R. L. Weisfield

Bio: R. L. Weisfield is an academic researcher. The author has contributed to research in topics: Fermi level. The author has an hindex of 1, co-authored 1 publications receiving 84 citations.

Space‐charge‐limited currents: Refinements in analysis and applications to a‐Si1−xGex: H alloys

Abstract: A new algorithm is described for deriving the density of states N(E) from the Fermi energy EF upwards toward the conduction band edge. This refinement in the analysis of space‐charge‐limited currents (SCLC) enables the accurate determination of N(E) by implicitly accounting for the spatial variations of physical quantities across the thickness of the diode. SCLC is measured in NiCr/n+/a‐Si1−xGex: H/Pt diode structures. For a‐Si:H samples, SCLC values for N(EF) are compared to those derived from admittance measurements on the same diodes. The two determinations agree in samples where 1016

Switching in coplanar amorphous hydrogenated silicon devices

Abstract: Switching has been observed in a wide variety of materials and devices. Hydrogenated amorphous silicon has become one of the most important cases because of interest in neural network applications. Although there are many reports regarding this phenomenon, not all of the physical processes involved are still determined precisely. Therefore, some more experimental information is needed in order to achieve this task. Much of the behavior of the devices has been ascribed to the existence of a filamentary region which is produced after the first switching process, called forming. We observed this filamentary region in its full extension by producing forming in amorphous silicon devices with coplanar metallic contacts placed near each other (∼5 μm). The I–V characteristics, filament optical and atomic force microscopy images and chemical etching led us to correlate changes in resistance to metal inclusion into the amorphous film. There are two stages: the first is related to contact stabilization, the second to metal transport into the film bulk. Optical images show a permanent filamentary region after forming. AFM images of these filaments showed that they are formed essentially by material accumulation between the contacts. This material tends to get some atomic arrangement, becoming a polycrystalline solid. If the device was led to breakdown, such accumulation becomes either a hillock or a thin conducting channel connecting both contacts. In the case of a switching filament, the accumulation tends to be a chain of smaller hillocks along the conduction path. Metal from the contacts remains in the conduction path after forming and chemical etching indicated that it is placed near the path core. Before forming, a tunneling transport process can be ascribed to the non-ohmic behavior of the samples during the first stage of metallic inclusion.

Characteristics of amorphous silicon staggered-electrode thin-film transistors

Abstract: Amorphous silicon staggered‐electrode thin‐film transistors (TFT’s) can show current crowding near the origin in the output characteristics. The degree of current crowding is governed by the voltage dependence of the current flowing from the n+ contact to the conducting channel. This current is a space‐charge‐limited current whose magnitude depends on the bulk density of states in the undoped intrinsic layer. For a 0.5‐μm‐thick i layer, calculations predict negligible current crowding for N(E) 3×1016 cm−3 eV−1. Experimental results are consistent with N(E) in the range 1016 cm−3 eV−1–2×1016 cm−3 eV−1. This is lower than the value derived from the transfer characteristic of the TFT (∼1017 cm−3 eV−1), which is evidence for an inhomogeneous distribution of deep gap states through the 0.5‐μm film of α‐Si:H.

Uniform multilevel switching of graphene oxide-based RRAM achieved by embedding with gold nanoparticles for image pattern recognition

Abstract: Traditional metal-oxide semiconductor devices are inadequate for use in artificial neural networks (ANNs) owing to their high power consumption, complex structures, and difficult fabrication techniques. Resistive random access memory (RRAM) is a promising candidate for ANNs owing to its simple structure, low power consumption, and excellent compatibility with CMOS. Moreover, it can mimic synaptic functions because of its multilevel resistive switching (RS) behavior. Herein, we demonstrate highly uniform RS and a high on/off ratio of RRAM based on graphene oxide by embedding gold nanoparticles into the device. This allowed reliable multilevel storage. Further, multilevel RRAM based on spike-timing-dependent-plasticity learning rules was used for image pattern recognition. These findings may offer a route to develop reliable digital memristors for ANNs.

Density-of-states distribution in the mobility gap of a-Si:H

Abstract: The evidence for the distribution of gap states g(E) in hydrogenated amorphous silicon (a-Si:H) is reviewed. In doped and defect-rich samples g(E) has near the gap center a peak that is proportional to the density of Si dangling bonds and a minimum about 0.4 eV below the electron mobility edge. g(E) below the gap center needs further exploration. The space charge limited current method can yield g(E) data for high quality undoped material which may have no peak due to dangling bond states.