Ratnabali Banerjee

Properties of tin doped indium oxide thin films prepared by magnetron sputtering

Indium tin oxide (ITO) films have been prepared by the magnetron sputtering technique from a target of a mixture of In2O3 and SnO2 in the proportion 9:1 by weight. By optimizing the deposition conditions it has been possible to produce highly transparent (transmission ∼90%) and conducting (resistivity ∼10−5 Ω cm) ITO films. A resistivity ∼10−4 Ω cm has been obtained for films of thickness ∼1000 A at a comparatively low substrate temperature of 50 °C and without using oxygen in the sputtering chamber. To characterize the films, the following properties have been studied, viz., electrical conductivity, thermoelectric power, Hall effect, optical transmission, and band gap. The effect of annealing in air and vacuum on the properties of the films have also been studied.

Degradation of tin‐doped indium‐oxide film in hydrogen and argon plasma

The degradation of tin‐doped indium‐oxide (ITO) films in glow‐discharge plasmas of hydrogen and argon have been investigated. Parameters which have been varied for the study include the temperature of ITO under ion bombardment, the rf power density, the time of exposure to plasma, and the gas flow rate. After bombardment, scanning electron micrograph observation, measurement of sheet resistance, transmittance and reflectance, and Auger analysis have been carried out to decide the extent of degradation. Magnetron‐sputtered ITO films have been found to be more resistant to ion bombardment damage compared to electron‐beam evaporated films. The degradation of ITO under the plasma of the reducing species such as hydrogen has been found to take place at lower temperature and power density compared to argon plasma.

Properties of electron-beam-evaporated tin oxide films

Abstract Transparent conducting thin films of tin oxide were prepared by electron beam evaporation of sintered pellets of SnO 2 under controlled conditions. Variations in such parameters as the substrate temperature T s and the post-deposition annealing temperature T A and time t A were studied. Structural, electrical and optical properties were measured to characterize the films. The film structure changed gradually from amorphous to crystalline (SnO phase) as T S was varied from 150 to 350 °C. A sharp decrease in the room temperature resistivity together with the growth of a crystalline phase occured in the as-deposited films at T S ≈ 250°C. On annealing in air ( T A = 550° C , t A = 2 h ) a radical structural transformation from amorphous to crystalline occurred with a sharp fall in resistivity for T S ⩽ 225°C. For T S = 350° C the lowest resistivity achieved for the undoped annealed films was 6.6×10 -3 Ω cm, the average visible transmittance was about 90% and the structure was characteristic of pure SnO 2 .

Properties of tin oxide films prepared by reactive electron beam evaporation

Tin oxide films were prepared by electron beam evaporation of pellets of Specpure SnO2 in the presence of added oxygen. By optimizing the deposition conditions, transparent and conducting tin oxide films exhibiting the structural characteristics of a predominant SnO2 phase were produced. The effect of annealing the films in air was also studied. The lowest resistivity obtained was 7.5 × 10−4 Ω cm, with a visible transmittance of over 90%. The properties studied to characterize the films were (1) structure by X-ray diffraction and transmission electron microscopy; (2) resistivity, Hall mobility and carrier concentration; (3) optical transmission and band gap. Films were also subjected to reduction tests by exposure to a hydrogen plasma to determine their suitability as electrodes for hydrogenated amorphous silicon solar cells.

Characterization of tin doped indium oxide films prepared by electron beam evaporation

Abstract Tin doped indium oxide (ITO) films have been prepared by electron beam evaporation of hot pressed powder of 90% In 2 O 3 10% SnO 2 by weight. The parameters varied for optimization of film properties have been the substrate temperature and the partial pressure of the oxygen added. Properties which have been studied for characterization are the resistivity, Hall effect, transmittance and optical band gap. The structural studies have been made by X-ray diffraction and transmission electron microscopy. D.c. resistivity in the range 10 −3 −10 −4 Ω cm and visible transmittance in excess of 90% have been obtained for the films, with proper parametric adjustments. A 〈111〉 texture has been generally exhibited by the ITO films, using X-ray diffraction. This has been corroborated by electron diffraction studies.

Properties of vacuum-evaporated CdS thin films

Thin films of highly purified CdS have been prepared by the vacuum evaporation method. The source has been maintained at 850°C and a semi-closed system has been used for evaporation. The following properties of the films have been studied, viz: (1) dark and photoconductivity as functions of temperature and thickness of the films (2) Hall mobility and carrier concentration at room temperature (3) optical absorption and spectral response and (4) structural studies by X-ray diffraction. The resistivity of the films varies from 0.15 to 3.7 Ωcm as the thickness of the films decreases from 13600 to 1200 A. The transmittance of the films has been found to be 80-90%. The results for Hall mobility and carrier concentration show that the comparatively low resistivity of CdS films obtained by us is primarily due to high carrier concentration. The photoconductive gain increases with a decrease in film thickness. The effect of heat treatment in air on dark and photoconductivity has been studied.

Control of the crystallite size and passivation of defects in porous silicon by a novel method

Abstract Porous silicon films were prepared by lateral anodization of crystalline silicon in HF based solutions at different current densities. At an optimum current density, passivation of the defects by an appropriate post-anodization treatment results in the significant enhancement in the photoluminescence (PL) efficiency. However, above the optimum current level, a phase is obtained which shows significant broadening of the PL spectrum indicating the quantum wire size distribution. The degraded PL intensity in the treated samples is higher as compared to that for the as-anodized samples. Infrared vibrational studies indicate that this enhancement is due to the H-passivation of defects in the Si-pore interface, though the presence of hydrogen-terminated silicon clusters cannot be ignored. Capacitance–voltage studies concur well with the photoluminescence and infrared results.

Short‐range order, microstructure and their correlation with light‐induced degradation in hydrogenated amorphous silicon deposited at high growth rates by cathode heating technique

Hydrogenated amorphous silicon (a‐Si:H) films were deposited at high growth rates by increasing the rf power density in a (SiH4+H2) discharge, while powder formation due to gas phase polymerization was controlled by heating the cathode together with the anode. A combination of Raman scattering, infrared absorption, and small angle x‐ray scattering experiments was used to study the short‐range order and microstructure of films deposited in different (dusty or otherwise) plasma conditions. The results were correlated with initial and light‐soaked photoresponse to demonstrate that films with more microstructure and less short‐range order were generally poorer.

Control of powder formation in silane discharge by cathode heating and hydrogen dilution for high‐rate deposition of hydrogenated amorphous silicon thin films

Hydrogenated amorphous silicon (a‐Si:H) films have been deposited at high growth rates by increasing the rf power density while the optoelectronic quality of the films has been concurrently taken care of by controlling powder formation due to gas‐phase polymerization in the plasma. This has been achieved by heating the cathode together with the anode in the capacitive coupling arrangement and keeping the cathode temperature close to that of the anode. This, together with hydrogen dilution of the source gas, has been used to control powder formation in the silane discharge. The films have been evaluated by optical and infrared vibrational spectroscopy, dark conductivity, secondary photoconductivity, and internal quantum efficiency measurements.

Some properties of indium- and antimony-doped vacuum-evaporated CdS thin films

Abstract The effects of doping of vacuum-evaporated CdS thin films with indium and antimony were studied. The properties specifically studied are (1) the dark conductivity and photoconductivity as functions of temperature and dopant concentration, (2) the Hall mobility and carrier concentration at room temperature, (3) the thermally stimulated current and (4) the spectral response and optical density. For indium-doped CdS films, in agreement with previous studies the dopant was found to act as a donor as it is a group III element and replaces cadmium in CdS. Thus the dark conductivity and carrier concentration are increased. Doping with antimony results in a sharp decrease in the dark conductivity, Hall mobility and carrier concentration. This behaviour is also expected as antimony is a group V element which replaces sulphur in CdS so that it acts as an acceptor. The nature of log σ D versus 10 3 / T curves for antimony-doped CdS thin films was found to be similar to that obtained for some amorphous semiconductor thin films. Study by X-ray diffraction showed the antimony-doped CdS films be amorphous.