C. Nunes de Carvalho

Effect of rf power on the properties of ITO thin films deposited by plasma enhanced reactive thermal evaporation on unheated polymer substrates

Abstract The influence of the radiofrequency (rf) deposition power on the properties of indium tin oxide (ITO) thin films deposited onto unheated polymer substrates is studied. The deposition technique used is the radiofrequency plasma enhanced reactive thermal evaporation (rf-PERTE). Results show that (1) the total transmittance at 500 nm is always around 80% and (2) that the electrical resistivity is 10−3 Ω cm for ITO films deposited in the rf power range 45–50 W. X-ray diffraction analysis showed the presence of a crystalline phase. Scanning electron microscopy (SEM) revealed that the surface morphology of the ITO films does not vary significantly with rf power.

Dependence of TFT performance on the dielectric characteristics

The study of thin film transistors (TFTs) and MIS structures using a variety of amorphous silicon nitride thin films (a-SiN x :H) as the gate dielectric is presented. These nitride films were deposited with N/Si ratios between 0.64 and 1.74, in order to evaluate the dependence of the TFT performance near the stoichiometric a-SiN x :H composition (1.33). These films were produced in a magnetically confined PECVD system. A set of samples was prepared for capacitance measurements (e r determination), FTIR measurements (Si-H and N-H bonds relative abundance), Rutherford backscattering spectrometry and elastic recoil detection measurements (elemental concentration and density calculation). TFT results show a close relationship between the field effect mobility (μ FE and the hydrogen concentration in the nitride films. Also, nitride films with the highest densities lead to superior electrical performance. These films are over-stoichiometric (N-rich), showing that, unlike CVD thermal nitride, the best a-SiN x :H are not necessarily stoichiometric. TFTs with N-poor a-SiN , ( : H films present a high degree of 1(V) hysteresis due to charge trapping on the a-Si:H/a-SiN x :H interface. This effect is also confirmed by C(V) measurements performed on MIS structures.

Effect of thickness on the properties of ITO thin films deposited by RF- PERTE on unheated, flexible, transparent substrates

Abstract The influence of thickness on the main properties of indium tin oxide (ITO) thin films deposited onto flexible, transparent polymer substrates at room temperature was studied. The deposition technique used was radio-frequency (RF) plasma-enhanced reactive thermal evaporation (RF-PERTE) of a 90% In–10% Sn alloy in the presence of oxygen. Results show that (1) the total transmittance is always approximately 80% at a wavelength of 500 nm when the thickness of the ITO films exceeds 70 nm and (2) ITO thin films with electrical resistivity of 6.2×10 −3 Ω cm, free carrier mobility of approximately 1.2 cm 2 V −1 s −1 and free carrier concentration of approximately 8.6×10 20 cm −3 are obtained, for films 100 nm thick. SEM investigations revealed that the surface morphology of the growing ITO thin film is dominated by the surface features of the flexible, transparent polymer substrate in the micron and submicron ranges, and does not vary significantly with thickness.

Influence of the initial layers on the optical and electrical properties of ITO films

Abstract The influence of early stage growth structure of indium tin oxide (ITO) thin films, deposited by reactive thermal evaporation (RTE) on optical and electrical properties, was studied by atomic force microscopy (AFM) measurements. ITO thin films were deposited at T s =440 K from an In:Sn alloy in the presence of added oxygen with (series A ), and without (series B ) a shutter between the substrate and the crucible. In series A , the presence of crystallisation seeds smaller than 20 nm was observed in the initial stages of growth. The mean grain size value and the number of grains per aggregate increased with film thickness reaching, respectively, 50 nm and 8 for t =100 nm. In series B , the initial stages show the presence of individual features with characteristics dimensions of up to 100 nm scattered on the surface. With increasing thickness ITO thin films of series B appear to grow similarly to series A . In series A , both transmittance and sheet-resistance were improved.

Properties of high growth rate amorphous silicon deposited by MC-RF-PECVD

Hydrogenated amorphous silicon (a-Si : H) thin films have been deposited on glass and crystalline silicon substrates by magnetically confined RF-PECVD (MC-RF-PECVD) at different RF power densities in order to verify the influence of this deposition parameter on the density of states (DOS) and growth rate (RG). It was found that the highest growth rate, 7.8 ( A is obtained for a-Si : H films deposited with an RF power density of 14.3 mW/cm 3 . For the DOS calculation, constant photocurrent method (CPM) data have been used. The lowest value of DOS is approximately 8 � 10 15 /eV/cm 3 and was obtained for a-Si : H films produced with an RF power density in the range of 10–20 mW/cm 3 . Infrared spectroscopy shows that when the RF power density increases, the concentration of SiH3 groups decreases and the concentration of SiH groups increases. At 8 mW/cm 3 , a maximum of the SiH2 concentration is obtained. At this point, a maximum of the optical gap (1.9 eV) is observed and a minimum of the dark conductivity is verified. We conclude that the best films are achieved in an RF power density range (7.1–21.4 mW/cm 3 ) for which an increase of SiH and a decrease of both SiH2 and SiH3 are simultaneously obtained. Thereafter, for higher power densities, an inversion of DOS and growth rate behaviour are observed due to ion bombardment. r 2002 Elsevier Science Ltd. All rights reserved.

ITO thin films deposited by RTE on flexible transparent substrates

Indium-tin oxide (ITO) thin films were successfully deposited onto transparent flexible substrates of hydroxypropylcellulose (HPC) cross-linked with 1,4-di-isocyanatobutane (BDI). The effect of O 2 plasma exposure on the transmittance and sheet resistance of the ITO coated flexible substrates has been studied. Atomic force microscopy (AFM) shows that these type of substrates have a large surface roughness (4.8 nm) which originates high values in the diffuse transmittance. The best properties of the resulting ITO films on flexible substrates are an average total transmittance in the visible region of about 80% and a sheet resistance of about 4 x 10 4 Ω/sq.

Photocurrent multiplication in ITO/SiOx/Si optical sensors

Abstract A visible/near-infrared optical sensor based on an ITO/SiOx/n-Si structure with internal gain is presented. This surface-barrier structure was fabricated by a low-temperature processing technique. The interface properties and carrier transport were investigated from dark current–voltage and capacitance–voltage characteristics. Examination of the multiplication properties was performed under different light excitation and reverse bias conditions. The spectral and pulse response characteristics are analyzed. The current amplification mechanism is interpreted by the control of electron current by the space charge of photogenerated holes near the SiOx/Si interface. The optical sensor output characteristics and device applications are discussed.

Flexible cellulose derivative PDLC type cells

In this work we perform a study of 250 ≈ μm thick flexible electro-optical PDLC type cells made from a biocompatible cellulose derivative film and several conductive substrates. The deposition of an ITO layer by reactive thermal evaporation on a polymeric substrate was referred to in the literature very recently and this type of coated substrate was used in the present work. In order to consider the influence of the substrates on the electro-optical behaviour of the cells, five cells were made using different substrates (three flexible polymers and two glass for comparison). Three of the substrates were coated under the same conditions, and the other two were commercially available substrates.

Influence of the a-Si:H structural defects studied by positron annihilation on the solar cells characteristics

The influence of the power density, P , on the density and structure of defects of undoped a-Si:H thin films, deposited by r.f.- D PECVD, is studied by the constant photocurrent method, (CPM), and by slow positron beam spectroscopy, respectively.Deep defect density, N , remains approximately constant at 10 cm , typical of device quality material, for P in the range 7-20 16 y3 DD D mWOcm , as calculated from CPM.Out of this range, N increases roughly one order of magnitude for both lower and higher y3 DD

Improvement of the ITO-p interface in a-Si:H solar cells using a thin SiO intermediate layer

The use of ITO thin films on glass/ITO/p-i-n/metal amorphous silicon solar cells is reviewed. It is suggested a new application for silicon monoxide thin films on the ITO-p interface, as an intermediate layer, to minimize the ITO thin film deterioration process, during the early stage of exposure to a silane plasma rich in hydrogen. The thickness of the silicon monoxide thin films is chosen not to worsen the optical and electrical properties of the ITO thin films. The ITO-p interface is optimized (due to impurities diffusion decrease), leading to an overall improvement of the device performance.