  A fully microscopic theory for the spontaneous emission from semiconductors
is discussed. The theory is evaluated for a quantum-well system and the role of
excitonic and unbound electron-hole-pair contributions to the emission is
analyzed. Simplifying aproximations to the full theory and their range of
validity are discussed. Numerical solutions are presented for experimentally
relevant situations and it is shown that a detailed analysis of measured
spectra requires the knowledge of both absorption and emission under identical
conditions.
