Graduate Thesis Or Dissertation
 

Transport properties of CuSc₁₋(subscript x)Mg(subscript x)O₂₊(subscript y) and BaCu₂S₂ transparent semiconductors

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  • Bulk properties of CuSc₁₋ₓMgₓO₂, CuSc₁₋ₓMgₓO₂₊y, BaCu₂S₂, Bai₁₋ₓKCu₂S₂, BaCu₂Se₂ and Bai₁₋ₓKₓCu₂Se₂ are investigated supporting the search for highly conductive p-type thin films. Mg is an efficient dopant in CuScO₂ with conductivity up to l.5.10⁻² S/cm. Oxidation of CuScO₂:Mg leads to further increase in conductivity up to 0.5 S/cm. The amount of oxygen entering the material is dependent on the Mg content with an observed maximum of y=0.23 in the 5 at. % Mg doped sample. Mg doping above 6 at. % leads to saturated or slightly decreased conductivities in CuScO₂. In the case of BaCu₂S₂:K and BaCu₂Se₂:K, conductivities of 420 S/cm and 740 S/cm are achieved at room temperature with 10 at. % potassium doping with no observable saturation, 2 orders of magnitude higher than in the corresponding undoped forms. A change from activated to metallic type conduction mechanism is observed in Bai₁₋ₓKCu₂S₂ at x>0.005. The Seebeck effect measurements demonstrate p-type conductivity for all samples. The temperature dependence of the Seebeck coefficient exhibits hopping type transport for CuSc₁₋ₓMgₓO₂₊y and metallic type for BaCu₂S₂:K. The optical properties of the 2H polymorph of CuScO₂ and CuScO₂:Mg show introduction of defects into the material compared to the 3R polymorph, and a change in color from light gray for 3R to dark gray for 2H CuScO₂:Mg was observed. Potassium doping and preparation temperature converts α-BaCu₂S₂ to β-BaCu₂S₂ which results in a change of measured band gap from 2.3 eV to 1.8 eV.
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