The Meyer-Neldel Rule in Conductivity of Microcrystalline Silicon

2002 ◽  
Vol 715 ◽  
Author(s):  
Sanjay K. Ram ◽  
Satyendra Kumar ◽  
P. Rocai Cabarrocas
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Film Thickness ◽  
Fermi Level ◽  
Carrier Transport ◽  
Dark Conductivity ◽  
Localized States ◽  
Microcrystalline Silicon ◽  
Thermally Activated ◽  
Density Of Localized States

AbstractThe dark conductivity (σd) has been measured from 300 to 440K on undoped hydrogenated microcrystalline silicon (μc-Si:H) films having different thicknesses. The carrier transport is found to be thermally activated with single activation energy (Ea) in all the samples. The Ea increases as the film thickness decreases. At the same time logarithmic of dark conductivity prefactor (σo) is found to follow a linear relation with activation energy, known as the Meyer-Neldel rule (MNR). Results are explained in terms of increased degree of disorder in thinner samples. Thus change in Ea with the film thickness is directly related to the density of localized states at the Fermi level in grain boundary (GB). Therefore varying the film thickness and, hence, the exponential density of states induces a statistical shift of Fermi level which gives rise to the observed MNR.

Defect states in amorphous Ge2Sb2Te5 phase change material

2014 ◽  
Vol 92 (7/8) ◽  
pp. 619-622
Author(s):  
N. Qamhieh ◽  
S.T. Mahmoud ◽  
A.I. Ayesh
Keyword(s):  
Fermi Level ◽  
Energy Gap ◽  
Continuous Distribution ◽  
Dark Conductivity ◽  
Localized States ◽  
Defect States ◽  
Thermally Activated ◽  
Level Shifts ◽  
Gap States ◽  
Change Material

Steady-state photoconductivity measurements in the temperature range 100–300 K on amorphous Ge2Sb2Te5 thin film prepared by dc sputtering are analyzed. The dark conductivity is thermally activated with a single activation energy that allocates the position of the Fermi level approximately in the middle of the energy gap relative to the valance band edge. The temperature dependence of the photoconductivity ensures the presence of a maximum normally observed in chalcogenides with low- and high-temperature slopes, which predict the location of discrete sets of localized states (recombination levels) in the gap. The presence of these defect states close to the valence and conduction band edges leaves the quasi Fermi level shifts in a continuous distribution of gap states at high temperatures, as evidenced from the γ values of the lux–ampere characteristics.

Carrier Transport Through Grain Boundaries in Hydrogenated Microcrystalline Silicon

1992 ◽  
Vol 283 ◽  
Author(s):  
S. Grebner ◽  
F. Wang ◽  
R. Schwarz
Keyword(s):  
Activation Energy ◽  
Grain Boundaries ◽  
Carrier Transport ◽  
Structural Information ◽  
Dark Conductivity ◽  
Microcrystalline Silicon ◽  
X Ray ◽  
Fermi Level Pinning ◽  
X Ray Scattering ◽  
Three Phase

ABSTRACTTo analyse the influence of the grain boundaries (gb) on the transport of carriers in hydrogenated microcrystalline silicon (μC-Si:H) the ambipolar diffusion length (LLMB) was measured by SSPG. In addition, the films were characterised by photo-conductivity, dark conductivity activation energy, Urbach energy (determined by CPM), hydrogen effusion, Raman spectroscopy, X-ray scattering and optical transmission.The sample series was prepared by PECVD of SiH4 diluted with increasing H2 content. Taking the structural information by Raman spectra and X-ray into account, we explain our optical and activation energy measurements within a three-phase-model (amorphous phase, crystalline phase, gb) and a Fermi level pinning in μc-Si:H.

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 %.

Density of Deep Bandgap States in Amorphous Silicon From the Temperature Dependence of Thin Film Transistor Current

1994 ◽  
Vol 336 ◽  
Author(s):  
T. Globus ◽  
H. C. Slade ◽  
M. Shur ◽  
M. Hack
Keyword(s):  
Thin Film ◽  
Activation Energy ◽  
Amorphous Silicon ◽  
Conduction Band ◽  
Energy Gap ◽  
Localized States ◽  
Flat Band ◽  
Gate Bias ◽  
Density Of Localized States ◽  
Wide Range

ABSTRACTWe have measured the current-voltage characteristics of amorphous silicon thin film transistors (a-Si TFTs) over a wide range of temperatures (20 to 160°C) and determined the activation energy of the channel current as a function of gate bias with emphasis on the leakage current and subthreshold regimes. We propose a new method for estimating the density of localized states (DOS) from the dependence of the derivative of activation energy with respect to gate bias. This differential technique does not require knowledge of the flat-band voltage (VFB) and does not incorporate integration over gate bias. Using this Method, we have characterized the density of localized states with energies in the range 0.15–1.2 eV from the bottom of the conduction band and have found a wide peak in the DOS in the range of 0.8–0.95 eV below the conduction band. We have also observed that the DOS peak in the lower half of the bandgap increases in magnitude and shifts towards the conduction band as a result of thermal and bias stress. We also measured an overall increase in the DOS in the upper half of the energy gap and an additional peak, centered at 0.2 eV below the conduction band, which appear due to the applied stress. These results are in qualitative agreement with the defect pool Model [1,2].

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.

Gated Nonlinear Transport in Organic Thin Film Transistors

2003 ◽  
Vol 771 ◽  
Author(s):  
Behrang H. Hamadani ◽  
Douglas Natelson
Keyword(s):  
Field Effect Transistors ◽  
Organic Thin Film Transistors ◽  
Localized States ◽  
Nonlinear Transport ◽  
Organic Thin Film ◽  
Thermally Activated ◽  
Density Of Localized States ◽  
Highly Nonlinear ◽  
Channel Lengths ◽  
Energy Dependent

AbstractCharge transport in poly(3-hexylthiophene) field effect transistors has been studied in a series of devices with channel lengths ranging from 3 μm down to 200 nm over a broad range of temperatures and gate voltages. We report gate-modulated highly nonlinear transport at temperatures below ∼200 K that is consistent in form with a Poole-Frenkel-like hopping mechanism in the space charge limited current regime. There is also consistency between this behavior and the hypothesis that density of localized states is strongly energy dependent. We also observe what appears to be a crossover from thermally activated to nonthermal hopping below 30 K.

Light-Induced Metastable Changes in a-SiSx:H

1995 ◽  
Vol 377 ◽  
Author(s):  
S. L. Wang ◽  
P. C. Taylor
Keyword(s):  
Activation Energy ◽  
Temperature Dependence ◽  
Annealing Temperature ◽  
Dark Conductivity ◽  
Sulfur Concentration ◽  
Thermally Activated ◽  
Dramatic Difference ◽  
The Creation ◽  
Sulfur Donor

ABSTRACTMetastable light-induced increases in the dark conductivities of a-SiSx:H alloys are explained as photo-activation of hydrogen-passivated sulfur donor sites. For a sulfur concentration (sulfur-to-silicon ratio) of 5.6 × 103 the excess dark conductivity as a function of illumination temperature is thermally activated with an activation energy of 0.72 eV. When the sulfur concentration is 3.3 × 102, the temperature dependence is very weak. This dramatic difference in the temperature dependence of the creation of increased dark conductivity is explained by a lowering of the annealing temperature for the metastable changes as the sulfur concentration increases. We discuss the influence of this new metastability on the possibility of obtaining more stable films.

scholarly journals Перенос заряда в планарных структурах на основе халькогенидной системы (As-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=-)-=SUB=-100-x-=/SUB=-Bi-=SUB=-x-=/SUB=-

2019 ◽  
Vol 53 (12) ◽  
pp. 1664
Author(s):  
Р.А. Кастро ◽  
С.Д. Ханин ◽  
А.П. Смирнов ◽  
А.А. Кононов
Keyword(s):  
Charge Transfer ◽  
Disordered Systems ◽  
Thin Layers ◽  
Localized States ◽  
Cbh Model ◽  
Thermally Activated ◽  
Transfer Processes ◽  
Density Of Localized States ◽  
Increasing Temperature ◽  
Thermally Activated Process

AbstractThe results of investigating charge-transfer processes in thin layers of a vitreous system (As_2Se_3)_100 – _ x Bi_ x are presented. A power-law dependence of the conductivity on the frequency and a decrease in the exponent s with increasing temperature are found. Charge transfer is a thermally activated process with two regions in the temperature dependence of the conductivity with the activation energies E _1 = 0.12 ± 0.01 eV and E _2 = 0.23 ± 0.01 eV, respectively. The results are explained in terms of the correlated barrier hopping (CBH) model of hopping conductivity in disordered systems. The main microparameters of the system are calculated: the density of localized states ( N ), the hopping length ( R _ω), and the largest height of the potential barrier ( W _ M ).

Metastable Changes in the Photoconductive Properties of Microcrystalline Silicon Upon Heat Treatment

2005 ◽  
Vol 862 ◽  
Author(s):  
R. Brüggemann
Keyword(s):  
Heat Treatment ◽  
Fermi Level ◽  
Carrier Mobility ◽  
Minority Carrier ◽  
Dark Conductivity ◽  
Effective Density ◽  
Ambient Conditions ◽  
Microcrystalline Silicon ◽  
Treatment Procedures ◽  
Minority Carrier Mobility

AbstractWe demonstrate that metastable changes or instabilities in the dark conductivity of microcrystalline silicon upon heat treatment and ambient conditions, which have been reported in the literature, are accompanied by changes in the photoconductivity or the majority-carrier mobility-lifetime product. The minority-carrier mobility-lifetime product and sub-gap absorption appear to be much less affected by different heat treatment procedures and ambient conditions. The observations can be related to Fermi-level induced change in defect occupancy by which the effective density of recombination centres is reduced for electrons but remains the same for holes. Minority carrier properties seem to be better suited as an indicator for sample quality and for comparison of microcrystalline silicon samples from different laboratories.

Transient photoconductivity measurements on halogenated a-Se1−x Tex photoconductors

1989 ◽  
Vol 67 (11) ◽  
pp. 1053-1064 ◽  
Author(s):  
S. O. Kasap
Keyword(s):  
Activation Energy ◽  
Electron Transport ◽  
Field Dependence ◽  
Drift Mobility ◽  
Hole Transport ◽  
Localized States ◽  
Zero Field ◽  
Thermally Activated ◽  
Transient Photoconductivity ◽  
Energy Location

Time-of-flight (TOF) transient photoconductivity measurements, as functions of temperature and applied field, were carried out on chlorinated a-Se1−x Tex (x < 0.1) chalcogenide semiconductor films to study the nature of charge transport in these commercially important xerographic alloys. The films were prepared by conventional vacuum-deposition techniques and were typically 60–70 μm thick. The TOF hole drift mobility was found to follow a power-law field dependence of the manner μh ~ Fn with the index n increasing with Te and Cl additions as well with decreasing temperature. At the highest fields the drift mobility increased sharply with the applied field. The strong field dependence became more pronounced as the temperature was decreased. TOF drift mobility measurements, as a function of temperature at various applied fields, indicated a thermally activated hole-transport process with a well-defined but field-dependent mobility activation energy, which exhibited an approximately linear field dependence, similar to the mobility activation energy reported for doped a-As2Se3. The zero-field extrapolated activation energy, Eμ0, was about ~ 0.43 eV for the whole range of compositions investigated from x ≈ 0.02 to 0.09, and for the Cl additions in the ~ 100 at. ppm range. Two possible interpretations are discussed. The first involves Te-or Cl-introduced shallow defects that result in a distinct feature on the density of localized states peaking at around ~ 0.43 eV above Ev. It is assumed that the the conductivity mobility in this model remains to represent microscopic transport via extended states as in pure a-Se, i.e., μ0 ~ T−n with n ≈ 1. The other possibility is that increased disorder, as a result of alloying with Te or Cl addition, causes the basic microscopic mobility to become thermally activated owing to hopping in the band-tail states with a hop activation energy of ~ 0.14 eV. It is assumed that the energy location of the shallow-hole traps at ~ 0.29 eV above Ev remains reasonably unaffected, but the energy width and the concentration of native defects controlling the mobility are modified. The latter model is essentially a trap-controlled hopping transport. The present TOF measurements could not conclusively infer one model over the other. There was no observable electron transport in chlorinated a-Se1−x Tex films, whereas in unhalogenated a-Se1−x Tex films the electron-drift mobility decreased with the Te content and exhibited a stronger power-law field dependence. The TOF electron photocurrents were highly dispersive and the drift mobility – temperature data indicated a thermally activated charge-transport process with a well-defined but field-dependent mobility activation energy. The zero-field activation energy was ~ 0.49 eV, which is ~ 0.14 eV higher than that for electron transport in pure a-Se. The two models discussed for hole transport may also be applied to electron transport. It is suggested that the Te addition modifies the already present defect population leaving their energy location below Ec unchanged so that the increase in the mobility activation energy of ~ 0.14 eV corresponds to the hop activation energy of electrons in the band-tail localized states.

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