Porous silicon (PS) layers have been prepared in this work by
electrochemical etching (ECE) technique of a (111) p-type silicon wafer
with resistivity (1.5-4 Ω.cm) in hydrofluoric (HF) acid of 20%
concentration. Various affecting parameters were studied such as the current
density (10, 20, 40, and 50 mA/cm2), and etching time (10, 20, and 40 min).
We have studied the optical properties (Reflectivity), vibration properties
(Raman), surface properties (FTIR), structural properties (XRD),
morphological properties (AFM), and electrical properties (I-V, C-V,
photocurrent, and photosensitivity). Also we prepared PS layers by ECE for
p-n silicon at different current densities (5, 10, and 40 mA/cm2) with fixed
etching time at 20 min, in 20% HF acid, in order to study the photovoltaic
measurements for solar cell.
The PS surface showed lower reflectance values compared with bulk
silicon. Raman spectra measurements showed a broadened peak and shifted
below 520 cm-1 for PS layers.
In freshly prepared PS layer, the FTIR studies demonstrated the
presence of silicon-hydrogen bonds, related to groups formed at the
extended PS surface. As the PS layers were stored, various silicon-oxygen
vibrational modes became apparent.
X-ray diffraction showed when crystal size was reduced toward
nanometric scale, then a broadening of diffraction peaks (111) were
observed and the width of the peak was directly correlated to the size of the
nanocrystalline domains.AFM images showed the PS layer had sponge like structure, and
average diameter of pore and thickness of PS layer increased with increasing
the current density and etching time.
The electrical properties of prepared PS; namely current densityvoltage
characteristics in dark, showed that the pass current through the PS
layer decreased by increasing the current density and etching time, due to
increase the resistivity of PS layer. The PS layer showed a rectifying
behaviour with different rectification ratio. C-V measurements demonstrated
that the charge carries decrease and width of depletion layer increase by
increasing the current density and etching time. The photosensitivity
measurements of prepared PS layer showed the peak value in visible region
at (400-600nm) increased with increasing the current density and etching
time.
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