Advertisements
Advertisements
Question
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.
Advertisements
Solution
(i) n-type wafer is created when As is implanted in Si crystal. The number of majority carriers electrons due to doping of As is
`n_e = N_D`
= `10^-6 xx 5 xx 10^28` atoms/m3
= `5 xx 10^22/m^3`
The number of minority carriers (holes) in an n-type wafer is
`n_h = n_i^2/n_e`
= `(1.5 xx 10^16)^2/(5 xx 10^22)`
= `0.45 xx 10^10/m^3`
The p-type wafer is created with the number of holes, when Boron is implanted in Si crystal,
`n_h = N_A`
= `200 xx 10^-6 xx (5 xx 10^28)`
= `1 xx 10^25/m^3`
Minority carriers (electrons) created in the p-type wafer is
`n_e = n_i^2/n_h`
= `(1.5 xx 10^16)^2/(1 xx 10^25)`
= `2.25 xx 10^7/m^3`
(ii) The minority carrier holes of the n-region wafer (nh = 0.45 × 1010/m3) would contribute more to the reverse saturation current than minority carrier electrons (ne = 2.25 × 107/m3) of the p-region wafer when the p-n junction is reverse biased.
APPEARS IN
RELATED QUESTIONS
Distinguish between 'intrinsic' and 'extrinsic' semiconductors
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 ______.
In n-type semiconductor, the fifth electron ______.
In p-type semiconductor, the dopant is ______.
In p-type semiconductor, ______.
State how a p-type semiconductor will be obtained from a pure crystal of a semiconductor.
Distinguish between n-type and p-type semiconductors.
In a pure semiconductor crystal of Si, if antimony is added then what type of extrinsic semiconductor is obtained. Draw the energy band diagram of this extrinsic semiconductor so formed.
The figure shows a piece of pure semiconductor S in series with a variable resistor R and a source of constant voltage V. Should the value of R be increased or decreased to keep the reading of the ammeter constant, when semiconductor S is heated? Justify your answer
Name the extrinsic semiconductors formed when pure germanium is doped with a trivalent impurity. Draw the energy band diagram of extrinsic semiconductors so formed.
Name the extrinsic semiconductors formed when pure germanium is doped with a Pentavalent impurity. Draw the energy band diagram of extrinsic semiconductors so formed.
- Statement I: By doping silicon semiconductor with pentavalent material, the electrons density increases.
- Statement II: The n-type semiconductor has net negative charge. In the light of the above statements, choose the most appropriate answer from the options given below:
In an extrinsic semiconductor, the number density of holes is 4 × 1020 m-3. If the number density of intrinsic carriers is 1.2 × 1015 m-3, the number density of electrons in it is ______.
Pieces of copper and of silicon are initially at room temperature. Both are heated to temperature T. The conductivity of ______.
What type of semiconductor is obtained when a crystal of silicon is doped with a trivalent element?
The majority charge carriers in a P-type semiconductor are ______.
