JPH05335619A - Light-emitting diode and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a light-emitting diode which has high luminance and excellent reliability by reducing the resistance of a window layer and suppressing the diffusion of a p-type impurity into an active layer in which crystals are being grown. CONSTITUTION:The hole concentration in a window layer 6a is set at p=1X10<18>cm<-3> in an 1-mum part near an active layer and at p=3X1018cm<-3> in the remaining 6-mum part. In other words, by lowering the Zn concentration in the part of the window layer 6a near the active layer, the diffusion of Zn into the active layer is suppressed and the generation of non-radiative recombination centers in the active layer can be prevented. When the Zn concentration in the part of the layer 6a far from the active layer is increased, the resistance in the layer 6a can be lowered.

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") made of a compound semiconductor and a method for manufacturing the same.

[0002]

2. Description of the Related Art Visible light LEDs are III-V group compound semiconductor gallium arsenide aluminum (GaAlAs), gallium phosphide (GaP), gallium arsenide phosphide (Ga).
AsP) has been put to practical use that has emission colors from red to green. These are not only indoor applications such as pilot lamps and numerical displays, but also outdoor applications such as outdoor information boards, signal lights, and high-mount stop lamps due to the high brightness of red LEDs using GaAlAs and green LEDs using GaP. Is expanding. However, in order to further expand the applications, it is essential to further increase the brightness of the green LED and the brightness of the orange and yellow LEDs. As a material satisfying this requirement, there is indium gallium aluminum phosphide (InGaAlP).

InGaAlP is inexpensive and can be lattice-matched with GaAs to obtain a high-quality crystal substrate.
It is obtained by epitaxial growth on an As substrate. Furthermore, the band gap can be set to 1.9 to 2.35 eV by changing the composition under the lattice matching condition with GaAs. Of these, 1.9 to 2.3 eV is a direct transition type, which is a wavelength of 650 (red) to 540.
Corresponds to (green) nm. These properties are high brightness LED
The conditions that are important for manufacturing are: (1) there are few crystal defects, (2) the active layer has a direct transition type band structure, and (3) the active layer has a larger bandgap than the active layer. It is satisfied that the so-called double hetero (DH) structure can be formed.

The epitaxial growth of InGaAlP is
Liquid phase epitaxy (LPE) method used for crystal growth of GaAlAs, GaP and GaAsP, chloride vapor phase epitaxy (CV)
It is difficult to perform the crystal growth method under the thermal equilibrium state such as PE) method, and the metal organic chemical vapor deposition (MOVPE) method, the molecular beam epitaxy (MB) method, which is the crystal growth method under the non-thermal equilibrium state.
E) method. Recently, especially MOVP
Method E is used. Further, Zn, Mg, Be or the like is used as a p-type impurity in order to grow a p-type crystal.

FIG. 5 is a sectional view of a chip of a light emitting diode of a first conventional example. This light emitting diode is an InGaAlP orange LED having an emission wavelength of 620 nm, and a low pressure MOVPE method is used for crystal growth. In, Ga, A
As the raw materials of Zn as the 1- and p-type impurities, trimethylindium (TMI), triethylgallium (TEG), trimethylaluminum (TMA), and dimethylzinc (DMZ), which are organic metals, are used, respectively. The raw materials are phosphine (PH
₃ ), arsine (AsH ₃ ), hydrogen selenide (H ₂ S
e) is used. Growth temperature is 700 ° C, growth pressure is 60T
It is constant at orr. The growth rate of each layer is 2 μm /
Hour.

N-GaAs substrate 1 (electron concentration n = 2 × 1
0¹⁸cm^-3, Thickness of 350 μm), firstly n-GaAs
Buffer layer 2 (n = 1 × 10¹⁸cm^-3) Is 0.5 μm
After a long time, n-In_0.5(Ga_0.3Al_0.7)_0.5P crack
Layer 3 (n = 1 × 10¹⁸cm ^-3) Is 1.0 μm, and
Loop In_0.5(Ga_0.8Al_0.2)_0.5P active layer 4
0.5 μm, p-In_0.5(Ga_0.3Al_0.7)_0.5P
Cladding layer 5 (hole concentration p = 5 × 10¹⁷cm^-3) To 1.
It grows to 0 μm. The composition of each of these layers is GaAs substrate 1
The active layer 4 which is lattice-matched with
The length is 620 nm and the clad layers 3, 5
Has a band gap larger than that of the active layer 4.
To do. In this way, the active layer 4 is more
The structure sandwiched between the clad layers 3 and 5 having a large gap is called the DH structure.
The clad layers 3 and 5 injected into the active layer 4
Plays the role of confining the rear. Thereby, the active layer 4
As a result, the density of injected carriers in the interior increases and the recombination probability increases.
As a result, the luminous efficiency is significantly improved.

Following this DH structure, p-Ga _0.3 Al
_{A 0.7} As window layer 6 (p = 3 × 10 ¹⁸ cm ⁻³ ) is grown to 7 μm. Since the window layer 6 takes out the light generated in the active layer 4 to the outside, it is transparent to the emission wavelength. Also, the p-side electrode 7
In order to spread the current from the above to the entire chip before reaching the active layer 4, Zn is doped at a high concentration to lower the specific resistance and grow thick. On top of that, p-GaAs
Contact layer 8 (p = 5 × 10 ¹⁸ cm ⁻³ ) 0.5 μm
grow up. Then, a diameter of 140 μm on the contact layer 8
The circular p-side electrode 7 and the n-side electrode 9 are formed on the entire back surface of the GaAs substrate 1 by vacuum deposition. Further, after removing the p-GaAs contact layer 8 except the portion under the p-side electrode 7 by wet etching, one side is 300
Cut into μm square chips.

The LED chip manufactured by the above method is fixed on the stem with silver (Ag) paste, and the gold (Au) wire is connected. Applying a voltage to this in the forward direction,
It emits light when energized.

[0009]

However, in the above conventional structure, the forward current is 20 mA despite the adoption of the DH structure, the thickening of the window layer 6 and the high concentration doping of Zn.
At that time, a satisfactory brightness of about 70 millilumens (mlm) cannot be obtained. Further, when an energization test was performed at room temperature with a forward current of 50 mA, it deteriorated to about 30% of the initial luminance after 200 hours, and the reliability was insufficient. This is because Zn doped in the window layer 6 at a high concentration is thermally diffused to the active layer 4 in a large amount during the crystal growth, and the Zn diffused in the active layer 4 is a non-radiative center in the active layer 4. Make crystal defects such as. This lowers the internal quantum efficiency and causes high brightness not to be obtained. Further, during the current-carrying test, the crystal defects cause the dislocations to multiply, which causes the deterioration of the brightness.

As another conventional example, in order to suppress the diffusion of Zn into the active layer 4 during crystal growth, only the carrier concentration of the window layer 6 was changed to a low value of 1 × 10 ¹⁸ cm ^-3. The luminance value at a forward current of 20 mA was about 80 mlm, which was not so improved. However, in the above-mentioned energization test, the deterioration of luminance was not observed until 1000 hours. This is because the Zn concentration in the window layer 6 is lowered, so that the diffusion of Zn into the active layer 4 during crystal growth is suppressed, while the window layer 6 is suppressed.
Is increased, the current from the p-side electrode 7 does not spread sufficiently before reaching the active layer 4, and the light extraction efficiency is reduced.

The present invention solves such a problem by lowering the resistance of the window layer and suppressing the diffusion of p-type impurities into the active layer during crystal growth, resulting in high brightness and excellent reliability. Another object of the present invention is to provide a light emitting diode and a method for manufacturing the same.

[0012]

According to a first aspect of the present invention, a light emitting diode has a low p-type impurity concentration in a portion of the window layer close to the active layer and a high p-type impurity concentration in a portion of the window layer far from the active layer. It is characterized by having done. The method for manufacturing a light emitting diode according to a second aspect of the present invention is characterized in that, when the window layer is grown, the growth temperature of the portion farther from the growth temperature of the portion closer to the active layer of the window layer is lowered.

[0013]

According to the structure of claim 1, the p-type impurity concentration in the portion of the window layer close to the active layer is lowered, so that diffusion of the p-type impurity into the active layer is suppressed and non-light emission in the active layer is achieved. You can prevent the occurrence of heart. Further, the resistance in the window layer can be lowered by increasing the p-type impurity concentration in the portion of the window layer far from the active layer. As a result, it is possible to realize an LED having high brightness and excellent reliability.

According to the manufacturing method of the second aspect, the efficiency of incorporating the p-type impurities into the crystal is higher as the growth temperature is lower. Therefore, when the window layer is grown, the portion of the window layer near the active layer is grown. By lowering the growth temperature of the portion farther than the growth temperature of p, the p-type impurity concentration of the portion farther from the portion closer to the active layer can be made higher even if the source supply amount of the p-type impurity is the same. By lowering the growth temperature, diffusion of p-type impurities into the active layer can be suppressed, and generation of non-radiative centers in the active layer can be prevented. As a result, an LED with high brightness and excellent reliability can be manufactured.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment; Corresponding to Claim 1] FIG. 1 is a sectional view showing a chip structure of a light emitting diode according to a first embodiment of the present invention. In FIG. 1, 1 is an n-GaAs substrate, 2 is n-G
aAs buffer layer, 3 is n-In _0.5 (Ga _0.3 Al
_0.7 ) _0.5 P clad layer, 4 is undoped In _0.5 (G
a _0.8 Al _0.2 ) _0.5 P active layer, 5 is p-In _0.5 (G
a _0.3 Al _0.7 ) _0.5 P clad layer, 6a is p-Ga
_0.3 Al _0.7 As window layer, 7 p-side electrode, 8 p-GaA
The s contact layer 9 is an n-side electrode.

This light emitting diode has an emission wavelength of 620n.
m InGaAlP orange LED, p-Ga _0.3 A
The hole concentration of the l _0.7 As window layer 6 a is the same as that of the conventional example except that the hole concentration of the p-Ga _0.3 Al _0.7 As window layer 6 of the conventional example shown in FIG. 5 is different. FIG. 2 shows a hole concentration distribution, which is a difference from the conventional example. That is, in this light emitting diode, the supply amount of dimethylzinc (DMZ) is changed during the growth of the window layer 6a so that the hole concentration of the window layer 6a is only 1 μm close to the active layer 4 and the hole concentration p = 1 × 10. ¹⁸ cm ⁻³ and the remaining 6 μm is p = 3 × 10 ¹⁸ cm ⁻³ . The other crystal growth methods and growth conditions are the same as in the conventional example.

According to this embodiment, the forward current is 20 mA.
The brightness at was about 150 mlm. This value is about twice that in the case of the conventional example, and the brightness is significantly improved. When an energization test was conducted at room temperature with a forward current of 50 mA, a value of about 90% of the initial luminance was shown after 1000 hours. As described above, by lowering the Zn concentration in the region close to the active layer 4 in the window layer 6a, diffusion of Zn into the active layer 4 can be suppressed and generation of non-radiative centers in the active layer 4 can be prevented. it can. Further, by increasing the Zn concentration in the region distant from the active layer 4, the resistance in the window layer 6a can be lowered. As a result, it is possible to realize an LED having high brightness and excellent reliability.

[Second Embodiment: Corresponding to Claim 1] Next, a light emitting diode of a second embodiment will be described. The light emitting diode of the second embodiment is p-type in the first embodiment.
Differ only Ga _0.3 Al _{0. 7} hole concentration distribution of As window layer 6a, the other configurations are the same as in the first embodiment, sectional view is omitted, the p-Ga _0.3 Al _0.7 As window layer The hole concentration distribution is shown in FIG.

That is, the light emitting diode according to the second embodiment is DM-diffused during the growth of the p-Ga _0.3 Al _0.7 As window layer.
The hole concentration is changed to p = 5 × 1 by continuously changing the supply amount of Z.
It is changed in proportion to the distance from the active layer from 0 ¹⁷ cm ^-3 to p = 5 × 10 ¹⁸ cm ^-3 . Similar to the first embodiment, the other crystal growth methods and growth conditions are the same as in the conventional example.

According to the second embodiment, the same effect as that of the first embodiment can be obtained. [Third Embodiment: Corresponding to Claim 2] A method of manufacturing a light emitting diode according to a third embodiment of the present invention will be described. Note that FIG. 1 used in the first embodiment will be used as a cross-sectional structural view of the light emitting diode in this embodiment.

In this embodiment, the n-GaAs buffer layer 2, n-In _0.5 (Ga _0.3 A) on the n-GaAs substrate 1 is used.
l _0.7 ) _0.5 P cladding layer 3, undoped In _0.5 (G
a _{0. 8} Al _{0.2) 0.5} P active layer 4, p-In _0.5 (Ga
_0.3 Al _0.7 ) _0.5 P clad layer 5, p-side electrode 7, p-
The method for forming the GaAs contact layer 8 and the n-side electrode 9 is the same as in the conventional example, and p-Ga _0.3 Al _0.7 A
The method for forming the s window layer 6a is characterized. Hereinafter, differences from the conventional example will be described with reference to FIG.

FIG. 4 shows changes in the growth temperature during crystal growth in this embodiment. The crystal growth method and the growth conditions are almost the same as those in the conventional example, but the growth of the window layer 6a is started with the hole concentration p = 1 × 10 ¹⁸ cm ⁻³ while supplying DMZ at the growth temperature of 700 ° C. After a minute, the growth temperature is changed from the former 700 ° C. to 650 ° C. The supply rate of DMZ was constant, and the growth rate was 2 μm / ho as in the conventional example.
ur. Ga of the growth temperature of 650 ℃ of Zn _{0 .3} Al
_Since the incorporation efficiency into _0.7 As is about three times higher than the growth temperature of 700 ° C., the hole concentration distribution in the window layer 6a is shown in FIG.
Is almost the same as

According to this embodiment, the forward current is 20 mA.
The luminance in Example was about 150 mlm, which was the same value as in the first and second examples. At room temperature, forward current 50m
When the energization test was carried out with A, no deterioration was observed even after 1000 hours, and excellent results were obtained as compared with the first and second examples. That is, according to this example, even if the supply amount of Zn raw material is the same, the efficiency of incorporation of Zn into the crystal is higher as the growth temperature is lower.
The Zn concentration in the crystal can be increased. Therefore, by lowering the growth temperature in the region apart from the active layer 4 in the window layer 6a compared to the growth temperature in the region close to the active layer 4, the same Zn source supply amount as compared to the region close to the active layer 4 is obtained. The Zn concentration in the distant region can be increased, and further, by lowering the growth temperature during the growth of the window layer 6a, the diffusion of Zn into the active layer 4 can be further suppressed, and the non-radiative center of the active layer 4 can be suppressed. It can be prevented from occurring. As a result, it is possible to realize an LED with high brightness and excellent reliability.

In the above embodiment, the active layer is made of In
_{Although 0.5} (Ga _0.8 Al _0.2 ) _0.5 P was used, it can be applied to other compositions or In _0.5 Ga _0.5 P.
Further, although Ga _0.3 Al _0.7 As is used for the window layer, it can be applied by using another composition or InGaAlP. Although Zn is used as the p-type impurity, it can be applied to the case of using other impurities. Furthermore, although the MOVPE growth method was used, it goes without saying that it can be applied to other growth methods.

[0025]

In the light emitting diode according to the first aspect of the present invention, the concentration of the p-type impurity in the portion of the window layer close to the active layer is lowered, so that diffusion of the p-type impurity into the active layer is suppressed, and the non-existence of the non-active layer in the active layer. Generation of emission centers can be prevented. Further, the resistance in the window layer can be lowered by increasing the p-type impurity concentration in the portion of the window layer far from the active layer. As a result, with high brightness,
It is possible to realize an LED with excellent reliability.

In the method for manufacturing a light-emitting diode according to the second aspect, since the efficiency of incorporating p-type impurities into the crystal is higher as the growth temperature is lower, when the window layer is grown, it is closer to the active layer of the window layer. By lowering the growth temperature of the portion farther from the growth temperature of the portion, the p-type impurity concentration in the portion farther from the portion closer to the active layer can be made higher even if the source supply amount of the p-type impurity is the same. By lowering the growth temperature, the diffusion of p-type impurities into the active layer can be suppressed,
Generation of non-radiative centers in the active layer can be prevented. As a result, an LED with high brightness and excellent reliability can be manufactured.

[Brief description of drawings]

FIG. 1 is a chip cross-sectional structural view of a light emitting diode according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a hole concentration distribution in the first embodiment of the present invention.

FIG. 3 is a diagram showing a hole concentration distribution in the second embodiment of the present invention.

FIG. 4 is a diagram showing changes in the growth temperature during crystal growth in the method for manufacturing a light emitting diode according to the third embodiment of the present invention.

FIG. 5 is a cross-sectional structural diagram of a conventional light emitting diode chip.

[Explanation of symbols]

1 n-GaAs substrate 3 n-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P clad layer 4 undoped In _0.5 (Ga _0.8 Al _0.2 ) _0.5 P
Active layer 5 p-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P clad layer 6 a p-Ga _0.3 Al _0.7 As window layer

Claims (2)

[Claims] 1. An n-type semiconductor substrate on which an n-type cladding layer made of n-type indium gallium aluminum phosphide, an active layer made of indium gallium phosphide or indium gallium aluminum phosphide, and p-type phosphide are formed. A light-emitting diode comprising a p-type clad layer made of indium gallium-aluminum successively grown, and a window layer made of indium gallium-aluminum phosphide or gallium arsenide arsenide grown on the p-type clad layer. A light emitting diode, wherein a p-type impurity concentration of a portion of the window layer close to the active layer is lowered and a p-type impurity concentration of a portion of the window layer far from the active layer is increased. 2. An n-type clad layer made of n-type indium gallium aluminum phosphide, an active layer made of indium gallium phosphide or indium gallium phosphide aluminum, and p-type phosphide on an n-type semiconductor substrate. A step of sequentially growing a p-type cladding layer made of indium gallium aluminum; and a step of growing a window layer made of indium gallium aluminum phosphide or gallium arsenide phosphide on the p type cladding layer. A method of manufacturing a light emitting diode, wherein, when growing the window layer, a growth temperature of a portion farther from a growth temperature of a portion of the window layer closer to the active layer is lowered. ..