JP5054622B2 - Surface emitting laser array, optical scanning device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the product yield of a surface-emitting laser array. <P>SOLUTION: The surface-emitting laser array includes a substrate 101, multiple semiconductor layers laminated on the substrate 101 and having a plurality of light projection portions, a plurality of p-side electrodes 113 provided corresponding to the plurality of light projection portions and having an opening serving as a path for light, a plurality of electrode pads provided corresponding to the plurality of p-side electrodes 113, and a plurality of interconnections electrically connecting the plurality of p-side electrodes 113 to the corresponding electrode pads. Then, a maximum value of the opening width of the opening of the p-side electrodes 113 is set to be smaller than a minimum width of an electrically insulated region. Consequently, even if a metal piece which peels in a lift-off process re-sticks, a "simultaneous light emission phenomenon" is suppressed to improve the product yield. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a surface emitting laser array, an optical scanning device, and an image forming apparatus. More specifically, the present invention relates to a surface emitting laser array having a plurality of light emitting units, an optical scanning device having the surface emitting laser array, and the optical scanning device. The present invention relates to an image forming apparatus.

  In electrophotographic image recording, an image forming method using laser light is widely used as an image forming means for obtaining high-definition image quality. In the case of electrophotography, a method of forming a latent image on the drum surface by rotating (sub-scanning) the drum while scanning (main scanning) laser light using a polygon mirror in the axial direction of the photosensitive drum Is common.

  In such an electrophotographic field, high definition of image quality and high speed of image output are required. For high definition of image quality, when the image resolution is doubled, twice the time is required for both main scanning and sub-scanning, so four times are required for image output. Therefore, in order to realize high definition of image quality, it is necessary to simultaneously achieve high speed image output.

  As methods for realizing high-speed image output, it is conceivable to increase the output of laser light, increase the number of beams, increase the sensitivity of the photosensitive member, and the like. In particular, in a high-speed output machine, it is common to use a multi-beam writing light source (multi-beam light source). Compared with the case of using one laser beam, when n laser beams are used at the same time, the latent image forming area in one scan is n times, and the time required for image formation is 1 / n. Become.

  For example, Patent Document 1 discloses a photoelectric conversion element including a plurality of photoelectric conversion units on the same substrate. Patent Document 2 discloses a semiconductor light emitting element including a plurality of light emitting portions on the same substrate. Each element disclosed in Patent Document 1 and Patent Document 2 has a configuration in which a plurality of edge-emitting semiconductor lasers (edge-emitting lasers) are arranged one-dimensionally. In these cases, the power consumption increases as the number of beams increases, and a new cooling system is required. Therefore, the cost is limited to about 4 beams or 8 beams.

  On the other hand, a surface emitting laser (Vertical Cavity Surface Emitting Laser), which has been actively researched in recent years, consumes about an order of magnitude less power than an edge emitting laser. In addition, in the surface emitting laser, many light emitting portions can be easily two-dimensionally integrated and arrayed. Therefore, a surface emitting laser array having a plurality of light emitting units is expected as a light source for achieving high speed and high density in an image forming apparatus (see, for example, Patent Documents 3 to 5).

  By the way, when each of the plurality of light emitting units is individually driven and controlled, a phenomenon in which a light emitting unit different from the light emitting unit to emit light simultaneously unintentionally emits light (hereinafter abbreviated as “simultaneous light emitting phenomenon” for convenience) A surface emitting laser array showing) was observed. This degrades the image quality, so such a surface emitting laser array becomes a defective product. As a result, the product yield is reduced.

  For example, Patent Document 6 discloses a multi-channel optical element mounting substrate that suppresses crosstalk between channels caused by electromagnetic induction between a common impedance and signal wiring wires due to a common electrode structure.

JP 11-340570 A JP 11-354888 A JP 2005-274755 A JP 2005-234510 A JP 2001-272615 A JP 2003-14994 A

  The inventors have intensively studied why the above-mentioned “simultaneous light emission phenomenon” occurs in a surface emitting laser array. And in the surface emitting laser array in which the “simultaneous light emission phenomenon” occurred, it was found that there is an abnormality in the electrode pad corresponding to the light emitting part. Specifically, foreign matter is attached to a region (gap) between adjacent electrode pads that should be electrically insulated originally, and this foreign matter makes the adjacent electrode pads conductive (short-circuited). When various analyzes such as composition analysis were performed on the foreign matter, it was found that the foreign matter was a metal piece having the same component as the patterned electrode.

  Further, the inventors searched for where in this process the metal piece originated, and found that it occurred in the lift-off process in the manufacturing process. That is, the metal piece was a reattachment of the metal piece removed during the manufacturing process.

  Thus, the “simultaneous light emission phenomenon” in the surface emitting laser array is unique to the surface emitting laser array, and it has been difficult to improve the product yield by the method disclosed in Patent Document 6.

  The present invention has been made based on the new knowledge obtained by the inventors described above, and has the following configuration.

According to a first aspect of the present invention, there is provided a substrate whose surface normal direction is inclined at a predetermined angle from the crystal orientation [1 0 0] direction to the crystal orientation [1 1 1] direction ; A multilayer semiconductor layer having a plurality of light emitting portions; a plurality of electrodes provided corresponding to the plurality of light emitting portions and having openings serving as light passages; provided corresponding to the plurality of electrodes A plurality of wirings electrically connecting each of the plurality of electrodes to a corresponding electrode pad, wherein the maximum value of the opening width in the opening is electrically insulated. The opening is smaller than a minimum width of the region, and the opening corresponds to the opening width in the first direction orthogonal to the plane including the crystal orientation [1 0 0] direction and the crystal orientation [1 1 1] direction, Includes the normal direction and the first direction The first ratio, which is the ratio of the aperture width in the second direction orthogonal to the plane, is the ratio of the beam width in the second direction to the beam width in the first direction in the near field pattern. The first and second ratios are 1.01 and 1.05, respectively, in the surface emitting laser array.

According to this, it is possible to improve the product yield.

  From a second viewpoint, the present invention is an optical scanning device that scans a surface to be scanned with light, the light source having the surface emitting laser array of the present invention; a deflector that deflects the light from the light source; A scanning optical system that condenses the light deflected by the deflector onto the surface to be scanned.

  According to this, since the light source has the surface emitting laser array of the present invention, high-density optical scanning can be performed without increasing the cost.

  According to a third aspect of the present invention, there is provided at least one image carrier; and at least one optical scanning device according to the invention that scans the at least one image carrier with light including image information. An image forming apparatus provided.

  According to this, since at least one optical scanning device of the present invention is provided, as a result, a high-definition image can be formed at a high speed without incurring an increase in cost.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a laser printer 1000 according to an embodiment of the present invention.

  The laser printer 1000 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 feeding roller 1037, a paper feeding 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 1050, a printer control device 1060 that comprehensively controls the above-described units, and the like are provided. These are housed in predetermined positions in the printer housing 1044.

  The communication control device 1050 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  The photosensitive drum 1030 is a cylindrical member, and a photosensitive layer is formed on the surface thereof. That is, the surface of the photoconductor drum 1030 is a scanned surface. The photosensitive drum 1030 rotates in the direction of the arrow in FIG.

  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. Then, along the rotation direction of the photosensitive drum 1030, the charging charger 1031 → the developing roller 1032 → the transfer charger 1033 → the discharging unit 1034 → the cleaning unit 1035 are arranged in this order.

  The charging charger 1031 uniformly charges the surface of the photosensitive drum 1030.

  The optical scanning device 1010 irradiates 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. As a result, a latent image corresponding to the image information is formed on the surface of the photosensitive drum 1030. 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.

  The toner cartridge 1036 stores toner, and the toner is supplied to the 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, and 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 configuration of the optical scanning device 1010 will be described.

  As shown in FIG. 2 as an example, the optical scanning device 1010 includes an fθ lens 11a, a toroidal lens 11b, a polygon mirror 13, a light source 14, a coupling lens 15, an aperture plate 16, a cylindrical lens 17, a reflection mirror 18, and A scanning control device (not shown) is provided. These are assembled at predetermined positions in the housing 30.

  In the following, for convenience, the direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  The coupling lens 15 converts the light beam emitted from the light source 14 into substantially parallel light. The light source 14 and the coupling lens 15 are fixed to an aluminum holding member and unitized.

  The aperture plate 16 has an aperture and defines the beam diameter of the light beam through the coupling lens 15.

  The cylindrical lens 17 forms an image of the light flux that has passed through the opening of the aperture plate 16 in the vicinity of the deflection reflection surface of the polygon mirror 13 via the reflection mirror 18 in the sub-scanning corresponding direction.

  The optical system arranged on the optical path between the light source 14 and the polygon mirror 13 is also called a pre-deflector optical system. In the present embodiment, the pre-deflector optical system includes a coupling lens 15, an aperture plate 16, a cylindrical lens 17, and a reflection mirror 18.

  As an example, the polygon mirror 13 has a hexahedral mirror having an inscribed circle radius of 18 mm, and each mirror serves as a deflecting reflection surface. The polygon mirror 13 deflects the light flux from the reflection mirror 18 while rotating at a constant speed around an axis parallel to the sub-scanning corresponding direction.

  The fθ lens 11 a is disposed on the optical path of the light beam deflected by the polygon mirror 13.

  The toroidal lens 11b is disposed on the optical path of the light beam through the fθ lens 11a. Then, the light beam that passes through the toroidal lens 11b 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 13 rotates. That is, the surface of the photosensitive drum 1030 is optically 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 13 and the photosensitive drum 1030 is also called a scanning optical system. In the present embodiment, the scanning optical system includes an fθ lens 11a and a toroidal lens 11b. Note that at least one folding mirror may be disposed on at least one of the optical path between the fθ lens 11a and the toroidal lens 11b and the optical path between the toroidal lens 11b and the photosensitive drum 1030.

  As an example, the light source 14 includes a surface emitting laser array 100 as shown in FIG.

  The surface-emitting laser array 100 includes a plurality of light emitting units, a plurality of electrode pads corresponding to the plurality of light emitting units, and a plurality of wirings that electrically connect each electrode pad and the corresponding light emitting unit on the same substrate. Is formed. Note that the M direction in FIG. 3 is the main scanning corresponding direction, and the S direction is the sub scanning corresponding direction.

  Here, as shown in FIG. 4, the surface emitting laser array 100 includes a light emitting unit in which eight light emitting units are arranged at equal intervals along the T direction which is a direction inclined from the M direction toward the S direction. There are four rows. These four light emitting section rows are arranged at equal intervals d in the S direction so that they are equally spaced c when all the light emitting sections are orthogonally projected onto a virtual line extending in the S direction. That is, 32 light emitting units are two-dimensionally arranged. In this specification, the “light emitting portion interval” refers to the distance between the centers of two light emitting portions.

  Here, the interval c is 3 μm, the interval d is 24 μm, and the light emitting portion interval X (see FIG. 4) in the M direction is 30 μm.

  Each light-emitting portion includes a substrate 101, a lower semiconductor DBR 103, a lower spacer layer 104, an active layer 105, as shown in FIG. 5 which is an AA cross-sectional view of FIG. 4 and FIG. The upper spacer layer 106, the upper semiconductor DBR 107, the contact layer 109, and the like, and emits laser light having an oscillation wavelength of 780 nm. In this specification, the laser oscillation direction is defined as the Z-axis direction, and two directions orthogonal to each other in a plane perpendicular to the Z-axis direction are described as the X-axis direction and the Y-axis direction.

  The surface of the substrate 101 is a mirror-polished surface, and as shown in FIG. 7A, the normal direction of the mirror-polished surface is crystal orientation [1 1 1] with respect to the crystal orientation [1 0 0] direction. ] An n-GaAs single crystal substrate inclined by 15 degrees (θ = 15 degrees) in the A direction. That is, the substrate 101 is a so-called inclined substrate. Here, as shown in FIG. 7B, the crystal orientation [0 1 -1] direction is the + X direction, and the crystal orientation [0 -1 1] direction is the -X direction.

The lower semiconductor DBR 103 is stacked on the + Z side surface of the substrate 101 via a buffer layer (not shown), and is formed of a low refractive index layer 103a made of n-AlAs and n-Al _0.3 Ga _0.7 As. There are 40.5 pairs of high refractive index layers 103b. Between each refractive index layer, in order to reduce electrical resistance, a composition gradient layer (not shown) having a thickness of 20 nm, in which the composition is gradually changed from one composition to the other composition, is provided. Each refractive index layer includes 1/2 of the adjacent composition gradient layer, and is set to have an optical thickness of λ / 4 when the oscillation wavelength is λ.

The lower spacer layer 104 is stacked on the + Z side of the lower semiconductor DBR 103 and is a layer made of non-doped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P.

The active layer 105 is stacked on the + Z side of the lower spacer layer 104, and includes, as an example, as shown in FIG. 8, three quantum well layers 105a and four barrier layers 105b. Each quantum well layer 105a is made of GaInPAs having a composition that induces 0.7% compressive strain, and has a band gap wavelength of about 780 nm. Each barrier layer 105b is made of Ga _0.68 In _0.32 P, which is a composition that induces a tensile strain of 0.6%.

  By the way, when the distortion increases, the band separation between the heavy hole and the light hole increases, so that the increase in gain increases, lowering the threshold and increasing the efficiency (higher output). Furthermore, by improving the carrier confinement property and lowering the threshold value, the reflectivity of the upper semiconductor DBR can be reduced, and higher output can be realized.

The upper spacer layer 106 is laminated on the active layer 105 on the + Z side, and is a layer made of non-doped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P.

  A portion composed of the lower spacer layer 104, the active layer 105, and the upper spacer layer 106 is also called a resonator structure, and the thickness thereof is set to be an optical thickness of one wavelength. The active layer 105 is provided at the center of the resonator structure at 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 upper semiconductor DBR 107 is stacked on the + Z side of the upper spacer layer 106, and has 23 pairs of a low refractive index layer and a high refractive index layer. And between each refractive index layer, in order to reduce an electrical resistance, the composition inclination layer (illustration omitted) which changed the composition gradually toward the other composition from one composition is provided.

  In one of the low refractive index layers in the upper semiconductor DBR 107, as shown in FIG. 9 as an example, a selective oxidation layer 108 made of p-AlAs is inserted with a thickness of 30 nm. The selective oxidation layer 108 is inserted at a position optically separated from the upper spacer layer 106 by 5λ / 4, and is in the third pair of low refractive index layers from the upper spacer layer 106. The low refractive index layer including the selective oxidation layer 108 is set so as to have an optical thickness of 3λ / 4 including 1/2 of the adjacent composition gradient layer.

  Each refractive index layer except the low refractive index layer including the selective oxidation layer 108 in the upper semiconductor DBR 107 is set to have an optical thickness of λ / 4 including 1/2 of the adjacent composition gradient layer. Has been.

As shown in FIG. 9 as an example, an intermediate layer 107m made of p-Al _0.81 Ga _0.19 As and having a thickness of 38 nm is provided on the −Z side and + Z side of the selectively oxidized layer 108. .

A layer 107c (hereinafter referred to as “low refractive index layer 107c”) adjacent to each intermediate layer 107m in the low refractive index layer including the selectively oxidized layer 108 is made of p-Al _0.7 Ga _0.3 As. Is a layer.

The low refractive index layer 107 a other than the low refractive index layer including the selective oxidation layer 108 in the upper semiconductor DBR 107 is a layer made of p-Al _0.9 Ga _0.1 As.

The high refractive index layer 107 b in the upper semiconductor DBR 107 is a layer made of p-Al _0.3 Ga _0.7 As.

  The contact layer 109 is stacked on the + Z side of the upper semiconductor DBR 107 and is a layer made of p-GaAs.

  Note that a structure in which a plurality of semiconductor layers are stacked on the substrate 101 is also referred to as a “stacked body” for convenience in the following.

  Next, a method for manufacturing the surface emitting laser array 100 will be briefly described.

(1) The laminate is formed by crystal growth by metal organic vapor phase epitaxy (MOCVD) or molecular beam epitaxy (MBE).

Here, trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI) are used as Group III materials, and phosphine (PH ₃ ) and arsine (AsH ₃ ) are used as Group V materials. ing. Further, carbon tetrabromide (CBr ₄ ) and dimethyl zinc (DMZn) are used as the raw material for the p-type dopant, and hydrogen selenide (H ₂ Se) is used as the raw material for the n-type dopant. Note that H ₂ is used as the carrier gas. In particular, the MOCVD method can easily form a composition graded layer layer by controlling the supply amount of the source gas, so that it can be used as a crystal growth method for a surface emitting laser element including a semiconductor DBR compared to the MBE method. Is suitable. Further, high vacuum is not required as in the MBE method, and the supply flow rate and supply time of the source gas may be controlled, so that the mass productivity is excellent.

(2) A square-shaped resist pattern having a side of 20 μm is formed in each of a plurality of regions to be light emitting portions on the surface of the laminate.

(3) A square columnar mesa is formed by ECR etching using Cl ₂ gas, using the resist pattern as a photomask. Here, the bottom surface of the etching is positioned in the lower spacer layer 104.

  By the way, it is preferable that the groove | channel between two light emission parts shall be 5 micrometers or more for the electrical and spatial separation of each light emission part. This is because if it is too narrow, it becomes difficult to control etching during production. Further, the mesa size (length of one side) is preferably 10 μm or more. This is because if it is too small, heat will be accumulated during operation and the characteristics may be deteriorated.

(4) The photomask is removed.

(5) The laminated body is heat-treated in water vapor. As a result, Al (aluminum) in the selectively oxidized layer 108 is selectively oxidized from the outer peripheral portion of the mesa, and an unoxidized region 108b surrounded by the Al oxide layer 108a remains in the central portion of the mesa. (See FIG. 6). In other words, a so-called oxidized constriction structure is formed that restricts the drive current path of the light emitting part only to the central part of the mesa. The non-oxidized region 108b is a current passage region (current injection region). Here, from the results of various preliminary experiments, the heat treatment conditions (holding temperature, holding time, etc.) are appropriately selected so that the current passage region has a desired shape and size.

(6) The protective layer 111 made of SiN or SiO ₂ is formed using a vapor phase chemical deposition method (CVD method).

(7) The protective layer 111 on the contact layer 109 is partially removed. Here, the portion where the protective layer 111 is left is masked with a photoresist, and then the unmasked protective layer 111 is etched with BHF.

(8) A photoresist is applied on the mesa with a uniform film thickness using a spin coater or the like. Here, the film thickness of the photoresist is determined by the controllability of lift-off. In this embodiment, it is set to several μm.

(9) The photoresist is heated (baked) and cured. In the present embodiment, the bake temperature is set lower than a general temperature (about 80 ° C.) in consideration of lift-off controllability.

(10) The photoresist is exposed and developed by a photolithography technique to form a lift-off resist pattern. This resist pattern is a pattern that masks a region other than the region where the p-side electrode, electrode pad, and wiring are formed.

(11) A metal is vapor-deposited on the laminate on which the resist pattern for lift-off is formed. Here, it is necessary to perform wiring also on the side surface (inclined surface) of the mesa, and the film is formed extremely thick in order to ensure the film thickness of the wiring on the inclined surface. Compared with the thickness of the wiring in a general silicon semiconductor, the thickness is several tens of times.

  The metal to be vapor-deposited is preferably a laminated structure composed of a plurality of metal films in consideration of adhesion to the base and alloying. In the present embodiment, a stacked structure of Cr / AuZn / Au is used in consideration of p-type ohmic contact properties and the like. The Cr layer has a thickness of about 5 nm, the AuZn layer has a thickness of about 10 nm, and the Au layer has a thickness of about 1 μm.

(12) The whole is immersed in acetone to dissolve the photoresist. At this time, the metal on the photoresist surface (deposited metal) is also peeled off at the same time. Here, ultrasonic vibration or the like may be added, but it is preferable to make it as weak as possible in order to prevent a problem such as film peeling at a necessary portion. The processing time is determined by visually observing how the photoresist is dissolved.

(13) The whole is immersed in a cleaning solution such as ethanol or IPA (isopropyl alcohol). Thereby, the p-side electrode 113, the electrode pad, and the wiring are formed. Hereinafter, as illustrated in FIG. 10 as an example, a region surrounded by the p-side electrode 113 is referred to as an “opening”. Further, a / b is also referred to as “rectangular ratio of the opening” when the opening width in the Y-axis direction at the opening is a and the opening width in the X-axis direction is b.

In the present embodiment, the rectangular ratio of the opening is, for example, a rectangular ratio (hereinafter also referred to as “NFP” for convenience) of a near field pattern (see FIG. 11A and FIG. 11B). Ny / Nx). In this specification, the rectangular ratio of NFP refers to the rectangular ratio of a region having a light intensity of 1 / e ² or more when the central light intensity is 1. A method for obtaining the rectangular ratio of NFP will be described later.

  Further, the minimum value L (see FIG. 12) of the gap between adjacent electrode pads is set to be larger than the longest width R (see FIG. 13) of the opening. Furthermore, as shown in FIG. 14 as an example, the minimum value L ′ of the gap between the p-side electrode 113 and the wiring is also set to be larger than the longest width R of the opening. The minimum value of the gap between adjacent wirings is also set to be larger than the longest width R of the opening.

(14) After polishing the back side of the substrate 101 to a predetermined thickness (for example, about 100 μm), the n-side electrode 114 is formed. Here, the n-side electrode 114 is a laminated structure of AuGe / Ni / Au.

(15) Ohmic conduction is established between the p-side electrode 113 and the n-side electrode 114 by annealing. Thereby, each mesa becomes a light emission part.

(16) Cut for each chip.

  In the plurality of surface emitting laser arrays 100 manufactured as described above, the above-mentioned “simultaneous light emission phenomenon” was not observed.

  Here, a method of obtaining the above-described NFP rectangle ratio will be described.

(A) First, a surface emitting laser for measurement having a configuration similar to that of the light emitting portion of the surface emitting laser array 100 and having a sufficiently large opening so that the opening does not affect the light emission pattern is separately manufactured. To do. Here, the opening has a square shape with a side of 12 μm. Also, the conditions of the heat treatment in the selective oxidation step (holding temperature, holding time, etc.) so that the size of the current passing region is 4.0 μm in the X-axis direction and 4.05 μm in the Y-axis direction when observed with an IR microscope. It was set.

(B) Then, an objective lens having a magnification of 100 is disposed so that the focal position thereof coincides with the bottom of the opening of the surface emitting laser for measurement.

(C) A driving current is supplied to the surface emitting laser for measurement, and the driving current is adjusted so that the optical output of the surface emitting laser for measurement is about 1.4 mW.

(D) The CCD camera receives the light beam from the surface emitting laser for measurement via the objective lens. A filter may be disposed between the objective lens and the CCD camera for the purpose of adjusting the light intensity.

(E) The output image of the CCD camera is image-processed, and the light intensity distribution in the cross section parallel to the X-axis direction and the cross-section parallel to the Y-axis direction through the position where the light intensity is maximum is subjected to so-called Gaussian fitting. Use to find.

(F) Then, based on each light intensity distribution, the width of a region having a light intensity of 1 / e ² or more is obtained with respect to the X-axis direction and the Y-axis direction, where the central light intensity is 1, and then The “width in the Y-axis direction / width in the X-axis direction” is the rectangular ratio of the NFP. In this embodiment, the width in the X-axis direction is 6.5 μm, the width in the Y-axis direction is 6.2 μm, and the rectangular ratio of NFP is about 1.05. In the surface emitting laser for measurement, the rectangular ratio of the current passing region was about 1.01, and the rectangular ratio of NFP was considerably larger.

  Therefore, in the surface emitting laser array 100, the opening width a in the Y-axis direction at the opening is 10.0 μm, and the opening width b in the X-axis direction is 10.5 μm. In this case, the maximum value R (see FIG. 13) of the opening width in the opening is 14.5 μm. The minimum value L of the gap between adjacent electrode pads was 14.6 μm.

  By the way, as described above, the “simultaneous light emission phenomenon” in the surface emitting laser array is unique to the surface emitting laser array, and the metal piece removed during the manufacturing process is restored to the electrically insulated region. It is generated by adhering and degrading the insulation of the region. In particular, the plurality of metals removed to form the opening in the lift-off process of the manufacturing process float in the immersion liquid as metal pieces having the same shape as the opening without being finely pulverized due to its thickness. . The inventors have found that this metal piece is related to the “simultaneous light emission phenomenon” (see FIG. 15).

  Therefore, it is conceivable to reduce the size of the opening in order to reduce the size of the metal piece. However, if the size of the opening is too small, the far field pattern (hereinafter also referred to as “FFP” for convenience), which is one of laser characteristics, is deteriorated. Specifically, the emitted light is diffracted at the edge of the opening, resulting in an FFP larger than the desired FFP. In addition, as shown in FIG. 16 as an example, when viewed from the Z-axis direction, the center of the current passing region 108b is shifted from the center of the opening, and the emitted light is applied to the edge of the opening. Similarly, the FFP is larger than the desired FFP. Therefore, in order to realize a desired FFP, it is necessary to increase the size of the opening to some extent in consideration of the shift in the manufacturing process.

  In addition, the inventors investigated the relationship between the shape of the current passing region 108b and the shape of the NFP for a plurality of surface emitting lasers. The result is shown in FIG. According to this, the average value of the rectangular ratio (see FIG. 18) of the current passing region was 1.02, and the average value of the rectangular ratio of NFP was 1.04. That is, it has been found that the shape of the current passing region 108b and the shape of the NFP are not similar. The rectangular ratio of the current passing region was measured by observing with an IR microscope (see FIG. 19).

  In order to obtain an FFP having a desired size when the shape of the opening is similar to the shape of the current passing region (square, see FIG. 20A) as in the prior art, It is necessary to set a tolerance in the size of the opening in consideration of not only the deviation but also the difference between the rectangular ratio of the current passing region and the rectangular ratio of the NFP.

  On the other hand, when the rectangular ratio of the opening is the same as the rectangular ratio of NFP (see FIGS. 20B and 20D) as in the present embodiment, only the deviation in the manufacturing process is considered. Thus, a tolerance in the size of the opening can be set.

  That is, in the present embodiment, an FFP having a desired size can be obtained even if the size of the opening is made smaller than before. As a result, the maximum value of the opening width in the opening can be made smaller than before (see FIGS. 20C and 20D).

  Therefore, in the present embodiment, the size of the metal piece causing the “simultaneous light emission phenomenon” can be made smaller than the conventional one (see FIG. 21). As a result, the gap between adjacent electrode pads and the gap between adjacent wirings can be reduced. That is, the chip area can be reduced, and the number of chips per lot can be increased. As a result, the product yield can be improved and the production cost can be further reduced.

  As described above, according to the surface emitting laser array 100 according to the present embodiment, the substrate 101, the multi-layered semiconductor layer stacked on the substrate 101 and having a plurality of light emitting portions, and the plurality of light emitting portions. A plurality of p-side electrodes 113 provided correspondingly and having openings serving as light passages; a plurality of electrode pads provided corresponding to the plurality of p-side electrodes 113; and the plurality of p-sides Each of the electrodes 113 includes a plurality of wirings that are electrically connected to the corresponding electrode pads.

  The maximum value of the opening width at the opening of the p-side electrode 113 is set to be smaller than the minimum width of the electrically insulated region.

  Therefore, even if the metal piece peeled off in the lift-off process is reattached, the “simultaneous light emission phenomenon” can be suppressed, and the product yield can be improved.

  By the way, in the surface emitting laser array 100, since the intervals between the light emitting portions when the respective light emitting portions are orthogonally projected onto the virtual line extending in the sub-scanning corresponding direction are equal intervals c, the photosensitive drum 1030 is adjusted by adjusting the lighting timing. In the above, it can be considered that the configuration is the same as the case where the light emitting units are arranged at equal intervals in the sub-scanning direction.

  Since the distance c is 3 μm, if the magnification of the optical system of the optical scanning device 1010 is about 1.8, high-density writing of 4800 dpi (dot / inch) can be performed.

  As described above, according to the optical scanning device 1010 according to this embodiment, since the light source 14 includes the surface emitting laser array 100, the photosensitive drum 1030 can be scanned at a high density.

  Of course, it is possible to increase the density by increasing the number of light emitting portions in the main scanning direction, making the array arrangement in which the distance d is narrowed and the distance c is further reduced, or by reducing the magnification of the optical system. Quality printing is possible. Note that the writing interval in the main scanning direction can be easily controlled by the lighting timing of the light emitting unit.

  Further, the laser printer 1000 can perform printing without reducing the printing speed even if the writing dot density increases. Further, when the writing dot density is the same, the printing speed can be further increased.

  In addition, since the polarization state of the light flux from each light emitting unit is stably aligned, the laser printer 1000 can form a high-definition image at high speed.

  Thus, according to the laser printer 1000 according to the present embodiment, since the optical scanning device 1010 is provided, a high-definition image can be formed at high speed.

  In the above embodiment, the case where the surface emitting laser array 100 has 32 light emitting units has been described, but the present invention is not limited to this.

In the above embodiment has described the case where the selective oxidation layer is formed of p-AlAs, not limited to this, also include Ga as for example _{p-Al 0.98 Ga 0.02} As good.

  In the above embodiment, the case where the selective oxidation layer 108 is inserted at a position optically separated from the upper spacer layer 106 by 5λ / 4 has been described. However, the present invention is not limited to this. For example, the insertion position of the selective oxidation layer 108 may be a position optically separated from the upper spacer layer 106 by 3λ / 4 or 7λ / 4.

  In the above embodiment, the case where the mesa shape in the cross section perpendicular to the laser oscillation direction is square has been described. However, the present invention is not limited to this, and may be any shape such as a circle, an ellipse, or a rectangle. Can do.

  The shape of the opening may be an elliptical shape as shown in FIG. 22 as an example. In this case, the length a ′ in the Y-axis direction / the length b ′ in the X-axis direction may be set as the rectangular ratio of the opening, and the rectangular ratio of the opening may be set to match the rectangular ratio of NFP. At this time, as shown in FIG. 23 as an example, the gap L between the adjacent electrode pads is made larger than the length of the major axis (here, a ′) in the outer shape of the opening. At this time, the shape of the opening may be set to be similar to the shape of NFP.

  Moreover, in the said embodiment, when the rectangular ratio of NFP is about 1.0, it is good also considering the external shape of an opening part as square shape or circular shape. The maximum value of the opening width when the opening is square is the length of the diagonal of the square, and the maximum value of the opening width when the opening is circular is the diameter of the circle.

  In the above-described embodiment, the case where the normal direction of the main surface of the substrate is inclined 15 degrees toward the crystal orientation [1 1 1] direction with respect to the crystal orientation [1 0 0] direction has been described. However, the present invention is not limited to this. The normal direction of the main surface of the substrate may be inclined toward one direction of crystal orientation <1 1 1> with respect to one direction of crystal orientation <1 0 0>.

  Moreover, although the said embodiment demonstrated the case where the oscillation wavelength of a light emission part was a 780 nm band, it is not limited to this. The oscillation wavelength of the light emitting unit may be changed according to the characteristics of the photoreceptor.

  Further, the surface emitting laser array 100 can be used for applications other than the image forming apparatus. In that case, the oscillation wavelength may be a wavelength band such as a 650 nm band, an 850 nm band, a 980 nm band, a 1.3 μm band, and a 1.5 μm band depending on the application.

  In the above embodiment, a surface emitting laser array in which light emitting units similar to the surface emitting laser array 100 are arranged one-dimensionally may be used instead of the surface emitting laser array 100.

  In the above embodiment, the laser printer 1000 is described as the image forming apparatus. However, the present invention is not limited to this. In short, any image forming apparatus including the optical scanning device 1010 may be used.

  For example, an image forming apparatus that directly irradiates laser light onto a medium (for example, paper) that develops color with laser light may be used.

  Further, an image forming apparatus using a silver salt film as the image carrier may be used. In this case, a latent image is formed on the silver salt film by optical scanning, and this latent image can be visualized by a process equivalent to a developing process in a normal silver salt photographic process. Then, it can be transferred to photographic paper by a process equivalent to a printing process in a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.

  As an example, as shown in FIG. 24, a color printer 2000 including a plurality of photosensitive drums may be used.

  The color printer 2000 is a tandem multicolor printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow). The black “photosensitive drum K1, charging device K2, "Developing device K4, cleaning unit K5, and transfer device K6", cyan "photosensitive drum C1, charging device C2, developing device C4, cleaning unit C5, and transfer device C6", and magenta "photosensitive drum" M1, charging device M2, developing device M4, cleaning unit M5, and transfer device M6 ”,“ photosensitive drum Y1, charging device Y2, developing device Y4, cleaning unit Y5, and transfer device Y6 ”for yellow, and light A scanning device 2010, a transfer belt 2080, a fixing unit 2030, and the like are provided.

  Each photosensitive drum rotates in the direction of the arrow in FIG. 24, and a charging device, a developing device, a transfer device, and a cleaning unit are arranged around each photosensitive drum along the rotational direction. Each charging device uniformly charges the surface of the corresponding photosensitive drum. The optical scanning device 2010 irradiates the surface of each photosensitive drum charged by the charging device with light, and forms a latent image on each photosensitive drum. Each developing device forms a toner image on the surface of the corresponding photosensitive drum. Further, each transfer device transfers the toner image on the surface of the corresponding photosensitive drum onto the recording paper on the transfer belt 2080. The recording paper onto which all the toner images have been transferred is sent to the fixing unit 2030, where the image is fixed.

  The optical scanning device 2010 has a light source similar to the light source 14 for each color. Therefore, the same effect as that of the optical scanning device 1010 can be obtained. In addition, since the color printer 2000 includes the optical scanning device 2010, the same effect as the laser printer 1000 can be obtained.

  By the way, in the color printer 2000, color misregistration may occur due to manufacturing error or position error of each component. Even in such a case, the color misregistration can be reduced by changing the light emitting section to be lit.

  As described above, the surface emitting laser array according to the present invention is suitable for improving the product yield. Further, the optical scanning device of the present invention is suitable for scanning the surface to be scanned at a high density without increasing the cost. The image forming apparatus of the present invention is suitable for forming a high-definition image at high speed without incurring an increase in cost.

It is a figure for demonstrating schematic structure of the laser printer which concerns on one Embodiment of this invention. It is the schematic which shows the optical scanning device in FIG. It is a figure for demonstrating the surface emitting laser array contained in the light source of an optical scanning device. It is a figure for demonstrating the two-dimensional arrangement | sequence of the light emission part in a surface emitting laser array. It is AA sectional drawing of FIG. It is the figure which expanded a part of FIG. FIG. 7A and FIG. 7B are diagrams for explaining the substrate of the surface emitting laser array, respectively. It is the figure which expanded the active layer vicinity of the surface emitting laser array. It is the figure which expanded a part of upper semiconductor DBR of a surface emitting laser array. It is a figure for demonstrating the opening part of a surface emitting laser array. FIG. 11A and FIG. 11B are diagrams for explaining NFP, respectively. It is a figure for demonstrating the gap | interval between adjacent electrode pads. It is a figure for demonstrating the maximum value of the opening width in an opening part. It is a figure for demonstrating the clearance gap between the electrode of p side, and wiring. It is a figure for demonstrating the "simultaneous light emission phenomenon" peculiar to a surface emitting laser array. It is a figure for demonstrating the shift | offset | difference of the center of an electric current passage area | region, and the center of an opening part. It is a figure for demonstrating the relationship between the shape of an electric current passage area | region, and the shape of NFP. It is a figure for demonstrating the rectangular rate of an electric current passage area | region. It is a figure for demonstrating the oxide layer and electric current passage area | region observed with IR microscope. 20A is a diagram for explaining the shape of the current passage region, FIG. 20B is a diagram for explaining the shape of the NFP, and FIG. 20C is a size of the conventional opening. FIG. 20D is a diagram for explaining the size of the opening in the present embodiment. It is a figure for demonstrating the effect of this embodiment. It is a figure for demonstrating the modification of the opening part of a surface emitting laser array. FIG. 23 is a diagram for explaining a gap between electrode pads corresponding to the opening in FIG. 22. It is a figure for demonstrating schematic structure of a color printer.

Explanation of symbols

  11a: fθ lens (part of scanning optical system), 11b: toroidal lens lens (part of scanning optical system), 13: polygon mirror (deflector), 14: light source, 100: surface emitting laser array, 101: substrate 113 ... p-side electrode (electrode), 1000 ... laser printer (image forming apparatus), 1010 ... light scanning apparatus, 1030 ... photosensitive drum (image carrier), 2000 ... color printer (image forming apparatus), 2010 ... Optical scanning device, K1, C1, M1, Y1,... Photosensitive drum (image carrier).

Claims (10)

A substrate whose surface normal direction is inclined by a predetermined angle from the crystal orientation [1 0 0] direction toward the crystal orientation [1 1 1] direction ;
A multilayer semiconductor layer stacked on the substrate and having a plurality of light emitting portions;
A plurality of electrodes provided corresponding to the plurality of light emitting portions and having openings serving as light paths;
A plurality of electrode pads provided corresponding to the plurality of electrodes;
A plurality of wirings that electrically connect each of the plurality of electrodes to a corresponding electrode pad;
The maximum value of the opening width in the opening is smaller than the minimum width of the electrically insulated region ,
The opening includes the normal direction and the first direction with respect to an opening width related to a first direction orthogonal to a plane including the crystal orientation [1 0 0] direction and the crystal orientation [1 1 1] direction. The first ratio, which is the ratio of the aperture width in the second direction orthogonal to the plane including the first width, is the ratio of the beam width in the second direction to the beam width in the first direction in the near field pattern. The same as a certain second ratio,
The surface emitting laser array wherein each of the first and second ratios is 1.01 or more and 1.05 or less . 2. The surface emitting laser array according to claim 1 , wherein an outer shape of the opening is similar to a near field pattern. 3. The surface emitting laser array according to claim 1, wherein the minimum width of the electrically insulated region is a minimum value of a gap between the electrode pads. 3. The surface emitting laser array according to claim 1, wherein a minimum width of the electrically insulated region is a minimum value of a gap between wirings. 3. The surface emitting laser array according to claim 1, wherein the minimum width of the electrically insulated region is a minimum value of a gap between the electrode and the wiring. The outer shape of the opening is a square, the maximum value of the opening width of the opening, according to any one of claims 1 to 5, characterized in that a diagonal length of the square Surface emitting laser array. The outer shape of the opening is circular, the maximum value of the opening width of the opening is a surface emitting laser according to any one of claims 1 to 5, characterized in that the diameter of the circle array. An optical scanning device that scans a surface to be scanned with light,
A light source comprising the surface emitting laser array according to any one of claims 1 to 7 ;
A deflector for deflecting light from the light source;
A scanning optical system for condensing the light deflected by the deflector onto the surface to be scanned. At least one image carrier;
An image forming apparatus comprising: at least one optical scanning device according to claim 8 that scans the at least one image carrier with light including image information. The image forming apparatus according to claim 9 , wherein the image information is multicolor color image information.