HALL COEFFICIENT AND MAGNETORESISTANCE OF SOFT CARBONS DOPED WITH ACCEPTORS

Samples of soft type carbon heattreated from 1800° to 3000°C were doped with boron and bisulfate acceptors and their galvanomagnetic properties measured in the temperature range from 2° to 300°K. The Hall coefficient (A), relative resistance (ρ/ρ300°K) and magnetoresistivity (Δρ/ρ) as measured at 22 kG are plotted against temperature (T) in Figs. 1-6. Doping causes a change in A vs. T curves corresponding to a decrease in heat treatment temperature. This change is considered to be due to a Fermi level depression. In general the changes in curves ρ/ρ300°K vs. T caused by the doping consist of a decrease in the slope in agreement with findings of previous investigators. This is not true however in the liquid helium temperature range, where an opposite tendency is found. Observed changes in the dependence of Δρ/ρ on temperature caused by the doping are complicated and cannot be explained only by the shift of the Fermi level or by differences in sign of carriers. © 1969.