Arsenic diffusion in si: arsenic is diffused into a thick slice of silicon with no previous arsenic in it at 1100ºc. if the surface concentration of the arsenic is 5.0 × 1018 atoms/cm3 and its concentration at 1.2 µm below the silicon surface is 1.5 × 1016 atoms/cm3 , how long must be the diffusion time? (d = 3.0 × 10-14 cm2 /s for as diffusing in si at 1100ºc.)

Diffusion time is 7.42 h

Solution:

As per the question:

Temperature, T =

Surface concentration of arsenic,

Surface concentration below Silicon surface,

D =

x =

Initial concentration at t = 0,

Now, by using Flick's second eqn:

Thus by putting appropriate values:

             (1)

Now,

Now, from error function values tabulation:

For z = 2.0, erf(z) = 0.998

For z = 2.2, erf(z) = 0.995

Now,

With the help of linear interpolation method:

z = 2.12

Now, using eqn (1) and above value:

= 26700 s

t =

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.