Hopping transport in doped co-deposited mixed-phase hydrogenated amorphous/nanocrystalline silicon thin films

2011 ◽  
Vol 1321 ◽  
Author(s):  
L. R. Wienkes ◽  
C. Blackwell ◽  
J. Kakalios
Keyword(s):  
Temperature Dependence ◽  
Electronic Transport ◽  
Nanocrystalline Silicon ◽  
Dark Conductivity ◽  
Mixed Phase ◽  
Dependence Analysis ◽  
Thermally Activated ◽  
Silicon Thin Films ◽  
And Shifts ◽  
Hydrogenated Amorphous

ABSTRACTStudies of the electronic transport properties of n-type doped hydrogenated amorphous/nanocrystalline silicon (a/nc-Si:H) films deposited in a dual-plasma co-deposition reactor are described. For these doped a/nc-Si:H, the conductivity increases monotonically for increasing crystal fractions up to 60% and displays marked deviations from a simple thermally activated temperature dependence. Analysis of the temperature dependence of the activation energy for these films finds that the dark conductivity is best described by a power-law temperature dependence, σ = σo (T/To)n where n = 1 – 4, suggesting multiphonon hopping as the main transport mechanism. These results suggest that electronic transport in mixed-phase films occurs through the a-Si:H matrix at lower nanocrystal concentrations and shifts to hopping conduction between clusters of nanocrystals at higher nanocrystal densities.

Thermoelectric properties of doped and undoped mixed phase hydrogenated amorphous/nanocrystalline silicon thin films

2010 ◽  
Vol 1245 ◽  
Author(s):  
James Kakalios ◽  
Yves Adjallah ◽  
Charlie Blackwell
Keyword(s):  
Thin Films ◽  
Seebeck Coefficient ◽  
Temperature Dependence ◽  
Nanocrystalline Silicon ◽  
Dark Conductivity ◽  
Mixed Phase ◽  
Positive Temperature ◽  
Silicon Thin Films ◽  
Similar Temperature Dependence ◽  
Hydrogenated Amorphous

AbstractThe Seebeck coefficient and dark conductivity for undoped, and n-type doped thin film hydrogenated amorphous silicon (a-Si:H), and mixed-phase films with silicon nanocrystalline inclusions (a/nc-Si:H) are reported. For both undoped a-Si:H and undoped a/nc-Si:H films, the dark conductivity is enhanced by the addition of silicon nanocrystals. The thermopower of the undoped a/nc-Si:H has a lower Seebeck coefficient, and similar temperature dependence, to that observed for undoped a-Si:H. In contrast, the addition of nanoparticles in doped a/nc-Si:H thin films leads to a negative Seebeck coefficient (consistent with n-type doping) with a positive temperature dependence, that is, the Seebeck coefficient becomes larger at higher temperatures. The temperature dependence of the thermopower of the doped a/nc-Si:H is similar to that observed in unhydrogenated a-Si grown by sputtering or following high-temperature annealing of a-Si:H, suggesting that charge transport may occur via hopping in these materials.

Hydrogenated Amorphous Silicon Thin Films with Nanocrystalline Silicon Inclusions

2003 ◽  
Vol 762 ◽  
Author(s):  
T. J. Belich ◽  
S. Thompson ◽  
C.R. Perrey ◽  
U. Kortshagen ◽  
C.B. Carter ◽  
...  
Keyword(s):  
Thin Films ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Nanocrystalline Silicon ◽  
Dark Conductivity ◽  
Capacitively Coupled ◽  
Silicon Thin Films ◽  
High Resolution Tem ◽  
Hydrogenated Amorphous ◽  
Deposition Conditions

AbstractThin films of hydrogenated amorphous silicon containing nanocrystalline silicon inclusions (a/nc-Si:H) have been synthesized in an RF capacitively coupled PECVD system using a mixture of hydrogen diluted silane and helium, under deposition conditions at the edge of powder formation within the plasma. High resolution TEM confirms the presence of nanocrystallites as small as 2 nm in these films. Measurements of the optical absorption spectrum using CPM and PDS indicates a broadening of the Urbach slope in the a/nc-Si:H, compared to a-Si:H films, but no appreciable increase in midgap absorption. Despite the deposition conditions for the a/nc-Si:H being very different from those associated with producing optimal quality a-Si:H, the dark conductivity and photoconductivity values, and the sensitivity to light-induced defect creation in the a/nc-Si:H films are comparable to those in a-Si:H.

Electronic Transport in Co-deposited Hydrogenated Amorphous/Nanocrystalline Thin Films

2008 ◽  
Vol 1066 ◽  
Author(s):  
Y. Adjallah ◽  
C. Blackwell ◽  
C. Anderson ◽  
U. Kortshagen ◽  
J. Kakalios
Keyword(s):  
Thin Films ◽  
Amorphous Silicon ◽  
Volume Fraction ◽  
Crystalline Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Nanocrystalline Silicon ◽  
Dark Conductivity ◽  
Mixed Phase ◽  
Bonding Structure ◽  
Hydrogenated Amorphous

ABSTRACTMixed-phase hydrogenated amorphous silicon thin films containing nanocrystalline silicon inclusions have been synthesized in a dual chamber co-deposition system. A PECVD deposition system produces small crystalline silicon particles (3-5 nm diameter) in a flow-through reactor, and injects these particles into a separate capacitively-coupled plasma chamber in which hydrogenated amorphous silicon is deposited. Raman spectroscopy is used to determine the volume fraction of nanocrystals in the mixed phase thin films, while infra-red spectroscopy characterizes the hydrogen bonding structure as a function of nanocrystalline concentration. At a moderate concentration of 5 nm silicon crystallites, the dark conductivity and photoconductivity are consistently found to be higher than in mixed phase films with either lower or higher densities of nanocrystalline inclusions.

Metastable Defect Kinetics in Hydrogen Passivated Polycrystalline Silicon

1994 ◽  
Vol 336 ◽  
Author(s):  
N. H. Nickel ◽  
R. A. Street ◽  
W. B. Jackson ◽  
N. M. Johnson
Keyword(s):  
Temperature Dependence ◽  
Polycrystalline Silicon ◽  
Direct Evidence ◽  
Slow Cool ◽  
Dark Conductivity ◽  
Active Hydrogen ◽  
Thermally Activated ◽  
Rate Dependent ◽  
Si Films ◽  
Metastable Defect

ABSTRACTThe temperature dependence of the dark conductivity, σD, of unhydrogenated and hydrogen passivated polycrystalline silicon (poly-Si) films was Measured. While σD of unhydrogenated poly-Si did not exhibit any influence of thermal treatment prior to the measurement, striking effects were observed in hydrogenated poly-Si films. Below 268 K a cooling-rate dependent metastable change of σD is observed. The dark conductivity increases by more than 8 orders of magnitude. This frozen-in state is metastable: Annealing and a slow cool restore the temperature dependence of the relaxed state. The time and temperature dependence of the relaxation reveal that this process is thermally activated with 0.74 eV. The lack of the quenching metastability in unhydrogenated poly-Si is direct evidence that the metastable changes in σD are due to the formation and dissociation of an electrically active hydrogen complex, in the grain-boundary regions.

Evolution of Structural and Electronic Properties in Boron-doped Nanocrystalline Silicon Thin Films

2007 ◽  
Vol 989 ◽  
Author(s):  
Hyun Jung Lee ◽  
Andrei Sazonov ◽  
Arokia Nathan
Keyword(s):  
Electronic Properties ◽  
Chemical Vapor ◽  
Boron Doping ◽  
Nanocrystalline Silicon ◽  
Dark Conductivity ◽  
Crystalline Fraction ◽  
Silicon Thin Films ◽  
Boron Doped ◽  
Structural And Electronic Properties ◽  
Effective Mobility

AbstractWe report on the boron-doping dependence of the structural and electronic properties in nanocrystalline silicon (nc-Si:H) films directly deposited by plasma- enhanced chemical vapor deposition (PECVD). The crystallinity, micro-structure, and dark conductivity of the films were investigated by gradually varying the ratio of trimethylboron [B(CH3)3 or TMB] to silane (SiH4) from 0.1 to 2 %. It was found that the low level of boron doping (< 0.2 %) first compensated the nc-Si:H material which demonstrates slightly n-type properties. As the doping increased up to 0.5 %, the maximum dark conductivity (ód) of 1.11 S/cm was obtained while high crystalline fraction (Xc) of the films (over 70 %) was maintained. However, further increase in a TMB-to-SiH4 ratio reduced ód to the order of 10-7 S/cm due to a phase transition of the films from nanocrystalline to amorphous, which was indicated by Raman spectra measurements.P-channel nc-Si:H thin film transistors (TFTs) with top gate and staggered source/drain contacts were fabricated using the developed p+ nc-Si:H layer. The fabricated TFT exhibits a threshold voltage (VTp) of -26.2 V and field effective mobility of holes (μp) of 0.24 cm2/V·s.

Growth of Mixed-Phase Amorphous and Ultra Nanocrystalline Silicon Thin Films in the Low Pressure Regime by a VHF PECVD Process

Silicon ◽  
2012 ◽  
Vol 4 (2) ◽  
pp. 127-135 ◽  
Author(s):  
Jhuma Gope ◽  
Sushil Kumar ◽  
Sukhbir Singh ◽  
C. M. S. Rauthan ◽  
P. C. Srivastava
Keyword(s):  
Thin Films ◽  
Nanocrystalline Silicon ◽  
Low Pressure ◽  
Mixed Phase ◽  
Silicon Thin Films ◽  
Pressure Regime
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