JP4845055B2 - Surface emitting laser device manufacturing method and surface emitting laser device - Google Patents

Description

  The present invention relates to a method for manufacturing a vertical cavity surface emitting laser element and a surface emitting laser element.

As a conventional surface emitting laser element, a vertical cavity surface emitting laser element is disclosed in which a plurality of semiconductor layers including an active layer are stacked between upper and lower multilayer reflectors which are DBR (Distributed Bragg Reflector) mirrors. (See Patent Documents 1 and 2). In addition, the surface emitting laser elements disclosed in Patent Documents 1 and 2 have a mesa post structure and a current confinement layer for limiting the current path and increasing the current injection efficiency. This current confinement layer has a current confinement portion made of Al ₂ O ₃ located on the outer periphery and a circular current injection portion made of AlAs located in the center of the current confinement portion. This current injection portion serves as a current path when current is injected into the surface emitting laser element, and also serves as an opening through which laser light is emitted.

Further, in the surface emitting laser elements disclosed in Patent Documents 1 and 2, in order to efficiently inject current from the p-side annular electrode, the uppermost layer of a plurality of semiconductor layers, and the uppermost layer and the current confinement layer Is provided with a low-resistance current path layer made of a p ⁺ type semiconductor. The current injected from the p-side annular electrode is efficiently injected to the active layer via the current confinement layer using these current path layers as current paths. As a result, the oscillation threshold current of the surface emitting laser element is reduced. The uppermost current path layer of the semiconductor layer also functions as a contact layer for the p-side annular electrode, and will be referred to as a contact layer below.

  Here, in the surface emitting laser element, it is necessary that the light having the wavelength to be oscillated forms a standing wave between the upper and lower multilayer reflectors. When this standing wave is formed, the lower multilayer The uppermost surface of the membrane reflector and the lowermost surface of the upper multilayer reflector are the antinodes of the standing wave. Further, the current confinement layer, the contact layer, and the current path layer described above are layers whose electrical characteristics are preferentially designed, and thus there is a possibility that laser oscillation light may be absorbed and scattered. Therefore, it is preferable that the current confinement layer, the contact layer, and the current path layer are disposed at the node of the standing wave of light. Therefore, in the conventional surface emitting laser element, the thickness and refractive index of each layer are adjusted in order to realize the positions of the antinodes and nodes of the standing wave of light described above.

  Further, the surface emitting laser elements disclosed in Patent Documents 1 and 2 include a phase adjustment layer called a rephase layer on the surface of the contact layer in the opening of the p-side annular electrode. This phase adjustment layer is made of a dielectric material such as silicon nitride, and is interposed between the contact layer and the lowermost surface of the upper multilayer reflector, and the contact layer is located at a node of the standing wave to reflect the upper multilayer film. The optical thickness is adjusted to about λ / 4 so that the lowermost surface of the mirror is located at the antinode of the standing wave. Here, the optical thickness of a certain layer is represented by the product of the layer thickness and the refractive index.

US Pat. No. 6,916,672 US Pat. No. 6750071

  However, when the present inventors manufactured a surface emitting laser element having a conventional structure, it has been found that there is a problem that the oscillation threshold current becomes larger than the design value. When the surface emitting laser element manufactured by the present inventors was examined closely, it was found that the element resistance was increased for the following reason.

FIG. 10 is a schematic cross-sectional view of a main part of a surface emitting laser element having a conventional structure. As shown in FIG. 10, the surface emitting laser element 300 includes a current confinement layer 307 having a current confinement portion 307a located on the outer periphery and a circular current injection portion 307b located in the center of the current confinement portion 307a, and p A type spacer layer 309, a p ⁺ type current path layer 310, a p type spacer layer 311 and a p ⁺ type contact layer 312 are sequentially stacked. A p-side annular electrode 313 is formed on the p ⁺ -type contact layer 312, and a disk-like phase adjustment layer 314 made of silicon nitride is formed in the opening of the p-side annular electrode 313. An upper DBR mirror 316 made of a dielectric multilayer film is formed on the p-side annular electrode 313 and the phase adjustment layer 314. Note that the active layer is located below the current confinement layer 307. At least from the active layer to the p ⁺ -type contact layer 312 has a cylindrical mesa post structure.

According to the findings of the present inventors, in the surface emitting laser element 300 having the conventional structure, the outer periphery of the phase adjustment layer 314 is disposed between the outer periphery of the phase adjustment layer 314 and the inner periphery of the p-side annular electrode 313. A gap 321 having a width of about 0.3 to 0.5 μm was formed over the groove, and a groove 324 was formed in the p ⁺ -type contact layer 312 at a portion immediately below the gap 321. Further examination by the present inventors revealed that this groove 324 is an etching solution between the outer periphery of the phase adjusting layer 314 and the inner periphery of the p-side annular electrode 313 in the step of forming the mesa post of the surface emitting laser element 300. And the p ⁺ -type contact layer 312 is eroded. When such a groove 324 is formed, the p ⁺ -type contact layer 312 becomes thin or breaks at that portion, so that the electrical resistance becomes high. As a result, the current injected from the p-side annular electrode 313 mainly flows in the plane direction of the p ⁺ type current path layer 310 as indicated by the arrow Ar3 and does not flow in the p ⁺ type contact layer 312. The resistance is thought to increase.

  The present invention has been made in view of the above, and an object thereof is to provide a method of manufacturing a surface emitting laser element having a small oscillation threshold current and a surface emitting laser element.

  In order to solve the above-described problems and achieve the object, a method for manufacturing a surface-emitting laser device according to the present invention is a method for manufacturing a vertical cavity surface-emitting laser device, in which a lower multilayer film is reflected on a substrate. A step of laminating a mirror, and laminating a plurality of semiconductor layers including an active layer and having a contact layer as an uppermost layer on the lower multilayer reflector, and a first dielectric in a partial region on the contact layer Forming a first dielectric layer, and forming an annular electrode having an opening at the center on the contact layer so that the first dielectric layer is disposed in the opening. A second dielectric layer forming a second dielectric layer so as to cover an electrode forming step, the first dielectric layer, and a gap formed between the first dielectric layer and the annular electrode; Forming the stacked semiconductor layer using the ring electrode as a mask; Characterized in that it comprises a mesa post forming step of etching the strike shape, a.

  The surface emitting laser device manufacturing method according to the present invention is the above-described invention, wherein in the above invention, after the mesa post forming step, an upper multilayer reflector comprising an upper multilayer reflector made of a dielectric is formed on the second dielectric layer. And forming the first and second dielectric layers, wherein the desired laser oscillation wavelength is λ, and the total optical thickness of the first and second dielectric layers is about λ / 4. It forms so that it may become.

  The method of manufacturing a surface-emitting laser device according to the present invention is the above-described invention, wherein in the first dielectric layer forming step, the first dielectric layer is formed as a lower dielectric, assuming that a desired laser oscillation wavelength is λ. And a lower dielectric having an optical thickness of about λ / 4. After the mesa post forming step, a dielectric is formed on the second dielectric layer. An upper multilayer reflector forming step of forming an upper multilayer reflector including the upper multilayer film and the second dielectric layer and having the upper dielectric layer as a lowermost layer. It is further characterized by including.

In the method of manufacturing a surface emitting laser element according to the present invention, in the above invention, the stacking step may include AlAs or Al _1-x Ga _x As (0 <x <1) between the contact layer and the active layer. And a current injection portion made of AlAs or Al _1-x Ga _x As by subjecting the stacked oxidized layer to a selective oxidation heat treatment after the mesa post forming step. And a current confinement layer forming step of forming a current confinement layer having a current confinement portion made of Al ₂ O ₃ or (Al _1-x Ga _x ) ₂ O ₃ .

  In the method of manufacturing a surface emitting laser element according to the present invention, in the above invention, the stacking step includes a current path layer having an acceptor concentration comparable to the contact layer between the contact layer and the oxidized layer. Including a current path layer laminating step of laminating.

  In the method of manufacturing a surface emitting laser element according to the present invention, in the above invention, at least a portion of the first dielectric layer in contact with the contact layer has a nitrogen composition ratio larger than a stoichiometric composition. It is made of silicon nitride.

  The surface-emitting laser element according to the present invention is a vertical cavity surface-emitting laser element, and includes a substrate, a lower multilayer reflector that is stacked on the substrate, and a stack that is stacked on the lower multilayer reflector. A plurality of semiconductor layers having a mesa post structure, including an active layer and having a contact layer as an uppermost layer, and an outer periphery formed on the contact layer and having an opening at the center and matching the outer periphery of the mesa post structure An annular electrode having a first dielectric layer formed in an opening of the annular electrode on the contact layer, the first dielectric layer, the first dielectric layer, and the annular electrode; And a second dielectric layer formed so as to cover a gap formed therebetween.

  Further, the surface emitting laser element according to the present invention further includes an upper multilayer reflector made of a dielectric formed on the second dielectric layer in the above invention, and a desired laser oscillation wavelength is λ, The total optical thickness of the first and second dielectric layers is about λ / 4.

  The surface emitting laser element according to the present invention may further include an upper multilayer film made of a dielectric formed on the second dielectric layer, wherein the first dielectric layer is a lower dielectric layer. And the upper dielectric layer, and when the desired laser oscillation wavelength is λ, the optical thickness of the lower dielectric is about λ / 4, and the upper multilayer film and the second dielectric layer And the upper dielectric layer constitutes an upper multilayer reflector having the upper dielectric layer as the lowest layer.

In the surface-emitting laser device according to the present invention, in the above invention, the plurality of semiconductor layers are AlAs or Al _1-x Ga formed by selective oxidation heat treatment between the active layer and the contact layer. A current confinement layer having a current injection portion made of _x As (0 <x <1) and a current confinement portion made of Al ₂ O ₃ or (Al _1-x Ga _x ) ₂ O ₃ is provided. .

  In the surface-emitting laser device according to the present invention as set forth in the invention described above, the plurality of semiconductor layers have an acceptor concentration similar to that of the contact layer formed between the current confinement layer and the contact layer. A current path layer is provided.

  In the surface emitting laser element according to the present invention, in the above invention, at least a portion of the first dielectric layer in contact with the contact layer is made of silicon nitride having a nitrogen composition ratio larger than the stoichiometric composition. It is characterized by becoming.

In the surface emitting laser element according to the present invention, the contact layer has a thickness of 50 nm or less, an acceptor concentration of 1 × 10 ¹⁹ cm ⁻³ or more, and a hydrogen concentration of 1 × 10 ^18. It is characterized by being cm ⁻³ or less.

  According to the present invention, no groove is formed in the contact layer in the portion immediately below the gap formed between the first dielectric layer and the annular electrode, and an increase in element resistance is prevented, so that the oscillation threshold is reduced. There is an effect that a surface emitting laser element with a small value current can be realized.

  Embodiments of a surface emitting laser element manufacturing method and a surface emitting laser element 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. The surface-emitting laser element according to the first embodiment includes a first and second dielectric layers having a laser oscillation wavelength in the 1100 nm band and a total optical thickness of λ / 4, where the laser oscillation wavelength is λ. I have.

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 substrate 101, a lower DBR mirror 102 that is a lower multilayer reflector formed on the substrate 101, a buffer layer 103, an n-type contact layer 104, A current confinement layer 107 having an active layer 105 having a multiple quantum well structure, a lower graded composition layer 106, a current confinement portion 107a located at the outer periphery, and a circular current injection portion 107b located at the center of the current confinement portion 107a. The upper graded composition layer 108, the p-type spacer layer 109, the p ⁺ -type current path layer 110, the p-type spacer layer 111, and the p ⁺ -type contact layer 112 are sequentially stacked. The active layer 105 to the p ⁺ -type contact layer 112 constitute a cylindrical mesa post M1.

The substrate 101 is made of undoped GaAs. The lower DBR mirror 102 is composed of 34 pairs of GaAs / Al _0.9 Ga _0.1 As layers. The n-type contact layer 104 is made of n-type GaAs. The active layer 105 has a structure in which a GaInNAs well layer having 3 layers and a GaAs barrier layer having 4 layers are alternately stacked, and the lowermost GaAs barrier layer also functions as an n-type cladding layer. To do. As for the current confinement layer 107, the current confinement portion 107a is made of Al ₂ O ₃ and the current injection portion 107b has a diameter of 6 to 7 μm and is made of AlAs. The lower graded composition layer 106 and the upper graded composition layer 108 are made of AlGaAs, and are configured such that their As compositions increase stepwise as they approach the current confinement layer 107 in the thickness direction. The p-type spacer layers 109 and 111, the p ⁺ -type current path layer 110, and the p ⁺ -type contact layer 112 are made of p-type and p ⁺ -type GaAs doped with carbon, respectively. The acceptor or donor concentration of each p-type or n-type layer is, for example, about 1 × 10 ¹⁸ cm ⁻³ , and the acceptor concentration of the p ⁺ -type layer is, for example, 1 × 10 ¹⁹ cm ⁻³ or more. The refractive index of each semiconductor layer made of GaAs is about 3.45.

On the p ⁺ -type contact layer 112, a p-side annular electrode 113 made of Pt / Ti, having an opening 113a at the center and having an outer periphery that coincides with the outer periphery of the mesa post M1 is formed. The outer diameter of the p-side annular electrode 113 is, for example, 30 μm, and the inner diameter of the opening 113a is, for example, 11 to 14 μm.

A disc-shaped first dielectric layer 114 made of silicon nitride (SiN _x ) is formed in the opening 113 a of the p-side annular electrode 113. A gap 121 having a width of about 0.3 to 0.5 μm is formed between the outer periphery of the first dielectric layer 114 and the inner periphery of the p-side annular electrode 113 over the outer periphery of the first dielectric layer 114. .

Further, a second dielectric layer 115 made of SiN _x is formed so as to cover the first dielectric layer 114 and the gap 121 and the outer periphery thereof reaches the p-side annular electrode 113.

Further, an upper DBR mirror 116, which is an upper multilayer film reflecting mirror made of a dielectric material, is formed from the second dielectric layer 115 to the outer periphery of the mesa post M1. The upper DBR mirror 116 is composed of, for example, 10-12 pairs of SiN _x / SiO ₂ , and for example, an α-Si / SiO ₂ or α-Si / Al ₂ O ₃ pair is formed depending on the refractive index of the material. The number of pairs may be such that an appropriate reflectance of about% is obtained. The n-type contact layer 104 extends radially outward from the lower portion of the mesa post M1, and a semi-annular n-side electrode 117 made of, for example, AuGeNi / Au is formed on the surface thereof. For example, the n-side electrode 117 has an outer diameter of 82 μm and an inner diameter of 42 μm. Further, a passivation film 118 made of a dielectric such as SiN _x is formed for protecting the surface in a region where the upper DBR mirror 116 is not formed.

  Further, an n-side lead electrode 119 made of Au is formed so as to contact the n-side electrode 117 through an opening formed in the passivation film 118. On the other hand, a p-side lead electrode 120 made of Au is also formed so as to contact the p-side annular electrode 113 through an opening formed in the passivation film 118. The n-side electrode 117 and the p-side annular electrode 113 are electrically connected to a current supply circuit (not shown) provided outside by an n-side extraction electrode 119 and a p-side extraction electrode 120, respectively.

The surface emitting laser element 100 applies a voltage from the current supply circuit via the n-side extraction electrode 119 and the p-side extraction electrode 120 to inject the current between the n-side electrode 117 and the p-side annular electrode 113, respectively. Then, the current mainly flows through the low-resistance p ⁺ -type contact layer 112 and the p ⁺ -type current path layer 110, and the current path is narrowed in the current injection portion 107 b by the current confinement layer 107, so It is supplied to the active layer 105. As a result, the active layer 105 is carrier-injected and emits spontaneous emission light. Of the spontaneous emission light, light having a wavelength λ which is a laser oscillation wavelength forms a standing wave between the lower DBR mirror 102 and the upper DBR mirror 116 and is amplified by the active layer 105. When the injection current becomes equal to or greater than the threshold value, the light that forms the standing wave oscillates, and the 1100 nm band laser beam is output from the opening 113a of the p-side annular electrode 113.

  Next, the standing wave of light and the current path in the surface emitting laser element 100 will be described more specifically. FIG. 2 is an explanatory diagram for explaining a standing wave of light and a current path in the surface emitting laser element 100.

First, the standing wave of light in the surface emitting laser element 100 will be described. In FIG. 2, a line L1 indicates the position in the stacked structure from the active layer 105 to the second dielectric layer 115 and the amplitude of the standing wave at that position. Here, the p-type spacer layers 109 and 111 are formed to have an optical thickness of λ / 4. Further, the total optical thickness of the first dielectric layer 114 and the second dielectric layer 115 is formed to be about λ / 4, and the first dielectric layer 114 and the second dielectric layer 115 are in phase. It functions as an adjustment layer. Note that the total optical thickness is not limited to λ / 4 accurately, but may be about λ / 4 for the sake of optical design and the like. As a result, as indicated by the line L1, the standing wave is located in the active layer 105 and the upper surface of the second dielectric layer 115, that is, the lowermost surface of the upper DBR mirror 116, and the current confinement layer 107 The p ⁺ type current path layer 110 and the p ⁺ type contact layer 112 are formed so that the node N is substantially located.

Since the refractive index of SiN _x varies depending on the composition ratio, the specific layer thicknesses of the first dielectric layer 114 and the second dielectric layer 115 are determined as follows according to the composition ratio. For example, when both the first dielectric layer 114 and the second dielectric layer 115 are made of SiN _{x with} x = 1.5, the refractive index n is 1.8, so that the laser oscillation wavelength λ is 1100 nm. The total thickness of the first dielectric layer 114 and the second dielectric layer 115 is 1100 / (4 · 1.8), that is, about 152.8 nm. Further, when both the first dielectric layer 114 and the second dielectric layer 115 are made of SiN _{x with} x = 1.2, since the refractive index n is 2.2, the first dielectric layer 114 and the second dielectric layer 115 The total layer thickness of the two dielectric layers 115 is about 125 nm.

Next, a current path in the surface emitting laser element 100 will be described with reference to FIG. In the surface emitting laser element 100, the second dielectric layer 115 is formed so as to cover the gap 121. As a result, as will be described later, even when the semiconductor layer is etched when the mesa post M1 is formed, there is no possibility that the etchant enters from the gap 121 and erodes the p ⁺ -type contact layer 112. Therefore, the current injected from the p-side annular electrode 113 flows in parallel through the p ⁺ -type current path layer 110 and the p ⁺ -type contact layer 112 having low resistance as indicated by the arrow Ar1. The resistance is kept low as designed. The current is further confined in the current injection portion 107b by the current confinement layer 107 and supplied to the active layer 105 at a high current density. As a result, the oscillation threshold current of the surface emitting laser element 100 becomes small. It should be noted that the thicknesses of the p ⁺ type current path layer 110 and the p ⁺ type contact layer 112 should be 50 nm or less so that the resistance is sufficiently low and the standing wave of light is not affected. Preferably, the thickness is 15 to 30 nm.

  As described above, the surface emitting laser element 100 has a small oscillation threshold current because an increase in element resistance is prevented.

  Next, a method for manufacturing the surface emitting laser element 100 will be described. 3-7 is explanatory drawing explaining an example of the manufacturing method of the surface emitting laser element 100. FIG.

First, as shown in FIG. 3, a lower DBR mirror 102, a buffer layer 103, an n-type contact layer 104, an active layer 105, a lower graded composition layer 106, an oxidizable layer 122 made of AlAs, by an epitaxial growth method, The upper graded composition layer 108, the p-type spacer layer 109, the p ⁺ -type current path layer 110, the p-type spacer layer 111, and the p ⁺ -type contact layer 112 are sequentially stacked, and one of the p ⁺ -type contact layers 112 is further formed by CVD. A disc-shaped first dielectric layer 114 made of SiN _x is formed in the partial region.

Next, a lift-off method is used to form a p-side annular electrode 113 on the p ⁺ -type contact layer 112 so that the first dielectric layer 114 is disposed in the opening 113a. Specifically, first, as shown in FIG. 4, a negative photoresist 123 is applied on the first dielectric layer 114 and the p ⁺ -type contact layer 112, and the pattern of the shape of the p-side annular electrode 113 is formed. P is formed. At this time, the pattern P is formed so that the width increases as it becomes deeper from the surface of the photoresist 123.

Next, as shown in FIG. 5, a Pt / Ti layer is deposited from above the photoresist 123 to form a p-side annular electrode 113 on the p ⁺ -type contact layer 112 in the pattern P. At this time, the p-side annular electrode 113 is formed in the same shape as the pattern P on the outermost surface of the photoresist 123. As a result, a gap 121 having a width of about 0.3 to 0.5 μm is formed across the outer periphery of the first dielectric layer 114 between the outer periphery of the first dielectric layer 114 and the inner periphery of the p-side annular electrode 113. Is done.

Next, as shown in FIG. 6, a second dielectric layer 115 made of SiN _x is formed so as to cover the first dielectric layer 114 and the gap 121 by, for example, plasma CVD. At this time, the second dielectric layer 115 is formed so as not to completely cover the surface of the p-side annular electrode 113 and to expose the outer peripheral region A1 of the p-side annular electrode 113.

Further, the second dielectric layer 115 is formed so that the total optical thickness of the first dielectric layer 114 and the second dielectric layer 115 is about λ / 4. As described above, since the refractive index of SiN _x varies depending on its composition ratio, the specific layer thicknesses of the first dielectric layer 114 and the second dielectric layer 115 are determined according to the composition ratio.

By the way, normal SiN _x contains a certain amount of hydrogen in its production process. When the composition ratio x of SiN _x constituting the first dielectric layer 114 is small, the density of SiN _x is increased. Therefore, in the subsequent heat treatment process, movement of contained hydrogen is limited, and the p ⁺ -type contact layer 112 is formed. May increase the electrical resistance. On the other hand, when a large composition ratio x of SiN _x, the density of the SiN _x decreases. As a result, hydrogen easily escapes from the surface in the heat treatment step, so that the penetration of hydrogen into the p ⁺ -type contact layer 112 is suppressed, and the increase in electrical resistance is also suppressed. Therefore, it is preferable that the composition ratio x of SiN _x constituting the first dielectric layer 114 is larger at least in a portion in contact with the p ⁺ type contact layer 112. That is, for example, when the first dielectric layer 114 has a multilayer structure, it is preferable that the composition ratio x of SiN _x constituting the layer in contact with the p ⁺ type contact layer 112 is larger in the multilayer structure. The composition ratio x is particularly preferably larger than the stoichiometric composition x = 1.33. Even when hydrogen enters the p ⁺ -type contact layer 112, the acceptor concentration of the p ⁺ -type contact layer 112 is 1 × 10 ¹⁹ cm ⁻³ or more and the hydrogen concentration is 1 × 10 ¹⁸ cm ⁻³ or less. For example, the p ⁺ -type contact layer 112 is preferable because it effectively functions as a current path. Since the second dielectric layer 115 has an extremely small area in contact with the p ⁺ -type contact layer 112, the composition ratio x of SiN _x constituting the second dielectric layer 115 is not particularly limited. From the viewpoint of optical characteristics, it is particularly preferable that the first dielectric layer 114 be the same.

Next, using the p-side annular electrode 113 as a metal mask, the semiconductor layer is etched to a depth reaching the n-type contact layer 104 using an acid etching solution or the like to form a cylindrical mesa post M1. Then, the n-type contact layer 104 is etched to a depth reaching the buffer layer 103. As a result, a structure in which the mesa post M1 shown in FIG. 7 is formed is obtained. In this etching step, since the second dielectric layer 115 is formed so as to cover the gap 121, there is no possibility that the acid etching solution enters from the gap 121 and erodes the p ⁺ -type contact layer 112. Further, since the second dielectric layer 115 is formed so that the outer peripheral area A1 of the p-side annular electrode 113 is exposed when the second dielectric layer 115 is formed, the second dielectric layer 115 The outer periphery does not protrude from the outer periphery of the p-side annular electrode 113. As a result, the outer periphery of the p-side annular electrode 113 and the outer periphery of the mesa post M1 can be matched with high accuracy.

Next, heat treatment is performed in a steam atmosphere to selectively oxidize the oxidized layer 122 from the outer peripheral side of the mesa post M1. At this time, a chemical reaction of AlAs + H ₂ O → Al ₂ O ₃ + AsH ₃ occurs in the oxidized layer 122, and AlAs becomes Al ₂ O ₃ from the outer peripheral side of the oxidized layer 122, thereby forming the current confinement portion 107 a. Since the chemical reaction proceeds uniformly from the outer peripheral side of the oxidized layer 122, a current injection portion 107b made of AlAs is formed at the center. Here, the heat treatment time or the like is adjusted so that the diameter of the current injection portion 107b is 6 to 7 μm. Since the current injection portion 107b is formed in this manner, the center of the mesa post M1, the center of the current injection portion 107b, and the center of the opening 113a of the p-side annular electrode 113 can be matched with high accuracy. As a result, the surface emitting laser element 100 can be a single transverse mode laser with a high yield.

Note that AsH ₃ generated by the above chemical reaction is scattered. The scattered AsH ₃ causes a chemical reaction of Pt included in the p-side annular electrode 113 and Pt + AsH ₃ → PtAs ₂ + 3H _{2 in} the exposed region A1 of the p-side annular electrode 113. As a result, the p-side annular electrode 113 is altered in the exposed region A1 and the electric resistance is increased, but the region covered with the second dielectric layer 115 is protected from such alteration and remains at a low resistance. is there.

  Next, a semi-annular n-side electrode 117 is formed on the surface of the n-type contact layer 104 on the outer peripheral side of the mesa post M1. Next, after forming a passivation film 118 on the entire surface, openings are formed in the passivation film 118 and the second dielectric layer 115 on the n-side electrode 117 and the p-side annular electrode 113, and the openings are formed through these openings. An n-side extraction electrode 119 that contacts the n-side electrode 117 and a p-side extraction electrode 120 that contacts the p-side annular electrode 113 are formed.

  Next, after forming the upper DBR mirror 116 by using the CVD method, the back surface of the substrate 101 is polished, and the thickness of the substrate 101 is adjusted to, for example, 150 μm. Thereafter, element isolation is performed to complete the surface emitting laser element 100 shown in FIG.

Next, as an example of the present invention, a surface emitting laser element having the structure shown in FIG. 1 was manufactured by the above manufacturing method. At this time, as SiN _x constituting the first dielectric layer and the second dielectric layer, those having a composition ratio x of x = 1.33 (Example 1) and 1.5 (Example 2). Using. On the other hand, as a comparative example, it is almost the same as the above manufacturing method, but the first dielectric layer made of SiN _x having a composition ratio x of x = 1.33 is set so that its optical thickness becomes λ / 4. A surface emitting laser element was manufactured without forming the second dielectric layer.

When the element resistances of these surface emitting laser elements were measured, the comparative example was 100Ω, the example 1 was 80Ω, and the example 2 was 70Ω. In other words, the device of Example 1 is considered to have a lower element resistance than that of the comparative example without the second dielectric layer as a result of the second dielectric layer preventing the p ⁺ -type contact layer from eroding. Furthermore, in Example 2, in addition to the erosion preventing effect of the second dielectric layer, the penetration of hydrogen contained in the first dielectric layer and the second dielectric layer into the p ⁺ type contact layer was prevented. As a result, it is considered that the element resistance is further reduced. In addition, the surface emitting laser elements of Examples 1 and 2 reflect the reduction of the element resistance, thereby improving the impedance matching in the high frequency characteristics and suppressing the band limitation due to CR (capacitance and resistance). Can be expected.

(Embodiment 2)
Next, a surface emitting laser element according to Embodiment 2 of the present invention will be described. Like the surface emitting laser element according to the first embodiment, the surface emitting laser element according to the second embodiment has a laser oscillation wavelength in the 1100 nm band, but the second dielectric layer is a part of the upper multilayer reflector. The difference is that it is part.

FIG. 8 is a schematic cross-sectional view of the surface emitting laser element 200 according to the second embodiment. In addition, the same code | symbol is attached | subjected to the same element as the surface emitting laser element 100 shown in FIG. As shown in FIG. 8, the surface emitting laser element 200 has the same structure as the surface emitting laser element 100. However, unlike the surface emitting laser element 100, the disk-shaped first dielectric layer 214 formed in the opening 113a of the p-side annular electrode 113 includes a lower dielectric layer 214a made of SiN _x and a lower dielectric layer 214a. It has a laminated structure with an upper dielectric layer 214b made of SiO ₂ laminated on the dielectric layer 214a. The lower dielectric layer 214a is formed so that its optical thickness is about λ / 4.

Further, a gap 221 having a width of about 0.3 to 0.5 μm is formed across the outer periphery of the first dielectric layer 214 between the outer periphery of the first dielectric layer 214 and the inner periphery of the p-side annular electrode 113. ing. A second dielectric layer 215 made of SiN _x is formed so as to cover the first dielectric layer 214 and the gap 221 and the outer edge thereof reaches the p-side annular electrode 113.

Further, an upper multilayer film 216 made of a dielectric is formed from the second dielectric layer 215 to the outer periphery of the mesa post M1. The upper multilayer film 216 is made of, for example, 10 to 12 pairs of SiN _x / SiO ₂ .

  The standing wave of light and the current path in the surface emitting laser element 200 will be described. FIG. 9 is an explanatory diagram for explaining a standing wave of light and a current path in the surface-emitting laser element 200.

First, the standing wave of light in the surface emitting laser element 200 will be described. In FIG. 9, a line L2 indicates the position in the stacked structure from the active layer 105 to the second dielectric layer 215 and the amplitude of the standing wave at that position. In the surface emitting laser element 200, the upper dielectric layer 214b, the second dielectric layer 215, and the upper multilayer film 216 constitute an upper DBR mirror, and the lower surface of the upper dielectric layer 214b is the upper DBR mirror. It is the bottom surface. That is, the upper dielectric layer 214b and the second dielectric layer 215 form a lowermost pair of DBR mirrors. Further, the lower dielectric layer 214a is formed to have an optical thickness of about λ / 4, and functions as a phase adjustment layer. As a result, as indicated by the line L2, the standing wave has the antinode AN substantially positioned on the lower surface of the active layer 105 and the upper dielectric layer 214b, that is, the lowermost surface of the upper DBR mirror, and the current confinement layer 107 and the p ⁺ type. The node N is formed in the current path layer 110 and the p ⁺ -type contact layer 112 so as to be substantially located.

Next, a current path in the surface emitting laser element 200 will be described. In the surface emitting laser element 200, the second dielectric layer 215 is formed so as to cover the gap 221. As a result, as in the surface emitting laser element 100, the current injected from the p-side annular electrode 113 is the low resistance p ⁺ type current path layer 110 and p ⁺ type contact layer 112 as indicated by the arrow Ar2. Since the current flows in parallel as a current path, the element resistance is kept low as designed. As a result, the oscillation threshold current of the surface emitting laser element 100 becomes small.

  The surface emitting laser element 200 can be manufactured by a method similar to the method for manufacturing the surface emitting laser element 100 described above.

  As described above, the surface emitting laser element 200 has a small oscillation threshold current because an increase in element resistance is prevented.

In the above embodiment, the layer to be oxidized is made of AlAs, but it may be made of Al _1-x Ga _x As (0 <x <1). When the layer to be oxidized is made of Al _1-x Ga _x As, the current confinement layer is made of (Al _1-x Ga _x ) ₂ O ₃ and the current injection portion is made of Al _1-x Ga _x As. It will consist of

  Moreover, in the said embodiment, although the p side annular electrode is formed using the lift-off method, it does not specifically limit about the formation method of a p side annular electrode. Even when the p-side annular electrode is formed by another method, a gap is formed between the p-side annular electrode and the first dielectric layer due to the difference in material. The effect can be obtained by applying.

  Further, in the above embodiment, two current path layers including the contact layer are formed. However, even if the current path layer is only the contact layer or three or more layers, the effect of the present invention can be obtained. It can be played.

1 is a schematic cross-sectional view of a surface emitting laser element according to Embodiment 1 of the present invention. It is explanatory drawing explaining the standing wave of light and the electric current path | route in the surface emitting laser element shown in FIG. It is explanatory drawing explaining the manufacturing method of the surface emitting laser element shown in FIG. It is explanatory drawing explaining the manufacturing method of the surface emitting laser element shown in FIG. It is explanatory drawing explaining the manufacturing method of the surface emitting laser element shown in FIG. It is explanatory drawing explaining the manufacturing method of the surface emitting laser element shown in FIG. It is explanatory drawing explaining the manufacturing method of the surface emitting laser element shown in FIG. It is typical sectional drawing of the surface emitting laser element which concerns on Embodiment 2 of this invention. It is explanatory drawing explaining the standing wave of light and an electric current path | route in the surface emitting laser element shown in FIG. It is typical sectional drawing of the principal part of the surface emitting laser element of a conventional structure.

Explanation of symbols

100 to 300 surface emitting laser element 101 substrate 102 lower DBR mirror 103 buffer layer 104 n-type contact layer 105 active layer 106 lower graded composition layer 107, 307 current confinement layer 107a, 307a current confinement part 107b, 307b current injection part 108 upper grade Composition layer 109, 111, 309, 311 p-type spacer layer 110, 310 p ⁺ type current path layer 112, 312 p ⁺ type contact layer 113, 313 p-side annular electrode 113a opening 114, 214 first dielectric layer 115 215 Second dielectric layer 116, 316 Upper DBR mirror 117 n-side electrode 118 passivation film 119 n-side extraction electrode 120 p-side extraction electrode 121-321 gap 122 oxidized layer 123 photoresist 214a lower dielectric layer 214b upper induction Body layer 216 upper multilayer 314 phase adjustment layer 324 trench region A1 AN belly Ar1~Ar3 arrows L1, L2 line M1 mesa post N nodes P pattern

Claims (13)

A method of manufacturing a vertical cavity surface emitting laser element,
Laminating a lower multilayer reflector on a substrate, and laminating a plurality of semiconductor layers including an active layer and having a contact layer on the uppermost layer on the lower multilayer reflector;
A first dielectric layer forming step of forming a first dielectric layer in a partial region on the contact layer;
Forming an annular electrode having an opening in the center on the contact layer so that the first dielectric layer is disposed in the opening; and
A second dielectric layer forming step of forming a second dielectric layer so as to cover the first dielectric layer and a gap formed between the first dielectric layer and the annular electrode;
A mesa post forming step of etching the laminated semiconductor layer into a mesa post shape using the annular electrode as a mask;
An upper multilayer reflector forming step of forming an upper multilayer reflector made of a dielectric on the second dielectric layer after the mesa post forming step;
Only including,
In the first and second dielectric layer forming steps, when the desired laser oscillation wavelength is λ, the first and second dielectric layers are formed so that the total optical thickness is about λ / 4. A method for manufacturing a surface-emitting laser element, comprising: A method of manufacturing a vertical cavity surface emitting laser element,
Laminating a lower multilayer reflector on a substrate, and laminating a plurality of semiconductor layers including an active layer and having a contact layer on the uppermost layer on the lower multilayer reflector;
A first dielectric layer forming step of forming a first dielectric layer in a partial region on the contact layer;
Forming an annular electrode having an opening in the center on the contact layer so that the first dielectric layer is disposed in the opening; and
A second dielectric layer forming step of forming a second dielectric layer so as to cover the first dielectric layer and a gap formed between the first dielectric layer and the annular electrode;
A mesa post forming step of etching the laminated semiconductor layer into a mesa post shape using the annular electrode as a mask;
An upper multilayer reflector forming step of forming an upper multilayer reflector made of a dielectric on the second dielectric layer after the mesa post forming step;
Including
In the first dielectric layer forming step, when a desired laser oscillation wavelength is λ, the first dielectric layer has a laminated structure of a lower dielectric layer and an upper dielectric layer, and the lower dielectric layer Formed so that the optical thickness is about λ / 4,
In the upper multilayer mirror forming step, by stacking the upper multilayer film made of dielectric on the second dielectric layer, the upper multilayer film and said second dielectric layer and it is included the upper dielectric layer There manufacturing method to that surface-emitting laser element, wherein the benzalkonium to form the upper multilayer reflector is the lowermost layer. 3. The surface emitting laser element according to claim 1, wherein, in the second dielectric layer forming step, the second dielectric layer is formed so as to cover at least a part of the annular electrode. Production method. The stacking step includes an oxidized layer stacking step of stacking an oxidized layer made of AlAs or Al _1-x Ga _x As (0 <x <1) between the contact layer and the active layer,
After the mesa post formation step, the stacked oxidation target layer is subjected to a selective oxidation heat treatment from a current injection portion made of AlAs or Al _1-x Ga _x As and Al ₂ O ₃ or (Al _1-x Ga _x ) ₂ O _3. The method for manufacturing a surface emitting laser element according to claim 1, further comprising a current confinement layer forming step of forming a current confinement layer having a current confinement portion.   5. The current path layer laminating process of laminating a current path layer having an acceptor concentration comparable to that of the contact layer between the contact layer and the oxidized layer. The manufacturing method of the surface emitting laser element of description.   The portion of the first dielectric layer in contact with at least the contact layer is made of silicon nitride having a nitrogen composition ratio larger than the stoichiometric composition. The manufacturing method of the surface emitting laser element as described in any one of. A vertical cavity surface emitting laser element,
A substrate,
A lower multilayer reflector mirror laminated on the substrate;
A plurality of semiconductor layers stacked on the lower multilayer reflector, having a mesa post structure, including an active layer and having a contact layer as an uppermost layer;
An annular electrode formed on the contact layer, having an opening at the center and having an outer periphery coinciding with the outer periphery of the mesa post structure;
A first dielectric layer formed in the opening of the annular electrode on the contact layer;
A second dielectric layer formed to cover the first dielectric layer and a gap formed between the first dielectric layer and the annular electrode;
An upper multilayer mirror made of a dielectric formed on the second dielectric layer;
Equipped with a,
A surface-emitting laser element , wherein a total optical thickness of the first and second dielectric layers is about λ / 4, where λ is a desired laser oscillation wavelength . A vertical cavity surface emitting laser element,
A substrate,
A lower multilayer reflector mirror laminated on the substrate;
A plurality of semiconductor layers stacked on the lower multilayer reflector, having a mesa post structure, including an active layer and having a contact layer as an uppermost layer;
An annular electrode formed on the contact layer, having an opening at the center and having an outer periphery coinciding with the outer periphery of the mesa post structure;
A first dielectric layer formed in the opening of the annular electrode on the contact layer;
A second dielectric layer formed to cover the first dielectric layer and a gap formed between the first dielectric layer and the annular electrode;
An upper multilayer mirror made of a dielectric formed on the second dielectric layer;
Equipped with a,
The first dielectric layer has a laminated structure of a lower dielectric layer and an upper dielectric layer. When a desired laser oscillation wavelength is λ, the optical thickness of the lower dielectric is about λ / 4. ,
An upper multilayer film made of a dielectric formed on the second dielectric layer and the second dielectric layer and said upper dielectric layer, the upper multilayer mirror the upper dielectric layer and the bottom layer surface-emitting laser element characterized in that it constitutes a. 9. The surface emitting laser device according to claim 7, wherein the second dielectric layer is formed so as to cover at least a part of the annular electrode. The plurality of semiconductor layers include a current injection portion made of AlAs or Al _1-x Ga _x As (0 <x <1) and Al formed between the active layer and the contact layer by a selective oxidation heat treatment. The surface emitting laser according to claim 7, further comprising a current confinement layer having a current confinement portion made of ₂ O ₃ or (Al _1-x Ga _x ) ₂ O _3. element.   11. The plurality of semiconductor layers include a current path layer formed between the current confinement layer and the contact layer and having an acceptor concentration comparable to the contact layer. Surface emitting laser element.   The portion of the first dielectric layer at least in contact with the contact layer is made of silicon nitride having a nitrogen composition ratio larger than that of the stoichiometric composition. The surface emitting laser element according to 1. The contact layer has a thickness of 50 nm or less, an acceptor concentration of 1 × 10 ¹⁹ cm ⁻³ or more, and a hydrogen concentration of 1 × 10 ¹⁸ cm ⁻³ or less. The surface emitting laser element according to any one of the above.

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