Oxygen rich p-type ZnO thin films using wet chemical route with enhanced carrier concentration by temperature-dependent tuning of acceptor defects

Abstract

This paper reports the temperature-dependent tailoring of acceptor defects in oxygen rich ZnO thin films, for enhanced p-type conductivity. The oxygen rich p-type ZnO thin films were successfully grown by pulsed laser deposition on silicon substrate at different postdeposition annealing temperatures (500-800 C). The oxygen rich ZnO powder was synthesized by wet chemical method using zinc acetate dihydrate [Zn(CH 3 COO) 2 Á2H 2 O] and potassium hydroxide (KOH) as precursors. The powder was then compressed and sintered to make pellets for pulsed laser deposition system. The x-ray diffraction analysis exhibits an improved crystallinity in thin films annealed at elevated temperatures with a temperature-dependent variation in lattice constants. An analysis of Auger Zn L 3 M 4,5 M 4,5 peak reveals a consistent decrease in interstitial zinc (Zn i) exhibiting its temperaturedependent reversion to zinc lattice sites. Room temperature photoluminescence of the p-type ZnO shows a dominant deep level emission peak at $3.12 eV related to oxygen interstitials (acceptors). The relative concentration of oxygen interstitials (O i) increases with increase in annealing temperature, resulting in enhanced hole carrier concentration. The maximum hole carrier concentration of 6.8 Â 10 14 cm À3 (indicating p-type conductivity) was estimated using Hall probe measurements for the thin film sample annealed at 700 C. V

Morphological, optical and X-ray photoelectron chemical state shift investigations of ZnO thin films

“…4 shows the XPS survey scan of the ZnO thin films at different thickness. In addition to the Zinc (Zn) and Oxygen (O) there is also an evidence for the presence of carbon which may be considered as an impurity during the transfer of samples from ALD to XPS chamber [35,36]. Fig.…”

Temperature-dependent stoichiometric alteration in ZnO:Mn nanostructured thin films for enhanced ferromagnetic response

“…Pelletized PLD targets of ZnO:Mn (with 5% Mn concentration) were synthesized through wet chemical method with the processing conditions reported elsewhere [10][11][12] in our previous studies. The PLD chamber was evacuated to a base pressure of the order of ~10 -6 mbar prior to thin film deposition.…”

Evolution of room temperature ferromagnetism with increasing 1D growth in Ni-doped ZnO nanostructures

“…Sanchez et al have reported that the uncompensated surface spins enhance the spin polarization induced by substitute Ni ions and even in the absence of magnetic ions, it might promote the formation of pderived extended magnetic states [54]. Further, presence of O i , in our samples is favorable to exhibit presence of holes due to the activation of acceptor states [40]. The activation of acceptor states for hole formation might be partly responsible for the enhancement in HTFM in the Ni doped ZnO NRs, also it is consistent with the Dietl's prediction of hole mediated ferromagnetism in Mn doped ZnO system [1].…”

“…Next an intense yellow emission (Peak IV) is observed from all of the samples, centered on~2.05 eV. This emission peak may be attributed to the recombination process associated with the ionized oxygen interstitials (O i ) induced transitions [35,40]. Most of the theoretical calculations agree that Zn V and O V are the lowest energy defects, while the Zn i, O i are to be higher in energy.…”