PHYSICAL ELECTRONICSECX 5239

PRESENTATION – 01

C.R.M. ANTHONY4090621372014-01-10

conductivity variation in semiconductors

It depends

on mainly two

factors ,

Atomic bond

Energy band

structure

conductivity

Conductors

Conductors are generally substances which have the property to pass different types of energy.

Semiconductors

Semiconductors are solids whose conductivity lies between the conductivity of conductors and insulators. Due to exchange of electrons - to achieve the noble gas config-uration - semiconductors arrange as lattice structure. Unlike metals, the conductivity increases with increasing temperature.

Insulators

Insulators possess no free charge carriers and thus are non-conductive.

Energy band structure

Semiconductor energy bands at room temperature

Full valanceband

Empty conductionband

+e- +e- +e- +e-Energy

ATOMIC BONDING

Conductivity of Semiconductors

Consider the conductivity of a semiconductors

conductivity of a semiconductors = Charge of electrons & = Concentration of electrons & holes & = Mobility of electrons & holes Conductivity of electrons, = Conductivity of holes, =

The variation of the drift mobility with dopant concentration in Si for electrons and holes at 300 K.

At room temperature T= 300 K. & Using the above graph conductivity of this sample at room temperature

= = 21.6//

The temperature dependence of the intrinsic concentration.

Intrinsic concentration == 1 ×

If Intrinsic ;

Using the above graph of (T) 1/T, we have:

1 × 1.9

= 526 K //

Q7).

𝐵𝑧

𝐵𝑧

𝐼 𝑥

Y𝐵𝑧𝐵𝑧

𝐵𝑧

P e

𝐹 𝑦

𝐸𝑝

𝐸𝑒

𝐸𝑝P

In the y-direction there is no net current, therefore ………………………………(1) ……………………………………………………….....(2)

There are driving forces activated on both electron & holes to drift along y axis. The net force experienced by the carriers…………………………………………..………(3)………………………………………………(4)Also, we can write the net force again as; ……………………………………….....(5) ………………………...............(6)Now we can equalize; (3)=(5) ………..….(7)& (4)=(6)…………………………………..(8)

P

e

−𝐹 𝑒𝑦

𝐹 𝑝𝑦

Using above equation (7) & (8) substituting in eq(2) ,we can solve & obtain ;

Finally represent hole coefficient is; …………………………………(9)After that; ; Substituting the mass action law into Equation (9) we get; ……………………………………….(10)

differentiation by n;

For maximize ; Resultant n is below which is leady for maximize ,

 

Thank you!