A far-infrared magneto-optical study was made of AlGaAs/AlGaAs multi quantum-well structures. These structures were selectively doped with Si donors in order to produce a stable population of shallow D- states (shallow neutral donors which trapped an additional electron) in some of them. A step-by-step increase in the Al content produced DX as the ground donor state, and provided useful information concerning DX centers as compared with shallow neutral and negatively charged donors. In particular, it was shown that the same donor ion could give rise to 2 different negative-donor states: the shallow D- state and the deep DX state. Either one or the other was populated, depending upon the history of the sample. The energy of the DX2 level (DX with two Al neighbors) was accurately determined.

S.Huant, A.Mandray, G.Martinez, B.Etienne: Materials Science Forum, 1995, 196-201, 395-402