1. WEEK ONE TOPIC: ELECTRONICS SOLID STATE MATERIALS  CONDUCTORS  INSULATORS  SEMICONDUCTORS

2. CONDUCTORS MATERIALS / SUBSTANCES THAT CAN CONDUCT ELECTRICITY, HEAT AND CHARGES CAN ALSO BE TRANSFERRED THROUGH THEM. EXAMPLES:  COPPER  IRON  SILVER  SALT  INORGANIC ACID SOLUTIONS

3. PROPERTIES OF CONDUCTORS 1.ALLOWS THE FLOW OF CURRENT 2. HAS LOW ELECTRICAL RESISTANCE AT ROOM TEMPERATURE 3. HAS A LARGE DENSITY OF MOBILE CHARGE CARRIERS (ELECTRONS) 4. A POSITIVE TEMPERATURE CO- EFFICIENT OF RESISTANCE (COPPER)

4. INSULATORS MATERIALS / SUBSTANCES THAT CANNOT ALLOW THE FLOW OF HEAT, ELECTRIC CURRENT OR CHARGES TRANSFER THROUGH THEM. EXAMPLES:  PLASTIC MATERIALS  GLASS  AIR  RUBBER

5. PROPERTIES OF INSULATORS 1.HIGH ELECTRICAL RESISTANCE 2.NO MOBILE CHARGE CARRIERS 3.NEGATIVE TEMPERATURE COEFFICIENT OF RESISTANCE (RUBBER, PLASTICS ETC)

6. SEMICONDUCTORS MATERIALS WHICH HAVE AN ELECTRIC CONDUCTIVITY INTERMEDIATE IN VALUE BETWEEN A GOOD CONDUCTOR (PURE METAL) AND A GOOD INSULATOR EXAMPLES  SILICON  GERMANIUM

7. PROPERTIES OF SEMICONDUCTORS 1.SMALL NUMBER DENSITY OF CHARGE CARRIERS 2. NEGATIVE TEMPERATURE COEFFICIENT OF RESISTANCE 3. INTERMEDIATE RESISTIVITY OF 10 1 AND 10 3 MM.  FREQUENT SENSITIVITY TO LIGHT  NEARLY OBEYS OHMS’ LAW OVER A WIDE RANGE OF CONDITIONS. EXCEPT AT A JUNTION OF MATERIALS  SILICON AND GERMANIUM HAVE FOUR VALENCE ELECTRONS AT THEIR OUTER SHELLS CRYSTALLINE IN NATURE.

8. MODES OF CONDUCTION IN SEMICONDUCTORS IN ELECTROLYTE, TWO TYPES OF IONS ARE CHARGE CARRIERS:  CATIONS – POSITIVE CHARGE CARRIERS  ANIONS – NEGATIVE CHARGE CARRIRS IN SEMICONDUCTORS, TWO TYPES OF CHARGE CARRIERS:  HOLES – POSITIVE CHARGE CARRIERS  ELECTRONS – NEGATIVE CHARGE CARRIERS

9. INTRINSIC AND EXTRINSIC SEMICONDUCTORS  INTRINSIC SEMICONDUCTORS INTRINSIC SEMICONDUCTORS ARE PURE SILICON AND GERMANIUM (I.E WITHOUT DOPING)  HAVE EQUAL NUMBER OF HOLES AND ELECTRONS, BUT DO NOT MAKE EQUAL CONTRIBUTION BECAUSE THEY HAVE DIFFERENT MOBILITIES AND ARE FEW IN NUMBER.  CURRENT CAN FLOW IN A PURE (INTRINSIC) SEMICONDUCTOR THERMAL EFFECT OF SEMICONDUCTORS THE DENSITY OF CHARGE CARRIERS (HOLES AND ELECTRONS) IN A SEMICONDUCTOR INCREASES RAPIDLY WITH TEMPERATURE

10. EXTRINSIC SEMICONDUCTORS THESE ARE SEMICONDUCTORS THAT HAVE HAD THEIR SEMICONDUCTING PROPERTIES ARTIFICIALLY MODIFIED BY ADDITION OF IMPURITY ATOMS TO THE CRYSTAL. TYPES OF EXTRINSIC SEMICONDUCTORS 1.N-TYPE SEMICONDUCTORS  PRODUCED BY ADDING A TINY AMOUNT OF IMPURITY SUCH AS ARSENIC OR PHOSPHORUS OR ANTIMONY, PENTAVALENT ELEMENTS TO A PURE SEMICONDUCTOR E.G GERMANIUM  CREATE MORE ELECTRONS THAN HOLES  HENCE N-TYPE MAJORITY CARRIERS ARE FREE ELECTRONS (NEGATIVE CHARGES)  MINORITY CARRIERS ARE HOLES (+CHARGES)  ARSENIC, PHOSPHORUS AND ANBTIMONY ARE CALLED DONOR ATOMS 2.P-TYPE SEMICONDUCTORS  PRODUCED BY ADDING IMPURITIES SUCH AS BORON OR INDIUM IN A TINY AMOUNT (A THREE-VALENT ELEMENT) TO SILICON, A PURE SEMICONDUCTOR  CREATES MORE HOLES THAN ELECTRONS  MAJORITY CARRIERS ARE HOLES  MINORITY CARRIERS ARE FREE ELECTRONS  BORON AND INDIUM ARE CALLED ACCEPTOR ATOMS

11. DOPING  A PROCESS OF ALTERING THE CRYSTALLINE STRUCTURE OF PURE SEMICONDUCTOR (GERMANIUM OR SILICON) BY ADDING IMPURITY CRYSTAL TO PRODUCE MORE FREE ELECTRONS OR MORE HOLES. P-N JUNCTION DIODE  A SINGLE SEMICONDUCTOR WHICH CONSISTS A P-TYPE AND N-TYPE SEMICONDUCTOR IN CONTACT.  ACTS AS A RECTIFIER (FULL WAVE OR HALF WAVE)  FUNCTIONS LIKE THERMIONIC DIODE CHANGING AC TO DC VOLTAGE  NON-OHMIC CONDUCTORS  SMALLER THAN THERMIONIC DIODE

12. A DIODE  IS FORWARD BIASED WHEN P-TYPE IS CONNECTED TO POSITIVE AND N-TYPE NEGATIVE TERMINAL OF A BATTERY.  REVERSE BIASED WHEN N-TYPE IS CONNECTED TO POSITIVE WHILE P-TYPE CONNECTS TO NEGATIVE TERMINAL OF A BATTERY.  A P-N JUNCTION DIODE HAS A LOW RESISTANCE IN FORWARD BIASED AND HIGH IN REVERSE BIASED SEMICONDUCTOR DEVICES  RECTIFIER  VALVE  DIODE  TRIODE ETC

13. IN A PURE CONDUCTOR, E.G PURE METAL ITS RESISTANCE INCREASES WITH INCREASE IN TEMPERATURE, BUT DECREASES ITS CONDUCTIVITY.

14. TRANSISTOR  THIS IS A SEMI CONDUCTOR WHICH CAN AMPLIFY HIGH FREQUENCY SIGNALS AS WELL AS PRODUCE ELECTRICAL OSCILLATIONS.  PERFORMS SIMILAR FUNCTIONS TO THOSE OF A TRIODE  HAS THREE (3) PN JUNCTIONS AND TERMINALS  EMITTER  COLLECTOR and  BASE

15. TYPES OF TRANSISTOR 1.nPn TRANSISTOR: A THIN LAYER p-TYPE SEMICONDUCTOR SANDWICHED BETWEEN TWO PIECES OF n-TYPE SEMICONDUCTOR 2. PnP TRANSISTOR: A THIN LAYER n-TYPE SEMICONDUCTOR SANDWICHED BETWEEN TWO PIECES OF p-TYPE SEMICONDUCTOR

16. ADVANTAGES OF TRANSISTOR: -HAS HIGH VOLTAGE GAIN, BUT LOWER SUPPLY VOLTAGE -NO HEATING EFFECT DISADVATAGE -LOW POWER DISSIPATION AND LOW INPUT IMPEDENCE -DEPENDENT ON TEMPERATURE

17. ASSIGNMENT 1.SKETCH A GRAPH TO SHOW HOW CURRENT THROUGH A JUNCTION DIODE VARIES WITH POTENTIAL DIFFERENCE ACROSS IT. 2. STATE THE TWO DEVICES WHICH OHM’S LAW DOES NOT APPLY (SSCE MAY/JUNE 2010) 3. (A) DIFFERENTIATE BETWEEN P-TYPE SEMICONDUCTOR AND N-TYPE SEMICONDUCTOR (B) INTRINSIC AND EXTRINSIC SEMICONDUCTOR.