JP2946781B2 - Semiconductor laser - 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 for a bar code reader such as a POS or FA system or a light source such as a laser printer, and more particularly to a high output and lateral mode control. And a structure of an AlGaInP-based visible light semiconductor laser having an oscillation wavelength of 680 nm or less.

[0002]

2. Description of the Related Art A conventional lateral mode control type AlGaInP.
An example of a visible light semiconductor laser is reported on page 165 of the Proceedings of the Japan Society of Applied Physics Autumn 1986.

A conventional semiconductor laser will be described with reference to FIGS. 3 (a) and 3 (b). FIG. 3 (a) shows a conventional lateral mode control type AlGaInP-based visible light semiconductor laser. FIG. 3B is a perspective view showing the structure of FIG. 3, and FIG. 3B is a sectional view taken along line EE of FIG. 3A and 3B, reference numeral 1 denotes an n-GaAs substrate, on which an n-GaAs buffer layer 2 is formed. On the buffer layer 2, n-AlGa
InP clad layer 3, GaInP active layer 4, p-AlG
aInP cladding layer 5, p-GaInP cap layer 6,
A double heterojunction structure including an n-GaAs current blocking layer 7 and a p-GaAs contact layer 8 is formed.

A semiconductor laser crystal having this structure is:
Usually, it is manufactured by the MOVPE method. However, since it is technically difficult to stack an AlGaInP layer on a substrate having a step, as shown in FIG. By forming the p-AlGaInP cladding layer 5 having a step and forming the n-GaAs current blocking layer 7 on this step, current confinement and optical waveguide action are performed in a self-aligned manner.

Here, the manufacturing process of the conventional semiconductor laser shown in FIGS. 3A and 3B will be briefly described. First, the first MOVPE growth starts with the n-GaAs buffer layer 2. A five-layer structure up to the p-GaInP cap layer 6 is sequentially formed. Subsequently, a stripe-shaped mask using a SiO ₂ film having a width of 5 μm is formed on the cap layer 6 by photolithography, and etched halfway through the p-AlGaInP clad layer 5 to form a stripe-shaped mesa. .

Next, n-Ga is added to the mesa portion excluding the stripe-shaped SiO ₂ film mask by the second MOVPE growth.
The As current blocking layer 7 is selectively formed. After that, Si
After removing the O ₂ film mask, a p-GaAs contact layer 8 is grown and formed on the entire surface by the third MOVPE growth, and a p-side electrode 9 is formed on the contact layer 8 and an n-side electrode 10 is formed on the n-GaAs substrate 1. By doing so, a laser element having the structure shown in FIGS. 3A and 3B is completed.

In this structure, current confinement is caused by n-GaAs.
This is performed by the current blocking layer 7. Also, p-GaInP
The cap layer 6 includes the p-AlGaInP clad layer 5 and the p-AlGaInP clad layer 5.
-Has the role of preventing an increase in electrical resistance caused by band discontinuity with the GaAs contact layer 8 (for example, Autumn 1987 Annual Meeting of the Japan Society of Applied Physics, p.
a-ZR-6), and as shown in FIG. 3 (b), up to both end faces in the resonator direction.

On the other hand, in the lateral mode control, the p-
N-Ga on both sides of the mesa of the AlGaInP cladding layer 5
Since light absorption loss is caused by the As current blocking layer 7, the formation is performed by forming a refractive index distribution on both sides of the mesa.

[0009]

In recent years, there has been an increasing demand for an AlGaInP-based visible light semiconductor laser which oscillates in a basic lateral mode and can realize a high output operation. However,
In the conventional refractive index guide type semiconductor laser as described above,
Since the p-GaInP cap layer 6 is formed up to both end faces in the resonator direction (see FIG. 3), the temperature in the active region (GaInP active layer 4) increases due to current injection, and furthermore,
At the end face of this active region, laser light is absorbed by the end face and heat is generated, the temperature of the end face rises, optical damage is apt to occur, the end face breakdown output decreases, and high output operation is difficult. Become.

The present invention solves the above-mentioned problems, and realizes a high-output operation capable of performing a high-output operation with a reduced temperature rise at the end face of the active region.
It is an object of the present invention to provide an lGaInP-based semiconductor laser.

[0011]

According to the semiconductor laser of the present invention, a current non-injection region is provided in the vicinity of a cavity facet, a temperature rise of the cavity facet due to current injection is reduced, and a facet breakdown output is increased. This enables high output operation.

That is, according to the present invention, the double heterojunction structure formed on the semiconductor substrate is (Al _x Ga _{1 -x} ) _0.5 In _0.5
In a P-based semiconductor laser, at least an active layer is sandwiched between a first cladding layer of a first conductivity type and a second cladding layer having a second conductivity type in a mesa shape. A semiconductor layer of the first conductivity type having a higher refractive index than the active layer in the portion and the outside, and a second conductivity type Ga _0.5 In _0.5 P layer only on the upper surface of the mesa having the second graded layer excluding the vicinity of the resonator end. And near both end faces of the resonator
Removing said second conductivity type Ga _0.5 In _0.5 P layer.
The width of the current non-injection region formed by
μm .

[0013]

According to the present invention, p-Ga is used only near the cavity end face.
By adopting a configuration in which the InP cap layer is removed, p
A band discontinuous junction between the -AlGaInP cladding layer and the p-GaAs contact layer is formed, and the electric resistance increases.

The width of the current non-injection region is at least 5
If it is μm, the effect of the present invention is not impaired, but the upper limit is preferably 10 μm.

[0015]

Next, the present invention will be described in detail with reference to FIGS. 1 (a) to 1 (d) and FIGS. 2 (a) and 2 (b). FIGS. 1A to 1D are views showing one embodiment of the present invention, and FIGS. 2A and 2B are views showing another embodiment of the present invention.

(Embodiment 1) FIG. 1A is a perspective view showing a structure of a semiconductor laser according to an embodiment of the present invention.
(b), (c) and (d) are cross-sectional views taken along the line AA shown in FIG.
FIG. 3 is a cross-sectional view taken along a line B and a line CC.

First, metal group III organic metals (trimethyl indium, triethyl gallium, trimethyl aluminum) and group V hydride (PH ₃ , AsH ₃ ) are used as raw materials.
The MOVPE method under reduced pressure using
A 0.5 μm thick n-GaAs buffer layer 12 (n concentration 1) was formed on a GaAs substrate 11 (n concentration 2 × 10 ¹⁸ cm ⁻³ ).
× 10 ¹⁷ cm ^-3 ), 1 μm thick n- (Al _0.6 G
a _0.4 ) _0.5 In _0.5 P clad layer 13 (n concentration 5 × 10 ¹⁷
cm ⁻³ ), Ga _0.5 In _0.5 P active layer 1 having a thickness of 0.06 μm
4. 1-μm-thick p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5
P clad layer 15 (p concentration 3 × 10 ¹⁷ cm ⁻³ ), thickness 0.1
μm p-Ga _0.5 In _0.5 P cap layer 16 (p concentration 1
× 10 ¹⁸ cm ^-3 ) is grown sequentially to form a double hetero wafer
To form

Subsequently, a rectangular SiO ₂ film having a width of 5 μm and a length of 280 μm is formed on the cap layer 16 by photolithography. Next, using an HCl-based etchant,
Only the p-Ga _0.5 In _0.5 P cap layer 16 except for the rectangular SiO ₂ film region having a width of 5 μm and a length of 280 μm is selectively etched away. Next, a stripe-shaped SiO ₂ film having a width of 5 μm is formed on the first rectangular SiO ₂ film by a second photolithography method.

[0019] Therefore, with H ₂ SO ₄ etchant, as shown in FIG. 1 (c), (d) , p- (Al 0.6 G
_a0.4 ) _{0.5 In0.5} P Etching is performed halfway through the clad layer 15, and the thickness of the clad layer 15 on both sides of the stripe-shaped mesa is controlled to be 0.2 to 0.3 μm.

Thus, the first rectangular SiO ₂
Under the film, as shown in FIG. 1D, p-Ga _0.5 In _0.5 P
Mesa cap layer 16 is the top layer, the top layer of the mesa except the rectangular SiO ₂ film of the under second striped SiO ₂ film, as shown in FIG. 1 (c), p- (A
1 _0.6 Ga _0.4 ) _0.5 In _0.5 P _0.5 cladding layer 15 is provided. The longitudinal direction of the rectangular SiO ₂ film is the resonator direction, and the rectangular SiO ₂ film having a length of 280 μm is 30
They are arranged at a pitch of 0 μm.

Next, by the second MOVPE growth, a thickness of 0.6 μm is formed on the mesa except for the stripe-shaped SiO ₂ film mask.
m (flat portion) n-GaAs current blocking layer 17 (n concentration 1
× 10 ^{1 8} cm ^-3) selectively grown form. Then, Si
After removing the O ₂ film mask, the third MOVPE growth
3 μm thick p-GaAs contact layer 18 on the entire surface
(P concentration 5 × 10 ¹⁸ cm ⁻³ ), and a p-side electrode 19 on the contact layer 18 and an n-side electrode 20 on the n-GaAs substrate 11 are formed. The wafer is completed.

Here, as shown in FIG. 1B, since the p-Ga _0.5 In _0.5 P cap layer 16 is not formed in the BB cross-sectional area, the p-GaAs contact layer 18 and the p-
A junction with the (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P _0.5 cladding layer 15 is formed, the electrical resistance increases due to band discontinuity, and the region becomes a current non-injection region. Further, this region is formed from the both end faces of the resonator to the inside of the resonator of 10 μm (X in the figure), the influence of heat generation near the end face due to current injection can be reduced, and high output operation can be performed. Also, in this embodiment,
Width of the current injection region X: is the case of 10 [mu] m, 10 [mu]
If m ≧ X ≧ 5 μm, the effect of the present invention is not impaired.

(Embodiment 2) FIG. 2A is a perspective view showing the structure of a semiconductor laser according to another embodiment of the present invention.
FIG. 2B is a sectional view taken along line DD in FIG. 2A.

The growth of the dovel heterostructure by the MOVPE method is performed in the same manner as in the first embodiment. In this embodiment, a thickness of 0.2 mm is formed on the active layer 14 by the first MOVPE growth.
After growing form ~0.3μm of _{p- (Al 0.6 Ga 0.4) 0.5} In 0.5 P cladding layer 15, a thickness of 40 angstroms p-Ga _0.5 In _0.5 P etching stop layer 21 (p concentration 3 × 10 ¹⁷ cm ^{- 3} ) is grown and formed, and the cladding layer 15 is formed to a thickness of 0.7 μm.
And different.

In this embodiment, the formation of the etching stopper layer 21 has the advantage that the thickness of the cladding layer 15 on both sides of the stripe-shaped mesa can be formed with good controllability by etching. Here, the thickness of the etching stop layer 21 needs to be as thin as 40 angstroms so as not to be absorbed by the oscillation light.

[0026]

As described above, according to the present invention,
By removing the second conductivity type Ga _0.5 In _0.5 P layer (p-Ga _0.5 In _0.5 P cap layer 16) near both end faces of the resonator, a current non-injection region is formed. Heat generation in the vicinity of the end face can be reduced, and high-output operation can be performed. In general, a high output operation of 10 to 15 mW, which is about 3 times the rated output of 3 to 5 mW, can be realized.

[Brief description of the drawings]

FIG. 1 (a) is a perspective view showing a structure of a semiconductor laser according to one embodiment of the present invention, and FIGS. 1 (b), (c) and (d) are
FIG. 2 is a sectional view taken along line AA, BB, and CC shown in FIG.

FIG. 2 (a) is a semiconductor laser according to another embodiment of the present invention.
FIG. 2 (b) is a perspective view showing the structure of
FIG. 4 is a sectional view taken along line D.

FIG. 3 (a) shows a conventional lateral mode control type AlGa.
FIG. 3B is a perspective view showing the structure of the InP-based visible light semiconductor laser, and FIG. 3B is a sectional view taken along the line EE of FIG. 3A.

[Explanation of symbols]

1, 11 n-GaAs substrate 2, 12 n-GaAs buffer layer 3 n-AlGaInP cladding layer 4 GaInP active layer 5 p-AlGaInP cladding layer 6 ... p-AlGaInP cap layer 7, 17 ... n-GaAs current blocking layer 8, 18 ... p-GaAs contact layer 9, 19 ... p-side electrode 10, 20 ... n-side electrode 13 ......- n- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P cladding layer 14 Ga _0.5 In _0.5 P active layer 15 p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P cladding layer 16 p-Ga _0.5 In _0.5 P cap layer 21 p-Ga _0.5 In _0.5 P etching stop layer

Claims (2)

(57) [Claims] 1. A double heterojunction structure formed on a semiconductor substrate (Al _X Ga _1-X) semiconductor laser composed of _0.5 an In _0.5 P system - in The, at least the active layer is first clad of the first conductivity type A semiconductor layer having a higher refractive index than the active layer of the first conductivity type on the side and the outside of the stripe-shaped mesa, sandwiched between the layer and a second cladding layer having a stripe-shaped mesa shape of the second conductivity type; The second conductivity type Ga _0.5 I is formed only on the upper surface of the second mesa layered mesa except for the vicinity of the resonator end.
an n _0.5 P layer, and the second conductive layer near both end faces of the resonator.
Formed by removing the Ga _0.5 In _0.5 P layer of
A width of the current non-injection region is 5 μm to 10 μm . 2. It has a striped mesa shape of a second conductivity type.
The second clad layer has an etch stop layer between the layers.
2. The semiconductor laser according to claim 1, wherein said semiconductor laser is formed.