222–282 nm AlGaN and InAlGaN-based deep-UV LEDs fabricated ...

Phys. Status Solidi A 206, No. 6, 1176–1182 (2009) / DOI 10.1002/pssa.200880961
physica
222–282 nm AlGaN
and InAlGaN-based deep-UV LEDs fabricated
on high-quality AlN on sapphire
pss
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applications and materials science
Hideki Hirayama *, 1, 2, 3 , Sachie Fujikawa 1, 2, 3 , Norimichi Noguchi 1, 2, 3 , Jun Norimatsu 1, 2, 3 , Takayoshi Takano 1, 4 ,
Kenji Tsubaki 1, 4 , and Norihiko Kamata 2, 3
1
RIKEN, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan
2
Saitama Univ. 255, Shimo-Okubo, Sakura-ku, Saitama, Saitama 388-8570, Japan
3
JST, CREST, 4-1-8, Honcho, Kawaguchi-shi, Saitama 322-0012, Japan
4
Panasonic Electric Works, Ltd., 1048 Kadoma, Osaka 571-8686, Japan
Received 22 September 2008, revised 14 January 2009, accepted 15 January 2009
Published online 25 March 2009
PACS 61.72.Lk, 78.55.Cr, 78.60.Fi, 81.05.Ea, 81.15.Gh, 85.60.Jb
* Corresponding author: e-mail hirayama@riken.jp, Phone: +81-48-462-1247, Fax: +81-48-462-1276
We demonstrate 222–282 nm AlGaN and InAlGaN-based
deep ultraviolet (DUV) light-emitting diodes (LEDs) fabricated
on low threading dislocation density (TDD) AlN template.
Low TDD AlN templates were realized by using ammonia
(NH 3 ) pulse-flow multilayer (ML) growth technique.
The edge- and screw-type dislocation densities of AlN layer
were reduced to 7.5 × 10 8 and 3.8 × 10 7 , respectively. Singlepeaked
electroluminescence (EL) were obtained for 222–
273 nm AlGaN multi quantum well (MQW) DUV-LEDs. We
obtained the maximum output power of 1.1 mW and 4.0 mW
for the AlGaN-QW LEDs with wavelengths of 241 nm,
256 nm, respectively, under room temperature (RT) CW operations.
The maximum output power of 227 nm and 222 nm
AlGaN-QW were 0.15 mW and 0.014 mW, respectively, under
RT pulsed operation. The maximum external quantum efficiency
(EQE) of the 227 nm and 250 nm AlGaN LEDs were
0.2% and 0.43%, respectively. We also fabricated 280 nm
band quaternary InAlGaN-MQW DUV-LEDs with n-type
and p-type InAlGaN layers on ML-AlN templates. We demonstrated
extremely high internal quantum efficiency (IQE)
of 284 nm InAlGaN-QW emission, which was confirmed by
the fact that the ratio of the integrated intensity of the RT-PL
against the 77 K-PL was 86%. The maximum output power
and EQE of the 282 nm InAlGaN LED were 10.6 mW and
1.2%, respectively, under RT CW operation.
© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1 Introduction Because of their wide direct transition
energy range in UV, which is between 6.2 eV (AlN) and
3.4 eV (GaN), AlGaN and quaternary InAlGaN are attracting
considerable attention as candidate materials for the realization
of deep ultraviolet (DUV) laser diodes (LDs) or
light-emitting diodes (LEDs) [1, 2]. DUV LEDs and LDs
with emission wavelengths in the range of 230–350 nm
are expected for a lot of applications, such as, sterilization,
water purification, medicine and biochemistry, light
sources for high density optical recording, white light illumination,
fluorescence analytical systems and related information
sensing fields, air purification equipment, and
zero-emission automobiles.
Research into AlGaN-based UV LEDs for wavelengths
shorter than 360 nm, i.e., wavelengths between 330–
355 nm [3–5], was initiated by several research groups between
1996–1999. The development of short-wavelength
UV LEDs is now becoming extremely competitive. Several
groups have reported AlGaN-, InAlGaN-, or AlNbased
DUV LEDs, 240–280 nm AlGaN multi-quantumwells
(MQWs) LEDs [6–10], quaternary InAlGaN MQW
LEDs [1, 11–13] and a 210 nm AlN LED [14].
We started our research into AlGaN-based deep-UV
LEDs in 1997. We reported first efficient DUV (230 nm)
photoluminescence (PL) from AlGaN QWs [15], and
333 nm AlGaN-QW UV LED on SiC in 1999 [3]. We have
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Phys. Status Solidi A 206, No. 6 (2009) 1177
also developed high-efficiency UV emission using quaternary
InAlGaN QWs [16, 17], and achieved high-efficiency
InAlGaN-based LEDs [11, 12, 18]. Recently we developed
low threading dislocation density (TDD) AlN template on
sapphire, and achieved efficient AlGaN-QW DUV-LEDs
with emission wavelengths at 231–261 nm [11]. We also
obtained sub-230 nm DUV-LEDs by the further reduction
of TDD and by using thin quantum well.
In this report, we demonstrate 222–282 nm AlGaN
and InAlGaN-based DUV-LEDs fabricated on high-quality
AlN buffers on sapphire. First, we describe on the fabrication
of low TDD AlN template on sapphire by using NH 3
pulse-flow multilayer (ML) growth technique, and describe
on remarkable increase of AlGaN-QW emission by introducing
the low TDD AlN templates. Then, we demonstrate
222–273 nm efficient AlGaN-QW DUV-LEDs fabricated
on ML-AlN templates. We also demonstrate quite high
IQE observed from an InAlGaN-QW with emission at
280 nm fabricated on a ML-AlN template. At last, we
demonstrate over 10 mW CW output power 280 nm-band
DUV-LED with quaternary InAlGaN emitting and p-type
layers.
2 Fabrication of low threading dislocation density
AlN template It is required to satisfy several conditions
for achieving high-quality AlGaN/AlN templates that
are applicable to deep-UV emitters, i.e., low threading dislocation
density (TDD), crack free, atomically flat surface
and stable Al (+c) polarity. In order to obtain all of the
conditions mentioned above, we proposed ammonia (NH 3 )
pulse-flow multi-layer (ML) growth method. Figure 1
shows the gas flow sequence used for NH 3 pulse-flow
growth, and schematic view of the growth control method
using pulse- and continuous-flow gas feeding growth.
The samples were grown on sapphire (0001) substrates
by low-pressure metal-organic chemical vapor deposition
(LP-MOCVD). First, an AlN nucleation layer and a burying
AlN layer were deposited, both by NH 3 pulse-flow
growth. Trimethylaluminum (TMAl) flow was continuous
during the NH 3 pulse-flow sequence, as shown in Fig. 1.
Low-TDD AlN can be achieved by the coalescence pro-
Figure 2 FWHM of X-ray diffraction (10 12) ω-scan rocking
curve (XRC) for various stage of ML-AlN growth.
cess of AlN nucleation layer. After the growth of the first
AlN layer, the surface is still rough because of the low
growth rate of the pulse-flow mode. We introduced the
high-growth-rate continuous-flow mode in order to reduce
the surface roughness. By repeating the pulse- and continuous-flow
modes, we obtained a crack-free, thick AlN
layer with an atomically flat surface. NH 3 pulse-flow
growth is effective for obtaining high-quality AlN because
of the enhancement of precursor migration. Furthermore, it
is effective for obtaining the stable Al (+c) polarity that is
necessary for realizing atomically flat surfaces, because of
the Al-rich growth condition. The growth rates in the
pulse- and continuous-flow modes were approximately
0.66 µm/hour and 6 µm/hour, respectively.
The advantage of the use of a ML-AlN for the DUV
LED is that low TDD AlN can be obtained without using
AlGaN layers, yielding a device structure with minimal
NH 3 pulse-flow growth
∑ Migration Enhance Epitaxy
∑ Al rich condition= stable Al (+c) polarity
TMAl
NH3
5s 3s 5s 3s 5s
AlN
AlN
AlN
AlN
Sapphire Sapphire Sapphire Sapphire
1. Growth of
nucleation AlN layer
(NH3 Pulse-flow)
2. Burying growth with
lateral enhancement
growth mode
(NH3 pulse-flow)
Reduction of threading
dislocation density (TDD)
3. Reduction of surface
roughness with
high-speed growth
(continuous flow)
4. Repeat 2 and 3
Crack-free thick AlN buffer
with atomically flat surface
Figure 1 (online colour at: www.pss-a.com) Gas flow sequence
and schematic of the growth control used for NH 3 pulse-flow
multilayer (ML)-AlN growth technique.
Figure 3 (online colour at: www.pss-a.com) AFM image of the
surface of ML-AlN (RMS value was 0.16 nm with 5 × 5 μm
square).
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1178 H. Hirayama et al.: 222–282 nm AlGaN and InAlGaN-based deep-UV LEDs
Figure 4 Schematic structure of an AlGaN/AlN template with
5-step ML-AlN buffer layer grown on sapphire used for 250 nm
band AlGaN MQW DUV-LED.
DUV absorption. An AlGaN-free buffer is believed to be
particularly important for realizing sub-250 nm-band highefficiency
LEDs.
Figure 2 shows the full width at half-maximum
(FWHM) of X-ray diffraction (1012) ω-scan rocking curve
(XRC) for various stages of ML-AlN growth. The total
thickness of ML-AlN layer for this sample was 3.3 μm.
The FWHM of XRC (1012) of AlN was reduced from
2160 arcsec to 550 arcsec by introducing the NH 3 pulseflow
ML-AlN growth method. Figure 3 shows an atomic
force microscope (AFM) image of the surface of ML-AlN
on sapphire. We confirmed the flat surface by observation
of the step-flow growth mode using AFM. The root mean
square (RMS) value of the surface roughness of the
ML-AlN obtained from the AFM image was 0.16 nm.
Figure 4 show a schematic structure of an AlGaN/AlN
template with 5-step ML-AlN buffer layer grown on sapphire
substrate used for a 250 nm AlGaN-MQW. The total
thickness of the ML-AlN buffer was 4.8 m. The fullwidth
at half maximum (FWHM) of the X-ray (0002) and
(1012) ω-scan rocking curves (XRC) of the AlN layer
were approximately 200 arcsec and 370 arcsec, respectively.
The edge-, screw- and mixed-type dislocation densities
of AlGaN layer on ML-AlN were 7.5 × 10 8 cm –2 ,
3.8 × 10 7 cm –2 and 2.4 × 10 8 cm –2 , respectively, as observed
from the cross-sectional transmission electron microscope
(TEM) image.
We observed remarkable enhancement of DUV emission
of AlGaN-QWs by fabricating them on the highquality
AlN template [19]. Figure 5 shows PL spectra of
AlGaN QWs with peak emission wavelength at around
254 nm fabricated on ML-AlN templates with various values
of XRC (1012) FWHM. The 254 nm QWs were excited
with 244 nm Ar-SHG laser. The excitation power
Figure 5 PL spectra of AlGaN QWs with peak emission wavelength
at around 254 nm fabricated on ML-AlN templates with
various values of XRC (10 12) FWHM.
density was approximately 200 W/cm 2 . As seen in Fig. 5,
the emission intensity was significantly increased by improving
the XRC (1012) FWHM. The PL intensity was increased
by more than 50 times by reducing the XRC
(1012) FWHM from 1400 arcsec to 500 arcsec. From
Fig. 5, we found that PL intensity of the QW was rapidly
increased when FWHM of XRC (1012) of AlGaN buffer is
reduced to 500–800 arcsec. We obtained similar emission
enhancement for the 260 nm, 270 nm and 280 nm band
AlGaN-QWs.
3 222–273 nm AlGaN QW LEDs fabricated on
ML-AlN templates Figure 6 shows a schematic of the
sample structure and emission image of an AlGaN MQW
DUV LED fabricated on a ML-AlN template. Table 1
shows the typical designed values of Al compositions x in
Al x Ga 1–x N wells, buffer and barrier layers, and electronblocking
layers (EBLs) used for 222–273 nm AlGaN-
MQW LEDs. High Al content AlGaN layers were used in
order to obtain short wavelength UV emissions, as shown
in Table 1. Figure 7 shows a cross-sectional TEM image of
an AlGaN MQW DUV LED with emission wavelength at
227 nm fabricated on a ML-AlN template. We grew an approximately
1 μm thick Si-doped Al 0.87 Ga 0.13 N buffer-layer,
followed by a 3-layer MQW region consisting of 1.3 nm
thick Al 0.79 Ga 0.21 N wells and 7 nm thick Al 0.87 Ga 0.13 N barriers,
a 21 nm thick undoped Al 0.87 Ga 0.13 N barrier, a 15 nm
thick Mg-doped Al 0.98 Ga 0.02 N electron-blocking layer
(EBL), a 10 nm thick Mg-doped Al 0.87 Ga 0.13 N p-layer and
an approximately 20 nm thick Mg-doped GaN contact
layer on the ML-AlN buffer. The quantum well thickness
was changed within the range of 1.3–2 nm. We used a thin
quantum well in order to obtain a high IQE by suppressing
the effects of the polarization field in the well. It is believed
to be particularly important to obtain atomically
smooth hetero-interfaces to obtain a high IQE from such a
thin QW, because the quantized energy level broadening
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Phys. Status Solidi A 206, No. 6 (2009) 1179
Ni/Au Electrode
Ni/Au
ML-AlN Buffer
(NH 3 Pulse-Flow Method)
Sapphire Sub.
GaN;Mg
Al 0.87Ga 0.13N;Mg
Al 0.98Ga 0.02N;Mg
E-Blocking Layer
Al 0.79Ga 0.21N/
Al 0.87Ga 0.13N
3-layer MQW
n-Al 0.87Ga 0.13N;Si
UV Output
Figure 7 Cross-sectional TEM image of an AlGaN MQW DUV
LED with emission wavelength of 227 nm.
Figure 6 (online colour at: www.pss-a.com) Schematic sample
structure and emission images of an AlGaN MQW DUV LED
with emission wavelength at 227 nm fabricated on a ML-AlN
buffer.
due to the roughened hetero-interfaces would cause the
reduction of emission intensity. The atomically flat heterointerfaces
for the 1.3 nm thick three-layer QWs are confirmed
by the cross-sectional TEM image, as seen in
Fig. 7. Ni/Au electrodes were used for both n-type and
p-type electrodes. The size of the p-type electrode was
300 × 300 µm. The output power radiated into the back of
the LED was measured using a Si photodetector located
behind the LED sample, which was calibrated to measure
luminous flux from LED sources using an integrated-
Table 1 Typical designed values of Al compositions x in
Al x Ga 1–x N wells, buffer and barrier layers, and electron-blocking
layers (EBLs) used for 222–273 nm AlGaN-MQW LEDs.
wavelength well barrier & buffer electron blocking layer
222 nm 0.83 0.89 0.98
227 nm 0.79 0.87 0.98
234 nm 0.74 0.84 0.97
248 nm 0.64 0.78 0.96
255 nm 0.60 0.75 0.95
261 nm 0.55 0.72 0.94
273 nm 0.47 0.67 0.93
spheres system. The LEDs were measured under bare wafer
condition.
Figure 8 shows electroluminescence (EL) spectra of
the fabricated AlGaN-MQW LEDs with wavelengths of
222, 227, 234, 248, 255 and 261 nm, and quaternary
InAlGaN-MQW LEDs with wavelengths of 282 nm, all
measured at room temperature (RT) with injection current
of around 50 mA. The pulse width and repetition
frequency used for the pulsed current injection were 10 μs
and 10 kHz, respectively. As can be seen in Fig. 8, singlepeaked
operations were obtained for every sample. The
222 nm is the shortest wavelength to date for an
AlGaN-based LED on sapphire.
Normalized Intensity
AlGaN QW
DUV LEDs
222nm Pulsed
227nm Pulsed
234nm CW
248nm CW
255nm CW
261nm CW
InAlGaN QW
DUV LED
282nm CW
Measured at RT
200 250 300 350 400
Wavelength (nm)
Figure 8 (online colour at: www.pss-a.com) EL spectra of the
fabricated AlGaN-MQW LEDs with wavelengths of 222, 227,
234, 248, 255 and 261 nm, and quaternary InAlGaN-MQW LEDs
with wavelengths of 282 nm, all measured at RT with injection
current of around 50 mA.
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1180 H. Hirayama et al.: 222–282 nm AlGaN and InAlGaN-based deep-UV LEDs
Output Power (mW)
2
DE EBL=420meV
l=250nm
(a)
DE EBL=280meV
Dl=254nm
1
RT CW
AlGaN-3MQW
DUV-LED
on ML-AlN
0
0 100 200 300 400
Current (mA)
EQE η ext (%)
0.5
0.4
0.3
0.2
0.1
DE EBL=420meV
l=250nm
DE EBL=280meV
l=254nm
(b)
RT CW
0
0 100 200 300 400
Current (mA)
Figure 9 (online colour at: www.pss-a.com) (a) I–L and (b)
I-EQE characteristics for two types 250 nm band AlGaN-MQW
LEDs under RT CW operation.
Figure 9 shows (a) current vs. output power (I–L) and
(b) current vs. EQE η ext characteristics for two types
250 nm band AlGaN-MQW LEDs under RT CW operation.
The electron barrier height of EBL and the peak wavelength
of the two types LEDs were 420 meV, 250 nm and
280 meV and 254 nm, respectively. As seen in Fig. 9(b),
the EQE of the LED was significantly increased by using
higher electron blocking height. This fact indicates that the
electron injection efficiency (EIE) into the QW is markedly
increased by the suppression of electron overflow.
The maximum output power and EQE were 2.2 mW and
0.43%, respectively, for the LED with wavelength of
250 nm under RT CW operation.
We also obtained single-peaked EL spectra for sub-
230 nm wavelength LEDs. The deep-level emissions were
more then two orders of magnitude smaller than the main
peak for the sub-230 nm wavelength LEDs. The output
power of the 227 nm LED was 0.15 mW with injection
current of 30 mA and the maximum EQE was 0.2%, under
RT pulsed operation. We also obtained the maximum output
power of 0.014 mW and EQE of 0.003% for 222 nm
AlGaN LED.
4 Over 10 mW CW power 280 nm band
InAlGaN-based DUV-LED Quaternary InAlGaN alloy is
attracting much attention as candidate material for realizing
DUV-LEDs, since efficient UV emission as well as
higher hole concentration can be obtained due to Inincorporation
effects [16–18]. Figure 10 shows a schematic
layer structure and a cross-sectional TEM image of a
282 nm InAlGaN-based UV-LED. On the ML-AlN/sapphire
template, we grew an approximately 2 μm thick
Si-doped AlGaN buffer layer, a 3 nm thick undoped
InAlGaN interlayer, a 20 nm thick Si-doped InAlGaN
buffer layer, a 2-layer MQW emitting region consisting
of 1.7 nm thick undoped wells and 7 nm thick Si-doped
InAlGaN barriers, a 10 nm thick undoped InAlGaN cap, a
7 nm thick Mg-doped InAlGaN electron blocking layer
(EBL), an approximately 50 nm thick Mg-doped InAlGaN
p-InGaN Contact
p-InAlGaN
n-AlGaN
AlN(NH3 pulse-flow
multi-layer growth)
Sapphire(0001)
p-InAlGaN
E-Block Layer (7nm)
InAlGaN Cap (10nm)
InAlGaN well
(1.7nm)
/InAlGaN:Si Barrier
(7nm) 2QW
InAlGaN:Si (20nm)
i-InAlGaN Interlayer
(3nm)
Figure 10 (online colour at: www.pss-a.com) Schematic layer
structure and a cross-sectional TEM image of a 282 nm InAl-
GaN-based UV-LED.
and a Mg-doped InGaN contact layer. The Al compositions
of the InAlGaN used for well and barrier layer were approximately
35% and 60%, respectively, in order to obtain
a 280 nm band emission from the QW. The In composition
of the InAlGaN layers was estimated to be below 1%. The
Al content used for InAlGaN EBL estimated by the growth
condition was more than 90%.
We achieved high-quality quaternary InAlGaN layers
with high Al content (>45%) by using quite low growth
rate, i.e., 0.03 μm/hour. The emission intensity of a 280 nm
band quaternary InAlGaN QW at RT was increased by
5 times by reducing the growth rate from 0.12 μm/hour to
0.03 μm/hour. We introduced Si-doped InAlGaN buffer
and barrier layers and undoped InAlGaN interlayer, for the
purpose of obtaining atomically flat hetero-interfaces of
the InAlGaN layers and reducing Piezoelectric field in the
QWs. The Si concentration of the InAlGaN barrier layer
was approximately 1 × 10 17 cm –3 . We confirmed that the
surface roughness of InAlGaN layer was significantly improved
by introducing Si-doped InAlGaN buffer layer. The
PL intensity of InAlGaN-QW with Si-doped InAlGaN barrier
was about 2 times higher than that with undoped
Figure 11 (online colour at: www.pss-a.com) Wavelength dependence
of the ratio of integrated PL intensity (PL at RT/PL at
low temperature).
10nm
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Output Power (mW)
10
l=282nm
1.5
5
RT CW 0.5
InAlGaN-2QW-LED
on AlN/AlGaN
/Sapphire Sub.
0
0
0 100 200 300
Current (mA)
1
External Quantum Efficiency (%)
Figure 12 Current vs. output power (I–L) and EQE characteristics
of the 282 nm InAlGaN QW UV-LED with Si-doped
InAlGaN layers.
InAlGaN barrier. We also obtained marked emission enhancement
of QWs by inserting Si-doped InAlGaN buffer
layer and i-InAlGaN interlayer.
Figure 11 summarizes the wavelength dependence of
the ratio of integrated PL intensity (PL at RT/PL at low
temperature). We usually measure the low temperature PL
at 10 K. As shown in Fig. 11, an AlGaN DUV emission
at RT is weak when we use high TDD AlN template
(TDD > 2 × 10 10 cm –2 ). We achieved high-efficiency emission
both for AlGaN and InAlGaN QWs, by fabricating
them on low TDD ML-AlN template. The maximum ratios
of the integrated PL intensity were 30% and 86% for
280 nm band AlGaN and InAlGaN QWs, respectively.
This result suggests that extremely high IQE can be obtained
from the InAlGaN-QW at RT by fabricating them
on a low TDD AlN buffer.
Figure 12 shows current vs. output power (I–L) and
EQE characteristics of the InAlGaN QW UV-LED with
Si-doped and Mg-doped InAlGaN layers. Single peaked
EL was obtained with the wavelength at 282 nm. The
maximum output power and EQE were 10.6 mW and
1.2%, respectively, under RT CW operation. From these
results, we found that quaternary InAlGaN QW and p-type
InAlGaN is quite useful for achieving high-efficiency
DUV-LEDs. We also found the control of n-type doping
layer around the InAlGaN-based QW was effective for obtaining
high-efficiency DUV-LEDs.
Figure 13 summarizes maximum output power of
AlGaN and InAlGaN based DUV-LEDs for the various
development stages of our group. When the TDD of the
AlN template was higher than 2 × 10 10 cm –2 , the emission
from the UV-LED was weak and not single-peak. We obtained
single-peaked 240–260 nm band LEDs by reducing
edge-type TDD to 3.2 × 10 9 cm –2 , as described in the
Ref. [9] in 2007. A significant increase of CW output
power was observed by reducing the TDD, as shown in
Fig. 13. We also found that the higher electron blocking
height is effective for obtaining high output power. The
Max. Output Power (mW)
10 2
10
1
10 -1
10 -2
10 -3
10 -4
10 -5
TDD(Edge)2×10 10 cm -2
Emission is weak and not
single peak.
200 220 240 260 280 300
Wavelength (nm)
Figure 13 (online colour at: www.pss-a.com) Maximum output
power of AlGaN and InAlGaN based DUV-LEDs for the various
development stages of our group.
output power of the 250 nm band LED was increased
by more than 30 times by reducing the TDD from
3.2 × 10 9 cm –2 to 7.5 × 10 8 cm –2 . We also used DOWA
Electronics Ltd. Corporation’s AlN/sapphire templates
with XRC (10 12) FWHM of 250–350 arcsec, in order to
obtain higher output power of AlGaN LEDs. We obtained
over 1 mW CW output power for 241–282 nm DUV-
LEDs. The maximum output power of the 241 nm and
256 nm LEDs were 1.1 mW and 4.0 mW, respectively, under
RT CW operations. We obtained over 10 mW CW
power with wavelength of 280 nm, which is available for
sterilization application.
Figure 14 summarizes the EQE of 200–300 nm band
III-nitride DUV-LEDs obtained by our group. The EQE
observed for the 220 nm band AlGaN LED were extremely
high compared with those for the 210 nm LED using AlN
emitting layer [14]. The reason of obtaining higher efficiency
for the AlGaN LED compared with AlN LED is
EQE η ext (%)
10 2
10 1
282nm
250nm 264nm 1.2% (CW)
0.43% 0.6%(CW)
10 0 227nm 0.2% (CW)
(Pulsed)
10 -1 222nm
InAlGaN-QW
0.003%
LED
(Pulsed)
10 -2
10 -3
AlGaN-QW
10 -4
LEDs
NTT
10 -5 AlN-LED
210nm, 10 -6 %
10 -6
200 220 240 260 280 300
Wavelength (nm)
Wavelength for
Sterilization
Figure 14 (online colour at: www.pss-a.com) EQE of 200–
300 nm band AlGaN and InAlGaN based DUV-LEDs achieved
by our group.
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1182 H. Hirayama et al.: 222–282 nm AlGaN and InAlGaN-based deep-UV LEDs
that a sufficient electron–hole confinement into QWs and
an efficient carrier injection can be obtained by utilizing an
AlGaN-based heterostructure. The maximum EQE of sub-
300 nm LED obtained by our group was 1.2%. One of the
reasons of low EQE for sub-300 nm nitride LEDs is considered
to be low light extraction efficiency (