Date of Award

1-1-2012

Document Type

Campus Access Thesis

Department

Electrical Engineering

First Advisor

Krishna C Mandal

Abstract

Two growth methods are investigated for producing detector-grade large volume layered chalcogenide gallium telluride (GaTe) single crystals. Growth method one utilizes a graphite crucible heated within an argon environment, yielding 2" diameter ingots. The second method uses a modified vertical Bridgman method which was designed and installed in our laboratory. For both growth methods, high purity (7N) Ga and zone refined (ZR) Te precursors were used, and the crystal growth was performed through a pre-determined temperature profile and a slow crystallization from the melt. GaTe crystals from the monocrystalline area of the grown ingot were cleaved mechanically and characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis by x-rays (EDAX), and x-ray photoelectron spectroscopy (XPS) measurements. Electrical properties, such as resistivity, carrier concentration, and mobility of the grown crystals, were determined using van der Pauw and Hall effect measurements. A new surface modification technique using sulfur passivation was developed for GaTe surfaces, which shows enhanced performance on Schottky barrier properties. Pulse height spectra (PHS) measurements were carried out using a 241Am (59.6 keV) radiation source and an energy resolution of 6.8% FWHM was obtained. These investigations demonstrate that both growth techniques produce high quality detector-grade GaTe crystals for nuclear radiation detection. These detectors will find a wide range of applications in Homeland security, nuclear non-proliferation, medical imaging for cancer diagnostics , and high energy nuclear physics research including nuclear power plants.

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