# How do experimentalists measure the exciton binding energy?

The exciton binding energy in semiconductors is determined theoretically by the energetic difference between the fundamental gap and the optical gap or, in other words, as the energetic difference of the fundamental gap and the first exciton peak in an optical spectrum.

My question is related to experiment. How would one obtain this energetic difference or the values of the fundamental and optical gap with good accuracy?

## 1 Answer

One can measure light absorption in a semiconductor. Peaks in absorption could appear corresponding to the photon -> exciton transition. They appear bellow optical gap

• But how would I then know the experimental value of the fundamental gap? This will only leave me with information about the energy of the exciton peak and not the exciton binding energy. Jun 1 at 10:09
• What is the initial condition ? You don't know the material and want to determine it from exciton spectrum do you? Jun 1 at 12:45
• No, I know the material and I want to understand how to measure the exciton binding energy (basically how to measure the two different gaps experimentally). Jun 1 at 14:10
• Regarding your answer, how could you measure where the optical gap is exactly, below which I find the excitonic peaks? Jun 1 at 14:28
• As far as I understand, one can measure absorption coefficient $\alpha$ and around the gap it should be $\alpha \propto \sqrt {(E - h \nu)}$. So if we want to know gap, we could fit the curve to the equation. Jun 1 at 15:52