1. Semiconductor basics 1. Vacuum tubes  Diode  Triode 2. Semiconductors  Diode  Transistors Bipolar Bipolar Field Effect Field Effect 3. What’s next?

2. Vacuum Tubes, diode Diode: a device that only allows current to flow in one direction. Filament to heat cathode ~6.3V V cathode anode

3. Vacuum Tubes, triode Triode: a device that controls (amplifies) a currents by a voltage.

4. Semiconductors, the p-n junction Doping provides charge carriers that are very close to conduction band.

5. Semiconductors, the p-n junction Forward biasing: current reverse biasing: high potential

6. Semiconductors, bipolar transistor An NPN transistor can be considered as two diodes with a shared anode region. The base region of the transistor must be made thin, so that carriers can diffuse across it in much less time than the semiconductor's minority carrier lifetime, to minimize the percentage of carriers that recombine before reaching the collector–base junction. The collector– base junction is reverse-biased, electrons that diffuse through the base towards the collector are swept into the collector by the electric field in the depletion region of the collector–base junction and this forms the collector current which is controlled by the base-emitter p-n junction. The first working transistor, Bell lab 1947

7. Semiconductors, field effect transistor Like an NPN bipolar transistor, but know bass current. The gate-source p-n junction is controlled by the potential applied to the gate. This in turn controls the current from drain to source. One may think that the voltage applied to gate controls the size of a conductive channel between the drain and source and hence the current in that channel. So a FET is a voltage controlled resistor.

8. Review questions How quantum physics changed our world? How quantum physics changed our world? Do you believe that future breakthroughs in physics will further change our world for better? Do you believe that future breakthroughs in physics will further change our world for better?