Question
Find the number density (concentration) of donor atoms to be added to an intrinsic germanium semiconductor to produce an ntype semiconductor of conductivity . The mobility of electron in ntype germanium is 3900 cm^{2}V^{–1}s^{–1}. Neglect the contribution of holes to the conductivity.




None of these
medium
Solution
The conductivity of an extrinsic semiconductor is given by
If the contribution of holes is negligible, then
The electron concentration is, thus, given by
.
Here,
.
.
because . Since one donor atom provides one free electron to the germanium, the number density of the required donor atoms is .
SIMILAR QUESTIONS
Pure Si at 300 K has equal electron (n_{e}) and hole (n_{h}) concentrations of . Doping by indium increases n_{h} to . Calculate n_{e} in the dopped Si.
A semiconductor has equal electron and hole concentrations of . On doping with a certain impurity, the hole concentration increases to . Calculate the new electron concentration of the semiconductor.
The number of electronhole pairs in an intrinsic semiconductor is at 27^{o}C. If this semiconductor is doped by a donor impurity such that the number of conduction electrons becomes, calculate the number of holes at 27^{o}C. Also calculate the dopant concentration.
A semiconductor has an electron concentration of m^{–3} and a hole concentration of . Calculate its conductivity. Given : electron mobility , hole mobility .
In a pure Ge sample at room temperature the electron and hole concentration is each equal to . It is doped with indium, 1 indium atom is added for 10^{6} Ge atoms. Find the conductivity of doped Ge. The concentration of Ge atoms in the sample is . Given :
.
A semiconductor is known to have an electron concentration of and a hole concentration of . Is the semiconductor ntype or ptype? What is the resistivity of the sample if the electron mobility is 23,000 cm^{2}V^{–1}s^{–1} and hole mobility is 100 cm^{2}V^{–1}s^{–1}.
The electrical conductivity of a semiconductor inceases when electromagnetic radiation of wavelength shorter than 2480 nm is incident on it. Find the band gap for the semiconductor. Given :
.
At absolute zero of temperature, the electrical conductivity of a pure semiconductor is
In pure silicon at 300 K the electron and hole concentration is each equal to . When doped with indium, the hole concentration increases to . What is the electron concentration in doped silicon?
In a transistor circuit, the collector current is 50 mA and the base current is 1 mA. The current gain is