Question

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 r refers to r valley in the transition of electron in the band structure of GaAs1-x Px. T-branchin the plot refers to direct band gap transition leading to radiative recombination. L branch refers to indirect band gap recombination which is not a radiative recombination. Finally, X refers to indirect bandgap transition but in this branch, the momentum 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 materialGaAs1-xPx, by finding the value of x for (a) Yellow LED (b)Red LED of t

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