Studies were made of the pulsed laser annealing of quantum-well structures in order to examine depth-dependent effects. Because the diffusion coefficients dependent strongly upon temperature, depth resolution was achieved because Mn diffusion from barriers and into the quantum wells was depth-dependent. The multiple quantum well structures were annealed using single pulses from a XeCl laser at 308nm. At a threshold value of 90mJ/cm2, 2 new emission bands were observed and were attributed to the diffusion of Mn from barrier layers to quantum wells. The diffusion which was associated with these bands, measured as an integrated product of diffusion constant and time, was found to amount to 300 and 30Å2. Calculations were made of the temperature, which was reached within the surface following pulsed laser annealing, by using an analytical solution to the heat diffusion equation; coupled with known high-temperature diffusion coefficients. The results predicted that diffusion decreased, by an order of magnitude, within one period at the top of the multiple quantum well stack. It was suggested that, at the threshold, surface-melting occurred and that the emission bands arose from the quantum wells which were immediately beneath the melt-front. The diffusion of Mn ions into the quantum wells was confirmed by magneto-optical data. A further emission band occurred at the same threshold, with a Mn concentration above that of the concentration in the barrier layers of the multiple quantum well stack. This emission was tentatively attributed to the segregation of Mn ions within the molten region following recrystallization.

Excimer Laser-Induced Diffusion in Magnetic Semiconductor Quantum Wells. H.Howari, D.Sands, J.E.Nicholls, J.H.C.Hogg, T.Stirner, W.E.Hagston: Journal of Applied Physics, 2000, 88[3], 1373-9