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Wednesday, April 22, 2015

Exploring Quantum Physics - Week 3 Extra Credit Question 8

Question: 

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What is the value of T for an electron in GaAs?

Solution:

It is a value hunting exercise. By one paper, we found out $ L = 175 \unicode{x212B} $. An $ \unicode{x212B} $ is a Angstrom, which is basically $ 10^{-10} $ meters.

On the effective mass of an electron in GaAs, another paper tell us the answer is $ 0.067 m_0 $, but what is $ m_0 $? Turn out $ m_0 $ is the electron mass and we can find it in the NIST values ,which is $ 9.10938291 \times 10^{-31} $ kg

To compute T, we will also need the Planck's constant, from the NIST website, it is $ 6.62606957 \times 10^{-34} $ J s.

So we compute $ T = \frac{8mL^2}{h} =2.2567 \times 10^{-13}$ s.
The last piece of the puzzle is a femtosecond, a femtosecond is basically $ 10^{-15} $ second, so the final answer is 225.67 femtoseconds.

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