## Question

####

A semiconductor is known to have an electron concentration of and a hole concentration of . Is the semiconductor *n*-type or *p*-type? 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}.

### Solution

Correct option is

The electron concentration in the semiconductor is higher than the hole concentration . Hence the semiconductor is *n*-type.

The resistivity of a doped semiconductor is given by

.

are electron and hole mobilities respectively.

Here,

.

.

#### SIMILAR QUESTIONS

Q1

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.

Q2

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.

Q3

The number of electron-hole 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.

Q5

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 :

.

Q6

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

Q7

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 :

.

Q8

At absolute zero of temperature, the electrical conductivity of a pure semiconductor is

Q9

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?

Q10

In a transistor circuit, the collector current is 50 mA and the base current is 1 mA. The current gain is