Measurements of Hall Effect and resistivity on semiconductors — implanted with radioactive ions — are able to point out additional aspects of the material. Properties like resistivity and carrier concentration, which are measured by the corresponding non-nuclear method, are influenced by the time dependence of the nuclear decay. Implanted radioactive ions decay exponentially and may change their electrical behaviour in the semiconductor if the doping characteristic of the new atom is different. Thereby: the macroscopic quantities resistivity and carrier concentration change.
The conclusions that these measurements provide are often useful to gather information complementary to techniques like Perturbed Angular Correlation for the investigation of defects in semiconductors. Nevertheless, the results of such Radio-Hall Effect measurements are interesting on their own.
Hall effect and resistivity measurements were performed on semi-insulating GaAs and p-GaAs implanted with
71As — (64h) → 71Ge — (11.2d) → 71Ga
in order to study the Ga-antisite-defect and on p-GaAs implanted with
125I — (60.14d) → 125Te.
The samples -- Zn pre-doped p-GaAs (dose 1013 cm-2) -- were implanted with 125I at a dose of 4·1012 cm-2 and 2·1012 cm-2. The pre-implantation has been performed at 160 keV, the 125I-implantations at 150 keV. The results of these measurements confirm the assumption, that the iodine acts as double donor. The exponential decrease of the resistivity can be explained by the change of the double donor iodine to the single donor tellurium, leading to a decreasing compensation of the p-conductivity.
The implantations with 71As were performed on different samples at the University of Bonn (p-type Zn-pre-implanted, dose 8.5·1012 cm-2 and 7·1012 cm-2 at 150 keV) and at the ISOLDE implanter at CERN (semiinsulating, 4·1012 cm-2 at 60 keV). The results of both measurements differ greatly.
While the 71GeAs and 71GaAs in the Bonn-samples act as an acceptor as expected, the behaviour of 71GaAs in the ISOLDE-sample is different. There it becomes a donor and compensates the p-conductivity of the sample [1]. It is possible to find reasons for the effects of the GaAs, but because of the different sample-types and different implantation-energies further measurements are necessary before any final conclusions can be drawn.