6. Doping <ul><li>Impurities that donate electrons called – DONORS </li></ul><ul><li>Impurities that ACCEPT electrons called – ACCEPTORS </li></ul><ul><li>Semi conductors can be - DOPED – with an impurity which changes the conduction properties. </li></ul>
7. Lattice <ul><li>The semi-conductor forms a LATTICE structure around the impurity. </li></ul>
8. N-type semiconductors
12. Forward Bias <ul><li>Electric field of battery overwhelms interface electric field allowing holes and electrons to be pushed across interface. Such a connection is called a " forward bias ", because it allows current to go forward. </li></ul>
13. Reverse bias
14. Graph <ul><li>pn junction diode "turns on" at about 0.6 V, but that varies according to the doping concentration. Notice the sharp rise in current near the turn-on voltage. This behavior will be exploited later in the construction of the transistor amplifier. </li></ul>
15. Graph Reverse current exaggerated; typical reverse current: 10 micro amperes. This is the "characteristic" curve of a pn junction diode. It shows the slow, then abrupt, rise of current as the voltage is raised. Under reverse bias, even very large voltages will cause only very small currents, essentially constant reverse bias currents. The reverse bias current depends mainly on the rate of thermal generation of electron-hole pairs
16. It points as "point" is spelled, with "p" first, and"n" later. Black band corresponds to the "point" in the diode symbol on the right.
17. Rectification of an AC Signal
18. Smoothing Capacitor charges up during the positive half-cycle, then releases its charge through the resistor during the negative half-cycle, causing current through the resistor that otherwise wouldn't exist.
19. Bipolar Junction Transistors Bipolar junction transistors (BJT). Two types of charge carriers are involved.
20. The PNP Transistor The junction on the left side of the base is forward-biased; the junction on the right side of the base is reverse-biased. Base is very narrow, and not drawn to scale.
21. Amplification Emitter-base junction is biased at the turn-on voltage, so even very small changes in voltage there will lead to very large changes in the emitter-base current ( see detail ). Electric field at the base-collector junction sweeps up almost all holes which enter the base. Weak input signal is amplified by the transistor (details follow).