Semiconductors Ch.4

thermal equilibrium

no external forces or excitation sources

time

what is thermal equilibrium independent of?

no=Nd

At thermal equilibrium, when an extrinsic semiconductor is only doped with donors…

po=Na

At thermal equilibrium, when an extrinsic semiconductor is only doped with acceptors…

nopo=ni²

At thermal equilibrium, the mass action law states that…

non-thermal equilibrium

when a semiconductor is under the influence of external forces or excitation sources

external forces/excitation sources

voltages sources, electric fields, magnetic fields, temperature gradients, radiations

does not apply

Under thermal non-equilibrium, the mass action law…

concentration under thermal equilibrium and excess concentration values

Under non-thermal equilibrium, the concentration of carriers is the sum of…

generation and injection

Under what processes are excess carriers the result of?

Low Level Injection

when the concentration of excess minority carriers in smaller than the majority carrier concentration

generation

creation of mobile charge carriers (electrons and holes)

thermal generation

some electrons in the valence band gain enough thermal energy to break free from their parent atoms, creating electron-hole pairs

bandgap energy and temperature

what is thermal generation dependent on?

optical generation

absorbs photons with energy greater than bandgap, enabling an electron to move to the conduction band and leaving a hole in the valence band, creating electron-hole pairs

recombination

removal or elimination of excess minority carriers by the process where mobile carriers (such as electrons and holes) combine and neutralize each other leading to a decrease in the number of free carriers

recombination

electron from conduction band falls into an energy state occupied by a hole in the valence band, eliminaitng both

excess minority carriers are surrounded by majority carriers

Recombination occurs when…

lifetime of minority carriers

average time it takes for excess minority carriers to recombine

impurities, temperature, defects

what factors influence minority carrier lifetimes?

position and time

recombination is a funciton of…

position

When excess carriers are created nonuniformly in a semiconductor, the electron and hole concentrations vary with…

net motion of the carriers

variation in concentration with position leads to a…

from areas of high concentration to low concentration

How do carriers move due to nonuniformity?

diffusion

What motion of carriers causes current?

continuity equation

what equation is used to determine the concentration of minority carriers?

continuity equation

describes the change in minority carrier concentration at a particular position with respect to time is equal to the difference between incoming and outgoing flux of minority carriers due to current flow plus the amount of carriers created by generation and minus the amount of carriers that are removed due to recombination