Influence of γ-Radiation on Optical and Electric Properties of 90Bi2Te3-10Bi2Se3 Doped Films of P-and N-Types Conductivity

Introduction

At present one of the main tasks in nanotechnology development, production of ordered nanodimensional structures fulfilling requirements of nanotechnology is significant prospects for high-efficient production of materials with physicochemical parameters of nanoparticles. One of its important properties is the creation of radiation –resistant nanostructures.

Bi-Te-based solid solutions attract many researchers as given materials by different Se atom substitution have high thermoelectric efficiency within temperatures as below as above room one at optimum compositions and concentrations of charge carriers (Ettenberg et al., 1996; Sveshnikova et al., 2005; Ivanova et al., 2007; Kutasov et al., 2006).

Interest in thin films of given layered solid solutions is due to the prospect of creation of miniature thermogenerators and thermorefrigerators on their base (Goltsman et al., 1985; Abdullayev, 2002). By investigating the influence of various type of radiation on Bi₂Te₃ properties two problems are especially of high-priority:

• 1.

  Just how strongly the electric properties of the materials change by irradiation.

• 2.

  How fast and by what external effects the restoration of original properties are taken place. γ-radiation is the electromagnetic radiation with λ ≤ 2∙^-10 m which can be considered as a plane wave with frequency ω, wave vector k and intensity I. By short waves like these the wave properties of γ-radiation have been manifested poorly.

There have been put forward corpuscular properties. γ-radiation is the gamma-quantum flow with energy, frequency, impulse:

Smith has considered Co gamma –irradiation on Hall constant R and specific resistance of p- and n- Bi₂Te₃ quasi-stoichiometric single crystal samples at 77K before and after irradiation; current heads for parallel to spall planes. There have been found out two effects on irradiated samples: the first one has been appeared after small irradiation dose (from 10¹⁶-10¹⁸ ph /cm²) and connects with “electron” excitement, the second one has been observed at exposure more than 10¹⁸ ph/cm² and caused by lattice distortions (Smith et al., 1963). Electron effect leads to decrease of Hall constant and specific resistance of n-Bi₂Te₃ and their growth in p-Bi₂Te₃.

It does not depend on radiation energy and saturates after very small dose. Given state is not stable. Annealing at room temperature for 10-24 hours returns p and R to initial values and defect annealing is in agreement with energy E_anneal.=0.7±0.1eV (Dins et al., 1960; Vavilov et al., 1963). Smith has suggested that in this case the decay of complexes formed from several interstitial atoms of Te being between quintets has been taken place. By cooling up to room temperature dissociated atoms come together at complexes. Reversibility on the effect is explained by this fact. Before the second stage E_anneal is equal to 0.9±0.1 eV that is very close to vacancy motion energy in magnitude in Bi₂Te₃.

In this work influence of γ-irradiation on optical (within 1÷6eV) and electric properties (within 1÷5V) of 90Bi₂Te₃-10Bi₂Se₃ film polycrystals of p-and n-type conductivity have been investigated.