Relative spacing of atoms 6N States Fig. 5 [Fig. 17 page 19] Formation of energy
ID: 475719 • Letter: R
Question
Relative spacing of atoms 6N States Fig. 5 [Fig. 17 page 19] Formation of energy bands from Outer hell discrete levels when Si atoms are far apart. When Si crystal or solid 2N Electron is formed, atoms get closer and Electrons their electrons start interacting 4N Electrons (like shown in Figs. 11/12 notes.) Middle shea Two bands are shown at the location of double headed arrow. Figure 3-3 Energy levels in Si as o function of interatomic spacing. The core levels in-1.21 in Sione completely with electrons. At the octuol atomic electrons in the 31 sub-hel cond the 2Nelectons in the 3p subshel undergo (valence bond, while the higher lying ANstates konduction bond one empty, separated by a Q.4 (a) In Fig. 5 the upper band which is identified by "4N states 0 electrons" is called Conduction band Valence band (b) Do all semiconductors have an energy gap Eg as shown in Fig 5. Circle one. False True (c) Generally at 0°K, the lower of the two energy bands is completely filled up with electrons and upper band is empty. Does this make Si an insulator semiconductor metal (d) At finite temperature T, some electrons statistically (though the probability is very small) leave the lower or valence band and make transition to the upper or conduction band. Will Si conduct electricity Circle one. YES No or (e) When few electrons from a fully filled valence band make transition to the upper band (conduction band), they leave behind unfilled energy states. What do we call these states? holes. OR acceptorsExplanation / Answer
a) Conduction band
The upper band which is identified as 4N= 0 is conduction band. The electrons will occupy the lowest energy states available to them thus, the 4N states in the valence band will be completely filled, and the 4N states in the conduction band will be completely empty.
b) True
The energy gap Eg represents the amount of energy needed to move electrons across from one band to another. All the Semiconductors, when undoped, will not conduct electricity readily because it has a band gap.
c) Semiconductor
At 0 K, the electrons will occupy the lowest energy states available to them thus, the lower energy band will be completely filled, and the upper energy band will be completely empty. This make silicon semiconductor.
d) Yes
With thermal excitation, some of these electrons can be excited from the valence band to the conduction band, and then they can contribute to the current transport process
e) Holes
The empty states in the valence band are called holes. If the conduction band electron and the valence band hole are created by thermal excitation of a valence band electron to the conduction band, then they are called electron-hole pair.