The Al-Ga interdiffusion which was produced by focussed Si ion-implantation and rapid thermal annealing was investigated in a Ga0.7Al0.3As/GaAs superlattice structure with equal (3.5nm) barrier and well widths. Ions of Si2+ were accelerated to 50 or 100kV and were implanted, parallel to the sample normal, to doses which ranged from 1013 to 1015/cm2. The effect of rapid thermal annealing (950C, 10s) was characterized by means of secondary ion mass spectrometry. It was found that, in the implanted region, the interdiffusion was significantly enhanced by Si implantation. Ion doses which were as low as 1014/cm2 led to a 2 orders of magnitude increase, in the interdiffusion coefficient, to a value of 4.5 x 10-14cm2/s. This led to a mixing effectiveness of about 90%. On the other hand, the use of rapid thermal annealing alone produced an interdiffusion coefficient of 1.3 x 10-16cm2/s; with very little mixing. A marked depth dependence of the mixing process was observed at an implantation energy of 100keV, with a more heavily mixed, so-called pinch-off, region being formed at a certain depth. It was noted that the depth at which this enhancement occurred was not associated with a maximum concentration of Si ions or of vacancies. It instead coincided with a positive maximum in the second derivative of the vacancy profile. This, in turn, represented a maximum in the vacancy injection process that was caused by the presence of a transient vacancy concentration gradient.

P.Chen, A.J.Steckl: Journal of Applied Physics, 1995, 77[11], 5616-24