JPH08186290A - Algainp-based light-emitting device - Google Patents

Abstract

PURPOSE: To provide an AlGaInP-based light-emitting device which is long-lived and whose reliability is high. CONSTITUTION: An n-type (Al0.7 Ga0.7 )0.51 In0.49 P clad layer 12 (thickness: about 1μm), an (Al0.15 Ga0.85 )0.51 In0.49 P active layer 13 (thickness: about 0.6μm) and a p-type (Al0.7 Ga0.3 )0.51 In0.49 P clad layer 14 (thickness: about 1μm) as well as a p-type Al0.7 Ga0.3 As layer 15a (thickness: about 3μm) and a p-type GaAs0.5 P0.5 layer 15b (thickness: about 7μm) which constitute a p-type current diffusion layer 15 are laminated and formed sequentially on an n-type GaAs substrate 11. Then, a surface electrode 16 is formed on the p-type GaAs0.5 P0.5 layer 15b, a rear-surface electrode 17 is formed on the rear surface of the n-type GaAs substrte, and a light-emitting device 10 is constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device using a compound semiconductor, and more particularly to a semiconductor light emitting device using AlGaInP as an active layer.

[0002]

2. Description of the Related Art AlGaInP-based materials have the largest direct transition type bandgap among III-V compound semiconductor mixed crystals excluding nitrides. Since the light emitting device using the AlGaInP-based material having such a large direct transition type band gap can emit light with high brightness in the wavelength range of 550 to 650 nm (green to red range), it is mainly used for outdoor display in recent years. Applications are being advanced.

FIG. 3 is a schematic sectional view showing an example of a conventional AlGaInP light emitting device. This conventional AlG
The aInP-based light emitting device 20 includes a first conductivity type (Al _x Ga _{1 -x} ) _0.51 In layer on a first conductivity type GaAs substrate 11.
_0.49 P cladding layer 12 (thickness: about 1μm), (Al _y Ga
_1-y ) _0.51 In _0.49 P active layer 13 (thickness about 0.6μ
m), the second conductivity type (Al _z Ga _1-z ) _0.51 In _0.49 P
The clad layer 14 (thickness: about 1 μm) and the second conductivity type current diffusion layer 25 (thickness: several μm or more) are sequentially laminated, and the upper electrode 16 and the GaAs substrate 11 are formed on the p-type current diffusion layer 25. The bottom surface electrode 17 is provided on the bottom surface.

Here, (Al _y Ga _1-y ) _0.51 In _0.49
P active layer 13 and two AlGaInP cladding layers having a bandgap larger than that of the active layer 13, that is, the first
Conductivity type (Al _x Ga _1-x ) _0.51 In _0.49 P cladding layer 12 and second conductivity type (Al _z Ga _1-z ) _0.51 In _0.49 P
The double heterojunction structure composed of the cladding layer 14 constitutes the light emitting layer portion 18, and the Al composition x, y, z of each AlGaInP layer composing the double heterojunction structure is 0 ≦.
The relations y ≦ 0.7, y <x, y <z are satisfied. Also,
The _{(Al y Ga 1-y)} 0.51 In 0.49 P active layer 13 functions as a light-emitting layer. In the following description, if there is no special circumstance, the above (Al _x Ga _1-x ) _0.51 In
_{0.49 P, (Al y Ga 1} -y) 0.51 In 0.49 P and (Al
_z Ga _1-z ) _0.51 In _0.49 P are collectively referred to as (Al _B Ga
_1-B ) _0.51 In _0.49 P or simply AlGaInP.

In the AlGaInP type light emitting device as described above, it is necessary to provide a current diffusion layer on the light emitting layer portion 18, and in particular, it is necessary to provide a current diffusion layer made of a material different from AlGaInP. The reason will be described with reference to FIG. In FIG. 3, the current distribution from the upper surface electrode 16 is indicated by reference numeral 19.

In energization light emission of the AlGaInP light emitting device, it is desirable that the current from the upper surface electrode 16 is effectively diffused throughout the light emitting layer portion 18, particularly the entire AlGaInP active layer 13 to allow efficient light emission. For that purpose, the distance (thickness) between the upper surface electrode 16 and the AlGaInP active layer 13 needs to be set to a predetermined value or more (several μm or more).

By the way, the AlGaInP type light emitting device is
Normally, as shown in FIG.
The AlGaInP-based layer 12 (thickness: about 1 μm) and the layer 13 (thickness: about 0.
6 μm), layer 14 (thickness about 1 μm) (Al _B G
a _1-B ) _0.51 In _0.49 P, but with a total thickness of more than 4 μm (Al _B Ga _1-B ) _0.51 In
It is extremely difficult to form a _0.49 P layer without impairing crystallinity. Therefore, in order to effectively diffuse the current from the upper surface electrode 16 to the entire area of the active layer 13, the thickness between the upper surface electrode 16 and the active layer 13 needs to be several μm or more. A layer of this thickness is formed by AlGaI
For nP-based materials, it is almost impossible due to the above reasons.

Therefore, conventionally, a layer made of a material other than AlGaInP is used as the current diffusion layer 25 and the light emitting layer portion 18 is formed.
Is formed on the upper surface, and the current from the upper surface electrode 16 is applied to AlGaInP.
Efficient light emission has been achieved by effectively diffusing the entire active layer 13.

As a material for the current diffusion layer 25, on the assumption that photons emitted from the AlGaInP active layer 13 are not absorbed, a direct band gap ([Equation 1]) larger than the energy of the photons is used.

[0010]

[Equation 1] Al _w Ga _1-w As (having a value of 0.45 ≦ w <1 and usually w≈0.7) or GaP has been conventionally used.

[0011]

However, the above Al _w G
When a _1-w As or GaP is used as the material of the current spreading layer, both have serious problems, which will be described below.

(Al _w Ga _1-w As current diffusion layer) AlG
Since the light emitted from the aInP active layer 13 is not absorbed by the Al _w Ga _1-w As current diffusion layer 25, the AlAs mixed crystal ratio w is usually large (for example, w≈0.7) and the Al _w G having a high Al concentration is used.
a _1-w As is used. Al _{w with} high Al concentration
When Ga _1-w As is used as the material of the current diffusion layer 25, such Al _w Ga _1-w As having a high Al concentration is very easy to oxidize. Then, there is a problem that the oxidation of the Al _w Ga _{1 -w} As current diffusion layer 25 causes deterioration of the emission luminance and further destruction. However, Al _w Ga
_Since the lattice mismatch ratio between _1-w As and (Al _B Ga _1-B ) _0.51 In _0.49 P is very low at about 0.1%, (Al _z G
a _1-z ) _0.51 In _0.49 P clad layer 14 and Al _w Ga _1-w As current diffusion layer 2 formed on the clad layer 14.
5 and a good crystal interface is formed,
It has the advantage that an Al _w Ga _1-w As current spreading layer with good crystal quality can be obtained.

(GaP current spreading layer) GaP is (Al _B G
a _1-B ) _0.51 In _0.49 P, which has a very high lattice mismatch rate of about 4%, so that it is extremely difficult to grow GaP crystals on the (Al _z Ga _1-z ) _0.51 In _0.49 P cladding layer 14. Is. Further, when the lattice mismatch rate is about 4%, dislocations of about 1 × 10 ¹² cm ^-2 occur at the interface between the cladding layer 14 and the GaP current diffusion layer 25 formed on the cladding layer 14. At the same time, a local internal stress is generated at this interface. These dislocations and internal stress affect the light emitting layer portion 18, especially the AlGaInP active layer 13 that plays a major role in light emission. Therefore, when the AlGaInP-based light emitting device 20 is used for energization and light emission, there is a problem that the device characteristics, particularly, the emission brightness is deteriorated. However, Ga
Since P is a material that is difficult to oxidize, the high Al concentration of A
It has the advantage of not causing problems like l _w Ga _1-w As.

Therefore, the present invention has good lattice matching with (Al _B Ga _{1 -B} ) _0.51 In _0.49 P forming the light emitting layer portion, and is provided with a current diffusion layer which is hard to be oxidized, and emits current for a long time. It is an object of the present invention to provide an AlGaInP-based light emitting device that has a long life and high reliability, in which the light emitting characteristics and the like do not deteriorate.

[0015]

In order to solve the above problems, the present invention provides a light emitting layer portion having an AlGaInP double heterojunction structure on a GaAs substrate and a current spreading layer formed on the light emitting layer portion. In the AlGaInP-based light emitting device having, the current spreading layer may be formed of (Al
_y Ga _1-y ) _0.51 In _0.49 P Direct type band gap ([Equation 1]) larger than the energy of photons emitted from the active layer

[0016]

[Equation 1] Al _w Ga _1-w As layer having Al and the Al _w Ga _1-w A
The GaAs layer is composed of two layers, a GaAs _1-v P _v layer formed on the s layer.

The Al composition y of the (Al _y Ga _1-y ) _0.51 In _0.49 P active layer is 0 ≦ y ≦ 0.7, and the Al _w
Ga _1-w As AlAs mixed crystal ratio w and GaAs _1-v
The GaP mixed crystal ratio v of P _v is preferably 0.45 ≦ w <1 and 0.4 ≦ v <0.8, respectively.

The total thickness of the current spreading layer (Al _w Ga
Sum of _1-w As layer thickness and GaAs _1-v P _v layer thickness)
Is required to be 5 μm or more in order to maintain the crystallinity of the light emitting layer portion and to sufficiently perform the current diffusion layer. The thicker the efficiency, the higher the efficiency of extracting emitted light to the outside.

Al _w Ga _1-w As was grown to be lattice-matched with a GaAs substrate (Al _B Ga _1-B ) _0.51 In _0.49.
Since the lattice constant is very close to that of P, a good crystal interface is formed between the AlGaInP light emitting layer portion and the Al _w Ga _1-w As layer grown on the light emitting layer portion, and a good crystal quality is obtained. An Al _w Ga _1-w As layer is obtained.
Although the lattice constant of GaAs _1-v P _v changes with the change of the mixed crystal ratio v, for example, when a GaAs _0.5 P _0.5 layer is formed on the Al _w Ga _1-w As layer, Al _w G
The lattice mismatch between a _1-w As and GaAs _0.5 P _0.5 is 2
%, And a GaAsP layer having a low dislocation density can be grown as compared with the case where GaP is directly grown as a current diffusion layer. In addition, in the double current diffusion layer of the present invention, the interface where dislocations occur is Al _w Ga _1-w.
Since it is the interface between the As layer and the GaAs _1-v P _v layer, the interface is separated from the light emitting layer portion by the thickness of the Al _w Ga _1-w As layer, and the dislocation generated at the interface is generated. Is less likely to affect the light emitting layer portion. Thereby, the high crystal quality of the light emitting layer portion can be maintained.

Furthermore, since GaAs _1-v P v is a hard material that is highly oxidized similarly to GaP, GaAs _1-v P
_{The v} layer has an effect of serving as a protective film for preventing oxidation of the Al _w Ga _1-w As layer.

[0021]

EXAMPLES An AlGaInP light emitting device of the present invention will be described below with reference to FIGS. However, chemical formulas, elements, layer constitutions, film thicknesses, relative positions and the like stored in this example are not merely intended to limit the scope of the present invention unless otherwise specified, and are simply explained. It's just an example.

The MOVPE method (metalorganic vapor phase epitaxy) is used to grow each layer of the AlGaInP light emitting devices of the present example and the comparative example. The raw materials of Al, Ga, In, P, and As are trimethylaluminum [Al (CH ₃ ), respectively.
₃ : TMAl], trimethylgallium [Ga (CH ₃ ).
₃ : TMGa], trimethylindium [In (C
H ₃ ) ₃ : TMIn], phosphine (PH ₃ ) and arsine (AsH ₃ ) are used. Further, hydrogen selenide (H ₂ Se) and dimethyl zinc [Zn (CH ₃ ) ₂ : DMZn] are used as n-type and p-type dopant sources, respectively.

FIG. 2 shows an example of the structure of a growth apparatus used when growing each layer by the MOVPE method. In the same figure, vapors of the various Group III metal organic materials and hydrides of vapor phase Group V elements are mixed by selecting the partial pressure and the flow rate according to the composition of growth, and the obtained mixed gas is It is supplied to the reaction chamber 50 and a desired growth layer is formed on the n-type or p-type GaAs substrate arranged in the reaction chamber 50. In the figure, 51 is phosphine (P
H ₃ ), a gas cylinder for storing gas phase hydrides such as arsine (AsH ₃ ), and is supplied to a carrier gas flow passage 55 for hydrogen or the like via a pressure / flow rate regulator 52 and a control valve 53. Reference numeral 56 is a bubbling tank for producing vapors of metals such as trimethylaluminum [TMAl], trimethylgallium [TMGa], and trimethylindium [TMIn], and is bubbled with hydrogen gas whose pressure / flow rate is controlled by the pressure / flow rate regulator 52. The organic metal vapor is sent to the carrier gas passage 55 such as hydrogen through the control valve 53. The group III metal organic vapor and the group V element hydride are mixed with each other to generate a predetermined mixed gas by selecting a partial pressure and a flow rate according to the composition of growth through the gas passage 55. The gas is supplied to a reaction chamber 50 surrounded by a heating element and adjusted to a predetermined pressure and a predetermined temperature, and a desired growth layer is laminated on an n-type or p-type GaAs substrate arranged in the reaction chamber 50. Specifically, under a reduced pressure of 50 Torr, V
A gas mixed so that the supply amount ratio (V / III ratio) of the group element and the group III element is 100 is used as a source gas for the growth layer, and GaAs is grown under the growth conditions of a growth temperature of 710 ° C. and a growth rate of 4 μm / hour. Each layer of the AlGaInP light emitting device is laminated on the substrate. By forming the epitaxial wafer thus obtained into a device, AlGaI
An nP light emitting device can be obtained.

According to the above manufacturing method, the Al of this embodiment is
A GaInP light emitting device 10 was manufactured. FIG. 1 is a schematic sectional view showing an embodiment of the AlGaInP light emitting device of the present invention. In the figure, the same members as those in FIG. The light emitting device 10 is an n-type GaA.
On the s substrate 11, n-type (Al _0.7 Ga _0.3 ) _0.51 In _0.
49 P clad layer 12 (thickness about 1 μm), (Al _0.15 Ga
_0.85 ) _0.51 In _0.49 P active layer 13 (thickness 0.6 μ
m), p-type (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P clad layer 14 (thickness: about 1 μm), and p-type Al _0.7 Ga _0.3 As layer 15 a (thickness: about 3 μm) constituting the p-type current diffusion layer 15.
m), p-type GaAs _0.5 P _0.5 layer 15b (thickness about 7μ
m) are sequentially laminated, and the upper surface electrode 16 is provided on the p-type GaAs _0.5 P _0.5 layer 15b and the lower surface electrode 17 is provided on the lower surface of the n-type GaAs substrate.

(Evaluation results of various characteristics) [Table 1] shows the evaluation results of various characteristics of the AlGaInP-based light emitting device of the present embodiment, as well as the AlGaIn of the conventional structures of Comparative Example 1 and Comparative Example 2.
This is shown in comparison with that of the P-based light emitting device. The AlGaInP-based light-emitting devices of Comparative Example 1 and Comparative Example 2 are the AlGaInP-based light-emitting devices of the conventional structure shown in FIG. 3, and the p-type current diffusion layers 25 are each formed of p-type Al.
_0.7 Ga _0.3 As current diffusion layer (about 10 μm) and p-type G
The same as the example except that the aP layer (thickness: about 10 μm) was formed.

As is clear from [Table 1], the AlGaInP-based light-emitting device of this example has a higher emission brightness and emission brightness than the conventional AlGaInP-based light-emitting devices (Comparative Example 1 and Comparative Example 2). AlGaIn with almost no deterioration
It is a P-type light emitting device, and the effectiveness of the present invention has been proved. That is, when the current diffusion layer is formed only by the Al _0.7 Ga _0.3 As layer (Comparative Example 1), the light emitting layer portion is formed (Al _B
Since the lattice matching with Ga _1-B ) _0.51 In _0.49 P is good, the initial emission luminance is as high as 100, but the current diffusion layer is easily oxidized and deteriorates due to long-term use, resulting in a poor life of 66%. On the other hand, when the current diffusion layer is formed of GaP only (Comparative Example 2), the light emitting layer portion is formed (Al _B
Ga _1-B ) _0.51 In _0.49 P has a high lattice mismatch rate, so that dislocations and internal stress existing at the interface between the light emitting layer portion and the GaP current diffusion layer affect the AlGaInP active layer as well. Has a low luminance of 83 and a life of 8
It turns out that it is inferior to 8%. On the other hand, in the example, the initial emission luminance is as high as 100 and the life is as good as 98%, and it can be seen that the effect of forming the current diffusion layer by the above two layers is remarkable.

[0027]

[Table 1]

In Table 1, the evaluation data is (10
Epitaxial wafer) × (10 light emitting device / epitaxial wafer) = 100 Average value of light emitting device. Luminance measurement current: 20 mA Life (also called afterglow rate) Afterglow rate = (I / I ₀ ) × 100 (%) I ₀ : Initial luminance I: 85 ° C., 85% humidity, DC 50 mA It is the luminance after energization and light emission for 1000 hours.

[0029]

As described above, according to the present invention,
Constituting the light emitting layer (Al _B Ga _1-B ) _0.51 In _0.49 P
Al _w Ga _1-w As layer having good lattice matching with Al and the Al
oxidizable GaA formed on _w Ga _1-w As layer
By providing the current diffusion layer composed of two layers, s _{1 -v} P _v layer, a long-life and highly reliable AlGaInP-based light emitting device that does not cause deterioration in light emission characteristics even when used for long-time light emission is obtained. To be

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional explanatory view showing an embodiment of an AlGaInP-based light emitting device of the present invention.

FIG. 2 is a schematic explanatory view showing an example of a manufacturing apparatus used when growing each layer by the MOVPE method.

FIG. 3 shows a conventional AlGaInP light emitting device (Comparative Example 1,
It is a schematic cross section explanatory drawing which shows one Example of the comparative example 2 and a general example.

[Explanation of symbols]

10 AlGaInP-based light emitting device according to an embodiment of the present invention 11 GaAs substrate 12 Clad layer 13 Active layer 14 Clad layer 15 Current diffusion layer of AlGaInP-based light emitting device according to an embodiment of the present invention 15a AlGaAs layer 15b GaAsP layer 16 Top electrode 17 Lower surface electrode 18 Light emitting layer portion (double heterojunction structure) 19 Current distribution 20 Conventional AlGaInP-based light emitting device 25 Current diffusion layer of conventional AlGaInP-based light emitting device

Claims (5)

[Claims] 1. An AlGaInP-based light emitting device having a light emitting layer portion having an AlGaInP double heterojunction structure on a GaAs substrate and a current spreading layer formed on the light emitting layer portion, wherein the current spreading layer is the light emitting layer. Part of (Al _y Ga _1-y )
_0.51 In _0.49 P Direct type band gap larger than the energy of photons emitted from the active layer ([Equation 1]) [Equation 1] Al _w Ga _1-w As layer having Al and the Al _w Ga _1-w A
An AlGaInP-based light-emitting device comprising two layers of a GaAs _1-v P _v layer formed on an s layer. 2. The (Al _y Ga _1-y ) _0.51 In _0.49 P
The Al composition y of the active layer is 0 ≦ y ≦ 0.7, and the AlGaIn according to claim 1.
P-based light emitting device. 3. The AlGaInP-based light emitting device according to claim 1, wherein the AlAs mixed crystal ratio w of the Al _w Ga _1-w As is 0.45 ≦ w <1. Wherein said GaAs _1-v P _v of the GaP mixed crystal ratio v
Is 0.4 ≦ v <0.8. 4. The AlGaInP-based light emitting device according to claim 1, wherein 5. The AlGaInP-based light emitting device according to claim 1, wherein the current diffusion layer has a total thickness of 5 μm or more.