In a semiconductor crystal the breaking of bonds results in the release of free electrons and equal number of holes. When potential difference is applied then current flows through it due to the free electrons. Such semiconductors are known as intrinsic semiconductors. On the other hand,in extrinsic semiconductors,the flow of current is due to the addition of impurity in pure semiconductors by the process of doping.

Introduction:
In a semiconductor crystal, the flow of electric current can occur due to the breakage of crystal bonds. This phenomenon is associated with the behavior of electrons within the crystal lattice. Semiconductors can be classified as either intrinsic or extrinsic based on the presence or absence of impurities.

Intrinsic Semiconductors:
- An intrinsic semiconductor is a pure semiconductor material that does not contain any impurities.
- In an intrinsic semiconductor crystal, the current flow is primarily due to the movement of electrons and holes, which are created by thermal excitation.
- At room temperature, some electrons gain enough energy to break free from their covalent bonds and become mobile charge carriers.
- These free electrons are responsible for the conduction of electric current in the crystal.
- Simultaneously, the breaking of covalent bonds also creates positively charged holes, which can also contribute to the current flow.
- The concentration of free electrons and holes in an intrinsic semiconductor is determined by the temperature and the energy band structure of the crystal.

Extrinsic Semiconductors:
- Extrinsic semiconductors are doped with impurity atoms to alter their electrical properties.
- Doping introduces impurity atoms into the crystal lattice, which can either donate or accept electrons to create excess charge carriers.
- When impurity atoms with more valence electrons than the host semiconductor are added, they are called donor impurities.
- Donor impurities create additional free electrons in the crystal, increasing its conductivity.
- On the other hand, acceptor impurities have fewer valence electrons than the host semiconductor.
- Acceptor impurities create additional holes in the crystal, thereby increasing its conductivity.
- In both cases, the flow of current in extrinsic semiconductors is primarily due to the movement of impurity-generated charge carriers.

Conclusion:
In summary, a semiconductor crystal that conducts current due to the breakage of crystal bonds is called an intrinsic semiconductor. Intrinsic semiconductors have mobile charge carriers, such as free electrons and holes, generated by thermal excitation. Extrinsic semiconductors, on the other hand, are doped with impurities to intentionally introduce excess charge carriers, either through donor or acceptor impurities.