Space charge limited current conduction in Bi 2Te 3 thin films

Abstract

Bi 2Te 3 is known for its large thermoelectric coefficients and is widely used as a material for Peltier devices. Bi 2Te 3 thin films with thicknesses in the range 125–300 Å have been prepared by Flash Evaporation at a pressure of 10 − 5 m bar on clean glass substrates at room temperature. An Al–Bi 2Te 3–Al sandwich structure has been used for electrical conduction properties in the temperature range 303 to 483 K. I– V characteristics showed Ohmic conduction in the low voltage region. In the higher voltage region, a Space Charge Limited Conduction (SCLC) takes place due to the presence of the trapping level. The transition voltage ( V t), between the Ohmic and the SCLC condition was proportional to the square of thickness. Further evidence for this conduction process was provided by the linear dependence of V t on t 2 and log J on log t. The hole concentration in the films were found to be n 0 = 1.65 * 10 10 m − 3 . The carrier mobility increases with increasing temperature whereas the density of trapped charges decreases with increasing temperature. The barrier height decreases with an increase in temperature. The increase in the trapping concentration V t is correlated with ascending the degree of preferred orientation of the highest atomic density plane. The activation energy was estimated and the values found to decrease with increasing applied voltage. The zero field value of the activation energy is found to be 0.4 eV.