnO, MgO, BeO, and CdO, respectively. In the case of a ZnMgBeCdO-based material, there are data points on or in the sides of the quadrilateral connecting the black circles according to the composition ratio of each composition. Here, the refractive index changes due to a difference in crystal quality such as a carrier concentration and an impurity concentration accompanying a difference in manufacturing method and a difference in emission wavelength (wavelength dispersion of refractive index).

  Point P2 indicates a data point corresponding to an example of an average composition in the lower DBR mirror 2. The point P2 and the point P1 in FIG. 2 show the same composition. A broken line L2 indicates the value of the lattice constant of ZnO constituting the substrate 1 (3.24３). A broken line L3 indicates a lattice constant value (3.14３) at which the strain amount with respect to the crystal lattice of ZnO is −3%. A broken line L4 indicates a lattice constant value (3.34Å) at which the strain amount with respect to the crystal lattice of ZnO is + 3%.

  As shown in FIG. 3, the average composition of the lower DBR mirror 2 is such that the average lattice constant is between the broken line L3 and the broken line L4, that is, the strain amount with respect to ZnO is ± 3% or less, as indicated by the point P2. If the composition is such that the influence of the strain on the active layer 6 is extremely reduced, the surface emitting laser element 100 having good emission characteristics and reliability is realized and preferable.

Next, specific examples of the composition of the low refractive index layer 2a and the composition of the high refractive index layer 2b that are preferable in the lower DBR mirror 2 will be given. Hereinafter, when the composition of the low refractive index layer 2a is specified, the composition formula Zn _1-x1-y1-z1 Mg _x1 Be _y1 Cd _z1 O (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, 0 ≦ z1 ≦) 1), when the composition of the high refractive index layer 2b is clearly indicated, the composition formula Zn _1-x2-y2-z2 Mg _x2 Be _y2 Cd _z2 O (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1, 0 ≦ z2 ≦ 1).

(MgBeO / ZnO)
First, the characteristics of the lower DBR mirror 2 when the low refractive index layer 2a is Mg _x1 Be _y1 O (x1 + y1 = 1) and the high refractive index layer 2b is ZnO will be described.

FIG. 4 shows the high refractive index layer 2b and the low refractive index when the low refractive index layer 2a is Mg _x1 Be _y1 O, the high refractive index layer 2b is ZnO, and the Mg composition of the low refractive index layer 2a is changed. It is a figure which shows the relationship between the refractive index difference (dn) with the layer 2a, and the reflectance (R [%]) of the lower DBR mirror 2. FIG. The high refractive index layer 2b has a refractive index of 2.1 and a thickness of 63.1 nm. FIG. 4 shows a case where the number of pairs of the high refractive index layer 2b and the low refractive index layer 2a of the lower DBR mirror 2 is 15 pairs and 10 pairs.

  In FIG. 4, broken lines L5 to L9 indicate positions that are compositions when the distortion amount of the lower DBR mirror 2 with respect to ZnO is 0%, −3%, + 3%, −1%, and + 1%, respectively. Broken lines L10 and L11 indicate positions where R is 99% and 99.9%, respectively.

Further, FIG. 5 is similar to FIG. 4 in which the low refractive index layer 2a is Mg _x1 Be _y1 O, the high refractive index layer 2b is ZnO, and the Mg composition of the low refractive index layer 2a is changed. The average strain amount [%] of the lower DBR mirror 2 with respect to the refractive index (n), thickness (t [nm]) and Mg composition of the low refractive index layer 2a, and the high refractive index layer 2b and the low refractive index. It is a figure which shows the relationship between the refractive index difference (dn) with the layer 2a, and the reflectance (R [%]) of the lower DBR mirror 2. FIG. The data in FIG. 4 and the data in FIG. 5 partially overlap.

  As shown in FIGS. 4 and 5, when the Mg composition (x1) described above is 0.76, the strain amount is 0%, and dn is sufficiently large as 0.54. Even when the number of pairs in the lower DBR mirror 2 is relatively small, 15 pairs, a high reflectance of 99.9% or more can be realized.

The lower DBR mirror 2 using the low refractive index layer 2a made of Mg _x1 Be _y1 O having an Mg composition (x1) of 0.76 to 0.89 has a distortion amount of 0% to + 3% (compression strain). The lower DBR mirror 2 using the low refractive index layer 2a made of Mg _x1 Be _y1 O having an Mg composition (x1) of 0.76 to 0.62 has a strain amount of 0% to −3% (tensile strain). In any case, a high reflectivity of 99% or more, particularly 99.9% or more, is realized as a relatively small number of 15 pairs or even a smaller number of 10 pairs.

Further, the lower DBR mirror 2 using the low refractive index layer 2a made of Mg _x1 Be _y1 O having an Mg composition (x1) of 0.76 to 0.84 has a distortion amount of 0% to + 2% (compression) The lower DBR mirror 2 using the low refractive index layer 2a made of Mg _x1 Be _y1 O having an Mg composition (x1) of 0.76 to 0.67 has a distortion amount of 0% to -2% (strain). Tensile strain), and in either case, a relatively low number of 15 pairs or even a smaller number of 10 pairs realizes a high reflectance of 99% or more, particularly 99.9% or more.

Further, the lower DBR mirror 2 using the low refractive index layer 2a made of Mg _x1 Be _y1 O having an Mg composition (x1) of 0.76 to 0.80 has a distortion amount of 0% to + 1% (compression) The lower DBR mirror 2 using the low refractive index layer 2a made of Mg _x1 Be _y1 O having an Mg composition (x1) of 0.76 to 0.71 has a distortion amount of 0% to -1% ( Tensile strain), and in either case, a relatively low number of 15 pairs or even a smaller number of 10 pairs realizes a high reflectance of 99% or more, particularly 99.9% or more.

  Further, in order to achieve a particularly preferable reflectance of 99.9% while suppressing the distortion amount within ± 3%, the Mg composition (x1) in the low refractive index layer 2a is set to 0.62 to 0.84. The number of pairs may be 15 pairs.

(ZnCdO / MgBeO)
Next, the low refractive index layer 2a is Mg _x1 Be _y1 O (x1 + y1 = 1), but the high refractive index layer 2b is made of ZnO having a higher refractive index than ZnO by mixing Cd into ZnO instead of ZnO. The characteristics of the lower DBR mirror 2 when _1-z2 Cd _z2 O (0 <z2 <1) will be described. Thus, by combining Zn _{1 -z 2} Cd _{z 2} O having a larger lattice constant than ZnO and Mg _x1 Be _y1 O having a smaller lattice constant than ZnO, the refractive index difference can be further increased. At the same time, the composition of Zn _{1 -z 2} Cd _{z 2} O (the amount of strain is positive) and the composition of Mg _x1 Be _y1 O (the amount of strain is negative) are different in the sign of the amount of distortion with respect to ZnO but have the same absolute value. By combining these, distortion in the lower DBR mirror 2 is compensated. As a result, the lower DBR mirror 2 having a high reflectivity and a compensated distortion can be realized with a smaller number of pairs. The surface emitting laser element 100 using the lower DBR mirror 2 in which the distortion is compensated in this way has particularly good emission characteristics and reliability.

In FIG. 6, the low refractive index layer 2a is Mg _x1 Be _y1 O, the high refractive index layer 2b is Zn _1-z2 Cd _z2 O, and the Mg composition of the low refractive index layer 2a and the Zn composition of the high refractive index layer 2b are shown. It is a figure which shows the relationship between the refractive index difference (dn) of the high refractive index layer 2b and the low refractive index layer 2a, and the reflectance (R [%]) of the lower DBR mirror 2 at the time of changing. The combination of the Mg composition of the low refractive index layer 2a and the Zn composition of the high refractive index layer 2b is selected so that the absolute value of the strain amount with respect to ZnO is the same. Further, FIG. 6 shows a case where the number of pairs of the high refractive index layer 2b and the low refractive index layer 2a of the lower DBR mirror 2 is 15 pairs and 10 pairs.

  In FIG. 6, broken lines L12 to L15 indicate that the absolute values of the distortion amounts of the low refractive index layer 2a and the high refractive index layer 2b with respect to the ZnO crystal lattice are 3%, 2%, 1%, and 0.5%, respectively. The position of the refractive index difference when the composition is as follows is shown. A broken line L16 indicates a position where R is 99.9%.

7, similarly to FIG. 6, the low refractive index layer 2 a is Mg _x1 Be _y1 O and the high refractive index layer 2 b is Zn _1-z2 Cd _z2 O, and the Mg composition and the high refractive index layer 2 a are high. When the Zn composition of the refractive index layer 2b is changed, the absolute value [%] of the distortion amount of the low refractive index layer 2a and the high refractive index layer 2b with respect to ZnO, and the Zn composition and refractive index of the high refractive index layer 2b ( n), thickness (t [nm]), Mg composition, refractive index (n), and thickness (t [nm]) of the low refractive index layer 2a, high refractive index layer 2b and low refractive index layer It is a figure which shows the relationship between the refractive index difference (dn) with 2a, and the reflectance (R [%]) of the lower DBR mirror 2. FIG. The data in FIG. 6 and the data in FIG. 7 overlap.

As shown in FIGS. 6 and 7, and the high refractive index layer 2b made Zn composition of (1-z2) from _{Zn 1-z2 Cd} z2 O which was .94 to .75, Mg composition of (x1) 0. The lower DBR mirror 2 using the low refractive index layer 2a made of Mg _x1 Be _y1 O from 73 to 0.62 is compensated for internal distortion and has a large refractive index difference (dn). As a result, even when the number of pairs in the lower DBR mirror 2 is 10, a reflectance of 99.9% or more can be realized. Furthermore, if the number of pairs is set to 15, the reflectance of 99.9% or more can be realized more easily.

(ZnO / ZnBeO, ZnO / ZnMgO, ZnCdO / ZnO)
Next, when the low refractive index layer 2a is Zn _1-y1 Be _y1 O (0 <y2 <1) or Zn _1-x1 Mg _x1 O (0 <x1 <1), and the high refractive index layer 2b is ZnO , or a low refractive index layer 2a and ZnO, explaining the high refractive index layer _{2b Zn 1-z2 Cd z2 O} (0 <z2 <1) and the characteristics of the lower DBR mirror 2 in the case of the. In these lower DBR mirrors 2 combining ZnO and ZnBeO, ZnMgO, or ZnCdO, the difference in refractive index between the high refractive index layer 2b and the low refractive index layer 2a is small, so the number of pairs is increased in order to increase the reflectance. Is increasing. Hereinafter, characteristics of the lower DBR mirror 2 in each combination will be described.

FIG. 8 shows the Be of the low refractive index layer 2a when the low refractive index layer 2a is Zn _1-y1 Be _y1 O, the high refractive index layer 2b is ZnO, and the Be composition of the low refractive index layer 2a is changed. Composition, refractive index (n), refractive index difference (dn) between high refractive index layer 2b and low refractive index layer 2a, thickness of low refractive index layer 2a (t [nm]), and lower part with respect to ZnO It is a figure which shows the relationship between the average distortion amount [%] of the DBR mirror 2, and the reflectance (R [%]) when the number of pairs of the lower DBR mirror 2 is 45 pairs.

As shown in FIG. 8, the lower DBR mirror 2 using the low refractive index layer 2a made of Zn _1-y1 Be _y1 O with a Be composition (y1) of 0.11 has a strain amount of −2%. Further, the reflectance is preferably about 99%. Further, when the Be composition (y1) is set to 0.17, the strain amount is −3%, and the reflectance is more preferably 99.9% or more.

FIG. 9 shows the Mg of the low refractive index layer 2a when the low refractive index layer 2a is Zn _1-x1 Mg _x1 O, the high refractive index layer 2b is ZnO, and the Mg composition of the low refractive index layer 2a is changed. Composition, refractive index (n), refractive index difference (dn) between high refractive index layer 2b and low refractive index layer 2a, thickness of low refractive index layer 2a (t [nm]), and lower part with respect to ZnO It is a figure which shows the relationship between the average distortion amount [%] of the DBR mirror 2, and the reflectance (R [%]) when the number of pairs of the lower DBR mirror 2 is 45 pairs.

As shown in FIG. 9, the lower DBR mirror 2 using the low refractive index layer 2a made of Zn _1-x1 Mg _x1 O having an Mg composition (x1) of 0.36 has a strain amount of 2%, and The reflectance is preferably about 99%. Further, when the Mg composition (x1) is 0.56, the strain amount is 3% and the reflectance is 99.9% or more, which is more preferable.

FIG. 10 shows the Cd of the high refractive index layer 2b when the low refractive index layer 2a is ZnO and the high refractive index layer 2b is Zn _1-z1 Cd _z1 O, and the Cd composition of the high refractive index layer 2b is changed. Composition, refractive index (n), refractive index difference (dn) between high refractive index layer 2b and low refractive index layer 2a, thickness of high refractive index layer 2b (t [nm]), and lower part with respect to ZnO It is a figure which shows the relationship between the average distortion amount [%] of the DBR mirror 2, and the reflectance (R [%]) when the number of pairs of the lower DBR mirror 2 is 45 pairs.

As shown in FIG. 10, the lower DBR mirror 2 using the high refractive index layer 2b made of Zn _1-z1 Cd _z1 O having a Cd composition (z1) of 0.26 has a strain amount of 3%, and The reflectivity is about 97%.

(Relationship between in-plane distribution of thickness of lower DBR mirror and reflection characteristics)
Next, the relationship between the in-plane distribution of the thickness of the lower DBR mirror 2 and the reflection characteristics will be described. First, a case where ZnO and ZnMgO are combined will be described as an example where the refractive index difference between the high refractive index layer 2b and the low refractive index layer 2a is small. Next, as an example where the refractive index difference is large, ZnO and MgBeO The case where it combines is demonstrated.

  First, in the lower DBR mirror 2 in which ZnO and ZnMgO are combined, since the difference in refractive index between the high refractive index layer 2b and the low refractive index layer 2a is small, the number of pairs is increased in order to increase the reflectance. However, if the refractive index difference is small, the stop bandwidth (reflection bandwidth) of the lower DBR mirror 2 is narrowed. In addition to this, since the number of pairs increases, a deviation from the design values of the thickness and composition of the high refractive index layer 2b and the low refractive index layer 2a, which occurs depending on the performance of the growth apparatus, accumulates. The uniformity and reproducibility of the in-plane distribution of the sheath composition decreases. As a result, it becomes difficult to match the stop band to the wavelength at which laser oscillation is desired over the entire surface of the substrate. Therefore, the reflectance of the lower DBR mirror 2 is lowered at the designed laser oscillation wavelength, and there is a possibility that good light emission characteristics cannot be obtained. Therefore, the deviation from the design values of the thickness and composition of each refractive index layer should be in an appropriate range.

FIG. 11 shows the lower DBR mirror 2 in which the low refractive index layer 2a is Zn _0.64 Mg _0.36 O, the high refractive index layer 2b is ZnO, and the number of pairs is 45 pairs. The figure which shows the reflection spectrum in case the deviation | shift amount with respect to the design value in the surface of each thickness of each low refractive index layer 2a is 0% (namely, as design value), 1%, 2%, 5% It is. The amount of deviation refers to a deviation from the design value of the individual thickness of each high refractive index layer 2b and each low refractive index layer 2a in the wafer plane. The lower DBR mirror 2 has an average strain amount of + 2% with respect to ZnO.

  In FIG. 11, the horizontal axis indicates the wavelength (λ wavelength [nm]), and the vertical axis indicates the reflectance (R [%]). A broken line L17 indicates 530 nm as a design value of the laser oscillation wavelength. As shown in FIG. 11, in the lower DBR mirror 2 having a large number of pairs, the stop band width is narrow, and the tolerance for the deviation from the design value of the lower DBR mirror 2 is narrowed.

FIG. 12 is a diagram showing the relationship between the amount of deviation and the reflectance at a wavelength of 530 nm in the reflection spectrum shown in FIG. In FIG. 11, the reflectivities when the deviation amounts are 0%, 1%, 2%, and 5% are 99.3%, 98.9%, 93.9%, and 11.7%, respectively. Thus, in the lower DBR mirror 2 in which the low refractive index layer 2a is made of Zn _0.64 Mg _0.36 O, the high refractive index layer 2b is made of ZnO, and the number of pairs is 45 pairs, the thickness design in the plane is designed. By suppressing the deviation from the value within ± 2%, which is easy to realize, even if the number of pairs is as large as 45 pairs, the decrease in reflectance is suppressed, and a reflectance of 90% or more can be realized. Can be mass-produced.

When the low refractive index layer 2a is made of Zn _1-x1 Mg _x1 O and the Mg composition (x1) is too small, the number of pairs is more than 45 pairs in order to realize a reflectance of 90% or more. Therefore, it becomes difficult to make the amount of deviation within ± 2%, and the mass productivity decreases. However, if the Mg composition (x1) is 0.3 or more, it is easy to suppress the deviation amount within ± 2% by setting the number of pairs to 45 pairs or less, and a reflectance of 90% or more can be realized. Therefore, mass productivity becomes high and is preferable.

  Incidentally, in this lower DBR mirror 2, if the Mg composition of the low refractive index layer 2a is 0.15 or more at which the strain amount is 1% or more and 0.60 or less at which the strain amount is 3% or less, A high reflectance of 90% or more can be realized with the number of pairs within 45 pairs.

  In addition, even in other combinations where the refractive index difference between the high refractive index layer 2b and the low refractive index layer 2a is small, for example, a combination of ZnO / ZnBeO, ZnO / ZnMgO, or ZnCdO / ZnO, the number of pairs is 45 pairs or less. If the composition is such that the amount of deviation is suppressed to within ± 2% and a reflectance of 90% or more can be realized, mass productivity becomes high.

  Next, in the lower DBR mirror 2 in which ZnO and MgBeO are combined, the difference in refractive index between the high refractive index layer 2b and the low refractive index layer 2a is large, so the number of pairs for increasing the reflectance is reduced. In this case, the stop band width of the lower DBR mirror 2 is widened, and accumulation of deviations from the design values of the thickness and composition of the high refractive index layer 2b and the low refractive index layer 2a is suppressed, so that the in-plane distribution is uniform. And reproducibility increase. As a result, it becomes easier to match the stop band to the wavelength to be laser-oscillated over the entire surface of the substrate, and the high reflectivity of the lower DBR mirror 2 is more reliably realized, which is suitable for realizing good light emission characteristics. is there.

FIG. 13 is a diagram illustrating a lower DBR mirror 2 in which the low refractive index layer 2a is Mg _0.76 Be _0.24 O, the high refractive index layer 2b is ZnO, and the number of pairs is 15 pairs. Reflection spectrum when the amount of deviation of the individual thickness of each low refractive index layer 2a from the in-plane design value is 0% (that is, as designed value), 1%, 5%, 10%, 15% FIG. The lower DBR mirror 2 is lattice-matched to the ZnO crystal as described above.

  In FIG. 13, a broken line L18 indicates 530 nm which is a design value of the laser oscillation wavelength. As shown in FIG. 13, in the lower DBR mirror 2 with a small number of pairs, the stop band width is wide, and the tolerance for the deviation from the design value of the lower DBR mirror 2 is extremely large.

FIG. 14 is a diagram showing the relationship between the amount of deviation and the reflectance at a wavelength of 530 nm in the reflection spectrum shown in FIG. In FIG. 14, the reflectance when the deviation amount is 0%, 1%, 5%, and 10% is about 100%, and the reflectance when the deviation amount is 15% is 62.8%. It was. Thus, in the lower DBR mirror 2 (lattice matching with ZnO crystal) in which the low refractive index layer 2a is Mg _0.76 Be _0.24 O, the high refractive index layer 2b is ZnO, and the number of pairs is 15 pairs, Even if the deviation from the design value of the thickness in the plane is ± 10%, an extremely high reflectivity of about 100% can be realized, so that the mass productivity is further increased. Although the in-plane distribution of thickness and the change in reflectance are described here, in-plane distribution of composition must actually be considered.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. The surface emitting laser element according to the second embodiment has the same structure as the surface emitting laser element according to the first embodiment, but the composition of the lower DBR mirror is set with respect to the active layer. The point is different. Hereinafter, the lower DBR mirror will be described in detail.

The lower DBR mirror in the surface emitting laser element according to the second embodiment has a low refractive index layer of Mg _x1 Be _y1 O (x1 + y1 = 1) and a high refractive index, as in the case shown in FIGS. The layer is Zn _1-z2 Cd _z2 O (0 <z2 <1), which realizes high reflectivity with a small number of pairs by increasing the difference in refractive index and compensating for distortion in the lower DBR mirror It is. However, the surface-emitting laser element according to the second embodiment differs from the surface-emitting laser element according to the first embodiment in that the sign of the strain amount is different from the GaInN crystal constituting the active layer, but the absolute value is the same. The lower DBR mirror and the active layer are lattice-matched by combining the composition of Zn _{1 -z 2} Cd _{z 2} O (the amount of strain is positive) and the composition of Mg _x1 Be _y1 O (the amount of strain is negative).

  As described above, the lattice matching between the active layer and the lower DBR mirror also greatly reduces the influence of the strain on the active layer, thereby realizing a surface emitting laser element having good light emission characteristics and reliability. .

FIG. 15 shows the low refractive index layer of the surface emitting laser element according to the second embodiment, in which the low refractive index layer of the lower DBR mirror is Mg _x1 Be _y1 O and the high refractive index layer is Zn _{1 -z2} Cd _z2 O. The refractive index difference (dn) between the high refractive index layer and the low refractive index layer and the reflectance (R [%]) of the lower DBR mirror when the Mg composition and the Zn composition of the high refractive index layer are changed. It is a figure which shows a relationship. As the combination of the Mg composition of the low refractive index layer and the Zn composition of the high refractive index layer, a combination having the same absolute value of the strain amount with respect to GaInN constituting the active layer is selected. The thickness and In composition of each layer of GaInN which is a constituent material of the active layer are set such that the well layer is 4 nm and 0.35, the barrier layer is 10 nm and 0.1. At this time, the lattice constant of the active layer is 3.3Å.

  FIG. 15 shows the case where the number of pairs of the high refractive index layer and the low refractive index layer of the lower DBR mirror is 5 pairs, 10 pairs, and 15 pairs. In FIG. 15, broken lines L19 to L22 indicate that the absolute values of the distortion amounts of the low refractive index layer and the high refractive index layer with respect to the GaInN crystal constituting the active layer are 3%, 2%, 1%, The position of the refractive index difference when the composition is 0.5% is shown.

Further, in FIG. 16, similarly to FIG. 15, the low refractive index layer is Mg _x1 Be _y1 O, the high refractive index layer is Zn _1-z2 Cd _z2 O, the Mg composition of the low refractive index layer and the high refractive index layer The absolute value [%] of the distortion amount of the low refractive index layer and the high refractive index layer with respect to the active layer, the Zn composition of the high refractive index layer, the refractive index (n), and the thickness (T [nm]), Mg composition, refractive index (n), and thickness (t [nm]) of the low refractive index layer, and refractive index difference (dn) between the high refractive index layer and the low refractive index layer It is a figure which shows the relationship between and the reflectance (R [%]) of a lower DBR mirror. The data in FIG. 15 and the data in FIG. 16 overlap.

As shown in FIGS. 15 and 16, and the high refractive index layer made of _{Zn 1-z2 Cd} z2 O with Zn composition of (1-z2) and from 0.78 to 0.57, Mg composition of (x1) 0.82 The lower DBR mirror using the low refractive index layer made of Mg _x1 Be _y1 O from 0.70 to 0.70 is lattice-matched with the active layer, compensates for internal distortion, and has a refractive index difference (dn ) Also increases. As a result, even when the number of pairs in the lower DBR mirror is 5, a reflectance of 90% or more can be realized. Furthermore, if the number of pairs is 10 or 15 pairs, a reflectance of 99.9% or more can be easily realized. Further, since tolerance against deviation from the design value of the lower DBR mirror becomes extremely large, the mass productivity is high.

  In the second embodiment, the active layer and the lower DBR mirror are lattice-matched and distortion is compensated for in the lower DBR mirror. However, the present invention is not limited to this. That is, the average composition of the lower DBR mirror is such that the average strain amount with respect to the active layer is ± 3% or less, preferably ± 2% or less, more preferably ± 1% or less, or the active layer and the lower DBR mirror If the composition is such that the lattice matching is achieved, the influence of the strain on the active layer is greatly reduced, so that a surface-emitting laser element having good emission characteristics and reliability is realized. In this case, the number of pairs in the lower DBR mirror is appropriately set according to a desired reflectance.

For example, the lower refractive index layer is made of Zn _1-x1 Mg _x1 O (0 <x1 <1), the high refractive index layer is made of ZnO as a lower DBR mirror, the thickness of each layer of GaInN which is a constituent material of the active layer, and In A case where the composition is set such that the well layer is 4 nm and 0.35, and the barrier layer is 10 nm and 0.1 is illustrated. In this case, the Mg composition (x1) for which the strain amount of the lower DBR mirror with respect to the active layer is 0.5% or more is 0.3 or more, and the Mg composition (x1) for which the strain amount is 3% or less is 0. When a lower DBR mirror having a composition of 9 or less and 45 pairs is used, a reflectance of 99% or more can be realized.

  The thickness, the number of pairs, and the reflectance of the low refractive index layer and the high refractive index layer described above are shown when the reflection center wavelength of the lower DBR mirror is set to a wavelength of 530 nm. Since the ZnMgBeCdO-based material has a wavelength dispersion characteristic and its refractive index changes according to the wavelength, the thickness and the number of pairs of the low refractive index layer and the high refractive index layer are set to a desired reflectance at a predetermined reflection center wavelength. Adjust appropriately to achieve

(Production method)
Next, an example of a method for manufacturing the surface emitting laser element 100 according to Embodiment 1 will be described.

(Semiconductor layer growth)
First, a substrate 1 made of ZnO is prepared. As for a substrate made of ZnO, a large-diameter substrate having a diameter of 2 to 3 inches (50.8 to 76.2 mm) is realized, which is suitable for mass production of elements. A substrate made of ZnO is preferable because it has higher thermal conductivity than a sapphire substrate.

  Next, using the substrate 1 as a growth substrate, adjusting the composition of the lower DBR mirror 2 on the substrate 1 so that the low refractive index layer 2a and the high refractive index layer 2b have a desired strain amount and refractive index, Epitaxial growth is performed for the desired number of pairs. The lower DBR mirror 2 is grown using a PLD (pulse laser deposition) method, an MBE (molecular beam epitaxy) method, an MOCVD (metal organic chemical vapor deposition) method, or the like.

  In the PLD method and the MBE method, an oxygen plasma cell capable of generating oxygen radicals as an oxygen source can be used. In the PLD method, ZnO, MgO, BeO, and CdO having a desired composition and their compounds, ZnMgO, ZnBeO, ZnCdO, MgBeO, and ZnMgBeCdO are used as target materials, and in the MBE method, Zn, Mg, Be, and Cd are used as metal raw materials. It can be supplied using a cell.

In MOCVD, diethyl zinc (DEZn) and dimethyl zinc (DMZn) as Zn raw materials that are Group II materials, diethyl magnesium (DEMg) and dimethyl magnesium (DMMg) as Mg raw materials, and diethyl cadmium (DECd) as Cd raw materials The lower DBR mirror 2 is supplied with organic metal materials such as dimethyl cadmium (DMCd), diethyl beryllium (DEBe) and dimethyl cadmium (DMCd) as Be raw materials, and oxygen (O ₂ ) as O raw materials. Can be formed.

  Note that it is more preferable to use the PLD method or the MBE method because the crystal growth can be performed without hydrogen, and the interface reaction between the lower DBR mirror 2 and the AlGaInN-based material can be suppressed.

  Next, the lower contact layer 3, the lower cladding layer 5, the active layer 6, the upper cladding layer 7, and the upper contact layer 8 are sequentially epitaxially grown on the lower DBR mirror 2. The growth of each layer made of GaInN, which is a nitride semiconductor, is performed using a PLD method, an MBE method, an MOCVD method, or the like.

  In the PLD method and the MBE method, a nitrogen plasma cell that generates nitrogen radicals can be used as a nitrogen source. In addition, as a group III material, AlN, GaN, InN, AlGaN, GaInN, AlGaInN or the like having a desired composition is supplied as a target material in the PLD method, and Al, Ga, In is supplied using a Knudsen cell in the MBE method.

In the MOCVD method, ammonia (NH ₃ ) can be used as a nitrogen source. Further, as group III materials, trimethylaluminum (TMA) and triethylaluminum (TEA) as Al materials, trimethylgallium (TMG) and triethylgallium (TEG) as Ga materials, trimethylindium (TMI) and triethyl as In materials Each nitride semiconductor layer is grown by appropriately supplying indium (TEI).

In addition, since ammonia and an oxide semiconductor react at a relatively low temperature and the oxide semiconductor is sublimated, the MBE method or the like is used to form the lower contact layer 3 on the lower DBR mirror 2 made of an oxide semiconductor. Is preferred. Then, after the lower DBR mirror 2 is covered with the nitride semiconductor, each nitride semiconductor layer with better crystal quality can be obtained by using the MOCVD method. Further, the side surfaces and the back surface of the substrate 1 made of ZnO and the lower DBR mirror 2 may be sublimated by reacting with ammonia during the growth of each nitride semiconductor layer by the MOCVD method, so that Si ₃ N It is preferable to protect it with an insulating film such as ₄ or SiO ₂ , a metal or the like.

(Element fabrication)
Next, a circular mask pattern corresponding to the outer periphery of the upper electrode 11 is formed by photolithography, and wet etching or dry etching is performed from the upper contact layer 8 to the lower contact layer 3 using the mask pattern as a mask. Form. Next, after a mask having a pattern corresponding to the shape of the lower electrode 4 is formed, a metal layer of Ti / Al structure or Ti / Pt / Au structure as a material of the lower electrode 4 is formed by resistance heating vapor deposition (RH), electron Deposited by line evaporation (EB), sputter deposition or the like, lifted off to form the lower electrode 4, and further subjected to heat treatment to form ohmic contact.

Next, a SiO ₂ layer or a Si ₃ N ₄ layer is deposited on the upper contact layer 8 by sputtering, PCVD (plasma chemical vapor deposition), or the like, and the current confinement layer 9 is formed by photolithography. Thereafter, for example, an ITO film is deposited on the entire surface to form the transparent conductive film 10. Next, an upper electrode 11 having a Ni / Au structure or a Ni / Pd / Pt structure is formed on the transparent conductive film 10 so as to surround the opening 9 a of the current confinement layer 9. Subsequently, the upper DBR mirror 12 is formed in the opening of the upper electrode 11 by sputtering or PCVD. Thereafter, the element is separated by dicing to complete the surface emitting laser element 100.

  A plurality of surface emitting laser elements arranged one-dimensionally or two-dimensionally during dicing may be cut out to form a surface emitting laser array element. Further, when these elements are mounted on a CAN package such as TO-CAN, for example, the following is performed. First, after the cut-out element is bonded on a heat sink or a submount, it is bonded on a heat sink such as copper. Then, the device is bonded to the CAN, and the electrode portion of the device and the CAN are wire-bonded. Finally, the CAN is sealed in a vacuum or a nitrogen atmosphere to complete the mounting of the element on the CAN.

  In the embodiment and the manufacturing method described above, the lower DBR mirror 2 and the active layer 6 are grown using the substrate 1 made of ZnO as the growth substrate, and also used as the support substrate in the surface emitting laser element 100. However, the present invention is not limited to this. For example, after a semiconductor layer stacked structure including a lower DBR mirror and an active layer is grown using a substrate made of ZnO as a growth substrate, the growth substrate and the semiconductor stacked structure are separated, and the semiconductor The laminated structure may be mounted on a support substrate, a heat sink or the like having a higher thermal conductivity than the ZnO substrate, such as a Si substrate. As described above, when a support substrate having higher thermal conductivity is used, a surface emitting laser element having good light emission characteristics and reliability and suitable for a higher temperature environment can be obtained. Further, without separating the growth substrate, a part of the growth substrate may be removed by polishing such as CMP (Chemical Mechanical Polishing) to reduce the thickness, and the substrate may be mounted on another support substrate having high thermal conductivity. Good.

  For example, a known laser lift-off technique as disclosed in Non-Patent Document 1 can be used to separate the growth substrate and the semiconductor multilayer structure. Alternatively, the growth substrate may be removed from the semiconductor multilayer structure by polishing such as CMP (Chemical Mechanical Polishing). Further, it is preferable to form a thick semiconductor layer by HVPE (hydride vapor phase epitaxy) method for growing a nitride semiconductor because part or all of the growth substrate can be easily separated or removed by polishing. Part or all of the growth substrate can be removed by separation or polishing before or after the above-described device fabrication.

  When the growth substrate and the semiconductor stacked structure are separated, the lower DBR mirror may be an n-type conductivity type, and the n-side electrode may be formed on the back surface of the lower DBR mirror. Alternatively, the lower DBR mirror may be n-type conductivity, the growth substrate or the support substrate may be n-type conductivity, and the n-side electrode may be formed on the back surface of the substrate.

  In the above embodiment, the active layer 6 is grown on the lower DBR mirror 2 via the lower contact layer 3 and the lower cladding layer 5, but it is further separated between the lower DBR mirror 2 and the active layer 6. Alternatively, the active layer 6 may be directly grown on the lower DBR mirror 2.

  Further, in the above embodiment, the lower DBR mirror side is n-type conductivity type with respect to the active layer, but the lower DBR mirror may be p-type conductivity type. In this case, the lower DBR mirror may be a p-type conductivity type, and the substrate may be a p-type conductivity type, and a p-side electrode may be provided on the back surface of the substrate.

  Further, an n-type or p-type conductivity type ZnO layer may be epitaxially grown on the substrate, and this may be used as a base layer of the lower DBR mirror.

  In addition, if the composition and thickness of the AlGaInN material are appropriately selected for the active layer, a surface emitting laser element having a desired laser oscillation wavelength can be realized over a wide range from the ultraviolet region to the visible region.

  Further, the present invention is not limited by the above embodiment. What was comprised combining the above-mentioned each component suitably is also contained in this invention.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower DBR mirror 2a Low refractive index layer 2b High refractive index layer 3 Lower contact layer 4 Lower electrode 5 Lower cladding layer 6 Active layer 7 Upper cladding layer 8 Upper contact layer 9 Current confinement layer 9a Opening 10 Transparent conductive film 11 Upper electrode 12 Upper DBR mirror 100 Surface emitting laser element L1 to L19 Broken line M Mesa post P1, P2 point

Claims (14)

A multilayer reflector grown using a growth substrate made of ZnO;
An active layer made of an AlGaInN-based material grown on the multilayer mirror;
The multilayer mirror includes a low refractive index layer made of Zn _1-x1-y1 Mg _x1 Be _y1 O (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1) and a refractive index higher than that of the low refractive index layer. A surface-emitting laser element characterized by having a structure in which high refractive index layers made of ZnO having a high thickness are alternately laminated and having a strain amount of ± 3% or less with respect to the ZnO crystal or the active layer. A multilayer reflector grown using a growth substrate made of ZnO;
An active layer made of an AlGaInN-based material grown on the multilayer mirror;
The multilayer mirror includes a low refractive index layer made of Zn _1-x1-y1 Mg _x1 Be _y1 O (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1) and a refractive index higher than that of the low refractive index layer. And a high refractive index layer made of Zn _{1-z 2} Cd _{z 2} O (0 ≦ z 2 ≦ 1) having a high thickness, and the strain amount with respect to the ZnO crystal or the active layer is ± 3% or less. A surface emitting laser element characterized by the above. A multilayer reflector grown using a growth substrate made of ZnO;
An active layer made of an AlGaInN-based material grown on the multilayer mirror;
The multilayer mirror includes a low refractive index layer made of Zn _1-x1 Mg _x1 O (0.3 ≦ x1 ≦ 0.9) and a high refractive index made of ZnO having a higher refractive index than the low refractive index layer. A surface-emitting laser element comprising a structure in which refractive index layers are alternately laminated and having a strain amount of ± 3% or less with respect to a ZnO crystal or the active layer. 2. The surface emitting laser element according to claim 1, wherein the low refractive index layer of the multilayer mirror is Mg _x1 Be _y1 O (0.62 ≦ x1 ≦ 0.89, x1 + y1 = 1). 2. The surface emitting laser element according to claim 1, wherein the low refractive index layer of the multilayer reflector is Zn _1-y1 Be _y1 O (0.11 ≦ y2 ≦ 0.17).   6. The surface emitting laser element according to claim 1, wherein a distortion amount of the multilayer mirror is ± 2% or less.   The surface emitting laser element according to claim 1, wherein the multilayer mirror has a distortion amount of ± 1% or less.   The surface emitting laser element according to claim 1, wherein the multilayer mirror is lattice-matched with a ZnO crystal or the active layer.   9. The low refractive index layer and the high refractive index layer of the multilayer-film reflective mirror have a distortion amount that is different from each other and has the same absolute value with respect to the ZnO crystal or the active layer. The surface emitting laser element according to any one of the above. The low refractive index layer of the multilayer mirror is Mg _x1 Be _y1 O (0.62 ≦ x1 ≦ 0.73, x1 + y1 = 1), and the high refractive index layer is Zn _1-z2 Cd _z2 O (0 3. The surface emitting laser element according to claim 2, wherein .75 ≦ 1-z2 ≦ 0.94). The low refractive index layer of the multilayer mirror is Mg _x1 Be _y1 O (0.70 ≦ x1 ≦ 0.82, x1 + y1 = 1), and the high refractive index layer is Zn _1-z2 Cd _z2 O (0 .5 ≦ 1−z2 ≦ 0.78) 3. The surface emitting laser element according to claim 2, wherein: A multilayer reflector growth step for growing a multilayer reflector on a substrate made of ZnO; an active layer growth step for growing an active layer made of an AlGaInN-based material on the multilayer reflector;
In the multilayer mirror growth step, a low refractive index layer made of Zn _1-x1-y1 Mg _x1 Be _y1 O (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1) and more than the low refractive index layer The high refractive index layer made of ZnO having a high refractive index is laminated alternately by adjusting the composition of each refractive index layer so that the strain amount with respect to the ZnO crystal or the active layer is ± 3% or less. A method of manufacturing a surface-emitting laser element, which is characterized. A multilayer reflector growth step for growing a multilayer reflector on a substrate made of ZnO; an active layer growth step for growing an active layer made of an AlGaInN-based material on the multilayer reflector;
In the multilayer mirror growth step, a low refractive index layer made of Zn _1-x1-y1 Mg _x1 Be _y1 O (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1) and more than the low refractive index layer Each refractive index layer having a high refractive index layer made of Zn _{1 -z 2} Cd _{z 2} O (0 ≦ z 2 ≦ 1) having a high refractive index is adjusted so that the strain amount with respect to the ZnO crystal or the active layer is ± 3% or less. A method of manufacturing a surface-emitting laser element, wherein the composition is adjusted and stacked alternately. A multilayer reflector growth step for growing a multilayer reflector on a substrate made of ZnO; an active layer growth step for growing an active layer made of an AlGaInN-based material on the multilayer reflector;
In the multilayer reflector growth step, a low refractive index layer made of Zn _1-x1 Mg _x1 O (0.3 ≦ x1 ≦ 0.9) and ZnO having a higher refractive index than the low refractive index layer A surface-emitting laser comprising: a high-refractive-index layer that is alternately laminated with a composition of each refractive-index layer adjusted so that a strain amount with respect to the ZnO crystal or the active layer is ± 3% or less Device manufacturing method.

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