Homework 5

Question 1

Conductivity Equation for a cylindrical specimen.

Answer 1

σ=1/p = I(Seperation Distance)/(Voltage)(π)(d/2)^2

Question 2

How do you compute number of free electrons per cubic meter?

Answer 2

Equation 18.8 : e= 1.602x10^-19C

Question 3

How do you calculate number of free electron per atom?

Answer 3

N_atom=(Avogrados #)(density g/cm^3)(10^6 cm^3/m^3)/(atomic weight) Then divide answer from Eq. 18.8 by N_atom. (Unitless)

Question 4

What is the lever rule used for?

Answer 4

Computing room temp conductivity:
W_α= (C_Σ-C_0)/(C_Σ-C_α)
W_Σ= (C_0-C_α)/(C_Σ-C_α)

C_Σ=Sn on the right side
C_0= Sn on the left side
C_α= Initial Value at Room Temp

Question 5

How do you convert mass fractions using Lever Rule?

Answer 5

V_α=(W_α/p_α)/((W_α/p_α)+(W_e/p_e)

Wapa/wapa plus wepe

You can now find impurity resistivity with eq 18.12 and find conductivity Eq. 18.4

Question 6

difference in certain free-electron-per-atom values?

Answer 6

magnitudes of the band gap energies (Table 18.3). The larger the band gap energy the smaller the chance for excitation

Question 7

how donor impurities in semiconductors give rise to free

electrons in numbers in excess of those generated by valence band–conduction band excitation

Answer 7

Impurities with 5 valence electrons, the impurity atom replaces some of the semi conductor atoms in the crystal structure where 4 of the valence electron would be involved in bonding with 4 neighboring semi-conductors while leaving the 5th electron to be free.

Question 8

how acceptor impurities give rise to holes in numbers in excess of those
generated by valence band–conduction band excitations

Answer 8

Instead of an excess electron, there will be excess holes developed. A tri-valence atom will replace some tetra-valence semi-conductor atom

Question 9

Compare the temperature dependence of the conductivity for metals and intrinsic
semiconductors

Answer 9

electrical conductivity decreases with increasing temperature. Eq 18.4.

As the temperature rises, n will remain constant, whereas the mobility (µe) will
decrease, because the thermal scattering of free electrons will become more efficient. Since |e| is
independent of temperature, the net result will be diminished in the magnitude of σ. Eq. 18.8

For intrinsic semiconductors, the temperature-dependence of conductivity is just the
opposite of that for metals—i.e, conductivity increases with rising temperature Eq. 18.15

Question 10

What are the two functions that a transistor may perform in an electronic circuit?

Answer 10

amplify an electrical signal

act as a switching device in computers

Question 11

compute the plate spacing of a parallel-plate capacitor

Answer 11

Combine eq. 18.26 & 18.27. Set one side of the equal signs with with subscript 1 and oposite with subscript 2. solve for missing value.

Question 12

Absorption occurrence using Energy equation?

Answer 12

Energy Band Gap: h*c/gamma

If energy bandgap>energy of light no absorption will occur

Question 13

why the current

in channel increases as gate voltage, VG increases with more positive values,

Answer 13

When more electrons in the channel, higher current flows between source and drain.