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Semiconductor Electronics: Materials, Devices and Simple Circuits Test 4

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Semiconductor Electronics: Materials, Devices and Simple Circuits Test 4
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Weekly Quiz Competition
  • Question 1
    1 / -0
    The mobility of free electrons is greater than that of free holes because 
    Solution
    Electrons require low energy for mobility as they suffer low resistance during their motion as compared to holes.
  • Question 2
    1 / -0
    Forbidden gap in a pure conductor is
    Solution
    Forbidden band gap is the group of energy levels that cannot be occupied by the electrons, these energies lies in between conduction band and valence band. In pure conductors, electrons are loosely bound to the nucleus hence, can detach easily at room temperature also. A large number of free electrons thus, available are conduction electrons. The energy level of these electrons corresponds to the conduction level, hence valence level and conduction level are overlapped. Due to this, there is no forbidden band gap present in between conduction band and valence band hence, for metals the forbidden band gap is $$0\ eV$$.
  • Question 3
    1 / -0
    Which of the following are correct for insulators?
    Solution
    In insulators, the electrons are very tightly bound to the nucleus. At a room temperature, thermal energy is not enough to push electrons into conduction band. The energy band gap is very high. Thus the conduction band is empty and the valence band is filled with electrons.
  • Question 4
    1 / -0
    The conduction band and valency band of a good conductor are
    Solution
    In conductors, electrons are loosely bound to the nucleus hence, can detach easily at room temperature also. A large number of free electrons thus, available are conduction electrons. The energy level of these electrons corresponds to the conduction level, hence valance level and conduction level are overlapped. 
  • Question 5
    1 / -0
    In a metal, the separation between conduction band and valence band is of the order
    Solution
    Energy band gap is the energy difference between conduction band and valence band, i. e., energy required to an electron to overcome the energy levels between conduction band and valence band. In conductors, electrons are loosely bound to the nucleus hence, can detach easily at room temperature also. A large number of free electrons thus, available are conduction electrons. The energy level of these electrons corresponds to the conduction level, hence valance level and conduction level are overlapped. Due to this, there is no gap between conduction band and valence band hence, for metals their separation is of the order of $$0\ eV$$.
  • Question 6
    1 / -0
    The value indicated by Fermi energy level in an intrinsic semiconductor is
    Solution
    In an intrinsic semiconductor, $$n = p$$, where, $$n$$ is number of electrons and $$p$$ is number of holes in intrinsic semiconductor.
    This implies that there is an equal chance of finding an electron at the conduction band edge as there is of finding a hole at the valence band edge. Thus, the average energy level of electrons and holes is half of the energy band gap in intrinsic semiconductors. Also the Fermi energy level lie exactly in the middle of energy band gap in intrinsic semiconductors. Thus, the value indicated by Fermi energy level in an intrinsic semiconductor is the average energy of electrons and holes.
  • Question 7
    1 / -0
    Which of the following contains a covalent bond?
    Solution

    A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding. As the valency of germanium is $$4$$, it can share $$4$$ electrons of neighboring atom to complete the octet. Hence, Ge has covalent bond. NaCl is an example of an ionic bond and helium and copper both have valency $$2$$ and $$1$$ respectively.

  • Question 8
    1 / -0
    The bond, that exists in a semiconductor is
    Solution
    Semi-conductors are made of 14th Group elements which form covalent bonding.
  • Question 9
    1 / -0
    There is no hole current in conductors, because they have
    Solution
    In conductors, electrons are loosely bound to the nucleus hence, can detach easily at room temperature. Also, a large number of free electrons thus, available are conduction electrons. When the covalent bond breaks, electrons are freed from the atom. The departure of an electron from valence band creates the vacancy in bond, this vacancy is known as hole. This hole is captured by another free electron. Also, the energy level of free electrons corresponds to the conduction level, hence valance level and conduction level are overlapped. So there are no holes in conduction level to carry hole current.
  • Question 10
    1 / -0
    p-n junction diode acts as
    Solution


    We know that in the case of metallic conductors, the potential difference varies in direct proportion to the current flowing. The $$I-V$$ graph of a ohmic conductor is a straight line. But, a p-n junction diode is not in according with Ohm's law. The current voltage characteristic curve of a p-n junction diode shows both forward bias as well as reverse bias characteristics as shown as in the graph.

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