Insulating epitaxial films of BaF 2, CaF 2 and Ba xCa 1− xF 2 grown by MBE on InP substrates

• Published in: Journal of crystal growth Vol. 60; no. 2; pp. 403 - 413
• Main Authors: Sullivan, P.W., Farrow, R.F.C., Jones, G.R.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1982
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/0022-0248(82)90118-X

Thin films (≤ 5000 Å) of BaF 2, CaF 2, and Ba x Ca 1− x F 2 have been grown onto InP (001) substrates in a vacuum locked MBE system. Electron diffraction was used to monitor film nucleation and growth at a variety of substrate temperatures. Subsequent ex-situ analysis included X-ray diffraction, electron microscopy and Auger sputter profiling. In addition, capacitance-voltage and current-voltage analyses were performed on MIS sandwich devices formed by evaporating aluminium onto the semiconductor-flouride samples. Deposition of flourides onto room temperature substrates resulted in the growth of smooth, pinhole free, stoichiometric polycrystalline films with little or no preferred orientation. TEM analysis indicates a grain size of the same order as the film thickness (∼ 1000 Å). Deposition of BaF 2 and CaF 2 onto cleaned, well-ordered (001) InP held at temperatures above 200°C resulted in single-crystal, heteroepitaxial growth. In the case of CaF 2, the increase in lattice mismatch on cooling to room temperature resulted in crazing of the epitaxial layer. Film resistivity values around 10 12–10 13 ω cm and breakdown strengths of 5x10 5V cm -1 have been achieved for both polycrystalline and single-crystal layers. In initial experiments on the growth of Ba x Ca 1− x F 2 alloys onto (001) epitaxial films of a single-phase cubic alloy with x ∼ 0.2 were obtained.