Simultaneously Enhanced Potential Gradient and Nonlinearity of ZnO Varistor Ceramics by MnO Doping with Nano-Sized ZnO Powders

ZnO varistor ceramics with a high potential gradient, as well as a high nonlinear coefficient, were reported and analyzed in this paper. With the use of nano-sized ZnO powders, the average grain size was reduced to about 2.6 μm, which successfully raised the potential gradient to 1172 V/mm. Moreover, the nonlinear coefficient increased to 48, and the leakage current was decreased to 8.4 μA/cm2 by doping a moderate amount of MnO (0.9 mol%). This was proven to be caused by the high Schottky barrier height formed at the grain boundary, where the Mn element segregated and, consequently, led to the increased density of interface states. Therefore, this could be considered as a potential method to simultaneously enhance the potential gradient and the nonlinear coefficient of ZnO varistor ceramics.

Computer simulations of solar cells based on silicon/boron phosphide selective contacts

Silicon solar cells with selective contacts based on boron phosphide (BP) demonstrate a high potential according to simulation. However, the influence of defects created at the BP/Si interface during BP deposition is a critical issue for solar cell performance. The computer simulations were performed to understand how the defects in the near-surface region and at the interface affect the photovoltaic properties. Calculations of the dependence of the characteristics of solar cells on parameters such as the density of interface states, the concentration of defects in the near-surface region, and its width were made.

Improving ALD-Al2O3 Surface Passivation of Si using Native SiOx

Al2O3 has rapidly become the surface passivation material of choice for the n-type Si solar cells with p + emitter due to its high negative fixed charge, good long-term and thermal stability, and no parasitic absorption. In this study, the surface saturation current density, fixed charge, and interface state density is compared for Al2O3 grown on Si substrates where the native SiOx was not removed, with substrates where the SiOx was removed by hydrofluoric acid. The depositions are performed by atomic layer deposition at temperatures in the 150–300 ˚C range, using trimethylaluminium, H2O, and O3 as precursors. The samples where the native oxide was not removed achieve a higher level of surface passivation for every tested deposition temperature, with the sample deposited at 200 ˚C exhibiting a surface saturation current density of only 1.9 fA/cm2, a fixed charge of 4.2×1012 cm− 2, and a density of interface states of 9.8×109 cm− 2 ev− 1. Capacitance and conductance voltage characteristics reveal a strong correlation between the surface saturation current density and the density of interface states and fixed charges. It is also determined that the long-term stability of the surface passivation depends on the deposition temperature, with higher deposition temperatures resulting in improved long-term stability.

Effect of annealing temperature on the interface state density of n-ZnO nanorod/p-Si heterojunction diodes

The effect of post-growth annealing treatment of zinc oxide (ZnO) nanorods on the electrical properties of their heterojunction diodes (HJDs) is investigated. ZnO nanorods are synthesized by the low-temperature aqueous solution growth technique and annealed at temperatures of 400 and 600°C. The as-grown and annealed nanorods are studied by scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. Electrical characterization of the ZnO/Si heterojunction diode is done by current–voltage (I–V) and capacitance–voltage (C–V) measurements at room temperature. The barrier height (ϕ B), ideality factor (n), doping concentration and density of interface states (N SS) are extracted. All HJDs exhibited a nonlinear behavior with rectification factors of 23, 1,596 and 309 at ±5 V for the as-grown, 400 and 600°C-annealed nanorod HJDs, respectively. Barrier heights of 0.81 and 0.63 V are obtained for HJDs of 400 and 600°C-annealed nanorods, respectively. The energy distribution of the interface state density has been investigated and found to be in the range 0.70 × 1010 to 1.05 × 1012 eV/cm2 below the conduction band from E C = 0.03 to E C = 0.58 eV. The highest density of interface states is observed in HJDs of 600°C-annealed nanorods. Overall improved behavior is observed for the heterojunctions diodes of 400°C-annealed ZnO nanorods.

High Resolution Mapping of Subsurface Defects at SiO2/SiC Interfaces by Time-Resolved Scanning Nonlinear Dielectric Microscopy

High resolution observation of density of interface states (Dit) at SiO2/4H-SiC interfaces was performed by time-resolved scanning nonlinear dielectric microscopy (tr-SNDM). The sizes of the non-uniform contrasts observed in the map of Dit were in the order of several tens of nanometers, which are smaller than the value reported in the previous study (>100 nm). The simulation of the tr-SNDM measurement suggested that the spatial resolution of tr-SNDM is down to the tip radius of the cantilever used for the measurement and can be smaller than the lateral spread of the depletion layer width.