Study On The Dielectric Properties Of Wide Bandgap Semiconductor Oxides

Due to their large band gaps, high breakdown electric fields and high thermal conductivities, wide-band-gap semiconductors are suitable for preparation (or production) of electronic integrated devices with high frequency, high power output, anti-radiation and high density electronic. The unique property of band gap can be used for not only blue and green detector, but also for ultraviolet devices and photo-detecting devices, which are well suitable in more stringent work conditions. Meanwhile, as one of the basic characteristics of the material, it has significance to study the dielectric property of wide-band-gap semiconductor. In general, metal material has narrow band gap, while insulator has wide band gap. At the same time, insulator material is a good insulator and dielectric material with high dielectric constant. Thus it is great deal to study the dielectric performance of wide-band-gap material. In this study, we systematically studied a series of wide-band-gap oxide materials, such as HfO2, Gd2O3 and TbFeO3 by using dielectric spectra:(1)The pure,2 at.%, and 20 at.% Gd-doped HfO2 ceramics were prepared by the standard solid-state reaction technique. Dielectric properties of these ceramics were investigated in the temperature range of 300-1050 K and frequency range of 20-5×106 Hz. Our results revealed an intrinsic dielectric constant around 20 in the temperature below 450 K for all tested ceramics. Two oxygen-vacancy-related relaxations R1 and R2 were observed at temperatures higher than 450 K, which were identified to be a dipolar relaxation due to grain response and a Maxwell-Wagner relaxation due to grain-boundary response, respectively. The dielectric properties of the pure and slightly doped (2 at.%,) samples are dominated by the grain-boundary response, which results in a colossal dielectric behavior similar to that found in CaCu3Ti4O12. The doping level of 20 at.% leads to the structural transformation from monoclinic phase to cubic phase. The dielectric properties of the heavily doped HfO2 are dominated by the grain response without no colossal dielectric behavior.(2)Ceramic samples of Gd2O3-doped CeO2 (GDC) were fabricated by the co-precipitation method. The dielectric properties were investigated as functions of temperature (350-950 K) and frequency (100 Hz to 10 MHz). Three relaxations with the activation energies of 0.76,0.88, and 1.03 eV in the order of ascending temperature were observed in GDC. The low-, middle-, and high-temperature relaxations are argued to be related to the bulk response caused by the Gd dopant-oxygen vacancy pairs, grain boundary, and contact effects, respectively.(3)TbFeO3 ceramics were prepared via conventional solid-state reaction route. By means of the complex dielectric permittivity, electric modulus, and impedance analysis, the high-temperature dielectric properties of TbFeO3 were investigated in the temperature range from 300 to 1073 K and frequency range of 102-107 Hz. Rich dielectric phenomena, including three dielectric responses (R1-R3), a relaxor-like dielectric anomaly and negative capacitance were found in the order of ascending temperature. The low-temperature relaxation (R1) near room temperature is caused by the surface-layer effect. The high-temperature relaxations R2 and R3 were argued to be related to the dipolar and Maxwell-Wagner relaxation, The anomaly is confirmed to be caused by the negative capacitance effect.