Wafer Replacement Cluster Tool

This presentation on wafer replacement cluster tool discusses: (1) Platform for advanced R and D toward SAI 2015 cost goal--crystal silicon PV at area costs closer to amorphous Si PV, it's 15% efficiency, inexpensive substrate, and moderate temperature processing (<800 C); (2) Why silicon?--industrial and knowledge base, abundant and environmentally benign, market acceptance, and good efficiency; and (3) Why replace wafers?--expensive, high embedded energy content, and uses 50-100 times more silicon than needed

New Microscopic Model of the Staebler-Wronski Effect in Hydrogenated Amorphous Silicon

A new microscopic and kinetic model of light-induced metastability in hydrogenated amorphous silicon (a-Si:H) was recently proposed. Carrier recombination excites H from deep Si-H bonds into a mobile configuration, leaving a threefold-coordinated Si dangling bond (DB) defect at the site of excitation - a process long suspected to be an element of metastable DB production. Normally, mobile H are recaptured at DB defects and neither metastability nor net DB production results. However, when two mobile H collide, they form a metastable two-hydrogen complex and leave two spatially-uncorrelated Staebler-Wronski DBs. The model leads to differential equations describing the evolution of the mobile H and DB densities and a variety of new predictions. New directions for improving the stability of a-Si:H are discussed

Understanding the Clean Interface between Covalent Si and Ionic Al2O3

The atomic and electronic structures of the (001)-Si/(001)-gamma-Al2O3 heterointerface are investigated by first principles total energy calculations combined with a newly developed "modified basin-hopping" method. It is found that all interface Si atoms are fourfold coordinated due to the formation of Si-O and unexpected covalent Si-Al bonds in the new abrupt interface model. And the interface has perfect electronic properties in that the unpassivated interface has a large LDA band gap and no gap levels. These results show that it is possible to have clean semiconductor-oxide interfaces

New Mechanism for Non-Radiative Recombination at Light-Induced Boron-Oxygen Complexes in Silicon

First-principles study of BO2 complex in B-doped Czochralski silicon (Cz-Si) reveals a novel, self-trapping-enhanced carrier recombination mechanism, in sharp contrasts to the standard fixed-level Shockley-Read-Hall theory for carrier recombination. We found that an O2 dimer, distant from any B, would cause only weak carrier recombination under illumination -- only enough to drive its diffusion to find B and form the BO2 complexes. Surprisingly, BO2 and O2 produce nearly identical defect gap states. Despite this, recombination at BO2 is substantially faster than that at O2, because the charge state of the latter inhibits hole capture, the key step for such recombination

Silicon Heterojunction Solar Cell Characterization and Optimization Using In Situ and Ex Situ Spectroscopic Ellipsometry

The summary of this report is that: in situ SE gives insight into growth mechanisms and accurate layer thickness; (2) ex situ SE measures completed device structures to determine integrated optical properties; and (3) the combination of in situ and ex situ SE provides a powerful method for pinpointing the effects of processing changes in actual SHJ devices and guiding optimization

SIMS Study of Elemental Diffusion During Solid Phase Crystallization of Amorphous Silicon

Crystallization of hydrogenated amorphous silicon (a-Si:H) films deposited on low-cost substrates shows potential for solar cell applications. Secondary ion mass spectrometry (SIMS) was used to study impurity incorporation, hydrogen evolution, and dopant diffusion during the crystallization proces

Silicon Heterojunction Solar Cell Characterization and Optimization Using In Situ and Ex Situ Spectroscopic Ellipsometry: Preprint

We use in-situ and ex-situ spectroscopic ellipsometry to characterize the optical, electronic, and structural properties of individual layers and completed silicon heterojunction devices. The combination of in-situ measurements during thin film deposition with ex-situ measurements of completed devices allows us to understand both the growth dynamics of the materials and the effects of each processing step on material properties. In-situ ellipsometry measurements enable us to map out how the optical properties change with deposition conditions, pointing the way towards reducing the absorption loss and increasing device efficiency. We use the measured optical properties and thickness of the i-, n-, and p-layers in optical device modeling to determine how the material properties affect device performance. Our best solar energy conversion efficiencies are 16.9% for a non-textured, single-sided device with an aluminum back surface field contact on a p-type float zone silicon wafer, and 17.8% for a textured double-sided device on a p-type float zone silicon wafer

Atomic Structure and Electronic Properties of c-Si/a-Si:H Interfaces in Si Heterojunction Solar Cells

The atomic structure and electronic properties of crystalline silicon/hydrogenated amorphous silicon (c-Si/a-Si:H) interfaces in silicon heterojunction (SHJ) solar cells are investigated by high-resolution transmission electron microscopy, atomic-resolution Z-contrast imaging, and electron energy loss spectroscopy. We find that all high-performance SHJ solar cells exhibit atomically abrupt and flat c-Si/a-Si:H interfaces and high disorder of the a-Si:H layers. These atomically abrupt and flat c-Si/a-Si:H interfaces can be realized by direct deposition of a-Si:H on c-Si substrates at a substrate temperature below 150 deg C by hot-wire chemical vapor deposition from pure silane

Well-Passivated a-Si:H Back Contacts for Double-Heterojunction Silicon Solar Cells: Preprint

We have developed hydrogenated amorphous silicon (a Si:H) back contacts to both p- and n-type silicon wafers, and employed them in double-heterojunction solar cells. These contacts are deposited entirely at low temperature (<250 C) and replace the standard diffused or alloyed back-surface-field contacts used in single-heterojunction (front-emitter only) cells. High-quality back contacts require excellent surface passivation, indicated by a low surface recombination velocity of minority-carriers (S) or a high open-circuit voltage (Voc). The back contact must also provide good conduction for majority carriers to the external circuit, as indicated by a high light I-V fill factor. We use hot-wire chemical vapor deposition (HWCVD) to grow a-Si:H layers for both the front emitters and back contacts. Our improved a-Si:H back contacts contribute to our recent achievement of a confirmed 18.2% efficiency in double-heterojunction silicon solar cells on p type textured silicon wafers

Radiative open charm decay of the Y(3940), Z(3930), X(4160) resonances

We determine the radiative decay amplitudes for decay into $D^*$ and $\bar{D} \gamma$, or $D^*_s$ and $\bar{D}_s \gamma$ of some of the charmonium like states classified as X,Y,Z resonances, plus some other hidden charm states which are dynamically generated from the interaction of vector mesons with charm. The mass distributions as a function of the $\bar{D} \gamma$ or $\bar{D}_s \gamma$ invariant mass show a peculiar behavior as a consequence of the $D^* \bar{D}^*$ nature of these states. The experimental search of these magnitudes can shed light on the nature of these states.Comment: 18 pages, 9 figure