It was recalled that, due to the negative-U property of the donor DX center, the Fermi energy tended to become pinned to the DX center free energy level when the Si dopant concentration was increased. At the same time, the carrier concentration tended to saturate. This was a general characteristic of n-type compound semiconductors when donor impurities induced negative-U DX levels in the energy gap. Here, in a series of Ga0.7Al0.3As epitaxial layers with Si doping concentrations ranging from 1017 to 1.5 x 1018/cm3, a carrier concentration saturation effect was detected by means of Hall measurements.

A.Y.Du, M.F.Li, T.C.Chong, S.J.Chua: Materials Science Forum, 1995, 196-201, 279-84