1. Based on current conduction, materials are classifieds as 1)Insulators Ex: Wood, Mica, Diamond 2) Conductors Ex: Copper, Aluminium 3) Semiconductors Ex: Silicon, Germanium Classification of Materials

2. Energy Bands

3. Semiconductors They are of two types 1)Intrinsic Semiconductors (Pure) 2)Extrinsic Semiconductors (Impure) Intrinsic is doped to form Extrinsic Adding Impurities is called as Doping

4. Depending on the impurities, there are two types of Extrinsic Semiconductors 1)n-type 2) p-type N-type are formed when pentavalent impurities like arsenic are added to pure semiconductor P-type are formed when trivalent impurities like gallium are added to pure semiconductor

5. Formation of n-type semiconductor

6. Formation of p-type semiconductor

7. p-n junction as diode

8. p-n junction forward biased

9. p-n junction reverse biased

10. V-I Characteristics of Diode

11. d.c resistance (static resistance) It is the ratio of Voltage to the current in forward biased Diode a.c resistance (dynamic resistance) r f = ΔV/ΔI Reverse resistance It is the resistance offered by Diode under reverse bias Diode Resistance

12. Diode Current Equation I = I o (e v/η.vt -1) I = Diode Current V = External Voltage I 0 = reverse saturation current η = 1 for Ge, 2 for Si V T = kT/q = T/11600; k=1.38x10 -23 J/K, q=1.6x10 -19 C T = Temperature of Diode (K) = ( 0 C + 273 0 )