JP2014017448A - Surface emitting laser, surface emitting laser array, optical scanner device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface emitting laser which can be manufactured with high yield in a simple method in a surface emitting laser having laser beams with a polarization direction stabilized in a single direction.SOLUTION: A surface emitting laser has a laminate including a lower semiconductor DBR formed on a substrate by lamination, a lower spacer layer, an active layer, an upper spacer layer and an upper semiconductor DBR. The laminate includes a mesa formed by forming a groove on the laminate around the mesa. A depth of the groove in the laminate in one direction is formed deeper then a depth of the groove in the other direction orthogonal to the one direction.

Description

  The present invention relates to a surface emitting laser, 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 that emits light in a direction perpendicular to a substrate, and is an edge-emitting type that emits light in a direction parallel to the substrate. Compared with a semiconductor laser, it has features such as low price, low power consumption, small size, high performance, and easy two-dimensional integration.

  Such a surface emitting laser generally has a constricted structure in order to increase current inflow efficiency. As this constriction structure, a constriction structure by selective oxidation of an Al (aluminum) As (arsenic) layer (sometimes referred to as “oxidized constriction structure” for convenience) is often used.

This oxidized constriction structure exposes the side surface of the current confinement layer made of p-AlAs by forming a mesa having a predetermined size, and then selectively oxidizes Al from the mesa side surface in a high-temperature steam atmosphere. Thus, a selective oxidation region is formed, and in the current confinement layer in the central portion of the mesa, a region for passing a driving current of the surface emitting laser (current injection region) is formed by the non-oxidized region. By such a method, a current confinement structure can be easily formed. In such an oxide confinement structure, the refractive index of the region (Al _x O _y ) where Al is selectively oxidized in the current confinement layer is about 1.6, which is lower than that of the semiconductor layer. Therefore, a lateral refractive index difference is generated in the resonator structure, and light can be confined in the center of the mesa, so that the light emission efficiency can be improved. As a result, excellent characteristics such as low threshold current and high efficiency can be realized.

  Applications of the surface emitting laser include a light source for optical writing in a printer (oscillation wavelength: 780 nm band), a light source for writing in an optical disk device (oscillation wavelengths: 780 nm band and 850 nm band), and a LAN (Local Area Network) using an optical fiber. ) And the like light source (oscillation wavelength: 1.3 μm band, 1.5 μm band). Furthermore, it is also expected as a light source for optical transmission between boards, within a board, between chips of an integrated circuit (LSI: Large Scale Integrated circuit), and within a chip of an integrated circuit.

  However, the surface emitting laser has a problem that it is difficult to control the polarization direction of the laser beam due to its structure. That is, in the edge-emitting semiconductor laser, since the resonator is constituted by a waveguide, the reflectivity of the waveguide end face is larger in the TE wave than in the TM wave, and the TE wave in the direction in which the electric field vector is horizontal to the semiconductor substrate. It oscillates at. That is, the light emitted from the end facet type semiconductor laser has a stable polarization plane and does not fluctuate.

  On the other hand, in the surface emitting laser, it is difficult to increase the reflectivity of the mirror with respect to light in a specific polarization direction and increase the gain of the active layer. That is, the surface emitting laser has a problem that the polarization direction becomes unstable because it is structurally isotropic with respect to the polarization. However, the reflectivity of most optical elements such as beam splitters and diffraction gratings depends on the polarization direction. Therefore, when a semiconductor laser is incorporated in an optical device, the variation in the polarization direction in a surface emitting laser is a hindrance in use, and if the polarization direction is unstable, the polarization directions orthogonal to each other are irregular. May cause noise.

  In general, as a method for controlling the polarization direction in a surface emitting laser, a method using an inclined substrate is known. That is, by using an inclined substrate, the crystal structure becomes asymmetric with respect to the main surface of the substrate, and anisotropy can be generated in the optical gain. This makes it possible to align the polarization direction with a specific direction in which the optical gain increases.

  For example, in Patent Document 1, [1 1 0] with respect to a plane having a crystal plane orientation equivalent to the (1 0 0) plane, based on the [1 0 0] direction, using a GaAs / AlGaAs semiconductor material. The polarization is controlled using a substrate tilted at an angle in the range of −5 ° to + 5 ° in the direction]. Further, in Patent Document 2, an inclined substrate is used, and two small areas are provided in the area where the laser beam is emitted, which is off the center of the emission area, and the reflectance of each small area is emitted. There is disclosed a technique in which high-order transverse mode oscillation control and polarization direction control are made compatible by forming a transparent dielectric film lower than the reflectance of the central portion of the region.

  In addition to the method using an inclined substrate, there is a method for generating an anisotropic stress by applying a strain load to the periphery of the active layer. For example, in Patent Document 3, a method of controlling polarization by applying an anisotropic stress to a resonator by distorting the resonator by arranging a strain load portion adjacent to the resonator of the surface emitting laser. Is disclosed.

  Further, in Patent Document 4, in a surface emitting laser fabricated on a substrate having a plane orientation (1 0 0) plane or the like, an active region is formed by forming an asymmetric selective oxidation structure in an Al high concentration layer portion inside a mesa. A method for improving polarization controllability by applying anisotropic stress to the center of the layer is disclosed.

  Further, in Patent Document 5, an anisotropic layer corresponding to the non-uniform distribution is formed by forming an oxide layer that is non-uniformly distributed in the direction of rotation around the light emitting region around the region corresponding to the light emitting region. A method is disclosed in which a stress is generated in an active layer to enhance polarization controllability.

  However, as in the methods disclosed in Patent Document 1 and Patent Document 2, when an inclined substrate is used, it is difficult to control the epitaxial growth conditions, and it is difficult to manufacture easily and stably. The surface emitting laser is expensive.

  In addition, in the methods disclosed in Patent Documents 3 to 5, the manufacturing process is complicated, and thus the yield is reduced during manufacturing. Similarly, the surface-emitting laser manufactured is expensive. . In particular, in the method disclosed in Patent Document 5, it is difficult to control the uniformity when forming an oxide film, and there is a further concern about a decrease in yield.

  As described above, conventionally, it has been difficult to manufacture a high-power surface emitting laser in which the polarization direction of laser light is stabilized in one direction with a simple method and with a high yield.

  Therefore, the present invention has been made in view of such problems, and a surface-emitting laser in which the polarization direction of laser light is stabilized in one direction and can be manufactured with a high yield by a simple method. The purpose is to provide.

  According to one aspect of the present invention, in a surface emitting laser having a stacked body including a lower semiconductor DBR, a lower spacer layer, an active layer, an upper spacer layer, and an upper semiconductor DBR stacked on a substrate, the stacked body includes: A mesa is formed, and the mesa is formed by forming a groove in the laminated body around the mesa, and the depth of the groove in one direction in the laminated body is It is characterized by being formed deeper than the depth of the groove in the other direction orthogonal to the one direction.

  According to the present invention, since the surface emitting laser in which the polarization direction of the laser beam is stabilized in one direction can be manufactured by a simple method with a high yield, the polarization direction of the laser beam is stabilized in one direction. The surface emitting laser can be provided at low cost.

Top view of surface emitting laser according to the first embodiment Sectional drawing of the surface emitting laser in 1st Embodiment Explanatory drawing in the manufacturing process of the surface emitting laser in 1st Embodiment Illustration of relationship between pattern width and etching depth Explanatory drawing (1) of the surface emitting laser in 1st Embodiment Explanatory drawing of surface emitting laser produced for comparison Explanatory drawing (2) of the surface emitting laser in 1st Embodiment Explanatory drawing (3) of the surface emitting laser in 1st Embodiment Explanatory drawing (4) of the surface emitting laser in 1st Embodiment Correlation diagram between exposure length and threshold current of resonator structure Structure diagram of surface emitting laser array in the first embodiment Configuration diagram of laser printer in second embodiment The block diagram of the optical scanning device in 2nd Embodiment The block diagram of the color printer in 3rd Embodiment

  The form for implementing this invention is demonstrated below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

[First Embodiment]
(Surface emitting laser)
The surface emitting laser according to the present embodiment will be described with reference to FIGS. As shown in FIG. 1, a surface emitting laser 100 according to the present embodiment is a surface emitting laser having an oscillation wavelength band of 780 nm, for example, and includes a substrate 101, a buffer layer 102, a lower semiconductor DBR 103, a lower spacer layer 104, an active A layer 105, an upper spacer layer 106, an upper semiconductor DBR 107, a contact layer 109, and the like are included. 1 is a top view of the surface emitting laser according to the present embodiment, FIG. 2A is a cross-sectional view taken along the alternate long and short dash line 1A-1B in FIG. 1, and FIG. It is sectional drawing cut | disconnected in the dashed-dotted line 1C-1D in FIG. That is, FIG. 2A and FIG. 2B are cross-sectional views in directions orthogonal to each other in the surface emitting laser according to the present embodiment.

  The substrate 101 is an n-GaAs substrate having a mirror-polished surface, and this GaAs substrate is preferably a (100) plane substrate, for example, but may be an inclined substrate.

  The buffer layer 102 is laminated on the + Z side surface of the substrate 101 and is a layer made of n-GaAs.

The lower semiconductor DBR 103 is stacked on the surface of the buffer layer 102 on the + Z side, and includes a low refractive index layer made of n-Al _0.9 Ga _0.1 As and n-Al _0.3 Ga _0.7 As. There are 40.5 pairs of high refractive index layers. Between each refractive index layer, in order to reduce an electrical resistance, a composition gradient layer 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 formed to have an optical thickness of λ / 4 when the oscillation wavelength is λ. When the optical thickness is λ / 4, the actual thickness D of the layer is D = λ / 4n (where n is the refractive index of the medium of the layer).

The lower spacer layer 104 is laminated on the + Z side of the lower semiconductor DBR 103 and is a layer made of non-doped Al _0.6 Ga _0.4 As.

The active layer 105 is stacked on the + Z side of the lower spacer layer 104 and is an active layer having a triple quantum well structure made of Al _0.12 Ga _0.88 As—Al _0.3 Ga _0.7 As.

The upper spacer layer 106 is laminated on the + Z side of the active layer 105 and is a layer made of non-doped Al _0.6 Ga _0.4 As.

  The 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 includes an optical component having a thickness of one wavelength including 1/2 of the adjacent composition gradient layer. It is formed to have a thickness. 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 as to obtain a high stimulated emission probability.

The upper semiconductor DBR 107 is laminated on the + Z side of the upper spacer layer 106, and has a low refractive index layer made of p-Al _0.9 Ga _0.1 As and a high refractive index made of p-Al _0.3 Ga _0.7 As. It has 24 pairs of layers. A composition gradient layer is provided between the refractive index layers. Each refractive index layer is formed so as to have an optical thickness of λ / 4, including 1/2 of the adjacent composition gradient layer.

A current confinement layer 108 made of p-Al _0.99 Ga _0.01 As and having a thickness of about 30 nm is inserted into one of the low refractive index layers in the upper semiconductor DBR 107. The insertion position of the current confinement layer 108 is preferably in the second pair of low refractive index layers from the upper spacer layer 106.

  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 may be referred to as a “stacked body” for convenience.

  In the surface emitting laser according to the present embodiment, the mesa 120 is formed by removing a part of the contact layer 109, the upper semiconductor DBR 107, the current confinement layer 108, and the like by etching. A selective oxidation region 108a is formed in the current confinement layer 108 by selective oxidation from the periphery of the mesa 120, and the current confinement region 108b is formed in the central portion of the mesa 120 by a region where the current confinement layer 108 is not oxidized. Is formed. A dielectric protective film 111 is formed so as to cover the side surface and the like of the mesa 120 formed in this way, and a p-side electrode 113 in contact with the contact layer 109 is formed on the dielectric protective film 111. An n-side electrode 114 is formed on the back surface of the substrate 101. The p-side electrode 113 is connected to an electrode pad 118 provided outside the mesa 120.

  In the surface emitting laser according to the present embodiment, the mesa 120 is formed in a substantially square shape or a substantially rectangular shape, and grooves 121 and 122 for forming the mesa 120 are formed around the mesa 120. The groove 121 is a groove along the X-axis direction and is formed so that the width in the Y-axis direction is d1. The groove 122 is a groove along the Y-axis direction and is formed so that the width in the X-axis direction is d2. That is, grooves 121 and 122 are formed around the mesa to form a mesa. The groove 121 is a groove in the Y-axis direction, and is a groove along the X-axis direction that is formed in the Y-axis direction. Further, the groove 122 is a groove in the X-axis direction, and is a groove along the Y-axis direction that is formed in the X-axis direction.

  In the present embodiment, the relationship between the width d1 of the groove 121 in the Y-axis direction and the width d2 of the groove 122 in the X-axis direction is such that d2> d1. In the present embodiment, the groove 121 having a width d1 in the Y-axis direction is formed by removing the contact layer 109, the upper semiconductor DBR 107, and the current confinement layer 108, and has a width in the X-axis direction. The groove 122 to be d2 is formed by removing the contact layer 109, the upper semiconductor DBR 107, the current confinement layer 108, the upper spacer layer 106, and the active layer 105. Therefore, the depths of the groove 121 and the groove 122 are different, and the groove 122 is formed deeper than the groove 121.

  In the present embodiment, the X-axis direction and the Y-axis direction are directions orthogonal to each other, and when one of them is set as one direction, the other may be described as the other direction. Therefore, one direction and the other direction are directions orthogonal to each other.

(Method for manufacturing surface emitting laser)
Next, a method for manufacturing the surface emitting laser in the present embodiment will be described.

(1) First, the laminate is formed by crystal growth by a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxy (MBE) method. Here, an example by the MOCVD method is shown. In the MOCVD method, 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. Used. 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.

  (2) Next, as shown in FIG. 3, a resist pattern 131a and a resist pattern 131b for forming the mesa 120 are formed. Specifically, a square-shaped resist pattern 131a with a side of 25 μm corresponding to the shape of the desired mesa 120 on the surface of the laminate, and a square-shaped resist on the outside so as to surround the square-shaped resist pattern 131a A pattern 131b is formed. Between the resist pattern 131a and the resist pattern 131b, the width between the resist pattern 131a and the resist pattern 131b in the Y-axis direction is d1r, and the width between the resist pattern 131a and the resist pattern 131b in the X-axis direction is It forms so that it may become d2r. The mesa 120 is formed by the resist pattern 131a thus formed. As will be described later, the groove portions 121 and 122 are formed by removing the stacked body in the region between the resist pattern 131a and the resist pattern 131b where the resist pattern is not formed by etching.

  At this time, the resist pattern 131a and the resist pattern 131b are formed so that the width d1 in the groove 121 along the X-axis direction is different from the width d2 in the groove 122 along the Y-axis. That is, the resist pattern 131a and the resist pattern 131b are formed so that the grooves 121 and 122 satisfying d2> d1 are formed. In the present embodiment, the resist pattern 131a and the resist pattern 131b are formed so that the width d1 in the Y-axis direction is 10 μm and the width d2 in the X-axis direction is 30 μm.

  In consideration of the dielectric protective film 111 to be formed later, in order to form the groove 121 along the X-axis direction so that the width (width in the Y-axis direction) is d1, a resist in the Y-axis direction is used. The width d1r between the pattern 131a and the resist pattern 131b needs to be formed slightly wider than the width d1. Similarly, the width d2r between the resist pattern 131a and the resist pattern 131b in the X-axis direction is formed so that the width of the groove 122 along the Y-axis direction (the width in the X-axis direction) is d2. Needs to be formed slightly wider than the width d2. That is, the resist pattern 131a and the resist pattern 131b are formed so that d1 <d1r and d2 <d2r. Thereby, as described later, the groove 121 along the X-axis direction in which the width in the Y-axis direction is d1 can be formed, and the groove 122 along the Y-axis direction in which the width in the X-axis direction is d2 is formed. Can be formed.

  (3) Next, by performing inductively coupled plasma (ICP) dry etching using the resist pattern 131a and the resist pattern 131b as masks, a square columnar mesa 120 is formed. In the present embodiment, the etching bottom surface of the groove 121 along the X-axis direction is the center position of the resonator structure formed by the active layer 105 and the pair of spacer layers (the lower spacer layer 104 and the upper spacer layer 106). Dry etching is performed as described above. Thereby, the etching bottom surface of the groove 122 along the Y-axis direction is a position where the upper spacer layer 106 remains about 30 nm due to the loading effect by dry etching.

  In the present embodiment, as shown in FIG. 2, in the groove 122 along the Y-axis direction, the groove 122 along the Y-axis direction extends from the interface between the current confinement layer 108 and the upper spacer layer 106. The length to the etching bottom is defined as the exposure length R1.

  Here, the loading effect in dry etching will be described. The loading effect in dry etching means that the etching rate depends on the ratio of the mask opening area (area to be etched) to the entire resist pattern, the partial pattern density of the mask opening, and the absolute value of the pattern width of the mask opening. Is a phenomenon that changes.

  Specifically, when the pattern width of the mask opening is narrow and the aspect ratio (ratio of the etching depth to the opening pattern width) is high, the etching speed is higher than when the pattern width is wide and the aspect ratio is low. The etching depth is reduced.

  FIG. 4 is a graph for explaining the loading effect in dry etching in the AlGaAs layer. The horizontal axis of the graph is the pattern width, and the vertical axis is the difference in the etching depth of each pattern width with respect to the etching depth at a pattern width of 10 μm. As shown in FIG. 4, the etching depth tends to increase as the pattern width increases. Based on FIG. 4, when the same dry etching is performed, the difference between the etching depth at the pattern width of 10 μm and the etching depth at the pattern width of 60 μm is about 0.3 μm (300 nm).

  Therefore, in the method of manufacturing the surface emitting laser according to the present embodiment, the resist pattern 131a and the resist pattern 131b for forming the quadrangular columnar mesa 120 are between the resist pattern 131a and the resist pattern 131b in the Y-axis direction. The width d1r is formed to be narrower than the width d2r in the X-axis direction. As a result, the etching rate in the region having the width d1r becomes slower than the etching rate in the region having the width d2r wider than the width d1r due to the loading effect in the dry etching, and thus the groove 122 along the Y-axis direction that becomes the width d2 is formed. The etching bottom surface becomes the active layer 105 or the lower spacer layer 104, whereas the etching bottom surface of the groove 121 along the X-axis direction having the width d1 becomes the upper spacer layer 106. Therefore, the depth of the groove 122 along the Y-axis direction can be made deeper than the depth of the groove 121 along the X-axis direction, and the depth of the groove 121 along the X-axis direction and along the Y-axis direction. The depth of the groove 122 can be different.

  (4) Next, the resist pattern 131a and the resist pattern 131b are removed.

(5) Next, the laminated body is heat-treated in water vapor. In the present embodiment, Al contained in the current confinement layer 108 is selectively oxidized from the outer periphery of the mesa 120 to form a selective oxidation region 108a, and the current confinement region that is not oxidized is formed in the central portion of the mesa 120. 108b is formed. As a result, it is possible to form an oxidized constriction structure that can limit the drive current path of the light emitting unit only to the central part of the mesa 120. In the present embodiment, the non-oxidized current confinement region 108b becomes a current passage region (current injection region). It should be noted that, based on the results of various preliminary experiments, heat treatment conditions (holding temperature, holding time, etc.) are appropriately selected so that the current confinement region 108b serving as a current passing region has a desired size. Here, the area of the current passing region is formed to be about 20 μm ² .

  (6) Next, a resist pattern for forming a separation (chip cutting) groove is formed on the surface of the laminate.

  (7) Next, using the resist pattern described above as an etching mask, a groove for separation (chip cutting) is formed by dry etching.

  (8) Next, a dielectric protective film 111 made of SiN is formed by plasma CVD. Specifically, the dielectric protective film 111 is formed so that the optical thickness is λ / 2. In this embodiment, since the refractive index n of SiN is 1.86 and the oscillation wavelength λ is 780 nm, the actual film thickness (= λ / 2n) is formed to be about 210 nm.

  (9) Next, an etching mask for opening a window for the p-side electrode contact is formed on the upper surface of the mesa 120 serving as the laser light emission surface.

  (10) Next, the periphery of the upper surface of the mesa 120 is left, and the p-side electrode contact is opened by etching with BHF.

  (11) Next, the etching mask is removed.

  (12) Next, a square resist pattern having a side of 10 μm is formed in a region to be a light emitting portion (opening portion of the metal layer) on the upper surface of the mesa 120, and the p-side electrode material is deposited. As the p-side electrode material, a multilayer film made of Ti / Pt / Au is used.

  (13) Next, the p-side electrode 113 is formed by removing the electrode material deposited in the region (light emitting region) serving as the light emitting portion by lift-off. A region surrounded by the p-side electrode 113 is a light emission region.

  (14) Next, 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 multilayer film made of AuGe / Ni / Au.

  (13) Next, ohmic conduction is established between the p-side electrode 113 and the n-side electrode 114 by annealing. Thereby, the mesa 120 becomes a light emitting unit.

  (14) Next, it cut | disconnects for every chip | tip and each mounts in a ceramic package. In this manner, the surface emitting laser in this embodiment can be manufactured. FIG. 5 shows the outer shape of the surface emitting laser chip thus formed in the present embodiment.

  When the surface emitting laser manufactured by the surface emitting laser manufacturing method in the present embodiment described above was emitted with an optical output of 0.3 mW, stable polarization characteristics were obtained in the X direction indicated by the arrow A in FIG. Obtained.

  For comparison, a surface emitting laser as shown in FIG. 6 was fabricated using the same laminate. Specifically, the mesa 920 has a substantially square shape, and the widths of the groove 921 along the X-axis direction and the groove 922 along the Y-axis formed around the mesa 920 are both 30 μm. A simple surface emitting laser was fabricated. That is, a resist pattern for forming the groove portion 921 along the X-axis direction and the groove portion 922 along the Y-axis direction is formed, and the etching bottom surface of the groove portion 921 along the X-axis direction becomes the center of the resonator structure. When dry etching was performed as described above, the etching bottom surface of the groove 922 along the Y-axis direction was also the center of the resonator structure. In the surface emitting laser manufactured in this way, the polarization characteristics of the laser beam when the light output was 0.3 mW were measured. As a result, the operation was not stable and good polarization characteristics were not obtained.

  A surface emitting laser as shown in FIG. 7 was fabricated using the same laminate. Specifically, a surface emitting laser in which the width d1 of the groove 121 along the X-axis direction is 30 μm and the width d2 of the groove 122 along the Y-axis is 10 μm was manufactured by the same method as the manufacturing method described above. In this surface emitting laser, when the polarization characteristic of the laser beam was measured when the light output was 0.3 mW, as shown by the arrow B, a stable polarization characteristic in the Y-axis direction was obtained.

Next, as shown in FIGS. 8 and 9, a surface emitting laser in which a circular mesa 220 having a diameter of 20 μm was formed was manufactured. Note that the area of the current passing region formed in the circular mesa 220 is 16 μm ² .

  In the surface emitting laser shown in FIG. 8, the mesa 220 has a circular shape, and a groove 221 in the Y-axis direction and a groove 222 in the X-axis direction are formed. The width e1 of the narrowest region in the groove 221 in the Y-axis direction is formed to be 10 μm, and the width e2 of the narrowest region in the groove 222 in the X-axis direction is formed to be 30 μm.

  In the surface emitting laser shown in FIG. 9, the mesa 220 has a circular shape, and a groove 221 in the Y-axis direction and a groove 222 in the X-axis direction are formed. The width e1 of the narrowest region in the groove portion 221 in the Y-axis direction is formed to be 30 μm, and the width e2 of the narrowest region in the groove portion 222 in the X-axis direction is formed to be 10 μm.

  In the surface emitting laser shown in FIGS. 8 and 9, the polarization characteristics of the laser light when the optical output is 0.3 mW were measured. As shown in the arrow A in the surface emitting laser shown in FIG. In addition, a stable polarization characteristic was obtained in the X-axis direction. Further, in the surface emitting laser shown in FIG. 9, as shown by the arrow B, a stable polarization characteristic was obtained in the Y-axis direction.

  As described above, in the groove formed when forming the mesa, the depth of the etching bottom surface of the groove portion in one direction is made deeper than the depth of the etching bottom surface of the groove portion in the other direction. It is possible to form a surface emitting laser having the polarization characteristics. The stable polarization characteristics obtained in this way are considered to be obtained by the difference in optical loss due to the difference in the depth of the etching bottom of the groove. One direction and the other direction are orthogonal to each other.

  That is, when the mesa 120 is formed by etching, if the etching bottom surface of the groove formed when the mesa 120 is formed is shallow and the remaining film that is not etched in the resonator structure is thick, the active layer 105 The emitted spontaneous emission light propagates laterally through these layers, and the light is likely to leak to the outside of the mesa 120 and the like.

  In contrast, if the bottom surface of the groove formed when forming the mesa 120 or the like is deep and the remaining film remaining unetched in the resonator structure is thin, the effective refractive index of the portion where the remaining film is thin is mesa. It becomes relatively lower than the effective refractive index at 120 or the like. Accordingly, since the effective refractive index difference in the lateral direction becomes large, light is confined in the mesa 120. As a result, loss due to leakage of spontaneously emitted light in the lateral direction can be reduced, so that the oscillation threshold current of the polarization mode polarized in this direction is lowered and preferentially oscillates. In the direction perpendicular to this direction, as described above, spontaneous emission light propagates through the spacer layer and leaks, so that the oscillation threshold current increases and oscillation is suppressed. Therefore, it is possible to oscillate in a state where the polarization directions are stably aligned in a certain direction.

  As shown in FIG. 2, in the groove portions 121 and 122 formed around the mesa 120, the depth of the etching bottom surface of the groove portion 121 along the X axis direction and the depth of the etching bottom surface of the groove portion 122 along the Y axis direction. In other words, the etching bottom surface of the groove 121 along the X-axis direction becomes the upper spacer layer 106, and the etching bottom surface of the groove 121 along the X-axis direction becomes the center of the resonator structure, that is, along the X-axis direction. When the etching bottom surface of the groove 121 becomes the lower spacer layer 104, the active layer 105, or the like, the loss due to the influence of light leakage increases particularly in the Y-axis direction, and the threshold current increases.

  FIG. 10 shows the relationship between the exposed length R1 of the resonator structure and the threshold current. The threshold current tends to increase as the exposed length R1 of the resonator structure is shorter, that is, as the etching bottom surface of the groove is shallower. Therefore, in the surface-emitting laser having the structure shown in FIG. 5, the threshold current in the X-axis direction is lower than the Y-axis direction, and oscillation preferentially in the X-axis direction. Therefore, a stable polarization characteristic in the X-axis direction can be obtained. As described above, in this embodiment, by forming grooves having different etching depths in one direction and the other direction orthogonal to each other, stable polarization characteristics can be obtained without using an inclined substrate or the like. A surface emitting laser can be obtained. Accordingly, it is possible to easily obtain a surface emitting laser having stable polarization characteristics with a high yield.

  In the above embodiment, the case where the shape of the mesa 120 in the cross section orthogonal to the laser oscillation direction is square has been described. However, the present invention is not limited to this. For example, as shown in FIGS. As described above, any shape such as a circle, an ellipse, or a rectangle may be used.

  In the embodiment described above, the case where the oscillation wavelength of the light emitting unit is in the 780 nm band has been described. However, the present invention is not limited to this. The oscillation wavelength of the light emitting unit may be changed according to the characteristics of the photoconductor and the like.

  In the above embodiment, the active layer 105 employs a quantum well structure of AlGaAs. However, the present invention is not limited to this. For example, a material containing InP such as GaInAsP is used as a material for forming the active layer 105. May be.

  In addition, the surface emitting laser in the present embodiment can be used for applications other than the image forming apparatus. In this 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, or a 1.5 μm band depending on the application.

(Surface emitting laser array)
Next, the surface emitting laser array in the present embodiment will be described. The surface emitting laser array in the present embodiment has a structure in which the above-described surface emitting lasers are arranged in a plurality of arrays.

  As shown in FIG. 11, the surface emitting laser array 300 includes a plurality (32 in this case) of light emitting units 310 arranged two-dimensionally on the same substrate. The M direction in FIG. 11 is the main scanning corresponding direction, and the S direction is the sub scanning corresponding direction. The number of light emitting units 310 is not limited to 32. In addition, each light emitting unit 310 is connected to the electrode pad 320 corresponding to each light emitting unit 310 by wiring 330.

  Each light emitting unit 310 has the same structure as the surface emitting laser 100 described above, and is manufactured by the same manufacturing method as the surface emitting laser 100. That is, the surface emitting laser array 300 is a surface emitting laser array in which the surface emitting lasers 100 are integrated. Therefore, the surface emitting laser array in the present embodiment can obtain the same effect as the surface emitting laser 100 in the present embodiment.

  As shown in FIG. 11, in the present embodiment, the surface emitting laser array 300 has an equal interval between the light emitting portions when each light emitting portion is orthogonally projected onto a virtual line extending in the sub-scanning corresponding direction. By adjusting the lighting timing, it can be understood that the configuration is similar to the case where the light emitting units are arranged at equal intervals in the sub-scanning direction on the photosensitive drum 1030.

  In addition, it is preferable that the groove | channel between the two light emission parts 310 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.

  The size of the mesa 120 (length of one side) is preferably 10 μm or more. This is because if it is too small, heat is accumulated during operation, and the characteristics of the surface emitting laser or the like may be deteriorated.

  For example, when the center interval of the light emitting unit 210 is 3 μm, high density writing of 4800 dpi (dots / inch) can be performed if the magnification of the optical system of the optical scanning device is about 1.8 times. Of course, if the number of light emitting portions in the main scanning direction is increased or the magnification of the optical system is decreased, the density can be increased, and higher quality printing can be achieved. The writing interval in the main scanning direction can be easily controlled by the lighting timing of the light emitting unit.

[Second Embodiment]
Next, a second embodiment will be described. The present embodiment is an optical scanning device 1010 using the surface emitting laser or the surface emitting laser array in the first embodiment and a laser printer 1000 as an image forming apparatus.

  Based on FIG. 12, the laser printer 1000 in the present embodiment will be described. The laser printer 1000 according to this embodiment includes an optical scanning device 1010, a photosensitive drum 1030, a charging device 1031, a developing roller 1032, a transfer charger 1033, a charge eliminating unit 1034, a cleaning unit 1035, a toner cartridge 1036, a paper supply roller 1037, A paper 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, and a printer control device 1060 that comprehensively controls each of the above units 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 printer control device 1060 includes a CPU, a program described in a code decipherable by the CPU, a ROM storing various data used for executing the program, a RAM as a working memory, an analog, An AD conversion circuit for converting data into digital data is included. The printer control device 1060 controls each unit in response to a request from the host device, and sends image information from the host device to the optical scanning device 1010.

  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 is rotated in the direction indicated by the arrow X in FIG.

  The charging device 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 device 1031 → the developing roller 1032 → the transfer charger 1033 → the discharging unit 1034 → the cleaning unit 1035 are arranged in the order of rotation of the photosensitive drum 1030.

  The charging device 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 device 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 toner-attached image (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 is removed returns to the position facing the charging device 1031 again.

  Next, the optical scanning device 1010 will be described with reference to FIG. As shown in FIG. 13, the optical scanning device 1010 includes a light source 1114, a coupling lens 1115, an aperture plate 1116, a cylindrical lens 1117, a reflection mirror 1118, a polygon mirror 1113, a first scanning lens 1111a, and a second scanning lens 1111b. , And a scanning control device (not shown). These are assembled at predetermined positions of the optical housing 1130. The light source 1114 includes the surface emitting laser or the surface emitting laser array in the first embodiment.

  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 1115 converts the light beam emitted from the light source 1114 into substantially parallel light.

  The aperture plate 1116 has an aperture and defines the beam diameter of the light beam that has passed through the coupling lens 1115.

  The cylindrical lens 1117 forms an image of the light beam that has passed through the opening of the aperture plate 1116 in the vicinity of the deflection reflection surface of the polygon mirror 1113 via the reflection mirror 1118 in the sub-scanning corresponding direction.

  The optical system arranged on the optical path between the light source 1114 and the polygon mirror 1113 is also called a pre-deflector optical system. In the present embodiment, the pre-deflector optical system includes a coupling lens 1115, an aperture plate 1116, a cylindrical lens 1117, and a reflection mirror 1118.

  The polygon mirror 1113 is made of a regular hexagonal columnar member having a low height, and six deflecting reflecting surfaces are formed on the side surface. The polygon mirror 1113 deflects the light beam from the reflection mirror 1118 while rotating at a constant speed around an axis parallel to the sub-scanning corresponding direction.

  The first scanning lens 1111 a is disposed on the optical path of the light beam deflected by the polygon mirror 1113.

  The second scanning lens 1111b is disposed on the optical path of the light beam that passes through the first scanning lens 1111a. Then, the light beam that has passed through the second scanning lens 1111b 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 1113 rotates. That is, the photosensitive 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 1113 and the photosensitive drum 1030 is also called a scanning optical system. In this embodiment, the scanning optical system includes a first scanning lens 1111a and a second scanning lens 1111b. Even if at least one folding mirror is disposed on at least one of the optical path between the first scanning lens 1111 a and the second scanning lens 1111 b and the optical path between the second scanning lens 1111 b and the photosensitive drum 1030. Good.

  In this embodiment, since the light source 1114 has the surface-emitting laser or the surface-emitting laser array in the first embodiment, the optical scanning device 1010 is low-cost without reducing the accuracy of optical scanning. Can be achieved. In addition, since the laser printer 1000 includes the optical scanning device 1010, the cost can be reduced without degrading the image quality.

  In the above embodiment, the case of the laser printer 1000 as the image forming apparatus has been described. However, the present invention is not limited to this.

  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.

  For example, the medium may be a printing plate known as CTP (Computer to Plate). That is, the optical scanning device 1010 is also suitable for an image forming apparatus that forms a printing plate by directly forming an image on a printing plate material by laser ablation.

  For example, the medium may be so-called rewritable paper. For example, a material described below is applied as a recording layer on a support such as paper or a resin film. Then, reversibility is imparted to color development by thermal energy control by laser light, and display / erasure is performed reversibly.

  There are a transparent cloudy type rewritable marking method and a color developing / erasing type rewritable marking method using a leuco dye, both of which can be applied.

  The transparent cloudy type is a polymer thin film in which fine particles of fatty acid are dispersed. When heated to 110 ° C. or higher, the resin expands due to melting of the fatty acid. Thereafter, when cooled, the fatty acid becomes supercooled and remains in a liquid state, and the expanded resin solidifies. Thereafter, the fatty acid solidifies and shrinks to become polycrystalline fine particles, and voids are formed between the resin and the fine particles. Light is scattered by this gap and appears white. Next, when heated to an erasing temperature range of 80 ° C. to 110 ° C., the fatty acid partially melts, and the resin thermally expands to fill the voids. If it cools in this state, it will be in a transparent state and an image will be erased.

  The rewritable marking method using a leuco dye utilizes a reversible color development and decoloration reaction between a colorless leuco dye and a developer / decolorant having a long-chain alkyl group. When heated by laser light, the leuco dye and the developer / decolorant react to develop color, and when rapidly cooled, the colored state is maintained. Then, when it is slowly cooled after heating, phase separation occurs due to the self-aggregating action of the long-chain alkyl group of the developer / decolorant, and the leuco dye and developer / decolorizer are physically separated and decolored.

  In addition, when the medium is exposed to ultraviolet light, it develops in C (cyan) and is decolored by visible R (red) light, and when exposed to ultraviolet light, it develops in M (magenta). A photochromic compound that is decolored by G (green) light, a photochromic compound that develops color when exposed to ultraviolet light (Y) and is decolored by visible B (blue) light. It may be a so-called color rewritable paper provided on the body.

  This is a method of expressing full color by controlling the color density of the three types of materials that develop color in Y, M, and C by the time and intensity of applying R, G, and B light once it is made black by applying ultraviolet light. However, if the strong light of R, G, and B is continuously applied, all three types can be decolored to become pure white.

  Such an apparatus that imparts reversibility to color development by light energy control can also be realized as an image forming apparatus including an optical scanning device similar to the above-described embodiment.

  Further, an image forming apparatus using a silver salt film as an 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.

[Third Embodiment]
Next, a third embodiment will be described. The present embodiment is a color printer 2000 including a plurality of photosensitive drums.

  A color printer 2000 according to the present embodiment will be described with reference to FIG. The color printer 2000 in this embodiment is a tandem multicolor printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and is a black station (photosensitive drum K1). , Charging device K2, developing device K4, cleaning unit K5, and transfer device K6), cyan station (photosensitive drum C1, charging device C2, developing device C4, cleaning unit C5, and transfer device C6), and magenta. Station (photosensitive drum M1, charging device M2, developing device M4, cleaning unit M5, and transfer device M6) and yellow station (photosensitive drum Y1, charging device Y2, developing device Y4, cleaning unit Y5, And transfer device Y6) and optical scanning device 2010 Includes a transfer belt 2080, a fixing unit 2030.

  Each photoconductor drum rotates in the direction of the arrow in FIG. 14, and a charging device, a developing device, a transfer device, and a cleaning unit are arranged around each photoconductor drum along the rotation direction. Each charging device uniformly charges the surface of the corresponding photosensitive drum. The surface of each photoconductive drum charged by the charging device is irradiated with light by the optical scanning device 2010, and a latent image is formed on each photoconductive drum. Then, a toner image is formed on the surface of each photosensitive drum by a corresponding developing device. Further, the toner image of each color is transferred onto the recording paper on the transfer belt 2080 by the corresponding transfer device, and finally the image is fixed on the recording paper by the fixing unit 2030.

  The optical scanning device 2010 has a light source provided with the surface emitting laser or the surface emitting laser array in the first embodiment for each color. Therefore, the same effect as that of the optical scanning device 1010 in the second embodiment can be obtained. In addition, since the color printer 2000 includes the optical scanning device 2010, it is possible to obtain the same effect as the laser printer 1000 in the second embodiment.

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

  As mentioned above, although the form which concerns on implementation of this invention was demonstrated, the said content does not limit the content of invention.

101 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 confinement region 109 contact layer 111 protective film 113 p side electrode 114 n side electrode 118 electrode pad 120 mesa 121 groove 122 groove 131a, 131b resist pattern 220 mesa 221 groove 222 groove 1000 laser printer ( Image forming device)
1010 Optical scanning device 2000 Color printer (image forming apparatus)

Japanese Patent No. 4010095 JP 2010-153768 A JP-A-11-54838 JP 2005-142361 A JP 2008-16824 A

Claims (10)

In a surface emitting laser having a stacked body including a lower semiconductor DBR, a lower spacer layer, an active layer, an upper spacer layer, and an upper semiconductor DBR stacked on a substrate,
Mesa is formed in the laminate,
The mesa is formed by forming a groove in the laminated body around the mesa,
The surface emitting laser according to claim 1, wherein the depth of the groove portion in one direction of the laminate is formed deeper than the depth of the groove portion in the other direction orthogonal to the one direction.   2. The surface emitting laser according to claim 1, wherein the width of the groove portion in the one direction is formed wider than the width of the groove portion in the other direction.   The surface emitting laser according to claim 1, wherein the groove is formed by dry etching. The upper semiconductor DBR is formed with a current confinement layer, and the current confinement layer is formed by oxidizing a portion around the mesa,
The bottom surface of the groove in the one direction is the active layer or the lower spacer layer,
4. The surface according to claim 1, wherein a bottom surface of the groove portion in the other direction is an upper semiconductor DBR formed on the substrate side with respect to the upper spacer layer or the current confinement layer. 5. Light emitting laser.   The surface emitting laser according to any one of claims 1 to 4, wherein a shape of the upper surface of the mesa is substantially circular or elliptical. The shape on the top surface of the mesa is a square or a rectangle,
The groove in the one direction is formed along the other direction,
5. The surface emitting laser according to claim 1, wherein the groove portion in the other direction is formed along the one direction.   A surface-emitting laser array comprising a plurality of surface-emitting lasers according to claim 1. An optical scanning device that scans a surface to be scanned with light,
A surface-emitting laser according to any one of claims 1 to 6, or a light source having the surface-emitting laser array according to claim 7,
A light deflector for deflecting light from the light source;
A scanning optical system for condensing the light deflected by the light deflection unit on the surface to be scanned;
An optical scanning device comprising: An image carrier;
The optical scanning device according to claim 8, wherein the image carrier is scanned with light modulated according to image information;
An image forming apparatus comprising:   The image forming apparatus according to claim 9, wherein there are a plurality of the image carriers, and the image information is multicolor color information.

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