Date of Award

Spring 1983

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Physics

First Advisor

Pedrotti, Frank L.

Second Advisor

Burch, T. J.

Third Advisor

Deshotels, Warren

Abstract

Two samples, GaAs:Mg (p-type) and GaAs:Si (n-type), ion-implanted to the same dose of 5 x 1012 ions/cm2, were investigated to study their temperature dependent electrical properties. The resistivity and Hall constant were determined directly by Van der Pauw technique. Sheet carrier concentration and carrier mobility were then calculated. The Silicon sample, in which the properties were relatively temperature independent, was found to be in the metallic conduction range. Hence the Magnesium sample was chosen for further temperature dependency investigation. In the case of the Magnesium sample, selecting the data points in the linear region of the p vs 1/T curve permitted a computer-fit to the theoretical expression. Optimized values for acceptor and donor concentrations, as well as impurity ionization energy, were determined in this way. Using these estimated values in the theoretical expression the carrier concentration was calculated and plotted against 1/T. The deviation between the experimental and theoretical curve was found to be due to impurity band conduction and phonon-assisted carrier hopping in the low temperature range, and to deep lying acceptor(s) levels due to substrate impurities as well as movement of the acceptor level towards the valence band in the high temperature range. The effective mobility due to optical phonon scattering, acoustic phonon scattering, neutral impurity scattering and ionized impurity scattering, was determined and compared with the experimental results. Very good agreement was found between calculated and experimental mobility down to a temperature of 40 oK. The deviation below 40 oK is associated with an increased effective mass of impurity band holes in impurity band conduction, compared with the value assumed in the mobility calculation. The resistivity vs 1/T variation also indicates impurity band conduction at temperatures of 40 oK and below, and allows a calculation of impurity activation energy in good agreement with the value determined from the computer-fit of the carrier concentration data.

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