JP2016127236A - Surface light-emitting laser element, surface light-emitting laser array, optical scanner, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light-emitting laser element that includes both a high heat dissipation property and a wide process window.SOLUTION: The present surface light-emitting laser element comprises: a reflection mirror that includes a first layer and a second layer having larger thermal conductivity than that of the first layer; a resonator structure that has a first spacer layer, active layer, and second spacer layer sequentially laminated on the second layer of the reflection mirror; and a lamination film that is laminated on the resonator structure, where the lamination film forms a mesa, and the resonator structure extends from a lower part of the mesa to the periphery of the mesa when viewed from a light emission direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface emitting laser element, a surface emitting laser array, an optical scanning device, and an image forming apparatus.

  A vertical cavity surface emitting laser (VCSEL) is a semiconductor laser having a structure in which a lower semiconductor DBR, a lower spacer layer, an active layer, an upper spacer layer, an upper semiconductor DBR, and the like are sequentially stacked on a semiconductor substrate. . In the surface emitting laser element, the lower spacer layer, the active layer, and the upper spacer layer form a resonator structure.

  When the surface emitting laser element emits light, heat is generated in the active layer. However, if the heat generated in the active layer is quickly dissipated, an increase in junction temperature (active layer temperature) is suppressed, and a decrease in gain is suppressed. Output is obtained. Also, the so-called temperature characteristics are good and the life is long.

  The lower semiconductor DBR has a structure in which low refractive index layers and high refractive index layers are alternately stacked, and an AlGaAs-based material is usually used. The AlGaAs-based material greatly varies in thermal conductivity depending on the Al composition, and AlAs has the highest thermal conductivity. Therefore, in the lower semiconductor DBR on the heat dissipation path side, it is most desirable that the low refractive index layer adjacent to the lower spacer layer of the resonator structure is an AlAs layer.

  As an example of realizing this structure, the upper semiconductor DBR is made of an AlGaAs material, the resonator structure including the lower spacer layer, the active layer, and the upper spacer layer is made of an AlGaInPAs material, and all the low refractive index layers of the lower semiconductor DBR are made of AlAs. A surface emitting laser element having a layer may be mentioned.

  In this surface emitting laser element, since the etching rate of the resonator structure can be made smaller than the etching rate of the upper semiconductor DBR, it is possible to easily determine that the etching bottom surface has reached the resonator structure. As a result, it is possible to perform etching accurately to the vicinity of the center of the resonator structure, and to make all the low refractive index layers of the lower semiconductor DBR into AlAs layers (see, for example, Patent Document 1).

  However, in the surface emitting laser element described above, in order to obtain a sufficient heat dissipation effect, it is necessary to minimize the thickness of the lower spacer layer. However, if the thickness of the lower spacer layer is minimized, the remaining thickness of the lower spacer layer becomes extremely thin from the distribution of the etching rate, and the AlAs layer of the lower semiconductor DBR may be partially exposed.

  In particular, when the AlAs layer of the lower semiconductor DBR is exposed on the side surface of the mesa, the AlAs layer exposed on the side surface of the mesa is oxidized from the side surface to increase resistance or insulation in the manufacturing process of the surface emitting laser element, thereby reducing the yield. It becomes a factor to do. In order to avoid this problem and obtain a wide process window, it is necessary to increase the thickness of the lower spacer layer, and as a result, heat dissipation is sacrificed.

  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 both high heat dissipation and a wide process window.

  The surface-emitting laser element includes a first layer and a reflecting mirror including a second layer having a thermal conductivity larger than that of the first layer, a first spacer layer, an active layer on the second layer of the reflecting mirror, And a resonator structure in which the second spacer layer is sequentially laminated, and a laminated film laminated on the resonator structure, and a mesa is formed by the laminated film, as viewed from the light emitting direction, It is a requirement that the resonator structure extends around the mesa from below the mesa.

  According to the disclosed technique, it is possible to provide a surface emitting laser element having both high heat dissipation and a wide process window.

It is sectional drawing which illustrates the surface emitting laser element which concerns on 1st Embodiment. FIG. 3 is a diagram (part 1) illustrating the method for manufacturing the surface emitting laser element according to the first embodiment; FIG. 6 is a diagram (No. 2) illustrating the method for manufacturing the surface emitting laser element according to the first embodiment; FIG. 4 is a diagram (No. 3) illustrating the method for manufacturing the surface emitting laser element according to the first embodiment; FIG. 6 is a diagram (No. 4) for exemplifying the method for manufacturing the surface emitting laser element according to the first embodiment; It is sectional drawing which illustrates the surface emitting laser element which concerns on a comparative example. It is sectional drawing which illustrates the surface emitting laser element which concerns on the modification 1 of 1st Embodiment. FIG. 10 is a diagram (part 1) illustrating a method for manufacturing the surface emitting laser element according to the first modification of the first embodiment; FIG. 11 is a diagram (No. 2) illustrating the method for manufacturing the surface emitting laser element according to the first modification of the first embodiment; It is sectional drawing which illustrates the surface emitting laser element which concerns on the modification 2 of 1st Embodiment. It is a figure which illustrates the laser printer which concerns on 2nd Embodiment. It is a figure which illustrates the optical scanning device concerning a 2nd embodiment. It is a figure explaining a surface emitting laser array.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

<First Embodiment>
[Structure of surface emitting laser element]
First, the structure of the surface emitting laser element will be described. FIG. 1 is a cross-sectional view illustrating a surface emitting laser element according to the first embodiment. The surface emitting laser element 100 according to the first embodiment is a vertical cavity type laser element having an oscillation wavelength λ of, for example, a 780 nm band.

  Referring to FIG. 1, in a surface emitting laser device 100, a buffer layer 102, a lower semiconductor DBR (Distributed Bragg Reflector) 103, a lower spacer layer 104, an active layer 105, an upper spacer layer 106, and an upper semiconductor are formed on a semiconductor substrate 101. A DBR (Distributed Bragg Reflector) 107 and a contact layer 109 are sequentially stacked.

  A current confinement layer 108 is formed in the upper semiconductor DBR 107. A p-side electrode 110 is formed on the upper surface side of the contact layer 109, and an n-side electrode 111 is formed on the lower surface side of the semiconductor substrate 101. The + Z direction indicates the light emission direction of the surface emitting laser element 100 (laser light emission direction).

  In the surface emitting laser element 100, a part of the upper semiconductor DBR 107 is removed by etching to form a mesa 150 (mesa structure). For example, the side surface of the mesa 150 may have a tapered shape that widens toward the upper spacer layer 106 side. Reference numeral 150a denotes a bottom surface around the mesa 150 (hereinafter referred to as an etching bottom surface 150a). Note that a surface-emitting laser array having a plurality of surface-emitting laser elements 100 can be realized. In this case, the etching bottom surface 150 a is formed between the mesas 150 of the adjacent surface-emitting laser elements 100.

  In this embodiment, for the sake of convenience, the p-side electrode 110 side is the front side or the upper side, and the n-side electrode 111 side is the back side or the lower side. Further, the surface on the p-side electrode 110 side of each part is referred to as a front surface or an upper surface, and the surface on the n-side electrode 111 side is referred to as a back surface or a lower surface. However, the surface emitting laser element 100 can be used upside down, or can be arranged at an arbitrary angle. In addition, the shape of each component of the surface emitting laser element 100 viewed from the light emitting direction (from the + Z direction) may be referred to as a planar shape.

  Hereinafter, each component of the surface emitting laser element 100 will be described in detail. The semiconductor substrate 101 is, for example, an n-GaAs single crystal substrate. The buffer layer 102 is stacked on the upper surface of the semiconductor substrate 101. The buffer layer 102 is made of, for example, n-GaAs.

The lower semiconductor DBR 103 is stacked on the upper surface of the buffer layer 102. The lower semiconductor DBR 103 includes, for example, 40.5 pairs of a low refractive index layer made of n-AlAs and a high refractive index layer made of n-Al _0.3 Ga _0.7 As. The low refractive index layer constituting the lower semiconductor DBR 103 has a significantly higher thermal conductivity than the high refractive index layer.

  AlAs has particularly high thermal conductivity and excellent heat dissipation. For this reason, in the lower semiconductor DBR 103, the low refractive index layer in contact with the lower spacer layer 104 is preferably made of AlAs. In this case, heat dissipation can be further improved by making the low refractive index layer in contact with the lower spacer layer 104 as thick as possible. Hereinafter, an example in which the low refractive index layer in contact with the lower spacer layer 104 is an AlAs layer will be described.

  In the lower semiconductor DBR 103, a composition gradient layer having a composition gradually changed from one composition to the other composition is provided between the refractive index layers in order to reduce electric resistance. Each refractive index layer is set to have an optical thickness of λ / 4, including 1/2 of the adjacent composition gradient layer. The lower semiconductor DBR 103 is a typical example of a reflecting mirror according to the present invention. The high refractive index layer of the lower semiconductor DBR 103 is a typical example of the first layer according to the present invention, and the low refractive index layer is a typical example of the second layer according to the present invention.

The lower spacer layer 104 is stacked on the upper surface of the lower semiconductor DBR 103 (the upper surface of the uppermost AlAs layer in the lower semiconductor DBR 103). The lower spacer layer 104 is made of, for example, non-doped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P. The lower spacer layer 104 is a typical example of the first spacer layer according to the present invention.

The active layer 105 is stacked on the upper surface of the lower spacer layer 104. The active layer 105 has, for example, three quantum well layers and four barrier layers. Each quantum well layer is made of, for example, GaInPAs having a composition that induces compressive strain, and has a band gap wavelength of about 780 nm. Each barrier layer is made of, for example, Ga _0.6 In _0.4 P, which is a composition that induces tensile strain.

The upper spacer layer 106 is stacked on the upper surface of the active layer 105. The upper spacer layer 106 is made of, for example, non-doped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P. The upper spacer layer 106 is a typical example of the second spacer layer according to the present invention.

  A portion in which the lower spacer layer 104, the active layer 105, and the upper spacer layer 106 are sequentially stacked constitutes the resonator structure 120. The thickness of the resonator structure 120 can be set to have an optical thickness of one wavelength. The active layer 105 can be provided at substantially the center of the resonator structure 120 that is a position corresponding to the antinode in the standing wave distribution of the electric field so that a high stimulated emission probability can be obtained.

  The heat generated in the active layer 105 is radiated to the semiconductor substrate 101 mainly through the lower semiconductor DBR 103. The semiconductor substrate 101 is attached to the package by, for example, a conductive adhesive via an n-side electrode 111 formed on the lower surface, and the heat generated in the active layer 105 is radiated from the semiconductor substrate 101 to the package.

The upper semiconductor DBR 107 is stacked on the upper surface of the upper spacer layer 106. The upper semiconductor DBR 107 has, for example, 24 pairs of a low refractive index layer made of p-Al _0.9 Ga _0.1 As and a high refractive index layer made of p-Al _0.3 Ga _0.7 As. ing.

  In the upper semiconductor DBR 107, a composition gradient layer in which the composition is gradually changed from one composition to the other composition is provided between the refractive index layers in order to reduce electrical resistance. Each refractive index layer is set to have an optical thickness of λ / 4, including 1/2 of the adjacent composition gradient layer.

  In one of the low refractive index layers in the upper semiconductor DBR 107, a current confinement layer 108 made of p-AlAs having a thickness of, for example, about 30 nm is formed. The current confinement layer 108 is formed, for example, in the third pair of low-refractive index layers from the upper spacer layer 106 at a position optically separated from the upper spacer layer 106 by 5λ / 4 inside the upper semiconductor DBR 107. .

  The current confinement layer 108 includes an oxidized selective oxidation region 108a and an unoxidized current passing region 108b. The selective oxidation region 108 a can be formed by oxidizing the current confinement layer 108 from the side surface of the mesa 150.

  The contact layer 109 is stacked on the upper surface of the upper semiconductor DBR 107. The contact layer 109 is made of, for example, highly doped p-GaAs. The contact layer 109 is a layer necessary for forming ohmic contact with the p-side electrode 110.

  The p-side electrode 110 is selectively formed on the upper surface of the contact layer 109. The p-side electrode 110 is formed of a film in which metals such as Ti / Pt / Au and Cr / AuZn / Au are stacked. Note that a region where the p-side electrode 110 is not formed on the contact layer 109 is an emission surface for emitting laser light.

  The n-side electrode 111 is provided on the lower surface of the semiconductor substrate 101 and is formed in ohmic contact with the semiconductor substrate 101. The n-side electrode 111 is formed of a film in which metals such as Ti / Pt / Au and AuGe / Ni / Au are laminated, for example.

  Note that an insulating film covering the top surface of the mesa 150, the side surface of the mesa 150, and the etching bottom surface 150a excluding the portion where the p-side electrode 110 is formed and the portion where the laser beam is emitted may be formed to a thickness of about 150 nm. . As the insulating film, for example, a silicon nitride film (SiN film) can be used.

  In the surface emitting laser element 100 according to the present embodiment, the mesa 150 is formed of a laminated film including the upper semiconductor DBR 107 and the like laminated on the resonator structure 120. Then, the entire surface of the etching bottom surface 150 a that is the bottom surface around the mesa 150 is formed by any layer (for example, the lowermost layer) in the upper semiconductor DBR 107.

  The resonator structure 120 remains in the entire region below the layer that forms the etching bottom surface 150a (for example, the lowermost layer in the upper semiconductor DBR 107). That is, as viewed from the light emitting direction, the resonator structure 120 extends from below the mesa 150 to the periphery of the mesa 150, and the resonator structure 120 remains in the entire region below the layer forming the etching bottom surface 150a.

[Method for Manufacturing Surface Emitting Laser Element]
Next, a method for manufacturing the surface emitting laser element 100 will be described with reference to FIGS.

  First, as shown in FIG. 2A, on a semiconductor substrate 101 made of n-GaAs or the like, a buffer layer 102, a lower semiconductor DBR 103, a lower spacer layer 104, an active layer 105, an upper spacer layer 106, an upper semiconductor DBR 107, The contact layers 109 are sequentially stacked to form a stacked body 180. Note that a part of the film constituting the stacked body 180 may be referred to as a stacked film.

  The stacked body 180 can be formed by, for example, a metal organic chemical vapor deposition (MOCVD) method. In addition, the stacked body 180 may be formed by molecular beam epitaxy (MBE).

For example, trimethylaluminum (TMA), trimethylgallium (TMG), or trimethylindium (TMI) can be used as the Group III material. Further, for example, an arsine (AsH ₃ ) gas or a phosphine (PH ₃ ) gas can be used as the group V raw material. Further, for example, carbon tetrabromide (CBr ₄ ) can be used as a raw material for the p-type dopant. Further, for example, hydrogen selenide (H ₂ Se) can be used as a raw material for the n-type dopant.

  Next, as illustrated in FIG. 2B, a resist pattern 500 is formed on the upper surface of the stacked body 180 (the upper surface of the contact layer 109). The resist pattern 500 is necessary for forming the mesa 150 and can be formed by, for example, photolithography. The planar shape of the resist pattern 500 may be a square having a side of about 20 μm, for example.

  Next, as shown in FIG. 3A, the laminate 180 is etched using the resist pattern 500 as a mask to form a mesa 150 having a substantially trapezoidal cross section. The mesa 150 can be formed using, for example, the ICP plasma etching apparatus 300 shown in FIG. This will be specifically described below.

  First, the laminated body 180 on which the resist pattern 500 shown in FIG. 2B is formed is placed in the vacuum chamber 301 of the ICP plasma etching apparatus 300, and is evacuated by the dry pump 321 for 10 minutes. Open and transport to reaction chamber 303. The reaction chamber 303 is provided with a ring-shaped silicon 304, and the reaction product contributes to the etching of the GaAs material.

In the reaction chamber 303, after the stacked body 180 is held for 10 minutes, for example, 1 sccm of Cl ₂ gas is introduced from a gas cylinder 305 for chlorine (Cl ₂ ). Further, for example, 1 sccm of SiCl ₄ gas is introduced from a gas cylinder 306 for carbon tetrachloride (SiCl ₄ ), and 1 sccm of Ar gas is introduced from a gas cylinder 307 for argon (Ar). Mass flow controllers 308, 309, and 310 are attached to the gas cylinders 305, 306, and 307, and the flow rates of the respective gases are controlled by the mass flow controllers 308, 309, and 310.

The reaction chamber 303 is evacuated by a turbo molecular pump 322 and a dry pump 323, and a valve 311 with an opening degree adjusting function is provided between the reaction chamber 303 and the turbo molecular pump 322. In addition, a vacuum gauge 312 for measuring the pressure in the reaction chamber 303 is provided. The pressure in the reaction chamber 303 is monitored with the vacuum gauge 312, and for example, the opening of the valve 311 with an opening adjustment function is controlled and etched so as to keep the pressure in the reaction chamber 303 at 0.3 Pa. Specifically, for example, after the pressure of the reaction chamber 303 is adjusted to 0.3 Pa for 30 seconds from the introduction of Cl ₂ gas, SiCl ₄ gas, and Ar gas, 400 W of power is supplied to the induction coil 314.

  Thereafter, for example, the power supplied to the induction coil 314 when the bottom surface of the etching reaches the position of the lowermost layer of the upper semiconductor DBR 107 is cut off. In this case, the etching bottom surface 150 a is formed by the lowermost layer of the upper semiconductor DBR 107 that is an upper layer than the upper spacer layer 106. The resonator structure 120 remains below the etching bottom surface 150a and is not removed at all.

  In this etching step, the position of the etching bottom can be measured as a change in reflectance by a reflectance measuring device 315 provided via a sapphire window provided in the upper part of the reaction chamber 303. The measured reflectivity is displayed on the reflectivity monitor 316. By performing etching while checking the status displayed on the reflectivity monitor 316, it is possible to confirm which layer is currently being etched. is there. Therefore, the etching can be stopped at a desired position and a desired layer can be exposed to the etching bottom surface 150a.

  Next, as shown in FIG. 3B, the resist pattern 500 is removed, and a current confinement layer 108 is formed. The current confinement layer 108 can be formed using, for example, the oxidation apparatus 400 shown in FIG. This will be specifically described below.

  The oxidizer 400 includes a water vapor supply unit 410, a stainless steel reaction vessel 420, an introduction pipe 430, an exhaust pipe 440, a water collector 450, a temperature controller, and the like. The water vapor supply unit 410 includes a mass flow controller 411, a vaporizer 412, a liquid mass flow controller 413, and a water supply unit 414, and water vapor is supplied to the stainless steel reaction vessel 420.

  In the stainless steel reaction vessel 420, a tray 421 for installing an object to be oxidized (in this case, a laminate 180 in which the mesa 150 is formed) is provided. In addition, a disc-shaped heating table 422 with a built-in ceramic heater 424 for heating an object to be oxidized via the tray 421, a thermocouple 425 for measuring the temperature of the object to be oxidized, and a heating table 422 are held and rotated. A possible base 423 is provided.

  The temperature controller controls the current (or voltage) supplied to the ceramic heater 424 while monitoring the output signal of the thermocouple 425, and keeps the object to be oxidized at a set temperature (holding temperature) for a set time (holding). Time) hold.

In the oxidizer 400, when nitrogen (N ₂ ) gas is introduced into the water supply unit 414 in the water vapor supply unit 410, the flow rate of water (H ₂ O) is controlled by the liquid mass flow controller 413 and supplied to the vaporizer 412. Become. When the flow rate of N ₂ carrier gas is controlled by the mass flow controller 411 and introduced into the vaporizer 412, the N ₂ carrier gas containing water vapor is introduced from the vaporizer 412 into the stainless steel reaction vessel 420 through the introduction pipe 430. Supplied.

The N ₂ carrier gas containing water vapor supplied into the stainless steel reaction vessel 420 is supplied around the laminate 180 in which the mesa 150 is formed. As a result, the stacked body 180 on which the mesa 150 is formed is exposed to a water vapor atmosphere, and in the region where the current confinement layer 108 of the mesa 150 is formed, oxidation gradually proceeds from the surroundings.

For example, in the stacked body 180 in which the mesa 150 is formed, the radius of the current passage region 108b is about 3.5 μm under the condition that the flow rate of water is 80 g / hr, the flow rate of N ₂ carrier gas is 20 SLM, and the holding temperature is 410 ° C. Oxidize only for hours. Here, the oxidation time can be calculated by calculating the required oxidation distance from the oxidation rate obtained by processing samples of the same laminate structure in advance and the finished dimensions of the mesa 150.

  As a result, the selective oxidation region 108a made of Al oxide is selectively oxidized from the side surface of the mesa 150, and the central portion of the mesa 150 is oxidized and surrounded by the selective oxidation region 108a in plan view. A current passing region 108b, which is a non-existing region, remains. That is, the current confinement layer 108 including the selective oxidation region 108a and the current passage region 108b is formed.

After the current confinement layer 108 is formed, the N ₂ carrier gas containing water vapor is discharged through the exhaust pipe 440 and the water collector 450.

  Thereafter, a silicon nitride film (SiN film) covering the upper surface of the mesa 150, the side surface of the mesa 150, and the etching bottom surface 150a is formed by a plasma CVD method to a thickness of about 150 nm. Then, a resist pattern having a substantially square opening with a side of, for example, 18 μm is formed on the silicon nitride film covering the upper surface of the substantially trapezoidal mesa 150. Then, the silicon nitride film in the region where the resist pattern is not formed is etched by, for example, buffered hydrofluoric acid, and an opening of, for example, 18 μm is formed on the upper surface of the mesa 150.

  Next, after forming a resist pattern for forming the p-side electrode 110, a metal film is formed in a stacked order such that, for example, Cr / AuZn / Au in the order of Cr / AuZn / Au by a vacuum deposition method or the like, The p-side electrode 110 is formed by performing lift-off. Further, after the lower surface of the semiconductor substrate 101 is polished, a metal film is stacked on the polished surface in the order of, for example, AuGe / Ni / Au by a vacuum deposition method or the like, and the n-side electrode 111 is formed.

  Thereafter, heat treatment is performed, for example, at 400 ° C. for 4 minutes in a sinter furnace. Through the above steps, the surface emitting laser element 100 shown in FIG. 1 is completed.

  Here, a specific effect produced by the surface emitting laser element 100 according to the present embodiment will be described with reference to a comparative example. FIG. 6 is a cross-sectional view illustrating a surface emitting laser element according to a comparative example. Referring to FIG. 6, the surface emitting laser element 100X according to the comparative example is that the entire bottom surface 150a of the etching is formed by the lower spacer layer 104, which is the surface emitting laser element 100 according to the present embodiment (FIG. 1). Different from reference).

In the surface emitting laser element 100X, the lower semiconductor DBR 103, which is the lower layer of the lower spacer layer 104, includes, for example, a low refractive index layer (AlAs layer) made of n-AlAs having a high thermal conductivity, and n-Al _0.3 Ga _{0. .7} A pair of high refractive index layers made of As. In order to enhance the heat dissipation effect of the heat generated in the active layer 105, the uppermost layer of the lower semiconductor DBR 103 is an AlAs layer, and the thickness of the lower spacer layer 104 is minimized to increase the thermal conductivity with the active layer 105. It is preferable to make the AlAs layer as close as possible.

  However, in the surface emitting laser element 100X, the lower spacer layer 104 is the etching bottom surface 150a. Therefore, if the thickness of the lower spacer layer 104 is minimized, the remaining thickness of the lower spacer layer 104 becomes extremely thin from the distribution of the etching rate, and the AlAs layer constituting the lower semiconductor DBR 103 may be partially exposed. There is.

  For example, when the AlAs layer is exposed on the side surface of the mesa 150, the AlAs layer exposed on the side surface of the mesa 150 is oxidized from the side surface to increase resistance or insulation in the step of forming the current confinement layer 108. It becomes a factor to decrease. Therefore, in order to obtain a wide process window, it is necessary to increase the thickness of the lower spacer layer 104. As a result, the heat dissipation effect is sacrificed.

  On the other hand, in the surface emitting laser element 100, unlike the surface emitting laser element 100X, the etching bottom surface 150a becomes a middle layer of the laminated film formed on the resonator structure 120, and resonates below the etching bottom surface 150a. The vessel structure 120 remains. Specifically, in the surface emitting laser element 100, the etching bottom surface 150a is, for example, the lowermost layer of the upper semiconductor DBR 107.

  In the structure of the surface emitting laser element 100, the lower spacer layer 104 is not etched when the etching bottom surface 150a is formed. Therefore, the thickness of the lower spacer layer 104 can be minimized, the active layer 105 and the AlAs layer (low refractive index layer) having a large thermal conductivity can be made as close as possible, and a wide process window can be obtained.

  Thus, in the surface emitting laser element 100, both high heat dissipation and a wide process window can be achieved.

  In the surface emitting laser element 100, since all of the resonator structure 120 remains below the etching bottom surface 150a, there is a concern that light leakage may occur in the lateral direction other than the light emitting direction, and the light output may be reduced. there were.

  However, according to the study by the inventors, in a surface emitting laser array having a plurality of surface emitting laser elements 100, the light output at 0.25 mA energization before laser oscillation was 6 to 7 μW per channel.

  This is a slight increase compared to 2-3 μW per channel in the case of a surface emitting laser array having a plurality of surface emitting laser elements 100X (conventional structure), but the light output (mW in the laser oscillation state). Compared to (order), the amount of light is negligible, and it is not a problem level. In particular, when a surface emitting laser array having a plurality of surface emitting laser elements 100 is used as a light source of an image forming apparatus, the level is not affected at all.

<Variation 1 of the first embodiment>
In the first modification of the first embodiment, an example is shown in which an etching bottom surface around the mesa is formed by etching deeper than in the first embodiment. In the first modification of the first embodiment, the description of the same components as those of the already described embodiments may be omitted.

[Structure of surface emitting laser element]
First, the structure of the surface emitting laser element will be described. FIG. 7 is a cross-sectional view illustrating a surface emitting laser element according to Modification 1 of the first embodiment. In the surface emitting laser element 100A according to the first modification of the first embodiment, the entire etching bottom surface 150a is formed by the upper spacer layer 106.

  In the surface emitting laser element 100A, the etching bottom surface 150a includes an inclined surface 150b and a flat surface 150c. The inclined surface 150b is inclined from the mesa 150 side toward the flat surface 150c side. However, the flat surface 150c may not be completely flat, and all or part of the flat surface 150c may be a surface that is inclined more gently than the inclined surface 150b.

  That is, in the surface emitting laser element 100A, the entire etching bottom surface 150a is formed by the upper spacer layer 106, and the upper spacer layer 106 has a region (a portion of the inclined surface 150b) in which the thickness decreases with increasing distance from the mesa 150 side. Yes. Since a part of the resonator structure 120 remains in the entire region below the etching bottom surface 150a, the lower layer than the upper spacer layer 106 is not exposed on the etching bottom surface 150a.

[Method for Manufacturing Surface Emitting Laser Element]
Next, a method for manufacturing the surface emitting laser element 100A will be described with reference to FIGS.

First, the same steps as those in FIGS. 2A to 3A of the first embodiment are performed to form a mesa 150 having a substantially trapezoidal cross section as shown in FIG. 8A. . Specifically, in the reaction chamber 303 shown in FIG. 4, after holding the stacked body 180 for 10 minutes, for example, 1 sccm of Cl ₂ gas is introduced from a gas cylinder 305 for chlorine (Cl ₂ ). Further, for example, 1 sccm of SiCl ₄ gas is introduced from a gas cylinder 306 for carbon tetrachloride (SiCl ₄ ), and 1 sccm of Ar gas is introduced from a gas cylinder 307 for argon (Ar).

Then, the pressure in the reaction chamber 303 is monitored by the vacuum gauge 312, and for example, the opening of the valve 311 with an opening adjustment function is controlled and etched so as to keep the pressure in the reaction chamber 303 at 0.3 Pa. Specifically, for example, after the pressure of the reaction chamber 303 is adjusted to 0.3 Pa for 30 seconds from the introduction of Cl ₂ gas, SiCl ₄ gas, and Ar gas, 400 W of power is supplied to the induction coil 314.

  Thereafter, the power supplied to the induction coil 314 is cut off when the bottom surface of the etching reaches the position of the lower surface of the layer that becomes the current confinement layer 108. Thereby, the mesa 150 is formed, and at this time, a flat etching bottom is formed by the upper semiconductor DBR 107.

Next, as shown in FIG. 8B, the amount of the introduced gas is changed and further etching is performed to form the inclined surface 150b and the flat surface 150c. Specifically, for example, by changing the Cl ₂ gas to 1.5 sccm, the SiCl ₄ gas to 1 sccm, and the Ar gas to 3.0 sccm, the opening degree is adjusted so as to keep the pressure in the reaction chamber 303 at 0.1 Pa, for example. The opening degree of the function-equipped valve 311 is controlled.

  Next, for example, after maintaining this pressure for 30 seconds, 400 W of power is again supplied to the induction coil 314 to perform etching. Then, the power supplied to the induction coil 314 is cut off when the etching bottom surface is positioned on the upper spacer layer 106. As a result, an etching bottom surface 150a having an inclined surface 150b and a flat surface 150c is formed, and the upper spacer layer 106 constituting the etching bottom surface 150a is a region where the thickness decreases as the distance from the mesa 150 side increases (part of the inclined surface 150b). ).

  Thus, in this embodiment, as described with reference to FIGS. 8A and 8B, the etching conditions are changed in two stages when the etching bottom surface 150a is formed.

  Specifically, the etching conditions in the first stage described with reference to FIG. 8A are mainly the source gas contributing to the chemical reaction, and the conditions for forming a flat etching bottom surface are selected. doing. On the other hand, the etching conditions of the second stage described with reference to FIG. 8B are conditions in which the raw material gas contributing to physical evaporation is mainly used and the reaction pressure is further reduced. The conditions for forming a certain etching bottom surface are selected.

Here, SiCl ₄ is a source gas that contributes to a chemical reaction with the object to be etched, Ar is a source gas that activates the surface to be etched while maintaining the plasma state and induces physical evaporation, and Cl _2. Is a source gas that contributes to both chemical reaction and induction of physical evaporation.

FIG. 9 is a diagram illustrating a concept in which raw materials contributing to physical evaporation are shielded by mesas. As shown in FIG. 9, since ions (Ar ⁺ ) of Ar, which is a raw material gas for inducing physical evaporation, are attracted to the surface to be etched having a GND potential, an ion assist effect occurs. Further, under the second stage etching conditions, the reaction pressure is lowered, and therefore the mean free path of molecules becomes large.

In this case, in the region where the distance from the mesa 150 on the surface to be etched is small, Ar ⁺ is shielded by the mesa 150, so that the ion assist effect is reduced and the etching rate is reduced (slowed). Further, as the distance from the mesa 150 is increased, the shielding effect by the mesa 150 is reduced and the ion assist effect is increased, so that the etching rate is increased (increased).

  As a result, a region (a portion of the inclined surface 150 b) whose thickness decreases as the distance from the mesa 150 side is formed in the upper spacer layer 106. However, since the shielding effect by the mesa 150 is lost when it is away from the mesa 150 side to some extent, the thickness of the upper spacer layer 106 becomes substantially uniform (part of the flat surface 150c).

  Thereafter, the surface emitting laser element 100A shown in FIG. 7 is completed by executing the same steps as those in FIG. 3B and thereafter in the first embodiment.

  As described above, in the surface emitting laser element 100A, the etching bottom surface 150a is formed by the upper spacer layer 106, and the upper spacer layer 106 has a region where the thickness decreases as the distance from the mesa 150 side increases. However, the etching bottom surface 150a is formed only by the upper spacer layer 106, and the lower layer than the upper spacer layer 106 is not exposed on the etching bottom surface 150a.

  Even in the structure of the surface emitting laser element 100A, as in the structure of the surface emitting laser element 100, the lower spacer layer 104 is not etched when the etching bottom surface 150a is formed. Therefore, as in the first embodiment, both high heat dissipation and a wide process window can be achieved.

  According to the study by the inventors, in the surface emitting laser array having a plurality of surface emitting laser elements 100A, the light output at 0.25 mA energization before laser oscillation was 2 to 3 μW per channel.

  This is the same amount of light as in the case of a surface emitting laser array having a plurality of surface emitting laser elements 100X (conventional structure). As a result, it was confirmed that even if a part of the resonator structure 120 remains around the mesa 150 as in the structure of the surface emitting laser element 100A, light leakage does not increase compared to the conventional structure. .

<Modification 2 of the first embodiment>
In the second modification of the first embodiment, an example is shown in which an etching bottom surface around the mesa is formed by deeper etching than in the first modification of the first embodiment. In the second modification of the first embodiment, the description of the same components as those of the already described embodiment may be omitted.

  FIG. 10 is a cross-sectional view illustrating a surface emitting laser element according to Modification 2 of the first embodiment. In the surface emitting laser element 100B according to the second modification of the first embodiment, the etching bottom surface 150a includes an inclined surface 150b and a flat surface 150c, as in the surface emitting laser element 100A (see FIG. 7). .

  However, unlike the surface emitting laser element 100A, when viewed from the light emitting direction, the inclined surface 150b is a first region where the end surface of the upper spacer layer 106 is exposed and the end surface of the active layer 105 is exposed from the mesa 150 side. 2 region, and a third region where the end face of the lower spacer layer 104 is exposed. Further, the flat surface 150 c is formed by the lower spacer layer 104. However, the flat surface 150c may not be completely flat, and all or part of the flat surface 150c may be a surface that is inclined more gently than the inclined surface 150b.

  That is, in the surface-emitting laser element 100B, a part of the etching bottom surface 150a is formed from the upper spacer layer 106, and the thickness of the upper spacer layer 106 decreases with increasing distance from the mesa 150 side, and then disappears (part of the inclined surface 150b). ). The remaining portion of the etching bottom surface 150a is formed of the active layer 105 and the lower spacer layer 104 (the remaining portion of the inclined surface 150b and the flat surface 150c). The active layer 105 and the lower spacer layer 104 have a region where the thickness decreases as the distance from the mesa 150 side increases.

  The surface emitting laser element 100B can be manufactured by the same manufacturing method as the surface emitting laser element 100A. Specifically, in the step shown in FIG. 8B, the electric power supplied to the induction coil 314 is cut off when the etching bottom surface is positioned on the lower spacer layer 104, whereby the surface emitting laser element 100B. The structure can be as follows.

  In the structure of the surface emitting laser element 100 </ b> B, a part of the etching bottom surface 150 a is formed from the lower spacer layer 104. However, a region where the lower spacer layer 104 is not etched exists on the mesa 150 side (a first region where the end surface of the upper spacer layer 106 of the inclined surface 150b is exposed and a second region where the end surface of the active layer 105 is exposed). ).

  Therefore, unlike the structure of the surface emitting laser element 100X according to the comparative example, the AlAs layer is not exposed on the side surface of the mesa 150 even if the etching conditions vary. As a result, the AlAs layer exposed on the side surface of the mesa 150 is oxidized from the side surface to increase resistance or insulation, and there is no possibility that the yield decreases.

  That is, also in the structure of the surface emitting laser element 100B, high heat dissipation and a wide process window can be achieved at the same time as in the first embodiment and the first modification thereof.

  According to the study by the inventors, in the surface emitting laser array having a plurality of surface emitting laser elements 100B, the light output at 0.25 mA energization before laser oscillation was 2-3 μW per channel.

  This is the same amount of light as in the case of a surface emitting laser array having a plurality of surface emitting laser elements 100X (conventional structure). As a result, it was confirmed that even if a part of the resonator structure 120 remains around the mesa 150 as in the structure of the surface emitting laser element 100B, light leakage does not increase as compared with the conventional structure. .

<Second Embodiment>
In the second embodiment, an example in which the surface emitting laser element according to the first embodiment or the modification thereof is mounted on a laser printer 1000 which is an image forming apparatus will be described. In the second embodiment, description of the same components as those of the already described embodiments may be omitted.

  FIG. 11 is a diagram illustrating a laser printer according to the second embodiment. Referring to FIG. 11, a laser printer 1000 according to the second embodiment includes an optical scanning device 1010, a photosensitive drum 1030, a charging charger 1031, a developing roller 1032, a transfer charger 1033, a charge eliminating unit 1034, a cleaning unit 1035, A toner cartridge 1036, a paper feed roller 1037, a paper feed tray 1038, a registration roller pair 1039, a fixing roller 1041, a paper discharge roller 1042, a paper discharge tray 1043, a communication control device, a printer control device, and the like are provided. These units are housed in predetermined positions in the printer housing 1044. The communication control device controls bidirectional communication with a host device (for example, a personal computer) via a network or the like. The printer control device controls the above-described units in an integrated manner.

  The photosensitive drum 1030 is a columnar member, and is an image carrier having a photosensitive layer formed on the surface thereof. That is, the surface of the photoconductor drum 1030 is a scanned surface. Then, the photosensitive drum 1030 rotates in the direction indicated by the arrow X.

  The charging charger 1031, the developing roller 1032, the transfer charger 1033, the charge removal unit 1034, and the cleaning unit 1035 are each disposed in the vicinity of the surface of the photosensitive drum 1030. The charging charger 1031, the developing roller 1032, the transfer charger 1033, the charge removal unit 1034, and the cleaning unit 1035 are arranged in this order along the rotation direction of the photosensitive drum 1030.

  The charging charger 1031 uniformly charges the surface of the photosensitive drum 1030. The optical scanning device 1010 scans the surface of the photosensitive drum 1030 charged by the charging charger 1031 with a light beam modulated based on image information from the host device, and corresponds to the image information on the surface of the photosensitive drum 1030. A latent image is formed. The latent image formed here moves in the direction of the developing roller 1032 as the photosensitive drum 1030 rotates. The configuration of the optical scanning device 1010 will be described later.

  Toner cartridge 1036 stores toner, and this toner is supplied to developing roller 1032.

  The developing roller 1032 causes the toner supplied from the toner cartridge 1036 to adhere to the latent image formed on the surface of the photosensitive drum 1030 to visualize the image information. Here, the latent image to which the toner is attached (hereinafter also referred to as “toner image” for the sake of convenience) moves in the direction of the transfer charger 1033 as the photosensitive drum 1030 rotates.

  Recording paper 1040 is stored in the paper feed tray 1038. A paper feed roller 1037 is disposed in the vicinity of the paper feed tray 1038. The paper feed roller 1037 takes out the recording paper 1040 one by one from the paper feed tray 1038 and conveys it to the registration roller pair 1039. The registration roller pair 1039 temporarily holds the recording paper 1040 taken out by the paper supply roller 1037, and in the gap between the photosensitive drum 1030 and the transfer charger 1033 according to the rotation of the photosensitive drum 1030. Send it out.

  A voltage having a polarity opposite to that of the toner is applied to the transfer charger 1033 in order to electrically attract the toner on the surface of the photosensitive drum 1030 to the recording paper 1040. With this voltage, the toner image on the surface of the photosensitive drum 1030 is transferred to the recording paper 1040. The recording sheet 1040 transferred here is sent to the fixing roller 1041.

  In the fixing roller 1041, heat and pressure are applied to the recording paper 1040, whereby the toner is fixed on the recording paper 1040. The recording paper 1040 fixed here is sent to the paper discharge tray 1043 via the paper discharge roller 1042 and is sequentially stacked on the paper discharge tray 1043. The neutralization unit 1034 neutralizes the surface of the photosensitive drum 1030.

  The cleaning unit 1035 removes the toner remaining on the surface of the photosensitive drum 1030 (residual toner). The surface of the photosensitive drum 1030 from which the residual toner has been removed returns to the position facing the charging charger 1031 again.

  Next, the optical scanning device 1010 will be described with reference to FIG. FIG. 12 is a diagram illustrating an optical scanning device according to the second embodiment. The optical scanning device 1010 controls the light source unit 1100, the coupling lens 1111, the aperture 1112, the cylindrical lens 1113, the polygon mirror 1114, the fθ lens 1115, the toroidal lens 1116, the two mirrors (1117, 1118), and the above parts. A control device for controlling is provided. The light source unit 1100 includes a surface emitting laser array LA in which a plurality of surface emitting laser elements 100, 100A, or 100B are formed. In FIG. 13 described later, a surface emitting laser array LA in which 40 surface emitting laser elements (VCSEL) are formed is illustrated.

  The coupling lens 1111 shapes the light emitted from the light source unit 1100 into substantially parallel light. The aperture 1112 defines the beam diameter of the light that has passed through the coupling lens 1111. The cylindrical lens 1113 condenses the light beam that has passed through the aperture 1112 in the vicinity of the deflection reflection surface of the polygon mirror 1114 that is a light deflection unit, via the mirror 1117.

  The polygon mirror 1114 is made of a regular hexagonal columnar member having a low height, and six deflection reflection surfaces are formed on the side surface. And it is rotated at a constant angular velocity in the direction shown by the arrow Y by the rotation mechanism.

  Accordingly, the light emitted from the light source unit 1100 and condensed near the deflection reflection surface of the polygon mirror 1114 by the cylindrical lens 1113 is deflected at a constant angular velocity by the rotation of the polygon mirror 1114.

  The fθ lens 1115 has an image height proportional to the incident angle of light from the polygon mirror 1114, and moves the image surface of light deflected by the polygon mirror 1114 at a constant angular velocity with constant speed in the main scanning direction. The toroidal lens 1116 forms an image of the light from the fθ lens 1115 on the surface of the photosensitive drum 1030 via the mirror 1118.

  The toroidal lens 1116 is disposed on the optical path of the light beam through the fθ lens 1115. Then, the light beam that has passed through the toroidal lens 1116 is irradiated onto the surface of the photosensitive drum 1030 to form a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 1030 as the polygon mirror 1114 rotates. That is, the photoconductor drum 1030 is scanned. The moving direction of the light spot at this time is the “main scanning direction”. The rotation direction of the photosensitive drum 1030 is the “sub-scanning direction”.

  The optical system arranged on the optical path between the polygon mirror 1114 and the photosensitive drum 1030 is also called a scanning optical system. In this embodiment, the scanning optical system includes an fθ lens 1115 and a toroidal lens 1116. Note that at least one folding mirror may be disposed on at least one of the optical path between the fθ lens 1115 and the toroidal lens 1116 and on the optical path between the toroidal lens 1116 and the photosensitive drum 1030.

  In this case, it is assumed that the surface emitting laser array LA is arranged as shown in FIG. Then, in the surface emitting laser array LA, the positional relationship of each surface emitting laser element in the direction corresponding to the sub-scanning direction when a perpendicular is drawn from the center of each surface emitting laser element (VCSEL) in the direction corresponding to the sub-scanning direction. Become equal intervals (interval d2). Therefore, by adjusting the lighting timing, it can be understood that the light source is arranged on the photosensitive drum 1030 at equal intervals in the sub-scanning direction. For example, if the pitch d1 of the surface emitting laser elements in the direction corresponding to the sub-scanning direction is 26.5 μm, the interval d2 is 2.65 μm.

  If the magnification of the optical system is doubled, writing dots can be formed on the photosensitive drum 1030 at intervals of 5.3 μm in the sub-scanning direction. This corresponds to 4800 dpi (dots / inch). That is, high-density writing of 4800 dpi (dot / inch) can be performed. Of course, higher density can be achieved by increasing the number of surface emitting lasers in the direction corresponding to the main scanning direction, making the array arrangement in which the pitch d1 is reduced and the interval d2 is further reduced, or the magnification of the optical system is reduced. And higher quality printing becomes possible. Note that the writing interval in the main scanning direction can be easily controlled by the lighting timing of the light source.

  In addition, the surface emitting laser element 100, 100A, or 100B according to the first embodiment or the modification thereof has a structure that is low in cost but does not easily oscillate a high-order transverse mode even when the output is increased. Therefore, a high light output can be obtained in the single basic transverse mode. Therefore, a minute circular beam spot can be formed with high accuracy, and since the output is high, the linear speed on the photosensitive drum 1030 can be increased, and a high-definition image can be formed at high speed in the laser printer 1000. .

  Further, in this case, since the polarization directions of the light beams from the respective light emitting units are stably aligned, the laser printer 1000 can stably form a high quality image.

  Further, since the surface emitting laser element 100, 100A, or 100B according to the first embodiment or its modification has both high heat dissipation and a wide process window, low cost while maintaining high heat dissipation. By increasing the number of elements, a surface emitting laser array can be realized. Thus, the laser printer 1000 can form a high-definition image at high speed at a low cost.

  As described above, according to the optical scanning device 1010 according to the second embodiment, since the light source unit 1100 includes the surface emitting laser array LA, a high-definition latent image is formed on the surface of the photosensitive drum 1030 at high speed. An optical scanning device capable of performing scanning can be realized at low cost.

  Further, according to the laser printer 1000 according to the second embodiment, since the optical scanning device 1010 including the surface emitting laser array LA is provided, a laser printer that forms high-definition images at high speed at low cost is realized. it can.

  In the second embodiment, the laser printer 1000 is described as an example of the image forming apparatus, but the present invention is not limited to this. In short, an image forming apparatus having a surface emitting laser array using the surface emitting laser elements 100, 100A, or 100B can form a high-definition image at high speed.

  In the image forming apparatus, the image information may be multicolor color information. Even an image forming apparatus that forms a color image can form a high-definition image at a high speed by using an optical scanning device corresponding to the color image.

  The image forming apparatus corresponds to a color image. For example, the photosensitive drum for black (K), the photosensitive drum for cyan (C), the photosensitive drum for magenta (M), and the photosensitive drum for yellow (Y). A tandem color machine including a plurality of photosensitive drums such as a photosensitive drum may be used.

  The preferred embodiments and the like have been described in detail above, but the present invention is not limited to the above-described embodiments and the like, and various modifications can be made to the above-described embodiments and the like without departing from the scope described in the claims. Variations and substitutions can be added.

100, 100A, 100B Surface emitting laser element 101 Semiconductor substrate 102 Buffer layer 103 Lower semiconductor DBR
104 Lower spacer layer 105 Active layer 106 Upper spacer layer 107 Upper semiconductor DBR
108 current confinement layer 108a selective oxidation region 108b current passage region 109 contact layer 110 p-side electrode 111 n-side electrode 120 resonator structure 150 mesa 150a etching bottom surface 150b inclined surface 150c flat surface 1000 laser printer (image forming apparatus)
1010 Optical scanning device

JP 2009-272389 A

Claims (10)

A reflecting mirror including a first layer and a second layer having a higher thermal conductivity than the first layer;
A resonator structure in which a first spacer layer, an active layer, and a second spacer layer are sequentially stacked on the second layer of the reflector;
A laminated film laminated on the resonator structure,
A mesa is formed by the laminated film,
A surface-emitting laser element in which the resonator structure extends from below the mesa to the periphery of the mesa as viewed from the light emitting direction. The second spacer layer includes a region whose thickness decreases as the distance from the mesa side increases.
The surface emitting laser element according to claim 1, wherein at least a part of a bottom surface around the mesa is formed by the second spacer layer. Viewed from the light exit direction, the bottom surface around the mesa is from the mesa side,
A first region where the second spacer layer is exposed;
A second region where the active layer is exposed;
The surface emitting laser element according to claim 2, further comprising: a third region in which the first spacer layer is exposed.   4. The surface emitting laser element according to claim 3, wherein the active layer and the first spacer layer include a region whose thickness decreases as the distance from the mesa side increases. 5.   3. The surface emitting laser element according to claim 2, wherein the entire bottom surface around the mesa is formed by the second spacer layer.   The surface emitting laser element according to claim 1, wherein the entire bottom surface around the mesa is formed of the multilayer film, and the resonator structure remains below the multilayer film forming the bottom surface.   The surface emitting laser element according to claim 1, wherein the second layer is made of AlAs.   A surface-emitting laser array comprising a plurality of surface-emitting laser elements according to claim 1. An optical scanning device that scans a surface to be scanned with a light beam,
A light source unit comprising the surface emitting laser array according to claim 8;
Deflecting means for deflecting the light beam from the light source unit;
And a scanning optical system for condensing the light beam deflected by the deflecting means on the surface to be scanned. An image carrier;
An image forming apparatus comprising: the optical scanning device according to claim 9, wherein the image carrier scans a light beam including image information.

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