JP3277711B2 - Semiconductor laser and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device using an AlGaAs-based material, and more particularly, to a ridge waveguide type self-aligned semiconductor laser and a self-aligned semiconductor laser capable of realizing a high refractive index and high output. More particularly, the present invention relates to a method for manufacturing such a ridge waveguide type self-aligned semiconductor laser with improved processing controllability.

[0002]

2. Description of the Related Art FIG. 10 shows a conventional complex refractive index waveguide type Al.
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a GaAs semiconductor laser. The semiconductor laser shown in FIG. 10 is a semiconductor laser having a double hetero structure in which the upper and lower portions of an active layer 3 are sandwiched between an upper cladding layer 4 and a lower cladding layer 2, and are sequentially formed on an n-type GaAs substrate 1. Lower cladding layer 2, active layer 3, upper cladding layer 4 formed in an inverted mesa ridge shape, contact layer 8a
The upper cladding layer 4 and the contact layer 8a formed in an inverted mesa ridge shape are sandwiched between the current constriction layer and the buried layer 7 made of GaAs regrown on both sides thereof. Further, ohmic electrodes 9a and 9b are provided on the upper and lower surfaces of these laminates.

With reference to FIGS. 11 and 12, a description will be given of a process for fabricating the above-mentioned complex refractive index waveguide type AlGaAs semiconductor laser formed on an n-type GaAs substrate as an example.
On an n-type GaAs substrate 1, a lower cladding layer 2 made of n-type AlGaAs, an active layer 3 made of intrinsic AlGaAs, and a p-type AlGa
An upper cladding layer 4 made of As and a contact layer 8a made of p-type GaAs are laminated. Then, on the entire surface contact layer 8a, dielectric, such as SiO ₂ and a thickness of 200nm laminated by a plasma CVD method to form a dielectric film (SiO ₂ film) F, then, SiO ₂ film by conventional photolithography [0
11] A resist mask G having a width of 8 μm is formed in the direction (see FIG. 11A).

Next, using the resist mask G as a mask,
Etching is performed by RIE to form a SiO ₂ film F in a stripe shape (see FIG. 11B). Next, this SiO
_{2 Using the} film F as an etching mask, the contact layer 8a and the upper cladding layer 4 are etched with, for example, a sulfuric acid-based wet etchant to form the ridge 11, and when the cladding layer 4 has a predetermined thickness T, The etching is stopped (see FIG. 12C). At this time, the etching is stopped when a predetermined time has elapsed by the time control.

Further, using the SiO ₂ film F as a mask for selective growth, a current blocking layer 7 made of n-type GaAs is epitaxially grown on the upper cladding layer 4 until the height is substantially the same as the upper surface of the contact layer 8a ( FIG. 12D). After the SiO ₂ film F is removed by etching with hydrofluoric acid or the like,
P-type Ga is formed on the entire surface of the contact layer 8a and the current blocking layer 7.
A contact layer 8b made of As is grown (FIG. 12).
(E)). Finally, ohmic electrodes 9a and 9b are deposited on the upper surface of the contact layer 8a and the back surface of the substrate 1, and then cleaved to a predetermined length to obtain a complex index guided AlGaAs semiconductor laser shown in FIG. be able to.

[0006]

The conventional complex-index-guided AlGaAs semiconductor laser shown in FIG. 10 has various problems as described below. First, since the conventional AlGaAs-based semiconductor laser uses the buried layer as a current confinement layer and an absorption layer, light and current are lost due to absorption in the buried layer.
There is a problem that it is difficult to increase the output and lower the threshold of the device. Second, there is a problem that heat generated by absorption lowers the reliability and high output resistance of the device.
Thirdly, there is a problem in that internal stress is generated due to a difference in lattice constant between GaAs and AlGaAs, and the internal stress is easily damaged, resulting in poor high output resistance.

On the other hand, the conventional manufacturing method of the ridge waveguide type semiconductor laser also has a problem. First, when etching the upper cladding layer for forming the ridge, by adjusting the etching time, the residual thickness of the upper cladding layer left on both sides of the ridge on the active layer is reduced to a predetermined thickness. The etching was controlled so as to be as follows. However, it is actually extremely difficult to control the etching by adjusting the etching time, and since the residual thickness of the upper cladding layer varies, the laser characteristics of the product semiconductor laser easily vary from product to product and maintain uniformity. It was difficult. In other words,
In the conventional method, it is difficult to control the residual thickness of the upper cladding layer uniformly and with good reproducibility, so that it has been difficult to improve the product yield of the semiconductor laser. Furthermore,
In the conventional method, the buried layer made of GaAs is regrown using the SiO ₂ film or the like as a mask. However, the conventional method is used to make the buried layer of Al _z Ga _{1 -z} As (z ≧ 0.3). If an attempt is made to introduce a buried layer, a polycrystal is formed on the mask, and it has been very difficult to suppress it.

A conventional self-pulsation type semiconductor laser is
About 30mW required for writing on rewritable optical disks
And a threshold current value of about 60 mA, and an operating current value of about 8 at a light output of 5 mW.
0 mA was required, and there was a problem that power consumption was large, and further, reliability was not satisfactory.

A first object of the present invention is to provide a ridge waveguide type semiconductor laser capable of increasing the output and lowering the threshold of the device, and improving the reliability and the high output resistance.
A second object is to provide a manufacturing method which can manufacture a ridge waveguide type semiconductor laser having uniform laser characteristics, is self-aligned, and has good processing controllability. A third object is to provide a highly reliable self-pulsation type semiconductor laser having a large maximum light output, a low threshold current value and a low operating current value.

[0010]

The first object of the present invention is to realize a ridge waveguide type self-aligned semiconductor laser in which a cladding layer is processed into a ridge shape by using an optical guide layer as an etching stop layer. This is achieved by: The second purpose is to introduce a window structure, to form a ridge by using, for example, hydrofluoric acid-based selective etching, and to form AlGa.
This can be achieved by providing a step of entirely growing the As buried layer. The details will be described below.

In order to achieve the above object, a semiconductor laser according to the present invention is an AlGaAs ridge waveguide semiconductor laser comprising a first cladding layer, an active layer, and an active layer, each of which is composed of an AlGaAs layer sequentially laminated on a substrate. 2 clad layers and Al formed sequentially on the second clad layer and formed in a ridge shape.
An optical guide layer comprising a GaAs layer and a third cladding layer;
Furthermore, Al having a band gap larger than the oscillation wavelength
It is characterized in that a current blocking layer made of a GaAs layer is formed on both sides of the ridge. In the present invention, the material and structure of the active layer are not particularly limited.
Or a quantum well structure.

In a preferred embodiment of the present invention, the A1 content X of the A1 _x Ga _{1 -x} As layer constituting the light guide layer is X ≦ 0.3.
And the A1 content Y of the A1 _y Ga _{1 -y} As layer constituting the third cladding layer is Y> 0.45. In a further preferred embodiment of the present invention, A1 content Z of A1 _z Ga _1-z As layer constituting the current blocking layer is characterized by a Z <0.6.

In another more preferred embodiment of the present invention,
Each layer is formed on the compound semiconductor substrate so that the {100} crystal plane is the main surface and the [011] crystal axis direction is the resonator direction, and the ridge is formed in an inverted mesa shape near the resonator end face of the compound semiconductor substrate. It is characterized in that it is formed and extends in the [0-11] crystal axis direction. Or {100}
Each layer is formed on the compound semiconductor substrate such that a crystal plane is a main surface and a [0-11] crystal axis direction is a resonator direction,
The ridge is formed in an inverted mesa shape in the vicinity of the resonator end face of the compound semiconductor substrate and extends in the [011] crystal axis direction. In this specification, [0-11] is
It means that-is added above the first 1 in the crystal axis [011] represented by the Miller index.

In another preferred embodiment of the present invention,
{111} A crystal plane, or {111} A and {011}
[011] The light guide layer in the ridge extending in the crystal axis direction has a window formed so as to cover the end face of the active layer composed of the crystal plane and [0-11] in the vicinity of the window. ] It is characterized in that it extends in the crystal axis direction.

In another more preferred embodiment of the present invention,
The active layer is formed flat, and in the cladding layer above the active layer, the light guide layer is buried in stripes with the current blocking layers sandwiched on both sides, and the current blocking layer and the third cladding layer are the same. Formed in composition. In a preferred embodiment of the present invention, the third cladding layer and the current blocking layer are, as described above,
Y> 0.45, Z <0.6, that is, made of AlGaAs having an Al content in the range of 0.45 to 0.6, and the light guide layer has X ≦ 0.3, that is, 0 to 0, as described above. It is formed of AlGaAs having an Al content in the range of 0.3.

The method for manufacturing a semiconductor laser according to the present invention comprises the steps of:
A method for manufacturing a GaAs-based ridge waveguide type self-aligned semiconductor laser, comprising: a first cladding layer 2 made of AlGaAs of a first conductivity type; an active layer 3 made of intrinsic AlGaAs; The second cladding layer 4 made of AlGaAs is formed of an A1 _x Ga _{1 -x} As layer of the second conductivity type, and its A1 content X
Is a light guide layer 5 where X ≦ 0.3, and A1 of the second conductivity type
_y Ga _1-y As layer, whose A1 content Y is Y> 0.4
5, a step of sequentially laminating a third cladding layer 6 and a step of sequentially laminating an etching mask layer A made of GaAs of the second conductivity type; a step of etching the etching mask layer A in a stripe form; Mask layer A
The step of selectively etching the third cladding layer 6 into a ridge shape using the mask as an etching mask, and the step of selectively removing the light guide layer 5 excluding a portion existing in the ridge. Features.

The etchant used in the step of selectively etching the third cladding layer 6 and processing it into a ridge is not particularly limited as long as it is an etchant having such an action. For example, an aqueous hydrofluoric acid solution can be used. . The etchant used in the step of selectively removing the light guide layer 5 other than the portion inside the ridge is not particularly limited as long as it is an etchant having such an effect. For example, a mixed solution of ammonia water and hydrogen peroxide solution is used. Can be used.

In a preferred embodiment of the method of the present invention, a current blocking layer 7 of AlGaAs of the first conductivity type is formed so as to cover the entire surface of the ridge, and the current blocking layer 7 remains on both sides of the ridge and the ridge remains. Removing the current blocking layer 7 so that the top third cladding layer is exposed; and forming a contact layer 8 of GaAs of the second conductivity type on the ridge top and the entire surface of the current blocking layer 7. It is characterized by being in.

According to a third aspect of the present invention, there is provided a self-pulsation type semiconductor laser according to the present invention, wherein the thickness of the buried stripe-shaped light guide layer and the thickness of the light guide are reduced. By controlling the effective refractive index difference in the lateral direction of the active layer to a predetermined value by adjusting the distance between the layer and the active layer and the composition of the current blocking layer, the active layer was formed into a predetermined multiple quantum well structure. Features.

In order to cause self-sustained pulsation, the built-in active layer must have a refractive index difference in the lateral direction of 1 × 10 ^{−3 to} 3 × 10 ⁻³ . This is because the value of this order is almost equal to the decrease in the refractive index just due to the plasma effect. This refractive index difference is, as shown in FIG. 16, the distance (d2) between the light guide layer and the multiple quantum well active layer.
And the width (d3) of the light guide layer can be obtained.

In a preferred embodiment of the present invention, the distance between the light guide layer and the multiple quantum well active layer is 0.1 to 0.6 μm, and the width of the light guide layer is 10 to 60 nm.

A supersaturated absorber is indispensable for causing self-excited vibration. In the present invention, the active layer outside the stripe and into which no current is injected functions as a saturable absorber. In this case, absorption does not occur unless the thickness of the active layer exceeds a certain level. In the case of a multiple quantum well structure, empirically, it is desirable that the total thickness including the SCH guide layer is 60 nm or more. Therefore, in a further preferred embodiment of the present invention, the multiple quantum well active layer is formed of a quantum barrier layer and a quantum well layer which are alternately and repeatedly arranged, and the thickness of the multiple quantum well active layer includes the SCH guide layer. It is 60 nm or more. Here, the SCH guide layer refers to an optical guide layer having a Separated Confinement Hetrostructure.

In a further preferred aspect of the present invention, the width of the quantum barrier layer and the width of the quantum well layer are 5 to 10 nm and 5 to 8 nm, respectively. This is because the width of the quantum barrier layer and the quantum well layer in the range specified here is such that the quantum effect can be sufficiently exerted and at the same time, the thickness is easy to manufacture. In a further preferred aspect of the present invention, the multiple quantum well active layer has 2 to 4 wells. This is because, when the width of the quantum barrier layer and the width of the quantum well layer are limited, it is necessary to increase the number of wells in order to make the thickness of the active layer a predetermined thickness. Absorption can be enhanced. However, if the number of wells is increased unnecessarily, the threshold value increases as a result, and the number of wells is most preferably 2 to 4 in view of light loss. In a further preferred aspect of the present invention, the ridge formed at the center of the laser has an upper width and a lower width of 1 to 3 μm, respectively.
m and 4 to 6 μm.

Another preferred embodiment of the self-sustained pulsation type semiconductor laser according to the present invention is characterized in that the rear end face is coated with high reflection to increase the reflectivity and the front end face is suppressed to a low reflectivity.

[0025]

In the AlGaAs ridge waveguide self-aligned semiconductor laser described above, since the current blocking layer is made of AlGaAs having a band gap larger than the oscillation wavelength, loss of light and current due to absorption and generation of heat are avoided. As a result, a lower threshold value, higher output, and higher reliability of the device can be realized. In addition, since the optical guide layer is provided in the ridge, the current blocking layer and the buried layer are formed while maintaining the actual refractive index in the stripe higher than the actual refractive index outside the stripe.
The content can take any value in a wide range from a lower value to a higher value than the Al content of the cladding layer. Thereby, the allowable setting range of the actual refraction difference inside and outside the stripe can be widened.
Further, the cladding layer, the light guide layer, and the buried layer are all made of Al.
Since it is made of GaAs, generation of internal stress such as thermal stress due to a difference in lattice constant between layers can be suppressed.

Further, Al _x Ga constituting the light guide layer
By the _1-X As layer Al content x is x ≦ 0.3 in and Al _y Ga _1-y YAs layer of Al content Y constituting the third cladding layer has a Y> 0.45, When the ridge is formed by etching using a hydrofluoric acid-based etchant, the light guide layer functions as an etching stop layer because the etching rate of the light guide layer is much lower than that of the third clad layer thereon. Thereby, highly selective etching can be performed.

By the way, Al _{Z is applied} so as to cover the entire ridge.
When forming a current blocking layer composed of a Ga _{1 -Z} As layer, Al
When _Z Ga _1-Z As layer of Al content Z becomes too large, the region Al _Z Ga _1-Z As layer does not grow higher the rate occurring on the ridge or on the side wall, the surface condition becomes poor risk Occurs. For this, the Al content Z of Al _Z Ga _1-Z As layer constituting the current blocking layer Z <
By setting the ratio in the range of 0.6, deterioration of the surface state can be suppressed. In addition, a high output and high reliability of the device can be ensured by a configuration in which the so-called window structure (see FIG. 13) in which the vicinity of the end face is formed of a cladding layer material and the active layer is not exposed is introduced.

The higher the Al content of the AlGaAs layer, the more
It is not appropriate to use a resist as an etching mask for a hydrofluoric acid-based or hydrochloric acid-based selective etchant that increases the etching rate. Therefore,
As an etching mask for forming a ridge, a GaAs layer etched in a stripe shape is used, and an optical guide layer is formed of Al _x Ga ₁ -x having an Al content X of X ≦ 0.3.
In the As layer and the third cladding layer, the Al content Y is Y>
It is composed of an Al _y Ga _1-y As layer of 0.45.
As a result, the light guide layer remains almost without being etched by the hydrofluoric acid-based or hydrochloric acid-based selective etchant, while the third cladding layer is etched to form a ridge. Therefore, the third clad layer can be left in a desired ridge shape in a self-aligned manner with good controllability, and the manufacturing yield of the semiconductor laser can be improved. Further, in the next step, a selective etchant whose etching rate becomes faster as the Al content is smaller, for example, a mixed solution of ammonia water and hydrogen peroxide is used to selectively remove the light guide layer other than the portion inside the ridge. And the light guide layer can be left only in the ridge, so that the refractive index difference can be realized in a self-aligned manner with good controllability, and unnecessary protrusion of the GaAs etching mask can be removed.

Further, by growing a current blocking layer over the entire surface of the second and third cladding layers, Al _Z Ga _{1 -Z} As
Even when the Al content Z of the current blocking layer composed of layers is Z ≧ 0.3, polycrystals are formed on the mask as in the conventional method of selectively growing the buried layer using a SiO ₂ film or the like as a mask. This can be avoided. In addition, by forming the contact layer made of GaAs on the top of the third cladding layer and on the entire surface of the current blocking layer, the contact resistance can be reduced and heat generation can be suppressed as compared with the conventional striped contact layer. Furthermore, when a conventional dielectric film such as a SiO ₂ film is used as a mask, the semiconductor layer immediately below the dielectric film undergoes thermal denaturation, and the regrowth interface of the contact layer has a problem of increasing the resistance. By removing the semiconductor layer at the top of the ridge and forming a GaAs contact layer on the entire surface, it is possible to avoid an increase in resistance at the regrowth interface of the contact layer.

By changing the thickness of the stripe-shaped light guide layer, the distance between the active layer and the light guide layer, and the composition of the current blocking layer, the effective refractive index difference in the lateral direction of the active layer can be changed to a desired value. Can be controlled. In addition, by introducing a multiple quantum well structure in the active layer, selecting the optimal number of wells, and making the rear end face high reflectivity and the front end face low reflectivity, kink generation output is increased and self-excited oscillation is achieved. Can be increased. Furthermore, the threshold current,
The operating current can be reduced, and the lifetime can be increased and the reliability can be improved in combination with the introduction of the multiple quantum well structure.

Hereinafter, the present invention will be described in more detail based on embodiments with reference to the accompanying drawings. The following description of the epitaxial growth method and the etching method, etc., or the description of the components related to the etchant, the GaAs layer and the ALGaAs layer, and the numerical values such as the composition and the layer thickness are merely examples for explanation and limit the present invention. It does not do. Example 1 FIG. 3 (j) is a cross-sectional view of Example 1 of an AlGaAs ridge waveguide semiconductor laser according to the present invention, and FIGS.
It is sectional drawing which shows each process of Example 1 which manufactures the semiconductor laser shown by (j) by the method of this invention.

Referring to FIGS. 1 to 3, a first embodiment of a semiconductor laser according to the present invention and a first embodiment of a method of the present invention will be described. First, a compound semiconductor substrate 1 made of n-type GaAs
2 μm of n-type A1 _u Ga _1-u As (u = 0.5) on a {100} crystal plane, for example, a main surface of a (100) crystal plane.
The first cladding layer 2 having a thickness of m is epitaxially grown. Epitaxial growth is performed by a liquid or gas phase crystal growth method, for example, an MOCVD method (metal organic chemical vapor deposition method). As a crystal material, a material such as a methyl-based material, for example, trimethylaluminum, trimethylgallium, or arsine is used. .

Subsequently, the intrinsic Al _V Ga _{1 -V} As (v =
0.13), the active layer 3 having a thickness of 0.05 μm
Type Al _w Ga _1-w As the (w = 0.5) second cladding layer 4 having a thickness of 0.3μm made of, p-type Al _X Ga
_A 0.09 μm-thick optical guide layer 5 made of _1-X As (X = 0.3) is applied to a p-type Al _y Ga _1-y As (y = 0.
5) a third cladding layer 6 having a thickness of 2.5 μm
Mask layer A having a thickness of 0.5 μm, which is made of GaAs, of a thickness sufficiently larger than the thickness of the light guide layer 5.
Are sequentially epitaxially grown. Next, [01] is formed on the etching mask layer A by photolithography.
A resist film B having a width of 6 μm extending in the [-1] direction is formed (see FIG. 1A).

Next, using phosphoric acid: hydrogen peroxide solution: water = 3: 1: 50 as an etching solution, the etching mask layer A is etched using the resist mask B as an etching mask until the etching reaches the third cladding layer 6. Then, it is processed into a stripe shape (see FIG. 1B).

Subsequently, the third cladding is performed using a 30% aqueous solution of hydrofluoric acid as an etching solution until the light guide layer 5 is exposed and the ridge width W under the etching mask layer A is about 4 μm. The layer 6 is etched to form a normal mesa ridge 11. (See FIG. 1 (c)). At this time, the etchant enters irregularly between the etching mask layer A and the resist film B, but the etching mask layer A acts as an etching mask because GaAs constituting the etching mask layer A is insoluble in the hydrofluoric acid aqueous solution. I do. The light guide layer 5 has an etching rate of about 1/50 of that of the third cladding layer 6, and thus acts as an etching stop layer.

Immediately before the etching reaches the light guide layer 5, interference fringes are observed due to the action of the third cladding layer 6 remaining thin on the light guide layer surface. Therefore,
If the etching is stopped when the interference fringes have just disappeared,
The ridge width can be controlled to about 4 μm with good reproducibility. In this embodiment, the ridge width is set to about 4 μm. However, the width of the ridge is changed to an arbitrary size by changing the width of the etching mask layer A by adjusting the width of the resist mask B or by changing the thickness of the cladding layer 6. Can be

Next, ammonia water: hydrogen peroxide solution = 1:
Using the etching liquid 30 as an etchant, the light guide layer 5 other than the portion inside the ridge, the etching mask layer A and the resist mask layer B protruding from the upper part of the ridge are removed by etching, and the third cladding layer 6 is formed into a forward mesa type The ridge 11 is formed (see FIG. 2D). Each of the etching mask layer A and the light guide layer 5 is about 1 μm by the above-mentioned etching solution.
The third cladding layer 6 and the second cladding layer 4 are hardly etched by the same etching solution, while being etched at an etching rate of about 0.15 μm / min. Therefore, while keeping the third cladding layer 6 formed by hydrofluoric acid-based etching in a ridge shape and without etching the second cladding layer 4, the light guide layer 5 and the etching mask layer A other than the portion inside the ridge are etched. The extra overhang can be removed. As described above, the third cladding layer 6 can be formed on the forward mesa ridge 11 with good controllability and reproducibility, that is, in a self-aligned manner, by the steps shown in FIGS. 1A to 2D. .

Next, a 2 μm thick current blocking layer 7 of n-type A1 _z Ga _{1 -z} As (z = 0.5) is epitaxially grown on the entire surface by MOCVD (see FIG. 2E).
Next, a resist layer C is applied to the entire surface of the current blocking layer 7 so that the flat portion has a thickness of at least about 0.8 μm. Further, RIE using oxygen gas is performed for several tens of seconds to etch the resist layer C, so that the surface of the current blocking layer 7 is exposed only at the top of the ridge having the smallest resist thickness (FIG. 1F).
reference).

Subsequently, phosphoric acid: hydrogen peroxide solution: water = 3:
The current blocking layer 7 exposed from the top of the ridge is etched using the mixed solution having a component composition of 1:50 as an etching solution and the resist layer C as a resist mask to expose the lower current blocking layer 7 and the cladding layer 6 on the surface. And flatten the surface. As a result, a current blocking layer 7 having no light absorption loss is formed on both sides of the ridge formed in the previous step.

Next, the resist layer C is removed by etching (see FIG. 3H). Next, a contact layer 8 of p-type GaAs having a thickness of 0.5 μm to 1 μm is epitaxially grown on the entire top surface of the current blocking layer 7 and the cladding layer 6 by MOCVD. (See FIG. 3 (i))
The contact resistance can be kept low without heat denaturation of the semiconductor layer, thereby suppressing heat generation and thermal resistance.

Then, electrodes 9a and 9b are formed on the upper surface of the contact layer 8 and the rear surface of the compound semiconductor substrate 1 in an ohmic manner, and then cleaved to a predetermined length. Now, FIG.
The semiconductor laser 10 according to the present invention shown in (j) can be obtained. In the present embodiment, AlGa constituting the current blocking layer 7 is
The band gap of the As layer is 2.050 eV, which is larger than the oscillation wavelength of 1.494 eV. In the above embodiment, Al
Although the case of the GaAs active layer has been described, the active layer may be InGaAs or the like, or may have a quantum well structure. In the above embodiment, the thickness of the etching mask layer A is 0.5 μm. However, if the thickness is about 0.01 μm or more, the layer functions as an etching mask. It has no meaning.

Embodiment 2 FIG. 8 is a perspective view of Embodiment 2 of an AlGaAs ridge waveguide semiconductor laser according to the present invention, and FIGS. 4 to 8 show Embodiment 2 of the semiconductor laser shown in FIG. It is a perspective view which shows each process of Example Method 2 manufactured by the method. FIG. 9 is an enlarged view of the laminated structure in the steps of FIGS. 6 (f), 7 (g) and 7 (h).

First, a resist film D is formed on the main surface of the (100) crystal plane of the {100} crystal plane of the compound semiconductor substrate 1 made of n-type GaAs, and is patterned by photolithography. [011] A resist pattern is formed in which a plurality of grooves having a groove width of about 1 µm extending in the [01-1] direction are formed at a period of 500 µm (see FIG. 4A). Then
Using a mixture of lactic acid and hydrogen peroxide as an etchant, the substrate 1 is etched using the resist film D as an etching mask to form an inverted mesa-shaped ridge 1a and a forward mesa-shaped groove 1b (FIG. 4 ( b)). The step of the ridge 1a or the groove depth H of the groove 1b is set to H> 5 μm.
Has an opening width W of 1 μm to 5 μm. In this embodiment,
The step H is 26 μm, and the opening width W is 4 μm.

Next, after the resist film D is removed by etching, vapor-phase growth is performed by MOCVD using a methyl-based material, for example, a material such as trimethylaluminum, trimethylgallium, arsine, etc., so that gr _[111] ≧ 3 ^{− 0.5} gr _[100] + (2/3) ^0.5 gr _[011] (1) n-type A1 _u Ga _{1-u under} crystal growth conditions satisfying the condition of equation (1)
A first cladding layer 2 of As (u = 0.5) having a thickness of 2 μm is epitaxially grown. Here, gr _[111] is the growth rate of the {111} crystal plane, gr _[100] is the growth rate of the {100} crystal plane, and gr _[011] is the growth rate of the {011} crystal plane. Subsequently, similarly, the intrinsic A1 _v Ga _1-v As (v
= 0.13) with an active layer 3 having a thickness of 0.05 μm,
Thickness 0.3 made of p-type A1 _w Ga _1-w As (w = 0.5)
The second cladding layer 4 of μm is formed by p-type A1 _X Ga _{1 -X} As (X =
0.3) of a light guide layer 5 having a thickness of 0.09 μm,
Thickness 2.5 made of p-type A1 _y Ga _1-y As (y = 0.5)
A third cladding layer 6 of μm and a 0.5 μm-thick etching mask layer A of p-type GaAs are sequentially epitaxially grown (see FIG. 5C, (II) is an enlarged view of the laminated portion of (I)). Is).

A resist mask B is formed on the above-described etching mask layer A (see FIG. 5D). Next, the resist mask B is processed by a photolithography technique to form a resist mask B ′ having a resist pattern including a stripe having a width of 6 μm extending in the [01-1] direction and a stripe having a width of 14 μm covering a groove extending in the [011] direction. Is formed (see FIG. 6E). The resist used here is selected to be highly viscous, for example, MP1400-37, so as to prevent the stripes from becoming fine near the ridge that forms the resonator end face.

Next, using the resist mask B as an etching mask, phosphoric acid: hydrogen peroxide solution: water =
Using 3: 1: 50, the etching mask layer A is etched until it reaches the third cladding layer 6, and processed into a stripe shape (see FIG. 9I). Subsequently, using a 30% aqueous hydrofluoric acid solution as an etching solution, the third cladding layer 6 is exposed until the light guide layer 5 is exposed and the ridge width W under the etching mask layer A is about 4 μm. Is etched to form a forward mesa type ridge 11 (FIG. 9).
(II)). At this time, the etching liquid enters irregularly between the etching mask layer A and the resist mask B,
The etching mask layer A functions as an etching mask because GaAs constituting the layer is insoluble in a hydrofluoric acid aqueous solution. The light guide layer 5 has an etching rate of about 1/50 of that of the third cladding layer 6, and thus acts as an etching stop layer.

Immediately before the etching progresses to the light guide layer 5, interference fringes are observed due to the action of the third cladding layer 6 remaining thin on the surface of the light guide layer. Therefore,
If the etching is stopped when the interference fringes have just disappeared,
The ridge width can be controlled to about 4 μm with good reproducibility. In this embodiment, the ridge width is set to about 4 μm. However, the width of the resist mask B is adjusted to change the width of the etching mask layer A processed into a stripe shape, or
By changing the thickness of the cladding layer 6, the ridge width W can be set to an arbitrary size.

Next, ammonia water: hydrogen peroxide solution = 1:
Using 30 as an etchant, the light guide layer 5 other than the portion inside the ridge, the etching mask layer A and the resist mask layer B projecting from the upper part of the ridge are removed by etching (see FIG. 9 (III)). The etching mask layer A and the optical guide layer 5 are etched at the etching rates of about 1 μm / min and about 0.15 μm / min, respectively, by the above-mentioned etching solution, while the third cladding layer 6 is etched.
The second cladding layer 4 is hardly etched by the same etchant. Therefore, while maintaining the third clad layer 6 formed by hydrofluoric acid-based etching in a ridge shape, the second clad layer 4 is not etched, and the light guide layer 5 and the etching mask layer A other than the portion inside the ridge are etched. Remove excess overhang. As described above,
The steps shown in FIGS. 4A to 6F allow the third cladding layer 6 to be formed in a ridge shape with good controllability and reproducibility, that is, in a self-aligned manner (see FIG. 6F).

Next, n-type A1 _z Ga _{1 -z} As (for example, when z = 0.
A 5 μm thick current blocking layer 7 composed of 5) is epitaxially grown on the entire surface of the second cladding layer 4 and the third cladding layer 6 by MOCVD (FIGS. 7 (g) and 9 (I)).
V)).

Next, a resist, for example, MP1400-37, is applied on the entire surface of the current blocking layer 7, and then the resist film E is left only in the groove by exposure and development. Further, a resist is applied to the entire surface so as to have a thickness of about 0.8 μm at the flat portion, thereby forming a resist layer C (see FIG. 9 (V)). Thereafter, RIE using oxygen gas is performed for several tens of seconds to etch the resist layer C, exposing the surface of the current blocking layer 7 only at the top of the ridge having the smallest resist thickness. Subsequently, a mixture of phosphoric acid and hydrogen peroxide having a composition of phosphoric acid: hydrogen peroxide: water = 3: 1: 50 is used as an etchant, and the current blocking layer 7 is etched from the exposed top of the ridge. The third cladding layer 6 is exposed on the etched surface and the surface is flattened. As a result, current blocking layers 7 having no light absorption loss are formed on both sides of the ridge formed in the previous step. Next, the resist layer C is removed by etching (FIG. 7).
(H) and FIG. 9 (VI)).

Subsequently, p-type Ga is applied to the entire surface by MOCVD.
A 0.5 μm to 1 μm thick contact layer 8 made of As is epitaxially grown (see FIGS. 8 and 9 (VII)). Thereby, the contact resistance can be suppressed low without heat denaturation of the semiconductor layer, thereby suppressing heat generation and thermal resistance. The cross section taken along the line AA 'in FIG.
(I) is provided with the same cross section,
3 is provided. Note that (I) to (VI) in FIG.
The cross section shown in I) is a cross section parallel to the arrow BB 'at a position away from the arrow BB' in FIG. 8, for example, a cross section taken along the line CC '. Also, (I) to (VII) of FIG.
In the cross section shown in FIG. 13 and the cross section in FIG.
The active layer 3 and the light guide layer 5 are formed in the clad layers 2, 4 and 6, and have a so-called window structure in which the light guide layer 5 is not exposed. By introducing such a window structure, high output and high reliability of the element can be guaranteed. Note that such a window structure is formed by applying MOCVD to the substrate 1 provided with a groove of a specific shape and epitaxially growing each layer.

Then, the contact layer 8 except for the vicinity of the ridge is formed.
(Not shown) is formed on the entire surface of the substrate and the back surface of the compound semiconductor substrate 1 in an ohmic manner.
An As-based ridge-guided self-aligned semiconductor laser can be obtained. In this embodiment, the current blocking layer 7 is formed.
The band gap of the AlGaAs layer is 2.050 eV, which is larger than the oscillation wavelength of 1.494 eV.

Embodiment 3 FIG. 14 is a cross-sectional view of Embodiment 3 of the semiconductor laser device according to the present invention, and FIG. 15 is a diagram showing a conduction band energy structure of a multiple quantum well structure constituting an active layer of the semiconductor laser device shown in FIG. It is a figure showing an outline. The fabrication of the semiconductor laser device 20 will be described. First, a liquid or gas phase crystal growth method, for example, M, is formed on a {100} crystal plane of a compound semiconductor substrate 1 made of n-type GaAs, for example, on a main surface of a (100) crystal plane.
By OCVD method, for example, methyl-based material or trimethyl aluminum, trimethyl gallium, and subjected to gas-phase growth of a material such as arsine, n-type Al _u Ga _1-u As (e.g. u
= 0.5) with a thickness of, for example, 3 μm.

Subsequently, an active layer 3 made of intrinsic AlGaAs
(Undoped Al _V Ga _1-V AsSCH guide layer (for example, v =
0.3) 10 nm thick, undoped Al _W Ga _1-W As (for example, w = 0.3) quantum barrier layer 5 nm thick, 4-layer repeating undoped Al _X Ga _1-X As (for example, x = 0.09) A quantum well layer (thickness: 8 nm) is formed. Furthermore, p-type Al _Y Ga
_A second cladding layer 4 made of _1-Y As (for example, y = 0.5) is formed into a p-type AlzGal-zA having a thickness of, for example, 0.4 μm.
s (e.g., z = 0.3) light guide layer 5 having a thickness of
For example, the thickness of the third cladding layer 6 made of p-type AlαGa ₁ -αAs (for example, α = 0.5) is set to 0.04 μm, for example, and the thickness of the third mask layer 6 made of p-type GaAs is set to 2.5 μm. For example, epitaxial growth is performed sequentially with a thickness of 0.5 μm.

Next, a resist mask having a width of 6 μm extending in the [01-1] direction is formed on the etching mask layer by photolithography. Next, etching is performed using a phosphoric acid-based aqueous solution as an etchant until the third clad layer 6 is reached, and the etching mask layer is processed into a stripe shape. Subsequently, the third clad layer 6 is etched using a 30% aqueous solution of hydrofluoric acid as an etchant.
The third cladding layer 6 is etched until the etching reaches the light guide layer 5 and the width under the ridge becomes about 4 μm.
Next, using the aqueous ammonia solution as an etchant, the light guide layer 5 other than the lower part of the ridge and the etching mask layer protruding from the upper part of the ridge are etched. Through the above-described steps, a ridge can be formed with good controllability and reproducibility.

Next, n-type AlβGa ₁ -βAs (for example, β = 0.
The current blocking layer 7 of 5) is epitaxially grown to a thickness of 2 μm over the entire surface by, for example, MOCVD. After applying a resist on the entire surface so that the thickness at the flat portion becomes about 0.8 μm, RIE using an oxygen gas is performed for several tens of seconds, so that only the top of the ridge having the smallest thickness of the resist is subjected to an etching mask. Exposed from the surface of the layer. The etching mask layer is etched using a phosphoric acid-based aqueous solution as an etching solution from the exposed top of the ridge to expose the third cladding layer 6 to the etching surface and flatten the surface. Thus, a current blocking layer having no light absorption loss is formed on both sides of the ridge formed in the previous step. After removing the resist, a contact layer 8 of p-type GaAs having a thickness of 0.5 to 1 μm is epitaxially grown on the entire surface by, for example, MOCVD. Thereby, the contact resistance can be suppressed low without heat denaturation of the semiconductor layer, thereby suppressing heat generation and thermal resistance.

Then, after the electrodes are formed on the upper surface of the contact layer 8 and the back surface of the compound semiconductor substrate 1 in an ohmic manner, the electrodes are cleaved with a predetermined length, and the semiconductor laser device 2 is cut.
Set to 0. Further, in the above embodiment, the thickness of the etching mask layer is set to 0.5 μm. However, if the thickness is about 0.01 μm or more, it serves as an etching mask. There is no.

Test Example Using the semiconductor laser device 20 described above, an evaluation test of its performance was performed. In the sample semiconductor laser device, the distance d2 between the optical guide layer and the multiple quantum well active layer was 0.4 μm, and SC
The total thickness of the active layer including H is 67 nm, the width of the quantum barrier layer is 5 nm, the width of the quantum well layer is 8 nm, and the number of wells is 4
And the width d3 of the light guide layer is set to 2 of 40 nm and 50 nm.
As a seed, a high reflection coating was applied to the rear end face so as to have a reflectance of 94%, and the reflectance of the front end face was suppressed to as low as 10%. The obtained semiconductor laser device was used as an example sample. d3 =
For the 40 nm and 50 nm example samples, the built-in refractive index differences were 1.5 × 10 ⁻³ and 2.1 × 1 respectively.
It became 0 ^-3 . For comparison, a comparative example in which an asymmetric coat having a rear end face of 94% and a front end face of 30% was also prepared.

FIG. 17A shows the oscillation spectrum of the example sample at an output of 5 mW, and FIG. 17B shows the oscillation spectrum of the comparative example at the same output. FIG. 17 is a graph in which the horizontal axis indicates the wavelength of the laser beam and the vertical axis indicates the ratio to the maximum output. The same applies to FIG. 18 described later. The sample of the example in which the reflectance at the front end face was kept low produced strong self-pulsation, and the maximum light output causing self-pulsation was about 10 mW and the kink level was about 70 mW. The COD level was about 100 mW. On the other hand, in the comparative sample, the maximum light output causing self-pulsation was about 5 mW, the kink level was about 50 mW,
The COD level was about 80 mW.

The oscillation threshold current of the sample is as low as about 25 mA. In addition, the operating current at a light output of 5 mW causing self-excited oscillation is as low as about 30 mA. The RIN (relative noise intensity) at a light output of 5 mW where self-pulsation occurs is -130 dB / H at a return light quantity of 1% under the conditions of a center frequency of 700 kHz, a bandwidth of 30 kHz, and an optical path length of 30 mm.
A very good value of not more than z was obtained. The value of RIN required for reproducing digital recordings such as CDs and MDs satisfies the condition of RIN <-120 dB / Hz, so that it can sufficiently withstand practical use. In the life test of the device, the device was operated stably at an ambient temperature of 50 ° C. and a constant output of 30 mW for 500 hours or more.

For reference, an asymmetric coat of 94% at the rear end face and 30% at the front end face was applied, and the width d3 of the light guide layer was 3
Two samples, 40 nm and 50 nm, were made and tested. FIG. 18A shows d3 = 40 nm at an optical output of 3 mW.
18 (b) shows the oscillation spectrum of the sample at d3 = 50 nm at the same output.
The sample of d3 = 40 nm caused self-pulsation at 3 mW, but the sample of d3 = 50 nm did not cause self-pulsation.

[0062]

According to the present invention, since the current blocking layer is made of AlGaAs having a band gap larger than the oscillation wavelength, loss of light and current and heat generation due to absorption can be prevented. Output and improvement of reliability can be realized. Further, an optical guide layer is disposed in the ridge, and the clad layer, the optical guide layer and the buried layer are formed of Al.
By using a GaAs layer, the generation of internal stress such as thermal stress due to a difference in lattice constant is suppressed, and an element having high output resistance and a long life can be realized.

A GaAs layer etched in a stripe shape is used as an etching mask for the ridge shape, and selective etching is performed, so that the cladding layer having a predetermined thickness can be formed with good controllability without etching the optical guide layer. In other words, it can be left in a self-aligned manner. Therefore, by using the method of the present invention, the laser characteristics of the device can be made uniform, and the production yield of the semiconductor laser can be improved. Also, by performing selective etching in the next step, it is possible to selectively remove the light guide layer other than the portion inside the ridge and leave the light guide layer only in the ridge in a self-aligned manner. The laser characteristics of the element can be made uniform.

Further, by removing the semiconductor layer at the top of the ridge serving as a current path and forming a GaAs contact layer on the entire surface, a semiconductor laser can be realized in which the resistance at the regrowth interface of the contact layer is avoided.

The effective refractive index in the lateral direction of the active layer can be changed to a desired value by changing the thickness of the striped light guide layer, the distance between the light guide layer and the active layer, and the composition of the current blocking layer. Value can be controlled. Also,
By selecting the optimal number of wells by introducing a multiple quantum well structure into the active layer, and by reducing the reflectivity of the front end face by making the rear end face highly reflective coating, the kink generation output and the maximum optical output that can obtain self-excited oscillation Can be higher. Further, the threshold current and the operating current can be reduced by adopting the real index guide structure. This, combined with the introduction of the multiple quantum well structure, contributes to prolonging the lifetime and increasing the reliability. As described above, according to the present invention,
A built-in refractive index difference can be realized with good controllability,
The high-output low-noise characteristics of the semiconductor laser can be improved as compared with the conventional technology, and the operating current and the threshold current can be reduced, and the life can be prolonged.

[Brief description of the drawings]

FIGS. 1A to 1C are cross-sectional views showing steps of a method 1 according to an embodiment.

2 (d) to 2 (f) are cross-sectional views showing respective steps of the method 1 of the embodiment following FIG.

FIGS. 3 (g) to 3 (j) are cross-sectional views showing each step of the method 1 of the embodiment following FIG. 2;

FIGS. 4 (a) and 4 (b) are perspective views showing steps of a method 2 of an embodiment.

5 (c) to 5 (d) are perspective views showing each step of the method 2 of the embodiment following FIG. 4. FIG.

6 (e) to 6 (f) are perspective views showing each step of the method 2 of the embodiment following FIG.

7 (g) to 7 (h) are perspective views showing respective steps of Example Method 2 following FIG. 6;

FIG. 8 is a perspective view showing a step of the method 2 of the embodiment following FIG. 7;

FIG. 9 is an enlarged cross-sectional view showing the configuration of the laminate in the steps shown in FIGS. 7 and 8.

FIG. 10 is a cross-sectional view schematically showing a conventional complex-index guided AlGaAs semiconductor laser.

FIGS. 11A and 11B are cross-sectional views showing steps of a conventional method for manufacturing a semiconductor laser.

12 (c) to 12 (e) are cross-sectional views showing respective steps of a conventional method for manufacturing a semiconductor laser following FIG.

FIG. 13 is a cross-sectional view showing the configuration of each layer taken along the line BB 'in FIG.

FIG. 14 is a sectional view of a semiconductor laser device according to a third embodiment.

15 is a diagram schematically showing a conduction band energy structure of a multiple quantum well structure constituting an active layer of the semiconductor laser device shown in FIG.

FIG. 16 is a graph showing the relationship between the distance (d2) between the light guide layer and the multiple quantum well active layer and the refractive index difference, using the width (d3) of the light guide layer as a parameter.

17 (a) and 17 (b) show respective spectral curves of an example sample and a comparative example sample.

FIGS. 18 (a) and (b) show samples (d3 = 40).
(nm and 50 nm).

[Explanation of symbols]

 Reference Signs List 1 n-type GaAs substrate 2 n-type AlGaAs cladding layer 3 active layer 4 p-type AlGaAs cladding layer 5 p-type AlGaAs optical guide layer 6 p-type AlGaAs cladding layer 7 n-type AlGaAs current blocking layer 8 a p-type GaAs contact layer 8 b p-type GaAs Contact layer 9a Ohmic electrode 9b Ohmic electrode 20 Semiconductor laser of Example 3 Ap type GaAs etching mask layer B, C, D, E Resist film

──────────────────────────────────────────────────続 き Continuation of the front page (72) Kazuhiko Nemoto, Inventor 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Yoshinobu Higuchi 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo (56) References JP-A-1-184973 (JP, A) JP-A-5-235467 (JP, A) JP-A-4-349679 (JP, A) JP-A-6-21579 (JP JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A first cladding layer made of an AlGaAs layer, an active layer, and a compound semiconductor substrate having a {100} crystal plane as a main surface.
A second clad layer is sequentially laminated, and a ridge extending on the [011] crystal axis direction is formed on the second clad layer, where the optical guide layer and the third clad layer are laminated. A groove or a step extending in the [0-11] crystal axis direction is formed in an inverted mesa shape in the compound semiconductor substrate in the vicinity of the resonator end face, and the end face of the active layer in the resonator length direction is {111}. A window is formed by a {A} crystal plane or a {111} A crystal plane and a {011} crystal plane, and an end face of the active layer is covered by the third cladding layer. A semiconductor laser comprising a current blocking layer formed of an AlGaAs layer having a band gap larger than an oscillation wavelength. 2. A method according to claim 1, wherein a first conductive type of A is formed on the compound semiconductor substrate.
a first cladding layer made of lGaAs and intrinsic AlGaAs
s, InGaAs, InAlGaAs or an active layer having a quantum well made of at least one of them, a second cladding layer made of AlGaAs of the second conductivity type, and an Al content X of X ≦ 0.3 A of the second conductivity type
a light guide layer made of l _x Ga _1-x As and an Al content Y
Is formed by sequentially laminating a third cladding layer made of Al _y Ga _1-y As of the second conductivity type with Y> 0.45, and further made of GaAs of the second conductivity type thicker than the light guide layer on this. Laminating the etching mask layer A, etching the etching mask layer A in a stripe shape, using the stripe-shaped etching mask layer A as an etching mask, and containing Al in the light guide layer and the third cladding layer. Using the difference in etching properties due to the difference in rate,
Selectively etching the third clad layer by etching using the light guide layer as an etching stop layer to form a ridge; and providing the light guide layer with Al in the light guide layer and the third clad layer. A step of selectively removing other portions except for a portion existing in the ridge by using a difference in etching property due to a difference in rate; and forming an AlGaAs having a band gap larger than an oscillation wavelength so as to cover the entire surface of the ridge. Forming a current blocking layer, and leaving the current blocking layer on both sides of the ridge and exposing and removing the top of the ridge.