JPH07111340A - Manufacture of light emitting diode - Google Patents

Abstract

PURPOSE:To enable an N-type window layer of ideal carrier concentration profile which has such a concentration gradient that concentration is high on an active layer side and low on a surface side to be easily obtained at a low cost, with the same growth solution. CONSTITUTION:A P-type active layer growth solution 14 is cooled down at a prescribed cooling rate, and a GaAs substrate 18 is made to come into contact with the solution 14 when it, reaches a prescribed temperature and left to stand till it reaches a certain temperature, whereby a P-type Al0.35Ga0.65 As active layer is grown on the GaAs substrate 18. Then, the Gaps substrate 18 is brought into contact with an N-type window layer growth solution 15 and left to stand till it reaches a certain temperature to grow a low carrier concentration N-type Al0.7 Ga0.3 As window layer 4 on the GaAs substrate 18. When the solution 15 reaches a lower temperature, additional impurity Te 16 is dropped in it to enhance the solution 15 in Te concentration, and a high carrier concentration N-type Al0.7 Ga0.3 As window layer is made to grow on the GaAs substrate 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a GaAlAs light emitting diode, and more particularly to a method for manufacturing a high brightness light emitting diode for display, communication and the like.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional single hetero structure Ga.
AlAs red light emitting diode (hereinafter, SH structure red LE
(Abbreviated as D). In this SH structure red LED, a Zn-doped p-type Al _0.35 Ga _0.65 As active layer 2 and a Te-doped n-type Al _0.7 Ga _0.3 As window layer 3 are sequentially laminated on a Zn-doped p-type GaAs substrate 1 by a liquid phase epitaxial growth method. Then, the p-side electrode 6 is
The n-side electrode 7 is formed, and the n-side electrode 6 has a structure in which a part of the n-side electrode 6 is removed by a photolithography technique to form a circular shape.

An example of the impurity concentration profile of the n-type window layer 3 of the SH structure red LED is shown in FIG. n
When Te is added to the growth solution as a type impurity, it is more likely to be taken into the growth layer at a lower temperature when grown by the slow cooling method, so that the impurity profile has a gradient type as shown by the solid line.
However, when grown by the temperature difference method, it becomes constant as shown by the dotted line.

Regardless of whether the growth method is the slow cooling method or the temperature difference method, the impurity concentration varies depending on the amount of Te added to the growth solution. The shape of the impurity profile shown is basically unchanged. However, due to the carrier concentration profile of this n-type GaAlAs window layer, the SH structure red L
Since the light emission output and electric characteristics of the ED are greatly affected, this carrier concentration profile becomes important. This will be described by taking the SH structure red LED of FIG. 5 as an example.

Ideally, the carrier concentration profile of the n-type window layer 3 is as follows. In the vicinity of the interface with the p-type active layer 2, if the Te concentration is high, the crystallinity is deteriorated and the emission output is reduced, so that 1 to 3 × 10 ¹⁷ cm ^−3.
A low carrier concentration of the order is desirable. Further, in the vicinity of the interface with the n-side electrode 7, in order to easily obtain a good ohmic junction and to improve the spread of electrons injected from the n-side electrode 7, about 1 × 2 × 10 ¹⁸ cm ^−3. A high carrier concentration is desirable.

Therefore, it has been proposed that the carrier concentration profile of the n-type window layer be improved by positively utilizing the characteristic that the impurity Te is more likely to be taken into the growth layer at lower temperatures and devising a temperature program in the slow cooling method. (For example, JP-A-63-278383). Since this method uses the same n-type window layer growth solution, there is no need to prepare two or more kinds of growth solutions for growth.

[0007]

However, in the above proposed slow cooling method, the carrier concentration in the vicinity of the interface with the p-type active layer and in the vicinity of the interface with the n-side electrode cannot be controlled independently. However, optimization is difficult because parameters such as cooling rate, temperature, and thickness are involved in the temperature program in a complicated manner. Further, if the cooling rate is slowed down, the time required for growth becomes long, so that workability is poor. In particular, it takes a long time to optimize the carrier concentration near the interface with the n-side electrode. Therefore, it is difficult to obtain an ideal carrier concentration profile of the n-type window layer.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to provide an LED with high emission output and good electrical characteristics.
An object of the present invention is to provide a method for manufacturing an LED that can easily obtain the above.

[0009]

According to the method of manufacturing an LED of the present invention, a GAlAs active layer is provided on a GaAlAs active layer.
There is a step of growing the aAlAs window layer as a single heterojunction by a liquid phase epitaxial method, and during the growth of the opposite conductivity type GaAlAs window layer,
By adding the impurities of the opposite conductivity type to the growth solution for the window layer at least once, the impurity carrier concentrations of the window layer before and after the addition of the impurities are independently controlled.

The LED manufacturing method of the present invention is based on Ga
A step of growing a GaAlAs active layer of the same conductivity type, an opposite conductivity type, or an undoped GaAlAs active layer and a GaAlAs window layer of the opposite conductivity type to the cladding layer on the AlAs clad layer by a liquid phase epitaxial method as a double heterojunction; The impurity carrier concentration of the window layer before and after the impurity is added by adding the impurity of the opposite conductivity type to the growth solution of the window layer at least once during the growth of the GaAlAs window layer of the opposite conductivity type. Is controlled independently.

[0011]

The GaAlAs active layer has a lower impurity carrier concentration than that of a GaAlAs window layer growth solution in which a predetermined amount of impurities of the opposite conductivity type are added to the GaAlAs active layer.
The AlAs window layer is grown by liquid phase epitaxial method. Next, an impurity of opposite conductivity type is added to the same growth solution, and subsequently a GaAlAs window layer of opposite conductivity type having a high impurity carrier concentration is continuously grown. This growth by adding impurities is repeated as necessary.

As described above, during the growth of the GaAlAs window layer, the impurity carrier concentration of the window layer can be independently controlled by adding impurities of the opposite conductivity type to the growth solution of the window layer at least once. become.

Therefore, LE having a single heterostructure
Regardless of the LED having the D or double hetero structure, the impurity concentration can be easily controlled, and an ideal carrier concentration profile of the n-type window layer can be obtained. Further, since the impurity concentration can be changed on the way, the temperature program can be simplified and the time required for growth can be shortened. Further, since the window layers having different concentrations can be grown from the same solution, the manufacturing cost can be kept low.

Since the carrier concentration near the interface with the GaAlAs active layer can be reduced to a predetermined low concentration, the light output of the LED can be significantly improved, and the carrier concentration near the window layer surface can be increased to a predetermined high concentration. The characteristics are greatly improved.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 3 is a sectional view showing an embodiment of the SH structure red LED, and FIG. 4 is a view showing an embodiment of the carrier concentration profile of the n-type window layer.

The LED structure of this embodiment has a Zn-doped p-type.
Zn-doped p-type Al _0.35 Ga on the GaAs substrate 1
_{A 0.65} As active layer 2 is formed, and two n-type window layers having different carrier concentrations are formed thereon. The two-layer n-type window layer is a low carrier concentration Te-doped n-type Al _0.7 Ga _0.3 A located on the active layer 2 side.
The s window layer 4 and the high carrier concentration Te-doped n-type Al _0.7 Ga _0.3 As window layer 5 located on the front surface side of the LED. The n-type window layer may be composed of three or more layers if the active layer side has a low concentration and the surface side has a high concentration. A p-side electrode 6 is provided on the entire back surface of the substrate 1 and has a high carrier concentration Te-doped n-type Al _0.7 Ga.
_An n-side electrode 7 is partially provided on the surface of the _0.3 As window layer 5.

As shown in FIG. 4, the low carrier concentration T
The carrier concentration profile of the e-doped n-type Al _0.7 Ga _0.3 As window layer is as shown in the region of the growth layer thickness of 0 to 15 μm, and is ideally 1 to 3 × 10 ¹⁷ cm ^−3.
Meets Further, the carrier concentration profile of the high carrier concentration Te-doped n-type Al _0.7 Ga _0.3 As window layer 5 is as shown in the region of 15 to 20 μm and satisfies the ideal 1-2 × 10 ¹⁸ cm ⁻³ . ing.

Next, an embodiment of a method of manufacturing the LED having the above structure by the horizontal boat method will be described with reference to FIG. In this embodiment, a graphite slide boat is used as a jig for crystal growth. Slide boat
It comprises a pedestal 8, a slider 9, a growth solution holder 10, and an additional impurity holder 11. The slider 9 has a G on its surface.
The aAs substrate 18 is placed and slidable on the pedestal 8 by the slider operating rod 12. Further, the additional impurity holder 11 is slidable on the growth solution holder 10 by an additional impurity holder operating rod 13.

The growth solution holder 10 is provided with two tanks. The first tank contains the p-type active layer growth solution 14 and the second tank contains the n-type window layer growth solution 15.
Then, Te16, which is an additional impurity, is put into the additional impurity holder 11, and the additional impurity holder operation rod 13 is provided.
This operation allows Te16 to be dropped into the second tank, and Te16 can be added to the n-type window layer growth solution 15 in the tank.

The p-type active layer growth solution 14 is composed of a Ga solvent, an Al solute having an AlAs mixed crystal ratio of 0.35, and a G solute.
It is composed of aAs polycrystal and Zn in such an amount that the p-type impurity concentration becomes 5 × 10 ¹⁷ cm ⁻³ . Further, the n-type window layer growth solution 15 has a Ga solvent, an Al solute having an AlAs mixed crystal ratio of 0.7, a GaAs polycrystal, and an n-type impurity concentration segregated at the interface with the active layer 1. The amount of T which is 5 × ¹⁷ cm ^-3
e (0.007 mg / Galg).

Now, referring to the temperature program of FIG. 2 using the above slide board, SH structure red LE
A method of manufacturing D will be described. First, the entire slide boat is left in an H ₂ atmosphere at 820 ° C. for 2 hours to purify the growth solution. Next, the temperature is lowered at a cooling rate of -1 ° C / min, and
When the temperature reaches ℃, the slider operation rod 12 is pulled as shown in FIG.
4 and let stand until it reaches 760 ° C. During this time,
A p-type Al _0.35 Ga _0.65 As active layer 2 is epitaxially grown on the GaAs substrate 18 by about 20 μm.

Next, when the temperature reaches 760 ° C., the operating rod 12 is pulled to bring the GaAs substrate 18 into contact with the n-type window layer growth solution 15 as shown in FIG. During this time, the low carrier concentration n-type Al _0.7 Ga _0.3 As window layer 4 is formed on the GaAs substrate 18 in an amount of about 1 _%.
Epitaxial growth of 5 μm.

When the temperature reaches 720 ° C., as shown in FIG. 1C, the additional impurity holder operating rod 13 is pushed to
The additional impurity Te16 in the additional impurity holder 11 is dropped into the n-type window layer growth solution 15. As a result, the Te concentration in the n-type window layer growth solution 15 increases, and the high-concentration impurity-containing n-type window layer growth solution 17 is added.
Changes to. In this state, it is left to 703 ° C. During this time, a high carrier concentration n-type Al is formed on the GaAs substrate 18.
_{The 0.7} Ga _0.3 As window layer 5 is epitaxially grown to a thickness of about 5 μm. The temperature control program described above is shown in FIG.

In this way, a GaAlAs red LED having a two-layer window layer structure shown in FIGS. 3 and 4 and having a carrier concentration profile which is different stepwise was produced.

The light output of the manufactured LED of this example was compared with the light output of the LED having the conventional single-layer n-type window layer carrier concentration profile shown in FIGS. 5 and 6, and the light output was 30%. Increased. Further, the contact resistance of the n-side electrode 7 was reduced and the series resistance component of the LED element was reduced.

Therefore, according to the above embodiment, the carrier concentration near the interface with the p-type active layer and the carrier concentration near the interface with the n-side electrode can be independently controlled by a simple method of adding impurities during the growth. Therefore, a complicated temperature program is not required and the concentration control is extremely easy. Further, it is possible to easily optimize the carrier concentration in the vicinity of the interface with the n-side electrode simply by increasing the amount of Te added to the growth solution, so that time is not required and workability is good. Also, the growth solution for the n-type window layer can be one type,
Since it is not necessary to prepare two or more types, the cost can be reduced.

In the above embodiment, the SH structure red LED is used.
However, the present invention can be applied not only to the SH structure but also to the DH structure and the LED of the DDH structure. Further, the emission wavelength range is not limited to red, but can be applied to infrared LEDs. Further, although the substrate and the active layer are p-type and the window layer is n-type in the above embodiment, the conductivity type opposite to this may be adopted.

Further, since the present invention uses growth solutions having different concentrations, it is possible to realize an ideal concentration profile of the window layer even by the temperature difference method. Further, the growing method can be applied to a batch type growing method such as a dipping method as well as a single-wafer method using a slide boat. The number of impurities added during the growth is not limited to once, but may be two or more if necessary. Also LED
As a matter of course, the structure may include other layers such as a buffer layer other than the active layer, the clad layer, and the window layer.

[0029]

【The invention's effect】

(1) According to the invention of claim 1, the emission output is high,
It is possible to easily obtain an LED having a single hetero structure with easy formation of electrodes and excellent electric characteristics.

(2) According to the invention described in claim 2, it is possible to easily obtain an LED having a double hetero structure, which has a higher light emission output, is easy to form an electrode, and has good electric characteristics.

[Brief description of drawings]

FIG. 1 is a process chart of carrying out the LED manufacturing method of the present invention by a slide boat method.

FIG. 2 is an explanatory view showing a temperature control program for carrying out the manufacturing method of FIG.

FIG. 3 SH structure red LE manufactured by the method of the present invention
It is sectional drawing which shows one Example of D.

FIG. 4 is a characteristic diagram showing an example of a carrier concentration profile of an n-type window layer of an LED according to this example.

FIG. 5 is a sectional view showing a conventional single heterostructure LED.

FIG. 6 is a characteristic diagram showing a carrier concentration profile example of an n-type window layer of a conventional LED.

[Explanation of symbols]

1 p-type GaAs substrate 2 p-type Al _0.35 Ga _0.65 As active layer 4 low carrier concentration Te-doped n-type Al _0.7 Ga _0.3 A
s window layer 5 high carrier concentration Te-doped n-type Al _0.7 Ga _0.3 A
s window layer 6 p-side electrode 7 n-side electrode 8 frame 9 slider 10 growth solution holder 11 additional impurity holder 12 slider operation rod 13 additional impurity holder operation rod 14 p-type active layer growth solution 15 n-type window layer growth solution 16 Additional impurity Te 17 High-concentration impurity-containing n-type window layer growth solution after addition of impurity 18 GaAs substrate

Front Page Continuation (72) Inventor Seiji Mizuba 5-1-1 Hidaka-cho, Hitachi-shi, Ibaraki Hitachi Cable Company Hidaka Plant

Claims (2)

[Claims] 1. A step of growing a GaAlAs window layer of opposite conductivity type on the GaAlAs active layer as a single heterojunction by a liquid phase epitaxial method, wherein during the growth of the opposite conductivity type GaAlAs window layer, A method for manufacturing a light emitting diode, wherein the impurity carrier concentration of the window layer before and after the addition of impurities is independently controlled by adding the impurities of the opposite conductivity type to the growth solution of the window layer at least once. 2. A GaAlAs clad layer of the same conductivity type, opposite conductivity type, or undoped GaAlAs is formed on the GaAlAs clad layer.
An active layer and GaAlAs having a conductivity type opposite to that of the clad layer.
A step of growing the window layer as a double heterojunction by a liquid phase epitaxial method, and adding the opposite conductivity type impurity to the growth solution of the window layer at least once during the growth of the opposite conductivity type GaAlAs window layer. By so doing, the impurity carrier concentration of the window layer before and after the addition of impurities is independently controlled, and the structure of the light emitting diode and the method for manufacturing the same.