JP2010080532A - Light emitting element, light emitting element head, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device or the like which suppresses total reflection on an interface of an inside and external of the light emitting device and extracts light to the external efficiently. <P>SOLUTION: An LED (light emitting diode) 102 includes: a substrate 202; a light emitting layer 206 which emits light when a current is supplied, and has a first recessed and projected structure on a surface; a coating layer 208 which has a second recessed and projected structure corresponding to the first recessed and projected structure, is formed to be in contact with the light emitting layer 206, and transmits the light emitted from the light emitting layer 206; and a reflection layer 204 which is formed between the substrate 202 and the light emitting layer 206, and reflects the light emitted from the light emitting layer 206. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light emitting element and the like, for example, a light emitting element that can be used in a light emitting element head.

  In image forming apparatuses such as printers, copiers, and facsimiles that employ an electrophotographic method, after obtaining an electrostatic latent image by irradiating image information onto a uniformly charged photoreceptor by optical recording means The electrostatic latent image is visualized by adding toner, and the image is formed by transferring and fixing on the recording paper. As such an optical recording means, in addition to an optical scanning method in which a laser beam is scanned in a main scanning direction using a laser for exposure, in recent years, a large number of LED (Light Emitting Diode) array light sources are arranged in the main scanning direction. An optical recording means using an LED head is employed.

  The image forming apparatus using the LED array light source does not require a scanning space and does not require a drive system, as compared with an optical scanning type image forming apparatus, so that the entire image forming apparatus is downsized and reliable. There is an advantage of improvement. There is also an advantage that it is strong against deformation of the optical system due to vibration and heat.

  Here, in Patent Document 1, in order to increase the external extraction efficiency of the emitted light, the side surface of the GaAlAs light-emitting element pellet is subjected to a process of forming a flat surface without processing distortion on the side surface, and then the side surface is finely formed. A method of manufacturing a GaAlAs light-emitting element that performs a process for forming a surface having irregularities has been proposed.

  In Patent Document 2, an n-type cladding layer, an undoped active layer, and a p-type cladding layer made of an InGaAlP-based material are grown on an n-type GaAs substrate to form a light-emitting layer, and the light-emitting layer formed on the light-emitting layer Alternatively, a semiconductor light emitting element having a lattice irregular lattice plus a light scattering layer whose surface is roughened with respect to the substrate has been proposed.

  Further, in Patent Document 3, a substrate layer, a buffer layer, an n-type cladding layer, an active layer, a p-type cladding layer, a first current blocking layer disposed under the anode electrode, and a first ring formed so as to be exposed on the side surface. A semiconductor light emitting device has been proposed in which a cathode electrode is formed on the lower surface of a semiconductor substrate comprising two current blocking layers and a contact layer, an anode electrode is formed in the center of the upper surface, and the upper surface and side surfaces are roughened.

JP-A-6-151959 JP-A-8-102548 JP-A-8-167738

A light emitting element such as an LED element is required to extract a large amount of light emitted inside the light emitting element.
An object of the present invention is to provide a light emitting element that can suppress total reflection at the interface between the inside and the outside of the light emitting element and can efficiently extract light to the outside.

  The invention according to claim 1 has a substrate, a light emitting layer that emits light by supplying a current and has a first uneven structure on a surface, and a second uneven structure corresponding to the first uneven structure. And a coating layer formed in contact with the light emitting layer and transmitting light emitted from the light emitting layer, and a reflective layer formed between the substrate and the light emitting layer and reflecting light emitted from the light emitting layer. A light-emitting element comprising:

The invention according to claim 2 is the light emitting element according to claim 1, wherein the light emitting layer is a pnpn type or npnp type thyristor.
The invention according to claim 3 is the light emitting device according to claim 1, wherein the reflective layer is made of a Bragg mirror.
The invention according to claim 4 is the light emitting device according to any one of claims 1 to 3, wherein the first concavo-convex structure is constituted by convex portions and concave portions arranged in a bowl shape. is there.
The invention according to claim 5 is the light-emitting element according to any one of claims 1 to 3, wherein the first concavo-convex structure is constituted by convex portions and concave portions arranged in a lattice pattern. is there.
The invention according to claim 6 is the light-emitting element according to any one of claims 1 to 3, wherein the first concavo-convex structure is constituted by convex portions and concave portions arranged in a staggered manner. is there.

  The invention according to claim 7 includes a substrate, a light emitting layer that emits light when current is supplied and has a first uneven structure on a surface, and a second uneven structure corresponding to the first uneven structure. A light emitting device having a coating layer formed in contact with the light emitting layer and transmitting light emitted from the light emitting layer, and a reflective layer formed between the substrate and the light emitting layer and reflecting light emitted from the light emitting layer. A light emitting element head comprising: a light emitting element array in which a plurality of light emitting element array chips each including an element are arranged in a main scanning direction; and an optical element that forms an image of a light output of the light emitting element array.

  The invention according to claim 8 is the light emitting element head according to claim 7, wherein the light emitting element array chip is a self-scanning light emitting element array chip.

  The invention according to claim 9 includes a substrate, a light emitting layer that emits light when current is supplied and has a first uneven structure on a surface, and a second uneven structure corresponding to the first uneven structure. A light emitting device having a coating layer formed in contact with the light emitting layer and transmitting light emitted from the light emitting layer, and a reflective layer formed between the substrate and the light emitting layer and reflecting light emitted from the light emitting layer. A toner image forming unit for forming a toner image, a transfer unit for transferring the toner image to a recording medium, and a fixing unit for fixing the toner image to the recording medium. The image forming apparatus is characterized.

According to the first aspect of the present invention, it is possible to realize a light emitting element capable of suppressing total reflection at the interface between the inside and the outside of the light emitting element and efficiently extracting light to the outside.
According to the second aspect of the present invention, it is possible to realize a light emitting device having a higher light output intensity than when the present configuration is not adopted.
According to the invention of claim 3, the reflective layer can be more easily formed as compared with the case where this configuration is not adopted.
According to the invention of claim 4, the concavo-convex structure can be formed more easily as compared with the case where this configuration is not adopted, and in particular, the concavo-convex structure is formed by the convex portions and the concave portions arranged in a bowl shape in the main scanning direction. When formed, the directivity of the condensed light in the sub-scanning direction can be improved.
According to the invention of claim 5, it is possible to extract light from the light emitting element more efficiently than in the case where this configuration is not adopted.
According to the sixth aspect of the present invention, it is possible to extract light from the light emitting element even more efficiently than in the case where this configuration is not adopted.
According to the invention of claim 7, it is possible to realize a light emitting element head having a higher light output intensity as compared with the case where this configuration is not adopted.
According to the eighth aspect of the present invention, the size of the light emitting element array chip can be further reduced as compared with the case where this configuration is not adopted.
According to the ninth aspect of the present invention, a light emitting element head having a higher light output intensity than that in the case where the present configuration is not employed, as compared with the case where the present configuration is not employed, is provided, and image formation is performed with higher image quality. Thus, an image forming apparatus that can be performed in the above manner can be realized.

  Embodiments of the present invention will be described below. However, the present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of the gist. Also, the drawings used are used to describe the present embodiment and do not represent the actual size.

FIG. 1 is a diagram showing the overall configuration of the image forming apparatus according to the present embodiment.
An image forming apparatus 1 shown in FIG. 1 is an image forming apparatus generally called a tandem type, and performs image formation corresponding to gradation data of each color, and image output control for controlling the image process system 10. Image processing unit (IPS: Image Processing System) connected to a unit 30, for example, a personal computer (PC) 2 or an image reading device (IIT: Image Input Terminal) 3, and performs image processing on image data received from these 40.

  The image processing system 10 includes an image forming unit 11 as an example of a toner image forming unit including a plurality of engines arranged in parallel at a constant interval in the horizontal direction. The image forming unit 11 is composed of four image forming units 11Y, 11M, 11C, and 11K of yellow (Y), magenta (M), cyan (C), and black (K). A photosensitive drum 12 that is an image holding member (photosensitive member) that forms an image by forming an image, a charger 13 that uniformly charges the surface of the photosensitive drum 12, and a photosensitive drum that is charged by the charger 13. The light emitting device head 14 is a light emitting device that exposes a light source 12 and a developing device 15 that develops a latent image obtained by the light emitting device head 14. Further, the image process system 10 multiplex-transfers each color toner image formed on the photosensitive drum 12 of each image forming unit 11Y, 11M, 11C, 11K onto a recording sheet as an example of a recording medium. A sheet conveying belt 21 that conveys the recording sheet, a driving roll 22 that is a roll for driving the sheet conveying belt 21, and a transfer roll 23 as an example of a transfer unit that transfers the toner image on the photosensitive drum 12 to the recording sheet are provided. Yes.

  Image signals input from the PC 2 or IIT 3 are subjected to image processing by the image processing unit 40 and supplied to the image forming units 11Y, 11M, 11C, and 11K through the interface. The image process system 10 operates based on a control signal such as a synchronization signal supplied from the image output control unit 30. First, in the yellow image forming unit 11Y, an electrostatic latent image is formed by the light emitting element head 14 on the surface of the photosensitive drum 12 charged by the charger 13 based on the image signal obtained from the image processing unit 40. . A yellow toner image is formed on the formed electrostatic latent image by the developing device 15, and the formed yellow toner image is transferred to a recording sheet on a sheet conveying belt 21 that rotates in the direction of the arrow in the figure. 23 is transferred. Similarly, magenta, cyan, and black toner images are formed on the respective photosensitive drums 12 and are multiple-transferred onto the recording paper on the paper transport belt 21 using the transfer roll 23. The multiple transferred toner image on the recording paper is conveyed to a fixing device 24 as an example of a fixing unit, and is fixed on the recording paper by heat and pressure.

  Next, the light emitting element head 14 will be described in detail. FIG. 2 shows an enlarged cross-sectional view of the light emitting element head 14 of the present embodiment. The light-emitting element head 14 supports the light-emitting element array 51, which is a staggered arrangement of light-emitting element array chips 100 in which LEDs as a large number of light-emitting elements are arranged in a straight line, as will be described later. A printed circuit board 52 on which a circuit for controlling the driving of the light emitting element array 51 is formed, a support member 53 that supports the printed circuit board 52, and an optical element that forms an image of the light output of each light emitting element array on the photosensitive drum 12. The image forming optical element 54, a support member 53 to which the printed circuit board 52 is attached, and a housing 55 for holding the image forming optical element 54 are provided.

  FIG. 3 is a perspective view of the light emitting element head 14. In the light emitting element head 14, the housing 55 is formed so as to protrude from both ends of the imaging optical element 54 in the main scanning direction. In the housing 55, these protruding portions are referred to as a first protruding portion 55a and a second protruding portion 55b. Here, the 1st protrusion part 55a has a function as a site | part to protrude, and the 1st protrusion part 55a is set longer than the 2nd protrusion part 55b. Bolts 58a and 58b for positioning the light-emitting element head 14 with respect to a frame (not shown) provided in the image forming apparatus 1 (see FIG. 1) are vertically provided on the protrusions 55a and 55b. Each is arranged through. Further, a printed circuit board to which a light emitting element array 51 (see FIG. 2) is attached to one end side of the light emitting element head 14 in the main scanning direction, specifically, an upper portion of the first protrusion 55a provided in the housing 55. 52 is extended and arranged. A driver IC 64 for driving the light emitting element array 51 is attached to the upper surface of the printed circuit board 52 exposed on the first protrusion 55a.

  A power cable 61 for supplying power to the driver IC 64, the light emitting element array 51, and the like is attached to the upper surface of the printed board 52 between the driver IC 64 and the bolt 58a attachment position. Furthermore, video data from the image processing unit 40 (see FIG. 1), a clock and a synchronization signal from the image output control unit 30 (see FIG. 1), etc. are provided on the upper surface of the printed circuit board 52 outside the mounting position of the bolts 58a. A harness 62 for receiving the signal is attached. As described above, in the present embodiment, the light emitting element array 51 is driven to a position substantially in series with the imaging optical element 54 (light emitting element array 51) on the one end side in the main scanning direction of the light emitting element head 14. The driver IC 64, the power supply power line connector to which the power cable 61 is attached, and the communication signal line connector to which the harness 62 is attached are arranged.

FIG. 4 is a schematic diagram illustrating the structure of the light emitting element array 51.
The light emitting element array 51 shown in FIG. 4 is formed by arranging a plurality of light emitting element array chips 100 in a staggered manner in the main scanning direction.
The light emitting element array chip 100 includes a bonding pad 101 that is a space for wiring and the like on both sides of a rectangular substrate. By providing the bonding pad 101 in this way, there is an advantage that the chip width can be reduced to a width almost required by the bonding pad 101 itself.

In the region between the bonding pads 101 on both sides of the light emitting element array chip 100, the LEDs 102 as light emitting elements are arranged linearly at equal intervals along the long side of the rectangle in the main scanning direction. Here, the LED 102 is arranged close to one long side of the light emitting element array chip 100. The odd-numbered light-emitting element array chip 100 and the even-numbered light-emitting element array chip 100 are arranged so that the LEDs 102 face each other and the bonding pads 101 are overlapped. With this arrangement, all the LEDs 102 can be arranged at equal intervals in the main scanning direction.
In addition, a microlens 103 (not shown) made of a transparent resin is attached to a light emitting element portion where each LED 102 is formed and an adjacent portion adjacent to the light emitting element portion.

FIGS. 5A and 5B are diagrams illustrating the structure of the light emitting element array chip 100. FIG.
FIG. 5A is a view of the light emitting element array chip 100 as viewed from the direction in which the light of the LED 102 is emitted. FIG. 5B is a cross-sectional view taken along the line AA in FIG.
As described above, the bonding pads 101 are arranged on both sides of the light emitting element array chip 100, and the LEDs 102 are arranged in a straight line at equal intervals in a region sandwiched between the bonding pads 101 on both sides. Each LED 102 is formed with a microlens 103 on the light emitting side. The microlens 103 collects the light emitted from the LED 102 and allows the light to efficiently enter the photosensitive drum 12 (see FIGS. 1 and 2).
The microlens 103 is made of a transparent resin such as a photocurable resin, and the surface thereof preferably has an aspherical shape in order to collect light more efficiently. In addition, the size, thickness, focal length, and the like of the microlens 103 are determined by the wavelength of the LED 102 used, the refractive index of the photocurable resin used, and the like.

  In the present embodiment, it is preferable to use a self-scanning light emitting element array chip as the light emitting element array chip 100. The self-scanning light-emitting element array chip uses a light-emitting thyristor having a pnpn structure as a component of the light-emitting element array, and is configured to realize self-scanning of the light-emitting element. It is disclosed in Japanese Laid-Open Patent Publication No. 2-14584, Japanese Laid-Open Patent Publication No. 2-92650, and Japanese Laid-Open Patent Publication No. 2-92651. Japanese Patent Application Laid-Open No. 2-263668 discloses a self-scanning light emitting element array having a structure separated from a light emitting element array as a light emitting part using the transfer element array as a transfer part.

FIG. 6 is an equivalent circuit diagram of a separation type self-scanning light emitting element array. This self-scanning light emitting element array includes transfer thyristors T ₁ , T ₂ , T ₃ ,... And write light emitting thyristors L ₁ , L ₂ , L ₃ ,. The configuration of the transfer unit uses a diode connection. V _GK is a power supply (usually 5 V), and is connected to the gate electrodes G ₁ , G ₂ , G ₃ ,... Of each transfer thyristor through the load resistance _RL from the power line 72. Further, the gate electrodes G ₁ , G ₂ , G ₃ ,... Of the transfer thyristor are also connected to the gate electrode of the write light-emitting thyristor. The gate electrode of the transfer thyristor T ₁ is the start pulse phi _S is applied to the anode electrode of the transfer thyristor, transfer clock pulses φ1 alternately, .phi.2 is applied. These transfer clock pulses φ 1 and φ 2 are supplied via clock pulse lines 74 and 76. The anode electrode of the write light emitting thyristor, via a signal line 78, a write signal phi _I is added.

Next, the operation will be briefly described. First voltage of the transfer clock pulses φ1 to the transfer thyristor T ₂ at the H level is on. At this time, the potential of the gate electrode _{G 2} is lowered to approximately 0V from 5V to _{V GK.} The effect of this potential drop is transmitted by the diode D ₂ to the gate electrode G _3, it is set to the potential of about 1V (forward threshold voltage of the diode D ₂ (equal to the diffusion potential)). However, the connection of the potential of the gate electrode G ₁ for the diode D ₁ is reverse biased state is not performed, the potential of the gate electrode G ₁ remains at 5V. ON potential of the write light emitting thyristor, since is approximated by a diffusion potential of the gate electrode potential + pn junction (approximately 1V), H-level voltage of the next transfer clock pulse φ2 turns on about 2V (the transfer thyristor T ₃ and a voltage) than necessary and about 4V (only the transfer thyristor T ₃ by setting the voltage) or less necessary to turn on the transfer thyristor T ₄ is turned on, other than the transfer thyristor for Can be left off. Therefore, the ON state is transferred by two transfer clock pulses.

The start pulse φ _S is a pulse for starting such a transfer operation. At the same time, the start pulse φ _{S is set} to L level (about 0 V), and at the same time, the transfer clock pulse φ 2 is set to H level (about 2 to about 4 V). , to turn on the transfer thyristor _{T 1.} Shortly thereafter, a start pulse φ _S is returned to the H level.

Assuming that the transfer thyristor T ₂ is in the ON state, the potential of the gate electrode G ₂ is, lower than V _{GK (here} assumed to 5V), becomes substantially 0V. Accordingly, the voltage of the write signal phi _I is, if the diffusion potential of the pn junction (approximately 1V) above, it is possible to write for the light-emitting thyristors L ₂ and the light-emitting state.

In contrast, the gate electrode _{wherein G 1} is about 5V, the gate electrode _{G 3} are approximately 1V. Accordingly, the write voltage of the write light-emitting thyristor L ₁ of about 6V, the write voltage of the write light-emitting thyristor L ₃ is about 2V. Now, the voltage of the write signal phi _I can write only to the write light-emitting thyristor _{L 2} is a range of 1 to 2 V. When the write light-emitting thyristor L ₂ is turned on, i.e., enters the emission state, the light emission intensity is decided to the amount of current flowing to the write signal phi _I, it is possible to image writing at any intensity. Further, in order to transfer the light-emitting state to the next light emitting element is dropped voltage of the write signal phi _I line once to 0V, it is necessary to once turn off the light-emitting element that emits light.

Next, the LED 102 will be described in detail.
FIG. 7 is a cross-sectional view illustrating an example of the LED 102.
FIG. 7 shows the structure of the LED 102. The LED 102 basically includes a substrate 202 and a light emitting layer 206 that emits light when supplied with current. In this embodiment mode, the cover layer 208 that is formed in contact with the light-emitting layer 206 and transmits light emitted from the light-emitting layer 206 and the light emitted from the light-emitting layer 206 that is formed between the substrate 202 and the light-emitting layer 206 are used. Is formed.

  The substrate 202 serves as a base for epitaxially growing the reflective layer 204 and the light emitting layer 206. In this embodiment, since a crystal film made of GaAlAs is used for the reflective layer 204 and the light emitting layer 206, a film made of GaAs having substantially the same lattice constant as this is preferably used.

  The reflective layer 204 is for reflecting the light emitted from the light emitting layer 206 toward the substrate 202 and changing the light path to the coating layer 208 side which is the light extraction side. In this embodiment, the reflective layer is a Bragg mirror, which is a semiconductor multilayer mirror layer made of p-type AlGaAs and configured by alternately stacking compound semiconductor layers having different compositions. Specifically, a semiconductor multilayer structure in which AlGaAs layers having different Al composition ratios are alternately stacked can be used. The reflective layer 204 can be formed by performing epitaxial growth by, for example, a MOCVD (metal organic chemical vapor deposition) method.

  In the present embodiment, the light emitting layer 206 is a pnpn type thyristor. Specifically, a p-type AlGaAs layer 206a, an n-type AlGaAs layer 206b, a p-type AlGaAs layer 206c, and an n-type AlGaAs layer 206d are sequentially stacked. In this embodiment, zinc (Zn) is used as the p-type dopant and tellurium (Te) is used as the n-type dopant. The light emitting layer 206 can be formed, for example, by performing epitaxial growth by MOCVD (metal organic chemical vapor deposition).

  This pnpn-type thyristor emits light mainly between the n-type AlGaAs layer 206b and the p-type AlGaAs layer 206c, and emits light of a preset wavelength. This light has no directivity and is spherically symmetric. The light emitted to the substrate 202 side is reflected by the reflective layer 204 as described above and travels toward the coating layer 208 side. At the same time, the light emitted toward the coating layer 208 should be emitted to the outside through the coating layer 208. However, as described above, the difference in refractive index between the semiconductor layer constituting the light emitting layer 206 and the outside air is large. Therefore, much light is totally reflected on the surface portion of the n-type AlGaAs layer 206d, which is the uppermost portion of the light emitting layer 206, and is reflected toward the reflective layer 204. In this case, reflection is again caused by the reflection layer 204, but this reflection angle does not change. Therefore, the light emitted at an angle causing total reflection at the n-type AlGaAs layer 206d remains inside, and the reflection angle is somehow changed. As long as it does not change, it does not exit to the outside.

Therefore, in the present embodiment, the first concavo-convex structure is formed on the surface of the n-type AlGaAs layer 206d which is the uppermost part of the light emitting layer 206.
This concavo-convex structure has, for example, a rectangular shape, and the width L1 of the convex portion 210 can be 1 μm. Similarly, the width L2 of the recess 212 can be set to 1 μm. Further, the step H between the concave portion 212 and the convex portion 210 can be set to 0.1 μm to 0.2 μm, for example. Although the width L1 and the width L2 may be smaller values, in this embodiment, the width L1 and the width L2 are 1 μm or more because they are manufactured by a photolithography method as described later. It is preferable. The width L1 at each location is a region where the rectangular uneven structure is formed, and is preferably substantially the same length. If there is a large variation in the length of the width L1 at each location, the amount of light extracted from the LED 102 is likely to vary from location to location, and uneven brightness is likely to occur. This also applies to the width L2. That is, in the region where the rectangular uneven structure is formed, the width L2 at each location is preferably substantially the same length.

  By forming such a concavo-convex structure, the light emitted from the light emitting layer 206 and reaching the surface of the n-type AlGaAs layer 206d is hardly totally reflected. That is, the presence of the convex portion 210 and the concave portion 212 increases the amount of components incident on the surface of the n-type AlGaAs layer 206d at an angle deviating from the angle at which total reflection occurs. This effect is particularly likely to occur at the corners 218a and 218b of the convex portion 210 and the concave portion 212. For this reason, it becomes easy to suppress generation | occurrence | production of total reflection, and it becomes easy to radiate | emit light outside.

  In order to produce the first concavo-convex structure by a photolithography method, for example, a photoresist solution is first applied to the surface of the n-type AlGaAs layer 206d by spin coating to form a resist layer. Then, when the resist layer is covered with a mask on which a fine pattern corresponding to the pattern of the first concavo-convex structure is drawn and exposed by ultraviolet (UV), electron beam (EB), etc., the resist layer A fine pattern is exposed. Next, when the exposed portion of the resist layer is removed using a developing solution, the portion of the resist layer corresponding to the fine pattern is removed, and a hole is formed in the resist layer. Then, the recess 212 is formed by removing the surface of the n-type AlGaAs layer 206d which is the bottom of the hole by etching. Finally, when the remaining resist layer is removed, a first uneven structure is formed on the surface of the n-type AlGaAs layer 206d. As etching, either dry etching or wet etching can be used.

In the present embodiment, the concavo-convex structure is a rectangular shape, but the present invention is not limited to this and may have other shapes. Specific examples include a spindle shape, a cone shape, a truncated cone shape, a polygonal pyramid shape, and a polygonal truncated cone shape.
In this embodiment mode, a pnpn type thyristor is described as an example of the light emitting layer 206. However, an npnp type thyristor may be used.

The covering layer 208 is formed of a transparent film that transmits the light emitted from the light emitting layer 206.
The covering layer 208 has a second concavo-convex structure on the surface corresponding to the first concavo-convex structure. That is, as shown in FIG. 7, a convex portion 214 of the covering layer 208 is formed by laminating on the convex portion 210 of the first concave-convex structure formed on the surface of the n-type AlGaAs layer 206d of the light emitting layer 206. Is done. In addition, the concave portion 216 of the covering layer 208 is formed by being stacked on the upper portion of the concave portion 212. Therefore, in the case of the present embodiment, the second concavo-convex structure has a rectangular shape similarly to the first concavo-convex structure. On the other hand, the convex part 214 of the second concavo-convex structure has a rounded corner 220a with respect to the convex part 210 of the first concavo-convex structure. Such a second concavo-convex structure can be formed by forming the coating layer 208 to a thickness that is approximately the same as or slightly thicker than the step H of the first concavo-convex structure. Specifically, it can be formed by depositing SiO ₂ by a CVD (Chemical Vapor Deposition) method.

  Since the coating layer 208 is a transparent film, light that has passed through the light emitting layer 206 can also pass through the coating layer 208 and be emitted to the outside. By forming the coating layer 208, the difference in refractive index between the light emitting layer 206 and the outside air is further reduced and reflection is further suppressed, so that the light extraction efficiency can be further increased.

Next, the first uneven structure will be described in more detail.
FIGS. 8A to 8D are perspective views illustrating the concavo-convex structure.
The LEDs 102a, 102b, 102c, and 102d shown in FIGS. 8A to 8D do not have the coating layer 208 drawn for the sake of simplicity. Then, various patterns of the first uneven structure are illustrated.

  Here, the LED 102a illustrated in FIG. 8A includes a convex portion 210 and a concave portion 212 arranged in a bowl shape in the sub-scanning direction. Further, the LED 102b shown in FIG. 8B includes a convex portion 210 and a concave portion 212 arranged in a bowl shape in the main scanning direction. The LED 102a and the LED 102b have a concavo-convex structure formed by a pattern in which convex portions 210 and concave portions 212 arranged in a substantially parallel bowl shape as shown in the figure are repeated. Further, the width of the convex portion 210 is substantially the same at any location where the convex portion 210 is formed. Similarly, the width of the recess 212 is substantially the same.

  Further, the LED 102c shown in FIG. 8C includes a convex portion 210 and a concave portion 212 arranged in a lattice pattern. Further, the LED 102d shown in FIG. 8D is configured by a convex portion 210 and a concave portion 212 arranged in a staggered manner. In the LED 102c and the LED 102d, the shape of the top portion of the convex portion 210 is substantially square as shown in the figure. That is, the width in the main scanning direction and the sub-scanning direction of the top of the convex portion 210 is substantially equal. Further, the width of the convex portion 210 in the main scanning direction and the sub-scanning direction is substantially the same at any location where the convex portion 210 is formed.

  In any of the forms shown in FIGS. 8A to 8D, the extraction efficiency of light emitted from the LEDs 102a, 102b, 102c, and 102d as the light emitting elements can be increased. However, the more corners 218a and 218b formed by the convex part 210 and the concave part 212, the more difficult it is to produce total reflection, and light can be extracted more efficiently. For example, in the structure of the LED 102c and the LED 102d, the number of corner portions 218a and 218b formed by the convex portions 210 and the concave portions 212 is larger than in the case of the structure of the LED 102a and the LED 102b. Therefore, total reflection is less likely to occur, and light can be extracted more efficiently. In addition, the structure of the LED 102b is more likely to collect light in the sub-scanning direction than the structure of the LED 102a. In other words, the amount of light that can be collected by the imaging optical element 54 increases due to the relationship between the effective angles at which the imaging optical element 54 (see FIG. 2) can collect light. Therefore, the directivity in the sub-scanning direction can be improved. Therefore, in the light emitting element head 14 as in the embodiment described with reference to FIG. 2, since it is easier to collect light more efficiently, it becomes easier to form more light output on the photosensitive drum 12 (see FIG. 2). .

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an exemplary embodiment. The expanded sectional view of the light emitting element head of this Embodiment is shown. The perspective view of the light emitting element head is shown. It is the schematic explaining the structure of the light emitting element array. It is a figure explaining the structure of the light emitting element array chip. It is an equivalent circuit diagram of a separation type self-scanning light emitting element array. It is sectional drawing explaining an example of LED. It is the perspective view explaining the uneven structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 11K, 11C, 11M, 11Y ... Image forming unit, 14 ... Light emitting element head, 23 ... Transfer roll, 24 ... Fixing device, 51 ... Light emitting element array, 54 ... Imaging optical element, 100 ... Light emission Element array chip, 101 ... bonding pad, 102 ... LED, 202 ... substrate, 204 ... reflective layer, 206 ... light emitting layer, 208 ... covering layer, 210, 214 ... convex, 212,216 ... concave

Claims (9)

A substrate,
A light emitting layer that emits light by supplying current and has a first uneven structure on the surface;
A coating layer that has a second concavo-convex structure corresponding to the first concavo-convex structure, is formed in contact with the light emitting layer, and transmits light emitted from the light emitting layer;
A reflective layer that is formed between the substrate and the light emitting layer and reflects light emitted from the light emitting layer;
A light-emitting element comprising:   The light emitting device according to claim 1, wherein the light emitting layer is a pnpn type or npnp type thyristor.   The light emitting device according to claim 1, wherein the reflective layer is made of a Bragg mirror.   4. The light emitting device according to claim 1, wherein the first concavo-convex structure includes a convex portion and a concave portion arranged in a bowl shape. 5.   4. The light emitting device according to claim 1, wherein the first concavo-convex structure is constituted by convex portions and concave portions arranged in a lattice pattern. 5.   4. The light emitting device according to claim 1, wherein the first concavo-convex structure includes convex portions and concave portions arranged in a staggered manner. 5. A substrate, a light-emitting layer that emits light by supplying current and has a first uneven structure on a surface, and a second uneven structure corresponding to the first uneven structure, is formed in contact with the light-emitting layer, and A light-emitting element array chip comprising a light-emitting element having a covering layer that transmits light emitted from a light-emitting layer, and a reflective layer that is formed between the substrate and the light-emitting layer and reflects light emitted from the light-emitting layer A plurality of light emitting element arrays arranged in the main scanning direction;
An optical element for imaging the light output of the light emitting element array;
A light-emitting element head comprising:   The light emitting element head according to claim 7, wherein the light emitting element array chip is a self-scanning light emitting element array chip. A substrate, a light-emitting layer that emits light by supplying current and has a first uneven structure on a surface, and a second uneven structure corresponding to the first uneven structure, is formed in contact with the light-emitting layer, and A light emitting element head comprising: a light emitting element having a coating layer that transmits light emitted from the light emitting layer; and a reflective layer that is formed between the substrate and the light emitting layer and reflects light emitted from the light emitting layer. Toner image forming means for forming a toner image;
Transfer means for transferring the toner image to a recording medium;
Fixing means for fixing the toner image on a recording medium;
An image forming apparatus comprising:

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