Date of Award

3-24-2016

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Engineering Physics

First Advisor

Yung Kee Yeo, PhD.

Abstract

Two different semiconductor materials received neutron radiation for assessment of radiation damage. The two materials are undoped bulk Ge and epitaxial Ge0.991Sn0.009, which is doped heavily with phosphorous. At room temperature, the Ge sample has direct and indirect bandgaps at 0.78 eV and 0.66 eV, respectively. The Ge0.991Sn0.009 sample has direct and indirect bandgaps at 0.72 eV and 0.63 eV, respectively. Two samples of each material were exposed to research reactor neutrons, delivering a 1 MeV equivalent neutron fluence of 2.52 × 1015 n/cm2. In order to assess the radiation damage and recovery, photoluminescence (PL) measurements were taken before and after irradiation weekly. The Ge experienced heavy neutron radiation damage, decreasing the direct and indirect bandgap PL intensity to about 4% and 1%, respectively, from the pre-neutron irradiation value. Room temperature annealing of the Ge sample over four weeks brought the recovery of the direct and indirect bandgap PL intensities only to about 7% and 3%, while an accumulated 60°C annealing for 100 minutes brought the PL recoveries to about 11% and 3%, respectively. The Ge0.991Sn0.009 sample experienced neutron damage that decreased the direct bandgap PL intensity to about 37% of the pre-neutron irradiation PL intensity. The direct bandgap PL intensities recovered to 88% and 86%, respectively after five weeks for a sample annealed only at room temperature and a sample that was also annealed at 60 deg C for 130 minutes. The significantly different radiation responses of bulk Ge and epitaxial Ge0.991Sn0.009 highlights that GeSn-based materials should be further researched for their neutron radiation hardness capabilities.

AFIT Designator

AFIT-ENP-MS-16-M-077

DTIC Accession Number

AD1053912

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