JP2681431B2 - Light emitting element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device, and more particularly to a light emitting device having a double hetero structure.

[0002]

2. Description of the Related Art A light emitting element is an element that emits light in the visible or near infrared region when a forward current is applied to a pn junction of a semiconductor, and is used as a point light source such as a pilot lamp, It is also used as a light source in communications, and its applications are expanding.

A light emitting device generally has a three-layer double hetero structure in which an active layer is sandwiched by a pair of cladding layers, and electrodes are formed on both surfaces of this three-layer double hetero structure to form a light emitting device. can get. Each layer of the three-layer structure is composed of a semiconductor, and the ones currently in practical use are mainly III-V.
It is a group compound semiconductor. Among them, a GaAlAs semiconductor can provide particularly high luminance, and is therefore used for a light emitting element for high luminance.

[0004] The light emitting element as described above is, for example, GaAs.
It is manufactured by growing a three-layer double heterostructure on a substrate by an epitaxial growth method. As this growth method, either vapor phase growth or liquid phase growth may be used.
The liquid phase epitaxy method is often used in that a growth layer having good crystals can be obtained.

[0005]

As the range of application of the light emitting element is expanded, a light emitting element with higher luminance has been desired. However, none of the conventional light emitting devices as described above can obtain sufficient brightness, and it has been desired to develop a light emitting device having further improved brightness.

Therefore, it is an object of the present invention to provide a light emitting device which can obtain higher brightness than conventional light emitting devices.

[0007]

According to the present invention, there is provided (a) a first cladding layer made of a p-type mixed crystal compound semiconductor (b) a p-type mixed crystal having a mixed crystal ratio necessary for light emission of a predetermined wavelength. (C) n having the same mixed crystal ratio as that of the first cladding layer
Consists of three layers of the second cladding layer made of the type of mixed crystal compound semiconductor, the active layer is the first and second class
In a light-emitting device including a double-hetero structure having a three-layer structure formed between pad layers, a key of the first cladding layer is included.
As the carrier concentration gradually decreases toward the active layer side,
Minimum value of 5 × 10 ¹⁶ cm ⁻³ or less near the junction with the layer
And the carrier concentration of the second cladding layer is
As the distance from the vicinity of the junction between the clad layer of 1 and the active layer increases,
Has a gradually increasing concentration profile, and has the three-layer structure described above.
An electrode is formed on the surface .

The carrier concentration of the active layer is 1 × 10.
^It is desirable that it is ¹⁷ cm ⁻³ or less, and the carrier concentration in the vicinity of the junction of the second cladding layer with the active layer is
It is preferably 5 × 10 ¹⁶ cm ⁻³ or more. Also,
The respective lower limits of the carrier concentration in the vicinity of the junction of the first cladding layer with the active layer and the carrier concentration of the active layer are:
The concentration is set such that the first conductivity type is maintained, and the upper limit of the carrier concentration of the second cladding layer is set by the addition of impurities that does not deteriorate the crystallinity. Sa
In addition, the carrier concentration of the first cladding layer is
In the region far from the layer, it is 1 × 10 ¹⁷ cm ⁻³ or more.
Is desirable. Note that Zn and C are used as impurities in the active layer and the first cladding layer, and Te and Sn are used as impurities in the second cladding layer.

The first and second cladding layers are made of Ga.
_The active layer may be composed of a mixed crystal type compound semiconductor represented by _1-x Al _x As (x is a number where 0 <x <1), and the active layer is Ga _1-y Al _y As (y is 0). A mixed crystal type compound semiconductor represented by <y <1) may be used. In this case, the range of values of x and y is 0.6 to 0.
It is preferably 85 and 0.3 to 0.45.

[0010]

In the present invention, the carrier concentration near the junction of the first cladding layer with the active layer is 5 × 10 ¹⁶ c.
By setting m ^-3 or less, the brightness of the light emitting element is improved. Conventionally, the carrier concentration of this cladding layer was generally 5 × 10 ¹⁶ cm ⁻³ or more, but as described above, it is rather 5 × 10 ¹⁶ c near the active layer.
It has been confirmed by the inventor of the present invention that the brightness of the light emitting device is improved under the condition of the carrier concentration of m ⁻³ or less.
The reason for this is that by decreasing the concentration of impurities added in the vicinity of the active layer, the positive effect such as the reduction of crystal defects is larger than the negative effect such as the reduction of carriers, and as a result, the effect of increasing the brightness is obtained. Is considered to have occurred.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing the structure in the depth direction of one embodiment of the light emitting device of the present invention. In the figure, a p-type GaAs <100> substrate 1 to which Zn having a concentration of about 1 to 3 × 10 ¹⁹ cm ⁻³ is added as an impurity
0, a three-layer epitaxial growth layer forming the light emitting device of the present invention is formed. That is, Ga _0.25 Al doped with Zn as an impurity so as to have a predetermined profile in the depth direction on the p-type GaAs substrate 10.
_0.75 As Mixed crystal type compound semiconductor 150 μm thick
m p-type clad layer 11 and Ga _0.62 Al _0,38 A doped with Zn as an impurity to a predetermined concentration
1 μm thick p-type active layer 12 made of s mixed crystal type compound semiconductor, and Ga doped with Te as an impurity
Each layer of the n-type cladding layer 13 made of _0.25 Al _0.75 As mixed crystal type compound semiconductor and having a thickness of 50 μm is continuously formed by the epitaxial growth method. Note that p
The type GaAs substrate 10 is removed by selective etching after forming the epitaxial growth layer.

Next, an example of a method of manufacturing the light emitting device of this embodiment will be described with reference to FIG. The light emitting device of this embodiment can be manufactured by growing each layer by a liquid phase growth method. Here, an example by a slide boat method using a slide boat will be described. In addition, a case is shown in which a slow cooling method in which growth is performed by gradually lowering the temperature is employed.

In FIG. 2, the p-type GaAs substrate 10 is
The upper surface should be flush with the upper surface of the boat body 20.
Is fixed on the upper surface of the boat body 20. Boat body 20
The slide type solution reservoir 21 that slides on the top has a p-type
The first solution reservoir 22 containing the solution 22a for growing the bed layer, p
A second solution reservoir 23 for containing the active layer growing solution 23a,
And a third solution containing the n-type cladding layer growth solution 24a.
Each liquid reservoir 24 is provided, each solution reservoir has no bottom,
Each solution is directly immersed in the upper surface of the boat body 20.
ing. p-type and n-type cladding layer growth solution 22a and
24a is Ga 0_{.twenty five}Al_0.75P is added to the As melt.
Type impurity Zn or n type impurity Te is added.
And the p-type active layer growth solution 23a is Ga_0.62Al
_0.38Zn melt, which is a p-type impurity, was added to the melt of As.
is there. The slide type solution reservoir 21 is operated by the operation rod 25.
It is designed to move depending on the work.

Next, a process of forming three epitaxial growth layers on the p-type GaAs substrate 10 using the above apparatus will be described. First, the slide type solution reservoir 21 is connected to the operation rod 25.
2 is slid in the direction of the arrow from the position shown in FIG. 2A, and the p-type clad layer growing solution 22 in the first solution reservoir 22 is slid.
a is set on the p-type GaAs substrate 10 and, for example, 900
The p-type cladding layer 11 is grown under the condition of lowering the temperature from ℃ to 800 ℃ (Fig. 2 (b)). Next, the slide type solution reservoir 21 is further slid in the direction of the arrow, and the p-type active layer growth solution 23a in the second solution reservoir 23 is replaced with p-type GaAs.
Set on the substrate 10 and grow the p-type active layer under the condition of lowering the temperature from 800 ° C. to 795 ° C. (FIG. 2).
(C)). Next, the slide type solution reservoir 21 is further slid in the direction of the arrow to grow the n-type cladding layer 13 under the condition of lowering the temperature from 795 ° C. to 650 ° C., for example (FIG. 2 (d)). Then, the slide type solution reservoir 21 is further slid in the direction of the arrow to complete the growth process (FIG. 2 (e)).

In order to set the carrier concentration in the vicinity of the active layer of the p-type cladding layer 11 to 5 × 10 ¹⁶ cm ^-3 or less, p
The p-type impurity Zn added to the type cladding layer growth solution 22a is extremely small or not added at all. However, a high temperature Zn added to the p-type GaAs substrate 10 diffuses to the cladding layer side by the subsequent heat step, and so-called autodoping is performed. As a result, the clad layer becomes the p-type clad layer 11 having a predetermined concentration profile, and a low carrier concentration (1 × 10 ¹⁶ cm ⁻³ ) region is formed near the p-type active layer 12.

After the three-layer double hetero structure is formed on the p-type GaAs substrate 10 as described above, the substrate is removed by selective etching and electrodes are formed on both sides of the three-layer structure to complete a light emitting device. .

FIG. 3 shows a concentration profile in the depth direction of the carrier concentration of the light emitting device of this example manufactured as described above. The carrier concentration of the p-type cladding layer 11 is p
In the vicinity of the type GaAs substrate 10, the carrier concentration is about the same as the substrate concentration (1 to 3 × 10 ¹⁹ cm ⁻³ ), but the carrier concentration decreases toward the p-type active layer 12 side, and the p-type active layer 12 1 × 10 ¹⁶ cm near the junction with layer 12
^It has fallen to ^-3 . On the other hand, the carrier concentration of the p-type active layer 12 is about 1 × 10 ¹⁷ cm ⁻³ . Further, the carrier concentration of the n-type cladding layer 13 increases from about 1 × 10 ¹⁷ cm ^−3, which is the same as the carrier concentration of the p-type active layer 12, to about 6 × 10 ¹⁷ cm ⁻³ in the uppermost layer. There is.

FIG. 4 shows the relationship between the carrier concentration near the active layer of the p-type cladding layer 11 and the relative brightness of the light emitting device. It can be seen that the relative luminance of the light emitting element increases as the carrier concentration in the p-type clad layer 11 near the p-type active layer 12 decreases. FIG. 5 shows the luminance distribution in the concentration range of the example of the present invention (1 to 2 × 10 ¹⁶ cm ⁻³ ) and the concentration range of the conventional light emitting element (1 to 2 × 10 ¹⁷ cm ⁻³ ). The concentration range of this example (1 to 2 × 10 ¹⁶ cm
^{In -3} ), it can be seen that the relative luminance shows an extremely high value of about 400.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made. For example, the carrier of the p-type clad layer 11 is Zn in the present embodiment, but the same effect can be obtained by substituting it with C or compound doping. Also, regarding the carrier of the n-type cladding layer 13,
Composite doping may be performed instead of Te.

[0020]

As described above, according to the present invention,
(A) A first cladding layer made of a mixed crystal compound semiconductor of the first conductivity type, and (b) An active layer made of a mixed crystal compound semiconductor of the first conductivity type having a mixed crystal ratio necessary for light emission of a predetermined wavelength. And (c) a second clad layer made of a mixed crystal compound semiconductor of the second conductivity type having a mixed crystal ratio equivalent to that of the first clad layer, and three layers of the first and second clad layers. In a light emitting device including a double hetero structure in which the active layer is formed between clad layers, a carrier concentration near the junction of the first clad layer with the active layer is 5 × 1.
By setting it to be 0 ¹⁶ cm ⁻³ or less, higher brightness than conventional light emitting devices can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure in a depth direction of an embodiment of a light emitting device of the present invention.

FIG. 2 is an explanatory view showing an example of a method for manufacturing a light emitting device of the present invention.

FIG. 3 is a diagram showing a carrier concentration profile in a depth direction of an embodiment of a light emitting device of the present invention.

FIG. 4 is a diagram showing a relationship between carrier concentration in the vicinity of an active layer of a p-type cladding layer and relative luminance of a light emitting device.

FIG. 5 is a concentration range of the embodiment of the present invention (1-2 × 10 ¹⁶ c
m ^-3 ) and the concentration range of a conventional light emitting device (1-2 x 10 ¹⁷ c
It is a figure which shows the brightness ^| luminance distribution in (m- ³ ).

[Explanation of symbols]

 10 p-type GaAs substrate 11 p-type clad layer 12 p-type active layer 13 n-type clad layer 20 boat body 21 slide type solution reservoir 22 first solution reservoir 22a p-type clad layer growth solution 23 second solution reservoir 23a p-type activity Layer growth solution 24 Third solution reservoir 24a n-type clad layer growth solution 25 Control rod

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-54-141592 (JP, A) JP-A-52-28885 (JP, A) JP-A-60-17969 (JP, A) JP-A-51- 147985 (JP, A) JP 63-278383 (JP, A) JP 63-278384 (JP, A)

Claims (8)

(57) [Claims] 1. A first clad layer made of (a) a p-type mixed crystal compound semiconductor (b) An active layer made of a p-type mixed crystal compound semiconductor having a mixed crystal ratio necessary for light emission of a predetermined wavelength. (C) n having the same mixed crystal ratio as that of the first cladding layer
Of a double heterostructure, which is composed of three layers of a second clad layer made of a mixed-type compound semiconductor of the same type, and the active layer is a three-layer structure formed between the first and second clad layers. In the device, the carrier concentration of the first cladding layer approaches the active layer side .
In near the junction with said active layer gradually decreases in accordance with Ku 5 × 10
The minimum value of ¹⁶ cm ⁻³ or less , and the second cladding
The carrier concentration of the layer is different from that of the first cladding layer and the active layer.
Concentration profile that gradually increases with distance from the vicinity of the junction
And a light emitting device having electrodes formed on both surfaces of the three-layer structure . 2. The carrier concentration of the active layer is 1 × 10.
The light emitting device according to claim 1, having a size of ¹⁷ cm ⁻³ or less. 3. The carrier concentration of the second cladding layer near the junction with the active layer is 5 × 10 ¹⁶ cm ^−3.
It is above, The light emitting element of Claim 1 or Claim 2. 4. The light emitting device according to claim 1, wherein the impurities added to the active layer and the first cladding layer are zinc (Zn) or carbon (C). 5. The first and second cladding layers are Ga
_1-x Al _x As (x is a number where 0 <x <1) is formed of a mixed crystal type compound semiconductor, and the active layer is Ga.
_{1 -y} Al _y As _(y is 0 <y <1 number becomes) claims 1 to 4 consisting of a mixed crystal compound semiconductor represented by
The light-emitting device according to item 1. 6. The light emitting device according to claim 5, wherein the x is a number in the range of 0.6 to 0.85 and the y is a number in the range of 0.3 to 0.45. 7. The light emitting device according to claim 1, wherein the impurity added to the second cladding layer is Te or Sn. 8. The carrier concentration of the first cladding layer is
Far from the active layer 1 × 10 in area ¹⁷ cm ^-3 that's all
The light emitting device according to claim 1, wherein