JPH06268259A - Gallium nitride compound semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To enable a gallium nitride compound semiconductor light emitting element to be lessened in forward potential and improved in emission efficiency by a method wherein a P-type GaN contact layer is formed on a specific Mg- doped clad layer. CONSTITUTION:A buffer layer 2 is grown on a sapphire substrate 1, and then an Si-doped N-type GaN layer 3 is made to grow thereon. Thereafter, an Si- doped Ga0.86Al0.14N layer is grown as an N-type clad layer 4, and furthermore an Si-doped In0.01Ga0.99N layer is grown as an N-type active layer 5. Then, an Mg-doped P-type GaN layer is grown as a P-type contact layer 6. Thereafter, the substrate 1 is taken out of a reaction oven and annealed to lessen a P-type GaAl layer 6 and a P-type GaN contact layer 7 in resistance. The wafer obtained as above is etched to make the N-type GaN layer 3 exposed, an Au electrode 8 is provided to the P-type GaN contact layer 7, an Al electrode 9 is provided onto the N-type GaN layer 3, and then the wafer is annealed again and then cut into chips.

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).
And a gallium nitride-based compound semiconductor light emitting device having a high emission output.

[0002]

2. Description of the Related Art GaN, GaAlN, InGaN, In
Since gallium nitride-based compound semiconductors such as AlGaN have a direct transition and the bandgap changes from 1.95 eV to 6 eV, they are regarded as promising materials for light emitting devices such as light emitting diodes and laser diodes. At present, a light emitting device using this material is a so-called MIS in which a high-resistance i-type gallium nitride compound semiconductor doped with a p-type dopant is stacked on an n-type gallium nitride compound semiconductor.
Blue light emitting diodes with a structure are known.

A light emitting device having a MIS structure generally has a very low light emission output, which is still insufficient for practical use. As a technique for realizing a pn junction light emitting device in which a high resistance i-type is changed to a low resistance p-type and a light emission output is improved, for example, in JP-A-3-218325, an i-type gallium nitride compound is disclosed. A technique of irradiating a semiconductor layer with an electron beam is disclosed. In addition, in Japanese Patent Application No. 3-357046, we proposed a technique of making a low resistance p-type by annealing an i-type gallium nitride compound semiconductor layer at 400 ° C. or higher.

As a light emitting device using a pn junction gallium nitride compound semiconductor, for example, Japanese Patent Application Laid-Open No. 4-2429.
Japanese Laid-Open Patent Publication No. 85-8595 proposes a laser device having a double-hetero structure, and Japanese Laid-Open Patent Publication No. 4-209577 proposes a light-emitting diode having a double-hetero structure having InGaAlN as a light emitting layer.

[0005]

In the semiconductor light emitting device having the pn junction, the double hetero structure has a larger light emission output than the homo structure, and the laser device can be realized only at least in the 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 remarkably differs depending on factors such as the type and composition ratio of the gallium nitride-based compound semiconductor used. A big difference appears in the output. In the extreme case, the reality is that an element that does not emit light is formed. Moreover, when an electrode is actually provided to form an element structure, the p-type crystal of the gallium nitride-based compound semiconductor and the electrode formed on the p-type crystal are not in ohmic contact with each other. , The forward voltage (Vf) becomes high,
There is a problem that the luminous efficiency is reduced. Therefore, in the gallium nitride-based compound semiconductor light emitting device, a light emitting diode having a heterostructure has not yet been commercialized, and even a laser device does not even oscillate.

Therefore, it is a first object of the present invention to provide a structure of a gallium nitride-based compound semiconductor capable of making ohmic contact with a p-type crystal to reduce Vf and improve luminous efficiency. A second object is to improve the light emission output of the light emitting device by providing a novel double hetero structure light emitting device structure using the gallium nitride compound semiconductor.

[0007]

By forming an electrode on p-type gallium nitride laminated on a specific p-type gallium nitride-based compound semiconductor, we have established ohmic contact between the electrode and the p-type gallium nitride layer. It was newly found that the obtained luminous efficiency was improved. Further, the light emitting element using the p-type gallium nitride compound semiconductor layer has a specific double hetero structure, and by limiting the types of gallium nitride compound semiconductors forming the double hetero structure, gallium nitride having the best crystallinity is obtained. It has been found that a device in which a 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 double heterostructure gallium nitride-based compound semiconductor light emitting device having a pn junction, Mg-doped p
A p-type GaN contact layer doped with Mg is provided as a layer on which an electrode is to be formed on a cladding layer of Ga _{1 -X} Al _X N type (where X is 0 <X <0.5). And a specific double-heterostructure light emitting element is
On the n-type gallium nitride-based compound semiconductor layer, n-type Ga _{1 -Y}
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
It is characterized in that a type Ga _1-x Al _x N cladding layer and the p-type GaN contact layer are laminated.

Gallium Nitride Compound Semiconductor Light Emission of the Present Invention
A sectional view showing the structure of the element is shown in FIG. From bottom to top
On the plate 1, the buffer layer 2 and the 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 layer 7 and the layer 7 are sequentially stacked. In addition, 8 is Mg
An electrode provided on the doped p-type GaN contact layer 7, 9
Is an electrode provided on the n-type gallium nitride-based compound semiconductor layer 3.
It is a pole. Substrate 1 has sapphire, ZnO, SiC, S
i, etc. are used. The buffer layer 2 has AlN, GaN,
GaAlN or the like is used.

In the above-mentioned 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, and includes GaN, GaAlN, In.
For example, Si, Ge, Te, S is added to a non-doped (non-added) gallium nitride-based compound semiconductor such as GaN or InAlGaN, or a non-doped gallium nitride-based compound semiconductor.
A layer grown by doping with an n-type dopant such as e so as to show n-type characteristics can be used.

Next, the n-type Ga _{1 -Y} Al _Y N cladding layer 4 is formed.
Must have a composition of ternary mixed crystal gallium aluminum nitride containing no In. Because n-type Ga
_{This is because if the 1-Y} Al _Y N clad layer 4 is newly made to contain indium, the crystallinity of the clad layer 4 is deteriorated and the light emission output is reduced. Further, by setting the Y value of the n-type Ga _{1 -Y} Al _Y N cladding layer within the range of 0 <Y <1, it is possible to act as an n-type cladding layer and form 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. The n-type Ga _1-Y Al _Y N cladding layer 4, as described above, were grown to indicate the non-doped Ga _1-Y Al _Y N or n-type dopant by doping n-type characteristics, Ga _{1- Y} Al _Y N can be used.

Next, the n-type In _Z Ga _{1 -Z} N active layer 5 must have a composition of ternary mixed crystal indium gallium nitride containing no Al. This is because the active layer is a light emitting layer, and when Al is contained in this light emitting layer, deep level light emission appears, which tends to hinder the interband light emission of InGaN, and therefore it is not preferable to use it as an 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 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. Further, as emission centers, 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, the Mg-doped p-type Ga _1-x Al _x N cladding layer 6 has the same composition as the n-type Ga _1-y Al _y N cladding layer 4 and is nitrided by a ternary mixed crystal containing no In. 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. In addition, _{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. When it is larger than 0, the double hetero structure can be obtained by acting as a p-type clad layer, and when it is smaller than 0.5, the p-type clad layer 6 having few lattice defects and good crystallinity can be obtained. Conversely, if it is 0.5 or more, p
The crystallinity of the p-type GaN contact layer 7 laminated on the type cladding layer 6 is deteriorated, and ohmic contact between the contact layer 7 and the electrode 8 cannot be obtained. Furthermore, this Mg-doped p-type Ga _1-X Al _X N
The film thickness of the clad layer 6 is 10 angstroms or more,
The range is preferably 0.2 μm or less. If the thickness is less than 10 angstroms, the n-type In _Z to be stacked underneath
It becomes easy to electrically short-circuit with the Ga _{1 -Z} N active layer 5, and it is difficult to act as a cladding layer. On the other hand, if the thickness is more than 0.2 μm, the crystal tends to be cracked and the crystallinity tends to deteriorate. Further, in this p-type Ga _1-x Al _x N clad layer, what is important is to use Mg as the p-type dopant,
This is to obtain the p-type characteristic by this Mg. This M
Other p-type dopants instead of g, such as Zn, Cd,
Doping with a p-type dopant such as Be or Ca makes it difficult to obtain p-type characteristics and tends to reduce the light emission output.

Next, the Mg-doped p-type GaN contact layer 7 needs to have 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 reduces the luminous efficiency. In particular, the film thickness of the p-type GaN contact layer is 10
It is preferable to adjust the thickness to at least angstrom and at most 0.5 μm. If the thickness is less than 10 angstrom, it is easy to electrically short-circuit with the p-type GaAlN cladding layer 6,
Hard to act as a contact layer. In addition, the ternary mixed crystal G
Since a binary mixed crystal GaN contact layer having a different composition is stacked on the aAlN cladding layer 6, if the thickness is made thicker than 0.5 μm, lattice defects due to misfit between crystals may cause GaN contact layer. 7 is likely to occur and crystallinity tends to decrease. The thinner the contact layer 7 is, the lower Vf can be made to improve the luminous efficiency. In addition, this p-type GaN contact layer 7
The p-type dopant of 1 must be Mg. Doping with another p-type dopant in place of Mg tends to make it difficult to obtain p-type characteristics, and also makes it difficult to obtain ohmic contact.

The p-type Ga _1-x Al _x N cladding layer 6,
As a means for further reducing the resistance of the p-type GaN layer, the annealing treatment at 400 ° C. or higher disclosed in the above-mentioned 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 have resistance, and the light emission output can be further improved.

[0015]

[Function] A double heterostructure nitride nitride film using a pn junction.
Mg-doped p
Type Ga_1-XAl_XMg-doped p-type on the N-clad layer 6
A GaN contact layer 7 is formed and its GaN contact is formed.
By forming the electrode 8 on the layer, ohmic contact is obtained.
Thus, 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/cm³And
The p-type GaN layer is about 10¹⁷/cm³And an order of magnitude higher
It was That is, the electrode with the higher hole carrier concentration
It may be easier to obtain ohmic contact by forming
I guess. In addition, the p-type GaAlN cladding layer 6
Forming p-type GaN contact layers 7 having different compositions on top
As a result, a lattice defect due to a misfit in the p-type GaN layer
Cavities are likely to occur and the crystallinity decreases. Misfit
In order to reduce the amount of Al, the Al of the p-type GaAlN cladding layer 6 is reduced.
The lower the mixed crystal ratio, the better. Therefore, p-type GaN contact
Layer 7 has good crystallinity and ohmic contact with electrode 8.
Is the limit value, that is, X value less than 0.5 is the limit value
It was

[0016]

EXAMPLES A method for producing the gallium nitride-based compound semiconductor light emitting device of the present invention by the metal organic chemical vapor deposition method will be described below.

Example 1 The sapphire substrate 1 was placed in a reaction vessel, 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 (source gas were used as source gases. Trimethylgallium) is used to grow the GaN buffer layer 2 on the sapphire substrate to a film thickness of about 200 Å.

After growing the buffer layer 2, stop only TMG,
The temperature is raised to 1030 ° C. When the temperature reached 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 source gas and the dopant gas are stopped, the temperature is set to 800 ° C., TMG and TMA (trimethylaluminum) and ammonia are used as the source gas, and the silane gas is used as the dopant gas. 4, a Si-doped Ga0.86Al0.14N layer is grown to a thickness of 0.15 μm.

Next, the source gas and the dopant gas are stopped,
The temperature is set to 800 ° C., the carrier gas is switched to nitrogen, TMG, TMI (trimethylindium) and ammonia are used as source gases, and silane gas is used as a dopant gas, and Si-doped In0.01Ga0.
A 99N layer is grown to 100 Å.

Then, the raw material gas and the dopant gas are stopped,
The temperature is again raised to 1020 ° C. and T is used as a source gas.
Using MG, TMA, ammonia, and Cp2Mg (cyclopentadienylmagnesium) as a dopant gas, a Mg-doped p-type Ga0.86Al0.14N layer of 0.15 μm is grown as the p-type cladding layer 6.

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

After the growth, the substrate is taken out of the reaction vessel and annealed at 700 ° C. for 20 minutes in a nitrogen atmosphere to anneal the p-type Ga0.86Al0.14N layer and the p-type GaN contact layer to further reduce the resistance. .

The wafer thus obtained is shown in FIG.
The n-type GaN layer 3 is exposed by etching as shown in FIG. 3, the p-type GaN contact layer 7 is provided with an electrode 8 made of Au, and the n-type GaN layer 3 is provided with an electrode 9 made of Al.
Annealing is performed again at 00 ° C. to make the electrode and the gallium nitride-based compound semiconductor conform to each other. After that, 500 according to the usual method
After being cut into chips having a square of μm, it was used as a light emitting diode. As a result, when the forward current was 20 mA, Vf was 5 V, the emission output was 700 μW at an emission wavelength of 370 nm, and the emission efficiency was 0.7%, which were 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 emission output were the same, but Vf dropped to 4 V, and the emission efficiency improved to 0.88%.

Example 2 In Example 1, p-type Mg
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 0.1 μm. At a forward current of 20 mA, the emission wavelength and emission output were the same, but Vf Was reduced to 4 V, and the luminous efficiency was 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 similarly obtained except that 0.55Al0.45N was used. Vf was 6 at a forward current of 20 mA.
It shows almost the limit value at which 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, and a forward current of 20 mA 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 0.5Al0.5N was used, and Vf was 30 at a forward current of 20 mA.
It was confirmed that the voltage rose to V and ohmic contact was not obtained. Since this device had a large Vf, it 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 an electrode was directly formed on the p-type cladding layer 6, and a forward current flow was obtained. 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 the p-type cladding layer 6 was grown, TMI was newly added to the source gas, the carrier gas was switched to nitrogen, and the growth temperature was set to 800.
A light emitting diode was obtained in the same manner except that the Mg-doped p-type In0.01Al0.14Ga0.85N cladding layer was grown at a temperature of 0 ° C., and no light was emitted immediately when a forward current of 20 mA was applied.

[0032]

As described above, the gallium nitride-based compound semiconductor light-emitting device of the present invention has the p-type GaN layer as a contact layer on the p-type GaAlN cladding layer, and thus emits light with low Vf. It is possible to obtain an element having excellent efficiency. Moreover, by limiting the Al mixed crystal ratio of the p-type GaAlN layer, the p-type cladding layer having excellent crystallinity,
The p-type contact layer can be obtained, which greatly contributes to the reduction of Vf.

Further, an n-type gallium nitride-based compound semiconductor layer, an n-type GaAlN cladding layer, and an n-type InGaN layer are stacked to form the p-type GaAlN cladding layer and the p-type GaN.
By stacking the contact layers, it is possible to realize a light-emitting element having excellent light-emission output and light-emission efficiency. Therefore, it has a great industrial utility value as a hint for the structure of a laser element that has not been realized yet.

[0034]

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a light emitting device according to an embodiment of the 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

Claims (4)

[Claims] 1. A double-heterostructure gallium nitride-based compound semiconductor light-emitting device having a pn junction, wherein 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 p-type GaN contact layer doped with Mg as a layer on which an electrode is to be formed, on the clad layer. 2. The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein the p-type Ga _1-x Al _x N clad layer has a film thickness of 10 angstroms or more and 0.2 μm or less. 3. The film thickness of the p-type GaN contact layer is 1
The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein the thickness is 0 angstrom or more and 0.5 μm or less. 4. An n-type Ga _{1 -Y} Al _Y N cladding layer (where Y is 0 <Y <
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
The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein the p-type Ga _1-x Al _x N clad layer is stacked on the active layer.