Thermodynamic relation between optical emission and absorption processes in quantum dot lasers

Summary form only given.It is widely assumed that there is a thermodynamic balance between the optical emission and absorption processes in semiconductor systems under high electrical injection. Indeed this assumption is commonly used to obtain gain spectra for laser diodes by transformation of their spontaneous emission. It is also used within theoretical work where the reverse transformation of gain to emission produces a calculated spontaneous emission spectrum. However, it is arguable whether this detailed balance premise holds under all conditions, material systems or emitting structures. Certainly recent theoretical work on excitonic systems has indicated a breakdown in the absorption-emission balance. Quantum dot lasers provide another interesting system in which to probe this question as the localised electronic states can become de-coupled at low temperature. This inhibits the use of globally determined population statistics and so the absorption and emission spectra can no longer be related by thermodynamic equilibrium functions such as the Fermi-Dirac distribution.