Exciton fine structure in interfacial quantum dots

We have studied, by 'micro-magneto-photoluminescence', the eigenstates of excitons localised in the interfacial potential of narrow GaAs/Al0.31Ga0.69As quantum wells. These behave in many respects as quantum dot excitons, and give narrow emission lines that permit direct resolution of Zeeman splittings. Some dots show small zero-field splitting (< 100 mueV), varying down to below the limit of resolution of our technique (approximate to 25 mueV). For these dots the excitonic g-factor depends on well-width, and also shows variation with the applied field B. The variation with B is related to the band mixing which is more prominent in these weakly-confined dots than in, for example, typical Stranski-Krastanow dots. The magnitude of the term linear in B can be calculated in a simplified model of the confined state, which gives a method of estimating the lateral extent of the confining potential. For particular transitions which are found at the extreme low-energy end of the emission from wells of 2 nm and 3 nm width, a different behaviour is found. These show much larger zero-field splitting of around 1 meV, and much smaller diamagnetic shift than that in the more usual dots with small zero-field splitting. The measured spin fine structure of these states is compared with that calculated from a spin Hamiltonian for a heavy-hole exciton, which gives a unique determination of the full three-dimensional g-factor for a single quantum dot.