JP2002050790A - Compound semiconductor light-emitting diode array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compound semiconductor light-emitting diode array for reduced manufacturing cost and improved yield, related to the formation of an electrode. SOLUTION: In a light-emitting diode array, a plurality of light-emitting parts, in which a p-type layer is jointed to an n-type layer are formed into a single chip, while an anode electrode 7 and a cathode electrode 8, which drive the light-emitting part, is formed on the surface of the chip in a light- emitting side. Here, the two electrodes are formed on the surface of the layers of the same type, while a tunnel junction is formed from the anode electrode 7 to the cathode electrode 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor light-emitting diode array in which an anode electrode and a cathode electrode are formed on a light-emitting surface of a chip, and more particularly to a reduction in manufacturing cost and an improvement in yield related to electrode formation. The present invention relates to a compound semiconductor light-emitting diode array capable of performing the following.

[0002]

2. Description of the Related Art An LED array in which a plurality of light emitting diodes (LEDs) are formed on the same chip has attracted attention as a light source for an electrophotographic printer, particularly a color printer. Then, from the viewpoint of reducing the price of the printer device, L
There is a strong demand for a reduction in the manufacturing cost of the ED array.

FIG. 7 shows a sectional structure of a light emitting portion of a conventional general AlGaAs LED array having a double hetero (DH) structure. This LED array is
An epitaxial layer mainly grown on the GaAs substrate 1;
It comprises an anode electrode 7, a cathode electrode 8, and an insulating film 9 formed on the surface of the epitaxial layer.

In an actual LED array, an electrode pad for electrically connecting to an external circuit, a wiring metal between the electrode pad and an anode electrode or a cathode electrode, an insulating film for insulating between these wiring metals, and the like. Is formed,
These are not shown in FIG.

The epitaxial layer is formed by a molecular beam epitaxy method (MBE method) or a metalorganic vapor phase epitaxy method (MO method).
In general, it is grown by the VPE method. The structure of the epitaxial layer is, in order from the GaAs substrate 1, p-type GaAs.
An s electrode contact layer 2, a p-type AlGaAs cladding layer 3, a p-type AlGaAs active layer 4, an n-type AlGaAs cladding layer 5, and an n-type GaAs electrode contact layer 6.

[0006] By separating the light emitting portion formed of a pn junction from other light emitting portions (not shown) by photoetching, adjacent light emitting portions are electrically insulated. Further, a part of the p-type GaAs electrode contact layer 2 is exposed by photoetching, and an anode electrode 7 is formed on the exposed surface. On the surface of the n-type GaAs electrode contact layer 6, a cathode electrode 8 is formed.
Since the n-type GaAs electrode contact layer 6 becomes a light absorbing layer, portions other than immediately below the cathode electrode are removed.

By applying a voltage between the anode electrode 7 and the cathode electrode 8 so that the anode side is positive, a current flows in the forward direction of the pn junction, and mainly a p-type AlGa
Light emission occurs in the As active layer 4. This light is emitted outside from a portion around the anode electrode.

An electrophotographic printer uses an LED array having an emission peak wavelength of about 660 nm to 850 nm, and a desired emission peak wavelength is obtained by controlling the AlAs mixed crystal ratio of the p-type AlGaAs active layer.

The cladding layer is made of AlGaAs having a wider band gap than the active layer. This structure is D
This structure is called an H structure, in which carriers injected into the active layer easily recombine with light. Recently, in order to obtain a higher emission output, studies have been made to use an AlGaAs quantum well structure for the active layer.

[0010] In the LED array, the density of the light emitting section is being increased, and a high density LED array having a density of 1000 DPI (dots per inch) or more has already been developed. High density LED
In the array, it is difficult to provide an electrode pad (not shown) for electrically connecting to the outside for each light emitting unit due to space restrictions. Therefore, for example, a method is adopted in which a matrix-shaped metal wiring layer is formed on the surface of the LED array chip, and a set of electrode pads is provided for four light emitting units. In this case, as shown in FIG. 7, both the anode electrode and the cathode electrode are formed on the surface on the light extraction side (light emission side).

Conventionally, an AuGe-based alloy has been used as a material for obtaining ohmic contact with the n-type GaAs electrode contact layer. On the other hand, an AuZn-based alloy is used as a material for obtaining ohmic contact with the p-type GaAs electrode contact layer.

[0012]

In the conventional AlGaAs-based LED array, it is necessary to use different materials for the anode electrode and the cathode electrode, respectively. This is because the conductivity type of the underlying GaAs is different. Usually, an electrode is formed by forming a photoresist pattern, depositing an electrode metal on the entire surface, and removing unnecessary electrode metal (in this case, the electrode metal deposited on the photoresist) by a lift-off method. . Therefore, in the conventional LED array, in order to form an anode electrode and a cathode electrode,
It is necessary to repeat the photoresist pattern forming step, the vapor deposition step, and the lift-off step twice. For this reason, the manufacturing cost related to the electrode formation increases, and it is difficult to reduce the cost of the LED array.

An object of the present invention is to provide a compound semiconductor light-emitting diode array that solves the above-mentioned problems and can reduce the manufacturing cost and improve the yield related to electrode formation.

[0014]

In order to achieve the above object, according to the present invention, a plurality of light-emitting portions formed by joining a p-type layer and an n-type layer are formed on one chip, and these light-emitting portions are driven. In a compound semiconductor light-emitting diode array in which an anode electrode and a cathode electrode are formed on the light-emitting side surface of the chip, the two electrodes are formed on the surface of the same type layer, and the two electrodes are formed from the anode electrode to the cathode electrode. A tunnel junction is formed between them.

The material constituting the active layer of the light emitting section is GaIn.
N may be included.

AlGa is used as a constituent material of the active layer of the light emitting section.
At least one of As, GaAs, AlGaInP, and GaInP may be included.

Both the p-type layer and the n-type layer forming the tunnel junction may be made of GaAs.

The p-type layer forming the tunnel junction is Al
It may be made of GaAs.

The n-type layer forming the tunnel junction is Ga
It may be made of InP or AlGaInP.

The dopant material of the p-type layer forming the tunnel junction may be C or Mg.

[0021] The dopant material of the n-type layer forming the tunnel junction may be Si or Se.

[0022]

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

As shown in FIG. 1, the LE according to the present invention
In the D array, an anode electrode 7 and a cathode electrode 8 are formed on the surface of the same layer, and a tunnel junction is formed between the anode electrode 7 and the cathode electrode 8.
The tunnel junction is a p-type layer with a high carrier concentration (p ⁺
(Type layer) 13 and an n-type layer (n ⁺ type layer in the figure) 12 having a high carrier concentration. When a forward current is applied to the pn junction of the light emitting portion formed by joining the p-type layer 10 and the n-type layer 11,
The tunnel junction is reverse biased. Therefore, LE
In order to suppress the power consumption of D, it is preferable that the electrical resistance in the reverse direction of the tunnel junction is sufficiently low.

FIG. 6 is a conceptual diagram of the conventional LED array shown in FIG. One light emitting part of the LED array,
It is basically a pn junction, and a light emission output can be obtained by flowing a current in the forward direction of this diode. As shown, in the conventional LED array, the anode electrode 7 and the cathode electrode 8 are formed on the surface of the epitaxial layer of different conductivity type. In order to form both anode and cathode electrodes on the same conductivity type epitaxial layer, for example, the n-type layer 11
It is necessary to provide a p-type layer between the electrode and the cathode electrode 8.
However, when the p-type layer is formed directly on the n-type layer 11, a pn junction in the direction opposite to the pn junction of the light emitting unit is formed. In such a configuration, a high voltage is required to cause a forward current to flow through the pn junction of the light emitting unit, and the power consumption of the LED increases significantly. To overcome this problem, it is effective to use a tunnel junction as shown in FIG.

FIG. 2 shows an example of a reverse current-voltage characteristic of a GaAs tunnel junction. The contact specific resistance of the tunnel junction calculated from the reverse current-voltage characteristics is 1 × 10 ⁻⁴ Ωcm ²
And the contact resistance when applied to an LED array can be suppressed to 1Ω or less. This is a level at which there is no problem in the operation of the LED array.

FIG. 3 shows an AlGaAs DH according to the present invention.
1 shows a cross-sectional structure of one light emitting unit of a structured LED array. This LED array is made of GaAs as in the prior art.
It comprises an epitaxial layer grown on the s-substrate 1 by the MOVPE method, an anode electrode 7, a cathode electrode 8, and an insulating film 9 formed on the surface of the epitaxial layer. The structure of the epitaxial layer is, in order from the GaAs substrate 1, an n ⁺ -type GaAs layer 15, a p ⁺ -type GaAs layer 16, and a p-type AlGa
As clad layer 3, p-type AlGaAs active layer 4, n-type A
An lGaAs cladding layer 5 and an n-type GaAs electrode contact layer 6 are provided.

By separating the light emitting portion formed of a pn junction from other light emitting portions (not shown) by photoetching, adjacent light emitting portions are electrically insulated. Further, a part of the n ⁺ -type GaAs layer 15 is exposed by photoetching, and the anode electrode 7 is formed on the exposed surface. On the surface of the n-type GaAs electrode contact layer 6, a cathode electrode 8 is formed. n-type GaAs
Since the s-electrode contact layer 6 absorbs light emitted from the p-type AlGaAs active layer 4, portions other than immediately below the cathode electrode are removed.

Since the anode electrode 7 and the cathode electrode 8 are both formed on the n-type GaAs layer, they are made of the same electrode material.

The tunnel junction is composed of an n ⁺ -type GaAs layer 15 and a p ⁺ -type GaAs layer 16. It is preferable to use Si or Se as a dopant of the n ⁺ -type GaAs layer 15. C or Mg is preferably used as a dopant for the p ⁺ -type GaAs layer 16.

The light emitting portion of this LED array and a conventional LED
A comparison with the light emitting portion of the array revealed that substantially the same light output was obtained under the same driving conditions. Also, 1 in the forward direction
When a current of 0 mA was passed, the rise of the forward voltage observed in the present invention was 10 mV or less, which was a negligible level.

In the structure of FIG. 3, the tunnel junction
History of the growth of the n-type AlGaAs cladding layer 3, the p-type AlGaAs active layer 4, the n-type AlGaAs cladding layer 5, and the n-type GaAs electrode contact layer 6 (normally 700 ° C.)
For about 2 hours). It is generally known that the characteristics of the tunnel junction deteriorate when subjected to such a heat history. This is because the dopant doped at a high concentration in the tunnel junction layer thermally diffuses, and the carrier concentration of the n ⁺ -type GaAs layer 15 and the p ⁺ -type GaAs layer 16 is reduced. In order to suppress this thermal diffusion, it is necessary to select an appropriate dopant.

C or Mg is suitable as a dopant for the p ⁺ -type GaAs layer 16 of the tunnel junction. Also, n
The dopant of the ⁺ type GaAs layer 15 is Si or S
e is suitable. These dopants were extremely stable thermally, and no reduction in carrier concentration due to diffusion was observed even after a thermal history of 3 hours at 700 ° C. Also,
The increase in the electrical resistance of the tunnel junction was also at a negligible level.

FIG. 4 shows an AlGaAs DH according to the present invention.
1 shows a cross-sectional structure of one light emitting unit of a structured LED array. The epitaxial layer was grown by the MOVPE method, and the structure of the epitaxial layer was GaAs substrate 1
P-type GaAs electrode contact layer 2, p-type Al
GaAs cladding layer 3, p-type AlGaAs active layer 4, n
-Type AlGaAs cladding layer 5, n ⁺ -type GaInP layer 1
7, a p ⁺ -type AlGaAs layer 18 and a p-type GaAs electrode contact layer 2.

The anode electrode 7 is formed on a part of the p-type GaAs electrode contact layer 2 exposed by photo-etching. A cathode electrode 8 is formed on the uppermost p-type GaAs electrode contact layer 2. These electrodes are all formed on the p-type GaAs electrode contact layer 2 and use the same electrode material.

The tunnel junction is an n ⁺ -type GaInP layer 17.
And a p ⁺ -type AlGaAs layer 18.
GaInP is grown with a composition lattice-matched to GaAs, and has a band gap of about 1.9 eV. This material has a hole trap and cannot obtain a high carrier concentration in a p-type, but can obtain a high carrier concentration applicable to a tunnel junction in an n-type.

On the other hand, AlGaAs is GaAs regardless of the composition.
It is lattice-matched with s, and the band gap involved in direct transition can be changed between about 1.4 eV to 3 eV. In this material, when the AlAs mixed crystal ratio increases, electron traps increase and it becomes difficult to obtain a high carrier concentration in the n-type, but a high carrier concentration applicable to the tunnel junction can be obtained in the p-type.

Therefore, the tunnel junction formed by the n ⁺ -type GaInP layer 17 and the p ⁺ -type AlGaAs layer 18 can prevent the light emitted from the active layer (in the case where AlGaAs is used for the active layer, to fall within a range of about 660 nm to 850 nm). )
Can be suppressed extremely low, and can be arranged on the light extraction side of the active layer. For this reason, the condition of the thermal history applied to the tunnel junction is relaxed, and the range of selection of the dopant material can be expanded.

In the embodiment shown in FIGS. 3 and 4, even if the conductivity type of each epitaxial layer other than the active layer is reversed, substantially the same performance can be obtained.

Further, in the embodiment shown in FIG. 4, instead of the n ⁺ -type GaInP layer forming the tunnel junction, n
The same characteristics can be obtained by using a ⁺ type AlGaInP layer.

According to the present invention, the constituent material of the active layer is AlGaAs.
For example, the present invention can be applied to an LED array including a group III-V compound semiconductor such as GaInP and AlGaInP.

Next, the manufacturing process related to the electrode formation of the LED array of the present invention will be compared with the conventional technology. As shown in FIG. 5, in the related art, after forming a first photoresist pattern, a step S1 of removing an insulating film, a step S2 of depositing an electrode metal and then performing a lift-off, and a second step After forming the photoresist pattern, a step S3 of removing the insulating film and a step S4 of performing lift-off after depositing the electrode metal were required.

In the present invention, when the epitaxial layer serving as the light emitting portion is grown on the GaAs substrate 1, the epitaxial layer forming the tunnel junction is simultaneously grown. By providing this tunnel junction, it becomes possible to form both the anode and cathode electrodes on the same conductivity type epitaxial layer. Therefore, it is not necessary to use different electrode metals for the anode electrode and the cathode electrode as in the related art. For this reason, as shown in FIG. 5, after forming a photoresist pattern, a step S of removing the insulating film is performed.
1 and a step S of performing lift-off after depositing an electrode metal
By simply performing step 2, both the anode and the cathode can be simultaneously formed, and the manufacturing process can be greatly reduced.

[0043]

The present invention exhibits the following excellent effects.

(1) Since the manufacturing cost related to the formation of the electrodes is reduced, a high-performance LED array can be supplied at a low price.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a cross section of one light emitting unit of an LED array according to an embodiment of the present invention.

FIG. 2 is a reverse current-voltage characteristic diagram of a tunnel junction.

FIG. 3 is a cross-sectional view of one light emitting unit of the LED array showing one embodiment of the present invention.

FIG. 4 is a cross-sectional view of one light-emitting portion of an LED array showing another embodiment of the present invention.

FIG. 5 is a manufacturing process diagram relating to the present invention and a conventional LED array electrode formation.

FIG. 6 is a conceptual diagram of a cross section of one light emitting section of a conventional LED array.

FIG. 7 is a cross-sectional view of one light emitting unit of a conventional LED array.

[Explanation of symbols]

Reference Signs List 1 GaAs substrate 2 p-type GaAs electrode contact layer 3 p-type AlGaAs cladding layer 4 p-type AlGaAs active layer 5 n-type AlGaAs cladding layer 6 n-type GaAs electrode contact layer 7 anode electrode 8 cathode electrode 9 insulating film 10 p-type layer 11 n Type layer 12 n ⁺ type layer 13 p ⁺ type layer 14 photoresist film 15 n ⁺ type GaAs layer 16 p ⁺ type GaAs layer 17 n ⁺ type GaInP layer 18 p ⁺ type AlGaAs layer

Claims (8)

[Claims] 1. A plurality of light-emitting portions each formed by joining a p-type layer and an n-type layer are formed on one chip, and an anode electrode and a cathode electrode for driving these light-emitting portions are provided on the light-emitting side of the chip. Wherein the two electrodes are formed on the surface of the same type layer, and a tunnel junction is formed between the anode electrode and the cathode electrode. Compound semiconductor light emitting diode array. 2. The method according to claim 1, wherein the active layer of the light emitting section is made of GaI.
The compound semiconductor light-emitting diode array according to claim 1, wherein nN is included. 3. An AlG material for the active layer of the light emitting section.
The compound semiconductor light-emitting diode array according to claim 1, wherein at least one of aAs, GaAs, AlGaInP, and GaInP is included. 4. A p-type layer forming said tunnel junction and n
4. The compound semiconductor light emitting diode array according to claim 3, wherein each of the mold layers is made of GaAs. 5. The semiconductor device according to claim 1, wherein the p-type layer forming the tunnel junction is A
4. The semiconductor device according to claim 3, wherein the substrate is made of lGaAs.
The compound semiconductor light-emitting diode array according to claim 1. 6. An n-type layer forming the tunnel junction is formed of G
4. The compound semiconductor light emitting diode array according to claim 3, wherein the array is made of aInP or AlGaInP. 7. The compound semiconductor light emitting diode array according to claim 4, wherein a dopant material of the p-type layer forming the tunnel junction is C or Mg. 8. The compound semiconductor light emitting diode array according to claim 4, wherein a dopant material of the n-type layer forming the tunnel junction is Si or Se.