JP3234323B2 - Semiconductor laser and method of manufacturing the same - 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 used for optical information processing and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, semiconductor lasers grown by using a metal organic chemical vapor deposition (MOCVD) method, which is excellent in mass productivity and yield of devices, have become widespread. FIG. 8 shows an optical pickup for a compact disk, for example.
It is a typical sectional view showing the structure of the conventional semiconductor laser produced using the MOCVD method. In the figure, reference numeral 81 denotes a substrate made of n-type GaAs. On the substrate 81, a first cladding layer 82 made of AlGaAs and an active layer 83 made of undoped AlGaAs are stacked. A second stripe formed in the <01 bar 1> direction
The ridge portion 84 of the cladding layer is buried by a current blocking layer 89 made of GaAs. A cap layer 88 is formed on the ridge portion 84, and a contact layer 90 is stacked on the cap layer 88 and the current block layer 89.

[0003]

A semiconductor laser having such a structure is often used for a read-only optical pickup, and has an optical output of about 5 mW. However, a semiconductor laser used for an optical pickup capable of writing on a magneto-optical disk requires an optical output of about 30 mW. When a particularly high output is required as in this writable semiconductor laser, as shown in FIG. 8, when the ridge portion 84 has a so-called curled shape in which the area is increased toward the bottom surface,
There is a problem that a current flows through the bottom side portion 84a having an increased area, the reactive current increases, the operating current increases, and a high output cannot be obtained. In addition, since the light emission spot becomes large, the light absorption in the current block layer adjacent to the bottom side portion 84a becomes large, and there is a problem that the external quantum differential efficiency is deteriorated.

In order to solve these problems, it is desirable to form the ridge portion in an inverted mesa shape, that is, a shape whose area is increased in the laminating direction, or a shape in which the side surface of the ridge portion is perpendicular to the substrate. The smaller the bottom area of the ridge, that is, the area on the active layer side, and the closer the side of the ridge is perpendicular to the substrate, the more the reactive current can be reduced and the smaller the operating current is, and the light absorption on the side of the ridge becomes less. External quantum differential efficiency is improved as the size becomes smaller.

When a stripe-shaped ridge portion is formed in the <011> crystal orientation, the upper portion of the ridge portion 94 has an inverted mesa shape as shown in a schematic sectional view showing the shape of the ridge portion in FIG. Although it can be formed, in the wet etching process at the time of formation, the conditions such as the composition of the etchant and the etching temperature must be carefully adjusted, and the lower part of the ridge portion 94 is oriented in the above-described crystal orientation <01 bar 1> direction. There is a problem that a mesa shape similar to the case of forming is formed. In particular, in the case of an Al _x Ga _{1 -x} As-based laser, when the mixed crystal ratio (x) of the ridge formed by the second cladding layer is large, the (111) A surface on the side of the ridge is etched. The ridge portion 84 shown in FIG.
There is a problem that the shape tends to increase in the depth direction as described above.

In addition, reactive ion etching (RIE)
By performing B), a ridge portion having a side surface perpendicular to the substrate can be formed, but there is a problem that the etched substrate surface is damaged and deteriorated.

The present invention has been made in view of such circumstances, and a ridge portion having a small bottom area can be easily formed on an active layer side by etching, a reactive current is reduced, and an operating current is reduced. It is another object of the present invention to provide a semiconductor laser in which the light emission spot is small, the light absorption in the current block layer is small, and the external quantum differential efficiency is improved, and a method for manufacturing the same.

[0008]

According to the present invention, there is provided a semiconductor laser in which a ridge is formed by etching on an opposite side of a substrate with respect to an active layer, and a periphery thereof is buried with a current blocking layer. Is etching
And a ridge shape adjusting layer having a composition such that the etching rate decreases stepwise or continuously from the active layer side in the laminating direction.

A method for manufacturing a semiconductor laser according to the present invention comprises:
In a method for manufacturing a semiconductor laser in which a ridge portion is formed by etching on a side opposite to a substrate with respect to an active layer and a periphery thereof is buried with a current blocking layer, a composition for stopping etching is provided on the active layer formed on the substrate. Laminating an etching stop layer, a step of laminating a ridge shape adjusting layer having a composition in which the etching rate is gradually or continuously reduced in the laminating direction from the active layer side on the etching stop layer, and a step of adjusting the ridge shape. Forming a residual portion by etching the layer to the surface of the etching stop layer, wherein the ridge portion is formed by the residual portion .

[0010]

According to the semiconductor laser and the method of manufacturing the same of the present invention,
An etching stop layer is formed on the active layer, and a ridge shape adjusting layer having a composition that reduces the etching rate in the laminating direction is stacked thereon. Therefore, when forming a ridge portion by etching, a ridge having a high etching rate is formed. The degree of side etching increases toward the bottom side of the shape adjustment layer, the bottom area of the ridge shape adjustment layer decreases, and the side surface is formed substantially perpendicular to the substrate.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. 1, 3 to 7 are schematic cross-sectional views showing the structure of a semiconductor laser formed according to the present invention at a manufacturing stage. First, a method of forming a semiconductor laser according to the present invention, as shown in FIG.
0) The first clad layer 2, the active layer 3, the second clad layer 4, the etching stop layer 5, the ridge shape adjusting layer 6, the third clad layer 7 are formed on the substrate 1 made of n-type GaAs by MOCVD. And the cap layer 8 are laminated in this order. The conductivity type, composition, carrier concentration and thickness of each layer are as follows. First cladding layer 2: n-Al _0.4 Ga _0.6 As _, n = 5
× 10 ¹⁷ cm ⁻³ , 2.0 μm Active layer 3: Al _0.1 Ga _0.9 As _, undoped, 0.07 μm Second cladding layer 4: p-Al _0.4 Ga _0.6 As _, p = 3
× 10 ¹⁸ cm ⁻³ , 0.3 μm Etching stop layer 5: p-Al _0.2 Ga _0.8 As _, p = 3
× 10 ¹⁸ cm ⁻³ , 0.03 μm Ridge shape adjusting layer 6: p-Al _x Ga _1-x As _, p = 3
× 10 ¹⁸ cm ⁻³ , 0.5 μm Third cladding layer 7: p-Al _0.4 Ga _0.6 As _, p = 3
× 10 ¹⁸ cm ⁻³ , 0.8 μm Cap layer 8: p-GaAs _, p = 5
× 10 ¹⁸ cm ^-3 , 0.2μm

At this time, the distribution of the mixed crystal ratio x of Al in the ridge shape adjusting layer 6 is as shown in FIG. FIG. 2 shows the mixed crystal ratio x on the vertical axis and the lamination direction on the horizontal axis, and shows the mixed crystal ratio x of the second clad layer 4, the etching stop layer 5, the ridge shape adjusting layer 6, and the third clad layer 7. Is shown. The ridge shape adjusting layer 6 has the highest mixed crystal ratio x in the surface area of the etching stop layer 5 and continuously decreases in the laminating direction, so that the mixed area of the third clad layer 7 in the contact area with the third clad layer 7 is increased. The crystal is grown so as to have the same value as the crystal ratio x.

Next, as shown in FIG. 3, a stripe-shaped ridge having a width of 5 to 6 μm is formed in the crystal orientation <01 bar 1> direction using the SI ₃ N ₄ layer 11 having a thickness of 2500 ° or more as a mask. First etching is performed as follows. As the etchant, a commonly used one such as sulfuric acid: hydrogen peroxide: water or phosphoric acid: hydrogen peroxide: methanol is used. At this time, in the first etching, the ridge shape adjusting layer 6 is
The ridge shape adjusting layer 6 has a shape in which the area is increased toward the etching stop layer 5.

Then, a second etching is performed using a hydrofluoric acid stock solution as an etchant. First, etching is performed for about 30 seconds to remove the remaining layer of the ridge shape adjusting layer 6 at the time of the first etching. This can be confirmed by a change in color due to the exposure of the surface of the etching stop layer 5. At this time, the surface of the Si ₃ N ₄ layer 11 is also etched and the thickness becomes thin. Thereafter, etching is further performed for several seconds to several tens of seconds, whereby the ridge shape adjustment layer 6 is side-etched. Since the ridge shape adjusting layer 6 has a different mixed crystal ratio x in the lamination direction and has a maximum value on the etching stop layer 5 side, the etching rate is highest on the etching stop layer 5 side. As a result, the ridge shape adjustment layer 6 remaining in a shape in which the area is increased toward the etching stop layer 5 in the first etching is formed such that the side surface thereof is substantially perpendicular to the substrate 1 as shown in FIG. You.

Next, as shown in FIG. 5, a current blocking layer 9 made of n-type GaAs is deposited to a thickness of 1.0 μm on the etching stopper layer 5 around the ridge. The carrier concentration of the current blocking layer 9 is 3 × 10 ¹⁸ cm ⁻³ . At this time, Si ₃ N ₄ layer 11 current blocking layer 9 is formed on the not deposited, by remove the Si ₃ N ₄ layer 11, for example with hydrofluoric acid, to expose the cap layer 8 surface.

Then, as shown in FIG. 6, a contact layer 10 of p-type GaAs is deposited on the current blocking layer 9 and the cap layer 8 to a thickness of 3.0 μm. Contact layer 10
Has a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ . Contact layer 10
(Not shown) are formed on the upper surface of the substrate 1 and the lower surface of the substrate 1, respectively.

The semiconductor laser formed as described above has
On the active layer 3, the second cladding layer 4, the etching stop layer 5,
A stripe-shaped ridge portion composed of the ridge shape adjusting layer 6 and the third cladding layer 7 is formed, and the ridge shape adjusting layer 6 is formed with a composition having a smaller etching rate in the laminating direction. Further, the side surface of the third cladding layer 7 is formed substantially perpendicular to the substrate 1. Thereby, in the semiconductor laser of this embodiment, the reactive current is reduced, the operating current is small, the light absorption on the side surface of the ridge is small, and the external quantum differential efficiency is improved.

Further, an AlGaInP-based semiconductor laser can be manufactured by the method as described above. FIG. 7 is a schematic sectional view showing the structure of an AlGaInP-based semiconductor laser formed by the method of the present invention. Plane orientation (10
0) The first clad layer 2, the active layer 3, the second clad layer 4, the etching stop layer 5, the ridge shape adjusting layer 6, the third clad layer 7 are formed on the substrate 1 made of n-type GaAs by MOCVD. And the cap layer 8 are laminated in this order. The conductivity type and composition of each layer are as follows. First cladding layer 2: n- (Al _0.5 Ga _0.5 ) _0.5 In
_0.5 P active layer 3: undoped Al _0.1 Ga _0.9 A
s _, second cladding layer 4: p- (Al _0.5 Ga _0.5 ) _0.5 In
_0.5 P etching stop layer 5: p- (Al _0.2 Ga _0.8 ) _0.5 In
_0.5 P Ridge shape adjusting layer 6: p- (Al _x Ga _{1 -x} ) _0.5 In
_0.5 P third cladding layer 7: p- (Al _0.5 Ga _0.5 ) _0.5 In
_0.5 P cap layer 8: p-GaAs _,

Such an AlGaInP-based semiconductor layer is laminated, and HCl is used as an etchant for the second etching.
Except for using H ₂ O = 1: 1, it is the same as the above-mentioned method, and the same reference numerals are given to the same parts, and the description of the structure and the forming method is omitted.

In this embodiment, hydrofluoric acid or hydrochloric acid is used as an etchant in the second etching step.
However, the present invention is not limited to this. When the mixed crystal ratio x of the ridge shape adjusting layer 6 is large, the etching rate is large, and the mixed crystal ratio x
If the etching rate is small, an etchant having a small etching rate may be used.

In this embodiment, the case where the stripe-shaped ridge portion is formed in the crystal orientation <01 bar 1> direction is described. However, the present invention is not limited to this, and the stripe ridge portion is formed in the crystal orientation <011> direction. May be.

[0022]

As described above, according to the present invention, the ridge shape adjusting layer having a small etching rate in the laminating direction is etched to form the remaining portion in an inverted mesa shape, or to make the side surface substantially opposite to the substrate. Since it is formed vertically, a ridge having a small area on the active layer side can be easily formed by etching. As a result, the present invention has excellent effects such as a reduction in reactive current and a reduction in operating current, and a reduction in light absorption on the side surface of the ridge and an improvement in external quantum differential efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a structure of a semiconductor laser formed according to the present invention at a manufacturing stage.

FIG. 2 is a graph showing a distribution of an Al mixed crystal ratio x of a semiconductor layer forming a ridge portion.

FIG. 3 is a schematic cross-sectional view showing a structure of a semiconductor laser formed according to the present invention at a manufacturing stage.

FIG. 4 is a schematic cross-sectional view showing a structure of a semiconductor laser formed according to the present invention at a manufacturing stage.

FIG. 5 is a schematic cross-sectional view showing a structure of a semiconductor laser formed by the present invention at a manufacturing stage.

FIG. 6 is a schematic cross-sectional view showing a structure of a semiconductor laser formed according to the present invention at a manufacturing stage.

FIG. 7 is a schematic cross-sectional view showing a structure of a semiconductor laser formed according to the present invention at a manufacturing stage.

FIG. 8 is a schematic sectional view showing the structure of a conventional semiconductor laser.

FIG. 9 is a schematic cross-sectional view illustrating a shape of a ridge portion of a conventional semiconductor laser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 1st clad layer 3 Active layer 4 2nd clad layer 5 Etch stop layer 6 Ridge shape adjustment layer 7 3rd clad layer 9 Current block layer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (2)

(57) [Claims] 1. A active layer a ridge portion is formed by etching the substrate opposite to the semiconductor laser embedded around its in the current blocking layer, the ridge portion, et
Laminated on etch stop layer with composition that stops etching
And a ridge shape adjusting layer having a composition in which the etching rate is reduced stepwise or continuously from the active layer side in the stacking direction.
A semiconductor laser, characterized in that there Ete. 2. A method for manufacturing a semiconductor laser in which a ridge portion is formed by etching on a side opposite to a substrate with respect to an active layer and a periphery thereof is buried with a current blocking layer. A step of laminating an etching stop layer having a composition for stopping the etching, and a step of laminating a ridge shape adjusting layer having a composition such that the etching rate is gradually or continuously reduced in the laminating direction from the active layer side on the etching stop layer. Forming a remaining portion by etching the ridge shape adjusting layer to the surface of the etching stop layer, wherein the ridge portion is formed by the remaining portion .