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