Reduced temperature-quenching of photoluminescence from indium nitride nanotips grown by metalorganic chemical vapor deposition

Article abstract of DOI:10.1063/1.2128484

We report metalorganic chemical vapor deposition of indium nitride (InN) nanotips with apex angles of 10° and length and base diameter of around 1 μm and 200 nm, respectively. The structure of the hexagonal InN nanotips growing along [002] was studied by electron microscopy and x-ray diffraction, and the optical properties were studied using temperature-dependent photoluminescence (PL) measurements. A narrow emission peak with a 18 meV full width at half maximum positioned at 0.77 eV was obtained with no visible emission. A PL quenching of only 14% was observed with a temperature scan of 15-320 K.

Full text of DOI:10.1063/1.2128484

Reduced temperature-quenching of photoluminescence from indium nitride nanotips
grown by metalorganic chemical vapor deposition
Shih-Chen Shi, Chia-Fu Chen, Geng-Ming Hsu, Jih-Shang Hwang, Surojit Chattopadhyay, Zon-Huang Lan, Kuei-
Hsien Chen, and Li-Chyong Chen
Citation: Applied Physics Letters 87, 203103 (2005); doi: 10.1063/1.2128484
View online: http://dx.doi.org/10.1063/1.2128484
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APPLIED PHYSICS LETTERS 87, 203103 ͑2005͒
Reduced temperature-quenching of photoluminescence from indium nitride
nanotips grown by metalorganic chemical vapor deposition
Shih-Chen Shi and Chia-Fu Chen
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 300, Taiwan,
Republic of China
Geng-Ming Hsu and Jih-Shang Hwang
Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung 202, Taiwan,
Republic of China
Surojit Chattopadhyay, Zon-Huang Lan, and Kuei-Hsien Chen
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan, Republic of China
a͒
Li-Chyong Chen
Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan,
Republic of China
͑
Received 24 June 2005; accepted 14 September 2005; published online 8 November 2005͒
We report metalorganic chemical vapor deposition of indium nitride ͑InN͒ nanotips with apex angles
of 10° and length and base diameter of around 1 ␮m and 200 nm, respectively. The structure of the
hexagonal InN nanotips growing along ͓002͔ was studied by electron microscopy and x-ray
diffraction, and the optical properties were studied using temperature-dependent photoluminescence
͑
PL͒ measurements. A narrow emission peak with a 18 meV full width at half maximum positioned
at 0.77 eV was obtained with no visible emission. A PL quenching of only 14% was observed with
a temperature scan of 15–320 K. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2128484͔
Indiun nitride ͑InN͒ is a key element in InGaN-based
used as growth precursors and high purity nitrogen was used
1
,2
light emitting diodes ͑LEDs͒ and also for high speed
as a carrier gas. Figure 1 shows a series of InNNT images
taken collectively by high resolution scanning electron mi-
croscopy ͑JEOL 5700F HRSEM͒ ͓Figs. 1͑a͒, 1͑b͒, and 1͑c͔͒
and high resolution transmission electron microscopy
3
electronics owing to its low electronic effective mass and
1
,2
high mobility. However, the recent controversy about the
fundamental band gap of InN has generated renewed interest
4
͓
HRTEM/ JEOL JEM 4000 EX͒ ͓Figs. 1͑e͒ and 1͑f͔͒. The
in the material. The initial estimation at near 1.9 eV has
5
sharply faceted, hexagonal InNNTs growing along ͓002͔ are
shown to carry a catalyst ͑Au in this case͒ at its apex which
is less than 10 nm in diameter ͓1͑b͔͒ and having an apex
angle of ϳ10°. To our knowledge this is the first observation
been challenged by Davydov et al. suggesting it to be near
0
.7 eV evident from photoluminescence ͑PL͒ measurements
and absorption spectroscopy. Several other reports have con-
6
,7
firmed such finding and the apparent band gap near 1.9 eV
was generally ascribed to the contribution from indium oxide
1
6
of solid InN nanotips, whereas that reported by Yin et al.
5
was a tubular form of InN. The schematic of the individual
related phase in the sample. Other possible origins for the
8
visible emission are the quantum size effect, the Burstein–
9
10
Moss shift and nitrogen excesses in InN. InN thin films
have been prepared by several routes including metalorganic
chemical vapor deposition ͑MOCVD͒, molecular beam epi-
11
taxy, chemical beam epitaxy, and vapor phase epitaxy. The
window for the growth temperature is narrow because of
nitrogen dissociation from InN around 550 °C. Reports on
1
2
nanostructured InN are scarce. InN nanoparticles and
1
3–15
nanowires
have been reported by the wet chemical syn-
thesis and vapor-liquid-solid ͑VLS͒ routes. Recently, there
has been a report on InN nanotube synthesis by a controlled
1
6
carbonitridation reaction. The scarcity of reports suggests
that there are challenges involved in growing good quality
InN nanostructures. This letter describes the MOCVD of
single crystalline InN ‘nanotips’ ͑InNNTs͒ and evaluates the
structural quality and the optical behavior of the material.
InNNTs were grown by the resistively heated MOCVD
on gold ͑2 nm͒ coated quartz substrates held at 550°C and 50
1
7
Torr pressure for 90 min. Epi-grade tri-methyl indium ͑EP-
ICHEM, UK͒ and high purity ͑99.999%͒ ammonia were
FIG. 1. ͑a͒ SEM image and ͑b͒ backscattered SEM image of InN nanotips;
͑
c͒ low magnification SEM image and ͑d͒ schematic diagram of a single InN
nanotip; ͑e͒ low magnification TEM image of a single nanotip and ͑f͒ HR-
TEM of the InN nanotip area marked in ͑e͒; inset showing the selected area
diffraction pattern of h-InN nanotip.
a͒Author to whom correspondence should be addressed; electronic mail:
chenlc@ccms.ntu.edu.tw
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003-6951/2005/87͑20͒/203103/3/$22.50 87, 203103-1 © 2005 American Institute of Physics
30.102.42.98 On: Sun, 23 Nov 2014 02:39:58
0
1

203103-2
Shi et al.
Appl. Phys. Lett. 87, 203103 ͑2005͒
FIG. 3. ͑a͒ The temperature dependent PL spectra of InN nanotips measured
with 100 mW incident laser power and 3 mm slit width. ͑b͒ Two sets of
Arrhenius plot of the normalized integrated photoluminescence intensity as
a function of inverse temperature: ͑ᮀ͒ 15–300 K, 488 nm laser, 3 mm slit
width ͑᭿͒ 15–320 K, 514 nm laser, 0.5 mm slit width.
FIG. 2. ͑a͒ EELS result showing the N–K edge and the In M4,5 -edge spectra
for the InN nanotips; ͑b͒ the x-ray diffraction spectrum of the InN nanotips
showing the hexagonal signature.
InNNT ͓Fig. 1͑d͔͒ shows its representative dimensions. The
selected area electron diffraction ͑SAED͒ of the InNNT ͓in-
set, Fig. 1͑f͔͒ also speaks of the good quality single crystal-
line hexagonal phase. The presence of polycrystalline InN
grains, which can complicate the interpretations of the PL
data presented later, can be ruled out from the observed
SAED pattern ͓inset, Fig. 1͑f͔͒ and the HRTEM images
Pr
␩
=
,
͑1͒
A
B
͓
P + P + P ͔
r
nr nr
A
B
where P , and P , are transition probabilities for two non-
nr
nr
radiative mechanisms in different temperature regimes. The
temperature dependence of the nonradiative transition prob-
abilities can be written as
͓
Figs. 1͑e͒ and 1͑f͔͒.
EX
X
Pnr = X exp
ͩ
−
ͪ
͑2͒
The composition of the InNNTs has been established
␬
T
from electron energy loss spectroscopy ͑EELS͒. The nitrogen
with X=A, or B, where E and E are the thermal activation
K edge and the In M edges, along with the fine structures,
A
B
4
,5
1
8
energies for the two processes, and A and B are temperature
independent prefactors. The temperature dependent effi-
ciency can hence be written as
were clearly seen in EELS data ͓Fig. 2͑a͔͒. Further infor-
mation on the structural quality of the InNNTs can be ob-
tained from the x-ray diffraction ͑XRD͒ ͑Rigaku DMAX/C
x-ray diffractometer͒. The XRD spectrum ͓Fig. 2͑b͔͒ shows
signature peaks of the hexagonal InN phases ͑Joint Commit-
tee for Powder Diffraction Standards, card No. 02-1450͒.
The infrared ͑IR͒ range PL was taken from a conven-
tional PL setup equipped with an InGaAs detector using Ar-
gon 488 and 514 nm line for excitation. The PL spectra of
the InNNTs measured with 488 nm laser and a 3 mm slit on
the detector path are shown in Fig. 3͑a͒. A sharp emission
1
␩͑T͒ =
.
͑3͒
A
1 + exp
Pr
EA
B
EB
ͫ
ͩ
−
ͪ
+
exp
ͩ ͪ
ͬ
−
␬T
Pr
␬T
Here, P is assumed to be independent of temperature. As-
r
suming the efficiency, ␩, to be solely governing the PL in-
tensity and that ␩͑15 K͒=100%, a high internal efficiency at
room temperature can be estimated from Fig. 3. Indication
5
,6
about the magnitude of the activation energies ͑E and E ͒
peak at 0.77 eV was observed with a linewidth full width
at half maximum of 18 meV with no significant emission
around the visible. A weak peak near 0.754 eV may be due to
A
B
can be obtained from the Arrhenius plot of the normalized
PL intensity as a function of inverse temperature ͓Fig. 3͑b͔͒
and its linear fit according to Eq. ͑3͒. Generally, two distinct
regions, one with a high activation near room temperatures
and another with low activation at low temperatures, were
obtained. Two features stand out from Fig. 3͑b͒. First, is the
extremely small value of the activation energy ͑EA
Ͻ6 meV͒ at low temperatures that supports the assumption
1
9
2
0-meV-deep donor level in InN. The peak at ϳ0.735 eV
could not be assigned at the present. Temperature depen-
dence of the IR-PL peak measured with an incident laser
power of 100 mW shows less than 14% ͑factor of 1.15͒
decrease in the emission intensity when the temperature was
varied from 15 to 300 K ͓open squares, Fig. 3͑b͔͒. The PL
efficiency ͑␩͒ defined as the ratio of the radiative transition
͑
␩͑15 K͒=100%͒ made earlier. Second, is the absence of
the PL quenching near room temperature, which, when
present, will give rise to the second region with a high ther-
probability ͑P ͒ and the sum of radiative and nonradiative
r
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transition probabilities, can be written as
mal activation energy ͑E ͒. For multiple quantum wells, such
B
1
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203103-3
Shi et al.
Appl. Phys. Lett. 87, 203103 ͑2005͒
as InGaP/AlGaInP, the thermal activation energy EA ac-
High resolution TEM demonstrated the nearly defect free
structure of the nanotips corroborated by the weak quenching
͑Ͻ14%͒ of the 0.76 eV photoluminescence peak intensity
over a 285 K temperature scan.
counts for loss mechanism within the well, whereas E ac-
B
counts for carrier emission outside the well followed by non-
2
1
radiative recombination in the barriers.
The small
activation energy ͑E ͒ below room temperature can be attrib-
A
Support from Academia Sinica, NSC and MOE, Taiwan,
and the U.S. Air Force of Scientific Research/Asian Office of
Aerospace Research and Development is gratefully acknowl-
edged. The authors thank Professor Y. F. Chen, National Tai-
wan University, for useful discussion and the use of the
IR-PL setup.
uted to excitonic binding energy with impurities. But Lam-
2
0
bkin et al. specified E to be responsible for carriers ther-
A
malizing from localized regions of order induced band edge
fluctuations in InGaP materials. In some cases the activation
energy, E , was attributed to nonradiative recombination in
B
2
2
the dislocations.
The absence of the room temperature PL quenching was
somewhat unusual and double checked with a 514 nm exci-
tation and a 0.5 mm slit on the detector path. The narrowing
of the slit width did reduce the overall intensity of the 0.77
eV line but the temperature dependence carried out from 15
to 320 K, in this case, showed a similar absence of quench-
ing ͓filled circles, Fig. 3͑b͔͒ and a small activation energy of
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