Characterization of Monolayer-Level Composition and Optical Gap Profiles in Amorphous Silicon-Carbon Alloy Bandgap-Modulated Structures

1997 ◽  
Vol 467 ◽  
Author(s):  
H. Fujiwara ◽  
Joohyun Koh ◽  
C. R. Wronski ◽  
R. W. Collins
Keyword(s):  
Amorphous Silicon ◽  
Chemical Vapor ◽  
Interface Layer ◽  
Open Circuit ◽  
Rf Plasma ◽  
Continuous Increase ◽  
Optical Gap ◽  
Silicon Carbon ◽  
Graded Layers ◽  
Interface Layers

ABSTRACTOver the past few years we have applied real time spectroscopie ellipsometry (RTSE) to characterize the structural, compositional, and optical gap profiles in continuously-graded amorphous silicon-carbon alloy films (a-Si1-xCx:H). Most recently, we have extended the RTSE methods to their monolayer sensitivity and resolution limits. In this study, continuous triangular variations in the carbon content × (0.02≤x≤0.24) within ∼25 to 130 Å thick graded layers were introduced at the i/p interfaces of the n-i-p solar cell structures using continuous variations in the flow ratio z=[CH4]/{[SiH4]+[CH4]} during rf plasma-enhanced chemical vapor deposition (PECVD). A virtual interface approximation has been applied to interpret the RTSE data collected during the growth of the graded interface layers. This analysis yields C-content depth-profiles with monolayer-level resolution and a compositional uncertainty of ±0.004. Even compositional gradients in which x changes by >0.2 within a few monolayers’ thickness are readily characterized. Lastly, a continuous increase in open circuit voltage with increasing graded interface layer thickness, saturating at ΔVoc=0.1 V after 100 Å, is observed in the n-i-p solar cells with graded layers. These results demonstrate the importance of the RTSE analysis in assessing bandgap engineered device designs.

Advances in the Characterization of Compositionally-graded Layers in Amorphous Semiconductor Solar Cells by Real Time Spectroellipsometry

1996 ◽  
Vol 420 ◽  
Author(s):  
R. W. Collins ◽  
Sangbo Kim ◽  
Joohyun Koh ◽  
J. S. Burnham ◽  
Lihong Jiao ◽  
...  
Keyword(s):  
Solar Cells ◽  
Real Time ◽  
Gas Flow ◽  
Chemical Vapor ◽  
Interface Layer ◽  
Open Circuit ◽  
Amorphous Semiconductor ◽  
Deposition Parameters ◽  
Gas Flow Ratio ◽  
Graded Layers

AbstractWe have developed a real time spectroellipsometry data analysis procedure that allows us to characterize compositionally- graded amorphous semiconductor alloy thin films prepared by plasma-enhanced chemical vapor deposition (PECVD). As an example, we have applied the analysis to obtain the depth-profile of the optical gap and alloy composition with ≤15 Å resolution for a hydrogenated amorphous silicon-carbon alloy (a-Si1−xCx:H) film prepared by continuously varying the gas flow ratio z=[CH4]/{[CH4]+[SiH4]} in the PECVD process. The graded layer has been incorporated at the p/i interface of widegap a-Si1−xCx:H (x∼0.05) p-i-n solar cells, and consistent improvements in open-circuit voltage have been demonstrated. The importance of the graded-layer characterization is the ability to relate improvements in device performance directly to the physical properties of the interface layer, rather to the deposition parameters with which they were prepared.

Protocrystalline Si:H p-type Layers for Maximization of the Open Circuit Voltage in a-Si:H n-i-p Solar Cells

2002 ◽  
Vol 715 ◽  
Author(s):  
R. J. Koval ◽  
Chi Chen ◽  
G. M. Ferreira ◽  
A. S. Ferlauto ◽  
J. M. Pearce ◽  
...  
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
Gas Flow ◽  
Open Circuit Voltage ◽  
Film Growth ◽  
Chemical Vapor ◽  
Open Circuit ◽  
Single Step ◽  
Rf Plasma ◽  
Growth Regime

AbstractWe have revisited the issue of p-layer optimization for amorphous silicon (a-Si:H) solar cells, correlating spectroscopic ellipsometry (SE) measurements of the p-layer in the device configuration with light current-voltage (J-V) characteristics of the completed solar cell. Working with p-layer gas mixtures of H2/SiH4/BF3 in rf plasma-enhanced chemical vapor deposition (PECVD), we have found that the maximum open circuit voltage (Voc) for n-i-p solar cells is obtained using p-layers prepared with the maximum possible hydrogen-dilution gas-flow ratio R=[H2]/[SiH4], but without crossing the thickness-dependent transition from the a-Si:H growth regime into the mixed-phase amorphous + microcrystalline [(a+μc)-Si:H] regime for the ∼200 Å p-layers. As a result, optimum single-step p-layers are obtained under conditions similar to those applied for optimum i-layers, i.e., by operating in the so-called “protocrystalline” Si:H film growth regime. The remarkable dependence of the p-layer phase (amorphous vs. microcrystalline) and n-i-p solar cell Voc on the nature of the underlying i-layer surface also supports this conclusion.

Photoelectron spectroscopy study of amorphous silicon-carbon alloys deposited by plasma-enhanced chemical vapor deposition

1996 ◽  
Vol 11 (12) ◽  
pp. 3017-3023 ◽  
Author(s):  
G. Cicala ◽  
G. Bruno ◽  
P. Capezzuto ◽  
P. Favia
Keyword(s):  
Amorphous Silicon ◽  
Vapor Deposition ◽  
Photoelectron Spectroscopy ◽  
Optical Transmission ◽  
Chemical Vapor ◽  
Spectroscopy Study ◽  
Air Oxidation ◽  
X Ray ◽  
Silicon Carbon

X-ray photoelectron spectroscopy (XPS) coupled with Fourier transform infrared (FTIR) and optical transmission spectroscopy (OTS) has been used for the characterization of silicon-carbon alloys (a-Si1−xCx: H, F) deposited via plasma, by varying the CH4 amount in SiF4–CH4–H2 feeding mixture. XPS measurements have shown that carbon-rich a-Si1−xCx: H, F alloys include large amounts of fluorine (>11 at. %), which make the films susceptible to the air oxidation. In addition, the effect of the alloying partner carbon on the valence band (VB) and on the VB edge position of amorphous silicon is also described.

Amorphous Silicon-Carbon Alloys for Solar Cells

1993 ◽  
Vol 297 ◽  
Author(s):  
Yuan-Min Li
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
Amorphous Silicon ◽  
Light Exposure ◽  
Open Circuit ◽  
Hydrogen Dilution ◽  
Silicon Carbon ◽  
Hydrogenated Amorphous ◽  
Substrate Temperatures ◽  
Open Circuit Voltages

Recent efforts to optimize undoped, glow-discharge hydrogenated amorphous silicon-carbon alloys (a-SiC:H) with 1.9-2.0 eV bandgaps for solar cell applications are reviewed. Hydrogen dilution coupled with relatively low substrate temperatures (below 200 °C) have led to great improvements in the optical and phototransport properties of a-SiC:H films. The issue of alternative carbon feedstocks other than methane (CH4) will be explored. The improved a-SiC:H alloys have resulted in solar cells with high open circuit voltages (V∞ > 1.0 volt) and high fill factors (> 0.7). Further, the a-SiC:H solar cell instability upon prolonged light exposure has been much reduced. Correlation will be made between the properties of bulk undoped a-SiC:H films and the performance of p-i-nsingle junction solar cells using corresponding a-SiC:H thin i-layers.

Amorphous Silicon Carbide Film Formation at Room Temperature by Monomethylsilane Gas

2013 ◽  
Vol 740-742 ◽  
pp. 235-238
Author(s):  
Hitoshi Habuka ◽  
Masaki Tsuji ◽  
Yusuke Ando
Keyword(s):  
Silicon Carbide ◽  
Amorphous Silicon ◽  
Room Temperature ◽  
Film Formation ◽  
Argon Plasma ◽  
Chemical Vapor ◽  
Amorphous Silicon Carbide ◽  
Silicon Carbide Film ◽  
Silicon Carbon ◽  
Thin Film Formation

The silicon carbide thin film formation process, completely performed at room temperature, was developed by argon plasma and a chemical vapor deposition using monomethylsilane gas. Silicon-carbon bonds were found to exist in the obtained film, the surface of which could remain specular after exposure to hydrogen chloride gas at 800 oC. The silicon dangling bonds formed at the silicon surface by the argon plasma are considered to react with the monomethylsilane molecules at room temperature to produce the amorphous silicon carbide film.

Doping Efficiency of N-Type a-Si:H Doped with a Liquid Organic Source

1993 ◽  
Vol 297 ◽  
Author(s):  
K. Gaughan ◽  
ZHAOHUI Lin ◽  
J.M. Viner ◽  
P.C. Taylor ◽  
P.C. Mathur
Keyword(s):  
Activation Energy ◽  
Chemical Vapor Deposition ◽  
Amorphous Silicon ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Dark Conductivity ◽  
Band Tail ◽  
Optical Gap ◽  
Heavily Doped ◽  
Pl Intensity

N-type amorphous silicon films were grown using a mixture of silane and tertiarybutylphosphine (TBP-C4H11P) vapor in a plasma enhanced chemical vapor deposition system. The concentration of TBP in silane was varied from 0 to 3% by volume. As expected, at low doping levels, the photoluminescence (PL) intensity associated with both the band-tail recombination (peak at 1.3 eV) and deep-defect recombination (peak at 0.8 eV) decreased as the impurity concentration increased, but for TBP concentrations > 0.1% the PL intensity increased again. For moderate doping levels the activation energy for conductivity leveled off at ∼ 0.2 eV. For concentrations of TBP > 0.1% the activation energy for dark conductivity increased. A shift in the optical gap was observed for the highest impurity concentrations due to the incorporation of carbon from the TBP. These results are interpreted as a pronounced decrease in the doping efficiency for heavily doped films (> 0.1%) perhaps influenced by the increased carbon concentration.

Hydrogenated amorphous silicon carbon nitride films prepared by PECVD technology: properties

2012 ◽  
Vol 63 (5) ◽  
pp. 333-335 ◽  
Author(s):  
Jozef Huran ◽  
Albín Valovič ◽  
Michal Kučera ◽  
Angela Kleinová ◽  
Eva Kovačcová ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Amorphous Materials ◽  
Carbon Nitride ◽  
Hydrogenated Amorphous Silicon ◽  
Electrical Characterization ◽  
Chemical Vapor ◽  
Silicon Carbon ◽  
Two Peaks ◽  
Hydrogenated Amorphous ◽  
Silicon Carbon Nitride

Hydrogenated amorphous silicon carbon nitride films were grown by plasma enhanced chemical vapor deposition (PECVD) technique. The flow rates of SiH4 , CH4 and NH3 gases were 6 sccm, 30 sccm and 8 sccm, respectively. The deposition temperatures were 350, 400 and 450 ◦C. The RBS and ERD results showed that the concentrations of Si, C, N and H are practically the same in the films deposited at substrate temperatures in the range 350-450 ◦C. In photoluminescence spectra we identified two peaks and assigned them to radiative transitions typical for amorphous materials, ie band to band and defect-related ones. The electrical characterization consists of I(V ) measurement in sandwich configuration for voltages up to 100 V. From electrical characterization, it was found that with increased deposition temperature the resistivity of the amorphous SiCN film was reduced.

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