Question

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 cm2V–1s–1. Neglect the contribution of holes to the conductivity.

Solution

Correct option is

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

Q1

Pure Si at 300 K has equal electron (ne) and hole (nh) concentrations of . Doping by indium increases nh to . Calculate ne 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 27oC. If this semiconductor is doped by a donor impurity such that the number of conduction electrons becomes, calculate the number of holes at 27oC. Also calculate the dopant concentration.  

Q4

A semiconductor has an electron concentration of m–3 and a hole concentration of . Calculate its conductivity. Given : electron mobility , hole mobility 

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 106 Ge atoms. Find the conductivity of doped Ge. The concentration of Ge atoms in the sample is . Given :    

.

Q6

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 cm2V–1s–1 and hole mobility is 100 cm2V–1s–1.

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