Search

In this work, we demonstrate multi-channel GaN varactors with enhanced quality-factor (Q-factor) and cutoff frequency (f0) and present a comprehensive investigation of their current conduction mechanisms. The varactors were based on 1x-, 2x-, and 3x-channel GaN-on-SiC epitaxy with excellent channel conductivity, showing great enhancement of ∼270% both in Q-factor and in f0, thanks to the reduced resistance and capacitance by multi-channels in AC conduction. The DC leakage current (I) in the three types of devices is dominated by Poole–Frenkel (PF) emission and trap-assisted tunneling, before the depletion of the topmost channel and after the depletion of the bottommost channel, respectively. The I in multi-channel devices is dominated by two-dimensional variable range hopping of electrons along the vertical direction between channels, when the topmost channel is depleted while the bottommost channel is not. The analysis is supported by excellent agreement between experimental results and theoretical models, along with activation energies (EA) quantitatively and statistically determined, presenting a promising technology with key understandings for future performance enhancement. [ABSTRACT FROM AUTHOR]

Pyroelectric energy harvesters based on lead-free ceramics cannot meet the requirement for practical applications due to their low energy conversion capacity. In this work, high-performance thermal energy harvesting with the greatly enhanced pyroelectric coefficient and rate of temperature change has been achieved by compositing the zinc oxide (ZnO) semiconductor into 0.94Bi0.5Na0.5TiO3-0.06BaZr0.2Ti0.8O3 (BNT-BZT) ceramic matrixes. The ZnO semiconductor not only provides charge carriers for accelerating the transportation of free charge to improve the pyroelectric coefficient of BNT-BZT: ZnO but also enhances the temperature variation rate dT/dt of the samples because of its high thermal conductivity. Owing to the electrothermal synergetic effect of the ZnO semiconductor, a highly improved energy harvesting performance of the energy density reaching up to 130 μJ cm−3 is achieved, which is over three times compared to that of the pristine BNT-BZT ceramics. This work will provide an effective and facile approach to develop high-performance pyroelectric composite ceramics for thermal energy harvesting applications. [ABSTRACT FROM AUTHOR]

(Pb,La)(Zr,Sn,Ti)O3 (PLZST) antiferroelectric (AFE) materials have been widely investigated for advanced pulsed power capacitors because of their fast charge-discharge rates and superior energy-storage capacity. For practical applications, pulsed power capacitors require not only large energy density but also high energy efficiency, which are very difficult to achieve simultaneously. To address this problem, we herein investigate the energy-storage properties of PLZST AFE ceramics with a high Sn content by considering that the introduction of Sn can make the polarization versus electric-field (P-E) hysteresis loops slimmer. The results show that an optimum Sn content leads to the realization of both large recoverable energy density (Wre) and high energy efficiency (η) in a single material. With a Sn content of 46%, the PLZST AFE ceramic exhibits the best room-temperature energy storage properties with a Wre value as large as 3.2 J/cm3 and an η value as high as 86.5%. In addition, both its Wre and η vary very slightly in the wide temperature range of 20–120 °C. The high Wre and η values and their good thermal stability make the Pb0.97La0.02(Zr0.50Sn0.46Ti0.04)O3 AFE ceramic a promising material for making pulsed power capacitors usable in various conditions. [ABSTRACT FROM AUTHOR]