DE2942540A1 - Semiconductor chip for channel-type laser - has lower substrate with raised section to limit current flow to narrow strip, extending in direction of emitted light - Google Patents

Abstract

The channel-type laser has several, different, doped semi-conductor layers on a lower semiconductor substrate, defining the current flow over a small range of a strip, which extends in the direction of the emitted light. The substrate has a raised section (12), which extends over the width of the strip and in the same direction. The strip limits the current flow on it. The raised section (12) has an upper, ever surface and steep side surface, which taper off on each side. The side-surfaces and part of the substrate surfaces, which extend out from the raised section (12) are covered with a sealing layer (13). The sealing layer consists of a semiconductor material, which is of a different conductivity to that of the substrate. The layer (13) is defined by a concave meniscus at the raised section (12).

Description

Strip laser

The U.S.A. priority is claimed with Serial No. 954,702 of October 25, 1978.

The invention relates to strip lasers such as those used in optical Communications technology can be used as a transmitter. In this application, it comes down to it on, as much of the emitted light as possible into a connected optical fiber to couple. Efforts have therefore been made to develop laser structures in which the light only emerges over a very small area. This is done on the one hand by that the laser is built up from several semiconductor layers on a substrate, the dopings and the compositions of the semiconductor layers being selected in this way are that charge carrier injection takes place only in very narrow areas, and that the light emitted during the charge carrier recombination only in a thin layer is guided, which is bordered by layers with a higher refractive index. These However, measures only lead to a limitation of the light flux in a thin one Layer.

To restrict the flux of light within this thin layer a narrow band is required, as is the current flow through the laser to limit it to a narrow band. This band extends in the direction of the emitted light and has the width less / um. The regression takes place in previous embodiments in that the top layer of the semiconductor laser is not contacted over its entire surface, but that on the top semiconductor layer First an insulating SiO2 layer is applied, from which a narrow strip is etched out of a few µm width. On this insulating layer with the etched A metal contact layer is applied to the strip. Because of the contact only along a narrow strip these semiconductor lasers also become strip lasers, in English usage "stripe-geometry laser" or "narrow stripe laser", called. Manufacturing techniques and embodiments of various structures for strip lasers are in the article by M.B. Panish "IEEE Transactions on Microwave Theory Technology, Vol. MTT-23, pages 20-30 January 1975 ".

The contacting of the top layer only along a narrow line Stripping leads, as desired, to the charge carrier injection and the light emission are only limited to a narrow band in the active layer. This leads to, that the light emerges only over a small area and therefore well into an optical fiber are coupled in channel. The measure also lowers the laser threshold. However, the aim is to further limit the laser-active volume in order to thereby obtaining even lower laser thresholds and smaller exit areas.

On this basis, the invention is based on the object of a structure To specify a strip laser in which the current flows through the active layer only runs along a band with such a narrow width, as has not been done before was attainable.

The solution to the problem is given in the first claim. The measure consists in the fact that the strip-shaped contact is not at the top, or not only on the top layer of the semiconductor laser, but that the semiconductor layer applied to the substrate by a special embodiment of the substrate along a narrow strip is contacted. All measures that have been found in previous embodiments of strip lasers as have proven advantageous, can also be used in this structure of a strip laser will. When contacting the top semiconductor layer along a narrow one Strip as with conventional strip lasers and simultaneous contacting of the semiconductor layer applied to the substrate is narrow in length Stripes, as in the proposed stripe laser, are particularly low Laser thresholds and small light exit areas can be achieved.

The invention is illustrated below with the aid of four figures Exemplary embodiments explained. They show: FIG. 1: Section through an embodiment of a strip laser according to the invention. Direction of view in the direction of the laser.

2: side view of a section through a strip laser according to Figure 1.

Fig. 3: Section through a second embodiment of an inventive Strip laser. Direction of view in the direction of the laser.

Fig. Lt: side view of a section through a semiconductor laser with a mirrored end face.

The basic structure of semiconductor lasers with a layer structure and their creation is generally known to the person skilled in the art and it is only in the following shortly thereafter.

Figures 1 - 4 represent sections through semiconductor layer lasers, however, for the sake of clarity, the layer dimensions are not true to scale are enlarged.

When producing a laser structure 10 according to FIG. 1, a Substrate 11 made of doped semiconductor material made of e.g.

Run out of gallium and arsenic. The material is p- or rì-guiding e.g. n-type gallium arsenide. The layer 11 is initially much thicker drawn in FIG. 1 and has a thickness as denoted by A in FIG. on a narrow strip of photoresist is applied to the substrate of thickness A, after which the substrate is etched to the thickness B, whereby on the substrate a strip-shaped increase in width C is produced. A solution comes as an etching agent in question, which contains H2O2 and NaIS40H in a ratio of 10 to 1. The etching time is usually 10 to 30 seconds depending on the width of the strip and more desired Limiting the increase. At present an elevation 12 can easily be made, which has a flat upper surface and steeply sloping side surfaces, wherein the dimensions of sizes B and C are approximately 2.5 µm.

Although only a single strip-shaped one for a laser of the type proposed If an increase is necessary, it is usual in practice on a large substrate wafer to simultaneously apply a large number of wafer structures and this wafer after All layers applied are divided into individual chips, each of which represents a component, which can then be attached to a carrier and with electrical connections can be provided. A proposed laser is also used produced by placing a considerable amount on a relatively large flat wafer Number of parallel elevations is produced by applying parallel strips of paint and then etched on the wafer. The remaining layers, which in the following are described, all are also spread over the entire wafer, before it is divided into the individual stripe lasers.

With the geometrical structure of the raised scoop described so far on the (m substrate it is not yet possible to establish a Kotttaktierung the next, on make the substrate to be applied semiconductor layer along a strip. Therefore, first a barrier layer is applied, which is from the elevation leaves essentially only the upper flat surface exposed. Applying the locking Layer and that of the other layers are carried out by liquid phase epitaxy. The growing conditions in growing furnace are set so that the semiconductor material, which the blocking Layer only forms on the sides of each elevation but not on the upper level Area of elevation is deposited. The conductivity of the material of the barrier layer is opposite to that of the substrate material. If e.g. for the substrate n-gallium arsenide would be used, p-gallium arsenide is used for the material of the barrier layer or p-gallium aluminum arsenide is used. In Figure 1 there are barrier layers 13, which is concave meniscus from the edges of the upper planes The surface extend over part of the surface of the substrate 11. The shape of the concave meniscus is due to the wetting properties of the molten, the locking Layer-forming material established against the substrate. The upper flat surface the elevation remains free of the maserial of the blocking layer as it is another crystalline structure like the etched surfaces of the substrate it has. Even if the upper flat surface with molten material, which is the barrier layer forms, is covered, it nevertheless succeeds in removing the blocking layer up to a distance from 15 pm to grow from the edges of the elevation before the blocking Layer-forming material also grows on the upper flat surface of the elevation. As already mentioned, the blocking layers cause a current to flow essentially only through the upper flat surface and not over the entire substrate surface he follows.

The remaining manufacturing steps for the deposition of a double heterostructure laser The necessary layers 14-17 in FIG. 1 are those during the production of the layers Manufacturing steps familiar to liquid phase epitaxy. The layers consist e.g. of Gallium arsenide or gallium aluminum arsenide.

The middle layer 15 is the active light-emitting recombination layer and the layer 17 is the cover layer, which is also called the contact layer.

The next step in manufacturing a laser structure according to FIG. 1 consists in depositing a thin insulating layer 18 made of silicon oxide. This layer is then down to a narrow strip, which it runs in the direction of the Rise on the substrate is covered with a photoresist, followed by a narrow one Strip 19 is etched out of the silicon oxide layer. The strip 19 and the Elevations 12 are symmetrical about a plane 20 which is perpendicular to the layers and runs in the direction of the laser light to be emitted.

By means of a metal layer 21 applied to the silicon oxide the contact layer 17 along the strip 19 contacted.

After that, the relatively large wafer is split into individual stripe lasers divided into a rectangular cross-section. In the case of an injection laser, it is important that the end faces are cleaved precisely along crystallographic planes thereby obtaining parallel and flat end faces. Also the mutual distance of the cleavage surfaces is crucial, as they must form a Fabry-Perot resonator, to emit strong laser light in the plane of the light-emitting layer 15 to ensure when a DC voltage or DC voltage pulses are applied to the component be created. These rays coherentficht that are within a desired Frequency spectrum are itt Figure 2 shown schematically by the arrows 22 and 23, the emerge from the end faces in opposite directions.

In order to make contact with the semiconductor laser, it is on the substrate side metallized by a conventional method and coated with a layer of solder 26 on top of a MetaI carrier 25 attached. The voltage supply to the uppermost metal layer 21 takes place by a connecting shoe 24. The carrier 25 serves as a holder and as a heat sink for the laser.

The upper strip contact 19 in FIG. 1 corresponds essentially the strip contact as described in the quoted article by M.B. Panish in Figure 12 (a) is shown. Together with the proposed strip-shaped contact through the elevation 12 and the blocking layers 13 a limitation of the diaphragmatic becomes Layer 15 penetrating current achieved on a particularly narrow band. the The Stronjfade is limited by the dashed lines, which can be seen in Figure 1 extending from the edges of the strip 19 to the edges of the elevation 12 is shown.

If, however, more value is placed on a cheap laser instead of a laser with a low laser threshold and a very small exit area of the laser light is, so can on the upper strip-shaped contact through the contact strip 19 can be dispensed with, and instead the metal layer 21 over the entire surface the top semiconductor layer 17 are applied. But then it is necessary the blocking layer 13 over the entire substrate surface except over the upper plane Expand area of elevation 12. This is in FIG. 3 in the case of the stripe laser 10A shown, in which the blocking layers 13A and 13B from the increase 12 extend over the entire remaining surface of the substrate 11. Only the upper flat surface of the elevation 12 remains uncovered. In Figure 2, parts of the Lasers which are identical to the structure according to FIG. 1 have the same reference numerals provided, while similar parts the Figure 1 corresponding reference numerals together with a suffix. The limitation of the current path through the component is as indicated in Figure 1 by dashed lines.

In semiconductor laser structures it is possible to use the emerging laser light focus in a direction in which one of the end faces with a reflective Oold film is mirrored, as shown, for example, in the structure according to FIG is. On one end face there is initially an insulating layer made of silicon oxide or aluminum oxide is applied and a reflective layer 27, e.g. vapor-deposited from gold. A further increase in optical efficiency and a Suppression of the laser modes which depend on the desired exit direction of the laser light differ can be achieved in a known manner in that the side surfaces of the laser and are therefore rough compared to the optically flat polished end faces. As a result, light emerging from the side is weakened and becomes thus deprived of the reinforcement by the laser effect.

In the previous it was described that the laser end faces, either vacuumed and polished flat optically, or that they can be by splitting the Wafers are achievable. The latter method is to be given preference. By doing In the event that the end faces are made by splitting, it is necessary to that the raised portion applied to the substrate runs in the direction which is perpendicular stands to the cleavage plane.

Claims (5)

Stripe lasers Claims: 1) Stripe lasers with a plurality differently doped semiconductor layers on a lowermost semiconductor substrate, in which laser the current flow to a small width of a band, which is extends in the direction of the emitted light, is limited, d a d u 1 c h g e it is not indicated that the substrate (11) has an elevation (12) approximately in width of the band and in the direction of the band to which the current flow is limited it should be that the elevation has an upper, flat surface and steeply sloping side surfaces and that the side surfaces and at least part of the substrate surfaces, which extend from the elevation, covered with a blocking layer (13) are. 2) Stripe laser according to claim 1, d a d u r c h e k e n n n z e i c It should be noted that the blocking layer made of a semiconductor material is opposite Conductivity type exists like the substrate. 3) strip laser according to claim 1 or 2, d a d u r c h g e k e n n z e i c ii n e t that the blocking layer covers the entire substrate area except for the upper, flat surface of the elevation covered. 4) strip laser according to one of claims 1 to 3, d a d u r c h g It is not noted that the blocking layer (13) has a concave meniscus adjoins the elevation (12). 5) strip laser according to one of claims 1 to 4, d a d u r c h g It is not noted that the top layer (17) is along a strip on the width and in the direction of the band to which the current flow is limited should be contacted. G) strip laser according to one of claims 1 to 11, d a d u r c h it is not noted that the top layer (17) covers its entire surface contacted (21A).