Localization of the electrical activity of structural defects in polycrystalline silicon

Abstract

In order to improve the capabilities of the electron-beam-induced current method, a technique based on scanning transmission electron-beam-induced current has been developed. It is shown that it enables the direct correlation of structural defects with their electrical activity. It implies the fabrication of ultrathin Schottky diodes (thickness ≤600 nm). From an approximate theoretical model it was inferred that the spatial resolution reaches about 200 nm in our experimental conditions. Experimental data are obtained on electron-grade and on upgrade metallurgical grade polycrystalline silicon, grown by the heat exchange method on which the behavior of carbon at grain boundaries and defects has been studied by transmission electron microscopy, high-resolution electron microscopy, and electron energy loss. There is a good agreement between the experimental data on electrical activity and the calculated approximation. The present method shows that the electrical activity is mainly related to the presence of impurities. Carbon seems to trap recombining impurities and specifically oxygen. Isolated dislocations are always electrically active whereas ‘‘clean’’ twin boundaries are not active. The activity at boundaries is always localized on extrinsic dislocations or on precipitates. Asymmetric profiles are also observed on boundaries and stacking faults. This was related to the existence of segregated zones lying on one side of these defects which are likely to act as diffusion barriers.

Luminescence emission from forward- and reverse-biased multicrystalline silicon solar cells

“…Carrier recombination at dislocations occurs primarily due to the presence of metallic impurities. [31][32][33] First direct evidence for this was given by McHugo et al 34 comparing light beam induced current mappings with synchrotron-based x-ray fluorescence. However, not only metal impurities but also oxygen seems to play a major role.…”

Influence of the organic solvents on the properties of the phosphoric acid dopant emulsion deposited on multicrystalline silicon wafers

“…It is well known that high-temperature processes applied to solar-grade multicrystalline wafers lead to a drastic degradation of minority carrier life time via the electrical activation of oxygen related defects [10][11][12]. On the other hand, some authors [13][14][15] attribute this behaviour to the dissolution of the precipitates, which contain metal transition elements such as copper and iron known as charge carrier lifetime killers. Emitter characterizations of the elaborated n + p emitters were performed by measuring sheet resistance with a fully automatic four point probe resistivity measurement system and the junction depth using an Accent Hall Profiling System HL-5900.…”

Structural Basis of Interface Engineering

“…These are, for example, the in situ methods consisting of annealing or straining the interfaces directly into the electron microscope for measurements of interfacial diffusivity [13][14][15] and mechanical properties [16], respectively. The in situ measurements of the electron beam induced current (ERIC) [17] and local resistivity [18] can be applied to determine the electrical properties of individual interfaces. Moreover, an interface cannot act independently of its environment, which makes it impossible to measure interfacial properties separately from the matrix.…”