Preparation Of Mn/Fe-Doped Germanium-Based Diluted Magnetic Semiconductor Materials

The concept, properties and applications of diluted magnetic semiconductor materials are introduced in this thesis. Mn- or Fe-doped germanium-based diluted magnetic semiconductor samples were prepared by sol-gel, sodium borohydride deoxidization, acid-induced liquid phase deposition under water bath condition, and thermal evaporation approaches. Various samples have been prepared under different conditions such as different pH value of precursor solution, type and concentration of Mn or Fe salt, heat treatment temperature and time, etc. The morphology, composition, structure, photoluminescence, semiconductor transport behavior and magnetic property of as-obtained samples were investigated.The sol-gel-derived germanium samples with 5% (mol) Fe dopants have two sorts of morphologies and crystal structures. The 1% (mol) Fe-doped Ge exhibits a single crystal phase. The room-temperature ferromagnetism of the 1% (mol) sample can be considered as an intrinsical behavior, and the Curie temperature of the sample is above 300 K.Mn-doped Ge powder samples prepared using sodium borohydride deoxidization method remain amorphous. The 2.5% (mol) Mn-doped sample fabricated under a pH of about 7 shows a weak room-temperature ferromagnetic behavior. Further increase of Mn concentration leads to transformation from ferromagnetism to paramagnetism.0.84~4.16% (mol) Fe-doped samples with one single phase structure were obtained through a liquid phase deposition process under water bath condition. It is found that the ratio of amorphous phase/crystal phase increases with increase of Fe content. The electrical resistivity does not increase linearly as the Fe concentration goes up from 0.84 to 4.16% (mol). The Fe-doped Ge films are p-type and the hole concentration reaches ~1021cm-3. All the film samples show room-temperature ferromagnetisms.Mn- or Fe-doped Ge films were obtained by thermal evaporation of sol-gel products derived from chemical reaction between sodium borhydride and Mn or Fe salt. The crystallity degree of the sample prepared using diacetylmanganese as the Mn source is higher than that of the sample obtained using manganous nitrate as Mn precursor. Quality of the Mn-doped film is improved by shortened the heat treatment time from 6 to 2 hours. The as-obtained film sample has a hole concentration about five times higher in magnitude than that of a bulk germanium, while its hole mobility is quite low. The Mn- or Fe-doped films have paramagnetisms, and a very weak ferromagnetism is observed in the sample with 1% (mol) Mn or Fe dopants.