JP4155368B2 - Semiconductor laser array element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser array element and a semiconductor laser array apparatus.
[0002]
[Prior art]
Semiconductor lasers are widely used as light sources for optical communication and light sources for information equipment.
As one of semiconductor lasers, a semiconductor laser array (multi-beam laser) that emits a plurality of laser beams is known.
[0003]
The semiconductor laser array is formed monolithically on a compound semiconductor substrate (hereinafter also simply referred to as a semiconductor substrate). This semiconductor element (semiconductor chip) is referred to as a semiconductor laser array element (semiconductor laser array chip). A semiconductor laser array product incorporating this semiconductor laser array element is called a semiconductor laser array device.
[0004]
A monolithic three-beam semiconductor laser element (semiconductor laser array element) is disclosed in “Electronic Materials”, June 1987 issue, P107 to P111, issued by the Industrial Research Council. This document describes a visible light semiconductor laser as a signal reading light source used in a document file system or the like including a CD, VD device, laser printer, POS, and barcode reader.
[0005]
Also, Hitachi, Ltd., Semiconductor Division, “Hitachi Opto Device Data Book”, February 1996, 7th edition, P12 ~ P18, GaAlAs multiple quantum well (MQW) structure 0.78μm band A visible laser diode is described.
[0006]
[Problems to be solved by the invention]
As one of the structures of a semiconductor laser (laser diode), there is a structure in which current confinement is performed with a pair of block layers sandwiching a ridge generated in a cladding layer.
[0007]
For example, as shown in FIG. 19, the semiconductor laser device (semiconductor laser chip) 1 having this structure has a first conductivity type cladding layer on one surface (upper surface) side of the first conductivity type compound semiconductor substrate (semiconductor substrate 2). 3, the active layer 4 and the second conductivity type cladding layer 5 are sequentially laminated.
[0008]
The second conductivity type cladding layer 5 is provided with a striped ridge 6. The ridge 6 is formed by etching the surface of the second conductivity type cladding layer 5 over a certain thickness.
[0009]
Further, both sides of the ridge 6 are buried with a block layer 7 of the first conductivity type. The ridge 6 and the block layer 7 are covered with a cap layer 8 of the first conductivity type. The electrodes 9 and 10 made of an anode electrode or a cathode electrode are formed on the cap layer 8 and on the other surface (back surface) side of the semiconductor substrate 2.
[0010]
In such a semiconductor laser, laser light is emitted from the end of the active layer 4 corresponding to the ridge 6 by applying a predetermined voltage to the electrodes 9 and 10.
[0011]
FIG. 20 is a cross-sectional view showing a semiconductor laser chip using an N-type GaAs substrate as a semiconductor substrate, and FIG. 21 is a cross-sectional view showing a semiconductor laser chip using a P-type GaAs substrate. In these figures, the reference numerals indicating the respective parts are the same as those in FIG. 19, but in the case of a semiconductor laser chip using an N-type GaAs substrate, N is appended to the reference numeral and a semiconductor laser using a P-type GaAs substrate is used. In the case of a chip, P is attached after the reference numeral.
[0012]
Further, the circles in the ridge 6 part indicate holes 11 in FIG. 20 and electrons 12 in FIG.
For clarity of illustration, hatching is omitted except for electrode portions.
[0013]
In the semiconductor laser chips 1N and 1P having such a structure, the flow region of the holes 11 is narrowed by the N-type cladding layer 5N as shown in FIG. 20, or the P-type cladding layer 5P as shown in FIG. This narrows the flow region of the electrons 12.
[0014]
Electrons have a higher mobility than holes and are easy to spread, spreading current. As a result, the reactive current increases and the threshold value I _th Increases and efficiency decreases.
[0015]
Thus, since electrons have a higher mobility than holes, semiconductor laser chips using an N-type substrate are frequently used as semiconductor substrates.
[0016]
A conventional semiconductor laser chip has a structure in which a cathode electrode (or anode electrode) is provided on one surface (front surface) of the front and back surfaces of a semiconductor substrate, and a cathode electrode (or anode electrode) is provided on the other surface (back surface). ing.
[0017]
As a result, in a semiconductor laser device having a structure in which the back surface potential of the semiconductor substrate is the substrate potential of the package body, the substrate potential is specified and may not be directly mounted on the electronic device as it is, and the circuit design of the electronic device is devised. May be required. For example, in a laser beam printer, there is a circuit configuration (drive circuit) that is used with the substrate potential of the semiconductor laser chip set to a negative potential for the purpose of reducing noise.
[0018]
On the other hand, in order to increase the speed of a laser beam printer (LBP), an optical disk, a magneto-optical disk, etc., it is known to use a multi-beam semiconductor laser as a light source.
[0019]
An object of the present invention is to provide a semiconductor laser array element capable of lowering a threshold value.
Another object of the present invention is to provide a semiconductor laser array element and a semiconductor laser array apparatus whose usability is not affected by the electrical polarity of the semiconductor substrate of the semiconductor laser array element.
The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.
[0020]
[Means for Solving the Problems]
The following is a brief description of an outline of typical inventions disclosed in the present application.
(1) A semiconductor laser array element in which a plurality of laser diodes are monolithically provided in parallel on a semiconductor substrate, and all the anode electrodes and cathode electrodes of the respective laser diodes are provided on one surface side of the semiconductor substrate. Yes. Each laser diode is formed in a multilayer semiconductor layer portion provided on one surface side of the semiconductor substrate, and each laser diode is an insulating means formed under the lowermost semiconductor layer constituting the laser diode. And an isolation groove provided on one surface of the semiconductor substrate and reaching the insulating means. A semiconductor layer of reverse conductivity type is interposed between the semiconductor substrate and the lowermost semiconductor layer, and these three layers constitute the insulating means as an NPN structure or a PNP structure, or the semiconductor substrate is a semi-insulating semiconductor The insulating means is configured by using a substrate and disposing the lowermost semiconductor layer on the semiconductor substrate. The laser diode has a current confinement structure that defines a hole flow region with an N conductivity type block layer.
[0021]
A semiconductor laser array apparatus incorporating such a semiconductor laser array element has the following configuration.
A package comprising a package body and a lid having a light transmission window through which laser light is transmitted; a semiconductor laser array element fixed to the package body and emitting a plurality of laser beams; and the package attached to the package body and the package A semiconductor laser array device having a plurality of external electrode terminals extending inside and outside, and connection means for connecting each electrode of the semiconductor laser array element and the external electrode terminal, wherein the semiconductor laser array element is The means (1) is configured.
[0022]
(2) In the configuration of the means (1), all the anode electrodes and cathode electrodes of the laser diodes are provided on one surface side of the semiconductor substrate, and the semiconductor surface is disposed on the other surface side of the semiconductor substrate. An electrode that is electrically connected to at least one electrode provided on the one surface side of the substrate via a connecting portion is provided.
[0023]
(3) In the configuration of the means (1) or (2), one of the anode electrode and the cathode electrode of the laser diode is connected to another laser through a conductive layer provided on one surface side of the semiconductor substrate. It is electrically connected to the electrode of the same polarity of the diode.
[0024]
According to the means of (1), (a) each laser diode constricts holes with low mobility, so that it is possible to suppress the spread of current in the current confinement portion and to reduce the reactive current. it can. As a result, the threshold value is reduced, and a reduction in operating current can be achieved.
[0025]
(B) Each laser diode formed in the semiconductor laser array element is electrically independent from the semiconductor substrate, and the anode and cathode electrode of each laser diode are provided on one surface of the semiconductor substrate. Usability is improved regardless of the electrical polarity of the semiconductor substrate. The ease of use is the same for a semiconductor laser array device incorporating a semiconductor laser array element.
[0026]
According to the means (2), in addition to the effect of the means (1), the other surface side of the semiconductor substrate is electrically connected to at least one electrode provided on the one surface side of the semiconductor substrate via a connecting portion. Since an electrode to be connected is provided, the electrode on the other surface side of this semiconductor substrate can also be used as one electrode for driving the laser diode. Electrode extraction design is facilitated.
[0027]
According to the means of (3), in addition to the effects of the means (1) or means (2), some of the electrodes of the same polarity of the plurality of laser diodes are conductive surfaces provided on one surface side of the semiconductor substrate. Since the layers are connected to each other via layers, the number of external electrode terminals in the semiconductor laser array device can be reduced.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment of the invention, and the repetitive description thereof is omitted.
[0029]
(Embodiment 1)
1 to 13 are diagrams relating to a semiconductor laser array element and a semiconductor laser array apparatus according to an embodiment (Embodiment 1) of the present invention.
[0030]
In the first embodiment, an example in which the present invention is applied to a semiconductor laser that emits two 0.78 μm band laser beams will be described.
[0031]
As shown in FIG. 1, the semiconductor laser array element (semiconductor laser array chip) 20 of the first embodiment has a vertical (depth) length of 250 μm, a horizontal width of 300 μm, and a thickness along the extending direction of the optical waveguide, for example. Is made of a 100 μm rectangular body.
[0032]
An isolation groove (insulation isolation groove) 21 is provided along the vertical direction in the central portion of the width of the surface (one surface, upper surface in the figure) of the semiconductor laser array chip 20. Laser diodes 22 are provided on both sides of the isolation groove 21, respectively.
[0033]
In each laser diode 22, an electrode separation groove 23 is provided along the vertical direction on the upper surface side of the semiconductor laser chip 1. An anode electrode 25 is provided on the upper surface of the mesa portion 24 between the electrode separation groove 23 and the isolation groove 21, and the upper surface of the electrode lead-out portion 26 between the electrode separation groove 22 and the end of the semiconductor laser chip 1. Is provided with a cathode electrode 27.
[0034]
The surface (one surface) of the semiconductor laser array chip 20 is covered with an insulating film 29 except for the electrodes 25 and 27.
[0035]
The semiconductor laser array chip 20 is formed on the compound semiconductor substrate as shown in the enlarged sectional view of FIG. In the first embodiment, the compound semiconductor substrate is an N conductivity type (N type) GaAs substrate (semiconductor substrate) 30. The N-GaAs substrate 30 has a thickness of less than 100 μm, Si is an impurity, and the impurity concentration is 2 × 10. ¹⁸ cm ~ ^Three It is formed with a GaAs plate of the order.
[0036]
A semiconductor layer is formed in multiple layers on one surface side of the semiconductor substrate (N-GaAs substrate) 30, that is, on the surface (upper surface) side in FIG. 1, and a laser diode is formed in this portion.
[0037]
The isolation groove 21 penetrates the multilayer semiconductor layer and reaches the surface layer of the N-GaAs substrate 30. The isolation groove 21 electrically separates the N-GaAs substrate 30 from side to side.
[0038]
The left and right laser diodes 22 provided across the isolation groove 21 have a symmetric structure with respect to the isolation groove 21.
[0039]
On one surface (front surface) side of the N-GaAs substrate 30, a semiconductor layer 31 having a conductivity type opposite to that of the N-GaAs substrate 30 (P conductivity type), that is, a P-GaAs layer 31 is provided. This P-GaAs layer 31 has Zn as an impurity and an impurity concentration of 1 × 10 5. ¹⁸ cm ~ ^Three The layer is about 3 μm thick.
[0040]
An N-GaAs buffer layer 32 is provided on the P-GaAs layer 31. The N-GaAs buffer layer 32 uses Se as an impurity and has an impurity concentration of 1 × 10 6. ¹⁸ cm ~ ^Three The layer is about 3 μm thick. This N-GaAs buffer layer 32 becomes the lowermost semiconductor layer constituting the laser diode 22.
[0041]
The N-GaAs substrate 30, the P-GaAs layer 31, and the N-GaAs buffer layer 32 form an insulating means by NPN bonding, and each laser diode 22 is electrically connected by the NPN structure and the isolation groove 21. Becomes an independent structure.
[0042]
When the semiconductor laser array element is formed with a P-type substrate, the insulating means has a PNP structure.
[0043]
On the N-GaAs substrate 30 defined by the isolation groove 21, the P-GaAs layer 31 and the N-GaAs buffer layer 32 overlap and extend. The electrode separation groove 23 reaches the surface layer of the N-GaAs buffer layer 32.
[0044]
In the mesa portion 24 and the electrode lead-out portion 26, an N-GaAlAs cladding layer 33 is provided on the N-GaAs buffer layer 32. The N-GaAlAs cladding layer 33 uses Se as an impurity and has an impurity concentration of 1 × 10 5. ¹⁸ cm ~ ^Three The layer is about 1.5 μm thick. The mixed crystal ratio x of Al is 0.5.
[0045]
An N-GaAs contact layer 34 is provided on the N-GaAlAs cladding layer 33 of the electrode lead-out portion 26, and a cathode electrode 27 is provided on the N-GaAlAs cladding layer 33. The N-GaAs contact layer 34 has Se as an impurity and an impurity concentration of 2 × 10 6. ¹⁸ cm ~ ^Three The thickness is about 1 μm.
[0046]
An active layer 40 made of multiple quantum wells (MQW) is provided on the N-GaAlAs cladding layer 33 of the mesa portion 24. The active layer (MQW active layer) 40 is a layer in which, for example, a barrier layer made of GaAlAs (thickness 5 nm) and a well layer made of GaAlAs (thickness 10 nm) are alternately stacked, and the well layer is a three-layer layer. And provided between guide layers made of GaAlAs each having a thickness of 10 nm.
[0047]
A P-GaAlAs cladding layer 41 is provided on the MQW active layer 40. A part of the P-GaAlAs cladding layer 41 is provided with a striped ridge 42 having a trapezoidal cross section. The ridge 42 extends in the vertical direction of the semiconductor laser array chip 20, and the MQW active layer 40 portion immediately below the ridge 42 serves as an optical waveguide.
[0048]
The distance between the two optical waveguides of the semiconductor laser array element 20 is, for example, about 100 μm.
[0049]
The P-GaAlAs cladding layer 41 uses Zn as an impurity and has an impurity concentration of 8 × 10. ¹⁷ cm ~ ^Three The layer is about 1.5 μm thick. The ridge 42 protrudes from the P-GaAlAs cladding layer 41 by about 1.2 μm. The width of the ridge 42 is about 5 μm at the lower thick portion.
[0050]
On the P-GaAlAs cladding layer 41 on both sides of the ridge 42, an N-GaAs block layer 43 for current confinement is provided. The N-GaAs block layer 43 uses Se as an impurity and has an impurity concentration of 2 × 10. ¹⁸ cm ~ ^Three The thickness is about 1.2 μm.
[0051]
A P-GaAs cap layer 44 is provided on the ridge 42 and the N-GaAs block layer 43. This P-GaAs cap layer 44 uses Zn as an impurity and has an impurity concentration of 5 × 10 5. ¹⁹ cm ~ ^Three The thickness is about 2.0 μm.
[0052]
An anode electrode 25 is provided on the P-GaAs cap layer 44.
Further, the surface of the semiconductor laser array chip 20 excluding the anode electrode 25 and the cathode electrode 27 has a single-layer or multi-layer SiO 2 surface. ₂ It is covered with an insulating film 29 made of a film or a PSG film.
[0053]
Next, a method for manufacturing the semiconductor laser array element 20 according to the first embodiment will be described with reference to FIGS.
[0054]
In manufacturing the semiconductor laser array element 20, a semiconductor substrate is first prepared. In actual manufacturing, a semiconductor substrate called a wafer having a large size is prepared, and in the final stage of element formation, the wafer is divided vertically and horizontally to manufacture a semiconductor laser array element composed of small pieces. A description will be given below in a state where a single semiconductor laser array element is manufactured.
[0055]
The semiconductor substrate 30 is composed of an N conductivity type GaAs substrate having a thickness of several hundred μm. This N-GaAs substrate 30 has Si as an impurity and an impurity concentration of 2 × 10. ¹⁸ cm ~ ^Three It is about.
[0056]
Next, as shown in FIG. 3, a multi-layered semiconductor layer is sequentially formed by MOCVD (Metalorganic Chemical Vapor Deposition) method or MBE (Molecular Beam Epitaxy) method. The multi-layered semiconductor layer includes a lowermost P-GaAs layer 31, an N-GaAs buffer layer 32, an N-GaAlAs cladding layer 33, an MQW active layer 40, and a P-GaAlAs cladding sequentially formed on the P-GaAs layer 31. It consists of layer 41.
[0057]
The P-GaAs layer 31 has Zn as an impurity and an impurity concentration of 1 × 10 5. ¹⁸ cm ~ ^Three The layer is about 3 μm thick.
[0058]
The N-GaAs buffer layer 32 uses Se as an impurity and has an impurity concentration of 1 × 10 5. ¹⁸ cm ~ ^Three This is a layer having a thickness of about 3 μm, and becomes the lowermost semiconductor layer constituting the laser diode 22.
[0059]
Further, the N-GaAs substrate 30, the P-GaAs layer 31, and the N-GaAs buffer layer 32 form an insulating means by NPN bonding.
[0060]
The N-GaAlAs cladding layer 33 has Se as an impurity and an impurity concentration of 1 × 10 5. ¹⁸ cm ~ ^Three The layer is about 1.5 μm thick. The mixed crystal ratio x of Al is 0.5.
[0061]
The MQW active layer 40 is, for example, a layer in which barrier layers made of GaAlAs (thickness 5 nm) and well layers made of GaAlAs (thickness 10 nm) are alternately stacked, and the well layers are three layers. The layer is provided between guide layers made of GaAlAs having a thickness of 10 nm, and has a thickness of about 60 nm as a whole.
[0062]
The P-GaAlAs cladding layer 41 uses Zn as an impurity and has an impurity concentration of 8 × 10 8. ¹⁷ cm ~ ^Three The layer is about 1.5 μm thick.
[0063]
Next, as shown in FIG. 4, after two striped masks 50 are formed on the surface of the N-GaAs substrate 30, the P-GaAlAs cladding layer 41 is formed with a thickness of 0. Etching is performed so that about 3 μm remains.
The mask 50 has a width of about 5 μm and an interval of about 100 μm.
[0064]
By this etching, a trapezoidal ridge 42 is formed immediately below the mask 50 from the crystallinity of the GaAs surface GaAlAs and the crystal plane of the surface of the N-GaAs substrate 30. The width of the lower portion of the ridge 42 is about 5 μm and the height is about 1.2 μm.
[0065]
Next, as shown in FIG. 5, an N-GaAs block layer 43 is formed on the P-GaAlAs cladding layer 41 on both sides of the ridge 42 by selectively performing burying growth using the mask 50 and the mask 50. Then, the entire surface of the N-GaAs substrate 30 is covered with the P-GaAs cap layer 44.
[0066]
The N-GaAs block layer 43 uses Se as an impurity and has an impurity concentration of 2 × 10. ¹⁸ cm ~ ^Three Thus, a layer having a thickness of about 1.2 μm is formed, and a recessed portion is embedded by the etching.
[0067]
The P-GaAs cap layer 44 uses Zn as an impurity and has an impurity concentration of 5 × 10 5. ¹⁹ cm ~ ^Three The thickness is about 2.0 μm.
[0068]
Next, as shown in FIG. 6, a mask 51 is formed on the central region including the two ridges 42. Thereafter, etching is performed up to the MQW active layer 40 using the mask 51 as a mask to expose the N-GaAlAs cladding layer 33. The portion exposed by this etching becomes the electrode lead-out portion 26.
[0069]
Next, as shown in FIG. 7, an N-GaAs contact layer 34 is formed on the surface of the N-GaAlAs cladding layer 33 exposed by the MOCVD method or the like. The N-GaAs contact layer 34 has Se as an impurity and an impurity concentration of 2 × 10. ¹⁸ cm ~ ^Three The thickness is about 1 μm. After forming the N-GaAs contact layer 34, the mask 51 is removed.
[0070]
Next, as shown in FIG. 8, after forming a mask 52 on the surface of the N-GaAs substrate 30, a V-shaped isolation groove (insulating isolation groove) 21 is formed using the mask 52 as a mask. The isolation groove 21 penetrates through the multiple semiconductor layers and reaches the surface layer portion of the N-GaAs substrate 30. This isolation groove 21 is for forming in parallel two laser diodes that are driven and controlled independently of each other. After the formation of the isolation groove 21, the mask 52 is removed.
[0071]
Next, as shown in FIG. 9, an electrode separation groove 23 is formed on the outside of the electrode lead-out portion 26. The electrode separation groove 23 reaches the surface layer portion of the N-GaAs buffer layer 32. By forming the electrode separation groove 23, a mesa portion 24 is formed between the electrode separation groove 23 and the isolation groove 21. The ridge 42 is located in the mesa portion 24.
[0072]
Next, as shown in FIG. 9, SiO 2 is selectively formed on the surface of the N-GaAs substrate 30. ₂ A single-layer or multilayer insulating film 29 made of a film, a PSG film, or the like is formed, an anode electrode 25 is formed on the mesa portion 24, and a cathode electrode 27 is formed on the electrode lead-out portion 26.
[0073]
As a result, the semiconductor laser array element 20 shown in FIGS. 1 and 2 is manufactured.
[0074]
Such a semiconductor laser array element 20 is incorporated in a sealed container to form a semiconductor laser array device 60 as shown in FIG. FIG. 10 is a perspective view of the semiconductor laser array device with a part cut away.
[0075]
The semiconductor laser array device 60 includes a package main body 61 that is a main component of the assembly, and a lid 62 that is attached to the surface side of the package main body 61. The package is formed by a package body 61 and a lid body 62.
[0076]
The package main body 61 is made of a circular metal plate having a thickness of several millimeters, and a copper heat sink 63 is fixed to the part off the center of the surface with a brazing material or the like.
[0077]
A submount 64 made of silicon carbide (SiC) is fixed to the tip side of the side surface (front surface) facing the center of the package body 61 of the heat sink 63.
[0078]
As shown in FIG. 13, the submount 64 is made of a rectangular plate larger than the semiconductor laser array element 20, and four wirings 65 are provided on one mounting surface. One end of these wirings 65 is a connecting portion overlapping the anode electrode 25 and the cathode electrode 27 of the semiconductor laser array element 20. A solder layer 66 made of PbSn is formed at this connection portion. The solder layer 66 is formed such that the side with respect to the cathode electrode 27 is thicker than the side with respect to the anode electrode 25, and a reliable connection can be obtained between the anode electrode 25 and the cathode electrode 27.
[0079]
The semiconductor laser array element 20 is fixed to the submount 64 with the electrodes on the fixed side. A submount 64 to which the semiconductor laser array element 20 is fixed is fixed to the heat sink 63.
[0080]
FIG. 13 is a view showing the submount 64 and the semiconductor laser array element 20 before the semiconductor laser array element 20 is fixed, and FIG. 12 shows the submount 64 in a state where the semiconductor laser array element 20 is fixed (mounted). FIG.
[0081]
As can be seen from these drawings, the other end of the wiring 65 is a lead portion extending away from the semiconductor laser array element 20 and a wire bonding portion 67 for connecting wires.
[0082]
Further, a metallized layer 68 is formed on the other surface of the submount 64, that is, a fixed surface fixed to the heat sink 63.
[0083]
The wiring 65 and the metallized layer 68 have, for example, a three-layer structure of Ti / Pt / Au.
[0084]
A light receiving element 70 that receives laser light emitted from the rear end of the semiconductor laser array element 20 is fixed at the center of the package body 61.
[0085]
Further, six external electrode terminals (leads) 71 are fixed to the package body 61. The five leads 71 are fixed to the package body 61 through the insulator 72 in a penetrating manner. The remaining one lead 71 is fixed to the back surface of the package body 61 in a butted manner.
[0086]
The tip of the lead 71 protruding to the surface side of the package body 61 and the one electrode of the wire bonding portion 67 of the wiring 65 of the submount 64 and the light receiving element 70 are electrically connected by a conductive wire 73. . The electrode on the back surface of the light receiving element 70 is electrically connected to one lead 71 through the package body 61.
[0087]
FIG. 11 is an equivalent circuit diagram of the semiconductor laser array device 60. The electrodes of the two laser diodes 22 and the light receiving element 70 are connected to electrically independent leads 71, respectively.
[0088]
On the other hand, the lid 62 has a cap structure and has a light transmission window 76 through which a laser beam (laser beam) 75 is transmitted. The light transmission window 76 is formed by overlapping and fixing a transparent glass plate 77 on a hole provided in the lid 62.
[0089]
In such a semiconductor laser array device 60, by applying a predetermined voltage to each of the predetermined leads 71, one or both of the laser diodes 22 can be operated to emit laser light 75 from the light transmission window 76. it can. Further, these light outputs can be monitored by the light receiving element 70.
[0090]
FIG. 14 is a schematic diagram showing a state in which the semiconductor laser array device 60 of Embodiment 1 is incorporated in a laser beam printer.
[0091]
Two laser beams (laser beams) 75 emitted from the semiconductor laser array device 60 are reflected by a polygon mirror 80 whose rotation is controlled, and focused on the surface of a photosensitive drum 82 of a laser beam printer through an fθ lens 81. The laser beam 75 is scanned along the axial direction of the photosensitive drum 82. Further, the photosensitive drum 82 rotates.
[0092]
Since the photosensitive drum 82 is uniformly charged before writing, the portion irradiated with the laser beam 75 loses its potential, and carbon powder (toner) adheres to it and is developed. A laser beam printer is performed by copying the toner onto paper by an electrostatic force at a transfer portion (not shown).
[0093]
Since the semiconductor laser array device 60 emits two laser beams 75, a wide image can be visualized by the two laser beams 75 in a single scan, compared to the case of one laser beam 75. Also, the printing time for a given line is halved.
[0094]
According to the first embodiment, the following effects can be obtained.
(1) Since each laser diode 22 confines holes with low mobility, current spreading at the current confinement portion can be suppressed, and reactive current can be reduced. As a result, the threshold value is reduced, and a reduction in operating current can be achieved.
[0095]
(2) Each laser diode 22 formed in the semiconductor laser array element 20 is electrically independent from the semiconductor substrate 30, and the anode electrode 25 and the cathode electrode 27 of each laser diode 22 are provided on one surface of the semiconductor substrate 30. Therefore, in use, the usability is improved regardless of the electrical polarity of the semiconductor substrate 30. This usability is the same for the semiconductor laser array device 60 incorporating the semiconductor laser array element 20.
[0096]
(Embodiment 2)
FIG. 15 is a sectional view showing a semiconductor laser array device according to another embodiment (Embodiment 2) of the present invention.
[0097]
The semiconductor laser array element 20 according to the second embodiment has a structure in which the cathode electrode 27 is provided on the N-GaAs buffer layer 32 without providing the N-GaAs contact layer 34 in the first embodiment.
According to the second embodiment, the manufacturing process can be simplified.
[0098]
(Embodiment 3)
FIG. 16 is a cross-sectional view showing a semiconductor laser array device according to another embodiment (Embodiment 3) of the present invention.
[0099]
In the semiconductor laser array element 20 of the third embodiment, the electrode lead-out portion is formed when the electrode separation groove 23 is formed without performing the etching reaching the N-GaAlAs cladding layer 33 in the electrode lead-out portion 26 in the first embodiment. 26, a contact hole 85 is formed, and a cathode electrode 27 is formed in the contact hole 85 portion.
[0100]
In the third embodiment, the area of the cathode electrode 27 is widened, the wettability of solder (solder) is improved, and the reliability of electrical connection is increased.
[0101]
(Embodiment 4)
FIG. 17 is a sectional view showing a semiconductor laser array device according to another embodiment (Embodiment 4) of the present invention.
[0102]
The semiconductor laser array element 20 of the fourth embodiment has a structure in which a plurality of contact holes 85 are used in the third embodiment.
[0103]
In the fourth embodiment, the area of the cathode electrode 27 is further increased as compared with the third embodiment, the wettability of solder (solder) is improved, and the reliability of electrical connection is increased.
[0104]
(Embodiment 5)
FIG. 18 is a sectional view showing a semiconductor laser array device according to another embodiment (embodiment 5) of the present invention.
[0105]
In the fifth embodiment, the conductivity type of each part is opposite to that in the third embodiment. Accordingly, the reference numerals of the respective parts will be described by adding the letter P after the numeral in the third embodiment (first embodiment).
[0106]
In the semiconductor laser array element 20P of the fifth embodiment, in the semiconductor laser array element 20P of the third embodiment, the hole 86 is provided in the insulating film 29P at the bottom of the isolation groove 21P, and the isolation groove 21P is covered. The conductive layer 87 is provided on the insulating film 29P. The conductive layer 87 is connected to the anode electrode 25P of the laser diode 22P on both sides of the isolation groove 21P, and is electrically connected to the semiconductor substrate 30P at the hole 86. Further, a back electrode 88 is provided on the other surface (back surface) of the semiconductor substrate 30P.
[0107]
That is, in the semiconductor laser array element 20P of the fifth embodiment, the anode electrode 25P of the laser diode 22P is electrically connected to the back electrode 88 through the conductive layer 87 and the semiconductor substrate 30P.
[0108]
In other words, in the fifth embodiment, all the anode electrodes 25P and cathode electrodes 27P of each laser diode 22P are provided on one surface side of the semiconductor substrate 30P, and are provided on one surface side of the semiconductor substrate 30P. A structure in which a back surface electrode 88 electrically connected to at least one electrode, that is, the anode electrode 25P through a conductive layer 87 and a semiconductor substrate 30P as a connection portion is provided on the other surface side of the semiconductor substrate 30P. It has become.
[0109]
According to the fifth embodiment, since all the electrodes of all the laser diodes 22P are arranged on one surface side of the semiconductor substrate 30P and the back surface electrode 88 is provided on the other surface side, this semiconductor The back surface electrode 88 on the other surface side of the substrate 30P can also be used as one electrode for driving the laser diode 22P, and when incorporated in the semiconductor laser array device, the electrode extraction design is facilitated.
[0110]
According to the fifth embodiment, some of the electrodes having the same polarity (anode electrode 25P) among the plurality of laser diodes 22P are connected to each other via the conductive layer 87 provided on one surface side of the semiconductor substrate 30P. Because of the structure, the number of external electrode terminals in the semiconductor laser array device can be reduced.
[0111]
Although the invention made by the present inventor has been specifically described based on the embodiment, the present invention is not limited to the embodiment described above, and various modifications can be made without departing from the scope of the invention. For example, a structure in which more laser diodes are arranged may be used.
[0112]
【The invention's effect】
The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.
(1) In a semiconductor laser array element incorporating a plurality of laser diodes, each laser diode has a structure for confining holes with low mobility, so that current spreading at the current confinement portion can be suppressed. The threshold value and the operating current can be reduced.
(2) Each laser diode formed in the semiconductor laser array element is electrically independent from the semiconductor substrate, and the anode and cathode electrode of each laser diode are provided on one surface of the semiconductor substrate. Usability is improved regardless of the electrical polarity of the semiconductor substrate.
(3) From the above (2), in the semiconductor laser array apparatus incorporating the semiconductor laser array element of the present invention, the external electrode terminals of the laser diodes are independent from each other. It is not affected by this and its usability is good.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a semiconductor laser array element according to an embodiment (Embodiment 1) of the present invention.
FIG. 2 is an enlarged cross-sectional view of a part of the semiconductor laser array element according to the first embodiment.
3 is a cross-sectional view of a semiconductor substrate in which semiconductor layers are formed in multiple layers on the main surface in the manufacture of the semiconductor laser array element of Embodiment 1. FIG.
4 is a cross-sectional view of a semiconductor substrate in which two ridges for forming a laser diode are formed on the main surface in the manufacture of the semiconductor laser array element of Embodiment 1. FIG.
5 is a cross-sectional view of a semiconductor substrate in which a semiconductor layer including a buried layer is formed on the main surface in the manufacture of the semiconductor laser array element of Embodiment 1. FIG.
6 is a cross-sectional view of a semiconductor substrate obtained by etching several layers of a semiconductor layer in a region where a cathode electrode is to be formed in the manufacture of the semiconductor laser array element of Embodiment 1. FIG.
7 is a cross-sectional view of a semiconductor substrate in which a contact layer is formed on a semiconductor layer in a region where a cathode electrode is to be formed in the manufacture of the semiconductor laser array element of Embodiment 1. FIG.
8 is a cross-sectional view of a semiconductor substrate in which an insulating separation groove is provided between ridges in the manufacture of the semiconductor laser array element of Embodiment 1. FIG.
9 is a cross-sectional view of a semiconductor substrate in which an electrode separation groove is provided and a cathode electrode and an anode electrode are formed on a main surface in the manufacture of the semiconductor laser array element of Embodiment 1. FIG.
10 is a perspective view in which a part of the semiconductor laser array device incorporating the semiconductor laser array element according to the first embodiment is cut away. FIG.
FIG. 11 is an equivalent circuit diagram of the semiconductor laser array device.
FIG. 12 is a perspective view showing a state where a semiconductor laser array element is mounted on a submount in the semiconductor laser array device.
FIG. 13 is a perspective view showing a fixed positional relationship between the submount and the semiconductor laser array element.
FIG. 14 is a partial schematic perspective view showing a state in which the semiconductor laser array device is incorporated in a laser beam printer.
FIG. 15 is a sectional view showing a semiconductor laser array device according to another embodiment (Embodiment 2) of the present invention.
FIG. 16 is a cross-sectional view showing a semiconductor laser array device according to another embodiment (Embodiment 3) of the present invention.
FIG. 17 is a cross-sectional view showing a semiconductor laser array device according to another embodiment (Embodiment 4) of the present invention.
FIG. 18 is a sectional view showing a semiconductor laser array device according to another embodiment (Embodiment 5) of the present invention.
FIG. 19 is a cross-sectional view showing a conventional semiconductor laser chip.
FIG. 20 is a schematic diagram showing the movement of holes that are current confined in a conventional semiconductor laser chip.
FIG. 21 is a schematic diagram showing the movement of electrons that are current confined in a conventional semiconductor laser chip.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser array element (semiconductor laser chip), 2 ... Semiconductor substrate, 3 ... 1st conductivity type cladding layer, 4 ... Active layer, 5 ... 2nd conductivity type cladding layer, 7 ... 1st conductivity type block Layer, 8 ... cap layer of first conductivity type, 9, 10 ... electrode, 11 ... hole, 12 ... electron, 20 ... semiconductor laser array element (semiconductor laser array chip), 21 ... isolation groove (insulation) Separation groove) 22 ... laser diode, 23 ... electrode separation groove, 24 ... mesa portion, 25 ... anode electrode, 26 ... electrode lead-out portion, 27 ... cathode electrode, 29 ... insulating film, 30 ... semiconductor substrate (N-GaAs substrate) , 31... Reverse conductivity type semiconductor layer (P-GaAs layer), 32... N-GaAs buffer layer, 33... N-GaAlAs cladding layer, 34... N-GaAs contact layer, 40. Layer), 41 ... P-GaAlAs cladding layer, 42 ... ridge, 43 ... N-GaAs block layer, 44 ... P-GaAs cap layer, 50-52 ... mask, 60 ... semiconductor laser array device, 61 ... package body, 62 ... Lid, 63 ... Heat sink, 64 ... Submount, 65 ... Wiring, 66 ... Solder layer, 67 ... Wire bonding part, 68 ... Metallized layer, 70 ... Light receiving element, 71 ... External electrode terminal (lead), 72 ... Insulation 73, wire, 75, laser beam (laser light), 76, light transmission window, 77, transparent glass plate, 80, polygon mirror, 81, fθ lens, 82, photosensitive drum, 85, contact hole, 86, hole 87 ... conductive layer, 88 ... back electrode.

Claims (4)

A semiconductor laser array element in which a plurality of laser diodes are monolithically provided in parallel on a semiconductor substrate,
A multilayer semiconductor layer is provided on one main surface side of the semiconductor substrate,
Between the lowermost semiconductor layer in the multilayer semiconductor layer and the semiconductor substrate, a semiconductor layer having a conductivity type opposite to that of the lowermost semiconductor layer and the semiconductor substrate is provided,
Each laser diode is formed in the multilayer semiconductor layer,
Each of the laser diodes has a PNP structure or NPN structure comprising the semiconductor substrate, the reverse conductivity type semiconductor layer, and the lowermost semiconductor layer, and an isolator that reaches the semiconductor substrate through the multilayer semiconductor layer. Is electrically independent by the
All the anode electrodes and cathode electrodes of each laser diode are provided on one main surface side of the semiconductor substrate, and a back electrode is provided on the other surface side opposite to the one main surface of the semiconductor substrate. And
The back electrode is electrically connected to at least one electrode provided on one main surface side of the semiconductor substrate via the conductive layer connected to the semiconductor substrate at the bottom of the isolation groove and the semiconductor substrate. the semiconductor laser array device characterized by being. The isolation groove is covered with an insulating film,
2. The semiconductor laser array element according to claim 1, wherein the conductive layer is connected to the semiconductor substrate through a hole formed in the insulating film at the bottom of the isolation groove. One electrode of the anode electrode or cathode electrode of the laser diode, according to claim 1, characterized in that via the front Kishirube conductive layer is electrically connected to the electrodes of the same polarity of the other laser diode The semiconductor laser array element according to 1. 2. The semiconductor laser array device according to claim 1 , wherein the laser diode has a current confinement structure that defines a hole flow region by an N conductivity type block layer.

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