JPH1051030A - Group iii nitride semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent ohmic contact with a metal electrode, without decreasing the injection efficiency of holes, by forming an electrode on a second layer to which acceptor impurities are added in a concentration range wherein a driving voltage becomes almost minimum. SOLUTION: A P-type layer 61 consists of at least a first layer 62 to which acceptor impurities are added in a concentration range wherein the hole concentration becomes almost maximum, and a second layer 63 to which acceptor impurities are added in a concentration range wherein a driving voltage becomes almost minimum. Electrodes 17, 18 are formed on the second layer 63. Thereby the driving voltage can be decreased, and the injection efficiency of holes to a light emitting layer can be improved. As a result, excellent ohmic contact with metal electrodes can be obtained without deteriorating the injection efficiency of holes.

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 group III nitride semiconductor.

[0002]

2. Description of the Related Art Conventionally, AlGaIn has been used as a blue light emitting diode.
A device using an N-based compound semiconductor is known. The compound semiconductor has attracted attention because of its direct transition type, which has high luminous efficiency, and that one of the three primary colors of light, blue, is used as the luminescent color.

Recently, it has been revealed that an AlGaInN-based semiconductor can be made p-type by doping with Mg and irradiating an electron beam or by heat treatment. As a result, instead of the conventional MIS type in which an n-layer and a semi-insulating layer (i-layer) are joined, AlGaN
There has been proposed a light emitting diode having a double hetero pn junction using a p-layer, a Zn-doped InGaN light-emitting layer, and an AlGaN n-layer.

[0004]

The above-mentioned double hetero p
In the n-junction type light emitting diode, GaN doped with magnesium on the order of 10 ¹⁹ / cm ³ is used as the contact layer for the p layer. The carrier concentration of this contact layer is as high as 7 × 10 ¹⁷ / cm ³ , and the hole injection efficiency is high. However, the present inventors have clarified, for the first time, that this contact layer forms a Schottky barrier with respect to the metal electrode, and this causes a reduction in drive voltage.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to newly devise a structure of a contact layer capable of obtaining good ohmic contact with a metal electrode without lowering the hole injection efficiency. It is to lower the drive voltage.

[0006]

According to the first aspect of the present invention, there is provided a group III nitride semiconductor (Al _x Ga _Y In _{1 -XY} N (0 ≦ X ≦ 1, 0
≦ Y ≦ 1, 0 ≦ X + Y ≦ 1)
A light-emitting element in which a layer, a light-emitting layer, and an n-layer exhibiting n-type conductivity are heterojunction, wherein the p-layer is at least a first layer doped with an acceptor impurity in a concentration range such that the hole concentration substantially takes a maximum value; It is characterized by comprising a second layer to which an acceptor impurity is added in a concentration range in which a driving voltage takes a substantially minimum value, and an electrode is formed on the second layer.

According to a second aspect of the present invention, a group III nitride semiconductor (Al _x Ga _Y In _1-XY N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ X + Y
≦ 1), a p-type layer having a p-type conductivity, a light-emitting layer, and an n-type layer having an n-type conductivity are heterojunction, and a p-type contact layer is provided between the electrode and the p-type layer. An acceptor impurity is added to the mold contact layer at a higher concentration than an acceptor impurity concentration at which the hole concentration takes a maximum value.

According to a third aspect of the present invention, a group III nitride semiconductor (Al _x Ga _Y In _1-XY N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ X + Y
≦ 1), a p-type layer having a p-type conductivity, a light-emitting layer, and an n-type layer having an n-type conductivity are heterojunction, and a p-type contact layer is provided between the electrode and the p-type layer. An acceptor impurity is added to the mold contact layer in such a concentration range that the driving voltage of the element takes a substantially minimum value.

Further, the invention according to claim 4 is characterized in that the acceptor impurity is magnesium (Mg) and the acceptor impurity concentration at which the hole concentration takes the maximum value is 5 × 10 ¹⁹ / cm ^3. The invention of claim 5 is characterized in that the acceptor impurity is magnesium (Mg), and the acceptor impurity concentration at which the drive voltage takes a substantially minimum value is 2 × 10 ²⁰ / cm ^3. The mold contact layer is made of gallium nitride (GaN).

[0010]

The present invention is based on the discovery of the present inventors that the magnesium concentration and the hole concentration are not in a proportional relationship and that the contact resistance does not become the minimum when the hole concentration takes the maximum value. is there. That is, there is an acceptor impurity concentration at which the hole concentration becomes maximum, and there is an acceptor impurity concentration at which the contact resistance takes the minimum value. Join the electrode to the layer where the contact resistance takes the minimum value,
By joining the layer having the maximum hole concentration to the light emitting layer or the p layer, the driving voltage can be reduced and the efficiency of hole injection into the light emitting layer can be improved.

[0011] As described above, the p layer is formed at least in the first layer to which the acceptor impurity is added in a concentration range in which the hole concentration substantially takes the maximum value, and in the concentration range in which the driving voltage takes a substantially minimum value. Second doped with acceptor impurities
The drive voltage could be reduced by forming the electrodes on the second layer.

Further, by adding an acceptor impurity to the p-type contact layer at a concentration higher than the acceptor impurity concentration at which the hole concentration takes the maximum value, the driving voltage can be reduced.

Further, by adding an acceptor impurity to the p-type contact layer in such a concentration range that the driving voltage of the element takes a substantially minimum value, the driving voltage can be reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment In FIG. 1, a light emitting diode 10 has a sapphire substrate 1 on which 500.degree.
An N 2 buffer layer 2 is formed. The buffer layer 2
On the top, in order, a film thickness of about 2.0 μm and an electron concentration of 2 × 10 ¹⁸ / c
a high carrier concentration n ⁺ layer 3 composed of m ³ silicon-doped GaN, a film thickness of about 2.0 μm, and an electron concentration of 2 × 10 ¹⁸ / cm ³ silicon-doped (Al _x2 Ga _1-x2 ) _y2 In _1-y2 N High carrier concentration n ⁺ layer 4, film thickness of about 0.5 μm, magnesium (Mg), cadmium (Cd) and silicon doped (Al _x1 Ga _1-x1 ) _y1 In _1-y1
N-type p-type light-emitting layer 5 having a thickness of about 1.0 μm, a hole concentration of 5 × 10 ¹⁷ / cm ³ , and a magnesium concentration of 1 × 10 ²⁰ / cm ³ magnesium-doped (Al _x2 Ga _1-x2 ) _y2 In _A p-layer 61 of _1-y2 N, a film thickness of about 0.2 μm, a hole concentration of 5 × 10 ¹⁷ / cm ³ ,
Magnesium doped with magnesium concentration of 1 × 10 ²⁰ / cm ³
The second contact layer 62 made of GaN, the film thickness is about 500 Å, the hole concentration is 2 × 10 ¹⁷ / cm ³ , and the magnesium concentration is 2 × 10 ²⁰ / cm ³
A first contact layer 63 made of magnesium-doped GaN is formed. Then, the first contact layer 63
And an electrode 8 formed of nickel connected to the high carrier concentration n ⁺ layer 4. The electrode 7 and the electrode 8 are electrically insulated and separated by the groove 9.

Next, a method of manufacturing the light emitting diode 10 having this structure will be described. The light emitting diode 10 includes:
It was manufactured by vapor phase growth by metal organic compound vapor phase epitaxy (hereinafter referred to as "M0VPE"). The gas used was NH
₃ and carrier gas H ₂ or N ₂ and trimethylgallium (Ga
(CH ₃ ) ₃ ) (hereinafter referred to as “TMG”), trimethylaluminum (Al (CH ₃ ) ₃ ) (hereinafter referred to as “TMA”), and trimethylindium (In (CH ₃ ) ₃ ) (hereinafter referred to as “TMI”). ), Dimethylcadmium (Cd (CH ₃ ) ₂ ) (hereinafter referred to as “DMCd”), silane (SiH ₄ ), and cyclopentadienyl magnesium (Mg
(C ₅ H ₅ ) ₂ ) (hereinafter referred to as “CP ₂ Mg”).

First, a single-crystal sapphire substrate 1 whose main surface is the a-plane cleaned by organic cleaning and heat treatment is mounted on a susceptor mounted in a reaction chamber of an MOVPE apparatus. Next, while flowing H ₂ at normal pressure into the reaction chamber at a flow rate of 2 liter / min, the temperature was 1100
The sapphire substrate 1 was subjected to gas-phase etching at a temperature of ℃.

Next, by lowering the temperature to 400 ° C., and H ₂
20 liter / min, NH ₃ 10 liter / min, TMA 1.8 × 10 ^-5
Supplying at mol / min, an AlN buffer layer 2 was formed to a thickness of about 500 °. Next, the temperature of the sapphire substrate 1 was set to 1150
℃ to retain a thickness of about 2.2 [mu] m, the electron concentration of 2 × 10 ¹⁸ / cm high carrier concentration of GaN silicon doped ³ n ⁺ layer 3
Was formed.

Hereinafter, the composition ratio of the light emitting layer 5 (active layer) and the cladding layers 4 and 6 and the implementation of crystal growth conditions when the light emission peak wavelength is set to 430 nm using cadmium (Cd) and silicon (Si) as light emission centers. Here is an example. After the formation of the high carrier concentration n ⁺ layer 3, the sapphire substrate 1
Is maintained at 850 ° C., N ₂ or H ₂ is 10 liter / min, NH
₃ for 10 liter / min, TMG for 1.12 × 10 ^-4 mol / min, TMA for
0.47 × 10 ^-4 mol / min, TMI 0.1 × 10 ^-4 mol / min and silane introduced, film thickness about 0.5 μm, concentration 1 × 10 ¹⁸ / c
A high carrier concentration n ⁺ layer 4 made of (Al _0.47 Ga _0.53 ) _0.9 In _0.1 N doped with m ³ silicon was formed.

Subsequently, the temperature was maintained at 850 ° C. and N ₂ or H ₂
20 liter / min, NH ₃ 10 liter / min, TMG 1.53 × 10
^-4 mol / min, TMA 0.47 × 10 ^-4 mol / min, TMI 0.02 ×
10 ^-4 mol / min, and 2 × 10 ^-4 mol / min of CP ₂ Mg and DMCd
^Was introduced at 2 × 10 ⁻⁷ mol / min and silane at 10 × 10 ⁻⁹ mol / min, and magnesium (Mg) and cadmium (C) having a thickness of about 0.5 μm were introduced.
A light emitting layer 5 composed of d) and silicon (Si) doped (Al _0.3 Ga _0.7 ) _0.94 In _0.06 N was formed. In this state, the light emitting layer 5 still has high resistance. Magnesium in the light emitting layer 5
(Mg) concentration is 1 × 10 ¹⁹ / cm ³ , cadmium (Cd) concentration is 5
× 10 ¹⁸ / cm ³ and the concentration of silicon (Si) is 1 × 10 ¹⁸ / cm ³
It is.

Subsequently, the temperature is maintained at 1100 ° C. and N ₂ or H ₂
20 liter / min, NH ₃ 10 liter / min, TMG 1.12 × 10
^-4 mol / min, TMA 0.47 × 10 ^-4 mol / min, TMI 0.1 ×
10 ^-4 mol / min, and 2 × 10 ^-4 mol / min of CP ₂ Mg were introduced, and a magnesium (Mg) -doped (Al
_A p-layer 61 of _0.47 Ga _0.53 ) _0.9 In _0.1 N was formed.
The magnesium concentration of the p layer 61 is 1 × 10 ²⁰ / cm ³ .
In this state, the p layer 61 is still an insulator having a resistivity of 10 ⁸ Ωcm or more. Next, the temperature was maintained at 850 ° C. and N ₂ or
The H ₂ 20 liter / min, the NH ₃ 10liter / min, 1.12 × the TMG
10 ^-4 mol / min and CP ₂ Mg were introduced at a rate of 2 × 10 ^-4 mol / min, and a magnesium (Mg) -doped film having a thickness of about 0.2 μm was introduced.
A second contact layer 62 made of GaN was formed. The concentration of magnesium in the second contact layer 62 is 1 × 10 ²⁰ / cm ³ . In this state, the second contact layer 62 still has
It is an insulator with a resistivity of 10 ⁸ Ωcm or more. Then, set the temperature to 85
Keep at 0 ° C, N ₂ or H ₂ at 20 liter / min, NH ₃ at 10 lit
er / min, TMG at 1.12 × 10 ^-4 mol / min, and CP ₂ Mg at 4
The first contact layer 63 made of GaN doped with magnesium (Mg) and having a thickness of about 500 し is introduced at a rate of × 10 ^-4 mol / min.
Was formed. The concentration of magnesium in the first contact layer 63 is 2 × 10 ²⁰ / cm ³ . In this state, the first contact layer 63 is still an insulator having a resistivity of 10 ⁸ Ωcm or more.

Next, using a reflection electron beam diffractometer, the first
The contact layer 63, the second contact layer 62, the p layer 61, and the light emitting layer 5 were uniformly irradiated with an electron beam. The electron beam irradiation conditions were as follows: acceleration voltage: about 10 KV, sample current: 1 μA, beam moving speed: 0.2 mm / sec, beam diameter: 60 μm, vacuum degree: 5.0 × 10 ^-5
Torr. By the irradiation of the electron beam, the first contact layer 63, the second contact layer 62, the p layer 61, and the light emitting layer 5
Are the hole concentrations of 2 × 10 ¹⁷ / cm ³ and 5 × 10 ¹⁷ / c, respectively.
m ³ , 5 × 10 ¹⁷ / cm ³ , resistivity 2 Ωcm, 0.8 Ωcm, 0.8 Ωcm
Of p-type semiconductor. Thus, a wafer having a multilayer structure as shown in FIG. 2 was obtained.

FIGS. 3 to 7 described below are cross-sectional views showing only one device on the wafer. In actuality, processing is performed on a wafer in which this device is continuously repeated. It is cut for each element.

As shown in FIG. 3, the first contact layer 63
A SiO ₂ layer 11 was formed to a thickness of 2000 ° by sputtering. Next, a photoresist 12 was applied on the SiO ₂ layer 11. And by photolithography,
On the first contact layer 63, a high carrier concentration n ⁺
The photoresist at the electrode formation site A corresponding to the hole 15 formed so as to reach the layer 4 and the photoresist at the site B where the groove 9 for insulating and separating the electrode formation region from the electrode of the p layer 61 is removed.

Next, as shown in FIG. 4, the SiO ₂ layer 11 not covered by the photoresist 12 was removed with a hydrofluoric acid-based etchant. Next, as shown in FIG.
The p layer 6, which is not covered by the photoresist 12 and the SiO ₂ layer 11, and the lower light emitting layer 5 and a part of the upper surface of the high carrier concentration n ⁺ layer 4 are partially vacuumed at a pressure of 0.04 Torr and a high frequency power of 0.
After dry-etching by supplying 44 W / cm ² and BCl ₃ gas at a rate of 10 ml / min, dry-etching was performed with Ar. In this step, a hole 15 for extracting an electrode from the high carrier concentration n ⁺ layer 4 and a groove 9 for insulating and separating were formed.

Next, as shown in FIG. 6, the SiO ₂ layer 11 remaining on the p layer 61 was removed with hydrofluoric acid. next,
As shown in FIG. 7, a Ni layer 13 was formed on the entire surface of the sample by vapor deposition. Thereby, the Ni layer 13 electrically connected to the high carrier concentration n ⁺ layer 4 is formed in the hole 15. Then, as shown in FIG. 7, a photoresist 14 is applied on the Ni layer 13, and the photoresist 14 is applied with a high carrier concentration n ⁺ layer 4 by photolithography.
Then, a pattern was formed in a predetermined shape so that an electrode portion for the p layer 61 remained.

Next, as shown in FIG. 7, the exposed portion of the lower Ni layer 13 was etched with a nitric acid-based etchant using the photoresist 14 as a mask. At this time, the Ni layer 13 deposited on the groove 9 for insulation separation is completely removed.
Next, the photoresist 14 was removed with acetone, and the electrode 8 of the high carrier concentration n ⁺ layer 4 and the electrode 7 of the first contact layer 63 were left. Thereafter, the wafer processed as described above was cut into individual devices to obtain a gallium nitride-based light emitting device having a ppn structure shown in FIG.

The light emitting device thus obtained had a driving current of 20 mA, a driving voltage of 4 V, a light emission peak wavelength of 430 nm and a light emission intensity of 1 cd.

Cadmium (C) in the light emitting layer 5
The concentrations of d) and silicon (Si) are respectively 1 × 10 ¹⁷ to 1
A range of × 10 ²⁰ is desirable from the viewpoint of improving the emission intensity.
Also, the concentration of silicon (Si) is lower than that of cadmium (Cd).
It is more desirable that the amount is as small as 1/2 to 1/10.

In the above embodiment, the p layer 6 having the band gap of the light emitting layer 5 on both sides and the high carrier concentration n ⁺ layer 4
Is formed in a double heterojunction that is smaller than the band gap. Also, Al, G of these three layers
The component ratios of a and In are selected so as to match the lattice constant of the high carrier concentration n ⁺ layer of GaN.

Second Embodiment The light emitting layer 5 of the first embodiment is doped with magnesium (Mg), cadmium (Cd) and silicon (Si). As shown in 8, magnesium (Mg)
And zinc (Zn) and silicon (Si). After forming the high carrier concentration n ⁺ layer 3, the temperature of the sapphire substrate 1 is maintained at 800 ° C. and N ₂ is reduced to 20 liter /
Min, NH ₃ at 10 liter / min, TMG at 1.12 × 10 ^-4 mol / min,
TMA 0.47 × 10 ^-4 mol / min, TMI 0.1 × 10 ^-4 mol / min
Min and silane are introduced, the film thickness is about 0.5 μm, and the concentration is 2 ×
10 ¹⁹ / cm ³ silicon doped (Al _0.3 Ga _0.7 ) _0.94 In _0.06 N
, A high carrier concentration n ⁺ layer 4 was formed.

[0031] Subsequently, the temperature was kept at 1150 ° C., the N ₂ 20 l
iter / min, the NH ₃ 10liter / min, 1.53 × 10 ^-4 mol / min TMG, 0.47 × 10 ^-4 mol / min TMA, 0.02 × 10 ^-4 mol / min TMI, 2 × the CP ₂ Mg 10 ^-4 mol / min, silane 10 × 10 ^-9
Mol / min, DEZ was introduced at 2 × 10 ^-4 mol / min for 7 minutes, and magnesium (Mg), silicon (Si) and zinc (Z
A light-emitting layer 5 of (n) doped (Al _0.09 Ga _0.91 ) _0.99 In _0.01 N was formed. The concentration of magnesium in the light emitting layer 5 was 1 × 10 ¹⁹ / cm ³ , and the concentration of zinc (Zn) was 2 × 10 ¹⁹ / cm ^3.
10 ¹⁸ / cm ³ , and the concentration of silicon (Si) is 1 × 10 ¹⁸ / cm ³ .

Subsequently, the temperature was maintained at 1100 ° C. and N ₂ was added in an amount of 20 l.
iter / min, the NH ₃ 10liter / min, 1.12 × 10 ^-4 mol / min TMG, 0.47 × 10 ^-4 mol / min TMA, 0.1 × 10 ^-4 mol / min TMI, and the CP ₂ Mg 2 × 10 ^-4 mol / min introduced, magnesium (Mg) doped (Al _0.3 Ga _0.7 ) with a film thickness of about 1.0 μm
_A p-layer 61 of _0.94 In _0.06 N was formed. The magnesium concentration of the p layer 61 is 1 × 10 ²⁰ / cm ³ . In this state, the p layer 61 is still an insulator having a resistivity of 10 ⁸ Ωcm or more.

Further, the temperature is maintained at 850 ° C. and N ₂ or H ₂
20 liter / min, NH ₃ 10 liter / min, TMG 1.12 × 10
^-4 mol / min and CP ₂ Mg are introduced at a rate of 2 × 10 ^-4 mol / min, and a magnesium (Mg) -doped Ga having a thickness of about 0.2 μm is introduced.
A second contact layer 62 made of N was formed. The concentration of magnesium in the second contact layer 62 is 1 × 10 ²⁰ / cm ³ . In this state, the second contact layer 62 is still an insulator having a resistivity of 10 ⁸ Ωcm or more. Then raise the temperature to 850
° C, N ₂ or H ₂ at 20 liter / min, NH ₃ at 10 liter
/ Min, TMG at 1.12 × 10 ^-4 mol / min, and CP ₂ Mg at 4 ×
The first contact layer 63 made of GaN doped with magnesium (Mg) and having a thickness of about 500 μm was formed at a rate of 10 ⁻⁴ mol / min. The concentration of magnesium in the first contact layer 63 is 2 × 10 ²⁰ / cm ³ . In this state, the first contact layer 63 is still an insulator having a resistivity of 10 ⁸ Ωcm or more.

Next, using a reflection electron beam diffractometer, the first
As in the example, the first contact layer 63, the second contact layer 62, the p layer 61, and the light emitting layer 5 were uniformly irradiated with an electron beam. As a result, the first contact layer 63, the second contact layer 62, the p-layer 61, and the light emitting layer 5 could be of p-conduction type. The light emitting diode 10 has a drive current of 20 mA, a drive voltage of 4 V, a peak emission wavelength of 430 nm, and a light emission intensity of 1000 mcd.

The light emitting diode of the third embodiment The third embodiment is different from the light emitting diode of the second embodiment, as shown in FIG. 9, zinc and magnesium (Mg) in the light emitting layer 5 of p conductivity type (Zn ) And silicon (Si) simultaneously doped Ga _y In _1-y N, p layer 61 is made of magnesium
(Mg) doped Al _x1 Ga _1-x1 N, high carrier concentration n ⁺
Layer 4 was formed by doped Al _x2 Ga _1-x2 N silicon (Si). The composition ratios x1, y, and x2 are set such that a double hetero junction in which the band gap of the light emitting layer 5 is smaller than the band gaps of the high carrier concentration n ⁺ layer 4 and the p layer 61 is formed. Note that the first contact layer 62 and the second
The contact layer 63 is the same as in the first embodiment and the second embodiment.

In FIG. 10, the light emitting diode 10 is
A sapphire substrate 1 is provided.
An AlN buffer layer 2 of 500 Å is formed thereon. On the buffer layer 2, a high carrier concentration n ⁺ layer 4 of silicon-doped GaN having a thickness of about 4.0 μm and an electron concentration of 2 × 10 ¹⁸ / cm ³ , a thickness of about 0.5 μm, magnesium, zinc, and A light emitting layer 5 made of silicon-doped Ga _0.94 In _0.06 N, a film thickness of about 0.5 μm, a p-layer 61 made of magnesium-doped Al _0.1 Ga _0.9 N having a hole concentration of 5 × 10 ¹⁷ / cm ³ , a film thickness of about
0.2 μm, hole concentration 5 × 10 ¹⁷ / cm ³ , magnesium concentration
1 × 10 ²⁰ / cm ³ magnesium-doped GaN
Contact layer 62, thickness about 500 mm, hole concentration 2 × 10 ¹⁷
A first contact layer 63 made of magnesium-doped GaN having a density of 2 × 10 ²⁰ / cm ³ and a magnesium concentration of 2 × 10 ²⁰ / cm ³ is formed. Then, an electrode 7 made of nickel connected to the first contact layer 63 and an electrode 8 made of nickel connected to the high carrier concentration n ⁺ layer 4 are formed. The electrode 7 and the electrode 8 are electrically insulated and separated by the groove 9.

Next, a method of manufacturing the light emitting diode 10 having this structure will be described. As in the first embodiment, the process is performed up to the AlN buffer layer 2. Next, the temperature of the sapphire substrate 1 was maintained at 1150 ° C., the film thickness was about 4.0 μm, and the electron concentration was 2 ×
A high carrier concentration n ⁺ layer 4 made of GaN doped with silicon at 10 ¹⁸ / cm ³ was formed.

Hereinafter, the light emitting layer 5, the cladding layer, that is, the p layer 61, and the second contact layer 6 when the light emission peak wavelength is set to 450 nm with zinc (Zn) and silicon (Si) as light emission centers.
2, Examples of the composition ratio of the first contact layer 63 and the crystal growth conditions will be described. After forming the high carrier concentration n ⁺ layer 4, the temperature of the sapphire substrate 1 is maintained at 850 ° C., N ₂ or H ₂ is 20 liter / min, NH ₃ is 10 liter / min, TM
G is 1.53 × 10 ⁻⁴ mol / min, TMI is 0.02 × 10 ⁻⁴ mol / min,
CP ₂ Mg 2 × 10 ^-4 mol / min, DMZ 2 × 10 ^-7 mol / min,
Silane was introduced at a ^rate of 10 × 10 ⁻⁹ mol / min, and a magnesium (Mg), zinc (Zn), and silicon (Si)
A light emitting layer 5 of _0.94 In _0.06 N was formed. In this state, the light emitting layer 5 still has high resistance.

Subsequently, the temperature was maintained at 850 ° C. and N ₂ or H ₂
20 liter / min, NH ₃ 10 liter / min, TMG 1.12 × 10
^-4 mol / min, 0.47 × 10 ^-4 mol / min of TMA and CP ₂ Mg
^Is introduced at a ^rate of 2 × 10 ⁻⁷ mol / min for 7 minutes to form a p-layer of magnesium (Mg) doped Al _0.1 Ga _0.9 N having a thickness of about 0.5 μm.
Layer 61 was formed. The p layer 61 still has a resistivity of 10
It is an insulator of ⁸ Ωcm or more. The concentration of magnesium (Mg) in p layer 61 is 1 × 10 ¹⁹ / cm ³ .

Subsequently, the temperature was maintained at 850 ° C. and N ₂ or H ₂
20 liter / min, NH ₃ 10 liter / min, TMG 1.12 × 10
^-4 mol / min, and 2 × 10 ^-4 mol / min of CP ₂ Mg,
A second contact layer 62 made of GaN doped with magnesium (Mg) and having a thickness of about 0.5 μm was formed. The concentration of magnesium in the second contact layer 62 is 1 × 10 ²⁰ / cm ³ . In this state, the second contact layer 62 still has a resistivity of 10 ⁸
It is an insulator of Ωcm or more. Subsequently, the temperature was maintained at 850 ° C., N ₂ or H ₂ was 20 liter / min, NH ₃ was 10 liter / min, TM
G is introduced at a rate of 1.12 × 10 ⁻⁴ mol / min and CP ₂ Mg is introduced at a rate of 4 × 10 ⁻⁴ mol / min.
A first contact layer 63 made of doped GaN was formed. The concentration of magnesium is 2 × 10 ²⁰ / cm ³ .

Next, the light emitting layer 5, the p layer 61, the second contact layer 62, and the first contact layer 63 were uniformly irradiated with an electron beam using a reflection electron beam diffractometer. The irradiation conditions of the electron beam are the same as in the first embodiment. Due to this electron beam irradiation, the p layer 61, the second contact layer 62, and the first contact layer 63 have a hole concentration of 5 × 10 ¹⁷ / cm ³ and 5 × 1, respectively.
It became a p-type semiconductor having 0 ¹⁷ / cm ³ , 2 × 10 ¹⁷ / cm ³ and resistivity of 0.8, 0.8, 2 Ωcm.

When the electrode area is 6 × 10 ⁻⁴ cm ² , the driving voltage of this light emitting device is 4 V at a current of 20 mA, and the contact resistance is 30 V.
４０40Ω. Also, when the electrode area is 1.6 × 10 ^-3 cm ² ,
The driving voltage of this light emitting element is 3.5 V at a current of 20 mA,
The contact resistance was 10 to 15Ω.

When forming the first contact layer 63 of GaN, the light emitting element was formed by changing the Mg concentration from 1 × 10 ¹⁹ / cm ³ to 2 × 10 ²¹ / cm ³ . FIG. 11 shows the current at this time.
It shows the drive voltage of the device at 20 mA. The drive voltage changed from 11.2 V to 4.0 V, and the contact resistance between the electrode 7 and the first contact layer 63 changed from 250 Ω to 30 Ω. When the concentration of Mg is 2 × 10 ²⁰ / cm ³ , the driving voltage is 4.
0 V, the lowest value of contact resistance 30Ω, Mg concentration is 2 × 10
^{At 21} / cm ³ , the drive voltage increased to 5.0 V and the contact resistance increased to 70Ω. From this, in order to reduce the driving voltage to 5 V or less, the Mg concentration of the first contact layer 63 is set to 1 × 10 ²⁰ to 1 × 10 ²¹ / cm ^3.
It was found that it was desirable to set the range.

FIG. 12 shows the second contact layer 62 or p.
This shows the relationship between the Mg concentration when forming the layer 61 and the hole concentration in the layer. Mg concentration of 5 × 10 ¹⁹ / c
When the hole concentration is increased to m ³ , the hole concentration increases to 7 × 10 ¹⁷ / cm ³ and saturates. Thereafter, when the Mg concentration is increased, the hole concentration is decreased, and the luminous efficiency of the device is undesirably decreased. Therefore, it is desirable that the Mg concentration of the second contact layer 62 or the p-layer 61 be lower than the Mg concentration of the first contact layer 63 within the range of 1 × 10 ¹⁹ to 5 × 10 ²⁰ / cm ³ . Since the hole concentration can be increased, the luminous efficiency of the element does not decrease.

In the above embodiment, the concentrations of zinc (Zn) and silicon (Si) in the light emitting layer 5 were 1 × 10
It has been found that a range of ¹⁷ to 1 × 10 ²⁰ is desirable from the viewpoint of improving the emission intensity. More preferably, 1 × 10 ¹⁸ to 1 ×
Range of 10 ¹⁹ is good. If it is less than 1 × 10 ¹⁸ , the effect is small, and if it is more than 1 × 10 ¹⁹ , the crystallinity becomes poor. The concentration of silicon (Si) is preferably 10 times to 1/10, more preferably about 1 to 1/10 or less, as compared with zinc (Zn).

In the above embodiment, the first contact layer 63 having a high concentration of magnesium (Mg) added and the second contact layer having a lower concentration of magnesium (Mg) than the first contact layer 63 were used. It has a two-layer structure with the two contact layers 62. However, magnesium (Mg) of p layer 5
A single contact layer having a magnesium (Mg) concentration higher than the concentration may be provided immediately below the electrodes 7 and 8. Although GaN is used as the contact layer, a mixed crystal having the same composition ratio as the p-layer 5 may be used.

The acceptor impurity is beryllium (B
e), magnesium (Mg), zinc (Zn), cadmium (Cd), and mercury (Hg) may be used. In addition, donor impurities include carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead.
(Pb) can be used.

Further, as a donor impurity, sulfur (S)
, Selenium (Se) and tellurium (Te) can also be used. p
Molding can be performed by electron beam irradiation, thermal annealing, heat treatment in N ₂ plasma gas, or laser irradiation.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a light emitting diode according to a first specific example of the present invention.

FIG. 2 is a sectional view showing a manufacturing process of the light-emitting diode of the embodiment.

FIG. 3 is a sectional view showing a manufacturing step of the light-emitting diode of the embodiment.

FIG. 4 is a sectional view showing a manufacturing step of the light-emitting diode of the same embodiment.

FIG. 5 is a sectional view showing the manufacturing process of the light emitting diode of the same embodiment.

FIG. 6 is a sectional view showing the manufacturing process of the light-emitting diode of the example.

FIG. 7 is a sectional view showing the manufacturing process of the light emitting diode of the same embodiment.

FIG. 8 is a configuration diagram showing a configuration of a light emitting diode according to a second embodiment.

FIG. 9 is a configuration diagram showing a configuration of a light emitting diode according to a third embodiment.

FIG. 10 is a configuration diagram showing a configuration of a light emitting diode according to a third embodiment.

FIG. 11 is a measurement diagram showing a relationship between a magnesium concentration in a first contact layer and a driving voltage of the element.

FIG. 12 is a measurement diagram showing a relationship between a magnesium concentration and a hole concentration in a second contact layer or a p-layer.

[Explanation of symbols]

Reference Signs List 10 light-emitting diode 1 sapphire substrate 2 buffer layer 3 high carrier concentration n ⁺ layer 4 high carrier concentration n ⁺ layer 5 light emitting layer 6 p layer 61 p layer 62 second contact layer 63 first Contact layer 7, 8 ... electrode 9 ... groove

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoki Shibata 1 Ochiai Nagahata, Kasuga-cho, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyota Gosei Co., Ltd. Inside Toyoda Gosei Co., Ltd. (72) Inventor Masayoshi Koike 1 Ochiai, Nagahata, Kasuga-cho, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. Co., Ltd. (72) Inventor Takahiro Ozawa 41-41, Yokomichi, Nagakute-cho, Aichi-gun, Aichi-gun 1 Toyota Central Research Laboratory Co., Ltd.

Claims (6)

[Claims] 1. A group III nitride semiconductor (Al _x Ga _Y In _1-XY N (0 ≦
X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ X + Y ≦ 1), wherein a p-layer having a p-conductivity type, a light-emitting layer, and an n-layer having an n-conductivity type are hetero-junctioned. At least a first layer to which an acceptor impurity is added in a concentration range in which a hole concentration substantially takes a maximum value, and a second layer to which an acceptor impurity is added in a concentration range in which a driving voltage takes a substantially minimum value. And a group III nitride semiconductor light emitting device, wherein an electrode is formed on the second layer. 2. A group III nitride semiconductor (Al _x Ga _Y In _1-XY N (0 ≦
X ≤ 1, 0 ≤ Y ≤ 1, 0 ≤ X + Y ≤ 1), a p-layer showing a p-conductivity type, a light-emitting layer, an n-layer showing an n-conductivity type are heterojunction, and an electrode and the p-layer A group III nitride, wherein an acceptor impurity is added to the p-type contact layer at a higher concentration than an acceptor impurity concentration at which a hole concentration takes a maximum value. Semiconductor light emitting device. 3. A group III nitride semiconductor (Al _x Ga _Y In _1-XY N (0 ≦
X ≤ 1, 0 ≤ Y ≤ 1, 0 ≤ X + Y ≤ 1), a p-layer showing a p-conductivity type, a light-emitting layer, an n-layer showing an n-conductivity type are heterojunction, and an electrode and the p-layer Wherein the acceptor impurity is added to the p-type contact layer in a concentration range such that the driving voltage of the element substantially takes a minimum value. Semiconductor light emitting device. 4. The method according to claim 1, wherein the acceptor impurity is magnesium (M
The group III nitride semiconductor light-emitting device according to claim 1 or 2, wherein g) and the acceptor impurity concentration at which the hole concentration has a maximum value is 5 × 10 ¹⁹ / cm ³ . 5. The method according to claim 1, wherein the acceptor impurity is magnesium (M
g), wherein the acceptor impurity concentration at which the drive voltage takes a substantially minimum value is 2 × 10 ²⁰ / cm ³ , wherein the group III nitride semiconductor light emission according to claim 1 or 3, wherein element. 6. The p-type contact layer is formed of gallium nitride.
The group III nitride semiconductor light emitting device according to claim 2 or 3, wherein the device is (GaN).