JP2013168581A - Light-emitting thyristor, light source head, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting thyristor that further suppresses drive voltage compared to the case not having a configuration of the present invention, a light source head, and an image forming apparatus.SOLUTION: In a light-emitting thyristor 100, an intermediate layer 112 having an Al composition x4 smaller than an Al composition x2 of a gate layer 110 is provided on the gate layer 110, and thereby a band gap of the intermediate layer 112 can be equal to or more than a band gap of a light-emitting layer 108, and less than a band gap of a second gate layer. Accordingly, a band gap of a diode junction area formed by the gate layer 110 and a cathode layer 114 is made smaller, and drive voltage can be suppressed.

Description

  The present invention relates to a light emitting thyristor, a light source head, and an image forming apparatus.

  In Patent Document 1, a second conductivity type semiconductor layer, a first conductivity type semiconductor layer, and a second conductivity type semiconductor layer are provided on a first conductivity type semiconductor substrate with or without a first conductivity type semiconductor layer interposed therebetween. In the light-emitting thyristor that is stacked in this order and configured to extract light generated inside the stacked semiconductor layers to the outside, the two second-conductivity-type semiconductor layers of the first-conductivity-type semiconductor layers. The impurity concentration of the first conductivity type semiconductor layer sandwiched between the semiconductor substrate is a high concentration on the opposite side of the semiconductor substrate and a low concentration on the semiconductor substrate side, and / or, among the second conductivity type semiconductor layers, The impurity concentration of the second conductivity type semiconductor layer sandwiched between two first conductivity type semiconductor layers or between the first conductivity type semiconductor layer and the first conductivity type semiconductor substrate is opposite to that of the semiconductor substrate. The side has a low concentration and the semiconductor It describes a light-emitting thyristor, wherein the substrate is a high concentration.

  In Patent Document 2, a first semiconductor layer of either N-type or P-type conductivity, a second semiconductor layer having a conductivity type opposite to the first semiconductor layer, and the same conductivity type as the first semiconductor layer are formed on a substrate. In the light emitting thyristor in which the third semiconductor layer and the fourth semiconductor layer having the opposite conductivity type to the first semiconductor layer are stacked in this order, the band gap of the third semiconductor layer is equal to the band gap of the second semiconductor layer. The third semiconductor layer is substantially the same and narrower than the band gap of the first and fourth semiconductor layers, and the third semiconductor layer includes a first region on the substrate side and a second region on the opposite side of the substrate. And the impurity concentration of the first region is lower than the impurity concentration of the second region, and the impurity concentration of the second semiconductor layer is equal to the impurity concentration of the first region of the third semiconductor layer. Approximately the same or higher concentration And the impurity concentration of the fourth semiconductor layer is substantially the same as or higher than the impurity concentration of the second region of the third semiconductor layer. A light-emitting thyristor is described.

JP 08-153890 A JP 2007-180460 A

  An object of the present invention is to provide a light-emitting thyristor, a light source head, and an image forming apparatus in which a drive voltage is suppressed as compared with a case where the present configuration is not provided.

  In order to achieve the above object, a light emitting thyristor according to the present invention includes a second conductive type first gate layer formed on a first conductive type anode layer, and a light emitting layer formed on the first gate layer. A second gate layer of the first conductivity type formed on the light emitting layer, and a band gap of the second gate layer formed on the second gate layer and having a band gap greater than or equal to the band gap of the light emitting layer. An intermediate layer that is less than the gap; and a cathode layer of the second conductivity type formed on the intermediate layer.

  In the light emitting thyristor of the present invention, the intermediate layer is of the first conductivity type.

  In the light-emitting thyristor of the present invention, the intermediate layer is the second conductivity type.

  In the light-emitting thyristor of the present invention, the cathode layer is provided in a partial region on the intermediate layer, and includes a gate electrode provided in a region on the intermediate layer where the cathode layer is not provided.

  In the light emitting thyristor according to the present invention, the intermediate layer is provided in a part of the region on the second gate layer, and the gate is provided in a region on the second gate layer where the intermediate layer is not provided. With electrodes.

  In the light emitting thyristor of the present invention, the cathode layer is provided in a partial region on the intermediate layer, the region where the cathode layer is not provided, and the region where the cathode layer is provided. A gate electrode provided on the intermediate layer having a thickness smaller than that of the intermediate layer.

  The light source head of the present invention includes a plurality of light emitting thyristors of the present invention as light sources.

  The light source head of the present invention includes a plurality of light emitting thyristors of the present invention, a transfer thyristor provided for each of the plurality of light emitting thyristors, a coupling diode for electrically coupling the transfer thyristors, and the light emitting thyristor. There are provided a plurality of chips each including a gate electrode and a gate resistor for connecting the gate electrode of the transfer thyristor corresponding to the light emitting thyristor to a reference potential.

  The image forming apparatus of the present invention includes a photosensitive member, a charging unit for charging the surface of the photosensitive member, and a light source head of the present invention, and forms an electrostatic latent image on the surface of the photosensitive member charged by the charging unit. In order to accomplish this, an exposure unit that exposes light emitted from the light source head, a developing unit that develops the electrostatic latent image formed by the exposure unit, and the electrostatic latent image developed by the developing unit are fixed. Fixing means.

  According to the first, second, seventh, eighth, and ninth aspects of the invention, the drive voltage can be suppressed as compared with the case where the present configuration is not provided.

  According to the third aspect of the present invention, the probability of light emission recombination in the intermediate layer is lower than when the intermediate layer and the cathode layer have different conductivity types.

  According to the fourth aspect of the present invention, the drive voltage can be further suppressed as compared with the case where this configuration is not provided.

  According to the fifth aspect of the present invention, control when etching the intermediate layer is facilitated as compared with the case where the present configuration is not provided.

  According to the sixth aspect of the present invention, an excellent ohmic contact is formed as compared with the case where no gate electrode is provided on the intermediate layer.

1 is a schematic configuration diagram showing an outline of an example of an image forming apparatus according to the present embodiment. It is a schematic sectional drawing which shows the internal structure of an example of the light source head which concerns on this Embodiment. It is a perspective view which shows the external appearance of an example of the semiconductor light-emitting element array which concerns on this Embodiment. It is a schematic diagram which shows an example of the chip | tip of this Embodiment. It is an equivalent circuit diagram which shows an example of the chip | tip of this Embodiment. It is sectional drawing which shows schematic structure of an example of the basic light emitting thyristor of this Embodiment. 3 is a cross-sectional view illustrating a schematic configuration of an example of a light-emitting thyristor according to Example 1. FIG. 4 is an explanatory diagram showing a specific example of the Al composition and film thickness of each layer of the light-emitting thyristor of Example 1. FIG. 6 is a cross-sectional view illustrating a schematic configuration of an example of a light-emitting thyristor of Example 2. FIG. 6 is an explanatory diagram showing a specific example of the Al composition and film thickness of each layer of the light-emitting thyristor of Example 2. FIG. 6 is a cross-sectional view illustrating a schematic configuration of an example of a light-emitting thyristor of Example 3. FIG. 6 is an explanatory diagram showing a specific example of the Al composition and film thickness of each layer of the light-emitting thyristor of Example 3. FIG. It is sectional drawing which shows schematic structure of an example of the conventional light emitting thyristor.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an outline of an example of an image forming apparatus according to the present embodiment. FIG. 2 is a schematic cross-sectional view showing the internal configuration of an example of the light source head of the present embodiment. FIG. 3 is a perspective view showing the appearance of an example of the light-emitting thyristor array according to the present embodiment.

  As shown in FIG. 1, the image forming apparatus 10 according to the present exemplary embodiment includes a photoconductor 12 that rotates at a constant speed in an arrow A direction.

  In order to form an electrostatic latent image on the surface of the photoconductor 12 around the photoconductor 12 along the rotation direction of the photoconductor 12, the charger 14 that charges the surface of the photoconductor 12 and the surface of the photoconductor 12 charged by the charger 14. A light source head 16 (exposure means) for exposing the toner image, a developing device 18 (developing means) for developing the electrostatic latent image with a developer to form a toner image, and transferring the toner image to a paper 28 (recording medium). A transfer body 20 (transfer means), a cleaner 22 for removing residual toner remaining on the photoconductor 12 after transfer, and an erase lamp 24 for discharging the photoconductor 12 to make the potential uniform are arranged in this order.

  That is, the surface of the photoconductor 12 is charged by the charger 14, and then a light beam is irradiated by the light source head 16 to form a latent image on the photoconductor 12. The light source head 16 is connected to a driving unit (not shown), and the lighting of the light emitting thyristor 100 is controlled by the driving unit to emit a light beam based on the image data.

  To the formed latent image, toner is supplied by the developing unit 18 to form a toner image on the photoreceptor 12. The toner image on the photoconductor 12 is transferred onto the conveyed paper 28 by the transfer body 20. The toner remaining on the photoconductor 12 after the transfer is removed by the cleaner 22, neutralized by the erase lamp 24, charged by the charger 14 again, and the same processing is repeated.

  On the other hand, the paper 28 onto which the toner image has been transferred is conveyed to a fixing device 30 (fixing means) composed of a pressure roller 30A and a heating roller 30B and subjected to a fixing process. As a result, the toner image is fixed and a desired image is formed on the paper 28. The paper 28 on which the image is formed is discharged out of the apparatus.

  Next, the configuration of the light source head 16 of the present embodiment will be described in detail. The light source head 16 of the present embodiment uses an SLED (Self-scanning LED). The SLED is obtained by integrating an LED array and a driving portion thereof, and includes a light emitting unit (light emitting thyristor 100, which will be described later in detail) having a plurality of thyristor structures. As shown in FIG. 2, a mounting board on which a light emitting thyristor array 50 and a circuit (not shown) for supporting the light emitting thyristor array 50 and supplying various signals for controlling the driving of the light emitting thyristor array 50 are mounted. 52 and a rod lens array 54 (Selfoc is a registered trademark of Nippon Sheet Glass Co., Ltd.) such as a Selfox lens array.

  The mounting substrate 52 is disposed in the housing 56 with the mounting surface of the light emitting thyristor array 50 facing the photoconductor 12 and is supported by a plate spring 58.

  As shown in FIG. 3, the light-emitting thyristor array 50 includes, for example, a chip 62 configured by arranging a plurality of light-emitting thyristors 100 along the axial direction of the photoconductor 12 according to the resolution in the axial direction. A plurality of light beams are arranged in series, and light beams are irradiated in the axial direction of the photosensitive member 12 with a predetermined resolution.

  In the present embodiment, an example in which a plurality of chips 62 are arranged in a one-dimensional manner in series is shown. However, the present invention is not limited to this, and the chips 62 may be arranged in a plurality of rows and arranged in a two-dimensional manner. For example, when arranged in a zigzag pattern, the plurality of chips 62 are arranged in a row so as to be aligned along the axial direction of the photoconductor 12 and are arranged in two rows with a certain interval in the direction intersecting the axial direction. Is done. Even if the light emitting thyristors 100 are divided into a plurality of chips 62, each of the light emitting thyristors 100 is arranged so that the distance between the two light emitting thyristors 100 adjacent to each other in the axial direction of the photoconductor 12 is substantially constant. ing.

  As shown in FIG. 2, the rod lens array 54 is supported by a holder 64 and forms an image of the light beam emitted from each light emitting thyristor 100 on the photoconductor 12.

  A schematic diagram of an example of the chip 62 is shown in FIG. Further, an equivalent circuit diagram of an example of the chip 62 is shown in FIG. On the chip 62, the light emitting thyristor 100, the transfer thyristor 70, the coupling diode 72 that electrically couples the transfer thyristors 70 of adjacent bits, the gate electrode of the light emitting thyristor 100, and the gate electrode of the transfer thyristor 70 are used as a reference. A gate resistor 74 connected to the potential line Vg is provided for each bit.

  The anode electrodes of the light emitting thyristor 100 and the transfer thyristor 70 are connected to the substrate on the chip 62. The gate electrode is connected to the reference potential line Vg through the gate resistor 74. The cathode electrode of the light emitting thyristor 100 is connected to the transfer signal line φI. On the other hand, in transfer thyristor 70, transfer thyristor 70 having a cathode electrode connected to transfer signal line φ1 and transfer thyristor 70 having a cathode electrode connected to transfer signal line φ2 are alternately arranged.

  Here, before describing the light-emitting thyristor 100 of this embodiment in detail, first, a conventional light-emitting thyristor will be described for comparison.

In a light emitting thyristor having a double hetero structure using an Al _x Ga _1-x As-based semiconductor layer, generally, the Al composition of a gate layer functioning as a barrier layer is made higher than that of the light emitting layer so that the band gap is larger than that of the light emitting layer. It is necessary to spread. FIG. 13 shows a schematic cross-sectional view of an example of a conventional light-emitting thyristor having such a double hetero structure. Here, as an example, a PNPN light-emitting thyristor is shown from the substrate side.

  A conventional light-emitting thyristor 1000 shown in FIG. 13 includes a p-type AlGaAs anode layer 1004, an n-type AlGaAs gate layer 1006, a light-emitting layer 1008, and a p-type AlGaAs gate on a p-type GaAs substrate 1002. A layer 1010, an n-type AlGaAs-based cathode layer 1014, and an n-type GaAs-based contact layer 1016 are sequentially stacked.

  A cathode electrode 1022 is formed on the contact layer 1016. A gate electrode 1020 is formed on the p-type gate layer 1010 from which a part of the cathode layer 1014 is removed and a part of the surface is exposed. An anode electrode 1018 is formed on the back surface of the substrate 1002 (the surface where the anode layer 1004 is not provided). Further, a protective layer 1024 provided in the emission region of the light emitting surface provided with the cathode electrode 1022 and the gate electrode 1020 is formed.

  As the Al composition x of the light emitting layer 1008, 0 <x <0.2, and as the Al composition x of the gate layer 1010 and the gate layer 1006, 0.2 <x <0.35 is used as a representative value. The greater the difference between the Al composition of the light emitting layer 1008 and the Al composition of the gate layer 1010 and the gate layer 1006, the greater the confinement of carriers in the light emitting layer 1008, and the higher the light output.

  In such a chip (see FIGS. 4 and 5 and chip 62) having the light emitting thyristor 1000 using the double hetero structure for the light emitting layer 1008, the Al composition of the p-type AlGaAs gate layer 1010 is increased as described above. In addition to an increase in the p-gate resistance, the operating voltage of the coupling diode 70 is increased. As the gate resistance 74 is increased and the operating voltage of the coupling diode 70 is increased, the driving voltage for operating the light emitting thyristor array 50 provided with the chip is increased.

  Next, the light-emitting thyristor 100 of this embodiment will be described in detail.

First, a schematic configuration of a basic light-emitting thyristor 100 according to the present embodiment will be described. FIG. 6 shows a cross-sectional view of a schematic configuration of an example of a basic light-emitting thyristor 100 of the present embodiment. Here, a case where the light emitting thyristor 100 is an Al _x Ga _1-x As-based PNPN type from the substrate side is shown.

  The light-emitting thyristor 100 according to the present embodiment has a light-emitting layer 108 having a double heterostructure, thereby enhancing the confinement of carriers (electrons and holes) and increasing the recombination probability of carriers, thereby increasing the light output. It is realized.

  The light emitting thyristor 100 includes a p-type GaAs substrate 102, a p-type AlGaAs anode layer 104, an n-type AlGaAs gate layer 106, an AlGaAs light-emitting layer 108, and a p-type AlGaAs gate layer 110. An AlGaAs intermediate layer 112, an n-type AlGaAs cathode layer 114, and a contact layer 116. The cathode layer 114 is laminated on a partial region of the surface of the gate layer 110 via the intermediate layer 112.

  The Al composition of the anode layer 104 is x1, the Al composition of the gate layer 106 and the gate layer 110 is x2, the Al composition of the light emitting layer 108 is x3, the Al composition of the intermediate layer 112 is x4, and the Al composition of the cathode layer 114 is x5. In this case, the following relationships (1) to (6) are satisfied. In addition, about the relationship of (5) and (6), although it is desirable to satisfy | fill the said relationship, it does not need to satisfy | fill.

0 <x3 <0.2 (1)
0.2 <x2 <0.35 (2)
x3 <x2 (3)
x3 ≦ x4 <x2 (4)
x1> x2 (5)
x5> x2 (6)
The light emitting thyristor 100 includes an anode electrode 118, a gate electrode 120, and a cathode electrode 122. The anode electrode 118 is provided on the back surface of the p-type GaAs substrate 102 (the surface on which the anode layer 104 is not formed). A part of the surface of the surface of the p-type AlGaAs gate layer 110 (a region where the cathode layer 114 is not provided) is exposed, and the gate electrode 120 is provided in the exposed region. In the light emitting thyristor 100 shown in FIG. 13, the gate electrode 120 is stacked on the gate layer 110 with the intermediate layer 112 interposed therebetween. On the other hand, the cathode electrode 122 is formed on the contact layer 116 provided on the cathode layer 114.

  As the materials for the anode electrode 118, the gate electrode 120, and the cathode electrode 122, materials suitable for maintaining good ohmic contact with the semiconductor layer or the p-type GaAs substrate 104 that are in contact with each other are used. Specific examples include gold (Au), an alloy of gold and germanium (AuGe), an alloy of gold and zinc (AuZn), nickel (Ni), and the like.

  In the light-emitting thyristor 100 according to the present embodiment, the n-type AlGaAs cathode layer 114 and the p-type AlGaAs anode layer 104 have large band gaps, and a signal (voltage) is applied to the gate electrode 120, and the gate electrode 120 By flowing a gate current to the electrode 122, the anode electrode 118 and the cathode electrode 122 are made conductive. As a result, carriers (electrons and holes) are recombined in the light emitting layer 108 having a smaller band gap than the n-type AlGaAs cathode layer 114 and the p-type AlGaAs anode layer 104, and the light emitted by the recombination is emitted. The light is emitted from the light emitting surface. Note that the wavelength of the emitted light is determined by the value of the band gap of the light emitting layer 108. In the case where the light emitting thyristor 100 of this embodiment is formed of an AlGaAs system, the band gap is increased as the Al composition x3 is increased, and the Al composition x3 is 0.12 to 0. The light having a wavelength of about .13 and a peak in the vicinity of 780 nm can be obtained.

  In the light-emitting thyristor 100 according to the present embodiment, a protective film 124 is provided in a region where light on the light-emitting surface is emitted (region outside the region where the cathode electrode 122 and the gate electrode 120 are formed). The protective film 124 is an antireflection film having a function of preventing light reflection. Examples of the protective film 124 include SiNx, for example.

  As in the light-emitting thyristor 100 of this embodiment, an intermediate layer 112 having an Al composition x4 smaller than the Al composition x2 of the gate layer 110 is provided on the gate layer 110, thereby forming the gate layer 110 and the cathode layer 114. The band gap of the diode junction region is reduced. Along with this, the carrier diffusion potential also decreases. When the diffusion potential is thus reduced, the threshold voltage at which an effective current flows in the diode (light emitting thyristor 100) is lowered, and as a result, the driving voltage of the diode (light emitting thyristor 100) is suppressed.

  In the light emitting thyristor 100 of this embodiment, the gate electrode 120 is formed on the intermediate layer 112. Since the intermediate layer 112 has a small Al composition x4 as described above, a good ohmic contact is formed when the gate electrode 120 is formed. Therefore, the contact resistance at the contact portion is smaller than that of the conventional light emitting thyristor 1000 (see FIG. 13).

  Therefore, as described above, in the light-emitting thyristor array 50 including the chip 62 using the light-emitting thyristor 100, the light-emitting thyristor array 50 is controlled in order to suppress the increase in the gate resistance 74 and the operating voltage of the coupling diode 70. The drive voltage is suppressed from increasing.

  Next, a specific example of the light emitting thyristor 100 of the present embodiment will be described. Note that description of the configuration and operation common to the embodiments may be omitted.

Example 1
A light-emitting thyristor 100 in which an intermediate layer 112 is provided above the gate layer 110 and below the cathode layer 114 is shown.

  FIG. 7 shows a cross-sectional view of a schematic configuration of an example of a basic light-emitting thyristor 100 of the present embodiment. FIG. 8 shows a specific example of the Al composition and film thickness of each layer of the light emitting thyristor 100 of this embodiment. In the light emitting thyristor 100 of this embodiment, as an example, Zn is used as a dopant in the case of p-type, and Si is used as a dopant in the case of n-type.

  A p-type AlGaAs anode layer 104 having an Al composition x1 of 0.35 and a film thickness of 0.500 μm is formed on a p-type GaAs substrate 102. On the anode layer 104, an n-type AlGaAs-based gate layer 106 having an Al composition x2 of 0.30 and a film thickness of 0.282 μm, and non-doped light emission having an Al composition x3 of 0.15 and a film thickness of 0.109 μm. A layer 108 and a p-type AlGaAs-based gate layer 110 having an Al composition x2 of 0.30 and a thickness of 0.335 μm are sequentially stacked.

  A p-type AlGaAs intermediate layer 112 having an Al composition x4 of 0.15 and a film thickness of 0.065 μm is formed on a partial region of the gate layer 110. On the intermediate layer 112, the Al composition x5 is An n-type AlGaAs cathode layer 114 having a thickness of 0.35 and a thickness of 0.500 μm and an n-type GaAs contact layer 116 having a thickness of 0.025 μm are sequentially formed.

  In the light emitting thyristor 100 of this embodiment, an anode electrode 118 is provided on the back surface of the substrate 102, and a cathode electrode 122 is provided on the contact layer 116.

  Furthermore, in the light emitting thyristor 100 of this embodiment, the gate electrode 120 is formed in a region on the gate layer 110 where the intermediate layer 112 is not provided. In order to form the gate electrode 120 in this way, first, an intermediate layer 112, an n-type AlGaAs-based cathode layer 114, and a contact layer 116 are sequentially formed on the gate layer 110. Thereafter, the contact layer 116, the n-type AlGaAs cathode layer 114, and a part of the intermediate layer 112 are removed by etching to the surface of the gate layer 110, and the gate electrode 120 is formed on the exposed surface of the gate layer 110. . For crystal growth of each layer of the light-emitting thyristor 100, for example, a MOCVD (Metal Organic Chemical Vapor Deposition) method is applied.

  Carriers (electrons) injected as fractional carriers from the n-type AlGaAs-based gate layer 106 move to the light emitting layer 108. Also, carriers (holes) injected as fractional carriers from the p-type AlGaAs-based gate layer 110 move. In the light emitting layer 108, the moved electrons and holes recombine with each other.

  Also in the light emitting thyristor 100 of this embodiment, the intermediate layer 112 having an Al composition x4 smaller than the Al composition x2 of the gate layer 110 is provided on the gate layer 110, thereby forming the gate layer 110 and the cathode layer 114. The band gap of the diode junction region is reduced. Therefore, the drive voltage is suppressed as described above.

  In the light emitting thyristor 100 of this embodiment, the gate electrode 120 is formed on the gate layer 110 without the intermediate layer 112 as described above. Since the intermediate layer 112 is thinner than the other layers, it may be difficult to control the etching to stop in the intermediate layer 112 immediately above the intermediate layer 112. On the other hand, the etching control is facilitated by removing all the intermediate layer 112 as in this embodiment.

(Example 2)
A light-emitting thyristor 100 in which an intermediate layer 112 is provided on the gate layer 110 and etched to a middle portion of the intermediate layer 112 and a gate electrode 120 is formed is shown.

  FIG. 9 shows a cross-sectional view of a schematic configuration of an example of a basic light-emitting thyristor 100 of the present embodiment. FIG. 10 shows a specific example of the Al composition and film thickness of each layer of the light-emitting thyristor 100 of this embodiment.

  A p-type AlGaAs anode layer 104 having an Al composition x1 of 0.35 and a film thickness of 0.500 μm is formed on a p-type GaAs substrate 102. On the anode layer 104, an n-type AlGaAs-based gate layer 106 having an Al composition x2 of 0.30 and a film thickness of 0.282 μm, and non-doped light emission having an Al composition x3 of 0.15 and a film thickness of 0.109 μm. A layer 108 and a p-type AlGaAs-based gate layer 110 having an Al composition x2 of 0.30 and a film thickness of 0.300 μm are sequentially stacked.

  A p-type AlGaAs-based intermediate layer 112 having an Al composition x4 of 0.15 is formed on the gate layer 110. The thickness of the intermediate layer 112 is different between the region where the n-type AlGaAs cathode layer 114 (cathode electrode 122) is formed and the region where the gate electrode 120 is formed. On the intermediate layer 112 having a thickness of 0.095 μm, an n-type AlGaAs cathode layer 114 having an Al composition x5 of 0.35 and a thickness of 0.500 μm, and an n-type GaAs system having a thickness of 0.025 μm. A contact layer 116 is sequentially formed. A cathode electrode 122 is formed on the contact layer 116.

  Further, in the light emitting thyristor 100 of this embodiment, the gate electrode 120 is formed in a region on the intermediate layer 112 whose film thickness is thinner than the region where the cathode layer 114 is formed. In order to form the gate electrode 120 as in this embodiment, first, the intermediate layer 112, the n-type AlGaAs-based cathode layer 114, and the contact layer 116 are sequentially formed on the gate layer 110. Thereafter, the contact layer 116, the n-type AlGaAs-based cathode layer 114, and a part of the intermediate layer 112 are removed to the middle of the intermediate layer 112 by etching. Then, the gate electrode 120 is formed on the intermediate layer 112. In order to stop the etching in the intermediate layer 112 in this way, the thickness of the intermediate layer 112 is made larger than that in the first embodiment. Further, how far etching is performed (how the film thickness of the intermediate layer 112 under the gate electrode 120 is made) is determined from the viewpoint of control of etching and driving voltage.

  Also in the light emitting thyristor 100 of this embodiment, the intermediate layer 112 having an Al composition x4 smaller than the Al composition x2 of the gate layer 110 is provided on the gate layer 110, thereby forming the gate layer 110 and the cathode layer 114. The band gap of the diode junction region is reduced. Therefore, the drive voltage is suppressed as described above.

  Further, in the light emitting thyristor 100 of this example, since the gate electrode 120 is provided on the intermediate layer 112 having a small Al composition x4 as described above, a good ohmic contact is formed. Therefore, contact resistance at the contact portion is suppressed. Therefore, as described above, the driving voltage of the light emitting thyristor array 50 as a whole can be suppressed.

(Example 3)
The light-emitting thyristor 100 in which an intermediate layer 112 is provided over the gate layer 110 and the intermediate layer 112 is formed as part of the cathode layer 114 is shown.

  FIG. 11 shows a cross-sectional view of a schematic configuration of an example of a basic light-emitting thyristor 100 of the present embodiment. FIG. 12 shows a specific example of the Al composition and film thickness of each layer of the light-emitting thyristor 100 of this embodiment.

  A p-type AlGaAs anode layer 104 having an Al composition x1 of 0.35 and a film thickness of 0.500 μm is formed on a p-type GaAs substrate 102. On the anode layer 104, an n-type AlGaAs-based gate layer 106 having an Al composition x2 of 0.30 and a film thickness of 0.282 μm, and non-doped light emission having an Al composition x3 of 0.15 and a film thickness of 0.109 μm. A layer 108 and a p-type AlGaAs-based gate layer 110 having an Al composition x2 of 0.30 and a thickness of 0.330 μm are sequentially stacked.

  An n-type AlGaAs-based intermediate layer 112 having an Al composition x4 of 0.15 and a film thickness of 0.065 μm is formed on a partial region of the gate layer 110, and the Al composition x5 is formed on the intermediate layer 112. An n-type AlGaAs cathode layer 114 having a thickness of 0.35 and a thickness of 0.500 μm and an n-type GaAs contact layer 116 having a thickness of 0.025 μm are sequentially formed. A cathode electrode 122 is provided on the contact layer 116.

  Furthermore, in the light emitting thyristor 100 of this embodiment, the gate electrode 120 is formed in a region on the gate layer 110 where the intermediate layer 112 is not provided.

  In the light emitting thyristor 100 of this embodiment, the intermediate layer 112 is formed as a part of the cathode layer 114. Specifically, the intermediate layer 112 and the cathode layer 114 are formed to have the same conductivity type. Since the intermediate layer 112 has a small band gap, emission recombination occurs when carriers are confined in the intermediate layer 112. However, since the intermediate layer 112 is close to the cathode electrode 122, light emitted from the intermediate layer 112 has many components that are shielded from light by the cathode electrode 122, and the light extraction efficiency is low. If the intermediate layer 112 has the same conductivity type as the cathode layer 114 (n-type in this embodiment), carriers (electrons in this embodiment) are difficult to confine. Therefore, the probability of light emission recombination in the intermediate layer 112 is reduced, and invalid light emission is suppressed.

  As described above, in the light emitting thyristor 100, the intermediate layer 112 having the Al composition x 4 smaller than the Al composition x 2 of the gate layer 110 is provided on the gate layer 110 in the light emitting thyristor 100. The band gap is greater than or equal to the band gap of the light emitting layer 108 and less than the band gap of the second gate layer. Thereby, the band gap of the junction region of the diode formed by the gate layer 110 and the cathode layer 114 is reduced. Therefore, the drive voltage is suppressed as described above.

  It should be noted that each of the above embodiments and examples is an example of the present invention, which may be combined, and can be changed according to the situation without departing from the gist of the present invention. Absent.

  For example, the light emitting layer 106 may be non-doped, p-type, or n-type as shown in the above embodiments and examples. Note that holes are less p-type or non-doped because they have a lower mobility than electrons and thus have a small spatial expansion (expansion in the thickness direction and in-plane direction of the layer) and high luminous efficiency.

  The light-emitting thyristor 100 may be a PNPN type or an NPNP type as described above.

  In this embodiment, the light emitting thyristor 100 using an AlGaAs-based material has been described as a specific example. However, the present invention is not limited to this, and the present invention is not limited to this. You may apply to.

  Further, in the present embodiment, the case where it is applied to the light source head 16 of the self-scanning electrophotographic image forming apparatus 10 has been described. However, the present invention is not limited to this, and the light emitting thyristor 100 of the present embodiment is used as another light source head. And may be applied to other image forming apparatuses. Further, the light emitting thyristor 100 may be applied to a light source of another device such as a scanner.

10 Image forming apparatus 16 Light source head 62 Chip 70 Transfer thyristor 72 Coupling diode 74 Gate resistor 100 Semiconductor light emitting element 104 Anode layer 106 Gate layer 108 Light emitting layer 110 Gate layer 112 Intermediate layer 114 Cathode layer

Claims (9)

A first gate layer of the second conductivity type formed on the anode layer of the first conductivity type;
A light emitting layer formed on the first gate layer;
A second gate layer of a first conductivity type formed on the light emitting layer;
An intermediate layer formed on the second gate layer, the band gap being equal to or greater than the band gap of the light emitting layer and less than the band gap of the second gate layer;
A cathode layer of the second conductivity type formed on the intermediate layer;
Light-emitting thyristor with   The light emitting thyristor according to claim 1, wherein the intermediate layer is of the first conductivity type.   The light-emitting thyristor according to claim 1, wherein the intermediate layer is of the second conductivity type. The cathode layer is provided in a partial region on the intermediate layer, and includes a gate electrode provided in a region on the intermediate layer where the cathode layer is not provided.
The light emitting thyristor according to any one of claims 1 to 3. The intermediate layer is provided in a part of the region on the second gate layer, and includes a gate electrode provided in a region on the second gate layer where the intermediate layer is not provided.
The light emitting thyristor according to any one of claims 1 to 3. The cathode layer is provided in a partial region on the intermediate layer, is a region where the cathode layer is not provided, and is a film than the intermediate layer below the region where the cathode layer is provided. A gate electrode provided on the intermediate layer having a small thickness;
The light emitting thyristor according to any one of claims 1 to 3.   A light source head comprising a plurality of light-emitting thyristors according to any one of claims 1 to 6 as a light source. A plurality of light-emitting thyristors according to any one of claims 1 to 6;
A transfer thyristor provided in accordance with each of the plurality of light emitting thyristors;
A coupling diode for electrically coupling the transfer thyristors;
A gate resistor for connecting the gate electrode of the light emitting thyristor and the gate electrode of the transfer thyristor corresponding to the light emitting thyristor to a reference potential;
A light source head comprising a plurality of chips each having A photoreceptor,
Charging means for charging the surface of the photoreceptor;
An exposure means comprising the light source head according to claim 7 or claim 8, and exposing with light emitted from the light source head to form an electrostatic latent image on the surface of the photoreceptor charged by the charging means. When,
Developing means for developing the electrostatic latent image formed by the exposure means;
Fixing means for fixing the electrostatic latent image developed by the developing means;
An image forming apparatus.