Question

Experiment 11: Investigating Bandgap Energies, Materials, and Design of Light-Emitting Diodes (LED) 3. For a device to be a good conductor, there must be a significant electron population in the conduction band. When no energy is supplied to a semiconductor, the relative population of the conduction band follows Boltzmann's population law. In the case of a diode, the equation is: CB Population = e /RT VB Population Where CB and VB population are the respective electron populations in the conduc- tion and valence bands, E. is the intrinsic band gap in ev, k is Boltzmann's constant (8.617 * 10- eV/K), and T' is the temperature in kelvin. a. Calculate the population ratio for the intrinsic silicon diode at room temperature. A general rule of thumb for a device to be considered a good conductor is that the population ratio should be around y. Based on your calculations, is it a good con- ductor or semiconductor? If not, how is it made into a conductor or semiconductor? b. Could temperature be used to make the intrinsic silicon conductive? Comment on the practicality of this method.

Answer 1

Answer (a)

a CB population - Ea/kTNE VB Population : Eg for Silicon Semiconductor = 1.1 ev . Te room temperature = 29.8K K= Bultzman constant = 8.617 X10 el .. 1.1 en 30, Population ratio=.e- 8.617x 105 evok x298k berli = 2:35x10-20 ne. Population ratio value not around 1/3 so it is not good conductor or semi- - Conductor So; to made. Ento conductor or Semicondu- ctor we must need to decrease Eg gap of Dope an impurities. : : :

Answer (b)

Population ratio = exp ( - Eg/ KT), So, with increasing temperature population ratio also increase and conductivity of intrinsic semiconductor increase the electrons surrounding the semiconductor atoms can break away from their covalent bond and move freely about the lattice.

The main effect of temperature on an intrinsic semiconductor is that resistivity decreases with an increase in temperature. This is because heating increases the concentration of electrons and holes because electron/hole pairs are thermally generated at a higher rate.

1. Semiconductors act as insulators at low temperatures and conductors at higher temperatures.
2. Conduction occurs at a higher temperature because the electrons surrounding the semiconductor atoms can break away from their covalent bond and move freely about the lattice
3. The conductive property of semiconductors forms the basis for understanding how we can use these materials in electrical devices.