As an engineer you are asked to design LEDS for traffic light signals. Specifically, you are asked to design LEDS for yellow light at wavelength A, = 590 nm and

red light at wavelength A, = 625 nm. You are provided gallium arsenide and gallium phosphide material systems to reach these designs. Consider the plot on the left. Here T refers to T valley in the transition of electron in the band structure of GaAs1-x Px. T-branch in the plot refers to direct band gap transition leading to radiative recombination. L branch refers to indirect bandgap radiative recombination. Finally, X refers to indirect band gap transition but in this branch, the momentum recombination which is not a conservation during recombination is sufficient enough for a photon emission (refer notes for details). That is, X branch is indirect recombination but still produces radiative recombination, and therefore can be used for LED material. Find out the formula for the ternary semiconductor material GaAs1-xPx, by finding the value of x for(a) Yellow LED (b) Red LED of t