Upheaval of Negative Dielectric Permittivity and Semiconductor to Metallic Transition in a Thermally Induced Sn-Doped β-Ga₂O₃ (−201) Single Crystal

Thermally induced dielectric and conductivity properties of an Sn-doped β-Ga₂O₃ (-201) single crystal were investigated by frequency-domain impedance spectroscopy in the frequency window from 100 Hz to 1 MHz with temperatures between 293 and 873 K. The (-201) plane-orientated single crystalline nature and the presence of an Sn dopant in β-Ga₂O₃ were confirmed by X-ray diffraction (XRD) and X-ray photoelectron (XPS) spectroscopy. Two different trends of impedance spectra have been discussed by the modulation of relaxation times and semiconductor to metallic transition after ∼723 K due to activation of a significant number of Sn dopants and their movements with temperature. The negative impedance values were encountered in the Nyquist plots (<i>Z</i>' vs <i>Z</i>″) after 573 K and constitute a reverse movement after 723 K with temperature. The average normalized change (Δ<i>Z</i>'/Δ<i>f</i>)/<i>Z</i>₀ of impedance exhibits a broad downward relaxation plateau near 723 K, indicating a weak electrical transition. The increases in the positive value of the dielectric constant (<i>ε</i>_r') below a percolating threshold temperature 573 K is attributed to the interfacial and dipolar polarizations, and the plasma oscillation of delocalized electrons governed by the Drude theory is responsible for the negative dielectric constant above 573 K. The 3D projections of the real dielectric constant create a sharp downward sinkhole near 723 K, indicating the existence of negative dielectric permittivity. The electrical conductivity dramatically changes its trends after 523 K and confirms a transition from hopping conduction (dielectric or semiconductor) following Jonscher's power law to metallic conduction by Drude theory. Below the percolating threshold temperature, a nonoverlapping small polaron tunneling conduction mechanism was unveiled with defect-induced activation energy of 0.21 eV. The Sn-doped β-Ga₂O₃ exhibits unique and tailored electromagnetic responses with temperatures that can be associated with a variety of applications in electromagnetic wave manipulations, cloaking devices, antennas, sensors, medical imaging, seismic wave propagation, etc.