Anomalous behaviour of galvanomagnetic effects in very lightly n-type bulkGaAs: Possible role of reverse-contrast centres

Magnetoresistance and Hall effect measurements in very lightly Te-doped n-t ype GaAs samples grown by the Liquid Encapsulated Czochralski (LEC) process in the temperature range 10 to 290 K were carried out. The transverse and longitudinal magnetoresistance coefficients for n-GaAs increase with increa sing sample temperatures up to 70 and 80 K and decrease in the range 70 to 290 K and 80 to 290 K, respectively. As the temperature increases, the expe rimental carrier concentration obtained from the Hall effect measurements i n the GaAs sample increases up to 140 K, decreases in the range of 140 to 2 20 K, and increases for T > 220 K. The change of the theoretical carrier co ncentration as a function of temperature in accordance with a new model con cerning the behaviour of Reverse Contrast (RC) is in agreement with the exp erimental carrier concentration. The electron Hall mobility increases with increasing temperature and the electrical conductivity exhibits conventiona l behaviour in the measurement temperature range of 10 to 290 K.