JP2007250961A - Light-emitting element array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting element array capable of preventing flow of a current from an upper electrode to an immediate below portion and ensuring conduction between a substrate electrode and a light emitting element without allowing a semiconductor multilayer mirror to employ an embedding structure requiring re-growth of an epitaxial layer. <P>SOLUTION: A reflection layer 25, a p-type first layer 24, an n-type second layer 23, a p-type third layer 22 and an n-type fourth layer 21 are successively formed on a p-type substrate 51. A cathode electrode 36 is formed on the fourth layer 21, a gate electrode 37 is formed on the third layer 22 partially exposed by etching, and a short circuit electrode 63 connects the fourth layer 24 partially exposed by etching to the substrate 51 exposed by etching. A rear surface common electrode 53 is formed on the rear surface of the substrate 51. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention provides a light emitting element array, particularly a light emitting element having a common electrode on the back surface and taking out light from the upper surface, and the current density flowing directly under the upper electrode is the highest, and the light emission intensity here is the highest. Nevertheless, there is a problem that light cannot be extracted because it is blocked by the electrodes. To solve this problem, the flow path of the current flowing directly under the upper electrode is changed by inserting an insulating film (or high resistance film) between the light emitting layer and the conductive substrate or by providing a pn junction. Attempts have been made to increase the proportion of light emission in the parts not blocked by the electrodes.

  Further, in the light emitting diode (LED), since light is emitted in a random direction, the light emitted to the substrate side is absorbed by the substrate and cannot be extracted from the upper surface. In order to solve this problem, an attempt has been made to provide a mirror formed of a semiconductor multilayer film structure between a light emitting layer and a conductive substrate, reflect light emitted to the substrate side, and extract it from the upper side.

In order to obtain a high reflectance with a small number of layers in a semiconductor multilayer mirror, it is necessary to increase the refractive index difference of the semiconductor multilayer film, and considering the case where the semiconductor multilayer film is composed of Al _x Ga _1-X As, Since the refractive index decreases as x increases, it is necessary to increase x in the low refractive index layer in order to increase the difference in refractive index. However, when x increases, the dopant activation rate decreases and the series resistance increases. On the other hand, if x is made small to increase the refractive index of the high refractive index layer, for example, a composition near 0 is used, the band offset at the heterojunction interface becomes large, and the series resistance also increases. In particular, in the case of a self-scanning light-emitting element array, an increase in series resistance causes an increase in operating voltage, so it is necessary to minimize it.

  The self-scanning light-emitting element array is a light-emitting element array proposed by the present applicant using a light-emitting thyristor having a pnpn structure (Japanese Patent No. 2744504, Japanese Patent No. 2758857, etc.). The light-emitting unit thyristors corresponding to are sequentially emitted.

  In addition, a method has been proposed in which the insulating film, the pn junction, and the reflective film are formed in a buried structure. For this purpose, it is necessary to perform epitaxial growth once again on the substrate once patterned, which complicates the process.

The object of the present invention is to prevent the current from flowing directly from the upper electrode to the semiconductor multilayer mirror without taking a buried structure that requires the regrowth of the epitaxial layer, and to ensure conduction between the substrate electrode and the light emitting element. An object of the present invention is to provide a light emitting element array that can be used.
Another object of the present invention is to provide an optical writing head using such a light emitting element array.
Still another object of the present invention is to provide a printer, a facsimile machine, and a copying machine using such an optical writing head.

  According to the light-emitting element array of the present invention, an insulating layer, a high-resistance layer, or a semiconductor multilayer mirror is continuously grown in advance between the light-emitting layer and the conductive substrate, and the insulating layer, the high-resistance layer, or The upper and lower layers of the semiconductor multilayer mirror are short-circuited by ohmic electrodes.

Since the current flows toward the ohmic electrode, the position where the current density is maximum in the light emitting area is shifted from directly below the electrode toward the ohmic electrode. Therefore, light can be extracted without being blocked by the electrodes. In addition, when the multilayer mirror is provided, light traveling toward the conductive substrate is reflected, so that the light extraction efficiency is further increased.
In addition, since a conductive substrate having a low resistivity can be used as the common electrode, in this case, it is not necessary to form a low-resistance metal wiring for the common electrode on the chip surface side, so that the chip width can be reduced.
According to a first aspect of the surface-emitting light-emitting element array of the present invention, a first conductive type conductive substrate and an insulating layer, a high resistance layer, or a conductive layer formed on the first conductive type conductive substrate are provided. A semiconductor multilayer mirror; a first first conductivity type semiconductor layer formed on the insulating layer, a high resistance layer, or the semiconductor multilayer film mirror; and the first first conductivity type semiconductor layer. A plurality of light-emitting elements each including a first electrode formed on the substrate and an ohmic electrode that short-circuits between the first conductive type conductive substrate and the first first conductive type semiconductor layer. The light emitting elements are separated by mesa etching.
According to a second aspect of the surface-emitting light-emitting element array of the present invention, there is provided a first conductive type conductive substrate and an insulating layer, a high resistance layer, or a conductive layer formed on the first conductive type conductive substrate. A semiconductor multilayer mirror; a first second-conductivity-type semiconductor layer formed on the insulating layer, the high-resistance layer, or the semiconductor multilayer-film mirror; a first first-conductivity-type semiconductor layer; Two second conductivity type semiconductor layers, a second first conductivity type semiconductor layer, a first electrode formed on the second first conductivity type semiconductor layer, and the first A second electrode formed on a back surface of a conductive substrate of a conductive type, and an ohmic electrode that short-circuits between the first conductive substrate of the first conductive type and the first second conductive semiconductor layer. A plurality of light emitting elements provided are arranged, and the light emitting elements are separated by mesa etching.
In the structure as described above, the position where the current density in the light emitting area of the light emitting element is maximized is not hidden by the first electrode.
The light emitting element array of the present invention can also be applied to a self-scanning light emitting element array having a pnpn structure.
Furthermore, a printer, a facsimile machine, and a copier using an optical writing head using the light emitting element array of the present invention can be realized.

According to the light emitting element array of the present invention, it is possible to further increase the light extraction efficiency by shifting the light emitting area and further using a multilayer mirror. Further, since the insulating layer, the high resistance layer, or the semiconductor multilayer mirror is not a buried structure, the process can be simplified.
A printer, a facsimile machine, and a copying machine can be provided by using an optical writing head using such a light emitting element array.

  Embodiments of the present invention will be described below with reference to the drawings.

  A sectional view of a single light-emitting thyristor of the first embodiment is shown in FIG. Here, the pnpn structure of GaAs grown on a p-GaAs substrate by metal organic chemical vapor deposition (MOCVD) will be described as an example, where p is the first conductivity type and n is the second conductivity type. In this pnpn structure, the same effect can be obtained when the first conductivity type is n and the second conductivity type is p.

  On the p-type substrate 51, a reflective layer 25, a p-type first layer 24, an n-type second layer 23, a p-type third layer 22, and an n-type fourth layer 21 are sequentially formed.

A cathode electrode 36 is formed on the fourth layer 21, a gate electrode 37 is formed on the third layer 22 that is partially exposed by etching, and the fourth layer 24 that is partially exposed by etching is etched. The exposed substrate 51 is connected with a short-circuit electrode 63. A back surface common electrode 53 is formed on the back surface of the substrate 51. Each electrode is formed so as to be in ohmic contact with each formed layer. Specifically, p-type semiconductor layer / AuZn / Au was used as the p-type electrode, and n-type semiconductor layer / AuGe / Ni / Au was used as the n-type electrode.
These structures are covered with a SiO ₂ protective film 61, and an aluminum wiring 62 is formed thereon. The aluminum wiring and the gold electrode are connected via a contact hole.

In the above configuration, as the reflection layer 25, non-doped AlAs (n = 2.97) and Al _0.1 Ga _0.9 As (n = 3.52) were used. When the emission wavelength is 780 nm, the respective layer thicknesses are 65.7 nm and 55.4 nm. Here, 8 pairs of these two layers were grown to obtain a reflectance of about 84%. Although the reflection layer 25 is non-doped, by doping it n-type, a pn junction is formed between the reflection layer 25 and the p-type layer 24, and current flowing to the substrate side can be blocked. Even with p-type doping, the series resistance of the reflective layer 25 needs to be sufficiently high so that the current passing through the short-circuit electrode 63 is larger than the current passing through the reflective layer 25. In the figure, a current flowing from the cathode electrode 36 to the short-circuit electrode 63 is indicated by a broken line arrow.
Since the current flows from the electrode 36 toward the short-circuit electrode 63, the light emitting area shifts from directly below the electrode. Therefore, the light output increases without being blocked by the electrode 36.

Next, a manufacturing process of the light-emitting thyristor of FIG. 1 will be described with reference to FIGS. 2A to 2H.
First, as shown in FIG. 2A, on a p-type GaAs substrate 51, a reflective layer 25, a p-type first layer 24, an n-type second layer 23, a p-type third layer 22, and an n-type fourth layer. Layer 21 is deposited by MOCVD.

Next, as shown in FIG. 2B, a cathode electrode 36 which is a current supply electrode is formed by lift-off. The electrodes are formed in the order of AuGe, Ni, and Au by vacuum deposition.
Next, as shown in FIG. 2C, the n-type fourth layer 21 is removed by etching, and a gate electrode 37 is formed by lift-off. The electrodes are formed in the order of AuZn and Au by vacuum deposition.

Next, as shown in FIG. 2D, a part of the n-type second layer 23 and the p-type third layer 22 is removed by etching, and a part of the p-type first layer 24 is exposed.
Subsequently, as shown in FIG. 2E, a part of the reflective layer 25 and the p-type first layer 24 is removed by etching, and a part of the p-type substrate 51 is exposed.

  Next, as shown in FIG. 2F, the short-circuit electrode 63 is formed by lift-off. The short-circuit electrode is formed in the order of AuZn and Au by vacuum deposition. Subsequently, the back electrode 53 is formed by vacuum deposition. Thereafter, each electrode is brought into ohmic contact by annealing.

Next, as shown in FIG. 2G, a protective film 61 is formed.
Finally, as shown in FIG. 2H, contact holes were opened, an aluminum film was formed by sputtering, and the aluminum wiring 62 was patterned by wet etching.

  2A to 2H schematically show a manufacturing process of a single light-emitting thyristor. The structure of an actual self-scanning light emitting element array using such a light emitting thyristor is shown in FIG. 4A and 4B are sectional views taken along lines AA ′ and BB ′ in FIG. FIG. 5 shows an equivalent circuit corresponding to FIG.

In the equivalent circuit of FIG. 5, 10 is a shift unit composed of a resistor 82, a coupling diode D, light emitting thyristors T ₁ , T ₂ , T ₃ ,..., 12 is a light emitting thyristor L ₁ , L ₂ , L ₃ ,... Are shown.
3, 4A, 4B, and 5, reference numerals 71 to 74 denote aluminum wirings, and 81 denotes a resistance. Reference numeral 84 denotes a thyristor island, on which a coupling diode island 86, a shift thyristor island 88, and a light emitting thyristor island 91 are provided. Each of the islands 86, 88, and 91 is a place where the n-type fourth layer 21 is left. Conversely, except for this part of the thyristor island, the n-type fourth layer 21 is removed by etching, and the p-type third layer is removed. The layer 22 is the uppermost layer as a semiconductor. On each island 86, 89, 91, n-type ohmic electrodes 87, 89, 90 are formed. On the other hand, a gate electrode 85 is formed on the thyristor island 84 and the p-type third layer 22.

The shift portion thyristor island 88 is electrically separated by an etching groove reaching the p-type first layer 24. 63 is a short-circuit electrode, which short-circuits between the p-type first layer 24 and the p-type substrate 51. Here, reference numeral 110 denotes a boundary line for removing the p-type first layer 24 and the mirror layer 25 by etching, and the p-type substrate 51 is exposed at a portion below the boundary line 110 in the drawing. An exposed portion is indicated by 101. The reason why the exposed portion 101 is crank-shaped is that a forward mesa / reverse mesa may appear depending on the etched surface, and the electrode is prevented from being disconnected when the reverse mesa is exceeded.
Each electrode is connected to aluminum wiring through a contact hole.

  FIG. 6 shows an example of the current-light output characteristics of the prototype self-scanning light emitting element array. In the figure, a solid line indicates a case with a mirror structure, and a broken line indicates a case without a mirror structure. When a current of 10 mA was applied, the light output was about 85 μW without the conventional mirror structure, but 270 μW with the mirror structure, which was about 3.2 times that of the conventional one. This is considered to be that the effect of reflection by the mirror is about 1.8 times, and the effect that the light emitting area is shifted from directly below the electrode is about 1.8 times.

In the first embodiment, light reflected toward the substrate is reflected by the mirror structure 25, and the current flowing directly under the electrode is blocked by utilizing the high series resistance of the mirror structure 25, thereby increasing the light extraction efficiency. Yes. However, since these two effects are independent, a high resistance layer may be inserted in place of the mirror structure 25 when the former effect is not expected. Here, non-doped Al _0.5 Ga _0.5 As having a thickness of 0.2 μm was inserted. As a result, 1.8 times the light output expected from the current blocking effect was obtained. Although the high resistance layer is inserted here, for example, the second conductivity type layer may be inserted to block the current by pn junction.

  The self-scanning light emitting element array as described above is linearly arranged and used for an optical writing head of an optical printer. FIG. 7 shows an example of an optical writing head using the light emitting element array of the present invention. A plurality of light emitting element array chips 71 in which light emitting elements are arranged in a row are mounted on the chip mounting substrate 70 in the main scanning direction, and on the optical path of light emitted from the light emitting elements of the light emitting element array chip 71. An erecting equal-magnification rod lens array 72 that is long in the main scanning direction is fixed by a resin housing 73. A photosensitive drum 74 is provided on the rod lens array 72. Further, a heat sink 75 for releasing heat of the light emitting element array chip 71 is provided on the base of the chip mounting substrate 70, and the housing 73 and the heat sink 75 are fixed by a fastener 76 with the chip mounting substrate 70 interposed therebetween. ing.

  An optical printer using such an optical writing head is shown in FIG. An optical writing head 100 is installed in the optical printer. A photoconductive material (photosensitive member) such as amorphous Si is formed on the surface of the cylindrical photosensitive drum 102. This drum rotates at the speed of printing. The surface of the photosensitive drum of the rotating drum is uniformly charged by the charger 104. Then, the optical writing head 100 irradiates the photosensitive member with the light of the dot image to be printed, neutralizes the charge where the light hits, and forms a latent image. Subsequently, the developing device 106 applies toner to the photoconductor according to the charged state on the photoconductor. The transfer device 108 transfers the toner onto the paper 112 sent from the cassette 110. The sheet is heated and fixed by the fixing device 114 and sent to the stacker 116. On the other hand, the drum that has been transferred is neutralized by the erasing lamp 118 over the entire surface, and the remaining toner is removed by the cleaner 120.

  Such an optical writing head can be used not only for a printer but also for a facsimile machine and a copying machine. FIG. 9 shows the basic structure of a facsimile or copying machine. The same constituent elements as those in FIG. 8 are denoted by the same reference numerals. Light is emitted from the light source 124 to the read original 122 conveyed by the paper feed roller 130, and the reflected light is received by the image sensor 128 through the imaging lens 126. Based on the output of the image sensor 128, the light emitting element array 132 of the optical writing head 100 is turned on and irradiated to the photosensitive drum 102 through the rod lens array 134. Printing on the paper 112 is as described for the optical printer.

It is a figure which shows sectional drawing of the single light emitting thyristor which is a 1st Example. It is sectional drawing which shows the manufacturing process of the light emitting thyristor of FIG. It is sectional drawing which shows the manufacturing process of the light emitting thyristor of FIG. It is sectional drawing which shows the manufacturing process of the light emitting thyristor of FIG. It is sectional drawing which shows the manufacturing process of the light emitting thyristor of FIG. It is sectional drawing which shows the manufacturing process of the light emitting thyristor of FIG. It is sectional drawing which shows the manufacturing process of the light emitting thyristor of FIG. It is sectional drawing which shows the manufacturing process of the light emitting thyristor of FIG. It is sectional drawing which shows the manufacturing process of the light emitting thyristor of FIG. It is a figure which shows the structure of a self-scanning light emitting element array. FIG. 4 is a cross-sectional view taken along line AA ′ in FIG. 3. FIG. 4 is a sectional view taken along line BB ′ in FIG. 3. It is an equivalent circuit diagram of a self-scanning light emitting element. It is a graph which shows the electric current-light output characteristic of a self-scanning light emitting element array. It is a figure which shows the structure of an optical writing head. It is a figure which shows the structure of the optical printer using the optical writing head using a self-scanning light emitting element array. It is a figure which shows the basic structure of a facsimile or a copying machine.

Explanation of symbols

21 n-type fourth layer 22 n-type third layer 23 n-type second layer 24 p-type first layer 25 reflective layer 36 cathode electrode 51 p-type substrate 61 SiO ₂ protective film 62 aluminum wiring 84 thyristor island 85 gate electrode 86 coupling Diode island 88 Shift portion thyristor island 91 Light emitting portion thyristor island 87, 89, 90 n-type ohmic electrode 100 Optical writing head 102 Photosensitive drum 104 Charger 106 Developer 108 Transfer device 110 Cassette 112 Paper 114 Fixing device 116 Stacker 118 Erase lamp 120 Cleaner

Claims (12)

A first conductive type conductive substrate;
An insulating layer, a high resistance layer, or a semiconductor multilayer mirror formed on the conductive substrate of the first conductivity type;
A first first-conductivity-type semiconductor layer formed on the insulating layer, the high-resistance layer, or the semiconductor multilayer mirror;
A first electrode formed on the first first conductivity type semiconductor layer;
A plurality of light emitting devices including an ohmic electrode that short-circuits between the first conductive type conductive substrate and the first first conductive type semiconductor layer are arranged, and the light emitting devices are separated by mesa etching. Light emitting element array. A first conductive type conductive substrate;
An insulating layer, a high resistance layer, or a semiconductor multilayer mirror formed on the conductive substrate of the first conductivity type;
A semiconductor layer of a first second conductivity type formed on the insulating layer, the high-resistance layer, or the semiconductor multilayer mirror;
A first electrode formed on the first second conductivity type semiconductor layer;
A plurality of light emitting elements each having an ohmic electrode that short-circuits between the first conductive type conductive substrate and the first second conductive type semiconductor layer are arranged, and the light emitting elements are separated by mesa etching. Light emitting element array. A first conductive type conductive substrate;
An insulating layer, a high resistance layer, or a semiconductor multilayer mirror formed on the conductive substrate of the first conductivity type;
A first first-conductivity-type semiconductor layer, a first second-conductivity-type semiconductor layer, and a second first-conductivity-type formed on the insulating layer, high-resistance layer, or semiconductor multilayer mirror. A semiconductor layer of the second conductivity type,
A first electrode formed on the second second conductivity type semiconductor layer;
A second electrode formed on the back surface of the conductive substrate of the first conductivity type;
A plurality of light emitting devices including an ohmic electrode that short-circuits between the first conductive type conductive substrate and the first first conductive type semiconductor layer are arranged, and the light emitting devices are separated by mesa etching. Light emitting element array. A first conductive type conductive substrate;
An insulating layer, a high resistance layer, or a semiconductor multilayer mirror formed on the conductive substrate of the first conductivity type;
A first second-conductivity-type semiconductor layer, a first first-conductivity-type semiconductor layer, and a second second-conductivity-type formed on the insulating layer, the high-resistance layer, or the semiconductor multilayer mirror. A semiconductor layer of the second conductivity type, a semiconductor layer of the second first conductivity type,
A first electrode formed on the second first conductivity type semiconductor layer;
A second electrode formed on the back surface of the conductive substrate of the first conductivity type;
A plurality of light emitting elements each having an ohmic electrode that short-circuits between the first conductive type conductive substrate and the first second conductive type semiconductor layer are arranged, and the light emitting elements are separated by mesa etching. Light emitting element array.   The light emitting element array according to claim 1 or 2, wherein a position at which a current density in the light emitting area of the light emitting element is maximum is not hidden by the first electrode.   5. The light emitting element array according to claim 3, wherein a position where a current density in the light emitting area of the light emitting element is maximum is not hidden by the first electrode.   The light emitting element array according to claim 6, wherein the light emitting element is a light emitting element thyristor having a pnpn structure.   The light emitting element array according to claim 7, wherein the light emitting element array is a self-scanning element array.   The optical writing head using the light emitting element array in any one of Claims 1-8.   A printer comprising the optical writing head according to claim 9.   A facsimile comprising the optical writing head according to claim 9.   A copying machine comprising the optical writing head according to claim 9.