JP3420417B2 - Light emitting diode array - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode array, and more particularly, to a light emitting diode array used as an exposure source of a photosensitive drum for a page printer. 2. Description of the Related Art A conventional light emitting diode array is shown in FIGS. FIG. 6 is a sectional view taken along line AA of FIG.
5 and 6, 21 is a semiconductor substrate, 22 is an island-shaped semiconductor layer, 23 is an individual electrode, and 24 is a common electrode. The semiconductor substrate 21 is made of, for example, silicon (S
i) or a single crystal semiconductor substrate such as gallium arsenide (GaAs). The island-shaped semiconductor layer 22 is made of a compound semiconductor layer such as gallium arsenide or aluminum gallium arsenide, and is composed of a layer 22a containing one conductivity type impurity and a layer 22b containing the opposite conductivity type impurity. A semiconductor junction is formed at the interface between the layer 22a containing one conductivity type impurity and the layer 22b containing the opposite conductivity type impurity. This island-shaped semiconductor layer 22 is formed, for example, by MOCVD (metal organic chemical vapor deposition).
After a single crystal semiconductor layer made of gallium arsenide, aluminum gallium arsenide, or the like is formed by a method or MBE (Electron Beam Epitaxy), it is formed into an island shape by mesa etching or the like. [0004] On the surface portion of the island-shaped semiconductor layer 22, for example a protective film 25 made of a silicon nitride film (Si _x N _y)
Are formed, and individual electrodes 23 made of, for example, gold (Au) are formed on the surface of the protective film 25. This individual electrode 23 is connected to a semiconductor layer 22b containing an impurity of the opposite conductivity type via a through hole formed in the protective film 25. This individual electrode 23 is formed of a layer 22 b containing an impurity of the opposite conductivity type in the island-shaped semiconductor layer 22.
Is formed so as to alternately extend to the other end face side for each adjacent island-shaped semiconductor layer 22 from the upper surface part to the vicinity of the end face of the semiconductor substrate 21 via the wall face part. A common electrode 24 is formed on almost the entire back surface of the semiconductor substrate 21. Each light emitting diode is constituted by the island-shaped semiconductor layer 22, the individual electrode 23, and the common electrode 24. The light emitting diodes are formed on the semiconductor substrate 21 in a line. In this case, for example, the individual electrode 23 becomes the anode electrode of the light emitting diode, and the common electrode 24 becomes the cathode electrode. The individual electrode 23 is connected to an external circuit at a wide portion thereof by a bonding wire or the like. In such a light emitting diode array, for example, when a current flows in a forward direction from the individual electrode 23 to the common electrode 24, electrons are injected into the layer 22b containing the opposite conductivity type impurity, and the one conductivity side impurity is removed. Holes are injected into the layer 22a containing. Some of these minority carriers emit light by radiative recombination with majority carriers. In addition, any one of the individual electrodes 2 of the light emitting elements formed in a row
By selecting 3 and causing a current to flow to emit light, for example, it is used as an exposure light source for a photosensitive drum for a page printer. However, in this conventional light emitting diode array, individual electrodes 23 are provided on the island-shaped semiconductor layer 22 formed on the front side of the semiconductor substrate 21 and a common electrode 24 is provided on the back side of the semiconductor substrate 21. Therefore, the step of forming the individual electrode 23 and the common electrode 24 is performed twice, and there is a problem that the manufacturing process becomes complicated. In addition, when the individual electrode 23 and the common electrode 24 are on both the front and back surfaces of the semiconductor substrate 21, there is a problem that the connection work is difficult when connecting to an external circuit by a wire bonding method or the like. Accordingly, the present inventors have filed a Japanese Patent Application No. 7-192.
No. 857, as shown in FIGS. 7 and 8, a lower semiconductor layer 22a containing one conductivity type impurity is provided on a semiconductor substrate 21, and an upper layer containing an opposite conductivity type impurity is provided on the lower semiconductor layer 22a. The semiconductor layer 22b is provided so as to have a smaller area than the lower semiconductor layer 22a, the common electrodes 24a and 24b are connected to the exposed portions of the lower semiconductor layer 22a, and the individual electrodes 23 are connected to the upper semiconductor layer 22b. Proposed that. With this configuration, the individual electrode 23 and the common electrodes 24a and 24b can be provided on the same side of the semiconductor substrate 21, and the individual electrode 23 and the common electrodes 24a and 24b can be provided.
Can be simultaneously formed in a single process, so that the manufacturing process of the light emitting diode array is simplified and the individual electrodes 2 are formed.
3 and the common electrodes 24a and 24b are located on the same side, so that a connection operation with an external circuit by a wire bonding method or the like is facilitated. In FIG. 8, reference numeral 25 denotes an insulating film made of a silicon nitride film or the like. As shown in FIG. 7, the common electrodes 24a and 24b are provided in two groups so as to belong to different groups for each adjacent island-shaped semiconductor layer 22, and the individual electrodes 23 are formed by the adjacent island-shaped semiconductor layers 22. Same individual electrode 23
It is provided to be connected by. As described above, when the common electrodes 24a and 24b are provided in two groups and the individual electrodes 23 are provided so that the adjacent island-shaped semiconductor layers 22 are connected to the same individual electrode, the electrode pattern is simplified. It is possible to prevent short-circuiting of the electrodes, etc.
There is an advantage that the connection area between the third circuit and the external circuit can be increased. In such a light emitting diode array, each light emitting diode is selectively caused to emit light by selecting a combination of the individual electrode 23 and the common electrodes 24a and 24b and flowing a current. However, in this conventional light emitting diode array, electrical separation between adjacent light emitting diodes is not sufficient, and in particular, the common electrodes 24a, 2b provided in two groups are provided.
There was a problem that a current leaked between 4b. The cause is that when the first semiconductor layer 22a is formed on the semiconductor substrate 21 by a high-temperature process, semiconductor impurities diffuse from the first semiconductor layer 22a having one conductivity type to the semiconductor substrate 21,
This is because the surface of the semiconductor substrate 21 has one conductivity type. As a result, when used as a light emitting diode array for an optical print head, the printing quality of an optical printer is degraded, and an expensive high resistance substrate having a resistivity ρ of 1000 to 2000 Ω · cm is used as a semiconductor substrate for forming a light emitting diode. There is a problem that a semiconductor substrate must be used. The present invention has been made in view of the above-mentioned problems of the prior art, and solves the problem that the manufacturing process becomes complicated and connection work with an external circuit becomes difficult.
It is an object of the present invention to provide a light emitting diode array in which current leakage between adjacent light emitting diodes is eliminated. In order to achieve the above object, in a light emitting diode array according to the present invention, an island-shaped first semiconductor layer having one conductivity type is formed in a row on a semiconductor substrate. Provided, a second semiconductor layer having a reverse conductivity type is provided on the first semiconductor layer, and in the light emitting diode array provided by connecting electrodes to the first semiconductor layer and the second semiconductor layer, respectively. A third semiconductor layer having a reverse conductivity type is provided between the semiconductor substrate and the first semiconductor layer, and the first semiconductor layers are arranged in a row on the third semiconductor layer so as to be concave in alternate directions. And a rectangular second semiconductor layer is separately provided on the first semiconductor layer, and the same common electrode is connected and provided every other one of the first semiconductor layers. One separate electrode for each adjacent two semiconductor layers Are connected to each other. An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a view showing one embodiment of a light emitting diode array according to the present invention, wherein 1 is a semiconductor substrate, 2 is a third semiconductor layer, 3 is a first semiconductor layer,
4 is a second semiconductor layer, 5 is a common electrode, 6 is an individual electrode, 7
Is a protective film. The semiconductor substrate 1 is made of, for example, silicon (Si).
And a single crystal semiconductor substrate such as gallium arsenide (GaAs). In the light-emitting diode array according to the present invention, as described later, any one of a semiconductor having one conductivity type, a semiconductor substrate having a reverse conductivity type, and a high-resistance semiconductor substrate can be used as the semiconductor substrate. For formation, a semiconductor substrate other than the high-resistance semiconductor substrate is desirable. The third semiconductor layer 2 is made of gallium arsenide or gallium arsenide and aluminum gallium arsenide (Al _x Ga _{1 -x}
As), which is formed of a two-layer film or the like, and contains impurities of the opposite conductivity type. The third semiconductor layer 2 is formed, for example, by MOCVD or M
It is formed by a BE method or the like. That is, the natural oxide film of the semiconductor substrate 1 is removed at a high temperature of 800 to 1000 ° C.
An amorphous silicon gallium arsenide film, which is a nucleus at a low temperature of 50 ° C. or less, is formed to a thickness of 0.1 to 2 μm by MOCVD or MBE.
After being grown to a thickness of about the same, the temperature is raised to 500 to 700 ° C. and recrystallized to grow a gallium arsenide single crystal film (two-step growth method). In this case, trimethylgallium ((CH ₃ ) ₃ Ga) or the like is used as a raw material of gallium, and arsine (AsH ₃ ) or the like is used as a raw material of arsenic. Next, post-annealing such as repeating annealing at a high temperature of 750 ° C. to 1000 ° C. and rapid cooling to a low temperature of 600 ° C. or less several times (temperature cycle method) is performed. When an aluminum gallium arsenide film is further formed on the gallium arsenide film, trimethyl aluminum ((CH ₃ ) ₃ Al) or the like is used as a raw material of aluminum. The third semiconductor layer 6 contains semiconductor impurities such as S, Se, Te, Ge, and Si at about 10 ¹⁶ to 10 ¹⁹ cm ⁻³ . This third semiconductor layer 6 is formed on substantially the entire surface of the semiconductor substrate 1. On the third semiconductor layer 2, first semiconductor layers 3 are formed so as to be concave in alternate directions. That is, it is formed continuously for each adjacent island via the continuous portion 2a. The first semiconductor layer 3 is also made of a compound semiconductor film such as aluminum gallium arsenide and contains one conductivity type impurity of about 10 ¹⁶ to 10 ¹⁹ cm ⁻³ . Such one conductivity type impurities include Zn, Cd, Sr, Ba,
Ra and the like. On the first semiconductor layer 3, a rectangular second semiconductor layer 4 is formed. That is, the rectangular second semiconductor layer 3 is formed at two places except for the continuous portion 3 a of the first semiconductor layer 3. This second semiconductor layer 3
Is made of a compound semiconductor film such as aluminum gallium arsenide and contains impurities of the opposite conductivity type at about 10 ¹⁶ to 10 ¹⁹ cm ⁻³ . A semiconductor junction is formed at the interface between the first semiconductor layer 2 containing one conductivity type impurity and the second semiconductor layer 3 containing the opposite conductivity type impurity. The semiconductor impurities contained in the second semiconductor layer 3 also include S, Se, Te, Ge, Si and the like. The second semiconductor layer 4 may be formed of a plurality of layers having different mixed crystal ratios of aluminum arsenide (AlAs) and gallium arsenide (GaAs). After the third semiconductor layer 2, the first semiconductor layer 3, and the second semiconductor layer 4 are formed on the entire surface or a part of the semiconductor substrate 1, the first semiconductor layer 3, Then, the second semiconductor layer 4 is etched so as to be concave in an alternate direction, and further etched so that the second semiconductor layer 4 remains in a rectangular shape. The second semiconductor layer 3 may be formed of a plurality of layers having different mixed crystal ratios of aluminum arsenide (AlAs) and gallium arsenide (GaAs). The first semiconductor layer 3 formed in a concave shape and the second semiconductor layer 4 formed in a rectangular shape are covered with a protective film 7 made of, for example, a silicon nitride film. Common electrodes 5a and 5b made of, for example, gold (Au) are formed so as to extend from the connecting portions 3a of the same to the vicinity of the end face of the semiconductor substrate 1. In this case, since the first semiconductor layer 3 is formed continuously for each adjacent light emitting diode, only one lead portion of the common electrodes 5a and 5b may be formed for every two light emitting diodes.
The electrode pattern is simplified. In addition, since it is only necessary to connect one common electrode 5a, 5b for every two light emitting diodes, the connection area between the first semiconductor layer 3 and the common electrodes 5a, 5b can be increased, and the first semiconductor The connection resistance between the layer 3 and the common electrodes 5a and 5b can be reduced. An individual electrode 6 made of, for example, gold (Au) is formed so as to extend from the surface of the second semiconductor layer 4 to the vicinity of the end face of the semiconductor substrate 1 via the wall surface. One individual electrode 6 is formed for each adjacent second semiconductor layer 4. That is, the individual electrode 6 is provided for each adjacent light emitting diode belonging to a different group.
The wide portion of the individual electrode 6 becomes an electrode pad for performing wire bonding for connection to an external circuit. By selecting a combination of the individual electrode 6 and the common electrodes 5a and 5b and passing a current, each individual light emitting diode can be selected to emit light. That is,
As shown in FIGS. 1 and 2, it is assumed that the semiconductor substrate 1 is p-type, the third semiconductor layer 2 is p-type, the first semiconductor layer 3 is n-type, and the second semiconductor layer 4 is p-type. If the second semiconductor layer 4
When a current flows in the forward direction between the first common electrode 5b and the first common electrode 5b, the light emission connected to the common electrode 5b can be achieved by connecting the other common electrode 5b with one common electrode 5a opened. Only the diode emits light. Therefore, even if the common individual electrode 6 is provided for each of the adjacent second semiconductor layers 4, the common electrodes 5a and 5b are separately connected. By changing the voltage application state between the light emitting diodes, the adjacent light emitting diodes can be selectively made to emit light. The present invention is not limited to the case where the common electrodes 5a and 5b are connected to every two island-shaped semiconductor layers, but the common electrodes 5a and 5b may be provided for every more island-shaped semiconductor layers. EXAMPLES Example 1 n having a thickness of 350 μm and a resistance of 0.02 Ω · cm
A p-type gallium arsenide layer (third semiconductor layer) doped with Zn at a concentration of 1 × 10 ¹⁸ cm ⁻³ is formed on a silicon substrate at a thickness of 2 μm, and a concentration of 1 × 10 ¹⁷ cm ⁻³ is formed. An n-type gallium arsenide layer (first semiconductor layer) doped with silicon is formed to a thickness of 0.6 μm, and a p-type gallium arsenide layer (first layer) doped with Zn at a concentration of 1 × 10 ¹⁸ cm ⁻³ is formed. FIG. 3 shows a current (I) -voltage (V) characteristic between the common electrodes 5a and 5b of the light emitting diode array in which the distance between the light emitting elements is set to 20 μm by forming the two semiconductor layers) at a thickness of 1.2 μm. Shown in Even when a voltage of ± 10 V was applied between the common electrodes 5a and 5b, the leakage current between the common electrodes 5a and 5b was about 1 mA, and extremely good IV characteristics were obtained. Comparative Example As shown in FIG. 8, a common electrode 2 of a light emitting diode in which a first semiconductor layer 22a is directly formed on a semiconductor substrate 21 is formed.
FIG. 4 shows a current (I) -voltage (V) characteristic between 4a and 24b. A high-resistance silicon substrate having a resistance of 1000 Ω · cm was used as the semiconductor substrate 21, and the same semiconductor layers as those in Example 1 were used as the first semiconductor layer and the second semiconductor layer. Semiconductor substrate 2
In the light emitting diode array in which the first semiconductor layer 22a is formed directly on the first electrode 1, when a voltage of ± 10 V is applied to the common electrodes 24a and 24b, the leakage current between the common electrodes 24a and 24b is about 2 mA, The leakage current is much larger than that of the light emitting diode array of the present invention in which the third semiconductor layer having the opposite conductivity type is provided below the first semiconductor layer having the shape, and the IV curve is also a dull curve. As described above, according to the light emitting diode array according to the present invention, the semiconductor substrate on which the light emitting diode is formed and the island-shaped first semiconductor of one conductivity type constituting the light emitting diode. Since the third semiconductor layer having the opposite conductivity type is provided between the light emitting diodes, the current leakage between the adjacent light emitting diodes can be effectively prevented. As a result, element separation between adjacent light emitting diodes can be completely performed,
When used as an optical printer head, print quality is improved. Further, it is not necessary to use a high-resistance substrate as a semiconductor substrate, and the range of selection of a semiconductor substrate such as an n-type substrate, a p-type substrate, and a high-resistance substrate is widened. Furthermore, a high-resistance substrate is expensive, and if a high-resistance substrate is not used, an inexpensive light-emitting diode can be provided. In addition, the first semiconductor layers are provided in rows so as to be concave in alternate directions on the third semiconductor layer, and a rectangular second semiconductor layer is separated on the first semiconductor layer. Because the same common electrode is connected and provided every other first semiconductor layer, and one individual electrode is connected and provided every adjacent second semiconductor layer, the electrode pattern And the connection resistance between the first semiconductor layer and the common electrode can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing one embodiment of a light emitting diode array according to the present invention. FIG. 2 is a sectional view of a light emitting diode array according to the present invention. FIG. 3 is a diagram showing current-voltage characteristics between adjacent common electrodes in a light emitting diode array according to the present invention. FIG. 4 is a diagram showing current-voltage characteristics between adjacent common electrodes in a conventional light emitting diode array. FIG. 5 is a view showing a conventional light emitting diode array. FIG. 6 is a sectional view taken along line AA of FIG. 5; FIG. 7 is a diagram showing another conventional light emitting diode array. 8 is a cross-sectional view of another conventional light emitting diode array shown in FIG. [Description of Signs] 1 ... semiconductor substrate, 2 ... third semiconductor layer, 3 ...
· First semiconductor layer, 3a ··· connection part of first semiconductor layer, 4 ··· second semiconductor layer, 5a and 5b ··· common electrode, 6 ··· individual electrode

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-104482 (JP, A) JP-A-55-124180 (JP, A) JP-A-3-194978 (JP, A) JP-A 8- 274374 (JP, A) JP-A-6-232454 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 33/00

Claims (1)

(57) Claims 1. An island-shaped first semiconductor layer having one conductivity type is provided in a row on a semiconductor substrate, and a reverse conductivity type is provided on the first semiconductor layer. In a light emitting diode array in which a second semiconductor layer is provided and electrodes are respectively connected to the first semiconductor layer and the second semiconductor layer, a reverse conductivity type is provided between the semiconductor substrate and the first semiconductor layer. A third semiconductor layer having a concave shape in an alternate direction on the third semiconductor layer.
The first semiconductor layers are provided in rows so that
Separating the rectangular second semiconductor layer on the first semiconductor layer
The same common for every other first semiconductor layer
While connecting and providing electrodes, the second semiconductor layer
A light-emitting diode array , wherein one individual electrode is connected to each adjacent electrode .