Photodetector on silicon-on-insulator

1. A system comprising a source of illumination and a photodetector, comprising:

an SOI-type semiconductor layer including a first region of a first conductivity forming an emitter of a photodetecting phototransistor, and a second region of the first conductivity type forming a collector of the photodetecting phototransistor, said first and second regions separated from each other by a central region of a second conductivity type forming a base of the photodetecting phototransistor, and

said SOI-type semiconductor layer having a bottom surface in contact with an insulator layer and a top surface opposite the bottom surface and having a transverse surface at said central region, said transverse surface extending orthogonally to top and bottom surfaces of the SOI-type semiconductor layer,

wherein the source of illumination generates a beam of light that orthogonally illuminates the transverse surface at said central region.

2. The system of claim 1 , wherein the first conductivity type is type N and the second conductivity type is type P.

3. The system of claim 2 , further including a first contact configured to receive a ground voltage for application to the first region and a second contact configured to receive a positive voltage for application to the second region, wherein the central region is left floating.

4. The system of claim 1 , further comprising a contact arranged on the upper surface of the central region.

5. The system of claim 4 , wherein the first conductivity type is type N and the second conductivity type is type P.

6. The system of claim 5 , further comprising circuitry configured to apply a positive voltage to the second region and a ground voltage to the first region and the central region.

7. The system of claim 1 , further comprising a contact arranged astride the first region and the central region.

8. The system of claim 1 , further comprising:

an extension of the central region configured to interrupt the first region; and

a contact arranged on an upper surface of the extension.

9. The system of claim 1 , further comprising:

extensions of the central region configured to interrupt the first region and the second region; and

a contact is arranged on an upper surface of each extension.

10. A system comprising a source of illumination and a photodetector, comprising:

an insulating layer;

a semiconductor layer on said insulating layer;

wherein said semiconductor layer includes:

a first region doped with a first conductivity type and in contact with a top surface of the insulating layer;

a second region adjacent the first region and in contact with a top surface of the insulating layer, the second region doped with a second conductivity type in; and

a third region adjacent the second region and in contact with a top surface of the insulating layer, the third region doped with the first conductivity type;

said first, second and third regions forming a photodetecting bipolar phototransistor device; and

a transverse surface at said second region that receives an illumination, said transverse surface extending orthogonally to an upper surface of the semiconductor layer.

11. The system of claim 10 , further comprising:

a first contact on said first region configured to receive a ground voltage; and

a second contact on said third region configured to receive a positive voltage.

12. The system of claim 11 , where the central region is left floating.

13. The system of claim 10 , wherein the second region includes an overdoped region and further comprising a contact on said overdoped region.

14. The system of claim 10 , wherein the second region includes an overdoped region and further comprising:

a first contact overlapping said first region and said overdoped region; and

a second contact on said third region.

15. The system of claim 10 , wherein said third region comprises first and second sub-regions separated from each other by an extension of the second region and further comprising:

a first contact on said first region;

a second contact on first sub-region; and

a third contact on said second sub-region.

16. The system of claim 15 , wherein the second region includes an overdoped region and further comprising a fourth contact on said overdoped region.

17. The system of claim 10 , wherein said first, second and third regions form, respectively, emitter, base and collector nodes of said bipolar phototransistor device.

18. A system comprising a source of illumination and a photodetecting phototransistor, comprising:

an insulating layer;

a semiconductor layer having a bottom surface on said insulating layer and having a top surface opposite the bottom surface;

wherein said semiconductor layer includes:

an emitter region of the photodetecting phototransistor doped with a first conductivity type and in contact with a top surface of the insulating layer;

a base region of the photodetecting phototransistor in contact with the emitter region and in contact with a top surface of the insulating layer, the base region doped with a second conductivity type; and

a collector region of the photodetecting phototransistor in contact with the base region and in contact with a top surface of the insulating layer, the collector region doped with the first conductivity type; and

a transverse surface at said base region extending between the top and bottom surfaces of the semiconductor layer; and

wherein the source of illumination applies a beam of light that orthogonally illuminates the transverse surface at said base region.

19. The system of claim 18 , wherein the base region includes an overdoped region and further comprising a contact on said overdoped region.

20. The system of claim 18 , wherein the base region includes an overdoped region and further comprising:

a first contact overlapping said emitter region and said overdoped region; and

a second contact on said collector region.

21. The system of claim 18 , wherein said collector region comprises first and second sub-regions separated from each other by an extension of the base region and further comprising:

a first contact on said emitter region;

a second contact on first sub-region; and

a third contact on said second sub-region.

22. The system of claim 18 , wherein the base region includes an overdoped region and further comprising a fourth contact on said overdoped region.