Comparative investigations of structural, electronic, optical, and thermoelectric properties of pure and 2 at. % Al-doped ZnO

Abstract

Context: We comparatively investigate the properties of pure ZnO and 2 at. % Al doping concentration of ZnO, AZO, as potential candidates for specific applications.

Methods: Calculations were carried out, using Wien2k package, to deduce structural, electronic, optical thermoelectric, and properties of both ZnO and AZO materials via the combination of GGA and mBJ approximations.

Results: It is shown that Al doping of ZnO (AZO) improves its optical properties; the deduced direct fundamental gap is enhanced due to the Burstein-Moss effect. Moreover, the dielectric function, at lower energies, confirms the existence of an extra strong fluctuation in the dispersive real part ɛ₁(ω) and a high peak for absorptive imaginary parts ɛ₂(ω) which are due to a variation in specific molecular bonding and the transition between the occupied and the non-occupied states. The critical point, observed at 2.81 eV for pure ZnO, is shifted to 3.3 eV in 2 at. % AZO, confirming a larger optical band gap. The reflectivity values slightly decreased for 2% AZO. The investigation of thermoelectric parameters as a function of chemical potential at different temperatures ranging from 300 to 900°C showed that these structures can be considered for good thermoelectric devices with (i) high absolute values of Seebeck coefficient: ׀S_ZnO׀ = 1.16 mV/K and ׀S_AZO׀ = 0.746 mV/K, (ii) no effect of temperature on electrical conductivity but a strong effect on thermal conductivity, (iii) a high value approaching unity for the figure of merit. Hence, these properties and their improvements, introduced by Al doping of ZnO, lead specific and more uses in optoelectronics, energy, and piezoelectric applications.

Keywords: AZO; GGA-mBJ; Wien2k; ZnO.