JPH08288548A - Light-emitting diode - Google Patents

Abstract

PURPOSE: To provide an LED of a structure wherein even if a semiconductor substrate is made thin, a warpage and a crack, which are caused by a residual stress, are not generated and a high luminous efficiency can be maintained. CONSTITUTION: A light-emitting diode has a double heterojunction luminous layer 6, which consists of an n-type clad layer 3 formed using an InGaAlAs semiconductor material, an active layer 4 and a p-type clad layer 5, on a semiconductor substrate 1 and a second clad layer 7 consisting of an Alz Ga1-z Asc P1-c (0.4<=z<=1.0, 0.85<=c<=0.97) layer is provided on the side, which is opposite to the substrate 1, of the layer 6.

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 (hereinafter referred to as LED) having a double heterojunction structure. More specifically, the present invention relates to an LED in which the semiconductor substrate does not warp or crack even if the lattice mismatch is reduced and the semiconductor substrate is thinned.

[0002]

2. Description of the Related Art Among LEDs, a material is selected such that an active layer is sandwiched between an n-type clad layer and a p-type clad layer, and a bandgap energy of the active layer is smaller than bandgap energies of clad layers on both sides. The LED of the double-heterojunction structure has high brightness, and its demand is expanding to traffic lights, tail lamps of automobiles, and outdoor displays.

A conventional method of manufacturing such an LED will be described with reference to FIG.

First, a reduced pressure MO is formed on the n-type GaAs substrate 21.
A buffer layer 22 made of n-type GaAs by the CVD method,
InGaA doped with silicon (hereinafter referred to as Si)
n-type cladding layer 23 made of IP, undoped InGa
Active layer 24 made of AlP, zinc (hereinafter referred to as Zn)
P-type cladding layer 2 made of InGaAlP
5, current diffusion layer 26 made of p-type AlGaAs, p-type G
The contact layer 27 made of aAs is sequentially crystal-grown,
Then, the p-side electrode 28 made of Au-Zn alloy or the like, A
An n-side electrode 29 made of u-Ge-Ni alloy or the like is formed by vapor deposition or the like, and a p-side electrode 28 and a contact layer 27 are formed.
Is etched away except the central portion as shown in FIG. 2 so as not to interfere with the extraction of light.

In the current diffusion layer 26, the current flowing from the p-side electrode 28 provided in the central portion of the chip to the n-side electrode 29 spreads to the peripheral portion of the chip, and the current flows through the entire active layer 24.
It is provided to improve the luminous efficiency. That is, the current easily flows directly below the p-side electrode 28,
Even if a current flows through the active layer directly below the p-side electrode 28 and emits light, the upward light is blocked by the metal p-side electrode 28 and cannot be extracted to the outside. This is because it is more effective to pass an electric current there.

[0006]

[Problems to be Solved by the Invention] Conventional InGaAlP
As described above, the LED using the compound semiconductor of the system is such that the current is prevented from concentrating on the lower part of the upper (p-side) electrode and the low-resistance AlGaAs layer is p-type clad to spread the current over the entire chip. It is provided on the layer.

However, InGaAl for the clad layer and the active layer
The P-based compound semiconductor is a quaternary compound and the substrate GaAs
However, the AlGaAS-based compound semiconductor cannot be lattice-matched with GaAs, and residual stress remains. On the other hand, if the chip size is about 150 μm square aiming at downsizing of the LED chip from the viewpoint of cost, if the wafer thickness is about 250 to 300 μm as before, it becomes vertically long and unstable during assembly, and the yield decreases. Therefore, it is necessary to polish the substrate to make it thinner. However, when the substrate is thinned by polishing, there is a problem that the substrate is easily warped or cracked due to the above-mentioned residual stress.

Further, if the current diffusion layer is not provided, the distance between the active layer and the upper electrode becomes short, the current from the upper electrode to the active layer cannot be sufficiently spread, and the light is emitted only under the upper electrode. There is a problem that the ratio does not increase, the bonding pressure is applied to the active layer at the time of wire bonding to the upper electrode, the crystallinity is impaired, and the light emission efficiency is reduced. However, when trying to form a thick cladding layer, In
When a compound semiconductor made of GaAlP is grown by the MOCVD method, the growth rate is very small as 3 μm / hr, it takes a very long time to form a thick layer, and when the compound semiconductor layer of InGaAlP is made thick. Crystallinity deteriorates and becomes impractical. Also, GaAs
Since these absorb light, they cannot be provided on the light extraction side.

The present invention solves such a problem, and even if the semiconductor substrate is made thin, warpage or cracking due to residual stress does not occur, and the light emission efficiency can be kept high.
The purpose is to provide.

[0010]

The LED of the present invention comprises a light emitting layer having a double heterojunction structure composed of an n-type clad layer, an active layer and a p-type clad layer made of an InGaAlP based semiconductor material, on a semiconductor substrate. An LED having the same, wherein Al _z Ga _1-z As _c P is provided on the side of the light emitting layer opposite to the semiconductor substrate.
_1-c (0.4 ≦ z ≦ 1.0, 0.85 ≦ c ≦ 0.97)
A second clad layer made of is provided.

The second cladding layer is made of P so that the lattice mismatch with the semiconductor substrate is within a range of ± 1.5 × 10 ^-3.
It is preferable that the ratio is defined because warpage and cracks are less likely to occur even when the semiconductor substrate is thinly polished.

Here, the lattice mismatch means a value obtained by subtracting the lattice constant of the substrate from the lattice constant of the epitaxial growth layer, divided by the lattice constant of the substrate.

[0013]

According to the present invention, since the second cladding layer made of AlGaAsP is provided on the side of the light emitting layer opposite to the semiconductor substrate, the lattice constant can be matched with that of the semiconductor substrate made of GaAs, for example. That is, for example, Al _0.7 Ga _0.3 As has a lattice mismatch with GaAs of about 2.4 × 10 ⁻³ , but by adding P by about 8%, the lattice mismatch becomes about 4 × 10 ⁻⁴ or less, and P By including it, the lattice constant can be made almost equal to that of GaAs.

As a result, the wafer thickness is reduced to 100-150.
Even if the thickness is reduced to about μm, residual stress does not remain, warpage and cracks are less likely to occur in the manufacturing process, and defects due to crystal change due to use do not occur, and reliability is significantly improved.

Further, AlGaAsP has a small specific resistance,
In addition to having the effect of spreading the current to the outer periphery of the chip, the distance between the bonding portion and the active layer can be increased, and the crystallinity of the active layer does not deteriorate during bonding.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the LED of the present invention will be described with reference to the drawings.
Will be described.

FIG. 1 is a sectional view showing an embodiment of the LED of the present invention.

First, the surface of an n-type GaAs substrate 1 doped with Si at a concentration of about 1 × 10 ¹⁸ / cm ³ is depressurized MOC.
Selenium (hereinafter referred to as Se) is 1 × 10 ¹⁸ by the VD method.
The n-type buffer layer 2 made of GaAs doped to about ³ / cm ^{3 is} grown to about 0.5 μm, and then Se is added to 3 × 1.
In _a (Ga _1-x Al _x ) doped to about 0 ¹⁷ / cm ³
_1-a P (0.48 ≦ a ≦ 0.50, 0.5 ≦ x ≦ 1.
0, for example, a = 0.5, x = 0.7), the n-type clad layer 3 of about 1 μm and undoped In _b (Ga _{1 -y
Al y) 1-b P (} 0.48 ≦ b ≦ 0.50,0 ≦ y ≦ 0.
4, y <x, for example b = 0.5, y = 0.3), the active layer 4 is about 0.5 μm, and Zn is 7 × 10 ¹⁷ / cm 3.
^The p-type cladding layer 5 made of In _a (Ga _1-x Al _x ) _1-a P doped to about ^{3 is} about 1 μm, and Zn is 2 × 10 ¹⁸ / c.
Al doped to about _{^{m 3 z Ga 1-z As}} c P 1-c (0.4
≦ z ≦ 1.0, 0.85 ≦ c ≦ 0.97, for example z =
0.7, c = 0.92) and the second clad layer 7 composed of 5
p doped with Zn at about 2 × 10 ¹⁹ / cm ³
A contact layer 8 made of type GaAs is sequentially epitaxially grown to a thickness of about 0.4 μm. InGa as a semiconductor layer
When an AlP-based compound semiconductor material is used, the bandgap energy becomes large when the ratio of Al is large, and by setting y <x as described above, the bandgap energy of the active layer 4 becomes larger than that of the cladding layers 3 and 6. It is smaller than that, and a double heterojunction structure is constructed.

After that, p made of a Ti--Au alloy or the like is used.
The side electrode 9 and the n-side electrode 10 made of Au—Ge—Ni alloy or the like are formed on the surface of the laminated contact layer 8 and the back surface of the n-type GaAs substrate 1 by vapor deposition or the like, respectively, and as shown in FIG. The p-side electrode 9 and the contact layer 8 are removed by etching except the central portion. Next, the LED according to the present invention is obtained by dicing each chip and molding with an epoxy resin or the like.

In the LED of the present invention, the n-type cladding layer 3,
The light emitting layer 6 of the double heterojunction structure composed of the active layer 4 and the p-type clad layer 5 has the same conductivity type as the clad layer (p-type clad layer 5 in this embodiment) opposite to the GaAs substrate 1. (P-type in this embodiment) Second cladding layer 7
To Al _z Ga _1-z As _c P _1-c (0.4 ≦ z ≦ 1.0, 0.
85 ≦ c ≦ 0.97), the feature is that it is formed to about 5 μm. That is, Al _z Ga _1-z As _c P which is a material having a bandgap energy larger than that of the active layer 4.
_Since the second cladding layer 7 made of _1-c is provided, the growth rate is high even in the epitaxial growth by the MOCVD method, and a film having a thickness of about 5 μm can be formed in about 40 minutes.

In the present invention, AlG is used as the second cladding layer 7.
By adding P to the aAs-based material, the lattice constant of AlGaAs, which has a larger lattice constant due to GaAs, can be reduced to match the lattice constant with GaAs.
Difference between lattice constant Δa of GaAsP and GaAs and GaAs
The lattice mismatch (Δa / a), which is the ratio to the lattice constant a of, can be set to approximately 4 × 10 ⁻⁴ by setting, for example, z = 0.7 and c = 0.92. As a result, even if the semiconductor substrate is lapped to a thickness of about 150 μm, warpage and cracks hardly occur, and it is not necessary to perform work such as die bonding in a vertically unstable state, and workability in a post process is improved. Improves yield and improves yield. AlGaA mentioned above
The larger the ratio of P to sP, the smaller the lattice constant, but in the normal case, the sum of As and As is 0.03 to
By setting it to about 0.15, the lattice mismatch is ± 1.5.
Within a range of about 10 ^−3, it can be set to a level at which problems such as warpage hardly occur.

Further, in the present invention, AlG is used as the second cladding layer.
Since an aAsP-based compound semiconductor is used, the specific resistance is small, the current easily diffuses not only directly under the upper electrode but also around the chip, and it is possible to increase the proportion of light emission in areas other than directly under the upper electrode. The luminous efficiency can be improved.

As the second cladding layer, AlGaA is used.
In may be further added to the sP-based material. I
The bandgap energy can be adjusted by adding n.

[0024]

As described above, according to the present invention, Al is formed on the opposite side of the light emitting layer of the double heterojunction structure from the semiconductor substrate.
Since the second cladding layer made of a GaAsP-based compound semiconductor is provided, a thick layer having a small lattice mismatch with the semiconductor substrate can be formed between the light emitting layer and the upper electrode in a short time. As a result, there is almost no residual stress in the semiconductor layer, and even if the semiconductor substrate is thinly polished to a thickness of about 100 to 150 μm, warpage and cracks do not occur, which facilitates the handling in subsequent working steps and improves the yield. .

Further, pressure is not applied to the active layer during wire bonding to the upper electrode, so that crystallinity is not impaired and luminous efficiency is not lowered. In addition, since the AlGaAsP-based compound semiconductor has a small specific resistance, the current is likely to spread to areas other than directly below the upper electrode. Therefore, the light emitted from the light emitting layer other than directly below the upper electrode can be efficiently extracted without being blocked by the upper electrode. The luminous efficiency can be improved.

The band gap energy can be increased by adding P to AlGaAs. This means that if the band gap energy is the same, the Al mixed crystal ratio can be lowered by adding P. Therefore, by lowering the Al mixed crystal ratio, it is possible to prevent the reliability of the element from lowering due to oxidation.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view of an embodiment of an LED of the present invention.

FIG. 2 is a cross-sectional explanatory view of a conventional LED.

[Explanation of symbols]

 1 GaAs substrate 3 n-type clad layer 4 active layer 5 p-type clad layer 6 light emitting layer 7 second clad layer

Claims (2)

[Claims] 1. A light emitting diode having a light emitting layer of a double heterojunction composed of an n-type clad layer using an InGaAlP-based semiconductor material, an active layer and a p-type clad layer on a semiconductor substrate. the semiconductor substrate opposite _{Al z Ga 1-z as c} P 1-c (0.4 ≦ z ≦ 1.0,0.
A light emitting diode provided with a second cladding layer of 85 ≦ c ≦ 0.97). 2. The light emitting diode according to claim 1, wherein the P ratio of the second cladding layer is determined so that the lattice mismatch with the semiconductor substrate is within a range of ± 1.5 × 10 ^−3. .