C.M. Fortmann

Optoelectronic Properties of Thin Amorphous and Micro-Crystalline p-Type Films Developed for Amorphous Silicon-Based Solar Cells

VIIF-PECVD at 110 MI-z was used to deposit micro-crystalline p-layers on glass substrates for detailed analysis and onto ZnO coated substrates for incorporation into p-i-n solar cell structures. Solar cell and film analysis confirmed that the films incorporated into the solar cells contained significant crystalline silicon volume fractions despite being only 30 nm thick. The p-i-n solar cells employing a micro-crystalline silicon p-layer deposited on ZnO coated substrates had series resistances, fill factors and V oc similar to those of the reference solar cells deposited onto SnO 2 coated substrates and having optimized amorphous silicon-carbon p-layers. The short circuit current of the micro-crystalline p-layer case was 10 percent lower than that of the reference cell indicating that further optimization is required.

Modulation of Growing Surface with Atomic Hydrogen and Excited Argon to Fabricate Narrow Gap a-Si:H

Hydrogenated amorphous silicon (a-Si:H) with a gaps narrower than 1.7 eV were made by repeating the deposition of a thin layer (1--3 nm thick) and the treatment of growing surface with a mixture of H and Ar*. Crystallization induced by permeation of hydrogen into the sub-surface at high substrate temperature (>200 C) was efficiently prevented by treating with a mixture of H and Ar*. The activation of growing surface may arise from releasing a part of hydrogen on surface by treating with Ar*. High quality a-Si:H films containing hydrogen of 3 atom % with a gap of 1.6 eV were made by chemical annealing with a mixture of H and Ar*.

Prospects for utilizing low temperature amorphous to crystalline phase transformation to define circuit elements; a new frontier for very large scale integrated technology

A new concept by which nanometer scale circuit elements can be defined through a relatively simple writing process employing a hydrogen radical beam to convert thin amorphous silicon layers to crystalline silicon is introduced. Later unwanted amorphous regions are removed through exposure to a lower energy hydrogen radical flux (not necessarily focused as the crystalline regions are etch resistant). Through the repeat process of amorphous deposition, regional crystallization, and amorphous etching it should be possible to construct both vertically and horizontally integrated circuit elements with dimensions of the order of a few nm. Dopant species can be co-deposited with the amorphous layers. The circuit writing sequence has other potential applications such as mask patterning.

Hot-wire deposition of photonic-grade amorphous silicon

Abstract A new amorphous silicon application related to the patterning of refractive index for the purpose of defining and integrating photonic-device elements is emerging. Photonic device elements include waveguides, splitters, mirrors, optical memories, etc. Hot-wire-deposited amorphous silicon has several attributes that make it an exceedingly attractive matrix for photonic device patterning, including: high hydrogen solubility limits; relatively little sub-gap absorption; low stress; non-peeling films; and fast, economical deposition of thick (≥5 μm) films, as well as optically smooth as-deposited surfaces, even on thick films. The growing catalog of proposed and/or demonstrated amorphous silicon-based optical devices is rapidly expanding.

Fabrication of high quality silicon related films with band-gap of 1.5 eV by chemical annealing

Abstract Hydrogen radical flux tended to promote crystallization at substrate temperature higher than 200°C accompanying reduction in the hydrogen content. By the addition of Ar∗ into H, the crystallization was partly prevented with the aid of ion-bombardment. Addition of a small amount of Ge efficiently prevented the crystallization induced by chemical annealing at higher substrate temperature. Consequently, a-SiGe0.1:H with a band-gap of 1.67 eV with a defect density less than 6 × 1015 cm−3 was fabricated by chemical annealing at Ts = 250°C. a-SiGe0.2:H with a band-gap of ∼ 1.5 eV showing low defect density was successfully made by preventing permeation of hydrogen into Si-network with the aid of Ar∗.

A structural basis for the Hodgkin and Huxley relation

Neural channel transport was analyzed using a previously reported relation for charged particle transport in two energy-type gradients: the electric field and here a water/strucural deformation energy. Neural channels are lined with α-helix structures filled with water vapor and sequestered hydrophobic amino acids arranged to present minimum water vapor and water-hydrophobic interface. Cation point charges generate enormous electric fields on sub-nanometer distances. Electrostatic energy reduction is characterized by dielectric water being pulled toward the transporting ion deforming the neural channel. An ion-water-structure coupling energy is induced by changes in channel diameter width. The resultant two energy gradient relation for cation transport: reduces to the Hodgkin-Huxley relation [A. L. Hodgkin and A. F. Huxley, J. Physiol. (London) 116, 449 (1952)], explains channel selectivity and environmental sensitivity, predicts fast non-dispersive transport under a narrow range of conditions, and produc...

Einstein relations for energy coupled particle systems

Einstein relations define ratios for diffusion and drift currents for an ensemble of particles moving via probabilistic events such as hops. An Einstein relation was derived for charged particles constrained to move as an integral part of a system having an energy consideration routed in its material matrix. For example, the cases where a deformation of a matrix or lattice structure stores or releases free energy upon electron concentration change. Using an analysis based on energy gradients, diffusion, and the steady state, a thermodynamic framework for energy-coupled motion was developed and applied to protein folding. Findings include an infinite mobility condition arising from finite free energy gradients.

Hot-wire photonics: materials, science, and technology

The prospect of an integrated photonic technology has fueled an effort to understand the optical properties and to gauge the photonic engineering potential of hydrogenated amorphous silicon-based materials. Of particular interest for photonic engineering is the tunable range of the refractive index in amorphous silicon and the fast and slow light induced optical changes. The advance of photonic-engineered amorphous silicon technology requires an investigation into the relationships among fabrication processes, material properties, and the interrelations among the various optically important parameters. Here, the experimental investigation into H-implant refractive engineered amorphous silicon materials is detailed. Interestingly, the H-implant can interact with the amorphous structure to produce compacting of the structure, which may indicate refractive index increase. In addition, the evolving prospects for an amorphous silicon-based photonic technology will be up-dated. Waveguide-based light valve structures for the further scientific investigation of light induced refractive index change in amorphous silicon and technological applications are described.

Prospects of amorphous-silicon-based photonic networks

The prospects for a thin film amorphous silicon based integrated photonic technology spanning materials, devices, and physics are described. Impurity implantation is an effective technique for the preparation of permanent refractive index patterning due to the very high solubility limits of the amorphous phase. Methods of preparing films of the requisite thickness and smoothness for photonic application have been identified. Other experiments suggest that there is a light induced refractive index change of sufficient magnitude for patterning light adaptive and/or light defined optical elements. Two light induced refractive index changes, one fast and one slow, were observed in amorphous silicon materials. These changes were observed over temperatures ranging from room temperature to 250 degree(s)C and do not appear to diminish with increasing temperature over this range. Simulations were used to elucidate the physics of light induced change. Several classes of thin film devices were developed which span a wide range of functionality.

An Alternative Approach to Protein Folding

A diffusion theory-based, all-physical ab initio protein folding simulation is described and applied. The model is based upon the drift and diffusion of protein substructures relative to one another in the multiple energy fields present. Without templates or statistical inputs, the simulations were run at physiologic and ambient temperatures (including pH). Around 100 protein secondary structures were surveyed, and twenty tertiary structures were determined. Greater than 70% of the secondary core structures with over 80% alpha helices were correctly identified on protein ranging from 30 to 200 amino-acid sequence. The drift-diffusion model predicted tertiary structures with RMSD values in the 3–5 Angstroms range for proteins ranging 30 to 150 amino acids. These predictions are among the best for an all ab initio protein simulation. Simulations could be run entirely on a desktop computer in minutes; however, more accurate tertiary structures were obtained using molecular dynamic energy relaxation. The drift-diffusion model generated realistic energy versus time traces. Rapid secondary structures followed by a slow compacting towards lower energy tertiary structures occurred after an initial incubation period in agreement with observations.