Andrzej Kolodziej

Density of states in the pseudo‐gap of amorphous silicon‐germanium alloys from electrical and optical measurements

Amorphous hydrogenated silicon‐germanium alloys a‐Si1−xGex:H in the form of thin films were prepared by rf sputtering and chemical vapor deposition methods with x varying from 0 to 0.63. Optical transmission, reflection, and photoconductivity measurements in the visible and near‐infrared regions of light enabled determination of the optical energy gap, band‐tail states distribution, and density of defect states near midgap. Dark conductivity and photoconductivity were measured in the temperature range of 300–500 K. Electronic band structure (density of states versus energy) for a‐Si0.74Ge0.26:H thin film was derived on the basis of optical measurements, dark conductivity, and photoconductivity.

Low temperature manufacturing of Si nanocrystallites in the SiO x matrix applicable in solar cells

Progress in fabrication and application of the nanocrystalline silicon thin films in opto-electronic devices like solar cells, thin film transistors, memory cells, etc., is a way to further enhance their parameters. Those films exhibit increased stability, absorption, carrier mobility. They also exhibit scattering and anti-/reflection properties. This paper is focused on the technology of manufacturing such films by means of Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RF PECVD). The authors describe the manufacturing process based on periodical variation of the process parameters, such as hydrogen to silane ratio (Rh), gas flows, RF power and pressure in the process chamber, during the deposition process. Additionally, the influence of chamber pre-annealing on resulting type of matrix with nanocrystalline inclusions, a-Si:H or SiOx, and differences between them are discussed. The authors also present the Secondary Ion Mass Spectrometry (SIMS) analyses and the measurements of typical samples with High Resolution Transmission Electron Microscopy (HRTEM), which confirms the existence of the nanocrystallites in the a-Si:H or SiOx matrix.

Modeling of top amorphous cell in four-terminal configuration with poly-silicon solar cell on the base of I-V-C and QE research

The investigation of top amorphous cells in four-terminal configuration with bottom polycrystalline silicon cell was carried out. The top structures were made at low pressure as well as in multistep hydrogen conditions by Capacitatively Coupled Radio Frequency (13.56 MHz) Plasma Enhancement Chemical Vapor Deposition (RF PECVD) on a glass plate and a foil as well as on a polysilicon structure. However, the authors focused on fabrication of protocrystalline solar cells with 6–8% efficiency and on their properties among others studied by analysis of defect states of intrinsic layer. Finally a selection of the thickness with respect to the current and optical matching with the bottom cell is made.

Properties of Image Sensor Structure Obtained Below 120°C On The Foil By Reactive Magnetron Sputtering

Polyimide substrates are of interest because of their thermal stability, light weight, and good mechanical characteristics. This paper reports thermal control multilayer deposition experiments which have strongly affected the properties of the image sensor structure (TFT + photodiode). Particularly TFT properties have been studied with respect to difficulties of obtaining of good quality a-SiN x :H films at temperature below 120°C. We characterize the structural properties using infrared absorption, refractive index measurements, small angle x-ray diffraction and the optoelectrical measurements of the TFT and PIN diode structure. The linear image sensor consisting of two rows, 40 pixels per row, with dimensions 0.6 mm 2 was made on the polyimide foil.

Methods of nano-crystallization of thin silicon films

In the paper the authors are analyzing differences in the nature of crystallization between: the nano-crystallization during deposition in multilayer RF PECVD process, in which hydrogen concentration and other parameters were changing over time, and crystallization of the same samples during temperature annealing in the range 200-1000°C. Observed behavior differs from columnar crystallization of μc-Si:H films deposited in homogeneous process. The analysis is carried out with respect on application of the films to solar structures.

Nanostructures in thin film opto-electronics

Recent investigations in the area of photovoltaics and microelectronics generated interest in thin-film technologies with nanostructural modifications. In this paper we concentrate on technological experiments, structure and composition control of the components of a thin silicon solar cell and opto-electonic devices. The results of high resolution electron microscopy and optical transmission and reflection analysis are presented. Additionally, the authors carried out theoretical calculations of scattering, absorption and reflection of the Ag nanoparticles located at the surface and also within the films on the absorber border.

Nanostructures applied to bit-cell devices

In this work split-gate charge trap FLASH memory with a storage layer containing 3D nano-crystals is proposed and compared with existing sub-90 nm solutions. We estimate electrical properties, cell operations and reliability issues. Analytical predictions show that for nano-crystals with the diameter < 3 nm metals could be the preferred material. The presented 3D layers were fabricated in a CMOS compatible process. We also show what kinds of nano-crystal geometries and distributions could be achieved. The study shows that the proposed memory cells have very good program/erase/read characteristics approaching those of SONOS cells but better retention time than standard discrete charge storage cells. Also dense nano-crystal structure should allow 2-bits of information to be stored.

X-ray matrix sensors

In this paper we present some of the newest solutions of the direct and the indirect methods of x-ray and (gamma) -ray detection applicable in medicine. We mainly describe technological postulations and several properties of linear and 2D x-ray and (gamma) -ray sensors using scintillator films, pin photodiode matrices and amorphous silicon thin film transistors.

Optimization of properties of ion-sensitive amorphous silicon (a-Si:H) based transistors

In this work the application of a-Si:H thin film transistor technology in the field of chemical sensors is presented. In particularly, the optimization of magnetron deposition process for obtaining various silicon nitride films and TFT structures are described as well as adequate structures of Ion Sensitive Field Effect Transistor with respect to the ion sensitive hydrogen properties are studied. The device shows a good Nernst response and high reproducibility but not acceptable stability yet.