Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Nanos tructured GaN on Silicon Fabricated by Electrochemical and Laser-induced Etching
Asmiet Ramizy 1 , Z. Hassan 1 *and Khalid Omar 1
1 Neon-Optoelectronics Research and Technology Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang, Malaysia
Abstract-Nanostructured GaN layers have been fabricated by electrochemical and laser-induced etching (LIE) processes. The etched samples
exhibited dramatic increase in photoluminescence intensity as compared to the as-grown samples. The Raman spectra also displayed stronger
intensity peaks which were shifted and broadened as a function of etching parameters.
Wide-gap III–V nitride semiconductors such as GaN are
most promising for blue or ultraviolet (UV)-emitting
devices. For the fabrication of GaN nanostructures-based
devices, it is important to control the size of nanocrystals as
well as to develop a reliable means of monitoring the size
distributions of the nanocrystallites in these luminescent
materials. In recent years, processing techniques for III– V
nitrides nanostructures have been successfully established,
especially for crystal growth, while the most suitable etching
method is not still concrete because of the excellent chemical
stability and high hardness of these compounds. Plasma
etching [1] and reactive ion etching (RIE) [2, 3] have mainly
been applied so far to etching of III–V nitride crystals. With
these processes, however, damage by ion or plasma
bombardment is a serious problem.
In this work, the fabrication of nanostructured porous GaN
by electrochemical etching (Figure 1) and laser-induced
etching (Figure 2) have been attempted. Laser processing
has the advantages of not causing damage or contamination,
as well as of special selectivity with high resolution and high
efficiency; however, there are few reports on the laser
processing of III–V nitride crystals. The studies on the
fundamental properties of these nanostructures are very
important due to their unique structural and optical
properties relative to the bulk form of the corresponding
materia l.
Figure 1. The electrochemical etching set-up
GaN thin films were grown on n-type Si (111) substrate
using Veeco model Gen II molecular beam epitaxy (MBE)
system. The GaN samples with (0001) orientation, carrier
concentration of 2.1 10 19 cm -3 , and thickness of 0.47 um
were placed in an electrolyte solution with ethanol 99.999%:
HF40% (4:1), and applied with current density of 75mA/cm 2
for the electrochemical etching, and for the laser-induced
etching, power density of 12 W/cm 2 fro m a laser diode
(=635 nm, 1.90 eV) was applied. The etching duration was
12 min.
The as-grown samp les exh ibited relatively surface
morphology. Electrochemical etching resulted in the
formation of pores structures with different sizes and shape.
The etched surface became hexagonal, and pores structures
are confined to smaller size. In addition, the pores walls were
very thin with some short thin tips at the top. On the other
hand, the surface morphology of the sample obtained after
laser induced etching process shows deep and extremely thin
pores.
Photoluminescence (PL) spectra showed blue shift
luminescence relative to the as-grown sample. The band
edge emission wavelength shifted from 362.0 to 335.0 nm
for the electrochemically etched sample, and to 346.5 for the
laser-induced etched sample. The average diameter of the
GaN crystallites was about 7-10 n m, as determined fro m the
PL data. The Raman spectra for the etched samples revealed
shifted and broadened peaks relative to the as grown GaN
which can be attributed to the quantum confinement effects
on electronic wave function of the GaN nanocrystals.
In summary, GaN nanostrutures have been fabricated by
two different etching techniques. The quantum confinement
effects are considered to control the mechanism of the
lu minescence in the nanocrystallites.
This study was supported by FRGS grant and Universiti
Sains Malaysia.
*Corresponding author: zai@usm.my
[1] S.A. Smith, C.A. Wolden, M.D. Bremser, A.D. Hanser, R.F.
Davis, W.V. Lampert. Appl. Phys. Lett. 71, 3631 (1997)
[2] D. Basak, M. Verdú, M.T. Montojo, M.A. Sánchez-Garcia, F.J.
Sánchez, E. Munõz, E. Calleja. Semicond. Sci. Technol. 12, 1654
(1997)
[3] J. B. Fedison, T. P. Chow, H. Lu, I. B. Bhat, J. Electrochem.
Soc. 144, L221 (1997)
Figure 2. The laser-induced etching set-up
6th Nanoscience and Nanotechnology Conference, zmir, 2010 353