JP4885688B2 - Semiconductor laser device - Google Patents

Description

  The present invention relates to a DVD / CD semiconductor laser device, and more particularly to a two-wavelength semiconductor laser device having a surge protection circuit.

In recent years, reproducible DVD / CD has become widespread all over the world and has become an indispensable technology in AV and storage devices. A semiconductor laser is used for reading DVD / CD, and the wavelength is properly selected according to various media.
Usually, a 650 nm band red semiconductor laser is used for DVD, and a 780 nm band infrared semiconductor laser is used for CD. From the viewpoint of cost reduction and the reduction in the number of parts, the 650 nm band and 780 nm band semiconductor lasers are combined into one package. Embedded two-wavelength semiconductor lasers are the mainstream.

However, so-called short-wave semiconductor lasers in the 650 nm band and the 780 nm band are vulnerable to electrical stress such as surge current. One of the causes is largely due to a destruction phenomenon peculiar to a short-wave semiconductor laser device, that is, COD (Catalytic Optical Damage). COD is a phenomenon in which, when a surge voltage or the like is applied, light exceeding the maximum rating is emitted by applying an excessive current in the forward direction, and the light emitting end face portion that has become high temperature is destroyed.
Recording DVD / CD semiconductor lasers that are used with large light output suppresses heat generation by reducing light absorption, such as by providing a window structure at the light emitting end face, and has a sufficient margin for the light output level at which COD occurs. It is However, in a semiconductor laser used in a reproducible DVD / CD having a small light output, the light emitting end face part only forms a protective film on the end face after cleaving the crystal. Therefore, as one of measures for preventing COD due to surge current, a technique of providing a protection circuit in a semiconductor laser is known.

  An example of a technique in which a protection circuit is provided in a two-wavelength semiconductor laser device is disclosed in Patent Document 1. A protective circuit is provided only in the semiconductor laser chip of 650 nm band having a weaker surge resistance, and the surge withstand voltage as an apparatus is improved. As the protective element, a thyristor formed by laminating two semiconductor laser layers is formed in a laser chip and connected in parallel to a 650 nm band semiconductor laser. Patent Document 2 discloses a semiconductor laser chip provided with a protection circuit in parallel. The device configuration is such that a protection circuit including a normal diode and a Zener diode is formed on a Si heat sink, and one semiconductor laser is mounted. In addition, Patent Document 3 discloses a configuration of a protection circuit using LEDs.

JP-A-2005-217381 JP 05-102602 A Japanese Patent No. 3787648

  In Patent Document 1, a thyristor layer formed by laminating two semiconductor laser layers is used as a protective element and integrated on a laser chip. Inevitably, the thyristor layer is thicker than the semiconductor laser layer from the substrate. From the viewpoint of heat dissipation, it is usually mounted on a heat sink by so-called junction down. However, in the above configuration, irregularities are formed on the laser chip. An assembly process is required, which increases the cost of the apparatus.

  By the way, the protection circuit must be turned on at a voltage somewhat higher than the operating voltage of the semiconductor laser in a normal operation. On the other hand, a simple configuration of the protection circuit is easier to manufacture and is advantageous in terms of cost. In particular, a two-wavelength semiconductor laser device used for a DVD / CD device has a strong demand for cost reduction, and low cost is important. As in Patent Document 2, in a circuit configuration in which a normal diode and a Zener diode are connected one by one, different elements are used, so that the manufacturing process becomes complicated and the cost reduction of the apparatus is limited. As in Patent Document 1, if a thyristor is used, a high turn-on voltage can be realized even in one stage. However, since the thyristor has a pnpn structure, the structure is more complicated than a diode, and the cost reduction of the device is limited.

The two-wavelength semiconductor laser device of the present invention includes a first semiconductor laser and a protection circuit connected in parallel with the first semiconductor laser, and the protection circuit has a second surge breakdown voltage higher than that of the first semiconductor laser. A semiconductor laser is provided.

  According to the present invention, a low-cost two-wavelength semiconductor laser device including a protection circuit is realized.

Next, a preferred embodiment of a two-wavelength semiconductor laser device according to the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a circuit diagram of a two-wavelength semiconductor laser device 10 showing a first embodiment of the present invention. The protection circuit 12 is connected in parallel to the first semiconductor laser 11, and the protection circuit includes a second semiconductor laser 13. The protection circuit 12 includes a two-stage diode 14 having the same pn junction structure as that of the second semiconductor laser 13. The second semiconductor laser 13 has a surge withstand voltage higher than that of the first semiconductor laser 11. The p-side terminal / n-side terminal of the diode 14 is connected to the p-side of the first semiconductor laser 11 and the p-side terminal of the second semiconductor laser 13, respectively. Further, current introduction portions 15 and 16 for introducing an operating current are provided on the p-side terminal of the first semiconductor laser 11 and the p-side terminal of the second semiconductor laser 13, respectively. Further, an n-side common terminal 17 is provided by connecting the n-side terminal of the first semiconductor laser 11 and the n-side terminal of the second semiconductor laser 13. The forward rising voltage of the protection circuit 12 is higher than the operating voltage of the first semiconductor laser 11. The reverse breakdown voltage of the diode 14 is higher than the forward surge breakdown voltage of the second semiconductor laser 13. Further, the resistance of the protection circuit 12 is smaller than the resistance of the first semiconductor laser 11.

  FIG. 2 is a perspective view of the two-wavelength semiconductor laser device 10 according to the first embodiment of the present invention, and FIG. 3 is a cross-sectional view taken along A-A ′ of FIG. Two n-type regions 22 are provided on the surface of the p-type Si substrate 21 serving as a heat sink, and a p-type region 23 is provided in the n-type region 22 to form two diodes 14 having the same pn junction structure. It is included. A first electrode 25 and a second electrode 26 are provided on the Si substrate 21 via an insulating film 24. Each of the first electrode 25 and the second electrode 26 is connected to the p region 23 / n region 22 through a contact hole opened in the insulating film 24, and is connected to the p-side terminal / It is an n-side terminal. In addition, the diode 14 is disposed at a position straddling the first electrode 25 and the second electrode 26, and the diodes 14 are connected by a wiring 27 through a contact hole opened in the insulating film 24. . The first electrode 25 and the second electrode 26 are respectively connected via a solder 28 to a p-side electrode 29 serving as a p-side terminal of the first semiconductor laser 11 and a p-side terminal serving as a p-side terminal of the second semiconductor laser 13. The side electrode 30 is fused. The first semiconductor laser 11 and the second semiconductor laser 13 are fused by so-called junction down. The first semiconductor laser 11 and the second semiconductor laser 13 are integrated in one chip on a semiconductor substrate 31 made of GaAs, and an n-side electrode 32 serving as a common n-side terminal is provided. The first electrode 25 and the second electrode 26 are current introduction portions for applying operating currents of the first semiconductor laser 11 and the second semiconductor laser 13, respectively, and a wire 33 is bonded thereto. A wire 33 is also bonded to the n-electrode side 33.

Next, the manufacturing process of the two-wavelength semiconductor laser device showing the first embodiment of the present invention will be described. An n-type impurity is thermally diffused in a p-type Si substrate 21 serving as a heat sink to form two n-type regions 22. For example, phosphorus, arsenic, or antimony is used as the n-type impurity. A p-type region 23 is formed by thermally diffusing a high-concentration p-type impurity in the n-type region 22, thereby forming the diode 14. For example, boron is used as the p-type impurity. The diode 14 has a pn junction carrier profile so that its reverse breakdown voltage is higher than the forward surge breakdown voltage of the second semiconductor laser 13. Next, an insulating film 24 is formed on the Si substrate 21. For example, the insulating film 24 is preferably silicon oxide, silicon nitride, titanium oxide, aluminum oxide, or aluminum nitride, and is formed with a thickness of at least 10 nm. Next, a contact hole is formed in the insulating film 24 on the p region 23 and the n region 22, a first electrode 25 and a second electrode 26 are formed on the insulating film 24, and The electrode 25, the n region 23, and the second electrode 26 are connected to each other.
Next, the p-side electrode 29 of the first semiconductor laser 11 and the p-side electrode 30 of the second semiconductor laser 13 are batched, and solder 28 is applied to the first electrode 25 and the second electrode 26, respectively. Fusing through. For example, a gold-tin alloy is used for the solder 28. Next, wires 33 are bonded to the first electrode 25, the second electrode 26, and the n-electrode 31, respectively. Although not shown in the figure, the Si substrate 21 is mounted on a submount or a stem, and the wire 33 is connected to an external circuit.

Next, the effect of this embodiment will be described. As described above, the protection circuit 12 includes the diode 14 having the same pn structure and the second semiconductor laser 13. The diode 14 is simply formed on the Si substrate 21 by two impurity diffusions and has a two-stage configuration, and the element structure, circuit configuration, and manufacturing process are simple. Further, the second semiconductor laser 13 is used as a part of the protection circuit 12, and circuit connection with the diode 14 is also performed together with the first semiconductor laser 11. Therefore, although the protection circuit 12 includes two types of diodes, this does not increase the manufacturing process or complicate the manufacturing process. In addition, since the number of diodes can be reduced, that is, the number of elements can be reduced as compared with the case where the protection circuit is formed with only the diodes, the manufacturing cost can be reduced. Furthermore, since the first semiconductor laser 11 and the second semiconductor laser 13 have substantially the same crystal growth thickness and the height of the fusion surface is uniform, a special configuration or special assembly is used for the heat sink during fusion. I don't need a method.
The diode 14 is disposed at a position straddling the first electrode 25 and the second electrode 26. In this arrangement, when the semiconductor substrate 31 is covered, a part of the light output of the first semiconductor laser 11 or the second semiconductor laser 13 is prevented from entering the diode 14 as stray light. Therefore, it is possible to prevent generation of photocurrent due to stray light entering the diode 14 and to prevent the operation of the first semiconductor laser 11 or the second semiconductor laser 13 from becoming unstable. In addition, the size of the Si substrate 21 serving as a heat sink can be minimized. Note that the diode 14 may be disposed at a position where the semiconductor substrate 31 is covered, and therefore may be disposed in a direction perpendicular to the paper surface in FIG.
Since the Si diode 14 has a two-stage configuration, its forward rise voltage is 0.6Vx2 = 1.2V, and the forward rise voltage of the second semiconductor laser 13 which is a 780 nm band semiconductor laser is 1.4V. The forward rising voltage of the protection circuit 12 is 2.6V. On the other hand, the first semiconductor laser 11 which is a 650 nm band semiconductor laser has an operating voltage of about 2.3 V in the case of a small optical output used for reading a DVD, and the conditions under which the first semiconductor laser 11 operates normally. Below, no current flows into the protection circuit.

  When an excessive voltage exceeding the rising voltage of the protection circuit 12 is applied to the first semiconductor laser 11 due to a surge in the forward direction, the excessive current applied thereby is shunted to the protection circuit, and effectively the first The surge breakdown voltage of the semiconductor laser 11 is improved.

  By the way, in general, a 650 nm band semiconductor laser is composed of an AlGaInP-based material, and a 780 nm band semiconductor laser is composed of an AlGaAs-based material, and the 780 nm band semiconductor laser is more resistant to ESD due to the difference in electric resistance and thermal resistance. In fact, according to an ESD (Electro-Static-Discharge) test using a man-machine model, the 780 nm band semiconductor laser has an ESD breakdown voltage, that is, a surge breakdown voltage of 100 V or more, whereas the 650 nm band semiconductor laser has only about 50 V. Make sure that there is.

  Therefore, in this embodiment, since the second semiconductor laser 13 having a surge withstand voltage higher than that of the first semiconductor laser 11 is used as a part of the protection circuit 12, the surge breakdown voltage of the first semiconductor laser 11 is less than or equal to The second semiconductor laser 13 is not destroyed.

Conversely, under the condition that the second semiconductor laser 13 operates normally, the diode 14 is reverse-biased, so that no current flows into the first semiconductor laser 11. Further, even when an excessive voltage is applied to the second semiconductor laser 13 due to a surge in the forward direction, the reverse breakdown voltage of the diode 14 is higher than the forward surge breakdown voltage of the second semiconductor laser 13. An excessive current applied to the semiconductor laser 13 does not flow into the first semiconductor laser 11.
In the present embodiment, the surge withstand voltage of the second semiconductor laser 13 is maintained, and the surge withstand voltage of the first semiconductor laser 11 is effectively improved from 50 V to 80 V, thereby providing a two-wavelength semiconductor laser device. The surge withstand voltage was greatly improved from 50V to 80V.
(Second embodiment)
FIG. 4 is a perspective view of the two-wavelength semiconductor laser device 40 of the second embodiment. In this embodiment, a light output monitor photodiode 41 for monitoring the laser output is formed on the Si substrate 21, and the monitor output is taken out from the wire 43. Since other configurations are the same as those of the first embodiment, detailed description thereof is omitted. Therefore, the effect in the configuration / operation of the protection circuit is the same as that described in the first embodiment.
In the present embodiment, for example, unlike Patent Document 2, since the diode 14 is formed in a region straddling the first electrode and the second electrode 26, the light output monitor photodiode 41 is located in the immediate rearward direction of the laser. This has the advantage that a sufficient monitor current can be obtained. Compared with the first embodiment, for example, the n-type impurity is thermally diffused simultaneously to form the pn junction region of the photodiode 41 when the n-type region is formed. If the n-side electrode 42 of 41 is also formed at the same time when the electrode of the diode 14 is formed, the number of processes will not increase.
Note that the number of stages of the diodes 14 is not limited to two, and when the operating voltage of the first semiconductor laser 11 and the forward rising voltage of the second semiconductor laser 13 are different from those of the present embodiment, the above-described embodiment is used. What is necessary is just to decide suitably according to the main point of. In addition, although the first semiconductor laser 11 and the second semiconductor laser 13 are examples of semiconductor lasers in the 650 nm band and the 780 nm band, it goes without saying that lasers in other wavelength bands can also be configured.

  As an application example of the two-wavelength semiconductor laser device of the present invention, there is a DVD / CD semiconductor laser device.

The circuit diagram of the two-wavelength semiconductor laser device of the first embodiment of the present invention 1 is a perspective view of a two-wavelength semiconductor laser device according to a first embodiment of the present invention. A-A 'sectional view of FIG. The perspective view of the two-wavelength semiconductor laser device of the second embodiment of the present invention

Explanation of symbols

10: two-wavelength semiconductor laser device 11: first semiconductor laser 12: protection circuit 13: second semiconductor laser 14: diode 15, 16: current introduction part 17: common terminal 21: Si substrate 22: n-type region 23: p-type region 24: insulating film 25: first electrode 26: second electrode 27: wiring 28: solder 29: p-side electrode 30: p-side electrode 31: semiconductor substrate 32: n-side electrode 33: wire 41: light Output monitor photodiode 42: n-side electrode 43: wire

Claims (9)

A first semiconductor laser, and a protection circuit connected in parallel with the first semiconductor laser,
The protection circuit includes a second semiconductor laser having a surge breakdown voltage higher than that of the first semiconductor laser and a diode having a pn junction structure ,
The diode has a p-type terminal connected to the p-type terminal of the first semiconductor laser and an n-type terminal connected to the p-type terminal of the second semiconductor laser,
The p-type terminal of the diode and the p-type terminal of the first semiconductor laser are connected to a first current introduction unit that introduces an operating current of the first semiconductor laser,
The semiconductor is characterized in that the n-type terminal of the diode and the p-type terminal of the second semiconductor laser are connected to a second current introducing portion for introducing an operating current of the second semiconductor laser. Laser device. The diode has a structure in which a plurality of diode elements having the same pn junction structure are connected in series ,
The p-type terminal of the diode element closest to the first semiconductor laser is connected to the first current introduction unit;
2. The semiconductor laser device according to claim 1, wherein the n-type terminal of the diode element closest to the second semiconductor laser is connected to the second current introduction unit . 3. The semiconductor laser device according to claim 1, wherein a forward rising voltage of the protection circuit is higher than an operating voltage of the first semiconductor laser. Reverse breakdown voltage of the diode, and wherein the higher than a forward surge resistance of the second semiconductor laser, a semiconductor laser device according to claims 1 to 3. Comprising a Si heat sink, the diodes, characterized in that it is built into the heat sink, the semiconductor laser device according to claims 1 to 4. The heat sink includes a first electrode and a second electrode for mounting the first semiconductor laser and the second semiconductor laser, and the diode is connected to the first electrode and the second electrode. The semiconductor laser device according to claim 5 , wherein the semiconductor laser device is disposed in a straddling position. The heat sink is characterized in that the optical output monitor photo diode is fabricated, the semiconductor laser device according to 6 the preceding claims 5. It said first semiconductor laser is 650nm band semiconductor laser, a semiconductor laser device according to claims 1 to 7, characterized in that said second semiconductor laser is 780nm band semiconductor laser. Wherein the first semiconductor laser and said second semiconductor laser is characterized in that it is a one-chip integrated semiconductor laser device according to claims 1 to 8.

Images