Condensed Matter Physics, Ch The junction: diodes, transistors, lamps and solar cells
Problem
An engineer needs a red LED at about 630nm and has two candidate materials in the same family: material A, gap 1.97eV, direct; material B, gap 1.95eV, indirect.
((a)) Find the emission wavelength each gap would give if it worked at all.
((b)) Say which material would actually make a usable LED, and why, and estimate the turn-on voltage of the one that works.