A QUANTUM-STATISTICAL THEORY OF EXCITONIC LINEWIDTH IN SEMICONDUCTOR QUANTUM-WELL STRUCTURES

We have developed a very general and a powerful formalism to calculate the linewidths of excitonic transitions in semiconductor quantum well structures with arbitrary potential profiles in the presence of appli ed electric and magnetic fields. We assume that at low temperatures th e dominant mechanism responsible for line broadening is the interface roughness which is always present even in the so called ''perfect' sam ples. We have calculated the variation of the linewidth of the heavy-h ole exciton (sigma) as a function of well size and magnetic and electr ic fields in GaAs-Al0.3Ga0.7As based quantum well structures with thre e different potential well profiles, namely, rectangular, parabolic, a nd asymmetric triangular. We find that for a given value of the magnet ic field the value of sigma increases as the well width is reduced, in all three different structures. For well sizes larger than about 100 A-degrees, the value of sigma is the highest in the triangular wells a nd lowest in the rectangular wells. However, for well width less than 100 A-degrees, the value of sigma falls below those in rectangular or parabolic wells. Also, for a given value of the well size the value of sigma increases with the magnetic field in all three different quantu m well structures. It should be pointed out that our values of the exc itonic linewidths am the lowest possible in these structures.