Preparation of Indium Telluride Thin Films for Device Applications

Abstract

The main objectives of this thesis work are to attain device quality of indium telluride (In2Te3 and InTe) thin films using thermal evaporation technique and to evaluate the suitability of these films for device applications. The key motivation point to this investigation is that these materials are exhibiting similar type of structures, band gaps, lattice constants and chemically compatible with traditional semiconductors such as III-V, II-VI and VI group compounds. The annealing temperature played a major role to get mono-phased and stoichiometric In2Te3 and InTe films. Hence, all the films were prepared at different substrate temperatures and annealed at optimized temperature and variations in the properties of these films were reported. The optical band gap and electrical conductivity of In2Te3 films were found to be 0.99 ± 0.02 eV and 10-1 Ω-1cm-1 respectively. Moreover, these films have shown 90% of transmittance in IR region. The optical band gap of InTe films was varied from 1.61 eV to 1.42 eV with an increase in the substrate temperature from 298 K to 473 K. The electrical conductivity of InTe films was found of the order of 101 Ω-1cm-1. The absorption coefficient of InTe films was found to be of the order of 106 cm-1. The optical properties accompanied with electrical properties of indium telluride films makes them suitable for absorbent layer in photovoltaic cells. Thermoelectric properties need specific requirements such as high seebeck coefficient with good electrical conductivity and low thermal conductivity. Accordingly, growth parameters were optimized by varying substrate temperature and thickness to investigate the thermoelectric properties. The In2Te3 films shown good thermoelectric properties when compared with InTe films with maximum thermoelectric power of 27 µ W m-1 K-2 at 450 K. To enhance thermoelectric power, various dopants such as Bi, Sb2Te3, Al, Sb, Se and Te were added in the range of 1-7 at% separately. The 3 % Se doping enhanced the power factor of In2Te3 films by 14 times which in turn 4.7 times greater than Sb2Te3 films. Finally, heterojunctions of n-Si/In2Te3 and n-Si/InTe were fabricated and interface properties were studied to understand the performance of indium telluride in opto-electronic devices. Among all diodes, as-deposited n-Si/In2Te3heterojunction had higher rectification ratio of 61.2 at ± 5V with affordable barrier heights of 0.11 eV which allows easy carrier transport across the barrier.