Automated PECVD System for Fabrication of a-Si:H Devices

AbstractThis paper reports a fully automated plasma-enhanced plasma chemical vapor deposition (PECVD) system for thin-film deposition. This system can be used for the deposition of hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon for devices like solar cells or optical sensors with good film homogeneity and material properties reproducibility. The control software enables two modes of system operation: semi-manual and full-auto. In the semi-manual mode the user sets all process parameters and controls all depositions steps. In the full-auto mode, the program performs the process steps according to script commands in a recipe file. This way, complex multilayered devices can be fabricated, with a high degree of reproducibility of the device characteristics

Preparation and Characterization of a-SiC:H Absorber Layer for Semi-transparent Solar Cells

AbstractThis paper reports on device-quality silicon-carbon alloy (a-SiC:H) application as an absorber material in semi-transparent solar cells. Films with an optical bandgap ranging from 2 to 2.3 eV were prepared by plasma enhanced chemical vapour deposition (PECVD). The n-i-p structures with undoped SiC:H layers deposited under the same experimental conditions were also fabricated and characterized. The optimized devices showed forward current-voltage characteristics with a diode ideality factor in the range from 1.4 to 1.8, and an open circuit voltage up to 0.92 V. The density of deep defect states in a SiC:H was estimated from the transient current measurements and correlated with the optical bandgap

Automated reactive thermal evaporation system for transparent conductive coatings

This work presents fully automated plasma-enhanced reactive thermal evaporation system (rf-PERTE) that can be used for the deposition of transparent metal oxide films with high reproducibility of their electrical and optical properties. The developed hardware/software platform enables the full control over the critical deposition conditions such as mass flow of oxygen, process pressure, current flowing through crucible and rf-power. For indium oxide films on glass substrates a resistivity of 9×10-4 Ω-cm and a transmittance of 90% in the visible spectral range were achieved without substrate heating. The system is also suitable for the deposition of transparent conducting coatings in a wide range of plastic substrates, for applications in the field of flexible sensors or solar cells. In particular, we have successfully deposited indium oxide on PEN (polyethylene naphthalate) sheets with electrical and optical properties approaching the ones of the films deposited on glass substrates

Lightweight amorphous silicon photovoltaic modules on flexible plastic substrate

Solar cells on lightweight and flexible substrates have advantages over glass-or wafer-based photovoltaic devices in both terrestrial and space applications. Here, we report on development of amorphous silicon thin film photovoltaic modules fabricated at maximum deposition temperature of 150 degrees C on 100 mu m thick polyethylene-naphtalate plastic films. Each module of 10 cm x 10 cm area consists of 72 a-Si:H n-i-p rectangular structures with transparent conducting oxide top electrodes with Al fingers and metal back electrodes deposited through the shadow masks. Individual structures are connected in series forming eight rows with connection ports provided for external blocking diodes. The design optimization and device performance analysis are performed using a developed SPICE model

Automated rf-PERTE system for room temperature deposition of TCO coatings

In this work we present a fully automated plasma-enhanced reactive thermal evaporation system (rf-PERTE) that can be used for the deposition of transparent metal oxide films without intentional heating of the substrate. The system and developed software enables the full control over critical deposition conditions such as mass flow of oxygen, process pressure, current flowing through crucible and rf-power. These parameters are automatically adjusted during the deposition thus keeping them in a narrow process window. This way, highly transparent and conductive coating can be deposited with a high degree of reproducibility of the optical and electrical characteristics. The resistivity of 9×10-4 Ω-cm and the peak transmittance of 90% in the visible spectral range were achieved for indium oxide films deposited on glass substrates. This technique is also suitable for the deposition of transparent conducting coatings in a wide range of plastic materials for flexible solar cells. In particular, we have successfully deposited indium oxide on PEN (polyethylene naphthalate) sheets with electrical and optical properties approaching the ones for films on glass.info:eu-repo/semantics/publishedVersio

High-mobility nanocrystalline indium oxide TFTs with silicon nitride gate dielectric

A variety of oxide semiconductors such as ZnO, SnO2, In 2O3 and other multi-component oxide compounds have been successfully used as channel materials in thin-film transistors (TFTs). Compared with amorphous silicon and organic semiconductor counterparts, the unique features of these materials include good performance, stability, low temperature processing, and transparency. In this work, we report on room-temperature deposition of indium oxide thin films by reactive ion beam assisted evaporation (IBAE) and their application to TFTs. By modifying the deposition parameters, nanocrystalline indium oxide (nc-In2O3) with an average grain size of 12 nm was achieved. TFTs with IBAE nc-In2O3 channel and silicon nitride gate dielectric deposited by conventional plasma-enhanced chemical vapour deposition (PECVD), were fabricated. The n-channel TFT has a threshold voltage of ∼2.5 V, a field-effect mobility of ∼32 cm2/Vs, along with an ON/OFF current ratio of ∼10 8, and a sub-threshold slope of 2.5 V/decade. The TFT reported here has one of the best performance characteristics in terms of device mobility, ON/OFF current ratio, and OFF current, using conventional, and large area foundry-compatible PECVD gate dielectrics. The device performance coupled with its low-temperature processing makes IBAE-derived nc-In2O3 TFT a promising candidate for active matrix flat panel displays. © 2008 Materials Research Society

Fabrication and characterization of NiO/ZnO/ITO p-i-n heterostructure

Transparent oxide semiconductors (TOSs) are promising materials for a variety of optoelectronic applications such as UV detectors. While several TOS-based p-n and p-i-n diodes have been recently reported, the high reverse dark current still poses a major issue. In this work, we report on a NiO/ZnO/ITO p-i-n heterostructure with reduced dark current level suitable for practical applications. Ion beam-assisted e-beam evaporation was used to deposit both p-type NiO and intrinsic ZnO layers, while a conventional sputtering system was used to prepare the ITO layer. Samples with sputtered ZnO layer were also fabricated for comparison. The diodes demonstrated clear rectifying I-V characteristics with a current rectification ratio up to 104 at bias voltages of ± 1 V. The lowest level of reverse dark current (∼ 10 nA/cm2 at - 5 V) is observed in samples with ZnO deposited by ion beam-assisted e-beam evaporation. In comparison, diodes with sputtered ZnO layer show two orders of magnitude higher dark current. Analysis of the quasi-static J-V characteristics, including time dependence behavior, shows that the dark current can be attributed to thermal generation of charge carriers via deep defects states in the ZnO layer and charge injection from the contacts. Electrical and optical properties of the TOS films are presented and discussed along with deposition conditions and device performance. © 2007 Elsevier B.V. All rights reserved

Phototransistor with nanocrystalline Si/amorphous Si bilayer channel

We report a field-effect phototransistor with a channel comprising a thin nanocrystalline silicon transport layer and a thicker hydrogenated amorphous silicon absorption layer. The semiconductor and dielectric layers were deposited by radio-frequency plasma enhanced chemical vapor deposition. The phototransistor with channel length of 24 microns and photosensitive area of 1.4 mm2 shows an off-current of about 1 pA, and high photoconductive gain in the subthreshold region. Measurements of the quantum efficiency at different incident light intensities and biasing conditions, along with spectral-response characteristics, and threshold voltage stability characterization demonstrate the feasibility of the phototransistor for low light level detection. © 2010 American Institute of Physics

Indium oxides by reactive ion beam assisted evaporation: From material study to device application

Indium oxides were deposited by reactive ion beam assisted e-beam evaporation at room temperature. A material study was conducted through a variety of material characterization including crystal structure, electrical properties, optical properties, and chemical composition, along with an investigation of material properties as a function of primary deposition parameters such as ion flux and deposition rate. Implementing the developed semiconducting indium oxide as a channel material, the authors further demonstrated high-performance indium oxide thin-film transistors (TFTs) with conventional silicon dioxide gate dielectric derived by plasma-enhanced chemical vapor deposition (PECVD). The n -channel TFT has a threshold voltage of ∼2.0 V, a field-effect mobility of 33 cm2 /V s at a gate bias of 20 V, an ON/OFF current ratio of 108, and a subthreshold slope of 2.0 V/decade. The stability study displays a small threshold voltage shift of ∼0.6 V under a 60 h constant current stress condition. The TFT reported here has one of the best performance characteristics in terms of field-effect mobility, ON/OFF current ratio, OFF current and device stability, using conventional and large-area foundry-compatible PECVD gate dielectrics. The device performance coupled with PECVD dielectrics makes ion beam assisted e-beam evaporation derived indium oxide TFT a promising candidate for active matrix flat-panel displays. © 2009 American Vacuum Society