JP2001094145A - Epitaxial substrate for infrared light-emitting element and light-emitting element provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epitaxial substrate for manufacturing a fast, high-output, and long-life GaAlAs infrared light-emitting diode of DDH structure. SOLUTION: The dopant of a p-type clad layer and a p-type active layer is Ge, with its carrier concentration in the range of 8×1017 to 12×1017 cm-3, the thickness of the p-type active layer is set to 0.5 to 1.2 μm, and the oxygen concentration is set less than 3×1016 cm-3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial substrate for producing a high-speed and high-output infrared light-emitting diode used for optical communication and spatial transmission using infrared light, and
The present invention relates to an infrared light emitting device manufactured from this epitaxial substrate.

[0002]

2. Description of the Related Art Light emitting devices (hereinafter, referred to as LEDs) using a GaAlAs-based compound semiconductor are widely used as light sources for infrared to red light. Infrared LEDs are used for optical communication and space transmission, but with the increase in the capacity of data to be transmitted and the transmission distance, the demand for high-output, high-speed infrared LEDs is increasing. .

As conventionally known, GaAlA
In an s-based LED, a double heterostructure (hereinafter referred to as DH) in which an active layer serving as a light emitting region is sandwiched between cladding layers having a larger band gap than a single heterostructure.
Structure) has a higher output, and the method of removing the substrate (hereinafter referred to as DDH structure) further increases the output. At this time, the active layer has a thickness of about 1 μm in consideration of the diffusion distance of carriers. Also,
When epitaxially growing a GaAlAs-based LED substrate, it is necessary to remove as much as possible oxygen from the growth system, which has a strong affinity with Al, forms a deep level in the crystal, lowers the crystallinity, and lowers the light emission output. Therefore, vacuum evacuation and baking of a growth furnace and a jig and purification of raw materials are generally performed.

When manufacturing an epitaxial substrate having a DDH structure, it is a standard configuration to add an epitaxial layer for securing the entire thickness of the finished substrate after the substrate is removed, in addition to a normal DH structure. Of course, the epitaxial layer has a wider band gap than the active layer, and is designed so as not to absorb the light emitted from the active layer. In addition, the epitaxial layer, in consideration of suppressing the total resistance of the device,
It is advantageous to add an n-type layer to the n-type cladding layer side. This is because in the GaAs-AlAs system, the mobility of electrons is 10 times or more higher than that of holes, and if the carrier concentration and the Al composition are the same, the n-type can lower the resistance. . When an n-type layer is added to the n-type cladding layer side to make the p-type cladding layer the LED surface side,
Using a p-type GaAs substrate as shown in FIG.
A structure in which a first p-type layer using Zn as a dopant, a p-type cladding layer using Ge as a dopant, a p-type active layer using Ge as a dopant, an n-type cladding layer, and a second n-type layer are effective. is there.

[0005]

However, when Ge is used as a dopant for the p-type cladding layer and the p-type active layer in epitaxial growth from a p-type substrate as shown in FIG. 3, depending on the carrier concentration, There has been a problem that the light emission output and response speed of the LED are affected and the characteristics are not stable. Further, as other factors that hinder the stabilization of the characteristics, there have been variations in the thickness of the active layer and variations in the oxygen concentration in the active layer.

SUMMARY OF THE INVENTION The present invention solves this problem and provides a DDH structure having an infrared LED which is stable, has high speed and high output, has low forward voltage (hereinafter abbreviated as VF), and has excellent life characteristics.
It is an object of the present invention to provide an epitaxial substrate for producing the same and an infrared light emitting device produced from the epitaxial substrate.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have reached the present invention.
That is. The present invention provides [1] a p-type GaAs single crystal substrate
First p-type layer (Ga _1-x1 Al _x1 As, 0.18 ≦ x1 ≦
0.25), p-type cladding layer (Ga _1-x2 Al _x2 As,
0.15 ≦ x2 ≦ 0.23), the emission wavelength is 850 to 90
P-type active layer (Ga _1-x3 Al
_x3 As, 0 ≦ x3 ≦ 0.03), n-type cladding layer (Ga
_1-x4 Al _x4 As, 0.10 ≦ x4 ≦ 0.33) and a second n-type layer (Ga _1-x5 Al _x5 As, 0.10 ≦ x5 ≦
0.33) are sequentially laminated by a liquid phase epitaxial method, and then the p-type GaAs single crystal substrate is removed. In the infrared-emitting device epitaxial substrate, the p-type GaAs single crystal substrate is used as a dopant for the p-type cladding layer and the p-type active layer. An epitaxial substrate for an infrared light-emitting device, wherein germanium is used and the carrier concentration thereof is 8 × 10 ¹⁷ cm ⁻³ or more and less than 12 × 10 ¹⁷ cm ⁻³ ; [2] Layer thickness of a p-type active layer Is 0.5 μm or more and 1.2 μm or less, and the concentration of oxygen in the p-type active layer is less than 3 × 10 ¹⁶ cm ^−3. The present invention also relates to a substrate, and a light emitting device manufactured using the epitaxial substrate for an infrared light emitting device according to [3] [1] or [2].

[0008]

Embodiments of the present invention will be described below. FIG. 1 schematically shows the structure of an infrared-emitting LED manufactured from the epitaxial substrate described in the present application. Each epitaxial layer is a first p-type layer Ga _1-x1 Al _x1 As
(0.18 ≦ x1 ≦ 0.25), p-type cladding layer (Ga
_1-x2 Al _x2 As, 0.15 ≦ x2 ≦ 0.23), p-type active layer (Ga _1-x3 Al _x3 As, 0 ≦ x3 ≦ 0.03), n
Type cladding layer (Ga _1-x4 Al _x4 As, 0.10 ≦ x4 ≦
0.33), and a second n-type layer (Ga _1-x5 Al _x5 As,
0.10 ≦ x5 ≦ 0.33) in this order on the p-type GaAs single crystal substrate. Regarding the mixed crystal ratio of each layer, the active layer is selected so that the emission wavelength becomes 850 to 900 nm, and the first p-type layer, the p-type cladding layer, the n-type cladding layer, and the second n-type layer The band gap is selected to be wider than the active layer so as not to absorb the light emitted from the active layer. For the dopant, Zn is used for the first p-type layer, Ge is used for the p-type cladding layer and the p-type active layer, and Te is used for the n-type layer.

As a method for growing the epitaxial substrate, for example, an apparatus based on a liquid phase growth method as shown in FIG. 4 can be used. The p-type GaAs substrate 20 is fixed to a substrate holder 21, and the plurality of substrate holders 21 are fixed by hangers 22. The hanger 22 has a structure that can be moved in the vertical direction by an appropriate driving mechanism (not shown). The crucibles 23 to 28 are fixed to the crucible table 29, and the crucible table can be moved right and left by an appropriate driving mechanism (not shown). Crucible 23,
25, 26, 27 and 28 each have a composition suitable for growing the first p-type layer, p-cladding layer, p-type active layer, n-cladding layer and second n-type layer shown in FIG. Ga
Metal, GaAs polycrystal, Al, and a dopant are set, and each is covered with a crucible lid 30 made of glassy carbon.

The actual growth is performed as follows.
The jig of FIG. 4 is set in a quartz reaction tube (not shown),
The raw material is dissolved by heating in a hydrogen stream. During this time, the holder 21 is held inside the empty crucible 24 to prevent As from coming off at high temperatures. Subsequently, the ambient temperature is lowered, and the holder 2
Then, the crucible table 29 is pulled rightward in FIG. 4 and the crucible 23 is set under the holder 21. Next, the holder 21 is lowered to immerse the wafer in the crucible 23.
Subsequently, the temperature of the atmosphere is gradually lowered to grow the first p-type layer of FIG. Next, the wafer is separated from the melt by raising the holder 21, and the crucible table 29 is pushed to the left in FIG. 4 to set the empty crucible 24 under the holder 21.
At this time, by raising and lowering the holder 21 several times, Zn
The residue of the crucible 23 containing is shaken off to prevent the melt from being brought into the next crucible. Subsequently, the holder 21 is raised and the crucible table 29 is pushed to set the crucible 25 under the holder 21, and then the holder 21 is lowered to make contact with the melt in the crucible 25. Hereinafter, the structure as shown in FIG. 1 can be grown by repeating the cooling and the movement of the holder and the crucible table.

After the completion of the epitaxial growth, the epitaxial substrate is taken out, the surface of the second n-layer shown in FIG. 1 is protected with an acid-resistant sheet, and p-type is treated with an ammonia-hydrogen peroxide-based etchant.
The type GaAs substrate is selectively removed. After that, electrodes are formed on both surfaces of the epitaxial substrate and separated by dicing to produce an infrared LED in which the first p-type layer is on the front side.

[0012]

Embodiments of the present invention will be described below. Example 1 The jig of FIG. 4 was set in a quartz reaction tube (not shown), and heated to 940 ° C. in a hydrogen stream to dissolve the raw materials. During this time, the holder 21 was held in an empty crucible 24. Subsequently, the ambient temperature was lowered to 925 ° C., and the holder 21 was raised. Then, the crucible table 29 was pulled to the right in FIG. Next, the wafer was immersed in the crucible 23 by lowering the holder 21. Subsequently, the temperature of the atmosphere is increased to 905 at a rate of 0.5 ° C./min.
The temperature was lowered to ℃ to grow the first p-type layer of FIG. Next, the holder 2 is kept at an ambient temperature of 905 ° C.
1 was lifted to separate the wafer from the melt. Next, the crucible table 29 was pushed to the left in FIG. 4 to set the empty crucible 24 under the holder 21. Here, the residue of the crucible 23 containing Zn was shaken off by raising and lowering the holder 21 several times. Subsequently, the holder 21 is raised,
After pressing the crucible base 29 to set the crucible 25 under the holder 21, the holder 21 was lowered and brought into contact with the melt in the crucible 25. Thereafter, the structure as shown in FIG. 1 was grown by repeating the cooling and the movement of the holder and the crucible table.
After growing the p-type active layer in the crucible 26, the crucible 2
The holder 21 was lightly moved up and down on 6 to shake off the p-type melt residue. In the embodiment, in order to vary the carrier concentration level of the p-type cladding layer and the p-type active layer, G
Epitaxial growth was performed by changing the amount of e added to the melt.

After completion of the epitaxial growth, the mixed crystal ratio of each layer, the layer thickness of each layer, and the carrier concentration were measured. The mixed crystal ratio was calculated from the wavelength of photoluminescence, the layer thickness was measured by a microscope, and the carrier concentration was measured by a CV method.

As a result, the mixed crystal ratio is such that the first p-type layer is Ga
_1-x1Al_x1As (0.20 ≦ x1 ≦ 0.22), p-type
Rad layer is Ga_1-x2Al_x2As (0.18 ≦ x2 ≦ 0.
20), the p-type active layer is Ga_1-x3Al_x3Al (x3 = 0.
01), the n-type cladding layer is Ga _1-x4Al_x4As (0.1
0 ≦ x4 ≦ 0.30), and the second n-type layer is Ga_1-x5Al_x5
As (0.10 ≦ x5 ≦ 0.30). Mixing each layer
There is a range in the crystal ratio because each layer is grown by slow cooling method
Composition ratio of epitaxial layer other than p-type active layer
Is to decrease toward the element surface side. In addition,
The rear concentration is the average value of each layer and the first p-type layer is 2 × 10¹⁸c
m^-3, The n-type cladding layer is 1 × 10¹⁸cm^-3, The second n-type
The layer is 1.5 × 10¹⁸cm^-3, The thickness of each layer is the first p-type layer
30 μm, p-type cladding layer 15 μm, n-type cladding
The layer was 75 μm and the second n-type layer was 75 μm.

Further, the epitaxial substrate was taken out, the surface of the second n-type layer in FIG. 1 was protected with an acid-resistant sheet, and the p-type GaAs substrate was selectively removed with an ammonia-hydrogen peroxide-based etchant. Thereafter, electrodes are formed on both sides of the epitaxial substrate, and separated by dicing, so that the first p-type layer is on the front side and a 350 μm square LED is formed.
Was prepared.

FIG. 5 shows the relationship between the carrier concentration of the p-type cladding layer and the light emission output and VF of the fabricated LED when only the amount of Ge added to the p-type cladding layer is changed. If the carrier concentration is less than 8 × 10 ¹⁷ cm ⁻³ , VF increases and the target is not satisfied. Also, 12 × 10 ¹⁷
It was found that the light emission output was reduced when cm ^-3 or more. Therefore, it can be seen that the carrier concentration of the Ge-doped p-type cladding layer should be in the range of 8 × 10 ¹⁷ cm ⁻³ or more and less than 12 × 10 ¹⁷ cm ⁻³ .

FIG. 6 shows the relationship between the carrier concentration of the p-type active layer and the light emission output and response speed (light emission rise time) of the fabricated LED when only the amount of Ge added to the p-type active layer is changed. Show. Carrier concentration is 8 × 10 ¹⁷ cm ^-3
If it is less than 1, the rise time is extended and the target is not satisfied. In addition, it was found that the emission output was lower than the target when the density was 12 × 10 ¹⁷ cm ⁻³ or more. Therefore, the carrier concentration of the Ge-doped p-type active layer is 8 × 10 ¹⁷ cm ^−3.
It can be seen that the range should be less than 12 × 10 ¹⁷ cm ⁻³ .

(Embodiment 2) Based on the results of Embodiment 1,
In the above embodiment, both the p-type cladding layer and the p-type active layer are 10 × 1
Under the condition of 0 ¹⁷ cm ^-3 , epitaxial growth and LED fabrication were repeated several times. 7 and 8 show the relationship between the light emission output and the response speed with respect to the active layer thickness and the oxygen concentration in the active layer at that time. The oxygen concentration in the active layer is S
Estimated by IMS. Active layer thickness is 0.5 to 1.2
The light emission output falls below the target when it is out of the range of μm,
It was found that the response speed was reduced when the thickness exceeded μm. The oxygen concentration in the active layer was 3 × 10 ¹⁶ cm ^−3.
It was found that the light emission output was reduced when the value exceeded. Furthermore, it is possible to suppress the oxygen concentration in the active layer to less than 3 × 10 ¹⁶ cm ⁻³ with good reproducibility by extending the duration of the jig baking and the duration of the raw material baking performed immediately before the epitaxial growth. I found it to be. From the above, it is understood that the layer thickness of the p-type active layer should be 0.5 μm or more and 1.2 μm or less, and the oxygen concentration should be less than 3 × 10 ¹⁶ cm ⁻³ .

[0019]

By implementing the present invention, DDH
A high-speed, high-output characteristic of the structure can be stably obtained, and an infrared LED with a low VF can be provided.

[Brief description of the drawings]

FIG. 1 schematically shows the structure of the LED of the present application.

FIG. 2 shows a DDH structure in which an epitaxial layer is added to an n-type cladding layer using an n-type GaAs substrate.

FIG. 3 shows a DDH structure in which an epitaxial layer is added to an n-type cladding layer using a p-type GaAs substrate.

FIG. 4 shows an epitaxial growth jig used for carrying out the present invention.

FIG. 5 shows the carrier concentration of a p-type cladding layer and the L
5 shows the relationship between the ED light emission output and VF.

FIG. 6 shows the carrier concentration of the p-type active layer and the produced LED.
2 shows the relationship between the light emission output and the response speed (rise time).

FIG. 7 shows a relationship between an active layer thickness, a light emission output, and a response speed (rise time).

FIG. 8 shows the relationship between the oxygen concentration in the active layer, the light emission output, and the response speed.

[Explanation of symbols]

 Reference Signs List 1 p-type GaAs substrate 2 first p-type layer 3 p-type cladding layer 4 p-type active layer 5 n-type cladding layer 6 second n-type layer 7 element surface side 8 n-type GaAs substrate 9 second n-type layer Reference Signs List 10 n-type cladding layer 11 p-type active layer 12 p-type cladding layer 13 element surface side 14 p-type GaAs substrate 15 element surface side 16 p-type cladding layer 17 p-type active layer 18 n-type cladding layer 19 second n-type layer Reference Signs List 20 p-type GaAs substrate 21 holder 22 hanger 23 crucible (for growing first p-type layer) 24 crucible (empty) 25 crucible (for growing p-type cladding layer) 26 crucible (for growing p-type active layer) 27 crucible (n 28 (for growing the second n-type layer) 29 crucible table 30 crucible lid

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G077 AA03 AB01 BE47 CG02 ED06 EG06 EG13 FJ04 HA02 HA06 HA12 5F041 AA02 AA04 CA04 CA35 CA36 CA49 CA53 CA57 CA63 CA67 CA74 CA76 CB36 FF14 5F053 AA03 BB04 BB08 BB04 BB08 BB04 BB04 JJ01 JJ03 KK02 KK04 KK08 LL02

Claims (3)

[Claims] A first p-type GaAs single crystal substrate is provided on a p-type GaAs single crystal substrate.
Layer (Ga_1-x1Al_x1As, 0.18 ≦ x1 ≦ 0.2
5), p-type cladding layer (Ga_1-x2Al_x2As, 0.15
≦ x2 ≦ 0.23), the emission wavelength is 850-900 nm
The p-type active layer (Ga_1-x3Al_x3As,
0 ≦ x3 ≦ 0.03), n-type cladding layer (Ga _1-x4Al
_x4As, 0.10 ≦ x4 ≦ 0.33), and the second n-type
Layer (Ga_1-x5Al_x5As, 0.10 ≦ x5 ≦ 0.33)
Are sequentially laminated by a liquid phase epitaxial method, and then the p-type G
Infrared light emitting device comprising removing aAs single crystal substrate
P-type cladding layer and p-type
Using germanium as a dopant of the active layer, and
The carrier concentration is 8 × 10¹⁷cm^-3More than 12 × 10¹⁷
cm^-3Epi for infrared light emitting device, characterized by being less than
TAXIAL PCB. 2. The p-type active layer has a thickness of 0.5 μm or more and 1.2 or more.
μm or less and the oxygen concentration in the p-type active layer is 3 ×
The epitaxial substrate for an infrared light emitting device according to claim 1, wherein the epitaxial substrate is less than 10 ¹⁶ cm ^-3 . 3. A light emitting device produced using the epitaxial substrate for an infrared light emitting device according to claim 1.