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Optically Driven Switch with Reduced Turnoff Time

IP.com Disclosure Number: IPCOM000094605D
Original Publication Date: 1965-Mar-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Roy, MM: AUTHOR [+3]

Abstract

For many applications it is desirable to reduce the turnoff time of a semiconductor device such as an optically driven silicon switch 10. This includes a pair of spaced planar emitter regions 11 and 12 disposed in base region 13 formed above collector region 14. Passivating silicon dioxide members 15 and 16 cover those portions 17 and 18 of emitter-base junctions 19 and 20 which extend to the upper semiconductor surface 21. Windows 22 and 23 of a transparent material cover the upper surfaces of emitter regions 11 and 12 except for small portions engaged by electrodes 24 and 25. These make ohmic contact with those regions and serve as the input and output electrodes of the switch.

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Optically Driven Switch with Reduced Turnoff Time

For many applications it is desirable to reduce the turnoff time of a semiconductor device such as an optically driven silicon switch 10. This includes a pair of spaced planar emitter regions 11 and 12 disposed in base region 13 formed above collector region 14. Passivating silicon dioxide members 15 and 16 cover those portions 17 and 18 of emitter-base junctions 19 and 20 which extend to the upper semiconductor surface 21. Windows 22 and 23 of a transparent material cover the upper surfaces of emitter regions 11 and 12 except for small portions engaged by electrodes 24 and 25. These make ohmic contact with those regions and serve as the input and output electrodes of the switch.

When a light source such as forward biased gallium arsenide diode 26 irradiates upper surface 21 of the normally off switch 10, an electrical circuit is established between emitter regions 11 and 12. Removal of the light turns switch 10 off.

I the absence of opaque coatings 27 and 28 of a suitable material over the silicon dioxide members 15 and 16, the turnoff time for the silicon switch 10 is as great as a few milliseconds. The use of the described opaque coatings has proved to be advantageous in greatly reducing the turnoff delay of the switch, turnoff times up to 80 microseconds having been realized. The opaque coatings prevent photon absorption so that carriers are not trapped or stored in the surface of base region 13.

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