In:
Journal of Materials Research, Springer Science and Business Media LLC, Vol. 12, No. 5 ( 1997-05), p. 1214-1236
Abstract:
Epitaxial Tl 2 Ba 2 CaCu 2 O 8 thin films with excellent electrical transport characteristics are grown in a two-step process involving metal-organic chemical vapor deposition (MOCVD) of a BaCaCuO(F) thin film followed by a postanneal in the presence of Tl 2 O vapor. Vapor pressure characteristics of the recently developed liquid metal-organic precursors Ba(hfa) 2 • mep (hfa = hexafluoroacetylacetonate, mep = methylethylpentaglyme), Ca(hfa) 2 • tet (tet = tetraglyme), and the solid precursor Cu(dpm) 2 (dpm = dipivaloylmethanate) are characterized by low pressure thermogravimetric analysis. Under typical film growth conditions, transport is shown to be diffusion limited. The transport rate of Ba(hfa) 2 • mep is demonstrated to be stable for over 85 h at typical MOCVD temperatures (120 °C). In contrast, the vapor pressure stability of the commonly used Ba precursor, Ba(dpm) 2 , deteriorates rapidly at typical growth temperatures, and the decrease in vapor pressure is approximately exponential with a half-life of ∼9.4 h. These precursors are employed in a low pressure (5 Torr) horizontal, hot-wall, film growth reactor for growth of BaCaCuO(F) thin films on (110) LaAlO 3 substrates. From the dependence of film deposition rate on substrate temperature and precursor partial pressure, the kinetics of deposition are shown to be mass-transport limited over the temperature range 350–650 °C at a 20 nm/min deposition rate. A ligand exchange process which yields volatile Cu(hfa) 2 and Cu(hfa) (dpm) is also observed under film growth conditions. The MOCVD-derived BaCaCuO(F) films are postannealed in the presence of bulk Tl 2 Ba 2 CaCu 2 O 8 at temperatures of 720–890 °C in flowing atmospheres ranging from 0–100% O 2 . The resulting Tl 2 Ba 2 CaCu 2 O 8 films are shown to be epitaxial by x-ray diffraction and transmission electron microscopic (TEM) analysis with the c -axis normal to the substrate surface, with in-plane alignment, and with abrupt film-substrate interfaces. The best films exhibit a T c = 105 K, transport-measured J c = 1.2 × 105 A/cm 2 at 77 K, and surface resistances as low as 0.4 mΩ (40 K, 10 GHz).
Type of Medium:
Online Resource
ISSN:
0884-2914
,
2044-5326
DOI:
10.1557/JMR.1997.0171
Language:
English
Publisher:
Springer Science and Business Media LLC
Publication Date:
1997
detail.hit.zdb_id:
54876-5
detail.hit.zdb_id:
2015297-8
