Question 14.7: Determine the output wavelength of a GaAs1-xPx material for ...

GaAs has a bandgap energy of E_{g}=1.42 \mathrm{eV}. This material would produce a photon output at a wavelength of

\lambda=\frac{1.24}{E}=\frac{1.24}{1.42}=0.873 \mu \mathrm{m}

This wavelength is in the infrared range and not in the visible range. If we desire a visible output with a wavelength of \lambda=0.653 \mu \mathrm{m}, for example, the bandgap energy would have to be

E=\frac{1.24}{\lambda}=\frac{1.24}{0.653}=1.90 \mathrm{eV}

This bandgap energy would correspond to a mole fraction of approximately x=0.4.

Comment

By changing the mole fraction in the \mathrm{GaAs}_{1-x} \mathrm{P}_{x} system, the output can change from the infrared to the red spectrum.