Gallium phosphide is a compound semiconductor of gallium and phosphorus, with chemical formula . Its electronic band structure determines which photon energies can excite mobile charge carriers and which transitions can produce light.
Its bulk band gap is indirect: a transition near the lowest gap involves a change of crystal momentum, so a phonon or another momentum-transfer mechanism matters. Consequently a band gap value alone does not predict an efficient light-emitting diode. Impurity states, radiative and nonradiative recombination, and extraction of emitted photons all affect the observable device output.
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