ZnO thin films grown with spatially tuned electrical and optical properties at room
temperature
F. Gherendi
1
, N. B. Mandache
1
, L. Ion
2
M. Nistor
1
1
National Institute for Lasers, Plasma and Radiation Physics (NILPRP), L22, P.O. Box. MG-
36, 77125 Bucharest-Magurele, Romania
2
University of Bucharest, Faculty of Physics, 77125 Bucharest-Magurele, Romania
E-mail
ZnO thin films are a widely adopted alternative for replacing doped and non-doped
indium oxide films for transparent electronics and photovoltaic device applications. In this
study, undoped ZnO thin films were grown by pulsed electron beam deposition (PED), an
ablation technique similar to pulsed laser deposition (PLD), where a pulsed electron beam is
used instead of the pulsed laser beam. The films were grown at room temperature, using
different working parameters for the PED device,
on SiO
2
/ Si wafer or large area glass
substrates. The optical and electrical properties of the films were spatially tuned using a
shadow mask placed at a distance from the substrate as an obstacle, constraining the ablation
plasma plume to bypass the obstacle by surrounding it and thus changing
the film
composition (Zn/O ratio) over a range of several centimeters. The electrical resistivity was
spatially mapped on the film across the obstacle shadow, using in-line four point probes. The
film resistivity varies between 7x10
-4
Ω cm in the non-shadowed region, and 1 Ω cm in the
center of the shadowed region, for a film grown at 1.4x10
-2
mbar working pressure of oxygen.
Optical transmittance measurements in UV-visible-near infrared region and
photoluminescence spectroscopy were performed in the shadowed and non-shadowed regions.
From Tauc plots, the band gap was determined, varying between 3.23 eV, in the non-
shadowed regions, and 3.28 eV in the center of the shadowed region. Hall effect
measurements were also performed for the regions of the film, revealing a spatial variation of
the carrier density up to a few orders of magnitude. The tunable resistivity, carrier density,
stoichiometry and optical properties of ZnO thin films grown in these conditions make this
growth method interesting for low-cost transparent electronics. One can obtain, by
downscaling the deposition geometry, source-channel-drain structures for thin film transistors
[1], or resistive random access memory devices, in a single fabrication step.
[1] F. Gherendi, M. Nistor, S. Antohe, L. Ion, I. Enculescu, N.B. Mandache,
Semicond. Sci.
Technol.
28
(8), 085002 (2013)
PS2 3
-197-
