Interaction between Na and Li in ZnO

Abstract

The interaction between group-Ia elements in ZnO have been studied by implanting Na into hydrothermally grown ZnO samples containing ∼4×1017 Li/cm3 and employing secondary ion mass spectrometry for sample analysis. Postimplantation annealing above 500 °C results in a diffusion of Na and concurrently Li is efficiently depleted from the regions occupied by Na. The data show unambiguously that Na and Li compete for the same trapping site and the results provide strong experimental evidence for that the formation energies of Na on Zn site together with that of interstitial Li are lower than those of Li on Zn site and interstitial Na in highly resistive ZnO. This conclusion is also supported by recent theoretical estimates of the formation energies of these species as a function of the Fermi-level position in ZnO.

Acceptor Type Vacancy Complexes In As-Grown ZnO

“…The small increase can be related to an outward relaxation of the atoms around the resulting complex. Similar defects has been observed in Hydrothermal ZnO with high content of Li (10 17 cm -3 ) where Li and Na are in substitutional position of Zn [10,11].…”

Defect evolution and impurity migration in Na-implanted ZnO

“…1(a), a measurable Na diffusion is found at 800 • C (A 3), while the redistribution of Li occurs already at 600 • C (A 2), indicating Li/Na interaction at 600 • C or below. 22 The 800 • C anneal results in a boxlike Na profile with a plateau at ∼4 × 10 17 cm −3 (A 3), characteristic of trap-limited diffusion (TLD), while the sample annealed at 950 • C (A 4) exhibits a long Na tail resembling Fickian diffusion. For the wafer B, Fig.…”

“…1(a)-1(d), respectively, and they are found to exhibit qualitatively different behavior. Firstly, competition between Na and Li occurs in wafers A and B upon the heat treatment, e.g., Li is depleted from the Na-rich region after 600 • C. 22 Subsequently, Li returns to this region when the Na concentration decreases at higher temperatures. 23 In the wafer A, Fig.…”

“…Wardle et al 18 also predicted that Na would be more stable on a zinc site as compared to Li, which has been experimentally confirmed. 22 Since E form (Na Zn ) + E form (Li i ) < E form (Na i ) + E form (Li Zn ), Na i causes Li Zn to change the configuration to Li i , which will diffuse and eventually get trapped in the sample bulk.…”

Intrinsic Point-Defect Balance in Self-Ion-Implanted ZnO

“…However, a high Li content in HT ZnO is an issue of concern and postgrowth treatment is required for its reduction [7,8]; especially, Li exhibits a so-called amphoteric behavior resulting in highly compensated material [9,10]. In as-grown HT ZnO, Li resides predominantly on Zn site [9], forming Li Zn acceptors, but can be potentially kicked out to an interstitial donor position (Li I ) during, for instance, postimplantation anneals [11]. Accordingly, HT ZnO, naturally containing $2 Â 10 17 Li=cm 3 , is a suitable model system to identify dominating residual point defects involved in the Li Zn kick-out mechanism.…”