JPH11214746A - Nitride semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the output of a nitride semiconductor device such as an LED and an LD and to improve the reliability of the device by lowering Vf and a threshold value. SOLUTION: Between a substrate 1 and an active layer 6, a first nitride semiconductor layer 3 having an n-type impurity of 1 × 10 ¹⁷ / cm ³ or less and a 3 × 10 ¹⁸ n-type impurity in order from the substrate side. / Cm ³ or more of the second nitride semiconductor layer 4 and an n-type impurity of 1 × 10 ¹⁷
/ Cm ³ or less, and an n-electrode is formed on the second nitride semiconductor layer 4. Since the first layer 3 and the third layer 5 have a low n-type impurity concentration, they are base layers having good crystallinity, and the second layer 4 having a high n-type impurity concentration is formed on the first layer 3 having good crystallinity. It can grow with good crystallinity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (In _{XA).
l Y Ga 1-XY N,} 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) consists,
The present invention relates to a nitride semiconductor light emitting device used for a light emitting device such as a light emitting diode device and a laser diode device.

[0002]

2. Description of the Related Art A nitride semiconductor is a high-brightness pure green light emitting LE.
D and blue LEDs have already been put to practical use in various light sources such as full-color LED displays, traffic signal lights, and image scanner light sources. These LED elements basically have a buffer layer made of GaN on a sapphire substrate,
An n-side contact layer made of Si-doped GaN; an active layer made of InGaN having a single quantum well structure; a p-side clad layer made of Mg-doped AlGaN;
And a p-side contact layer made of N in order. At 20 mA, 5 mW for a blue LED with an emission wavelength of 450 nm, external quantum efficiency of 9.1%, 520 n
The green LED of 3 m has an excellent characteristic of 3 mW and an external quantum efficiency of 6.3%.

[0003] Further, the present applicant has announced the world's first laser oscillation of 410 nm at room temperature under pulse current using this material {for example, Jpn. J. Appl. Phys. 35 (1996) L74, Jp.
nJAppl.Phys.35 (1996) L217}. This laser element
Multiple quantum well structure (MQW: Multi-
It has a double hetero structure having an active layer of Quantum-Well, a threshold current of 610 mA, a threshold current density of 8.7 kA / cm ² , and a pulse width of 2 μs and a pulse period of 2 ms.
10 nm oscillation is shown. The present applicant has also succeeded for the first time in continuous oscillation at room temperature and has announced. {For example, Nikkei Electronics December 2, 1996 Technical Bulletin, Appl.Phys.L
ett.69 (1996) 3034-, Appl.Phys.Lett.69 (1996) 4056-
Etc.], the laser device exhibits continuous oscillation for 27 hours at 20 ° C., at a threshold current density of 3.6 kA / cm ² , a threshold voltage of 5.5 V, and an output of 1.5 mW.

[0004]

As described above, nitride semiconductors have already been put to practical use in LEDs and continuous oscillations have been achieved for several tens of hours in LDs. However, LEDs have been used, for example, as light sources for illumination and outdoor displays exposed to direct sunlight. In order to achieve the same, the output needs to be further improved. Further, in order to reduce the threshold value of the LD to extend its life and to put it to practical use as a light source such as an optical pickup, further improvement is required. The LED element has a Vf of 3 at 20 mA.
It is near 6V. By further lowering Vf, the amount of heat generated by the element is reduced, and the reliability is improved. In a laser device, lowering the voltage at the threshold is very important for improving the life of the device. The present invention has been made in view of such circumstances, and an object of the present invention is to mainly improve the output of nitride semiconductor devices such as LEDs and LDs, and reduce the Vf and threshold to reduce the device output. The purpose is to improve the reliability.

[0005]

That is, the present invention can achieve the present invention by the above-mentioned constitutions (1) to (3). (1) Between the substrate and the active layer, a first nitride semiconductor layer having an n-type impurity of 1 × 10 ¹⁷ / cm ³ or less and an n-type impurity of 3 × 10 ¹⁸ / cm ³ or more in order from the substrate side And a third nitride semiconductor layer having an n-type impurity of 1 × 10 ¹⁷ / cm ³ or less, and an n-electrode is formed on the second nitride semiconductor layer. A nitride semiconductor light-emitting device, comprising:

(2) The nitride semiconductor light emitting device according to the above (1), wherein the second nitride semiconductor layer is doped with an n-type impurity of 5 × 10 ¹⁸ / cm ³ or more. (3) The thickness of the third nitride semiconductor layer is 0.5 μm
The nitride semiconductor light emitting device according to the above (1) or (2), wherein:

That is, as described above, according to the present invention, the forward voltage (Vf) and the forward voltage (Vf) can be significantly reduced by defining the n-type impurity concentration of the specific first, second and third nitride semiconductor layers within a specific range. The threshold can be lowered. Further, in the present invention, the forward voltage can be more favorably reduced by setting the thickness of the third nitride semiconductor layer to 0.5 μm or less.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first nitride semiconductor layer has an n-type impurity concentration of 1 × 10 ¹⁷ / cm ³ or less, preferably 5 × 10 ¹⁷ / cm ^3.
It may be undoped at 10 ¹⁶ / cm ³ or less. When the n-type impurity concentration is reduced as described above, the second nitride semiconductor layer having a high n-type impurity concentration can be formed with good crystallinity even when formed on the first nitride semiconductor layer. If the impurity concentration is out of the above range, it becomes difficult to form a second nitride semiconductor layer having good crystallinity, and a leak current of the device tends to occur.

The first nitride semiconductor layer is grown at a higher temperature, for example, 900 ° C. to 1100 ° C. than a buffer layer to be described later, and is made of In _x Al _Y Ga ₁ -XYN (0 ≦ X, 0 ≦ Y, X + Y ≦
It can be composed of 1), and its composition is not particularly limited.
Preferably, GaN, Al _X Ga ₁ -XN having an X value of 0.2 or less.
Then, a nitride semiconductor layer with few crystal defects is easily obtained. The film thickness is not particularly limited, and it is preferable that the film is grown with a thickness larger than that of the buffer layer, and is usually grown with a thickness of 0.1 μm or more and 20 μm or less.

The n-type impurity concentration of the second nitride semiconductor layer is 3 × 10 ¹⁸ / cm ³ or more, preferably 5 × 10 ¹⁸ / cm ^3.
cm ³ or more, more preferably 8 × 10 ¹⁹ / cm ³ or more. By doping a large amount of n-type impurities and using this layer as a contact layer, Vf and the threshold value can be reduced. If the impurity concentration deviates from the above range, Vf tends to be less likely to decrease. In addition, a nitride semiconductor doped with an n-type impurity at a high concentration generally tends to have difficulty in forming a good crystallinity.
Is formed on the first nitride semiconductor layer having a low n-type impurity concentration and good crystallinity, and thus has a high crystallinity despite having a high concentration of the n-type impurity. It can be formed well. Although the upper limit of the n-type impurity concentration of the second nitride semiconductor layer is not particularly limited, the limit that crystallinity of the contact layer becomes too poor is 5 × 10 ²¹ /.
cm ³ or less is desirable.

The second nitride semiconductor layer has a superlattice structure in which two types of nitride semiconductor layers having different band gap energies are laminated or a nitride semiconductor layer having the same composition is laminated. Is also good. When a superlattice layer is used, the mobility of the second nitride semiconductor layer is increased and the resistivity is further reduced, so that Vf and the threshold value can be reduced, and an element having particularly high light emission efficiency can be realized. In the case of a superlattice structure, the thickness of the nitride semiconductor layer constituting the superlattice is adjusted to 100 Å or less, more preferably 70 Å or less, and most preferably 50 Å or less. In the case of a superlattice structure, the nitride semiconductor layer forming the superlattice may be modulation-doped with an n-type impurity such as Si or Ge. What is a modulation dope?
This means that the nitride semiconductor layers constituting the superlattice layer have different impurity concentrations, and in this case, one of the layers may be undoped, that is, undoped. Preferably, the second nitride semiconductor layer has a superlattice structure in which layers having different band gap energies are stacked, and one of the nitride semiconductors is heavily doped with n-type impurities, for example, 5 × 10 ¹⁸ / cm ³ or more. It is desirable to dope,
It is preferable that the other nitride semiconductor layer is undoped. When performing modulation doping, the difference in impurity concentration is desirably one digit or more.

[0012] The second nitride semiconductor layer in the same manner as in the first nitride semiconductor _{layer, In X Al Y Ga 1-} X- Y N (0 ≦ X, 0 ≦
Y, X + Y ≦ 1), and the composition thereof is not particularly limited, but is preferably GaN, Al _X having an X value of 0.2 or less.
When Ga ₁ -xN is used, a nitride semiconductor layer with few crystal defects is easily obtained. There is no particular limitation on the film thickness, but since it is a layer for forming an n-electrode, it is preferable to grow the film to a film thickness of 1 μm or more and 20 μm or less.

The n-type impurity concentration of the third nitride semiconductor layer is 1 × 10 ¹⁷ / cm ³ or less, preferably 5 × 10 ¹⁶ / cm ³
/ Cm ³ or less and may be undoped. Thus n
When the type impurity concentration is reduced, the crystallinity of the third nitride semiconductor layer is improved. When the active layer is formed on the third nitride semiconductor layer having good crystallinity, the third nitride semiconductor layer can be formed with high crystallinity. When the impurity concentration is out of the range, it becomes difficult to form the third nitride semiconductor layer with good crystallinity, and the crystallinity of the active layer formed on the third nitride semiconductor layer is reduced, and the output is reduced. Or, a leak current of the element tends to occur easily.

The thickness of the third nitride semiconductor layer is 0.5 μm.
m or less, preferably 0.2 μm or less, more preferably 0.15 μm or less. The lower limit is not particularly limited, but is desirably adjusted to 10 angstroms or more, preferably 50 angstroms or more, and more preferably 100 angstroms or more. As described above, the third nitride semiconductor layer has the doping amount of the n-type impurity of 1 × 10 ¹⁷ / cm.
Since it is ³ or less, the resistivity is higher than that of the second nitride semiconductor layer, and when the third nitride semiconductor layer is grown as a thick film layer, Vf and the threshold value tend to be hardly reduced. When the film thickness is in the above range, Vf and the threshold value can be favorably reduced, which is preferable.

Further, it is preferable that the third nitride semiconductor layer be thinner than the first nitride semiconductor layer. The first nitride semiconductor layer functions as a buffer layer (high-temperature growth) for growing the second nitride semiconductor layer as a thick film. The third nitride semiconductor layer also acts as a buffer layer during the growth of the active layer. However, if the third nitride semiconductor layer is grown as a thick film, the resistance in the vertical direction increases, so that the first nitride semiconductor layer It is desirable that the thickness be smaller than 0.5 μm.

The third nitride semiconductor layer 5 is made of In _x Al _Y Ga _{1 -XYN} (0 ≦) similarly to the first and second nitride semiconductor layers.
X, 0 ≦ Y, X + Y ≦ 1), and the composition thereof is not particularly limited, but is preferably GaN, Al _X Ga _1-X N having an X value of 0.2 or less, or Y having a value of 0. 1 or less In _Y Ga
_{When 1-YN} is used, a nitride semiconductor layer with few crystal defects is easily obtained. When InGaN is grown, it is possible to prevent cracks in the Al-containing nitride semiconductor layer when growing a nitride semiconductor containing Al thereon.

In the present invention, the first nitride semiconductor layer, the second nitride semiconductor layer, and the third nitride semiconductor layer may be formed by growing nitride semiconductors having the same composition. Is desirable.

In the present invention, examples of the n-type impurities doped into the first to third nitride semiconductor layers include Group 4 elements, such as Si, Ge, Sn, and S. Is Si or Ge, more preferably S
i.

In the present invention, the undoped nitride semiconductor layer refers to a nitride semiconductor layer which is not intentionally doped with impurities.
For example, a layer in which an impurity is mixed by an impurity contained in a raw material, contamination in a reactor, or an unintentional diffusion from another layer intentionally doped with an impurity is also defined as undoped in the present invention.

Further, in the present invention, a buffer layer grown at a lower temperature than the first nitride semiconductor layer may be provided between the substrate and the first nitride semiconductor layer. This buffer layer is made of, for example, AlN, GaN, AlGaN or the like at 400 ° C.
A base layer that can be grown at a temperature of up to 900 ° C. with a thickness of 0.5 μm or less, to reduce lattice mismatch between the substrate and the nitride semiconductor, or to grow the first nitride semiconductor layer with good crystallinity. Act as

The light emitting device of the present invention has a nitride semiconductor layer having at least a three-layer structure between the active layer and the substrate. First, the first nitride semiconductor layer is undoped or doped with a small amount of n-type impurities in order to grow the second nitride semiconductor layer containing n-type impurities with good crystallinity.
Next, the second nitride semiconductor layer is heavily doped with n-type impurities, and functions as a contact layer for forming an n-electrode having a low resistivity and a high carrier concentration.

Next, similarly to the first nitride semiconductor layer, the third nitride semiconductor layer is undoped or doped with a small amount of n-type impurities. The second nitride semiconductor layer having a high n-type impurity concentration is not so good in crystallinity as compared with the nitride semiconductor layer having a low n-type impurity concentration, and an active layer or a cladding layer is formed directly on the second nitride semiconductor layer. When these are grown, the crystallinity of the active layer and the like tends to deteriorate. Therefore, by interposing the third nitride semiconductor with good crystallinity doped with a small amount of n-type impurities between the second nitride semiconductor layer and the active layer, it acts as a buffer layer before growing the active layer. Thus, the active layer and the like can be grown with good crystallinity.
Further, by interposing a third nitride semiconductor layer doped with a small amount of n-type impurities and having a relatively high resistivity between the active layer and the second nitride semiconductor layer, a leak current of the element is prevented. In addition, the withstand voltage in the reverse direction can be increased.

In the present invention, the active layer preferably has a single quantum well structure having a well layer made of an undoped nitride semiconductor containing In, preferably InGaN, or a multiple quantum well structure.

The other layers constituting the light-emitting device of the present invention are not particularly limited. For example, preferred device configurations include the layer configurations shown in the following examples. However, the present invention is not limited to this.

[0025]

[Embodiment 1] FIG. 1 is a schematic sectional view showing the structure of an LED device according to an embodiment of the present invention. Hereinafter, a method of manufacturing the device of the present invention will be described with reference to this drawing. .

The substrate 1 made of sapphire (C plane) is set in a reaction vessel, and after sufficiently replacing the inside of the vessel with hydrogen, the temperature of the substrate is increased to 1050 ° C. while flowing hydrogen to clean the substrate. . Another sapphire C face substrate 1, a sapphire having the principal R-plane, A plane, other, including other insulating substrate such as spinel _{(MgA1 2 O 4), SiC} (6H, 4H, and 3C ), Si, Zn
A semiconductor substrate such as O, GaAs, or GaN can be used.

(Buffer Layer 2) Subsequently, the temperature is set to 510 ° C.
The buffer layer 2 made of GaN is grown on the substrate 1 to a thickness of about 200 angstroms using hydrogen as a carrier gas and ammonia and TMG (trimethylgallium) as a source gas.

(First Nitride Semiconductor Layer 3) Buffer Layer 2
After growth, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C, TM
Using G and ammonia gas, a first nitride semiconductor layer 3 made of undoped GaN is grown to a thickness of 1.5 μm.

(Second nitride semiconductor layer 4)
At 0 ° C., TMG, ammonia gas and silane gas were used as the source gas and the impurity gas, and Si was added at 5 × 10 ¹⁸ / cm 3.
^A second nitride semiconductor layer 3 made of ^3- doped GaN is grown to a thickness of 3 μm.

(Third nitride semiconductor layer 5) Next, only silane gas is stopped, and undoped Ga
A third nitride semiconductor layer 5 made of N is grown to a thickness of 0.15 μm.

(Active Layer 6) Next, the temperature is set to 800 ° C., the carrier gas is switched to nitrogen, and TMG, TMI
An active layer 6 having a single quantum well structure is grown by growing an undoped In _0.15 Ga _0.85 N layer with a thickness of 30 Å using (trimethylindium) and ammonia.

(P-side cladding layer 7)
0 ℃, TMG, TMA, ammonia, Cp2Mg
Using (cyclopentadienyl magnesium), a p-side cladding layer 7 of p-type Al _0.1 Ga _0.9 N doped with Mg at 1 × 10 ²⁰ / cm ³ is grown to a thickness of 0.1 μm. This layer acts as a carrier confinement layer, and is a nitride semiconductor containing Al, preferably Al _Y Ga _1-Y N (0 <Y
It is desirable to grow <1). In order to grow a layer having good crystallinity, Al _Y Ga ₁ -YN having a Y value of 0.3 or less is preferred.
It is desirable to grow the layer to a thickness of 0.5 μm or less.

(P-side contact layer 8) Subsequently, at 1050 ° C.
And using TMG, ammonia, and Cp2Mg,
A p-side contact layer 8 made of p-type GaN doped with × 10 ²⁰ / cm ³ is grown to a thickness of 0.1 μm. The p-side contact layer 8 is also formed of In _X Al _Y Ga _{1 -XYN} (0 ≦ X, 0 ≦ Y, X
+ Y ≦ 1), and the composition thereof is not particularly limited. However, when it is preferably GaN, a nitride semiconductor layer with few crystal defects is easily obtained, and a preferable ohmic contact with a p-electrode material is easily obtained.

After the completion of the reaction, the temperature was lowered to room temperature, and the wafer was placed in a reaction vessel in a nitrogen atmosphere at a temperature of 700.degree.
Anneal at ℃ to further reduce the resistance of the p-type layer.

After annealing, the wafer is taken out of the reaction vessel, a mask having a predetermined shape is formed on the surface of the uppermost p-side contact layer 8, and etching is performed from the p-side contact layer side by an RIE (reactive ion etching) apparatus. Do
As shown in FIG. 1, the surface of the second nitride semiconductor layer 4 is exposed.

After the etching, almost 200 nm of a translucent p-electrode 9 containing Ni and Au is formed on almost the entire surface of the uppermost p-side contact layer, and a bonding Au is formed on the p-electrode 9. p pad electrode 10
It is formed with a film thickness of μm. On the other hand, the surface of the second nitride semiconductor layer 4 exposed by etching has n containing W and Al
The electrode 11 is formed. Finally, an insulating film 12 made of SiO ₂ is formed as shown in FIG. 1 to protect the surface of the p-electrode 9, and the wafer is separated by scribing to form a film 35.
An LED element of 0 μm square is used.

The forward voltage (V) of the obtained LED element
f) and the relationship between the forward current (If) and the conventional LED element
In order to compare the relationship between Vf and If of FIG.
Indicated. As a conventional LED element, it has a
And emits blue light of 450 nm, on a sapphire substrate.
GaN buffer layer and Si 2 × 10¹⁸/ Cm
^ThreeN-side contact layer of doped GaN
An active layer made of InGaN having a quantum well structure;
P-side cladding layer made of AlGaN and Mg-doped G
Conventionally, a p-side contact layer made of aN is sequentially stacked
Blue light emitting LED was used.

As a result, compared with the conventional LED element (line b in FIG. 3), the LED element of Example 1 had a Vf of 0.4 to 0.5 V and an output of 5 to 20 mA compared to the conventional LED element (line b in FIG. 3). % To 10%, and even if If increases, the increase in Vf is extremely small as compared with the conventional one. Thus, Embodiment 1
It can be seen that in the LED element of No. 5, the Vf is remarkably reduced with an increase in current as compared with the conventional LED element. Also, -5
The leakage current at V was less than 0.1 μA.

Example 2 In Example 1, the first nitride semiconductor layer 3 was doped with 1 × 10 ¹⁷ / cm ³ of Si,
An element was obtained in the same manner as above except that the second nitride semiconductor layer 4 was doped with 8 × 10 ¹⁸ / cm ³ of Si and the third nitride semiconductor layer 5 was undoped. As a result, although Vf was almost the same as that of the first embodiment, since the first nitride semiconductor layer 3 was more doped with Si than in the first embodiment, a slight leak current was generated from the device. Output is Example 1
It was slightly lower than.

Example 3 In Example 1, the third nitride semiconductor layer 5 was doped with 1 × 10 ¹⁷ / cm ³ of Si,
An element was obtained in the same manner as above except that the second nitride semiconductor layer 4 was doped with 8 × 10 ¹⁸ / cm ³ of Si and the first nitride semiconductor layer 3 was undoped. As a result, although the Vf was almost the same as that of the first embodiment, since the third nitride semiconductor layer 5 was more doped with Si than in the first embodiment, a slight leak current was generated from the device. Output is Example 1
It was slightly lower than.

Example 4 An element was fabricated in the same manner as in Example 1 except that the first nitride semiconductor layer 3 and the third nitride semiconductor layer 5 were each doped with 8 × 10 ¹⁶ / cm ^{3 of} Si. Obtained. As a result, Vf was almost the same as in Example 1, and the leak current was hardly generated as in Example 1 because the n-type impurity concentrations of the first and third nitride semiconductor layers were reduced. The output was slightly lower than in Example 1.

Fifth Embodiment In the first embodiment, when growing the third nitride semiconductor layer 5, the temperature is set to 800.degree.
Undoped In _0.05 G using G, TMI and ammonia
An LED element was obtained in the same manner as in Example 1, except that a _0.95 N layer was grown to a thickness of 200 Å.
An element having substantially the same characteristics as in Example 1 was obtained.

[Embodiment 6] FIG. 2 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention, which is taken when the device is cut in a direction perpendicular to the resonance direction of laser light. 3 shows the structure. The sixth embodiment will be described below based on this drawing.

On the substrate 20 made of sapphire (C-plane), a buffer layer 21 is grown to a thickness of 200 angstroms in the same manner as in the first embodiment.

(First Nitride Semiconductor Layer 22) After the growth of the buffer layer 20, the temperature is increased to 1020 ° C.
At 5 ° C., a first nitride semiconductor layer 22 made of undoped GaN is grown to a thickness of 5 μm.

(Second nitride semiconductor layer 23)
At 020 ° C., silane gas was used as an impurity gas, and Si was
A second nitride semiconductor layer 22 of 10 ¹⁸ / cm ³ doped n-type GaN is grown to a thickness of 3 μm.

(Third Nitride Semiconductor Layer 24) Next, the temperature is raised to 800 ° C., and the third nitride semiconductor layer 24 made of undoped In _0.05 Ga _0.95 N is formed using TMG, TMI, and ammonia by 500 Å. It grows with the film thickness of.

(N-side cladding layer 25)
0 ° C and TMA, TMG, NH ₃ , Si
N-type Al doped with 1 × 10 ¹⁷ / cm ³ using H _4
An n-side clad layer having a superlattice structure in which 40 Å of _0.25 Ga _0.75 N layers and 40 Å of undoped GaN layers are alternately stacked is grown. This n-side cladding layer acts as a carrier confinement layer and a light confinement layer.

(N-side light guide layer 26)
An n-side optical guide layer 26 of n-type GaN doped with Si at 1 × 10 ¹⁹ / cm ³ is grown at a temperature of 0.2 ° C. to a thickness of 0.2 μm. The n-side light guide layer 26 functions as a light guide layer of an active layer, and is preferably used for growing GaN or InGaN, and is usually formed to have a thickness of 100 Å to 5 μm, more preferably 200 Å to 1 μm. desirable. This n-side light guide layer may be undoped.

(Active Layer 27) At a temperature of 800 ° C., a well layer of Si-doped In _0.2 Ga _0.8 N is first grown to a thickness of 25 Å. Next, only by changing the molar ratio of TMI, the Si-doped In _0.01
A barrier layer made of Ga _0.99 N is grown to a thickness of 50 Å. This operation is repeated twice to finally form a multiple quantum well structure in which well layers are stacked.

(P-side cap layer 28)
20 ° C, TMG, TMA, ammonia, Cp_TwoM
g, the band gap energy is larger than that of the active layer.
Ki, Mg 1 × 10²⁰/cm ^ThreeDoped Al_0.3Ga
_0.7300 angstrom of the p-side cap layer 28 made of N
Grow with a ROHM film thickness. This p-side cap layer 28
Preferably, it is p-type, but since the film thickness is small, n-type impurities
May be doped to form an i-type in which carriers are compensated.
The thickness of the p-side cap layer 28 is 0.1 μm or less, more preferably.
Preferably less than 500 angstroms, most preferably
Adjust to 300 angstrom or less. 0.1 μm
If the layer is grown to a thicker thickness,
Nitride semiconductor layer with good crystallinity, easy to enter rack
Is difficult to grow. And the carrier is this energy
The tunnel cannot pass through the energy barrier due to the tunnel effect. A
When the composition ratio of Al is large, the thinner the AlGaN, the LD element
The child easily oscillates. For example, A with a Y value of 0.2 or more
l_YGa_1-YIf N, adjust to 500 Å or less
Adjustment is desirable. Below the thickness of the p-side cap layer 28
The thickness is not particularly limited, but a film of 10 Å or more
It is desirable to form it with a thickness.

(P-side light guide layer 29)
A p-side light guide layer 26 made of GaN doped with Mg at 1 × 10 ¹⁸ / cm ³ is grown at 0.2 ° C. to a thickness of 0.2 μm. The p-side light guide layer 29 acts as a light guide layer of an active layer, like the n-side light guide layer 26, and serves as a GaN, I
It is desirable to grow nGaN, preferably to a thickness of 100 Å to 5 μm, more preferably 200 Å to 1 μm. The p-side light guide layer is doped with a p-type impurity, but may be made of an undoped nitride semiconductor.

(P-side cladding layer 30)
P-type Al doped with Mg at 1 × 10 ²⁰ / cm ³
_A p-side cladding layer 30 having a superlattice structure in which 40 layers of _0.25 Ga _0.75 N layers and 40 angstroms of undoped GaN layers are alternately laminated is grown. This p-side cladding layer acts as a carrier confinement layer and an optical confinement layer like the n-side cladding layer.
By making the side cladding layer side a superlattice, the resistance of the p-layer tends to decrease and the threshold value tends to decrease more.

(P-side contact layer 31) Finally, Mg was deposited on the p-side cladding layer 30 at 1050 ° C. at 2 × 10 ²⁰ / Mg.
A p-side contact layer 31 made of GaN doped with cm ³ is grown to a thickness of 150 Å.

After completion of the reaction, the temperature was lowered to room temperature, and the wafer was placed in a reaction vessel in a nitrogen atmosphere.
Annealing is performed at ° C. to further reduce the resistance of the layer doped with the p-type impurity.

After the annealing, the wafer was taken out of the reaction vessel, and as shown in FIG.
The side contact layer 31 and the p-side cladding layer 30 are etched to form a ridge shape having a stripe width of 4 μm. In particular, by forming a layer of a nitride semiconductor layer containing Al or higher which is higher than the active layer into a ridge shape, light emission of the active layer is concentrated on the lower portion of the ridge, the transverse mode is easily united, and the threshold value is lowered. Cheap. After the formation of the ridge, a mask is formed on the surface of the ridge, and the surface of the second nitride semiconductor layer 23 on which the n-electrode 34 is to be formed is exposed, as shown in FIG. Let it.

Next, a p-electrode 32 made of Ni and Au is formed on almost the entire top surface of the ridge of the p-side contact layer 31. On the other hand, an n-electrode 34 made of Ti and Al is formed on almost the entire surface of the stripe-shaped second nitride semiconductor layer 23.
It should be noted that substantially the entire surface refers to an area of 80% or more. Thus, the second nitride semiconductor layer 2 is symmetrical with respect to the p-electrode 32.
Exposing 3 and providing an n-electrode on almost the entire surface of the second layer 23 is also very advantageous in lowering the threshold value. Further, after an insulating film 35 made of SiO ₂ is formed between the p electrode and the n electrode, the p pad electrode 3 made of Au is electrically connected to the p electrode 32 via the insulating film 35.
Form 3

As described above, the wafer on which the n-electrode and the p-electrode are formed is transferred to the polishing apparatus, and the sapphire substrate 20 on which the nitride semiconductor is not formed is wrapped using a diamond abrasive. The thickness of the substrate is 50 μm. After lapping, the substrate surface is mirror-finished by polishing with a finer abrasive at 1 μm.

After the substrate is polished, the polished surface side is scribed,
Cleavage is performed in a bar shape in a direction perpendicular to the stripe-shaped electrodes, and a resonator is formed on the cleavage plane. SiO ₂ and TiO ₂ on the resonator surface
A dielectric multilayer film is formed, and finally the bar is cut in a direction parallel to the p-electrode 32 to form a laser device. When this device was placed on a heat sink and laser oscillation was attempted at room temperature, the threshold current density was 2.5 kA / c at room temperature.
At m ² and a threshold voltage of 4.0 V, continuous oscillation at an oscillation wavelength of 405 nm was confirmed. The lifetime was 500 hours or more, and the lifetime was improved 10 times or more as compared with the conventional nitride semiconductor laser device.

Example 7 An LD device was obtained in the same manner as in Example 6, except that the first nitride semiconductor layer 22 was doped with 1 × 10 ¹⁷ / cm ³ of Si. As a result, Example 5
And almost good results were obtained, but Example 6 was slightly better.

[0061]

As described above, in the device of the present invention, 1 × 10 ¹⁷ n-type impurities between the active layer and the substrate are removed.
/ Cm ³ or less of the first nitride semiconductor layer, the n-type impurity can be grown so as to maintain the crystallinity of the second nitride semiconductor doped, 3 an n-type impurity then × 10 ¹⁸ / c
The second nitride semiconductor layer of m ³ or more can be grown as a thick film with good crystallinity. Further, a third nitride semiconductor having an n-type impurity of 1 × 10 ¹⁷ / cm ³ or less serves as a base layer having good crystallinity for a nitride semiconductor layer grown on the third nitride semiconductor. Therefore, the resistivity of the second nitride semiconductor layer can be reduced and the carrier concentration can be increased, so that a very efficient nitride semiconductor element can be realized. As described above, according to the present invention, a light-emitting element having a low Vf and a low threshold value can be realized while improving the output, so that the heat generation of the element is reduced and an element with improved reliability can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of an LED element according to one embodiment of the present invention.

FIG. 2 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention.

FIG. 3 is a diagram comparing the relationship between the forward voltage and the forward current of the LED element of the present invention and the conventional LED element.

[Explanation of symbols]

 1, 20 ... substrate 2, 21 ... buffer layer 3, 22 ... first nitride semiconductor layer 4, 23 ... second nitride semiconductor layer 5, 24 ... third Nitride semiconductor layer 6, 27 ... Active layer 7, 30 ... p-side cladding layer 8, 31 ... p-side contact layer 25 ... n-side light guide layer 26 ... n-side cladding layer 28 ... p-side cap layer 29 ... p-side light guide layer 9, 32 ... p electrode 10, 33 ... p pad electrode 11, 34 ... n electrode 35, 12 ... insulating film

Claims (3)

[Claims] 1. A method according to claim 1, further comprising the step of:
1 × 10 n-type impurities ¹⁷/ Cm^ThreeThe following first nitride half
Conductive layer and 3 × 10 n-type impurities¹⁸/ Cm^ThreeThe second above
Nitride semiconductor layer and n-type impurity is 1 × 10¹⁷/ Cm^Three
A third nitride semiconductor layer described below, wherein the second nitride
Characterized in that an n-electrode is formed on the semiconductor layer
Nitride semiconductor light emitting device. 2. The nitride semiconductor light emitting device according to claim 1, wherein the second nitride semiconductor layer is doped with an n-type impurity at a concentration of 5 × 10 ¹⁸ / cm ³ or more. 3. The semiconductor device according to claim 1, wherein said third nitride semiconductor layer has a thickness of 0.5.
3. The nitride semiconductor light emitting device according to claim 1, wherein the thickness is 5 μm or less.