JP2002299763A - Semiconductor laser element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser element of a ridge waveguide type, which has large θpara and has proper light output/injected current characteristic, i.e., a high kink level up to the high-output region. SOLUTION: The semiconductor laser element of a ridge waveguide type includes a p-contact layer 26 of a stripe-shaped ridge 28 formed on a p-clad layer 24, an insulation film 42 formed as a current path narrowing layer on the clad layer at both side faces of the ridge and on the sides thereof, and a p-side electrode 32 electrically connected to an upper surface of the ridge through a window of the insulating film and extended onto the clad layer at both the side faces of the ridge and on the sides thereof. A spin-on-glass(SOG) film, having absorption coefficient of 2000 cm<-1> or more, is formed as the insulation film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ridge waveguide type semiconductor laser device, and more particularly, to a hetero interface, in which a half-width θ _para of a horizontal far-field image (FFP) is large,
The present invention relates to a ridge waveguide type semiconductor laser device having good optical output-injection current characteristics at the time of high output operation.

[0002]

2. Description of the Related Art Semiconductor laser devices, including GaAs-based and InP-based semiconductor laser devices in a long wavelength region and nitride III-V compound semiconductor laser devices in a short wavelength region, are easy to manufacture. For this reason, ridge waveguide type semiconductor laser devices are widely used in various fields. In a ridge waveguide type semiconductor laser device, the upper part of the upper cladding layer and the contact layer are formed as stripe-shaped ridges, and both sides of the ridge and the upper cladding layer on both sides of the ridge are covered with an insulating film to form a current confinement layer. And an index guide type (refractive index guided type) semiconductor laser device which provides a lateral effective refractive index difference and performs mode control.

[0005] Here, a configuration of a ridge waveguide type nitride III-V compound semiconductor laser device (hereinafter, referred to as a nitride semiconductor laser device) in a short wavelength region will be described with reference to FIG. FIG. 5 is a sectional view showing the configuration of the nitride-based semiconductor laser device. The nitride-based semiconductor laser device 10 is basically formed on a sapphire substrate 12 as shown in FIG.
An n-GaN contact layer 14 and a 1.0 μm-thick n-AlGaN (Al
N-G having a cladding layer 16 and a film thickness of 0.1 μm
aN light guide layer 18, MQW active layer 20 having three well layers, p-GaN light guide layer 22 having a thickness of 0.1 μm,
p- (GaN: Mg / AlGaN) -SLS cladding layer 24 and 0.1 μm-thick p-GaN contact layer 2
6 are provided.

In the laminated structure, the upper part of the p-cladding layer 24 and the p-contact layer 26 are
8 are formed. Also, the n-contact layer 14
, N-cladding layer 16, n-light guiding layer 18, M
The remaining layer 24a of the QW active layer 20, the p-light guide layer 22, and the p-cladding layer 24 is formed as a mesa structure extending in the same direction as the ridge 28. The ridge width W of the ridge 28 is, for example, 1.8 μm, the ridge height H is, for example, 0.6 μm, and the film thickness T of the remaining layer 24 a of the p-cladding layer 24 on both sides of the ridge 28 is, for example, 0.3 μm. is there.

Then, both sides of the ridge 28, the ridge 28
On the remaining layer 24a of the p-cladding layer 24 on both sides of
The O ₂ insulating film 30 is formed as a current confinement layer. P
A p-side electrode 32 made of a d / Pt / Au multilayer metal film is formed on the insulating film 30 and is in contact with the p-contact layer 26 through a window of the insulating film 30. Further, on the n-contact layer 14, an n-side electrode 34 made of a multilayer metal film of Ti / Pt / Au is formed.

[0006]

By the way, the use of the nitride-based semiconductor laser device has been expanded, and the nitride-based semiconductor laser device has a horizontal far-field image (FFP) at the hetero interface of the resonator structure. Half width (hereinafter referred to as θ _para )
And maintaining a good optical output-injection current characteristic up to a high output region by increasing the kink level. For example, when a nitride-based semiconductor laser device is applied to a light source of an optical pickup, θ _para is 7 degrees or more and a high kink level, for example, 50 mW is required. However, it has been difficult for conventional nitride-based semiconductor laser devices to satisfy such severe conditions.

In the above description, the problem has been described by taking a nitride-based semiconductor laser device as an example. However, this problem is not limited to the nitride-based semiconductor laser device but has a longer oscillation wavelength than the nitride-based semiconductor laser device. , GaAs, and InP-based ridge waveguide type semiconductor laser devices.

Accordingly, an object of the present invention is to provide a ridge waveguide type semiconductor laser device having a large θ _para and good optical output-injection current characteristics up to a high output region, that is, a high kink level, and a method of manufacturing the same. It is to be.

[0009]

In the course of research for solving the above-mentioned problems, the present inventor obtained the results of various experiments conducted on a nitride-based semiconductor laser device as shown in FIG. _As shown in FIG. 6, _para is closely related to the effective refractive index difference Δn of the ridge waveguide, and it has been found that Δn needs to be increased in order to increase θ _para . In FIG. 6, marks indicating experimental results are omitted because of complexity. Here, the effective refractive index difference Δn of the ridge waveguide is, as shown in FIG. 5, the difference between the effective refractive index n _eff1 in the ridge and the effective refractive index n _eff2 beside the ridge with respect to the oscillation wavelength, and n _{ef f1} −n _{In the experiment} for _{obtaining the} result shown in FIG. 6, the thickness T of the remaining layer 24a of the p-cladding layer 24 was _eff2 .
Is changed to change Δn.

However, when trying to increase Δn, the cutoff ridge width in the higher-order horizontal / lateral mode becomes narrower. The cut-off ridge width in higher-order horizontal / transverse mode refers to the ridge width where higher-order horizontal / transverse mode does not occur. To the primary mode. FIG. 7 schematically shows a basic mode and a first-order higher-order mode in the horizontal and horizontal modes. When a hybrid mode composed of the basic horizontal / lateral mode and the higher-order horizontal / lateral mode occurs, as shown in FIG. 8, a kink occurs in the light output-injection current characteristic (LI characteristic), and the light is illuminated during the high output operation. The linearity of the output-injection current characteristics cannot be maintained.

Therefore, the present inventor has conducted various experiments,
As shown in FIG. 6, the kink level is closely related to the effective refractive index difference Δn of the ridge waveguide, and it has been found that it is necessary to reduce Δn in order to increase the kink level. Note that various different marks shown in FIG. 6 indicate experimental results. According to the study of the present inventors, in particular, the nitride-based semiconductor laser device has a small Δn and a short oscillation wavelength, and therefore, as shown in FIG. . FIG. 9 shows the relationship between the effective refractive index difference Δn of the GaN layer ridge and the cutoff ridge width (μm) when the refractive index of the GaN layer is 2.504 and the oscillation wavelength λ is 400 nm. It is a graph shown. For example, the refractive index difference Δn of the ridge waveguide is 0.005.
When the value is set to 0.01, the ridge width must be reduced to about 1 μm in order to make the ridge width smaller than the cutoff ridge width.

To further explain, the nitride semiconductor laser device has a stripe width of GaAs for controlling the transverse mode.
Although the stripe width is smaller than the stripe width of the system or InP-based semiconductor laser device, for example, 2.5 μm, for example, 3 to 4 μm, a higher-order (first-order) transverse mode as shown in FIG. -Kink occurs in the injection current characteristic. According to the study of the present inventor, the main factor is that the effective refractive index difference Δn, which is a main parameter of lateral confinement, is large as described above.

As described above, when Δn is increased to increase θ _para , the cutoff ridge width is reduced, so that the laser characteristics at the time of high-output operation are deteriorated. That is, with respect to the ridge width, increasing θ _para and enhancing laser characteristics during high-power operation have a trade-off relationship as shown in FIG. In FIG. 10, marks such as black circles, white circles, triangles, black squares, white squares, and the like indicate experimental results.

In the course of the research, the present inventor conducted experiments on the absorption loss of the primary mode and the fundamental mode by changing the material of the insulating film provided as the current confinement layer in various ways. as a result,
When an SOG (Spin On Glass) film is used as the insulating film, if the absorption coefficient α is larger than 2000 cm ⁻¹ ,
As shown in FIG. 11, as the absorption coefficient α increases, Δn hardly changes, and the loss in the primary mode in the horizontal and transverse mode is more selective than in the basic (0th-order) mode in the horizontal and transverse mode. To increase.

In other words, the kink is caused by an increase in the light intensity of the primary mode in the horizontal and transverse modes. Therefore, if the loss in the primary mode is larger than the loss in the fundamental mode, the injection current is increased. Increase the light output
Kink generation is suppressed. Also, for example, T
By adding an impurity such as i to the SOG to increase the absorption coefficient of the SOG, the loss of the first-order mode is reduced to the fundamental (0
It is significantly increased compared to the loss of the (second) mode. Thus, without reducing Δn, that is, when θ
_The present invention has been experimentally demonstrated that a linear light output-injection current characteristic without kink can be obtained while suppressing the generation of the first mode while maintaining _para .

To achieve the above object, based on the above findings, a semiconductor laser according to the present invention has at least an upper part of an upper cladding layer formed in a stripe-shaped ridge,
A ridge waveguide type semiconductor laser having an insulating film formed as a current confinement layer on both sides of a ridge and an upper cladding layer beside a ridge, and an electrode film electrically connected to the ridge upper surface through a window of the insulating film. In the device, as an insulating film, S
It is characterized in that an OG (Spin On Glass) film is formed.

Preferably, an SOG (Spin On Glass) film
Has an absorption coefficient of 2000 cm^-1The above SOG (Spin On
Glass) film. SOG (Spin On Glass) film thickness
Depends on the absorption coefficient of the SOG film.
The thickness is 0.05 μm or more on the remaining layer of the cladding layer beside
Is preferred. Preferably, SOG (Spin On Glass)
The film is made of SiO_Two, ZrO_TwoAnd TiO _TwoIn any of
Is formed. Further, preferably, S
The absorption coefficient of OG (Spin On Glass) film is 2000cm
^-1As described above, the impurity is SOG (Spin On Glass).
 ). The impurities are, for example, Ti, Zn,
At least Ni, Fe, Co, Al, Zr, and Si
Is an absorption medium at the oscillation wavelength.

The method for fabricating a semiconductor laser device according to the present invention is a method for fabricating a ridge waveguide type semiconductor laser device, wherein an insulating film is formed as a current confinement layer on both sides of the ridge and on the upper cladding layer beside the ridge. In doing so, S
A step of applying an OG (Spin On Glass) film by a spin coating method, a step of heat-treating and curing the SOG film, and an etching of the SOG film to expose an upper surface of the ridge without forming an etching mask on the SOG film. And a step of causing

By performing heat treatment in an atmosphere of 100 ° C. or more, that is, by performing baking, a solid SOG film can be obtained. When etching the SOG film,
For example, the SOG film is etched by a dry etching method using an etching gas containing CF ₄ gas so that the contact layer on the ridge upper surface is exposed. In the method of the present invention, when etching the SOG film, an etching mask is not required. Therefore, a process for forming an etching mask is not required, and accordingly, the number of process steps is reduced, and the manufacturing cost can be reduced.

The present invention and the method of the present invention can be applied without limitation to the composition and film type of the compound semiconductor layer forming the laser structure. For example, GaAs, InP, AlGaAs, G
It can be suitably applied to an aN-based semiconductor laser device.

[0021]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The film forming method, the composition and thickness of the compound semiconductor layer, the ridge width, the process conditions, and the like described in the following embodiments are merely examples for facilitating understanding of the present invention. It is not limited to this example. Embodiment 1 This embodiment is an embodiment in which the semiconductor laser device according to the present invention is applied to a ridge waveguide type nitride III-V compound semiconductor laser device (hereinafter, referred to as a nitride semiconductor laser device). FIG. 1 is a cross-sectional view showing a configuration of a nitride-based semiconductor laser device of this embodiment. 1 that are the same as those shown in FIG. 5 are given the same reference numerals, and descriptions thereof are omitted. The nitride-based semiconductor laser device 40 of the present embodiment is a semiconductor laser device having an oscillation wavelength of 400 nm, and has p-sides on the side surfaces of the ridge and on the side of the ridge.
(GaN: Mg / AlGaN) -SLS cladding layer 24
5 has the same configuration as the conventional nitride-based semiconductor laser device 10 shown in FIG. 5 except that the type of the insulating film on the remaining layer 24a is different.

In this embodiment, an SOG (Spin On Glass) film 42 having an absorption coefficient α of 4500 cm ^-1 is used as an insulating film.
Is formed by spin coating. SOG film 42
Contains Ti in order to increase the absorption coefficient α.

In order to evaluate the nitride semiconductor laser device of this embodiment, effective refraction is performed by changing the thickness of the remaining layer 24a of the p-clad layer 24 of the nitride semiconductor laser device of this embodiment. The kink level height was measured by changing the rate difference Δn to various sizes, and the result shown in FIG. 2 was obtained. The mark Δ indicates the measurement result. Further, for a conventional nitride-based semiconductor laser device provided with a SiO ₂ film by a vapor deposition method or a CVD method as a current confinement layer, the height of the kink level was measured by changing Δn in the same manner, and FIG. It was shown to. The circles indicate the measurement results. From a comparison between the two, it can be seen that the kink level of the nitride-based semiconductor laser device of the present embodiment is significantly higher than that of the conventional nitride-based semiconductor laser device at the same Δn.

EXAMPLE The present example is a specific example of the present embodiment, and the SOG film 42 has an absorption coefficient α of 4500 cm ⁻¹ , and FIG.
As shown in (c), the thickness t on the p-clad layer 24 beside the ridge is 135 nm. Examples of the material for forming the SOG film 42 include a hard coat agent manufactured by Nissan Chemical Industries, Ltd.
The trade name NHC CT-1100C can be used. This hard coat agent is hexylene glycol 51
%, Butyl cellosolve 19%, ethanol 13%, and the like. With the above configuration, the nitride-based semiconductor laser device 40 of this example had θ _para of 10.5 ° and a kink level of 80 mW.

Hereinafter, a method of forming the SOG film 42 will be described with reference to FIG. FIG. 3A to FIG. 3C are cross-sectional views for respective steps when the SOG film 42 of the embodiment is formed. First, as shown in FIG. 3 (a), the p-contact layer 26 and the p-cladding layer 24 are partially etched to form a stripe-shaped ridge 28 comprising the p-cladding layer 24 and the p-contact layer 26. Form. Next, the above-mentioned hard coat agent is applied by a spin coat method, and an SOG film is formed as shown in FIG. By applying the SOG film by spin coating, the SOG film on the p-contact layer 26 is thin,
-The SOG film on the remaining layer 24a of the cladding layer 24 becomes thicker. Then, a heat treatment is performed at a temperature of 300 ° C. for 30 minutes to bake and harden the SOG film. Subsequently, without forming an etching mask, a dry etching method using an etching gas containing CF ₄ was performed as shown in FIG.
As shown in (c), the SOG film is etched to such an extent that the p-contact layer 26 is exposed. Thus, p-
On the remaining layer 24a of the cladding layer 24, a thickness of 135 n
Thus, m SiO ₂ films 42 are formed.

As shown in FIG. 4A, when a SiO ₂ film is formed on the ridge 28 by a vapor deposition method or a CVD method, the p-cladding layer 24 is formed on the p-contact layer 26 as shown in FIG. Of the same thickness as on the remaining layer 24a of
An O ₂ film is deposited. Therefore, when exposing the p-contact layer 26 and opening a window as shown in FIG. 4B, an etching mask is required as shown in FIG. 4A. Further, even when an etching mask is not used, a photoresist process that is difficult to control such as flattening with a resist is required. In this embodiment, since an etching mask is not required, a process for forming an etching mask becomes unnecessary, and accordingly, the number of process steps is reduced and the manufacturing cost can be reduced.

[0027]

According to the present invention, an absorption coefficient of 2 is formed as a current confinement layer on both sides of the ridge and on the cladding layer beside the ridge.
By forming a SOG (Spin On Glass) film of 000 cm ^-1 or more, a ridge waveguide type semiconductor laser device having a large θ _{para and} excellent light output-injection current characteristics at the time of high output operation is realized. . Further, the method of the present invention realizes a method of manufacturing a ridge waveguide type semiconductor laser device which does not require a process of forming an etching mask in a step of opening a window of an insulating film and reduces the manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a nitride-based semiconductor laser device according to an embodiment.

FIG. 2 is a graph showing a comparison between a nitride-based semiconductor laser device according to an embodiment and a conventional nitride-based semiconductor laser device with respect to a relationship between Δn and a kink level.

FIGS. 3A to 3C are cross-sectional views for each process when forming an SOG film according to an embodiment.

FIGS. 4A and 4B are process diagrams illustrating a conventional method of forming an insulating film.

FIG. 5 is a cross-sectional view showing a configuration of a conventional nitride-based semiconductor laser device.

FIG. 6 is a graph showing the relationship between Δn and θ _para and the relationship between Δn and kink level, respectively, obtained by experiments.

FIG. 7 is a schematic diagram illustrating a basic lateral mode and a higher-order lateral mode.

FIG. 8 is a schematic diagram illustrating a kink.

FIG. 9 is a graph showing a relationship between an effective refractive index difference Δn and a cutoff ridge width.

FIG. 10 is a graph showing a relationship between θ _para and a kink level obtained by an experiment.

FIG. 11 is a graph showing the relationship between the absorption coefficient of SOG and Δn, and the relationship between the absorption coefficient of SOG and the zero-order mode (fundamental mode) and the first-order mode absorption loss, respectively, obtained by experiments.

[Explanation of symbols]

10 ... conventional nitride semiconductor laser element, 12 ... sapphire substrate, 14 ... n-GaN contact layer, 16
... n-AlGaN (8% Al composition) cladding layer, 1
8 n-GaN optical guide layer, 20 MQW active layer,
22 p-GaN light guide layer, 24 p- (Ga
N: Mg / AlGaN) -SLS clad layer, 26 ...
p-GaN contact layer, 28: stripe ridge, 30: SiO ₂ film, 32: p-side electrode, 34:
n-side electrode, 40... nitride semiconductor laser device of the embodiment, 42... SOG (Spin On Glass) film.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F058 BC02 BC03 BC04 BC08 BF46 BJ01 BJ07 5F073 AA13 AA45 AA74 BA04 CB05 DA24 EA16 EA19

Claims (6)

[Claims] At least an upper portion of an upper cladding layer is formed as a stripe-shaped ridge, an insulating film formed as a current confinement layer on both side surfaces of the ridge and an upper cladding layer beside the ridge, and a ridge formed through a window of the insulating film. A semiconductor laser device having a ridge waveguide type semiconductor laser device having an electrode film electrically connected to an upper surface thereof, wherein an SOG (Spin On Glass) film is formed as an insulating film. 2. The semiconductor laser device according to claim 1, wherein the SOG (Spin On Glass) film is an SOG (Spin On Glass) film having an absorption coefficient of 2000 cm ⁻¹ or more. 3. The SOG (Spin On Glass) film is made of SiO
₂ , ZrO ₂ , TiO ₂ , MgF, SiN, and CeO
_3. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is formed of any one of the following. 4. An absorption loss for an oscillation wavelength of SOG (Spin On Glass) is set to 2000 cm ⁻¹ or more.
4. The semiconductor laser device according to claim 1, wherein an impurity is mixed in the SOG (Spin On Glass) film. 5. 5. The method according to claim 1, wherein the impurities are Ti, Zn, Ni, Fe, C
The semiconductor laser device according to claim 4, wherein the semiconductor laser device is at least one of o, Al, Zr, and Si. 6. A method of manufacturing a ridge waveguide type semiconductor laser device, comprising: forming an insulating film as a current confinement layer on both side surfaces of a ridge and an upper cladding layer beside the ridge; On glass) A step of applying a film by a spin coating method, a step of heat-treating and curing the SOG film, and a step of forming an SOG film without forming an etching mask on the SOG film.
Exposing the upper surface of the ridge by etching the OG film.