JPH11145566A - Manufacture of 3-nitride semiconductor laser diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve light deflectivity at an end surface by improving flatness at a surface of the resonator end face of a laser diode. SOLUTION: On a substrate 1, a plurality of layers 2-9 of 3-nitride semiconductor are formed. An active layer 6 of MQW(multiple quantum well) structure is sandwiched between an n-guide layer 6 and an n-clad layer 4 on one side and a p-guide layer 7 and a p-clad layer 8 on the other side. By removing the other part except for a resonator part by etching, the resonator is formed into a mesa-type. The mesa-type etching of the resonator is so executed that width which is parallel to a substrate surface at the end surface of the resonator is wider than that of the main body part of the resonator, where a current flows vertical to the substrate surface, so that the resonator becomes I-shaped. When the resonator is to be retained by mesa-etching, an edge part of the end surface is etched round, which does not appear at a center part of the end surface. Thus, the flatness at the end surface where light is reflected is substantially improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a laser diode using a group III nitride semiconductor. In particular, it relates to a method for forming an end face of a laser-diode resonator.

[0002]

2. Description of the Related Art Heretofore, there have been known devices formed of a gallium nitride-based compound semiconductor (AlGaInN) on a sapphire substrate to form a blue light emitting diode (LED) and a blue laser diode (LD). In order to efficiently reflect and oscillate the light of the laser diode (LD), it is necessary to keep the perpendicularity and parallelism of the cavity end face high. Cleavage is preferably used to form the resonator end face with high precision. However, in the above-described device, cleavage is difficult because the substrate and the device layer are formed of different materials. For this reason, an end face is formed by dry etching.

[0003]

However, when forming a ridge waveguide type laser diode in which only the resonator portion is left in a mesa shape by dry etching as described above, the end face has a curvature with respect to the optical axis. Has and is rounded. As a result, there is a problem that the mirror end face of the ideal resonator is not formed, the laser does not oscillate, and the oscillation efficiency is low.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to improve the flatness of the surface of a cavity end face of a laser diode and improve the light reflectance at the end face. Thus, the effect of confining light is enhanced and the oscillation threshold current is reduced.

[0005]

Means for Solving the Problems and Effects and Effects of the Invention
A feature of the invention for achieving the object is that a plurality of layers made of a group III nitride semiconductor are formed on a substrate, and the other portions are removed by etching while leaving the resonator portion, thereby forming the mesa in the resonator. In the method for manufacturing a group III nitride semiconductor laser diode formed in a mold, each layer made of a group III nitride semiconductor is formed on a substrate, and the mesa-type etching of the resonator is performed so that the width parallel to the substrate surface at the end face of the resonator is reduced. The etching is performed so as to be longer than the width of the main body of the resonator in which the current flows perpendicular to the substrate surface.

The width of the end face of the resonator parallel to the substrate surface is longer than the width of the main body of the resonator. Therefore, when the resonator is left by mesa etching, the edge portion of the end face is etched round, but this roundness does not appear at the center of the end face.
Thereby, the flatness of the end face on which light is substantially reflected is improved, and an ideal mirror surface can be obtained. As a result, the specularity of the end face is improved, the effect of confining light is improved, and the lasing threshold current of the laser is reduced.

[0007] By forming the resonator in the shape of the capital letter "I" when viewed from the direction perpendicular to the substrate surface, a structure having the above-described effect can be specifically configured. The group III nitride semiconductor is preferably Al _x Ga _Y In _1-XY N (0 ≦ X ≦
1,0 ≦ Y ≦ 1,0 ≦ X + Y ≦ 1), whereby a blue short-wavelength laser diode can be obtained. In particular, the semiconductor laser diode is changed to Al _x1 Ga _1-x1 N
(0 ≦ X1 ≦ 1) and Ga _x2 In _1-x2 N (0
≦ X2 ≦ 1) / GaN active layer with MQW structure
Blue laser output can be improved. In addition, the end face can be efficiently formed by using the reactive ion beam etching (RIBE) as the dry etching. Further, desirably, the reactive ion beam etching is performed,
By performing etching using Cl ₂ gas, etching with a high etching rate can be performed. Thereby, the mirror surface accuracy of the resonator end face can be further improved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on specific embodiments. Note that the present invention is not limited to the following examples. FIG. 1 is a sectional view showing a configuration of a light emitting device (semiconductor laser) 100 according to a specific embodiment of the present invention. The light emitting device 100 has a sapphire substrate 1, and a 50 nm AlN buffer layer 2 is formed on the sapphire substrate 1.

On the buffer layer 2, a film thickness of about 4.0 μm, an electron density of 1 × 10 ¹⁸ / cm ³ , and silicon (S
i) n layer 3 made of doped GaN, thickness 500 nm, electron density 1 × 10 ¹⁸ / cm ³ , silicon (Si) doped Al _0.1 Ga
N-cladding layer 4 of _0.9 N, n-guide layer 5 of silicon (Si) -doped GaN having a thickness of 100 nm and electron density of 1 × 10 ¹⁸ / cm ³ , and barrier layer 6 of GaN having a thickness of about 35 °
An active layer 6 of a multiple quantum well structure (MQW) in which well layers 61 of Ga _0.95 In _0.05 N having a thickness of about 35 ° are alternately stacked.
Are formed. The barrier layer 62 has six layers, and the well layer 61 has five layers. Then, on the active layer 6, a film thickness of 100
nm, magnesium with a hole density of 5 × 10 ¹⁷ / cm ³ (M
g) p guide layer 7 made of doped GaN, thickness 500 nm,
A p-cladding layer 8 made of magnesium (Mg) -doped Al _0.1 Ga _0.9 N with a hole density of 5 × 10 ¹⁷ / cm ³ and a thickness of 200 n
m, hole density 5 × 10 ¹⁷ / cm ³ , magnesium (Mg)
A p-contact layer 9 made of doped GaN is formed. Then, a Ni electrode 10 is formed on the p contact layer 9. An electrode 11 made of Al is formed on the n-layer 3.

The plane of the light emitting device 100 is configured as shown in FIG. 2, and the layers 4 to 9 are formed in an “I” shape. Region A in FIG. 2 is the exposed surface of layer 3. The electrode 11 is formed on the exposed surface A of the layer 3.
Lines L1 and L2 in FIG. 2 are etching lines for forming a mirror surface of a resonator described later. In the "I" -shaped element, the current confinement portion at the center is the main body and the width is W.
Is displayed in.

Next, a method of manufacturing a light emitting device (semiconductor laser) having this structure will be described. Light emitting element 100
Was produced by vapor phase epitaxy by metalorganic compound vapor phase epitaxy (hereinafter referred to as "MOVPE"). The gases used were NH ₃ and carrier gas H ₂ or N ₂ and trimethylgallium.
(Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”), trimethylaluminum (Al (CH ₃ ) ₃ ) (hereinafter referred to as “TMA”), and trimethylindium (In (CH ₃ ) ₃ ) (hereinafter referred to as “TMI”). ]) And silane
(SiH ₄ ) and cyclopentadienyl magnesium (Mg (C
₅ H ₅ ) ₂ ) (hereinafter referred to as “CP ₂ Mg”).

First, a single-crystal sapphire substrate 1 is mounted on a susceptor placed in a reaction chamber of a MOVPE apparatus, with the a-plane cleaned by organic cleaning and heat treatment as a main surface. Next, the sapphire substrate 1 was baked at a temperature of 1100 ° C. while flowing H ₂ at a normal pressure and a flow rate of ₂ liter / min into the reaction chamber for about 30 minutes.

[0013] Next, by lowering the temperature to 400 ° C., H ₂
20 liter / min, NH ₃ 10 liter / min, TMA 1.8 ×
The buffer layer 2 of AlN was formed to a thickness of about 50 nm by supplying at a rate of 10 ^-5 mol / min for about 90 seconds. Next, the temperature of the sapphire substrate 1 was maintained at 1150 ° C., and H ₂ was 20 liter / min.
NH ₃ at 10 liter / min, TMG at 1.7 × 10 ^-4 mol / min,
Silane (SiH ₄ ) diluted to 0.86 ppm with H ₂ gas was introduced at 20 × 10 ⁻⁸ mol / min, the film thickness was about 4.0 μm, the electron density was 1 × 10 ¹⁸ / cm ³ , and silicon (Si ) An n layer 3 made of doped GaN was formed.

After the formation of the n-layer 3, the temperature is maintained at 1100 ° C., H ₂ is 20 liter / min, and NH ₃ is 10 l / min.
ter / min, TMA 5.0 × 10 ^-6 mol / min, TMG 5.0
Silane (SiH ₄ ) diluted to 8 × 10 ⁻⁵ mol / min and 0.86 ppm with H ₂ gas was introduced at 8 × 10 ⁻⁹ mol / min, and the film thickness was 500 nm and the electron density was 1 × 10 ¹⁸ / cm. ³ , silicon (S
i) An n-cladding layer 4 made of doped Al _0.1 Ga _0.9 N was formed.

Next, the temperature was kept at 1100 ° C., the H ₂ 2
0 liter / min, TMG was 5 × 10 ⁻⁵ mol / min, and (SiH ₄ ) diluted to 0.86 ppm with H ₂ gas was 8 × 10 ⁻⁹ mol / min.
Minutes, the film thickness is 100 nm, and the electron density is 1 × 10 ¹⁸ / c.
An n guide layer 5 made of m ³ silicon (Si) doped GaN was formed.

Next, N ₂ or H ₂ , NH ₃ and TMG were supplied to form a barrier layer 62 of GaN having a thickness of about 35 °. Next, supply N ₂ or H ₂ , NH ₃ , TMG and TMI,
A well layer 61 of Ga _0.95 In _0.05 N with a thickness of about 35 ° was formed. Further, a barrier layer 62 and a well layer 61 were formed four times under the same conditions, and a barrier layer 62 made of GaN was formed thereon. Thus, the active layer 6 having the MQW structure having five periods was formed.

Subsequently, the temperature was maintained at 1100 ° C., N ₂ or H ₂ was 20 liter / min, NH ₃ was 10 liter / min, and TMG was 0.1 liter / min.
5 × 10 ⁻⁴ mol / min, Cp ₂ Mg is introduced at 2 × 10 ⁻⁷ mol / min, and a magnesium (Mg) -doped p-guide made of magnesium (Mg) -doped GaN with a thickness of about 10 nm is introduced. Layer 7 was formed.

Next, the temperature is maintained at 1100 ° C. and N ₂ or
H _{2 20} liter / min, NH ₃ 10 liter / min, TMA 5 × 1
0 ^-6 mol / min, 5 × 10 ^-5 mol / min of TMG and Cp ₂ M
g was introduced at 2 × 10 ⁻⁷ mol / min, and magnesium (Mg) was introduced.
Doped with about 100 nm thick magnesium
A p-cladding layer 8 made of (Mg) -doped Al _0.1 Ga _0.9 N was formed.

Next, the temperature is maintained at 1100 ° C. and N ₂ or
H _{2 20} liter / min, NH ₃ 10 liter / min, TMG 5 × 1
0 ^-5 mol / min, was introduced Cp ₂ Mg at 2 × 10 ^-7 mol / min, magnesium (Mg) is doped, the thickness of about 20
A p-contact layer 9 made of 0 nm magnesium (Mg) -doped GaN was formed.

Next, the p-contact layer 9, p-cladding layer 8 and p-guide layer 7 were uniformly irradiated with an electron beam using an electron beam irradiation apparatus. The irradiation conditions of the electron beam are as follows:
kV, sample current 1 μA, beam moving speed 0.2 mm /
sec, beam diameter 60 μmφ, degree of vacuum 5.0 × 10 ⁻⁵ T
orr. Due to the irradiation of the electron beam, the p-contact layer 9, the p-cladding layer 8 and the p-guide layer 7 have hole concentrations of 5 × 10 ¹⁷ / cm ³ , 5 × 10 ¹⁷ / cm ³ and 5 respectively.
× 10 ¹⁷ / cm ³ . Thus, a wafer having a multilayer structure could be formed.

Next, as shown in FIG. 3, an SiO ₂ layer 12 is formed on the p-contact layer 9 by sputtering for 200 nm.
m, and a photoresist 13 was applied on the SiO ₂ layer 12. Then, as shown in FIG. 3, the photoresist 13 at the electrode formation site A ′ for the n-layer 3 was removed by photolithography. Next, as shown in FIG. 4, the SiO ₂ layer 12 not covered with the photoresist 13 was removed with a hydrofluoric acid-based etchant.

Next, the photoresist 13 and the SiO ₂ layer 12
P contact layer 9, p clad layer 8, p guide layer 7, active layer 6, n guide layer 5,
A part of the n-cladding layer 4 and the n-layer 3 is vacuumed to 0.04
rr, high frequency power 0.44 W / cm ² , BCl ₃ gas 10
dry etching by supplying at a rate of
Was dry-etched. In this step, as shown in FIG. 5, a region A for extracting an electrode from the n-layer 3 was formed. Thereafter, the SiO ₂ layer 12 was removed.

Next, an electrode 10 was formed on the p-contact layer 9 through uniform deposition of Ni, application of a photoresist, a photolithography step, and an etching step. On the other hand, aluminum is deposited on the
1 was formed.

Next, dry etching for forming a resonator end face was performed as follows. A photoresist is uniformly applied on the entire upper surface of the wafer, and a stripe-shaped region B (FIG. 2) having a width in the y-axis direction and a length in the x-axis direction is removed by photolithography. A resist mask 12 covered along the x-axis with a width of y was formed as shown in FIG.

Next, Cl at a vacuum of 1 mTorr and high frequency power of 300 W
₂ Supply gas at a rate of 5 ml / min.
Reactive ion beam etching (R) until the sapphire substrate 1 exposes the striped region B not covered with
Dry etching by IBE).

Thereafter, the wafer processed as described above is scribed along the length direction (y-axis) of the laser resonator (direction perpendicular to the end face S of the resonator) to form a scribe groove. A die strip was obtained by die-sinking in the x-axis direction parallel to the end face.

Next, in order to protect the cavity facet S, SiO ₂ was deposited on the cavity facet S by sputtering. Then, each strip was pressed by a roller, and separated into each element chip by using a scribe groove already formed along the y-axis direction. In this way, a resonator end face S having a high degree of perpendicularity to the substrate 1 and a high degree of parallelism between the end faces, and a high flatness of the surface and a high specularity was obtained. As a result, the reflectivity of light at the cavity end face S was increased, the effect of confining light was high, and the threshold current could be reduced. The laser diode 100 thus obtained has a drive current of 1000 mA, an emission output of 10 mW, and an oscillation peak wavelength.
380 nm.

A protective film of SiO ₂ is formed on the resonator end face S. Silicon oxide such as SiO ₂ , silicon nitride such as Si ₃ N ₄ ,
A multi-layer made of another dielectric such as TiO ₂ may be formed on the end face S. By optimally designing the thickness of each of the multiple layers, the reflectance at the end face S can be further improved.

As shown in FIG. 2 and FIG.
Since the layers 4 to 9 as the functional layers are etched in an “I” shape, the width D in the x-axis direction of the resonance end face S is formed to be wider than the width W of the main body portion in which the current path is narrowed. As a result,
The flatness of the resonance end face S can be improved while achieving the function of current constriction.

FIG. 8 shows the SE of the etched resonance end face S.
It is an M photograph. (A) shows a case where the width D is 5 μm, (b) shows a case where the width D is 10 μm, and (c) shows a case where the width D is 30 μm. Width D
It can be seen that the longer the is, the more the center portion of the resonance end face S is etched flat without roundness. That is,
When the width D is small, the edges e1, e2, e3, and e4 are rounded as shown in FIG. 9A schematically showing the end face S, but when the width D is large, , Edge e
1, e2, e3, and e4 are straight lines, and the end face S at the center is flat.

The width D is desirably 30 μm or more. It has been measured that when the width D is 30 μm, the smoothness (degree of surface irregularities) of the end face S is 10 nm or less.
Further, the width H in the y direction shown in FIG. 2 is not particularly related to the flatness of the end face S, but is preferably 5 to 50 μm.

In the above embodiment, the crystal material of the layers 2 to 9 may be a gallium nitride-based compound semiconductor, and there is no particular limitation on the crystal material and composition ratio. General formula, Al _x Ga _Y
It is possible to use any binary, ternary or quaternary Group 3 nitride semiconductor represented by In _{1- XY} N (0 ≦ X ≦ 1,0 ≦ Y ≦ 1,0 ≦ X + Y ≦ 1). it can. Further, the active layer 6 has the MQW structure, but may have the SQW structure. The composition ratio between the active layer 6 and the cladding layers 4 and 8 is such that when a double hetero junction is formed, the band gap of the active layer 6 is
8 may be selected so as to be narrower than the band gap and to match the lattice constant. When an arbitrary quaternary Group III nitride semiconductor is used, the band gap and the lattice constant can be independently changed, so that a double heterojunction having the same lattice constant in each layer can be realized. Although it is desirable to configure a double hetero junction, the present invention is not limited to a double hetero junction and may be a single hetero junction, a homo junction, or the like.

Although the resistance of the p guide layer, the p clad layer and the p contact layer has been reduced by electron beam irradiation, it may be performed by thermal annealing, heat treatment in N ₂ plasma gas, or laser irradiation. In the above embodiment, the electrode 11
The mask for the formation of the etching step, other SiO _2, metal, resist or the like, there are etching resistance to dry etching can be adopted if it can selectively etched or peeling the semiconductor of the underlying GaN-based . further,
Photoresist was used as a mask in the enchanting step for forming the cavity end face, but it also has etching resistance to dry etching of SiO ₂ or the like, and is selectively etched with respect to the lower electrodes 10 and 11. Alternatively, any material that can be separated can be used.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a semiconductor laser according to a first specific example of the present invention.

FIG. 2 is a plan view of the semiconductor laser of the embodiment.

FIG. 3 is a sectional view showing a manufacturing step of the semiconductor laser according to the embodiment.

FIG. 4 is a sectional view showing a manufacturing process of the semiconductor laser according to the embodiment.

FIG. 5 is a sectional view showing a manufacturing step of the semiconductor laser of the embodiment.

FIG. 6 is a sectional view showing a manufacturing step of the semiconductor laser according to the embodiment.

FIG. 7 is a perspective view showing a configuration of the semiconductor laser of the embodiment.

FIG. 8 is a SEM micrograph of the etched resonance end face.

FIG. 9 is a schematic diagram for explaining an SEM photograph.

[Explanation of symbols]

 100 laser diode 1 sapphire substrate 2 buffer layer 3 n layer 4 n clad layer 6 active layer 7 p p clad layer 8 p guide layer 10, 11 electrode 61 well layer 62 barrier layer 12 Photoresist S: cavity facet

Claims (4)

[Claims] A resonator is formed in a mesa shape by forming a plurality of layers made of a group III nitride semiconductor on a substrate and removing other portions by etching while leaving a resonator portion.
In the method for manufacturing a group III nitride semiconductor laser diode, each layer made of a group III nitride semiconductor is formed on the substrate, and the width of the mesa-type etching of the resonator is parallel to the substrate surface at the end face of the resonator. A method of manufacturing a group III nitride semiconductor laser diode, characterized in that etching is performed so as to be longer than a width of a main body of a resonator flowing perpendicularly to a substrate surface. 2. The method for manufacturing a group III nitride semiconductor laser diode according to claim 1, wherein the shape of the mesa etching of the resonator is an I-shape when viewed from above the substrate. 3. The group III nitride semiconductor according to claim 1, wherein the group III nitride semiconductor is Al _x Ga _Y In
3. The group III nitride semiconductor laser diode according to claim _{1, wherein 1-XYN} (0 ≦ X ≦ 1,0 ≦ Y ≦ 1,0 ≦ X + Y ≦ 1). Production method. 4. The method according to claim 1, wherein said dry etching is reactive ion beam etching (RIBE).
A method for manufacturing a group III nitride semiconductor laser diode according to claim 1.