Question

(a) Cadmium telluride (CdTe) is a semiconductor witha band gap, Eg, of 1.45 eV. Calculate the value of the absorption edge of this material. Express your answer in meters.


(b) Shown below are several % absorption vs. wavelength diagrams. Identify the correct diagram for a semiconductor.
I)a
II)b
III)c
IV)d

(c) Cadmium sulfide (CdS) is also a semiconductor. Do you expect the band gap of this material to be greater, less than, or equal to the band gap of CdTe? Select the solution with the most appropriate explanation.

I)Greater, as sulfur is in the n=3 period while tellurium is in the n=5 period, hence sulfur forms stronger bonds than tellurium, hence electrons in CdS will be more tightly bound.

II)Less, due to the lower nuclear charge of sulfur, it will form weaker bonds, hence electrons in CdS will be more weakly bound.

III)The same, as both S and Te are in the same group on the periodic table they should undergo exactly the same chemical bonding.

IV)Not enough information is given to roughly estimate the value of band gap, which is fairly independent of position on the periodic table.

Answer 1

I) greater

Answer 2

(a) and (b) ??

Answer 3

8.57e-7, b, greater

Answer 4

Thank you anonymous and Ibvda

Answer 5

You are not allowed to post answers to exam problems. Collaboration of any form is strictly
forbidden in the midterms and the final exams.

Answer 6

greater