Cavity solitons in passive bulk semiconductor microcavities. I. Microscopic model and modulational instabilities

We consider a broad-area vertical microresonator with an active layer const ituted by bulk GaAs driven by an external coherent homogeneous electromagne tic field, and we adopt a microscopic model that describes the field and ca rrier dynamics in the quasi-equilibrium regime. The theory is developed wit hin the free-carrier approximation, with some relevant effects, such as the Urbach tail and the bandgap renormalization, which are taken into account in a phenomenological way. We include in the model the description of parax ial diffraction and carrier diffusion. A detailed study of the instabilitie s, both modulational and plane wave, affecting the homogeneous stationary s tate of the output field is performed. In this way we address the numerical research of cavity solitons, which appear as self-organized light peaks em bedded in a homogeneous background, as discussed in a companion paper [J. O pt. Sec. Am. B 16, 2095 (1999)]. Optimal conditions for cavity solitons' ex istence are found in extended regions of the parameter space. (C) 1999 Opti cal Society of America [S0740-3224(99)01011-5].