Charge transport in liquid and solid rare gases.

This work forms an extension to krypton and xenon of previous studies of argon in this laboratory, and aims at a critical comparison between the charge transport properties of argon, krypton and xenon. A pulse of 40KeV electrons, of between 5 and 300 nanoseconds duration penetrates one of the electrodes between which the specimen is contained. Electron-hole pairs are generated in a region near the surface of the specimen, and carriers of one sign are extracted by an applied electric field. The drift of carriers through the specimen is detected by amplifying and displaying on an oscilloscope the voltage pulse which appears across a load resistor in series with the electrodes and the battery. The drift velocity v of electrons has been measured in these substances at electric fields E between 20V.cm-1 and 40kV.cm-1. In all cases, v is determined principally by acoustic mode scattering. The low field mobilities at temperatures near the triple point are: Units: cm2V-1sec-1. In both solid and liquid, there is a transition at intermediate fields to a region where v ? E1/2. This behaviour has been described in terms of the Shockley 'hot electron' theory. At high fields v becomes independent of E in both liquids and solids. Deviations from Shockley's theory have been explained qualitatively in terms of the recent theory of Cohen and Lekner. Holes have been found to be mobile only in solid xenon, and a tentative interpretation of the results in terms of the small polar on theory is given. The drift velocity of holes was found to depend linearly on electric field up to at least 30kV.cm-1. The hole mobility at 158°K is approximately 2 x 10-2cm2V-1sec-1. It is suggested that deviations from the small polar on theory below about 130°K are caused by hole trapping. It is important to obtain very pure samples for drift velocity measurements, and an evaluation of two purification techniques employed is given.