Ring-shaped luminescence pattern in biased quantum wells studied as a   steady state reaction front
  Under certain conditions, focused laser excitation in semiconductor quantum well structures can lead to charge separation and a circular reaction front, which is visible as a ring-shaped photoluminescence pattern. The diffusion-reaction equations governing the system are studied here with the aim of a detailed understanding of the steady state. The qualitative asymmetry in the sources for the two carriers is found to lead to unusual effects which dramatically affect the steady-state configuration. Analytic expressions are derived for carrier distributions and interface position for a number of cases. These are compared with steady-state information obtained from simulations of the diffusion-reaction equations. 
Masudul Haque