Origin of the hot phonon effect in group-III nitrides

Lifetimes of the zone-center A₁(LO) and higher-E₂ modes in group-III-nitride wurtzite semiconductors have been calculated by employing a theoretical treatment of three-phonon and four-phonon processes based on realistic phonon dispersion curves and an elastic continuum model for crystal anharmonicity. The hot phonon effect observed in GaN and InN has been identified to originate from the ineffectiveness of these modes to decay into two or three lower frequency optical modes. This effect is predicted to be significantly reduced in AlGaN and AlInN alloys. Explanations have been forwarded for the observations that the lifetime of the LO mode strongly depends on photoexcited carrier density in GaN and that it follows a weak temperature dependence in AlGaN∕GaN.