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)