Partap Kumar

Electrical properties of Te-rich, Cd-rich and hydrogen-exposed polycrystalline CdTe thin films

Polycrystalline films of CdTe, stoichiometric, Te-rich, and Cd-rich, were grown using a vacuum evaporation technique on glass substrates kept at room temperature. The as-grown films were exposed to hydrogen gas at high pressure (200-500 PSI). Measurements of DC conductivity in the temperature range 77-300K, X-ray diffraction studies and electron probe microanalyses were made on these films. The conductivity data for the stoichiometric, Te-rich and Cd-rich films in the low temperature region have been analysed for variable range hopping conduction on the basis of Motts model. The analysis of the high temperature conductivity data for Te-rich and hydrogen-exposed films has been based on Setos model of thermionic emission. It is found that addition of Te and Cd improves the conductivity of the films by four and six orders of magnitude respectively. However, the density of trap states near the Fermi level, N(EF), also increases with increase of Cd and Te content. In the case of hydrogen-exposed films the conductivity decreases with increase of gas pressure.

Growth and properties of well-oriented In2Te3 thin films

Abstract Well-oriented thin films of In 2 Te 3 were grown on sapphire substrates by thermal evaporation at 350°C and were then annealed in an argon atmosphere at 400°C for 2 h. Studies of the d.c. conductivity and Hall effect for these films were carried out in the temperature range 77–295 K. The variation in the Hall mobility with temperature indicated that there is a considerable contribution from lattice scattering above 220 K.

Electrical transport properties of heavily indium- doped polycrystalline CdS films

Abstract CdS was doped with up to 1.5 at.% In by means of a chemical method. Films were produced from the chemically prepared charge by evaporation onto glass. Measurements of the d.c. conductivity and the Hall effect were made on these films. It was observed that the carrier concentration in the films increases by two orders of magnitude on the addition of 1.0 at.% In. The carrier concentration remains almost constant, however, on further addition of indium. In contrast, the mobility increases on the addition of indium up to 1.0 at.% but it decreases when further indium is added.

Growth and electrical properties of cuprous telluride thin films

Abstract Polycrystalline thin films of cuprous telluride were grown on mica substrates by vacuum evaporation at 350 °C and were then annealed at the same temperature in a vacuum for about 2 h. The films, which were grown using a stoichiometric charge, were found to have large numbers of copper vacancies. Hall coefficient and Hall mobility studies of these films were made in the temperature range 77–300 K. The observed variation in the Hall mobility with temperature indicated that the mobility is mainly limited by defect scattering and ionized impurity scattering in the temperature range 77–200 K, while lattice scattering is predominant at temperatures above 200 K.

The effect of hydrogen on the electrical properties of n-type Pb0.9Cd0.1Te thin films

Abstract Measurements of the Hall coefficient and the d.c. conductivity were made on flash evaporated n -type Pb 0.9 Cd 0.1 Te epitaxial films exposed to molecular hydrogen gas at high pressures (upto 500 psi) in the temperature range 77–300 K. It has been found that the effect of hydrogen on the films is to reduce the concentration of the extrinsic carriers and to increase their mobility. It is believed that hydrogen gas removes cadmium ions and neutral cadmium atoms from these films.

Electrical transport properties of p-type Pb1−xCdxS epitaxial thin films

Abstract Measurements were made of the Hall coefficient and d.c. conductivity of p-type Pb 1− x Cd x S thin films grown on mica substrates. It was found that films with x x ≈ 0.1 is comparable with that in films grown on other substrates, e.g. NaCl and BaF 2 .

Electrical transport properties of thallium-doped p-type PbTe films

Abstract Hall measurements were made in the temperature range 77–700 K on thallium- doped p-type epitaxial films of PbTe having free carrier concentrations in the range 5×1017−6×1019cm−3 at 300 K. The various band parameters, i.e. mobility, effective mass and population ratios for light and heavy holes, were estimated as functions of temperature and carrier concentration. These results were compared with reported data on bulk samples.

Effect of hydrogen on electrical transport properties of polycrystalline CulnTe2 thin films

The effect of molecular hydrogen on the electrical transport properties of p-type CulnTe2 films was studied by exposing the films at high pressures (up to 700 psi). It was observed that the Hall coefficient increased initially with the increase of pressure up to 500 psi and then started decreasing. The mobility was found to increase with pressure of the gas. The results are explained in terms of a grain-boundary scattering mechanism and in terms of donor action provided by hydrogen diffusion into the thin film.

Electrical effects of thallium on the Hall mobility in p-PbTe thin films

Abstract The Hall coefficient and Hall mobility were measured for epitaxial p-type PbTe films doped with thallium. It was observed that doping of the films with thallium leads to a decrease in the mobility and an increase in the concentration of charge carriers. The mobility μD limited by defect scattering was calculated and was found to be independent of temperature and to decrease with increases in the carrier concentration p. For films with carrier concentrations exceeding 7 × 1018 cm-3 the value of μD decreases as p- 4 3 , whereas for films with lower carrier concentrations the decrease in μD with p is at a slower rate.

Electrical effects of thallium, sodium and silver impurities on lead telluride thin films

Abstract Thin epitaxial films of PbTe incorporating Ag and Tl impurities were deposited by coevaporating these elements with PbTe from two separate boats onto heated mica and sapphire. Na doped films were prepared by coevaporating NaCl and PbTe. The rates of the various constituents were carefully monitored in order to have a wide concentration range. DC conductivity and Hall measurements have been reported on these films in the temperature range of 100–700 K. Various band parameters, i.e. mobility, effective mass and population ratios for light and heavy holes, have been estimated as a function of carrier concentration and temperature on the basis of a two-valence band model. All these impurities have been found to give p-type behaviour. For a given carrier concentration, the mobility ratio of light to heavy holes ( b= μ 1 μ h ) for Ag doped films was larger as compared to those doped with Na and Tl. It has been observed that the values of b for all these films decrease with increasing carrier concentration. However, this decrease is smaller in the case of Tl and Na doped films than in Ag doped films. The effect of various dopants on the valence band separation (ΔEv) has been found to be almost independent of dopant and its concentration. The Hall mobility has been observed to decrease with increasing carrier concentration. Data on the variation of the mobility temperature have been found and were analysed in terms of different scattering mechanisms.