Date of Graduation

Spring 2009

Degree

Master of Science in Materials Science

Department

Physics, Astronomy and Materials Science

Committee Chair

Kartik Ghosh

Keywords

semiconductors, transparent conducting oxide, pulsed laser deposition, indium oxide, opto-electronic properties

Subject Categories

Materials Science and Engineering

Abstract

Recently, enormous research efforts have been directed at diluted magnetic semiconductors (DMS) critical for realization for multi-functional spintronic devices. However, the origin of electronic and magnetic properties in DMS is not well understood. This study is aimed to better understand the structural, optical, magnetic, and magneto-transport property relationships of Cr-doped In2O3 (In2O3:Cr) DMS grown under different partial oxygen pressures on sapphire substrates using pulsed laser deposition technique. The thin films were characterized using various state-of-the-art techniques such as x-ray diffraction (XRD), UV-VIS spectroscopy, magnetotransport, and SQUID magnetometer. Expansions in lattice parameter (10.10 Å to 10.34 Å) and crystal size (13.9 nm to 35.5 nm) in these films with an increase in oxygen growth pressure as observed from XRD analysis are traceable to the reduction in oxygen vacancies (OVA). Optical analysis showed a redshift in absorption edges of the samples from 3.93 eV to 3.76 eV with an increase in oxygen growth pressure, which is attributed to the significant improvement in crystallinity. Magnetotransport results revealed that films grown at low oxygen pressures (high OVA) exhibited semiconductor-to-metallic transitions while film growth at high oxygen pressure (low OVA) showed typical semiconductor behavior. The films exhibited paramagnetism/antiferromagnetism as observed from magnetization data collected using a SQUID magnetometer. The observed magnetic behavior is possibly due to Cr clustering. This investigation reveals the important role of oxygen vacancies in the structural and electro-magneto-optical properties of In2O3:Cr DMS. Understanding of DMS is critical for the realization of spintronic devices such as spin field effect transistors.

Copyright

© Ndubuisi Benjamin Ukah

Open Access

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