Electron drift and Hall mobility in γ-irradiated 10<i>M</i> NaOH glassy alkaline ice

Abstract

The drift and Hall mobility of electrons in 10M NaOH glassy alkaline ice has been studied to determine the relevant charge transport mechanisms in this disordered system. The electrons are photoexcited to a conduction state after being trapped in the matrix at 77 K by γ irradiation. The dominant electron scattering mechanisms have been deduced from variation of voltage and temperature, and it appears that electron transport in this matrix is well characterized by a band model. Field dependent mobilities are observed and indicate that hot electron effects exist. In the field independent mobility region, the limit of which depends on temperature, the dominant mechanism is scattering by acoustical and optical phonons. This holds above 77 K and probably to much lower temperatures. In the field dependent mobility region, the dominant mechanism is ionic species scattering, notably by O−, at lower temperatures, and acoustical and optical phonon scattering at higher temperatures. The dividing temperature decreases with increasing field and is ∼50 K at 4 kV cm−1. At constant temperature versus field, the mobility is dominated by phonon scattering in the field independent mobility region, by ionic species scattering in the initial part of the field dependent mobility region, and by phonon scattering again at high fields. Drift mobility, Hall mobility, and photoconductivity results all interrelate and give a consistent picture of electron transport in 10M NaOH. The super-Ohmic photocurrents, previously observed, are seen to be due to dominance of ionic species scattering. The temperature and field dependence of the mobility is satisfactorily predicted by a simple band model and the mobility magnitude is at least semiquantitatively predicted. However, the critical field, at which hot electron effects occur, is predicted to be too high by the band model.