ZnO Homojunction for Cross-Bar Memory
Ł. Wachnicki1,2, A. Szczepanik1,2, T. Krajewski1, P. Kruszewski1, K. Kopalko1,
E. Guziewicz1, M. Godlewski1,2
1
Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668,
Poland
2
Cardinal Stefan Wyszynski University, College of Science, Department of Mathematics and
Natural Sciences, Warszawa, Poland
Zinc oxide is a II-VI semiconductor with a direct band gap energy of 3.37 eV at room
temperature. This semiconductor shows advantageous physical and chemical properties,
which makes this material very attractive for many applications, including transparent
electrodes in solar cells and Light Emitting Devices (LEDs). For the latter application of ZnO
in optoelectronic devices, it is necessary to grow the ZnO based p-n junction.
At present there are only limited reports on ZnO homojunction LEDs due to the
absence of a reliable p-type doping of zinc oxide. Only a few groups made homojunctions
using p-type ZnO with such dopants as N, As, Sb and sputtering, Molecular Beam Epitaxy,
Pulsed Laser Deposition, Metalorganic Chemical Vapour Deposition. Electric parameters of
such homojunctions are rather poor [1].
We report on first ZnO-based homojunction based on thin films grown by the Atomic
Layer Deposition (ALD) method. We used an ammonia water precursor, which plays a double
role in the process. It delivers oxygen to an exchange reaction with diethylzinc and, on the
other hand, introduces nitrogen which is the p-type dopant in ZnO. In our reaction we used
low temperature, in comparison with other growth methods, which is important for
implementation of so obtained junctions in cross-bar (3D) memory devices.
Our ZnO thin films have a polycrystalline structure and show very reproducible
electrical properties [2, 3]. We can control their electrical properties by adjusting conditions
of the ALD process such as temperature, precursor pulse time, etc.
The homojunction is based on two layers of ZnO, grown at different temperature and a
different oxygen precursor with n-type ZnO at the bottom and p-type ZnO on the top. These
two ZnO layers were deposited at the range of temperature between 600C and 2000C using a
very reactive metalorganic precursor (diethylzinc) [2-3]. We used ITO as a back contact to ntype ZnO. The I(V) characteristics were measured. We report rectification ratio of 1.98×102 at
1.5 V, showing that homojunction has a good quality.
The work was supported by polish grant SPUB No. 180/6.PR UE/2006/7 (6 Framework
Programme – priorytet 2 (IST)) and European project FP6 026714 VERSATILE.
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