Studying electronic properties in GaN without electrical contacts using γ-γ vs e^--γ Perturbed Angular Correlations.

Area of Science:

• Materials Science
• Solid State Physics
• Nuclear Physics

Background:

• Hall effect measurements are crucial for material characterization but can be limited by poor ohmic contact quality.
• Perturbed Angular Correlations (PAC) is a nuclear spectroscopy technique sensitive to the local electronic and magnetic environment of probe atoms.

Purpose of the Study:

• To demonstrate the utility of combined electron-gamma (e-γ) and gamma-gamma (γ-γ) PAC experiments as an alternative method for studying electronic properties.
• To investigate the lattice site and electronic recombination dynamics of implanted 181Hf/181Ta in Si- and Zn-doped Gallium Nitride (GaN) as a function of temperature and doping.

Main Methods:

• Utilized combined e-γ and γ-γ PAC spectroscopy.
• Performed experiments on Si- and Zn-doped GaN samples implanted with 181Hf.
• Integrated PAC results with Density Functional Theory (DFT) simulations.
• Varied experimental temperature to study charge state dynamics and recombination processes.

Main Results:

• Identified a single stable lattice site for Ta in GaN with a double-donor character.
• Observed a metastable charge state for Ta at specific temperatures using e-γ PAC.
• Characterized thermally activated electronic recombination with activation energies of 15(2) meV (Si-doped) and 12(1) meV (Zn-doped), attributed to Si shallow donors.
• Observed reduced electron availability in Zn-doped GaN due to donor compensation by Zn acceptors.
• Suggested Variable Range Hopping for recombination at low temperatures.
• Successfully distinguished doping characteristics of Si- and Zn-doped GaN samples.

Conclusions:

• Combined e-γ and γ-γ PAC spectroscopy is a viable alternative for probing electronic properties, especially when Hall effect measurements are challenging.
• The study elucidated the site-specific electronic behavior of Ta impurities in doped GaN.
• PAC experiments effectively differentiated the doping profiles and compensation mechanisms in Si- and Zn-doped GaN.