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What is the Variation of mobility with electric field?

At smaller electric fields mobility is constant. At higher electric fields mobility varies inversely with the electric field. At such higher fields the velocity of charge carriers will be constant and is of the order of 2*10^5 m/s. There exists a transition period between these two phases where mobility varies inversely to the square root of electric field.

Intrinsic band diagram extrinsic band diagrams?

Intrensic semiconductor band diagram

Intrensic semiconductor band diagram

Band diagrams of N-type semiconductor

Band diagrams of N-type semiconductor

 

Band diagrams of P-type semiconductor

Band diagrams of P-type semiconductor

Comparison of silicon vs. germanium?

Silicon and Germanium
Property Silicon Germanium
Atomic number 14 32
Ego, eV at 0 k 1.21 0.785
Ego, eV at 0 k 1.1 0.72
Intrinsic concentration at 300 K 1.5 * 1010 2.5 * 1013
Mobility(holes, electrons) at 300k 1300,500 3800,1800
Diffusion constants 34,13 99,47

Why silicon is preferred over germanium in electronic devices?

Silicon is preferred over germanium for the following reasons:

  • Silicon is abundant in nature is available cheaply.
  • The electrical properties of germanium are more sensitive to temperature than silicon. Fine control of conduction properties of germanium is difficult compared to silicon
  • Silicon has wider band gap than germanium.
  • Silicon is Stable and strong material.

How bands occur in semiconductor?

In a crystal it is found out that the electronic energy levels of atoms gets altered. At interatomic distances the inner shell electros will not be affected much but the outer most energy levels are changed considerably. The outermost shells of all the atoms gets spreads out and forms a large number of discret but closely spaced energy levels called energy bands. In silicon energy band splits into two one is valence band and the other is conduction band.

How can you experimentally differentiate P –type SC and N-type Semi conductor?

Hall affectIf the semiconductor material is of N-type then the carriers will be electrons which are forced towards side 2 by the Lorentz force exerted by the magnetic filed B. Hence the induced hall voltage of side 2 measured with respect to 1(the opposite face to 2) will be negative (Recall that the electrons are negative charge carriers).

If the semiconductor material is of P-type then the carriers will be holes which are forced towards side 2 by the Lorentz force exerted by the magnetic filed B (assuming the flow of current is in the same direction as electrons, conventional current is in the direction opposite to the flow of electrons). Hence the induced hall voltage of side21 measured with respect to 1 (the opposite face to 2) will be positive (Recall that the holes are positive charge carriers).

What is photo electric effect?

When light falls on metal electrons are emitted from the surface of the metal. This phenomena is termed as photo electric effect. The energy the impinging photons (light consists of tiny mass less particles called photons which carry energy of h*v where h is Planck’s constant and v is frequency of light) should be at least equal to work function (characteristic property of metal). If the impinging photon on metal is having energy greater than the work function of metal the extra energy will appear as kinetic energy of ejected electron. Accordingly we can write

                                                h*v = Wf + K.E

Where Wf is the work function of metal, K.E is the kinetic energy of ejected electron.

 What is florescence?

Certain substances after absorbing some form of incident electromagnetic radiation releases the absorbed energy in chunks. The emitted radiation will be having lesser energy or frequency compared to the incident radiation. This is termed Fluorescence.

 What is the motion of charge particle in electric and magnetic field?

In electrostatic field alone electron moves in straight line. The electron’s travel is in the direction opposite to the direction of electric field.

If an electron enters a magneto static field alone with non zero velocity electron moves in circular path. The electron motion will be in a plane perpendicular to the direction of magnetic field.

If an electron enters a combined electric and magnetic field with non zero velocity electron travels in a helical path whose patch vary with time.                          

Motion of electron in combined Electric and Magnetic fields

Motion of electron in combined Electric and Magnetic fields

 What is thermistor and sensistor?

In semiconductors as temperature increases conductivity increases i.e. it can exhibit positive temperature coefficient of conductivity, this property finds applications in control devices, as a thermal relay e.t.c. Such a semiconductor is called as thermistor.

Sensistor is a heavily doped semiconductor which exhibits positive temperature coefficient of resistance.

What is photo ionization?

When light falls on an atom it will eject one or more electrons (depending on energy of photons) from it forming ions. This process is called Photo ionization. Photo ionization and photo electric effects are one and same process which essentially involves interaction of matter with electromagnetic radiation. The term Photo ionization is used with regard to isolated or non interacting atoms whereas photo electric effect is used with regard to metals.

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