(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.
I) greater
(a) and (b) ??
8.57e-7, b, greater
Thank you anonymous and Ibvda
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greater
(a) To calculate the value of the absorption edge of cadmium telluride (CdTe), we need to convert its band gap energy from electron volts (eV) to meters. The formula relating energy to wavelength is given by:
E = hc/λ
Where:
E is the energy of the photon
h is Planck's constant (6.626 x 10^-34 J·s)
c is the speed of light (3.00 x 10^8 m/s)
λ is the wavelength
To convert electron volts to joules, we use the conversion factor: 1 eV = 1.602 x 10^-19 J.
Given that the band gap energy (Eg) of CdTe is 1.45 eV, we can now calculate the corresponding wavelength using the formula:
E = hc/λ
Rearranging the formula, we get:
λ = hc/E
Plugging in the values, we have:
λ = (6.626 x 10^-34 J·s * 3.00 x 10^8 m/s) / (1.45 * 1.602 x 10^-19 J)
Simplifying the expression:
λ ≈ 1.374 x 10^-6 meters
Therefore, the value of the absorption edge of cadmium telluride (CdTe) is approximately 1.374 x 10^-6 meters.
(b) To identify the correct diagram for a semiconductor based on the % absorption vs. wavelength diagrams, we need to look for the characteristic behavior of a semiconductor material. Semiconductors typically exhibit an absorption edge, beyond which there is a significant increase in absorption.
Without the diagrams provided, it is not possible to determine which one corresponds to a semiconductor accurately. However, in a semiconductor diagram, the % absorption will be relatively low for most wavelengths until reaching a certain cutoff point (the absorption edge), at which the % absorption sharply increases.
(c) To determine whether the band gap of cadmium sulfide (CdS) is greater than, less than, or equal to the band gap of cadmium telluride (CdTe), we can consider the chemical properties of sulfur (S) and tellurium (Te).
Sulfur is in the n=3 period of the periodic table, while tellurium is in the n=5 period. Generally, as one moves down a group in the periodic table, the atomic radius increases, resulting in weaker bonding. However, it is important to note that the position on the periodic table alone does not determine the strength of bonding in the compound.
Considering the answer options provided:
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 the band gap, which is fairly independent of position on the periodic table.
Option IV is the most appropriate answer. While the position on the periodic table can provide some insight into the behavior of elements, it is not sufficient to determine the band gap in this case. Other factors such as electronegativity, atomic size, and crystal structure also play significant roles in determining the band gap of a semiconductor material.