  We present a model to derive the state of the photon pairs generated by the
biexciton cascade decay of a self-assembled quantum dot, which agrees well with
the experimental result. Furthermore we calculate the concurrence and
entanglement sudden death is found in this system with temperature increasing,
which prevents quantum dot emits entangled photon pairs at a high temperature.
The relationship between the fine structure splitting and the sudden death
temperature is provided too.
