JP2002009331A - Light emitting diode array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting diode array which can improve light emission output by raising current density passing through an active layer. SOLUTION: A cathode electrode 3 and an anode electrode 4 are disposed at both sides of a light emission part 2 provided to a surface of a diode 1, and form a current path 19 passing through immediately below the light emission part 2. Recombination characteristic of electron and hole inside a crystalline layer immediately below a light emission part is increased by disposing an electrode to form a current path immediately below a light emission part, thus improving light emission output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 for an electrophotographic printer light source.

[0002]

2. Description of the Related Art Conventionally, a laser system and a light emitting diode array system have been widely used as a light source of an electrophotographic printer. In particular, the light-emitting diode array system does not require a long optical path length unlike the laser system, so that the printer can be downsized and large-size printing is easy. 2. Description of the Related Art In recent years, printers have been downsized, and a light-emitting diode array with higher definition and higher output has been required.

FIG. 4 shows a conventional light-emitting diode array viewed from above, in which diode portions 1 are arranged at predetermined intervals on a semi-insulating n-type GaAs substrate 10. The diode unit 1 has a plurality of light emitting units 2, and a cathode electrode 3 and an anode electrode 4 for applying a voltage to the light emitting unit 2.
And a bonding pad 6 connected to the cathode electrode 3 and the Au wiring layer 5. The diode portion 1 is separated from the bonding portion 8 by a mesa etching groove 7.

FIG. 5 is a cross-sectional view of the light emitting diode array shown in FIG. 4 taken along the line AA. On a semi-insulating GaAs substrate 10, a p-type GaAs conductive layer 11, a p-type AlGaAs etching stopper layer 12, a p-type AlGaAs Clad layer 13,
It has a double hetero structure in which an n-type AlGaAs active layer 14, an n-type AlGaAs cladding layer 15, and an n-type GaAs cap layer 16 are stacked, a PSG film 17 covering the n-type GaAs cap layer 16, and a p-type GaAs conductive layer. 1
An anode electrode 4 formed by evaporating and alloying a metal on the first electrode 1 and an Au wiring layer 5 formed on the PSG film 17 are provided.

The diode section 1 is formed by laminating a cathode electrode 3 on the top surface of a mesa of an n-type GaAs cap layer 18 laminated on an n-type AlGaAs clad layer 15.

The diode section 1 forms the light emitting section 2 by removing the n-type GaAs cap layer 16 by etching. The light emitting section 2 of the current path 19 flowing from the anode electrode 4 toward the cathode electrode 3 is formed. N-type A directly below
The light L emitted from the lGaAs active layer 14 is irradiated.

[0007]

However, according to the conventional light emitting diode array, the current supplied from the anode electrode to the cathode electrode passes through the active layer immediately below the light emitting portion at a current density corresponding to the size of the cathode electrode. Therefore, if the size of the cathode electrode is increased, there is a problem that the current density passing through the active layer is reduced and the light emission output is reduced. For example, when the length of the cathode electrode is six times or more the width of the active layer immediately below the light emitting portion, the light emission output is significantly reduced.

Accordingly, it is an object of the present invention to provide a light emitting diode array capable of increasing the current density passing through the active layer and increasing the light emitting output.

[0009]

According to the present invention, in order to achieve the above object, an epitaxial layer formed by stacking a plurality of crystal layers on a semiconductor substrate is divided by a mesa etching groove to form a plurality of light emitting diode portions. In the provided light emitting diode array, there is provided a light emitting diode array having electrode portions arranged on both sides of a light emitting portion provided on a surface of the light emitting diode portion and forming a current path passing immediately below the light emitting portion.

According to the light emitting diode array described above,
By arranging the electrodes so that a current path is formed immediately below the light emitting section of the light emitting diode section, the recombination of electrons and holes in the crystal layer immediately below the light emitting section increases, which means that As a result, the light emission output is increased.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a light emitting diode array according to the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a light emitting diode array according to the present invention from above, in which diode portions 1 are arranged on a semi-insulating GaAs substrate 10 at predetermined intervals. The diode unit 1 has a plurality of light emitting units 2, a cathode electrode 3 and an anode electrode 4 for applying a voltage to the light emitting unit 2,
It has a bonding pad 6 connected to the cathode electrode 3 by the Au wiring layer 5, and is formed so that the length L of the cathode electrode 3 is three times or less the width W of the light emitting unit 2. The diode section 1 is separated from the bonding section 8 by a mesa etching groove 7.

FIG. 2 shows a cross section taken along line BB of the light emitting diode array shown in FIG. 1. On a semi-insulating GaAs substrate 10, a p-type GaAs conductive layer 11, a p-type AlGaAs etching stopper layer 12, a p-type AlGaAs Clad layer 13,
It has a double hetero structure in which an n-type AlGaAs active layer 14, an n-type AlGaAs cladding layer 15, and an n-type GaAs cap layer 16 are stacked, a PSG film 17 covering the n-type GaAs cap layer 16, and a p-type GaAs conductive layer. 1
1 has an anode electrode 4 formed by evaporating a metal and alloying the same, and an Au wiring layer 5 formed on the PSG film 17. The length l of the cathode electrode 3 is determined by the width W ( (Rearward in the drawing).

The diode section 1 is formed by laminating a cathode electrode 3 on the top surface of a mesa of an n-type GaAs cap layer 18 laminated on an n-type AlGaAs clad layer 15.

The diode section 1 forms the light emitting section 2 by removing the n-type GaAs cap layer 16 by etching. The light emitting section 2 of the current path 19 flowing from the anode electrode 4 to the cathode electrode 3 is formed. N-type A directly below
The light L emitted from the lGaAs active layer 14 is irradiated.

Hereinafter, a method for manufacturing a light emitting diode array according to the present invention will be described.

First, a carrier concentration of 4 × 10 ¹⁹ cm− is applied to the surface of the semi-insulating GaAs substrate 10 by MOVPE.
³ p-type GaAs conductive layer 11 is 1 μm, and carrier concentration is 3
The p-type AlGaAs etching stopper layer 12 of × 10 ¹⁹ cm ⁻³ is 0.5 μm, and the carrier concentration is 3 × 10 ¹⁸ cm −3.
³ An n-type AlGaAs active layer 14 having a p-type AlGaAs cladding layer 13 of 1 μm and a carrier concentration of 1 × 10 ¹⁸ cm ^−3.
Is 1 μm and the carrier concentration is 2 × 10 ¹⁸ cm ⁻³ n-type Al
The GaAs cladding layer 15 is 3 μm, and the carrier concentration is 1 × 1.
0 ¹⁸ cm- ³ of 0.5μ the n-type GaAs cap layer 16
grow m successively.

Next, the n-type GaAs cap layer 16 is removed by wet etching while leaving a part 18 of the cap layer for forming the cathode electrode 3.

Next, a mesa etching groove 7 is formed by wet etching in order to electrically isolate each diode portion 1 from the bonding portion 8. Note that the depth of the mesa etching groove 7 is 7.0 μm so that the n-type GaAs layer 12 is exposed.
And

Next, a PSG film 17 is grown to a thickness of 0.5 μm so as to cover the entire surface by CVD.

Next, the PSG film 17 where the cathode electrode 3 and the anode electrode 4 are to be formed is removed with hydrofluoric acid.
The cathode electrode 3 is formed by depositing and alloying AuGe / Ni / Au on the n-type GaAs cap layer 18. Further, the anode electrode 4 is provided with a mesa etching groove 7.
Au on the p-type GaAs conductive layer 11 exposed at the bottom of
It is formed by depositing and alloying Zn / Ni / Au.

Finally, the Au electrode 5 connects the cathode electrode 3
Is connected to the bonding pad 6 to form a light emitting diode array.

In the light emitting diode array described above, when a voltage is applied between the cathode electrode 3 and the anode electrode 4,
A current based on the current path 19 flows from the anode electrode 4 to the cathode electrode 3. At this time, the n-type A immediately below the light emitting section 2
In the 1GaAs active layer, a current having a current density corresponding to the size of the cathode electrode 3 passes.

FIG. 3 shows the light emission output of the light emitting section 2. When the length L of the cathode electrode 3 was 13.5 μm, a light emission output of about 38 μW was obtained. On the other hand, when the length L of the cathode electrode 3 is 58 μm, which is the conventional design value, the light emission output is about 23 μW (not shown). Therefore, in the light emitting diode array of the present invention, It was confirmed that double light output was obtained.

In the above-described embodiment, a p-type crystal in which a p-type crystal is placed on a semi-insulating GaAs substrate 10 is used.
The light-emitting diode array having the n-type order crystal structure has been described.
Even in a light emitting diode array having an n-type and a p-type crystal structure in which the type crystal is placed downward, the same effect can be obtained only by changing the polarity of the diode.

In the present embodiment, the semi-insulating Ga
Although the As substrate 10 is used, even if the substrate is a conductive substrate, a high-resistance layer such as undoped GaAs may be provided thereon.
A crystal structure of pnp or npn can be applied since it can be electrically insulated.

[0027]

As described above, according to the light-emitting diode array of the present invention, the electrode portions arranged on both sides of the light-emitting portion provided on the surface of the light-emitting diode portion and forming a current path passing immediately below the light-emitting portion are formed. As a result, the light emitting output can be increased by increasing the current density passing through the active layer.

[Brief description of the drawings]

FIG. 1 is a plan view showing a light emitting diode array according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along a line BB in FIG. 1;

FIG. 3 is an explanatory diagram showing light emission output characteristics of the light emitting diode array according to the embodiment of the present invention.

FIG. 4 is a plan view showing a conventional light emitting diode array.

FIG. 5 is a sectional view taken along the line AA in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diode part 2 Light emitting part 3 Cathode electrode 4 Anode electrode 5 Au wiring layer 6 Bonding pad 7 Mesa etching groove 8 Bonding part 10 GaAs substrate 11 p-type GaAs conductive layer 12 p-type AlGaAs etching stopper layer 13 p-type AlGaAs cladding layer 14 n -Type AlGaAs active layer 15 n-type AlGaAs cladding layer 16 n-type GaAs cap layer 17 PSG film 18 n-type GaAs cap layer 19 current path

Claims (2)

[Claims] 1. A light emitting diode array in which a plurality of light emitting diode portions are provided by dividing an epitaxial layer formed by laminating a plurality of crystal layers on a semiconductor substrate by a mesa etching groove, and provided on a surface of the light emitting diode portion. A light emitting diode array, comprising: an electrode portion disposed on both sides of a light emitting portion to form a current path passing immediately below the light emitting portion. 2. The light-emitting diode array according to claim 1, wherein said electrode portion has a configuration in which an electrode length adjacent to said light-emitting portion is formed to be three times or less the width of said light-emitting portion.