Nethala Manikanthababu

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 (Z' vs Z″) after 573 K and constitute a reverse movement after 723 K with temperature. The average normalized change (ΔZ'/Δf)/Z₀ 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 (ε_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.

β-Ga₂O₃ has become an ultimate choice of emerging new-generation material for its wide range of compelling applications in power electronics. In this review, we have explored the available radiations in the atmosphere and the effects of radiation on the β-Ga₂O₃ material and devices. The focus in this review summarizes various studies covering different radiation such as swift heavy ions, protons, neutrons, electrons, Gamma, and X-rays to understand the radiation-induced effects on the structure and their reliable performance in harsh environments. In addition, we focused on the various pre-existing defects in β-Ga₂O₃ and the emergence of radiation-induced defects that provoke a severe concern, especially from the device performance point of view. This review presents the irradiation-induced effects on the devices such as high-power devices such as Schottky barrier diodes (SBDs), field-effect transistors (FETs), metal-oxide-semiconductor (MOS) devices, and photodetectors. Some key studies including the changes in carrier concentration with a removal rate, Schottky barrier height (SBH), ideality factor, defect dynamics dielectric damage, interface charge trapping, a thermally activated recovery mechanism for charge carriers at elevated temperature, and diffusion length of minority charge carriers. These reports show that β-Ga₂O₃-based devices could be deployable for space or high-radiation terrestrial applications. These results provide/suggest a better device design based on the radiation degradation studies in the state-of-the-art β-Ga₂O₃ devices.

The electrical device characteristics of Ni/β-Ga₂O₃ vertical Schottky barrier diodes (SBDs) were measured in situ during the irradiation of 120 MeV Ag⁷⁺ swift heavy ions (SHIs). These devices exhibit SHI irradiation-induced degradation with 120 MeV Ag⁷⁺ ions in the ion fluence ranges of 1 × 10¹⁰ to 1 × 10¹² ions/cm². The height of the Schottky barrier is found to decrease from 1.11 to 0.93 eV, and the ideality factor increases from 1.16 to 2.06. These changes indicate the degradation of the device with SHI irradiation. A significant four orders increase is observed in the leakage current density from 4.04 × 10⁻⁸ to 1.98 × 10⁻⁴ A/cm² at −1 V, and the series resistance also increases from 3.38 × 10³ to 1.15 × 10⁴ Ω. X-ray photoelectron spectroscopy measurements show that the Ga ions are present in divalent and trivalent states with the spectral features having the binding energies centered at 20.2 eV and 19.9 eV (Ga 3d core-levels) before and after ion irradiation. The O 2s peak shifts to 23.7 eV, and there is an increase in intensity and peak broadening due to the change in the trivalent to divalent state of Ga due to the irradiation. The O(I) peak appears at 530.7 eV in the pristine sample with the Ga–O bonding with the Ga³⁺ state in pure Ga₂O₃. Moreover, there is a significant change in the intensity and the peak width of O(II) centered at 533.0 eV after ion irradiation at the fluence of 1 × 10¹² ions/cm². This indicates that there is an increase in the surface adsorbed/lattice oxygen, resulting in GaO.