JPH10150220A - Semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light emitting device which is cheap and requires no etching process for mounting an N electrode. SOLUTION: An N-electrode 6 is mounted covering a part of the one side of a substrate 1 which is electrically conductive and transmits light rays emitted from a light emitting device. An N-type first semiconductor layer 2, a light emitting layer 3, and a P-type second semiconductor layer 4 are successively formed on the other side of the substrate 1 in this sequence to form a light emitting device structure. A P-electrode 5 is mounted substantially covering all the surface of the P-type second semiconductor layer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a semiconductor light emitting device. The present invention can be applied to a light emitting diode or a laser diode formed of a GaN-based compound semiconductor.

[0002]

2. Description of the Related Art As a light emitting device in the visible light short wavelength region, a device using a compound semiconductor is known. Above all, group III nitride semiconductors have attracted particular attention because they are of direct transition type and have high luminous efficiency and emit blue light, which is one of the three primary colors of light.

[0003] Such a light-emitting element has, for example, a structure in which a buffer layer, an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer are sequentially stacked on a sapphire substrate.

In such a light emitting device, since the sapphire substrate is an insulator, electrodes cannot be attached so as to sandwich the p-type semiconductor layer and the n-type semiconductor layer. Therefore, it is necessary to form electrodes on the p-type and n-type semiconductor layers on the upper surface of the element, that is, on the same surface without the sapphire substrate, and remove a part of the p-type semiconductor layer and the light-emitting layer, and Separate steps such as etching for exposing the semiconductor layer are required.

[0005] Since the p-type semiconductor layer has a high electric resistance, the carrier to be injected from the electrode is not diffused into the entire p-type semiconductor layer simply by bonding the electrode to the electrode. Therefore, in order to transmit the light emitted from the light emitting layer and uniformly diffuse the carriers throughout the p-type semiconductor layer, the light-transmissive electrode is made of p-type.
It had to be provided on substantially the entire upper surface of the semiconductor layer of the mold. Then, an electrode pad for bonding is mounted on the translucent electrode.

When an electrode is connected to the upper surface of the n-type semiconductor layer exposed by etching, a current flows in parallel in the n-type semiconductor layer.
The resistance increases, causing unnecessary voltage drop and heat generation.

Since the sapphire substrate is connected to the lead frame, heat generated in the light emitting layer is released to the lead frame through the substrate. The sapphire substrate occupies most of the entire device thickness, and it is not efficient to dissipate heat through such a thick sapphire substrate.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve at least one of the above-mentioned problems. The light-emitting element is a light-emitting element formed using a GaN-based compound semiconductor, which is conductive and covers a part of one surface of a substrate that transmits light emitted by the light-emitting element. A light emitting device structure formed on another surface of the substrate, the first electrode being a n-type semiconductor layer, the light emitting layer, and the second p-type semiconductor layer from the substrate side. Are sequentially laminated, and a p-electrode is provided on the second semiconductor layer.

[0009]

According to the semiconductor light-emitting device having the above-described structure, the n-electrode is attached to the substrate and the p-electrode is attached to the p-type second semiconductor layer, so that an etching step for attaching the electrode is not required. Become. Therefore, an inexpensive light-emitting element can be provided.

[0010] When the n-electrode and the p-electrode are attached to each other with the light-emitting element structure interposed therebetween, current flows substantially perpendicular to the element. Therefore, the resistance can be reduced as much as possible, and unnecessary voltage drop and generation of heat can be prevented.

Since the substrate transmits the emitted light and the n-electrode covers only a part of it, the p-type second
Since the p-electrode is provided on substantially the entire surface of the semiconductor layer, the p-electrode can be directly mounted on the lead frame with the substrate facing upward. As a result, heat generated in the light emitting layer can be efficiently released to the lead frame without passing through any substrate. Therefore, the linearity of the current-light output (IL) characteristics is improved. Further, since the p-electrode is directly mounted on the lead frame, wire bonding between the lead frame and the p-electrode becomes unnecessary.

Carriers are injected substantially uniformly from the p-electrode to substantially the entire surface of the second semiconductor layer. That is, the current density in the p-type second semiconductor layer becomes uniform. To do so, for example, a p-electrode is attached to the second semiconductor layer so as to cover substantially the entire surface. Thus, the light-transmitting electrode provided between the p-electrode and the p-type second semiconductor layer becomes unnecessary. Therefore, an inexpensive light-emitting element with few components can be provided.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples. FIG. 1 is a sectional view of a light emitting diode 10 according to the embodiment. In this light emitting diode 10, an n-cladding layer (n-type first semiconductor layer) 2, a light-emitting layer 3, and a p-cladding layer (p-type second semiconductor layer) 4 are sequentially laminated on a substrate 1 to form a light-emitting element structure. An n-electrode 6 and a p-electrode 5 are attached to one surface (the lower surface in FIG. 1) of the substrate 1 and the surface of the p-cladding layer 4, respectively.

The specifications of each semiconductor layer are as follows. Semiconductor layer: composition: dopant (film thickness) p-cladding layer 4: p-GaN: Mg (50 nm) light-emitting layer 3: quantum well structure quantum well layer: In _0.15 Ga _0.85 N (3.5 nm) barrier layer: GaN (3.5 nm) ) Number of repetitions of quantum well layer and barrier layer: 5 n cladding layer 2: n-GaN: Si (3 μm) Substrate 1: n-GaN (200 μm)

The p electrode 5 is laminated so as to cover substantially the entire surface of the p clad layer 4. This p electrode 5 is made of gold, platinum,
It is formed of palladium, nickel, an alloy containing these, or a composite metal layer obtained by laminating a plurality of these metals. It is preferable that the thickness of the p electrode 5 is 0.5 μm or more. If the thickness of the p-electrode 5 is less than 0.5 μm, when the p-electrode 5 is mounted on a lead frame, a solder or a metal paste for fixing the two may short-circuit to the p-cladding layer 4.

The n-electrode 6 is formed by covering a part of one surface of the substrate 1. Wire bonding is performed on the n-electrode. This n-electrode 6 is formed of aluminum. Alternatively, the n-electrode can be formed of vanadium, niobium, zirconia, chromium, or an alloy containing these. Since the resistance of the n-GaN layers 1 and 2 can be made relatively small, if the n-electrode 6 is in contact with a part of the substrate 1, carriers can be sufficiently diffused over the entire surface. Therefore, in order to minimize the light shielding, the area of the n-electrode 6 is set to the minimum size required for the wire bonding operation.

As shown in FIG. 2, the light emitting element 10 having such a configuration is directly connected to the lead frame 20 with the p electrode 5 on the lower side. Reference numeral 21 in the drawing is a solder.

As shown in FIG. 2, the light emitting device 20 of the embodiment
Then, the substrate 1 is on the upper side. Therefore, the substrate 1 is formed of a material through which light generated in the light emitting layer 3 can be transmitted. In addition, since the light emitting element structure (the n-cladding layer 2, the light-emitting layer 3, and the p-cladding layer 4) and the n-electrode 6 conduct electricity, they need to have conductivity. In this embodiment, since blue light is generated in the light emitting layer 3, n-type GaN (carrier concentration: 2 × 10 ¹⁸ / carrier concentration) having a band gap capable of transmitting this light and having a sufficient carrier concentration to have conductivity. cm ³ )
Thus, the substrate 1 is formed.

The substrate 1 is made of a GaN-based compound semiconductor, that is, Al _X1 In _Y1 Ga _{1 -X1 -Y1} N (X1 = 0, Y1) in order to achieve lattice matching with each of the layers 2 to 4 of the light emitting element structure.
= 0 and X1 = Y1 = 0). When the substrate is formed of the same GaN-based compound semiconductor as that of the light emitting element structure, the coefficient of thermal expansion between the substrate and the light emitting element structure becomes equal. Thereby, thermal distortion is eliminated, crystallinity of the light emitting element structure is improved, and luminous efficiency is increased. This substrate 1 may or may not be intentionally doped. Note that impurities which are included in the semiconductor layer due to being present in a background atmosphere when the semiconductor layer is grown do not correspond to intentional impurities in this specification.

The n cladding layer 2 is made of Al _X2 In _Y2 Ga
_1-X2-Y2 N (including X2 = 0, Y2 = 0, and X2 = Y2 = 0). Its film thickness is 1-3 μm
It is preferable that Here, X2 = X1, Y
If 2 = Y1, the n-cladding layer 2 and the substrate 1 are integrated, and there is no boundary between them. By doing so, the substrate 1 and the n-cladding layer 2 can be grown under the same semiconductor growth conditions, and the manufacturing becomes easy. This n-cladding layer 2 may or may not be intentionally doped with impurities.

A stopper layer having a larger band gap than that of the n-cladding layer 2 for confining holes can be interposed between the n-cladding layer 2 and the light emitting layer 3. Similarly, a guide layer for confining light can be provided.

The light emitting layer 3 can be of an MQW (multiple quantum well) type, an SQW (single quantum well) type, or a bulk type (double hetero structure, single hetero structure) in addition to the MQW (multi quantum well) type of the embodiment. These layers are made of Al _X3 In _Y3 Ga _1-X3-Y3 N (X
3 = 0, Y3 = 0, and X3 = Y3 = 0), and intentional impurities may or may not be added.

The p-cladding layer 4 is made of Al _X4 In _Y4 Ga
_1-X4-Y4N (including X4 = 0, Y4 = 0, and X4 = Y4 = 0). The film thickness is 30 to 80
It is preferably set to nm.

A contact layer for lowering the contact resistance can be interposed between the p clad layer 4 and the electrode layer 5. An impurity is added to this contact layer at a higher concentration than the p-cladding layer 4.

A stopper layer having a band gap larger than that of the p-cladding layer 4 for confining electrons can be interposed between the p-cladding layer 4 and the light emitting layer 3. Similarly, a guide layer for confining light can be provided.

Each semiconductor layer is formed by metalorganic compound vapor phase epitaxy (hereinafter, referred to as "MOVPE") (see, for example, JP-A-6-268257 and JP-A-8-97471). In this growth method, ammonia gas and an organic metal gas of a group III element are used as raw material gases,
For example, trimethyl gallium (TMG), trimethyl aluminum (TMA) or trimethyl indium (TM
I) In addition, silane, cyclopentadienylmagnesium, etc. are supplied on a substrate heated to an appropriate temperature to add impurities, and are thermally decomposed to grow a desired semiconductor crystal on the substrate. . See, for example, JP-A-63-188934 for a gas-phase reactor for performing the MOVPE method.

After each semiconductor layer is formed, the p-cladding layer 5 in a semi-insulating state is uniformly irradiated with an electron beam using an electron beam irradiation apparatus. The irradiation conditions of the electron beam were as follows: an acceleration voltage of about 10 kV,
Specimen current 1 .mu.A, the beam moving speed 0.2 mm / sec, a beam diameter 60Myuemufai, a vacuum degree of 5.0X 10 ^{over 5} Torr. The resistance of the p-cladding layer 5 is reduced by such electron beam irradiation.

On the semiconductor wafer thus formed, an n-electrode 6 made of aluminum is formed by vapor deposition at a predetermined portion of a portion to be the substrate 1. Then, as shown in FIG. 3, a p-electrode 5 of gold / nickel or the like is deposited on a portion to be the p-cladding layer 4 and patterned. At this time,
The material of the solder 21 can be laminated on the p-electrode 5. This facilitates the work when fixing the light emitting element 10 to the lead frame 20.

The semiconductor wafer formed as described above is cut by scribing or dicing at a portion 30 indicated by a dotted line in FIG.

The light emitting diode 10 thus formed is fixed to the lead frame 20 by the solder 21 with its p electrode 5 facing downward. Since the solder 21 has conductivity, wire bonding to the p-electrode 5 becomes unnecessary. Instead of the solder 21, the p electrode 5 of the light emitting diode 10 may be fixed to the lead frame 20 using a paste of a conductive metal such as silver. And n on the top surface of the element
Wire bonding is performed on the electrodes according to a standard method.

The present invention is not at all limited to the description of the above-described embodiments and examples. Various modifications are included in the present invention without departing from the scope of the claims and within the scope of those skilled in the art. Needless to say, the present invention can be applied to a laser diode.

[Brief description of the drawings]

FIG. 1 is a sectional view of a light emitting device according to an embodiment of the present invention.

FIG. 2 is a view showing a state where the light emitting device is mounted on a lead frame.

FIG. 3 is a perspective view showing a wafer in a manufacturing process of the light emitting device.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 n-cladding layer (first semiconductor layer) 3 light-emitting layer 4 p-cladding layer (second semiconductor layer) 5 p-electrode 6 n-electrode 10 light-emitting diode 20 lead frame 21 solder

Claims (3)

[Claims] 1. A light-emitting element formed of a GaN-based compound semiconductor, comprising: a substrate that is conductive and transmits light emitted by the light-emitting element; and covers a part of one surface of the substrate. An n-electrode, which is mounted as above, and a light-emitting element structure formed on another surface of the substrate, wherein the n-type first semiconductor layer, the light-emitting layer, and the p-type second semiconductor are arranged from the substrate side A semiconductor light-emitting device comprising: a plurality of layers sequentially stacked; and a p-electrode on the second semiconductor layer. 2. The p-electrode covers substantially the entire surface of the second semiconductor layer and is attached to the second semiconductor layer.
The semiconductor light emitting device according to claim 1, wherein: 3. The substrate according to claim 1, wherein the substrate is formed of an n-type GaN-based compound semiconductor, and a material of the substrate also serves as the n-type first semiconductor layer.
3. The semiconductor light emitting device according to item 1.