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
Energy Bands
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
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
Formation of n-type semiconductor
Formation of p-type semiconductor
p-n junction as diode
p-n junction forward biased
p-n junction reverse biased
V-I Characteristics of Diode
d.c resistance (static resistance)It is the ratio of Voltage to the current in forward biased Diode
a.c resistance (dynamic resistance)rf = ΔV/ΔI
Reverse resistanceIt is the resistance offered by Diode under reverse bias
Diode Resistance
Diode Current Equation
I = Io (ev/η.vt -1)I = Diode Current
V = External Voltage
I0 = reverse saturation current
η = 1 for Ge, 2 for Si
VT = kT/q = T/11600; k=1.38x10-23 J/K , q=1.6x10-19 C
T = Temperature of Diode (K) = (0 C + 2730)
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