JP2778405B2 - Gallium nitride based compound semiconductor light emitting device - 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 using a gallium nitride compound semiconductor, and more particularly to a forward voltage (Vf).
The present invention relates to a gallium nitride-based compound semiconductor light emitting device having a low light emission and high light emission output.

[0002]

2. Description of the Related Art GaN, GaAlN, InGaN, In
Gallium nitride-based compound semiconductors such as AlGaN have direct transitions and change in band gap from 1.95 eV to 6 eV. Therefore, they are promising as materials for light-emitting elements such as light-emitting diodes and laser diodes. At present, a light-emitting element using this material includes a so-called MIS in which a high-resistance i-type gallium nitride-based compound semiconductor doped with a p-type dopant is laminated on an n-type gallium nitride-based compound semiconductor.
A blue light emitting diode having a structure is known.

[0003] Light emitting devices of the MIS structure generally have a very low light emission output, and are still insufficient for practical use. As a technique for realizing a pn junction light-emitting element in which a high-resistance i-type is changed to a low-resistance p-type and an emission output is improved, for example, Japanese Patent Application Laid-Open No. 3-218325 discloses an i-type gallium nitride compound. A technique of irradiating a semiconductor layer with an electron beam has been disclosed. In addition, in Japanese Patent Application No. 3-357046, we have proposed a technique of forming a low-resistance p-type by annealing an i-type gallium nitride-based compound semiconductor layer at 400 ° C. or higher.

A light emitting device using a gallium nitride-based compound semiconductor having a pn junction is disclosed in, for example, Japanese Patent Laid-Open No. 4-2429.
No. 85 proposes a laser element having a double hetero structure, and Japanese Patent Application Laid-Open No. 4-209577 proposes a light emitting diode having a double hetero structure using InGaAlN as a light emitting layer.

[0005]

As for a semiconductor light emitting device having a pn junction, a double hetero structure has a larger light emission output than a homo structure, and a laser element cannot be realized unless it has at least a hetero structure. Are known. However, when a gallium nitride-based compound semiconductor light emitting device having a double hetero structure is realized, the crystallinity of the gallium nitride-based compound semiconductor is significantly different depending on factors such as the type and composition ratio of the gallium nitride-based compound semiconductor used. A large difference appears in the output. In an extreme case, an element that does not emit light at all is actually produced. In addition, when an electrode is actually provided to form an element structure, the p-type crystal of the gallium nitride-based compound semiconductor does not have ohmic contact with the electrode formed on the p-type crystal, so that a predetermined forward current cannot be obtained. , The forward voltage (Vf) increases,
There is a problem that luminous efficiency is reduced. For this reason, in the gallium nitride-based compound semiconductor light emitting device, a light emitting diode having a hetero structure has not yet been commercialized, and the laser device has not even oscillated.

Accordingly, a first object of the present invention is to provide a structure of a gallium nitride-based compound semiconductor capable of obtaining ohmic contact with a p-type crystal, thereby lowering Vf and improving luminous efficiency. A second object is to provide a novel double heterostructure light emitting device using the gallium nitride-based compound semiconductor, thereby improving the light emitting output of the light emitting device.

[0007]

Means for Solving the Problems By forming an electrode on p-type gallium nitride laminated on a specific p-type gallium nitride compound semiconductor, the ohmic contact between the electrode and the p-type gallium nitride layer can be reduced. It was newly found that the luminous efficiency was improved. Further, the light-emitting element using the p-type gallium nitride-based compound semiconductor layer has a specific double heterostructure, and the type of gallium nitride-based compound semiconductor constituting the double heterostructure is limited, so that gallium nitride having the most excellent crystallinity can be obtained. It has been found that an element in which a series compound semiconductor is laminated is obtained, and the light emission output is improved. That is, the gallium nitride based compound semiconductor light emitting device of the present invention,
In a gallium nitride-based compound semiconductor light emitting device having a double hetero structure having a pn junction, Mg-doped p
A p-type GaN contact layer doped with Mg as a layer on which an electrode is to be formed on a cladding layer of the type Ga _1-x Al _x N (where x is 0 <x <0.5) Wherein the specific double heterostructure light emitting element is n
N-type Ga _1-Y on the gallium nitride-based compound semiconductor layer
Al _Y N cladding layer (where Y is 0 <Y <1) and n-type I
n _Z Ga _1-Z N active layer (where, Z is 0 <Z <1) and the p
And a p-type GaN contact layer laminated with a p _- type Ga _1-x Al _x N cladding layer.

The gallium nitride compound semiconductor light emission of the present invention
FIG. 1 is a sectional view showing the structure of the element. From the bottom,
A buffer layer 2 and an n-type gallium nitride-based compound
Semiconductor layer 3 and n-type Ga_1-YAl_YN cladding layer 4 (0
<Y <1) and n-type In_ZGa _1-ZN (0 <Z <1) active layer
5 and Mg-doped p-type Ga_1-XAl_XN (0 <X <0.
5) Cladding layer 6 and Mg-doped p-type GaN contact
It has a structure in which the layers 7 are sequentially stacked. 8 is Mg
An electrode provided on the doped p-type GaN contact layer 7;
Represents an electric current provided on the n-type gallium nitride-based compound semiconductor layer 3.
It is a pole. Sapphire, ZnO, SiC, S
i and the like are used. AlN, GaN,
GaAlN or the like is used.

In the gallium nitride-based compound semiconductor light emitting device, the type of the n-type gallium nitride-based compound semiconductor layer 3 is not particularly limited.
Non-doped gallium nitride-based compound semiconductors such as GaN and InAlGaN or non-doped gallium nitride-based compound semiconductors include, for example, Si, Ge, Te, and S.
A layer doped with an n-type dopant such as e and grown so as to exhibit n-type characteristics can be used.

Next, the n-type Ga _1-Y Al _Y N cladding layer 4
Must have a ternary mixed crystal gallium aluminum nitride containing no In. Because n-type Ga
_This is because if indium is newly added to the _1-Y Al _Y N cladding layer 4, the crystallinity of the cladding layer 4 deteriorates, and the light emission output decreases. Further, by setting the Y value of the n-type Ga _1-Y Al _Y N clad layer in the range of 0 <Y <1, it is possible to function as an n-type clad layer and obtain a preferable double hetero structure. More preferably, by setting the Y value to 0.5 or less, the n-type cladding layer 4 having few lattice defects and good crystallinity can be obtained. As described above, the n-type Ga _1-Y Al _Y N cladding layer 4 is doped with non-doped Ga _1-Y Al _Y N or Ga _1- grown by doping with an n-type dopant to exhibit n-type characteristics. _Y Al _Y N can be used.

[0011] Then, n-type In _Z Ga _1-Z N active layer 5, it is necessary to its composition and indium gallium nitride ternary mixed crystal containing no Al. This is because the active layer is a light-emitting layer, and when Al is contained in the light-emitting layer, deep-level light emission appears, which tends to inhibit inter-band light emission of InGaN. Therefore, it is not preferable to use the active layer as the active layer. n-type In _Z Ga _1-Z N active layer 5, by the range and the Z value 0 <Z <1, and for the emission wavelengths can be converted from purple to red is highly advantageous . n-type In
_{As described above, the Z} Ga _{1 -Z} N active layer is made of a non-doped I
n _Z Ga _{1 -Z} N layer or n-type dopant doped with n
In _Z Ga _1-Z layer grown as indicating the type characteristic may be used. In addition, Mg, Zn, Cd, Be, C
It is also possible to use In _Z Ga _1-Z N layer grown as an n-type characteristics by doping p-type dopant in a like.
Further n-type dopant, and In _Z Ga _1-Z layer grown as a p-type dopant by doping an n-type characteristics can be used. By doping these dopants to make them n-type, the color purity of the emission color can be improved and the emission output can be improved.

Next, similarly to the n-type Ga _1-Y Al _Y N cladding layer 4, the Mg-doped p-type Ga _1-x Al _x N cladding layer 6 has a ternary mixed crystal nitride containing no In. It must be gallium aluminum. This is because the inclusion of indium as described above deteriorates the crystallinity of the p-type cladding layer 6 and makes it difficult to exhibit p-type characteristics. The _{X of the} p-type Ga _1-x Al _x N cladding layer 6
The value must be in the range 0 <X <0.5. By setting it to be larger than 0, it can function as a p-type cladding layer and obtain a preferable double hetero structure, and by making it smaller than 0.5, a p-type cladding layer 6 having few lattice defects and good crystallinity can be obtained. Conversely, if it is 0.5 or more, p
Since the crystallinity of the p-type GaN contact layer 7 laminated on the mold clad layer 6 deteriorates and ohmic contact between the contact layer 7 and the electrode 8 cannot be obtained, the limit value is set to less than 0.5. Further, the Mg-doped p-type Ga _1-x Al _x N
The thickness of the cladding layer 6 is 10 Å or more,
It is preferable that the thickness be 0.2 μm or less. If it is thinner than 10 Å, the n-type In _Z
An electrical short-circuit easily occurs with the Ga ₁ -ZN active layer 5, and it is difficult to function as a cladding layer. Conversely, if the thickness is more than 0.2 μm, the crystal tends to crack, and the crystallinity tends to deteriorate. Further, in this p-type Ga _1-x Al _x N cladding layer, what is important is that the p-type dopant is Mg,
The p-type characteristic is obtained by this Mg. This M
Instead of g, other p-type dopants such as Zn, Cd,
If a p-type dopant such as Be or Ca is doped, it becomes difficult to obtain p-type characteristics, and the light emission output tends to decrease.

Next, it is necessary that the Mg-doped p-type GaN contact layer 7 has a composition of binary mixed crystal gallium nitride containing no In and Al. This is because the inclusion of indium and aluminum makes it difficult to obtain ohmic contact with the electrode 8 and lowers the luminous efficiency. In particular, the thickness of the p-type GaN contact layer is 10
It is preferable to adjust the thickness to angstrom or more and 0.5 μm or less. If the thickness is less than 10 angstroms, electrical short-circuit with the p-type GaAlN cladding layer 6 is likely to occur,
Difficult to act as a contact layer. The ternary mixed crystal G
Since a binary mixed crystal GaN contact layer having a different composition is laminated on the aAlN cladding layer 6, if the thickness of the GaN contact layer is made larger than 0.5 μm, lattice defects due to misfit between the crystals may occur. 7 tends to occur, and the crystallinity tends to decrease. The thinner the thickness of the contact layer 7, the lower the Vf and the higher the luminous efficiency. Further, the p-type GaN contact layer 7
Need to be Mg. Doping with another p-type dopant instead of Mg tends to make it difficult to obtain p-type characteristics, and also tends to make it difficult to obtain ohmic contact.

Further, a p-type Ga _{1 -x} Al _x N cladding layer 6,
As means for further reducing the resistance of the p-type GaN layer, an annealing treatment at 400 ° C. or higher disclosed in Japanese Patent Application No. 3-357046 may be performed. When the annealing is performed, both the p-type cladding layer and the p-type contact layer become resistant, and the light emission output can be further improved.

[0015]

The double-heterostructure nitride gas using a pn junction is provided.
In a lithium-based compound semiconductor light emitting device, Mg-doped p
Type Ga_1-XAl_XMg-doped p-type on N cladding layer 6
A GaN contact layer 7 is formed and the GaN contact
By forming the electrode 8 on the layer, the ohmic contact
As a result, the luminous efficiency is improved. The detailed principle is unknown
But we measured the hole carrier concentration in those layers
As a result, p-type Ga_{1- X}Al_XN layer is about 10¹⁶/cm^ThreeIn
The p-type GaN layer is about 10¹⁷/cm^ThreeAnd one digit higher
Was. In other words, the electrode with the higher hole carrier concentration
Ohmic contact is easier to obtain by forming
I guess. The p-type GaAlN cladding layer 6
A p-type GaN contact layer 7 having a different composition is formed thereon.
As a result, lattice mismatch due to misfit in the p-type GaN layer
Depression is likely to occur, and crystallinity decreases. Misfit
Can be reduced by reducing the Al content of the p-type GaAlN cladding layer 6.
A smaller mixed crystal ratio is better. Therefore, the p-type GaN contact
Layer 7 has good crystallinity and is in ohmic contact with electrode 8
Limit value, that is, the X value less than 0.5 is the limit value
Was.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing a gallium nitride-based compound semiconductor light emitting device of the present invention by metal organic chemical vapor deposition will be described.

Example 1 After the sapphire substrate 1 was placed in a reaction vessel and the sapphire substrate 1 was cleaned, the growth temperature was set to 510 ° C., hydrogen was used as a carrier gas, and ammonia and TMG ( GaN buffer layer 2 is grown on a sapphire substrate to a thickness of about 200 Å using trimethylgallium).

After growing the buffer layer 2, only TMG is stopped,
Raise the temperature to 1030 ° C. When the temperature reaches 1030 ° C., n-type G doped with Si using TMG and ammonia gas as the source gas and silane gas as the dopant gas.
The aN layer 3 is grown to 4 μm.

After the growth of the n-type GaN layer 3, the raw material gas and the dopant gas are stopped, the temperature is set to 800 ° C., and TMG, TMA (trimethylaluminum) and ammonia are used as the raw material gas, and silane gas is used as the dopant gas. As No. 4, a Si-doped Ga 0.86 Al 0.14 N layer is grown to a thickness of 0.15 μm.

Next, the source gas and the dopant gas are stopped,
The temperature was set to 800 ° C., the carrier gas was switched to nitrogen, TMG, TMI (trimethyl indium) and ammonia were used as source gases, silane gas was used as dopant gas, and Si-doped In 0.01 Ga 0.
A 99N layer is grown for 100 Å.

Next, the source gas and the dopant gas are stopped,
The temperature was raised again to 1020 ° C. and T
Using Mg, TMA, ammonia, and Cp2Mg (cyclopentadienylmagnesium) as a dopant gas, a p-type Ga0.86Al0.14N layer doped with Mg is grown as the p-type cladding layer 6 by 0.15 .mu.m.

Next, only TMA is stopped, and a Mg-doped p-type GaN layer is grown as the p-type contact layer 7 by 0.4 μm.

After the growth, the substrate is taken out of the reaction vessel and annealed in a nitrogen atmosphere at 700 ° C. for 20 minutes to further reduce the resistance of the p-type Ga 0.86 Al 0.14 N layer and the p-type GaN contact layer. .

The wafer obtained as described above is shown in FIG.
The n-type GaN layer 3 is exposed by etching as shown in (1), an electrode 8 made of Au is provided on the p-type GaN contact layer 7, and an electrode 9 made of Al is provided on the n-type GaN layer 3.
Annealing is again performed at 00 ° C., so that the electrode and the gallium nitride-based compound semiconductor are adapted. After that, 500
After cutting into chips of μm square, a light emitting diode was obtained. At a forward current of 20 mA, Vf was 5 V, the light emission output was 700 μW at a light emission wavelength of 370 nm, and the light emission efficiency was 0.7%, showing excellent characteristics.

Example 2 A light emitting diode was obtained in the same manner as in Example 1 except that the thickness of the Mg-doped p-type GaN contact layer was changed to 0.1 μm.
At a forward current of 20 mA, the emission wavelength and the emission output were the same, but Vf was reduced to 4 V, and the emission efficiency was improved to 0.88%.

Example 2 In Example 1, p-type Mg was used.
A light-emitting diode was obtained in the same manner as in Example 1 except that the thickness of the doped p-type GaN contact layer was changed to 0.1 μm. At a forward current of 20 mA, the light-emitting wavelength and light-emitting output were the same. Decreased to 4 V, and the luminous efficiency improved to 0.88%.

Example 3 In Example 1, the flow rate of TMA was increased and the Al mixed crystal ratio of the p-type cladding layer 6 was changed to Ga.
A light-emitting diode was obtained in the same manner except that 0.55 Al0.45 N was used, and Vf was 6 at a forward current of 20 mA.
It shows almost the limit value where ohmic contact with V is obtained,
The emission wavelength was the same, the emission output was 400 μW, and the emission efficiency was 0.2%.

Example 4 A light-emitting diode was obtained in the same manner as in Example 1 except that the n-type cladding layer 4 was not grown. At a forward current of 20 mA, a light-emitting diode was obtained.
Although Vf was 5 V, the light emission output was 200 μW and the light emission efficiency was 0.2%.

[Comparative Example 1] In Example 1, the flow rate of TMA was increased and the Al mixed crystal ratio of the p-type cladding layer 6 was changed to Ga.
A light emitting diode was obtained in the same manner except that 0.5 Al 0.5 N was used. At a forward current of 20 mA, Vf was 30
V, and it was confirmed that ohmic contact was not obtained. Since this device had a large Vf, the device stopped emitting light immediately.

Comparative Example 2 A light-emitting diode was obtained in the same manner as in Example 1 except that the p-type contact layer 7 was not formed and the electrode was formed directly on the p-type cladding layer 6. At 20 mA, Vf increased to 30 V, and no ohmic contact was obtained, so that light emission stopped immediately as in Comparative Example 1.

COMPARATIVE EXAMPLE 3 In Example 1, when growing the p-type cladding layer 6, TMI was newly added to the raw material gas, the carrier gas was changed to nitrogen, and the growth temperature was set to 800.
A light-emitting diode was obtained in the same manner except that a Mg-doped p-type In0.01Al0.14Ga0.85N cladding layer was grown at a temperature of ° C. When a forward current of 20 mA was passed, light emission stopped immediately.

[0032]

As described above, the gallium nitride-based compound semiconductor light-emitting device of the present invention has a low Vf because it has a p-type GaN layer as a contact layer on a p-type GaAlN cladding layer. An element with excellent efficiency can be obtained. Moreover, the p-type clad layer excellent in crystallinity by limiting the Al mixed crystal ratio of the p-type GaAlN layer,
The p-type contact layer can be obtained, which greatly contributes to a decrease in Vf.

Further, an n-type gallium nitride compound semiconductor layer, an n-type GaAlN cladding layer, and an n-type InGaN layer are laminated, and the p-type GaAlN cladding layer, the p-type GaN
By laminating the contact layers, a light emitting device having excellent light emitting output and light emitting efficiency can be realized. Therefore, as a hint of the structure of a laser device which has not been realized, its industrial utility value is great.

[0034]

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a light emitting device according to one embodiment of the present invention.

[Explanation of symbols]

1 sapphire substrate 2 GaN buffer layer 3 n-type gallium nitride compound semiconductor layer 4 n-type Ga _1-Y Al _Y N clad layer 5 ····· n-type In _Z Ga _{1 -Z} N active layer 6 ···· p-type Ga _1-x Al _x N cladding layer 7 ····· p-type GaN contact layer 8, 9 ··· electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 33/00

Claims (4)

(57) [Claims] In a gallium nitride-based compound semiconductor light emitting device having a double heterostructure having a pn junction, Mg-doped p-type Ga _1-x Al _x N (where X is 0 <X <
0.5) A gallium nitride-based compound semiconductor light emitting device comprising a Mg-doped p-type GaN contact layer as a layer on which an electrode is to be formed, on a cladding layer. 2. The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein the thickness of the p-type Ga _1-x Al _x N cladding layer is not less than 10 Å and not more than 0.2 μm. 3. The p-type GaN contact layer has a thickness of 1
2. The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein said gallium nitride based compound semiconductor light emitting device has a thickness of not less than 0 Å and not more than 0.5 μm. 4. An n-type Ga _1-Y Al _Y N cladding layer (where Y is 0 <Y <) on the n-type gallium nitride-based compound semiconductor layer.
And 1), n-type In _Z Ga _1-Z N active layer (where, Z is 0 <Z <
1) and are layered in this order, the n-type In _Z Ga _1-Z N
On the active layer, the p-type Ga _1-X Al _X N gallium nitride compound semiconductor light-emitting device according to claim 1, the cladding layer is characterized in that it is laminated.