Abnormal frequency dispersion of the admittance associated with a chromium/plasma deposited a-SiNx : H/p-Si structure

Admittance (Y-m) versus applied gate bias (V-G) on MIS structure (Cr/a-SiNx:H/p-Si) was measured as a function of frequency (mHzMHz)/ternperature (77-400 K) as parameters to investigate minority carrier behavior. Strong frequency dispersion in measured capacitance at inverting gate bias (positive biases for p-type silicon substrate) and low frequency behavior in capacitance-voltage (C-PI curves under high measuring frequencies (above kHz) at 300-400 K temperature interval are reported. This phenomenon is interpreted via lateral hopping conductivity of self-inversion charges beyond the gate inside a-SiNx:H film near interface as generation mechanism of minorities with a lower activation energy (0.11 eV) rather than prevailing mechanisms of much higher activation energies (namely, generation-recombination and diffusion)

Transmission electron microscope imaging of plasma grown electroformed silicon nitride-based light emitting diode for direct examination of nanocrystallization

We report for the first time a direct transmission electron microscope (TEM) imaging of a cross-section of a silicon nitride-based light emitting diode (LED), produced via a method patented by our research group. Grown by plasma enhanced chemical vapor deposition (PECVD) technique the LED structure (glass/Cr/p+-nc-Si:H/i-SiNx:H/n+-nc-Si:H/ITO) was then subjected to a high forward voltage stress for one time only, i.e. electroforming process. After electroforming the LED exhibited a boosted visible light emission and memory effect. To study the structural effect of the electroforming on the as-deposited LED the cross-section was extracted by focused ion beam (FIB) technique directly from the electroformed diode and thus prepared for TEM imaging. Since the electroforming process caused crystallization of ITO and its breakup in some parts of the diode surface, the FIB was conducted for the cross-section containing some regions with ITO layer and some without ITO. TEM examination revealed the nanocrystalline phase formation within the intrinsic layer (i-SiNx:H) caused by the electroforming process. The average size and distribution of Si nanocrystallites formed inside i-SiNx:H was determined. The Si nanocrystallization within i-SiNx:H was compared for the regions with and without ITO layer. The previously proposed model describing the changes taken place in the diode during electroforming process was reconsidered in the light of this TEM analysis

SEM, EDX spectroscopy and real-time optical microscopy of electroformed silicon nitride-based light emitting memory device

An ordinary amorphous silicon nitride-based p-i-n diode was electroformed under optimized process conditions, which led to its instant transformation to a semiconductor device with two-in-one properties: a bright visible light emitting diode and a resistive memory switching device; i.e. light emitting memory (LEM). In the present work, for a thorough understanding of the changes that occur during electroforming, SEM images and EDX analyses were performed on both top-view and cross-section of both as-deposited and electroformed diodes. It was seen from the top-view images that while the diode surface of the as-deposited diode had a smooth and homogeneous ITO top electrode, the electroformed diode exhibited a rough ITO surface. EDX analyses showed that ITO was completely removed from many point-like regions on the diode surface. Cross-sectional SEM images showed no clue of any material diffusion through the diode structure during electroforming, which was one of the suspected situations about our model. EDX results also showed no considerable increase of any of the ingredients of the ITO alloy (In, Sn or O) across the semiconductor (p-i-n) layers of the electroformed diode. In contrast to the roughened surface of the electroformed diode, the silicon-based layers of the diode below the ITO electrode seemed to be well-preserved. Real-time optical microscopy showed that the light is emitted through the regions of the diode surface where the residual ITO top electrode is present

Similar admittance behavior of amorphous silicon carbide and nitride dielectrics within the MIS structure

PECVD grown a-SiNx:H and a-SiCx:H films were investigated as dielectric films in the form of metal/insulator/p-silicon (MIS) structures. AC admittance of MIS structures was measured as a function of dc gate bias voltages and frequencies (1-1000 kHz) of the superimposed ac bias voltage (10mV). For each applied bias voltage (from accumulating to inverting bias regimes), temperature (7) dependence of both capacitance (C) and conductance (G/omega) were measured to investigate majority/minority carrier behavior under various frequencies omega(kHz-MHz) as parameters. C and G/omega - T - omega measurements reveal that observed pairs of capacitance steps and conductance peaks are related to traps lying on the same energy value, residing in the insulator and at the interface of insulator/semiconductor structure and differing only through capture cross-sections. On the other hand, surface band bending (0,) of silicon and activation energy (EA) deduced from the Arrhenius plot of the frequency vs. reciprocal temperature as a function of gate bias (VG) seem linearly dependent, implying that EA reflects the 0, variation

On the Size of Full Element-Indexes for XML Keyword Search

Abstract. We show that a full element-index can be as space-efficient as a direct index with Dewey ids, after compression using typical techniques. 1 Full Element-Index for XML Keyword Search Keyword search is a crucial operation that has to be supported on XML data. Earlier works attacking this problem from information retrieval (IR) perspective essentially consider disjunctive query semantics (e.g., see [2]); whereas works representing the database (DB) perspective mainly concentrate on Web-style conjunctive semantics (e.g., [1,4]). Typically, an inverted index is the preferred data structure for XML keyword search in both communities. In this respect, a straightforward approach is indexing each element in the XML data as a separate document, which is formed of the text contained in the element itself and that in all of its descendants [2]. This is called a full (element-)index. While a full index can support both disjunctive and conjunctive keyword search semantics 1, the nested structure of XML data poses some efficiency challenges on its use in practice [1]. Most crucially, in a full index, a term t tha

Effects of tail states on the conduction mechanisms in silicon carbide thin films with high carbon content

Hydrogenated amorphous silicon carbide (a-SiCx:H) films of different carbon content (x) were deposited by radio frequency plasma enhanced chemical vapor deposition (PECVD) system. Apart from the X-ray photoelectron spectroscopy (XPS) and UV-Visible transmission analyses, the resistivity measurements between 293 K and 450 K were emphasized to assess the eventual transport mechanisms. The film resistivities are unexpectedly found relatively low, especially for high carbon content. In the frame of exclusive band conduction, the apparent thermal activation energies, evaluated from Arrhenius type plot remain too low compared to half values of the optical gaps

Electroluminescence properties of a PIN structure made by nearly stoichiometric a-SiCx:H active layer

a-SiCx:H PIN diode has been fabricated within a single pump-down process under the same deposition conditions used for doped and undoped PECVD grown thin films, whose optical and electrical properties are determined and compared with a-Si:H. Current-voltage characteristics of PIN diode are evaluated and concluded to be limited by tunnelling of holes at p-i interface into valence band tail states. Electroluminescence measurements revealed radiative monomolecular recombinations. Deconvolution of the luminescence spectra is utilized to analyse recombination mechanism to be dominated by the transitions between band tails and deep states, which are created by the large density of both silicon and carbon dangling bonds, probable in the stoichiometric a-SiCx:H film. Finally, a small luminescence peak around 1.9 eV would be an evidence of reduced probability of tail to tail transitions, than that of the transitions between tail and deep states

Electroforming of thin film silicon based homojunction pin diode

The recent observations of bright visible electroluminescence (EL) from electroformed thin film silicon based wide-gap alloys are further clamped down in a simpler structure. For this purpose, a standard quality, ordinary hydrogenated amorphous silicon (a-Si:H) homojunction pin diode was fabricated by plasma enhanced chemical vapor deposition. The fresh diode was characterized by temperature scanned current-voltage (I-V) and constant photocurrent measurements. The energy distribution of density of states within the forbidden gap of the intrinsic a-Si:H layer was determined by space charge limited current and optical absorption spectroscopies. Then the diode was intentionally subjected to a sufficiently high, calibrated electric field leading to its Joule heating assisted rapid crystallization at ambient atmosphere. The fresh and the formed diodes exhibit different I-V and EL characteristics. The current density of the formed diode increases drastically at low voltages while remaining unchanged at high voltages when compared to that of the fresh diode. Parallelly, the room temperature EL intensity under a particular current stress is boosted with electroforming. These interesting phenomena have been discussed in the frame of a self-consistent model