スライド 1

Spatial variation of luminescence
of InGaN alloys measured by
highly-spatially-resolved scanning
cathodoluminescence
F.Bertram et al.
Material Science and Engineering
B93 (2002) 19-23
Itoh Lab.
Takahiro Doki
Contents
・Introduction
-InGaN
-Cathodoluminescence
・Motivation
・Sample
・Experimental Results
・Summary
InGaN
laser diodes (LD)
Ultraviolet
Blue
light-emitting diodes (LED)
Green
(http://www.marumet.co.jp/closeup/led.htm )
( InN )x
+
(Eg~0.80 eV)
( GaN )1- x =
( Eg~3.40 eV)
EInGaN(x) = xEInN + (1-x)EGaN –bx(1-x)
b: bowing parameter
EInN = 0.80(eV), EGaN= 3.40(eV)
b= 2.0(eV)
InxGa1-xN
Bandgap energy of InxGa1-xN
InGaN
Potential Energy
Thermal
Nonradiative
High quantum efficiency
despite high defect densities
Exciton
Lattice defect
In-rich
Radiative
Position
Effective localization of
carriers in Indium-rich
potential minima
Cathodoluminescence
・Cathodoluminescence (CL)
：Luminescence under
electron beam irradiation
Wavelength of an electron
beam is very short.
Small excitation spot (to ~10nm)
High
spatial resolution
Electron beam
Auger
electron
Secondary electron
Cathodoluminescence
（CL）
Ｘ-ray
Sample
・Secondary electron
→Observation of an image by the
scanning electron microscope (SEM)
Motivation

It is said that strong localization of carriers due to
inhomogeneity of In concentration results in the high
quantum efficiency.

The structural dependence of optical properties of InGaN
have been extensively investigated by CL, Micro-PL and
SNOM. SNOM: Scanning Near Field Optical Microscope
CL measurement to reveal a correlation of
microstructures with luminescence for InGaN
Sample
InxGa1-xN
(x= 0.03-0.20)
AFM image (x = 0.17)
30nm
100nm
4μm
Buffer layer
Substrate
InGaN
GaN
AlGaN
sapphire
20nm
10nm
0nm
AFM: Atomic Force Microscope
Experimental Results ①
CL overview spectra (a, d) & The images of emission peaks (b, e)
x=0.03 Main peak
InxGa1-xN
Single peak
x=0.17
Narrow
spectral
range
Main peak
Additional peaks
First peak
Second peak
x> 0.1
Wide
spectral
range
Experimental Results ②
SEM image of InGaN sample with x=0.13.
Spike
Plateau
3nm
Craters (density of 2.9 × 108 cm-2)
Spikes (density of 1.9 × 107 cm-2)
Crater
Experimental Results ③
Images of CLI in the main peak(430nm), the first(450nm),
second peak(468nm) of CL overview spectra from InGaN sample with x=0.13.
430nm(Main peak)
450nm(First peak)
468nm(Second peak)
Almost homogeneous
Exclusively from craters and spikes
Summary

Highly-spatially-resolved cathodoluminescence was measured
for InGaN alloys.

The samples with the low In concentration show one main peak
in CL spectra.

The sample with the high In concentration has many
nanostructures of craters and spikes. CL spectrum shows a
main peak originating from all the area and the additional
peaks at the lower energy side originating from the
nanostructures.

As a result, it was suggested that craters and spikes has In-rich
composition and the carriers are strongly localized at them.

Download Report