JPH07321401A - Semiconductor laser array and its driving method - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser array in which a light-emitting point can be moved at a very small interval required for the tracking operation of an optical disk by a method wherein a position in which a second stripe electrode is installed is set in a position on a semiconductor substrate corresponding to a first adjacent stripe electrode and a part between the stripe electrodes is installed. CONSTITUTION:First, 23mA is electrified across a stripe electrode 111 and a stripe electrode 112, and only a stripe electrode 115 is grounded. Then, a current density in an active layer has a shape in which a recess is formed in the center, and the central position of a near-visual-field image is situted in A. Then, a current of 50mA is injected from the stripe electrode 112, and stripe electrodes 115, 116 are grounded. Then, the current density in the active layer has a shape in which a recess is formed in the center, and the central position of the near-visual-field image is shifted to B. Then, a current of 25mA is made to flow through the stripe electrode 112 and a stripe electrode 113, and only the stripe electrode 1116 is grounded. Then, the current density in the active layer has a shape in which the recess is formed in the center, and the central position of the near-visual-field image is shifted to C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser array used for exposing a photosensitive drum mounted on a laser printer or a laser copying machine and writing information on an optical disk, and more particularly to emitting a semiconductor laser array. The present invention relates to a semiconductor laser array capable of moving the beam position of laser light on a plane at small intervals.

[0002]

2. Description of the Related Art A multi-beam semiconductor laser array having a plurality of individually addressable light emitting points arranged at a narrow interval is used in optical disk technology, laser printing technology, optical interconnection,
It is important for many applications such as optical fiber communication.

When the multi-beam semiconductor laser array is applied to each of the above techniques, it is desirable that the laser elements of the laser array be as close as possible in order to make the optical device associated with the semiconductor laser array a simple structure. For example, when a multi-beam semiconductor laser array is mounted as a light source of a laser printer that scans a laser beam with a polygon mirror to write an electrostatic latent image on a photoconductor drum, the printing time can be shortened. However, if the distance between the laser elements is wide, there are restrictions that the optical system between the light source and the photosensitive drum becomes complicated and that a complicated control system such as an interlacing operation must be used.

As an individually addressable multi-beam semiconductor laser array, there is a ridge stripe type dual-beam semiconductor laser as shown in the sectional view of FIG.
In the figure, 301 is an n-side electrode and 302 is n-type GaAs.
Substrate, 303 is n-type AlGaAs cladding layer, 304 is active layer, 305 is p-type AlGaAs cladding layer, 306
Is an n-type GaAs current blocking layer, 307 is a p + type GaA
The s contact layer and 308 are p electrodes. This dual-beam semiconductor laser has a mesa stripe structure 3 in the lateral direction.
By producing No. 09, a difference in refractive index in the lateral direction is embodied and a stable transverse mode is obtained. However, since the lateral mesa stripe structure 309 undergoes etching and regrowth processes, the element spacing 310 is currently limited to 25 μm.

Further, as shown in the sectional view of FIG. 7 disclosed in Japanese Patent Laid-Open No. 2-39583, a Si impurity diffusion layer 40 is used.
1 is applied to an AlGaAs infrared semiconductor laser to form an embedded structure. This buried structure can provide a multi-beam semiconductor laser having a low threshold value and a narrow interval 402 because it does not use a regrowth process, but the interval is still limited to 10 μm.

If a gain-guiding semiconductor laser is used without making a lateral refractive index difference as shown in FIGS. 6 and 7, photolithography can be performed in principle without being restricted by processes such as etching and diffusion. The electrode spacing can be narrowed to the limit of technology, and a semiconductor laser array with a small beam spacing can be manufactured. However, a gain-guided laser without a lateral structure is fatal as a practical laser for lateral mode instability in which the position of the light emitting point naturally changes before and after the occurrence of kink, high threshold current, and wide-near-field image. It inherently has a problem.

On the other hand, Research Report 93, Electrotechnical Laboratory
No. 4 "Study on Nonlinear Operation of Twin Stripe Laser and Application to Optical Logic Operation" and Japanese Patent Application No. 3-278490.
The publication describes the operating characteristics of the twin stripe laser. 8A and 8B show a cross section and a plan view of the twin stripe laser. In the figure, 501 is an n-type GaAs substrate, 502 is an n-type GaAs buffer layer,
503 is an n-type AlGaAs clad layer, 504 is an active layer, 505 is a p-type AlGaAs clad layer, and 506 is p.
A + -type GaAs contact layer, 507 is a p-electrode, 508 is an etching groove, and 509 is an n-side electrode.

Here, if the currents are equally injected from the two stripe electrodes 507, the current density distribution becomes a shape having a depression in the central portion (see solid line G in FIG. 9), so that the plasma effect makes it effective in the central portion. The refractive index is increased, light is confined in this region, and a low threshold value (see solid line G in FIG. 11) can be realized in a narrow near-field image (see solid line G in FIG. 10). By the way, the dotted line T in FIGS. 9 to 11 is the experimental data when the current is injected only through one of the two stripe electrodes 507 of the twin stripe laser. Therefore, also in the gain waveguide type semiconductor laser array, the lateral refractive index difference can be embodied by injecting current so that the current density distribution has a recess in the central portion.

On the other hand, information is recorded on the optical disc,
Further, in order to optically reproduce the recorded information, it is necessary to irradiate a track on the optical disk with a beam of laser light emitted from the optical head at an appropriate position on the track. The device is provided with a so-called tracking servo mechanism. However,
This tracking servo mechanism has a structure in which a lens is mechanically moved by a motor and its frequency band is limited to several kHz, so that the rotation speed of the disk cannot be increased and the data transfer rate cannot be increased. There is.

As a method of solving this problem, there is a method of using the function of moving the light emitting point of the semiconductor laser array instead of or in combination with the tracking servo mechanism by the motor.

FIG. 12 shows an example of the structure of a semiconductor laser array in which a large number of stripe electrodes are arranged on a semiconductor contact layer to move the light emitting point. Also,
13A, 13B and 13C are a graph showing a light emitting point in the semiconductor laser array shown in FIG. 12, a plan view showing a stripe electrode, and a graph showing a current density in the semiconductor laser array.

In the figure, 901 is an n-type GaAs substrate,
902 is an n-type GaAs buffer layer, 903 is an n-type AlG
aAs buffer layer, 904 is n-type AlGaAs cladding layer, 905 is active layer, 906 is p-type AlGaAs cladding layer, 907 is AlGaAs contact layer, and 908 is p-type.
+ Type GaAs contact layer, 909 is a p electrode (stripe electrode), 910 is a high resistance region, and 911 is a p electrode 909.
, 912 is an interval between p electrodes 909, and 913 is an n-side electrode. Further, reference numerals 1001, 1002 and 1003 denote adjacent electrodes among the plurality of p electrodes 909.

In the semiconductor laser array shown in FIG. 12, when a current is simultaneously injected from two adjacent stripe electrodes, the middle of the two stripe electrodes becomes a light emitting point.
Therefore, the light emitting point can be moved by switching the position of the stripe electrode for injecting the current.

If the laser beam is aligned with the information track on the optical disk by the direct modulation of the semiconductor laser in this way, the spot position can be corrected at several MHz, and the data transfer rate can be greatly increased. be able to.

[0015]

However, as shown in FIG.
In a semiconductor laser array in which a large number of stripe electrodes are arranged on the semiconductor contact layer, that is, in the case of a semiconductor laser array in which a large number of twin stripe lasers are arranged, when the current is injected by the stripe electrodes 1001 and 1002, the light emitting point becomes the above-mentioned 2 One stripe electrode 1001,1
002 intermediate position (reference numeral A in FIGS. 12 and 13)
), And then stripe electrodes 1002 and 100
When a current is injected by means of 3, the light emitting point becomes an intermediate position (indicated by a symbol C in FIGS. 12 and 13) between the two stripe electrodes 1002 and 1003. Therefore,
Continuous beam movement is not possible.

Although continuous movement of the light emitting point is required for tracking the optical disk, the light emitting point is point A as described above.
Tracking cannot be performed by the discontinuous movement of the light emitting points at a large interval 1004 such as jumping from the point C to the point C.

Therefore, the problem to be solved by the present invention is, as described above, in a semiconductor laser array in which a light emitting point can be moved, which employs a current injection method for realizing a shape in which a current density distribution has a depression at the center. It is to realize the movement of the light emitting points at the minute intervals necessary for tracking.

[0018]

A basic device structure is a semiconductor substrate, and at least a first clad layer of a first conductivity type, an active layer, and a second clad layer of a second conductivity type on the semiconductor substrate. And a semiconductor layer of a contact layer of the second conductivity type are sequentially laminated, and in a semiconductor laser having a plurality of first stripe electrodes on the contact layer of the second conductivity type, on the side opposite to the contact layer of the second conductivity type. A plurality of second stripe electrodes are also provided on the semiconductor substrate, and the second stripe electrodes are provided at positions on the semiconductor substrate corresponding to the adjacent first stripe electrodes, and the stripe electrodes It is a semiconductor laser array characterized by insulating between them or having good conductivity just below the electrodes.

Further, the driving method is such that N adjacent first stripe electrodes of the first stripe electrodes are adjacent to each other and the electrodes at both ends of the N first stripe electrodes are located inside. N−M (where M is an integer and a value of 1 ≦ M <N) a method of passing a current between the second stripe electrodes and a method of connecting adjacent N of the second stripe electrodes.
N second stripe electrodes and N−M (where M is M) inside the positions of the electrodes at both ends of the N second stripe electrodes.
Is an integer and a value of 1 ≦ M <N). By alternately performing the above two methods, beam movement with a small interval can be realized. In the case of N = 2, if the currents injected into the plurality of electrodes are equally injected into the two electrodes, the current density distribution in the active layer naturally has a shape having a recess in the center in the structure of the present invention. be able to. When N ≧ 3, the current injection amount of each electrode is controlled so that the current density distribution in the active layer has a shape having a recess in the center. It is characterized by the above device structure and driving method.

[0020]

According to the present invention, since the stripe electrodes are offset by half the distance between the stripe electrodes on the front and back of the substrate,
By passing a current between two adjacent strip electrodes on one surface and one strip electrode on the other surface located between these two strip electrodes, the current density distribution in the active layer is centered. The beam position of the laser light on the emission surface can be moved at a small interval while having a shape having a recess.

[0021]

EXAMPLES The present invention will be specifically described below based on Examples and Comparative Examples.

[First Embodiment] FIG. 1 is a sectional view of a spot moving laser having a plurality of electrodes provided on a p-type semiconductor contact layer. On the n-type GaAs substrate 101, an n-type GaAs buffer layer 102, an n-type A buffer layer 102, and an n-type A are formed by a crystal thin film growth apparatus such as a metal organic chemical vapor deposition method or a molecular beam epitaxial growth apparatus.
lGaAs buffer layer 103, n-type AlGaAs cladding layer 104, GaAs active layer 105, p-type AlGaA
s clad layer 106, p-type AlGaAs contact layer 1
07 and the p-type GaAs contact layer 108 are sequentially laminated. p-side stripe electrodes 111, 112, 113, 11
4 is an alloy containing Au as a main component, or a laminated structure of metal is formed by vapor deposition, and the width 118 of this electrode is 2 μm.
And the electrode spacing 119 is 5 μm or less.
In the region 109, protons accelerated at 75 keV are incident, and the dose amount is 3 × 10 ¹⁵ ions / cm ² ,
The p-type contact layer and the p-type cladding layer are made to have a high resistance without being mixed. As a result, it is possible to suppress the lateral diffusion of the current in the upper layer portion above the active layer, and to prevent the adjacent p-side electrodes 1
When currents are equally injected from 11 and 112, a current density distribution having a depression in the center is realized in the active layer. Alternatively, the same effect can be expected by dry etching the region 109.

Next, the n-type GaAs substrate 101 is polished or etched to reduce the device thickness to 100 μm or less. Next, parallel to the extending direction of the p-side stripe electrode,
Further, the n-side stripe electrode is provided on the polished surface of the n-type GaAs substrate corresponding to the position between the p-side stripe electrode and the p-side stripe electrode.

In this case, it becomes difficult to perform the alignment by the usual patterning of photoresist exposure. Therefore, FIG.
As shown in FIG. 5, a photoresist 1302 is applied in advance by a spin coater on the polished surface of the n-type GaAs substrate from which the oxide film generated by polishing is removed, and the p-side stripe electrode 1303 is used as a mask to remove the p-side stripe electrode side. From the infrared light source 1301. Then, since the infrared ray 1304 at the p-side stripe electrode position is absorbed, the infrared ray 1305 at the position without the p-side stripe electrode passes through the AlGaAs semiconductor film 1300 and exposes the photoresist 1302 applied to the polished surface of the GaAs substrate. . By using the method described above, the position of the n-type stripe electrode can be easily aligned.

Through the above steps, an AuGe / Ni alloy was used as an n-type stripe electrode material as shown in FIG.
5, 116, 117 are formed on the polishing surface in stripes.

Insulating region 11 in n-type GaAs substrate 101
In the case of 0, protons are incident and insulated in advance before the epitaxial growth of the laser structure is performed, or photolithography is performed again after the electrodes are formed and dry etching is performed between the electrodes, and then protons are incident and insulated. Alternatively, it is etched by dry etching. Alternatively, n-type GaA
A pn junction is formed by vapor phase diffusion of zinc between the electrodes 110 on the s substrate side, and the current path is limited.

Next, a method of driving the above semiconductor laser array will be described.

First, the stripe electrode 111 has a length of 25 m.
When 25 mA is applied to A and the striped electrode 112 and only the striped electrode 115 is grounded, the current path becomes as shown by a thick arrow 121, and the current density in the active layer has a shape having a depression at the center, which results in a near-field image. The center position is A. Next, when 50 mA is injected from the stripe electrode 112 and the stripe electrodes 115 and 116 are grounded, the current path becomes as indicated by the dotted arrow 122, and the current density in the active layer becomes a shape having a depression in the center, which results in a near-field image. The center position moves to B. Next, apply 25 to the stripe electrode 112.
When current of 25 mA is applied to the mA and stripe electrode 113 and only the stripe electrode 116 is grounded, the current path becomes as indicated by the thin arrow 123, and the current density in the active layer has a recess in the center, which is the center of the near-field image. Position is C
Move on to. In the conventional current injection method, the center position of the near-field image can be moved only from A to C, but the center position of the near-field image is sequentially changed from A to C at small intervals due to the device configuration and the current injection method. It becomes possible to move from B to C.

[Second Embodiment] In the first embodiment, the current injection is performed by the two stripe electrodes, but in the second embodiment, the stripe structure of the first embodiment is used without changing the device configuration of the first embodiment. An example will be given in which the interval of the movement of the light emitting point is smaller and smoother than that of the first embodiment by making the width of the electrode smaller and injecting the current from a larger number of stripe electrodes.

3 (a) and 3 (b) show a laser sectional view and the movement of the near-field image on the end face in the second embodiment of the present invention. The members corresponding to those in the first embodiment are designated by the same reference numerals. In the figure, 201 to 204 indicate p-side stripe electrodes, and 205 to 207 indicate n-side stripe electrodes.

The width 207 of the stripe electrodes and the distance 211 between the electrodes are smaller than those of the first embodiment.
The current injection method is 20 mA for the stripe electrode 201, 2
02 is 10 mA and 203 is 20 mA, and only the stripe electrodes 205 and 206 are grounded. At this time, in the current density distribution, a recess is formed immediately below the stripe electrode 202, and the light is confined at this point. As a result, the near-field image becomes like 208 (see FIG. 3B). Next, by injecting 25 mA into the stripe electrode 202 and 25 mA into the stripe electrode 203, and grounding the stripe electrodes 205, 206, and 207, light is now confined between the stripe electrodes 202 and 203, and as a result, the near-field image becomes 209. Become. If the above current injection method is repeated in the same manner one after another, the beam moves on the end faces at small intervals. For example, stripe electrode width 2
07 and the distance between electrodes 211 is 1 μm, the distance of movement of the near-field image on the end face is 2 μm as in the conventional current injection method.
Half of m is 1 μm.

[Third Embodiment] In the third embodiment, the device structure is the p-type GaAs contact layer 1 as shown in FIG.
The region 1101 immediately below the electrodes 111 to 114 of 08 is a good conduction region by zinc diffusion, and the current path is 1102.

[Fourth Embodiment] In the fourth embodiment, the device structure is a p-type GaAs contact layer 1 as shown in FIG.
A region 1210 directly below the electrodes 1208 and 1209 of 206 is etched by reactive ion etching, and the etched region 1210 is filled with stripe electrodes 1208 and 1209. In this manner, by injecting the current from a position closer to the active layer 1204, the lateral current spreading of the current can be suppressed, and the current density distribution in the active layer 1204 can be easily controlled. Etched area 121
At the bottom of 0, the carrier concentration is increased by zinc diffusion to form a resistive electrode. Alternatively, p, which has a high carrier concentration in advance,
A type GaAs thin film layer is epitaxially grown. This is realized by a combination of the following semiconductor thin film multilayer structure and process.

Si-doped G on the n-type semiconductor substrate 1201
aAs buffer layer 1202, Si-doped AlGaAs
Cladding layer 1203, active layer 1204, Zn-doped Al
GaAs clad layer 1205, high-concentration Zn-doped GaA
s contact layer 1206, GaAs cap layer 1207
Are sequentially laminated. Next, the region 1210 is subjected to reactive ion etching to perform high-concentration Zn-doped GaAs contact layer 1
Etch until 206 is reached. Then, the electrode material is vapor-deposited.

In such a structure, current injection is performed at a position closer to the active layer as compared with the first embodiment, so that the current density distribution in the active layer can be easily controlled. In addition, the position between electrodes 12
When 12 is irradiated with protons to have high resistance, the controllability of the current density distribution in the active layer is further improved.

In addition, in the present specification, as examples,
Although four types of the fourth embodiment have been described, the present invention can be applied to all device structures that can be realized by a combination of these four types regardless of the first stripe electrode and the second stripe electrode. .

As described above, in the embodiments, only the AlGaAs material is described, but the material is not limited to this material and AlGaI is used.
It is applicable to nP-based materials, GaInAsP-based materials, CdZnSSe-based materials, ZnMgSSe-based materials, and other material systems that can be used as semiconductor lasers.

[0038]

According to the present invention, in a gain waveguide type semiconductor laser array having a narrow beam interval, a beam position is moved at a small interval, and a semiconductor laser array having a narrow near-field image and a low threshold is realized. You can Therefore, if this laser is used in a laser printer or a laser copying machine, the burden on the polygon mirror is reduced, or a polygon mirror is not required, and a low-cost and high-speed printer can be provided. Is possible.

[0039]

[Simple Drawing Description]

[0040]

FIG. 1 is a sectional view of a semiconductor laser array according to a first embodiment of the present invention.

[0041]

FIG. 2 is a cross-sectional view illustrating a manufacturing method of forming stripe electrodes on both surfaces.

[0042]

FIG. 3A is a sectional view of a semiconductor laser array according to a second embodiment of the present invention, and FIG. 3B is an explanatory view showing movement of a light emitting point.

[0043]

FIG. 4 is a sectional view of a semiconductor laser array according to a third embodiment of the present invention.

[0044]

FIG. 5 is a sectional view of a semiconductor laser array according to a fourth embodiment of the present invention.

[0045]

FIG. 6 is a sectional view of a dual beam semiconductor laser having a ridge stripe structure.

[0046]

FIG. 7 is a cross-sectional view of an embedded dual-beam semiconductor laser by diffusing Si impurities.

[0047]

FIG. 8A is a sectional view of a twin stripe laser,
(B) is the same top view.

[0048]

FIG. 9 is a graph showing a difference in lateral current density distribution in an active layer according to an injection method in a twin stripe laser.

[0049]

FIG. 10 is a graph showing a difference in near-field image depending on an injection method in a twin stripe laser.

[0050]

FIG. 11 is a difference in current light output characteristics depending on the injection method in the twin stripe laser.

[0051]

FIG. 12A is a plan view of a multi-beam laser of a twin stripe laser, and FIG. 12B is a sectional view of the same.

[0052]

FIG. 13 is a beam position and current density distribution of a multi-beam twin stripe laser.

[0053]

[Explanation of symbols]

301: n-side electrode, 302: n-type GaAs substrate, 30
3: n-type AlGaAs cladding layer, 304: active layer, 3
05: p-type AlGaAs cladding layer, 306: n-type Ga
As current blocking layer, 307: p + type GaAs contact layer, 308: p electrode, 401: Si impurity diffusion region,
402: beam spacing, 501: n-type GaAs substrate, 50
2: n-type GaAs buffer layer, 503: n-type AlGaA
s clad layer, 504: active layer, 505: p-type AlGa
As clad layer, 506: p + type GaAs contact layer, 507: p electrode, 508: etching groove, 509:
n-side electrode, 901: n-type GaAs substrate, 902: n-type G
aAs buffer layer, 903: n-type AlGaAs buffer layer, 904: n-type AlGaAs cladding layer, 905: active layer, 906: p-type AlGaAs cladding layer, 907:
AlGaAs contact layer, 908: p + type GaAs contact layer, 909: p electrode, 913: n-side electrode, 10
01 to 1003: p electrode, 1004: beam movement interval

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Nakayama 2274 Hongo, Ebina, Ebina, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor, Houji Seko 2274, Hongo, Ebina, Kanagawa Fuji Xerox Co., Ltd. (72) ) Inventor Mario Fuse 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (4)

[Claims] 1. A semiconductor substrate, and a semiconductor layer of at least a first clad layer of a first conductivity type, an active layer, a second clad layer of a second conductivity type, and a contact layer of a second conductivity type on the semiconductor substrate. A semiconductor laser having a plurality of first stripe electrodes on a second-conductivity-type contact layer, and a plurality of second stripe electrodes on a semiconductor substrate opposite to the second-conductivity-type contact layer. And a position where the second stripe electrode is provided is a position on the semiconductor substrate corresponding to the adjacent first stripe electrodes, and the stripe electrodes are insulated from each other. Semiconductor laser array. 2. A semiconductor substrate, and a semiconductor layer of at least a first clad layer of a first conductivity type, an active layer, a second clad layer of a second conductivity type, and a contact layer of a second conductivity type on the semiconductor substrate. A semiconductor laser having a plurality of first stripe electrodes on a second-conductivity-type contact layer, and a plurality of second stripe electrodes on a semiconductor substrate opposite to the second-conductivity-type contact layer. And the position where the second stripe electrode is provided is a position on the semiconductor substrate corresponding to the space between the adjacent first stripe electrodes, and only the region directly below the stripe electrode has good conductivity. A semiconductor laser array characterized in that 3. Among the first striped electrodes, any N first striped electrodes adjacent to each other and N−M (not provided) inside the electrodes of both ends of the N first striped electrodes are provided. M is an integer and a value of 1 ≦ M <N). A current density distribution in the active layer has a shape having a recess in the center by causing a current to flow between the second stripe electrode and the second stripe electrode. A method of driving a semiconductor laser array according to claim 1 or 2. 4. Of the second stripe electrodes, any N second stripe electrodes adjacent to each other and N−M (where provided on the inner side of the electrodes at both ends of the N second stripe electrodes) M is an integer and a value of 1 ≦ M <N). A current density distribution in the active layer has a shape having a recess in the center by causing a current to flow between the first stripe electrode and the first stripe electrode. The method of driving a semiconductor laser array according to claim 1 or 2.