[SolidState] Highest wavelength to excite an electron in CdTe

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SUMMARY

The highest allowable wavelength to excite an electron in Cadmium Telluride (CdTe) is determined to be 1.45 eV. This value corresponds to the energy difference between the valence band and the conduction band, specifically in the \Gamma direction, where the energy levels B_{4V} and B_{5C} are referenced. The calculation for wavelength is derived using the formula λ = hc/ε, where h is Planck's constant and c is the speed of light. Precision in reading values from the graph is limited to approximately 0.2 eV due to the lack of additional markers.

PREREQUISITES
  • Understanding of semiconductor physics, particularly band theory.
  • Familiarity with energy band diagrams and the significance of valence and conduction bands.
  • Knowledge of the relationship between energy, wavelength, and the constants h and c.
  • Ability to interpret graphical data and extract numerical values accurately.
NEXT STEPS
  • Study the principles of semiconductor band gaps and their implications on electron excitation.
  • Learn about the calculation of wavelength from energy using the formula λ = hc/ε.
  • Explore the properties of Cadmium Telluride (CdTe) as a semiconductor material.
  • Investigate methods for improving precision in graphical data interpretation.
USEFUL FOR

Students in materials science, physicists studying semiconductor properties, and engineers working with photovoltaic materials will benefit from this discussion.

Ran4
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I'm reading through old exams, but there's not very much in the way of explanation, and this is one of the problems I have that I'm not sure that I fully understand.

We have the material CdTe. What is the highest allowable wavelength that incoming light can have in order to excite an electron from the valence band to the conduction band?

The relevant figure is this one:
jNlgNgV.png


The index V signifies valence electrons, C signifies the conduction band.

The highest wavelength is going to have the lowest energy, so I figure that you want the smallest difference between two energy levels of valence electrons and conduction band electrons. According to the figure that should happen in the \Gamma direction, and if we look at B_{4V} and B_{5C} that would give us about 1.6 eV.

The answer is supposed to be 1.45 eV (which is then used to calculate λ from λ=hc/ε), so I'm not sure if I'm doing this right.
 
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If at least one value is estimaged based on the graph, those "different" values could have the same origin.
Without additional markers and/or pixel counting, I don't think I could read off that value with a precision better than 0.2
 

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