Ac Hall and Magnetostrictive Effects in Photoconducting Alkali Halides

This paper reports the results of room-temperature measurements of the Hall and magnetoresistive effects for single-crystal potassium bromide containing a low concentration of $F$ centers. Measurements were carried out with strong steady illumination in the $F$-absorption band by means of a new ac technique which avoids space-charge polarization effects. The current carriers were found to be negative in sign with a Hall mobility of 12.5 ${\mathrm{cm}}^2$/volt-sec and are undoubtedly electrons photoexcited from $F$ centers. Their maximum concentration was of the order of ${10}^{10}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The mobility was found to be substantially independent of light intensity and signal frequency over the limited ranges investigated. Transverse magnetoresistive effects of both positive and negative sign were also observed. Finally, a phenomenological discussion of the experimental results is given.