Data were presented which showed that the Al-Ga interdiffusion coefficient for an AlxGa1-xAs-GaAs quantum-well heterostructure or a superlattice was highly dependent upon the crystal encapsulation conditions (table 4). The activation energy for Al-Ga interdiffusion, and thus layer-disordering, was smaller (about 3.5eV) for dielectric encapsulated samples than after capless annealing (about 4.7eV). The interdiffusion coefficient for Si3N4-capped samples was almost an order of magnitude smaller than for the cases of capless or SiO2-capped samples at temperatures of between 800 and 875C. As well as the type of encapsulant, the encapsulation geometry (stripes or capped stripes) was important because of strain effects. These were a major source of anisotropic Al-Ga interdiffusion.

L.J.Guido, N.Holonyak, K.C.Hsieh, R.W.Kaliski, W.E.Plano, R.D.Burnham, R.L.Thornton, J.E.Epler, T.L.Paoli: Journal of Applied Physics, 1987, 61[4], 1372-9

Table 4

Interdiffusivity (Al-Ga) in AlGaAs/GaAs