KR20000035300A - Semiconductor laser - Google Patents

Abstract

PURPOSE: A semiconductor laser is provided to be capable of widening a bandgap around an end portion, to increase a yield, and to improve a reliability. CONSTITUTION: In a semiconductor laser, a stripe width of an end portion(100b) is set in a resonator direction so as to be more than that of a center portion(100c). A bandgap of an active layer of the end portion(100b) is constructed so as to be more than that of an active layer of the center portion(100c). An adjustment of the bandgap is executed by a thickness of the active layer film.

Description

Semiconductor Laser {SEMICONDUCTOR LASER}

The present invention relates to a semiconductor laser having a SDH (Separated Double Heterostructure) structure.

10 and 11 show a conventional semiconductor laser having an SDH structure, FIG. 10 is a plan view, and FIG. 11 is a sectional view taken along the line A-A of FIG.

In the semiconductor laser 10, one main surface of the p-type compound semiconductor (GaAs) substrate 11 has a (100) crystal plane, and the main surface 11a has a stripe shape (in Fig. 11, A mesa type projection 11b is formed in a stripe extending in the direction orthogonal to the ground.

On the main surface 11a of the semiconductor substrate 11 having the stripe mesa protrusion 11b, the p-type was continuously formed by one MOCVD (metal organic chemical vapor deposition) crystal growth step. An epitaxially grown cross section of the first cladding layer 12, the low impurity or undoped active layer 13, and the n-type second cladding layer 14 is three. An epitaxial growth layer having a rectangular shape is formed.

The p-type current block layer 15 of the epitaxial layer including the p-type first cladding layer 12, the active layer 13, and the second cladding layer 14 formed on the mesa-type protrusion 11b. It is formed in contact with both sides.

Further, an n-type cladding layer 16 is formed on the second cladding layer 14 formed on the current block layer 15 and the mesa-type protrusion 11b, and the n-type cladding layer 16 is formed on the cladding layer 16. Cap layer 17 is formed.

On the n-type cap layer 17, n-side electrodes 18 such as Ti / Pt / Au electrodes are formed.

On the other hand, the p-side electrode 19 similar to the AuGe / Ni / Au electrode is formed on the back surface of the p-type substrate 11.

And the width | variety of the stripe part 10a of the resonator direction of the semiconductor laser 10 is set uniformly.

As described above, since the semiconductor laser 10 uses the SDH structure, a complex structure can be produced by one MOCVD crystal growth step, and thus a relatively stable and uniform characteristic can be obtained.

However, in the above-described laser structure, the bandgap Eg emits light due to the interface level, deterioration of heat emission efficiency, high optical density, and other factors in the vicinity of the cross section of the resonator. It tends to be smaller than the area, absorbs the laser light generated inside, may cause more heat generation, limit the maximum oscillation output, and possibly cause cross-sectional breakdown, thereby degrading the reliability of the laser.

In particular, when outputting a watt (W) class laser beam from a broad stripe laser in which the stripe width is set to 10 µm or more, deterioration from a cross section may proceed.

Therefore, it is important to perform end surface protection from the point of view of laser reliability.

In this regard, a so-called window structure for raising the band gap Eg near the cross section is proposed.

This includes a method of embedding a material having a high band gap (Eg), or a method of diffusing impurities (such as Zn), destroying a superlattice structure, and raising the band gap (Eg). Two methods of are known.

However, since both methods rely on complicated process technology, there is a high possibility that the yield and the like are bad.

This invention is made | formed in view of such a situation, The objective is providing the semiconductor laser which can widen the bandgap of a cross section vicinity, aiming at the improvement of a yield, and also the improvement of reliability and the increase of the maximum light output are attained. It is in doing it.

1 is a plan view showing a first embodiment of a semiconductor laser according to the present invention.

2 is a cross-sectional view taken along the line A-A of FIG.

3 is a cross-sectional view taken along the line B-B in FIG.

4 is a diagram for explaining the effect of migration on MOCVD growth.

FIG. 5 is a view for explaining the change in the film thickness at the cross-sectional triangle portion on the mesa projection enclosed by the (111) B surface. FIG.

Fig. 6 is a diagram for explaining the migration effect when the SDH structure is also present at both sides.

7 is a plan view showing a second embodiment of a semiconductor laser according to the present invention.

8 is a simplified cross-sectional view taken along the line A-A of FIG.

9 is a simplified cross-sectional view taken along the line B-B in FIG. 7.

10 is a plan view of a conventional semiconductor laser.

11 is a cross-sectional view taken along the line A-A of FIG.

<Explanation of symbols for main parts of drawing>

100, 100A: semiconductor laser, 100a: stripe portion, 100b: end face portion, 100c: center portion, 101: p-type semiconductor substrate, 101a: main surface, 101b: mesa-type protrusion, 102: p-type first cladding layer 103: active layer, 103b: active layer in cross section, 100c: active layer in center, 104: n-type second clad layer, 105: p-type current block layer, 106: n-type clad layer, 107: n-type cap layer, 108: n Side electrode, 109 p-side electrode, 110: second stripe portion.

In order to achieve the above object, according to the first embodiment of the present invention, a first cladding layer of the first conductivity type, an active layer, and a second conductive semiconductor layer are formed on a semiconductor substrate having a stripe mesa protrusion formed on the principal surface of the crystal plane. The second double cladding layer has an epitaxial growth layer that is epitaxially grown in turn, has a refractive index difference in the transverse direction of the active layer, and a SDH (Separated Double Heterostructure) structure in which a current block layer exists for current narrowing. A semiconductor laser comprising: a stripe width in the cross section in the resonator direction is set larger than a stripe width in the center portion, and a band gap of the active layer in the cross section is wider than a band gap of the active layer in the center portion.

In the present invention, the thickness of the active layer in the cross section is thinner than the thickness of the active layer in the center.

Further, according to the second embodiment of the present invention, the first cladding layer of the first conductivity type, the active layer, and the second conductivity type of the second conductive type are formed on the semiconductor substrate on which the mesa-shaped projections of the stripe type are formed on the main surface of the crystal plane. A semiconductor laser having an SDH structure in which a cladding layer has an epitaxial growth layer in which epitaxially grown layers are in turn, a refractive index difference in the transverse direction of an active layer, and a current block layer for current narrowing exists. The plurality of second stripe portions having a width narrower than that of the resonator direction are formed.

In the present invention, the second stripe portion is formed in the center portion in the resonator direction, and the second stripe portion is fused in the cross-section portion to form one wide stripe.

Moreover, in this invention, the band gap of the active layer in a cross section is wider than the band gap of the active layer in a center part.

Moreover, in this invention, the thickness of the active layer in a cross section is thinner than the thickness of the active layer in a center part.

According to the present invention, due to the so-called migration effect, the active layer is easily formed upward in the cross-sectional triangle portion on the mesa projection in the center portion where the stripe width is set small. In other words, the thickness of the active layer in the center portion becomes thick.

On the other hand, in the cross section in which the stripe width is set large, the active layer tends to be formed downward in the cross section triangle on the mesa projection. That is, the thickness of the active layer of the cross section becomes thin.

As described above, since the thickness of the active layer at the cross section is thinner than the thickness of the active layer at the center, the band gap energy rises when the quantum well structure is used in comparison with the center at the cross section.

As a result, the amount of light absorption of the end face portion decreases and the heat generation decreases. That is, the cross section is strengthened.

Further, according to the present invention, since the center portion of the stripe portion has an array type SDH structure, the film of the quantum well active layer is thickly formed by the migration enhancement effect from both sides.

On the other hand, since the film thickness of the active layer of the cross section is large in stripe width, there is less migration effect and is formed thinner than the center portion.

As described above, since the thickness of the active layer at the cross section is thinner than the thickness of the active layer at the center, the band gap energy increases when the quantum well structure is used in comparison with the center at the cross section.

As a result, the amount of light absorption of the end face portion decreases and the heat generation decreases. That is, the cross section is strengthened.

In the cross-section, the second stripe portion is fused to form one wide stripe, so that the near-field image becomes uniform light emission.

In addition, since the SDH structure is used, a complex structure can be produced by one MOCVD growth.

Next, a preferred embodiment of the present invention will be described with reference to the drawings.

First embodiment

1 is a plan view showing a first embodiment of a semiconductor laser according to the present invention, FIG. 2 is a sectional view taken along the line A-A of FIG. 1, and FIG. 3 is a sectional view taken along the line B-B of FIG.

The semiconductor laser 100 has a multi-layer semiconductor laser structure composed of a cladding layer, an active layer, and the like on a compound semiconductor substrate having a stripe-shaped non-uniform shape in the reverse mesa direction. The growth step has a so-called SDH structure of a BH (Buried Hetero Structure) structure in which the refractive index difference is made in the transverse direction of the active layer, and a current block layer for current narrowing is formed, and a p-type substrate is used.

In the semiconductor laser 100, as shown in Fig. 1, the stripe width of the cross-section 100b is set larger than the stripe width of the central portion 100c in the resonator direction of the stripe portion 100a. The band gap Egb of the active layer in 100b) is configured to be larger than the bandgap Egc of the active layer in the center portion 100c.

This band gap is adjusted by the thickness of the active layer. Specifically, the thickness of the active layer in the cross section 100b is formed thinner than the thickness of the active layer in the central portion 100c.

Next, the specific structure of the semiconductor laser 100 is demonstrated.

As shown in Figs. 2 and 3, this semiconductor laser 100 has one main surface of the first conductive type, for example, p-type compound semiconductor (GaAs) substrate 101, having a (100) crystal plane. The mesa-type protrusion 101b is formed in 101a of stripe form (a stripe extended in the direction orthogonal to the surface in FIGS. 2 and 3).

On the main surface 101a of the semiconductor substrate 101 having the stripe mesa protrusion 101b, the first p-type cladding layer (Al _0.4 Ga _0.6 As) 102 is successively subjected to one MOCVD crystal growth step. Epitaxially), a low impurity or undoped active layer (Al _0.12 Ga _0.88 As) 103, and a second conductive layer (n-type) second clad layer (Al _0.4 Ga _0.6 As) 104. An epitaxial growth layer having a triangular triangular cross section is formed.

Here, since the thickness of the active layer 103 is set to be larger than the stripe width of the center portion 100c in the resonator direction, the stripe width of the cross section portion 100b of the stripe portion 100a is reduced by the migration effect described later. The thickness of the active layer 103b (FIG. 2) in the part 100b is formed thinner than the thickness of the active layer 100c (FIG. 3) in the center part 100c.

As such, an epitaxial growth layer having a triangular cross section is formed, but this is due to the following reason.

That is, the relationship between the shape of the stripe mesa protrusion 101b and its crystal orientation is selected to have a predetermined relationship, and the (111) B crystal plane whose angle is about 55 ° with respect to the (100) plane of the upper surface thereof. The tomographic part of the inclined surface is formed.

This means that once the (111) B surface is formed in the epitaxial layer grown on the mesa protrusion 101b on the substrate 101, the epitaxial growth rate on the (111) B surface is different, for example ( 100) Since the growth rate of the crystal plane is about one tenth or less, the monolayer portion is formed along the slope by (111) B.

Therefore, on the mesa protrusion 101b, an epitaxial growth layer having a triangular cross section is sandwiched between the monolayer portions.

The p-type current block layer 105 includes an epitaxy including a p-type first cladding layer 102, an active layer 103, and a second cladding layer 104 formed on the mesa-type protrusion 101b. It is formed in contact with both sides of the ear layer.

In addition, an n-type cladding layer 106 is formed on the second cladding layer 104 formed on the current block layer 105 and the mesa-type protrusion 101b, and the n-type cladding layer 106 is formed on the cladding layer 106. Cap layer 107 is formed.

On the n-type cap layer 107, an n-side electrode 108 such as a Ti / Pt / Au electrode is formed.

On the other hand, the p-side electrode 109 like the AuGe / Ni / Au electrode is formed on the back surface of the p-type substrate 101.

In addition, the current block layer (Al _0.1 Ga _0.9 As) 105 can freely select its composition and polarity as a feature of the SDH structure fabrication.

In the semiconductor laser 100 having the above structure, as described above, the thickness of the active layer 103 is greater than the stripe width of the center portion 100c in the resonator direction of the stripe portion 100a. Since the setting is large, the thickness of the active layer 103b in the cross section 100b is made thinner than the thickness of the active layer 100c in the central portion 100c due to the migration effect. It demonstrates with reference to FIG. 4, FIG. 5, FIG.

4 is a diagram for explaining a migration effect in MOCVD growth.

When growing on a nonuniform substrate like an SHD structure, it is known that (111) B surface is formed and growth is suppressed on it as mentioned above.

In this state, when the active layer thin film is formed in the triangular cross section on the mesa protrusion 101b surrounded by the (111) B surface, growth of the raw material supplied to the region indicated by the broken line in FIG. 4 is inhibited. By migration, film formation takes place by moving to a nearby growthable region.

Although the migration distance of a raw material changes with growth conditions and a raw material, it is about 2 micrometers with A1 raw material, and about 10 micrometers with Ga raw material.

That is, it turns out that the raw material supplied to the growth inhibiting area performs the function of thickening the thickness of the active layer at such a distance.

5 is a figure for demonstrating the change of the film thickness in the triangular part of the cross section on the mesa protrusion 101b enclosed by the (111) B surface.

As shown in Fig. 5, the more the progress is performed upward from the cross-sectional triangle on the mesa projection 101b, that is, the larger the crystal growth is, the wider the width of the growth inhibiting region (the region indicated by the broken line in Fig. 4) is. The effect becomes stronger and the film thickness becomes thicker.

That is, forming an active layer at the top in the cross-sectional triangle portion on the mesa protrusion 101b means that the thickness formed at the bottom becomes small.

Therefore, in the center part 100c in which stripe width was set small, an active layer tends to be formed in the top in the cross-sectional triangular part on the mesa protrusion 101b. That is, the thickness of the active layer 103c of the central portion 100c becomes thick.

In contrast, in the end face portion 100b having a large stripe width, an active layer is likely to be formed at the bottom in the cross-sectional triangle portion on the mesa protrusion 101b. That is, the thickness of the active layer 103b of the cross section 100b becomes thin.

Thus, since the thickness of the active layer 103b (FIG. 2) in the cross section 100b is formed to be thinner than the thickness of the active layer 100c (FIG. 3) in the central portion 100c, the center portion in the cross section 100b. When the quantum well structure is used in comparison with, the bandgap energy Egb can be increased.

As a result, the amount of light absorption of the end surface portion 100b decreases and the heat generation decreases.

That is, the cross section is strengthened.

For example, electrostatic resistance is enhanced. In other words, damage to the laser cross-section due to surge current application is suppressed.

6 is a view for explaining the migration effect when the SDH structure is also present on both sides.

In this way, if the growth inhibition region also exists in the adjacent region, the migration effect also occurs from both sides, so that the film thickness of the region is formed thicker.

As described above, according to the first embodiment, a MOCVD crystal is formed on a compound semiconductor substrate having a stripe non-uniform shape in the reverse mesa direction, having a multilayer film semiconductor laser structure composed of a cladding layer, an active layer, and the like. In the semiconductor laser 100 having the SDH structure of the BH configuration, which has a refractive index difference in the transverse direction of the active layer by the growth step and forms a current block layer for current narrowing, the end face portion 100b of the stripe portion 100a. ), The stripe width is set to be larger than the stripe width of the center portion 100c in the resonator direction, and the thickness of the active layer in the cross section portion 100b is made thinner than the thickness of the active layer in the center portion 100c, and the cross section portion 100b is formed. Since the bandgap (Egb) of the active layer in the structure is larger than the bandgap (Egb) of the active layer in the center portion, the cross section of the laser beam generated inside Absorption can be reduced, heat generation is suppressed, the band gap near the end face can be widened while improving the yield and cost reduction, and there is no fear of end face breakage. Is increased.

In addition, since the SDH structure is used, a complicated structure can be produced by one MOCVD growth step.

Incidentally, in the first embodiment, the AlGaAs-based semiconductor laser has been described as an example, but the present invention can also be applied to other material-based semiconductors, for example, AlGaInP-based semiconductor lasers. to be.

Second embodiment

7 is a plan view showing a second embodiment of the semiconductor laser according to the present invention, FIG. 8 is a simplified sectional view taken along the line A-A of FIG. 7, and FIG. 9 is a simplified sectional view taken along the line B-B of FIG.

The semiconductor laser 100A according to the second embodiment is a super high power (SHP) semiconductor laser of a so-called broad stripe structure whose stripe width is set to 10 µm or more and whose output is of watt (W) class. .

This semiconductor laser 100A has a multilayer film semiconductor laser structure composed of a cladding layer, a guide layer, an active layer, and the like on a compound semiconductor substrate having a stripe-shaped non-uniform shape in the reverse mesa direction as in the first embodiment. Has a SDH structure of a BH configuration in which the refractive index difference is made in the transverse direction of the active layer by one MOCVD (organic metal vapor deposition) crystal growth step and forms a current block layer for current narrowing, and a p-type substrate is used. However, it differs from 1st Example in the following point.

That is, in the semiconductor laser 100A, as shown in Fig. 7, a plurality of second stripe portions 110 having a narrower width are formed in the stripe portion 100a in the resonator direction from the center portion 100c thereof.

That is, in the semiconductor laser 100A, as shown in Fig. 9, the center portion 100c of the stripe portion 100a has an array type SDH structure.

In such a structure, the entire stripe portion in the center of the resonator is not activated. In other words, no current is injected into the entire region, but there is no problem in the characteristics.

However, if the stripe is separated in all the resonator directions, the application is limited to an array type SHP semiconductor laser. However, in the second embodiment, the second stripe section 111 is formed at the end face 110b of the stripe section 110. ) Are fused to form one wide stripe.

In this way, the stripes are fused at a wide width at the end face, so that the near-field image is uniform light emission.

As described above, since the center portion 110a of the stripe portion 110 is formed in an array type SDH structure, the active layer 103c in the center portion has enhanced migration from both sides as described with reference to FIG. 6. Due to the effect, a thick film of the quantum well active layer is formed.

On the other hand, the film thickness of the active layer 103b in the end face portion 100b has a wide stripe width, so that the migration effect is small and is thinner than the center portion.

Thus, also in this second embodiment, since the thickness of the active layer 103b (FIG. 8) in the cross section 100b is formed thinner than the thickness of the active layer 100c (FIG. 9) in the central portion 100c, When the quantum well structure is used in the cross section 100b as compared with the center portion, the band gap energy Egb may be increased.

As a result, the amount of light absorption of the end surface portion 100b decreases and the heat generation decreases.

That is, the cross section is strengthened.

As described above, according to the second embodiment, it is possible to widen the band gap near the end face while improving the yield and reducing the cost, and there is no fear of causing end face breakage, and furthermore, the reliability is improved and the maximum light is achieved. There is an advantage that the output can be increased.

As described above, according to the present invention, it is possible to widen the band gap near the end face while improving the yield and reducing the cost, and there is no fear of causing end face breakage, and furthermore, the reliability is improved and the maximum light output is increased. There is an advantage that can be planned.

In addition, since the SDH structure is used, a complex structure can be produced by one MOCVD growth.

While the invention has been described with reference to specific embodiments selected for purposes of illustration, those skilled in the art may, of course, make various modifications without departing from the basic concept and scope of the invention.

Claims (8)

On a semiconductor substrate on which a mesa-shaped projection of stripe shape is formed on a main surface of a crystal surface, The first cladding layer of the first conductivity type, the active layer, and the second cladding layer of the second conductivity type have an epitaxial growth layer epitaxially grown, A semiconductor laser having a SDH (Separated Double Heterostructure) structure having a refractive index difference in the transverse direction of the active layer and having a current block layer for current narrowing, The stripe width of the cross section in the resonator direction is set larger than the stripe width of the central portion, The bandgap of the active layer at the cross section is greater than the bandgap of the active layer at the center. Semiconductor laser. The method of claim 1, A semiconductor laser in which the thickness of the active layer at the cross section is thinner than the thickness of the active layer at the center. On a semiconductor substrate having a stripe mesa protrusion formed on the main surface of the crystal plane, The first cladding layer of the first conductivity type, the active layer, and the second cladding layer of the second conductivity type have an epitaxial growth layer epitaxially grown, A semiconductor laser having an SDH structure having a refractive index difference in a lateral direction of the active layer and having a current block layer for current narrowing, The stripe portion includes a plurality of second stripe portions narrower in width than the resonator direction. Semiconductor laser. The method of claim 3, And the second stripe portion is formed in the center portion in the resonator direction, and the second stripe portion is fused in the cross-section portion to form one wide stripe. The method of claim 3, A semiconductor laser in which the bandgap of the active layer in the cross section is larger than the bandgap of the active layer in the center. The method of claim 4, wherein A semiconductor laser in which the bandgap of the active layer in the cross section is larger than the bandgap of the active layer in the center. The method of claim 5, A semiconductor laser in which the thickness of the active layer at the cross section is thinner than the thickness of the active layer at the center. The method of claim 6, A semiconductor laser in which the thickness of the active layer at the cross section is thinner than the thickness of the active layer at the center.