JP2008066406A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device which is equipped with a built-in photodiode for optical output monitoring and capable of demonstrating its high reliability in spite of a low manufacturing cost. <P>SOLUTION: The semiconductor laser device has a first clad layer 102 formed on a semiconductor substrate 101, an active layer 103 formed on the first clad layer 102, a second clad layer 104 having a ridge structure formed on the active layer 103, and a current block layer 105 which is formed on the second clad layer 104 and composed of a semiconductor different in polarity from that of the second clad layer 104. The current block layer 105 is divided into two regions, one is a first region 105a adjacent to a gain region formed in the ridge structure and the other is a second region 105b which is other than the first region 105a. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device, and more particularly to a high-cost semiconductor laser device incorporating a photodiode for monitoring optical output.

  In recent years, digital information devices using optical disks such as CDs and DVDs are rapidly spreading. A semiconductor laser device is used for reading and writing data on an optical disk, but there is a strong demand for cost reduction of the semiconductor laser device and its peripheral members.

  While the optical output of a semiconductor laser is required to be constant over time, it is actually constant with respect to the drive current due to the effects of element temperature, usage time from the start of use, and element variations. It will not be. Therefore, the drive current is controlled so as to obtain a desired light output while monitoring the light output (Auto Power Control: APC). In addition, when writing data to the optical disc, the laser beam is turned on / off according to the write signal. However, in order to perform stable writing, the tracking of the laser beam output with respect to the write signal is accurately controlled. There is a need to.

  Conventionally, such an optical output monitor has been performed by separately providing a photodiode outside the semiconductor laser, but in particular, the period of the write signal has become shorter with the recent increase in write speed, In order to make the laser beam output follow the write signal that has become a short cycle, the optical output monitor is also required to have higher responsiveness. In order to satisfy such requirements and to reduce the cost of the entire apparatus and ensure high reliability, it has been studied to form a light output monitoring photodiode inside the semiconductor laser element.

  8 and 9 show a conventional semiconductor laser device in which a light output monitoring photodiode is formed inside the device. FIG. 8 is a schematic plan view of a conventional semiconductor laser device, and FIG. 9 is a schematic cross-sectional view of a portion indicated by an alternate long and short dash line FF ′ in FIG.

As shown in FIGS. 8 and 9, the conventional semiconductor laser device 900 includes a first cladding layer 902, an active layer 903, a second cladding layer 904 having a ridge structure on the top, a contact layer 909 on a semiconductor substrate 901. Are sequentially stacked. A portion between the two broken lines shown in FIG. 8 which is a top view is a ridge structure portion. Since the ridge structure is formed by etching the contact layer 909 and the second cladding layer 904 other than the region remaining as the ridge, the contact layer 909 exists only on the ridge. An opening is provided in the center of the portion of the insulating film 910 provided on the second cladding layer 904 and the contact layer 909 formed on the ridge structure, and a metal electrode provided on the insulating film 910 The upper electrode 906 for driving the laser and the contact layer 909 are directly connected. A current is injected into this portion from the upper electrode 906 for driving the laser to become a gain region for oscillating the laser beam. Further, another opening is provided in the peripheral portion of the insulating film 910 formed on the ridge structure (the portion near the right end of the ridge structure in FIGS. 8 and 9), and the insulating film is insulated via this opening. The upper electrode 907 for the photodiode, which is another metal electrode formed on the film 910, and the contact layer 909 are directly connected to each other to form a photodiode portion. In FIG. 8, only the outer shapes of the laser driving upper electrode 906 and the photodiode upper electrode 907 are shown by solid lines so that the planar positional relationship can be easily understood. Further, the insulating film 910 in the portion between the two metal electrodes 906 and 907 is recognized as a portion separating the gain region and the photodiode portion.
JP-A-8-56048

However, in the above conventional configuration, since the laser driving upper electrode 906 and the photodiode upper electrode 907 are both in direct contact with the contact layer 909, the laser driving current from the laser driving upper electrode 106 is the same. Tends to leak to the photodiode side. Conversely, it is conceivable that the current that should flow to the photodiode electrode 907 leaks into the current path for driving the laser. In such a case, not only accurate light output monitoring cannot be performed, but also the laser drive current is lost and the light emission efficiency is lowered.
An object of the present invention is to solve the above-mentioned problems in the prior art and to provide a semiconductor laser device incorporating a photodiode for monitoring optical output, which can obtain high reliability despite low manufacturing cost. And

  In order to solve the above problems, a semiconductor laser device of the present invention is formed on a first cladding layer formed on a semiconductor substrate, an active layer formed on the first cladding layer, and the active layer. A second cladding layer having a ridge structure and a current blocking layer made of a semiconductor having a polarity different from that of the second cladding layer formed on the second cladding layer, wherein the current blocking layer includes the ridge structure. It is divided into two regions, a first region adjacent to the gain region formed in the structure portion and a second region other than the first region.

  In the semiconductor laser device of the present invention, the current blocking layer in a region other than the region adjacent to the gain region of the ridge structure can be used as a photodiode. For this reason, since the current for driving the laser does not leak to the photodiode portion, the semiconductor light emitting device with a built-in light output monitor can be obtained in which the light emission efficiency of the laser does not decrease and the light output monitor current is stable.

  In the semiconductor laser device of the present invention, the voltage applied to the current blocking layer in the first region is equal to or lower than the voltage applied to the current blocking layer in the second region. Is preferred. Further, the end region other than the gain region forms a window structure in which a dopant is implanted at a high concentration, and further, the first region and the second region of the current blocking layer It is more preferable to form a dielectric film between them.

  A semiconductor laser device according to an embodiment of the present invention will be described below with reference to the drawings.

(First embodiment)
A semiconductor laser device 100 according to a first embodiment of the present invention is shown in FIG. 1, FIG. 2, and FIG. 1 is a schematic plan view of the semiconductor laser device according to the present embodiment, FIG. 2 is a schematic cross-sectional view of a portion indicated by a one-dot chain line AA ′ in FIG. 1, and FIGS. ) Show schematic cross-sectional views of portions indicated by alternate long and short dash lines BB ′, CC ′, and DD ′ in FIG. 1, respectively.

  In the semiconductor laser device 100 according to the present embodiment, a substrate 101 made of an n-type GaAs semiconductor, a first clad layer 102 of an n-type semiconductor, an active layer 103, and a second clad layer 104 of a p-type semiconductor having a ridge structure on the upper portion thereof. A contact layer 109 is stacked on top of the ridge that is sequentially stacked and later becomes a gain region. The ridge structure of the second cladding layer 104 is formed in the longitudinal direction in the central portion of the semiconductor laser device 100 as indicated by a broken line in FIG. An n-type semiconductor current blocking layer 105, which is a semiconductor having a polarity different from that of the second cladding layer, is formed on the second cladding layer 104. In the current blocking layer 105, a notch is formed in a portion overlapping the ridge structure portion provided in the second cladding layer 104, and an upper electrode for laser driving stacked on the current blocking layer 105 106 and the contact layer 109 on the ridge structure portion of the second cladding layer 104 can be directly electrically connected. This portion becomes a gain region having a laser function.

  The current blocking layer 105 is divided into two regions, a first region 105a adjacent to the gain region and a second region 105b other than the first region 105a. A photodiode upper electrode 107 is formed on the second region 105b of the current blocking layer. In the semiconductor laser device 100 according to the present invention, unlike the conventional semiconductor laser device 900 shown in FIGS. 8 and 9, the current blocking layer 105 is provided between the photodiode upper electrode 107 and the second cladding layer 104. Is formed. In FIG. 1 as well, the laser driving upper electrode 106 and the photodiode upper electrode 107 are shown in the same manner as in FIG. 8 showing the conventional example so that the planar configuration of the semiconductor laser device 100 according to this embodiment can be easily understood. Only the outer shape is represented by a solid line.

  Here, the specific structure of each layer will be described in detail. The substrate 101 is made of an n-type GaAs semiconductor and has a thickness of 100 μm. The first cladding layer 102 is made of n-type AlGaInP and has a thickness of 2 μm. The active layer 103 is made of AlGaInP. It consists of a multiple quantum well structure with GaInP, the total thickness is 0.05 μm, the second cladding layer is made of p-type AlGaInP, the thickness is 1.5 μm, the ridge width is 3 μm, the height is 1.2 μm, the contact layer 109 is a laminated film of p-type GaInP on the second cladding layer side and p-type GaAs on the electrode side, and the thicknesses are 0.05 μm and 0.2 μm, respectively. The current blocking layer 105 is made of n-type AlInP and has a thickness of 0.5 μm. Further, the laser driving upper electrode 106 and the photodiode upper electrode 107 are both laminated films of Ti / Pt / Au and have a thickness of 0.05 μm / 0.1 μm / 3 μm.

  In the present embodiment, the current blocking layer 105a in the first region and the current blocking layer 105b in the second region are formed from layers of the same material and the same thickness. In this way, the current blocking layers 105a and 105b divided into two regions can be easily formed in the manufacturing process. That is, after the current blocking layer 105 is formed on the entire semiconductor chip, this is patterned into a predetermined shape, or a dielectric or the like is previously disposed in a place where the current blocking layer 105 is not formed, and the current is selectively selected. The current blocking layers 105a and 105b having such a shape can be formed by using a conventional method such as growing the blocking layer 105, and the manufacturing cost can be reduced. This also applies to the two metal electrodes, the laser driving upper electrode 106 and the photodiode upper electrode 107.

  On the other hand, by changing the composition and film thickness of the two current blocking layers 105a and 105b, for example, in order to increase the light receiving sensitivity of the photodiode, the current blocking layer is more than the current blocking layer 105a. For example, the carrier concentration of 105b may be reduced and the film thickness may be increased.

  Furthermore, in the semiconductor laser device 100 according to the present embodiment, the semiconductor laser device 100 is located in a portion other than the gain region of the ridge structure formed in the second cladding layer 104 (a portion corresponding to both sides of the gain region in the left-right direction in FIGS. 1 and 2). A so-called window structure 108 is formed by doping the active layer 103, the first cladding layer 102, and the second cladding layer 104 with a dopant such as Zn or Mg deeper than the gain region. In this window structure 108 portion, by widening the band gap of the active layer, light absorption with respect to the emission wavelength can be extremely reduced. 2 and 3, the region where the window structure 108 is formed is indicated by a dotted line. As described above, by forming a portion of the gain region where the semiconductor laser is not formed with a window structure, the end portion of the active layer 903 as in the conventional semiconductor laser device 900 shown in FIGS. Compared with the structure of the light receiving portion, light absorption in a so-called current non-injection region other than the gain region is eliminated, thereby improving the efficiency of the semiconductor laser and end face destruction (COD: Catalytic Optical Damage) caused by heat generation at the light emitting end face. ) Can be improved.

  Next, the operation of the semiconductor laser device 100 according to this embodiment will be described. FIG. 4 shows the relationship between potential and current when driving the semiconductor laser device 100 according to the present embodiment.

  As shown in FIG. 4, in the semiconductor laser device 100 according to the present embodiment, when the voltage applied to the photodiode upper electrode 107 is Vmon and the voltage applied to the laser driving upper electrode 106 is Vop, Vmon ≧ Vop. By satisfying this relationship, there is a gap between the current blocking layer 105b formed in the photodiode region that is the light output monitoring unit, that is, the second region, and the second cladding layer 104 formed of the p-type semiconductor. A reverse bias is applied. Even when the relationship between the two applied voltages is Vmon = Vop, a built-in potential is generated between the block layer 105b that is an n-type semiconductor and the second cladding layer 104 that is a p-type semiconductor. Actually, the state is the same as when a reverse bias is applied. Here, the voltage Vsub is applied to the lower electrode of the semiconductor substrate 101 not shown in FIG.

  When a laser driving voltage Vop is applied to the laser driving upper electrode 106 of the semiconductor laser device 100 according to the present embodiment, a driving current Iop is generated, and light is emitted from the active layer 103 located under the electrode 106 that is a current injection region. Occurs. This light emission reaches the end face of the semiconductor laser device 100 along a waveguide formed by the first cladding layer 102 and the second cladding layer 104 and a stripe shape. Here, the light distribution inside the waveguide is considered to be distributed from the active layer 103 to the inside of the current blocking layer 105. Here, due to the relationship between the driving voltages described above, a reverse bias is applied between the current blocking layer 105b and the second cladding layer 104 in the photodiode region, and a depletion layer is generated in the boundary region between the two. When the light generated in the active layer 103 enters the depletion layer, a monitor current Imon is generated, and this Imon is a value reflecting the light output of the semiconductor laser device 100 according to the present embodiment. Therefore, by monitoring Imon, it is possible to grasp the output of the semiconductor laser and control it so as to obtain a predetermined output light based on it.

  On the other hand, when Vmon <Vop, a forward bias is applied between the current blocking layer 105 b and the second cladding layer 104. Since a built-in voltage of about 1 V is generated between the current blocking layer 105 b and the second cladding layer 104, the current blocking layer 105 b and the second cladding layer 104 have a voltage up to Vop−Vmon <built-in voltage (about 1 V). A depletion layer exists at the boundary and functions as a photodiode. However, when Vop−Vmon ≧ built-in voltage (about 1 V), the depletion layer disappears and the function as a photodiode is lost. In addition, when Vop−Vmon ≧ built-in voltage (about 1V) and the depletion layer disappears, a part of the driving current Iop leaks to the electrode 107 of the photodiode portion, and not only the light output cannot be monitored, The laser emission efficiency is also reduced.

  Furthermore, Ion reflects the optical output of the semiconductor laser device 100, but is also affected by the width of the depletion layer generated at the boundary between the current blocking layer 105b and the second cladding layer 104 (the light receiving region is larger when the depletion layer width is wider). It gets bigger and Imon gets bigger). In general, it is difficult to control the width of the depletion layer with a forward bias, and in order to realize a stable optical output monitor, it is desirable that Vmon ≧ Vop.

  When an ordinary photodiode is used as an output monitor of the semiconductor laser device, the light in the high-concentration doping layer that serves as an electrode before the light reaches the pn junction (= depletion layer) of the photodiode. Absorption will always occur. Further, considering the case where a Si-based photodiode is used as a monitor of semiconductor laser output light, the response speed is limited to about several hundred MHz. Compared to this, according to the configuration of the semiconductor laser device of the present embodiment, the generated laser light directly reaches the pn junction (= depletion layer) of the photodiode portion without passing through the light absorption layer. High sensitivity can be realized. In the case of this embodiment, since the pn junction is formed of a compound semiconductor having a carrier mobility higher than that of Si, a high-speed response on the order of GHz is possible as a response speed.

  Further, as described above, in the semiconductor laser device 100 according to the present embodiment, the photoelectric conversion of the photodiode portion that monitors the output light of the semiconductor laser is performed on a semiconductor having a polarity different from that provided on the second cladding layer 104. Since the conversion is performed by the current blocking layer 205b, which is a layer, it is possible to monitor the optical output with higher accuracy than in the conventional semiconductor laser device 900 in which this conversion is performed by the active layer 903. In addition, since the portion other than the gain region around the semiconductor laser region can have a window structure in which light absorption does not occur, the light emission efficiency as a laser does not decrease, and the cost is low but the self A semiconductor laser device to which a photodiode function capable of monitoring the light output is added can be obtained.

(Second Embodiment)
Next, a schematic view of a semiconductor laser device 200 according to the second embodiment of the present invention is shown. FIG. 5 is a schematic plan view of the semiconductor laser device 200 according to the second embodiment, and FIG. 6 is a schematic cross-sectional view of a portion indicated by a dashed line EE ′ in FIG.

  The basic structure of the semiconductor laser device 200 according to this embodiment is the same as that of the semiconductor laser device 100 according to the first embodiment shown in FIGS. That is, a substrate 101 made of an n-type GaAs semiconductor, a first cladding layer 102 of an n-type semiconductor, an active layer 103, a second cladding layer 104 of a p-type semiconductor having a ridge structure thereon, a contact layer 109, and a second cladding layer 104 An n-type semiconductor current blocking layer 105, which is a semiconductor having a polarity different from that of the second cladding layer formed thereon, and a laser driving upper electrode 106 and a photodiode upper electrode 107 are sequentially stacked thereon. For this reason, the same code | symbol is attached | subjected to the part of the same structure, and detailed description is abbreviate | omitted. Similarly to the semiconductor laser device 100 of the first embodiment, the contact layer 109 is located above the ridge serving as the gain region, and the window region 108 is centered on the active layer 103 at both ends other than the gain region. Is provided.

  This embodiment is different from the first embodiment in that the gain region has a ridge structure provided in two regions of the current blocking layer 105, that is, the second cladding layer 104, which is a current injection region functioning as a semiconductor laser. A dielectric film 209 is provided between the first region 105a adjacent to the second region 105b and the second region 105b which is a non-current injection region functioning as a photodiode. The dielectric film 209 is made of, for example, SiO 2 or SiN, and has a thickness of, for example, 0.3 μm.

  In the absence of the dielectric film 209, a small amount of foreign matter is present at the boundary portion between the second cladding layer 104, which is a p-type semiconductor layer, and the current blocking layer 105, which is a semiconductor layer having the opposite polarity, that is, the pn junction portion. It is conceivable that even if only attached, it leaks easily. Specifically, when Vmon ≧ Vop, that is, when a reverse bias is applied between the second cladding layer 104 and the current blocking layer 105b, a depletion layer is generated in the pn junction region of both, and light is emitted. Unless n is incident, only a minute current of nA order called dark current flows. However, when a foreign substance adheres to the pn junction region, a leakage current having a value larger than the dark current is generated through the foreign substance. In this case, Imon is generated regardless of the presence or absence of incident light, and accurate light output monitoring cannot be performed. In particular, when the semiconductor laser device according to the present invention is mounted by junction down soldering (solder bonding between the electrodes 106 and 107 and the submount), the solder that has spread during mounting can easily become the above-mentioned foreign matter. It is preferable to take For the above reason, by providing the dielectric film 209, it is possible to prevent the exposure of the junction part at the boundary part between the second cladding layer 104 and the current blocking layer 105 and realize a highly reliable semiconductor laser device. it can.

(Third embodiment)
In each of the embodiments of the present invention described above, the portion where the photodiode is formed is the portion of the current blocking layer 105 formed so as to overlap the ridge structure formed in the second cladding layer 104. However, the present invention is not limited thereto, and may be formed in parallel with a gain region formed on the ridge structure, for example. A schematic plan view of the semiconductor laser device 300 in this case is shown in FIG. 7 as a third embodiment.

  As shown in FIG. 7, in the semiconductor laser device 300 according to the third embodiment, an opening is formed at the center in the left-right direction of the ridge structure (shown by the dotted line in the drawing) provided in the second cladding layer 104. In addition, the upper electrode 106 for laser driving and the contact layer 109 that are shown only by the solid line in the drawing are in direct contact with each other. This portion forms a gain region. As a region other than the first region 105a of the current blocking layer 105 adjacent to the gain region, the second region 105b is parallel to the ridge structure as shown in FIG. It is formed in two places (vertical direction). The photodiode upper electrode 107 for detecting the current of the photodiode portion formed in the second region 105b is also provided at two locations parallel to the ridge structure so as to correspond to the region 105b of the current blocking layer. Is formed.

  By doing so, the area of the photodiode portion can be increased and a larger monitor current can be taken out as compared with the first and second embodiments in which the photodiode is formed on the ridge structure described above. An excellent effect of being able to be obtained can be obtained.

  As described above, specific embodiments of the semiconductor laser device of the present invention have been described with reference to the drawings. However, it is needless to say that the present invention is not limited to these specific examples. For example, in each of the above embodiments, the first cladding layer and the current blocking layer are described as n-type semiconductor layers, and the second cladding layer is described as a p-type semiconductor layer. However, there is no problem even if these polarities are reversed. There is no. In the above embodiments, the AlGaInP red semiconductor laser device is used. However, an AlGaAs infrared semiconductor laser, a GaN blue-violet semiconductor laser, or the like may be used. Furthermore, although the AlInP type is used as the current blocking layer in each of the above embodiments, a GaAs-based or different material type laminated film may be used.

  The position of the monitoring photodiode is preferably on the rear side of the semiconductor laser device, but may be provided on the front side or both. The front side refers to the end surface side from which laser light directed toward the optical disk or the like is emitted, and the rear side refers to the opposite side. In general, the amount of heat generated in the semiconductor laser device is larger on the front side, so it is desirable to increase the mounting area on the front side.To this end, the photodiode part is arranged on the rear side and the electrode area on the front side is increased. It is better to make it larger.

  As described above, according to the present invention, it is possible to obtain a semiconductor laser device incorporating a photodiode that can be used for stable light output monitoring with high light emission efficiency without increasing the manufacturing cost. Therefore, it can be used as a semiconductor laser device used for reading and writing of digital information equipment using an optical disk.

1 is a schematic plan view showing a semiconductor laser device according to a first embodiment of the present invention. 1 is a schematic cross-sectional view showing a cross section of a semiconductor laser device according to a first embodiment of the present invention. 1 is a schematic cross-sectional view showing a cross section of a semiconductor laser device according to a first embodiment of the present invention. The figure which shows the use condition of the semiconductor laser apparatus which concerns on the 1st Embodiment of this invention Schematic plan view showing a semiconductor laser device according to a second embodiment of the present invention. Schematic sectional view showing a section of a semiconductor laser device according to a second embodiment of the present invention Schematic plan view showing a semiconductor laser device according to a third embodiment of the present invention. Schematic plan view showing a conventional semiconductor laser device incorporating a photodiode Schematic cross-sectional view showing a cross section of a conventional semiconductor laser device incorporating a photodiode

Explanation of symbols

100, 200, 300, 900 Semiconductor laser device 101, 901 Semiconductor substrate 102, 902 1 Clad layer 103, 903 Active layer 104, 904 Second clad layer 105 Current blocking layer 105a First region 105b Second region 106, 906 Upper electrode for laser drive 107, 907 Upper electrode for photodiode 108 Window region 109, 909 Contact layer 209 Dielectric film 910 Insulating film

Claims (4)

  A first cladding layer formed on a semiconductor substrate; an active layer formed on the first cladding layer; a second cladding layer having a ridge structure formed on the active layer; and the second cladding layer A current blocking layer made of a semiconductor having a polarity different from that of the second cladding layer formed on the first cladding layer, and the current blocking layer includes a first region adjacent to a gain region formed in the ridge structure portion; The semiconductor laser device is divided into two regions including a second region other than the first region.   2. The semiconductor laser device according to claim 1, wherein a voltage applied to the current blocking layer in the first region is equal to or lower than a voltage applied to the current blocking layer in the second region.   3. The semiconductor laser device according to claim 1, wherein an end region other than the gain region forms a window structure in which a dopant is implanted at a high concentration.   4. The semiconductor laser device according to claim 1, wherein a dielectric film is formed between the first region and the second region of the current blocking layer. 5.

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