A. K. Batabyal

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.

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 undoped and p-type hydrogenated amorphous silicon carbide films

The properties of undoped and p-type hydrogenated amorphous silicon carbide (a Si C:H) films were studied. Thea Si C:H films were prepared under different deposition conditions by the r.f. glow discharge decomposition of gas mixtures of silane and methane in an inductively coupled system. The p-typea Si C:H films were prepared from mixtures of silane, methane and diborane gases. The dark conductivity, photoconductivity, optical absorption, band gap and spectral response of these films were studied. By analysing the dark and photoconductivity data, information about the transport mechanism and the recombination processes in these films was obtained. It is suggested that there is possibly a significant change in the structure ofa Si C:H films with an increase in the carbon concentration that influences various properties of the material.

The influence of deposition parameters on the properties of amorphous silicon thin films produced by the magnetron sputtering method

The influence of various deposition parameters on the properties of amorphous silicon (a-Si) thin films produced by r.f. magnetron sputtering was studied. The following parameters were varied: the incident r.f. power, the argon pressure in the sputtering chamber and the substrate temperature. The films were characterized by studying the dark conductivity and optical absorption from which the values of the band gaps were obtained. The most interesting result was that a-Si films prepared at high argon pressures showed significant photoconductivity. The results show that the magnetron sputtering method has good potential for producing high quality a-Si films.

Performance dependence of a-Si/a-Si double junction solar cell on the quality of the a-Si:C:H buffer layer at p+-Si:C:H/i-a-Si:H interface

Abstract The use of a highly photoconductive a-SiC:H buffer layer at the p+-SiC:H and i-Si:H interface of an a-Si/a-Si double junction tandem cell results in a high value for the fill factor of the cell. It has been observed that the collection efficiency of the bottom cell measured under a forward bias condition greatly depends upon the quality of the a-SiC:H buffer layer. With no a-SiC:H buffer layer at p+-SiC:H and i-Si:H junction or with an inferior quality a-SiC:H buffer the collection efficiency of the bottom cell has been observed to decrease at any wavelength. With a highly photoconductive a-SiC:H buffer layer the collection efficiency of the bottom cell below a certain wavelength has been found to be maximum at a positive bias voltage corresponding to the maximum power point of the cell. Enhancement of the bottom cell collection efficiency at short wavelength on application of forward bias has been explained by injection of photogenerated carriers in the a-SiC:H layer into the bottom cell i-layer.

Electronic and optical properties of boron doped hydrogenated amorphous silicon thin films

Abstract The electronic and optical properties of p-type a-Si:H films prepared by the rf glow discharge decomposition of a mixture of silane and diborane gases have been studied. The films have been prepared under different conditions which include variation of volume ration of B 2 H 6 and SiH 4 and rf power. The properties of compensated a-Si:H films prepared with very small boron doping have also been studied. The effects of mixing Ar with SiH 4 + B 2 H 6 mixture have been investigated. The properties actually studied include (1) dark conductivity, (2) steady state photoconductivity, (3) spectral response, (4) optical absorption and band gap. Attempts have been made to analyse the data to yield information about the transport mechanism, and the existence of hole and electron traps.

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.

Thickness dependence of light-induced effects in a-Si solar cells

Abstract A systematic study of the changes in photovoltaic properties of amorphous silicon p-i-n-type solar cells upon 100 h of white light (air mass (AM) 1.5 G) soaking has been made with the thickness of the i layer as variable parameter. The thickness of the i layer ranged from 700 to 7500 A. A significant rise in open-circuit voltage was observed in cells having an i layer less than 2500 A thick. This is explained as an effect of doping enhancement in the p and n layers of the cell upon light soaking. A study of collection efficiency spectra revealed that with an increase in i layer thickness the degradation increases towards longer wavelengths.

Hydrogenated amorphous silicon films prepared at high substrate temperature : properties and light induced degradation

Of the different deposition parameters, the substrate temperature Ts has a profound effect on the microstructure and optoelectronic properties of hydrogenated amorphous silicon (a‐Si:H). A detailed study was done to evaluate a‐Si:H materials deposited at high substrate temperatures (≥325 °C). Their characteristics and nature of light induced degradation were compared to a‐Si:H deposited at 200 °C. Electrical properties were studied with coplanar electrode structure as well as on Schottky barrier devices. Absorption measurements in the visible and infrared regions and spin‐density measurements were carried out. For high Ts (≥325 °C) the presence of acceptorlike defects are indicated in addition to the neutral dangling bonds. Annealing recovery from the light soaked state is slower as compared to a film deposited at 200 °C. The results have been discussed in connection with the role of hydrogen motion in the annealing of light induced defects.