Feasible solution to n-type doping of high-resistance solar-blind 4.43 eV bandgap
Mg
0.51
Zn
0.49
O by fluorine
Lishu Liu
1
, Zengxia Mei
1
*, Yaonan Hou
1
, Huili Liang
1
, Alexander Azarov
2
,
VishnukanthanVenkatachalapathy
2
, Andrej Kuznetsov
2
, and Xiaolong Du
1
1
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of
Sciences, Beijing 100190, P. R. China
2
Department of Physics, University of Oslo, Oslo P.O. Box 1048, NO-0316, Norway
Contact e-mail
Wurtzite Mg
x
Zn
1-x
O possesses unique merits of large tunable band gap (3.37-6.3eV),
low growth temperature (100-450
C), and capabilities of wet etching processing etc. The
environment-friendly and biocompatible characteristics also make MgZnO appealing for UV
device applications. Moreover, ZnO is remarkably resistant to high-energy particle irradiation,
which is extremely important for UV photodetectors (PDs) working in the outer space.
However, a crucial issue restricting the practical use of high-Mg-content Mg
x
Zn
1-x
O is its
notably high resistance. Tuning the conductivity is therefore specifically necessary for these
films and related devices. Heterovalent cation dopants – Ga
3+
and Al
3+
for instance – have
been added into Mg
x
Zn
1-x
O to create electron carriers. However, the effectiveness of these
dopants as donors appears to decrease drastically as the Mg content (x) in Mg
x
Zn
1-x
O
increases. There has been no report on tuning the electrical properties of high-Mg-content
MgZnO with bandgap in solar-blind range using the popular Ga and Al dopants yet.
Therefore, it is worth exploring some new methods for effective n-type doping in Mg
x
Zn
1-x
O
(x>0.4) films in order to promote the corresponding device performance.
In present work, via comparative studies of doping with different cations and anion, a
route was developed to replace O atoms with F for tuning the electrical properties of
single-crystalline W-Mg
0.51
Zn
0.49
O films having a solar-blind 4.43 eV bandgap
[1]
. Fluorine
dopants were demonstrated to be effective donors, with an average concentration of 1.0×10
19
F/cm
3
. The dramatically increased carrier concentration (2.85×10
17
cm
-3
vs ~10
14
cm
-3
) and
decreased resistivity (129
cm vs ~10
6
cm) indicate that the electrical properties of
semi-insulating Mg
0.51
Zn
0.49
O film can be delicately regulated by F doping. Interestingly, two
donor levels (17 meV and 74 meV) associated with F were revealed by
temperature-dependent Hall measurements, which may be ascribed to two different
configurations of the substitutional fluorine atoms with different polarization fields along the
c-axis. A Schottky type metal-semiconductor-metal UV PD manifests a remarkably enhanced
photocurrent, two orders of magnitude higher than that of the undoped counterpart. These
results exhibit F doping serves as a promising pathway for improving the performance of
high-Mg-content Mg
x
Zn
1-x
O-based devices. In addition, the purification and solidification
process to the chosen doping source --ZnF
2
powder and their unique advantages, high-purity
and solid phase for example, may offer a new approach for fluorine doping attempts in other
wide bandgap oxides.
[1] Lishu Liu, et al. Fluorine doping
：
A feasible solution to enhancing the conductivity of
high-resistance wide bandgap MgZnO active components.
Scientific Reports
5, 15516 (2015).
O 41
-103-
