Evidence for the AlZn-Oi defect-complex model for magnetron-sputtered aluminum-doped zinc oxide: A combined X-ray absorption near edge spectroscopy, X-ray diffraction and electronic transport study

Abstract

Al-doped ZnO and Zn1 − xMgxO films, deposited by magnetron sputtering at substrate temperatures from about 25 °C to 500 °C and exhibiting a strong variation of the carrier concentration, were investigated by X-ray absorption spectroscopy (XAS), analyzing the X-ray absorption near-edge structures. The near-order structure, derived from the X-ray absorption spectra, shows that the dopant Al was built-in onto Zn lattice sites, independently of the deposition temperature up to 450 °C. FEFF calculations confirm the lattice location of the dopant on zinc lattice sites. The formation of secondary (spinel) phases occurs only at deposition temperatures above 450 °C, more pronounced for the Zn1 − xMgxO:Al films. In contrast to the XAS measurements, the electrical parameters of the films—carrier concentration and Hall mobility—exhibit a strong dependence on the substrate temperature, with a variation of the electron concentration by a factor of 4.5 from 25 °C to about 300 °C. This shows that the XAS method is significantly less sensitive compared to electrical measurements for the characterization of electrically active dopant elements. This fact is tentatively explained by the formation of oxygen interstitial defects Oi during deposition, annealing out at low temperatures, and by the formation of defect complexes of dopant atoms with intrinsic lattice defects, like Al-Oi or Al-Mg-Oi, which induce the observed electrical effects but are not detectable by XAS methods.

Electrical and Optical Properties of Amorphous SnO2:Ta Films, Prepared by DC and RF Magnetron Sputtering: A Systematic Study of the Influence of the Type of the Reactive Gas

“…The quite low carrier concentrations of the SnO 2 :Ta films could be caused by an inactivation/compensation of the donors (Ta Sn ) by other defects, already mentioned above (O i , V O etc.). Similar compensation effects were recently reported by T-Thienprasert et al and by us for Al-doped ZnO[49,50].…”

“…It is nearly constant at a concentration of 1.5 at%. This means that the observed variation in the electrical parameters as a function of the reactive gas pressure is not caused by a variation in the chemical dopant amount, but by a varying electrical activation of the dopant Ta and/or by compensation of the electrons by acceptor-like defects-see, for instance, [49,50].…”

High performance GZO/p-Si heterojunction diodes fabricated by reactive co-sputtering of Zn and GaAs through the control of GZO layer thickness

“…71 It is also known that nonstoichiometric Ga x O y phases can be formed during the sputtering of Ga 2 O 3 lms, leading to a wide range of oxygen substoichiometry 72 and there is also a possibility of forming ZnGa 2 O 4 phase. 73,74 Another possibility is the strong compensation due to the formation of acceptor complexes, such as, (Ga Zn + O i ) and (Al Zn + O i ), [75][76][77] respectively reported in Ga and Al doped ZnO lms, grown under O-rich conditions. A recent X-ray absorption study of reactively sputtered GZO lms from our group 47 has shown that the formation of (Ga Zn + O i ) acceptor complex depends critically on the availability oxygen during sputtering.…”

Ce doping induced trapping states and local electronic structure modifications in SrZnO2 nanophosphors

“…Such alterations can be studied well by X-ray absorption spectroscopy (XAS), which is an efficient technique to investigate the local electronic structure around the atom of interest. 10,11 Apart from that, thermoluminescence (TL) is a widely employed technique to characterize electron and hole trapping states present in the system. 12 TL deals with the detection of radiative signal caused by the recombination of electron and holes from such trapping states when defect centres are excited with various irradiation sources.…”

“…Such alterations can be studied well by X-ray absorption spectroscopy (XAS), which is an efficient technique to investigate the local electronic structure around the atom of interest. 10,11…”