DE4234404A1 - Optoelectronic semiconductor element - Google Patents

Abstract

The invention relates to an optoelectronic semiconductor component in the form of an electro-optical modulator with an integrated optical waveguide in the sphere of influence of a diode structure and with external electrical connections. In order to realize the high charge carrier densities required for the switching function, with relatively low switching currents at low power loss, the waveguide and the diode structure have in common a central silicon-germanium layer (2) of predetermined germanium content and on both sides of this central layer (2) a silicon coating (21, 22) or another silicon-germanium layer (3, 4) with relatively low germanium content. The silicon coatings (21, 22) or the other silicon-germanium layers (3, 4) are in each case of opposite conductivity type.

Description

The invention relates to an opto-electronic Semiconductor component as an electro-optical modulator with an integrated optical waveguide in the influence area of a diode structure and with external electrical Connections.

In a known semiconductor device of this type (DE 40 11 861 A1) are those for the injection of cargo carriers in the integrated optical waveguide agile diode wells with regard to the waveguide attenuation is relatively far from the waveguide arranges. This creates the problem that with Volume of the semiconductor to be flooded by charge carriers Component is relatively large, which is why for operation of the known semiconductor device relatively large Switching currents with associated relatively high Power loss are required.

Furthermore, there is an optoelectronic semiconductor component known as an electro-optical modulator ("Applied Physics Letters "51 (1), July 6, 1987, pages 6 to 8), at which is the vertical wave guide of the in this semiconductor Component formed optical waveguide on the small real part of the refractive index in highly doped silicon is based. However, this semiconductor construction closes element of the optical waveguide highly doped areas one, resulting in high additional losses due to absorption through free charge carriers.

The invention has for its object an opto electronic semiconductor component as electro-optical To propose modulator in which the switch function necessary high charge density with comparative wise small switching currents and small power losses are reachable.

To solve this problem point at an opto electronic semiconductor element of the aforementioned Type of waveguide and diodes according to the invention structure together a central silicon germanium Layer of predetermined germanium content and both on the part of this central silicon germanium layer in each case attached a silicon coating or another Silicon germanium layer with comparatively little Germanium content, with the silicon coatings or the further silicon germanium layers of each are of opposite conductivity type.

A major advantage of the semiconductor according to the invention Component is that with him the optical field is concentrated in a small volume and the high Charge carrier concentrations only in this small volume are generated, which advantageously with ver relatively small switching currents and relatively small power losses can be worked. This is through the use of the central silicon germanium Layer possible, on the one hand the germanium in this central layer increases the real part of the refractive index, so that the optical performance in this silicon germanium Layer is largely bundled, and secondly Silicon germanium has a smaller band gap than silicon has, so that the charge carriers in the area of this focus central layer.  

In the semiconductor component according to the invention, the Germanium content in the central layer varies to be high; however, it will be advantageous seen when the central silicon germanium layer has a germanium content of at most 20% because with a higher proportion of germanium in this central Layer the damping of light waves in the semiconductor component at a common wavelength of 1.3 µm increases very sharply.

It is considered particularly advantageous if at the component of the invention the central silicon Germanium layer has a germanium content between 15 and 20% and a layer thickness of at most 200 nm having. With such a central layer the energy barriers remain at the hetero-interfaces above the thermal energy and the necessary Switching currents can be relatively small.

In a further advantageous embodiment of the semiconductor component according to the invention have the further Silicon germanium layers on each of their central side facing away from silicon-germanium layer Silicon layers of the same conductivity type as that neighboring additional silicon germanium layer on.

As is known per se, so can the invention Semiconductor component advantageously a rib for lateral waveguide that have an outer carries electrical contact.

Furthermore, the semiconductor construction according to the invention element can advantageously also be designed so that  it has a support plate made of an insulating material which is suitable for the application of silicon (SOI material = Silicon On INsulator material).

In a further advantageous embodiment of the Invention has the semiconductor device under formation an integrated optical Mach-Zehnder Inferfero meters next to one rib, another rib for lateral wave guide on, giving the possibility is given, the phase modulation by interference in an intensity modulation of the waveguide-guided To implement light.

In a further advantageous embodiment of the The semiconductor component according to the invention has this Formation of an optical switch next to the one rib with an additional electrical contact additional rib on the two additional outer carries electrical contacts.

To explain the invention is in

Fig. 1 shows an embodiment of the semiconductor device according to the invention cross-sectioned perspective view, in

Fig. 2 shows a further embodiment of the semiconductor device according to the invention cross-section in perspective, in

Fig. 3 shows another embodiment of the semiconductor device according to the invention as a Mach-Zehnder interferometer in two representations and in

Fig. 4 shows an additional embodiment as an optical switch in two representations.

The exemplary embodiment shown in FIG. 1 shows an optoelectronic semiconductor component 1 which contains a central silicon-germanium layer 2 which, for example, has a germanium content of 15% and a thickness of 100 nm. Both sides of the central silicon germanium layer 2 are directly adjacent to further silicon germanium layers 3 and 4 which, for example, have a germanium content of 5%. One further silicon germanium layer 3 is p-doped, while the other further silicon germanium layer 4 is n-doped. With this layer structure, an optical waveguide running in the direction of an arrow shown is realized with regard to its vertical waveguide.

In FIG. 1, there is a silicon layer 5 , which is also p-doped, directly above another silicon germanium layer 3 . This silicon layer 5 forms with a supplementary silicon layer 6 with p⁺ doping a rib through which the optical wave is guided laterally.

In Fig. 1 below the other further silicon-germanium layer 4, a further silicon layer 7 is a further additional silicon layer having n-type doping and below this 8 - n-doped also - arranged. On the outside of the one additional silicon layer 6 there is an external electrical contact 9 and on the outside of the other additional silicon layer 8 there is another external electrical contact 10 ; to the outer contacts 9 and 10 , a voltage is applied in the direction of flow when operating the semiconductor component in a manner not shown. On the top, the semiconductor component is covered with layers 11 and 12 of silicon dioxide or silicon nitride for insulation.

In the exemplary embodiment according to FIG. 1, the central silicon germanium layer 2 is therefore surrounded by layers of different conductivity types, as a result of which a pn hetero diode structure is formed. Due to the relatively high gemanium content in the central silicon germanium layer 2 , energy barriers form, so that the recombination of the charge carriers injected into the pn junction area in the case of current flow takes place mainly in this layer 2 . So it comes to the desired charge carrier bundling in this silicon germanium layer 2 . This layer 2 determines both the optical and the electrical properties of the semiconductor component. A relatively large thickness of the layer 2 means that a large proportion of the optical wave is guided in this layer. On the other hand, the critical thickness of layer 2 for a dislocation-free crystal growth must not be exceeded, so that a large thickness of layer 2 only allows a small proportion of germanium and thus the concentration of the injected charge carriers in layer 2 is reduced. The values given above for the dimensioning of layer 4 represent an optimum.

The table below shows the dimensions for the different layers 2 to 8 :

As can be seen from the table above, the layers 3 , 4 , 5 and 7 are weakly doped in order to keep the absorption by free charge carriers low. However, the doping is not so low that this results in higher series resistances and higher power losses.

In deviation from the described configuration of the semiconductor component according to FIG. 1, the p-doped layers 3 , 5 and 6 above the central layer 2 can also be n-doped; layers 4 , 7 and 8 are then p-doped accordingly.

In the exemplary embodiment according to FIG. 2, a central silicon germanium layer 20 is provided on its upper side in FIG. 2 with a silicon coating 21 with n-doping and on its lower side in FIG. 2 with another silicon -Coating 22 provided with p-doping. Outside the layer structure formed in this way there is also an outer n⁺-doped silicon layer 23 and a further outer p⁺-doped silicon layer 24 ; layers 23 and 24 are relatively highly doped for technological reasons. One outer silicon layer 23 is contacted by means of an outer electrical contact 25 , while an approximately V-shaped further outer electrical contact 26 is used to contact the further outer silicon layer 24 . The electrical contacts 25 and 26 are insulated from one another by an insulating coating 27 made of silicon dioxide or silicon nitride; Another insulating covering 28 made of the same material is located on the side of the one contact 25 facing away from the further contact 26 .

As FIG. 2 also shows, the layers 21 and 23 are also designed to form a rib.

In addition to FIG. 2, it should also be noted that the doping on both sides of the central silicon germanium layer 20 can also be exchanged here without the mode of operation of the semiconductor component changing as a result. It should also be noted that the semiconductor component according to this figure is carried by a plate 29 made of an insulating material which is suitable for the application of silicon (SOI material).

The embodiment of FIG. 3 shows in the upper representation a plan view of a basic Dar position of a Mach-Zehnder interferometer 30 as a semiconductor component in which a light beam L runs through branches 31 and 32 from an input 33 to an output 34 , wherein the branches have a length D.

The lower representation of FIG. 3 shows in section ent along the line III-III after the upper representation, the perspective of the configuration of the semiconductor component 30 again and reveals that a central silicon germanium layer 35 is again present, in addition to which - as was explained in detail in connection with the explanation of FIG. 1 - extend further silicon germanium layers 36 and 37 and silicon layers 38 and 39 . Together with the one silicon layer 38 , advantageously n dot-doped additional silicon layers 40 and 41 each form a rib 42 or 43 . The additional silicon layer 41 is provided with an external electrical contact 44 , while the further silicon layer 40, like the other surface areas of the semiconductor component 30, is covered with an insulating layer 45 made of silicon dioxide or silicon nitride.

Below the further silicon layer 39 there is a further supplementary silicon layer 46 , advantageously piert-doped, on the outside of which there is another external electrical contact 47 .

In the case of use, a voltage is applied to the electrical contacts 44 and 47 in the direction of flow.

In the embodiment according to FIG. 3, phase modulation takes place in the branch of the Mach-Zehnder interferometer formed in this way, which is below the electrical contact 44 , as in the embodiments according to FIGS . 1 and 2. By interference formation, the phase modulation is in a Intensity modulation of the light emerging at the output 34 of the interferometer 30 implemented. The necessary length D of the branches 31 and 32 of the interferometer results from the possible charge carrier concentration in the central silicon germanium layer 35 and the proportion of the optical power that is conducted there, so that an injected charge carrier density of, for example, 3 × 10 ¹⁸ cm ^-3 and an optical power share of 10% within the central layer 2 results in a length D of approximately 4 mm. The design of the individual layers of the exemplary embodiment according to FIG. 3 is made in the same way as for the layers according to the exemplary embodiment according to FIG. 1.

In the upper diagram of Fig. 4 is a top view is shown of an embodiment of a semiconductor device according to the invention as an optical switch 50 in a schematic representation. It can be seen that light inputs 51 and 52 can be optically connected to light outputs 53 and 54 in such a way that, for example, the light entering via input 51 can exit either at output 53 or at output 54 . Blocks 55 and 56 and 57 and 58 are intended to schematically identify external electrical contacts.

In a section along the line IV-IV of the upper Dar position of FIG. 4, the lower representation shows the structural design of the semiconductor component 50 in perspective.

As the lower illustration in FIG. 4 shows, the semiconductor component in turn contains a central silicon germanium layer 60 , above and below which, in the same way as is shown in the lower illustration of FIG. 3, further silicon Germanium layers 61 and 62 and silicon layers 63 and 64 extend. Complementary silicon layers 65 and 66 are arranged above the one silicon layer 63 to form two ribs 67 and 68 , which run parallel to one another. The additional silicon layers 65 and 66 are contacted by two outer electrical contacts 55 , 56 , 57 and 58 , while a further outer electrical contact 73 rests on another additional silicon layer 74 , which in turn is connected to the further silicon layer 75 is adjacent. On the upper side of the semiconductor component 50, in turn, is an insulating layer 75 of silicon dioxide or Silizumnitrid.

In the embodiment of FIG. 4, when voltage sources are connected in the direction of flow, the relative position of two modes of the light guided by the semiconductor component 50 to one another is changed, which leads to a switchover of the light with a corresponding length of the semiconductor component.

Claims (8)

1. Optoelectronic semiconductor component as an electro-optical modulator with an integrated optical waveguide in the area of influence of a diode structure and with external electrical connections, characterized in that the waveguide and the diode structure together have a central silicon-germanium layer ( 2 ) of predetermined germanium content and on both sides of this central Silicon-germanium layer ( 2 ) each having a silicon coating ( 21 , 22 ) or a further silicon-germanium layer ( 3 , 4 ) with a comparatively low germanium content, the silicon coatings ( 21 , 22 ) or the are further silicon germanium layers ( 3 , 4 ) of opposite conductivity type. 2. Semiconductor components according to claim 1, characterized in that the central silicon germanium layer ( 2 ) has a germanium content of at most 20%. 3. Semiconductor component according to claim 1 or 2, characterized in that the central silicon germanium layer ( 2 ) has a germanium content between 15 and 20% and a layer thickness of at most 200 nm. 4. Semiconductor component according to one of the preceding claims, characterized in that the further silicon germanium layers ( 3 , 4 ) on their respective side facing away from the central silicon germanium layer ( 2 ) side silicon layers ( 5 , 7 ) from have the same conductivity type as the respectively adjacent further silicon germanium layer ( 3 , 4 ) and that the further silicon germanium layers ( 3 , 4 ) and the silicon layers ( 5 , 7 ) have an acceptor or donor concentration of at most 10 ¹⁶ cm ^-3 on show. 5. Semiconductor component according to one of the preceding claims, characterized in that it has a rib for lateral wave guidance and that the rib carries an external electrical contact ( 9 ). 6. Semiconductor component according to one of the preceding claims, characterized in that it has a support plate ( 29 ) made of an insulating material which is suitable for the application of silicon. 7. Semiconductor component according to one of the preceding claims, characterized in that it has a further rib ( 42 ) for lateral wave guidance to form an integrated Mach-Ten optical interferometer in addition to the one rib ( 43 ). 8. Semiconductor component according to one of claims 1 to 7, characterized in that it has an additional rib ( 68 ) with an additional contact ( 69 ), forming an optical switch next to the one rib ( 67 ), which has two additional external electrical contacts ( 70 , 71 ).