JPH03174780A - Light emitting diode - Google Patents

Abstract

PURPOSE:To omit a strength reinforcing GaAlAs substrate by providing a surface electrode and a rear-surface-part electrode on the upper surface and the rear surface of a double-heterojunction structure comprising a clad layer, an active layer and a window layer, and lining the entire rear surface with a conductive resin. CONSTITUTION:A surface electrode 1 and a rear electrode 7 are provided on the upper surface and the rear surface of a double-heterojunction structure comprising a clad layer 4, an active layer 3 and a window layer 2. A reinforcing conductive resin film 9 is formed on the rear surface. As the reinforcing conductive resin, a heat resisting resin paste containing noble metal powder can be used. As the resin paste, epoxy resin and polyimide based resin can be used. As the noble metal powder, silver powder, gold powder or the powder of alloy containing the silver powder and the gold powder can be utilized. Thus a strength reinforcing GaAlAs substrate can be omitted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a light emitting diode (1, ED), particularly a high brightness light emitting diode.

[Prior art] L E of conventional tuple/\terror structure (D I-f)
The D chip is shown in FIGS. 4 and 5. In the figure, 1 is a surface electrode, 2 is GaAJ! As window layer, 3 is GaAfJA
s active layer, 4 is GaAfJAs cladding layer, 5 is GaA
jA, s substrate, 6 is GaAs substrate, 7 is back partial electrode,
8 is a back electrode.

In the back reflection type GaA, Q As LED shown in Fig. 4, the light emitted from the active layer between the substrates is reflected by the back surface, so the back reflection type GaA, Q As LED shown in Fig.
Compared to D, it is possible to achieve a high luminance of 2 (?i or more -L),
It has a wide range of uses including outdoor use.

However, L E
In order to handle a D epitaxial wafer or an LED chip manufactured using the same, both the wafer and the chip require a certain degree of mechanical strength. For this reason,
In the back reflection type G a A j A s LED ebitaxial wafer, as shown in FIG.
．． Active layer 3. In addition to the parts that directly contribute to light emission, such as the cladding layer 4, there is a G a AJ for strength reinforcement with a thickness of about 200 μm.
! 6GaAJ that requires forming the As substrate 5 and making the total thickness about 300 μII! In As crystal growth, A
Since the segregation coefficient of J is large, it is generally not possible to grow large and uniform crystals. For this reason, GaAJIAs substrates are generally difficult to obtain.

There are two typical manufacturing methods for back-reflection type GaA, Q As LEDs:

(1) For the growth of the epitaxial wafer, a liquid phase epitaxial growth method, which has a proven track record for light emitting devices, is used. GaA
GaAJIAs layer 5 of approximately 200 μIIl on the s substrate.
After growing the cladding layer 4, the active layer 3. The DH tank structure of the wind layer 2 is grown. Thereafter, the GaAs substrate is removed by polishing, etching, or the like.

(2) GaA of about 200tzTn on a GaAs substrate,
After growing the ffAs layer 5, the evaporator is taken out and the G
The aAs substrate is removed and the surface of the GaAjAs layer 5 is mirror-finished. Thereafter, this GaAJAs substrate 5 is used to form a cladding layer 4. Active layer 3. DHI growth of the window layer 2 is performed.

[Problem to be solved by the invention] However, the back reflection type GaAJfAs manufactured using the conventional technology
In an epitaxial wafer for LED, a GaA or OAs layer for strength reinforcement with a thickness of about 200 μm is required for strength reinforcement.

Therefore, in the above-mentioned manufacturing method (1), it is necessary to perform growth at a high temperature such as (1) a cooling start temperature of 100°C. For this reason,
The epitaxial furnace wears out rapidly, resulting in high equipment depreciation costs. Furthermore, it is difficult to uniformly grow a 200 μm thick film, the characteristics vary widely, and mass production is difficult.

(2) The temperature difference method in which the Ga solution has a temperature gradient requires gas phase transport of the dopant, a transport mechanism for the substrate, etc., and the equipment becomes expensive.

In addition, in the above-mentioned manufacturing method (2), (1) after growing the GaAJIAs layer, −30% is removed and the GaAJIAs layer is grown.
Removal of the As substrate requires a number of steps to mirror-finish the surface. Furthermore, since GaA and QAs are brittle and easily cracked, the yield of this process is low.

(2) The surface of the GaAJIAs taken out is oxidized, and normal epitaxial growth cannot be performed by normal methods. Furthermore, since light absorption occurs even in the GaA and QAS substrates, the light output decreases.

The purpose of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a back-reflection type GaA that does not require a GaA or QAs substrate for strength reinforcement.
, II AsLED.

[Means for Solving the Problems] The present invention provides a back reflection type GaA, OAs light emitting diode in which a front electrode and a back partial electrode are provided on the front and back surfaces of a double heterostructure consisting of a cladding layer, an active layer, and a window layer. The entire back surface is lined with conductive resin. Instead of lining with the conductive resin described above, a metal plate may be attached to the back surface on which the back electrode is formed.

[Function] Since the conventional GaAJIAs substrate for strength reinforcement is eliminated, and the entire back side of the double heterostructure is reinforced with conductive resin or pasted with a metal plate, it is possible to handle wafers of about 150 μm. , it is possible to significantly reduce wafer prices and reduce characteristic variations. Also,
Since the conductive resin or metal plate absorbs less light than the GaAJIAs substrate, the light output can also be made brighter.

As the reinforcing conductive resin, a heat-resistant resin paste containing noble metal powder can be used. An epoxy resin or a polyide resin can be used for the resin paste, and a silver powder, a gold powder, or an alloy powder containing these can be used as the noble metal powder.

The appropriate thickness of the resin film is 50 μm to 300 μm. A compound semiconductor wafer can be used as the semiconductor wafer.

Paste is suitable for metal plates such as iron and aluminum.

Copper and brass conductive metal plates can be used.

[Example] Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of an LED chip reinforced with conductive resin. The emission wavelength is 660 μm. Here, the normal cladding layer 4. Active layer 3. On the front and back surfaces of the double heterostructure (DH) of the window layer 2, surface electrodes 1. A back surface partial voltage #17 is provided, and a reinforcing conductive resin film 9 is formed on the back surface.

The manufacturing method is liquid phase epitaxial growth method.
A 4.1μ cladding layer with a film thickness of 100μ is formed from a GaAs substrate.
DH consisting of an active layer of 3.50 μm and a window layer 2 of
Form a s structure. Thereafter, gold electrodes 1 with a diameter of 150 μm are formed on the surface such that the distance between the electrode centers is 350 μm.

The electrodes were formed by forming an electrode pattern in advance in a photolithography process, depositing the electrodes on top, and then forming them in a lift-off process.

Thereafter, alloying was performed at 400° C. for 3 minutes in a N2 atmosphere.

The wafer on which the surface electrode #11 was formed was set on a quartz tray with the surface facing downward. After this, the wafer and the tray are
The GaAs substrate is removed by placing it in an As selective etching solution. The etching solution contains N202:NH40H=1
A 0:1 mixed solution was used at room temperature.

The GaA, QAs wafer from which the GaAs substrate has been removed is dried while being placed on a quartz tray, and a metal mask is placed on top and fixed. Holes with a diameter of 30 μm were formed in the metal mask such that the distance between the centers of the holes was 100 μl and 11 m. The wafer is set in the wafer evaporation apparatus in this state, and all the electrodes 7 are evaporated from above the metal mask, and alloyed as in the surface electrode@1.

As a result, a partial electrode 7 or 10 with a diameter of 30μ is placed on the back side.
They are formed at intervals of 0 μm.

Since these steps can be performed while the wafer is placed on the quartz tray, wafer cracking can be prevented even with a wafer having a total thickness of 150 μm. Therefore, the yield is improved.

After removing the metal mask, silver-epoxy conductive resin 9 is applied to the back surface to a thickness of 200 μm. After this,
Heat to 170°C for 30 minutes to harden the resin.

After the resin has been cured, the wafer is separated into elements in a normal process step, and then fully cut by tying and separated into chips. That is, by forming the conductive resin layer 9, even a wafer with a total thickness of 150 μm can be processed in the post-process.

Figure 2 shows L reinforced with metal plate 1o instead of conductive resin 9.
An example of an ED chip is shown.

As in the above actual filter example, all chambers @7 were formed on the back surface, and after removing the metal mask, an aluminum plate (metal plate 10) was pasted on the back surface with silver-epoxy conductive resin 9. The thickness of the aluminum plate is 200 μm. Thereafter, the resin is cured by heating at 170° C. for 30 minutes. After the resin has been cured, the wafer is separated into chips in a normal process.

The chip manufactured as described above was bonded onto the stem by epoxy die bonding, and an LBD was manufactured through wire bonding and resin molding.

Figure 3 shows the measurement of the light emission output of this LED and the GaAJI
The results are shown in comparison with ED using an As substrate and a GaAs substrate. The light emission output characteristic (curve A) of this LED is G
It can be seen that higher brightness can be obtained than the LED using the aAjAs substrate (curve B) and the LED using the GaAs substrate (curve C). This is because there is no light absorption in the GaAρAs substrate, and means that the luminous intensity can be improved by about 20%.

The features of the above embodiment can be summarized as follows.

(i) In the z-pitaxial growth, growth conditions of 900'C or less are used, similar to the normal DH ellipse, so that generally uniform wafers can be manufactured.

(2) Since there is no light absorption in the G a AJ) A s substrate, the luminous intensity of the emitted light could be improved by about 20%.

(3) Since normal process steps and device manufacturing can be used, no special equipment is required.

(4) Wafer cracking, etc. has decreased, and yield has improved.

In the above embodiments, the red LED with a wavelength of 660 μm was described, but the present invention is also applicable to GaAJlA LEDs such as infrared LEDs.
It can be widely used in general light emitting devices in which the S layer is grown thick to reinforce it.

[Results of the Invention] As described above, the present invention can produce the following remarkable effects.

(1) Eliminating the conventional GaAJIAs substrate for strength reinforcement,
The entire back side of the double-hetero structure is lined with conductive resin or reinforced with a metal plate, so 1.
It is possible to handle wafers with a diameter of about 50 μm, and the wafer price can be significantly reduced and variations in characteristics can be reduced. This reduces wafer cracking, improves yield, and allows use of conventional process techniques and device manufacturing.
No special equipment required.

(2) Also, there is no GaAlAs substrate for strength reinforcement,
Since no light is absorbed in the GaAJIAs substrate, the luminous intensity of light emission can be improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an LED chip, not showing one embodiment of the present invention, FIG. 2 is a cross-sectional view of an LED chip, not showing another example of the present invention, and FIG. A diagram showing an example of measuring characteristics, Figure 4 is a conventional back reflection type GaAjA, 5LED.
Cross-sectional view of the chip. FIG. 5 is a cross-sectional view of a conventional LED chip using a GaAs substrate. In the figure, 1 is a surface electrode, 2 is a GaA, QAs window layer, 3 is a Ga, A, QAs active layer, 4 is a Ga1A, ClAs cladding layer, 5 is a GaA, f! As substrate,
6 is a GaAs substrate, 7 is a back partial electrode, 8 is a back electrode,
9 indicates a conductive resin, and 10 indicates a metal plate.

Claims (1)

[Claims] 1. In a back reflection type GaAlAs light emitting diode,
A light emitting diode characterized in that a front electrode and a back partial electrode are provided on the front and back surfaces of a double heterostructure consisting of a cladding layer, an active layer, and a window layer, and the entire back surface is lined with a conductive resin. 2. The light emitting diode according to claim 1, characterized in that instead of being lined with the conductive resin, a metal plate is attached to the back surface on which the back electrode is formed.