PREPARATION AND CHARACTERIZATION OF GERMANIUM SUBSTRATES FOR MIS ELECTRONIC DEVICES

For electronic and optoelectronic devices on germanium substrates, it is necessary to analyse, to understand and to control the surface properties of the samples. In this work, surface samples have been investigated by Auger electron spectroscopy under high vacuum conditions. The germanium oxide which is hygroscopic and unstable has been removed. The decrease in the oxide contents is correlated with the evolution of the intensity of the oxygen Auger peak. The adsorption of nitrogen atoms on the surface does not give a stable insulating film when the sample is heated That is not the case for alumina film condensed on a substrate previously cleaned by cycles of proton sputtering (t = 20 mn, E(o) = 500 eV, J(o) = 3 mu A cm(-2)). The electrical measurements of the MIS structure (Ge/Al2O3/Hg) indicate a high density of states which induces the Fermi level pinning observed for different polarizations. These results can be connected with the damage to the surface by the energetic proton beam. On the other hand, better results have been obtained on the same type of structures but realised on substrates prepared by thermal effect. The measured value of the density of states in the mid-gap is then 9 x 10(11) eV(-1) cm(-2). It can be reduced by thermal annealing in the 'forming-gas' down to 8 x 10(10) eV(-1) cm(-2), quite close to the value of the Si/SiO2 interface used up to now for microelectronic components. So germanium can be a good candidate for electronic engineering, moreover it has the advantage of a high speed carrier mobility.