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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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A semiconductor has almost _____ band.
Empty valence
Empty conduction
Full conduction
None of the above
Empty conduction
Quick Summary: At absolute zero temperature (0 K), a semiconductor has a completely filled valence band and an empty conduction band. The conduction band remains nearly empty even at room temperature, as only a small fraction of electrons gain sufficient thermal energy to jump the narrow energy gap.
At absolute zero temperature (0 K), a semiconductor has a completely filled valence band and an empty conduction band. The conduction band remains nearly empty even at room temperature, as only a small fraction of electrons gain sufficient thermal energy to jump the narrow energy gap.
Eg=Ec−Ev — Energy band gap definition where Ec is conduction band edge and Ev is valence band edge
f(E)=1+ekTE−EF1 — Fermi-Dirac distribution function for occupation probability
In a semiconductor, the forbidden energy gap (Eg) is small, typically around 1 eV. At 0 K, there is insufficient thermal energy for electrons in the valence band to overcome this gap. As temperature increases, some electrons gain thermal energy E≥Eg and jump to the conduction band, leaving behind holes in the valence band. However, compared to metals, the density of charge carriers in the conduction band remains very low, keeping it 'almost empty'.
Semiconductors behave as insulators at 0 K because the conduction band is empty.
The Fermi level (EF) for an intrinsic semiconductor lies approximately in the middle of the forbidden energy gap.
Thermal excitation is the primary mechanism for creating carriers in the conduction band.
Conductivity of a semiconductor increases with temperature due to the filling of the conduction band.
Ability to control electrical conductivity through doping.
Compact size and lower power consumption compared to vacuum tubes.
Sensitive to temperature fluctuations.
Limited power handling capacity.
Fabrication of Transistors, Diodes, and Logic Gates.
Solar cells and Photodetectors.
The energy gap for Silicon is approximately 1.1 eV and for Germanium is 0.72 eV at 300 K.
Option A is incorrect because the valence band is full at 0 K. Option C is incorrect because a full conduction band would make the material a conductor.
B is correct — In a semiconductor, the conduction band is nearly empty because the forbidden energy gap prevents electrons from transitioning from the valence band at low temperatures.
Always remember that in metals, the valence and conduction bands overlap, whereas in insulators, the forbidden gap is very large (> 5 eV), preventing conduction.