JPH05259565A - Multi-beam semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a multi-beam semiconductor laser applicable to an A GaInP based semiconductor laser. CONSTITUTION:The title semiconductor laser has two beams A, B on the same semiconductor substrate 1, and is constituted as follows; a common electrode 10 is formed on the rear of the semiconductor substrate 1, and electrodes 9 which are isolated for each of the beams are formed on the surface, in order to be able to mutually independently drive the beam A and the beam B. Active layers 4 and clad layers 3, 5 for the respective beams are integrated in a unified body, respectively, as the common layers. The thickness (d) of the upper side clad layer 5 between the beam A and the beam B is smaller than that of the beam part. Thereby crosstalk between the beam A and the beam B can be prevented, and independent operation is enabled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a multi-beam semiconductor laser having a plurality of beams which can be independently driven on the same semiconductor chip.

[0002]

2. Description of the Related Art Currently, semiconductor lasers are widely used in laser printers and optical disks, but the drawing speed of the printer and the data transfer speed of the optical disk are not necessarily sufficiently high. In this case, if two laser beams that are close to each other and can be driven independently can be provided on one semiconductor laser substrate, then a system having double the writing speed or data transfer speed with one optical system can be created. Since it is expected that such multi-beam semiconductor lasers can be produced, research on such multi-beam semiconductor lasers has recently been conducted. This type of laser currently used is of the AlGaAs type,
The wavelength is about 0.78 to 0.84 μm. In this material system, as a method for electrically separating the beams, a method of diffusing impurities between the beams to increase the resistance, or a method of etching deeper than the active layer at the time of beam formation and then lowering the refractive index A method of burying with a high resistance crystal is known.

On the other hand, aside from this, the development of a red semiconductor laser based on AlGaInP and having a wavelength of 0, 6 to 0, 7 μm is in progress. If the AlGaAs semiconductor laser is replaced with an AlGaInP semiconductor laser,
In the laser printer, it is possible to use a photosensitive material with higher sensitivity, and it is expected that the printing speed can be increased. Further, in the optical disc, since the light spot can be narrowed down further, the capacity can be increased.

[0004]

[Problems to be Solved by the Invention]
In the case of using an aInP-based material, the technique of forming a multi-beam as in the AlGaAs-based material has not been sufficiently developed.
That is, the multi-beam technology for AlGaAs semiconductor lasers, such as the technology of increasing the resistance by impurity diffusion or the technology of etching deeper than the active layer and burying with a low-refractive-index high-resistance crystal, may not be applied to the AlGaInP semiconductor laser as it is. As a multi-beam semiconductor laser capable of driving each beam independently of each other, sufficient characteristics could not be obtained. It is known that the beams are not driven independently of each other, but are driven simultaneously to simply increase the output (Reference “High-power AlGaInP
three-ridge type LASER diode array "ELECTRONICS
LETTERS 17th 1988 Vol.24 No.6).

An object of the present invention is to obtain a multi-beam semiconductor laser capable of driving a plurality of beams independently of each other, even in an AlGaInP-based semiconductor laser.

[0006]

In the multi-beam semiconductor laser of the present invention, the active layer and the clad layer of each beam are integrated as a common layer, and the thickness of the upper clad layer between the beams is equal to the beam part. It is thinner than that.

[0007]

According to the conventional wisdom so far, it was considered that each beam cannot be driven independently of each other due to electrical crosstalk unless the active layer is electrically separated. This can be seen, for example, in the literature “Properties of closly
spaced independently addressable lasors fabricated
by impurity-induced disordering '' Appl.Phys.Lett.
56. (17), 23 April 1990. However, it has been found that even if the active layer and the clad layer are not separated for each beam, electrical crosstalk can be sufficiently reduced if the clad on the separation electrode side, that is, the upper clad layer is thin between the beams. It was also found that removing the upper clad layer between the beams rather deteriorates the oscillation characteristics of each beam. The present invention is based on this experimental fact.

[0008]

FIG. 1 is a sectional view of a multi-beam semiconductor laser showing an embodiment of the present invention. In FIG.
Is a GaAs substrate with Si added, 3 is A with Se added
A cladding layer made of 1GaInP, 4 is an active layer having a strained multiple quantum well structure, and 5 is AlGaIn to which Zn is added.
A cladding layer made of P, 6 is a current blocking layer made of GaAs to which Si is added, and 7 is Ga to which Zn is added.
A cap layer made of InP is shown. Reference numeral 8 denotes a contact layer made of GaAs to which Zn is added, and 9 and 1
Reference numeral 0 indicates a p-electrode and an n-electrode, respectively. Reference numeral 12 is a silicon nitride film formed so as to fill the separation groove 11 provided between the beams A and B. In addition,
This embodiment can be referred to as an AlGaInP-based semiconductor laser. In the AlGaInP-based semiconductor laser described here, the Al composition of the active layer is zero, that is, GaInP and the Ga composition of the cladding layer are zero, that is, AlInP. Shall also be included. FIG. 3B is an energy band diagram showing the strained multiple quantum well structure of the active layer 4. As shown in the figure, the active layer 4 is composed of an undoped Ga _0.47 In _0.57 P well layer 41 having a thickness of 100 Å and an undoped (Al _0.4 Ga _0.6 ) _0.5 I layer separating the well layer 41.
A barrier layer 42 made of n _0.5 P and having a thickness of 80 Å, and a thickness 80 made of the same material as the barrier layer 42.
The optical confinement layer 43 has a thickness of 0 angstrom. It is a known technique to form the active layer with such a multiple quantum well structure. Moreover, when the material having the composition ratio as described in this embodiment is used for the active layer, the active layer is subjected to compressive strain.

FIG. 1 schematically shows the structure,
The dimensional ratio of each part does not necessarily represent the dimensional ratio of an actual device. For example, the thickness of the GaAs substrate 1 is actually 7
While the thickness is about 0 μm, the total thickness from the cladding layer 3 to the cap layer 7 thereover is 2 to 3 μm, and the thickness of the contact layer 8 thereon is about 2 μm.

The active layer 4 and the cladding layers 3 and 5 are formed in common for each of the beams A and B, but the upper cladding layer 5
Is thinned between the beams, and the thickness d of the thin portion is 2000 angstrom. An isolation groove 11 reaching the surface of the current block layer 6 is formed in the contact layer 8, and is separated into two beams by a silicon nitride film 12 formed so as to fill the groove 11.
By thinning the upper cladding layer 5 between the beams A and B as in this embodiment, the electrical crosstalk between the beams can be sufficiently reduced in practical use. Note that if the upper clad layer in this portion is removed, the oscillation characteristics of each beam deteriorate, so it is important to make the thickness sufficiently thin so as not to remove it.

Further, in order to obtain a practical multi-beam semiconductor laser, it is necessary to suppress not only electrical crosstalk but also thermal crosstalk. That is, since the semiconductor laser has a characteristic that its output decreases as the temperature rises, it is necessary to suppress the adverse effect that the output of another beam decreases due to heat generation during driving. As a method therefor, a method of preventing heat transfer between the beams, a method of making each beam less susceptible to heat, a method of making each beam less likely to generate heat, and the like are considered. In this embodiment, the third method is adopted, and by forming the active layer 4 into a strained multiple quantum well structure,
The threshold current is lowered to suppress heat generation. That is, the threshold current is reduced by applying compressive strain to the active layer, and the effect is enhanced by forming a multiple quantum well structure. Therefore, heat generation of each beam is suppressed, and the outputs of the other beams are not reduced by heating.

Next, a method of manufacturing such a multi-beam semiconductor laser will be described with reference to FIGS.

After the clad layer 3, the active layer 4, the clad layer 5 and the cap layer 7 are sequentially epitaxially grown on the GaAs substrate 1, a silicon nitride film 21 is formed (FIG. 2A). The crystal growth temperature at this time is 740 ° C. Doping amount of n and P clad is 2 × 10 each
^{Both 17} cm ⁻³ and 4 × 10 ¹⁷ cm ^{−3 have} a thickness of 1 μm. The silicon nitride film 21 is patterned so as to serve as a mask when the portion indicated by the broken line is removed by etching in the next step. Buffered hydrofluoric acid was used as an etchant for this patterning. Here, the width of the two patterned silicon nitride films 21 is 5 μm, and the distance between the centers of the two is 15 μm.
I am trying.

Then, next, mesa etching is performed. Here, mixed acid (sulfuric acid: hydrogen peroxide:
Etching is performed for 6 minutes using water = 3: 1: 1) to leave the upper cladding layer 5 at 2000 angstroms (FIG. 2B). Then, GaAs with Si added to the portion removed by etching (impurity concentration is 2 × 10 ¹⁷
cm ^-3 ) is grown to form the current blocking layer 6. The silicon nitride film 21 is removed with an etchant of hydrofluoric acid: water = 1: 1 (FIG. 2C). After that, a silicon nitride film is formed on the entire surface, and the silicon nitride film 22 is left only between the beams by resist patterning and etching (FIG. 2D).

Next, Zn-added GaAs (impurity concentration: 1 × 10 ¹⁹ cm ⁻³ ) was grown to 1 μm, and the contact layer 8 separated at the portion where the silicon nitride film 22 was left.
Are formed (FIG. 3A). Then, the silicon nitride film 2
2 is removed, and a silicon nitride film 11 'is newly formed on the entire surface. Then, the resist pattern 30 is left on the separated portion of the contact layer 8, the silicon nitride film 11 'is removed by etching using the resist pattern 30 as a mask, and the patterned silicon nitride film 11 is left (FIG. 3B. )).

Further, after a metal film 9'consisting of a Ti / Pt / Au3 layer film is formed on the entire surface by vapor deposition (FIG. 3).
(C)) By removing the resist pattern 30 with acetone, the metal film 9'above is lifted off to leave the p-electrode 9 for each beam. Subsequently, the substrate is etched from the back to a thickness of about 70 μm, and then the n-electrode is vapor-deposited on the back surface and alloyed at 400 ° C. for 1 minute in a nitrogen atmosphere to remove the AuGe / Ni / Au3 layer film. Then, the n-electrode 10 is formed (FIG. 3D).

The multi-beam semiconductor laser thus manufactured is cleaved into a chip having a width of 400 μm and a cavity length of about 250 μm to form a multi-beam semiconductor laser having two beams. So-called epi-up mounting was performed with the above as the upper side. Figure 4
The current-light output characteristics of each beam of the multi-beam semiconductor laser thus mounted are shown. The characteristics indicated by solid lines A and B in the figure are those when the beams A and B are driven independently, and the characteristics indicated by solid line C are those when the p electrodes of both beams are short-circuited. The threshold current when short-circuited is almost twice the threshold current when each beam is driven independently. Also, when the near-field image when only one beam was turned on was seen, the other beam did not emit light. Furthermore, when the resistance between the p-electrodes of both beams, that is, the voltage-current characteristic is examined, the resistance value is non-linear, and the resistance value decreases as the applied voltage decreases, but it is in a minute voltage region of 0.1 V or less. Then, the resistance value became almost constant and was about 10 KΩ. That is, it can be seen that the semiconductor laser of this example has a resistance value between the p electrodes which is always 10 KΩ or more, and the current crosstalk is very small. If the resistance value between the p electrodes is 1 KΩ or more, the beams can be driven independently of each other to some extent. For example, the thickness d of the p-clad layer (upper clad layer) between the beams is set to 0.2 μm in the present embodiment, but if it is set to 0.3 μm, the resistance value between the p-electrodes increases and the current crossing is increased. Although an increase in talk was recognized, sufficient independent driveability for practical use can be secured.

The present invention is intended to realize a multi-beam semiconductor laser having AlGaInP as a cladding, but the present invention is not limited to this material system. For example, the so-called A in the 0.78-1.1 μm band
It can also be applied to a 1GaAs semiconductor laser. In that case, (Al) GaInAs is used as the strain active layer.
Further, when a semiconductor laser of the same wavelength band (0.78-1.1 μm band) is realized, it is possible to use GaInP or AlGaInP instead of AlGaAs in the clad, and the present invention can be applied in that case as well. further,
It can also be applied to a GaInAsP semiconductor laser in the 1.3 to 1.6 μm band.

FIG. 5 shows a second embodiment of the multi-beam semiconductor laser of the present invention. The same elements as those in the first embodiment are designated by the same reference numerals, and their description will be omitted. Although this embodiment has five beams, the p-electrode 9 for the two beams on the left and the p-electrode 9 for the three beams on the right are common. As a result, the two left beams are simultaneously driven, the three right groups are similarly driven simultaneously, and the left and right groups are independently driven.

[0020]

As described above, according to the present invention, the active layer and the cladding layer of each beam are integrated as a common layer, and the thickness of the upper cladding layer between the beams is smaller than that of the beam portion. By doing so, a multi-beam semiconductor laser with less crosstalk can be obtained. In particular, it is useful in a GaInP or AlGaInP-based laser in which it is difficult to form a structure in which an active layer separated for each beam is buried, and it is possible to use a multi-beam semiconductor laser having a shorter wavelength than that of an AlGaAs-based laser. is there.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a multi-beam semiconductor laser showing an embodiment of the present invention.

2A to 2D are process cross-sectional views showing a manufacturing method according to an embodiment of the present invention.

FIG. 3 is a process sectional view showing the manufacturing method of the embodiment of the present invention.

FIG. 4 is a diagram showing current-light output characteristics of one embodiment of the present invention.

FIG. 5 is a sectional view showing a second embodiment of the present invention.

[Explanation of symbols]

1 ... GaAs substrate, 3 ... lower cladding layer, 4 ... active layer having strained multiple quantum well structure, 5 ... upper cladding layer, 6 ...
Current blocking layer, 8 ... Contact layer, 9 ... P electrode, 10
... n electrode.

Claims (6)

[Claims] 1. Beams can be driven independently of each other by having a plurality of beams on the same semiconductor substrate, and providing a common electrode on the back surface of the semiconductor substrate and providing electrodes separated for each beam on the front surface. In the multi-beam semiconductor laser configured as described above, the active layer and the clad layer of each beam are integrated as a common layer, and the thickness of the upper clad layer between the beams is smaller than that of the beam part. Characteristic multi-beam semiconductor laser. 2. The multi-beam semiconductor laser according to claim 1, wherein the resistance between the electrodes separated for each beam is 1 kΩ or more. 3. The material of the active layer is (Al) GaInP
(However, the case where the Al composition ratio is zero is included), and the material of the cladding layer is Al (Ga) InP (however, the case where the Ga composition ratio is zero is included).
The multi-beam semiconductor laser described in. 4. The multi-beam semiconductor laser according to claim 3, wherein the active layer is subjected to compressive strain. 5. The multi-beam semiconductor laser according to claim 4, wherein the active layer has a strained multiple quantum well isolation confinement type hetero structure. 6. The conductivity type of the upper cladding layer is p-type,
6. The multi-beam semiconductor laser according to claim 3, wherein the cladding layer has a thickness of 0.3 μm or less between the beams.