Graduation Semester and Year

2006

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering

Department

Materials Science and Engineering

First Advisor

Meng Tao

Abstract

Copper oxides, including cuprous oxide and cupric oxide, are prepared by electrochemical deposition. The structural, optical and electrical properties of as-deposited copper oxides are evaluated, based on which cuprous oxide is selected as a promising material for photovoltaic applications. Electrodeposited cuprous oxide is a p-type semiconductor with a direct band gap of 2.06 eV. The mechanism of how pH affects the structural and electrical properties of electro-deposited cuprous oxide films is studied. In the pH range of 7.5 to 12.0, there are three different preferred crystal orientations: (100), (110) and (111). With different orientations, cuprous oxide shows different surface morphology and grain size. Bath pH effect on structural properties is explained by its effect on the growth rate of different crystallographic planes with different Cu+/O2- ratios. Capacitance-voltage measurements are performed to study electrical properties of differently oriented cuprous oxide films. The results show that the flat band potential shifts negatively as the bath pH increases. Electrodeposited cupric oxide is a p-type cupric oxide with an indirect band gap of 1.32 eV. Different cleaning methods are used to clean the substrate surface for electrodeposition of cupric oxide. Electrochemical etching is proven to be an effective method for Cu substrate cleaning in cupric oxide deposition. In particular, in-situ electrochemical etching is developed, which prevents the cleaned substrate from exposure to air. Current-voltage characterization shows that cupric oxide deposited on electrochemically etched Cu substrates has favorable electrical properties and better rectification behavior. Cuprous oxide is selected for the fabrication of p-n homo-junction because it has better crystallinity, bigger grains, better control over crystal quality and a direct band gap. Based on the model that bath pH can control the stoichiometry and native point defects in electrodeposited cuprous oxide films, both p-type and n-type cuprous oxides are successfully deposited at different bath pH values. For samples deposited at pH below 7.5, cuprous oxides are n-type semiconductors, while at bath pH above 9.0, cuprous oxides are p-type semiconductors. Furthermore, a two-step deposition process is developed to fabricate a p-n homo-junction in cuprous oxide. Current-voltage measurements show a typical rectification behavior of a p-n junction for these samples, which suggest that a p-n homo-junction of cuprous oxide is achieved, which is, to our knowledge, the first p-n homo-junction of cuprous oxide prepared by any method. The significance of this invention is because it enables the fabrication of solar cell with a reasonable high conversion efficiency (~10%) at a very low cost.

Disciplines

Engineering | Materials Science and Engineering

Comments

Degree granted by The University of Texas at Arlington

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