MOCVD, optical, and electrical properties of CuCrO2 : a novel transparent and p-type conducting oxide with delafossite structure

Abstract

Deposition and Optoelectronic Properties of CuCrO Thin Films by MOCVD

Abstract and Synopsis Introduction This thesis focuses on the deposition of phase-pure thin films of the delafossite-type oxide CuCrO using Metal-Organic Chemical Vapor Deposition (MOCVD). CuCrO exhibits p-type conductivity and significant transmittance in the visible region, though both values are lower than required for transparent conducting oxide (TCO) technologies.

The motivation was to enhance electrical conductivity by selecting Cr³ as the octahedral site cation. Its smaller ionic radius was expected to reduce the lattice parameter, increase overlap between Cu d-orbitals, and thereby improve carrier mobility. The work combines thin-film growth with optoelectronic property characterization, including attempts to fabricate an all-oxide transparent p-n junction using p-CuCrO and n-SnO .

Key Findings

Thin Film Growth

Films deposited on glass and sapphire (012) substrates at 450-600 °C.

Polycrystalline films with no preferred orientation.

Phase purity favored at lower deposition temperatures.

Morphology: large angular grains with high aspect ratios.

XPS revealed Cu in both +1 and +2 oxidation states.

Optical Properties

Transmittance: 40-50% for ~350 nm films on glass; higher for sapphire substrates.

Reflectance: <20% in the visible region.

Direct bandgap: 3.05 ± 0.03 eV; possible indirect transitions at lower energies.

Absence of plasma frequency in IR suggests low mobile carrier concentration.

Electrical Properties

Conductivity: thermally activated near room temperature; variable-range polaron hopping dominant below 150 K.

Carrier type, concentration, and mobility estimated via Hall and Seebeck measurements.

Activation energies from Seebeck and Arrhenius plots differ slightly, supporting polaron hopping as the main conduction mechanism even at room temperature.

p-n Junction Fabrication

Attempted junction between p-CuCrO and n-SnO .

Did not exhibit proper rectifying behavior, likely due to degradation from high deposition temperatures.

Conclusions and Outlook

CuCrO thin films show promise as transparent p-type conducting oxides.

Improvements in conductivity and carrier concentration are essential for device applications.

Future work should:

Explore delafossite compositions with varied Cu content and oxygen partial pressures.

Conduct systematic studies of mobility, carrier concentration, and Seebeck coefficient across temperatures.

Optimize CVD growth for uniform coatings over large areas and complex geometries.

An in-depth understanding of optoelectronic properties, coupled with successful low-temperature CVD deposition, could enable novel devices such as transparent field-effect transistors (FETs) and UV-emitting diodes.