Effects of Ga doping on the properties of the Ag/GZO/Si:p/Au heterostructures for photovoltaic applications

Abstract

Nanostructured layers of zinc oxide are promising compounds for sensor and solar cell applications. Such layers can be obtained by combining both sol–gel and pulsed laser deposition (PLD) preparation methods. Gallium-doped zinc oxide (GZO) nanoparticles were synthesized using the sol–gel method. The obtained powder was used to deposit thin films of GZO on glass and p-silicon substrates by PLD. The effect of Ga doping concentration on the morphological, optical and electrical properties of the GZO thin films was investigated. Scanning electron microscopy images reveals particle homogenous surface and particles in nonmetric size. GZO thin films showed more than 90% transparency in the entire visible region. The relationship between electrical properties and Ga doping concentration was clarified by analyzing the current–voltage (I-V), capacitance–voltage (C-V), and conductance-frequency (G-ω) characteristics of the Ag/GZO/Si:p/Au structure over a wide range of temperature, frequency, and voltage bias. I-V and C-V characteristics show that our structure is formed by two back-to-back diodes. The GZO/Si:p heterojunction governs the electrical response at low temperatures and the Ag/GZO Schottky junction takes over at higher temperatures. At low temperature (T ≤ 160 K), high rectifying behavior of the Si:p/GZO p-n heterojunction was observed for Ga doping concentration 1 at%. The carrier concentration of the GZO thin films is calculated from the C⁻²-V characteristics. The analysis of impedance dependent on frequency, reveals that the relaxation is a thermally activation process. Activation energies of defects in GZO thin films and their effects on the electronic properties of Ag/GZO/Si:p/Au structure are obtained. This investigation makes a valuable contribution to the behavior of defects in GZO thin films to optimize their properties for solar cell applications.