Hall effect measurements were carried out at 4K on molecular beam epitaxially grown -doped AlxGa1-xAs/GaAs heterostructures. The persistent photoconductivity effect was used to determine the DX level and the conduction band offset independently by comparing the experimental results with self-consistent calculations. When x was less than 0.38, the variation of the DX level energy as a function of composition could be described by:

E(eV) = 1.38x - 0.25

This was in accord with the negative-U model for DX centers. A conduction band, to valence band, offset ratio of 68:32 was found when x was less than 0.38. The valence band offset was proportional to x over the entire compositional range. A valence band offset of 0.544x (eV) gave the best fit to the data. Secondary ion mass spectrometric measurements revealed a strong enhancement of Si segregation, towards the surface, with increasing Al concentration. The full-width at half-maximum of the Si -doping layers was found to be equal to 67 + 13.7x (nm) at a growth temperature of 620C.

A.Leuther, A.Förster, H.Lüth, H.Holzbrecher, U.Breuer: Semiconductor Science and Technology, 1996, 11[5], 766-71