Semiconductors Slides Ch.3 Part 2 and 3

fermi level

average energy of the free carriers in the system

constant

At equilibrium, the average energy must always be the same so E_F must be…

temperature

What is the intrinsic carrier concentration dependent on?

zero

According to charge neutrality, the net charge in a small portion of a uniformly doped semiconductor should be…

if not there will be a net flow of charge resulting in current flow; goes against assumption of thermal equilibrium

Why should the net charge in a uniformly doped semiconductor be zero?

n-type

When the fermi level is closer to the conduction band what type of extrinsic semiconductor is it?

p-type

When the fermi level is closer to the valence band, what type of extrinsic semiconductor is it?

free electrons

When the fermi level is closer to the conduction band, what are the majority carriers?

holes

When the fermi level is closer to the valence band, what are the majority carriers?

Eg

?=Ec-Ev

the energy of the intrinsic carriers

What is Ei?

halfway

Where is Ei located between Ec and Ev?

thermal energy

Where do electrons get kinetic energy from?

random

thermal motion is…

space charge neutrality

if the material is to remain electrostatically neutral, the sum of the positive charges must balance the sum of the negative charges

random electron movement cancels out charge (no net current)

Why is there no current from just moving electrons?

an electric field

What does a voltage source create across a device?

creates an electric force that cause carriers to move

What does an electric field do to the carriers?

spatially homogeneous carrier concentration with no applied electric field

When assuming thermal equilibrium, there is…

scatters

As a result of thermal motion, electrons move in a random direction until it…

interacting with the crystal lattice, impurities, other carriers, or defects

Why does an electron scatter?

constant, random motion of electrons

Drift and Diffusion depend on…

electric field

impurities are ionized so they produce an…

drift

in the presence of an electric field, a carrier movement due to the presence of the electric field superimposed on the random motion

average velocity

charged particles within a semiconductor move with an _____ ____ proportional to the electric field.

carrier velocity and carrier concentration

Drift current is proportional to the…

scattering events

the mobility of the carriers depends on the mean time between…

t bar

the mean time between scattering events

m_n^*

effectibe mass of electrons

majority carriers

conductivity is dominated by…

the scattering mechanism

the mean time between scattering depends upon…

lattice scattering, impurity scattering, defect scattering, carrier carrier scattering

what are the differnet types of scattering mechanisms?

temperature

Different scattering mechanisms exhibit different _________ dependence.

impurity scattering

What scattering mechanism dominates at low temperatures?

lattice scattering

What scattering mechanism dominates at high temperatures?

diffusion

due to thermally induced random motion, mobile particles tend to mov from a region of high concentration to a region of low concentration

less time

At higher temperatures, the steering from the electric fields have _____ _____ to act upon the moving electrons.

decreased stability

At higher temperatures, the atoms within the lattice vibrate more so the lattice has…

scattering effect

interaction with atom/doping causes carrier to move in a direction