JP2001244501A - Epitaxial wafer for infrared-emitting diode and light emitting diode formed thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaAlAs infrared LED which is hardly lowered in luminous efficiency even if a small current is applied. SOLUTION: In an epitaxial wafer for an infrared-emitting diode having a structure of a junction of an Si-doped N-type Ga1-xAlxAs (0<=X<1) epitaxial layer and an Si-doped P-type Ga1-yAlyAs (0<=y<1) epitaxial layer, the Si content of the PN junction of the Si-doped N-type Ga1-xAlxAs (0<=X<1) epitaxial layer and the Si-doped P-type Ga1-yAlyAs (0<=y<1) epitaxial layer is made to range from 2×1019 cm-3 to 9×1019 cm-3, and an Al compositional ratio (y) at the PN junction is so set as to satisfy a formula, 0.01<=y<=0.1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to Ga _{1 -Z} Al _Z As.
The present invention relates to an epitaxial wafer for infrared light emitting diode using (0 ≦ z <1) (hereinafter abbreviated as GaAlAs) crystal and a light emitting diode manufactured using the epitaxial wafer.

[0002]

2. Description of the Related Art An infrared light-emitting diode (LED) epitaxial wafer in which a pn junction is formed by a silicon-doped n-type GaAlAs epitaxial layer and a silicon-doped p-type GaAlAs epitaxial layer is provided by a photocoupler, various optical sensors, and a remote control. It is used as a light source for controllers. For the infrared LED,
Devices used under high-current energizing conditions, such as remote controllers, and those used under low-current energizing conditions, such as photocouplers, are broadly classified.

In general, the pn junction of these infrared LEDs is manufactured by a slow cooling method liquid phase epitaxial growth method utilizing np natural inversion of silicon, which is an amphoteric impurity. When silicon is used as a dopant in the liquid phase epitaxial growth of GaAs or GaAlAs, an n-type epitaxial layer grows at a high temperature and a p-type epitaxial layer grows at a low temperature. Therefore, by starting epitaxial growth from a temperature higher than the np inversion temperature at which the n-type is changed to n-type and growing to a temperature lower than the np inversion temperature, the n-type epitaxial layer and the p-type epitaxial layer can be formed from one growth solution. It can be grown continuously. Such a growth method has the advantages of easy production and high productivity.

[0004]

However, a GaAlAs infrared LED manufactured using np spontaneous inversion has a problem that its luminous efficiency is lower when used at a low current flow than under a high current flow condition.

It is an object of the present invention to solve this.

[0006]

Means for Solving the Problems The present inventor has made intensive studies to solve the above-mentioned problems, and as a result, it has been found that, in the conventional principle, the crystallinity is deteriorated and the luminous efficiency is reduced to the np natural range. By defining the Si concentration of the inversion part,
It has been found that the luminous efficiency when applying a low current is greatly improved. In addition, the present inventor has found that, when the Si concentration is increased, the emission wavelength becomes longer. Therefore, when the wavelength characteristics on the light receiving side are limited, such as in a photocoupler, the shift of the emission wavelength becomes a problem. It has been found that the emission wavelength, which has been made longer by increasing the Al mixed crystal ratio, is shortened, and the luminous efficiency when a low current is applied is further improved, thereby completing the present invention. That is, the present invention relates to [1] Si-doped n
Infrared LED having a structure in which an epitaxial layer of Ga _1-x Al _x As (0 ≦ x <1) and a p-type Ga _1-y Al _y As (0 ≦ y <1) epitaxial layer doped with Si are joined. The p-type Ga _1-y Al _y As epitaxial layer and the n-type Ga _1-x Al _x As epitaxial layer
The Si concentration at the n-junction is 2 × 10 ¹⁹ cm ^{−3 to} 9 × 10 ¹⁹
Infrared LED epitaxial wafer, which is a range of cm ^-3, [2] of the p-type Ga _1-y Al y As epitaxial layer, pn of the n-type Ga _1-x Al x As epitaxial layer The Al composition ratio at the joint is 0.01 ≦ y
≦ 0.1, the infrared ray L according to [1],
ED epitaxial wafer, [3] infrared LED epitaxial wafer according to [1] or [2], wherein the emission peak wavelength is 900 nm or more and 950 nm or less, [4] [1] to [3] And a photocoupler and a photointerrupter using the light-emitting diode according to [5] or [4].

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An epitaxial wafer for infrared LED of the present invention is a Si-doped n-type Ga _1-x Al _x As (0
≦ x <1) epitaxial layer and Si-doped p-type Ga
It has a structure in which it is bonded to a _1-y Al _y As (0 ≦ y <1) epitaxial layer.

According to the present invention, in order to increase the luminous efficiency at the time of driving the LED at a low current, the Si concentration at the interface between the p-type Ga _1-y Al _y As epitaxial layer and the n-type Ga _1-x Al _x As epitaxial layer is improved. From 2 × 10 ¹⁹ cm ^{−3 to} 9 × 10 ¹⁹ cm ⁻³
Within the range. According to the conventional principle, when the Si concentration is increased to the above range, the luminous efficiency is reduced due to the deterioration of crystallinity, and a structure having a lower Si concentration than the above range has been used.

The Si concentration mentioned here is not the carrier concentration but the concentration of Si itself. Si is an amphoteric impurity, and in GaAlAs, both a Si donor and a Si acceptor are present and have a compensation relationship. Therefore, the difference between the donor concentration including Si and the acceptor concentration is the carrier concentration.

Further, in the present invention, in order to enhance the luminous efficiency at the time of driving the LED at a low current, the interface between the p-type Ga _{1- y} Al _y As epitaxial layer and the n-type Ga _1-x Al _x As epitaxial layer is improved. When the Al composition ratio y is 0.01 ≦ y ≦ 0.
It is preferably set to 1.

The epitaxial wafer for an infrared LED of the present invention has an emission peak wavelength of 900 nm or more, particularly 950 nm.
It is preferable to use m or less in order to increase the luminous efficiency. Further, the light emitting diode manufactured using the epitaxial wafer for infrared LED of the present invention is preferably used for a photocoupler, a photointerrupter, and the like, which are used particularly for a low-current application.

[0012]

Next, the present invention will be described in detail with reference to examples and comparative examples.

(Example 1) An apparatus for liquid phase epitaxial growth having two graphite solution tanks for holding a Ga melt was prepared.
n made of GaAlAs doped with silicon on s substrate
After forming a p-negative inversion epitaxial layer, the G
An epitaxial layer made of GaAlAs, which is transparent to the emission wavelength of light emitted from the aAlAs epitaxial layer, was laminated. Specific film formation was performed as follows.

[0014] In the first tank of the graphite solution tank of the growth apparatus,
Metal Ga as a solvent, GaAs polycrystal as a solute, and Si as a dopant were charged as the first melt. The charged amounts were 145 g of GaAs polycrystal and 6 g of Si per kg of Ga.

In a second tank of the graphite solution tank, metal Ga as a solvent, GaAs polycrystal as a solute, Al and Zn as a dopant were charged as a second melt. The charged amount was 80 g of GaAs polycrystal per kg of Ga, and A
l1.3 g and Zn 1.5 g.

The GaAs substrate was placed on a growth apparatus, and the growth apparatus was placed in a growth furnace and heated from room temperature to 910 ° C. in a hydrogen atmosphere. After the respective solutions were completely dissolved, the temperature was lowered to 905 ° C., and the substrate was brought into contact with the first melt. Then, 1 ℃ /
After the temperature was lowered to 870 ° C. at a cooling rate of 1 minute to grow an np spontaneous inversion epitaxial layer on the GaAs substrate, the substrate and the first melt were separated. Subsequently, the substrate was brought into contact with the second melt. Thereafter, the temperature was lowered to 820 ° C. at a cooling rate of 1 ° C./min to further grow an epitaxial layer. Then, the substrate and the second melt were separated, and the atmosphere gas was changed to argon and allowed to cool. Through this step, the epitaxial wafer shown in FIG. 1 was obtained.

The characteristics of the epitaxial wafer thus obtained were evaluated. The Si concentration was measured by SIMS. The pn junction position was examined by measuring the carrier concentration distribution in the epitaxial growth direction by a CV evaluation method. As a result, the Si concentration at the pn junction becomes 5.
It was 6 × 10 ¹⁹ cm ⁻³ .

The characteristics of this epitaxial wafer were evaluated as LEDs. The emission peak wavelength was 950 nm.

Example 2 An epitaxial wafer was obtained by epitaxially growing the first melt in the first tank in the same manner as in Example 1 except that the amount of Si added was varied. These wafers were processed into LEDs as in Example 1, and the characteristics were evaluated.

Example 3 Epitaxial growth was carried out in the same manner as in Example 1 except that as a first melt in a first tank, Al was added to metal Ga in addition to desired GaAs polycrystal and Si. Thus, an epitaxial wafer was obtained. First
The charge amount of the melt was 1 kg of Ga per 1 kg of GaAs polycrystal.
45 g, Al 0.5 g, and Si 6 g. As a result of evaluating the characteristics of this wafer, the Si concentration near the pn junction was 5.4 × 10 ¹⁹ cm ⁻³ . The Al mixed crystal ratio in the vicinity of the pn junction was 0.06. This wafer was processed into LEDs in the same manner as in Example 1, and the characteristics were evaluated. As a result, the emission peak wavelength of the LED was 935 nm.

Example 4 Example 1 was repeated except that the amounts of Si and Al added to the first melt in the first tank were varied.
The epitaxial growth was performed in the same manner as in the above to obtain an epitaxial wafer. These wafers were replaced with LEDs as in Example 1.
And the characteristics were evaluated.

(Comparative Example 1) For comparison, the same as Example 1 except that, among the manufacturing conditions and manufacturing steps of the above example, the amount of Si added to the first melt was adjusted so as to fall outside the range of the present invention. To obtain an epitaxial wafer.

Comparative Example 2 For comparison, the amount of Si added to the first melt and Al
An epitaxial wafer was obtained by epitaxial growth in the same manner as in Example 3, except that the addition amounts were adjusted so as to be outside the range of the present invention.

The characteristics of the LEDs using the epitaxial wafers obtained in Examples 1 and 2 and Comparative Example 1 were evaluated, and the relationship between the Si concentration in the vicinity of the pn junction and the relative light emission output was investigated by changing the flowing current. The results are shown in FIG.

As is clear from FIG. 2, the Si concentration in the vicinity of the pn junction is 2 × 10 ¹⁹ cm ⁻³ or more and 9 × 10 ¹⁹ cm ⁻³ or less, preferably 4 × 10 ¹⁹ cm ⁻³ or more and 8 × 10 ¹⁹ cm ^−3. cm
It has been clarified that the relative luminous output at the time of applying a low current can be increased by setting ^-3 or less.

The characteristics of the infrared LEDs using the epitaxial wafers obtained in Examples 3 and 4 and Comparative Example 2 were evaluated.
FIG. 3 shows the relationship between the Al mixed crystal ratio and the luminous output at the interface between the n _- type Ga _1-y Al _y As layer and the n-type Ga _1-x Al _x As epitaxial layer, while varying the flowing current. Show. G
When Al is added to aAs, the band gap increases and the emission peak wavelength shifts to the shorter wavelength side. There is no problem if there is no effect even if the wavelength becomes shorter, but if it is necessary to match the wavelength characteristics on the light receiving side, such as for a photocoupler, it is necessary to adjust the wavelength to fall within a predetermined wavelength. A
The addition amount of 1 and the addition amount of Si were adjusted, and the emission peak wavelength was in the range of 900 nm to 950 nm, and the dependence of the output characteristics on the Al mixed crystal ratio was compared.

As is clear from FIG. 3, the Al mixed crystal ratio at the pn junction interface is 0.01 to 0.1, preferably 0.02 to 0.09, more preferably 0.04 to 0.09. By setting the content to 0.08 or less, it is possible to achieve a high efficiency output when a low current is applied.

In this embodiment, the case where a p-type GaAlAs epitaxial layer using Zn as a dopant is used as a window layer (transparent layer) on a pn junction layer has been described.
Similar effects were obtained in an epitaxial wafer obtained when the aAlAs epitaxial layer (window layer) was grown using a p-type dopant other than Zn, and in an LED manufactured using the same.

Further, in the embodiment, the case where the p-type GaAlAs epitaxial layer is used as the window layer (transparent layer) on the pn junction layer has been described, but the epitaxial wafer having the structure in which the p-type GaAlAs epitaxial layer is not mounted as the window layer is described. And the LED manufactured using the same can obtain the same effect.

Further, in the embodiment, the case where an epitaxial layer is grown on a GaAs substrate and used as it is has been described. However, in an epitaxial wafer having a structure in which the GaAs substrate layer is removed by etching or the like, and in an LED manufactured using the same, Has the same effect.

[0031]

In the infrared LED epitaxial wafer of the present invention, the pn of the p-type Ga _1-y Al _y As epitaxial layer and the n-type Ga _1-x Al _x As epitaxial layer
The Si concentration at the junction is 2 × 10 ¹⁹ cm ^{−3 to} 9 × 10 ¹⁹ c
When it is within the range of m ⁻³ , it is possible to manufacture an LED that can obtain a high relative emission output even when a low current is applied.

In particular, the Al composition ratio at the pn junction is
By setting 0.01 ≦ y ≦ 0.1 and the emission peak wavelength to be 900 nm or more and 950 nm or less, the luminous efficiency can be further increased.

When an LED manufactured by using the epitaxial wafer of the present invention is used particularly for a photocoupler or a photointerrupter, an element having high current efficiency can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of an epitaxial wafer of the present invention shown in an embodiment.

FIG. 2 is a diagram showing a relationship between a Si concentration at a pn junction and a relative light emission output.

FIG. 3 is a diagram showing a relationship between an Al mixed crystal ratio at a pn junction and a relative light emission output.

[Explanation of symbols]

 Reference Signs List 1 GaAs substrate 2 n-type GaAs epitaxial layer (Si-doped) 3 p-type GaAs epitaxial layer (Si-doped) 4 p-type GaAlAs epitaxial layer

Claims (5)

[Claims] 1. An Si-doped n-type Ga _1-x Al _x As (0 ≦
x <1) epitaxial layer and Si-doped p-type Ga _1-y
An epitaxial wafer for an infrared light-emitting diode having a structure in which an Al _y As (0 ≦ y <1) epitaxial layer is bonded, comprising a p-type Ga _{1- y} Al _y As epitaxial layer and an n-type Ga _1-x Al _x As epitaxial Si of pn junction of layer
An epitaxial wafer for an infrared light-emitting diode, wherein the concentration is in the range of 2 × 10 ¹⁹ cm ^{−3 to} 9 × 10 ¹⁹ cm ⁻³ . 2. An Al composition ratio at a pn junction of a p-type Ga _1-y Al _y As epitaxial layer and an n-type Ga _1-x Al _x As epitaxial layer is 0.01 ≦ y ≦ 0.1. The epitaxial wafer for an infrared light emitting diode according to claim 1, wherein: 3. An emission peak wavelength of 950 at 900 nm or more.
3. The epitaxial wafer for an infrared light emitting diode according to claim 1, wherein the thickness is not more than nm. 4. 4. A light emitting diode manufactured using the infrared light emitting diode epitaxial wafer according to claim 1. 5. A photocoupler or photointerrupter using the light emitting diode according to claim 4.