Date of Award

8-1986

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical Engineering

Supervisor

Dr. D.A. Thompson

Abstract

This thesis is concerned with investigating the production of thin film Bi-Sb alloys by ion beam mixing. Samples were composed of a thin Sb film sandwiched between two Bi layers; the thicknesses of the films were varied to produce composition range from 0 to ~45% Sb. The overall thickness was about 55 nm.

Analysis of the films by Rutherford Backscattering Spectrometry (RBS) and Auger Electron Spectroscopy (AES) indicated that ion beam mixing can produce uniform Bi-Sb alloys with doses of about 2.8X10¹⁵ cmˉ² of 80 KeV Ar⁺ at room temperature. The results of Electron Microscopy showed a grain growth due to ion bombardment.

The mixing was characterized by the increase in the full width at half maximum (FWHM) of the Sb signal in the RBS spectra. It was measured as a function of ion dose, dose rate, mass, and energy. The dependence of mixing on the temperature was also investigated. A square-root dependence of mixing on the dose confirmed a diffusion like mixing process. The rate of mixing per ion dose was found to increase with the elastic energy deposited at the Bi/Sb interface. The mixing is temperature independent in the range of ~40 to ~266 K, i.e., collision cascade mixing dominates. An effective diffusion coefficient, D*, of about 4.9X10ˉ²⁸cm⁴/ion was determined. At temperatures higher than ~266 K, the mixing increases with the temperature. This suggests that a radiation enhanced diffusion mechanism is the dominant mixing process. An effective diffusion coefficient of ~1.7X10ˉ²⁷cm⁴/ion at room temperature was calculated: an activation energy of ~0.15 eV was found.

Thermoelectric characteristics of the alloys were investigated by measuring the thermal voltage, V₃, as a function of the temperature, T, in the range 300-500 K, for alloys with various composition. The thermal voltage was found to have a linear dependence on temperature. The thermoelectric power, dV₃/dT, reaches a maximum of about 70 μV/deg, for Bi₈₇Sb₁₃. The dependence of the thermoelectric power on Sb concentration agrees with the model put forward to explain the transport properties of bulk Bi-Sb alloys. An empirical model has been proposed to relate the state of mixing with the measured thermoelectric power.