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The CdSe Nanocrystalline Growth in solutions
Shima Fardad
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Introduction
Compound semiconductor deposition from liquid )aqueous or non-aqueous solutions( is becoming increasingly popular because :• capability of large-area deposition.• It has the advantages of economy.
The II/VI semiconductors has been the focus of attention recently for, Optoelectronic Photovoltaic solar cells Photocatalytics Photoelectro Chemicals Laser diodes ...
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CdSe growth in:
Glasses Organic glasses Colloidal solutions Chemical solutions Solution Gels (Sol-gel)
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Chemical Deposition(Fabrication Techniques) :
ELECTROCD Electro Chemical Deposition
PCD Photo Chemical Deposition
CBD Chemical Bath Deposition
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CdSe Chemical Deposition
Basic idea Reaction between slowly released Se anion with a
free Cd cation. Controlling the crystalline size by
Growth time Light intensity Heating temperature Wavelength
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Effective factorson size R
e
R
hE
2
2
22 8.1
2
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Electrodeposition
Plating Technologies
Electroplating Electroless plating
Use DC Vol. Source No Vol. Source
Restricted to electrically conductive materials
The films can be made in any thickness from ~1µm to >100µm
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Photo Chemical Deposition Controlling Deposition by light.
As discussed above Changing the intensity Turning off/on
Chemical reaction catalyzed by hv Need some species (sulfite ions) can supply
solvated electrons. Sulfite ions will release electrons when photo
activated.
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CdSe PCD reactions
Thickness = 300nm ; Time = 120minsRate = 150nm/h
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Chemical Bath Deposition
Large variety of chalcogenide semiconductors
Purely chemical reaction between dissolved precursors (without any charge transfer)
Large area deposition Various substrates
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CdSe CBD
Cadmium acetate + Sodium selenosulfite
Adding small amount of heteropolyacid improves greatly the photoelectrochemical response
Example : Silicotungstic (STA) ; SiW12O40H4
Changing bath composition gives different mass
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CdSe CBD (contd.)
With STA
Less Noisy
Saturated
Without STA
Noisy
Decreases to ZERO
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CdSe Growth in CBD
According to Figures we have two-peak profile. Proves the process
takes place in 2 steps. Two dimensional
growth (Cylindrical) Three dimensional
growth (Hemispheroids )
TEM
STM
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Change in Color (Bulk to Nanocrystal)
As the CdSe grows on the substrate it’s Color changes from yellow to Dark Red.
An aggregation process of the COLLOIDS form.
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CdSe in Sol-Gel Films
Sol-Gel Films are prepared by incorporating Cadmium acetate into a Glass matrix.
Sol-Gel can stabilize cubic forms of nanocrystalline CdSe against transformation to the hexagonal phase. Causes separation between nanocrystalls. viscosity will lower the mobility of
nanocrystalls. Porosity of the Sol-Gel
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XRD spectra
CdSe CD. Fimls CdSe in TiO2 sol-gel CdSe in ZrO2 sol-gel
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An application of Electrodepositionfor CdSe
CdSe Nanowire Arrays (embedded in anodic aluminia membrane, AAM)
Uses in Electronic Magnetic Optical devices
Filling the pores of AAM by Electrodeposition method we have a CdSe nanowire.
60nm in diameter ; 5um in length Cd/Se significantly depends on the PH (9)
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SEM images (highly ordered CdSe nanowire arrays)
A Cross sectional view
A top view image
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Best Wishes