Ambipolar Phototransport (μτe = μτh) Observed as an Intrinsic Property of a-SiGe:H

1997 ◽  
Vol 467 ◽  
Author(s):  
Paul Wickboldt ◽  
Dawen Pang ◽  
William Paul ◽  
Joseph H. Chen ◽  
Chih-Chiang Chen ◽  
...  
Keyword(s):  
Gas Phase ◽  
Diffusion Length ◽  
Dopant Concentration ◽  
Intrinsic Property ◽  
Dark Conductivity ◽  
Air Leak ◽  
Cathodic Deposition ◽  
Conductivity Activation Energy ◽  
Unusual Behavior ◽  
Film Properties

ABSTRACTA study is presented of a series of high quality PECVD a-Si0.33Ge0.67 films, produced by cathodic deposition, in which small concentrations of PH3, B2H6 or air impurities were added during deposition. The quantum efficiency-mobility-lifetime product (ημτ) increases, and the ambipolar diffusion length (Lamb) decreases monotonically with dopant concentration for both PH3 and B2H6. This result is strong evidence that for these films neither photocarrier is dominant (μτe= μτh) at zero doping. This result is very different from what has been typically observed by other researchers, that the electron is the dominant photocarrier for undoped a-SiGe:H.Drive level capacitance (DLC) measurements of these alloys show an unusual behavior of being temperature-independent, and the dark conductivity activation energy is maximum for zero doping. It is proposed that all of these unusual properties are due to the unusually low impurity concentration of these films, and that these properties are, in fact, the intrinsic properties for a-SiGe:H alloys. To verify this, films were prepared with a calibrated and controlled air leak introduced during deposition. As the air leak was increased, the film properties changed to typical behavior. Even for air concentrations as low as 2 ppm (gas phase), the transport measurements showed changes consistent with a shift in the Fermi level toward the conduction band.

Possible Origin of Large Response Times and Ambipolar Diffusion Lengths in Hot-Wire-Cvd Silicon Films

1998 ◽  
Vol 507 ◽  
Author(s):  
R. Schwarz ◽  
T. Múrias ◽  
J.P. Conde ◽  
P. Brogueira ◽  
V. Chu
Keyword(s):  
Response Time ◽  
Diffusion Length ◽  
Response Times ◽  
Chemical Vapor ◽  
Dark Conductivity ◽  
Ambipolar Diffusion ◽  
Silicon Films ◽  
Hot Wire ◽  
Film Properties ◽  
Positive Effect

ABSTRACTWe measured the response time zR and the ambipolar diffusion length Lamb in amorphous (a-Si:H) and microcrystalline silicon films (μ-Si:H) prepared by hot-wire chemical vapor deposition (HW-CVD). The response times in the amorphous and microcrystalline HW films were larger by factors of 100 and 1000, respectively, than in standard PE-CVD a-Si:H films (1-2 μs). The ambipolar diffusion length of the HW-CVD films was about twice as large as in conventional glow-discharge films. Strong doping of microcrystalline HW films with trimethylboron (TMB) led to a reduction of the response time. The results hint to a positive effect of the compact microstructure of HW-CVD films. We suggest the dark conductivity activation energy, Eact, and response time, τR, to be used as suitable parameters to describe optoelectronic film properties.

Electronic Transport Properties of a-Si:H,F/a-Si,Ge:H,F Superlattices

1987 ◽  
Vol 95 ◽  
Author(s):  
J. P. Conde ◽  
S. Aljishi ◽  
D. S. Shen ◽  
V. Chu ◽  
Z E. Smith ◽  
...  
Keyword(s):  
Barrier Layer ◽  
Electronic Transport ◽  
Thermal Emission ◽  
Parallel Transport ◽  
Dark Conductivity ◽  
Alloy Layer ◽  
Conductivity Activation Energy ◽  
Superlattice Structures ◽  
Deposition Conditions ◽  
Extract Information

AbstractWe study the dark conductivity σd, dark conductivity activation energy Ea and photoconductivity σph of a-Si:H,F/a-Si,Ge:H,F superlattices both perpendicular and parallel to the plane of the layers. In parallel transport, both the σph and σd are dominated by the alloy layer characteristics with the superposition of carrier confinement quantum effects. In perpendicular transport, the σd shows an interplay of quantum mechanical tunneling through the barriers and of classical thermal emission over the barrier layer and the σph is controlled by the decreasing absorption by the silicon barrier layer as the optical gap Eopt of the structure decreases.We also found that the multilayer structure allows to grow lower gap a-Si,Ge:H,F alloys than achievable under the same deposition conditions for bulk materials. This stabilizing effect allowed us to study low-gap superlattice structures and extract information about these very low gap (<1.2 eV) a- Si,Ge:H,F alloys.

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.

Effect of electron bombardment during deposition of cadmium sulfide films using a hot-wall technique

1985 ◽  
Vol 63 (6) ◽  
pp. 712-715 ◽  
Author(s):  
A. Haque ◽  
A. E. Dixon ◽  
D. E. Brodie
Keyword(s):  
Dark Conductivity ◽  
Electron Bombardment ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
Film Properties ◽  
X Ray ◽  
Glass Substrates ◽  
Hall Effect Measurements ◽  
Decoration Technique ◽  
Cds Films

The use of electron-beam irradiation combined with a hot-wall technique during deposition of CdS films is described. CdS films 2–10 μm thick were thermally deposited with and without electron bombardment on glass substrates using a hot-wall technique under a pressure greater than 1 × 10−6 Torr (1 Torr = 133.3 Pa). Film properties were studied using low-angle X-ray diffraction, scanning electron microscopy, optical microscopy using a chemical decoration technique, Hall-effect measurements, and temperature-dependent dark conductivity. The surface grain size varied from 2 to 5 μm and films were brownish orange with a smoky appearance.

The Effect of Temperature and Si Concentration on the Mixing of AlAs/GaAs Superlattices

1986 ◽  
Vol 77 ◽  
Author(s):  
Ping Mei ◽  
H. W. Yoon ◽  
T. Venkatesan ◽  
S. A. Schwarz ◽  
J. P. Harbison
Keyword(s):  
Activation Energy ◽  
Molecular Beam ◽  
Secondary Ion Mass Spectrometry ◽  
Diffusion Length ◽  
Dopant Concentration ◽  
Effect Of Temperature ◽  
Surface Layers ◽  
Near Surface ◽  
Depth Profiles ◽  
Secondary Ion

ABSTRACTThe intermixing of AlAs/GaAs superlattices has been investigated as a function of Si concentration following anneals in the range of 500 to 900 C. The superlattice samples were grown by molecular beam epitaxy(MBE) and the near surface layers were doped with silicon at concentrations of 2×10 to 5×1018 cm-3. Si and Al depth profiles were measured with secondary ion mass spectrometry (SIMS).The diffusion length and activation energy of Al as a function of silicon dopant concentration are derived from the SIMS data. In the temperature range studied an activation energy for the Al interdiffusion of -4eV is observed with the diffusion coefficients increasing rapidly with Si concentration.

A Low Temperature Plasma-Assisted Deposition Process for Microcrystalline Thin Film Transistors, TFTS

1994 ◽  
Vol 336 ◽  
Author(s):  
S.S. He ◽  
G. Lucovsky
Keyword(s):  
Low Temperature ◽  
Deposition Process ◽  
Dark Conductivity ◽  
Low Temperature Plasma ◽  
Conductivity Activation Energy ◽  
Temperature Plasma ◽  
Threshold Voltages ◽  
Gate Structure ◽  
Saturation Region ◽  
Effective Channel

ABSTRACTThe drive-current of low-temperature (∼300°C) deposited TFTs has been increased by replacing the a-Si:H channel, and source and drain materials with μc-Si. Lightly B2H6 doped, near-intrinsic μc-Si has been used as the channel layer of the TFTs, and n+ μc-Si was used for the source and drain contacts. The compensation of intrinsic defects in the undoped μc-Si by boron doping increases the dark conductivity activation energy from -0.35 eV to 0.8 eV. TFTs were fabricated in a bottom gate structure, and required an H2 plasma treatment to produce devices with effective channel mobilities of -6.8 cm2/V-s and threshold voltages of -3.7 V in the saturation region.

Deposition of Device Quality Amorphous Silicon by Hot-Wire CVD

1997 ◽  
Vol 467 ◽  
Author(s):  
K. F. Feenstra ◽  
C. H. M. Van Der Werf ◽  
E. C. Molenbroek ◽  
R. E. I. Schropp
Keyword(s):  
Growth Rate ◽  
Electrical Properties ◽  
Amorphous Silicon ◽  
Diffusion Length ◽  
Hydrogenated Amorphous Silicon ◽  
Dark Conductivity ◽  
Hot Wire ◽  
Tungsten Filaments ◽  
Wire Method ◽  
Hydrogenated Amorphous

ABSTRACTIn this paper we present the results of the optimization of hydrogenated amorphous silicon films deposited by the hot-wire method in a larger area system. Using a two-wire design, we succeeded in depositing films that exhibit uniform electrical properties over the whole 4” x 4” Corning 7059 glass substrate. At a substrate temperature of 430 °C. and a pressure of 20 μbar we obtained a growth rate of ∼2 nm/s. The temperature of the tungsten filaments was kept at 1850 °C. The values for the photoconductivity and dark conductivity were 8.9×10−6 S/cm and 1.6×10−10 S/cm respectively, whereas the ambipolar diffusion length, as measured with the Steady-State Photocarrier Grating technique (SSPG), amounted to 145 nm. This value is higher than for our device quality glow-discharge (GD) films, which yield devices with efficiencies higher than 10%. The hydrogen content was 9.5%.We report on the density-of-states (DOS) distribution in the films, which was measured with the techniques of Thermally Stimulated Conductivity (TSC) and Constant Photocurrent Method (CPM). Furthermore, we describe the behavior of the electrical properties on light-induced degradation. Finally, we incorporated these films in solar cells, using conventional GD doped layers. Preliminary SS/n-i-p/ITO devices yielded efficiencies in excess of 3% under 100 mW/cm2 AM 1.5 illumination. Further work concerning the optimization of the interfaces is in progress.

Properties of amorphous silicon-germanium films and devices deposited at higher growth rates

2002 ◽  
Vol 715 ◽  
Author(s):  
Yong Liu ◽  
Vikram L. Dalal
Keyword(s):  
Amorphous Silicon ◽  
Growth Rates ◽  
Silicon Germanium ◽  
Urbach Energy ◽  
Dark Conductivity ◽  
Film Properties ◽  
Ecr Plasma ◽  
Device Properties ◽  
Amorphous Silicon Germanium ◽  
Defect Densities

AbstractWe report on the growth and properties of amorphous Silicon-Germanium [a–(Si,Ge):H] films and devices fabricated at growth rates of ∼ 5 Å/sec using a remote ECR plasma growth process. The films and devices were made using mixtures of germane and silane along with dilution with hydrogen and helium. The addition of He to the gas mixture significantly increased the growth rates. It was found that hydrogen was always necessary in order to achieve the best film and device properties. Films and devices were made across the entire bandgap range, from a-Si to a-Ge. High ratios of photo/dark conductivity and low values of Urbach energy ( > 50 meV) indicate good film properties. The defect densities were measured using space charge limited current techniques. The defect densities were in the range of 1-2 x 10 16/cm 3 –eV, about 5 times higher than for a-Si:H. Electron mobility-lifetime products were measured and found to be in the range of 2-4 x 10-7 cm2/V, even for low gap materials (1.35 eV). Single and graded gap devices were fabricated in these materials. Device fill factors of ∼ 70% were obtained in graded gap devices.

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