Investigation of large Seebeck effect by charge mobility engineering in CuAlO2 thin films grown on Si substrate by thermal evaporation

In this research paper, we have reported giant enhancement in Seebeck coefficient of AlCuO2 thin films by charge mobility engineering. Thin films of AlCuO2 were grown by the evaporation of Al and Cu powder in tube furnace on Si (100) substrate. The experimental conditions were sets as; tube pressure (0.2 Torr), source to substrate distance (3 cm), evaporation temperature (1000 °C), oxygen flow rate (60 sccm) and evaporation time was (30 min). The charge mobility and diffusion of oxygen atoms were controlled by annealing the grown samples in oxygen environment at various temperatures from 600 to 800 °C with a step of 100 °C for one hour in muffle furnace. The observed giant enhancement in Seebeck coefficient (150-1050 μV/K) can be explained as; The annealing generates oxygen interstitials and causes the charge scattering mechanism shift from lattice to impurity scattering mechanism. In the impurity scattering mechanism, mobility of charge carriers increased with temperature. This increase in mobility results in the giant enhancement of Seebeck coefficient. The argument was verified by Hall data which suggested that concentration of oxygen interstitials increased by annealing temperature. To further strengthened our argument we have performed XRD and FTIR measurements. XRD data has showed that as grown sample consists of one peak at angle 32° related to (006) phase of CuAlO2. Annealing resulted in the generation of new phases at angles 35°, 42.5° and 48.4° which were related to CuO (111), CuAlO2 (104) and CuAlO2 (009) respectively. FTIR spectrum verified the presence of Cu-O and Al-O at wavenumbers 450 cm−1 and 600 cm−1 respectively.