Estimation of Defect State Densities from Bulk Photoelectronic Properties of a-Si,Ge:H Alloys

1987 ◽  
Vol 95 ◽  
Author(s):  
G. N. Parsons ◽  
G. Lucovsky
Keyword(s):  
Activation Energy ◽  
Incident Light ◽  
Film Surface ◽  
Dark Conductivity ◽  
State Density ◽  
Defect State ◽  
Oxide Interface ◽  
Conductivity Activation Energy ◽  
State Densities

AbstractWe have studied the photoelectronic properities of a- Si(x),Ge(1−x):H alloy films and have concluded that there are depletion layers at the film surface and film/oxide interface that effect the determination of bulk quantum effieciencymobility- lifetime (nuT) products. From changes in dark conductivity activation energy with film thickness and the nuT product with wavelength of incident light we have estimated defeci sta:e lensitles. Our best x=0.5 film has an nuT value of 9×10−8 cm2 V−1 andaj defect state density near the Fermi level of approximately 5×10 cm−3 eV−1.

Measurements of Light-Induced Degradation in A-Si, Ge:H, F Alloys,

1986 ◽  
Vol 70 ◽  
Author(s):  
J. Kolodzey ◽  
S. Aljishi ◽  
Z E. Smith ◽  
V. Chu ◽  
R. Schwarz ◽  
...  
Keyword(s):  
Activation Energy ◽  
Electronic Properties ◽  
Dark Conductivity ◽  
Narrow Gap ◽  
Conductivity Activation Energy ◽  
Optical And Electronic Properties ◽  
Amorphous Si

ABSTRACTThe effects of illumination on the optical and electronic properties of narrow gap hydrogenated and fluorinated amorphous Si-Ge (a-Si1-xGex:H, F) alloys have been evaluated. A series of alloys with optical gaps ranging from 1.30 eV to 1.64 eV has been light soaked at ∼1 sun intensity for 354 hours. Measurements of sub-gap absorption, photo- and dark conductivities and dark conductivity activation energy were made on alloys in the annealed and the light-soaked states. The results indicate that samples with optical gaps ≳ 1.4 eV degrade significantly. The 1.3 eV sample shows no degradation in its optical or electronic properties except for a factor of 5 increase in the dark conductivity.

The Study of Deep Levels in CdS/CdTe Solar Cells Using Admittance Spectroscopy and its Modifications

2003 ◽  
Vol 763 ◽  
Author(s):  
A.S. Gilmore ◽  
V. Kaydanov ◽  
T.R. Ohno
Keyword(s):  
Solar Cells ◽  
Energy Levels ◽  
Wide Frequency Range ◽  
State Density ◽  
Defect State ◽  
Stress Tests ◽  
Frequency Range ◽  
Cdte Solar Cells ◽  
State Densities ◽  
As Stress

AbstractMeasurements of an admittance over a wide frequency range were used to detect the defect electronic states and evaluate their properties in CdTe based solar cells. Cells prepared in various ways, from various facilities all exhibited a high defect state density (>1014cm-3, and often >1015cm-3). Two distinct energy levels or bands were observed at approximately 0.37eV and 0.61eV above the valence band. These were tentatively attributed to CuCd- and VCd-- respectively. Various post-CdTe deposition treatments, as well as stress tests, were applied to alter the defect state densities. The high defect concentration measured was not observed to inhibit cell performance in any way.

Increasing The Dark Conductivity Activation Energy in Undoped Microcrystalline Silicon by Post-Growth Anneals

2001 ◽  
Vol 664 ◽  
Author(s):  
Jong-Hwan Yoon
Keyword(s):  
Activation Energy ◽  
Oxygen Concentration ◽  
Dark Conductivity ◽  
Low Energy ◽  
Microcrystalline Silicon ◽  
Conductivity Activation Energy ◽  
Constant Rate ◽  
Annealing Effects ◽  
Annealing Cycle ◽  
Type Character

ABSTRACTUndoped µc-Si:H film of the strong n-type character with the dark conductivity activation energy of about 0.28 eV was annealed. Annealing was carried out by slowly increasing the temperature from 25 °C to 450 °C at a constant rate of 12 °C/min (one annealing cycle). Annealing effects were monitored by measuring the changes in dark conductivity, oxygen and hydrogen concentrations, and photoluminescence (PL). Dark conductivity activation energy gradually increases with increasing the number of annealing cycles to a saturation value of about 0.6 eV. There is little or no change in the oxygen concentration, but the hydrogen concentration decreases with increasing the number of annealing cycles. The PL band near 1.2 eV disappears with annealing, while the low energy PL band near 0.85 eV dominates rather as the number of annealing cycles increases. A possible explanation will be discussed.

Intrinsic microcrystalline silicon by postgrowth anneals

2001 ◽  
Vol 16 (6) ◽  
pp. 1531-1534 ◽  
Author(s):  
Jong-Hwan Yoon
Keyword(s):  
Activation Energy ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Dark Conductivity ◽  
Microcrystalline Silicon ◽  
Conductivity Activation Energy ◽  
High Hydrogen ◽  
Constant Rate ◽  
Annealing Cycle

Hydrogenated microcrystalline silicon (μc-Si:H) grown by a conventional plasma-enhanced chemical vapor deposition from high hydrogen-diluted silane was annealed by increasing the temperature from 25 to 450 °C at a constant rate of 12 °C/min (one annealing cycle). Dark-conductivity activation energy gradually increases with increasing the number of annealing cycle to a saturation value of about 0.6 eV, observed in truly intrinsic μc-Si:H films. For the saturated state, the dark conductivity of the order of 10−8 S/cm was obtained. Little or no change in the oxygen content was observed after the annealing.

Minority Carrier Diffusion Lengths And Photoconductivity In a-Si,N:H Deposited By Remote Pecvd

1994 ◽  
Vol 336 ◽  
Author(s):  
M.J. Williams ◽  
S.M. Cho ◽  
S.S. He ◽  
G. Lucovsky
Keyword(s):  
Activation Energy ◽  
Minority Carrier ◽  
Dark Conductivity ◽  
Wide Bandgap ◽  
Conductivity Ratio ◽  
Conductivity Activation Energy ◽  
Active Materials ◽  
Atom Source ◽  
Staebler Wronski Effect ◽  
Deposited Films

ABSTRACTWe have deposited films of a-Si,N:H by remote PECVD from N2 and SiH4 for N-concentrations, [N], to about 12 atomic percent (at. %). Bonded-H concentrations were ∼7–10 at. %, Mostly in Si-H groups. The films with [N] = 9–12 at. % have εθ4 bandgaps of ∼2.0 to 2.2 eV, which makes them potentially useful as wide bandgap photo-active materials in tandem PV cells. Several properties are of special interest for PV applications. First, like many other a-Si:H-based alloys, the photoconductivity relative to a-Si:H is degraded by alloying, but less than for a-Si,C:H alloys with the same bandgaps. Second, the ambipolar diffusion lengths (Ld) obtained with the Steady State Photocarrier Grating (SSPG) technique for films with [N] = 10 at. % and εθ4 = 2.1eV, are comparable to those of a-Si:H. For lightly-nitrided films to [N] ∼5 at. %, Ld first decreases with respect to a-Si:H and then increases as [N] increases from ∼7 at.% to 10–12 at. %. These trends follow the dark conductivity activation energy, Ea, which initially drops due to doping, and then increases into an alloy regime for [N] > 5 at. %. Films with [N1=10 at. % have dark conductivities and Ea's comparable to those of undoped a-Si:H. Third the magnitude of the Staebler-Wronski effect, as monitored by the photo- to dark conductivity ratio after a 1000 Minute lightsoak, was about the same as in a-Si:H. Finally, we contrast the properties of these films prepared from N2 with a-Si,N:H alloys with the same [N] and E04, but prepared from an ammonia N-atom source gas and attribute differences in their photoelectronic behavior such as a significantly enhanced Staebler-Wronski effect.to the presence of Si-NH bonding arrangements in the films grown from NH3.

Deposition and Characterization of Near “Intrinsic” μc-Si Films Deposited by Remote Plasma-Enhanced Chemical-Vapor Deposition - RPECVD

1991 ◽  
Vol 219 ◽  
Author(s):  
M. J. Williams ◽  
C. Wang ◽  
G. Lucovsky
Keyword(s):  
Activation Energy ◽  
Vapor Deposition ◽  
Room Temperature ◽  
Boron Concentration ◽  
Chemical Vapor ◽  
Dark Conductivity ◽  
Conductivity Activation Energy ◽  
Boron Doped ◽  
Si Films

ABSTRACTUndoped films of μc-Si deposited by RPECVD are n-type with a room temperature dark conductivity of ∼6×10-4 S/cm and an activation energy of ∼0.3 eV. This is due to native donor-like defects. We report on the conductivity and photoconductivity of boron-doped μc-Si, with emphasis on low doping levels that are designed to compensate exactly these native donor-like defects. We describe the dark conductivity and the photoconductivity as functions of dark conductivity activation energy and the average boron concentration, and present a model for the photoconductivity based on band off sets between the crystalline and amorphous regions of the μc-Si.

Adsorption on evaporated tungsten films I. Oxygen and carbon monoxide chemisorption and the determination of film surface areas

1951 ◽  
Vol 205 (1082) ◽  
pp. 409-421 ◽  
Keyword(s):  
Activation Energy ◽  
Carbon Monoxide ◽  
Film Surface ◽  
Layer Formation ◽  
Surface Areas ◽  
Air Temperatures ◽  
Gas Pressures

The chemisorption of oxygen and of carbon monoxide by evaporated tungsten films has been studied between 20 and - 195° C and at pressures up to 10 -2 mm., with the primary aim of measuring the surface areas of the films. The two methods give results which agree, and the film areas have been determined to an accuracy of about 5 %. Chemisorption of oxygen is followed by a second process, probably an oxidation, which slows very rapidly as gas is taken up, and for which an activation energy of 7000 cal. has been evaluated. The heat of carbon monoxide chemisorption is so low in densely packed layers that measurable equilibrium gas pressures are required even at liquid-air temperatures for completion of chemisorption. Values for the fraction of the surface atoms covered at various temperatures and pressures have been obtained, together with isothermal heats at various coverages. At the lowest temperatures onset of second-layer formation has been observed; first- and second-layer formations do not form a stepwise process.

High Temperature n- and p-type Doped Microcrystalline Silicon Layers Grown by VHF PECVD Layer-by-Layer Deposition

2003 ◽  
Vol 762 ◽  
Author(s):  
A. Gordijn ◽  
J.K. Rath ◽  
R.E.I. Schropp
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
High Temperatures ◽  
Continuous Wave ◽  
Hydrogen Plasma ◽  
Silicon Layer ◽  
Dark Conductivity ◽  
High Deposition Rate ◽  
Layer By Layer ◽  
Microcrystalline Silicon

AbstractDue to the high temperatures used for high deposition rate microcrystalline (μc-Si:H) and polycrystalline silicon, there is a need for compact and temperature-stable doped layers. In this study we report on films grown by the layer-by-layer method (LbL) using VHF PECVD. Growth of an amorphous silicon layer is alternated by a hydrogen plasma treatment. In LbL, the surface reactions are separated time-wise from the nucleation in the bulk. We observed that it is possible to incorporate dopant atoms in the layer, without disturbing the nucleation. Even at high substrate temperatures (up to 400°C) doped layers can be made microcrystalline. At these temperatures, in the continuous wave case, crystallinity is hindered, which is generally attributed to the out-diffusion of hydrogen from the surface and the presence of impurities (dopants).We observe that the parameter window for the treatment time for p-layers is smaller compared to n-layers. Moreover we observe that for high temperatures, the nucleation of p-layers is more adversely affected than for n-layers. Thin, doped layers have been structurally, optically and electrically characterized. The best n-layer made at 400°C, with a thickness of only 31 nm, had an activation energy of 0.056 eV and a dark conductivity of 2.7 S/cm, while the best p-layer made at 350°C, with a thickness of 29 nm, had an activation energy of 0.11 V and a dark conductivity of 0.1 S/cm. The suitability of these high temperature n-layers has been demonstrated in an n-i-p microcrystalline silicon solar cell with an unoptimized μc-Si:H i-layer deposited at 250°C and without buffer. The Voc of the cell is 0.48 V and the fill factor is 70 %.

Sign in / Sign up

Export Citation Format

Share Document