From the silicon's crystal structure to discuss how to make doped semiconductors and the mechanics.
To see how we can make silicon a useful electronic material, we
will have to go back to its crystal structure. Suppose somehow(and we will talk about how this is done later) we could substitute a few atoms of phosphorus for
some of the silicon atoms.
A silicon crystal "doped" with phosphorus If you sneak a look at the periodic table, you will see that
phosphorus is a group V element, as compared with silicon whichis a group IV element. What this means is the phosphorus atom
has
five outer or
valence electrons, instead of the four which silicon has. In a lattice
composed mainly of silicon, the extra electron associated withthe phosphorus atom has no "mating" electron with which it can
complete a shell, and so is left loosely dangling to thephosphorus atom, with relatively low binding energy. In fact,
with the addition of just a little thermal energy (from thenatural or latent heat of the crystal lattice) this electron can
break free and be left to wander around the silicon atom freely.In our "energy band" picture, we have something like what we see
in
. The phosphorus atoms are
represented by the added cups with P's on them. They are newallowed energy levels which are formed within the "band gap"
near the bottom of the first empty band. They are located closeenough to the empty (or "conduction") band, so that the
electrons which they contain are easily excited up into theconduction band. There, they are free to move about and
contribute to the electrical conductivity of the sample. Notealso, however, that since the electron has left the vicinity of
the phosphorus atom, there is now one more proton than there areelectrons at the atom, and hence it has a net positive charge of
1
. We have represented this by
putting a little "+" sign in each P-cup. Note that thispositive charge is fixed at the site of the phosphorous atom
called a
donor since it "donates" an electron up
into the conduction band, and is not free to move about in thecrystal.
Silicon doped with phosphorus How many phosphorus atoms do we need to significantly change the
resistance of our silicon? Suppose we wanted our 1 mm by 1 mmsquare sample to have a resistance of one ohm as opposed to more
than 60 MΩ. Turning the resistance equation around we get
And hence (If we continue to assume an electron mobility of
Now adding more than
phosphorus atoms per cubic centimeter might seem like
a lot of phosphorus, until you realize that there are almost
silicon atoms in a cubic centimeter and hence only one
in every 1.6 million silicon atoms has to be changed into aphosphorus one to reduce the resistance of the sample from
several 10s of MΩdown to only oneΩ. This is the real
power of semiconductors. You can make dramatic changes in theirelectrical properties by the addition of only minute amounts of
impurities. This process is called "
doping " the semiconductor.
It is also one of the great challenges of the semiconductormanufacturing industry, for it is necessary to maintain
fantastic levels of control of the impurities in the material inorder to predict and control their electrical properties.
Questions & Answers
A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
A mouse of mass 200 g falls 100 m down a vertical mine shaft and lands at the bottom with a speed of 8.0 m/s. During its fall, how much work is done on the mouse by air resistance
Chemistry is a branch of science that deals with the study of matter,it composition,it structure and the changes it undergoes
Adjei
please, I'm a physics student and I need help in physics
Adjanou
chemistry could also be understood like the sexual attraction/repulsion of the male and female elements. the reaction varies depending on the energy differences of each given gender. + masculine -female.
Pedro
A ball is thrown straight up.it passes a 2.0m high window 7.50 m off the ground on it path up and takes 1.30 s to go past the window.what was the ball initial velocity
2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.
you have been hired as an espert witness in a court case involving an automobile accident. the accident involved car A of mass 1500kg which crashed into stationary car B of mass 1100kg. the driver of car A applied his brakes 15 m before he skidded and crashed into car B. after the collision, car A s
can someone explain to me, an ignorant high school student, why the trend of the graph doesn't follow the fact that the higher frequency a sound wave is, the more power it is, hence, making me think the phons output would follow this general trend?
Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
Joseph
Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
Joseph
"Generation of electrical energy from sound energy | IEEE Conference Publication | IEEE Xplore" ***ieeexplore.ieee.org/document/7150687?reload=true
A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?
