JPH09148678A - Nitride semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve light emission output of a light emitting element, by forming an active layer of multiple quantum well structure wherein well layers composed of nitride semiconductor containing In and barrier layers composed of nitride semiconductor containg In are laminated. SOLUTION: A buffer layer 2, an N-type contact layer 3, a first N-type layer 4 acting as a buffer layer, a second N-type layer 5 acting as a light confining layer, and a third N-type layer 6 acting as a guide layer are formed on a sapphire substrate 1. An active layer 7 composed of multiple quantum well structure is formed by alternately laminating a plurality of well layers composed of undoped InGaN and a plurality of barrier layers composed of undoped InGaN. A first P-type layer 8 acting as a cap layer, a second P-type layer 9 acting as a light guide layer, and a third P-type layer 10 acting as a light confining layer are formed. A P-type contact layer 11 is formed, selective etching is performed, the surface of the N-type contact layer is exposed, and a positive electrode and a negative electrode are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode (LE).
D), nitride semiconductors (In _X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y used for laser diodes (LD), etc.
≦ 1) for a light emitting device.

[0002]

2. Description of the Related Art In _X Al _Y Ga _1-XY N (0≤X, 0≤
The nitride semiconductor represented by Y, X + Y ≦ 1) is MOVPE.
It is epitaxially grown on the substrate using a vapor phase growth method such as (organic metal vapor phase epitaxy method), MBE (molecular beam vapor phase epitaxy method) and HDVPE (halide vapor phase epitaxy method).
Since this semiconductor material is a direct transition type wide wide-gap semiconductor, it is known as a material for light-emitting elements from ultraviolet to red. Recently, this material has a high brightness of blue LE.
Realization of D and green LEDs, and realization of a laser diode (LD) is desired as the next target.

As a light emitting device using a nitride semiconductor, for example, an LED device is disclosed in Japanese Patent Laid-Open No. 6-21511. In this publication, a well layer made of InGaN and having a thickness of 100 angstroms and a GaN film having a thickness of 100 are formed.
An LED device including an active layer having a multiple quantum well structure stacked with an angstrom barrier layer is shown.

[0004]

According to the above publication, I
An LED element having a double confinement type double hetero structure in which an active layer having a multiple quantum well structure composed of nGaN and GaN is sandwiched between GaN and a cladding layer composed of AlGaN is shown. When the active layer has a multi-quantum well structure, an LED device excellent in light emission output can be obtained.
However, in the LD, it is necessary to further increase the light emission output as compared with the LED. Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to realize a semiconductor laser by increasing the light emission output of a light emitting element made of a nitride semiconductor. By improving the layer structure, a high-power light emitting device is realized.

[0005]

The light emitting device of the present invention is I
It is characterized by comprising an active layer having a multiple quantum well structure in which a well layer made of a nitride semiconductor containing n and a barrier layer made of a nitride semiconductor containing In are stacked.

The active layer having a multiple quantum well structure is characterized in that the well layer has a thickness of 70 Å or less and the barrier layer has a thickness of 150 Å or less.

Further, the light emitting device of the present invention has a film thickness of 1 μm made of a p-type nitride semiconductor containing at least Al in the active layer.
It is characterized in that a p-type clad layer of m or less is in contact.

In the light-emitting device of the present invention, the well layer made of a nitride semiconductor containing In forming a multi-quantum well structure (MQW: Multi-quantum-well) has a ternary mixed crystal of In.
XGa1-XN (0 <X≤1) is preferable, and the barrier layer is also preferably InYGa1-YN (0 <Y <1) of ternary mixed crystal. Since ternary mixed crystal InGaN has a better crystallinity than that of the quaternary mixed crystal, the light emission output is improved. The barrier layer has a bandgap energy larger than that of the well layer and is stacked so as to be well + barrier + well + ... + Barrier + well layer to form a multiple quantum well structure. As described above, when the active layer is an MQW in which InGaN is laminated,
It is possible to realize a high-power LD in the range of about 365 nm to 660 nm by light emission between quantum levels.

When realizing an LD, it is preferable that the thickness of the active layer, that is, the total thickness of the active layer in which the well layer and the barrier layer are laminated is adjusted to 200 angstroms or more. 200
If the thickness is thinner than angstrom, the output is not sufficiently increased and laser oscillation tends to be difficult. Further, if the thickness of the active layer is too thick, the output tends to decrease, and it is desirable to adjust the thickness to 0.5 μm or less.

Further, the thickness of the well layer is preferably adjusted to 70 angstroms or less, and more preferably 50 angstroms or less. FIG. 2 is a diagram showing the relationship between the film thickness of the well layer and the light emission output, and the light emission output is shown for the LED element. Regarding the output, the same can be said for the LD. This indicates that this film thickness is below the critical film thickness of the InGaN well layer. In InGaN, the Bohr radius of electrons is about 30 angstroms, which is why I
The quantum effect of nGaN appears below 70 Å.

The thickness of the barrier layer is preferably adjusted to 150 angstroms or less, more preferably 100 angstroms or less. FIG. 3 is a diagram showing the relationship between the barrier layer, the film thickness, and the light emission output, and the light emission output is shown for the LED element as in FIG. 2, but the same can be said for the LD.

Next, in the light emitting device of the present invention, a p-type nitride semiconductor containing at least Al in contact with the active layer, preferably a ternary mixed crystal or a binary mixed crystal of AlZGa1-ZN (0 <Z≤
It is desirable that the p-type clad layer of 1) be formed. Further, this AlGaN is adjusted to 1 μm or less, more preferably 10 angstroms or more and 0.5 μm or less. By forming the p-type clad layer in contact with the active layer, the output of the device is remarkably improved. On the contrary, if the cladding layer in contact with the active layer is made of GaN, the output of the device will be reduced to about 1/3. It is presumed that this is because AlGaN is more likely to be p-type than GaN and has the effect of suppressing decomposition of InGaN during growth of the p-type cladding layer, but details are unknown. Further, if the thickness of the p-type clad layer is thicker than 1 μm, cracks are likely to occur in the clad layer itself, and it tends to be difficult to manufacture the device.

[0013]

In the light emitting device of the present invention, the active layer is made of InGaN and the In layer has a band gap larger than that of the well layer.
This is a multiple quantum well structure in which barrier layers made of GaN are stacked. It differs from JP-A-6-21511 in that the barrier layer is GaN. This is because the MQW in which a thin film well layer and a barrier layer are stacked has different stresses in each layer. When a barrier layer made of InGaN is stacked on the well layer as in the present invention, the barrier layer made of InGaN has a softer crystal than GaN and AlGaN crystals. Therefore, the Al of the clad layer
Since the thickness of GaN can be increased, laser oscillation can be realized. On the other hand, when the barrier layer is GaN, AlG is formed on the active layer.
When a clad layer made of aN is grown, cracks tend to occur in the clad layer.

Further, the crystal growth temperature is different between InGaN and GaN. For example, in the MOVPE method, InGaN is grown at 600 ° C. to 800 ° C., whereas GaN is grown at a temperature higher than 800. Therefore, InGaN
If a barrier layer made of GaN is to be grown after the growth of a well layer made of GaN, it is necessary to raise the growth temperature. When the growth temperature is raised, the previously grown InGaN
Since the well layer is decomposed, it is difficult to obtain a well layer with good crystallinity. Further, the thickness of the well layer is only several tens of angstroms, and it becomes difficult to manufacture the MQW when the well layer of the thin film is decomposed. On the other hand, in the present invention, since the barrier layer is also InGaN, the well layer and the barrier layer can be grown at the same temperature. Therefore, since the well layer formed earlier does not decompose, an MQW with good crystallinity can be formed.

[0015]

EXAMPLES A method for producing an LD element by the MOVPE method will be described below. The light-emitting element of the present invention is not limited to the MOVPE method, but other known nitride semiconductors such as MBE and HDVPE can be vapor-phase grown. It can be grown using the method and is applicable not only to LD but also to LED.

Example 1 A well-cleaned sapphire substrate 1 (0001 surface) was placed in a reaction vessel of a MOVPE apparatus, and then TMG (trimethylgallium) was used as a source gas.
Then, using ammonia, a buffer layer 2 made of GaN was grown to a thickness of 200 angstroms on the surface of the sapphire substrate at a temperature of 500 ° C.

This buffer layer has a function of alleviating the lattice mismatch between the substrate and the nitride semiconductor, and in addition, AlN and AlG.
It is also possible to grow aN or the like. In addition to sapphire, spinel 111 surface (MgAl ₂ O ₄ ), S
A conventionally known substrate made of a single crystal of iC, MgO, Si, ZnO or the like is used. It is known that by growing this buffer layer, the crystallinity of the n-type nitride semiconductor grown on the substrate is improved, but the buffer layer may not be grown depending on the growth method, the type of the substrate and the like. .

Then, the temperature is raised to 1050 ° C., TMG and ammonia are used as a source gas, and SiH is used as a donor impurity.
_An n-type contact layer 3 made of Si-doped GaN was grown to a thickness of 4 μm using ₄ (silane) gas. By using GaN for the n-type contact layer 3, a layer having a high carrier concentration can be obtained, and a preferable ohmic contact with the electrode material can be obtained.

Next, the temperature is lowered to 750 ° C., TMG, TMI (trimethylindium), ammonia is used as a source gas, and silane gas is used as an impurity gas.
A first n-type layer 4 of 1 Ga 0.9 N was grown to a film thickness of 500 Å.

The first n-type layer 4 is grown from an n-type nitride semiconductor containing In, preferably InGaN, so that a nitride semiconductor containing Al to be grown next can be grown as a thick film. Becomes In the case of LD, it is necessary to grow the layers serving as the light confinement layer and the light guide layer to have a film thickness of, for example, 0.1 μm or more. Conventionally, GaN, AlG
When a thick AlGaN film was grown directly on the aN layer, it was difficult to fabricate the device because the AlGaN grown later had cracks, but the first n-type layer acts as a buffer layer. That is, this layer serves as a buffer layer, and it is possible to prevent cracks from occurring in the nitride semiconductor layer containing Al to be grown next. Moreover, even if the nitride semiconductor layer containing Al to be grown next is grown as a thick film, it can be grown with good film quality. The first n-type layer is preferably grown to a film thickness of 100 angstroms or more and 0.5 μm or less. If it is thinner than 100 angstrom, it is difficult to act as a buffer layer as described above, and if it is thicker than 0.5 μm, the crystal itself tends to turn black. The first n-type layer 4 may be omitted.

Next, the temperature is set to 1050 ° C., TEG, TMA (trimethylaluminum) and ammonia are used as source gases, and silane gas is used as an impurity gas.
0.5 μ of the second n-type layer 5 made of Al0.3Ga0.7N
It was grown to a film thickness of m. In the case of LD, this second n-type layer acts as a light confining layer, and it is usually desirable to grow it to a film thickness of 0.1 μm to 1 μm.

Then, TMG, ammonia, and
Si-doped n-type GaN using silane gas as impurity gas
The third n-type layer 6 was grown to a film thickness of 500 angstroms. In the case of LD, this third n-type layer 6 acts as a light guide layer, and usually has a thickness of 100 Å.
It is desirable to grow it to a film thickness of 1 μm, and it is also possible to grow n-type nitride semiconductors containing In such as InGaN in addition to GaN. In particular, by using InGaN or GaN, the next active layer has a quantum well structure. It becomes possible to do.

Next, the active layer 7 was grown using TMG, TMI, and ammonia as source gases. The active layer 7 has a temperature of 7
While maintaining the temperature at 50 ° C., first, a well layer made of non-doped In0.2Ga0.8N is grown to a thickness of 25 Å. Next, a barrier layer made of non-doped In0.01Ga0.95N was deposited at the same temperature by changing only the molar ratio of TMI.
It is grown to a film thickness of 0 angstrom. This operation is 1
Repeat 3 times, and finally grow the well layer to a total film thickness of 0.1μ
An active layer 7 having a multiple quantum well structure with a thickness of m was grown. The preferable thickness of the well layer is 100 angstroms or less, and the thickness of the barrier layer is 150 angstroms or less. By growing the well layer and the barrier layer elastically, crystal defects are reduced, and the output of the device is dramatically increased. Therefore, laser oscillation becomes possible. In addition, the well layer is InG
Nitride semiconductor containing InGaN such as aN, the barrier layer is Ga
It is desirable to use N, InGaN, or the like. In particular, if the well layer and the barrier layer are both InGaN, the growth temperature can be kept constant, which is very preferable in terms of production technology.

After growth of the active layer 7, the temperature is set to 1050 ° C. and TMG, TMA, ammonia, and Cp 2 Mg (cyclopentadienyl magnesium) as an acceptor impurity source.
Was used to grow a first p-type layer 8 of Mg-doped p-type Al0.2Ga0.8N to a film thickness of 100 angstrom. This first p-type layer 8 is grown to a film thickness of 1 μm or less, more preferably 0.1 μm or less,
It has a function as a cap layer for preventing the active layer made of GaN from being decomposed, and p containing Al on the active layer.
By growing the first p-type layer 8 made of the type nitride semiconductor, the light emission output is improved. The p-type nitride semiconductor layer can be obtained by doping acceptor impurities such as Zn, Mg, Cd, Ca, Be and C during growth.
Among them, Mg exhibits the most preferable p-type characteristics. Furthermore, more preferable p-type is obtained by performing annealing at 400 ° C. or higher in an inert gas atmosphere after doping the acceptor impurities.

Next, while maintaining the temperature at 1050 ° C., T
Mg-doped p-type G using MG, ammonia, and Cp2Mg
A second p-type layer 9 made of aN was grown to a film thickness of 500 Å. In the case of LD, this second p-type layer 9 acts as a light guide layer, and it is usually desirable to grow it with a film thickness of 100 angstrom to 1 μm.
It is also possible to grow a p-type nitride semiconductor containing In, such as InGaN, in addition to N. In particular, by using InGaN or GaN, the third p-type layer 10 containing Al can be grown with good crystallinity.

Subsequently, TMG, TMA, ammonia and C
A third p-type layer 10 made of Mg-doped Al0.3Ga0.7N was grown to a thickness of 0.5 μm using p2Mg. In the case of LD, this third p-type layer 10 acts as a light confining layer, and it is desirable to grow it to a film thickness of 0.1 μm to 1 μm, and it is a p-type nitride semiconductor containing Al such as AlGaN. Therefore, it preferably acts as a light confining layer.

Subsequently, TMG, ammonia, Cp2Mg
Was used to grow a p-type contact layer 11 made of Mg-doped p-type GaN with a film thickness of 0.5 μm. If this p-type contact layer is GaN containing Mg, a p-type layer having the highest carrier concentration can be obtained, and good ohmic contact with the material of the positive electrode can be obtained.

The wafer in which the nitride semiconductors are laminated as described above is taken out of the reaction container and, as shown in FIG. 1, the uppermost p-type contact layer 11 is selectively etched to expose the surface of the n-type contact layer 3. Let exposed n
After forming striped electrodes on the surfaces of the p-type contact layer 3 and the p-type contact layer 11, respectively, etching is further performed from a direction orthogonal to the striped electrodes to form a vertical etching end face, and the etching surface is formed. A reflecting mirror was formed in accordance with a conventional method to form a resonance surface. A cross-sectional view of the laser device as seen from the resonance surface side is the cross-sectional view shown in FIG.
When this laser element was placed on a heat sink and used as an LD, a very excellent crystal was laminated, so at normal temperature, laser oscillation with a threshold current density of 4.0 kA / cm ² and an emission wavelength of 410 nm and a half width of 2 nm was obtained. showed that.

[0029]

As described above, the light emitting device of the present invention has an MQW active layer in which a well layer made of a nitride semiconductor containing In and a barrier layer made of a nitride semiconductor containing In are stacked. Therefore, the output of the light emitting element was improved and a laser diode was realized. This is because the active layer with good film quality has been grown. Thus, in the present invention, the short wavelength L
By realizing D, the capacities as a writing light source and a reading light source are dramatically improved as compared with conventional ones, and their industrial utility value is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of an LD according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a well layer of an active layer and a light emission output of an element according to an example of the present invention.

FIG. 3 is a diagram showing a relationship between a barrier layer of an active layer and a light emission output of an element according to an example of the present invention.

[Explanation of symbols]

 1 ... Substrate 2 ... GaN buffer layer 3 ... n-type GaN (n-type contact layer) 4 ... n-type InGaN (first n-type layer) 5 ... n-type AlGaN (second N-type layer) 6 ... n-type GaN (third n-type layer) 7 ... active layer 8 ... p-type AlGaN (first p-type layer) 9 ... p-type GaN (third Second p-type layer) 10 ... p-type AlGaN (third p-type layer) 11 ... p-type GaN (p-type contact layer)

Claims (3)

[Claims] 1. A nitride semiconductor light emitting device, comprising: an active layer having a multiple quantum well structure in which a well layer made of a nitride semiconductor containing In and a barrier layer made of a nitride semiconductor containing In are stacked. element. 2. The nitride semiconductor laser device according to claim 1, wherein the well layer has a thickness of 70 Å or less, and the barrier layer has a thickness of 150 Å or less. . 3. The active layer is in contact with a p-type clad layer having a thickness of 1 μm or less made of a p-type nitride semiconductor containing at least Al.
The nitride semiconductor laser device described in 1 ..