JPH1027923A - Group-iii nitride semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting element which can emit light in a wide wavelength range with a high luminous efficiency. SOLUTION: A luminous layer 5 is made of GaN doped with Fe and Si, and also sandwiched at both its sides by a cladding later 4 of n-Al0.08 Ga0.92 N and a cladding layer 71 got p-Al0.08 Ga0.92 N. As a result of doping the luminous layer withtransition metals, the luminous layer using GaN having a high crystallization can emit having wavelength sufficiently longer than those of a GaN forbidden band width. Because the luminous layer 5 can produce light of long wavelengths, the luminous layer can employ group-III nitride semiconductor having high crystallization and a low In crystallization ratio, thus improving its luminous efficiency.

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 and capable of emitting light in a wide wavelength range. In particular, the present invention relates to a light-emitting element in which luminance of light emission in a short wavelength region such as blue is improved.

[0002]

2. Description of the Related Art Heretofore, there has been known a material using an AlGaInN-based compound semiconductor as a material for a light emitting device in a blue or short wavelength region. 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 or green, is used as the luminescent color.

An AlGaInN-based semiconductor can also be made p-type by doping with Mg and irradiating an electron beam or by heat treatment.
As a result, a light emitting diode (LED) having a double heterojunction structure using an AlGaN p-type cladding layer, a Zn and Si doped InGaN light emitting layer, and a GaN n layer has been proposed. This light-emitting diode has a buffer layer on a sapphire substrate and an n ^{+ -type} Ga doped with silicon at a high concentration.
An N layer, a cladding layer composed of an n-type GaN layer doped with silicon, a light emitting layer composed of InGaN, a cladding layer composed of a p-type AlGaN,
A first contact layer of p-type GaN and a second contact layer of p ^{+ -type} GaN are formed.

[0004]

However, in the light emitting diode having such a structure, the emission wavelength is increased by using InGaN for the light emitting layer and increasing the mixed crystal ratio of In to narrow the forbidden band width. It is shifted to the wavelength side. However, it is difficult to control the mixed crystal ratio of InGaN, and its crystallinity is not good. For this reason, there is a problem that the luminous efficiency is reduced as the mixed crystal ratio of In is increased.

Accordingly, an object of the present invention is to enable long-wavelength highly efficient light emission without increasing the mixed crystal ratio of In.

[0006]

According to a first aspect of the present invention, in a light emitting device having a light emitting layer made of a group III nitride semiconductor, a transition metal is added to the light emitting layer. Since the impurity level is formed at a deep energy level in the forbidden band by the addition of the transition metal, the wavelength of light emission due to the transition of electrons through the impurity level becomes longer. According to the second aspect of the present invention, since the light emitting layer is doped with the donor impurity and / or the acceptor impurity, the level difference between the impurity level due to the transition metal and the donor impurity level or the acceptor impurity level is compared with the forbidden bandwidth. Can be further narrowed. For this reason, even if the forbidden bandwidth of the semiconductor in the light emitting layer is wide, light emission with a wavelength sufficiently longer than the wavelength corresponding to the forbidden bandwidth can be obtained.

According to a third aspect of the present invention, the group III nitride semiconductor is
(Al _x Ga _1-x ) _y In _1-y N (0 ≤ x ≤ 1; 0 ≤ y ≤ 1), depending on the mixed crystal ratio and transition metal, a wide range from blue to red Emission having the following wavelength can be obtained.

According to the fourth aspect of the present invention, since the light emitting layer is made of GaN, a decrease in crystallinity due to a large mixed crystal ratio of In is improved, and a GaN forbidden substance is added because a transition metal is added. Light having a wavelength sufficiently longer than the wavelength corresponding to the bandwidth can be obtained with high luminous efficiency.

In the invention of claim 5, the transition metal added to the light emitting layer is nickel (Ni), copper (Cu), iron (Fe), chromium (C
By using r), manganese (Mn), gold (Au), and cobalt (Co), light having a wavelength sufficiently longer than the wavelength corresponding to the band gap of the light emitting layer can be obtained. According to the invention of claim 6, the donor impurity is silicon (Si) or sulfur (S),
By using magnesium (Mg), zinc (Zn), and cadmium (Cd) as the acceptor impurities, light emission of a longer wavelength can be realized.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on specific embodiments. The present invention is not limited to the following examples. FIG. 1 shows an overall view of a light emitting device 100 according to an embodiment of the present invention. The light emitting device 100 has a sapphire substrate 1, and a 0.05 μm AlN buffer layer 2 is formed on the sapphire substrate 1.

On the buffer layer 2, a film thickness of about
4.0 μm, silicon (Si) doped with 2 × 10 ¹⁸ / cm ³ electron concentration
High carrier concentration n ⁺ layer 3 made of GaN, thickness about 0.5 μm
Electron concentration of 5 × 10 ¹⁷ / cm ³ silicon (Si) doped n-Al
Cladding layer 4 of _0.08 Ga _0.92 N, thickness of about 200 nm, iron (F
e) and silicon (Si) are 5 × 10 ¹⁸ / cm ³ doped GaN light-emitting layer 5, thickness of about 10 nm, hole concentration 2 × 10 ¹⁷ / cm ³ , magnesium (Mg) concentration 5 × 10 ¹⁹ / c
A cladding layer 71 made of p-Al _0.08 Ga _0.92 N doped with m ³ , magnesium (Mg) having a thickness of about 100 nm and a hole concentration of 3 × 10 ¹⁷ / cm ³ doped with a concentration of 5 × 10 ¹⁹ / cm ³ GaN
A first contact layer 72 of about 50 nm, a hole concentration of 6 × 10 ¹⁷ / cm ³ , and a concentration of magnesium (Mg) of 1 × 10 ²⁰
A p ^{+ -type} second contact layer 73 made of GaN doped at / cm ³ is formed. A transparent electrode 9 composed of a double layer of Ni / Au is formed on the entire upper surface of the second contact layer 73, and a pad 10 for bonding composed of a double layer of Ni / Au is formed at a corner of the transparent electrode 9. Have been. Further, an electrode 8 made of Al is formed on the n ⁺ layer 3.

Next, a method of manufacturing a semiconductor device having this structure will be described. The light emitting device 100 was manufactured by vapor phase growth using metal organic chemical vapor deposition (hereinafter, MOVPE). The gases used were ammonia (NH ₃ ), carrier gas (H ₂ ), and trimethylgallium (Ga (CH ₃ ) ₃ ) (hereinafter “TMG
), Trimethyl aluminum (Al (CH ₃ ) ₃ ) (hereinafter referred to as “TMA”), silane (SiH ₄ ), cyclopentadienyl magnesium (Mg (C ₅ H ₅ ) ₂ ) (hereinafter “CP ₂ Mg ”)
Cyclopentadienyl iron _{(Fe (C 5 H 5)} 2) ( hereinafter "CP ₂ Fe"
).

First, a single-crystal sapphire substrate 1 is mounted on a susceptor placed in a reaction chamber of an MOVPE apparatus, with the a-plane cleaned by organic cleaning and heat treatment as a main surface. Next, the sapphire substrate 1 was baked at a temperature of 1100 ° C. while flowing H ₂ into the reaction chamber at a flow rate of 2 liter / min at normal pressure for about 30 minutes.

[0014] Next, by lowering the temperature to 400 ° C., and H ₂
20 liter / min, NH ₃ 10 liter / min, TMA 1.8 × 10 ^-5
The AlN buffer layer 2 was supplied at about 0.1 mol / min for about 90 seconds.
It was formed to a thickness of 05 μm. Next, the temperature of the sapphire substrate 1 was maintained at 1150 ° C., H ₂ was 20 liter / min, and NH ₃ was 10 lite.
r / min, TMG 1.7 × 10 ^-4 mol / min, 0.86p by H ₂ gas
Silane diluted at 20 × 10 ⁻⁸ mol / min was introduced for 40 minutes at a film thickness of about 4.0 μm, an electron concentration of 1 × 10 ¹⁸ / cm ³ , and a silicon concentration of 4 × 10 ¹⁸ / cm ³ (Si). 3.) A high carrier concentration n ⁺ layer 3 made of doped GaN was formed.

After forming the high carrier concentration n ⁺ layer 3, the temperature is maintained at 1100 ° C. and N ₂ or H ₂ is reduced to 20 lit.
er / min, NH ₃ at 10 liter / min, TMG at 0.5 × 10 ^-4 mol /
Min, 0.47 × 10 ^-5 mol / min TMA, and by H ₂ gas 0.
Silane diluted to 86 ppm was introduced at 10 × 10 ⁻⁹ mol / min for 30 minutes, and Al _0.08 Ga having a film thickness of about 0.5 μm, an electron concentration of 5 × 10 ¹⁷ / cm ³ , and a silicon concentration of 1 × 10 ¹⁸ / cm ^3. _A cladding layer 4 of _0.92 N was formed.

Subsequently, the temperature was maintained at 1100 ° C., and H ₂ was reduced to 20 l.
iter / min, NH ₃ at 10 liter / min, TMG at 1.7 × 10 ⁻⁴ mol / min, and silane diluted to 0.86 ppm with H ₂ gas at 25 ×
10 ^-8 mol / min, CP ₂ Fe was supplied at 2 × 10 ^-7 mol / min for 2 minutes, and silicon and iron having a thickness of 200 nm were converted to 5 × 10
^The light emitting layer 5 made of GaN doped at ¹⁸ / cm ³ was formed.

Subsequently, the temperature is maintained at 1100 ° C. and N ₂ or H ₂
20 liter / min, NH ₃ 10 liter / min, TMG 0.5 × 10
^-4 mol / min, TMA 0.47 × 10 ^-5 mol / min, and CP ₂ Mg
^Was introduced at 2 × 10 ⁻⁷ mol / min for 2 minutes to form a cladding layer 71 made of magnesium (Mg) -doped Al _0.08 Ga _0.92 N and having a thickness of about 10 nm. The magnesium concentration of the cladding layer 71 is 5 × 10 ¹⁹ / cm ³ . In this state, the cladding layer 7
1 is an insulator having a resistivity of 10 ⁸ Ωcm or more.

Next, the temperature is maintained at 1100 ° C. and N ₂ or H ₂ is added.
20 liter / min, NH ₃ 10 liter / min, TMG 0.5 × 10 ^-4
Mol / min and CP ₂ Mg were introduced at 2 × 10 ⁻⁸ mol / min for 5 minutes, and magnesium (Mg) -doped GaN having a thickness of about 100 nm was used.
The first contact layer 72 made of was formed. The magnesium concentration of the first contact layer 72 is 5 × 10 ¹⁹ / cm ³ .
In this state, the first contact layer 72 still has the resistivity
It is an insulator of 10 ⁸ Ωcm or more.

Next, the temperature was maintained at 1100 ° C. and N ₂ or H ₂ was added.
20 liter / min, NH ₃ 10 liter / min, TMG 0.5 × 10 ^-4
Mol / min and CP ₂ Mg were introduced at 4 × 10 ⁻⁸ mol / min for 2 minutes to form a p ⁺ second contact layer 73 of magnesium (Mg) -doped GaN having a thickness of about 50 nm. The magnesium concentration of the second contact layer 73 is 1 × 10 ²⁰ / cm ³ . In this state, the second contact layer 73 is still an insulator having a resistivity of 10 ⁸ Ωcm or more.

Next, the second contact layer 73, the first contact layer 72, and the cladding layer 7 are formed by using an electron beam irradiation device.
1 was uniformly irradiated with an electron beam. Electron beam irradiation conditions are: acceleration voltage about 10KV, data current 1μA, beam moving speed 0.2m
m / sec, beam diameter 60 μmφ, vacuum degree 5.0 × 10 ⁻⁵ Torr. By the irradiation of the electron beam, the second contact layer 73,
The first contact layer 72 and the cladding layer 71 have a hole concentration of 6 × 10 ¹⁷ / cm ³ , 3 × 10 ¹⁷ / cm ³ , 2 × 10 ¹⁷ / c, respectively.
It became a p-conduction type semiconductor having m ³ and resistivity of 2Ωcm, 1Ωcm, 0.7Ωcm. Thus, a wafer having a multilayer structure was obtained.

Next, as shown in FIG. 2, an SiO ₂ layer 11 is formed on the second contact
Then, a photoresist 12 was applied on the SiO ₂ layer 11. Then, by photolithography, as shown in FIG. 2, on the second contact layer 73, the photoresist 12 at the electrode formation site A ^′ for the high carrier concentration n ⁺ layer 3 was removed. Next, as shown in FIG.
SiO ₂ layer 11 not covered by photoresist 12
Was removed with a hydrofluoric acid-based etching solution.

Next, the photoresist 12 and the SiO ₂ layer 11
The second contact layer 73 not covered by the second contact layer 73,
First contact layer 72, cladding layer 71, light emitting layer 5, n
The layers 4, vacuum 0.04 Torr, RF power 0.44W / cm ^2, BCl ₃
After gas was supplied at a rate of 10 ml / min to perform dry etching, dry etching was performed using Ar. In this step, as shown in FIG. 4, a hole A for extracting an electrode from the high carrier concentration n ⁺ layer 3 was formed. Then, photoresist 1
2 and the SiO ₂ layer 11 were removed.

Next, two layers of Ni / Au were uniformly deposited, and a transparent electrode 9 was formed on the second contact layer 73 through application of a photoresist, a photolithography step, and an etching step. Then, Ni / Au is applied to a part of the transparent electrode 9.
Were deposited to form the pad 10. On the other hand, the electrode 8 was formed on the n ⁺ layer 3 by evaporating aluminum. Thereafter, the wafer processed as described above was cut into individual devices to obtain light emitting diodes having the structure shown in FIG. This light-emitting element emits light at a peak emission wavelength of 45 at a driving current of 20 mA.
The emission intensity was 0 nm and the emission intensity was 2000 mCd. By using the luminescent layer 5 as GaN having high crystallinity, light emission having a wavelength sufficiently longer than the wavelength corresponding to the band gap of GaN could be obtained. In addition, as a result of using GaN having good crystallinity for the light emitting layer 5, the luminous efficiency was doubled as compared with the LED having the conventional structure.

The light emitting layer 5 is made of nickel (Ni) at 5 × 10 ¹⁹ / c
was prepared an LED was added to a concentration of m ^3, likewise, the emission peak wavelength of 450 nm by driving current 20 mA, the emission intensity 2000mC
d is obtained.

In the above embodiment, Fe or Ni was used as the transition metal, but in addition to Fe and Ni, copper (Cu), chromium (Cr),
Metals such as manganese (Mn), gold (Au), and cobalt (Co) can be used. As an organic metal gas for adding a transition metal, cyclopentadienyl M metal (M (C ₅ H ₅ ) ₂ ) (“CP ₂ M”) can be used for the transition metal M ₂ .

Although GaN is used for the light emitting layer 5 in the above embodiment, In _x Ga ₁ -xN may be used. In this case, since the transition metal M is added, emission of a long wavelength can be obtained even if the mixed crystal ratio X of In is small. Specifically, light emission in the range of 450 to 550 nm is possible. further,
Generally, (Al _x Ga _1-x ) _y In _1-y N (0 ≦ x ≦
1; 0 ≤ y ≤ 1) can be used. Thus, by changing the mixed crystal ratios x and y, it is possible to obtain an element capable of emitting light over a wide range from a short wavelength to a long wavelength.

The thickness of the light emitting layer 5 is desirably 1000 to 3000 °. If the angle is 1000 ° or less, or 3000 ° or more, the emission intensity is undesirably reduced. In the above embodiment, the light emitting layer 5 is constituted by a single layer. However, a single or multiple quantum well structure may be employed. In the case of a multiple quantum well structure, the transition metal is added to the well layer, to both the well layer and the barrier layer, and further to the case where a donor impurity or an acceptor impurity is added, a donor impurity or an acceptor is added. Adding impurities to the well layer, adding to the barrier layer, adding donor impurities to the well layer, acceptor impurities to the barrier layer, adding the impurities in a reverse manner, and so on.
Various methods of addition are conceivable.

In the above embodiment, Si is added to the light emitting layer 5 as a donor impurity, but only the transition metal may be added. The range of the addition concentration of the transition metal is 1 × 10 ¹⁷ to
1 × 10 ²⁰ / cm ³ is desirable. When the concentration is 1 × 10 ¹⁷ / cm ³ or less, the luminous efficiency is reduced due to the shortage of the luminescent center, and 1 × 10 ²⁰
If it exceeds / cm ³ , the crystallinity deteriorates and the Auger effect occurs, which is not desirable. More preferably 1
The range of × 10 ¹⁸ to 1 × 10 ¹⁹ / cm ³ is good. Also, instead of Si, group 4 elements such as carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and group 6 element sulfur (S) and selenium (Se) , Tellurium (Te) can be used. In addition, beryllium (Be), magnesium (Mg), zinc (Zn), cadmium (Cd), or mercury (Hg) of a Group 2 element may be used as the acceptor impurity. Its concentration range is 1 × 10 ¹⁷ to 1 × 10 ²⁰ / c
m ³ is preferred. More preferably, 1 × 10 ¹⁸ to 1 × 10 ¹⁹ / c
range of m ³ is good. Desirable reasons for the range are the same as those for the transition metal concentration range.

In the above embodiment, the contact layer has a two-layer structure, but may have a one-layer structure. The thickness of the cladding layer 71 is 2 nm to 70 nm, and the thickness of the first contact layer 72 is 2 nm.
To 100 nm, and the thickness of the second contact layer 73 is preferably 2 nm to 50 nm. When the thickness of the cladding layer 71 is smaller than 2 nm,
Since the effect of confining carriers is reduced, the luminous efficiency is reduced, which is not desirable. If the thickness of the first contact layer 72 is smaller than 2 nm, the number of holes to be injected is reduced, so that the luminous efficiency is reduced, which is not desirable. If the second contact layer 73 is thinner than 2 nm, the ohmic property becomes poor and the contact resistance increases, which is not desirable. On the other hand, when the thickness of each layer exceeds the above upper limit thickness, the time during which the light emitting layer is exposed to a temperature higher than its growth temperature becomes longer, and the effect of improving the crystallinity of the light emitting layer is not desirable.

The hole concentration of the cladding layer 71 is 1 × 10
¹⁷ to 1 × 10 ¹⁸ / cm ³ is desirable. Hall concentration 1 × 10 ¹⁸
/ Cm ³ or more and becomes undesirable since crystallinity becomes higher impurity concentration is lowered luminous efficiency decreases, 1 × 10 ¹⁷ /
If it is less than cm ³ , the series resistance becomes too high, which is not desirable.

The first contact layer 72 is made of magnesium (M
g) is added at a concentration lower than the magnesium (Mg) concentration of the second contact layer 73 in the range of 1 × 10 ^{19 to} 5 × 10 ²⁰ / cm ³ to form a layer exhibiting the p-conduction type, so that the hole of the layer is formed. The concentration can be an area including the maximum value of 3 × 10 ¹⁷ to 8 × 10 ¹⁷ / cm ³ . Thus, the luminous efficiency does not decrease.

The second contact layer 73 is made of magnesium (M
g) It is desirable that the concentration be 1 × 10 ²⁰ to 1 × 10 ²¹ / cm ³ . Magnesium (Mg) is 1 × 10 ²⁰ -1 × 10 ²¹ /
The p-type layer added to the cm ³ layer can improve the ohmic property of the metal electrode, but the hole concentration is slightly reduced to 1 × 10 ¹⁷ to 8 × 10 ¹⁷ / cm ³ . (The Mg concentration is preferably in the above range from the viewpoint of improving ohmic properties, including the range in which the driving voltage can be reduced to 5 V or less.)

In addition, as the acceptor impurity, beryllium (Be), magnesium (Mg), zinc (Zn), cadmium (Cd), or mercury (Hg) of a Group 2 element may be used. When a group II element is used as an acceptor impurity, carbon (C), silicon (Si), germanium (G)
e), tin (Sn), and lead (Pb) can be used. When the group 4 element is used as an acceptor impurity, the group 6 element sulfur (S), selenium (Se), tellurium (Te) is used as the donor impurity.
Can also be used. The p-type conversion 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 specific embodiment 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.

[Explanation of symbols]

100 semiconductor device 1 sapphire substrate 2 buffer layer 3 high carrier concentration n ⁺ layer 4 cladding layer 5 light emitting layer 71 cladding layer 72 first contact layer 73 second contact layer 8 electrode 9 transparent Electrode 10 ... Pad

 ──────────────────────────────────────────────────の Continuing on the front page (72) Norikatsu Koide, No. 1, Nagahata, Ochiai, Kasuga-machi, Nishikasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. (72) Masayoshi Koike, Nagahata, Ochiai, Kasuga-cho, Nishikasugai-gun, Aichi No. 1 Toyoda Gosei Co., Ltd. (72) Inventor Isamu Akasaki 1-38-805, Nishi-ku, Nagoya-shi, Aichi 1-38-805 (72) Inventor Hiroshi Amano 2-104 Yamanote, Meito-ku, Nagoya-shi, Aichi No. 508 Takara Mansion Yamanote

Claims (6)

[Claims] 1. A light emitting device having a light emitting layer made of a Group III nitride semiconductor, wherein a transition metal is added to the light emitting layer. 2. The light emitting device according to claim 1, wherein a donor impurity and / or an acceptor impurity are further added to the light emitting layer. 3. The group III nitride semiconductor is (Al _x Ga _1-x ) _y In _1-y
The light emitting device according to claim 1, wherein N (0 ≦ x ≦ 1; 0 ≦ y ≦ 1). 4. The light emitting device according to claim 1, wherein said light emitting layer is made of GaN. 5. The transition metal added to the light emitting layer includes nickel (Ni), copper (Cu), iron (Fe), chromium (Cr), manganese (Mn),
2. The method according to claim 1, wherein the material is gold (Au) or cobalt (Co).
The light-emitting device according to item 1. 6. The method according to claim 1, wherein the donor impurity is silicon (Si) or
3. The light emitting device according to claim 2, wherein the element is sulfur (S), and the acceptor impurities are magnesium (Mg), zinc (Zn), and cadmium (Cd).