JPH1174621A - Nitride group semiconductor luminous element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve total element characteristics while a threshold value current is reduced and cracking is suppressed. SOLUTION: Relating to a nitride based semiconductor laser comprising separate confinement hetero structure wherein an MQW (multiplex quantum well structure) active layer 16 of InGaN based semiconductor is sandwiched between a pair of GaN light confinement layers 15 and 17 whose band gap is larger than the active layer 16, which is further sandwiched between a pair of, p-type and n-type, clad layers 14 and 18 of AlGaN whose band gap larger than the light confinement layers 15 and 17, further comprising GaN contact layers 13 and 19, p-type and n-type, outside of them, such a light confinement layer 15 as on n-side, out of the pair of light confinement layers 15 and 17, is formed of InGaN whose reflectance factor is larger than the GaN contact layers 13 and 19, for improved light confinement effect and also for preventing occurrence of crack at the active layer 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride-based semiconductor light emitting device used in technical fields such as optical information processing, optical communication, and optical measurement, and more particularly to a separated confinement heterostructure (SC).
H: a nitride-based semiconductor light emitting device having a separate confinement heterostructure).

[0002]

2. Description of the Related Art In recent years, demand for short-wavelength light emitting devices has increased,
Research and development of short-wavelength light emitting devices using ZnSe-based and GaN-based materials have been actively conducted. In a ZnSe-based material,
Although continuous oscillation at room temperature of a short-wavelength semiconductor laser having an oscillation wavelength of about 500 nm has been achieved, device deterioration due to the growth of crystal defects becomes a problem, and a longer life of the device cannot be achieved.
It has not been put to practical use.

On the other hand, in recent years, a blue light emitting diode (LED) has been put to practical use as a GaN-based material, and research and development of a GaN-based blue semiconductor laser are currently being vigorously conducted. Recently, continuous oscillation at room temperature has also been achieved in a GaN-based semiconductor laser. However, in this material system, there are still many unknown parts regarding physical properties, and there are many problems to be solved in practical use. The main reasons are that the threshold current is high,
There is also a problem that cracks (cracks) occur. In this material system, it seems that there are many problems that cannot be solved by an element structure similar to that of a material system which has been practically used conventionally.

In a GaN-based blue semiconductor laser, conventionally, p
Between an AlGaN cladding layer having n-type and n-type conduction,
An SCH structure having an InGaN-based active layer having a multiple quantum well structure (MQW) is often used. To reduce the threshold current, it is necessary to reduce the number of pairs of the MQW well layer and the barrier layer. However, in reality, when the number of MQW pairs is reduced, a problem occurs in which cracks occur in the growth layer. Therefore, there is a trade-off between reducing the threshold value and suppressing the occurrence of cracks, and it is difficult to improve the total element characteristics.

[0005] In addition, insufficient light confinement in the conventional element structure is also a factor of high threshold. In order to sufficiently confine the light, it is effective to increase the Al composition and increase the film thickness of the AlGaN cladding layer, but this causes a problem that cracks become noticeable. Therefore, in order to sufficiently confine light and reduce the threshold value, a method other than increasing the Al composition and increasing the film thickness of the cladding layer is required.

[0006]

As described above, conventionally, Ga
For the practical use of N-based semiconductor lasers, it is essential to reduce the threshold current and to suppress the occurrence of cracks. However, these are in a trade-off relationship, and the total element characteristics must be reduced. It was difficult to improve.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to simultaneously reduce the threshold current and suppress cracks, thereby improving the total element characteristics. It is an object of the present invention to provide a nitride-based semiconductor light-emitting device that can solve the problem.

[0008]

[Means for Solving the Problems]

(Structure) In order to solve the above problem, the present invention employs the following structure. That is, the present invention comprises a plurality of nitride-based semiconductor layers laminated on a substrate, an active layer sandwiched between a pair of optical confinement layers, and the outside thereof sandwiched between a pair of p-type and n-type cladding layers. A nitride-based semiconductor light-emitting device having a heterostructure and having p-type and n-type contact layers outside thereof, wherein the refractive index of the p-side light confinement layer of the pair of light confinement layers is The refractive index of the n-side light confinement layer is the same as or larger than that of the contact layer, and is larger than that of the p-side light confinement layer.

Further, according to the present invention, an active layer made of a nitride-based semiconductor is sandwiched between a pair of optical confinement layers made of a nitride-based semiconductor having a larger band gap than the active layer. Having a separate confinement heterostructure sandwiched between a pair of p-type and n-type cladding layers made of a nitride-based semiconductor containing Al having a large diameter, and made of a nitride-based semiconductor having a band gap smaller than that of the cladding layer on the outside thereof. A nitride-based semiconductor light-emitting device having p-type and n-type contact layers, wherein, of the pair of light confinement layers, an n-side light confinement layer has a higher refractive index than the contact layer, and a p-side light confinement layer. The confinement layer has a lower refractive index than the n-side optical confinement layer, and has the same or higher refractive index as the contact layer.

Here, preferred embodiments of the present invention include the following. (1) Each cladding layer is formed by _{Al z Ga 1-z N (} 0 <z ≦ 1), each contact layer is formed of GaN, the light confinement layer of n-side _{In x Ga 1-x N (} 0 <X ≦ 1), and the p-side optical confinement layer is In _y Ga _1-y N (0 ≦ y).
<X).

(2) The active layer has an InGaN-based multiple quantum well structure. (3) The thickness of the p-side optical confinement layer is larger than the thickness of the n-side optical confinement layer.

According to the present invention, a plurality of nitride-based semiconductor layers are stacked on a substrate, and the active layer is sandwiched between a pair of optical confinement layers having a band gap larger than that of the active layer. P with a larger band gap than the layer
A nitride-based semiconductor light-emitting device having a separate confinement heterostructure sandwiched between a pair of n-type and n-type cladding layers, wherein the active layer is separated into a first active layer and a second active layer; A crack preventing layer having a smaller band gap than the light confinement layer and a larger band gap than the first and second active layers is provided between the first active layer and the second active layer. I do. Here, the active layer has a quantum well structure including a well layer and a barrier layer, and the band gap of the crack prevention layer is desirably larger than the well layer of the active layer and smaller than the barrier layer.

(Function) In a nitride semiconductor light emitting device having an SCH structure, it is essential to reduce the number of pairs of well layers and barrier layers of an InGaN MQW active layer in order to reduce the threshold current. is there. In addition, in order to solve the problem that the threshold current cannot be reduced due to insufficient light confinement, the thickness of the AlGaN cladding layer or A
It is effective to increase the l composition. However, MQ
Reduction of the number of W pairs, thickness of AlGaN cladding layer or Al
As the composition increases, the occurrence of cracks becomes remarkable. Conventionally, there is an example in which a layer for preventing cracks is inserted below the SCH structure. This method has some effects of preventing cracks, but the effect is not perfect and cannot withstand practical use. Things. Further, this method cannot solve the problem that the threshold value cannot be reduced due to insufficient light confinement.

Therefore, in the present invention, the number of MQW pairs can be reduced,
Provided is a short-wavelength semiconductor light-emitting device having a low threshold value, which can increase an optical confinement effect while suppressing the occurrence of cracks and can be sufficiently practically used. That is, in the present invention, a light confinement layer,
In particular, by using InGaN for the n-side optical confinement layer,
Even if the number of MQW pairs is reduced, the occurrence of cracks can be suppressed, and the light confinement effect can be greatly increased. In addition, a low-threshold semiconductor light emitting device can be realized.

In either the n-side or the p-side light confinement layer, In
Even if GaN is used, a crack preventing effect and an optical confinement effect can be obtained, but in actuality, it is necessary to design an element structure for comprehensively improving element characteristics. That is, it is necessary to design an element structure in consideration of structural restrictions and physical property restrictions. When the conventional structure shown in FIG. 3 is mainly used,
(1) Since the overflow of electrons to the p-side is remarkable, a structure capable of suppressing this is desirable. (2) It is necessary to have a structure that can prevent re-evaporation of the active layer during the re-heating process after the growth of the InGaN-based active layer. In consideration of physical properties, (3)
Obtaining InGaN having a high carrier concentration by p-type conduction is difficult with the current technology. (4) The crack prevention effect is greater when InGaN is used for the n-side optical confinement layer than for the p-side optical confinement layer.

From the above structural and physical restrictions, it is effective to use InGaN for the n-side optical confinement layer. The I-side of the n-side InGaN optical confinement layer
The n composition must be lower than the In composition of the well layer. As an example, when the In composition of the well layer is 20%, n
The In composition of the side InGaN light confinement layer is preferably about 5 to 8%. On the other hand, a large effect can be obtained by using p-type GaN for the p-side optical confinement layer as before, but in order to further enhance the light confinement effect and crack prevention effect, InGaN is also used for the p-side optical confinement layer. Is also good. However, for the reasons (1), (2) and (3) described above, it is necessary to lower the In composition of the n-side InGaN optical confinement layer. In the case of the above example, the In composition is preferably about 2 to 3%. Also, (1)
In consideration of the problem of electron overflow to the p-side and the asymmetry of the light intensity distribution, for example, it is not necessary to provide a light confinement layer on the p-side.

On the other hand, since the In compositions (refractive indexes) of the n-side and p-side light confinement layers are different, the confinement of light in the active layer becomes asymmetric, and the center of the light intensity distribution is shifted from the center of the active layer. This light intensity distribution can be controlled by changing the thickness of the n-side and p-side light confinement layers. For example, when InGaN is used for the n-side optical confinement layer and GaN is used for the p-side optical confinement layer, if both have the same film thickness,
The center of the light intensity distribution is shifted to the n side. However, by making the thickness of the p-side light confinement layer larger than that of the n-side light confinement layer, this shift can be returned to the center position.

It is also possible to provide a crack prevention layer at the center of the n- and p-side light confinement layers. In this case, active layers are provided above and below the crack prevention layer, that is, on the n-side and p-side. Structure.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. (Embodiment 1) FIG. 1 shows a cross section of the device structure of a nitride semiconductor laser according to a first embodiment of the present invention, and FIG. 2 shows a band diagram of the SCH structure in the device structure of FIG. For reference, a schematic structural diagram of a conventional nitride-based semiconductor laser having an SCH structure is shown in FIG. 3, and a band diagram in the device structure is shown in FIG.

First, the nitride semiconductor laser having the SCH structure according to the present embodiment will be explained with reference to FIG. The laser according to the present embodiment has an undoped GaN underlayer 12, an n-type GaN contact layer 13, a thickness of 0.33 μm on a sapphire substrate 11 via a buffer layer (not shown).
m n-type Al _0.16 Ga _0.84 N cladding layers 14 are sequentially formed. In order to sufficiently confine the light of the active layer and produce a semiconductor laser with a low threshold value, it is necessary to make the Al composition of the AlGaN cladding layer 14 sufficiently high or to make the film thickness sufficient. However, the AlGaN cladding layer 1
By increasing the Al composition or increasing the film thickness of No. 4, a problem arises in that a crack occurs in the laser multilayer film. This crack becomes more remarkable as the Al composition is higher and the film thickness is larger.

In this embodiment, in order to solve this problem, 0.2 μm thick In _0.07 Ga having both effects of confining n-side light and preventing cracks is formed on the n-type AlGaN cladding layer 14. _A crack prevention / light confinement layer 15 made of _0.93 N is formed. On top of the crack prevention / optical confinement layer 15, a 2 nm thick In _0.15 Ga
_{An IW} having a multiple quantum well structure (MQW) comprising three pairs of a _0.85 N well layer and a 4 nm thick In _0.05 Ga _0.95 N barrier layer.
An nGaN-based active layer 16 is formed, and a p-side GaN light confinement layer 17 having a thickness of 0.25 μm and a p-type Al
_{The 0.16} Ga _0.84 N cladding layer 18 and the p-type GaN contact layer 19 are formed in the above order.

A part of the multilayer structure is removed by the dry etching method up to the n-type GaN contact layer 13, and an n-side electrode 20 made of Ti / Al is formed on the exposed contact layer 13. Then, a p-side electrode 21 is formed on the p-type GaN contact layer 19.

Next, a method of manufacturing the laser according to the present embodiment will be described. This laser was produced by a well-known metal organic chemical vapor deposition (MOCVD) method. As organic metal raw materials, trimethylgallium (TMG), trimethylaluminum (TMA), trimethylindium (TMI),
Biscyclopentadienyl magnesium (Cp ₂ Mg)
Was used. In addition, ammonia (NH
₃ ), silane (SiH ₄ ) was used. Further, hydrogen and nitrogen were used as carrier gases.

First, a sapphire substrate 11 treated by organic cleaning and acid cleaning was introduced into a reaction chamber of a MOCVD apparatus, and was placed on a susceptor heated by high frequency.
Next, while flowing hydrogen at a flow rate of 25 L / min at normal pressure,
Vapor phase etching was performed at a temperature of 1200 ° C. for about 10 minutes to remove a natural oxide film formed on the surface.

Next, a 550 ° C.
After growing the buffer layer at a low temperature, the substrate temperature is set to 1100 ° C. and 20.5 L of hydrogen is used as a carrier gas.
/ Min, ammonia 9.5 L / min, TMG 10
By supplying the solution at 0 cc / min for 60 minutes, an undoped GaN underlayer 12 (2.0 μm) was formed. Then S
10 cc of iH ₄ was added, and an n-type GaN contact layer 13 (4.0 μm) was continuously formed. Then, TMA is 6
By adding 0 cc / min, n-type Al _0.16 Ga _0.84 N
A cladding layer (0.33 μm) was formed.

Next, the temperature of the sapphire substrate 11 is lowered to 760 ° C., the carrier gas is switched from hydrogen to nitrogen 20.5 L / min, ammonia is 9.5 L / min, and TMG is 10
By flowing TMI at a rate of 150 cc / min for about 8 minutes, a 0.2 μm-thick crack prevention / optical confinement layer 15 was grown. Next, the supply amount of TMI was increased to 450 c.
By alternately switching between c and 50 cc, the thickness 2n
m In _0.15 Ga _0.85 N well layer, 4 nm thick In _0.05
Multiple quantum well structure (MQW) consisting of Ga _0.95 N barrier layer
Was formed.

Next, the sapphire substrate 11 is heated to 1080 ° C.
The temperature was increased to 20.5 L / min of nitrogen carrier gas, 9.5 L / min of ammonia, 100 cc / min of TMG, and 50 cc of CP ₂ Mg as a p-type dopant raw material, whereby a 0.25 μm thick p-side light was added. The confinement layer 17 is grown for 3 minutes, after which 60 cc / min of TMA is supplied and CP ₂
By increasing Mg to 100 cc, p-type Al _0.16
A Ga _0.84 N cladding layer 18 (0.33 μm) is formed. Subsequently, the supply of TMA was stopped, and the supply amount of CP ₂ Mg was set to 50 cc to form the p-type GaN contact layer 19.

After the formation of the p-type GaN contact layer 19, the supply of the organometallic material is stopped and the nitrogen carrier gas 2
Subsequently, only 0.5 L / min and 9.5 L / min of ammonia were continuously supplied, and the substrate temperature was naturally lowered. However, the supply of ammonia was stopped when the substrate temperature reached 350 ° C.

The wafer prepared by the above method is subjected to MOCV
When taken out of the D apparatus, it was confirmed that a good quality multilayer film for a nitride-based semiconductor laser having excellent flatness and no cracks was obtained.

Next, the laser multilayer film formed by the above-described method is etched by dry etching to form an n-side electrode, exposing the n-type contact layer 13, and made of Ti / Al on the upper portion. An n-side electrode 20 was formed. Further, a p-side electrode 21 was formed on the p-type GaN contact layer 19.

FIG. 2 shows a band diagram of the SCH structure in the element structure of FIG. 1 prepared as described above. As shown in this figure, in the laser multilayer film according to the present embodiment, the number of MQW pairs is as small as 3 pairs in order to reduce the threshold current.
Further, in order to solve the problem of crack generation which becomes a problem due to the reduction in the number of MQW pairs,
InGaN crack prevention and light confinement layer 1 having a band gap between a well layer and a barrier layer in MQW active layer 16
5 are provided.

This n-side crack prevention and light confinement layer 1
5 has a higher refractive index (lower In composition) than the light confinement layer 17 above (p side) the MQW active layer 16,
The light confinement effect is also large. However, if the crack prevention and light confinement layer 15 on the n side has the same thickness as the light confinement layer 17 on the p side, light confinement to the active layer 15 will be biased toward the n side. Therefore, this is prevented by making the thickness of the n-side crack prevention and light confinement layer 15 smaller than that of the p-side light confinement layer 17.

As described above, in the present embodiment, by providing the crack prevention and light confinement layer 15, a laser element which suppresses cracks, has a large light confinement effect, and can reduce the number of MQW pairs is realized. It is possible,
The threshold current density can be greatly reduced.

Next, the IV characteristics of the semiconductor device on which the n-side electrode 20 and the p-side electrode 21 were formed were measured.
Good ohmic contact was obtained. Next, the wafer on which the semiconductor multilayer film having the above-mentioned electrodes was formed was 350 μm × 5
A cavity mirror was formed by cleaving to a size of 00 μm, and a semiconductor laser was fabricated. When a current was injected into this semiconductor laser, continuous oscillation at room temperature continued at a wavelength of 417 nm. The operating voltage of the device was 5.0 V, and the threshold current density was 1.
It was ² kA / cm ² . The element life is 10
It has increased to more than 00 times, and the reliability of the device has been greatly improved.

On the other hand, in order to verify the effect of the present invention,
A laser device having the conventional SCH structure shown in FIG. 3 was also prepared, and its device characteristics were examined and compared with the device according to the present embodiment. In the laser device having the conventional SCH structure shown in FIG. 3, the device portions other than the SCH structure portion, the method of growing the same, and the method of manufacturing the device are the same as those of the laser device according to the embodiment shown in FIG.

1. Reference numerals 31 to 41 in FIG. 3 denote reference numerals 11 to 2 in FIG.
Corresponds to 1. Although the basic configuration is the same as that of FIG. 1, in this reference example, both the optical confinement layers 35 and 37 are G layers.
aN. The number of pairs of the well layer and the barrier layer in the MQW active layer 36 is two, three pairs and ten pairs.

On a sapphire substrate 31, a GaN underlayer 32
After forming a multilayer film for the laser from the P-type GaN contact layer 39 to the p-type GaN contact layer 39 by using the MOCVD apparatus, it was taken out of the reaction furnace. As a result, cracks were extremely found on the growth layer surface of the laser multilayer film having three pairs of MQW structures. Occurred many times. On the other hand, cracks occurred in a part of the wafer on the growth layer surface of the laser multilayer film having the 10 pairs of MQW structure, but it is clear that the density is smaller than that of the 3 pairs.

Next, with respect to the above two samples, a part of the multilayer structure was removed to the n-type GaN contact layer 33 by dry etching, and an n-side electrode 40 made of Ti / AI was formed thereon. Further, a p-side electrode 41 was formed on the p-type GaN contact layer 39.

FIG. 4 shows a band diagram of the SCH structure in the conventional GaN-based blue semiconductor laser fabricated as described above. When the IV characteristics of the semiconductor element were measured, good ohmic contact was obtained.

Next, the semiconductor mirror was formed by cleaving the wafer on which the semiconductor multilayer film having the above-mentioned electrodes was formed into a size of 350 μm × 500 μm to form a resonator mirror. When current was injected into these semiconductor lasers, the following results were obtained. The device having 10 pairs of MQW active layers continuously oscillated at room temperature at a wavelength of 417 nm, and the operating voltage during oscillation was about 5V. However, the threshold current density is 1
As high as 5 kA / cm ² , the device lifetime is as short as less than 30 minutes. In addition, variations in element characteristics within the wafer surface are small.

On the other hand, in a device having three pairs of MQW active layers, many cracks are generated, and there are many cut portions due to cracks in one device during the device fabrication process. And the yield is very low.
However, for about 10% of the devices in the wafer plane, the wavelength 417n
m and continuous oscillation at room temperature, and the operating voltage during oscillation was about 5V. The threshold current density was lower than the device having 10 pairs of MQW active layers, that is, 7 kA / cm ² . The life of the oscillated element was about 30 hours for a long one from 30 seconds.

As described above, in the conventional GaN-based semiconductor laser, the InGaN-based MQW is used to reduce the threshold current.
When the number of pairs of active layers is reduced, cracks occur frequently, and the yield and characteristics of the device are greatly impaired. Further, in the conventional structure, light was not sufficiently confined, so that it was difficult to reduce the threshold value. On the other hand, in the present embodiment, the number of pairs of InGaN-based MQW active layers can be reduced, and the conventional G
By using GaN having a higher refractive index than aN, the effect of confining light was enhanced, and the threshold current was able to be significantly reduced. As a result, the reliability and the yield of the device were greatly improved.

Also, as an unexpected effect, the flatness of the growth layer surface was improved when InGaN according to the present embodiment was used as compared with the case where conventional GaN was used as the n-side optical confinement layer. The roughness of the growth layer surface measured by an atomic force microscope (AFM) is about 100 nm in the conventional structure,
In the growth layer according to the present embodiment, the thickness was about 20 nm. Due to the improvement of the flatness, the yield and reliability in an element process such as electrode formation have been improved. The improvement in the flatness of the surface of the growth layer is, of course, due to the M
The ordering of the QW structure can be improved, adverse effects such as light scattering in the conventional structure can be reduced, and adverse effects on electrical characteristics such as carrier injection and recombination can be excluded.

As described above, according to the present embodiment, it is possible to reduce the threshold current which has been difficult in the GaN-based short wavelength laser. In this material laser, generally MQ
Although an InGaN-based active layer having a W structure is used, when the number of MQW pairs is reduced to reduce the threshold current, cracks occur frequently, and the threshold is reduced and the crack is generated by reducing the number of MQW pairs. (Crack density) had a trade-off relationship. That is, in the structure in which the generation of cracks is suppressed, the threshold current is high, and in the structure in which the threshold current is low, cracks occur frequently, and the yield and reliability of the device are significantly reduced. The present embodiment can solve the above problem, suppress the occurrence of cracks, and at the same time, reduce the number of MQW pairs, and as a result,
The threshold current can be greatly reduced. As a result, the yield, initial characteristics, and reliability of the device are greatly improved.

(Embodiment 2) FIG. 5 is a sectional view of the element structure showing a semiconductor laser according to a second embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, in the device structure of the semiconductor laser similar to that of the first embodiment, an MQW type InGaN
Single quantum well structure (SQW) instead of active layer 16
P-side optical confinement layer 2 using p-type InGaN-based active layer 26
7 is InGa instead of GaN in the first embodiment.
N is used. The structure other than the active layer 26 and the p-side light confinement layer 27 is the same as that of the first embodiment.

In this embodiment, since the active layer 26 is made of SQW, cracks are more likely to occur and light confinement is severer than in the case of the first embodiment. Therefore, in the present embodiment, it is necessary to increase the crack prevention effect and the light confinement effect by using InGaN for the p-side light confinement layer 27 similarly to the n-side light confinement layer. However, the p-side InGaN optical confinement layer 27 is also provided for the reason described in the section (Means for solving the problem).
If the In composition is too high, the device characteristics deteriorate. In this embodiment, the p-side optical confinement layer 27 has a thickness of 0.2 μm
_0.03 Ga _0.97 N was used.

The surface flatness of the laser multilayer film formed under the same growth conditions as in the first embodiment is extremely good.
Measurement showed that the roughness was about 10 nm. Next, the same process as that of the first embodiment was applied to the above-described laser multilayer film to form an n-side electrode 20 and a p-side electrode 21. After measuring the IV characteristics, a good ohmic contact was obtained. Was done.

Next, the wafer on which the above-mentioned electrodes are formed is moved to 35
A cavity was formed by cleaving to a size of 0 μm × 500 μm, and a semiconductor laser was fabricated. When a current was injected into this semiconductor laser, continuous oscillation at room temperature continued at a wavelength of 417 nm. The operating voltage of the device was 4.8 V, and the threshold current density was 1 kA / cm ² . In addition, the life of the device was increased to 1000 times or more as compared with the conventional device, and the reliability of the device was greatly improved.

When an InGaN-based active layer having the SQW structure is used, cracks occur frequently in the conventional structure, making it difficult to fabricate the device. However, in the laser device fabricated in this embodiment, the n-side and p-side Is provided with an InGaN light confinement layer, crack generation is suppressed, and at the same time, the light confinement effect is increased, and the threshold current can be significantly reduced. As a result, the yield and reliability of the device are significantly reduced. Improved.

(Third Embodiment) In the present embodiment, the element structure is designed to prevent carrier overflow in the active layer, and the number of MQW wells is reduced.
An example for providing a nitride-based low-threshold semiconductor laser that can enhance the light confinement effect and suppress the occurrence of cracks will be described.

In the nitride semiconductor laser, the overflow of electrons in the active layer poses a problem. In order to further increase the recombination probability of electrons and holes, it is necessary to suppress the overflow of electrons. In the present embodiment, in order to suppress the overflow of electrons, high Al is deposited on the InGaN-based MQW active layer.
GaAlN layer of composition (Al composition 20%, film thickness 5n
m) and no p-side light confinement layer is provided.

FIG. 6 shows a cross section of the device structure of the nitride semiconductor laser according to the present embodiment, and the layer structure will be briefly described below. The growth was performed by the MOCVD method. A GaN buffer layer 82a and an undoped Ga
N underlayer 82, n-type GaN contact layer 83, n-type Ga
_0.84 Al _0.16 N current injection layer (0.3 μm) 91, undoped In _0.05 Ga _0.95 N light confinement layer (0.3 μm) 9
2. Undoped InGaN-based MQW active layer (4 pairs) 93
Are sequentially formed, and a Ga _0.8 Al _0.2 N layer (5 nm) 94 is formed thereon as a carrier overflow prevention layer.
On top of that, a p-type Ga _0.93 Al _0.07 N current injection layer (0.4
μm) 95, a p-type GaN current injection layer 85, and an n-type GaN current confinement layer 86 are sequentially formed.

Next, the n-type GaN current confinement layer 86 is partially patterned, and the p-type GaN current injection layer 85 is exposed to the outermost surface by etching or the like. Then, p-type Ga
On the N current injection layer 85 and the n-type GaN current confinement layer 86, a p-type GaN contact layer 87 is formed again by the MOCVD method.

Next, etching is performed partially to the p-type GaN contact layer 83 by masking with SiO ₂ or the like, an n-side electrode 96 is formed on the exposed contact layer 83, and a p-type GaN contact layer 87 is formed on the p-type GaN contact layer 87. The side electrode 97 is formed.

The semiconductor laser thus produced is
It oscillated at a low threshold of 910 A / cm ² at an oscillation wavelength of 410 nm. By using InGaN for the n-side light confinement layer as in the present embodiment, it is possible to suppress the occurrence of cracks and at the same time improve the light confinement effect.
The overflow of electrons to the p-side, which is a problem in the nitride-based semiconductor laser, is caused by the high Al composition GaAl
This can be suppressed by inserting the N layer. Therefore, in the case of the structure as in the present embodiment, it is not always necessary to provide the p-side light confinement layer. However, if the crack generation suppressing effect or the light confinement effect is insufficient due to the structure, in FIG.
A GaAlN carrier overflow prevention layer (5 nm) 94 is formed on the InGaN-based MQW active layer 93, a p-side optical confinement layer is further provided thereon, and a p-type GaAlN current injection layer 95 similar to that of the present embodiment is formed thereon. It may be a structure to be formed.

(Embodiment 4) FIG. 7 is a sectional view showing an element structure of a semiconductor laser according to a fourth embodiment of the present invention.

In this embodiment, an n-type GaN contact layer 53 is formed on a sapphire substrate 51 via a buffer layer 52, and an n-type AlGaN cladding layer (Al composition: 0.32) 54 is formed on the contact layer 53. GaN optical confinement layer 55, InGa of first multiple quantum well structure (MQW)
An N-based active layer 56 is formed sequentially. Here, the active layer 56
Has a two-pair MQW structure in which an InGaN well layer and a GaN barrier layer having an In composition of 20% are combined.

On the first MQW active layer 56, a thickness of 40 n
m InGaN-based crack prevention layer (In composition: 7%) 5
7 was formed. Further, an InGaN-based active layer 58 having a second MQW structure having the same structure as the active layer 56 having the first MQW structure was formed thereon. Further, a p-type GaN light confinement layer 59 and a p-type AlGaN
A cladding layer (Al composition: 0.32) 60 is sequentially formed,
The layers from the n-type AlGaN cladding layer 54 to the p-type AlGaN cladding layer 60 were formed in a mesa stripe shape as shown in FIG.

On the side of the mesa stripe, an i-type GaN layer 61 is embedded, and a p-type AlGaN cladding layer 60 and an i-type GaN layer 61 are formed.
On the p-type GaN layer 61, a p-type GaN contact layer 62 was formed. That is, a double hetero structure having a buried mesa structure was formed, and a contact layer with the p-side electrode was further formed thereon. A high-resistance GaN layer was used for embedding.

The semiconductor laser according to this embodiment is manufactured by the MOCVD method as in the first embodiment. There is no crack in the laser wafer created in this way,
Good crystals were obtained.

FIG. 8 shows a band diagram in the vicinity of the active layer of the laser multilayer film formed as described above. Crack preventing layer 57 inserted between first active layer 56 and second active layer 58
Is smaller than that of the optical confinement layers 55 and 59 and larger than that of the first and second active layers 56 and 58. More specifically, the band gap of the crack prevention layer 57 is larger than that of the MQW well layers constituting the active layers 56 and 58, and smaller than that of the barrier layers. Note that only one of the two active layers 56 and 58 may have an MQW configuration, and the other may have a normal undoped active layer or SQW configuration.

Next, on the n-type GaN contact layer 53, T
An n-side electrode 63 made of i / Au was formed. p-type GaN
A p-side electrode 64 was formed on the contact layer 62. Subsequently, the laser structure was cleaved from the substrate side using a scriber or the like, and a resonator mirror was formed.

The semiconductor laser thus produced oscillated continuously at a wavelength of 420 nm. The operating voltage of this element was 4.2 V, and the threshold current density was 1 kA / cm ² . Further, there was almost no variation in device characteristics in the prepared laser wafer, and the device life was extended to about 1000 times that of the conventional device, and the reliability was greatly improved.

The present invention is not limited to the above embodiments. The substrate for growing the semiconductor layer is not limited to sapphire, and GaN, SiC, Si or the like can be used. Further, in the embodiment, the structure in which the n layer in the pn structure is provided on the substrate side with respect to the active layer and the p layer is provided on the opposite side (upper part) is described as an example, but the p layer is provided on the substrate side and the upper part of the growth layer is provided. Alternatively, a structure in which an n-layer is formed on the substrate may be used.

Further, in the embodiment, the example of the GaN-based semiconductor laser has been described. However, the present invention is not limited to the semiconductor laser but can be applied to a light emitting diode (LED). Further, Ga
The present invention is not limited to N-based materials, and can be applied to light-emitting elements using nitride-based semiconductors. In addition, various modifications can be made without departing from the scope of the present invention.

[0067]

As described in detail above, according to the present invention, S
In a nitride-based semiconductor light emitting device having a CH structure,
By forming the light confinement layer on the side of InGaN or the like having a refractive index larger than that of GaN or the like as the contact layer, it is possible to simultaneously reduce the threshold current and suppress cracks, and the total Device characteristics can be improved. As a result, the yield, initial characteristics, and reliability of the device are greatly improved.

[Brief description of the drawings]

FIG. 1 is an element structure cross-sectional view showing a nitride-based semiconductor laser having an SCH structure according to a first embodiment.

FIG. 2 is a band diagram of an SCH structure in the element structure of FIG.

FIG. 3 is an element structure sectional view showing a conventional nitride-based semiconductor laser having an SCH structure shown for comparison in the first embodiment.

FIG. 4 is a band diagram of an SCH structure in the conventional nitride semiconductor laser of FIG. 5;

FIG. 5 is an element structure sectional view showing a semiconductor laser according to a second embodiment.

FIG. 6 is a sectional view of an element structure showing a semiconductor laser according to a third embodiment.

FIG. 7 is an element structure sectional view showing a semiconductor laser according to a fourth embodiment.

FIG. 8 is a band diagram near an active layer in the structure of FIG. 7;

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 sapphire substrate 12 undoped GaN underlayer 13 n-type GaN contact layer 14 n-type AlGaN cladding layer 15 n-side InGaN light confinement layer and anti-crack layer 16 MQW InGaN-based active layer 17 p-side GaN light Confinement layer 18 p-type AlGaN cladding layer 19 p-type GaN contact layer 20 n-side electrode 21 p-side electrode

Claims (4)

[Claims] An isolated confinement in which a plurality of nitride-based semiconductor layers are laminated on a substrate, an active layer is sandwiched between a pair of optical confinement layers, and the outside thereof is sandwiched between a pair of p-type and n-type cladding layers. A nitride-based semiconductor light-emitting device having a heterostructure and having p-type and n-type contact layers outside thereof, wherein the refractive index of a p-side light confinement layer of the pair of light confinement layers is A nitride-based semiconductor light-emitting device characterized by being equal to or larger than that of a contact layer and having a refractive index of an n-side light confinement layer larger than that of a p-side light confinement layer. 2. An active layer made of a nitride-based semiconductor is sandwiched between a pair of optical confinement layers made of a nitride-based semiconductor having a larger band gap than the active layer, and the outside of the pair is made of Al having a larger band gap than the optical confinement layer. Having a separate confinement heterostructure sandwiched between a pair of p-type and n-type cladding layers made of a nitride-based semiconductor including, and a p-type and a nitride-based semiconductor having a band gap smaller than that of the cladding layer on the outside thereof. A nitride-based semiconductor light emitting device having an n-type contact layer, wherein, of the pair of light confinement layers, an n-side light confinement layer has a larger refractive index than the contact layer, and a p-side light confinement layer has A nitride-based semiconductor light-emitting device having a lower refractive index than the n-side light confinement layer and a refractive index equal to or higher than that of the contact layer. Wherein each said cladding layer is _{Al z Ga 1-z N (} 0
<Z ≦ 1), each of the contact layers is formed of GaN, and the n-side optical confinement layer is In _x Ga ₁ -xN.
It is formed by (0 <x ≦ 1), an optical confinement layer of the p-side _{In y Ga 1-y N (} 0 ≦ y <x) of claim 1 or 2, wherein the are formed of Nitride based semiconductor light emitting device. 4. A semiconductor device comprising: a plurality of nitride-based semiconductor layers laminated on a substrate; an active layer sandwiched between a pair of optical confinement layers having a larger band gap than the active layer; What is claimed is: 1. A nitride semiconductor light emitting device having a separated confinement heterostructure sandwiched between a pair of p-type and n-type cladding layers having a large band gap, wherein said active layer is separated into a first active layer and a second active layer. A crack preventing layer having a smaller band gap than the light confinement layer and a larger band gap than the first and second active layers is provided between the first active layer and the second active layer. A nitride-based semiconductor light-emitting device.