JP2003078214A - Nitride semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor light emitting device which is markedly improved in device life when it operates at high temperatures while outputting a high power and furthermore improved in long-term service life. SOLUTION: A nitride semiconductor light emitting device is equipped with an active layer 110 of quantum well structure composed of laminated well layers and barrier layers. The active layer 110 is equipped with a high- dislocation density region 116 and a low-dislocation density region 104 which are different from one another in dislocation density. The low-dislocation density region 104 is lower in dislocation density than the high-dislocation density region 116. Furthermore, at least a current injection region is provided to a part of the low-dislocation density region 104, and the impurity concentration of the active layer is below 1018 cm<-3> .

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] The present invention relates to a blue-violet semiconductor laser.
The present invention relates to a nitride semiconductor light emitting device such as a semiconductor device. [0002] 2. Description of the Related Art A nitride semiconductor is a material for a blue-violet laser device.
Is very promising, and Nakamura et al.
ys. vol. 36 (1997), pp. L1568-1571
As mentioned above, at room temperature, 2mW output for more than 10,000 hours
The oscillation lifetime has been reported. FIG. 4 shows the cross-sectional structure of the laser.
The drawing is shown. Generally, to extend the life of the laser element
It is essential to reduce the dislocation density for
In a laser device, a GaN film on a sapphire substrate 101
A stripe-shaped SiO2 film (mask) 103 is formed on
Selective growth by forming and growing GaN on it
To form GaN with low dislocation density grown laterally on the mask.
And a p-electrode 105 is formed on the low dislocation density region 104.
A laser element is manufactured to be formed. Made by the above method by Nakamura et al.
GaN substrate is ELOG (Epitaxial Lateral Overgrowth GaN)
The part without the SiO2 mask called the substrate (window area)
Above the GaN film on the sapphire substrate
Position is taken over as it is and the film grows,
(Ten¹²m^-2Above) Dislocation density, but SiO2 mask
Mask disturbs the propagation of dislocations above
Low (10¹¹m^-2Less) dislocation density is realized.
However, near the center of the SiO2 mask, the window
Dislocations are newly generated because GaN that has grown in
It has a high dislocation density. Then, the low dislocation region (the center on the SiO2 mask)
Part away from: Areas without dot pattern in the figure
Area) 104 so that the p-electrode 105 is formed
When a laser element is fabricated, the low dislocation density region in the active layer is charged.
Current is injected into the device, causing the degradation of the device due to the dislocation.
It is considered that the element life becomes longer and the life of the element becomes longer. The laser device shown in FIG. 4 is a Si-doped n-type GaN-ELO
On a G substrate 106, an Si-doped n-type In0.1Ga0.9N layer 107, 12
Zero-period Si-doped n-type GaN layer (2.5 nm thick) and undoped Al
N-type cladding layer 1 consisting of 0.14Ga0.86N layer (2.5nm thickness)
08, n-type photo-closed made of Si-doped n-type GaN (0.1 μm thick)
Confinement layer 109, Si-doped n-type In0.15Ga0.85N quantum well layer
(3.5 nm thick) and Si-doped n-type In0.02Ga0.98N barrier layer (thick
Multi-quantum well active layer 210 made of Mg
P-type Al0.2Ga0.8N cap layer (thickness: 20 nm) 111, Mg
P-type optical confinement layer 1 made of low-p-type GaN (0.1 μm thick)
12,120 cycles of Mg-doped p-type GaN layer (2.5 nm thick)
A p-type clad consisting of a doped Al0.14Ga0.86N layer (2.5 nm thick)
Layer 113, made of Mg-doped p-type GaN (0.05 μm thick).
After the p-type contact layer 114 is sequentially grown,
The ridge structure as shown in Fig. 4 is formed by etching etc.
And finally a p-electrode 105 composed of Ni and Au, and Ti and Al
N electrode 115 formed by evaporation. In addition to the above-described method using a mask, dislocation density
Nakamura et al. Applied applied physics
As described in Vol. 68, No. 7, pp. 793-796,
Dry etching of GaN film on fire substrate and stripe
Leaving a GaN film in the shape of
To form a flat film using lateral growth
There is also "Screth ELOG"). In this way, the remaining
Threading dislocations of GaN film are inherited on top of tripe GaN
GaN is etched by sapphire
The dislocation density is low above the region where is exposed. And this
Forming a laser device in the low dislocation density region
A long element life is obtained. On the other hand, the inventors have disclosed Jpn. J. Appl. Phys.
l. 36 (1997), pp. L899-902 or NEC Research and
 Development vol.41 (2000) No.1 pp.74-85
FIELO (Facet-Initiated Epitaxial Lateral
Substrate or activity by a method called Overgrowth)
Successfully reducing the dislocation density over the entire layer
You. In FIELO, on the sapphire substrate like ELOG
Of SiO2 film (mask) in stripes on GaN film
Selective growth by hydride vapor phase epitaxy
Can be used to bend threading dislocations, like ELOG
No regions with high dislocation density occur in the
The density can be reduced. As described above, GaN with low dislocation density is produced.
With the development of manufacturing technology, the wavelength range of about 400-450nm
Life of blue-violet nitride semiconductor laser oscillating at high speed
Has been improved. On the other hand, lasers such as threshold current density
As a technology to improve the device characteristics itself,
The addition of a pure substance is mentioned. Nagahama et al., JP 10-12969
As described in the report, Si impurities (or
10 other impurities such as Mg)¹⁹-Ten^{twenty one}cm^-3At a concentration of
This improves the laser threshold. Chichibu et al., Applied Physics Letter 73 (1
998), pp. 496-498. And Proc. Of the 2nd Int. Symp. On B
lue Laser and Light Emitting Diodes, (1998), p.38
In 1, the threshold by adding Si impurity to the active layer
It describes the mechanism of value reduction, and
Electric field shielding effect and flatness improvement of the quantum well structure.
He mentioned several possibilities. As described above,
The mechanism of laser characteristics improvement by
Although not always the case, the laser characteristics were improved by adding this impurity.
Good is widely recognized in the industry, and recently produced nitrogen
Addition of Si impurity to active layer in nitride semiconductor laser
Is common sense. [0010] SUMMARY OF THE INVENTION
Application point of view for conventional nitride semiconductor laser devices
Says that sufficient device reliability has been achieved
No. Nitride semiconductor oscillating in the wavelength range of 400-450nm
In order to use a laser for an optical disc such as a DVD,
In addition, when taking into account the
A device life of at least 00 hours is required. Nevertheless
Nakamura et al., JSAP International No.1 pp.5-17 (2000)
So far, at 60 ° C,
Also achieves a device life of only 500 hours at 30mW output.
Absent. The present invention has been made in view of the aforementioned problems.
Dramatically improved device life at high temperature and high output operation
And a longer device life.
It is an object to provide a compound semiconductor light emitting device. [0012] SUMMARY OF THE INVENTION The present inventors have developed a nitride
As a result of conducting research on semiconductor laser manufacturing technology,
For nitride semiconductor laser device fabricated on FIELO-GaN substrate
Low threshold without adding impurities to the active layer
And the life of those devices
There was also a sign that it was long. The present inventors have proposed a pellet (one chip).
Dislocation density distribution of the active layer
Further study the relationship between the pure substance concentration, the threshold value of the laser
In order to investigate in detail, the same
The laser structure is grown by time growth, and the laser element is fabricated.
Was. Then, the concentration of Si impurities added to the active layer quantum well is
About undoped, 1 × 10¹⁸cm^-3, 5 × 10¹⁸cm^-3Three kinds
Was made. The structure of the laser device is described in the first embodiment described later.
This is the same as that described in the embodiment. ELOG base used here
For the board, a SiO2 mask with a mask width of 20 μm and a window of 5 μm
ELOG (mask)
(The width is usually about 10 μm or less). This
When the mask width is wide, the lateral growth is
Since a mask must be embedded, create a flat film.
Area that is not easy to manufacture but has low dislocation density
Area can be increased. Here, buried flat
Growth conditions (flow ratio of group III raw material to group V raw material)
ELOG with wider mask width than before
Was realized. Table 1 shows several lasers produced from these.
Average of initial threshold current density of device and 10 at 70 ° C and 30mW
This shows the state of element deterioration after APC operation for 0 hours. [Table 1] The initial threshold current density is large in the six kinds of samples.
No difference is seen, and the undoped and 1 ×
Ten¹⁸cm^-3Doping tends to lower the threshold slightly
ing. That is, when the Si impurity concentration is 10¹⁹cm^-3Up to the level
Not reached, but the threshold value largely depends on the Si impurity concentration
No, and at least on FIELO
Although there is a possibility of the range of the key, but do not add Si impurities
Tended to lower the threshold. And the element
5 × 10 on ELOG¹⁸cm^-3Doping
A slight voltage increase (deterioration) was observed only in the device. From the above experimental results, it can be seen that high-temperature, high-power operation
Deterioration of the device caused by the existence of a high dislocation density region and the Si impurity concentration
Both degrees are thought to be involved. That is, the substrate
Element on FIELO where dislocation density is reduced over the entire surface
Is less likely to occur in the device, but the current injection area is low
High dislocation density region exists in the pellet even in the dislocation density region
Degradation is likely to occur in the case of existing ELOG elements
Can be Furthermore, a high dislocation density region exists in the pellet.
The concentration of impurities added to the active layer
When the value is small, it is considered that deterioration hardly occurs. The mechanism of these phenomena is presumed as follows.
Measured. In high-temperature, high-power operation, the device has a large current
Flow, generate a large amount of heat, and generate a high intensity of light. this
Due to the energy of heat and light,
The active layer region (where the current is flowing)
Minutes), there is a possibility that the element may be degraded
Can be The presence or absence of impurity addition to the active layer depends on the dislocation.
The reason for affecting growth and exercise is that
Therefore, local strain was introduced into the crystal, and the dislocation grew.
Laser light absorption due to the effect of easy movement and impurity levels
It is considered that the heat generated by heat promotes dislocation growth and movement.
available. In order to prevent such deterioration of the element,
It is most desirable to reduce the dislocation density in all regions.
No. If a FIELO substrate is used, all areas within the substrate surface are low.
Although the dislocation density will occur, MOV
Use not only PE growth equipment but also hydride VPE growth equipment
Needs to be considered, and the cost is high at present. future,
If the mass production of FIELO substrates becomes possible, this cost
Is expected to be resolved, but at present, ELOG and
Use of GaN substrate by screen ELOG is more cost effective
It is advantageous. Uses GaN substrate by ELOG or maskless ELOG
The operating life of high-temperature, high-output laser devices
To do this, the following two methods can be considered. One is EL
SiO2 mask width for OG production or maskless ELOG production
Sapphire exposed area is made sufficiently wide to achieve high dislocation density
This is a method to reduce the influence of the area. The other is the active layer
Lower impurity concentration to lower dislocation density from high dislocation density region
This is a method of suppressing the growth and movement of dislocations into the region. In the former method, it is necessary to embed by lateral growth.
Area required for embedding.
Long time is long and it is difficult to produce a flat film
It becomes difficult. However, growth conditions for easy lateral growth
(Eg, TMG flow rate should be 1μmol or less per minute)
30μm mask width (or sapphire exposure area
Area can be buried with a flat film. In the latter method, the threshold is better when the Si impurity is added.
Nitride semiconductor laser with low current density
Although it is in a direction contrary to common sense of the element, as described above,
It depends on the Si impurity concentration at least in the range where the inventors experimented.
No significant change in the threshold current density was observed. This is FI
Inventors made it so that the result on the ELO board tells the story
Active layer (current injection region) has low dislocation density and few defects
I speculate that nothing is relevant. In the dislocation, the carrier is not released through the dislocation core.
Radiation recombination is thought to occur, but to reduce this
Increase impurity concentration in active layer to shorten carrier diffusion length
By doing so, the flow of carriers into the dislocation core can be suppressed.
It is considered effective. However, on the other hand, when the impurity concentration is 10¹⁹cm
^-3Above, non-radiative recombination called Auger recombination
It has been reported that many semiconductors have become popular. Conventionally, it was necessary to increase the impurity concentration.
Has a high dislocation density in the active layer,
It is thought that this was to prevent binding. On the other hand, dislocation density
Laser to inject current into the region where
Reduces Auger recombination over non-radiative recombination at dislocation cores
The experimental results show that it is important to
available. The active layer is not a quantum well structure but has a thickness
In the case of a single layer film of 10 nm or more, the Si impurity concentration should be 10¹⁸cm^-3Yo
Even if it is smaller, the life extension is as large as that of the quantum well structure.
Not noticeable. However, even if the active layer is an InGaN single layer
Even if a film is used, the effect of the quantum well structure (state density
The optical gain increases due to the sharp rise,
The active layer thickness is 10
In the case of less than nm (single quantum well structure), the impurity concentration is 10
¹⁸cm^-3If it is made smaller, as in the case of the quantum well active layer,
The life extension was remarkable. [0026] Longer life effect with single layer active layer of thickness 10nm or more
One of the reasons that the results are not significant is that thick active layers
When the concentration of pure substance is reduced, its series resistance increases and the calorific value increases.
Dislocation multiplication and migration even with a small amount of impurity added.
It is conceivable that the movement easily occurs. Also, departure
Large impurity concentration in the case of quantum well structure separately from the calorific value
The reason why the life is shortened is that in the case of a thick monolayer active layer
The proportion of the interface in the active layer volume is significantly increased compared to
In addition, segregation of impurities at these interfaces occurs, and interface recombination occurs.
Not only increase the speed, but also increase the dislocation
It is thought to be to increase. Accordingly, the present invention has been made based on the above findings.
Technology to solve the above-mentioned problems, the following configuration
Adopted. That is, in the nitride semiconductor light emitting device of the present invention,
Has a quantum well structure in which a well layer and a barrier layer are laminated.
A nitride semiconductor light emitting device having an active layer,
The dislocation layer has a high dislocation density region and a low dislocation density
And the low dislocation density region includes the high dislocation density region.
Dislocation density lower than dislocation density region and at least partially
A current injection region is formed, and the active layer has an impurity concentration of 10
¹⁸cm^-3Less than. In this nitride semiconductor light emitting device, low dislocation density
Current injection region is formed in at least a part of the
Impurity concentration of active layer of child well structure is 10¹⁸cm^-3Is less than
Because the impurity concentration in the active layer is low, Auger recombination
Is reduced, and from the high dislocation density region to the low dislocation density region.
The propagation and migration of dislocations into the current injection region in the region
, Dramatically extending device life at high temperature and high output operation
can do. Also, the nitride semiconductor light emitting device of the present invention
The low dislocation density region is the dislocation density of the high dislocation density region.
This is suitable when the dislocation density is 1/10 or less. Ma
Further, the nitride semiconductor light emitting device of the present invention is characterized in that the current injection region
The average dislocation density in the region is 10% of the average dislocation density in the entire active layer region.
It is suitable when it is less than one-half. Further, the nitride semiconductor light emitting device of the present invention
Indicates that the high dislocation density region has at least a portion of the dislocation density.
Is 10¹²m^-2And the current injection in the low dislocation density region
The average dislocation density in the region is 10¹¹m^-2Suitable when less than
It is. Further, the nitride semiconductor light emitting device of the present invention,
The active layer has an average dislocation density of 10¹²m^-2Is over
And the average displacement of the current injection region in the low dislocation density region.
Phase density is 10¹¹m^-2It is suitable when it is less than. In these nitride semiconductor light emitting devices, a small number
At least the dislocation density in the region where current is injected in the active layer
Degree is 1/10 or less of the high dislocation density region in other regions.
The active layer has an impurity concentration of 10¹⁸cm^-3By being less than
Effect (suppression of dislocation migration / proliferation from the high dislocation density region)
Remarkably). Also, the nitride semiconductor light emitting device of the present invention
The active layer has an average dislocation density of 10 in the current injection region.¹¹
m^-2Less than 5 μm from the current injection area.
Region average dislocation density is 10¹²m^-2It is suitable when it is above
You. Further, the nitride semiconductor light emitting device of the present invention is characterized in that
A current injection electrode is formed on the layer via another semiconductor layer.
And the active layer is formed in a flat area in a region immediately below the current injection electrode.
Average dislocation density of 10¹¹m^-2And less than 5 from the area
The average dislocation density in the region within μm is 10¹²m^-2If more than
It is suitable for. Also, the nitride semiconductor light emitting device of the present invention
The active layer has an average dislocation density in the current injection region,
10 min of the average dislocation density in the region within 5 μm from the implantation region
It is suitable when it is 1 or less. The nitride of the present invention
The semiconductor light emitting device may include another semiconductor layer on the active layer.
A current injection electrode is formed through the active layer, and the active layer
The average dislocation density in the region directly below the flow injection electrode is
1/10 or less of the average dislocation density in the area within 5 μm
It is suitable for the case. In these nitride semiconductor light emitting devices, the current
Region having a dislocation density 10 times or more than the region where
Area is within 5 μm of the area where the current is injected.
In this case, the impurity concentration of the active layer is 10¹⁸cm^-3Less than
Effect (movement of dislocations from the high dislocation density region
Inhibition of proliferation) is particularly remarkably obtained. Also, the nitride semiconductor light emitting device of the present invention
The nitride semiconductor was patterned on the exposed substrate surface
Made by selectively growing nitride after forming mask material
Preferably. In other words, this nitride semiconductor
Optical devices are manufactured on so-called ELOG substrates, so
Can be manufactured at low cost compared to loose FIELO substrates
You. Also, the nitride semiconductor light emitting device of the present invention
The substrate surface on which the nitride semiconductor layer is formed is etched.
Nitride after partially removing the nitride semiconductor layer
It is preferable that the substrate be made by growing an object. That is,
In this nitride semiconductor light emitting device, a so-called maskless EL
Since it is manufactured on an OG substrate, it is
It can be manufactured at low cost. The nitride semiconductor light emitting device of the present invention has a well layer
And an active layer having a quantum well structure
Nitride semiconductor light emitting device, wherein the nitride semiconductor is exposed.
Form a patterned mask material on the exposed substrate surface
After the selective growth of nitride, the mask
The material is patterned with a mask width of 25 μm or more
It is characterized by the following. In this nitride semiconductor light emitting device,
When manufacturing on a so-called ELOG substrate, the mask material
Is patterned with a mask width of 25 μm or more,
Wide enough low dislocation density for high reliability at high temperature and high output
Degree region is secured, and the influence from the high dislocation density region is large.
Be suppressed. The nitride semiconductor light emitting device of the present invention has a well layer
And an active layer having a quantum well structure
Nitride semiconductor light emitting device, wherein the nitride semiconductor layer is
Process the formed substrate surface by etching and partially
After removing the nitride semiconductor layer, the nitride
And the processing by the etching has a width of 25 μm or more.
It is characterized in that it is applied to the area. This nitride semiconductor
In the case of body light emitting devices, they are fabricated on so-called maskless ELOG substrates.
Processing by etching is more than 25μm width
High reliability with high temperature and high output because it is applied to the upper area
A low dislocation density region wide enough to obtain
The influence from the potential density region is greatly suppressed. The nitride semiconductor light emitting device of the present invention
Preferably, the impurity added to the active layer is Si.
No. [0040] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described.
And will be described with reference to FIG. Figure 1 shows the first implementation
FIG. 3 is a cross-sectional structural view of a nitride semiconductor laser device according to an embodiment.
You. The semiconductor laser device of the first embodiment
The structure will be described together with its manufacturing steps. First, sapphire
A GaN film 102 is grown on a substrate 101 by MOCVD.
Then, on the GaN film 102, a stripe-shaped SiO2 film (ma
Mask) 103 is formed in the [1, -1,0,0] direction, and Si is
Selective growth by MOCVD growth of doped n-type GaN
To form GaN with low dislocation density grown laterally on the mask.
Then, an n-type GaN-ELOG substrate 106 is manufactured. At this time,
For comparison, a substrate having a SiO2 film mask width of 10 μm and
Both substrates having a mask width of 25 μm were prepared. Further on this substrate, Si-doped n
Type In0.1Ga0.9N layer 107, Si-doped n-type GaN layer with 120 periods
(2.5nm thick) and undoped Al0.14Ga0.86N layer (2.5n thick)
m), an n-type clad layer 108 composed of
N-type optical confinement layer 109 of 0.1 μm)
In0.15Ga0.85N quantum well layer (3.5nm thick) and undoped
Multiquantum composed of In0.02Ga0.98N barrier layer (10.5nm thickness)
Well active layer 110, Mg-doped p-type Al0.2Ga0.8N cap layer
(Thickness 20nm) 111, Mg-doped p-type GaN (0.1μm thickness)
P-type optical confinement layer 112 composed of 120 periods of Mg-doped p-type
GaN layer (2.5nm thickness) and undoped Al0.14Ga0.86N layer (thickness
2.5 nm) p-type cladding layer 113, Mg-doped p-type
P-type contact layer 114 made of GaN (0.05 μm thick)
After growing in order, dry etching etc.
Form ridge structure as shown, and finally consist of Ni and Au
A p-electrode 105 and an n-electrode 115 made of Ti and Al are deposited by evaporation.
Thus, the semiconductor laser device shown in FIG. 1 is manufactured. For comparison, the barrier layer of the active layer and
1 × 10 Si impurity in quantum well layer¹⁸cm^{- Three}Laser element added
5 × 10 Si impurities in element and active layer¹⁸cm^-3Laser added
An element was also manufactured. For these laser elements, transmitted electrons
Observation of dislocations with a microscope showed that all elements
On the other hand, the above-described high dislocation density region 116 and low dislocation density region 1
04 was clearly observed, and the dislocation density was high.
5 × 10 in area 116¹²m^-2Degree, 2 in low dislocation density region 104
× 10^Tenm^-2It was about. Thus, in this embodiment,
Means that the high dislocation density region 116 and the low dislocation density region 104
It is formed in the direction of the active layer and has a dislocation density in the plane of the active layer.
It has changed significantly. The dislocation density was measured by a transmission electron microscope.
It can be checked by inspection, but more easily the etch pit
You can also check by density. In nitride semiconductors, phosphoric acid
Heat the mixture of sulfuric acid and sulfuric acid to about 200 ° C,
Etch pits are formed by soaking
You. Basically, the etch pit is where the dislocation exists
As a result, the etch pit density is almost equivalent to the dislocation density.
Respond. When the dislocation (etch pit) density is low
Must count the number of dislocations (etch pits) in a large area
Accurate density measurement is not possible. For example, dislocation density 10
¹¹m^-2At least 10 if the degree^-Tenm^TwoIn the area of about
Measurement is required. This area corresponds to a 10 μm square
However, the film grown on the ELOG substrate turns in the direction perpendicular to the stripe.
The measurement is "stripe"
100μm in direction × 1μm in direction perpendicular to the stripe
Must be done in the area. Different SiO2 mask width or Si impurity concentration
The initial threshold current densities for these six devices and 70
Table 2 shows the state of device deterioration after 100 hours of APC operation at 30mW and 30mW.
Shown in [Table 2] The initial threshold current density is almost the same for the six elements.
Although there is no difference, the deterioration of the device
Is 10 μm, and 5 × 10¹⁸cm^-3
Significant deterioration was seen in the element added, 100 hours
Oscillation stopped before the end of operation. The other five
No deterioration was observed for the sample. Ma
In addition, the deteriorated element was examined with a transmission electron microscope.
Observation of dislocations revealed that the dislocation density ranged from high to low.
It was observed that the dislocation migrated to the region and proliferated. In this sample, the high dislocation density region is
Before the operation test, about 3 μm from the active layer area where current is injected
Although it was far away, the high dislocation density region
It has advanced to the active layer (current injection region). to this
On the other hand, in a device in which an impurity is not added to the active layer, dislocations
Was in the same condition as before the operation test. Ma
Also, the SiO2 mask width is 25 μm, and the active layer has no Si
5 × 10 pure¹⁸cm^-3High dislocation density
Dislocations move from the degree region 116 to the low dislocation density region 104
Proliferation was observed, but high dislocation density regions 116
Advance is limited to a distance of about 5 μm and the active layer (current
Injection region). As described above, in this embodiment, the high dislocation density
The region 116 is within 5 μm from the active layer (current injection region)
Impurity concentration is low even if it exists near
I (10¹⁸cm^-3Less), the effect is remarkably obtained,
Dislocation movement and proliferation can be suppressed. In addition,
Do not add Si impurity to active layer
Or make the SiO2 mask width sufficiently wide (2
5 μm or more), the low dislocations from the high dislocation density region 116
The movement and proliferation of dislocations to the density region 104 are suppressed,
・ Dramatic improvement in laser element life at high output. Note that the element longevity effect in this embodiment is
In order to show the high dislocation density region and low dislocation density
In which the dislocation density in various regions is varied.
A device degradation test was performed for each of them at high temperature and high output operation.
Was. The dislocation density depends on the growth conditions for selective growth.
And can be controlled to some extent. As a result, in this embodiment, the high dislocation density region
Of the dislocation density between the region and the low dislocation density region
By adding no Si impurity
A prolonged life phenomenon occurs remarkably and deterioration of the element is suppressed.
And was confirmed. Movement / increase of dislocations from high dislocation density region
Considering that the device has deteriorated due to
Spatial distribution of dislocation densities (eg, dislocations in the plane of the active layer)
If the change in density is not very large, the effect is small.
This result should be taken for granted, and the dislocation density is actually
Do not add impurities in a laser element that is uniformly uniform
No effect of extending the life was observed at all. Further, the impurity addition to the active layer described here
Means either the quantum well layer or the barrier layer, or both
Refers to the addition of impurities to the active layer.
Layer is undoped or the amount of Si impurity added
To 10¹⁸cm^-3The length of the element only by making it smaller
Life extension is realized. Further, the active layer is made of InGa instead of a quantum well structure.
As a result of conducting an experiment using an N monolayer film,
If the thickness is 10 nm or more, the Si impurity concentration should be 10¹⁸cm^-3Than
Even if it is small, the life extension is not as pronounced as in the quantum well structure.
It was not written. However, even if the active layer is an InGaN single layer film
Active layer thickness that shows the effect as quantum well structure
Is less than 10 nm (single quantum well structure)
Degree 10¹⁸cm^-3If it is smaller, the case of the quantum well active layer and
Similarly, the prolongation of the service life was remarkable. As described above, an InGaN single-layer film having a thickness of 10 nm or more
One of the reasons why the effect of extending the life in the active layer is not remarkable
Is because a large amount of heat is generated in a thick active layer as described above.
Growth of dislocations even in the active layer with no Si impurity added
It is conceivable that the movement occurs easily. Also,
As mentioned above, apart from the calorific value, the quantum well structure
The life is shortened if the Si impurity concentration is high
As a result, the active layer occupies a larger volume than the thick single-layer active layer.
Significantly increase the proportion of
Segregation occurs, resulting in an increase in the interface recombination rate
Or increase the dislocation growth and migration. Further, Nagahama et al. Described in JP-A-10-12969.
Add impurities other than Si, such as Mg, as described
It is also possible to reduce the threshold of the laser element
However, even in such a laser element, impurities are added.
The life of high-temperature, high-power laser elements
It is thought to be improved. In fact we have Mg in the active layer
Laser elements with and without impurities
As a result of comparing the device degradation at 70 ° C and 30mW,
The deterioration of the element added was more remarkable than that of the element without the element. Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. FIG. 2 shows a second embodiment.
1 is a cross-sectional structural view of a nitride semiconductor laser device according to the present invention. Structure of Semiconductor Laser Device of Second Embodiment
Will be described together with the manufacturing process. First, the sapphire group
A GaN film is grown on the plate 101 by MOCVD. On it
Form tripe-shaped SiO2 mask for dry etching
The GaN in the window was further etched to sapphire. Then S
After removing the iO2 mask, the stripe-shaped GaN 301
Regrown n-type GaN 302 with Si added by MOCVD
You. After growing for some time, from the side
Are connected to form a flat GaN film. Striped Ga
High-density threading dislocations are inherited directly above N
High dislocation density region (dot pattern is not
Region) 116, but Ga formed by side growth
N becomes the low dislocation density region 104. Also, from left and right
New dislocations occur in the region where GaN that has grown
It has a high dislocation density. For comparison, the width of the sapphire exposed area was set to 10
Prepare both a substrate with a width of 25 μm and a substrate with a width of 25 μm
did. On this substrate, a Si-doped n-type In0.1Ga0.9N layer 10
7, 120 cycles of Si-doped n-type GaN layer (2.5 nm thick) and AND
N-type cladding made of Al0.14Ga0.86N layer (2.5nm thick)
Layer 108, n made of Si-doped n-type GaN (0.1 μm thick)
Type optical confinement layer 109, undoped In0.15Ga0.85N quantum
Well layer (3.5nm thickness) and undoped In0.02Ga0.98N barrier layer
(Thickness 10.5 nm) multi-quantum well active layer 110, Mg
Doped p-type Al0.2Ga0.8N cap layer (20 nm thick) 111,
P-type optical confinement made of Mg-doped p-type GaN (0.1μm thick)
Layer 112, Mg-doped p-type GaN layer with 120 periods (2.5 nm thickness)
Composed of undoped Al0.14Ga0.86N layer (thickness 2.5nm)
-Type cladding layer 113, Mg-doped p-type GaN (0.05 μm thick)
After sequentially growing a p-type contact layer 114 made of
The ridge structure as shown in FIG.
Finally, a p-electrode 105 made of Ni and Au and Ti and A
The n-electrode 115 made of l is deposited on the semiconductor shown in FIG.
A laser device is manufactured. For comparison, the barrier layer of the active layer and the quantum well
1 × 10 Si impurity in door layer¹⁸cm^-3Added laser element and
5 × 10 Si impurities in active layer¹⁸cm^-3Laser element added
Produced. For these laser elements, a transmission electron microscope
Observing the dislocations by
The above-mentioned high dislocation density region and low dislocation density region are clearly
Observed, dislocation density is 5 × 10 in high dislocation density region¹²m^-2About
Degree, 2 × 10 in low dislocation density region^Tenm^-2It was about. Different SiO2 mask width or Si impurity concentration
The initial threshold current densities for these six devices and 70
Table 3 shows the element deterioration status after 100 hours of APC operation at 30mW at ℃.
Shown in [Table 3] The initial threshold current density is almost the same for the six elements.
Although there is no difference, the sapphire exposure
The output region width is 10 μm, and the active layer is
Ten¹⁸cm^-3In the element added, remarkable deterioration is seen,
Oscillation stopped before 100 hours of operation. After that
Almost no deterioration was seen for the other five samples
Was. Further, regarding the deteriorated element, a transmission electron
Observation of dislocations under a microscope showed that
Dislocations migrate from the dislocation density region to the low dislocation density region and grow.
I was guessed. In this sample, the high dislocation density region
Before the test, leave about 3 μm from the active layer area where current is injected.
However, after the operation test, the high dislocation density region became active.
Into the active layer (region where current is injected). On the other hand, impurities are added to the active layer.
The dislocation distribution is completely the same as before the operation test.
It was a bad situation. The sapphire exposed area width is 25 μm
And 5 × 10 Si impurities in the active layer¹⁸cm^-3Add
In a device having a low dislocation density,
It is observed that the dislocations move to the
However, the advance of the high dislocation density region 116 has a distance of about 5 μm.
Stays and advances to the active layer (current injection area)
I didn't. As a result, in this embodiment, the active layer (current
High dislocation density region 1 within 5 μm from the region to be implanted
Even if 16 exists, the impurity concentration is low.
(Ten ¹⁸cm^-3), The effect of
Movement and proliferation of the position can be suppressed. In addition,
Do not add Si impurities to the active layer
Or make the sapphire exposed area wide enough.
As a result, from the high dislocation density region 116 to the low dislocation density region 1
04 dislocation movement and proliferation are suppressed, and at high temperature and high output
It can be seen that the life of the laser element is significantly improved. Next, a third embodiment of the present invention will be described with reference to FIG.
3 will be described. FIG. 3 shows a third embodiment.
FIG. 1 is a cross-sectional structural view of a surface-emitting nitride semiconductor laser device according to the present invention.
You. Structure of Semiconductor Laser Device of Third Embodiment
Will be described together with the manufacturing process. First, the sapphire group
A GaN film 102 is grown on a plate 101 by MOCVD. That
Then, a 20-period ZrO2 / Si in a stripe pattern is formed on the GaN film 102.
An O2 film (mask) 403 is formed in the [1, -1,0,0] direction.
MOCVD growth of n-type GaN doped with Si
Selective growth and low dislocation density grown laterally on the mask
GaN is formed, and an n-type GaN-ELOG substrate 106 is manufactured. The ZrO2 / SiO2 film is a dielectric multilayer film reflecting mirror (D
BR). Continue on this board
Undoped In0.15Ga0.85N quantum well layer (3.5nm thick)
And undoped In0.02Ga0.98N barrier layer (10.5nm thickness)
Multi-quantum well active layer 110, Mg-doped p-type Al0.4Ga0.6
N / GaN 40 periodic multilayer reflector (DBR) 413, Mg-doped p-type G
The p-type contact layer 114 made of aN (0.05 μm thick) is
After being grown to a thickness of
A ridge structure is formed, and finally p
The electrode 105 and the n-electrode 115 made of Ti and Al are deposited by evaporation.
Make it. In this surface emitting laser, the back surface (that is,
Laser light is emitted from the fire substrate side). Comparison
1 × 1 Si impurity in barrier layer and quantum well layer of active layer
0¹⁸cm^-35 × Si impurities in the doped laser element and active layer
Ten¹⁸cm^-3The added laser element was also manufactured. From these aspects
In the optical laser element, the active layer
Element that does not add impurities to
The service life has been extended. In each of the above embodiments, the nitride semiconductor
Applied to semiconductor lasers as light emitting devices, but other semiconductors
It may be used for a light emitting element. For example, LED or SL
It may be used for D (Super Luminescent Diode). [0071] As described above, the nitride semiconductor of the present invention is
According to the body light emitting device, at least a part of the low dislocation density region
Current injection region is formed in the active layer having the quantum well structure.
Pure substance concentration is 10¹⁸cm^-3Less than the
Low pure concentration reduces Auger recombination and high
Transition from dislocation density region to current injection region in low dislocation density region
Temperature and high power operation.
Can dramatically increase the life of laser devices
Wear. Further, according to the nitride semiconductor light emitting device of the present invention,
Patterning on the substrate surface where the nitride semiconductor is exposed
Nitride is selectively grown after forming the patterned mask material.
The mask material is patterned with a mask width of 25 μm or more.
Or a nitride semiconductor layer is formed
The substrate surface is processed by etching and partially nitrided
It is manufactured by growing nitride after removing the conductor layer.
Processing by etching is applied to the area of 25μm or more in width.
High enough to provide high reliability at high temperatures and high output.
Low dislocation density region is secured and shadows from high dislocation density region
Sound is greatly suppressed. Therefore, according to the present invention, writable
Nitride semiconductor lasers that can be used as
Users can be realized, and the industrial utility value is
Always big.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a nitride semiconductor laser device showing a first embodiment of a nitride semiconductor light emitting device according to the present invention. FIG. 2 is a sectional view of a nitride semiconductor laser device showing a second embodiment of the nitride semiconductor light emitting device according to the present invention. FIG. 3 is a sectional view of a nitride semiconductor laser device showing a third embodiment of the nitride semiconductor light emitting device according to the present invention. FIG. 4 is a sectional view of a nitride semiconductor laser device showing a conventional example of a nitride semiconductor light emitting device according to the present invention. [Description of Signs] 101 Sapphire substrate 102 GaN film 103 Striped SiO2 film (mask) 104 Low dislocation density region (region without dot pattern) 105 p electrode 106 ELOG substrate 107 InGaN layer 108 n-type cladding layer 109 n Light confinement layer 110 undoped active layer 111 cap layer 112 p-type light confinement layer 113 p-type cladding layer 114 p-type contact layer 115 n-electrode 116 high dislocation density region (dotted region) 210 Si-doped active layer 301 stripe GaN 302 n-type GaN 403 Striped ZrO2 / SiO2 multilayer 413 p-type AlGaN / GaN multilayer mirror

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Masaaki Nichido             NEC Corporation 5-7-1 Shiba, Minato-ku, Tokyo NEC Corporation             In the formula company F term (reference) 5F073 AA13 AA45 AA74 BA05 CA07                       CB05 DA05 DA35 EA28

Claims (1)

1. A nitride semiconductor light emitting device having an active layer having a quantum well structure in which a well layer and a barrier layer are stacked, wherein the active layers have different dislocation densities from each other. It has a dislocation density region and a low dislocation density region, wherein the low dislocation density region has a lower dislocation density than the high dislocation density region and at least a current injection region is formed, and the high dislocation density region is A nitride semiconductor light emitting device, which is located at a position away from a current injection region, wherein the impurity concentration of the active layer is less than 10 ¹⁸ cm ⁻³ .