JP4138731B2 - Semiconductor laser device and manufacturing method thereof - Google Patents

Description

  The present invention includes DVD-RAM (digital versatile disk random access memory), DVD-R (digital versatile disk recordable), DVD-RW (digital versatile disk rewritable), DVD + R, DVD + RW, CD-R (compact disk recordable), CD-RW, DVD-ROM (digital versatile disk read only memory), CD-ROM, DVD-Video and CD-DA, etc., or semiconductors used for optical information processing, optical communication, optical measurement, etc. The present invention relates to a laser device and a manufacturing method thereof.

  An AlGaInP red laser having a wavelength of 650 nm is used as a read / write pickup light source such as a DVD-RAM. On the other hand, an AlGaAs infrared laser having a wavelength of 780 nm band is used as a pickup light source for reading and writing such as CD-R. In order to support both of these disks, both a red laser and an infrared laser are required for one drive. Therefore, a drive provided with two optical integrated units for DVD and CD is generally popular.

  However, due to recent demands for miniaturization, cost reduction, and simplification of the optical system assembly process, a dual wavelength laser in which two lasers are integrated on the same substrate has been put into practical use so that it can be handled by one optical integrated unit. It's getting on. The following patent document 1 is mentioned as a conventional example of such a two-wavelength laser. This is a monolithically integrated 650 nm band AlGaInP red laser and 780 nm band AlGaAs infrared laser on a GaAs substrate, and an optical pickup having both DVD / CD lasers on one optical integrated unit. Has proposed.

  A dual wavelength laser, like a conventional laser, forms a resonator by cleavage. Since the cavity length is determined by the cleavage positions at both ends, the cavity lengths of the red laser and the infrared laser are necessarily the same. Cavity length is one of the parameters that affect laser characteristics such as maximum light output, oscillation threshold current, and efficiency. In the case of a dual wavelength laser, the cavity length is optimized independently for the red laser and infrared laser. There was a restriction that it was not possible.

For example, in a laser in which a high-power red laser and a high-power infrared laser are monolithically integrated, when trying to realize a high output of 200 mW with a red laser, the resonator length is practically required to be at least 900 μm or more. However, when the cavity length of the infrared laser is 900 μm or more, the operating current is greatly increased as compared with the conventional laser, and there are concerns about adverse effects such as an increase in power consumption and promotion of element deterioration due to heat generation. Under such circumstances, it may be difficult to increase the output of the dual wavelength laser.
JP 2000-11417 A

  In order to solve the above-mentioned conventional problems, the present invention can independently control the effective resonator length, that is, the length of the active layer that contributes to laser oscillation in the resonator direction. Provided are a semiconductor laser device of a two-wavelength laser capable of improving the laser characteristics by setting an optimum resonator length for each laser, and a method for manufacturing the same.

A semiconductor device according to the present invention includes a plurality of resonators formed in parallel to each other on a substrate and having the same resonator length, an active layer formed on the plurality of resonators, and near both end faces of the plurality of resonators. And a current injection region formed in the plurality of resonators and having different lengths from each other .

  The dual wavelength laser according to the present invention adopts a structure that prevents current injection into the active layer in a partial region from the end face of one or both lasers toward the center of the resonator, thereby providing an effective resonator length, That is, the length of the active layer contributing to laser oscillation in the resonator direction can be independently controlled. As a result, the optimum resonator length is set for each of the red and infrared lasers, and the laser characteristics can be improved.

  In the present invention, if the length of the resonator in the region where the current of the active layer is injected is 1000 μm for the red laser and 700 μm for the infrared laser, the desired operating current, light output, and temperature characteristics are obtained. The device it has can be realized.

  In the present invention, “two resonators are parallel to each other” is preferably parallel within a range of ± 1 degree or less.

  The at least one active layer is preferably composed of a quantum well. The quantum well structure has the same effect as a conventional laser in reducing the operating current density by increasing the light emission efficiency for injected carriers. In addition, the quantum well structure allows crystal disorder when Zn diffusion is applied. If this is applied to the non-gain region (region where no current is injected) of the element with the shorter effective resonator length, the deterioration of characteristics such as an increase in operating current due to light absorption can be prevented. it can.

  In a part of the region from one or both end faces of the at least one resonator toward the center of the resonator, a region where no current is injected into the active layer is formed, and the length of this region is between the two resonators. It is preferable that the lengths of the active layers in the direction of the resonator are different from each other because they are different from each other. Because the red laser has lower carrier confinement and higher thermal resistance than the infrared laser, so the optical output limit due to thermal saturation is low, so the output length is increased by improving the end face reflectance loss and heat dissipation by increasing the cavity length. It is necessary to improve the temperature characteristics. On the other hand, when the infrared laser is lengthened to the same cavity length as that of the red laser, the operating current is greatly increased as compared with the conventional single laser due to the increase of the light emitting area.

  The band gap energy of the semiconductor layer in the region where the propagation light exists in the region where no current is injected into the active layer is preferably larger than the energy of the active layer emission wavelength. This is because, if the band gap of the region is smaller than the energy of the active layer emission wavelength, light absorption occurs, leading to deterioration of characteristics such as increase in threshold current, operating current, and decrease in light output.

The two active layers are respectively (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) and Al _z Ga _1-z As (0 ≦ z ≦ 1). The wavelengths obtained from the two active layers are preferably 630 nm to 690 nm and 760 nm to 810 nm, respectively. This is because laser light in the above-described wavelength band is necessary for reading and writing data on DVD optical disks and CD optical disks, respectively.

  It is preferable that each maximum light output from one end face obtained from the two active layers is 80 mW or more. The above is the optical output required to write data on the optical disc at about twice the speed or higher.

  Widening the band gap of at least a part of the quantum well active layer from one or both end faces of the at least one resonator toward the center of the resonator by disordering by impurity diffusion or impurity implantation, and current The semiconductor layer or the electrode corresponding to the current injection path is partially removed, and the length from the end face to which the above process is performed to the center of the resonator is mutually reduced by the two resonators. Preferably they are different. By adopting such a manufacturing method, it is possible to precisely control the light emitting end face position interval, and it is possible to form an element having an optimum resonator length for each.

Each of the at least two active layers is composed of a layer containing (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). The light output of the element having the higher maximum light output is preferably 50 mW or more, and the operating current of the element having the lower maximum light output is preferably 35 mA or less at the light output of 2 mW or more. A conventional optical disc that performs both writing and reading with a single high-power laser by using one element as a high-power laser that can write to the disc and the other as a low-power laser that can read the disc with a low operating current. Since the power consumption when reading data can be reduced from the device, it is easier to deploy to products such as portable DVDs.

  According to the present invention, in a two-wavelength laser, the effective resonator lengths of a plurality of lasers having different characteristics such as an infrared laser and a red laser are independently designed and manufactured, exceeding the resonator length limitation determined by cleavage. Therefore, by adopting a resonator length suitable for each desired characteristic, it is possible to improve each laser characteristic.

  Embodiments of the present invention will be described below.

(Embodiment 1)
1A to 1C and FIG. 2 show a dual-wavelength high-power laser having an optical output of 200 mW according to Embodiment 1 of the present invention, FIG. 1A is a plan view thereof, and FIG. 1B is a cross-sectional view taken along the line II of FIG. 1C is a sectional view taken along line II-II in FIG. 1A, and FIG. 2 is a perspective view thereof. The same reference numbers indicate the same material or part.

FIGS. 3A to D, FIGS. 4A to B ′, and FIGS. 5A to 5D are cross-sectional views (however, FIGS. 4A ′ and 4B ′ are plan views) showing the manufacturing process of the semiconductor laser according to the first embodiment of the present invention. . Here, a description will be given along the manufacturing process of FIGS.
(1) As shown in FIG. 3A, an infrared laser n-type cladding layer 102, an infrared laser active layer 103, and an infrared laser p-type cladding layer 104 are sequentially stacked on an n-type GaAs substrate 101. The infrared laser active layer 103 has a quantum well structure.
(2) As shown in FIG. 3B, the infrared laser n-type cladding layer 102, the infrared laser active layer 103, and the infrared laser p-type cladding layer 104 are removed in a part of the region including the red laser region.
(3) As shown in FIG. 3C, a red laser n-type cladding layer 105, a red laser active layer 106, and a red laser p-type cladding layer 107 are sequentially stacked. The red laser active layer 106 has a quantum well structure.
(4) As shown in FIG. 3D, the red laser n-type cladding layer 105, the red laser active layer 106, and the red laser p-type cladding layer 107 are removed in a part of the region including the infrared laser region.
(5) As shown in FIG. 4A, the zinc oxide film 301 extends from the both end faces of the red laser p-type cladding layer 107 to a region of 10 μm and from the end face of the infrared laser p-type cladding layer 104 to regions of 10 μm and 310 μm, respectively. Form.
(6) As shown in FIG. 4B, Zn is diffused in the active layer immediately below each of the 202, 203, 205, and 206 regions where the zinc oxide film is formed by heating. By this step, the band gap is expanded by disordering the heterojunction between the quantum well layer forming the active layer and the adjacent barrier layer. This region is transparent to the wavelength emitted from the active layer. After the heating, the zinc oxide film is removed. The lengths of the regions 201 and 204 are 680 μm and 980 μm, respectively.
(7) As shown in FIG. 5A, the infrared laser p-cladding layer 104 and the red laser p-cladding layer 107 are partially etched to form striped mesa structures. The width of the mesa is 1 μm at the top and 3 μm at the bottom.
(8) As shown in FIG. 5B, selective regrowth of the current blocking layer 108 is performed.
(9) As shown in FIG. 5C, regrowth of the contact layer 109 is performed. (10) As shown in FIG. 5D, the vicinity of the boundary between the infrared laser and the red laser is etched to the substrate 101 to perform element isolation. P-side electrodes 110 and 111 are formed on a region excluding 202 and 203 on the infrared laser and on a region excluding 205 and 206 on the red laser, respectively. Further, an n-side electrode 112 is deposited under the substrate to form an element.

  The material, conductivity type, film thickness, and carrier concentration of each layer are as shown in Table 1 below.

(Remarks) * 1 Mesa internal 1.4μm, mesa external 0.2μm
* 2 This is the thickness of the region grown in the direction perpendicular to the substrate.

  The feature of the present invention is that the lengths of the infrared laser current injection region 201 and the red laser current injection region 204 in the cavity direction are different.

  In the case of a conventional dual wavelength laser, the cavity lengths of the infrared laser and the red laser are the same. FIG. 6 shows current-light output characteristics of a red laser and an infrared laser of a dual wavelength laser each having a cavity length of 700 μm. The red laser cannot obtain the desired light output due to thermal saturation near 180 mW. In order to obtain an optical output of 200 mW or more, it is necessary to increase the cavity length of the red laser.

  On the other hand, FIG. 7 shows current-light output characteristics of a red laser and an infrared laser of a two-wavelength laser each having a cavity length of 1000 μm. Although both the infrared laser and the red laser obtain an optical output of 200 mW or more, the operating current of the infrared laser increases as the active layer volume increases as compared with a laser having a cavity length of 700 μm. Due to this increase in power consumption, the battery operable time when mounted on a portable device driven by a battery is shortened compared to a device using a single laser.

In this embodiment, the effective resonator lengths of the infrared laser and the red laser are 680 μm and 980 μm, respectively. In the infrared laser, the actual cavity length is 1000 μm, but the region where current is not injected is provided 310 μm from the end surface and 10 μm from the other end surface, and does not contribute to light emission in that region, and the quantum well activity Since the band gap is widened by layer disorder, no waveguide loss due to light absorption occurs. As a result, as shown in FIG. 8, while the optical output of the red laser achieves 200 mW, the operating current of the infrared laser shows a value comparable to an element having a resonator length of 700 μm. The red laser is also provided with a 10 μm current non- injection region and an active layer disordered region on both end faces, which are provided to avoid optical breakdown due to light absorption at the end faces.

(Embodiment 2)
9A is a plan view of a high-power / low-power integrated red laser according to Embodiment 2 of the present invention, FIG. 9B is a cross-sectional view taken along line III-III in FIG. 9A, and FIG. 9C is a cross-sectional view taken along line IV-IV in FIG. .

FIGS. 10A to 10E are cross-sectional structure diagrams illustrating the manufacturing steps of the semiconductor laser according to the second embodiment of the present invention. Here, it demonstrates along the manufacturing process of FIG. 10A-E.
(1) As shown in FIG. 10A, a low-power laser n-type cladding layer 402, an active layer 403, and a p-type cladding layer 404 are sequentially stacked on an n-type GaAs substrate 401. The active layer 403 has a quantum well structure. In the present embodiment, the n-type cladding layer 405, the active layer 406, and the p-type cladding layer 407 of the high-power laser are also used as the respective layers.
(2) As shown in FIG. 10B, part of the p-type cladding layers 404 and 407 are etched to form a ridge-type waveguide.
(3) As shown in FIG. 10C, parts of the p-type cladding layers 404 and 407 are further etched up to the substrate 401 , and element separation of the low-power laser and the high-power laser is performed. In this embodiment, the resonator width is made smaller than that of the high-power laser in order to reduce the operating current of the low-power laser.
(4) As shown in FIG. 10D, Zn diffusion is applied to the active layer immediately below the regions indicated by 502, 503, 505, and 506 in FIG. The lengths of the regions 501 and 504 in FIG. 9 are 480 μm and 980 μm, respectively.
(5) As shown in FIG. 10E, a p-side electrode 408 and an n-side electrode 409 are formed.

  The current-light output characteristics of this element are shown in FIG. The high-power laser achieves an optical output exceeding 200 mW, while the low-power laser realizes the 10 mW optical output required for readout with a low operating current of about 20 mA.

  Conventional high-power red lasers for rewritable DVDs have a long resonator length, so the operating current during low-power operation for reading data is higher than that for low-power red lasers with a short read-only resonator length. End up. However, as shown in this embodiment, two red lasers with different effective resonator lengths are monolithically integrated, a high-power laser with a long resonator length is used for data writing, and a low-power laser with a short resonator length is used for data reading. This makes it possible to realize an optical pickup that consumes less power than before in data reading without degrading data writing performance.

  As described above, the present invention is not limited to the dual wavelength laser but can be applied to monolithic integration of the same wavelength band laser.

1A is a cross-sectional view of a dual wavelength laser according to Embodiment 1 of the present invention, FIG. 1B is a cross-sectional view taken along the line II of FIG. 1A, and FIG. 1C is a cross-sectional view taken along the line II-II of FIG. FIG. 2 is a perspective view of the dual wavelength laser according to Embodiment 1 of the present invention. 3A to 3D are cross-sectional views illustrating a manufacturing process of the dual wavelength laser according to Embodiment 1 of the present invention. 4A-B are cross-sectional views of the manufacturing process of the dual wavelength laser according to Embodiment 1 of the present invention, and FIGS. 4A'-B 'are plan views thereof. 5A to 5D are cross-sectional views illustrating a manufacturing process of the dual wavelength laser according to Embodiment 1 of the present invention. FIG. 6 is a current-light output characteristic diagram of a dual wavelength laser having a resonator length of 700 μm. FIG. 7 is a current-light output characteristic diagram of a dual wavelength laser with a resonator length of 1000 μm. FIG. 8 is a current-light output characteristic diagram of the dual wavelength laser according to Embodiment 1 of the present invention. 9A is a plan view of a high-power and low-power red laser monolithic integrated chip according to Embodiment 2 of the present invention, FIG. 9B is a cross-sectional view taken along line III-III of A, and FIG. 9C is a cross-sectional view taken along line IV-IV of A. 10A to 10E are cross-sectional views showing a manufacturing process of a high-power and low-power red laser monolithic integrated chip according to Embodiment 2 of the present invention. FIG. 11 is a current-light output characteristic diagram of the dual wavelength laser according to Embodiment 2 of the present invention.

Explanation of symbols

101, 401 Substrate 102 Infrared laser n-type cladding layer 103 Infrared laser active layer 104 Infrared laser p-type cladding layer 105 Red laser n-type cladding layer 106 Red laser active layer 107 Red laser p-cladding layer 108 Current blocking layer 109 Contact Layer 110 Infrared laser p-side electrode 111 Red laser p-side electrode 112, 410 n-side electrode 201 Infrared laser current injection region 202 Infrared laser front end surface side current non-injection region 203 Infrared laser rear end surface side current non-injection region 204 Red laser current injection region 205 Red laser front end face side current non-injection region 206 Red laser rear end face side current non-injection region 301 Zinc oxide film 402 Low power red laser n-type cladding layer 403 Low power red laser active layer 404 Low power red laser p-type cladding layer 405 high power red laser n-type cladding layer 406 high power Red laser active layer 407 High output red laser p cladding layer 408 Low output red laser p side electrode 409 High output red laser p side electrode 501 Low output red laser current injection region 502 Low output red laser front end side current non-injection region 503 Low Output red laser rear end face side current non-injection area 504 High output red laser current end injection area 505 High output red laser front end face side current non-injection area 506 High output red laser rear end face side current non-injection area

Claims (8)

A plurality of resonators formed in parallel to each other on the substrate and having the same resonator length;
An active layer formed in the plurality of resonators;
Current non-injection regions formed near both end faces of the plurality of resonators;
A semiconductor laser device comprising: current injection regions formed in the plurality of resonators and having different lengths. Even without least semiconductor laser device according to different claims 1 emission wavelength obtained from two of the active layer, respectively. One of the active layer even without least a semiconductor laser device according to configured claim 1 by the quantum well. The semiconductor laser device according to claim 1 , wherein a band gap energy of a semiconductor layer in a region where propagation light exists in the current non-injection region is larger than an energy of an active layer emission wavelength. At least two of the active layers are (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) and Al _z Ga _1-z As (0 ≦ z ≦ 1) is composed of a layer containing the two wavelengths obtained from the active layer is 630nm or more 690nm or less, and a semiconductor laser device according to claim 1 is 760nm or more 810nm or less.   6. The semiconductor laser device according to claim 5, wherein each of the maximum light outputs from one end face obtained from the two active layers is 80 mW or more. The semiconductor laser device according maximum light output obtained from the active layer to 請 Motomeko 1 that different respectively. Each of the at least two active layers is composed of a layer containing (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). 8. The semiconductor laser device according to claim 7 , wherein the light output of the element having the higher maximum light output is 50 mW or more, and the operating current of the element having the lower maximum light output is 35 mA or less at the light output of 2 mW or more.

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