DE2804371C2 - Injection laser with semiconductor heterostructure and a stripe geometry of the electrically active area - Google Patents

Description

active material η-conductive Ga ^ A ^ As (2) adjoins, while the strips are surrounded by p-conductive and likewise optically active Ga,., Al ₁ As (3).

under BHdung a pn junction (11) as an optically 35 layer 2 of Ga _1x AUAs adjoins χ , for example

'"""' a value of 0.08. Otherwise it is strip-shaped

Area 4 of a zone 3 of p-type Gai, AUAs limited Here the x-value for zones 2 and 3 is identical. Zones 2 and 3 are through to the outside

5. Injection laser according to claim 4, characterized in that 40 further semiconductor layers 1 and 5 are delimited, which are characterized by the fact that the optically active, or p-conductive Gai.jALAs consist; y is always greater

Gai.jAUAs layers (2,3) existing area of '

Semiconductor areas (1,5) with a smaller refractive index made of p- or η-conducting Gai. ^ AI ^ As is surrounded

where y> χ

6. Injection laser according to one of the preceding claims, characterized in that the Carrier body (6) of the multilayer arrangement produced by epitaxial deposition processes consists of GaAs

7. Injection laser according to one of the preceding claims, characterized in that the optically active area (2, 3) is approximately 2μιη wide and contains three electrically active strip-shaped areas (4a- Ac) .

as χ and can have a value of 03, for example. The pn junction 11 comes to the surface at the light exit area. The electrically active area, in which a high inversion current density of the charge carriers is generated, consists essentially of the p-conducting GaAs zone 4, while the optically active area in which the light wave is guided is formed by zones 2, 3 and 4 will. This light guide area is delimited by the outer zones 1 and 5 made of a material with a smaller refractive index.

Instead of forming the entire semiconductor crystal as an optical resonator, the Use of corrugations due to partial wave reflections; it is then the so-called type of a DFB laser with distributed feedback; see IEEE Journal of Quantum Electronics Vol. QE-12, No. 10, Oct 76, pp. 597-603. The in F i g. The basic structure shown in FIG. 1 would be in to be modified in a known manner if the starting material used in place of GaAs z. B. InP would be used where the other layers of the composition GaInAsP used have a smaller band gap

In the manufacture of injection lasers based on There are different designs of semiconductor heterojunctions. For example, there is the so-called SH laser, which consists of a single heterojunction. The straight transition comes for example between a basic 65 as InP.

material made of GaAs and an epitaxial layer from Furthermore, from DE-OS 25 29 406 semiconductor injection

GaAlAs comes about. There is also the so-called DH laser with a double heterojunction. Of the tion laser according to the features of the preamble of claim 1 known. The electrically active

Areas consist of several parallel, strip-shaped partial areas, which with the surrounding Semiconductor material heterojunctions and, with an adjacent layer, pn junctions form the inactive ones Intermediate areas serve and should improve the dissipation of heat from the active areas due to their relatively low refractive index, the strip-shaped subregions are optical Form waveguides.

In semiconductor laser diodes, structures are currently used in which the width d \ of the gallium arsenide strip 4 is of the order of 10 to 20 μm

The strip thickness in the direction of the current is in the order of magnitude of 1 μm or less. To get into the However, it is essential to achieve a range of operating currents of the order of magnitude of 10 to 20 mA find narrower electrically active areas use. With a strip width of 1 μπι can for example, a threshold current for laser excitation in the order of magnitude of approx. 15 mA can be realized.

With the reduction of the stripe width, however, there is an inevitable broadening of the emission lobe in the Far field hand in hand. In the case of a diode with a stripe width di = 1 μm, the emission lobe has an opening angle of 2 s angle of approx. 50 °. The emission lobe comprises 50% of the maximum radiation power. For even narrower strips that form the electrically active area, the Radiation cone even wider, and the coupling of other optical components, such as Fiberglass, is becoming increasingly difficult, if not impossible. In either case, there is a strong performance hit to be expected when coupling further components or light guide media.

The invention is therefore based on the object for an injection laser according to the preamble of Claim 1 to specify a structure that manages with very low threshold currents, but at the same time has a small opening angle of the emission lobe in the far field. This object is achieved according to the invention solved by the characterizing features of claim 1

The incision laser according to the invention is again preferably an SCH laser (Seperate Confinement Heterostructure) in which the electrically active areas are buried in the semiconductor body and are narrower than the likewise limited optically active area. The electrically active areas are preferably narrower than 1 μm, and the distance between two subregions is likewise preferably below 1 μΐη.

The inventive division of the electrically active strip-shaped semiconductor area has the significant advantage that the emission lobe in the far field has a significantly smaller opening angle, for example when using three partial strips, the total area of which corresponds to a 1 μm wide individual strip, so that the same operating current is required to excite the laser is achieved with a suitably selected coupling distance between the individual sections, a reduction of the opening angle of the emission lobe at about 20 ⁰ C. This means a more than two times better focusing of the laser beam. The emission lobe with an opening angle of 20 ° is created by adding up the individual vectors, if one takes into account that all sub-areas are driven with the same power and the same phase. The superposition of the individual wave fields is similar to that of antenna fields.

Embodiments of the invention are described below with reference to FIG. 2 and 3 explained

FIG. 2 shows the basic structural design of an injection laser. The figure shows the direction of the current and the layering of the individual semiconductor regions running perpendicular to it. The excited laser light beam emerges from the illustrated end face of the arrangement, which is mirrored. The emission lobe with an opening angle of approx. 20 ° in the far field is shown in FIG. 2 also indicated. The structure of the structure shown in FIG. 2 corresponds essentially to that of FIG. 1. The main difference is that the electrically active area 4 of FIG. 1 in the arrangement according to FIG. 2 was divided into three adjacent sub-areas 4a, 46 and 4c. Each of the strips 4a to 4c is, for example, 0.3 μm wide (d \) and separated from the adjacent strip by a distance tk of the same order of magnitude, so that the total width rf of the arrangement in FIG. 2 is about 2 μΐη

In FIG. 3 shows a top view of the light exit surface of the overall arrangement of the laser diode. The multi-layer structure is located on a, for example, η-conductive gallium arsenide carrier body 6. The multi-layer arrangement has a mesa-shaped structure, with the edge areas of the mesa mountain being made of a material are surrounded, which limits the optically active area of the multi-layer structure and prevents the light wave from escaping in this direction. This delimitation area of the mesa structure is shown in FIG. 3 denoted by 10 and consists, for example, of η-conductive GawAlojAs. Starting from the base body 6, the multi-layer arrangement initially consists of an η-conductive layer 1 made of Gao.7Alo.3As. This layer delimits the optically active area of the semiconductor arrangement. In the exemplary embodiment according to FIG. 3, the layer 2, which is already used for guiding the light waves, consists of n-conducting Gaoj92Alo.o8As. The electrically active areas 4a to 4c made of p-conductive gallium arsenide adjoin this zone 2 and are, for example, d = 0.3 μm wide in the image plane. The distance di between the individual subregions is of the same order of magnitude, so that the entire mesa structure according to FIG. 3 is approximately </ = 2μπι wide in the image plane. The p-conducting subregions 4a to 4c form a hetero-pn junction with zone 2. They are also surrounded by the p-conductive layer 3 made of Gao.92Alo.oeAs. This layer 3 also serves to guide the light of the optical wave. The top of the optically active area is limited by the p-conductive layer 5 made of Gao.7Alo3As. The strip-shaped subregions Aa to 4c have the greatest refractive index. This refractive index decreases towards the outer layers, the largest jump occurring between zones 3 and 5 or zones 2 and 1, and between zones 2 and 3 on the one hand and zone 10 on the other. This limits the optical wave to zones 2, 3 and 4.

On the semiconductor zone 5 there is also a connection zone 7 made of p-conductive and relatively high doped gallium arsenide, which is laterally bounded by an oxide layer ring 12. The metal connection contact 9 covers this gallium arsenide layer 7 as well as the weakly doped and poorly conductive

Semiconductor regions 10 surrounding the multi-layer structure. The second connection contact 8 of the diode is located on the underside of the support body 6, so that the current direction through the multi-layer arrangement is determined by the position of the connection contacts 8 and 9.

The doping of zones 2 and 3 is of the order of magnitude of approx. 10 ¹⁷ atoms / cm ³ , while that of the electrically active areas 4a to 4c is higher at approx. 5 10 ¹⁷ atoms / cm ³ . The delimitation zones 1 and S for the optically active area are, for example, approximately 1 μm thick. The thickness of the zones 2, 3 and 4 is below t μπι, preferably in the range between 0.1 and 0.2 μπι.

The multi-layer structure of Figure 3 is preferred produced by epitaxial deposition processes. The molecular beam epitaxy, which occurs in the Literature has been described several times, can be used advantageously. The sub-areas 4a to 4c are preferably produced by first epitaxially forming a continuous layer of gallium arsenide deposited and then divided into sub-areas with the help of photolithographic processes and by etching will.

It should be pointed out again that the optical coupling makes it very narrow, more electrically active strip-shaped areas according to the invention, the opening angle of the scattering lobe in the far field is considerable could be reduced. This results in the coupling of additional components or light-conducting media only very low radiation losses, since the emerging light is focused in a very small space Power lobes lying outside the emission lobe have only a low level of energy.

For this purpose 2 sheets of drawings

Claims (4)

Patent claims: 1. Injection laser with semiconductor heterostructure and a strip geometry of the electrically active area, the electrically active, strip-shaped area having a pn hetero-transition into several, parallel strip-shaped sub-areas, each with a pn- Transition are provided, is divided, and in which the strip-shaped sub-areas are arranged in a plane perpendicular to the direction of flow and the coupling medium between the sub-areas consists of a material whose band gap is greater than that of the is material of the sub-areas, characterized in that the sub-areas (4a- Ac) are so closely spaced that they are optically coupled. 2. Injection laser according to claim 1, characterized electrically active area made of one semiconductor material is in this case with one material on both sides With this arrangement, the charge carriers and the optical Waveguide matching edge areas on both sides of the recombination zone. There are also so-called SCH lasers (Separate Confinement Heterostructures) (IEEE journal of Quantum Electronics VoL QE-12, No. 10, Oct 76, pp 597-603), in which the injected charge carriers act on a small electrically active area within the optically active area are limited. Recently, laser arrays have also been produced with very low current density and in which the electrically active areas in the form of a narrow Strips are buried in the semiconductor body. The advantage of this strip-like arrangement of the electrical active area in the form of a structure buried in the semiconductor body lies in the fact that marked that it was a SCH laser (Seperate 20 stood lower and more uniform temperatures in the " "* '· ■ · active area prevail. This is because the total thermal power that has to be given off by the structure, proportional to the area of the With these structures, the active area can be used for the Laser excitation achieve the required inversion current density on charge carriers. Such a structure is shown in FIG. 1 shown schematically The arrangement consists essentially of five semiconductor layers, the planes of which are perpendicular to the direction of the current. Inside the forest is for example an elongated strip-shaped Area 4 made of GaAs, which is p-conductive and with the formation of a pn-heterojunction to the n-conductive Confinement heterostructure) in which the electrically active areas (Aa-Ac) are buried in the semiconductor body and are narrower than the likewise delimited optically active area (2, 3). 3. Injection laser according to claim 1 or 2, characterized in that the electrically active areas (Aa-Ac) are narrower than 1 μm and the distance between two sub-areas is also less than 1 μm 4. Injection laser according to one of the preceding claims, characterized in that the electrically active areas (Aa-Ac) consist of p-conductive GaAs, on at least one side