EBB215. 2015.Classroom Exercise Part IICarrier generation in an intrinsic semiconductor 1. A semiconductor is said to be intrinsic if it contains _____________ impurities. 2. The unit of the concentration of electrons in a semiconductor is ___________________. 3. In an intrinsic semiconductor, the number of electrons in the conduction band is equal/less than the number of holes in the valance band. 4. In an intrinsic semiconductor at absolute zero (0 K), all electrons occupy the electronic energy states in the _________band. The conduction band is full/empty. 5. At 0 K, every electron will be found in the lowest possible energy state = T/F. 6. At high temperatures, electrons acquire some thermal energy which is transferred to them from the crystal lattice = T/F. 7. Atoms in the crystal lattice vibrate and the lattice vibration can be transmitted through the crystals as wave. = T/F. 8. These waves are called photons = T/F. 9. When electrons are excited to the conduction band, empty states or _______are formed in the valance band. 10. The electrons are quasi free and can move if _____________________________. 11. When electrons and holes are formed by thermal generation, ________________ pairs are formed. 12. When electrons and holes are formed by optical generation, _________ is supplied to the semiconductor. 13. When the electron is in the higher energy state, it no longer contributes to the covalent bonding. = T/F 14. How does hole move? ______________________________________15. The larger the semiconductor band gap, the smaller the number of electrons and holes = T/F?16. In an intrinsic semiconductor, the equilibrium concentration of electrons, no is the same as the po = T/F. 17. no = po = ni = intrinsic T/F?18. The electrons in the conduction band can move to the empty state in valance band filling the hole, this process is called ______________________. 19. When this happens, quasi-free electrons and quasi-free holes disappear. 20. The energy lost by the process is given out as ___________ or __________ or both. 21. Electrons will remain the conduction band at an average time, n before _______________ with holes in the valance band. 22. The average time between generation and recombination is called _____________________ (typical value is 10-10 to 10-3s). 23. List down three typical semiconductor materials: ____________, ____________, _____________.

Carrier generation in an extrinsic semiconductor 1. By adding __________ atoms, the number of electrons in the conduction band is no longer equal to the number of holes in the valance band. 2. In an extrinsic semiconductor, no = po = T/F3. Extrinsic semiconductor is created by incorporating impurity atoms into an intrinsic semiconductor (host) by a process call __________________. 4. If no > po then the semiconductor is said to be ______ type. 5. If no < po then the semiconductor is said to be _______ type. 6. If a material is a p-type then the majority carrier is _________________. 7. If a material is n-type then the majority carrier is _______________. 8. Assume an atom with five electrons on its outer shell, is substituted for a silicon atom in crystal of silicon, the atom will contribute 4 of its electrons for covalent boding, and ______ electron left not needed for the covalent bonding. This is electron is loosely bound to P. 9. This extra electron can be _________________ to the conduction band of silicon when energy is applied to Si. 10. Draw P atom as donor in silicon crystal. 11. Then draw an energy band diagram of silicon doped with P atom. 12. P is ________________ atom. 13. The electron P contributes to Si is called __________________. 14. The P atom has a slightly different set of energy level than the surrounding Si atoms, some of the levels will actually be in the ____________________ of Si. 15. The donor state is ______________. It is close to the conduction band of Si = T/F16. The P atom will lose its electron to the host and the P atom left behind is ionized positively. 17. The ionized positive atoms can move = T/F. 18. Boron doped in silicon is called _________________ atoms. 19. When B is added to silicon, the silicon becomes _______________ type. 20. Draw how holes can be produced by B addition to Si.