RESUMO
Betavoltaic power sources based on the conversion of radioisotope energy to electrical power are considered an appealing option for remote applications due to extended period of operation and high energy densities. However, to be competitive with other power sources, their efficiency must be increased. This can be done through optimization of the beta source and selection of the semiconductor absorber. This paper evaluates available on the market and developing wideband gap semiconductors as prospective absorbers with 3H and 63Ni sources. Simulation results indicate that among wide band gap materials 4H-SiC and diamond are two optimal semiconductors due to the combination of good coupling efficiencies with isotope sources and good electronic transport properties. Additionally, having good coupling efficiency, an ultra-wide bandgap, and the capability for both n- and p-type doping, c-BN is a promising material for betavoltaic applications.
RESUMO
We investigate charge injection into the gate dielectric of single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) having Al(2)O(3) and HfO(2) gate dielectrics. We demonstrate the use of electric field gradient microscopy (EFM) to identify the sign and approximate the magnitude of the injected charge carriers. Charge injection rates and saturation levels are found to differ between electrons and holes and also vary according to gate dielectric material. Electrically, Al(2)O(3) gated devices demonstrate smaller average hysteresis and notably higher average on-state current and p-type mobility than those gated by HfO(2). These differences in transfer characteristics are attributed to the charge injection, observed via EFM, and correlate well with differences in tunneling barrier height for electrons and holes formed in the conduction and valence at the SWCNT/dielectric interface, respectively. This work emphasizes the need to understand the SWCNT/dielectric interface to overcome charge injection that occurs in the focused field region adjacent to SWCNTs and indicates that large barrier heights are key to minimizing the effect.