JP2001313441A - Semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting element of a double- heterojunction structure, having a high light-emitting efficiency and low operating voltage. SOLUTION: The semiconductor light-emitting element of a double- heterojunction structure comprises at least a sandwich structure of an n-type clad layer 4, an active layer 5 and a p-type clad layer 6 in such a manner that the band gap energy of the active layer is formed of a material, having a smaller band gap energy than those of both the clad layers. In this case, a material of both the clad layers is selected, so that the band gas energy of the n-type clad layer is smaller than that of the p-type clad layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device. More specifically, the present invention relates to a semiconductor light emitting device capable of emitting light with high luminance by lowering the operating voltage.

Here, a semiconductor light emitting device is a light emitting diode (hereinafter, referred to as an LED) having a double hetero junction such as a pn junction or a pin, a superluminescent diode (SLD), or a semiconductor laser diode (hereinafter, referred to as an LED).
LD).

[0003]

2. Description of the Related Art Conventionally, a blue LED has low luminance compared to red and green, and has been difficult to put into practical use. However, in recent years, a low-resistance p-type semiconductor layer using a gallium nitride compound semiconductor and Mg as a dopant has been used. As a result, the brightness has improved and the spotlight has been hit.

Here, the gallium nitride compound semiconductor is a compound of Ga of a group III element and N of a group V element or
A compound in which part or all of Ga of a group III element is substituted with another group III element such as Al or In and / or a compound in which part of N of a group V element is substituted with another group V element such as P or As. Semiconductor.

A conventional LED using a gallium nitride compound semiconductor is manufactured as follows. FIG. 4 shows a perspective view of a completed gallium nitride compound semiconductor LED chip.

First, an organic metal compound gas together with a carrier gas H 2 is deposited on a substrate 21 made of sapphire (Al ₂ O ₃ single crystal) at a low temperature of 400 to 700 ° C. by a metal organic compound vapor phase growth method (hereinafter referred to as MOCVD method). (Hereinafter, referred to as TMG), ammonia (NH ₃ ), SiH ₄ as a dopant, and the like, and a low-temperature buffer layer 22 composed of an n-type GaN layer is set to 0.1.
About 0.01 to 0.2 μm, and then 700 to 1200
The same gas is supplied at a high temperature of ° C. to form a high-temperature buffer layer 23 of n-type GaN having the same composition of about 2 to 5 μm.

Then, a source gas of trimethylaluminum (hereinafter referred to as TMA) is further added to the above-described gas into the reaction tube, and n-type Al _z G containing n-type dopant Si is added.
a _1-z N (0 <z ≦ 1) layer is formed, and the n-type cladding layer 2 is formed.
4 is formed in a thickness of about 0.1 to 0.3 μm.

Next, a material whose band gap energy becomes smaller than that of the cladding layer, for example, trimethylindium (hereinafter referred to as T
MI) and In _y Ga _1-y N (0 ≦ y ≦ 1)
An active layer 25 of about 0.05 to 0.1 μm is formed.

Further, the same source gas as that used for forming the n-type cladding layer 24 is replaced with SiH4 and Mg or Zn as a p-type impurity is replaced with biscyclopentadienyl magnesium (hereinafter referred to as Cp ₂ Mg). That)
Alternatively, it is added as dimethylzinc (hereinafter referred to as DMZn) and introduced into a reaction tube, and p-type A
An lz Ga1-z N layer is grown in vapor phase. Here, the reaction gas is supplied such that the Al composition ratio z becomes the same value as z of the n-type cladding layer 24 from the viewpoint of ease of manufacture. These n
A double hetero junction is formed by the mold cladding layer 24, the active layer 25, and the p-cladding layer 26.

Next, in order to form the cap layer 27, Cp ₂ Mg or DMZn is supplied as an impurity source gas with the same source gas as the buffer layer 23 described above, and a p-type GaN layer is grown to about 0.3 to 2 μm.

After that, a protective film is provided and heat treatment for annealing the p-type layer or electron beam irradiation is performed to activate the p-type cladding layer 26 and the cap layer 27.

Then, after removing the protective film, a resist is applied and patterned to form an n-side electrode, and a part of each grown semiconductor layer is removed by etching to form an n-type cladding layer. 24 or the buffer layer 23 is exposed.

Next, a metal film of Au, Al, or the like is formed by, for example, vapor deposition, sputtering, or the like to form both the p-side and n-side electrodes 29, 30, respectively.
LED chips are formed by dicing.

[0014]

In a conventional gallium nitride compound semiconductor, a double heterojunction semiconductor light emitting device has high luminous efficiency but high operating voltage. When a material having a small band gap energy is used for the n-type cladding layer and the p-type cladding layer in order to lower the operating voltage, that is, a material having a small Al composition ratio z of Al _z Ga ₁ -zN, the operating voltage is low. However, there is a problem that the outflow of electrons from the active layer to the p-type cladding layer increases, and the luminous efficiency decreases.

An object of the present invention is to provide a semiconductor light emitting device having a double hetero structure, which does not decrease the luminous efficiency and has a low operating voltage.

[0016]

The semiconductor light emitting device of the present invention has at least a sandwich structure of an n-type cladding layer made of a gallium nitride compound semiconductor, an active layer and a p-type cladding layer, and the band of the active layer is A double heterojunction type semiconductor light emitting device having a gap energy smaller than the band gap energy of both cladding layers, wherein a difference between a band gap energy of the n-type cladding layer and a band gap energy of the active layer. Is 1 / (the difference between the bandgap energy of the p-type cladding layer and the bandgap energy of the active layer).
The n-type cladding layer is n-type so as to be about 3 to 1/2.
Type Al _x Ga ₁ -xN (0 ≦ x ≦ 0.5), wherein the active layer is made of In _y Ga _1-y N (0 ≦ y ≦ 1);
The type cladding layer is made of p-type Al _z Ga _{1 -zN} (0 <z ≦ 1), and the materials of the two cladding layers are selected so as to constitute a light emitting diode.

In the semiconductor light emitting device according to the present invention, the sandwich structure is formed so as to constitute a semiconductor laser.

In the semiconductor light emitting device of the present invention, in the semiconductor laser according to claim 2, the materials of the active layer and the cladding layers are selected such that the refractive index of the active layer is larger than the refractive indexes of the cladding layers. Be done. 4. The semiconductor light emitting device according to claim 2, wherein the n-type cladding layer is n-type Al _x Ga _{1 -x.}
N (0 ≦ x ≦ 0.5), and the active layer is made of In _y G
a _1-y N (0 ≦ y ≦ 1), and the p-type cladding layer is made of p-type Al _z Ga _1-z N (0 <z ≦ 1). The semiconductor light emitting device of the present invention is the semiconductor laser according to claim 2, 3 or 4, wherein the sandwich structure is provided on a substrate, and a buffer layer made of at least GaN is provided between the sandwich structure and the substrate. It is characterized by being obtained. The semiconductor light emitting device of the present invention is the semiconductor laser according to claim 2, 3, 4 or 5, wherein the sandwich structure is provided on a substrate, and at least GaN is provided on a surface of the sandwich structure opposite to the substrate. Characterized in that a cap layer is provided. According to a sixth aspect of the present invention, in the semiconductor laser according to the sixth aspect, the cap layer and a part of the sandwich structure are etched to form a mesa shape.

Embodiments of the present invention will be described below. In the semiconductor laser, the materials of the active layer and the cladding layers are selected such that the refractive index of the active layer is higher than the refractive indexes of the cladding layers. Further, the n
N _- type Al _x Ga _1-x N (0 ≦ x ≦ 0.5)
And the active layer is made of In _y Ga _1-y N (0 ≦ y ≦ 1).
And the p-type cladding layer is p-type Al _z Ga _{1 -z} N
(0 <z ≦ 1). The sandwich structure is provided on a substrate, and at least Ga is provided between the sandwich structure and the substrate.
The provision of the buffer layer made of N can alleviate the strain in the cladding layer, prevent crystal defects and dislocations in the cladding layer, and lower the resistance of the semiconductor layer. preferable. Also, at least G is provided on the surface of the sandwich structure opposite to the substrate.
A structure in which a cap layer made of aN is provided can be employed. Further, a mesa-shaped semiconductor laser is obtained by etching a part of the cap layer and the sandwich structure into a mesa shape.

According to the semiconductor light emitting device of the present invention, since a material having a smaller band gap energy than that of the p-type cladding layer is used for the n-type cladding layer, the injection of electrons from the n-type cladding layer to the active layer requires a low voltage. Is easily done with On the other hand, since the p-type cladding layer is made of a material having a large band gap energy as in the conventional case, the escape of electrons from the active layer to the p-type cladding layer is small, and the recombination of electrons and holes in the active layer is prevented. Contribute. Since holes have a larger effective mass than electrons, even if the band gap energy of the n-type cladding layer is small, holes injected into the active layer do not escape to the n-type cladding layer side. This contributes to recombination in the active layer without wasting holes, and the operating voltage can be reduced by the reduction of the band gap energy of the n-type cladding layer. I do.

The rate at which the band gap energy of the n-type cladding layer can be reduced can be reduced to about 1/3 since the effective mass of holes is about three times that of electrons.
The difference between the p-type cladding layer and the active layer is smaller than the band gap energy difference between the p-type cladding layer and the active layer.
/ 3 or more, preferably about 1/2
_{If the} lzGa1 _-zN material is used for the cladding layer, the ratio z of Al can be reduced to half or less of the ratio of Al in the p-type cladding layer, and the operating voltage can be reduced by 5 to 10%.

Next, the semiconductor light emitting device of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is an explanatory cross-sectional view of a semiconductor laser chip having a mesa shape, which is an embodiment of a semiconductor light emitting device of the present invention.
FIG. 2 is a manufacturing process diagram, and FIG. 3 is a schematic view of an energy band mainly showing a forbidden band of the n-type cladding layer, the active layer and the p-type cladding layer of the semiconductor light emitting device of the present invention.

In FIG. 1, 1 is sapphire (Al 2 O).
3 single-crystal), n-type GaN,
Low temperature buffer layer 2 of about 1 to 0.2 μm, n-type GaN
High temperature buffer layer 3 of about 2-3 μm, n-type
Gap energy (forbidden band width) is p-type cladding layer
Smaller material, for example Al_xGa_1-xN (0 ≦ x ≦
0.5, for example, x = 0.07), from 0.1 to
N-type cladding layer 4 of about 0.3 μm, non-doped or
n-type or p-type
Materials with low energy and high refractive index
If In_yGa_1-yN (0 ≦ y ≦ 1), from 0.05 to
Active layer 5 of about 0.1 μm, p-type Al_zGa_{1 -z}N (0 <
z ≦ 1, 2x ≦ z, for example, z = 0.15)
P-type cladding layer of about 0.1 to 0.3 μm, p-type GaN
And a cap layer 7 of about 0.3 to 2 μm is sequentially stacked.
A p-side electrode made of Au or the like on the cap layer 7
8. A part of the laminated semiconductor layer is removed by etching.
An n-side electrode made of Al or the like is placed on the exposed high-temperature buffer layer 3.
The poles 9 are formed, further forming a current stripe.
Therefore, the cap layer 7 and part of the p-type cladding layer are etched.
To form a mesa, and the semiconductor laser chip
Is formed.

In the semiconductor light emitting device of the present invention, the band gap energy of the n-type cladding layer 4 is smaller than the band gap energy of the p-type cladding layer 6 as shown in the above-described embodiment of the semiconductor laser. The cladding layers 4 and 6 and the active layer 5 are made of a material having a gap energy larger than the band gap energy of the active layer 5.
Is formed.

A double heterojunction structure in which an active layer 5 made of a material having a small bandgap energy is sandwiched by a cladding layer made of a material having a large bandgap energy in order to efficiently perform recombination of electrons and holes and increase luminous efficiency. Are used in semiconductor lasers and high-brightness LEDs. When a material with a large band gap energy is used for the cladding layer, the effect of confining electrons and holes increases, which contributes to light emission without waste. However, the operating voltage increases, and in fact, the leakage of electrons and holes from the active layer is ignored. A material having a bandgap energy that is as large as possible is selected. However, the operating voltage is higher than that of the pn junction. In the present invention, the operating voltage can be reduced while maintaining the leakage of the electrons and holes to a negligible level. That is, the effective mass of holes is as large as about three times the effective mass of electrons, and leakage is smaller than that of electrons even if the band gap energy is small. Therefore, by using a material having a bandgap energy smaller than the bandgap energy of the p-type cladding layer for the n-type cladding layer, electrons can be injected into the active layer at a low voltage, thereby preventing holes from leaking from the active layer. It is made possible.

The operation of the present invention will be described in detail with reference to FIG. 3, which is a schematic diagram showing the energy band diagram of the semiconductor laser shown in FIG. In FIG. 3, V indicates a valence band, F indicates a forbidden band, C indicates an energy band of a conduction band, and A indicates n.
High-temperature buffer layer 3 made of n-type GaN, B is n-type Al _0.07
An n-type cladding layer 4 made of Ga _0.93 N, where D is In _y Ga
_The active layer 5 made of _1-yN , G shows a p-type cladding layer made of Al _0.15 Ga _0.85 N, and J shows an energy band of a cap layer 7 made of p-type GaN.

In the semiconductor laser of this embodiment, as shown in FIG. 3, the band gap energy of the n-type cladding layer indicated by B is smaller than the band gap energy of the p-type cladding layer indicated by G. . Broken line B1
Indicates the case of the same band gap energy as that of the p-type cladding layer in the conventional structure.

In this configuration, when a voltage is applied between the p-side electrode 8 and the n-side electrode 9, the electrons E flow from the n-type GaN (high-temperature buffer layer A) side to the p-side, and the conduction band of the active layer K1
Flows into. At this time, since the bandgap energy of the n-type cladding layer is low, the electrons E easily flow into the conduction band K1 of the active layer, and the electrons are supplied to the active layer even at a low voltage.
The electrons E flowing into the conduction band K1 of the active layer are pulled by the p-side electrode, but are confined in the active layer because the band gap energy of the p-type cladding layer is large. On the other hand, the holes H flow from the p-type GaN (contact layer J) side to the n-side and flow into the valence band K2 of the active layer. The holes H flowing into the valence band K2 of the active layer are pulled by the n-side electrode, but the effective mass of the holes H is as large as about three times the effective mass of the electrons, and the band gap energy of the n-type cladding layer B is increased. Cannot be overcome even if it is low, and is effectively confined within the valence band of the active layer. As a result, electrons and holes are efficiently recombined in the active layer, and high luminous efficiency is obtained.

As described above, according to the present invention, each semiconductor layer is selected so that the band gap energy of the n-type cladding layer is smaller than that of the p-type cladding layer. The electron injection can be performed, and the luminous efficiency can be improved without increasing the reactive current. The extent to which the bandgap energy of the n-type cladding layer is smaller than that of the p-type cladding layer is determined by the bandgap energy of the active layer, and the difference in bandgap energy from the active layer is 1/3 to 1 of that in the case of the p-type layer. / 低 く, that is, about ３ to ２.

The general formula Al _p Ga _q In _1-pq N (0 ≦ p <
In order to reduce the bandgap energy using a gallium nitride compound semiconductor composed of 1, 0 <q ≦ 1, 0 <p + q ≦ 1), p is reduced, that is, the composition ratio of Al is reduced, or p + q is reduced. That is, it can be obtained by increasing the composition ratio of In. Therefore, by adjusting the composition ratio of Al and In so that the band gap energy of the cladding layer is larger than that of the active layer and the band gap energy of the n-type cladding layer is smaller than that of the p-type cladding layer, A semiconductor layer having a band gap energy of

Further, since the embodiment shown in FIG. 1 is a semiconductor laser, it is necessary to confine light in the active layer and oscillate, and the refractive index of the cladding layer is made smaller than that of the active layer. In the case of an LED, it is not always necessary. However, when the Al composition ratio is increased in the above composition ratio, the refractive index decreases.

Next, a method of manufacturing the semiconductor laser shown in FIG. 1 will be described with reference to FIG.

First, as shown in FIG. 2A, a low-temperature buffer layer 2 made of, for example, a gallium nitride-based compound semiconductor such as n-type GaN is deposited on a substrate 1 made of sapphire or the like by the MOCVD method in a range of 0.01 to 0.01. A high-temperature buffer layer 3 made of n-type GaN having the same composition at a high temperature of about 700 to 1200 ° C.
Degree formed.

Next, TMI is further supplied to, for example, an n-type Alx Ga1-x N (0 ≦ x ≦ 0.5, for example, x
= 0.07).
It is formed about 3 μm. Then, instead of TMA, TMI
To supply undoped or n-type or p-type In _y G
An active layer 5 made of a _1-y N (0 ≦ y ≦ 1, for example, y = 0.06) is grown to a thickness of about 0.05 to 0.1 μm. Then, using the same source gas as that used for forming the n-type cladding layer 4, TMA was applied to the n-type cladding layer 4.
A p-type Al _z Ga ₁ -z which is a p-type cladding layer 6 is supplied to the reaction tube at a flow rate of about 20 to 100 sccm which is about twice as large as that of the case.
An N (0 <z ≦ 1, 2x ≦ z, for example, z = 0.15) layer is formed to a thickness of about 0.1 to 0.3 μm. Further, the same source gas as that for forming the buffer layer 3 is supplied to form the cap layer 7 made of p-type GaN to a thickness of 0.3 to 2 μm.

In order to form the buffer layer 3 and the cladding layer 4 to be n-type, Si, Ge, and Te are converted to SiH ₄ , G
In order to form the clad layer 6 and the cap layer 7 into p-type by mixing them into the reaction gas as impurity source gases such as eH ₄ and TeH ₄ , Mg or Zn is converted into an organic metal gas such as Cp ₂ Mg or DMZn. Mix in gas. However, in the case of n-type, even if impurities are not mixed, N is easily evaporated at the time of film formation and naturally becomes n-type.

After that, a protective film 10 such as SiO ₂ or Si ₃ N ₄ is provided on the entire surface of the growth layer of the semiconductor layer (see FIG. 2B), and annealing is performed at 400 to 800 ° C. for about 20 to 60 minutes. Then, the p-type clad layer 6 and the cap layer 7 which are p-type layers are activated.

When the annealing is completed, as shown in FIG. 2 (c), a mask such as a resist film 11 is provided, and the layers are stacked until the n-type cladding layer 4 or the n-type high temperature buffer layer 3 is exposed. Etch the semiconductor layer. This etching is performed by, for example, reactive ion etching under an atmosphere of a mixed gas of Cl ₂ and BCl ₃ .

Next, a metal film of Au, Al, or the like is formed by sputtering or the like, and the p-side electrode 8 electrically connected to the p-type layer on the surface of the laminated compound semiconductor layer and the exposed surface of the high-temperature buffer layer 3 An n-side electrode 9 electrically connected to the n-type layer is formed, and a portion of the cap layer 7 and a part of the p-type cladding layer 6 are mesa-etched (see FIG. 1).

Next, dicing is performed on each chip to form a semiconductor laser chip.

In the above embodiment, a semiconductor laser having a mesa-shaped current stripe structure has been described. However, a semiconductor laser having various structures such as a current limiting layer embedded type or a gallium nitride compound semiconductor such as an LED having a double hetero junction structure. The present invention can also be applied to a semiconductor light emitting device using a.
Further semiconductor material is not limited to the material of Example composition, the _{Al p Ga q In 1-pq} N of some or all substituted with such as As and / or P materials and gallium arsenide-based compound semiconductor N The present invention can be similarly applied to a semiconductor light-emitting device using the same.

[0041]

According to the semiconductor light emitting device of the present invention, the semiconductor material is selected so that the band gap energy of the n-type cladding layer is smaller than the band gap energy of the p-type cladding layer. Less,
In addition, high-luminance light can be emitted at a low operating voltage, and a semiconductor light-emitting element with high luminous efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of one embodiment of a semiconductor light emitting device of the present invention.

FIG. 2 is an explanatory sectional view showing the manufacturing process of FIG. 1;

FIG. 3 is an energy band diagram mainly showing a forbidden band of a cladding layer and an active layer in one embodiment of the semiconductor light emitting device of the present invention.

FIG. 4 is a perspective view showing an example of a conventional semiconductor light emitting device.

[Explanation of symbols]

 Reference Signs List 1 substrate 4 n-type cladding layer 5 active layer 6 p-type cladding layer

Claims (7)

[Claims] 1. A semiconductor comprising a gallium nitride compound semiconductor
Sandwich of n-type cladding layer, active layer and p-type cladding layer
And at least a band gap of the active layer.
The energy is the band gap energy of the cladding layers.
Double heterojunction type
A semiconductor light emitting device, comprising: a band of the n-type cladding layer.
Gap energy and band gap energy of the active layer
Difference from the bandgap of the p-type cladding layer.
Energy and the band gap energy of the active layer
So that the difference between the n-type
Pad layer is n-type Al_xGa_1-xN (0 ≦ x ≦ 0.5)
The active layer is In_yGa_{1 -y}N (0 ≦ y ≦ 1)
The p-type cladding layer is p-type Al_zGa_1-zN (0 <z
≦ 1), so as to constitute a light emitting diode,
A semiconductor light emitting device in which the materials of the cladding layers are selected
Child. 2. The semiconductor laser according to claim 1, wherein said sandwich structure is formed to constitute a semiconductor laser. 3. The semiconductor laser according to claim 2, wherein the materials of the active layer and the cladding layers are selected so that the refractive index of the active layer is higher than the refractive index of the cladding layers. 4. The method according to claim 1, wherein the n-type cladding layer is an n-type Al _x Ga _{1 -x}
N (0 ≦ x ≦ 0.5), and the active layer is made of In _y G
_{a 1-y N (0 ≦} y ≦ 1) consists, said p-type cladding layer is p-type _{Al z Ga 1-z N (} 0 <z ≦ 1) consists of claim 2
Or the semiconductor laser according to 3. 5. The semiconductor laser according to claim 2, wherein said sandwich structure is provided on a substrate, and a buffer layer made of at least GaN is provided between said sandwich structure and said substrate. 6. The sandwich structure is provided on a substrate, and a cap layer made of at least GaN is provided on a surface side of the sandwich structure opposite to the substrate. Semiconductor laser. 7. The semiconductor laser according to claim 6, wherein a part of said cap layer and said sandwich structure is etched to form a mesa shape.