Electron Spin Resonance Investigations of Rapid Thermal Oxidized Porous Silicon
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ELECTRON SPIN RESONANCE
INVESTIGATIONS OF RAPID THERMAL
OXIDIZED POROUS SILICON H. LINKE 1, P. OMLING 1, B.K. MEYER2 , V. PETROVA-KOCH2 , T. MUSCHIK2 V. LEHMANN' 1) Solid State Physics Department, University of Lund, S-22100 Lund, Sweden 2) Physics Department, Tech. Univ Munich, D 8046 Garching, Germany 3) Siemens Research Laboratories,D 8000 Munich, Germany ABSTRACT We studied the defect properties present in rapid thermal oxidized porous silicon (RTOPS) by Electron Spin Resonance (ESR). Two different types of defects are distinguished, one similar to the ones observed in damaged c-Si, and in a-Si.The second one is probably related to the Pbocenter at the Si/SiO2 interface. The minimum dens-lty of 10 6 cm- 3 is observed for the as etched and for the 900 C oxidized samples, but reaches a maximum of 8x018 cm-3 for the 600 C samples. The PL intensity anticorrelates with the defect densities, which shows that nonradiative recombination via defects is a very powerful channel in quenching the PL efficiency.
1.
INTRODUCTION With the discovery of the efficient visible photoluminescence
(PL) at room temperature (RT) /1/, porous silicon (PS) became an optoelectronics. Unfortunately (VIS) light illumination /2/, electron beam /4/ 3
orders
etc.
ultraviolet (UV) and visible heating /3/, exposure to an
cause a pronounced PL degradation
of magnitude).
The main reason for this
the very low structural stability bond
strength
only
the electrolytically etched interesting material for
/5/)
of the hydrides SiHx
covering
the
internal
(up to
behaviour
is
(ca.3 eV
surface
of
the
as-prepared material /3/. The understanding of the PL degradation goes hand in hand with the understanding of the origin of light in the PS. The latter is controversially discussed recovery
in
the
when
high
internal surface spectra of thick emission
is
not
literature.
The
quality
thermal
recent
observation
oxide
is
formed
of on
PL the
/11,12/ (no traces of SiHx bonds in the IR samples /16/) brings evidence that the light related
to
surface
luminous
agents
Mat. Res. Soc. Symp. Proc. Vol. 283. @1993 Materials Research Society
(hydrides
252
SiHx /6/ or siloxene Si6H6-m 0 3+n/7/) (crystallites). Independent of the
but to the Si remnants different mechanisms of
radiative recombination which can take place in the remnants (band to band recombinations /1/, or recombination via surface confined states /19/) the PL gain will be affected by the density of electronic defects acting as nonradiative recombination centers (the nonradiative recombination process is faster than the radiative ones, in the considered PS and RTOPS the decay is slow (ps) /14/). Electron Paramagnetic Resonance (EPR) investigations can provide valuable information about the nature, microscopic neighbourhood and density of these defects. So far only a few publications dealing with spin dependent properties of PS are known /2,8-11,13/. They were dealing with samples with hydride and oxyhydride coverage. Here we present an EPR study of rapid therm
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