JP3329753B2 - Nitride semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light emitting diode,
A nitride semiconductor (In _X A) used for a light emitting element such as a laser diode or a light receiving element such as a solar cell or an optical sensor.
The present invention relates to a nitride semiconductor laser device comprising 1 _Y Ga _{1 -XYN} , 0 ≦ X, 0 ≦ Y, and X + Y ≦ 1).

[0002]

2. Description of the Related Art In recent years, a blue laser diode made of a nitride semiconductor has become practical. For example, the present inventors, Japanese Journal of Aplide Physics. Vol. 37 (1
998) pp. L309-L312, Ga grown on sapphire
Forming a protective film made of SiO ₂ partially on the N layer;
GaN was again grown on the protective film by metal organic chemical vapor deposition (M
By growing by a vapor phase growth method such as OVPE), the growth starts from a portion where the protective film is not formed (hereinafter, referred to as a window portion), and the lateral growth of GaN gradually occurs on the upper portion of the protective film, and the GaN is gradually grown. GaN grown in the lateral direction from the window to be joined continues to grow by bonding on the protective film, and crystal defects (hereinafter, referred to as “crystal defects”).
It is disclosed that a nitride semiconductor having extremely few dislocations can be obtained. A nitride semiconductor laser device obtained by using an obtained nitride semiconductor having few crystal defects as a substrate and forming an element structure on the nitride semiconductor substrate can achieve continuous oscillation of 10,000 hours or more. It has been disclosed. After forming such a protective film, a method of growing a nitride semiconductor using lateral growth of the nitride semiconductor is performed by using an epitaxial lateral overgrowth method.
) (Hereinafter sometimes referred to as ELOG growth).

[0003] The above-mentioned method uses GaN on a sapphire substrate.
After the layer is once grown to 2 μm, a protective film made of striped SiO ₂ having a thickness of 2 μm and a width of 13 μm is formed at intervals of 3 μm (window portion), and halide vapor phase growth is performed on the protective film. A GaN substrate having few crystal defects can be obtained by growing a GaN layer by about 10 μm again by utilizing a lateral growth of GaN by a vapor phase growth method such as an HVPE method or a metal organic chemical vapor deposition method (MOVPE). It is a technology that can be obtained. GaN substrate obtained by the above method, according to the surface transmission electron microscope (surface TEM) observations, as compared to the growth process of a conventional nitride semiconductor, generally the crystal defects is significantly reduced, in particular the protection of SiO ₂ Almost no crystal defects are found in the nitride semiconductor located above the film. The nitride semiconductor element in which the ridge-shaped stripe laser waveguide is formed on the protective film having almost no crystal defects is located on the upper side of the window in comparison with the ridge-shaped stripe formed on the window. Has good life characteristics.

[0004]

However, in some cases, the life characteristics are reduced even though a ridge-shaped stripe is formed on the protective film. As a result of various studies, it was confirmed that when an n-type contact layer made of GaN having an element structure was grown on GaN grown by ELOG, fine cracks were generated inside the n-type contact layer. Was done. This is probably due to ELOG
Although no crystal defects are found in the grown GaN, the lattice constant and thermal expansion of the GaN grown by ELOG during the process of growing from the space between the protective films and covering the protective film by lateral growth to form a thick film. It is considered that the coefficient is different from those of the n-type contact layer.

[0005] Even if the dislocation density inside GaN obtained by ELOG growth can be reduced, if fine cracks are generated in the n-type contact layer grown on GaN grown by ELOG, the activity to grow on this is increased. It may be propagated to a layer or the like, and it is difficult to sufficiently exhibit performance even when an element structure capable of high life characteristics and high output is formed. In order to obtain good life characteristics, it is desired that a substrate or the like for growing an element structure has no crystal defects or fine cracks.

[0006] Further, a laser device having good life characteristics such as the above-mentioned JJAP has been announced. However, in consideration of application of the laser device to various products, the threshold value is further lowered to reduce heat generation in the device. It is desired to lower it and improve the life characteristics. Methods for lowering the threshold include improving the crystallinity of the laser device, preventing propagation loss in the laser waveguide, enhancing light confinement in the laser waveguide, good confinement of electrons in the active layer, It is possible to reduce the bulk resistance of each layer of the structure. Various methods have been proposed and studied for each layer in order to lower such a threshold value. However, in order to further reduce the threshold value, each layer of the element structure constituting the element is required. It is desired to consider the relationship in the above and the entire element structure.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a nitride semiconductor laser device which reduces dislocations and fine cracks in the laser device, lowers the threshold value, and has better life characteristics. is there.

[0008]

That is, the present invention can achieve the object of the present invention by the following constitutions (1) to (12). (1) In a nitride semiconductor laser device having a ridge-shaped stripe in which at least an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially stacked on a substrate, the substrate is made of a nitride semiconductor After forming a protective film made of a material on which a nitride semiconductor does not grow or hardly grow on a nitride semiconductor grown on the heterogeneous substrate and a nitride semiconductor grown on the heterogeneous substrate, And an n-type nitride semiconductor is formed on the substrate by Al _a
A nitride semiconductor laser device having an n-type contact layer made of Ga1 _- aN (0 <a <1). (2) the active _{layer, In b Ga 1-b N} (0 ≦ b <
The nitride semiconductor device according to (1), wherein the nitride semiconductor device has a quantum well structure including (1). (3) The p-type nitride semiconductor layer has at least one or more p-type electron confinement layers made of Al _d Ga _1-d N (0 <d ≦ 1) in contact with the active layer. The nitride semiconductor laser device according to the above (1) or (2), wherein (4) In the n-type nitride semiconductor layer, G
(1) An n-type guide layer made of aN, and a p-type guide layer made of GaN in contact with the n-type electron confinement layer in the p-type nitride semiconductor layer. The nitride semiconductor laser device according to any one of (1) to (3). (5) a nitride including an n-type cladding layer made of a nitride semiconductor containing Al in contact with the substrate side of the n-type guide layer, and a nitride containing Al in contact with a side of the p-type guide layer opposite to the active layer; The nitride semiconductor laser device according to any one of the above (1) to (4), comprising a p-type cladding layer made of a semiconductor. (6) Mg-doped GaN on the p-type cladding layer
The nitride semiconductor laser device according to any one of the above (1) to (5), comprising a p-type contact layer made of (7) the said between the n-type contact layer and the n-type cladding _layer, an _{In g Ga 1- g N (0.05} ≦ g ≦ 0.2) characterized by having a crack preventing layer (1)
The nitride semiconductor laser device according to any one of (1) to (6). (8) The p-type impurity concentration of each layer of the n-type nitride semiconductor layer is 1 × 10 ¹⁹ to 1 × 10 ²¹ / in order from the substrate side.
cm ³ p-type electron confinement layer, 1 × 10 ¹⁶ to 1 × 10
¹⁸ / cm ³ p-type guide layer, 1 × 10 ¹⁷ to 1 × 10
¹⁹ / cm ³ p-type cladding layer, 1 × 10 ¹⁹ to 1 × 1
The nitride semiconductor laser device according to any one of the above (1) to (7), wherein the nitride semiconductor laser device is a p-type contact layer of 0 ²² / cm ³ . (9) The nitride according to any one of (1) to (8), further comprising a high-temperature buffer layer made of undoped GaN between the contact layer and the nitride semiconductor substrate. Semiconductor laser device. (10) The nitride semiconductor laser device according to any one of (1) to (9), wherein the C-plane of sapphire is stepwise off-angled in the different substrate. (11) The off-angle of the sapphire substrate that is off-angled in the step shape is 0.1 ° to 0.3 °.
The nitride semiconductor laser device according to any one of the above (1) to (10), (12) The protective film has a stripe shape, and the width of the stripe and the width of the window portion where the protective film is not formed are 16
To 18: 3.
The nitride semiconductor laser device according to 1).

That is, according to the present invention, as described above, ELOG
By using a grown nitride semiconductor as a substrate and forming an n-type contact layer made of AlGaN thereon,
Even if the lattice constant is different from that of the nitride semiconductor grown by G, generation of fine cracks inside the n-type contact layer can be prevented, whereby fine cracks can be formed from the n-type contact layer to an upper layer (for example, an active layer). Can be prevented from being propagated, the threshold value can be reduced as compared with the conventional case, and a nitride semiconductor laser device having good life characteristics can be provided.

[0010] If a fine crack is generated in a nitride semiconductor substrate for forming an element structure constituting a laser element or an n-type contact layer formed close to the substrate,
Fine cracks are liable to propagate to various element structures (for example, an active layer) grown on the n-type contact layer, thereby deteriorating element characteristics such as life characteristics. On the other hand, the present inventors have conducted various studies in order to prevent fine cracks which are considered to be caused by a difference in lattice constant between the nitride semiconductor grown by ELOG and the n-type contact layer. It has been found that the generation of fine cracks is favorably prevented by growing the layer with a ternary mixed crystal of AlGaN. Further, when the n-type contact layer is grown with a ternary mixed crystal as described above, n
Generation of fine cracks inside the n-type contact layer can be prevented, and even if fine cracks occur in the nitride semiconductor substrate grown by ELOG, the fine cracks can be prevented from being propagated to the n-type contact layer. can do. If the n-type contact layer grown on the nitride semiconductor substrate has good crystallinity, various layers with good characteristics are formed on the n-type contact layer to prevent the crystallinity from being lowered and to prevent the entire laser device from being deteriorated. Can be improved, and the characteristics of each layer can be sufficiently exhibited. As a result, the threshold value can be further reduced, and the life characteristics of the nitride semiconductor laser device can be improved.

Further, according to the present invention, the various nitride semiconductor layers of the element structure constituting the element are individually examined and the entire element is examined comprehensively at the same time, thereby lowering the threshold voltage and improving the device performance. In order to make a laser device with long life characteristics,
The layer structure is specified as described above.

Further, according to the present invention, the concentration of the p-type impurity in each layer of the p-type nitride semiconductor layer is 1 × 10 ¹⁹ from the substrate side.
~ 1 × 10 ²¹ / cm ³ p-type electron confinement layer, 1 × 10
¹⁶ to 1 × 10 ¹⁸ / cm ³ p-type guide layer, 1 × 10 ¹⁷ to
1 × 10 ¹⁹ / cm ³ p-type cladding layer, 1 × 10 ¹⁹ to 1
By using a p-type contact layer of × 10 ²² / cm ³ , the bulk resistance of the entire device is reduced, the contact resistance with the p-electrode is further reduced, and the portion of the laser waveguide through which light propagates, in particular, By suppressing the propagation loss by suppressing the amount of Mg doping in the guide layer of the waveguide, the threshold value can be reduced and the life characteristics can be more improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to FIG. FIG. 1 is a schematic sectional view showing a nitride semiconductor laser device according to an embodiment of the present invention.
FIG. 1 shows that an n-type impurity (for example, S) is formed on a nitride semiconductor substrate 1 grown by ELOG on a heterogeneous substrate such as sapphire.
i) an n-type contact layer 2 made of Al _a Ga _1-a N (0 <a <1) doped with Si; a Si-doped In _g Ga _1-g
A crack prevention layer 3 made of N (0.05 ≦ g ≦ 0.2), an n-type clad layer 4 of a multilayer film containing Al _e Ga _1-e N (0.12 ≦ e <0.15), Undoped GaN
N-type guide layer 5 of In _b Ga ₁ -bN (0 ≦ b <
An active layer 6 having a multiple quantum well structure comprising 1) and at least 1 comprising Mg-doped Al _d Ga _{1 -d} N (0 <d ≦ 1).
Layers above the p-type electron confinement layer 7, p-type guide layer 8 made of undoped _{GaN, Al f Ga 1-f} N (0 <f ≦ 1)
1 shows a nitride semiconductor laser device having a ridge-shaped stripe formed of a p-type cladding layer 9 of a multilayer film and a p-type contact layer 10 of Mg-doped GaN. The p-electrode is formed on the uppermost layer of the ridge-shaped stripe, and the n-electrode is formed on the n-type contact layer. Hereinafter, each layer will be described in more detail.

The ELOG growth will be described below. ELOG growth that can be used in the present invention is to at least partially temporarily stop vertical growth of nitride semiconductors,
There is no particular limitation on the growth method as long as dislocations can be suppressed by utilizing lateral growth. For example, specifically, on a heterogeneous substrate made of a material different from that of the nitride semiconductor, a protective film made of a material that does not or hardly grow a nitride semiconductor is partially formed, and the nitride semiconductor is grown thereon. As a result, the nitride semiconductor grows from the portion where the protective film is not formed, and grows laterally toward the protective film by continuing the growth, thereby obtaining a thick nitride semiconductor.

The heterogeneous substrate is not particularly limited as long as the substrate is made of a material different from that of the nitride semiconductor. For example, sapphire, spinel (C), R (plane) and A (plane) shown in FIG. an insulating substrate such as MgA1 ₂ O _4), S
iC (including 6H, 4H, 3C), ZnS, ZnO, G
A substrate material different from a conventionally known nitride semiconductor, such as an oxide substrate that lattice-matches with aAs, Si, and a nitride semiconductor, can be used. Among the above-mentioned different kinds of substrates, sapphire is preferable, and the C-plane of sapphire is more preferable. Further, the C-plane of sapphire is off-angled in a step-like manner from the viewpoint that generation of fine cracks in the nitride semiconductor obtained by ELOG growth can be prevented, and the off-angle angle θ (θ shown in FIG. 3). ) Is 0.
Those having a range of 1 ° to 0.3 ° are preferred. If the off-angle angle θ is less than 0.1 °, the characteristics of the laser element tend to be stable, and fine cracks tend to be easily generated inside the nitride semiconductor grown by ELOG. When the angle exceeds 0.3 °, the surface state of the nitride semiconductor grown by ELOG becomes step-like, and when the element structure is grown thereon, the steps are slightly emphasized, which tends to cause short-circuiting of the element and an increase in threshold voltage. There is.

A protective film is formed on a heterogeneous substrate such as sapphire that is off-angled in a step-like manner as described above, either directly or once a nitride semiconductor is grown. The protective film is not particularly limited as long as the material has a property that the nitride semiconductor does not grow or hardly grows on the surface of the protective film. Examples of the material include silicon oxide (SiO _x ), silicon nitride (Si _x N _y ), and oxide. Oxides such as titanium (TiO _x ) and zirconium oxide (ZrO _x ), nitrides, multi-layered films thereof, and metals having a melting point of 1200 ° C. or more can be used. A preferred protective film material is SiO 2
₂ and SiN. To form a protective film material on the surface of a nitride semiconductor or the like, for example, vapor deposition, sputtering, CV
For example, a vapor deposition technique such as D can be used. Further, in order to partially (selectively) form, a photomask having a predetermined shape is manufactured by using a photolithography technique, and the material is vapor-phase-formed through the photomask. A protective film having a predetermined shape can be formed. Although the shape of the protective film is not particularly limited, it can be formed, for example, in a dot, stripe, or checkerboard shape, and is preferably formed in a stripe shape so that the stripe is perpendicular to the orientation flat surface (Sapphire A surface). Is done. When the surface area where the protective film is formed is larger than the surface area where the protective film is not formed, dislocation is prevented and a nitride semiconductor substrate having good crystallinity can be obtained.

When the protective film has a stripe shape, the relationship between the stripe width of the protective film and the width of the portion (window) where the protective film is not formed is 10: 3 or more, preferably 16 to 18: 3. When the stripe width of the protective film and the width of the window portion have the above relationship, the nitride semiconductor can easily cover a good protective film, and dislocation can be prevented well. The stripe width of the protective film is, for example, 6 to 27 μm.
m, preferably 11 to 24 μm, and the width of the window is, for example, 2 to 5 μm, preferably 2 to 4 μm.
In the case where a device structure is formed on a nitride semiconductor obtained by ELOG growth and a ridge-shaped stripe is formed on the uppermost layer of the p-type nitride semiconductor layer, the ridge-shaped stripe is located above the protective film, In addition, it is preferable that the protective film is formed so as to avoid the central portion of the protective film, since the threshold value can be lowered and the reliability of the element is improved. This is because the crystallinity of the nitride semiconductor in the upper part of the protective film is better than that in the upper part of the window, and is therefore preferable for lowering the threshold value. Also, near the center of the protective film,
Adjacent nitride semiconductors grown from the window are joined by lateral growth, and a gap may be formed at such a joint.When a ridge-shaped stripe is formed at the top of the gap, This is because, during operation of the laser element, the dislocation tends to propagate from the gap, and thus the reliability of the element tends to deteriorate.

The protective film may be formed directly on a heterogeneous substrate. However, forming a buffer layer grown at a low temperature and growing a nitride semiconductor grown at a high temperature and then forming a nitride semiconductor prevents dislocation. Preferred. Examples of the low-temperature growth buffer layer include AlN, GaN, AlGaN, and InG.
aN or the like is grown at a temperature of 900 ° C. or less and 200 ° C. or more with a film thickness of several tens angstroms to several hundred angstroms. This buffer layer is preferable for alleviating lattice constant irregularities between the heterogeneous substrate and the nitride semiconductor layer grown at a high temperature and preventing the occurrence of dislocation. As the nitride semiconductor grown at a high temperature, undoped GaN, GaN doped with an n-type impurity, or GaN doped with Si can be used, and undoped GaN is preferable. In addition, these nitride semiconductors are used at a high temperature, specifically 9
It is grown on the buffer layer at a temperature between 00C and 1100C, preferably at 1050C. The thickness is not particularly limited, but is, for example, 1 to 20 μm, and preferably 2 to 10 μm.

Next, after forming a protective film, a nitride semiconductor is grown by ELOG to obtain a nitride semiconductor substrate 1. In this case, as the nitride semiconductor to be grown, undoped GaN or impurities (for example, Si, Ge, Sn, Be, Z
GaN doped with n, Mn, Cr, and Mg). The growth temperature is, for example, 900 ° C. to 1100
C., more specifically, at a temperature around 1050.degree. Doping with an impurity is preferable for suppressing dislocation. MOCVD (Metal-Organic Chemical Vapor Deposition), in which the growth rate is easy to control at the beginning of the growth on the protective film
The growth after the protective film is covered with the nitride semiconductor of the ELOG growth may be performed by HVPE (halide vapor phase epitaxy) or the like.

The nitride half obtained by the above LOG growth
An element structure is grown on the conductive substrate 1. First, n-type
A contact layer 2 is grown on the nitride semiconductor substrate 1. n
The n-type impurity (preferably S
i) Al doped_aGa_1-aN (0 <a <1)
Al, preferably a is 0.01 to 0.05 Al_aG
a_1-aGrow N. n-type contact layer contains Al
When formed with a ternary mixed crystal, fine nitride semiconductor substrate 1
Prevents the propagation of minute cracks even if cracks have occurred
Nitride nitride, which has been a problem in the past.
Lattice constant and thermal expansion between conductive substrate 1 and n-type contact layer
Fine cracks in n-type contact layer due to difference in coefficient
This is preferable because the occurrence of phenomena can be prevented. n-type impurity
1 x 10¹⁸/ Cm^Three~ 5 × 10¹⁸/ C
m^ThreeIt is. An n-electrode is formed on this n-type contact layer 2.
It is. The thickness of the n-type contact layer 2 is 1 to 10 μm.
m. Also, the nitride semiconductor substrate 1 and the n-type contact
Between layer 2 and undoped Al _aGa_1-aN (0 <a <
1) may be grown, and this undoped layer may be grown
The crystallinity becomes good when it is
preferable. The thickness of the undoped n-type contact layer is several μm.
m.

Next, a crack preventing layer 3 is grown on the n-type contact layer 2. The crack preventing layer 3 is made of Si
A doped In _g Ga _1-g N (0.05 ≦ g ≦ 0.2) is grown, and preferably, In _g G having a g of 0.05 to 0.08.
a _1-g N is grown. Although the crack preventing layer 3 can be omitted, it is preferable to form the crack preventing layer 3 on the n-type contact layer 2 to prevent cracks from occurring in the device. The doping amount of Si is 5 × 10
¹⁸ / cm ³ . When growing the crack preventing layer 3, if the mixed crystal ratio of In is large (x ≧ 0.1),
The crack preventing layer 3 is preferable because it can absorb light emitted from the active layer 6 and leaked from the n-type cladding layer 4 and can prevent disturbance of a far field pattern of laser light. The thickness of the crack prevention layer is a thickness that does not impair the crystallinity.
5 to 0.3 μm.

Next, an n-type cladding layer 4 is grown on the crack preventing layer 3. As the n-type cladding layer 4, Al _e
It is formed as a layer of a multilayer film including a nitride semiconductor containing Ga ₁ -eN (0.12 ≦ e <0.15). What is a multilayer film?
₁ shows a multilayer structure in which nitride semiconductor layers having different compositions are stacked, for example, Al _e Ga _{1 -e} N (0.12 ≦ e <
0.15) layer and a nitride semiconductor having a different composition from Al _e Ga _{1 -e} N, for example, a compound having a different mixed crystal ratio of Al, a ternary mixed crystal containing In, or GaN. It is formed by laminating layers in combination. As a preferable combination among them, a multilayer film formed by stacking Al _e Ga _{1 -e} N and GaN is preferable because a nitride semiconductor layer having good crystallinity can be stacked at the same temperature. A more preferred multilayer film is a combination of undoped Al _e Ga _{1 -e} N and GaN doped with an n-type impurity (for example, Si). The n-type impurity may be doped into Al _e Ga _1-e N. The doping amount of the n-type impurity is 4 × 10 ¹⁸ / c
m ³ -5 × 10 ¹⁸ / cm ³ . When the n-type impurity is doped in this range, the resistivity can be lowered and the crystallinity is not impaired. Such a multilayer film has a single layer thickness of 100.
Angstroms or less, preferably 70 Angstroms or less, more preferably 40 Angstroms or less,
Preferably, a nitride semiconductor layer having a thickness of 10 Å or more is laminated. If the single film thickness is less than 100 angstroms, the n-type cladding layer has a superlattice structure, so that cracks can be prevented and the crystallinity can be improved irrespective of containing Al. Also,
The total thickness of the n-type cladding layer 4 is 0.7 to 2 μm. The average composition of Al in the entire n-type cladding layer is:
0.05 to 0.1. When the average composition of Al is within this range, the composition ratio is such that cracks are not generated, and is a preferable composition ratio for sufficiently obtaining a difference in refractive index from the laser waveguide.

Next, the n-type guide layer 5 is replaced with the n-type clad layer 4.
Grow on. As the n-type guide layer 5, a nitride semiconductor made of undoped GaN is grown. When the film thickness of the n-type guide layer 5 is 0.1 to 0.07 μm, the threshold value is lowered, which is preferable. By undoping the n-type guide layer 4, the propagation loss in the laser waveguide is reduced,
The threshold is low, which is preferable.

Next, an active layer 6 is grown on the n-type guide layer 5. As the active layer, In _b Ga _1-b N (0 ≦ b <
1) A multi-quantum well structure including (1). As the well layer of the active layer 6, In _b Ga _1-b N where b is 0.1 to 0.2
And the barrier layer is made of In _b G in which b is 0 to 0.01.
a _{1 -bN} . Further, one or both of the well layer and the barrier layer constituting the active layer 6 may be doped with impurities. It is preferable that the barrier layer is doped with an impurity, since the threshold value is reduced. The thickness of the well layer is 30
６０60 Å, and the thickness of the barrier layer is 90-150 Å.

The multi-quantum well structure of the active layer 6 may start with the barrier layer and end with the well layer, start with the barrier layer and end with the barrier layer, start with the well layer and end with the barrier layer.
Further, it may start from the well layer and end at the well layer. Preferably, starting from the barrier layer, the pair of the well layer and the barrier layer
It is preferable to repeat five times, preferably three times the pair of the well layer and the barrier layer, in order to lower the threshold value and improve the life characteristics.

Next, a p-type electron confinement layer 7 is grown on the active layer 6. The p-type electron confinement layer 7 is formed by growing at least one layer made of Mg-doped Al _d Ga _{1 -dN} (0 <d ≦ 1). Preferably d
Is 0.1 to 0.5 Mg-doped Al _d Ga ₁ -dN. The thickness of the p-type electron confinement layer 7 is 10 to 1000 Å, preferably 50 to 200 Å. When the film thickness is in the above range, electrons in the active layer 6 can be satisfactorily confined, and the bulk resistance can be suppressed low, which is preferable. The doping amount of Mg in the p-type electron confinement layer 7 is 1 × 10 ¹⁹ / cm ³ to 1 × 10
²¹ / cm ³ . When the doping amount is within this range, in addition to lowering the bulk resistance, Mg is well diffused into a p-type guide layer grown by undoping described later, and Mg is added to the p-type guide layer 8 which is a thin film layer. × 10 ¹⁶ / cm ³ or more
It can be contained in the range of 1 × 10 ¹⁸ / cm ³ .
The p-type electron confinement layer 7 is formed at a low temperature, for example, 850 to 9
It is preferable to grow the active layer at a temperature similar to the temperature at which the active layer is grown at about 50 ° C., because decomposition of the active layer can be prevented. The p-type electron confinement layer 7 may be composed of two layers: a layer grown at a low temperature and a layer grown at a high temperature, for example, at a temperature of about 100 ° C. higher than the growth temperature of the active layer. As described above, when the layer is composed of two layers, the layer grown at a low temperature prevents the decomposition of the active layer, and the layer grown at a high temperature lowers the bulk resistance. When the p-type electron confinement layer 7 is composed of two layers, the thickness of each layer is not particularly limited, but the low temperature growth layer is preferably 10 to 50 angstroms, and the high temperature growth layer is preferably 50 to 150 angstroms.

Next, a p-type guide layer 8 is grown on the p-type electron confinement layer 7. The p-type guide layer 8 is grown as a nitride semiconductor layer made of undoped GaN. The film thickness is 0.1 to 0.07 μm,
This range is preferable because the threshold value is lowered. As described above, the p-type guide layer is grown as an undoped layer.
g is diffused and 1 × 10 ¹⁶ / cm ³ to 1 × 10 ¹⁸ / cm ³
Mg is contained within the range.

Next, the p-type cladding layer 9 is replaced with the p-type guide layer 8.
To grow. The p-type cladding layer, Al _f Ga _1-f
Of a multilayer film having a nitride semiconductor layer containing N (0 <f ≦ 1), preferably a nitride semiconductor layer containing Al _f Ga _{1 -fN} (0.05 ≦ f ≦ 0.15). Formed as a layer. The multilayer film is a multilayer film structure in which nitride semiconductor layers having different compositions are stacked, for example, Al _f Ga _{1 -fN}
A combination of a layer and a nitride semiconductor having a different composition from Al _f Ga ₁ -fN, for example, a compound having a different mixed crystal ratio of Al, a ternary mixed crystal containing In, or a layer made of GaN or the like It is formed by laminating. Preferred combinations in this, when a multilayer film formed by laminating a GaN and Al _f Ga _1-f N, preferably be laminated excellent crystallinity nitride semiconductor layer at the same temperature. And more preferred multilayer film is a combination formed by laminating a GaN undoped Al _f Ga _1-f N and p-type impurities (e.g., Mg) doped. p-type impurity may be doped in the Al _f Ga _1-f N. The doping amount of the p-type impurity is 1 × 10 ¹⁷ / cm ³ to 1 × 10 ¹⁹
/ Cm ³ . It is preferable that the p-type impurity is doped in this range because the doping amount is such that the crystallinity is not impaired and the bulk resistance is low. Such a multilayer film has a single layer thickness of 100 Å or less, preferably 70 Å or less.
A nitride semiconductor layer having a thickness of not more than Å, more preferably not more than 40 Å, preferably not less than 10 Å is formed. 1 single film thickness
When the thickness is less than 00 Å, the n-type cladding layer has a superlattice structure, and although it contains Al,
Cracks can be prevented and crystallinity can be improved. The total thickness of the p-type cladding layer 9 is 0.4 to
0.5 μm, and within this range, the forward voltage (V
Preferred for reducing f). The average composition of Al in the entire p-type cladding layer is 0.05 to 0.1. This value is preferable for suppressing the occurrence of cracks and obtaining a difference in refractive index from the laser waveguide.

Next, a p-type contact layer 10 is grown on the p-type cladding layer 9. As the p-type contact layer, M
This is obtained by growing a nitride semiconductor layer made of g-doped GaN. The film thickness is 10 to 200 angstroms. The doping amount of Mg is 1 × 10 ¹⁹ / cm ³ -1 × 1
0 ²² / cm ³ . By adjusting the film thickness and the doping amount of Mg in this manner, the carrier concentration of the p-type contact layer increases, and the p-electrode is easily made ohmic.

In the device of the present invention, the ridge-shaped stripe is formed by being etched from the p-type contact layer to the lower side (substrate side) than the p-type contact layer. For example, a stripe formed by etching from the p-type contact layer 10 to the middle of the p-type cladding layer 9 as shown in FIG.
To the n-type contact layer 2.

On the side surface of the ridge-shaped stripe formed by etching or on the plane of the nitride semiconductor layer continuous with the side surface, for example, as shown in FIG. A film is formed.
As the insulating film formed on the side surface of the stripe or the like, for example, S has a refractive index of about 1.6 to 2.3.
an oxide containing at least one element selected from the group consisting of i, V, Zr, Nb, Hf, and Ta, BN, Al
N and the like, and preferably one or more elements of oxides of Zr and Hf, and BN. Further, a p-electrode is formed on the surface of the p-type contact layer 10 at the uppermost layer of the stripe via the insulating film. The width of the ridge-shaped stripe formed by etching is 0.5
４4 μm, preferably 1-3 μm. When the width of the stripe is in this range, the horizontal / lateral mode is easily changed to a single mode, which is preferable. Further, the etching is performed in the p-type cladding layer 9.
It is preferable to make the aspect ratio close to 1 when the distance is set to be closer to the substrate than the interface between the laser waveguide region and the laser waveguide region. As described above, when the etching amount of the ridge-shaped stripe, the stripe width, and the refractive index of the insulating film on the side surface of the stripe are specified, a single-mode laser beam can be obtained, and the aspect ratio can be made closer to a circle. This is preferable because the design of the laser beam and the lens becomes easy. In the device of the present invention, various types of conventionally known p-electrodes and n-electrodes can be appropriately selected and used.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment which is an embodiment of the present invention will be described below. However, the present invention is not limited to this. In addition, although the present embodiment shows MOVPE (metal organic chemical vapor deposition), the method of the present invention is not limited to MOVPE, for example, HVPE (halide vapor phase epitaxy),
All known methods for growing nitride semiconductors, such as MBE (Molecular Beam Epitaxy), can be applied.

Example 1 As Example 1, the nitride semiconductor laser device according to one embodiment of the present invention shown in FIG. 1 is manufactured.

As shown in FIG. 3, the main surface of the hetero-substrate is a stepped off-angled C-plane, with an off-angle of θ = 0.15 °, a step height of about 20 Å, and a terrace width W of about 800 Å. In this case, a sapphire substrate is prepared in which the orientation flat surface is the A surface and the steps are perpendicular to the A surface. This sapphire substrate was set in a reaction vessel, the temperature was set to 510 ° C., hydrogen was used as a carrier gas, ammonia and TMG (trimethylgallium) were used as source gases, and a low-temperature growth buffer layer made of GaN was formed on the sapphire substrate. It is grown to a thickness of 200 angstroms. After the growth of the buffer layer, only TMG was stopped, the temperature was raised to 1050 ° C., and when the temperature reached 1050 ° C., a high-temperature grown buffer layer of undoped GaN was formed to a thickness of 5 μm using TMG, ammonia, and silane gas as source gases. Grow with. Next, a stripe-shaped photomask is formed on the wafer on which the buffer layer grown at a high temperature is laminated, and a stripe width of 18 μm is formed by a CVD apparatus.
m, a protective film made of SiO _{2 having} a window portion having a width of 3 μm is 0.1
It is formed with a film thickness of μm. The stripe direction of the protective film is a direction perpendicular to the sapphire A plane. After forming the protective film,
The wafer is transferred to a reaction vessel, and a nitride semiconductor layer made of undoped GaN is grown to a thickness of 15 μm at 1050 ° C. using TMG and ammonia as source gases to obtain a nitride semiconductor substrate 1. Using the obtained nitride semiconductor as a nitride semiconductor substrate 1, the following element structure is stacked and grown.

(Undoped n-type contact layer) [not shown in FIG. 1] On the nitride semiconductor substrate 1, a source gas of TM
An n-type contact layer made of undoped Al _0.05 Ga _0.95 N is grown to a thickness of 1 μm using A (trimethylaluminum), TMG, and ammonia gas. (N-type contact layer 2) Next, at the same temperature, TMA
N-type contact layer 2 made of Al _0.05 Ga _0.95 N doped with Si at 3 × 10 ¹⁸ / cm ³ using TMG and ammonia gas, silane gas (SiH ₄ ) as an impurity gas;
Is grown to a thickness of 3 μm. Fine cracks are not generated in the grown n-type contact layer 2, and the generation of fine cracks is well prevented. In addition, even if a fine crack is generated in the nitride semiconductor substrate 1, the growth of the n-type contact layer 2 can prevent the propagation of the fine crack and grow an element structure having good crystallinity. The improvement in the crystallinity can be improved by growing the undoped n-type contact layer as described above, as compared with the case where only the n-type contact layer 2 is used.

(Crack prevention layer 3) Next, the temperature was set to 800
℃, TMG, TMI (trimethyl in
Silane and ammonia as impurity gas
5 × 10 ¹⁸/ Cm^ThreeDoped In
_0.08Ga_0.920.15 μm of crack prevention layer 3 made of N
It is grown to a thickness of m.

(N-type cladding layer 4) Next, the temperature was set to 105
At 0 ° C., a layer A of undoped Al _0.14 Ga _0.86 N is grown to a thickness of 25 Å using TMA, TMG and ammonia as source gases,
Stop MA, use silane gas as impurity gas, Si
Is grown at a thickness of 25 angstroms from a B layer made of GaN doped with 5 × 10 ¹⁸ / cm ³ . This operation is repeated 160 times to laminate the A layer and the B layer to grow the n-type cladding layer 4 composed of a multilayer film (superlattice structure) having a total film thickness of 8000 Å.

(N-type guide layer 5) Next, at the same temperature,
Using TMG and ammonia as source gases, an n-type guide layer made of undoped GaN is grown to a thickness of 0.075 μm.

(Active Layer 6) Next, the temperature was raised to 800 ° C., and TMI, TMG and ammonia were used as raw material gases.
Using silane gas as an impurity gas, Si is 5 × 10 ¹⁸
A barrier layer made of In _0.01 Ga _0.99 N doped with / cm ³ is grown to a thickness of 100 Å. Subsequently, the silane gas was stopped, and undoped In _0.11 Ga _0.89
A well layer made of N is grown to a thickness of 50 angstroms. This operation is repeated three times, and finally, the active layer 6 having a multiple quantum well structure (MQW) having a total film thickness of 550 Å, on which the barrier layers are stacked, is grown.

(P-type electron confinement layer 7) Next, at the same temperature, TMA, TMG and ammonia are used as source gases, Cp ₂ Mg (cyclopentadienyl magnesium) is used as an impurity gas, and Mg is 1 ×. A p-type electron confinement layer 7 of 10 ¹⁹ / cm ³ doped Al _0.4 Ga _0.6 N is grown to a thickness of 100 Å.

(P-type guide layer 8) Next, the temperature was set to 1050
° C, and using TMG and ammonia as source gases, a p-type guide layer 8 made of undoped GaN was set to 0.075.
It is grown to a thickness of μm. The p-type guide layer 8 is grown as undoped, but the Mg concentration becomes 5 × 10 ¹⁶ / cm ³ due to the diffusion of Mg from the p-type electron confinement layer 7, indicating p-type.

(P-type cladding layer 9) Next, at the same temperature, using TMA, TMG and ammonia
An A layer made of undoped Al _0.1 Ga _0.9 N is grown to a thickness of 25 Å, followed by stopping TMA, using Cp ₂ Mg as an impurity gas, and adding 5 × 1 Mg.
A B layer of GaN doped with 0 ¹⁸ / cm ³ is grown to a thickness of 25 Å. This operation is repeated 100 times to stack the A layer and the B layer, thereby growing the p-type cladding layer 9 composed of a multilayer film (superlattice structure) having a total thickness of 5000 Å.

(P-type contact layer 10) Next, at the same temperature, TMG and ammonia are used as source gases, Cp ₂ Mg is used as an impurity gas, and Mg is 1 × 10 ²⁰ / cm ^3.
The p-type contact layer 10 made of doped GaN is
It is grown to a thickness of 0 Å.

After the completion of the reaction, the wafer is annealed at 700 ° C. in a nitrogen atmosphere in a reaction vessel to further reduce the resistance of the p-type layer. After annealing, the wafer is taken out of the reaction vessel, a protective film made of SiO ₂ is formed on the surface of the uppermost p-side contact layer, and is etched by SiCl ₄ gas using RIE (reactive ion etching). As shown, the surface of the n-side contact layer 2 where the n-electrode is to be formed is exposed. Next, as shown in FIG. 4A, almost the entire surface of the uppermost p-side contact layer 10 is
Si oxide (mainly SiO ₂ ) by PVD equipment
After forming a first protective film 61 of 0.5 μm in thickness, a mask of a predetermined shape is applied on the first protective film 61, and a third protective film 63 of a photoresist is It is formed with a width of 1.8 μm and a thickness of 1 μm. Next, as shown in FIG. 4B, after forming the third protective film 63, RIE is performed.
(Reactive ion etching) The first protective film is etched into a stripe shape by using a CF ₄ gas with the third protective film 63 as a mask. Thereafter, the photoresist is removed only by treating with an etchant, thereby forming the p-side contact layer 1 as shown in FIG.
A first protective film 61 having a stripe width of 1.8 μm can be formed on the first protective film 61.

Further, as shown in FIG. 4D, after the first protection film 61 in the form of a stripe is formed, S is formed again by RIE.
The p-side contact layer 10 and the p-side cladding layer 9 are etched using iCl ₄ gas to obtain a stripe width of 1.
An 8 μm ridge-shaped stripe is formed. However, the ridge-shaped stripe is, as shown in FIG.
The protective film is formed above the protective film formed during the growth and so as to avoid the central portion of the protective film. After forming the ridge stripe, the wafer is transferred to a PVD apparatus, and a second protective film 62 made of Zr oxide (mainly ZrO ₂ ) is placed on the first protective film 61 as shown in FIG. 0.5 μm on the p-side cladding layer 9 exposed by etching.
It is formed continuously with a film thickness of. The formation of the Zr oxide in this way is preferable because the pn plane is insulated and the transverse mode can be stabilized. Next, the wafer is immersed in hydrofluoric acid to form a first protective film 61 as shown in FIG.
Is removed by a lift-off method.

Next, as shown in FIG. 4 (g), the first protective film 61 on the p-side contact layer 10 is removed and the exposed surface of the p-side contact layer is made of Ni / Au.
An electrode 20 is formed. However, the p-electrode 20 has a stripe width of 100 μm and is formed over the second protective film 62 as shown in FIG. After forming the second protective film 62,
As shown in FIG. 1, an n-electrode 21 made of Ti / Al is formed on the exposed surface of the n-side contact layer 2 in a direction parallel to the stripe.

As described above, the sapphire substrate of the wafer on which the n-electrode and the p-electrode are formed is polished to 70 μm, and then cleaved in a bar shape from the substrate side in a direction perpendicular to the stripe-shaped electrodes. A resonator is formed on a cleavage plane (11-00 plane, a plane corresponding to the side surface of a hexagonal columnar crystal = M plane).
A dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on the cavity surface, and finally, the bar is cut in a direction parallel to the p-electrode to obtain a laser device as shown in FIG. The resonator length is 30
It is desirable to set it to 0 to 500 μm. The obtained laser element was set on a heat sink, and the respective electrodes were wire-bonded, and laser oscillation was attempted at room temperature. As a result, continuous oscillation at an oscillation wavelength of 400 nm was confirmed at room temperature with a threshold value of 2.5 kA / cm ² and a threshold voltage of 5 V, and a lifetime of 10,000 hours or more was shown at room temperature.

Example 2 A nitride semiconductor laser device is manufactured in the same manner as in Example 1, except that the p-type electron confinement layer 7 is constituted by two layers as follows. (P-type electron confinement layer 7) The temperature is set to 800 ° C.
Using MA, TMG, and ammonia, using Cp ₂ Mg (cyclopentadienyl magnesium) as an impurity gas, and adding Al _0.4 Ga doped with 5 × 10 ¹⁸ / cm ^{3 of} Mg.
A low-temperature-grown A layer of _0.6 N is grown to a thickness of 30 Å, and then the temperature is set to 900 ° C.
Consists of two layers, a low-temperature-grown A layer and a high-temperature-grown B layer formed by growing a high-temperature-grown B layer of Al _0.4 Ga _0.6 N doped with 5 × 10 ¹⁸ / cm ³ to a thickness of 70 Å. A p-type electron confinement layer 7 is grown. The obtained laser element has good life characteristics as in Example 1.

Example 3 In Example 1, when growing the crack prevention layer 3, the composition ratio of In was set to 0.2, and In _0.2 Ga doped with 5 × 10 ¹⁸ / cm ^{3 of} Si was used.
_A laser device is manufactured in the same manner except that the crack prevention layer 3 of _0.8 N is grown to a thickness of 0.15 μm. The obtained laser device has good life characteristics as in Example 1, and light emitted from the active layer 6 and leaked from the n-type cladding layer is satisfactorily formed in the laser device (cladding prevention layer 3). It is absorbed and the far field pattern becomes better than that of the first embodiment.

[0050]

According to the present invention, it is possible to provide a nitride semiconductor laser device which reduces dislocations and fine cracks in the laser device, lowers the threshold value, and has better life characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a nitride semiconductor laser device according to one embodiment of the present invention.

FIG. 2 is a unit cell diagram showing a plane orientation of sapphire.

FIG. 3 is a schematic cross-sectional view showing a partial shape of an off-angle heterogeneous substrate.

FIG. 4 is a schematic cross-sectional view showing a partial structure of a wafer in each step of a method according to an embodiment for forming a ridge-shaped stripe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Nitride semiconductor substrate 2 ... N-type contact layer 3 ... Crack prevention layer 4 ... N-type cladding layer 5 ... N-type guide layer 6 ... Active layer 7 ... p -Type electron confinement layer 8 ... p-type guide layer 9 ... p-type cladding layer 10 ... p-type contact layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-10-290047 (JP, A) JP-A-9-293935 (JP, A) JP-A-5-190903 (JP, A) JP-A-7- 201745 (JP, A) WO 97/11518 (WO, A1) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (12)

(57) [Claims] 1. A nitride semiconductor laser device having a ridge-shaped stripe in which at least an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially stacked on a substrate. A nitride different from a semiconductor and a nitride film formed on a nitride semiconductor grown on the different substrate by forming a protective film made of a material on which the nitride semiconductor does not grow or hardly grows, and then selectively growing GaN. A n-type nitride semiconductor is formed on the substrate by Al _a Ga
_1-a A nitride semiconductor laser device having an n-type contact layer made of N (0 <a <1). Wherein said active layer _{is, In b Ga 1-b N} (0
2. The nitride semiconductor device according to claim 1, wherein the nitride semiconductor device has a quantum well structure including ≦ b <1). 3. 3. The p-type nitride semiconductor layer has at least one or more p-type electron confinement layers made of Al _d Ga _1-d N (0 <d ≦ 1) in contact with the active layer. The nitride semiconductor laser device according to claim 1, wherein: 4. An n-type nitride semiconductor layer, comprising: an n-type guide layer made of GaN in contact with an active layer;
Ga in contact with the n-type electron confinement layer
4. The nitride semiconductor laser device according to claim 1, further comprising a p-type guide layer made of N. 5. An Al contacting the n-type guide layer on the substrate side.
Having an n-type cladding layer made of a nitride semiconductor containing
5. The nitride semiconductor according to claim 1, further comprising a p-type clad layer made of a nitride semiconductor containing Al in contact with a side of the mold guide layer opposite to the active layer. Laser element. 6. The nitride semiconductor laser device according to claim 1, further comprising a p-type contact layer made of Mg-doped GaN on said p-type cladding layer. 7. between the n-type contact layer and the n-type cladding _{layer, In g Ga 1-g N} (0.05 ≦ g ≦ 0.2
7. The nitride semiconductor laser device according to claim 1, comprising a crack preventing layer. 8. The p-type impurity concentration of each layer of the n-type nitride semiconductor layer is 1 × 10 ¹⁹ to 1 × 10 in order from the substrate side.
²¹ / cm ³ p-type electron confinement layer, 1 × 10 ¹⁶ -1
× 10 ¹⁸ / cm ³ p-type guide layer, 1 × 10 ¹⁷ to 1
× 10 ¹⁹ / cm ³ p-type cladding layer, 1 × 10 ¹⁹ to
The nitride semiconductor laser device according to claim 1, wherein the nitride semiconductor laser device is a p-type contact layer of 1 × 10 ²² / cm ³ . 9. The nitride according to claim 1, further comprising a high-temperature buffer layer made of undoped GaN between said contact layer and said nitride semiconductor substrate. Semiconductor laser device. 10. The nitride semiconductor laser device according to claim 1, wherein the sapphire C-plane is off-angled in a step-like manner in the different substrate. 11. An off-angle angle of the sapphire substrate that is off-angled in a step shape is 0.1 ° to 0.1 °.
The nitride semiconductor laser device according to claim 1, wherein the angle is 0.3 °. 12. The protective film has a stripe shape,
The width of the stripe and the width of the window where the protective film is not formed are 16 to 18: 3.
12. The nitride semiconductor laser device according to item 11.