APPLIED PHYSICS LETTERS
VOLUME 83, NUMBER 2
14 JULY 2003
Electrical activity of nitrogen acceptors in ZnO films grown by metalorganic
vapor phase epitaxy
a)
`
J. F. Rommeluere, L. Svob, F. Jomard, J. Mimila-Arroyo, A. Lusson, V. Sallet,
and Y. Marfaingb)
`
Laboratoire de Physique des Solides et de Cristallogenese, CNRS, 92195 Meudon Cedex, France
͑Received 2 January 2003; accepted 15 May 2003͒
The electrical activity of nitrogen as an acceptor in ZnO has been investigated in two ways. First,
nitrogen was introduced by means of diallylamine during metalorganic vapor phase epitaxy
͑MOVPE͒ yielding incorporation of nitrogen in the range 1016–1021 cmϪ3. This led to significant
compensation of the natural donors with a minimum electron concentration of 5ϫ1014 cmϪ3
.
Second, diffusion of nitrogen was carried out on undoped MOVPE layers under high pressure
conditions stemming from the decomposition of NH4NO3 . Conversion to p-type conductivity was
observed in a systematic way with measured hole concentrations up to 6.5ϫ1017 cmϪ3
American Institute of Physics. ͓DOI: 10.1063/1.1592621͔
. © 2003
The current high interest in wide band gap semiconduc-
tors has led to reconsider the case of zinc oxide ͑ZnO͒. Non-
intentionally doped ZnO is usually n type, which has been
linked to either the presence of native defects, groups III and
VII impurities and more recently to hydrogen.1 By contrast
realization of p-type conductivity is more problematic and
this topic is now attracting much attention at the theoretical
and experimental levels.
led to minimum electron concentration in undoped layers
(2–3ϫ1017 cmϪ3).
In situ nitrogen doping of ZnO layers grown on ͑0001͒
sapphire was achieved by introducing diallylamine in the
reactor at a partial pressure P. The concentration of incorpo-
rated dopant ͓N͔ was measured by secondary ion mass spec-
trometry ͑SIMS͒. Resistivity and Hall effect measurements
were performed at 300 K in the Van der Pauw configuration
with four In contacts deposited on the ZnO layers. The con-
centration ͓N͔ increased with increasing P and decreasing
A few papers have claimed achievement of hole conduc-
tivity by doping with the acceptor NO coming from various
doping sources: NH3 ,2 N2O,3 N2 ,4 monomethyl-hydrazine.5
Furthermore p type was also mentioned as a result of doping
with As,6 Sb7 and of interaction with oxygen-rich
atmospheres.8,9 On the theoretical side several papers have
dealt with the energetics of native defects10–13 and the spe-
cific aspects of incorporation and compensation of nitrogen
in ZnO.13–15 A general conclusion is that a number of point
defects and defect complexes can act as compensating do-
R
VI/II, the ratio of the oxygen to zinc precursors partial pres-
sures, as seen in Figs. 1 and 2. ͓N͔ spanned the range
1016–1021 cmϪ3
.
The corresponding electrical properties are given in
Table I. The electron concentration decreases as ͓N͔ in-
creases, reaching the minimum value n0ϭ5ϫ1014 cmϪ3 for
N ϭ1021 cmϪ3. These results give evidence of the electri-
͓ ͔
cal activity of N as a compensating acceptor. However,
p-type conversion was not obtained, due to either a limited
electrical activity of nitrogen or a high concentration of do-
nor defects.
nors on the p-type side: Zn2i ϩ , Zn2Oϩ , VO2ϩ , (N2)2Oϩ
,
(NO–Zni)ϩ. These defects are generally favored in the Zn-
rich conditions of growth. Moreover it was stressed that us-
ing NO or NO2 is the most efficient way to dope ZnO p
type.14
In a second series of experiments diffusion of nitrogen
The earlier considerations are the background of the
present work which comprises two separate experiments.
First, nitrogen was incorporated during the growth of ZnO
films, leading to significant electrical compensation of the
residual or induced donors. Second, diffusion of nitrogen in
oxidizing atmosphere were performed on undoped layers
which allowed one to overcome the compensated state, then
yielding p-type conductivity.
ZnO epitaxial layers were grown at atmospheric pressure
by metalorganic vapor phase epitaxy ͑MOVPE͒ in a horizon-
tal reactor on sapphire substrates.16 The organic sources were
dimethylzinc-triethylamine, tert-butanol and the growth tem-
perature Tg was 420 °C. The layer thickness was in the range
1–2 m. In these conditions, use of the carrier gas N2 has
a͒
Present address: Cinvestav-IPN, Mexico D.F., Mexico.
Electronic mail: marfaing@cnrs-bellevue.fr
FIG. 1. Concentration of nitrogen incorporated in MOVPE grown ZnO
layers vs the pressure of the N precursor.
b͒
0003-6951/2003/83(2)/287/3/$20.00 287 © 2003 American Institute of Physics
129.12.233.101 On: Tue, 02 Dec 2014 15:29:33