1 Higher Physics Unit 3 Optoelectronics Semiconductors.

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Presentation transcript:

1 Higher Physics Unit 3 Optoelectronics Semiconductors

2 Silicon ( undoped ) paired bonding electrons Silicon nucleus  Temp. will free some electrons ( make them more mobile ) and so  Resistance ADD Impurities ( add atoms that are DIFFERENT from the main material 1 ppm )

3 Doping the intentional adding of “impuirity” atoms to  increase the conductivity of a semi-conductor &  specify particular semiconductor propeties.

4 Introduce gaps in the bonding structure of electrons into which other electrons can move into “ holes “, and leave a positive charge behind called p-type semiconductors. Introduce atoms with unbound “ floating” electrons which are free to move called n-type semi-conductor.

5 n - Type Semiconductor extra free electron from Arsenic

6 p - Type Semiconductor Gallium (Ga) nucleus hole due to “missing” electron

7 p-Type Conduction I electrons flowing

8 p-Type Conduction I holes flowing

9 PN Junctions & Diodes n-type semi-conductor p-type semi-conductor Note: both types are neutral

10 PN Junction. pnpn pn depletion zone

11 Connecting Diodes ( PN junctions ) in circuits. pn depletion zone If forward voltage greater than 0.7 V, depletion zone collapses and diode conducts

12 Reverse Bias. pn depletion zone

13 Light Emitting Diodes ( L.E.D.’s ) pn depletion zone positive HOLE negative ELECTRON released PHOTON Energy of releasedPhoton E = h. f

14 Photoconductive Mode. p n depletion zone Connected in REVERSE BIAS I  light falling on depletion zone Very FAST& SENSITIVE

15 Photovoltaic Mode. p n depletion zone

16 Photovoltaic Mode. p n depletion zone  p - type  n - type The PN junction is NOT connected to a d.c supply. Here the PN junction is used itself as a d.c. source to drive a device ( e.g. calculator ) n-type acts as the negative terminal p-type acts as positive terminal