Hello,
The result of Silicon crystal analyzation shown that there is an amount of arsenic As atoms in silicon crystal at Concentrate percentage which is 0.0002%. assuming if conductivity concentration which promote by heat is an eliminated amount.
Find out the electrical conducting density?


Where Molarity of silicon = 12.1cm3/mole
my humble ideas goes like,
Density= w/v....1
V= Moles#/Molarity....2

1/Calculation of moles number:

Moles#=w/M.wt....3
= .0002*100/28.1
=7.117*10^-4 mole

2/ Calculation of volume:
back to equation #2
V=7.117*10^-4/12.1
=5.88*10-5 cm3

If I do it in appropriate way why I couldn't find the Weight in grams of Si. Hold on, silicon is the conductive and arsenic is a blotch which give us a N-type conducting. Avoiding the weight of Si we can go throw this rule which says: Density =the number of conductive * 1 cm3
Where 1 cm3 = 1mole =Avogadro’s number
1 mole = 6.022 x 10^23 atoms
Now, how could I figure out the number of conductive?
How can I solve this, Am I doing well ?!

Draw the diagram of band and name the form of boundary


Finding out the Si weight
W of Si =moles#/atomic mass
= 7.117*10^-4/28.086
= 2.534*10^-5gm
Back to density
D = 2.534*10^-5/5.88*10^-5
= 0.4309gm/cm3
Another solution
segma= 1/D
Log segma = 4.247 –(92924/T)
=2.7221998*10^-6 ms
D = 367.349*10^3

Electrical conductivity or specific conductance

is a measure of a material's ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current. The conductivity s is defined as the ratio of the current density J to the electric field strength E

J=sE

where electrical conductivity s is has been calculated
means it can be found in table as a constant.

!!!!!!!!!
Any Ideas!
I really need help.