JPH0156547B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface-emitting semiconductor laser and such a semiconductor laser, in which optical integrated circuits and the like can be easily constructed by forming an optical resonator in a direction perpendicular to the wafer surface. This relates to a two-dimensional laser array consisting of.

Various proposals have been made regarding such semiconductor lasers. However, with conventional semiconductor lasers,
Since both ends of the thin film serving as the laser medium are cleaved to serve as the reflective surfaces of the optical resonator, the oscillated laser light is emitted in a direction tangential, that is, parallel, to the wafer surface. In doing so, there were major restrictions regarding the direction of light. For example, conventionally proposed laser arrays are difficult to process, and even more so, it is not easy to manufacture a two-dimensional laser array.

Furthermore, in conventional semiconductor lasers, a part of the laser medium is used as a reflective surface, so the influence of optical damage becomes a problem during high-output operation. Moreover, since it is formed by an optical resonator cleavage method, it is difficult to operate in a single longitudinal mode.

SUMMARY OF THE INVENTION An object of the present invention is to propose a novel surface-emitting semiconductor laser having a completely different structure from conventional semiconductor lasers, in order to solve the above-mentioned drawbacks. In order to achieve the above object, according to the present invention, an active layer with a large refractive index is sandwiched on one side of a semiconductor substrate made of an InP substrate transparent to laser light, and a plurality of semiconductor layers with different polarities are formed. a first electrode which also serves as a first reflecting mirror surface and which is made of a metal thin film provided on one side of the laser body opposite to the substrate; A second metal thin film is provided on the other side surface of the main body on the substrate side without cutting a groove, and is coated with a metal thin film for forming a Fabry-Perot resonator with the first reflecting mirror surface. a second electrode that also serves as a dual-reflection mirror surface, and a bias power source is connected between these first and second electrodes to bias the active layer in the forward direction to form an active region. It is characterized in that the laser beam can be extracted in a direction perpendicular to the first and second reflecting mirror surfaces.

Furthermore, in another embodiment of the present invention, an active layer with a large refractive index is sandwiched on one side of a semiconductor substrate made of an InP substrate transparent to laser light, and a plurality of semiconductor layers having different polarities are almost mutually arranged. a laser body formed parallel to each other; and a first mirror surface, the laser body having a substantially circular metal thin film deposited on one side of the laser body opposite to the substrate, and acting as a first reflecting mirror surface of the Fabry-Perot resonator. an electrode, and a reflective coating that is provided without cutting a groove on the other side of the laser body on the substrate side and acts as a second reflective mirror surface of the resonator, and the active region of the active layer is A region around the outer periphery of the region to be formed and from one side of the laser body to a part of the substrate is a diffusion layer doped with p-type impurities, and a metal thin film is deposited on the diffusion layer. A bias power source is connected between the first and second electrodes to bias the active layer in the forward direction to form an active region, and the laser light generated in the active region is transmitted to the first and second electrodes. It is characterized in that the laser beam can be extracted in a direction perpendicular to the second reflecting mirror surface.

Furthermore, in another embodiment of the present invention, a semiconductor substrate is made of an InP substrate that is transparent to laser light, and has a convex portion having a substantially circular cross section in a portion thereof, and a semiconductor substrate is provided on the semiconductor substrate around the convex portion. a reverse bias layer consisting of a semiconductor layer of one polarity and an active layer grown sequentially; a semiconductor layer of one polarity and an active layer grown sequentially on the surface of the convex portion separately from the reverse bias layer; a semiconductor layer of the other polarity grown on the reverse bias layer so as to surround the semiconductor layer on the surface of the convex portion and the active layer; is a first electrode which also serves as a first reflecting mirror surface and is made of a metal thin film provided on one side surface on the opposite side; A reflective mirror surface and a second electrode which also serves as a second reflective mirror surface and which is coated with a metal thin film to form a Fabry-Perot resonator are provided, and a bias power source is connected between these first and second electrodes to The active layer grown in the shaped portion is biased in the forward direction to form an active region, and the laser light generated in the active region can be extracted in a direction perpendicular to the first and second reflecting mirror surfaces. It is characterized by being formed as follows.

Embodiments of the invention will be explained in detail with reference to the drawings.

FIG. 1 is an explanatory diagram for explaining the structure of the surface-emitting semiconductor laser of the present invention in the order of its manufacturing steps. First, as shown in FIG. 1, an n-type InP layer 2, an active layer 3 made of a GaInAsP intermetallic compound, and a p-type InP layer 4 are successively crystal-grown on an n-type InP substrate 1.

Next, as shown in Figure 1, on the P-type InP layer 4,
The SiO ₂ insulating film 5 is sputtered and further etched to form circular holes in the SiO ₂ film.

Next, as shown in FIG. 1, the back surface of the n-type InP substrate 1 is polished to a desired thickness to give a mirror surface 6.

Next, as shown in Figure 1, SiO ₂ film 5 with holes is
An electrode 7 made of an Au-Zn alloy is coated on the entire upper surface of the electrode.

Next, as shown in Fig. 1, Au-
An electrode 8 made of Sn-based alloy is provided.

In this case, there is a hole in the SiO ₂ film 5 and a portion 7A where the Au-Zn alloy electrode 7 is in direct contact with the semiconductor.
It is preferable to correspond to the hole 8A of the An-Sn alloy electrode 8.

To explain this in more detail, it is preferable that the center line of one hole 7A and the center line of the other hole 8A substantially coincide with each other.

Next, as shown in FIG. 1(vi), gold is deposited on the entire upper surface of the Au-Sn alloy electrode 8 and its hole 8A.
A layer 9 is provided.

Next, the surface emitting type semiconductor laser 10 is obtained by cutting as shown in FIG. 1(vii).

FIG. 2 shows an enlarged view of this surface-emitting semiconductor laser 10. As shown in FIG. The reference numerals correspond to those in FIG. 1, and the same reference numerals indicate the same parts.
The Au-Zn alloy electrode 7 is connected to the DC power source E with the anode side (+) and the Au-Sn alloy electrode 8 as the negative electrode side (-) to apply a forward bias. In this way, the bandgap (forbidden band width) of the active layer 3 made of GaInAsP is smaller than the bandgap of the InP layers 2 and 4 on both sides thereof, and a so-called oxide stripe region is formed by the SiO ₂ insulating film 5, and the carrier is
Hole 7 of Au-Zn alloy electrode 7 of GaInAsP active layer 3
It is confined in the part facing A, and an active region 3A is formed here. As a result, a so-called energy population inversion is formed, and when electrons in the conduction band recombine with holes in the valence band, the difference in energy is emitted as laser light. Conventional GaInAsP-InP double heterojunction semiconductor lasers have 1 to 4 semiconductor crystal layers in each layer.
The surface created by cleavage in the direction perpendicular to is used as a Fabry-Perot resonator, and the laser beam is extracted in a direction parallel to the main surface of the semiconductor chip, but in the present invention, the laser beam is extracted in this direction. and
90° difference. In other words, as mentioned above, the bandgap of InP is larger than that of GaInAsP, so almost no light entering it is absorbed.
The Au film 9 and the Au-Zn alloy film 7A are reached.
The semiconductor surface directly under the Au film 9 is particularly finished as a mirror surface 6, and since the Au film and the Au-Zn alloy film are formed almost parallel to each other, both become reflective mirror surfaces and form a Fabry-Perot resonator. and generates laser oscillation. Then, a part of the light that propagates as shown in the light propagation loop 11 indicated by the arrow in FIG. Proceed in the direction shown. That is, laser light can be extracted in a direction perpendicular to the main surface of the semiconductor chip. According to the present invention, a surface emitting semiconductor laser is formed in the manner described above.

As a result of experiments, the surface-emitting semiconductor laser 1 of the present invention
It was confirmed that 0 laser oscillates at an absolute temperature of 77K. From this data, the threshold current density at room temperature is estimated to be about 110 KA/cm ² .
Therefore, if the thickness of the active layer 3 can be doubled and the reflectance can be increased, the threshold current density will be
It is less than 1/2 of 110KA/cm ² and can be about 50KA/cm ² . Therefore, it is considered that room temperature oscillation is also possible with the semiconductor laser of the present invention. For example, here, as the P side electrode, the diameter is about 5 μm.
If a circular electrode is adopted, the oscillation threshold current will be as low as about 10 mA from the above estimation, and it will be possible to obtain a laser with little optical damage even at high output.

Hereinafter, some modified examples of the embodiment shown in FIG. 3 will be described in which further improvements are made.

FIG. 3a shows an example of another embodiment of the present invention, in which, unlike the embodiment of FIG. 2, a p-type impurity is diffused after crystal growth to form a p-type region 13, and carriers are introduced from the lateral direction. This shows a surface-emitting laser that uses an injection method. According to this method, the thickness of the active layer 3 can be made thicker than in the embodiment shown in FIG. 1, and a laser with a lower threshold current can be obtained.
Further, FIG. 3b shows a modification based on this method in which both electrodes are installed on one side, and in this case, a semi-insulating substrate 1 can also be used.

FIG. 4a shows another embodiment of the present invention, in which an optical confinement mechanism is incorporated into the embodiment of FIG. 2, in addition to carrier injection mechanisms from the vertical and lateral directions. As a method of incorporating these two mechanisms, it is possible to consider something like the one shown in Figure 4b, but here we will first introduce its basic form, Figure 4a.
The manufacturing method and operation of this embodiment will be described. First, the n-type InP substrate 1 is etched into a convex shape, and the n-type InP substrate 1 is etched into a convex shape.
The InP layer 2 and the GaInAsP layer 3 are grown separately. It has already been confirmed that this is possible by appropriately selecting crystal growth conditions. Then, crystal growth is performed so that the p-type InP layer 4 surrounds the active region 3A. The subsequent processing method is the same as that shown in FIG.

Next, the operation of this embodiment will be explained. First, when a forward voltage E is applied to this laser diode, the current is limited by the SiO ₂ film 5, and at the same time flows more concentrated in the active region 3A in the horizontal and vertical directions due to the difference in diffusion voltage. Since the active region 3A has a high refractive index, the light acts like a lens and is focused near the active region 3A, forming the Fabry-Perot resonator 1.
Resonance occurs between the electrodes 7 and 9 of 0, causing laser oscillation as described in the embodiment of FIG. As a result, by growing the active layer 3A thickly and separately, a single mode laser with a low threshold current can be obtained.

FIG. 4b shows that in order to more completely inject carriers into the active region, reverse bias layers 2A and 2B are further formed on the substrate 1 and the substrate 1 by crystal growth twice.
This figure shows a surface emitting type laser provided between the type InP layer 4 and the surface emitting type laser. With such a structure, current flows only near the active region 3A, and shallow current leakage becomes extremely small. Therefore, it is possible to obtain a surface emitting type semiconductor laser having the characteristics of higher efficiency and lower threshold current than the embodiment shown in FIG. 4a.

FIG. 5 shows a two-dimensional laser array using the surface emitting type semiconductor laser of the present invention, and the lasers can be integrated on one wafer using only a normal wafer process. 14 is a laser element, 15 is a wafer, and 16 is an electrode. Such a laser array takes advantage of the characteristic that the light output direction of the surface emitting laser is perpendicular to the main surface of the wafer, and is suitable as a light source for a multi-fiber cable.

In each of the above embodiments, GaInAsP and InP are used.
Although a semiconductor laser in which a system compound is superimposed by crystal growth is taken as an example, the present invention is not limited to this, and it goes without saying that other semiconductors forming a heterostructure can also be used.

As explained in detail above, according to the present invention,
A Fabry-Perot resonator is provided on the main surface of the wafer, and optical output can be extracted perpendicularly to the main surface of the wafer. When assembled into a two-dimensional laser array, lasers can be easily placed on a single wafer. Can be accumulated. Furthermore, by incorporating the semiconductor element according to the present invention into an optical integrated circuit, restrictions on the direction of light emission can be relaxed, and a new optical integrated circuit can be created. Therefore,
The present invention is expected to be widely used in constructing new optical integrated circuits, and is extremely useful in this type of industry.

Next, the differences between the surface emitting type semiconductor laser according to the present invention and the conventional edge emitting type semiconductor laser will be explained.

Near-field pattern: Width 0.5 to 1 μ in the direction perpendicular to the active layer for edge-emitting type
The width (or diameter) of the surface-emitting type is 10 m.
~20μm, which can be wide.

Far-field pattern In the end-radial type, the near-field pattern is narrow as mentioned above, so it spreads out to about 40 degrees, and the directivity is extremely poor. On the other hand, with a surface-emitting type, the radiation is in the form of a sharp beam, with a spread of only about 1°, and has excellent directivity.

light output Both the edge-emitting type and the surface-emitting type are approximately the same.

Light density Edge-emitting type has a small near-field pattern, so the light density is high and optical damage is likely to occur. The light density is
It is ^about 1mw/μm2. On the other hand, the surface-emitting type has a wide near-field pattern, so the light density can be kept low and there is no risk of optical damage. The light density is ~
It is about 10 ^-2 mw/ ^μm2 .

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of a method for manufacturing a surface-emitting semiconductor laser of the present invention, FIG. 2 is a cross-sectional view showing an example of a surface-emitting semiconductor laser of the present invention, and FIGS.
The figure is a schematic cross-sectional view showing another embodiment of the semiconductor of the present invention. FIG. 5 is a schematic diagram showing an application to a two-dimensional laser array. 1... n-type InP substrate, 2... n-type InP layer, 3...
...GaInAsP active layer, 3A... active region, 4...
P-type Inp layer, 5...SiO ₂ insulating film, 6... Mirror surface, 7
...Au-Zn alloy electrode, 8...Au-Sn alloy electrode, 7A, 8A...electrode hole, 9...Au layer,
10... Surface-emitting semiconductor laser, 11... Light propagation loop.

Claims (1)

[Claims] 1. A semiconductor substrate made of an InP substrate that is transparent to laser light, with an active layer having a large refractive index sandwiched between them, and a plurality of semiconductor layers having different polarities formed substantially parallel to each other. a first electrode that also serves as a first reflecting mirror surface and is made of a metal thin film provided on one side of the laser body opposite to the substrate; and a first electrode that also serves as a first reflecting mirror surface; a second electrode that also serves as a second reflecting mirror surface, which is provided on the other side surface without cutting a groove on the side surface, and is coated with a metal thin film for forming a Fabry-Perot resonator with the first reflecting mirror surface; , a bias power source is connected between the first and second electrodes to bias the active layer in the forward direction to form an active region, and the laser beam generated within the Fabry-Perot resonator is transmitted to the first and second electrodes. A surface emitting type semiconductor laser characterized in that it is configured to be able to emit laser light in a direction perpendicular to a second reflecting mirror surface. 2 The InP substrate is n-type, and the active layer is
Claim 1 characterized in that a GaInAsP active layer is used, a semiconductor layer of the active layer on the side of the InP substrate is an n-type InP layer, and a semiconductor layer on the other side of the active layer is a p-type InP layer. The surface-emitting semiconductor laser described in . 3. The first electrode, which also serves as the first reflecting mirror surface, is provided on the one side surface of the laser body and has a substantially circular hole in a portion corresponding to the resonator. 3. A surface-emitting semiconductor laser according to claim 1, wherein the surface-emitting semiconductor laser is attached to a side surface. 4. The first electrode that also serves as the first reflecting mirror surface is connected to the one side surface of the laser body through an insulating layer transparent to the laser light provided on the one side surface of the laser body and corresponding to the resonator. 3. A surface-emitting semiconductor laser according to claim 1 or 2, wherein the surface-emitting semiconductor laser is coated with a semiconductor laser. 5. A region around the outer periphery of the active region of the active layer and extending from the one side surface of the laser body to a part of the substrate is a diffusion layer doped with p-type impurities. The surface-emitting semiconductor laser according to any one of the first to fourth items. 6. A laser body formed by forming a plurality of semiconductor layers with different polarities substantially parallel to each other with an active layer having a large refractive index sandwiched between one side of a semiconductor substrate made of an InP substrate transparent to laser light; a first electrode comprising a substantially circular metal thin film deposited on one side of the laser body opposite to the substrate and acting as a first reflecting mirror surface of a Fabry-Perot resonator; and the substrate of the laser body. a reflective coating that is provided without cutting a groove on the other side of the side and acts as a second reflective mirror surface of the resonator; A region from one side of the laser body to a part of the substrate is a diffusion layer doped with p-type impurities, and a second electrode made of a metal thin film is deposited on the diffusion layer, and a second electrode made of a metal thin film is provided on the diffusion layer. and a bias power source is connected between the second electrodes to bias the active layer in the forward direction to form an active region, and the laser beam generated in the active region is directed in a direction perpendicular to the first and second reflecting mirror surfaces. A surface-emitting semiconductor laser characterized by being configured to be able to extract laser light. 7 A semiconductor substrate made of an InP substrate that is transparent to laser light and has a convex portion with a substantially circular cross-section in one part, and a semiconductor of one polarity grown sequentially on the semiconductor substrate around the convex portion. a reverse bias layer consisting of a layer and an active layer, a semiconductor layer and an active layer of one polarity grown in sequence on the surface of the convex portion separately from the reverse bias layer, and on the surface of the convex portion. a laser body having a semiconductor layer of the other polarity grown on the reverse bias layer so as to surround the semiconductor layer and the active layer; and a laser body provided on one side of the laser body opposite to the substrate. a first electrode that also serves as a first reflecting mirror surface made of a metal thin film; and a first electrode that is provided without cutting a groove on the other side of the laser body on the substrate side, and that forms a Fabry-Perot resonator with the first reflecting mirror surface. a second electrode which also serves as a second reflecting mirror surface, and a bias power source is connected between the first and second electrodes to sequentially apply the active layer grown on the convex portion. A surface emitting surface emitting device characterized in that an active region is formed by biasing the active region so that the laser light generated in the active region can be extracted in a direction perpendicular to the first and second reflecting mirror surfaces. shaped semiconductor laser.