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.

Materials and Interface Optimization of Heterojunction Silicon (HIT) Solar Cells Using in-situ Real-Time Spectroscopic Ellipsometry

2004 ◽  
Vol 808 ◽  
Author(s):  
D.H. Levi ◽  
C.W. Teplin ◽  
E. Iwaniczko ◽  
R.K. Ahrenkiel ◽  
H.M. Branz ◽  
...  
Keyword(s):  
Solar Cells ◽  
Real Time ◽  
Spectroscopic Ellipsometry ◽  
Crystalline Silicon ◽  
Surface Recombination ◽  
Chemical Vapor ◽  
Energy Conversion Efficiency ◽  
Open Circuit ◽  
Analysis Tool

ABSTRACTWe have applied real-time spectroscopic ellipsometry (RTSE) as both an in-situ diagnostic and post-growth analysis tool for hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) heterojunction with intrinsic thin-layer (HIT) solar cells grown by hot-wire chemical vapor deposition. RTSE enables precise thickness control of the 5 to 25 nm layers used in these devices, as well as monitoring crystallinity and surface roughness in real time. Utilizing RTSE feedback, but without extensive optimization, we have achieved a photovoltaic energy conversion efficiency of 14.1% on an Al-backed p-type Czochralski c-Si wafer coated with thin i and n layers on the front. Open-circuit voltages above 620 mV indicate effective passivation of the c-Si surface by the a-Si:H intrinsic layer. Lifetime measurements using resonant coupled photoconductive decay indicate that surface recombination velocities can approach 1 cm/s. RTSE and transmission electron microscopy show that the intrinsic a-Si:H i-layers grow as a mixture of amorphous and nano-crystalline silicon.

High Rates and Very Low Temperature Fabrication of Polycrystalline Silicon From Fluorinated Source GAS and Their Transport Properties

1999 ◽  
Vol 557 ◽  
Author(s):  
T. Kamiya ◽  
K. Nakahata ◽  
K. Ro ◽  
C. M. Fortmann ◽  
I. Shimizu
Keyword(s):  
Growth Rate ◽  
Solar Cells ◽  
Low Temperature ◽  
Polycrystalline Silicon ◽  
Gas Flow ◽  
Open Circuit ◽  
Glow Discharge Plasma ◽  
Very High Frequency ◽  
Crystalline Films ◽  
Gas Flow Ratio

AbstractLow temperature (50-300°C) growth of polycrystalline silicon (poly-Si) by very high frequency (100MHz) glow-discharge plasma enhanced CVD using SiF4 and H2mixtures was studied. The poly-Si microstructure was strongly affected by the SiF4/H2 gas flow ratio. For example, either (220) or (400) preferentially oriented films were prepared by appropriate SiF4/H2 ratio selection. The addition of small SiH4 flows to the SiF4/H2 mixtures could be used to increase the growth rate while the SiF4/H2 continued to control the film structures such as preferential orientation. Highly crystalline films were grown at a growth rate of 0.52nm/s using SiF4/H2/SiH4 flow rates of 30/90/2.Osccm (respectively). However, at higher SiH4 flows amorphous films were deposited. Under the small SiF4/H2 ratio condition, highly crystallized poly-Si was grown at temperatures as low as 50°C. N/i/Pt Schottky diode solar cells were prepared using these poly-Si for both the n- and the i-layers. These solar cells exhibited good performance; for example, open circuit voltages over 0.32V. N-i-p solar cell results are very promising with 6.2% of conversion efficiency being achieved in the initial trials.

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.

Heteroepitaxial Growth of Ge-Rich SiGe Films on Si for Solar Cells

2014 ◽  
Vol 1014 ◽  
pp. 216-219 ◽  
Author(s):  
Jin Wang ◽  
Ke Tao ◽  
Guo Feng Li
Keyword(s):  
Solar Cells ◽  
Silicon Germanium ◽  
Gas Flow ◽  
Hole Concentration ◽  
Chemical Vapor ◽  
Threading Dislocation ◽  
Heteroepitaxial Growth ◽  
Gas Flow Ratio ◽  
Threading Dislocation Density ◽  
P Type

Germanium-rich silicon-germanium (Si1-xGex: 0.98≤x≤1) films were epitaxially grown on Si (001) substrate by reactive thermal chemical vapor deposition at low temperature. Si2H6and GeF4were used as source gases. The effect of gas flow ratio between Si2H6and GeF4was studied to optimize the film quality. The results indicated that Si1-xGex(x≥0.99) epilayer can be prepared directly on Si wafer at 350°C with a threading dislocation density of ~7×105/cm2and surface RMS roughness of 1.0 nm. Hall-effect and conductivity measurements revealed that the epilayer was p-type conduction with the hall mobility of 767 cm2/Vs and the hole concentration of 6.08×1016/cm3. Those results indicated the Ge-rich Si1-xGexwas an excellent candidate for bottom cells of multijunction solar cells.

Control and Variation of Stress in Pecvd SiNx Films on InP

1988 ◽  
Vol 130 ◽  
Author(s):  
J. Lopata ◽  
W. C. Dautremont-Smith ◽  
J. W. Lee
Keyword(s):  
Compressive Stress ◽  
High Frequency ◽  
Gas Flow ◽  
Plasma Reactor ◽  
Low Frequency ◽  
Chemical Vapor ◽  
Flow Ratio ◽  
Deposition Parameters ◽  
Chemical Vapor Deposited ◽  
Gas Flow Ratio

AbstractStress in plasma enhanced chemical vapor deposited (PECVD) SiNx films on InP has been evaluated as a function of source gases (NH3 /SiH4 or N2/SiH4) and plasma operating frequency (high, » 1 MHz or low, « 1 MHz). All films were deposited at 300°C in the same parallel-plate, radial flow plasma reactor. Levels of stress in PECVD SiNx on InP within a continuous range from moderately high tensile (∼ 5 × 109 dyne cm−2) to very high compressive (2 × 1010 dyne cm−2 ) were obtained from appropriate choices of deposition parameters. Deposition from NH3/SiH4 at high frequency produces tensile stress, of magnitude increasing with NH3/SiH4 flow ratio. Deposition from N2/SiH4 at high frequency produces zero to low compressive stress. At low frequency compressive stress is always produced; for N2/SiH4 increasing the gas flow ratio from 25:1 to 500:1 reduces the compressive stress from 1.8 X 1010 to 7 × 108 dyne cm−2. The ability to vary the stress in a dielectric film of approximately constant chemical composition over such a broad range is beneficial for assessing the effects of stress on device performance.

Hydrogen Concentration Analysis in Pecvd and Rtcvd Silicon Nitride Thin Films and It's Impact on Device Performance

2001 ◽  
Vol 664 ◽  
Author(s):  
C. Y. Wang ◽  
E. H. Lim ◽  
H. Liu ◽  
J. L. Sudijono ◽  
T. C. Ang ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
Threshold Voltage ◽  
Vapor Deposition ◽  
Gas Flow ◽  
Chemical Vapor ◽  
Gate Oxide ◽  
Nitride Film ◽  
Device Performance ◽  
Gas Flow Ratio ◽  
The Impact

ABSTRACTIn this paper the impact of the ESL (Etch Stop layer) nitride on the device performance especially the threshold voltage (Vt) has been studied. From SIMS analysis, it is found that different nitride gives different H concentration, [H] in the Gate oxide area, the higher [H] in the nitride film, the higher H in the Gate Oxide area and the lower the threshold voltage. It is also found that using TiSi instead of CoSi can help to stop the H from diffusing into Gate Oxide/channel area, resulting in a smaller threshold voltage drift for the device employed TiSi. Study to control the [H] in the nitride film is also carried out. In this paper, RBS, HFS and FTIR are used to analyze the composition changes of the SiN films prepared using Plasma enhanced Chemical Vapor deposition (PECVD), Rapid Thermal Chemical Vapor Deposition (RTCVD) with different process parameters. Gas flow ratio, RF power and temperature are found to be the key factors that affect the composition and the H concentration in the film. It is found that the nearer the SiN composition to stoichiometric Si3N4, the lower the [H] in SiN film because there is no excess silicon or nitrogen to be bonded with H. However the lowest [H] in the SiN film is limited by temperature. The higher the process temperature the lower the [H] can be obtained in the SiN film and the nearer the composition to stoichiometric Si3N4.

Temperature Dependent Transport in Microcrystalline PIN Diodes

2000 ◽  
Vol 609 ◽  
Author(s):  
T. Brammer ◽  
H. Stiebig ◽  
A. Lambertz ◽  
W. Reetz ◽  
H. Wagner
Keyword(s):  
Solar Cells ◽  
Fill Factor ◽  
Extraction Efficiency ◽  
Chemical Vapor ◽  
Open Circuit ◽  
Microcrystalline Silicon ◽  
Temperature Dependent ◽  
Dependent Transport ◽  
Silane Concentration ◽  
Interface Effects

ABSTRACTThe optoelectronic behavior of diodes deposited by plasma enhanced chemical vapor deposition was investigated for a series of different silane concentrations in the gas phase. The purpose of this work was to correlate device characteristics with inherent properties of microcrystalline silicon by experiments and numerical simulations. Dark diode characteristics and, therefore, the open circuit voltage behavior of this series were dominated by the bulk properties of the i-layer (equilibrium carrier concentration) as shown by numerical modeling. Measurement of the solar cell output parameters as a function of the temperature showed that the fill factor of solar cells with small silane concentrations is dominated by the dark diode characteristics. This is in contrast to the temperature dependent fill factor of solar cells with large silane concentration which is limited by the extraction efficiency of the photogenerated carriers. Interface effects dominated the temperature dependent blue response. The gain in blue response increased with temperature and silane concentration by up to 200 % which revealed transport limiting material properties in the vicinity of the p/i-interface. This behavior was attributed to the nucleation region.

Dependence of PECVD Silicon Oxynitride Properties on Deposition Parameters

1988 ◽  
Vol 131 ◽  
Author(s):  
Aubrey L. Helms ◽  
Robert M. Havrilla
Keyword(s):  
Gas Flow ◽  
Chemical Vapor ◽  
Silicon Oxynitride ◽  
Gas Flow Rate ◽  
Process Gas ◽  
Deposition Parameters ◽  
Chemical Vapor Deposited ◽  
Passivation Layers ◽  
Parallel Plate Reactor ◽  
Deposition Conditions

ABSTRACTThe properties of Plasma Enhanced Chemical Vapor Deposited (PECVD) silicon oxynitride thin films were determined for a variety of deposition conditions. The films were characterized with respect to stress, refractive index, deposition rate, hydrogen content, dielectric constant, and uniformity. The films were deposited in an Electrotech ND6200 parallel plate reactor using a silane - ammonia - nitrous oxide process gas chemistry. Deposition parameters which were investigated include process gas flow rate, power, and total pressure. The possible application of these films as both inter-layer and final passivation layers for use on GaAs ICs will be discussed.

Sign in / Sign up

Export Citation Format

Share Document