JP2003218468A - Semiconductor laser element and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GaN semiconductor laser element that has no occasion to introduce Al and continuously oscillates a laser beam in a wavelength region of visible light such as blue and green at a room temperature. <P>SOLUTION: This semiconductor laser element comprises at least a cladding layer, a guiding layer and an active layer. The cladding layer consists of GaN, and the guiding layer and the active layer consist of InGaN. An In composition of the active layer is higher than that of the guiding layer, and further the In composition of the active layer is 20 atom % or more. A blue semiconductor laser element is provided by making an energy difference between band gaps of the cladding layer and the active layer 0.5 eV or more, the In composition of the active layer 20-30 atom % and a thickness of the active layer 1-10 nm. A green semiconductor laser element is provided by making the In composition of the active layer 30-50 atom %, and the thickness of the active layer 1-10 nm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device made of a nitride semiconductor and a method for manufacturing the same, and more particularly to a semiconductor laser device having a novel structure in which GaN and InGaN are combined and a method for manufacturing the same. .

[0002]

2. Description of the Related Art GaN-based compound semiconductors have attracted attention as semiconductor materials for semiconductor lasers, and device design and trial manufacture have been advanced from various viewpoints. The oscillation wavelength of the GaN-based semiconductor laser device is in the short wavelength region such as blue and green. For example, in the field of optical recording, shortening the wavelength of recording light or reproducing light leads to higher density and higher capacity. It is expected to be used as a light source.

As a semiconductor laser device using the GaN compound semiconductor, a semiconductor laser device having a double hetero structure using an InGaN layer has been developed.
The structure in which the InGaN layer is sandwiched by N layers is effective for confining injected carriers and light, and is therefore adopted as a structure of a semiconductor laser device for high-luminance or short-wavelength light emission. For example, in a semiconductor laser device in which a GaN guide layer is provided above and below the InGaN active layer and an AlGaN clad layer is provided adjacent to the outside of this GaN guide layer, the refractive index of the InGaN active layer is n.
₁ , where n _{2 is} the refractive index of the GaN guide layer and n ₃ is the refractive index of the AlGaN cladding layer, InGaN having the highest refractive index can be obtained by setting n ₁ > n ₂ > n _3.
Laser emission occurs due to the index guided mode along the active layer.

[0004]

By the way, as described above, in the GaN-based semiconductor laser, the cladding layer is made of Al.
Although GaN is used, introduction of Al is technically difficult. For example, Al has a very low vapor pressure and is difficult to diffuse, and abnormal growth tends to occur during selective growth. In order to avoid catastrophic optical damage (COD) and to prolong the life, Al-free is desired.

The present invention has been proposed in view of the above-mentioned conventional circumstances, and is a novel G that does not require the introduction of Al.
It is an object of the present invention to provide an aN-based semiconductor laser device, and further to provide a manufacturing method thereof. Another object of the present invention is to provide a GaN-based semiconductor laser device that is capable of continuously oscillating laser light in the visible light wavelength region such as blue and green at room temperature and is simple to manufacture.
It is an object to provide a manufacturing method thereof. A further object of the present invention is to provide a GaN-based semiconductor laser device capable of changing the emission wavelength by adjusting the In composition and thickness of the active layer, and an object thereof is to provide a manufacturing method thereof. .

[0006]

As a result of various studies, the inventors of the present invention have found that in a semiconductor laser in the visible wavelength region such as blue and green, even if GaN is used for the cladding layer, the cladding layer and the active layer We have obtained the knowledge that the band gap energy difference between the two can oscillate at room temperature.

The present invention has been completed based on the above findings. A semiconductor laser device of the present invention has at least a clad layer, a guide layer and an active layer, and the clad layer is made of GaN. The guide layer and the active layer are made of InGaN, the In composition of the active layer is higher than the In composition of the guide layer, and the In composition of the active layer is 2
It is characterized by being 0 atomic% or more. The method for manufacturing a semiconductor laser device of the present invention is a method for manufacturing a semiconductor laser device in which a clad layer, a guide layer, an active layer, a guide layer, and a clad layer are sequentially laminated.
While forming each of the clad layers using GaN,
Each of the guide layers and the active layer is formed using InGaN, and the In composition is adjusted so that the In composition of the active layer is higher than that of the guide layer and the In composition of the active layer is 20 atomic% or more. It is characterized by that.

The semiconductor laser device of the present invention does not use AlGaN for the cladding layer and is Al-free. Therefore, catastrophic optical damage (COD) due to the introduction of Al is avoided, and problems such as abnormal growth are solved. Further, it is easier to manufacture the clad layer with GaN. Further, when the structure of the semiconductor laser device of the present invention is adopted, the band gap can be changed only by the In composition, and the emission wavelength can be adjusted by adjusting the In composition and the thickness of the active layer.

For example, the energy difference between the bandgap of the cladding layer and the bandgap of the active layer is 0.5 eV or more, the In composition of the active layer is 20 to 30 atomic%, and the active layer thickness is 1 to 10 nm. The emission wavelength is 460n
It becomes a blue semiconductor laser device of m to 490 nm. Also,
The energy difference between the bandgap of the cladding layer and the bandgap of the active layer is 0.5 eV or more, the In composition of the active layer is 30 to 50 atomic%, and the active layer thickness is 1 to 10 nm. It becomes a 550 nm green semiconductor laser device.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a semiconductor laser device to which the present invention is applied and a method for manufacturing the same will be described in detail with reference to the drawings.

The semiconductor laser of the present invention is a semiconductor laser in which the cladding layer is made of GaN on the substrate, the guide layer is InGaN, and the active layer is InGaN.
The composition is set higher than the In composition of the guide layer. The In composition of the active layer is 20 atomic% or more. In a nitride semiconductor laser, AlGaN is usually used for the clad layer, but in a semiconductor laser in the visible wavelength region such as blue and green, even if GaN is used for the clad layer, the band between the clad layer and the active layer is increased. The gap energy difference can be sufficiently oscillated at room temperature. Since introducing Al is technically difficult, it is easier to manufacture the clad layer with GaN as in the present invention.

Further, in the above structure, since the band gap is changed only by the composition of In, the composition change can be changed gradually or stepwise. Therefore, compared to the AlGaN / GaN / InGaN structure which has been used so far, it has various merits in terms of technology and characteristics.

For example, the band gap energy difference is set to 0.5 eV or more for the following reason. For example, conventional AlGaN / GaN / InGa
In the semiconductor laser device made of N (active layer), as shown in FIG. 1, the threshold current density Jth decreases as the energy difference in the band gap increases, and the energy difference in the band gap becomes 0. Continuous oscillation at 5 eV (CW
Oscillation) is occurring. Based on these results, here, the energy difference of the band gap is 0.5 eV.
That is all.

Particularly, as the first optimum value, for example, the energy difference between the bandgap of the cladding layer and the bandgap of the active layer is 0.5 eV or more, the In composition of the active layer is 20 to 30 atomic%, and the active layer thickness is Is set to 1 to 10 nm, whereby a blue semiconductor laser device having an emission wavelength of 460 nm to 490 nm can be obtained. For continuous oscillation at room temperature, a bandgap energy difference of 0.5 eV or more is required between the active layer and the cladding layer. Here, if the composition of In and the thickness of the active layer are adjusted to produce the above wavelength, a blue semiconductor laser is obtained, and the industrial application range is greatly expanded. However, the semiconductor laser device of the present invention does not use Al. Therefore, the overall bandgap cannot be increased. Therefore, the above numerical range is adopted as the first optimum value.

FIG. 2 shows the relationship between the In composition in InGaN and the band gap energy Eg (eV). In InGaN, the band gap energy Eg decreases as the In composition increases, but I
When the n composition becomes 20 atomic%, the band gap energy difference from In0 atomic% (that is, GaN) is 0.
Greatly exceeds 5 eV. Therefore, the In composition of the active layer is set to 20 atomic% or more. Further, as shown in FIG. 3, the thickness of the active layer is set to 10 nm or less because the emission intensity (PL intensity) decreases when it exceeds 10 nm.

Similarly, as a second optimum value, the energy difference between the band gap of the cladding layer and the band gap of the active layer is 0.5 eV or more, and the In composition of the active layer is 30 to 30.
By setting the atomic layer thickness to 50 atomic% and the active layer thickness to 1 to 10 nm, a green semiconductor laser device having an emission wavelength of 500 nm to 550 nm can be obtained. As in the case of the blue semiconductor laser, the green semiconductor laser can be obtained by simply adjusting the In composition and the thickness of the active layer, so that the industrial application range is greatly expanded. Further, under this condition, it is easy to set the energy difference between the band gap of the cladding layer and the band gap of the active layer to 0.5 eV or more.

Further, in the active layer, In / (I
It is desirable to set n + Ga) to 0.9 or more. I
The threshold current density can be reduced by setting n / (In + Ga) to 0.9 or more.

In any case, In of the guide layer
The composition may be, for example, 2 to 10 atomic%, and the thickness of the guide layer may be set to, for example, 10 nm or more and 100 nm or less. In the guide layer, it is said that the optical confinement is sufficient because the refractive index difference Δn is several%. Furthermore, the degree of difference is also required for the clad layers. From such a viewpoint, the In composition of the guide layer is set within the above range. By setting the In composition of the guide layer to 2 atomic% or more, the refractive index difference Δn can be set to several% or more. Further, the In composition of the guide layer is set to 10 atomic% or less so that the defect does not occur even when the film thickness of the guide layer is 10 to 100 nm. On the contrary, when the thickness of the guide layer is 10 to 100 nm in the above In composition of 2 to 10 atomic%, the thickness is below the critical film thickness and no defects are introduced.

The semiconductor laser device of the present invention has the above-mentioned active layer, guide layer, clad layer, electrodes, contact layers in contact with the electrodes, and the like, and has the same structure as a normal semiconductor laser device. Here, the contact layer is In
It is preferably composed of GaN: Mg. In the semiconductor laser device of the present invention, since Al is not used for all layers and long-wave light is emitted, even if it is InGaN, there is little problem of blocking light.

Further, the present invention can be applied to semiconductor laser devices having various structures. For example, a so-called planar structure may be used, or various structures such as a vertical structure, a selective growth structure, or a combination thereof can be adopted. In particular, if the above layers are formed on the (1-101) plane (so-called S plane) formed by selective growth, a semiconductor laser device having excellent characteristics can be realized.

To manufacture the above semiconductor laser device, a clad layer, a guide layer, an active layer, a guide layer, and a clad layer may be sequentially laminated on the substrate, and further, an electrode and a contact layer may be laminated. . For example, in the case of a selective growth structure, it is formed of nitride (1-101)
The clad layer, the guide layer and the active layer may be sequentially grown on the surface. The (1-101) plane can be formed by growing a nitride on a selective mask by selective growth, and the inclined surface that has been selectively grown becomes the S plane. Alternatively,
The nitride grown on the sapphire substrate may be processed into a seed crystal, and the cladding layer, the guide layer, and the active layer may be sequentially grown on the growth surface obtained by growing the nitride on the seed crystal.

When the clad layer, the guide layer, the active layer, the guide layer, and the clad layer are sequentially laminated as described above, each clad layer is formed using GaN, and each guide layer and the active layer is formed of InGaN. The In composition of the active layer is adjusted so that the In composition of the active layer is higher than that of the guide layer and the In composition of the active layer is 20 atomic% or more.

For example, in the case of a blue semiconductor laser device, the In composition of the active layer is 20 to 30 atomic%, the thickness of the active layer is 1 to 10 nm, and the emission wavelength is 460 nm to 490 n.
to be m. In the case of a green semiconductor laser device, the In composition of the active layer is 30 to 50 atomic%, the active layer thickness is 1 to 10 nm, and the emission wavelength is 500 nm to 550 n.
to be m. In either case, the guide layer I
The n composition is, for example, 2 to 10 atomic%.

Next, a specific structure of the semiconductor laser device to which the present invention is applied will be described. First, FIG. 4 shows an example of a blue semiconductor laser device having a planar structure in which the present invention is applied to a semiconductor laser device having a planar structure.

This planar structure blue semiconductor laser device comprises a cladding layer 2, a guide layer 3, an active layer 4,
The guide layer 5 and the clad layer 6 are laminated.
Then, a contact layer 7 is formed on the uppermost clad layer 6, and a p-electrode 9 is laminated via an insulating film 8, and the p-electrode 9 is formed through an opening formed in the insulating film 8.
The electrode 9 is connected to the contact layer 8. Also,
Each of the above layers is partially etched until the cladding layer 2 is exposed, and the n-electrode 10 is formed on the exposed cladding layer 2.

As the substrate 1, for example, a sapphire substrate or a bulk GaN substrate is used. When a sapphire substrate is used, a sapphire substrate having a C-plane as a main surface, which is often used when growing a gallium nitride-based compound semiconductor material, is suitable. In this case, the C plane as the main surface of the substrate includes a plane orientation inclined in the range of 5 to 6 °. In addition, SiC, ZnS, ZnO, AlN, In
AlGaN, Si, LiMgO, LiGaO ₂ , GaA
It is also possible to use a substrate made of s, MgAl ₂ O ₄ or the like, and a hexagonal crystal substrate or a cubic crystal substrate made of these materials is preferable, and a hexagonal crystal substrate is more preferable.

The cladding layer 2 is formed of an n-type GaN layer. The GaN layer has the property of becoming n-type even if it is undoped because of the nitrogen vacancies formed in the crystal.
By doping donor impurities such as i, Ge, and Se during crystal growth, an n-type having a preferable carrier concentration can be obtained. Further, in order to suppress dislocations and the like formed in the GaN layer, a buffer layer may be formed on the substrate 1 by changing the temperature in advance (for example, at a low temperature). This buffer layer can be formed by growing a thin (for example, about 20 to 30 nm) GaN layer at a low temperature (for example, 500 ° C.).

Further, once a GaN layer is formed on the substrate 1,
A selection mask having an opening formed thereon is formed, and Ga is
The dislocation can also be suppressed by forming the N layer by selective growth. By forming the GaN layer by selective growth, it is possible to suppress the density of threading dislocations, and it is possible to form a GaN layer having high crystallinity. Furthermore, the dislocation density of the crystal layer grown on the GaN layer can also be reduced.

In this example, a buffer layer (not shown) is grown on the substrate 1 while changing the temperature, and Ga is grown thereon.
N: Si is used as the cladding layer 2 and has a thickness of 4 .mu.m.
It was grown at ℃.

An n-type guide layer 3 is formed on the clad layer 2. In this example, In is formed on the cladding layer 2.
GaN: Si was grown as the guide layer 3. The In composition of InGaN: Si forming the n-type guide layer 3 was 10 atomic%. The bandgap of the GaN forming the cladding layer 2 is 3.1 eV as compared with the bandgap of 3.4 eV. The guide layer 3 of InG
The growth temperature for growing aN: Si is 800 here.
C. and the film thickness was 50 nm.

Further, an active layer 4 was formed on the guide layer 3. The active layer 4 is made of InGaN at a growth temperature of 700 ° C.
(In composition 25 atomic%) was grown to 3 nm. The active layer 4 has a higher In composition than the guide layer 3 and the guide layer 5 described later, and exceeds 20 atomic%.

On the active layer 4, a p-type guide layer 5,
The p-type clad layer 6 is sequentially laminated. To make the nitride semiconductor p-type, Mg, Zn, C, B
Although it can be obtained by doping an acceptor impurity such as e, Ca, or Ba, in order to obtain a p-layer having a high carrier concentration, after the acceptor impurity is doped, nitrogen,
Annealing is preferably performed at 400 ° C. or higher in an atmosphere of an inert gas such as argon. There is also a method of activation by electron beam irradiation or the like, and a method of activation by microwave irradiation or light irradiation.

In this example, InG is used as the p-type guide layer 5.
aN: Mg was grown on the active layer 4. This InGa
The In composition of N: Mg is 10 atomic%. In addition, this p
When forming the guide layer 5 of the mold, it is preferable to separate Mg doping from the active layer 4 in order to prevent impurities from being mixed into the active layer 4, which results in relatively good characteristics.

Next, a p-type clad layer 6 is laminated on the p-type guide layer 5. The p-type clad layer 6 is
GaN: Mg is grown so that the growth temperature is not so raised from the time of growing InGaN which is the p-type guide layer 5. The thickness is, for example, 0.5 μm.

Further, as the contact layer 7, InGa
N: Mg is grown on the p-type cladding layer 6. The In composition of the contact layer 7 is, for example, 10 atom%. An insulating film 8 made of SiO ₂ or the like is formed on the contact layer 7, the stripe portion is insulated, and a p-electrode 9 is formed by vapor deposition. The p electrode 9 is made of Al, Ag, Au, Ti, Pt,
A metal thin film such as Pd, or a laminated structure in which these metal thin films are combined can be used. In this example, Pd /
The combination was Pt / Au.

Further, in order to connect the n-electrodes, the above-mentioned laminated body is etched to partially expose the n-type cladding layer 2, and the n-electrode 10 is formed thereon. The n-electrode 10 is T
A combination of i / Pt / Au was formed, and this was formed by vapor deposition. Finally, this is cleaved to form an end face for forming a resonator, and a semiconductor laser device is completed.

The semiconductor laser device having the above structure has the active layer 4
Has an In composition of 20 to 30 atomic% (25 atomic%), an active layer thickness of 1 to 10 nm (3 nm), and an emission wavelength of 460.
It becomes a blue semiconductor laser element of nm to 490 nm. Further, with this structure, by lowering the growth temperature of the active layer 4 by about 50 ° C. and further increasing the In composition to 30 atomic% or more, a green semiconductor laser device having an emission wavelength of 500 nm to 550 nm is obtained.

Next, as a second example, an S-plane blue semiconductor laser device in which each layer is grown on the (1-101) plane (so-called S-plane) will be described. The S-plane blue semiconductor laser device is formed by laminating a cladding layer, a guide layer, and an active layer on the inclined surface (S-plane) of the selectively grown nitride semiconductor.

In the S-plane blue semiconductor laser device, as shown in FIG. 5, an underlayer 12 is formed on a substrate 11, and a nitride semiconductor such as G is formed on the underlayer 12 via a mask layer 13.
aN: Si is selectively grown and has an inclined surface (S surface) 3
A prismatic selective growth layer 14 is formed, and an n-type cladding layer 15, an n-type guide layer 16, an active layer 17, a p-type guide layer 18, a p-type cladding layer 19, a contact layer 20 and a p-layer.
It is configured by stacking the electrodes 21. Also,
An n electrode 22 is formed in a region of the underlayer 12 where the selective growth layer 14 is not formed. In the region where the n-electrode 22 is formed, the mask layer 13 is removed to expose the underlying layer 12, and the n-electrode 22 serves as the underlying layer 1.
It is directly connected to 2.

The substrate 11 used here is not particularly limited as long as it can form a crystal layer having an S-plane or a plane equivalent to the S-plane, and various substrates can be used. For example, the substrate that can be used is sapphire (including Al ₂ O ₃ , A plane, R plane, and C plane) SiC (6
H, 4H and 3C are included. ) GaN, Si, ZnS, Zn
O, AlN, LiMgO, GaAs, MgAl ₂ O ₄ ,
A substrate made of InAlGaN or the like, preferably a hexagonal substrate or a cubic substrate made of these materials, more preferably a hexagonal substrate. For example, when using a sapphire substrate, gallium nitride (Ga
It is possible to use a sapphire substrate having a C-plane as the main surface, which is often used when growing a N) -based compound semiconductor material. In this case, the C plane as the main surface of the substrate is 5 to
It includes the plane orientation inclined in the range of 6 °.

The selective growth layer 14, which is a crystal layer formed on the substrate 11, has an S plane inclined with respect to the main surface of the substrate or a plane substantially equivalent to the S plane. The selective growth layer 14 may be a material layer capable of forming a clad layer, a guide layer, and an active layer on a surface parallel to an S surface or a surface substantially equivalent to the S surface described later, and is not particularly limited. However, among them, it is preferable to have a wurtzite crystal structure. As such a selective growth layer 14, for example, I
Group II compound semiconductors and BeMgZnCdS compound semiconductors can be used, and gallium nitride (Ga
N) -based compound semiconductors, aluminum nitride (AlN) -based compound semiconductors, indium nitride (InN) -based compound semiconductors, indium gallium nitride (InGaN) -based compound semiconductors, aluminum gallium nitride (AlGaN) -based compound semiconductors are preferably formed. In particular, gallium nitride-based compound semiconductors are preferable. In the present invention, InGaN, AlGaN, GaN, etc. are not necessarily
The present invention is not limited to ternary mixed crystal only and binary mixed crystal only nitride semiconductors. For example, in the case of InGaN, even if a trace amount of Al and other impurities are contained within a range that does not change the action of InGaN, the scope of the present invention. Needless to say. Further, a surface substantially equivalent to the S surface is 5 to 6 with respect to the S surface.
It includes the plane orientation inclined in the range of °.

As a method of growing the selective growth layer 14,
Various vapor phase epitaxy methods can be mentioned, for example, vapor phase epitaxy methods such as organometallic compound vapor phase epitaxy method (MOCVD (MOVPE) method) and molecular beam epitaxy method (MBE method),
A hydride vapor phase epitaxy method (HVPE method) or the like can be used. Among them, according to the MOVPE method, a material having good crystallinity can be obtained quickly. In the MOVPE method, Ga
TMG (trimethylgallium) as source, TEG
(Triethylgallium), TMA as Al source
Alkyl metal compounds such as TMI (trimethylindium) and TEI (triethylindium) are often used as (trimethylaluminum), TEA (triethylaluminum), and In sources, and gases such as ammonia and hydrazine are used as nitrogen sources. It Also,
As the impurity source, Si is silane gas, Ge is germane gas, Mg is Cp2Mg (cyclopentadienyl magnesium), and Zn is DEZ.
A gas such as (diethyl zinc) is used. MOCV
In the D method, these gases are supplied to the surface of the substrate 11 heated to, for example, 600 ° C. or higher to decompose the gases, so that the InAlGaN-based compound semiconductor can be epitaxially grown.

Before forming the selective growth layer 14, the underlayer 1
2 is preferably formed on the substrate 11. The underlayer 12 is composed of, for example, a gallium nitride layer or an aluminum nitride layer, and the underlayer 12 is composed of a combination of a low temperature buffer layer and a high temperature buffer layer or a combination of a buffer layer and a crystal seed layer functioning as a crystal seed. May be Like the selective growth layer 14, the underlayer 12 can also be formed by various vapor phase epitaxy methods, for example, a metal organic compound vapor phase epitaxy method (MOCVD method) and a molecular beam epitaxy method (MBE).
Method), a hydride vapor phase epitaxy method (HVPE method), or the like. When the growth of the selective growth layer 14 is started from the low temperature buffer layer, polycrystals are likely to be deposited on the mask, which becomes a problem. Therefore, a crystal having a better crystallinity can be grown by including a crystal seed layer and then growing a surface different from the substrate 11 thereon. Also,
In order to perform crystal growth using selective growth, it is necessary to form from the buffer layer if there is no crystal seed layer, but if selective growth is performed from the buffer layer, growth is hindered. Is more likely to occur. Therefore, by using the crystal seed layer, it is possible to grow the crystal with good selectivity in the region where the growth is required. The buffer layer also has the purpose of alleviating the lattice mismatch between the substrate and the nitride semiconductor. Therefore, a substrate having a lattice constant close to that of the nitride semiconductor,
The buffer layer may not be formed in some cases when the substrates having the same lattice constant are used. For example, Al on SiC
A buffer layer may be added without lowering the temperature of N.
In some cases, AlN and GaN may grow as a buffer layer on the i substrate without being kept at a low temperature.
aN can be formed. Further, the structure may be such that no buffer layer is provided, and a GaN substrate may be used.

Then, in this example, the selective growth method is used to form the S-plane or a plane substantially equivalent to the S-plane. The S-plane is a stable plane that can be seen when selectively grown on the C + plane, is a plane that is relatively easy to obtain, and has a hexagonal plane index of (1-101). Similar to the C + and C− planes on the C plane, there are S + and S− planes on the S plane, but in the present specification, unless otherwise specified, S + on the C + plane GaN. The surface is growing, and this is S
It is described as a surface. Regarding the S surface, the S + surface is the stable surface. The surface index of the C + surface is (0001). Regarding the S-plane, when the selective growth layer 14 is made of a gallium nitride-based compound semiconductor as described above,
On the surface, the number of bonds from Ga to N is 2 or 3, which is the second largest after the C-plane. Here, since the C-plane cannot be practically obtained on the C + plane, the number of bonds on the S-plane becomes the largest. For example, when a nitride is grown on a sapphire substrate having a C-plane as the main surface, the surface of the wurtzite type nitride is generally the C + plane, but the S-plane can be formed by using selective growth. , The bond of N, which tends to be easily detached on the plane parallel to the C-plane, is bonded by one bond from Ga, whereas it is bonded by at least one bond on the inclined S-plane. . Therefore, effectively V /
The III ratio is increased, which is advantageous for improving the crystallinity of the laminated structure. Further, when grown in a direction different from that of the substrate, dislocations extending upward from the substrate may be bent, which is also advantageous in reducing defects.

A specific selective growth method is carried out selectively on the underlying layer 12 or by utilizing the opened portion of the mask layer 13 formed before the underlying layer 12 is formed. The mask layer 13 can be composed of, for example, a silicon oxide layer or a silicon nitride layer. In this example, the opening formed in the mask layer 13 has a slit shape, the triangular columnar selective growth layer 14 is grown along the slit, and the inclined surfaces on both sides are S surfaces.

In the experiment conducted by the present inventors, when the hexagonal truncated pyramid shape grown by using cathode luminescence is observed, the crystal of the S plane is of good quality and the luminous efficiency is higher than that of the C + plane. Has been shown. Especially I
Since the growth temperature of the nGaN active layer is 700 to 800 ° C., the decomposition efficiency of ammonia is low and more N species are required. Also, when the surface was observed with an AFM, the steps were aligned and a surface suitable for incorporation of InGaN was observed. Furthermore, it is known that the growth surface of the Mg-doped layer generally has a poor surface condition at the AFM level, but the growth of the S-plane also causes the Mg-doped layer to grow in a good surface condition and the doping conditions are considerably different. . Further, when microphotoluminescence mapping is performed, it is possible to measure with a resolution of about 0.5 to 1 μm, but in a normal method grown on the C + plane, there is unevenness of about 1 μm pitch,
Uniform results were obtained for the samples obtained by S-plane by selective growth. Further, the flatness of the slope viewed by SEM is smoother than that of the C + surface.

Further, in the case of selective growth using a selective growth mask, there is no lateral growth when growing only on the opening of the selective mask. Therefore, lateral growth is performed using microchannel epitaxy. It is possible to make the shape larger than the window region. It is known that the lateral growth using such microchannel epitaxy makes it easier to avoid threading dislocations and reduces dislocations.

In this example, GaN: Si to be the base layer 12
Were grown to a thickness of 1-2 μm at 1000 °. A selective mask (mask layer 13) made of SiO ₂ was formed thereon by using a photolithography technique. In this example, a 10 μm wide stripe-shaped opening is formed in the mask layer 13, and the selective growth layer 14 is further selectively grown on the opening. The constituent material of the selective growth layer 14 is GaN: Si. The selectively grown GaN: Si grows in a roof-like structure at the top and has a triangular prism shape with a triangular cross section.

Further, the selectively grown layer 14 that has been selectively grown.
GaN: Si is grown on the S-plane of
This was used as the n-type cladding layer 15. An n-type guide layer 16 is further formed on the n-type cladding layer 15. In this example, InGaN: Si is formed on the n-type cladding layer 15.
Was grown as the n-type guide layer 16. The In composition of InGaN: Si forming the n-type guide layer 16 was 10 atomic%. The bandgap of the n-type cladding layer 15 is 3.1 eV as compared with the bandgap of GaN which is 3.4 eV. The growth temperature for growing the InGaN: Si that is the n-type guide layer 16 was 800 ° C. here, and the film thickness thereof was 50 nm.

Further, an active layer 17 was formed on the n-type guide layer 16. The active layer 17 has a growth temperature of 700 ° C.
nGaN (In composition: 25 atomic%) was grown to 3 nm. The active layer 17 has a higher In composition than the n-type guide layer 16 and a p-type guide layer 18 described later, and exceeds 20 atomic%.

A p-type guide layer 1 is formed on the active layer 17.
8 and the p-type clad layer 19 are sequentially laminated. To make the nitride semiconductor p-type, Mg, Zn,
It can be obtained by doping an acceptor impurity such as C, Be, Ca, and Ba. In order to obtain a p-layer having a high carrier concentration, after doping the acceptor impurity,
Annealing is preferably performed at 400 ° C. or higher in an atmosphere of an inert gas such as nitrogen or argon. There is also a method of activation by electron beam irradiation, microwave irradiation,
There is also a method of activation by light irradiation.

In this example, InG is used as the p-type guide layer 18.
aN: Mg was grown on the active layer 17. This InG
The In composition of aN: Mg is 10 atomic%. When forming the p-type guide layer 18, the impurity active layer 17 is formed.
In order to prevent contamination with Mg, it is preferable that the Mg doping be separated from the active layer 17 to some extent, which results in relatively good characteristics.

Next, a p-type clad layer 19 is laminated on the p-type guide layer 18. The p-type clad layer 19 is
GaN: Mg is grown so that the growth temperature is not so raised from the time of growing InGaN that is the p-type guide layer 18. The thickness is, for example, 0.5 μm.

Further, as the contact layer 20, InG is used.
aN: Mg is grown on the p-type cladding layer 19. The In composition of the contact layer 20 is, for example, 10 atom%.
On the contact layer 20, a p electrode 21 is further formed by vapor deposition. The p electrode 21 is made of Al, Ag, Au, Ti, P
A metal thin film of t, Pd or the like, or a laminated structure in which these metal thin films are combined can be used. In this example, P
The combination was d / Pt / Au.

In order to connect the n-electrode, the mask layer 13 is etched with a hydrofluoric acid-based etchant,
The underlying layer 12 is partially exposed, and the n electrode 22 is formed thereon. The n-electrode 22 was a combination of Ti / Pt / Au and was formed by vapor deposition. Finally, this is cleaved to form an end face for forming a resonator, and a semiconductor laser device is completed.

The S-plane blue semiconductor laser device having the above structure is
The blue semiconductor laser device has an In composition of the active layer 17 of 20 to 30 atomic% (25 atomic%), an active layer thickness of 1 to 10 nm (3 nm), and an emission wavelength of 460 nm to 490 nm. Further, with this structure, by lowering the growth temperature of the active layer 17 by about 50 ° C. and further increasing the In composition to 30 atomic% or more, a green semiconductor laser device having an emission wavelength of 500 nm to 550 nm is obtained.

Finally, a special S-plane blue semiconductor laser device corresponding to a modification of the S-plane blue semiconductor laser will be described. Also in this example, similar to the S-plane blue semiconductor laser device, the cladding layer, the guide layer, and the active layer are laminated on the inclined surface (S-plane) of the selectively grown nitride semiconductor. The take-out structure is different from that of the S-plane blue semiconductor laser device.

As shown in FIG. 6, the special S-plane blue semiconductor laser device has a nitride semiconductor such as Ga on a substrate 31.
N: Si is selectively grown to form a triangular column-shaped selective growth layer 32 having an inclined surface (S surface), on which an n-type cladding layer 33, an n-type guide layer 34, an active layer 35, a p-type guide are formed. The layer 36, the p-type cladding layer 37, the contact layer 38, and the p-electrode 39 are laminated and formed.

In this example, the substrate 31 is a sapphire substrate,
Alternatively, a bulk GaN substrate is used. If necessary, a buffer layer or the like is grown while changing the temperature, and GaN: Si serving as an underlayer is further grown to a thickness of 1 to 2 μm.
Grew at 0 °. A selective mask made of SiO ₂ was formed thereon by using a photolithography technique. The selection mask masks the portion other than the 10 μm-wide stripe, and the GaN is etched at all openings. A selective growth layer 32 was further selectively grown thereon. The constituent material of the selective growth layer 32 is GaN: Si. The selectively grown GaN: Si grows in a roof-like structure at the top and has a triangular prism shape with a triangular cross section.

Further, the selectively grown layer 32 that has been selectively grown.
GaN: Si is grown on the S-plane of
This was used as the n-type cladding layer 33. An n-type guide layer 34 is further formed on the n-type cladding layer 33. In this example, InGaN: Si is formed on the n-type cladding layer 33.
Was grown as an n-type guide layer 34. The In composition of InGaN: Si forming the n-type guide layer 34 was 10 atomic%. The bandgap of the n-type cladding layer 33 is 3.1 eV as compared with the bandgap of GaN which is 3.4 eV. The growth temperature for growing InGaN: Si, which is the n-type guide layer 34, was 800 ° C. here, and the film thickness thereof was 50 nm.

Further, an active layer 35 was formed on the n-type guide layer 34. The active layer 35 has a growth temperature of 700 ° C.
nGaN (In composition: 25 atomic%) was grown to 3 nm. The In composition of the active layer 35 is higher than that of the n-type guide layer 34 and a p-type guide layer 36 described later, and exceeds 20 atomic%.

The p-type guide layer 3 is formed on the active layer 35.
6 and the p-type clad layer 37 are sequentially laminated. To make the nitride semiconductor p-type, Mg, Zn,
It can be obtained by doping an acceptor impurity such as C, Be, Ca, and Ba. In order to obtain a p-layer having a high carrier concentration, after doping the acceptor impurity,
Annealing is preferably performed at 400 ° C. or higher in an atmosphere of an inert gas such as nitrogen or argon. There is also a method of activation by electron beam irradiation, microwave irradiation,
There is also a method of activation by light irradiation.

In this example, InG is used as the p-type guide layer 36.
aN: Mg was grown on the active layer 35. This InG
The In composition of aN: Mg is 10 atomic%. When the p-type guide layer 36 is formed, the impurity active layer 35 is formed.
In order to prevent the impurities from being mixed into the active layer 35, it is preferable that the Mg doping be separated from the active layer 35, which results in relatively good characteristics.

Next, a p-type clad layer 37 is laminated on the p-type guide layer 36. The p-type clad layer 37 is
GaN: Mg is grown so that the growth temperature is not raised so much from the time of growing InGaN which is the p-type guide layer 36. The thickness is, for example, 0.5 μm.

Further, as the contact layer 38, InG is used.
aN: Mg is grown on the p-type cladding layer 37. The In composition of the contact layer 38 is, for example, 10 atom%.
A p-electrode 39 is further vapor-deposited on the contact layer 38. The p electrode 39 is made of Al, Ag, Au, Ti, P
A metal thin film of t, Pd, or the like, or a laminated structure in which these metal thin films are combined can be used. In this example, P
The combination was d / Pt / Au.

The semiconductor laser device of this example is different from the previous example in the structure of taking the n-electrode. Specifically, conductive Ti is previously formed on a portion other than GaN of the substrate 31 made of sapphire or the like.
It is sufficient to form a film such as the above, grow InGaN: Mg, and then etch the portion on Ti to establish conduction only there. Alternatively, the stripe portion may be entirely embedded in polyimide or the like and transferred to form the n-electrode on the back surface side. At the time of transfer, the back surface is irradiated with an excimer laser or the like and peeled from the substrate by laser ablation. However, since the part exposed by the excimer laser from the back surface and exposed by the peeling is the n layer, the Ti / Pt /
Au or the like may be vapor-deposited.

The special S-plane blue semiconductor laser device having the above structure also has an In composition of the active layer 17 of 20 to 30 atomic% (25 atomic%), an active layer thickness of 1 to 10 nm (3 nm), and an emission wavelength of 460 nm. It becomes a blue semiconductor laser device of ˜490 nm. With this structure, the growth temperature of the active layer 17 is lowered by about 50 ° C., and the In composition is further increased to 30 atomic% or more, whereby the emission wavelength is 500 nm to 550 nm.
It becomes a green semiconductor laser device.

[0068]

As is apparent from the above description, according to the present invention, it is possible to provide a novel GaN-based semiconductor laser device that does not require the introduction of Al, and the disadvantages of introducing Al are encountered. It can be resolved.

The semiconductor laser device of the present invention is blue,
Laser light in the visible light wavelength range such as green can be continuously oscillated at room temperature, and it can be the strongest light emitting element (light source) to date. Therefore, the semiconductor laser device of the present invention can be applied to a full-color display or the like. The semiconductor laser device of the present invention is a laser device using GaN, but the GaN-based material is relatively durable and can easily be made high power.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a bandgap energy difference and a threshold current density J in a semiconductor laser device made of AlGaN / GaN / InGaN (active layer).

FIG. 2 is a characteristic diagram showing a relationship between In composition and bandgap energy Eg in InGaN.

FIG. 3 is a characteristic diagram showing the relationship between active layer thickness and emission intensity.

FIG. 4 is a schematic perspective view showing an example of a planar semiconductor laser device to which the present invention is applied.

FIG. 5 is a schematic perspective view showing an example of an S-plane semiconductor laser device to which the present invention is applied.

FIG. 6 is a schematic perspective view showing an example of a special S-plane semiconductor laser device to which the present invention is applied.

[Explanation of symbols]

1,11,31 substrate, 2,15,33 n-type clad layer, 3,16,34 n-type guide layer, 4,17,35
Active layer, 5,18,36 p-type guide layer, 6,19,3
7 p-type clad layer, 7, 20, 38 contact layer,
9,21,39p electrode, 10,22n electrode

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takeshi Biwa             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation (72) Inventor Toyoji Ohata             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F term (reference) 5F073 AA04 AA45 AA73 AA89 BA06                       CA07 CB10 DA05 EA07

Claims (20)

[Claims] 1. A cladding layer, a guide layer, and an active layer, at least the cladding layer is made of GaN, the guide layer and the active layer are made of InGaN, and the In composition of the active layer is the In composition of the guide layer. And the In composition of the active layer is 20 atomic% or more. 2. The semiconductor laser device according to claim 1, wherein the energy difference between the band gap of the cladding layer and the band gap of the active layer is 0.5 eV or more. 3. The active layer has an In composition of 20 to 30 atomic%, an active layer thickness of 1 to 10 nm, and an emission wavelength of 460.
The semiconductor laser device according to claim 2, wherein the semiconductor laser device has a wavelength of nm to 490 nm. 4. The semiconductor laser device according to claim 3, wherein the In composition of the guide layer is 2 to 10 atomic%. 5. The In composition of the active layer is 30 to 50 atomic%, the thickness of the active layer is 1 to 10 nm, and the emission wavelength is 500.
The semiconductor laser device according to claim 2, wherein the semiconductor laser device has a thickness of nm to 550 nm. 6. The semiconductor laser device according to claim 5, wherein the In composition of the guide layer is 2 to 10 atom%. 7. In / (In + G) in the active layer
The semiconductor laser device according to claim 1, wherein a) ≧ 0.9. 8. The semiconductor laser device according to claim 1, further comprising a contact layer in contact with the electrode, the contact layer being composed of InGaN: Mg. 9. The thickness of the guide layer is 10 nm or more, 1
The semiconductor laser device according to claim 1, wherein the semiconductor laser device has a thickness of 00 nm or less. 10. A crystal layer of (1-
The semiconductor laser device according to claim 1, wherein each of the layers is crystal-grown on the (101) plane. 11. The semiconductor laser device according to claim 10, wherein the crystal layer is formed by selective growth. 12. A method of manufacturing a semiconductor laser device in which a clad layer, a guide layer, an active layer, a guide layer, and a clad layer are sequentially laminated, wherein each clad layer is formed of GaN, and
Each of the guide layers and the active layer is formed using InGaN, and the In composition is adjusted so that the In composition of the active layer is higher than that of the guide layer and the In composition of the active layer is 20 atomic% or more. A method of manufacturing a semiconductor laser device, comprising: 13. The method for manufacturing a semiconductor laser device according to claim 12, wherein the energy difference between the band gap of the cladding layer and the band gap of the active layer is 0.5 eV or more. 14. The active layer has an In composition of 20 to 30 atomic%, an active layer thickness of 1 to 10 nm, and an emission wavelength of 460.
14. The method for manufacturing a semiconductor laser device according to claim 13, wherein the blue semiconductor laser device has a wavelength of nm to 490 nm. 15. The method of manufacturing a semiconductor laser device according to claim 14, wherein the In composition of the guide layer is 2 to 10 atom%. 16. The active layer has an In composition of 30 to 50 atomic%, an active layer thickness of 1 to 10 nm, and an emission wavelength of 500.
14. The method for manufacturing a semiconductor laser device according to claim 13, wherein the green semiconductor laser device has a wavelength of nm to 550 nm. 17. The method of manufacturing a semiconductor laser device according to claim 16, wherein the In composition of the guide layer is 2 to 10 atomic%. 18. A nitride formed of (1-10)
13. The method of manufacturing a semiconductor laser device according to claim 12, wherein the clad layer, the guide layer and the active layer are sequentially grown on the surface 1). 19. The semiconductor according to claim 18, wherein nitride is grown on the selective mask by selective growth, and the cladding layer, the guide layer and the active layer are sequentially grown on the selectively grown growth surface. Laser element manufacturing method. 20. A nitride grown on a sapphire substrate is processed to form a seed crystal, and the cladding layer, the guide layer and the active layer are sequentially grown on the growth surface obtained by growing the nitride on the seed crystal. 19. The method of manufacturing a semiconductor laser device according to claim 18, wherein the method is performed.