Amorphous silicon

About: Amorphous silicon is a research topic. Over the lifetime, 26777 publications have been published within this topic receiving 423234 citations.

Substrate selectivity in the formation of microcrystalline silicon: Mechanisms and technological consequences

Abstract: We report the results of an in situ spectroscopic ellipsometry study concerning the substrate dependence of the evolution of microcrystalline silicon films deposited by alternating amorphous silicon deposition and hydrogen plasma treatment. The evolution of the composition of the films during growth, up to thicknesses of ∼100 nm, indicates that besides etching, the diffusion of atomic hydrogen efficiently promotes the growth (and/or nucleation) of buried crystallites. Moreover, the evolution of the films strongly depends on the nature of the substrate. This substrate selectivity is discussed in terms of initial growth processes. The effect of the hydrogen plasma well below the film surface, which produces the thickness‐dependent film composition, along with the substrate selectivity, may be of prime importance in technological applications of microcrystalline silicon.

Interaction of aluminum with hydrogenated amorphous silicon at low temperatures

Abstract: Annealing effects on aluminum/hydrogenated amorphous silicon (a‐Si:H) contacts in the temperature range from 100 to 300 °C were studied. Al was evaporated on device‐quality, phosphorus‐doped (n+) a‐Si:H films deposited in a UHV plasma‐enhanced chemical‐ vapor‐deposition system. Both electrical measurements and surface morphological analyses were performed to characterize the interaction. The transmission line model technique was used to measure sheet resistance and contact resistivity. For samples where Al covered the entire a‐Si:H surface during annealing, sheet resistance and contact resistivity were found to decrease monotonically with annealing temperature; whereas, samples annealed after patterning of the Al pads exhibited a minimum in sheet resistance and contact resistivity at temperatures between 150 and 200 °C. Optical and scanning electron microscopy, surface profilometry, and Raman spectroscopy were used to study the surface morphology. Interaction of Al with a‐Si:H was observed to initiate at ...

Direct evidence for the amorphous silicon phase in visible photoluminescent porous silicon

Abstract: We report on micro‐Raman spectroscopy studies of porous silicon which show an amorphous silicon Raman line at 480 R cm−1 from regions that emit visible photoluminescence. A Raman line corresponding to microcrystalline silicon at 510 R cm−1 is also observed. X‐ray photoelectron spectroscopy data is presented which shows a high silicon‐dioxide content in porous silicon consistent with an amorphous silicon phase.

Origins of structural and electronic transitions in disordered silicon

Abstract: Structurally disordered materials pose fundamental questions1–4, including how different disordered phases (‘polyamorphs’) can coexist and transform from one phase to another5–9. Amorphous silicon has been extensively studied; it forms a fourfold-coordinated, covalent network at ambient conditions and much-higher-coordinated, metallic phases under pressure10–12. However, a detailed mechanistic understanding of the structural transitions in disordered silicon has been lacking, owing to the intrinsic limitations of even the most advanced experimental and computational techniques, for example, in terms of the system sizes accessible via simulation. Here we show how atomistic machine learning models trained on accurate quantum mechanical computations can help to describe liquid–amorphous and amorphous–amorphous transitions for a system of 100,000 atoms (ten-nanometre length scale), predicting structure, stability and electronic properties. Our simulations reveal a three-step transformation sequence for amorphous silicon under increasing external pressure. First, polyamorphic low- and high-density amorphous regions are found to coexist, rather than appearing sequentially. Then, we observe a structural collapse into a distinct very-high-density amorphous (VHDA) phase. Finally, our simulations indicate the transient nature of this VHDA phase: it rapidly nucleates crystallites, ultimately leading to the formation of a polycrystalline structure, consistent with experiments13–15 but not seen in earlier simulations11,16–18. A machine learning model for the electronic density of states confirms the onset of metallicity during VHDA formation and the subsequent crystallization. These results shed light on the liquid and amorphous states of silicon, and, in a wider context, they exemplify a machine learning-driven approach to predictive materials modelling. Machine learning models enable atomistic simulations of phase transitions in amorphous silicon, predict electronic fingerprints, and show that the pressure-induced crystallization occurs over three distinct stages.

Steady‐state photocarrier grating technique for diffusion‐length measurement in semiconductors: Theory and experimental results for amorphous silicon and semi‐insulating GaAs

Abstract: The theory underlying the steady‐state photocarrier grating technique is presented, including the effect of surface recombination. Experimental results for amorphous hydrogenated silicon and semi‐insulating GaAs prove that diffusion lengths ranging from 200 A to 10 μm can be measured with an accuracy of better than 5%.