Electrons and Holes

• For T> 0 K, there would be some electrons in otherwise empty conduction band, and some empty states in otherwise filled valence band.
• The empty states in valence band are referred as holes.
• If conduction band electron and the valence band hole are created by the thermal excitation of the valence band electron to conduction band, then they are called as electron-hole pair (EHP).
• After excitation to conduction band, an electron is surrounded by the large number of empty states, for example the equilibrium number of EHPs at the temperature 300 K in Si is ≈ 10¹⁰/cm³, whereas Si atom density is  ≈ 10²²/cm³.

• Therefore, electrons in the conduction band are free to move about using many available empty states.
• The corresponding problem of charge transport in the valence band is a bit more complex.
• Current transport in valence band can be accounted for by keeping track of holes themselves.
• In the filled band, all the available energy states are pre occupied.
• For every electron moving with the given velocity, there is equal and opposite electron motion somewhere else in band.
• Under the applied electric field, net current is zero, as for every electron j moving with the velocity V_j, there is corresponding electron j' moving with the velocity -V_j .
• In the unit volume, current density J can be given as

  (filled band)                                    (2.2)

here N is number of  electrons/cm³ in band, and q is electronic charge.

• Now, if j^th electron is removed and the hole is created in valence band, then the net current density can be given as

• Therefore, the current contribution of empty state (hole), obtained by removing jth electron, is equivalent to that of the positively charged particle with the velocity V_j.
• Note that this transport is accounted for by the motion of the uncompensated electron J' possesing a charge of q and moving with the velocity  V_j.
• The current contribution (- q)(-  V_j) is equivalent to that of the positively charged particle with the velocity +  V_j .
• For simplicity, the empty states in valence band are called as holes, and they are assigned positive charge and the positive mass.
• The electron energy increases as one moves up the conduction band, and electrons gravitate downward towards bottom of conduction band.
• Conversely hole energy increases as one moves down the valence band (as the holes have positive charges), and holes gravitate upwards towards the top of valence band.

Email based Digital Electronics assignment help - homework help at Expertsmind

Are you searching Electronics Engineering assignment help expert for help with Electrons and Holes questions?  Electrons and Holes topic is not easier to learn without any external help?  We at www.expertsmind.com offers free lecture notes for Digital Electronics assignment help and Digital Electronics homework help. Live tutors are available 24x7 hours for helping students in their Electrons and Holes related problems. We provide step by step Electrons and Holes question's answers with 100% plagiarism free content. We prepare quality content and notes for Electrons and Holes topic under digital electronics theory and study material. These are avail for subscribed users and they can get advantages anytime.

Why Expertsmind for assignment help

1. Higher degree holder and experienced experts network
2. Punctuality and responsibility of work
3. Quality solution with 100% plagiarism free answers
4. Time on Delivery
5. Privacy of information and details
6. Excellence in solving electronics engineering questions in excels and word format.
7. Best tutoring assistance 24x7 hours