JP3722680B2 - LED array - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device, and more particularly to an LED array suitable for a printer used as an exposure light source for a photosensitive drum for a page printer.
[0002]
[Prior art]
Conventional LED arrays for printers are shown in FIGS.
3 is a cross-sectional view of one LED, FIG. 4 is a plan view of an LED array for a printer, and FIG. 5 is a plan view of another LED array for a printer.
[0003]
In the LED shown in FIG. 3, reference numeral 21 denotes a high-resistance silicon substrate, and a one-conductivity-type semiconductor layer 22 and a reverse-conductivity-type semiconductor layer 23 are sequentially stacked on the high-resistance silicon substrate 21. Reference numeral 24 is an individual electrode, 25 is a common electrode, and 26 is a protective film made of a silicon nitride film or the like.
[0004]
The reverse conductivity type semiconductor layer 23 is provided so as to have an area smaller than that of the one conductivity type semiconductor layer 22, and the common electrode 25 is connected to the exposed portion of the one conductivity type semiconductor layer 22. An individual electrode 24 is connected to the type semiconductor layer 23.
[0005]
Also, according to the printer LED array shown in FIG. 4, a plurality of LEDs (light emitting elements) having the above-described configuration are arranged, and two electrodes connected to the reverse conductivity type semiconductor layer 23 are connected to one pad. In summary, the number of pads is halved. The common electrode 25 (25a to 25d) is provided in two groups so as to belong to different groups for each adjacent light emitting element, and an electrode pad D is provided for this purpose. Two adjacent light emitting elements form one unit, and both are connected to the same individual electrode 24.
[0006]
In such an LED array, each light emitting element is made to emit light selectively by selecting a combination of the individual electrode 24 and the common electrode 25 (25a to 25d) and passing a current.
[0007]
Further, in the LED array for a printer shown in FIG. 5, the number of the conventional one-fourth is obtained by collecting the individual electrodes 24 connected on the reverse conductivity type semiconductor layer 3 into one electrode pad P with four lines. I have to. In addition, all the electrode pads P are arranged on one side of the LED array.
[0008]
The common electrodes 25 (25a to 25d) are provided by being divided into four groups so as to belong to different groups for each adjacent light emitting element, and an electrode pad D is provided for this purpose.
[0009]
In this LED array as well, each LED is selectively caused to emit light by selecting a combination of the individual electrode 24 and the common electrode 25 (25a to 25d) and passing a current in the same manner.
[0010]
[Problems to be solved by the invention]
However, according to the LED array for a printer as shown in FIG. 5, it is divided into the common electrodes 25a and 25c arranged on the inner side of the LED array and the common electrodes 25b and 25d arranged on the outer side. The contact position between the common electrode 25b and the one conductive type semiconductor layer 22 connected by the common electrode 25d is compared with the contact position of the one conductive type semiconductor layer 22 connected by the inner common electrodes 25a and 25c. Therefore, the distance from the reverse conductivity type semiconductor layer 23 is longer, and the current must flow through the one conductivity type semiconductor layer 22 for a longer distance. As a result, the drive voltage is increased.
[0011]
However, an IC for driving an LED (light emitting element) has a drawback that it cannot supply a constant current when a predetermined voltage value is exceeded, and the value also varies. Therefore, if the driving voltage of the light emitting element varies, There is a problem in that the supplied current varies and the light emission intensity varies between the light emitting elements due to this.
[0012]
Therefore, the present invention has been completed in view of the above description, and the object thereof is to make the emission intensity uniform between the light emitting elements by reducing or eliminating the variation in the driving voltage value among the light emitting elements. This provides a high quality LED array.
[0013]
Another object of the present invention is to provide an LED array suitable for a printer used as an exposure light source for a photosensitive drum for a page printer.
[0014]
[Means for Solving the Problems]
In the LED array of the present invention, a one-conductivity-type semiconductor layer, a reverse-conductivity-type semiconductor layer, and one electrode are sequentially stacked on a single crystal substrate, and the other electrode is formed on an extension portion that extends the one-conductivity-type semiconductor layer. A plurality of formed light emitting elements are arranged, and an electrode pad for commonly energizing each one electrode of these light emitting elements is provided to form a light emitting element group, and the plurality of light emitting element groups are arranged in an array. In addition, the electrode spacing to the other electrode in the extending portion of each light emitting element in one light emitting element group is different, and the electrode spacing is the same between the light emitting elements in the other light emitting element group. Each of the other electrodes is electrically connected to each other, and the width of the extending portion of the light emitting element is increased as the distance between the electrodes reaching the other electrode is increased.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to FIGS.
FIG. 1 is a schematic cross-sectional view of each LED (light emitting element) constituting the LED array of the present invention, and FIG. 2 is a plan view showing an embodiment of the LED array for a printer of the present invention.
[0016]
In the LED shown in FIG. 1, reference numeral 1 denotes a high-resistance silicon substrate, and a one-conductivity type semiconductor layer 2 and a reverse-conductivity type semiconductor layer 3 are sequentially stacked on the high-resistance silicon substrate 1. 4 is an individual electrode which is the one electrode, 5 is a common electrode which is the other electrode, 6 is a protective film made of a silicon nitride film or the like, and the individual electrode 4 and the common electrode 5 are regions where the protective film 6 is not covered. Formed.
[0017]
As described above, in the stacked configuration, the reverse conductivity type semiconductor layer 3 is provided so as to have a smaller area than the one conductivity type semiconductor layer 2, and the common electrode 5 is formed on the extended portion 7 where the one conductivity type semiconductor layer 2 is extended. Are connected.
[0018]
The high-resistance silicon substrate 1 is preferably composed of a high-resistance silicon single crystal, and a substrate with its (100) plane turned off by 2 to 7 ° in the <011> direction is particularly suitable.
[0019]
The one conductivity type semiconductor layer 2 includes a buffer layer 2a, an ohmic contact layer 2b, and an electron injection layer 2c.
[0020]
The buffer layer 2a is formed to a thickness of about 2 to 4 μm, the ohmic contact layer 2b is formed to a thickness of about 0.1 to 4 μm, and the electron injection layer 2c is formed to a thickness of about 0.2 to 4 μm.
[0021]
The buffer layer 2a and the ohmic contact layer 2b are formed of gallium arsenide or the like, and the electron injection layer 2c is formed of aluminum gallium arsenide or the like.
[0022]
The ohmic contact layer 2b contains about 1 × 10 ¹⁶ to 10 ¹⁹ atoms / cm ³ of one conductivity type semiconductor impurity such as silicon, and the electron injection layer 2c also contains 1 × 10 ¹⁶ to 10 ¹⁹ of one conductivity type semiconductor impurity such as silicon. Contains about atoms / cm ³ .
[0023]
The buffer layer 2a is provided in order to prevent misfit dislocation based on mismatch of lattice constant between the high resistance silicon substrate 1 and the semiconductor layer, and does not have to contain semiconductor impurities.
[0024]
The reverse conductivity type semiconductor layer 3 includes a light emitting layer 3a, a second cladding layer 3b, and a second ohmic contact layer 3c.
[0025]
The light emitting layer 3a and the second cladding layer 3b are formed to a thickness of about 0.2 to 4 μm, and the ohmic contact layer 3c is formed to a thickness of about 0.01 μm to 1 μm.
[0026]
The light emitting layer 3a and the second cladding layer 3b are made of aluminum gallium arsenide or the like, and the second ohmic contact layer 3c is made of gallium arsenide or the like.
[0027]
The light emitting layer 3a, the second cladding layer 3b, and the ohmic contact resistance reduction layer 3c have a mixed crystal ratio of aluminum arsenide (AlAs) and gallium arsenide (GaAs) in order to obtain an electron confinement effect and a light extraction effect. Make it different.
[0028]
The light emitting layer 3a and the second cladding layer 3b contain about 1 × 10 ¹⁶ to 10 ²¹ atoms / cm ³ of a reverse conductivity type semiconductor impurity such as zinc (Zn), and the second ohmic contact layer 3c is a reverse layer of zinc or the like. About 1 × 10 ¹⁹ to 10 ²¹ atoms / cm ^{3 of} conductive semiconductor impurities are contained.
[0029]
The protective film 6 is made of silicon nitride or the like and has a thickness of about 3000 mm.
[0030]
The individual electrode 4 and the common electrode 5 are made of gold / chromium (Au / Cr) or the like and are formed with a thickness of about 1 μm.
[0031]
In the LED array having the above configuration, four light emitting elements are arranged as shown in FIG. 2, and an electrode pad 8 for energizing these individual electrodes 4 in common is provided to form a light emitting element group. Light emitting element groups are arranged in an array.
[0032]
In the figure, the light-emitting element shown in FIG. 1 is shown with an overlapping structure of a rectangular one-conductive semiconductor layer 2 and a rectangular reverse-conductive semiconductor layer 3.
[0033]
The common electrode 5 is connected to the extending portion 7 of each reverse conductivity type semiconductor layer 3, and the connecting portion is shown as a contact portion in the drawing. In extending the common electrode 5 to other light emitting elements, the common electrode 5 may be formed over the protective film 6.
[0034]
In the light emitting element group, the electrode spacing S reaching the common electrode 5 in the extending portion 7 of the reverse conductivity type semiconductor layer 3 is different between the light emitting elements. The common electrodes 5 are electrically connected so that the electrode spacing S is the same between the light emitting elements of the other light emitting element group.
[0035]
Furthermore, in the present invention, as the electrode spacing S reaching the common electrode 5 in the extending portion 7 of the light emitting element becomes longer, the width is increased, thereby making the driving voltage for each light emitting element constant. That is, as the electrode spacing S increases, the electrical resistance increases and the driving voltage increases. However, by increasing the width of the electrode spacing S, the increase in electrical resistance is suppressed and the driving voltage decreases. An increase in the amount can also be suppressed.
(Method for manufacturing LED array for printer)
Next, the manufacturing method of the above LED array for printers is demonstrated.
[0036]
First, a one-conductivity-type semiconductor layer 2 and a reverse-conductivity-type semiconductor layer 3 are sequentially stacked on a high-resistance silicon substrate 1 made of a high-resistance silicon single crystal by MOCVD or the like.
[0037]
When these semiconductor layers 2 and 3 are formed, the substrate temperature is first set to 400 to 500 ° C., an amorphous gallium arsenide film is formed to a thickness of 200 to 2000 mm, and then the substrate temperature is set to 700 to 900 ° C. The semiconductor layers 2 and 3 having a desired thickness are formed.
[0038]
In this case, as source gases, TMG ((CH ₃ ) ₃ Ga), TEG ((C ₂ H ₅ ) ₃ Ga), arsine (AsH ₃ ), TMA ((CH ₃ ) ₃ Al), TEA ((C ₂ H ₅ ) ₃ Al) or the like is used, and silane (SiH ₄ ), hydrogen selenide (H ₂ Se), DMZ ((CH ₃ ) ₂ Zn) or the like is used as the gas for controlling the conductivity type. As the carrier gas, H ₂ or the like is used.
[0039]
Next, the semiconductor layers 2 and 3 are patterned in an island shape so that adjacent elements are electrically separated. This etching is performed by wet etching using a sulfuric acid hydrogen peroxide-based etching solution, dry etching using CCl ₂ F ₂ gas, or the like.
[0040]
Thereafter, the reverse conductivity semiconductor layer 3 is exposed to the one-conductivity-type semiconductor layer 2 so that a part of the one-conductivity-type semiconductor layer 2 on one end side is exposed and an adjacent region portion of the one-conductivity-type semiconductor layer 2 is exposed. The reverse conductivity type semiconductor layer 3 is etched so as to be formed narrower. This etching is also performed by wet etching using a sulfuric acid hydrogen peroxide-based etching solution or dry etching using CCl ₂ F ₂ gas.
[0041]
Thereafter, an insulating film made of silicon nitride is formed and patterned by plasma CVD using silane gas (SiH ₄ ) and ammonia gas (NH ₃ ).
[0042]
Finally, chromium and gold are formed by vapor deposition or sputtering and patterned.
[0043]
In addition, this invention is not limited to the said embodiment, A various change, improvement, etc. do not interfere in the range which does not deviate from the summary of this invention. For example, in this example, the light emitting element group is composed of four light emitting elements, but the number of light emitting elements may be five, six, or more.
[0044]
【The invention's effect】
As described above, according to the LED array of the present invention, the one-conductivity-type semiconductor layer, the reverse-conductivity-type semiconductor layer, and the one electrode are sequentially stacked on the single crystal substrate, and the one-conductivity-type semiconductor layer is extended. A plurality of light emitting elements each having the other electrode formed thereon are arranged, and an electrode pad for energizing each one of the light emitting elements in common is provided to form a light emitting element group. Are arranged in an array, and the electrode spacing to the other electrode in the extending portion of each light emitting element in one light emitting element group is different, and the electrode spacing between the light emitting elements in the other light emitting element group In the configuration in which the other electrodes are electrically connected so that they are the same, the width of the electrode extending to the other electrode in the extending portion of the light emitting element is increased to increase the width of each light emitting element. Drive between elements Or to reduce the variation in the pressure value, it can be eliminated, thereby, the emission intensity becomes uniform in between each light-emitting element, as a result, high-quality and high reliability of the LED array could be provided.
[0045]
Further, according to the present invention, since the light emission intensity is uniform between the light emitting elements, an LED array suitable for a printer used as an exposure light source for a photosensitive drum for a page printer can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a light emitting device constituting an LED array of the present invention.
FIG. 2 is a plan view showing an embodiment of the LED array of the present invention.
FIG. 3 is a schematic cross-sectional view of a light-emitting element forming a conventional LED array.
FIG. 4 is a plan view showing an embodiment of a conventional LED array.
FIG. 5 is a schematic cross-sectional view of a light emitting device forming another conventional LED array.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... High resistance silicon substrate 2 ... One conductivity type semiconductor layer 3 ... Reverse conductivity type semiconductor layer 4 ... Individual electrode 5 ... Common electrode 6 ... Protective film 7 ... Extension Part 8 ... Electrode pad

Claims (1)

A light-emitting element in which a one-conductivity-type semiconductor layer, a reverse-conductivity-type semiconductor layer, and one electrode are sequentially stacked on a single crystal substrate, and the other electrode is formed on an extended portion obtained by extending the one-conductivity-type semiconductor layer. A plurality of light emitting elements are arranged to form a light emitting element group by arranging an electrode pad for energizing each one of the light emitting elements in common, and the plurality of light emitting element groups are arranged in an array, and one light emitting element group The distance between the electrodes reaching the other electrode in the extending portion of each light emitting element is different, and the other electrode is electrically connected so that the electrode distance is the same between the light emitting elements of the other light emitting element group. An LED array connected to the LED array, wherein the width of the LED array is increased as the distance between the electrodes reaching the other electrode in the extending portion of the light emitting element is increased.

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