JP2005294633A - Semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a pulsation in a pulsation laser and expand a margin for a temperature and a power band to expand a usable range of the pulsation laser.
A pulsation laser having an active layer and a lower clad layer and an upper clad layer sandwiching the active layer has a refractive index higher than that of the lower clad layer at least in the lower clad layer. A light control layer 32 that largely controls the light distribution is provided.
[Selection] Figure 1

Description

  The present invention relates to a so-called semiconductor light emitting device such as a semiconductor laser mainly composed of a pulsation laser, a multilaser, or an optical integrated circuit.

  As a semiconductor laser for an optical disk, for example, a semiconductor laser (pulsation laser) that operates in a pulsation (self-pulsation) mode capable of suppressing noise generated by light returned to the semiconductor laser in an information reading application has been proposed. (See Patent Documents 1 and 2). This pulsation laser has a SAL type with a saturable absorbing layer (SAL) near the active layer and a weak refractive index difference that realizes an intermediate waveguide guide between the index guide and the gain guide. There is a WI (Weakly Index guide) type in which a saturable absorption region is formed in the active layer during operation.

FIG. 5 shows a schematic configuration of a conventional WI type pulsation laser. In this pulsation laser 1, for example, an n-type buffer layer 3, an n-type cladding layer 4, an active layer 5, a p-type cladding layer 6, an n-type intermediate layer 7 and an n-type contact layer 8 are laminated on an n-type substrate 2. The n-type contact layer 8, the n-type intermediate layer 7, and the p-type cladding layer 6 are mesa-etched over a part thereof, and n-type current blocking layers 9 are formed on both sides of the mesa-etching. An n-electrode 10 is formed on the back surface of the substrate 1, and a p-electrode 11 is formed on the contact layer 8.
In the pulsation laser 1, as shown in FIG. 6, supersaturated absorption regions 14 are formed on both sides of the laser oscillation region 13 in the active layer 3 during operation, and the pulsation operation is performed. The laser oscillation region 13 is formed in a region where the light distribution 16 and the current distribution 15 overlap, and the supersaturated absorption region 14 is formed in a region where the light distribution 16 of the active layer 5 overlaps. In such a pulsation laser 1, as shown in FIG. 6, the light distribution 16 is usually formed close to the p-type cladding layer 6 side.
JP 2001-237491 A JP-A-6-260716

In the pulsation laser, the pulsation operation depends on the temperature and power band (laser output power) of the laser element, and the range in which the pulsation can be stably used, that is, the temperature and power band range to be used is Limited. In the conventional pulsation structure, the pulsation becomes unstable at high temperature, high power, low temperature and low power, and the usable range is limited. For example, when the temperature rises, carriers are generated according to the temperature, and the carriers are also absorbed in the supersaturated absorption region, and the light absorption capacity of the supersaturated absorption region is reduced. Further, when the power is increased, a large amount of current flows, and the spread of the current increases accordingly, and the volume of the supersaturated absorption region decreases. That is, the range of use is limited due to a decrease in light absorption capability.
Therefore, it has been desired to increase the margin for the temperature and power band of the pulsation and expand the range that can be used as a pulsation laser.

  In view of the above, the present invention provides a semiconductor light-emitting device that stabilizes pulsation and increases the margin for temperature and power band to widen the usable range.

  The semiconductor light emitting device according to the present invention has a refractive index larger than that of the lower cladding layer in at least the lower cladding layer of a pulsation laser having an active layer and a lower cladding layer and an upper cladding layer sandwiching the active layer. A light control layer for controlling the light distribution is provided.

According to the present invention, in the semiconductor light emitting device, a light distribution is controlled by the light control layer so as to be closer to the active layer, and a supersaturated absorption region is formed in the active layer.
In the semiconductor light emitting device according to the present invention, a light control layer having a higher refractive index than that of the upper cladding layer and controlling the light distribution is further provided in the upper cladding layer.

  In the semiconductor light emitting device of the present invention, a light control layer having a higher refractive index is provided on at least the lower cladding layer of the pulsation laser, for example, the lower cladding layer, or both the upper cladding layer and the lower cladding layer. As a result, the light distribution during operation is attracted to the lower clad layer side and approaches the active layer. As the light distribution approaches the active layer, the supersaturated absorption region where the active layer overlaps with the light distribution formed on both sides of the laser oscillation region is expanded.

  According to the semiconductor light emitting device of the present invention, the supersaturated absorption region is expanded without changing the current distribution in the pulsation laser, so that the pulsation is stabilized. Thereby, the margin with respect to temperature and a power band can be expanded, and the range which can use a pulsation laser can be expanded. In addition, the degree of freedom in designing the pulsation laser can be expanded.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an embodiment in which a semiconductor light emitting device according to the present invention is applied to a pulsation laser. The pulsation laser 21 according to the present embodiment includes a first conductivity type buffer layer 23, a first conductivity type cladding layer 24, an active layer 25, and a second conductivity type cladding on a first conductivity type semiconductor substrate 22. The layer 26, the second conductivity type intermediate layer 27, and the second conductivity type contact layer 28 are stacked, and mesa etching is performed over part of the second conductivity type contact layer 28, the intermediate layer 27, and the clad layer 26, and the mesa A first conductivity type current blocking layer 29 is formed over both sides of the portion and the upper surface of the second conductivity type cladding layer 26 continuous from the mesa portion. A first conductive side electrode 30 is formed on the back surface of the substrate 22, and a second conductive side electrode 31 is formed so as to extend to the upper surface of the contact layer 28, in this example, the upper surface of the current block layer 29.

  In the present embodiment, the light control layer 32 for controlling the distribution of light formed during operation is formed particularly in the first conductivity type cladding layer 24. The light control layer 32 is formed of a layer having a refractive index larger than that of the first conductivity type cladding layer 24 and is formed of a layer that does not absorb light. The light control layer 32 can be formed over the entire length of the laser 21 in the resonator length direction and the entire width perpendicular to the length. The distance d1 between the light control layer 32 and the active layer 25 and the layer thickness t1 of the light control layer 32 can be set by a control amount that brings the light distribution toward the light control layer 32 side.

In this example, an n-GaAs substrate is used as the substrate 22, and an n-type buffer layer 23 composed of an n-GaAs layer (substrate side) and an n-GaInP layer (cladding layer side) is formed on the n-type substrate 22. — (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer (thickness 1.1 μm) n-type cladding layer 24, Ga _0.5 In _0.5 P layer n-type light control layer 32, n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer (thickness 0.4 μm) n-type cladding layer 24, non-doped Ga _0.5 In _0.5 P layer activity Layer 25, p-type cladding layer 26 of p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer (thickness 0.4 μm), p-Ga _0.5 In _0.5 P layer P-type intermediate layer 27, p-GaAs layer p-type contact layer 28, and n-GaAs layer current blocking layer 29 are formed. Then, an n electrode 30 in which AuGe / Ni / Au is sequentially laminated from the bottom is ohmically connected to the back surface of the n-type substrate 22, and a p electrode 31 in which Ti / Pt / Au is sequentially laminated from the bottom is ohmic connected to the p-type contact layer 28. Connected. Since the optical control layer 32 has a higher refractive index than that of the n-type cladding layer 24, the Al amount in the AlGaInP system can be set to a composition in which the amount of Al is smaller than that of the n-type cladding layer 24 (including 0). .

The active layer may have a multiple quantum well structure (MQW), for example, an MQW formed by repeatedly laminating an AlGaInP layer and a GaInP layer. Moreover, it can also be set as the structure which has a guide layer between an active layer and a clad layer.
Each layer of the pulsation laser 21 is not limited to the above composition, and can be formed with various compositions depending on the purpose, for example, depending on the laser wavelength.

  In the pulsation laser 21 of the present embodiment, a laser oscillation region 43 is formed in a region where the light distribution 41 and the current distribution 42 in the active layer 25 overlap as shown in FIG. Supersaturated absorption regions 44 are formed on both sides of 43, and a pulsation operation is performed. At this time, the light control layer 32 provided in the n-type cladding layer 24 causes the light distribution 41 to be closer to the active layer 25 than the conventional light distribution 16 indicated by a chain line. In other words, in a conventional case, the flat elliptical light distribution 16 may be out of the active layer depending on the layer structure. However, in the present embodiment, the light control layer 32 causes the light distribution 41 to approach the center of the active layer 25, so that both tip portions 41 a exist in the active layer 25 in the light distribution 41. For this reason, the supersaturated absorption region 44 where the light distribution 41 and the active layer 25 overlap is expanded. By widening the supersaturated absorption region 44, the light absorption capability is improved, the pulsation is stabilized, and the use range can be expanded.

  Thus, the light control layer 32 brings the light distribution 41 closer to the center of the active layer 25, so that the difference between the current distribution 42 and the light distribution 41, that is, the region into which carriers are injected (current distribution), The difference between the regions where the current injection is insufficient and the light gain is not obtained (light distribution) becomes large, and the pulsation can be strengthened. FIG. 3 shows γ temperature characteristics when γ is used as a parameter indicating the strength of pulsation. The γ temperature characteristic is measured with a digital video disc (DVD). γ is called coherence and indicates the degree of laser interference, and is defined as follows. Let γ be the second peak when the maximum level of the wavelength data measured with the λ-designated light output 1 is 1. A large γ value means strong interference, and pulsation (self-excited oscillation) becomes weak.

  In FIG. 3, curve I is a pulsation laser having a conventional structure without a light control layer, and curve II is a pulsation laser having a structure of the present invention in which a light control layer is inserted. As the γ value, 0.5 or less is considered desirable. According to FIG. 3, in the pulsation laser 1 having the conventional structure, the γ value greatly exceeds 0.5 at 80 ° C. (high temperature), whereas in the pulsation laser 21 having the structure of the present invention, 80 ° C. (high temperature). Thus, the γ value is suppressed to 0.5 or less.

  According to the pulsation laser 21 according to the present embodiment, pulsation can be stabilized, and a margin for temperature and power band (so-called laser emission power range) can be expanded. Therefore, the range that can be used as a pulsation laser can be expanded. Further, since the margin for the temperature and power band can be expanded, the degree of freedom in designing the pulsation laser can be expanded.

  Incidentally, in the conventional structure of FIG. 5, if the distance between the active layer and the current block layer is increased, the light confinement is weakened and the light distribution is widened to expand the supersaturated absorption region. As a result, the operating current is increased and heat is generated, resulting in poor pulsation. In the present embodiment, the light distribution 41 is suppressed by the light control layer 32 without suppressing the spread of the current distribution 42 without changing the distance L1 between the active layer 25 and the current blocking layer 29, and without excessively widening the light distribution. Since the supersaturated absorption region can be expanded by attracting more to the active layer 25 side, the pulsation can be strengthened without changing the characteristics.

  On the other hand, when applied to a pulsation laser having a light guide layer between the active layer and the clad layer, the static characteristics can be improved by finely adjusting the thickness of the light guide layer, the p-type clad layer, and the volume of the active layer. The pulsation can be strengthened without changing it.

  The pulsation laser 21 according to the embodiment in FIG. 1 described above has a configuration in which the light control layer 32 is provided in the n-type cladding layer 24, but a configuration in which a light control layer is also provided on the p-cladding layer 26 side. be able to.

FIG. 4 shows another embodiment of the pulsation laser according to the present invention in which the light control layer 36 is provided on the n-type cladding layer 24 and the p-type cladding layer 26.
The pulsation laser 35 according to the present embodiment includes a buffer layer 23, a first conductivity type n-type cladding layer 24, an active layer 25, a second conductivity type p-type cladding, etc. It has a layer 26, an intermediate layer 27, a contact layer 28, a current blocking layer 29, and both electrodes 30 and 31. The first light control layer 32 is formed in the n-type cladding layer 24, and the second light control layer 36 is formed in the p-type cladding layer 26. The second light control layer 36 can also be used as an etching stop layer. For example, when each layer is formed with the same composition as described above, the second light control layer 36 can be formed of a Ga _0.5 In _0.5 P layer. The second light control layer 36 is formed of a layer having a refractive index larger than that of the p-type cladding layer 26 and does not absorb light. For example, the second light control layer 36 has the same composition as that of the first light control layer 32 but of a different conductivity type. Can be formed.

That is, in this example, on the n-GaAs substrate 22, an n-type buffer layer 23 composed of an n-GaAs layer (substrate side) and an n-GaInP layer (cladding layer side), n- (Al _0.7 Ga _{0. 3) 0.5} in _0.5 n-type cladding layer ₂₄ of the P _layer, Ga _{0.5 in} 0.5 P n-type optical control layer of the layer 32, n chromatography _{(Al 0.7 Ga 0.3) 0. 5} In _0.5 P layer n-type cladding layer 24, non-doped Ga _0.5 In _0.5 P layer active layer 25, p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P P-type cladding layer 26 of layer, p-type light control layer 36 of Ga _0.5 In _0.5 P layer, p-type of p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer p-type Con cladding layer 26, p chromatography _{Ga 0.5 in} 0.5 P layer p-type intermediate layer 27, p over GaAs layer The n-type GaAs layer is formed on the back surface of the n-type substrate 22, and an n-electrode 30 in which AuGe / Ni / Au is sequentially laminated from the bottom is ohmically connected to the p-type contact layer 28. The p-electrodes 31 in which Ti / Pt / Au are sequentially stacked are ohmically connected.

  According to the pulsation laser 35 according to the present embodiment, the first light control layer 32 provided in the n-type cladding layer 24 and the second light control layer 36 provided in the p-type cladding layer 26. The distribution of light is controlled, and the supersaturated absorption region can be expanded by bringing the light distribution 41 closer to the active layer 25 as in FIG. Therefore, even in this configuration, the pulsation can be stabilized and the margin for the temperature and power band can be expanded. Therefore, the range that can be used as a pulsation laser can be expanded. Further, since the margin for the temperature and power band can be expanded, the degree of freedom in designing the pulsation laser can be expanded.

  FIG. 5 shows still another embodiment of the pulsation laser according to the present invention. In this example, the light control layer 36 is provided in the n-type cladding layer 24 and the p-type cladding layer 26, but the configuration is different from that in FIG. The pulsation laser 37 according to the present embodiment has a buffer layer 23, a first conductivity type, for example, an n-type cladding layer 24, an active layer 25, and a second conductivity type, for example, on the substrate 22 as in FIG. A p-type cladding layer 26, an intermediate layer 27, a contact layer 28, a current blocking layer 29, and both electrodes 30 and 31 are provided. The first light control layer 32 is formed in the n-type cladding layer 24, and the second light control layer 36 is formed in the p-type cladding layer 26.

  In the present embodiment, in particular, the second light control layer 36 and the p-type cladding layer 26, the intermediate layer 27, and the contact layer 28 thereon are formed in a structure in which the width is regulated by the current blocking layer 29. The composition of each layer can be formed, for example, with the same composition as in FIG.

  According to the pulsation laser 37 according to the present embodiment, in the first light control layer 32 and the p-type cladding layer 26 provided in the n-type cladding layer 24 as in the case of the pulsation laser 35 of FIG. The distribution of light is controlled by the provided second light control layer 36, and the supersaturated absorption region can be expanded by moving the light distribution 41 closer to the active layer 25 as in FIG. Therefore, even in this configuration, the pulsation can be stabilized and the margin for the temperature and power band can be expanded. Therefore, the range that can be used as a pulsation laser can be expanded. Further, since the margin for the temperature and power band can be expanded, the degree of freedom in designing the pulsation laser can be expanded.

  The pulsation laser of the present invention can be applied to a laser having a configuration in which a light guide layer is provided between the active layer and the clad layer in addition to the above example.

  In the above-described embodiment, the present invention is applied to a pulsation laser element. In addition, a multi-laser mainly including a pulsation laser, or an optical integrated circuit such as a laser coupler incorporating a pulsation laser, etc. It can also be applied to.

It is a block diagram which shows one Embodiment of the semiconductor light-emitting device based on this invention. It is explanatory drawing with which it uses for operation | movement description of the pulsation laser which is a semiconductor light-emitting device concerning this invention. It is a graph which shows (gamma) temperature characteristic which compared this invention and the conventional pulsation laser. It is a block diagram which shows other embodiment of the semiconductor light-emitting device based on this invention. It is a block diagram which shows other embodiment of the semiconductor light-emitting device concerning this invention. It is a block diagram which shows the example of the conventional pulsation laser. It is explanatory drawing with which it uses for operation | movement description of the conventional pulsation laser.

Explanation of symbols

  21, 35, 37 ..Pulsation laser, 22 ..Substrate, 23 ..Buffer layer, 24 ..n-type cladding layer, 25 ..active layer, 26 ..p-type cladding layer, 27. 28..Contact layer, 29..Electrode block layer, 30, 31..Electrode, 32, 36..Light control layer, 41..Light distribution, 42..Electrode distribution, 43..Laser oscillation region, 44. ..Supersaturated absorption region

Claims (3)

A pulsation laser having an active layer, and a lower clad layer and an upper clad layer sandwiching the active layer,
A semiconductor light emitting device characterized in that at least the lower clad layer is provided with a light control layer having a refractive index larger than that of the lower clad layer and controlling the light distribution. 2. The semiconductor light emitting device according to claim 1, wherein a light distribution is controlled by the light control layer so as to be closer to the active layer, and a saturable absorption region is formed in the active layer. 2. The semiconductor light emitting device according to claim 1, wherein a light control layer having a refractive index larger than that of the upper cladding layer and controlling the light distribution is provided on the upper cladding layer.

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