JP4131293B2 - Nitride semiconductor laser device and nitride semiconductor device - Google Patents

Description

The present invention relates to a nitride semiconductor laser element and a laser diode, a light emitting diode (LED), a light receiving element, a high frequency transistor, a high voltage transistor, and the like provided with an active layer containing In. In particular, the present invention relates to a nitride semiconductor laser device and a nitride semiconductor device in which device characteristics are improved by using a nitride semiconductor substrate having a specific off angle.

A laser element made of a nitride semiconductor such as GaN can be used in a wide range of oscillation wavelengths from an ultraviolet region of 370 nm or less to a wavelength region of 500 nm or more. Some substrates on which such laser elements are formed are formed by utilizing lateral growth called an ELOG (Epitaxially Lateral Overgrowth) method.

This technique, on the underlying substrate formed with SiO ₂ mask pattern having periodic stripe-shaped opening, and the GaN is laterally grown to form a GaN layer. Next, the substrate made of only the GaN layer is manufactured by removing the base substrate. GaN in laterally grown regions
Is a region with low dislocations. Since the crystallinity of low dislocation GaN is good, this GaN
Can be used as a substrate, the lifetime characteristics of the nitride semiconductor laser device can be improved.

Nitride semiconductor laser elements are also required to have improved element characteristics. Therefore, the substrate is required not only to lower the dislocation of the substrate itself but also to allow a nitride semiconductor layer having good crystallinity to be grown thereon. Furthermore, in order to put nitride semiconductor elements into practical use, it is necessary to increase the diameter of the substrate itself.
Therefore, a substrate made of a hexagonal nitride-based semiconductor has been proposed in which an off angle is formed in a predetermined direction from 1 ° to 20 ° from the (0001) plane (Reference Document 1).
JP 2002-16000 A

However, since this nitride semiconductor substrate has a wide range of off-angle tilts and off-angle tilt directions, the composition of In and Al, the distribution of impurities, and the like in the laser element vary. In particular, I
In the case of a laser element having an active layer containing n, the threshold current increases depending on the oscillation wavelength. Theoretically, a nitride semiconductor laser element can oscillate in a wide wavelength band, but in practice, this can be realized unless the composition distribution, for example, the In distribution in the active layer is made uniform. There are issues such as being unable to do so.
In addition, when manufacturing a substrate having a large diameter of 1 inch or more, pits and grooves remain on the main surface of the substrate. Therefore, it is necessary to planarize the surface with a nitride semiconductor layer formed on the substrate. There is also a problem of becoming.

The present invention has been made in view of the above points, and in a wide wavelength band, the composition distribution of the nitride semiconductor layer, for example, the crystallinity of the active layer and the In content are made uniform, and the lifetime characteristics and device characteristics are obtained. An object of the present invention is to provide a more excellent device.

A first nitride semiconductor laser element according to the present invention includes a first conductivity type nitride semiconductor layer, an active layer containing In, and a conductivity type different from the first conductivity type on a main surface of a nitride semiconductor substrate. A nitride semiconductor layer of the second conductivity type, and a stripe-shaped ridge portion in the nitride semiconductor layer of the second conductivity type, wherein the main surface of the nitride semiconductor substrate is relative to a reference crystal plane. And at least an off-angle a (θ _a ) in a direction substantially parallel to the stripe-shaped ridge portion.

Further, the second nitride semiconductor laser element includes a first conductivity type nitride semiconductor layer, an active layer, and a second conductivity having a conductivity type different from the first conductivity type on the main surface of the nitride semiconductor substrate. A nitride semiconductor layer of the type, and a stripe-shaped ridge portion in the nitride semiconductor layer of the second conductivity type, wherein the main surface of the nitride semiconductor substrate is the stripe shape with respect to a reference crystal plane off angle direction substantially parallel to the ridge of _a (θ a), characterized in that it has a off angle _b (θ b) in a substantially vertical direction.

Furthermore, the nitride semiconductor device of the present invention has a first conductivity type nitride semiconductor layer, an active layer, and a second conductivity type having a conductivity type different from the first conductivity type on the main surface of the nitride semiconductor substrate. Of the nitride semiconductor layer, and the main surface of the nitride semiconductor substrate has an off angle a (θ _a ) in a direction substantially perpendicular to the M plane (1-100) and an off angle in a direction substantially parallel to the M surface (1-100). b (θ _b ), and | θ _a | >> |
It is characterized by satisfying the relationship of θ _b |.

In these elements, (1) the reference crystal plane is (0001) plane, (11-20)
Or (1) the main surface of the nitride semiconductor substrate is (0001)
A first region comprising a plane and a second region having a crystal growth surface different from at least the first region; or (3) whether the second region is a (000-1) plane. (4) The main surface of the nitride semiconductor substrate has the first region and the second region substantially in parallel, or (5
) The first region is arranged immediately below the ridge or (6) 0.1 ° ≦ | θ _a | ≦ 0.7
Meet or _{°, (7) | θ a} |> | θ b | To meet or (8) a nitride semiconductor layer of a first conductivity type, either containing Al obtained by lateral growth, (9) first It is preferable that the region and the second region include at least one of the polarities separated in a stripe shape.

Further, in these elements, a core region including an active layer is formed between the first conductive type nitride semiconductor layer and the second conductive type nitride semiconductor layer,
At least one of the first conductivity type and the second conductivity type nitride semiconductor layer has a first nitride semiconductor layer and a second nitride semiconductor layer in order from the outermost layer of the core region,
It is preferable that there is a difference in refractive index between the outermost layer of the core region and the first nitride semiconductor layer and between the first nitride semiconductor layer and the second nitride semiconductor layer.

In this case, (a) the first nitride semiconductor layer has a lower refractive index than the outermost layer of the core region, or (b) the second nitride semiconductor layer has a refractive index lower than that of the first nitride semiconductor layer. Or (c) the refractive index difference (Δn ₁ ) between the outermost layer in the core region and the first nitride semiconductor layer and / or the refraction between the first nitride semiconductor layer and the second nitride semiconductor layer. The rate difference (Δn ₂ ) is 0.004 to 0.03, or (d) the n-type nitride semiconductor layer is formed in order from the first n-type nitride semiconductor layer in contact with the outermost layer of the core region. having an n-type nitride semiconductor layer of m (m ≧ 2),
The p-type nitride semiconductor layer has a first p-type nitride semiconductor layer in contact with the outermost layer of the core region,
The refractive index of the mth (m ≧ 2) n-type nitride semiconductor layer is higher than the refractive index of the first p-type nitride semiconductor layer. (E) The mth (m ≧ 2) n-type nitride semiconductor. The refractive index difference (Δn) between the layer and the first p-type nitride semiconductor layer is 0.004 to 0.03, or (f) the m-th (m ≧ 2) n-type nitride semiconductor layer The refractive index difference (Δn _m ) between the core region and the outermost layer is preferably 0.007 to 0.05 or more.

According to the element of the present invention, since the main surface of the nitride semiconductor substrate has an off angle in a predetermined direction, the composition distribution and film thickness distribution of the nitride semiconductor layer, for example, the crystallinity of the active layer And In content can be made uniform. This is because flat crystal growth can be performed starting from the step on the atomic plane. Thereby, the interface of the semiconductor layer grown on the main surface of the substrate can suppress an uneven step having a height difference, and can realize a range from an ultraviolet region having an oscillation wavelength of 365 nm or less to a long wavelength region having a wavelength of 500 nm or more. In the active layer, the composition distribution can be made uniform. In addition, an element having excellent lifetime characteristics and element characteristics can be obtained in such a wide wavelength band.

Further, when the element of the present invention has a predetermined refractive index difference relationship in a predetermined semiconductor layer, the stay region of light generated in the active layer is appropriately adjusted to stabilize the light. By performing confinement, the COD level can be improved. Further, the spread angle of the light intensity distribution in the vertical direction can be reduced, and the aspect ratio can be optimized or reduced to 2 or less. As a result, an increase in threshold voltage due to light leakage can be prevented, light output efficiency can be improved, a light collection rate is good, and a highly reliable element can be obtained.

The nitride semiconductor laser element and the nitride semiconductor element of the present invention (including both of them may be simply referred to as “element”) are the first main elements of the nitride semiconductor substrate (sometimes referred to as “substrate”). A nitride semiconductor layer of a first conductivity type on the surface (sometimes simply referred to as “semiconductor layer”), an active layer,
A nitride semiconductor layer of the second conductivity type (conductivity type different from the first conductivity type) is provided in this order. The nitride semiconductor element may be a laser element or an LED. In particular, in the case of a laser element, it is preferable that the second conductivity type nitride semiconductor layer has a striped ridge portion.

This element includes a second electrode on a second conductivity type nitride semiconductor layer, and a second main surface (
A counter electrode structure including a first electrode on a main surface facing the first main surface can be obtained. With this structure, the manufacturing process can be stabilized, a large current can be input, and a high-quality element capable of high output oscillation can be realized with a high yield. Further, both the first and second electrodes may be arranged on the first main surface side.

Hereinafter, the nitride semiconductor laser device of the present invention will be described together with its manufacturing method.
As shown in FIGS. 1B and 2A, the device includes a nitride semiconductor substrate 101 having a first conductivity type nitride semiconductor layer, an active layer, and a second conductivity type nitride semiconductor. They are formed in order, and a striped ridge portion is formed on the surface of the second conductivity type nitride semiconductor layer.
As shown in FIGS. 1A, 3A and 3B, the main surface of the substrate 101 is off from a direction A substantially parallel to the ridge portion, for example, the [0001] direction and the [1-100] direction. Angle a (θa °)
Tilted. That is, the main surface of the substrate refers to a surface having an off angle a with respect to a predetermined reference crystal surface (a surface having no off angle inclination, for example, a C surface).

Further, as shown in FIGS. 4 (a) and 4 (b), the main surface of the substrate is inclined in an off-angle a in a direction A substantially parallel to the ridge portion with respect to a predetermined reference crystal plane. The off-angle b (θb °) may be inclined in a direction substantially perpendicular to the orientation flat (OF) plane, for example, in the [11-20] direction.
Here, the reference crystal plane indicates a crystal plane such as a C plane, an M plane, an A plane, or an R plane. Of these, the C-plane (0001), M-plane (1-100), A-plane (11-20) plane and the like are preferable.

The “off angle” is an inclination angle with respect to a predetermined reference crystal plane formed on the substrate surface. The off angle is preferably formed at least in a direction substantially parallel to the striped ridge portion (off angle a), and further formed in a direction orthogonal to the direction in which the off angle a is formed (off angle). b) is preferred. “Formed in a substantially parallel direction” means, for example, formed so as to descend in the direction of the light exit surface of the resonance surface, formed so as to descend in the direction of the light reflection surface of the resonance surface, or M It includes being formed in a direction substantially perpendicular to the plane (1-100). As a result, the surface morphology and composition (for example, In mixed crystal ratio) of the active layer located immediately below the ridge portion can be made uniform.

The off angle a has an absolute value | θ _a | of about 0.02 ° to 5 °, about 0.1 ° to 0.7 °, further about 0.15 ° to 0.6 °, and 0.1 ° to 0. .5 °, 0.15 ° -0.4 °, 0
. It is preferably about 2 ° to 0.3 °. The off-angle b has an absolute value | θ _b | larger than 0 °, about 0 ° to 0.7 °, about 0 ° to 0.5 °, 0 ° to less than 0.5 °, 0 ° to 0.0. It is preferably about 3 °. When the substrate has off angles a and b, it is preferable that | θ _a |> | θ _b |. As a result, the surface morphology of the semiconductor layer grown on the main surface of the substrate is planarized in the plane. Further, the composition distribution of Al, In, etc. in the semiconductor layer can be made more uniform. In particular, the composition distribution can be made uniform even in a semiconductor layer in which the In composition in the active layer exceeds 5%, which is difficult with a conventional substrate.

That is, if the off-angle as described above is formed, the device characteristics can be improved in a range from the ultraviolet region of 365 nm or less to the long wavelength region of 500 nm or more. When the micro-PL observes the inside of the ridge or chip, the In composition fluctuation of the active layer in the semiconductor layer grown on the substrate having no off-angle is large (FIG. 5), whereas the above-mentioned off-state When a substrate having a corner is used, fluctuations in the In composition of the active layer can be suppressed (FIG. 6).
.

The semiconductor layer has a separated light confinement structure (Separate Confinement Heterostructu) in which an active layer is sandwiched between a first conductivity type (eg, n-type) semiconductor layer and a second conductivity type (eg, p-type) semiconductor layer.
re).
The active layer preferably contains In. Thereby, an element having a wide wavelength band can be realized. Further, either a multiple or single quantum well structure may be used. Luminous efficiency can be improved by using a quantum well structure. An optical waveguide is configured by providing semiconductor layers having a band gap larger than that of the active layer above and below the active layer. Furthermore, by forming a clad layer (a layer having a low refractive index) on both sides of the active layer, both light and carriers can be confined.

(First step)
The nitride semiconductor substrate having an off angle can be formed as follows.
First, as shown in FIG. 7A, a heterogeneous substrate 10 made of a material different from a nitride semiconductor is prepared. Heterogeneous substrates are sapphire, GaAs, SiC, Si, spinel, SiO ₂ , Si
N, ZnO, etc. are mentioned. The surface of the heterogeneous substrate 10 preferably has a growth surface of a nitride semiconductor to be grown later as a (0001) plane, a (11-20) plane, or a (1-100) plane.

A buffer layer (not shown) made of Al _x Ga _1-x N (0 ≦ x ≦ 1) is grown on the surface of the heterogeneous substrate 10. The buffer layer is grown at a growth temperature of 900 ° C. or lower, for example, by a MOCVD method, under reduced pressure to atmospheric pressure. In the present invention, the semiconductor layer is grown by a vapor phase growth method such as a metal organic chemical vapor deposition (MOCVD) method, a halide vapor phase epitaxy (HVPE) method, a molecular beam epitaxy (MBE) method, or a nitride semiconductor. It can be formed using all known methods.

Thereafter, as shown in FIG. 7B, for example, a convex portion 10a is formed on the surface of the heterogeneous substrate 10 via a buffer layer.
Subsequently, the nitride semiconductor layer 100 with reduced dislocations is grown. The film thickness of the semiconductor layer 100 is about 50 μm to 10 mm, preferably about 100 μm to 1000 μm. Within this range, it is possible to facilitate the formation and handling of the off-angle in the subsequent process.

Next, as shown in FIG. 7C, the heterogeneous substrate is removed by polishing, grinding, electromagnetic wave irradiation (excimer laser irradiation, etc.), CMP, etc., and the single nitride semiconductor layer 100 is taken out. Get the substrate. In this substrate, a growth surface of the semiconductor layer 100 is a first main surface, and an exposed surface obtained by removing the heterogeneous substrate 10 is a second main surface.
It is not always necessary to remove the heterogeneous substrate here. It may be removed before formation of an n-electrode described later, or may not be removed.

The first surface of the obtained nitride semiconductor substrate preferably includes, for example, a (0001) plane, a (11-20) plane, a (1-100) plane (M plane), and the like. Thereby, dislocations generated from the interface between the substrate and the nitride semiconductor layer can be reduced. Further, cleavage and the like in the process of dividing from the wafer can be performed with good reproducibility.

Dislocations may be periodically distributed in the plane on the first surface of the substrate. For example, using the ELO method, a low dislocation density region (for example, the first region) and a high dislocation density region (for example, the first region)
And the second region) are alternately formed in a stripe shape. Thereby, the stress in a board | substrate can be relieved and a nitride semiconductor layer can be grown on it, without forming a stress relaxation layer on a board | substrate.
The first region and the second region are preferably separated in polarity from each other in a stripe shape. Thereby, the stress and distortion which generate | occur | produce in a board | substrate can be suppressed. Further, cleavage and the like in the wafer dividing process can be performed with good reproducibility.

Here, the low dislocation density regions, dislocations per unit area 1 × 10 ⁷ / cm ² or less, preferably 1 × 10 ⁶ / cm ² or less, more preferably ⁵ × 10 5 / cm ² or less in the region It is. The high dislocation density region may be a region having a dislocation density higher than that of the low dislocation density region.
When the first region and the second region alternately form stripes, the width of the first region is 10
It is preferably from μm to 500 μm, more preferably from 100 μm to 500 μm. The width of the second region is 2 μm
˜100 μm, 10 μm to 50 μm are preferable.
These dislocation measurements can be performed by CL observation, TEM observation, or the like.

For example, if the low dislocation density region formed on the first surface is the (0001) plane, the high dislocation density region is different from the (0001) plane (000-1) plane, (11-20) plane, ( 10-14
) Plane, (10-15) plane, (11-24) plane and the like. In particular, (00
The 0-1) plane is preferable. By using a substrate having a partially different crystal growth surface in this way, stress and strain generated in the substrate can be relaxed, and a semiconductor layer can be formed without forming a stress relaxation layer on the substrate. Lamination can be performed with a film thickness of 5 μm or more. That is, the occurrence of wafer warpage and cracks can be reduced. The above stripe shape is
Including those formed in a broken line shape.

The second surface of the nitride semiconductor preferably has at least two or more different crystal growth planes. Specifically, the (000-1) plane, the (0001) plane, the (11-20) plane, 1
0-15) plane, (10-14) plane, (11-24) plane, and the like. In the present specification, a bar (-) in parentheses representing a face index is attached on the back number.
Further, the outer peripheral shape of the substrate is not particularly limited, and may be a wafer shape, a rectangular shape, or the like. In the case of a wafer, a size of 1 inch or more, and further 2 inches or more is preferable.

Full width of half-width of (0002) diffraction X-ray rocking curve by biaxial crystal method
th at Half Maximum) is preferably 2 minutes or less, and more preferably 1 minute or less.
Examples of the nitride semiconductor substrate include a compound of III group element (B, Ga, Al, In, etc.) and nitrogen or a mixed crystal compound (GaN, AlN, AlGaN, InAlGaN, etc.). The substrate preferably contains an n-type or p-type impurity. Examples of the impurity concentration include 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ .
This substrate may partially have an insulating substrate such as sapphire.
The nitride semiconductor substrate may be formed using the above-described two-stage growth ELO method, selective growth method, or the like, or a hydrothermal synthesis method, a high pressure method, a flux method, a melting method for crystal growth in a supercritical fluid. A bulk single crystal formed by the above method may be used. Moreover, you may use a commercial item.

Next, as shown in FIG. 7D, an off angle is formed on the surface of the obtained substrate 101. The off-angle is formed by forming a mask (not shown) having a film thickness distribution on the first surface of the substrate 101, and then removing the mask by etching, and further etching the exposed first surface of the substrate. Etching is wet etching, dry etching (reactive ion etching: RIE, reactive ion beam etching: RIBE, electron cyclotron resonance: EC
R, high frequency inductively coupled plasma: ICP, focused ion beam: FIB, etc.), CMP treatment or the like. In particular, it is preferable to use a dry etching method because the off angle can be easily controlled. Thereby, since an in-plane distribution occurs during the etching time on the first surface of the substrate, a desired off angle can be formed in a desired size with respect to a desired direction.

Alternatively, the first surface of the substrate may be polished, ground, or surface treated by laser irradiation, or a bulk nitride semiconductor substrate may be cut out with a wire saw to have an off angle. Good. In particular, when forming an off angle by dry etching,
Alternatively, the substrate may be tilted and set in a dry etching apparatus, or the substrate may be set in an inclined substrate holder and subjected to etching. Further, an off-angle may be formed in advance on a different substrate, and a nitride semiconductor layer may be grown on the off-angle so that the off-angle is inherited from the different substrate to the nitride semiconductor layer, and the substrate may be obtained from the nitride semiconductor layer. .
The first main surface of the obtained substrate 101 has an off angle a with respect to the original surface of the nitride semiconductor substrate.
Have By forming an element using this, the stress is suppressed in the semiconductor layer grown on the substrate, and it becomes possible to withstand damage during cleavage.

(Second step)
Next, as shown in FIG. 8A, a lower layer (on the first main surface of the substrate 101 having an off angle (
For example, an n-side layer, an active layer, and a p-side layer are stacked in this order as the nitride semiconductor layer 200 via an optional crack prevention layer or the like. The semiconductor layer _{200, In x Al y Ga 1-} xy N (0
≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) and the like.

First, as an n-side layer, an n-side cladding layer: n-type impurity-doped Al _x Ga _1-x N (0 ≦ x ≦ 0
. 5) N-side light guide layer: Al _x Ga _1-x N (0 ≦ x ≦ 0.3) is grown. Note that the names of the cladding layer, the light guide layer, and the like do not necessarily mean that they have only their functions, but also have other functions (the same applies to the p-side layer). If the n-side cladding layer is a single layer, the general formula is Al _x Ga _1-x N (0 ≦ x ≦ 0.2), and the film thickness is 0.
It is preferable that it is 5-5 micrometers. If multi-layer, the first _{layer: Al x Ga 1-x N} (0 ≦ x ≦
0.5, 0 ≦ x ≦ 0.1, more preferably 0 <x ≦ 0.3) and the second layer: Al _y Ga _1-y
A laminated structure with N (0.01 ≦ y ≦ 1) may be used. The n-side layer, particularly the first layer (semiconductor layer containing Al) in the case of a multilayer, is preferably formed by lateral growth. Thereby, further planarization of the surface of the semiconductor layer and suppression of composition fluctuation in the semiconductor layer can be realized.
In the lateral growth, the growth temperature in the furnace is preferably 1000 ° C. or higher and the pressure is 600 Torr or lower. For the first and second layers in the case of a multilayer, for example, a film thickness of 0.5 to 5 μm is appropriate.

Next, as an active layer, the general formula _{In x Al y Ga 1-xy} N (0 <x ≦ 1,0 ≦ y <1,0 <
It is preferable to grow a semiconductor layer having a multiple quantum well structure represented by x + y ≦ 1). The composition of the well layer is preferably such that the In mixed crystal satisfies 0 <x ≦ 0.5. The film thickness of the well layer and the barrier layer is, for example, 10 to 300 mm, 20 to 300 mm, and the total film thickness is, for example, 100 to
About 3000 mm is appropriate. Moreover, by setting the total film thickness to a range of about 10 to 300 mm,
V _f and the threshold current density can be reduced. Furthermore, by adjusting the Al content, the light emitted from the ultraviolet region is changed to the light emitted on the long wavelength side (for example, 300 nm to 650 nm, further 360 nm).
˜580 nm).

A multi-quantum well structure may start with a barrier layer and end with a well layer, start with a barrier layer and end with a barrier layer, start with a well layer and end with a barrier layer, start with a well layer and end with a well layer . Preferably, the structure starts with the barrier layer and repeats the pair of the well layer and the barrier layer 2 to 8 times and ends with the barrier layer. In particular, those in which this pair is repeated 2 to 3 times are preferable for lowering the threshold and improving the life characteristics.

Subsequently, as a p-side layer, an electron confinement layer (can be omitted): p-type impurity-doped Al _x Ga _1-x
N (0 ≦ x ≦ 0.5), p-side light guide layer: Al _x Ga _1-x N (0 ≦ x ≦ 0.3), p-side cladding layer: p-type impurity doped Al _x Ga _1-x N (0 ≦ x ≦ 0.5), p-side contact layer: p-type impurity doped Al _x Ga _1-x N (0 ≦ x ≦ 1) is grown in this order. These semiconductor layers may be mixed with In. The thickness of each layer is about 30 to 5 μm.

The semiconductor layer 200 is formed on the first main surface of the substrate 101 with a low-temperature growth buffer layer: Al _x Ga _1-x N
(0 ≦ x ≦ 0.3), the intermediate layer _{202: Al x Ga 1-x} N (0 ≦ x ≦ 0.3) and / or anti-cracking _{layer: In x Al y Ga 1-} xy N (0 <x ≦ 1, 0 ≦ y <1, 0 <x + y ≦ 1) may be used to grow the n-side layer. Further, a structure having a stress buffer layer between each layer or G
An RIN structure may be used. The intermediate layer or the like may be either a single layer or a multilayer stacked structure. This intermediate layer or the like can reduce dislocations (threading dislocations and the like) and pits generated on the surface of the semiconductor layer.

The n-side cladding layer and the p-side cladding layer may have a single layer structure, a two-layer structure, or a superlattice (SL) structure including two layers having different composition ratios. The total film thickness of the n-side and p-side cladding layers is
It is preferable that it is 0.4-10 micrometers. Thereby, the forward voltage (Vf) can be reduced. Moreover, it is preferable that the average composition of Al of the whole cladding layer is 0.02-0.15. Thereby, generation | occurrence | production of a crack can be suppressed and the refractive index difference with a laser waveguide can be obtained.

Examples of the n-type impurity include Si, Ge, Sn, S, O, Ti, Zr, and Cd.
Examples of the p-type impurity include Mg, Be, Zn, Mn, Ca, and Sr. Impurity concentration is 5x
It is preferably about 10 ¹⁶ / cm ³ to 1 × 10 ²¹ / cm ³ . In particular, the doping amount of n-type impurities is 1
× is preferably ^{10 17 / cm 3 ~5 × 10} 19 / cm 3. Thereby, a resistivity can be made low and crystallinity is not impaired. The doping amount of the p-type impurity is 1 × 10 ¹⁹ / cm ³ to 1 × 1
It is preferably 0 ²¹ / cm ^3. Thereby, crystallinity is not impaired. The impurity doping may be modulation doping.

(Third step)
The wafer in which the semiconductor layer 200 is stacked on the substrate 101 is taken out from the reaction vessel of the semiconductor growth apparatus, and the n-side layer is etched to expose, for example, the n-side cladding layer.
Thereby, stress can be relieved. This step can be omitted,
The surface exposed by etching is not necessarily the n-side cladding layer. Etching can be performed using a RIE method and a chlorine-based gas such as Cl ₂ , CCl ₄ , BCl ₃ , or SiCl ₄ gas.

Next, as shown in FIG. 8B, a stripe-shaped ridge portion is formed on the surface of the p-side layer.
In forming the ridge portion, first, a protective film (not shown) is formed on the surface of the p-side contact layer 209 which is the uppermost layer of the p-side layer. This protective film is a pattern corresponding to the shape of the ridge portion.
Using this protective film as a mask, the p-side layer is removed by etching. The ridge portion defines the waveguide region, the width is about 1.0 μm to 100.0 μm, and the height (etching depth) is
What is necessary is just to be a range that exposes at least the p-side cladding layer. The resonator length is 300 μm to 100
About 0 μm is preferable. In the case of a single mode laser beam, the width is 1.0 μm to 3.
The thickness is preferably 0 μm. If the width of the ridge portion is 5 μm or more, a high output of 1 W or more is possible. Also, if a large current is passed, the current spreads in the lateral direction immediately below the ridge,
The height of the ridge portion is preferably up to the p-side light guide layer. Note that the ridge is preferably formed so as to be disposed above the low dislocation density region (first region) described above.

(Fourth process)
Thereafter, as shown in FIG. 8C, the side surface of the ridge portion is protected with a buried film 220. The buried film 220 is preferably selected from insulating materials having a refractive index smaller than that of the semiconductor layer. Specifically, a single layer or a multilayer of oxides such as ZrO ₂ , SiO ₂ , V, Nb, Hf, Ta, and Al can be given.
Subsequently, a p-electrode 230 is formed on the upper surface of the ridge portion of the p-side contact layer 209. Preferably, a p-electrode 230 is formed on the p-side contact layer 209 and the buried film 220. The p-electrode has a multilayer structure, for example, Ni (50 to 200 mm: lower layer) / Au (500 to 3000 mm: upper layer), Ni / Au / Pt (500 to 5000 mm) or Ni / Au / Pd (500 to 5000).
I) is preferred.
After forming the p-electrode 230, it is preferable to perform ohmic annealing in a nitrogen and / or oxygen atmosphere at 300 ° C. or higher, preferably 500 ° C. or higher.

Next, as shown in FIG. 8D, a protective film 240 is formed on the side surface of the n-side layer exposed in the previous step. As shown in FIG. 2B, the protective film only needs to cover at least the side surfaces of the n-side layer and the p-side layer, and may not cover a part of the p-electrode 230.
Further, a pad electrode 250 is formed on the p electrode 230. The pad electrode 250 is made of Ni
, Ti, Au, Pt, Pd, W, and the like, for example, W / Pd / Au (1
000Å or more) or Ni / Ti / Au (1000Å or more).

(Fifth step)
As shown in FIG. 8E, an n-electrode 210 is formed on the second main surface of the substrate 101.
The n electrode is a part or the whole of the second main surface by at least one metal selected from the group consisting of Ti, Ni, Au, Pt, Al, Pd, W, Rh, Ag, Mo, V, and Hf. It is preferable to form. As a result, ohmic characteristics between the substrate and the n-electrode can be easily obtained, adhesion is good, and electrode peeling in a cleavage step or the like for dividing the wafer can be prevented.

When the n-electrode has a multilayer structure, the uppermost layer is preferably Pt or Au. Thereby, the heat dissipation from an electrode can be improved. The film thickness of the n electrode is preferably 10000 mm or less, more preferably 6000 mm or less. In the case of a multilayer structure, for example, the substrate side is V, Ti, Mo, W
, Hf, etc. (500 Å or less, in the case of W, 300 Å or less). In the case of V, the film thickness is preferably 50 to 300 mm or less, and more preferably 70 to 200 mm. Thereby, a favorable ohmic characteristic can be obtained and heat resistance can be improved. Specifically, Ti
(100Å: substrate side) / Al (5000Å), Ti / Pt / Au (60Å / 1000Å /
3000 Å), Ti (60 Å) / Mo (500 Å) / Pt (1000 Å) / Au (210
0Å), Ti (60Å) / Hf (60Å) / Pt (1000Å) / Au (3000 ／),
Ti (60 Å) / Mo (500 ／) / Ti (500 Å) / Pt (1000 Å) / Au (2
100mm), W / Pt / Au, W / Al / W / Au, Hf / Al, Ti / W / Pt / Au
Ti / Pd / Pt / Au, Pd / Pt / Au, Ti / W / Ti / Pt / Au, Mo / P
t / Au, Mo / Ti / Pt / Au, W / Pt / Au, V / Pt / Au, V / Mo / Pt
/ Au, V / W / Pt / Au, Cr / Pt / Au, Cr / Mo / Pt / Au, Cr / W /
Pt / Au etc. are mentioned. After forming the n-electrode, annealing may be performed at 300 ° C. or higher.

The n-electrode is preferably formed in a rectangular shape on the second main surface side in a range excluding a region that becomes a scribe line in a scribing process for forming a substrate in a subsequent process. Further, a metallized electrode may be formed on the n electrode in the same pattern shape as the n electrode. Thereby, it becomes easy to scribe and cleavage is improved. For metallized electrodes, Ti
-Pt-Au- (Au / Sn), Ti-Pt-Au- (Au / Si), Ti-Pt-Au
-(Au / Ge), Ti-Pt-Au-In, Au / Sn, In, Au / Si, Au / G
e and the like.

Further, an off-angle or uneven step may be formed on the second main surface of the substrate.
If the second main surface is the (000-1) plane by forming the uneven step, (000-1)
An inclined surface other than the surface can be exposed. The inclined surface other than the (000-1) plane is preferably 0.5% or more and more preferably about 1 to 20% of the surface area of the n-polar surface. As a result, n
The ohmic characteristics of the electrode can be improved.
Here, the step is an interface step of 0.1 μm or more, and the step shape includes a taper shape and an inverse taper shape. The planar shape of the step can be selected from a stripe shape, a lattice shape, an island shape, a circular shape, a polygonal shape, a rectangular shape, a comb shape, and a mesh shape. For example, if a circular convex portion is formed, the diameter width of the circular convex portion can be set to 5 μm or more. In addition, it is preferable that the width of the concave groove has an area of at least 3 μm because there is no peeling of the electrode.
In order to expose the inclined surface other than the (000-1) plane in the second main surface, the off angle is set to 0.2.
It is suitable to form in the range of ~ 90 °.

(Sixth step)
In order to form a resonance surface of the semiconductor layer in a direction perpendicular to the striped p-electrode 230, the wafer is divided into bars. The resonance plane is preferably an M plane (1-100) and an A plane (11-20). Examples of the dividing method include blade break, roller break or press break.
This division is preferably performed in two stages in which a cleavage assist groove is first formed and then divided.
Thereby, the resonance surface can be formed with a high yield.
That is, first, a cleavage assist groove is formed by scribing from the first or second main surface side of the substrate. These grooves are formed on the entire surface of the wafer or both ends of the wafer in a region to be a bar. The grooves are preferably formed at intervals in the form of broken lines in the cleavage direction for forming the bars. As a result, bending of the cleavage direction can be suppressed and cleavage can be easily performed. Further, by forming this groove on the second main surface, it is possible to suppress the ripple of FFP and to prevent the electrode from peeling off.

Next, the wafer is divided into bars by a breaker. Examples of the cleavage method include blade break, roller break, press break and the like.
A reflection mirror may be formed on the light reflection side and / or the light emission surface of the resonance surface formed by cleavage. The reflection mirror can be formed of a dielectric multilayer film such as SiO ₂ , ZrO ₂ , TiO ₂ , Al ₂ O ₃ , and Nb ₂ O ₅ . In particular, Al ₂ O ₃ or Nb ₂ O ₅ is preferable on the emission end face side. Thereby, a lifetime characteristic becomes favorable. If the resonance surface is formed by cleavage, the reflection mirror can be formed with good reproducibility.
Further, the bar-shaped substrate is divided in parallel with the stripe direction of the electrodes, and the device is made into chips. The shape after chip formation is preferably rectangular, and the width of the resonance surface is 500 μm.
Hereinafter, it is further preferably 400 μm or less.

The laser element thus obtained has characteristics such as a long lifetime in which the ripple of FFP is suppressed. Further, since the element has a counter electrode structure, the contact resistivity can be reduced to 1.0E ⁻³ Ωcm ² or less.
This element may be a laser element having a plurality of waveguide regions on a substrate, or may be a laser element having a wide ridge portion.

Moreover, it is preferable that the element of the present invention mainly has a core region including an active layer between a first conductivity type (for example, n-type) layer and a second conductivity type (for example, p-type) layer.
Here, the core region means an optical waveguide region, that is, a region where light generated in the active layer can be confined and the light wave can be guided without being attenuated. Usually, the active layer and the light guide layer sandwiching the active layer constitute the core region, and it is appropriate that the film thickness is, for example, about 100 to 1.5 μm.
The semiconductor layers constituting the n-type and p-type layers are not particularly limited, and examples thereof include the nitride semiconductor layers described above.

In this element, a first nitride semiconductor layer (hereinafter referred to as “first layer”) is adjacent to at least one of the n-type layer and the p-type layer, in particular, the n-type layer and adjacent to the outermost layer of the core region. ) And a second nitride semiconductor layer (hereinafter referred to as “second layer”) are preferably arranged in this order.
In the n-type layer, each of the first layer and the second layer is a layer for adjusting the light emission angle,
Although it functions as an optical guide layer and a clad layer, these functions can be adjusted by laminating these layers.
In other words, by making the n layer or the p layer multi-layered, in particular by making the n layer multi-layered, F.I. F. P. N. is reduced and N.I. F. P can be expanded. Thereby, the threshold current can be maintained. Furthermore, the light emission angle can be adjusted upward, downward, etc., and the light output efficiency can be improved to obtain an element with a good light collection rate.

The first layer and the outermost layer of the core region, and the second layer and the first layer preferably have different refractive indexes, and in particular, the first layer has a lower refractive index than the outermost layer of the core region and It is preferable that the second layer has a lower refractive index than the first layer. These layers are preferably set so that the refractive index decreases in order from the outermost layer of the core region. Thereby, the beam irradiated from the active layer can be stabilized by stable light confinement. As a result, the application as a laser light source spreads.

Furthermore, the refractive index difference (Δn ₁ ) between the outermost layer and the first layer in the core region and / or the refractive index difference (Δn ₂ ) between the first layer and the second layer is 0.004 to 0.03. It is preferable. This
The stay region of light generated in the active layer can be more appropriately adjusted, and stable light confinement can be performed. As a result, F.I. F. The spread angle of P can be controlled.

In the n-type layer, the layer formed adjacent to the outermost layer of the core region is not limited to two layers,
Three or more layers, for example, m layers (m ≧ 2) may be formed. The upper limit is not particularly limited. Considering the light confinement effect, 10 layers or less, 8 layers or less, and 6 layers or less are appropriate. In particular,
The refractive index difference (Δn _m ) between the outermost layer and the m-th layer in the core region is 0.008 to 0.05, 0.07 to
It is preferable to be within the range of 0.05. By setting in such a range, the light confinement is relaxed and the F.V. F. While controlling the spread angle of P, light leakage can be prevented.

The refractive index of the n-type layer can usually be adjusted by its composition. For example, the refractive index can be reduced by increasing the mixed crystal ratio of Al. For example, in order to obtain a refractive index difference of 0.004 to 0.03 between the first layer and the second layer, the composition ratio of Al is 0 in both.
. It is appropriate to provide a difference of about 01 to 0.07.

Further, when the first layer and / or the second layer has a superlattice structure of an X layer and a Y layer, only the film thickness of one of the layers is changed. For example, in the first layer, the X layer has The refractive index of the n-type layer can be adjusted by increasing the thickness of the X-layer in the second layer.
In the n-type layer, the first layer and the second layer have a thickness of about 1000 to 10,000 mm, for example. Moreover, when it is formed from the first layer to the m-th layer, the total is 2000 to 40.
It is appropriate to be about 000 mm.

In particular, when the n-type layer is formed to contain Al _x Ga _1-x N (0 <x <1), at least 0.004 at a position of about 500 to 5000 mm from the outermost layer of the core region. ~ 0.03
A layer having a refractive index difference of about 0.004 to 0.03 at a position of about 1500 to 20000 mm
It is preferable that a layer having a refractive index difference of about a degree is arranged, and further 2500 to 25000 mm
More preferably, a layer having a refractive index of about 0.004 to 0.03 is arranged at a position of about. Thereby, regardless of the composition and film thickness, generation of cracks inside the layer can be prevented. Therefore, more appropriate light confinement can be realized.

The m-type n-type nitride semiconductor layer includes m-type n-type nitride semiconductor layers on the n-type nitride semiconductor layer side, and the p-type nitride semiconductor layer includes the first p-type semiconductor layer. However, when the refractive index is higher than the refractive index of the first p-type nitride semiconductor layer, the light confinement effect on the p side can be strengthened, so that more stable light confinement can be performed. . In addition, by making the confinement on the n side weaker than that on the p side, it is possible to prevent the occurrence of kinks on the n side.

If the first layer and the second layer described above are formed in the n-type layer, the first layer and the second layer are not necessarily formed in the p-type layer. In the case where the first layer is formed in the p-type layer, the refractive index difference between the first layer and the outermost layer of the core region is not particularly limited.
. A value of about 01 to 0.2 is appropriate. In addition, it is preferable that a 1st layer has a refractive index smaller than the outermost layer of a core area | region. Thereby, it is possible to reliably confine light. The mth
The difference in refractive index between the layer and the first layer is preferably about 0.004 to 0.03, for example.
The first layer preferably has a refractive index smaller than that of the mth layer. Further, the film thickness of the first layer is, for example, about 1000 to 10,000 mm. The first layer preferably has a superlattice structure in which GaN and AlGaN are stacked. Moreover, even if the mixed crystal ratio of Al is set high in order to make the refractive index on the p side smaller than that on the n side, the occurrence of internal cracks can be prevented by reducing the film thickness, The stability of the device can be maintained, that is, the leakage current can be reduced.

The optical guide layer is made of a nitride semiconductor and has an energy band gap sufficient for waveguide formation. The composition, film thickness, etc. are not particularly limited, and the single layer, multilayer, superlattice layer Any of these structures may be used. Specifically, at wavelengths of 370 to 470 nm, Ga
It is appropriate to use N and use a multilayer or superlattice layer of InGaN / GaN for longer wavelengths. The composition, film thickness, structure, and the like of the nitride semiconductor constituting the light guide layer may be the same or different on the n side and the p side.

In the present invention, the specific laminated structure of the core region, the n-type layer and the p-type layer is, for example,
First p-type nitride semiconductor layer: AlGaN single layer, AlGaN / GaN multilayer or superlattice layer,
p-type light guide layer: AlGaN single layer, GaN single layer, AlGaN / GaN multilayer or superlattice layer,
Active layer: InGaN single layer, InGaN / InGaN multilayer or superlattice layer, InGaN
/ GaN multilayer or superlattice layer,
n-type light guide layer: GaN single layer, InGaN single layer, AlGaN single layer, GaN / AlGa
N multilayer or superlattice layer, InGaN / AlGaN multilayer or superlattice layer, AlGaN / Al
GaN multilayer or superlattice layer,
First n-type nitride semiconductor layer: AlGaN single layer, GaN / AlGaN multilayer or superlattice layer, InGaN / AlGaN multilayer or superlattice layer, AlGaN / AlGaN multilayer or superlattice layer,
Second n-type nitride semiconductor layer: AlGaN single layer, GaN / AlGaN multilayer or superlattice layer, InGaN / AlGaN multilayer or superlattice layer, AlGaN / AlGaN multilayer or superlattice layer, and the like. These layers can be arbitrarily combined. In particular, in the case of a superlattice layer, the refractive index and refractive index of each layer can be changed by changing the composition, changing the film thickness, or changing the composition and film thickness in one or both layers. The difference can be set as described above.

Examples of the element of the present invention are shown below.
Example 1
The structure of the semiconductor laser device of this example is shown in FIGS. 1 (b) and 2 (a).
This laser element has a low temperature growth buffer layer on a substrate 101 made of GaN having a dislocation density of 1 × 10 ⁶ / cm ² or less as a main surface and an off angle a of 0.3 ° with respect to the (0001) plane. (Not shown) and an intermediate layer (not shown) through the n-side cladding layer 203 and the n-side light guide layer 20
4, active layer 205, p-side cap layer 206, p-side light guide layer 207, p-side cladding layer 20
8, p-side contact layer 209 is laminated in this order.

Striped ridges are formed on the surface of the p-side contact layer 209, and the surface of the p-side cladding layer 208 is exposed on both sides of the ridge.
A buried layer 220 is formed on the exposed surface of the p-side cladding layer 208 and the side surface of the ridge portion.
A p-electrode 230 is formed in a region in contact with the upper surface of the ridge portion and over the buried film 220. A protective film 240 is formed so as to cover the side surface of the above-described semiconductor laminate from a part on the p-electrode 230.
Further, a p-pad electrode 250 is formed on the p-electrode 230, and the GaN substrate 10
An n-electrode 210 is formed on the back surface of 1.

Such a semiconductor laser device can be formed by the following manufacturing method.
(Nitride semiconductor substrate 101)
First, in the MOCVD reactor, a dissimilar substrate made of sapphire or GaAs is placed and the temperature is set to 500 ° C. Next, trimethylgallium (TMG), ammonia (N
A buffer layer (200 mm) made of GaN is grown using H ₃ ). Then set the temperature to 1
The first nitride semiconductor layer (4 μm) made of GaN is grown at 050 ° C.
Subsequently, the wafer is taken out from the reaction vessel, a striped photomask is formed on the surface of the first nitride semiconductor, and a SiO 2 having a stripe width of 10 to 300 μm and a stripe interval (window) of 5 to 300 μm is formed by a CVD apparatus. forming a protective film made of _2.

Thereafter, the wafer is transferred to an HVPE apparatus, Ga metal, HCl gas, and ammonia are used as raw materials, and Ga (Si) or oxygen (O) is doped as an n-type impurity.
A second nitride semiconductor (400 μm) made of N is grown. Thus, by growing a GaN thick film of 100 μm or more on the protective film by the HVPE method, crystal defects can be reduced by two orders of magnitude or more.

By removing the heterogeneous substrate or the like, the nitride semiconductor substrate 101 is obtained from GaN composed of the second nitride semiconductor layer. The thickness of the substrate 101 is about 400 μm, and the dislocation density is 1 × 10 ⁶ / cm ² or less in at least the region where the waveguide is intended to be formed.
The obtained substrate 101 is set at a predetermined angle in a dry etching apparatus and subjected to dry etching, whereby the main surface of the substrate 101 ((0001 surface))
An off angle a of 0.3 ° is given in the direction intended to form the ridge.

(N-side cladding layer 203)
Subsequently, TMA (trimethyl aluminum) at 1000 ℃ ~1080 ℃, TMG, ammonia, Al ₀ to using silane gas was ^{1 × 10 18 / cm 3 ~1} × 10 19 / cm 3 doped with _Si.
An n-side cladding layer (thickness: 2 μm) made of ₀₃ Ga _0.97 N is grown.

(N-side light guide layer 204)
Next, the silane gas is stopped, and an n-side light guide layer (0.175 μm) made of undoped GaN is grown at 1000 ° C. to 1080 ° C. This layer may be doped with n-type impurities or may contain IN.

(Active layer 205)
Next, the temperature is set to 900 ° C. or lower, and a barrier layer (1) made of Si-doped In _0.02 Ga _0.98 N
Next, a well layer (70Å) made of undoped In _0.07 Ga _0.93 N is grown at the same temperature. A barrier layer and a well layer are alternately stacked twice, and finally a barrier layer is formed to form an active layer of a multiple quantum well structure (MQW) having a total film thickness of 560 mm.

(P-side cap layer 206)
Next, at 900 ° C. or elevated temperature, TMG, TMA, ammonia, Cp ₂ Mg (cyclopentadienylmagnesium) is used, and the band gap energy is larger than that of the p-side light guide layer, and Mg is 1 × 10 ¹⁹ / A p-side cap layer (100Å) made of p-type Al _0.25 Ga _0.75 N doped with cm ³ to 1 × 10 ²⁰ / cm ³ is grown. This layer can be omitted.

(P-side light guide layer 207)
Subsequently, Cp ₂ Mg and TMA are stopped, and a p-side light guide layer made of undoped GaN (band gap energy is smaller than that of the p-side cap layer 10 at 1000 ° C. to 1050 ° C. (
About 0.14 μm). This layer may be doped with p-type impurities, or I
n may be contained.

(P-side cladding layer 208)
Thereafter, a layer made of undoped Al _0.10 Ga _0.90 N (at 25 ° C. at 1000 ° C. to 1050 ° C.
Then, TMA is stopped, and a layer (25 cm) made of Mg-doped GaN is grown, and a p-side cladding layer made of a superlattice layer having a total film thickness of 0.4 μm is grown.

(P-side contact layer 209)
At 1050 ° C., on the p-side cladding layer, p-type GaN was 1 × 10 ²⁰ / cm ³ doped with Mg
A p-side contact layer (150 Å) made of is grown.
Next, the wafer is taken out of the reaction vessel, and SiO ₂ is deposited on the surface of the uppermost p-side contact layer.
A protective film made of this is formed as a mask and etched by RIE using SiCl ₄ gas. As a result, the n-side cladding layer 203 is exposed.

A protective film made of striped SiO ₂ is formed on the surface of the p-side contact layer 209 as a mask, and is etched with SiCl ₄ gas using RIE. Thereby, a ridge portion which is a striped waveguide region is formed.
Subsequently, the side surface of the ridge portion is protected by the buried layer 220 made of ZrO ₂ .

In addition, a resist pattern having a plurality of openings is formed in the vicinity of the end face of the ridge portion, which is the waveguide region, at a position separated from the ridge using photolithography technology, and the n-side cladding is formed by SiCl ₄ gas using RIE. Etch until the layer is reached. As a result, p
For example, a hexagonal recess is formed on the surface of the side contact layer. The longest distance between the apexes of the recesses is 1 to 10 μm, preferably 2 to 5 μm. Ripple can be suppressed by forming the recess. This step may be omitted.
Next, Ni (100 Å) / Au is formed on the surface above the p-side contact layer 209 and the buried layer 220.
A p-electrode 230 made of (1500 mm) is formed.
Thereafter, a protective film 240 (0.5 μm) made of Si oxide film (SiO ₂ ) is applied to the p electrode 230.
A film is formed by sputtering on the top and the buried film 220 and on the side surface of the semiconductor layer.

Next, ohmic annealing is performed at 600 ° C.
Subsequently, Ni (10) is continuously formed on the exposed p-electrode 230 that is not covered with the protective film.
00Å) / Ti (1000Å) / Au (8000Å) in this order, and the p-pad electrode 2
50 is formed.
Thereafter, V (100 Å) / Pt (2000 Å) / Au (3000) is formed on the second main surface of the substrate.
An n-electrode 210 made of i) is formed.

Next, a concave groove (depth: 10 μm, width in parallel with the resonance surface: 50 is formed on the first main surface side of the substrate.
μm, vertical width: 15 μm). This groove is used as a cleavage assist line, and the substrate is cleaved from the n-electrode formation surface side, and the cleavage surface (1-100 surface, surface corresponding to the side surface of the hexagonal columnar crystal = M
A bar having a plane) as a resonance plane is obtained.
A dielectric multilayer film is formed on the resonator surface.
Finally, the bar is divided in the direction parallel to the p-electrode 230 and formed into chips to obtain a semiconductor laser element.

A plurality of the obtained laser elements were respectively installed on a heat sink, and p electrodes were wire-bonded, and laser oscillation was attempted at room temperature. As a result, all the laser elements exhibited good continuous oscillation at room temperature at an oscillation wavelength of 400 to 420 nm and a threshold current density of 2.9 kA / cm ² . In addition, the resonance surface has no cleavage and the applied current is 140 to 170 m as shown in FIG.
A. A laser device having a lifetime of 10,000 hours and particularly good lifetime characteristics with a light output of CW 80 mW and an operating temperature of 70 ° C. could be manufactured with good reproducibility.

Furthermore, the fluctuation of the In composition in the active region of the laser element was measured by microphotoluminescence (μ-PL) for a cross section in the depth direction of 100 μm to 400 μm from the active layer surface under the ridge portion.
As a result, as shown in FIG. 6, fluctuations in the In composition of the active layer were suppressed.

For comparison, the same measurement was performed on an element manufactured in the same manner as in Example 1 except that the substrate had no off-angle. As a result, as shown in FIG. 5, the In composition fluctuation of the active layer was large.

Example 2
A laser element substantially the same as that of Example 1 was fabricated except that the configuration shown in the following table was changed.

The obtained element was oscillated in the same manner as in Example 1.
Good continuous oscillation is exhibited at room temperature at an oscillation wavelength of 460 to 480 nm and a threshold current density of 2.0 kA / cm ² .
In addition, a long wavelength laser element having particularly good life characteristics can be manufactured with good reproducibility, with no cracks on the resonance surface, a light output of CW 80 mW, an operating temperature of 60 ° C., and a life of 3000 hours.

Example 3
The GaN substrate used in this example has a C-plane (0001) as the main surface and an M-plane (1-100).
The off angle a is inclined 0.23 ° in the vertical direction and the off angle b is inclined 0.06 ° in the parallel direction.
Further, on the first and second main surfaces of the GaN substrate, there are a first region (1st) composed of a C plane (0001) and a second region (2nd) composed of a (000-1) surface. 400μ each
m and an interval of 20 μm. Further, the laser element of this example has a configuration shown in the following table. The other laser elements are substantially the same as those of the first embodiment.

The obtained device was subjected to laser oscillation in the same manner as in Example 1.
Good continuous oscillation is exhibited at room temperature at an oscillation wavelength of 400 to 420 nm and a threshold current density of 2.9 kA / cm ² . In addition, the resonance surface is free of cleavage, optical output is CW80mW, operating temperature is 7
A laser element having a lifetime of 10,000 hours in a state of 0 ° C. and particularly excellent lifetime characteristics can be manufactured with good reproducibility.

Furthermore, the mixed crystal fluctuations in the active region of this laser element are microphotoluminescence (
(μ-PL).
As a result, as shown in FIG. 10A, the wavelength is uniform in the first region.
In addition, the surface state of the nitride semiconductor layer was observed.
As a result, as shown in FIG. 10B, the surface step of the semiconductor layer is 0 in the first region.
. It is flattened to 1 μm or less.

Examples 4-8
A device substantially similar to that of Example 3 is manufactured except that the off angle a (θ _a ) and the off angle b (θ _b ) are set to values shown in the following table.

得られた素子について、実施例１と同様にレーザ発振させると、いずれも、実施例３と
同様に、長寿命で、優れた表面平坦性が得られる。

When the obtained element was laser-oscillated in the same manner as in Example 1, all of them had a long life and excellent surface flatness as in Example 3.

Example 9
The GaN substrate has an off angle a of 0.3 ° and an off angle b of 0.05 °, and is substantially the same as that of Example 1 except for having the configuration shown in the following table. It is a laser element.

The obtained device was subjected to laser oscillation in the same manner as in Example 1.
Good continuous oscillation is exhibited at room temperature at an oscillation wavelength of 403 to 407 nm and a threshold current density of 1.8 to 2.0 kA / cm ² . Further, it is possible to manufacture a laser element with particularly good life characteristics with a reproducibility of 10000 hours or more in a state where the optical output is CW 200 mW and the operating temperature is 25 ° C.

Example 10
The GaN substrate has an off angle a of 0.3 ° and an off angle b of 0.05 °, and is substantially the same as that of Example 1 except for having the configuration shown in the following table. It is a laser element.

The obtained device was subjected to laser oscillation in the same manner as in Example 1.
Oscillation wavelength 373～376Nm, in threshold current density 3.4~3.5kA / cm ^2, indicating good continuous oscillation at room temperature. Further, it is possible to manufacture a laser element with particularly good life characteristics with a reproducibility of 8000 hours with a light output of CW 30 mW and an operating temperature of 25 ° C.

Example 11
The GaN substrate has an off angle a of 0.3 ° and an off angle b of 0.05 °, and is substantially the same as that of Example 1 except for having the configuration shown in the following table. It is a laser element.

The obtained device was subjected to laser oscillation in the same manner as in Example 1.
Good continuous oscillation is exhibited at room temperature at an oscillation wavelength of 373 to 376 nm and a threshold current density of 2.2 to 2.3 kA / cm ² . Further, it is possible to manufacture a laser element having particularly good life characteristics with a good reproducibility, in which the light output is CW 100 mW, the operating temperature is 25 ° C., and the life is 1000 hours or more.

Example 12
The GaN substrate has an off angle a of 0.3 ° and an off angle b of 0.05 °, and is substantially the same as that of Example 1 except for having the configuration shown in the following table. It is a laser element.

The obtained element was subjected to laser oscillation in the same manner as in Example 1.
Good continuous oscillation is exhibited at room temperature at an oscillation wavelength of 442 to 449 nm and a threshold current density of 2.5 kA / cm ² . In addition, the lifetime is 100 when the optical output is CW 30 mW and the operating temperature is 50 ° C.
It is possible to manufacture a laser element having particularly good life characteristics with 00 hours with good reproducibility.

Example 13
The GaN substrate has an off angle a of 0.3 ° and an off angle b of 0.05 °, and is substantially the same as that of Example 1 except for having the configuration shown in the following table. It is a laser element.

The obtained device was subjected to laser oscillation in the same manner as in Example 1.
Good continuous oscillation is exhibited at room temperature at an oscillation wavelength of 442 to 449 nm and a threshold current density of 1.7 to 1.8 kA / cm ² . In addition, a laser element having particularly good life characteristics with a light output of CW 150 mW and an operating temperature of 25 ° C. and a life of 10,000 hours can be manufactured with good reproducibility.

Example 14
The GaN substrate has an off angle a of 0.3 ° and an off angle b of 0.05 °, and is substantially the same as that of Example 1 except for having the configuration shown in the following table. It is a laser element.

The obtained device was subjected to laser oscillation in the same manner as in Example 1.
Good continuous oscillation is exhibited at room temperature at an oscillation wavelength of 467 to 475 nm and a threshold current density of 2.9 kA / cm ² . In addition, the lifetime is 500 when the optical output is CW20mW and the operating temperature is 50 ℃.
It is possible to manufacture a laser element with good reproducibility, particularly with 0 hours.

Comparative Examples 1-3
A device substantially similar to that of Example 3 is fabricated except that the off angles shown in the following table are used.

これらの素子の活性領域の混晶揺らぎ及び窒化物半導体層の表面状態を、実施例３と同
様に測定した。その結果、いずれの比較例においても、第１の領域内において波長が不均
一となった。また、第１の領域内において半導体層に段差があり、平坦化されていない。

The mixed crystal fluctuation in the active region and the surface state of the nitride semiconductor layer of these devices were measured in the same manner as in Example 3. As a result, in any of the comparative examples, the wavelength was not uniform in the first region. Further, the semiconductor layer has a step in the first region and is not flattened.

Example 15
The element of this example is substantially the same as that of Example 1 except that the configuration of the semiconductor layer is changed as described below.
As the second layer in -n-side _{layer, Al 0.08 Ga 0.92 N (25Å} ) / GaN (25Å) to 220 repetitions total thickness 1.1μm superlattice structure (average Al mixed crystal 4%),
-As a first layer, a superlattice structure having a total film thickness of 3000 mm obtained by repeating Al _0.05 Ga _0.95 N (25 Å) / GaN (25 ６０) 60 times (average Al mixed crystal is 2.5%),
A GaN layer (1700 mm) as an n-type light guide layer in the core region,
-As an active layer, a barrier layer composed of In _0.05 Ga _0.95 N (1405) / In _0.1 Ga _0.9 N
A multiple quantum well structure (MQW) having a total film thickness of about 720 mm, in which a well layer (70 mm) made of is repeated twice and a barrier layer (300 mm) made of In _0.05 Ga _0.95 N is formed thereon,
-As a p-type guide layer, GaN (1500 mm),
As the first layer in the −p side layer, 3 Al _0.1 Ga _0.9 N (20Å) / GaN (20Å)
It has a superlattice structure (average Al mixed crystal is 4.9%) having a total thickness of 4500 mm repeated 00 times.

The p electrode is Ni / Au, the n electrode is Ti / Al, and the pad electrode is Ni-Ti.
-Au (1000? -1000? -8000?) Is formed. The resonator length is 650
μm.

As for this element, any laser element has an oscillation wavelength of 405 nm and a threshold current density of 2.8.
Good continuous oscillation was exhibited at room temperature at kA / cm ² .
In addition, it was possible to manufacture a laser device with particularly good life characteristics with good reproducibility, with no resonance on the resonance surface, a light output of CW 5 mW, an operating temperature of 60 ° C., and a life of 2000 hours or more.
Furthermore, the divergence angle and aspect ratio of this device were measured and compared with the devices of the comparative examples shown below. As a result, it was possible to reduce the divergence angle by about 8% and the aspect ratio by about 6%.

In the comparative example, in the element described above, instead of providing the second n-type nitride semiconductor layer and the first n-type nitride semiconductor layer, Al _0.08 Ga _0.92 N (25Å) / Ga is used as the n-type cladding layer.
N (25 （) was repeated to form only one layer of a superlattice structure (average Al mixed crystal of 4%) having a total film thickness of 1.4 μm.

Example 16
This example is the same as the element of Example 15 except that the n-side second layer has a superlattice two-layer structure. That is, the temperature is set to 1050 ° C., TMA, TMG, and ammonia are used as source gases, and an A layer made of undoped Al _0.12 Ga _0.88 N is grown to a thickness of 25 mm, and then TMA is stopped as an impurity gas. Si is 5 × 10 ¹⁸ / cm using silane gas.
^A B layer made of ³ doped GaN is grown to a thickness of 25 mm. Then, this operation is repeated 160 times to laminate the A layer and the B layer, and a multilayer film (superlattice structure) having a total film thickness of 8000 mm.
A lower layer of the second n-type nitride semiconductor layer is formed. The average Al mixed crystal in the lower layer of the second layer is 6%.

Subsequently, the temperature was set to 1050 ° C., and TMA, TMG, and ammonia were used as source gases.
An A layer made of undoped Al _0.08 Ga _0.92 N is grown to a thickness of 25 mm, followed by TM
A was stopped, G was doped with Si at 5 × 10 ¹⁸ / cm ³ using silane gas as impurity gas.
A B layer made of aN is grown to a thickness of 25 mm. Then, this operation is repeated 60 times so that the A layer and the B layer are stacked, and the upper layer of the second layer made of a multilayer film (superlattice structure) having a total film thickness of 3000 mm is grown. The average Al mixed crystal in the upper layer of the second layer is 4%.
Thereafter, in the same manner as in Example 15, the first n-type nitride semiconductor layer and the subsequent layers are formed to obtain a nitride semiconductor element.

The obtained device was evaluated in the same manner as in Example 1, and the divergence angle and aspect ratio were measured.
As a result, the same effect as in Example 1 was obtained.
Further, compared with the above comparative example, the divergence angle was reduced by about 20% and the aspect ratio was reduced by about 13%. In other words, the F.E.
F. P. It was confirmed that the spread angle of light in can be suppressed, and that the aspect ratio can be reduced.

The element of the present invention can be used in various devices such as optical disk applications, optical communication systems, printing presses, optical communication systems, exposure applications, and measurement. In addition, specific wavelength (470-490
It is also useful for bio-related excitation photons and the like that can detect the presence or position of the substance by irradiating the substance having sensitivity in the vicinity of nm) with light obtained from the element of the present invention.

1 is a schematic perspective view of a nitride semiconductor laser device of the present invention. It is typical sectional drawing of the nitride semiconductor substrate of this invention. It is a figure for demonstrating the off angle of the nitride semiconductor substrate of this invention. It is a figure for demonstrating another off angle of the nitride semiconductor substrate of this invention. It is the micro PL measurement data of the conventional nitride semiconductor laser element. It is the micro PL measurement data of the nitride semiconductor laser device of the present invention. It is sectional drawing which shows one manufacturing process of the nitride semiconductor substrate of this invention. It is sectional drawing which shows one manufacturing process of the nitride semiconductor laser element of this invention. It is a figure which shows the life data of the nitride semiconductor laser element of this invention. The sectional view (a) which measured the mixed crystal fluctuation of the active region in the nitride semiconductor laser element of the present invention by microphotoluminescence (μ-PL) and the sectional view (b) which observed the surface state of the nitride semiconductor layer is there. Sectional view (a) obtained by measuring the mixed crystal fluctuation of the active region by micro-photoluminescence (μ-PL) in the nitride semiconductor laser device of Comparative Example 1 and sectional view (b) observing the surface state of the nitride semiconductor layer It is. Sectional view (a) obtained by measuring the mixed crystal fluctuation in the active region by micro-photoluminescence (μ-PL) in the nitride semiconductor laser device of Comparative Example 2 and sectional view (b) observing the surface state of the nitride semiconductor layer It is. Sectional view (a) obtained by measuring mixed crystal fluctuation in the active region in the nitride semiconductor laser device of Comparative Example 3 by micro-photoluminescence (μ-PL) and sectional view obtained by observing the surface state of the nitride semiconductor layer (b) It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Nitride semiconductor substrate, 200 ... Nitride semiconductor layer, 203 ... N side clad layer, 20
4 ... n-side light guide layer, 205 ... active layer, 206 ... p-side cap layer, 207 ... p-side light guide layer, 208 ... p-side cladding layer, 209 ... p-side contact layer, 220 ... buried film, 230 ... p
Electrode, 240 ... protective film, 250 ... pad electrode

Claims (15)

A nitride semiconductor layer of the first conductivity type on the main surface of the nitride semiconductor substrate and a multiple or single quantum well structure, at least an active layer containing In in the well layer, is different from the first conductivity type. A nitride semiconductor laser device comprising: a second conductivity type nitride semiconductor layer having a conductivity type; and a stripe-shaped ridge portion on the second conductivity type nitride semiconductor layer,
The main surface of the nitride semiconductor substrate has an off angle a (θa) from the C plane (0001) in a direction substantially parallel to the stripe-shaped ridge portion and in a direction substantially perpendicular to the M plane (1-100). ) And an off angle b (θb) in a direction substantially perpendicular to the ridge portion and in a direction substantially parallel to the M-plane (1-100), 0.05 ° ≦ | θb | ≦ 0.14 And 0.2 ° ≦ | θa | ≦ 0.3 °.   2. The device according to claim 1, wherein the main surface of the nitride semiconductor substrate includes a low dislocation density region made of a C plane (0001) and a high dislocation density region having a dislocation density higher than that of the low dislocation density region.   The element according to claim 2, wherein a main surface of the nitride semiconductor substrate has the low dislocation density region and the high dislocation density region substantially in parallel.   The element according to claim 2, wherein the low dislocation density region is disposed immediately below the ridge.   The element according to claim 1, wherein the first conductivity type nitride semiconductor layer includes a laterally grown Al-containing nitride semiconductor layer. The device according to claim 2, wherein the low dislocation density region has a number of dislocations per unit area of 1 × 10 ⁷ / cm ² or less. Active layer, the general formula _{In x Al y Ga 1-xy} N (0 <x ≦ 1,0 ≦ y <1,0 <x + y ≦ 1) formed by forming a semiconductor layer represented by the claims 1 to 6 An element according to any one of the above.   The device according to claim 1, wherein the active layer has an In composition exceeding 5%. A core region including an active layer is formed between the first conductivity type nitride semiconductor layer and the second conductivity type nitride semiconductor layer,
At least one of the first conductivity type and the second conductivity type nitride semiconductor layer has a first nitride semiconductor layer and a second nitride semiconductor layer in order from the outermost layer of the core region,
A refractive index difference between the outermost layer of the core region and the first nitride semiconductor layer and between the first nitride semiconductor layer and the second nitride semiconductor layer;
The refractive index of the first nitride semiconductor layer is lower than that of the outermost layer of the core region, and the refractive index of the second nitride semiconductor layer is lower than that of the first nitride semiconductor layer. Elements. The refractive index difference (Δn ₁ ) between the outermost layer of the core region and the first nitride semiconductor layer and / or the refractive index difference (Δn ₂ ) between the first nitride semiconductor layer and the second nitride semiconductor layer is The element according to claim 9, which is 0.004 to 0.03. The n-type nitride semiconductor layer which is the first conductivity type nitride semiconductor layer is an m-th (m ≧ 2) n-type nitride in order from the first n-type nitride semiconductor layer in contact with the outermost layer of the core region. Having a semiconductor layer,
The p-type nitride semiconductor layer which is the second conductivity type nitride semiconductor layer has a first p-type nitride semiconductor layer in contact with the outermost layer of the core region,
The element according to claim 1, wherein a refractive index of the m-th (m ≧ 2) n-type nitride semiconductor layer is higher than a refractive index of the first p-type nitride semiconductor layer.   The refractive index difference (Δn) between the m-th (m ≧ 2) -th n-type nitride semiconductor layer and the first p-type nitride semiconductor layer is 0.004 to 0.03. element. The refractive index difference (Δn _m ) between the m-th (m ≧ 2) -th n-type nitride semiconductor layer and the outermost layer of the core region is 0.007 to 0.05. element.   The device according to claim 7, wherein a composition of In in the well layer is 0 <x ≦ 0.5.   The element according to claim 14, wherein the well layer has a thickness of 10 to 300 mm.

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