How can a model separate wavelength from material choice?
The two controls answer different questions: wavelength changes the supplied photon energy; the selected gap changes the required energy. An illustrative 1.50 eV gap has a boundary near 827 nm, shorter than the 1.12 eV boundary.
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EXPLORE THE MODEL
Photon energy and an ideal threshold
E = hc/λ; λthreshold = hc/Eg
Read sampled numerical values
| Vacuum wavelength (nm) | Photon energy | Assumed band gap |
|---|---|---|
| 350 | 3.542 | 1.12 |
| 480 | 2.583 | 1.12 |
| 610 | 2.033 | 1.12 |
| 740 | 1.675 | 1.12 |
| 870 | 1.425 | 1.12 |
| 1,000 | 1.24 | 1.12 |
| 1,130 | 1.097 | 1.12 |
| 1,260 | 0.984 | 1.12 |
| 1,390 | 0.892 | 1.12 |
| 1,520 | 0.816 | 1.12 |
| 1,650 | 0.751 | 1.12 |
| 1,700 | 0.729 | 1.12 |
A photon at or above the chosen band gap satisfies the simple energy comparison. That does not mean every such photon is absorbed or collected as a useful electrical signal.
What this model can establish
An assumed band gap is a threshold, not a complete absorption or detection model. Silicon has an indirect gap; phonons, thickness, reflection, carrier collection and noise matter.
Optional: check your understanding
MAKE THE CONNECTION
At 900 nm, what happens if the model gap rises from 1.12 to 1.50 eV?
Sources for this view
HISTORY THROUGH EVIDENCE
The threshold that challenged light theory
Light-driven electron emission helped distinguish energy per photon from beam intensity.
Explore how the evidence changed the explanation →