Measurements were made of interdiffusion coefficients in CdTe/HgTe (001) superlattices which had been grown by means of molecular beam epitaxy (figure 9). The interdiffusion coefficients were deduced from double-crystal X-ray diffraction studies of post-growth annealed samples. The annealing was carried out, at temperatures of between 200 and 240C, in a Hg saturated ambient. The results indicated that interdiffusion was dependent upon the concentration. The diffused profiles were calculated from an expression for D(C,T), and simulated X-ray spectra were fitted to the experimental ones. It was found that, at temperatures ranging from 200 to 220C:

Cd:     C (cm2/s) = 1.0 exp[-1.46(eV)/kT]exp[-0.63CCd(eV)/kT]

while, at 240C:

Cd:     C (cm2/s) = 1.0 exp[-1.45(eV)/kT]exp[-0.49CCd(eV)/kT]

The activation energies, of 1.46eV for Hg and 2.0eV for Cd, were consistent with interdiffusion via a vacancy mechanism. It was shown that intermixing was not negligible during growth at 180C.

A.Tardot, A.Hamoudi, N.Magnea, P.Gentile, J.L.Pautrat: Semiconductor Science and Technology, 1993, 8[1], S276-80

Figure 9

Interdiffusion in CdTe/HgTe Superlattices

upper points: diffusion in HgTe, lower points: diffusion in CdTe