Hopping of Electrons in Hybrid Band Tails of a-Si1-xGex:H

1990 ◽  
Vol 192 ◽  
Author(s):  
C. E. Nebel ◽  
H. C. Weller ◽  
G.H. Bauer
Keyword(s):  
Conduction Band ◽  
Alloy Composition ◽  
Time Of Flight ◽  
State Density ◽  
Mobility Edge ◽  
Medium Temperature ◽  
Tail State ◽  
Current Decay ◽  
Thermally Activated ◽  
Multiple Trapping

ABSTRACTThe thermalization of electrons in the medium temperature range (120K ≤ T ≤ 200K) is investigated by time-of-flight experiments on a-SiGe:H mim structures. The evaluation of the pre-transit current decay reveals a dual slope characteristic which reflects an initial hopping down (I ∼ t−1) followed by a thermally activated (I ∼ t−p 0 < p < 1) process. The transition time from hopping down to multiple trapping sensitively depends on temperature and alloy composition. The experimentally deduced features can be explained by the increased tail state density at the conduction band mobility edge of a-SiGe:H samples compared to a-Si:H.

Electron Transport and Conduction-Band-Tail States in a-Si:H Deposited with a Remote Hydrogen Plasma

1993 ◽  
Vol 297 ◽  
Author(s):  
C.E. Nebel ◽  
R.A. Street ◽  
N.M. Johnson ◽  
J. Walker
Keyword(s):  
Electron Transport ◽  
Conduction Band ◽  
Defect Density ◽  
Plasma Deposition ◽  
Hydrogen Plasma ◽  
Band Tail ◽  
Mobility Edge ◽  
Characteristic Energy ◽  
Tail State ◽  
Electron Transport Properties

Electron transport properties of a-Si:H prepared in a remote hydrogen plasma deposition reactor (RHPD) at TD = 400°C were investigated in the temperature regime 110 K ≤ T ≤ 300 K by time-of-flight and post-transit spectroscopy experiments. Based on these data the conduction-band-tail state distribution was calculated. In the energy range 85 meV ≤ Ec- E ≤ 350 meV below the mobility edge Ec the tail is well described by an exponential distribution with a characteristic energy of ≃ 21 meV. Deeper in the mobility gap (Ec-E > 350 meV) the tail smoothly passes over into the defect density which is approximately six orders of magnitude smaller than at the mobility edge. Comparisons with data deduced on conventionally prepared a-Si:H (RF-, DC-glow discharge) at TD = 230 °C show that electron transport and the conduction band tail of the RHPD material are comparable.

scholarly journals Localised States in Microcrystalline Silicon Photovoltaic Structures Studied by Post-Transit Time-of-Flight Spectroscopy

2003 ◽  
Vol 762 ◽  
Author(s):  
Steve Reynolds ◽  
Vladimir Smirnov ◽  
Charlie Main ◽  
Reinhard Carius ◽  
Friedhelm Finger
Keyword(s):  
Transit Time ◽  
Carrier Transport ◽  
Time Of Flight ◽  
Microcrystalline Silicon ◽  
Mobility Edge ◽  
Cell Structures ◽  
Multiple Trapping ◽  
Multiple Trapping Model ◽  
Localised States ◽  
Time Of Flight Spectroscopy

AbstractPost-transit time-of-flight spectroscopy has been used to study the density of states distribution in hot-wire CVD microcrystalline silicon pin solar cell structures. For an absorber layer Raman scattering intensity ratio ICRS of 0.4 or less, behaviour consistent with multiple-trapping carrier transport is observed and may be interpreted in terms of a conduction-band tail of some 18 meV slope plus a broad defect bump of order 1017 cm-3 centered at 0.55 eV relative to the mobility edge. As ICRS is increased beyond 0.4, the temperature-dependence of the photocurrent transient becomes inconsistent with multiple-trapping and above 0.6 the decays are almost temperature-independent. By comparing data taken at 300 K, it may be inferred from the multiple-trapping model that localised states between 0.35 and 0.5 eV are associated with the presence of columns or clusters of nanocrystals and those deeper than 0.5 eV with the amorphous tissue. Results are compared with previous work on coplanar and sandwich structures.

Electron Time-of-Flight Measurements in a-Si1−XCX:H

1993 ◽  
Vol 297 ◽  
Author(s):  
Qi Wang ◽  
Eric A. Schiff ◽  
Yuan-Min Li
Keyword(s):  
Time Of Flight ◽  
Drift Mobility ◽  
Electron Drift ◽  
Temperature Dependent ◽  
Thermally Activated ◽  
Multiple Trapping ◽  
Silicon Carbon ◽  
Solar Conversion ◽  
Hydrogenated Amorphous ◽  
Electron Drift Mobility

We have measured the temperature-dependent electron drift mobility in a series of hydrogenated amorphous silicon-carbon alloys using time-of-flight. The specimens were prepared at Solarex using the gas mixture procedures which have recently yielded improvement in the solar conversion efficiency of wide bandgap solar cells. As the bandgap increased due to carbon alloying the electron drift mobility decreased by as much as a factor 30 at some temperatures. The cells with 1.75 eV, 1.81 eV, and 1.87 eV bandgaps had thermally activated drift mobilities over the temperature range 120 K ‐ 200 K; this is associated with simple multiple-trapping behavior. Specimens with bandgaps near 1.90 eV did not have simply activated drift mobilities; we have not accounted for this behavior, but it suggests that the bandtail broadening description used to account for the effects of germanium alloying on the electron drift mobility may not be simply applicable to carbon alloying.

Variable Temperature Measurement on Operating Pentacene-Based OTFT

2008 ◽  
Vol 1091 ◽  
Author(s):  
Hung-Keng Chen ◽  
Po-Tsun Liu ◽  
Ting-Chang Chang ◽  
S.-L. Shy
Keyword(s):  
Conduction Mechanism ◽  
Variable Temperature ◽  
Electrical Measurement ◽  
Isokinetic Temperature ◽  
Trap States ◽  
Band Tail ◽  
Thermally Activated ◽  
Multiple Trapping ◽  
Higher Temperature ◽  
Release Model

AbstractVariable temperature electrical measurement is well-established and used for determining the conduction mechanism in semiconductors. There is a Meyer¡VNeldel relationship between the activation energy and the prefactor with a Meyer¡VNeldel energy of 30.03 meV, which corresponds well with the isokinetic temperature of about 350 K. Therefore, the multiple trapping and release model is properly used to explain the thermally activated phenomenon. By the method, an exponential distribution of traps is assumed to be a better representation of trap states in band tail. Samples with higher temperature during measurement are observed to show better mobility, higher on-current and lower resistance, which agree well with the multiple trapping and release model proposed to explain the conduction mechanism in pentacene-based OTFTs.

Band Tailing and Transport in a-SiGe:H-Alloys

1989 ◽  
Vol 149 ◽  
Author(s):  
G. H. Bauer ◽  
C. E. Nebel ◽  
M. B. Schubert ◽  
G. Schumm
Keyword(s):  
Raman Scattering ◽  
Valence Band ◽  
State Density ◽  
Conduction Band Edge ◽  
Compound Structure ◽  
Tail State ◽  
Photocurrent Spectroscopy ◽  
Transport Studies ◽  
Small X ◽  
Band Tailing

ABSTRACTOptical and transport studies of both cb- and vb-tail states in a-Si1−xGex:H such as subband absorption (PDS), instationary photocurrent experiments (TOF, PTS) for electrons and holes, Modulated Photocurrent Spectroscopy (MPS), and Raman scattering have been performed. The main consequences of Ge-alloying into the a-Si:H network are i) an increase in cb-tail state density at the conduction band edge and in the exponential cb- tail even for small x (O<x<0.3), accompanied by ii) a rise in deep cb-tail and midgap states which to some extent can be reduced by appropriate deposition methods; iii) at the valence band side up to x≈0.3 the tail seems not to be affected at all and for 0.3<x<0.9 the vb-tail obviously can be kept similar to that of a-Si:H (Evo≈(50–60) meV). Halfwidths of Raman TO-like modes point to the existence of a rigid Si-network in O<x<0.3 in which Ge is incorporated and to a transition at x>0.35 into a Si-Ge compound structure with maximum disorder at x≈0.5.

Photoconductivity study of amorphous CdTe

1977 ◽  
Vol 55 (3) ◽  
pp. 265-269 ◽  
Author(s):  
R. T. S. Shiah ◽  
D. E. Brodie ◽  
P. C. Eastman
Keyword(s):  
Light Intensity ◽  
Fermi Level ◽  
Conduction Band ◽  
Localized States ◽  
Effective Density ◽  
Transition Rates ◽  
Mobility Edge ◽  
Energy Parameters ◽  
Density Of Localized States ◽  
Mobility Gap

Photoconductivity measurements as a function of light intensity and temperature for amorphous CdTe are analyzed on the basis of the Mott and Davis model and some ideas of the Arnoldussen, Bube, Fagen, and Holmberg model. Energy parameters within the mobility gap of amorphous CdTe were evaluated. The effective density of localized states is found to be 1017and 1019 per cm3 per eV near the valence and conduction band edges respectively. The localized-to-localized recombination transition rates are also given. The dark Fermi level is found to be 0.54 eV above the valence mobility edge. Localized states extend into the mobility gap 0.37 eV from the valence mobility edge. These results are consistent with earlier measurements by Ng, Webb, and Brodie.

Amorphous Silicon/Silicon Germanium Alloy Superlattices with Periods from 1 to 100 NM

1989 ◽  
Vol 149 ◽  
Author(s):  
J. P. Conde ◽  
V. Chu ◽  
S. Wagner
Keyword(s):  
Silicon Germanium ◽  
Hole Mobility ◽  
State Density ◽  
Hole Transport ◽  
Barrier Thickness ◽  
Tail State ◽  
Recombination Lifetime ◽  
Germanium Alloy ◽  
The Individual ◽  
Silicon Silicon

ABSTRACTThe electron and hole transport perpendicular to the plane of the layers in a-Si:H, F/a-Si, Ge:H, F multilayers is analyzed. We measure the electron dark conductivity σd and its activation energy Ea, d, the photo conductivity σph and its exponent γ, the electron and hole mobility-deep trapping lifetime (μτd)e, h and the hole mobility-recombination lifetime (μτr)h. We identify three regions of barrier thickness ds with very different transport properties: (a) ds≲50Å, dominated by tunnelling between quantum confined states in the bottom of the wells; (b) 50Å ≲ds≲200Å, in which the well acts as the provider of an extra, controllable tail state density; and (c) ds≳200Å, where the individual layers are essentially decoupled.

Improved Interface Trap Density Close to the Conduction Band Edge of a-Face 4H-SiC MOSFETs Revealed Using the Charge Pumping Technique

2017 ◽  
Vol 897 ◽  
pp. 143-146 ◽  
Author(s):  
Gerald Rescher ◽  
Gregor Pobegen ◽  
Thomas Aichinger ◽  
Tibor Grasser
Keyword(s):  
Silicon Carbide ◽  
Conduction Band ◽  
State Density ◽  
Trap Density ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Power Mosfets ◽  
Charge Pumping ◽  
Wide Range ◽  
Reduced Mobility

We study the interface properties of 4H silicon carbide Si-face 0001 and a-face 11220 power MOSFETs using the charge pumping technique. MOSFETs produced on the a-face show a higher electron mobility than Si-face devices, although their charge pumping signal is 5 times higher, indicating a higher interface/border trap density. We show the main contribution to the interface/border trap density on a-face devices originates from deep states in a wide range around midgap, whereas Si-face devices show a higher and exponentially increasing interface/border state density close to the conduction band edge of 4H silicon carbide, resulting in reduced mobility.

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