Hydrogenated Amorphous Silicon Speed Sensor Based on the Flying Spot Technique

1995 ◽  
Vol 377 ◽  
Author(s):  
M. Vieira ◽  
A. Fantoni ◽  
A. Maçarico ◽  
F. Soares ◽  
G. Evans ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Material Characterization ◽  
Diffusion Length ◽  
Hydrogenated Amorphous Silicon ◽  
Effective Lifetime ◽  
Object Position ◽  
The Past ◽  
Speed Sensor ◽  
Hydrogenated Amorphous ◽  
Flying Spot

ABSTRACTIn the past we have developed a transient technique, called the Flying Spot Technique (FST). FST allows, not only to infer the ambipolar diffusion length but also the effective lifetime of the photogenerated carriers once the light spot velocity and geometry of the structure were known.In this paper, we propose to apply this technique backwards in order to detect the path and velocity of an object that is moving in the direction of a light source. The light reflected back from the object is analyzed through a p.i.n structure being the transient transverse photovoltage dependent on the movement of the object (position and velocity). Assuming that the transport properties of the material and the geometry of the device are known and using a triangulation method we show that it is possible to map the movement of the object. Details concerning material characterization, simulation and device geometry are presented.

Hydrogenated amorphous silicon speed sensor based on the flying spot technique

1995 ◽  
Author(s):  
Manuela Vieira ◽  
Alessandro Fantoni ◽  
A. Felipe Macarico ◽  
Fernando Soares ◽  
Rodrigo Martins
Keyword(s):  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Speed Sensor ◽  
Hydrogenated Amorphous ◽  
Flying Spot

Deposition of Device Quality Amorphous Silicon by Hot-Wire CVD

1997 ◽  
Vol 467 ◽  
Author(s):  
K. F. Feenstra ◽  
C. H. M. Van Der Werf ◽  
E. C. Molenbroek ◽  
R. E. I. Schropp
Keyword(s):  
Growth Rate ◽  
Electrical Properties ◽  
Amorphous Silicon ◽  
Diffusion Length ◽  
Hydrogenated Amorphous Silicon ◽  
Dark Conductivity ◽  
Hot Wire ◽  
Tungsten Filaments ◽  
Wire Method ◽  
Hydrogenated Amorphous

ABSTRACTIn this paper we present the results of the optimization of hydrogenated amorphous silicon films deposited by the hot-wire method in a larger area system. Using a two-wire design, we succeeded in depositing films that exhibit uniform electrical properties over the whole 4” x 4” Corning 7059 glass substrate. At a substrate temperature of 430 °C. and a pressure of 20 μbar we obtained a growth rate of ∼2 nm/s. The temperature of the tungsten filaments was kept at 1850 °C. The values for the photoconductivity and dark conductivity were 8.9×10−6 S/cm and 1.6×10−10 S/cm respectively, whereas the ambipolar diffusion length, as measured with the Steady-State Photocarrier Grating technique (SSPG), amounted to 145 nm. This value is higher than for our device quality glow-discharge (GD) films, which yield devices with efficiencies higher than 10%. The hydrogen content was 9.5%.We report on the density-of-states (DOS) distribution in the films, which was measured with the techniques of Thermally Stimulated Conductivity (TSC) and Constant Photocurrent Method (CPM). Furthermore, we describe the behavior of the electrical properties on light-induced degradation. Finally, we incorporated these films in solar cells, using conventional GD doped layers. Preliminary SS/n-i-p/ITO devices yielded efficiencies in excess of 3% under 100 mW/cm2 AM 1.5 illumination. Further work concerning the optimization of the interfaces is in progress.

Crystalline Silicon Surface Passivation by Pecv-Deposited Hydrogenated Amorphous Silicon Oxide Films [a-SiOx:H]

2007 ◽  
Vol 989 ◽  
Author(s):  
Thomas Mueller ◽  
Wolfgang Duengen ◽  
Reinhart Job ◽  
Maximilian Scherff ◽  
Wolfgang Fahrner
Keyword(s):  
Solar Cells ◽  
Amorphous Silicon ◽  
Thermal Annealing ◽  
Surface Passivation ◽  
Crystalline Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Window Layer ◽  
Effective Lifetime ◽  
Si Solar Cells ◽  
Hydrogenated Amorphous

AbstractIn the research field of crystalline silicon (c-Si) solar cells, electronic surface passivation has been recognized as a crucial step to achieve high conversion efficiencies. The main issue of this article is to analyze the surface passivation properties of both, n-type and p-type crystalline silicon wafers by hydrogenated amorphous silicon sub oxide [a-SiOx:H] films the for use in hetero-junction (a-Si/c-Si) solar cells. A window layer is obtained with a certain fraction of oxygen in the a-SiOx:H layers.The a-SiOx:H films were deposited by decomposition of silane, carbon dioxide and hydrogen as source gases using plasma enhanced chemical vapor deposition (PECVD). Films with varying deposition parameters such as gas flow ratio (oxygen fraction) and plasma frequency (13.56, 70.0 and 110.0 MHz) are compared.To determine the passivation quality of the a-SiOx:H films, microwave-detected photo conductance decay (µ-PCD) provides a contactless measurement of the effective recombination lifetime of free carriers. The film compositions and also the changes in the microscopic structure of the amorphous network upon thermal annealing are studied using Raman spectroscopy and optical profiling techniques.The Raman spectra reveal the generation of Si-(OH)x and Si-O-Si bonds after thermal annealing in the layers, leading to a higher effective lifetime, as it reduces the defect absorption of the sub oxides.For n-type FZ material, lifetime values as high as 1650 µs are obtained, resulting in a surface recombination velocity Seff < 9.5 cm/s.

Assessment of Intrinsic-Layer Growth Temperature to High-Deposition-Rate a-Si:H n-i-p Solar Cells Deposited by Hot-Wire CVD

1999 ◽  
Vol 557 ◽  
Author(s):  
Qi Wang ◽  
Eugene Iwaniczko ◽  
Yueqin Xu ◽  
Brent P. Nelson ◽  
A. H. Mahan
Keyword(s):  
Solar Cells ◽  
Substrate Temperature ◽  
Amorphous Silicon ◽  
Diffusion Length ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Ambipolar Diffusion ◽  
Hot Wire ◽  
Top Contact ◽  
Hydrogenated Amorphous

AbstractWe report progress in hydrogenated amorphous silicon n-i-p solar cells with the i-layer grown by the hot-wire chemical vapor deposition technique. Early research showed that we grew device-quality materials with low saturated defect density (2 × 106/cm3), high initial ambipolar diffusion length (~2000 Å) and low hydrogen content (<1%). One of the major barriers to implementing this material into solar cells is the high substrate temperature required (>400°C). We re-assess the effects of low substrate temperature on the property of the films and the performance of the solar cells as an alternative avenue to solving this problem. We find that the material grown at 300°C can have similar values of saturated defect density and ambipolar diffusion length as the one grown greater than 400°C. We also study the effect of i-layer substrate temperature ranging from 280° to 440°C for n-i-p solar cells. We now consistently grow devices with Fill Factor (FF) greater than 0.66, with the best close to 0.70 at lower substrate temperature. A collaboration with United Solar System, in where they grew the p-layer and top contact, produced devices with initial efficiencies as high as 9.8%. We produce n-i-p solar cells with initial efficiencies as high as 8% when we grow all the hydrogenated amorphous silicon and top contact layers. All these i-layers are grown at deposition rates of 16 to 18 Å/sec. We need to further improve our p-layer and transparent conductor layer to equal the collaborative cell efficiency. We also report light-soaking results of these devices.

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