Slajd 1

1
Compositional dependence of damage buildup in
Ar-ion bombarded AlGaN K.
Pagowska1, R. Ratajczak1, A. Stonert 1, L.
Nowicki1 and A. Turos 1,2
1 Soltan Institute for Nuclear Studies, 05-400
Swierk/Otwock, Poland
2 Institute of Electronic Materials
Technology, Wólczynska 133, 01-919 Warsaw, Poland
AIM   The detailed understanding of defect
formation and transformations in AlGaN is of
great interest for further material and device
improvement. Because of the complexity of
processes involved in defect buildup, many
important issues are still to be elucidated.
Nucleation Layer
SAMPLE PREPARATION GaN, Al0.4Ga0.6N and AlN
layers of 1 µm thickness were grown on sapphire
substrates using the MOVPE technique. Epitaxial
layers were bombarded with 320 keV Ar ions to
fluence ranging from 5?1012 to 1?1017/cm2 at RT.
EXPERIMENTAL RBS/channeling with 1.70 MeV
4He-ions was used for analysis. The Monte Carlo
simulation code McChasy was applied for spectra
evaluation.
Fig. 1. Random and aligned RBS/channeling spectra
for 1 µm thick GaN film bombarded to different
fluences of 320 keV Ar ions.

• RESULTS
• Fig. 1 shows random and (0001) aligned spectra
  (Ga peak only) for 1 µm thick GaN epilayers
  subjected to Ar-ion bombardment to different
  fluences. Some characteristic features of spectra
  should be pointed out
• with increasing Ar fluence Ga damage peak
  increases monotonically due to the progressing
  damage builup in GaN layer,
• for the highest fluence the implanted region was
  amorphized,
• peak in the vicinity of the rear edge is due to
  the lattice mismatch between the layer and the
  substrate and is characteristic for
  heteroepitaxial GaN growth.
• Similar spectra were obtained for Ar-ion
  implanted Al0.4Ga0.6N and AlN layers.

Fig. 2. Depth distributions of displaced lattice
atoms due to Ar-ion bombardment
DISCUSSION AND CONCLUSIONS Fig. 3 shows the
defect buildup curves for studied alloys. The
multistep damage accumulation model 1 has been
fitted to the data. For comparison results of
Ar-ion bombardment at 15 K 2 were also shown.
At a given fluence phase transformations in
bombarded epilayers occur, which are visualized
as steps in calculated curves. Three step process
has been assumed. Parameters of corresponding
transitions are listed in Table 1. One notes that
the critical fluence for the second step is
independent of the Al molar quotient. Our
preliminary HRXRD data indicate that the driving
force for this effect is the strain accumulation
in implanted layer. Besides of GaN the
amorphization cannot be attained with 320 keV
Ar-ion bombardment. Further increase of the ion
fluence leads only to enhanced sputtering and
cannot produce more damage.
Table 1. MSDA model parameters
fdi- level of damage at saturation
, si-cross-section for damage formation
(slope), xi- irradiation fluence in dpa,
where i stage number.
GaN GaN Wendler Al0.4Ga0.6N AlN
fd1 6 7.5 6 0.5
s1 0.77 2.15 4.8 0.5
fd2 70 75 42 6.5
s2 0.151 0.258 0.16 7.8
x2 3 2.1 0.7 0.06
fd3 100 100 54 63.5
s3 0.02 0.079 0.022 0.168
x3 88 14 60 1.26
REFERENCES 1 J. Jagielski et al. NIMB 266
(2008) 2902. 2 E. Wendler et al. NIMB 206
(2003) 1028.
Fig. 3. Accumulated damage in GaN, AlGaN and AlN
epilayers bombarded with 320 keV Ar ions. Solid
lines are fits to RBS/C data using the MSDA model
assuming a three-step process
ACKNOWLEDGEMENTS This work was supported by the
Polish Ministry of Science and Higher Education,
Grant No. N 51502931/1104. RBS/channeling
analysis has been carried out at the AIM of the
Institute of Ion Beam Physics and Materials
Research of the Forschungszentrum
Dresden-Rossendorf within the framework of the
specific research and technological development
programme of the European Community "Structuring
the European Research Area Research
Infrastructures Transnational Access (RITA
Contract Number 025646).