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The CdSe Nanocrystalline Growth in solutions
Shima Fardad
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 ...
CdSe growth in:
Glasses Organic glasses Colloidal solutions Chemical solutions Solution Gels (Sol-gel)
Chemical Deposition(Fabrication Techniques) :
ELECTROCD Electro Chemical Deposition
PCD Photo Chemical Deposition
CBD Chemical Bath Deposition
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
Effective factorson size R
e
R
hE
2
2
22 8.1
2
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
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.
CdSe PCD reactions
Thickness = 300nm ; Time = 120minsRate = 150nm/h
Chemical Bath Deposition
Large variety of chalcogenide semiconductors
Purely chemical reaction between dissolved precursors (without any charge transfer)
Large area deposition Various substrates
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
CdSe CBD (contd.)
With STA
Less Noisy
Saturated
Without STA
Noisy
Decreases to ZERO
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
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.
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
XRD spectra
CdSe CD. Fimls CdSe in TiO2 sol-gel CdSe in ZrO2 sol-gel
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)
SEM images (highly ordered CdSe nanowire arrays)
A Cross sectional view
A top view image
Best Wishes
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