Hydrogenated Amorphous Silicon Grown by Hot-Wire CVD at Deposition Rates up to 1 µm/minute

2000 ◽  
Vol 609 ◽  
Author(s):  
Brent P. Nelson ◽  
Yueqin Xu ◽  
A. Harv Mahan ◽  
D.L. Williamson ◽  
R.S. Crandal
Keyword(s):  
Amorphous Silicon ◽  
Deposition Rate ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Conductivity Ratio ◽  
Hot Wire ◽  
Single Filament ◽  
Deposition Rates ◽  
X Ray ◽  
Hydrogenated Amorphous

ABSTRACTWe grow hydrogenated amorphous-silicon (a-Si:H) by the hot-wire chemical vapor deposition (HWCVD) technique. In our standard tube-reactor we use a single filament, centered 5 cm below the substrate and obtain deposition rates up to 20 Å/s. However, by adding a second filament, and decreasing the filament-to-substrate distance, we are able to grow a-Si:H at deposition rates exceeding 167 Å/s (1 µm/min). We find the deposition rate increases with increasing deposition pressure, silane flow rate, and filament current and decreasing filament-tosubstrate distance. There are significant interactions among these parameters that require optimization to grow films of optimal quality for a desired deposition rate. Using our best conditions, we are able to maintain an AM1.5 photoconductivity-to-dark-conductivity ratio of 105 at deposition rates up to 130 Å/s, beyond which the conductivity ratio decreases. Other electronic properties decrease more rapidly with increasing deposition rate, including the ambipolar diffusion length, Urbach energy, and the as-grown defect density. Measurements of void density by small-angle X-ray scattering (SAXS) reveal an increase by well over an order of magnitude when going from one to two filaments. However, both Raman and X-ray diffraction (XRD) measurements show no change in film structure with increasing deposition rates up to 144 Å/s, and atomic force microscopy (AFM) reveals little change in topology.

Low Hydrogen Content, High Quality Hydrogenated Amorphous Silicon Grown by Hot-Wire CVD

1999 ◽  
Vol 557 ◽  
Author(s):  
Brent P. Nelson ◽  
Richard S. Crandall ◽  
Eugene Iwaniczko ◽  
A. H. Mahan ◽  
Qi Wang ◽  
...  
Keyword(s):  
Substrate Temperature ◽  
Amorphous Silicon ◽  
Hydrogen Content ◽  
Defect Density ◽  
Flow Direction ◽  
Scale Up ◽  
Hydrogenated Amorphous Silicon ◽  
Hot Wire ◽  
High Quality ◽  
Hydrogenated Amorphous

AbstractWe grow hydrogenated amorphous silicon (a-Si:H) by Hot-Wire Chemical Vapor Deposition (HWCVD). Our early work with this technique has shown that we can grow a-Si:H that is different from typical a-Si:H materials. Specifically, we demonstrated the ability to grow a-Si:H of exceptional quality with very low hydrogen (H) contents (0.01 to 4 at. %). The deposition chambers in which this early work was done have two limitations: they hold only small-area substrates and they are incompatible with a load-lock. In our efforts to scale up to larger area chambers—that have load-lock compatibility—we encountered difficulty in growing high-quality films that also have a low H content. Substrate temperature has a direct effect on the H content of HWCVD grown a-Si:H. We found that making dramatic changes to the other deposition process parameters—at fixed substrate temperature and filament-to-substrate spacing—did not have much effect on the H content of the resulting films in our new chambers. However, these changes did have profound effects on film quality. We can grow high-quality a-Si:H in the new larger area chambers at 4 at. % H. For example, the lowest known stabilized defect density of a-Si:H is approximately 2 × 1016 cm-3, which we have grown in our new chamber at 18 Å/s. Making changes to our original chamber—making it more like our new reactor—did not increase the hydrogen content at a fixed substrate temperature and filament-to-substrate spacing. We continued to grow high quality films with low H content in spite of these changes. An interesting, and very useful, result of these experiments is that the orientation of the filament with respect to silane flow direction had no influence on film quality or the H content of the films. The condition of the filament is much more important to growing quality films than the geometry of the chamber due to tungsten-silicide formation on the filament.

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.

Hydrogenated Amorphous Silicon Films by the Pyrolysis of Disilane(1)

1985 ◽  
Vol 49 ◽  
Author(s):  
T. L. Chu ◽  
Shirley S. Chu ◽  
S. T. Ang ◽  
D. H. Lo ◽  
A. Duong ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Amorphous Silicon ◽  
Deposition Rate ◽  
Hydrogenated Amorphous Silicon ◽  
Conductivity Ratio ◽  
Helium Flow ◽  
Photothermal Deflection Spectroscopy ◽  
Photothermal Deflection ◽  
Gap States ◽  
Hydrogenated Amorphous

AbstractThe thermal decomposition of disilane in a hydrogen or helium flow has been used for the deposition of hydrogenated amorphous silicon (a-Si:H) films on the surface of several substrates at 450°-500°C. The concentration of disilane in the reaction mixture has been found to affect strongly the deposition rate and the photoconductivity of a-Si:H films. The AMI conductivity of a-Si:H films increases with increasing disilane concentration and approaches lO−5(ohm-cm)−l at disilane concentrations higher than about 4%, and the conductivity ratio is about lO5. The density of gap states in CVD a-Si:H films have been determined by the photothermal deflection spectroscopy, capacitancetemperature, capacitance-frequency, and space-charged-limited current measurements with similar results.

A Defect Density of ∼ 1014 cm-3 in Hydrogenated Amorphous Silicon Deposited at High Substrate Temperatures

1992 ◽  
Vol 258 ◽  
Author(s):  
Gautam Ganguly ◽  
Akihisa Matsuda
Keyword(s):  
Substrate Temperature ◽  
Amorphous Silicon ◽  
Deposition Rate ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
High Substrate ◽  
Surface Mobility ◽  
Surface Hydrogen ◽  
Hydrogenated Amorphous ◽  
Substrate Temperatures

ABSTRACTThe idea of surface mobility of growth precursors determined material quality has been exploited by raising the substrate temperature above the conventional 250°C and the ensuing thermal depletion of the surface hydrogen coverage compensated by increasing the precursor flux (deposition rate) to prepare ultra low defect density hydrogenated amorphous silicon.

Hydrogenated Nanocrystalline Silicon Thin Film Transistor Array for X-ray Detector Application

2008 ◽  
Vol 1066 ◽  
Author(s):  
Kyung-Wook Shin ◽  
Mohammad R. Esmaeili-Rad ◽  
Andrei Sazonov ◽  
Arokia Nathan
Keyword(s):  
Thin Film ◽  
Amorphous Silicon ◽  
Threshold Voltage ◽  
Hydrogenated Amorphous Silicon ◽  
Nanocrystalline Silicon ◽  
Amorphous Selenium ◽  
Breakdown Field ◽  
Storage Capacitor ◽  
X Ray ◽  
Hydrogenated Amorphous

ABSTRACTHydrogenated nanocrystalline silicon (nc-Si:H) has strong potential to replace the hydrogenated amorphous silicon (a-Si:H) in thin film transistors (TFTs) due to its compatibility with the current industrial a-Si:H processes, and its better threshold voltage stability [1]. In this paper, we present an experimental TFT array backplane for direct conversion X-ray detector, using inverted staggered bottom gate nc-Si:H TFT as switching element. The TFTs employed a nc-Si:H/a-Si:H bilayer as the channel layer and hydrogenated amorphous silicon nitride (a-SiNx) as the gate dielectric; both layers deposited by plasma enhanced chemical vapor deposition (PECVD) at 280°C. Each pixel consists of a switching TFT, a charge storage capacitor (Cpx), and a mushroom electrode which serves as the bottom contact for X-ray detector such as amorphous selenium photoconductor. The chemical composition of the a-SiNx was studied by Fourier transform infrared spectroscopy. Current-voltage measurements of the a-SiNx film demonstrate that a breakdown field of 4.3 MV/cm.. TFTs in the array exhibits a field effect mobility (μEF) of 0.15 cm2/V·s, a threshold voltage (VTh) of 5.71 V, and a subthreshold leakage current (Isub) of 10−10 A. The fabrication sequence and TFT characteristics will be discussed in details.

Sign in / Sign up

Export Citation Format

Share Document