Question

(iv) Write down an expression for the electrical conductivity of a material and define all the variables in your equation. (2) (v) Now use your equation from (iv) and the sketches of band structure from (iii) to explain the differences in electrical conductivity between metals, semiconductors and insulators. (4)

Answer 1

the ratio cnit per area Soluhon. Electrical condctivity (a) is defined as of charge flow across unit in a condector Potential gradient expression for elechóical Conductivity is C = Teo2mt - The ne?? smi? where number of electrons Applied electron charge C16X1019c) au e - T Relaxation time of electron - mass baud 6 From electrical condctivity expression, the structure for metal, semiconductor and conductor cine

Solution - Conductor Energy Band: Fermi level Conduction Band overlap In conductors like metals the valence Band overlaps the Condochon baud. There is no forbidden energy gap E=0. valence Band the Conduction Bond Insulator Energy Band: In insulators electrons in the valence Baud Sare separated by a large gap the conduction Baud. The farbidden erorgt geep Ester large enorgt geup less condichvuity Fermi level gip from valence Band Energy Band. Scri conductor an Fermi lever Sean conductors there is Small enough gap between the Conduction Band and valence conduction that bands valence Band thermal other excitations can bridge the forbidden gap Vogues E: 0.7ev to lev. or the gap