Advertisements
Advertisements
Question
The number of silicon atoms per m3 is 5 × 1028. This is doped simultaneously with 5 × 1022 atoms per m3 of Arsenic and 5 × 1020 per m3 atoms of Indium. Calculate the number of electrons and holes. Given that ni= 1.5 × 1016 m−3. Is the material n-type or p-type?
Advertisements
Solution
Number of silicon atoms, N = 5 × 1028 atoms/m3
Number of arsenic atoms, nAs = 5 × 1022 atoms/m3
Number of indium atoms, nIn = 5 × 1020 atoms/m3
Number of thermally-generated electrons, ni = 1.5 × 1016 electrons/m3
Number of electrons, ne = 5 × 1022 − 1.5 × 1016 ≈ 4.99 × 1022
Number of holes = nh
In thermal equilibrium, the concentrations of electrons and holes in a semiconductor are related as:
nenh = ni2
`therefore "n"_"h" = ("n"_"i"^2)/"n"_"e"`
`= (1.5 xx 10^16)^2/(4.99 xx 10^22) ~~ 4.51 xx 10^9`
Therefore, the number of electrons is approximately 4.99 × 1022 and the number of holes is about 4.51 × 109. Since the number of electrons is more than the number of holes, the material is an n-type semiconductor.
RELATED QUESTIONS
Distinguish between 'intrinsic' and 'extrinsic' semiconductors
In a p-type semiconductos, which of the following statement is true:
Distinguish between intrinsic and extrinsic semiconductor. (Give any two points).
In a p-type semiconductor, the acceptor impurity produces an energy level ______
Semiconductors formed by doping germanium (Ge) with aluminium (Z = 13) and antimony (Z = 51) are ______.
Distinguish between n-type and p-type semiconductors.
The conductivity of a semiconductor increases with increase in temperature because ______.
Why are elemental dopants for Silicon or Germanium usually chosen from group XIII or group XV?
Sn, C, and Si, Ge are all group XIV elements. Yet, Sn is a conductor, C is an insulator while Si and Ge are semiconductors. Why?
Suppose a ‘n’-type wafer is created by doping Si crystal having 5 × 1028 atoms/m3 with 1 ppm concentration of As. On the surface 200 ppm Boron is added to create ‘P’ region in this wafer. Considering n i = 1.5 × 1016 m–3, (i) Calculate the densities of the charge carriers in the n and p regions. (ii) Comment which charge carriers would contribute largely for the reverse saturation current when diode is reverse biased.
Name the extrinsic semiconductors formed when pure germanium is doped with a Pentavalent impurity. Draw the energy band diagram of extrinsic semiconductors so formed.
With an increase in the temperature, the electrical conductivity of a semiconductor ______.
What is the process of adding a suitable impurity to increase a semiconductor's electrical conductivity called?
What is a doped semiconductor called?
Which type of dopant is boron (B)?
Which type of dopant is aluminium (Al)?
What are the two types of extrinsic semiconductors?
