JP2733210B2 - Semiconductor stripe laser - Google Patents

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 structural improvement for improving characteristics of a stripe type semiconductor laser (semiconductor stripe laser).

[0002]

2. Description of the Related Art Semiconductor lasers have been gradually improved in characteristics since the 1970s, but in the first place, semiconductor lasers emit spontaneous emission light upon injection of carriers, and a part thereof is an optical resonator. The mode is amplified as a mode, and when the amplification factor exceeds the loss, the optical resonance mode becomes dominant, and it follows the principle that efficient electron-light conversion can be achieved by stimulated emission.

[0003]

However, the conventional semiconductor laser has few means for suppressing the leakage of the spontaneous emission light at the beginning, and has a certain large threshold current for efficient light emission. I was Furthermore, there is no disclosure of a structure that is particularly advantageous with respect to the problem of recombination on the side surface or the emission end face of the active layer or the physical protection of the emission end face. The present invention basically addresses these drawbacks of the conventional example, and employs the distributed feedback principle among semiconductor lasers.
In the stripe laser, extremely low threshold,
Ideally, it is intended to provide a semiconductor stripe laser having a structural principle capable of driving without a threshold value or having an excellent recombination suppressing effect.

[0004]

Since the present invention SUMMARY OF] To achieve the above object, sandwiching the active layer to cause laser oscillation in the vertical clad layer, a semiconductor stripe laser for outputting laser light from an end face of the active layer, a semiconductor stripe laser To
It is proposed to configure a distributed feedback laser and cover the entire periphery of the active layer including the laser light emitting end face with a cladding layer. Furthermore, it is proposed that the clad layer covering the periphery of the active layer is formed of a semiconductor multilayer film.

[0005]

FIGS. 1, 2 and 3 show an embodiment of a semiconductor laser manufactured according to the present invention. Here, for the sake of convenience, a semiconductor laser according to the present invention is first used. A basic example of one step of a semiconductor fine processing method is described with reference to FIGS.

[0006] First, as shown in FIG.
As shown in FIG. 4A, an AlGaAs layer 11 formed by epitaxial growth on a GaAs substrate 10 or a tungsten (about 100 nm thick) the W) thin film by sputtering is formed as an etching resist film, existing, by conventional lithography dedicated machine, after patterning the resist film by optical lithography or electron lithography according to the desired pattern, a desired pattern by CF ₄ plasma etching tungsten The thin film (etching mask) 12 is left.

[0007] Thereafter, the processing apparatus 13 shown in FIG.
That is, the sample introduction chamber 14 and the horizontal MOCVD growth furnace 15
The sample shown in FIG. 4A is carried into the sample introduction chamber 14 of the processing apparatus 13 provided with an ECR etching apparatus 16 therebetween, and is not shown in the figure. 4) for the sample transferred from the sample introduction chamber to the ECR etching apparatus 16
As shown in FIG. 3B, ECR etching is performed to a depth of about 1 μm using the tungsten thin film 12 as an etching mask. GaAs layer epitaxially grown on GaAs substrate 10.
In the case of a sample having 11, the substrate is etched to a depth such that the substrate surface is exposed.

Next, the sample is immediately transferred from the ECR etching chamber 16 into the MOCVD growth furnace 15 by the sample transfer device (not shown) without breaking the vacuum (without exposing the sample to the atmosphere), as shown in FIG. This time, the AlGaAs layer 17 is selectively grown using the tungsten thin film 12 as a selective growth mask.

At this time, when the Al composition is large or when Zn is used as a dopant, a polycrystal grows on the tungsten mask 12 as shown by a virtual line 18 in FIG. Sometimes. If this is unnecessary or inconvenient, after regrowth, the sample may be transferred to the ECR etching chamber 16 again, and the polycrystalline thin film 18 may be removed. In practice, the polycrystalline thin film 18 thus formed is so thin that it can be easily removed. By repeating such regrowth and etching as many times as necessary, the regrowth surface is flattened as shown in FIG. 4D, or a multilayer structure or a semiconductor (not shown in FIG. 4) is formed. A multilayer structure can be obtained. Then, the regrown AlGaAs thus planarized
As shown in FIG. 4E, a GaAs layer 19 and the like can be further provided on the layer 17.

When the fine structure thus formed was actually observed by a scanning electron microscope, a polycrystalline thin film 18 was grown on the tungsten thin film (tungsten mask) 12, but because of its thinness, it was easily re-etched. In addition, no adverse reaction was observed between the tungsten thin film 12 and the GaAs layer 19 at all. In addition, the verticality of the side surface of the fine structure was sufficiently high, and the result of the fine processing with high accuracy was confirmed.

As described above, the characteristics of semiconductor lasers have been gradually improved up to now.
Nevertheless, in view of the power consumption, for example, the power consumption per element was several milliwatts or more even if the power consumption was low.
In order to obtain an integration density comparable to electronic integrated circuits in the future, it is necessary to reduce this to at least tens of microwatts.

On the other hand, one of the conventional semiconductor lasers having a small size and high efficiency is a so-called quantum well semiconductor laser. In this case, the geometric dimensions of the quantum well layer or active layer in which laser oscillation actually occurs have a thickness of about 10
It has been downsized to about 2 μm in width, about 2 μm in width, and about 200 μm in length, and about 4 μm ³ in volume. But this is not enough.

On the other hand, when the fine processing method described above with reference to FIGS. 4 and 5 is applied, the width of the active layer can be accurately reduced to about 0.2 μm.
It can be reduced to about 20μm in the length direction. In this case, the volume of the active layer and the threshold current are one-hundredth of that of the above-mentioned existing laser, and the threshold is usually 3 to
From 10 mA to 0.03 mA, the volume decreases to about 0.04 μm ³ .

However, not only the distributed feedback type but also the miniaturization method alone does not consider the consideration of spontaneous emission light and the problem of recombination mentioned above at all. The present invention provides an answer to these questions, and proposes a structure in which a cladding layer (in some cases, preferably a multilayer reflective layer) is provided around the active layer. In this case, first, since the spontaneous emission light cannot freely exit the resonance cavity, a laser structure having an apparently no oscillation threshold (or extremely low) can be obtained.
That is, if the periphery of the active layer is covered with a three-dimensional high-reflectance mirror, the modes allowed in the optical resonator are reduced and discretized, so that spontaneous emission light is also emitted as a limited mode.
Since spontaneous emission in such a limited mode occurs at random in time, their temporal coherency is not maintained, but the emission distribution and wavelength are determined by cavity parameters, so the apparent In addition, it is almost indistinguishable from laser light. Therefore, such a semiconductor laser can be regarded as having substantially no threshold value or extremely low threshold value,
Highly efficient laser oscillation can be realized at extremely low current.
An example of this is given in FIG. 2 below. In addition, the consideration itself regarding such apparent thresholdless or low threshold laser is described in Conventional Document A: “Microcavity Laser: Current Status and Outlook”, Applied Physics, Vol. 61, No. 9 (1992) , Pp.890-901.

On the other hand, FIG. 1 shows an embodiment of the semiconductor laser of the present invention. In particular, as an embodiment for expecting an effect of suppressing recombination, a semiconductor stripe laser adopting the distributed feedback principle will be described. The case where the present invention is applied is shown. To explain, an n-type lower cladding layer 2 is formed on an n-type GaAs substrate 10 by a normal epitaxial growth technique.
1. After a pair of upper and lower green layers 22 and 22 and a p-type upper cladding layer 24 having a laser active layer or a quantum well layer 23 interposed therebetween are sequentially laminated, as shown in FIG. The tungsten thin film 12 is patterned into a desired shape by the dedicated lithography machine. In the case shown in the figure, the patterned tungsten thin film 12 has a width of about 200 mm.
nm, the length is 30 μm or less, and the planar shape is such that the side surface periodically repeats irregularities in the length direction.

The period of the side surface irregularities is one quarter of the wavelength in the medium of the light, and the central portion in the length direction has a half convex portion so that the phase shifter 29 is formed thereunder. It is designed to be continuous over one wavelength, thereby realizing an optical resonator at the Bragg reflection wavelength. In addition,
In order to correspond to the process example described with reference to FIG. 4, the above-described n-type lower cladding layer 21, laser active layer (in this case, a quantum well layer) 23, a pair of upper and lower grin layers 22, 22 , P
It can be considered that the laminated structure composed of the mold upper cladding layer 24 all corresponds to the epitaxial layer 11 on the substrate 10 shown in FIG.

The tungsten thin film 12 of the pattern as described above
Is used as an etching mask, and then the etching and regrowth processing apparatus 13 described with reference to FIG.
After being introduced into the CR etching chamber 16, the etching is performed. Immediately thereafter, the wafer is transferred to the MOCVD regrowth furnace 15 without being exposed to the air, and the tungsten thin film 12 is used as a selective mask for regrowth, and the remaining portion is etched. All around, regrown i-type (ie semi-insulating) AlGaAs
It is embedded with a surrounding cladding layer (embedding layer) 17. Then, an appropriate metal electrode, desirably an Au electrode 25 is formed on the tungsten pattern 12 to complete a fine distributed feedback semiconductor stripe laser.

As a result of the laser according to the present invention, both ends of the stripe-shaped active layer 23 in the longitudinal direction, which are light emission end faces, are also formed on the AlGaAs cladding layer 17 similarly to the side surfaces.
In other words, the entire periphery of the stripe-shaped laser structure becomes a completely buried structure. As described above, since the structure in which the emission end face having a high light intensity is covered with the cladding 17 from the side surface can be expected to have the effect of suppressing recombination, it is particularly necessary to obtain a distributed feedback stripe laser that oscillates short-wavelength laser light. This is a desirable structure. Of course, there is also a physical output end face protection effect.

In order to reduce the element resistance, as described earlier with reference to FIG. 4C, a polycrystal which may be deposited on the tungsten thin film 12 through a regrowth step is used. After removing AlGaAs 18 by etching, p-doped Al
It is also effective to selectively grow a GaAs layer or a GaAs layer. Also, in the actual production of the semiconductor stripe laser shown in FIG. 1, the pattern shape of the tungsten thin film 12 as a minute pattern has a precision of several tens of nm so as to correspond to a quarter of the wavelength in the medium of light. Formed with precision. In the fine processing method described above with reference to FIG. 4, if the patterning accuracy can be improved to several nm accuracy with higher accuracy in the future, depending on the shape in the horizontal direction perpendicular to the length direction, the quantum level of the quantum wire can be improved. Can be controlled, so that the quantum level of the light emitting section can be made smaller than that of the waveguide section, and the light absorption in the waveguide section can be further reduced. further,
It is extremely advantageous to produce the minute distributed feedback laser of the embodiment shown in FIG. 1 by the above-mentioned fine processing method in another sense. Since the quantum well width and the like are determined by the initial uniform crystal growth, and the side shape is determined by an arbitrary pattern of the planar shape of the dry etching mask regardless of the crystal orientation, the direction of the laser stripe is free. Because it can be set to

Incidentally, the microfabrication method described with reference to FIGS. 4 and 5 is, in a sense, applicable to the production of an electron waveguide as a basic functional element, and also to a quantum wire having an arbitrary planar shape or a path pattern. Useful. The quantum wire structure is basically the same or similar to the cross-sectional structure of the semiconductor laser shown in FIG. 1 as an embodiment of the present invention, but in the case of a GaAs system, at least a lower cladding layer is formed on a GaAs substrate. AlGa
An As layer, a GaAs layer having a thickness on the order of the wavelength of electrons (approximately 10 nm) as a substantial waveguide layer or a core layer, and an AlGaAs layer as an upper cladding layer are formed by lamination. Is patterned in a linear shape (stripe shape), and then an AlGaAs layer is regrown on both side surfaces to form left and right clad layers.

In addition, in the fine processing method shown in FIGS. 4 and 5, when the above-described quantum wires are manufactured, the pattern is formed into a Y-shaped branched shape when the etching and regrowth mask 12 is patterned. By making it into a shape, the structure itself is also useful for forming a well-known Y-shaped electron or optical branching path, and is once divided into two parts so that it can be combined into one line or waveguide again. By patterning,
It can also be advantageously used for producing a so-called Mach-Cheander interferometer or the like. Furthermore, a four-terminal directional coupler can be realized by patterning a single main waveguide such that the sub-waveguide approaches and moves away in the middle of its length. In other words, the microfabrication method described with reference to FIGS. 4 and 5 is also necessary for producing various electronic or optical passive functional elements that realize a specific function by the features related to the patterning shape of the waveguide. This is a very useful technique.

FIG. 2 shows a semiconductor microlaser generally called a microcavity laser as another embodiment of the present invention. The laser function portion has a laser structure portion in which a GaAs quantum well layer 23 as a stripe-shaped active layer is sandwiched between upper and lower cladding layers, similarly to the semiconductor laser described above. In particular, in this case, an n-type AlGaAs multilayer film (for example, when the Al composition ratio is
Alternating structure of 0.2 AlGaAs layer and 0.7 AlGaAs layer) 26
And a multilayer film 27 having a p-type AlGaAs alternately laminated structure having similarly different Al composition ratios. Further, the cladding layer of the regrown AlGaAs layer provided so as to cover the left and right sides and the laser emission end face of the active layer 23 according to the present invention is also an i-type.
The AlGaAs multilayer films 28 having different Al composition ratios are used. In this way, the left, right, top and bottom of the active layer or core layer are all semiconductor multilayer films.
By embedding with 28, high reflection characteristics can be obtained, so even if the optical resonator has a small volume as described above, the loss can be reduced, and the free emission of spontaneous radiation can be limited. As far as spatial emission patterns and emission wavelengths are concerned, it is possible to obtain characteristics close to no threshold value.
However, although it is most desirable that the semiconductor laser of the present invention be manufactured in a microstructure, the structure principle of the present invention can be applied to a structure having a slightly larger dimension. May be formed to the size of the existing class, that is, about 2 μm in width and about 100 μm in length.

The microcavity laser shown in FIG. 2 can be used for obtaining an electron-optical coupling device as shown in FIG. 5 in combination with a quantum wave device represented by a so-called micro FET. That is, in the electron-optical coupling device shown in FIG. 5, a microcavity structure 71 which may be the same as the microcavity already described with reference to FIG. Therefore, in the microcavity 71, the electron system and the photon system can strongly interact with each other, and the state in which light can be taken is limited to several or less, so that the photon and the electron-hole pair are reversibly formed. It can be converted. That is, the quantum wave element
By performing a logical operation at 50 and designing the result to be expressed as a change in the charge distribution or built-in electric field of the quantum dot 63, the moment the quantum level in the quantum dot 63 matches the resonance wavelength of the microcavity 71, In addition, specific photons can be efficiently emitted.

Further, if a plurality of microcavities 71 having such a structure are connected by an optical waveguide 72, arithmetic and storage operations are performed by an electronic system, transmission is performed by light, and so on. This has been proposed in the past,
In other words, the "role sharing" method can be performed even in a micro device. In an electron waveguide, one electron can be accommodated in one state because the electron is fermion, and there is a premise that an ideal state requires a resistance of 12.9 KΩ per mode. If a certain photon is used for transmission, the number of particles that can be accommodated in the fundamental mode of the optical waveguide is not limited, and the transmission speed is significantly improved.

Although several embodiments of the present invention have been described in detail above, various modifications are free as long as they conform to the gist of the present invention.

[0026]

According to the present invention, there is provided a structural principle capable of solving the conventional problems and obtaining a semiconductor laser having an extremely low threshold value, ideally no threshold value. In addition, since the side surface and the emission end face are all covered with the cladding layer, an effect of suppressing recombination there can be expected, and in addition to providing an advantageous structure for constructing a laser having a relatively short wavelength, in any case, In addition, it is possible to protect the emission end face.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a minute distribution feedback laser as one embodiment of a semiconductor stripe laser of the present invention.

FIG. 2 is a schematic configuration diagram of an edge-emitting microcavity laser as another embodiment of the semiconductor stripe laser of the present invention.

FIG. 3 is a schematic configuration diagram of an example of an electron-optical coupling device that can incorporate the semiconductor stripe laser of the present invention.

FIG. 4 is an explanatory diagram of a process example of a fine processing method suitable for application to the production of a semiconductor stripe laser of the present invention.

FIG. 5 is an explanatory diagram of an example of an apparatus configuration suitable for executing the fine processing method shown in FIG. 4;

[Explanation of symbols]

10 Semiconductor or semi-insulating substrate, 12 Etching and regrowth mask, 13 Etching and regrowth processing equipment, 14 Sample introduction chamber, 15 MOCVD growth furnace, 16 ECR etching chamber, 17 Covering around regrowth layer or active layer Cladding layer, 21 lower cladding layer, 23 laser active layer or quantum well layer, 24 upper cladding layer, 26 lower semiconductor multilayer film, 27 upper semiconductor multilayer film, 28 semiconductor multilayer film as cladding layer surrounding active layer.

Claims (2)

(57) [Claims] 1. A semiconductor stripe laser in which an active layer causing laser oscillation is sandwiched between upper and lower cladding layers, and a laser beam is output from an end face of the active layer ; form
The shape is such that the side surface periodically repeats irregularities in the length direction.
That the period of the side irregularities is a quarter of the wavelength in the medium of light.
And a phase shifter is formed in the central part in the longitudinal direction.
The convex part is continuous over half the wavelength so that
When; semiconductor stripe laser, wherein; including emitting facet of the laser beam, it was covered with cladding layers all around the active layer. 2. An active layer that causes laser oscillation is vertically
And a laser beam output from the end face of the active layer.
A conductor stripe laser; including a laser light emitting end face, and a light emitting element having a laser beam emitted from the entire periphery of the active layer;
A semiconductor cladding layer, wherein the cladding layer is formed of a semiconductor multilayer film.