Thin-Film Phototransistor with nc-Si:H/a-Si:H Bilayer Channel

2012 ◽  
Vol 1426 ◽  
pp. 205-210
Author(s):  
Y. Vygranenko ◽  
A. Sazonov ◽  
M. Fernandes ◽  
M. Vieira ◽  
A. Nathan
Keyword(s):  
Thin Film ◽  
Optical Sensors ◽  
Spectral Response ◽  
Chemical Vapor ◽  
Nanocrystalline Silicon ◽  
Light Level ◽  
Transport Layer ◽  
Photon Flux ◽  
Flat Panel Display ◽  
Threshold Voltage Shift

ABSTRACTThere is significant interest in optical sensors whose fabrication process is fully compatible with existing flat panel display thin film transistor (TFT) technology. Here, we report a field-effect phototransistor with a channel comprising a thin nanocrystalline silicon (nc-Si:H) transport layer and a thicker hydrogenated amorphous silicon (a-Si:H) absorption layer. The implementation of nc-Si:H layer improves device stability in comparison with a-Si:H phototransistors, resulting in reduced threshold voltage shift. Semiconductor and dielectric layers were deposited by radio-frequency plasma enhanced chemical vapor deposition at 280°C. The device characterization included the dark and light transfer characteristics, spectral-response and dynamic measurements. The external quantum efficiency was measured as a function of incident photon flux at different biasing conditions. The phototransistor with channel length of 24 microns and photosensitive area of 1.4 mm2shows an off-current of about 1 pA, and photo-conductive gain up to 200 at low incident intensities. Thus, the results demonstrate the feasibility of the phototransistor for low light level detection.

scholarly journals Versatility of Nanocrystalline Silicon Films: from Thin-Film to Perovskite/c-Si Tandem Solar Cell Applications

Coatings ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 759
Author(s):  
Luana Mazzarella ◽  
Anna Morales-Vilches ◽  
Lars Korte ◽  
Rutger Schlatmann ◽  
Bernd Stannowski
Keyword(s):  
Thin Film ◽  
Solar Cells ◽  
Carrier Transport ◽  
Silicon Oxide ◽  
Short Circuit ◽  
Chemical Vapor ◽  
Nanocrystalline Silicon ◽  
Silicon Films ◽  
Two Phase ◽  
Nanocrystalline Silicon Films

Doped hydrogenated nanocrystalline (nc-Si:H) and silicon oxide (nc-SiOx:H) materials grown by plasma-enhanced chemical vapor deposition have favourable optoelectronic properties originated from their two-phase structure. This unique combination of qualities, initially, led to the development of thin-film Si solar cells allowing the fabrication of multijunction devices by tailoring the material bandgap. Furthermore, nanocrystalline silicon films can offer a better carrier transport and field-effect passivation than amorphous Si layers could do, and this can improve the carrier selectivity in silicon heterojunction (SHJ) solar cells. The reduced parasitic absorption, due to the lower absorption coefficient of nc-SiOx:H films in the relevant spectral range, leads to potential gain in short circuit current. In this work, we report on development and applications of hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) from material to device level. We address the potential benefits and the challenges for a successful integration in SHJ solar cells. Finally, we prove that nc-SiOx:H demonstrated clear advantages for maximizing the infrared response of c-Si bottom cells in combination with perovskite top cells.

Ambipolar Thin-Film Transistors Fabricated by PECVD Nanocrystalline Silicon

2006 ◽  
Vol 910 ◽  
Author(s):  
Czang-Ho Lee ◽  
Andrei Sazonov ◽  
Mohammad R. E. Rad ◽  
G. Reza Chaji ◽  
Arokia Nathan
Keyword(s):  
Thin Film ◽  
Thin Film Transistors ◽  
Field Effect ◽  
Chemical Vapor ◽  
Hole Mobility ◽  
Complementary Metal Oxide Semiconductor ◽  
Nanocrystalline Silicon ◽  
Oxide Semiconductor ◽  
Hole Injection ◽  
Current Ratio

AbstractWe report on directly deposited plasma-enhanced chemical vapor deposition (PECVD) nanocrystalline silicon (nc-Si:H) ambipolar thin-film transistors (TFTs) fabricated at 260 °C. The ambipolar operation is achieved adopting Cr metal contacts with high-quality nc-Si:H channel layer, which creates highly conductive Cr silicided drain/source contacts, reducing both electron and hole injection barriers. The n-channel nc-Si:H TFTs show a field-effect electron mobility (meFE) of 150 cm2/Vs, threshold voltage (VT) ~ 2 V, subthreshold slope (S) ~0.3 V/dec, and ON/OFF current ratio of more than 107, while the p-channel nc-Si:H TFTs show a field-effect hole mobility (mhFE) of 26 cm2/Vs, VT ~ -3.8 V, S ~0.25 V/dec, and ON/OFF current ratio of more than 106. Complementary metal-oxide-semiconductor (CMOS) logic integrated with two ambipolar nc-Si:H TFTs shows reasonable transfer characteristics. The results presented here demonstrate that low-temperature nc-Si:H TFT technology is feasible for total integration of active-matrix TFT backplanes.

Thin-film Photodiode with an a-Si:H/nc-Si:H Absorption Bilayer

2011 ◽  
Vol 1321 ◽  
Author(s):  
Y. Vygranenko ◽  
M. Vieira ◽  
A. Sazonov
Keyword(s):  
Thin Film ◽  
Leakage Current ◽  
Near Infrared ◽  
Spectral Response ◽  
Nanocrystalline Silicon ◽  
Depletion Region ◽  
Long Wavelength ◽  
Near Ultraviolet ◽  
High Bias ◽  
Bias Range

ABSTRACTWe report on the fabrication and characterization of n+-n-i-δi-p thin-film photodiodes with an active region comprising a hydrogenated nanocrystalline silicon (nc-Si:H) n-layer and a hydrogenated amorphous silicon (a-Si:H) i-layer. The combination of wide- and narrow-gap absorption layers enables the spectral response extending from the near-ultraviolet (NUV) to the near-infrared (NIR) region. Moreover, in the low-bias range, when only the i-layer is depleted, the leakage current is significantly lower than that in the conventional nc-Si:H n+-n-p+ photodiode deposited under the same deposition conditions. Device with the 900nm/400nm thick n-i-layers exhibits a reverse dark current density of 3 nA/cm2 at −1V. In the high-bias range, when the depletion region expands within the n-layer, the magnitude of the leakage current depends on electronic properties of nc-Si:H. The density of shallow and deep states, and diffusion length of holes in the n-layer have been estimated from the capacitance-voltage characteristics and from the bias dependence of the long-wavelength response, respectively. To improve the quantum efficiency in the NIR-region, we have also implemented a Cr / ZnO:Al back reflector. The observed long-wavelength spectral response is about twice as high as that for a reference photodiode without ZnO:Al layer. Results demonstrate the feasibility of the photodiode for low-level light detection in the NUV-to-NIR spectral range.

Hydrogen in Ultralow Temperature SiO2for Nanocrystalline Silicon Thin Film Transistors

2004 ◽  
Vol 814 ◽  
Author(s):  
Alex Kattamis ◽  
I-Chun Cheng ◽  
Steve Allen ◽  
Sigurd Wagner
Keyword(s):  
Thin Film ◽  
Leakage Current ◽  
Current Density ◽  
Thin Film Transistors ◽  
Secondary Ion Mass Spectrometry ◽  
Crystalline Silicon ◽  
Chemical Vapor ◽  
Nanocrystalline Silicon ◽  
Film Deposition ◽  
Silicon Thin Film

AbstractNanocrystalline silicon is a candidate material for fabricating thin film transistors with high carrier mobilities on plastic substrates. A major issue in the processing of nanocrystalline silicon thin film transistors (nc-Si:H TFTs) at ultralow temperatures is the quality of the SiO2gate dielectric. SiO2deposited at less than 250°C by radio frequency plasma enhanced chemical vapor deposition (rf-PECVD), and not annealed at high temperature after deposition, exhibits high leakage current and voltage shifts when incorporated into TFT's. Secondary ion mass spectrometry (SIMS) measurements show that the hydrogen concentration (NH) in PECVD oxide deposited at 150°C on crystalline silicon (x-Si) is ∼ 0.8 at. %. This is much higher than in thermal oxides on x-Si, which display concentrations of less than 0.003 at. %. The leakage current density for thermal oxides on x-Si at a bias of 10 V is ∼9×10−6A/cm2whereas for 200°C PECVD oxides on nc-Si:H the current is ∼1×10−4A/cm2. As the temperature of the SiO2deposition is reduced to 150°C the current density rises by up to two orders of magnitude more. The H which is suspected to cause the leakage current across the PECVD oxide originates from the nc-Si:H substrate and the SiH4source gas. We analyzed the 300-nm gate oxide in capacitor structures of Al / SiO2/n+nc-Si:H / Cr / glass, Al / SiO2/ n+nc-Si:H / x-Si, and Al / SiO2/ x-Si. Vacuum annealing the nc-Si:H prior to PECVD of the oxide drives H out of the nc-Si:H film and reduces the amount of H incorporated into the oxide that is deposited on top. SiO2film deposition from SiH4and N2O at high He dilution has a still greater effect on lowering NH. The leakage current at a 10 V bias dropped from ∼1×10−4A/cm2to about ∼2×10−6A/cm2using He dilution at 250°C, and the vacuum anneal of the nc-Si:H lowered it by an additional factor of two. Thus we observe that both the nc-Si:H anneal and the SiO2deposition at high He dilution lessen the gate leakage current.

Visible Light Emitting Diode Employing Electrochemically Anodized Nanocrystalline Silicon Thin Film

1996 ◽  
Vol 452 ◽  
Author(s):  
T. Toyama ◽  
T. Yamamoto ◽  
T. Matsui ◽  
H. Okamoto
Keyword(s):  
Thin Film ◽  
Light Emitting Diode ◽  
Light Output ◽  
Chemical Vapor ◽  
Nanocrystalline Silicon ◽  
Rf Plasma ◽  
Silicon Thin Film ◽  
Light Emitting ◽  
Plasma Chemical Vapor Deposition ◽  
Boron Doped

AbstractVisible electroluminescence (EL) has been achieved on the entirely solid state thin film light emitting diode (TFLED) employing electrochemically anodized nanocrystalline Si (nc-Si) as a light emitting active layer. The TFLED consisting of p-type nc-Si, and intrinsic and n-type amorphous layers was fabricated on a SnO2-coated glass substrate. The nc-Si was formed in HF aqueous solution from boron doped microcrystalline Si (μc-Si) deposited by rf plasma chemical vapor deposition (CVD). The TFLED exhibits clear rectification with a forward threshold voltage of about 1.5 V, whereas visible EL emission is observed upon applying reverse bias voltages. The diode ideality factor is more than 2, and the light output increases with the square of the diode current. The EL emission color is orange-red and the spectral peak energy is 1.8 eV.

DC and AC Gate-Bias Stability of Nanocrystalline Silicon Thin-Film Transistors Made on Colorless Polyimide Foil Substrates

2011 ◽  
Vol 1321 ◽  
Author(s):  
I-Chung Chiu ◽  
I-Chun Cheng ◽  
Jian Z. Chen ◽  
Jung-Jie Huang ◽  
Yung-Pei Chen
Keyword(s):  
Thin Film ◽  
Threshold Voltage ◽  
Thin Film Transistors ◽  
Nanocrystalline Silicon ◽  
Gate Bias ◽  
Threshold Voltage Shift ◽  
Voltage Shift ◽  
Bias Stress ◽  
Mechanical Tensile ◽  
Gate Bias Stress

ABSTRACTStaggered bottom-gate hydrogenated nanocrystalline silicon (nc-Si:H) thin-film transistors (TFTs) were demonstrated on flexible colorless polyimide substrates. The dc and ac bias-stress stability of these TFTs were investigated with and without mechanical tensile stress applied in parallel to the current flow direction. The findings indicate that the threshold voltage shift caused by an ac gate-bias stress was smaller compared to that caused by a dc gate-bias stress. Frequency dependence of threshold voltage shift was pronounced in the negative gate-bias stress experiments. Compared to TFTs under pure electrical gate-bias stressing, the stability of the nc-Si:H TFTs degrades further when the mechanical tensile strain is applied together with an electrical gate-bias stress.

Effects of Various Hydrogen Dilution Ratios on the Performance of Thin Film Nanocrystalline/Crystalline Silicon Solar Cells

1998 ◽  
Vol 536 ◽  
Author(s):  
Y. J. Song ◽  
W. A. Anderson
Keyword(s):  
Thin Film ◽  
Low Temperature ◽  
Electron Cyclotron Resonance ◽  
Crystalline Silicon ◽  
Low Cost ◽  
Silicon Film ◽  
Chemical Vapor ◽  
Nanocrystalline Silicon ◽  
Maximum Efficiency ◽  
Crystalline Silicon Solar Cells

AbstractLow temperature growth of hydrogenated nanocrystalline silicon film (nc-Si:H) by microwave electron cyclotron resonance chemical vapor deposition has been performed employing a double dilution of silane, using a He carrier for SiH4 and its subsequent dilution by H2. A series of Raman spectra and AFM pictures has shown that a very thin (<100Å) nc-Si:H layer initially grown with high H2 dilution on a glass substrate can serve as a seed layer for the subsequent growth of the film with lower H2 dilution, which results in a higher crystallinity of the whole film. The role of this thin layer in low temperature junction formation has been examined by the insertion of the layer between the interface of both nc-Si:H (deposited with lower H2 dilution)/c-Si and a-Si:H/c-Si heterojunction type photovoltaic cells. This is to address the knowledge that the device's performance is strongly influenced by the quality of the thin film silicon/crystalline silicon interface. Various thicknesses and H2 dilution ratios have been used to find the optimized condition providing the best performance of the cells. The maximum efficiency of 10.5% (Jsc=35.1mA/cm2, Voc=0.51V and FF=0.59) has been obtained, without an AR coating, by the successive deposition of nc-Si:H film with four different H2 dilution ratios on a crystalline silicon substrate. This is potentially a low-temperature, low-cost solar cell fabrication process.

Nanocrystalline Silicon by Microwave CVD for Thin Film Transistors and Solar Cells

2000 ◽  
Vol 638 ◽  
Author(s):  
Young J. Song ◽  
Hak-Gyu Lee ◽  
Lihong Teng ◽  
Wayne A. Anderson
Keyword(s):  
Thin Film ◽  
Solar Cells ◽  
Thin Film Transistors ◽  
Chemical Vapor ◽  
Nanocrystalline Silicon ◽  
Dark Conductivity ◽  
Antireflection Coating ◽  
Process Conditions ◽  
Hydrogen Dilution ◽  
Partial Pressures

AbstractMicrowave chemical vapor deposition (MCVD) is utilized to deposit nanocrystalline silicon (nc-si) thin films onto a variety of substrates for application to thin film transistors (TFT's) and solar cells. It is especially important to gain reproducible control of the processing. Thus, an in-situ mass spectrometer (MS) records the plasma conditions with variation of process conditions such as gas selection, pressures, partial pressures, and substrate temperature. These data are correlated with electrical and optical properties of the films. Raman spectra show a FWHM of 11/cm with position at 522/cm as desired for crystalline Si. Typical film thickness is 100nm with grain size of 20-30 nm, using standard deposition, and 50-80 nm when the substrate is intensely optically illuminated during deposition, called photon assist (PA). Hydrogen dilution serves to increase the crystallinity of the films. The ratio of photo-to dark conductivity exceeds 10+5 with dark conductivity as low as 1.5 × 10-10 S/cm. Thin film transistors have been fabricated with Ion/Ioff of 10+7. Hetrojunction solar cells were fabricated using amorphous Si/ nc-Si/ crystlline Si giving a conversion efficiency of above 10.5%, without an antireflection coating. The use of MS in device design will be emphasized.

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