A Significant Decrease in Thermal Conductivity in Eu- and Cd-Doped ZnO Films

Area of Science:

• Materials Science
• Solid State Physics
• Semiconductor Research

Background:

• Non-polar ZnO films are promising for electronic and optoelectronic applications.
• Controlling thermal properties is essential for device performance and thermal management.
• Dopant incorporation can significantly alter material characteristics, including thermal conductivity.

Purpose of the Study:

• To investigate the effect of Cadmium (Cd) and Europium (Eu) co-doping on the thermal conductivity of non-polar a-plane ZnO films.
• To correlate dopant distribution and inhomogeneity with measured thermal transport properties.
• To understand the mechanisms of thermal conductivity suppression in doped ZnO.

Main Methods:

• Plasma-assisted molecular beam epitaxy (MBE) for growing a-plane ZnO films on r-plane sapphire.
• X-ray diffraction (XRD) for structural characterization and phase purity assessment.
• Cross-sectional scanning electron microscopy (SEM) for film morphology and interface analysis.
• Secondary-ion mass spectrometry (SIMS) for depth profiling of dopant incorporation.
• Frequency-domain photothermal infrared radiometry (PTR) for measuring cross-plane thermal conductivity at room temperature.
• Multilayer heat-diffusion modeling for analyzing PTR data.

Main Results:

• Successfully grown Cadmium/Europium (Cd/Eu) co-doped, a-plane-oriented ZnO films on r-plane sapphire without secondary phases.
• Confirmed uniform Cd/Eu incorporation throughout the film thickness via SIMS.
• Measured cross-plane thermal conductivity (κ) ranging from approximately 3.7 to 6.3 W·m⁻¹·K⁻¹.
• Demonstrated a strong correlation between increased Europium (Eu) distribution inhomogeneity and suppressed thermal conductivity.
• Observed enhanced phonon scattering as the primary mechanism for reduced heat transport.

Conclusions:

• Dopant inhomogeneity, particularly of Europium (Eu), is a critical factor in suppressing thermal conductivity in non-polar ZnO films.
• The findings highlight the importance of controlling dopant distribution for optimizing thermal management in ZnO-based devices.
• The study provides valuable insights into phonon scattering mechanisms influenced by dopant inhomogeneity in semiconductor thin films.