Anharmonic decay of confined optical phonons in quantum dots

Due to the anharmonicity of lattice forces, the lifetime of confined optical phonons in semiconductor quantum dots is studied by considering the typical channel of decay into two bulk acoustic phonons. The model in which the three-phonon coupling strength is expressed in terms of the Grüneisen constant enables us to obtain a compact expression for the lifetime from standard perturbation theory. The lifetime is shown to be weakly size dependent, which increases with decreasing dot size. For GaAs quantum dots, the results are found to be completely consistent with other theoretical approaches and experimental data in bulk GaAs. Furthermore, we present a brief discussion for the carrier relaxation in quantum dots. Due to the decay of the confined phonons, we find that the carrier relaxation time can be as short as tens of picoseconds in a wide energy detuning of tens of meV; thus the so-called phonon-bottleneck effect is not a serious problem in quantum-dot-based device applications.