Phenomena transport in the semiconductors
1) Characterization of the devices analogic you:
to) creation of mathematical models to us or circuita them deriving from the mathematical description of the physical processes that regulate the operation of the device
b) creation of models circuita them deriving from the characteristics to the clips expressed in graphical shape.
2) Device "Bulk":
It is an electronic device that directly takes advantage of some property of the semiconductor and not the property of the splices.
3) intrinsic Semiconductor:
Draft of a material whose reticulum is constituted from joined tetravalenti atoms between they from covalenti ties, is had that to growing of the temperature some of the ties are broken off generating free electrons to move in the reticulum and an equal gap number.
4) extrinsic Semiconductor of type ânâ?:
Inserting impurità pentavalenti (…P4 Phosphorus, As Arsenic, Sb Antimony) in the reticulum of the tetravalente silicon, ciascuna of they will replace to an atom of silicon having created 4 covalenti ties with the first neighbors while supplying one small energy (…0,1eV for the Ge and 0,05eV for) 5° the electron of valence of the donor can be removed from the same one. In the representation to bands that corresponds to create a level of energy (…Donor level) to ridosso immediately of the conduction band, it is popolato from fifth electrons supplied from the donors who however already to ambient temperature pass in conduction band.
5) extrinsic Semiconductor of type âpâ?:
Inserting impurità trivalenti (…B Boron, Ga Gallium, Indian In) in the reticulum of the tetravalente silicon, ciascuna of they will replace to an atom of silicon having created 3 covalenti ties with the first neighbors remain therefore incomplete a covalent bond which it attracts near electrons of valence forcing them to break off their covalent bond.
In the representation to bands ci² it corresponds to create a level of energy (…Acceptor level) to ridosso immediately of the valence band, which already to ambient temperature it comes to completely being occupied from valence electrons that therefore leave of free gaps to lead in the valence band.
6) Law of action of mass:
It is observed that if increase the concentration of
bearers of type "n" (…drugging with impurità
tetravalenti) reduces the number of bearers "p" in how much is
recombined and viceversa, is had therefore that to one given to
temperature the product of the number of bearers of type "p" for the
number of type bearers "n" he is constant and it is worth 
where To0 is one
constant independent from the temperature and and0 are the energy gap that to 0K it is worth 0,785eV
for GE and 1,21eV for.
7) Density of loads in a semiconductor:
It is obtained from the law of action of mass 
and from the relation of 
neutrality:
to) in a type semiconductor ânâ? the electrons prevail and their concentration is equal to the concentration of the donors that is n = Nd while the concentration of gaps is p = n2/Nd .
b) in a type semiconductor âpâ? the gaps prevail and their concentration is equal to the concentration of the accepters that is p = Nto while the concentration of electrons is n = nthe 2/Nto .
8) Mobility:
It is the constant of proportionality between the field
applied and the assumed average speed from the bearers, for the gaps
ha 
while for the electrons 
therefore the two types of bearers come move to you
from the field in opposite backs.
9) Conductivity:
quindi 
10) Hall Effect:
One has a semiconductor to rectangular section with base w
and height d, and slides in direction trasversa one current in the
back of x the crescents, has moreover a B field in the sense of the z
increasing, the bearers in motion are subject to the force of of
Lorentz 
that independently pushes them towards
the bottom from their nature, have themselves therefore that in the
case of a type semiconductor "n" the bearers are the free electrons
and therefore is had low loads negative and up loads positive while in
the case of a type semiconductor "p" the bearers are the gaps for
which he has low loads positive and up he loads negative.
In both the cases a double layer is created of loads and
therefore an electric field who opposes itself to the force of
Lorentz, its value to the equilibrium is obtained from the budget of
the forces 
from which being 
ha 
and quindi 
.
In particular the constant of Hall is defined 
that concurs to gain mobility in case is famous the
conductivity s has in fact 
and wanting to hold account of the fact that all the
charges do not move with the same speed it has 
.
11) Describe the spread:
_ S' image to sezionare ideal a semiconductor so that the
concentration of bearer that have to sx be various from that one that
have to dx, since every bearer for effect of the temperature move in
direction randomica, have that the number of bearer that cross the
section from sx to dx be greater of the n° of that one that it cross
from dx to sx, create that is a density of current of spread in
direction opposite to the gradient of concentration, in the case of
the gap have 
while in the case of the
electron free have 
where Dp and Dn they are
the spread constants.
12) Relation of Einstein:
It puts in relation the constant of spread with respective
mobility in how much both subject to considerations statistics, finds
the equivalent in tension of the 
temperature.
